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Abstract: Aberrations introduced during fabrication degrade the performance of X-ray optics and their ability to achieve diffraction limited focusing. Corrective optics can counteract these errors by introducing wavefront perturbations prior to the optic which cancel out the distortions. Here we demonstrate two-dimensional wavefront correction of an aberrated Kirkpatrick-Baez mirror pair using adaptable refractive structures. The resulting two-dimensional wavefront is measured using hard X-ray ptychography to recover the complex probe wavefield with high spatial resolution and model the optical performance under coherent conditions. The optical performance including the beam caustic, focal profile and wavefront error is examined before and after correction with both mirrors found to be diffraction limited after correcting. The results will be applicable to a wide variety of high numerical aperture X-ray optics aiming to achieve diffraction limited focussing using low emittance sources.

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Abstract: In the last two decades, X-ray imaging techniques have been used increasingly to study metal solidification in real-time as, thanks to advances in X-ray sources (synchrotron and laboratory-based) and detector technology, images can now be obtained with spatio-temporal resolutions sufficient to record key phenomena and extract quantitative information, primarily relating to crystal growth. This paper presents an overview of the research conducted at the University of Oxford over the last 6 years as a partner in the UK’s Future Liquid Metal Engineering (LiME) Manufacturing Hub. The focus is on in situ X-ray radiography to investigate the solidification of Al alloys, including the formation of primary α -Al crystals, and the formation and growth of secondary intermetallic phases. Technologically, the thrust is to understand how to control as-cast phases, structures and element distributions, particularly elements associated with recycling, as a means to facilitate greater recirculation of aluminium alloys. We first present studies on refinement of primary α -Al, including extrinsic grain refinement using inoculation and intrinsic refinement based on dendrite fragmentation. Second, we describe studies on intermetallic phase formation and growth, because intermetallic fraction, morphology and distribution are frequently a limiting factor of alloy mechanical properties and recyclability. Then we present some of the latest progress in studying liquid flow during solidification and associated hot tear formation. Finally, future research directions are described.

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Abstract: The aim of this thesis was to provide methods of correlation and co-localization to investigate element compositions of human bone sample. The μ-XRF generated images were collected at the ESRF and Diamond synchrotron radiation facilities and depict the distributions of the elements Ar, Ca, Cr, Fe, Co, Ni, Cu, Zn, Gd and W which are given with an approximated image size between 10 μm (ESRF) and 500 μm (Diamond) and a resolution of 50 nm and 500 nm respectively. The whole data set consists of 31 single scan locations on the bone samples, taken from five patients suffering from tumorous or osteoporotic diseases.The main elements of interest are Ca, Cr, Fe, Ni, Cu, Zn and Gd where the origin is very well known. Ca, Cr, Fe, Ni, Cu and Zn are natural or age-related (due to the environment in the life of the patient) elements of bone tissue. Possible Gd accumulations are explored about used Gd based contrast agents for magnetic resonance imaging investigations during patient treatments.The investigated methods are based on image correlation and overlap measurements. To obtain a value quantifying the correlation, the Pearson’s Correlation Coefficient (linear correlation) and the Spearman’s Correlation Coefficients (monotonic correlation) were determined. Furthermore, the Manders Overlap Coefficient was determined as a measure of the overlap between two element distributions.Furthermore, to get a qualitative overview, correlation graphs and overlap images are presented for better interpretations. Statistical methods were used to show element correlations and co-localizations for the whole data set. Finally, the statistical methods are applied to compare two different patients and extract differences between them for the correlation and overlap coefficients.Not surprisingly, Ca was found in each pixel for all samples. Between Ca and Zn, a high correlation and high overlap was found. Regarding GD1 (osteoporotic) and GD5 (tumorous), the Ca-Fe relationship for overlap measurements shows less Fe for patient GD1 compared to GD5. Due to the small number of samples (n= 7) for patient GD1 and n= 15 for patient GD5, more data would be required to solidify the results.Concerning the overlap coefficients M1 and M2, the following element combinations are significant differ- ent between patient GD1 and GD5:-) For GD5, Ca overlaps Fe to 53% more (median), in compare to GD1. Fe overlaps Ca to 100% for GD1 and GD5. The co-localization is significant higher for GD5 in compare to GD1.-) For GD5, Fe overlaps Ni to 71% less (median), in compare to GD1. The co-localization is significant higher for GD1 in compare to GD5.-) For GD5, Gd overlaps Fe to 55% more (median), in compare to GD1. The co- localization is significant higher for GD5 in compare to GD1.-) For GD5, Gd overlaps Ni to 44% less (median), in compare to GD1. The co-localization is significant higher for GD1 in compare to GD5.-) For GD5, Zn overlaps Fe to 51% more (median), in compare to GD1. The co-localization is significant higher for GD5 in compare to GD1.

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Abstract: We investigate local deformation within a dual-phase Ti6242 alloy by considering the interaction between α orientation (i.e., slip system) and the presence of β phase (i.e., fraction and morphology), and the corresponding evolution of stored dislocations. In situ micropillar compression combined with microLaue diffraction and high angular resolution electron backscatter diffraction (HR-EBSD) shows that the high rate of geometrically necessary dislocation (GND) accumulation was observed in basal-slip oriented pillar, while easy formation of glide step with minimal GND accumulation was found in prism-slip oriented pillar. The difference is explained due to the role of the phase boundary for these slip configurations, where local stress concentrations can arise even in pillar with easy slip orientation (i.e., prism slip) if the phase boundary acts as a barrier to slip and results in inhomogeneity of local deformation. This study reveals significance of β phase in potentially modulating the local dislocation based hardening and hence local stress states within Ti polycrystalline aggregate.

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Abstract: Experiments involving the irradiation of water contained within magnesium hydroxide and alumina nanoparticle sludges were conducted and culminated in observations of an increased yield of molecular hydrogen when compared to the yield from the irradiation of bulk water. We show that there is a relationship linking this increased yield to the direct nanoscale ionization mechanism in the nanoparticles, indicating that electron emission from the nanoparticles drives new radiative pathways in the water. Because the chemical changes in these sludges are introduced by irradiation only, we have a genuinely unstirred system. This feature allows us to determine the diffusivity of the dissolved gas. Using the measured gas production rate, we have developed a method for modelling when hydrogen bubble formation will occur within the nanoparticle sludges. This model facilitates the determination of a consistent radiolytic consumption rate coinciding with the observations of bubble formation. Thus, we demonstrate a nanoscale radiation effect directly influencing the formation of molecular hydrogen.