The arrangement of atoms in most ceramic materials is not perfect and point defects such as vacancies and interstitials, as well as extended defects like grain boundaries exist. In general these defects dominate the properties and processes that are important for the applications of the material. The capture and emission of charge at point defects can affect the stability of dielectrics such as those used in MOS devices. The presence of grain boundaries is also known to lower both the electric and thermal conductivity of a material. Collectively the diffusion of point defects at grain boundaries play a role in mechanisms such as creep and have also been suggested to be involved in the corrosion of metals. In this thesis simulation techniques were used to investigate properties of defects in amorphous silica and near grain boundaries in MgO. Atomistic methods were used to determine the migration barriers of defects at MgO grain boundaries, the effect of electric field on the stability of the defects, and also the effect of temperature on the structure and stability of the grain boundaries. The nudged elastic band method was used to determine the activation energy for vacancy and interstitial migration at the Σ17 {410}/[001] tilt and the Σ5 twist grain boundaries. At the tilt and the twist grain boundaries it was found that the activation energies for vacancy migration were up to 1.31 eV and 1.41 eV lower than those in bulk MgO respectively. A finite MgO film model was produced to investigate the effect of electric field on point defects at the tilt grain boundary. The electric field was added to the system by sandwiching the MgO between two layers of point charges. It was found that the field anisotropically lowers the activation energies for vacancy migration by up to 0.37 eV with respect to those determined in the absence of the field. Molecular dynamics simulations were used to investigate the effect of temperature on the stability of the tilt grain boundary and two of its metastable structures and also on the twist grain boundary. The twist grain boundary was found to have the highest entropy in the temperature range 300 - 3000 K which suggests that it may be the most commonly occurring grain boundary in MgO. An ab initio study was also carried out on the structure and electronic structure of the neutral oxygen vacancy in amorphous silica in order to investigate mechanisms associated with dielectric breakdown such as negative bias temperature instability. Contrary to published suggestions the positively charged and neutral vacancy defects studied were found to have one electron energy levels below the Si valence band which suggests that these defects do not contribute to threshold voltage shifts.

The predictions of quantum mechanics cannot be resolved with a completely classical view of the world. In particular, the statistics of space-like separated measurements on entangled quantum systems violate a Bell inequality [Bell1964]. We put forward a computational perspective on a broad class of Bell tests that study correlators, or the statistics of joint measurement outcomes. We associate particular maps, or functions to particular theories. The violation of a Bell inequality then implies the ability to perform some functions, or computations that classical, or more generally, local hidden variable (LHV) theories cannot. We derive an infinite class of Bell inequalities that establish a link to so-called "non-local games" [Cleve2004]. We then make the connection between Raussendorf and Briegel's formulation of Measurement-based Quantum Computing (MBQC) [Raussendorf2001], and these non-local games. Not only can we show that a quantum violation implies a computational advantage in this model, we show that adaptive measurements are required to perform all quantum computations. Finally, we explore post-selection of data in Bell tests from both a practical and conceptual point-of-view, with particular consideration to so-called "loopholes". Loopholes allow LHV theories to simulate quantum correlations through post-selection. We give a computational description of how loopholes can emerge in different post-selection scenarios. This motivates us to find a form of post-selection that does not lead to loopholes. Central again to this discussion is the description of LHV theories in terms of computations. Interestingly, quantum correlators can be made more "non-classical" with this loophole-free post-selection. This method of post-selection also can simulate information processing tasks, such as MBQC, that have time-like separated components. This opens up new avenues for the study of time-like tasks studied within the space-like separated scenario of the Bell test.

Cylindrical vector beams (CVBs) are the class of laser beams which exhibit azimuthal symmetry in their polarisation structure. These beams exhibit a `donut' intensity profile due to an on-axis polarisation vortex. CVBs have received significant recent interest due to their similarities to the modes of an optical fibre and their interesting focusing properties in the limit of high numerical aperture. This thesis contains an investigation into the properties of CVBs and their applications for optical micromanipulation, using a variety of experimental geometries. First I describe methods for the synthesis of CVBs and explain why CVBs are appealing for optical trapping. This is followed by an experimental investigation of focal volume control using the polarisation state of CVBs in an optical tweezers. Experimental results are complemented by numerical calculations of trapping forces obtained from a theoretical model derived from electromagnetic scattering theory in the T-matrix framework. Next I consider the use of CVBs in a dual-beam fibre-optic trap for trapping of low refractive index particles, such as ultrasound contrast agent microbubbles. The optical trapping forces are calculated numerically for a wide range of parameters. Additionally, the photonic stress profile over the surface of the microbubble is presented together with the resulting optically-induced deformation. The next chapter is an investigation of CVBs in an alternative trapping geometry. Experimental results are presented, demonstrating optical trapping and propulsion of microscopic particles using the evanescent field in the region around a tapered optical fibre. I also consider the plasmonic optical forces on metallic nanoparticles in the evanescent field of a tapered fibre. Finally, I present results of experiments probing the optical coherence properties of higher order CVBs to clarify the differences between coherence and correlation properties of stochastic beams which have a non-uniform polarisation direction.

Electron re-scattering in a strong laser field provides an important probe of molecular structure and processes, and can allow for time resolved study of nuclear and electronic dynamics at sub-femtosecond timescales with Angstrom spatial resolution. In such experiments a molecule is ionised in a strong, few cycle, laser field. The changes in sign of the laser field during the cycle can cause the electron to re-collide with its parent molecular ion. Under these circumstances the electron can either recombine leading to high harmonic generation, or it can be re-scattered. This scattering can be thought of as electron self-diffraction and the process has the potential to act as a detailed probe of the target molecule. It is usual for such experiments to be performed on aligned molecules, as the dynamics of the ionisation and re-collision changes with alignment. This introduces extra physics compared to the standard gas-phase, electron-molecule scattering problem. It is important for the understanding and analysis of such experiments to have a physically sound theoretical model of re-scattering which is capable of treating quantum mechanically the complicated scattering dynamics of an electron-molecular ion collision. This thesis explores the use of sophisticated ab initio quantum mechanical techniques to model this part of the re-scattering process. Previous theoretical models of the re-collision problem have thus greatly simplified this aspect of the problem. An introduction to attosecond physics, and a review of the relevant scattering and R-matrix theory is given. A simple preliminary model not including molecular alignment is described for molecules of experimental interest. Then the formalism for scattering from aligned linear molecules is presented. For linear molecules consisting of more than two atoms we use the polyatomic R-matrix codes. However the polyatomic version of the code only uses Abelian point groups which means that calculations on symmetric or asymmetric linear molecules are performed using the D2h or C2v point groups respectively. A further step is required, involving the reconstruction of T-matrices into the linear molecule symmetry groups D1h or C1v. The formalism for this is also presented. Finally differential and integral cross sections are presented for re-scattering for H2 and CO2.

No description available.

This thesis investigates electronic and optical properties of graphene, graphene oxide (GO) and low-gap polymers, and their applications in light-emitting diodes (LEDs) and photovoltaics (PVs). Charge transport is crucial for achieving high efficiency in polymer photovoltaics. Few-layer graphene (FLG) was synthesized via liquid-phase exfoliation and served as an intermediary in a ternary structure to facilitate charge transport rather than acting as an electron acceptor. To investigate the role GO can play, a bilayer photovoltaic device incorporation of poly (3-hexylthiophene-2,5-diyl) (P3HT) was fabricated which demonstrated that P3HT/GO heterojunctions could be created. The flexibility of GO is also discussed. Molecule interchain interaction can adversely affect optical properties such as photoluminescence (PL) and electroluminescence (EL). OLEDs incorporated with GO quantum dots (GOQDs) have been fabricated. PL quenching is observed with the addition of GOQDs, which is a result of a competition between energy transfer from polymer to GOQDs and prevention of interchain interaction by GOQDs. A blue-shift in PL as well as EL is observed. The addition of GOQDs could shift the value of light-on voltage due to a higher mobility of GOQDs compared with the host polymer. Also, application of GOQDs can balance charge carriers. Finally, a low-gap polymer with a broad absorption in the near infrared range has been studied both in PVs and LEDs. Binary blends have been investigated in terms of donor:acceptor ratio, annealing treatment, open circuit voltage (Voc) and fill factor (FF), showing different performance, especially with respect to thermal annealing and FF. Polymer-polymer PV with a high Voc has been achieved. For infrared LEDs, we have demonstrated ~ 1 μm EL emission from the pure polymer device and a blue-shift in the blended device, due to the reduction of polymer aggregation.

The particle tracking software package, GPT, has been developed and utilised to simulate the beam optics of the EMMA injection line and ring, constructed at the Daresbury Laboratory, UK. EMMA is a proof-of-principle machine for a new type of accelerator: a non-scaling fixed-field alternating gradient (ns-FFAG) accelerator. As such the beam dynamics of the magnetic lattice require benchmarking, with GPT chosen for its space-charge self-field simulation package. Tune and time-of-flight measurements have been successfully simulated and compared to experimental data, recorded during the first few runs of the machine. Measurements confirm the successful operation of EMMA as a ns-FFAG accelerator and simulations highlight that space-charge effects are observable in the EMMA bunch-charge and energy regime. Such accelerators have many applications within and outside particle physics, ranging from cancer therapy and accelerator driven thorium reactors to neutrino factories and muon colliders. The application of FFAGs and the design of the COMET/PRISM experiment, which is seeking to measure muon-to-electron conversion at the 10^−18 level, is investigated. Simulations of the COMET experiment, staged in two phases, have been performed with a focus on optimisation of the stopping target design. A number of geometries have been tested, with a cone then disk structure preferred for Phase-I then Phase-II respectively. Initial data from the COMET precursor experiment, MuSIC, have also been analysed and successfully compared to simulation.

Between 1965 and 1979 ideas about the meaning of the 47 XYY chromosome complement shifted considerably. Moreover, both the question of the significance of the extra Y, and research intended to resolve that question, have repeatedly been the subject of controversy. This thesis is an attempt to examine these controversies from the standpoint of the sociology of scientific knowledge. It is argued that the development of knowledge about the chromosome abnormality was shaped by: 1) Features of the organisation of the biomedical and behavioural science communities in Britain and the USA during the 1960's and 1970's - in particular, the pattern of competitive pressures that structured the activities of individuals as members of disciplines, institutions, and professions in their struggles over the accumulation of symbolic capital. 2) The availability of "common-sense" schemas, rhetorical resources, and scientific traditions that facilitated the conceptualisation and presentation of research results in such a way as to appear to bear upon the quest ions of a biological (and therefore "natural") basis for masculinity, aggression, and criminality. 3) The politics of crime and concern with crime in the period - and the way in which rising anxiety about the decline of law and order created an opportunity for particular groups of scientists to make use of these rhetorical resources in order to advance their claims of technical and professional authority.

The importance of active drug transport in determining chemical fate is becoming increasingly clear, with efflux transporters such as MDR1, MRP2 and BCRP recognised as key determinants of drug action. The impact have been shown to impact compound bioavailability through first-pass effects; determine target site drug concentrations through affecting drug distribution; and drive drug resistance through their up-regulation following chronic drug exposure. While the role of these transporters is well established, less is known about transporters such as MRP3 and MRP4, which act to move chemicals back into the systemic circulation rather than target them for elimination. In this thesis the hypothesis examined states, “transport and metabolism processes are balanced to allow for efficient handling of both endogenous and xenobiotics substrates into the excreta and systemic circulation”. To examine this hypothesis a portion of the molecular interaction network of active drug transporters, passive transport and drug metabolising enzymes that determines the biological fate of 17β-estradiol in the liver was reconstructed. The model was parameterised using experimentally-derived kinetic and abundance values where available, or biologically realistic estimates. The behaviour of the model was validated against in vitro measurement of estradiol fate in primary human hepatocytes. As such the model represents, to the best of our knowledge, the situation occurring in the liver. Under steady-state conditions and physiologically relevant concentrations of 17β-estradiol robust network behaviour was predicted, with network flux predominantly via passive processes. To examine the role of dietary constituents on network behaviour, the impact of the flavonoid compounds hesperidin and naringin on MRP3 and MRP4-dependent transport was determined experimentally. Inhibitory constants were then applied to the in silico model of estradiol metabolism, predicting a complete loss of basolateral efflux by MRP4 and redirection of estradiol glucuronide transport via apical transporters. In summary, we present a computational approach to examine the relative input of network components in determining drug fate, and the impact of food chemical interactions. Such computational approaches provide novel systems to examine the impact of genetic variation or transporter-specific inhibitors on drug fate and, hence, efficacy.

The mitotic spindle is a key cellular structure responsible for aligning and separating chromosomes during mitosis. It is vital that this process is performed faithfully, as errors can result in disease causing genome instability. The mitotic spindle is primarily composed of an organised mass of dynamic microtubules that form a bipolar structure. Different cells have been shown to employ varying molecular pathways to generate these microtubules; however how these multiple pathways coexist and coordinate in a single cell type is poorly understood. Using the Drosophila syncytial embryo as a model cell type, the work presented in this thesis provides evidence of multiple spindle assembly routes employed within this system. Development of a technique to disrupt the temporal controls on microtubule generation combined with high speed confocal microscopy has allowed for the direct visualisation of a chromatin mediated microtubule generation pathway, a process shown to require Ran-GTP, D-HURP and the Augmin complex, but surprisingly not by a Drosophila homologue of the vertebrate spindle assembly factor TPX2, also identified here. Disruption of centrosome assembly has also revealed the importance of Augmin in generating microtubules for spindle assembly from multiple acentrosomal microtubule organising centres. Additionally, work presented here demonstrates that spindle assembly pathways can increase their microtubule generating capacity when the activity of another pathway has been perturbed, showing a degree of coordination. This thesis demonstrates the remarkable robustness with which the mitotic spindle can assemble while providing an insight into the mechanisms behind this flexibility.