UMD Theses and Dissertations

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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 given thesis/dissertation in DRUM.

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1/f noise and Luttinger liquid phenomena in carbon nanotubes
(2007-08-03) Tobias, David; Lobb, Christopher; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Carbon nanotubes (CNTs) provide an ideal medium for testing the behavior of one-dimensional electron systems and are promising candidates for electronic applications such as sensors or field-effect transistors. This thesis describes the use of low frequency resistance fluctuations to measure both the properties of the one-dimensional electron system in CNTs, and the sensitivity of CNT devices to their environment. Low frequency noise was measured in CNTs in field effect transistor (FET) geometry. CNTs have a large amount of surface area relative to their volume and are expected to be strongly affected by their environment, leading to speculation that CNTs should have large amounts of 1/f noise. My measurements indicate that the noise level is in the same range as that of traditional FETs, an encouraging result for possible electronic applications. The temperature dependence of 1/f noise from 1.2 K to 300 K can be used to extract the characteristic energies of the fluctuators responsible for the noise. The characteristic energies allows for the elimination of structural and electronic transitions within the CNT itself as possible sources of 1/f noise in CNTs, leaving the motion of defects in the gate dielectric, or possibly strongly physisorbed species, as the likely culprits. Another form of low frequency noise found in CNTs is random telegraph signal (RTS), which manifests as the alternation between two current states at a stable voltage bias. In CNTs, this phenomenon occurs due to the tunneling of electrons into and out of the CNT from a nearby defect, and thus provides a way to probe the tunneling density of states of the CNT itself. The tunneling density of states in turn provides information on the strength of the electron-electron interaction in CNTs. Due to the one-dimensional structure of CNTs their electronic state is expected to be a Luttinger liquid, which should manifest as a power-law suppression of the tunneling density of states at the Fermi energy. The power law exponent is measured in both the temperature dependence and energy dependence of the tunneling rates. In agreement with theory, the power-law exponent is significantly larger in semiconducting CNTs than found in previous experiments on metallic CNTs. The RTS can also be used as a "defect thermometer" to probe the electron temperature of the CNT. The effect of the bias voltage on the electron temperature provides a means to determine the energy relaxation length for the electrons in the CNT.
13 Episodes for String Quartet
(2019) Dizon, Quinn Gareth; Wilson, Mark E; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
13 Episodes for String Quartet is an original composition with an approximate duration of 38 minutes. A dramatic narrative unfolds over a 13-movement arch form as two intervals, a tritone and a perfect fifth, are presented and explored in different harmonic and melodic contexts. As these two opposing forces compete for the foreground, a gradual shift takes place from musical material that is audibly tritone based to material that is audibly perfect fifth based. To help realize the structure and content for this composition, I developed a computational method to generate and parse pitch-class sets based on user supplied interval content and filter criteria. I call this Binary Harmony. In this method, I generate sequences of pitches, where each dyadic adjacency in the sequence forms one of two provided pitch class-intervals. The principal musical material for each movement is generated using this computational method.
13C and 15N Metabolic Flux Analysis on the Marine Diatom Phaeodactylum tricornutum to Investigate Efficient Unicellular Carbon and Nitrogen Assimilation Mechanisms
(2013) Zheng, Yuting; Sriram, Ganesh; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Photosynthesis is indispensable in carbon cycling and obtaining renewable carbon. Operated by cyanobacteria, algae and plants, this process provides reduced carbon and molecular oxygen, consumes atmospheric CO₂ and harnesses solar energy. Photosynthesis is also central to the production of biofuels. Diatoms, a class of marine algae, contribute 20% to 40% of global photosynthetic productivity despite surviving in CO₂-depleted and nitrogen-limited environments. This makes diatoms ideal models to study efficient photosynthetic, specifically carbon concentrating mechanisms (CCM). It has been long debated that whether the unicellular marine diatom Phaeodactylum tricornutum operates a CCM, and whether the CCM is biophysical or biochemical (C4) in nature, with existing (circumstantial) experimental evidence divided amongst the two possibilities. Through isotope labeling experiments (ILE) and metabolic flux analysis (MFA), we provide for the first time significant, direct evidence for a biochemical CCM and the potential combined operation of a biochemical and a biophysical CCM. Additionally, we shed light on how genes regulating this complex process respond to critical environmental variables. Furthermore, we report the use of isotope-assisted metabolic flux analysis to study organic carbon (especially glucose) assimilation in P. tricornutum. Our steady state ILEs reveal glucose assimilation under light and potentially which genes may be responsible for glucose metabolism. We then studied nitrogen (mainly urea) assimilation through instationary 15N and 13C labeling experiments, to find indications of an unusual pathway of urea assimilation. Gene expression trends under various environmental conditions suggest the possible participation of the urea cycle in assimilating nitrogen in P. tricornutum, and how this metabolically differs from nitrate and ammonium assimilation. We anticipate that this work will not only improve understanding of unicellular C4 CCMs, but provide insights to explain the ecological success of diatoms in adapting to challenging environments.
The 1974 Bilingual Education Amendments: Revolution, Reaction or Reform
(1976) Schneider, Susan Gilbert; Baird, Janet R.; Languages, Literatures, & Cultures; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Purpose: The study examined in detail the legislative history of the 1974 Bilingual Education Act, Section 105 of the Education Amendments of 1974, Public Law 93-380. The study examined the roles of Representatives, Senators, lobbyists, judicial decisions, minority groups and Administration officials in developing the 1974 Bilingual Education Act.
1D-CROSSPOINT ARRAY AND ITS CONSTRUCTION, APPLICATION TO BIG DATA PROBLEMS, AND HIGHER DIMENSION VARIANTS
(2022) An, Taeyoung; Oruc, Yavuz A; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Increased chip densities offer massive computation power to deal with fundamental bigdata operations such as sorting. At the same time the proliferation of processing elements (PEs) in settings such as High Performance Computers(HPCs) or servers together with the employment of more aggressive parallel algorithms cause the interprocessor communications to dominate the overall computation time, potentially resulting in reduced computational efficiency. To overcome this issue, this dissertation introduces a new architecture that uses simple crosspoint switches to pair PEs instead of a complex interconnection network. This new architecture may be viewed as a “quadratic” array of processors as it uses O(n^2) PEs rather than O(n) as in linear array processor models. In addition, three different models for sorting big data in a distributed com- puting environment such as Cloud computing are presented. With the most realistic model of the three, we demonstrate that the high parallelism made possible by the simple communication channels overcomes the seemingly excessive hardware complexity and performs comparable to or better than existing algorithms. Furthermore, two additional algorithms of matrix multiplica- tion and triangle counting for the 1D-Crosspoint Array are introduced and analyzed. Lastly, two higher dimensional variants, 2D- and 3D-Crosspoint Array are also proposed with a construction method, which succeeds in reducing the number of PEs required by utilizing the communication channels in the added dimensions.
2-DIMENSIONAL ZEOLITES FOR ADSORPTIVE DESULFURIZATION
(2018) Fang, Jingyu; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The removal of sulfur-containing compounds from transportation fuels is of growing urgency due to the increasingly government stringent regulations. Adsorptive desulfurization at ambient conditions is a promising strategy for sulfur-containing compound removal compared to traditional hydrodesulfurization (HDS) that requires high temperature and pressure. In this thesis, we studied zeolite adsorbents for adsorptive desulfurization of model fuels. Three zeolite frameworks (MFI, MWW and FAU) in both 2-dimensional (2D) and 3D structures were synthesized and ion-exchanged to both proton-form and Ag+-form. The adsorption of thiophene and benzothiophene, respectively, in n-octane was done using both H+- and Ag+-form zeolites in both 2D and 3D structures. The results show that 2D zeolites have high adsorption capacity than 3D analogues in removal of benzothiophene. The Ag+-form zeolites increase the adsorption capacity compared with that of H+-form. In terms of zeolite framework effects, MWW zeolites possesses the highest adsorption capacity.
A 20-YEAR CLIMATOLOGY OF GLOBAL ATMOSPHERIC METHANE FROM HYPERSPECTRAL THERMAL INFRARED SOUNDERS WITH SOME APPLICATIONS
(2022) Zhou, Lihang; Warner, Juying; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Atmospheric Methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2), and accounts for approximately 20% of the global warming produced by all well-mixed greenhouse gases. Thus, its spatiotemporal distributions and relevant long-term trends are critical to understanding the sources, sinks, and global budget of atmospheric composition, as well as the associated climate impacts. The current suite of hyperspectral thermal infrared sounders has provided continuous global methane data records since 2002, starting with the Atmospheric Infrared Sounder (AIRS) onboard the NASA EOS/Aqua satellite launched on 2 May 2002. The Cross-track Infrared Sounder (CrIS) was launched onboard the Suomi National Polar Orbiting Partnership (SNPP) on 28 October 2011 and then on NOAA-20 on 18 November 2017. The Infrared Atmospheric Sounding Interferometer (IASI) was launched onboard the EUMETSAT MetOp-A on 19 October 2006, followed by MetOp-B on 17 September 2012, then Metop-C on 7 November 2018. In this study, nearly two decades of global CH4 concentrations retrieved from the AIRS and CrIS sensors were analyzed. Results indicate that the global mid-upper tropospheric CH4 concentrations (centered around 400 hPa) increased significantly from 2003 to 2020, i.e., with an annual average of ~1754 ppbv in 2003 and ~1839 ppbv in 2020. The total increase is approximately 85 ppbv representing a +4.8% change in 18 years. More importantly, the rate of increase was derived using satellite measurements and shown to be consistent with the rate of increase previously reported only from in-situ observational measurements. It further confirmed that there was a steady increase starting in 2007 that became stronger since 2014, as also reported from the in-situ observations. In addition, comparisons of the methane retrieved from the AIRS and CrIS against in situ measurements from NOAA Global Monitoring Laboratory (GML) were conducted. One of the key findings of this comparative study is that there are phase shifts in the seasonal cycles between satellite thermal infrared measurements and ground measurements, especially in the middle to high latitudes in the northern hemisphere. Through this, an issue common in the hyperspectral thermal sensor retrievals were discovered that was unknown previously and offered potential solutions. We also conducted research on some applications of the retrieval products in monitoring the changes of CH4 over the selected regions (the Arctic and South America). Detailed analyses based on local geographic changes related to CH4 concentration increases were discussed. The results of this study concluded that while the atmospheric CH4 concentration over the Arctic region has been increasing since the early 2000s, there were no catastrophic sudden jumps during the period of 2008-2012, as indicated by the earlier studies using pre-validated retrieval products. From our study of CH4 climatology using hyperspectral infrared sounders, it has been proved that the CH4 from hyperspectral sounders provide valuable information on CH4 for the mid-upper troposphere and lower stratosphere. Future approaches are suggested that include: 1) Utilizing extended data records for CH4 monitoring using AIRS, CrIS, and other potential new generation hyperspectral infrared sensors; 2). Improving the algorithms for trace gas retrievals; and 3). Enhancing the capacity to detect CH4 changes and anomalies with radiance signals from hyperspectral infrared sounders.
20th Century French Oboe Repertoire from Two Groups of Composers: "Le Triton and "Le Jeune France"
(2006) Kim, Yeong Su; Hill, Mark; Music; University of Maryland (College Park, Md.); Digital Repository at the University of Maryland
21st CENTURY AMERICAN TRUMPET SONATAS: THE PERFORMANCE PRACTICE AND PEDAGOGICAL INFLUENCES OF FOUR SONATAS
(2024) Rudy, Brennan; Gekker, Paul C; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Sonatas for trumpet and piano have played an impactful role in the development of the trumpet as a recital instrument. Thorvald Hansen’s 1903 sonata for cornet and piano was the earliest sonata for our instrument, later leading to the first two sonatas for the Bb trumpet and piano in 1939 by German composer Paul Hindemith and Soviet composer Boris Asafiev. The first American sonata for trumpet and piano was written by Harold Shapero in 1940 and was dedicated to his teacher, Aaron Copland. These early sonatas led to other prominent 20th Century trumpet sonatas that were written by American composers Kent Kennan, Halsey Stevens, and Eric Ewazen. As a modern solo instrument, performance and pedagogical practices for the trumpet are strongly based on compositions of the 20th Century or earlier. As we are now almost 25 years into the 21st Century, trumpet sonatas and their composers have continued to evolve and create a lasting impact on the use of the trumpet and its pedagogy. This dissertation will discuss the pedagogical impacts and musical developments of several 21st Century sonatas for trumpet and piano. Accompanying this dissertation are four recordings of some of the most recently published trumpet sonatas from 2015-2023, each by American composers of diverse backgrounds. The four recorded sonatas previously had very few or no professional recordings and exemplify modern developments on traits originally established by composers of early trumpet sonatas. Through this dissertation and accompanying recordings, I hope to encourage the use of modern trumpet sonatas for application in pedagogical instruction, performances, and college and university juries and entrance auditions.
The 25th Year
(2023) Bronson Boddie, Sebastian; Weiner, Joshua; Creative Writing; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
THE 25TH YEAR is a collection that seeks to understand what it means to bear witness. Cataloging their environment is how the speaker reconciles their fraught reality, making sense of the disorder of living. This disorder is reflected in the form of the work, as most of the poems are in free verse, with occasional variation. The poems in this collection explore themes of memory, community, and ordinary human kindness – and meditate on how powerful the practice of witness can be. In the tradition of Baldwin, Baudelaire, and the flâneur, the speaker observes what can often be missed, in order to connect to their community and themselves.
THE 3' UTR OF TURNIP CRINKLE VIRUS INTERACTS LOCALLY AND DISTALLY TO REGULATE TRANSCRIPTION AND TRANSLATION OF THE VIRUS
(2012) Young, Megan Yoke Len; Simon, Anne E; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Turnip crinkle virus (TCV) is a 4054 b positive-strand RNA virus of the genus Carmovirus in the Family Tombusviridae. Upon entry into cells, TCV is translated using host translational machinery to produce its RNA-dependent RNA polymerase (RdRp). The RNA is proposed to undergo a conformational rearrangement, mediated by recruitment of the RdRp to the 3' ends of the viral RNA, which represses translation and promotes negative-strand synthesis. A second RNA switch is proposed to occur that inhibits minus-strand synthesis and promotes recruitment of the RdRp to the 3' ends of negative-strands for the asymmetrical production of positive-strands. Within the 3' UTR of TCV is a tRNA-shaped structure (TSS) that is capable of binding ribosomes and overlaps with structures necessary for translational enhancement. The RdRp has been shown to bind within this region and result in a widespread conformational shift. The binding of RdRp to the 3' end of the virus is very sensitive to perturbations of sequence or structure, with many mutations resulting in non-specific binding of the RdRp. The elements within the 3' UTR have been shown to be very interactive with alterations affecting the structure of regions hundreds of bases away. A second-site mutation study indicated that regions upstream of the 3' UTR may also be interacting with the 3' UTR. Some second-site mutations located in this upstream region were found to increase accumulation in protoplasts and additional studies are under way to explain this phenomenon. The 3' viral contribution in a luciferase reporter construct was increased to incorporate the second-site mutations. While the second-site mutations had little effect on translation, it was surprising to find that extension of the viral 3' sequence enhanced translation. Translational enhancement was mapped to just an additional twenty bases and further study revealed that a hairpin (H3) is important for viral translation and accumulation and may also be interacting with the 3' UTR.
3-alkyl-[delta](2)-cyclohexenones and m-dialkylbenzenes
(1951) Plapinger, Robert Edwin; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
30+ YEARS OF LAND COVER AND LAND USE CHANGE IN SOUTH AMERICA
(2020) Zalles Ballivian, Viviana; Hansen, Matthew C.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The modification of the Earth’s surface constitutes the most impactful way in which humans affect their surrounding environment, with broad and lasting consequences. Changes in land cover accelerate biodiversity loss, contribute to climate change, and affect the provisioning of ecosystem services. Such negative environmental impacts can have important effects on human health and livelihoods. The South American continent, in particular, has undergone significant transformations over the past decade, due in large part to the conversion of natural land to more economically productive land uses, such as crops, pastures, and tree plantations. The agricultural commodities produced in South America are traded and consumed globally, and land will likely continue to be converted if demand for these commodities continues to rise. Despite the environmental and commercial importance of land cover and land use change dynamics in South America, the extent and rates of land change have not yet been thoroughly characterized and quantified. This dissertation aims to advance scientific knowledge on the extent and rates of change of important land covers and land uses, especially as they relate to the production of agricultural commodities, by leveraging the 34-year Landsat archive of Earth observation data. The general approach employed throughout follows a two-step process of mapping and sampling, in order to provide spatially explicit information on the patterns of land cover/land use change, as well as associated unbiased area estimates. This approach is first employed for the use-case of Brazilian cropland expansion from 2000 to 2014, and results show a near doubling of cropland area, the majority of which (80%) came about through the conversion of existing pastures. The methodology is then repeated at broader thematic, temporal, and geographic scales, resulting in area estimates of changes in cropland, pasture, plantation, natural tree regrowth, semi-natural land, tree cover and degraded tree cover from 1985 to 2018. Altogether, these changes amount to a 60% increase in human impact on natural land over the study period. Finally, an analysis and evaluation of the methodology employed for mapping and sampling when there is a multitude of target classes instead of a single one is provided as an assessment of methodological approaches.
3D ENGINEERING OF VIRUS-BASED PROTEIN NANOTUBES AND RODS: A TOOLKIT FOR GENERATING NOVEL NANOSTRUCTURED MATERIALS
(2018) Brown, Adam Degen; Culver, James N; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Technological innovation at the nanometer scale has the potential to improve a wide range of applications, including energy storage, sensing of environmental and medical signals, and targeted drug delivery. A key challenge in this area is the ability to create complex structures at the nanometer scale. Difficulties in meeting this challenge using traditional fabrication methods have prompted interest in biological processes, which provide inspiration for complex structural organization at nanometer to micrometer length scales from self-assembling components produced inexpensively from common materials. From that perspective, a system of targeted modifications to the primary amino acid structure of Tobacco mosaic virus (TMV) capsid protein (CP) has been developed that induces new self-assembling behaviors to produce nanometer-scale particles with novel architectures. TMV CPs contain several negatively charged carboxylate residues which interact repulsively with those of adjacent CP subunits to destabilize the assembled TMV particle. Here, the replacement of these negatively charged carboxylate residues with neutrally charged or positively charged residues results in the spontaneous assembly of bacterially expressed CP into TMV virus-like particles (VLPs) with a range of environmental stabilities and morphologies and which can be engineered to attach perpendicularly to surfaces and to display functional molecular patterns such as target-binding peptide chains or chemical groups for attachment of functional targets. In addition, the distinct electrostatic surface charges of these CP variants enable the higher-level coassembly of TMV and VLP into continuous rod-shaped nanoparticles with longitudinally segregated distribution of functionalities and surface properties. Furthermore, the unique, novel, environmentally responsive assembly and disassembly behaviors of the modified CPs are shown to act as simple mechanisms to control the fabrication of these hierarchically structured functional nanoparticles.
3D Fast Geometric Collision Avoidance Algorithm (FGA) and Decision-Making Approach based on the Balance of Safety and Cost for UAS
(2021) lin, zijie; Xu, Mumu; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Unmanned Aircraft System (UAS) is a fast-growing industry with extensive economic implications and would be integrated into the national airspace system (NAS), which requires UAS to have the efficient sense and avoidance capability. This thesis develops a fast geometry-based algorithm FGA which shortens the collision avoidance computation time, path length and balances the probability of safety and energy cost by calculating and giving UAS proper selective avoidance starting time tc, meaning the last possible point for the UAS to avoiding the potential threaten and itis based on the UAS kinematic, conflicts likelihood map, and navigation constraints. This operation enables the update path to be as close as possible to the UAVs resume designed path, decreasing the length of path variation and the corresponding time cost. In comparison to a current geometry method, the sampling-based method and the search algorithm, the FGA algorithm shows 40% to 90% of reduction in computational time and length of path for the same obstacle avoidance scenarios. Quantitative analysis of the efficiency by different avoiding trigger times is also provided. FGA with critical avoidance time tc not only could improve the geometry methods, but also could be used for (1) research on the bounds of general geometry based collision avoidance, and (2) solving the multiple obstacles avoidance problem.For a scenarios with crowded obstacles which cannot be avoided at the same time, an applicable algorithm for obstacles classification is provided. It divides the obstacles into small groups with different urgent levels by their critical avoidance trigger time tc, and then avoids them in sequence. Simulation validates the efficiency of this application. Extremely difficult obstacle avoidance such as the UAV working under maneuver limitation and the obstacles are time-variant are discussed and solved in the following chapters. Monte Carlo simulation, statistical method and Machine learning algorithms especially the supervised logistic learning methods are implemented later to analyze the weight of the factors such as sensor detection distance, ratio of the speed, number of obstacles, which have impacts on the geometric based obstacle avoidance methods. Finally, flight missions in an aircraft simulator and the hardware fixed-wing aircraft experiments validate the algorithm effectiveness with successful results.
3D IMAGE ANALYSIS OF CT DATA OF CONCRETE CYLINDER SUNDERGOING DELAYED ETTRINGTIE FORMATION
(2019) Shi, Kuo; Amde, Amde M; Livingston, Richard A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The strains in a concrete caused by delayed ettringite formation (DEF) are conventionally expressed in terms of the one-dimensional linear expansion. However, concrete is not a homogeneous material, and differences in the volume change between the inert aggregates and the reactive cement paste will produce variations in local displacements that cannot be detected by the linear expansion variable. With CT slices offered by Simultaneous neutron and X-ray computed tomography (SNXCT), this thesis applies image analysis algorithms to quantify the distortion of cylinder over time due to delayed ettringite formation. The research reported in this thesis concerned the development of several MATLAB programs to apply image analysis algorithms to quantify the distortion of cylinder over time in terms of summary variables. These included mean radial expansion, deviation from circularity, vertical tilt angle and rotation, void area fraction and the displacement of microbead internal reference points.
3D Integration, Temperature Effects, and Modeling
(2005-05-02) Parker, Latise; Goldsman, Neil; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Practical limits to device scaling are threatening the growth of integrated circuit (IC) technology. A breakthrough architecture is needed in order to realize the increased device density and circuit functionality that future high performance ICs demand. 3D integration is being considered as this breakthrough architecture. In this thesis, the limits to scaling are noted and the feasibility of overcoming these limits using 3D integration is presented. The challenges and considerations, most notably dangerously high chip temperatures, are provided. To address the temperature concern, a mixed-mode simulator that calculates temperature as a function of position on chip is detailed. The simulator captures the important link between individual device and full chip heating. Lastly, circuit simulations and lab experiments are performed to experimentally validate the claims that differences in device activity on chip leads to dangerously high local and overall chip temperatures.
3D Ionospheric Effects on HF Propagation and Heating
(2015) Zawdie, Katherine A.; Papadopoulos, Konstantinos; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The thesis uses a three-dimensional, first-principles model of the ionosphere in combination with High Frequency (HF) raytracing model to address key topics related to the physics of HF propagation and artificial ionospheric heating. In particular: 1. Explores the effect of the ubiquitous electron density gradients caused by Medium Scale Traveling Ionospheric Disturbances (MSTIDs) on high-angle of incidence HF radio wave propagation. Previous studies neglected the all-important presence of horizontal gradients in both the cross- and down-range directions, which refract the HF waves, significantly changing their path through the ionosphere. The physics-based ionosphere model SAMI3/ESF is used to generate a self-consistently evolving MSTID that allows for the examination of the spatio-temporal progression of the HF radio waves in the ionosphere. 2. Tests the potential and determines engineering requirements for ground- based high power HF heaters to trigger and control the evolution of Equatorial Spread F (ESF). Interference from ESF on radio wave propagation through the ionosphere remains a critical issue on HF systems reliability. Artificial HF heating has been shown to create plasma density cavities in the ionosphere similar to those that may trigger ESF bubbles. The work explores whether HF heating may trigger or control ESF bubbles. 3. Uses the combined ionosphere and HF raytracing models to create the first self-consistent HF Heating model. This model is utilized to simulate results from an Arecibo experiment and to provide understanding of the physical mechanism behind observed phenomena. The insights gained provide engineering guidance for new artificial heaters that are being built for use in low to middle latitude regions. In accomplishing the above topics: (i) I generated a model MSTID using the SAMI3/ESF code, and used a raytrace model to examine the effects of the MSTID gradients on radio wave propagation observables; (ii) I implemented a three- dimensional HF heating model in SAMI3/ESF and used the model to determine whether HF heating could artificially generate an ESF bubble; (iii) I created the first self-consistent model for artificial HF heating using the SAMI3/ESF ionosphere model and the MoJo raytrace model and ran a series of simulations that successfully modeled the results of early artificial heating experiments at Arecibo.
3D Magnetic Imaging using SQUIDs and Spin-valve Sensors
(2016) Jeffers, Alex; Wellstood, Frederick C; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
We have used 2 µm by 4 µm thin-film Cu-Mn-Ir spin-valve sensors and high Tc YBa2Cu3O7-x dc SQUIDs to take magnetic images of test samples with current paths that meander between 1 and 5 metallization layers separated by 1 µm to 10 µm vertically. I describe the development and performance of a 3D magnetic inverse for reconstructing current paths from a magnetic image. I present results from this inverse technique that demonstrate the reconstruction of the 3D current paths from magnetic images of samples. This technique not only maps active current paths in the sample but also extracts key parameters such as the layer-to-layer separations. When imaging with 2 µm by 4 µm spin-valve sensors I typically applied currents of 1 mA at 95 kHz and achieved system noise of about 200 nT for a 3 ms averaging time per pixel. This enabled a vertical resolution of 1 µm and a lateral resolution of 1 µm in the top layers and 3 µm in the bottom layer. For our roughly 30 µm square SQUID sensors, I typically applied currents of 1 mA at 5.3 kHz, and achieved system noise of about 200 pT for a 3 ms averaging time per pixel. The higher sensitivity compared to the spin-valve sensor allowed me to resolve more deeply buried current paths.
3D Multimodal Image Registration: Application to equine PET and CT images
(2017) Regani, Sai Deepika; Chellappa, Rama; Beylin, David; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Positron Emission Tomography (PET) is being widely used in veterinary medicine in recent years. Although it was limited to small animals because of its classical design and the large amount of radionuclide doses required, PET imaging in horses became possible with the introduction of a portable PET scanner developed by Brain Biosciences Inc. It was observed that this new modality could capture abnormalities like lesions that Computed Tomography (CT), Magnetic Resonance Imaging (MRI) and other modalities could not. Since 2016, PET imaging in horses is being studied and analysed. While PET provides functional information characterizing the activity of lesions, it is useful to combine information from other modalities like CT and match the structural information to develop an accurate spatial representation of the data. Since biochemical changes occur much earlier than structural changes, this helps detect lesions and tumours during the early stages. Multimodal image registration is used to achieve this goal. A series of steps are proposed to automate the process of registration of equine PET and CT images. Multimodal image registration using landmark-based and intensity-based techniques are studied. It is observed that a few tissues are not imaged in the PET, which makes image segmentation, an important preprocessing step in the registration process. A study of the segmentation algorithms relevant to the field of medical imaging is presented. The performance of segmentation algorithms improved with the extent of manual interaction and intensity-based registration gave the smallest time complexity with reasonable accuracy.

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