Advanced high strength steels (AHSS) have high susceptibility to hydrogen embrittlement, and are often exposed to hydrogen environments in processing. In order to study the embrittlement and recovery of steel, tensile tests were conducted on two different types of AHSS over time after hydrogen charging. Concentration measurements and hydrogen microprinting were carried out at the same time steps to visualize the hydrogen behavior during recovery. The diffusible hydrogen concentration was found to decay exponentially, and equations were found for the two types of steel. Hydrogen concentration decay rates were calculated to be -0.355 /hr in TBF steel, and -0.225 /hr in DP. Hydrogen concentration thresholds for embrittlement were found to be 1.04 mL/100 g for TBF steel, and 0.87 mL/100g for DP steel. TBF steel is predicted to recover from embrittlement within 4.1 hours, compared to 7.2 hours in DP steel. A two-factor method of evaluating recovery from embrittlement, requiring hydrogen concentration threshold and decay rate, is explained for use in predicting recovery after exposure to hydrogen. Anisotropic hydrogen diffusion rates were also observed on the surface of both steels for a short time after charging, as hydrogen left the surface through <001> and <101> grains faster than grains with <111> orientations. This could be explained by differences in surface energies between the different orientations.

Titanium nitride (TiN) films are widely applied as diffusion barrier layers in microelectronic devices. The continued miniaturization of such devices not only poses new challenges to material systems design, but also puts high demands on characterization techniques. To gain understanding of diffusion processes that can eventually lead to failure of the barrier layer and thus of the whole device, it is essential to develop routines to chemically and structurally investigate these layers down to the atomic scale. In the present study, model TiN diffusion barriers with a Cu overlayer acting as the diffusion source were grown by reactive magnetron sputtering on MgO(001) and thermally oxidized Si(001) substrates. Cross-sectional transmission electron microscopy (XTEM) of the pristine samples revealed epitaxial, single-crystalline growth of TiN on MgO(001), while the polycrystalline TiN grown on Si(001) exhibited a [001]-oriented columnar microstructure. Various annealing treatments were carried out to induce diffusion of Cu into the TiN layer. Subsequently, XTEM images were recorded with a high-angle annular dark field detector, which provides strong elemental contrast, to illuminate the correlation between the structure and the barrier efficiency of the single- and polycrystalline TiN layers. Particular regions of interest were investigated more closely by energy dispersive X-ray (EDX) mapping. These investigations are completed by atom probe tomography (APT) studies, which provide a three-dimensional insight into the elemental distribution at the near-interface region with atomic chemical resolution and high sensitivity. In case of the single-crystalline barrier, a uniform Cu-enriched diffusion layer of 12 nm could be detected at the interface after an annealing treatment at 1000 °C for 12 h. This excellent barrier performance can be attributed to the lack of fast diffusion paths such as grain boundaries. Moreover, density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N-sublattice for the experimental N/Ti ratio. In comparison, the polycrystalline TiN layers exhibited grain boundaries reaching from the Cu-TiN interface to the substrate, thus providing direct diffusion paths for Cu. However, the microstructure of these columnar layers was still dense without open porosity or voids, so that the onset of grain boundary diffusion could only be found after annealing at 900 °C for 1 h. The present study shows how to combine two high resolution state-of-the-art methods, TEM and APT, to characterize model TiN diffusion barriers. It is shown how to correlate the microstructure with the performance of the barrier layer by two-dimensional EDX mapping and three-dimensional APT. Highly effective Cu-diffusion barrier function is thus demonstrated for single-crystal TiN(001) (up to 1000 °C) and dense polycrystalline TiN (900 °C).

The objective of the research presented in this thesis has been to develop a physics-based dislocation density-based numerical framework to simulate microstructure evolution in severe plastic deformation (SPD) manufacturing processes for different materials. Different mechanisms of microstructure evolution in SPD manufacturing processes were investigated and summarized for different materials under dynamic or high strain rates over a wide temperature range. Thorough literature reviews were performed to clarify discrepancies of the mechanism responsible for the formation of nanocrystalline structure in the machined surface layer under both low-temperature and high-temperature conditions. Under this framework, metallo-thermo-mechanically (MTM) coupled finite element (FE) models were developed to predict the microstructure evolution during different SPD manufacturing processes. Different material flow stress responses were modeled subject to responsible plastic deformation mechanisms. These MTM coupled FE models successfully captured the microstructure evolution process for various materials subjected to multiple mechanisms. Cellular automaton models were developed for SPD manufacturing processes under intermediate to high strain rates for the first time to simulate the microstructure evolution subjected to discontinuous dynamic recrystallization and thermally driven grain growth. The cellular automaton simulations revealed that the recrystallization process usually cannot be completed by the end of the plastic deformation under intermediate to high strain rates. The completion of the recrystallization process during the cooling stage after the plastic deformation process was modeled for the first time for SPD manufacturing processes at elevated temperatures.

Scandate cathodes, where scandia is added to the tungsten cathode pellets, have recently received substantial and renewed research interest owing to significantly improved electron emission capabilities at lower temperatures, as compared with conventional dispenser cathodes. However, there are several persistent issues including non-uniform electron emission, lack of understanding regarding scandium’s role in the emission mechanism, and unreliable reproducibility in terms of scandate cathode fabrication. As a result, scandate cathodes have not yet been widely implemented in actual vacuum electron devices (VEDs). The surface structure and chemical composition of multiple scandate cathodes – prepared with the powder using the liquid-solid (L-S) technique – and exhibiting excellent emission behavior were characterized to give insight into the fundamental mechanism(s) of operation. This was achieved with high-resolution electron microscopy techniques that include high-precision specimen lift-out. These studies showed that the micron-sized tungsten particles that compose the largest fraction of the cathode body are highly faceted and decorated with nanoscale Ba/BaO (~10 nm), as well as larger (~150 nm) Sc2O3 and BaAl2O4 particles. The experimentally identified facets were confirmed through Wulff analysis of the tungsten crystal shape and were determined to consist of {110}, {100}, and {112} facets, in increasing order of surface area prevalence. Furthermore, it is estimated that Ba atoms decorating the tungsten crystal surfaces are present in quantities such that monolayer coverage is possible at elevated temperatures. The high-resolution electron microscopy techniques used to investigate the cross section (near-surface) of the L-S scandate cathodes also revealed that the BaAl2O4 particles (100-500 nm) that attach to the larger tungsten particles are either adjacent to the smaller Sc2O3 nanoparticles or encompass them. Furthermore, high-resolution chemical analysis and 3D elemental tomography show that the two oxides always appear to be physically distinct from each other, despite their close proximity. 3D elemental tomography also showed that the Sc2O3 particles can sometimes appear inside the larger tungsten particles, but are inhomogeneously distributed. Nanobeam electron diffraction confirmed that the crystal structure of the tungsten particles are body-centered cubic, and imply that the structure remains unchanged despite the numerous complex chemical reactions that take place throughout the impregnation and activation procedures. The role of Sc and the emission mechanism for scandate cathodes are discussed. Based on characterization results and materials computation, the role of Sc in scandate cathodes is possibly related to tuning the partial pressure of oxygen in order to establish an oxygen-poor atmosphere around the cathode surface, which is a necessary condition for the formation of the (near) equilibrium tungsten shape. A thin Ba-Sc-O surface layer (~8 nm) was detected near the surface of tungsten particles, using electron energy loss spectroscopy in the scanning transmission electron microscope. This stands in stark contrast to models invoking a ~100 nm Ba-Sc-O semiconducting surface layer, which are broadly discussed in the literature. These results provide new insights into understanding the emission mechanism of scandate cathodes.

This dissertation is an investigation into the effect of different zinc sources and levels on eggshell quality and microstructure, as well as keel bone damage. Eggshell function is two-fold; eggshells function to protect the developing embryo, as well as act as a barrier against bacterial penetration, optimizing food safety of the egg for human consumption (Mabe et. Al., 2003). Two small trials were conducted in order to determine differences in eggshell microstructure of eggs produced from hens at peak lay (26 weeks of age) and at the end of lay (88 weeks of age). Two groups of hens were fed a calcium sufficient or a calcium deficient diet. From this it was determined that eggs with higher breaking strengths had some differences in eggshell microstructure. Eggs with greater breaking strengths had a greater density of ‘normal’ structures, compared to ‘abnormal’ structures. Additionally, eggs requiring a greater breaking force, had a thicker micro-structure, compared to shells requiring less breaking force. With this knowledge on microstructure, a larger, 36-week study was conducted using different zinc sources. Every four weeks, eggs were collected and standard egg quality measurements were taken and keel bones were scored. At the end of the study, keel bones were collected from randomly selected hens representing each treatment. Picture of these keel bones were taken and measurements were taken to determine type and degree of deformation, in comparison to scores taken on the live bird. Pens selected for keel bone analysis, were the same pens that eggs were taken for imaging by the scanning electron microscope, to determine eggshell microstructure. From this data, it was determined that egg quality differences were detected, as well as differences in eggshell microstructure. Additionally, keel bone scores progressively worsened throughout the 36-week long study, with type and degree of deformation differing depending on zinc source.

Titanium alloys are widely used for aerospace and biomaterial applications since their high specific strength, and high corrosion resistivity. Besides these properties, titanium is an excellent biocompatible material widely used for internal body implants. Because the products have complex geometries in both applications, Additive Manufacturing (AM) methods have been recently applied for production. AM methods can process a direct 3-D shape of the final product, decrease total production time and cost. However, high residual stress of the final product limits the application of AM components, especially the ones that are exposed to cyclic loading. In the present study, the initial microstructures and impact toughness of Ti6Al4V processed by EBM and CMT, and CP:Ti processed by SLM were experimented. In addition to initial microstructure and impact toughness, their response to different heat treatments were examined. Gleeble® 3500 was used for rapid heat treatment process. The change of mechanical properties due to different heat treatments were monitored with impact tests. Phase transformation kinetics of CP:Ti and Ti6Al4V were investigated with a Differential Scanning Calorimeter at slow heating and cooling rates. Microstructure examination was done with a scanning electron microscope. EBSD data was used to analyze the microstructure behavior. It is observed that toughness of the samples that are produced by powder-based AM methods were improved. Overall, residual stress, strain values, and grain orientation are the key elements that affected impact toughness AM produced components.

[pt] O presente trabalho visa generalizar a modelagem do tempo entre os negócios ocorridos no mercado financeiro, doravante chamado duração, e estudar os impactos destas duraçõoes sobre a volatilidade instântanea. O estudo foi realizado por meio do modelo linear ACD (autoregression conditional duration) proposto por Engel e Russel[3], os quais usaram a distribuição Exponencial e Weibull para as inovações, e o modelo GARCH-t para dados com alta freqüência para modelar a volatilidade instântanea, também usando a proposição de Engel e Russel[3]. A generalização faz uso da Gama Generalizada proposta em Zhang, Russel & Tsay[9] em um modelo de duração não linear conhecido como TACD (threshold autoregressive conditional duration). A justificativa para o estudo das durações com a Gama Generalizada é obter uma modelo mais flexível que o proposto por Engel e Russel[3]. Os resultados do modelo ACD com as inovações seguindo uma Gama Generalizada se mostrou mais adequado capturando a sub-dispersão dos dados. A seguir estimamos o modelo de volatilidade instantânea usando as durações estimadas como variáveis explicativas encontrando resultados compatíveis com a literatura. / [en] This work generalizes the duration model, the time elapsed between two consecutive transactions, such as financial transactions data; and explores the consequences of durations in the instantaneous volatility. The approach have been motivated by Engel and Russel[3], that proposed an autoregressive conditional duration (ACD) model to explain the variation of volatility, where the innovations proposes were Exponential andWeibull distributions. Besides they used the GARCH-t to modeling the instantaneous volatility in high frequency data. This work uses the Generalized Gamma to the innovations in order to generalize the ACD model, this distribution has been first suggested by Zhang, Russel and Tsay[9], in the threshold ACD (TACD) framework. We justify the generalized Gamma specification in order to allow for more flexibility than the ACD model of Engel and Russel[3]. We find evidences that the ACD model with this specification was better to captur the behavior such as sub- dispersion.

Z-pinning is a through-thickness reinforcement technology for polymer composite materials that has been developed and commercialised over the past fifteen years. The through-thickness reinforcement of composites with thin metallic or fibrous pins aids in suppressing delamination, improving impact damage tolerance and increasing joint strength. Z-pins are applied to the composite part during its manufacture. Pins are embedded within sheets of foam and placed over the unconsolidated part. Subsequently, the foam is compacted and the pins transferred into the part, which is usually an uncured prepreg. In this manner, large numbers of pins can be inserted quickly and easily. The pinned composite is then cured using conventional processes. The use of z-pins is currently limited to several high performance composite structures, most notably Formula One racing cars and F/A-18 E/F (Superhornet) fighter aircraft, although the technology has potential applications in a d iverse variety of aerospace and non-aerospace composite structures. A limited understanding of the mechanical performance of z-pinned parts under high load and fatigue loading conditions currently hinders the application of z-pinned composites. The aim of this PhD project is to investigate the mechanical properties, strengthening mechanics and failure mechanisms of z-pinned carbon/epoxy laminates and joints. The effect of z-pin reinforcement on the tensile and flexural properties of laminates under monotonic and fatigue loading is studied. The sensitivity of these properties to the volume content and diameter of the z-pins is systematically studied by experimentation and analytical modelling. This PhD also evaluates the efficacy of z-pins in improving the load-bearing properties of carbon/epoxy lap joints. Improvements to the room temperature and elevated temperature properties of z-pinned lap joints under monotonic and fatigue tensile loading were determined. The effect of strain rate on the load-bearing properties of z-pinned lap joints was also evaluated. A further aim of the PhD project was to assess the z-pin manufacturing process and the microstructural damage caused by that process. The outcome of this study augments the analysis of the me chanical properties of z-pinned laminates and joints.

This dissertation consists of 3 essays that examine the impact of electronic screen trading in futures markets. The research provides empirical evidence on increasingly significant issues given the rapid global advances in technology used in securities markets. Each essay addresses the scarcity of conclusive research in order to aid researchers, regulators, exchange policy makers and systems builders as they confront issues related to electronic trading systems.

This study was carried out to determine the characteristics of common carp surimi. In Australia, common carp (Cyprinus carpio) is an environmental pest, strongly coloured (dark-muscle fish), large (2-3 kg), low cost (AUD 2.5/kg) and not highly valued as it is every where else. Surimi could add value to carp, but the colour would have to be modified as surimi manufacturers prefer white coloured flesh. So, firstly the efficiency of Hydrogen peroxide (H2O2; 1-3% v/v) solution at alkaline side of pH (7.0-11.5) on whitening of light fillets of common carp was examined. The whiteness (L*-3b*) of surimi produced from treated (3% H2O2, pH 8.2) common carp light fillets was significantly (p less than 0.05) greater than that of threadfin bream surimi and was not significantly different to that of Alaska pollock. Based on a temperature sweep test, a similar pattern in G of tested surimi was observed which started at ca. 47?C and was completed at ca. 73-74?C. However, thread fin bream kamaboko showed better texture profile characteristics (hardness and gel strength) than that of the other kamaboko tested. To improve the quality of common carp surimi and kamaboko, alternative methods were applied such as modified conventional method (MCM), alkaline-aided method (AAM) and pH modified method (PMM) and the resultant surimi and kamaboko were compared with those produced by the traditional method (TM). In MCM each washing cycle was followed by a centrifugation step for a more effective dewatering and removal of sarcoplasmic proteins (Sp-P). Kamaboko prepared from MCM was whiter and had significantly (p less than 0.05) improved textural characteristics (hardness and gel strength) than that from TM, AAM and PMM. Furthermore, SEM of surimi and kamaboko showed higher number of polygonal structure/mm2 in the gel matrix of MCM kamaboko, as a result of more cross-linking of the myofibrillar proteins, than that recorded for TM, AAM and PMM samples tested. Finally, this study examined the effect of adding common carp sarcoplasmic proteins (Sp-P) on the gel characteristics of threadfin bream surimi and kamaboko. Based on the temperature sweep test, the depths of the valley in the G thermograph of the gels decreased as the concentration of added Sp-P increased from 5% to 35%. Storage modulus (G) of the gels showed greater elasticity in the samples with added Sp-P compared with the control samples without added Sp-P. Furthermore, the breaking force and breaking distance and consequently gel strength of the resultant kamaboko were improved, significantly (p less than 0.05) with added Sp-P. Thus, added Sp-P did not interfere with the gelling of myofibrillar proteins during sol-gel transition phase and was associated with textural quality enhancement for the resultant kamaboko. However, the addition of freeze-dried Sp-P from the dark muscle of the carp decreased the whiteness of the resultant surimi. Furthermore, the gel strength could not be associated with either the number of polygonal structures/mm2 or the area of the polygonal structures.