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Reproduction de : Thèse de doctorat : physique : Le Mans : 2006. / Titre provenant de l'écran-titre.

Thesis (Ph. D.)--University of Washington, 2001. / Includes bibliographical references (leaves 156-168).

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 174-184).

Thesis (M. S.)--Physics, Georgia Institute of Technology, 2010. / Committee Chair: Kennedy, Brian; Committee Member: Chapman, Michael; Committee Member: Zangwill, Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Among the many examples of Bose condensation considered in physics, electron-hole-pair (exciton) condensation has maintained special interest because it has been difficult to realize experimentally, and because of controversy about condensate properties. In this thesis, we studied the various aspects of spontaneous symmetry broken state of exciton in bilayer using mean field theory. We calculated the photoluminescence of excitonic condensation created by laser. We developed a one-dimensional toy model of excitonic supercurrent using mean field theory plus non-equilibrium Green’s function (NEGF) which give qualitatively consistent results with experiments. We proposed graphene bilayer as a novel system for excitonic condensation to occur and estimate it to exist even at temperature as high as room temperature. / text

In this dissertation, the applications of many-body physics in neutral bosons and electronic systems in transition metal oxides are discussed. In the first part of the thesis, I will introduce the concepts of Bose condensation, emphasize the significance of the order parameter in superfluids (macroscopic wave function), and its consequence such as the emergence of exotic vortex states under rotation. Dated back to the importance of the vortex dynamics in the properties of high T[subscript c] superconductors, people have introduced a dual vortex description to describe the dynamics of charged bosons in a magnetic field. Similarly, the dual description is adapted to the problems of neutral bosons under rotation. Based on that picture, vortices behave like charges in an effective magnetic field which has been known to demonstrate different quantum phases such as Wigner crystal phase, and fractional quantum Hall liquid phases depending on the relative fraction of the number of bosons and vortices. In this work, we would like to address the validity of the picture by low energy effective theory. We can identify the origin of the vortex masse and the parameter regimes in which the vortex dual description is appropriate. In the second part of the dissertation, density functional theory is used to describe the strongly correlated matters with local density approximation and local Hubbard U interaction(LDA+U). We are particularly interested in the interface states in the heterojunction systems of two different perovskite oxides. What we found is that the interface states can be engineered to appear in certain transitional metal oxide layers by controlling the number of positive and negative charged layers, leading to the formation of quantum wells in two dimension. This type of systems ignite the hope to search for broken symmetry states in the interface which can be tunable with chemical doping or electric field doping. Even room temperature superconducting state may or may not exist in the interface is still an intriguing issue. / text

Distillers’ spent grain (DSG) is a by-product of ethanol production and used for swine feed supplement due to its nutrient composition. Lowering the moisture content of DSG using superheated steam (SS) drying can be more energy efficient compared to hot air drying. One objective was to investigate parameters associated with SS drying on DSG including maximum condensation, condensation time, and restoration time. Increasing SS temperature from 120 to 180 °C and SS velocity from 1.0 to 1.4 m/s resulted in a 97% and 67% decrease in maximum condensation, respectively. Another objective was to determine the effect of SS temperature, velocity, and pellet orientation on effective moisture diffusivity of DSG pellets. The diffusion model was based on finite cylinder geometry accounting for volumetric shrinkage. The diffusivity coefficient was determined to be 1.56 × 10-8 m2/s. A significant effect of pellet orientation on moisture diffusivity was found during the constant drying-rate period. / October 2015

Thesis (MTech. degree in Chemistry)--Tshwane University of Technology, 2008. / This work is aimed at experimental verification of the theory about the advantages of the two-step sample vapour release in a fast-heated ballast furnace. The term “ballast” was introduced earlier in electrothermal atomic absorption spectrometry, as an alternative to a platform to describe a compact body of refractive material loosely located on the bottom of a tube furnace atomiser. The thermal behaviour of the ballast furnace is similar to that of the platform, but without restriction created by the platform area. Compared with the flat or concave platform, a compact ballast of similar mass to the platform should have less impact on gas temperature because of the smaller surface area. The theoretical predictions concerning atomisation efficiency in the fast-heated ballast furnace were examined by the determination of metals in organic and inorganic matrices using a Quantum Z.ETA atomic absorption spectrometer. The instrument provided fast heating of the tube atomizer, 10 K ms-1. It is shown that in the employed ballast furnace the vapour released into the gas phase occurs after interim condensation on the ballast. For the samples of tetraethyllead, base oil and aqueous solutions of various metals, analytical signals are observed after stabilisation of tube temperature, independent of volatility of the analyte and level of temperature setting. For those samples, a high gas phase temperature provides complete recovery of the analyte without involvement of chemical modifiers and the reduction of spectral interferences from chloride matrices.

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