Oxygen Diffusion Rate Research Articles

Fabrication and oxidation resistance of the non-stoichiometric tantalum-hafnium carbonitride

This research was conducted to obtain non-stoichiometric tantalum-hafnium carbonitride powder of the Fm3m (225) structural type using a combination of mechanical activation (MA) and self-propagating high-temperature synthesis (SHS) methods. Mechanical activation for 60 min in a low-energy mode (347 rpm) forms Ta/Hf/C composite particles 1 to 20 μm in size with a layered structure and contributes to a uniform distribution of elements. SHS of a mechanically activated Ta + Hf + C mixture in a nitrogen atmosphere (0.8 MPa) leads to the formation of a single-phase tantalum-hafnium carbonitride powder with the Ta0.25Hf0.75C0.5N0.3 composition where particles feature by a ≪spongy≫ morphology with pores and caverns and consist of submicron grains. Spark plasma sintering (SPS) was used to obtain a bulk sample of tantalum-hafnium carbonitride with a grain size of 3 to 5 μm, relative density of 98.2 Ѓ} 0.3 %, hardness of 19.8 Ѓ} 0.2 GPa, and crack resistance of 5.4 Ѓ} 0.4 MPa・m1/2. The kinetics of (Ta,Hf)CN oxidation at 1200 °C in air is described by a parabolic law suggesting the formation of an Hf6Ta2O17 + mHfO2 oxide layer with a low oxygen diffusion rate where the oxidation rate is 0.006 mg/(cm2・s). A (Ta,Hf)CN oxidation mechanism is proposed, which states that Ta2O5 and HfO2 are formed on the surface of grains at the first stage that react with each other at the second stage to form a Hf6Ta2O17 homologous superstructure and monoclinic HfO2. CO, CO2, NO and NO2 gaseous oxidation products are released with the formation of pores and cracks.

The Race to Equilibrate

Background: While it is well documented that culture in hypoxic conditions produces superior outcomes, the mechanics of establishing such conditions within the embryo’s liquid environment is less clear. It is not uncommon for laboratories, while ‘culturing’ in low-oxygen, to equilibrate dishes in CO2 only environments prior to use, meaning embryos are exposed to high oxygen tension in their media even after placing into the hypoxic environment, but for how long is so far unclear. Aim: To assess the equilibration rate of oxygen within embryo culture media when exposed to hypoxic conditions. Method: A handheld blood gas analyser (EPOC system, ‘BGEM’ cartridges) was used to determine the pO2 of G1+ culture media after exposure to a reduced oxygen environment. Results: Culture media in atmospheric oxygen (with or without the presence of CO2) showed mean pO2 values of 150mmHg. Media fully equilibrated over 24 hours in 5% oxygen fell to approximately 70mmHg. This was well above the theoretically expected value but shown to be consistent across multiple measurements including various dish and incubator types. Initial equilibration to hypoxic conditions occurred relatively rapidly, with dishes undergoing 50% of the required oxygen reduction in only 30 minutes. Within 1.5 hours of exposure 5% O2, media achieved 83% of the required change, with full equilibration reached at approximately 2.5 hours. Pre-equilibration of dishes in 6% CO2 did not appear to affect the oxygen diffusion rate compared with non-equilibrated media. Oxygen exhibited similarly rapid diffusion into culture media when dishes equilibrated at 5% O2 were exposed to atmospheric conditions, with pO2 increasing by 1.46mmHg per minute. Conclusion: The diffusion rate of oxygen appears to be significantly faster than the more widely studied CO2, however, oxygen tension in media still requires greater than 2 hours to reach optimum levels, requiring us to consider oxygen in our equilibration practices.

Extremely Stable, Highly Conductive Boron‐Hydrogen Complexes in Forsterite and Olivine

AbstractBoron is an important tracer in the mantle but its fate during deep subduction is poorly constrained. In this work we use density functional theory and a thermodynamic model to study the stability of boron‐hydrogen defects in forsterite and olivine and predict their effect on olivine properties. In the absence of water/hydrogen we predict that in all conditions B3+ replaces Si4+ charge balanced by an oxygen vacancy and thus pure boron increases oxygen diffusion rates. In the presence of hydrogen two boron‐hydrogen defects are found to be stable, an “associated” boron‐silicon hydrate (B‐Si‐H) with planar BO3 at low temperatures and an attached hydrogen and a “dissociated” B‐Si‐H with tetrahedral BO4 and interstitial free hydrogen at high temperatures. These B‐Si‐H complexes are extremely stable compared to non‐hydrous boron and form to the exclusion of all other water defects regardless of pressure, temperature, SiO2 activity and Fe# thus forsterite and olivine should behave identically. The stability of B‐Si‐H defects against pressure and temperature suggests that dissolved boron will remain dissolved deep into the mantle and that boron should induce a near linear increase in the solubility of water in olivine. We predict that at high temperatures water associated with boron in olivine will not have FTIR signals in the standard measurement range 3,000–3,600 cm−1 and that instead a large rise in conductivity will be seen. The change in the coordination of boron in B‐Si‐H with temperature will impact upon its fractionation.

Influence of temperature on aerobic granular sludge formation and stability treating municipal wastewater with high nitrogen loadings

This study investigated the influence of temperature (20 and 30 °C) on the formation and stability of aerobic granules in sequential batch reactors (SBR). Therefore, two lab-scale SBRs operated at 20 and 30 °C (SBR20 and SBR30) were used. The reactors were fed with municipal wastewater (CODt:TN:TP 100:15:1.7), leading to mean organic loading rates (OLR) of 1.3 ± 0.4 kgCODt m−3 day−1. Both reactors had the same height/diameter ratio of 4.2 and were inoculated with activated sludge from a municipal wastewater treatment plant. The operational conditions were also the same for both temperatures and lasted in stable process parameters for over 100 days. By optimizing the aeration and oxygen concentration, a high removal efficiency of NH4–N (∼99%) and COD (∼90%) was achieved in both reactors, despite the poor C:N:P ratio at the influent. Furthermore, a relatively low oxygen concentration of 2 mg L−1 was defined as the set point for the control strategy. Nevertheless, granulation at 30 °C was significantly faster, resulting in more stable sludge volume index (SVI) values (SVI10/SVI30 < 1.1). The granules formed at 30 °C were also larger, more compact, and considerably more stable against system disturbances. However, at higher temperatures, larger granules might be required for nitrate removal because of the increased oxygen diffusion rates. Finally, microbiological 16S rRNA gene amplicon analysis for both systems indicated major differences relatively to the inoculum sludge only for nitrogen-degrading organisms.

Study of high burnup effect on steam oxidation of Zircaloy and its regulatory implications via the developement of a pre-transient oxide model of TRANOX

A mechanisitc model that gives oxygen distribution of Zircaloy cladding with pre-transient oxide and absorbed hydrogen under steam oxidation environments has been developed. The model has been incorporated into TRANOX. The model has been validated against steam oxidation experiments with Zircaloy-4 specimens that were pre-oxidized in simulated PWR environments and past experimental data available in open literature. The high burnup effects on cladding oxidation owing to pre-transient oxide and hydrogen can be categorized into: thinning of initial Zr-matrix by the formation of pre-transient ZrO2, increasing diffusion resistance of oxygen with pre-transient ZrO2, and increasing oxygen diffusion rate with a thicker β-phase by β-stabilizing hydrogen. Relative magnitudes of these effects with temperature, pre-transient oxide thickness, and hydrogen content determine the dynamics of high burnup fuel oxidation. Mechanistically modeling the high burnup effect, the model comprehensively simulates the integrated effects of pre-transient oxide and absorbed hydrogen. This study confirms that the corrected Cathcart Pawel correlation-based Equivalent Cladding Reacted evaluation method employed by the U.S Nuclear Regulatory Commission is an effective, yet accurate, simplification of the high burnup cladding oxidation modeling for safety analysis of representative LBLOCA of current PWR systems. The application of the developed model to safety analysis revealed allowable discharge burnup limits of 59 and 76 MWd/kgU for Zircaloy-4 and Zr-Nb alloy, respectively from the view point of fuel accident safety.

Impacts of A-site gadolinium doping on electrocatalytic performance of La0.33Ba0.62Gd0.05Co0.7Fe0.3O3-δ to realize promising cathode for intermediate-temperature solid oxide fuel cells

With respect to intermediate-temperature solid oxide fuel cells (IT-SOFCs), electrocatalytic activity of the cathodes dominates their output power. Herein A-site gadolinium-doped La0.33Ba0.62Gd0.05Co0.7Fe0.3O3-δ (LBG0.05CF) perovskite is synthesized and systematically evaluated as the cathode for IT-SOFCs. We demonstrate outstanding catalytic activity of LBG0.05CF toward oxygen reduction reaction (ORR). Benefiting from enhanced electrical conductivity, oxygen surface exchange and diffusion rates, the ORR activity of LBG0.05CF outperforms that of La0.33Ba0.67Co0.7Fe0.3O3-δ (LBCF), as evidenced by the lower polarization resistance (0.035 Ω cm2) at 700 °C. The Ce0.9Gd0.1O1.95 (CGO) electrolyte-supported fuel cell with the LBG0.05CF cathode delivers a peak power density (PPD) of 371 mW cm−2 at 700 °C, which surpasses the PPD (278 mW cm−2) for LBCF-based cell. Furthermore, LBG0.05CF exhibits an improved CO2 tolerance compared with pristine LBCF. These results highlight a promising strategy of A-site replacement of Ba by lanthanide for optimizing catalytic ORR activity of the perovskite materials.

Modulating Nucleus Oxygen Concentration by Altering Intramembrane Cholesterol Levels: Creating Hypoxic Nucleus in Oxic Conditions.

We propose a novel mechanism by which cancer cells can modulate the oxygen concentration within the nucleus, potentially creating low nuclear oxygen conditions without the need of an hypoxic micro-environment and suited for allowing cancer cells to resist chemo- and radio-therapy. The cells ability to alter intra-cellular oxygen conditions depends on the amount of cholesterol present within the cellular membranes, where high levels of cholesterol can yield rigid membranes that slow oxygen diffusion. The proposed mechanism centers on the competition between (1) the diffusion of oxygen within the cell and across cellular membranes that replenishes any consumed oxygen and (2) the consumption of oxygen in the mitochondria, peroxisomes, endoplasmic reticulum (ER), etc. The novelty of our work centers around the assumption that the cholesterol content of a membrane can affect the oxygen diffusion across the membrane, reducing the cell ability to replenish the oxygen consumed within the cell. For these conditions, the effective diffusion rate of oxygen becomes of the same order as the oxygen consumption rate, allowing the cell to reduce the oxygen concentration of the nucleus, with implications to the Warburg Effect. The cellular and nucleus oxygen content is indirectly evaluated experimentally for bladder (T24) cancer cells and during the cell cycle, where the cells are initially synchronized using hydroxeaurea (HU) at the late G1-phase/early S-phase. The analysis of cellular and nucleus oxygen concentration during cell cycle is performed via (i) RT-qPCR gene analysis of hypoxia inducible transcription factors (HIF) and prolyl hydroxylases (PHD) and (ii) radiation clonogenic assay every 2 h, after release from synchronization. The HIF/PHD genes allowed us to correlate cellular oxygen with oxygen concentration in the nucleus that is obtained from the cells radiation response, where the amount DNA damage due to radiation is directly related to the amount of oxygen present in the nucleus. We demonstrate that during the S-phase cells can become hypoxic in the late S-phase/early G2-phase and therefore the radiation resistance increases 2- to 3-fold.

A high-speed variable-temperature ultrahigh vacuum scanning tunneling microscope with spiral scan capabilities.

We present the design and development of a variable-temperature high-speed scanning tunneling microscope (STM). The setup consists of a two-chamber ultra-high vacuum system, including a preparation and a main chamber. The preparation chamber is equipped with standard preparation tools for sample cleaning and film growth. The main chamber hosts the STM that is located within a continuous flow cryostat for counter-cooling during high-temperature measurements. The microscope body is compact, rigid, and highly symmetric to ensure vibrational stability and low thermal drift. We designed a hybrid scanner made of two independent tube piezos for slow and fast scanning, respectively. A commercial STM controller is used for slow scanning, while a high-speed Versa Module Eurocard bus system controls fast scanning. Here, we implement non-conventional spiral geometries for high-speed scanning, which consist of smooth sine and cosine signals created by an arbitrary waveform generator. The tip scans in a quasi-constant height mode, where the logarithm of the tunneling current signal can be regarded as roughly proportional to the surface topography. Scan control and data acquisition have been programmed in the experimental physics and industrial control system framework. With the spiral scans, we atomically resolved diffusion processes of oxygen atoms on the Ru(0001) surface and achieved a time resolution of 8.3 ms per frame at different temperatures. Variable-temperature measurements reveal an influence of the temperature on the oxygen diffusion rate.

Performance Evaluation of Nonacosan-10-ol-Based Polyethylene Packaging Material Using Molecular Dynamics Simulations.

Packaging material has a significant role in maintaining or altering the shelf life of different products. Polymer materials are extensively used as packaging materials for different perishable and non-perishable products both during transportation and storage. This article aims at developing a new polymer composite which can be used as packaging material. This new composite addresses the challenge of controlling oxygen diffusion rates during the storage of perishable goods such as vegetables, meat and produce, etc. The proposed new composite primarily consists of nonacosan-10-ol and polyethylene. Molecular dynamics simulations (MDS) are performed by mixing 5.2%, 17.1%, 29.2%, 40.8% and 45.2% (wt/wt) of nonacosan-10-ol to amorphous polyethylene. Mechanical properties such as Young’s modulus/glass transition temperature, and gas transport properties such as diffusion coefficient and diffusion volume are estimated from the MDS and diffusion related simulations consisting of different oxygen concentrations in polyethylene-alone system and polyethylene- nonacosan-10-ol blends. The impact of adding different weight percent of nonacosan-10-ol to polyethylene is quantitatively assessed and optimal composition of the proposed additive is suggested corresponding to minimal oxygen diffusion rate, high elastic modulus and good thermal stability.

Microstructural Defects of Epoxy–Phenolic Polymers on Metal Substrates during Acidic Corrosion

This study uses confocal microscopy and image processing to investigate the microstructural changes of coating–metal systems immersed in a heated acidic bath. Unlike standard optical microscopy techniques, 3D confocal microscopy images can quantitatively reveal microscopic defects formed at early stages of cathodic delamination. The coatings are made of fluorescent epoxy–phenolic resins cured at high temperatures onto tinplate (T23) and tin-free steel (TFS) substrates. When the coated metal substrates are immersed in acetic acid, a series of microscopic corrosion events occur at the polymer–metal interface. These events are quantified by changes in the thickness distribution of the degraded samples relative to that of intact coatings. The degradation rate is highest for epoxy–phenolic polymers on TFS substrates, represented by multiple orders of magnitude increase in the number density of defect sites. Higher molecular weight coatings provide slightly better resistance against delamination. The coating thickness dictates the rate of oxygen diffusion and ion transport along the polymer–coating interface, where raised asperities serve as localized sites for metal oxidation and formation of alkaline species, leading to subsequent delamination of the cured polymers from the surfaces. The results show that the metal surface topology is as important as chemistry when designing the corrosion resistance of products containing acidic liquids, and that confocal microscopy is useful in quality control through early detection of mesoscale polymer failure.

Biochemical-thermal-hydro-mechanical coupling model for aerobic degradation of landfilled municipal solid waste

Ventilating solid waste landfills with an oxygen supply can effectively accelerate the degradation of waste, achieve rapid stabilization, and realize the sustainable utilization of landfills. Aiming to understand and verify the aerobic degradation process in landfills, this paper proposed a biochemical-thermal-hydro-mechanical coupling model. The model considers aerobic biochemical reactions, dissolved solute migration, heat transport, two-phase flow, and skeleton deformation. The model was verified by comparison with an in-situ experiment at Jinkou landfill. The results showed the model could accurately represent the observed degradation phenomena during the experiment. The modelling results indicated that the rate of temperature increase and peak temperature of the upper layer, which were lower than those of the middle layer, were affected by heat exchange at the landfill surface. The lowest temperatures occurred near the bottom because of high water content and low oxygen concentrations. The high temperature zone migrated out from the injection well during degradation, reflecting the degradation of degradable organic matter associated with oxygen diffusion rates and aerobic degradation reactions. The initial accumulated settlement value was fast, but slowed and finally stabilized. The surface subsidence also developed from the center around the injection well to the surrounding area, and 70% of the total subsidence occurred within 150 days. This newly developed model provides a theoretical framework for analyzing the multi-field coupling of aerobic degradation of landfilled municipal solid waste (MSW).

Hydrogen Peroxide Production from Water Oxidation on a CuWO4 Anode in Oxygen-Deficient Conditions for Water Decontamination.

Hydrogen peroxide, an environmentally benign oxidant, is an effective chemical agent for water purification. On-site production of H2O2 is considered economical because it avoids the cost of storage and transportation. Traditional generation of H2O2 from oxygen reduction, as a heterogeneous electrochemical reaction, suffers from mass transfer problems because of the limited solubility and low diffusion rate of oxygen in water. These limitations can be overcome if H2O2 is formed by water oxidation. Herein, conversion of water to hydrogen peroxide was achieved efficiently on a CuWO4 anode. This water oxidation strategy can generate H2O2 at a rate of ∼11.8 μmol min-1 cm-2 at 3.0 V versus reversible hydrogen electrode. Importantly, this on-site H2O2 production shows high efficiency in water purification in O2-deficient conditions. This water oxidation anode offers a feasible way to provide a green purification agent with only water as the final byproduct, avoiding toxic intermediates and residues during the production and application.

Inhibition effect of N2/CO2 blends on the minimum explosion concentration of agriculture and coal dusts

Minimum explosion concentration (MEC) of three agriculture dusts and two coal dusts was studied via a 20-L explosion chamber to reveal the role of gaseous inhibitors. Both active method (CO2 diluting air) and passive method (CO2 replacing O2) were used. The TG and DTG thermal analysis tests were conducted to study the pyrolysis and combustion characteristics of dust samples. An alternative explosion criterion based on combustion duration time was used to determine MEC, and compared with the standardized overpressure method. Under 10-kJ ignition condition, as oxygen mole fraction (XO2) decreased from 21% to 10%, MEC of agriculture dusts and coal dusts respectively increased by around 5 times and 2 times. The active inerting method with a lower N2/CO2 ratio was found to have a better suppression effect on the explosion of the five carbonaceous dusts because the blend has a higher specific heat and a lower oxygen diffusion rate.

Articular Cartilage Regeneration in Veterinary Medicine.

Cartilage is an avascular tissue with a limited rate of oxygen and nutrient diffusion, resulting in its inability to heal spontaneously. Articular cartilage defects eventually lead to osteoarthritis (OA), the endpoint of progressive destruction of cartilage. In companion animals, OA is the most common joint disease, and many pain management and surgical attempts have been made to find an appropriate treatment. Pain management of OA is usually the first choice of OA therapy, which is often managed with nonsteroidal anti-inflammatory drugs (NSAIDs). To avoid known negative side effects of NSAIDs, other approaches are being considered, such as the use of anti-nerve growth factor monoclonal antibodies (anti-NGF mAB), hyaluronic acid (HA), platelet-rich plasma (PRP), and mesenchymal stem cells (MSCs). The latter is increasingly being recognized as effective in reducing or even eliminating pain and lameness associated with OA. However, the in vivo mechanisms of MSC action do not relate to their differentiation potential, but rather to their immunomodulatory functions. Achieving actual regeneration of cartilage to prevent OA from developing or even revert already existing OA condition has not yet been achieved. Several techniques have been tried to overcome cartilage's inability to regenerate, from osteochondral transplantation, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). Combinatory use of MSCs unique features and biomaterials is also being investigated with the aim to as much as possible recapitulate the native microenvironment of the cartilage, yet so far none of the methods have produced reliable and truly effective results. Although OA, for now, remains an incurable disease, novel techniques are being developed, rendering hope for the future accomplishment of actual cartilage regeneration. The aim of this chapter is firstly to summarize known and developing pain management options for OA, secondly to present surgical attempts to regenerate articular cartilage, and finally to present the attempts to improve existing regenerative treatment options using mesenchymal stem cells, with the vision for the possible use of developing strategies in veterinary medicine.

Foaming mechanism of polishing porcelain stoneware tile residues via adding C, Al and Si powder

Polishing porcelain stoneware tile residues (PPR) is used to prepare foamed ceramic to solve the problem of solid waste discharge in ceramic industry. In this study, C, Al and Si powder were added to the simulated PPR to control foaming, and the mechanism of silicon carbide foaming in the PPR was discussed in detail. After these powders were introduced into the simulated PPR, the phenomenon of alumina crystallization on the pore wall of the foamed ceramic and the diffusion of gas in the foamed ceramic were discovered to be exciting. The foaming mechanism of PPR is detailed as follows: the diffusion rate of oxygen in silicate liquid is faster than that of CO during sintering, so the CO generated by incomplete oxidation of silicon carbide in PPR accumulates in the liquid, which makes the volume of ceramics expand and causes foaming.

Vaporization, Diffusion and Combustion of Laser-Induced Individual Magnesium Microparticles in Inert and Oxidizing Atmospheres

Although the gas phase combustion of metallic magnesium (Mg) has been extensively studied, the vaporization and diffusive combustion behaviors of Mg have not been well characterized. This paper proposes an investigation of the vaporization, diffusion, and combustion characteristics of individual Mg microparticles in inert and oxidizing gases by a self-built experimental setup based on laser-induced heating and microscopic high-speed cinematography. Characteristic parameters like vaporization and diffusion coefficients, diffusion ratios, flame propagation rates, etc., were obtained at high spatiotemporal resolutions (μm and tens of μs), and their differences in inert gases (argon, nitrogen) and in oxidizing gases (air, pure oxygen) were comparatively analyzed. More importantly, for the core–shell structure, during vaporization, a shock wave effect on the cracking of the porous magnesium oxide thin film shell-covered Mg core was first experimentally revealed in inert gases. In air, the combustion flame stood over the Mg microparticles, and the heterogeneous combustion reaction was controlled by the diffusion rate of oxygen in air. While in pure O2, the vapor-phase stand-off flame surrounded the Mg microparticles, and the reaction was dominated by the diffusion rate of Mg vapor. The diffusion coefficients of the Mg vapor in oxidizing gases are 1~2 orders of magnitude higher than those in inert gases. However, the diffusive ratios of condensed combustion residues in oxidizing gases are ~1/2 of those in inert gases. The morphology and the constituent contents analysis showed that argon would not dissolve into liquid Mg, while nitrogen would significantly dissolve into liquid Mg. In oxidizing gases of air or pure O2, Mg microparticles in normal pressure completely burned due to laser-induced heating.

Stabilization of natural and synthetic indigo on nanocellulose network - Towards bioactive materials and facile dyeing processes

Synthetic dyes are vastly used for colouring numerous materials, although the adverse effects on environment are well recognized. In addition to developing the existing dyeing technologies more efficient and cleaner, the valorisation of natural dyes can enhance the sustainable development of dyeing industry. Natural indigo, derived from Isatis tinctoria, is a bio-based alternative for indigo produced via chemical synthesis routes. Owing to the insoluble character of indigo pigment, the dye requires conversion into soluble leucoindigo form prior to dyeing, which is often accomplished by using harsh sodium dithionite vat technique. During the processing from plant to dye attached on a fabric, indigo is transferred from the soluble leucoindigo form to the oxidized insoluble indigo and once more back to leucoindigo. Additionally, the oxidation is difficult to control and with traditional vat technique maintaining the leucoindigo through the dyeing often requires adding more reducing agent chemicals. Maintaining the soluble form throughout the process would enable lower number of processing steps and reduce the use of harmful chemical agents. In the present study, the stabilization of leucoindigo on nanocellulose matrix carrier was investigated with spectroscopic and photophysical methods. According to the results, leucoindigo was successfully stabilized on nanocellulose suspension, most likely due to the limited rate of oxygen diffusion into the viscous medium. Visual observations revealed that the leuco-form was retained even longer with natural indigo than synthetic indigo. This enhanced stability was attributed to the presence of radical scavenging species in natural indigo since the synthetic indigo did not show notable antioxidant properties. Given the promising results the paste formulation was demonstrated to be applicable for creating patterns on cotton using a screen-printing technique. Since the leucoindigo was stabilized on nanocellulose carrier, the need for re-reduction prior to dyeing was avoided and the amount of harmful reducing chemicals was reduced. These findings also show that the characteristics of natural dyes that are often considered disadvantageous compared to synthetic dyestuff, i.e. presence of co-products in the mixture, can however, create more value to the dyed material through new functionalities.

Sequestration of soil carbon by burying it deeper within the profile: A theoretical exploration of three possible mechanisms

Subsoil carbon is generally older and decomposes more slowly than topsoil carbon. It has, therefore, been suggested that carbon stocks could be increased by burying carbon-rich topsoil at depth to slow its decomposition. This has been supported by recent experiments that showed that buried topsoil carbon indeed decomposed more slowly, but the mechanisms causing the reduction have not yet been identified. We investigated three theoretical mechanisms that may explain reduced decomposition rates at depth: (1) lower soil-temperature variability, (2) lower oxygen concentrations/redox potential and (3) less priming (biological synergy). Temperature variability decreases with soil depth. As decomposition rates vary non-linearly with temperature, reduced temperature variability should, therefore, reduce annual decomposition rates. However, detailed simulations showed that it changed annual decomposition rates by only a few percent. Maximal decomposition rates also require adequate oxygen, but our simulations showed that oxygen diffusion rates would need to be reduced 1000 to 10 000-fold compared to the topsoil for it to protect buried soil carbon. Oxygen limitation is, therefore, likely to be confined to soils that are water-logged for extended periods. Priming (or biological synergy) is assumed to be the stimulation of decomposition rates by the availability of labile organic carbon. Our simulations showed that lower labile carbon inputs could reduce priming and potentially preserve up to half of buried carbon for centuries. If experimental work can further substantiate the role of this mechanism, carbon burial at depth could become a practical and useful climate-change mitigation option.

Influence of Oxidation Temperature on Structure and Mechanical Properties of Titanium

Surface oxidation of pure titanium was performed in the atmosphere to increase the mechanical properties. The effect of oxidation temperature (650-900°C) for 2 h on the microstructure, composition, and mechanical properties of the treated samples was investigated using X-ray diffraction, hardness tester and indentation modulus tester, respectively. The diffusion rate of oxygen in grade-2 pure Ti with different processing temperatures discussed in present research. Based on a result of the examination, the surface hardness was increased first and then decreased as the processing temperature increased. And when the processing temperature at 850°C, the surface hardness reached the maximum value. In addition, the Young's modulus of the treated samples also showed a maximum value of 198.9 GPa for a processing temperature of 850°C. An oxidation condition of 850°C is considered optimal as it provides sufficiently high hardness during practical use.

Factors determining barrier properties to oxygen transport across model and cell plasma membranes based on EPR spin-label oximetry.

This review is motivated by the exciting new area of radiation therapy using a phenomenon termed FLASH in which oxygen is thought to have a central role. Well-established principles of radiation biology and physics suggest that if oxygen has a strong role, it should be the level at the DNA. The key aspect discussed is the rate of oxygen diffusion. If oxygen freely diffuses into cells and rapidly equilibrates, then measurements in the extracellular compartment would enable FLASH to be investigated using existing methodologies that can readily measure oxygen in the extracellular compartment. EPR spin-label oximetry allows evaluation of the oxygen permeability coefficient across lipid bilayer membranes. It is established that simple fluid phase lipid bilayers are not barriers to oxygen transport. However, further investigations indicate that many physical and chemical (compositional) factor can significantly decrease this permeation. In biological cell plasma membranes, the lipid bilayer forms the matrix in which integral membrane proteins are immersed, changing organization and properties of the lipid matrix. To evaluate oxygen permeability coefficients across these complex membranes, oxygen permeation across all membrane domains and components must be considered. In this review, we consider many of the factors that affect (decrease) oxygen permeation across cell plasma membranes. Finally, we address the question, can the plasma membrane of the cell form a barrier to the free diffusion of oxygen into the cell interior? If there is a barrier then this must be considered in the investigations of the role of oxygen in FLASH.