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1
Stamm, Matthew T. "Particle Dynamics and Particle-Cell Interaction in Microfluidic Systems." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/308886.
Full textAbstract:
Particle-laden flow in a microchannel resulting in aggregation of microparticles was investigated to determine the dependence of the cluster growth rate on the following parameters: suspension void fraction, shear strain rate, and channel-height to particle-diameter ratio. The growth rate of an average cluster was found to increase linearly with suspension void fraction, and to obey a power-law relationships with shear strain rate as S^0.9 and channel-height to particle-diameter ratio as (h/d)^-3.5. Ceramic liposomal nanoparticles and silica microparticles were functionalized with antibodies that act as targeting ligands. The bio-functionality and physical integrity of the cerasomes were characterized. Surface functionalization allows cerasomes to deliver drugs with selectivity and specificity that is not possible using standard liposomes. The functionalized particle-target cell binding process was characterized using BT-20 breast cancer cells. Two microfluidic systems were used; one with both species in suspension, the other with cells immobilized inside a microchannel and particle suspension as the mobile phase. Effects of incubation time, particle concentration, and shear strain rate on particle-cell binding were investigated. With both species in suspension, the particle-cell binding process was found to be reasonably well-described by a first-order model. Particle desorption and cellular loss of binding affinity in time were found to be negligible; cell-particle-cell interaction was identified as the limiting mechanism in particle-cell binding. Findings suggest that separation of a bound particle from a cell may be detrimental to cellular binding affinity. Cell-particle-cell interactions were prevented by immobilizing cells inside a microchannel. The initial stage of particle-cell binding was investigated and was again found to be reasonably well-described by a first-order model. For both systems, the time constant was found to be inversely proportional to particle concentration. The second system revealed the time constant to obey a power-law relationship with shear strain rate as τ∝S^.37±.06. Under appropriate scaling, the behavior displayed in both systems is well-described by the same exponential curve. Identification of the appropriate scaling parameters allows for extrapolation and requires only two empirical values. This could provide a major head-start in any dosage optimization studies.
2
Stoica, Cristina. "Particle systems with quasihomogeneous interaction." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ52774.pdf.
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3
Lindemann, Dirk, Kristin Stirnnagel, Daniel Lüftenegger, Annett Stange, Anka Swiersy, Erik Müllers, Juliane Reh, et al. "Analysis of Prototype Foamy Virus particle-host cell interaction with autofluorescent retroviral particles." BMC, 2010. https://tud.qucosa.de/id/qucosa%3A28868.
Full textAbstract:
Background
The foamy virus (FV) replication cycle displays several unique features, which set them apart from orthoretroviruses. First, like other B/D type orthoretroviruses, FV capsids preassemble at the centrosome, but more similar to hepadnaviruses, FV budding is strictly dependent on cognate viral glycoprotein coexpression. Second, the unusually broad host range of FV is thought to be due to use of a very common entry receptor present on host cell plasma membranes, because all cell lines tested in vitro so far are permissive.
Results
In order to take advantage of modern fluorescent microscopy techniques to study FV replication, we have created FV Gag proteins bearing a variety of protein tags and evaluated these for their ability to support various steps of FV replication. Addition of even small N-terminal HA-tags to FV Gag severely impaired FV particle release. For example, release was completely abrogated by an N-terminal autofluorescent protein (AFP) fusion, despite apparently normal intracellular capsid assembly. In contrast, C-terminal Gag-tags had only minor effects on particle assembly, egress and particle morphogenesis. The infectivity of C-terminal capsid-tagged FV vector particles was reduced up to 100-fold in comparison to wild type; however, infectivity was rescued by coexpression of wild type Gag and assembly of mixed particles. Specific dose-dependent binding of fluorescent FV particles to target cells was demonstrated in an Env-dependent manner, but not binding to target cell-extracted- or synthetic- lipids. Screening of target cells of various origins resulted in the identification of two cell lines, a human erythroid precursor- and a zebrafish- cell line, resistant to FV Env-mediated FV- and HIV-vector transduction.
Conclusions
We have established functional, autofluorescent foamy viral particles as a valuable new tool to study FV - host cell interactions using modern fluorescent imaging techniques. Furthermore, we succeeded for the first time in identifying two cell lines resistant to Prototype Foamy Virus Env-mediated gene transfer. Interestingly, both cell lines still displayed FV Env-dependent attachment of fluorescent retroviral particles, implying a post-binding block potentially due to lack of putative FV entry cofactors. These cell lines might ultimately lead to the identification of the currently unknown ubiquitous cellular entry receptor(s) of FVs.
4
Lindemann, Dirk, Kristin Stirnnagel, Daniel Lüftenegger, Annett Stange, Anka Swiersy, Erik Müllers, Juliane Reh, et al. "Analysis of Prototype Foamy Virus particle-host cell interaction with autofluorescent retroviral particles." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-176566.
Full textAbstract:
Background
The foamy virus (FV) replication cycle displays several unique features, which set them apart from orthoretroviruses. First, like other B/D type orthoretroviruses, FV capsids preassemble at the centrosome, but more similar to hepadnaviruses, FV budding is strictly dependent on cognate viral glycoprotein coexpression. Second, the unusually broad host range of FV is thought to be due to use of a very common entry receptor present on host cell plasma membranes, because all cell lines tested in vitro so far are permissive.
Results
In order to take advantage of modern fluorescent microscopy techniques to study FV replication, we have created FV Gag proteins bearing a variety of protein tags and evaluated these for their ability to support various steps of FV replication. Addition of even small N-terminal HA-tags to FV Gag severely impaired FV particle release. For example, release was completely abrogated by an N-terminal autofluorescent protein (AFP) fusion, despite apparently normal intracellular capsid assembly. In contrast, C-terminal Gag-tags had only minor effects on particle assembly, egress and particle morphogenesis. The infectivity of C-terminal capsid-tagged FV vector particles was reduced up to 100-fold in comparison to wild type; however, infectivity was rescued by coexpression of wild type Gag and assembly of mixed particles. Specific dose-dependent binding of fluorescent FV particles to target cells was demonstrated in an Env-dependent manner, but not binding to target cell-extracted- or synthetic- lipids. Screening of target cells of various origins resulted in the identification of two cell lines, a human erythroid precursor- and a zebrafish- cell line, resistant to FV Env-mediated FV- and HIV-vector transduction.
Conclusions
We have established functional, autofluorescent foamy viral particles as a valuable new tool to study FV - host cell interactions using modern fluorescent imaging techniques. Furthermore, we succeeded for the first time in identifying two cell lines resistant to Prototype Foamy Virus Env-mediated gene transfer. Interestingly, both cell lines still displayed FV Env-dependent attachment of fluorescent retroviral particles, implying a post-binding block potentially due to lack of putative FV entry cofactors. These cell lines might ultimately lead to the identification of the currently unknown ubiquitous cellular entry receptor(s) of FVs.
5
Adera, Gashaw Bekele. "Strange particle production via the weak interaction." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2777.
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Thesis (MSc (Physics))--University of Stellenbosch, 2009.In this thesis a general relativistic formalism for neutrino-induced weak production of strange particles is presented. In our formalism it is shown that the differential cross section is constructed as a contraction between a leptonic tensor and a hadronic tensor. The electroweak theory of Glashow, Salam and Weinberg is used to calculate the leptonic tensor exactly. The hadronic current is determined from the newly derived general form of the weak hadronic current which is expressed in terms of eighteen invariant amplitudes that parametrize the hadron vertex. The Born diagram is used to approximate the unknown hadronic vertex and the numerical calculation is made by evaluating the tree diagrams in terms of standard weak form factors and the strong coupling constants in the framework of the Cabibbo theory and SU(3) symmetry. The investigation is made for charged current reactions in terms of the angular distribution of the differential cross section with respect to the outgoing kaon angle and the results are discussed.
6
Paleo, Cageao Paloma. "Fluid-particle interaction in geophysical flows : debris flow." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/27808/.
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Small scale laboratory experiments were conducted to study the dynamic mor- phology and rheological behaviour of fluid-particle mixtures, such as snout-body architecture, levee formation, deposition and particle segregation effects. Debris flows consist of an agitated mixture of rock and sediment saturated with water. They are mobilized under the influence of gravity from hill slopes and channels and can reach long run-out distance and have extremely destructive power. Better understanding of the mechanisms that govern these flows is required to assess and mitigate the hazard of debris flows and similar geophysical flows. Debris flow models are required to accurately deal with evolving behaviours in space and time, to be able to predict flow height, velocity profiles and run-out distances and shapes. The evolution of laboratory debris flows, both dry glass beads and mixtures with water or glycerol, released from behind a lock gate to flow down an inclined flume, was observed through the channel side wall and captured with high speed video and PIV analysis to provide velocity profiles through out the flow depth. Pore pressure and the normal and shear stress at the base of the flow were also measured. Distinct regions were characterized by the non-fluctuating region and the in- termittent granular cloud surrounding the flows. The extent of these regions was shown to be related to flow properties. The separation of these two regions allowed the systematic definition of bulk flow characteristics such as characteristic height and flow front position. Laboratory flows showed variations in morphology and rheological characteristics under the influence of particle size, roughness element diameter, interstitial fluid viscosity and solid volume fraction. Mono-dispersed and poly-dispersed components mixed with liquids without fine sediments, reveal a head and body structure and an appearance similar to the classic anatomy of real debris flows. Unsaturated fronts were observed in mono-dispersed flows, suggesting that particle segregation is not the only mechanism. A numerical simulation of laboratory debris flows using the computer model RAMMS (RApid Mass Movements Simulation) was tested with dry laboratory flows, showing close similarity to calculated mean velocities.
7
Tehranchi, Shiela. "Particule « enfin » en français parlé et ses fonctions en discours et l'interaction." Thesis, Lyon 2, 2011. http://www.theses.fr/2011LYO20059.
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Dans les interactions langagières, l'usage de la particule enfin traduit diverses activités discursives des locuteurs. L'objectif de cette étude est de déterminer la fréquence et les variétés d’occurrence de ce petit mot dans les interactions, selon les situations et les types d’activités dans lesquels les sujets s’engagent, afin d'appréhender au mieux ses caractéristiques interactionnelles et fonctionnelles. Nous mobiliserons à cette fin un cadre d'analyse pluridimensionnel (analyse conversationnelle, discours en interaction). Notre méthode de travail repose sur une analyse des activités verbales des interactions, à partir d'enregistrements audio/ vidéo. Dans cette perspective, nous recensons les éléments récurrents gravitant autour de la particule enfin, les collectons, pour ensuite les convertir en formats. Ces formats nous conduisent à dégager sept valeurs principales de enfin dont chacune se subdivise en plusieurs sous-catégories et qui peuvent parfois avoir une portée contradictoire (conclusive/ introductive, interruptive/progressive, etc.). Dans une approche inter-discursive, enfin montre aussi une dissemblance de modalités d'usage conditionnées par le contexte. Enfin intervient de manière divergente selon que le cadre formel de la même manière que dans un cadre informelIn linguistic interaction, the use of the particle enfin provide various discursive activities of the speakers. In this study, we aim at determining the frequency and the occurrence varieties of this short word in the interaction, according to situations and types of activity in which the subjects commit themselves, in order to understand its interactionnal and functional characteristics. Following this purpose, we decide to adopt a multidimensional analysis framework (Conversation Analysis , Discourse in Interactions ). Our work method relies on the analysis of the participants verbal activities. It is based on audio/ video recordings. Therefore, we take notice of the recurring elements surrounding the particle, we collect these elements to convert them into the formats: seven usages of enfin have been identified, each of them subdivided in several subcategories and which can sometimes have a contradictory range (conclusive/ introductory, discontinuity/continuity, etc). In an inter-discursive approach, enfin betrays a dissimilarity in its use due to the context. As a conclusion, we can say that enfin operates differently depending to the framework nature (formal / informal)
8
Alton, Andrew K. "Evidence for the existence of jets in photon-parton interaction events at center of mass energies from 18 to 28 GEV." Virtual Press, 1995. http://liblink.bsu.edu/uhtbin/catkey/1014850.
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Experiment E683 at Fermi National Accelerator Laboratory (FNAL) in Batavia, Illinois, uses a modular, high-energy sampling calorimeter as the basis of the detector system. This detector provides information on the energy and position of particles that exit a collision of a photon or pion with a target proton. While exiting particles are thought to form what are described as "jets", and several E683 projects involve working with these jets, it has not yet been demonstrated that jets indeed have been detected.The solution proposed here involves demonstrating that E683 data has a statistically significant "jettiness" even in a data sample which has not been biased. Towards this, a data sample was selected based on criteria unrelated to the presumption of jets. Planarity and the Et Flow were chosen as measures of how oblong(jetlike) an event is. The sample was then examined for planarity and Et flow in a number of kinematic ranges and the results demonstrate that over a certain kinematic range, events in our sample are increasingly planar, as we hypothesized.Department of Physics and Astronomy
9
Pan, Kai Ph D. Massachusetts Institute of Technology. "Simulating fluid-solid interaction using smoothed particle hydrodynamics method." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/109642.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 97-102).
The fluid-solid interaction (FSI) is a challenging process for numerical models since it requires accounting for the interactions of deformable materials that are governed by different equations of state. It calls for the modeling of large deformation, geometrical discontinuity, material failure, including crack propagation, and the computation of flow induced loads on evolving fluid-solid interfaces. Using particle methods with no prescribed geometric linkages allows high deformations to be dealt with easily in cases where grid-based methods would introduce difficulties. Smoothed Particle Hydrodynamics (SPH) method is one of the oldest mesh-free methods, and it has gained popularity over the last decades to simulate initially fluids and more recently solids. This dissertation is focused on developing a general numerical modeling framework based on SPH to model the coupled problem, with application to wave impact on floating offshore structures, and the hydraulic fracturing of rocks induced by fluid pressure. An accurate estimate of forces exerted by waves on offshore structures is vital to assess potential risks to structural integrity. The dissertation first explores a weakly compressible SPH method to simulate the wave impact on rigid-body floating structures. Model predictions are validated against two sets of experimental data, namely the dam-break fluid impact on a fixed structure, and the wave induced motion of a floating cube. Following validation, this framework is applied to simulation of the mipact of large waves on an offshore structure. A new numerical technique is proposed for generating multi-modal and multi-directional sea waves with SPH. The waves are generated by moving the side boundaries of the fluid domain according to the sum of Fourier modes, each with its own direction, amplitude and wave frequency. By carefully selecting the amplitudes and the frequencies, the ensemble of wave modes can be chosen to satisfy a real sea wave spectrum. The method is used to simulate an extreme wave event, with generally good agreement between the simulated waves and the recorded real-life data. The second application is the modeling of hydro-fracture initiation and propagation in rocks. A new general SPH numerical coupling method is developed to model the interaction between fluids and solids, which includes non-linear deformation and dynamic fracture initiation and propagation. A Grady-Kipp damage model is employed to model the tensile failure of the solid and a Drucker-Prager plasticity model is used to predict material shear failures. These models are coupled together so that both shear and tensile failures can be simulated within the same scheme. Fluid and solid are treated as a single system for the entire domain, and are computed using the same stress representation within a uniform SPH framework. Two new stress coupling approaches are proposed to maintain the stress continuity at the fluid-solid interface, namely, a continuum approach and stress-boundary-condition approach. A corrected form of the density continuity equation is implemented to handle the density discontinuity of the two phases at the interface. The method is validated against analytic solutions for a hydrostatic problem and for a pressurized borehole in the presence of in-situ stresses. The simulation of hydro-fracture initiation and propagation in the presence of in-situ stresses is also presented. Good results demonstrate that SPH has the potential to accurately simulate the hydraulic-fracturing phenomenon in rocks.
by Kai Pan.
Ph. D.
10
Xu, Zhenghe. "A study of hydrophobic interaction in fine particle coagulation." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39945.
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Rodier, Elisabeth. "Le passage et la rétention de particules colloidales dans un milieu poreux." Vandoeuvre-les-Nancy, INPL, 1993. http://docnum.univ-lorraine.fr/public/INPL_T_1993_RODIER_E.pdf.
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Cette thèse a pour objet l'étude du passage et de la rétention de particules colloïdales au sein d'un milieu poreux. Dans un premier temps, on effectue une étude bibliographique, d'une part sur les caractéristiques de base de l'interface liquide-solide, d'autre part sur les études théoriques et expérimentales réalisées au sujet de la déposition des colloïdes sur une surface collectrice. On s'intéresse ici plus particulièrement au cas où l'on est dans des conditions répulsives. Des expériences de migration de suspensions colloïdales dans un milieu poreux sont ensuite présentées. Auparavant, on a choisi un colloïde et un milieu poreux modèles que l'on caractérise d'un point de vue potentiel de surface par des mesures électrophorétiques et des mesures de courant d'écoulement. Ils sont ensuite mis en contact dans diverses conditions physico-chimiques, d'une part en système fermé en l'absence d'hydrodynamique et d'autre part en système ouvert pour lequel les conditions hydrodynamiques varient. On étudie ainsi l'influence de plusieurs paramètres tels que le débit d'entrée, la force ionique, le pH, le temps, etc. . .
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Oduwole, Olayinka. "Particle interactions in a magnetophoretic system." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:f01cbb33-4dd4-4057-8891-7097e6493bce.
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The continuous flow separation of magnetic particles from a mixture of particles could improve the performance of magnetic bead based assays but the formation of agglomerates limit the separation efficiency. Bead agglomerates are formed as a result of magnetic binding forces while the hydrodynamic fluid environment strongly influences their movement. The ability to predict the interaction between nearby beads will help to determine a threshold separation distance which will be recommended for use when obtaining measurement within a magnetic bead assay for a specified time interval. The introductory part of this thesis explored the development of a two dimensional numerical model in Matlab which predicts the trajectory pattern as well as magnetic induced velocities between a pair of super-paramagnetic beads suspended in water within a uniform field. The movement of a bead pair interacting due to both magnetic and hydrodynamic forces within a magnetophoretic system was recorded using an optical system; the beads' movements were compared with the simulated trajectories and gave a good agreement. The model was used to predict the shortest agglomeration time for a given separation distance which is of practical benefit to users of bead based assays. The concluding part of this thesis expanded the simulation into a three dimensional model to predict the interactions among three super-paramagnetic beads within a magnetophoretic system. In order to determine the height of the magnetic beads, a Huygens-Fresnel model was implemented in Matlab which was compared with off-focused diffracted images of the beads viewed under an optical system. A good comparison was obtained by comparing the simulated three-dimensional trajectories with experimental data.
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Goy, Jérôme. "Mesures des observables tensorielles dans la réaction H(p,d)pion pour des énergies comprises entre 580 et 1300 MeV et stabilité des systèmes borroméens." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10019.
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L'essentiel du travail de cette these se rapporte a la mesure des observables tensorielles de polarisation dans la reaction h(p,d)pion pour des energies comprises entre 580 et 1300 mev. Ces observables sont obtenues en mesurant la polarisation des protons incidents et la polarisation tensorielle des deutons de recul par le polarimetre polder. Les resultats concernant les pouvoirs polarisants et les coefficients de transfert de spin de cette reaction apportent des contraintes nouvelles sur les analyses en ondes partielles et permettent d'acceder a une meilleure comprehension du processus d'absorption du pion pour des energies superieures au pic d'excitation de la resonance delta. La mesure du pouvoir d'analyse vectoriel fait egalement ressortir une structure autour de l'energie centre de masse de 2. 38 gev qui n'est pas reproduite par les analyses en ondes partielles. L'etude detaillee des erreurs systematiques associees aux mesures de polarisation du deuton servira aussi dans l'analyse d'une experience de diffusion elastique electron-deuton qui se monte actuellement au tnjaf (usa) et qui doit permettre d'isoler les facteurs de forme de charge et quadrupolaire du deuton a haut moment de transfert. La seconde partie de la these se refere a un travail effectue sur les systemes borromeens. L'objectif etait de determiner par une methode variationnelle, le jeu des constantes de couplage des potentiels d'interaction qui autorise la stabilite a trois corps sans qu'aucun sous-systeme a deux corps ne puisse etre lie
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Lyberatos, Andreas. "Monte Carlo simulations of interaction effects in fine particle ferromagnets." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38088.
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Javed, Ali. "Investigation on meshfree particle methods for fluid structure interaction problems." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/386297/.
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The research aims to investigate the application of meshfree particle methods for computational modelling of the Fluid Structure Interaction problems with particular emphasis on flow around cylindrical objects and aerofoils. For this purpose, a solution scheme has been developed for solving incompressible, viscous Navier-Stokes (N-S) equations over meshfree particles. Spatial derivatives appearing in N-S equations are dealt with using radial basis functions infinite difference mode (RBF-FD). A comparative study has also been conducted between implicit and explicit in time solution schemes for N-S equations over meshfree nodes. Subsequently, a coupled meshfree and mesh-based solution scheme is proposed, over hybrid fluid grid, for incompressible, viscous flow around stationary as well as moving objects. The aim of this coupled solver is to provide efficiency and flexibility by combining the advantages of both meshfree and mesh-based methods. The coupled solution scheme suggests generating a body conformal meshfree nodal cloud around the solid body in the near field. A static Cartesian grid surrounds the meshfree cloud in the far field. The Meshfree nodes offer flexibility in dealing with solid motion by moving along the solid boundary without necessitating re-meshing. The Cartesian grid, on the other hand, provides improved performance by allowing faster computation owing to the use of efficient mesh based method. Flow equations, in Arbitrary Lagrangian-Eulerian (ALE) formulation, are solved using RBF-FD based scheme over moving meshfree nodes. Conventional infinite differencing is used over static Cartesian grid for flow equations in Eulerian formulation. The coupled solution scheme, on hybrid grid, is employed for closely coupled Fluid Structure Interaction problems. The equations for solid motion are solved using classical Runge-Kutta method. Close coupling between fluid and structural solvers is realized by a sub-iterative prediction-correction algorithm. In order to reduce computational overhead due to sub-iterations, only near field flow (in meshfree zone) is solved during inner iterations. Solution over full fluid domain is sought during outer (time step) iterations only, when the convergence at fluidsolid interface has already been reached. The solution scheme is also applied for high Reynolds number problems. For this purpose, a stabilization term is included in the flow equations to suppress the spurious oscillations. The stabilization term is derived using vimomentum balance equation over control volume and applying higher order Taylor series expansion of momentum flux and fluid forces. In order to avoid ill-conditioning and accuracy problems related to RBF matrices in domains having varying nodal density, use of shape adaptive RBFs are proposed. In that, the shape parameter of the radial basis function is varied according to local nodal density. Moreover, adaptive sizing of influence domain has also been introduced to maintain suitable number of neighbouring particles. These adaptive techniques are found to be useful as they allow much finer nodal distribution at regions of interest enabling accurate capturing of flow gradients and leading to better results. The use of hybrid grid offers flexibility in dealing with moving boundaries. Moreover, in addition to allowing faster computing over Cartesian grid, it also enables using the reduced fluid domain during inner FSI iterations and therefore helps reduce the number of computations in the fluid domain during fluid-solid coupling. The solution scheme was tested for problems relating to flows around static as well as moving cylinders and aerofoils. Flow induced vibrations have been studied with one and two degrees of freedom. The results are found to be in good agreement with previous numerical work and experimental results.
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Dieste, Martina. "Random-vortex-particle methods applied to broadband fan interaction noise." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/192591/.
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The general aim of this thesis is to investigate the suitability of a stochastic method for computational aeroacoustics, the specific objective being to devise a stochastic method to generate synthetic turbulence and combine it with the linearised Euler equations to predict broadband fan interaction noise. In modern turbofan designs broadband fan noise is a dominant source of aircraft noise, the most efficient source being the interaction between upstream turbulence and the stator vanes. The stochastic method developed to generate synthetic turbulence reproduces twodimensional isotropic turbulent flows by filtering a random field. The fillter is expressed in terms of the energy spectrum and controls the spatial properties of the synthetic turbulence. In contrast with previous work, non-Gaussian filters are developed to model more realistic energy spectra such as Liepmann and von Karman spectra. The temporal decorrelation present in turbulent flows is modelled using Langevin Equations. A standard Langevin equation and a second-order Langevin model are derived in details and validated for fan interaction noise. In contrast with classical methods to generate synthetic turbulence, random-vortex-particle methods can be extended to cope with inhomogeneous non-stationary turbulence with little modification from the formulation for homogeneous turbulence. The stochastic method is applied for first time to broadband fan interaction noise. The method is firstly validated for frozen turbulence interacting with an airfoil. The temporal decorrelation is then included in the method to assess the influence of the integral time scale on the radiated acoustic sound field. The method is also combined with an existing wake model to represent the inhomogeneous non-stationary turbulent flow found downstream of a fan. Finally, comparison with existing experimental data for an isolated airfoil in a turbulent jet demonstrates the benefits of using more realistic energy spectra
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Denz, Markus [Verfasser]. "Convergence results for stochastic particle systems with social interaction / Markus Denz." Mainz : Universitätsbibliothek Mainz, 2014. http://d-nb.info/1046966782/34.
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Keisling, John Davis 1969. "Approach to equilibrium for Markovian infinite particle systems with exclusion interaction." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/282248.
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The N-exclusion process is an interacting particle system that generalizes the simple exclusion process by allowing up to N particles at each site. In this work, we define the jump rates to be 1 if any particles are present and 0 if not, and we consider the infinite-volume limit of this process in arbitrary dimension. Assuming symmetry and translation invariance of the underlying Markov chain, we show that the extremal translation-invariant stationary measures are product measures, one for each given "density" of particles. With the further assumption of irreducibility, we generalize a coupling argument of Liggett to show that every translation-invariant measure converges to a mixture of these product measures.
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Bethke, Nastja. "Vortex ring interaction with a particle layer : implications for sediment transport." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611495.
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Qin, Tong. "Numerical Simulations of Interactions of Solid Particles and Deformable Gas Bubbles in Viscous Liquids." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19225.
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Studying the interactions of solid particles and deformable gasbubbles in viscous liquids is very important in many applications,
especially in mining and chemical industries. These interactions
involve liquid-solid-air multiphase flows and an
arbitrary-Lagrangian-Eulerican (ALE) approach is used for the direct
numerical simulations. In the system of rigid particles and
deformable gas bubbles suspended in viscous liquids, the
Navier-Stokes equations coupled with the equations of motion of the
particles and deformable bubbles are solved in a finite-element
framework. A moving, unstructured, triangular mesh tracks the
deformation of the bubble and free surface with adaptive refinement.
In this dissertation, we study four problems. In the first three
problems the flow is assumed to be axisymmetric and two dimensional
(2D) in the fourth problem.
Firstly, we study the interaction between a rising deformable bubble
and a solid wall in highly viscous liquids. The mechanism of the
bubble deformation as it interacts with the wall is described in
terms of two nondimensional groups, namely the Morton number (Mo)
and Bond number (Bo). The film drainage process is also
considered. It is found that three modes of bubble-rigid wall
interaction exist as Bo changes at a moderate Mo.
The first mode prevails at small Bo where the bubble deformation
is small. For this mode, the bubble is
hard to break up and will bounce back and eventually attach
to the rigid wall. In the second mode, the bubble may break up after
it collides with the rigid wall, which is determined by the film
drainage. In the third mode, which prevails at high Bo, the bubble
breaks up due to the bottom surface catches up the top surface
during the interaction.
Secondly, we simulate the interaction between a rigid particle and a
free surface. In order to isolate the effects of viscous drag and
particle inertia, the gravitational force is neglected and the
particle gains its impact velocity by an external accelerating
force. The process of a rigid particle impacting a free surface and
then rebounding is simulated. Simplified theoretical models are
provided to illustrate the relationship between the particle
velocity and the time variation of film thickness between the
particle and free surface. Two film thicknesses are defined. The
first is the thickness achieved when the particle reaches its
highest position. The second is the thickness when the particle
falls to its lowest position. The smaller of these two thicknesses
is termed the minimum film thickness and its variation with the
impact velocity has been determined. We find that the interactions
between the free surface and rigid particle can be divided into
three regimes according to the trend of the first film thickness.
The three regimes are viscous regime, inertial regime and jetting
regime. In viscous regime, the first film thickness decreases as the
impact velocity increases. Then it rises slightly in the inertial
regime because the effect of liquid inertia becomes larger as the
impact velocity increases. Finally, the film thickness decreases
again due to Plateau-Rayleigh instability in the jetting regime.
We also find that the minimum film thickness corresponds to an
impact velocity on the demarcation point between the viscous and
inertial regimes. This fact is caused by the balance of viscous
drag, surface deformation and liquid inertia.
Thirdly, we consider the interaction between a rigid particle and a
deformable bubble. Two typical cases are simulated: (1) Collision of
a rigid particle with a gas bubble in water in the absence of
gravity, and (2) Collision of a buoyancy-driven rising bubble with a
falling particle in highly viscous liquids. We also compare our
simulation results with available experimental data. Good agreement
is obtained for the force on the particle and the shape of the
bubble.
Finally, we investigated the collisions of groups of bubbles and
particles in two dimensions. A preliminary example of the oblique
collision between a single particle and a single bubble is conducted
by giving the particle a constant acceleration. Then, to investigate
the possibility of particles attaching to bubbles, the interactions
between a group of 22 particles and rising bubbles are studied. Due
to the fluid motion, the particles involved in central collisions
with bubbles have higher possibilities to attach to the bubble.
Ph. D.
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Farnoud, Amir Mohammad. "Interaction of polymeric particles with surfactant interfaces." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/4627.
Full textAbstract:
Films of phospholipids and biologically relevant surfactants at the air-water interface provide a well-defined medium to study molecular alignment, phase behavior and interactions of biomembranes and lung surfactant with exogenous materials. Interactions between lung surfactant interfaces and solid particles are of particular interest due to the increased use of nanomaterials in industrial applications and the promise of polymeric particles in pulmonary drug delivery. Understanding such interactions is necessary to avoid potential adverse effects on surfactant function after exposure to particles.
In this thesis, the mechanisms of surfactant inhibition after exposure to submicron particles via different routes were investigated. The effects of carboxyl-modified polystyrene particles (200 nm) on films of dipalmitoyl phosphatidylcholine (DPPC) and Infasurf (calf lung surfactant extract) were studied. Surfactants were exposed to different concentrations of particles in a Langmuir trough with symmetric surface compression and expansion. Surface tension, potential, microstructure and topology were examined to monitor particle effects on surfactant function. Several methods of surfactant exposure to particles were studied: particle injection into the subphase after spreading surfactant monolayers (subphase injection), mixing the particles with the subphase and spreading the surfactant on top (monolayer addition) and particle aerosolization onto surfactant films.
Studies with DPPC monolayers revealed that particle-surfactant interactions are dependent on the particle introduction method. In the subphase injection method, particles did not penetrate the monolayer and no inhibitory effects on surfactant function were observed. However, in the monolayer addition method, particles caused a premature monolayer collapse and hindered surfactant respreading likely by penetrating into the DPPC monolayer. Finally, particle aerosolization on surfactant was performed to mimic the physiologically relevant route of surfactant exposure to particles. Particle aerosolization on DPPC monolayers significantly inhibited surfactant function in the lung-relevant surface tension range. When aerosolized on Infasurf, particles caused inhibitory effects as a function of time suggesting adsorption of surfactant components on particle surfaces as the main mechanism of interaction. This research will enhance understanding of the mechanisms of particle-induced surfactant dysfunction, thereby providing information for the safe design of polymeric particles for drug delivery and for developing guidelines for particles used in occupational settings.
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Olsson, Martin Wexö. "GPU based particle system." Thesis, Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-3761.
Full textAbstract:
GPGPU (General purpose computing on graphics processing unit) is quite common in today's modern computer games when doing heavy simulation calculations like game physics or particle systems. GPU programming is not only used in games but also in scientific research when doing heavy calculations on molecular structures and protein folding etc. The reason why you use the GPU for these kinds of tasks is that you can gain an incredible speedup in performance to your application. Previous research shows that particle systems scale very well to the GPU architecture. When simulating very large particle-system on the GPU it can run up to 79 times faster than the CPU. But for some very small particle systems the CPU proved to be faster. This research aims to compare the difference between the GPU and CPU when it comes to simulating many smaller particle-systems and to see what happen to the performance when the particle-systems become smaller and smaller.
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Salama, I. M. "High temperature particle -to-metal interaction in a simulated gas turbine environment." Thesis, Cranfield University, 2002. http://dspace.lib.cranfield.ac.uk/handle/1826/4610.
Full textAbstract:
An experimental study of the particle-to-metal
interaction during high temperatures and velocity impact
conditions is presented. A novel continuous erosion
testing facility have been used to study the effect of
particle and metal target temperatures as well as impact
particle velocity on the erosion/deposition behaviour of
the stainless steel 321, Nimonic 75, and aluminium target
materials. The study was carried out to provide database
information on the behaviour of those metals under
simulated gas turbine conditions. The erosive particles
used were quartz sand with diameters ranging from 20-30
μm. The erosion characteristics of stainless steel 321
were recorded at target surface temperature of 285°C,
415°C, 570°C and 715°C. The tests were carried out at two
different impingement angles of 30° and 60° and at
particle impact velocities of up to 300m/s. The effects
of particle temperatures of 550°C, 750°C and 950°C on
erosion/deposition rates were examined. The Nimonic 75
target temperatures were slightly modified to give a
similar surface to melting point ratio as the stainless
steel. The Nimonic 75 was tested at 545°C, 685°C, 825°C
and 965°C surface temperatures and at the same particle
velocities and temperature used for the stainless steel
tests. The Nimonic targets were only tested at one impact
angle of 30°. The aluminium targets were only tested at an
impact angle of 60° and particle impact velocity of 100
m/s. The surface temperature was modified to give a ratio
up to 0.8 of the melting point temperature, where the
particle temperature was set to be 350°C, 550°C and 750°C.
It was found that particle and target temperatures,
impact velocity and angle have a significant effect on
the erosion/deposition characteristics. There is a
threshold target and particle temperature for which
deposition begins, and it depends on impact velocity and
angle. The Nimonic 75 targets exhibit a better resistance
to particle deposition over the stainless steel 321 at
high impact velocity and temperatures. Simple models of
the erosion/deposition were established to describe the
conditions of particle deposition on the stainless steel
and Nimonic targets. The aluminium targets show an
increase in the erosion rate as target temperature
reaches certain level, which then drops as target
temperature continues to increase beyond this point.
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Zhang, Hao. "Numerical investigation of particle-fluid interaction system based on discrete element method." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/284833.
Full textAbstract:
This thesis focuses on the numerical investigation of the particle-fluid systems based on the Discrete Element Method (DEM). The whole thesis consists of three parts, in each part we have coupled the DEM with different schemes/solvers on the fluid phase. In the first part, we have coupled DEM with Direct Numerical Simulation (DNS) to study the particle-laden turbulent flow. The effect of collisions on the particle behavior in fully developed turbulent flow in a straight square duct was numerically investigated. Three sizes of particles were considered with diameters equal to 50 µm, 100 µm and 500 µm. Firstly, the particle transportation by turbulent flow was studied in the absence of the gravitational effect. Then, the particle deposition was studied under the effect of the wall-normal gravity force in which the influence of collisions on the particle resuspension rate and the final stage of particle distribution on the duct floor were discussed, respectively. In the second part, we have coupled DEM with Lattice Boltzmann Method (LBM) to study the particle sedimentation in Newtonian laminar flow. A novel combined LBM-IBM-DEM scheme was presented with its application to model the sedimentation of two dimensional circular particles in incompressible Newtonian flows. Case studies of single sphere settling in a cavity, and two particles settling in a channel were carried out, the velocity characteristics of the particle during settling and near the bottom were examined. At last, a numerical example of sedimentation involving 504 particles was finally presented to demonstrate the capability of the combined scheme. Furthermore, a Particulate Immersed Boundary Method (PIBM) for simulating the fluid-particle multiphase flow was presented and assessed in both two and three-dimensional applications. Compared with the conventional IBM, dozens of times speedup in two-dimensional simulation and hundreds of times in three-dimensional simulation can be expected under the same particle and mesh number. Numerical simulations of particle sedimentation in the Newtonian flows were conducted based on a combined LBM - PIBM - DEM showing that the PIBM could capture the feature of the particulate flows in fluid and was indeed a promising scheme for the solution of the fluid-particle interaction problems. In the last part, we have coupled DEM with averaged Navier-Stokes equations (NS) to study the particle transportation and wear process on the pipe wall. A case of pneumatic conveying was utilized to demonstrate the capability of the coupling model. The concrete pumping process was then simulated, where the hydraulic pressure and velocity distribution of the fluid phase were obtained. The frequency of the particles impacting on the bended pipe was monitored, a new time average collision intensity model based on impact force was proposed to investigate the wear process of the elbow. The location of maximum erosive wear damage in elbow was predicted. Furthermore, the influences of slurry velocity, bend orientation and angle of elbow on the puncture point location were discussed.Esta tesis se centra en la investigación numérica de sistemas partícula-líquido basado en la técnica Discrete Element Method (DEM). La tesis consta de tres partes, en cada una de las cuales se ha acoplado el método DEM con diferentes esquemas/solucionadores en la fase fluida. En la primera parte, hemos acoplado los métodos DEM con Direct Numerical Simulation (DNS) para estudiar casos de "particle-laden turbulent flow". Se investigó numéricamente el efecto de las colisiones en el comportamiento de las partículas en el flujo turbulento completamente desarrollado en un conducto cuadrado recto. Tres tamaños de partículas se consideraron con diámetros de 50, 100 y 500 micrometros. En primer lugar, el transporte de partículas por el flujo turbulento se estudió en la ausencia del efecto gravitacional. Entonces, la deposición de partículas se estudió bajo el efecto de la fuerza de gravedad normal a la pared, en el que se discutieron la influencia de la tasa de colisiones en re-suspensión de las partículas y la fase final de la distribución de partículas en el suelo del conducto, respectivamente. En la segunda parte, se ha acoplado los métodos DEM con Lattice Boltzmann Method (LBM) para estudiar la sedimentación de partículas en flujo laminar newtoniano. Un nuevo metodo combinado LBM-IBM-DEM se presentó y ha sido aplicado para modelar la sedimentación de dos partículas circulares bi-dimensionales en flujos Newtonianos incompresibles. Se estudiaron casos de sedimentación en una cavidad de una sola esfera, y sedimentación de dos partículas en un canal, las características de la velocidad de la partícula durante la sedimentación y cerca de la base fueron también examinados. En el último caso, un ejemplo numérico de sedimentación de 504 partículas fue finalmente presentado para demostrar la capacidad del método combinado. Además, se ha presentado un método "Particulate Immersed Boundary Method" (PIBM) para la simulación de flujos multifásicos partícula-fluido y ha sido evaluado en dos y tres dimensiones. En comparación con el método IBM convencional, se puede esperar con el mismo número de partículas y de malla un SpeedUp docenas de veces superior en la simulación bidimensional y cientos de veces en la simulación en tres dimensiones. Se llevaron a cabo simulaciones numéricas de la sedimentación de partículas en los flujos newtonianos basados en una combinación LBM - PIBM - DEM, mostrando que el PIBM podría capturar las características de los flujos de partículas en el líquido y fue en efecto un esquema prometedor para la solución de problemas de interacción fluido-partícula. En la última parte, se ha acoplado el método DEM con las ecuaciones promediadas de Navier-Stokes (NS) para estudiar el transporte de partículas y el proceso de desgaste en la pared de una tubería. Se utilizó un caso de transporte neumático para demostrar la capacidad del modelo acoplado. Entonces se simuló el proceso de bombeo de hormigón, de donde se obtuvo la presión hidráulica y la distribución de la velocidad de la fase fluida. Se monitoreó la frecuencia de impacto de las partículas en la tubería doblada, se propuso un nuevo modelo de intensidad de colisión promediado en tiempo para investigar el proceso de desgaste del codo basado en la fuerza de impacto. Se predijo la ubicación del daño máximo desgaste por erosión en el codo. Además, se examinaron las influencias de la velocidad de pulpa, la orientación y el ángulo de curvatura del codo en la ubicación del punto de punción.
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Ballard, Nicholas. "Anisotropic colloids in soft matter environments : particle synthesis and interaction with interfaces." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/54360/.
Full textAbstract:
We have shown new applications and synthetic routes for polymer colloids in the field of home and personal care products by controlling polymer and/or colloidal architectures. Our initial aim was to develop functional particles that imparted beneficial properties to fibrous substrates and as such our first goal was to develop a method for depositing particles onto such surfaces. Chapter 2 describes the method by which we achieved this goal, namely adding a small amount of a low glass transition polymer to an otherwise non-adhesive polymer to enhance colloidal deposition. Following on from this work we looked into ways in which to impart desirable characteristics from the particles onto fibres. In Chapter 3 we describe how the use of a hydrazide functional monomer in polymer gels can provide a continuing slow release of fragrance molecules that reacts to the environment it is held in such that if the local fragrance concentration is low then more is released. In Chapter 4 we describe the synthesis of highly porous particles with controlled pore sizes and the use of such particles in oil absorption for applications in water-free cleaning systems. The particles are capable of carrying many times their own weight in oil and are shown to be reusable. In Chapter 5 we describe a computational model that predicts the ability of a particle to stabilize emulsions. The model is highly adaptable and can be used to predict the surface activity of almost any particle morphology. Chapter 6 builds on this work and described the synthesis of highly anisotropic polymer particles by templating preexisting structures and explains their surface activity, or lack thereof.
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Early, Juliana Marie. "Investigation of orthogonal blade-vortex interaction using a particle image velocimetry technique." Thesis, University of Glasgow, 2006. http://theses.gla.ac.uk/619/.
Full textAbstract:
The complex flowfield which is associated with a rotor wake gives rise to the multitude of aerodynamic interactions that may occur during rotorcraft operation. These interactions may give rise to undesirable noise and lead to an unacceptable performance degradation, and as such the investigation of the fundamental mechanics of such interactions, that which occurs between the tail rotor and the trailing tip vortices shed from the main rotor assembly, is the focus of the current investigation. As the purpose of the tail rotor is to provide balance for the torque of the main rotor, these types of interaction will adversely impact on the overall rotorcraft performance. The basis of the present thesis has been an experimental investigation of the orthogonal BVI, in which the axis of the interacting vortex (in the plane of the vortex core axial flow) is nominally orthogonal to the interacting blade chordline, representing the tail rotor interaction. The tests have been conducted using a specifically designed facility at the University of Glasgow, with the flow interrogated using a Particle Image Velocimetry (PVI) technique. The PVI method allows global flowfield information to be obtained pertaining to the nature of the interaction. The methodology was benchmarked against synthetic flowfields, and with the accuracy of the flowfield measurements improved dramatically with the implementation of the Forward/Reverse Tile Test (FRTT), which improved the accuracy in the flowfields to 3% in two-dimensional interrigation, and 5% in three-dimensional. The interrogation of the flowfield around the representative tail rotor blade demonstrated that the characteristics imparted vortex due to the BVI event could be attributed to the manner in which the axial flow component of the vortex was affected by the interaction. The results for the isolated flow conditions agreed well with those from previous measurements of the vortical structure, and the post interaction structure clearly indicated distinct differences determined by the direction of the axial flow relative to the blade chordline. Initial testing indicated that the thickness ratio had a marked effect on the progression of the OBVI, and for a suitably high thickness ratio, there was little evidence to suggest that the vortex core axial flow is 'cut' by the interacting body in the manner observed for the lower thickness ratios. For lower thickness ratios, as the vortex core is blocked by the interacting blade surface, the retardation of the axial component on the blade lower surface leads to rapid redistribution of the fluid into the surrounding flow, and the corresponding enlargement and distortion to the vortex tangential velocity components promoted by the radial outflow. On the upper blade side, regions of negative axial flow velocity indicate the presence of some fluid passing down through the core towards the surface of the blade, which are accompanied by a split divergence pattern around the vortex core. The effects immediately behind the trailing edge continue to be of interest due to the manner in which the vortex might be regenerated after the interaction and before any subsequent interactions with following blades. A relative lack of distortion within the out-of-plane component indicates that a rapid regeneration of the axial flow component may occur once the vortex has passed over the trailing edge. The use of passive control techniques in reduction of the effects associated with the orthoganal BVI have also been addressed, considering the effect of a counter-rotating vortex pair on the progression of the interaction. Although the inclusion a notch in the leading edge and outboard sweep on the rotor blade producing the representative trailing tip vortex did produce a well defined inboard vortex structure, there is evidence to suggest that this structure is ingested into the outboard tip vortex, as there is no significant modification to the progression of the OBVI.
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Schimmoller, Brian Keith. "A bubble-particle interaction model for flotation combining hydrodynamic and surface forces." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09192009-040332/.
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Bigongiari, Alessandra. "High Intensity Laser-Plasma Grating Interaction : surface wave excitation and particle acceleration." Palaiseau, Ecole polytechnique, 2012. http://pastel.archives-ouvertes.fr/docs/00/75/83/55/PDF/alebigo_TESI_rapporteurs.pdf.
Full textAbstract:
Les ondes de surface ont été observées pour la première fois par Wood en 1902 qui note des anomalies dans le spectre de diffraction d'une lumière continue sur un réseau métallique. Pour certaines longueurs d'onde, le spectre diffracté présente des lignes noires que Fano interprète quelques années plus tard (1941) comme dues à l'excitation d'ondes de surface. De façon analogue, on peut exciter par laser de façon résonante une onde plasma de surface à la surface d'un plasma sur-dense créé par interaction laser-solide, si les conditions d'excitation de l'onde sont satisfaites. L'onde de surface se propage le long de l'interface plasma-vide et se caractérise par un champ électrique résonant haute-fréquence localisé. Dans ce travail, la dynamique du plasma et les champs associés à l'excitation par laser de l'onde de surface sont décrits numériquement avec des simulations bidimensionnelles Particule-In-Cell dans lesquelles la surface du plasma est initialement pré-structurée de sorte à satisfaire les conditions d'excitation de l'onde de surface. L'intensité laser a été variée entre Iλ2 =10^15 et 10^20 μm^2/Wcm^2 afin d'étudier la transition entre un régime d'excitation non-relativiste et relativiste. Les simulations dans lesquelles l'onde de surface est excitée sont comparées à celles où elle ne l'est pas et le couplage du laser avec la cible est analysé. Pour différents paramètres du laser et de la cible, nous avons considéré les quatre aspects suivants de l'interaction laser plasma : i) l'absorption laser et le champ électrique à la surface du plasma, ii) le champ magnétique quasi-statique généré, iii) le chauffage électronique et iiii) l'accélération des ions. Nous avons démontré la possibilité d'exciter une onde plasma de surface pour une large gamme d'intensité laser. Lorsque l'onde de surface est excitée, la composante perpendiculaire à la surface du plasma du champ électrique est amplifiée par rapport au champ laser sur la surface plasma-vide d'un facteur allant de 3. 2 à 7. 2 selon les cas. L'absorption augmente également fortement de 27% lorsque l'onde de surface n'est pas excitée à 73% lorsqu'elle l'est pour Iλ2=10^19 μm^2/Wcm^2 par exemple. Cette étude nous a permis de définir les conditions optimales pour lesquelles le couplage entre le laser et l'onde de surface est le plus efficace. Elles correspondent au régime d'intensité laser relativiste dans lequel le mécanisme d'absorption principale est le " vacuum heating " : les particules gagnent de l'énergie en oscillant dans le champ électrique perpendiculaire à la cible. En présence de l'onde de surface, cette oscillation est fortement augmentée par la présence du champ localisé de l'onde de surface plus intense que le celui du laser. La possibilité de créer des champs magnétiques quasi-statiques auto-générés en présence d'une onde de surface a de plus été étudiée analytiquement et les résultats ont été comparés à ceux des simulations. Les structures de champ obtenues suggèrent que l'intensité du champ magnétique généré induit un confinement partiel des particules sur la surface de la cible lorsque l'onde de surface est excitée. Enfin, nous avons observé un effet induit par l'excitation de l'onde de surface encore plus fort dans des cibles minces dans lesquelles les électrons peuvent circuler d'un bord à l'autre de la cible et interagir plusieurs fois avec le champ de l'onde. Le champ de charge d'espace ainsi créé au cours de l'interaction induit une augmentation importante de l'énergie des ions émis sur les deux faces de la cible mince. L'ensemble de ce travail nous a permis de montrer que l'excitation d'une onde de surface par interaction laser-plasma structuré est un mécanisme physique prometteur pour augmenter l'énergie des particules émises. C'est un point particulièrement intéressant pour les applications liées à la production de protons énergétiques telles que la thérapie hadronique ou à celle d'électrons de hautes énergies indispensables dans le processus de fusion inertiel dans lequel le schéma de l'allumeur rapide est utiliséeSurface waves in solids were first observed by Wood in 1902 as an anomaly in the diffraction of a continuous light source from a metal grating: the diffracted spectrum presented dark lines corresponding to certain wavelengths, which were later explained (Fano, 1941) in terms of the excitation of a surface wave sustained by the grating. Similarly to the metal grating case, a surface plasma wave (SPW) can be resonantly excited by a laser pulse at the surface of a laser-produced over-dense plasma, if the correct matching conditions are provided. SPWs propagate along the plasma-vacuum interface and are characterized by a localized, high frequency, resonant electric field. In the present work we describe numerically the dynamics of the plasma and the field distribution associated to SPW excitation, using two-dimensional particle-in-cell (PIC) simulations, where the plasma surface is initially pre-formed so that the SPW excitation conditions are fulfilled. We examine the surface wave excitation for a large range of laser intensities (Iλ2 =10^15-10^20 μm^2/Wcm^2) in order to study the transition from the non-relativistic to the relativistic regime. The simulations in which the wave is resonantly excited are compared to cases in which the resonant conditions are not provided and the coupling of the laser with the target is analyzed. We have considered the following aspects of the laser-plasma interaction, for different laser and target parameters: i) the laser absorption and the electric field at the surface ii) the generation of a quasi-static magnetic field iii) the electron heating and iiii) the ion acceleration. The possibility to excite a surface plasma wave on a structured target for a large range of laser energies has been demonstrated. In the cases where the surface wave is excited the electric field component normal to the target is amplified at the surface by a factor ranging from 3. 2 to 7. 2 with respect to the laser field. The absorption is also increased,for example it raises from 27% when the SPW is not excited up to 73% for Iλ^2=10^9 μm^2/Wcm^2. We have defined the optimal conditions for efficient coupling which increase laser absorption, that correspond to the relativistic laser intensities (Iλ^2>10^19 μm^2/Wcm^2). In this regime the main absorption mechanism is vacuum heating, associated to particles oscillating in the field perpendicular to the target, which is enhanced by the stronger, localized field of the SPW. The generation of a quasi-static magnetic field has been studied analytically and compared to the result of PIC simulations. The different field structure in presence of a SPW and for a flat target suggests that the enhanced field strength has caused partial confinement of particles at the target surface when SPW is present. The effects of the surface wave are more pronounced in thin laminar targets where electrons recirculate into the target interacting several times with the wave. Efficient electron heating increases the energy of the ions which are accelerated at both the irradiated and not irradiated target surface by the hot electrons space charge field. For the thinnest target (3. 5 μm) the ion cut-off energy is about 14 Mev, approximately twice the value obtained when the SPW is not excited
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Calabretta, Jacob S. "A Three Dimensional Vortex Particle-Panel Code For Modeling Propeller-Airframe Interaction." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/336.
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Analysis of the aerodynamic effects of a propeller flowfield on bodies downstream of the propeller is a complex task. These interaction effects can have serious repercussions for many aspects of the vehicle, including drag changes resulting in larger power requirements, stability changes resulting in adjustments to stabilizer sizing, and lift changes requiring wing planform adjustments.
Historically it has been difficult to accurately account for these effects at any stage during the design process. More recently methods using Euler solvers have been developed that capture interference effects well, although they don't provide an ideal tool for early stages of aircraft design, due to computational cost and the time and expense of setting up complex volume grids. This research proposes a method to fill the void of an interference model useful to the aircraft conceptual and preliminary designer.
The proposed method combines a flexible and adaptable tool already familiar to the conceptual designer in the aerodynamic panel code, with a pseudo-steady slipstream model wherein rotational effects are discretized onto vortex particle point elements. The method maintains a freedom from volume grids that are so often necessary in the existing interference models. In addition to the lack of a volume grid, the relative computational simplicity allows the aircraft designer the freedom to rapidly test radically different configurations, including more unconventional designs like the channel wing, thereby providing a much broader design space than otherwise possible.
Throughout the course of the research, verification and validation studies were conducted to ensure the most accurate model possible was being applied. Once the vortex particle scheme had been verified, and the ability to model an actuator disk with vortex particles had been validated, the overall product was compared against propeller-wing wind tunnel results conducted specifically as benchmarks for numerical methods.
The method discussed in this work provides a glimpse into the possibility of pseudo-steady interference modeling using vortex particles. A great groundwork has been laid that already provides reasonable results, and many areas of interest have been discovered where future work could improve the method further. The current state of the method is demonstrated through simulations of several configurations including a wing and nacelle and a channel wing.
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Chandramohan, Rajiv. "Measurement of particle interaction properties for the incorporation into Discrete Element Methods." Thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/5565.
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Includes bibliographical references (leaves 213-215).The principle aim of this research project is to measure parameters which are pertinent for numerical simulations in discontinuous media. One such numerical tool, the Discrete Element Method (DEM), is a promising technique for predicting the dynamics of charge motion with in a mill. Particle interactions in DEM are calculated by contact force and force displacement laws at each particle contact. These contact events are characterized by parameters that are often fitted or estimated due to the lack of accurate experimental measurements. The aim of this project is to experimentally measure the necessary interaction properties required for the DEM analysis and to test the DEM models against the measured experimental results. An in-flight binary collisions drop tester is constructed to measure the material interaction properties of two spheres. The collision event is captured photographically and pre- and post- relative velocities are measured. The binary collisions of the particles are carefully controlled by relay timing circuits and they are captured on digitized images using a SLR digital camera. The particles are illuminated using digital strobes controlled by a signal generator. The heights of the colliding particles are adjusted to vary the drop velocities prior to collision. The measured relative velocities arc applied in rigid body theory of binary impact to extract the required material interaction properties. The parameters measured from the binary collision include coefficients of tangential and normal restitution and friction. The analysis presented here draws on the work of Maw et al and Foerster et al, which is an extension of the Hertz theory of impact to the oblique impact of the elastic bodies with circular contacts. Initial numerical simulations using the viscous damping model is performed in Particle Flow Code (PFC) and a comparison between experimental and numerical results presented.
31
Jones, Peter Michael. "A silicon array for conversion electron detection." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309867.
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Maity, Tuhin Subhra Weeks Kevin. "Temporal order of interaction directs native assembly of the mammalian signal recognition particle." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2007. http://dc.lib.unc.edu/u?/etd,778.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2007.Title from electronic title page (viewed Dec. 18, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry." Discipline: Chemistry; Department/School: Chemistry.
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Klotzky, Jens [Verfasser], and Christian [Gutachter] Klingenberg. "Well-posedness of a fluid-particle interaction model / Jens Klotzky ; Gutachter: Christian Klingenberg." Würzburg : Universität Würzburg, 2018. http://d-nb.info/1170061613/34.
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Chen, Qiang. "Development of a full particle PIC method for simulating nonlinear wave-structure interaction." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760902.
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During the past few decades, Computational Fluid Dynamics (CFD) modelling hasbecome very popular in the coastal and offshore engineering community. Both Eulerianand Lagrangian methods have achieved great successes; typical examples are thegrid-based OpenFOAM® model and the meshless Smoothed Particle Hydrodynamics(SPH) method based model (e.g. SPHysics). While the former tends to be moreefficient and has advantages in enforcing incompressibility and boundary conditionsvia use of a grid, the latter is more suitable for handling large free-surface deformationsusing particles. In an attempt to combine the advantages of both methods, theParticle-In-Cell (PIC) method was devised through a combined use of particles andgrid. However, so far this hybrid method has not been very well exploited for use inthe coastal and offshore engineering field, where modelling complex wave-structureinteraction with computational efficiency still remains an important challenge. This thesis develops a novel "full particle" PIC based numerical model that solves theincompressible Newtonian Navier-Stokes equations for single-phase free-surface flowswith an emphasis on fluid-structure interaction. The use of the phrase "full particle"here indicates that all of the fluid properties, such as the mass and momentum,are assigned only to the particles, rather than being split between the particles andgrid as is the case in "classical" PIC. The novelty of the model lies in the fact thatthe particles are employed to solve the nonlinear advection term and track the fluidconguration (including the free surface), while the underlying grid is solely usedfor computational convenience for solving the non-advection terms. In addition, atailored Distributed Lagrange Multiplier method and a Cartesian cut cell based two-waystrong coupling algorithm are incorporated for fluid-structure interaction. Themodel is developed in both two and three spatial dimensions, and the 3D modelis parallelised using the Message Passing Interface (MPI) approach. The model isvalidated using benchmark tests in the coastal and offshore engineering field withsimulating nonlinear wave-structure interaction being the principal interest. It isshown that the present "full particle" PIC model is flexible, efficient (in terms ofCPU cost) and accurate when modelling complex free-surface flows and the violentinteraction of such flows with (surface-piercing) structures of arbitrary shape anddegree of freedom. With new innovations, the model has great potential to become ahigh quality numerical tool for use in coastal and offshore engineering applications.
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Harvey, David Richard. "Measuring the self-interaction cross-section of dark matter with astronomical particle colliders." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/10447.
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The dark matter paradigm has been a great source of speculation in both the 20th and 21st Centuries. Since its proposed existence in 1933, the mounting evidence has led to this theoretical particle becoming one of the greatest mysteries of modern physics. However, despite its dominant presence in the Universe, little is known about its nature and how it behaves. In this thesis I critically analyse one particular property of dark matter: the self-coupling. The self-interacting dark matter paradigm hypothesises that dark matter is not collisionless as assumed in most cosmological simulations, and in-fact has some probability that it will scatter off itself. Such a self-coupling will resolve many discrepancies that exist between observations and theory, particularly on small, non-linear scales. Moreover, any detection of a self-interaction cross-section will place considerable limitations on the acceptable particle physics models of dark matter and hence has grown to become an important question. In this thesis I develop and implement a method to constrain the self-interaction cross-section of dark matter that exploits continually accreting and merging groups of galaxies as they fall into galaxy clusters. Utilising the ubiquitous nature of accreting substructure, I measure the offsets between dark matter and baryonic gas as they become separated due to their differing interaction properties. Studying this effect over a sample of events, I will be able to make the first ever statistical estimate of the cross-section of dark matter, while averaging over many different unknown merging scenarios. I begin my thesis by deriving an analytical description of sub-halo in-fall, allowing me to constrain dark matter self-interaction models directly from observations. In this study, I find that current archival data should be able to detect a difference in the dynamical behaviour of dark matter and standard model particles at 6σ, and measure the total interaction cross-section σDM/m with 68% confidence limits of ±1 cm2g-1. Having constructed a new method to derive constraints on the cross-section of dark matter I carry out a study into the potential systematics that may affect a measurement. I determine the accuracy of weak gravitational lensing, which is the distortion of light due to intervening mass, as a tool to estimate the positions of substructure in galaxy clusters. I find that the public Lenstool software can measure the position of individual 1:5 x 1013Mʘ peaks with ~ 0:3" systematic bias, as long as they are at least ~ 30" from the cluster centre. Finally, I develop a pipeline that can analyse a sample of inhomogeneous observations from The Hubble Space Telescope and the Chandra X-ray Observatory. By measuring the positions of dark matter, gas and galaxies for 68 individual merging events, from a total of 28 galaxy clusters, I detect a 7:4σ offset between gas and an unobserved dark mass. I make the first ever measurement of cross-section of dark matter from a sample of clusters finding σDM < 0:50cm2/g [95% CL], the best constraints to date. In addition to this I find that the brightest group galaxy in-fact tends to lead the dark matter halo during merging events. Although evidence for the existence of interacting dark matter, I conclude that the astrophysics of the BCG is complicated, and that this apparent directional bias should be considered in all galaxy cluster analyses. Moreover, I show that this technique is easily extendable for future surveys that have larger samples of galaxy clusters, with constraints of σDM < 0:001cm2/g potentially attainable.
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Payan, Oldouz. "Detailed modelling of fluid-particle interaction in sediment transport with applications in rivers." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/10489/.
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Flood risks, channel and bank erosions are directly related to the sediment transport discharge, its understanding and control. Moreover the prediction of sediment entrainment, transport and deposition, predicting the river bed-form (e.g. ripples and dunes) changes is an important research field due to its substantial practical worth. The prediction process of sediment transport over bed-forms in open-channel flow is strongly affected by the complex turbulence structures. Witnessing effects of small and large turbulent scales on particles while considering inter-particle collisions remain challengeable. On the other hand it is clear that, not only the movement of sediments at river beds is influenced by turbulent flows the but also on most cases the solid particles have a direct impact on the flow regime. One of the tasks remain in this regard is to measure the aforementioned effects, on a very small scales where the momentum exchange at the particulate scales occurs. In order to study such challenges in a more faithful approach, four-way coupling through open source code of CFD-DEM (a coupling code between Computational Fluid dynamics (CFD) and Discrete Element Method (DEM)), is demonstrated in this research for bed-load sediment transport on a particulate scale. Understanding the fluid-particle interaction for application in rivers where the presence of micro and macro turbulent structures in the fluid plays a significant role, have been the focus of this study. Furthermore this thesis is furnished by conducting numerical and experimental investigations to obtain better understanding of turbulent flows in geometries similar to river bed-forms, e.g. dune-form and bar-form. This research demonstrates that complexity of particle-laden turbulent flows is a result of particle-fluid, fluid-particle, particle-particle and particle-structures that takes place close to bed. Turbulence and near-bed flow velocity along with its irregular risings and fallings have a direct impact on the sediment particles motion. By utilising Large Eddy Simulation (LES) turbulent modelling, turbulent scales are captured. Moreover inter-particle collision of sediments has been highlighted by the means of four-way coupling. Consequently the effect of fluid on the particles and vice versa is demonstrated. It is revealed that the presence of sediment particles in turbulent flows affect the fluid motion along with its accompanying turbulent activities. Particles are lifted as a result of applied forces from eddies and significant influence is therefore captured on the moving particles that are in the vicinity of eddies. The effects that sediments apply on the turbulent structures in the flow have also been captured due to momentum exchange between particle and fluid phase. This has been shown by the means of fluctuation variations at the location of interacting particles.
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Doche, Antoine. "Particle acceleration with beam driven wakefield." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX023/document.
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Les accélérateurs par onde de sillage plasma produites par faisceaux de particules (PWFA) ou par faisceaux laser (LWFA) appartiennent à un nouveau type d’accélérateurs de particules particulièrement prometteur. Ils permettent d’exploiter des champs accélérateurs jusqu’à cent Gigaélectronvolt par mètre alors que les dispositifs conventionnels se limitent à cent Megaélectronvolt par mètre. Dans le schéma d’accélération par onde de sillage plasma, ou par onde de sillage laser, un faisceau de particules ou une impulsion laser se propage dans un plasma et créé une structure accélératrice dans son sillage : c’est une onde de densité électronique à laquelle sont associés des champs électromagnétiques dans le plasma. L’un des principaux résultats de cette thèse a été la démonstration de l’accélération par onde de sillage plasma d’un paquet distinct de positrons. Dans le schéma utilisé, un plasma de Lithium était créé dans un four, et une onde plasma était excitée par un premier paquet de positrons (le drive ou faisceau excitateur) et l’énergie était extraite par un second faisceau (le trailing ou faisceau témoin). Un champ accélérateur de 1,36 GeV/m a ainsi été obtenu durant l’expérience, pour une charge accélérée typique de 40 pC. Nous montrons également ici la possibilité d’utiliser différents régimes d’accélération qui semblent très prometteurs. Par ailleurs, l’accélération de particule par sillage laser permet quant à elle, en partant d’une impulsion laser femtoseconde de produire un faisceau d’électron quasi-monoénergétique d’énergie typique de l’ordre de 200 MeV. Nous présentons les résultats d’une campagne expérimentale d’association de ce schéma d’accélération par sillage laser avec un schéma d’accélération par sillage plasma. Au cours de cette expérience un faisceau d’électrons créé par laser est refocalisé lors d’une interaction dans un second plasma. Une étude des phénomènes associés à cette plateforme hybride LWFA-PWFA est également présentée. Enfin, le schéma hybride LWFA-PWFA est prometteur pour optimiser l’émission de rayonnement X par les électrons du faisceau de particule crée dans l’étage LWFA de la plateforme. Nous présentons dans un dernier temps la première réalisation expérimentale d’un tel schéma et ses résultats prometteursPlasma wakefield accelerators (PWFA) or laser wakefield accelerators (LWFA) are new technologies of particle accelerators that are particularly promising, as they can provide accelerating fields of hundreds of Gigaelectronvolts per meter while conventional facilities are limited to hundreds of Megaelectronvolts per meter. In the Plasma Wakefield Acceleration scheme (PWFA) and the Laser Wakefield Acceleration scheme (LWFA), a bunch of particles or a laser pulse propagates in a gas, creating an accelerating structure in its wake: an electron density wake associated to electromagnetic fields in the plasma. The main achievement of this thesis is the very first demonstration and experimental study in 2016 of the Plasma Wakefield Acceleration of a distinct positron bunch. In the scheme considered in the experiment, a lithium plasma was created in an oven, and a plasma density wave was excited inside it by a first bunch of positrons (the drive bunch) while the energy deposited in the plasma was extracted by a second bunch (the trailing bunch). An accelerating field of 1.36 GeV/m was reached during the experiment, for a typical accelerated charge of 40 pC. In the present manuscript is also reported the feasibility of several regimes of acceleration, which opens promising prospects for plasma wakefield accelerator staging and future colliders. Furthermore, this thesis also reports the progresses made regarding a new scheme: the use of a LWFA-produced electron beam to drive plasma waves in a gas jet. In this second experimental study, an electron beam created by laser-plasma interaction is refocused by particle bunch-plasma interaction in a second gas jet. A study of the physical phenomena associated to this hybrid LWFA-PWFA platform is reported. Last, the hybrid LWFA-PWFA scheme is also promising in order to enhance the X-ray emission by the LWFA electron beam produced in the first stage of the platform. In the last chapter of this thesis is reported the first experimental realization of this last scheme, and its promising results are discussed
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Hosein, Falahaty. "Enhanced fully-Lagrangian particle methods for non-linear interaction between incompressible fluid and structure." Kyoto University, 2018. http://hdl.handle.net/2433/235070.
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Arai, Nozomi. "Self-Assembly of Colloidal Particles with Controlled Interaction Forces." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263693.
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Sun, Guangyuan. "Stochastic Simulation of Lagrangian Particle Transport in Turbulent Flows." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5838.
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This dissertation presents the development and validation of the One Dimensional Turbulence (ODT) multiphase model in the Lagrangian reference frame. ODT is a stochastic model that captures the full range of length and time scales and provides statistical information on fine-scale turbulent-particle mixing and transport at low computational cost. The flow evolution is governed by a deterministic solution of the viscous processes and a stochastic representation of advection through stochastic domain mapping processes. The three algorithms for Lagrangian particle transport are presented within the context of the ODT approach. The Type-I and -C models consider the particle-eddy interaction as instantaneous and continuous change of the particle position and velocity, respectively. The Type-IC model combines the features of the Type-I and -C models. The models are applied to the multiphase flows in the homogeneous decaying turbulence and turbulent round jet. Particle dispersion, dispersion coefficients, and velocity statistics are predicted and compared with experimental data. The models accurately reproduces the experimental data sets and capture particle inertial effects and trajectory crossing effect. A new adjustable particle parameter is introduced into the ODT model, and sensitivity analysis is performed to facilitate parameter estimation and selection. A novel algorithm of the two-way momentum coupling between the particle and carrier phases is developed in the ODT multiphase model. Momentum exchange between the phases is accounted for through particle source terms in the viscous diffusion. The source term is implemented in eddy events through a new kernel transformation and an iterative procedure is required for eddy selection. This model is applied to a particle-laden turbulent jet flow, and simulation results are compared with experimental measurements. The effect of particle addition on the velocities of the gas phase is investigated. The development of particle velocity and particle number distribution are illustrated. The simulation results indicate that the model qualitatively captures the turbulent modulation with the presence of difference particle classes with different solid loadings. The model is then extended to simulate temperature evolution of the particles in a nonisothermal hot jet, in which heat transfer between the particles and gas is considered. The flow is bounded by a wall on the one side of the domain. The simulations are performed over a range of particle inertia and thermal relaxation time scales and different initial particle locations. The present study investigates the post-blast-phase mixing between the particles, the environment that is intended to heat them up, and the ambient environment that dilutes the jet flow. The results indicate that the model can qualitatively predict the important particle statistics in jet flame.
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Cross, Andrew John. "The electron-phonon interaction in GaAs/(AlGa)As quantum wells." Thesis, University of Nottingham, 2001. http://eprints.nottingham.ac.uk/14316/.
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This thesis presents a study of the electron-phonon interaction in two dimensional electron gases (2DEGs), by measuring of the acoustic phonon emission from a sequence of n-type doped GaAs/(AlGa)As quantum wells. Previous studies of emISSIon from 2DEGs confined in GaAs heterojunctions (Chin et al., 1984) have shown a surprising absence of longitudinal acoustic (LA) mode phonon emission, in contrast with theoretical studies (Vass, 1987) which predict that deformation potential coupled LA mode emission should dominate the energy relaxation processes. This may be attributed to the finite width of the quasi-2D sheet, which imposes a restriction on the maximum emitted phonon wavevector component perpendicular to the 2DEG, leading to a suppression of the emission (the "1Iao cutoff') at smaller phonon wavevectors than predicted by the earlier theory. By using the quantum well width w as a means of modulating the thickness of the 2DEG, the dependence of the 1Iao cutoff on the phonon emission can be directly measured. In the present work, significant LA phonon emission from the quantum well samples is observed. To complement the experimental measurements, the theory of emission from a 2DEG has been modelled in detail using computer simulation techniques. Calculations of the electron-phonon interaction, including matrix element anisotropy and dynamic screening, as well as phonon focusing effects, can be combined to produce accurate predictions of the experimentally detected phonon emission energy spectra.
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Crowe, Adam. "Inclined Negatively Buoyant Jets and Boundary Interaction." Thesis, University of Canterbury. Civil and Natural Resources Engineering, 2013. http://hdl.handle.net/10092/7895.
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Inclined negatively buoyant jets are commonly used to dispose brine effluent produced by desalination plants. Desalination and associated research has expanded in recent years due to the continued depletion and degradation of natural potable water sources. Desalination plants are the preferred option for meeting water demand deficits in many countries around the world. Inclined negatively buoyant jets are produced when the brine is discharged at an upward inclined angle via an offshore pipeline and diffuser system. Previous experimental studies have focused on the rapid mixing and dilution achieved by these discharges, as well as geometric parameters. Dilution measurements between these experimental studies vary significantly, which is possibly due to variations in the location of a lower boundary on observed flow behaviour. In the present study, velocity field information is experimentally measured for inclined negatively buoyant jets and compared to integral model predictions. Experiments are conducted with and without a lower boundary influencing observed flow behaviour, thus allowing the effects of a lower boundary to be determined.
The particle tracking velocimetry experimental technique is employed to measure near field velocities of these discharges. Firstly, discharges with source angles between 15\degree and 75\degree are investigated without boundary influence in stationary ambient conditions. The source was a minimum of 655 mm above the bottom of the experimental tank to ensure there was no lower boundary influence on observed behaviour. Time-averaged and fluctuating data are extracted along the trajectory of discharges. All non-dimensionalised geometric and centreline velocity parameters are found to collapse. Empirical coefficients are compared to previous experimental studies and integral model predictions.
A new detrainment model is developed to predict the behaviour of inclined negatively buoyant jets without boundary influence. The model further develops recent attempts to allow for buoyancy flux reduction along the flow path. The reduction in buoyancy flux is dependent on the local parameters of the flow and simulates experimentally observed detrainment. Dilution, geometric, and velocity predictions are found to be improved over previous models when compared to experimental data.
Finally, a raised platform was placed inside the experimental tank to determine the influence of a lower boundary on inclined negatively buoyant jets. Source angles of 30\degree, 45\degree, and 60\degree are investigated at three different non-dimensional source heights. The lower boundary is horizontal and ambient conditions are again stationary. Discharges impinge the lower boundary before forming a radially spreading layer along the boundary. Geometric and velocity data are compared to the first set of experiments in this study to determine the influence of the lower boundary on observed flow behaviour. Empirical coefficients at maximum height are similar with and without the influence of the boundary, whereas coefficients are substantially influenced at the return point when the boundary is present.
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Sharp, David Keith. "Trends in single-particle energies in N=51 nuclei." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/trends-in-singleparticle-energies-in-n51-nuclei(fe5f71e3-c0ab-4ace-98ae-af674f923b44).html.
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A systematic study of the neutron single-particle states in N=51 isotones has been performed. Final states in 89Sr, 91Zr and 93Mo have been populated using the (d,p) and (alpha,3He) single-neutron adding reactions. The Yale tandem provided beams of 15-MeV deuterons and 50-MeV alpha particles with the outgoing ejectiles momentum analysed using an Enge split-pole spectrometer. A supplementary measurement of the d(86Kr,p)87Kr reaction, at a beam energy of 10 MeV/u, was made in inverse kinematics using the HELIOS spectrometer. Outgoing protons execute a helical orbit in a uniform field before detection, before they return to axis, using a position-sensitive silicon array. Absolute cross sections were measured for states up to 4 MeV in excitation. The transferred angular momentum was identified through a comparison of angular distributions and the ratio of cross section between reactions. Relative spectroscopic factors were extracted through a DWBA analysis.The measured centroids for the single-particle energies of the s1/2, d3/2, d5/2, g7/2 and h11/2 orbitals were compared to calculations using a Gaussian central potential with and without the addition of a tensor interaction. Through this comparison it was deduced that the inclusion of a tensor interaction is required to explain the observed shifts in the single-particle energies of the d3/2 and g7/2 orbitals. This system provided an observation of a switch in behaviour, from repulsive to attractive and vice versa, of the effect of the tensor interaction. This occurs due to a change from j> to j< proton occupancy at Z=40.
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Martinez, Bertrand. "Effets radiatifs et quantiques dans l'interaction laser-matière ultra-relativiste." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0442/document.
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L'avènement d'une nouvelle génération de lasers ultra-relativistes (d'éclairement supérieur à 10^22 W/cm2), tels le laser APOLLON sur le plateau de Saclay, donnera lieu à un régime d'interaction laser-matière sans précédent, couplant physique des plasmas relativistes et effets électrodynamiques quantiques. Sources de particules et de rayonnements aux propriétés énergétiques et spatio-temporelles inédites, ces lasers serviront, entre autres applications, à la mise au point de nouveaux concepts d'accélérateurs et de diagnostics radiographiques, au chauffage de plasmas denses, comme à la reproduction de configurations astrophysiques en laboratoire. En prévision des futures expériences, les codes particle-in-cell (PIC), qui constituent les outils de référence pour la simulation de l'interaction laser-plasma, doivent être enrichis des processus radiatifs et quantiques propres à ce nouveau régime d'interaction. C'est le cas du code CALDER développé au CEA/DAM, qui modélise désormais l'émission de photons énergétiques et la conversion de ceux-ci en paires électron-positron ; autant d'effets susceptibles d'affecter le bilan d'énergie de l'interaction laser-cible et, plus précisément, le rendement du laser en particules et rayonnements énergétiques. L'objet de ce stage théorique est d'étudier, à l'aide du code CALDER, l'influence de ces processus dans un certain nombre de scénarios physiques en champ extrême (accélération électronique et ionique dans un plasma surcritique, production de rayonnement, génération de choc non-collisionnel…)Forthcoming multi-petawatt laser systems, such as the French Apollon and European Extreme Light Infrastructure facilities, are expected to deliver on-target laser intensities exceeding 10^22 W/cm^2. A novel regime of laser-matter interaction will ensue, where ultra-relativistic plasma effects are coupled with copious generation of high-energy photons and electron-positron pairs. This will pave the way for many transdisciplinary applications in fundamental and applied research, including the development of unprecedentedly intense, compact particle and radiation sources, the experimental investigation of relativistic astrophysical scenarios and tests of quantum electrodynamics theory.In recent years, most theoretical studies performed in this research field have focused on the impact of synchrotron photon emission and Breit-Wheeler pair generation, both directly induced by the laser field and believed to be dominant at intensities >10^22 W/cm^2. At the lower intensities (≲10^21 Wcm^(-2)) currently attainable, by contrast, photon and pair production mainly originate from, respectively, Bremsstrahlung and Bethe-Heitler/Trident processes, all triggered by atomic Coulomb fields. The conditions for a transition between these two regimes have, as yet, hardly been investigated, particularly by means of integrated kinetic numerical simulations. The purpose of this PhD is precisely to study the aforementioned processes under various physical scenarios involving extreme laser-plasma interactions. This work is carried out using the particle-in-cell CALDER code developed at CEA/DAM which, over the past few years, had been enriched with modules describing the synchrotron and Breit-Wheeler processes.Our first study aimed at extending the simulation capabilities of CALDER to the whole range of photon and positron generation mechanisms arising during relativistic laser-plasma interactions. To this purpose, we have implemented modules for the Coulomb-field-mediated Bremsstrahlung, Bethe-Heitler and Trident processes. Refined Bremsstrahlung and Bethe-Heitler cross sections have been obtained which account for electronic shielding effects in arbitrarily ionized plasmas. Following validation tests of the Monte Carlo numerical method, we have examined the competition between Bremsstrahlung/Bethe-Heitler and Trident pair generations by relativistic electrons propagating through micrometer copper foils. Our self-consistent simulations qualitatively agree with a 0-D theoretical model, yet they show that the deceleration of the fast electrons due to target expansion significantly impacts pair production.We then address the competition between Bremsstrahlung and synchrotron emission from copper foils irradiated at 10^22 Wcm^(-2). We show that the maximum radiation yield (into >10 keV photons) is achieved through synchrotron emission in relativistically transparent targets of a few 10 nm thick. The efficiency of Bremsstrahlung increases with the target thickness, and takes over synchrotron for >2μm thicknesses. The spectral properties of the two radiation processes are analyzed in detail and correlated with the ultrafast target dynamics.Finally, we investigate the potential of nanowire-array targets to enhance the synchrotron yield of a 10^22 Wcm^(-2) femtosecond laser pulse. Several radiation mechanisms are identified depending on the target parameters and as a function of time. A simulation scan allows us to identify the optimal target geometry in terms of nanowire width and interspacing, yielding a ∼10% radiation efficiency. In this configuration, the laser-driven nanowire array rapidly expands to form a quasi-uniform, relativistically transparent plasma. Furthermore, we demonstrate that uniform sub-solid targets can achieve synchrotron yields as high as in nanowire arrays, but that the latter enable a strong emission level to be sustained over a broader range of average plasma density
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Vera, Gomis Pablo de. "Charged particle interaction with biological materials: modelling and application to ion beam cancer therapy." Doctoral thesis, Universidad de Alicante, 2016. http://hdl.handle.net/10045/56995.
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En esta tesis se presenta un estudio teórico sobre la interacción de partículas cargadas aceleradas con materiales de interés radioterapéutico, con miras a su posible aplicación en el tratamiento del cáncer mediante haces de iones. El trabajo se centra en el cálculo de las probabilidades de interacción electrónica (secciones eficaces de excitación y de ionización) de partículas cargadas (haces de iones y de electrones) con materia condensada, incluyendo materiales inorgánicos y orgánicos de interés para el problema estudiado, así como su uso en programas de simulación de la interacción de la radiación con materiales biológicos. Tras una introducción general (capítulo 1), la primera parte de la tesis (capítulos 2-4) trata sobre el cálculo de las secciones eficaces. El formalismo dieléctrico se ha utilizado para obtener las magnitudes básicas de frenado, tales como el poder de frenado, el straggling en la pérdida de energía, o el recorrido libre medio, para haces de iones y electrones. También se ha desarrollado un método para aplicar el formalismo dieléctrico al cálculo de secciones eficaces de ionización, incluyendo el cálculo de las distribuciones energéticas y angulares de electrones secundarios. Además, se ha implementado una metodología para extender estos cálculos a materiales biológicos arbitrarios, incluyendo blancos complejos, tales como el hueso, el ADN y sus componentes moleculares, proteínas, o compartimentos celulares. Las secciones eficaces obtenidas se han utilizado como dato de entrada en el código de simulación SEICS para la propagación de haces de iones en materia condensada (capítulos 5 y 6). Este programa se ha ampliado para tener en cuenta los efectos específicos sufridos por protones relativistas (correcciones relativistas y reacciones nucleares de fragmentación nuclear) y se ha utilizado para simular situaciones de interés en la terapia del cáncer mediante haces de iones. Mediante el programa de simulación SEICS se ha reproducido una serie de experimentos de irradiación de blancos cilíndricos micrométricos, para poner a prueba el programa, así como para evaluar el poder de frenado de protones en agua líquida (el principal componente de los tejidos vivos). Además, se ha utilizado SEICS para obtener cantidades tales como la dosis en función de la profundidad, los perfiles de dosis lateral, y otras cantidades relacionadas, útiles en terapia. Por último, se han desarrollado técnicas analíticas, en contraste con la técnica de simulación (capítulo 7). Se ha implementado un algoritmo de haces tipo pincel para el cálculo rápido de la dosis, aprovechando los resultados obtenidos con el programa SEICS. Además, se ha desarrollado un modelo analítico para describir la interacción de haces de iones con compartimentos subcelulares realistas. Este modelo es muy útil para evaluar el depósito de energía y el número de ionizaciones producidas en el núcleo y el citoplasma celular, cantidades que son relevantes en radiobiología, ya que la energía depositada en el núcleo puede relacionarse con la probabilidad de muerte celular, mientras que existen otros efectos biológicos relacionados con el depósito de energía fuera del núcleo. Los resultados presentados en esta tesis exploran diferentes procesos físicos implicados en los mecanismos que subyacen a la terapia del cáncer mediante haces de iones.
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Jin, Hanbing. "Particle-in-Cell Simulation of Electromagnetic Pulse Generated by High-power Laser-target Interaction." Thesis, KTH, Fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231339.
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Bouzid, Djallel. "Study of high impact polypropylene morphology : interaction between the polymerisation process and particle morphology." Lyon 1, 2004. http://www.theses.fr/2004LYO10185.
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La fragmentation du catalyseur au début de la polymérisation a un effet déterminant sur la morphologie final du polymère, aussi bien sur la cinétique de polymérisation. La connaissance du comportement du catalyseur et du développement de la morphologie de la particule durant la réaction est très importante du point de vue de l’optimisation du produit et du processus. L’orientation originale de cette étude devrait donc fournir l’analyse en profondeur de l’évolution de la morphologie des particules de catalyseur/polymère avec pour but de comprendre le rapport entre la morphologie, la densité apparente et la teneur en caoutchouc dans les processus d’iPP. L’objectif concret principal était d’obtenir le contenu en caoutchouc le plus haut en gardant une morphologie appréciable. Les objectifs secondaires étaient de comprendre le rapport entre la morphologie du catalyseur, le contenu en caoutchouc et la cinétique de la réactionThe principal objective of this thesis is to elucidate how the rubber phase produced in the copolymerisation step is distributed inside growing particles of high impact polypropylene, and how the amount of rubber incorporated in the original polypropylene matrix influences the overall morphology and mechanical properties of the final product. To this end, polymer was made under different conditions, and the products were characterised and analysed in order to attempt to understand how the morphology of the isotactic polypropylene matrix changes during particle growth, how rubber flows in the porous network, and how the EPR arrives at, and pools on the surface of the particle. All of these phenomena are obviously dependent on each other, which complicates the problem. A representation which incorporates the rheological properties of the copolymer combined with the structure of the homopolymer polypropylene matrix is probably a more realistic approach to take
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Slapak, Rikard. "O⁺ heating in the high altitude cusp and mantle due to wave-particle interaction." Licentiate thesis, Luleå tekniska universitet, Rymdteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26562.
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This thesis is composed of three articles, which have the common denominator that they are studies of heating of oxygen ions in the high altitude cusp and mantle in the terrestrial magnetosphere. All data analysis are based on observational data from the Cluster satellites. Oxygen ions originate in the ionosphere, from where they flow up along open cusp field lines. This upflowing ionospheric plasma is generally gravitationally bound and will return as ionospheric downflow. However, if the plasma is sufficiently energized it may overcome gravity and reach the magnetosphere. Further energization is able to put the plasma on trajectories leading downstream along the magnetotail, which may cause the plasma to escape into the magnetosheath. This thesis considers energization of oxygen ions through wave-particle interactions. We show that the average electric spectral densities in the altitude range of 8-15 Earth radii are able to explain the average perpendicular temperatures, using a simple gyroresonance model and 50% of the observed spectral density at the O+ gyrofrequency. We also show that the phase velocities derived from the observed low frequency electric and magnetic fields are consistent with Alfvén waves. Strong heating is sporadic and spatially limited. For three case studies of strong heating, we show that the regions of enhanced wave activity are at least one order of magnitude larger than the gyroradius of the ions, which is a condition for the gyroresonance model to be valid. An analysis indicates that enhanced perpendicular temperatures can be observed over several Earth radii after heating has ceased, suggesting that high perpendicular-to-parallel temperature ratio is not necessarily a sign of local heating. This also explains why we sometimes observe enhanced temperatures and low spectral densities. Three events of very high temperatures and simultaneously observed high spectral densities were studied, and we showed that the temperatures could be explained with the simple gyrofrequency model. We have also provided average diffusion coefficients at different altitudes, which can be used for ion heating and outflow modeling.Godkänd; 2011; 20111007 (riksla); LICENTIATSEMINARIUM Ämnesområde: Rymdteknik/Space Engineering Examinator: Docent Hans Nilsson, IRF Kiruna Diskutant: Doktor Stephan Buchert, IRF Uppsala Tid: Fredag den 11 november 2011 kl 10.00 Plats: IRF, Kiruna
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Pachler, Klaus, Thomas Frank, and Klaus Bernert. "Simulation of Unsteady Gas-Particle Flows including Two-way and Four-way Coupling on a MIMD Computer Architectur." Universitätsbibliothek Chemnitz, 2002. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200200352.
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The transport or the separation of solid particles or droplets suspended in a fluid flow is a common task in mechanical and process engineering. To improve machinery and physical processes (e.g. for coal combustion, reduction of NO_x and soot) an optimization of complex phenomena by simulation applying the fundamental conservation equations is required. Fluid-particle flows are characterized by the ratio of density of the two phases gamma=rho_P/rho_F, by the Stokes number St=tau_P/tau_F and by the loading in terms of void and mass fraction.
Those numbers (Stokes number, gamma) define the flow regime and which relevant forces are acting on the particle. Dependent on the geometrical configuration the particle-wall interaction might have a heavy impact on the mean flow structure. The occurrence of particle-particle collisions becomes also more and more important with the increase of the local void fraction of the particulate phase. With increase of the particle loading the interaction with the fluid phase can not been neglected and 2-way or even 4-way coupling between the continous and disperse phases has to be taken into account.
For dilute to moderate dense particle flows the Euler-Lagrange method is capable to resolve the main flow mechanism. An accurate computation needs unfortunately a high number of numerical particles (1,...,10^7) to get the reliable statistics for the underlying modelling correlations. Due to the fact that a Lagrangian algorithm cannot be vectorized for complex meshes the only way to finish those simulations in a reasonable time is the parallization applying the message passing paradigma.
Frank et al. describes the basic ideas for a parallel Eulererian-Lagrangian solver, which uses multigrid for acceleration of the flow equations. The performance figures are quite good, though only steady problems are tackled. The presented paper is aimed to the numerical prediction of time-dependend fluid-particle flows using the simultanous particle tracking approach based on the Eulerian-Lagrangian and the particle-source-in-cell (PSI-Cell) approach. It is shown in the paper that for the unsteady flow prediction efficiency and load balancing of the parallel numerical simulation is an even more pronounced problem in comparison with the steady flow calculations, because the time steps for the time integration along one particle trajectory are very small per one time step of fluid flow integration and so the floating point workload on a single processor node is usualy rather low.
Much time is spent for communication and waiting time of the processors, because for cold flow particle convection not very extensive calculations are necessary. One remedy might be a highspeed switch like Myrinet or Dolphin PCI/SCI (500 MByte/s), which could balance the relative high floating point performance of INTEL PIII processors and the weak capacity of the Fast-Ethernet communication network (100 Mbit/s) of the Chemnitz Linux Cluster (CLIC) used for the presented calculations. Corresponding to the discussed examples calculation times and parallel performance will be presented. Another point is the communication of many small packages, which should be summed up to bigger messages, because each message requires a startup time independently of its size. Summarising the potential of such a parallel algorithm, it will be shown that a Beowulf-type cluster computer is a highly competitve alternative to the classical main frame computer for the investigated Eulerian-Lagrangian simultanous particle tracking approach.
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Idouakass, Malik. "Linear and nonlinear study of the precessional fishbone instability." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4756/document.
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L'interaction onde-particule dans les plasma est un sujet de recherche important, pour la compréhension des phénomènes physiques fondamentaux comme pour l'opération de réacteurs à fusion tels que les tokamaks. Cette intéraction peut être responsable de l'existence de modes instables, comme l'instabilité "fishbone" dans les plasmas de tokamak. Celle-ci est causée par l'interaction résonante entre un mode vivant dans la plasma et une population de particules supra-thermiques. Cette instabilité cause l'éjection d'une partie de ces particules énergétiques. Elle est par ailleurs caractérisée par une diminution de sa fréquence durant son évolution. Dans cette thèse, un modèle pour l'instabilité "fishbone", décrivant le plasma thérmique avec un traitement fluide et les particlules énergétiques avec un traitement cinétique, est développé. Ce modèle est simplifié de manière à permettre la compréhension des mécanismes les plus basiques qui causent la destabilisation du mode, sa diminution en fréquence durant son évolution ainsi que l'éjection de particules qu'il engendre. La théorie linéaire de ce modèle est faite, montrant les conditions qui permettent l'existence de l'instabilité, et permettant la caractérisation de son comportement linéaire. Les résultats analytiques sont ensuite comparés aux résultats linéaires numériques, obtenus grâce à un code développé durant cette thèse et basé sur les hypothèses du modèle, et ils sont en accord. Enfin, ce code est utilisé pour explorer le comportement non linéaire des particules énergétiques. Le mécanisme principalement responsable du changement de fréquence du mode ainsi que de l'éjection des particules est identifié et étudié en detailThe wave-particle interaction in plasmas is an important research subject, for fundamental physical understanding as well as for the operation of fusion devices such as tokamaks. This interaction can cause the existence of unstable modes, such as the fishbone instability that is observed in tokamak plasmas. It results from the resonant interaction between an electro-magnetic wave living in the plasma and a population of supra-thermal particles. This mode causes the ejection of a portion of these energetic particles, and is thus detrimental to the confinment of energy in a tokamak, and it is characterized by a frequency down-chirping, i.e. a decrease of frequency of the mode during its evolution. In this thesis, a model for the fishbone instability is developed, that describes the thermal plasma with fluid equations and the supra-thermal particles with the kinetic Vlasov equation. This model is highly simplified in order to understand the basic mechanisms leading to destabilization, frequency chirping, and particle ejection. The linear theory of this model is then done, showing the conditions that lead to the existence of an instability, and that allow the characterization of its linear behavior. The linear analytic results are then compared to numerical linear results obtained with a code, based on the assumptions of the model, that was developed during this PhD and the results are found to be in good agreement. Finally, the code is used to explore the nonlinear behavior of energetic particles in the later phase of the fishbone instability. The main mechanism responsible for the frequency chirping and energetic particle ejection is identified and studied in detail