Internal Oxygen Research Articles

Effect of internal oxygen substituents on the properties of bowl-shaped aromatic hydrocarbons

In this study, we compare a bowl-shaped aromatic hydrocarbon with internal methoxy groups to related derivatives with hydrogen, methyl, and anisyl groups, evaluating their electron-accepting properties, electronic absorption spectra, and fullerene-binding behavior.

Oxygen-carrying acid-responsive Cu/ZIF-8 for photodynamic antibacterial therapy against cariogenic Streptococcus mutans infection.

Caries as a result of acid demineralization is the most common oral microbial infectious disease. Due to the small and complex intraoral operating space, it is challenging to completely remove Streptococcus mutans (S. mutans) and other cariogenic bacteria. As an intelligent acid-responsive photosensitive nanomaterial, O2-Cu/ZIF-8@Ce6/ZIF-8@HA (OCZCH) was chosen to adapt to the anaerobic and acidic microenvironment for inactivating S. mutans. In this work, OCZCH not only exhibits a regular nanomorphology in SEM and TEM images but also shows intelligent acid responsiveness as evidenced by the release of Ce6 and oxygen. When excited by near-infrared light at 650 nm, Ce6 releases reactive oxygen species (ROS) that act synergistically with internal oxygen to significantly enhance the antimicrobial therapeutic effect of photodynamic therapy (PDT). In vitro antimicrobial experiments showed that OCZCH could achieve an impressive sterilization effect against S. mutans and biofilm. Notably, the acid-producing ability of the bacteria was also significantly inhibited. With its oxygen-carrying photosensitizing properties, excellent responsiveness to acidic environments, and antimicrobial capacity under anaerobic conditions, OCZCH is considered an innovative candidate for clinical application in treating dental caries.

High-efficiency water splitting catalyzed by NiMoO4 nanorod arrays decorated with vacancy defect-rich NiTex and MoOy layers

Nickel molybdate is a promising non-noble metal candidate for alkaline hydrogen evolution reaction (HER), but its insufficient activity due to its low conductivity and slow reaction kinetics hinders its application for large-scale commercial hydrogen production. Here, we report an efficient self-supporting electrocatalyst consisting of NiMoO4 nanorods modified by MoOy with abundant internal oxygen vacancies and epitaxially grown NiTex with high specific surface area for alkaline HER. Benefiting from the structural advantages of nanorods/nanosheets integrated electrode, a larger specific surface area and abundant active centers can be provided for the HER. Such constructed NiTex/MoOy/NiMoO4 catalyst achieves a low overpotential of 59 mV to drive a current density of 10 mA cm−2 and a low Tafel slope of 32.8 mV dec−1 in 1.0 M KOH solution with sustainable durability. Additionally, a two-electrode electrolytic cell system assembled with NiTex/MoOy/NiMoO4 and NiMoO4 employed as cathode and anode, respectively, extraordinary performance with a voltage of 1.49 V at a current density of 10 mA cm−2 was achieved in alkaline electrolyte. This work demonstrates a novel idea for metalloid Te-modified transition metal oxides, which is expected to expand the family of stable and efficient transition metal oxide (such as CoMoO4, Co3O4, NiCo2O4, etc.)-based catalysts for energy electrocatalysis.

A novel epoxy coating with nanocatalytic anticorrosion performance achieved by single-atom Fe-N-C catalyst

In view of the critical importance of oxygen to corrosion evolution, to starve corrosion via depleting oxygen in coatings is a promising strategy. In this work, a novel nanocatalytic anticorrosion concept is proposed to design new coating with outstanding corrosion resistance. Different from the passive barrier of traditional coatings and self-repair after corrosion of current stimuli-feedback coatings, such coating could spontaneously eliminate internal diffused oxygen and greatly suppress the corrosion process. As a proof of concept, single-atom Fe-N-C electrocatalyst with isolated FeN4 active sites is synthesized by a simple confined carbonization method, exhibiting excellent oxygen reduction performance (E1/2 = 0.902 V). In composite coating, the evenly dispersed Fe-N-C compensates for the coating defects and serves as oxygen scavengers, which could actively adsorb and consume ambient oxygen, thereby preventing oxygen penetration to the metal substrate surface, eliminating the oxygen contribution to corrosion and significantly boosting the anticorrosion performance of epoxy coating. This in-situ mediation for oxygen in coating prevents metal substrate from receiving new supply of oxygen, while imparting active anticorrosion property to the coating.

Performance and mechanism study of Ce2(SO4)3 for methane chemical looping partial oxidation

Partially oxidizing methane into syngas via a two-step chemical looping scheme was a promising option for methane transformation. Ce2(SO4)3 was selected to explore the performance and mechanism of methane chemical looping partial oxidation (CLPOM) to syngas. Thermodynamic and kinetic analysis forecast the Ce2(SO4)3 as a promising candidate for CLPOM. Compared with literature, Ce2(SO4)3 not only had an outstanding syngas selectivity, but also an appropriate CH4 conversion and molar ratio, and CH4 conversion could reach 90.5 % of thermodynamic result. As revealed via characterization, Ce2(SO4)3(102) surface had the highest peak intensity and the migration of lattice oxygen played an important role in CLPOM. Some of them were tend to agglomeration and these small particles were less than 5 μm. Density functional theory calculations demonstrated that CH4 series dehydrogenation products tended to adsorb at O site and CH3 → CH2 + H was the rate-determining step. The reaction of surface lattice oxygen atoms and migration of the internal lattice oxygen atoms could inhibit carbon deposition, promote CH4 conversion and syngas generation in experiment. Compared with NiO, Ce2(SO4)3 had a lower energy barrier of lattice oxygen migration, which could increase the reaction rate.

Effects of oxygen on the response of mitochondria to X-irradiation and reactive oxygen species-mediated fibroblast activation

Purpose In living organisms, sensitivity to radiation increases in the presence of oxygen (O2) compared with that under anoxic or hypoxic conditions. Here, we investigated whether O2 concentration affected the response of mitochondria to X-rays radiation, which is associated with tumor microenvironment formation via fibroblast activation in radiation-related tumors. Materials and methods O2 concentrations were controlled at <5% (internal environmental oxygen condition) or anoxic levels during culture of normal human diploid lung fibroblasts TIG-3 and MRC-5. Protein expression associated with the response of mitochondria to radiation was assessed using immunostaining or western blotting. Results Induction of DNA damage (marker: γ-H2A histone family member X) and mitochondrial signaling (AMP-activated protein kinase), suppression of mitochondrial metabolic activity, and generation of reactive oxygen species occurred with radiation in cells cultured under 5% and 20% O2 conditions. However, reducing O2 concentration mitigated the effects of radiation on cell growth, mitochondrial damage (parkin), induction of antioxidant responses (nuclear factor E2-related factor 2), and fibroblast activation (α-smooth muscle actin). Radiation did not affect the markers used in this study in the absence of O2. Conclusion O2 concentration affected the response of mitochondria to radiation and reactive oxygen species-mediated fibroblast activation. Higher O2 concentrations enhanced the effects of radiation on mitochondria in human fibroblasts. In vitro studies may overestimate in vivo radiation effects due to high O2 concentrations.

Contrasting seasonal dynamics of dormancy, respiratory metabolism and cell cycle state in grapevine buds of a subtropical and Mediterranean climate

AbstractGrapevine (Vitis vinifera L.) is the most widely cultivated fruit crop worldwide, contributing substantially to rural economies. The production cycle and productivity depend on seasonal cues and can range from a strongly deciduous habit in cool‐temperate climates to evergreen in subtropical and tropical climates. The influence of the different seasonal conditions on the dynamics of the perennating bud, including the degree of growth and metabolic quiescence, cell cycle status and internal tissue oxygen status between different climatic zones is largely unknown. This knowledge is important for adapting to changing climate conditions and for crop expansion to wider regions. This study investigated the growth and metabolic physiology of the perennating bud of commercially grown cv. Flame Seedless table grapes from Mediterranean and subtropical climate in Western Australia, from summer until late winter. Climate data were obtained, showing differences in minimum (night) temperature between the two climates, reflected by differences in calculated chilling units. Bud dormancy increased during autumn of both climates;however, the onset and depth of dormancy of buds from the subtropical region were attenuated relative to the Mediterranean condition. Stark contrasts were also observed in metabolism. The respiration of subtropical‐grown buds increased over fivefold during late autumn and winter, while that of Mediterranean‐grown buds increased less than twofold. This was also reflected in less desiccation of the subtropical‐grown buds, and an apparently greater degree of hypoxia within the bud during late winter, prior to bud burst. Collectively, these data show pronounced differences in growth and metabolic physiology of commercially grown table grapes, which provide a foundation for investigating the influence of differing climate and seasonality on the growth and productivity of table grapes and how these may be managed through breeding and agronomy.

Bimetallic ZIFs derived 3D acetylene black loading La2O3/Co bifunctional ORR/OER catalysts

A new type of acetylene black (AB) loading La2O3-Co/AB catalyst derived from rare earth (RE) La-doped zeolite imidazole framework-67 (ZIF-67) was prepared by composite synthesis strategy to make up for the defects of the weak activity and conductivity of single transition metal catalysts. The different coordination forms of La and cobalt hinder the growth of La-ZIF-67 crystals and promote the exposure of active sites, and the La2O3 in the pyrolysis product improves the stability of the catalyst. The introduction of AB provided abundant anchor sites to facilitate the heterojunctions formation and the electronic transfer at the interface. Remarkably, La2O3-Co/AB showed high ORR half-wave potential and low OER overpotential, which is believed to benefit from the rich CoNx local environment, heterostructure with internal electric field and oxygen vacancies.

Predicting physiologically-relevant oxygen concentrations in precision-cut liver slices using mathematical modelling.

Precision cut liver slices represent an encouraging ex vivo method to understand the pathogenesis of liver disease alongside drug induced liver injury. Despite being more physiologically relevant compared to in vitro models, precision cut liver slices are limited by the availability of healthy human tissue and experimental variability. Internal oxygen concentration and media composition govern the longevity and viability of the slices during the culture period and as such, a variety of approaches have been taken to maximise the appropriateness of the internal oxygen concentrations across the slice. The aim of this study was to predict whether it is possible to generate a physiologically relevant oxygen gradient of 35-65mmHg across a precision cut liver slice using mathematical modelling. Simulations explore how the internal oxygen concentration changes as a function of the diameter of the slice, the position inside the well and the external incubator oxygen concentration. The model predicts that the desired oxygen gradient may be achieved using a 5mm diameter slice at atmospheric oxygen concentrations, provided that the slice is positioned at a certain height within the well of a 12-well plate.

Selection of a suitable photosynthetically active microalgae strain for the co-cultivation with mammalian cells.

Preventing hypoxic zones in 3D bioprinted mammalian cell-laden constructs using an internal oxygen supply could enable a more successful cultivation both in vitro and in vivo. In this study, the suitability of green microalgae as photosynthetic oxygen generators within bioprinted constructs was evaluated by defining and investigating important parameters for a successful co-culture. First, we assessed the impact of light–necessary for photosynthesis–on two non-light adapted mammalian cell types and defined red-light illumination and a temperature of 37°C as essential factors in a co-culture. The four thermotolerant microalgae strains Chlorella sorokiniana, Coelastrella oocystiformis, Coelastrella striolata, and Scenedesmus sp. were cultured both in suspension culture and 3D bioprinted constructs to assess viability and photosynthetic activity under these defined co-culture conditions. Scenedesmus sp. proved to be performing best under red light and 37°C as well as immobilized in a bioprinted hydrogel based on alginate. Moreover, the presence of the antibiotic ampicillin and the organic carbon-source glucose, both required for mammalian cell cultures, had no impact on bioprinted Scenedesmus sp. cultures regarding growth, viability, and photosynthetic activity. This study is the first to investigate the influence of mammalian cell requirements on the metabolism and photosynthetic ability of different microalgal strains. In a co-culture, the strain Scenedesmus sp. could provide a stable oxygenation that ensures the functionality of the mammalian cells.

Investigation of local sensitivity for vehicle-oriented fuel cell stacks based on electrochemical impedance spectroscopy

The lifetime of fuel cells is a severe constraint on fuel cell industrialization, which is significantly influenced by the consistency of the fuel cell stack. This paper is the first to measure the impedance of a whole high-power fuel cell stack throughout its ten equal areas based on a multi-channel impedance test system. Based on the equivalent circuit model combined with the relaxation time distribution, the differences in the local polarization dynamics processes of the stack and its sensitivity to working condition variations are analyzed in detail. Additionally, the Pearson correlation between the local voltage and internal state parameters is quantified. The results show that the distribution characteristics of the local polarization dynamics losses are inherent to the stack structure and assembly errors, but are less influenced by the working conditions without extreme conditions. Furthermore, the robust correlations between the local voltage and the internal ohmic resistance and oxygen diffusion resistances in the stack are revealed. More importantly, this study would support the variance assessment of the internal state based on the local voltage, which will have comprehensive applications in controlling fuel cell systems.

The effects of low oxidation-reduction potential on the performance of full-scale hybrid membrane-aerated biofilm reactors

Membrane-Aerated Biofilm Reactors (MABRs) are becoming a popular process intensification alternative within wastewater treatment plants (WWTP). Indeed, the nitrogen removal capacity of aerobic/anoxic/anaerobic reactors can be substantially enhanced with reduced energy consumption and footprint requirements. However, little is known about how oxidation–reduction potential (ORP) may impact their overall process performance. This study aims to report some of these effects by showing the results of almost three years of monitoring of two hybrid MABRs (R1, R2) adjacent to an existing Biodenipho™ facility. In Period 1 (P1), R1 and R2 were fed with anaerobic mixed liquor from the selector for the biological phosphorus removal zone. In Period 2 (P2), external aeration was introduced to increase ORP values (R1, R2), and membranes were replaced (R1) or cleaned (R2). Results show an increase in nitrification rates: from 0.27 and 0.33 g N m−2 d−1 in R1/R2 during P1 to 1.0 and 0.80 g N m−2 d−1 in R1/R2 during P2. 16 s rRNA amplicon sequencing analysis revealed that the relative abundance of nitrifying organisms increased from 0.2 to 6.7 % in R1 and 0.8 to 5.3 % in R2 in P2 (in detriment of microbes with fermenting capabilities). Energy dispersive X-ray spectroscopy confirmed the presence of coating substances under the lowest ORP (P1), which could be pyrite and its precursors like mackinawite. Overall, it is hypothesized that low ORP conditions (P1) had a detrimental effect on nitrification performance, as it promoted the reduction of different iron and sulfur compounds, which in turn a) precipitate in the biofilm as FeS increasing mass transfer limitations and competing with biomass for space; b) re-oxidize increasing the internal oxygen demand; c) inhibit nitrifiers growth.

Prognostic predictive value of intracranial pressure and cerebral oxygen metabolism monitoring in patients with spontaneous intracerebral hemorrhage

ObjectiveOur study aimed to investigate the predictive value of intracranial pressure (ICP) and cerebral oxygen metabolism monitoring in the postoperative prognosis of patients with spontaneous intracerebral hemorrhage (SICH).MethodsThe clinical data of 55 patients with SICH treated by neurosurgery were analyzed retrospectively. These patients were divided into two groups based on postoperative Glasgow Outcome Scale (GOS) scores, i.e., the poor prognosis group (GOS I-III) and the good prognosis group (GOS IV and V). Next, the ICP and cerebral oxygen metabolism indexes, such as brain temperature (BT), cerebral perfusion pressure (CPP), internal jugular venous oxygen saturation (SjvO2), and arterial partial pressure of carbon dioxide (PaCO2), were recorded after the operation. Further, the prognostic differences between the two groups were compared, and the predictive values were evaluated using the receiver operating characteristic curve (ROC) and area under the curve (AUC).ResultsThe results showed that the average ICP and BT in the good prognosis group were lower than those in the poor prognosis group. However, the CPP and SjvO2 in the good prognosis group were higher than those in the poor prognosis group. Moreover, the incidence of low PaCO2 in the poor prognosis group was higher than that in the good prognosis group.ConclusionsOur results demonstrated that the average ICP, BT, CPP, SjvO2, and arterial PaCO2 may reflect the changes in brain function and cerebral blood flow, which are significantly correlated with the prognosis of patients. Further, our findings indicated that the combined postoperative ICP levels with cerebral oxygen metabolism indexes could guide clinical treatments and predict prognosis.

A novel mechanism for visible-light degradation of phenol by oxygen vacancy Bi2MoO6 homojunction

Homojunctions formed between two same semiconductors can notably facilitate charge transfer and separation. It is mainly used in solar cells to improve power conversion efficiency, and there is great potential for its application in photo-catalytic wastewater degradation. Herein, we designed an oxygen vacancy of Nanorods/Nanosheets Bi2MoO6 homojunction photo-catalyst, prepared by calcining pure Bi2MoO6 at high temperature and annealing it at the ambient temperature. Various characterization methods analyzed the chemical ingredient, microstructure, and optical characteristics. They are degrading phenol during visible illumination to survey the photo-catalytic performance of the homojunction. Density function theory (DFT) and other characterization methods demonstrate that the enhanced activity of the photo-catalyst is the efficient interfacial charge transfer and separation induced by the internal electric field and oxygen vacancies in the homojunction. This work provides a new strategy for constructing a novel homojunction to treat phenol wastewater.

Improvement of Device Characteristics of Low Temperature IGZO Thin-film Transistors through Laser Post Annealing

High-performance thin-film transistors (TFTs) produced at low temperatures are required for ultrahigh- resolution and flexible display applications. The scientific community has been studying unconventional techniques to investigate low voltage flexible devices and low power flexible circuits for the past decade. In particular, metal oxide semiconductors, such as indium gallium zinc oxide (IGZO), have made significant progress as amorphous silicon replacements for electronics and commercial displays. On the other hand, developing metal oxide transistors with low processing temperatures remains a difficulty. The hightemperature annealing process causes very instability in the plastic substrate. Here, we introduce IGZO TFTs that shows enhanced electrical properties environmental stability by laser post-annealing. After annealing process, the laser post-annealing process was given at 80 MHz, pulse width 140 fs, for 50 seconds. The improved electrical characteristics of this laser post-annealed IGZO TFTs were: 9.03 cm&lt;sup&gt;2&lt;/sup&gt;/Vs; 2.2×10&lt;sup&gt;7&lt;/sup&gt; on/off current ratio. The IGZO TFT to which laser post-annealing was applied had a flat surface, and it was confirmed that the combination of internal metal and oxygen was urged, and the leakage current problem was improved by suppressing excessive generation of oxygen vacancy. Furthermore, the voltage transfer curve was measured after fabricating the N-MOS logic inverter circuit, this inverter showed a value of 80.8% the total noise margin.

The onset of active gill respiration in post-embryonic zebrafish (Danio rerio) larvae triggers an increased sensitivity to neurotoxic compounds.

Originally designed as a general alternative to acute fish toxicity testing (AFT), the fish embryo toxicity test (FET) has become subject to concerns with respect to neurotoxic substances. Whereas oxygen uptake in the fish embryo primarily occurs via diffusion across the skin, juvenile and adult fish rely on active ventilation of the gills. As a consequence, substances including, e.g., neurotoxicants which prevent appropriate ventilation of gills ("respiratory failure syndrome") might lead to suffocation in juvenile and adult fish, but not in skin-breathing embryos. To investigate if this respiratory failure syndrome might play a role for the higher sensitivity of juvenile and adult fish to neurotoxicants, a modified acute toxicity test using post-embryonic, early gill-breathing life-stages of zebrafish was developed with chlorpyrifos, permethrin, lindane, aldicarb, ziram and aniline as test substances. Additionally, a comparative study into bioaccumulation of lipophilic substances with logKow > 3.5 and swimbladder deflation as potential side effects of the respiratory failure syndrome was performed with 4 d old skin-breathing and 12 d old gill-breathing zebrafish. With respect to acute toxicity, post-embryonic 12 d larvae proved to be more sensitive than both embryos (FET) and adult zebrafish (AFT) to all test substances except for permethrin. Accumulation of chlorpyrifos, lindane and permethrin was 1.3- to 5-fold higher in 4 d old than in 12 d old zebrafish, suggesting that (intermediate) storage of substances in the yolk might reduce bioavailability and prevent metabolization, which could be a further reason for lower toxicity in 4 d than in 12 d old zebrafish. Whereas ziram and aniline showed no significant effect on the swimbladder, zebrafish exposed to chlorpyrifos, lindane and permethrin showed significantly deflated swimbladders in 12 d old larvae; in the case of aldicarb, there was a significant hyperinflation in 4 d old larvae. Swimbladder deflation in post-embryonic 12 d zebrafish larvae might be hypothesized as a reason for a lack of internal oxygen supplies during the respiratory failure syndrome, whereas in 4 d old embryos cholinergic hyperinflation of the swimbladder dominates over other effects. Regarding acute lethality, the study provides further evidence that the switch from transcutaneous to branchial respiration in post-embryonic zebrafish life-stages might be the reason for the higher sensitivity of juvenile and adult fish to neurotoxic substances.

Marine Sponges in a Snowstorm - Extreme Sensitivity of a Sponge Holobiont to Marine Oil Snow and Chemically Dispersed Oil Pollution.

Holobionts formed by a host organism and associated symbionts are key biological units in marine ecosystems where they are responsible for fundamental ecosystem services. Therefore, understanding anthropogenic impacts on holobionts is essential. Sponges (Phylum Porifera) are ideal holobiont models. They host a complex microbial community and provide ecosystem services including nutrient cycling. At bathyal depths, sponges can accumulate forming dense sponge ground habitats supporting biodiverse associated communities. However, the impacts of spilled oil and dispersants on sponge grounds cannot be understood without considering exposures mediated through sponge filtration of marine snow particles. To examine this, we exposed the model sponge Halichondria panicea to oil, dispersant and “marine oil snow” contaminated seawater and elucidate the complex molecular response of the holobiont through metatranscriptomics. While the host response included detoxification and immune response pathways, the bacterial symbiotic response differed and was at least partially the result of a change in the host environment rather than a direct response to hydrocarbon exposure. As the sponge host reduced its pumping activity and internal tissue oxygen levels declined, the symbionts changed their metabolism from aerobic to anaerobic pathways possibly via quorum sensing. Furthermore, we found evidence of hydrocarbon degradation by sponge symbionts, but sponge mortality (even when exposed to low concentrations of hydrocarbons) implied this may not provide the holobiont with sufficient resilience against contaminants. Given the continued proposed expansion of hydrocarbon production into deep continental shelf and slope settings where sponge grounds form significant habitats it is important that dispersant use is minimised and that environmental impact assessments carefully consider the vulnerability of sponge holobionts.

Heterostructure design of MoO2/FeCo/NPC nanocomposites via supramolecular self-assembly for efficient electromagnetic wave absorption

To date, the development of high-efficiency absorbing materials is still the most effective method to solve increasingly serious problem of electromagnetic pollution. Herein, molybdenum dioxide/iron cobalt alloy/nitrogen phosphorus doped carbon (MoO2/FeCo/NPC) nanocomposites were prepared by combination of supramolecular self-assembly and carbonization. The microstructure, morphology and performance of MoO2/FeCo/NPC nanocomposites were characterized by various test methods. Maximum reflection loss (RL) reached −42.3 dB at 10.4 GHz and 2.1 mm thickness. Adjusting the thickness from 1.5 to 3 mm could achieve effective absorption bandwidth of 8.4 GHz. The dispersion of dielectric MoO2 in system generated synergistic effect with magnetic coupling network formed by FeCo nanoparticles. In addition, local charge accumulation caused by Schottky barrier between two interfaces also contributed to interface polarization. Moreover, internal oxygen vacancy defects and unique electric double layer structure on the surface of ionic crystal MoO2, as well as the existence of capacitor-like structure between carbon nanosheets further optimized absorption performance of MoO2/FeCo/NPC. Thus, such a satisfactory achievement is closely related to the unique morphology and structure of MoO2/FeCo/NPC and the synergistic effect of various components.

Gas exchange model using heterogeneous diffusivity to study internal browning in ‘Conference’ pear

Internal gas gradients in pear fruit during controlled atmosphere storage depend on the effective gas diffusivity of the tissue. The diffusivity varies over the fruit organ due to the heterogeneous tissue microstructure across the fruit. This study implemented effective diffusivity maps reflecting the heterogeneous structure to predict internal gas gradients and relate the result to the occurrence of internal browning. Diffusivity maps of different pears were calculated from X-ray CT based porosity maps. Internal oxygen (O2), carbon dioxide (CO2) and respiratory quotient (RQ) levels were computed using a reaction-diffusion model incorporating the heterogeneous effective diffusivity map. Critical O2 and RQ levels for the shift from respiration to fermentation were defined based on the respiratory-fermentative energy balance of the cells. The model was indirectly validated by comparing RQ level contours with non-destructive 3D images of the internal browning of the pears after storage at 1.0 kPa and 0.5 kPa O2, combined with 0.7 kPa CO2 at 1 °C. The distribution of the internal gas concentrations and RQ was affected by the heterogeneity of the diffusivity. The results also confirmed the incidence of internal browning when the O2 and RQ were under or above critical O2 and RQ limits, respectively. The fermentation process was indicated to be dominant when the tissue’s RQ limit (RQ*) went above 2.12 (or at 0.044 kPa O2). The tissue volumes where O2 and RQ levels were critical corresponded reasonably well to browning-affected tissues of pears with different shapes. The pear with more shallow gas gradients showed less symptoms of browning.

Study on the Ignition Mechanism of Inert Fuel Tank Subjected to High-Velocity Impact of Fragments.

Nowadays, aircraft fuel tanks are protected by measures such as inerting, fire and explosion suppression, which significantly improve their ability to mitigate mechanical damage and prevent fire in the case of an accidental attack. In this study, an equivalent inert fuel tank with fire and explosion suppression was designed according to the vulnerabilities of a typical fighter. Then, a ballistic gun, a 37 mm gun and a two-stage light-gas gun were used to propel different fragments in tank damage experiments at different speeds (1400 m/s–2600 m/s). Experimental results show that the disassembly of a fuel tank is a prerequisite for igniting fuel. When the fragments hit the gas phase of the tank, the fuel tank was not disassembled and the fuel was not ignited. The calculation results show that the internal oxygen concentration was always lower than the limiting oxygen concentration (12%) before the fuel tank was disassembled. In addition, the minimum ignition speeds of inerted fragments with different masses as predicted by the ignition criterion when hitting the liquid fuel are consistent with the test results. This shows that increasing the mass of inert fragments will increase the minimum ignition speed and reduce the probability of ignition of the fuel. However, the implosion effect of the energetic fragments released about 3 times the chemical energy of its own kinetic energy, and the high-temperature and high-pressure products were very beneficial to the disintegration and ignition of the fuel tank compared to inert fragments.