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Experimental and Numerical Investigation of Rock Drilling Accelerated Through Cracking
No full textThis research aims to provide experimental and numerical methodologies to study the effect of pre-induced cracks on rock drilling processes. Plasma induced micro-cracks, a novel technology to improve the drilling of hard rock formations in geothermal wells, was investigated and its effectiveness was quantified. Lab-scale rock cutting tests using single PDC techniques were carried out to study the differences between uncracked and cracked (plasma treated rocks). The cutting and thrust forces were analyzed using a novel cutting configuration. The effect of parameters such as the feed rate were also considered. The results showed a general trend of reduction in the forces, but the magnitude of reduction was found to depend on the feed rate. A maximum force reduction of around 50% is found with statistical significance. Further analysis showed that cases with a higher force reduction were also found to have rougher surface topography, which indicates more excessive fracturing and, thus, a crack-accelerated material removal process. Additionally, the guidelines, practical considerations, advantages, and limitations of the cutting technique were also discussed. The effect of pre-induced cracks in reducing the cutting forces is further studied under high-pressure downhole conditions using finite element analysis. A 3-D finite element model rock cutting model was created using a pressure sensitive yield criterion in conjunction with a damage criterion to model element erosion. The results showed that the pre-induced cracks reduce the cutting force under the tested pressure range (0-100 MPa). The overall effectiveness decreased as the confining pressure increased because the pressure compacted the rock, restricting fracturing ahead of the cutter surface. Additionally, the rock cutting mechanism was found to change from a continuous removal of material at atmospheric pressure to a more intermittent form at higher pressures
Effects of Developmental Restriction on Neural Progenitor Cell Graft-derived V2a Interneurons After Spinal Cord Injury
Get PDFSpinal cord injury (SCI) is a devastating condition that leads to lasting deficits in motor, sensory, and autonomic functions, and dramatically decreases quality of life. There are currently no effective treatments that can even partially restore function to those living with SCI. However, neural progenitor cell (NPC) transplantation is a promising potential treatment to restore function after SCI. Neural progenitor cells are cells in the developing central nervous system that retain a limited proliferative capacity and give rise to mature neurons and glial cells following transplantation into sites of SCI. Transplanted NPCs have been shown to form new synaptic connections with host neurons and differentiate into a diversity of spinal interneuron populations. Specific subtypes of graft-derived cells may play significant roles in restoring specific types of neurological function. To maximize the effectiveness of cell transplantation therapies, the diversity of neurons must be considered in order to support the formation of functionally relevant neuronal relays. One of the prominent players in motor function is the Chx10-expressing V2a interneuron. In the intact spinal cord, distinct subpopulations of V2a interneurons are involved diverse motor functions such as gait, left-right coordination, skilled reaching, and respiratory activity. We have previously found that V2a interneurons are present in NPC grafts, but little characterization of these cells has previously been performed. This project will investigate the abundance, morphology, distributions, and molecular phenotypes of V2a interneurons in NPC grafts of different developmental stages. We hypothesize that earlier-stage grafts will contain greater abundances of V2a interneurons than later-stage grafts, and that distributions of type I/type II V2a neurons will be significantly different in different graft types. To test this hypothesis, we transplanted NPCs obtained from E11.5, E12.5, or E13.5 Chx10-Cre;Ai14 embryos into sites of cervical SCI in adult wild-type mice. Four weeks post-transplantation, we performed immunohistochemical analysis on graft tissue to examine abundances, morphology, and distributions of tdTomato/Chx10+ neurons, and data analysis is still ongoing. Findings from this work will guide future efforts to improve the effectiveness of stem cell treatments after spinal cord injury
Assessment of Corrosion Prevention and Mitigation Techniques for Steel Bridges
No full textCorroded steel members cause a significant risk to the durability of steel bridges, leading to costly failures and endangering public safety. Hence, it is essential to implement effective corrosion prevention and mitigation strategies to ensure the long-term durability of steel girders and reduce risks associated with corrosion activities. The Texas Department of Transportation uses corrosion-resistant materials and painting of steel elements to mitigate corrosion on steel girder bridges. Weathering steel provides excellent corrosion resistance and forms an adhesive oxide layer over time known as patina that enhances its resistance to atmospheric corrosion, ultimately resulting in longer service life. This study provides a comprehensive literature analysis documenting the complexity of corrosion prevention and mitigation in steel bridges, including various protective systems and corrosion-resistant steel. The literature also includes information about more durable duplex paint systems with more than 50 years of durability before any need for touchup or maintenance repaint.
To assess the performance efficacy of weathering and painted steel bridges in Texas, 25 weathering bridges and 20 painted bridges across the state were inspected visually, along with field and laboratory tests. The field testing included ultrasonic thickness measurement, pH test, chloride test, paint thickness measurement, tape adhesion test, and pull off adhesion test at several exterior and interior girders locations such as web, top and bottom flange. Rust and paint samples were scraped from the exterior and interior web of the girders. The laboratory test included scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), optical microscopy, x-ray photoelectron spectroscopy (XPS), and powdered x-ray diffraction (XRD). The particle size analysis of tape adhesion test samples collected from 25 bridges led to the development of a quantifiable patina rating index based on the particle size and area of particle that can determine the performance of the weathering steel patina on a 0 to 10 scale. The powdered XRD analysis was able to classify the rust into protective, inactive, and active categories, whereas the active category means there is no adhering patina that can protect the weathering steel surface from undergoing further corrosion. Moreover, the results of the XRD analysis corroborated the findings of the developed patina rating index. In addition, optical microscopy and SEM/EDS analysis could distinguish between epoxy-based, zinc-based, and lead-based paint systems. Findings from this study showed weathering steel girders exhibited long-term durability in low- to medium-corrosive environments. However, an increased volume of akaganeite and splines within the patina decreases the functionality of the rust layer as the corrosivity rises. In such environments, an alternative protection system for steel structures is a zinc-based paint system consisting of three layers of zinc and epoxy coatings, known as Paint System III. It was concluded that Paint System III is a durable corrosion prevention and mitigation method for protecting steel structures in high-corrosive regions, such as regions with high airborne chloride and regions where deicing salt is frequently used
Menaquinone Biosynthesis: Mechanistic Studies on 5,8-Dihydroxy-2-Naphthoate Synthase and Dehypoxanthine Futalosine Cyclase
Get PDFThis work details mechanistic studies of two enzymes in the futalosine dependent biosynthetic pathway of menaquinone (vitamin K), 5,8-Dihydroxy-2- naphthoate synthase (MqnD) and dehypoxanthine futalosine cyclase (MqnC). MqnD catalyzes the conversion of cyclic dehypoxanthine futalosine to 5,8-dihydroxy-2- naphthoic acid and an uncharacterized product. The main limitation in the study of this enzyme was the lack of substrate availability due to either difficult chemical synthesis or poor activity of an upstream enzyme in this pathway.
This study describes a chemoenzymatic synthesis of cyclic dehypoxanthine futalosine. This synthesis achieved a 2-fold yield enhancement by using titanium(III) citrate as the reducing agent and another 5-fold yield enhancement using a fluorinated analog of dehypoxanthine futalosine which was converted to cyclic dehypoxanthine futalosine by an ipso substitution mechanism. This synthetic route enabled the synthesis of cyclic dehypoxanthine futalosine in sufficient quantity to identify the second reaction product and to determine that the MqnD-catalyzed reaction proceeds by a hemiacetal ring opening-tautomerization-retroaldol sequence.
The radical S-Adenosylmethionine (SAM) enzyme, MqnC, found in the alternative menaquinone biosynthetic pathway catalyzes the conversion of dehypoxanthine futalosine to cyclic dehypoxanthine futalosine. This work reports the second successful use of an SRN1 fragmentation to trap an aryl radical anion intermediate, the use of a reducing agent gradient to pinpoint the branch point of the SRN1 fragmentation, and further work in understanding an unexpected 5-fold product enhancement when using a fluorinated substrate analog
Reconstructing the History of a Patagonian Peatland
Get PDFPlant macrofossils in peatlands decay very slowly over time due to the high water saturation, low temperatures, and anoxia. Therefore, the peat layers that have accumulated in these ecosystems over millennia are an excellent archive to study past climates and how they have affected the composition of these landscapes. The biological and chemical content of these peat layers contains the history of the site, and they can be ���read��� from the bottom of the peatland all the way to its top layers. The Beef Penguin peatland in Patagonia has been radiocarbon dated to around 15,600 years ago. This presents an opportunity to reconstruct the history of past regional climatic trends. A research team collected a peat core from this Patagonian peatland that is 770 cm long. Plant macrofossil identification was done on samples of this core at 8-cm increments in order to determine when changes in vegetation occurred. Samples were also taken from places in the core where there appeared to be abrupt changes in vegetation in order to view the changes at a higher resolution. The results of this study show that this site switched from a minerotrophic fen to an ombrotrophic bog. Bioaccumulation began at this site when ligneous and herbaceous plants began to grow atop a light brown mineral material at 15,590 �� 225 cal. BP. The site switched to a brown moss-dominated landscape at approximately 14,500 cal. BP. This lasted until around 12,000 cal. BP, when the site dried enough for herbaceous plants to take over dominance. Brown mosses stopped occurring about 5,600 cal. BP. Around 4,600 cal. BP, the site went through a dry period where ligneous plants saw a brief period of dominance. From approximately 3,600 cal. BP to present, Sphagnum mosses have been the dominant vegetation at this site. These vegetation reconstructions can then be used to infer past temperature and precipitation regimes because we know which conditions are preferred by different plant communities based on modern-day observations across large landscapes. In the case of my study site, I believe that this region has been seeing a climatic trend of increasing drying over the last 12,000 years. This information will allow the prediction of how projected climate change could influence the vegetation communities of these important ecosystems, and their capacity to store carbon
The Brain and Beyond: Maternal and Fetal Targets of Chronic Alcohol Exposure in Pregnancy
Get PDFFetal alcohol spectrum disorders (FASD) persists as significant a public health threat partly due to enmeshment of drinking culture in modern society and partly because of the inherent complexity of alcohol-mediated pathogenesis. Discernment of FASD pathogenesis remains warranted because of the persistence of this threat coupled with extremely limited treatment options for affected patients. In the following studies (Chapters 2 & 3) we used classic approaches to describe a potential mechanism for alcohol-mediated pathogenesis in an atypical focal point of FASD investigation: the maternal uterine artery. The latter part of this work (Chapters 5 & 6) applied advanced technologies (HPLC, next-gen RNA sequencing) to identify new foci in a classic FASD target: the fetal brain. All studies were completed using a well characterized in vivo model of chronic binge prenatal alcohol exposure with clinical relevance. In the uterine artery, alcohol impaired the myogenic response and endothelial-mediated vasodilation, and dysregulation of the nitric oxide (NO) pathway and the enzyme responsible for NO synthesis (eNOS) were presented as susceptible candidates for this dysfunction. Brain studies described here bolster support for pursuing investigation of how excitatory amino acid imbalances influence neurotoxicity, expressly in the developing cerebellum and hippocampus. Transcriptome analysis also identified new hippocampal genes and canonical pathways of investigational interest based on their previous linkage to alcohol and FASD-adjacent pathology but were not tied to FASD contextually to FASD until now. Ultimately, we affirmed that alcohol use during pregnancy is unsafe and poses significant health risks not only to fetal development but to maternal physiology essential for sustaining this development
Plant Disease Diagnosis Form
Get PDFRequest form for plant disease going to Texas High Plains Plant Disease Diagnostic La