UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Now showing 1 - 7 of 7
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    Mechanical Adaptability of Ovarian Cancer Tumor Spheroids
    (2021) Conrad, Christina Barber; Scarcelli, Giuliano; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A major obstacle in ovarian cancer treatment is the onset of ascites, an abnormal build-up of fluid in the peritoneal cavity. Using in vitro perfusion models, ascitic flow has been shown to drive epithelial-mesenchymal-transition (EMT) biomarker expression, promote epidermal growth factor receptor (EGFR) downstream signaling, and upregulate chemoresistance. Given the close ties between cell mechanics and behaviors, it is of interest to establish if mechanotransduction serves a role in cell signaling dysfunction. Here, we identified the mechanical behavior of tumor spheroids subjected to flow using Brillouin confocal microscopy, a non-contact optical method based on the interaction between incident light and microscopic mechanical waves within matter. We validated this technique by establishing a relationship with the traditionally derived Young’s modulus measured using atomic force microscopy and a parallel-plate compression device. Following characterization, we used Brillouin confocal microscopy to map mechanical properties of tumor spheroids embedded in a microfluidic chip and found that continuous flow for 7 days caused a decreased Brillouin shift (i.e., stiffness) compared to tumors in a static condition. Another physical phenomenon related to ascites is dysregulated osmolality. Maintaining cell water homeostasis is driven by the transport of water to balance solute concentration and can have direct consequences on mechanics and biochemical signaling in cells. Recently, it was demonstrated in single cells that cell volume correlated with mechanical properties; but the effects in tumor spheroids which exhibit multi-cellular interfaces has remained unclear. Here, we derived relationships between osmolality and nuclear volume, tumor cell density, and Young’s modulus, and found the correlations in spheroids resembled single cell relationships previously described in literature. Additionally, we looked at the impact of osmotic shocks on E-cadherin junctions and found aggregates formed with a unique timescale compared to morphology. Lastly, we observed reversibility of the mechanical, morphological, and molecular properties which showed the tumor’s dynamic ability to respond to physical cues. Altogether, this work demonstrated how flow and osmosis associated with ovarian cancer ascites can trigger phenotype transformations. These findings warrant future investigations into how the regulation of mechanotransduction pathways can be harnessed to prevent chemoresistance and signaling dysfunction.
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    A Numerical Study of Vortical Structure in a Turbulent Backward Facing Step Flow
    (2018) Leonard, Eric; Bernard, Peter; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A vortex filament scheme, termed the GVFS or gridfree vortex filament scheme, in which the vorticity field away from the immediate vicinity of solid boundaries was represented by convecting, gridfree vortex tubes, was used to simulate flow over a backward-facing step with curved edges. The backward-facing step geometry, which possesses a fixed separation point at the step edge, is largely used to study the physics of separation, reattachment, recirculation, and reattachment. Changes to the vortex filament scheme, termed the vortex insertion scheme, were added to the original vortex filament scheme which consisted of inserting vortex tubes into the flow immediately downstream of the step edge based on local vorticity. Running the vortex filament scheme in conjunction with the vortex insertion scheme produced a separated region suitable for comparison to flow over a backward-facing step with straight edges. By utilizing an alternative definition of structure which considered the entirety of the vorticity field it was demonstrated that roller vortices which form in the separated region: (i) result from the roll-up of fluid induced by the shear layer in the separated region, (ii) extend across the span but possess spanwise gaps which underlie the extensions of furrows which convect into the separated region, and (iii) break up due to shearing motion generated by the shear layer in the separated region. It was also discovered that flapping of the shear layer in the separated region results from changes in the spanwise positions of the furrows. The results of the present thesis demonstrate that vortex filament schemes are useful tools to tie together the structure in the upstream boundary layer of a step flow with the structure present in the mixing layer that occurs downstream of the step edge. In addition, a tentative connection was found between the structural make-up of the fluid upstream of the step edge and reattachment. This potential link was used to suggest an area for future research.
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    HANDS FOUR AND PASS IT DOWN: GENERATIONAL ENCOUNTERS IN MODERN URBAN CONTRA DANCE
    (2017) Byrd, Deborah; Rios, Fernando; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Contra dance is a form of folk dance with a heritage dating back hundreds of years. Now, in the early twenty-first century, contra dance is thriving, its participants successfully navigating elements of their multi-faceted lives to bring the living tradition into a relevant and meaningful present. In this dissertation, I examine generational encounters, with both vertical (from one generation to the next within contra dance) and horizontal (between members of the same generation but across genres) flows of ideas, as a means by which contra dance communities and practices are perpetuated. I approach this through a variety of perspectives. Culminating in the recent electronically-infused music crossover trend, which I locate as part of a larger twenty-first century remix phenomenon, this study delineates the younger generation’s contribution to the community while observing the interaction of the community as a whole. I describe contra dance as a community of practice in which participation is a key component for individuals to engage in and contribute to the practices of their communities, and for communities to refine their practice and ensure new generations of members. I analyze contra dance as a participatory practice in which style characteristics of the choreography and the music combine with a spirit of invitation to provide opportunities for people of varying levels of commitment, interests, and skills. This is valuable in bridging states of competence and challenge, and creating the possibility of optimal experience (flow). These practices allow contra dance to evolve with the times. Through this examination, contra dance is seen as a practice that has proven consistently malleable and open to transformation in both social context and in regard to music and dance capable of absorbing aspects of other styles. Contra dance, in all its facets, is not a vestige of the past, nor is it a passive form, but a practice fully in the present.
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    SOCIAL AND ECOLOGICAL FACTORS INFLUENCING COLLECTIVE BEHAVIOR IN GIANT DANIO
    (2016) Chicoli, Amanda; Paley, Derek A; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A fundamental problem in biology is understanding how and why things group together. Collective behavior is observed on all organismic levels - from cells and slime molds, to swarms of insects, flocks of birds, and schooling fish, and in mammals, including humans. The long-term goal of this research is to understand the functions and mechanisms underlying collective behavior in groups. This dissertation focuses on shoaling (aggregating) fish. Shoaling behaviors in fish confer foraging and anti-predator benefits through social cues from other individuals in the group. However, it is not fully understood what information individuals receive from one another or how this information is propagated throughout a group. It is also not fully understood how the environmental conditions and perturbations affect group behaviors. The specific research objective of this dissertation is to gain a better understanding of how certain social and environmental factors affect group behaviors in fish. I focus on two ecologically relevant decision-making behaviors: (i) rheotaxis, or orientation with respect to a flow, and (ii) startle response, a rapid response to a perceived threat. By integrating behavioral and engineering paradigms, I detail specifics of behavior in giant danio Devario aequipinnatus (McClelland 1893), and numerically analyze mathematical models that may be extended to group behavior for fish in general, and potentially other groups of animals as well. These models that predict behavior data, as well as generate additional, testable hypotheses. One of the primary goals of neuroethology is to study an organism's behavior in the context of evolution and ecology. Here, I focus on studying ecologically relevant behaviors in giant danio in order to better understand collective behavior in fish. The experiments in this dissertation provide contributions to fish ecology, collective behavior, and biologically-inspired robotics.
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    Analysis of Flow-Based Microfluidic Gradient Generators for the Study of Bacterial Chemotaxis
    (2015) Wolfram, Christopher James; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. This behavior is best understood in the bacteria Escherichia coli, which exhibits chemotaxis towards a variety of energy sources and signaling molecules. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis are not sufficient for such complex applications. The field of microfluidics offers solutions in the form of gradient generators. Many of these gradient generators are flow-based, where a chemical species diffuses across a solution moving through a microchannel. A microfluidic gradient generator was explored as a chemotaxis platform. Sources of error during experimental operation and methods of mitigating this error were demonstrated, and the fundamental theory behind these devices was examined. These devices were determined to be inadequate for the study of bacterial chemotaxis.
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    Design of a Novel Portable Flow Meter for Measurement of Average and Peak Inspiratory Flow
    (2009) Jamshidi, Shaya; Johnson, Arthur T; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The maximum tolerable physical effort that workers can sustain is of significance across many industrial sectors. These limits can be determined by assessing physiological responses to maximal workloads. Respiratory response is the primary metric to determine energy expenditure in industries that use respirator masks to protect against airborne contaminants. Current studies fail to evaluate endurance under conditions that emulate employee operating environments. Values obtained in artificial laboratory settings may be poor indicators of respiratory performance in actual work environments. To eliminate such discrepancies, equipment that accurately measures peak respiratory flows in situ is needed. This study provides a solution in the form of a novel portable flow meter design that accurately measures average and peak inspiratory flow of a user wearing an M40A1 respirator mask.
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    RECRUITMENT RESPONSES OF BENTHIC INFAUNA TO MANIPULATED SEDIMENT GEOCHEMICAL PROPERTIES IN NATURAL FLOWS
    (2004-05-18) Engstrom, Steven John; Marinelli, Roberta L; Marine-Estuarine-Environmental Sciences
    Recent studies have shown that local variation in sediment geochemistry can have significant effects on settlement rates of benthic invertebrates. For example, elevated porewater ammonium concentrations in soft-sediment benthic systems may result in decreased recruitment rates of settling larvae. Recruitment responses of the benthic polychaete Arenicola cristata and the bivalve Mercenaria mercenaria to varying ammonium concentrations were measured in realistic flow environments. Experiments made novel use of ammonium-spiked polyacrylamide gels placed beneath field-collected sediment, which produced predictable porewater ammonium concentrations. Post-larval arenicolids and Mercenaria were allowed to settle in an annular flume containing sediment treatments with varying ammonium concentrations. Porewater ammonium data indicated successful manipulation of geochemical properties without contamination of overlying water. In Mercenaria trials, recruit retention was low. For Arenicola trials, significant retention differences were observed as a function of ammonium concentration, and indicate that ammonium plays a significant role in determining recruitment patterns and hence juvenile abundance.