The type of feedstock and host rock utilised in ex situ and in situ Carbon Capture and Storage by Mineralisation (CCSM) is an important aspect of these technologies, and detailed appraisal of candidate mineral/rock performance in the presence of CO2 may greatly improve CCSM efficiency. Here, a detailed mineralogical and geochemical investigation of serpentine minerals and ultramafic rocks under laboratory-controlled experiments simulating ex situ and in situ process conditions is presented. Feedstock serpentine minerals were analysed comprehensively, prior to experimental processing. The identification of antigorite was unequivocal using a combination of X-ray diffraction, Fourier Transform Infrared Spectroscopy and/or Thermo-gravimetric Analysis. However, the analysis of chrysotile and lizardite proved to be more challenging, especially when the two polymorphs were finely inter-grown. This study highlighted the structural, textural and chemical complexity of serpentines and showed that great care must be taken when analysing this mineral group for CCSM. Investigation of the acid leaching of serpentine minerals under conditions of 70°C and 1.4M NH4HSO4 provided fundamental insights into the rate and extraction efficiency (EE) of Mg2+ and associated controlling factors, under conditions relevant for ex situ CCSM. It is demonstrated that EE is a function of mineral reactivity and depend on a complex interplay between crystal structure and chemistry. Generally, poorly crystalline and highly disordered phases with low levels of Al3+ were found to be suitable feedstock materials for acid digestion pre-treatment. Chrysotile, lizardite 2H1 and poorly crystalline serpentines showed up to 85% Mg2+ EE after 3 h of acid leaching, and hence are recommended as best feedstock materials for CCSM, whilst antigorite and Al3+-rich serpentines proved to be largely unsuitable, showing low levels of EE of ~ 20%. Examination of dunite, harzburgite and serpentinite under conditions relevant for in situ CCSM, i.e. 70°C and 100 bar CO2 pressure, provided insights into rock reactivity as a function of composition and texture, and the progression of in situ mineral carbonation. The rate of net Mg release and thus the extent of subsequent carbonation were greatest for serpentinite, providing ca. 3% carbonation after six months. However, mineral reactivity within serpentinite was preferential, i.e. significantly enhanced within secondary vein serpentine, being thus, the main source of Mg2+ for magnesite precipitation. Reaction-induced transformation and hence mineral carbonation of dunite and harzburgite were less pronounced over the same time-scale. The reaction of serpentinite with wet supercritical CO2, as opposed to CO2-saturated brine, significantly affected rock integrity, with the exposure of more surface area and promotion of fluid-rock interaction. In particular, it is shown that ferric iron oxidation and the precipitation of goethite impacts upon surface mineral dissolution at exposed surfaces, thereby hindering subsequent carbonation. Overall, this study highlighted the importance of host rock choice for in situ CCSM and the need for detailed petrographical and geochemical investigation of any proposed CCSM repository prior to technological process modelling.

The direct radiative capture reactions D(p,⋎)He³ and O¹⁶(p,⋎)F¹⁷, both of which are of interest in astrophysical processes, have been studied theoretically using a simple two-body direct radiative capture model in order to estimate the cross sections at low energies. In addition, the time inverse of the first reaction, namely the photodisintegration of He³, has been studied for high excitation energies in He³ by applying the reciprocity relations to the direct capture theory. The calculations involve taking matrix elements of the particle-radiation interaction Hamiltonian between bound and continuum states and using first-order perturbation theory to obtain the cross sections. Bound state wave functions are generated in simple potentials involving square-well and Saxon-Woods forms with appropriate Coulomb barriers and with one free parameter which is adjusted to fit the binding energy. The potential parameters for the continuum state wave functions are adjusted to fit available scattering data. For the reaction O¹⁶(p,⋎)F¹⁷ the cross sections for transitions to both the ground and first excited states are in good agreement with the somewhat limited experimental data from 150 KeV to 2.5 MeV and the astrophysical S-factors are shown to be energy dependent even at energies below 100 KeV. The photodisintegration cross section for the reaction He³(⋎,p)D is well fitted in the neighbourhood of the peak at around 11 MeV as well as at lower energies. The D(p,⋎)He³ direct capture cross sections in the energy range around 1 MeV are shown to be sensitive to admixtures of ²S-state of mixed symmetry and of ⁴D-state in the ground state of He³, which is predominantly Symmetric ²S. The same model including the ²S-state of mixed symmetry leads to a capture cross section for thermal neutrons by deuterons in good agreement with the experimental value. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A fossil magnetic field embedded in the radiative core of the Sun has been thought possible for some time now. However, such a fossil magnetic field has, a priori, not been considered a visible phenomenon due to the effects of turbulence in the solar convection zone. Since a well developed theory (referred to herein as magnetohydrodynamic dynamo theory) exists for describing the regeneration of magnetic fields in astrophysical objects like the Sun, it is possible to quantitatively evaluate the interaction of a fossil magnetic field with the magnetohydrodynamic dynamo operating in the solar convection zone. In this work, after a brief description of the basic dynamo equations, a spherical model calculation of the solar dynamo is introduced. First, we calculate the interaction of a fossil magnetic field with a dynamo in which the regeneration mechanisms of cyclonic convection and large-scale, nonuniform rotation are confined to spherical shells. It is argued that the amount of amplification or suppression of a fossil magnetic field will be smallest for a uniform distribution of cyclonic convection and nonuniform rotation, as expected in the Sun. Secondly, we calculate the interaction of a fossil magnetic field with a dynamo having a uniform distribution of cyclonic convection and large-scale, nonuniform rotation. We find that the dipole or quadrupole moments of a fossil magnetic field are suppressed by factors of -0.35 and -0.37, respectively. The dynamo modified fossil field, superimposed on the theoretically calculated magnetic fields of the solar magnetic cycle, are compared with the actual sunspot cycle and solar magnetic fields as observed by others, indicating that a fossil magnetic field may be responsible for asymmetries in the sunspot cycle and an observed solar magnetic quadrupole moment. Further observations and reduction of the data are required before the presence of a fossil magnetic field can be established. A discussion is given of the implications for the Sun if a fossil magnetic field is observed and identified. It is considered most likely that a fossil magnetic field would be a remnant of the possible Hayashi phase of a fully convective, protosun. Other possibilities also exist.

Gravitational lensing of photons in the Cosmic Microwave Background (CMB) can be described by an integrated potential along the line of sight, the CMB lensing potential. Covariances in maps of the CMB are generated by the lensing effect, and are used to reconstruct the lensing potential itself, which is a useful probe of the matter distribution. The CMB lensing potential has been measured to high significance with CMB temperature data. However, signal to noise for lensing reconstruction from CMB polarization data is expected to be much better due to the presence of the lensing B-mode. Upcoming data from ground based CMB polarization instruments will provide high resolution maps over small patches of the sky. This will provide much better lensing reconstruction, but also presents data analysis challenges. This thesis begins with an introduction to the field of CMB lensing and CMB lensing reconstruction. The second chapter details the biases present in reconstructing the lensing potential from CMB polarization maps considering first the full sky, and then small patches of sky. It also shows that using the pure-B mode formalism for the CMB polarization leads to improved lensing reconstruction over the naive case on the cut sky. Given the upcoming improvement in the CMB lensing reconstruction, it is expected that cross-correlations of the CMB lensing with other structure tracers, such as galaxies, will yield improved information for cosmology. It is also expected that the CMB lensing will become useful to help constrain uncertainties in the galaxy power spectrum, and provide information on the linear galaxy bias and redshift distribution. The third chapter of the thesis forecasts the power of cross correlation science for a number of galactic and non-galactic parameters. Finally, the CMB lensing effects the level of non-Gaussianity observed in the CMB. The fourth chapter of the thesis is a study of the lensing effect on the primordial squeezed bispectrum. We conclude in the fifth chapter.

Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

The study of outer radiation belt dynamics has been ongoing for over 5 decades. Outer radiation belt dropouts involve the rapid lost of electron fluxes at the main phase of a storm and subsequent recovery. The characteristics of the dropouts are many and varied. This study examines the Geosynchronous Earth Orbit (GEO) and the ionospheric responses during Stream Interface (SI) andMagnetic Cloud (MC) events, using a combination of ground based and satellite instruments. SI- and MC-driven dropout events were inspected from summary plots of the Synchronous Orbit Particle Analyser (SOPA) instruments from the year 1996 to 2007. Comprehensive studies were done on six selected events. Analysis of the data from the instruments indicate that SIs and MCs are important lost drivers with significant differences in GEO and ionospheric environment. To validate the data and test for consistent response of the events, the Superposed Epoch Analysis (SEA) technique was used. The ground based measurements also revealed how the absorption peaks in the ionosphere correlated with dropouts and geophysical activity. Ionospheric absorption during SI associated dropouts was enhanced for 5 < L < 6, while significant peaks in ionospheric absorption extended to lower L during MC driven dropouts. Wave-particle interactions and southward Interplanetary Magnetic Field (IMF-Bz) are apparent causes for the precipitation. This analysis showed that, within the confines of the selected events, SI driven dropouts were more dominant at the declining phase of the solar cycle while the MC driven dropouts were more dominant during solar maximum. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

The knowledge of the dynamics and characteristics of space plasma during solar-terrestrial coupling has been greatly enriched by process that aids the determination of the instantaneous frequencies which support the non-stationary and non-linear nature of signals. Such plasmas are observed in the magnetosheath in the downstream of bow shock. In this thesis a technique was applied which extracts the various contributing oscillatory modes reflecting the waveforms observed in the space by Cluster spacecraft instruments such as FGM, CIS and EFW, and decompose the frequency of each extracted mode using Instantaneous Frequency method that is based on Simple Hilbert Transform (SHT). This is achieved through the use of Empirical Mode Decomposition (EMD). To eliminate the negative frequency of the various extracted modes referred to as intrinsic mode function which appears with Fourier transform, we apply Hilbert transform leading to analytic representation of the signals. This process aids the determination of the instantaneous frequencies of the extracted modes. The combined process of EMD and Hilbert transform is called the Hilbert-Huang transform. The results in this thesis have been based on the improved EMD. To contribute to the understanding of plasma dynamics, the computed instantaneous frequencies are compared with the results obtained from the application of Simple Hilbert Transform. Instantaneous frequencies of overriding waves are easily separated as opposed to the application of just SHT. They offer the advantage of 3-dimensional study of the spatial characteristics of waves. The understanding of the instantaneous wave number has been achieved through the EMD and SHT combination. This provides the results which give the wave vector for a known frequency at a given instant of time. The instantaneous dispersion relation is determined using the knowledge of the instantaneous frequency and wave vector in the satellite frame, the plasma bulk velocity and the spacecraft velocity (found to be negligible compared with the plasma bulk velocity). This is accomplished using a Doppler shift relation. Wave modes identifications have been carried out by considering the proton temperature anisotropies, plasma beta and plasma bulk velocity and instantaneous phase velocity in the satellite frame. We report Alfvén mode close to the bow shock, spreading out to mirror mode which dominates the middle of magnetosheath. The mirror mode then diminishes towards the magnetopause.

Thesis (Ph.D.)--Tufts University, 2002. / Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 95-98). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph.D.) - University of St Andrews, January 2008.

Accretion discs efficiently transport angular momentum by a wide variety of as yet imperfectly understood mechanisms, with profound implications for the disc lifetime and planet formation. We discuss two different methods of angular momentum transport: first, generation of acoustic waves by mixing of inertial waves, and second, the generation of a self-sustaining magnetic field via the magnetorotational instability (MRI) which would be a source of dissipative turbulence. Previous local simulations of the MRI have shown that the dynamo changes character on addition of vertical stratification. We investigate numerically 3D hydrodynamic shearing waves with a conserved Hermitian form in an isothermal disc with vertical gravity, and describe the associated symplectic structure. We continue with a numerical investigation into the linear evolution of the MRI and the undular magnetic buoyancy instability in isolated flux regions and characterise the resultant quasi-linear EMFs as a function of height above the midplane. We combine this with an analytic description of the linear modes under an assumption of a poloidal-toroidal scale separation. Finally, we use RAMSES to perform full MHD simulations in a zero net flux shearing box, followed by spatial and a novel temporal averaging to reveal the essential structure of the dynamo. We find that inertial modes may be efficiently converted into acoustic modes for "bending waves", despite a fundamental ambiguity in the inertial mode structure. With our linear MRI and the undular magnetic buoyancy modes we find the localisation of the instability high in the atmosphere becomes determined by magnetic buoyancy rather than field strength for small enough azimuthal wavenumber, and that the critical Alfven speed below which the dynamo can operate increases with increasing distance from the midplane. We calculate analytically quasi-linear EMFs which predict both a vertical propagation of toroidal field and a method for creation of radial field. From our fully nonlinear calculations we find an electromotive force in phase with the toroidal field, which is itself 3π/2 out of phase with the radial (sheared) field at the midplane, and good agreement with our quasi-linear analytics. We have identified an efficient mechanism for generating acoustic waves in a disc. In our investigation of the accretion disc dynamo, we have reproduced analytically the EMFs calculated in our simulations, given arguments based on the phase of relevant quantities, several correlation integrals and the scalings suggested by our analytic work. Our analysis contributes significantly to an explanation for the dynamo in an accretion disc.