This thesis is concerned with Calabi-Yau threefolds and vector bundles upon them, which are the basic mathematical objects at the centre of smooth supersymmetric compactifications of heterotic string theory. We begin by explaining how these objects arise in physics, and give a brief review of the techniques of algebraic geometry which are used to construct and study them. We then turn to studying multiply-connected Calabi-Yau threefolds, which are of particular importance for realistic string compactifications. We construct a large number of new examples via free group actions on complete intersection Calabi-Yau manifolds (CICY's). For special values of the parameters, these group actions develop fixed points, and we show that, on the quotient spaces, this leads to a particular class of singularities, which are quotients of the conifold. We demonstrate that, in many cases at least, such a singularity can be resolved to yield another smooth Calabi-Yau threefold, with different Hodge numbers and fundamental group. This is a new example of the interconnectedness of the moduli spaces of distinct Calabi-Yau threefolds. In the second part of the thesis we turn to a study of two new `three-generation' manifolds, constructed as quotients of a particular CICY, which can also be represented as a hypersurface in dP6 x dP6, where dP6 is the del Pezzo surface of degree six. After describing the geometry of this manifold, and especially its non-Abelian quotient, in detail, we show how to construct on the quotient manifolds vector bundles which lead to four-dimensional heterotic models with the standard model gauge group and three generations of particles. The example described in detail has the spectrum of the minimal supersymmetric standard model plus a single vector-like pair of colour triplets.

In this thesis, we consider heterotic string vacua based on a warped product of a four-dimensional domain wall and a six-dimensional internal manifold preserving only two supercharges. Thus, they correspond to half-BPS states of heterotic supergravity. The constraints on the internal manifolds with $SU(3)$ structure are derived. They are found to be a generalization of half-flat manifolds with a particular pattern of torsion classes and they include half-flat manifolds and Strominger's complex non-Kahler manifolds as special cases. We also verify that heterotic compactifications on half-flat mirror manifolds are based on this class of solutions. Furthermore, within this context, we construct specific examples based on six-dimensional nearly-Kahler homogeneous manifolds and non-trivial vector bundles thereon. Our solutions are based on three specific group coset spaces satisfying the half-flat torsion class conditions. It is shown how to construct line bundles over these manifolds, compute their properties and build up vector bundles consistent with supersymmetry and the heterotic anomaly cancellation. It turns out that the most interesting solutions are obtained from SU(3)/U(1)². This space supports a large number of vector bundles leading to consistent heterotic vacua with GUT group and, for some of them, with three chiral families.

This portfolio of eleven scores and an accompanying commentary is an in depth investigation into the use and development of compositional techniques over a wide range of instrumental and vocal combinations.  The scores submitted trace my development as a composer by considering research questions related to structural organisation, harmonic and rhythmic development and how external sources, particularly visual and literary, can be used as a starting point for the compositional process. Included in the portfolio are eleven works, categorised into three sections: instrumental music, solo works, and vocal music. The portfolio researches and examines elements of composition such as harmony, texture and timbral relationships, as well as the use of visual and literary art as a stimulus for composition across all of the instrumental and vocal combinations included.  My interest in the combination of pre-existing compositional methods such as serialism, with particular regards to pitch, and atonality is also examined in many of the scores and documented in the accompanying commentary.

Autosomal dominant adult onset neuronal ceroid lipofuscinoses (ANCL/CLN4) is a rare neurodegenerative disorder caused by mutations in the human gene DNAJC5 which encodes cysteine string protein alpha (CSPα). ANCL is characterized by the appearance of aberrant lysosomal storage material in the post-mortem brains of patients, who usually die from widespread neuronal loss within 10 years from the onset of symptoms. CSPα is a neuroprotective co-chaperone specifically localized to synaptic vesicles (SVs) and is evolutionarily conserved in all animals. CSPα forms a chaperone complex with HSC70 to properly fold a limited number of synaptic proteins. Complete loss of CSP leads to neurodegeneration and reduced lifespans in flies and mice. However, the mechanism of degeneration induced by ANCL mutations is currently unknown and there are no available animal models to study the dysfunctional proteins in situ. In this thesis, I describe the generation and subsequent characterization of the first animal model of ANCL, using the fruit fly Drosophila melanogaster. First, I show that human CSPα (hCSPα) is conserved functionally from humans to flies. Wildtype hCSPα expressed in flies localizes properly to SVs and is able to rescue lifespan defects in CSP null mutant flies. Overexpression of hCSPα proteins with the ANCL causing L115R and L116Δ mutations recapitulates numerous phenotypes consistent with human disease pathology. This includes the appearance of high molecular weight (HMW) SDS-resistant aggregates on western blots, accumulation of aberrant osmophilic membrane structures observed via electron microscopy, and a dose-dependent reduction in adult viability. Mutant hCSPα is mislocalized from SVs to enlarged abnormal endosomes, which accumulate in neuronal axons and somata. These endosomes strongly co-localize with the endosomal sorting required for transport (ESCRT) complex protein HRS, contain large amounts of ubiquitinated proteins, and lack markers of lysosomal maturation. This suggests that the ANCL causing mutations may cause disruptions in endo-lysosomal trafficking via an ESCRT related mechanism. To probe the genetic nature of the mutant alleles I expressed the mutant hCSPα transgenes with various doses of endogenous Drosophila CSP (dCSP). I show that loss of dCSP suppresses toxicity, as well as the aberrant endosomal accumulations and HMW aggregates induced by overexpression of mutant hCSPα. Additionally, expression of a combination of the wildtype and mutant hCSPα showed a super-additive effect on viability and HMW aggregates. This suggests that the disease-causing mutations may act as hypermorphic gain of function alleles, contrary to existing models, which suggest a dominant-negative mechanism. I also performed an F1 candidate screen for genetic modifiers of toxicity, using a robust and easy-to-score adult eye morphology and pigmentation phenotype. Using this approach, I discovered several strong interactors, both enhancers and suppressors, including member of the ESCRT trafficking pathway and other known CSP-interacting proteins. Of particular interest was the CSP co-chaperone Hsc70, which had several loss of function alleles among the strongest observed suppressors. Loss of Hsc70 also greatly reduces toxicity and endosomal accumulations of overexpressed mutant hCSPα but interestingly does not have a significant effect on the levels of HMW CSPα aggregates. This further supports the model that ANCL mutations act as hypermorphs, with a toxic mechanism involving CSP’s endogenous interactions with HSC70. Finally, I discuss the implications of these findings in relation to previous studies of the ANCL causing mutations and endogenous CSPα/HSC70 function and propose a novel mechanistic disease model. This model postulates that mutant CSP is properly trafficked to synapses but, after a brief lifespan as a properly functioning HSC70 co-chaperone, is then ubiquitinated and localized onto endosomes. Ubiquitinated mutant CSP is then clustered by HRS but is unable to mature properly through an ESCRT dependent degradation pathway. These endosomes are retrogradely trafficked through the axon to the soma where they fuse, accumulate, and persist, eventually leading to cellular toxicity via an unknown mechanism. The hypermorphic nature of the mutants can be explained by the novel observation that normal endogenous CSP also traffics through a retrograde ESCRT dependent pathway, where it intersects and co-accumulates with mutant CSP, potentially contributing to toxicity.

Bela Bartok's six string quartets are generally regarded as the next most significant works in the medium after the quartets of Beethoven. Unlike some of his contemporaries in the field, e.g, Hindemith, Milhaud, and Schoenberg, Bartok's quartets are representative of his musical growth and, as such, are worthy of equal status with those of such recognized masters as Haydn and Mozart, as well as Beethoven...

I have been overwhelmed by curiosity, a curiosity that is keeping my desire to make valid. I have an endless infatuation with growth and constructing. My aim is to juxtapose an academic and a "rudimentary" approach that will set up contradictions in which traditional woodworkers may find irreverence towards.

The purpose of this thesis is to study a symmetry of string theory known as T-duality. We focus on a particular example establishing the equivalence between a quantized string moving in a circular space of radius R and a dual string moving in a similar space of radius 1/R . We will show that this duality implies that the momentum of the string in one picture becomes the number of times the string is wound around the circle in the dual picture. We present two proofs of T-duality. The first reflects the standard interpretation of T-duality as an isomorphism of quantum theories. The second approach is based on Hull's Double Field Theory.

In this Thesis I explore aspects of dark radiation and its role in String Phenomenology. Dark radiation is any additional hidden type of relativistic matter present in the Universe today, conventionally labelled as an "excess effective number of neutrino species", Δ N_eff. It provides a powerful test of hitherto untested theoretical models based on fundamental theories such as String Theory. I begin by considering dark radiation in the LARGE Volume Scenario, a phenomenologically viable class of string compactifications. First I review how the minimal setup slightly overproduces axionic dark radiation via modulus decay. I then demonstrate that loop corrections to the main competing visible-sector decay process have a negligible effect and are unable to alleviate the tension with observations. In the following chapter I explore fibred extensions of the LARGE Volume Scenario. The predictions for Δ N_eff are qualitatively different: in particular, models with a sequestered visible sector on D3 branes at a singularity are swamped by massless axions and decisively ruled out. I then consider TeV-scale supersymmetry in a model with anisotropic modulus stabilisation. If the Standard Model is realised on D7 branes wrapping the small volume cycle a hierarchy of soft terms is generated, which may have applications to natural supersymmetry. The final chapter takes a different approach and investigates the proposition that dark radiation, in the form of a Cosmic Axion Background, could explain the long-standing soft X-ray excess from galaxy clusters. I show for the Coma cluster that the morphology of the excess can be reproduced by axion-photon conversion in the intracluster magnetic field, provided the field is allowed to have more structure on smaller scales than typically assumed based on Faraday rotation data. This explanation requires an inverse axion-photon coupling M ∼ 10¹¹ - 10¹² GeV and a mean axion energy (E_CAB) ∼ 50 - 250 eV.

Master of Music / Department of Music / David Littrell / An aspect of instrument choice that has not been studied in such abundance as the topics of timbre and gender associations of instruments are the influences of external factors, such as ensemble director, parent and family, friends, academic diversity, travel opportunities, and medical reasons as examples; however, these factors have been briefly addressed in word alone in many of the studies completed for related examinations. This study is integral in defining how music educators can better identify supplementary factors in addition to the timbre and gender association studies that will further influence students to choose to play an instrument and more specifically a string instrument. The findings can be applied to band, choir, theater, ROTC, and any other student organization as these factors are contributions and experiences from the student’s life previous to the presentation of the new activity. The current study focuses primarily on string instrument choice as gathered from a pilot survey using a string youth symphony ensemble from the Midwest as subjects and then high school students from three different but similar districts also in the Midwest. The information provided by the students was in agreement with previously performed studies; however, it also featured truths specifically unique to the ensemble and communities in which they were gathered. The researcher will seek to answer the following research questions: 1) What are the three most influential external factors that contributed to the student’s choice to begin string instruction? 2) How are these factors related to the musical culture of the student including opportunities for participation as well as observations? 3) Are family influences stronger than teacher/friend influences? 4) How does the strength of the string community (school and community) affect the beginning string student based on student perceptions of the two communities? Using descriptive statistics, the three most influential external factors contributing to the student’s string instrument choice in the pilot study were Parents, Private lesson teacher, and Other family. The three most influential external factors for the high school students were Parents, Live performance, and Friends. The three most influential external factors for High School #1 were Parents, Live performance, and Elementary Orchestra Teacher. For High School #2, the top three were Parents, High School Orchestra Teacher, and Friends. In High School #3, Parents, Live Performance, and Private Lesson Teacher were shown to be the student’s most influential external factors. In each case, Parents were reported as the most influential external factor for string instrument choice among the populations of students surveyed. When teachers determine recruitment activities, they must recruit the parent, which begins the moment the public school teacher is hired in the orchestra teaching position. Overall, parental influences trump all other external factors in the list examined by this population, which was slightly dissimilar than the review of the literature suggested.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. 27 January 2016. / The direct and inverse spectral problems for an inhomogeneous string with an interval of zero density and a concentrated mass at the end point moving with damping are investigated. The partial differential equation is mapped into an ordinary differential equation using separation of variables which in turn is transformed into a Sturm-Liouville differential equation with boundary conditions depending on these parathion variable. The Marchenko approach is employed in the inverse problem to recover the potential, density and other parameters from the knowledge of the two spectra and length of the string.