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.
Browse
8 results
Search Results
Item A Survey of Bees in the University of Maryland Campus Area(2021) Striegel, Theodore; Hawthorne, David; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I sampled the wild bee community in the University of Maryland campus area in College Park, Maryland for one season and combined those data with that from previous years. The protocol was modified to significantly expand the geographic scope of the survey, covering a much wider spatial range of the campus. This combined data was used to assess population trends, best practices, and determine whether or not the expanded protocol offers advantages in capturing local wild bee diversity and/or analytical benefits over the previous survey. New data allowed for characterization of the local wild bee community and discerned a landscape driver of spatial variance in local diversity. Appropriateness of different geographic parameters was found to depend on survey goals.Item SUBAQUEOUS SOILS OF SOUTH RIVER, MARYLAND: SOIL-LANDSCAPE MODEL EVALUATION(2021) Park, Cedric Evan; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The way soils form, their distribution on the landscape, and their interactions with their ecosystems must be understood if they are to be managed well. Our incipient understanding of subaqueous soils limits successful management, but recent research efforts have sought to address this problem. The goal of this study was to evaluate the protocols for describing, characterizing, classifying, and mapping subaqueous soils. To this end, a subaqueous soil-landscape model (Wessel, 2020) was used to predict the distribution of soils in South River, a western shore Chesapeake Bay subestuary. The soils of South River were surveyed, and the observed soils were compared to the predictions. The model provided significant positive guidance for mapping subaqueous soils, confirming that a pedological approach is useful in subaqueous settings. Pedological data were used to generate a subaqueous soils map for South River and make recommendations to refine the model. Protocols related to soil porewater halinity and mineralogy were also investigated.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 SIFTING FOR SAPPHIRES IN THE TRANSIENT SKY: THE SEARCH FOR TIDAL DISRUPTION EVENTS IN THE OPTICAL TIME DOMAIN(2018) HUNG, TZU-YU; Gezari, Suvi; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal disruption events (TDEs) refer to the scenario where a star passes within the tidal disruption sphere of a supermassive black hole (SMBH) and becomes torn apart by tidal stresses. In the classical picture, a thermal flare is expected once the bound stellar debris circularize to form an accretion disk that feeds onto the black hole. This flare of radiation provides a unique window to study the demographics of black holes within distant and quiescent galaxies that cannot be probed by other means. In addition, TDEs serve as a powerful probe of the accretion process, where the mass fallback rate can be super-Eddington for \Mbh{} $<$ a few $\times$ 10$^7$ \Msun{}. In recent years, ground-based wide-field optical surveys have successfully detected about a dozen of TDEs. Yet our knowledge of these events is still limited due to their low occurrence rate ($\approx$ 10$^{-4}$--10$^{-5}$ gal$^{-1}$ yr$^{-1}$). In the first part of this thesis, we present results from a systematic selection of TDEs in the Intermediate Palomar Transient Factory (iPTF). Our selection targets typical optically-selected TDEs: blue transients ($g-r$ $<$ 0 mag) residing in the center of resolved red galaxies that are absent of previous nuclear activity. Our photometric selection has led to discoveries of two TDEs in $\sim$4 months, iPTF16axa and iPTF16fnl, in 2016. With the most stringent criteria, we significantly reduced the contamination rate from SN Ia and AGN from 200:1 to 4.5:1. We derived a TDE rate of 1.7$^{+2.9}_{-1.3}$ $\times$ 10$^{-4}$ gal$^{-1}$ yr$^{-1}$ and forecast a discovery rate of 32$^{+41}_{-25}$ TDEs per year for ZTF. The second part of this thesis features a detailed analysis of the photometric and spectroscopic observations on iPTF16axa. We compared iPTF16axa with 11 other TDEs in the literature with well-sampled optical light curves. We concluded that most of these TDE candidates have peak luminosities confined between log(L [erg s$^{-1}$]) = 43.4--44.4, with constant temperatures of a few $\times$ 10$^4$ K during their power-law declines, implying blackbody radii on the order of ten times the tidal disruption radius, that decrease monotonically with time. For TDE candidates with hydrogen and helium emission, the high helium-to-hydrogen ratios suggest that the emission arises from high-density gas, where nebular arguments break down. In the last part of this thesis, I present statistical analyses on the Zwicky Transient Facility (ZTF) data and comments on the TDE rate from the first few months of the survey. Finally, I close this chapter with an analysis on the optical spectra of the first ZTF TDE -- AT2018zr.Item A COMPARISON OF EX-ANTE, LABORATORY, AND FIELD METHODS FOR EVALUATING SURVEY QUESTIONS(2014) Maitland, Aaron; Presser, Stanley; Survey Methodology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A diverse range of evaluation methods is available for detecting measurement error in survey questions. Ex-ante question evaluation methods are relatively inexpensive, because they do not require data collection from survey respondents. Other methods require data collection from respondents either in the laboratory or in the field setting. Research has explored how effective some of these methods are at identifying problems with respect to one another. However, a weakness of most of these studies is that they do not compare the range of question evaluation methods that are currently available to researchers. The purpose of this dissertation is to understand how the methods researchers use to evaluate survey questions influence the conclusions they draw about the questions. In addition, the dissertation seeks to identify more effective ways to use the methods together. It consists of three studies. The first study examines the extent of agreement between ex-ante and laboratory methods in identifying problems and compares the methods in how well they predict differences between questions whose validity has been estimated in record-check studies. The second study evaluates the extent to which ex-ante and laboratory methods predict the performance of questions in the field as measured by indirect assessments of data quality such as behavior coding, response latency and item nonresponse. The third study evaluates the extent to which ex-ante, laboratory, and field methods predict the reliability of answers to survey questions as measured by stability over time. The findings suggest (1) that a multiple method approach to question evaluation is the best strategy given differences in the ability to detect different types of problems between the methods and (2) how to combine methods more effectively in the future.Item Identity and philanthropy: Designing a survey instrument to operationalize lesbian, gay, bisexual, transgender, and queer alumni giving(2013) Garvey, Jason C.; Drezner, Noah D.; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigated philanthropic giving to higher education among lesbian, gay, bisexual, transgender, and queer (LGBTQ) alumni. The primary purpose was to create a multi-institutional survey instrument that operationalizes philanthropic involvement and motivation among LGBTQ alumni. Additional objectives included creating factors and items specific to philanthropic involvement and motivations of LGBTQ alumni, and ensuring validity and reliability of this instrument. I used a variety of analyses to create the instrument and to ensure validity and reliability of constructs within the survey. I followed DeVellis' (2003) model for scale development, utilizing his eight steps to create and validate the survey for LGBTQ alumni giving. Before administration, expert reviewers checked for both content and construct validity, providing feedback regarding both the overall functioning of the survey and specific critiques within items and factors. Surveying LGBTQ alumni from one institution, my sample yield was 21.89% (197 of approximately 900 potential participants). Following data collection, I conducted three different analyses to create a valid, reliable, and more parsimonious survey instrument: social desirability, construct validity, and principal components analysis (PCA). The final instrument yielded five empirically and conceptually valid factors across 22 items. Results from all analyses and validations led to the conclusion that the final instrument and accompanying factors are useable in measuring LGBTQ alumni giving.Item Beyond Response Rates: The Effect of Prepaid Incentives on Measurement Error(2012) Medway, Rebecca; Tourangeau, Roger; Survey Methodology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As response rates continue to decline, survey researchers increasingly offer incentives as a way to motivate sample members to take part in their surveys. Extensive prior research demonstrates that prepaid incentives are an effective tool for doing so. If prepaid incentives influence behavior at the stage of deciding whether or not to participate, they also may alter the way that respondents behave while completing surveys. Nevertheless, most research has focused narrowly on the effect that incentives have on response rates. Survey researchers should have a better empirical basis for assessing the potential tradeoffs associated with the higher responses rates yielded by prepaid incentives. This dissertation describes the results of three studies aimed at expanding our understanding of the impact of prepaid incentives on measurement error. The first study explored the effect that a $5 prepaid cash incentive had on twelve indicators of respondent effort in a national telephone survey. The incentive led to significant reductions in item nonresponse and interview length. However, it had little effect on the other indicators, such as response order effects and responses to open-ended items. The second study evaluated the effect that a $5 prepaid cash incentive had on responses to sensitive questions in a mail survey of registered voters. The incentive resulted in a significant increase in the proportion of highly undesirable attitudes and behaviors to which respondents admitted and had no effect on responses to less sensitive items. While the incentive led to a general pattern of reduced nonresponse bias and increased measurement bias for the three voting items where administrative data was available for the full sample, these effects generally were not significant. The third study tested for measurement invariance in incentive and control group responses to four multi-item scales from three recent surveys that included prepaid incentive experiments. There was no evidence of differential item functioning; however, full metric invariance could not be established for one of the scales. Generally, these results suggest that prepaid incentives had minimal impact on measurement error. Thus, these findings should be reassuring for survey researchers considering the use of prepaid incentives to increase response rates.Item Survey of Maryland Dentists' Knowledge, Opinions and Practices About Oral Cancer Prevention and Early Detection(2010) Maybury, Catherine A.; Green, Kerry; Public and Community Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To reduce the morbidity and mortality associated with oral cancer, dentists must have oral cancer prevention and early detection knowledge and skills, and they must perform routine screening examinations. Maryland dentists were surveyed to assess their knowledge, opinions and screening practices relating to oral cancer prevention and early detection. Thirty-eight percent of dentists had a high level of knowledge of oral cancer risk factors, thirty-nine percent had a high level of knowledge of oral cancer diagnostic procedures, and thirty-eight percent received a high score for provision of oral cancer examinations. Dentists who strongly agreed or agreed that their oral cancer knowledge is current were more likely to receive a high score for knowledge of oral cancer diagnostic procedures and knowledge of risk factors and diagnostic procedures combined. Deficiencies exist in dentists' knowledge and practices relating to oral cancer. Actions are needed in education, policy and research to address these deficiencies.