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Towards Understanding the Influence of Surface Integrity on Mechanical Behavior of Additively Manufactured Ti-6Al-4V
No full textAdditively manufactured components often exhibit shorter fatigue lives in their
unmachined state compared to machined or wrought counterparts mainly due to the presence of
surface micro-notches. While post-processing treatments can improve performance, they increase
lead times, may not always be feasible or desired, and can compromise the advantages of AM,
such as near-net shape fabrication. This dissertation aims to investigate the influence of surface
integrity on the mechanical behavior of laser powder bed fused (L-PBF) Ti-6Al-4V specimens.
First, a novel framework was developed to quantify surface micro-notches using X-ray computed
tomography, where key geometrical features such as width, depth, opening angle, and radius of
curvature were captured. These features were then combined in the fatigue stress concentration
formula, Kf, to assess the fatigue criticality of each notch. It was found that the crack-initiating
features ranked within the top 1% of all notches based on the calculated Kf. Fatigue life predictions,
employing the fatigue notch factor approach that incorporated localized geometrical features of
micro-notch, demonstrated reasonable accuracy for unmachined L-PBF Ti-6Al-4V specimens.
This framework was then further validated for conditions where process parameters were
systematically varied (i.e., specifically, combination of different infill and contour parameters),
and a wide range of surface and near-surface conditions were produced. Moreover, the modelling
approach was further applied to partially treated specimens to assess its broader applicability. The
results demonstrated that the developed fatigue modelling framework could reasonably predict
lives across a wide range of surface textures including partially treated specimens. In addition toiii
modelling, the influence of a wide range of surface conditions on the mechanical performance was
investigated. Results showed that avoiding contour passes increased surface roughness and
reduced tensile ductility due to early void nucleation. While contour passes enhanced fatigue life
for default and underheated infill settings, this beneficial effect was diminished for overheated
conditions due to increased roughness and near-surface defects. Moreover, the impact of surface
material removal methods, including direct polishing, shallow machining and polishing, deep
machining (DM), and deep machining with polishing (DM+P) on the mechanical performance was
evaluated. The results showed that polishing alone did not improve tensile behavior and fatigue
resistance due to persistence of surface valleys, while DM and DM+P improved tensile ductility
and fatigue life by removing surface and near-surface defects
Exploring Fungal Diversity and Interactions with Lecanosticta acicola in Brown Spot Needle Blight
No full textBrown spot needle blight is a foliar disease that affects loblolly pines. It is characterized by small, necrotic spots on the needles that expand into brown lesions surrounded by a yellowish halo, often culminating in defoliation when conditions are favorable. Loblolly pine is the most abundant pine found in the southeast U.S. It is of a high economic value, however in recent years it has been threatened by brown spot needle blight disease, thereby impacting the region’s forest economy. In this study morphological and molecular techniques were used to identify co-occurring foliar pathogens with Lecanosticta acicola, the causative pathogen of the disease. Twenty-one different fungi genera were recovered from these methods of which Pestalotiopsis, Cladosporium, Hendersonia, and Trichoderma were found to be the predominant fungi associated with L. acicola. The study further tested the susceptibility of seventeen different loblolly pine families to L. acicola. We ranked the best three families that had better tolerance to the pathogen, based on growth parameters such as mean height, disease rating root collar diameter and relative water content. Finally, we investigated how spore traps could be used to assess L. acicola spore loads in BSNB-infected plots. We found that climatic variables such as rainfall, relative humidity and temperature affected spore release throughout the sampling period, with rainfall having the best association with spore release.
Keywords: Loblolly pine, foliar pathogens, Brown spot needle bligh
Characterization of RHIM Domain Functionality in Viral Pathogens Through Interaction with Necroptotic Machinery
Get PDFNecroptotic cell death occurs following cellular stress conditions in which there is a
potential benefit to the host to encouraging an inflammatory response. Often, this is an additional
defense against pathogens, although the exact mechanism of activation is often unclear. This
signaling cascade, unlike apoptotic cell death, does not involve the activation of caspases and is
dependent on the kinase activity and interaction of RIP homotypic interaction motifs (RHIM)
contained within several proteins within the cascade. However, non-mammalian RHIM domains
have been observed with a range of potential positive and negative effects on the cell. Through a
novel RHIM-swap screen, we evaluated the cellular localization of these proposed RHIMs as a
predictive measure of binding ability. These predictions were corroborated through protein
interaction experiments. The results of these experiments suggest a role in RHIM binding in
some coronavirus infections and may indicate a novel approach to understanding inflammatory
responses to some viral infections
“Racism is Not Getting Worse, It’s Getting Reposted”: Exploring the Biopsychosocial Impact of Online Vicarious Racism
No full textOnline vicarious racism, or indirect exposure to racially traumatic content via digital platforms, has become an increasingly salient contributor to racial stress and health disparities among Black Americans. The conceptual study introduces a biopsychosocial model to define and contextualize online vicarious racism, illustrating how it may serve as a unique risk factor for adverse health outcomes and influence social determinants of health. Complementing this work, the following quantitative study employed a repeated measures experimental design to examine the psychological and physiological effects of viewing racially distressing online content. Findings revealed significant increases in anxiety, negative affect, somatic symptoms, and racial trauma, depending on the degree of racialized violence presented. Together, these studies underscore the pervasive and multidimensional impact of online vicarious racism, highlighting the urgent need for trauma-informed clinical interventions and systemic policy reforms to mitigate its harmful effects in an increasingly digital world
Autonomy, Guidance, and Control Strategies for Safe Operation of Aerospace Vehicles
No full textThis dissertation is structured around three core research problems, each addressing a fundamental challenge in enabling safer operation of aerospace vehicles. While the primary motivation stems from the growing use of multirotor Unmanned Aerial Vehicles (UAVs) in civilian and industrial applications, the methodologies developed apply to a broader class of autonomous systems. The three focus areas include: 1) obstacle avoidance (collision safety) -- learning-based obstacle avoidance for real-time motion planning in cluttered environments, 2) noise control (acoustic safety) -- phase and crossover angle control for propellers to reduce aerodynamic interference and noise, and 3) robust guidance (safety from sensitive parameters) -- desensitization of optimal control problems to parametric uncertainties using desensitization techniques. Each of these research topics is explored independently with the goal of advancing autonomy, guidance, and control strategies for reliable and safe operations of aerospace vehicles.
The first part of this dissertation addresses the challenge of collision safety by developing a learning-based framework for real-time UAV motion planning and guidance in cluttered environments. In this section, Neural Networks (NNs) are configured and trained on a dataset of optimal trajectories generated using a convex optimization-based planner. The convex optimizer generates dynamically-compliant, energy-optimal trajectories. To ensure effective learning across various obstacle configurations, hyperparameter tuning is performed for the NN models using Optuna. The proposed motion planning framework employs a cascaded planning architecture in which a high-level path planning NN model first predicts a set of waypoints around detected obstacles, followed by a second NN to generate a smooth, dynamically feasible trajectory using B-spline representations. This two-stage design improves interpretability and post-processing of the waypoints generated. A safety margin correction step is also introduced, which adjusts the predicted trajectories to enforce a buffer zone around obstacles and guarantee collision-free paths. Additionally, an object detection and localization (ODL) software stack is also developed, which leverages stereo vision and a tiny YOLOv3 network to estimate the 3D positions of obstacles. The complete perception-guidance pipeline, including object detection, depth-based obstacle localization, and trajectory generation, is deployed onboard a quadcopter equipped with a stereo camera and a Jetson Nano as a companion computer. Flight experiments validate the system's ability to navigate safely and autonomously in an indoor arena with up to two obstacles.
The second part of this dissertation focuses on controlling the phase angles of rotating propellers, which improves the acoustic signatures of multi-rotor UAVs. Initially, a phase control algorithm is developed that enables precise adjustment of the phase angles. This controller is experimentally tested on various propeller configurations, including single, side-by-side, and coaxial, to validate its effectiveness in different aerodynamic coupling conditions. The phase controller is extended to specifically address counter-rotating configurations, where the two propellers spin in opposite directions and periodically overlap in angular space. This region of overlap, referred to as the crossover, influences the noise propagation characteristics of the system. A crossover position controller is developed to enable the shifting of the angular alignment of the propellers. To assess the controller’s accuracy and performance, a non-invasive image-based validation method is introduced using a high-speed video system and centroid tracking of reflective markers affixed to the propellers. This technique allows for precise measurement of phase and crossover angles without the need for onboard sensors or encoders. Experimental results demonstrate that the controller can achieve desired crossover alignments with an average error of less than 4 degrees across a wide range of propeller speeds and configurations.
The third part of this dissertation addresses the challenges associated with uncertainties in dynamical systems and focuses on the development of a novel trajectory optimization framework that minimizes sensitivity to parametric uncertainties. The investigation begins with a standard low-thrust spacecraft trajectory optimization problem, where an initial attempt is made to improve robustness of the cost (i.e., the final mass of the spacecraft) to the uncertainties in the thrust magnitude of the propulsion system using a costate-based (a.k.a. Lagrange multipliers) desensitized optimal control approach. However, this method does not yield any improvements in the robustness to uncertainties. Further analysis revealed that the costate profiles arising from the hybrid nature of the direct-indirect formulation are non-unique. Using this property of the costates, a new approach, called the Reduced Desensitization Formulation (RDF), is developed for desensitizing optimal control problems. To investigate the effect of desensitization at specific intervals during the flight, a time-triggered variant of RDF is also introduced. The base and time-triggered RDF is applied to a broad range of optimal control problems. Simulation results demonstrate that RDF reduces the dispersion of the trajectory cost functional under parametric uncertainties
The Synergistic Effects of Dietary Nitrate Supplementation and 12 Weeks of Resistance Training on Skeletal Muscle and Vascular Function in Middle-aged and Older Adults
Get PDFIncreasing dietary nitrate (NO3-) through beetroot juice (BRJ) supplementation elicits acute ergogenic benefits. However, it is unknown whether chronic NO3- supplementation can enhance resistance training (RT) adaptations in middle-aged and older adults. Therefore, we sought to determine whether 12 weeks of combined RT and NO3- supplementation enhanced hypertrophic, vascular, strength, and skeletal muscle angiogenesis adaptations in this population. Twenty-eight apparently healthy, untrained men and women (56±7 years old, 29.1 kg/m2 body mass index) completed 12 weeks of supervised full-body RT (2x/week) while ingesting either BRJ (140 mL daily, providing 800 mg NO3-; n=14 with 7M/7W) or NO3--depleted BRJ placebo (PLA; n=14 with 7M/7W). Participants underwent a whole-body dual-energy x-ray absorptiometry scan, right mid-thigh ultrasonography for muscle imaging, right leg popliteal artery flow-mediated dilation (FMD) assessments, a biopsy of the right mid-thigh vastus lateralis, and strength testing prior to and following the 12-week intervention. Biopsy analyses included a NO3-/nitrite (NOx) fluorometric assay, immunoblotting for proteins involved in angiogenesis, and immunohistochemistry to quantify fiber type-specific capillaries and cross-sectional areas. Muscle NOx values did not significantly change: +15.4% in BRJ (p=0.073) and +7.8% (p=0.514) in PLA. Both groups significantly improved measures related to muscle hypertrophy, strength, and FMD. However, no significant group × time interactions were observed for whole-body lean mass, mid-thigh muscle cross-sectional area, popliteal artery FMD outcomes, or histological or molecular markers. In conclusion, BRJ supplementation does not enhance RT adaptations in middle-aged and older adults.
The impact of commercial feeder types on feeding and feed-spillage related behaviors of broiler chickens.
No full textThe behavior of birds at the feeder can cause feed spillage, which can have economic consequences. This research aimed to evaluate the impact of different commercial feeder types on feeding and feed-spillage related behaviors of broilers by assessing the frequency of behaviors performed by each bird at the feeder. The first study was conducted during the starter phase. A total of 720 male broiler chicks (YP x Ross708) were randomly placed into 24 floor pens at a stocking density of 30 birds/pen. Feeder treatments were C2 plus feeder (C2), C2 feeder with supplemental turbo grow (C2TG), C2 feeder with supplemental feed tray (C2FT), and Konavi feeder (KON). Behaviors were continuously recorded on days 1, 4, 7, and 14 with a 5-minute observation every 30 minutes. Behaviors were categorized as, eating from outside the feeder, eating perched on the edge of the feeder, eating from inside the feeder, entering-exiting the feeder, attempts to enter the feeder, moving inside the feeder, pecking at litter within the feeder, feed scratching, feed selection, jostling at the feeder, displacing other birds from the feeder, and repetitive pecking at the feeder. Behavioral frequencies were analyzed by using a one-way ANOVA (PROC GLIMMIX, SAS 9.4) with Poisson distribution to assess the impact of feeder treatments on bird behavior. Means were separated via Tukey-Kramer. Birds ate more from outside the C2TG (9.98) and KON (9.68), whilst birds ate more from inside the C2FT (6.10). More birds ate while perching on the edge of C2 (0.44), while fewer birds ate from the edge of KON (0.1). Birds had the highest successful entering and exiting with C2FT (4.12), and the highest unsuccessful attempts with KON (0.78). Birds were most active inside C2FT (2.10), then C2 (0.74), followed by C2TG (0.29), and least active inside KON (0.01). Pecking at litter within the feeder, feed scratching, and feed selection were more frequently observed with C2FT (P<0.01). Both jostling at the feeder and displacement of chicks from the feeder occurred the most with KON and least with C2 (P<0.01). These results indicate that feeders such as C2FT and C2 allowed birds to enter feeders, subsequently increasing the occurrences of eating, moving, feed-scratching, and feed selection inside the feeder. With these behaviors, birds spilled the feed while sorting or scratching the feed. Whereas feeders such as C2TG and KON limited birds from entering the feeder and had higher frequencies of birds eating from outside, jostling, and displacement at the feeder. These behaviors have led to the feeder swinging or shaking, forcing out the feed particles from the feeder. The second study was conducted on the grower and finisher phases of broiler chickens. On the day of hatch, a total of 720 male broiler chicks (YP x Ross708) were randomly placed into 24 floor pens (30 birds/pen) in a randomized block design. Treatments were: C2 feeders at opening setting 4 (C2 (4)), C2 feeders at opening setting 5 (C2 (5)), C2 feeders at opening setting 6 (C2 (6)), KON feeders at opening setting 1 (KON (1)), KON feeders at opening setting 2 (KON (2)), and KON feeders at opening setting 3 (KON (3)). Experimental feeder treatment started on day 14, and behaviors were observed on days 27, 34, and 41 with a similar method used in Study 1. Behaviors assessed were straight eating, neck flexion with head outside feeder, neck flexion with head in-feeder, lateral eating, moderate feeder shaking, violent feeder shaking, feeder movement with birds’ activity, jostling at the feeder, displacement of birds from the feeder, and substrate flicking. To assess the impact of feeder treatments on bird behavior, a one-way ANOVA (PROC GLIMMIX, SAS 9.4) with negative binomial distribution was used. Overall, birds ate from all the treatments at a similar frequency. However, birds ate less in an neck flexion with head outside the feeder posture in all C2 feeders (C2 (4) = 0.45, C2 (5) = 0.49, C2 (6) = 0.50) then KON feeders, with the frequency being higher for KON (2) (1.52) then for KON (3) (1.23) but not differing from KON (1) (1.28). Similarly, fewer birds ate in lateral posture at all C2 treatments (C2 (4) = 0.20, C2 (5) = 0.19, C2 (6) = 0.23) compared to KON treatments; however, within KON feeders, birds ate more with KON (1) (0.95) and KON (2) (0.93), then with KON (3) (0.71). Birds were moderately shaking C2 (6) (0.36), and KON (2) (0.18) the most, and KON (3) (0.18) the least. Whilst birds were violently shaking all KON feeders (KON (4) = 0.04, KON (5) = 0.04, and KON (6) = 0.04) more than all the C2 feeders (C2 (4) = 0.00, C2 (5) =0.00, C2 (6) = 0.01). No effect of feeder treatments was seen on straight feeding, feeder movement, jostling, displacement, and substrate flicking. These results indicate that behavior such as moderate and violent feeder shaking, feeder movement, jostling, and displacement caused by feeder disturbances led to spillage, as explained in study 1. However, the greater amount of spillage in KON feeders (1, 2, 3) than in C2 feeders (4, 5, 6) can be attributed to the violent feeder-shaking behavior of birds and feeder features. Feeder design influenced the feeding and feed-spillage related behaviors of birds, and KON had greater spillage in both studies. Design features of KON, such as lower pan height and the feed being presented near the edge, made it prone to spilling the feed when birds performed behavior at the feeder. Overall, these studies in different phases of broiler chickens highlight the influence of feeder design on behaviors that cause feed spillage
Sustainable Waste Valorization through Coupled Anaerobic Digestion and Biofilm Photobioreactor Systems
No full textAbstract
Methane and carbon dioxide are two of the most significant greenhouse gases, responsible for global warming. A primary source of these emissions is the improper disposal of organic waste, including food waste and fish sludge. Developing sustainable strategies for managing such waste streams is crucial to human beings. This thesis studies two projects for the valorization of food waste and fish sludge. The first project investigates the anaerobic digestion of fish sludge and food waste under mesophilic conditions, aiming to maximize biogas production. The second project aims to construct and test the bench-scale circulation coculture biofilm photobioreactor (CCBP) to convert biogas produced from the first project into microbial biomass, which can be subsequently converted into an aquafeed.
In Chapter 1, the need for conducting this project and the purpose of the research are investigated by treating waste and converting it into value-added materials, such as methane and nutrient-rich compounds, to utilize this biogas in the CCBP, which is equipped with a conveyor belt and membrane to grow single-cell protein for fishmeal. These justifications were based on the fundamentals and need to build and develop the proposed waste2feed biotechnology.
In chapter 2, the co-digestion of the fish sludge and food waste is examined. The effect of the ratio of food waste and fish sludge on the methane and biogas volume production is studied. The results show that food waste was responsible for increasing the percentage of the solid content and contributing more carbon content to the process. Eventually, the increase in food waste can lead to a rise in methane and biogas production. The analysis of the Chemical Oxygen Demand (COD)
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reveals that the COD of the food waste and fish sludge decreases after the anaerobic digestion process. Therefore, the co-digestion of fish sludge and food waste not only improves anaerobic digestion but also enhances waste management by reducing the COD of the two waste streams. In the previous chapter, the co-digestion of fish sludge and food waste was studied. The effect of the ratio of food waste and fish sludge on the methane and biogas volume production is investigated. The results show that food waste was responsible for increasing the percentage of the solid content and contributing more carbon to the system. Consequently, as the food waste portion increases, the amount of methane and gas also increases. The analysis of the Chemical Oxygen Demand (COD) reveals that the COD of the food waste and fish sludge decreases after the anaerobic digestion process. The co-digestion of fish sludge and food waste not only improves anaerobic digestion but also enhances waste management by reducing the COD of the two waste streams.
In Chapter 3, the construction and development of the CCBP are discussed. The main components, necessary items, and sensors were designed and customized using design software such as Fusion 360 and manufactured in the maker space at Auburn University. Our challenge is to maintain the temperature and utilize intelligent monitoring by leveraging Arduino sensors. This challenge was addressed by using the BMP280 Arduino sensor, coil heating, and specialized insulation. Different candidates for conveyor belts were tested using methanotrophs in this chapter as well. The results showed that all the tested materials had the potential to be used as a conveyor belt, as there was no significant inhibition from them. The need for producing fish meal out of fish sludge is discussed in this chapter, too. The CSTR configuration, using a Bioflo bioreactor, was employed to convert the 10% anaerobic digestion (AD) effluent from Chapter 2 into single-cell protein. All parameters, including the growth rate and biomass concentration during the process, as well as the amounts of protein and lipid, are studied in this chapter.
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In Chapter 4, the conclusion of the chapters above is discussed. The co-digestion of food waste and fish sludge resulted in a synergistic effect that can improve biogas and methane yield. The COD removal parameters indicated that this system could help convert organic matter into inorganic matter. The effluent coming from the codigestion was diluted 10 times and used in the coculture of methanotrophs and microalgae to produce fish meal. The results for this coculture showed that not only was the growth rate high, but also the protein and lipid content of the biomass made this product a good candidate for the fish meal. Since these results come from laboratory scales. The real application requires some modifications and improvements, such as scaling up the process and conducting more analyses of the liquid and gas to understand better and monitor the process. For the future, the CCBP and co-digestion of fish sludge and food waste should be integrated as a single process, not only to remove organic matter from food waste and fish sludge but also to produce single-cell protein for the fish
Improving Dielectric and Piezoelectric Property of Flexible Composite for Energy Applications Using CNC and Related Fundamentals
No full textWith the rapid advancement of modern electronic devices, there is a growing demand for miniaturized, high-energy-output, and flexible energy storage and generation/conversion systems. Among energy storage technologies, dielectric capacitors are widely adopted due to their ultrafast charge–discharge capability compared to conventional electrochemical batteries. However, their application is often limited by its low energy density, restricting their use to "temporary" energy storage functions. The key to achieving higher energy storage performance lies in simultaneously enhancing the dielectric breakdown strength and the dielectric permittivity.
In the first part of this study, a new methodology is proposed to eliminate the intrinsic thickness dependence of dielectric breakdown strength (DBS) and recoverable energy storage density in ceramic dielectric materials. This method references all DBS and recoverable energy storage density measurements to a standardized value, thereby providing a unified benchmark for comparing the DBS and energy storage performance of ceramic films across different materials and fabrication methods. It can also be extended to polymer dielectrics, enabling a more accurate evaluation of the true energy storage potential of thicker polymer films.
For improving the DBS of polymer-based material, fluorinated trichlorosilane was identified as a highly effective organic additive for polymer matrices, including P(VDF-HFP), P(VDF-CTFE), and PMMA. Incorporating this fluorinated silane compound resulted in up to a 40% increase in dielectric permittivity and an 80% enhancement in DBS compared to unmodified polymers. This demonstrates its dual functionality in improving both polarization response and breakdown strength, independently of inorganic filler surface interactions.
Furthermore, due to environmental concerns related to the potential chemical pollution caused by small molecule fluorinated silane compounds, biofriendly and renewable cellulose nanocrystals (CNC) were explored as fillers for PVDF copolymers. During the development of CNC–P(VDF-HFP) composites, a novel low-water-content fabrication process was established. This process enabled the incorporation of CNC into P(VDF-HFP) while maintaining low moisture levels, resulting in approximately 40% improvements in both DBS and maximum chargeable energy density.
As for the energy conversion, piezoelectric nanogenerators (PENG) have garnered considerable attention for energy‐harvesting applications because their compact size and power output are sufficient to operate modern electronic sensors. Cellulose nanocrystals (CNC) are promising candidates for PENG fabrication due to their high intrinsic piezoelectric coefficient (e.g., d_25~210 pC/N) and inherent flexibility. To fully exploit this large coefficient, CNC–polymer composites with well-aligned CNC were produced by shear casting using the low-water-content methods described earlier. Computational analyses confirm that aligned CNC make a substantial contribution to the composite’s overall piezoelectric response. Experimental measurements revealed that incorporating CNC into P(VDF-TrFE) results in an approximately eightfold increase in piezoelectric output.
Taken together, these four complementary strategies—thickness normalization, fluorinated silane additive incorporation, CNC-based bio-fillers, and alignment-enhanced CNC composites—offer a robust and integrative framework for both the accurate evaluation and targeted enhancement of dielectric and piezoelectric materials. These advancements pave the way for the development of next-generation high-energy-density capacitors and advanced piezoelectric nanogenerators
Microplastic contamination in the Alabama River and effects on Daphnia magna
Get PDFThis thesis research focused on assessing microplastic (MP) contamination in the Alabama River and evaluating the impacts of different MP types on Daphnia magna. Chapter 1 was an overview of MP pollution including sources, ecological impacts, and rationale for
conducting this thesis research. Chapter 2 investigated MP contamination in the Alabama River at which sources, temporal and spatial distributions, and MP load into Mobile Bay were studied. Chapter 3 focused on the chronic effects of three environmentally representative MPs: nylon and Kevlar microfibers and MPs made from a single use plastic cup on D. magna. Effects on survival, growth, reproduction, and MP uptake were determined. Chapter 4 was a preliminary risk assessment for MPs in the Alabama River through comparing the results of chapter 2 and chapter 3 using the probabilistic risk assessment approach to determine the bioavailability of MPs and potential risk to aquatic organisms in the Alabama River