UMD Theses and Dissertations
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Item TRANSFORMING VACANT LOTS: INVESTIGATING AN ALTERNATIVE APPROACH TO REDUCING FEAR OF CRIME(2015) De Biasi, Alaina Marie; McGloin, Jean; Criminology and Criminal Justice; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vacant lots deserve criminological attention insofar as their disorderly conditions create opportunities for a host of negative outcomes including “fear of crime.” The present study considers whether incorporating fundamental standards of Crime Prevention through Environmental Design (CPTED) into traditional urban greening practices of vacant lots provides added value with regard to fear of crime above and beyond the traditional endeavor. This study conducted an experiment (N=523) from a sample of undergraduate students. Research participants were asked to report their level of fear of crime in regards to one of three randomly assigned computer-adjusted images: 1) A disorderly lot; 2) A traditional greened lot; and 3) A CPTED lot. This study found that on average participants who viewed a CPTED lot had lower levels of fear of crime than all other participants. This study discusses the implications of this finding for future research.Item VOTING FOR CORRUPTION: WHEN DO VOTERS SUPPORT CORRUPT POLITICIANS?(2015) McNally, Darragh Charles; Calvo, Ernesto; Uslaner, Eric; Government and Politics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation explores the determinants of when voters are willing to support corrupt politicians. The first paper presents a unique survey experiment that asks respondents to choose between pairs of politicians who have different ideological positions, and are accused of corruption. The survey goes some way toward recreating the tradeoffs one makes when voting in the real world. Results show that voters are more likely to choose corrupt politicians who agree with their position on an issue when issue salience is high. Results also show that institutional trust decreases the likelihood of choosing a corrupt politician, while perceptions of corruption increase the likelihood. Institutional trust and perceptions of corruption also have a modifying effect on issue salience. The second paper uses several datasets to test the effects of several mechanisms on the likelihood of a person voting for Silvio Berlusconi. Taking Berlusconi as the archetypal corrupt yet electorally successful politician I show that social norms that justify corruption in one’s peer group extend to voting and increase the likelihood of supporting Berlusconi. I find that perceptions of political corruption have an effect on the likelihood of supporting Berlusconi, and that this effect is not constant over time. I also find that trust in the judiciary has no effect on the likelihood of supporting Berlusconi – contrary to Berlusconi’s claims of persecution by the judiciary – and that trusting the institution of television has a strong effect on the likelihood of voting for Berlusconi. The third paper uses a unique survey experiment to measure changes in the support of voters for corrupt politicians. Results show that context matters, with voters’ sensitivity to corruption being shaped by the type of political post held by politicians and the overall corruption in the political system. Experimental results show that voters are more forgiving of acts of corruption among higher ranked politicians in executive politicians, when corruption is common. Overall, I provide evidence showing that voters are often willing to support corrupt politicians, and that transparency alone will have a limited effect in increasing the likelihood that corrupt politicians will be punished electorally.Item One-Dimensional Analytical Model Development of a Plasma-Based Actuator(2014) Popkin, Sarah Haack; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation provides a method for modeling the complex, multi-physics, multi-dimensional processes associated with a plasma-based flow control actuator, also known as the SparkJet, by using a one-dimensional analytical model derived from the Euler and thermodynamic equations, under varying assumptions. This model is compared to CFD simulations and experimental data to verify and/or modify the model where simplifying assumptions poorly represent the real actuator. The model was exercised to explore high-frequency actuation and methods of improving actuator performance. Using peak jet momentum as a performance metric, the model shows that a typical SparkJet design (1 mm orifice diameter, 84.8 mm3 cavity volume, and 0.5 J energy input) operated over a range of frequencies from 1 Hz to 10 kHz shows a decrease in peak momentum corresponding to an actuation cutoff frequency of 800 Hz. The model results show that the cutoff frequency is primarily a function of orifice diameter and cavity volume. To further verify model accuracy, experimental testing was performed involving time-dependent, cavity pressure and arc power measurements as a function of orifice diameter, cavity volume, input energy, and electrode gap. The cavity pressure measurements showed that pressure-based efficiency ranges from 20% to 40%. The arc power measurements exposed the deficiency in assuming instantaneous energy deposition and a calorically perfect gas and also showed that arc efficiency was approximately 80%. Additional comparisons between the pressure-based modeling and experimental results show that the model captures the actuator dependence on orifice diameter, cavity volume, and input energy but over-estimates the duration of the jet flow during Stage 2. The likely cause of the disagreement is an inaccurate representation of thermal heat transfer related to convective heat transfer or heat loss to the electrodes.Item Effects of Inequality and Transmissivity in a Common Pool Aquifer - Theory, Experimental Evidence and Policy Implications(2013) Chfadi, Tarik; Chambers, Robert G; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The early literature on common pool resources focused on the race for appropriation among users and its damaging effects on the resource stock and on the aggregate welfare of all users. The differential game framework was widely used to examine each user's actions under non-cooperative management and to assess the losses from deviating from an optimal resource management under cooperation. Interest has recently shifted toward the effects of characteristics such as heterogeneity among users and level of commonality in the resource on the use of common resources. This article is interested in combining both effects: I consider a dynamic model of a common pool aquifer with a finite transmissivity used by two farmers with dissimilar efficiencies. I unravel the players' behavior under different strategies and estimate their respective profits in order to evaluate the welfare effects of inequality and transmissivity. Solving for the aggregate profit of all players allowed me to revisit of a widespread result found in the common pool resource literature, which is that well enforced property rights are always associated with higher profitability; indeed, in the case of highly unequal players I reach a rather counterintuitive result as increasing transmissivity is proven to increase the overall profits. Such a result was never established in the literature at hand. However, on the distributional aspect, the model shows that the benefits of less efficient users always suffer from more transmissivity, even when the inequality is high enough to generate a raise in aggregate profits. For the validation of my theoretical results I carried out a series of experiments in the experimental laboratory at the Department of Agricultural and Resource Economics with volunteer subjects recruited from the University of Maryland. I used four experimental treatments. In the first two treatments the transmissivity is infinite; the players are highly differentiated in one treatment and identical in the other. The last two treatments are a replica of the earlier ones but with no transmissivity. The laboratory data were compared to the theoretical solution following four benchmark paths: the social optimum, the subgame perfect equilibrium, the semi-myopic, and the myopic. The results show that the decisions of a significant share of players follow the myopic path. All the theoretical findings were corroborated by the experimental results including the increasing effect of transmissivity in the presence of users highly unequal. In Chapter 5 on policy implications, I try to extend the analysis on the combined (or individual) effects of transmissivity and inequality on the aquifer use to the case when the possibility of communication between users, or the existence of a central agency, allows the emergence of alternative resource management modes. The first mode corresponds to the case of social optimum resource management; when users coordinate their actions to maximize the benefits to the community from the aquifer. The second mode of management corresponds to the case where, from a certain round, only one user, a priori the most effective, is allowed to use the resource, while the other user abandons extraction activities for the remaining duration of the game.Item Design of Discrete Auction(2010) Sujarittanonta, Pacharasut; Cramton, Peter; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chapter 1: Efficient Design of an Auction with Discrete Bid Levels This paper studies one of auction design issues: the choice of bid levels. Full efficiency is generally unachievable with a discrete auction. Since there may be more than one bidder who submits the same bid, the auction cannot completely sort bidders by valuation. In effort to maximize efficiency, the social planner tries to choose the partition rule-a rule dictating how type space is partitioned to group bidders who submit the same bid together-to maximize efficiency. With the efficient partition rule, we implement bid levels with sealed-bid and clock auctions. We find that the efficient bid levels in the sealed-bid second-price auction may be non-unique and efficient bid increments in a clock auction with highest-rejected bid may be decreasing. We also show that revealing demand is efficiency-enhancing even in the independent private valuation setting where price discovery is not important. Chapter 2: Pricing Rule in a Clock Auction We analyze a discrete clock auction with lowest-accepted bid (LAB) pricing and provisional winners, as adopted by India for its 3G spectrum auction. In a perfect Bayesian equilibrium, the provisional winner shades her bid while provisional losers do not. Such differential shading leads to inefficiency. An auction with highest-rejected bid (HRB) pricing and exit bids is strategically simple, has no bid shading, and is fully efficient. In addition, it has higher revenues than the LAB auction, assuming profit maximizing bidders. The bid shading in the LAB auction exposes a bidder to the possibility of losing the auction at a price below the bidder's value. Thus, a fear of losing at profitable prices may cause bidders in the LAB auction to bid more aggressively than predicted assuming profit-maximizing bidders. We extend the model by adding an anticipated loser's regret to the payoff function. Revenue from the LAB auction yields higher expected revenue than the HRB auction when bidders' fear of losing at profitable prices is sufficiently strong. This would provide one explanation why India, with an expressed objective of revenue maximization, adopted the LAB auction for its upcoming 3G spectrum auction, rather than the seemingly superior HRB auction. Chapter 3: Discrete Clock Auctions: An Experimental Study We analyze the implications of different pricing rules in discrete clock auctions. The two most common pricing rules are highest-rejected bid (HRB) and lowest-accepted bid (LAB). Under HRB, the winners pay the lowest price that clears the market; under LAB, the winners pay the highest price that clears the market. Both the HRB and LAB auctions maximize revenues and are fully efficient in our setting. Our experimental results indicate that the LAB auction achieves higher revenues. This also is the case in a version of the clock auction with provisional winners. This revenue result may explain the frequent use of LAB pricing. On the other hand, HRB is successful in eliciting true values of the bidders both theoretically and experimentally.Item Cryogenic test of gravitational inverse square law below 100-micrometer length scales(2010) Yethadka Venkateswara, Krishna Raj; Paik, Ho Jung; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The inverse-square law is a hallmark of theories of gravity, impressively demonstrated from astronomical scales to sub-millimeter scales, yet we do not have a complete quantized theory of gravity applicable at the shortest distance scale. Problems within modern physics such as the hierarchy problem, the cosmological constant problem, and the strong CP problem in the Standard Model motivate a search for new physics. Theories such as large extra dimensions, ‘fat gravitons,’ and the axion, proposed to solve these problems, can result in a deviation from the gravitational inverse-square law below 100 μm and are thus testable in the laboratory. We have conducted a sub-millimeter test of the inverse-square law at 4.2 K. To minimize Newtonian errors, the experiment employed a near-null source, a disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, were positioned on the two sides of the source mass at a nominal distance of 280 μm. As the source was driven sinusoidally, the response of the test masses was sensed through a superconducting differential accelerometer. Any deviations from the inverse-square law would appear as a violation signal at the second harmonic of the source frequency, due to symmetry. We improved the design of the experiment significantly over an earlier version, by separating the source mass suspension from the detector housing and making the detector a true differential accelerometer. We identified the residual gas pressure as an error source, and developed ways to overcome the problem. During the experiment we further identified the two dominant sources of error - magnetic cross-talk and electrostatic coupling. Using cross-talk cancellation and residual balance, these were reduced to the level of the limiting random noise. No deviations from the inverse-square law were found within the experimental error (2σ) down to a length scale λ = 100 μm at the level of coupling constant |α|≤2. Extra dimensions were searched down to a length scale of 78 μm (|α|≤4). We have also proposed modifications to the current experimental design in the form of new tantalum source mass and installing additional accelerometers, to achieve an amplifier noise limited sensitivity.Item An Experimental Evaluation of After School Program Participation on Problem Behavior Outcomes: Does Pre-Existing Risk Moderate the Effects of Program Participation?(2009) Cross, Amanda Brown; Gottfredson, Denise C; Criminology and Criminal Justice; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Background: Some prevention programs negatively affect participants. Previous research indicates that peers can cause these negative effects. However, little is known about which students may be most vulnerable to negative peer effects in prevention interventions. Purpose: This study tests the effect of participation in an after-school program (ASP) on student outcomes of peer delinquency, problem behavior and antisocial attitudes and beliefs for students of differing pre-test levels of risk for those outcomes. Drawing on social learning theory, this study examines whether low- and moderate- risk students in the intervention are more likely to acquire delinquent behaviors and beliefs in the ASP than their already-delinquent counterparts. Participants: 447 middle school students attending underperforming schools in Baltimore County, Maryland. Intervention: The data are drawn from an experimental evaluation of an after school program which operated in five middle schools in Baltimore County during the 2006-2007 academic year. The overall evaluation of the program found null effects on the wide range of measured outcomes (including academic achievement and delinquency). I explore whether the lack of beneficial program effects is partially attributable to negative effects among low and moderate risk participants who absorbed negative beliefs and behaviors from high-risk peers in the ASP. Research Design: Randomized, controlled field trial. Findings: Results indicate that low- and moderate- risk youth are not more likely to experience negative outcomes than high-risk youths. On the contrary, low-risk participants are less likely to experience negative effects than high-risk participants. Students who began the program with elevated negative peer influences grew in this characteristic if they often participated in the ASP but declined in negative peer influences if they less often attended the program. Implications for universal prevention are discussed.Item Contributions to the Measurement and Analysis of Helicopter Blade Tip Vortices(2004-10-18) Ramasamy, Manikandan; Leishman, John G; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The physical structure and the evolution of helicopter blade tip vortices, particularly the effect of the filament strain and flow rotation effects on the turbulent structure, were investigated through model-scale hovering rotor experiments as well as by developing a mathematical model from the Navier-Stokes (N--S) equations. The flow properties were measured using a high-resolution, three-component Laser Doppler Velocimetry (LDV) system. Images of the tip vortices were also obtained using laser sheet flow visualization. A strain field on the tip vortices was introduced by placing a solid boundary downstream of the rotor. As the vortices approached this boundary, they were convected radially outwards enabling measurements to be obtained in a known strain field. Comparing these measurements with vortex measurements in free-air provided considerable insight into the interdependence of strain and diffusion and their impact on the evolution of rotor tip vortices. The measurements also served to validate a mathematical model developed to predict the core growth of the tip vortices, which included the effects of both filament strain and diffusion. The measurements also laid the groundwork for the development of a comprehensive engineering tip vortex core growth model, which combined the effects of vortex filament strain and Reynolds number effects. Laser sheet flow visualization of the vortex core structure indicated the presence of three distinct regions --- an inner laminar region, an intermediate transition region and an outer turbulent region. Analysis of the velocity profiles measured across the vortex core at various wake ages further supported this hypothesis. The effects of flow rotation on the turbulence present inside the vortex core was quantified based on a Richardson number concept. This results in a laminar flow structure until a particular distance from the vortex center that correlated with the location where the Richardson number fell below a threshold value Based on these observations an eddy viscosity intermittency function was developed, which modeled the flow transition within the three regions of the core. This function was incorporated into a comprehensive tip vortex model formulated in terms of vortex Reynolds number. The empirical constants used in the present model were obtained from the present measurements, as well as several other sources. The dependence of the results on vortex Reynolds number ensured that the model successfully predicted the core growth of tip vortices for both sub-scale as well as full-scale rotors.