Ambient Oxygen Concentration Research Articles

Reproduction of I‐type cosmic spherules and characterization in an Fe‐Ni‐O system

AbstractThe chemical composition and texture of cosmic spherules are influenced by atmospheric conditions and the characteristics of their parent interplanetary particles. The objective of this study was to reproduce I‐type cosmic spherules, which consist mainly of Fe oxide and Fe‐Ni metal, and compare their textural characteristics with those of natural I‐type cosmic spherules. Thus, a series of rapid heating and quenching experiments were performed on free falling iron meteorite powders obtained from Canyon Diablo, in the United States. The experiments were conducted using a high‐temperature furnace with controlled gas flow rates at oxygen fugacities of FMQ + 2.4, FMQ, and FMQ − 2.5 log unit. The resulting Fe‐Ni metal and oxide phases showed the nonequilibrium state of the melted spherules formed during quenching. Two types of magnetite crystals in different orientations were found in iron oxide. As temperatures decreased, the molten metal was oxidized to form immiscible molten iron oxide that then covered the former. As the oxide melt increased at the expense of metal, magnetite began to crystallize from the iron oxide melt, as the liquidus phase, either on the surface or within the melt phase. The characteristics of the run products obtained under different oxygen fugacities were similar to those of natural I‐type cosmic spherules, which have textures and compositions that may contain information regarding the oxygen content of the upper atmosphere. Our study suggests that CO2‐bearing molecules in the atmosphere could form iron oxide with a texture similar to natural I‐type cosmic spherules. During this process, rapid crystallization of magnetite plays an important role in texture formation in disequilibrium states.

One-for-All Nanoplatform for Synergistic Mild Cascade-Potentiated Ultrasound Therapy Induced with Targeting Imaging-Guided Photothermal Therapy.

Ameliorated therapy based on the tumor microenvironment is becoming increasingly popular, yet only a few methods have achieved wide recognition. Herein, targeting multifunctional hydrophilic nanomicelles, AgBiS2@DSPE-PEG2000-FA (ABS-FA), were obtained and employed for tumor treatment. In a cascade amplification mode, ABS-FA exhibited favorable properties of actively enhancing computed tomography/infrared (CT/IR) imaging and gently relieving ambient oxygen concentration by cooperative photothermal and sonodynamic therapy. Compared with traditional Bi2S3 nanoparticles, the CT imaging capability of the probe was augmented (43.21%), and the photothermal conversion efficiency was increased (33.1%). Furthermore, remarkable ultrasonic dynamic features of ABS-FA were observed, with increased generation of reactive oxygen species (24.3%) being obtained compared to Ce6, a commonly used sonosensitizer. Furthermore, ABS-FA exhibited obvious inhibitory effects on HeLa cell migration at 6 μg/mL, which to some extent, demonstrated its suppressive effect on tumor growth. A lower dose, laser and ultrasonic power, and shorter processing time endowed ABS-FA with excellent photothermal and sonodynamic effects. By mild cascade mode, the hypoxic condition of the tumor site was largely improved, and a suitable oxygen-rich environment was provided, thereby endowing ABS-FA with a superior synergistically enhanced treatment effect compared with the single-mode approach, which ultimately realized the purpose of "one injection, multiple treatment". Moreover, our data showed that ABS-FA was given with a biological safety profile while harnessing in vivo. Taken together, as a synergistically enhanced medical diagnosis and treatment method, the one-for-all nanoplatform will pave a new avenue for further clinical applications.

The influence of oxygen deprivation and donor age on the effect of statins on human mesenchymal stromal cells

To date, no study evaluated the effect of oxygen deprivation together with statins pretreatment on human mesenchymal stromal cells (MSCs). The aim of our study was to establish the influence of atorvastatin and rosuvastatin on MSC proliferation and cytotoxicity in different oxygenic conditions. Human MSCs isolated from the bone marrow (n = 12) were incubated with statins. The proliferation rate and cytotoxic effect were evaluated in normoxic (21 %O2) and hypoxic (2%O2) conditions, also in relation to donor age. The treatment with atorvastatin was associated with significantly higher proliferation rate compared to control, both in hypoxic (19 % median increase) and normoxic conditions (20 %), p = 0.02 and p = 0.04, respectively. Atorvastatin had no significant cytotoxic effect on MSCs. Treatment with rosuvastatin in hypoxia resulted in significantly higher proliferation rate (15 %, p = 0.02) comparing to control with no significant cytotoxicity. In atmospheric oxygen concentration, rosuvastatin was associated with no significant change in proliferation and higher cytotoxicity compared to untreated control (p = 0.042 and p = 0.015, for 0.04 μM and 1 μM solutions respectively). There were no differences in the effect of statins on MSC from young donors vs. aged donors. These results suggest that statins could support MSC-based therapy of acute myocardial infarction.

Metabolic Activity of Human Embryos after Thawing Differs in Atmosphere with Different Oxygen Concentrations.

The vitrification of human embryos is more and more frequently being utilized as a method of assisted reproduction. For this technique, gentle treatment of the embryos after thawing is crucial. In this study, the balance of amino acids released to/consumed from the cultivation media surrounding the warmed embryos was observed in the context of a cultivation environment, which was with the atmospheric oxygen concentration ≈20% or with a regulated oxygen level—hysiological (5%). It is the first time that total amino acid turnover in human embryos after their freezing at post compaction stages has been evaluated. During this study, progressive embryos (developed to blastocyst stage) and stagnant embryos (without developmental progression) were analyzed. It was observed that the embryos cultivated in conditions of physiological oxygen levels (5% oxygen) showed a significantly lower consumption of amino acids from the cultivation media. Progressively developing embryos also had significantly lower total amino acid turnovers (consumption and production of amino acids) when cultured in conditions with physiological oxygen levels. Based on these results it seems that a cultivation environment with a reduced oxygen concentration decreases the risk of degenerative changes in the embryos after thawing. Therefore, the cultivation of thawed embryos in an environment with physiological oxygen levels may preclude embryonal stagnation, and can support the further development of human embryos after their thawing.

The influence of oxygen concentration during embryo culture on obstetric and neonatal outcomes: a secondary analysis of a randomized controlled trial.

Does oxygen concentration during 3-day embryo culture affect obstetric and neonatal outcomes? Oxygen concentration during 3-day embryo culture does not seem to affect the obstetric and neonatal outcomes measured. Atmospheric oxygen appears to be harmful during extended embryo culture. Embryo culture conditions might therefore be a potential risk factor for subsequent fetal development and the health of future children. No data are available concerning the obstetrics and neonatal outcomes after Day 3 transfer of embryos cultured under reduced and atmospheric oxygen tensions. A secondary analysis of a previous randomized controlled trial assessing clinical pregnancy outcomes was carried out. This analysis included 1125 consecutive oocyte donation cycles utilizing ICSI or IVF and Day 3 embryo transfers between November 2009 and April 2012. The whole cohort of donated oocytes from patients who agreed to participate in the study were randomly allocated (1:1 ratio) to a reduced O2 tension group (6% O2) or an air-exposed group (20% O2) based on a computer-generated randomization list. Fresh and vitrified oocytes were used for oocyte donation. Only those pregnancies with a live birth at or beyond 24 weeks of gestation were included. Day 3 embryos were cultured in an atmosphere of 5.5% CO2, 6% O2, 88.5% N2 versus a dual gas system in air. From the eligible 1125 cycles, 564 were allocated to the 6% O2 group and 561 cycles to the 20% O2 group. However, 50 and 62 cycles did not reach embryo transfer in the 6% and 20% O2 groups, respectively. No differences were found between 6% O2 and atmospheric O2 tension in the number of livebirths per embryo transfer (mean ± SD, 0.5 ± 0.7 versus 0.5 ± 0.7), pregnancy complications or neonatal outcomes. Both groups (6% and atmospheric O2) had similar single and twin delivery rates (40.8% versus 38.1% and 10.7% versus 12.3%, respectively). Preterm delivery rates and very preterm delivery rates (10.80% versus 13.24% and 1.25% versus 2.94%, respectively), birthweight (3229 ± 561 g versus 3154 ± 731 g), low birthweight (2.92% versus 2.45%), birth height (50.18 ± 2.41 cm versus 49.7 ± 3.59 cm), head circumference (34.16 ± 1.87 cm versus 33.09 ± 1.85 cm) and 1 min Apgar scores (8.96 ± 0.87 versus 8.89 ± 0.96) were also similar between 6% and atmospheric O2 groups, respectively. The number of liveborns finally analyzed is still small and not all obstetric and neonatal variables could be evaluated. Furthermore, a small proportion of the obstetric and neonatal data was obtained through a questionnaire filled out by the patients themselves. One reason for the lack of effect of oxygen concentration on pregnancy outcome could be the absence of trophectoderm cells at cleavage stage, which may make Day 3 embryos less susceptible to hypoxic conditions. Nowadays many IVF laboratories use a more physiological oxygen concentration for embryo culture. However, the benefits of using low oxygen concentration on both laboratory and clinical outcomes during embryo culture are still under debate. Furthermore, long-term studies investigating the effect of using atmospheric O2 are also needed. Gathering these type of clinical data is indeed, quite relevant from the safety perspective. The present data show that, at least in egg donation cycles undergoing Day 3 embryo transfers, culturing embryos under atmospheric oxygen concentration seems not to affect perinatal outcomes. The present project was supported by the R + D program of the Regional Valencian Government, Spain (IMPIVA IMDTF/2011/214). The authors declare that they have no conflict of interest with respect to the content of this manuscript. NCT01532193.

Effects of relative humidity and elevated oxygen concentrations on egg‐hatching success of American alligator, Alligator mississippiensis

AbstractTwo experiments were conducted to determine effects of relative humidity (RH) and atmospheric oxygen concentration on hatching success of artificially incubated alligator eggs. In one study, 216 eggs were subjected to one of four treatments involving two levels of RH (80 or 93% RH) and two atmospheric oxygen concentrations (21 or 28% O2). Hatching success of eggs in the 80/21 and 80/28 treatments, combined, totaled only 1.8% (one hatchling produced in each treatment), while hatching success of eggs in the 93/21 and 93/28 treatments averaged 83.3% in both groups, with no significant difference (p > .05) between treatments. In a second study, 300 alligator eggs were incubated at 93% RH and one of three atmospheric oxygen concentrations (21, 25, or 28% O2). Hatching success averaged 66.3, 56.3, and 62.5% in the 21, 25, and 28% oxygen treatments, respectively, with no significant difference (p > .05) among treatments. Results of the two experiments indicated that 80% RH reduced egg‐hatching success to nearly zero, regardless of atmospheric oxygen concentration, while 93% RH produced good hatching success. Elevated atmospheric oxygen concentrations up to one‐third higher than ambient air had no effect on egg‐hatching success under the conditions of either study.

Downward burning of PMMA cylinders: The effect of pressure and oxygen

Better understanding the burning behavior of solid fuels is necessary in order to be able to estimate more accurately the fire risk that they might represent. The burning rate is an essential component when assessing the growth of a fire, since it determines the heat released during the fuel burning. The objective of the present work is to study the effect of ambient pressure and oxygen concentration on the burning of cylindrical samples of polymethyl-methacrylate (PMMA) in opposed flow flame spread conditions. Experiments are conducted using pressures ranging between 100 and 30 kPa and oxygen concentrations between 19% and 23%, with a forced flow velocity of 100 mm/s. The experimental conditions reflect environments potentially encountered in future spacecraft cabins. The data collected show that during downward opposed flame spread the surface regression rate, and consequently the mass burning rate, decreases with decreasing ambient pressure and increases with decreasing oxygen concentration. The data presented is correlated with a simplified model to estimate the surface regression rate based on the mixed heat convection coefficient and the B number. Model predictions are made based on fuel properties as well as the relevant environmental conditions. The predictions of the model agree well capturing the effect of ambient pressure and oxygen concentration. The correlations provide information about the variations in the burning rate in environments with variable pressure and oxygen concentration, providing guidance for potential for fire safety testing and design in different ambient conditions.

Spray combustion and soot formation characteristics of the acetone-butanol-ethanol/diesel blends under diesel engine-relevant conditions

The acetone–butanol–ethanol (ABE) is considered as a promising biofuel to partially substitute the diesel fuel. In this paper, the optical constant volume combustion chamber was used to record the chamber pressure, and measured the soot mass and distribution for ABE and diesel blends. Then, the CFD KIVA-3V code coupled with the CANTERA was used to simulate the formation and oxidation processes of soot during the spray combustion. In addition, the CFD simulation cases for pure diesel and ABE20 were comprehensively validated against the experimental data under different initial ambient oxygen concentrations. Finally, a series of CFD cases were performed to investigate the effects of different ABE/diesel blends (up to 50% by volume), different initial ambient temperatures (mimic the traditional combustion and low temperature combustion modes) and oxygen concentrations (represent the free, low and high EGR conditions) on the combustion and soot formation characteristics under the diesel engine-relevant conditions. The results indicated that with the increase of ABE ratio in the ABE/diesel blends, the combustion pressure and heat release rate decreased and the combustion phase was delayed, the combustion temperature distribution was more uniform, while the flame lift-off length was increased gradually. In addition, the soot mass was decreased and its corresponding generation rate was also decreased with increasing the ABE ratio in blends. Furthermore, high concentration of soot mainly distributed in the temperature range of 1800–2000 K and the equivalent ratio range of 1.8–2.0.

The Role of Reversible Protein Phosphorylation in Regulation of the Mitochondrial Electron Transport System During Hypoxia and Reoxygenation Stress in Marine Bivalves

Fluctuations in the ambient oxygen concentrations represent a major stressor for aerobic organisms causing ATP deficiency during hypoxia and excessive production of reactive oxygen species during reoxygenation. Modulation of the mitochondrial electron transport system activity was proposed as a major mechanism involved in both the mitochondrial injury and adaptive response, but the mechanisms of ETS regulation during hypoxia/reoxygenation (H/R) stress remain poorly understood in hypoxia-tolerant organisms. To address this gap, we focused on the effects of H/R on activities of the mitochondrial Complexes I and IV in hypoxia-tolerant marine bivalves, the blue mussel Mytilus edulis, the Arctic quahog Arctica islandica and the Pacific oyster Crassostrea gigas, exposing them for one or six days to extreme hypoxia (<0.1% O2) followed by one hour of reoxygenation. We used a combination of bioinformatics analysis, biochemical and molecular studies to examine the potential role of the reversible protein phosphorylation in regulation of the Complex I and IV activities and in the mitochondrial responses to H/R stress. Our results showed a strong species-specific modulation of two important kinases, the serine/threonine protein kinase A (PKA) and protein kinase C (PKC) by H/R stress in the studied bivalves. The mitochondrial Complexes I and IV emerged as important targets for modulation by H/R stress, mediated in part through reversible phosphorylation by PKA and PKC. The effects of the reversible phosphorylation on the enzyme activities were species- and condition-specific. In mussels and quahogs, phosphorylation by PKA and PKC led to a strong increase in activity of Complexes I and IV. In oysters, Complexes I and IV were insensitive to PKA and PKC activation except after prolonged hypoxia and reoxygenation when elevated sensitivity to PKA and PKC activation indicated a change in the configuration and/or isoform composition of these enzymes. Non-site-specific dephosphorylation strongly suppressed the activity of Complex I and IV in all three studied species. Because in mammals PKA and PKC can have either damaging or protective effects depending on the timing of activation, our findings underscore the need to further study the physiological implications of H/R-induced modulation of the PKA and PKC activity in hypoxia-tolerant organisms.

Pyrolysis-gasification of wastes plastics for syngas production using metal modified zeolite catalysts under different ratio of nitrogen/oxygen

The aim of this study was the syngas production by the gasification of plastic waste (polyethylene, polypropylene and terephthalate polyethylene). Ca, Ce, La, Mg and Mn were used to promote the Ni/ZSM-5 catalyst in order to enhance the production of higher syngas yield. The modified catalysts can enhanced the reaction rate of the pyrolysis process and resulting in high syngas in the product yields. Especially cerium, lanthanum promoted catalysts can enhance the yield of syngas. The effect of the reaction temperature and nitrogen/oxygen ratio of the carrier gas was also investigated. The maximum syngas production was obtained with lanthanum catalyst (112.2 mmol/g (95%N2 and 5%O2), and 130.7 mmol/g (90%N2 and 10%O2) at 850 °C. Less carbon depositions was found at 850 °C or even by the using of catalyst and more oxygen in the carrier gas. The oxygen content of the pyrolysis-gasification atmosphere had a key role to the syngas yield and affects significantly the carbon-monoxide/carbon-dioxide ratio. Catalysts can also accelerate the methanization reactions and isomerize the main carbon frame. Increasing in both temperature and oxygen in the atmosphere led to higher n-paraffin/n-olefin ratio and more multi-ring aromatic hydrocarbons in pyrolysis oils. The concentration of hydrocarbons containing oxygen and branched compounds was also significantly affected by catalysts.

Microstructure and mechanical properties of additively manufactured CoCrW alloy using laser metal deposition

We successfully used CoCrW alloy as the feedstock for directly shaping wear-resistant products by additive manufacturing. We present a guideline for forming substantive, high-density, crack-free CoCrW alloys via laser metal deposition (LMD) and evaluated the relationship between the microstructure and mechanical properties. CoCrW alloy with a scale of several tens of cubic centimeters has not been previously reported because the brittle material undergoes cracking due to residual stresses. Densification and crack suppression were achieved by controlling the oxygen concentration in an Ar atmosphere and preheating the base plate to 400 °C. The tensile strength (MPa) of the LMDed CoCrW alloy was 1492 ± 141 along the scan direction, 1464 ± 234 along the overlap direction, and 1359 ± 72 along the build direction. The overlap direction had almost the same strength as the scan direction. In the microtensile test for the overlap direction, the fracture ratio in the overlap region was only 17.4%, and it was found that softening in this region did not contribute to the decrease in strength.

Spray Auto-ignition Behaviors of Diesel and Jet Fuel at Reduced Oxygen Environments

ABSTRACT Spray auto-ignition behaviors of the RP-3 jet fuel were compared to those of a conventional diesel fuel on a constant-volume combustion chamber. The experiments were conducted at changed ambient temperatures and oxygen concentrations, with adjusted fuel injection pressure and duration as well. Compared to diesel fuel, the RP-3 jet fuel exhibits less auto-ignition propensity and lower burn rate, its ignition delay, and combustion delay times are more sensitive to the change in temperature and oxygen concentration, and more obviously staged heat releases and pressure rises are observed at lower oxygen ambience. Also, the peak heat release rate of diesel fuel exhibits an apparent non-monotonic trend versus increased temperature at high oxygen environments, due to the reduced premixed burn intensity with increased ambient temperature, while this non-monotonic trend for the RP-3 jet fuel is less significant, as the peak burn intensity is less influenced by changed ambient temperature. Finally, both elevated injection pressure and extended injection duration significantly reduce the combustion delay time at lower ambient oxygen concentrations, because the interval between the two-stage pressure rises, that occur at lower ambient oxygen environments, are apparently shortened.

Natural radioactivity and formation of oxygen in Earth's atmosphere: Decay of radioactive 40K and radiolysis of ocean water

The important role of radioactivity in the conversion of primary hydro- and atmosphere is substantiated considering the decay of 40 K isotope in seawater. By now, the total energy resulting from the decay of 40 K in the ocean amounts to 6.3 × 1026 J. The calculations show that the concentration of oxygen formed over the last 3.8 Ga is approximately 8 × 1017 kg, i.e., it is of the same order of magnitude as the content of oxygen in the modern atmosphere. The ocean was an intermediate reservoir in which oxygen was formed and which was purified from toxic components. The radiation provides the threshold concentrations of oxygen (Urey, Pasteur, and Berkner-Marshall points) important for the development of oxygen-breathing life. The radical and ionic products of water radiolysis induced chemical transformations of the compounds dissolved in the ocean. The calculations show that their total concentration over a period of 3.8 Ga was approximately 0.3 mol L−1. Seawater radiolysis resulted in water purification, saturation with oxygen, and formation of simple organic molecules.

Impact of Electron Acceptor Availability on Methane-Influenced Microorganisms in an Enrichment Culture Obtained From a Stratified Lake.

Methanotrophs are of major importance in limiting methane emissions from lakes. They are known to preferably inhabit the oxycline of stratified water columns, often assumed due to an intolerance to atmospheric oxygen concentrations, but little is known on the response of methanotrophs to different oxygen concentrations as well as their preference for different electron acceptors. In this study, we enriched a methanotroph of the Methylobacter genus from the oxycline and the anoxic water column of a stratified lake, which was also present in the oxic water column in the winter. We tested the response of this Methylobacter-dominated enrichment culture to different electron acceptors, i.e., oxygen, nitrate, sulfate, and humic substances, and found that, in contrast to earlier results with water column incubations, oxygen was the preferred electron acceptor, leading to methane oxidation rates of 45–72 pmol cell−1 day−1. Despite the general assumption of methanotrophs preferring microaerobic conditions, methane oxidation was most efficient under high oxygen concentrations (>600 μM). Low (<30 μM) oxygen concentrations still supported methane oxidation, but no methane oxidation was observed with trace oxygen concentrations (<9 μM) or under anoxic conditions. Remarkably, the presence of nitrate stimulated methane oxidation rates under oxic conditions, raising the methane oxidation rates by 50% when compared to oxic incubations with ammonium. Under anoxic conditions, no net methane consumption was observed; however, methanotroph abundances were two to three times higher in incubations with nitrate and sulfate compared to anoxic incubations with ammonium as the nitrogen source. Metagenomic sequencing revealed the absence of a complete denitrification pathway in the dominant methanotroph Methylobacter, but the most abundant methylotroph Methylotenera seemed capable of denitrification, which can possibly play a role in the enhanced methane oxidation rates under nitrate-rich conditions.

Comparative Study on NO2 and H2s Sensing Mechanisms of Gas Sensors Based on WS2 Nanosheets

Introduction Metal sulfides have been actively explored in a wide range of potential applications in optoelectronic [1], energy storage [2], sensor [3], and photocatalytic devices [4] because of their excellent electrical properties and active defects sites . In particular, metal sulfides such as SnS2, MoS2 and WS2 are of interest to researchers because of their narrow band gap, large surface-to-volume ratio and excellent gas selectivity. However, the exploration of the sensing mechanism of metal sulfide-based gas sensors is still in its infancy and lacks experimental verification. Especially the research on the sensing mechanism of WS2 is very scarce. In this paper, we report a facile synthesis of WS2 nanosheets with an average cross-sectional size of about 10 nm by sulfurization of the WO3 nanomesh. The sensor based on WS2 nanosheets exhibits p-type sensing behavior and excellent selectivity to NO2 gas at a low temperature of 160 °C. Its excellent sensing performance can be attributed to the active sites of the thin nanosheets for the adsorption of NO2 and the strong physical affinity between WS2 nanosheets and NO2 gas molecules. In addition, we designed sensing experiments of WS2 nanosheets toward NO2 and H2S in different background atmospheres. Surprisingly, the effect of oxygen in the background gas on the sensing response of NO2 and H2S gas is different, revealing the different sensing mechanisms of WS2 nanosheets for NO2 and H2S gas. The study of the influence of oxygen content in the background atmosphere on the gas response of the sensor is of great significance for the application of the sensor in some anaerobic environments such as aerospace, mine and plateau. Synthesis of WS2 nanosheets The WO3 nanomesh was synthesized according to the procedures detailed in our previous report. In brief, WO3 nanomesh was synthesized by hydrothermal recrystallization of H2WO4 in oxidizing environment at 180 °C for 12 h under autogenic pressure with 0.2 M thiourea as the morphology-controlling agent. The WS2 nanosheets were obtained by sulfurization of the WO3 nanomesh. In a tipical process, 1g sulphur powder and 0.1 g WO3 nanomesh were placed at left end of heating zone (the upstream side) and the hot center of the tube furnace, respectively. The tube furnace was evacuated by using a mechanical pump and then filled up with N2. The evacuation and flushing steps were repeated three times to minimize O2 in the tube furnace. Then, the furnace was heated from room temperature to 500 °C using a heating rate of 5 oC/min, and the sulfurization was performed for a period of 1h at 500 oC in a flow of 80 sccm N2. After the sulfurization, the furnace was naturally cooled down to room temperature. Method The as-prepared WS2 was mixed with a few drops of deionized water and absolute ethanol to form a slurry by grounding in an agate mortar. The sensing slurry was deposited on the Au interdigital electrode by a hand-brushing method, and then the electrode was placed in an oven and dried at 70 °C overnight. The gas sensing measurements were performed by a computer-controlled gas mixing and data-acquisition system. The sensor response was defined as the ratio of resistance ([(Ra /Rg )-1]×100) (%) to oxidizing gas and ([(Rg /Ra )-1]×100) (%) to reducing gas), where where Ra and Rg were the sensor resistance in air and in target gas atmosphere, respectively. The response and recovery times of the sensors were defined as the time required for 90% of the total resistance change. Results and Conclusions In summary, we have reported the gas sensor based on WS2 nanosheets synthesized by the sulfurization of the WO3 nanomesh. The p-type WS2 nanosheets sensor exhibits excellent NO2 sensing characteristics in terms of high response, short response/recovery time, low detection limit and good selectivity. This is attributed to the interactions between the gas molecules and edge and in-plane sites of the thin units of WS2 nanosheets. Moreover, we tested the response of WS2 nanosheets sensor to NO2 and H2S under different background atmospheres. We found that WS2 nanosheets do not require oxygen for NO2 sensing, but oxygen is required for H2S sensing. This result indicates that WS2 nanosheets have different sensing mechanisms for different gases. Specifically, the NO2-sensing mechanism of WS2 nanosheets is based on NO2 physisorption model, while the H2S-sensing mechanism is based on classical oxidation reaction model. This study presents the basic mechanism of the WS2 nanosheets sensor that can be used as reference for other metal sulfide sensors.

Computational fluid dynamics modeling in a fixed adsorbent layer during separation of gas mixtures

The paper discusses the numerical analysis results of the aerodynamic structure of a flow in the granular adsorbent layer in a pressure swing adsorption unit adsorber during atmospheric air separation and oxygen concentration. The computational experiments were carried out using one-dimensional and two-dimensional mathematical models to calculate the velocity field in the adsorbent bulk layer. While assessing the accuracy of calculating the aerodynamic structure of the gas flow in the adsorbent, it was found that the use of a two-dimensional mathematical model provides an increase in the accuracy of calculations by an average of ~1-2% compared with the one-dimensional model.

Reactive carbonyls and the formation of the heterocyclic aromatic amine 2-amino-3,4-dimethylimidazo(4,5-f)quinoline (MeIQ)

Reactions involving reactive carbonyls, creatinine, and ammonia-producing compounds were investigated in order to clarify the formation of the heterocyclic aromatic amine (HAA) 2-amino-3,4-dimethylimidazo(4,5-f)quinoline (MeIQ). Obtained results showed that MeIQ was only produced when 2-butenal (crotonaldehyde) was present. Reaction yields depended on the pH, with a maximum around pH 6.5, and on concentrations of crotonaldehyde and creatinine. Ammonia was also required for MeIQ formation, but ammonia was produced by creatinine decomposition. The amount of MeIQ formed increased with reaction time, temperature, and oxygen content in the reaction atmosphere. Activation energy for MeIQ formation from crotonaldehyde, creatinine, and glutamine was 72.2 ± 0.4 kJ·mol−1. A reaction pathway that explains MeIQ formation is proposed. Obtained results suggest a main role of reactive carbonyls formed in foods (the food carbonylome) on HAA formation. In addition, they provide scientific basis for the understanding of how HAAs are formed and could be mitigated.

Variability in lag-duration of Campylobacter spp. during enrichment after cold and oxidative stress and its impact on growth kinetics and reliable detection

Campylobacter jejuni and Campylobacter coli continue to be the leading cause of zoonotic gastroenteritis in the European Union, making reliable detection in food important. Low storage temperatures and atmospheric oxygen concentrations during food production can cause sub-lethal damage or transient non-culturability which is why ISO 10272-1:2017 includes an enrichment step to repair cell damage and increase cell concentrations, thereby supporting detection of campylobacters from foods.The aim of this study was to assess the variability in lag-duration of C. jejuni and C. coli during enrichment after different food-relevant stress treatments and evaluate its impact on growth kinetics and reliability of detection outcomes. Therefore, 13 C. jejuni and 10 C. coli strains were subjected to cold stress during refrigerated and frozen storage. Refrigerated storage did not significantly reduce culturability, but frozen storage reduced cell concentrations by 1.6 ± 0.1 log10cfu/ml for both species.Subsequently, cells were enriched following ISO 10272-1:2017-A and cell concentrations were determined over time and lag-duration and growth rate were determined by fitting the Baranyi-model. Without prior stress treatment, mean lag-duration for C. jejuni and C. coli was 2.5 ± 0.2 h and 2.2 ± 0.3 h, respectively. Refrigerated storage increased lag-duration for C. jejuni to 4.6 ± 0.4 h and for C. coli to 5.0 ± 0.4 h and frozen storage increased lag-duration to 5.0 ± 0.3 h and 6.1 ± 0.4 h for C. jejuni and C. coli, respectively.Comparison of strain- and biological variability showed that differences in recovery after cold stress can be attributed mainly to strain variability since strain variability after refrigeration and freeze stress increased respectively 3-fold and 4-fold while biological variability remained constant.A subset of strains was also subjected to oxidative stress that reduced cell concentrations by 0.7 ± 0.2 log10 cfu/ml and comparison of recovery patterns after oxidative and freeze stress indicated that recovery behaviour was also dependent on the stress applied. A scenario analysis was conducted to evaluate the impact of heterogeneity in outgrowth kinetics of single cells on the reliability of detection outcomes following ISO protocol 10272-1:2017. This revealed that a ‘worst-case’-scenario for successful detection by a combination of the longest lag-duration of 7.6 h and lowest growth rate of 0.47 h−1 still resulted in positive detection outcomes since the detection limit was reached within 32.5 h. This suggests that other factors such as competitive microbiota can act as a causative factor in false-negative outcomes of tested food samples.

Mouse embryos exposed to oxygen concentrations that mimic changes in the oviduct and uterus show improvement in blastocyst rate, blastocyst size, and accelerated cell division

After in vivo fertilisation, the preimplantation embryo goes through cleavage during migration along the oviduct in mammals or the fallopian tube in a woman and ends up inside the uterus. This study investigates the effect of a protocol aimed at closely reproducing that natural oxygen concentration in the oviduct (7 % O2 from day 1 to day 3 and 2 % from day 3 to day 5), in contrast to the concentrations (5 % or 20 %) widely used in practice in ART using morphokinetic. Female mice (BI6/CBAca) were sacrificed, and zygotes were isolated 20 h after mating and randomly allocated to three parallel groups, which were grown under high atmospheric, low, or sequential oxygen concentrations. Zygotes were cultured in GTL medium (Vitrolife) and observed by the Primovision time-lapse system. Blastocyst rate at 120 h in the sequential group (91.3 %) was significantly increased over the high (76.3 %) and low (74.4 %) groups. Blastocyst size was also enlarged in the sequential group compared to the high and low groups. Moreover, cell division in the sequential group was significantly faster at almost every cleavage stage than it was in the other groups. Notably, the duration of the interims between stages also differed significantly between the groups. This study demonstrated that, in comparison to routinely used high or low oxygen conditions, oxygen concentrations mimicking changes in the oviduct and uterus significantly improve the blastocyst rate and size and accelerate cell division at several stages as well as the interims between cleavage events.

Chemical archeoceanography

Elemental fluxes to the ocean are expected to increase with the surface area of continental exposure to weathering and atmospheric PCO2. The record of phosphorus in sediments, which has no notable source within the ocean, and the radiogenic strontium isotopes in Archean carbonates indicate that, prior to the Great Oxidation Event (GOE), subaerial expanses represented only about 20% of the modern continental surface area, i.e. 7% of the surface of the Earth. Because these simple first-order observations, in contrast to the low oxygen content of the pre-GOE atmosphere, have so far received only little attention in the appraisal of the marine chemistry of the early Earth, a reassessment of the chemistry of the pre-GOE ocean is warranted. Here we discuss some of the geochemical cycles of the Archean world, including protons, alkalinity, electrons, and other electrolytes, and attempt to build a first conceptual framework for Chemical Archeoceanography. The smaller subaerial exposures characterizing the Archean and the low abundance of Archean carbonates and mudstones imply that the flux of alkalinity to the ocean was much weaker than today and therefore that the capacity of the runoff to neutralize the high-temperature hydrothermal fluids was less important. Such a reduced flux in turn entails lower seawater pH and higher chlorinity. The lack of atmospheric O2 allowed iron to be in its soluble Fe(II) form and to reduce HCO3− to CH4 while liberating large amounts of protons. The low pH of the pre-GOE ocean and the reduced alkalinity input, reinforced by scant P supply, account for reduced carbonate precipitation. Ocean chemistry evolved under the control of two changing factors: (i) the balance between chemical weathering and hydrothermal fluxes and (ii) the oxygen pressure in the ocean and the atmosphere. Seawater iron concentration was controlled by high [Fe2+]/[H+]2 ratios. With the temperature of hydrothermal fluids at mid-ocean ridges and other active volcanic edifices being determined by the expansion properties of seawater, the chemistry of hydrothermal fluids is controlled by the chlorinity of the ocean. Of all the major element cycles in seawater, those of Na, Mg, and P seem to be unbalanced when runoff falls below the modern value. The very low P content of banded iron formations is inconsistent with a major role of biological activity in the oxidation of Fe2+ dissolved in the Archean ocean. Prior to the GOE, banded iron formations were the major sedimentary sink of seawater cations, a role now played by carbonates. The controls of seawater alkalinity, which today are exerted by the Ca2+–CaCO3 couple, was exerted by dissolved Fe2+-magnetite or Fe2+-ferrihydrite. Plain language summaryWe here evaluate the constraints on seawater chemistry before free oxygen was introduced into the atmosphere some 2.4 billion years ago. We suggest a simple conceptual framework which we validated on modern seawater and which is based on two so-far largely overlooked observations, namely that the phosphorus concentration and strontium isotopic records in ancient sediments require that emerged continental land masses were covering only ~7% of Earth's surface at the time of the Great Oxidation Event instead of 30% today. Atmospheric and seawater chemistry critically depend on this proportion as well as on the chlorinity of the ocean. The oxygen-free atmosphere allowed iron to remain in solution and to reduce atmospheric carbon dioxide to methane. The pH of the ancient oceans must have been lower because less river water was available to neutralize the acidic submarine high-temperature hydrothermal fluids emitted at mid-ocean ridges. Limited continental surface starved the sedimentary column for clays. The low pH and scant phosphorus drainage led to rare carbonate deposition. We conclude by proposing a new scheme for Archean marine chemistry and geochemical cycles that can explain the chemical and geological observations from the Archean and early Proterozoic rock record.