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The application of pesticides in agriculture production systems is a complex process and involves a series of factors that dynamically interact to impact overall pesticide application efficacy. Spray droplet formation, target impaction and deposition, plant uptake, and subsequent biological response are all functions of pesticide active ingredient, nozzle selection, application pressure, and carrier volume. Smaller spray droplets with a lower kinetic energy result in greater spray droplet retention on the leaf surface relative to larger droplets. Consequently, larger spray droplets with higher kinetic energy are poorly retained on the leaf surface and yield minimal coverage of leaf surface tissue. While smaller droplets maximize target coverage and spray droplet retention, larger spray droplets minimize off-target movement and agrichemical transport. Consequently, application factors that maximize pesticide efficacy and minimize off-target movement are often incongruous elements. Therefore, the objective of this research was to evaluate the impact of carrier volume and spray droplet size on the efficacy of various pesticide applications in Mississippi. These data indicate that 1) for thrips and tarnished plant bug control, acephate and sulfoxaflor are superior dicamba application partners relative to dimethoate and thiamethoxam, respectively, insecticide efficacy did not vary due to spray droplet size when applied without dicamba, and maximum efficacy was achieved with a carrier volume of 187 L ha-1; 2) dicamba + acephate and dicamba + thiamethoxam or sulfoxaflor are efficacious options to control Palmer amaranth relative to dicamba applied alone, and maximum Palmer amaranth control was achieved with a carrier volume of 187 L ha-1; 3) cotton defoliation efficacy is positively and negatively correlated with carrier volume and spray droplet size, respectively, and maximum efficacy was achieved with cotton defoliation programs consisting of two-applications, each with a carrier volume of 187 L ha-1 and 200 µm droplets; 4) soybean harvest aid efficacy is primarily a function of the harvest aid applied and that the impact of carrier volume and spray droplet size varies across harvest aids. However, when paraquat is applied, a carrier volume between 47 and 187 L ha-1 should be utilized with droplets of 200-500 µm to maximize harvest aid efficacy.

Distributed Generators (DGs) are being increasingly utilized in power system distribution networks to provide electric power at or near load centers. These are generally based on technologies like solar, wind and biomass and range from 10 kW to 50 MW. Research work carried out in this thesis relates to the optimal siting and sizing of DGs in order to maximize the system voltage stability and improve voltage profile. This has been formulated as an optimization problem and solved using LINGO software. Power flow equations have been embedded in the LINGO formulation, along with other operating constraints. The solution provides optimal values of the bus voltage magnitudes and angles, which have been utilized to compute a stability index. Finally, a multi-objective formulation has been developed to simultaneously optimize the size and placement of the DGs. The impact of the DGs on voltage stability and voltage profile has been studied on I standard distribution test systems and verified using three-phase unbalanced power flow software developed at Mississippi State University (MSU). Results indicate that the sizing and siting of DGs are system dependent and should be optimally selected before installing the distributed generators in the system.

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</p> I investigated the effects of habitat fragmentation in terms of spatial scale (enclosures of different sizes) and the degree of isolation (different mesh sizes) on benthic macroinvertebrates in the littoral zone of a shallow lake. I hypothesized that decreasing diversity and increasing temporal variation will occur with decreasing size and increasing isolation of enclosures. This hypothesis was tested by examining spatial and temporal variation (coefficient of variation) among replicate enclosures. Variation in benthic diversity was further examined within and among enclosures. The degree of isolation and habitat size interacted to determine variation of species abundance in the benthic community. Specifically, at higher levels of isolation (plastic enclosures), variance among enclosures of the same and of different sizes was the greatest compared to less isolated enclosures. We also investigated the persistence of benthic macroinvertebrates where persistence is defined as constancy in the number of organisms through time. We hypothesized that persistence is lower in small and more isolated enclosures as opposed to large less isolated ones. We simultaneously tested the hierarchical nature of community persistence as outlined by Rahel (1990) to determine if there is a difference in the assessment of persistence of the assemblage depending on the analytical scale used. There is a possible scale effect at the level of abundance rank since small (1 and 4 m2 ) enclosures had lower persistence than large (9 and 16m2 ) enclosures. Low persistence in both abundance and abundance rank over time prevented a conclusive test of the hierarchical nature of community persistence. I conclude that it is important for benthic enclosure experiments to be conducted at various spatial and analytical scales and that, where replication is possible, spatial and temporal variation allows a thorough examination of different community responses. </p> / Thesis / Master of Science (MSc)

My current thesis is regarding the application of Gel Permeation Chromatography (GPC) equipment and principles to the study of polyelectrolyte configuration in solution. The main focus of this study is the effect of salt on the hydrodynamic volume/solution properties of polyelectrolytes and the ability of GPC to effectively determine the degree of variation. This involves the comparison of different salt types and concentrations in aqueous solution. The specific polyelectrolyte examined is poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC), a zwitterionic polymer (i.e. one having both positive and negative charges on the monomer). PMPC is a fairly new and promising polyelectrolyte for use in protein drug delivery and biomaterial surface applications. Understanding the effects of salt on this polyelectrolyte will aid in the development of technologies involving this polymer as well as other zwitterionic polymers. Different salts were utilized to formulate an effect of salt ions so that a systematic analysis could be performed. Using a control as reference it was determined that the salt does have an effect on the solution properties of the polyelectrolytes, as expected. The specific properties examined were characterized into two categories; solution properties and ion properties. Solution properties involved the investigation of salt concentration, solution ionic strength and solution pH effects. For ion properties, salts were selected on the basis of ion charge, charge type and ion size, so that the effects of both the cation and anion components could be analyzed. Two parameters, namely, ion size/type and ion valency were examined for both the cation and the anion. In addition the configuration of the anion was also investigated. vSpecific conclusions found in this study were as follows: 1) The salt concentration has an effect up to a certain "saturation" point. 2) The ionic strength has no visible effect (any effect is related to the concentration component). 3) There is no observable solution pH effect. 4) There is no observable cation effect. This includes no cation type/size or cation valency effect. 5) There is a significant anion effect. 6) A smaller anion has a greater effect than a larger anion. 7) A divalent anion has a greater effect than a monovalent anion. 8) A monatomic anion has a greater effect than a polyatomic anion. It was found that the effect of ion properties is related to mechanisms associated with the geometry of the polyelectrolyte. The negative charge group of the polyelectrolyte which is situated closer to the backbone (inside) is less important to the change in hydrodynamic volume resulting from ionic interactions with the salts since it is shielded by the positive charge group situated at the end of the side chain (outside). The observed phenomena were also explained by other chemical and physical properties such as charge density and ionic potential. In addition to the original plan of study, other phenomena were observed and later explained, such as the presence of four distinct regions associated with salt concentration and the variation m the degree of hydrodynamic volume change with different molecular weight samples. The application of aqueous GPC equipment (including a differential refractive index detector (DRI)) and principles to the study of polyelectrolyte solution effects minimizes the detection equipment required and, provides sufficient resolution and accuracy for examination of solution properties while remaining time and cost effective. The project discoveries have shown that size exclusion chromatography provides an excellent means of obtaining a complete and accurate set of correlations between polyelectrolyte charge and salt effects. / Thesis / Master of Applied Science (MASc)

Test equating is important to large-scale testing programs because of the following two reasons: strict test security is a key concern for high-stakes tests and fairness of test equating is important for test takers. The question of adequacy of sample size often arises in test equating. However, most recommendations in the existing literature are based on classical test equating. Very few research studies systematically investigated the minimal sample size which leads to reasonably accurate equating results based on item response theory (IRT). The main purpose of this study was to examine the minimal sample size for desired IRT equating accuracy for the common-item nonequivalent groups design under various conditions. Accuracy was determined by examining the relative magnitude of six accuracy statistics. Two IRT equating methods were carried out on simulated tests with combinations of test length, test format, group ability difference, similarity of the form difficulty, and parameter estimation methods for 14 sample sizes using Monte Carlo simulations with 1,000 replications per cell. Observed score equating and true score equating were compared to the criterion equating to obtain the accuracy statistics. The results suggest that different sample size requirements exist for different test lengths, test formats and parameter estimation methods. Additionally, the results show the following: first, the results for true score equating and observed score equating are very similar. Second, the longer test has less accurate equating than the shorter one at the same sample size level and as the sample size decreases, the gap is greater. Third, concurrent parameter estimation method produced less equating error than separate estimation at the same sample size level and as the sample size reduces, the difference increases. Fourth, the cases with different group ability have larger and less stable error comparing to the base case and the cases with different test difficulty, especially when using separate parameter estimation method with sample size less than 750. Last, the mixed formatted test is more accurate than the single formatted one at the same sample size level. / Ph. D.

Empirical object recognition research indicates that objects are represented and perceived as hierarchical part-whole arrangements that vary according to bottom-up and top-down biases. An ongoing debate within object recognition research concerns whether local or global image properties are more fundamental for the perception of objects. Similarly, there is also disagreement about whether the visual system is guided by holistic or analytical processes. Neuroimaging findings have revealed functional distinctions between low and higher-level visual processes across lateral occipital-temporal cortex (LOC), primary visual cortices (V1/V2) and ventral occipital-temporal cortex. Recent studies suggest activations in these object recognition areas and others, such as the fusiform face area (FFA) and extra-striate body area (EBA), are collinear with activations associated with the perception scenes and buildings. Together, this information warrants the focus of the proposed study: to investigate the neural correlates of object recognition and perceived size. During the experiment subjects tracked a fixation stimulus while simultaneously being presented with images of shape contours and faces. Contours and face stimuli subtended small, medium and large visual angles in order to evaluate variance in neural activation across perceived size. In the present study visual areas were hypothesized to modulate as a function of visual angle, meaning that the part-whole relationships of objects vary with their perceived size. / Master of Science