Function Of Oxygen Concentration Research Articles

Spontaneous combustion characteristics of coal based on the oxygen consumption rate integral

According to the different characteristics of coal spontaneous combustion (CSC), different countermeasures can effectively prevent CSC. In this paper, a new characteristic parameter, the oxygen consumption rate integral (OCRI), was proposed. The characteristics of CSC during the latent period and the effect of low oxygen concentration (0–20.96 %) on the CSC were comprehensively examined. Using a lab-built closed oxidation system, isothermal oxidation experiments were performed on different grades of coals at different temperatures. The OCRI was obtained by integrating the oxygen consumption rate as a function of oxygen concentration. The OCRI expresses the sum of the rates of oxygen consumption at different concentrations of oxygen and can be used as an identification index for the propensity of CSC. The kinetic basis for this approach is the variability of initial oxygen consumption rates and oxygen reaction orders for different coals. Finally, the physicochemical structure of the coal was measured by N2 adsorption and IR analysis. The results were correlated with the OCRI. On this basis, the main microscopic reaction pathways affecting the CSC were revealed. The results can aid in the future direction for research and development of high-efficiency inhibitors.

Photophysical Rate Constants and Oxygen Dependence for Si and Ge Rhodamine Zwitterions.

The family of group XIV rhodamine zwitterions are fluorescence probes with carbon, silicon, germanium, or tin substituted in the 10-position of the xanthene ring. Because of their inherent near-infrared fluorescence, photostability and high quantum yields in aqueous solutions, the Si and Ge containing fluorophores in this class have become increasingly important for fluorescent labeling of proteins and biological molecules. This study fully characterizes photophysical rates derived from a model consisting of a singlet ground state, the lowest singlet excited state, and the lowest triplet excited state for two exemplar group XIV rhodamine zwitterions, one containing Si and the other Ge. Within a simple Jablonski diagram, all radiative and non-radiative rates, including intersystem crossing and triplet depopulation rates, were measured as a function of oxygen concentration. It was shown that the triplet depopulation rates are intrinsically fast in comparison with traditional xanthene containing fluorophores, probably due to the increased spin-obit coupling from the Si and Ge substitution in the xanthene ring. Dissolved oxygen increases both the intersystem crossing and triplet depopulation rates. Stern-Volmer analysis was conducted to estimate rates of quenching by oxygen. The experimental data was used to estimate the initial rates for reactive oxygen production by Si and Ge containing fluorophores in aqueous solutions containing different concentrations of dissolved O2. These estimates showed a significantly slower initial rate of reactive oxygen production in comparison with rhodamine 6G. This goes a long way to explaining their inherent photostability. Spectroscopic experiments were also conducted in 77 K viscous aqueous glasses where it was observed that the fluorescence spectra remained unchanged, and the quantum yields increased from 0.53 to 0.84 and from 0.52 to 0.89 for the Si and Ge containing fluorophores respectively; no phosphorescence was observed. All intersystem crossing and triplet depopulation rates were measured using fluorescence correlation spectroscopy (FCS) and analyzed using a new method that extrapolated the power dependence of the FCS curves to optical saturation. This method was verified using published data.

Mechanistic modelling of oxygen enhancement ratio of radiation via Monte Carlo simulation-based DNA damage calculation

Objective. Oxygen plays an important role in affecting the cellular radio-sensitivity to ionizing radiation. The objective of this study is to build a mechanistic model to compute oxygen enhancement ratio (OER) using a GPU-based Monte Carlo (MC) simulation package gMicroMC for microscopic radiation transport simulation and DNA damage calculation. Approach. We first simulated the water radiolysis process in the presence of DNA and oxygen for 1 ns and recorded the produced DNA damages. In this process, chemical reactions among oxygen, water radiolysis free radicals and DNA molecules were considered. We then applied a probabilistic approach to model the reactions between oxygen and indirect DNA damages for a maximal reaction time of t 0. Finally, we defined two parameters P 0 and P 1, representing probabilities for DNA damages without and with oxygen fixation effect not being restored in the repair process, to compute the final DNA double strand breaks (DSBs). As cell survival fraction is mainly determined by the number of DSBs, we assumed that the same numbers of DSBs resulted in the same cell survival rates, which enabled us to compute the OER as the ratio of doses producing the same number of DSBs without and with oxygen. We determined the three parameters (t 0, P 0 and P 1) by fitting the OERs obtained in our computation to a set of published experimental data under x-ray irradiation. We then validated the model by performing OER studies under proton irradiation and studied model sensitivity to parameter values. Main results. We obtained the model parameters as t 0 = 3.8 ms, P 0 = 0.08, and P 1 = 0.28 with a mean difference of 3.8% between the OERs computed by our model and that obtained from experimental measurements under x-ray irradiation. Applying the established model to proton irradiation, we obtained OERs as functions of oxygen concentration, LET, and dose values, which generally agreed with published experimental data. The parameter sensitivity analysis revealed that the absolute magnitude of the OER curve relied on the values of P 0 and P 1, while the curve was subject to a horizontal shift when adjusting t 0. Significance. This study developed a mechanistic model that fully relies on microscopic MC simulations to compute OER.

The modulated oxygen evolution reaction performance in La2/3Sr1/3CoO3 by a design of stoichiometry offset

The accurate stoichiometry control of single-crystalline transition metal oxide thin film and the electrochemical performance such as in oxygen evolution reaction (OER) offer a useful pathway towards the mechanism understanding and the strategy of improving electrochemical activity at the atomic level. As a stable, low cost, and high active OER catalyst, La2/3Sr1/3CoO3 (LSCO) has drawn substantial attention recently. Here we report a modulated OER performance of LSCO by different stoichiometry offsets, an overall ∼2074.63% tunability can be seen. Meanwhile, the overpotential of LSCO exhibits a volcano trend as a function of oxygen concentration. These phenomena can be understood on the competition of double- and super-exchanges in Co3+/Co4+ with the help of the overlap of O 2p and Co 3d orbits. Our investigation provides an effective platform for obtaining a narrow window of improved electrochemical activity in correlated transition metal oxides.

The Evolution of Photoluminescence Properties of PEA2SnI4 Upon Oxygen Exposure: Insight into Concentration Effects

AbstractThe time evolution of the photoluminescence properties in phenylethylammonium tin halide perovskite (PEA2SnI4) film as a function of oxygen concentration is reported. Photo‐brightening and reversible photoluminescence quenching are observed in PEA2SnI4 film at ultralow oxygen concentration (< 1.5 vol%). In the case of 1.5 vol% < [O2] < 21 vol%, the photoluminescence emission of PEA2SnI4 film can be partially recovered after resetting the samples to nitrogen box. As the oxygen concentration further increases with the range of 21 to 95 vol%, the photoluminescence emission of PEA2SnI4 film is significantly quenched and can only be slightly recovered after removing it to the nitrogen box. By correlating the material characterizations and theoretical analysis, the interactions between PEA2SnI4 and oxygen contain physisorption and chemical reactions are illustrated. Depending on the oxygen concentration, the chemical reactions between PEA2SnI4 and oxygen can be reversible and/or irreversible. The insights into oxygen concentration effects provide a guideline to optimize the stability of PEA2SnI4 for achieving high‐performance optoelectronic devices.

Oxygen Consumption by Phalaenopsis Plantlets and Chrysanthemum Cuttings as a Function of Temperature and Time: Model Structure Validation

Phalaenopsis spp. and Chrysanthemum are ornamentals with an important economic value. Currently, quality loss during storage and transport of plantlets and cuttings is a limiting factor for spreading the workload, broadening the export range, and the use of slower but more environmentally friendly transport. In the agro-food sector, equilibrium modified atmosphere packaging has enhanced the shelf-life of minimally processed produce. The required properties for an equilibrium modified atmosphere packaging system can be estimated from the respiration rate of the packaged commodity under specified atmospheric composition and storage temperature. In this work, a model structure is validated to estimate the respiration rate as a function of oxygen concentration and temperature for Phalaenopsis and Chrysanthemum. The oxygen concentration as a function of time was monitored in a closed system for different storage temperatures. The models show a good fit to the data. The model coefficients were dependent on the plant species and characteristics. The resulting formulae can be used to estimate the oxygen consumption rate of the produce under a range of oxygen concentrations and a temperature range from 15 °C to 32 °C for Phalaenopsis and from 2 °C to 14 °C for Chrysanthemum. The oxygen concentrations for which the formulae are valid depend on the storage temperature and plant species. The models can be used to estimate a dynamic oxygen consumption rate profile during storage and transport.

A Self-Powered, Biodegradable Dissolved Oxygen Microsensor

We report a biodegradable, self-powered sensor for measurement of dissolved oxygen in the body. The principle of operation is the competition of an oxygen reduction reaction against the ordinarily dominant hydrogen reduction reaction at the cathode of a corroding electrochemical couple. Because the relative contribution of the oxygen reduction reaction to the overall electrochemical reaction depends on the local oxygen concentration, the output voltage of the couple is also dependent on local oxygen concentration. The sensor is formed by embedding the biodegradable metals magnesium and molybdenum within a biodegradable poly(lactic acid) substrate using lamination; external physiological solution is utilized as the electrolyte. The output voltage of the sensor (i.e., the voltage generated across the corroding couple) was measured as a function of oxygen concentration over typical physiological oxygen concentration ranges of 0–60% that of atmospheric oxygen. A linear output voltage response of approximately 6 mV per percentage point oxygen concentration was observed; oxygen concentrations above this range resulted in sensor saturation. [2020-0192]

Partial inertion as basis of safety for pharmaceutical operations involving highly ignition sensitive powders and modeling combustion properties as a function of oxygen concentration

AbstractPharmaceutical operations often require inertion or other suitable explosion protection systems when handling highly ignition sensitive materials. Regulating bodies typically require full inertion, which may be difficult and expensive to maintain. This work measured the influence of oxygen concentration on the values of the minimum ignition energy (MIE) as well as the explosion severity (Kst and Pmax) for several of the most easily ignitable pharmaceutical powders. We found a significant increase in the MIE and decreases in the Kst and Pmax by reducing the oxygen level to 12% to 15% v/v. The changes in MIE and explosion severity mean that partial inertion along with control of static should provide a satisfactory basis of safety for most unit operations handling these powders. We share these results to encourage others to examine the behavior of similar organic powders. Further, we have used the adiabatic flame temperature from combustion calculations to model the Pmax, limiting oxygen concentration, and MIE at reduced oxygen concentrations, and find very good agreement with the experimental values. This modeling can be a useful tool as a safe and economical alternative to testing when material is not available or for highly potent/toxic materials where testing is not preferred to avoid personnel exposure.

Rate-Limiting Steps Elucidated By Electrochemical Impedance Spectroscopy of a Yttria-Stabilized Zirconia 2-in-1 Temperature and Oxygen Gas Sensor Measured at Extreme Temperatures

Introduction Yttria-stabilized zirconia (YSZ) is known for its good ionic conductivity, essentially being synonymous with the term “lambda sensor”. Automotive lambda sensors have been fabricated with YSZ as the electrolyte for 30+ years and have operated in a temperature region of 600oC to 800oC. There is an increasing demand for higher operating temperature sensors, specifically a 2-in-1 temperature and oxygen sensor which is stable, selective, and sensitive in extreme environments. However, there remains a disagreement among scholars about the effects on oxygen vacancy activation energy at temperatures higher than 800oC. Also, the rate-limiting step of oxygen reduction on the platinum electrode is not inherently clear. A 2-in-1 temperature and oxygen sensor was fabricated and characterized with the analysis of electrochemical impedance spectroscopy (EIS), DC resistance, and open circuit potential measurements at temperatures between 600oC and 1200oC. The temperature dependence on individual activation energies within the sensor was elucidated directly through these techniques. Methods Yttria-stabilized zirconia (MTI Corp) was employed as the solid-state electrolyte in sensor fabrication, with the primary electrode material as porous platinum (ESL 5570). Platinum paste was screen printed onto planar YSZ substrates in an interdigitated electrode configuration, then fired at 1500oC for 2 hours in nitrogen atmosphere (1 atm). The sensor was placed in a ThermoScientific tube furnace capable of reaching 1500oC, with mass flow controllers varying oxygen gas concentration throughout electrical measurements. Platinum foil acted as a Faraday cage around the sensor to shield from furnace inductive fluctuations and minimize noise during low frequency EIS measurements. A thermocouple placed next to the sensor validated furnace operating temperature and cooling endcaps on the furnace tube created a natural temperature gradient between sensor placement and the electrical connections outside of the furnace. Figure 1 displays the environmental testing setup. Results and Conclusions Figure 2a displays an impedance Nyquist spectrum that contains real and imaginary components of impedance measured at 0.21 atm PO2, where electrolyte resistance decreases with an increase in temperature. Figure 2b displays the Arrhenius plot of isolated YSZ electrolytic resistance extracted from figure 2a, where there are distinct activation regions at moderate and high temperatures. In agreement with Badwal [1], the shift to lower EA at higher temperatures was due to a gradual transition between an association region where oxygen vacancies are bound to dopant cations, and a dissociation region where vacancies are free and mobile.At a known temperature, EIS also elucidates oxygen concentration dependence on sensor electrode resistance. Figure 3a shows sensor electrode resistance, fitted from figure 2a, as a function of oxygen concentration. Investigating the oxygen reduction reaction (ORR) variation on platinum at various temperature regions, it is suggested that ORR on platinum is co-limited by oxygen adsorption and by oxygen transport along the surface of the electrode, in agreement with Adler [2]. Figure 3b shows that electrode 2 is dominant at temperatures below 1050oC, indicative of oxygen diffusion limitation on the surface and through platinum. Electrode 1 is dominant at temperatures above 1050oC, where dissociative adsorption of oxygen on the electrode surface is predominant.

Oxy-combustion characteristics as a function of oxygen concentration and biomass co-firing ratio in a 0.1 MWth circulating fluidized bed combustion test-rig

Oxy-combustion with a circulating fluidized bed (Oxy-CFBC) can facilitate the separation of high CO2 concentration and reduce emissions by biomass co-firing. This study investigated Oxy-CFBC characteristics such as temperature, solid hold-up, flue gas concentrations including CO2, pollutant emissions (SO2, NO, and CO), combustion efficiency and ash properties (slagging, fouling index) with increasing input oxygen levels (21–29 vol%), and biomass co-firing ratios (50, 70, and 100 wt% with domestic wood pellet). The possibility of bio-energy carbon capture and storage for negative CO2 emission was also evaluated using a 0.1 MWth Oxy-CFBC test-rig. The results show that combustion stably achieved with at least 90 vol% CO2 in the flue gas. Compared to air-firing, oxy-firing (with 24 vol% oxygen) reduced pollutant emissions to 29.4% NO, 31.9% SO2 and 18.5% CO. Increasing the biomass co-firing from 50 to 100 wt% decreased the NO, SO2 and CO content from 19.2 mg/MJ to 16.1 mg/MJ, 92.8 mg/MJ to 25.0 mg/MJ, and 7.5 mg/MJ to 5.5 mg/MJ, respectively. In contrast to blends of sub-bituminous coal and lignite, negative CO2 emission (approximately −647 g/kWth) was predicted for oxy-combustion only biomass.

Mechanical properties of VMoNO as a function of oxygen concentration: Toward development of hard and tough refractory oxynitrides

Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl-structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem that may compromise material properties and performance. Here, the authors explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1−xOx solid solutions as a function of the oxygen concentration x. Elastic constant and intrinsic hardness calculations show that oxidation does not degrade the mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate that the presence of oxygen reduces the covalent bond character, which slightly lowers the alloy strength and intrinsic hardness. Nevertheless, the character of metallic d-d states, which are crucial for allowing plastic deformation and enhancing toughness, remains unaffected. Overall, the authors’ results suggest that VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high intrinsic hardness, while still being ductile.

Characterizing flame stability and radiative heat transfer in non-swirling oxy-coal flames using different multiphase modeling frameworks

The ability of two multiphase modeling frameworks (Euler-Lagrangian and Euler-Euler) to capture the experimentally observed flame ignition characteristics in non-swirling oxy-coal flames were investigated. The interphase interaction terms were modeled employing identical phenomenological laws. Simulations of inert particles were carried out first and were found to yield identical predictions across both frameworks. Next, user-defined functions were utilized to: model the diffusional and kinetic resistances associated with the heterogeneous char oxidation (in the Euler-Euler framework), the non-gray effects of gas radiation, and the variations in the radiative properties of the solid phase (in the Euler-Lagrangian framework). Only the Euler-Euler framework was able to capture the experimental observed trends in flame stand-off as a function of oxygen concentration in the primary burner. The interval between the devolatilization and char combustion processes varied between the two frameworks and were a contributing factor to the prediction differences. Representing the coal PSD by a single granular phase in the Eulerian framework was deemed adequate for capturing flame stand-off since solving additional phase equations did not significantly impact the flame stand-off predictions. Further, the experimentally observed effects of: primary oxidizer composition variations, secondary oxidizer temperature and wall temperature on flame stand-off were also adequately predicted reasonably well by the Euler-Euler framework. Radiation was the dominant mode of heat transfer in these flames with the radiant heat loss fraction (Radiative heat loss/Total chemical heat release) determined to be 0.6 for both flames. Radiation from the participating gases accounted for 75% of the total radiative heat transfer.

Abstract 1914: Acute myeloid leukemia cell and stem-progenitor cell behavior studied in mimetic bone marrow microenvironment

Abstract The bone marrow (BM) microenvironment plays a pivotal role in the survival and chemoresistance of leukemia stem cells (LSC) in acute myeloid leukemia (AML). However, conventional culture approaches do not reflect physiological conditions of crucial anatomical districts and signals of incubation-induced dysregulation may confound leukemic transcriptome results. In vivo mimetic cultures of the LSC districts will significantly aid in the disentanglement of LSC mechanisms and in the assessment of the therapy. We engineered Petri dishes able to mimic the “hypoxic” conditions found in the stem cell niches and in BM district. Our approach is based on a patented method which controls the physiological concentrations of oxygen, glucose and pH in the culture environment. Cell proliferation and hypoxia-induced apoptosis in the engineered device were investigated for OCI-AML3 and KG1 AML cell lines. We observed a slight but significant reduction in cell proliferation compared with control cells for OCI AML-3, which is in line with a more quiescent cell condition. No significant differences were obtained by culturing KG-1 cells, which are more resistant to low oxygen concentrations. We have analyzed the effects of cell culturing in the hypoxic dishes on the expression of MYC and p21. Immunofluorescence analysis of HIF-1α levels and HIF-1α nuclear localization as a function of oxygen concentration were determined. Time-lapse experiments of AML cell lines and primary BM cells were performed in the in vivo mimetic device to elucidate the response of CD34+ AML cells to different oxygen concentrations. We tested an innovative cell culturing device able to mimic the dynamical conditions of oxygen content, which are found in vivo. Our results shed light on AML cells and progenitor-stem cells behavior in response to oxygen conditions in the BM niche and allow to disentangle the LSCs complex biology. This ”in vivo mimetic” approach will generate crucial information on the molecular mechanisms preserving LSC in AML, thus providing novel potential therapeutic targets to eradicate leukemia initiating cells in their own microenvironment, contrasting therapy resistance. Supported by: Associazione Italiana per la Ricerca sul Cancro, MFAG id. 19044. Citation Format: Giorgia Simonetti, Marco Malferrari, Maila Becconi, Samantha Bruno, Giovanni Martinelli, Stefania Rapino. Acute myeloid leukemia cell and stem-progenitor cell behavior studied in mimetic bone marrow microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1914.

Thermal stability of aluminum oxide nanoparticles: role of oxygen concentration

Oxygen incorporation yields an Al2O3 nanoparticle with a Janus-like morphology.

Uphill Diffusion of Antioxidant in Cross-Linked Polyethylene

Cross-linked polyethylene (XLPE or PEX) is a major material for cable insulation. Antioxidants are usually added to XLPE to prevent the insulation from oxidation. However, antioxidants diffuse out of an XLPE matrix during thermal ageing, which accelerates oxidation, causing the degradation of the insulation. Few models have been developed to represent the diffusion behavior of the antioxidant. One paper has reported that the antioxidant in XLPE migrates from low to high concentration but no explanation has been given. Starting with the theories of uphill diffusion and reaction-diffusion, this paper has developed a physics-based model explicating why the antioxidant migrates against the concentration gradient. In addition to the concentration, the activity coefficient (y) of the antioxidant is considered. With physical significance, this study mathematically proves the inhomogeneous distribution of the diffusing oxygen in XLPE makes y a function of oxygen concentration. y determines the driving force rendering the uphill diffusion of the antioxidant. Besides the y function, the decomposition rate of the antioxidant has been modeled. Experimental data are used to validate the proposed model.

Resolving phase stability in the Ti-O binary with first-principles statistical mechanics methods

The Ti-O system consists of a multitude of stable and metastable oxides that are used in wide ranging applications. In this work we investigate phase stability in the Ti-O binary from first principles. We perform a systematic search for ground state structures as a function of oxygen concentration by considering oxygen-vacancy and/or titanium-vacancy orderings over four parent crystal structures: (i) hcp Ti, (ii) $\ensuremath{\omega}$-Ti, (iii) rocksalt, and (iv) hcp oxygen containing interstitial titanium. We explore phase stability at finite temperature using cluster expansion Hamiltonians and Monte Carlo simulations. The calculations predict a high oxygen solubility in hcp Ti and the stability of suboxide phases that undergo order-disorder transitions upon heating. Vacancy ordered rocksalt phases are also predicted at low temperature that disorder to form an extended solid solution at high temperatures. Predicted stable and metastable phase diagrams are qualitatively consistent with experimental observations, however, important discrepancies are revealed between first-principles density functional theory predictions of phase stability and the current understanding of phase stability in this system.

The effect of pressure and oxygen concentration on the ignition and combustion of aluminum–magnesium fuel-rich propellant

In order to better understand how future candidate solid propellants may affect combustion characteristics in ramjet motor, the aluminum–magnesium fuel-rich propellant was tested on a sealed high-pressure laser ignition platform. The laser ignition experimental device was designed and built, then the ignition and combustion characteristics of aluminum–magnesium fuel-rich propellant under different pressures and oxygen concentrations in environment gas were studied. The comprehensive impacts of pressure and oxygen concentration on ignition delay time and burning rate were appraised. The results displayed that the ignition delay time was decreased with the increase of pressure and oxygen concentration. The effect of pressure on ignition delay time was weaker than oxygen concentration. The impact of oxygen concentration on ignition was very complex. When the oxygen concentration of environment gas was less than that of the oxidizing gas from the propellant pyrolysis products, the ignition gas phase reaction occurred in the dispersion region of the solid propellant pyrolysis product, the initial flame was close to the propellant surface. In contrast, when the oxygen concentration was larger than the pyrolysis oxidizing gas, the ignition gas phase reaction occurred in the diffusion zone of the propellant pyrolysis products and the environment gas, the initial flame appeared far from the propellant surface. The burning rate of aluminum–magnesium fuel-rich propellant increased with the increase of pressure and oxygen concentration, where their effect on burning rate is accord with B-number theory. Comparing the experimental measurements with an analytical model, the results showed good consistency. The function of oxygen concentration and pressure could explain the effect on burning rate and ignition delay time, because pressure and oxygen concentration were favorable for the heat transfer, radiation and convection from the flame. The function of the combined influences of pressure and oxygen concentration on burning rate was established by a power law fitting. The good fitting is consistent with the experimental measurements, and shows that the scaling is valid for a full range of pressure and oxygen concentration tests to predict burning rate.

Effect of oxygen on dislocation multiplication in silicon crystals

This paper aims to clarify the effect of oxygen on dislocation multiplication in silicon single crystals grown by the Czochralski and floating zone methods using numerical analysis. The analysis is based on the Alexander–Haasen–Sumino model and involves oxygen diffusion from the bulk to the dislocation cores during the annealing process in a furnace. The results show that after the annealing process, the dislocation density in silicon single crystals decreases as a function of oxygen concentration. This decrease can be explained by considering the unlocking stress caused by interstitial oxygen atoms. When the oxygen concentration is 7.5 × 1017 cm−3, the total stress is about 2 MPa and the unlocking stress is less than 1 MPa. As the oxygen concentration increases, the unlocking stress also increases; however, the dislocation velocity decreases.

The Warburg effect as an adaptation of cancer cells to rapid fluctuations in energy demand.

To maintain optimal fitness, a cell must balance the risk of inadequate energy reserve for response to a potentially fatal perturbation against the long-term cost of maintaining high concentrations of ATP to meet occasional spikes in demand. Here we apply a game theoretic approach to address the dynamics of energy production and expenditure in eukaryotic cells. Conventionally, glucose metabolism is viewed as a function of oxygen concentrations in which the more efficient oxidation of glucose to CO2 and H2O produces all or nearly all ATP except under hypoxic conditions when less efficient (2 ATP/ glucose vs. about 36ATP/glucose) anaerobic metabolism of glucose to lactic acid provides an emergency backup. We propose an alternative in which energy production is governed by the complex temporal and spatial dynamics of intracellular ATP demand. In the short term, a cell must provide energy for constant baseline needs but also maintain capacity to rapidly respond to fluxes in demand particularly due to external perturbations on the cell membrane. Similarly, longer-term dynamics require a trade-off between the cost of maintaining high metabolic capacity to meet uncommon spikes in demand versus the risk of unsuccessfully responding to threats or opportunities. Here we develop a model and computationally explore the cell’s optimal mix of glycolytic and oxidative capacity. We find the Warburg effect, high glycolytic metabolism even under normoxic conditions, is represents a metabolic strategy that allow cancer cells to optimally meet energy demands posed by stochastic or fluctuating tumor environments.

Durability Evaluations and Rapid Ageing Methods in Commercial Emission Catalyst Development for Diesel, Natural Gas and Gasoline Applications

The ageing conditions were analyzed with gasoline, diesel and natural gas (NG) catalysts to find the simplified, rapid thermal and chemical (sulfur) ageing methods for catalyst development. Rich-stoichiometric conditions prevented the deactivation of TWCs in gasoline and NG applications. Active metals and support are sintered thermally during short lean periods by increasing deactivation as a function of oxygen concentration. Air ageing for 3–10 h is an appropriate rapid ageing method for TWCs. Active regeneration conditions for DPF with a higher carbon concentration deactivated DOCs less than normal diesel exhaust conditions at 700 °C. Natural gas oxidation catalysts were sulfated in use conditions but almost complete recovery was possible above 600 °C with higher methane feeds at lean. In addition to sulfur, other chemical poisoning was also included in the rapid ageing methods by fittings to the diesel and NG field aged catalysts.