http://hdl.handle.net/2097/4 2013-06-20T10:24:42Z 2013-06-20T10:24:42Z Paul, George http://hdl.handle.net/2097/15914 2013-06-18T19:17:22Z 2013-06-18T00:00:00Z

EVALUATION OF SURFACE ENERGY BALANCE MODELS FOR MAPPING EVAPOTRANSPIRATION USING VERY HIGH RESOLUTION AIRBORNE REMOTE SENSING DATA Paul, George Agriculture is the largest (90%) consumer of all fresh water in the world. The consumptive use of water by vegetation represented by the process evapotranspiration (ET) has a vital role in the dynamics of water, carbon and energy fluxes of the biosphere. Consequently, mapping ET is essential for making water a sustainable resource and also for monitoring ecosystem response to water stress and changing climate. Over the past three decades, numerous thermal remote sensing based ET mapping algorithms were developed and these have brought a significant theoretical and technical advancement in the spatial modeling of ET. Though these algorithms provided a robust, economical, and efficient tool for ET estimations at field and regional scales, yet the uncertainties in flux estimations were large, making evaluation a difficult task. The main objective of this study was to evaluate and improve the performance of widely used remote sensing based energy balance models, namely: the Surface Energy Balance Algorithm for Land (SEBAL), Mapping Evapotranspiration at high Resolution and with Internalized Calibration (METRIC), and Surface Energy Balance System (SEBS). Data used in this study was collected as part of a multi-disciplinary and multi-institutional field campaign BEAREX (Bushland Evapotranspiration and Agricultural Remote Sensing Experiment) that was conducted during 2007 and 2008 summer cropping seasons at the USDA-ARS Conservation and Production Research Laboratory (CPRL) in Bushland, Texas. Seventeen high resolution remote sensing images taken from multispectral sensors onboard aircraft and field measurements of the agro-meteorological variables from the campaign were used for model evaluation and improvement. Overall relative error measured in terms of mean absolute percent difference (MAPD) for instantaneous ET (mm h-1) were 22.7%, 23.2%, and 12.6% for SEBAL, METRIC, and SEBS, respectively. SEBAL and METRIC performances for irrigated fields representing higher ET with limited or no water stress and complete ground cover surfaces were markedly better than that for dryland fields representing lesser ET and greater soil water deficits with sparser vegetation cover. SEBS algorithm performed equally well for both irrigated and dryland conditions but required accurate air temperature data. Overall, this study provides new insights into the performance of three widely used thermal remote sensing based algorithms for estimating ET and proposed modifications to improve the accuracy of estimated ET for efficient management of water resources.

2013-06-18T00:00:00Z Li, Hui http://hdl.handle.net/2097/15913 2013-06-18T19:14:36Z 2013-06-18T00:00:00Z

STUDY ON MOLECULAR PHOTOIONIZATION IN FEMTOSECOND LASER FIELD Li, Hui This thesis consists of two major parts. The first part concerns studies of the orientation dependence of the ionization of diatomic molecules in intense, femtosecond two-color laser fields. The second part is about studies on the ionization mechanisms of the C[subscript]6[subscript]0 molecule in femtosecond near-infrared and ultraviolet laser fields. In the first part, experimental and theoretical results on the asymmetric ion emission of the heteronuclear molecules CO and NO in two-color laser fields are discussed. The two-color fields, which can be tailored by a relative phase, are used to ionize and dissociate CO and NO molecules, both of which are molecules with small polarizabilities. The resulting C[superscript]+, C[superscript]2[superscript]+, N[superscript]+ and O[superscript]+ ions are detected by a velocity map imaging (VMI) setup. The photoelectrons from above-threshold ionization (ATI) of Xe are studied under such a two-color field to assign the phase. For both CO and NO we find that enhanced ionization occurs when the molecule is oriented with the electric field pointing from the C or N atom toward the O atom. This is in agreement with the molecular orbital Ammosov-Delone-Krainov (MO-ADK) theory and the Stark-corrected strong-field-approximation (SFA) calculations. The second part is devoted to the investigation of the ionization mechanism of neutral C[subscript]60 molecules with 30 fs laser pulses at about 800 nm and with 50 fs pulses at about 400 nm. The angular distributions of photoelectrons are measured utilizing VMI. Measurements under different intensities are carried out for the two wavelengths. In our work, thermal electron emission is highly suppressed by the use of short pulses. For near-infrared excitation, photoelectron angular distributions (PADs) that contain six lobes are observed for low energy electrons. This behavior is different from studies for longer pulses of about 120 fs [1]. Further analysis indicates that the PADs might originate from single photon ionization of a super atomic molecular orbital (SAMO), however, a detailed assignment requires further theoretical work. The PADs for the ultraviolet excitation show very similar structures to earlier results [1]. For the near-infrared excitation, we have carried out studies as a function of the chirp of the pulses and find effects on photoelectron spectra and on PADs, which are tentatively explained by sequential multiphoton ionization via “doorway” states.

2013-06-18T00:00:00Z Madamadakala, Ganapathi http://hdl.handle.net/2097/15911 2013-06-18T18:44:05Z 2013-06-18T00:00:00Z

HEAT TRANSFER AND FLOW CHARACTERISTICS OF SONIC NOZZLE Madamadakala, Ganapathi The current research presents the experimental investigation of heat transfer and flow characteristics of sonic multiphase flow in a converging-diverging nozzle. R134a and R123 are used in this study. Four different nozzle assemblies with two different throat sizes (2.43mm and 1.5 mm with 1° growth angle with the centerline of the nozzle in the diverging section) and two different heater lengths (200 mm and 125 mm) were tested. Each test section was an assembly of aluminum nozzle sections. The experimental facility design allowed controlling three variables: throat velocity, inlet temperature, back pressure saturation temperature. The analysis used to find the average heat transfer of the fluid to each nozzle section. This was achieved by measuring the nozzle wall temperature and fluid pressure in a steady state condition. Two methods for finding the average heat flux in sonic nozzle were included in the data analysis: infinite contact resistance and zero contact resistance between nozzle sections. The input variables ranges were 25 °C and 30 °C for inlet temperature and back pressure saturation temperatures, 1100-60,000 kg/m 2 s for mass flux, and 1.4-700 kW/m2 heat flux. The effect of the mass flux and heat flux on the average two-phase heat transfer coefficients was investigated. The flow quality, Mach number(M), and Nusselt number ratio (φ) were also calculated for each section of the nozzle. As the fluid flowed through the nozzle, the pressure of the liquid dropped below the inlet saturation pressure of the liquid due to sonic expansion in the nozzle. This temperature drop was significantly lower in the case of R134a than R123. The results showed that the two-phase heat transfer coefficients were above of 30000 W/m^2 K in the first 75 mm of the nozzle, and they decreased along the nozzle. The Mach number profile appeared similar to the temperature profile, and the fluid was in the sonic region as long as temperature of the fluid dropped in the nozzle. Nusselt number ratios were compared with the Mach numbers and showed that the Nusselt number ratio were increased in the sonic region. The results showed that the length of the sonic region was larger for R123 than for R134a, and the Mach numbers were higher for R123. The Nusselt ratios of R123 were low compared to the R134a cases, and the trend in the Nusselt ratios was notably different as well.

2013-06-18T00:00:00Z Horst, Kyle http://hdl.handle.net/2097/15910 2013-06-18T15:03:19Z 2013-06-18T00:00:00Z

TRAIT MINDFULNESS AS A PREDICTIVE FACTOR FOR INTIMATE PARTNER VIOLENCE PERPETRATION AMONG YOUNG ADULTS Horst, Kyle Recent literature has highlighted the importance of considering personal and relationship factors in predicting IPV perpetration. The present study sought to investigate whether trait mindfulness is associated with IPV, as well as the mechanisms by which mindfulness might predict IPV. Utilizing longitudinal data collected from 247 undergraduate students, the study tested a hurdle model of IPV occurrence and frequency at Time 3 being predicted by trait mindfulness at Time 1 and other known risk factors at Time 2. Results indicated that trait mindfulness at time 1 was associated with IPV perpetration at Time 3; however, when controlling for other known risk factors at time 1, the association between mindfulness at Time 1 and IPV at Time 3 was no longer significant. Finally, results from the mediational analysis revealed a significant indirect effect of trait mindfulness on IPV through relationship satisfaction and conflict resolution while all variables were measured at the same time point, but no indirect effect of trait mindfulness at time 1 on IPV at time 3.These results indicate that although mindfulness might not be a significant direct predictor of IPV when other known risk factors are controlled for, it is important since mindfulness indirectly predicts IPV through other relationship processes when measured at the same time point. Suggestions for future research and clinical intervention are offered.

2013-06-18T00:00:00Z