Oxygen Flux Research Articles

Impacts of climate change on estuarine stratification and implications for hypoxia within a shallow subtropical system

Vertical density stratification often plays an important role in the formation and expansion of coastal hypoxic zones through its effect on near-bed circulation and vertical oxygen flux. However, the impact of future climate change on estuarine circulation is widely unknown. Here, we developed and calibrated a three-dimensional hydrodynamic model for Pensacola Bay, a shallow subtropical estuary in the northeastern Gulf of Mexico. Model simulations based on years 2013–2017 were applied to examine changes in salinity, temperature, and density under future climate scenarios, including increased radiative forcing (IR) and temperature (T), increased freshwater discharge (D), sea level rise (SLR), and wind intensification (W). Simulations showed that the impacts of climate change on modeled state variables varied over time with external forcing conditions. The model demonstrated the potential for sea level rise and increased freshwater discharge to episodically increase vertical density gradients in the Bay. However, increased wind forcing destabilized vertical gradients, at times reducing the spatial extent and duration of stable stratification. For time periods with low freshwater discharge, moderate increases in wind speed (10%) can destabilize density gradients strengthened by increased discharge (10%) and sea level rise (0.48 m). In contrast, destruction of strong density gradients that form near the mid-Bay channel following flood events requires stronger wind forcing. These results highlight the importance of considering natural variability in freshwater and wind forcing, as well as local phenomena that are generally unresolved by global climate models.

High-Entropy Perovskites Pr1-xSrx(Cr,Mn,Fe,Co,Ni)O3-δ (x = 0-0.5): Synthesis and Oxygen Permeation Properties.

High-entropy perovskite oxides have already been studied in various fields owing to their high-entropy-induced properties. Partial substitution of an element by a lower valence element usually improves the oxygen permeability of perovskite oxides, but high substitution amounts may lead to structural instability. In this work, pure high-entropy perovskites Pr1-xSrx(Cr,Mn,Fe,Co,Ni)O3-δ with high amounts Sr up to x = 0.5 were synthesized via a sol-gel method. Several characterization methods prove that the solubility of Sr increases with higher temperatures of the heating treatment. The ceramic with x = 0.5 shows a transition from semi-conductive to metallic behavior when the temperature reaches 873K. Its oxygen flux is comparable to the low-entropy counterpart La0.6Sr0.4Co0.5Fe0.5O3-δ. A stable run of ca. 46.2 h was documented for oxygen permeation under an air/CO2 gradient.

Real-world impacts of microplastic pollution on seafloor ecosystem function

Emerging research shows that microplastic pollution could be impacting seafloor ecosystem function, but this has been primarily demonstrated without environmental and ecological context. This causes uncertainty in the real-world effects of microplastic pollution and leaves out essential information guiding policy and mitigation. In this study, we take a well-supported sampling design and statistical approach commonly employed in benthic ecology to evaluate real-world effects of microplastic pollution on coastal, benthic ecosystem function. We utilised environmental gradients in the Waitemata Harbour of Auckland, New Zealand to evaluate the importance of commonly assessed biological, chemical, and geological sediment variables and the characteristics of microplastic contaminants in driving essential ecosystem functions. Our results showed that models including microplastic terms were more accurate and explained more variability than those without microplastic terms, highlighting that microplastics impact real-world seafloor ecosystem function. Specifically, microplastic fibers significantly influenced oxygen flux (p < 0.03) and the diverse forms of microplastics (i.e., richness) significantly influenced ammonium flux (p < 0.02). Additionally, interactions between microplastic fiber concentrations and mollusc abundances significantly contributed to oxygen flux (p < 0.02). These results provide the first evaluation of in situ relationships between microplastics and ecosystem function. Even more importantly, this study suggests the value of environmental and ecological context for addressing microplastic impacts on benthic ecosystems and argues for further field examination.

Aerobic respiration controls on shale weathering

The weathering of shale exerts an important control on the hydrochemical fluxes to river systems, thus influencing the global carbon, nutrient, and geochemical cycles. However, the quantitative understanding of shale weathering and its impact on global biogeochemical cycles remains inadequate due to the complex interplay between hydrological, biogeochemical, and physical processes. In this study, we develop a novel modeling approach to quantitatively interpret the long-term chemical weathering of shale occurring since the last glaciation period (15,000 years) leading to the present geochemical conditions. The model explicitly considers processes occurring across multiple phases and involved in the weathering, including: (i) the infiltration of meteoric water, (ii) the interactions between the water and the mineral assemblage via dissolution/precipitation reactions, (iii) the microbially-mediated oxidation of organic matter, (iv) the evolution of porosity induced by mineral reactions, and (v) the exchange of gases between the subsurface and the atmosphere. To implement and test our model, we conduct this study at a well-instrumented hillslope underlain by Mancos Shale and located at the East River study site, Western Colorado. Consistent with field observations, the model successfully reproduces the stratified weathering front, the complex spatial distribution of organic carbon, and the gaseous emissions of carbon dioxide from the subsurface. Model simulations show that aerobic respiration exerts a fundamental control on the weathering of shale. While previous studies have highlighted the diffusion of oxygen from the atmosphere as the primary mechanism for shale weathering, our model simulations demonstrate that aerobic respiration limits the propagation of oxygen in the shallow subsurface, and thereby inhibits the dissolution of pyrite at depth. Aerobic respiration is particularly favored in the top soil horizon due to the constant flux of oxygen from the atmosphere, the replenishment of fresh litter/plant-derived organic matter, and to a lesser extent the presence of fossil shale-associated organic matter. The acidic pore water generated through aerobic respiration within the shallow subsurface is transported to greater depths, where it sustains the dissolution of carbonate (dolomite in this example). Overall, our results demonstrate that the evolution of pyrite and carbonate depletion fronts are significantly different, and primarily depend on the ability of microorganisms to carry out microbial respiration and the various transport pathways of reactants controlling the mineral reactions under partially saturated conditions.

Large-Scale Spatial and Temporal Patterns and Importance of Sediment–Water Oxygen and Nutrient Fluxes in the Chesapeake Bay Region

Large-Scale Spatial and Temporal Patterns and Importance of Sediment–Water Oxygen and Nutrient Fluxes in the Chesapeake Bay Region

Abstract 13646: APOL1 Nephropathy Risk Variant Alters Macrophage Metabolism

The common G1 and G2 variants in the APOL1 gene, specific to patients with African ancestry, increase the risk of developing chronic kidney disease and stroke. These variants also confer a survival benefit against African trypanosomiasis, but the effects of G1 and G2 variants on macrophage function remain unclear despite their role in innate immunity. Crucial to both innate immunity and tissue homeostasis, macrophages can promote cardiometabolic disease if dysregulated. Others have shown that metabolic changes can alter macrophage phenotype and function, and the G1 and G2 variants have been linked to mitochondrial dysfunction in epithelial cells. We therefore hypothesize that APOL1 risk variants promote cardiometabolic disease traits by altering macrophage metabolism and, thus, function. To test our hypothesis, we established CRISPR-Cas9 genome-edited induced pluripotent stem cell (iPSC) lines with the G0/G0 (major allele) genotype and the G1/G1 genotype on isogenic backgrounds. We then differentiated these iPSC lines into macrophage-like cells (iPSDMs) and evaluated their phenotype and function at baseline and under stimulation with 5 - 50 ug/mL interferon-γ, a potent inducer of APOL1 expression. We measured inflammatory markers via QPCR and ELISA, mitochondrial oxygen flux with the Agilent Seahorse XF Analyzer, and intracellular hydrophilic metabolites via LCMS. We found that G1/G1 iPSDMs express higher levels of pro-inflammatory markers and exhibited lower basal respiration as well as lower ATP production compared to G0/G0 controls. Because APOL1 risk variants have been linked to defective autophagy and ER stress, we treated the G1/G1 iPSDMs with rapamycin (autophagy inducer) or TUDCA (ER stress inhibitor) but found that they did not abrogate these genotype-specific differences in metabolic flux. Upon examination of metabolomics profiles of G1/G1 vs G0/G0 iPSDMs, differentially abundant metabolites were enriched for SMPDB pathways including spermidine biosynthesis (needed for anti-inflammatory reprogramming), gluconeogenesis, Warburg effect, homocysteine degradation, and fatty acid oxidation. Taken together, G1/G1 iPSDMs exhibit metabolic differences that may contribute to their proinflammatory phenotype.

Comparing CrN and TiN Coatings for Accident-Tolerant Fuels in PWR and BWR Autoclaves

The development of coatings for accident-tolerant fuels (ATFs) for light water reactor (LWR) applications promises improved corrosion resistance under accident conditions and better performances during operation. CrN and TiN coatings are characterized by high wear resistance coupled with good corrosion resistance properties. They are generally used to protect materials in applications where extreme conditions are involved and represent promising candidates for ATF. Zr cladding tubes coated with 5 µm-thick CrN or TiN, exposed in an autoclave to simulated PWR chemistry and BWR chemistry, were characterized with SEM, EDS, and STEM. The investigation focused on the performance and oxidation mechanisms of the coated claddings under simulated reactor chemistry. Both coatings provided improved oxidation resistance in a simulated PWR environment, where passivating films of Cr2O3 and TiO2, less than 1 µm-thick, formed on the CrN and TiN outer surfaces, respectively. Under the more challenging BWR conditions, any formed Cr2O3 dissolved into the oxidizing water, resulting in the complete dissolution of the CrN coating. For the TiN coating, the formation of a stable TiO2 film was observed under BWR conditions, but the developed oxide film was unable to stop the flux of oxygen to the substrate, causing the oxidation of the substrate.

Modulation of oxidative neurometabolism in ischemia/reperfusion by nitrite.

Nitrite has been viewed essentially as an inert metabolic endpoint of nitric oxide (•NO). However, under certain conditions, nitrite can be a source of •NO. In the brain, this alternative source of •NO production independent of nitric oxide synthase activity may be particularly relevant in ischemia/reperfusion (I/R), where low oxygen availability limits enzymatic production of •NO. Notably, in vivo concentration of nitrite can be easily increased with diet, through the ingestion of nitrate-rich foods, opening the window for a therapeutic intervention based on diet. Considering the modulation of mitochondrial respiration by •NO, we have hypothesized that the protective action of nitrite in I/R may also result from modulation of mitochondrial function. We used high-resolution respirometry to evaluate the effects of nitrite in two in vitro models of I/R. In both cases, an increase in oxygen flux was observed following reoxygenation, a phenomenon that has been coined "oxidative burst". The amplitude of this "oxidative burst" was decreased by nitrite in a concentration-dependent manner. Additionally, a pilot in vivo study in which animals received a nitrate-rich diet as a strategy to increase circulating and tissue levels of nitrite also revealed that the "oxidative burst" was decreased in the nitrate-treated animals. These results may provide mechanistic support to the observation of a protective effect of nitrite in situations of brain ischemia.

Controlling factors of the climatological annual cycle of the surface mixed layer oxygen content: A global view

The annual cycle of global dissolved oxygen content (O2C) and mean oxygen concentration in the surface mixed layer are estimated using monthly climatological oxygen fields from the World Ocean Atlas 2018 (WOA18). The largest seasonal variability in the mixed layer O2C occurs in the extra-tropics between 30° and 70° latitude of each hemisphere. A global view of the role of entrainment, air-sea flux, and biological activity in controlling the oxygen content/concentration annual cycle in the mixed layer is determined using an oxygen mass balance model. Based on the relative percentage from the mass balance model, entrainment is only a significant driver (contributing to 20-40% of the total changes) from mid-fall to early spring when the mixed layer deepens and transfers oxygen to deeper waters. Both the air-sea oxygen flux and biological activity show strong annual cycles and play critical roles in the annual cycle of O2C in the mixed layer. Air-sea oxygen flux is ingassing from late fall to early spring and outgassing between late spring and early fall. It is a substantial factor throughout the year and controls 40-60% of the oxygen changes in most months. Biological activity is a net source (production) in the spring and summer and a net sink (consumption) in the late fall and winter for the mixed layer oxygen content. Biological activity plays a more important role during spring/summer (40-60%) than that during fall/winter (10-30%) in controlling the overall oxygen change in each month. The model estimates a mean value (±SD) of 3.06±1.61 mol C m-2 yr-1 and a total of 863.7±73.8 Tmol C yr-1 for the global annual net ocean community production (ANCP) between 60°S and 60°N latitude, which are in fairly good agreement with previous studies.

The Role of Boundary Mixing for Diapycnal Oxygen Fluxes in a Stratified Marine System

AbstractInsufficient diapycnal oxygen transport through the halocline is the key reason for the anoxic conditions typically observed in the deeper parts of the Baltic Sea. The variability of turbulent oxygen fluxes through the halocline was investigated seasonally and in space during three cruises (summer, fall, winter). Turbulence dissipation rates and oxygen fluxes showed a pronounced seasonal pattern, with the lowest values during summer. At the basin boundaries, halocline oxygen fluxes increased by an order of magnitude as a result of boundary mixing. A simple box model, distinguishing between interior, intermediate, and boundary regions, was used to extrapolate the locally observed fluxes to the central Baltic Sea. The boundary area, covering less than 23% of the total basin area, contributed more than 80% of the basin‐scale oxygen transport through the halocline. According to this model, the annual oxygen flux through the halocline is of the order of 20–28 Gmol per year.

A three-dimensional model to describe complete human corneal oxygenation during contact lens wear.

We perform a novel 3D study to quantify the corneal oxygen consumption and diffusion in each part of the cornea with different contact lens materials. The oxygen profile is calculated as a function of oxygen tension at the cornea-tear interface and the oxygen transmissibility of the lens, with values used in previous studies. We aim to determine the influence of a detailed geometry of the cornea in their modeling compared to previous low dimensional models used in the literature. To this end, a 3-D study based on an axisymmetric volume element analysis model was applied to different contact lenses currently on the market. We have obtained that the model provides a valuable tool for understanding the flux and cornea oxygen profiles through the epithelium, stroma, and endothelium. The most important results are related to the dependence of the oxygen flux through the cornea-lens system on the contact lens thickness and geometry. Both parameters play an important role in the corneal flux and oxygen tension distribution. The decline in oxygen consumption experienced by the cornea takes place just inside the epithelium, where the oxygen tension falls to between 95 and 16 mmHg under open eye conditions, and 30 to 0.3 mmHg under closed eye conditions, depending on the contact lens worn. This helps to understand the physiological response of the corneal tissue under conditions of daily and overnight contact lens wear, and the importance of detailed geometry of the cornea in the modeling of diffusion for oxygen and other species.

Disparate relationships between pH and goethite-water 18O/16O and D/H fractionation factors

For goethites synthesized at low (∼1–2) and high (∼13–14) extremes of pH, the values of 1000ln18αgt-w at ca. 25 °C are, respectively, +6.2(±0.6) and + 0.9(±0.6). Note that 18αgt-w = (18O/16O)gt/(18O/16O)w and gt = goethite (α-FeOOH); w = liquid water. A steady-state, flux-balance model indicates that this pH-related difference in values of 1000ln18αgt-w arises because of an effectively irreversible oxygen flux associated with aqueous Fe(III) hydroxide adsorption on, and incorporation in, goethite during growth at crystal surfaces. The model predicts that the transition from a low-pH to a high-pH value of 1000ln18αgt-w is relatively abrupt. At 22 to 25 °C, extant data indicate that the transition occurs in the interval of pH from about 6 to 8. Consequently, uncertainty about the pH of ancient waters could be a factor in interpretations of goethite δ18O values. However, an experimentally determined equation for the temperature dependence of 1000ln18α(LpH) has been applied with apparent success to natural goethites that formed in the presence of meteoric waters (18α(LpH) = low-pH 18αgt-w). This suggests that those ancient waters may have been acidic (pH < 6) in the immediate environments of goethite crystallization.Published values of D/H fractionation between synthetic goethite and water (Dαgt-w) show no systematic effect of either pH or temperature (T) over a range of pH from 1 to 14 and a range of T from 22 °C to 62 °C. Within these ranges, the average value of Dαgt-w is 0.905(±0.005) – a value which seems to characterize the D/H fractionation observed in natural goethites. If hydrogen in transitional, chemisorbed Fe(III) hydroxides – represented here as Fe(OH)3A – rapidly exchanges D/H with ambient water during crystal growth, there is a model-based expectation that Dαgt-w will not be affected by pH. This postulated D/H exchange would cease when Fe(OH)3A irreversibly transitions to FeOOH during crystallization – i.e., when Fe, O, and H are incorporated in the structure of the growing crystal.Thus, the flux balance model suggests that the observed dichotomy in the effects of pH on 18αgt-w and Dαgt-w is a result of distinctly different exchangeabilities of 18O/16O and D/H in transitional Fe(III) hydroxides that are chemisorbed on growing surfaces of goethite crystals. Observed values of 18αgt-w and Dαgt-w may represent steady-state – but not necessarily thermodynamic equilibrium – distributions of isotopes between H2O and the oxygen or hydrogen in the interiors of crystallizing goethites. Nevertheless, these steady-state values of Dαgt-w and 18αgt-w are generally reproducible and systematically relate δ18O and δD values of goethite to environmental variables.

Asymmetric Ba0.5Sr0.5Co0.8Fe0.2O3-Δ Membrane for Oxygen Permeation: Synergetic Fabrication By Magnetron Sputtering Deposition and Selective Laser Annealing

The Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) mixed ionic electronic conductor (MIEC) is considered to be one of the most promising perovskite-based materials for oxygen transport exhibiting high oxygen permeability. Such oxygen-permeable perovskite membrane maybe applied to increase efficiency of combustion or reforming processes of new fuels such as green ammonia. An approach to elevate the oxygen permeability of BSCF membranes is reduction of membrane thickness, as the permeation process is mostly controlled by bulk diffusion. Since self-standing thin membranes are not sufficiently mechanically stable, asymmetric membranes consisting of a thin layer membrane deposited onto a porous bulk support are usually employed. . In this work, planar BSCF thin film membranes of 1 to 2 and 15 to 20 µm thickness were successfully synthesized by a combination of magnetron sputtering (MS) and thermal annealing (TA) and/or selective laser annealing (SLA) processes. Thin films appeared to be pinhole-free with a high crystallinity of a single perovskite phase and a microstructure that showed suitability for oxygen permeation applications. Correlations between thin film properties and MS process parameters (e.g. power, Ar/O2 ratio, pressure, etc.) and TA&/SLA parameters were established and optimised as key factors for producing thin film membrane exhibiting high oxygen flux and good stability. A variation of the oxygen flux through the BSCF asymmetric membrane as well as the porous substrate is presented as a function of temperature and also oxygen partial pressures applied to both sides of the membrane allowing for calculation of permeability of the deposited thin film. Figure 1

Investigating Oxygen Reduction Reaction Using a Multiscale Modeling Approach for Polymer Electrolyte Membrane Fuel Cell

Cathode catalyst layer (CCL) modeling is an important tool in elucidating the coupled transport-reaction phenomena and optimizing electrode architectures for greater efficiency, power density, and durability and thereby, reducing fuel cell costs. State-of-the-art catalyst use a high surface area carbon black (HSC) that supports platinum (Pt) nanoparticles, where some of the Pt particles reside on the carbon surface and a significant fraction of particles are found in the nm-scale pores of the carbon support. Within the electrode, the catalyst in bound by a polymer electrode binder (i.e., ionomer) that coats the external surface of the catalyst but does not penetrate the internal pores that are filled with liquid water due to capillary condensation. The contact of ionomer with Pt is known to reduce electrocatalytic activity due to site-blocking by the ionomer anion as well as increase the oxygen transport resistance. There is very little prior work on modeling the distinct performance of the internal Pt and the external Pt in contact with the ionomer. Most prior attempts to model CCLs with HSC catalyst supports at the MEA-scale and cell-scale have used an uncoupled approach, that separately considered the transport to the internal and external Pt particles, not considering the combined flux of oxygen through the ionomer film. Thus, the prior uncoupled model could potentially underestimate the oxygen concentration drop through the ionomer film. Here, we have adopted a numerical model of the catalyst that simultaneously considers the transport to the internal and external Pt as well as the different transport properties in the water and ionomer domains in single primary particle of the catalyst. The single spherical catalyst support model is upscaled to a 3D fuel cell model using a parametric linear regression fitting to model the local source/sink terms in the CCL. This multi-scale model is then applied to study the impact of the catalyst morphology.This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office, Award Number DE-EE0008822.

Air-water CO2 and water-sediment O2 exchanges over a tidal flat in Tokyo Bay

Despite the potential for carbon storage in tidal flats, little is known about the details of relevant processes because of the complexity of intertidal physical and chemical environments and the uniqueness of the biota. We measured air-water carbon dioxide (CO2) fluxes and water-sediment oxygen (O2) fluxes over a tidal flat in Tokyo Bay by the eddy covariance method, which has the potential to facilitate long-term, broad-scale, continuous monitoring of carbon flows in tidal flats. The results indicated that throughout the tidal flat in Tokyo Bay, CO2 was taken up from the atmosphere at a rate of 6.05 ± 7.14 (mean ± SD) mmol m−2 hour−1, and O2 was taken up from the water into the sediment at a rate of 0.62 ± 1.14 (mean ± SD) mmol m−2 hour−1. The fact that the CO2 uptake rate was about 18 times faster than the previously reported average uptake rate in the whole area of Tokyo Bay was attributable to physical turbulence in the water column caused by bottom friction. Statistical analysis suggested that light intensity and water temperature were the major factors responsible for variations of CO2 and O2 exchange, respectively. Other factors such as freshwater inputs, atmospheric stability, and wind speed also affected CO2 and O2 exchange. High rates of O2 uptake from the water into the sediment surface and high rates of atmospheric CO2 uptake into the water column occurred simultaneously (R2 = 0.44 and 0.47 during day and night, respectively). The explanation could be that photosynthetic consumption of CO2 and production of O2 in the water column increased the downward CO2 (air to water) and O2 (water to sediment) fluxes by increasing the concentration gradients of those gases. Resuspension of sediment in the low-O2 layer by physical disturbance would also increase the O2 concentration gradient and the O2 flux in the water.

Spatial characterization of microbial sulfur cycling in horizontal-flow constructed wetland models

Constructed wetlands (CWs) are a cost-effective technology for wastewater treatment in which plant-microorganism relationships play a key role in transforming pollutants. However, there is little knowledge about the spatial organization of microbial metabolic processes in CWs. Here we show the structuring of microbial transformation of inorganic sulfur compounds (ISCs) in two horizontal subsurface-flow CW models fed with sulfate-rich artificial wastewater. One model was fully planted with Juncus effusus, while the other was planted only in the middle to investigate further the influence of the plant on ISC transformations. Chemical analyses revealed that sulfate reduction and re-oxidation of sulfide/sulfur occurred simultaneously along the flow paths, with net reduction at the beginning of the CWs, where organic carbon from the influent was still present, and predominant re-oxidation in the downstream sections. Porewater ISC concentrations hardly differed between the two CWs. However, analysis of the bacterial communities showed that sulfur cycling in the fully planted CW was much higher. Total bacterial abundances were about 50 times and 3–4 orders of magnitude higher in the rhizoplane than in porewater and on gravel, respectively, as quantified by qPCR determination of the 16S rRNA gene. Sequencing of 16S rRNA gene amplicons revealed that bacterial communities on the roots and in the porewater differed substantially, apparently a consequence of the fluxes of oxygen and exudates from the roots. Furthermore, we observed partitioning of ISC transforming bacteria into different niches of the CWs. The results of the chemical and microbial analyses collectively support that extensive sulfur cycling occurred in the rhizospheres of the CW models. The study is relevant to the treatment of sulfur-containing wastewater and the elucidation of microbial communities involved in biogeochemical activities to improve water quality.

Processing, microstructure, electrical properties and cytotoxic behaviour of lead-free 0.99K0.5Na0.5NbO3-0.01BiFeO3 piezoceramics prepared using Spark Plasma Sintering (SPS)

In this work, “lead free” 0.99K0.5Na0.5NbO3-0.01BiFeO3 (KNN–BF) piezoceramics were prepared by a combination of mechanochemical activation, Spark Plasma Sintering and post-annealing treatment. Results show that the annealing treatment causes important microstructural and electrical changes. The SPS sample was characterized by low electrical resistance, while the air annealed samples showed better insulating properties due to a partial compensation of the oxygen vacancy. The best piezoelectric properties were found for the samples annealed at 1000 and 1050 ​°C for 2h due to the optimum grain size and oxygen vacancy compensation achieved. A further enhancement of the dielectric and piezoelectric properties was achieved through a second annealing treatment in oxygen flux at 1050 ​°C for 30 ​min. Moreover, the toxicity of the pellets was evaluated through exposure experiments to the pulverized KNN–BF pellets, employing two widely used human and environmental cellular models.

Ractopamine and age alter oxygen use and nitrogen metabolism in tissues of beef steers.

The objective was to quantify the effects of age and ractopamine (RAC) on whole body oxygen consumption and Leu flux, and oxygen flux and metabolism of nitrogenous compounds by the portal-drained viscera (PDV), liver, and hindquarters (HQ) of steers. Multicatheterized steers were fed a high energy diet every 2 h in 12 equal portions. Five younger steers (body weight, [BW] = 223 ± 10.1 kg) were 6 mo old and five older steers (BW = 464 ± 16.3 kg) were 14 mo old. Treatments were control (Cont) or 80 mg RAC per kg diet in a crossover design. Nitrogen (N) balance was measured on day 9 to 13. Whole body oxygen consumption and net flux were measured on day 11 and day 13, and net flux of N variables, Phe and Leu kinetics were measured on day 13. Whole body oxygen consumption increased (P < 0.05) in response to RAC in older but not younger steers. Retained N was greater (P = 0.009) for younger than older steers and increased (P = 0.010) with RAC in both ages of steers. Nitrogen retained as a percentage of N apparently absorbed increased (P < 0.05) in the older steers but not the younger steers in response to RAC. Oxygen uptake was greater (P < 0.05) in PDV, liver, and total splanchnic tissues in the younger steers and there was no response to RAC. In contrast, oxygen uptake in HQ increased (P < 0.05) with RAC in the older but not the younger steers. Concentration and net PDV release of α-amino N (AAN) were not affected by age or RAC. Uptake of AAN by liver decreased with RAC (P = 0.001). Splanchnic release of AAN was greater in younger steers (P = 0.020) and increased (P = 0.024) in response to RAC. For HQ tissues, uptake (P = 0.005) and extraction (P = 0.005) of AAN were lesser in older than younger steers and both increased (P = 0.001) in response to RAC. Based on Phe kinetics in HQ, RAC increased (P < 0.05) protein synthesis in older steers but not in younger steers. In contrast, protein breakdown decreased (P < 0.05) in response to RAC in younger steers. In response to RAC, protein degradation was less (P < 0.05) in younger than older steers. Based on Leu kinetics, whole body protein synthesis was greater in the younger steers (P = 0.022) but not altered in response to RAC. Ractopamine enhanced lean tissue growth by increasing supply of AAN to peripheral tissues and altering protein metabolism in HQ. These metabolic responses are consistent with established responses to RAC in production situations.

Can We Estimate Air‐Sea Flux of Biological O2 From Total Dissolved Oxygen?

AbstractIn this study, we compare mechanistic and empirical approaches to reconstruct the air‐sea flux of biological oxygen () by parameterizing the physical oxygen saturation anomaly (ΔO2[phy]) in order to separate the biological contribution from total oxygen. The first approach matches ΔO2[phy] to the monthly climatology of the argon saturation anomaly from a global ocean circulation model's output. The second approach derives ΔO2[phy] from an iterative mass balance model forced by satellite‐based physical drivers of ΔO2[phy] prior to the sampling day by assuming that air‐sea interactions are the dominant factors driving the surface ΔO2[phy]. The final approach leverages the machine‐learning technique of Genetic Programming (GP) to search for the functional relationship between ΔO2[phy] and biophysicochemical parameters. We compile simultaneous measurements of O2/Ar and O2 concentration from 14 cruises to train the GP algorithm and test the validity and applicability of our modeled ΔO2[phy] and . Among the approaches, the GP approach, which incorporates ship‐based measurements and historical records of physical parameters from the reanalysis products, provides the most robust predictions (R2 = 0.74 for ΔO2[phy] and 0.72 for ; RMSE = 1.4% for ΔO2[phy] and 7.1 mmol O2 m−2 d−1 for ). We use the empirical formulation derived from GP approach to reconstruct regional, inter‐annual, and decadal variability of based on historical oxygen records. Overall, our study represents a first attempt at deriving from snapshot measurements of oxygen, thereby paving the way toward using historical O2 data and a rapidly growing number of O2 measurements on autonomous platforms for independent insight into the biological pump.

Critical conditions at liftoff limit of a laminar n-butane-air jet diffusion flame

The stability mechanism of laminar coflow jet diffusion flames in normal gravity has been studied computationally and experimentally. N-butane, the heaviest alkane in a gaseous state at ambient temperature and pressure, is used as the fuel since the reaction mechanism is similar to that of higher (liquid) hydrocarbons. The critical mean n-butane jet and coflowing air velocities at flame stability limits are measured using a small fuel tube burner (0.8 mm inner diameter). The time-dependent, axisymmetric numerical code with a detailed reaction mechanism (58 species and 540 reactions), molecular diffusive transport, and a radiation model, reveals a flame structure. A fuel-lean peak reactivity spot (i.e., reaction kernel), possessing the hybrid nature of diffusion-premixed flame structure at a constant temperature of ≈1560 K, is formed at the flame base and controls the flame stability. In a near-quiescent environment, the flame base resides below the fuel tube exit plane and thereby premixing is limited. As the coflowing air velocity is increased incrementally under a fixed fuel jet velocity, the flame base moves slightly above (≈1 mm) the burner exit and vigorous premixed combustion becomes prevailing. The local heat-release rate at the reaction kernel nearly doubles due to the increased convective oxygen flux (i.e., a blowing effect). The local Damköhler number, newly defined as a ratio of the square root of the local heat-release rate and the local velocity, decreases gradually first and drops abruptly at a critical threshold value and the flame base lifts off from the burner rim. The calculated coflow air velocity at liftoff is ≈0.38 m/s at the fuel jet velocity of 2 m/s, which is consistent with an extrapolated measured value of 0.41 m/s. This work has determined the critical Damköhler number at the stability limit quantitatively, for the first time, for laminar jet diffusion flames.