Charge Transport in Dielectric: The Pulsed Electroacoustic Method

Understanding and predicting charge accumulation and transport in dielectric materials is vital in applications where excess charge can accumulate including semiconductor devices, high-power electronic devices, high voltage DC cabling, high-energy physics facilities, plasma chambers, and spacecraft charging. Excess charge accumulation may result in electrostatic discharge events, which are the leading cause of spacecraft failure due to the space environment. The pulsed electroacoustic method allows you to “pop the hood” and non-destructively directly measure the embedded charge distributions in dielectric materials. Charge transport in disordered dielectric materials, measurements with the pulsed electroacoustic system, and comparison to models will be presented

Videogame Intervention for Improved Control of Type 1 Diabetes in Adolescents

Type 1 diabetes is a metabolic disease characterized by an inability to produce insulin, leading to hyperglycemia and other serious complications. Type 1 diabetes can be managed with exogenous insulin and careful dietary monitoring. However, adolescents with type 1 diabetes often have difficulty adhering to optimal treatment regimens, resulting in poorer diabetic control than patients in any other age group. In this study, we will test the efficacy of a serious videogame for increasing adherence to effective treatment regimens. We hypothesize that this intervention will lead to a significant reduction in glycosylated hemoglobin A1c, the standard assessment of diabetic control. We will randomize patients to the videogame intervention or a control group and measure hemoglobin A1c levels before and after intervention. This study will evaluate an engaging, age-appropriate tool to allow clinicians to connect with adolescent patients with the goal of decreasing their incidence of future diabetes-related complications

The Role of the Dispersion Parameter in Electrical Properties of Highly Disordered Insulating Materials

Charge transport in disordered solids can be described with use of a dispersion parameter. The dispersion parameter can be defined simply as either the thermal energy (low electric field regime) or the field energy (high field regime) scaled by the reciprocal of a characteristic energy of the material. A transitionary temperature and electric field are defined when the ratio of thermal or field energy over the characteristic energy is one, respectively. This indicates a transition from dispersive transport to normal transport. Dispersive transport can be described simply by the dispersion parameter for many disordered materials. Models involving the dispersion parameter describe anomalous behavior for disordered materials in measurements of charge transport for photoconductivity, DC conductivity, radiation induced conductivity, permittivity, and electrostatic breakdown onset, among others. Dispersive to normal transport transitions have been measured with pulsed electroacoustic measurements of internal charge distributions for high field induced transitions. Temperature induced transitions have been measured in photoconductivity and DC conductivity experiments. Low-density polyethylene (LDPE) is a ubiquitous disordered polymer and will be used as an example to show the connections between various measurements through the dispersion parameter

The Physical Significance of α for Electron Transport

Charge transport in crystalline materials can be well understood through the use of Bloch functions, band theory, and extended state transport. Disordered materials do not allow the same luxury, and different methods have to be considered. It turns out that band structures still exist. Although extended state conduction can still occur, localized states within the band gap allow for alternative mechanisms of charge transport in disordered materials. Conduction can be understood through such models as hopping, multiple trapping, and percolation, but all of them can lead to a broad distribution of event times. For example, the hopping-time distribution proposed by Scher and Montroll based on continuous time random walk formalism to describe transient photocurrent time-of-flight experiments, where ‘α’ is referred to as the dispersion parameter. This form of distribution exhibits a long tail. If the distribution of event times is broad enough to contain times on the order of the experiment then dispersive transport is observed. At sufficiently high temperatures or electric fields a transition from dispersive to normal transport can occur due to a shift in the occupancy of the states extending into the mobility gap to shallow traps. This results in shorter event times, leaving out times on the order of the experiment and dispersive transport is no longer observed. In the case of an exponential energetic density of states extending into the mobility gap, the dispersion parameter α is linearly proportional to either temperature or electric field. In overlapping regimes, descriptions are more complex. The dispersion parameter is scaled by the reciprocal of a characteristic energy that corresponds to the width of the density of states in the mobility gap and defines both a temperature and electric field corresponding to a transition from dispersive to normal transport when the dispersion parameter is one. These transition temperatures and fields appear to have significant meaning for a given material, such as the electric field strength associated with the onset of breakdown or a glassy transition temperature. While the dispersion parameter shows up in models involving other ψ(t) ∝ t-(1+α), density of states, the simplicity of the insight is lost in more complex descriptions

Charge Transport in Disordered Materials and the Dispersion Parameter

Charge transport in disordered solids can be described with use of a dispersion parameter. The dispersion parameter can be defined simply as either the thermal energy (low electric field regime) or the field energy (high field regime) scaled by the reciprocal of a characteristic energy of the material. A transitionary temperature and electric field are defined when the ratio of thermal or field energy over the characteristic energy is one, respectively. This indicates a transition from dispersive transport to normal transport. Dispersive transport can be described simply by the dispersion parameter for many disordered materials. Models involving the dispersion parameter describe anomalous behavior for disordered materials in measurements of charge transport for photoconductivity, DC conductivity, radiation induced conductivity, permittivity, and electrostatic breakdown onset, among others. Dispersive to normal transport transitions have been measured with pulsed electroacoustic measurements of internal charge distributions for high field induced transitions. Temperature induced transitions have been measured in photoconductivity and DC conductivity experiments. Low-density polyethylene (LDPE) is a ubiquitous disordered polymer and will be used as an example to show the connections between various measurements through the dispersion parameter. Our group is in the process of measuring temperature dependent conductivity for LDPE with the constant voltage conductivity method

Once Upon a Time/There was a Story that Began: Novelty, Endings, and Chronotope in John Barth’s The Tidewater Tales

This thesis examines the use of frame tales, genre blending, multi-voiced narration, and circular structure in John Barth’s 1987 novel, The Tidewater Tales. It tracks the isomorphy of Barth’s general aesthetic project, set forth in his essays, “The Literature of Exhaustion,” “The Literature of Replenishment,” and “Very Like an Elephant: Reality Versus Realism,” onto the theoretical aesthetics of Russian philosopher Mikhail Bakhtin. Both Barth and Bakhtin praise the novel its omnivorous capability to accommodate, and juxtaposes conflicting genres against one another; they each see the novelist as an “arranger” or “orchestrator,” who reassembles pre-existing forms to make them “sound in new ways.” Using Bakhtin’s concepts of novelness, heteroglossia, and unfinalizability this essay works to present The Tidewater Tales as an active embodiment of the Bakhtinian worldview, which locates truth and knowledge in dialogue between two subjects. By aligning Barth’s novel with Bakhtin’s philosophy, which emphasizes intersubjective dependence between the I and the other, this essay seeks to work as a corrective rehabilitation of Barth’s writing, which has been maligned as solipsistic self-consciousness by critics such as John Gardner, Christopher Lasch, and David Foster Wallace

Pulsed Electroacoustic Measurements of Polymers Irradiated With Low Energy Monoenergetic Electrons

Understanding the dynamics and accumulation of embedded charge in dielectric materials is paramount for many applications from HVDC power transmission to spacecraft charging. The pulsed electroacoustic (PEA) method allows for nondestructive measurements of embedded charge distributions in dielectrics. The spatial resolution of PEA measurements are typically ~10 μm. However, some of the most deleterious spacecraft charging events result from electron fluxes with 10 keV to 50 keV energies, resulting in electron ranges of 1\u27s to 10\u27s of μm. Due to the resolution of the PEA method and the superposition of the interfacial charge with the deposited charge distribution, it is difficult to measure charge deposited at these critical energies. A novel analysis method is proposed to measure these shallow charge distributions

Uncertainties of the Pulsed Electroacoustic Method: Peak Positions of Embedded Charge Distributions

Understanding the accumulation and dynamics of embedded charge in insulating materials is paramount for myriad of applications from HVDC power transmission to spacecraft charging. PEA systems allow for nondestructive measurements of embedded charge distributions. The spatial resolution of PEA measurements are typically defined as the FWHM of the leading interfacial peak, ~10 µm is typical. However, this is only one moment of the charge distribution. There are also the magnitude, peak position, and skewness of the charge distribution. Precise knowledge of the peak position of embedded charge distributions is important for understanding the electrical properties of insulators such as conductivity (slow charge migration), radiation induced conductivity (and delayed radiation induced conductivity), and electron range/penetration depth (as a function of dose and incident energy). This study focuses on the resolution of the peak position of embedded charge distributions measured via the PEA method