¡@¡@¡@¡@¡@¡@¡@­^¡@¤å¡@ºK¡@­n¡@¡@¡@¡@¡@¡@¡@ Heat transfer of a molten splat to a thin layer rapidly solidified on a cold substrate and the heat transfer coefficient at the bottom surface of a splat is extensively and self-consistently investigated. Rapid freezing in the splat is governed by a nonequilibrium kinetics at the solidification front in contrast to the melting in the substrate simulated by the traditional phase change problem. Solving one-dimensional unsteady heat conduction equations and accounting for distinct properties between phases and splat and substrate, the results show the effects of dimensionless parameters such as the dimensionless kinetic coefficient, stefan number, latent heat ratio, initial, equilibrium melting, and nucleation temperature, and conductivity, density, and specific heat ratios between solid and liquid and splat and substrate on unsteady temperature fields and freezing and melting rates in the splat and substrate and on unsteady variation of Biot number are presented. The unsteady variation of the heat coefficient or Biot number can be divided by five regimes: liquid splat-solid substrate, liquid splat-liquid substrate, solid splat-solid substrate, solid splat-liquid substrate, and the nucleation of the splat. Appropriate choices of dimensionless parameters to control the time for freezing and melting of the splat and substrate and an understanding and estimation of the heat coefficient at the bottom surface of the splat therefore are presented. The velocity distribution function and transport variables of the positive ions and electrons in the collisionless presheath and sheath of a plasma near a wall partially reflecting ions and electrons are determined from a kinetic analysis. Since velocities of the ions and electrons near the wall are highly non-Maxwell-Boltzmann distributions, accurate predictions of transport variables such as density, fluid velocity, mean pressure, fluidlike viscous stress and conduction require kinetic analysis. The result find that dimensionless transport variables of ions and electrons in the presheath and sheath can be exactly expressed in terms of transcendental functions determined by dimensionless independent parameters of ions and electrons reflectivities of the wall, ion-to-electron mass ratio, charge number and electron-to-ion temperature ratio at the presheath edge. The effects of the parameters on transport variables at the wall are also obtained. The computed transport variables in the presheath and sheath show agreement with available theoretical data for a completely absorbing wall.

Analytical and numerical studies are carried out to investigate spacecraft charging and plasma interactions in the solar wind. The physics of spacecraft charging in solar wind is determined by the mesothermal flow and the photoelectron sheath. In order to properly resolve both plasma flow and the photoelectron sheath, a 3-D full particle PIC model is applied. In this model, all plasma species (ambient ions and electrons, and photoelectrons) are modeled as macro-particles so the detailed dynamics of each species can be resolved around a charged spacecraft. In order to correctly resolve the mesothermal velocity ratio, PIC simulations are carried out using the real ion to electron mass ratio. A charging model based on the capacitance matrix method is integrated into the PIC model so the floating potential can be calculated self-consistently with the PIC code from charges deposited on the surface. We first investigate the photoelectron sheath in the solar wind. Previous analytical studies of monotonic and non-monotonic sheath profiles in stationary electrons have suggested that there can exist two solutions of the sheath profiles when photoelectron emissions are significant. We extend the previous analytical approach to include the effects of drifting electrons. Full particle PIC simulations suggest that the non-monotonic sheath profile is the stable solution under solar wind conditions. We found that the current balance calculation is not an accurate method to predict the floating potential when photoelectron emissions are significant. We next apply the simulation model to study spacecraft charging under various solar wind conditions. Due to photoelectron emissions, spacecraft charging is typically not a serious problem. The floating potential is ~2.5V under the mean solar wind condition. We also investigate the plasma interactions of a multi-body system consisting of a large platform and a small free flyer in the absence of photoelectron emissions where we set a free flyer at 2*Debye length behind the platform in the wake. For the particular system studied in this dissertation, the simulation shows that wake charging is not severe under both the mean solar wind condition and severe magnetosheath charging condition. / Ph. D.

ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Electrostatic approach is considered for mitigation of communication attenuation during the testing of laser powered directed energy weapon. Mitigation analysis is carried out for two target materials Al and Ti. Plasma parameters are obtained using one dimensional coupled analysis of laser-target interaction. Influence of laser beam frequency on plasma parameters is addressed. Sheath thickness is obtained using transient sheath calculations. It is found that uninterrupted telemetry can be achieved | using a maximum bias voltage of 10 kV, through Al plasma for fluences below 5 J/cm² and through Ti plasma for fluences below 2 J/cm².

The 5-year survival rate for ovarian cancer is only 45% largely due to lack of effective screening methods. Current methods include palpation, transvaginal ultrasound, and the CA-125 blood test. Finding disease reliably and at an early stage increase survival to 92%. We have designed and built a 0.7 mm endoscope for the early detection of ovarian cancer. Inserted transvaginally through the working channel of a hysteroscope, the falloposcope creates a minimally invasive procedure for the screening of high risk women. To improve the ease-of-use and safety of falloposcope deployment, we are working to create an everting balloon. Currently, the falloposcope would require a skilled user to operate due to the challenging anatomy of the fallopian tubes - a small opening from the uterus (< 1 mm), tortuous path, and delicate lumenal features. A balloon delivery system would gently open the fallopian tube and guide the falloposcope down the center of lumen. We show balloon design and discuss integration with the falloposcope prototype. We test possible mechanical damage to the tissue due to scraping, puncture, or overstretching. Successful introduction of the everting balloon to simplify falloposcope delivery could expand screening beyond specialized centers to smaller clinical locations.

This study uses the PIC (Particle-in-cell) method to simulate unsteady three-dimensional dynamics of particles in argon plasma under low pressure, high density, and weak ionization between two planar electrodes subject to a sudden biased voltage. Plasma has been widely used in materials processing, film manufacturing, nuclear fusion, lamps, etc. Properties of plasmas are also becoming important area for research. This work includes elastic collisions between electrons and neutrals, ions and neutrals, and inelastic collisions resulting in ionization from impacting neutrals by electrons, and charge exchange between ions and neutrals, and Coulomb collisions between electrons and ions. The model ignores magnetic field, secondary electron emission, recombination between ions and electrons, and assumes uniform distribution of the neutrals having velocity of Maxwellian distribution. The computed results show the effects of elastic and inelastic collisions on the characteristics of plasma and sheath (space charge region) in front of the workpiece surface. Unsteady mass, momentum and energy transport from the bulk plasma through sheath to the workpiece is confirmatively and exploratorily studied after successful comparison between PIC prediction and experimental data has been made.

Thesis (M.Sc.). / Written for the Dept. of Neurology and Neurosurgery. Title from title page of PDF (viewed 2008/05/14). Includes bibliographical references.

Thesis (Ph. D.)--Case Western Reserve University, 2006. / [School of Medicine] Department of Neurosciences. Includes bibliographical references. Available online via OhioLINK's ETD Center.

Thesis (M.S.)--University of Tennessee Health Science Center, 2008. / Title from title page screen (viewed on February 27, 2009). Research advisor: Terrence L. Geiger, MD, PhD. Document formatted into pages (xi, 74 p. : ill.). Vita. Abstract. Includes bibliographical references (p. 64-74).

Multiple sclerosis (MS) is a chronic autoimmune inflammatory disease of the central nervous system (CNS) whereby abnormal autoimmune responses cause damage to myelin, the lipid-rich layer that surrounds and insulates axons. This results in interruptions in communication within the CNS and between the CNS and peripheral nervous system (PNS). This dysfunction contributes to a variety of symptoms that negatively impact the lives of individuals with MS. Sleep disturbances and memory difficulties are two common challenges faced by MS patients, but are not comprehensively understood within the MS literature. Additionally, despite general consensus with regard to the important role that sleep plays in memory function, studies investigating the links between sleep disturbance and memory in MS are sparse. As such, the purpose of this dissertation was to determine whether sleep disturbance helps to explain differential memory functioning in individuals with MS, both cross-sectionally and over time. A sample of 165 early MS patients participated in cognitive measures, gait assessments, sensorimotor assessments, and self-report questionnaires once at baseline, and again 3 years after their initial assessment. Magnetic Resonance Imaging (MRI) data were collected at baseline. The primary predictor variable for the present study was sleep disturbance, as measured by two validated self-report measures of sleep functioning, the Insomnia Severity Index (ISI) and Pittsburgh Sleep Quality Index (PSQI). This study’s primary outcome was memory function, which was assessed by the CANTAB Paired Associate Learning (CANTAB PAL), Brief Visuospatial Memory Test, Revised (BVMT-R), Selective Reminding Test (SRT), and Verbal Paired Associate Learning (VPAL). Additional predictors included mood, disease burden, estimated premorbid intelligence, and demographic variables (age, sex, BMI). As hypothesized, results revealed that changes in sleep significantly predicted changes in memory over time. Patients with stable sleep and worsened sleep demonstrated an average decline in memory z-score from baseline to follow up, whereas patients whose sleep improved demonstrated an average improvement in memory z-score. Cross-sectionally, the presence of sleep disturbance significantly predicted worse memory performance when the ISI was used a measure of sleep disturbance, but not when the PSQI was used as a measure of sleep disturbance. Taken together, results highlight the importance of acknowledging sleep disturbance as an important predictor of memory function in individuals with early MS, paving the way for highly needed efforts toward prevention and intervention. However, findings should be extended to both objective and subjective sleep measures beyond the ISI.

In a wide variety of applications such as the Hall thruster and the tokamak, understanding the plasma-material interactions which take place at the wall is important for improving performance and preventing failure due to material degradation. In the region near a surface, the plasma sheath forms and regulates the electron and ion fluxes into the material. Emission from the material has the potential to change sheath structure drastically, and must be modeled rigorously to produce accurate predictions of the fluxes into the wall. Continuum kinetic codes offer significant advantages for the modeling of sheath physics, but the complexity of emission physics makes it difficult to implement accurately. This difficulty results in major simplifications which often neglect important energy-dependent physics. A focus of the work is on proper simulation of the sheath. The implementation of source and collision terms is discussed, alongside a brief study of the Weibel instability in the sheath demonstrating the necessity of proper collision implementation to avoid missing relevant physics. A novel implementation of semi-empirical models for electron-impact secondary electron emission into the boundary conditions of a continuum kinetic code is presented here. The features of both high and low energy regimes of emission are represented self-consistently, and the underlying algorithms are flexible and can be easily extended to other emission mechanisms, such as ion-impact secondary electron emission. The models are applied to simulations of oxidized and clean lithium for fusion-relevant plasma regimes. Oxidized lithium has a high emission coefficent and the sheath transitions into space-charge limited and inverse modes for different parameters. The breakdown of the classical sheath results in an increase of energy fluxes to the surface, with potential ramification for applications. / Doctor of Philosophy / Great advances are being made in a variety of promising applications of plasma physics, such as the development of spacecraft thrusters and fusion devices. Many of these devices constrain the flow of plasma within a material channel, leading degradation of the wall due to particle impact to be a serious concern for durability and lifespan. The plasma sheath is a region next to these material surfaces where ions are accelerated towards the wall, while electrons are repelled. As particles from the sheath impact the material, they cause the emission of secondary particles back into the sheath. This can drastically change the expected fluxes into the material and consequently the degradation expected to occur. Continuum kinetic simulations are a valuable tool for predicting and modeling the evolution of the sheath, but they are limited in their ability to rigorously do material emission physics by their inability to directly represent particle interactions with the surface. As such, past treatments of material emission in continuum kinetics tend to sacrifice valuable energy-dependent physics for simplified models.par To facilitate better understanding of the effects of emission on the sheath and the ramifications it might have for applications, the work here seeks to develop a framework for capturing the entire range of energy-dependent emission physics within a continuum kinetic framework. The implementation relies on semi-empirical models of beam emission data, focusing on simplicity and flexibility while still capturing the separate emission mechanisms which dominate in different energy regimes. The model is applied to simulations of lithium, an important material for fusion applications. Oxidized lithium has significantly enhanced emission properties over clean lithium, and is found to undergo a shift to non-monotonic sheath modes. The results show that the fundamental changes in the sheath structure due to the increased emission lead to greater energy fluxes into the surface. In this work, only secondary electron emission from the impact of electrons on a surface is examined. However, the underlying algorithms are easily extended to other energy-dependent energy mechanisms, such as ion-impact secondary electron emission.