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Structural Composite Electrode for Space Applications
No full textStructural batteries offer a solution for more range-efficient vehicles with its multifunctional ability to hold mechanical load and store energy. The earth���s atmosphere and space environment require vehicles and satellites to have structures which are sturdy against potential environmental debris collisions and able to withstand low temperature. This thesis focuses on the material processing and electrochemical performance of a multifunctional structural composite electrode which consists of carbon fibers for structural reinforcement and a structural biphasic bicontinuous electrolyte (SBBE) for the composite matrix. The SBBE-coated carbon fiber versus lithium half-cell is studied in coin cell configuration. The solid biphasic bicontinuous electrolyte is made from lithium bis(trifluoromethanesulfonyl)imide salt, diglyme, and fluoroethylene carbonate for the liquid electrolyte ionic-conducting phase and resin for high modulus phase.
The effect of the pre-cured volume of SBBE (i.e., volume of SBBE pipetted on top of carbon fiber fabric prior to curing) on the electrochemical performance of the carbon fiber versus lithium foil half-cell in coin cell configuration was studied. After the solid biphasic electrolyte is cured as a layer on the carbon fiber fabric composite electrode, electrochemical characterizations were performed on structural composite electrode half cells with pre-cured SBBE volumes ranging from 25 to 100 ��������. Results indicated that the optimal structural battery volume is 50 �������� because it has the highest electrochemical charge and discharge capacity for the structural composite electrode versus lithium metal foil half-cell at 180 mAh/g for the first cycle, the lowest charge transfer resistance from the electrochemical impedance spectra, and relatively the highest anodic peak when comparing 5th cycle cyclic voltammograms of structural composite electrode with pre-cured SBBE volumes ranging from 25 to 100 ��������. Future work includes testing samples with biphasic electrolyte coated on desized carbon fiber tows on an in-situ electrochemo-mechanical coupling machine
Semi-Synthetic Analogs of Occidiofungin
No full textFungal infections are a global healthcare concern. Multi-drug resistant fungal infections present a great challenge for the treatment of infected individuals. Current classes of antifungal agents each have their own limitations. The last class of antifungal agent approved for treating systemic fungal infection was echinocandins in the early 2000s. Occidiofungin is a natural product produced by the soil bacterium Burkholderia contaminans MS14. The structure is a cyclic glycolipopeptide consisting of 8 animo acids. The mechanism of action of occidiofungin is unique compared to current antifungal agents. Murine models demonstrated that occidiofungin had minimal toxicity and was effective in treating vulvovaginal candidiasis. Occidiofungin is currently in phase 1 clinical trials for the treatment of recurrent vulvovaginal candidiasis. This dissertation is focused on the characterization of novel occidiofungin variants, and the production and characterization of semi-synthetic occidiofungin analogs. Semi-synthetic occidiofungin analogs were produced by modifying the sidechain of novel amino acid 2. These analogs were used to investigate the structure-activity relationship of occidiofungin. The diol group on novel amino acid 2 plays an important role in the antifungal activity of occidiofungin, likely contributing to cellular uptake. A newly identified occidiofungin variant was identified which contains aspartic acid instead of asparagine at position 7. The aspartic acid variant could be utilized to produce semi-synthetic analogs by targeting the terminal carboxylic acid on the aspartic acid. The aspartic acid residue presents a region that is highly amenable to modification without reducing antifungal activity. A phosphate prodrug semi-synthetic analog designed to treat systemic infection has been developed. Occidiofungin was not able to reduce the fungal load in a systemic candidiasis murine model, which may be due to high levels of binding to serum proteins. The phosphate prodrug analog demonstrated in vitro antifungal activity and reduced binding to serum proteins. Future investigation into the efficacy of the phosphate prodrug analog in treating systemic fungal infections will be performed
John Bickham field notebook: AK1501-AK2000.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK2001-AK2500 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
Genetic Architecture of Nodule Traits in Guar
No full textGuar (Cyamopsis tetragonoloba L.) is an annual, diploid legume crop cultivated primarily for the galactomannan gum contained in the seed endosperm, which is used widely in foods, pharmaceuticals, and other industrial applications. As a legume, guar forms root nodules to fix atmospheric nitrogen, but nodulation has been noted to be poor in the field. Phenotypic evaluation of 225 diverse guar accessions from the United States Department of Agriculture germplasm collection revealed significant variation among genotypes for plant height, nodule diameter, fresh and dry nodule weight and dry aboveground plant biomass. However, no significant differences were found for fresh aboveground plant biomass. Broad-sense heritability was highest for nodule diameter (92%) indicating potential for genetic gain through selection. Significant positive correlations occurred between nodule number and weight, and between plant biomass and nodule weight, revealing increased plant growth with greater nodule mass. Several promising genotypes such as PI 288747 were identified that can serve as parents in breeding initiatives to improve nodulation capacity. Population structure analysis on 225 accessions from India, Pakistan, and the United States genotyped with 7,000 SNPs revealed three main genetic clusters largely corresponding to geographic origin. In which Q1 included genotypes from all three countries while Q2 and Q3 included genotypes only from India. Genome-wide association studies using 19,007 filtered SNPs identified SNP markers associated with plant height, nodule number and diameter, nodule weight, and plant biomass across multiple models. Several SNPs were shown to be connected to various guar nodulation traits. SNP Chr6_56449898 showed a strong correlation with the weight and number of nodules. Chr2_51078296 and Chr2_51010513 SNPs showed a strong correlation with nodule characteristics as well as other variables including biomass and plant height. Together, these results further scientific understanding of guar genetic diversity, nodulation traits, and potential genomic regions controlling nodulation. This knowledge and germplasm can aid guar breeding programs seeking to improve nitrogen fixation and yields through enhanced nodulation, which would also increase ecological services. This research provides an important foundation and resources to enable marker-assisted breeding and selection for superior nodulation capacity and associated increased productivity in this economically important legume crop
A Test for Stationarity Using a Local Average of the Autocovariance of the Discrete Fourier Transform
No full textThe discrete Fourier transform of a second-order stationary process has been found to be asymptotically uncorrelated, a property which can be leveraged to create a test statistic for stationary. Building off this, we propose a version of the test where the test statistic is created by taking the local average over several partitions of the canonical frequencies, standardized using the heteroskedicity-consistent standard errors. Under the null hypothesis of stationarity this test statistic will be distributed as the sum-of-F distributions, while under the alternative hypothesis of local stationarity it will be distributed as the sum of non-central F distributions. Simulation studies show that locally averaging the DFT can result in a significant increase of power compared to globally averaging the DFT, and performs similarly to the Wavelet Packet Test, another contemporary test for stationarity
Ultra-High Strain Rate Impact Behavior in High Molecular Weight Thermoplastics
No full textThe advent of commercial and military hypersonic vehicles introduces formidable challenges to existing thermal protection systems and ballistic armor. Concurrently, all spacecraft face escalating threats from hypervelocity impacts (HVIs) by micrometeoroids and orbital debris (MMOD). Overcoming these obstacles requires materials/structures capable of withstanding extreme conditions. Yet, a clear knowledge gap exists in the fundamental understanding of the complex multiphysics phenomena generated when materials are subjected to ultra-high strain rate (>10^6 s^ ���1 ) collisions. This is especially true for polymers, despite their capacity for energy absorption and tailorability. This dissertation endeavors to bridge this knowledge gap by exploring the ultra-high strain rate impact behavior of three high molecular weight thermoplastics, ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and polycarbonate (PC). The primary objective is to help answer fundamental questions about their behavior and illuminate their applications. This goal necessitated a four-pronged strategy: (i) the establishment of an impact testing facility; (ii) the execution of HVI experiments; (iii) the application of numerical simulations to infer impacted target conditions; and (iv) the integration of these findings with existing literature to explain the role a polymer���s microstructure plays in its macroscopic energy absorption. The ensuing findings (i) revealed the difference in UHMWPE and HDPE���s HVI deformation, failure, and energy absorption was governed by an interplay between strain rates and rates of polymer chain disentanglement and reorientation and (ii) demonstrated the viability of threat-optimized protective structures. The dissertation also includes a novel study on similar impact phenomena, generated by decreasing spatial scale instead of increasing velocity. A Laser Induced Projectile Impact Test (LIPIT) apparatus and gas gun were used to launch alumina spheres ranging five orders of magnitude in diameter (3 ��m���10 mm) into scaled PC targets at 550 m/s. Length scale reduction set in motion a remarkable 230% amplification in specific energy absorption and a 240% increase in relative impact deformation area. In all, the dissertation leads to an irrefutable conclusion: while the behavior of polymers at lower rates (<10^3 s^ ���1 ) is well understood, there remains much to discover about their behavior as loading conditions become extreme. Data from lower rates and smaller scales cannot be extrapolated to higher rates and larger scales
An Innovative Algorithm for Assessing Instance Segmentation in Autofluorescence Microscopy Images
No full textNumerous methods have been created to segment individual cells in microscopy images, highlighting the need for an effective way to evaluate segmented results. Traditionally, the comparison of segmented images with their corresponding ground-truth images is conducted on a pixel-by-pixel basis. However, this approach often overlooks the misallocation of pixels between adjacent objects. In response, we introduce a per-object segmentation evaluation algorithm (POSEA), which assesses the accuracy of segmentation for each object in comparison to a ground truth image. The efficacy of POSEA is validated through the analysis of precision, recall, and f-measure scores, contrasting these with those derived from traditional pixel-based assessments across simulated and segmented fluorescence microscopy images of three distinct cell types. Notably, POSEA identifies a higher rate of segmentation errors due to its accurate recognition of pixels misattributed to adjacent objects. As a result, POSEA offers precise metrics for evaluating the segmentation of adjacent objects, proving its effectiveness for evaluating segmentation algorithms for autofluorescence microscopy images
Immunomodulatory Roles of Renal Lymphatic Endothelial Cells in Kidney Injury
No full textAcute Kidney Injury (AKI) is defined as a sudden decrease in renal filtration and is found to be associated with increased risk of developing chronic renal conditions such as Chronic Kidney Disease (CKD) and End-Stage Renal Disease (ESRD). While the mechanisms of the AKI-to-CKD transition remain unclear, AKI associated injury promotes an environment of persistent renal inflammation and fibrotic remodeling which may drive irreversible loss of nephrons and other renal cell types. Inflammation associated lymphangiogenesis (IAL) maintains tissue homeostasis through the uptake of proteins, fluids, macromolecules, and immune cells. IAL occurs upon AKI insult and is driven by Vascular endothelial growth factor D (VEGF-D) and VEGF-C. Recent work has demonstrated lymphatics and their components, lymphatic endothelial cells (LECs), have immunomodulatory roles such as antigen presentation, major histocompatibility complex (MHC) expression, and chemokine receptors. This dissertation investigates how renal lymphangigogenesis and LEC genetic adaptations in various models of kidney injury alter the adaptive immune cells in the kidney and the outcomes of renal function post-injury. Increased renal lymphatic density prior to the onset of kidney injury in a mouse model of kidney specific inducible overexpression of VEGF-D (KidVD) demonstrated an altered CD4:CD8 T cell ratio, decreased fibrotic remodeling, and improved functional recovery. Single cell RNA sequencing (scRNA seq) revealed that after AKI isolated renal LECs have T cell related immunomodulatory roles. To address the direct effect of LEC- T cell interactions, a murine genetic model with a LEC specific deletion of the Sphingosine-1- Phosphate (S1P) transporter Spinster 2 (SPNS2), key for S1P chemokine gradients to direct tissue immune cell egress, revealed altered renal immune cell subtypes and differential responses to injury challenge. Additionally, mice with disrupted LEC-S1P signaling demonstrate increased renal immunoglobulin deposition and, with nephrotoxic serum challenge, increased B cell activation and B effector subtype presence. This dissertation strengthens the connection between lymphangiogenesis and immunomodulation in kidney injury through the alteration of the adaptive immune response and demonstrates lymphatic targeted therapeutics may provide a novel renal targeted treatment option to prevent inflammatory progression to CKD
Views of Rural Community Members on Building or Rebuilding Public Trust in Healthcare
No full textHow, why, and what determines public trust in health entities is a critical element that is yet to be well documented particularly among rural residents. Identifying the perceptions of rural community members on trust in health entities is considered a fundamental strategy for improving health outcomes. To investigate the views of rural community members on trust in health entities, the purpose of this study was to assess and conceptualize a framework of building and rebuilding public trust in health entities among rural communities in the U.S.
Two different research strategies were utilized to complete this dissertation. First, a mixed-methods approach including a review process with systematic elements was performed to locate and evaluate the literature followed by a narrative approach to complete a scoping review. Second, a qualitative research study was used to explore the views of rural community members on trust in health entities using three different interview formats (intercept, dyadic, and focus groups).
Three major themes emerged based on both the scoping review and the qualitative research study. The themes included sources of information, trust barriers, and rebuilding trust which further resulted in other subthemes within each of them. The most common sources of information identified by both studies were medical professionals. Trust barriers according to the scoping review were specific to the health outcome and therefore the response identified varied from what was recorded in the qualitative studies. The qualitative study identified low expectations as the most dominant barrier of all others listed. Likewise, strategies identified for rebuilding trust included the inclusion of leadership engagement strategies, increasing awareness through information, and availability of services as the most presented.
In conclusion, the findings of the dissertation noted that strategic and multidimensional measures are required that are sustainable and long-term in order to increase public trust in health entities among rural communities in the U.S
Salmonella Survival, Growth, and Presence in Onion Bulbs, Extracts, and Production Environment
No full textThe purpose of this research was to investigate the presence, survival, and growth of Salmonella in onions and their environment as a prerequisite to understanding the risk that Salmonella poses to the consumer. Extracts from red and white onions grown under blue light significantly (P < 0.05) inhibited the growth of Salmonella. Extracts from genotype 1104 showed an optical density (OD) that was significantly lower than all other extracts, with total inhibition in extracts from the outer scales. Salmonella Newport was inoculated at various depths using a syringe (wounding) in and on red, white, and yellow onions and stored at room temperature for up to 18 days. At intervals, samples were collected from the top layer (skin) and inner layers of each onion and were tested for Salmonella. In all cases, the outer layer of all onion varieties not only inhibited S. Newport growth, but the populations of this pathogen were reduced by 3.2, 2.4, and 2.5 log cycles on red, white, and yellow onions, respectively within the first 3 days of storage, with no significant further changes in counts over 18 days. In contrast, Salmonella Newport grew by 1.7, 2.3, and 2.5 log cycles over the 18-d storage time in the inner layers of red, white, and yellow onions. In the trials to track the presence of Salmonella in onion-producing environments, a total of 255 samples (101 from fields, and 154 from packing plants) were collected and subjected to qualitative and quantitative Salmonella assay in a BAX system with the SalQuant kit. Salmonella was detected in 3 (13%) of 23 samples of well water collected from one onion field, 3 (4%) of 75 samples of soil collected from 3 fields, and 16 (10%) of 151 surface samples collected from 3 onion packing plants. In field samples that tested positive, the quantitative assay gave mean counts of 0.1 log CFU/50 L in water and 1.2 log CFU/g in soil. For environmental samples from packing plants, the mean counts for positive samples ranged between 1.9 and 3.2 CFU/cm2 , no significant differences between types of surfaces were found in the Salmonella counts