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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item INTEGRATION OF SUPERCONDUCTORS INTO WIDE BANDGAP SEMICONDUCTOR ENVIRONMENTS FOR DEPLOYABLE SINGLE PHOTON DETECTORS(2024) Drechsler, Annaliese Grace; Christou, Aristos; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Superconducting nanowire single photon detectors (SNSPDs) are the photon detecting devices of the future. These devices offer exceptional detecting capabilities over a wide range of wavelengths, which will enable next generation systems for optical communications, light detection and ranging, quantum key decryption, and astronomy among others. There are substantial materials, fabrication, and device development challenges that need to be addressed before these devices are ready for large scale deployment in arrays. This dissertation demonstrates novel approach to SNSPD development by monolithically integrating superconducting materials with wide bandgap semiconductor systems to scale these devices. Specifically, this work explores the integration of niobium nitride (NbN) with multi-channel aluminum gallium nitride (AlGaN)/gallium nitride (GaN) superlattice devices to leverage the benefits of materials similarity and lattice matching to provide high quality detector performance in the proposed system. The multichannel superlattice device selected for this work, the superlattice castellated field effect transistor (SLCFET) utilizes a novel δ-doping approach to generate conducting channels. Epitaxial structures were studied between 300K and 4K. This structure exhibits a substantial reduction in epitaxial resistance, determined to be a result of mobility improvement to 4151.5 cm2/Vs through Hall effect analysis. Phonon scattering modelling indicates that the device is limited by polar optical phonon scattering at high temperatures and interface roughness between the channels at cryogenic conditions. Field effect transistors fabricated from this epitaxial structure were tested and shown to exhibit exceptionally high performance at low temperatures, proving feasibility of device integration. A production-scalable NbN deposition process was developed for SNSPD fabrication. Thorough analyses determined the relationship between deposition parameters and the resultant crystallinity, defectivity, and surface morphology. Analysis of ultra-thin films determined that the NbN films grow through a step-flow growth mechanism. This data was used to develop a temperature-dependent empirical model of the kinetics of the surface morphology and growth mechanism evolution based on the Avrami equation. Fabrication processes were developed using these films to pattern SNSPDs with narrow linewidths down to 50 nanometers composing the meander structure for long wavelength performance. Thorough analysis of the impact of electron beam lithography write conditions were conducted to propose ideal fabrication conditions. Methods were proposed and implemented to address defectivity by reducing the impact of elasto-capillary forces on line collapse including chemical surface modification using hexamethyldisilazane and resist thinning using polymethyl methacrylate (PMMA) and ZEP and implementing charge dissipation layers. Additional processes were proposed and implemented to enable integration into the SLCFET fabrication flow. The SLCFET devices and NbN structures were tested and determined to be functional, thus demonstrating the feasibility of integration. An initial integrated device was designed and modelled by combining a SLCFET with NbN SNSPDs, using the RF output as a readout approach. The devices were successfully fabricated using the processes developed within this dissertation. Testing of the devices showed a 30dB signal difference between the normal and detecting states, thus demonstrating the first device of its kind, representing a substantial contribution to the field. This will open the door for full-scale array development using novel on and off chip signal processing approaches proposed in this work.Item SOCIAL URBANISM IN MEDELLIN – INTEGRATION OF LANDSCAPE, LIFE, AND CULTURE(2023) Farieta, Maria Fernanda; Matthews, Georgeanne; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over the last 50 years, the city of Medellín, Colombia has experienced a drastic urban transformation. The drug war and armed conflict in the late 20th century expedited urbanization as people were forced to leave their rural homes and seek shelter in major cities. However, the infrastructural capacity of larger cities has been unable to accommodate the basic needs of the growing population. As a result, people had to build habitats in the peripheries of the cities. These “informal settlements” were born out of necessity, with limited resources, and often under unsafe conditions. Nonetheless, these self-built neighborhoods are “the most common form of urbanization on the planet,” and as such, the processes behind “informal city making” are key to understanding the potential for development, innovation, and integration of a city. This paradigm shift regarding informality intends to bring visibility to the perseverance and creativity of migrants under limited resources, to challenge policies that shape urbanization and to explore alternative methods to address population growth.Item A New Chapter...Refugee Housing: From Enclave to Hub(2020) Neugebauer Peters, Taina; Williams, Joseph C.; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ref.u.gee (noun): “A person who has been forced to leave their country in order to escape war, persecution, or natural disaster.” 30,000 refugees were resettled to the United States in 2019. Coming from countries all around the world, refugees experience the tough reality of leaving their homes in search of a better life in a distant and unfamiliar place. With little knowledge and understanding of new customs, many struggle to establish daily routines and complete simple tasks. Resettlement Agencies also struggle to find adequate accommodations, especially in California, where the current housing crisis has led to a shortage of affordable housing. This thesis proposes an affordable housing model that facilitates refugee integration into new communities by providing housing options that meet their needs as well as community spaces that educates and promotes cultural diversity throughout the greater urban community.Item SysML Executable Model of an Energy Efficient House and Trade-Off Analysis(2018) Cawasji, Kersasp Aspi; Baras, John S.; Systems Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the growing complexity of energy efficient buildings, the methods of modeling and simulating such structures must account for monitoring several thousand design parameters across multiple diverse domains. As a result, modeling tools are now very specific to their respective domains and are growing more and more incongruous with each other. This calls for a way to integrate multiple modeling tools in the effort to create a single, large model capable to encapsulate data from multiple, different models. Thus, in this thesis, different methods to perform an integration with Systems Modeling Language (SysML) and a simulation tool were identified, described and evaluated. Then, a new method was developed and discussed. Finally, the new method was demonstrated by developing a SysML executable model of a simple two-room house that utilizes solar power for space heating, with a heat pump used as a backup. Using the Functional Mock-up Interface (FMI) standard, the SysML model is integrated with a Modelica model, and a simulation is run in Simulink. Finally, a tradeoff analysis was performed for the purpose of design space exploration.Item Development and Integration of Tactile Sensing System(2018) Agarwal, Rishabh; Bergbreiter, Sarah; Systems Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To grasp and manipulate complex objects, robots require information about the interaction between the end effector and the object. This work describes the integration of a low-cost 3-axis tactile sensing system into two different robotic systems and the measurement of some of these complex interactions. The sensor itself is small, lightweight, and compliant so that it can be integrated within a variety of end effectors and locations on those end effectors (e.g. wrapped around a finger). To improve usability and data collection, a custom interface board and ROS (Robot Operating System) package were developed to read the sensor data and interface with the robots and grippers. Sensor data has been collected from four different tasks: 1. pick and place of non-conductive and conductive objects, 2. wrist-based manipulation, 3. peeling tape, and 4. human interaction with a grasped object. In the last task, a closed loop controller is used to adjust the grip force on the grasped object while the human interacts with it.Item The Power of Synthesis: the Pursuit of Environmental Sustainability and Social Equity Through Design Practice(2017) Kedar, Boaz Ahi Omri; Rockcastle, Garth C; Howeland, Marie; Urban and Regional Planning and Design; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The paradigm of architecture and design is changing. Centuries of industrialization and rapid urbanization have placed profound stress on the earth’s natural systems, presenting new challenges for architects and urban planners. As our collective awareness towards these challenges increases, designers are increasingly called upon to partake in the global transition towards a low-carbon future. These professionals are re-assessing their priorities and practices, striving for better ecological and social scenarios. This dissertation explores how architects and designers successfully integrate environmental sustainability and social equity deliberations into architectural design practice by implementing more holistic sustainable design approaches. It advocates for a future reality where these considerations are naturally incorporated into the design process of any architectural project, and suggests a framework for their more effective integration. The dissertation opens with a review of current sustainable design approaches and practices in the architectural design profession, focusing on the tools and methods commonly used for their integration in the design process. Next, it presents three case studies of exemplary architectural projects, each demonstrating a progressive design approach that successfully integrates both environmental and social sustainability agendas within the design process. Data collection methods included a series of semi-structured interviews with designers, architects, developers, clients and other stakeholders in the respective projects, as well as site visits. In each case study project, the process of its inception, development, settings, and design methodologies were explored, aiming to evaluate the potentialities and effectiveness of these attributes for better integration of socially and environmentally sustainable design agendas. Synthesis of the collected data ultimately offers a framework for more effective integration of these virtues within architectural design processes. The conclusions point to a multivariate threshold containing a combination of external conditions, recommended processes and design-based tactics to achieve such projects. The conclusions underscore the method for application of these factors, not as isolated deliberations but as parts of a holistic, integrated process. When applied concurrently, these factors perform synergistically to produce holistic, well-rounded living environments that foster environmental stewardship alongside social and cultural wellbeing, empowering a community to flourish.Item Factors that Influence Technology Integration in the Classroom(2017) Montgomery, Maureen Cathryn; McLaughlin, Margaret J; Richardson, Patricia M; Education Policy, and Leadership; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Education is one area where the use of technology has had great impact on student learning. The integration of technology in teaching and learning can significantly influence the outcome of education in the classroom. However, there are a myriad of factors that influence technology integration in the classroom. The purpose of this study was to investigate the variation of teacher integration of technology into classroom instruction. Factors that teachers perceive as being the most influential will be analyzed. The investigation also serves to inform school leaders about specific ways to ensure maximum use of instructional technology by all staff members. The study involved a comprehensive high school centrally located in a suburban county in Maryland with an on-time graduation of above 95%. This study surveyed 49 teachers who are employed at this high school and represent various years’ experience. Their teaching assignments range from standard level to advanced placement courses in one of the following content areas: English, science, social studies, or math. The research design in this study is quantitative in nature and was conducted through an on-line anonymous, eleven question survey using the Qualtrics platform. A total of 44/49 participants, or 90%, provided responses to all of the questions asked on the anonymous survey. Results indicated that content, grade, skill level of student, and years’ experience had no effect on the integration of technology in the classroom as 84% reported daily integration. Smart Boards and Laptops were the most frequently used while responders/clickers and the document camera were the least frequently used. Teachers reported using the Internet to develop lessons, Moodle, and video clips from the Internet were the most common uses of technology. Furthermore, results indicated that personal interest, availability, and professional development had the greatest influence over a teacher’s decision to integrate technology.Item REFUGEES AND RESETTLEMENT: A QUALITATIVE ANALYSIS OF REFUGEE INTEGRATION THROUGH SOCIAL & SUPPORT SERVICES(2016) Enekwe, Blessing; McIntosh, Wayne; Government and Politics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation studies refugee resettlement in the United States utilizing the Integration Indicator’s framework developed by Ager and Strang for the U.S. context. The study highlights the U.S. refugee admissions program and the policies in the states of Maryland and Massachusetts while analyzing the service delivery models and its effects on refugee integration in these locations. Though immigration policy and funding for refugee services are primarily the domain of the federal government, funds are allocated through and services are delivered at the state level. The Office of Refugee Resettlement (ORR), which operates under the Department of Health and Human Services, was established after the Refugee Act of 1980 to deliver assistance to displaced persons. The ORR provides funds to individual states primarily through The Refugee Social Service and Targeted Assistance Formula Grant programs. Since the inauguration of the ORR three primary models of refugee integration through service delivery have emerged. Two of the models include the publicly/privately administered programs, where resources are allocated to the state in conjunction with private voluntary agencies; and the Wilson/Fish Alternative programs, where states sub-contract all elements of the resettlement program to voluntary agencies and private organizations —in which they can cease all state level participation and voluntary agencies or private organizations contract directly from the ORR in order for all states to deliver refugee services where the live. The specific goals of this program are early employment and economic self-sufficiency. This project utilizes US Census, state, and ORR data in conjunction with interviews of refugee resettlement practitioners involved in the service delivery and refugees. The findings show that delivery models emphasizing job training, English instruction courses, institutional collaboration, and monetary assistance, increases refugee acclimation and adaptation, providing insight into their potential for integration into the United States.Item Integration of SysML with Trade-off Analysis Tools(2012) Spyropoulos, Dimitrios; Baras, John S.; Systems Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Changes in technology, economy and society create challenges that force us to rethink the way we develop systems. Model-Based Systems Engineering is an approach that can prove catalytic in this new era of systems development. In this work we introduce the concept of the modeling "hub" in order to realize the vision of Model-Based Systems Engineering and especially we focus on the trade-off analysis and design space exploration part of this "hub". For that purpose the capabilities of SysML are extended by integrating it with the trade-off analysis tool Consol-Optcad. The integration framework, the implementation details as well as the tools that were used for this work are described throughout this thesis. The implemented integration is then applied to analyze a very interesting multi-criteria optimization problem concerning power allocation and scheduling of a microgrid.Item African American Women's Politics, Organizing, and Activism in 1920s-Washington, D.C.(2012) Murphy, Mary-Elizabeth Bradley; Barkley Brown, Elsa; History; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation offers a social history of African American women's political activism and organizing in 1920s-Washington, D.C. Specifically, I examine the ways that black women worked to reform the school system, protested segregation in the offices of the federal government and neighborhoods, fought for the passage of an anti-lynching law, formed Republican organizations, upheld African American citizenship through commemoration, and recruited more than one thousand women and men to join a labor union, the National Association of Wage Earners. I argue that black women in 1920s-Washington, D.C., reached into the knowledge and skills they derived from black institutional culture, from their location in the city, from their work experiences, friendships, and family life to organize their campaigns and participate in politics. Black institutional culture formed a bridge to women's formal political activism. As churchgoers, dues-paying members of fraternal orders, fundraisers for the Young Women's Christian Association (YWCA), or participants in social clubs, African American women developed important skills, including fundraising, publicity, and public speaking, which they applied to their more overtly political campaigns. Locating the origins of African American women's political campaigns and organizations within black institutions helps to explain how black women were sometimes able to mobilize hundreds of foot soldiers in a short period of time. Personal experiences also mattered tremendously in women's political activism. Stories and memories passed along from family and friends inspired African American women to wage their wide-ranging campaigns for justice. During the 1920s, black women in ways both large and small, individual and collective--from walking through the streets to recruit members to a labor organization to raising money for a YWCA organizing drive, from marching through the streets in support of anti-lynching bill, to staging protests in front of the Board of Education building--organized to sustain their communities, reform their city, and enact democracy in Washington and throughout the nation. This dissertation relies on a range of sources, including organizational records, personal papers, black and white newspapers, social scientific studies, government documents, court cases, oral histories, Sanborn maps, city directories, and the manuscript census.