O2 Pressure Research Articles

Tensile strain-induced disorder and weak localization in SrRuO3 thin films on (100) KTaO3 substrates

Abstract SrRuO3 (SRO) thin (∼12 nm) films have been grown on KTaO3 (001) substrates by RF magnetron sputtering. The as-prepared films are under enormous in-plane tensile strain, which corresponds to the elastic energy of ∼1.5 MJ. Annealing in oxygen at 900 °C for 6 h relaxes strain, partially lowering the elastic energy. The surface topography shows a transition from granularity as the Ar+O2 pressure increases from 5 mTorr to 200 mTorr, with a simultaneous change in the average surface roughness from 4 nm to 0.8 nm. Annealing transforms the topography to island-type and enhances surface roughness. The films deposited at 5 mTorr are semiconducting, and annealing further enhances the resistivity. The ρ-T of films grown at 200 mTorr shows a metallic behavior with an inflection in the ρ-T at TC ∼ 150 K, FM transition. The low-temperature resistivity upturn shows the disordered nature of these films. The eq. ρ T = 1 σ 0 + a T 1 2 + a 1 T p 2 + b T α (p = 2 & α = 2) describes the transport behavior from 2 K to 300 K of 5 mTorr deposited films. In the 200 mTorr deposited film, the above eq. is valid at T < 95 K with p = 2 and α = 1.5. At TC < T ≤ 300 K, the ρ-T follows eq. ρ T = ρ 0 + ρ 1 T α with α = 1.3 and 1.5 for the as-grown and annealed films. The lower temperature ρ-T upturn appears to have contributions from the disorder-enhanced renormalized e-e interaction (REEI) and weak localization (WL) effects. The magnetoresistance behavior supports a substantial WL effect in the films grown at 200 mTorr. Our results establish a strong correlation between the nature of strain, surface topography, and carrier transport mechanisms.

Reduced brain oxygen response to spreading depolarization predicts worse outcome in ischaemic stroke.

Spreading depolarization (SD) describes a propagating neuronal mass depolarization within the cerebral cortex that represents a mediator of infarct development and strongly stimulates the metabolic rate of O2 consumption. Here, we investigated the influence of Spreading Depolarization (SD) on brain tissue partial pressure of O2 (ptiO2) within the peri-infarct tissue of patients suffering malignant hemispheric stroke (MHS). This prospective observational trial included 25 patients with MHS that underwent decompressive hemicraniectomy followed by subdural placement of electrodes for electrocorticography (ECoG) and neighboring implantation of a ptiO2 probe within the peri-infarcted cortex. Continuous side-by-side ECoG + ptiO2 recordings were obtained for 3-6 days postoperatively and analyzed for the occurrence of SD-independent and SD-coupled ptiO2 changes, radiological findings, as well as their association with clinical outcome at 6 months. During the combined ECoG + ptiO2 monitoring period of 2,604 hours and among 1,022 SDs, 483 (47%) SD-coupled ptiO2 variations were identified as biphasic (59%), hypoxic (36%) or hyperoxic (5%) ptiO2 responses that differed significantly (*p<0.0001). Among the remaining 538/1,022 (53%) SDs, no SD-coupled ptiO2 response was detected, which we categorized as 'No response'. The overall infarct progression was 1.7% (IQR -2.5-10.9). Spreading Depolarization characteristics regarding type, duration and frequency, as well as SD-independent baseline ptiO2 had no association with outcome. In contrast, a high occurrence rate and amplitude of SD-coupled variations in ptiO2 were associated with improved outcome at 6 months (occurrence: r=-0.62, *p=0.035; amplitude: r=-0.57, *p=0.024; Spearman correlation). In conclusion, an absent or reduced ptiO2 response to SD could indicate tissue-at-risk and help direct targeted treatment strategies in ischemic stroke, which is further evidence that not all SDs are the same, but that tissue responses coupled to SD such as ptiO2 contain prognostic information. In particular, a lack of SD-coupled ptiO2 variations appears to be a predictor of worse outcome in large hemispheric stroke.

Respiratory responses and isocapnic buffering phase in child and youth soccer players during an incremental exercise test.

This study investigated the respiratory response and isocapnic buffering (IB) phase during an incremental exercise test to exhaustion in 16 child soccer players (11.9±0.9 years) and 18 youth soccer players (18.2±2.9 years). The IB phase was calculated as the difference in oxygen uptake (VO2) between the respiratory compensation point (RCP) and metabolic threshold (MT) and expressed in either absolute or relative values. The maximal oxygen uptake (VO2max) was higher in youth players than in child players. For youth players, VO2max was measured at 55.9 ± 3.6mLmin-1kg-1 and 74.9 ± 4.8mLmin-1kg-0.75, while for child players, VO2max was 50.8 ± 4.1mLmin-1kg-1 and 67.2 ± 6.1mLmin-1kg-0.75 (p < 0.001). MT and RCP occurred at 69.8 ± 6.7% and 90.9 ± 6.9% of VO2max in child players and at 73.9 ± 5.1% and 91.5 ± 4.5% of VO2max in youth players, respectively. The two groups had no significant difference (p > 0.05). Absolute IB (10.6 ± 2.8 vs 9.7 ± 3.1mLmin-1kg-1), relative IB (23.1 ± 5.7 vs 19.1 ± 6.1), and the ratio of RCP VO2 to MT VO2 (1.3 ± 0.09 vs 1.24 ± 0.09) were similar in child and youth players (p > 0.05). There was no difference in minute ventilation (V̇E, mLmin-1kg-1) and respiratory exchange ratio during exercise between the two groups (p > 0.05). During exercise, respiratory frequency, ventilatory equivalent for carbon dioxide (VE/VCO2) and oxygen (VE/VO2), VE/VCO2 slope, end-tidal O2 pressure were higher in child players than in youth players, while tidal volume (L kg-1), O2 pulse, and end-tidal CO2 pressure were lower (p < 0.05). Despite differences in aerobic capacity and ventilatory response to exercise, child players showed similar IB phase as youth players. Although child players have lower ventilation efficiency than youth players, the higher ventilation response for a given VCO2 may provide an advantage in regulating acid-base balance during intense exercise.

Epitaxial growth and characterization of copper gallate (CuGa2O4) thin films by pulsed laser deposition

High-quality crystalline copper gallate (CuGa2O4) thin films were grown on c-plane sapphire substrates using the pulsed laser deposition (PLD) technique by optimizing the growth parameters (i.e., temperature, oxygen chamber pressure, and laser energy density). The obtained XRD patterns validated that the preferred orientation of the crystalline CuGa2O4 thin film is along the [111] direction, and the crystallinity of the films improved with increasing substrate temperature while maintaining a constant O2 pressure, as assessed by measuring the full width at half maximum (FWHM) of the prominent (222) plane. Reducing the oxygen pressure leads to the emergence of β-Ga2O3 peaks rather than the CuGa2O4 peaks due to the incomplete oxidation of copper (Cu). Subsequent XRD phi (φ) scans revealed a sixfold rotational symmetry of CuGa2O4 and a 30° epitaxial relationship between the film and the sapphire substrate. X-ray photoelectron spectroscopy (XPS) spectra confirmed the presence of Cu1+, Cu2+, and Ga3+ oxidation states in the films. Increasing laser energy density resulted in the complete oxidation of Cu and an increase in the film thickness from 51.8 nm to 183.4 nm. The direct bandgap of CuGa2O4 films was determined to be approximately 4.50 eV by analyzing the UV–Vis absorbance spectra using the Tauc equation. The refractive index was found to be approximately 2.05 ± 0.01 based on the spectroscopic ellipsometry data. While the impact of increasing laser energy density was negligible on the parameters such as crystal structure, rotational symmetry, oxidation states of gallium (Ga), oxygen (O), bandgap, and refractive index of CuGa2O4 thin film, notable alterations in the oxidation state of Cu and film thickness were observed. The surface roughness (Rrms) measured from AFM images showed a strong correlation with the values derived from ellipsometry analysis.

Predictive Hypoxemic Threshold for Tolerating the Apnea Test While Assessing Death by Neurological Criteria

Abstract Background The apnea test (AT) plays a vital role in diagnosing brain death by evaluating the absence of spontaneous respiratory activity. It entails disconnecting the patient from mechanical ventilation to raise the CO2 partial pressure and lower the pH. Occasionally, the AT is aborted because of safety concerns, such as hypoxemia and hemodynamic instability, to prevent worsening conditions. However, the exact oxygen partial pressure level needed before commencing AT, indicating an inability to tolerate the test, is still uncertain. This study seeks to determine pre-AT oxygen levels linked with a heightened risk of test failure. Methods We conducted a retrospective cohort study involving patients suspected of having brain death at the Tel Aviv Medical Center from 2010 to 2022. The primary outcome was defined as an arterial partial O2 pressure (PaO2) level of 60 mmHg or lower at the conclusion of the AT. This threshold is significant because it marks the point at which the saturation curve deflects, potentially leading to rapid deterioration in the patient’s oxygen saturation. Results Among the 70 patients who underwent AT, 7 patients met the primary diagnostic criteria. Patients with a PaO2 ≤ 60 mmHg at the conclusion of the AT exhibited a significantly lower initial median PaO2 of 243.7 mmHg compared with those with higher pre-AT PaO2 levels of 374.8 mmHg (interquartile range 104.65–307.00 and interquartile range 267.8–444.9 respectively, P value = 0.0041). Pre-AT PaO2 levels demonstrated good discriminatory ability for low PaO2 levels according to the receiver operating characteristic (ROC) curve, with an area under the curve of 0.76 (95% confidence interval 0.52–0.99). Conclusions PaO2 values at the conclusion of the AT are closely associated with PaO2 values at the beginning of the test. Establishing a cutoff value of approximately 300 mmHg PaO2 at the onset of AT may assist in avoiding saturation drops below 90%.

Thermal corrosion behavior of Inconel 693, Hastelloy N and 310S in ceramic waste forming reactions

The thermal corrosion behavior of Inconel 693, Hastelloy N, and 310S was investigated in the reaction environment of ceramic waste forming reactions. Due to the difference in Cr content and the effect of chlorides, the high Cr Inconel 693 and 310S alloys exhibit selective corrosion by Cr, while the low Cr Hastelloy N exhibits uniform corrosion and the volatilization of MoO3 caused high dimensional losses. The different behavior of the alloys in different corrosive environmental regions is also discussed. In the sintered product region, due to the encapsulation of the sintered product and the corrosion inhibiting role played by O2−, Hastelloy N alloy and 310S alloy experienced milder corrosion compared to alloy in the atmosphere region. And in the atmosphere region, the more abundant gas supply and the open environment caused Hastelloy N alloy and 310S alloy to experience more severe erosion. However, for Inconel 693 alloy, it formed a continuous spinel phase layer containing FeCr2O4 due to the higher partial pressure of O2 in the atmosphere region, resulting in more slight corrosion compared to the sintered product region.

Insoluble HIFa protein aggregates by cadmium disrupt hypoxia-prolyl hydroxylase (PHD)-hypoxia inducible factor (HIFa) signaling in renal epithelial (NRK-52E) and interstitial (FAIK3-5) cells.

The kidney is the main organ that senses changes in systemic O2 pressure by hypoxia-PHD-HIFa (HPH) signaling, resulting in adaptive target gene activation, including erythropoietin (EPO). The non-essential transition metal cadmium (Cd) is nephrotoxic and disrupts the renal HPH pathway, which may promote Cd-associated chronic renal disease (CKD). A deeper molecular understanding of Cd interference with renal HPH signaling is missing, and no data with renal cell lines are available. In rat kidney NRK-52E cells, which model the proximal tubule, and murine fibroblastoid atypical interstitial kidney (FAIK3-5) cells, which mimic renal EPO-producing cells, the chemical hypoxia mimetic dimethyloxalylglycine (DMOG; 1 mmol/l) or hypoxia (1% O2) activated HPH signaling. Cd2+ (2.5-20 µmol/l for ≤ 24h) preferentially induced necrosis (trypan blue uptake) of FAIK3-5 cells at high Cd whereas NRK-52E cells specially developed apoptosis (PARP-1 cleavage) at all Cd concentrations. Cd (12.5 µmol/l) abolished HIFa stabilization and prevented upregulation of target genes (quantitative real-time polymerase chain reaction and immunoblotting) induced by DMOG or hypoxia in both cell lines, which was caused by the formation of insoluble HIFa aggregates. Strikingly, hypoxic preconditioning (1% O2 for 18h) reduced apoptosis of FAIK3-5 and NRK-52E cells at low Cd concentrations and decreased insoluble HIFa proteins. Hence, drugs mimicking hypoxic preconditioning could reduce CKD induced by chronic low Cd exposure.

Treatment of Anaerobic Digester Liquids via Membrane Biofilm Reactors: Simultaneous Aerobic Methanotrophy and Nitrogen Removal.

Anaerobic digestion (AD) produces useful biogas and waste streams with high levels of dissolved methane (CH4) and ammonium (NH4+), among other nutrients. Membrane biofilm reactors (MBfRs), which support dissolved methane oxidation in the same reactor as simultaneous nitrification and denitrification (ME-SND), are a potential bubble-less treatment method. Here, we demonstrate ME-SND taking place in single-stage, AD digestate liquid-fed MBfRs, where oxygen (O2) and supplemental CH4 were delivered via pressurized membranes. The effects of two O2 pressures, leading to different O2 fluxes, on CH4 and N removal were examined. MBfRs achieved up to 98% and 67% CH4 and N removal efficiencies, respectively. The maximum N removal rates ranged from 57 to 94 mg N L-1 d-1, with higher overall rates observed in reactors with lower O2 pressures. The higher-O2-flux condition showed NO2- as a partial nitrification endpoint, with a lower total N removal rate due to low N2 gas production compared to lower-O2-pressure reactors, which favored complete nitrification and denitrification. Membrane biofilm 16S rRNA amplicon sequencing showed an abundance of aerobic methanotrophs (especially Methylobacter, Methylomonas, and Methylotenera) and enrichment of nitrifiers (especially Nitrosomonas and Nitrospira) and anammox bacteria (especially Ca. Annamoxoglobus and Ca. Brocadia) in high-O2 and low-O2 reactors, respectively. Supplementation of the influent with nitrite supported evidence that anammox bacteria in the low-O2 condition were nitrite-limited. This work highlights coupling of aerobic methanotrophy and nitrogen removal in AD digestate-fed reactors, demonstrating the potential application of ME-SND in MBfRs for the treatment of AD's residual liquids and wastewater. Sensor-based tuning of membrane O2 pressure holds promise for the optimization of bubble-less treatment of excess CH4 and NH4+ in wastewater.

Reduced diffusional limitations in carnation stems facilitate higher photosynthetic rates and reduced photorespiratory losses compared with leaves.

Green stem photosynthesis has been shown to be relatively inefficient but can occasionally contribute significantly to the carbon budget of desert plants. Although the possession of green photosynthetic stems is a common trait, little is known about their photosynthetic characteristics in non-desert species. Dianthus caryophyllus is a semi-woody species with prominent green stems, which show similar photosynthetic anatomy with leaves. In the present study, we used a combination of gas exchange and chlorophyll fluorescence measurements, some of which were taken under varying O2 and CO2 partial pressures, to investigate whether the apparent anatomical similarities between the species' leaves and stems translate into similar photosynthetic physiology and capacity for CO2 assimilation. Both organs displayed high photosynthetic electron transport rates (ETR) and similar values of steady-state non-photochemical quenching (NPQ), albeit leaves could attain them faster. The analysis of OJIP transients showed that the quantum efficiencies and energy fluxes along the photosynthetic electron transport chain are largely similar between leaves and stems. Stems displayed higher total conductance to CO2 diffusion, similar biochemical properties, significantly higher photosynthetic rates and lower water use efficiency than leaves. Leaf ETR was more sensitive to sub-ambient O2 and super-ambient CO2 partial pressures, while leaves also displayed a higher relative rate of Rubisco oxygenation. We conclude that the highly responsive NPQ and the enhanced photorespiration and WUE in leaves represent photoprotective and water-conserving adaptations to the high incident light intensities they experience naturally, at the expense of higher CO2 assimilation rates, which the vertically orientated stems can readily attain.

Amphiphilic Janus Particles for Aerobic Alcohol Oxidation in Oil Foams.

Amphiphilic Janus silica particles, tunable with oleophobic-oleophilic properties and low fluorine content (8 wt % F), exhibited prominent foamability for a variety of aromatic alcohols at low particle concentrations (<1 wt %) compared to randomly functionalized silica particles. When selectively loaded with Pd nanoparticles on the oleophilic hemisphere, the particles displayed more than a 2-fold increase in catalytic activity for the aerobic oxidation of benzyl alcohol compared to nonfoam bulk catalysis under ambient O2 pressure. The particles were conveniently recycled with high foamability and catalytic activity maintained for at least five consecutive runs.

Ethnicity and Observed Oxygen Saturations, Fraction of Inspired Oxygen, and Clinical Outcomes: A Post-Hoc Analysis of the Oxy-PICU Trial of Conservative Oxygenation.

A conservative oxygenation strategy, targeting peripheral oxygen saturations (Sp o2 ) between 88% and 92% in mechanically ventilated children in PICU, was associated with a shorter duration of organ support and greater survival compared with Sp o2 greater than 94% in our recent Oxy-PICU trial. Sp o2 monitors may overestimate arterial oxygen saturation (Sa o2 ) in patients with higher levels of skin pigmentation compared with those with less skin pigmentation. We investigated if ethnicity was associated with changes in distributions of Sp o2 and F io2 and outcome. Post-hoc analysis of a pragmatic, open-label, multicenter randomized controlled trial. Fifteen PICUs across the United Kingdom and Scotland. Children aged 38 weeks corrected gestational age to 15 years accepted to a participating PICU as an unplanned admission and receiving invasive mechanical ventilation with supplemental oxygen for abnormal gas exchange. Hierarchical regression models for Sp o2 and F io2 , and ordinal models for the primary trial outcome of a composite of the duration of organ support at 30 days and death, were used to examine the effects of ethnicity, accounting for baseline Sp o2 , F io2 , and mean airway pressure and trial allocation. Ethnicity data were available for 1577 of 1986 eligible children, 1408 (89.3%) of which were White, Asian, or Black. Sp o2 and F io2 distributions did not vary according to Black or Asian ethnicity compared with White children. The trial primary outcome measure also did not vary significantly with ethnicity. The point estimate for the treatment effect of conservative oxygenation in Black children was 0.64 (95% CI, 0.33-1.25) compared with 0.84 (0.68-1.04) in the overall trial population. These data do not suggest that the association between improved outcomes and conservative oxygenation strategy in mechanically ventilated children in PICU is modified by ethnicity.

Effect of caspase inhibitors on hemodynamics and inflammatory factors in ARDS model rats

To study the effects of caspase inhibitors on hemodynamics and inflammatory factors in acute respiratory distress syndrome (ARDS) model rats. Sixty healthy male Wistar rats were randomly divided into three groups, namely, the control group, ARDS group and ARDS + Caspase inhibitor group, with 20 rats in each group. The control group was intraperitoneally injected with 2 mL/kg saline, and the ARDS model group was established by intraperitoneally injecting 4 mg/kg Lipopolysaccharide (LPS), ARDS + Caspase inhibitor group was adminstered 20 mg/kg caspase inhibitor after intraperitoneal LPS injection. Changes in pulmonary arterial pressure (PAP) and mean arterial pressure (MAP) at 6 and 12 h before and after administration were recorded. Moreover, arterial blood gas was evaluated with a blood gas analyzer and changes in the partial pressure of O2 (PaO2), partial pressure of CO2 (PaCO2), partial pressure of O2/fraction of inspired O2 (PaO2/FiO2) were evaluated. In addition, the lung wet/dry weight (W/D) ratio and inflammatory factor levels in lung tissue were determined. Finally, pathological sections were used to determine the pulmonary artery media thickness (MT), MT percentage (MT%), and the degree of muscle vascularization. The pulmonary arterial pressure of rats was determined at several time points. Compared with the control group, the model group had a significantly increased pulmonary arterial pressure at each time point (P < 0.01), and the mean arterial pressure significantly increased at 6 h (P < 0.05). Compared with that of rats in the model group, the pulmonary arterial pressure of rats in drug administration group was significantly reduced at each time point after administration (P < 0.01), and the mean arterial pressure was significantly reduced at 6 h (P < 0.05). The arterial blood gas analysis showed that compared with those in the control group, PaO2, PaCO2 and PaO2/FiO2 in the model group were significantly reduced (P < 0.01), and PaO2, PaCO2 and PaO2/FiO2 were significantly increased after caspase inhibitor treatment (P < 0.05 or 0.01). The levels of the inflammatory mediators tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in the model group were significantly higher than those in the control group (P < 0.01), and they were significantly decreased after caspase inhibitor treatment (P < 0.01). In the model group, pulmonary artery MT, MT% and the degree of muscle vascularization were significantly increased (P < 0.05 or 0.01), and pulmonary artery MT and the degree of muscle vascularization were significantly reduced after caspase inhibitor treatment (P < 0.05 or 0.01). Apoptosis Repressor with a Caspase Recuitment Domain (ARC) can alleviate the occurrence and development of pulmonary hypertension (PH) by affecting hemodynamics and reducing inflammation.

Multi objective optimization using artificial neural network to maximize the power output of PEMFCs

ABSTRACT Designing a PEM fuel cell model is exceedingly challenging because of its multivariate in nature. Optimization is required to achieve highest operating condition. Neural Network Model is one of the possible methods to solve complex problems. The polarisation curve of a PEMFC (Proton Exchange Membrane Fuel Cell) is investigated in this paper in relation to the effects of seven parameters, including temperature, relative humidity in the cathode, relative humidity in the anode, anode stoichiometry, cathode stoichiometry, partial pressure of H2, and partial pressure of O2, using an ANN (artificial neural network) model. Where model geometric parameters i.e. Channel width, Channel depth, Channel length, Rib width, Cell width, GDL thickness, CL thickness, Membrane thickness of PEMFC was constant. Initially single Objective Function (Output Power) is predicted. The research presented here makes predictions about a PEMFC stack's electrical performance under multiple operating conditions. Mathematical model was further verified using laboratory data. Co-efficient of Determination (R2), Mean Square Error (MSE), and Mean Absolute Error (MAE) was determined using the fuel cell stack voltage model and stack power model. The model results show the possibility of using ANN in the implementation of such models to predict the PEMFC system's steady-state behaviour.

Relative Severity of Human Performance Decrements Recorded in Rapid vs. Gradual Decompression.

INTRODUCTION: Cabin decompression presents a threat in high-altitude-capable aircraft. A chamber study was performed to compare effects of rapid (RD) vs. gradual decompression and gauge impairment at altitude with and without hypoxia, as well as to assess recovery.METHODS: There were 12 participants who completed RD (1 s) and Gradual (3 min 12 s) ascents from 2743-7620 m (9000-25000 ft) altitude pressures while breathing air or 100% O₂. Physiological indices included oxygen saturation (SPo₂), heart rate (HR), respiration, end tidal O₂ and CO₂ partial pressures, and electroencephalography (EEG). Cognition was evaluated using SYNWIN, which combines memory, arithmetic, visual, and auditory tasks. The study incorporated ascent rate (RD, gradual), breathing gas (air, 100% O₂) and epoch (ground-level, pre-breathe, ascent-altitude, recovery) as factors.RESULTS: Physiological effects in hypoxic "air" ascents included decreased SPo₂ and end tidal O₂ and CO₂ partial pressures (hypocapnia), with elevated HR and minute ventilation (<mml:math id="im1" display="inline"><mml:mrow><mml:mover><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math>E); SPo₂ and HR effects were greater after RD (-7.3% lower and +10.0 bpm higher, respectively). HR and <mml:math id="im2" display="inline"><mml:mrow><mml:mover><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math>E decreased during recovery. SYNWIN performance declined during ascent in air, with key metrics, including composite score, falling further (-75% vs. -50%) after RD. Broad cognitive impairment was not recorded on 100% O₂, nor in recovery. EEG signals showed increased slow-wave activity during hypoxia.DISCUSSION: In hypoxic exposures, RD impaired performance more than gradual ascent. Hypobaria did not comprehensively impair performance without hypoxia. Lingering impairment was not observed during recovery, but HR and <mml:math id="im3" display="inline"><mml:mrow><mml:mover><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math>E metrics suggested compensatory slowing following altitude stress. Participants' cognitive strategy shifted as hypoxia progressed, with efficiency giving way to "satisficing," redistributing effort to easier tasks.Beer J, Mojica AJ, Blacker KJ, Dart TS, Morse BG, Sherman PM. Relative severity of human performance decrements recorded in rapid vs. gradual decompression. Aerosp Med Hum Perform. 2024; 95(7):353-366.

Discharge mode and particle transport in radio frequency capacitively coupled Ar/O2 plasma discharges

Abstract Simulations are conducted on capacitively coupled Ar/O2 mixed gas discharges employing a one-dimensional fluid coupled with an electron Monte Carlo (MC) model. The research explores the impact of different O2 ratio and pressures on the discharge characteristics of Ar/O2 plasma. At a fixed Ar/O2 gas ratio, with the increasing pressure, higher ion densities, as well as a slight increase in electron density in the bulk region can be observed. The discharge remains dominated by the drift–ambipolar (DA) mode, and the flux of O(3P) at the electrode increases with the increasing pressure due to higher background gas density, while the fluxes of O(1D) and Ar* decrease due to the pronounced loss rate. With the increasing proportion of O2, a change in the dominant discharge mode from α mode to DA mode can be detected, and the O2-associated charged particle densities are significantly increased. However, Ar+ density shows a trend of increasing and then decreasing, while for neutral fluxes at the electrode, Ar* flux decreases, and O(3P) flux increases with the reduced Ar gas proportion, while trends in O(1D) flux show slight differences. The evolution of the densities of the charged particle and the neutral fluxes under different discharge parameters are discussed in detail using the ionization characteristics as well as the transport properties. Hopefully, more comprehensive understanding of Ar/O2 discharge characteristics in this work will provide a valuable reference for the industry.

Unraveling oxygen-driven surface segregation dynamics in platinum-gold alloys

In this study we use high-energy resolution and fast X-ray Photoelectron Spectroscopy (XPS) measurements combined with Density Functional Theory (DFT) calculations to investigate the interplay between surface segregation and bulk migration of Pt atoms on Au(111) in an oxygen environment. We demonstrate that the segregation of Pt atoms is significantly influenced by the oxygen partial pressure and identify a range of O2 pressure where PtAu surface alloy formation is inhibited while promoting the formation of Au oxide. These findings are essential to understand the compositional changes in the bimetallic surface alloy, which could potentially lead to modifying the catalytic properties of PtAu up to catalyst deactivation. Our results offer a strategy to control Pt surface coverage on Au(111), a quantity that is of paramount relevance given the applications of PtAu alloys as catalysts in reactions such as the oxygen reduction reaction or the oxidation of methanol and carbon monoxide. Additionally, our findings indicate a method for controlling the composition and properties of the surface of PtAu catalysts through adjustments made during the formation of the PtAu alloy.

Accelerated oxidation of epoxy thermosets with increased O2 pressure

Polymer oxidation is usually accelerated with temperature, which is therefore applied in nearly every experimental approach dealing with predictive materials aging. Because of this simple approach, we may tend to neglect that the effective concentration of oxygen also acts as a rate multiplier for oxidation. Increasing the oxygen partial pressure in an aging environment accelerates oxidation, and while there is often a near proportional increase initially, the effect of additional oxygen usually transitions to a saturation level at some elevated pressure. This has been theoretically described in the general autoxidation scheme and is well recognized. However, for many materials the exact rate behavior under moderately increased oxygen concentration remains to be established. We therefore review epoxy oxidation and offer a broader overview of its behavior under increased O2 partial pressure. Experimental data are given for a few thermoset materials demonstrating their rate behavior under O2 partial pressure up to 4 atm, meaning approximately 20 times more than under standard atmospheric conditions. Confirmative evidence suggests that epoxy materials will reach saturation oxidation rates only at significantly higher O2 partial pressure. In such a high-pressure regime it is theoretically possible to not only accelerate oxidation, but to transition into a condition where O2 diffusion can be increased without further accelerating the oxidation rate. This can reduce diffusion limited oxidation effects under specific accelerated aging conditions as a combination of temperature and O2 partial pressure.

Oxygenation and Carbon Dioxide Rebreathing of a Well-fitting Non-rebreathing EcoLite™ Mask with a Reservoir: A Single-center Prospective Observational Study in Healthy Volunteers.

The fitting of oxygen mask affects the performance of it such as oxygenation or CO₂ elimination. The intersurgical EcoLite™ adult high-concentration oxygen mask (EcoLite with a reservoir, Intersurgical, UK) was developed to give well-fitting. The purpose of this study is to evaluate the performance of EcoLite with a reservoir compared to the conventional mask. Ten healthy volunteers were included in this study. EcoLite with a reservoir and conventional mask were given to patients at different oxygen flow rates (5, 8, 10, 12, and 15 L/min). Fraction of inspiratory O₂ (FIO₂) and partial pressure of inspiratory CO₂ (PICO₂) were measured by a sampling tube at the middle pharynx inserted via nose. The EcoLite with a reservoir had a significantly higher FIO₂ than the control reservoir mask. However, the PICO₂ was significantly higher in the EcoLite with a reservoir than in the control reservoir mask, especially when the oxygen flow rate was low. The EcoLite with a reservoir provided improved oxygenation and a better fit than the conventional reservoir masks in healthy volunteers. However, the EcoLite with a reservoir might cause higher CO₂ rebreathing at low oxygen flow rates.

Influence of hypercapnia and hypercapnic hypoxia on the heart rate response to apnea.

We aimed to determine the relative contribution of hypercapnia and hypoxia to the bradycardic response to apneas. We hypothesized that apneas with hypercapnia would cause greater bradycardia than normoxia, similar to the response seen with hypoxia, and that apneas with hypercapnic hypoxia would induce greater bradycardia than hypoxia or hypercapnia alone. Twenty-six healthy participants (12 females; 23 ± 2 years; BMI 24 ± 3 kg/m2) underwent three gas challenges: hypercapnia (+5 torr end tidal partial pressure of CO2 [PETCO2]), hypoxia (50 torr end tidal partial pressure of O2 [PETO2]), and hypercapnic hypoxia (combined hypercapnia and hypoxia), with each condition interspersed with normocapnic normoxia. Heart rate and rhythm, blood pressure, PETCO2, PETO2, and oxygen saturation were measured continuously. Hypercapnic hypoxic apneas induced larger bradycardia (-19 ± 16 bpm) than normocapnic normoxic apneas (-11 ± 15 bpm; p = 0.002), but had a comparable response to hypoxic (-19 ± 15 bpm; p = 0.999) and hypercapnic apneas (-14 ± 14 bpm; p = 0.059). Hypercapnic apneas were not different from normocapnic normoxic apneas (p = 0.134). After removal of the normocapnic normoxic heart rate response, the change in heart rate during hypercapnic hypoxia (-11 ± 16 bpm) was similar to the summed change during hypercapnia+hypoxia (-9 ± 10 bpm; p = 0.485). Only hypoxia contributed to this bradycardic response. Under apneic conditions, the cardiac response is driven by hypoxia.

Soft-templating synthesis of mesoporous MnSiOx composites as catalytic supports for Pd nanoparticles towards solvent-free oxidation of benzyl alcohol under atmospheric pressure O2

Solvent-free and liquid-phase selective oxidation of aromatic alcohols using O2 as an oxidant is a green strategy for the synthesis of aromatic aldehydes and other carbonyl compounds. Wherein, the design and preparation of heterogeneous catalysts with high activity and selectivity is a hot topic in this process. Herein, a series of manganese oxide-silica (MnSiOx) composites were synthesized using cetyltrimethylammonium bromide as a soft template. During the preparation process, the amounts of tetraethyl orthosilicate and ammonia and the calcination temperature significantly affected the textural properties and Mn cation distributions of MnSiOx. The MnSiOx composites were then employed as catalysts for Pd nanoparticles. In the solvent-free and atmospheric conditions, Pd/MnSiOx materials showed high catalytic conversions of benzyl alcohol (BZA), and the catalytic activity thereof is related to the fractions of Pd0 and Mn3+. As the reaction time and temperature are 4 h and 90 °C, the conversion of BZA (feeding dosage: 4 mL) and the selectivity of benzaldehyde are 64.8 % and 94.9 %, respectively. The catalyst can be reused at least five times without any significant loss of activity. Furthermore, the correlation between physiochemical properties and catalytic activity of Pd/MnSiOx was analyzed.