Erstmalig wurden für die VGF-Züchtung von GaAs-Kristallen die verschiedenen Möglichkeiten der Beeinflussung der Kohlenstoffkonzentration untersucht und Möglichkeiten zu deren zielstrebigen Einstellung aufgezeigt. Dies eröffnet auch für die so gezüchteten Kristalle den semi-isolierenden Widerstandsbereich bei niedrigkompensiertem GaAs technologisch sicher einstellen zu können. Anhand umfangreicher experimenteller Daten und thermodynamischer Betrachtungen werden die komplexen Zusammenhänge untersucht und Lösungswege für die technologische Beherrschung aufgezeigt. Das auf die experimentellen Daten angewendete Modell erzeugte die notwendigen Regelparameter für einen gradientenfreien Verlauf der Kohlenstoffkonzentration entlang der Kristallachse. Die Ergebnisse der Dissertation konnten in eine industrielle Fertigungstechnologie übertragen werden.

The influence of human activity on surrounding environments is an important field of research. With respect to aquatic settings, lacustrine deposits provide excellent proxies of environmental change since the sediment accumulates at a relatively constant rate, recording environmental change. This study employs isotopic, mineral, and chemical records from Farmington Bay freeze cores, in particular δ13C, δ15N, and 210Pb isotopes as well as phosphorus level fluctuation and trace metal analysis. In particular, 210Pb isotopes permit estimation of the age of sediment with depth and δ15N, δ13C, and concentration of P provides a record of changing nutrient sources and level of eutrophication. Results from 210Pb isotopes have allowed ages to be assigned to depths along the core dating back roughly 100 years at 30 cm. At this depth, a dramatic shift in the δ15N isotope is observed. Initial δ15N levels indicated a nutrient source related to agriculture. However, beginning around 100 years ago, the δ15N shows the main nutrient source for the bay became wastewater which correlates to the completion of a sewage canal in 1911 that began routing wastewater directly into the bay. Results have also shown a large rise in phosphorus levels beginning around 1970 which may be due to the construction of the automobile causeway that isolated Farmington Bay from the rest of the Great Salt Lake.

This study focused on the dynamic behaviour of the freeze lining and slag bath, and the interactions between these components in an ilmenite-smelting furnace process. The purpose of the work was to gain a better understanding of these issues and to ultimately contribute to an improved understanding of the ilmenite-smelting process in its entirety, and to future improvements in the design, operation and control of these processes. A mathematical model of the freeze lining and furnace sidewall was developed. This model was used in isolation for focused characterisation of the dynamic behaviour and interactions of the freeze lining and slag bath. The influences of net power input and slag composition were studied and various aspects of the freeze lining and slag bath were considered. These aspects included freeze lining thickness, temperature distribution through the freeze lining and furnace sidewall, composition distribution through the freeze lining, slag bath temperature and slag bath composition. The thermal response of thermocouples installed in the furnace sidewall to changing conditions on the inside of the furnace was also investigated. A mathematical model of the crust that forms on the slag bath surface was developed. This model was not used in isolation, and was only incorporated into a complete model of the process. A mathematical model of the entire ilmenite-smelting furnace process was constructed. This model incorporated the two models mentioned above and was able to describe the metal bath, slag bath, furnace atmosphere, freeze lining, furnace sidewall and the crust that is sometimes present on top of the slag bath. The model was used to study the influence of changes in operational parameters on the slag bath and freeze lining. The operational parameters that were studied included electrical power and reductant feed rate, both relative to ilmenite feed rate. The influence of severe operational errors and furnace down time were also investigated. Operational errors included loss of all feed while maintain electrical power input, and loss of reductant feed while maintaining power input and ilmenite feed. The above-mentioned studies were conducted by executing numerous experiments with two of the mathematical models. The experimental results were processed into sets of graphs displaying variations in the aspects that were considered. Many valuable insights resulted from the interpretation of these results. One specific aspect that formed part of the scope of this work was the origin of the compositional invariance of the slag close to the stoichiometric M3O5composition. This invariance was studied and a mechanism was proposed that explains the observed behaviour. The proposed mechanism created some questions about other mechanisms in the process. These mechanisms were also considered and elaborated on. The models and results produced in this study provide valuable insights into the behaviour of the ilmenite-smelting process. It also represents a useful foundation for future modelling work, and finally, it presents numerous opportunities for organisations operating ilmenite-smelting furnaces to improve their understanding and even the performance of their processes. / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2004. / Materials Science and Metallurgical Engineering / unrestricted

No description available.

No description available.

The use of recycled concrete material (RCM) as pavement base material is a promising but unproven technique for road rehabilitation and construction. A telephone survey conducted to investigate the state of the practice concerning RCM usage in Utah County revealed that RCM is infrequently used in this application due primarily to a lack of practical knowledge about the engineering properties of the material. Therefore, this research was aimed at evaluating the physical properties, strength parameters, and durability characteristics of both demolition and haul-back sources of RCM available in Utah County for use as pavement base material. The study included extensive laboratory and field testing. Laboratory tests included California bearing ratio (CBR), unconfined compressive strength (UCS), stiffness, freeze-thaw cycling, moisture susceptibility, abrasion, salinity, and alkalinity evaluations. Non-destructive testing was utilized in the field to monitor seasonal variation in stiffness of an RCM pavement base layer over a 1-year period. The testing included a dynamic cone penetrometer, ground-penetrating radar, a heavy Clegg impact soil tester, a soil stiffness gauge, and a portable falling-weight deflectometer. The laboratory testing indicated that the demolition material exhibited lower strength and stiffness than the haul-back material and reduced UCS loss after freeze-thaw cycling. However, the demolition material received a moisture susceptibility rating of good in the tube suction test, while the haul-back material was rated as marginal. Both materials exhibited self-cementing effects that led to approximately 180 percent increases in UCS over a 7-day curing period. Seven-day UCS values were 1260 kPa and 1820 kPa for the demolition and haul-back materials, respectively, and corresponding CBR values were 22 and 55. The field monitoring demonstrated that the RCM base layer was susceptible to stiffness changes due primarily to changes in moisture. In its saturated state during spring testing, the site experienced CBR and stiffness losses of up to 60 percent compared to summer-time values. RCM compares well with typical pavement base materials in many respects. Given the laboratory and field data developed in this research, engineers should be able to estimate the strength and durability parameters of RCM needed for pavement design.

The objective of this research was to investigate emulsion-treated base (ETB) frost susceptibility in terms of both freeze-thaw cycling and frost heave. The research performed in this study involved laboratory testing of ETB materials sampled from both the Redwood Road and 7800 South reconstruction projects in northern Utah. The effects of freeze-thaw cycling were evaluated by comparing the stiffness and strength of tested specimens to the same properties of control specimens not subjected to freeze-thaw cycling. Frost heave testing enabled evaluation of the effects of emulsion content and degree of curing on the volumetric stability of ETB materials during sustained freezing. Since permeability affects the frost susceptibility of a material, samples were also prepared to specifically evaluate the effect of curing condition on the permeability of the two base materials when treated with emulsion. The results of freeze-thaw testing showed that both the Redwood Road and 7800 South specimens experienced decreases in modulus as a result of freeze-thaw damage. The results also showed that the Redwood Road specimens experienced substantial decreases in strength as a result of freeze-thaw damage. The specimens from 7800 South did not exhibit such strength loss; since those specimens initially had much lower modulus and unconfined compressive strength values than the Redwood Road specimens, they were less susceptible to stiffness and strength loss during the freeze-thaw test. Results for the frost heave tests showed that the untreated base materials were not susceptible to frost heave and that the addition of emulsion, with or without curing, did not change the frost heave behavior in a practically important way. While susceptibility to frost heave is not expected to be a problem with these base materials, the laboratory results revealed a significant increase in the permeability of the ETB specimens after curing, which could facilitate greater freeze-thaw damage. In consideration of these research results, engineers should ensure proper material sampling and laboratory testing to assess the efficacy of emulsion treatment for a given project. ETB to be constructed in cold regions should be subjected to freeze-thaw testing during the design phase, and designers should be aware that curing of the ETB may dramatically increase permeability and therefore increase frost susceptibility.

DEVELOPMENT AND VALIDATION OF A LIGHT WEIGHT, ENERGY DENSE, READY TO EAT (RTE) BAR Jacob Wilhelm-Maria Heick Providing additional calories in the form of an RTE bar to endurance athletes will increase performance and muscle re-synthesis, reduce muscle breakdown, and shorten recovery time. An RTE bar containing a blend of dairy proteins and carbohydrates will create a product with superior functionality, including bioactive and immunity enhancing properties from dairy derived ingredients. The protein will provide benefits in the form of easily digestible calories, essential amino acids and physical satiate. A formulation was developed and optimized, resulting in a final product that meets the required nutritional profile: 400kcal, 25grams protein per 100 gram serving size. The desired physical characteristics were achieved through processing by both conventional baking and freeze drying. The latter method improves the stability and functionality of the RTE bar. In order to meet the protein requirements of the RTE bar without compromising sensory properties, a unique protein source was developed. Using high concentrations of conventional protein sources like Whey Protein Concentrate (WPC) resulted in stale off-flavors and unappealing textures. Milk Protein Precipitate (MPP) was developed for this formulation. MPP is a curd-like ingredient created through the combined heat and acid precipitation of dairy proteins. MPP can be used effectively in high concentrations provides a subtle dairy flavor. MPP delivers a balance of casein and whey, similar to that found in milk. The effectiveness of the RTE bar formulation as a post exercise recovery food was evaluated in a human studies experiment conducted on the Cal Poly campus. The human subjects study utilized 34 Cal Poly students in a single-blind cross-over design experiment. The study compared the effects of this high protein RTE bar against a calorically equal carbohydrate bar. The bars were administered after subjects completed the pre-assigned hikes on three consecutive days. Following the cross-over design, subjects received the alternate bar in the second period of the experiment. Several blood markers involved in metabolism and inflammation were measured before and after the two treatment periods. No blood marker showed a statistically significant difference between bars, but several trends were observed. Body weight and fat percent were also unaffected by bar composition.

No description available.

No description available.