An optical, contact-free method for measuring minority carrier diffusion lengths is developed and demonstrated for a range of semiconductor materials used in high efficiency triple junction solar cells. This method uses a Scanning Electron Microscope (SEM) coupled with an optical microscope. The diffusion lengths, combined with minority carrier lifetime measured via time-resolved photoluminescence, allow for the computation of minority charge carrier mobility. The technique uses images to extract diffusion length measurements from GaAs, InGaAs, and InGaP heterostructures at different SEM beam energies and probe currents. Excellent correlation between measurements shows the reproducibility of this technique. Diffusion lengths from 2-63 microns have been measured in a variety of GaAs, InGaAs, and InGaP samples. Effects of alloy ordering, doping, and lattice matching have been investigated. Several areas for further research are offered, including detailed radiationdamage mapping of solar cell layers. Further anisotropic studies of the solar cell layers are suggested to investigate the directional dependence of diffusion length within the InGaP heterostructures. Finally, new and emerging solar cell materials would benefit from this technique, allowing for the complete characterization of minority charge transport properties before growing an entire solar cell.

The thesis is concerned with the derivation of anisotropic intermolecular potentials from experimental data. For the rare gas - hydrogen halide systems the most useful experimental results are those from molecular beam rotational spectra of van der Waals complexes and from pressure broadening of hydrogen halide rotational spectra by rare gases. Intermolecular potentials for the Ar.HCl system had previously been obtained from each of these experiments separately, but none of the potentials proposed succeeded in reproducing all the available data. In the present work, improved theoretical methods are developed for the calculation of molecular beam spectra and line broadening cross sections from a proposed intermolecular potential. The methods developed are substantially faster than those previously available, allowing their use in a least squares procedure to determine potential parameters. Several possible parameterisations of the intermolecular potential are then considered for Ar.HCl, and least squares fits of potential parameters to experimental results are performed for this system. Measurements of total differential cross sections and second virial coefficients are included in the least squares fits, in addition to the experiments mentioned above. The experimental data demonstrate conclusively that the equilibrium geometry of Ar.HCl is linear, with the atomic arrangement as written. The equilibrium intermolecular distance is 400±3 pm, with an absolute well depth of 18andpm;10 cm^-1 . The only feature of the potential which is not well determined by the experimental results is the behaviour around the linear Ar.Cl-H geometry. The results for Ar.HCl are then extended to the systems Ne.HCl, Kr.HCl and Xe.HCl, allowing the dependence of the intermolecular potential on the rare gas to be considered. The molecular beam spectra for Ne.HCl can be fitted only by a potential with a secondary minimum at the linear Ne.Cl-H geometry, in addition to the primary minimum at the linear Ne.H-Cl geometry. The experimental results for the other rare gas - HC1 systems are not very sensitive to this feature of the potential, and the potentials for these are constrained to be similar to that for Ne.HCl in this region. The potential surfaces for all the rare gas - HC1 systems have similar shapes, and appear to be nearly conformal. Finally, intermolecular potentials are obtained for the systems Ar.HF, Kr.HF and Xe.HF from molecular beam spectra. The experimental data for these systems are less extensive than for the HC1 systems, and the potentials obtained are reliable only in the region of the absolute minimum. The HF systems are considerably more anisotropic than the HC1 systems, and it is suggested that this is principally due to greater induction forces in the HF systems. Experiments are suggested which would provide further information on the intermolecular potentials for both HF and HC1 systems, and predictions of the results are made using the current best fit potentials.

Xu Bai Yu. / "August 22, 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. [164]-169). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

PhD, Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2010 / Informal settlements are a growing world-wide phenomenon. Up-to-date spatial information mapping settlements is essential for a variety of end-user applications from planning settlement upgrading to monitoring expansion and infill. One method of gathering this information is through the analysis of nadir-view aerial imagery and the automated or semi-automated extraction of individual shacks. The problem of shack detection and delineation in, particularly South African, informal settlements is a unique and difficult one. This is primarily due to the inhomogeneous appearance of shack roofs, which are constructed from a variety of disparate materials, and the density of shacks. Previous research has focused mostly on the use of height data in conjunction with optical images to perform automated or semi-automated shack extraction. In this thesis, a novel approach to automating shack extraction is presented and prototyped, in which the appearance of shack roofs is homogenised, facilitating their detection. The main features of this strategy are: construction of an anisotropic scale-space from a single source image and detection of hypotheses at multiple scales; simplification of hypotheses' boundaries through discrete curve evolution and regularisation of boundaries in accordance with an assumed shack model - a 4-6 sided, compact, rectilinear shape; selection of hypotheses competing across scales using fuzzy rules; grouping of hypotheses based on their support for one another, and localisation and re-regularisation of boundaries through the incorporation of image edges. The prototype's performance is evaluated in terms of standard metrics and is analysed for four different images, having three different sets of imaging conditions, and containing well over a hundred shacks. Detection rates in terms of building counts vary from 83% to 100% and, in terms of roof area coverage, from 55% to 84%. These results, each derived from a single source image, compare favourably with those of existing shack detection systems, especially automated ones which make use of richer source data. Integrating this scale-space approach with height data offers the promise of even better results.

No description available.

The code is developed for the calculation of the magneto-crystalline anisotropy (MAE) in thin films using a classical Heisenberg hamiltonian with a correction developed by Van Vleck. A Metropolis style Monte Carlo algorithm was used with adequate corrections to accelerate the calculation. The MAE was calculated for the case of a thin film with an increasing number of defects on the top layer for the cases where the defects were distributed randomly and when they assumed ordered positions. The results obtained agree qualitatively with the results provided by the literature and with the theory. / Graduation date: 2003

The thermodynamic and structural effects of highly anisotropic, short-ranged attraction are investigated for single- and four-site interaction models using Wertheim's multi-density graph theory of chemical association. Both models consist of associating hard spheres, where the saturable attraction sites are described by conical wells centered in the hard core and evaluated in the "sticky-spot" limit. The resulting fluids then mimic many of the directional and steric-constrained properties of hydrogen-bonded fluids. The single-site model is used to explore the effects of dimerization upon the well-known properties of a planar liquid-vapor interface. Apart from hard sphere repulsion and sticky-spot attraction, a van der Waals-like dispersion interaction is incorporated to generate the critical point. Association is treated within Wertheim's thermodynamic perturbation theory, along with classical density functional methods to determine the interfacial density profile. The direct correlation functions which carry all bonding information are derived by means of the associative Ornstein-Zernike equations with a Percus-Yevick-like closure relation. The primary effects of dimerization are manifest in system thermodynamics. Critical temperatures and densities are shifted from their non-associating values and small, non-monotonic shifts in the correlation length and surface tension are also observed. While these effects are accompanied by interface compositional changes, any influence upon the density profile seems to be subsumed by use of the proper T/T[subscript c]. The four-site, network-forming model is investigated as a prototype for the thermodynamics and structural properties of water. Bonding interactions occur between "hydrogen" and electron "lone pair" sites described in the sticky-spot limit. System properties are derived under the ideal network approximation using the same methods as for the one-site model and are found to qualitatively reproduce some thermodynamic and connectivity features characteristic of real water. Partial densities are calculated self-consistently within the theory, and most thermodynamic quantities can be written in terms of the average number of hydrogen bonds per molecule. An analytical structure factor is also derived for this model. / Graduation date: 2003

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Restricted until May 2006. Bibliography: leaves 75-77. Also available online.

The crust is the outer-most layer of the earth with thickness up to 80 km. Massive seismic waveform data have enabled imaging fine crustal structures with the aid of new imaging techniques. In this thesis, I develop seismic imaging techniques to take full advantage of the expanding dataset as well as apply the imaging techniques to understand crustal seismic structures. First, I apply receiver function techniques to image the crustal thickness and average Vp/Vs in Northeast China. I found an uplifted Moho in eastern flank of the Songliao Basin and the Changbaishan region and suggest that dynamic mantle upwelling might be the cause of the observed uplift. With accumulated waveform data available, it becomes possible to extract more subtle structural information from receiver function. Second, I develop a new technique to robustly estimate seismic azimuthal anisotropy with radial and transverse receiver functions. I apply this technique to estimate the crustal anisotropy in Southeast Yunnan region and found that the significant crustal anisotropy may be caused by lower crust flow in this region. Full-wave based imaging techniques such as reverse time migration and full-wave inversion does not assume flat interfaces or infinite frequency rays as that the receiver function techniques do and are desirable in imaging more complex crustal structures. However, their high computational cost is one of the issues that prevent their practical applications. In the last part, I developed an effective waveform modeling technique to efficiently simulate wave propagation in acoustic media. With this novel modeling technique, the full-wave based imaging techniques are accelerated by a factor up to 400%.

Includes bibliographical references (p. 124-135).