Nonuniform Distribution Of Oxygen Research Articles

Numerical modeling of non-uniform corrosion of concrete reinforcement considering calcium leaching and chloride diffusion coupling effect

A novel numerical model is proposed for characterizing the nonuniform corrosion of steel bars. The proposed model corrects the anodic Tafel slope through the concentration of chloride and accounts for the adsorption-binding impact of chloride. The viability of the presented model is confirmed with regard to chloride diffusion and the distribution of steel corrosion products. The rebar-concrete interface's non-uniform distribution of oxygen and chloride concentrations along the circumferential direction influences the corrosion current density. Calcium leaching influences the migration of oxygen and chloride, and speeds up the electrochemical corrosion of the rebar.

Effect of Interconnector Rib on Optimization of SOFC Structural Parameters

Interconnector (IC) is a key component for current collection in solid oxide fuel cell (SOFC) stacks, but leads to uneven distribution of gas (especially O2) and significantly reduces the power density. In this paper, a 3D numerical model is developed to study the effect of interconnector on the optimization of cathode structures of a planar SOFC. After model validation, parametric analyses are conducted to investigate the effects of cathode structural properties on the SOFC performance and temperature distribution, considering the interconnect dimensions and parameter variations along the flow channel. It is found that the interconnector causes more non-uniform distribution of oxygen in the downstream cathode than in the upstream. Increasing porosity or cathode thickness can improve the oxygen uniformity and the cell electrochemical performance especially in the downstream. However, too high porosity (ε > 0.4) or too thick cathode (t c > 250 μm) can cause significant ohmic or concentration losses, respectively. Besides, gradient porosity can increase the oxygen uniformity (up to 6.5%) and reduce the concentration loss (up to 10.6%) especially under the rib. In addition, a higher temperature region is observed in the cathode area under the channel, while increasing the porosity, the cathode thickness or using gradient porosity all cause a more uniform temperature distribution.

Heating Process Characteristics and Kinetics of Biomass at Different Oxygen Concentrations

Abstract Mass transfer is very important for the combustion of biomass fuels, especially pellets. The oxygen diffusion, which results in a nonuniform distribution of oxygen in the pellets, should be considered in the modeling of pellet combustion. In this study, the effect of oxygen on thermal degradation of biomass is studied by thermogravimetric (TG) experiments and then a kinetic model considering oxygen effect is developed. The fuels investigated are spruce, sophora, wheat straw, and peanut straw. TG curves are taken under different oxygen concentrations, ranging from 0 to 20 %. Oxygen concentration has little effect on the devolatilization but is critical for the behavior of char combustion. Reaction mechanism is proposed based on the observation of decomposition at different reaction conditions. The kinetic model consists of three devolatilization reactions (for cellulose, hemicellulose, and lignin) and one char combustion reaction. In the devolatilization steps, char and gas are formed as products and oxygen is not involved in the reactions. A power law dependence of oxygen is assumed for the char combustion stage. The model parameters are fitted by the experimental TG data and good agreement is observed between the experimental and modeled data at various oxygen concentrations and for different biomass fuels. It is expected that the developed kinetic model could be applied for the modeling of pellets combustion considering oxygen diffusion process.

A Phosphorescent Iridium(III) Complex-Modified Nanoprobe for Hypoxia Bioimaging Via Time-Resolved Luminescence Microscopy.

Oxygen plays a crucial role in many biological processes. Accurate monitoring of oxygen level is important for diagnosis and treatment of diseases. Autofluorescence is an unavoidable interference in luminescent bioimaging, so that an amount of research work has been devoted to reducing background autofluorescence. Herein, a phosphorescent iridium(III) complex‐modified nanoprobe is developed, which can monitor oxygen concentration and also reduce autofluorescence under both downconversion and upconversion channels. The nanoprobe is designed based on the mesoporous silica coated lanthanide‐doped upconversion nanoparticles, which contains oxygen‐sensitive iridium(III) complex in the outer silica shell. To image intracellular hypoxia without the interferences of autofluorescence, time‐resolved luminescent imaging technology and near‐infrared light excitation, both of which can reduce autofluorescence effectively, are adopted in this work. Moreover, gradient O2 concentration can be detected clearly through confocal microscopy luminescence intensity imaging, phosphorescence lifetime imaging microscopy, and time‐gated imaging, which is meaningful to oxygen sensing in tissues with nonuniform oxygen distribution.

Perturbed Angular Correlations Studies in the HgBa2CaCu2O6+δ high-TC Superconductor

The electric field gradients at Hg-199m nuclei have been measured via the perturbed angular correlation (PAC) technique, allowing a full characterization of the Hg neighborhood charge distribution at high oxygen doping on the Hg planes. The PAC technique has been applied to investigate the effect of high oxygen pressure during the measurement. Polycrystalline HgBa2CaCu2O6+delta (Hg-1212) samples have been annealed at 152 bar pressurized oxygen. The influence of oxygen pressure during the experiment was then investigated by measuring the samples at atmospheric pressure and under 152 bar oxygen pressure. The present set of PAC experiments shows that at high oxygen concentrations there is a non-uniform oxygen distribution. Moreover, the Hg environment is not free from oxygen and the results hint to a new type of ordering.

Three-dimensional multispecies nonlinear tumor growth—II: Tumor invasion and angiogenesis

We extend the diffuse interface model developed in Wise et al. (2008) to study nonlinear tumor growth in 3-D. Extensions include the tracking of multiple viable cell species populations through a continuum diffuse-interface method, onset and aging of discrete tumor vessels through angiogenesis, and incorporation of individual cell movement using a hybrid continuum-discrete approach. We investigate disease progression as a function of cellular-scale parameters such as proliferation and oxygen/nutrient uptake rates. We find that heterogeneity in the physiologically complex tumor microenvironment, caused by non-uniform distribution of oxygen, cell nutrients, and metabolites, as well as phenotypic changes affecting cellular-scale parameters, can be quantitatively linked to the tumor macro-scale as a mechanism that promotes morphological instability. This instability leads to invasion through tumor infiltration of surrounding healthy tissue. Models that employ a biologically founded, multiscale approach, as illustrated in this work, could help to quantitatively link the critical effect of heterogeneity in the tumor microenvironment with clinically observed tumor growth and invasion. Using patient tumor-specific parameter values, this may provide a predictive tool to characterize the complex in vivo tumor physiological characteristics and clinical response, and thus lead to improved treatment modalities and prognosis.

Effect of magnetic (phase) inhomogeneities on the conductivity of an antiferromagnetic La2CuO4 + δ single crystal at low temperatures

It has been established that, at a strongly nonuniform distribution of oxygen in a La2CuO4 + δ single crystal, isolated superconducting inclusions can be formed at an average hole concentration not higher than 0.0024 per copper atom. The behavior of the conductivity in a magnetic field below 20 K is consistent with possible existence of a insulating low-temperature magnetic phase (spin density waves), which is typical of cuprates with excess oxygen.

Competition between thermal donors and thermal acceptors in electron-irradiated silicon annealed at 400–700 °C

The formation of electrically active shallow centers in electron-irradiated silicon annealed in the range 400–700 °C was investigated. Radiation-enhanced formation of thermal donors (TDs) was observed at T∼400 °C. Non-uniform generation of TDs and thermal acceptors was found for an annealing temperature of 450 °C. The formation of areas with p- and n-type conductivity correlates with the non-uniform distribution of oxygen in silicon. The temperature interval of thermal acceptor generation in electron-irradiated, Cz-grown silicon was found to be very narrow around 450 °C.

Nonuniform Distribution of Electric Properties in Ferrite Ceramics

Electric and magnetic properties of Li–Ti ferrite ceramics depending on sintering modes and controlled by the diffusion-based specimen-to-environment oxygen exchange are considered. The relationship between the properties of ceramics and the character of nonuniform distribution of oxygen in the bulk of a specimen is determined. A physical model of the processes giving rise to nonuniform distribution of oxygen in polycrystalline ferrite ceramics is proposed. The empirical dependences of specific conductivity on sintering time at 1373 K are obtained.

Auger electron microscopy study of transfer film induced in an aircraft braking tribosystem

Microchemical analysis was carried out using a scanning Auger microscope on the transfer film induced in an aircraft brake tribosystem. The focus was placed on the study of the distribution of major elements in the transfer film, as well as the extent and uniformity of surface oxidation. Results showed that the as-worn surface of the transfer film consisted of large amounts of contaminant elements, primarily carbon and oxygen, along with minor quantities of S, Ca, Na, N and Cl. The transferred elements were distributed nonuniformly. The scale of the nonuniformity depended on the domain (particle) size of each component in the friction material. The high concentration and nonuniform distribution of oxygen indicated that the slideinduced oxidation process was severe and nonuniform. The carbon concentration was lower and metallic elements oxidized more severely in the high oxygen region than in the low oxygen region. With sputter time the Cu/Fe ratio continued to decrease, while the C/Cu ratio increased, suggesting that carbon was easier than copper to transfer and/or adhere to the steel suface.

Selective etching of YBCO targets by ion — plasma sputtering

Abstract Single-phase ceramics YBa2Cu3O7 produced by the solid-state sintering and used as a target at ion-plasma deposition of films was studied by the X-rays analysis, optical microscopy and microhardness measurement. Following changes occurred in the target during its use: 1. 1-grains having the orientation along the normal to the surface of the target were predominantly etched away by sputtering from the surface of the target; 2. 2 — Y2BaCuO5 compound appeared; 3. 3 — nonuniform distribution of oxygen appeared along the cross-section of the target.

Selective etching of YBCO target by ion-plasma sputtering

Single-phase ceramics YBa 2Cu 3O 7 produced by the solid-state sintering and used as a target at ion-plasma deposition of films was studied by the X-rays analysis, optical microscopy and microhardness measurement. Following changes occured in the target during its use: 1 - grains having the < 00 l orientation along to the normal to the surface of the target were predominantly etched away by sputtering from the surface of the target; 2 - Y 2BaCuO 5 compound appeared; 3 - nonuniform distribution of oxygen appeared along the cross-section of the target.