Direct observation via in situ heated stage EBSD analysis of recrystallization of phosphorous deoxidised copper in unstrained and strained conditions

Recrystallization of phosphorous deoxidised copper used for strength critical applications at elevated temperatures was investigated by means of in situ heated stage EBSD analysis using a Gatan Murano heated stage mounted within a Carl Zeiss Sigma FEGSEM electron microscope. The influence of applied strain as the result of deformation within a Nakajima test as an analogue for industrial forming on the recrystallization temperature was investigated, the impact of increased heating rates on microstructural evolution was also investigated. Inverse pole figure plots combined with regions of reduction in local misorientations and variations in geometrically necessary dislocations were used to establish the point of recrystallization and the recrystallized fraction of the material. Recrystallization was observed to occur at temperatures as low as 130 °C in highly strained samples compared to around 300 °C within the annealed samples dependent upon heating rate. Increased heating rates were observed to produce a finer final grain structure but had little effect on presence of 60° grain twins, which was influenced more by initial material condition

Closed Quasi-Fuchsian Surfaces In Hyperbolic Knot Complements

We show that every hyperbolic knot complement contains a closed quasi-Fuchsian surface.Comment: 69 pages, 27 figures. Made small changes suggested by refere

Output of a tidal farm in yawed flow and varying turbulence using GAD-CFD

Tidal stream turbine arrays will be subject to a range of flow conditions throughout the tidal cycle and it is important for developers to have an understanding of the impact of these on array performance when planning site design. A generalised actuator disk-computational fluid dynamics (GAD-CFD) model is used to conduct simulations on a three and fourteen turbine array arranged in two different configurations. Firstly, simulations of both arrays are conducted in straight flow conditions to understand the hydrodynamics around devices and evaluate their performance. Performance predictions for the three turbine array in straight flow conditions are in close agreement with previous studies. In the fourteen turbine array, wake recovery to free-stream conditions was better in the modified formation compared to the regular formation and the total power output was increased by over 10%. The influence of yaw angle and upstream TI (turbulence intensity) on both array performance was also studied. Strong sensitivity of overall farm power and thrust was found to exist in small variations in yaw angle. However, the overall wake structures were similar irrespective of the yaw angle. Finally, simulations of different turbulence intensities showed rapid decay shortly downstream of the inlet. In all arrays, turbulence intensity had little effect on the thrust and power of the upstream set of devices for the considered TI range but greatly influenced the individual downstream devices

Hollow micro/nanomaterials as nanoreactors for photocatalysis

Learning from nature, one of the most prominent goals of photocatalysis is to assemble multifunctional photocatalytic units in an integrated, high performance device that is capable of using solar energy to produce “solar hydrogen” from aqueous media. By analogy with natural systems it is clear that scaffolds with multi-scale structural architectures are necessary. In this perspective, recent progress related to the use of hollow micro/nanomaterials as nanoreactors for photocatalysis is discussed. Organised, multi-scale assemblies of photocatalytic units on hollow scaffolds is an emerging area that shows much promise for the synthesis of high performance photocatalysts. Not only do improved transport and diffusion characteristics play an import role, but increased electron/hole separation lifetimes as well as improved light harvesting characteristics by the hollow structures also do so and are touched upon in this short perspective

Theory and modelling of electrolytes and chain molecules

An aqueous solution of electrolytes can be modelled simplistically as charged hard spheresdispersed in a dielectric continuum. We review various classical theories for hard sphere systems including the Percus-Yevick theory, the mean spherical approximation, the Debye-Hückel theory and the hyper-netted chain theory, and we compare the predictions of the theories with simulation results. The statistical associating fluid theory (SAFT) has proved to be accurate for neutral polymers. It is modified to cope with charged polyelectrolyte systems. A chain term for the charged reference fluid is introduced into the theory. Some well-established results are reproduced in this study and we also introduce new terms and discuss their effects. The results show that the SAFT is semi-quantitatively correct in predicting the phase behaviour of polyelectrolytes. The electrostatic attraction between unlike charged particles at low temperature is very strong. The short-range attractions between unlike pairs are treated via an association theory while the remaining interactions are handled by hypernetted chain theory. This method works quite well with multiple associating sites. The phase prediction for the size and charge symmetric restricted primitive model is quantitatively correct as compared with simulation results. Furthermore, it also gives semi-quantitatively correct predictions for the phase behaviour of size- and charge-asymmetric cases. Dissipative particle dynamics (DPD) is a powerful simulation technique for mesoscopic systems. Molecules with specific shapes (rods and spheres) are simulated using this technique.By tuning the density of the system, some liquid crystal phase transitions can be observed.The properties of spider silk fibroin are also modelled by DPD, indicating a possible route offorming spider silk.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Expert Performance By Athletes In The Verbal Estimation Of Spatial Extents Does Not Alter Their Perceptual Metric Of Space

Athletes often give more accurate estimates of egocentric distance along the ground than do non-athletes. To explore whether cognitive calibration was accompanied by perceptual change, athletes and non-athletes made verbal height and distance estimates and also did a perceptual matching task between perceived egocentric distances and frontal vertical extents. Both groups were well calibrated for height estimation for poles viewed frontally, but athletes were much better calibrated at estimating longer egocentric distances (which are systematically underestimated by non-athletes). Athletes were more likely to have learned specific units of ground distance from relevant sports contexts. Both groups reported using human height as a metric for vertical extent. For non-athletes, verbal underestimation of ground distance corresponded to predictions based on perceptual matches between egocentric distances and vertical extents in conjunction with human-height-based verbal estimates of vertical extents. For athletes, the verbal scaling of egocentric distances of 10 m or more was more accurate and was not predicted by their egocentric distance matches to vertical extents

PopSparse: Accelerated block sparse matrix multiplication on IPU

Reducing the computational cost of running large scale neural networks using sparsity has attracted great attention in the deep learning community. While much success has been achieved in reducing FLOP and parameter counts while maintaining acceptable task performance, achieving actual speed improvements has typically been much more difficult, particularly on general purpose accelerators (GPAs) such as NVIDIA GPUs using low precision number formats. In this work we introduce PopSparse, a library that enables fast sparse operations on Graphcore IPUs by leveraging both the unique hardware characteristics of IPUs as well as any block structure defined in the data. We target two different types of sparsity: static, where the sparsity pattern is fixed at compile-time; and dynamic, where it can change each time the model is run. We present benchmark results for matrix multiplication for both of these modes on IPU with a range of block sizes, matrix sizes and densities. Results indicate that the PopSparse implementations are faster than dense matrix multiplications on IPU at a range of sparsity levels with large matrix size and block size. Furthermore, static sparsity in general outperforms dynamic sparsity. While previous work on GPAs has shown speedups only for very high sparsity (typically 99\% and above), the present work demonstrates that our static sparse implementation outperforms equivalent dense calculations in FP16 at lower sparsity (around 90%). IPU code is available to view and run at ipu.dev/sparsity-benchmarks, GPU code will be made available shortly

Galaxy Zoo and ALFALFA: Atomic Gas and the Regulation of Star Formation in Barred Disc Galaxies

We study the observed correlation between atomic gas content and the likelihood of hosting a large scale bar in a sample of 2090 disc galaxies. Such a test has never been done before on this scale. We use data on morphologies from the Galaxy Zoo project and information on the galaxies' HI content from the ALFALFA blind HI survey. Our main result is that the bar fraction is significantly lower among gas rich disc galaxies than gas poor ones. This is not explained by known trends for more massive (stellar) and redder disc galaxies to host more bars and have lower gas fractions: we still see at fixed stellar mass a residual correlation between gas content and bar fraction. We discuss three possible causal explanations: (1) bars in disc galaxies cause atomic gas to be used up more quickly, (2) increasing the atomic gas content in a disc galaxy inhibits bar formation, and (3) bar fraction and gas content are both driven by correlation with environmental effects (e.g. tidal triggering of bars, combined with strangulation removing gas). All three explanations are consistent with the observed correlations. In addition our observations suggest bars may reduce or halt star formation in the outer parts of discs by holding back the infall of external gas beyond bar co-rotation, reddening the global colours of barred disc galaxies. This suggests that secular evolution driven by the exchange of angular momentum between stars in the bar, and gas in the disc, acts as a feedback mechanism to regulate star formation in intermediate mass disc galaxies.Comment: 16 pages, 10 figures. In press at MNRAS. v2 contains corrections found in proof