Browsing by Author "Tabatabaei Sadeghi, Sahar"

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    Climatic drivers of Southeast U.S hydrology
    (University of Alabama Libraries, 2019) Tabatabaei Sadeghi, Sahar; Tootle, Glenn; University of Alabama Tuscaloosa
    The growing demand for water has raised concerns regarding future resource scarcity. For water management, agriculture, fisheries needs and hydro-climatic research, there has been conflict over water in Southeastern United States (SEUS). In this dissertation, I intend to evaluate the temporal (monthly) variability of El Nino on SEUS streamflow and Atlantic Ocean Sea Surface Temperature (AO SST) variability and SEUS streamflow. The development of an El Nino and the association of increased moisture (e.g., precipitation, streamflow) in coastal Mississippi and Alabama is misleading in agricultural practices (Sadeghi et al., 2019b). While annual increases were ~20%, this increase was in the winter and late-spring during the planting season for crops. Thus, moist soil conditions could delay crop planting. During the summer growing season, moisture was decreased and, thus, given the majority of agricultural lands are rain-fed and not irrigated, this could severely impact crop production (drought). A multi-decadal teleconnection was established between north Atlantic Ocean SSTs and SEUS streamflow (Sadeghi et al., 2019a). SEUS streamflow has been in a multi-decadal decline since ~1990 and the warming of north Atlantic Ocean SSTs exhibits a strong, linear relationship with this decline. The use of “raw” SSTs confirms previous efforts establishing an Atlantic Multidecadal Oscillation “like” signal in SEUS streamflow. Future research efforts will utilize the multi-decadal teleconnection of Atlantic Ocean SSTs to forecast SEUS streamflow. Future forecasts of Atlantic Oceans SSTs from multiple Global Climate Models (GCMs) will be used as independent variables in regression models to forecast future multi-decadal variability of SEUS streamflow. These results can be compared to “traditional” methods in which physically based distributed hydrologic models are developed and downscaled future “forcings” are input to determine future flows.
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    Evaluation of fluid dynamic effect on thin film growth in a horizontal type meso-scale chemical vapor deposition reactor using computational fluid dynamics
    (University of Alabama Libraries, 2013) Tabatabaei Sadeghi, Sahar; Klein, Tonya M.; University of Alabama Tuscaloosa
    To design and analyze chemical vapor deposition (CVD) reactors, computer models are regularly utilized. The foremost aim of this thesis research is to understand how thin film uniformity can be controlled in a CVD reactor. A complete understanding of chemical reactions that take place both in gas phase and at the deposition surface is required to predict thin film properties such as growth rate and composition precisely, however, deposition rates and surface topography can be determined by the arrival flux of reactants in a mass-transfer limited regime. In order to understand experimental thickness and roughness uniformity, a predictive model has been developed to study the fluid dynamic effect on thin film growth in a horizontal type reactor using velocity, temperature, pressure and viscosity as tunable parameters upon which velocity profiles within a CVD reactor have been evaluated using computational fluid dynamic (CFD) calculations. Through this predictive model, it is shown that fluid velocity is the major variable contributing to transverse roll cell formation compared to temperature and pressure gradients present during thin film deposition in a meso-scale CVD reactor. These results provide a physical insight regarding improved reactor operation conditions that influence uniformity.