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John Bickham field notebook: AK6001-AK6500.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK6501-AK7000 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
Sheep as a Potential Tool for In-Season Cotton Weed Management
No full textIncreased reliance on herbicides in crop production has led to many weed species becoming
resistant to multiple herbicide modes of action. Sheep herbivory may be a viable alternative
weed control method, as sheep have the potential to preferentially graze weeds and be averse to
eating the cotton plant due to the presence and concentration of gossypol. Common weeds such
as Palmer amaranth and field bindweed are major competitors with cotton plants in western
Texas but are also palatable to sheep. Field research on the integration of sheep into cotton
systems was performed at the Texas AgriLife extension and research center in San Angelo,
Texas during the 2022 and 2023 seasons. Treatments included three different cotton growth
stages to initiate grazing (4-leaf, 8-leaf, and mid-bloom) and three different levels of grazing
intensity based on weed removal (approximately 70%, 90%, and 100%) with presumably greater
cotton damage with increasing intensity. Treatment effects were quantified through monitoring
sheep grazing activity, assessments of weed biomass removal, cotton damage, and cotton yield.
During the 4-leaf, 8-leaf, and mid-bloom initiation for both years, sheep spent 87%, 86%, and
93% of feeding time, respectively, grazing on weeds rather than cotton. Final cotton biomass was
not influenced by year, intensity, or timing of treatments. Final weed biomass was affected by
year (P > 0.069) and timing (P > 0.036). The year 2022 had less final weed biomass than 2023
and grazing initiated at the 4-leaf stage resulted in greater weed biomass at the end of the
growing season when compared to grazing initiated at the 8-leaf stage. This trial emphasizes the
challenge of extrapolating small-scale findings to field conditions, where sheep grazing may
occur at different times. While small-plot research is valuable, its limitations highlight the need
for field-scale observations. Integrating sheep grazing into production systems shows promise for
farmers seeking reduced herbicide/organic management, but further refinement and consideration of economic impacts are necessary. Future research may assess grazing preferences relative to sheep age and breed to provide greater insight into integrated crop-livestock management practices
Essays in Law and Economics
No full textMy dissertation focuses on issues related to the criminal justice system in the United States, especially with respect to indigent defense and policing.
First, I ask whether indigent defense attorneys secure better deals for same-race defendants. This is important since 80 percent of criminal defendants rely on assigned counsel for legal defense. To do this, I employ a difference-in-differences approach, exploiting the quasi-random assignment of court-appointed attorneys to cases in Travis County, Texas. Results indicate that while Black and White attorneys are similarly effective at securing dismissals for White defendants, Black attorneys are less effective than White attorneys at securing dismissals for Black defendants. Specifically, Black defendants who are represented by White rather than Black attorneys are 20-22 percent more likely to have their charges dismissed and 17-27 percent less likely to be incarcerated. Moreover, Black defendants who are represented by White attorneys are not more likely to re-offend in the future.
Second, I study the effect of police-involved shootings on gun violence and civilian cooperation with police. To distinguish between crime reporting and crime incidence, I use administrative data on 911 calls and ShotSpotter data from Minneapolis. Exploiting the variation in the timing and the distance to these incidents, I show that exposure to a police shooting increases gun-related crimes by 3-6 percent and reduces civilian crime reports to police by 4-6 percent.
Finally, I study the impact of internal affair investigations, the most common accountability system in policing, on police behavior. Using data from a large city where there is conditionally random assignment of officers to 911 calls, I employ regression discontinuity and difference-indifferences methods to distinguish the impact of investigations from confounding factors. Results indicate that increased oversight from internal investigations does not change an officer���s likelihood of making an arrest or using force. This is true across different types of allegations, including those that are sustained
Electro-Chemo-Mechanics of Several Pure Metal Anodes for Rechargeable Batteries
No full textBy enabling constant access to electronic devices and seamless communication capabilities, energy storage devices have greatly improved our lives. With advances in technology over time, the demand for larger capacity and longer lifetime energy storage devices continues to increase. Still, technological hurdles, such as safety issues, kinetic limitations, and material degradation over time, remain that must be addressed to enable the next generation of high-capacity batteries. While battery research primarily has focused on improvements in electrochemistry, higher capacity technologies have necessitated a shift to the focus towards more multidisciplinary approaches in research.
This dissertation explores battery materials from a mechanical and coupled electro-chemo-mechanical perspective by evaluating various materials��� intrinsic mechanical properties and analyzing their mechanical behaviors during electrochemical cycling. Fracture behavior of sodium was investigated, highlighting its extreme ductility and flaw-insensitivity at room temperature. Furthermore, calcium was mechanically assessed at various length scales, which unveiled calcium���s relatively limited ���indentation size effects��� as compared to counterparts of Li and Na metal, likely due to its relatively high melting point and relatively low dislocation spacing. Additionally, various lithiated compositions and phases of Li���Mg alloy anode were mechanically evaluated via nanoindentation. XRD patterns on post-mortem lithiated Mg samples revealed that Li���Mg alloy anodes undergo a single-phase transformation electrochemically, from the Mg-rich �� phase (HCP) to Li-rich �� phase (BCC). Furthermore, the nanoindentation hardness and elastic modulus of Li���Mg was found to significantly decrease with increasing lithium concentration. This dissertation also investigates the mechanical behavior of pure lithium metal anodes under various electrochemical conditions. These tests uncovered a marked current-dependent mechanical stress response of lithium. Keeping in mind that the processes of electrodeposition of lithium and the growth of Li dendrites, while distinct, share similar underlying mechanisms, these measurements provide important insight into understanding the growth of Li dendrites.
Overall, this dissertation investigates the mechanics of various battery anode materials that exhibit an intimate interplay between mechanics and electrochemistry; their overall performance in practice is thus highly dependent on their mechanical behavior. As such, this dissertation provides general insight into understanding energy storage systems in terms of the intricate interactions between mechanics and electrochemistry
Combustion Solutions for Reduced Methane Emissions from Large Bore Natural Gas Engines
No full textLegacy large bore, natural gas two-stroke engines form a vital component of the pipeline industry, but with increasing stringent pushes to reduce emissions, the necessity of improving performance of an ageing engine fleet grows more critical than ever. Precombustion chambers are frequently implemented on these engines to improve ignition stability and extend the lean limit of operation, a process which brings an additional benefit of reducing harmful emissions such as oxides of nitrogen (NOx) and hydrocarbons (HC). While prechambers reduce the carbon footprint from pipeline compressor stations, the pathway to zero emissions of the future still contains a plethora of research avenues to explore.
This study sought to explore two potential combustion solutions for reducing methane emissions from large bore natural gas engines. First, the Cooper-Bessemer GMV4 engine was fully simulated using Converge CFD and validated using experimental data. Before igniting the primary prechamber, radical and intermediate species were seeded throughout the main combustion chamber by use of a second, deliberately quenched prechamber. This served to boost reactivity and promote flame propagation throughout unburned regions of the chamber. Multiple temperature levels, injection timings, and chemical species compositions were investigated, for which each was then examined for early ignition limits, surviving concentration of seeded species, and overall impact on residual methane and the combustion process.
Second, the Cooper Ajax E-565 engine in open-chambered configuration was fully simulated using Converge CFD software and validated using experimental data. The open-chambered configuration was then modified to a prechambered configuration, and input parameters, such as fuel delivery and spark timing, were adjusted using best real-world design practices. This model was then used as a foundation upon which to evaluate the sensitivity of in-cylinder mixing between prechamber and main chamber gases to changes in intake manifold and port design. Eight different manifolds designs were created and analyzed for overall air flow, mixing quality, and general combustion performance. The results were then examined for an extensive investigation of factors preventing oxidation of residual methane as well as the production mechanisms of NOx emissions
Teleoperation for Time-sensitive and Challenging Construction Environments: Dive into Cognitive Challenges
No full textDespite the dream of fully autonomous construction robots, the inherently unpredictable and dynamic scenarios of construction tasks make complete automation challenging. In many scenarios, situations that are outside the planned tasks or the pre-programmed robots��� capabilities underscore the necessity for human adaptability and decision-making. Teleoperation, therefore, has emerged as an effective approach in the construction domain and has been extensively studied. In the past two decades, prior studies primarily focused on technological advancements such as sensing for distant workplaces, computation algorithms, and automated control systems. However, this focus often neglected one crucial element of the teleoperation system: the human operator. As humans are decisionmakers and vital in addressing construction challenges effectively, a more in-depth understanding of human operators is necessary. Particularly, we must dive into the limited human cognition capacity and the challenges it poses during construction teleoperation, as cognitive workload directly influences their decision-making quality and control performance. This study thus employs a human-centric approach to navigate and manage the cognitive challenges faced by operators during the teleoperation of construction robots, especially those focused on the excavators. There are three research objectives: (1) the first objective aims to explore human factors that significantly affect teleoperation performance in construction from a systematic perspective, this objective involves identifying and prioritizing factors focused on cognitive aspects to understand their impact on operational efficiency and safety; (2) the second objective examines how various demanding and challenging construction scenarios impact teleoperators' cognitive and task performance along with safety behavior, this objective seeks to deepen understanding of the impact of the cognitive challenges identified in the first objective; and (3) the third objective is to assess the effectiveness of a novel assistive technology that has been specifically designed to reduce cognitive load and promote safer and more efficient performance, even under highly demanding conditions towards a cognitive-resilient teleoperation system. The findings reveal that excavator performance is negatively affected not only by tangible obstacles but also by intangible obstacles that impact the operator's cognitive state, such as time pressure and risk perception in remote environments. During our investigation, we found that teleoperators conducting demanding tasks performed the best under reasonable time pressure, even better than without pressure, whereas under excessive time pressure, they experienced cognitive overload and impaired risk perception, resulting in significant control errors as a result. However, teleoperators using electro-tactile feedback, a novel assistive technology, achieve high levels of safety and productivity regardless of the level of time pressure. This assistive technology is shown to help prevent cognitive overload by distributing cognitive tasks to the robotic system, enhancing awareness of remote hazards. This dissertation significantly contributes to the body of knowledge of construction teleoperation by bridging the gap in understanding human aspects within teleoperation systems. The research also offers valuable insights for designing user-centered systems for human-robot interaction or collaboration in construction teleoperation, applicable across various scenarios ranging from normal to highly demanding and challenging workplaces
The Role of Metformin in the Prevention and Treatment of Breast Cancer: Insights From Preclinical Studies
No full textMetformin, a commonly used medication for type II diabetes, has been reported to decrease breast cancer risk. However, results from observational and clinical trials show mixed results, questioning the efficacy of metformin for breast cancer treatment. In addition, determining what patient populations may experience optimal responses to the drug is warranted. Our goal was to improve our understanding of the circumstances under which metformin may exhibit maximal efficacy for breast cancer prevention and treatment. First, we assessed the effectiveness of metformin on tumor outcomes in ovary-intact and ovariectomized rodents. Our findings support metformin treatment being more effective in the postmenopausal setting, having observed prevention of new tumors and reduced tumor burden. The second objective was to elucidate how metformin affects mammary adipose tissue. We have previously shown that metformin reduces M2-like aromatase-expressing macrophages in the tumor border. Here, we investigated if treatment lowered inflammatory markers in tumor-distant mammary tissue. We found a small reduction in inflammatory markers in metformin-treated mammary adipose. However, RNA seq analysis from adipose tissue from treated and control rats showed no changes in gene expression. Our final aim centered on determining the optimal timeframe for metformin treatment during the menopause transition for improved tumor outcomes. We found that metformin treatment in the first four weeks post-ovariectomy was needed to improve tumor outcomes. This work underscores the significance of menopausal status and timing within the menopause transition in influencing the efficacy of metformin for treating mammary tumors and emphasizing the need for a targeted approach to metformin treatment for breast cancers
Unraveling the Complexity of Cdec Expression During Clostridioides difficile Sporulation: Insights into the Role of Sigma Factors and Non-Coding RNA on Cdec Expression
No full textGram-positive, obligatory anaerobic Clostridioides difficile (C. difficile) is a spore-forming, obligate anaerobic bacterium that causes diarrhea and other healthcare-associated illnesses globally. This study aimed to identify the sigma factor boxes in the promoter region of cdeC that affect the early and late stages of C. difficile sporulation. Therefore, we first identified the sigma factors' positions in the promoter region. Then, we constructed transcriptional fusions containing a different deletion of these sigma factors and introduced them into the C. difficile R20291CM210 WT strain. However, no detectable fluorescence was observed due to lack of sporulation in the C. difficile R20291CM210. Both increasing the time of incubation and increasing thiamphenicol concentrations failed to induce sporulation for R20291CM210. After that, we introduced all transcriptional fusions into the C. difficile R20291CM196 WT strain. We found out that only P���ncRNA-cdeC-mScarlett transcriptional fusion that contains the promoter region with a deletion of the ncRNA shows a modest fluorescence signal compared to other fusions. These results suggest that ncRNA located in the promoter region of cdeC may have an activity for cdeC expression during sporulation
New Directions in Indirect Detections: Gamma-Ray Observations of Globular Clusters and Dwarf Galaxies
No full textOne of the most elusive unknowns in particle physics and astrophysics today is the fundamental nature of dark matter. It is theoretically well-motivated that dark matter is a weakly interacting massive particle (WIMP) ��� a particle lying within the GeV to TeV energy ranges that interacts very weakly with Standard Model particles. Such behavior makes dark matter extremely difficult to detect with terrestrial detectors. However, there are still many ways to probe the fundamental nature of dark matter. One such way is by searching for astrophysical signatures of dark matter annihilation. Supposing that dark matter is a WIMP which self-annihilates, we can look for inexplicable excesses of Standard Model particles from astrophysical sources. In particular, we can look for high-energy gamma-rays with energies in the range of GeV to TeV. In this thesis, I will discuss recent results on both the dark matter distributions and gamma-ray emissions of a selection of Milky Way satellites and globular clusters with an emphasis on the Sagittarius dwarf galaxy system and the Omega Centauri globular cluster. In Chapter Two, I discuss an updated dynamical analysis of the Omega Centauri globular cluster. In Chapter Three, I discuss an in-depth analysis of the gamma-ray source associated with M54, the globular cluster at the center of the Sagittarius dwarf galaxy. In Chapter Four, I discuss a follow-up paper in which we use cosmological simulations to further test the physical origins of the M54/Sagittarius source. I conclude in Chapter Five by describing several unique ways in which it may be possible to differentiate between the signal of annihilating DM and that of astrophysical background sources
Essays on Microeconometrics
No full textThis dissertation consists of three essays on Microeconometrics and Applied Econometrics.
Chapter 2 provides nonparametric identification results in first-price auctions with unknown collusion schemes. This chapter shows that regardless of the unknown collusion scheme, collusive bidders in a partial cartel can be identified from winning bids, identities of winners, and auction-specific covariates satisfying an exclusion restriction. It can be shown that the value distributions of collusive bidders are identified under two types of cartels characterized by McAfee and McMillan (1992). This chapter proposes a test procedure to recover the identities of collusive bidders. The test method is applied to California highway procurement auctions.
Chapter 3, a joint work with Yonghong An, Matthew Gentry, and Daiqiang Zhang, examines the economic impacts of anti-bid-shopping legislation. We exploit the policy changes in Washington state to evaluate the impacts of anti-bid-shopping legislation on both ex-ante and ex-post procurement auction outcomes. With the engineer���s estimate of the cost and work types of projects, we can classify the contracts affected or not affected by anti-bid-shopping legislation. We estimate the effects of the policy using Regression Discontinuity Design (RDD) or Difference-in-Difference (DID). Findings indicate that the requirement for subcontractor listing can increase the winning bid while reducing the final total payment to the primary contractor. Moreover, disallowing substitutions may expedite project completion time and reduce the final total payment.
Chapter 4 proposes nonparametric estimation and uniform inference on counterfactual distributions in the presence of proxy variables. A two-step series estimator is developed to consistently estimate counterfactual distributions and their functionals under a general framework with latent variables. The uniform asymptotic theory is built on strong approximations of Gaussian processes introduced in Chernozhukov et al. (2013). The two-sample series counterfactual distribution estimator is applied to both simulations and an empirical study of the wage gap, in which the Armed Forces Qualifying Test (AFQT) score is used as a proxy variable for premarket human capital. The difference in the distribution of premarket human capital explains the racial wage ga