Dans cette thèse, les caractéristiques des plasmas MDECR ont été étudiées en utilisant des mesures d'émission optique (OES), de spectroscopie de masse (QMS) et de sonde Langmuir plane. Ces techniques combinées avec des observations sur la pression avec et sans plasma nous ont permis de construire une image assez claire sur les propriétés chimiques et physiques des plasmas MDECR, notamment des plasmas de silane. A cause des conditions de fonctionnement à faible pression (~ mTorr), grande puissance (~kW) et à cause du confinement électronique dû à l'effet ECR, la distribution électronique dans le plasma est divisé en deux familles : une famille d'électrons rapides et une autre d'électrons froids. Les mesures OES des plasmas d'argon et de silane ont montré le confinement des électrons rapides dans les zones ECR autour de chaque antenne, toute la chimie du plasma (la dissociation, l'excitation et l'ionisation) se produit essentiellement dans ces zones. Les mesures par sonde Langmuir plane ont montré que la température des électrons froids est dans la gamme 1-2 eV qui est en bon accord avec les résultats de l'équipe de S. Béchu. Ces mesures (OES, QMS, sonde Langmuir) et les mesures de la pression ont montré la présence très importante d'hydrogène atomique et ionique dans un plasma de silane. Les mesures de spectroscopie de masse ont montré que dans un plasma de silane, la présence des radicaux et d'ions à base de Si, SiH et SiH2 est aussi importante que celle des radicaux SiH3. La contribution de ces radicaux et ions avec un grand coefficient de collage à la croissance du film a également été observée par des études de dépôt à travers un masque contenant des petits orifices. Toutes les mesures ont montré que pour un plasma de silane, un rapport «puissance totale/débit du gaz» faible est favorable à la formation de radicaux SiH3, tandis qu'un rapport «puissance/débit du gaz» grand rend le rapport [SiH*]/[Hα] petit. Cela suggère que les conditions de fortes puissances, faibles débits de silane favorisent le dépôt du matériau microcristallin tandis que les conditions de faibles puissances, forts débits de gaz devraient favoriser la formation d'un matériau amorphe.

Graduation date: 2005

Graduation date: 1999

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (April 25, 2007) Vita. Includes bibliographical references.

Thermonuclear fusion has potential to offer an economically, environmentally and socially acceptable supply of energy. A promising reactor design to execute thermonuclear fusion is the toroidal magnetic confinement device, tokamak. The tokamak still faces challenges in the major areas which can be categorised into confinement, heating and fusion technology. This thesis addresses the problem of confinement, in particular the role of transport along magnetic field lines perturbed by diverse MHD instabilities. Unstable modes such as ideal ballooning-peeling, tearing etc., break closed magnetic surfaces and destroy the axisymmetry of the magnetic configuration in a tokamak, providing deviation of magnetic field lines from unperturbed magnetic surfaces. Radial gradients of plasma parameters have nonzero projections along such lines and drive parallel particle and heat flows which contribute to the radial transport. Such transport can significantly affect confinement as this takes place by the development of neoclassical tearing modes (NTMs) in the core and edge localised modes (ELMs) at the plasma periphery. In this thesis, transport of heat through non-overlapped magnetic island chains is first investigated using the 'Optimal path' approach, which is based on the principal of minimum entropy production. This model shows how the effective heat conduction through islands increases with parallel heat conduction and with the perturbation level. A more standard analytical approach for the limit cases of "small" and "large" islands is also presented. Transport of heat through internally heated magnetic islands is next investigated by further development of the 'Optimal path' method. In addition the approach by R. Fitzpatrick, has been extended for this investigation. By application of these approaches to experimental observations made at TEXTOR tokamak, heat flux limit, limiting parallel heat conduction in low collisional plasmas, is elucidated. Models to study transport of heat and particles due to ELMs have also been developed. Energy losses during ELMs have been estimated considering contribution from parallel conduction due to electrons and parallel convection of ions, with constant level of the magnetic field perturbation, steady profiles for density and temperature, and by accounting for the heat flux limit. The estimate shows good agreement with experimental observations. The model is developed further by accounting for the time evolution of the perturbation level due to ballooning mode, and of density and temperature profiles.

The Cassini spacecraft orbits Saturn since 2004, carrying a multitude of instruments for studies of the plasma environment around the planet as well as the constituents of the ring system. Of particular interest to the present thesis is the large E ring, which consists mainly of water ice grains, smaller than a few micrometres, referred to as dust. The first part of the work presented here is concerned with the interaction between, on the one hand, the plasma and, on the other hand, the dust, the spacecraft and the Langmuir probe carried by the spacecraft. In Paper I, dust densities along the trajectory of Cassini, as it passes through the ring, are inferred from measured electron and ion densities. In Paper II, the situation where a Langmuir probe is located in the potential well of a spacecraft is considered. The importance of knowing the potential structure around the spacecraft and probe is emphasised and its effect on the probe's current-voltage characteristic is illustrated with a simple analytical model. In Paper III, particle-in-cell simulations are employed to study the potential and density profiles around the Cassini as it travels through the plasma at the orbit of the moon Enceladus. The latter part of the work concerns large-scale currents and convection patterns. In Paper IV, the effects of charged E-ring dust moving across the magnetic field is studied, for example in terms of what field-aligned currents it sets up, which compared to corresponding plasma currents. In Paper V, a model for the convection of the magnetospheric plasma is proposed that recreates the co-rotating density asymmetry of the plasma. / QC 20120507

<p>Hydroxyapatite (HA), which is a natural component of bone tissue, is already being marketed as a coating for the metal shafts of hip implants as well as dental screws and other endoprostheses with the expectation of improved bonding to bone through osseointegration. Coatings prepared by the more widely used and commercial method, plasma spraying technique suffer from poor adhesion or delamination from the substrate. The high temperatures also results in a number of unstable decomposition phases compared to the more crystalline phase. The main purpose of the present research was to prepare and characterize HA coatings using low temperature sol-gel method with the specific aims of improving adhesion on both the HA/metal and HA/bone interface which have been reported failure modes of implants.</p>

Cellular behaviour depends ultimately on the transcription of genes. If we know how transcription is controlled we have a better chance of understanding cellular processes. This thesis presents six studies, all concerning cellular regulatory mechanisms. One study is purely experimental and five are computational studies. A large part of the research concerns the Epstein-Barr virus (EBV). We investigate the latency programme switching of EBV, with an equilibrium statistical mechanics model that describes the transcription activities of two central viral promoters. We demonstrate that this system is bistable and predict promoter activities that correlate well with experimental data. Further we study the switching efficiency of one of the promoters, highlighting how competitive binding of transcription factors generates a more efficient geneticswitch. The EBV protein EBNA1 is known to affect cellular gene expression. With a dinucleotide position weight matrix we search the complete human genome for regions with multiple EBNA1 binding sites. 40 potential binding regions are identified, with several of particular interest in relation to EBV infections. The final study on EBV is purely experimental, in which we demonstrate an interaction between the Syk kinase and integrin β4. Moreover, we show how reduced levels of these proteins affect migration of epithelial LMP2a positive cells, and hypothesise that these effects are due to the Syk-β4 interaction. The two remaining studies presented in this thesis concern other cellular systems. Dynamic properties of two different regulatory feedback mechanisms for transport and metabolism of small molecules are investigated. The synergetic effect of adding a regulatory loop is exemplified with the iron metabolism in bacteria. The final project concerns the λ phage. With the equilibrium statistical mechanics method for describing promoter activities we characterise the equilibrium properties of λ mutants and compare with experimental findings. We argue that the observed differences between model and experiment are due to a larger perturbation of the genetic circuit than presumed. The research presented in this thesis shed light on the properties of several regulatory mechanisms. As computational studies they add perspective to the experimental research in this field and provide new hypothesis for further research. / QC20100720

This thesis describes theoretical studies of adiabatic motion of relativistic charged particles in the radiation belts and numerical modeling of multi-dimensional diffusion due to interactions between electrons and plasma waves. A general Hamiltonian theory for the adiabatic motion of relativistic charged particles confined by slowly-varying background electromagnetic fields is presented based on a unified Lie-transform perturbation analysis in extended phase space (which includes energy and time as independent coordinates) for all three adiabatic invariants. First, the guiding-center equations of motion for a relativistic particle are derived from the particle Lagrangian. Covariant aspects of the resulting relativistic guiding-center equations of motion are discussed and contrasted with previous works. Next, the second and third invariants for the bounce motion and drift motion, respectively, are obtained by successively removing the bounce phase and the drift phase from the guiding-center Lagrangian. First-order corrections to the second and third adiabatic invariants for a relativistic particle are derived. These results simplify and generalize previous works to all three adiabatic motions of relativistic magnetically-trapped particles. Interactions with small amplitude plasma waves are described using quasi-linear diffusion theory, and we note that in previous work numerical problems arise when solving the resulting multi-dimensional diffusion equations using standard finite difference methods. In this thesis we introduce two new methods based on stochastic differential equation theory to solve multi-dimensional radiation belt diffusion equations. We use our new codes to assess the importance of cross diffusion, which is often ignored in previous work, and effects of ignoring oblique waves, which are omitted in the parallel-propagation approximation of calculating diffusion coefficients. Using established wave models we show that ignoring cross diffusion or oblique waves may produce large errors at high energies. Results of this work are useful for understanding radiation belt dynamics, which is crucial for predictability of radiation in space.

In this thesis we show that the entropy parameter PV5/3 , where P is the pressure and V is the volume of a flux tube with unit magnetic flux, plays a central role in the earthward plasma convection from the near- and middle-Earth plasma sheet to the inner magnetosphere. This work presents a series of numerical simulations, investigating the relationship between the value of PV5/3 and the different features of plasma earthward transport that occur during different types of events in geomagnetic active times. The simulations are conducted using the Rice-Convection-Model (RCM) and the Rice-Convection-Model-Equilibrium (RCM-E) that have carefully designed boundary conditions to simulate the effect of various values of PV 5/3. In Chapter 3 we present results of an RCM simulation of a sawtooth event where it is found that a dramatic reduction of PV5/3 on the boundary along a wide range of local times produces interchange convection in the inner magnetosphere and drives spatially quasi-periodic Birkeland currents that suggest an explanation for the finger-like aurora usually observed during this type of event. In Chapter 4 we present results of an RCM-E simulation of an isolated substorm, which is done by imposing depleted PV5/3 (a bubble) in the expansion phase. The results of this simulation reproduce typical features of a substorm and agree fairly well with multipoint observations. Chapter 6 presents a detailed analysis of the RCM-E expansion phase simulation which indicates that the reconfigurations of PV5/3, plasma pressure and magnetic field in an idealized bubble injection event can be quite complicated. Chapter 7 presents results of a superposed epoch study using Geotail data showing that the time variations of PV 5/3 are different in isolated substorms, pseudo-breakups and convection bay events, suggesting that bubbles have different characteristics in different modes of earthward transport. We follow this up with three corresponding RCM-E simulations by representing a sustained bubble, a transient bubble and sustained low PV5/3 plasma along the boundary. The simulations are roughly consistent with theoretical suggestions, superposed epoch results and some other observations. These simulations provide a systematic description of inner magnetospheric configuration during various active events, suggesting the temporal and spatial characteristics of PV5/3 in the plasma sheet as a key in the magnetospheric convection.