A Two-dimensional Hybrid-Direct Kinetic Model of a Hall Thruster

The goal of this dissertation is to improve the state-of-the art modeling approaches available for simulating the discharge plasma in a Hall effect thruster (HET). A HET is a space propulsion device that utilizes electrical energy to ionize and accelerate propellant, generating thrust. The device features a cross-field configuration, whereby the transverse magnetic field traps electrons, and the axial electric field electrostatically accelerates ions out of the thruster channel. This configuration enables desirable thruster performance characteristics typically characterized by a relatively high specific impulse (1000-3000 s) and a high thrust density (a few Newtons per square meter). High fidelity computational models are useful to investigate the physical processes that govern the HET's performance, efficiency, and lifetime limitations. The non-equilibrium nature of the plasma transport should be resolved so that the flow can be accurately characterized. A grid-based direct kinetic (DK) simulation is capable of modeling the non-equilibrium state of plasma without the numerical noise that is inherent to particle-based methods since the velocity distribution functions (VDFs) are obtained in a deterministic manner. As the primary objective of this work, a two-dimensional, hybrid-DK simulation of the discharge plasma in a HET is developed. As a secondary objective, a plasma sheath, one of the important physical structures that form in the discharge plasma of a HET near the channel walls, is examined via a two-dimensional full DK simulation that highlights slight spatial differences in the sheath as a result of electrically disparate, adjacent wall materials. The memory storage requirements and computational load for the parallelized DK simulation grow with additional species, physical space dimensions, and velocity space dimensions. Some of these numerical limitations are encountered within this work. The hybrid-DK HET model utilizes a quasi-one-dimensional fluid electron algorithm in conjunction with a two-dimensional DK method to simulate the motion of neutral atoms and ions in a HET channel and near-field plume. Upon its development, the hybrid-DK simulation is benchmarked against results obtained from a two-dimensional hybrid-particle-in-cell (PIC) simulation with an identical fluid electron algorithm. To achieve agreement between the simulation results, a boundary condition for the DK model that satisfies particle conservation at the wall boundaries is developed, and electron model boundary conditions that provide solution stability are sought and utilized. For both high-frequency and low-frequency oscillations, the two simulations show good agreement for both time-averaged and dynamic plasma properties. Statistical noise tends to randomize plasma oscillations in the PIC simulation results, whereas the DK results exhibit coherent oscillatory behavior. Furthermore, results indicate that the DK simulation is capable of responding to small changes in electron dynamics, which is promising for future work. The DK plasma sheath simulation models a two-dimensional plasma sheath that highlights slight spatial differences inside the sheath as a result of electrically disparate, adjacent materials. To accomplish this goal, a quasi-one-dimensional sheath model is first built in a two-dimensional framework, boundary conditions are developed, and results are verified against theoretical expectations. Then, the full two-dimensional plasma sheath is modeled. The proof-of-concept model shows that two-dimensional effects are present in the vicinity of the discontinuous plasma potential at the wall, and electron and ion VDFs both clearly exhibit changes due to these effects.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162983/1/astridr_1.pd

Who Belongs in Honors? Culturally Responsive Advising and Transformative Diversity

Despite a rich body of scholarship that engages with university honors advising, advising to support diversity in higher education, and the overall need for better attention to diversity within honors, the literature has not fully explored the vital role that advising plays in supporting diversity and fostering belonging within honors programs and colleges. This essay brings together the too-often disparate threads of advising, honors, and diversity to advocate for a practice of culturally responsive advising within the honors environment in order to pursue truly transformative diversity. Holistic academic advising and related programming must play a central role in any honors program or college with a true commitment to inclusivity because advising work is the work of diversity, equity, and inclusion

The Role of Hardiness, Family Hardiness, and Parenting Self-Efficacy on Parenting Stress in Adoptive Parents

Adoptive parents are at risk for experiencing a high level of parenting stress (McGlone, Santos, Kazama, Fong, & Mueller, 2002) throughout the duration of the adoption experience. Adoptee background factors have been found to contribute to increased levels of parenting stress and distress in adoptive parents (Brooks, Simmel, Wind, & Barth, 2005; McDonald, Lieberman, Partridge, & Homby, 1991; McGlone et al., 2002). Increased parenting stress has been associated with negative outcomes for both parent and child (Ang, 2008; Deater-Deckard, Smith, & Ivy 2005; Morgan, Robinsion, & Aldridge, 2002). Hardiness, family hardiness and parental self-efficacy are protective factors that have all been found to be negatively associated with distress (Beasley, Thompson, & Davidson, 2002; Sevigny & Loutzenhiser, 2009; Svavarsdottir & Rayens, 2005) but have not been studied in a population of adoptive parents. Given the unique challenges of parenting an adopted child, the current study evaluated the relationship between hardiness, family hardiness, parenting self-efficacy, and parenting stress in a sample of adoptive parents. Results demonstrated that hardiness, family hardiness, and parenting self-efficacy predicted parenting stress in adoptive parents. Both hardiness and parenting self-efficacy emerged as unique predictors of parenting stress whereas family hardiness did not. 1bis was the first study to demonstrate that hardiness, family hardiness, and parenting self-efficacy buffer against the negative effects of parenting stress for adoptive parents

Survival, Growth, Food Selection, and Alimentary Canal Development of Intensively Reared Walleyes and Yellow Perch

Five genera of invertebrates, collected from a municipal sewage lagoon, were fed to newly hatched larval walleyes, (Stizostedion vitreun vitreun), and yellow perch, (Perca flavescens), to document survival, growth, food selection, and alimentary canal development of these fishes. Mean survival of walleyes for the 18 day period after hatching was 14.1%: mean unaccountable mortality was 43.5%. Forty-three percent of the walleyes remaining after 18 days survived an additional 32 days; mean unaccountable mortality was 33.8%. Mean daily length gain over the 50 day period was 0.8 mm/day. The cladoceran, Moina brachiate, was selected for by walleyes and yellow perch; the copepod, Cyclops vernalis, was initially ingested in the same proportion as fed, but later was selected for; the rotifer, Brachionus sp., was selected against by walleyes but was selected for by yellow perch during the first five days of feeding and was selected against thereafter; the cladocerans, Daphina magna and D. pulex, and the rotifer, Asplanchna sieboldi, were selected against by walleyes and yellow perch. Initially, significantly (P\u3c.05) more organisms were ingested by walleyes collected at 1100 than at 2300 hours; after day 12, more organisms were ingested by walleyes collected at 2300 than at 1100 hours, but there was a significant (P\u3c.05) interaction between the time of feeding and day of feeding, indicating that the effect of feeding time on the mean number of organisms was ingested by walleyes was dependent upon the day of feeding. Mean number of organisms ingested by yellow perch collected at 1100 hours was significantly (p\u3c.05) greater than the mean number ingested by yellow perch collected at 2300 hours. As the fishes grew they ingested progressively larger cladocerans indicating size and selection in feeding. The alimentary canal progressed through a series of changes as the larvae grew. The alimentary canal was completely developed in walleyes (22 mm, total length) by day 32 and was approaching full development in yellow perch (15mm, total length) by day 32. Invertebrates, collected from a municipal sewage lagoon, appeared to be of adequate size and species to feed walleyes and yellow perch during larval development

Free healthy breakfasts in primary schools: A cluster randomised controlled trial of a policy intervention in Wales, UK

Objective: The present study evaluated the impact of a national school programme of universal free healthy breakfast provision in Wales, UK. Design: A cluster randomised controlled trial with repeated cross-sectional design and a 12-month follow-up. Primary outcomes were breakfast skipping, breakfast diet and episodic memory. Secondary outcomes were frequency of eating breakfast at home and at school, breakfast attitudes, rest-of-day diet and class behaviour. Setting: Primary schools in nine local education authority areas. Subjects: A total of 4350 students (aged 9–11 years) at baseline and 4472 at follow-up in 111 schools. Results: Students in intervention schools reported significantly higher numbers of healthy food items consumed at breakfast and more positive attitudes towards breakfast eating at 12 months. Parents in intervention schools reported significantly higher rates of consumption of breakfast at school and correspondingly lower rates of breakfast consumption at home. No other significant differences were found. Conclusions: The intervention did not reduce breakfast skipping; rather, pupils substituted breakfast at home for breakfast at school. However, there were improvements in children’s nutritional intake at breakfast time, if not the rest of the day, and more positive attitudes to breakfast, which may have implications for life-course dietary behaviours. There was no impact on episodic memory or classroom behaviour, which may require targeting breakfast skippers

Assessment of a Two-Dimensional Hybrid-Direct Kinetic Simulation of a Hall Thruster

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143095/1/6.2017-4727.pd

Conformal Antenna Array for Millimeter-Wave Communications: Performance Evaluation

In this paper, we study the influence of the radius of a cylindrical supporting structure on radiation properties of a conformal millimeter-wave antenna array. Bent antenna array structures on cylindrical surfaces may have important applications in future mobile devices. Small radii may be needed if the antenna is printed on the edges of mobile devices and in items which human beings are wearing, such as wrist watches, bracelets and rings. The antenna under study consists of four linear series-fed arrays of four patch elements and is operating at 58.8 GHz with linear polarization. The antenna array is fabricated on polytetrafluoroethylene substrate with thickness of 0.127 mm due to its good plasticity properties and low losses. Results for both planar and conformal antenna arrays show rather good agreement between simulation and measurements. The results show that conformal antenna structures allow achieving large angular coverage and may allow beam-steering implementations if switches are used to select between different arrays around a cylindrical supporting structure.Comment: Keywords: conformal antenna, millimeter-wave communications, patch antenna array. 11 pages, 10 figures, 1 tabl