<p> The main objective of this study was to gain an understanding of the oxidation properties of iron at low oxygen pressures and at high temperature. </p> <p> A thermogravimetric technique was employed to investigate the oxidation of iron in oxygen over the pressure range 2.5×10⁻³ - 3.0×10⁻¹ torr at temperatures ranging between 750ºC and 1000ºC. The oxidation curves exhibited distinct intervals of linear kinetics followed by transition to intervals of parabolic kinetics during exposures extending to 125 min. Linear kinetics governing the growth of uniformly thick wustite scales; the linear rate constants showed a proportional dependence on oxygen pressure due to reaction control by a phase boundary reaction involving non-dissociation adsorption of oxygen. Parabolic kinetics governed growth of wustite-magnetite scales containing magnetite as outermost layers. The value of the parabolic rate constants were independent of oxygen pressure since scale growth was directly dependent on the iron vacancy gradient in wustite established by the oxygen activities at the Fe/FeO and FeO/Fe₃O₄ interfaces. </p> <p> Scanning electron microscopy techniques were used to gain information on the growth of magnetite and hematite layers in the multilayer scale consisting largely of wustite formed at high temperature in the pressure range 2.5×10⁻³ to 760 torr. </p> / Thesis / Master of Science (MSc)

The Mississippi River Bridge in Vicksburg, MS is a 7 span cantilever bridge that is 3,389 feet long by 68.5 feet wide and is part of the Interstate-20 corridor. On March 23, 2011 at 1:30pm, a barge moving downstream struck a pier of the bridge. Infrasound stations located at the U.S. Army Engineer Research and Development Center (ERDC) detected the impact. Coincidentally, ERDC had instrumented the bridge with strain gages and accelerometers as part of a structural health monitoring project. Finite Element (FE) models were developed to investigate the structural behavior of the bridge due to the impact. The measurements and the FE models were used to determine the source mechanism of the infrasound from the bridge. Measurements from the sensors that were installed on the bridge will be presented along with FE models and infrasound data.

The development of whitening of the youngest leaves of actively growing ivy geranium (Pelargonium peltatum L.) has been observed as the season changes from late spring to summer. This study was conducted to determine the specific environmental causes of whitening, if micronutrients deficiencies cause similar whitening, whether low night temperatures can reverse whitening, and whether salicylic acid affects growth and whitening in ivy geraniums. Two cultivars, ‘Beach’ and ‘Butterfly’, with different susceptibility to whitening were chosen for this study. Elevated air temperature, but not elevated root-zone temperature, was found to be the environmental cause of whitening in ivy geranium. Elevated air temperatures severely reduced plant growth, leaf area, fresh weight, and dry weight in both cultivars. Elevated air temperature reduced photosynthetic pigments and their ratios in ivy geranium. Carotenoids and pheophytins decreased in ‘Butterfly’ at elevated air temperature. Foliar total Fe levels indicated no inhibition of Fe-uptake at elevated temperatures. Applications of Fe-chelate at elevated temperatures helped chlorophyll synthesis in ivy geraniums. Deficiency treatments of all micronutrients, Fe, Mn, Zn, S or Mg did not result in whitening in either cultivar of ivy geraniums. Salicylic acid did not affect whitening of ivy geraniums. It did not affect growth, leaf area, fresh or dry (stem, leaf or total) weight, fresh: dry weight ratio, leaf area ratio, specific leaf area or foliar nutrient (Fe, Mn, Zn, Mg and S) content in either cultivar. Cultivars varied in their response to low night temperature. ‘Beach’ reduced its plant growth and fresh to dry weight ratio whereas ‘Butterfly’ did not. Fe-chelate application did not reduce growth, leaf area, fresh weight, dry weight or fresh:dry weight ratio of either cultivar. Although Fe-application did not reduce whitening in ivy geraniums, it helped to preserve chlorophyll, particularly chlorophyll b as indicated by Chl a:b ratio in ‘Beach’. Whitening in ivy geranium is a heat stress response initially exhibited by young, developing leaves and is caused by elevated air temperatures. Whitening is the result of impaired photosynthetic pigments synthesis and/or degradation.

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<p>The application aluminum sheet alloy for light vehicle development was limited by the high cost of alloy fabrication. The impurity iron, which is easily picked up during fabrication, deteriorates its formability. The sheet alloy produced by continuous casting techniques was showing lower in-service performance than the one produced with traditional high-cost direct-chill casting technique. Therefore, enhancing the general formability of the aluminum alloy became .the aim of many researchers and engineers in past decades.</p><p>This project was launched to detect a possible modification effect of rare-earth (RE) element on a Al-Mg-Fe alloy, which is a simplified AA5754 alloy. Cerium was chosen as the RE element to test with. The influence of this rare-earth element on the alloy grain microstructure, phase morphology, and corresponding mechanical behavior was investigated.</p><p>It was found that cerium had a modification effect on the phase morphology to some extent. Its addition provided a great grain refinement in as-cast alloys. However, after thermo-mechanical processing, this effect would be eliminated by the small broken particles and recrystallized fine grains. It was found that the mechanical performance of the cerium-containing AA5754 was neither enhanced nor deteriorated. The AA5754 alloy remained non-heat-treatable after the addition of cerium.</p> / Thesis / Master of Applied Science (MASc)

The need for environmentally friendly and energy efficient high temperature components that can operate under mechanical and/or thermal stress has prompted interest in the development of Fe-Cr-Al based alloys. These alloys have been widely investigated, because of their ability to form a protective layer of a - Al203, which is able to withstand further oxidation degradation. However, despite their superior oxidation qualities, alpha-alumina scales are highly susceptible to mechanical damage when subjected to aggressive environments. The origins of such failure can be attributed to the generation and relaxation of stresses during the scaling process. As such, this study has experimentally investigated the interaction between oxidation and stress on Fe-Cr-Al based alloy, Kanthal Al. Oxidation experiments of Kanthal Al were conducted in two parts. First, the alloy's scaling process at rest with respect to intrinsic growth stress and oxide morphology was examined. Second, external stress was applied during oxidation to obtain a comprehensive understanding of its effect on scale growth with comparison to experiments conducted without stress. The formation of compact α - Al203 scales was accompanied by compressive growth stresses on the order of 1 GPa. Prolonged oxidation decreased growth stresses resulting in increased scale porosity. Maximum scale porosity occurred under oxidation at 1300°C. Consequently, the protectiveness of the scale was heavily degraded, as indicated by scale morphology, implying that in-service operation at this temperature or above would be detrimental. Applied tensile stress showed a significant decrease in the development of intrinsic growth stress, suggesting a strong interdependency between scale growth stress and creep deformation at high temperature. There was no measurable change in the scale growth rate, as compared to experiments conducted at rest. Possible explanations include insufficient tensile load and/or drastic increase in spallation/rehealing, both of which simultaneously influences the lifetime of a material under aggressive operational conditions. / Thesis / Master of Applied Science (MASc)

Iron-sulfur [Fe-S] clusters are protein cofactors that facilitate various life-sustaining biological processes. Their in vivo assembly is accomplished by three different systems known to date. These are: the NIF system which provides [Fe-S] clusters for nitrogenase and other nitrogen-fixing proteins, the SUF system which is induced during conditions of oxidative stress and iron starvation in E. coli, and the ISC system which serves as the housekeeping assembly apparatus. The latter is the focus of this dissertation and includes the proteins IscR, IscS, IscU, IscA, HscB, HscA, Fdx, and IscX. IscU is purified in its cluster-less (apo) form, but can serve as a scaffold to assemble [Fe-S] clusters in vitro in the presence of excess iron and sulfide. To test the scaffold hypothesis and gain insight into the events that occur during [Fe-S] cluster assembly and delivery, we developed two methods that allow the isolation of IscU and other ISC proteins in vivo. In the first method, Azotobacter vinelandii IscU is isolated from its native host, whereas in the second, it is isolated recombinantly from E. coli using a vector that allows expression of the entire isc operon. We found that IscU exists in vivo in two forms: apo-IscU and [2Fe-2S]2+ cluster-loaded IscU which are believed to be conformationally distinct. Both transient and stable IscU-IscS complexes were identified, indicating that the two proteins interact in vivo in a manner that involves their association and dissociation. The [2Fe-2S]2+-IscU species was present as a single entity, whereas significant amounts of apo-IscU were found associated with IscS, suggesting that IscU-IscS dissociation is triggered by the completion of [2Fe-2S] clusters. Both apo and [2Fe-2S]2+-IscU were predominantly monomeric whereas IscU-IscS complexes were determined to have an α2β2 composition. IscU was purified in the absence of the chaperones HscA and HscB and was also shown to accommodate a [2Fe-2S]2+ cluster similar to the one bound to IscU isolated from wild type cells. The findings suggest that [2Fe-2S]2+-IscU exists in one conformation in vivo and that any conformational changes on IscU are exerted after [2Fe-2S] cluster formation. In silico studies showed that a flexible loop containing the conserved LPPVK motif, which is responsible for interactions with HscA, may facilitate cluster exposure to either mediate its delivery to acceptor proteins or participation in the construction of [4Fe-4S] clusters. Experiments with NfuA, a protein similar to the C-terminal domain of NifU, demonstrated that NfuA and similar proteins might serve as [Fe-S] cluster carriers to accomplish the efficient delivery of nascent cofactors to the various recipient proteins. / Ph. D.

This thesis examines the ill-fated Texan Santa Fe Expedition of 1841 to analyze the state of a lucrative market network in the Southwest. Cut off from Santa Fe, the hub of the network, Texas struggled economically as an independent nation. Commercially isolated and dealing with near- worthless paper money, Texans hoped that trade with the people of Santa Fe would divert wealth into their nation. To justify the expedition, Anglo-Texans used the rhetoric of Manifest Destiny and turned the trek into a liberation mission. Moreover, Texans desired an overland route to Santa Fe to attract merchants to their otherwise inactive ports. Texans invested much into the expedition both economically and culturally; however, the Texan Santa Fe Expedition ended in utter failure and convinced many Texans that annexation to the United States was the wiser path to take. / Master of Arts

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