Lutetium 177 ions were implanted in iron and nickel foils using a mass separator. The rotations of the angular correlation pattern caused by the hyperfine fields acting on the implanted nuclei were measured for the 71-250 keV and the 208-113 keV cascades in the beta-decay product Hafnium 177. Using measured data, the g-factor for the 250 keV spin 11/2, second excited state in Hf177 was determined, as were the internal fields acting on the Hf177 impurity in iron and nickel. The results are as follows: g11/2 = 0.277 ± 0.080 HFe(int) = -133 ± 7 k0e HNi(int) = -58.6 ± 8 k0e / Thesis / Master of Science (MSc)

<p> A surface station consisting of a sample manipulator and transfer system was developed to allow the study of plasma - first wall interactions in ALCATOR at M.I.T. A disc shaped probe is located at the plasma edge and rotated past an aperture in a shield to obtain time resolved data. Samples can be analysed in situ or transported under vacuum to McMaster University. The transfer process from the surface station to the 'vacuum suitcase' is accomplished by means of pressure locks.</p> / Thesis / Master of Engineering (MEngr)

"A ¡°mixed cathodes¡± LIB recycling process was first proposed and developed in the CR3 center at Worcester Polytechnic Institute. This process can efficiently and economically recover all the valuable metal elements in LIB waste. In the end of the recovery process, lithium, nickel, manganese, and cobalt ions will be recovered in the leaching solution. The objective of this work is to utilize the leaching solution to synthesis NixMnyCoz(OH)2 precursors and their corresponding LiNixMnyCozO2 cathode materials. The synthesized cathode materials can be used to build new LIBs, allowing the overall process to be a ¡°closed loop¡±. "

In the quantum dot implementation of an intermediate band solar cell presented in this thesis, the offset of the intermediate band with respect to the conduction band is approximated by the ground state energy of a single electron in a single quantum dot heterojunction. The ground state energy is calculated with the radial Schrodinger equation with a Hamiltonian whose potential is composed from the step-like conduction band offset of the quantum dot heterojunction and the 1/r electrostatic potential of the hydrogenic impurity. The position of the intermediate band is tuned by adjusting the radius of the quantum dots. By assuming that the centrally located impurities are ionized, the location of the Fermi energy is guaranteed to be within the intermediate band. An intermediate band solar cell contains three bands: a conduction band, a valence band; and an intermediate band. The addition of an intermediate band augments the photogeneration of carriers. These additional carriers allow for an increased theoretical efficiency as compared to a conventional homojunction solar cell. The challenges in implementing an intermediate band solar cell involve centering the intermediate band at an energy level matched to the solar spectrum and aligning the Fermi energy within the intermediate band. The latter is necessary to ensure both a supply of electrons capable of photon induced transition to the conduction band as well as a large population of holes that allow photon induced electrons to transition from the valence band to the intermediate band. This thesis presents a novel material system, InPAs quantum dots enveloped in AlGaAs barriers grown on GaAs substrates, with which to implement an optimized QD-IBSC. This novel material system is selected based upon a refined set of design rules that include a requirement that the quantum dot/barrier pair offer a negligible valence band offset. With such a design rule the existence of hole levels is avoided, thus reducing bandgap narrowing at the valence band edge and the existence of minibands below the intermediate band.

No description available.

Electron scattering by a single or multiple impurities affects the quantizaton of conductance of a semiconductor nanochannel. The theoretical model of electron transport in a hardwall nanostructure with an impurity requires an analysis of the electronic transverse energy levels, eigenfunctions and hopping integrals resulting from cross channel or transverse confinement. Theoretical equations for the electronic transverse energy levels, wavefunctions and hopping integrals in the case of a repulsive, finite strength rectangular barrier arbitrarily positioned in the nanochannel are presented. The effects of size, strength and location of the impurity are discussed.In order to find the electronic transverse energy levels, wavefunctions and hopping integrals, two FORTRAN computer programs were developed. The first, called Program Data Input, writes the computational parameters to a data file. The second, Program Single Impurity, uses this data file in performing the calculations of the electronic transverse energy levels, eigenfunctions and hopping integrals. / Department of Physics and Astronomy

Experiments on several tokamaks convincingly demonstrated that a deliberate seeding of selected impurities can have a positive effect on the plasma performance. On the one hand, a significant reduction of the head load on divertor plates, one of the main concerns by constructing a thermonuclear reactor, has been achieved due to the increase of edge radiation. On the other hand, in some devices impurity seeding has led to an improvement of the energy confinement and the so called radiation improved (RI) mode has been established with the same or even better confinement than in the H-mode. However, in order to make use of these positive impacts, the behaviour of seeded impurity has to be strictly controlled and such negative developments as the accumulation of impurity ions in the plasma core accompanied by a strong increase of the central radiation losses should be avoided.<p><p>Plasma heating by radio-frequency (RF) waves has been proven to be a useful tool to control the behaviour of puffed impurities. In order to asses the prospective of impurity control by RF waves in larger devices and under reactor conditions, proper modelling approaches have been developed. One of the important parameters, which should be evaluated, is the averaged energy or temperature of heated impurity ions. The latter determines, in particular, the power transported to the main species, and, thus, the heating efficiency. Besides, the temperature of impurity ions characterizes the intensity of particle losses for heated impurities. An approach to compute the impurity temperature under such conditions is elaborated. It is based on the construction of a hierarchy of approximate solutions to the impurity heat balance equation and takes into account that the density and, thus, the heat conductivity of heated ion species can change by many orders of magnitude with the position in the plasma. The developed method has been incorporated into 1D transport code RITM. Coupled with the full wave code TORIC, the particle and heat balances for impurity and main plasma species provide a self-consistent approach to model the ion cyclotron resonance heating (ICRH) scenario. The modelling of various heating scenarios for several tokamaks displays the impacts of impurity heating on the heat and particles transport and heating efficiency. To investigate the possibility of impurity control at the large tokamak the experiment on selective impurity heating in the mode conversion H/D plasma was prepared and carried out in the tokamak JET.<p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p><p> / Doctorat en sciences, Spécialisation physique / info:eu-repo/semantics/nonPublished

Les performances des plasmas de fusion confinés magnétiquement peuvent être dégradées par l'accumulation d'impuretés. Plus particulièrement, les impuretés lourdes accumulées au centre du plasma diluent les réactifs, et peuvent aussi conduire à un collapse radiatif du plasma par de fortes pertes par rayonnement. La compréhension du transport des impuretés lourdes produites lors de l'interaction plasma-paroi est donc devenue cruciale.Le coeur du plasma est sujet à une instabilité magnétohydrodynamique (MHD) appelée ‘kink interne’, conduisant à des oscillations de relaxation nommées ‘dents de scie’. Les dents de scie entraînent une relaxation périodique de densité et de température dans le coeur du plasma, et affectent significativement le transport radial. Notamment, les particules et la chaleur sont redistribuées pendant un crash dont la durée est très courte par rapport au temps de confinement.En l'absence des instabilités MHD, le transport des impuretés est porté par les collisions (transport néoclassique) et la turbulence. Il est établi que le transport néoclassique est important pour les impuretés lourdes dans la région centrale du plasma de tokamak. Cependant, des mesures expérimentales du tokamak ASDEX-Upgrade montrent que la dynamique des impuretés en présence des dents de scie est différente des prédictions faites par les codes de transport.Dans cette thèse, l'outil numérique utilisé pour simuler les dents de scie est le code XTOR-2F, qui est un code non-linéaire tridimensionnel résolvant les équations de la MHD. Les équations fluides modélisant le transport des impuretés dans un régime de collisionalité élevée (Pfirsch-Schlüter) ont été implémentées et couplées avec l'ensemble des équations de la MHD bi-fluide.Les simulations montrent que les profils de densité d'impuretés sont affectés par les dents de scie, en accord avec les observations expérimentales. Ceci résulte d'une compétition entre processus néoclassiques et relaxations dues aux dents de scie. / Impurity accumulation can degrade the performance of magnetically confined fusion plasmas. In particular, heavy impurities accumulated in the core plasma dilute fusion reactants and may also lead to a radiative collapse of the plasma due to excessive cooling by radiation. Therefore, understanding the transport of heavy impurities produced by plasma-wall interaction has become a subject of utmost importance.The plasma core is likely to be affected by a magnetohydrodynamic (MHD) instability called 'internal kink' that induces relaxation oscillations named 'sawteeth'. Sawteeth are responsible for periodic relaxations of the core density and temperature and affect significantly the radial transport. Especially, particles and heat are redistributed during the crash phase the duration of which is short compared to the confinement time.In absence of MHD instabilities, impurity transport is governed by collisions (neoclassical transport) and turbulence. It is shown that neoclassical transport is important for heavy impurities in the core region of tokamak plasmas. Meanwhile, experimental measurements in the ASDEX-Upgrade tokamak show that the impurity dynamics in presence of sawteeth differs from the predictions made by transport codes.In this thesis, the numerical tool used to simulate sawteeth is the XTOR-2F code, which is a non-linear tridimensional code solving MHD equations. Fluid equations that model the transport of impurities in a highly collisional (Pfirsch-Schlüter) regime have been implemented and coupled to the set of two-fluid MHD equations.The simulations show a difference between the impurity profiles with and without sawteeth, which is consistent with experimental observations. This results from a competition between neoclassical processes and sawtooth relaxations.

A syngas compositional database with focus on trace impurities was established. For this work, ammonia (NH3) and benzene (C6H6) effects on cell growth, enzymatic activities of hydrogenase and alcohol dehydrogenase (ADH), and product formation were studied. NH3, after entering media, will be converted rapidly to NH4+, which will raise the total osmolarity of the media. NH3, as a common nutrient for the cell growth, is not the real culprit for cell growth inhibition. In essence, it is the high osmolarity resulting from the accumulation of NH4+ in the media which disrupts the normal regulation of the cells. It was concluded that at NH4+ concentration above 250 mM, the cell growth was substantially inhibited. However, P11 cells used in this study can likely adapt to an elevated osmolarity (up to 500 mM) although the mechanism is unknown. It was also found that higher osmolarity will eventually lead to higher ethanol per cell density. In conclusion, NH3 needs to be cleaned out of syngas feeding system. The realistic C6H6 concentration in the media coming from a gasifier was simulated in bioreactors and was measured by a GC/MS. The most realistic C6H6 concentration in the media was around 0.41 mM (upper limit 0.83 mM). However, five elevated concentrations of 0.64, 1.18, 1.72, 2.33, and 3.44 mM were doped into the media. It was found that at 3.44 mM cell growth and ethanol production were significantly affected. However, there was only negligible adverse effect on cell growth and ethanol production at 0.41 mM, which is the expected concentration in bioreactors exposed to syngas. Therefore, it is unnecessary to remove C6H6 from the gas feeding stream. A kinetic model for hydrogenase activity that included inhibition effects of NH4+ and C6H6 was developed. Experimental results showed that NH4+ is a non-competitive inhibitor for hydrogenase activity with KNH4+ of (649 ± 35) mM and KH2 of (0.19 ± 0.1) mM. This KH2 value is consistent with those reported in literature. C6H6 is also a non-competitive inhibitor but a more potent one compared to NH4+ (KC6H6=11.4 ± 1.32 mM). A KH2 value of (0.196 ± 0.022) mM is also comparable with literature and also with the NH4+ study. At a realistic C6H6 concentration of 0.41 mM expected in bioreactors exposed to syngas, hydrogenase activity is expected to be reduced by less than 5%. Forward ADH activity was not adversely affected up to 200 mM [NH4+].From the current work, NH3 should be targeted for removal but it is not necessary to remove C6H6 when designing an efficient gas cleanup system.

<p> High resolution measurements of the far-infrared absorption spectra due to a number of substitutional impurities in KBr and KCl are presented. Several Van Hove singularities of the phonon spectrum of the host lattice are directly observed and found to shift to higher frequencies as the impurity concentration is increased. The first direct experimental evidence for the change of shape or metamorphism of singularities is also presented. The experimental spectra are compared with numerical calculations based on the ordinary shell model for the defect together with phonon data obtained from inelastic neutron scattering experiments. Agreement between experiment and calculation is generally good when impurity resonant modes are absent.</p> / Thesis / Doctor of Philosophy (PhD)