Small scale turbulence in a magnetically confined fusion plasma drives energy and particle transport which determine the confinement. The plasma in a tokamak experiment has a toroidal rotation which may be driven externally, but can also arise spontaneously from turbulent momentum transport. This thesis investigates the interaction between turbulence and rotation via nonlinear numerical simulations, which use the gyrokinetic description in the frame that corotates with the plasma. A local gyrokinetic code is extended to include both the centrifugal force, and the stabilising effect of sheared equilibrium flow. Sheared flow perpendicular to the magnetic field suppresses the turbulence, and also breaks a symmetry of the local model. The resulting asymmetry creates a turbulent residual stress which can counteract diffusive momentum transport and contribute to spontaneous rotation. The competition between symmetry breaking and turbulence suppression results in a maximum in the nondiffusive momentum flux at intermediate shearing rates. Whilst this component of the momentum transport is driven by the sheared flow, it is also found to be suppressed by the shearing more strongly than the thermal transport. The direction of the residual stress reverses for negative magnetic shear, but also persists at zero magnetic shear. The parallel component of the centrifugal force traps particles on the outboard side of the plasma, which destabilises trapped particle driven modes. The perpendicular component of the centrifugal force appears as a centrifugal drift which modifies the phase relation between density and electric field perturbations, and is stabilising for both electron and ion driven instabilities. For ion temperature gradient dominated turbulence, an increased fraction of slow trapped electrons enhances the convective particle pinch, suggesting increased density peaking for strongly rotating plasmas. Heavy impurities feel the centrifugal force more strongly, therefore the effects of rotation are significant for impurities even when the bulk ion Mach number is low. For ion driven modes, rotation results in a strong impurity convection inward, whilst a more moderate convection outward is found for electron driven modes.

The influence of ordering on the structure of vanadium carbon alloys has been studied using electron microscopy and electron diffraction. Within the nominally cubic (rocksalt) phase field of the vanadium carbon system non-stoichiometry occurs by the formation-. of-carbon vacancies, and these have been shown to be always distributed in a non-random manner at low temperatures (below 1300°C). The cubic phase field has been shown to contain two ordered compounds both of which exist over a range of stoichiometry, and in addition a region exhibiting a form of short range order. The order-disorder temperature has been determined from metallographic changes occurring in quenched samples annealed at successively higher temperatures, and a revised equilibrium diagram proposed for this compositional region. In order to produce the high purity single crystals of different composition required for this structural study, a floating zone melting apparatus has beer, designed and built to operate with r.f. heating under a positive pressure of ambient-inert Gas to reduce volatalisation losses. Crystal growth experiments using this apparatus are described. The ordered compound V6C5 has been found to exist over a wide range of stoichiometry from VC0.75 to VC0.86. Two forms of ordered structure having monoclinic and trigonal symmetry are obtained, and duplex structures consisting of small highly faulted regions of both structures are obtained. Possible mechanisms and reasons for the formation of this type of structure are discussed. The alloys contain a high density of planar faults and these are analysed and discussed in terms of possible fault vectors for the proposed structures. A long period superlattice is formed at high temperatures at compositions near to VC0.84 whose formation is explained in terms of a crystallographic shear structure. At higher carbon contents the cubic V8C7 compound exists from VC0.87 to VC0.90 and is characterised by a foam structure of anti-phase domain boundaries which have been analysed in terms of possible fault vectors. Both the cubic V8C7 and non-cubic V6C5 forms of ordered carbon atom arrangements are seen in alloys with intermediate compositions and the formation of such structures is discussed. Above the order-disorder temperature and at lower carbon contents (< VC0.75 ) the carbon atom arrangement indicates a form of short range order detectable by broad diffuse bands in diffraction patterns. Possible models for this type of structure are discussed. In addition these lower carbon alloys contain large numbers of intrinsic stacking faults bounded bi Shockley partial dislocations. A dislocation mechanism is proposed whereby these faults are nuclei for the transformation to the ζ-phase detected at lower carbon contents. This phase has a complex twelve layer metal-atom stacking sequences Finally an explanation for the formation and stability of the ordered compounds is given in terms of both electronic and structural considerations, and the possible role these structures might have on mechanical properties is discussed.

Dilute nitride alloys of III–V semiconductors, and transparent conducting group-II oxides may both be categorised as highly mismatched compounds. The small size and high values of electronegativity of nitrogen and oxygen (see figure), compared to the substituted anion, in dilute nitrides, and the cation, in transparent conducting oxides, give rise to striking properties in these materials. The dilute nitride alloys GaNSb, InNSb, and GaInNSb, grown by molecular beam epitaxy, have been studied. Infrared absorption measurements of GaNSb are presented, showing the divergence of transitions from the valence band to E− and E+ conduction bands with increasing nitrogen incorporation. The fitting of the positions of the valence band to E+ transitions gives a value of 2.6 eV for the coupling parameter in this material. A reduction in the bandgap of InNSb from that of InSb is shown by modelling the competing effects of Moss-Burstein band filling and bandgap renormalisation. Finally, bandstructure calculations of the quaternary material GaInNSb, with dilute incorporations of nitrogen and indium, show that the material is suitable for the exploitation of the 8–14 μm atmospheric transmission window. Structural characterisation of GaInNSb shows that this material can be grown lattice matched to GaSb with nitrogen and indium incorporations of 1.8 and 8.4 per cent, respectively. The conducting oxide CdO, grown by metal-organic vapour-phase epitaxy, has also been studied. Analysis and simulation of infrared reflectance data, including conduction band non-parabolicity and Moss-Burstein band filling, reveal bandgap and band-edge effective mass values of 2.16 eV and 0.21 m0, respectively. In addition, high energy 4He+ ion irradiation was used to stabilise the Fermi level in CdO. Carrier statistics calculations were performed and the charge neutrality level was found to be 2.52 eV with respect to the "-point valence band maximum, corresponding to 0.36 eV above the conduction band minimum. The location of the charge neutrality level within the conduction band explains the propensity for high unintentional n-type doping, and the high conductivity observed in CdO.

A time-dependent amplitude analysis of B0 → K0 Sπ+π− decays is performed in order to extract the CP violation parameters of f0(980)K0 S and ρ0(770)K0 S and direct CP asymmetries of K∗+(892)π−. The results are obtained from the final BABAR data sample of (465 ± 5)106 BB decays, collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The time dependent CP asymmetry for f0(980)K0 S and ρ0(770)K0 S are measured to be S(f0(980)K0S) = −0.97±0.09±0.01±0.01, and S(ρ0(770)K0S) = 0.67±0.20± 0.06 ± 0.04, respectively. In decays to K∗+(892)π− the direct CP asymmetry is found to be ACP (K∗±(892)π∓) = −0.18 ± 0.10 ± 0.04 ± 0.00. The relative phases between B0 → K∗+(892)π− and B0 → K∗−(892)π+, relevant for the extraction of the unitarity triangle angle γ, is measured to be φ(K∗(892)π) = (34.9 ± 23.1 ± 7.5 ± 4.7)◦, where uncertainties are statistical, systematic and model-dependent, respectively. Fit fractions, direct CP asymemtries and the relative phases of different other resonant modes have also been measured. A new method for extracting longitudinal shower development information from longitudinally unsegmented calorimeters is also presented. This method has been implemented as a part of the BABAR final particle identification algorithm. A significant improvement in low momenta muon identification at BABAR is obtained.

We present a study of the theory and simulation of Liquid Crystals. A general introduction to the field is given, then the essential features of the Monte Carlo (MC) sampling algorithm are described and explained, along with some of the practical considerations in the implementation of MC. Several quantitative measures used to describe liquid crystalline systems are outlined, including the second rank order tensor, in addition to some of those from elastic theory and density functional theory. Monte Carlo Simulations were performed in bulk geometry in the canonical ensemble in order to calculate the Frank elastic constants of hard spherocylinders, hard platelets and hard cut-spheres at three thicknesses. Onsager’s density functional theory was also performed to yield the elastic constants for hard platelets, and this amounts to using a virial expansion in the free energy, truncated at second order. Our collaborators for O’Brien et al. [2008] provided results for the elastic constants from a calculation of the higher order virial coefficients. All of the results from theory are compared to simulation, with some experimental determinations available. All three elastic constants compared well with the high-order virial theory, there is quantitative agreement with the experimental values, and the effect of increasing thickness of discs was found to improve the agreement of the ratio of K1/K3. Aspects of translationally ordered phases are studied in the context of constrained non-equilibrium systems. Monte Carlo was also performed for platelets confined in wedge geometry, with several choices for the types of wall. A local approximation is utilised to yield the depletion force and potential as a function of the wall separation, as well as the adsorption between the walls. The adsorption for large separations exhibited general qualitative agreement with theory and Gibbs Ensemble simulations. The two different wall boundary conditions produced different orientational structural features, with repulsive and attractive depletion potentials measured, and a planar surface phase that does not appear in the bulk is categorised.

Identifying the ordered three-dimensional structures formed by atoms and molecules is essential to understanding the properties of solid-state materials. Solid-state NMR is an extremely sensitive structural probe and offers atomic-level information regarding the three-dimensional packing of molecules and the intermolecular interactions, for example, hydrogen bonding, which control this. Recently, the combination of advanced solid-state NMR experiments and complementary computational techniques have led to the emergence of the field of `NMR crystallography', which shows great potential for the structural determination of systems where traditional diffraction-based methods are not suitable. The work in this thesis uses a combined approach of high-resolution MAS NMR experiments and first-principles (GIPAW) calculations of NMR parameters to provide structural insight into a range of challenging organic systems. In particular, 1H-13C and 1H DQ (double-quantum) CRAMPS (combined rotation and multiple pulse spectroscopy) techniques are employed to identify 1H and 13C NMR chemical shifts and close 1H-1H interatomic proximities. A new 1H DQ-13C SQ (single-quantum) experiment is presented that better allows intra- and intermolecular 1H-1H distances to be identified in the pharmaceutical compound, penicillin and the disaccharide, β-maltose monohydrate, notably enabling, for the first time, the full 1H resonance assignment of the latter. Using a similar methodology, a `spectrum to structure' approach is applied to identify modes of self assembly for guanosine derivatives for which single-crystal diffraction structures could not be obtained. In addition, chemical shift calculations on the full unit cell (348 atoms) of a complex pyrazole allow the complete assignment of experimental 1H, 13C resonances for each of the six independent molecules of the asymmetric unit cell. Finally, hydrogen-bond mediated 2hJ15N17O and 2hJ15N13C couplings across NH...O and N...HC hydrogen bonds are determined experimentally for the first time by the use of heteronuclear spin-echo experiments. The J couplings, which have also been determined using first-principles calculations, are a quantitative measure of hydrogen-bonding strength.

Interest in termolecular association reactions of the type shown below, stems from their importance in the chemistry of planetary atmospheres, gas-cooled nuclear reactors and gas-phase cluster ions. This study is concerned with evaluating the rate constants of such X+ + X + M ------> X2+ + M k3 (1) reactions as both a function of temperature and of the third body M. The values of the third order rate constant k3 are expressed conventionally in terms of k3 = CT-m where T is the temperature and C and m are constants characteristic of the reaction which depend also on the nature of M. Literature now shows a general measure of agreement on values of C and m in several studies for which X=M, however, inconsistent values have been reported on the M=He system. This thesis describes an investigation of the two systems X=N2, CO and M= the reactant or a rare gas. Experiments were conducted in a conventional high pressure ion source and a pulsed drift ion source fitted to an updated Kratos MS9 mass spectrometer. Results obtained for the one component studies show good agreement with other literature values for the temperature dependence, m. In general, for both N2 and CO systems, He was found to have the same efficiency as the parent molecule as a third body at 300K, but the temperature dependence of k3 is markedly lower. Ar was found to behave very similarly to the parent molecule in both systems. For the CO system, although good agreement is found for the temperature dependence result with literature, there is still an uncertainty of about a factor of 2 in the room temperature values of k3.

The technique of medium energy ion scattering (MEIS) can be used to elucidate the structural details of surfaces, both in general terms and in a more qualitative manner, in order to help solve a number of outstanding uncertainties relating to the structures of a number of surface systems. MEIS, involving the back-scattering of light ions from a material of interest, in this case 100 keV H+ ions from adsorbate covered single crystal metal surfaces, can potentially be a powerful tool for obtaining either depth-dependent compositional information or quantitative structural details. MEIS has been used to study the surface relaxations at the Cu(410)-O stepped surface. The results have been compared to a number of models favoured by previous studies, and an optimisation of the structural parameters associated with the outermost Cu atoms was undertaken so as to determine the positions of these atoms to a reasonable degree of precision. In this thesis, MEIS has also been used to probe the surface reconstructions triggered by the adsorption of the methylthiolate species on the Cu(100), Au(111) and Pd(111) surfaces. Methylthiolate is derived from the n-alkylthiol molecule methylth- iol, the simplest molecule of a species which ubiquitously form so called self-assembled monolayers (SAMs) on single crystal metal surfaces. In the case of Cu(100), our study confirms the existence of a radial lateral distortion of the outermost Cu layer, and we quantify this distortion. For Au(111), two competing structural models for the methylth- iolate overlayer have been proposed, namely the Au-adatom-monothiolate (AAM) and Au-adatom-dithiolate (AAD). MEIS has been used to compare these two models, and we find in favour of the AAD model. Additionally, evidence has been found for a significant reconstruction of the Pd(111) surface triggered by adsorption of methylthiolate. We have carried out a MEIS investigation of the (3×2)-alaninate phase formed by adsorption of the chiral molecule alanine on Cu(110). Evidence is found for a small degree of lateral surface distortion.

This thesis describes the application of multinuclear solid-state NMR to three materials systems: first, components of polymer-based proton-exchange fuel cells including the fluoropolymer membranes (Chapter 4) and the precious metal supported catalysts (Chapter 5); secondly, the formation of a complex bismuth niobium aluminoborosilicate glass-ceramic with novel dielectric properties (Chapter 6); finally, platinum (II) dialkyldithiophosphates which belong to a class of compounds (metal dialkyldithiophosphates) some of which are used in mineral separation processing (Chapter 7). A full investigation into the effects of different conditions during sample preparation and 19F NMR experiments on fluoropolymer membranes recommended unmilled preparation, dry storage and magic angle spinning below 24 kHz for the study of structural differences between membranes. The application of 19F NMR to a range of commercial and experimental fluoropolymer membranes revealed that the equivalent weight does not affect the mobility of the polymer molecules such that can be detected by this technique. Calculations of equivalent weight from 19F NMR differed with quoted values by up to 14%. Discrepancies were smallest in the short sidechain polymers, as low as 3%. The assignment of spectra was invariant with sidechain structure apart from a change in the number of ester links. The presence or absence of oxygen affected chemical shielding even around nuclei separated by several bonds. Differences in 1H linewidths between membranes could not be interpreted without the control and comparison of manufacturing techniques. It is desirable to remove the necessity for organic solvents in membrane casting. However, membranes cast from aqueous solution do not possess the same properties as those from propanol. It had been proposed that rapid drying of water cast membranes would result in a structure more similar to those from organic solvent. 1H NMR revealed that the opposite is the case, rapid drying makes the ordinarily more inhomogeneous aqueous membranes even more so. The application of both 19F and 1H NMR revealed that the monomolecular layers of fluoropolymer deposited on the surface of fuel cell catalysts to aid proton conductivity are categorically different in nature to the same materials in the bulk state. 19F NMR suggests a polymer structure either more disordered, greatly less mobile or both. 1H NMR displayed water environments that could not be reconciled to the standard model of rapid exchange between bulk water and water associated with acid groups. Spectral differences caused by solvent and polymer loading were discussed. The first complete and quantitative Fourier transformed 195Pt NMR spectra of platinum fuel cell catalysts, acquired using a field sweeping method, are analysed for deviation from the cubooctohedral particle model and surface oxidation. A combination of 11B, 27Al and 29Si studies of the BN1 ceramic system after different temperature heat treatments confirmed much of the previous work on phase evolution. However, it was shown that kyanite does not make up a significant proportion of the material until heat treatment reaches 1000 ºC and that aluminium impurities in bismuthbiobate crystals appear to increase with treatment temperature. The nature and abundance of glassy phases in the system are explored for the first time. Field sweep 195Pt NMR was employed to characterise the 195Pt chemical shift anisotropy of five platinum (II) dialkyldithiophosphates complexes. Additionally the 31P chemical shift anisotropies of two of the complexes, previously unpublished are presented.

In this thesis the dynamic properties of unknotted ring polymers at high densities is investigated. We hypothesise an unusual type of glass transition which is purely attributed to the topological constraints between the penetrating rings. A mean-field model is developed to describe the strongly constrained ring polymers as ideal lattice trees. Equilibrium properties can be derived within the framework of statistical thermodynamics using an argument based on structural recurrence. Here each ring can be seen as a linear object|as a loop strand with branching protrusions. The ring polymers were simplified as loop strands without any branching. We focused on the constraints emerging from the circular topology, and the polymer dynamics was simulated using a Monte Carlo technique. The degree of inter-ring penetrations essentially controls the slowing of dynamics and represents a universal parameter for the glass transition. The penetrating rings form a percolating network involving reversible quasi-topological entanglements. As such, the stress relaxation of each ring is prolonged by the coupled penetrations which have limited pathways to release constraints from one another. The simulation data suggest the existence of a glassy material exclusively formed by the topological constraints associated with the circular structure. In order to test the picture of topological glass, the uorescence-labelled circular DNA was used to observe its self-diffusion in the entangled state. The experimental method has demonstrated its potential for the future investigation of the dynamics of entangled ring polymers despite the fact that it failed to provide evidence of the glassy state in our experiment.