The Internal Charge Evolution of Multilayered Materials Undergoing Mono-Energetic Electron Bombardment

The charging of multilayer materials as related to the charging of spacecraft is one of the primary concerns related to activities in the space environment. To understand how multilayer materials undergoing electron bombardment charge, an in-depth study of energy-dependent material properties must be undertaken. These properties include the electron penetration depth, secondary electron emission, charge transport and electrostatic discharge. By using energy dependent models of these properties, along with the geometry of the system, multilayer models can be developed to predict the time evolution of the internal charge distribution. Using these models, the net surface potential and the measurement of electrode currents can be used to extrapolate information about the internal charge distribution. The Utah State University Materials Physics Group, with the funding of NASA James Webb Space Telescope project, performed several tests to understand the charging of multilayer dielectrics in various configurations. By using the Surface Voltage Probe to measure the net surface potential, along with measured electrode currents, the internal charge distribution can be inferred by using the developed theory for multilayer materials. Because each scenario requires a unique analysis, the theory of multilayer charging for a multilayer dielectric is outlined for four configurations defined as (i) surface layer deposition with grounded conductive layer, (ii) surface deposition with ungrounded conductive layer, (iii) conductive layer deposition with grounded conductive layer, and (iv) conductive layer deposition with ungrounded conductive layer. The results for these tests are outlined along with the fits given by the predictive models. The results of the tests show that knowledge of the energy-dependent electronic properties of the material, the energy of the incident electrons and the geometry of the system are all vital to predict the outcome of the given scenario. It is shown that for multilayer materials with an ungrounded conductive layer, electrostatic discharge occurs after the material charges past the breakdown limits of the material. These results can help to design, construct, and model already deployed spacecraft to mitigate and prevent detrimental spacecraft charging effects

Incorporating Electron Range Approximations into Secondary Electron Emission Models

Secondary Electron Yield is a key parameter in spacecraft charging. In order to develop a robust model to predict the secondary electron yield for any given material, the work done by Utah State University’s Materials Physics Group on electron range is extended to the yield problem. This newly developed yield model uses the probabilistic nature of inelastic collisions to incorporate the material dependent inelastic mean free path model used in USU’s MPG’s range model

Multichannel Radiofrequency Lock-in Detection For Coherent Processing Of Optical Signals

The thesis deals with the extraction of weak radio frequency signals buried in noise by the technique of multichannel spectral analysis based on radio frequency lock-in detection. The technique and the developed instrument find extensive use in the fields of radio astronomy, remote sensing, and spectroscopy.;Radio frequency spectral resolution over a reception range of 0 - 512 MHz was achieved with a multichannel spectrum analyzer consisting of a radio-frequency pre-processor and a set of 64 parallel lock-in receivers. The reception range is divided uniformly into 64 evenly spaced channels of 8 MHz bandwidth. System control was facilitated through a user programmable microcomputer which performs data acquisition, data preprocessing, graphic display, and tape storage.;The technique for resolving weak radio frequency signals has been improved by the application of the concepts of parallel processing, modularity, and symmetry.;The concepts of parallel processing as applied to RF processing of weak signals were successfully employed in the multichannel spectrum analyzer. The resulting system is characterized by reduced hardware complexity, low-noise electronic circuitry, and improved reliability. The concepts of modularity and symmetry proved advantageous in reducing design and hardware development time.;The channel receiver is a novel design based on the principles of superheterodyne reception incorporating improved detection stages. A dual square-law detection scheme for thermal compensation significantly reduced the problem of thermal drift. The gated synchronous detector scheme eliminated contaminating noise that was asynchronous with the chopping signal and also chopper transition noise.;The minimum detectable power across all channels was measured to be -138 dBm (+OR-)1 dB. In addition, across all channels, a noise figure of 3.05 (+OR-) 0.3 dB and a receiver noise temperature of 306 (+OR-) 43 K was measured. Through software control, the system can perform auto-calibration, address any combination of receivers, perform preprocessing of data for graphical display, and perform digital integration for extended periods of time

Evaluating the effectiveness of using touch sensor capacitors as an input device for a wrist watch computer

On the go computing is becoming more important for users who wish to access information from anywhere. Wearable computers are an optimal solution to achieving this feat because it allows for easy accessibility and quick use. There are many challenges that arise with small computers worn on the body. One of the most common issues is the interaction between the computer and the user and more specifically how the user enters input. In this paper we research a potential effective way to interact with a wrist watch by mounting touch sensors on the watch band.Committee Member/Second Reader: Rebecca Grinter; Faculty Mentor: Thad Starne

Evaluation of Herbicides on the Establishment of Pearl Millet [Pennisetum glaucum (L.) R. Br.] x Napiergrass (Pennisetum purpureum Schumach.)

Pearl millet [Pennisetum glaucum (L.) R. Br.] x napiergrass (Pennisetum purpureum Schumach.) (PMN) hybrids have potential as a seeded, perennial bioenergy or forage crop. The PMN hybrid utilized in this study (PMN10TX13) was developed as an alternative to herbaceous bioenergy feed stocks that either require vegetative propagation, complicated planting strategies due to small seed size, or annual reseeding due to annual growth habit. However, PMN seedlings are impacted by competition from nearby weeds for water, nutrients, and sunlight during establishment. To date, there is limited agronomic information on strategies for effective establishment of weed-free PMN stands. The objective of this study was to develop herbicide response tests to determine the phytotoxic effects of selected pre-crop emergence (PRE) and post-crop emergence herbicides (POST) on the seeded establishment of PMN. Several herbicides with utility for weed free establishment of seeded PMN were successfully identified. Pre-emergent herbicides Balance Pro (isoxaflutole), Dual II (s-metolachlor,) Plateau (imazapic), and Permit (halosulfuron) were effective as long as sufficient rates of seed safener were used. Post-crop emergent herbicides Permit (halosulfuron), Prowl (pendimethalin), Banvel (dicamba), Aatrex (atrazine), AIM (carfentrazone-ethyl), Warrant (achetochlor), and Huskie (pyrasulfotole) were also found to be safe for use at the 5-7 leaf stage and beyond

Development and Application of Pseudoreceptor Modeling

Quantitative Structure-Activity Relationship (QSAR) methods are a commonly used tool in the drug discovery process. These methods attempt to form a statistical model that relates descriptor properties of a ligand to the activity of that ligand compound towards a specific desired physiological response. QSAR methods are known as a ligand-based method, as they specifically use information from ligands and not protein structural data. However, a derivation of QSAR methods are pseudoreceptor methods. Pseudoreceptor methods go beyond standard QSAR by building a model representation of the protein pocket. However, the ability of pseudoreceptors to accurately replicate natural protein surfaces has not been studied. The goal of this thesis work is to investigate the necessary descriptors to map a protein binding pocket and a method to accurately recreate the 3-D spatial structure of the binding pocket. In addition, additional applications of existing pseudoreceptor methods are explored