Hall Effect Thruster Characterization through Potential, Magnetic, and Optical Measurements

Electric propulsion is a promising method for providing ΔV to spacecraft on orbit. In general, much higher ISPS are obtained compared to their chemical counterparts. Hall thrusters are a subset of electric propulsion with moderately high specific impulse and thrust when compared to other forms of electric propulsion. Even though Hall thrusters have an extensive flight legacy around the world, there are still many unknowns associated with their operation. Experimental research was conducted in AFIT’s Space Propulsion Application Simulation System (SPASS) laboratory, to measure Hall current, plasma potential and visible emission from the 600W Hall thruster in a time correlated system at data rates up to 1MHz. Unfortunately issues would plague the experiment and ultimately prevent any data collection on the thruster understudy. Instead data collected prior was further analyzed in attempt correlate behavior of plasma instabilities to determine causal relationships between plasma properties and anomalous diffusion modes. This was done by performing a frequency analysis where frequencies associated with breathing mode and spoke mode were identified

Development of phosphate glass and multi-phase titanate ceramic compositions for thermal treatment of irradiated nuclear fuel residues

The highly heterogeneous nature of UK legacy damaged and degraded spent nuclear fuels and so called, 'orphan fuels', prohibits the use of standard conditioning methods. An inventory of UK residual fuels yielded an account for three main fuel types: Magnox, AGR (advanced gas-cooled reactor) and MOx (mixed oxides). A series of glass and ceramic type host systems have been investigated for potential conditioning of these high uranium content spent fuel materials. Electron microscopy and powder X-ray diffraction techniques were used to characterise the prototypical wasteforms. Two sets of low-melt temperature phosphate glass compositions were trialled with additions of CeO2 to simulate the fluorite structure and large ionic radius of U in oxide fuels. Evolution of monazite-type phases at simulant oxide fuel loadings above 15 wt.% highlighted a potential development into a glass-ceramic hybrid assemblage. Investigation into the use of an alkoxide nitrate synthesis route for SYNROC-F type ceramic precursors has allowed for the demonstration of a sintered host pyrochlore phase containing up to ~40 wt.% fuel simulant CeO2. Gas evolution has led to increased porosity at higher temperatures and longer sintering times, this may be mitigated by higher pre-calcination temperatures

Structural transformations and disordering in zirconolite (CaZrTi2O7) at high pressure

There is interest in identifying novel materials for use in radioactive waste applications and studying their behavior under high pressure conditions. The mineral zirconolite (CaZrTi2O7) exists naturally in trace amounts in diamond-bearing deep-seated metamorphic/igneous environments, and it is also identified as a potential ceramic phase for radionuclide sequestration. However, it has been shown to undergo radiation-induced metamictization resulting in amorphous forms. In this study we probed the high pressure structural properties of this pyrochlore-like structure to study its phase transformations and possible amorphization behavior. Combined synchrotron X-ray diffraction and Raman spectroscopy studies reveal a series of high pressure phase transformations. Starting from the ambient pressure monoclinic structure, an intermediate phase with P21/m symmetry is produced above 15.6 GPa via a first order transformation resulting in a wide coexistence range. Upon compression to above 56 GPa a disordered metastable phase III with a cotunnite-related structure appears that is recoverable to ambient conditions. We examine the similarity between the zirconolite behavior and the structural evolution of analogous pyrochlore systems under pressure.<br/

Assessment of Turbulent CFD Against STS-128 Hypersonic Flight Data

Turbulent CFD simulations are compared against surface temperature measurements of the space shuttle orbiter windward tiles at reentry flight conditions. Algebraic turbulence models are used within both the LAURA and DPLR CFD codes. The flight data are from temperature measurements obtained by seven thermocouples during the STS-128 mission (September 2009). The flight data indicate boundary layer transition onset over the Mach number range 13.5{15.5, depending upon the location on the vehicle. But the boundary layer flow appeared to be transitional down through Mach 12, based upon the flight data and CFD trends. At Mach 9 the simulations match the flight data on average within 20 F/11 C, where typical surface temperatures were approximately 1600 F/870 C

Greenhouse Aquaponics: Custom Aquaponic Systems at Home

Taking advantage of inherent natural systems, aquaponic practices hold the potential to serve as an educational, sustainable, and profitable hobby for home gardeners facing common constraints such as temperature, space, and pests. The goal of this research was to assess the feasibility of implementing a small scale (4,542-liter) home -based aquaponic system in a small (48.768 square meter) greenhouse to produce fresh produce and fish protein. System construction and maintenance costs were compared to the value of crops and fish produced to determine whether this aquaponic system is a feasible option for the home grower. It was hypothesized that this system will breakeven in five years. Results showed that such a system can be successfully built and operated to yield fresh produce, fish protein and a high value composted fertilizer on an annual basis. However, the payback period for the system can be five years or even longer, depending on the estimation of future costs and benefits and discount rates used. Results and experience from the greenhouse system have been and will continue to be used for system improvements, education into natural systems, designs for others, as well as a guide for aquaponic systems moving forward

Flat Plate Solar Collector Materials (and Designs with an Economic Methodology for Optimizing Collector Design)

The desirability of specific materials and designs for conventional flat-plate solar collector components is considered. Then a methodology for choosing the most economic component is presented, consisting of a computer simulation and a rate-of-return analysis. The effect of rising conventional fuel costs is examined. Examples of using the methodology are given, based on Southern California climatic and user-demand conditions. Selective absorber-plate coatings and film inner glazing are shown to be economic, yielding a rate-of-return of 23 percent and 29 percent, respectively

Evaluation of positive G sub Z tolerance following simulated weightlessness (bedrest)

The magnitude of physiologic changes which are known to occur in human subjects exposed to varying levels of + G sub Z acceleration following bed rest simulation of weightlessness was studied. Bed rest effects were documented by fluid and electrolyte balance studies, maximal exercise capability, 70 deg passive tilt and lower body negative pressure tests and the ability to endure randomly prescribed acceleration profiles of +2G sub Z, +3G sub Z, and +4G sub Z. Six healthy male volunteers were studied during two weeks of bed rest after adequate control observations, followed by two weeks of recovery, followed by a second two-week period of bed rest at which time an Air Force cutaway anti-G suit was used to determine its effectiveness as a countermeasure for observed cardiovascular changes during acceleration. Results showed uniform and significant changes in all measured parameters as a consequence of bed rest including a reduced ability to tolerate +G sub Z acceleration. The use of anti-G suits significantly improved subject tolerance to all G exposures and returned measured parameters such as heart rate and blood pressure towards or to pre-bed-rest (control) values in four of the six cases

Identification of specialists and abundance-occupancy relationships among intestinal bacteria of Aves, Mammalia, and Actinopterygii

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of American Society for Microbiology for personal use, not for redistribution. The definitive version was published in Applied and Environmental Microbiology 82 (2016): 1496-1503, doi:10.1128/AEM.02456-15.The coalescence of next generation DNA sequencing methods, ecological perspectives, and bioinformatics analysis tools is rapidly advancing our understanding of the evolution and function of vertebrate-associated bacterial communities. Delineating host-microbial associations has applied benefits ranging from clinical treatments to protecting our natural waters. Microbial communities follow some broad-scale patterns observed for macro-organisms, but it remains unclear how specialization of intestinal vertebrate-associated communities to a particular host environment influences broad-scale patterns in microbial abundance and distribution. We analyzed the V6 region of 16S rRNA gene amplified from 106 fecal samples spanning Aves, Mammalia, and Actinopterygii (ray-finned fish). The interspecific abundance-occupancy relationship—where widespread taxa tend to be more abundant than narrowly distributed taxa—among operational taxonomic units (OTUs) was investigated within and among host species. In a separate analysis, specialists OTUs that were highly abundant in a single host and rare in all other hosts were identified using a multinomial model without excluding under-sampled OTUs a priori. We also show that intestinal microbes in humans and other vertebrates studied follow a similar interspecific abundance-occupancy relationship compared to plants and animals, as well as microbes in ocean and soil environments; but because intestinal host-associated communities have undergone intense specialization, this trend is violated by a disproportionately large number of specialist taxa. Although it is difficult to distinguish the effects of dispersal limitations, host selection, historical contingency, and stochastic processes on community assembly, results suggest bacterial taxa can be shared among diverse vertebrate hosts in ways similar to those of ‘free-living’ bacteria