No description available.

No description available.

No description available.

Recovery, recrystallization, grain growth and precipitation constitute the fundamentals of thermomechanical controlled processing (TMCP) of microalloyed steels. In-depth understanding of these phenomena is indeed needed. In this work, the individual components and some of the potential mutual interactions have been investigated deliberately. The effect of alloying elements of Mn, Si, and Al on recovery and recrystallization has been systematically studied by conducting the stress relaxation tests on binary Fe-0.1%C and ternary Fe-0.1%C-X alloys. The effect of temperature on recovery kinetics was also investigated. The effects were considered by fitting the recovery model through the activation volume term. Higher temperature or lower solute content will accelerate the recovery process and then facilitate the onset of recrystallization. NbC precipitation behavior has been investigated using a nickel-based model alloy, having samples deformed at both room temperature and elevated temperature and subjected to annealing at 700℃ for different times, in order to elucidate the stages of nucleation, growth and coarsening for precipitation. The microstructures preserved by water quenching were examined using transmission electron microscopy (with both metal foil and carbon replica specimens). Results from mechanical response and microstructural evolution are linked and discussed. The precipitate number density and size evolution show good agreements with predictions from a classical strain-induced precipitation model. The in-situ laser-ultrasonics measurement of C-Mn steels provides a unique way to evaluate grain size evolution during TMCP, for different strains of 0.15, 0.25 and 0.35, at 950℃ and 1050℃. Effects of temperature and strain on recovery, recrystallization and grain growth have been covered and elucidated. Higher strains facilitate the onset of recrystallization and grain size refinement. However, higher temperatures only shorten the onset of recrystallization but lead to larger grain size. The effect of microalloying element of Nb on softening kinetics was also investigated by comparing C-Mn/C-Mn-Nb steels at the same conditions. The solute drag effect of Nb can be seen by the onset-delays of recrystallization and larger grain sizes. The laser-ultrasonics results can match well with stress relaxation measurements. The in-situ grain size evolution data has given the possibility to develop robust thermomechanical processing (TMP) models combining deformation, recovery, precipitation, recrystallization and grain growth. The application and validation of the TMP models have been attempted and remain ongoing. / Thesis / Doctor of Philosophy (PhD)

Measurement error (ME) in the factor levels of designed experiments is often overlooked in the planning and analysis of experimental designs. A familiar model for this type of ME, called the Berkson error model, is discussed at length. Previous research has examined the effect of Berkson error on two-level factorial and fractional factorial designs. This dissertation extends the examination to designs for second order models. The results are used to suggest optimal values for axial points in Central Composite Designs. The proper analysis for experimental data including ME is outlined for first and second order models. A comparison of this analysis to a typical Ordinary Least Squares analysis is made for second order models. The comparison is used to quantify the difference in performance of the two methods, both of which yield unbiased coefficient estimates. Robustness to misspecification of the ME variance is also explored. A solution for experimental planning is also suggested. A design optimality criterion, called the DME criterion, is used to create a second-stage design when ME is present. The performance of the criterion is compared to a D-optimal design augmentation. A final comparison is made between methods accounting for ME and methods ignoring ME. / Ph. D.

Experimental measurements ol N₂ resonant charge transfer cross sections were performed. It was found that the energy of electrons used to produce the N₂⁺ ions is an important variable with respect to cross section. An examination of the experimental precision was performed and it was found that the precision of measurement was insufficient to determine the exact form of this relationship. The effect of ion energy (collisional energy) was too small to be seen. Modulated detection was used to improve precision and permit measurement at high noise levels. A description of the apparatus is provided. Consideration of other systems and the suitability of their resonant charge transfer reactions for experimental investigation is discussed. Various theoretical models for estimation of cross section were examined. / M.S.

A theory and method have been developed and design change drawn, for the estimation of certain stability derivatives for wings of arbitrary platform in subsonic flow. / Ph. D.

The equations governing the thermodynamic behavior of a military aircraft have been implemented by the Air Force Research Lab (AFRL) and other Integrated Vehicle Energy Technology Demonstration (INVENT) contributors into a cohesive, adaptable, dynamic aircraft simulation program in Mathworks' Simulink®. The resulting model known as the "Tip-to-tail" model meets the design specifications set forth by the INVENT program. The system consists of six intimately linked subsystems that include a propulsion subsystem (PS), air vehicle subsystem (AVS), robust electrical power subsystem (REPS), high power electric actuation subsystem (HPEAS), advanced power and thermal management subsystem (APTMS), and a fuel thermal management subsystem (FTMS). The model's governing equations are augmented with experimental data and supported by defined physical parameters. In order to address the problems associated with the additional power and thermal loads for in more electric aircraft (MEA), this research utilizes exergy analysis and mission-integrated synthesis/design optimization to investigate the potential for improvement in tip-to-tail design/performance. Additionally, this thesis describes the development and integration of higher fidelity transient heat exchanger models for use in the tip-to-tail. Finally, the change in performance due to the integration of new heat exchanger models developed here is presented. Additionally, this thesis discusses the results obtained by performing mission-integrated synthesis/design optimization on the tip-to-tail using heat exchanger design parameters as decision variables. These results show that the performance of the tip-to-thermal management subsystems improves significantly due to the integration of the heat exchanger models. These results also show improvements in vehicle performance due to the mission-integrated optimization. / Master of Science

The relationships of the fourteen (14) species of Campylobacter were derived by comparison of the partial 16S ribosomal RNA sequences determined using reverse transcriptase and oligonucleotide primers specific for regions in the 16S rRNA molecule. These species formed three distinct RNA sequence homology groups. We propose that the following species remain in the genus Campylobacter (homology group I): C. coli, C. jejuni, C. laridis, C. fetus, C. hyointestinalis, C. concisus, C. mucosalis, C. sputorum and the "catalase-negative to weakly-positive" (CNW) strains. C. pylori, "C. cinaedi" and "C. fennelliae'' were not related to the true campylobacters at the genus level. However, they were related to each other and to Wolinella succinogenes at the genus level and constituted homology group II. These four species should be reclassified and placed within a single genus based on 16S rRNA sequence similarity. C. cryaerophila and C. nitrofigilis also exhibited a high level of RNA sequence homology with each other but not with any other species tested; they constituted homology group III and should be considered as being a single genus. A comparison of the 165 rRNA sequence data from the three homology groups with the same sequences from representatives of the three major phylogenetic branches of the purple bacteria indicated that these genera form a single phylogenetic branch which is only distantly related to the purple bacteria. / Master of Science

Studies were undertaken to determine the dispersal mechanisms of Verticicladiella procera Kendrick, the causal agent of Procera Root Disease (PRD). Propagule germinability in artificially infested soil decrease rapidly under natural and controlled conditions. Colonization of seedlings in artificially infested soil was rare and symptoms were not displayed by colonized seedlings. Natural populations of V. procera were closely associated with colonized root tissue. Colonization of field planted seedlings was related to proximity to root collars of diseased trees and insect activity on the seedlings. Insects (Coleoptera) contaminated with V. procera were found in plantations both with and without PRD. The percent of weevils and bark beetles contaminated with V. procera was 64 and 0.76 respectively. Verticicladiella procera was transmitted to white pine bolts in the field and under controlled conditions following visitation by contaminated insects. Verticicladiella procera was associated with larval galleries and frass in trap bolts and was observed fruiting in insect galleries in root systems of diseased trees. This evidence suggests that transmission by insects, especially weevils, is the more important mechanism for dispersal and that soil-borne propagules have a minor role in pathogen spread. / M.S.