Oxygen Concentration Gradient Research Articles

Pseudomonas aeruginosa in the Frontline of the Greatest Challenge of Biofilm Infection—Its Tolerance to Antibiotics

P. aeruginosa biofilms are aggregates of bacteria surrounded by a self-produced matrix which binds to some antibiotics such as aminoglycosides. P. aeruginosa biofilms are tolerant to antibiotics. The treatment of biofilm infections leads to a recurrence of symptoms after finishing antibiotic treatment, although the initial clinical response to the treatment is frequently favorable. There is a concentration gradient of oxygen and nutrients from the surface to the center of biofilms. Surface-located bacteria are multiplying and metabolizing, whereas deeper located bacteria are dormant and tolerant to most antibiotics. Colistin kills dormant bacteria, and combination therapy with colistin and antibiotics which kills multiplying bacteria is efficient in vitro. Some antibiotics such as imipenem induce additional production of the biofilm matrix and of chromosomal beta-lactamase in biofilms. Biofilms present a third Pharmacokinetic/Pharmacodynamic (PK/PD) micro-compartment (first: blood, second: tissue, third: biofilm) which must be taken into consideration when calculations try to predict the antibiotic concentrations in biofilms and thereby the probability of target attainment (PTA) for killing the biofilm. Treating biofilms with hyperbaric oxygen to wake up the dormant cells, destruction of the biofilm matrix, and the use of bacteriophage therapy in combination with antibiotics are promising possibilities which have shown proof of concept in in vitro experiments and in animal experiments.

Integrating cultural and natural assets in marine spatial planning: A new approach for joint management of cultural and natural assets

Effective sustainable marine management requires the integration of cultural and natural assets, a practice that is rarely attempted. This study developed and tested a new method for Marine Spatial Planning (MSP) that uses interdisciplinary knowledge of the spatial distribution of cultural and natural assets in marine ecosystems along environmental and human pressure gradients and seeks to understand their interrelationships. The study focused on Estonian marine areas in the north-eastern Baltic Sea. Environmental conditions and threats were assessed, and the extent of spatial overlap between underwater cultural heritage (UCH), natural assets and conservation measures was identified. Although nature reserves and UCH sites were generally exposed to different ranges of environmental and pressure gradients, significant overlap with UCH sites was observed for certain natural assets, as well as along gradients of current velocity, oxygen concentration, bottom sediment, and human pressure. These results highlight the value of joint archaeological and ecological analyses to identify natural assets specific to UCH regions that require protection from both a natural and cultural heritage perspective.

Long-term Monitoring of Oxygen Consumption Rates in Highly Differentiated and Polarized Retinal Pigment Epithelial Cultures.

Mitochondrial metabolism is critical for the normal function of the retinal pigment epithelium (RPE), a monolayer of cells in the retina important for photoreceptor survival. RPE mitochondrial dysfunction is a hallmark of age-related macular degeneration (AMD), the leading cause of irreversible blindness in the developed world, and proliferative vitreoretinopathy (PVR), a blinding complication of retinal detachments. RPE degenerative conditions have been well-modeled by RPE culture systems that are highly differentiated and polarized to mimic in vivo RPE. However, monitoring oxygen consumption rates (OCR), a proxy for mitochondrial function, has been difficult in such culture systems because the conditions that promote ideal RPE polarization and differentiation do not allow for easy OCR measurements. Here, we introduce a novel system, Resipher, to monitor OCR for weeks at a time in well-differentiated RPE cultures while maintaining the RPE on optimal growth substrates and physiologic culture media in a standard cell culture incubator. This system calculates OCR by measuring the oxygen concentration gradient present in the media above cells. We discuss the advantages of this system over other methods for detecting OCR and how to set up the system for measuring OCR in RPE cultures. We cover key tips and tricks for using the system, caution about interpreting the data, and guidelines for troubleshooting unexpected results. We also provide an online calculator for extrapolating the level of hypoxia, normoxia, or hyperoxia RPE cultures experience based on the oxygen gradient in the media above cells detected by the system. Finally, we review two applications of the system, measuring the metabolic state of RPE cells in a PVR model and understanding how the RPE metabolically adapts to hypoxia. We anticipate that the use of this system on highly polarized and differentiated RPE cultures will enhance our understanding of RPE mitochondrial metabolism both under physiologic and disease states.

O-214 The effect of constant 5% versus gradient 8%, 5%, 2% oxygen concentration on the development of sibling human embryos in vitro to the blastocyst stage

Abstract Study question Does a physiological gradient of oxygen concentration in embryo culture atmosphere yield a higher percentage of fertilized oocytes developing into morphologically optimal blastocysts? Summary answer Study favours sustaining a static 5% oxygen level, instead of a gradient, during extended embryo culture, resulting in more viable embryos for cryopreservation and transfer. What is known already To date, there’s ongoing research about the optimal oxygen concentration for embryo culture. The available data from studies based on animal models show that the O2 level in the fallopian tube is around 8%, and the in-utero O2 level is at around 2% (Wale & Gardner, 2010). Data on oxygen measurement in the human uterus is scarce, yet aligns with similar findings in other mammalian species (Ng et al., 2018). These findings support the use of sequential O2 levels for embryo culture. Our study stands as the first to implement such dynamic oxygen culture conditions within an in vitro setting. Study design, size, duration A prospective sibling-split oocyte study, analyzing 44 ICSI cycles from January 2022 to January 2023, with alternate allocation into a static 5% (Control group) during entire culture period or under an oxygen gradient (intervention group), starting with 8% from day-0 to day-3, continuing with 5% on day-3 and following with 2% of oxygen from the end of day-3 to day-5/6. Participants/materials, setting, methods 44 ICSI cycles, which produced a total of 521 metaphase II oocytes. A total of 353 2PN embryos were cultured and annotated in time-lapse for morphokinetic and morphometric analysis. Main results and the role of chance While morphological outcomes slightly favored the intervention group for day 2 and day 3 embryos, the trend reversed by day 5. The control group (5% O2) showed a notably higher proportion of zygotes developed to clinically utilized blastocysts (47% vs. 37%, p = 0.016) and consequently more of them were used for transfer on day 5 (10% vs. 4%, P = 0.008) compared to the intervention group. Additionally, though not statistically significant, the control group showed a higher percentage of morphologically optimal blastocysts on day 5 (10.3% vs. 14.7%, p = 0.1233). Morphokinetic timings, as revealed by time-lapse analysis, indicated a delayed development in the intervention group, notably seen in the initiation of blastulation (p = 0.0024), initiation of expansion (p < 0.0001), and full blastocyst formation (p < 0.0001). The speed of blastulation, however, does not necessarily reflect differences in implantation potential, as implantation (58.6% vs 57.1% p > 0.92) and clinical pregnancy rates (55.2% vs 57.1%, p > 0.92) after transferring blastocysts from either group were comparable. Limitations, reasons for caution Measuring the in vivo O2 levels in female reproductive tract should take into account possible oscillations and dynamic nature of gas and nutrient exchange. It’s also important to acknowledge the complexity of embryo’s adaptive response, making it challenging to attribute observed outcomes solely to the impact of targeted oxygen concentration. Wider implications of the findings Based on these clinical results, we will analyze the metabolomic footprint in spent embryo culture under static 5% or gradient 8-5-2% oxygen concentration, employing non-invasive NMR and chromatography methods. A randomized control trial should be conducted to explore the effect of different oxygen regimes on clinical outcomes. Trial registration number NCT05898178

Establishing mainstream partial nitrification in the membrane aerated biofilm reactor by limiting the oxygen concentration in the biofilm

The proliferation of nitrite oxidizing bacteria (NOB) still remains as a major challenge for nitrogen removal in mainstream wastewater treatment process based on partial nitrification (PN). This study investigated different operational conditions to establish mainstream PN for the fast start-up of membrane aerated biofilm reactor (MABR) systems. Different oxygen controlling strategies were adopted by employing different influent NH4+-N loads and oxygen supply strategies to inhibit NOB. We indicated the essential for NOB suppression was to reduce the oxygen concentration of the inner biofilm and the thickness of aerobic biofilm. A higher NH4+-N load (7.4 g-N/(m2·d)) induced higher oxygen utilization rate (14.4 g-O2/(m2·d)) and steeper gradient of oxygen concentration, which reduced the thickness of aerobic biofilm. Employing closed-end oxygen supply mode exhibited the minimum concentration of oxygen to realize PN, which was over 46% reduction of the normal open-end oxygen mode. Under the conditions of high NH4+-N load and closed-end oxygen supply mode, the microbial community exhibited a comparative advantage of ammonium oxidizing bacteria over NOB in the aerobic biofilm, with a relative abundance of Nitrosomonas of 30–40% and no detection of Nitrospira. The optimal fast start-up strategy was proposed with open-end aeration mode in the first 10 days and closed-end mode subsequently under high NH4+-N load. The results revealed the mechanism of NOB inhibition on the biofilm and provided strategies for a quick start-up and stable mainstream PN simultaneously, which poses great significance for the future application of MABR.

Assessing the Natural Source Zone Depletion of a Petroleum-Contaminated Clayey Soil Site in Southern China Combining Concentration Gradient Method and Metagenomics.

Natural source zone depletion (NSZD) is the main process of LNAPL (Light Non-Aqueous Phase Liquid) removal under natural conditions. The NSZD rates assessed ranged from 0.55 to 11.55 kg·m-2·a-1 (kilograms per square meter per year) in previous studies. However, most of these data were obtained from sandy sites, with few clayey sites. To gain knowledge of NSZD in clayey soil sites, the study assessed the NSZD of a petroleum hydrocarbon-contaminated clayey soil site in China, combining the concentration gradient method with metagenomic sequencing technology. The results show that the abundance of methane-producing key enzyme mcrA gene in the source zone was more abundant than in background areas, which suggests that there was methanogenesis, the key process of NSZD. The concentration gradients of oxygen and carbon dioxide existed only in shallow soil (<0.7 m), which suggests that there was a thin methane oxidation zone in the shallow zone. The calculated NSZD rates range from 0.23 to 1.15 kg·m-2·a-1, which fall within the moderate range compared to previous NSZD sites. This study expands the knowledge of NSZD in clayey soil and enriches the attenuation rate data for contaminated sites, which is of significant importance in managing petroleum contaminants.

Cable Bacteria Skeletons as Catalytically Active Electrodes.

Cable bacteria are multicellular, filamentous bacteria that use internal conductive fibers to transfer electrons over centimeter distances from donors within anoxic sediment layers to oxygen at the surface. We extracted the fibers and used them as free-standing bio-based electrodes to investigate their electrocatalytic behavior. The fibers catalyzed the reversible interconversion of oxygen and water, and an electric current was running through the fibers even when the potential difference was generated solely by a gradient of oxygen concentration. Oxygen reduction as well as oxygen evolution were confirmed by optical measurements. Within living cable bacteria, oxygen reduction by direct electrocatalysis on the fibers and not by membrane-bound proteins readily explains exceptionally high cell-specific oxygen consumption rates observed in the oxic zone, while electrocatalytic water oxidation may provide oxygen to cells in the anoxic zone.

Kabelbakterienskelette als katalytisch aktive Elektroden

AbstractKabelbakterien sind vielzellige, filamentöse Bakterien, die interne leitfähige Fasern verwenden, um Elektronen über Zentimeterdistanzen von Elektronenspendern in anoxischen Sedimentschichten zu Sauerstoff an der Oberfläche zu transportieren. Wir haben diese Fasern extrahiert und sie als freistehende biobasierte Elektroden verwendet, um ihr elektrokatalytisches Verhalten zu untersuchen. Die Fasern katalysieren die reversible Umwandlung von Sauerstoff und Wasser, kombiniert mit einem elektrischen Stromfluss durch die Fasern, selbst wenn die Potentialdifferenz ausschließlich durch einen Sauerstoffkonzentrationsgradienten erzeugt wird. Sowohl die Sauerstoffreduktion als auch die Sauerstoffentwicklung wurden durch optische Messungen bestätigt. Bei lebenden Kabelbakterien erklärt sich die Sauerstoffreduktion durch direkte Elektrokatalyse an den Fasern, und nicht durch membrangebundene Proteine, und führt zu den außergewöhnlich hohen zellspezifischen Sauerstoffverbrauchsraten, die in der oxischen Zone beobachtet werden, während die elektrokatalytische Wasseroxidation Zellen in der anoxischen Zone mit Sauerstoff versorgen kann.

Exploring the Mechanisms Driving Thermal Growth of Copper Oxide Nanowires

Copper oxide nanowires have gained attention in the scientific community due to their potential in a wide range of applications, including gas sensing, solar cells, energy storage, photocatalysis, and as antibacterial agents. Despite significant research on their thermal growth, the underlying mechanism remains unresolved, and the exact experimental conditions required for their growth are still unknown. To address these knowledge gaps, we conducted thermal oxidation of copper under various conditions and analyzed the resulting nanowires using electron microscopy techniques. Our study aimed to understand the processes occurring inside the copper oxide layers, which serve as the starting point for nanowire growth, as well as the driving force behind the one-dimensional growth of nanowires. Additionally, we explored the effects of experimental conditions on the microstructure of the copper oxide layers and nanowires. Our findings indicate that chemical processes inside the oxide layers are influenced by copper and oxygen concentration gradients, with oxygen concentration being the key factor in determining the prevalent copper oxide phase. Moreover, the microstructure of both the oxide layers and nanowires is affected by stress and defects in the oxide layers. We found that twin boundaries in the CuO grains are the main reason for the unidirectional elongation of nanowires. Our research provides important insights into the mechanisms driving the thermal growth of copper oxide nanowires, which can aid in their synthesis and applications in various fields.

Numerical Simulation of Local Entropy Generation of Oxygen Transport in Cathode Diffusion Media of PEFC

To further improve the power density and efficiency of polymer electrolyte fuel cells (PEFCs), it’s necessary to review the conventional flow fields consisting of porous electrodes and gas channels and reduce the overpotentials due to the electrochemical reaction and mass transport. In the past works, the voltage loss in fuel cells had been generally classified into the activation, ohmic and concentration polarizations and evaluated comprehensively. However, the factors of the energy loss should be identified in more detail to design the better electrode/channel structure, because the interaction of the heat and mass transfer, ionic and electronic transport and electrochemical reaction occurs complicatedly in porous electrodes. Several researchers [1-2] focused on entropy that is a physical property representing the thermodynamic irreversibility and evaluated the energy losses in fuel cells and electrochemical devices from the view of entropy generation. Especially, Charoen-amornkitt et al. [2] has attempted to design the diffusion field in a reaction-diffusion system with the use of a combination of entropy generation analysis and topology optimization. The analysis of entropy generation enables to identify the dominant process causing the overpotential in PEFCs and contributes to design the optimum electrode/channel structure minimizing the energy loss. This study introduced the evaluation technique using entropy generation into the conventional two-phase flow simulation for the gas diffusion layer (GDL) of a PEFC and succeeded to numerically estimate the distribution of entropy production rate due to the oxygen diffusion in the cathode GDL. Furthermore, the author investigated the effect of land-channel configuration on the local entropy generation of oxygen transport within the GDL in detail and discussed how to design the electrode/channel structure reducing the entropy generation.Fig. 1 presents the numerical results of the two-phase flow simulation and the entropy generation analysis in the cathode GDL. The two-phase model used in this study was developed by Natarajan and Nguyen [3]. The model domain consists of the flow channel, both lands, GDL and catalyst layer in the cross section of the cathode. Figs. 1(a) and 1(b) denote the distributions of the oxygen concentration (mole fraction) and the entropy production rate due to the oxygen diffusion, respectively. In the simulation, the fuel cell was operated for 200 s at the temperature of 80 oC and the constant current density of 1.0 A/cm2. The pressure and humidification of air supplied to the cathode were set to 1 atm and 80 %RH. As shown in Fig. 1(a), the oxygen concentration is lowered under the land because of its insufficient supply. The result of entropy generation analysis in Fig. 1(b) revealed that the entropy production rate due to the oxygen diffusion becomes remarkably high under the boundary between the flow channel and land that causes its large concentration gradient. To reduce the entropy generation in this area, it’s necessary to design the electrode/channel structure alleviating the gradient of oxygen concentration.

Study of Transcriptomic Analysis of Yak (Bos grunniens) and Cattle (Bos taurus) Pulmonary Artery Smooth Muscle Cells under Oxygen Concentration Gradients and Differences in Their Lung Histology and Expression of Pyruvate Dehydrogenase Kinase 1-Related Factors.

The aim of this study was to investigate the molecular mechanisms by which hypoxia affects the biological behavior of yak PASMCs, the changes in the histological structure of yak and cattle lungs, and the relationships and regulatory roles that exist regarding the differences in the distribution and expression of PDK1 and its hypoxia-associated factors screened for their role in the adaptation of yak lungs to the plateau hypoxic environment. The results showed that, at the level of transcriptome sequencing, the molecular regulatory mechanisms of the HIF-1 signaling pathway, glucose metabolism pathway, and related factors (HK2/PGK1/ENO1/ENO3/ALDOC/ALDOA) may be closely related to the adaptation of yaks to the hypoxic environment of the plateau; at the tissue level, the presence of filled alveoli and semi-filled alveoli, thicker alveolar septa and basement membranes, a large number of erythrocytes, capillary distribution, and collagen fibers accounted for all levels of fine bronchioles in the lungs of yaks as compared to cattle. A higher percentage of goblet cells was found in the fine bronchioles of yaks, and PDK1, HIF-1α, and VEGF were predominantly distributed and expressed in the monolayers of ciliated columnar epithelium in the branches of the terminal fine bronchioles of yak and cattle lungs, with a small amount of it distributed in the alveolar septa; at the molecular level, the differences in PDK1 mRNA relative expression in the lungs of adult yaks and cattle were not significant (p > 0.05), the differences in HIF-1α and VEGF mRNA relative expression were significant (p < 0.05), and the expression of PDK1 and HIF-1α proteins in adult yaks was stronger than that in adult cattle. PDK1 and HIF-1α proteins were more strongly expressed in adult yaks than in adult cattle, and the difference was highly significant (p < 0.01); the relative expression of VEGF proteins was not significantly different between adult yaks and cattle (p > 0.05). The possible regulatory relationship between the above results and the adaptation of yak lungs to the plateau hypoxic environment paves the way for the regulatory mechanisms of PDK1, HIF-1α, and VEGF, and provides basic information for studying the mechanism of hypoxic adaptation of yaks in the plateau. At the same time, it provides a reference for human hypoxia adaptation and a target for the prevention and treatment of plateau diseases in humans and plateau animals.

Experimental evolution of Pseudomonas aeruginosa to colistin in spatially confined microdroplets identifies evolutionary trajectories consistent with adaptation in microaerobic lung environments.

Antibiotic resistance remains one of the great challenges confronting public health in the world today. Individuals with compromised immune systems or underlying health conditions are often at an increased for bacterial infections. Patients with cystic fibrosis (CF) produce thick mucus that clogs airways and provides a very favorable environment for infection by bacteria that further decrease lung function and, ultimately, mortality. CF patients are often infected by bacteria such as Pseudomonas aeruginosa early in life and experience a series of chronic infections that, over time, become increasingly difficult to treat due to increased antibiotic resistance. Colistin is a major antibiotic used to treat CF patients. Clinical and laboratory studies have identified PmrA/PmrB and PhoP/PhoQ as responsible for increased resistance to colistin. Both have been identified in CF patient lungs, but why, in some cases, is it one and not the other? In this study, we show that distinct evolutionary trajectories to colistin resistance may be favored by the microaerobic partitioning found within the damaged CF lung.

Modification of accelerated thermal stabilization of polyacrylonitrile fibers by creating an oxygen concentration gradient in the production of carbon fiber

Objectives. The work set out to modify the technology of accelerated thermal stabilization of polyacrylonitrile (PAN) fibers used in the production of high-strength carbon fibers by reducing the formation of a heterophase core–shell structure to create an oxygen concentration gradient in heat treatment furnaces while maintaining a total thermal stabilization time of 30 min. The optimized process conditions led to milder thermal stabilization conditions, reducing both the final heat treatment temperature and the temperature difference between the thermal stabilization zones while simultaneously maintaining the target volume density parameter with respect to the previously developed accelerated thermal stabilization technology.Methods. The thermal stabilization study of an industrially produced 12S precursor under different conditions on an experimental carbon fiber production line included measurement of bulk density, analysis of the thermal effects of the oxidation reaction by differential scanning calorimetry (DSC), and a study of micrographs of the resulting samples.Results. The optimum process of thermal stabilization of PAN fiber was determined in four stabilization zones using selected compositions. The formation of the core–shell structure is significantly reduced when the target volume density and DSC thermal oxidation reaction effect of the stabilized polymer fiber are achieved in a given time (30 min).Conclusions. The resulting technology regime is promising for the production of high strength (4.5 GPa, 4.9 GPa) PAN fibers at a reduced cost. While maintaining the total thermal stabilization time of PAN at the level of 30 min, which is three times less than the industrial processes used, it was possible to reduce the formation of a heterophase structure, as well as lowering the final processing temperature and reducing the temperature difference between the stabilization zones. This is promising in terms of a positive effect on the stability and safety of the industrial process, as well as ensuring the quality of the obtained products.

Behavior of breast cancer cells under oxygen concentration gradients in a microfluidic device.

The tumor microenvironment (TME) is known as a chronic hypoxic environment, with spatiotemporal variation in oxygen concentration depending on the distance from blood vessels and the blood supply. In our previous studies, cancer cell behavior was observed under hypoxic conditions with spatial variation of oxygen concentration (oxygen concentration gradients); however, that under oxygen concentration gradients at low oxygen levels found in the TME has not been studied. In this study, we investigated the behavior of breast cancer cells at various oxygen concentration gradients, generated using a microfluidic device with oxygen concentration controllability. The results showed that cell distribution was altered in response to oxygen concentration, and tended to increase in a specific region at around 5% O2. Evaluation of changes in cell numbers due to proliferation, migration, and cell death indicated that proliferation strongly affected cell distribution.

Necrosis reduction efficacy of subdermal biomaterial mediated oxygen delivery in ischemic skin flaps

Inadequate tissue blood supply as may be found in a wound or a poorly vascularised graft, can result in tissue ischemia and necrosis. As revascularization is a slow process relative to the proliferation of bacteria and the onset of tissue necrosis, extensive tissue damage and loss can occur before healing is underway. Necrosis can develop rapidly, and treatment options are limited such that loss of tissue following necrosis onset is considered unavoidable and irreversible.Oxygen delivery from biomaterials exploiting aqueous decomposition of peroxy-compounds has shown some potential in overcoming the supply limitations by creating oxygen concentration gradients higher than can be attained physiologically or by air saturated solutions.We sought to test whether subdermal oxygen delivery from a material composite that was buffered and contained a catalyst, to reduce hydrogen peroxide release, could ameliorate necrosis in a 9 × 2 cm flap in a rat model that reliably underwent 40 % necrosis if untreated. Blood flow in this flap reduced from near normal to essentially zero, along its 9 cm length and subdermal perforator vessel anastomosis was physically prevented by placement of a polymer sheet. In the middle, low blood flow region of the flap, treatment significantly reduced necrosis based on measurements from photographs and histological micrographs. No change was observed in blood vessel density but significant differences in HIF1-α, inducible nitric oxide synthase and liver arginase were observed with oxygen delivery.

The aerotaxis of Dictyostelium discoideum is independent of mitochondria, nitric oxide and oxidative stress.

Spatial and temporal variations of oxygen environments affect the behaviors of various cells and are involved in physiological and pathological events. Our previous studies with Dictyostelium discoideum as a model of cell motility have demonstrated that aerotaxis toward an oxygen-rich region occurs below 2% O2. However, while the aerotaxis of Dictyostelium seems to be an effective strategy to search for what is essential for survival, the mechanism underlying this phenomenon is still largely unclear. One hypothesis is that an oxygen concentration gradient generates a secondary oxidative stress gradient that would direct cell migration towards higher oxygen concentration. Such mechanism was inferred but not fully demonstrated to explain the aerotaxis of human tumor cells. Here, we investigated the role on aerotaxis of flavohemoglobins, proteins that can both act as potential oxygen sensors and modulators of nitric oxide and oxidative stress. The migratory behaviors of Dictyostelium cells were observed under both self-generated and imposed oxygen gradients. Furthermore, their changes by chemicals generating or preventing oxidative stress were tested. The trajectories of the cells were then analyzed through time-lapse phase-contrast microscopic images. The results indicate that both oxidative and nitrosative stresses are not involved in the aerotaxis of Dictyostelium but cause cytotoxic effects that are enhanced upon hypoxia.

Film-forming investigation of NbC-modified HfC coating based on oxyacetylene ablation and argon-atmosphere heating above 2000 °C

Ablation test of NbC-modified HfC coatings using an oxyacetylene flame and heat treatment of HfO2–Nb2O5 plates up to 2100 °C were performed. The results indicate that HfC-30 mol% NbC coating forms a dense oxide film comprising HfO2 columnar crystals, achieving the best ablation property. At 2100 °C in an argon atmosphere, the solubility of niobium suboxide in HfO2 is in the range 27–30 mol%, and the stable phases are HfO2, Nb, and NbO. NbO liquids improve the transport of Hf and produce gradients of temperature and oxygen concentration, promoting the formation of a composite film under an oxyacetylene flame.

Metabolic-fluid dynamics model construction and scale-down design for an industrial penicillin chrysogenum fermentation with combined dissolved oxygen and glucose concentration dynamics

This study focuses on the metabolic impacts of simultaneous glucose and oxygen concentration gradients on penicillin production in an industrial-scale fermentor, using the computational fluid dynamics-cellular reaction dynamics approach. Inclusion of oxygen-coupling considerably impacts the glucose uptake and resulting penicillin productivity. This is characterised by six metabolic regimes; lifeline data reconstructed from experimental results, recorded from the cellular perspective, indicates rapid dynamics in glucose and dissolved oxygen uptake by the microorganisms. The results are highly sensitive to variations in the oxygen-related model parameters, requiring accurate insight into the multiphase hydrodynamics and metabolic processes. Hypothetical scenarios with stronger glucose-oxygen limitations than tested experimentally were further explored. A precision scale-down (SD) simulator was designed based on the lifeline data, requiring considerable operational dynamics, with increasing system complexity and implementation difficulty. These insights may inspire further research into alternative SD configurations better suited to mimic the rapid dynamics of large-scale fermentation processes.

Solubility, crystal growth, and film-formation mechanism of NbC-modified ZrC coating under oxyacetylene flame

Herein, the ablation resistance of plasma-sprayed NbC-modified ZrC (ZrC-NbC) coatings was firstly tested using an oxyacetylene flame. Next, the phase composition of the ZrO2-Nb2O5 (NbO2.5) plates heat-treated at 2100 °C in an argon atmosphere was determined. The results indicated that, the ZrC-20 mol% NbC coating formed a dense oxide layer after ablation for 120 s and a composite film consisting of self-bridged ZrO2 columnar crystals up to 300 s, achieving the best ablation property. At 2100 °C, the solubility (solid solubility and adsorption capacity) of niobium suboxide in ZrO2 was 30 mol%. The stable phases were t-ZrO2 and Nb as the NbO2.5-addition was no more than 20 mol%, and t-ZrO2, Nb, and NbO when it ranged from 25 to 40 mol%. Furthermore, ZrO2 increased the viscosity of Nb-O liquids and ensured the transformation of NbO2.5 into Nb and NbO phases, improving the thermal stability. Nb-O liquids improved the transfer of Zr and formed gradients of temperature and oxygen concentration, strengthening the film-forming ability of the ZrC coating under an oxyacetylene flame.

Effect of Cu-Sn Addition on Corrosion Property of Pressureless Sintered Fe-Cu-Co Substrate Alloys

Fe-Cu-Co prealloyed powder is used for bonding metal of diamond tools. In order to obtain diamond tools with good mechanical properties by pressureless sintering, it is necessary to add Cu-Sn sintering aids. The substrate also has high corrosion resistance requirements, which is conducive to the chemical erosion of diamond tools. This paper mainly studies the effects of Cu-Sn on the corrosion behavior of pressureless sintered Fe-Cu-Co substrate. The results show that the linear contraction rate and relative density of pressureless sintered Fe-Cu-Co alloy at 875 °C reach their peak when the Cu-Sn content is 8 wt.%, 15.13% and 97.5%, respectively. The substrate is mainly composed of α-Fe and Cu-rich phases, and selective corrosion occurs during electrochemical corrosion; namely, α-Fe grains are more prone to corrosion than Cu-rich grains to form porous corrosion surfaces. With the increase in Cu-Sn addition, the volume fraction of the Cu-rich phase increases, the corrosion current density and the passive current density gradually decrease, and the corrosion resistance of the alloy is improved. The amount and integrity of anodic passive film on the Fe-Cu-Co surface increases with the increase in Cu-Sn addition. The oxygen content of the anodic passivation film is lower than that of the active corrosion products of the α-Fe phase, thus reducing the oxygen concentration gradient and slowing down the corrosion. The addition of Cu-Sn is conducive to improving the corrosion resistance of Fe-Cu-Co alloy as the substrate of diamond tools.