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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    A Comparison of the Effectiveness of Demonstrations, Verbal Statements, and Hands-on Experiences on Correcting a Misconception of First-Graders Regarding Magnets
    (1987) Benbow, Ann E.; Lockard, J. David; Teaching, Learning, Policy & Leadership; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    The purpose of this study was to compare the relative effectiveness of five instructional interventions which were designed to correct a size-related science misconception in a group of first graders. The particular misconception chosen for the study is the belief that larger magnets are always of greater strength than smaller magnets. These interventions consisted of: a. a demonstration lesson, b. a hands-on lesson, c. a verbal statements lesson, d. a demonstration-plus-verbal statements lesson, and e. a hands-on-plus-verbal statements lesson. At the beginning of each magnet lesson, students were first exposed to evidence contradicting the size-related magnet misconception. This was followed by the introduction of cognitive conflict via the use of a small weak rectangular magnet and a larger strong rectangular magnet to pick up paper clips. Finally, students interacted with two (apparently) identical rectangular magnets of clearly differing strengths. The second major component of each intervention was the use of iron filings and a magnet to "show" lines of force. The purpose of this last activity was to give the students some information about magnets that would assist them in accommodating the events witnessed in the first part of the intervention. Subjects were tested three days before the treatment, one day after treatment to determine change of knowledge effect, then six weeks after treatment as a check for knowledge retention. Six subjects were randomly chosen from each treatment group to be interviewed using a format based upon Novak's Interview-about-Instances (1984) prior to the instruction, and on two occasions (one day, and six weeks) after the instruction. It was hypothesized that a demonstration treatment would result in the highest frequency of students who received a score of 100% on four misconception-related items on the post-test. It was also hypothesized that the demonstration treatment would result in the greatest retention. Analysis of both test scores and interview data indicates that, although there is strong support for the corrective properties of a demonstration which directly confronts the misconception that a necessary direct relation ship exists between magnetic strength and magnet size, a demonstration alone is not more effective than all of the remaining treatments in achieving change of knowledge or retention. Therefore, there is a lack of support for both research hypotheses. Both treatments containing demonstrations, however, were more effective in achieving correction of the size-related misconception than the treatments consisting of a hands-on treatment alone and verbal statements alone.
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    The interaction between a parasitic barnacle, Loxothylacus panopaei (Cirripedia, Rhizocephala), and three of its crab host species (Brachyura, Xanthidae) along the east coast of North America.
    (1993) Alvarez, Fernando; Reaka-Kudla, Marjorie; Animal & Avian Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    Rhizocephalan barnacles parasitize primarily decapod crustaceans (Bocquet-Vedrine 1968, Overstreet 1983). The principal effect of the parasites is often the permanent sterilization of the hosts (Bocquet-Vedrine 1972, O'Brien & Van Wyk 1984). Regardless of the processes involved, the end result of the infection is the creation of non-reproductive individuals that will use resources that otherwise would be available to the healthy traction of the host population. The potential impact on the host population then resides in the accumulation of sterile resource-using individuals in each generation. Prevalences of barnacles on anomuran and brachyuran crabs have been reported in a number of studies (e.g., Walker 1985, Hawkes et al. 1986, Johnson et al. 1986, Wardle & Tirpak 1991 ). Rhizocephalan infections can reach very high levels locally, suggesting that entire host populations may have a greatly reduced reproductive capacity. However, in most host species, the pattern of distribution of parasites is not uniform throughout the host's range. I examined the crab-rhizocephalan interaction using the system composed by the barnacle Loxothylacus panopaei and three of its crab host species: Panopeus lacustris, Eurypanopeus depressus, and Rhithropanopeus harrisii, occurring along the east coast of the North America. Through experimental infections conducted in the laboratory, it was determined that B. harrisii of a wide range of sizes could be infected by L. panopaei. The complete life-cycle of the parasite was manipulated in the laboratory. Neither host molting frequency nor host molt increments differed significantly between parasitized and control crabs. Host survival was significantly reduced during the parasite's developmental period; the heaviest mortality of the host occurred in the megalopal stage.
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    Women Correspondents in Vietnam: Historical Analysis and Oral Histories
    (1988) Martin, Christine; Hiebert, Ray; Journalism; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    Although women correspondents have covered wars since the Spanish-American conflict, it was not until the Vietnam War that they achieved full access to the battlefield and equal opportunities to cover all aspects of the conflict. Easily attained army accreditation, the burgeoning women's movement and the unique nature of the Vietnam War - a Third World, essentially, political conflict - combined to offer women reporters unprecedented opportunities to cover the war and to prove themselves as worthy members of journalism's elite crew - war correspondents. More women covered Vietnam than any other war. They focused their coverage primarily on the "human interest" angle and the effects of war on its civilian and military victims. This traditional women's focus took on a new prominence in Vietnam, where an understanding of the social and political underpinnings of Vietnamese culture was essential to the success of the American war effort. As a result, the traditional news definition of war as battlefield was widened and the "women's angle" became central to war correspondence. This study presents an historical analysis of the evolution of the role of the woman war correspondent, from the Spanish- American conflict to Vietnam, and presents the oral histories of 10 women who worked as war correspondents in Vietnam.
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    GABRIEL FAURE (1845-1924): INNOVATOR OF THE FRENCH MODERN STYLE AS SEEN IN HIS WORKS FOR CELLO AND PIANO
    (2003) Oh, Jooeun; Elsing, Evelyn; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    Gabriel Faure was a deeply influential leader in establishing modem trends in early twentieth-century French music. His individualistic compositions include both traditional and modern aspects incorporated into his own distinctive style. This doctoral project is a study of Faure's contributions to French chamber-music and explores especially his works for cello. In the first chapter of this dissertation, a brief biography of Faure is presented, and Faure's personal relationships with several influential contemporaries, including Camille Saint-Saens, are discussed. The second chapter describes Faure's highly effective career as Professor and then Director and reformer at the Paris Conservatoire. In the third chapter, Faure's chamber music is discussed, with emphasis on his works for cello. His works can be divided into three time periods, each representative of the composer's unique musical style and illustrative of Faure's stylistic development throughout his career. The fourth and final chapter examines the evolution of Faure's musical approach, while his complete works for the cello are analyzed and compared. Diverse reactions of his contemporary critics to Faure's late-period chamber works are also presented. As part of this doctoral project two recitals of works by Faure and his contemporaries were performed at the University of Maryland School of Music. The works performed in the first recital include Camille Saint-Saens' Romance for Violoncello and Piano, Opus 36 ( 1877); Maurice Ravel's Sonata for Violoncello and Violin ( 1920-22); Claude Debussy's Sonata for Violoncello and Piano ( 1915); and Faure's Violoncello Sonata No. I in d minor, Opus I 09 ( 1917). The second recital incorporated selections from all three of Faure's compositional periods: Elegie for Violoncello and Piano, Opus 2-1 ( 1880); Papillion for Violoncello and Piano, Opus 77 ( 1885), Romance for Violoncello and Piano, Opus 69 ( 1894 ), Sicilienne for Violoncello and Piano, Opus 78 ( 1898, originally 1893 ); Violoncello Sonata No. 2 in g minor, Opus I I 7 ( 1921 ); and Piano Trio in d minor, Opus I 20 ( 1922-1923 ).
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    PERFORMANCE OF THE VIOLIN CONCERTO AND SONATAS OF JOHANNES BRAHMS WITH AN ANALYSIS OF JOSEPH JOACHIM'S INFLUENCE ON HIS VIOLIN CONCERTO
    (1997) Hsieh, I-Chun; Heifetz, Daniel; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    This dissertation consists of a performance project and extensive studies of selected works by Johannes Brahms, including the Violin Concerto, Sonatensatz, and three Violin Sonatas. The performance project was presented in two recitals at the University of Maryland, College Park, on November 14, 1997, and November 16, 1997. The first recital featured Brahms' s Sonatensatz in C Minor, Violin Sonata No. I, Op. 78 in G Major, and Violin Sonata No. 3, Op. 108, in D Minor. The second recital included Brahms' s Violin Sonata No.2, Op. 100, in A Major and Violin Concerto Op. 77, in D Major. Section One gives an overview of this dissertation project. Section Two introduces the violin virtuoso Joseph Joachim, his relationship with Johannes Brahms, and Brahms' s life and major violin works. This section also analyzes Joachim' s performance practice and his teaching style. The end of this section focuses on the influence of Joseph Joachim on Brahms' s Violin Concerto and indicates the differences between Brahms' s original manuscript and the version suggested by Joachim. Section Three is composed of the programs of the two recitals. Section Four consists of program notes for the two recitals. The first recital was performed by I-Chun Hsieh, violin and Roy Hakes, piano. The second recital was performed by I-Chun Hsieh, violin and Chia-Hsuan Lee, piano.
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    Baroque Plague Imagery and Tridentine Church Reforms
    (1990) Boeckl, Christine M.; Pressly, William; Art History & Archaeology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    This dissertation aims to achieve two goals: one, to assemble as many facts as possible about the plague, regardless of period, and to relate this material to images; and two, to present a well-defined group of religious baroque plague paintings in the context of social, political and religious history. This inquiry is primarily concerned with scenes that portray saints actively involved in charitable pursuits, dispensing the sacraments to victims of the most dreaded disease, the bubonic plague. Chapter I contains a bibliographical essay, divided into three parts: medicine, theology, and art history. The next chapter considers the sources and the formation of baroque plague iconography. The remaining two chapters discuss "documentary" plague scenes and how they relate to historic events. They are presented in two sections: Italy and transalpine countries. This interdisciplinary research resulted in a number of observations. First, these narrative plague scenes were produced in Italy and in Catholic countries bordering Protestant regions: Switzerland, France, Flanders, and in the Habsburg Empire (excluding Spain). Second, the painters were mostly Italian or Italian-trained. Third, the artists observed not only the requirements specified by the Church in the 1563 Tridentine Decree on the Arts but also reflected in their work the catechetic teachings of the Council. Fourth, these religious scenes were not votive paintings but doctrinal images that served either didactic or polemic functions. Fifth, the scenes were not intended as memento mori; rather, the iconology conveyed positive images which emphasized that the faithful needed the Roman Catholic clergy to gain life-everlasting. Sixth, these plague paintings were important documents not as recordings of the conditions experienced during an epidemic but as historic testimony of liturgical practices. Last, these selected scenes mirrored the baroque Church's views on the ultimate questions about life and death.
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    The Effects of Instruction in Sentence Combining and Revision on Ninth and Tenth Graders' Explanatory Writing
    (1989) Horstman, Franklin; Slater, Wayne H.; Teaching, Learning, Policy & Leadership; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    In this study, I examined the effects of instruction in sentence combining on three measures of student writing : 1.) syntactic fluency; 2.) overall writing quality; and 3.) sentence -combining ability. Sentence combining is a method of writing instruction in which students rewrite a series of sentences into one syntactically more complex sentence. Two teachers instructed experimental group one (37 students) in sentence combining applied to revision. The same two teachers also instructed experimental group two (37 students) in sentence combining alone. A third teacher instructed the control students (38 students) in the standard ninth-grade English curriculum. To examine syntactic fluency, I analyzed students' writing for words per T-unit, clauses per T-unit, and words per clause. To examine overall writing quality, two trained raters assessed students' writing using forced choice holistic scoring. I also assessed students' sentence-combining ability. On syntactic fluency, the control group demonstrated statistically significant gains for mean number of words per clause. On overall writing quality, the control group also demonstrated statistically significant gains. On sentence-combining ability, both experimental group one and experimental group two demonstrated statistically significant gains. While the results do not support the first two research questions, on sentence-combining ability, the results suggest that ninth-grade writers can be taught sentence combining in a four-week, intensive instructional unit. Additionally, results suggest links between rhetorical and psychological theories and writing. However, the limitations of the results also suggest further sentence-combining research.
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    The Folklore and Life of My Native Country in Pictorial Terms
    (1967) Al-Harithi, Naziha Rashid; Maril, Herman; Art; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    The content of this thesis exhibition is involved in exploration of the folklore and life of the people of my native country in terms of a more contemporary painting language. Color symbols and patterns play a great role in these concepts.
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    Development and Preliminary Validation of the Religious Identity Development Scale
    (2002) Veerasamy, Suthkaran; Hoffman, Mary Ann; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    The purpose of this study was to examine the psychometric properties of a new measure of religious identity development, the Religious Identity Development Scale (RIDS). The study also explored the relationship among religious identity development, anxiety and dogmatism to determine convergent and discriminant validity for the RIDS. The concurrent validity for the RIDS was determined by exploring the relationship between intrinsic and extrinsic religious orientations. The religious identity measure that was validated in this study was based on a proposed model of religious identity development, the Experiential/Rational Model of Religious Identity Development. The participants for the study were 211 students and adults from the Midwest and East coast. They completed the Religious Identity Development Scale (RIDS; V. Suthakaran, 2002), the Rokeach Dogmatism Scale (Rokeach, 1960), the State subscale of the State-Trait Anxiety Scale (Spielberger, 1983), Age Universal Intrinsic-Extrinsic Scale (Gorsuch & Venable, 1983), and the Marlowe-Crowne Social Desirability Scale (Crowne & Marlowe, 1960). Exploratory factor analysis supported a six-factor model better than a seven-factor model. Discriminant validity was demonstrated by the negative correlations of the Acceptance status with anxiety and dogmatism, and the negative correlation of the Cognitive-Rationalization status with anxiety. Convergent validity was demonstrated by the positive correlations of the Concrete, Relational and Cognitive - Rationalization statuses with dogmatism, and the positive correlation of the Confusion status with anxiety. Some evidence, albeit modest, was found for concurrent validity, in that the Relational status was positively correlated with extrinsic religious orientation, and the Exploration status was positively correlated with intrinsic religious orientation. The negative correlation of the Cognitive-Rationalization status and the Confusion status with intrinsic religious orientation also provided tentative evidence for concurrent validity. Additional preliminary support for the concurrent validity of the RIDS was provided by examining the relationship of the six statuses with a two-dimensional definition of intrinsic and extrinsic religious orientation. Finally, results appeared to indicate that the internal consistencies and test-retest reliabilities were adequate, except for the Relational status. The methodological limitations of the study and implications for counseling psychology were discussed. Suggestions for future research for refinement of methodology were offered.
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    The Washington Bronze Dionysos
    (1994) Bennet, Susanne Klejman; Venit, Marjorie Susan; Art History & Archaeology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    A life-size bronze of a nude youth was discovered in a river in Asia Minor in the early 1960's. The bronze no longer had the iconographic attributes that it had once held in its hands, but the head presented features which made it possible to identity the figure as representing the god Dionysos. The sculptor drew upon earlier prototypes, specifically a figure called the Westmacott athlete, which has been tentatively attributed to the Greek sculptor Polykleitos. The head of the statue reflects a different, possibly female, prototype. An investigation of a group of Roman life-size and three quarter life-size bronzes reveals that the iconographic details which identity the Washington Bronze also place it outside the category of lamp hearers to which the majority of the other statues belong. The physiques of the majority of the lamp bearers and of the Washington Bronze, however, reflect the same Polykleitan prototypes. The identification of the Washington Bronze as a devotional rather than functional statue is made through a study of the literary, religious, and archaeological evidence. The evolution in the iconography of the god is traced through his portrayals on Greek vases and in Graeco-Roman bronze and marble statuary. The Bronze was created in the Eastern Roman Empire. Through a comparative analysis of other bronzes it can be dated within the period between the beginning of the Augustan era and the third quarter of the first century A. D. A setting in the home of a devotee of the Dionysian Mysteries is adduced.
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    The Effects of Variation in the Amount of Play Materials on the Play Behavior of the Preschool Child
    (1978) Rechsteiner, Ann E.; Leeper, Sarah L.; Human Development & Quantitative Methodology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    Major questions have arisen concerning the function of play in the development of the young child. Changing attitudes towards the significance of play reflect changing social patterns. The present study was concerned with the effect that a removal of a specified amount of play material had on the play behavior of young children. Ten intact groups of children from the Washington, D.C. Metropolitan Area ranging in age from three to five years old were studied by this researcher. A time sampling technique using a modified version of DUSOPAC was used to measure the play behavior of the groups. The data collected by the observers were compiled and analysed using a one way ANOVA for a repeated measure design for each of the eleven variables (Disruptive, Unoccupied, Solitary, Onlooker, Parallel, Associative, Cooperative, Not Play, Child-Child, Child-Adult, Child-Self.) The findings indicated that a significant relationship (at the .05 significance level) existed between the amount of social play observed and the amount of play equipment that was available to the young child. Less social play was observed when the material was removed on the first treatment day than when the material was present. No significant relationships were observed between the amount of equipment available and the amount of non-social play, the amount of child-child interaction, the amount of child-self interaction, or the amount of child-adult interaction that occurred. Investigation of the mean score values revealed trends for both interaction patterns and play behavior. Females were found to display more child-self interaction behavior and males more child-child interaction behavior. Also, for all days of observation, regardless of treatment, the most frequently occurring interaction behavior was child-child followed by child-self. The least frequently occurring interaction behavior was child-adult. For play behavior for all days of observation, regardless of treatment, males displayed more disruptive, unoccupied, associative, cooperative, parallel and social play behavior than did females. Females were found to display more solitary, onlooker, not-play and non-social play behavior than were males. These findings were not in agreement with Langlois, Gottfried and Seay (1973), and Sitzky, Haywood and Isett (1970 ). The results of this study seem to indicate that there is a need for more research to 1) update earlier studies; 2) study the role of play in the development of social interactions; 3) investigate saturation levels of equipment as they relate to a child's play; 4) to explore in more detail environmental influences on play behavior.
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    Land Use in Charles County
    (1962) Langen, John S.; Van Royen, W.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    The land use of Charles County does not basically differ from that in the past. Land in forest and land in farms are the two categories of land utilization. The great demand for tobacco on the overseas markets in the early days of the county's history, led to the introduction of this crop. Because of the favorable climate and soils, tobacco became soon the mainstay of the county's economy, a situation which still exists today. The purpose of the thesis was to determine which geographical factors and others accounted for the use of the land. In addition to field work, use was made of detailed statistical data. It was found, that the county could be divided into three sections. In the western section, land in forest was the dominating land use form. In the central section, land in forest and land in farms were about equal in areal extent, whereas in the eastern section, land in farms dominated. The reason was that soils in the western part became exhausted, and a shift to the eastern section took place. Landforms contributed much to the distribution of land in crops, especially for tobacco. Recently, a change in the use of the land is taking place. The encroachment of the Washington Metropolitan area, and the building of a major highway, connecting the North with the South, have induced farmers to sell their lands, which are converted into residential areas.
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    Juvenile Delinquency and the Negro in Charles County, Maryland
    (1966) Seaman, Thomas W.; Lejins, Peter P.; Sociology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    Are there differences between Negro and white juvenile delinquents? This was the question that constituted the basis for this exploratory study. The objectives of the project were to determine if Negro juveniles were proportionately overrepresented among juvenile delinquents and if there were differences in types of offenses committed by Negro and white delinquents. The differences found were analyzed in the light of socio-economic class differences between Negro and white delinquents. Previous research has tended to indicate that racial differences disappeared when socioeconomic class was held constant. The area selected for the project was Charles County, Maryland, because of the writer's access to court records and knowledge of the area. Delinquency rates were developed to determine if Negroes were proportionately overrepresented among delinquents and/or if lower class juveniles were overrepresented among delinquents. Delinquent offenses were divided into four types: offenses involving theft or attempted theft of property, offenses involving violence, offenses involving the destruction of property, and offenses injurious to the child himself. Delinquency rates were developed for Negro and white delinquents in each socio-economic class for each type of offense. A simple ecological investigation was conducted to determine if there were any significant patterns in the spatial distribution of the delinquents. The findings show that Negro juveniles were not significantly overrepresented among delinquents even though Negro delinquents were overrepresented among lower-lower class delinquents. White delinquents were found to be overrepresented among delinquents from the lower-middle and upper-lower classes. The analyses of types of offenses revealed that types of offenses could be identified with certain levels of the socio-economic structure regardless of race, but that differences existed between Negro and white delinquents within socio-economic classes. The ecological investigation indicated that there was no significant ecological pattern among county delinquents.
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    Exploring and Propagating Oboe Music From Composers of South Asian, African, and Middle Eastern Heritage
    (2023) Helgerman, Michael Andrew; Hill, Mark
    Though the oboe has enjoyed both a rich history and contemporary renaissance as a solo voice, the instrument's repertoire bears some rigidity and limitations in representing composers from diverse backgrounds. A repertoire survey from a 2001 edition of the Double Reed Journal denotes a clear tendency towards homogeneity of composer background in the instrument's canon. After contacting oboe professors employed at universities across the United States, compiler Susan Lundberg published lists of concerti, sonatas, chamber pieces, and other works that "oboists should know"; every piece listed in the top ten results of each genre was written by a male composer of European or American descent. This dissertation project will serve as a small step among the many needed for the oboe's solo repertoire to evolve into a canon that equitably represents composers from all backgrounds. In particular, composers with South Asian, African, and Middle Eastern roots will enjoy the spotlight in this dissertation, as these cultures boast rich musical foundations whose synthesis with the modern oboe has yet to receive significant research.
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    The Cowbell in Music and Culture
    (2023) McGovern, John; Votta, Michael; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Cowbells are used as percussion instruments in a variety of musical settings today. Such uses represent a number of distinct musical practices. In this dissertation I attempt to chronicle cowbells in music from the first such use (the mid-19th century) to the present day, with a focus on historically linking and differentiating cowbell practices in orchestral music, in early musical theater and popular music, and in Cuban and Cuban-derived music. I argue furthermore that perceptions of the cowbell and its connotations, in the cultures that produce these musical practices, affect the way that the instrument is used and perceived. The word “cowbell” makes no differentiation between cowbells used historically for farming and the modern instruments descended from them. This, coupled with historical associations between cowbells and the carnivalesque exemplified by charivari practices, has led to perceptions of the cowbell, throughout its musical history, as an object of othering, humor, and/or derision.
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    Essays on the Epistemology of Polycentriicty and Democracy
    (2023) Manor, Aylon; Kogelmann, Brian; Philosophy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation investigates the epistemic properties of two institutional types, polycentricity and democracy, and explores how these ideals can be translated into concrete plans for institutional design. The dissertation consists of four papers, with the first two papers investigating the epistemic case for polycentricity and its relation to moral arguments, while the remaining two papers investigate the epistemic properties of democracy. The first paper argues that the epistemic case and moral case for polycentricity point toward different polycentric arrangements, while the second paper highlights two dimensions through which polycentric arrangements can generate epistemic value. The third paper proposes a two-stage political process using a Wikipedia-inspired platform to filter for quality information and allow all citizens to participate, while the fourth paper argues for the normative significance of "epistemic equality" in voting methods and explores its implications for alternative methods. 
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    Evaluating the Potential Benefits and Sustainability of a Novel Living and Dead Cover Crop Mixture in Mid-Atlantic Crop Production
    (2023) Johnson, Veronica; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Modern vegetable production systems are often characterized by monoculture fields andthe intensive use of tillage and/or synthetic agrochemicals for managing weeds and insect pests. A growing public interest in more sustainable and eco-friendly production practices has resulted in increased demand that crops be produced with lower inputs. Incorporating flowering living mulches and cover crop residues within crop fields can create an environment more hospitable to beneficial organisms and less conducive to pest outbreaks. My dissertation research aims to advance our knowledge in this area by evaluating the impacts of a novel cover cropping tactic which involves combining a perennial flowering living mulch with cover crop residue on insects and/or weeds. Further, it is often suggested that weed management requires a holistic approach; and that cover cropping will not be successful as a sole weed management tactic. As such, another research aim is to investigate whether combining a cover cropping tactic with herbicide sprays would result in better weed suppression and increased yield in sweet corn compared to using cover crops alone. An economic assessment was also performed to further evaluate the practicality of sweet corn producers adopting the management practices being investigated. Cost of seeds, labor and other expenses can be a primary limitation to cover crop usage. To this point, I also evaluated the feasibility of using a single cover crop planting to suppress weeds over multiple cropping systems and field seasons. If a single cover crop planting can be used over multiple seasons, this could reduce the cost of cover crop use. Agricultural intensification and conversion of natural landscapes to crop production fields have contributed to declines in insect biodiversity including natural enemies and pollinators. Advancing our understanding of how increasing vegetational diversity within crop fields influences weed pressure and populations of herbivores and beneficial arthropods, as well as production costs, can facilitate the adoption of practices in annual cropping systems that favor beneficial organisms and conserves insect biodiversity.
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    UNVEILING THE SELF-ASSEMBLY OF POLYMER-GRAFTED NANOPARTICLES IN SELECTIVE SOLVENTS
    (2023) Lamar, Chelsey; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The self-assembly of inorganic nanoparticles (NPs) has garnered considerable attention due to the potential for fabricating functional structures with unique collective properties. In recent years, polymers have emerged as valuable candidates in assisting the organization of NPs into complex architectures with multiple capabilities. Researchers have shown that polymer-grafted nanoparticles (PGNPs) facilitate the use of advanced nanostructures with tailored properties in biomedical applications. Although, continued exploration of the rational design and tailoring of PGNP assemblies is needed to expand our understanding before we can fully realize the potential of these structures in desired applications. My dissertation aims to investigate the fundamental aspects and elucidate the underlying mechanisms in the self-assembly of PGNPs for modern biomedical applications. A facile and versatile solution-based strategy was utilized to explore the individual self-assembly of PGNPs with anisotropic NPs and the co-assembly of binary PGNPs with distinct sizes. We focused on designing, characterizing, and exploring the optical properties of hierarchical assembly structures produced from inorganic NPs tethered with amphiphilic block copolymers (BCPs). Individual PNGPs with anisotropic NPs and binary mixtures of small and large PGNPs produce vesicle structures with well-defined packing arrangements. My work shows how key parameters, including polymer chain length, nanoparticle size, and concentration, influence the self-assembly behavior and the formation of vesicles in each system. Through a combination of experimental observations and theoretical considerations, I highlight the significance of polymer shell shape in dictating the self-assembly behavior of individual anisotropic PGNPs. Moreover, I demonstrate that elevated temperatures impacted the stability and optical responses of the vesicle structures. In co-assembly studies, my work describes the macroscopic segregation of PGNPs with different sizes in the vesicular membrane, which is attributed to the conformation entropy gain of the grafted copolymer ligands. This research will provide valuable insights into the self-assembly behavior and fundamental design of PGNP structures relevant to biomedical applications.
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    MULTI-GEV LASER WAKEFIELD ACCELERATION IN OPTICALLY GENERATED PLASMA WAVEGUIDES
    (2023) Shrock, Jaron E; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Plasma based electron accelerators offer a promising path to overcoming the significant technological and economic challenges facing the evolution to higher energies by radiofrequency (RF) accelerator technology. In particular, laser-driven wakefield acceleration (LWFA) in plasmas can produce accelerating gradients 1000 times larger than linear RF accelerators, enabling the production of GeV-scale electron bunches in just a few centimeters of acceleration. Efficient LWFA of electrons to this energy scale requires the use of optical guiding to maintain drive laser intensity over much longer distances than the characteristic diffraction length of the pulse. In this dissertation, I will present the first successful implementations of optically generated plasma waveguides in multi-GeV laser wakefield acceleration. I will focus on three primary topics: (1) experimental considerations for generating and diagnosing meter-scale plasma waveguides and the wakefield acceleration process, (2) the experimental demonstration of electron bunches accelerated up to 5 GeV in an all-optical LWFA, and (3) development of a model of drive pulse evolution and electron injection in agreement with a broad range of our experimental results, including the demonstration of localized electron injection through modification of the waveguide properties.
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    IDENTIFICATION OF TRACE KRYPTON IN THE LUX-ZEPLIN DARK MATTER SEARCH
    (2023) Silk, John James; Hall, Carter; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Searches for Weakly Interacting Massive Particles (WIMPs) carried out by liquid xenon time projection chambers (TPCs) require a careful accounting of all background sources. Because WIMPs are a leading dark matter candidate, their possible existence is of great interest to particle physicists, astrophysicists, and cosmologists. The LUX-ZEPLIN (LZ) detector has completed an initial science run finding no evidence for WIMP scattering events. The data excludes scattering cross sections above 6.5x10$^{-48}$ cm$^{2}$ for a WIMP mass of 30 GeV/c$^{2}$. Background contributions from the beta decay of dispersed \isotope[85]{Kr} were reduced prior to the initial science run using charcoal chromatography to remove trace krypton. Over 10 tonnes of xenon were processed, and a custom mass spectrometry system measured a final mass averaged krypton concentration of 123 $\pm$ 22 parts-per-quadrillion (ppq) $\frac{gram}{gram}$ $\frac{ \isotope[nat]{Kr} }{\isotope[nat]{Xe}}$. A delayed coincidence $\beta$ - $\gamma$ search was also conducted to identify rare decays from \isotope[85]{Kr} in the LZ WIMP search data. The 11.0 $\pm$ 4.0 identified events are equivalent to a concentration of 183 $\pm$ 67 ppq. The total background contribution from \isotope[85]{Kr} to the WIMP search region of interest is 30 $ \pm $ 11 electron recoil events.