UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
4 results
Search Results
Item MY TRANS.PARENT WOMB: QUANTUM PLAY, ARTIFICIAL INTELLIGENCE, AND ASEXUAL REGENERATION FROM WITHIN THE US WAR MACHINE(2024) Leizman, Danielle; Collis, Shannon; Art; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)"FROM BENEATH" is a multimedia art installation which offers an immersive experience through three distinct works that act as “wombs.” The work aims to redefine conventional ideas of reproduction and futurity by transforming the gallery space into a realm of sensory exploration and non-linear time. Utilizing devices such as optical illusion, tactile sound, AI generation, and re-animation of archival media, the work advocates for embodiment as a catalyst for a queer navigational strategy which the artist defines as “quantum play.”Item Evaluation of an Additively Manufactured Ferritic-Martensitic Steel for Advanced Nuclear Applications(2018) Vega, Daniel; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A multidisciplinary investigation is presented in which the first known Additively Manufactured (AM) ferritic/martensitic (FM) steel alloys were evaluated for suitability as fast reactor structural components. As AM becomes more mainstream, it offers new possibilities in improving the design and cost of metal parts, especially those with weldability and workability limitations. However, questions remain about AM’s ability to reliably produce the types of high performance ferritic alloys that require carefully tailored microstructures. Laser-based AM produces heating patterns that interfere with the phase transformations from which wrought FM steels derive their ductility, high strength, and creep resistance. Additionally, study of irradiation effects on AM materials is immature. To address these questions, this dissertation presents an analysis of AM Grade 91 steel, an alloy with established pedigree in the nuclear and fossil fuel sectors, and whose ASME code case establishment was the first in a family of creep strength enhanced FM steels. Material from the first known successful AM build of Grade 91 steel was prepared, heat treated, analyzed using microstructural characterization techniques, subjected to a range of mechanical testing (to 600 °C), and irradiated up to 100 dpa with 5 MeV Fe2+ ions. Among the most salient findings were that i) AM material that was subjected to a prescribed normalization heat treatment developed a uniform microstructure and martensite fraction similar to wrought material, ii) normalized and tempered AM material had a similar distribution of carbide precipitates, but finer grain structure than wrought material, iii) AM material was slightly harder and less ductile than wrought material at room temperature, but at 300 °C and 600 °C, their mechanical strength/ductility were virtually the same, iv) AM heat treated material directly built and tested without heat treatments had an unpredictable and heterogeneous microstructure, but that when tensile tested, demonstrated extremely high strength and unexpectedly high ductility, especially at high temperatures, and iv) AM material showed less radiation-induced hardening, due to its fine grain structure. Indications are that AM Grade 91 steel may well be suitable for advanced nuclear applications, and additional research leading to a path forward for certification should be pursued.Item THE DESIGN AND STUDY OF THE SUB-MILLIMETER WAVE LENGTH GYROTRON AND FUNDAMENTAL AND SECOND CYCLOTRON HARMONICS(2015) Pu, Ruifeng; Granatstein, Victor L.; Nusinovich, Gregory S.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation documents research activities directed toward designing high power, high efficiency gyrotrons to operate in the sub-millimeter wavelength region. The gyrotron is to produce pulsed RF power at 670 GHz, with possible application to a novel scheme for detecting concealed radioactive materials. High efficiency is to be achieved by designing a cavity resonator in which the electrons interact with the high-order TE31,8 mode. The choice of resonating mode helps to alleviate Ohmic losses in the cavity walls, and simulation results show that the output efficiency could be more than 30%. The design study takes into account a variety of known effects that could affect efficiency, such as orbital velocity spread, voltage depression and after-cavity interaction. The 670GHz gyrotron was built using the resonator design; operation confirmed that record high efficiency was achieved at an output power level of about 200 kilowatts. In addition, the issue of radial spread in electron guiding centers, which is related to the design of the magnetron injection gun used in the 670GHz gyrotron, was also examined. This spread degrades the interaction between the electrons and the RF field. This often overlooked issue is important for future electron gun designs; this thesis presents analytical methods for estimating how much the degradation affects gyrotron efficiency. The analytical method was verified with numerical simulation, showing that the efficiency's sensitivity to spread in guiding centers is highly dependent on the location of an annular electron beam: when the beam is injected in the inner peak of the desired mode, the radial spread should be kept to less than 1/3 of the RF wavelength. Finally, the dissertation investigates the possibility of further extending the operating parameters of the gyrotron by using the second harmonic of the electron cyclotron resonance. An average output power could be increased by operating the gyrotron continuously rather than in pulses. Using the second cyclotron harmonic allows the magnetic field requirement for resonance condition to be reduced by a factor of two, so that in 670 GHz gyrotrons the pulsed solenoid can be replaced with a cryo-magnet. The investigation shows that for the TE31,8 mode at the second cyclotron harmonic, the operating mode has only one competing mode at the fundamental cyclotron harmonic that could present a mode stability issue. Numerical simulation shows that this mode is TE11,6, the operating mode can suppress this mode, while achieving 20% interaction efficiency. Results also reveal that the resonator for the operating mode at second cyclotron harmonic must be modified to increase the Q-factor. Continuously operating gyrotrons using cryo-magnets have been used for plasma heating in controlled thermonuclear fusion research, albeit at lower frequency than the 670 GHz of the current study.Item Integrated Methodology for Thermal-Hydraulics Uncertainty Analysis (IMTHUA)(2007-01-25) Pour-Gol-Mohamad, Mohammad; Modarres, Mohammad; Mosleh, Ali; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation describes a new integrated uncertainty analysis methodology for "best estimate" thermal hydraulics (TH) codes such as RELAP5. The main thrust of the methodology is to utilize all available types of data and information in an effective way to identify important sources of uncertainty and to assess the magnitude of their impact on the uncertainty of the TH code output measures. The proposed methodology is fully quantitative and uses the Bayesian approach for quantifying the uncertainties in the predictions of TH codes. The methodology also uses the data and information for a more informed and evidence-based ranking and selection of TH phenomena through a modified PIRT method. The modification considers importance of various TH phenomena as well as their uncertainty importance. In identifying and assessing uncertainties, the proposed methodology treats the TH code as a white box, thus explicitly treating internal sub-model uncertainties, and propagation of such model uncertainties through the code structure as well as various input parameters. A The TH code output is further corrected through a Bayesian updating with available experimental data from integrated test facilities. It utilizes the data directly or indirectly related to the code output to account implicitly for missed/screened out sources of uncertainties. The proposed methodology uses an efficient Monte Carlo sampling technique for the propagation of uncertainty using modified Wilks sampling criteria. The methodology is demonstrated on the LOFT facility for 200% cold leg LBLOCA transient scenario.