Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Burning Emulations of Condensed Phase Fuels Aboard The International Space Station(2022) Dehghani, Parham; Sunderland, Peter B; Quintiere, James G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Little is known about the fire hazards of solids and liquids in microgravity. Ground-based tests are too short to overcome ignition transients and testing dozens of condensed fuels in orbit is prohibitively expensive. Burning rate emulation is one way to address this gap. It involves emulating condensed fuels with gases using a porous burner with embedded heat flux gages. This is a study of microgravity burning rate emulation aboard the International Space Station. The burner had porous round surfaces with a diameter of 25 mm. The fuel mixture was gaseous ethylene, and it was diluted with various amounts of nitrogen. The resulting heats of combustion were 15 – 47.2 kJ/g. The flow rate, oxygen concentration in the ambient, and pressure were varied. Heat flux to the burner was measured with two embedded heat flux gages and a slug calorimeter. The effective heat of gasification was determined from the heat flux divided by the fuel flow rate. Radiometers provided the radiative loss fractions. A dimensional analysis based on radiation theory yielded a relationship for radiative loss fraction. RADCAL, a narrow-band radiation model, yielded flame emissivities from the product concentrations, temperature, flame length, and pressure. Previously published analytical solutions to these flames allowed prediction of flame heights and radius, and when combined with the radiation empirical relationship led to corrections of total heat release rate from the flames due to radiative loss. Average convective and radiative heat flux were obtained from the analytical solution and a model based on the geometrical view factor of the burner surface with respect to the flame sheet, that was used to calculate the heat of gasification. All flames burning in 21% by volume oxygen self-extinguished within 40 s. However, steady flames were observed at 26.5, 34, and 40% oxygen. The analytical solution was used to quantify flame steadiness just before extinction. The steadiest flames reached more than 94% of their steady-state heat fluxes and heights. A flammability map as a plot of the heat of gasification versus heat of combustion was developed based on the measurement and theory for nominal ambient oxygen mole fractions of 0.265, 0.34, and 0.4.Item DETERMINING ELONGATION AT BREAK OF CABLE INSULATIONS USING CONDITION MONITORING PARAMETERS(2022) Gharazi, Salimeh; Al-Sheikhly, Mohamad; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many United States nuclear power plants are seeking to renew life licenses to extend the operational life of the plant to an additional 20 or 40 years. Degradation of insulation and jacket of cables, which are originally designed for 40 years in the second round of operation, is a critical issue which can impair the safe and reliable function of cables and ultimately the plant. The main criterion for assessing the end of life of these insulations is defined when the elongation at break reaches 50% of its original value. However, measuring the elongation at break is done by tensile tests, which are destructive and need large samples; the feasibility of these tests is significantly limited on installed cables at nuclear power plants. A new model was developed to relate the changes in the activation energy corresponding to EAB in terms of the changes in the activation energies corresponding to non-destructive condition monitoring, NDE-CM, parameters. The coefficients of the model are obtained by normalizing the calculated activation energy of each CM parameter’s changes with the activation energy of EAB changes. Therefore, it is possible to estimate EAB values, in the present developed equations, from the substitution of activation energy corresponding to EAB changes with the correlated activation energy of the non-destructive condition monitoring parameters. Cable Polymer Aging database, C-PAD, which is provided by Electric Power Research Institute, and supported by the U.S. Department of Energy, along with experimental results done in the University of Maryland, UMD, laboratory was used as the database. While taking advantage of C-PAD database which contains condition monitoring parameters of insulation cables such as Elongation at break, Modulus and Density provided by many U.S. and international research institutes, extensive aging experimental results on two cables, each with two grades provided us with not only a database but also a better understanding of the aging mechanism. The published experimental results of cable insulations are used to validate the model. A good fit between the experimental and modeled results confirms the validity of the model.Item Multi-locus phylogenetic analysis of Amphipoda indicates a single origin of the pelagic suborder Hyperiidea(2019) Biancani, Leann M; Cummings, Michael P; Osborn, Karen J; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hyperiidea is an exclusively pelagic suborder of amphipod crustaceans, exhibiting a wide array of unique adaptations to life in the dark, open expanse of the oceanic midwater. No common morphological synapomorphy unites approximately 350 described species. Instead, hyperiid amphipods are defined only by their pelagic existence. Hyperiidea exhibits many of the characteristics of an adaptive radiation and could represent a midwater example of this phenomenon. Previous morphological and molecular analyses have led to uncertainty in the shared ancestry of Hyperiidea. The evolutionary history of their diverse adaptations, as well as their relationship to other amphipods, remains unknown. Here we present results of a multi-locus phylogenetic analysis of publicly available amphipod sequences for three nuclear loci (18S, 28S, and H3) and two mitochondrial loci (COI and 16S) from over 300 amphipod genera, 40 of which are hyperiids. We recover strong support for a monophyletic Hyperiidea as well as reciprocally monophyletic hyperiid infraorders Physocephalata and Physosomata (with enigmatic genera Cystisoma and Paraphronima more closely related to Physosomata). We also identify several benthic, commensal amphipods representing potential sister groups for Hyperiidea. These taxa have not previously been considered close hyperiid relatives and include the genera Amphilochus, Colomastix, Anamixis, Paranamixis, and Leucothoe. Our results support the current definition of Hyperiidea and inform the phylogenetic placement of the suborder within Amphipoda.Item A Method for Measurement of Spatially Resolved Radiation Intensity and Radiative Fraction of Laminar Flames of Gaseous and Solid Fuels(2016) Hamel, Catherine Marie; Stoliarov, Stanislav; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work introduces a new method for determination of the radiation intensity and radiative fraction for axisymmetric laminar diffusion flames for both solid and gaseous fuels by using a modified DSL-R camera employed to collect monochromatic (900 nm) images and a Schmidt-Boelter heat flux gauge. The high spatial resolution provided by the images of the camera allows for a multi-emitter treatment of the 2-6 cm flames. The flame’s radius and intensity are extracted from the images and presented as two curves that are functions of the flame-axis position. Each point on the flame sheet is discretized at pixel-level resolution and treated as a differential emitting surface. Radiation transport equations are formulated and solved numerically to compute a function that relates the camera’s readings to the total radiation heat flux detected by the gauge. The calculation yields spatially resolved radiation intensity information. Integration of this intensity over the flame surface divided by the total heat release rate yields the global radiative fraction. In this work, polyethylene (solid fuel) is studied and three gaseous fuels (methane, propane and acetylene) are studied to validate the methodologyItem Characterization of Luminescent Materials for Application in the Space Environment(2015) Sanders, Michael H.; Sedwick, Raymond; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The medium Earth orbital (MEO) altitudes are greatly underutilized due to the harsh radiation environment. In thinking of alternative ways to work in this environment, luminescent materials are proposed as a replacement or augmentation for power. An investigation into the radiation resilience of some luminescent materials for use in space was undertaken. The results have been integrated into a baseline design for utilizing such materials for power generation via luminescent solar concentrators (LSC) in the space environment. The performance of such a system is compared to that of existing solar cell based power generation. Rhodamine 6G, Fluorescein and Cytodiagnostics Large Stokes Shift 500 dye was used in the radiation experiments. Rhodamine 6G and Fluorescein were chosen due to their well-documented history, while Cytodiagnostics dye was selected to further characterize a non-traditional, potential luminophore. Concentrations of the luminescent materials were mixed with polymer host materials and dissolved in a solvent, then spin coated onto quartz substrates to produce thin film test samples. Absorption and emission measurements were taken and analyzed to determine the materials radiation tolerance. The results showed a good tolerance for Rhodamine 6G while the other materials did not perform as well. To enhance the understanding of the environmental constraints, a thermal simulation was performed to investigate the extreme operating temperatures, and how heating may affect the materials in the power generation system. An interesting trade caused by temperature effects was shown. The solar cell in the LSC system operates at a lower, more efficient temperature, but the luminophores become less efficient from solar heating. The end result is that the overall LSC system efficiency remains fairly constant as the system is heated.Item ESTIMATING SURFACE LONGWAVE RADIATION AND APPLICATIONS TO HIGH LATITUDE ISSUES(2012) Nussbaumer, Eric; Pinker, Rachel T; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Two models, with distinct advantages for calculating downwelling surface longwave (DSLW) radiation under all sky conditions are presented. Both models are driven with a combination of Moderate Resolution Imaging Spectroradiometer (MODIS) level-3 cloud parameters and information from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim model. To compute the clear sky component of DSLW the first model DSLW/UMD v1 utilizes a globally applicable parameterization. The second generation model DSLW/UMD v2 utilizes a two layer feed-forward artificial neural network with sigmoid hidden neurons and linear output neurons. When computing the cloud contribution to DSLW, DSLW/UMD v1 implements a commonly used statistical model to calculate cloud vertical height while in DSLW/UMD v2 the cloud base temperature is estimated by using an independent artificial neural network based on spatially and temporally co- located MODIS and Cloudsat Cloud Profiling Radar (CPR) and the Cloud-Aerosol Lidar and Infrared Pathfiner Satellite Observation (CALIPSO) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. Daily average estimates of DSLW for 2003 to 2009 are compared against ground measurements from the Baseline Surface Radiation Network (BSRN) and show significant improvements over currently available model estimates. DSLW/UMD v2 as optimized for Polar Regions along with a UMD develop shortwave model are used to investigate the role of radiative components in Arctic sea ice anomalies. The correlation between downwelling surface longwave and shortwave radiation and sea ice anomaly for the period from 2003 to 2007 is investigated using the latest Moderate Resolution Imagining Spectroradiometer (MODIS) level-3 cloud parameters and information from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim model. All sky downwelling surface longwave radiation (DSLW), all sky downwelling shortwave radiation (DSSW), all sky total downwelling shortwave and longwave radiation (DSSW + DSLW), and cloud total cloud forcing are individually examined to determine their respective correlation to sea ice anomaly. It is determined that these radiation components are not the primary drivers for major sea ice anomalies that occur during the investigated time frame within the 120o E to 210o E region.Item RADIATIVE FLUXES AND ALBEDO FEEDBACK IN POLAR REGIONS(2011) Niu, Xiaolei; Pinker, Rachel T.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Arctic is experiencing an unprecedented increase in surface temperature and decrease in sea ice extent. Discussion as to the causes that contribute to the Arctic warming is still ongoing. The ice-albedo feedback has been proposed as a possible mechanism for polar amplification of such warming. It states that more open water leads to more solar heat absorption, which results in more ice melting and more open water. In order to study this relationship there is a need for accurate information on the solar heat input into the Arctic Oceans. I have developed and improved inference schemes for shortwave radiative fluxes that respond to the needs of Polar Regions utilizing most recent information on atmospheric and surface states. A Moderate Resolution Imaging Spectroradiometer (MODIS) approach has been optimized for Polar Regions and implemented at 1° for 2002-2010 and at 5-km for 2007. A methodology was developed to derive solar fluxes from the Advanced Very High Resolution Radiometer (AVHRR) and implemented at 0.5° for 1983-2006. Evaluation against ground measurements over land and ocean at high latitudes shows that the MODIS shortwave flux estimates are in best agreement with ground observations as compared to other available satellite and model products, with a bias of -3.6 Wm-2 and standard deviation of 23 Wm-2 at a daily time scale. The AVHRR estimates agree with ground observations with a bias of -4.7 Wm-2 and a standard deviation of 41 Wm-2 at a daily time scale. The ice-albedo feedback was evaluated by computing the solar heating into the Arctic Ocean using the improved satellite flux estimates. A growth at a rate of 2 %/year in the trend of solar heating for 2003-09 was found at a 75 % confidence level; the trend for 1984-2002 was only 0.2 %/year at a 99 % confidence level. The ice retreat is correlated to the solar energy into the ocean at 0.7 at a 75 % confidence level. An increase in the open water fraction resulted in a maximum 300 % positive anomaly in solar heating in 2007 located where the maximum sea ice retreat is.Item Dose and image quality considerations in computed tomography(2011) Abboud, Samir; Kyprianou, Iacovos; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The increased use of Computed Tomography as an imaging modality is of concern because of the growing body of evidence linking radiation exposure to cancer incidence. However, a framework does not yet exist for balancing the immediate needs of the clinical task (image quality) with future risks due to the imaging procedure (dose). We developed a method to estimate the shape and thickness of materials yielding attenuation equivalent to that of bow-tie-shaped filters in clinical scanners. The results are especially useful for accurate modeling in Monte Carlo simulations of radiation transport. We then investigated measures of dose and image quality using both simulation and laboratory experimentation. We found that current measures of dose are robust under current clinical conditions. We also found that measures of image quality are object and task specific.