The Rosetta spacecraft is on route to rendezvous with the comet 67P/ Churyomov-Gerasimenko. One of the instruments onboard is the Langmuir probe instrument (LAP) developed by the Swedish Institute of Space Physics. The LAP includes two spherical probes used to measure a number of properties of the surrounding plasma. One measured property is the plasma density for which the spacecraft potential is a good proxy. By the determining the potential between spacecraft and Langmuir probe, the spacecraft potential can be measured. But such measurements are sometimes disturbed by the potential from the spacecraft itself, the influence from photoemitted electrons and the solar wind wake behind Rosetta. In order to correct for the errors caused by spacecraft-plasma interaction in the solar wind a model depending on the spacecraft (and Langmuir probe) orientation is developed. The data is obtained from three-dimensional simulations of Rosetta, with varying plasma parameters, using the software SPIS (Spacecraft Plasma Interaction System). Least squares fitting with a set of basis functions then provide the input for a parametric modelling. The developed model makes it possible to estimate the influence of each of the disturbing effects. The developed model gives good fits to data obtained in SPIS simulations. The two angular dependent factors, modelling perturbation on potential measurements caused by photoelectrons and wake effects, show errors below the 100 mV level in all cases. The model describing the influence from spacecraft potential is slightly less accurate, with errors at or below the 400 mV level in all relevant cases.

Tidal stream energy is a predictable source of renewable energy. Tidal stream turbines have been proposed as a way to extract useful energy from the tide. Many arrays of such devices will need to be installed to extract significant amounts of energy. The presence of an array of turbines within a tidal flow will impact the flowfield, as complex fluid interactions occur across multiple scales. This thesis is concerned with the behaviour of tidal turbines arrayed across channels. Experimental and analytical work is carried out to investigate array behaviour and to create new modelling tools to replicate this behaviour. Linear Momentum Actuator Disc Theory (LMADT) is employed to develop a new analytical model for a long row array of tidal turbines split into multiple smaller, co- linear row arrays. An argument of separation of scales is used to facilitate this model. It is found that increases in power extraction beyond that of a single continuous row array are possible. Experimental work is carried out on a row array of eight porous discs, simulating a short row array of tidal turbines. Disc porosity and spacing are varied to investigate thrust on the array, flow behaviour behind the array and an 'inferred' power removed from the flow. The results are compared to previously developed theoretical models. Good agreement is found with the trends of the analytical model, for example that there is a peak power coefficient which can be reached through appropriate selection of spacing and disc resistance. Differences from theory are found in the total thrust and power measurements, as well as in some aspects of the flow behaviour in the array wake. Reductions in thrust and power towards the ends of the array are also identified as 'end effects' which are not included in the analytical model. Based on these results a new semi-empirical model is proposed, using LMADT with experimental data closure. This model allows variation of the disc resistance across a row array. Values from the experimental work are used as inputs to the model, and the results compared to experimental measurements of flowspeed, thrust and power. Although agreement with experimental results is found in some areas, there are still some discrepancies between the analytical model and the experimental results. This indicates that there are additional factors that contribute to end effects on a short row array.

Economic evaluations provide a tool to estimate costs and health consequences of competing medical technologies, ultimately to aid decision makers when deciding which medical technologies should be funded from available resources. Such decisions inevitably need to be taken under uncertainty and it is not clear how to approach them in health care decision-making. Recent work in economic evaluation has proposed an analytic framework where two related, but conceptually different decisions need to be considered: (1) should a medical technology be adopted given existing evidence; and (2) whether more evidence should be acquired to support the adoption decision in the future. The proposed analytic framework requires a decision-analytic model appropriately representing the clinical decision problem under consideration, a probabilistic analysis of this model in order to determine cost-effectiveness and characterise current decision uncertainty, and estimating the value of additional information from research to reduce decision uncertainty. The main aim of this thesis is to apply the analytic framework on three case studies concerning treatment strategies for cardiovascular disease in order to establish whether the treatment strategies should be adopted given current available information and if more information should be acquired to support the adoption decisions in the future. The implications for policy and methodology of utilising the analytic framework employed in the case studies are also discussed in this thesis. The results of the case studies show that a screening programme for abdominal aortic aneurysm in 65-year-old men is likely to be cost-effective in a Swedish setting and there appears to be little value in performing further research regarding this decision problem; an early interventional strategy in non-ST-elevation acute coronary syndrome is cost-effective for patients at intermediate to high risk of further cardiac events in a UK setting; endarterectomy in patients with an asymptomatic carotid artery stenosis is cost-effective for men around 73 years of age or younger in a Swedish setting and conducting further research regarding this decision problem is potentially worthwhile. Comparing the results of the present analyses with current clinical practice shows a need for changing clinical practice in Sweden regarding screening for abdominal aortic aneurysm and endarterectomy in patients with asymptomatic carotid artery stenosis. Furthermore, employing the analytic framework applied in the case studies can improve treatment guidelines and recommendations for further research. In particular, treatment guidelines ought to consider in which particular subgroups of patients an intervention is cost-effective. The case studies indicate that it is feasible to apply the analytic framework for economic evaluation of health care. Methodological development can improve the accuracy with which cost-effectiveness and value of information is estimated, but may also lead to comprehensive and complex evaluations. The nature of the decision problem should determine the level of comprehensiveness required for a particular evaluation.