Beta-phase gallium oxide (β-Ga2O3), with its ultrawide band gap energy (~4.8 eV), high predicted breakdown field strength (6-8 MV/cm), controllable n-type doping and availability of large area, melt-grown, differently oriented native substrates, has spurred substantial interest for future applications in power electronics and ultraviolet optoelectronics. The ability to support bandgap engineering by alloying with Al2O3 also extends β-(AlxGa1-x)2O3 based electronic and optoelectronic applications into new regime with even higher critical field strength that is currently unachievable from SiC-, GaN- or AlxGa1-xN- (for a large range of alloy compositions) based devices. However, the integration of β-(AlxGa1-x)2O3 alloys into prospective applications will largely depend on the epitaxial growth of high quality materials with high Al composition. This is considerably important as higher Al composition in β-(AlxGa1-x)2O3/Ga2O3 heterojunctions can gain advantages of its large conduction band offsets in order to simultaneously achieve maximized mobility and high carrier density in lateral devices through modulation doping. However, due to the relative immaturity of β-(AlxGa1-x)2O3 alloy system, knowledge of the synthesis and fundamental material properties such as the solubility limits, band gaps, band offsets as well as the structural defects and their influence on electrical characteristics is still very limited. Hence, this research aims to pursue a comprehensive investigation of synthesis of β-(AlxGa1-x)2O3 thin films via metal organic chemical vapor deposition (MOCVD) growth methods, building from the growth on mostly investigated (010) β-Ga2O3 substrate to other orientations such as (100), (001) and (-201), as well as exploring other polymorphs, such as alpha (α) and kappa (κ) phases of Ga2O3 and (AlxGa1-x)2O3 to provide a pathway for bandgap engineering of Ga2O3 using Al for high performance device applications. Using a wide range of material characterization techniqu (open full item for complete abstract)

Nickel-base superalloys are routinely employed for structural components within the late-stage compressor and turbine sections of gas turbine propulsion engines due to their unique combination of ductility and strength at elevated temperatures. The desirable performance of this material class is a direct consequence of an aggregate microstructure containing a disordered γ-FCC phase strengthened by ordered γ'-L12 precipitates. In recent years, a novel alloying system with microstructural characteristics analogous to nickel-base superalloys has garnered significant interest within the aerospace community. At specific compositions, the ternary Co-Al-W system exhibits similar L12 precipitates within a FCC matrix, but with the added advantage of a solidus temperature approximately 100 - 150 °C higher than observed in nickel-based systems. This effort adds to other alloy development investigations assessing the potential of this new alloy class for commercial transition into aerospace propulsion applications. Two aspects of Co-Al-W-base alloys were probed in detail: (i) microstructural stability after exposure to an elevated temperature for extended times and (ii) the hot deformation behavior of polycrystalline alloys under conditions relevant to the industrial thermo-mechanical processes necessary for component fabrication. In many previous publications, the Co3 (Al,W)- γ' strengthening phase in the Co-Al-W ternary system has been proposed as thermodynamically metastable at desired application temperatures. Bulk specimens of five Co-rich compositions of the Co-Al-W ternary and Co-Al-W-Ni quaternary systems were characterized after isothermal aging near 850 °C to assess previously unevaluated γ' W:Al ratios and confirm the effect of Ni alloying at exposure times up to 5000 hours. The aged microstructures, phase fractions, and phase compositions were evaluated with the intent of informing computational thermodynamic simulations for the Co-rich end of Co-Al-W and Co-Al- (open full item for complete abstract)

The lattice parameters of the gamma iron as a function of chromium alloy content were determined using high temperature X-ray diffraction measurements for three Fe-rich alloys. The three concentrations were: (1) pure iron powder, (2) 1 at.% Cr, and (3) 1.8 at.% Cr, and the temperature range was between 800℃ to 1300℃. Linear relationships between lattice parameter and temperature were observed and determined in all three samples. The lattice parameters of the γ-phase of the three samples at room temperature were determined by extrapolating the high temperature data to 20℃. The values are (0.3572±0.0005) nm, (0.3604±0.0003) nm, and (0.3609±0.0003) nm for pure iron powder and iron-chromium powders with 1 at.% Cr and 1.8 at.% Cr, respectively. A linear least squares regression analysis yielded: a=0.0021(nm/(at.%))×CCr+0.3575(nm).

Studies from our lab demonstrated that a cold-sensitive gamma-tubulin mutant allele, mipAD159, causes defects in the coordination of late mitotic events at restrictive temperatures with observed phenotypes such as abnormal chromosome segregation and inhibition of anaphase A (Prigozhina et al., 2004). These abnormalities are not a result of defects in microtubule nucleation since gamma-tubulin localized normally to the spindle pole body (SPB), microtubules were abundant and mitotic spindle formation and elongation appeared to be normal (Prigozhina et al., 2004). Nayak et al. (2010) further examined gamma-tubulin's role in mitotic regulation and determined that, at restrictive temperatures, mipAD159 caused a failure of accumulation of cyclin B, cyclin dependent kinase 1 (Cdk1) and the phosphatase, Ancdc14, in a subset of nuclei. These nuclei were removed from the cell cycle while other nuclei in the same cell accumulated these proteins and cycled normally. Extensive analysis revealed that this failure of accumulation was due to a nuclear autonomous failure of inactivation of the anaphase promoting complex/cyclosome (APC/C) sometime between late mitosis and S phase. The two projects I have focused on are directed toward further elucidating gamma-tubulin's role in cell cycle regulation. Many mitotic regulatory proteins are known to localize to the SPB, or the centrosome, its functional equivalent in higher organisms, in mitosis. Therefore, gamma-tubulin might be interacting with such proteins and such interactions might be altered in strains carrying mipAD159. I decided to focus on the spindle assembly checkpoint (SAC) proteins Mad2, Mps1, Bub3, BubR1 and Cdc20. I identified the A. nidulans homolog of each, created fluorescent protein fusions, and observed them in vivo by spinning disk confocal microscopy. I found that these proteins are physically separate from each other in interphase, keeping the SAC inactive until mitosis, when they are all at the S (open full item for complete abstract)

Conventionally processed, fully lamellar, TiAl Based alloys ordinarily possess alpha2 laths having a thickness on the order of hundreds of nanometers. Polycrystalline samples, having compositions between Ti-42Al and Ti-46Al, can be solution heat treated in the alpha phase field, and then rapidly quenched, to produce a microstructure that consists entirely of supersaturated alpha2 phase. Upon aging the supersaturated solid solution, in the alpha2 + gamma phase field, a fully lamellar structure results. In contrast to the conventionally processed fully lamellar TiAl based alloys, the laths resulting from the aging treatment have a thickness on the order of tens of nanometers. Additionally, this nanoscale microstructure consists of rigidly alternating laths of gamma and alpha2. A transformation mechanism from the supersaturated alpha2 to the ultra-fine lamellar structure, via nucleation and glide of dislocation loops is proposed. Consideration is also given to the question of whether or not these ultra-fine lamellar structures can aid slip transmission between the two phases. The gettering of interstitial contaminants, by the alpha2 laths in fully lamellar TiAl based alloys, has been shown to be responsible for the enhanced slip activity observed in the gamma laths of these alloys. However, absorption of the impurities from the gamma, limits the number of active slip systems that can operate in the alpha2 phase. The result is that the alpha2, an already brittle phase, becomes even less likely to undergo plastic deformation. The brittle alpha2 laths constrain the gamma phase, and the overall ductility of the fully lamellar material is reduced. By suitably engineering the sequence of solid state phase transformations leading to microstructural development in TiAl based alloys, it is possible to employ the gettering benefits provided by the alpha2 phase, while eliminating the constraints imposed by it on the gamma phase. The addition of small amounts of the ternary alloyi (open full item for complete abstract)