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 Developing effective communication for climate change adaptation and disaster risk mitigation(2021) Lim, JungKyu Rhys; Liu, Brooke Fisher; Communication; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Preparing for natural disasters and adapting to climate change can save lives. However, little research has examined how organizations can effectively communicate climate change adaptation and disaster risk mitigation behaviors. This dissertation employs two studies to examine how to effectively communicate disaster mitigation and preparedness to help at-risk publics better prepare for natural disasters. Fragmented studies so far have not provided an integrated model to identify the most effective factors for explaining and predicting disaster preparedness behaviors and policy support. Moreover, studies have not yet developed and tested communication messages that can motivate publics’ disaster risk mitigation through experiments. Thus, in Study 1, this dissertation attempts to build an integrated model and identify the key factors that motivate disaster preparedness behaviors and policy support through three large-scale online surveys (N = 3,468). Two of the most common federally declared disasters in large disaster-prone states are studied: wildfires and hurricanes with floods. Study 1 finds that social norms and self-efficacy strongly motivate disaster preparedness behaviors, while response efficacy strongly motivates policy support behaviors. Then, based on Study 1 and consultation with eight communication experts, Study 2 develops messages using social norms and efficacy. Study 2 tests the social norms and coping appraisal messages through four between-subject online experiments (2 X 2 X 2 X 2) with an additional vicarious experience condition in flood- and hurricane-prone states (N = 5,027). Injunctive norms and disapproval rationale strongly encourage at-risk publics to take mitigation behaviors, and vicarious experience seems promising for message design. Additionally, this dissertation reveals at-risk publics’ awareness, behavioral engagement, preferred communication channels, and information sources for preparing for hurricanes and wildfire risks. Weather forecasters and the National Oceanic and Atmospheric Administration (NOAA), including the National Weather Service (NWS), were the preferred information sources for preparing for hurricane risks. Conversely, local and state fire departments were the preferred information sources for preparing for wildfire risks. By developing and testing messages on the strongest factors using preferred information sources, the dissertation provides guidance for risk communication researchers and professionals.Item Corruption, Reform, and Revolution in Africa's Third Wave of Protest(2019) Lewis, Jacob Scott; McCauley, John F; Government and Politics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)What explains diverging calls for reform and revolution in Africa over the past ten years? African countries have made substantial strides toward actual democratic devel-opment, including a concerted effort to address corruption. As African democracies have strengthened, calls by citizens for anti-corruption reform have grown, highlighting the progress that is being made. Yet, in recent years, some anti-corruption movements have called instead for revolution - completely replacing the state or seceding altogether. What explains these calls for revolution? I argue that we need to understand how differ-ent types of corruption shape contentious goals. When corruption generates material benefits, citizens lose trust in politicians but do not lose trust in the system. In response, they call for reform, seeking to improve the system. When corruption generates system-ic benefits (distorting the system altogether), citizens lose trust in the institutions and instead call for revolution. I test this using individual-level data from survey experi-ments as well as large-n surveys, and group-level data using statistical analysis of pro-test events as well as case studies. I find strong support that types of corruption matter greatly in shaping contentious politics in Africa.Item IMPROVING CHRONIC ILLNESS MEDICATION ADHERENCE: A COUNTERFACTUAL THINKING-BASED MODEL OF PERSUASIVE COMMUNICATION(2017) Iles, Irina; Nan, Xiaoli; Communication; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The World Health Organization estimates that, by 2020, the number of Americans affected by at least one chronic condition requiring medication therapy will grow to 157 million. Effective medications are a cornerstone of prevention and disease treatment, yet only about half of patients take their medications as prescribed, resulting in a common and costly public health challenge for the U.S. health care system. As with much of health care, drug adherence is primarily about human behavior. Therefore, patients who lack motivation to take their medication as prescribed cannot be forced or simply educated to take their medication; they must be persuaded and motivated to do so. However, existing literature on how persuasion-based behavioral change can be achieved for non-adherent patients is sparse. To help build more evidence on how effective communication can be used to promote drug adherence for patients who have been diagnosed with chronic illness, this research tested the effectiveness of counterfactual thinking as a message design strategy aimed at increasing drug adherence among individuals at risk for nonadherence. Findings from experiments 1 and 2 showed no effect of counterfactual thinking on medication adherence. Findings from experiment 3 showed that, in a sample of 303 patients with type 2 diabetes at risk for nonadherence, messages including upward counterfactual thinking (e.g., “if only I had taken my medication as prescribed, I would not be in the hospital right now!”), compared to messages including downward counterfactual thinking (e.g., “it could have been worse and I could have died!”) or no counterfactual thinking, increased perceptions of medication adherence self- and response efficacy, and behavioral intention to take one’s medications as prescribed. Counterfactual thinking-based messages are a promising and easy to use persuasion strategy for patients who are at risk for nonadherence. Counterfactual thinking can be incorporated in interventions aimed at increasing adherence, and in doctor-patient or pharmacist-patient communications. Future studies should replicate these findings patients who have other chronic illnesses. Furthermore, measuring actual medication adherence behavior as opposed to behavioral intention, would provide a better indicator of the effectiveness of counterfactual thinking in increasing adherence.Item Testing a Dual Path Framework of the Boomerang Effect: Proattitudinal versus Counterattitudinal Messages(2017) Zhao, Xinyan; Fink, Edward L.; Communication; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation aims to differentiate two types of boomerang effects on belief and attitude change: a boomerang effect under a proattitudinal message and a boomerang effect under a counterattitudinal message. By employing a 2 (Message valence: anti-policy vs. pro-policy) × 2 (Issues: legal age for drinking vs. legal age of marriage) × 2 (Threat to freedom: low threat vs. high threat) × 2 (Argument quality: low quality vs. high quality) plus 2 (Control groups: no-message control for the two issues) cross-sectional factorial design (N = 458), antecedents and mediators that bring about the two types of boomerang effect were examined. Under a counterattitudinal message, both argument quality and prior belief strength predicted a boomerang effect: Those receiving a low-quality argument or those with a strong prior belief, as compared with the control group, exhibited a boomerang on belief and attitude. The dominant mechanism that explained the relationship between argument quality and belief position boomerang was counterarguing (vs. anger). Under a proattitudinal message, there was an indirect effect of trait reactance on belief boomerang through anger (vs. negative cognitions). But the perceived threat to attitudinal freedom did not predict a boomerang effect. These results contribute to attitude change research by empirically separating cognitive and affective mechanisms for boomerang effects. Furthermore, this study refines the construct of negative cognitions and integrates reactance theory and the cognitive response perspective on boomerang effects. Both structural equation models and confirmatory factor analysis suggested that counterarguments and nonrefutational thoughts were two distinct types of negative cognitions. The two constructs were caused by different sets of antecedents and had different outcomes: Poor argument quality caused counterarguments, whereas perceived threat and trait reactance caused nonrefutational thoughts. Only counterarguments mediated the effects of argument quality on the boomerang effects for belief (e.g., the extent to which the legal drinking age should be decreased on a magnitude scale) and belief position (e.g., the legal age for drinking), which subsequently predicted the boomerang effect on attitude (e.g., the extent to which the legal drinking age is liked). This dissertation expands the theoretical scope of belief and attitude change research. Future research should explore the persuasive appeals for mitigating the cognitive or affective process resulting in a boomerang effect. Among those who are more prone to boomerang on certain issues, a boomerang appeal can be employed to persuade.Item UNDERSTANDING DIRECT BOROHYDRIDE - HYDROGEN PEROXIDE FUEL CELL PERFORMANCE(2013) Stroman, Richard O'Neil; Jackson, Gregory S; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Direct borohydride fuel cells (DBFCs) generate electrical power by oxidizing aqueous BH4- at the anode and reducing an oxidizer, like aqueous H2O2 for an all-liquid fuel cell, at the cathode. Interest in DBFCs has grown due to high theoretical energy densities of the reactants, yet DBFC technology faces challenges such as side reactions and other processes that reduce cell efficiency and power generation. Relationships linking performance to cell design and operation will benefit from detailed and calibrated cell design models, and this study presents the development and calibration of a 2D, single-cell DBFC model that includes transport in reactant channels and complex charge transfer reactions at each electrode. Initial modeling was performed assuming ideal reactions without undesirable side reactions. Results were valuable for showing how design parameters impact ideal performance limits and DBFC cell voltage (efficiency). Model results showed that concentration boundary layers in the reactant flow channels limit power density and single-pass reactant utilization. Shallower channels and recirculation improve utilization, but at the expense of lower cell voltage and power per unit membrane area. Reactant coulombic efficiency grows with decreasing inlet reactant concentration, reactant flow rate and cell potential, as the relative reaction rates at each electrode shift to favor charge transfer reactions. To incorporate more realistic reaction mechanisms into the model, experiments in a single cell DBFC were performed to guide reaction mechanism selection by showing which processes were important to capture. Kinetic parameters for both electrochemical and critical heterogeneous reactions at each electrode were subsequently fitted to the measurements. Single-cell experiments showed that undesirable side reactions identified by gas production were reduced with lower reactant concentration and higher supporting electrolyte concentration and these results provided the basis for calibrating multi-step kinetic mechanism. Model results with the resulting calibrated mechanism showed that cell thermodynamic efficiency falls with cell voltage while coulombic utilization rises, yielding a maximum overall efficiency operating point. For this DBFC, maximum overall efficiency coincides with maximum power density, suggesting the existence of preferred operating point for a given geometry and operating conditions.Item Outcomes of an elementary grades social competence experiment according to student self-report(2008-06-30) Harak, Elise Touris; Gottfredson, Gary D; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Problem behaviors that emerge in early childhood often persist through adolescence. Evaluations provide evidence that social skills programs in elementary schools can reduce student aggression. There is some evidence that social skills programs also increase social skills, academic commitment, and achievement. Outcome evaluations have more often focused on aggression than on social skills and academics, however. The present study is a randomized, controlled trial evaluating the effects of one popular social skills instructional program, Second Step, in six treatment and six control schools after two years of implementation. Despite the widespread use of Second Step, few evaluations have assessed its effects. The existing evaluations have either: (a) lacked randomization, (b) had small samples, (c) not measured implementation, or (d) were implemented for one year or less. In the present evaluation, implementation data were collected from all teachers as each lesson was completed. Overall implementation was high across two years. Treatment effects were assessed on nine self-report measures including Engagement in Learning, prosocial behaviors (Altruism, Empathy, and Self-Restraint) and problem behaviors and attitudes (Rebellious Behavior, Aggression, Victimization, Acceptability of Aggression, and Hostile Attribution Bias). Analyses completed using hierarchical linear modeling (HLM) implied that treatment did not statistically significantly affect individual student self-reports net of individual characteristics. In almost all cases, the non-significant estimates of treatment effects were in the desired direction but mirrored non-significant pre-intervention differences.Item MIXING CHARACTERISTICS OF SINGLE-PLUME AND MULTI-PLUME HIGH PRESSURE INJECTION TESTS(2007-06-13) Knowles, Philip; Kiger, Kenneth T; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this thesis is to examine effects of multiple plumes in a Pressurized Water Reactor downcomer under scaled Pressurized Thermal Shock conditions, then assess the flow patterns and mixing compared to a single plume. Most computational and experimental studies have been performed using only single plumes; the findings of multiple plume experiments indicate that plume interaction significantly changes the flow pattern in the downcomer. A globally-induced recirculation region was created by the collective interaction of the multiple plumes in the UMD experiments, which does not occur for a single plume under similar conditions. From the evolving concentration field measurements and entrainment theory, it's argued that two merged plumes experience lower entrainment rates than a single plume. This implies the possibility of a higher thermal stress on the downcomer wall than would be inferred from single plume tests. Flow visualization was employed to examine the differences in plume behavior.Item Is It More Profitable to Post Prices? - Market Structure with Endogeneous Search Costs(2006-08-07) Gong, Binglin; Rust, John; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation contains three chapters. It analyzes a market where firms can choose whether or not to publicly post their prices. Price posting rewards a firm by reducing search costs for customers and thus attracting more demand, at the risk of triggering more direct price competition. In the first two chapters, I use a continuous model and a discrete model to discuss possible market equilibria, respectively. In a non-cooperative and dynamic environment, I find that when the supporting information technology becomes available to all firms, a firm wants to post prices only when it has appropriate cost advantage over its competitors. A lower cost of posting prices encourages firms to post their prices. Price posting improves market efficiency unless one firm has too much cost advantage. When a more efficient entrant replaces the incumbent price-posting firm, the incumbent wants to hide its prices again. These results explain why in some markets firms or individual traders hesitate to publicly post their prices and some even impose search costs on their prices. In the third chapter, I use a laboratory experiment to show how a market evolves when firms or individual traders endogenously determine the search costs on their prices. In the experiment, human subjects play sellers and the computer calculates demands and profits, assuming consumers behave optimally. I assign costs and demand parameters to subjects and let them choose both their prices and whether or not to publicly post them. I alter the production costs, the fixed cost of posting prices, and the possibility of communication among subjects across treatments to show the effect of these factors on market structure. Experimental results show that one is more likely to post prices when he or she has lower unit cost and when the fixed cost of posting prices becomes lower. Price posting lowers effective prices when communication among subjects is not allowed but raises prices when subjects can communicate with each other.Item Liquid sodium model of Earth's outer core(2004-08-27) Shew, Woodrow Lee; Lathrop, Daniel P.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Convective motions in Earth's outer core are responsible for the generation of the geomagnetic field. We present liquid sodium convection experiments in a spherical vessel, designed to model the convective state of Earth's outer core. Heat transfer, zonal fluid velocities, and properties of temperature fluctuations were measured for different rotation rates and temperature drops across the convecting sodium. The small scale fluid motion was highly turbulent, despite the fact that less than half of the total heat transfer was due to convection. Retrograde zonal velocities were measured at speeds up to 0.02 times the tangential speed of the outer wall of the vessel. Power spectra of temperature fluctuations indicate a well defined knee characterizing the convective energy input. This frequency is proportional to the ballistic velocity estimate. In the context of Earth's outer core, our observations imply a thermal Rayleigh number Ra=10^22, a convective velocity near 10^-5 m/s, and length and time scales of convective motions of 100 m and 2 days.