A careful study of plasma-material interactions is essential to understand and improve the operation of devices where plasma contacts a wall such as plasma thrusters, fusion devices, spacecraft-environment interactions, to name a few. This work aims to advance our understanding of fundamental plasma processes pertaining to plasma-material interactions, sheath physics, and kinetic instabilities through theory and novel numerical simulations. Key contributions of this work include (i) novel continuum kinetic algorithms with novel boundary conditions that directly discretize the Vlasov/Boltzmann equation using the discontinuous Galerkin method, (ii) fundamental studies of plasma sheath physics with collisions, ionization, and physics-based wall emission, and (iii) theoretical and numerical studies of the linear growth and nonlinear saturation of the kinetic Weibel instability, including its role in plasma sheaths. The continuum kinetic algorithm has been shown to compare well with theoretical predictions of Landau damping of Langmuir waves and the two-stream instability. Benchmarks are also performed using the electromagnetic Weibel instability and excellent agreement is found between theory and simulation. The role of the electric field is significant during nonlinear saturation of the Weibel instability, something that was not noted in previous studies of the Weibel instability. For some plasma parameters, the electric field energy can approach magnitudes of the magnetic field energy during the nonlinear phase of the Weibel instability. A significant focus is put on understanding plasma sheath physics which is essential for studying plasma-material interactions. Initial simulations are performed using a baseline collisionless kinetic model to match classical sheath theory and the Bohm criterion. Following this, a collision operator and volumetric physics-based source terms are introduced and effects of heat flux are briefly discussed. Novel boundary conditions are developed and included in a general manner with the continuum kinetic algorithm for bounded plasma simulations. A physics-based wall emission model based on first principles from quantum mechanics is self-consistently implemented and demonstrated to significantly impact sheath physics. These are the first continuum kinetic simulations using self-consistent, wall emission boundary conditions with broad applicability across a variety of regimes. / Ph. D. / An understanding of plasma physics is vital for problems on a wide range of scales: from large astrophysical scales relevant to the formation of intergalactic magnetic fields, to scales relevant to solar wind and space weather, which poses a significant risk to Earth’s power grid, to design of fusion devices, which have the potential to meet terrestrial energy needs perpetually, and electric space propulsion for human deep space exploration. This work aims to further our fundamental understanding of plasma dynamics for applications with bounded plasmas. A comprehensive understanding of theory coupled with high-fidelity numerical simulations of fundamental plasma processes is necessary, this then can be used to improve improve the operation of plasma devices. There are two main thrusts of this work. The first thrust involves advancing the state-of-the-art in numerical modeling. Presently, numerical simulations in plasma physics are typically performed either using kinetic models such as particle-in-cell, where individual particles are tracked through a phase-space grid, or using fluid models, where reductions are performed from kinetic physics to arrive at continuum models that can be solved using well-developed numerical methods. The novelty of the numerical modeling is the ability to perform a complete kinetic calculation using a continuum description and evolving a complete distribution function in phase-space, thus resolving kinetic physics with continuum numerics. The second thrust, which is the main focus of this work, aims to advance our fundamental understanding of plasma-wall interactions as applicable to real engineering problems. The continuum kinetic numerical simulations are used to study plasma-material interactions and their effects on plasma sheaths. Plasma sheaths are regions of positive space charge formed everywhere that a plasma comes into contact with a solid surface; the charge inequality is created because mobile electrons can quickly exit the domain. A local electric field is self-consistently created which accelerates ions and retards electrons so the ion and electron fluxes are equalized. Even though sheath physics occurs on micro-scales, sheaths can have global consequences. The electric field accelerates ions towards the wall which can cause erosion of the material. Another consequence of plasma-wall interaction is the emission of electrons. Emitted electrons are accelerated back into the domain and can contribute to anomalous transport. The novel numerical method coupled with a unique implementation of electron emission from the wall is used to study plasma-wall interactions. While motivated by Hall thrusters, the applicability of the algorithms developed here extends to a number of other disciplines such as semiconductors, fusion research, and spacecraft-environment interactions.

Um eine verbesserte Therapieoption mit weniger Schmerzen und Nebenwirkun-gen für Patienten mit Depigmentierungsstörungen wie Vitiligo zu entwickeln, wurde eine Methode zur nichtinvasiven Gewinnung von autologen Melanozyten aus der Haarwurzel genutzt. Die Haarwurzel als einfach zugängliches Stammzell-reservoir bietet die Möglichkeit, Vorläufermelanozyten aus der äußeren Haar-wurzelscheide zu isolieren, differenzieren und zu proliferieren. Für zukünftige autologe Transplantationsversuche wurden in dieser Arbeit die kultivierten hu-manen Melanozyten aus der äußeren Haarwurzelscheide (Human Melanocytes from the Outer Root Sheath, HUMORS) auf drei unterschiedlichen Scaffolds getes-tet. Hinsichtlich mitochondrialer Aktivität (Marker für Zellproliferation), mela-nozytenspezifischer Markerexpression und ihrer Funktionalität (Tyrosinase-Enzymaktivität und Melaningehalt) wurden die Zellen auf Collagen Cell Carrier® (CCC), Poly-ε-Caprolacton-Scaffolds (PCL) und kollagen basierten Hydrogelen (cGEL) kultiviert und charakterisiert. Alle Scaffolds waren biokompatibel, immu-nologisch nur gering aktiv und wiesen eine dreidimensionale Struktur auf, die der extrazellulären Matrix nachempfunden war. Einen positiven Effekt auf die Prolife-ration wiesen die HUMORS auf den Collagen Cell Carrier® auf. Bei Untersuchun-gen der melanotischen Aktivität überzeugten die HUMORS auf dem cGEL Typ4 durch einen signifikant höheren Melaningehalt. Da Melanin das entscheidende Produkt der Repigmentierung bei Vitiligoläsionen ist, stellte sich damit das cGEL Typ4 als vielversprechender Zellträger für die Kultivierung und vorgesehene Transplantation der Melanozyten heraus.

The thesis is based on recent evidence of the presence and functionality of brown adipose tissue (in human body) which have brought increased interest in non-sheath thermogenesis and the role of BAT in metabolism. Since BAT is generally activated by cold exposure, there is a question of the relationship between the amount of body fat in human body (BMI index) and regular cold exposure. The study (cold showers several times a week for three months) was attended by a total of 49 probands in the age range of 19 - 25 years. They were all measured before and after cold showers on a Bodystat device where body fat percentage, the percentage of active body mass (ATH), the percentage of lean body mass, the percentage of body water, the BMI and the WHR index were found. Subsequently, the identified characteristics were compared and evaluated. An important result is the difference in body fat percentage where, due to the cold showers and anticipated activation of BAT, there was a statistically significant reduction in body fat in the experimental group of women. It can be stated that cold showers can have significant potential in the fight against obesity.

This investigation examines band gap engineering of the GaAsN alloy by means of plasma ion implantation. The strong redshift of the alloy's band gap is suitable for telecommunication applications and thus stimulated much interest in recent years. Nitrogen (N) ion implantation into gallium arsenide (GaAs) results in a thin shallow N-rich layer below the surface. However, the violent implantation process also modifies the concentrations of gallium and arsenide. The core of this thesis is a novel method for prediction of the band gap from the conditions in the processing plasma.<p>The first important variable, the number of implanted ions, is obtained from the Lieberman model for the current during high-voltage Plasma Ion Implantation (PII). A review of the model's assumptions is provided as well as a comprehensive discussion of the implantation which includes error boundaries. The predicted and measured ion currents agree within error boundaries. The number of implanted ions can therefore be obtained from the prediction.<p>The distribution of the implanted ions was subsequently explored by simulations such as TRIM and TRIDYN. It was found that the nitrogen content in GaAs is limited by the sputtering of the surface atoms. Furthermore, the content of gallium increases near the surface while the content of arsenic decreases. The predicted ratios of the constituents in the implanted layer is such that the alloy cannot form by ion implantation alone; it could be reconciled by annealing.<p>Preliminary samples were produced and tested for the formation of the GaAsN alloy by Raman spectroscopy. No evidence for bonds between N and either Ga or As was found in the as-implanted samples. The thesis concludes with a discussion of the necessary steps to synthesize the GaAsN alloy.

This investigation examines band gap engineering of the GaAsN alloy by means of plasma ion implantation. The strong redshift of the alloy's band gap is suitable for telecommunication applications and thus stimulated much interest in recent years. Nitrogen (N) ion implantation into gallium arsenide (GaAs) results in a thin shallow N-rich layer below the surface. However, the violent implantation process also modifies the concentrations of gallium and arsenide. The core of this thesis is a novel method for prediction of the band gap from the conditions in the processing plasma.<p>The first important variable, the number of implanted ions, is obtained from the Lieberman model for the current during high-voltage Plasma Ion Implantation (PII). A review of the model's assumptions is provided as well as a comprehensive discussion of the implantation which includes error boundaries. The predicted and measured ion currents agree within error boundaries. The number of implanted ions can therefore be obtained from the prediction.<p>The distribution of the implanted ions was subsequently explored by simulations such as TRIM and TRIDYN. It was found that the nitrogen content in GaAs is limited by the sputtering of the surface atoms. Furthermore, the content of gallium increases near the surface while the content of arsenic decreases. The predicted ratios of the constituents in the implanted layer is such that the alloy cannot form by ion implantation alone; it could be reconciled by annealing.<p>Preliminary samples were produced and tested for the formation of the GaAsN alloy by Raman spectroscopy. No evidence for bonds between N and either Ga or As was found in the as-implanted samples. The thesis concludes with a discussion of the necessary steps to synthesize the GaAsN alloy.

Diss. (sammanfattning) Linköping : Univ., 2002. / Härtill 4 uppsatser.

Le Chauffage Cyclotron Ionique (ICRH) par des ondes dans la gamme 30-80MHz est couramment utilisé dans les plasmas de fusion magnétique. Excitées par par des réseaux phasés de rubans de courant à la périphérie du plasma, ces ondes existent sous deux polarisations. L’onde rapide traverse le bord ténu du plasma par effet tunnel puis se propage à son centre où elle est absorbée. L’onde lente, émise de façon parasite, existe seulement à proximité des antennes. Quelle puissance peut être couplée au centre avec 1A de courant sur les rubans? Comment les champs radiofréquence (RF) proches et lointains émis interagissent-ils avec le plasma de bord par rectification de gaine RF à l’interface plasma-paroi? Pour répondre simultanément à ces deux questions, en géométrie réaliste sur l’échelle spatiale des antennes ICRH, cette thèse a amélioré et testé le code numérique SSWICH (Self-consitent Sheaths and Waves for ICH). SSWICH couple de manière auto-cohérente la propagation des ondes RF et la polarisation continue (DC) du plasma via des conditions aux limites non-linéaires de type gaine (SBC) appliquées à l’interface plasma / paroi. La nouvelle version SSWICH-FW est pleine onde et a été développée en deux dimensions (toroïdale/radiale). De nouvelles SBCs couplant les deux polarisations d’ondes ont été obtenues et mises en œuvre le long de parois courbes inclinées par rapport au champ magnétique de confinement. Avec ce nouvel outil en l'absence de SBCs, nous avons étudié l'impact d'une densité décroissant continûment à l'intérieur de la boîte d'antenne en traversant la résonance hybride basse (LH). Dans les limites mémoire de notre poste de travail, les champs RF au-dessous de la résonance LH ont changé avec la taille de maille. Par contre spectre de puissance couplée n’a que très peu évolué, et n’était que faiblement influencé par la densité à l'intérieur de l'antenne. En présence de SBCs, les simulations SSWICH-FW ont identifié le rôle de l'onde rapide sur l’excitation de gaines RF et reproduit certaines observations expérimentales clés. SSWICH-FW a finalement été adapté pour réaliser les premières simulations 2D électromagnétiques et de gaine-RF de la machine plasma cylindrique magnétisée ALINE / Ion Cyclotron Resonant Heating (ICRH) by waves in 30-80MHz range is currently used in magnetic fusion plasmas. Excited by phased arrays of current straps at the plasma periphery, these waves exist under two polarizations. The Fast Wave tunnels through the tenuous plasma edge and propagates to its center where it is absorbed. The parasitically emitted Slow Wave only exists close to the launchers. How much power can be coupled to the center with 1A current on the straps? How do the emitted radiofrequency (RF) near and far fields interact parasitically with the edge plasma via RF sheath rectification at plasma-wall interfaces? To address these two issues simultaneously, in realistic geometry over the size of ICRH antennas, this thesis upgraded and tested the Self-consistent Sheaths and Waves for ICH (SSWICH) code. SSWICH couples self-consistently RF wave propagation and Direct Current (DC) plasma biasing via non-linear RF and DC sheath boundary conditions (SBCs) at plasma/wall interfaces. Its upgrade is full wave and was implemented in two dimensions (toroidal/radial). New SBCs coupling the two polarizations were derived and implemented along shaped walls tilted with respect to the confinement magnetic field. Using this new tool in the absence of SBCs, we studied the impact of a density decaying continuously inside the antenna box and across the Lower Hybrid (LH) resonance. Up to the memory limits of our workstation, the RF fields below the LH resonance changed with the grid size. However the coupled power spectrum hardly evolved and was only weakly affected by the density inside the box. In presence of SBCs, SSWICH-FW simulations have identified the role of the fast wave on RF sheath excitation and reproduced some key experimental observations. SSWICH-FW was finally adapted to conduct the first electromagnetic and RF-sheath 2D simulations of the cylindrical magnetized plasma device ALINE

C4 plants have a biochemical carbon concentrating mechanism (CCM) that increases CO2 concentration around Rubisco in the bundle sheath (BS). Maize CCM has two CO2 delivery pathways to the Bundle Sheath (BS) (respectively via malate, MAL or aspartate, ASP); rates of PGA reduction, carbohydrate synthesis and PEP regeneration vary between BS and Mesophyll (M) cells. For these anatomical and biochemical complexities, C4 plants are highly sensitive to light conditions. Under limiting light, the activity of the CCM generally decreases, causing an increase in leakiness, (Φ), the ratio of CO2 retrodiffusing from the BS relative to C4 carboxylation processes. This increase in Φ had been theoretically associated with a decrease in biochemical operating efficiency (expressed as ATP cost of gross assimilation, ATP / GA) under low light and, because a proportion of canopy photosynthesis is carried out by shaded leaves, to potential productivity losses at field scale. In C4 leaves, because of the concentric anatomy, light reaches M cells before the deeper BS (Evans et al., 2007), and could alter the energetic partitioning balance between BS and M and potentially cause efficiency losses. In this experimental programme I investigated strategies deployed by C4 plants to adjust operating efficiency under different illumination conditions. Firstly, maize plants were grown under high and low light regimes (respectively HL, 600 vs LL, 100 μE m-2 s-1). Short term acclimation of Φ was compared from isotopic discrimination (Δ), gas exchange and photochemistry using an improved modelling approach which does not suffer from elements of circularity. Long term acclimation to low light intensities brought about physiological changes which could potentially increase the operating efficiency under limiting ATP supplies. Secondly, profiles of light penetration across a leaf were used to derive the potential ATP supply for M and BS cells induced by changing light quality. Empirical measurements of net CO2 uptake, ATP production rate and carbon isotope discrimination were made on plants under a low light intensity. The overall conversion efficiency was not affected by light quality. A comprehensive metabolic model highlighted the importance of both CO2 delivery pathways in maize. Further, metabolic plasticity allowed the balancing of ATP and NADPH requirements between BS and M. Finally, I tested the hypothesis that plants can modify their physiology so as to reach a status of higher operating efficiency when exposed to high light and then to low light, so as to mimic the transition which leaves undergo when shaded by newly emerging leaves in a crop canopy. Plants were grown under high light and low light for three weeks, then, HL plants were transferred to low light for a further three weeks. Re-acclimation was very effective in reducing ATP cost of net assimilation under low light intensities. In addition, the hyperbolic leakiness increase observed under low light intensities was not associated to operating efficiency loss. Overall, in the three experimental Chapters I showed compelling theoretical and empirical evidence proving the hypothesis that C4 plants deal with low light conditions and with different light qualities without losing operating efficiency.

Objectifs : (1) Évaluer l’effet de l’anesthésie intrathécale de la gaine carpienne sur la désensibilisation du membre distal et identifier les emplacements potentiels de désensibilisation des nerfs palmaires. (2) Investiguer l’utilisation de l’arthroscope aiguille pour la ténoscopie diagnostique de la gaine carpienne chez le cheval debout. Design : Études expérimentales ex vivo et in vivo. Animaux : Membres cadavériques (n=20+6) et chevaux (n=8+6). Matériel et méthodes : (1) Le seuil de sensibilité cutané a été mesuré sur le membre distal de 8 chevaux entre t0 et t180mn après anesthésie (mépivacaïne) intrathécale. Puis, 20 membres thoraciques ont été préparés et disséqués transversalement ou longitudinalement. (2) Les ténoscopies de la gaine carpienne avec arthroscopes aiguille et standard ont été comparées sur 6 cadavres avant de réaliser la ténoscopie avec un arthroscope aiguille chez 6 chevaux sous sédation. Résultats : (1) 6/8 chevaux ont été désensibilisés au niveau des glomes. Les nerfs palmaires sont en relation étroite avec la gaine à 2 sites de diffusion probables identifiés. (2) L’arthroscope aiguille a permis une exploration complète des structures proximales dans les modèles cadavérique et in vivo (6/6), la tension résiduelle des tendons fléchisseurs a toutefois limité la visualisation du fléchisseur superficiel du doigt chez 4/6 des chevaux in vivo. Conclusion : (1) L’anesthésie intrathécale de la gaine carpienne devrait être interprétée dans les 15min post-injection, et les autres anesthésies distales au carpe être repoussées plus de 3h après. (2) La ténoscopie debout a permis une évaluation complète et sécuritaire de la région proximale de la gaine, offrant ainsi une technique diagnostique alternative. / Objective: (1) To assess the effect of carpal sheath anaesthesia on skin sensitivity of the distal forelimb and to determine potential locations for desensitisation of palmar nerves. (2) To investigate the use of a needle arthroscope for diagnostic tenoscopy of the carpal sheath in standing horses. Study design: Experimental ex vivo and in vivo studies. Animals: Cadaveric limbs (n=20+6) and live horses (n=8+6). Methods: (1) Mechanical nociception of the distal forelimb was measured with a dynamometer on 8 horses between t0 and t180mn after intrathecal anesthesia (mepivacaine). Twenty cadaveric limbs were prepared and dissected transversally or longitudinally. (2) Needle and regular arthroscopes were compared during carpal sheath tenoscopy of 6 cadaveric limbs. Then, standing carpal sheath tenoscopy was performed in 6 sedated healthy horses with the needle arthroscope. Results: (1) Six out of 8 horses were completely desensitized on both heel bulbs. Cadaveric specimens revealed close proximity between the sheath and palmar nerves at 2 possible diffusion sites identified. (2) Needle arthroscopy allowed thorough visualization of the proximal region of the carpal sheath in cadaveric limbs and standing horses (6/6). However, remaining flexor tendons tension limited visualization of the superficial digital flexor tendon in 4/6 of horses. Conclusion: (1) Carpal sheath anaesthesia should be interpreted within 15min post-injection and perineural or articular blocks distal to the carpus should be delayed for more than 3 hours post-carpal sheath anesthesia. (2) Standing carpal sheath tenoscopy allows a safe and thorough evaluation of the proximal region of the sheath, offering an alternative diagnostic technique.

No description available.