Variations In PO2 Research Articles

Thermochemical reaction kinetics of Mn-Fe based particles for High-Temperature energy storage systems

Concentrated Solar Power (CSP) systems, augmented by Thermal Energy Storage (TES), are crucial for enhancing renewable energy stability. However, challenges in CSP technology, particularly efficiency and cost factors, persist. Elevating heat collection and storage temperature stands out as an effective strategy to improve efficiency and reduce costs. In this study, we investigated the use of Mn-Fe particles for thermal energy storage in CSP, highlighting their excellent cycling stability and suitability for high temperatures (>900 °C). We conducted a detailed analysis of the oxidation kinetics. The oxygen partial pressure at equilibrium of oxidation process (pO2,eql(Tox))​ was determined and the onset temperature was found to exceed 850 °C, with a noticeable lag at lower pO2, diminishing or disappearing at higher pO2. To sustain a high re-oxidation conversion during the oxidation process, it is crucial to maintain either a high pO2 (>0.16 bar) or a low cooling rate β. The kinetic parameters were subjected to polynomial fitting with pO2 and β as independent variables, followed by an investigation into the correlation between these parameters and the fundamental physical processes of the reaction. Subsequently, a definitive kinetic model for the oxidation of Mn-Fe particle was established, exhibiting a strong correlation with experimental results (R2 = 0.9993). This model accurately describes the oxidation process under diverse conditions, spanning variations in pO2 from 0.16 bar to 0.7 bar and β from 5 K/min to 20 K/min, and establishes a foundation for monitoring and controlling the oxidation dynamics of Mn-Fe particle for fluidized-bed heat transfer in CSP.

Oxygen Consumption In Vivo by Ultra-High Dose Rate Electron Irradiation Depends Upon Baseline Tissue Oxygenation

Purpose: This study aimed to assess the impact of tissue oxygen levels on transient oxygen consumption induced by ultra-high dose rate (UHDR) electron radiation in murine flank and to examine the effect of dose rate variations on this relationship. Methods: Real-time oximetry using the phosphorescence quenching method and Oxyphor PdG4 molecular probe was employed. Continuous measurements were taken during radiation delivery on a UHDR-capable Mobetron linear accelerator (linac). Oxyphor PdG4 was administered into the subcutaneous tissue of the flank skin one hour before irradiation. Skin oxygen tension (pO2) was manipulated by adjusting oxygen content in the inhaled gas mixture and/or by vasculature compression. A skin surface radiation dose of 19.8±0.3Gy was verified using a calibrated semiconductor diode dosimeter. Dose rate was varied across the UHDR range by changing linac cone length and pulse repetition frequency (PRF). Results: The decrease in pO2 per unit dose during radiation delivery, termed oxygen consumption g-value (gO2, mmHg/Gy), was significantly influenced by tissue oxygen levels in the range 0-65mmHg under UHDR conditions. Within the 0-20mmHg range, gO2 exhibited a sharp increase with rising baseline pO2, plateauing at 0.26mmHg/Gy. Dose rate variations (mean values 25-1170Gy/s, per-pulse doses of 2.5-9.8Gy) were explored by varying both cone length and PRF (10-120Hz) with no significant changes in gO2. Conventional dose rate irradiation resulted in no discernible changes in pO2. Conclusions: The results show significant differences in the radiation-chemical effects of UHDR radiation between hypoxic and well-oxygenated tissues. Similar trends between earlier published in vitro and in vivo experiments presented herein suggest the chemical mechanisms driving the dependencies of gO2 on pO2 are similar, potentially underpinning the FLASH effect. Importantly, significant variations in baseline pO2 were observed in animals kept under identical conditions, underscoring the necessity to control and monitor tissue oxygen levels for preclinical investigations and future clinical applications of FLASH-RT.

Sensitive simultaneous measurements of oxygenation and extracellular pH by EPR using a stable monophosphonated trityl radical and lithium phthalocyanine

The monitoring of acidosis and hypoxia is crucial because both factors promote cancer progression and impact the efficacy of anti-cancer treatments. A phosphonated tetrathiatriarylmethyl (pTAM) has been previously described to monitor both parameters simultaneously, but the sensitivity to tackle subtle changes in oxygenation was limited. Here, we describe an innovative approach combining the pTAM radical and lithium phthalocyanine (LiPc) crystals to provide sensitive simultaneous measurements of extracellular pH (pHe) and pO2. Both parameters can be measured simultaneously as both EPR spectra do not overlap, with a gain in sensitivity to pO2 variations by a factor of 10. This procedure was applied to characterize the impact of carbogen breathing in a breast cancer 4T1 model as a proof-of-concept. No significant change in pHe and pO2 was observed using pTAM alone, while LiPc detected a significant increase in tumor oxygenation. Interestingly, we observed that pTAM systematically overestimated the pO2 compared to LiPc. In addition, we analyzed the impact of an inhibitor (UK-5099) of the mitochondrial pyruvate carrier (MPC) on the tumor microenvironment. In vitro, the exposure of 4T1 cells to UK-5099 for 24 h induced a decrease in pHe and oxygen consumption rate (OCR). In vivo, a significant decrease in tumor pHe was observed in UK-5099-treated mice, while there was no change for mice treated with the vehicle. Despite the change observed in OCR, no significant change in tumor oxygenation was observed after the UK-5099 treatment. This approach is promising for assessing in vivo the effect of treatments targeting tumor metabolism.

Influence of pneumatic tube delivery system on laboratory results.

The pneumatic tube system (PTS) is an automated and fast modality of transportation of biological samples, but it has been reported to induce preanalytical errors. To study the influence of transportation by PTS on biochemistry tests which are particularly sensitive to haemolysis and atmospheric pressure variation. We compared laboratory results of arterial blood gas, sodium, potassium, chloride, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, glucose and haemolysis index of samples conveyed simultaneously by PTS and by courier. We recruited 30 patients from the sampling room and 40 patients from the intensive care unit. Transport through PTS resulted in a significant increase in aspartate aminotransferase and potassium without exceeding the limits of acceptability. Potassium was significantly more increased for samples transported in a higher speed line (p = .048) but without exceeding the limits of acceptability. No significant impact was noted on haemolysis indices. The pO2 variations due to PTS transportation exceeded the limit of acceptability with significant intra-individual variations. Our PTS is validated for biochemistry tests results. It reduces turnaround times without affecting sample quality. However, the interpretation of arterial blood gas results should be careful for samples transported by PTS.

Identifiability of the mechanisms governing the reaction kinetics of MIEC electrodes in solid oxide cells

The oxygen reduction reaction (ORR) is the main phenomenon occurring in mixed ionic and electronic conductors (MIECs) used as air electrodes in solid oxide cells. Their optimisation requires the identification of the ORR regime, which is typically performed via electrochemical impedance spectroscopy (EIS). In this study we present a physics-based model to simulate the impedance spectra of p-type oxygen-deficient perovskite MIEC materials. The EIS response of four extreme kinetic scenarios, characterised by the rate-determining step (electron-transfer or ion-transfer) and the high/low surface coverage of adsorbed oxygen, is mechanistically interpreted for both dense films and porous electrodes. A strategy for kinetic identification is proposed based on distinctive EIS fingerprints at different oxygen partial pressures (pO2) and cathodic bias. However, distinguishing the kinetic scenarios is not free from ambiguity even in dense films since some scenarios are discriminated only via a quantitative analysis, which may be susceptible to experimental errors in real measurements, and reverse behaviours appear when combining cathodic bias with pO2 variation. More difficulties arise in porous electrodes since bulk oxygen vacancy transport interacts with the ORR response. Application of the proposed strategy using literature data for some common MIEC materials shows the typical challenges of kinetic identification when relying solely on EIS.

Effects of abiotic processes on the correlation between pH and pO2 in the Norwegian Sea: Implications for GCS monitoring

In the absence of abiotic sources of CO2, variation in pCO2 and pO2 is expected to be inversely correlated in the water column due to biogenic processes. It has previously been suggested to use this correlation for leakage monitoring of offshore geological carbon storage (GCS) sites. In this study the aim is to investigate the extent of this correlation in ocean water masses with different origin and history in the Norwegian Sea, as well as in water masses in the vicinity of an active hydrothermal vent field at Mohn's Ridge, where pH is used as a proxy for pCO2. Over a hydrothermal vent site, a strong correlation between pH and pO2 is observed from 0 to 1700 m, whereas at depths >1700 m there is no correlation, likely due to CO2 emissions from the hydrothermal vents. However, at a reference site nearly 200 km from the hydrothermal vents, the intermediate Arctic water masses (700 – 1600 m depth) also show pH-pO2 correlations that are inconsistent with biogenic processes, but less pronounced compared to the hydrothermal vent site. These findings show that the suitability of this monitoring strategy will depend on a thorough site-specific evaluation of pH/CO2 and O2 relationships of relevant water masses.

MR-oximetry with fat DESPOT

PurposeThe R1 relaxation rate of fat is a promising marker of tissue oxygenation. Existing techniques to map fat R1 in MR-oximetry offer limited spatial coverage, require long scan times, or pulse sequences that are not readily available on clinical scanners. This work addresses these limitations with a 3D voxel-wise fat R1 mapping technique for MR-oximetry based on a variable flip angle (VFA) approach at 3 T. MethodsVarying levels of dissolved oxygen (O2) were generated in a phantom consisting of vials of safflower oil emulsion, used to approximate human fat. Joint voxel-wise mapping of fat and water R1 was performed with a two-compartment VFA model fitted to multi-echo gradient-echo magnitude data acquired at four flip angles, referred to as Fat DESPOT. Global R1 was also calculated. Variations of fat, water, and global R1 were investigated as a function of the partial pressure of O2 (pO2). Inversion-prepared stimulated echo magnetic resonance spectroscopy was used as the reference technique for R1 measurements. ResultsFat R1 from Fat DESPOT was more sensitive than water R1 and global R1 to variations in pO2, consistent with previous studies performed with different R1 mapping techniques. Fat R1 sensitivity to pO2 variations with Fat DESPOT (median O2 relaxivity r1, O2 = 1.57× 10−3 s−1 mmHg−1) was comparable to spectroscopy-based measurements for methylene, the main fat resonance (median r1, O2= 1.80 × 10−3 s−1 mmHg−1). ConclusionFat and water R1 can be measured on a voxel-wise basis using a two-component fit to multi-echo 3D VFA magnitude data in a clinically acceptable scan time. Fat and water R1 measured with Fat DESPOT were sensitive to variations in pO2. These observations suggest an approach to 3D in vivo MR oximetry.

Hyperoxic exposure monitoring in diving: A farewell to the UPTD

Depending on pO2 and exposure time hyperoxic breathing gas may cause injury in many organs including the lungs. Pulmonary oxygen toxicity (POT) may be asymptomatic, but will initially present as a tracheobronchitis in symptomatic subjects. A number of objective measurements of POT have been investigated, but the decrement in vital capacity (VC) has remained the most accepted outcome measure. The unit pulmonary toxic dose (UPTD) has been established as the most common exposure index for POT in diving. UPTD is calculated based on the pO2 and exposure time. A literature search identified five models predicting POT, but no model would accurately predict VC change for the full range of pO2 variation and exposure time relevant for surface-oriented diving. Nevertheless, compared to UPTD, the K-index(K = t2*pO24.57, where t = time (hours) and pO2 = inspired pO2 (atm)) suggested by Arieli performed better for pO2 > 150 kPa and allowed estimation of recovery. We recommend that the Arieli K-index should replace UPTD as the POT exposure index for all surface-oriented diving. Based on the limited data available we suggest a daily threshold of K = 120 for a maximum of two diving days followed by two days of recovery. For five consecutive days of diving, we recommend that the threshold should not exceed K=70 and two recovery days should be allowed. For multiday diving without days of recovery, the daily exposure should probably be limited to K = 40-50.

Effect of processing parameters on the defects state in Ni0.65Zn0.35Al0.8Fe1.2O4 thin films

Ferromagnetic resonance (FMR) technique is used to investigate the effect of oxygen partial pressure (PO2) and substrate temperature (TS) on the defect properties of Ni0.65Zn0.35Al0.8Fe1.2O4 (NZAFO) thin films. NZAFO thin films are deposited on MgAl2O4 (MAO) (100) substrates using pulsed laser deposition technique under various PO2 and TS. The FMR study reveals that the FMR parameters such as linewidth, line intensity and g-factor of the NZAFO thin films are sensitive to the variations in PO2 and TS. The observed changes in the FMR parameters are attributed to the variation of density and uniformity of defects in NZAFO thin films. Thus the significance of the present work suggests that the FMR may serve as an effective tool to monitor the growth condition of complex oxide films.

Model‐based analysis of microcirculatory parameters affecting O 2 transport in skeletal muscle subjected to fixed surface PO 2

Microcirculation in skeletal muscle determines both blood flow distribution and O2 transport. The partial pressure of oxygen (PO2) is a prime candidate to assess in tissue, as PO2 variations herald a functionality decline in skeletal muscle. Traditional non-invasive microcirculatory techniques such as Intra-vital Video Microscopy (IVVM) allowing for blood velocity and capillary saturation (SO2) measurements, are unable to directly assess skeletal muscle tissue PO2. Instead, modern microcirculatory O2 analysis relies on biophysical models to recreate tissue PO2 distributions. (Ellis et al, Microcirc 2012, 19:5). Recently, a continuous coupled partial differential equation (PDE) model of two layers of skeletal muscle coupled via diffusion at their boundaries was developed accounting for tissue O2 diffusion, capillary O2 convection, tissue O2 consumption, and capillary-tissue O2 transfer. This model was developed to study an IVVM protocol involving a controlled exposure of skeletal muscle using an O2 exchange chamber. In the protocol studied, hemodynamic parameters in the skeletal muscle region near to the O2 chamber are experimentally shown to exhibit substantial variations. The prevailing theory is capillary perfusion limits the depth of penetration of the chamber O2, and local hemodynamic parameter responses serve to regulate capillary SO2 in skeletal muscle; this would be towards either a fixed target value or homogeneity with neighboring capillary modules. The coupled PDE two-layer model was developed for steady-state PO2 distributions and was solved using traditional math techniques such as operator decoupling and Fourier decomposition, and exhibited the ability to rapidly and accurately calculate PO2 distributions in skeletal muscle which agreed with experimental values. (Afas and Goldman, Vasc Bio 2020). The solution affords for the unique ability not allowed in previous convection-diffusion analytic models of O2 transport, to observe the interaction of both skeletal muscle layers. This is achieved by assuming baseline hemodynamic parameters in the layer far from the O2 chamber and allowing the near layer to take on a range of parameter variations; these variations can be compared to experimental observations. In this study, the behavior of both layers of skeletal muscle adjacent to an O2 chamber will be modelled by the a-priori fixing of parameters in the region far from the O2 chamber and allowing near-layer parameters to be perturbed. Several parameters, including capillary density φ, velocity vB, inlet saturation SIN, hematocrit HT, and tissue consumption μ will have this variation method applied from previous baselines (Afas et al, Math Biosci 2021, in press), and the resultant two-layer O2 profiles will be visualized, as well as the conditions under which the capillary SO2 is homogenized in both layers of skeletal muscle.

Comparative studies on ferroelectric switching kinetics of sputtered Hf0.5Zr0.5O2 thin films with variations in film thickness and crystallinity

Ferroelectric Hf0.5Zr0.5O2 (HZO) thin film capacitors with Pt/HZO/TiN structures were characterized to investigate the effects of oxygen partial pressure (PO2) and film thickness on the ferroelectric properties and switching dynamics of sputter-deposited HZO thin films. The PO2 during deposition and the film thickness varied from 0% to 1.5% and from 20 to 30 nm, respectively. The ferroelectric remnant polarization (2Pr) was 24.8 μC/cm2 for the 20-nm-thick HZO thin film deposited at a PO2 of 0% and decreased with increasing PO2 and film thickness due to variation in the amount of ferroelectric orthorhombic phase. The 2Pr of the 30-nm-thick HZO film deposited at a PO2 of 1% was 9.60 μC/cm2. The switching times and related parameters of the HZO films were estimated and analyzed by Kolmogorov–Avrami–Ishibashi and nucleation-limited switching (NLS) models. The NLS model provided better fitting results over the full range of polarization switching. The switching times could be modulated with variations in PO2 and film thickness from 0.46 to 1.58 μs. The activation field for polarization reversal increased with increasing PO2, and the degree of PO2 dependence was higher for a thinner film.

Dynamic controlled atmosphere based on carbon dioxide production (DCA – CD): Lower oxygen limit establishment, metabolism and overall quality of apples after long-term storage

Abstract The present study aimed to estimate the lower oxygen limit (LOL) by DCA – CD (Dynamic controlled atmosphere based on CO2 production) for several apple cultivars and seasons and compare this method with DCA – RQ. The metabolism and overall quality maintenance of fruit stored under DCA – CD was also compared with CA – ULO, DCA – CF and DCA – RQ for ‘Imperial Gala’, ‘Fuji Suprema’, ‘Golden Delicious’ and ‘Cripps Pink’ apples after 9 months of storage plus 7 d of shelf life at 20 °C. The experiments were carried out over three years. The DCA – CD method, which is based only by CO2 production by the fruit, correctly estimated the LOL for cultivars and seasons, allowing the pO2 variation according to fruit metabolism during storage period, with a difference between 0.01 to 0.10 kPa O2, when compared to DCA – RQ. Storage under DCA – CD allowed the induction of anaerobic metabolism compounds in safe levels, below the odor threshold reported in the literature, and without damaging the cell membranes. Fruit under DCA – CD had lower flesh breakdown incidence and higher flesh firmness and reduced the decay incidence in ‘Imperial Gala’ and ‘Golden Delicious’.

Metabolic rate and hypoxia tolerance in Girardinichthys multiradiatus (Pisces: Goodeidae), an endemic fish at high altitude in tropical Mexico

The darkedged splitfin (Amarillo fish), Girardinichthys multiradiatus is a vulnerable endemic fish species inhabiting central Mexico's high altitude Upper Lerma Basin, where aquatic hypoxia is exacerbated by low barometric pressures (lower PO2s), large aquatic oxygen changes, poor aquatic systems management and urban, agricultural and industrial pollution. The respiratory physiology of G. multiradiatus under such challenging conditions is unknown - therefore the main goal of the present study was to determine metabolic rates and hypoxia tolerance to elucidate possible physiological adaptations allowing this fish to survive high altitude and increasingly eutrophic conditions. Fish came from two artificial reservoirs – San Elías and Ex Hacienda - considered refuges for this species. Both reservoirs showed high dial PO2 variation, with hypoxic conditions before midday and after 20:00 h, ~4 h of normoxia (15 kPa) from 16:00–20:00, and ~4 h of hyperoxia (16–33 kPa) from 12:00–16:00. Standard metabolic rate at 20 ± 0.5 °C of larvae from Ex Hacienda was significantly higher than those from San Elías, but these differences disappeared in juveniles and adults. Metabolic rate at 20 ± 0.5 °C for adults was 9.8 ± 0.1 SEM μmol O2/g/h. The metabolic scaling exponent for adults was 0.58 for San Elías fish and 0.83 for Ex Hacienda fish, indicating possible ecological effects on this variable. Post-larval fish in Ex Hacienda and all stages in San Elias site showed considerable hypoxia tolerance, with PCrit mean values ranging from 1.9–3.1 kPa, lower than those of many tropical fish at comparable temperatures. Collectively, these data indicate that G. multiradiatus is well adapted for the hypoxia associated with their high-altitude habitat.

ENSO drives near-surface oxygen and vertical habitat variability in the tropical Pacific

El Niño-Southern oscillation (ENSO) is the leading cause of sea surface temperature variability in the tropical Pacific with known impacts on tuna geographic range, but its effects on oxygen and available oxygenated habitat space are less clear. Variations in oxygenated vertical habitat space in the upper-ocean can alter interactions between predator and prey, as well as drive changes in the vulnerability of economically important tuna and other pelagic fish to surface fishing gear. Using in situ measurements, we show that ENSO is the primary driver of upper-ocean oxygen partial pressure (pO2) variability on year-to-year time scales in the tropical Pacific. Mechanistically, these pO2 variations are primarily caused by vertical shifts in thermocline depth, which alternately elevate and depress cold, hypoxic waters from the ocean interior depending on the ENSO phase and location. Transport-driven, isopycnal pO2 variations within the thermocline also play an important but secondary role. In the western tropical Pacific, waters within the exclusive economic zones of Palau, Micronesia, Nauru, and the Marshall Islands undergo the greatest variations in oxygenated tuna vertical habitat extent: approximately 19.5 m, 23.9 m, 19.5 m, and 19.3 m, respectively, between El Niño and La Niña phases. Oxygen thus plays an important role in altering available tuna vertical habitat space between different phases of ENSO.

Influence of A- and B-Site Modifications of (La1-xSrx)yCr0.5-zMn0.5-wNiz+wO3-δ on Electrochemical Impedance Characteristics of Reversible Solid Oxide Cell

Influence of A-site deficiency and chemical composition of B-site (concentration of Ni, Mn, and Cr) on electrochemical performance of hydrogen electrode in (La1-xSrx)yCr0.5-zMn0.5-wNiz+wO3-δ|(Sc2O3)0.10(CeO2)0.01(ZrO2)0.89|La0.8Sr0.2FeO3-δ reversible solid oxide fuel cell has been studied. Electrochemical characterization has been carried out in fuel cell and electrolysis regimes. Results indicate that in fuel cell regime most notable limiting steps were detected around 0.5 Hz frequency range and were attributed to gas-solid adsorption-desorption processes. pO2 variation in the oxygen electrode compartment led to small variations in a total impedance of single cells but was not the limiting process. In electrolysis mode, the dissociative adsorption was shown as an important limiting stage and limitations in kinetic region of charge transfer step were remarkable. Increase of A-site deficiency caused a significant increase in high-frequency series resistance as well as some increase of total polarization resistance. Variation in B-site composition had a significant influence on electrochemical performance with very different frequency dependence of impedance. Highest current density values of 0.27 and 0.66 A cm−2 at unit cell potentials of 0.9 and 1.5 V, respectively, at 850°C were measured for La0.75Sr0.25Cr0.3Mn0.5Ni0.2O3-δ (fuel cell mode) and (La0.8Sr0.2)xCr0.49Mn0.49Ni0.02O3-δ (electrolysis mode) in hydrogen fuel gas with pH2O = 0.03 and 0.30 atm, respectively.

Controlling porosity and ultraviolet photoresponse of crystallographically oriented ZnO nanostructures grown by pulsed laser deposition

We have synthesized a series of porous nanostructures of c-axis oriented wurtzite ZnO using glancing angle pulsed laser deposition. During deposition, the oxygen partial pressure (PO2) was varied to study the effects on growth, porosity and optical properties. With varied PO2 the growth of nanostructure changes gradually without losing its crystallographic orientation. The variation in PO2 causes systematic change in porosity of these nanostructures, which strongly influences ultraviolet photoresponse. These results show that the parameters such as surface morphology, growth and porosity as well as the optoelectronic properties can be controlled by variation in PO2 without compromising the crystalline structure.

Oxygen Sensing, Hypoxia Tracing and in Vivo Imaging with Functional Metalloprobes for the Early Detection of Non-communicable Diseases.

Hypoxia has been identified as one of the hallmarks of tumor environments and a prognosis factor in many cancers. The development of ideal chemical probes for imaging and sensing of hypoxia remains elusive. Crucial characteristics would include a measurable response to subtle variations of pO2 in living systems and an ability to accumulate only in the areas of interest (e.g., targeting hypoxia tissues) whilst exhibiting kinetic stabilities in vitro and in vivo. A sensitive probe would comprise platforms for applications in imaging and therapy for non-communicable diseases (NCDs) relying on sensitive detection of pO2. Just a handful of probes for the in vivo imaging of hypoxia [mainly using positron emission tomography (PET)] have reached the clinical research stage. Many chemical compounds, whilst presenting promising in vitro results as oxygen-sensing probes, are facing considerable disadvantages regarding their general application in vivo. The mechanisms of action of many hypoxia tracers have not been entirely rationalized, especially in the case of metallo-probes. An insight into the hypoxia selectivity mechanisms can allow an optimization of current imaging probes candidates and this will be explored hereby. The mechanistic understanding of the modes of action of coordination compounds under oxygen concentration gradients in living cells allows an expansion of the scope of compounds toward in vivo applications which, in turn, would help translate these into clinical applications. We summarize hereby some of the recent research efforts made toward the discovery of new oxygen sensing molecules having a metal-ligand core. We discuss their applications in vitro and/or in vivo, with an appreciation of a plethora of molecular imaging techniques (mainly reliant on nuclear medicine techniques) currently applied in the detection and tracing of hypoxia in the preclinical and clinical setups. The design of imaging/sensing probe for early-stage diagnosis would longer term avoid invasive procedures providing platforms for therapy monitoring in a variety of NCDs and, particularly, in cancers.

An innovative intermittent hypoxia model for cell cultures allowing fast Po2 oscillations with minimal gas consumption.

Performing hypoxia-reoxygenation cycles in cell culture with a cycle duration accurately reflecting what occurs in obstructive sleep apnea (OSA) patients is a difficult but crucial technical challenge. Our goal was to develop a novel device to expose multiple cell culture dishes to intermittent hypoxia (IH) cycles relevant to OSA with limited gas consumption. With gas flows as low as 200 ml/min, our combination of plate holders with gas-permeable cultureware generates rapid normoxia-hypoxia cycles. Cycles alternating 1 min at 20% O2 followed by 1 min at 2% O2 resulted in Po2 values ranging from 124 to 44 mmHg. Extending hypoxic and normoxic phases to 10 min allowed Po2 variations from 120 to 25 mmHg. The volume of culture medium or the presence of cells only modestly affected the Po2 variations. In contrast, the nadir of the hypoxia phase increased when measured at different heights above the membrane. We validated the physiological relevance of this model by showing that hypoxia inducible factor-1α expression was significantly increased by IH exposure in human aortic endothelial cells, murine breast carcinoma (4T1) cells as well as in a blood-brain barrier model (2.5-, 1.5-, and 6-fold increases, respectively). In conclusion, we have established a new device to perform rapid intermittent hypoxia cycles in cell cultures, with minimal gas consumption and the possibility to expose several culture dishes simultaneously. This device will allow functional studies of the consequences of IH and deciphering of the molecular biology of IH at the cellular level using oxygen cycles that are clinically relevant to OSA.

Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia

The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth’s oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen (pO2) leading to termination of an OAE after ∼1 Myr. Wildfire is highly responsive to changes in pO2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE. We report a sustained ∼800 kyr enhancement of fire-activity beginning ∼1 Myr after the onset of the T-OAE and peaking during its termination. This major enhancement of fire occurred across the timescale of predicted pO2 variations, and we argue this was primarily driven by increased pO2. Our study provides the first fossil-based evidence suggesting that fire-feedbacks to rising pO2 may have aided in terminating the T-OAE.

Performance of Proton-conducting Ceramic-electrolyte Fuel Cell with BZCY40 electrolyte and BSCF5582 cathode

In the present research, Proton conducting Ceramic electrolyte Fuel Cell (PCFC) has been fabricated with BaZr0.4Ce0.45Y0.15O3−δ electrolyte, NiO–BaZr0.4Ce0.45Y0.15O3−δ as anode and Ba0.5Sr0.5Co0.8Fe0.2O3−δ as a cathode material. The effects of anodic and cathodic gas flow rates and partial pressures on PCFC performance are studied by varying the gas flow rates between 50 and 200sccm while partial pressures between 0.25 and 1atm at one electrode by keeping constant gas flow rate and partial pressure at another electrode. The different electrode processes occurring at the electrodes and electrode/electrolyte interfaces are analyzed by electrochemical impedance spectroscopy. It is observed that gas flow rate doesn’t affect more on the fuel cell performance while increase in gas partial pressure changes the performance of PCFC. The variation in cathodic pO2 shows that the oxygen dissociation and charge transfer at cathode electrode are the major contributors toward overall electrode polarization resistance. A peak power density of ~0.80W/cm−2 is achieved at 700°C with 200sccm of wet H2 and air. The stability of the PCFC is also studied under CO2 condition and it has shown stable performance without any degradation.