Fluorescent proteins (FPs), particularly Enhanced Green Fluorescent Protein (EGFP), are essential tools in the study of intact biological systems. Whilst the photophysics of its progenitor, GFP, have been investigated extensively, far fewer studies of EGFP have been made. In this thesis, a full characterisation of EGFP excited state photophysics by singleand two-photon time-resolved fluorescence lifetime and anisotropy is presented. Furthermore, the two-photon transition tensor, determined by absorption and initial anisotropies, is shown to be dominated by a single element. The two-photon excited state of EGFP was subject to Stimulated Emission Depletion (STED), revealing the stimulated emission cross section, the ground state relaxation time and the time evolution of the higher order distribution moments to which anisotropy is not sensitive. The strong adherence to theoretical Debye diffusion reinforced the conclusions of the two-photon structure model, and showed EGFP to be an excellent molecule for the future development of STED. In addition, these studies provided a sound basis on which to employ single- and two-photon FRET in vivo and in vitro. Cell behaviour is governed by the transduction of molecular signals from the extracellular environment to intracellular compartments. At the centre of the PI 3-kinase signalling pathway is PDK1, a Serine/Threonine kinase, which phosphorylates numerous important downstream targets including Protein Kinase B (PKB). To date however, the regulatory mechanisms governing the behaviour of this protein remain poorly understood. Timeresolved fluorescence lifetime imaging microscopy (FLIM) was employed with FP tagged PDK1 to investigate dynamic interactions in intact cells in situ and in vivo. PDK1 was shown to dimerise in a manner dependent on PI 3-kinase activity and PDK1 PH domain lipid binding. To detail the structure of the observed intermolecular interaction, recombinant FP labelled PDK1 was produced with insect cells. Measurement of the rise in acceptor fluorescence during FRET in vitro indicated the PDK1 dimer pair exists in an antiparallel arrangement. These results provide the first insight on the structure of the dimer and demonstrate that the generation of 3-phosphorylated lipids is required for its formation.

Here is presented an experimental study of the low-temperature magnetic behaviour of the spin ice holmium titanate, Ho_2Ti_2O_7; stuffed spin ice, Ho_{2+x}Ti_{2-x}O_{7-x/2}; and neodymium zirconate, Nd_2Zr_2O_7. The main techniques utilised here are based on neutron scattering which gives information on the static and dynamic behaviour of materials. Stuffed spin ice represents the addition of holmium magnetic moments into holmium titanate. This addition of the Ho^3^+ affects the oxygen lattice which is responsible for the considerable magnetocrystalline anisotropy in these materials. Inelastic scattering measurements reveal that a crystal of Ho_{2.3}Ti_{1.7}O_{6.85} is a static magnetic system at the lowest energies. Elastic neutron scattering on the same crystal reveals short-range order that distinguishes it from spin ice. Neodymium zirconate, Nd_2Zr_2O_7, is a stoichiometric pyrochlore material isomorphous to holmium titanate in structure. Here a single crystal and a powder sample have been investigated by both elastic and inelastic scattering. The powder and crystals exhibit low temperature intensity in the same temperature range indicating a low temperature transition which has been shown to be second order. A field induced transition has also been studied, but its origin has not been established. Holmium titanate is a stoichiometric material unlike stuffed spin ice. Here a study has been conducted into scattering in the hhl plane under application of a magnetic field at a temperature of 60 mK. The results indicate a breaking of the ordered \alpha-chain structure within the material as the field is removed.

A positron is the antimatter counterpart of the electron with which it can form a short lived bound state called positronium (Ps). The interactions of both of these particles with matter is the concern of the present work. These are of relevance in a variety of fields, for example, galactic astronomy, condensed matter physics and positron emission tomography. In the present work, the progress toward the realisation of a positron reaction microscope is described which will hopefully lead to the measurement of fully differential cross sections for ionizing collisions. To achieve this, a crossed beam system has been developed, in which a positron beam is passed through a supersonic gas jet target. Ions produced in the resulting collisions are guided onto a position sensitive detector for imaging using a spectrometer. A complementary theoretical study of target ionization caused by positron collisions has also been carried out. This has involved the development of a 3-body classical trajectory Monte Carlo simulation which has been applied to the calculations of direct-ionization, Ps formation, and excited state Ps formation cross sections. The development of the code also included a study of numerical integrator techniques, as well as, by way of diagnostics, the calculation of cross sections for collision systems which have been previously studied (e.g. proton - hydrogen). Finally, the mono-energetic Ps beam line at UCL has been used to measure the Ps total scattering cross section (TCS) for collisions with CO2. This work has contributed towards the observation that the Ps TCS is remarkably similar to that of an equivelocity electron. An enhancement in the TCS has also been observed in the vicinity of the 2 \Pi u shape resonance in the electron - CO2 TCS.

The Rapid Temporal Survey explores the faint, variable sky. I have led the development of the data reduction and analysis pipeline for this survey and have played a leading role in the observation and analysis of follow-up data. The survey and follow-up work is presented in this thesis. The strategy of the survey is to observe fields close to the Galactic plane at a cadence of ~1 min for around two hours down to a depth of g' = 23 The data presented in this thesis cover 31 square degrees of which 16 are within 10^o of the Galactic plane. This is the first dedicated survey to explore this parameter space and such I have had to develop new techniques when dealing with the data. The photometry was performed using a difference imaging technique and resulted in over 3 × 10^6 light curves. This work primarily deals with periodic variability and with this aim I have developed a method which combines two algorithms (Lomb-Scargle and Analysis of Variance) to produce a sub-set of variable sources which contains a very low number of false positives –around 600 out of 1.2 × 10^5 detected variables. For sources brighter than g' = 21 this technique is able to detect – at a confidence above 90 per cent – variability on time-scales of less than 10 min to tens of minutes in source with semi-amplitudes of less than 0.04 mag. Spectroscopic follow-up observations of a number of these targets have been performed and have resulted in the discovery of many different variables from several different classes. I highlight three populations to study in more detail: short-period, variable A-stars; SX Phe and /delta Scuti stars; and pulsating white dwarfs. Of particular interest are the SX Phe stars which I have found to be as far away as 30 kpc from us. I also provide a detailed examination of two variables sources: one is a dwarf nova which was discovered through quasi-periodic oscillations in quiescence, the other a pulsating white dwarf which appears to have a hot companion. I conclude by looking to the future of the project which will continue with a similar strategy but surveying the Kepler field of view.

The field of transiting extrasolar planets and especially the study of their atmospheres is one of the youngest and most dynamic subjects in current astrophysics. To study the atmospheres of those foreign worlds, we typically require a 10^−4 to 10^−5 level of accuracy in flux. Currently available instruments were not designed with these precisions in mind. Calibrating an instrument without knowing its response function at the required level has become the central challenge of exoplanetary spectroscopy. A variety of parametric correction models are used in the literature. These show high degeneracies between the scientific result and the instrument correction used. Hence, an unbiased analysis of the data at the 10^−4 level of accuracy is difficult and the cause of much controversy in the field. In this thesis, I present three novel ways of de-trending exoplanetary data non-parametrically, i.e. without requiring auxiliary or prior information of the instrument or data. This removes correctional bias. These techniques are based on: 1) unsupervised machine-learning algorithms (Chapter 3) to de-convolve non-Gaussian sig- nals, i.e. the systematic noise, from the desired astrophysical feature. Such a ‘blind’ signal de-mixing is commonly known as the ‘Cocktail Party problem’ in signal-processing. I demon- strate its capabilities using spectroscopic Hubble/NICMOS measurements of the hot-Jupiters HD189733b and XO1b and demonstrate the removal of stellar noise in Kepler photometry (Chapter 4). 2) Fourier/Wavelet based self-filtering algorithms based on the concepts of sparsity of the exoplanetary signal in the frequency domain (Chapter 5). The robustness of this method is demonstrated for very low signal-to-noise conditions using four nights of ground-based observa- tions of the secondary eclipse of HD189733b in Chapter 6. Here I unambiguously confirm the detection of a strong non-LTE methane emission in the L-band and can test for residual telluric contamination using this method. 3) an Independent-component-analysis supported wavelet masking of multivariate data, which extends the non-parametric machine learning to Gaussian noise dominated data applications, Chapter 7. In the light of ever increasing data analysis challenges, as we probe ever smaller signals and fainter targets, techniques such as the ones presented in this thesis are paramount to the success of exoplanetary characterisation in the future.

In this thesis we use data from the Cassini spacecraft in order to investigate the influences on Saturn’s magnetosphere, and the dynamics and interactions that occur within it. The primary instrument for this study is the Cassini electron spectrometer (CAPS-ELS), analysing low energy electron data to examine three areas of research, which are discussed and developed in this thesis. The first study concerns the magnetopause of Saturn, the boundary between the region of space dominated by the planet’s magnetic field and the interplanetary magnetic field. We develop a new pressure balance model using a multi-instrument data analysis, building on past models and including new features. It has been shown that the model has improved on previous models due to the inclusion of the suprathermal plasma and variable static pressures in the pressure balance equation providing more realistic results. It is currently the most up to date model of Saturn’s magnetopause. The second study concerns flux tube interchange and injection events in Saturn’s inner magnetosphere. A new survey of these features was carried out across the entire dataset in order to learn more about plasma circulation, and to answer questions such as whether injection events with increases in magnetic field strength are always found at the equator. By examining the electron and ion data, we test previous interpretations of some events, analyse other such events in detail, and demonstrate a method through which the radial plasma flow direction of interchanging flux tubes can be determined. Pitch angle distributions, magnetic field data and plasma flow models were considered in order to help establish plasma circulation patterns in the kronian magnetosphere. We were able to determine the flow direction of 17 events and use magnetic field data from 32 events to conclude that generally increases in magnetic field strength are indeed found at the equator. We believe our work has shown that Saturn exhibits general and isolated plasma flow, with the isolated plasma flow occurring as “bubbles” in the plasma. The third study concerns low energy electron enhancements in the inner magnetosphere, specifically those associated with Saturn’s moon Enceladus. During an investigation of close flybys of Enceladus, discrete, short duration enhancements were found in the low energy electron plasma. We present the new features seen in the Enceladus L shell region of the kronian magnetosphere. The data from these new features were surveyed and some possible creation mechanisms are discussed. In total, over 600 spikes were found between L = 3.5 and 4.5 from data between Saturn Orbit Insertion and June 2010, showing a preference about the equatorial region but no obvious patterns in local time. Some spikes appear to extend to dispersive higher energy signatures, which are generally associated with injection events and hence these types of spikes were investigated accordingly. Although one formation process was not found to account for all the events, we rule out several processes, such as spacecraft charging and thruster engine firing as causes for the spikes. We believe that our results show that different creation mechanisms can be responsible for different types of low energy electron enhancements.

Coatings, typically painted films, one of the most important and widely-used surface treatment materials, were selected as the subject of this research project. In this dissertation, detailed three-dimensional (3D) spatial structures of three types of coating specimens: silver epoxy adhesive, iron oxide alkyd paint and aluminium epoxy marine coating were obtained by using different 3D X-ray imaging methods and comparative 3D electron imaging means. The shapes and spatial distributions of particles of the main functional ingredients of all these coating specimens were demonstrated. Specifically, for the aluminium epoxy marine coating, the quantitative analysis of the sizes, volumes, orientations and spatial distributions and correlations of the aluminium flakes in the matrix materials of the coating were carried out. Furthermore, the 3D structures of the aluminium epoxy marine coating samples were used for the finite element simulations of the (ion) percolation properties of the coating film. This potentially provides us with a practical method to engineer the efficacy of coatings by modelling their performances based on the actual structures instead of using assumed model structures. This is a new way to evaluate the performance of materials, and also can be an approach for validating their mechanistic assumptions. It could help to shorten the product research and development lifetime, complementing endurance studies of original specimens. The work presented in the dissertation is the first systematic research of 3D spatial structures of coatings and it could help guide coating researchers how to choose the most suitable 3D investigation method for a specific coating specimen. Through comparative experiments, transmission X-ray microscopy (TXM), ptychographic Xray computed tomography (PXCT), X-ray holo-tomography and serial block-face scanning electron microscopy (SBFSEM) have been verified as effective ways to reveal 3D spatial structures of complex industrial specimens. A comparison among these 3D imaging approaches and their advantages and disadvantages are discussed. The wave-front modulation coherent X-ray diffraction imaging was also implemented. It proved to be a capable method of measuring structures of coating samples and reaches similar resolution as TXM. Developing it into a 3D coherent X-ray imaging methodology with capabilities of obtaining a unique image solution from a single diffraction pattern is left as future work.

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