The Dynamics of Magnetised Warped Discs

The study of warped discs and the study of magnetised discs have generally been performed in relative isolation, and comparatively little attention has been given to the complex interplay between these two aspects of accretion disc physics. This thesis aims to provide a synthesis of these disparate areas of research and explore the effects of a mean magnetic field on warp evolution. Using a coordinate system based upon tilted spheres, a series of self-similar solutions are presented for the global structure of a potential magnetic field beyond a warped disc. Warped discs threaded by a mean magnetic field are investigated numerically and semi-analytically in both a warped shearing box and a corrugated disc model. An asymptotic analysis is used to demonstrate the relation between these distinct local perspectives. Interactions between the warp and what we have called ‘Alfv$\acute e$nic-epicyclic’ oscillation modes, the magnetic analogues to epicyclic oscillations, are found to have potentially profound and hitherto unexplored consequences for the evolution of the warp. Resonances between the vertical oscillation mode and the Alfv$\acute e$nic-epicyclic modes imbue magnetised discs with a rich and subtle structure compared to their hydrodynamic counterparts. Notably the anomalous rapid propagation of the warp in Keplerian inviscid discs is suppressed, while warp propagation in non-Keplerian discs may be considerably enhanced. Non-local angular momentum transport via the external magnetic field may also provide an additional important contribution to the warp evolution. The practical application of these results to numerical simulations is discussed.PhD supported by funding from the Science and Technology Facilities Council (STFC

Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka

Role of the Ce valence in the coexistence of superconductivity and ferromagnetism of CeO1−x_{1-x}Fx_{x}BiS2_{2} revealed by Ce L3L_3-edge x-ray absorption spectroscopy

We have performed Ce $L_3$-edge x-ray absorption spectroscopy (XAS) measurements on CeO$_{1-x}$F$_x$BiS$_2$, in which the superconductivity of the BiS$_2$ layer and the ferromagnetism of the CeO$_{1-x}$F$_x$ layer are induced by the F-doping, in order to investigate the impact of the F-doping on the local electronic and lattice structures. The Ce $L_3$-edge XAS spectrum of CeOBiS$_2$ exhibits coexistence of $4f^1$ (Ce$^{3+}$) and $4f^0$ (Ce$^{4+}$) state transitions revealing Ce mixed valency in this system. The spectral weight of the $4f^0$ state decreases with the F-doping and completely disappears for $x>0.4$ where the system shows the superconductivity and the ferromagnetism. The results suggest that suppression of Ce-S-Bi coupling channel by the F-doping appears to drive the system from the valence fluctuation regime to the Kondo-like regime, leading to the coexistence of the superconducting BiS$_2$ layer and the ferromagnetic CeO$_{1-x}$F$_x$ layer.Comment: 5 pages, 5 figure

An engineering database management system for spacecraft operations

Studies at ESOC have demonstrated the feasibility of a flexible and powerful Engineering Database Management System in support for spacecraft operations documentation. The objectives set out were three-fold: first an analysis of the problems encountered by the Operations team in obtaining and managing operations documents; secondly, the definition of a concept for operations documentation and the implementation of prototype to prove the feasibility of the concept; and thirdly, definition of standards and protocols required for the exchange of data between the top-level partners in a satellite project. The EDMS prototype was populated with ERS-l satellite design data and has been used by the operations team at ESOC to gather operational experience. An operational EDMS would be implemented at the satellite prime contractor's site as a common database for all technical information surrounding a project and would be accessible by the cocontractor's and ESA teams

Structured Pathways, Reinforced Plans: Exploring the Impact of a Dual Enrollment Program on the College Choice and Career Interests of Future Teachers of Color

In response to the critical shortage of a diverse teacher workforce, Temple Education Scholars is a “Grow Your Own dual enrollment program model designed to promote access to postsecondary education and educator diversity. Grow Your Own programs have frequently been cited as a promising and potentially sustainable model for addressing the disparity between the racial identifications of students and those of their teachers. Using social cognitive career theory, we explore how three participants in the Temple Education Scholars program develop academic and career interests in teaching and make educational choices related to their career aspirations. Following case study analysis, we illustrate how three participants with interests in teaching described what attracted them to the program, how the program supported their college and career aspirations, and their visions for careers in education

First Application of the Dakin-West Reaction to Fmoc Chemistry: Synthesis of the ketomethylene tripeptide Fmoc-Nα-Asp(tBu)-(R,S)Tyr(tBu)Ψ(CO-CH2)Gly-OH

International audienceA practical synthesis of a tripeptide containing a ketomethylene isostere, suitably protected for introduction in Fmoc SPPS, has been carried out for the first time in Fmoc chemistry by using a modified Dakin-West reaction

Exploring the “At-Risk” Student Label Through the Perspectives of Higher Education Professionals

Institutions of higher education often use the term “at-risk” to label undergraduate students who have a higher likelihood of not persisting. However, it is not clear how the use of this label impacts the perspectives of the higher education professionals who serve and support these students. Our qualitative study explores the descriptions and understandings of higher education professionals who serve and support at-risk students. We use thematic analysis (Braun & Clark, 2006) to interpret our data and develop our themes. These themes include conflicting views of the “at-risk” definition, attempts to normalize at-risk, fostering relationships, and “at-promise.

The Impact of Optional: Investigating the Effects of Test-Optional Admissions Policies

An increasing number of postsecondary institutions in the United States have introduced test-optional admissions policies primarily due to criticism of standardized admissions tests as potentially biased predictors of student success. However, the impact of the test-optional movement is largely unknown and continues to evolve amid the COVID-19 pandemic. Using institutional isomorphism as our theoretical framework, we update and extend existing research by broadening the number and type of test-optional institutions represented in the literature. We use 2x2 repeated measures multivariate analysis of variance (MANOVA) to examine change in applications received, acceptances, enrollment, and the racial and socioeconomic composition of the student body upon the implementation of a test-optional admissions policy. Findings demonstrate that test-optional policy implementation results in a statistically significant increase in applications and enrolled students. However, we find that test-optional policy adoption does not result in a statistically significant increase in the percentage of underrepresented racial minority students or Pell Grant recipients