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Dissertations / Theses on the topic 'Fast particles'

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Published: 8 June 2024
Last updated: 22 June 2025

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1

Müller, Matthias S. "Fast algorithms for the simulation of granular particles." [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9716193.

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2

Zegenhagen, Stefan. "Destabilization of Alfvén eigenmodes by fast particles in W7-AS." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=984442553.

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3

Pinches, Simon David. "Nonlinear interaction of fast particles with Alfven waves in tokamaks." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362917.

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4

Lilley, Matthew Keith. "Resonant interaction of fast particles with Alfvén waves in spherical tokamaks." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5487.

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The Spherical Tokamak (ST) concept has become one of the main avenues in magnetic nuclear fusion research since STs successfully demonstrated plasma operation at [Beta] = 2P[mu]0=B2~1. Next step ST machines aiming at achieving burning plasma conditions in high [Beta] plasmas are being planned, such as the Spherical Tokamak Power Plant (STPP) and the Component Testing Facility (CTF). Instabilities of fast particle-driven Alfven eigenmodes are often observed in present-day STs. Such instabilities, driven by fusion-born alpha particles as well as by fast ions produced with auxiliary heating schemes, in the next step STs may pose a major problem as these instabilities may affect confinement and losses of the fast ions. A theory of compressional Alfven eigenmodes (CAE) with frequencies above the deuterium cyclotron frequency,[omega] > [omega]cD, is developed for plasma parameters of a STPP, and modes in the ion-ion hybrid frequency range, [omega]cT < [omega] < [omega]cD, are also investigated in order to assess the potential of diagnosing the deuterium-tritium (D-T) ratio. For the 1-D character of a STPP equilibrium with [Beta]~1 , a `hollow cylinder' toroidal plasma model is employed for studying CAEs with arbitrary values of the parallel wave-vector k[||] = k[.]B/|B|. The existence of weakly-damped CAEs, free of mode conversion, is shown to be associated with the `well' in the magnetic field profile, B = B (R), that can exist at the magnetic axis. A significant part of this thesis focusses on the experimentally observed effects of resonant wave-particle interaction between Alfven waves and fast particles in the Mega Amp Spherical Tokamak (MAST) device at the Culham Laboratory, UK, and in the LArge Plasma Device (LAPD) in the University of California, Los-Angeles, USA. New robust experimental scenarios for exciting CAEs in the MAST spherical tokamak are developed, and interpretation of the observed CAEs in the frequency range [omega]cD/3 < [omega] < [omega]cD is given in the context of the 1-D ST model and the Doppler shifted cyclotron resonance. The e ciency of the Doppler resonance between co and counter directed fast ions and left and right hand polarised Alfven waves is further assessed experimentally on the LAPD device, with probe ions injected in the presence of Alfv en waves launched by an external antenna. The developed theory of CAEs is then applied to a calculation of the linear kinetic drive of CAEs in the MAST experiments. A model representation of the fast ion distribution function, produced by neutral beam injection (NBI), is used by fitting to the TRANSP Monte-Carlo NBI modelling results. The main free energy sources associated with temperature anisotropy and bump-on-tail are estimated analytically, and the CAE stability boundary is qualitatively assessed. In order to explain the experimentally observed difference between steady-state and pulsating Alfvenic modes, the non-linear theory of fast particle driven modes near marginal stability is extended to include dynamical friction (drag). For the bump-on-tail problem, the drag is shown to always give an explosive amplitude evolution in contrast to diffusion in velocity space in the vicinity of the wave-particle resonance. This is then extended to the case of experimentally observed NBI-driven toroidal Alfven eigenmodes (TAEs) in the MAST machine. The experimentally observed differences between TAEs driven by fast ions produced with ion cyclotron resonance heating (ICRH) and NBI are then interpreted. The problem of drag dominated collisions for modes excited by fusion-born alpha particles in burning plasmas such as a STPP and ITER is underlined.
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5

Vincenzi, Pietro. "Interaction between neutral beam fast particles and plasma in fusion experiments." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424363.

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Neutral beam injection (NBI) is one of the most used and reliable methods to heat plasmas in magnetically confined fusion devices. NBI is used in most of the present experiments, it will be used as dominant auxiliary power system in ITER experiment and studies are ongoing for DEMO reactor preconceptual designs with neutral beam (NB) systems. NBI is an essential actuator for plasma scenarios in terms of heating and driven current. This thesis presents the work performed during the 3 years of my Ph.D.. It focuses on numerical studies of the interaction between energetic particles coming from NBI and magnetically confined hot plasmas. The main aspects discussed in this thesis are the neutral beam ionization, fast ion confinement, fast ion losses, power deposition and driven current. A brief discussion of NBI as fuelling source is also presented. NBI modelling tools have been applied to study different devices with dominant NB power: the largest tokamak in operation (JET), the largest helical device in operation (LHD) and DEMO tokamak reactor concept. Detailed modelling of NBI by means of a Monte Carlo orbit following code has been provided for JET discharge analyses. A predictive simulation aimed at reconstructing the ion temperature profile with strong ion heating from NBI has been performed, resulting in a reliable prediction when the experimental measurement was not available due to a diagnostic fault. JET NBI-plasma interaction has been studied by predictive simulations for H discharges starting from reference D discharges in support of JET isotope studies. The isotopic change and the consequent effect on NBI-plasma interaction has been discussed also for LHD helical device, where studies in preparation of future D experiments (instead of H) are ongoing. NBI is one of the options as additional power system for a demonstrative fusion power plant (DEMO), and a pre-conceptual design of the reactor is ongoing within EUROfusion activities. DEMO scenario simulations have been carried out both for pulsed and steady-state concepts. The role of NBI as dominant heating and current drive system has been investigated by sensitivity studies, comparisons with other heating systems and transport investigations of transient phases (plasma ramp-up and ramp-down).<br>L’iniezione di fasci di particelle neutre (neutral beam injection NBI) é uno dei metodi piú utilizzati e affidabili per scaldare il plasma in esperimenti sulla fusione termonucleare confinata magneticamente. L’NBI é utilizzato nella maggior parte degli attuali esperimenti, verrá applicato come riscaldamento dominante in ITER e studi sono in corso per implementare l’NBI nel progetto europeo del futuro reattore dimostrativo DEMO. L’NBI gioca un ruolo fondamentale per i plasmi fusionistici in termini di riscaldamento e capacitá di indurre corrente nel plasma. Questa tesi presenta il lavoro svolto durante i tre anni del mio dottorato e si focalizza su studi numerici dell’interazione tra particelle energetiche provenienti dall’NBI e plasmi confinati magneticamente. Gli aspetti principali discussi sono la ionizzazione del fascio di neutri nel plasma, il confinamento e le perdite degli ioni veloci, la deposizione di potenza e la corrente di plasma indotta dal fascio. Viene inoltre presentata una breve discussione sull’NBI come sorgente di particelle. Diversi codici numerici sono stati applicati per lo studio di esperimenti caratterizzati da un riscaldamento dominante tramite NBI: sono stati studiati il piú grande tokamak attivo al mondo (JET), il piú grande stellarator attivo al mondo (LHD) e il progetto del reattore dimostrativo europeo DEMO. Accurate simulazioni dell’iniezione del fascio neutro sono state elaborate grazie ad un codice Monte Carlo per l’analisi di esperimenti di JET. Una simulazione predittiva é stata condotta con l’intento di ricostruire il profilo di temperature ionica del plasma nel caso di rilevante riscaldamento ionico da parte dell’NBI. Ció ha prodotto un’attendibile ricostruzione in un caso in cui le misure sperimentali non erano disponibili a causa di un problema con lo strumento di misura. L’interazione tra NBI e plasma al JET é stata studiata tramite simulazioni predittive anche per scariche in idrogeno, partendo da scariche di riferimento in deuterio, con l’obbiettivo di studiare gli effetti che il cambiamento isotopico provoca sul plasma di JET. Studi sugli effetti isotopici sono stati effettuati anche per LHD, esperimento a configurazione elicoidale, dove si stanno preparando i futuri esperimenti in deuterio al posto degli usuali esperimenti in idrogeno. L’iniezione di particelle neutre é una delle opzioni come riscaldamento addizionale del plasma per il futuro reattore dimostrativo DEMO. Attualmente uno studio pre-concettuale di questo reattore é in corso a livello europeo. Simulazioni degli scenari di DEMO sono state effettuate sia per il progetto di un DEMO pulsato, sia per un DEMO a funzionamento stazionario. Il ruolo dell’NBI come riscaldamento principale e sistema per indurre la corrente di plasma é stato investigato tramite studi di sensibilitá, confronti con altri sistemi di riscaldamento e simulazioni delle fasi transitorie del plasma (accensione - ramp-up - e spegnimento - ramp-down - della scarica).
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6

Girardo, Jean-Baptiste. "Control of instabilities and turbulence by fast particles in fusion plasmas." Palaiseau, Ecole polytechnique, 2015. http://www.theses.fr/2015EPXX0121.

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7

Chen, Li. "Fast pyrolysis of millimetric wood particles between 800°C and 1000°C." Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10258.

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Ces travaux de thèse s’intègrent au sein du projet Biocarb lancé par le Commissariat à l’Énergie Atomique dont l’objectif est de développer des procédés de production de carburants liquides ou gazeux à partir de gaz de synthèse riche en H2 et CO obtenu par gazéification de la biomasse lignocellulosique. L’objectif de cette étude est d’étudier le comportement de particules de biomasse millimétriques lors de la pyrolyse dans des conditions types de gazéifieurs industriels tels que les réacteurs à lit fluidisé ou à flux entraîné, qui fonctionnent pour des flux de chaleur élevés (105 – 106 W⋅m-2) et pour de hautes températures (&gt;800°C). Tout d’abord, des expériences de pyrolyse sont menées à 800 et 950°C dans un four à chute de laboratoire sur des particules de bois entre 350 et 800 μm. Les résultats montrent que dans les conditions de l’étude, l’augmentation de la taille de la particule augmente seulement la durée de la pyrolyse mais ne modifie pas les rendements ou la composition du solide et du gaz au cours de la pyrolyse. Par ailleurs, des mesures basées sur la technique de PTV (Particle Tracking Velocimetry) sont réalisées à température ambiante pour caractériser la taille et la densité des particules de bois brut et de résidu, et valider une corrélation donnant le coefficient de traînée qui sert à calculer le temps de séjour des particules dans le réacteur. On constate à la fin de la pyrolyse une diminution de la densité comprise entre 70 et 80% ainsi qu’une diminution de la taille des particules entre 25 et 40%. Les résultats montrent également que la vitesse de glissement de la particule et l’évolution de ses propriétés doivent être prises en compte lors du calcul de sa vitesse. Enfin, à partir des résultats expérimentaux, un modèle unidimensionnel à coeur rétrécissant est développé pour décrire le comportement d’une particule de bois lors de sa pyrolyse. Le modèle est capable de prévoir l’évolution du rendement en solide, en gaz total et en goudrons au cours de la pyrolyse ainsi que la vitesse de glissement de la particule et son temps de séjour dans le réacteur.L’analyse de sensibilité du modèle montre que même pour des particules millimétriques, une connaissance précise de la chaleur de réaction associée à la pyrolyse, de la densité du bois et de la conductivité thermique du résidu solide est essentielle<br>The present work is part of a project of the French energy research centre Commissariat à l’Energie Atomique. The goal of the project is to develop processes of production of gaseous or liquid fuel from synthesis gas obtained by gasification of lignocellulosic biomass. The objective of the present work is to study the pyrolysis behaviour of millimetric biomass particles under the operating conditions encountered in fluidized bed or entrained flow gasifiers, namely high external heat flux (105 – 106 W⋅m-2) and high temperature (&gt; 800°C). First, pyrolysis experiments are conducted at 800 and 950°C in a lab-scale drop tube reactor on wood particles between 350 and 800 μm. The results show that under the explored conditions, the increase of the particle size only increases the time required for pyrolysis but does not affect the product distribution during pyrolysis. Since in the pyrolysis experiments, the particle residence time cannot be directly measured, PTV (Particle Tracking Velocimetry) measurements are performed at room temperature to characterize the evolution of the particle size and density along pyrolysis and to validate a drag coefficient correlation for the particle residence time calculation. The optical measurements show that at the end of pyrolysis there is a decrease of particle density of 70 – 80% and of particle size of 25 – 40%. It is also proven that the particle slip velocity cannot be neglected and that the change of these particle properties must be taken into account for the calculation of the particle slip velocity and residence time. Finally, based on these experimental results, a 1D shrinking-core model is developed that is able to predict the solid/gas/tar yields and the residence time of a single particle along pyrolysis in the drop tube reactor. It is validated on both the pyrolysis and optical experiments. The model sensitivity analysis shows that even for millimetric particles, the accurate knowledge of the heat of pyrolysis, of the wood density and of the char thermal conductivity is essential
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8

Feher, Tamas Bela [Verfasser]. "Simulation of the interaction between Alfvén waves and fast particles / Tamas Bela Feher." Greifswald : Universitätsbibliothek Greifswald, 2014. http://d-nb.info/1048536556/34.

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9

Müller, Matthias S. [Verfasser]. "Fast algorithms for the simulation of granular particles / Rechenzentrum, Universität Stuttgart... Matthias S. Müller." Stuttgart : RUS [u.a.], 2001. http://d-nb.info/964089122/34.

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10

CORREA, DEISE A. C. "Estudo da fluencia do aco inoxidavel AISI-316 irradiado com neutrons rapidos e particulas alfa." reponame:Repositório Institucional do IPEN, 1986. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9886.

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Made available in DSpace on 2014-10-09T12:32:29Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T14:10:15Z (GMT). No. of bitstreams: 1 03180.pdf: 2623068 bytes, checksum: eb3adbfcbd2151a3b9e3f1cbe30c00e8 (MD5)<br>Dissertacao(Mestrado)<br>IPEN/D<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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11

Bergkvist, Tommy. "Non-linear dynamics of Alfvén eigenmodes excited by fast ions in tokamaks." Doctoral thesis, KTH, Fusionsplasmafysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4320.

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The tokamak is so far the most promising magnetic configuration for achieving a net production of fusion energy. The D-T fusion reactions result in 3.5 MeV alpha-particles, which may destabilize Alfvén eigenmodes through wave-particle interaction. These instabilities redistribute the alpha-particles from the central region of the plasma towards the edge, where they are thermalized, and hence result in a reduced heating efficiency. The high-energy alpha-particles may even be thrown out of the plasma and may damage the wall. To investigate the destabilization of Alfvén eigenmodes by high-energy ions, ion cyclotron resonance heating (ICRH) and neutral beam injection (NBI) are often used to create a high-energy tail on the distribution function. The ICRH does not only produce high-energy anisotropic tails, it also decorrelates the wave-particle interaction with the Alfvén eigenmodes. Without decorrelation of the wave-particle interaction an ion will undergo a superadiabatic oscillation in phase space and there will be no net transfer of energy to the mode. For the thermal ions the decorrelation from collisions dominates while for the high-energy ions the decorrelation from ICRH dominates. As the unstable modes grow up, the gradients in phase space, which drive the mode, are reduced, resulting in a weaker drive. The dynamics of the system becomes non-linear due to a continuous restoration of the gradients by D-T reactions and ICRH. In this thesis the non-linear dynamics of toroidal Alfvén eigenmodes (TAEs) during ICRH has been investigated using the SELFO code. The SELFO code, which calculates the distribution function during ICRH self-consistently using a Monte-Carlo metod, has been upgraded to include interactions with TAEs. The fast decay of the mode amplitude as the ICRH is switched off, which is seen in experiments, as well as the oscillation of the mode amplitude as the distribution function is repetetively built up by the ICRH and flattened by the TAE has been reproduced using numerical simulations. In the presence of several unstable modes the dynamics become more complicated. The redistribution of an alpha-particle slowing down distribution function as well as the reduced heating efficiency in the presence of several modes has also been investigated.<br>QC 20100628
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12

Tran, Nhan Thanh. "Numerical methods for solving wave scattering problems." Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32508.

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Doctor of Philosophy<br>Department of Mathematics<br>Alexander G. Ramm<br>In this thesis, the author presents several numerical methods for solving scalar and electromagnetic wave scattering problems. These methods are taken from the papers of Professor Alexander Ramm and the author, see [1] and [2]. In Chapter 1, scalar wave scattering by many small particles of arbitrary shapes with impedance boundary condition is studied. The problem is solved asymptotically and numerically under the assumptions a << d << λ, where k = 2π/λ is the wave number, λ is the wave length, a is the characteristic size of the particles, and d is the smallest distance between neighboring particles. A fast algorithm for solving this wave scattering problem by billions of particles is presented. The algorithm comprises the derivation of the (ORI) linear system and makes use of Conjugate Orthogonal Conjugate Gradient method and Fast Fourier Transform. Numerical solutions of the scalar wave scattering problem with 1, 4, 7, and 10 billions of small impedance particles are achieved for the first time. In these numerical examples, the problem of creating a material with negative refraction coefficient is also described and a recipe for creating materials with a desired refraction coefficient is tested. In Chapter 2, electromagnetic (EM) wave scattering problem by one and many small perfectly conducting bodies is studied. A numerical method for solving this problem is presented. For the case of one body, the problem is solved for a body of arbitrary shape, using the corresponding boundary integral equation. For the case of many bodies, the problem is solved asymptotically under the physical assumptions a << d << λ, where a is the characteristic size of the bodies, d is the minimal distance between neighboring bodies, λ = 2π/k is the wave length and k is the wave number. Numerical results for the cases of one and many small bodies are presented. Error analysis for the numerical method are also provided.
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13

Regan, Cyril. "Modéles réduits pour le transport de particules rapides dans le cadre de la fusion par confinement inertiel." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14138/document.

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Le transport de l'énergie dans le cadre du schéma d'allumage rapide pour la Fusion par Confinement Inertiel (FCI) se fait au moyen d'électrons relativistes ou d'ions rapides. Le transport des particules et le processus de dépôt d'énergie induisent une physique complexe dont la description détaillée requiert des calculs cinétiques multidimensionnels précis. Exigeant en ressources informatiques, ces modules de transport cinétiques sont peut compatibles avec les soucis d'efficacité des utilisateurs de codes hydrodynamiques.Un des enjeux actuels consiste à développer méthodes efficaces qui rendent compte des principales caractéristiques du processus de transport cinétique et qui soient suffisamment rapides pour être couplées à un calcul intégré d'assemblage de combustible et de combustion. J'ai étudié dans ce travail deux modèles de transport de particules chargées, qui tendent à répondre à ces besoins. Le premier modèle (Trumpet) est une extension à deux dimensions d'un modèle simplifié considérant un angle de diffusion moyen. Le second modèle (M1) est une simplification des équations de Fokker Planck basée sur une fermeture angulaire respectant le principe de minimisation d'entropie.Ces deux modèles ont été implémentés et intégrés dans le code hydrodynamique du CELIA (CHIC). Après avoir étudié les avantages et les limites de ces modèles, je les ai appliqué au calcul de dépôt d'ions énergétiques dans une cible compressée. Nous avons modélisé un diagnostic d'imagerie protonique d'une expérience de compression d'un cylindre par laser et analysé l'allumage d'une cible par des ions de deutérium tritium et de carbone accélérés au moyen d'impulsions ultra intense<br>The energy transport in the Fast Ignition scheme within the framework of Inertial Confinement Fusion (ICF) is done by means of energetic charged particles, relativistic electrons or fast ions. The particle transport and energy deposition process is rather complicated and its detailed description requires large scale kinetic multidimensional calculations. These codes are CPU time consuming and cannot be easily implemented in radiation hydrodynamic codes that describe the fuel assembly, resulting energy deposition and the combustion. Reduced methods are needed that account for the main features of the kinetic transport process and are sufficiently fast and efficient to be introduced directly in an hydrodynamic module. We have developed two reduced models of charged particles transport, suitable for integration in hydro-codes. The first model, called Trumpet, is a two-dimensional extension of a simplified 1D model for the average scattering angle. The second model called M1 is a simplification of the Fokker Planck equation, based one the angular closure respecting the minimum entropy principle. These two models have been integrated in the CELIA hydrodynamic code (CHIC). After considering the advantages and limitations of these models, we used them to calculate the ion energy deposition in a compressed target. We have modelled the protonic radiography of a cylindrical laser-driven impulsion, and analyse a new fast ignition scheme with fast deuterium tritium and carbon ions accelerated by laser
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14

Henkel, Marion [Verfasser]. "Measurements of ion temperatures and fast particles in the scrape-off layer of W7-X stellarator and EAST tokamak / Marion Henkel." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2021. http://d-nb.info/1239413556/34.

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15

Fomin, Alex. "Multiple Scattering Effects on the Dynamics and Radiation of Fast Charged Particles in Crystals. Transients in the Nuclear Burning Wave Reactor." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS272/document.

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Les effets cohérents dans l’interaction des particules à haute énergie avec les cristauxouvrent de nouvelles opportunités d’accélération et détection de particules. Les champs électromagnétiquesefficaces présents dans les cristaux qui se présentent dans ce cas peuvent dépassermille fois les champs qui sont maintenant réalisables dans les installations expérimentales.La première partie de la thèse est consacrée à l’étude théorique des effets de diffusion multiples surla dynamique et le rayonnement des particules chargées de haute énergie dans les cristaux. L’undes objectifs de cette étude est de trouver des conditions optimales pour effectuer la mesure dumoment magnétique anormal du baryon Lamda au LHC. En raison de la courte durée de vie de cetteparticule, le seul moyen de fournir une telle mesure est d’utiliser un cristal courbé, qui peut imiter lechamp magnétique de l’ordre de milliers de Tesla.L’optimisation des paramètres du set up expérimental a été réalisée sur la base de la simulation parordinateur du passage du Baryon Lamda à travers un cristal courbé à l’aide du modèle de collisions binaires, entenant compte de la diffusion incohérente sur les vibrations thermiques des atomes des noeuds enréseau et de la diffusion sur un sous-système électronique d’un cristal. Les résultats de la recherchemenée dans la thèse démontre la possibilité d’effectuer une telle expérience au LHC et sont devenusla base de la proposition correspondante.Les effets de diffusion multiple des électrons ultra relativistes et le rayonnement des positons dansles cristaux alignés sont également considérés dans la première partie de la thèse.Il est également démontré que la distribution angulaire spectrale et les caractéristiques de polarisationdu rayonnement diffèrent essentiellement des résultats de la théorie de Bethe–Heitler. Lesconditions d’observation expérimentale de ces effets sont présentées.La deuxième partie de la thèse est consacrée à l’étude des processus transitoires des réacteursrapides fonctionnant dans un régime d’onde de combustion nucléaire auto-entretenue (OCN). C’estun nouveau concept de réacteurs de fission nucléaire avec la soi-disant “sécurité intrinsèque”, danslaquelle le développement d’une réaction nucléaire à chaîne incontrôlable est impossible en raisondes principes physiques du fonctionnement du réacteur. Les concepts prometteurs du réacteur OCNdans le cas de sa mise en œuvre permettent d’utiliser l’uranium appauvri et fournit le traitement desdéchets radioactifs à longue durée de vie.Cette étude est basée sur la résolution numérique de l’équation de diffusion non linéaire non stationnairedu transport de neutrons avec un ensemble d’équations de combustion pour les composantsdu carburant et les équations de la cinétique nucléaire pour les noyaux précurseurs des neutronsretardés, en utilisant une approche “effective multigroup”. Le modèle du réacteur cylindrique homogèneavec le combustible métallique des cycles de carburant U–Pu, Th–U et mixte Th–U–Pu estconsidéré dans le cadre du concept de flambage.À la suite de ces études, l’existence du mode OCN dans le cas du combustible mixte Th–U–Puet de ses avantages essentiels est démontrée; l’analyse détaillée d’un type spécial de rétroactionnégative inhérente au régime OCN et sous-jacente à la “sécurité intrinsèque” d’un tel réacteur esteffectuée; les scénarios d’un démarrage en douceur, d’un arrêt forcé et d’un redémarrage ultérieurdu réacteur OCN sont développés<br>The coherent effects in the high energy particle interaction with crystals open up new opportunities for accelerating and detecting techniques. The effective electromagnetic fields that arise in this case can exceed a thousand times the fields that are now attainable at experimental installations. The first part of the thesis is devoted to the theoretical study of the multiple scattering effects on the dynamics and radiation of high energy charged particles in crystals. One of the goals of this study is to find optimal conditions to carry out the measurement of the anomalous magnetic moment of the charmed Lambda Baryon at the LHC. Due to the short lifetime of this particle the only way to provide such a measurement is to use a bent crystal, which can imitate the magnetic field of order of thousand Tesla. The optimization of the parameters for an experimental setup was carried out on the basis of computer simulation of the Lamda Baryon passage through a bent crystal using the binary collisions model, taking in to account incoherent scattering on thermal vibrations of atoms at lattice nodes, and scattering on an electronic subsystem of a crystal. The results of the research conducted in the thesis give an optimistic forecast for the possibility of carrying out such an experiment at the LHC and became the basis of the corresponding proposal. The multiple scattering effects of the thesis. This study is performed in the framework of classical electrodynamics approach for describing the relativistic particle radiation and the computer simulation of fast charged particles passing through a crystal using the above-mentioned model. It is shown, that the spectral-angular distribution and the polarization characteristics of radiation essentially differ from the results of the Bethe–Heitler theory. The conditions for the experimental observation of these effects are presented. The second part of the thesis is devoted to the study of transient processes in advanced fast reactor breeder working in a self-sustained nuclear burning wave (NBW) regime. It is a new concept of nuclear fission reactors with the so-called “intrinsic safety”, in which the development of uncontrolled chain nuclear reaction is impossible due to the physical principles of reactor operation. The promising concepts of NBW reactor in the case of its implementation allows to utilize the depleted Uranium and provides the treatment of long-lived radioactive waste. This study is based on numerical solving the non-stationary non-linear diffusion equation of neutron transport together with a set of the burn-up equations for fuel components and the equations of nuclear kinetics for precursor nuclei of delayed neutrons using effective multi-group approach. The model of cylindrical homogeneous reactor with metallic fuel of U–Pu, Th–U and mixed Th–U–Pufuel cycles is considered in the framework of the buckling concept. As a result of these studies the existence of the NBW mode in the case of mixed Th–U–Pu fuel and its essential advantages are demonstrated; the detailed analysis of a special kind of the negative reactivity feedback that is inherent to the NBW regime and underlies the “intrinsic safety” of such a reactor is performed; the scenarios of a smooth start-up, forced shutdown and subsequent restart of the NBW reactor are developed
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Laxåback, Martin. "Fast wave heating and current drive in tokamaks." Doctoral thesis, KTH, Alfvénlaboratoriet, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118.

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This thesis concerns heating and current drive in tokamak plasmas using the fast magnetosonic wave in the ion cyclotron range of frequencies. Fast wave heating is a versatile heating method for thermonuclear fusion plasmas and can provide both ion and electron heating and non-inductive current drive. Predicting and interpreting realistic heating scenarios is however difficult due to the coupled evolution of the cyclotron resonant ion velocity distributions and the wave field. The SELFO code, which solves the coupled wave equation and Fokker-Planck equation for cyclotron resonant ion species in a self-consistent manner, has been upgraded to allow the study of more advanced fast wave heating and current drive scenarios in present day experiments and in preparation for the ITER tokamak. Theoretical and experimental studies related to fast wave heating and current drive with emphasis on fast ion effects are presented. Analysis of minority ion cyclotron current drive in ITER indicates that the use of a hydrogen minority rather than the proposed helium-3 minority results in substantially more efficient current drive. The parasitic losses of power to fusion born alpha particles and beam injected ions are concluded to be acceptably low. Experiments performed at the JET tokamak on polychromatic ion cyclotron resonance heating and on fast wave electron current drive are presented and analysed. Polychromatic heating is demonstrated to increase the bulk plasma ion to electron heating ratio, in line with theoretical expectations, but the fast wave electron current drive is found to be severely degraded by parasitic power losses outside of the plasma. A theoretical analysis of parasitic power losses at radio frequency antennas indicates that the losses can be significantly increased in scenarios with low wave damping and with narrow antenna spectra, such as in electron current drive scenarios.<br>QC 20100506
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Dvornova, Anastasiia. "Simulations hybrides fluides-cinétiques de l'excitation des modes TAE via particules rapides et une antenne externe." Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0265.

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Dans ce travail de thèse, l’excitation de modes magnétohydrodynamique (MHD) spécifiques appelés les Toroidal Alfvèn Eigenmodes sont étudiés. Ces modes peuvent être facilement déstabilisés par plusieurs populations de particules rapides. L’excitation de modes TAE par une antenne externe en 3D est simulée pour la première fois dans les configurations point X et limiteur. Les simulations présentent une bonne concordance avec la difficulté d’exciter des modes TAE en géométrie X observée expérimentalement. L’utilisation du code Castor a permis de montrer que pour certains profils de densité, l’atténuation provenant d’une région de la séparatrice dont la limite est proche de la séparatrice peut être une source d’amplification de l’atténuation. Les résultats obtenus avec le code Jorek montrent que la région où les lignes de champ sont ouvertes est la principale source d’atténuation. Le code purement fluide Jorek a été modifié afin d’inclure les termes cinétiques fournis par son extension cinétique. Afin de confirmer l’implémentation du schéma, les taux de croissance linéaires de TAE sont calculés pour le cas de référence ITPA. Un pas supplémentaire a été fait à travers l’étude de l’évolution des modes TAE excités par une antenne externe en présence de particules rapides. L’intérêt principal de cette approche est d’investiguer la possibilité d’extraction d’information sur l’excitation des particules rapides depuis la réponse plasma à une excitation TAE. Une méthode permettant l’estimation de l’excitation de particules rapides à travers la mesure de la différence de réponse fréquentielle entre les deux directions des ondes progressives TAE est développé<br>In this thesis, the excitation of a specific types of the MHD modes called the Toroidal Alfven Eigenmodes is studied. These global modes can be easily destabilized by one of the several populations of the fast particles present in tokamaks. For the first time the modelling of the excitation of the TAE modes by a 3D external antenna is performed in case of limiter and X-point geometries. With the use of the code CASTOR it has been shown that the damping from the region inside the separatrix with plasma boundary approaching the separatrix can be a source of an increased damping for certain density profile shapes. The results obtained with the JOREK code identifies the region of the open-field lines as the main source of damping. Firther, the purely fluid code JOREK was modified to include the kinetic terms provided by the code's kinetic extension. Between the two commonly used hybrid schemes, pressure and current coupling schemes. In order to confirm the implementation of the scheme, the TAE linear growth rates are obtained for the ITPA benchmark case. A further step that was taken is to combine the previously used approaches by examining the evolution of the TAE modes excited by an external antenna now in the presence of fast particles. The principal interest in this approach is to investigate the possibility of extracting information on the fast particle drive from the plasma response on the TAE excitation. A method allowing an estimate of the fast particle drive by measuring the difference in the frequency response of the two directions of the traveling TAE waves was developed
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18

Yang, Minglin. "Computation of light scattering, radiation force, torque and stress of large non-spherical particles with Multilevel Fast Multipole Algorithm and Vectorial Complex Ray Model." Rouen, 2014. http://www.theses.fr/2014ROUES055.

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Cette thèse est dédiée à la validation du modèle de Tracé de Rayons Vectoriels Complexes (VCRM - Vectorial Complex Ray Model en anglais) par la comparaison des diagrammes de diffusion avec les résultats de SIE- MLFMA (Surface Integral Equation with Multilevel Fast Multipole Algorithm en anglais) et les applications de MLFMA développé à la prédiction de la force de pression de radiation, le couple et la tension exercés sur des grosses particules non-sphériques par un faisceau laser. En introduisant la courbure du front d’onde comme une nouvelle propriété des rayons lumineux, VCRM apporte une amélioration considérable sur la précision et l’applicabilité du modèle de rayons pour la diffusion de la lumière par les particules non-sphériques. Cependant ses résultats pour les particules non-sphériques restent à valider. Alors, MLFMA est une méthode numérique très efficace pour traiter l’interaction de la lumière avec des particules de forme quelconque. Afin d’étendre sa capacité pour les grosses particules, dans cette thèse, MLFMA est améliorée et parallélisée. Le code mis au point permet d’obtenir des résultats exacts pour les particules de paramètre de taille supérieur à 600. Le bon accord entre les diagrammes de diffusion des grosses particules ellipsoïdales calculées par MLFMA et VCRM illustre la grande capacité de ces deux méthodes. Ensuite, le code MLFMA développé est appliqué au calcul de la force de pression de radiation (FPR) et le couple sur des particules homogènes de forme quelconque. Pour éviter l’imprécision de la description mathématique en champ lointain de faisceau laser, l’expression analytique de champs électromagnétiques dans la région proche de la particule est utilisée. La FPR et le couple sont donc calculés par le flux du vecteur du tenseur de Maxwell sur une surface sphérique incluant la particule. Cette méthode est très puissante et flexible permettant de prédire la FPR et le couple exercés par un faisceau de forme quelconque sur une grosse particule, comme des particules sphéroïdales, des particules de forme de globule rouge ou moteur. La FPR et le couple sont des effets mécaniques globaux d’un faisceau de lumière exercés sur une particule. La tension sur la surface d’une particule peut être importante dans l’étude des propriétés élastiques de certaines particules. Le code MLFMA développé est donc étendu au calcul de la tension de surface et VCRM a été appliqué à l’analyse le mécanisme de la tension sur des particules sphéroïdales.
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Šesták, Jozef. "Rychlá separace výbušnin vysokoúčinnou kapalinovou chromatografií." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2011. http://www.nusl.cz/ntk/nusl-216722.

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The topic of the diploma thesis is fast separation of explosives by HPLC and development of miniaturized liquid chromatograph for application in a handheld explosives detection device. In this work the retention of some nitrated explosives and selectivity in reversed phase system as a function of mobile phase composition is studied while methanol, acetonitrile and acetone as an organic solvent is used. Best selectivity and good retention can be observed in methanol mobile phase. Acetonitrile and acetone are not suitable for fast isocratic separation of mixture containing pentaerythritol tetranitrate because of its strong retention. Efficiency and permeability of monolithic column (Chromolith CapRod RP-18e) and columns filled with superficially porous particles are compared (Kinetex 2,6 µm C-18, Poroshell 120 SB-C18). Monolithic column with satisfying efficiency and high column permeability is the most suitable solution for fast separation of explosives. Assuming use of explosives detection device in different conditions the separation was optimized on temperature 50 °C. Under these conditions the 35% v/v methanol gives good retention and selectivity. For very fast scan analysis of pentaerythritol tetranitrate or other nitroaromatics use of 70% v/v acetone mobile phase is suitable. Construction of miniaturized liquid chromatograph that enables preconcentration of explosives from aqueous solutions and fast separation in less than 1 minute is described. This concept will be incorporated into the handheld explosives detection device where the explosives vapor will be absorbed into the water and after the separation detected by chemiluminescence.
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20

Delshadi, Sarah. "Tests de diagnostic immunologique rapides combinant des nanoparticules magnétiques et des micro-aimants structurés." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAV070.

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Cette thèse présente le développement de tests immunologiques innovants, rapides et sensibles combinant des nanoparticules superparamagnétiques (SPN) fonctionnalisées et des micro-aimants : nos immuno-essais magnétiques exploitent les forts gradients de champ magnétique de ces micro-aimants pour capturer les complexes immunologiques liés aux SPN. L’attraction magnétique est souvent utilisée en biotechnologies car elle peut générér des forces capables de capturer des molécules d’intérêt. Les immuno-essais sur billes utilisent habituellement des aimants centi- et millimétriques pour capturer des micro-particules. Réduire la taille des particules magnétiques est très intéressant pour réduire les cinétiques de réactions, tout en diminuant les phénomènes de sédimentation et d’agrégation. Cette réduction d’échelle des particules permet aussi d’augmenter la surface de réaction et ainsi d’augmenter la sensibilité des tests. Cependant les aimants millimétriques génèrent des gradients faibles qui capturent difficilement les SPN, trop mobiles. Les micro-aimants de l’Institut Néel génèrent des forts gradients locaux et ainsi des forces magnétiques importantes. Ces technologies innovantes sont utilisées dans cette thèse pour développer des immuno-essais rapides tirant profit de la réduction d’échelle des particules et des aimants, par rapport aux technologies commerciales.Dans un premier temps, nous avons développé un test immunologique magnétique (MagIA) colorimétrique, comme approche innovante du test ELISA. Nous avons réalisé une preuve de concept pour la détection d’anticorps dirigé contre l’ovalbumine et comparé les résultats avec ceux de tests ELISA. Le test MagIA optimisé présente une limite de détection et une zone dynamique similaires au test ELISA développé avec les mêmes réactifs biologiques. Les micro-aimants fabriqués selon la méthode de micro-magnetic imprinting sont intégrés à bas coût dans les micro-puits des plaques multi-puits ELISA, et permettent la capture efficace des complexes immunologiques couplés aux SPN. La méthode est générique est permet de réaliser des tests ELISA en 30 minutes avec le même équipement.Nous avons ensuite développé un test magnétique immunologique avec une détection fluorescente locale tirant profit des propriétés de capture locale des SPN sur les micro-aimants. Ce test permet la quantification de la molécule d’intérêt en à peine 15 minutes sans étape de lavage. Une preuve de concept réalisée sur la détection de l’anticorps anti-ovalbumine a été réalisée, avec des anticorps de détection fluorescents et des micro-aimants fabriqués selon la méthode de thermo-magnetic patterning. La mesure différentielle entre le signal fluorescent provenant des complexes immunologiques couplés aux SPN localisées sur les micro-aimants, et le signal non spécifique (à l’extérieur des micro-aimants) permet la quantification d’une molécule. Ce test MLFIA (magnetically localized FIA) possède des performances jusqu’à 100 fois meilleures que les tests ELISA standard, pour la détection d’anticorps anti-ovalbumine en PBS. Le test MLFIA a ensuite été transféré à la détection de paramètres cliniques tels que la protéine C réactive, l'ostéopontine, et les sérologies de la toxoplasmose (IgG et IgM). La comparaison des résultats avec des méthodes automatisées a montré d’excellentes corrélations. Le test MLFIA présente plusieurs avantages : il est versatile, compatible avec les milieux biologiques, utilise de faibles volumes et requiert peu d’énergie. Ces résultats ouvrent la voie à une nouvelle génération de tests immunologiques sensibles et nous développons désormais un lecteur miniature pour le diagnostic portable<br>This thesis reports the development of innovative, sensitive and fast immunoassays combining functionalized superparamagnetic nanoparticles (SPN) and micro-magnets. Our magnetic immunoassays exploit high gradients generated by micro-magnets to capture immune-complexes captured on SPN. Magnetic attraction is widely used in biotechnology, because it provides long-range forces able to capture molecules of interest. Bead-based immunoassays use common centimetre-scale magnets to attract micro-particles. Those magnets generate low magnetic gradients and struggle to capture superparamagnetic nano-particles, which are too small and mobile to be efficiently trapped. Down-scaling the size of magnetic particles is very interesting since it allows diffusion-based transport to perform faster reactions, while avoiding particle sedimentation and aggregation. Furthermore, it increases the reaction surface, which improves the sensitivity of immunoassays. Thanks to the scaling law effects micro-magnets from Institut Néel generate high local gradients and therefore large magnetic volume forces: we use this innovative technology to develop fast immuno-assays that take advantage of a radical size reduction, compared to commercial technology.We first developed a colorimetric magnetic immunoassay (MagIA) as a new approach to standard ELISA. A proof-of-concept based on colorimetric quantification of anti-ovalbumin antibody in buffer was performed and compared with conventional ELISAs. After optimization, MagIA exhibits a limit of detection and dynamic range similar to ELISAs developed using the same biochemical tools. Micromagnets made by the micro-magnetic imprinting method can be fully integrated in multi-well plates at low cost, allowing the efficient capture of immuno-complexes carried by SPNs. The method is generic and performs magnetic ELISA in 30 min.We then developed a magnetically localized fluorescent immunoassay (MLFIA) exploiting the local capture of SPN on micro-magnets. The differential measurement of fluorescence localized on and besides micro-magnet arrays allows the detection and quantification of a molecule in only 15 minutes without fluid handling. We present a proof of concept based on the detection of monoclonal antibody anti-ovalbumin. Functionalized nanoparticles are incubated with fluorescent detection antibody and the sample containing the molecule to be detected. After a single incubation step, the nanoparticles are captured on micro-magnets made by thermo-magnetic patterning. Fluorescence is then read under a microscope. Differential measurement between the signal from the immunological complex localised on the micro-magnets and the non-specific signal localised besides micro-magnets allows the quantification of mAb anti-OVA. The performance of MLFIA was compared with conventional ELISA and exhibits a limit of detection up to 100 times better for anti-OVA mAb in PBS. For further validation, MLFIA was used to measure clinical parameters: we developed a sandwich assay to detect C-reactive protein, and a serology for Toxoplasma gondii immunoglobulin G and M or osteopontin in human samples. Comparisons with data obtained with routine clinical automatized methods show excellent correlation. Our MLFIA technology presents several key advantages: it is compatible with biological media (serum, plasma), uses small volumes and requires little energy. It also is versatile and thus can be used to detect any antigen or antibody in complex media. We are currently developing a portable prototype for point-of-care diagnostics. The results will open the way to a new generation of sensitive immunological lab-on-chip
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21

Saayman, Jean. "Combined hydrodynamic and reaction analysis of a bubbling to turbulent Fluidized Bed Reactor." Thesis, University of Pretoria, 2013. http://hdl.handle.net/2263/40221.

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There are many large-scale contacting methods for gas reactions requiring a solid catalyst. The catalytic gas-solid Fluidized Bed Reactor (FBR) is one of the popular methods in industry. In FBRs the bulk of the gas throughput is present as lean bubbles, mostly deprived of solids, bubbling through a solids-rich emulsion phase. The movement of gas into and out of the emulsion often dictates the performance of an FBR. During the past five decades major contributions have been made towards the understanding of FBRs, although numerous gaps still exist, especially at higher bubbling regime velocities. This work follows an integrated approach for the simultaneous measurement of hydrodynamics and reactor performance. Hydrodynamics are measured using fast X-Ray Tomography (XRT), pressure analysis techniques and an optical fibre probe. Reactor performance is measured by utilizing the ozone decomposition reaction. Performance is quantified using a basic two-phase reactor model with an apparent overall interphase mass transfer (K0) parameter. Two 14 cm (ID) fluidized bed columns are used, one setup supporting the ozone decomposition reaction and the other installed within a fast XRT facility. Special emphasis is placed on superficial velocities (U0) spanning the entire bubbling regime up to the onset of the turbulent regime (Uc). The particle types employed are Geldart B sand particles and highly dense ferro-silicon (FeSi) particles. Fines are added to both particle types, resulting in a total of four particle systems (sand baseline; sand with fines; FeSi baseline; FeSi with fines). Time constraints on the XRT equipment limited the tomography measurements to the sand baseline particle system. The hydrodynamics of the other particle systems were limited to the pressure signal and optical probe measurements of the ozone decomposition setup. The results of the sand baseline system suggest that a distinction should be made between the low-interaction bubbling regime and the high-interaction bubbling regime. A change in mass transfer behaviour occurs around a U0/Uc value of 0.25. Reactor performance increases up to U0/Uc = 0.7, after which a decreasing trend is observed. An empirical correlation is proposed for the specific interphase mass transfer (kbe) of the higher velocity bubbling regime. This correlation is based on the integration of the hydrodynamics determined by means of XRT and reactor performance: 4-12 The hydrodynamic parameter β gives the best fit for the entire velocity range with an average error of 8%, although it is not recommended for U0/Uc<0.17. It is observed that the classical approach of penetration theory for interphase mass transfer, performs exceptionally well at low velocities (U0/Uc<0.34). The addition of fines to the FeSi particle type decreases the overall reactor performance, despite decreased bubble sizes. The solids fraction, however, unexpectedly increases with the addition of fines and a collapse of the emulsion phase is measured. It is therefore postulated that though flow in the emulsion phase is much higher for the FeSi baseline system and decreases with the addition of fines. For the sand particle type, the behaviour expected from literature is observed: reactor performance increases, bubble sizes decrease and the solids fraction decreases. Very distinct hydrodynamic behaviour is observed for all the fluidization regimes with XRT. Probability density distributions show there are still two phases present in the turbulent regime and that the emulsion-phase solids fraction remains independent of velocity until fast fluidization sets in. The turbulent regime has unique hydrodynamic behaviour, although voids appear to be a transient structure between the structures of the bubbling and fast fluidization regimes.<br>Thesis (PhD)--University of Pretoria, 2013.<br>gm2014<br>Chemical Engineering<br>unrestricted
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22

Johansson, Dorota. "Colloids in fats the fat crystal as a functional particle /." Lund : Lund University, 1994. http://catalog.hathitrust.org/api/volumes/oclc/39676932.html.

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23

Taghavi, Ehsan, Fredrik Lindsten, Lennart Svensson, and Thomas B. Schön. "Adaptive stopping for fast particle smoothing." Linköpings universitet, Reglerteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-93461.

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Particle smoothing is useful for offline state inference and parameter learning in nonlinear/non-Gaussian state-space models. However, many particle smoothers, such as the popular forward filter/backward simulator (FFBS), are plagued by a quadratic computational complexity in the number of particles. One approach to tackle this issue is to use rejection-sampling-based FFBS (RS-FFBS), which asymptotically reaches linear complexity. In practice, however, the constants can be quite large and the actual gain in computational time limited. In this contribution, we develop a hybrid method, governed by an adaptive stopping rule, in order to exploit the benefits, but avoid the drawbacks, of RS-FFBS. The resulting particle smoother is shown in a simulation study to be considerably more computationally efficient than both FFBS and RS-FFBS.<br>CNDM<br>CADICS
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24

Laisney, Jérôme. "Influence de l’environnement sur la commutation et la bistabilité thermique de micro- et de nanoparticules à transition de spin." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112002.

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Les composés à transition de spin forment une classe spécifique de matériaux pour lesquels la commutation de l’état de spin du centre métallique peut être pilotée par divers stimuli (T, P, irradiation lumineuse, …) et s’accompagne de changements remarquables des propriétés physiques (magnétiques, optiques, structurales ou encore vibrationnelles). Ils se distinguent des autres matériaux commutables par l’observation, pour un certain nombre d’entre eux, de processus coopératifs à l’état solide, donnant lieu à l’ouverture d’une hystérèse thermique (bistabilité) particulièrement intéressante pour le stockage de l’information. Un des challenges technologiques actuels est de réduire la taille des matériaux susceptibles d’application et de les mettre en forme au sein de dispositifs sans altérer pour autant leurs propriétés. Les objectifs de la thèse ont été d’élaborer des micro- et nanoparticules à conversion de spin à partir de composés moléculaires présentant une transition de spin du premier ordre à l’état massif, puis d’étudier et analyser l’influence de la taille et de la matrice dispersante sur les processus de transition de spin. Après un premier chapitre introductif portant sur les matériaux à transition de spin, les méthodes de nanochimie et de mise en forme, le deuxième chapitre décrit l’élaboration de particules des composés FeII(phen)2(NCX)2 (X = S, Se) et [FeIII(3-OMeSalRen)2]PF6 (R = Me, Et). Comme la technique de précipitation rapide convient pour des composés ioniques, son application à FeII(phen)2(NCX)2 composé neutre, a nécessité la mise au point d’une synthèse indirecte de particules, basée sur l’extraction de ligand de précurseurs solubles, et le contrôle via des paramètres expérimentaux, des étapes de nucléation-croissance. De nouvelles particules de composés ioniques de Fe(III) [FeIII(3-OMeSalRen)2]PF6 (R = Me, Et) et des films minces contenant ces particules dispersées dans un polymère (PVP) ont été préparées. Les études magnétique et optique de ces films montrent que la matrice et la mise en forme modifient toujours les caractéristiques de la transition de spin des particules.La deuxième partie des travaux a été consacrée à l’étude des effets d’environnement. L’interaction entre des microparticules de Fe(phen)2(NCS)2 et des matrices vitreuses (Tg &gt; T1/2; T1/2, étant la température de transition) peut conduire à l’ouverture d’un large cycle d’hystérésis, déplacé vers les plus basses températures. Cette zone de bistabilité a été examinée à l’aide de la méthode FORC (First-Order Reversal Curves). L’analyse a permis d’établir l’existence de composantes réversibles attribuées aux interactions élastiques à l’interface matrice/particule et au changement de volume de la particule à transition de spin.L’étude des effets de matrice et de taille a été poursuivie avec des micro- et nanocristaux de [FeIII(3-OMeSalEen2]PF6 dispersés dans des polymères ou des liquides moléculaires formant des verres à basse température. L’encapsulation dans des verres rigides de particules haut-spin (T1/2 &lt; Tg) ou bas-spin (T1/2 &gt; Tg) donnent lieu à des conversions de spin déplacées respectivement vers les plus basses ou plus hautes températures, éventuellement des processus coopératifs avec hystérésis. Le renforcement de la coopérativité et la bistabilité observées dans le second cas ont été interprétés comme résultant des contraintes mécaniques vis-à-vis du changement de volume BS-HS de la particule. Enfin, le changement d’état de la matrice induit par des étapes de trempe (ou recuit) en-dessous (au-dessus) de la température de transition vitreuse, a été exploité pour moduler ces effets. Dans la perspective d’une application, de nouvelles études de composites ont été engagées avec des complexes présentant une transition de spin proche de la température ambiante. Le choix de la matrice dispersante selon certains critères (nature chimique, température de transition vitreuse) a permis de retrouver certains effets<br>Spin-transition compounds are a class of materials for which the spin-state switching of the metal center can be controlled by various stimuli (T, P, light irradiation,...) and produces dramatic changes of physical properties (magnetic, optical, structural or vibrational). With respect to the set of switchable materials, a number of spin-transition compounds exhibit at solid-state cooperative processes and thermal hysteresis loops (bistability), particularly suitable for information storage. One of the current technological challenges is to integrate in devices such potentially interesting materials without altering their properties. The goal of the research, recently developed by several teams, is to determine the smaller size of object in which an information can be stored, and thus to understand the effect of downsizing on cooperativity and bistability. Therefore, the objectives of the Ph-D thesis were (i) to synthesize spin-crossover nano- and microparticles from molecular materials that in the form of bulk undergo a first-order phase transition; (ii), to investigate the importance of particles size and matrix effects on the spin-transition process.After a first chapter in which the spin crossover materials are introduced, the second chapter describes the synthesis of particles of FeII(phen)2(NCX)2 (X = S, Se) and [FeIII(3-OMeSalRen)2]PF6 (R = Me, E) compounds. As the fast precipitation technique essentially suits for ionic compounds, its application to neutral ones like FeII(phen)2(NCX)2, has been made possible by an indirect syntheses based on the ligand extraction from soluble precursors and the control of nucleation and growth processes of neutral products via experimental parameters. New particles of [FeIII(3-OMeSalEen)2]PF6 and thin films containing them after their dispersion in a polymeric matrix (PVP) have been prepared. The study of these films with UV-vis and magnetic measurements has raised the issue of the impact of the polymeric matrix and processing on the spin transition properties of these particles.The second part of the manuscript focuses on the interaction between the spin-crossover particles and the dispersing medium. This interaction between microparticles of Fe(phen)2(NCS)2 and glassy matrices (Tg &gt; T1/2, T1/2, being the transition temperature) may result in the observation of large hysteresis loops shifted towards lower temperatures. This bistability has been examined with the FORC (First-Order Reversal Curves) method, magnetic measurements and a theoretical model. This analysis has shown the existence of reversible components associated to the particles/matrix interactions and the change of volume of spin-crossover particles.In a third part, the study of matrix and size effect has been pursued with micro- and nanocrystals of [FeIII(3-OMeSalEen2]PF6 encapsulated in polymeric or molecular liquids which form glasses at sufficiently low temperature. The encapsulation in rigid glasses of high spin (T1/2 &lt; Tg) or low spin (T1/2 &gt; Tg) particles give rise to transitions shifted towards lower or higher temperature respectively, possibly with cooperativity and hysteresis. The reinforcement of cooperativity and the bistability observed in the second case have been accounted for by the effect of the mechanical stress exerted by the glassy matrix on the particle volume. In addition, it has been shown that a thermal treatment of matrices (quenching or annealing steps below or above the glass transition) results in the modulation of the matrix effects. Finally, in the last chapter, a few composites including compounds undergoing a spin transition close to room temperature have been shortly investigated in presence of dispersing matrices. The choice of the matrices characteristics (chemical nature, glass transition temperature) has allowed some of these effects to be observed
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25

Kirk, John Daniel. "Particle beam LC/MS with fast atom bombardment." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/27127.

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Harvey, P. R. "Hyper-fast NMR imaging." Thesis, University of Nottingham, 1991. http://eprints.nottingham.ac.uk/13753/.

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The work presented in this thesis was carried out in the Physics Department at the University of Nottingham between October 1988 and October 1991. It is the original work of the author except where indicated by reference. This thesis describes the continuation of the development of Echo Volumar Imaging (EVI) to facilitate snapshot imaging of a volume within the human body. Variants of the technique which have also been investigated include a spin echo version, SE-EVI, and a zoomed version ZEVI. All formats acquired data in a modulus fashion in times ranging from 64 ms to 120 ms. Hardware limitations have restricted the image matrix size to 64 x 32 x 8 voxels and prompted the employment of more efficient gradient driver circuitry. A multi-mode resonant gradient circuit is described for use in both Echo Planar Imaging (EPI) and EVI. The circuit behaves in an overall resonant manner but at a fixed number of discrete frequencies. By choosing the number of resonant modes, the circuit can be used to generate approximations to a square wave or trapezoidal waveform. Because of the energy conserving nature of the circuit design much faster current rise times can be achieved with a given amplifier and gradient coil. The multi-mode gradient driver circuit was utilized both for planar imaging and to investigate the effect of rapidly modulated magnetic fields on the human body. A simple neural stimulation model is used to evaluate the stimulation threshold current density for a variety of magnetically induced waveforms and for sinusoidal stimulation as a function of frequency. Experimental results correlate well with the model showing that for short times, contrary to the widely held view, neural stimulation is independent of the magnetic field switching rate dB / dt, but depends on the final magnetic field value.
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Pippig, Michael. "Massively Parallel, Fast Fourier Transforms and Particle-Mesh Methods." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-197359.

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The present thesis provides a modularized view on the structure of fast numerical methods for computing Coulomb interactions between charged particles in three-dimensional space. Thereby, the common structure is given in terms of three self-contained algorithmic frameworks that are built on top of each other, namely fast Fourier transform (FFT), nonequispaced fast Fourier transform (NFFT) and NFFT based particle-mesh methods (P²NFFT). For each of these frameworks algorithmic enhancement and parallel implementations are presented with special emphasis on scalability up to hundreds of thousands of parallel processes. In the context of FFT massively parallel algorithms are composed from hardware adaptive low level modules provided by the FFTW software library. The new algorithmic NFFT concepts include pruned NFFT, interlacing, analytic differentiation, and optimized deconvolution in Fourier space with respect to a mean square aliasing error. Enabled by these generalized concepts it is shown that NFFT provides a unified access to particle-mesh methods. Especially, mixed-periodic boundary conditions are handled in a consistent way and interlacing can be incorporated more efficiently. Heuristic approaches for parameter tuning are presented on the basis of thorough error estimates<br>Die vorliegende Dissertation beschreibt einen modularisierten Blick auf die Struktur schneller numerischer Methoden für die Berechnung der Coulomb-Wechselwirkungen zwischen Ladungen im dreidimensionalen Raum. Die gemeinsame Struktur ist geprägt durch drei selbstständige und auf einander aufbauenden Algorithmen, nämlich der schnellen Fourier-Transformation (FFT), der nicht äquidistanten schnellen Fourier-Transformation (NFFT) und der NFFT-basierten Teilchen-Gitter-Methode (P²NFFT). Für jeden dieser Algorithmen werden Verbesserungen und parallele Implementierungen vorgestellt mit besonderem Augenmerk auf massiv paralleler Skalierbarkeit. Im Kontext der FFT werden parallele Algorithmen aus den Hardware adaptiven Modulen der FFTW Softwarebibliothek zusammengesetzt. Die neuen NFFT-Konzepte beinhalten abgeschnittene NFFT, Versatz, analytische Differentiation und optimierte Entfaltung im Fourier-Raum bezüglich des mittleren quadratischen Aliasfehlers. Mit Hilfe dieser Verallgemeinerungen bietet die NFFT einen vereinheitlichten Zugang zu Teilchen-Gitter-Methoden. Insbesondere gemischt periodische Randbedingungen werden einheitlich behandelt und Versatz wird effizienter umgesetzt. Heuristiken für die Parameterwahl werden auf Basis sorgfältiger Fehlerabschätzungen angegeben
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28

Gudmundsson, Magnus. "Heavy particle interference and diffraction in fast electron transfer collisions." Doctoral thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-57190.

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This thesis presents experimental results from the synchrotron cooler and storage ring CRYRING on charge transfer processes in fast electron transfer collisions using high-resolution cold target recoil-ion momentum spectroscopy. The main focus of these studies was to investigate a key concept of quantum mechanics: the wave-particle duality. One series of experiments has been dedicated to the study of heavy particle de Broglie wave interference due to scattering on a molecular ’double slit’. This is a fundamental manifestation of the wave properties of matter. Quantum interference oscillations were observed in the target orientation dependent cross section of single- and double-electron capture from H2 to 1.3 MeV protons and to 1.2 and 2.0 MeV He2+ ions. Another study, included in this work, is a series of angular differential cross section measurements for single-electron capture to 1.3-12.5 MeV kinetic energy protons from He that enabled us to systematically investigate the classically allowed non-radiative electron capture process in fast collisions predicted by L. H. Thomas in 1927. The cross section for this process is expected to have a nonrelativistic, asymptotic dependence on the projectile velocity, vp, of vp−11. This prediction (from 1927) was verified experimentally for the first time through the present measurements. Using the above mentioned experimental data in addition to measurements of double electron capture by 6.0 MeV He2+ from He, we have also studied the dominating, central part of the angular differential cross section, dσ/dΩ, where the peak shapes and widths surprisingly are very similar regardless of projectile energy and the number of captured electrons. We explain this with a diffraction model for the electron capture and calculate the corresponding diffracting electron capture ‘apertures’ from the shapes and widths of the measured cross sections and the projectile de Broglie wavelengths. We have on one hand established very strong experimental support for the picture suggested by Thomas in 1927 in which electrons and protons are described as classical particles. On the other hand, the diffraction picture describes the shapes of the central peaks in dσ/dΩ quite well, and nicely explains appearances of second and a third maxima in the angular differential cross section. It is hard to see how these seemingly contradicting results can be explained through complementary classical and quantum descriptions of the same underlying physical processes.<br>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.
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Cardinali, Matteo [Verfasser]. "Fast frontend electronics for high rate particle detectors / Matteo Cardinali." Mainz : Universitätsbibliothek Mainz, 2015. http://d-nb.info/1074160134/34.

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30

Vallar, Matteo. "Neutral beam fast particle physics in fusion plasma integrated scenarios." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3425245.

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Neutral beam injection heating is one of the most reliable ways to heat a plasma up to the temperatures needed to achieve steady-state thermonuclear fusion. This system injects neutral particles with energy much higher than the bulk ion energy, introducing a population of energetic particles which collide with the plasma ions and electrons. In this way energy and momen- tum are transferred to the plasma giving as final result an increase of the tar- get plasma temperature and, depending on the beam characteristics, possible modifications of its flow and current profile. Numerical modelling of the behaviour of fast particles in tokamak plasma is the subject of this thesis. Analytical and Monte Carlo models have been applied to different devices (RFX-mod, JT-60 SA and TCV) in order to study the impact of these particles in both inductive (standard) and non-inductive (advanced) scenarios. Comparison between the different codes have been made in order to assess if the different models apply correctly to the cases studied. RFX-mod device is under modification and the installation of a neutral beam injector (with fixed parameters and geometry) is in the upgrade hy- pothesis. The impact of energetic particles in RFX-mod tokamak plasmas is discussed in this work using METIS fast tokamak simulator and compared with NUBEAM Monte Carlo code. The impact of energetic particles in JT-60 SA superconducting tokamak is studied with ASCOT Monte Carlo orbit solver. This device relies on a wide and flexible set of beams for plasma heating and current drive, both for stan- dard and advanced scenarios. The behaviour of the fast particles in JT-60 SA standard and advanced tokamak plasmas is analysed, showing the reliability of the neutral beam system in this device. Neutral beam injection heating in TCV is the last topic studied in this thesis. The impact of electron cyclotron wave injection heating on energetic particles behaviour has been studied in advanced tokamak scenarios, where the expected performances are not achieved using the combination of the two heating systems. Comparison between ASCOT and NUBEAM code is performed in order to check which of the two codes<br>O aquecimento por injeção de feixes de neutros é um dos métodos mais fiáveis para aquecer um plasma até às temperaturas necessárias para atingir fusão termonuclear estacionária. Este tipo de sistema injeta neutros com ener- gias muito superiores à energia dos iões que constituem o grosso do plasma, introduzindo uma população de partículas energéticas que, colidindo com os iões e electrões do plasma, transmite a energia ao plasma. Adicionalmente, esta população de partículas energéticas também induz corrente no plasma, contribuindo para a manutenção da descarga. O tema central desta tese incide na modelização numérica do compor- tamento de partículas rápidas num plasma de Tokamak. Códigos analíti- cos e de numéricos de Monte Carlo foram aplicados a diferentes máquinas (RFX-mod, JT-60 SA and TCV) com vista a estudar o impacto destas partícu- las em cenários de operação indutivos (cenário standard) e não indutivos (avançado). A máquina RFX-mod está a ser melhorada e a instalação de injectores de feixes neutros (com parâmetros e geometria fixos) é uma das possíveis melhorias. Deste modo, o impacto das partículas energéticas nos plasmas do RFX-mod é discutida neste trabalho usando o código analítico METIS. O impacto de partículas energéticas no tokamak superconductor JT-60SA é estudado com o código de Monte Carlo ASCOT. Neste Tokamak, o aqueci- mento do plasma e a geração de corrente, seja em cenário de operação stan- dard ou avançado, é garantido em grande parte por um conjunto de feixes de injeção de neutros. Neste trabalho, a dinâmica das partículas rápidas nos cenários standard e avançado do JT-60SA é analisada, evidenciando a fiabili- dade do sistema de injeção de neutros no Tokamak. Um injector de feixes neutros foi instalado no Tokamak TCV há três anos. Este feixe é importante dado que deposita potência predominantemente nos iões e permite alargar o regime de operação do tokamak. Nesta tese, após uma revisão da condição atual do feixe de neutros e da operação com ele realizada nos últimos três anos, é feito um estudo sobre o impacto do aque- cimento por injeção de ondas electro-c
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31

Pringle, Gavin J. "Numerical study of three-dimensional flow using fast parallel particle algorithms." Thesis, Edinburgh Napier University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385914.

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32

Daniels, Graham Clinton. "Observing flow using fast neutron radiography and positron emission particle tracking." Doctoral thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33606.

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Dynamic flow of material has been studied using fast neutron radiography (FNR) and positron emission particle tracking (PEPT). A new fast neutron imaging system was commissioned at The South African Nuclear Energy Corporation, Pretoria, as part of this study, although FNR measurements were ultimately performed at PhysikalischTechnische Bundesanstalt (PTB), Braunschweig. The PEPT studies were undertaken at the PEPT Cape Town facility located at iThemba LABS, Cape Town. The steady state motion of media, within a laboratory-scale tumbling mill, was studied for a range of speed and media mixes, using both FNR and PEPT. Several operational parameters were derived from the data, which could be related to potential improvements to the milling efficiency. The blending of FNR and PEPT data for the study of steady state flow, was explored for the first time. In addition, the flow of water through porous media was studied using FNR, which enabled the determination of the hydraulic conductivity, and hence intrinsic permeability, of the media within the column. The potential of using FNR, without or without PEPT, for the study of material in motion is discussed.
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33

Sohl, Lukas. "Development of PICOSEC-Micromegas for fast timing in high rate environments." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP084.

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Les futures expériences de physique des particules devront être opérationnelles pour un flux de particules et une luminosité croissants. Plus particulièrement, les détecteurs proches du point d'interaction devront présenter une très bonne robustesse pour faire face à un flux de particules très élevé. De plus, une résolution temporelle de quelques dizaines de picosecondes pour les particules au minimum d’ionisation sera nécessaire pour assurer une séparation nette des vertex reconstruits et réduire l'empilement d’événements. Ce manuscrit a pour sujet l’instrument PICOSEC-Micromegas, un détecteur de particules innovant basé sur la lecture d’un détecteur Micromegas couplé à un radiateur Cherenkov et une photocathode. Dans ce dispositif, chaque électron primaire étant produit à la surface de la photocathode, l’étalement en temps du signal est minimal, alors qu’il peut atteindre plusieurs nanosecondes lorsque les ionisations primaires ont lieu sur le passage d'une particule dans l’espace de dérive. La hauteur de ce dernier est ici du même ordre de grandeur que celle de la région d'amplification (100-200 μm) afin de minimiser l'ionisation directe du gaz. L’espace de dérive est également utilisée comme espace de pré-amplification. Un modèle mathématique, basé sur des simulations GARFIELD++, a été développé pour décrire le développement de l'avalanche de pré-amplification. Il a permis de montrer que la longueur et la multiplication de l'avalanche dans l’espace de dérive sont les facteurs dominants dans la résolution temporelle. Le concept PICOSEC-Micromegas a été étudié avec plusieurs prototypes optimisant les champs électriques, la distance de dérive et le mélange gazeux auprès de l’installation laser du LIDYL (Laboratoire Interactions, Dynamiques et Lasers). Une résolution temporelle de ~44 ps a été obtenue pour un photo‑électron unique. Par ailleurs, des mesures effectuées en faisceau test au CERN ont permis d'obtenir une résolution temporelle de 24 ps pour des muons de 150 GeV, avec un espace de dérive de 200 μm et une photocathode en CsI (10 photoélectrons par MIP). Afin de passer du concept de détection à un démonstrateur plusieurs prototypes ont été développés, en se concentrant sur les propriétés spécifiques nécessaires aux applications futures: segmentation de l'anode, annulation des étincelles, efficacité de la photocathode et robustesse à haut flux de particules. Un prototype à pads hexagonaux a été testé en faisceau et montré une résolution temporelle de ~36 ps dans le pad central. Les performances à haut flux sont testées avec des détecteurs résistifs dans des faisceaux de muons et de pions. Des résolutions temporelles nettement inférieures à 100 ps et un fonctionnement stable en faisceau de pions sont obtenus avec tous les prototypes résistifs. Des matériaux de photocathode robustes, comme alternative au CsI, sont étudiés pour réduire la dégradation due au retour des ions. Les matériaux les plus prometteurs sont le “diamond-like carbon” (DLC) et le carbure de bore (B4C). Compte tenu des résultats obtenus, deux cas d'application sont considérés pour les perspectives de ce programme de R&amp;D. La première application considérée est l'utilisation du détecteur PICOSEC à l'intérieur d'un calorimètre comme couche de synchronisation ou de nombreuses particules secondaires sont produites dans un calorimètre électromagnétique après quelques longueurs de radiation. Une résolution temporelle de ~5 ps est attendue avec le PICOSEC-Micromegas. La seconde application est l'identification des particules par des mesures de temps de vol (TOF) ou PICOSEC-Micromegas devrait permettre de doubler la plage d’impulsion des détecteurs TOF actuels pour la séparation π/Κ avec 3σ<br>Future particle physics experiments will face an increasing particle flux with rising beam luminosity. Detectors close to the interaction point will need to provide robustness against the high particle flux. Moreover, a time resolution of tens of picosecond for Minimum Ionising Particles will be necessary to ensure a clear vertex separation of the reconstructed secondary particles and to reduce pile-up. This manuscript focusses on the PICOSEC-Micromegas, an innovative particle detector based on the Micromegas readout coupled to a Cherenkov radiator and a photocathode in front of the gaseous volume. In this way, each primary electron is located on the surface of the photocathode, suppressing thus the inevitable time jitter of several nanoseconds, due to the different ionisation positions created by the passage of a particle from the drift region of a gaseous detector. The drift region length is reduced to the same order of magnitude as the amplification region (100-200 μm) to minimise direct gas ionisation, and it is additionally used as a pre-amplification stage. A mathematical model, based on GARFIELD++ simulations, is developed to describe the propagation of the pre-amplification avalanche showing that the length and multiplication of the avalanche in the drift region is the dominant factor in the timing performance. The PICOSEC-Micromegas concept is studied with several prototypes optimising the electric fields, the drift distance, and the gas mixture in the LIDYL (Laboratoire Interactions, Dynamiques et Lasers) UV laser facility. A single photoelectron time resolution of ~44 ps is measured with the shortest tested drift region length of 119,μm and the highest stable field setting. Measurements performed in the secondary particle beam at CERN have resulted in a time resolution of 24 ps for 150 GeV muons with a drift region length of 200 μm and a CsI photocathode providing 10 photoelectrons per MIP. In order to evolve from the detection concept to a versatile instrument, several prototypes are developed, focusing on specific properties needed for future applications: anode segmentation, spark quenching, photocathode efficiency and robustness for higher particle flux. An hexagonal segmented multipad prototype is tested in the beam with a time resolution of ~36 ps in the central pad. The operation in high rate environments is studied with different resistive strip and floating strip anodes resistive detectors in muon and pion beams. Time resolutions significantly under 100 ps and stable operation in the pion beam are achieved with all resistive prototypes. Robust photocathode materials, as an alternative to CsI, are investigated to reduce degradation from the ion-backflow generated in the pre-amplification avalanche. The most promising materials are diamond-like carbon (DLC) and boron carbide (B4C). Considering all the results achieved, two application cases are projected with the PICOSEC-Micromegas detector. The first one is the use in a calorimeter as a timing layer. Many secondary particles are produced in an electromagnetic calorimeter after few radiation lengths and a time resolution down to ~5 ps is expected with the PICOSEC-Micromegas. The second one is particle identification trough time-of-flight (TOF) measurements. The PICOSEC-Micromegas is expected to double the momentum range of current TOF detectors for π/Κ separation with 3σ
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34

Park, Bum Jun. "Interactions between colloidal particles at oil-water interfaces." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 96 p, 2008. http://proquest.umi.com/pqdweb?did=1475189581&sid=20&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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35

Schlegel, Fabrice. "A fast 3D particle method for simulations of buoyant and reacting flows." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/42308.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2007.<br>Includes bibliographical references (p. 89-91).<br>This thesis describes progress in several areas related to three dimensional vortex methods and their application to multiphysics problems. The first is the solution of a generic scalar transport equation by advecting and diffusing the scalar gradient along a particle trajectory and onto a mesh, respectively, and recovering the scalar values using a Biot-Savart-like summation. The second is the accurate, high-resolution calculation of the velocity gradient using a fast treecode, which avoids using kinematic relations between the evolution of the gradients and the distortion of the flow map. The same tree structure is used to compute all the variables of interest and those required during the integration of the governing equations. Next, we apply our modified interpolation kernel algorithm for treating diffusion and remeshing to maintain long time accuracy. The coupling between the vorticity transport and that of a dynamic scalar, in this case the temperature or density in a gravitational field, is manifested by the generation of vorticity. We demonstrate the performance of the multiphysics algorithm by solving a number of buoyant and reacting flow problems.<br>by Fabrice Schlegel.<br>S.M.
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36

Lauber, Philipp. "Linear gyrokinetic description of fast particle effects on the MHD stability in tokamaks." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969890222.

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37

Pippig, Michael, and Daniel Potts. "Parallel Three-Dimensional Nonequispaced Fast Fourier Transforms and Their Application to Particle Simulation." Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-94926.

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In this paper we describe a parallel algorithm for calculating nonequispaced fast Fourier transforms on massively parallel distributed memory architectures. These algorithms are implemented in an open source software library called PNFFT. Furthermore, we derive a parallel fast algorithm for the computation of the Coulomb potentials and forces in a charged particle system, which is based on the parallel nonequispaced fast Fourier transform. To prove the high scalability of our algorithms we provide performance results on a BlueGene/P system using up to 65536 cores.
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38

Asquith, Nicola Louise. "Fast and thermal Accelerator Driven Systems: Studies of secondary particle production and transport." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14150.

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Accelerator Driven Systems (ADS) consist of a spallation neutron source coupled to a sub-critical nuclear assembly and are a proposed technology for the transmutation of nuclear waste and electricity generation. The Gamma-3 assembly of the Joint Institute for Nuclear Research (JINR), Dubna, Russia consists of a lead spallation target surrounded by graphite. The target was irradiated with 1.6 GeV deuterons and the neutron capture and fission rate of 232Th within the assembly were experimentally measured. These two reactions are fundamental to the performance and feasibility of 232Th in an ADS. The spatial distribution of slow neutrons on the surface of the graphite was also measured using CR-39 track detectors coupled to LR-115 2B film. The Quinta assembly, also located at the JINR, is composed of 512 kg of natural uranium surrounded by a lead reflector. It was irradiated with 1 and 4 GeV deuterons and the fission rate of natU, 232Th, 209Bi, natPb and 197Au was measured using mica track detectors. These materials are proposed fuel and/or target materials in future ADS. (n,γ) and (n,xn) reaction rates of 209Bi and 197Au were also determined through gamma spectrometry. Experimental reaction rates were compared to those calculated using the MCNPX 2.7 code with the INCL4/ABLA and CEM03 physics models. Evaluated cross-section libraries were used whenever available, otherwise reaction cross section data were retrieved from the literature or calculated using the TALYS and XSEX3 codes. Good agreement between the experimental and calculated results were found, although in general, the INCL4-ABLA model produced a closer agreement with the experimental results compared to CEM03. This study serves as a good validation for the computational models and cross section data used to simulate secondary particle production and transport in thermal and fast ADS. Future development of ADS will inevitably rely upon accurate and well validated simulation codes and nuclear data.
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39

Nestler, Franziska. "Efficient Computation of Electrostatic Interactions in Particle Systems Based on Nonequispaced Fast Fourier Transforms." Universitätsverlag der Technischen Universität Chemnitz, 2017. https://monarch.qucosa.de/id/qucosa%3A23376.

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The present thesis is dedicated to the efficient computation of electrostatic interactions in particle systems, which is of great importance in the field of molecular dynamics simulations. In order to compute the therefor required physical quantities with only O(N log N) arithmetic operations, so called particle-mesh methods make use of the well-known Ewald summation approach and the fast Fourier transform (FFT). Typically, such methods are able to handle systems of point charges subject to periodic boundary conditions in all spatial directions. However, periodicity is not always desired in all three dimensions and, moreover, also interactions to dipoles play an important role in many applications. Within the scope of the present work, we consider the particle-particle NFFT method (P²NFFT), a particle-mesh approach based on the fast Fourier transform for nonequispaced data (NFFT). An extension of this method for mixed periodic as well as open boundary conditions is presented. Furthermore, the method is appropriately modified in order to treat particle systems containing both charges and dipoles. Consequently, an efficient algorithm for mixed charge-dipole systems, that additionally allows a unified handling of various types of periodic boundary conditions, is presented for the first time. Appropriate error estimates as well as parameter tuning strategies are developed and verified by numerical examples.<br>Die vorliegende Arbeit widmet sich der Berechnung elektrostatischer Wechselwirkungen in Partikelsystemen, was beispielsweise im Bereich der molekulardynamischen Simulationen eine zentrale Rolle spielt. Um die dafür benötigten physikalischen Größen mit lediglich O(N log N) arithmetischen Operationen zu berechnen, nutzen sogenannte Teilchen-Gitter-Methoden die Ewald-Summation sowie die schnelle Fourier-Transformation (FFT). Typischerweise können derartige Verfahren Systeme von Punktladungen unter periodischen Randbedingungen in allen Raumrichtungen handhaben. Periodizität ist jedoch nicht immer bezüglich aller drei Dimensionen erwünscht. Des Weiteren spielen auch Wechselwirkungen zu Dipolen in vielen Anwendungen eine wichtige Rolle. Zentraler Gegenstand dieser Arbeit ist die Partikel-Partikel-NFFT Methode (P²NFFT), ein Teilchen-Gitter-Verfahren, welches auf der schnellen Fouriertransformation für nichtäquidistante Daten (NFFT) basiert. Eine Erweiterung dieses Verfahrens auf gemischt periodische sowie offene Randbedingungen wird vorgestellt. Außerdem wird die Methode für die Behandlung von Partikelsystemen, in denen sowohl Ladungen als auch Dipole vorliegen, angepasst. Somit wird erstmalig ein effizienter Algorithmus für gemischte Ladungs-Dipol-Systeme präsentiert, der zusätzlich die Behandlung sämtlicher Arten von Randbedingungen mit einem einheitlichen Zugang erlaubt. Entsprechende Fehlerabschätzungen sowie Strategien für die Parameterwahl werden entwickelt und anhand numerischer Beispiele verifiziert.
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Sghaier, Halim. "Electronique rapide de décision associée à un compteur Cherenkov de faisceau." Grenoble 1, 1993. http://www.theses.fr/1993GRE10015.

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Dans la phase ii de l'experience wa89 au cern, il est prevu d'etiqueter en ligne les hyperons du faisceau a 250 gev. L'identification des particules en physique des hautes energies fait appel a des techniques exploitant l'effet cherenkov, mais aucun type de detecteur ne permettait de satisfaire ces exigences en 1989. C'est pourquoi le compteur hypolit a ete concu. Le systeme de detection consiste en un intensificateur d'images relie a des photomultiplicateurs grace a une matrice de fibres optiques, divisee en huit secteurs de vingt couches chacun. Ces 160 pixels assurent la localisation des photons. Le principe de l'identification est base sur la reconstitution du cercle cherenkov a partir des 10 a 15 photons detectes en moyenne. A cet ensemble experimental est associe un systeme electronique rapide de traitement et d'acquisition rassemblant des caracteristiques de haute technicite: rapidite, compacite et modularite. L'electronique doit permettre, en moins de 5 microsecondes, de determiner le rayon du cercle cherenkov apres elimination des photons de bruit de fond et d'appliquer une correction pour tenir compte de la dispersion en impulsion des particules, mesuree par ailleurs. Le signal d'identification ainsi obtenu contribue a l'elaboration du signal de declenchement de l'experience. Les cartes electroniques sont realisees avec des methodes modernes de conception (cao) et des technologies de pointe telles que les composants montes en surface (cms), et les asic programmables. Les tests sur faisceau ont permis de verifier le bon fonctionnement de l'ensemble
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41

Hanazawa, Tomohito. "Effects of fat particles on the stability of complex food systems." Kyoto University, 2019. http://hdl.handle.net/2433/242551.

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42

Aston, David Eric. "Quantifying single oil-particle interactions in aqueous media /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9898.

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43

Perks, Jonathan Michael. "Phosphorus segregation and diffusion in nickel and Fe-Cr-Ni alloys under fast particle irradiation." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329993.

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44

Lloyd, Rhys David. "Collisional particle in cell modelling of the propagation of fast electrons in solid density plasma." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/14280.

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This thesis looks at the effects that electron-ion Coulomb collisions have on fast electron transport in solid density plasma. The study of the fast electrons generated in ultra-high intensity laser-plasma interactions is important due to their envisioned use in the fast ignition approach to inertial confinement fusion. Collisions have been added to the particle-in-cell (PIC) code EPOCH in order to study the propagation of fast electron beams in various solid density targets. By using a collisional PIC model several of the assumptions used in previous studies are not required. The code solves the full Maxwell equations (including the displacement current), does not require assumptions of Ohm’s law and of Spitzer resistivity and does not require the background distributions to be Maxwellian. The thesis begins with summaries of the background theory and of the previous work performed in this area. The PIC method is then discussed and the way in which collisions were added to EPOCH is outlined. The results from several collisional PIC simulations with different target Z values are then discussed and com- pared to both collisionless PIC simulation results and hybrid simulation results. The effects of collisions have then been examined by looking into numerous aspects of the simulations that have been performed. Firstly, the generation of fields within the plasma and the subsequent filamentation of the fast electron beam are examined. The effects that the collisions have on the electron distributions within the plasma are then investigated with particular attention given to the divergence of the fast electrons, the energy and momentum distributions of the electrons and the background temperatures within the plasma. Finally, the results of the simulations are used to assess the accuracy of the Spitzer resistivity approximation that is used in hybrid codes.
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45

Salyer, Zachary M. "Identification of Optimal Fast Charging Control based on Battery State of Health." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587037951166857.

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46

Hurtig, Tomas. "Plasma cloud penetration across magnetic boundaries." Doctoral thesis, KTH, Alfvén Laboratory, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3804.

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47

Gu, Chuan. "Development of a fast simulation method for particle-laden fluid interfaces and selected applications to problems involving drops." Thesis, Queen Mary, University of London, 2018. http://qmro.qmul.ac.uk/xmlui/handle/123456789/39752.

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Solid particles tend to adhere to fluid interfaces under the action of capillary force. This adsorption process is robust and has been exploited in lots of applications from stabilisation of emulsions to micro fluidic fabrications. The resulting particle laden fluid interfaces can manifest solid-like behaviours. The modifi cation of the surface tension and the emergence of surface shear elasticity of a particle-covered drops are attributed to the particle-induced surface stress. This stress represents at the continuum level the microscopic effect of particle-particle interactions. Understanding the link between the surface stress and the particle arrangement are crucial for creating novel soft materials in the future. A challenge remains when carrying out numerical simulations of particle-laden fluid interfaces: the large separation of scales makes the direct numerical simulations extraordinary expensive. Physical features present in the system come from both the liquid meniscus on the surface of each particle and the fluid interfaces containing thousands of particles. Motivated by the need for a fast simulation method to study problems involving particle-laden fluid interface, this thesis presents a new numerical formulation named Fast Interface Particle Interaction (FIPI) that can be used to simulate a large number of solid particles absorbed on fluid interfaces at a moderate computational cost. The outstanding performance of this new method is attributed to the fact that particle-level phenomena are modelled with analytical or semi-empirical expressions while hydrodynamics and fluid interface morphology at larger scales are fully resolved. Two important studies of particle-covered drops have been carried out with FIPI. In the first one a particle-covered pendant drop is simulated. The result reveals that the FIPI can successfully capture the modulation of surface tension made by absorbed particles. Moreover, the information of anisotropic surface stress is now directly available on the fluid interfaces. This capability has not been achieved previously in both experiments and simulations. The anisotropic stress emerged on the surface of a pendant drop is caused by anisotropic arrangement of the particles on the interface which in turn is induced by stretching of the interface due to gravity. Once the surface tension of the fluid interface is reduced below zero, the Laplace pressure inside the drop becomes negative and the drop can buckle like a thin solid elastic shell under compression. In the second study, the behaviours of a particle covered spherical drop under compression have been explored. The simulation results indicate the possibilities of particle desorption as well as fluid interface buckling. The onset of desorption is highly correlated to small-scale monolayer undulations which can greatly amplify the normal forces pushing particles out of the interface. The behaviours of a particle-covered drop under compression depend on the combination of several parameters related to the properties of the particle and the surface pressure created by the monolayer.
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Moraes, Marlene Silva de. "Convecção forçada de partículas poliméricas em fase diluída : curvas de pressão e distribuição de partículas." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266776.

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Orientador: Elias Basile Tambourgi<br>Tese (doutorado) - Universiade Estadual de Campinas, Faculdade de Engenharia Química<br>Made available in DSpace on 2018-08-20T13:24:06Z (GMT). No. of bitstreams: 1 Moraes_MarleneSilvade_D.pdf: 18744401 bytes, checksum: 214df2eb889315d588ba4e56ffbbc454 (MD5) Previous issue date: 2012<br>Resumo: O deslocamento de polímeros, cereais, minérios, produtos farmacêuticos e outros materiais particulados no interior de tubulações, tendo como fluido transportador o ar, é denominado de transporte pneumático. Esta técnica é comumente dividida em transporte em fase densa, com concentração de partículas acima de 30% em volume e transporte em fase diluída, com concentração inferior a 1%. A fase diluída, que não exige tubulações espessas e é de menor custo de aquisição, operação e manutenção, tem como principais inconvenientes: a) o desgaste da parte inferior do tubo transportador devido à má distribuição das partículas na seção transversal; b) a falta de dados da perda de carga de tê com saída de lado, que tem substituído curvas em unidades catalíticas de petróleo por criar um colchão amortecedor e reduzir o desgaste e c) a escassez de informações da relação entre a distribuição de partículas na seção transversal do duto e a perda de carga. O presente trabalho teve como objetivo geral projetar e montar uma unidade experimental, em escala piloto com duto de 117 mm de diâmetro, de transporte pneumático para estudar, em fase diluída, as perdas de carga no trecho vertical, singularidades e a distribuição de partículas na seção transversal. Visou como objetivos específicos: a) construir as curvas de perda de carga em função da velocidade do ar, tendo como parâmetro, as vazões de pellets de polipropileno; b) determinar o valor do coeficiente K, multiplicador da carga cinética da expressão geral de perda de carga localizada para tê com saída de lado, com três prolongamentos (balisas) distintos de 30, 60 e 90 mm e c) obter a distribuição das partículas na seção transversal do duto vertical. A unidade projetada e montada consistiu basicamente de um ventilador centrífugo, com pás semi abertas de 210 mm de diâmetro, acoplado a um motor de rotação variável de 1 cv, um tubo de Pitot horizontal e um vertical, uma válvula rotativa acionada por motor de rotação variável na base de um silo de alimentação, dutos de acrílico estrudados, com diâmetro interno de 117 mm, um sistema de coleta com nove dutos, de seção quadrada paralelos, para análise da distribuição das partículas na seção transversal dos dutos horizontal e vertical e um ciclone. A perda de carga foi determinada através de tomadas de pressão estática, acopladas a anéis piezométricos, com leitura simultânea de todas as tomadas de pressão em uma série de tubos em "U". A velocidade do ar foi obtida por Pitot e anemômetros. A vazão volumétrica do ar foi calculada pelo método das centróides de áreas iguais, com as medidas dos valores coletados pelo Pitot e anemômetro. As vazões dos sólidos particulados foram quantificadas pelo número de revoluções por unidade de tempo da válvula rotativa, aferida pela técnica da massa por tempo. A distribuição de partículas, na seção transversal dos tubos vertical e horizontal e após o tê com saída de lado, foi verificada por pesagem dos sólidos nos coletores. O trabalho forneceu, para o duto horizontal, curvas da perda de carga em função de cinco velocidades de ar de 13,45; 15,18; 16,90; 18,97 e 21,39 m/s e vazões de polipropileno de 0,08; 0,143 e 0,233 kg/s, com a distribuição de partículas em pontos de relevância para projeto. O tê com saída de lado forneceu um coeficiente K de 1,40; com prolongamento de 30 mm, um K de 1,58; com o de 60 mm, um K de 1,43 e com o de 90 mm, um multiplicador (K) igual a 1,47<br>Abstract: The displacement of polymers, pharmaceutical cereals, ores, pharmaceutical products and other particulate materials in the interior of tubing , having as fluid transporter the air, is called pneumatic transport. This technique is commonly divided in: transport in dense phase, with particles concentration above 30% in volume and transport in diluted phase, with inferior concentration at 1%. The diluted phase, that does not demand thick tubing and is acquired at lesser cost operation and maintenance, has as main inconveniences: a) the consuming of the inferior part of the transporting pipe due to bad distribution of particles in the transversal session; b) the lack of data of the loss of load of T with side exit, that has been replacing curves in catalytic units of oil for creating a cushioning mattress and reducing consuming and c) the scarcity of information of the relation between the particle distribution in the transversal section of the duct and the loading loss. The present work had as general objective to project and build up an experimental unit, in scale pilot with a 117 mm diameter duct, of pneumatic transport to study, in diluted phase, the losses of load in the vertical stretch, the particle singularities and distribution in the transversal section. It aimed as specific objective: a) to construct the curves of loss of load in function of the air speed, having as parameter, the outflows of pellets of polypropylene; b) to determine the value of coefficient K, multiplier of the kinetic load of the general expression of loss of located load for T with side exit, with three distinct prolongations (boundary-makers): 30, 60 and 90 mm and c) to get the distribution of particles in the transversal section of the vertical duct. The projected and built unit consisted basically on a centrifugal fan, with opened half 210 mm diameter shovels, connected to a 1cv changeable rotation engine, a pipe of horizontal Pitot and one vertical line, a rotating valve set in motion by engine of changeable rotation in the base of a feeding silo, extruded acrylic ducts, with internal diameter of 117 mm, a system of collection with nine ducts, square shaped section parallel, for analysis of the distribution of particles in the transversal section of the horizontal and vertical ducts and a cyclone. The loss of load was determined through static pressure heads, connected to piezometric surface rings, with simultaneous reading of all the pressure heads in a series of pipes in "U". The air speed was gotten by Pitot and anemometers. The volumetric outflow of air was calculated by the method of the centroids of equal areas, with the measures of the values collected by the Pitot and anemometer. The outflows of particulates solids were quantified by the number of revolutions per unit of time of the rotating valve, surveyed by the technique of the mass per time. The particle distribution, in the transversal section of the vertical and horizontal pipes and after T with side exit, was verified by weighing solids in the collectors. The work provided to, the horizontal duct, curves of the loss of load in function of five air speeds of 13,45; 15,18; 16,90; 18,97 and 21,39 m/s and polypropylene outflows of 0,08; 0,143 and 0,233 kg/s, with the particle distribution in points of relevance for project. The T with side exit, provided a 1,40 coefficient K; with a 30mm prolongation, a 1,58 K; with 60 mm, a K of 1,43 and with 90 mm, a multiplier (K) equals to 1,47<br>Doutorado<br>Sistemas de Processos Quimicos e Informatica<br>Doutora em Engenharia Quimica
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49

Masse, Lucie. "Anaerobic degradation of fat particles in slaughterhouse wastewater with and without hydrolysis pretreatment." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/9039.

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Lipids represent an important fraction of the particulate organic charge in slaughterhouse wastewater. Anaerobic treatment of slaughterhouse wastewater has been reported to be slowed down or impaired because of high concentrations of suspended solids, particularly fats. However, the fate of lipids during anaerobic digestion has been poorly defined, especially for wastewaters from the meat processing industry. The objectives of this thesis were thus (1) to evaluate the effect of hydrolysis pretreatment on the anaerobic digestion of fat particles in slaughterhouse wastewater; (2) to characterise and quantify neutral fat hydrolysis and long-chain fatty acid (LCFA) oxidation during anaerobic degradation of slaughterhouse wastewater with and without hydrolysis pretreatment; and (3) to determine the effect of particle size on fat hydrolysis. The efficiency of four pretreatments to hydrolyse and reduce the size of pork and beef fat particles during mixing at room temperature was tested: NaOH and three commercial lipases of plant, bacterial and animal origins. The most promising pretreatment was the pancreatic lipase PL-250 that could significantly reduce the initial average particle size (Din) of pork fat by a maximum of 40% after 4 h of mixing at room temperature. Approximately 35% of the neutral fat was hydrolysed after 5.5-h of pretreatment with 250 mg/l of PL-250 in a substrate containing approximately 2000 mg/l of pork fat particles. Most of the free LCFAs released during the hydrolytic pretreatment remained adsorbed on the fat particle surface. The effect of pretreatment with PL-250 on subsequent anaerobic digestion of the substrate was evaluated by feeding control and enzyme pretreated slaughterhouse wastewater containing pork fat particles to anaerobic sequencing batch reactors (ASBRs) operated at 25&deg;C. The main conclusions from the experiment were: (1) Pretreatment with PL-250 only had a small effect on pork fat particle digestion at 25&deg;C, marked by a decrease of about 5% in digestion time to achieve 80% reduction in initial neutral fat and free LCFA concentrations. (2) Anaerobic degradation of pork fat particles is mainly controlled by free LCFA oxidation and, in ASBRs operated at 25&deg;C, near maximum oxidation rate is reached at low free LCFA concentration. Consequently, increasing the initial free LCFA concentration by prehydrolysing the substrate will have limited effect on fat degradation rate. (3) At Din ranging from 60 to 450 mum, pork fat hydrolysis rate in anaerobic reactors is not a function of particle size. The fat particles became more filamentous and plate-like as their size was increased. Bacteria could probably colonise the inside as well as the outside of the particles. Consequently, specific surface area (m2/m3) available for hydrolysis was not significantly increased by decreasing the pork fat particle size. (4) Neutral fat hydrolysis and free LCFA oxidation rates can be adequately modelled using first-order and Monod-type kinetics, respectively. The first-order hydrolysis rate constant averaged 0.63 +/- 0.07 d-1, while the maximum oxidation rate (kmax) and half-saturation concentration (Ks) were estimated at 164 +/- 37 mg free LCFA /l/d and 35 +/- 31 mg free LCFA/1, respectively. (5) Fat hydrolysis rate will be underestimated if based on the increase in soluble compounds with respect to particulate organics. An analytical method that removes bound LCFAs from solids surface must be used to measure lipid hydrolysis.
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Jolly, Simon. "An intra-pulse fast feedback system for a future linear collider." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:3e17d216-7430-4869-9873-4a469fa9c4c5.

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An intra-pulse Interaction Point fast feedback system (IPFB) has been designed for the Next Linear Collider (NLC), to correct relative beam-beam misalignments at the Interaction Point (IP). This system will utilise the large beam-beam kick that results from the beam-beam interaction and apply a rapid correction to the beam misalignment at the IP within a single bunch train. A detailed examination of the IPFB system is given, including a discussion of the necessary electronics, and the results of extensive simulations based on the IPFB concept for fast beam correction are presented. A recovery of the nominal luminosity of the NLC is predicted well within the NLC bunch train of 266 ns. The FONT experiment - Feedback On Nanosecond Timescales - was proposed as a direct test of the IPFB concept and was realised at the NLC Test Accelerator at SLAC. As part of FONT, a novel X-band BPM was designed and tested at the NLCTA. The results of these tests with the NLCTA short and long-pulse beam are presented, demonstrating a linear response to the position of the 180 ns long-pulse beam: measurements show a time constant of ~1.5 ns and a precision of better than 20 microns. A novel BPM processor for use at X-band, making use of the difference-over-sum processing technique, is also presented in detail, with results given for both short and long-pulse beams. The FONT design concepts and modification of the IPFB system for use at the NLCTA are described. The design of a fast charge normalisation circuit, to process the difference and sum signals produced by the BPM processor, forming part of the FONT feedback circuit, is detailed extensively. Bench tests of the feedback electronics demonstrate the effectiveness of the normalisation and feedback stages, for which a signal latency of 11 ns was measured. These bench tests also show the correct operation of the normalisation and feedback principles. Finally, the results of a full beam test of the FONT system are presented, during which a system latency of 70 ns was measured. These rigorous tests establish the soundness of the IPFB scheme and show correction of a mis-steered bunch train within the full NLCTA pulse length of 180 ns.
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