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Dynamic Covalent Polymer Networks for Additive Manufacturing and Supersonic Impact
No full textThe use of dynamic covalent bonds enables self-healing, shape morphing, and energy dissipation in materials. During the past decade, significant progress has been made in advancing both network chemistry and structural design. Diels-Alder (DA) ���click��� reactions introduce room-temperature stability and thermal response to the polymer networks. This thesis explores the roles of temperature and stress in the unique behavior of DA dynamic polymer (DAP) materials for their use in additive manufacturing and supersonic impact. In the second chapter, we report highly conductive nanocomposites made of DAP networks containing branched multi-wall carbon nanotubes (b-CNTs). The ability of liquified DAP to wet, infiltrate, and chemically stabilize bCNTs at increased temperature, and then ���lock��� well-dispersed nanotubes upon cooling via the ���click��� DA reaction results in a low percolation threshold of 0.04 wt% b-CNTs. Moreover, the nanocomposites exhibit controlled network plasticity for permanent shape reconfiguration at solid state via Joule-heating-induced dynamic bond exchanges, and these transformations can be triggered selectively at different locations in printed multi-material hybrid constructs, enabling spatiotemporal control of the material's permanent shape. In the third chapter, we demonstrate that large puncture healing of ultra-thin DAP dynamic networks under supersonic impact by microprojectiles outperforms that of traditional glassy polymers, while showing energy absorption comparable to those materials. Post-mortem microscopies reveal efficient puncture healing that is likely enabled by stress- and temperature-induced viscoelastic responses of DAP networks. The progression of impact events was observed using in-situ imaging with a nanosecond, microscale resolution, while the recovery of DA bonds after the impact was confirmed by infrared nanospectroscopy. In the fourth chapter, we present a procedure design for manufacturing DAP microspheres and analyze their high-strain-rate deformation behaviors under supersonic impacts against a rigid substrate. The dynamic responses of these microspheres are associated with the viscoelastic and viscoplastic characteristics of the microspheres as well as interfacial adhesion. Unlike traditional polymers, the interfacial adhesion properties are governed by the thermomechanical responses of DAP networks, due to temperature- and stress-sensitive DA bonds. The role of thermomechanical network responses in microsphere impacts was unveiled by in-situ observations, post-mortem morphological analysis, and finite element analysis simulations
Spatial Transformer Network You Only Look Once (STN-YOLO) for Improved Object Detection
No full textObject detection plays a crucial role in the field of computer vision by enabling machines to identify and locate objects within images or videos. There are several state-of-the-art object detection approaches and the most common model is You Only Look Once (YOLO). YOLO is a single-shot algorithm that directly classifies an object in a single pass by having only one neural network predict the bounding boxes and class probabilities. The baseline YOLO model may encounter challenges in detecting objects within cluttered or partially occluded scenes. Furthermore, the model may face difficulty in detecting small objects or those with low contrast. To improve the performance of the baseline model, a spatial transformer network (STN) is incorporated into YOLO baseline model.
The results showcase the efficacy of the end-to-end pipeline, highlighting the innovative application of STN integrated with YOLO that demonstrates improved object detection performance through quantitative metrics (e.g., precision, accuracy, recall and intersection over union). This study also investigates of the impact of different localization network in the STN like RESNET18 and VGG16 on the object detection. The objective of incorporating the STN module into YOLO is to enhance the model���s capability not only to attend to the most relevant regions in an image but also to perform spatial transformations such that the image is aligned before the detection is performed. The detected image can be used to perform analysis by extracting relevant information in terms of features or statistics from images
Efficacy and Utility of MPP51AA2-Traited Cotton as a Management Tool for Cotton Fleahoppers [Pseudatomoscelis seraitus (Reuter)]
No full textIn Texas the cotton fleahopper (Pseudatomoscelis seriatus (Reuter)) is considered a highly economically damaging pest of cotton (Gossypium hirsutum L.). Current control methods rely heavily on the use of foliar applied chemical insecticides during the growing season. The Mpp51Aa2.834_16 gene in cotton (ThryvOn) has proven effective against thrips and Lygus spp. with piercing and sucking feeding behaviors, suggesting the trait may also provide similar efficacy on cotton fleahoppers.
Field trials were conducted in 2019, 2020, and 2021 comparing a ThryvOn cultivar to a non-traited isoline under insecticide-treated and untreated conditions. While cotton fleahopper population differences between the traited and non-traited plants were not consistently noted during the pre-bloom squaring period, there was a consistent increase in square retention in cotton expressing Mpp51Aa2 relative to non-traited cotton. Additionally, cotton expressing Mpp51Aa2 offered similar square protection relative to non-traited cotton treated with insecticides for cotton fleahopper. These findings indicate that the Mpp51Aa2 protein should provide benefits of delayed nymphal growth, population suppression, and increased square retention.
In the choice assay, feeding by cotton fleahoppers significantly reduced square retention in the non-traited cotton to 46%, while ThryvOn cotton retained 60% of squares. In the no-choice assay, cotton fleahopper nymph feeding significantly reduced square retention in the non-traited cotton to 61%, whereas ThryvOn cotton was unaffected. Our findings indicate that the Mpp51Aa2 protein influences cotton fleahopper feeding preference and the susceptibility of cotton plants to damage caused by cotton fleahoppers.
To evaluate the feeding behavior of the cotton fleahoppers on ThryvOn cotton an electropenetrography (EPG) coupled with a Giga-8 DC EPG amplifier was used to monitor the probing activity cotton fleahopper nymphs on ThryvOn and non-traited cotton squares. Nymphs were placed on a square for 8 hours and waveforms were characterized as non-probing, cell rupturing, and ingestion. There were significantly more cell rupturing events on ThryvOn (14.8) than on non-traited squares (10.3) but were no differences in ingestion events. However, the duration of ingestion events were significantly shorter at 509s on ThryvOn compared to 914s on non-traited squares. The results of this study provide evidence that ThryvOn affects the feeding behavior of cotton fleahoppers
The BAZ Family of Chromatin Remodelers in Colorectal Cancer: Insights into Oncogenesis, Alternative Splicing and Chemosensitization
No full textColorectal cancer (CRC) poses a significant healthcare challenge worldwide, necessitating a deeper understanding of the molecular mechanisms underlying its pathogenesis for improved therapeutic interventions. This thesis investigates the BAZ (Bromodomain Adjacent to Zinc finger) family of chromatin remodelers and their intricate involvement in CRC. The BAZ family members, including BAZ1A, BAZ1B, BAZ2A, and BAZ2B, exert critical regulatory functions in chromatin architecture and transcription, impacting various cellular processes from development to disease.
In colorectal cancer, BAZ1A is overexpressed, and its depletion resulted in diminished cell viability, increased apoptosis, augmented DNA damage, and cellular senescence, concomitant with the downregulation of components within the Wnt/��-catenin signaling pathway. In vivo studies corroborated these findings, revealing that knockdown of BAZ1A leads to diminished tumor growth and alterations in chromatin regulation. Interestingly, BAZ1A undergoes alternative splicing, which is promoted by treatment with histone deacetylase inhibitors, thereby highlighting its therapeutic potential. Remarkably, the full-length form of BAZ1A is implicated in DNA repair mechanisms, while its alternatively spliced counterpart is susceptible to increased DNA damage and sensitivity to DNA-damaging agents. These observations underscored the oncogenic role of BAZ1A in colorectal cancer and the importance of considering an oncogene���s alternative splicing patterns.
Similar to BAZ1A, BAZ2A is also upregulated in CRC and associated with reduced patient survival. Functional studies demonstrated their roles in inhibiting cell viability, colony formation, and modulating Wnt/��-catenin signaling. Inhibition of BAZ2A led to reduced tumor growth rates in mouse models, where it also affected histone modification patterns, favoring a less repressive chromatin state, and influencing major histocompatibility complex (MHC) regulation.
In contrast to BAZ1A and BAZ2A, BAZ1B knockdown enhanced cell viability, colony formation, and altered cell cycle progression, suggesting a tumor-suppressive role in metastatic CRC. BAZ1B impacted c-MYC expression independently of the Wnt/��-catenin pathway, and influenced p53 and p21 levels, implicating its involvement in tumor suppressive pathways.
Overall, the study underscores the potential of BAZ family members as therapeutic targets in CRC. Future research should focus on elucidating their molecular mechanisms, translating findings into clinical applications, and exploring combination therapies to improve treatment outcomes for CRC patients, thus advancing more personalized therapeutic approaches for CRC
Essays in Monetary Policy and Household Expectations
No full textThis dissertation focuses on the formation and implications of household beliefs and expectations with respect to monetary policy.
In the first chapter, I investigate whether consumer sentiment (analogously referred to as confidence) matters for monetary policy. Specifically, I consider whether consumer sentiment responds to monetary policy shocks, as well as whether the responses of output, inflation, and unemployment depend on the state of consumer sentiment. Although various methods of measuring confidence/sentiment exist, the underlying goal of each is to gauge how the normative economic attitudes of households change over time. As such, asking whether consumer sentiment responds to monetary policy shocks can alternatively be viewed as whether monetary policy shocks change households��� perceptions of the current/future state of the economy. Additionally, while some of the variation in sentiment reflects movement in aggregate fundamentals, a number of papers have established that the unaccounted for portion has predictive power for a variety of macroeconomic variables. This observation motivates considering whether the state of consumer sentiment suggests different macroeconomic impacts of monetary policy shocks.
Using an external identification scheme in a local projections (LP) approach, I find that contractionary monetary policy shocks have only minor negative effects on consumer sentiment. Consumer sentiment is measured by the headline index published by the Michigan Survey of Consumers. Further, I find that this minor response persists across various states of inflation, business cycles, and interest rates. In contrast, I do find evidence that the state of consumer sentiment matters for how output, inflation, and unemployment respond to these shocks. Specifically, positive interest rate shocks during periods of depressed consumer sentiment have quicker and more contractionary effects on output and unemployment, while inflation is not responsive over short nor long term horizons.
In the second chapter, I utilize a novel feature of the Michigan Survey of Consumers (MSC) to identify whether respondent expectations change within tight windows around macroeconomic data releases. This feature of the data is the interview dates of respondents between June 1979 ��� May 2019. Over this period, I include releases of the Employment Situation Summary (ESS), Consumer Price Index (CPI), Industrial Production (IP), and Gross Domestic Product (GDP), as well as Federal Open Market Committee (FOMC) meetings and calls. Incorporating the interview dates of each respondent alleviates a major identification problem that has prevented previous empirical work from using the MSC data to address such a question. Without them, one would only know which survey the person was interviewed for, but not when it was conducted. Thus, it was not possible to discriminate between the different information sets of the respondents, thereby preventing identification of the change in inflation expectations in response to a particular release.
My work in this paper furthers our understanding of household inflation expectations along a number of dimensions. First, I find that expectations significantly respond to information about the unemployment rate and CPI inflation, indicating that these are more salient to households than the other releases. I measure the information being conveyed by the releases by using the size and sign of changes in the release relative to the previous periods value. Second, I consider whether the relevance of these releases differs during recessions, the first paper to empirically address such a question. I find that information about the unemployment rate is particularly salient preceding, during, and following recessions. The final contribution I make in this paper is the finding that, over a shorter subsample, unanticipated changes in output growth prompt households to adjust their inflation expectations. Here, unanticipated refers to the difference between the realized value and Bloomberg consensus forecast value for each release, wherein inflation expectations respond to such deviations in IP and real GDP growth
Culturally Responsive Coaching for African American Parents of Children with Autism: A Single-Case Analysis, Qualitative Systematic, and Practitioner Paper
No full textAfrican American children and their families face a heightened susceptibility to disparities associated with autism (Dababnah et al., 2018). While advancements have been made in mitigating racial inequities in the identification of autism, Constantino et al. (2020) still report the existence of diagnostic delays for autism in Black children. This study suggests a gap of approximately three years between the period when parents initially express concerns about their child's developmental milestones and the eventual diagnosis of autism. The purpose of these three studies were (1) to identify how culturally responsive parent coaching for African American families of children with autism can increase parent implementation of naturalistic intervention strategies by conducting a multiple-probe single case experimental design across participants; (2) to conduct a qualitative systematic review on the experience and quality of studies on African American families of children with autism; 3) To provide a practitioner guideline of culturally responsive parent coaching, for educators and service providers working with African American families of children with autism.
The findings of the study indicated that culturally responsive parent coaching is effective in improving communication for African American parents and their children with autism. The findings from the second study reports the different experiences of African American families ranging from lack of source of support, cultural differences, cost of health care services, and parents lack of prior knowledge of autism. The third study provides a guideline for practitioners who serve culturally diverse families like African American parents.
The findings of these three studies presents several implications for practice and research. Service providers and healthcare professionals need to be trained to become more culturally responsive to better serve African American families. There is also a need for more research on the implementation of culturally responsive practice with African American families of children with autism
D-modules and the Cauchy-Kovlevskaya Theorem
No full textThis is an expository article served as an elementary introduction to the theory of algebraic D-modules. For the first part, we give the definition and basic properties of D-modules. We take advantage of the sheaf theory and compare the results of complex manifolds with those on affine spaces. We particularly focus on introducing the characteristic varieties of D-modules. For the second part, we introduce the classical Cauchy-Kovalevskaya theorem. Using the languages of category theory and homological algebra, we give a generalized version on affine spaces, which is a simplified version of the Cauchy-Kovalevskaya-Kashiwara theorem
John Bickham field notebook: AK20501-AK21000.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK21001-AK21500 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
Characterization of Soil Physical and Hydraulic Properties of TexMesonet Monitoring Sites
No full textOperated by the Texas Water Development Board, the TexMesonet comprises 100 monitoring stations across Texas. These stations record 11 environmental variables, which include soil moisture measurements at depths of 5, 10, 20, and 50 cm. While soil moisture data from other networks have been utilized to enhance crop yield estimation, develop drought indices, estimate potential groundwater recharge, and validate remote sensing soil moisture data, TexMesonet soil moisture data remain underutilized for such applications. This underutilization is due to the absence of comprehensive, site- and depth-specific data on soil physical and hydraulic properties. The objectives of this project are twofold: firstly, to characterize the soil physical and hydraulic properties at TexMesonet sites, and secondly, to estimate site- and depth-specific soil hydraulic parameters using the Rosetta3 pedotransfer function. This was achieved through extensive field sampling and laboratory measurements at 30 stations, including determining sand, silt, and clay percentages, bulk density, and volumetric water content at field capacity (-33 kPa) and permanent wilting point (-1500 kPa). These measurements were then applied in the Rosetta3 pedotransfer function to derive site-and depth-specific soil hydraulic parameters. The resulting database includes ten soil physical and hydraulic properties for each site and depth, leading to 218 data points across the 30 study sites. Within the TexMesonet, ten of the twelve USDA soil textural classes were identified, with silt and sand not represented. The mean absolute error (MAE) between the measured and predicted water retention curves ranged from 0.025 cm�� cm- �� to 0.13 cm�� cm- ��. Additionally, the MAE for volumetric water content estimates from TexMesonet sensors versus direct sampling was 0.081 cm�� cm- ��. With further sampling and expansion to all TexMesonet sites, this database has strong potential to provide critical information for improving water resource management applications in Texas, including irrigation scheduling and predicting floods and droughts
Colonial Calamities: The Politics of U.S. Disaster Relief and Economic Development in Puerto Rico, 1898-1979
No full textWhen Hurricanes Maria and Fiona battered Puerto Rico in 2017 and 2022, it reopened public conversations about Puerto Rico���s colonial status. With thousands out of electricity, displaced from their homes, and ruined economically, then- and only then- did U.S. policymakers debate the appropriate humanitarian response. In addition, the disaster relief aid overseen by the Federal Emergency Management Agency (FEMA) provided only temporary solutions but did nothing to address the ongoing structural issues of Puerto Rico. This type of response was not a new phenomenon. It was just the latest chapter in a century-long history of United States disaster relief operations that continually reinforced Puerto Rico���s colonial status.
This dissertation Colonial Calamities: The Politics of U.S. Disaster Relief in Puerto Rico, 1898-1979, is the first to explore the history of American disaster relief in Puerto Rico from the period 1898-1979. Disasters provide a window to reveal how structures of power determined who ���deserved��� aid and what conditions were attached to it. I argue that after disasters, the relief policies undertaken by U.S. government institutions were justifications to strengthen influence in the region and actually made Puerto Ricans more vulnerable to disasters. The American military, Red Cross, and colonial administrators prioritized short-term mitigation strategies that served U.S. strategic and economic interests. In this way the American colonial government constructed and maintained Puerto Rican vulnerability to disasters and the vagueness of status as subjects/citizens. American policymakers perpetuated the idea that if Puerto Ricans were poor and vulnerable to disasters, it could not have anything to do with the United States or colonialism. However, policymakers also thought that if Puerto Rican poverty and vulnerability to disasters was caused by Puerto Ricans themselves, then the U.S. and only the U.S. could help them. Together, these ideas inscribed Puerto Ricans as inferior, borderline citizens, while at the same time rejecting them as completely alien. To combat these positions and policies, Puerto Ricans developed local networks to promote solidarity and conduct disaster relief without relying on American agencies. This strategy proved important during the latter part of the twentieth century with the increasing effects of climate change causing more frequent disasters