The objectives of this research are to take advance steps to assess the potential impacts of sea level rise on our nation's estuarine environments and water resources management. Specific engineering solutions to control salinity intrusion are studied. Structure measures such as construction of tidal barriers, tidal locks, and through long term stream flow augmentation are investigated for their suitability. Quantification of the extent of the impacts is accomplished by means of computer model simulations. A laterally integrated two-dimensional. time dependent. finite difference numerical model is used to study time-varying tidal height. current and salinity. Through a selected estuary. parametric studies on scenarios of projected sea level rise, stream flow, channel roughness, change in cross-section profile, etc. are performed in order to have an in-depth understanding of estuarine processes for cases such as present condition versus future sea level rise, with or without control measures. The results of the parametric studies are summarized and engineering applications of individual control methods are discussed. / Master of Science

Analysis of three-phase, three-level VSIs is done for high-power high-voltage applications. Complete Space Vector Modulation (SVM) algorithm is developed for a three-phase, three-level converter. Special attention is given to minimization of output ripple and voltage balance of the dc-link input capacitors. Verification of the proposed SVM algorithm is done by computer simulation. Comprehensive small-signal modeling of the three-level converter with a resistive load is developed the first time. Steady-state solutions reveal that the voltage across dc-link input capacitors is constant at the half of the dc-link voltage. / Master of Science

As the use of unmanned vehicles continues to grow, so does the need for systems to safely test and operate these vehicles. While there are safety systems designed for this purpose, they are often developed for a specific vehicle platform. The Multi-Level Emergency Stop (MLES) system provides three user-defined emergency response contingencies that can be adapted to a wide variety of unmanned vehicles. The Multi-Level Emergency Stop system is designed to be an ad-on safety system that can be integrated into ground, air, or surface unmanned vehicles. A complete MLES system consists of a hand held transmitter and a vehicle mounted receiver. The three levels of contingencies are controlled by three switches on the transmitter. These switches engage and disengage contacts located in the receiver via a wireless link. The function of these contacts is determined by the user for each unique application. Presented in this thesis is the detailed hardware design and software layout of the Multi-Level Emergency Stop system. Also included are the performance results and operational tests. / Master of Science

The purpose of this study is to examine the relationship among student civic knowledge scores and several different variables each at the student, classroom/school, and national levels using the IEA CIVED study international data set collected in 1999 from 27 countries. The student level predictors included two elements of socioeconomic status (a student's parental education, their home literacy level measured by the number of books at home), student's perception of an open classroom climate, student aspiration of obtaining higher education, and other variables that were identified as relevant to the dependent variable in the literature. The classroom/school level predictors included teacher's degree in civics, in-service training, teaching confidence, and school safety in addition to the compositional variable created as the classroom/school averages by aggregating the student level variables. Then I investigated whether instructional methods focusing on the student activities the teacher employed in the classroom and an open classroom climate were associated after accounting for the above student and school level background variables. National level variables such as GNP, GINI index, democratic system, public education expenditure, and etc. as well as compositional variables obtained by aggregating the classroom/school variables were also added to the model to investigate if they were associated with students' civic knowledge scores and whether they could explain between nations variability. The study used a three-level hierarchical linear model to analyze the data, with number of students, N=56,579, number of classrooms/schools, J=3443, and number of countries, K=27. Some of the key findings was that there were significant variations of civics knowledge among nations, and significant variations of civic knowledge scores between school and within nations, no statistically significant association between teacher's practice and civics knowledge scores, however the student perception of an open classroom climate was significant at all 3 levels. These findings were interpreted in terms of policies and practices that could be implemented to improve students' civic knowledge. / Ph. D.

Coastal communities face threats of flooding associated with episodic storm events and high tides that are increasing in severity and frequency due to climate change and sea level rise (SLR). The Mid-Atlantic U.S. is experiencing SLR at rates faster than the global average, especially in Hampton Roads, Virginia where the rate of SLR is accelerating due to land subsidence. Adaptation plans for coastal flooding are mostly made at the municipality level, ignoring the propagation of water across its administrative boundaries. Impact assessment at the watershed scale identifies areas where municipalities will need to collaborate to mitigate the flood impact. The main purpose of this project was to evaluate the impact of flooding among watersheds in Hampton Roads and identify those most at risk that overlap one or more municipal boundary. Additionally, this research assessed the impact on land use/cover and population throughout the Hampton Roads region and within a case study watershed. To meet these objectives, we used U.S. Army Corps of Engineers 50-year floodplain and NOAA intermediate SLR scenarios for 2030, 2060, and 2090 to calculate the percent land area inundated for each watershed in Hampton Roads. Further, we assessed the flood impact on populations and specific land use/covers throughout the region for each SLR scenario, as well as within the Elizabeth River watershed. Key findings show that five watersheds will see a greater increase in inundated area than the surrounding watersheds, with two that overlap multiple municipalities. The anticipated land use impacts indicate significant inundation of land occupied by military, followed by commercial, industrial, and wetland covers both in Hampton Roads and within the Elizabeth River watershed. These findings not only highlight the need for more synchronized collaboration on adaptation between municipalities in Hampton Roads, but also provide a framework for the impact assessments in similar settings globally. / Master of Science / Coastal communities face numerous threats of flooding due to storm events and high tides. These events are becoming more frequent due to climate change and sea level rise (SLR). The Mid-Atlantic U.S. is experiencing SLR at rates faster than the global average, especially in Hampton Roads, Virginia where the rate of SLR is accelerating due to sinking land. Water movement does not recognize administrative boundaries but rather reflects physical features of the land. At the same time most plans to combat rising water levels are often made within administrative boundaries. The main objective of this research is to evaluate the flood impacts at the watershed scale and identify areas where localities will need to collaborate to reduce flood impact. This research further explores answers the following questions: 1.)Which watersheds in Hampton Roads are most prone to flooding?; and 2.) How many people will be impacted by flooding, and what kinds of land uses will be impacted? To answer these questions, we used floodplain data and SLR scenarios for 2030, 2060, and 2090 to determine land area inundated for each watershed in Hampton Roads. Further, we summarized population and land use impacts within the floodplain for the entire region, as well as within a case study of the Elizabeth River watershed in Norfolk and Portsmouth. Key findings include five watersheds that will see a greater increase in inundated area with SLR than surrounding watersheds, two of which contain multiple municipalities. Finally, we identified significant impacts for military, commercial, industrial, and wetland land covers both in Hampton Roads and within the Elizabeth River watershed.

Reservoir level and discharge data were collected for three Tennessee Valley Authority (TVA) dams (Chickamauga, Watts Bar and Douglas) on the Tennessee river in the Eastern Tennessee Seismic Zone (ETSZ). Earthquake catalog data was also collected for the ETSZ from 1980-2018. Well levels from 2 U.S. Geological Survey groundwater monitoring wells were also collected. Rainfall data were collected for the ETSZ. Reservoir, well and rainfall data were examined for correlation with earthquake occurrence rates. High Pearson correlation and anti-correlation coefficients (.7-.9) were obtained for the reservoir level and dam discharge volume rates vs monthly earthquake counts. Pearson correlation coefficients for rainfall and well level vs. monthly earthquake counts were small (.0-.2). A large difference in earthquake rates between the months of February (low rate) and April (high rate) over the 39 year study period was observed. The difference in earthquakes rates for February and April are statistically significant at the 95% confidence interval using the two sample Poisson rate test. The high correlations for the reservoir level and flow discharge vs. earthquake counts provides strong evidence of hydro-seismicity occurring in the ETSZ from seasonal fluctuations in reservoir level and discharge flow. / Master of Science / Reservoir level and discharge data were collected for three Tennessee Valley Authority (TVA) dams (Chickamauga, Watts Bar and Douglas) on the Tennessee river in the Eastern Tennessee Seismic Zone (ETSZ). Reservoir discharge and level data was collected for the three reservoirs. Also collected were rainfall data for the study area. This was provided by the TVA. Earthquake and well level data was collected from the USGS. High Pearson correlations for dam discharge and reservoir level vs. earthquake counts provided strong evidence of hydro-seismicity in the ETSZ.

The purpose of this thesis was to assess the repeatability and reproducibility of two high-speed macrotexture measuring systems. The first portion of the study collected macrotexture measurements using the two high-speed systems on the Virginia Smart Road facility and validated the reproducibility of the mean profile depth (MPD) measurements with reference CT Meter measurements. The various data sets were then compared with each other. The objective was to determine whether the two systems are collecting repeatable and reproducible data. The analysis showed that the two high-speed systems investigated have good repeatability (0.105 mm for the Ames and 0.113 mm for the SCRIM) when measuring the average MPD of the sections investigated. The two systems produce measurements that are highly-correlated (Ames R2 = 0.9591 and SCRIM R2 = 0.9157) with the reference ones obtained with the CT Meter. While the Ames systems, with the data processed using the Virginia Tech filter, measures MPD values that are very close to those of the CT Meter, with a virtually zero systematic bias. The SCRIM obtains slightly lower readings. The differences are thought to be due to the filtering of the raw pavement elevation measurements used by the SCRIM processing software to eliminate dropout and spikes in the laser measurements. / Master of Science / The researched compared two different devices used to record data for a surface property of pavement, macrotexture. The macrotexture is a measure of the spaces in between the particles making up the surface of the asphalt. This property is linked to the level of friction on the roadways affecting safety. The readings from each of the devices were validated through a reference device in order to insure they were obtaining reliable results on the Virginia Smart Road. The repeatability and reproducibility of each of the devices was examined to determine whether the two systems were collecting repeatable and reproducible data. It was determined the two devices had good repeatability and were highly correlated with the reference device. The first device called the Ames system obtained measurements very close to those of the reference device, with a virtually zero systematic bias. The second device called the SCRIM system obtained measurements close to the reference device but slightly lower. Through the comparisons and data analysis, an equation permitting users to convert readings from the SCRIM to Ames system and vice versa was computed. Because one device obtains slightly higher readings than the other, this equation is very important in order to have comparable results.

Yes / Background: Stroke has been linked to a lack of physical activity; however, the extent of the association between inactive lifestyles and stroke risk has yet to be characterized across large populations. Purpose: This study aimed to explore the association between activity-related behaviors and stroke incidence. Methods: Data from 1999 to 2018 waves of the concurrent cross-sectional National Health and Nutrition Examination Survey (NHANES) were extracted. We analyzed participants characteristics and outcomes for all participants with data on whether they had a stroke or not and assessed how different forms of physical activity affect the incidence of disease. Results: Of the 102,578 individuals included, 3851 had a history of stroke. A range of activity-related behaviors was protective against stroke, including engaging in moderate-intensity work over the last 30 days (OR = 0.8, 95% CI = 0.7–0.9; P = 0.001) and vigorous-intensity work activities over the last 30 days (OR = 0.6, 95% CI = 0.5–0.8; P < 0.001), and muscle-strengthening exercises (OR = 0.6, 95% CI = 0.5–0.8; P < 0.001). Conversely, more than 4 h of daily TV, video, or computer use was positively associated with the likelihood of stroke (OR = 11.7, 95% CI = 2.1–219.2; P = 0.022). Conclusion: Different types, frequencies, and intensities of physical activity were associated with reduced stroke incidence, implying that there is an option for everyone. Daily or every other day activities are more critical in reducing stroke than reducing sedentary behavior duration.

Storm surges induced by tropical cyclones have been ravaging coastal communities worldwide, where a growing number of people reside. Tremendous life and economic losses are caused by tropical cyclones, contributing to more than half of the damages induced by natural hazards. To improve the resilience of coastal communities to surge hazards, it is of great importance to provide reliable and efficient real time forecasts of the spatiotemporal evolution of storm surge, as well as reliable predictions of the probabilistic surge hazards under future conditions. Three specific goals are addressed in this work. Studies on characterization and prediction of surge before a hurricane landfall show that a dimensionless relationship between intensity scaled surge magnitude and wind-duration scaled surge timing may effectively be used for rapid and reliable forerunner surge forecasting. Investigation of how probabilistic surge hazard changes with sea level rise (SLR) shows that the probabilistic surge with SLR can be 1.0 m larger, while different individual storm's surge with the same magnitude can be 1.5 m larger or 0.1 m smaller, indicating the importance of not relying on results from a limited number of storm surge events to assess the probabilistic surge hazard change to SLR. Finally, studying the temporal evolution of coastal flooding changes with SLR shows forerunner surge responds differently to SLR than peak surge, and that storm forward speed is a key factor determining the forerunner-SLR response. / Ph. D. / Flooding induced by tropical cyclones have been ravaging coastal communities worldwide, where a growing number of people reside. Tremendous life and economic losses are caused by tropical cyclones, contributing to more than half of the damages induced by natural hazards. To improve the resilience of coastal communities to flood hazards, it is of great importance to provide reliable and efficient real time forecasts of the flooding time series, as well as reliable predictions of the statistical flood elevation under future conditions. Three specific goals are addressed in this work. Studies on forecasting early coastal flooding show that a dimensionless relationship between storm characteristics and flood elevation may effectively be used for rapid and reliable early flood forecasting. Investigation of how statistical flood elevation changes with sea level rise show the importance of modeling the physical processes and of the storm sample size to address this issue. Finally, studying the coastal flooding time series with sea level rise shows early flooding responds differently to sea level rise, compared to maximum flooding, and that storm’s moving speed is a key factor determining flooding response to sea level rise.

Master of Arts / Department of Modern Languages / Abby Franchitti / The role of first language (L1) has been controversial in foreign language (FL) learning and teaching. This study examines the relationship between L1 use and gender and level of education of EFL teachers as well as gender and EFL proficiency level of learners in an Afghan university setting. It also investigates the relationship between FL use and learner anxiety by learner gender and EFL proficiency level. The study hypothesized that female FL teachers use the L1 more than male teachers in FL classrooms. Second, low FL proficiency learners consider L1 use as necessary in FL classrooms. Third, low FL proficiency students experience more anxiety with the exclusive use of FL than higher level learners. Fourth, female learners experience more anxiety than male students with the exclusive use of FL by learners and teachers. Twenty EFL teachers participated in the study by completing a 19-item questionnaire and sixty EFL learners by completing a 27-item questionnaire about their views towards L1/FL use and learner anxiety. The data, analyzed through SPSS software, included calculating frequencies and percentages, computing correlations, and conducting independent-samples t-tests to compare the mean difference between the variables. The first hypothesis was not supported as male teachers reported using the L1 more than female teachers. The study also revealed that male teachers with BA and MA degrees used the L1 more than female teachers with BA degrees. In contrast, female teachers with MA degrees used the L1 more than male teachers with BA and MA degrees and also more than female teachers with BA degrees. The results supported hypothesis two. More elementary learners considered the use of L1 as necessary than intermediate and advanced students. The findings also supported hypotheses three and four. Elementary learners as well as female students experienced more anxiety with the exclusive use of FL than intermediate and advanced level students and male learners. The principal conclusion indicated a significant positive correlation between the exclusive use of FL and learner anxiety.