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.
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Item HIGH THROUGHPUT STIMULATED BRILLOUIN SCATTERING SPECTROSCOPY(2024) Rosvold, Jake Robert; Scarcelli, Giuliano; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Brillouin light scattering arises from the coupled interaction between light and material acoustic phonons. The measurand of Brillouin scattering is the characteristic frequency difference between incident and scattered light which depends on the local longitudinal modulus of the material. Spontaneous Brillouin scattering has been used in combination with confocal microscopy to provide non-contact, label-free mapping at micron-scale resolution in biological media. To date, spontaneous Brillouin microscopy has reached the speed limit (~20-50ms per spectrum) as determined by the theoretical scattering efficiency. While a great deal of research has been directed to speeding up Brillouin microscopy acquisition times, spontaneous Brillouin scattering is fundamentally an inefficient process thus limiting the ability to study faster biological phenomena and rapid processes. To combat this limitation, its nonlinear counterpart, stimulated Brillouin scattering (SBS) has been proposed for microscopy applications. For decades, stimulated Brillouin scattering has been used in fiber sensing and all-optical pulse control and leverages a nonlinear interaction where two counterpropagating light beams stimulate a more efficient scattering relationship. However, the small interaction volumes and photodamage constraints presented in microscopy have hindered the translation of stimulated Brillouin scattering into the biological realm. Recently, continuous wave stimulated Brillouin microscopy has led to competitive acquisition times (~5ms per spectrum) when compared to the spontaneous alternative but has yet to be widely adopted. Due to a plethora of factors, such as an inefficient power balance between pump and probe beams, lack of proper commercial laser sources, and nonoptimal detection schemes, the complete picture of what SBS spectroscopy has to offer has yet to be revealed. As such, there is a need to customize light sources and detection schemes in order to fully take advantage of the enhanced Brillouin efficiency possible in SBS. Herein we introduce novel methodology to improve the acquisition speed of Brillouin microscopy by designing and developing proper laser sources and detection schemes for efficient SBS spectroscopy. First, we showcase the potential utility of our state-of-the-art continuous wave SBS technology in a flow cytometry application, highly suitable for the counterpropagating geometry of SBS where the laser position is fixed while the sample is being moved at high speeds. Additionally, we will present an optimized receiver design based on polarization detection which enables 100x faster spectral measurements in the low-gain regime relevant to biological materials. Finally, we demonstrate an optimal pulsed laser source specifically designed for SBS Brillouin microscopy.Item Functionalized Nanoparticles for the Controlled Modulation of Cellular Behavior(2023) Pendragon, Katherine Evelyn; Fisher, John; Delehanty, James; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to control cellular behavior at the single-cell level is of great importance for gaining a nuanced understanding of cellular machinery. This dissertation focuses on the development of novel hard nanoparticle (NP) bioconjugate materials, specifically gold nanoparticles (AuNPs) and quantum dots (QDs), for the controlled modulation of cellular behavior. These hard NPs offer advantages such as small size on the order of 1 – 100 nm, high stability, unique optical properties, and the ability to load cargo on a large surface area to volume ratio, making them ideal tools for understanding and controlling cell behavior. In Aim 1, we demonstrate the use of AuNPs to manipulate cellular biological functions, specifically the modulation of membrane potential. We present the conception of anisotropic-shaped AuNPs, known as gold nanoflowers (AuNFs), which exhibit broad absorption extending into the near-infrared region of the spectrum. We demonstrate the effectiveness of utilizing the plasmonic properties AuNFs for inducing plasma membrane depolarization in rat adrenal medulla pheochromocytoma (PC-12) neuron-like cells. Importantly, this is achieved with temporal control and without negatively impacting cellular viability. Aim 2 explores the use of QDs as an optical, trackable scaffold for the multivalent display of growth factors, specifically erythropoietin (EPO), for the enhanced induction of protein expression of aquaporin-4 (AQPN-4) within human astrocytes. This results in enhanced cellular water transport within human astrocytes, a critical function in the brain's glymphatic system. We show that EPO-QD-induced augmented AQPN-4 expression does not negatively impact astrocyte viability and augments the rate of water efflux from astrocytes by approximately two-fold compared to cells treated with monomeric EPO, demonstrating the potential of EPO-NP conjugates as research tools and prospective therapeutics for modulating glymphatic system function. Overall, the body of work presented in this dissertation develops new NP tools, namely solid anisotropic AuNFs and growth factor-delivering QDs, for the understanding and control of cell function. These new functional nanomaterials pave the way for the continued development of novel NP-based tools for the precise modulation of cellular physiology.Item TRPV4, A CALCIUM-PERMEABLE CHANNEL, PLAYS A ROLE IN MATRIX STIFFNESS INDUCED MACROPHAGE POLARIZATION(2020) Dutta, Bidisha; Rahaman, Shaik Ohidar; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phenotypic polarization of macrophages is deemed essential in innate immunity and various pathophysiological processes, but little is known about how mechanical forces like matrix stiffness regulate the polarization and the associated signaling mechanisms. Here we report that calcium ion channel Transient Receptor Potential Vanilloid 4 (TRPV4), a mechanosensitive receptor/channel, mediates the substrate stiffness-induced macrophage polarization. Using atomic force microscopy, we show that fibrosis-induced tissue stiffness is dependent on TRPV4. M1 macrophages were found to be the predominant macrophage subtype in stiffer tissues and loss of TRPV4 significantly decreased the level of M1 macrophages. These findings were further validated by our in vitro assays indicating that increase in substrate stiffness leads to an increased secretion of M1 proinflammatory mediators, which is further enhanced by the addition of soluble factors. Taken together, these findings provide new insights about the role of TRPV4 in matrix stiffness-induced macrophage polarization that can be explored in tissue engineering and in the development of targeted therapeutics.Item Flip-Flops, Double Standards, and Other Political Sins: A Citizen's Guide to Hypocrisy in Politics(2020) Stonerook, Jason Port; Soltan, Karol; Government and Politics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)People detest hypocrisy, and one of the reasons people hold politics in such low regard is that politics appears rife with hypocrisy. The proliferation of hypocrisy in politics can leave many feeling disenchanted and cynical about political affairs. Yet even those with a strong aversion to political hypocrisy are likely to admit there are occasions when an act that has been characterized as hypocritical is actually acceptable in politics. In some cases, the offense of hypocrisy may not be very serious, or conditioned by circumstances; in other cases, the accusation may not even be valid. This study examines the question of when hypocrisy is more or less acceptable in politics. This issue is explored through a series of case studies drawn from events that occurred in American politics between 2014-2016, an era characterized by high political polarization, high-stakes showdowns between congressional Republicans and the Democratic administration of President Barack Obama, the 2016 presidential primaries, and 2016 presidential election between Hillary Clinton and Donald Trump. The study is organized by type, with a focus on basic violations of principle; logical inconsistencies; double standards involving partisan competition; discrepancies between the public affairs of public officials and their private lives; and flip-flops. The study finds that the most useful and powerful accusations of hypocrisy are those that effectively assert that a political figure has inappropriately prioritized narrow partisan concerns over a broader commitment to principles related to democratic norms, the exercise of civic virtue, and public-spiritedness.Item A Probe of Colored Medium Effects on Quarkonia Polarization in √s = 7 TeV pp collisions at CMS(2017) Ferraioli, Charles Christopher; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The suppression of quarkonia mesons is one of the signature indications of the presence of a quark-gluon plasma, the colored, asymptotically free state of matter believed to have existed moments after the Big Bang, and recreated by colliding heavy-ions. Two S-wave charmonia states, the J/ψ and the ψ(2S), along with three S-wave bottomonia states, the Υ(1S), Υ(2S), and Υ(3S), have been studied in heavy-ion collisions at both the Relativistic Heavy Ion Collider and the Large Hadron Collider (LHC), showing clear sequential suppression patterns, with the most tightly bound states less suppressed than the others, relative to scaled proton-proton (pp) collisions. Yet, the results remain difficult to interpret, owing to a combination of complicated feed-down processes from P-wave χ states, as well as regeneration of quarkonia occurring well after the initial collision. Further, the basic production mechanism of quarkonia is still far from certain, leaving open the possibility that changing mechanisms could affect the scaling of pp yields. This thesis aims to be the first in a line of studies into the effects of a colored medium on the basic production mechanism of quarkonia by measuring quarkonia polarization. Polarization can be measured using the angular distributions of dimuons emanating from quarkonia decays, and the Compact Muon Solenoid detector is well suited for these measurements. The polarizations of the three Υ(nS) and two ψ(nS) states were measured versus event multiplicity using a dimuon data sample collected during the 2011 LHC run of √s = 7 TeV pp collisions, with a total integrated luminosity of 4.9 fb−1. The measurements were integrated over the available rapidity range, for transverse momentum up to 35 GeV/c. All quarkonia states showed small polarizations, which were cross checked across several reference frames, and are consistent with multiplicity-integrated analyses. In the states for which a precise measurement could be made, the J/ψ and the Υ(1S), there was no variation with multiplicity, but these states are strongly affected by feed-down, preventing any definitive conclusions. Ultimately, this study leads the way for a polarization measurement in heavy-ion collisions, which would provide a more decisive look into the affect of a colored medium on quarkonium production.Item The Economy and the American Presidency in a Polarized Era: Changes to Income and Unemployment by Class, Race, and Gender(2017) Mugglestone, Konrad Peter; Morris, Irwin L; Government and Politics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)For decades, political scientists have debated, with little consensus, whether Democratic and Republican presidents have contrasting macroeconomic records. While some scholars have argued that presidents can (and do) target economic benefits to constituents, existing research on party differences in macroeconomic politics has assumed that the two major parties have constituencies distinguished by class and that each party managed the macroeconomy to benefit these class-based constituencies. However, political and economic conditions have changed over the past thirty years. Scholars have been concerned about the effects of increasing political polarization, which has caused unusually contentious and slow-paced policymaking. High debt levels have made major budgetary changes more difficult, and monetary policy has been checked by the zero lower bound. In light of these new political and economic challenges, this dissertation utilizes a unique dataset to examine presidential administrations from 1970 to 2014. Using this data, this project seeks to answer several key questions: Do modern presidents of opposing parties have contrasting macroeconomic records? In light of changing political and economic conditions, have these differences grown or decreased from the differences observed in the past? Finally, do modern presidents reflect the identity politics of the polarized, modern era by focusing not only on class constituencies, but on race and gender constituencies as well? Some of the findings are predictable, but others are surprising. In terms of the macroeconomy, Democratic presidents demonstrate economic records superior to their Republican counterparts. However, the party of the president rarely has any meaningful impact on income growth for specific class, race, and gender groups. Even so, the party of the president does have a consistently meaningful effect on unemployment rates. On average, Democratic presidents have greater impacts than Republicans on the overall unemployment rate and the unemployment rates of some of their constituent groups: the working class, and racial minorities. Moreover, evidence suggests that other political factors sometimes matter – both divided government and an election year variable capturing the Political Business Cycle have statistical relevance, especially in unemployment models. Finally, this study finds little statistical evidence that polarization is having a meaningful impact on presidential economic policymaking.Item ESSAYS ON GRADUATION(2011) Qian, Rong; Reinhart, Carmen M; Vegh, Carlos; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation attempts to address the elusive concept of "graduation", that is the emergence from frequent crisis suffering status. It contains two chapters. The first uses a data set covering over two hundred years of sovereign debt, banking and inflation crises to explore the question of how long does it take a country to "graduate" from the typical pattern of serial crises that most emerging markets experience. We find that for default and inflation crises, twenty years is a significant period, but the distribution of recidivism has extremely fat tails. In the case of banking crises, it is unclear whether countries ever graduate. We also examine the more recent phenomenon of IMF programs, which sometimes result in "near misses" but sometimes end in default even after a program is instituted. The second chapter investigates the impact of countries' institutions on their likelihood of sovereign default from both an empirical and theoretical perspective. By employing a dataset of more than 80 countries, two facts emerge: 1) high institutional quality is associated with a low frequency of sovereign default crisis, and 2) in particular, polarized governments tend to default more often. To explain these facts, we developed a model that establishes a link between institutions, government polarization and sovereign default crises. Countries that lack rules and institutional settings to limit the pressure of powerful groups on a central government's policies default more often than countries that do have good institutions. Given that there are no barriers to limit the influence of powerful groups, a more polarized government defaults more because groups do not coordinate, giving rise to a negative externality. Simulations of the model succeed in matching the cross-country differences in sovereign default frequencies, given their institutional quality and degree of government polarization in the data.