Dissertation Defenses

Doctoral students who have an upcoming dissertation oral defense are posted here. So why not take this opportunity to learn about the research that our graduate students are doing!

Dissertation Defense for Zhexuan Zhang

Program: Mechanical Engineering: PHD

Department Contact Email: tracey.harvey@unh.edu

Defense Title: The Stability and Nonlinear Dynamics of Spatially-Extended Langmuir Circulation

Defense Date and Time: 07/29/14 10:00 am

Defense Location: Kingsbury Hall, N334

Defense Advisor: Prof. Gregory Chini


Defense Abstract: Langmuir circulation (LC) is a wind- and surface-wave-driven convective flow on lateral scales from meters to several kilometers (the ocean submesoscales) in the mixed layer (ML), the upper 50-100 meters of the ocean. Despite the importance of LC to the transfer of heat, mass, and momentum between the atmosphere and oceans, ocean general circulation models (OGCMs) - a key component of computational climate models - cannot resolve these comparably fine-scale flows, whose effects must therefore be parameterized. While much is known about the physics of LC in small domains, having O(100) meter dimensions, a necessary prerequisite for parameterizing LC in OGCMs is a proper understanding of the stability and intrinsic nonlinear dynamics of spatially-extended arrays of Langmuir cells.

In this theoretical investigation, a complement of linear and secondary stability analysis and direct numerical simulation, strategically initialized using a superposition of the relevant base flow plus a small-amplitude contribution of the fastest-growing instability mode, is used to study three scenarios in which spatially-extended LC dynamics may be manifest.

First, the influence of downwind modulation on the dynamics of Langmuir cells is investigated using an asymptotically reduced version of the Craik-Leibovich (CL) equations governing LC. The reduced CL (rCL) equations render numerical simulations in very long downwind domains more feasible. Secondary stability analysis and numerical simulations of the rCL equations empirically demonstrate that the rCL equations admit dynamics reminiscent of LC. A key finding is a numerically-exact nonlinear defect traveling-wave solution of the rCL equations, associated with a novel downwind-modulated 2:1 spatial resonance phenomenon.

Next, the dynamics of LC in cross-wind extended domains is considered. For this purpose, downwind variability is suppressed. The effects of both density stratification and Coriolis accelerations are incorporated to study the effects of horizontal stratification, associated with submesoscale lateral fronts in the upper ocean, on LC. It is shown that LC, generally viewed as a prominent vertical mixing mechanism, may actually play a role in ML re-stratification.

Finally, the stability of steady downwind invariant LC states to long-wavelength cross-wind-varying disturbances and in the presence of (stable) vertical stratification is studied using spatial Floquet theory. A variety of secondary instabilities is identified and catalogued. Numerical simulations reveal the potential for certain long-wavelength instabilities to radically modify the uniformly patterned base state, deepening the ML in some cases and driving modulated internal-wave packets in others.


 

Dissertation Defense for Jessica Ulrich-Shad

Program: Sociology: PHD

Department Contact Email: deena.peschke@unh.edu

Defense Title: Migration, Views on Development, and Making Community in Rural Recreation Counties in hte U.S.

Defense Date and Time: 08/05/14 2:00 pm

Defense Location: MUB 330

Defense Advisor: Dr. Thomas Safford


Defense Abstract: Rural places rich in natural amenities and recreational opportunities have experienced consistent population growth since the 1970s, primarily because of in-migration. As these places continue to attract amenity migrants, questions about the nature and consequences of amenity-growth remain relevant. This dissertation is a collection of three interrelated papers that examine the effect natural and recreational amenities have on rural migration patterns, attitudes towards development, and community making.
The first paper uses Census Bureau population estimates to examine whether recreational amenities have independent effects on net migration in rural areas and whether the effects hold among different age groups and during periods of economic recession. Counties with desirable recreational amenities did experience net in-migration from 2000 to 2010 regardless of other county-level attributes, although the direction and magnitude of the effect varied when taking the age, or lifecycle, group of migrants into account. The Great Recession had a significant impact on migration trends in rural areas, including reducing the effect of recreational amenities in migration.
The second paper uses data form the Community and Environment in Rural America (CERA) survey to examine views on development in rural recreation counties, including to what extent there is evidence of a "culture clash," that is, whether values and attitudes of new and long-term residents differ about local development issues. Factors other than length of residence, such as residents' attachment to the natural enviornment and quality of life, their political party affiliation and educcation, and the rurality of their county were better predictors of attitudes toward development.
The final paper draws on a case study of a town in a rural recreation county in Colorado. Interviews and observations are used to examine what happens to community life as a rural place transitions to a rural amenity destination. Although residents continue to feel a strong sense of community, they see development as an increasingly controversial local issue that is dividing the community into two distinct social groups: one that is resistant to change and another that is open to development.
Overall, the research demonstrates the important role recreational amenities play in rural migration patterns in the context of an economic recession and among different age groups. It also challenges the idea that new and long-term residents of amenity growth communities have starkly different views on development and ways of making community.


 

Dissertation Defense for Desiree Wiesen-Martin

Program: Sociology: PHD

Department Contact Email: deena.peschke@unh.edu

Defense Title: The Interaction of Individual and Community Characteristics in Intimate Partner Violence Help Seeking

Defense Date and Time: 08/13/14 8:00 am

Defense Location: MUB 321

Defense Advisor: Dr. David Finkelhor


Defense Abstract: Intimate partner violence (IPV) is a public health concern and IPV help seeking is the focus of many intervention/prevention policies and programs. This dissertation increases the body of research examining IPV help seeking by examining the impact of community and state characteristics on IPV help seeking, as well as the impact of community and state characteristics on the relationship between individual characteristics and IPV help seeking. The literature which examines the relationship between individual characteristics in IPV help seeking is abundant, but the IPV help seeking literature gets smaller when considering community and state characteristics, and is virtually non-existent when looking at how community and state characteristics influence the relationship between individual characteristics and IPV help seeking.
Using data from an evaluation of STOP Violence against Women grant funded programs, multilevel modeling regression and logistic regression models are used to examine main effects of individual, community, and state characteristics as well as cross-level interactions between individual and community and individual, and individual and state characteristics. Further multilevel regression and logistic regression models are conducted to examine differences in IPV help seeking by sexual assault status in the IPV relationship.
Three significant and important findings deserve special attention. Findings indicate that coordinated community responses to domestic violence and sexual assault may not be meeting the needs of older females impacted by IPV. Informal social support was found to decrease the likelihood of failing to seek help when it was needed. The relationship between informal social support and IPV help seeking from formal supports suggests that more research is needed to see if the reduction in help seeking associated with informal social support negatively impacts victims of IPV. Lastly, progressive domestic violence and sexual assault laws were found to be associated with a decrease in help seeking. This suggests that progressive laws, often defined as being more punitive, may actually inhibit help seeking by victims of IPV. Together these findings indicate a need for consideration of paradoxical relationships when constructing and implementing policies to address IPV.


 

Dissertation Defense for Meghan Mills

Program: Sociology: PHD

Department Contact Email: deena.peschke@unh.edu

Defense Title: The Impact of Socioeconomic Status and Goal-Striving Stress on Depression and Delinquency among Rural Youth

Defense Date and Time: 03/18/15 10:00 am

Defense Location: Carsey Institute, Huddleston Hall

Defense Advisor: Dr. Karen Van Gundy


Defense Abstract: According to the stress process framework,both socioeconomic status and goal-striving stress serve as critical chronic stressors; however, little to no research has examined the relationship between socioeconomic status, goal-striving stres, and well-being using this theoretical framework. Using longitudinal data from Waves I (2009) & II (2011) of the Rural Youth Study (RYS), my dissertation examines how goal-striving stress varies by socioeconomic status, and it investigates the impact of goal-striving stress on delinquent behaviors and depressive symptoms among rural youth over time, and net of crucial components of the stress process framework (i.e., stressful life events, family attachment, and personal resources). More specifically, my research examines the unique effects of educational, occupational, and community goal-striving stress as well as the effects of a combined measure of overall goal-striving stress.
Analyses reveal a significant negative relationship between socioeconomic status and depressive symptoms, but this relationship is mediated by family attachment. Controlling for prior depressive symptoms, only a significant positive relationship between community goal-striving stress and depressive symptoms remains. However, with regard to delinquent behaviors, educational, community, and overall goal-striving stress are significantly positively related to delinquent behaviors net of prior delinquency. Such findings remain even with statistical adjustments for socioeconomic status, stressful life events, family attachment, and personal resources.
The findings of my dissertation illustrate the importance of considering various types of goal-striving stress and considering their unique effects on different outcomes. My findings highlight the importance of a "new" type of goal-striving stress among rural youth, community goal-striving stress. Additionally, my findings indicate that goal-striving stress may be especially important for understanding the unequal social distribution of outcomes such as delinquency that are not as clearly or directly associated with socioeconomic status. Such findings highlight the important role of the stress process framework for understanding socioeconomic disparities in outcomes. In sum, goal-striving stress is a critical topic for future research using the stress process framework with important policy implications for improving the well-being of rural youth.


 

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