O2 Distribution Research Articles

Assessing the influence of thermal structure variation on Fe and P mobility in sediments cores using Yellow Spring Instrument, diffusive gradient technology, and HR Peeper for sustainable water quality management.

The freshwater ecological characteristics in terms of the daily inventory of thermal stratification, spatial variation of O2 distribution, and the mobility of potentially toxic elements (PTEs) at the water sediment interface (WSI) are prudent freshwater assessment indices for water quality management protocol. The study conducted daily observations within a monsoon-influenced region, utilizing high-resolution techniques such as HR Peeper, Yellow Spring Instrument (YSI), and ZrO-Chelex diffusive gradient technology (DGT) to analyze PTEs, specifically phosphorus (P) and iron (Fe),within the water-sediment interface (WSI) under different temperatures and oxygen conditions. The 66-day field study showed that high thermal structure contributed significantly to production Fe ions and P from sediment under reductive dissolution of FeOOH. The study also revealed that P and Fe exhibited comparable spatial distribution patterns at the WSI, indicating a linked relationship between these PTEs. This correlation was reinforced by high Pearson correlation coefficients ranging from 0.7 to 0.9 (bilateral, p < 0.05) indicating that the concentrations of labile P were predominantly influenced by the release of phosphorus bound to iron. The fluxes of the PTEs were positive with a range of Fe, 3.3-81.5 mg/m2 day and P, 0.03-0.5 mg/m2 day showing the sediments liberated the PTEs into the benthic water. Again, high positive fluxes (Fe≈60 mg/m2 day, P≈0.5 mg/m2 day) for PTEs were obtained when stratification was high (anoxic conditions) and low (Fe≈5 mg/m2 day, P≈0.08 mg/m2 day) when stratification did not exist. This depicts that Fe/P dynamics were hinged mainly on hypoxic conditions in the benthic water under the reductive dissolution of FeOOH. The findings showed that organic materials (both solid and dissolved) correlated (> 0.7) significantly with (positive high values) Fe. This indicates that their interaction contributed to the reservoir water deterioration. However, Ca2⁺ and Mg2⁺ had little impact on the liberation of Fe-DOC-P from sediments due to their inability to compete with Fe for binding to DOC and P, as shown by their low correlation values. The research provides in-depth insights into the dynamics of PTEs on a daily timescale and offers valuable information for water management practices in inland reservoirs, particularly concerning the cycling of phosphorus (P) and its effects on ecosystem health.

In Vivo Lifetime Imaging of the Internal O2 Dynamics in Corals with near-Infrared-Emitting Sensor Nanoparticles.

Mapping of O2 with luminescent sensors within intact animals is challenging due to attenuation of excitation and emission light caused by tissue absorption and scattering as well as interfering background fluorescence. Here we show the application of luminescent O2 sensor nanoparticles (∼50-70 nm) composed of the O2 indicator platinum(II) tetra(4-fluoro)phenyltetrabenzoporphyrin (PtTPTBPF) immobilized in poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA). We injected the sensor nanoparticles into the gastrovascular system of intact colony fractions of reef-building tropical corals that harbor photosynthetic microalgae in their tissues. The sensor nanoparticles are excited by red LED light (617 nm) and emit in the near-infrared (780 nm), which enhances the transmission of excitation and emission light through biological materials. This enabled us to map the internal O2 concentration via time-domain luminescence lifetime imaging through the outer tissue layers across several coral polyps in flowing seawater. After injection, nanoparticles dispersed within the coral tissue for several hours. While luminescence intensity imaging showed some local aggregation of sensor particles, lifetime imaging showed a more homogeneous O2 distribution across a larger area of the coral colony. Local stimulation of symbiont photosynthesis in corals induced oxygenation of illuminated tissue areas and formation of lateral O2 gradients toward surrounding respiring tissues, which were dissipated rapidly after the onset of darkness. Such measurements are key to improving our understanding of how corals regulate their internal chemical microenvironment and metabolic activity, and how they are affected by environmental stress such as ocean warming, acidification, and deoxygenation. Our experimental approach can also be adapted for in vivo O2 imaging in other natural systems such as biofilms, plant and animal tissues, as well as in organoids and other cell constructs, where imaging internal O2 conditions are relevant and challenging due to high optical density and background fluorescence.

Novel design of a staggered-trap/block flow field for use in serpentine proton exchange membrane fuel cells

Enhancing the transverse velocity to the catalyst layer and exploiting the over-rib flow are two common methods of improving proton exchange membrane fuel cells (PEMFCs). The block flow field configuration significantly affects the augmentation of the transverse velocity to the catalyst layer, whereas the trap configuration significantly increases the molar concentration of O2 at the cathode catalyst layer without a pressure drop penalty. In this study, four-channel PEMFC models with different configurations were used, including the baseline and staggered-trap, -block, and -trap/block channels. The novel flow field with a combination of trap/block configurations exhibits a higher power output than those of the other designs. Furthermore, the novel staggered-trap/block channel induces a higher over-rib flow velocity than that of the baseline channel, leading to more uniform O2 and temperature distributions within the PEMFC. The optimal trap/block design increases the maximum net cell power by 8.04 % at V = 0.5 V.

A microscopic oxygen transport model for ultra-high dose rate radiotherapy in vivo: The impact of physiological conditions on FLASH effect.

Ultra-high dose rate irradiation (≥40Gy/s, FLASH) has been shown to reduce normal tissue toxicity, while maintaining tumor control compared to conventional dose-rate radiotherapy. The radiolytic oxygen (O2) depletion (ROD) resulting from FLASH has been proposed to explain the normal tissue protection effect; however, in vivo experiments have not confirmed that FLASH induced global tissue hypoxia. Nonetheless, the experiments reported are based on volume-averaged measurement, which have inherent limitations in detecting microscopic phenomena, including the potential preservation of stem cells niches due to local FLASH-induced O2 depletion. Computational modeling offers a complementary approach to understand the ROD caused by FLASH at the microscopic level. We developed a comprehensive model to describe the spatial and temporal dynamics of O2 consumption and transport in response to irradiation in vivo. The change of oxygen enhancement ratio (OER) was used to quantify and investigate the FLASH effect as a function of physiological and radiation parameters at microscopic scale. We considered time-dependent O2 supply and consumption in a 3D cylindrical geometry, incorporating blood flow linking the O2 concentration ([O2]) in the capillary to that within the tissue through the Hill equation, radial and axial diffusion of O2, metabolic and zero-order radiolytic O2 consumption, and a pulsed radiation structure. Time-evolved distributions of [O2] were obtained by numerically solving perfusion-diffusion equations. The model enables the computation of dynamic O2 distribution and the relative change of OER (δROD) under various physiological and radiation conditions in vivo. Initial [O2] level and the subsequent changes during irradiation determined δROD distribution, which strongly depends on physiological parameters, i.e., intercapillary spacing, ultimately determining the tissue area with enhanced radioresistance. We observed that the δROD/FLASH effect is affected by and sensitive to the interplay effect among physiological and radiation parameters. It renders that the FLASH effect can be tissue environment dependent. The saturation of FLASH normal tissue protection upon dose and dose rate was shown. Beyond ∼60Gy/s, no significant decrease in radiosensitivity within tissue region was observed. In turn, for a given dose rate, the change of radiosensitivity became saturated after a certain dose level. Pulse structures with the same dose and instantaneous dose rate but with different delivery times were shown to have distinguishable δROD thus tissue sparing, suggesting the average dose rate could be a metric assessing the FLASH effect and demonstrating the capability of our model to support experimental findings. On a macroscopic scale, the modeling results align with the experimental findings in terms of dose and dose rate thresholds, and it also indicates that pulse structure can vary the FLASH effect. At the microscopic level, this model enables us to examine the spatially resolved FLASH effect based on physiological and irradiation parameters. Our model thus provides a complementary approach to experimental methods for understanding the underlying mechanism of FLASH radiotherapy. Our results show that physiological conditions can potentially determine the FLASH efficacy in tissue protection. The FLASH effect may be observed under optimal combination of physiological parameters, not limited to radiation conditions alone.

Respiration and CO2 evasion dynamics in moving streambeds as a response to flow regimes

Streams and rivers are subject to discharge fluctuations that may be natural or man-made, which influence biogeochemical processes and the release of CO2 to the atmosphere. Fluctuations in discharge are also associated with changing streamwater velocity that directly affects the movement of bedforms in sandy streambeds. However, bedform movement is rarely considered when studying effects of flow dynamics on biogeochemical processes. We used planar optodes during moving-bed flume experiments to quantify the effects of different flow regimes on aerobic respiration dynamics and the subsequent release of CO2. The flow regimes included constant flow (C), sinusoidal flow (S), and single peak flow events (F). Flow regimes substantially influence aerobic respiration in the streambed and, hence, the distribution of O2 and CO2 in the streambed. Hyporheic exchange flux (HEF), bedform celerity, and respiration rates increased non-linearly with streamwater velocity. It was found that HEF and CO2 evasion were highest under dynamic flow regimes S and F. However, respiration rates, the total O2 consumed, and the total CO2 produced were highest under flow regime C. This is due to low reaction rates once the streambed became stationary in the low discharge periods of flow regimes S and F. Thus, the distribution of celerities controls total respiration. Our results highlight that substantial aerobic respiration occurs even in slow-moving streambeds and that it is important to consider bedform movement when studying biogeochemical reactions in the hyporheic zone or predicting greenhouse gas emissions from catchments.

Optimization of air distribution and coal blending in pulverized coal boilers for high-temperature corrosion prevention based on POD reduced-order modeling

High-temperature corrosion in coal-fired boilers poses a significant threat to safe operation. However, there is currently a lack of effective online monitoring and optimization methods for high-temperature corrosion. Therefore, this study proposes a novel approach to rapidly predict the distribution of chemical species and evaluate high-temperature corrosion degrees, along with optimizing operating conditions to prevent high-temperature corrosion. Firstly, a total of 564 Computational Fluid Dynamics (CFD) simulations are performed on a 330 MW tangentially fired boiler, covering various operating conditions, including coal blending, air distribution, boiler load, etc., to obtain a database of O2, CO, and H2S distributions within the boiler. Then a method based on Proper Orthogonal Decomposition (POD) and Support Vector Regression (SVR) is used to process the database to realize real-time prediction of boiler chemical species distribution, which is next utilized as inputs of a high-temperature corrosion evaluation to obtain in-situ corrosion degree distribution. Finally, Particle Swarm Optimization (PSO) is used to optimize coal blending and air distribution schemes, effectively reducing severe corrosion ratio from 36.34 % to 10.04 % in a typical case by improving the atmosphere near the water walls. This study thus provides a new perspective for online boiler diagnostics and digital twin construction, particularly by achieving online monitoring of high-temperature corrosion and optimizing operating conditions to prevent corrosion.

Selective H2 production from plastic waste through pyrolysis and in-line oxidative steam reforming

This study deals with the proposal of pyrolysis and in-line oxidative steam reforming (P-OSR) for plastic waste valorization and assesses the potential of this strategy for the selective production of H2. Overall, the study aims at progressing towards the fine-tuning of the pyrolysis-reforming technology by co-feeding O2. Thus, a multi-point O2 injection system has been developed to ensure a suitable O2 distribution in the reforming reactor and avoid the formation of hot spots, as they may cause catalyst deactivation by metal sintering. Moreover, as O2 is directly supplied into the catalytic bed, pre-combustion of the volatile stream before contacting the catalyst is avoided and in-situ coke combustion is promoted. The P-OSR of HDPE was carried out in a two-step reaction system, which combines CSBR (conical spouted bed reactor) and FBR (fluidized bed reactor) technologies. The experiments were conducted in continuous mode and the influence of the main process conditions at zero time on stream was analyzed. Thus, the effect of reforming temperature was studied in the 550–750 °C range, that of the space time from 3.12 to 15.62 gcat min gHDPE−1, steam to plastic (S/P) ratio between 2 and 5 and equivalence ratio (ER) from 0 to 0.3. Under the optimum conditions (700 °C, S/P of 3, 12.5 gcat min gHDPE−1 and ER of 0.2), a H2 production of 25.0 wt% was obtained, which is only 28.6 % lower than that obtained in the conventional pyrolysis-steam reforming (P-SR) process. The results obtained confirm the potential of continuous P-OSR process for the selective production of H2.

Engineering a High-Loading Sub-4 nm Intermetallic Platinum-Cobalt Alloy on Atomically Dispersed Cobalt-Nitrogen-Carbon for Efficient Oxygen Reduction in Fuel Cells.

Developing a high-performance membrane electrode assembly (MEA) poses a formidable challenge for fuel cells, which lies in achieving both high metal loading and efficient catalytic activity concurrently for MEA catalysts. Here, we introduce a porous Co@NC carrier to synthesize sub-4 nm PtCo intermetallic nanocrystals, achieving an impressive Pt loading of 27 wt %. The PtCo-CoNC catalyst demonstrates exceptional catalytic activity and remarkable stability for the oxygen reduction reaction. Advanced characterization techniques and theoretical calculations emphasize the synergistic effect between PtCo alloys and single Co atoms, which enhances the desorption of the OH* intermediate. Furthermore, the PtCo-CoNC-based cathode delivers a high power density of 1.22 W cm-2 in the MEA test owing to the enhanced mass transport, which is verified by the simulation results of the O2 distributions and current density inside the catalyst layer. This study lays the groundwork for the design of efficient catalysts with practical applications in fuel cells.

Cholesterol inhibits oxygen permeation through biological membranes: mechanism against double-bond peroxidation.

The presence of oxygen molecules (O2) in biological membranes promotes lipid peroxidation of phospholipids with unsaturated acyl chains. On the other hand, cholesterol is considered to be an antioxidant molecule as it has a significant barrier effect on the permeation of O2 across membranes. However, a comprehensive explanation of how cholesterol affects the distribution and diffusion of O2 within lipid bilayers is yet to be established. In this study, we investigated the interaction of oxygen molecules with polyunsaturated lipid bilayers using molecular dynamics (MD) simulations. The degree of lipid unsaturation and the concentration of cholesterol were varied to study the permeation of O2. The free energy profile of O2 diffusing from the water phase to the lipid bilayer was calculated using biased umbrella MD simulations. The results show that O2 passively translocates into the membrane without changing the physical properties of the bilayer. Interestingly, in the unsaturated lipid bilayers the presence of cholesterol led to a significantly decreased permeation of O2 and an increase in the lipid chain order. Our results indicate that the hydroxyl groups of cholesterol strongly interact with the O2 molecules effectively inhibiting interactions between the oxygens and the double bonds in unsaturated lipid tails. In addition, a linear relationship between permeation and the ratio of membrane thickness and area per lipid was found. These insights can help our understanding of how the degree of unsaturation in a lipid tail and cholesterol affect lipid peroxidation at the molecular level.

Ultrasound-Driven Non-Metallic Fenton-Active Center Construction for Extensive Chemodynamic Therapy.

Chemodynamic therapy (CDT) is an emerging tumor microenvironment-responsive cancer therapeutic strategy based on Fenton/Fenton-like reactions. However, the effectiveness of CDT is subject to the slow kinetic rate and non-homogeneous distribution of H2 O2 . In this study, a conceptual non-metallic "Fenton-active" center construction strategy is proposed to enhance CDT efficiency using Bi0.44 Ba0.06 Na0.5 TiO2.97 (BNBT-6) nanocrystals. The separated charge carriers under a piezoelectric-induced electric field synchronize the oxidation of H2 O and reduction of H2 O2 , which consequently increases hydroxyl radical (·OH) yield even under low H2 O2 levels. Moreover, acceptor doping induces electron-rich oxygen vacancies to facilitate the dissociation of H2 O2 and H2 O and further promote ·OH generation. In vitro and in vivo experiments demonstrate that BNBT-6 induces extensive intracellular oxidative stress and enhances cell-killing efficiency by activating necroptosis in addition to the conventional apoptotic pathway. This study proposes a novel design approach for nanomaterials used in CDT and presents a new treatment strategy for apoptosis-resistant tumors.

CFD modelling of longwall goaf atmosphere under vertical boreholes gas drainage

To effectively control and utilise large amounts of gas emissions from underground coal mining, Australia and many other countries rely heavily on a series of vertical boreholes to capture the gas during mining. This gas capture not only reduces the greenhouse gas impact but also recovers a significant amount of energy. Vacuum pumps are connected to surface boreholes to drive gas flow from the goaf and overlying fractured strata. However, applying high suction pressure to the boreholes may cause more oxygen to enter the goaf from the longwall working face. This influx of oxygen can potentially react with residual coal in the goaf, accelerating coal self-heating and possibly resulting in endogenous fires. By analysing extensive goaf gas drainage data collected from Australian longwalls, researchers have established the normal trend of goaf gas concentration and flow rate as a result of intensive goaf gas drainage. This paper further developed goaf gas flow CFD models with the operating vertical boreholes, which were then calibrated using field borehole production data under certain operating conditions. The CFD model simulated the distribution of O2 and CH4 as well as the gas flow pathways in the goaf, considering the complication of goaf gas drainage. This study found that the O2 concentration is higher on the goaf tailgate side under the influence of tailgate side boreholes compared to the maingate side. Furthermore, for the well-compacted goaf, a significant proportion of the ventilation air travels through ‘high permeability flow channels’ provided by the goaf edge on tailgate side, and then circulates back into the goaf boreholes. These CFD modelling results not only enable ventilation engineers to visualize the goaf gas flow patterns under the impact of multiple operating boreholes, but also to understand the impact on goaf atmosphere through sensitivity analysis of natural goaf characteristics, such as goaf permeability distributions and gas emission rates.

Numerical simulation to optimize passive aeration strategy for semi-aerobic landfill

Passive aeration has been proven to be efficient for oxygen supply in landfill. The combination of passive aeration and semi-aerobic landfill offers a cost-effective and energy-efficient approach to solid waste (SW) treatment. However, determining the optimal strategy for this combination has remained unclear. This study aimed to investigate the strategy of passive aeration in a semi-aerobic landfill using numerical simulation methods. A model coupled hydrodynamic model and compartment model for degradation of SW was implemented. The accuracy was well validated by comparing measured and simulated results in a pilot-scale landfill. Compared with natural convection, passive aeration by funnel caps could increase air input by 20 %. By simulating volumetric fraction distribution of CO2, CH4 and O2 in landfill, an orthogonal experiment including 4 factors was designed to identify that the diameter of tubes (DT), the spacing between tubes (ST) and the landfill depth (LD) have substantial impacts on aerobic zone ratio (AZR) of landfill. But the diameter of gas ports (DGP) has an indiscernible effect. The optimized factors were determined to be as follows: DT = 0.3 m, ST = 15.0 m, DGP = 0.05 m, and LD = 4.0 m, under which the semi-aerobic landfill could enhance SW degradation. Large diameter and spacing of tubes are favorable to improve the AZR at the top of the landfill, and the aerobic zone mainly exists near the ventilation tubes. These findings contribute to the development of more efficient and sustainable solid waste treatment strategies in semi-aerobic landfill.

O2-generating multifunctional polymeric micelles for highly efficient and selective photodynamic-photothermal therapy in melanoma

Photothermal therapy (PTT) and photodynamic therapy (PDT) have received tremendous attention owing to their great potential for tumor treatment. However, two main issues hamper the antitumor performance of PDT: overexpression of glutathione (GSH) in tumors, which consumes PDT-induced reactive oxygen species (ROS), and hypoxia within the tumor microenvironment. The drawbacks of PTT include uneven temperature distribution and the upregulation of the heat-shock proteins in tumors, both of which result in ineffective treatment. To address these issues, a MnO2 doped nano-delivery system (HTIM-PMs) was synthesized by one-step self-assembly of disulfide bond bridged copolymers for indocyanine green (ICG) and MnO2 loading. The surface of polymeric micelles was layered with hyaluronan (HA) and transactivator (TAT) peptides to improve active targeting and increase cell penetration. After internalization, HTIM-PMs showed responsiveness to the tumor microenvironment (acid pH, high glutathione, high H2O2). Breaking the disulfide bond reduced the intratumoral GSH level and simultaneously released the MnO2 and ICG. The released MnO2 further reduced the GSH level and promoted O2 generation, thus enhancing the PDT effect. The PTT-mediated hyperthermia accelerated blood flow, which is beneficial for O2 distribution, and promotes ROS diffusion. These PTT-mediated adjuvant effects further overcame the limitations of PDT and the robust PDT effect in turn compensated for the deficiency of PTT. This promising platform exhibited a significant improvement in the PTT-PDT cancer treatment strategy compared to previously reported nanostructures.

Effects of preheating temperature, O2 distribution concentration and combustion temperature on the formation of PM during preheating-low NO combustion

Clarifying the mechanism of multi-mode PM formation during pulverized coal preheating-combustion is expected to facilitate the synergistic control of NO and PM, and a significant low carbon way to achieve clean combustion. In this study, combustion experiments under different preheating-combustion conditions were conducted in a preheating-combustion furnace. Based on this, a system coupling design was explored by combining preheating-combustion with air staging. The results demonstrated a significant simultaneous reduction in both PM and NO during preheating-combustion, achieving a synergistic control of PM and NO emissions. With an increase in preheating temperature(Tp), the NO formation decreased, while the PM10 formation increased. Increasing the excess air coefficient(αp) reduced the PM10 formation, while the NO exhibited a trend of initially decreasing and then increasing. The impact of the combustion temperature(Tc) on NO and PM was more pronounced, especially with a significant increase of 80.59% in the PM0.3 (from 1300 K to 1700 K). Furthermore, the effect of the interaction of the three factors on NO: αp and Tc > αp and Tp > Tp and Tc. After coupling preheating-combustion with air staging, the formation of NO and PM0.3 decreased by 33.27% and 17.43%, respectively, compared to the preheating-combustion baseline.

Air distribution and coal blending optimization to reduce slagging on coal-fired boiler water wall based on POD reduced order modeling for CFD

Slagging is a common phenomenon interfering with the safe and efficient operation of coal-fired boilers. Due to the lack of monitoring methods for species and temperature distribution near the water wall, which is critical for slagging formation, it is a tricky problem to detect and reduce the slagging in real time. A method for slagging distribution prediction and anti-slagging optimization of a 330 MW tangentially coal-fired boiler is developed in this paper. Proper orthogonal decomposition (POD) reduced order modeling and support vector machine (SVM) are used to predict the distribution of temperature and O2 near the water wall by taking 15 variables as input parameters (load, coal types, primary air rate, secondary air rate, excess air coefficient, and secondary air velocities). Next, fuzzy comprehensive evaluation (FCE) is employed to quantify the slagging occurrence and distribution on the water wall. Furthermore, the real time slagging prediction is realized with the combination of POD, SVM, and FCE. Finally, the conventional genetic algorithm (CGA) and simulated annealing genetic algorithm (SAGA) are adopted to optimize the air distribution schemes and coal blending schemes to reduce the slagging ratio, and their performances are compared. The results indicate that the predictions of temperature and O2 with POD show a good agreement with CFD simulations. In the optimization process, whether air distribution is optimized alone or both coal blending and air distribution are optimized simultaneously, the performance of SAGA is better than that of CGA. After optimizing the air distribution with SAGA, the slagging ratio of a typical operating condition with a load of 330 MW is reduced from 14.21% to 7.16%. The slagging ratio is further reduced to 5.36% after optimizing air distribution and coal blending schemes simultaneously. The proposed slagging prediction and optimization for anti-slagging opens a new perspective to alleviate slagging of water walls effectively.

Steps to understand the role played by the main operating conditions in the oxidative steam reforming of biomass fast pyrolysis volatiles

Biomass pyrolysis and in-line catalytic oxidative steam reforming of the volatiles (P-OSR) has been analyzed in a two-step reaction system made up of a conical spouted bed reactor (CSBR) and a fluidized bed reactor (FBR). A novel O2 multi-point injection system has been designed in order to ensure suitable O2 distribution in the FBR, and hence avoid the formation of hot spots that may lead to irreversible catalyst deactivation by metal sintering. Optimization of the main process parameters has been approached in order to maximize H2 production and overcome the high energy requirements of the endothermic reforming reaction. The study has been conducted in the following ranges of the operating conditions: Reforming temperature, 550–700 °C; space time, 5–20 gcat min gvolatiles−1; steam/biomass (S/B) ratio, 2.5–5; and equivalence ratio (ER) from 0 to 0.19. Moderate reforming temperatures (600–650 °C), a S/B value of 3 and a space time of 15 gcat min gvolatiles−1 are the optimum conditions for the process. Furthermore, when low space time values are used, O2 feeding rates into the reforming step of up to an ER value of 0.12 (corresponding to autothermal operation (ATR)) revealed a synergistic effect promoting reforming reactions. Thus, an improvement in H2 production from 6.81 wt% to 8.26 wt% was observed by changing ER from 0 to 0.12, which means H2 production increases by 21.4% compared to the conventional pyrolysis-reforming (P-SR) process. Therefore, the promising results obtained in this study prove the suitability of the continuous P-OSR strategy for H2 production from biomass and involve a step forward towards the scaling up of the process.

Effects of bipolar plate flow channel configuration on thermal-electric performance of direct ammonia solid oxide fuel cell: Part I - Numerical study of channel section geometry

Direct ammonia SOFCs (DA-SOFCs) are numerical studied to investigate the effects of bipolar plate flow channel configuration on thermal-electric performance. This study establishes a planar DA-SOFC model and investigates triangular, quadrangular, and oval flow channel configurations’ impact using numerical simulations. Results reveal oval cross-section channels outperform trapezoidal and triangular ones, achieving power density increases of 15.6%, 16.1%, and 18.6%, respectively, compared to rectangular channels at 0.6V. The oval channel displays superior velocity and vorticity, enhancing mass transfer between the main flow and reaction zone. Increasing channel width reduces rib width, promoting O2 distribution, temperature improvement via exothermic reactions, NH3 decomposition into H2, and improved cell performance. Rib width increase shortens diffusion and reduces concentration polarization, but increases ion transport and ohmic polarization. A theoretical formula for optimal rib width (Wrib0) to minimize polarization loss is provided. These findings offer a comprehensive reference for optimizing DA-SOFC design.

A theoretical study of H2 O2 as the surrogate of dose in minibeam radiotherapy, with a diffusion model considering radical removal process.

Minibeam radiation therapy (MBRT) is an innovative dose delivery method with the potential to spare normal tissue while achieving similar tumor control as conventional radiotherapy. However, it is difficult to use a single dose parameter, such as mean dose, to compare different patterns of MBRT due to the spatially fractionated radiation. Also, the mechanism leading to the biological effects is still unknown. This study aims to demonstrate that the hydrogen peroxide (H2 O2 ) distribution could serve as a surrogate of dose distribution when comparing different patterns of MBRT. A free diffusion model (FDM) for H2 O2 developed with Fick's second law was compared with a previously published model based on Monte Carlo & convolution method. Since cells form separate compartments that can eliminate H2 O2 radicals diffusing inside the cell, a term describing the elimination was introduced into the equation. The FDM and the diffusion model considering removal (DMCR) were compared by simulating various dose rate irradiation schemes and uniform irradiation. Finally, the DMCR was compared with previous microbeam and minibeam animal experiments. Compared with a previous Monte Carlo & Convolution method, this analytical method provides more accurate results. Furthermore, the new model shows H2 O2 concentration distribution instead of the time to achieve a certain H2 O2 uniformity. The comparison between FDM and DMCR showed that H2 O2 distribution from FDM varied with dose rate irradiation, while DMCR had consistent results. For uniform irradiation, FDM resulted in a Gaussian distribution, while the H2 O2 distribution from DMCR was close to the dose distribution. The animal studies' evaluation showed a correlation between the H2 O2 concentration in the valley region and treatment outcomes. DMCR is a more realistic model for H2 O2 simulation than the FDM. In addition, the H2 O2 distribution can be a good surrogate of dose distribution when the minibeam effect could be observed.

Temporal succession and spatial heterogeneity of humification, pathogens and bacterial community in facultative heap composting

The oxygen (O2) content of heap composting pile gradually decreased with depth, mainly because of limitations to air diffusion. Owing to uneven distribution of O2, composting was aerobic in upper layer, facultatively anaerobic in middle layer, and anaerobic fermentation occurred in bottom layer. Therefore, this study investigated temporal succession and spatial heterogeneity of humification, pathogens and bacterial community in facultative heap composting. In this study, pig manure alone or mixed with cornstalk was composted for 90 days without ventilation or turning. Different compost layers exhibited discrepancies in maturity and bacterial community due to differences in air diffusion during heap composting. From the compost pile’s upper to lower levels, the maturity of both treatments decreased from 80.60% to 0%, and the Shannon index decreased from 4.09 to 2.08. Cornstalk regulation significantly improved compost maturity and humification, brought obvious improvements to bacterial diversity and cooperative interactions and accelerated transformation from anaerobic to aerobic bacteria by enhancing porosity and oxygen diffusion. Cornstalk addition would slow the rate of pathogen reduction but could inactivate more thoroughly. The structural equation model revealed oxygen content, temperature and bacterial community mainly influenced pathogen inactivation, and key factors affecting humification were dissolved organic carbon and bacterial community.

Shrinking of the Arabian Sea oxygen minimum zone with climate change projected with a downscaled model

In Arabian Sea (AS), land-locked northern boundary and strong seasonal productivity lead to the formation of one of the most intense open ocean Oxygen Minimum Zones (OMZs). Presence of this perennial OMZ has significant consequences on adjacent coastal fisheries and ecosystem. Simulations from CMIP5 suggest significant weakening of both monsoonal winds and productivity under high emission scenario. But the fate of AS OMZ in this scenario - whether it will expand or shrink - still remains elusive, mainly due to poor representation of extent and strength of AS OMZ in CMIP5 present-day simulations. To address this, we analyze the distribution of O2 in AS from a subset of three contrasted CMIP5 simulations, and complemented with a set of regional downscaled model experiments which we forced at surface and open boundaries using information from those three CMIP5 models. We tested two regional downscaling approaches - with and without correction of CMIP5 biases with respect to observations. Using a set of sensitivity experiments, we disentangle the contributions of local (atmospheric) forcing vs. remote (at the lateral boundaries) forcing in driving the future projected O2 changes. While CMIP5 projects either shrinking or expansion of the AS OMZ depending on the model, our downscaling experiments consistently project a shrinking of AS OMZ. We show that projected O2 changes in OMZ layer are affected by both local and remote processes. In the southern AS, the main response to climate change is oxygenation that originates from the boundaries, and hence downscalled and CMIP5 model responses are similar. In contrast, in northern AS, downscaling yields a substantial reduction in O2 projection discrepancies because of a minimal influence of remote forcing there leading to a stronger sensitivity to improved local physics and improved model representation of present-day conditions. We find that when corrected for present-day biases, projected deoxygenation in the northern AS is shallower. Our findings indicate the importance of downscaling of global models in regions where local forcing is dominant, and the need for correcting global model biases with respect to observations to reduce uncertainties in future O2 projections.