Medium-manganese steels (5-12 wt%) are candidates for third-generation advanced high strength steel (AHSS). Potential applications for these steels are centered around the automotive industry due to their combination of high tensile strength, high tensile ductility, and low alloying cost. Previous studies at VT have been primarily focused on the effect of chemistry on mechanical properties with only a minor emphasis on microstructure. This led to a detailed investigation into the effect of carbon content on the microstructure of Fe8Mn2AlSiC alloys. Six different chemistries with carbon contents of 0.30, 0.34, 0.39, 0.44, 0.49 and 0.52 wt% were produced at the Kroehling Advanced Materials Foundry. After a variety of heat treatments, the samples were characterized using x-ray diffraction (XRD), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), optical microscopy, and hardness testing. This thesis will discuss how the microstructure and hardness of these medium manganese steels is influenced by the carbon content. / Master of Science / This research will be used to help design steel alloys that might one day be used in automotive applications. These steels need to be tough and ductile so they can absorb impact without fracturing. This is especially important in the event of a car crash, in which the steel needs to deform without breaking and causing injury to the driver or passenger. In order to achieve such qualities today, expensive elements are often added to the steel which increases cost. Medium manganese steels hope to alleviate this issue by providing a less expensive alternative with similar deformation properties. The properties of steel can be correlated with its microstructure, and more specifically, the different phases that make up the microstructure. These phases give rise to the macroscopic properties that make steel so useful. Microstructure can be controlled through chemistry and through thermomechanical processes. This research focuses on the effects of carbon and on heat treatments. This research is unique in that it keeps the chemistry consistent between all of the samples, making the effect of carbon or of the heat treatment identifiable. A total of six different carbon contents were tested over eight different heat treatment conditions. After creating the samples, the hardness was measured. The samples were then characterized to understand the microstructure. The results of this research showed there is a direct connection between heat treatment and chemistry to the microstructure.

Rosmarinus officinalis L. (rosemary) is popular as a culinary herb, landscape plant, and potted florist's crop. Little research has been reported on the greenhouse production of this plant. Effects of irrigation rate, fertilizer concentration, and growing media on root and shoot growth were investigated for R. officinalis 'Athens Blue Spires'. In the first experiment, rooted cuttings were potted and received fertilizer treatments of 100, 200, or 300 mg?L-1 nitrogen (N) from 15N-2.2P-12.2K water-soluble fertilizer for twelve weeks. Two irrigation regimes were imposed - plants were irrigated with fertilizer solution when the growing media dried down to less than 30% or 20% volumetric soil moisture content. Root and shoot dry weights showed irrigation rate did not effect roots, but the higher irrigation rate produced larger shoots at all fertilizer concentrations. The largest roots and shoots were a product of the lowest fertilizer concentration. In the second experiment, rooted cuttings of the same cultivar were potted and received fertilizer treatments of 50, 100, 150, or 200 mg?L-1 N from 15N-2.2P-12.2K water-soluble fertilizer for 2, 4, 6, or 8 weeks. Plants were harvested at the end of each treatment. A third irrigation regime was imposed - plants were irrigated with fertilizer solution when the growing media dried down to less than 40%, 30%, or 20% volumetric soil moisture content. Root and shoot dry weights showed neither irrigation nor fertilizer were significant at week two, six, or eight. Dry weights showed irrigation was significant for roots at week four with the lowest irrigation rate producing the largest roots at all fertilizer concentrations except 100 mg?L-1 at the less than 30% irrigation rate. Irrigation was also significant at week four for shoots with the lowest irrigation rate producing the largest shoots at all fertilizer concentrations except 100 mg?L-1 at the less than 30% irrigation rate. In the third experiment 'Athens Blue Spires' rooted cuttings were potted in five different soilless media [Fafard 52 (24% peat, 60% bark, 8% perlite, 8% vermiculite); Fafard 3B (45% peat, 25% bark, 15% perlite, 15% vermiculite); Scott's Sierra Perennial Mix (25% peat, 65% bark, 10% perlite); Scott's Metro Mix 700 with Coir (25% coir, 50% bark, 10% perlite, 15% vermiculite); and a nursery mix (89% pine bark, 11% sand)]. Plants were irrigated for fourteen weeks with 150 mg?L-1N fertilizer solution when the growing media dried down to less than 30% or <20% volumetric soil moisture content. Growing media affected shoot dry weight with the highest-percentage peat media (Fafard 3B) producing the largest plants. All were of marketable quality. Irrigation rate did not affect root dry weight, but the higher rate produced larger shoots in each of the five media. The fourth experiment examined the growth of R. officinalis 'Tuscan Blue' rooted cuttings when planted in five different growing media [Fafard 52, Fafard 3B, Scott's Perennial, Metro Mix 560 with coir (30% coir, 15% peat, 40% bark, and 15% perlite), and 100% pine bark]. A third irrigation regime was imposed - plants were irrigated with 150 mg?L-1N fertilizer solution when the growing media dried down to less than 40%, 30%, or 20% volumetric soil moisture content. Treatments lasted for 2, 4, 6, or 8 weeks and plants were harvested at the end of each treatment. Dry weights showed neither media nor irrigation was significant for roots or shoots at weeks four or eight. However, at week two, media significantly affected root dry weight with the heaviest roots produced by the two perennial mixes (Scott's perennial and Fafard 52). Growing media affected shoot dry weight at week six with the highest-percentage peat media (Fafard 3B) producing the largest plants at the low and high irrigation rate. Irrigation also affected root dry weight at week six with the two lowest irrigation rates producing the heaviest roots in all media. / Master of Science

The production of high quality silicon requires the use of ultraclean coal containing less than 1.5% ash. The magnetite used to clean the coal in a dense medium process is a contaminant that seriously impacts the quality of the final silicon product. As such, research has been conducted to evaluate the potential to substitute the magnetite with fine silica–based alternative material generated during the silicon production process. Dense medium cyclone tests were performed based on a statistically designed program to determine the optimum conditions that maximize organic efficiency and minimize probable error and low–density bypass. The results revealed that a clean coal product with less than 1.5% ash can be produced using a medium formed from the silicon production waste with an organic efficiency value of around 99% and a probable error value below 0.02. There was no measurable bypass of high density particles into the product stream or low–density particles into the reject stream.

<p>The effect of stellar feedback on the interstellar medium is investigated using numerical simulation. In particular, the roles of supernova feedback and ionization feedback on the star formation rate and structure of the interstellar medium are compared. We use Enzo, an adaptive mesh code, and employ the MUSCL-Hancock hydrodynamics scheme to run simulations of a section of a stratified galactic disk. A turbulent velocity field is imposed in the central region of the disk and self-gravity is applied. Star clusters are formed when density and temperature conditions are met, which, in turn, provide ionization and supernova feedback into the interstellar medium. Simulations were run with and without supernova and ionization feedback and the runs are compared. Ionization feedback is found to dominate over supernova feedback in regulating star formation rates. With no feedback, all the gas is converted to stars by 200 Myr. When supernova feedback is added, 98% of the gas is used to create stars by 300 Myr. With ionization feedback instead, at 1 Gyr into the run, only 30% of the gas is in stars. Even with supernova feedback added to ionization feedback, the gas converted to stars is just 29% at 1 Gyr. Very strong supernovae take this fraction down to 25%. The star formation rates in the runs with supernova feedback are consistent with the low end of the Kennicutt-Schmidt relation, while the runs without ionization feedback have star formation rates that are an order of magnitude larger. Gas phase masses and volumes produced in the ionization runs are broadly consistent with observations.</p> / Master of Science (MSc)

This study was a research on the effects of the change in the tax system on small medium sized enterprises. Its focus was in Swaziland. It concludes by giving recommendations on how the tax system can be improved in view of what have succeeded in other countries with an almost similar economy. It also recommends more research in this field.

Winterreise : D. 911 / Franz Schubert. / text

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It has become increasingly clear that a complete picture of galaxy evolution requires a better understanding of the role of Active Galactic Nuclei (AGN). In particular, they could be responsible for regulating star formation and galaxy growth via feedback processes. There are also competing views about the main modes of stellar growth and supermassive black hole growth in galaxies that need to be resolved. With high infrared luminosities (thus star formation rates) and a frequent occurrence of AGN, galaxies selected in the far-infrared wavebands form an ideal sample to search for a connection between AGN and star formation. The first part of this thesis contains a detailed analysis of the molecular gas properties of nearby infrared luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs). We find that the enhanced molecular gas density in the most IR-luminous systems can be explained by major galaxy mergers, and that AGN are more likely to reside in higher-density systems. While the frequent concurrence of AGN and galaxy mergers in ULIRGs was already established, this work provides a coherent framework that explains trends observed with five molecular gas tracers with a broad range of critical densities, and a comparison with simulations that reproduce observed molecular line ratios without invoking AGN-induced chemistry. The second part of the thesis presents an analysis of the AGN content of intermediate redshift galaxies (0.3<z<1). However, identifying complete AGN samples at these redshift is challenging because it is difficult to find X-ray weak or absorbed AGN. To alleviate this problem, we developed the Mass-Excitation (MEx) diagram, which is applicable out to redshift of 1 with existing optical spectra. It improves the overall AGN census by detecting AGN that are missed in even the most sensitive X-ray surveys. The new diagnostic was used to study the concurrence of star formation and AGN in 70 micron-selected galaxies from the Far-Infrared Deep Extragalactic Legacy survey. When multiple AGN diagnostics are combined, we find not only a high AGN fraction in FIR-selected galaxies (as high as for nearby FIR-selected galaxies), but a high incidence of X-ray absorbed AGN. These findings may have considerable implications for current views about the main mode of AGN growth.

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