Pyramidal neurons (PyNs) in ‘higher’ brain are highly susceptible to acute stroke injury yet ‘lower’ brain regions better survive global ischemia, presumably because of better residual blood flow. Here we show that projection neurons in ‘lower’ brain regions of hypothalamus and brainstem intrinsically resist acute stroke-like injury independent of blood flow in the brain slice. In contrast `higher` projection neurons in neocortex, hippocampus, striatum and thalamus are highly susceptible. In live brain slices from rat deprived of oxygen and glucose (OGD), we imaged anoxic depolarization (AD) as it propagates through these regions. AD, the initial electrophysiological event of stroke, is a depolarizing front that drains residual energy in compromised gray matter. The extent of AD reliably determines ensuing damage in higher brain, but using whole-cell recordings we found that all CNS neurons do not generate a robust AD. Higher neurons generate strong AD and show no functional recovery in contrast to neurons in hypothalamus and brainstem that generate a weak and gradual AD. Most dramatically, lower neurons recover their membrane potential, input resistance and spike amplitude when oxygen and glucose is restored, while higher neurons do not. Following OGD, new recordings could be acquired in all lower (but not higher) brain regions, with some neurons even withstanding multiple OGD exposure. Two-photon laser scanning microscopy confirmed neuroprotection in lower, but not higher gray matter. Specifically pyramidal neurons swell and lose their dendritic spines post-OGD, whereas neurons in hypothalamus and brainstem display no such injury. Exposure to the Na+/K+ ATPase inhibitor ouabain (100 μM), induces depolarization similar to OGD in all cell types tested. Moreover, elevated [K+]o evokes spreading depression (SD), a milder version of AD, in higher brain but not hypothalamus or brainstem so weak AD correlates with the inability to generate SD. In summary, overriding the Na+/K+ pump using OGD, ouabain or elevated [K+]o evokes steep and robust depolarization of higher gray matter. We show that this important regional difference can be largely accounted for by the intrinsic properties of the resident neurons and that Na+/K+ ATPase pump efficiency is a major determining factor generating strong or weak spreading depolarizations. / Thesis (Ph.D, Anatomy & Cell Biology) -- Queen's University, 2012-10-02 17:59:20.589

No description available.

No description available.

No description available.

The patterns, stoichiometry, and kinetics of microbial benzene, toluene, p-xylene, m-xylene, and o-xylene degradation by a denitrifying activated sludge consortium was investigated in a sequencing batch reactor (SBR) receiving a mixed waste. After six months of acclimation, toluene and m-xylene were routinely degraded to below detection. Both toluene and m-xylene could serve as sole carbon and energy sources. The removal of o-xylene was also possible; however, its transformation was dependent upon gratuitous metabolism during toluene degradation. Benzene and p-xylene were recalcitrant throughout the study. The first order decay coefficient (b) of the denitrifying biomass was determined to be 0.016 ± 0.006 h⁻¹ on a theoretical oxygen demand (thOD) basis. The true growth yields (Y) for the biogenic and toluene/m-xylene components of the mixed waste were determined to be 0.41 ± 0.02 and 0.35 ± 0.04 mg thOD biomass per mg thOD substrate, respectively. The Monod parameters, qmax and KS, for toluene ranged from 0.059 to 0.14 mg toluene/mg protein/h and 0.84 to 6.9 mg/L, respectively. For m-xylene, the qmax and KS parameters ranged from 0.034 to 0.041 mg m-xylene/mg protein/h and 0.28 to 3.7 mg/L, respectively. Some of the variation observed between kinetic experiments was attributed to the different accumulation levels of the denitrification intermediate nitrite (NO⁻) and the inhibitory effects of its conjugate acid, nitrous acid (HNO₂). Other evidence suggested that part of the variation was also due to a continuous acclimation and refinement towards higher affinity toluene- and m-xylene-degrading enzyme systems within the biomass. / Master of Science

Three of Hampton Roads Sanitation District's (HRSD's) conventional activated sludge Water Resource Recovery Facilities (WRRFs) add methanol for post-anoxic denitrification: the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB). From 2017-2020, VIP averaged 0.49 ± 0.03 lb COD/lb N removed, while NP and AB averaged 1.48 ± 0.06 and 2.11 ± 0.15 lb COD/lb N, respectively. Significant methanol savings at VIP may result from post-anoxic denitrification using internal carbon that was stored in the anaerobic zone. An investigation into the factors affecting internal carbon-driven (internal C) denitrification was done via a series of batch tests. The capacity for internal C denitrification was demonstrated with sludge from all three WRRFs, despite not necessarily being used full-scale. For each WRRF, an increase in these rates correlated to higher phosphorus uptake rates, suggesting a dependence on the PAO population. Shorter aerobic times and more acetate in the anaerobic stage were shown to increase internal C denitrification rates to varying degrees, and this type of denitrification was only observed for bio-P biomass that was also nitrifying. Beyond internal carbon, other denitrification factors explored include moving the methanol dose point further into the anoxic zone, longer post-anoxic residence times, plug-flow conditions, solids residence time (SRT), and anoxic conditions prior to methanol dosing. Contributions from slowly biodegradable COD were minimal. Understanding the conditions that promote denitrification with internal carbon or other carbon sources would be required for effective strategies to achieve methanol savings at NP and AB that would rival those at VIP. / Master of Science / Three of Hampton Roads Sanitation District's (HRSD's) Water Resource Recovery Facilities (WRRFs) add methanol to facilitate denitrification in the post-anoxic zone: the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB). Significant methanol savings at VIP may result from denitrification using carbon that was stored in the biomass earlier in the treatment process. An investigation into the factors affecting this type of denitrification with internal carbon was done via a series of batch tests. All three WRRFs were able to use this internal carbon for denitrification in the batch tests, despite not necessarily using it full-scale. These denitrification rates were shown to relate to the performance of the biomass that is also responsible for phosphorus removal. Shorter aerobic times prior to the anoxic phase and more acetate in the stage where carbon is stored were shown to increase these denitrification rates, and this type of denitrification was only observed for biomass from WRRFs that implement nitrification. Beyond internal carbon, other denitrification factors explored include moving the methanol dose point further into the anoxic zone, longer post-anoxic residence times, plug-flow conditions, solids residence time (SRT), and anoxic conditions prior to methanol dosing. Contributions from carbon pushed downstream from overloading primary clarifiers was minimal. Understanding the conditions that promote denitrification with internal carbon or other carbon sources would be required for effective strategies to achieve methanol savings at NP and AB that would rival those at VIP.

Oceanic anoxic events (OAEs) are periods in Earth's history when oceans were depleted in dissolved oxygen and characterized by deposition of organic-rich sediments. The Oceanic Drilling Program (ODP) has drilled through OAEs in a number of areas worldwide, collecting core and borehole log data. This project attempts to identify a characteristic signature from known ODP OAE sections using these data and to apply the signature to identify OAE intervals in Gulf of Mexico wells where cores are lacking. Additionally, pseudo density curves were generated from ODP logs and compared to bulk density logs to determine if the deviation between the two would aid identification of OAE intervals. A general, though not fool proof, signature of high gamma ray, uranium, neutron porosity and low density was seen in nearly all of the ODP holes. Using this signature 20 potential OAE intervals were identified in the Gulf of Mexico.

abstract: Variations of 238U/235U in sedimentary carbonate rocks are being explored as a tool for reconstructing oceanic anoxia through time. However, the fidelity of this novel paleoredox proxy relies on characterization of uranium isotope geochemistry via laboratory experimental studies and field work in modern analog environmental settings. This dissertation systematically examines the fidelity of 238U/235U in sedimentary carbonate rocks as a paleoredox proxy focusing on the following issues: (1) U isotope fractionation during U incorporation into primary abiotic and biogenic calcium carbonates; (2) diagenetic effects on U isotope fractionation in modern shallow-water carbonate sediments; (3) the effects of anoxic depositional environments on 238U/235U in carbonate sediments. Variable and positive shifts of 238U/235U were observed during U uptake by primary abiotic and biotic calcium carbonates, carbonate diagenesis, and anoxic deposition of carbonates. Previous CaCO3 coprecipitation experiments demonstrated a small but measurable U isotope fractionation of ~0.10 ‰ during U(VI) incorporation into abiotic calcium carbonates, with 238U preferentially incorporated into the precipitates (Chen et al., 2016). The magnitude of U isotope fractionation depended on aqueous U speciation, which is controlled by water chemistry, including pH, ionic strength, carbonate, and Ca2+ and Mg2+ concentrations. Based on this speciation-dependent isotope fractionation model, the estimated U isotope fractionation in abiotic calcium carbonates induced by secular changes in seawater chemistry through the Phanerozoic was predicted to be 0.11–0.23 ‰. A smaller and variable U isotope fractionation (0–0.09 ‰) was observed in primary biogenic calcium carbonates, which fractionated U isotopes in the same direction as abiotic calcium carbonates. Early diagenesis of modern shallow-water carbonate sediments from the Bahamas shifted δ238U values to be 0.270.14 ‰ (1 SD) higher than contemporaneous seawater. Also, carbonate sediments deposited under anoxic conditions in a redox-stratified lake—Fayetteville Green Lake, New York, USA— exhibited elevated δ238U values by 0.160.12 ‰ (1 SD) relative to surface water carbonates with significant enrichments in U. The significant U isotope fractionation observed in these studies suggests the need to correct for the U isotopic offset between carbonate sediments and coeval seawater when using δ238U variations in ancient carbonate rocks to reconstruct changes in ocean anoxia. The U isotope fractionation in abiotic and biogenic primary carbonate precipitates, during carbonate diagenesis, and under anoxic depositional environments provide a preliminary guideline to calibrate 238U/235U in sedimentary carbonate rocks as a paleoredox proxy. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2018

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: George W. Luther, III., College of Marine and Earth Studies. Includes bibliographical references.

Standard geochemical analysis methods, such as aqueous geochemistry analysis and mineralogical analysis, frequently are utilized to evaluate the effectiveness of passive treatment systems, though they do not necessarily provide information regarding the mechanism of removal. Two emerging analytical techniques have shown promise by providing additional information to improve characterization of treatment systems: X-ray absorption spectroscopy (XAS) and stable isotope analysis. In this thesis, these novel analytical techniques were integrated with standard geochemical measurements to better characterize contaminated sites as well as potential treatment technologies used to mitigate aqueous contaminant mobility. Laboratory experiments were used to evaluate the removal of Se(VI) form simulated groundwater using granular Fe0 (GI) and organic carbon (OC). Greater than 90 % removal of Se(VI) was observed for systems containing GI after 5 days of reaction time and only 15 % removal was observed in systems containing OC. Synchrotron radiation-based XAS analysis of the treatment materials indicated the presence of both Se(IV) and Se(0) on the edges of GI grains after 6 hours reaction time, with no evidence of oxidized Se after 5 days of reaction. Several analytical techniques were integrated to characterize sediment contaminated with Hg and other contaminants through previous industrial practices. Analysis of the sediment by XAS indicated the possible presence of mercury selenide and copper sulfide. Resuspension tests were performed in oxic and anoxic conditions to simulate the effects of changing geochemical conditions of Hg release from sediments during dredging operations. The results indicated a higher release of Hg under oxic conditions in some sediment locations, suggesting that oxidative degradation of organic carbon or oxidative dissolution of Hg sulfides contributed to Hg release. The treatment of aqueous Hg(II) was evaluated with a variety of treatment media, including clay and GI. Treatment with GI was rapid, with 90 % removal observed after 2 hours reaction time. Extended X-ray absorption fine structure (EXAFS) analysis indicated the presence of Hg-O bonding on GI, suggesting that Hg was bound to Fe oxides formed on the surface of corroded GI. A new conceptual model for tracking the stable isotope fractionation of sulfur was coupled to the reactive transport model MIN3P to determine the effects of secondary transformations on sulfur cycling in passive treatment systems. Minor differences were noted when comparing the transport model-derived fractionation factor to calculations using a simplified Rayleigh distillation model, possibly indicating the effect of SO4 precipitation. The incorporation of stable isotope modeling provides a framework for the modeling of other isotope systems in treatment technologies.