145 research outputs found

    From a Distance: Teaching, Learning, and Parenting During the COVID-19 Pandemic

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    Genotypic and phenotypic characterization of response to aflatoxin and secondary traits in maize

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    One major problem facing maize producers in the southern US is contamination with the mycotoxin aflatoxin, produced by Aspergillus flavus (Link:fr). Aflatoxin is a serious threat to human and animal health, with no resistant commercial hybrid available. Development of resistance to aflatoxin production has several major limitations. Aflatoxin is highly variable both across and within environments, even under inoculation, requiring several locations and replications for breeding. Additionally, there is no screening method that is reliable, rapid, inexpensive, and allows for high throughput. Several secondary traits, such as kernel texture, kernel integrity, husk cover, and visible ear rot, have previously shown to be related to aflatoxin accumulation. These traits are easily characterized in the field and are candidates for indirect selection if they are correlated to aflatoxin concentration. Root lodging, a plantÂ’s inability to maintain upright stature, is another complex characteristic of root related traits that traditionally is selected for indirectly. It can greatly reduce harvestable yield. It is affected by morphological traits and environmental conditions, but its genetic components are little understood. This dissertation comprises three studies presented in chapters II, III, and IV. Chapter II involved white and yellow hybrid maize trials as well as quality protein maize trials from several years across Texas environments. Data was analyzed both per and across location to determine repeatability of response to aflatoxin. Additionally, aflatoxin levels were correlated to several secondary characteristics (female flowering, endosperm texture, husk cover, and ear rot ratings) to determine usefulness in indirect selection. Chapter III was a phenotypic evaluation of a recombinant inbred line (RIL) mapping population, which was derived from divergent parental inbreds Tx811 and CML176. The trials were conducted in two Texas locations, and phenotypic data for aflatoxin concentration, kernel integrity, endosperm texture, female flowering date, and root lodging was collected. Variance components for these traits and genetic and phenotypic correlations were determined. Chapter IV was a genotypic evaluation of the Tx811/CML176 mapping population using simple sequence repeat markers. Genotypic and phenotypic data were combined to identify quantitative trait loci (QTL) and epistatic interactions for response to aflatoxin and for root lodging

    Blood Chemistry of Free-Ranging and Captive White-tailed Deer (Odocoileus virginianus) in Texas

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    Blood samples were collected from 602 white-tailed deer (WTD) (Odocoileus virginianus) between October 2008 – October 2009, from 15 different counties throughout Texas. White-tailed deer were evaluated for serum biochemical parameters (total protein, albumin, calcium serum, phosphorus, glucose, blood urea nitrogen, creatinine, total bilirubin, creatine kinase, aspartate aminotransferase, glutamic-oxaloacetic transaminase, globulins, albumins to globulins ratio, gamma-glutamyl transferase, and magnesium) and the following variables were recorded: age, gender, county of collection, season, capture method, and status based on captive or free-ranging. The 14 biochemical parameters were compared for WTD among age groups fawns (<12 months), yearlings (≥12 months - <24 months) and adults (≥24 months), gender, season (Spring, Summer, Fall and Winter), status (captive or free-ranging) and capture method (physical restraint, anesthetized using physical restraint method of drug administration, anesthetized using dart gun method of drug administration, drop-netted, net-gunned, or hunter harvested). The data collected for these parameters was used to establish normal ranges for a comprehensive metabolic panel (serum chemistry panel) for WTD in Texas. These reference ranges will be used for both captive and free-ranging WTD to improve diagnostic screening and disease monitoring. Captive vs. free-ranging status was statistically significant in WTD for 7 of the 14 physiological parameters. Significant differences and trends were observed among the three age groups. Calcium and phosphorus had an inverse relationship with age, while glucose had a direct relationship with age. Gender was statistically significant for 7 of 14 parameters. Anesthetized WTD vs. non-anesthetized had the greatest impact on mean blood chemistry values. Values for total serum protein, albumin, calcium, phosphorus, and globulins were higher for non-anesthetized WTD. Glucose, BUN, and AST mean values for higher for anesthetized WTD

    Synthesis, Structure, and Activity of Enhanced Initiators for Olefin Metathesis

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    A series of ruthenium olefin metathesis catalysts of the general structure (H_2IMes)(PR_3)(Cl)_2Ru CHPh (H_2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) have been prepared; these complexes are readily accessible in two steps from commercially available (H_2IMes)(PCy_3)(Cl)_2Ru CHPh. Their phosphine dissociation rate constants (k_1), relative rates of phosphine reassociation, and relative reaction rates in ring-opening metathesis polymerization (ROMP) and ring-closing metathesis (RCM) have been investigated. The rates of phosphine dissociation (initiation) from these complexes increase with decreasing phosphine donor strength. Complexes containing a triarylphosphine exhibit dramatically improved initiation relative to (H_2IMes)(PCy_3)(Cl)_2Ru CHPh. Conversely, phosphine reassociation shows no direct correlation with phosphine electronics. In general, increased phosphine dissociation leads to faster olefin metathesis reaction rates, which is of direct significance to both organic and polymer metathesis processes

    Lipid biomarker and stable isotopic profiles through Early-Middle Ordovician carbonates from Spitsbergen, Norway

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    One of the most dramatic episodes of sustained diversification of marine ecosystems in Earth history took place during the Early to Middle Ordovician Period. Changes in climate, oceanographic conditions, and trophic structure are hypothesised to have been major drivers of these biotic events, but relatively little is known about the composition and stability of marine microbial communities controlling biogeochemical cycles at the base of the food chain. This study examines well-preserved, carbonate-rich strata spanning the Tremadocian through Upper Dapingian stages from the Oslobreen Group in Spitsbergen, Norway. Abundant bacterial lipid markers (elevated hopane/sterane ratios, average = 4.8; maximum of 13.1), detection of Chlorobi markers in organic-rich strata, and bulk nitrogen isotopes (delta N-15(total)) averaging 0 to -1 parts per thousand for the open marine facies, suggest episodes of water column redox-stratification and that primary production was likely limited by fixed nitrogen availability in the photic zone. Near absence of the C-30 sterane marine algal biomarker, 24-n-propylcholestane (24-npc), in most samples supports and extends the previously observed hiatus of 24-npc in Early Paleozoic (Late Cambrian to Early Silurian) marine environments. Very high abundances of 3 beta-methylhopanes (average = 9.9%; maximum of 16.8%), extends this biomarker characteristic to Early Ordovician strata for the first time and may reflect enhanced and sustained marine methane cycling during this interval of fluctuating climatic and low sulfate marine conditions. Olenid trilobite fossils are prominent in strata deposited during an interval of marine transgression with biomarker evidence for episodic euxinia/anoxia extending into the photic zone of the water column. (C) 2019 Elsevier Ltd. All rights reserved.Peer reviewe

    A Versatile Precursor for the Synthesis of New Ruthenium Olefin Metathesis Catalysts

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    The ruthenium complex (IMesH_2)(Cl)_2(C_5H_5N)_2Ru═CHPh [IMesH_2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene] (3) was prepared by the reaction of (IMesH_2)(PCy_3)(Cl)_2Ru═CHPh (2) with an excess of pyridine. Complex 3 contains substitutionally labile pyridine and chloride ligands and serves as a versatile starting material for the synthesis of new ruthenium benzylidenes

    Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts

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    This report details the effects of ligand variation on the mechanism and activity of ruthenium-based olefin metathesis catalysts. A series of ruthenium complexes of the general formula L(PR_3)(X)_2Ru ═ CHR^1 have been prepared, and the influence of the substituents L, X, R, and R^1 on the rates of phosphine dissociation and initiation as well as overall activity for olefin metathesis reactions was examined. In all cases, initiation proceeds by dissociative substitution of a phosphine ligand (PR_3) with an olefinic substrate. All of the ligands L, X, R, and R^1 have a significant impact on initiation rates and on catalyst activity. The origins of the observed substituent effects as well as the implications of these studies for the design and implementation of new olefin metathesis catalysts and substrates are discussed in detail
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