Theses and Dissertations from UMD

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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 give thesis/dissertation in DRUM

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

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    A SYNTHETIC TMRNA PLATFORM FOR ELUCIDATION OF BACTERIAL PROTEOME REMODELING UNDER STRESS
    (2022) Turner, Randi; McIver, Kevin; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Translational reprogramming is a key component of the bacterial stress response and is a function of mRNA stability, protein turnover and proteolysis. Total proteome measurements give a view of the stable proteome but can fail to capture dynamic changes under stress, including incomplete polypeptides that result from cleaved mRNAs or stalled translation events. Bacteria employ a nearly ubiquitous native ribosome rescue system, transfer-messenger RNA (tmRNA), that rapidly resolves stalled translational complexes and tags the incomplete polypeptides for degradation. Characterization of these tmRNA-tagged polypeptides could reveal previously unknown aspects of the bacterial stress response. To address this information gap, we have developed a synthetic tmRNA platform that reprograms the native system to allow for co-translational labeling of the incomplete polypeptides in live bacteria. A short tag reading frame (TRF) encoded on native tmRNA facilitates the addition of a natural peptidyl degradation tag to the polypeptides, and therefore offers an attractive modular domain to introduce synthetic peptide tag sequences and study the “degradome”. To study translational remodeling under stress, we modified the native tmRNA with an 6x-HIS isolation tag with the specific purpose of stabilizing, isolating, and characterizing the degradome in Escherichia coli. Using our inducible system, we have successfully isolated 6xHis-tagged proteins, verified dynamic controlled tagging, assessed broad-spectrum tag introduction with mass spectrometry. Our results capture known tmRNA substrates and excitingly show that tagged protein profiles are markedly different under stress. We investigated the shifting degradome in cells experiencing translational stress associated with serine starvation induced by serine hydroxamate. In cells lacking RelE, the mRNA interferease toxin that cleaves mRNA in the ribosome A site, we find a dramatic shift away from catalytic protein degradation and distinct, disparate enrichment of ribosomal proteins in the degradome under stress. These latter results suggest a new specific role for RelE in regulating ribosome protein abundance under translational stress conditions
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    Physiological dynamics of injury and regeneration in the clonal freshwater annelid Pristina leidyi
    (2022) Rennolds, Corey William; Bely, Alexandra E; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The threat that mechanical injury poses to homeostasis and survival has spurred the evolution of diverse processes to mitigate these effects. The most dramatic of these is regeneration, a process that restores the form and function of lost body parts. The apparent benefits of regeneration may come at considerable cost, however, and these may substantially diminish regeneration’s adaptive value in certain contexts, potentially contributing to evolutionary losses of regeneration. The costs and benefits of regeneration are poorly understood in most animals, precluding more than speculation of the evolutionary drivers of regeneration. Naids are a group of small, clonally reproducing freshwater annelids that feature great diversity of regenerative ability and are well suited to experimental studies. I used the species Pristina leidyi to determine how injury and regeneration affect organismal function and fitness, integrating physiological and molecular approaches. I first investigated how injury and regeneration differentially affect an individual’s ability to tolerate environmental stress, an ecologically relevant and energetically demanding task. I found that stress tolerance is reduced by regeneration in a stressor- and tissue-specific manner while, unexpectedly, tolerance is temporarily improved shortly after injury. These effects are unrelated to whole-organism metabolic rate, which surprisingly does not differ between early and late injury recovery. Using 3’ TagSeq, I found that, while injury and heat stress elicit largely distinct responses, both upregulate certain shared damage control pathways. I then tested whether the physiological cost of regeneration has potential to translate into fitness costs by examining the interaction between regeneration and reproduction, which occurs by asexual fission in this species. By modulating resource availability, I found evidence for an energetic trade-off between regeneration and reproduction that is masked when food is abundant. This tradeoff is manifested through a reduction in per-offspring allocation rather than reproductive rate. Overall, my results demonstrate that injury and regeneration costs are highly context dependent in P. leidyi. More broadly, these findings contrast in key ways from evolutionarily distant animals with very different life history traits, illustrating the importance of investigating the physiological mechanisms that may mediate selection on regeneration in diverse lineages.
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    “STARTED FROM THE BOTTOM, NOW WE’RE…WHERE?”” A QUALITATIVE ANALYSIS OF STRESS AND COPING AMONG HIGHLY EDUCATED BLACK WOMEN
    (2021) Ellick, Kecia Lurie; Lewin, Amy B; Roy, Kevin M; Family Studies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Rationale: Black women suffer disproportionate rates of stress-related diseases including heart disease, diabetes, cancer, maternal mortality, and depression. Education is promoted as a protective factor against these outcomes. An increasing number of Black women are leveraging advanced degrees to secure leadership positions in education, law, science, and technology. Yet, highly educated, middle-class Black women experience the same deleterious health outcomes, at the same rates, as Black women living in poverty. This suggests that neither education nor its correlates protect Black women from harmful outcomes. It further suggests that, for Black women, the cost of social mobility afforded by advanced education may result in diminishing returns by reproducing and reinforcing social inequalities that inform and exacerbate negative experiences.Purpose: The purpose of this study was to explore the experiences of highly educated Black women during their prime work, partnering, and reproductive years. This study examined the strategies that highly educated Black women employed to cope with stressors perceived while navigating, negotiating, and performing multiple roles, social identities, and responsibilities in their personal and professional lives. Methods: Data was collected from a sample of Black, middle-class women living in Georgia, ages 28 - 49, with doctorate degrees (n = 24, Mage = 40.2) via in-person, semi-structured interviews. Following a constructivist grounded theory approach, a triadic scheme of open, axial, and selective coding will be performed to uncover emergent themes from women’s narratives. Findings: Evaluation of the data revealed three central themes that serve as the main findings of this study and answer the study questions about how highly educated Black women experience and cope with stress: 1) redefining of the strong Black woman, 2) prioritization of self-care practices and, 3) unapologetic authenticity. Discussion: This study explored the heterogeneity of Black women and contributes to the body literature focused on the interactive effects of race, gender, and class. It provides empirical data on the ways in which Black women experience, perceive, and respond to stress and highlights the ways in which Black women take proactive approaches to protect their health and well-being.
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    TOXIN-ANTITOXIN SYSTEMS AND OTHER STRESS RESPONSE ELEMENTS IN PICOCYANOBACTERIA AND THEIR ECOLOGICAL IMPLICATIONS.
    (2020) Fucich, Daniel Christopher Ehlers; Chen, Feng; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Picocyanobacteria (mainly Synechococcus and Prochlorococcus) contribute significantly to oceanic primary production. Unlike Prochlorococcus, which is mainly constrained to the warm and oligotrophic ocean, Synechococcus has a ubiquitous distribution. Synechococcus is present in freshwater, estuarine, coastal, and open ocean habitats. They have also been found in polar regions and hot springs. Endemic to the hot and the cold, the saline and the fresh, and every condition in between, Synechococcus appears to have the capability to adapt and tolerate nearly any environment and climate. This ability to adapt to any aquatic environment is possible through their genome plasticity, a character that is not present in the Prochlorococcus.Due to the differential distribution of the genera, Synechococcus is considered a generalist and Prochlorococcus is considered a specialist in ecological theory. More than 400 picocyanobacterial genomes have now been sequenced, and this large genomic resource enables comprehensive genome mining and comparison. One possibility is to study the prevalence of Toxin-Antitoxin (TA) systems in picocyanobacterial genomes. TA systems are present in nearly all bacteria and archaea and are involved in cell growth regulation in response to environmental stresses. However, little is known about the presence and complexity of TA systems in picocyanobacteria. By querying 77 complete genomes of freshwater, estuarine, coastal and ocean picocyanobacteria, Type II TA systems (the most well studied TA family) were predicted in 27 of 33 (81%) Synechococcus strains, but no type II TA genes were predicted in any of the 38 Prochlorococcus strains. The number of TA pairs varies from 0 to 80 in Synechococcus strains, with a trend for more type II TA systems being predicted in larger genomes. A linear correlation between the genome size and the number of putative TA systems in both coastal and freshwater Synechococcus was established. In general, open ocean Synechococcus contain no or few TA systems, while coastal and freshwater Synechococcus contain more TA systems. The type II TA systems inhibit microbial translation via ribonucleases and allow cells to enter the “dormant” stage in adverse environments. Inheritance of more TA genes in freshwater and coastal Synechococcus could confer a recoverable persister state which would be an important mechanism to survive in variable environments. Different genotypes of Synechococcus are present in the Chesapeake Bay in winter and summer. Winter isolates of Synechococcus have shown high tolerance to cold conditions and other stressors. To explore their potential genetic capability, complete genomes of five representative winter Synechococcus strains CBW1002, CBW1004, CBW1006, CBW1107, and CBW1108 were fully sequenced. These five winter strains share many homologs that are unique to them and not shared with pelagic Synechococcus. Winter Synechococcus genomes are enriched with particular desaturases, chaperones, and transposases. Similar amino acid sequences and annotated features were not found in distantly related Synechococcus from Subcluster 5.1. These shared genomic features between the winter strains imply that maintaining membrane fluidity, protein stability, and genomic plasticity are important to cold adaption of Synechococcus. The winter strains also contain genes that are not traditionally considered with the canonical bacterial cold shock response. They contain a particularly high abundance of Type II TA pairs with complex association networks. They feature promiscuous toxins, like VapC, that pair with multiple antitoxins, which support the mix and match hypothesis. Winter strains also contain more monogamous toxins, such as BrnT, which tend to pair with their traditionally named antitoxin, BrnA. Expression of certain TA transcripts in response to environmental stress has been observed in the model strain CB0101, and the activity of one TA pair in CB0101 for growth arrest has been experimentally confirmed via heterologous expression in E. coli. My thesis work has identified interesting genetic systems related to niche partitioning of picocyanobacteria, particularly among the Chesapeake Bay Synechococcus. Future studies are paramount to understand the functional role of TA systems, desaturases, chaperons, and transposases of picocyanobacteria under various environmental stressors.
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    Stress, Mental Health, and Self-Care among Refugee Teachers in Malaysia
    (2020) Gosnell, Nicole; O'Neal, Colleen; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The mental health of post-conflict refugee teachers is understudied, yet critically important given the current refugee crisis which has displaced more than 70 million people (UNHCR, 2019). Teachers in hidden refugee schools are often refugees themselves, have little teacher education, and are faced with overwhelming classroom demands and other unique stressors. This study utilizes a mixed method design to examine stress, mental health (i.e., depression, and anxiety), and self-care among teachers in hidden refugee schools in Kuala Lumpur, Malaysia. Quantitative data are archival, collected in Malaysia in 2013. Quantitative study participants included 97 primarily Burmese refugee teachers and 26 non-refugee teachers living in Malaysia. Quantitative measures included (a) Depression, Anxiety, and Stress Scales (DASS); (b) a self-care strategies questionnaire, and (c) a demographic questionnaire. Quantitative results suggest that refugee teachers have significantly higher rates of mental health and stress, but lower rates of self-care as compared to their non-refugee peer teachers. In addition, higher rates of self-care are associated with lower rates of mental health symptoms and stress rates; the association is moderated by age. Qualitative data were collected in June 2018 via individual interviews with eleven Burmese refugee teachers working in Malaysia. Qualitative results shed light on the unique definitions and experiences of stress, mental health, and self-care among refugee teachers in the context of macrolevel factors. Overall, this dissertation found that macrolevel factors unique to being a refugee impact refugees’ rates, experiences, and definitions of microlevel mental health symptoms, stress, and self-care.
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    Stress and achievement in elementary school students: The mediating role of growth mindset
    (2019) Babaturk, Leyla; O'Neal, Colleen R; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The achievement gap is one of the most pernicious education problems in the United States, and stress has a negative impact on achievement. Growth mindset may explain how stress impacts achievement. This study used a short-term longitudinal design (n = 251; 36% DLL) to evaluate growth mindset as a mediator of the negative impact of stress on literacy achievement in 3rd - 5th grade students. Results confirmed that perceived stress was negative related to achievement. The present study also explored whether mediation model results differ between dual-language learning (DLL) and English-native students. Although growth mindset did not act as a mediator in the full sample, growth-minded attributions mediated the negative effect of stress on achievement for non-DLL students only. These results hold implications for understanding how to help students with the consequences of stress on their mindsets and academic performance.
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    Using Mindfulness to Reduce Occupational Stress and Burnout in Music Teachers: A Randomized Controlled Trial
    (2019) Varona, Dana Arbaugh; Hewitt, Michael P; Prichard, Stephanie; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of this study was to examine the effects of a mindfulness-based intervention (MBI) on K-12 music educators' self-reported responses to occupational stress and burnout. Secondary purposes were (a) to explore the experiences of K-12 music educators who underwent a four-week web-based MBI; and (b) to determine if there were any potential relations between participants' demographic and descriptive data and their pretest levels of self-reported responses to occupational stress and burnout. Two hundred fifty in-service music teachers were randomly assigned to either the treatment or waitlist-control group. Treatment group participants (n = 90) underwent a four-week online MBI known as the Mindfulness Training for Music Educators (MTME). Waitlist-control group participants (n = 160) were not provided with any mindfulness training but were given full access to the MTME following completion of the study. All participants completed assessments of self-reported responses to occupational stress and burnout at pretest, midpoint, and posttest. Following completion of the MTME, treatment group participants provided data regarding their experiences with the MTME and its feasibility. Results of mixed effects regression suggested that treatment group participants reported significantly steeper decreases in responses to occupational stress and burnout than waitlist-control group participants. Cross-sectional analyses at pretest indicated that age, female gender, salary dissatisfaction, perceived lack of administrative support, and perceived lack of parental support were significant predictors of increased responses to occupational stress, while teaching secondary school, salary dissatisfaction, perceived lack of administrative support, and perceived lack of parental support were significant predictors of increased responses to burnout. For each additional extracurricular hour worked beyond the school day, there was small but significant decrease in burnout. During the intervention period, the treatment group participants experienced a variety of occupational stressors including managing students, major events, interpersonal conflict, scheduling issues, and illness. Participants primarily responded to occupational stress with emotion-focused coping strategies such as breathing and meditation. Overall, treatment group participants found the MTME to be feasible for reducing stress and burnout while working as a music teacher and would recommend it to a fellow music educator.
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    Stress and Literacy Achievement: The Potential Moderating Role of Socioemotional Factors for Dual Language and Non-Dual Language Students
    (2019) Goldthrite, Antoinette Marie; O'Neal, Colleen R; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The achievement gap is one of the most pervasive education problems in the United States. Stress may contribute to this achievement gap, since it is inversely related to achievement. Dual Language Learners (DLLs) may face a wide variety of stressors that contribute to their lower grades, relative to their non-DLL peers. Researchers have turned to a slew of socioemotional factors to see which may help reduce the gap between ethnic minority and White students. However, in the face of stress, these factors may not all be equally protective. This study explored the potential protective effects of three socioemotional factors – grit, growth mindset, and anger regulation - by using moderation analyses within both a self-regulation and a risk and resilience framework in an ethnically diverse sample of 3rd, 4th, and 5th grade students. Results were compared between the DLL (N = 81) and non-DLL (N = 170) students. Results indicated that grit was a significant moderator of the relationship between stress and reading achievement for the for the DLL subsample; those with high grit outperformed those with low grit in times of high stress. Additionally, in the DLL group, growth mindset moderated this relationship; those with high growth mindset outperformed those with low growth mindset in times of low perceived stress, while those with low and high growth mindset performed similarly in times of high perceived stress. Anger regulation was a significant moderator for the non-DLL group; those with reporting high usage of anger regulation skills outperformed those with low use of anger regulation in times of high stress. The findings of this study suggest that there may be different protective factors for different groups facing stress, though more research needs to be conducted to explore this relationship. School administrators and school psychologists should continue to consider the potential benefits of fostering socioemotional skills to promote reading achievement but are cautioned to critically consider and tailor which interventions are selected for which students.
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    THE INFLUENCE OF STRESS AND SOCIAL SUPPORT ON PARENTING BEHAVIORS AMONG LOW-INCOME FAMILIES: MEDIATIONAL PATHWAYS TO CHILDREN’S SOCIAL DEVELOPMENT
    (2019) Kuhns, Catherine Emily; Cabrera, Natasha; Human Development; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Economic stress been shown to compromise children’s social development and undermine parenting behaviors in mothers of young children. A separate literature suggests that social support may attenuate the negative effects of maternal stress on parenting behaviors. Guided by the Family Stress Model and the Stress Buffering Model, this study examined the indirect pathways from maternal experiences of stress (economic and parenting) to children’s social competencies and behavior problems longitudinally in a sample of children from the Early Head Start Family and Child Experiences Survey (Baby FACES). It also tested the moderating effects of two types of social support (instrumental and emotional) on the negative association between stressors (economic and parenting) and children’s social skills. Using structural equation modeling (SEM) results demonstrated support for the Family Stress Model, such that economic stress (at age 1) was longitudinally and indirectly related to children’s social competencies and problem behaviors (at age 3) via observed maternal sensitivity (at age 2). That is, higher levels of economic stress were related to elevated levels of behavior problems and lower levels of social competencies because it increased parenting stress and decreased maternal sensitivity. However, there was no evidence that social support moderated the association between either type of stress and parenting. Findings are discussed in light of policy and programmatic efforts to broaden support of families and children by incorporating services that promote sensitive parent-child interactions and reduce maternal parenting stress.
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    Functional Neuroimaging of the Social Regulation of Emotion in Schizophrenia
    (2016) McCarthy, Julie McCarthy; Blanchard, Jack J; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Negative symptoms in schizophrenia are characterized by deficits in normative experiences and expression of emotion. Social anhedonia (diminished pleasure from social experiences) is one negative symptom that may impact patients’ motivation to engage in meaningful social relationships. Past research has begun to examine the mechanisms that underlie social anhedonia, but it is unclear how this lack of social interest may impact the typically positive effects of social buffering and social baseline theory whereby social support attenuates stress. The present pilot study examines how social affiliation through hand holding is related to subjective and neural threat processing, negative symptoms, and social functioning. Twenty-one participants (14 controls; 7 schizophrenia) developed social affiliation with a member of the research staff who served as the supportive partner during the threat task. Participants displayed greater subjective benefit to holding the hand of their partner during times of stress relative to being alone or with an anonymous experimenter, as indicated by self-reported increased positive valence and decreased arousal ratings. When examining the effects of group, hand holding, and their interaction on the neurological experience of threat during the fMRI task, the results were not significant. However, exploratory analyses identified preliminary data suggesting that controls experienced small relative increases in BOLD signal to threat when alone compared to being with the anonymous experimenter or their partner, whereas the schizophrenia group results indicated subtle relative decreases in BOLD signal to threat when alone compared to either of the hand holding conditions. Additionally, within the schizophrenia group, more positive valence in the partner condition was associated with less severe negative symptoms, better social functioning, and more social affiliation, whereas less arousal was correlated with more social affiliation. Our pilot study offers initial insights about the difficulties of building and using social affiliation and support through hand holding with individuals with schizophrenia during times of stress. Further research is necessary to clarify which types of support may be more or less beneficial to individuals with schizophrenia who may experience social anhedonia or paranoia with others that may challenge the otherwise positive effects of social buffering and maintaining a social baseline.