Higher Order QCD Corrections to Electroweak Boson Production at Colliders

In this thesis we consider the Next-to-Next-to-Leading Order (NNLO) corrections to single charged electroweak boson production with associated QCD radiation in hadron-hadron collisions, calculated using the antenna subtraction method to regulate infrared (IR) divergences. Results are presented alongside the neutral current case for the inclusive transverse momentum spectrum and subsequent ratios both with and without the addition of state-of-the-art resummation results. In the former case a comparison to CMS data is also provided. We also discuss the phenomenological implications of the results when one or more jets are reconstructed from the QCD radiation. Particular attention is given to the impact on valence quark content of Parton Distribution Functions (PDFs) through a comparison with experimental results from the ATLAS, CMS and LHCb collaborations. We then discuss the use of fixed-order QCD predictions for inclusive Drell-Yan production in the context of an effective Weinberg angle extraction using triple-differential data taken by the ATLAS collaboration at $\sqrt{s}=8~\mathrm{TeV}$, using the kinematics to extend the predictions to Next-to-Next-to-Next-to-Leading Order (N$^3$LO) for certain parts of the measurement. Finally, using the antenna subtraction method we derive the NNLO QCD corrections to di-jet production in charged-current Deep Inelastic Scattering (DIS), allowing the first comparison to ZEUS data at this order. These results are then combined with inclusive structure functions using the method of projection-to-Born (p2B) in order to derive the first exclusive fiducial predictions for single jet inclusive production in charged-current DIS to N$^3$LO. A comparison to data is performed, where we observe reasonable agreement with the experimental results from ZEUS

Experimental and computational study of hybrid diffusers for gas turbine combustors

Diffusers are essential in gas turbine combustors, decelerating the compressor efflux prior to the combustion chamber to reduce total pressure losses. Modern, low emission, radially staged combustors require even more diffusion due to the increased flame tube depth of this type of combustor. Furthermore, these high rates of deceleration are accompanied by large adverse pressure gradients and an associated risk of flow separation. Previous studies have shown that hybrid diffusers can achieve high rates of efficient diffusion in far shorter lengths than conventional faired diffusers or dump diffuser systems, representing a potential performance gain and weight saving. Hybrid diffusers consist of a wide angle diffuser immediately downstream of a sudden expansion, with flow separation prevented by bleeding off a small amount of the mainstream flow. However, previous studies have not provided a conclusive understanding of the associated flow mechanisms leading to hybrid diffusers currently being considered high risk. Additionally definitive data does not exist on the influence of bleed gap geometry and therefore hybrid diffusers cannot, currently, be optimised for use in a modern gas turbine. Further issues also not addressed by earlier studies, but concerning the use of hybrid diffuser in gas turbine combustors, are the effect of representative inlet conditions incorporating vane wakes at diffuser inlet, the quality of the bleed air and its potential for use for component cooling, the effect of radial struts within a hybrid diffuser and the quality of the flow delivered to the combustor feed annuli (total pressure losses). Therefore, a predominately experimental study, coupled with CFD predictions, was undertaken to investigate the controlling flow mechanisms of hybrid diffusers and address the questions necessary to evaluate the suitability of hybrid diffusers for use in modern, low emission, radially staged combustion systems. An existing isothermal test facility was used comprising a fully annular, staged combustor downstream of a single stage axial compressor incorporating engine representative outlet guide vanes. Initial experimental work led to rig modifications which allowed a range of hybrid diffusers to be studied. To act as a benchmark the performance of a conventional single-passage, dump diffuser system was first studied. A hybrid diffuser demonstrated a 53% increase in area ratio within the same axial length as the conventional diffuser. Results showed that this hybrid diffuser achieved a 13% increase in static pressure recovery which, in turn, improved the feed to the combustor feed annuli and decreased total pressure loses by 25%. Notably this brought the annulus losses within accepted target values; something the conventional diffuser system was unable to do. Additionally, it was clearly shown, in contradiction to previous studies, that bleeding air via a vortex chamber was not necessary. Bleeding air via a simple duct arrangement achieved the same results without altering the governing flow mechanisms. To provide a better understanding of these flow mechanisms, a computational investigation was also undertaken. A commercial CFD code, Fluent, was used to solve the Reynolds averaged Navier-Stokes equations for an incompressible flow regime, employing a blended second order upwind/central differencing scheme and the SIMPLE pressure correction algorithm. The turbulence was modelled using the k-ε model in conjunction with a standard wall function. Several generic two-dimensional hybrid diffusers were studied in order to reveal the controlling flow mechanisms and enable optimisation of the bleed gap geometry. Importantly, this revealed that many features previously thought to contribute to the flow mechanisms were, in fact, unnecessary. A detailed examination of the flow field, including an analysis of the terms within the momentum equation, demonstrated that the controlling flow mechanisms were not simply a boundary layer bleed but involve a much more complex interaction between the accelerating bleed flow and the diffusing mainstream flow. Firstly, momentum is transferred from the accelerating bleed flow to the diffusing mainstream flow, enabling a fresh boundary layer to be formed on the diffuser wall which is sufficiently energetic to overcome the high rates of diffusion and high adverse pressure gradient. Secondly, the radial pressure gradient created by the bleed causes deflection of the mainstream flow which also transports higher momentum fluid into the boundary layer. Understanding this resulted in a greatly simplified design for the hybrid diffuser not only potentially reducing weight but also reducing bleed flow total pressure losses. Predictions for a three-dimensional representation of the experimental facility displayed many similarities in the flow field and similar performance trends to the experimental data. However, predicted values of total pressure loss and static pressure recovery differed from experimental data and it was thought that this was due to an incomplete description of the turbulence (k and ε) at inlet and/or known problems the k-ε turbulence model has with predicting some unconfined flows. Nonetheless, three-dimensional predictions revealed an interaction between the OGV wake fluid and bleed flow causing localised, but small, modification of the flow mechanisms. Furthermore, it was shown that without the levels of turbulence produced downstream of an axial compressor the hybrid diffuser under study would, in fact, stall. Overall, experimental and computational results obtained in the current research suggest that the performance of hybrid diffusers is more than satisfactory for use within lowemission, staged, gas turbine combustion systems. An understanding of the governing flow mechanisms and the effect of features such as OGV wakes or radial struts has lead to a more practical design of hybrid diffuser, simplifying the geometry and reducing bleed flow total pressure losses (increasing the possibility of this air being used for component cooling)

Modelling the emergent dynamics and major metabolites of the human colonic microbiota

Funded by Scottish Government's Rural and Environment Science and Analytical Services Division (RESAS) Acknowledgements We would like to thank Thanasis Vogogias, David Nutter and Alec Mann for their assistance in developing the software for this model. We also acknowledge the Scottish Government’s Rural and Environment Science and Analytical Services Division (RESAS) for their financial support. Furthermore,many thanks go to the two anonymous reviewers whose hard work has greatly improved this paper.Peer reviewedPublisher PD

Noncanonical spike-related BOLD responses in focal epilepsy

Till now, most studies of the Blood Oxygen Level-Dependent (BOLD) response to interictal epileptic discharges (IED) have assumed that its time course matches closely to that of brief physiological stimuli, commonly called the canonical event-related haemodynamic response function (canonical HRF). Analyses based on that assumption have produced significant response patterns that are generally concordant with prior electroclinical data. In this work, we used a more flexible model of the event-related response, a Fourier basis set, to investigate the presence of other responses in relation to individual IED in 30 experiments in patients with focal epilepsy. We found significant responses that had a noncanonical time course in 37% of cases, compared with 40% for the conventional, canonical HRF-based approach. In two cases, the Fourier analysis suggested activations where the conventional model did not. The noncanonical activations were almost always remote from the presumed generator of epileptiform activity. In the majority of cases with noncanonical responses, the noncanonical responses in single-voxel clusters were suggestive of artifacts. We did not find evidence for IED-related noncanonical HRFs arising from areas of pathology, suggesting that the BOLD response to IED is primarily canonical. Noncanonical responses may represent a number of phenomena, including artefacts and propagated epileptiform activity

EEG–fMRI mapping of asymmetrical delta activity in a patient with refractory epilepsy is concordant with the epileptogenic region determined by intracranial EEG

We studied a patient with refractory focal epilepsy using continuous EEG-correlated fMRI. Seizures were characterized by head turning to the left and clonic jerking of the left arm, suggesting a right frontal epileptogenic region. Interictal EEG showed occasional runs of independent nonlateralized slow activity in the delta band with right frontocentral dominance and had no lateralizing value. Ictal scalp EEG had no lateralizing value. Ictal scalp EEG suggested right-sided central slow activity preceding some seizures. Structural 3-T MRI showed no abnormality. There was no clear epileptiform abnormality during simultaneous EEG–fMRI. We therefore modeled asymmetrical EEG delta activity at 1–3 Hz near frontocentral electrode positions. Significant blood oxygen level-dependent (BOLD) signal changes in the right superior frontal gyrus correlated with right frontal oscillations at 1–3 Hz but not at 4–7 Hz and with neither of the two frequency bands when derived from contralateral or posterior electrode positions, which served as controls. Motor fMRI activations with a finger-tapping paradigm were asymmetrical: they were more anterior for the left hand compared with the right and were near the aforementioned EEG-correlated signal changes. A right frontocentral perirolandic seizure onset was identified with a subdural grid recording, and electric stimulation of the adjacent contact produced motor responses in the left arm and after discharges. The fMRI localization of the left hand motor and the detected BOLD activation associated with modeled slow activity suggest a role for localization of the epileptogenic region with EEG–fMRI even in the absence of clear interictal discharges

Using Rural Household Income Survey Data to Inform Poverty Analysis: An Example from Mozambique

This paper demonstrates that income survey data can be very informative in explaining the variation across households in the incidence and severity of absolute poverty using a rural household income data set for Mozambique. Results from regression analysis of the sources of variation are used to simulate the impact of alternative agricultural interventions or strategies on rural poverty. Complementarities in the insights gained from consumption expenditure and income surveys may justify the collection and analysis of both types of information, especially in Sub-Saharan Africa, the one region of the world where the incidence of poverty is increasing.Poverty analysis, household income surveys, agricultural development, Millenium Development Goals, Mozambique, Consumer/Household Economics, Food Security and Poverty, C21, I3, O13, O2, Q18,

Investigation of wheelhouse flow interaction and the influence of lateral wheel displacement

The aim of this research was to improve the understanding of the complex flow features found around a wheel and wheelhouse and to examine how the lateral displacement of the wheel affects these features and the production of exhibited pressures and forces. A bespoke rotating wheel rig and accompanying wheelhouse with a fully-pressure-tapped wheel arch was designed and manufactured at Loughborough University. Wind tunnel tests were performed where force and pressure measurements and Particle Image Velocimetry (PIV), data were obtained. The experimental data were used to validate unsteady CFD predictions where a k-ω SST Improved Delayed Detached Eddy Simulation (IDDES) turbulence model was used in STAR-CCM+. The CFD showed good agreement with all trends of the experimental results providing a validated numerical methodology. For both methodologies, a lower amount of wheelhouse drag was found generated when the wheel was rotating. However, the CFD showed that whilst this was the case, total configuration drag had increased. This was attributed to an increase of the wheel and axle drag, illustrated by the change in separation over the wheel itself when located within a wheelhouse and so overcompensating the reduction in body and stand drag. Differences in vortex locations when comparing to previously-attained results were due to differences in housing geometry, such as blockage in the cavity or housing dimensions. Experimental and computational results showed that up until a 10-mm displacement outboard of the housing, overall drag decreased. The reduction in housing drag was credited to a reduction in the size of outboard longitudinal vortex structures. This led to the lateral width of the shear layer across the housing side being narrower. Overall, this study identified that there were potential benefits to be gained when offsetting a wheel outboard of the longitudinal edge of a model housing