Flux Ropes as Singularities of the Vector Potential

A flux rope is a domain of concentration of the magnetic field $\textbf{B}$. Insofar as $\textbf{B}$ outside such a domain is considered as vanishingly small, a flux rope can be described as the core of a singularity of the outer vector potential $\textbf{A}$, whose topological invariant is the magnetic flux through the rope. By 'topological' it is meant that $\oint_C\textbf{A}\cdot\mathrm d\textbf{s}$ measures along any loop $C$ surrounding the flux rope the same constant flux $\Phi$. The electric current intensity is another invariant of the theory, but non-topological. We show that, in this theoretical framework, the linear force-free field (LFFF) Lundquist model and the non-linear (NLFFF) Gold-Hoyle model of a flux rope exhibit stable solutions distributed over quantized strata of increasing energies (an infinite number of strata in the first case, only one stratum in the second case); each stratum is made of a continuous set of stable states. The lowest LFFF stratum and the unique NLFFF stratum come numerically close one to the other, and match with a reasonable accuracy the data collected by spacecrafts travelling across magnetic clouds. The other LFFF strata do not match these data at all. It is not possible at this stage to claim which model fits better the magnetic cloud data. We also analyze in some detail the merging of tubes belonging to the same stratum, with conservation of the magnetic helicity, and the transition of a tube from one stratum to another one, which does not conserve magnetic helicity.Comment: 24 pages, 1 figur

Imperfections in focal conic domains: the role of dislocations

It is usual to think of Focal Conic Domains (FCD) as perfect geometric constructions in which the layers are folded into Dupin cyclides, about an ellipse and a hyperbola that are conjugate. This ideal picture is often far from reality. We have investigated in detail the FCDs in several materials which have a transition from a smectic A (SmA) to a nematic phase. The ellipse and the hyperbola are seldom perfect, and the FCD textures also suffer large transformations (in shape or/and in nature) when approaching the transition to the nematic phase, or appear imperfect on cooling from the nematic phase. We interpret these imperfections as due to the interaction of FCDs with dislocations. We analyze theoretically the general principles subtending the interaction mechanisms between FCDs and finite Burgers vector dislocations, namely the formation of kinks on disclinations, to which dislocations are attached, and we present models relating to some experimental results. Whereas the principles of the interactions are very general, their realizations can differ widely in function of the boundary conditions.Comment: 19 pages, 18 figure

Graduation in an Era of Uncertainty: Student Loan Repayment Following the Great Recession

Many students have financed educational aspirations through burdening themselves with debt-a result of interplaying dynamics of finance, education, and the labor market, a financing strategy for higher education especially prevalent during and following the American Great Recession. By the time students graduated and entered a ravished employment landscape, many had educational experiences that were other than traditional. In order to attain a bachelor’s degree, some began at community colleges or for-profit institutions, others had transferred, and many had taken longer than expected. This interaction between the financial crisis and higher education had considerable consequences for students as the rise in student debt was accompanied by a rising trend of repayment distress. In the slow recovery following the recession, have some students been able to manage their educational debt better than others? In my thesis, I examine debt repayment patterns in a post-recession era persistently marked with uncertainty. I draw from the nationally representative Baccalaureate & Beyond 2007-08 survey conducted by the U.S. National Center for Education Statistics. Corroborating past research, this sample suggests that some students are more successful in loan repayment: those who come from an economically privileged class and those who began college at public and private not-for-profit four-year institutions. I find that many students who began at two-year institutions and for-profit school had taken on more debt to finance what was supposed to be cheaper education and graduated with substantially higher debt loads and weaker labor outcomes than their peers. This suggests that institution type first enrolled plays a role on student outcomes and ultimately loan repayment. The interplay of where a student begins college and post-baccalaureate labor market outcomes have become increasingly important in understanding social stratification: college has been regarded as an equalizer among demographic and economic groups; however, it may instead further replicate disadvantages.Undergraduate Research Scholarship, The Ohio State University Arts and Sciences Honors Committee, $2,000No embargoAcademic Major: Sociolog

Onion storage diseases and their headspace volatiles

Onion, Allium cepa, is one of the world’s most commonly produced and consumed vegetables. In order to be available year round in temperate climates onions must be stored for several months. During this time parts of the harvested weight of bulbs are lost to storage diseases, sprouting and respiration leading to loss of carbohydrates and water. Diseases developing in storage may be difficult to spot at early stages as bulbs are typically stored in large bins. However, storage diseases can change the volatile metabolite profile of the infected onions. Electronic sensors that detect the concentration of specific volatile compounds in the air could be deployed in storage facilities to detect these changes. This would provide an early warning system that could detect diseases developing in storage bins before it becomes obvious to a human observer. In this way, some of the losses that occur during storage of onions could be prevented. This introductory paper discusses some of the available literature on the facets of onion production that are connected to storage disease development and the detection of said storage diseases using headspace sampling and analysis. The focus of the paper is mainly on onion production and storage of long day cultivars in relatively cold, temperate climates, as the use of short day cultivars and warm storage in warmer climates comes with different challenges and diseases

Mobilize for Franchise: The Quest for African American Women’s Suffrage with the Creation of African American Organizations from the 1910s to the 19th Amendment

The presentation is about the mobilization of African American women during the Women\u27s suffrage movement and how they mobilized their community to seek the right to vote despite the racially motivated obstacles against them