AUETD (Auburn University)
Not a member yet
9771 research outputs found
Sort by
Four Essays in International Trade and Economic Development
Get PDFThis dissertation comprises four essays investigating the impact of trade agreements on trade outcomes and the relationship between export diversification and economic growth.
Chapter 1 investigates the effect of the U.S. African Growth and Opportunity Act (AGOA) on Sub-Saharan African (SSA) countries’ exports to the U.S. We used synthetic control method and U.S.-AGOA data. The study reveals that AGOA member nations experienced a significant 324.37 million yearly. State-level impacts varied, notably affecting areas with specific demographic characteristics such as higher poverty level, greater Black population, lower percentage of the population with a high school degree, and higher percent female population.
Chapter 4 investigates the relationship between export diversification and economic growth in thirty-nine Sub-Saharan African countries. We used macroeconomic data from United Nations Conference on Trade and Development (UNCTAD) and the Arellano-Bond difference generalized method-of-moment estimator, the study finds positive economic growth effects with better corruption control and governance quality, showcasing export diversification beyond the growth-optimized level. This was confirmed through robustness checks using country-fixed effect regression, ensuring the stability of the findings
Performance Properties of Recycled Plastic Modified (RPM) Asphalt Mixtures Added via the Dry Method
No full textAccording to the United States Environmental Protection Agency (EPA), approximately 35.7 million tons of plastic waste were generated in 2018, of which only 3.1 million tons were recycled, with the rest being buried in landfills, incinerated, or discarded as litter. Numerous possible solutions are being investigated to reuse waste plastics with considerable attention being given to using specific categories of plastics in asphalt pavements. The two methods for incorporating recycled plastics in asphalt mixtures are the dry method and the wet method. In the wet method, recycled plastics are added to the asphalt binder as a polymer modifier or an asphalt replacement. In the dry method, recycled plastics are added directly into the mixture as either an aggregate replacement, mixture modifier, binder modifier, or a combination of these. Of the seven categories of waste plastic, the majority of research has focused on high and low-density polyethylene (HDPE and LDPE), and polypropylene (PP) since these categories have melting points generally in the range of mixing temperatures for asphalt paving mixtures. However, there are currently no robust specifications on the source and properties of recycled plastics for use in asphalt. Therefore, evaluating recycled plastics with different properties is essential to understand their effects on the asphalt mixtures.
This research explored the potential of integrating recycled plastics into asphalt pavements and was structured on three experiments designed to assess the implications of incorporating post-consumer recycled (PCR) plastics into asphalt mixtures. These experiments focused on evaluating performance-based properties and friction-related characteristics of both plant-produced and laboratory-prepared recycled plastic-modified (RPM) asphalt mixtures. The first experiment delved into characterizing the performance and friction-related characteristics of plant-produced RPM asphalt mixtures from two field projects. By comparing these properties to control mixtures without PCR plastics, this phase aimed to evaluate the implications of using recycled plastics in real-world paving applications. Various performance tests were considered to provide a testing plan for evaluating the RPM mixture's behavior under various conditions. The test results revealed that incorporating PCR plastics via the dry method enhances stiffness and rutting resistance, yet adversely impacts workability, intermediate-temperature cracking resistance, and fatigue damage resistance. However, their effects on low-temperature cracking resistance, moisture susceptibility, surface texture, and friction properties appeared minimal.
The second experiment tried to develop a laboratory procedure that simulates the dry method of adding PCR plastics to asphalt mixtures at production plants. This experiment assessed the performance properties of mixtures prepared by four laboratory PCR addition methods and compared them with the plant-produced asphalt mixtures to identify the laboratory method that best replicates the plant-production process. Mix designs from two field projects used in the first experiment were used for this experiment. The second experiment revealed that none of the four PCR plastic addition methods accurately replicated the production of RPM mixtures at asphalt plants due to possible differences in production and storage aging processes between laboratory and plant production.
The third experiment expanded the scope to include laboratory-prepared RPM asphalt mixtures incorporating five different types and sources of PCR plastics. This was essential for evaluating the adaptability of various plastic materials in asphalt mixtures. Mix designs from the National Center for Asphalt Technology (NCAT) and Minnesota Road Research Facility (MnROAD) Additive Group (AG) experiments represented southern and northern mix designs, respectively, to assess the effects of different PCR plastics on the performance properties of both control and RPM asphalt mixtures. The test results showed that RPM mixtures maintained comparable workability, intermediate-temperature cracking resistance, surface characteristics, and low-temperature cracking resistance, but with slightly better rutting resistance and higher stiffness than the control mixtures. However, these RPM mixtures displayed reduced fatigue resistance. Results regarding moisture susceptibility were inconsistent for the two mix designs.
Additionally, the FlexPAVETM analysis was conducted on both plant-produced and laboratory-prepared control and RPM mixtures to assess the cracking damage performance over a 20-year analysis period. FlexPAVETM analysis was used for mechanistic asphalt mixture and pavement performance prediction based on fundamental properties and using moving vehicle loads and pavement temperature data. Different pavement structures, varying in the thickness of the asphalt concrete (AC) layer, were also simulated using FlexPAVETM to explore the effects of incorporating recycled plastics into various pavement designs. Based on the FlexPAVETM simulations, pavement test sections with RPM mixtures generally exhibited similar or higher final percent damage, except for two PCR plastics, compared to the control sections after 20 years of service life. However, the impact of different types of recycled plastics on the final percentage of damage varied.
Finally, a Pearson correlation analysis was performed to assess the relationship between the physical and thermal properties of recycled plastics and the performance test results of laboratory-prepared RPM asphalt mixtures. These mixtures incorporated five different types and sources of PCR plastics using the southern and northern mix designs. The analysis results indicated that among the various properties of PCR plastics, only the melt flow index (MFI) exhibited strong correlations with mixture workability, Glover-Rowe (G-Rm), and rutting resistance
Deep Integration of a Flight Vehicle Dynamic Model in a Vector Tracking Software Defined Receiver
Get PDFThe greater occurrence of signal interference on Global Navigation Satellite Systems
(GNSS) requires additional alternative navigation solutions to provide robust, reliable localization
of flight vehicles when measurements from GNSS are unavailable. This thesis proposes a
Flight Vehicle Dynamic Model (FVDM) that is deeply integrated with Global Positioning System
(GPS) correlator measurements for aircraft state estimates in GPS-challenged environments.
It is well-documented that large, modern aircraft feature an array of sensors that work in
tandem to provide robust positioning performance. However, the sizing limitations of low Size,
Weight, Power, and Cost (SWaP-C) do not allow for such redundant sensor suites, meaning
an alternative navigation solution is required. Furthermore, low cost flight vehicles typically
feature lower quality sensors that are subject to vibrations and subsequently faulty, unreliable
measurements that provide no benefit to the flight vehicle when GNSS measurements are also
considered unreliable.
The FVDM is a high-fidelity flight vehicle model based on the Diamond DA-40 singlepropeller
fixed wing aircraft. The aircraft model features a piston engine model that generates
thrust power through a shaft that spins a numerically modeled 3-blade propeller. The speed of
the propeller is controlled through a electric governor, and the pitch is controlled to maintain
efficient propeller action onto the incident airflow. The aerodynamics of the aircraft are modeled
using a discretized aerodynamic coefficient technique, also known as strip theory. Although not
used in this work, a landing gear model incorporates the three landing gear on the Diamond
DA-40 and evaluates the forces and moments applied during landing as a second-order springmass-
damper system. An International Standard Atmosphere (ISA) model is used to calculate
the density, temperature, and ambient pressure based on aircraft altitude. To close the loop of
the FVDM, a set of controllers in collaboration with a waypoint manager are used to actuate the
control surfaces on the aircraft. Multiple planned paths are demonstrated during this work and
are presented in their respective sections.
The proposed navigation filter presented in this work provides a closed loop solution fusion
of the vector tracking loop algorithms and the FVDM process model via a Vector Delay and
Frequency Lock Loop (VDFLL). Vector tracking loops are able to maintain channel lock on
satellite signals when either signal interference is present, or the dynamics of the collection
platform are too high for scalar loops to track the signal consistently.
The results within this work showcase the improvements in flight vehicle state estimates
when compared to a standard VDFLL zero-mean acceleration kinematic model. In simulation,
two trajectories are flown under varying levels of signal degradation. The first trajectory is
a steady-level, un-accelerated flight path where the aircraft is maintaining a constant altitude
and heading for the duration of the 60 second simulation. For this trajectory, it is expected
that the standard VDFLL implementation performs comparably to the proposed navigation
filter. The second trajectory features a more dramatic flight bath – full of oscillatory turns and a
constant climb segments. For the second trajectory, the proposed navigation filter out performs
the standard VDFLL due to its capability to predict the behavior of the aircraft given a set of
control inputs. Each of the trajectories and subsequent cases of signal degradation are tested in
100-run Monte-Carlo sims to further test the robustness of the proposed navigation filter
Evaluation of winter cover crops and biological control products to manage Meloidogyne incognita and insect pest damage in organic sweetpotatoes
Get PDFThere is a need to develop effective organic integrated pest management practices for sweetpotatoes. Our findings indicated that the combination of BotaniGard 22WP, Triple Threat Entomopathogenic Nematodes, and Majestene significantly reduced insect damage to sweetpotatoes under field conditions. The winter cover crops elbon rye and the mix containing crimson clover, daikon radish, elbon rye, and wheat resulted in lowered soil M. incognita populations compared with leguminous winter cover crops like field peas and crimson clover. Total insect pest damage was similar across winter cover crops, but lowest following crimson clover in North Carolina and black oats in Alabama. Soil health values measured by the Solvita CO2 Burst test were elevated following the winter cover crop mixes compared with the single winter cover crop treatments, indicating that the mixes stimulate higher maximal biological activity, which relates to increased soil health. Overall, the integration of biological control products and winter cover crops shows promise for enhancing organic sweetpotato production while promoting soil health and sustainability
Black women are F.I.R.E.- Fitting in resistance exercise: A culturally tailored and theory-based exercise intervention for young adult women
Get PDFBACKGROUND: Black women have the lowest rates of physical activity (PA) in the United States coupled with high prevalence of cardiometabolic risk factors. Resistance exercise (RE) has been shown to mitigate these health risks, however its effects and feasibility to increase exercise adherence in young Black women has been understudied. Concepts from the Social Cognitive Theory (SCT) and the Self-Determination Theory (SDT) have been associated with exercise adherence, but have not been used in conjunction with culturally-tailored strategies in this population to improve exercise adherence, physical and psychological outcomes. PURPOSE: This study examined the effects of a culturally tailored and theory-based RE intervention on adherence to RE, cardiometabolic disease risk factors, body composition, strength, behavioral aspects from the SCT (self-regulatory strategies and self-efficacy) and SDT concepts (competence, autonomy, relatedness, source of self-regulation) in young Black women over 24 weeks between a motivational exercise group (MEG) and a standard exercise group (SEG). METHODS: Thirty young, inactive Black women were randomized into MEG or SEG and received in-person RE training from a Black woman trainer in a fitness center in a predominantly Black neighborhood. Women in MEG discussed weekly topics about self-regulation and barriers and motivators for exercise in Black women while also working on improving competence and autonomy for RE. These discussions were followed up with text messages twice per week. Women in SEG only received one-on-one training. Cardiometabolic risk factors [total cholesterol, triglycerides, high-density lipoproteins (HDL), low-density lipoprotein (LDL), glucose, and waist circumference], body composition, and muscular strength were measured. Psychological outcomes included self-regulation, the basic psychological needs (competence, autonomy, relatedness), sources of motivation (amotivation, external, introjected, identified, integrated, and intrinsic motivation), and self-efficacy. All outcomes were assessed at pre-test, post-test, and a 3-month follow-up. RE adherence was measured for supervised and unsupervised RE sessions. RESULTS: Women in MEG (n = 14, mean age: 23.29±3.77 years) completed 93.9% of supervised sessions compared to 88.8% in SEG (n = 13, mean age: 26.15±3.29 years), and 14.3% completed at least 2 or more days of RE unsupervised versus 15.4% in SEG. Mixed ANOVAs showed no group by time interactions for physical or psychological outcomes, but there was a main effect of time. Bonferroni post-hoc analyses showed women in MEG significantly increased lean body mass (p < .001), decreased body fat percentage (p = .005), increased upper (p = .002) and lower body strength (p < .001) from pre-test to post-test, and upper and lower body muscular strength remained significantly higher than baseline at 3-month follow up (p < .001). Women in SEG exhibited increases in lean body mass at post-test (p = .023), upper body strength at 3-month follow-up (p < .001), and lower body strength at post-test and 3-month follow-up (p < .001). Bonferroni post-hoc analyses following the main effect of time revealed that women in both groups experienced increases in autonomy and competence at post-test (p < .001), but ultimately decreased from post-test to 3-month follow-up (MEG: p = .008, p < .001; SEG: p = .003, p = .002). Relatedness increased significantly for MEG (p = .001) and SEG (p < .001) from pre- to post-test, but showed a decrease from post-test to 3-month follow-up for MEG (p = .025). Significant increases in MEG and SEG occurred for identified regulation (p < .001; p = .004), integrated regulation (p < .001; p = .027), and intrinsic motivation (p < .001; p < .001) from pre- to post-test visits. For MEG, values were significantly higher at 3-month follow-up in comparison to pre-test for identified regulation (p < .001), integrated regulation (p = .002), and intrinsic motivation (p < .001). For SEG, only intrinsic motivation remained higher at 3-month follow-up in comparison to pre-test values (p = .034). Introjected regulation continually increased over the three timepoints for MEG (pre-test to 3-month follow-up: p = .003; post-test to 3-month follow-up: p = .006). Self-efficacy increased for MEG test (p < .001) and SEG (p = .014) from pre- to post-test, and decreased in MEG from post-test to 3-month follow-up (p = .011). Self-regulation increased in both groups at post-test (p < .001), and remained significantly higher at 3-month follow-up from baseline for MEG (p = .002) and SEG (p = .017). CONCLUSION: Ten weeks of surface level culturally-tailored RE can improve lean body mass, body fat percentage, and muscular strength in Black women. Additionally, those who successfully participated in more than 1 day of RE during the unsupervised period of the study increased basic psychological needs, and forms of autonomous and intrinsic motivation 12 weeks beyond in-person training. Deeper level cultural tailoring failed to significantly improve adherence. However, better methods are needed to improve adherence to RE during unsupervised training periods for young Black women
‘Structure - Processing - Property’ Relationships of Cellulose Nanocrystals for Optical and Sensing Applications
No full textThis research enhanced scientific understanding of the structure-processing-property relationships that govern the assembly of sulfated cellulose nanocrystals (CNCs) into films for photonic and sensing applications. CNCs are one-dimensional crystalline nanomaterials derived from cellulose. Their natural abundance, high strength, and ability to form lyotropic liquid crystalline phases make them an intriguing alternative to synthetic advanced materials. The first part of this research focused on CNC’s geometric polydispersity. The effects of a simple sedimentation technique on CNC size distribution, phase behavior, rheological properties, and photonic film properties were explored. Sedimentation of a primarily isotropic aqueous CNC dispersion resulted in two distinct phases. The top phase was isotropic and consisted of shorter nanocrystals, and the bottom phase was liquid crystalline and contained longer nanocrystals. Based on atomic force microscopy, the average length-to-diameter ratio of CNCs in the top and bottom phases was 70 and 51, respectively. Rheological measurements of nanomaterial aspect ratio are often used to augment atomic force microscopy measurements, but this is challenging for aqueous CNCs. Their ability to flow align can cause erroneous viscometer measurements. The low viscosity of dilute dispersions prevents measurement of the zero-shear viscosity on a rotational rheometer, which prevents the use of rotational rheology methods requiring measurement of a low-shear Newtonian plateau. These challenges were overcome by using Fedor's equation to determine the intrinsic viscosity and Bachelor's and Simha's equation to calculate the associated aspect ratio of the top, bottom, and parent phases. Additional rheological studies coupled with cross-polarized optical microscopy images were used to explore how the size distribution in each phase affected its rheology and phase behavior. As expected, the top phase comprised of shorter rods required a higher concentration for forming liquid crystal domains. The differences in dispersion properties directly affected the properties of dried CNC films. Image processing was used to quantify the relative abundance of tactoids, helices with planar anchoring, and helices with homeotropic anchoring for films made from the parent dispersions and each fraction. The bottom fraction containing the longer rods resulted in a higher abundance of the planar anchoring required for selective reflection.
The majority of this research focused on modifying CNCs to enable their use in sensing analytes in aqueous media. This work can be split into three segments: (a) surface functionalization of CNCs, (b) selective sensing of analytes using molecularly imprinted polymers coated onto CNC films, and (c) CNC-based microdevice fabrication and characterization. Commercially available sulfated CNCs exhibit high dispersibility in water, which enables manufacturing CNC materials from aqueous dispersions. However, CNCs’ water dispersibility prevents their use in applications requiring hydrolytic stability. To address this limitation, CNCs were modified 3-aminopropyltriethoxy silane (APTES). The functionalization was confirmed with several analytical techniques, including attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis coupled infrared spectroscopy, dynamic light scattering, inductively coupled plasma mass spectroscopy, and ultimate analysis. The change in dispersion characteristics was observed using dynamic light scattering, AFM, and optical microscopy. A 12.6% degree of APTES substitution of CNCs’ available hydroxyl groups significantly improved the hydrolytic stability of CNC films while having a minor impact on the films' mechanical properties. In addition, quartz crystal microbalance with dissipation (QCMD) and multiparametric surface plasmon resonance (MP-SPR) studies showed that the CNC-APTES films had a greater irreversible non-specific binding with carbofuran, a pesticide and emerging contaminant.
After overcoming the hydrolytic stability challenge, the need for specificity was achieved by synthesizing molecularly imprinted polymers (MIPs) for the detection of carbofuran, a model pesticide; amoxicillin, a model antibiotic residue; and β lactoglobulin, a model food allergen. Polymer synthesis, templating of the analyte, and analyte removal were characterized using ATR-IR, Raman, and CRAIC microspectrophotometer. CNC-APTES films were coated with MIP for sensing experiments, and their sensing capabilities were tested using QCMD and MP-SPR. The detection of β-lactoglobulin was troublesome due to water swelling of protein molecules. However, carbofuran and amoxicillin could both be detected by their corresponding MIPs. In fact, for carbofuran, the reversible sensitivity was 0.03 ppm, which is lower than that of standard commercial sensors. In addition, the MIP for carbofuran was found to be selective during tests with the herbicide 2,4-dichlorophenoxyacetic acid (2,4D) which has a similar benzene-based structure.
In the last segment of the research, CNC-APTES was employed to make micro-devices with the aim of using them as mass-dependent resonating microcantilevers to sense analyte adsorption. These devices were fabricated using clean room microfabrication techniques, including photolithography, shear film cast, electron beam physical vapor deposition (ePVD), etching, device release, critical point drying, and sputtering. While portable detection is ultimately envisioned, laboratory studies employed an atomic force microscope (AFM) to probe the cantilevers’ resonance frequencies. This necessitated coating the beams with a thin layer of gold to enable laser reflection and obtain a measurement of the beam resonance frequency. Together with advances in understanding CNC surface modification for the adsorption of analytes, the device fabrication and characterization pave the way for analyte detection using CNC-APTES based devices
Quantifying the influence of initial nutrient conditions on phytoplankton growth in response to low-level glyphosate exposure
No full textGlyphosate, the active ingredient in RoundUp®, is the most common herbicide in the United States. Glyphosate is efficient at eliminating nuisance terrestrial plants. However, the nitrogen and phosphorus that make up glyphosate are made bioavailable upon decomposition into aminomethylphosphonic acid (AMPA) and phosphate. In a natural environment, glyphosate is prone to rapid degradation. The impact of glyphosate on phytoplankton growth has been both positive and negative, with few definite results. This project investigated the influence of various parameters on the ability of glyphosate to impact phytoplankton, and therefore, what systems are most at risk of eutrophication due to glyphosate addition. Multiple laboratory bioassays were performed as well as a three-pond mesocosm field experiment conducted in Auburn, AL. Lab experiments, tested on a laboratory-cultured Microcystis aeruginosa strain, found systems with low pH (<7) and dissolved organic matter (DOM) had the most growth following glyphosate addition; these environments promoted up to a 30% increase in chlorophyll-a compared to the control. Glyphosate, in the form of RoundUp®, was added to field mesocosms in levels of 100 µg/L and 700 µg/L. The field experiment found the mesotrophic and eutrophic ponds had 50% more chlorophyll-a in the 700 µg/L treatment than the control. These results show that low levels of RoundUp® (<1 mg/L) can increase nutrient values significantly and be effective at causing excess phytoplankton growth and in some cases eutrophication
Can nutrition strategies, such as fiber and ketone supplementation, ameliorate the negative effects of high salt consumption on vascular health and immune cell phenotypes?
Get PDFBackground: Consuming high dietary salt (HS) is prevalent in the western diet and does not appear to be decreasing. HS consumption is the leading modifiable risk factor for the development of hypertension and subsequent cardiovascular disease (CVD) in the United States. Understanding that CVD is the leading cause of death, strategies are necessary to reduce the risk of CVD development. Dietary fiber and the ketone body β-hydroxybutyrate (βHB) have been demonstrated to be candidate nutrients in supporting cardiovascular health and reducing inflammation. Therefore, the purpose of this dissertation was to investigate the potential roles of dietary fiber and βHB in offsetting the negative effects of high dietary salt consumption and exposure. Methods: To investigate the role of fiber, a national dataset (NHANES) was collected from the Center of Disease Control; dietary patterns were quantified by total sodium consumption and sodium indexed to fiber and were correlated with blood pressure (BP) and markers of inflammation. A clinical trial was used to investigate the effect of βHB supplementation on BP reactivity, a measure prognostic of future CV incidence regardless of salt sensitivity status, despite concomitant salt supplementation; and a cell culture model was used to investigate whether direct βHB exposure would ameliorate the proinflammatory response induced by high salt observed in peripheral blood mononuclear cells. Results: While no linear relations were observed between recalled nutrition and measured BP, there were quadratic relations between sodium to fiber and all measures of BP (ps < 0.035). The clinical 2 trial remains underpowered at the time of this writing, and no significant effects of supplemental conditions were observed on BP reactivity, however the proinflammatory cytokine TNF-α was reduced in the HS+βHB condition (p = 0.035). There was a significant effect of the βHB exposure in the expression of pro- (p < 0.001) and anti-inflammatory (p = 0.008) cytokines the immune cells. Conclusion: Observing sodium to fiber ratios may provide an index into dietary habits, but are not linearly related to BP. With continued investigation βHB may provide cardioprotective benefits and has been demonstrated to decrease proinflammatory gene expression
Where’s the Music? Understanding Sense of Place in Asheville North Carolina Through Tourism Guidebooks and Stakeholder Interviews
Get PDFMy study seeks to investigate music’s role in Asheville’s tourism message. The
significance of my study is the opportunity to add to existing music tourism research on mid sized cities in geographic literature. Data will be collected by using on- on-one interviews and
content from Asheville tourism guidebooks to explore the development of Asheville’s tourism
promotion The respondents will be local musicians, venue promoters, and Asheville’s tourism
officials and discourse analysis will be done on guidebooks and interview responses. My study
will benefit Asheville’s tourism industry and local community as well as fill in gaps in tourism
development in midsized cites based on cultural characteristics such as music
Attosecond Pulse-Tailoring with a Two-Color Field and the Time-Resolved Quantum-Path Interference Measurement of Cu(111)
No full textThis work investigates high harmonics generated by electron dynamics in a strong, slowly varying electric field. Attosecond light sources based on high-harmonic generation have enabled probing dynamics in matter on the natural timescale of electron motion. Typically, attosecond measurements involve generating an electron wavepacket by absorbing the attosecond pulse, with dynamics being deduced from the wave packet’s attributes and known spectral components of the pulse. Theoretical models of previous experimental work on attosecond pulse trains show that the intensity ratio and phase shift are key control mechanisms. Spectral phases computed using Strong-Field Approximation (SFA) theory qualitatively match the spectral characteristics of high harmonic radiation in single- and multi-color fields. Calculations for a fundamental intensity of 200 TW/cm² and various intensity ratios and phases between 400 nm and 800 nm components of the driving field demonstrate precise periodicity control of the attosecond pulse and a novel method to experimentally retrieve temporal properties of the electron's ejection. Additionally, technical developments of an end-station for solid-state materials are presented, with initial measurements of time-resolved quantum-path interference on the Γ̅ symmetry axis in Cu(111) compared with a similar measurement in argon