Master of Science / Department of Statistics / Christopher Vahl / Non-inferiority trials have been widely used in many medical areas. The goal of a non-inferiority trial is to show that a new test therapy is either better or not too much worse than the active control rather than showing the test therapy is superior to a negative control (i.e. placebo). The appeal of a non-inferiority trial is that it is often unethical to give some patients a treatment with no therapeutic benefit. When designing a non-inferiority trial, the issues of assay sensitivity, sample size, constancy condition, and a suitable non-inferiority margin need to be considered. A poor choice of the non-inferiority margin is a major reason that many non-inferiority trials fail. A numerical example is presented to show how to estimate the non-inferiority margin without historical data.

Denna uppsats har ett särskilt fokus på Frankrikes förbud av ansiktstäckande plagg, såsom burkor, vilket är ett exempel på en grund för de konflikter som uppkommer vid Europas ökade religiösa mångfald. Av de cirka 15 miljoner muslimerna i Europa, bor 5 miljoner i Frankrike, vilket gör islam till den näst största religionen i landet. Genom att undersöka Frankrikes lagstiftning mot ansiktstäckande plagg på offentliga platser och deras senare prövning i Europadomstolen kan man påvisa ett betydelsefullt exempel på hur religiösa minoritetsgrupper behandlas i det moderna Europa.

T he casing treatment technique for the axial fan has never been more significant since its potential applications were recognized in gas turbines, tunnel ventilation and many other industrial applications where the axial fan would benefit from the casing treatment. In the last two decades experimental investigations were carried out at Cranfield University to examine the influence of recess casing treatment on stall margin, operating efficiency and flow field of a low-speed axial flow fan. They showed more than 50% improvement in the stall margin with a negligible loss in the efficiency. However, a little work has been done on the numerical simulation of casing treatments due to its complexities, even though in recent years computational fluid dynamics [CFD] analysis has been very active in the prediction of various phenomena in turbomachinery. This work presents numerical investigation of flow in a single axial-flow fan with and without recess casing treatment. It involves the detailed effect of the recess casing on stall margin improvement as well as its influence on global performance parameters. The project offers a contribution to the understanding of the physical processes occurring when approaching stall and the working mechanism by which recess casing treatments improve stall margin. A Reynolds-Averaged Navier-Stokes CFD code was used for the analysis using steady and unsteady simulations. The numerical investigation of the overall performance, efficiency and work-input characteristics of the fan were found to agree very well with the previously reported experimental results. The effect of casing treatment was investigated using two types of configurations, vaneless and vaned casing. The vaneless casing treatment produced a sizeable stall margin improvement with a measurable loss in both pressure rise and efficiency. The recess was fitted later with vanes and was shown to offer both a further stall margin improvement and an increase in the pressure rise coefficient without any significant drop in efficiency at design conditions. The effect of number of vanes inside the recess was also investigated by doubling and halving the number of vanes originally adopted. The predicted results highlighted the importance of the vane inside the casing. Unsteady simulations for the fan with solid and treated casing were carried out. The solid casing simulated for a single blade passage as well as for the entire fan containing all 27 blades highlighted the flow physics of the tip stall growth process, as a large amount of radial flow injected from the hub at the blade suction side near the trailing edge towards the outer casing and occupy this through a mechanism of radial low momentum flow transport. This transport process is the main contributor to the very large separation observed in the shroud region in addition to the locally induced separation due to high blade loading and tip clearance. Although the examination of the unsteady simulation of the recess treatment cavities does not offer an image of large scale unsteady activity at the flow condition investigated, this is on itself quite significant and enables the drawing of an important conclusion namely that large casing treatments rely primarily on a steady-state flow process. The corollary of this conclusion is of course that a steady-state simulation should then be sufficient to capture the essential features of the recess treatment.

This project was desgined to ascertain the origin of debris-bearing basal ice exposed in thick sequences at the margin of the Greenland ice sheet; an understanding of basal processes is fundamental to realistic modelling both of ice sheet behaviour and of the development of glaciated landscapes. Stratigraphic, isotopic (delta18O, deltaD), structural, dynamic and sedimentological analyses of ice and debris from the ice sheet margin indicate two zones of basal ice formation and debris entrainment beneath the ice. At some point in the interior, water freezes to the bed in small increments across a transition zone between warm and cold based areas. This interior derived basal ice re-crystalises during flow, may undergo pressure melting and regelation, and appears at the ice sheet margin as an isotopically distinctive ice facies with large clear crystals and with gas and debris pockets at crystal boundaries. Close to the margin, particularly in zones of faster flowing ice, some of this basal ice melts from the bed. Water derived from this melting, and from penetration of surface meltwater, re-freezes at the bed in a narrow freezing zone at the very edge of the ice sheet, forming a sequence several metres thick of ice and debris laminae. Compressive flow at the margin, related to seasonal freezing as well as to marginal thinning of the ice, causes folding and thrust-faulting within the glacier. This thickens the basal sequence, and raises material from the basal layers and from the basal transport zone into the body of the glacier to form debris bands. At the very margin, accumulations of snow, superimposed ice, and debris are overriden and incorporated into the lowest part of the basal sequence. These findings have implications for basal thermal conditions, ice rheology, the distribution of zones of sub-glacial geomorphic activity, and the structure of ice sheet sediments.

Glioma is one of the most challenging types of brain tumors to be treated or controlled locally. One of the main problems is to determine which areas of the apparently normal brain contain glioma cells, as gliomas are known to infiltrate several centimetres beyond the clinically apparent lesion that is visualized on standard CT or MRI. To ensure that radiation treatment encompasses the whole tumor, including the cancerous cells not revealed by MRI, doctors treat the volume of brain that extends 2cm out from the margin of the visible tumor. This approach does not consider varying tumor-growth dynamics in different brain tissues, thus it may result in killing some healthy cells while leaving cancerous cells alive in other areas. These cells may cause recurrence of the tumor later in time which limits the effectiveness of the therapy. In this thesis, we propose two models to define the tumor invasion margin based on the fact that glioma cells preferentially spread along nerve fibers. The first model is an anisotropic reaction-diffusion type tumor growth model that prioritizes diffusion along nerve fibers, as given by DW-MRI data. The second proposed approach computes the tumor invasion margin using a geodesic distance defined on the Riemannian manifold of brain bers. Both mathematical models result in Partial Differential Equations (PDEs) that have to be numerically solved. Numerical methods used for solving differential equations should be chosen with great care. A part of this thesis is dedicated to discuss in detail, the numerical aspects such as stability and consistency of different finite difference methods used to solve these PDEs. We review the stability issues of several 2D methods that discretize the anisotropic diffusion equation and we propose an extension of one 2D stable method to 3D. We also analyze the stability issues of the geodesic model. In comparison, the geodesic model is numerically more stable than the anisotropic diffusion model since it results in a rst-order PDE. Finally, we evaluate both models on actual DTI data from patients with glioma by comparing our predicted growth with follow-up MRI scans. Results show improvement in predicting the invasion margin when using the geodesic distance model as opposed to the 2cm conventional Euclidean distance.

No description available.

This thesis studies the effects of morphological factors of hexapod robots on their locomotion stability. In particular, an offset model for such robots is proposed. The stability margin as well as the error margin are used to indicate the stability of the hexapod robot, as it walks with different gaits in arbitrary directions. Two hexapod gaits are compared, which are the symmetric gait and the metachronal gait. The former is an artificial gait and the latter, on the contrary, is a natural gait which can be observed in many multiped animals. As we investigate advantages and disadvantages of the two gaits, we find that the stability of a hexapod robot can be enhanced by increasing the offset value. This is particularly true for a robot moving in the X and oblique directions with a symmetrical gait. However, altering the offset is less useful for metachronal gaits. In general, a hexapod robot moves most stably in the Y direction with a symmetrical gait, whereas it is most stable in the X direction with a metachronal gait.

This dissertation assesses the causes and consequences of gender wage discrimination in Ethiopia. In the first chapter, we estimate the distribution of Gender Wage Discrimination in the Ethiopian urban labor market using quantile counterfactual decompositions. The literature generally finds a u-shaped distribution suggesting the presence of both a sticky floor effect and a glass ceiling effect. Using repeated cross-section data for the years 2006, 2010 and 2014, we find a strong evidence of a sticky floor effect but not a glass ceiling effect in the Ethiopian urban labor market. Our paper also provides evidence that there is substantial difference in the extent of discrimination between working in private and public jobs. Public jobs are less discriminatory for women relative to the private jobs. In the second chapter, we investigate the determinants of the gender wage gap in the Ethiopian manufacturing sector between the years 1996 and 2010 with a particular focus on the impact of the export orientation. This is done both at the intensive and extensive margin. Accordingly, we find that more export orientation helps reduce the firm level gender wage gap regardless of whether it is at the intensive or extensive margin. Our results also provide evidence on the presence of sectoral variation on the association between export orientation and gender wage gap. Export orientation doesn’t have a significant impact on the gender wage gap in the construction and housing goods sector. Segmenting the data in to two we also find that the impact of export orientation in reducing gender wage gap is much stronger for the period 2003-2010 relative to the 1996-2002 period. Finally, we estimate the impact of gender earnings differentials on the technical efficiency of the firm in the Ethiopian manufacturing sector for the period 1996 through 2010. We adopt a two-step time-variant panel stochastic frontier model using a translog production function. Our results provide fresh evidence on the existence of a significant negative association between gender wage gap and predicted technical efficiencies of firms. Further subdividing the manufacturing sector into four different industries, we find that the negative association is consistent in most industries. Our results are also robust to the inclusion of other firm level explanatory variables at the sectoral level.

Passive tectonic margins, like the eastern North American margin (ENAM), represent the meeting of oceanic and continental material where no active deformation is occurring. The recent ENAM Community Seismic Experiment provides an opportunity to examine the crustal structure across the ENAM owing to the simultaneous deployment of offshore and onshore seismic instrumentation. Using Rayleigh wave phase and group velocities derived from ambient noise data, we invert for shear velocity across the ENAM. We observe a region of transitional crustal thicknesses that connects the oceanic and continental crusts. Associated with the transitional crust is a localized positive gravitational anomaly. Farther east, the East Coast magnetic anomaly (ECMA) is located at the intersection of the transitional and oceanic crusts. We propose that underplating of dense magmatic material along the bottom of the transitional crust is responsible for the gravitational anomaly and that the ECMA demarks the location of initial oceanic crustal formation.

This paper studied the extensive margin (EM) and intensive margin (IM)of liquefied natural gas(LNG) imports in Europe over the period 1996-2015. Two econometric models were used, a prob it estimation for the EM and an OLS for the IM. A time-varying approach was conducted to analyse the stability of the models in the studied time frame. The models were constructed through the application of known determinants of LNG trade as well as new factors that previously was unused in the investigation of LNG trade. The results indicated an overall stable EM, but a highly varying IM over the period. The findings inform that the EM is driven by income, diversification and lower bounds technological development and we found that itis inhibited by pipeline imports, domestic production and higher bounds technological development. The IM is determined by favourable pricing opportunities, lower bounds technological development and the diversification aspect of LNG. IM is negatively affected by domestic natural gas production and the higher bounds of technological development.