The interaction of a high-intensity laser beam with a solid target generates a large number of fast electrons with long mean free paths. The study of these fast electrons is still the subject of active research, given their relevance to Tabak's [2] proposed fast-ignition approach to inertial confinement fusion. Conventional methods for simulating this system fall into two categories: kinetic and hybrid codes. Kinetic codes (Vlasov Fokker-Planck (VFP) and Particle in Cell (PIC) codes) provide an almost complete description of the system, but are often computationally expensive. Conventional hybrid codes simulate the fast-electrons well using a PIC code, but simplify the simulation of the background by using a rudimentary fluid model. In this thesis I present a new approach to modelling relativistic electrons propagating through a background plasma. This novel approach includes an improved classical transport description of the background plasma by using the VFP code IMPACT [21]. The fast electrons are modelled in two ways. Firstly, a 1D crude rigid beam model is used for the fast electrons. This gives rise to interesting transport effects in the background, such as transverse heat flow and non-local transport. It is found that the transverse heat flow is sufficient to reverse the `beam hollowing' effect of Davies et al [74] , allowing the reemergence of a fast electron collimating magnetic field over picosecond timescales. The second approach is to couple a PIC code into IMPACT to model the dynamic evolution of the fast electron beam. The scheme is tested against relevant beam-plasma phenomena. The code is used to model fast electron transport in 2D through a near-solid density background plasma. The significant result from this 2D investigation is the suppression of the filamentation instability by the resistively collimating field that surrounds the main beam.

In this thesis we investigate properties of equilibrium and non-equilibrium systems by means of renormalization group (RG) analysis. In the study of the d-dimensional Coulomb gas we have formulated a continuum model from the underlying hyper-cubic lattice and employed the irreducible differential formulation of the Wilson RG.We have identified a Thouless-Kosterletz transition in d=2 and found no non-trivial fixed points for d>2. As an example of a non-equilibrium system, we have investigated properties of quasi-neutral plasmas which are governed by stochastic magnetohydrodynamic (MHD) equations. The present method is based upon the Martin-Siggia-Rose field-theory formulation of stochastic dynamics. We develop a diagrammatic representation for the theory and carry out a momentum-shell RG of Wilson-Kadanoff type. An infinite set of diagrams is identified which are marginal in the RG sense. We have shown, in accordance with previous literature, that the same problem arises for the randomly-forced Navier-Stokes equation. The problem of marginal variables can be suppressed by working near equilibrium, where stochastic forcing represents thermal fluctuations. In a similar manner we have considered regimes when MHD equations are subject either to kinetic or magnetic forcing only. In such models the macroscopic limit can be taken such that all marginal terms are irrelevant and the dynamics is governed by linear equations. Furthermore, non-trivial fixed points are identified in such regimes and limiting values of either kinematic viscosity or magnetic diffusivity are derived. A consistent description of MHD dynamics far from equilibrium is still absent. We highlight some of the aspects of the functional integral formulation with regards to the symmetries of the system and propose possible ways in which the system can be studied non-pertubatively.

Geometry and algorithm design for a novel highly miniaturised radiation monitor (HMRM) for spacecraft in medium Earth orbit are presented. The HMRM device comprises a telescopic configuration of application-specific active pixel sensors enclosed in a titanium shield, with an estimated total mass of 52 g and volume of 15 cm3. The monitor is intended to provide real-time dosimetry and identification of energetic charged particles in fluxes of up to 108 cm-2 s-1 (omnidirectional). Achieving this capability with such a small instrument could open new prospects for radiation detection in space. The methodology followed for the design and optimisation of the particle detector geometry is explained and analysis algorithms - for real-time use within the monitor and for post-processing reconstruction of spectra - are presented. Simulations with the Geant4 toolkit are used to predict operational results in various Earth orbits. Early test results of a prototype monitor, including calibration of the pixel sensors, are also reported.

In this thesis a new formulation is presented of the low energy, supergravity limit of type II string theory and M theory, including fermions to leading order. This is performed by utilising the language of generalised geometry, which is shown to be the natural setting for these theories. The core idea behind generalised geometry – an extension of ordinary differential geometry – and what makes it such a powerful tool for analysing supergravity, is that it recasts all the bosonic fields of the manifold as the natural geometric symmetries of an enlarged tangent space. There are two versions of generalised geometry which are of particular interest, namely O(d, d) generalised geometry which will be used to formulate the NSNS sector of type II theories, and Ed(d) generalised geometry (also known as exceptional generalised geometry) which enables the description of eleven-dimensional supergravity. For both cases, this work will show how one can introduce generalised connections to study the differential structure of the extended tangent spaces and define novel notions of generalised curvature. Specifying extra local structure defines a generalised notion of the Riemannian metric tensor, which contains all the relevant bosonic fields in a single, unified object. With these tools one can then reformulate the supergravity equations very naturally, as they become simply the generalised geometry analogue of Einstein gravity. One thus obtains a formalism which is automatically fully covariant under all the bosonic symmetries of supergravity. Furthermore, generalised connections are shown to be intimately related to supersymmetry, with important consequences for future applications. As an example, in the concluding chapter it will be shown how the classic problem of solving the Killing spinor equations of supersymmetric compactifications can be equivalently recast as the statement that the background possesses the generalised analogue of special holonomy.

T2K is a long-baseline neutrino oscillation experiment. It uses an accelerator- produced neutrino beam, whereby a beam of protons impinges on a nuclear target, producing kaon and pion mesons that decay to neutrinos. The main neutrino detectors are situated at 2.50 off-axis from the centre of the beam. An accurate flux prediction for this off-axis beam is crucial to achieve the sensitivity required for the goals of T2K. External experiments reduce the major flux uncertainty (hadronic interactions in the target), but are inherently independent of the real and variable beamline conditions of T2K. Therefore, in situ measurements are required to validate the flux. This thesis uses data from the T2K near detector (ND280) to validate the ux prediction. The normalisation of K+-originating neutrinos at the ND280 is measured. The K+ beam component is important since K+ daughters dominate the high energy part of the μ beam and contribute to the intrinsic e contamination. As many aspects of the beam simulation affect this measurement, including the hadron production at the target and the off-axis angle, it is used to validate the entire system. The November 2010 to March 2011 data set is used, corresponding to 7:837 x 1019 protons on target. μ charged-current interactions are selected (with 86.3% purity) using the ND280 tracker and binned according to the momentum and angle of the muon candidate. The Monte Carlo (MC) is fitted to the data to extract the normalisations of both K+ and π+ originating neutrinos, bK and bπ respectively. The flux, cross-section and detector systematic errors are considered. The best fit point is at bK = 0:86 and bπ = 0:78, consistent with the nominal MC at the 1σ level. Additionally, results of the first time calibration of the ND280 detector, primarily of the ECal sub-detector, are presented.

The use of plastic disks coated with a thin film ( ~1 µm) of Aluminium has been investigated as a control mechanism for the shockwave formed from a radial foil z-pinch in the presence of an ambient medium. Experiments were carried out on the MAGPIE (1:4MA, 250ns rise time) facility at Imperial College London. It has been found that plastic formers replicate the results seen in standard radial foil z-pinch configurations and dramatically increase the working pressure of the experimental setup. The configuration produces a strong radiative shockwave driven with constant velocity ( ≥ 25km/s) for long time ( ≥ 400ns) and spatial scales (cm). Through comparison with standard radial foil configuration results a new formation model for shockwaves from radial foil z-pinches is proposed. The model is found to be in good agreement with all experimental velocity and profile data. The model indicates a means to maximise the shockwave velocity and alter the profile. Investigation of the effect of ambient medium atomic mass on shockwave parameters was then undertaken using the plastic former configuration. Experimental results demonstrate scaling of shock compression opposite to that found in 1D radiation hydro-dynamic simulations. Evidence of a thermal instability in the post-shock cooling region is linked to a decrease in compression for higher atomic masses due to increased radiative cooling. Increases in post-shock temperature and ionization have been measured with decreased radial distance from a strongly cooling hydrodynamic jet. Regions of observed thermal instability for Xenon and Krypton agree with those expected from evaluation of theoretical cooling functions. The possibility of temporal oscillation of the shock velocity due to thermal instability is also investigated.

More advanced models of climate systems are needed for use in present day weather forecasting and climate projection, and there is a drive towards the use of coupled modelling of various processes to achieve this goal. This thesis seeks to investigate coupled ocean-atmosphere-wave modelling using the latest generation of models. The test basin for this investigation is the Caspian Sea, where accurate representation of the water budget is vital for prediction of water level changes, which have historically seen trends of up to 15 cm/year. The individual models of atmosphere, waves and ocean are first run separately to investigate their skill in predicting observed conditions in the Caspian. These models capture the behaviour of the basin when model results are compared with observed wind speeds, currents, wave heights, sea-surface temperatures and precipitation. The coupling of the ROMS ocean and WRF atmosphere models is seen to improve sea-surface temperature prediction, but, under the Janjic Eta surface layer scheme used here, increases evaporation above the level expected. The additional inclusion of wave coupling from the SWAN model decreases strong winds through wave dependent surface roughness, reduces sea-surface temperatures and increases precipitation; all leading to better agreement with measurements. Wave prediction is best when wave-atmosphere coupling is included, but not current-wave coupling - this is believed to be because of the “double counting” of currents, where they are included both implicitly in the model formulation and then explicitly through coupling. The final part of this study considers near-inertial oscillations, which are frequently observed in the measured current records. The model is able to accurately represent the observations, and sees significant near-inertial oscillations over most of the basin. The amplitude of the oscillations in the model is found to increase with distance from the coastline. This agrees with the mechanism of barotropic and baroclinic waves, which are generated by the no flow condition at the coast, controlling inertial oscillations.

In this thesis we report the development of a range of high-performance thin-film transistors utilising different solution processable organic dielectrics grown at temperatures compatible with inexpensive substrate materials such as plastic. Firstly, we study the dielectric properties and application of a novel low-k fluoropolymer dielectric, named Hyflon AD (Solvay). The orthogonal nature of the Hyflon formulation, to most conventional organic semiconductors, allows fabrication of top-gate transistors with optimised semiconductor/dielectric interface. When used as the gate dielectric in organic transistors, this transparent and highly water-repellent polymer yields high-performance devices with excellent operating stability. In the case of top-gate organic transistors, hole and electron mobility values close to or higher than 1 cm2/Vs, are obtained. These results suggest that Hyflon AD is a promising candidate for use as dielectric in organic and potentially hybrid electronics. By taking advantage of the non-reactive nature of the Hyflon AD dielectric, the p-doping process of an organic blend semiconductor using a molybdenum based organometallic complex as the molecular dopant, has also been investigated for the first time. Although the much promising properties of Hyflon AD were demonstrated, the resulting transistors need, however, to be operated at high voltages typically in the range of 50-100 V. The latter results to a high power consumption by the discrete transistors as well as the resulting integrated circuits. Therefore, reduction in the operating voltage of these devices is crucial for the implementation of the technology in portable battery-operated devices. Our approach towards the development of low-voltage organic transistors and circuits explored in this work focused on the use of self-assembled monolayer (SAM) organics as ultra-thin gate dielectrics. Only few nanometres thick (2-5 nm), these SAM dielectrics are highly insulating and yield high geometrical capacitances in the range 0.5 - 1 μF/cm2. The latter has enabled the design and development of organic transistors with operating voltages down to a few volts. Using these SAM nanodielectrics high performance transistors with ambipolar transport characteristics have also been realised and combined to form low-voltage integrated circuits for the first time. In the final part of this thesis the potential of Hyflon AD and SAM dielectrics for application in the emerging area of graphene electronics, has been explored. To this end we have employed chemical vapour deposited (CVD) graphene layers that can be processed from solution onto the surface of the organic dielectric (Hyflon AD, SAM). By careful engineering of the graphene/dielectric interface we were able to demonstrate transistors with improved operating characteristics that include; high charge carrier mobility (~1400 cm2/Vs), hysteresis free operation, negligible unintentional doping and improved reliability as compared to bare SiO2 based devices. Importantly, the use of SAM nanodielectrics has enabled the demonstration of low voltage (<|1.5| V) graphene transistors that have been processed from solution at low temperature onto flexible plastic substrates. Graphene transistors with tuneable doping characteristics were also demonstrated by taking advantage of the SAM’s flexible chemistry and more specifically the type of the chemical SAM end-group employed. Overall, the work described in this thesis represents a significant step towards flexible carbon-based electronics where large-volume and low-temperature processing are required.

Quantitative projections are routinely made for the future statistics of climate variables, such as the frequency and intensity of storms in the North Atlantic. The quantification of uncertainty in these projections is particularly important if such results are to be used for decision making. This thesis addresses the design, use, and interpretation of models in climate science, using the behaviour of North Atlantic extratropical storms as a detailed case study. Results from novel statistical models and state-of-the-art dynamical models are generated and evaluated, looking at the frequency and intensity characteristics of storms in the eastern North Atlantic and the clustering characteristics of the most intense storms. It is found that statistical models are extremely limited by the shortness of the calibration data set of historical observations, and therefore have little merit other than simplicity. Dynamical models are primarily constrained by the accuracy of their dynamical assumptions, which cannot be easily quantified. Some relevant properties of dynamical systems, including structural instability, are discussed with reference to predictability in the North Atlantic and other aspects of climate science. This thesis concludes that despite the existence of "statistically significant" results from some individual models, there is little evidence that we can correctly evaluate even the sign of 21st century change of North Atlantic storm characteristics (frequency, intensity or spatial position). Although climate models do suggest that the magnitude of overall change will be small, this could still result in very large percentage changes to the tails of the distribution, given the nonlinear nature of the climate system. In order to make more confident conclusions about the tails of such distributions, much longer runs are needed than the 30 year slices requested by the CMIP experiments. In addition, formal quantification of subjective opinions about model error would benefit climate science, scientists, and decision-makers.

This thesis presents how sources of coherent sources extreme ultraviolet (XUV) and soft X-ray wavelengths can be generated and how these sources may be used to study both the dynamics and structure of molecular systems. Developmental work on a beam line designed to generate XUV radiation using high harmonic generation is presented. In addition to commissioning experimental work using both a flat-field XUV spectrometer and magnetic bottle electron spectrometer, software development work towards building a scalable and future proof acquisition framework for future experiments is presented. The remainder of the thesis presents results obtained from experiments performed at the Linac Coherent Light Source (LCLS) X-ray free electron laser (FEL). We demonstrate that by using a UV femtosecond pulse and a weakly focused X-ray pulse of duration 70 fs, the evolution of UV induced photoisomerisation of 1-3 cyclohexadiene can be tracked. Over timescales of ≈1 ps after UV excitation, the ion yields of the H+ and C+ species were observed to increase by 10% and the observed kinetic energy of all fragments is observed to increase over the same time scale, which can be explained by the structural change of the molecule into the hexatriene isomers. There has been a recent focus in FEL science in using tightly focused X-rays to generate so called hollow atoms, with a completely empty inner shell. Study of the products of the creation of these states ideally requires a measurement in coincidence of multiple particles. We demonstrate that by using the technique of partial covariance mapping (PCM) in conjunction with a high efficiency electron time-of-flight spectrometer, multiple processes in the core ionisation of neon can be resolved. We also use the scheme to successfully measure single site double-core hole states in the hydrocarbons of acetylene and ethane. We discuss how this technique will be a powerful tool in future experiments designed for chemical analysis of the core hole states of systems.