Master's Theses (Fall 2009 to Present)
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New submissions to the University of Delaware Master's Theses collection are added as they are released by the Graduate College. The Graduate College deposits all master's theses from a given semester after the official graduation date.
University of Delaware master’s theses submitted between 1980 - Summer 2009 are available online through Dissertations & Theses @ University of Delaware. Use the library catalog, DELCAT, to search for all print or microform copies of master's theses 1980 - 2009 that are NOT available in Dissertations & Theses @ University of Delaware because Dissertations & Theses @ University of Delaware does NOT contain the complete collection of University of Delaware master's theses.
Master’s theses in the Longwood Graduate Program in Public Horticulture (now known as the Longwood Fellows Program) submitted between 1970 - 2004 are available online.
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Item 100 Hz 512x512 SLEDS system design(University of Delaware, 2014) Nabha, KassemInfrared (IR) detectors applications are widely used across fields from scientific and military to medical and industrial. IR can detect information that human eyes cannot perceive allowing the advancement in science and technology. ☐ Due to the importance of the infrared detectors in today's world, it is necessary to accurately test and characterize these detectors with a frame of reference related to the application. IR projection systems are a great way to characterize the detectors because they can be used as high accuracy reference. ☐ Described in this work is a 512x512 super-latticed light emitting diode system (SLEDS) operating at a frame rate of 100Hz. This system has been fully developed, tested, and corrected for non-uniformity (NUC). Further work will be done to achieve higher frame rates and two frequencies of emission (colors) instead of one.Item 210Polonium and 210lead radionucidles in the Delaware and Chesapeake estuarine and coastal regions(University of Delaware, 2013) Marsan, DavidOne of the primary objectives of this thesis is to present an integrated study of the 210Pb and 210Po radioactive tracers, and assess their use as tracers for particle and trace element export from different estuarine and coastal environments. In order to achieve this main objective, the thesis was split into three sections, each enhancing the understanding of the natural radionuclides 210Pb and 210Po in the estuarine and costal system. Chapter 1 is dedicated to testing the sampling and analytical methods of 210Po and 210Pb extraction from estuarine and coastal waters, specifically comparing the two most widely used scavenging methods, Fe(OH)3 and CoRAPDC. The chapter describes experiments conducted on about 100 samples collected from the Delaware estuary, Chesapeake estuary, Delaware intertidal marsh and an offshore continental slope site. Data in the chapter clarifies the accuracy and reliability of each method and includes suggestions to enhance them. Other details include results of calculations, error propagation, spike calibration, plating efficiency and the MnO2 scavenging method. Chapter 2 presents a synthesis of the estuarine and coastal biogeochemistry of 210Po and 210Pb in the Delaware and Chesapeake estuaries. A single box model is presented using steady state equations to determine residence times of the radionuclides. This chapter presents five highlights: 1) How 210Pb and 210Po dissolved and particulate data can revel key biogeochemical processes and rates in estuaries; 2) Are regional differences in estuaries dominated by a single or compilation of biogeochemical process; 3) Do subRoxic bottom waters affect the distribution of 210Po and 210Pb; 4) Can disequilibria between parent (210Pb) and grandRdaughter (210Po) be used to identify and quantify principle processes; 5) Will a simple mass balance model result in reliable net scavenging residence times for the Delaware and Chesapeake estuaries. Chapter 3 will advance the simple single boxRmodel from chapter 2 to a more complex twoRlayer model. The model will include evaluations of the fate of not only 210Po and 210Pb in the Delaware and Chesapeake estuaries but also the trace elements Fe, Cu, Cd, Ni, Zn, Pb, Cr, Co and Mn. Residences times, presented as halfRlives along with rates and partition coefficients will be identified for the water column including at the sediment water interface. The thesis will revisit the major conclusions obtained from the work presented along with suggestions for future work. Appendix sections include supporting hydrographic data and a compilation of salt marsh trace metal results conducted in Graz, Austria. Trace metal work included a suite of 26 elements measured in a core, two species of mussels, Spartina)alterniflora marsh plant and the sea surface microlayer (SML) from an intertidal Delaware salt marsh.Item 3D permeability characterization of fibrous media(University of Delaware, 2010) Okonkwo, KennethIn Liquid Composite Molding (LCM) processes, a liquid resin is forced to flow through dry fibrous preform, usually fabrics, to impregnate it and create the composite part in net or near-net shape. The principal advantage of LCM processes is their capacity to produce high fiber volume fraction and high quality parts under low pressure at low cost. The main conditions for successful manufacturing are complete filling of the mold and perfect impregnation of the reinforcement material. If these conditions are not met the structural properties of the finished part are significantly impaired by defects like voids. The mold filling depends on the permeability of the fibrous media. Permeability is an intrinsic property of fiber reinforcement, which includes all interactions between fibers and fluid and characterizes the ease of flow through the medium. The complete prediction of second-order permeability tensor is critical to understanding and prediction of flow in the resin transfer molding process of thick composites or where the flow process is three dimensional In this thesis a new approach for characterizing the three dimensional permeability tensor of fabrics used as reinforcement in liquid injection molding processes from a single experiment is presented and validated. In this approach, a liquid is injected into a preform placed in a mold containing 192 electrical resistance flow sensors radially embedded in the top and the bottom platens of the mold. The proposed method uses an optimization routine in which the permeabilities in a 3D flow simulation of the identical mold is updated continuously until the error between the simulation arrival times at all the 192 sensor locations and the experimental arrival time is minimum. The optimization routine systematically changes the values of the components of the permeability tensor using golden search method until the best match is obtained. The validation and sensitivity of this method is explored and it has been shown that this technique is promising for permeability characterization. The approach is shown to be valid for reinforcements with anisotropic and isotropic nature The advantage of this approach is that it can be used to obtain permeability values from a single experiment; there is no need to scale the circular injection inlet, and it is not limited to principal permeability values. The sensors utilized are unobtrusive to the flow unlike say optic fibers embedded in the fabric that interfere with the flow of the test fluid. The electrical resistance sensors used in this approach are embedded in mold platens instead and which flush with the surface. The method can be used to help predict and understand resin flow behavior during liquid molding of advanced composite materials.Item 95 GHz silicon germanium low noise amplifier as front-end receiver for sparse aperture millimeter wave imaging(University of Delaware, 2015) Wright, Andrew AlexanderDemand for the ability to navigate in degraded visual environments (DVE) such as dust, smoke, and fog, has lead the development of millimeter wave (mm-wave) real-time imaging systems. Millimeter wavelength radiation has shown that the wavelengths are long enough to penetrate the obscurants while also allowing sufficient resolution. A low attenuation atmospheric window in the 95 GHz region has pushed for these systems to operate at these millimeter wavelength frequencies. Due to low signal levels at these frequencies, the system requires high gain in the front-end to boost the signals of mm-wave frequencies. This involves collecting the electromagnetic waves with a horn antenna and then amplifying the signal with a low noise amplifier (LNA) to maximize the signal to noise ratio (SNR). In photonics-based imaging systems, the mm-wave signal is then up-converted to optical domain, where it then propagates through optical fibers to an infrared camera for further processing. The horn, LNA and up-converter comprise a single module. A large distributed array of modules, around 200, are required for a real-time mm-wave imaging system capable of peering through DVE. As a result, pushing this technology to higher frequencies can be very costly, due to the high prices of individual high frequency components. Therefore, an alternative technology is required to keep the costs to a minimum. One approach to controlling costs of components operating at higher frequencies is to adopt an alternative amplifier technology. Conventionally, commercially available GaAs and InP LNAs are used to obtain high gain at the high frequencies, but at 95 GHz, each amplifier used to be thousands of dollars. Since then, costs for each amplifier decreased to $100. With each module requiring three or more amplifiers, costs become prohibitively high for many applications. Therefore, this thesis focuses on the development of a 95 GHz amplifier using silicon germanium (SiGe) technology to obtain the required high gain while maintaining low costs. To date, extensive efforts have been made in the development of SiGe amplifier technology and high gain was demonstrated at the W-band. However, existing amplifier technology does not meet the requirements of the mm-wave imager. In particular, major limitation is the 3-dB bandwidth of the gain curve. A distributed aperture system with a wide field of view and broadband response will experience a phenomenon known as fringe-washing if an off-axis signal arrives with significant delay between the receivers on the opposite ends of the longest baseline. Severe fringe-washing occurs when this delay of the projected baseline is comparable to the correlation time of the signal, i.e. the inverse bandwidth of the system. To mitigate fringe-washing, each module must limit the bandwidth of operation, which can be accomplished either with a filter or an amplifier. Since filters can be lossy, ideally a narrow-band amplifier is preferred. In this thesis, using the basic principle of amplifier design, an LNA is developed based on advanced SiGe-foundry processes to operate in the 95 GHz regime. The advantage of a custom SiGe amplifier is the ability to design it to meet the imager's specific demands, including gain, noise figure, bandwidth, and power consumption in a single low cost device. This thesis details such design, and includes the discussion of tradeoffs and limitations imposed by the commercial SiGe-foundry processes employed.Item A ballast box to study the effect of sand fouling on ballast, track stiffness, track deformation, and predicting maintenance time(University of Delaware, 2023) Alzhrani, Mohammed Abdullah JRailroad track crossings through sandy areas, like deserts, face the unique challenge of sand infiltrating into the ballast, leading to ballast fouling. Geographical conditions make these areas particularly prone to windblown sand infiltration, causing fine sand to gradually fill the ballast voids, ultimately resulting in fouling issues. Over time, fouled ballasts become a significant concern because of their negative impacts on track performance. ☐ This study explores the impact of ballast fouling primarily caused by sand infiltration on track deflection, stiffness (modulus), and overall track degradation. The main goal is to establish a clear relationship between these factors and fouling levels due to sand infiltration. ☐ The research was conducted at the University of Delaware's Civil Engineering laboratory, utilizing an 18-cubic-foot (0.67 cubic yards) ballast box. A rail/tie/fastener assembly was placed on the ballast and subjected to cyclic loading at a rate of 12 cycles per minute. The testing began with clean ballast, and dynamic load tests were carried out under simulated vehicle wheel loading conditions for up to five hours, with load-deflection behavior recorded during each cycle. Sand was introduced to the ballast in two series: Series 1, representing unconsolidated tests, and Series 2, simulating progressive fouling. These tests were repeated with varying levels of sand fouling, ranging from moderate to severe. Load deflection curves were analyzed using the Beam on Elastic Foundation (BOEF) theory to determine track modulus (stiffness) values and cumulative deformation, corresponding to cumulative plastic strain under repeated wheel loading. ☐ The study's results reveal a consistent pattern in load deflection curves, track modulus values, and cumulative plastic strain for different levels of sand fouling. It was observed that as sand fouling increased, both track stiffness (modulus) and track settlement also increased, aligning with field measurements conducted under similar conditions. ☐ As a result of these findings, a predictive application was developed to estimate maintenance time based on the degree of fouling. This application can offer valuable insights into maintenance planning and decision-making for tracks traversing sandy regions.Item A Bayesian Cue Integration approach to racial bias in pain assessment and treatment(University of Delaware, 2023) Goharzad, AzaadehPatients' reports of subjective pain experience are at least nominally a primary diagnostic cue in assessment and treatment of pain. Despite this, there is low concordance between provider assessments and self-reported pain ratings, such that patient pain is regularly underestimated and undertreated. Such discrepancies in care are particularly stark for Black patients, who receive less adequate pain care compared to White patients. While attending to facial expressions of pain marginally improves concordance in patient-provider pain ratings, it is not clear that this would improve concordance for Black patients given previous work demonstrating blunted recognition of pain on Black faces. Moreover, it is unclear how self-reported pain information is integrated with facial expressions of pain, and whether this integration is similarly biased as a function of patient race. In the present paper we construct three models of pain assessment for both Black and White targets to examine how individuals use facial expression and self-reported pain cues in making holistic judgements of pain intensity as well as subsequent treatment decisions. Overall, we find that the Bayesian Cue Integration model (compared to Face Dominant and Self-Report Dominant models) best predict participant assessments of pain as well as treatment outcomes for both Black and White targets, suggesting that both facial expression and self-report are integrated in pain assessment. ☐ Keywords: Social cognition, pain, race, cue integrationItem A depth of terrible endurance": the construction of incarcerated labor at Eastern State Penitentiary(University of Delaware, 2024) Dombrovskaya, EmEastern State Penitentiary (ESP) opened its doors with the goals of reforming incarcerated Pennsylvanians in 1829. Utilizing the penal method commonly referred to as the Pennsylvania System, the institution intended to operate through “solitary confinement at labour, with instruction in labour, in morals, and in religion.” The incarcerated people at ESP were trained in weaving, shoe-making, chair seat caning, and cigar making, among other occupations. While other penal systems were investing in industrial scale production in prisons for economic profit, ESP embodied the tension between moral commitment to reform and rehabilitation, and the economic pressures of running the penitentiary in a rapidly industrializing context. The evidence of labor practices at ESP demonstrates that the enacted version of carceral labor became a balance of equipment and material costs, the skills of the incarcerated population, and the judgements of character based on socioeconomic factors that predisposed people to certain tasks. These practices had bodily effects on incarcerated people. A consideration of the record relating to the human body serves to supplement the missing glimpses of personal experience in relation to labor which have been written out of the archive. This constellation of human contact within the penitentiary reveals the forces of medical neglect, institutional racism and sexism, against which incarcerated individuals struggled as individuals and laborers. This analysis uncovers how the moral aspirations underlying the labor program at ESP were overshadowed by the institution's prioritization of efficiency and economic gains over the period ideals of moral reform, resulting in the failure of the system by the 1870s with overcrowding making solitary confinement wholly impossible.Item A detailed look into the performance of bifacial solar arrays in Delaware's climate(University of Delaware, 2023) Purnell, RyanThis paper studies the effectiveness of bifacial solar arrays in Delaware’s climate, analyzing several factors that influence the anticipated benefits of using bifacial modules over their monofacial counterparts, with the goal of advising future solar installers and to see if bifacial modules would be beneficial in an upcoming agrivoltaic project. We compared the effects that white tarps, black tarps and gravel had on array output, and covered the rear sides of two modules, making them monofacial, then comparing them to their bifacial neighbors to quantify the benefit of rear surface light collection. Over the course of the year, the covered modules produced 9.99% and 9.93% less energy and were between 1.5% and 3.5% less efficient than their bifacial counterparts depending on the ground cover. High albedo ground covers like the white tarps increased the disparity between the power production and efficiency of the covered versus uncovered modules as the increased insolation on the rear side causes the uncovered modules to produce more energy. Additionally, the impact of inverter clipping on the bifacial gain was analyzed, with white tarps providing the highest bifacial gain in all categories. On days with inverter clipping, a lot of the bifacial gains were eliminated, but still provided gains between 5-6% for white tarps. On days without clipping, the bifacial gain from white tarps reached as high as 16.7%, vastly outperforming the other ground cover types for similar conditions. Overall, the effectiveness of bifacial modules and the benefits that come with increasing the albedo of the ground cover underneath the array were analyzed and proven, especially for cloudy and winter days where the bifacial gains were not partially eliminated by inverter clipping.Item "A free woman... carved from life": uncovering the embodied lived, networks, and identities in the Bust of Nora August(University of Delaware, 2023) Ford-Dirks, GraceThis thesis centers on the Bust of Nora August from St. Simons Island, Georgia. Carved in 1865 by an unknown maker, this large ivory bust is an unusual rendering of a young Black woman celebrating the moment of her emancipation. The Bust of Nora August is an archive within an object, offering clues about broad global connections and individual histories alike. The thesis unpacks this object’s relationship to nineteenth-century artistic, material, and social exchange networks and places the object within historical racial discourses surrounding Black agency and emancipation. ☐ This analysis draws on decades of historical, art historical, literary, and archival studies in order to offer a first step towards a holistic understanding of the object and its networks. The paper is divided into three sections that analyze the object as archive, as narrative, and as relic. The first section uses the bust as a window into the interconnected material and personal worlds of the coastal South during the post-emancipation period. It reflects on the bust as “archive within an object” and as a material repository for individual and collective memory of emancipation and enslavement. The second section argues that the Bust of Nora August is a material slave narrative that uses a potent combination of text and likeness to convey Nora’s story. Blending the visual, haptic, and textual languages of the slave narrative and portrait bust genres, the bust acted as a material extension of Nora’s being and offered a tool to seek connection and belonging amid a deeply uncertain political and social climate. Finally, the third section analyzes the role of the bust on present-day St. Simons Island. It assesses how the island’s privatized objects and landscapes of historical memory have impacted the ways in which historical narratives are conveyed. Ultimately, the Bust of Nora August is an important artifact that complicates scholarly assumptions about Civil War-era material and social networks. Its evocative appearance demands a deeper examination of the lasting impacts of transatlantic slavery on art, commerce, and global ecologies.Item A low-energy dense dietary pattern: a narrative review(University of Delaware, 2021) Burns, Kaelyn F.A low-energy dense dietary pattern is promoted throughout dietary recommendations for the purpose of promoting diet quality and overall health. However, little work has identified effective approaches for achieving a low-energy dense diet, making the implementation of dietary recommendations challenging. The purpose of this thesis project was to conduct a narrative review to examine energy density used within extant literature. The narrative review aims to examine the approaches used to implement a low-energy dense dietary pattern within dietary interventions while describing the success of the intervention and how a low-energy dense dietary pattern compares to other dietary strategies in improving dietary and health outcomes. The narrative review underscores the work of basic feeding studies and observational research which have demonstrated that a diet low in energy density is associated with a reduced energy intake and positive health outcomes. Ten dietary intervention studies with the explicit goal of altering participant dietary energy density were reviewed and the impact the intervention had on dietary energy density, diet quality, energy intake, and weight were described. Implementation of a low-energy dense diet was accomplished through two different approaches; modifying the consumption of food/nutrient groups that impact energy density or applying one of various proposed energy density classification methods. Across interventions, consuming a low-energy dense dietary pattern had similar results compared to other dietary intervention strategies in regard to impact on the reviewed health outcomes. Interventions that used an energy density classification method to implement a low- energy dense dietary pattern appeared to have more consistency across studies in regard to reducing participant dietary energy density, diet quality, energy intake, and weight management when compared to the approach of modifying the consumption of food/nutrient groups that impact energy density.Item A sociological examination of disordered eating and body satisfaction among transgender and nonbinary individuals(University of Delaware, 2023) Gavnik, AdamTransgender, nonbinary, and other gender nonconforming communities have grown in visibility over recent years, and this visibility is associated with an increase in academic research on the health and wellbeing of these communities. Social science research has established that, compared to cisgender individuals, transgender and nonbinary people face an increased risk of mental health concerns such as disordered eating and body dissatisfaction. However, there is a dearth of research that explains this disparity. The current study uses 20 in-depth interviews with transgender and nonbinary adults to explore the factors that produce their eating habits and attitudes towards their bodies. Findings reveals the impact of micro-level factors such as individual health, gender dysphoria, and gender affirming care. Meso-level analysis emphasized the role of gender attribution and accountability in shaping participants’ relationship with food and their bodies, as well as social learning processes of food and body-related norms. Macro-level themes highlighted unique ways that trans and nonbinary identity shape experiences of embodiment and beauty ideals. Overall, this research elucidates the individual, interactional, and institutional factors that may contribute to elevated rates of disordered eating among trans and nonbinary people. Such findings indicate the complexity of these phenomena and the need for explanations that go beyond physical gender dysphoria.Item A suite of agronomic factors can offset the effects of climate variability on rainfed maize production in Kenya(University of Delaware, 2022) Oluoch, Kevin Ong'areAchieving food security in sub-Saharan Africa (SSA) is a multidimensional challenge. SSA reliance on food imports is expected to grow in the coming decades to meet the population's demand, projected to double to over 2 billion people by 2050. In addition, climate change is already affecting food production and supply chains across the region. Addressing these multiple food security challenges will necessitate rapid enhancements in agricultural productivity, which is influenced by a host of demographic, agronomic, and climatic factors. We use statistical approaches to examine rainfed maize in Kenya, where maize cultivation and consumption are widespread and central to livelihoods and national food security. We find that improving a suite of agronomic factors will have a greater effect on rainfed maize productivity than demographics and can offset the effects of climate change. These findings could also offer insights into similar challenges for other crops in Kenya and other SSA countries.Item A supervisory control approach for Digit navigation on inclined terrain(University of Delaware, 2024) Sinha, ShantaniHumanoid robots are engineered to replicate human capabilities, including navigating inclined terrains with stable locomotion. Humans exhibit remarkable adaptive capability to safely traverse inclined terrains without sight, adjusting their gait dynamically based on proprioceptive feedback and tactile sensations. Therefore, to enable bipedal robot Digit to navigate on inclined terrains without sight, we have implemented a high level planner called Supervisory Control System. ☐ In this thesis, we have proposed the development and implementation of the Supervisory Control System capable of operating in the presence of potentially large parametric uncertainties, specifically addressing the inclination angle of the terrain. Supervisory Control is designed as a combination of an online estimation unit and a controller library, where a suitable controller is selected based on the current estimate of ground inclination and the system behavior is adapted accordingly. In this control design, optimal controller is selected by the means of logic-based switching among the family of controllers and is placed in the feedback loop based on the current estimation of the inclination angle. We illustrate the effectiveness of our method by applying it on Digit walking on inclined terrain. Our results show that by switching to the optimal controller that is best according to the current estimate of uncertainty maintains robustness and stability across varying inclinations.Item The abdominal fat contribution to adiposity in chickens divergently selected for fatness or growth: Cross-model elucidation and validation of gene expression(University of Delaware, 2013) Resnyk, ChristopherThe domestic chicken (Gallus domesticus) is an important global source of high-quality dietary protein and a widely used biological model. Decades of intensive genetic selection have established the remarkable growth rate of the commercial broiler today; however, increased growth rate has been accompanied by the magnification of several unfavorable traits. This thesis addresses abdominal fatness, one of the traits that are incidentally amplified by selection for increased growth. Excessive fatness, coupled with several unique avian features of metabolism (i.e., fasting hyperglycemia and insulin insensitivity), parallels conditions observed in humans with metabolic diseases. Thus, understanding the genetic influence on excessive fatness in chickens will not only serve to improve the quality of production from an agricultural standpoint, but will also advance the knowledge of metabolic disorders in humans. Four experimental lines of meat-type chickens that were divergently selected for either a large difference in abdominal (visceral) fatness or in growth rate were used to characterize the role of adipose tissue (classically thought to have a minimal lipogenic contribution) in regulating adiposity. At the age of selection (9 weeks), the fat line (FL) and lean line (LL) chickens exhibit a 2.5-fold difference in abdominal adipose weight, while their body weight and feed intake are similar. The high growth (HG) and low growth (LG) chickens were divergently selected for either high (HG) or low (LG) body weight at 8 and 32 weeks of age resulting in a 2.7-fold increase in bodyweight and an 8-fold increase in abdominal fatness (as a percentage of BW) in HG chickens on average from 1 through 11 weeks. The adipose transcriptomes of these four genotypes (FL compared to LL and HG compared to LG) were analyzed at 1 through 11 weeks of age using the Del-Mar 14K Chicken Integrated Systems microarray, and at a single age (7 weeks) by RNA sequencing. Microarray analysis of abdominal fat in FL and LL chickens revealed 131 differentially expressed (DE) genes (FDR≤0.05) as the main effect of genotype, 254 DE genes as an interaction of age and genotype and 3,194 DE genes (FDR≤0.01) as the main effect of age. The most notable discoveries in the abdominal fat transcriptome during juvenile development were higher expression of many genes involved in hemostasis in the LL and up-regulation of numerous adipogenic and lipogenic genes in FL chickens. Many of these DE genes belong to pathways controlling the synthesis, metabolism and transport of lipids or endocrine signaling pathways activated by adipokines, retinoids and thyroid hormones. The importance of these processes in regulating adiposity in abdominal fat of FL and LL chickens was reinforced by the deep RNA sequencing analysis at 7 weeks. Remarkably, the highest expressed genes at this age included those involved in the metabolism of lipid and carbohydrates which are functionally associated with endocrine system and metabolic disorders. There were 1,687 DE genes between fat and lean chickens at 7 weeks including transcription factors and metabolic enzymes which have direct influences on lipogenesis and adipogenesis. The findings of the microarray analysis were further verified by the abundance of DE hemostatic factors uncovered by RNA sequencing analysis. This deep sequencing analysis also revealed a number of ectopically expressed genes suggesting that visceral fat functions autonomously as well as an endocrine organ in the regulation of lipid metabolism and perhaps feed intake. Microarray analysis of HG and LG chickens at 1 through 11 weeks of age revealed DE genes (FDR≤0.05) as the main effect of genotype (321 genes), the interaction of age and genotype (718 genes), and the main effect of age (2,918 genes). RNA sequencing at 7 weeks uncovered 280 DE genes (FDR≤0.1). Similar to the FL, HG chickens over-express many genes involved in adipogenesis and lipogenesis (including biosynthesis of fatty acids, cholesterol and triglycerides) which could at least partially account for their increase in abdominal fatness. Conversely, LG chickens up-regulate several energy producing processes (i.e., peroxisomal -oxidation, mitochondrial -oxidation, ketogenesis and oxidative phosphorylation) early on in juvenile development which are likely responsible for their extreme leanness. Hemostasis also appears to have a critical role in the maintenance of the lean phenotype at the age of maximal difference in adiposity in these chickens (7 weeks). These findings validate abdominal fat as a major contributor to adiposity in response to either divergent selection on abdominal fatness in the FL and LL or body weight in the HG and LG chickens.Item Abundance and size of the sea scallop population in the Mid-Atlantic Bight(University of Delaware, 2013) Walker, JustinThe stock of the Mid-Atlantic Bight sea scallop fishery is assessed every year through the use of various dredging and imaging techniques. The sustainability of the fishery depends on the proper setting of the yearly catch limits based on the assessment of the preceding year. Within the past 10 years, digital image surveys have been explored as a potential method to supplement the yearly dredged based surveys. AUVs have been shown to be a successful platform for rapidly and accurately performing seafloor image surveys of benthic habitats. In 2011, a Teledyne-Gavia autonomous underwater vehicle (AUV) with a hull-mounted camera was used to non-invasively optically and acoustically image 313 km of the seafloor within the Mid-Atlantic Bight at a constant altitude of 2 m. Survey transects were completed at 24 open access ground locations and 3 additional locations within the Elephant Trunk Access Area. Trained image analysts, using a scallop counting and sizing algorithm developed for this stock assessment, were able to enumerate and size sea scallops within the collected 250,000 seafloor images, finding that the region had an overall scallop density of 0.027 scallops/m2. Georeferenced data was tagged by the AUV inertial navigation system (INS) to every seafloor image, allowing for unprecedented meter scale spatial analysis of the sea scallop distribution. The relationship between image subsampling and the accuracy of the resulting scallop density was explored via simulations run on the image analysis results. Eight AUV transects were resurveyed by a New Bedford commercial scallop dredge for shell height calibration data and to calculate the harvest efficiency of the dredge (0.60). Image analysis and backscatter data collected by the AUV’s 900 kHz side-scan sonar were used to classify seafloor substrate types. The surveyed scallop strata were classified as 98.6% sandy seafloor with the remaining 1.4% representing intermittent shell hash, mounds, and ripples. The side-scan backscatter data revealed other varied seafloor texture, including escarpments from scallop dredge trawling and wave created sorted bedforms. Seafloor dredge scar area measured from the side-scan backscatter data and National Oceanic and Atmospheric Administration (NOAA) vessel monitoring system (VMS) tracking data were used as a proxy for fishing effort. Increased dredging was found to positively skew shell height distributions.Item Abundance of the Asian shore crab Hemigrapsus sanguineus in and adjacent to the Delaware Bay: evidence of invasive crash and return of native species(University of Delaware, 2013) Schab, CoreyThe Asian shore crab Hemigrapsus sanguineus has been introduced to multiple rocky habitats outside its native range and is considered an invasive species on the East Coast. The Delaware Bay region represents one of these locations and contains established populations of this intertidal, brachyuran species. Previous studies conducted in the University of Delaware Harbor, a location within this invaded region, indicated that H. sanguineus had displaced native mud crabs as the dominant species in this habitat. This trend had been observed at many locations in the North American range of the species. However, surveys conducted a decade later, during 2011 and 2012, have indicated a reverse in the previous trend and have shown significantly higher abundance and biomass of Panopeus herbstii, a native mud crab, compared to H. sanguineus. These results document the first evidence of a decline in the population of H. sanguineus along the East Coast of the USA.Item Abundance, diversity, and activity of ammonia-oxidizing prokaryotes in the coastal arctic ocean in summer and winter(University of Delaware, 2009) Christman, GlennAmmonia oxidation, the first step in nitrification, is performed by certain Betaand Gammaproteobacteria and mesophilic Crenarchaea to generate metabolic energy. Ammonia monooxygenase (amoA) genes from both Bacteria and Crenarchaea have been found in a variety of marine ecosystems, but the relative importance of Bacteria versus Crenarchaea in ammonia oxidation is unresolved, and seasonal comparisons are rare. In this study, we compare the abundance of betaproteobacterial and crenarchaeal amoA genes in the coastal Artic Ocean during summer and winter seasons over two years. Betaproteobacterial and crenarchaeal amoA genes were present in both seasons, but were more abundant during the winter. Archaeal amoA genes were more abundant than betaproteobacterial amoA genes in the first year, but betaproteobacterial amoA was more abundant than archaeal amoA the following year. Summer and winter betaproteobacterial amoA clone libraries were significantly different. Gene sequences of amoA were similar to those found in temperate and polar environments. The ratio of archaeal amoA gene copies to Marine Group I crenarchaeal 16S rRNA genes averaged 2.9 over both seasons, implying that ammonia oxidation was common in Crenarchaea at this location. Nitrification rates were highest in the winter when ammonia oxidizer abundance was greatest, suggesting that ammonia oxidation plays an important role in coastal arctic waters during the winter when the ocean is ice covered and photosynthesis is at a minimum.Item Acculturation, diet and psychological health of Asian international students at the University of Delaware(University of Delaware, 2015) Jiang, HengBackground: Accumulating evidence showed that immigrants change their diet and experience various psychological problems in acculturation process. International students in United States are increasing rapidly and more than 50% of them are from Asian countries. However, little is known about the diet and psychological health of Asian international students along with acculturation level. Aims: This study aims to describe the dietary nutrient intakes and psychological health status of Asian international students at the University of Delaware after their immigration to the U.S. Methods: Online survey was sent out including demographic questionnaire, dietary screener questionnaire (DSQ), Asian American Multidimensional Acculturation Scale (AAMAS) and Kessler 6 (psychological screener). Linear regression models were fit to examine the association between normally distributed diet and acculturation data and demographic characteristics. Beta and 95% CI were reported. For non-normally distributed diet and acculturation data, Kruskal-Wallis was performed and median and interquartile range were presented. Results: We observed a trend for bicultural food consumption. Individuals more acculturated to American culture had lower Kessler 6 score (Beta -0.04; 95% CI -0.3, 0.2),those showed higher attachment to original culture had higher Kessler 6 score (Beta 1.1; 95% CI -0.3, 2.4). Specifically, the higher host culture language acquirement and original language maintenance, the better performance on Kessler 6.Item Accumulation of sediment and radionuclides in tidal marshes of the Murderkill River Estuary, Delaware(University of Delaware, 2010) Stuart, DackThis thesis examines patterns and rates of sediment accumulation and tidal marsh accretion in the Murderkill River estuary, Delaware, with special emphasis placed on changes in accumulation rates and sediment physical properties associated with historical land-use practices, such as mosquito ditching. Over 90% of United States Atlantic East coast salt marshes have been ditched to some degree, but little quantitative work has been done to examine the specific effects on marsh sedimentary processes. An understanding how these ditches have affected sediment delivery to and retention on the marsh platform will provide insight into how ditched marshes are likely to respond to changes in sea level, sediment availability and vegetative growth. To investigate historical changes in sediment composition of the marsh sediment column, the specific contributions of mineral and organic solids and water/entrapped gas were determined from measurements of sediment dry-bulk density and loss-on-ignition. Additionally, grain-size analysis was conducted to determine the textural composition of sedimentary particles delivered to the marsh. Downcore profiles of the radionuclides 210Pb and 137Cs were used to determine sediment accumulation and marsh accretion rates, to develop chronologies for the sediment column, and also as indicators of sediment transport pathways within the marsh. In addition, an historical investigation was conducted to learn more about past land-use practices and sources of human disturbance in the estuarine system. Spatial and temporal variations in the relative contributions of organic and mineral matter to total sediment volume show that marsh accumulation in the Murderkill is dominated by mineral matter and that the organic contribution has varied little over the past century. At two upriver sites, changes in dry-bulk density, loss-on-ignition and grain size were observed and interpreted to correspond to the transition from freshwater marsh to brackish marsh. Although the cause of this change is unknown, it cannot be directly associated with mosquito ditching in the lower estuary due to the distance separating these sites from ditched areas. Vertical accretion rates (0.3−0.7 cm/yr) determined for undisturbed marsh sites are comparable to rates computed for other salt marshes of the greater Delaware Estuary. Radionuclide focusing factors for the marsh sites indicate that the Murderkill is a well-mixed estuary, consistent with results from a previous study of hydrodynamics of the Murderkill River. Temporal changes in accumulation (organic vs. mineral) were observed at one inter-ditch site, but the change cannot be directly associated with ditching activities because similar trends are not evident in other inter-ditch cores. Ditches filled rapidly with mineral mud after being excavated but have not matched the adjacent marsh elevation, possibly because they are acting as the preferred tidal pathways into and out of the marsh. Ditches have not significantly affected the median grain size and sorting of inter-ditch or ditch sites compared to a similarly located non-ditched location. There is no evidence to suggest ditches have deprived the marsh platform of suspended sediment in order to infill. The sedimentary record suggests that the effects of ditching on the adjacent marsh platform are subtle and not always similar among depositional sites. Thus, the results of this study suggest that there is no specific sedimentary response to ditching in ditched or non-ditched areas of the same marsh.Item Accuracy and convergence of the Asymptotic Single Risk Factor formula in a large credit portfolio(University of Delaware, 2016) Houser, Madelyn R.According to international banking standards, all financial institutions must classify the risks associated with the credit portfolios they hold. Mathematical approximations of default distributions are among the most common ways of assessing such risk. Understanding the errors of these approximations is crucial for generating reliable credit portfolio default risk calculations. We consider the error associated with Vasicek’s Asymptotic Single Risk Factor model for the cumulative distribution of losses in a portfolio of N companies. We analytically and numerically verify the scaling of the error to be O(N–1), scaling as the reciprocal of the number of companies. Our results provide insight into the error associated with one of the most commonly used credit risk models and serve as a model for future work in examining the errors of more complex, hierarchical structural models.