Oxygen Concentration Distribution Research Articles

Optimization-based image reconstruction from sparsely sampled data in electron paramagnetic resonance imaging

Electron paramagnetic resonance imaging (EPRI) can yield information about the 3-dimensional (3D) spatial distribution of the unpaired-electron-spin density from which the spatial distribution of oxygen concentration within tumor tissue, referred to as the oxygen image or electron paramagnetic resonance (EPR) image in this work, can be derived. Existing algorithms for reconstruction of EPR images often require data collected at a large number of densely sampled projection views, resulting in a prolonged data-acquisition time and consequently numerous practical challenges especially to in vivo animal EPRI. Therefore, a strong interest exists in shortening data-acquisition time through reducing the number of data samples collected in EPRI, and one approach is to acquire data at a reduced number of sparsely distributed projection views from which existing algorithms may reconstruct images with prominent artifacts. In this work, we investigate and develop an optimization-based technique for image reconstruction from data collected at sparsely sampled projection views for reducing scanning time in EPRI. Specifically, we design a convex optimization program in which the EPR image of interest is formulated as a solution and then tailor the Chambolle-Pock (CP) primal-dual algorithm to reconstruct the image by solving the convex optimization program. Using computer-simulated EPRI data from numerical phantoms and real EPRI data collected from physical phantoms, we perform studies on the verification and characterization of the optimization-based technique for EPR image reconstruction. Results of the studies suggest that the technique may yield accurate EPR images from data collected at sparsely distributed projection views, thus potentially enabling fast EPRI with reduced acquisition time.

Integration of an oxygen sensor into a polydymethylsiloxane hepatic culture device for two-dimensional gradient characterization

This paper presents a new hepatic culture device, in which oxygen concentration gradient formed by cellular respiration can be visualized as a two-dimensional optical image. An oxygen sensor layer containing Pt (II) octaethylporphyrin (PtOEP) was embedded at the bottom of the device, allowing visualization of oxygen concentration distribution over the cell culture area. Oxygen concentration was determined by analyzing the modulation of fluorescence intensity emitted by the sensor, which is negatively correlated to the concentration. The results in HepG2 cell culture showed that the oxygen gradient and local oxygen partial pressure could be regulated by controlling the perfusion flow rate in the device. The local and physiological oxygen gradient comparable to the in vivo liver lobules can successfully be reproduced in the device. Therefore, periportal and perivenous hepatic like-zones were successfully realized in vitro. The present device would be helpful in the development of novel in vitro methods recapitulating the liver physiology for investigation of hepatic zonation and drug screening system recapitulating the liver physiology.

Effects of agglomerate model parameters on transport characterization and performance of PEM fuel cells

A three-dimensional, non-isothermal and two-phase flow model for proton exchange membrane (PEM) fuel cells is developed. In the cathode catalyst layer, a spherical agglomerate model with consideration of catalyst layer structure and liquid water effect is applied to determine the electrochemical kinetics. The size and structure of the agglomerates are determined by the following parameters, i.e., the agglomerate radius (ragg), the volume fraction of ionomer within the agglomerate (Li,agg), and the thickness of the ionomer film over the agglomerate (δi). It is noted that a random combination of the three above parameters is widely used in agglomerate models by researchers. In this paper, the effects of ragg and Li,agg on the cell performance and local transport characteristics are numerically investigated by using the developed model with consideration of the relationships between agglomerate parameters. It is concluded that the cell performance is significantly improved by decreasing ragg and increasing Li,agg at medium and high current densities when the volume fractions of the solid phase (LPt/C) and ionomer phase (Li) are maintained constant. In addition, the distributions of oxygen concentration, liquid water saturation, volumetric current density and effectiveness factor are also strongly influenced by the variation of the two parameters.

Developing transmission line equations of oxygen transport for predicting oxygen distribution in the arterial system

The oxygen content in the arterial system plays a significant role in determining the physiological status of a human body. Understanding the oxygen concentration distribution in the arterial system is beneficial for the prevention and intervention of vascular disease. However, the oxygen concentration in the arteries could not be noninvasively monitored in clinical research. Although the oxygen concentration distribution in a vessel could be obtained from a three-dimensional (3D) numerical simulation of blood flow coupled with oxygen transport, a 3D numerical simulation of the systemic arterial tree is complicated and requires considerable computational resources and time. However, the lumped parameter model of oxygen transport derived from transmission line equations of oxygen transport requires fewer computational resources and less time to numerically predict the oxygen concentration distribution in the systemic arterial tree. In this study, transmission line equations of oxygen transport are developed according to the theory of oxygen transport in the vessel, and fluid transmission line equations are used as the theoretical reference for the development. The transmission line equations of oxygen transport could also be regarded as the theoretical basis for developing lumped parameter models of other substances in blood.

Prediction of Necrotic Core and Hypoxic Zone of Multicellular Spheroids in a Microbioreactor with a U-Shaped Barrier.

Microfluidic devices have been widely used for biological and cellular studies. Microbioreactors for three-dimensional (3D) multicellular spheroid culture are now considered as the next generation in in vitro diagnostic tools. The feasibility of using 3D cell aggregates to form multicellular spheroids in a microbioreactor with U-shaped barriers has been demonstrated experimentally. A barrier array is an alternative to commonly used microwell traps. The present study investigates oxygen and glucose concentration distributions as key parameters in a U-shaped array microbioreactor using finite element simulation. The effect of spheroid diameter, inlet concentration and flow rate of the medium are systematically studied. In all cases, the channel walls are considered to be permeable to oxygen. Necrotic and hypoxic or quiescent regions corresponding to both oxygen and glucose concentration distributions are identified for various conditions. The results show that the entire quiescent and necrotic regions become larger with increasing spheroid diameter and decreasing inlet and wall concentration. The shear stress (0.5–9 mPa) imposed on the spheroid surface by the fluid flow was compared with the critical values to predict possible damage to the cells. Finally, optimum range of medium inlet concentration (0.13–0.2 mM for oxygen and 3–11 mM for glucose) and flow rate (5–20 μL/min) are found to form the largest possible multicellular spheroid (500 μm), without any quiescent and necrotic regions with an acceptable shear stress. The effect of cell-trap types on the oxygen and glucose concentration inside the spheroid was also investigated. The levels of oxygen and glucose concentration for the microwell are much lower than those for the other two traps. The U-shaped barrier created with microposts allows for a continuous flow of culture medium, and so improves the glucose concentration compared to that in the integrated U-shaped barrier. Oxygen concentration for both types of U-shaped barriers is nearly the same. Due to the advantage of using U-shaped barriers to culture multicellular spheroids, the results of this paper can help to choose the experimental and design parameters of the microbioreactor.

Modelling for reactor-style aerobic composting based on coupling theory of mass-heat-momentum transport and Contois equation

This study establishes an optimal mathematical modelling to rationally describe the dynamic changes and spatial distribution of temperature and oxygen concentration in the aerobic composting process using coupling mass-heat-momentum transfer based on the microbial mechanism. Two different conditional composting experiments, namely continuous aeration and intermittent aeration, were performed to verify the proposed model. The results show that the model accurately predicted the dynamic changes in temperature (case I: R2 = 0.93, RMSE = 1.95 K; case II: R2 = 0.86, RMSE = 4.69 K) and oxygen concentration (case I: R2 = 0.90, RMSE = 1.26%; case II: R2 = 0.75, RMSE = 2.93%) in the central point of compost substrates. It also systematically simulated fluctuations in oxygen concentration caused by boundary conditions and the spatial distribution of the actual temperature and oxygen concentration. The proposed model exhibits good applicability in simulating the actual working conditions of aerobic composting process.

Analytical solution of coal self-heating characteristics incorporating the effect of oxygen concentration

A novel analytical solution, which included the effects of temperature distribution and oxygen concentration distribution on coal self-heating system, was presented. It was derived by combining the travelling wave reduced form method and the intermediate variable method. Coal self-heating results were consistent between theory and experiments. Using the analytical solution, the effects of kinetic parameters on coal self-heating were explicitly discussed. For Killoch6015 coal, an increase of pre-exponential and a decrease of other parameters (i.e., activation energy and inlet velocity) was observed at a reference temperature of 350K, and the temperature and oxygen consumption within the coal self-heating system raised in varying degrees. However, an increase in porosity had almost no influence on the coal self-heating process, only exhibiting a weak increase in oxygen concentration and temperature within the system. Finally, the evolution processes of the temperature and oxygen concentration distributions were discussed. [Received: May 24, 2017; Accepted: October 10, 2017]

Analytical solution of coal self-heating characteristics incorporating the effect of oxygen concentration

A novel analytical solution, which included the effects of temperature distribution and oxygen concentration distribution on coal self-heating system, was presented. It was derived by combining the travelling wave reduced form method and the intermediate variable method. Coal self-heating results were consistent between theory and experiments. Using the analytical solution, the effects of kinetic parameters on coal self-heating were explicitly discussed. For Killoch6015 coal, an increase of pre-exponential and a decrease of other parameters (i.e., activation energy and inlet velocity) was observed at a reference temperature of 350K, and the temperature and oxygen consumption within the coal self-heating system raised in varying degrees. However, an increase in porosity had almost no influence on the coal self-heating process, only exhibiting a weak increase in oxygen concentration and temperature within the system. Finally, the evolution processes of the temperature and oxygen concentration distributions were discussed. [Received: May 24, 2017; Accepted: October 10, 2017]

Numerical simulation of the oxygen distribution in silicon melt for different argon gas flow rates during Czochralski silicon crystal growth process

The effects of argon gas flow rate on the oxygen concentration in Czochralski (CZ) grown silicon crystal were examined. To analyze the influence of the argon gas flow rate in CZ growth process, a 200 mm length silicon single crystal was grown. Different argon gas flow rates are considered. The melt flow pattern, temperature and oxygen concentration distributions in the melt and crystal-melt interface are calculated. The results show that the transport of oxygen impurity is quite dependent on the flow motion in the melt. As the argon gas flow rate increases, there is no fundamental change in flow motion of the melt and the oxygen concentration decreases to a minimum value. When the argon gas flow rate increases further, the flow pattern under the melt-crystal interface starting changes and the oxygen concentration has increased after. Therefore, there is an optimum value for the argon gas flow rate for obtaining the lowest oxygen concentration in the melt.

Numerical Simulation of the Behavior of Toroidal and Spheroidal Multicellular Aggregates in Microfluidic Devices with Microwell and U-Shaped Barrier.

A microfluidic system provides an excellent platform for cellular studies. Most importantly, a three-dimensional (3D) cell culture model reconstructs more accurately the in vivo microenvironment of tissue. Accordingly, microfluidic 3D cell culture devices could be ideal candidates for in vitro cell culture platforms. In this paper, two types of 3D cellular aggregates, i.e., toroid and spheroid, are numerically studied. The studies are carried out for microfluidic systems containing U-shaped barrier as well as microwell structure. For the first time, we obtain oxygen and glucose concentration distributions inside a toroid aggregate as well as the shear stress on its surface and compare its performance with a spheroid aggregate of the same volume. In particular, we obtain the oxygen concentration distributions in three areas, namely, oxygen-permeable layer, multicellular aggregates and culture medium. Further, glucose concentration distributions in two regions of multicellular aggregates and culture medium are investigated. The results show that the levels of oxygen and glucose in the system containing U-shaped barriers are far more than those in the system containing microwells. Therefore, to achieve high levels of oxygen and nutrients, a system with U-shaped barriers is more suited than the conventional traps, but the choice between toroid and spheroid depends on their volume and orientation. The results indicate that higher oxygen and glucose concentrations can be achieved in spheroid with a small volume as well as in horizontal toroid with a large volume. The vertical toroid has the highest levels of oxygen and glucose concentration while the surface shear stress on its surface is also maximum. These findings can be used as guidelines for designing an optimum 3D microfluidic bioreactor based on the desired levels of oxygen, glucose and shear stress distributions.

Oxide Dissolution and Oxygen Diffusion in Solid-State Recycled Ti-6Al-4V: Numerical Modeling, Verification by Nanoindentation, and Effects on Grain Growth and Recrystallization

The oxide dissolution and oxygen diffusion during annealing of Ti-6Al-4V solid-state recycled from machining chips by equal-channel angular pressing (ECAP) have been investigated using nanoindentation and numerical modeling. The hardness profile from nanoindentation was converted into the oxygen concentration distribution using the Fleisher and Friedel model. An iterative fitting method was then employed to revise the ideal model proposed previously, leading to correct predictions of the oxide dissolution times and oxygen concentration profiles and verifying nanoindentation as an effective method to measure local oxygen concentrations. Recrystallization started at the prior oxide boundaries where local strains were high from the severe plastic deformation incurred in the ECAP recycling process, forming a band of ultrafine grains whose growth was retarded by solute dragging thanks to high oxygen concentrations. The recrystallized fine-grained region would advance with time to eventually replace the lamellar structure formed during ECAP.

Oxygen Concentration Measurement in the Porous Cathode of Aqueous Lithium–Air Battery By Fine Optical Fiber

Spatial and temporal oxygen concentration distribution in the porous cathode of discharging aqueous lithium-air secondary battery was successfully measured. Lithium-air battery attracts great attention because of its high energy density. In this study, we focus on the aqueous lithium–air secondary battery. The aqueous electrolyte realizes cost reduction and ensures the safe use of a battery. On the other hand, low solubility of oxygen in aqueous electrolyte limits oxygen transport to the reaction site. To realize a more powerful aqueous lithium–air battery, it is necessary to clarify and improve the oxygen transport phenomena in the porous cathode. In this study, we developed the measurement technique of oxygen concentration in the porous cathode under operating condition by inserting a fine optical fiber oxygen sensor. In this study, platinum tetrakis pentrafluoropheny porphine (PtTFPP) was employed as oxygen indicator [1]. When the PtTFPP is exposed to excitation light (λ = 405 nm), phosphorescence emission (λ= 650 nm) is produced, and its intensity depends on oxygen partial pressure. Thus, quantitative oxygen concentration can be obtained by measuring phosphorescence intensity and using calibration data. The PtTFPP was painted at the edge of optical fiber of which diameter was 110 μm. In order to measure the phosphorescence intensity, bifurcated optical fibers were connected to excitation light source and spectrometer, respectively. As shown in Figure 1, phosphorescence intensity changed at 650 nm depending on oxygen concentration. The experimental setup is shown in Figure 2. The porous cathode (SIGRACET® 10AA, SGL Group, USA) was fixed near electrolyte interface horizontally. The tiny optical fiber sensor was moved up and inserted in the cathode. The temporal oxygen concentration change from the start of discharge was measured at arbitrary positions in the porous cathode. The composite anode was water-stable and had a multilayer structure for the aqueous lithium air battery [2]. Measurement of spatial and temporal distribution of oxygen concentration has been conducted under the assumption that discharge experiment had reproducibility. Initial position (z = 0 μm) was defined arbitrary, and the sensor was moved up each 70 μm. Time variation of oxygen concentration was measured at each point. Finally, spatiotemporal distribution of oxygen concentration for each current density was obtained. As shown in Figure 3, the spatial and temporal oxygen concentration distribution at 0.10 mA/cm2 was successfully observed. When the discharge was started, the oxygen concentration gradually decreased in the cathode, and finally, oxygen concentration reached considerably low value even in the condition of 0.10 mA/cm2. In this experiment, oxygen concentration gradients are present at both ends of the atmosphere side (0-140 μm) and electrolyte side (490-910 μm) of the cathode. Flux for both side of cathode, upper side and lower side, was discussed and comprehensible interpretation was obtained. Although dissolved oxygen that forms flux from the lower side of cathode has an effective supply to the porous electrode, electrolyte layer formed at between the atmosphere and the cathode causes oxygen transport resistance. Acknowledgement: This work was supported by JSPS KAKENHI Grant Number 15K13881, 15H02347. Reference: [1] CS Chu., CA Lin, Sensors and Actuators B: Chemica, 2014, 195, 259-265. [2] T. Zhang, N. Imanishi, S. Hasegawa, A. Hirano, J. Xie, Y. Takeda, O. Yamamoto, N. Sammes, J. Electrochem. Soc., 2008, 155, A965. Figure 1

Measurement of oxygen concentrations in bacterial biofilms using transient state monitoring by single plane illumination microscopy

Oxygen is required for respiration in aerobic bacteria and hence plays an essential role in the generation of energy necessary for cell maintenance and growth. The distribution of oxygen within a biofilm can be heterogeneous and may result in bacterial cells exhibiting distinct physiological states depending on their local oxygen availability. Here, we have employed transient state (TRAST) monitoring, a non-invasive method that can measure the relative populations of triplet states by time-modulated illumination, to determine the distribution of oxygen concentrations in biofilm colonies. The method was implemented on a single plane illumination microscope that can perform optical slicing, making it a suitable approach for imaging thick samples. We present a map of triplet relaxation times measured inside a Pseudomonas aeruginosa biofilm at micrometre resolution. We also provide a calibration method that can evaluate oxygen concentration based on TRAST contrast. Our results indicate that anoxic zones exist within the colonies, and oxygen consumption extends outside the areas of high cell densities, establishing a gradient until levels return to air saturation.

Numerical Modeling with Electrochemical Active Area (ECA) Distribution in the Lateral Direction in a PEM Fuel Cell

Abstract In a PEM fuel cell, local current density distribution is very critical to the overall cell performance. From our previous experimental research on the current performance between land and channel in a PEM fuel cell, current density under the land is significantly larger than that under the channel in the most operating voltage regions [1] . This could lead to very severe problems such as accelerating membrane and catalyst degradation, thus reduce the lifetime and durability of a PEM fuel cell. In order to understand the mechanism of the current density distribution in this lateral direction, and for the better future design of a PEM fuel cell with higher performance, we construct a three-dimensional CFD model with electrochemical active area (ECA) equation implemented, while the ECA distribution is directly from previous research. The numerical results coincide well with the experimental results, and the lateral current density distribution and oxygen concentration distribution have also been studied.

Experimental Study of an On-board Fuel Tank Inerting System

A simulated aircraft fuel tank inerting system was established and experiments were conducted to investigate the performance of the system. The system uses hollow fiber membrane which is widely used in aircraft as the air separation device and a simplified 20% scale multi compartment fuel tank as the inerting object. Experiments were carried out to investigate the influences of different operating parameters on the inerting effectiveness of the system, including NEA (nitrogen-enriched air) flow rate, NEA oxygen concentration, NEA distribution, pressure of bleeding air and fuel load of the tank. Results showed that for the multi compartment fuel tank, concentrated flow washing inerting would cause great differences throughout the distribution of oxygen concentration in the fuel tank, and inerting dead zone would exist. The inerting effectiveness was greatly improved and the ullage oxygen concentration of the tank would reduce to 12% successfully when NEA entered three compartments evenly. The time span of a complete inerting process reduced obviously with increasing NEA flow rate and decreasing NEA concentration, but the trend became weaker gradually. However, the reduction of NEA concentration will decrease the utilization efficiency of the bleeding air. In addition, the time span can also be reduced by raising the pressure of bleeding air, which will improve the bleeding air utilization efficiency at the same time. The time span decreases linearly as the fuel load increases.

Analytical prediction of coal spontaneous combustion tendency: Velocity range with high possibility of self-ignition

Coal spontaneous combustion is an inherent problem in coal mines throughout the world. The analysis of stationary-states, including stable point and critical point, is an effective method to judge its ignition tendency. A lower critical point temperature means that it is more likely to cause fire. In the past, due to the limitation of mathematical methods, the consumption and distribution of oxygen concentration are usually neglected. In order to accurately analyze coal ignition tendency, this paper takes coal bulk as a porous system and develops an improved model by a combination of oxygen species and energy equation. The model is solved for stationary-states of the system. Qualitative analysis of the stationary-states gives a mechanism explanation for the reason why coal spontaneous ignition is hard to be extinguished and indicates that the temperature of initial endpoint and that of internal site can be uniquely determined from each other. It further points out a trend that the location of critical point moves inward as the inlet air velocity increases, which correlates well with simulation results of the existing literatures. Then, for stationary-states, calculation results of Killoch 6015 coal are obtained. Quantitative analysis of them finds a trend that the temperature of critical point rises rapidly after its slow increase. At last, a velocity range, in which the possibility of fire is extremely high, is presented by simulation computation, e.g., the range of Killoch 6015 coal is determined as 8×10−5–3×10−3m/s when the critical ignition temperature is set as 150°C.

Study on the operation mode of air conditioning system for plateau passenger train

It is very necessary to ensure the oxygen level and obtain the good air quality inside when the plateau passenger train runs at high altitude. Therefore, integrated regulation of the oxygen supply and the fresh air should be carried out. Numerical calculation by Matrix Laboratory (MATLAB) is used in this study. The concentration distributions of oxygen and carbon dioxide in the carriage under different operation modes of the oxygen supply system and the fresh air system are investigated, as well as the system energy consumption under the corresponding operation mode. The results show that the frequency conversion operation mode can effectively reduce the system energy consumption on the premise of ensuring the concentrations of oxygen and carbon dioxide in the carriage.

対向流燃焼を適用したストーカ式焼却炉の低NOx化に関する性能評価

JFE Engineering has developed the advanced stoker-type incineration system “JFE Hyper 21 Stoker System”, which adopts high temperature air combustion technology. With this technology, the incinerator realizes stable combustion in the condition of low excess air ratio, which results in reduction of NOx formation. In this paper, we describe a newly developed stoker-type incinerator which utilizes counter flow combustion in addition to high temperature air combustion technology. Verification experiment was conducted and further reduction of NOx formation was achieved. Experiment and numerical simulation were carried out to consider the reduction mechanism of NOx. Flat combustion region which contributes to stable combustion was observed in both experiment and simulation. Oxygen concentration distribution in the furnace implies that effective two-staged combustion is formed. From the view of fluid analysis, strong turbulence region is formed in the downstream of the furnace. These factors are considered to interact with each other and contribute to suppress the NOx formation.

Research of the influence of flue gas recirculation on the processes in the ltv furnace

The combustion of solid low-grade fuel in LTV-boiler furnaces is a pressing research questions currently. The aim of this work is to study the influence of flue gas entering the process fully-the boiler furnace. The result of the calculation of the resulting distribution of temperatures and oxygen concentrations along the height of the furnace. The analysis of the obtained results.

Experimental investigation of interfacial mass transfer mechanisms for a confined high‐reynolds‐number bubble rising in a thin gap

Interfacial mass transfer is known to be enhanced for confined bubbles due to the efficiency of the transfer in the thin liquid films between them and the wall. In the present experimental investigation, the mechanisms of gas–liquid mass transfer are studied for isolated bubbles rising at high Reynolds number in a thin gap. A planar laser induced fluorescence (PLIF) technique is applied with a dye the fluorescence of which is quenched by dissolved oxygen. The aim is to measure the interfacial mass fluxes for pure oxygen bubbles of various shapes and paths rising in water at rest. In the wakes of the bubbles, patterns due to the presence of dissolved oxygen are observed on PLIF images. They reveal the contrasted contributions to mass transfer of two different regions of the interface. The flow around a bubble consists of both two thin liquid films between the bubble and the walls of the cell and an external high‐Reynolds‐number in‐plane flow surrounding the bubble. Mass transfer mechanisms associated to both regions are discussed. Measurement of the concentration of dissolved oxygen is a difficult task due to the nonlinear relation between the fluorescence intensity and the concentration in the gap. It is however possible to accurately measure the global mass flux transferred through the bubble interface. It is determined from the fluorescence intensity recorded in the wakes when the oxygen distribution has been made homogeneous through the gap by diffusion. Assuming a reasonable distribution of oxygen concentration through the gap at short time also allows a measurement of the mass fluxes due to the liquid films. A discussion of the results points out the specific physics of mass transfer for bubbles confined between two plates as compared to bubbles free to move in unconfined flows. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2394–2408, 2017