Oxygen Profiles Research Articles

Field performance and numerical simulation study on the toe to heel air injection (THAI) process in a heavy oil reservoir with bottom water

Extra-heavy oil and bitumen (EHOB) comprise 30 percent of the remaining recoverable fossil fuel resources on Earth. This means EHOB could play an important role in a secure transition towards net zero emissions (NZE) by 2050. Technological developments, such as toe to heel air injection (THAI), have been shown to efficiently recover heavy oil with reduced environmental footprint. The Kerrobert project was the first to utilise the THAI technology in presence of bottom water (BW) in the reservoir. The project demonstrated a good performance (with average oil rate of 10 m3/day per well) compared to the conventional ISC operations in a BW situation. Lessons taken from the Kerrobert operational experience can assist the forthcoming THAI operations explicitly in the presence of BW. Dynamic field data for one of the best performing THAI pilot well pairs (K2), were analysed in this work. It was found that the K2 pilot must have experienced interference from K5, which is the closest neighbouring THAI well pair to the K2. Previously developed THAI models have not been validated against actual field data. A new field-scale THAI model in the presence of BW was constructed and, for the first time, validated against the field data from the Kerrobert project in this work. In addition, the quasi-staggered line drive well arrangement, as used for the K2 pilot, was studied. The daily and cumulative oil production rates were predicted well (the final agreement with field data was within 3 percent). The history matched model was then used to investigate the effect of the variation in air injection rates on THAI performance in presence of BW. Major developed zones during the propagation of the combustion front were numerically examined. It was demonstrated that extra air ingress from the neighbouring THAI well pair has caused a reduction in oxygen utilisation throughout the process. As a result, the simulated temperature profile declined with the increasing combustion time. The oxygen profile around the horizontal producer (HP) well was studied via the new history-matched model. An inversely proportional relationship was detected between the coke concentration and the oxygen profile around the HP well. It was found that the size of the steam zone, ahead of the combustion front, differs with variation in air injection rates. It was observed that some of the mobilised oil sank into the BW, leaving a significant amount of oil trapped in the reservoir. To prevent such an event, the location of the HP well was altered as a potential strategy to optimise the THAI efficiency. Consequently, the oxygen utilisation was improved by 13%, resulting in 73% higher cumulative oil production in comparison with the history-matched model.

Perspectives of the extra corporeal membrane oxygenation – Key insights from mathematical analysis

Extracorporeal membrane oxygenator is a life-saving critical medical equipment for cardio-pulmonary support, for treatment of severe chronic respiratory distress. The equipment performance is dependent on the type of membrane, flow configuration, and blood physiology. Lot of research efforts are focused on the development of novel membrane. However, the cardiovascular pulsations and blood physiological conditions on the flow and associated transport is important, which was not explored significantly. Here, we investigate the impact of the frequency of flow oscillations on the oxygenation profile. The physiological parameters which affect the blood oxygenation profile is investigated in detail. The oscillations in the oxygen transfer rate profiles are suppressed, as the blood flow rate is reduced, and the oxygen saturation is completely out-of-phase with the flow rhythm (saturation is maximum when the flow is minimum). We present the phase space to easily decide on the required combination of process variables or design specifications, needed to achieve the target oxygen saturation, based on the patient blood physiology. The present effort in understanding the process, can lead to improved performance and design of this life-supporting equipment. The results provide clear recommendations from the clinical perspectives. The outcome of the work will be useful to the engineering (biomedical) community in realizing the role of fluid flow and transport phenomena in extracorporeal oxygenation, under varied physiological conditions.

Biological processes of nitrogen removal and modeling oxygen diffusion in flocculent sludge and in granular sequencing batch reactors

AbstractBACKGROUNDSimultaneous nitrification‐denitrification (SND) in biological wastewater treatment occurs under aerobic conditions in flocs and granules, exhibiting aerobic and internal anoxic zones; SND depends on dissolved oxygen concentration. Aerobic denitrification (AD) is an advantageous process because control of aeration is not required. In the present study, the effects of anoxic/aerobic conditions and size of microbial aggregates on the AD process were evaluated using sequencing batch reactors (SBR) with activated sludge (anoxic/aerobic SBRAS) or aerobic granules (SBRAG).RESULTSNitrogen mass balances were used to estimate nitrogen assimilation, nitrification and denitrification. An oxygen diffusion model was proposed to evaluate oxygen profiles in the microbial aggregates determining the contribution of AD on nitrogen removal. At COD:N ratio = 100:10, fully aerobic biomass was predicted for all flocs in SBRAS and for 82% of the granules in SBRAG. In SBRAS, intracellular carbon storage was favored in the anoxic phase; nitrification was followed by AD, achieving 67% inorganic nitrogen (Ni) removal. In SBRAG, SND was 55% and Ni removal 51%. For SBRAG, genomic analysis described microbial community and nitrogen metabolic pathways were proposed. Heterotrophic nitrification‐aerobic denitrification (HNAD) was proposed as the main nitrogen removal process. At COD:N = 100:15, 80% of the granules developed internal anoxic zones; anoxic denitrification predominated, allowing treatment of a higher nitrogen load with similar Ni removal.CONCLUSIONSBiological processes without oxygen control are simpler to operate. For anoxic/aerobic SBR, high Ni removal efficiency was achieved even with 3.5–5.4 mg O2 L−1 at the center of the flocs, as predicted by the diffusion model. In aerobic granular systems, SND carried out by HNAD bacteria constitutes a promising approach for nitrogen removal. © 2022 Society of Chemical Industry (SCI).

Spatio-temporal profile of atomic oxygen in a 1 kHz repetition atmospheric-pressure plasma jet in He–O2–H2O mixture

Atomic oxygen (O) is one of the essential reactive species in plasma oxidation processes. We investigated the behavior of atomic oxygen in a 1 kHz-repetition pulsed plasma jet in atmospheric-pressure He/O2/H2O mixture. By two-photon absorption laser-induced fluorescence, the spatio-temporal profiles of O density were measured under various conditions. In the dry ([H2O] 100 ppm) condition, the rate of O production did not depend on the [O2] fraction in the range of [O2] = 275–8600 ppm. The analysis of the O-production rate indicates that the atomic oxygen in this plasma jet arises from electron-impact dissociation and quenching of O(1 D), similar to the O-production mechanism in radio-frequency plasma jet. The dependence of O-production in each discharge pulse (Δ[O]) on the discharge energy and [O2] in the plasma region at dry condition is formulated as . The decay rate of atomic oxygen was not explained by self-recombination or ozone-generation reactions; it was consistent with the reaction rate of O + OH O2 + H at [OH] = cm−3. This result suggests that the small amount of [OH] with 1013 cm−3 density is more responsible for O behavior than [O2] with large fraction of 1015 cm−3. We conducted a chemical reaction simulation considering the measured results of [O] and [OH] production, resulting in good agreement with the spatial distribution of [O]. Chemical reaction analysis revealed that the cyclic reproduction of OH via chain reaction with O and O2 is important, therefore a small amount of OH catalytically consumes atomic oxygen with two-order higher density.

Aeration control strategy design based on dissolved oxygen and redox potential profiles for nitrogen and phosphorus removal from sewage in a sequencing batch reactor

Oxygen availability during different stages of biological nutrient removal (BNR) plays utmost critical role in all wastewater treatment techniques. Inadequate aeration control results in low treatment efficiencies and may lead to significantly higher costs. Hence, a strategically designed aeration scheme is very crucial. This study was carried out with the objective of maximising nitrogen and phosphorus removal from sewage by implementing an optimised aeration strategy. To achieve this, a 4-hour Anaerobic/Aerobic/Anoxic (AOA) cycle based on dissolved oxygen (DO) and oxidation-reduction potential (ORP) values was strategically designed, implemented and monitored in a 4.5 l laboratory-scale Sequencing Batch Reactor (SBR). On an average, feed waste consisted of 170 mg/l of biological oxygen demand (BOD), 228 mg/l of chemical oxygen demand (COD), 64 mg/l of total nitrogen (TN) and 33 mg/l of ortho-phosphate (PO43−). The average BOD, COD, TN and PO43− loading rates of 0.510, 0.684, 0.192 and 0.099 kg/(m3-d), respectively were applied to the reactor. During the 90-day operation of the SBR, it was observed that BOD, COD, TN and PO43− removal were achieved with 91%, 93%, 90% and 75% efficiencies, with removal rates of 0.477, 0.614, 0.173 and 0.075 kg/(m3-d), respectively. Also, the cycle study revealed that P removal occurred during the aerobic phase, while N removal occurred during the anoxic phase through denitrification. A mass balance analysis for N also revealed that denitrification and microbial uptake accounted for 59% and 41% of nitrogen removal, respectively. Study revealed that nutrient removal was achieved successfully while avoiding any unnecessary extended aeration costs. Such aeration strategy based on DO and ORP values could be deployed not only to optimise the aeration phase lengths, but could also be used for dynamic process control to manage fluctuations in influent characteristics and system conditions.

Effects of Acute Moderate Hypoxia versus Normoxia on Metabolic and Cardiac Function and Skeletal Muscle Oxygenation during Endurance Exercise at the Same Heart Rate Level.

This study aimed to investigate the effects of acute moderate hypoxia (HYP), compared with those of normoxia (NORM), during endurance exercise with the same HR level on metabolic function, skeletal muscle oxygenation, and cardiac function. Twelve healthy men (aged 25.1 ± 2.3 years) completed 30 min of endurance exercise using a cycle ergometer with the same HR level (136.5 ± 1.5 bpm) corresponding to 70% maximal heart rate (HRmax) under NORM (760 mmHg) and HYP (526 mmHg, simulated 3000 m altitude) after a 30 min exposure in the respective environments on different days, in random order. Exercise load, rating of perceived exertion (RPE), metabolic function (saturation of percutaneous oxygen; SpO2, minute ventilation; oxygen uptake; VO2, carbon dioxide excretion; respiratory exchange ratio; RER, and oxygen pulse), skeletal muscle oxygen profiles (oxyhemoglobin, oxhb, deoxyhemoglobin, dxhb, total hemoglobin, and tissue oxygenation index; StO2), and cardiac function (heart rate, stroke volume, cardiac output, end-diastolic volume, end-systolic volume, and ejection fraction) were measured during endurance exercise. HYP showed a lower exercise load with the same RPE during exercise than did NORM. In addition, HYP showed a lower SpO2, VO2, oxygen pulse, oxhb, and StO2, and a higher RER and dxhb during exercise than NORM. We found that HYP showed lower exercise load and VO2 at the same RPE than NORM and also confirmed a higher anaerobic metabolism and oxygen inflow into skeletal muscle tissue due to the limitation of oxygen delivery capacity.

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

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

Pharmaceutical Biotransformation is Influenced by Photosynthesis and Microbial Nitrogen Cycling in a Benthic Wetland Biomat

In shallow, open-water engineered wetlands, design parameters select for a photosynthetic microbial biomat capable of robust pharmaceutical biotransformation, yet the contributions of specific microbial processes remain unclear. Here, we combined genome-resolved metatranscriptomics and oxygen profiling of a field-scale biomat to inform laboratory inhibition microcosms amended with a suite of pharmaceuticals. Our analyses revealed a dynamic surficial layer harboring oxic-anoxic cycling and simultaneous photosynthetic, nitrifying, and denitrifying microbial transcription spanning nine bacterial phyla, with unbinned eukaryotic scaffolds suggesting a dominance of diatoms. In the laboratory, photosynthesis, nitrification, and denitrification were broadly decoupled by incubating oxic and anoxic microcosms in the presence and absence of light and nitrogen cycling enzyme inhibitors. Through combining microcosm inhibition data with field-scale metagenomics, we inferred microbial clades responsible for biotransformation associated with membrane-bound nitrate reductase activity (emtricitabine, trimethoprim, and atenolol), nitrous oxide reduction (trimethoprim), ammonium oxidation (trimethoprim and emtricitabine), and photosynthesis (metoprolol). Monitoring of transformation products of atenolol and emtricitabine confirmed that inhibition was specific to biotransformation and highlighted the value of oscillating redox environments for the further transformation of atenolol acid. Our findings shed light on microbial processes contributing to pharmaceutical biotransformation in open-water wetlands with implications for similar nature-based treatment systems.

Benthic nitrogen cycling in the deep ocean of the Kuroshio Extension region

Benthic nitrogen cycling, including nitrification, N-loss, and other nitrogen transformations, plays a crucial role in the marine nitrogen budget. However, studies on benthic nitrogen cycling mainly focus on marginal seas, while attention to the deep ocean, which occupies the largest area of the seafloor, is severely lacking. In this study, we investigate the benthic nitrogen cycling in the Kuroshio Extension region (KE) of the northwest Pacific Ocean at water depths greater than 5,000 m through 15N enrichment slurry incubation and pore-water dissolved oxygen and inorganic nitrogen profiles. The slurry incubation indicates nitrification is the predominant process in benthic nitrogen cycling. The potential nitrification rates are nearly an order of magnitude higher than dissimilatory nitrate reduction. Nitrification and total N-loss flux estimated from pore-water nitrate and ammonium profiles are 6–42 and 5–30 μmol N m−2 d−1, respectively. Generally, anammox is the predominant N-loss process in KE sediment. The temperature gradient experiment indicates that the optimum temperature for anammox and denitrification is 13 and 41°C, respectively, partially explaining anammox as the dominant process for deep-ocean benthic N-loss. Both the low concentration of ammonium in pore-water and the discrepant results between anoxic incubation amended with 15NO3− and 15NH4++14NO3− suggest that ammonium is another limiting factor for benthic anammox. N-loss activity gradually declines with the distance from the Oyashio–Kuroshio transition zone. However, nitrification has the opposite trend roughly. This reveals that the sediment in KE transfers from nitrate sink to source from north to south. This trend is mainly caused by the variation of primary production and the supplement of active organic matter, which is the energy source for microbes and the potential source for ammonium through remineralization. Overall, our results highlight temperature and ammonium as two limiting factors for deep-ocean benthic N-loss and also exhibit a tight coupling relationship between pelagic primary production and the benthic nitrogen cycle in KE.

Role of insulin in pancreatic microcirculatory oxygen profile and bioenergetics.

BACKGROUNDThe pancreatic islet microcirculation adapts its metabolism to cope with limited oxygen availability and nutrient delivery. In diabetes, the balance between oxygen delivery and consumption is impaired. Insulin has been proven to exert complex actions promoting the maintenance of homeostasis of the pancreas under glucotoxicity.AIMTo test the hypothesis that insulin administration can improve the integrated pancreatic microcirculatory oxygen profile and bioenergetics.METHODSThe pancreatic microcirculatory partial oxygen pressure (PO2), relative hemoglobin (rHb) and hemoglobin oxygen saturation (SO2) were evaluated in nondiabetic, type 1 diabetes mellitus (T1DM), and insulin-treated mice. A three-dimensional framework was generated to visualize the microcirculatory oxygen profile. Ultrastructural changes in the microvasculature were examined using transmission electron microscopy. An Extracellular Flux Analyzer was used to detect the real-time changes in bioenergetics by measuring the oxygen consumption rate and extracellular acidification rate in islet microvascular endothelial cells (IMECs).RESULTSSignificantly lower PO2, rHb, and SO2 values were observed in T1DM mice than in nondiabetic controls. Insulin administration ameliorated the streptozotocin-induced decreases in these microcirculatory oxygen parameters and improved the mitochondrial ultrastructural abnormalities in IMECs. Bioenergetic profiling revealed that the IMECs did not have spare respiratory capacity. Insulin-treated IMECs exhibited significantly greater basal respiration than glucotoxicity-exposed IMECs (P < 0.05). An energy map revealed increased energetic metabolism in insulin-treated IMECs, with significantly increased ATP production, non-mitochondrial respiration, and oxidative metabolism (all P < 0.05). Significant negative correlations were revealed between microcirculatory SO2 and bioenergetic parameters.CONCLUSIONGlucotoxicity deteriorates the integrated pancreatic microcirculatory oxygen profile and bioenergetics, but this deterioration can be reversed by insulin administration.

New Estimates of Southern Ocean Annual Net Community Production Revealed by BGC‐Argo Floats

AbstractUsing an expanding Southern Ocean fleet of biogeochemical Argo (BGC‐Argo) floats, we developed a novel approach to estimate annual net community production (ANCP) by integrating subsurface oxygen drawdown from all available BGC‐Argo oxygen profiles. Our results suggest that, on average, 14% of remineralization occurs between 500 and 1,000 m and 15% occurs between the euphotic depth and 100 m. Using the improved methodology, we estimated total basin‐integrated ANCP in the Southern Ocean to be 3.89 GT C year−1 suggesting a more important role for the Southern Ocean in regulating oceanic carbon storage, atmospheric CO2 exchange and climate than previously assumed.

Revisiting weight-gain correlations for as-fabricated Zircaloy-4 cladding tubes during steam oxidation

During a loss of coolant accident, elevated temperatures and steam environment induce fuel cladding oxidation. During cladding high-temperature oxidation, the weight increase is considered as a material property when divided by the surface exposed to the environment, this is the so-called weight-gain. Many laboratories tested Zircaloy-4 specimens and used several approaches to determine weight-gain correlations. Two frequently used methods are weight measurements and metallographic measurements of scale thickness combined with diffusion simulations. Usually, assuming that weight-gain is controlled by diffusion processes, the correlations have a parabolic dependency to steam exposure duration. In the present study, a metallographic method relying on scale thickness measurements is proposed with few assumptions on the oxygen transport process in the oxide and α(O) layers. These two layers contain the main oxygen inventory. The local weight-gain is obtained by the integration of a simplified oxygen profile across the specimen thickness. The proposed method is compared to specimen weighing approach and leads to accurate predictions. The method was applied to five experimental campaigns performed in different laboratories combining more than 375 tests. A single non-parabolic weight-gain correlation covering a large temperature range (900–1500 °C) is finally provided.

Oxygen Saturation Profiles in Healthy Term Infants in Early Postnatal Life.

Oxygen saturation profiles generated by pulse oximetry are used as a clinical tool in the neonatal intensive care unit (NICU). There is limited evidence on normal oxygen saturation profile values in term infants. This study aimed to determine oxygen saturation profiles over an 8-hour monitoring period among healthy term neonates between 24 and 48 hours after birth. A prospective cohort study of healthy term neonates born at 37 to 41 weeks of gestation. Preductal oxygen saturations were continuously monitored for an 8-hour period between 24 and 48 hours of life using pulse oximetry. Oxygen profile histograms were recorded for analysis. The average percent oxygen saturation (SpO2) was measured over the entire study duration for each neonate and was characterized as the fraction of time of their SpO2 reading was in each of five intervals: ≤80, 81 to 84, 85 to 89, 90 to 94, and 95 to 100%. Seventy-five neonates were included in the study. Median SpO2 was 95.4%. Percentage time spent in each of the five SpO2 intervals was as follows: 0.07 (≤80), 0.15 (81-84), 0.88 (85-89), 26.9 (90-94), and 67.3% (95-100%). Eighteen infants (24%) spent the highest percentage of time in SpO2 of 90 to 94%. This study provides reference ranges for oxygen profiles in healthy term neonates during 24 to 48 hours of life. Nearly one-quarter of newborns spent the highest percentage of time in SpO2 of 90 to 94%. This data is important when interpreting oxygen saturation profiles of term neonates admitted to the NICU. · This study provide reference ranges for oxygen profiles in healthy term neonates during 24 to 48 hours.. · Median SpO2 was 95.4%.. · Nearly one quarter of newborns spent the highest percentage of time in SpO2 of 90 to 94%..

New DA white dwarf models for asteroseismology of ZZ Ceti stars

Context. Asteroseismology is a powerful tool used to infer the evolutionary status and chemical stratification of white dwarf stars and to gain insights into the physical processes that lead to their formation. This is particularly true for the variable hydrogen-rich atmosphere (DA) white dwarfs, known as DAV or ZZ Ceti stars. They constitute the most numerous class of pulsating white dwarfs. Aims. We present a new grid of white dwarf models that take into account advances made over the last decade in modeling and input physics of both the progenitor and the white dwarf stars. As a result, it is possible to avoid several shortcomings present in the set of white dwarf models employed in the asteroseismological analyses of ZZ Ceti stars that we carried out in our previous works. Methods. We generate white dwarf stellar models appropriate for ZZ Ceti stars with masses from ∼0.52 to ∼0.83 M⊙, resulting from the whole evolution of initially 1.5–4.0 M⊙ mass star models. These new models are derived from a self-consistent way with the changes in the internal chemical distribution that result from the mixing of all the core chemical components induced by mean molecular-weight inversions, from 22Ne diffusion, Coulomb sedimentation, and from residual nuclear burning. In addition, the expected nuclear-burning history and mixing events along the progenitor evolution are accounted for, in particular the occurrence of third dredge-up, which determines the properties of the core and envelope of post-AGB and white dwarf stars, as well as the white dwarf initial-final mass relation. The range of hydrogen envelopes of our new ZZ Ceti models extends from the maximum residual hydrogen content predicted by the progenitor history, log(MH/M⊙)∼ − 4 to −5, to log(MH/M⊙) = − 13.5, thus allowing for the first stellar models that would enable the search for seismological solutions for ZZ Ceti stars with extremely thin hydrogen envelopes – if, indeed, they do exist in nature. We computed the adiabatic gravity(g)-mode pulsation periods of these models. Calculations of our new evolutionary and pulsational ZZ Ceti models were performed with the LPCODE stellar evolution code and the LP-PUL stellar pulsation code. Results. Our new hydrogen-burning post-AGB models predict chemical structures for ZZ Ceti stars that are substantially different from those we used in our previous works, particularly in connection with the chemical profiles of oxygen and carbon near the stellar centre. We also discuss the implications of these new models for the pulsational spectrum of ZZ Ceti stars. Specifically, we find that the pulsation periods of g modes and the mode-trapping properties of the new models differ significantly from those characterizing the ZZ Ceti models of our previous works, particularly for long periods. Conclusions. The improvements in the modeling of ZZ Ceti stars we present here lead to substantial differences in the predicted pulsational properties of ZZ Ceti stars, which are expected to impact the asteroseismological inferences of these stars. This is extremely relevant in view of the abundant amount of photometric data from current and future space missions, resulting in discoveries of numerous ZZ Ceti stars.

Asteroseismology of the DAV Star L19-2

L19-2 is a DAV star, which was intermittently observed from 1976 to 2013. Five independent pulsation modes of 350, 192, 143, 118, and 113 s are identified. The five modes can be used to constrain the fitting models. The rates of period change can be obtained through the O–C method for the modes of 192 and 113 s, which can be used to study the evolution effect of DAV stars. Using the White Dwarf Evolution Code (WDEC; 2018 version), a large sample of DAV star models are evolved. The theoretical modes are calculated and used to fit the observed modes. After fine model fittings, we obtain an optimal model with an absolute difference of Φ = 0.06 s. By parameterizing the core oxygen profile, the WDEC procedure can greatly reduce the fitting error of asteroseismological models. According to our optimal model, the distance obtained through the model luminosity is only 1% different from that reported by the Gaia Data Release 2. L19-2 is a massive and hot DAV star with a relatively thick H atmosphere and a thick He layer. The stellar parameters and the rates of period change of our optimal model are slightly modified from that of the previous work. Our optimal model has a large central oxygen abundance. The central oxygen abundance is strongly correlated with the previous physical process of stellar evolution. A lot of asteroseismological work on white dwarfs presents an opportunity to explore the progenitor stars.

Three-Dimensional Numerical Study of the inlet Temperature Effects on the Performance of Planar PEMFCs

In the present study, a CFD (computational fluid dynamics) three-dimensional model is performed to investigate the effects of the inlet temperature on the power density, pressure and local transport phenomena of a single cell PEMFC (proton exchange membrane fuel cell) with straight channels. Deferent inlet temperatures of the reactants (333, 343 and 353 K) have been investigated using ANSYS-FLUENT. The interest of our work is focused on obtaining I-P and I-V curves as well as the pressure, hydrogen, oxygen and water mass fraction profiles to analyze the effect of the oxygen and hydrogen inlet temperature on the current, voltage and power densities of the studied PEMFC. From the results obtained its appears that the variation in the inlet temperature values of the PEMFC has a significant influence on the cell performances at medium and higher current density. Therefore, the results analysis of the three-dimensional and single-phase model indicates that the increase in the reactants’ inlet temperature of the studied PEMFC shows a negative impact on the generated power densities, which have an inversely proportional effect.

Muscle oxygenation during normoxic and hypoxic cycling exercise in humans with high-affinity haemoglobin.

What is the central question of this study? Do humans with high-affinity haemoglobin (HAH) demonstrate attenuated skeletal muscle deoxygenation during normoxic and hypoxic exercise? What is the main finding and its importance? Examination of near-infrared spectroscopy-derived muscle oxygenation profiles suggests that fractional oxygen extraction is blunted during hypoxic exercise in humans with HAH compared with control subjects. However, muscle tissue oxygen saturation levels were higher in humans with HAH during exercise in normoxia compared with control subjects. These alterations in fractional oxygen extraction in humans with HAH might influence blood flow regulation and exercise capacity during hypoxia. Recently, researchers in our laboratory have shown that humans with genetic mutations resulting in high-affinity haemoglobin (HAH) demonstrate better maintained aerobic capacity and peak power output during hypoxic exercise versus normoxic exercise in comparison to humans with normal-affinity haemoglobin. However, the influence of HAH on tissue oxygenation within exercising muscle during normoxia and hypoxia is unknown. Therefore, we examined near-infrared spectroscopy-derived oxygenation profiles of the vastus lateralis during graded cycling exercise in normoxia and hypoxia among humans with HAH (n=5) and control subjects with normal-affinity haemoglobin (n=12). The HAH group elicited a blunted increase of deoxygenated haemoglobin+myoglobin during hypoxic exercise compared with the control group (P = 0.03), suggesting reduced fractional oxygen extraction in the HAH group. In addition, the HAH group maintained a higher level of muscle tissue oxygen saturation during normoxic exercise (HAH, 75 ± 4% vs. controls, 65 ± 3%, P = 0.049) and there were no differences between groups in muscle tissue oxygen saturation during hypoxic exercise (HAH, 68 ± 3% vs. controls, 68 ± 2%, P = 0.943). Overall, our results suggest that humans with HAH might demonstrate divergent patterns of fractional oxygen extraction during hypoxic exercise and elevated muscle tissue oxygenation during normoxic exercise compared with control subjects.

Prognostic implications of comorbidity patterns in critically ill COVID-19 patients: A multicenter, observational study.

SummaryBackgroundThe clinical heterogeneity of COVID-19 suggests the existence of different phenotypes with prognostic implications. We aimed to analyze comorbidity patterns in critically ill COVID-19 patients and assess their impact on in-hospital outcomes, response to treatment and sequelae.MethodsMulticenter prospective/retrospective observational study in intensive care units of 55 Spanish hospitals. 5866 PCR-confirmed COVID-19 patients had comorbidities recorded at hospital admission; clinical and biological parameters, in-hospital procedures and complications throughout the stay; and, clinical complications, persistent symptoms and sequelae at 3 and 6 months.FindingsLatent class analysis identified 3 phenotypes using training and test subcohorts: low-morbidity (n=3385; 58%), younger and with few comorbidities; high-morbidity (n=2074; 35%), with high comorbid burden; and renal-morbidity (n=407; 7%), with chronic kidney disease (CKD), high comorbidity burden and the worst oxygenation profile. Renal-morbidity and high-morbidity had more in-hospital complications and higher mortality risk than low-morbidity (adjusted HR (95% CI): 1.57 (1.34-1.84) and 1.16 (1.05-1.28), respectively). Corticosteroids, but not tocilizumab, were associated with lower mortality risk (HR (95% CI) 0.76 (0.63-0.93)), especially in renal-morbidity and high-morbidity. Renal-morbidity and high-morbidity showed the worst lung function throughout the follow-up, with renal-morbidity having the highest risk of infectious complications (6%), emergency visits (29%) or hospital readmissions (14%) at 6 months (p<0.01).InterpretationComorbidity-based phenotypes were identified and associated with different expression of in-hospital complications, mortality, treatment response, and sequelae, with CKD playing a major role. This could help clinicians in day-to-day decision making including the management of post-discharge COVID-19 sequelae.FundingISCIII, UNESPA, CIBERES, FEDER, ESF.

Modelling the effect of vascular status on tumour evolution and outcome after thermal therapy

Microscale oxygenation plays a prominent role in tumour progression. Spatiotemporal variability of oxygen distribution in the tumour microenvironment contributes to cellular heterogeneity and to the emergence of normoxic and hypoxic populations. Local levels of oxygen strongly affect the response of tumours to the administration of different therapeutic modalities and, more generally, to the phenomenon of resistance to treatments. Several interventions have been proposed to improve tumour oxygenation, being the elevation of the local temperature (hyperthermia) an important one. While other factors such as the metabolic activity have to be considered, the proficiency of the tumour vascular system is a key factor both for the tissue oxygenation and for its temperature maps. Consequently, the interplay of these factors has attracted considerable attention from the mathematical modelling perspective. Here we put forward a transport-based system of partial differential equations aimed at describing the dynamics of healthy and tumour cell subpopulations at the microscale in a region placed between two blood vessels. By using this model with diverse flow conditions, we analyse the oxygen and temperature profiles that arise in different scenarios of vascular status, both during free progression and under thermal therapy. We find that low oxygen levels are associated to elevations of temperature in locations preferentially populated by hypoxic cells, and hyperthermia-induced cell death, being strongly dependent on blood flow, would only appear under highly disrupted conditions of the local vasculature. This results in a noticeable effect of heat on hypoxic cells. Additionally, when pronounced cell death occurs, it is followed by a significant increase in the oxygen levels. Our results provide quantitative insight to the physiological and biological processes taking place at sub-voxel sizes, currently not accessible to standard functional imaging due to spatial resolution limitations.

Weak Hypoxia Enhanced Denitrification in a Dissimilatory Nitrate Reduction to Ammonium (DNRA)-Dominated Shallow and Eutrophic Coastal Waterbody, Jinhae Bay, South Korea

The effects of seasonal hypoxia on sediment-water interface nitrogen (N) transformations in Jinhae Bay were examined from 2015 to 2019. The rates of benthic denitrification, anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, and sediment oxygen consumption were measured seasonally. The oxygen (O2) and hydrogen sulfide (H2S) depth profiles were measured using microelectrodes. Neither penetration nor consumption of oxygen decreased during hypoxia. Denitrification, anammox, and DNRA ranged from 0 to 0.73, 0.13, and 1.09 mmol N m-2 day-1, respectively. Denitrification, the dominant N removal pathway, increased by 75% while anammox ceased, which led to an overall increase of 55% in the total N2 gas production during hypoxia relative to that during normoxia. Enhanced denitrification is the result of increased coupled nitrification–denitrification due to the intermittent supply of oxygen during bottom water hypoxia (“weak hypoxia”). In the hypoxic period, DNRA decreased by 62%, and the relative contribution of DNRA to the total nitrogen reduction process decreased from 81 to 58%, but it still outperformed denitrification as the main nitrate reduction pathway. Sediments were strong sources of ammonium for the water column, both under normoxia and hypoxia, whereas they were a sink of nitrate from the water column during hypoxia. Bioturbation may be important for maintaining oxygen penetration and consumption in sediments. The dominance of DNRA was mainly due to the relatively high content of sulfide and organic-rich sediments. The repressed macrofaunal activity and increased coupling of nitrification and denitrification during hypoxia may have contributed to enhanced denitrification. Taken together, the overall dominance of DNRA might contribute to the development and maintenance of eutrophication and seasonal hypoxia in this system. However, in contrast to the previous results, denitrification was enhanced during “weak hypoxia,” which might be helpful in alleviating eutrophication.