Influence of Enhanced O2 Provision on the Discharge Performance of Li-air Batteries by Incorporating Fluoroether.

PubMed

Wan, Hao; Mao, Ya; Liu, Zixuan; Bai, Qingyou; Peng, Zhe; Bao, Jingjing; Wu, Gang; Liu, Yang; Wang, Deyu; Xie, Jingying

2017-04-10

As the first step during discharge, the mass transfer of oxygen should play a crucial role in Li-air batteries to tailor the growth of discharge products, however, not enough attention has been paid to this issue. Herein, we introduce an oxygen-enriching cosolvent, 1,2-(1,1,2,2-tetrafluoroethoxy) ethane (FE1), into the electrolyte, and investigate its influence on the discharge performance. The incorporation of this novel cosolvent consistently enhances the oxygen solubility of the electrolyte, and improves the oxygen diffusivity following a volcano-shape trend peaking at 50 % FE1. It is interesting that the discharge capacities obtained with the investigated electrolytes share the similar volcano trends as the oxygen transport under 50 mA g carbon -1 and higher current densities. The improved oxygen diffusion could benefit the volumetric utilization of the air cathode, especially at the separator side, probably owing to the fast oxygen transport to moderate its concentration gradient. Our results demonstrate the importance of oxygen provision, which easily becomes the capacity-determining factor. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of oxygen content of Nd-Fe-B sintered magnet on grain boundary diffusion process of DyH2 dip-coating

NASA Astrophysics Data System (ADS)

Bae, Kyoung-Hoon; Lee, Seong-Rae; Kim, Hyo-Jun; Lee, Min-Woo; Jang, Tae-Suk

2015-11-01

We investigated the effect of oxygen content on the microstructural and magnetic properties of a DyH2 dip-coated Nd-Fe-B sintered magnet. When the magnet had a low oxygen content (1500 ppm), the volume and size of the rare-earth-rich oxide (Nd-Dy-O) phase was reduced, and a uniform and continuous thin Nd-rich grain boundary phase (GBP) was well developed. The grain boundary diffusion depth of Dy increased from 200 to 350 μm with decreasing oxygen content from ˜3000 to 1500 ppm. The coercivity of the low-oxygen magnet increased from 19.98 to 23.59 kOe after grain boundary diffusion process (GBDP) while the remanence reduction was minimized. The formation of an fcc-NdOx Nd-rich phase in the high-oxygen magnet hindered the formation of a Nd-rich triple-junction phase and GBP. In contrast, a metallic dhcp-Nd phase, which was closely related to coercivity enhancement after GBDP, was formed in the low-oxygen magnet.

Microscale diffusion measurements and simulation of a scaffold with a permeable strut.

PubMed

Lee, Seung Youl; Lee, Byung Ryong; Lee, Jongwan; Kim, Seongjun; Kim, Jung Kyung; Jeong, Young Hun; Jin, Songwan

2013-10-10

Electrospun nanofibrous structures provide good performance to scaffolds in tissue engineering. We measured the local diffusion coefficients of 3-kDa FITC-dextran in line patterns of electrospun nanofibrous structures fabricated by the direct-write electrospinning (DWES) technique using the fluorescence recovery after photobleaching (FRAP) method. No significant differences were detected between DWES line patterns fabricated with polymer supplied at flow rates of 0.1 and 0.5 mL/h. The oxygen diffusion coefficients of samples were estimated to be ~92%-94% of the oxygen diffusion coefficient in water based on the measured diffusion coefficient of 3-kDa FITC-dextran. We also simulated cell growth and distribution within spatially patterned scaffolds with struts consisting of either oxygen-permeable or non-permeable material. The permeable strut scaffolds exhibited enhanced cell growth. Saturated depths at which cells could grow to confluence were 15% deeper for the permeable strut scaffolds than for the non-permeable strut scaffold.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perriot, Romain; Uberuaga, Blas P.

We use molecular dynamics simulations to investigate the role of cation disorder on oxygen diffusion in Gd 2Zr 2O 7 (GZO) and Gd 2Ti 2O 7 (GTO) pyrochlores, a class of complex oxides which contain a structural vacancy relative to the basic fluorite structure. The introduction of disorder has distinct effects depending on the chemistry of the material, increasing the mobility of structural carriers by up to four orders of magnitude in GZO. In contrast, in GTO, there is no mobility at zero or low disorder on the ns timescale, but higher disorder liberates the otherwise immobile carriers, allowing diffusionmore » with rates comparable to GZO for the fully disordered material. Here, we show that the cation disorder enhances the diffusivity by both increasing the concentration of mobile structural carriers and their individual mobility. The disorder also influences the diffusion in materials containing intrinsic carriers, such as additional vacancies VO or oxygen interstitials OI. And while in ordered GZO and GTO the contribution of the intrinsic carriers dominates the overall diffusion of oxygen, OI in GZO contributes along with structural carriers, and the total diffusion rate can be calculated by assuming simple additive contributions from the two sources. Although the disorder in the materials with intrinsic defects usually enhances the diffusivity as in the defect-free case, in low concentrations, cation antisites AB or BA, where A = Gd and B = Zr or Ti, can act as traps for fast intrinsic defects. The trapping results in a lowering of the diffusivity, and causes a non-monotonic behavior of the diffusivity with disorder. Conversely, in the case of slow intrinsic defects, the main effect of the disorder is to liberate the structural carriers, resulting in an increase of the diffusivity regardless of the defect trapping.« less

Enhanced oxygen vacancy diffusion in Ta2O5 resistive memory devices due to infinitely adaptive crystal structure

NASA Astrophysics Data System (ADS)

Jiang, Hao; Stewart, Derek A.

2016-04-01

Metal oxide resistive memory devices based on Ta2O5 have demonstrated high switching speed, long endurance, and low set voltage. However, the physical origin of this improved performance is still unclear. Ta2O5 is an important archetype of a class of materials that possess an adaptive crystal structure that can respond easily to the presence of defects. Using first principles nudged elastic band calculations, we show that this adaptive crystal structure leads to low energy barriers for in-plane diffusion of oxygen vacancies in λ phase Ta2O5. Identified diffusion paths are associated with collective motion of neighboring atoms. The overall vacancy diffusion is anisotropic with higher diffusion barriers found for oxygen vacancy movement between Ta-O planes. Coupled with the fact that oxygen vacancy formation energy in Ta2O5 is relatively small, our calculated low diffusion barriers can help explain the low set voltage in Ta2O5 based resistive memory devices. Our work shows that other oxides with adaptive crystal structures could serve as potential candidates for resistive random access memory devices. We also discuss some general characteristics for ideal resistive RAM oxides that could be used in future computational material searches.

Brain tissue oxygen tension is more indicative of oxygen diffusion than oxygen delivery and metabolism in patients with traumatic brain injury.

PubMed

Rosenthal, Guy; Hemphill, J Claude; Sorani, Marco; Martin, Christine; Morabito, Diane; Obrist, Walter D; Manley, Geoffrey T

2008-06-01

Despite the growing clinical use of brain tissue oxygen monitoring, the specific determinants of low brain tissue oxygen tension (P(bt)O2) following severe traumatic brain injury (TBI) remain poorly defined. The objective of this study was to evaluate whether P(bt)O2 more closely reflects variables related to cerebral oxygen diffusion or reflects cerebral oxygen delivery and metabolism. Prospective observational study. Level I trauma center. Fourteen TBI patients with advanced neuromonitoring underwent an oxygen challenge (increase in FiO2 to 1.0) to assess tissue oxygen reactivity, pressure challenge (increase in mean arterial pressure) to assess autoregulation, and CO2 challenge (hyperventilation) to assess cerebral vasoreactivity. None. P(bt)O2 was measured directly with a parenchymal probe in the least-injured hemisphere. Local cerebral blood flow (CBF) was measured with a parenchymal thermal diffusion probe. Cerebral venous blood gases were drawn from a jugular bulb venous catheter. We performed 119 measurements of PaO2, arterial oxygen content (CaO2), jugular bulb venous oxygen tension (PVO2), venous oxygen content (CVO2), arteriovenous oxygen content difference (AVDO2), and local cerebral metabolic rate of oxygen (locCMRO2). In multivariable analysis adjusting for various variables of cerebral oxygen delivery and metabolism, the only statistically significant relationship was that between P(bt)O2 and the product of CBF and cerebral arteriovenous oxygen tension difference (AVTO2), suggesting a strong association between brain tissue oxygen tension and diffusion of dissolved plasma oxygen across the blood-brain barrier. Measurements of P(bt)O2 represent the product of CBF and the cerebral AVTO2 rather than a direct measurement of total oxygen delivery or cerebral oxygen metabolism. This improved understanding of the cerebral physiology of P(bt)O2 should enhance the clinical utility of brain tissue oxygen monitoring in patients with TBI.

Structure Evolution of Graphene Oxide during Thermally Driven Phase Transformation: Is the Oxygen Content Really Preserved?

PubMed Central

Sun, Pengzhan; Wang, Yanlei; Liu, He; Wang, Kunlin; Wu, Dehai; Xu, Zhiping; Zhu, Hongwei

2014-01-01

A mild annealing procedure was recently proposed for the scalable enhancement of graphene oxide (GO) properties with the oxygen content preserved, which was demonstrated to be attributed to the thermally driven phase separation. In this work, the structure evolution of GO with mild annealing is closely investigated. It reveals that in addition to phase separation, the transformation of oxygen functionalities also occurs, which leads to the slight reduction of GO membranes and furthers the enhancement of GO properties. These results are further supported by the density functional theory based calculations. The results also show that the amount of chemically bonded oxygen atoms on graphene decreases gradually and we propose that the strongly physisorbed oxygen species constrained in the holes and vacancies on GO lattice might be responsible for the preserved oxygen content during the mild annealing procedure. The present experimental results and calculations indicate that both the diffusion and transformation of oxygen functional groups might play important roles in the scalable enhancement of GO properties. PMID:25372142

Locally enhanced sampling molecular dynamics study of the dioxygen transport in human cytoglobin.

PubMed

Orlowski, Slawomir; Nowak, Wieslaw

2007-07-01

Cytoglobin (Cyg)--a new member of the vertebrate heme globin family--is expressed in many tissues of the human body but its physiological role is still unclear. It may deliver oxygen under hypoxia, serve as a scavenger of reactive species or be involved in collagen synthesis. This protein is usually six-coordinated and binds oxygen by a displacement of the distal HisE7 imidazole. In this paper, the results of 60 ns molecular dynamics (MD) simulations of dioxygen diffusion inside Cyg matrix are discussed. In addition to a classical MD trajectory, an approximate Locally Enhanced Sampling (LES) method has been employed. Classical diffusion paths were carefully analyzed, five cavities in dynamical structures were determined and at least four distinct ligand exit paths were identified. The most probable exit/entry path is connected with a large tunnel present in Cyg. Several residues that are perhaps critical for kinetics of small gaseous diffusion were discovered. A comparison of gaseous ligand transport in Cyg and in the most studied heme protein myoglobin is presented. Implications of efficient oxygen transport found in Cyg to its possible physiological role are discussed.

Water has no effect on oxygen self-diffusion rate in forsterite

NASA Astrophysics Data System (ADS)

Fei, H.; Yamazaki, D.; Wiedenbeck, M.; Katsura, T.

2014-12-01

Water is thought to play an essential role in dynamical processes in the Earth's interior. Even several tens wt. ppm of water may enhance the creep rates in olivine by orders of magnitude based on deformation experiments [1, 2]. High temperature creep in olivine is believed to be controlled by self-diffusion of the slowest species, which is silicon in olivine. However, silicon self-diffusion experiments suggest that the role of water on olivine rheology is overestimated in previous deformation studies because of the experimental difficulties [3].On the other hand, oxygen is the second slowest species with similar diffusion rate as silicon. It may also play an essential role in olivine creep. By comparing the oxygen self-diffusion coefficient (DO) in olivine at ambient pressure and dry conditions [4] with those at 2 GPa and hydrous conditions, it is found that even 30-50 wt. ppm of water could enhance DO by one order of magnitude [5]. However, comparison of experimental results obtained at different pressures could lead to misinterpretations because different experimental setups have different error sources [6]. In this study, we systematically measured DO in an iron-free olivine, namely, forsterite, at 8 GPa and 1600-1800 K over a wide range of water content (CH2O) from <1 up to 800 wt. ppm. Our results show that DO∝(CH2O)0.05±0.06≈(CH2O)0. Thus, water has no significant effect on oxygen self-diffusion rate in forsterite. Since the water content dependence of silicon self-diffusion rate is also very small [3], the role of water on olivine rheology is not as significant as previously thought by assuming the diffusion controlled creep mechanism. [1] Karato &Jung (2003), Philosophical Mag. 83, 401-414.[2] Hirth & Kohlstedt (2003) Geophys. Monogr. 138, 83-105.[3] Fei et al. (2013), Nature 498, 213-215.[4] Dohmen et al. (2002), GRL 29, 2030.[5] Costa & Chakraborty (2008), PEPI 166, 11-29.[6] Fei et al. (2012), EPSL 345, 95-103.

Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores

DOE PAGES

Perriot, Romain; Uberuaga, Blas P.

2015-04-21

We use molecular dynamics simulations to investigate the role of cation disorder on oxygen diffusion in Gd 2Zr 2O 7 (GZO) and Gd 2Ti 2O 7 (GTO) pyrochlores, a class of complex oxides which contain a structural vacancy relative to the basic fluorite structure. The introduction of disorder has distinct effects depending on the chemistry of the material, increasing the mobility of structural carriers by up to four orders of magnitude in GZO. In contrast, in GTO, there is no mobility at zero or low disorder on the ns timescale, but higher disorder liberates the otherwise immobile carriers, allowing diffusionmore » with rates comparable to GZO for the fully disordered material. Here, we show that the cation disorder enhances the diffusivity by both increasing the concentration of mobile structural carriers and their individual mobility. The disorder also influences the diffusion in materials containing intrinsic carriers, such as additional vacancies VO or oxygen interstitials OI. And while in ordered GZO and GTO the contribution of the intrinsic carriers dominates the overall diffusion of oxygen, OI in GZO contributes along with structural carriers, and the total diffusion rate can be calculated by assuming simple additive contributions from the two sources. Although the disorder in the materials with intrinsic defects usually enhances the diffusivity as in the defect-free case, in low concentrations, cation antisites AB or BA, where A = Gd and B = Zr or Ti, can act as traps for fast intrinsic defects. The trapping results in a lowering of the diffusivity, and causes a non-monotonic behavior of the diffusivity with disorder. Conversely, in the case of slow intrinsic defects, the main effect of the disorder is to liberate the structural carriers, resulting in an increase of the diffusivity regardless of the defect trapping.« less

Insights into thermal diffusion of germanium and oxygen atoms in HfO{sub 2}/GeO{sub 2}/Ge gate stacks and their suppressed reaction with atomically thin AlO{sub x} interlayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogawa, Shingo, E-mail: Shingo-Ogawa@trc.toray.co.jp; Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871; Asahara, Ryohei

2015-12-21

The thermal diffusion of germanium and oxygen atoms in HfO{sub 2}/GeO{sub 2}/Ge gate stacks was comprehensively evaluated by x-ray photoelectron spectroscopy and secondary ion mass spectrometry combined with an isotopic labeling technique. It was found that {sup 18}O-tracers composing the GeO{sub 2} underlayers diffuse within the HfO{sub 2} overlayers based on Fick's law with the low activation energy of about 0.5 eV. Although out-diffusion of the germanium atoms through HfO{sub 2} also proceeded at the low temperatures of around 200 °C, the diffusing germanium atoms preferentially segregated on the HfO{sub 2} surfaces, and the reaction was further enhanced at high temperatures withmore » the assistance of GeO desorption. A technique to insert atomically thin AlO{sub x} interlayers between the HfO{sub 2} and GeO{sub 2} layers was proven to effectively suppress both of these independent germanium and oxygen intermixing reactions in the gate stacks.« less

Oxygen Transfer in Moving Bed Biofilm Reactor and Integrated Fixed Film Activated Sludge Processes.

PubMed

2017-11-17

A demonstrated approach to design the, so-called, medium-bubble air diffusion network for oxygen transfer into the aerobic zone(s) of moving bed biofilm reactor (MBBR) and integrated fixed-film activated sludge (IFAS) processes is described in this paper. Operational full-scale biological water resource recovery systems treating municipal sewerage demonstrate that medium-bubble air diffusion networks designed using the method presented here provide reliable service. Further improvement is possible, however, as knowledge gaps prevent more rational process designs. Filling such knowledge gaps can potentially result in higher performing and more economical systems. Small-scale system testing demonstrates significant enhancement of oxygen transfer capacity due to the presence of media, but quantification of such effects in full-scale systems is lacking, and is needed. Establishment of the relationship between diffuser submergence, aeration rate, and biofilm carrier fill fraction will enhance MBBR and IFAS aerobic process design, cost, and performance. Limited testing of full-scale systems is available to allow computation of alpha valuess. As with clean water testing of full-scale systems, further full-scale testing under actual operating conditions is required to more fully quantify MBBR and IFAS system oxygen transfer performance under a wide range of operating conditions. Control of MBBR and IFAS aerobic zone oxygen transfer systems can be optimized by recognizing that varying residual dissolved oxygen (DO) concentrations are needed, depending on operating conditions. For example, the DO concentration in the aerobic zone of nitrifying IFAS processes can be lowered during warm weather conditions when greater suspended growth nitrification can occur, resulting in the need for reduced nitrification by the biofilm compartment. Further application of oxygen transfer control approaches used in activated sludge systems to MBBR and IFAS systems, such as ammonia-based oxygen transfer system control, has been demonstrated to further improve MBBR and IFAS system energy-efficiency.

An Investigation into the Effects of Process Conditions on the Tribological Performance of Pack Carburized Titanium with Limited Oxygen Diffusion

NASA Astrophysics Data System (ADS)

Bailey, R.; Sun, Y.

2018-04-01

In the present study, a new pack carburization technique for titanium has been investigated. The aim of this treatment is to produce a titanium carbide/oxycarbide layer atop of an extended oxygen diffusion zone [α-Ti(O)]. The effects of treatment temperature and pack composition have been investigated in order to determine the optimal conditions required to grant the best tribological response. The resulting structural features were investigated with particular interest in the carbon and oxygen concentrations across the samples cross section. The optimization showed that a temperature of 925 °C with a pack composition of 1 part carbon to 1 part energizer produced surface capable of withstanding a contact pressure of ≈ 1.5 GPa for 1 h. The process resulted in TiC surface structure which offers enhanced hardness (2100 HV) and generates a low friction coefficient (μ ≈ 0.2) when in dry sliding contact with an alumina (Al2O3) ball. The process also produced an extended oxygen diffusion zone that helps to improve the load bearing capacity of the substrate.

Sooting Limits Of Diffusion Flames With Oxygen-Enriched Air And Diluted Fuel

NASA Technical Reports Server (NTRS)

Sunderland, P. B.; Urban, D. L.; Stocker, D. P.; Chao, B. H.; Axelbaum, R. L.

2003-01-01

Oxygen-enhanced combustion permits certain benefits and flexibility that are not otherwise available in the design of practical combustors, as discussed by Baukal. The cost of pure and enriched oxygen has declined to the point that oxygen-enhanced combustion is preferable to combustion in air for many applications. Carbon sequestration is greatly facilitated by oxygen enrichment because nitrogen can be eliminated from the product stream. For example, when natural gas (or natural gas diluted with CO2) is burned in pure oxygen, the only significant products are water and CO2. Oxygen-enhanced combustion also has important implications for soot formation, as explored in this work. We propose that soot inception in nonpremixed flames requires a region where C/O ratio, temperature, and residence time are above certain critical values. Soot does not form at low temperatures, with the threshold in nonpremixed flames ranging from about 1250-1650 K, a temperature referred to here as the critical temperature for soot inception, Tc. Soot inception also can be suppressed when residence time is short (equivalently, when the strain rate in counterflow flames is high). Soot induction times of 0.8-15 ms were reported by Tesner and Shurupov for acetylene/nitrogen mixtures at 1473 K. Burner stabilized spherical microgravity flames are employed in this work for two main reasons. First, this configuration offers unrestricted control over convection direction. Second, in steady state these flames are strain-free and thus can yield intrinsic sooting limits in diffusion flames, similar to the way past work in premixed flames has provided intrinsic values of C/O ratio associated with soot inception limits.

Forging Fast Ion Conducting Nanochannels with Swift Heavy Ions: The Correlated Role of Local Electronic and Atomic Structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sachan, Ritesh; Cooper, Valentino R.; Liu, Bin

2016-12-19

Atomically disordered oxides have attracted significant attention in recent years due to the possibility of enhanced ionic conductivity. However, the correlation between atomic disorder, corresponding electronic structure, and the resulting oxygen diffusivity is not well understood. The disordered variants of the ordered pyrochlore structure in gadolinium titanate (Gd 2Ti 2O 7) are seen as a particularly interesting prospect due to intrinsic presence of a vacant oxygen site in the unit atomic structure, which could provide a channel for fast oxygen conduction. In this paper, we provide insights into the subangstrom scale on the disordering-induced variations in the local atomic environmentmore » and its effect on the electronic structure in high-energy ion irradiation-induced disordered nanochannels, which can be utilized as pathways for fast oxygen ion transport. With the help of an atomic plane-by-plane-resolved analyses, the work shows how the presence of various types of TiO x polyhedral that exist in the amorphous and disordered crystalline phase modify the electronic structures relative to the ordered pyrochlore phase in Gd 2Ti 2O 7. Finally, the correlated molecular dynamics simulations on the disordered structures show a remarkable enhancement in oxygen diffusivity as compared with ordered pyrochlore lattice and make that a suitable candidate for applications requiring fast oxygen conduction.« less

Sediment-Overlying Water Relationships Affecting Wintertime Dissolved Oxygen Conditions in the Big Eau Pleine Reservoir, Wisconsin.

DTIC Science & Technology

1992-07-01

22202-4302. and to the Office of Managel ent and Bidget . P worki Reduction Pfo4ect(07T4-016 Wahington. DC 20S03. -1. AGENCY USE ONLY (Leave blank) 2...higher pool elevation can not be maintained, it is likely that additional aerators must be installed for incremental use to meet periodic heavy oxygen...install additional aerators throughout the reservoir for incremental use as needed to enhance oxygen diffusion processes. The difficulty with this

Meso-pores carbon nano-tubes (CNTs) tissues-perfluorocarbons (PFCs) hybrid air-electrodes for Li-O2 battery

NASA Astrophysics Data System (ADS)

Balaish, Moran; Ein-Eli, Yair

2018-03-01

Adding immiscible perfluorocarbons (PFCs), possessing superior oxygen solubility and diffusivity, to a free-standing (metal-free and binder-free) CNTs air-electrode tissues with a meso-pore structure, fully maximized the advantages of PFCs as oxygenated-species' channels-providers. The discharge behavior of hybrid PFCs-CNT Li-O2 systems demonstrated a drastic increase in cell capacity at high current density (0.2 mA cm-2), where oxygen transport limitations are best illustrated. The results of this research revealed several key factors affecting PFCs-Li-O2 systems. The incorporation of PFCs with higher superoxide solubility and oxygen diffusivity, but more importantly higher PFCs/electrolyte miscibility, in a meso-pore air-electrode enabled better exploitation of PFCs potential. Consequently, the utilization of the air-electrode' surface area was enhanced via the formation of artificial three phase reaction zones with additional oxygen transportation routes, leading to uniform and intimate Li2O2 deposit at areas further away from the oxygen reservoir. Associated mechanisms are discussed along with insights into an improved Li-O2 battery system.

Double perovskite cathodes for proton-conducting ceramic fuel cells: are they triple mixed ionic electronic conductors?

NASA Astrophysics Data System (ADS)

Téllez Lozano, Helena; Druce, John; Cooper, Samuel J.; Kilner, John A.

2017-12-01

18O and 2H diffusion has been investigated at a temperature of 300 °C in the double perovskite material PrBaCo2O5+δ (PBCO) in flowing air containing 200 mbar of 2H216O. Secondary ion mass spectrometry (SIMS) depth profiling of exchanged ceramics has shown PBCO still retains significant oxygen diffusivity ( 1.3 × 10-11 cm2s-1) at this temperature and that the presence of water (2H216O), gives rise to an enhancement of the surface exchange rate over that in pure oxygen by a factor of 3. The 2H distribution, as inferred from the 2H216O- SIMS signal, shows an apparent depth profile which could be interpreted as 2H diffusion. However, examination of the 3-D distribution of the signal shows it to be nonhomogeneous and probably related to the presence of hydrated layers in the interior walls of pores and is not due to proton diffusion. This suggests that PBCO acts mainly as an oxygen ion mixed conductor when used in PCFC devices, although the presence of a small amount of protonic conductivity cannot be discounted in these materials.

Kinetic Monte Carlo Simulation of Oxygen and Cation Diffusion in Yttria-Stabilized Zirconia

NASA Technical Reports Server (NTRS)

Good, Brian

2011-01-01

Yttria-stabilized zirconia (YSZ) is of interest to the aerospace community, notably for its application as a thermal barrier coating for turbine engine components. In such an application, diffusion of both oxygen ions and cations is of concern. Oxygen diffusion can lead to deterioration of a coated part, and often necessitates an environmental barrier coating. Cation diffusion in YSZ is much slower than oxygen diffusion. However, such diffusion is a mechanism by which creep takes place, potentially affecting the mechanical integrity and phase stability of the coating. In other applications, the high oxygen diffusivity of YSZ is useful, and makes the material of interest for use as a solid-state electrolyte in fuel cells. The kinetic Monte Carlo (kMC) method offers a number of advantages compared with the more widely known molecular dynamics simulation method. In particular, kMC is much more efficient for the study of processes, such as diffusion, that involve infrequent events. We describe the results of kinetic Monte Carlo computer simulations of oxygen and cation diffusion in YSZ. Using diffusive energy barriers from ab initio calculations and from the literature, we present results on the temperature dependence of oxygen and cation diffusivity, and on the dependence of the diffusivities on yttria concentration and oxygen sublattice vacancy concentration. We also present results of the effect on diffusivity of oxygen vacancies in the vicinity of the barrier cations that determine the oxygen diffusion energy barriers.

Oxygen self-diffusion mechanisms in monoclinic Zr O2 revealed and quantified by density functional theory, random walk analysis, and kinetic Monte Carlo calculations

NASA Astrophysics Data System (ADS)

Yang, Jing; Youssef, Mostafa; Yildiz, Bilge

2018-01-01

In this work, we quantify oxygen self-diffusion in monoclinic-phase zirconium oxide as a function of temperature and oxygen partial pressure. A migration barrier of each type of oxygen defect was obtained by first-principles calculations. Random walk theory was used to quantify the diffusivities of oxygen interstitials by using the calculated migration barriers. Kinetic Monte Carlo simulations were used to calculate diffusivities of oxygen vacancies by distinguishing the threefold- and fourfold-coordinated lattice oxygen. By combining the equilibrium defect concentrations obtained in our previous work together with the herein calculated diffusivity of each defect species, we present the resulting oxygen self-diffusion coefficients and the corresponding atomistically resolved transport mechanisms. The predicted effective migration barriers and diffusion prefactors are in reasonable agreement with the experimentally reported values. This work provides insights into oxygen diffusion engineering in Zr O2 -related devices and parametrization for continuum transport modeling.

Restricted diffusion in a model acinar labyrinth by NMR: Theoretical and numerical results

NASA Astrophysics Data System (ADS)

Grebenkov, D. S.; Guillot, G.; Sapoval, B.

2007-01-01

A branched geometrical structure of the mammal lungs is known to be crucial for rapid access of oxygen to blood. But an important pulmonary disease like emphysema results in partial destruction of the alveolar tissue and enlargement of the distal airspaces, which may reduce the total oxygen transfer. This effect has been intensively studied during the last decade by MRI of hyperpolarized gases like helium-3. The relation between geometry and signal attenuation remained obscure due to a lack of realistic geometrical model of the acinar morphology. In this paper, we use Monte Carlo simulations of restricted diffusion in a realistic model acinus to compute the signal attenuation in a diffusion-weighted NMR experiment. We demonstrate that this technique should be sensitive to destruction of the branched structure: partial removal of the interalveolar tissue creates loops in the tree-like acinar architecture that enhance diffusive motion and the consequent signal attenuation. The role of the local geometry and related practical applications are discussed.

Benthic Oxygen Demand in Three Former Salt Ponds Adjacent to South San Francisco Bay, California

USGS Publications Warehouse

Topping, Brent R.; Kuwabara, James S.; Athearn, Nicole D.; Takekawa, John Y.; Parcheso, Francis; Henderson, Kathleen D.; Piotter, Sara

2009-01-01

Sampling trips were coordinated in the second half of 2008 to examine the interstitial water in the sediment and the overlying bottom waters of three shallow (average depth 2 meters). The water column at all deployment sites was monitored with dataloggers for ancillary water-quality parameters (including dissolved oxygen, salinity, specific conductance, temperature, and pH) to facilitate the interpretation of benthic-flux results. Calculated diffusive benthic flux of dissolved (0.2-micron filtered) oxygen was consistently negative (that is, drawn from the water column into the sediment) and ranged between -0.5 x 10-6 and -37 x 10-6 micromoles per square centimeter per second (site averages depicted in table 2). Assuming pond areas of 1.0, 1.4, and 2.3 square kilometers for ponds A16, A14, and A3W, respectively, this converts to an oxygen mass flux into the ponds' sediment ranging from -1 to -72 kilograms per day. Diffusive oxygen flux into the benthos (listed as negative) was lowest in pond A14 (-0.5 x 10-6 to -1.8 x 10-6 micromoles per square centimeter per second) compared with diffusive flux estimates for ponds A16 and A3W (site averages -26 x 10-6 to -35 x 10-6 and -34 x 10-6 to -37 x 10-6 micromoles per square centimeter per second, respectively). These initial diffusive-flux estimates are of the order of magnitude of those measured in the South Bay using core-incubation experiments (Topping and others, 2004), which include bioturbation and bioirrigation effects. Estimates of benthic oxygen demand reported herein, based on molecular diffusion, serve as conservative estimates of benthic flux because solute transport across the sediment-water interface can be enhanced by multidisciplinary processes including bioturbation, bioirrigation, ground-water advection, and wind resuspension (Kuwabara and others, 2009).

The Steady-State Transport of Oxygen through Hemoglobin Solutions

PubMed Central

Keller, K. H.; Friedlander, S. K.

1966-01-01

The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated. PMID:5943608

The role of water management on the oxygen transport resistance in polymer electrolyte fuel cell with ultra-low precious metal loading

NASA Astrophysics Data System (ADS)

Srouji, A. K.; Zheng, L. J.; Dross, R.; Aaron, D.; Mench, M. M.

2017-10-01

Limiting current measurements are used to evaluate oxygen transport resistance in the catalyst layer of a polymer electrolyte fuel cell (PEFC). The pressure independent oxygen transport resistance in the electrode is quantified for two cell architectures and two cathode Pt loadings (0.4 and 0.07 mgPt.cm-2). The compounded effect of the flow field and Pt loading is used to shed light on the nature of the observed transport resistance, especially its response to fundamentally different flow fields, which is shown to directly or indirectly scale with Pt loading in the open literature. By varying gas pressure and using low oxygen concentrations, the total oxygen transport resistance is divided into intermolecular gas diffusion (a pressure-dependent component) and a pressure independent component, which can be attributed to Knudsen diffusion or dissolution film resistance. The pressure-independent oxygen transport resistance in the catalyst layer varies between 13.3 and 34.4 s/m. It is shown that the pressure independent oxygen transport resistance increases with reduced Pt loading, but that effect is greatly exacerbated by using conventional channel/lands. The results indicate that open metallic element architecture improves the oxygen transport resistance in ultra-low Pt loading electrodes, likely due to enhanced water management at the catalyst layer.

Diffuse optical tomography and spectroscopy of breast cancer and fetal brain

NASA Astrophysics Data System (ADS)

Choe, Regine

Diffuse optical techniques utilize light in the near infrared spectral range to measure tissue physiology non-invasively. Based on these measurements, either on average or a three-dimensional spatial map of tissue properties such as total hemoglobin concentration, blood oxygen saturation and scattering can be obtained using model-based reconstruction algorithms. In this thesis, diffuse optical techniques were applied for in vivo breast cancer imaging and trans-abdominal fetal brain oxygenation monitoring. For in vivo breast cancer imaging, clinical diffuse optical tomography and related instrumentation was developed and used in several contexts. Bulk physiological properties were quantified for fifty-two healthy subjects in the parallel-plate transmission geometry. Three-dimensional images of breast were reconstructed for subjects with breast tumors and, tumor contrast with respect to normal tissue was found in total hemoglobin concentration and scattering and was quantified for twenty-two breast carcinomas. Tumor contrast and tumor volume changes during neoadjuvant chemotherapy were tracked for one subject and compared to the dynamic contrast-enhanced MRI. Finally, the feasibility for measuring blood flow of breast tumors using optical methods was demonstrated for seven subjects. In a qualitatively different set of experiments, the feasibility for trans-abdominal fetal brain oxygenation monitoring was demonstrated on pregnant ewes with induced fetal hypoxia. Preliminary clinical experiences were discussed to identify future directions. In total, this research has translated diffuse optical tomography techniques into clinical research environment.

Oxygen diffusion: an enzyme-controlled variable parameter.

PubMed

Erdmann, Wilhelm; Kunke, Stefan

2014-01-01

Previous oxygen microelectrode studies have shown that the oxygen diffusion coefficient (DO₂) increases during extracellular PO₂ decreases, while intracellular PO₂ remained unchanged and thus cell function (spike activity of neurons). Oxygen dependency of complex multicellular organisms requires a stable and adequate oxygen supply to the cells, while toxic concentrations have to be avoided. Oxygen brought to the tissue by convection diffuses through the intercellular and cell membranes, which are potential barriers to diffusion. In gerbil brain cortex, PO₂ and DO₂ were measured by membrane-covered and by bare gold microelectrodes, as were also spike potentials. Moderate respiratory hypoxia was followed by a primary sharp drop of tissue PO₂ that recovered to higher values concomitant with an increase of DO₂. A drop in intracellular PO₂ recovered immediately. Studies on the abdominal ganglion of aplysia californica showed similar results.Heterogeneity is a feature of both normal oxygen supply to tissue and supply due to a wide range of disturbances in oxygen supply. Oxygen diffusion through membranes is variable thereby ensuring adequate intracellular PO₂. Cell-derived glucosamine oxidase seems to regulate the polymerization/depolymerisation ratio of membrane mucopolysaccharides and thus oxygen diffusion.Variability of oxygen diffusion is a decisive parameter for regulating the supply/demand ratio of oxygen supply to the cell; this occurs in highly developed animals as well as in species of a less sophisticated nature. Autoregulation of oxygen diffusion is as important as the distribution/perfusion ratio of the capillary meshwork and as the oxygen extraction ratio in relation to oxygen consumption of the cell. Oxygen diffusion resistance is the cellular protection against luxury oxygen supply (which can result in toxic oxidative species leading to mutagenesis).

Interferometric study on the mass transfer in cryogenic distillation under magnetic field

NASA Astrophysics Data System (ADS)

Bao, S. R.; Zhang, R. P.; Y Rong, Y.; Zhi, X. Q.; Qiu, L. M.

2017-12-01

Cryogenic distillation has long been used for the mass production of industrial gases because of its features of high efficiency, high purity, and capability to produce noble gases. It is of great theoretical and practical significance to explore methods to improve the mass transfer efficiency in cryogenic distillation. The negative correlation between the susceptibility of paramagnetic oxygen and temperature provides a new possibility of comprehensive utilization of boiling point and susceptibility differences in cryogenic distillation. Starting from this concept, we proposed a novel distillation intensifying method by using gradient magnetic field, in which the magnetic forces enhance the transport of the oxygen molecules to the liquid phase in the distillation. In this study, a cryogenic testbed was designed and fabricated to study the diffusion between oxygen and nitrogen under magnetic field. A Mach-Zehnder interferometer was used to visualize the concentration distribution during the diffusion process. The mass transfer characteristics with and without magnetic field, in the chamber filled with the magnetized medium, were systematically studied. The concentration redistribution of oxygen was observed, and the stable stratified diffusion between liquid oxygen and nitrogen was prolonged by the non-uniform magnetic field. The experimental results show that the magnetic field can efficiently influence the mass transfer in cryogenic distillation, which can provide a new mechanism for the optimization of air separation process.

Optimization of perfluoro nano-scale emulsions: the importance of particle size for enhanced oxygen transfer in biomedical applications.

PubMed

Fraker, Christopher A; Mendez, Armando J; Inverardi, Luca; Ricordi, Camillo; Stabler, Cherie L

2012-10-01

Nano-scale emulsification has long been utilized by the food and cosmetics industry to maximize material delivery through increased surface area to volume ratios. More recently, these methods have been employed in the area of biomedical research to enhance and control the delivery of desired agents, as in perfluorocarbon emulsions for oxygen delivery. In this work, we evaluate critical factors for the optimization of PFC emulsions for use in cell-based applications. Cytotoxicity screening revealed minimal cytotoxicity of components, with the exception of one perfluorocarbon utilized for emulsion manufacture, perfluorooctylbromide (PFOB), and specific w% limitations of PEG-based surfactants utilized. We optimized the manufacture of stable nano-scale emulsions via evaluation of: component materials, emulsification time and pressure, and resulting particle size and temporal stability. The initial emulsion size was greatly dependent upon the emulsion surfactant tested, with pluronics providing the smallest size. Temporal stability of the nano-scale emulsions was directly related to the perfluorocarbon utilized, with perfluorotributylamine, FC-43, providing a highly stable emulsion, while perfluorodecalin, PFD, coalesced over time. The oxygen mass transfer, or diffusive permeability, of the resulting emulsions was also characterized. Our studies found particle size to be the critical factor affecting oxygen mass transfer, as increased micelle size resulted in reduced oxygen diffusion. Overall, this work demonstrates the importance of accurate characterization of emulsification parameters in order to generate stable, reproducible emulsions with the desired bio-delivery properties. Copyright © 2012 Elsevier B.V. All rights reserved.

Formation of tungsten oxide nanowires by ion irradiation and vacuum annealing

NASA Astrophysics Data System (ADS)

Zheng, Xu-Dong; Ren, Feng; Wu, Heng-Yi; Qin, Wen-Jing; Jiang, Chang-Zhong

2018-04-01

Here we reported the fabrication of tungsten oxide (WO3-x ) nanowires by Ar+ ion irradiation of WO3 thin films followed by annealing in vacuum. The nanowire length increases with increasing irradiation fluence and with decreasing ion energy. We propose that the stress-driven diffusion of the irradiation-induced W interstitial atoms is responsible for the formation of the nanowires. Comparing to the pristine film, the fabricated nanowire film shows a 106-fold enhancement in electrical conductivity, resulting from the high-density irradiation-induced vacancies on the oxygen sublattice. The nanostructure exhibits largely enhanced surface-enhanced Raman scattering effect due to the oxygen vacancy. Thus, ion irradiation provides a powerful approach for fabricating and tailoring the surface nanostructures of semiconductors.

Kinetic bottlenecks to chemical exchange rates for deep-sea animals - Part 1: Oxygen

NASA Astrophysics Data System (ADS)

Hofmann, A. F.; Peltzer, E. T.; Brewer, P. G.

2012-10-01

Ocean warming will reduce dissolved oxygen concentrations which can pose challenges to marine life. Oxygen limits are traditionally reported simply as a static concentration thresholds with no temperature, pressure or flow rate dependency. Here we treat the oceanic oxygen supply potential for heterotrophic consumption as a dynamic molecular exchange problem analogous to familiar gas exchange processes at the sea surface. A combination of the purely physico-chemical oceanic properties temperature, hydrostatic pressure, and oxygen concentration defines the ability of the ocean to supply oxygen to any given animal. This general oceanic oxygen supply potential is modulated by animal specific properties such as the diffusive boundary layer thickness to define and limit maximal oxygen supply rates. Here we combine all these properties into formal, mechanistic equations defining novel oceanic properties that subsume various relevant classical oceanographic parameters to better visualize, map, comprehend, and predict the impact of ocean deoxygenation on aerobic life. By explicitly including temperature and hydrostatic pressure into our quantities, various ocean regions ranging from the cold deep-sea to warm, coastal seas can be compared. We define purely physico-chemical quantities to describe the oceanic oxygen supply potential, but also quantities that contain organism-specific properties which in a most generalized way describe general concepts and dependencies. We apply these novel quantities to example oceanic profiles around the world and find that temperature and pressure dependencies of diffusion and partial pressure create zones of greatest physical constriction on oxygen supply typically at around 1000 m depth, which coincides with oxygen concentration minimum zones. In these zones, which comprise the bulk of the world ocean, ocean warming and deoxygenation have a clear negative effect for aerobic life. In some shallow and warm waters the enhanced diffusion and higher partial pressure due to higher temperatures might slightly overcompensate for oxygen concentration decreases due to decreases in solubility.

Oxygen Tracer Diffusion in LA(z-x) SR(X) CUO(4-y) Single Crystals

NASA Technical Reports Server (NTRS)

Opila, Elizabeth J.; Tuller, Harry L.; Wuensch, Berhardt J.; Maier, Joachim

1993-01-01

The tracer diffusion of O-18 in La(2-x)Sr(x)CuO(4-y) single crystals (x = 0 to 0.12) has been measured from 400 to 700 C in 1 atm of oxygen using SIMS analysis. Evidence for diffusion by a vacancy mechanism was found at low strontium contents. Oxygen diffusivities for x greater than or = 0.07 were depressed by several orders of magnitude below the diffusivity for undoped La2CuO(4+/-y). The observed effects of strontium doping on oxygen diffusivity are discussed in terms of defect chemical models. The decreasing oxygen diffusivity with increasing strontium was attributed to the ordering of oxygen vacancies at large defect concentrations. A diffusion anisotropy D(sub ab)/D(sub c) of nearly 600 was also found at 500 C.

Double perovskite cathodes for proton-conducting ceramic fuel cells: are they triple mixed ionic electronic conductors?

PubMed Central

Téllez Lozano, Helena; Druce, John; Cooper, Samuel J.; Kilner, John A.

2017-01-01

Abstract 18O and 2H diffusion has been investigated at a temperature of 300 °C in the double perovskite material PrBaCo2O5+δ (PBCO) in flowing air containing 200 mbar of 2H2 16O. Secondary ion mass spectrometry (SIMS) depth profiling of exchanged ceramics has shown PBCO still retains significant oxygen diffusivity (~1.3 × 10−11 cm2s−1) at this temperature and that the presence of water (2H2 16O), gives rise to an enhancement of the surface exchange rate over that in pure oxygen by a factor of ~3. The 2H distribution, as inferred from the 2H2 16O− SIMS signal, shows an apparent depth profile which could be interpreted as 2H diffusion. However, examination of the 3-D distribution of the signal shows it to be nonhomogeneous and probably related to the presence of hydrated layers in the interior walls of pores and is not due to proton diffusion. This suggests that PBCO acts mainly as an oxygen ion mixed conductor when used in PCFC devices, although the presence of a small amount of protonic conductivity cannot be discounted in these materials. PMID:29383047

Body mass scaling of passive oxygen diffusion in endotherms and ectotherms

PubMed Central

Gillooly, James F.; Gomez, Juan Pablo; Mavrodiev, Evgeny V.; Rong, Yue; McLamore, Eric S.

2016-01-01

The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick’s law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption. PMID:27118837

Body mass scaling of passive oxygen diffusion in endotherms and ectotherms.

PubMed

Gillooly, James F; Gomez, Juan Pablo; Mavrodiev, Evgeny V; Rong, Yue; McLamore, Eric S

2016-05-10

The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick's law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption.

Engineering amorphous-crystalline interfaces in TiO2-x/TiO2-y-based bilayer structures for enhanced resistive switching and synaptic properties

NASA Astrophysics Data System (ADS)

Bousoulas, P.; Asenov, P.; Karageorgiou, I.; Sakellaropoulos, D.; Stathopoulos, S.; Tsoukalas, D.

2016-10-01

The operating principle of resistive random access memories (RRAMs) relies on the distribution of ionic species and their influence on the electron transport. Taking into account that formation and annihilation of conducting filaments (CFs) is the driving mechanism for the switching effect, it is very important to control the regions where these filaments will evolve. Thus, homolayers of titanium oxide with different oxygen contents were fabricated in order to tune the local electrical and thermal properties of the CFs and narrow down the potential percolation paths. We show that the oxygen content in the top layer of the TiO2-x/TiO2-y bilayer memristors can directly influence the morphology of the layers which affect the diffusion barrier and consequently the diffusivity and drift velocity of oxygen vacancies, yielding in important enhancement of switching characteristics, in terms of spatial uniformity (σ/μ < 0.2), enlarged switching ratio (˜104), and synaptic learning. In order to address the experimental data, a physical model was applied, divulging the crucial role of temperature, electric potential and oxygen vacancy density on the switching effect and offering physical insights to the SET/RESET transitions and the analog switching. The forming free nature of all the devices in conjunction with the self-rectifying behavior, should also be regarded as important assets towards RRAM device optimization.

Nitrogen diffusion in hafnia and the impact of nitridation on oxygen and hydrogen diffusion: A first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sathiyanarayanan, Rajesh, E-mail: rajessat@in.ibm.com, E-mail: rajesh.sathiyanarayanan@gmail.com; Pandey, R. K.; Murali, K. V. R. M.

2015-01-21

Using first-principles simulations, we have computed incorporation energies and diffusion barriers of ammonia, the nitrogen molecule and atomic nitrogen in monoclinic hafnia (m-HfO{sub 2}). Our calculations show that ammonia is likely to dissociate into an NH{sub 2} molecular unit, whereas the nitrogen molecule remains as a molecule either in the interstitial space or at an oxygen lattice site. The lowest energy pathway for the diffusion of atomic nitrogen interstitials consists of the hopping of the nitrogen interstitial between neighboring three-coordinated lattice oxygen atoms that share a single Hf atom, and the barrier for such hops is determined by a switchingmore » mechanism. The substitutional nitrogen atom shows a preference for diffusion through the doubly positive oxygen vacancy-mediated mechanism. Furthermore, we have investigated the impact of nitrogen atoms on the diffusion barriers of oxygen and hydrogen interstitials in m-HfO{sub 2}. Our results show that nitrogen incorporation has a significant impact on the barriers for oxygen and hydrogen diffusion: nitrogen atoms attract oxygen and hydrogen interstitials diffusing in the vicinity, thereby slowing down (reducing) their diffusion (diffusion length)« less

Effect of hemoglobin polymerization on oxygen transport in hemoglobin solutions.

PubMed

Budhiraja, Vikas; Hellums, J David

2002-09-01

The effect of hemoglobin (Hb) polymerization on facilitated transport of oxygen in a bovine hemoglobin-based oxygen carrier was studied using a diffusion cell. In high oxygen tension gradient experiments (HOTG) at 37 degrees C the diffusion of dissolved oxygen in polymerized Hb samples was similar to that in unpolymerized Hb solutions during oxygen uptake. However, in the oxygen release experiments, the transport by diffusion of dissolved oxygen was augmented by diffusion of oxyhemoglobin over a range of oxygen saturations. The augmentation was up to 30% in the case of polymerized Hb and up to 100% in the case of unpolymerized Hb solution. In experiments performed at constant, low oxygen tension gradients in the range of physiological significance, the augmentation effect was less than that in the HOTG experiments. Oxygen transport in polymerized Hb samples was approximately the same as that in unpolymerized samples over a wide range of oxygen tensions. However, at oxygen tensions lower than 30 mm Hg, there were more significant augmentation effects in unpolymerized bovine Hb samples than in polymerized Hb. The results presented here are the first accurate, quantitative measurements of effective diffusion coefficients for oxygen transport in hemoglobin-based oxygen carriers of the type being evaluated to replace red cells in transfusions. In all cases the oxygen carrier was found to have higher effective oxygen diffusion coefficients than blood.

Why Are High Altitude Natives So Strong at High Altitude? Nature vs. Nurture: Genetic Factors vs. Growth and Development.

PubMed

Brutsaert, Tom

Among high-altitude natives there is evidence of a general hypoxia tolerance leading to enhanced performance and/or increased capacity in several important domains. These domains likely include an enhanced physical work capacity, an enhanced reproductive capacity, and an ability to resist several common pathologies of chronic high-altitude exposure. The "strength" of the high-altitude native in this regard may have both a developmental and a genetic basis, although there is better evidence for the former (developmental effects) than for the latter. For example, early-life hypoxia exposure clearly results in lung growth and remodeling leading to an increased O2 diffusing capacity in adulthood. Genetic research has yet to reveal a population genetic basis for enhanced capacity in high-altitude natives, but several traits are clearly under genetic control in Andean and Tibetan populations e.g., resting and exercise arterial O2 saturation (SaO2). This chapter reviews the effects of nature and nurture on traits that are relevant to the process of gas exchange, including pulmonary volumes and diffusion capacity, the maximal oxygen consumption (VO2max), the SaO2, and the alveolar-arterial oxygen partial pressure difference (A-aDO2) during exercise.

Reaction rates of oxygen with hemoglobin measured by non-equilibrium facilitated oxygen diffusion through hemoglobin solutions.

PubMed

Bouwer, S T; Hoofd, L; Kreuzer, F

2001-02-16

The purpose of this study was to verify the concept of non-equilibrium facilitated oxygen diffusion. This work succeeds our previous study, where facilitated oxygen diffusion by hemoglobin was measured at conditions of chemical equilibrium, and which yielded diffusion coefficients of hemoglobin and of oxygen. In the present work chemical non-equilibrium was induced using very thin diffusion layers. As a result, facilitation was decreased as predicted by theory. Thus, this work presents the first experimental demonstration of non-equilibrium facilitated oxygen diffusion. In addition, association and dissociation rate parameters of the reaction between oxygen and bovine and human hemoglobin were calculated and the effect of the homotropic and heterotropic interactions on each rate parameter was demonstrated. The results indicate that the homotropic interaction--which leads to increasing oxygen affinity with increasing oxygenation--is predominantly due to an increase in the association rate. The heterotropic interaction--which leads to decreasing oxygen affinity by anionic ligands--appears to be effected in two ways. Cl- increases the dissociation rate. In contrast, 2,3-diphosphoglycerate decreases the association rate.

Ion-barrier for memristors/ReRAM and methods thereof

DOEpatents

Haase, Gad S.

2017-11-28

The present invention relates to memristive devices including a resistance-switching element and a barrier element. In particular examples, the barrier element is a monolayer of a transition metal chalcogenide that sufficiently inhibits diffusion of oxygen atoms or ions out of the switching element. As the location of these atoms and ions determine the state of the device, inhibiting diffusion would provide enhanced state retention and device reliability. Other types of barrier elements, as well as methods for forming such elements, are described herein.

Novel mesoporous MnCo2O4 nanorods as oxygen reduction catalyst at neutral pH in microbial fuel cells.

PubMed

Kumar, Ravinder; Singh, Lakhveer; Wahid, Zularisam Ab; Mahapatra, Durga Madhab; Liu, Hong

2018-04-01

The aim of this work was to evaluate the comparative performance of hybrid metal oxide nanorods i.e. MnCo 2 O 4 nanorods (MCON) and single metal oxide nanorods i.e. Co 3 O 4 nanorods (CON) as oxygen reduction catalyst in microbial fuel cells (MFC). Compared to the single metal oxide, the hybrid MCON exhibited a higher BET surface area and provided additional positively charged ions, i.e., Co 2+ /Co 3+ and Mn 3+ /Mn 4+ on its surfaces, which increased the electro-conductivity of the cathode and improved the oxygen reduction kinetics significantly, achieved an i o of 6.01 A/m 2 that was 12.4% higher than CON. Moreover, the porous architecture of MCON facilitated the diffusion of electrolyte, reactants and electrons during the oxygen reduction, suggested by lower diffusion (R d ), activation (R act ) and ohmic resistance (R ohm ) values. This enhanced oxygen reduction by MCON boosted the power generation in MFC, achieving a maximum power density of 587 mW/m 2 that was ∼29% higher than CON. Published by Elsevier Ltd.

Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

USGS Publications Warehouse

Molins, S.; Mayer, K.U.

2007-01-01

The two‐way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate‐rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O2 consumption.

Position-Dependent Diffusion Tensors in Anisotropic Media from Simulation: Oxygen Transport in and through Membranes.

PubMed

Ghysels, An; Venable, Richard M; Pastor, Richard W; Hummer, Gerhard

2017-06-13

A Bayesian-based methodology is developed to estimate diffusion tensors from molecular dynamics simulations of permeants in anisotropic media, and is applied to oxygen in lipid bilayers. By a separation of variables in the Smoluchowski diffusion equation, the multidimensional diffusion is reduced to coupled one-dimensional diffusion problems that are treated by discretization. The resulting diffusivity profiles characterize the membrane transport dynamics as a function of the position across the membrane, discriminating between diffusion normal and parallel to the membrane. The methodology is first validated with neat water, neat hexadecane, and a hexadecane slab surrounded by water, the latter being a simple model for a lipid membrane. Next, a bilayer consisting of pure 1-palmitoyl 2-oleoylphosphatidylcholine (POPC), and a bilayer mimicking the lipid composition of the inner mitochondrial membrane, including cardiolipin, are investigated. We analyze the detailed time evolution of oxygen molecules, in terms of both normal diffusion through and radial diffusion inside the membrane. Diffusion is fast in the more loosely packed interleaflet region, and anisotropic, with oxygen spreading more rapidly in the membrane plane than normal to it. Visualization of the propagator shows that oxygen enters the membrane rapidly, reaching its thermodynamically favored center in about 1 ns, despite the free energy barrier at the headgroup region. Oxygen transport is quantified by computing the oxygen permeability of the membranes and the average radial diffusivity, which confirm the anisotropy of the diffusion. The position-dependent diffusion constants and free energies are used to construct compartmental models and test assumptions used in estimating permeability, including Overton's rule. In particular, a hexadecane slab surrounded by water is found to be a poor model of oxygen transport in membranes because the relevant energy barriers differ substantially.

Insensitivity of cerebral oxygen transport to oxygen affinity of hemoglobin-based oxygen carriers.

PubMed

Koehler, Raymond C; Fronticelli, Clara; Bucci, Enrico

2008-10-01

The cerebrovascular effects of exchange transfusion of various cell-free hemoglobins that possess different oxygen affinities are reviewed. Reducing hematocrit by transfusion of a non-oxygen-carrying solution dilates pial arterioles on the brain surface and increases cerebral blood flow to maintain a constant bulk oxygen transport to the brain. In contrast, transfusion of hemoglobins with P50 of 4-34 Torr causes constriction of pial arterioles that offsets the decrease in blood viscosity to maintain cerebral blood flow and oxygen transport. The autoregulatory constriction is dependent on synthesis of 20-HETE from arachidonic acid. This oxygen-dependent reaction is apparently enhanced by facilitated oxygen diffusion from the red cell to the endothelium arising from increased plasma oxygen solubility in the presence of low or high-affinity hemoglobin. Exchange transfusion of recombinant hemoglobin polymers with P50 of 3 and 18 Torr reduces infarct volume from experimental stroke. Cell-free hemoglobins do not require a P50 as high as red blood cell hemoglobin to facilitate oxygen delivery.

Combined diffusion-weighted, blood oxygen level-dependent, and dynamic contrast-enhanced MRI for characterization and differentiation of renal cell carcinoma.

PubMed

Notohamiprodjo, Mike; Staehler, Michael; Steiner, Nicole; Schwab, Felix; Sourbron, Steven P; Michaely, Henrik J; Helck, Andreas D; Reiser, Maximilian F; Nikolaou, Konstantin

2013-06-01

To investigate a multiparametric magnetic resonance imaging (MRI) approach comprising diffusion-weighted imaging (DWI), blood oxygen-dependent (BOLD), and dynamic contrast-enhanced (DCE) MRI for characterization and differentiation of primary renal cell carcinoma (RCC). Fourteen patients with clear-cell carcinoma and four patients with papillary RCC were examined with DWI, BOLD MRI, and DCE MRI at 1.5T. The apparent diffusion coefficient (ADC) was calculated with a monoexponential decay. The spin-dephasing rate R2* was derived from parametric R2* maps. DCE-MRI was analyzed using a two-compartment exchange model allowing separation of perfusion (plasma flow [FP] and plasma volume [VP]), permeability (permeability surface area product [PS]), and extravascular extracellular volume (VE). Statistical analysis was performed with Wilcoxon signed-rank test, Pearson's correlation coefficient, and receiver operating characteristic curve analysis. Clear-cell RCC showed higher ADC and lower R2* compared to papillary subtypes, but differences were not significant. FP of clear-cell subtypes was significantly higher than in papillary RCC. Perfusion parameters showed moderate but significant inverse correlation with R2*. VE showed moderate inverse correlation with ADC. Fp and Vp showed best sensitivity for histological differentiation. Multiparametric MRI comprising DWI, BOLD, and DCE MRI is feasible for assessment of primary RCC. BOLD moderately correlates to DCE MRI-derived perfusion. ADC shows moderate correlation to the extracellular volume, but does not correlate to tumor oxygenation or perfusion. In this preliminary study DCE-MRI appeared superior to BOLD and DWI for histological differentiation. Copyright © 2013 AUR. Published by Elsevier Inc. All rights reserved.

Enhancement of the Laser Transmission Weldability between Polyethylene and Polyoxymethylene by Plasma Surface Treatment

PubMed Central

Tan, Wensheng; Wang, Xiao

2017-01-01

Due to their large compatibility difference, polyethylene (PE) and polyoxymethylene (POM) cannot be welded together by laser transmission welding. In this study, PE and POM are pretreated using plasma that significantly enhances their laser transmission welding strength. To understand the mechanism underlying the laser welding strength enhancement, surface modification is analyzed using contact angle measurements, atomic force microscopy (AFM), optical microscopy, and X-ray photoelectron spectroscopy (XPS). Characterization results show that the plasma surface treatment improves the surface free energy, significantly enhancing the wettability of the materials. The increase in surface roughness and the generation of homogeneous bubbles contribute to the formation of mechanical micro-interlocking. The oxygen-containing groups introduced by the oxygen plasma treatment improve the compatibility of PE and POM, and facilitate the diffusion and entanglement of molecular chains and the formation of van der Waals force. PMID:29278367

Enhancement of the Laser Transmission Weldability between Polyethylene and Polyoxymethylene by Plasma Surface Treatment.

PubMed

Liu, Huixia; Jiang, Yingjie; Tan, Wensheng; Wang, Xiao

2017-12-26

Due to their large compatibility difference, polyethylene (PE) and polyoxymethylene (POM) cannot be welded together by laser transmission welding. In this study, PE and POM are pretreated using plasma that significantly enhances their laser transmission welding strength. To understand the mechanism underlying the laser welding strength enhancement, surface modification is analyzed using contact angle measurements, atomic force microscopy (AFM), optical microscopy, and X-ray photoelectron spectroscopy (XPS). Characterization results show that the plasma surface treatment improves the surface free energy, significantly enhancing the wettability of the materials. The increase in surface roughness and the generation of homogeneous bubbles contribute to the formation of mechanical micro-interlocking. The oxygen-containing groups introduced by the oxygen plasma treatment improve the compatibility of PE and POM, and facilitate the diffusion and entanglement of molecular chains and the formation of van der Waals force.

Dopants Diffusion in Silicon during Molecular Oxygen/nitrogen Trifluoride Oxidation and Related Phenomena

NASA Astrophysics Data System (ADS)

Kim, U. S.

1990-01-01

To date, chlorine has been used as useful additives in silicon oxidation. However, rapid scaling of device dimensions motivates the development of a new dielectric layer or modification of the silicon dioxide itself. More recently, chemically enhanced thermal oxidation by the use of fluorine containing species has been introduced to verify the potential of fluorine in the silicon oxidation process. In this study, gaseous nitrogen trifluoride (NF _3) was selected as the fluorine oxidizing source based on ease of use and was compared with the dichlorofluoroethane (C_2H _3Cl_2F) source. Two different kinds of boron marker samples were prepared and oxidized in O_2/NF_3 ambient for the comparison of surface vs bulk oxidation enhanced/retarded diffusion (OED/ORD). The phosphorus, arsenic and antimony diffusion in silicon during fluorine oxidation has been studied using the various covering layers such as SiO_2, Si_3 N_4, and SiO_2 + Si_3N_4 layers. The oxidation related phenomena, i.e. enhanced silicon and silicon nitride oxidation in fluorine ambient were studied and correlated with the point defect balance at the oxidizing interface. The results of this investigation were discussed with special emphasis on the effect of fluorine on enhanced oxidation and dopant diffusion.

A computational model of oxygen delivery by hemoglobin-based oxygen carriers in three-dimensional microvascular networks.

PubMed

Tsoukias, Nikolaos M; Goldman, Daniel; Vadapalli, Arjun; Pittman, Roland N; Popel, Aleksander S

2007-10-21

A detailed computational model is developed to simulate oxygen transport from a three-dimensional (3D) microvascular network to the surrounding tissue in the presence of hemoglobin-based oxygen carriers. The model accounts for nonlinear O(2) consumption, myoglobin-facilitated diffusion and nonlinear oxyhemoglobin dissociation in the RBCs and plasma. It also includes a detailed description of intravascular resistance to O(2) transport and is capable of incorporating realistic 3D microvascular network geometries. Simulations in this study were performed using a computer-generated microvascular architecture that mimics morphometric parameters for the hamster cheek pouch retractor muscle. Theoretical results are presented next to corresponding experimental data. Phosphorescence quenching microscopy provided PO(2) measurements at the arteriolar and venular ends of capillaries in the hamster retractor muscle before and after isovolemic hemodilution with three different hemodilutents: a non-oxygen-carrying plasma expander and two hemoglobin solutions with different oxygen affinities. Sample results in a microvascular network show an enhancement of diffusive shunting between arterioles, venules and capillaries and a decrease in hemoglobin's effectiveness for tissue oxygenation when its affinity for O(2) is decreased. Model simulations suggest that microvascular network anatomy can affect the optimal hemoglobin affinity for reducing tissue hypoxia. O(2) transport simulations in realistic representations of microvascular networks should provide a theoretical framework for choosing optimal parameter values in the development of hemoglobin-based blood substitutes.

Solid state oxygen sensor

DOEpatents

Garzon, Fernando H.; Chung, Brandon W.; Raistrick, Ian D.; Brosha, Eric L.

1996-01-01

Solid state oxygen sensors are provided with a yttria-doped zirconia as an electrolyte and use the electrochemical oxygen pumping of the zirconia electrolyte. A linear relationship between oxygen concentration and the voltage arising at a current plateau occurs when oxygen accessing the electrolyte is limited by a diffusion barrier. A diffusion barrier is formed herein with a mixed electronic and oxygen ion-conducting membrane of lanthanum-containing perovskite or zirconia-containing fluorite. A heater may be used to maintain an adequate oxygen diffusion coefficient in the mixed conducting layer.

Desorption of oxygen from YBa2Cu3O6+x films studied by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Bock, A.; Kürsten, R.; Brühl, M.; Dieckmann, N.; Merkt, U.

1996-08-01

Phonons of laser-deposited YBa2Cu3O6+x films on MgO(100) substrates are investigated in a Raman setup as a function of laser power density. Investigations of YBa2Cu3O7 films allow us to study oxygen out-diffusion, where the onset of out-diffusion is indicated by the appearance of disorder-induced modes in the Raman spectra. At a pressure of 5×10-6 mbar the temperature threshold of the out-diffusion is (490+/-15) K. With increasing oxygen pressure the observed temperature thresholds rise only moderately in contrast to the behavior expected from the pox-T phase diagram of YBa2Cu3O6+x. Even at 1 bar oxygen partial pressure out-diffusion is observed and tetragonal sites with x=0 develop. These observations can be explained by photon-stimulated desorption of oxygen. Investigations of YBa2Cu3O6 films allow us to study oxygen in-diffusion. In 1 bar oxygen we observe competing oxygen fluxes due to thermally activated diffusion and photon-stimulated desorption. From these measurements we determine an upper bound of the thermal activation energy of the oxygen in-diffusion into YBa2Cu3O6 films of (0.19+/-0.01) eV.

Augmentation of oxygen transport by various hemoglobins as determined by pulsed field gradient NMR.

PubMed

Budhiraja, Vikas; Hellums, J David; Post, Jan F M

2002-11-01

Diffusion of oxyhemoglobin has been shown to augment the oxygen transport inside the red blood cells. Measurement of hemoglobin diffusion coefficients by pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) technique can be used for estimating this augmentation effect. Self-diffusion coefficients of polymerized and unpolymerized bovine hemoglobin (Hb) and several other proteins were measured using this technique. The Hb diffusion coefficient was used to determine the effective permeability of oxygen and augmentation of oxygen transport through samples of Hb solutions due to diffusion of oxyhemoglobin. The values compared well with our previous diffusion cell measurements of effective diffusivity and augmentation. Our NMR studies show that even at low concentrations the augmentation of oxygen transport due to diffusion can be significant. The PFG NMR technique can thus provide an accurate and easy method for measuring augmentation of oxygen transport, especially in dilute samples of Hb. The results on polyhemoglobin and high-molecular-weight hemoglobin are of both basic interest and practical value in assessing the promise and performance of hemoglobin-based blood substitutes.

Assessment of tumor response to oxygen challenge using quantitative diffusion MRI in an animal model.

PubMed

Zhang, Zhongwei; Yuan, Qing; Zhou, Heling; Zhao, Dawen; Li, Li; Gerberich, Jenifer L; Mason, Ralph P

2015-11-01

To assess tumor response to oxygen challenge using quantitative diffusion magnetic resonance imaging (MRI). A well-characterized Dunning R3327-AT1 rat prostate cancer line was implanted subcutaneously in the right thigh of male Copenhagen rats (n = 8). Diffusion-weighted images (DWI) with multiple b values (0, 25, 50, 100, 150, 200, 300, 500, 1000, 1500 s/mm(2) ) in three orthogonal directions were obtained using a multishot FSE-based Stejskal-Tanner DWI sequence (FSE-DWI) at 4.7T, while rats breathed medical air (21% oxygen) and with 100% oxygen challenge. Stretched-exponential and intravoxel incoherent motion (IVIM) models were used to calculate and compare quantitative diffusion parameters: diffusion heterogeneity index (α), intravoxel distribution of diffusion coefficients (DDC), tissue diffusivity (Dt), pseudo-diffusivity (Dp), and perfusion fraction (f) on a voxel-by-voxel basis. A significant increase of α (73.9 ± 4.7% in air vs. 78.1 ± 4.5% in oxygen, P = 0.0198) and a significant decrease of f (13.4 ± 3.7% in air vs. 10.4 ± 2.7% in oxygen, P = 0.0201) were observed to accompany oxygen challenge. Correlations between f and α during both air and oxygen breathing were found; the correlation coefficients (r) were -0.90 and -0.96, respectively. Positive correlations between Dt and DDC with oxygen breathing (r = 0.95, P = 0.0003), f and DDC with air breathing were also observed (r = 0.95, P = 0.0004). Quantitative diffusion MRI demonstrated changes in tumor perfusion in response to oxygen challenge. © 2015 Wiley Periodicals, Inc.

Theranostic Oxygen Delivery Using Ultrasound and Microbubbles

PubMed Central

Kwan, James J.; Kaya, Mehmet; Borden, Mark A.; Dayton, Paul A.

2012-01-01

Means to overcome tumor hypoxia have been the subject of clinical investigations since the 1960's; however these studies have yet to find a treatment which is widely accepted. It has been known for nearly a century that hypoxic cells are more resistant to radiotherapy than aerobic cells, and tumor hypoxia is a major factor leading to the resistance of tumors to radiation treatment as well as several cytotoxic agents. In this manuscript, the application of ultrasound combined with oxygen-carrier microbubbles is demonstrated as a method to locally increase dissolved oxygen. Microbubbles can also be imaged by ultrasound, thus providing the opportunity for image-guided oxygen delivery. Simulations of gas diffusion and microbubble gas exchange show that small amounts (down to 5 vol%) of a low-solubility osmotic gas can substantially increase microbubble persistence and therefore production rates and stability of oxygen-carrier microbubbles. Simulations also indicate that the lipid shell can be engineered with long-chain lipids to increase oxygen payload during in vivo transit. Experimental results demonstrate that the application of ultrasound to destroy the microbubbles significantly enhances the local oxygen release. We propose this technology as an application for ultrasound image-guided release of oxygen directly to hypoxic tissue, such as tumor sites to enhance radiotherapy. PMID:23382774

Interactions of Oxygen and Hydrogen on Pd(111) surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demchenko, D.O.; Sacha, G.M.; Salmeron, M.

2008-06-25

The coadsorption and interactions of oxygen and hydrogen on Pd(1 1 1) was studied by scanning tunneling microscopy and density functional theory calculations. In the absence of hydrogen oxygen forms a (2 x 2) ordered structure. Coadsorption of hydrogen leads to a structural transformation from (2 x 2) to a ({radical}3 x {radical}3)R30 degree structure. In addition to this transformation, hydrogen enhances the mobility of oxygen. To explain these observations, the interaction of oxygen and hydrogen on Pd(1 1 1) was studied within the density functional theory. In agreement with the experiment the calculations find a total energy minimum formore » the oxygen (2 x 2) structure. The interaction between H and O atoms was found to be repulsive and short ranged, leading to a compression of the O islands from (2 x 2) to ({radical}3 x {radical}3)R30 degree ordered structure at high H coverage. The computed energy barriers for the oxygen diffusion were found to be reduced due to the coadsorption of hydrogen, in agreement with the experimentally observed enhancement of oxygen mobility. The calculations also support the finding that at low temperatures the water formation reaction does not occur on Pd(1 1 1).« less

SIMS study of oxygen diffusion in monoclinic HfO2

NASA Astrophysics Data System (ADS)

Mueller, Michael P.; De Souza, Roger A.

2018-01-01

The diffusion of oxygen in dense ceramics of monoclinic HfO2 was studied by means of (18O/16O) isotope exchange annealing and subsequent determination of isotope depth profiles by Secondary Ion Mass Spectrometry. Anneals were performed in the temperature range of 573 ≤T /K ≤ 973 at an oxygen partial pressure of p O2=200 mbar . All measured isotope profiles exhibited two features: the first feature, closer to the surface, was attributed mainly to slow oxygen diffusion in an impurity silicate phase; the second feature, deeper in the sample, was attributed to oxygen diffusion in bulk monoclinic HfO2 . The activation enthalpy of oxygen tracer diffusion in bulk HfO2 was found to be ΔHD∗≈0.5 eV .

Scaling oxygen microprofiles at the sediment interface of deep stratified waters

NASA Astrophysics Data System (ADS)

Schwefel, Robert; Hondzo, Miki; Wüest, Alfred; Bouffard, Damien

2017-02-01

Dissolved oxygen microprofiles at the sediment-water interface of Lake Geneva were measured concurrently with velocities 0.25 to 2 m above the sediment. The measurements and scaling analyses indicate dissolved oxygen fluctuations and turbulent fluxes in exceedance of molecular diffusion in the proximity of the sediment-water interface. The measurements allowed the parameterization of the turbulent diffusion as a function of the dimensionless height above the sediment and the turbulence above the sediment-water interface. Turbulent diffusion depended strongly on the friction velocity and differed from formulations reported in the literature that are based on concepts of turbulent and developed wall-bounded flows. The dissolved oxygen microprofiles and proposed parameterization of turbulent diffusion enable a foundation for the similarity scaling of oxygen microprofiles in proximity to the sediment. The proposed scaling allows the estimation of diffusive boundary layer thickness, oxygen flux, and oxygen microprofile distribution in the near-sediment boundary layer.

Solid state oxygen sensor

DOEpatents

Garzon, F.H.; Chung, B.W.; Raistrick, I.D.; Brosha, E.L.

1996-08-06

Solid state oxygen sensors are provided with a yttria-doped zirconia as an electrolyte and use the electrochemical oxygen pumping of the zirconia electrolyte. A linear relationship between oxygen concentration and the voltage arising at a current plateau occurs when oxygen accessing the electrolyte is limited by a diffusion barrier. A diffusion barrier is formed herein with a mixed electronic and oxygen ion-conducting membrane of lanthanum-containing perovskite or zirconia-containing fluorite. A heater may be used to maintain an adequate oxygen diffusion coefficient in the mixed conducting layer. 4 figs.

Fast oxygen diffusion in bismuth oxide probed by quasielastic neutron scattering

DOE PAGES

Mamontov, Eugene

2016-09-24

In this paper, we present the first, to our knowledge, study of solid state oxygen translational diffusion by quasielastic neutron scattering. Such studies in the past might have been precluded by relatively low diffusivities of oxygen anions in the temperature range amenable to neutron scattering experiments. To explore the potential of the quasielastic scattering technique, which can deduce atomic diffusion jump length of oxygen anions through the momentum transfer dependence of the scattering signal, we have selected the fastest known oxygen conductor, bismuth oxide. Finally, we have found the oxygen anion jump length in excellent agreement with the nearest oxygen-vacancymore » distance in the anion sublattice of the fluorite-related structure of bismuth oxide.« less

Kinetic Monte Carlo Simulation of Oxygen Diffusion in Ytterbium Disilicate

NASA Astrophysics Data System (ADS)

Good, Brian

2015-03-01

Ytterbium disilicate is of interest as a potential environmental barrier coating for aerospace applications, notably for use in next generation jet turbine engines. In such applications, the diffusion of oxygen and water vapor through these coatings is undesirable if high temperature corrosion is to be avoided. In an effort to understand the diffusion process in these materials, we have performed kinetic Monte Carlo simulations of vacancy-mediated oxygen diffusion in Ytterbium Disilicate. Oxygen vacancy site energies and diffusion barrier energies are computed using Density Functional Theory. We find that many potential diffusion paths involve large barrier energies, but some paths have barrier energies smaller than one electron volt. However, computed vacancy formation energies suggest that the intrinsic vacancy concentration is small in the pure material, with the result that the material is unlikely to exhibit significant oxygen permeability.

Effect of Normobaric versus Hypobaric Oxygenation on Gaseous Microemboli Removal in a Diffusion Membrane Oxygenator: An In Vitro Comparison

PubMed Central

Schuldes, Matthew; Riley, Jeffrey B.; Francis, Stephen G.; Clingan, Sean

2016-01-01

Abstract: Gaseous microemboli (GME) are an abnormal physiological occurrence during cardiopulmonary bypass and extracorporeal membrane oxygenation (ECMO). Several studies have correlated negative sequelae with exposure to increased amounts of GME. Hypobaric oxygenation is effective at eliminating GME in hollow-fiber microporous membrane oxygenators. However, hollow-fiber diffusion membrane oxygenators, which are commonly used for ECMO, have yet to be validated. The purpose of this study was to determine if hypobaric oxygenation, compared against normobaric oxygenation, can reduce introduced GME when used on diffusion membrane oxygenators. Comparison of a sealed Quadrox-iD with hypobaric sweep gas (.67 atm) vs. an unmodified Quadrox-iD with normal atmospheric sweep gas (1 atm) in terms of GME transmission during continuous air introduction (50 mL/min) in a recirculating in vitro circuit, over a range of flow rates (3.5, 5 L/min) and crystalloid prime temperatures (37°C, 28°C, and 18°C). GME were measured using three EDAC Doppler probes positioned pre-oxygenator, post-oxygenator, and at the arterial cannula. Hypobaric oxygenation vs. normobaric oxygenation significantly reduced hollow-fiber diffusion membrane oxygenator GME transmission at all combination of pump flows and temperatures. There was further significant reduction in GME count between the oxygenator outlet and at the arterial cannula. Hypobaric oxygenation used on hollow-fiber diffusion membrane oxygenators can further reduce GME compared to normobaric oxygenation. This technique may be a safe approach to eliminate GME during ECMO. PMID:27729706

Carbon, oxygen and their interaction with intrinsic point defects in solar silicon ribbon material: A speculative approach

NASA Technical Reports Server (NTRS)

Goesele, U.; Ast, D. G.

1983-01-01

Some background information on intrinsic point defects is provided and on carbon and oxygen in silicon in so far as it may be relevant for the efficiency of solar cells fabricated from EFG ribbon material. The co-precipitation of carbon and oxygen and especially of carbon and silicon self interstitials are discussed. A simple model for the electrical activity of carbon-self-interstitial agglomerates is presented. The self-interstitial content of these agglomerates is assumed to determine their electrical activity and that both compressive stresses (high self-interstitial content) and tensile stresses (low self-interstitial content) give rise to electrical activity of the agglomerates. The self-interstitial content of these carbon-related agglomerates may be reduced by an appropriate high temperature treatment and enhanced by a supersaturation of self-interstitials generated during formation of the p-n junction of solar cells. Oxygen present in supersaturation in carbon-rich silicon may be induced to form SiO, precipitates by self-interstitials generated during phosphorus diffusion. It is proposed that the SiO2-Si interface of the precipates gives rise to a continuum of donor stables and that these interface states are responsible for at least part of the light inhancement effects observed in oxygen containing EFG silicon after phosphorus diffusion.

Effect of hypolimnetic oxygenation on oxygen depletion rates in two water-supply reservoirs.

PubMed

Gantzer, Paul A; Bryant, Lee D; Little, John C

2009-04-01

Oxygenation systems, such as bubble-plume diffusers, are used to improve water quality by replenishing dissolved oxygen (DO) in the hypolimnia of water-supply reservoirs. The diffusers induce circulation and mixing, which helps distribute DO throughout the hypolimnion. Mixing, however, has also been observed to increase hypolimnetic oxygen demand (HOD) during system operation, thus accelerating oxygen depletion. Two water-supply reservoirs (Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR)) that employ linear bubble-plume diffusers were studied to quantify diffuser effects on HOD. A recently validated plume model was used to predict oxygen addition rates. The results were used together with observed oxygen accumulation rates to evaluate HOD over a wide range of applied gas flow rates. Plume-induced mixing correlated well with applied gas flow rate and was observed to increase HOD. Linear relationships between applied gas flow rate and HOD were found for both SHR and CCR. HOD was also observed to be independent of bulk hypolimnion oxygen concentration, indicating that HOD is controlled by induced mixing. Despite transient increases in HOD, oxygenation caused an overall decrease in background HOD, as well as a decrease in induced HOD during diffuser operation, over several years. This suggests that the residual or background oxygen demand decreases from one year to the next. Despite diffuser-induced increases in HOD, hypolimnetic oxygenation remains a viable method for replenishing DO in thermally-stratified water-supply reservoirs such as SHR and CCR.

Insights into the role of wettability in cathode catalyst layer of proton exchange membrane fuel cell; pore scale immiscible flow and transport processes

NASA Astrophysics Data System (ADS)

Fathi, H.; Raoof, A.; Mansouri, S. H.

2017-05-01

The production of liquid water in cathode catalyst layer, CCL, is a significant barrier to increase the efficiency of proton exchange membrane fuel cell. Here we present, for the first time, a direct three-dimensional pore-scale modelling to look at the complex immiscible two-phase flow in CCL. After production of the liquid water at the surface of CCL agglomerates due to the electrochemical reactions, water spatial distribution affects transport of oxygen through the CCL as well as the rate of reaction at the agglomerate surfaces. To explore the wettability effects, we apply hydrophilic and hydrophobic properties using different surface contact angles. Effective diffusivity is calculated under several water saturation levels. Results indicate larger diffusive transport values for hydrophilic domain compared to the hydrophobic media where the liquid water preferentially floods the larger pores. However, hydrophobic domain showed more available surface area and higher oxygen consumption rate at the reaction sites under various saturation levels, which is explained by the effect of wettability on pore-scale distribution of water. Hydrophobic domain, with a contact angle of 150, reveals efficient water removal where only 28% of the pore space stays saturated. This condition contributes to the enhanced available reaction surface area and oxygen diffusivity.

Oxygen transport enhancement by functionalized magnetic nanoparticles (FMP) in bioprocesses

NASA Astrophysics Data System (ADS)

Ataide, Filipe Andre Prata

The enhancement of fluid properties, namely thermal conductivity and mass diffusivity for a wide range of applications, through the use of nanosized particles' suspensions has been gathering increasing interest in the scientific community. In previous studies, Olle et al. (2006) showed an enhancement in oxygen absorption to aqueous solutions of up to 6-fold through the use of functionalized nanosized magnetic particles with oleic acid coating. Krishnamurthy et al. (2006) showed a remarkable 26-fold enhancement in dye diffusion in water. These two publications are landmarks in mass transfer enhancement in chemical systems through the use of nanoparticles. The central goal of this Ph.D. thesis was to develop functionalized magnetic nanoparticles to enhance oxygen transport in bioprocesses. The experimental protocol for magnetic nanoparticles synthesis and purification adopted in this thesis is a modification of that reported by Olle et al. (2006). This is facilitated by employing twice the quantity of ammonia, added at a slower rate, and by filtering the final nanoparticle solution in a cross-flow filtration modulus against 55 volumes of distilled water. This modification in the protocol resulted in improved magnetic nanoparticles with measurably higher mass transfer enhancement. Magnetic nanoparticles with oleic acid and Hitenol-BC coating were screened for oxygen transfer enhancement, since these particles are relatively inexpensive and easy to synthesize. A glass 0.5-liter reactor was custom manufactured specifically for oxygen transport studies in magnetic nanoparticles suspensions. The reactor geometry, baffles and Rushton impeller are of standard dimensions. Mass transfer tests were conducted through the use of the sulphite oxidation method, applying iodometric back-titration. A 3-factor central composite circumscribed design (CCD) was adopted for design of experiments in order to generate sufficiently informative data to model the effect of magnetic nanoparticles on interfacial area and mass transfer coefficient. The parameters ranges used were: 250-750 rpm for stirring speed, 0-2 vvm for aeration and 0-0.00120 g g?1 magnetic nanoparticles mass fraction. It was found that 36 nm-sized nanoparticles produced during the course of this dissertation enhanced the volumetric mass transfer coefficient up to 3.3-fold and the interfacial area up to 3.3-fold in relation to gas-liquid dispersions without nanoparticles. These results are concordant with previously published enhancement data (kLa enhancement by 7.1-fold and a enhancement by 4.1-fold) (Olle et al. 2006). The magnetic nanoparticles synthesized in this thesis were stable (constant diameter) over a 1wide pH range (2-9). Statistical regression models showed that both kLa and a have high sensitivity to the nanoparticles loading. Empirical correlation models were derived for kLa and for interfacial area, a, as function of physical properties and nanoparticles loading. These correlations lay out a methodology that can help the scientific community to design and scale-up oxygen transfer systems that are based on nanoparticle suspensions. None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None

Oxygen diffusion in nanocrystalline yttria-stabilized zirconia: the effect of grain boundaries.

PubMed

De Souza, Roger A; Pietrowski, Martha J; Anselmi-Tamburini, Umberto; Kim, Sangtae; Munir, Zuhair A; Martin, Manfred

2008-04-21

The transport of oxygen in dense samples of yttria-stabilized zirconia (YSZ), of average grain size d approximately 50 nm, has been studied by means of 18O/16O exchange annealing and secondary ion mass spectrometry (SIMS). Oxygen diffusion coefficients (D*) and oxygen surface exchange coefficients (k*) were measured for temperatures 673

Molecular dynamics analysis of diffusion of uranium and oxygen ions in uranium dioxide

NASA Astrophysics Data System (ADS)

Arima, T.; Yoshida, K.; Idemitsu, K.; Inagaki, Y.; Sato, I.

2010-03-01

Diffusion behaviours of oxygen and uranium were evaluated for bulk and grain-boundaries of uranium dioxide using the molecular dynamics (MD) simulation. It elucidated that oxygen behaved like liquid in superionic state at high temperatures and migrated on sub-lattice sites accompanying formation of lattice defects such as Frenkel defects at middle temperatures. Formation energies of Frenkel and Shottky defects were compared to literature data, and migration energies of oxygen and uranium were estimated by introducing vacancies into the supercell. For grain-boundaries (GB) modelled by the coincidence-site lattice theory, MD calculations showed that GB energy and diffusivities of oxygen and uranium increased with the misorientation angle. By analysing GB structures such as pair-correlation functions, it also showed that the disordered phase was observed for uranium as well as oxygen in GBs especially for a large misorientation angle such as S5 GB. Hence, GB diffusion was much larger than bulk diffusion for oxygen and uranium.

Enhanced Organic Solar Cell Stability through the Effective Blocking of Oxygen Diffusion using a Self-Passivating Metal Electrode.

PubMed

Lee, Hansol; Jo, Sae Byeok; Lee, Hyo Chan; Kim, Min; Sin, Dong Hun; Ko, Hyomin; Cho, Kilwon

2016-03-08

A new and simple strategy for enhancing the stability of organic solar cells (OSCs) was developed by using self-passivating metal top electrodes. Systematic investigations on O2 permeability of Al top electrodes revealed that the main pathways for oxidation-induced degradation could be greatly suppressed by simply controlling the nanoscale morphology of the Al electrode. The population of nanoscale pinholes among Al grains, which critically decided the diffusion of O2 molecules toward the Al-organic interfaces that are vulnerable to oxidation, was successfully regulated by rapidly depositing Al or promoting lateral growth among the Al grains, accompanied by increasing the deposition thickness. Our observations suggested that the stability of OSCs with conventional architectures might be greatly enhanced simply by controlling the fabrication conditions of the Al top electrode, without the aid of additional secondary treatments. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Insensitivity of cerebral oxygen transport to oxygen affinity of hemoglobin-based oxygen carriers

PubMed Central

Koehler, Raymond C.; Fronticelli, Clara; Bucci, Enrico

2008-01-01

The cerebrovascular effects of exchange transfusion of various cell-free hemoglobins that possess different oxygen affinities are reviewed. Reducing hematocrit by transfusion of a non-oxygen-carrying solution dilates pial arterioles on the brain surface and increases cerebral blood flow to maintain a constant bulk oxygen transport to the brain. In contrast, transfusion of hemoglobins with P50 of 4–34 Torr causes constriction of pial arterioles that offsets the decrease in blood viscosity to maintain cerebral blood flow and oxygen transport. The autoregulatory constriction is dependent on synthesis of 20-HETE from arachidonic acid. This oxygen-dependent reaction is apparently enhanced by facilitated oxygen diffusion from the red cell to the endothelium arising from increased plasma oxygen solubility in the presence of low or high-affinity hemoglobin. Exchange transfusion of recombinant hemoglobin polymers with P50 of 3 and 18 Torr reduces infarct volume from experimental stroke. Cell-free hemoglobins do not require a P50 as high as red blood cell hemoglobin to facilitate oxygen delivery. PMID:18230370

A Role of the Reaction Kernel in Propagation and Stabilization of Edge Diffusion Flames of C1-C3 Hydrocarbons

NASA Technical Reports Server (NTRS)

Takahashi, Fumiaki; Katta, Viswanath R.

2003-01-01

Diffusion flame stabilization is of essential importance in both Earth-bound combustion systems and spacecraft fire safety. Local extinction, re-ignition, and propagation processes may occur as a result of interactions between the flame zone and vortices or fire-extinguishing agents. By using a computational fluid dynamics code with a detailed chemistry model for methane combustion, the authors have revealed the chemical kinetic structure of the stabilizing region of both jet and flat-plate diffusion flames, predicted the flame stability limit, and proposed diffusion flame attachment and detachment mechanisms in normal and microgravity. Because of the unique geometry of the edge of diffusion flames, radical back-diffusion against the oxygen-rich entrainment dramatically enhanced chain reactions, thus forming a peak reactivity spot, i.e., reaction kernel, responsible for flame holding. The new results have been obtained for the edge diffusion flame propagation and attached flame structure using various C1-C3 hydrocarbons.

Study of Oxygen Diffusion in Reduced LiNbO3 Crystals

NASA Astrophysics Data System (ADS)

Yatsenko, A. V.; Pritulenko, A. S.; Yagupov, S. V.; Sugak, D. Yu.; Sol'skii, I. M.

2018-03-01

Using the method of impedance spectroscopy and optical density measurements, the diffusion of oxygen in single crystals of lithium niobate of the congruent composition after the reductive thermochemical processing is studied. The parameters describing the diffusion of oxygen in the temperature range 493-693 K are established.

Modelling oxygen self-diffusion in UO 2 under pressure

DOE PAGES

Cooper, Michael William D.; Grimes, R. W.; Fitzpatrick, M. E.; ...

2015-10-22

Access to values for oxygen self-diffusion over a range of temperatures and pressures in UO 2 is important to nuclear fuel applications. Here, elastic and expansivity data are used in the framework of a thermodynamic model, the cBΩ model, to derive the oxygen self-diffusion coefficient in UO 2 over a range of pressures (0–10 GPa) and temperatures (300–1900 K). Furthermore, the significant reduction in oxygen self-diffusion as a function of increasing hydrostatic pressure, and the associated increase in activation energy, is identified.

Oxygen transport in off-stoichiometric uranium dioxide mediated by defect clustering dynamics

DOE PAGES

Yu, Jianguo; Bai, Xian -Ming; El-Azab, Anter; ...

2015-03-05

In this study, oxygen transport is central to many properties of oxides such as stoichiometric changes, phase transformation and ionic conductivity. In this paper, we report a mechanism for oxygen transport in uranium dioxide (UO 2) in which the kinetics is mediated by defect clustering dynamics. In particular, the kinetic Monte Carlo (KMC) method has been used to investigate the kinetics of oxygen transport in UO 2 under the condition of creation and annihilation of oxygen vacancies and interstitials as well as oxygen interstitial clustering, with variable offstoichiometry and temperature conditions. It is found that in hypo-stoichiometric UO 2-x, oxygenmore » transport is well described by the vacancy diffusion mechanism while in hyper-stoichiometric UO 2+x, oxygen interstitial cluster diffusion contributes significantly to oxygen transport kinetics, particularly at high temperatures and high off-stoichiometry levels. It is also found that diinterstitial clusters and single interstitials play dominant roles in oxygen diffusion while other larger clusters have negligible contributions. However, the formation, coalescence and dissociation of these larger clusters indirectly affects the overall oxygen diffusion due to their interactions with mono and di-interstitials, thus providing a explanation of the experimental observation of saturation or even drop of oxygen diffusivity at high off-stoichiometry.« less

Effect of cation structure on the oxygen solubility and diffusivity in a range of bis{(trifluoromethyl)sulfonyl}imide anion based ionic liquids for lithium-air battery electrolytes.

PubMed

Neale, Alex R; Li, Peilin; Jacquemin, Johan; Goodrich, Peter; Ball, Sarah C; Compton, Richard G; Hardacre, Christopher

2016-04-28

This paper reports on the solubility and diffusivity of dissolved oxygen in a series of ionic liquids (ILs) based on the bis{(trifluoromethyl)sulfonyl}imide anion with a range of related alkyl and ether functionalised cyclic alkylammonium cations. Cyclic voltammetry has been used to observe the reduction of oxygen in ILs at a microdisk electrode and chronoamperometric measurements have then been applied to simultaneously determine both the concentration and the diffusion coefficient of oxygen in different ILs. The viscosity of the ILs and the calculated molar volume and free volume are also reported. It is found that, within this class of ILs, the oxygen diffusivity generally increases with decreasing viscosity of the neat IL. An inverse relationship between oxygen solubility and IL free volume is reported for the two IL families implying that oxygen is not simply occupying the available empty space. In addition, it is reported that the introduction of an ether-group into the IL cation structure promotes the diffusivity of dissolved oxygen but reduces the solubility of the gas.

Hemoglobin diffusion and the dynamics of oxygen capture by red blood cells.

PubMed

Longeville, Stéphane; Stingaciu, Laura-Roxana

2017-09-05

Translational diffusion of macromolecules in cell is generally assumed to be anomalous due high macromolecular crowding of the milieu. Red blood cells are a special case of cells filled quasi exclusively (95% of the dry weight of the cell) with an almost spherical protein: hemoglobin. Hemoglobin diffusion has since a long time been recognized as facilitating the rate of oxygen diffusion through a solution. We address in this paper the question on how hemoglobin diffusion in the red blood cells can help the oxygen capture at the cell level and hence to improve oxygen transport. We report a measurement by neutron spin echo spectroscopy of the diffusion of hemoglobin in solutions with increasing protein concentration. We show that hemoglobin diffusion in solution can be described as Brownian motion up to physiological concentration and that hemoglobin diffusion in the red blood cells and in solutions at similar concentration are the same. Finally, using a simple model and the concentration dependence of the diffusion of the protein reported here, we show that hemoglobin concentration observed in human red blood cells ([Formula: see text]330 g.L -1 ) corresponds to an optimum for oxygen transport for individuals under strong activity.

Hemoglobin diffusion and the dynamics of oxygen capture by red blood cells

DOE PAGES

Longeville, Stéphane; Stingaciu, Laura-Roxana

2017-09-05

Translational diffusion of macromolecules in cell is generally assumed to be anomalous due high macromolecular crowding of the milieu. Red blood cells are a special case of cells filled quasi exclusively (95% of the dry weight of the cell) with an almost spherical protein: hemoglobin. Hemoglobin diffusion has since a long time been recognized as facilitating the rate of oxygen diffusion through a solution. We address in this paper the question on how hemoglobin diffusion in the red blood cells can help the oxygen capture at the cell level and hence to improve oxygen transport. We report a measurement bymore » neutron spin echo spectroscopy of the diffusion of hemoglobin in solutions with increasing protein concentration. We show that hemoglobin diffusion in solution can be described as Brownian motion up to physiological concentration and that hemoglobin diffusion in the red blood cells and in solutions at similar concentration are the same. Finally, using a simple model and the concentration dependence of the diffusion of the protein reported here, we show that hemoglobin concentration observed in human red blood cells (≃330 g.L -1) corresponds to an optimum for oxygen transport for individuals under strong activity.« less

Hemoglobin diffusion and the dynamics of oxygen capture by red blood cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Longeville, Stéphane; Stingaciu, Laura-Roxana

Translational diffusion of macromolecules in cell is generally assumed to be anomalous due high macromolecular crowding of the milieu. Red blood cells are a special case of cells filled quasi exclusively (95% of the dry weight of the cell) with an almost spherical protein: hemoglobin. Hemoglobin diffusion has since a long time been recognized as facilitating the rate of oxygen diffusion through a solution. We address in this paper the question on how hemoglobin diffusion in the red blood cells can help the oxygen capture at the cell level and hence to improve oxygen transport. We report a measurement bymore » neutron spin echo spectroscopy of the diffusion of hemoglobin in solutions with increasing protein concentration. We show that hemoglobin diffusion in solution can be described as Brownian motion up to physiological concentration and that hemoglobin diffusion in the red blood cells and in solutions at similar concentration are the same. Finally, using a simple model and the concentration dependence of the diffusion of the protein reported here, we show that hemoglobin concentration observed in human red blood cells (≃330 g.L -1) corresponds to an optimum for oxygen transport for individuals under strong activity.« less

Enhancement of oxygen transfer and nitrogen removal in a membrane separation bioreactor for domestic wastewater treatment.

PubMed

Chiemchaisri, C; Yamamoto, K

2005-01-01

Biological nitrogen removal in a membrane separation bioreactor developed for on-site domestic wastewater treatment was investigated. The bioreactor employed hollow fiber membrane modules for solid-liquid separation so that the biomass could be completely retained within the system. Intermittent aeration was supplied with 90 minutes on and off cycle to achieve nitrification and denitrification reaction for nitrogen removal. High COD and nitrogen removal of more than 90% were achieved under a moderate temperature of 25 degrees C. As the temperature was stepwise decreased from 25 to 5 degrees C, COD removal in the system could be constantly maintained while nitrogen removal was deteriorated. Nevertheless, increasing aeration supply could enhance nitrification at low temperature with benefit from complete retention of nitrifying bacteria within the system by membrane separation. At low operating temperature range of 5 degrees C, nitrogen removal could be recovered to more than 85%. A mathematical model considering diffusion resistance of limiting substrate into the bio-particle is applied to describe nitrogen removal in a membrane separation bioreactor. The simulation suggested that limitation of the oxygen supply was the major cause of inhibition of nitrification during temperature decrease. Nevertheless, increasing aeration could promote oxygen diffusion into the bio-particle. Sufficient oxygen was supplied to the nitrifying bacteria and the nitrification could proceed. In the membrane separation bioreactor, biomass concentration under low temperature operation was allowed to increase by 2-3 times of that of moderate temperature to compensate for the loss of bacterial activities so that the temperature effect was masked.

Integrative Conductance of Oxygen During Exercise at Altitude.

PubMed

Calbet, José A L; Lundby, Carsten; Boushel, Robert

2016-01-01

In the oxygen (O2) cascade downstream steps can never achieve higher flows of O2 than the preceding ones. At the lung the transfer of O2 is determined by the O2 gradient between the alveolar space and the lung capillaries and the O2 diffusing capacity (DLO2). While DLO2 may be increased several times during exercise by recruiting more lung capillaries and by increasing the oxygen carrying capacity of blood due to higher peripheral extraction of O2, the capacity to enhance the alveolocapillary PO2 gradient is more limited. The transfer of oxygen from the alveolar space to the hemoglobin (Hb) must overcome first the resistance offered by the alveolocapillary membrane (1/DM) and the capillary blood (1/θVc). The fractional contribution of each of these two components to DLO2 remains unknown. During exercise these resistances are reduced by the recruitment of lung capillaries. The factors that reduce the slope of the oxygen dissociation curve of the Hb (ODC) (i.e., lactic acidosis and hyperthermia) increase 1/θVc contributing to limit DLO2. These effects are accentuated in hypoxia. Reducing the size of the active muscle mass improves pulmonary gas exchange during exercise and reduces the rightward shift of the ODC. The flow of oxygen from the muscle capillaries to the mitochondria is pressumably limited by muscle O2 conductance (DmcO2) (an estimation of muscle oxygen diffusing capacity). However, during maximal whole body exercise in normoxia, a higher flow of O2 is achieved at the same pressure gradients after increasing blood [Hb], implying that in healthy humans exercising in normoxia there is a functional reserve in DmcO2. This conclusion is supported by the fact that during small muscle exercise in chronic hypoxia, peak exercise DmcO2 is similar to that observed during exercise in normoxia despite a markedly lower O2 pressure gradient driving diffusion.

On the mobility of carriers at semi-coherent oxide heterointerfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dholabhai, Pratik P.; Martinez, Enrique Saez; Brown, Nicholas Taylor

In the quest to develop new materials with enhanced ionic conductivity for battery and fuel cell applications, nano-structured oxides have attracted attention. Experimental reports indicate that oxide heterointerfaces can lead to enhanced ionic conductivity, but these same reports cannot elucidate the origin of this enhancement, often vaguely referring to pipe diffusion at misfit dislocations as a potential explanation. However, this highlights the need to understand the role of misfit dislocation structure at semi-coherent oxide heterointerfaces in modifying carrier mobilities. Here, we use atomistic and kinetic Monte Carlo (KMC) simulations to develop a model of oxygen vacancy migration at SrTiO 3/MgOmore » interfaces, chosen because the misfit dislocation structure can be modified by changing the termination chemistry. We use atomistic simulations to determine the energetics of oxygen vacancies at both SrO and TiO 2 terminated interfaces, which are then used as the basis of the KMC simulations. While this model is approximate (as revealed by select nudged elastic band calculations), it highlights the role of the misfit dislocation structure in modifying the oxygen vacancy dynamics. We find that oxygen vacancy mobility is significantly reduced at either interface, with slight differences at each interface due to the differing misfit dislocation structure. Here, we conclude that if such semi-coherent oxide heterointerfaces induce enhanced ionic conductivity, it is not a consequence of higher carrier mobility.« less

On the mobility of carriers at semi-coherent oxide heterointerfaces

DOE PAGES

Dholabhai, Pratik P.; Martinez, Enrique Saez; Brown, Nicholas Taylor; ...

2017-08-17

In the quest to develop new materials with enhanced ionic conductivity for battery and fuel cell applications, nano-structured oxides have attracted attention. Experimental reports indicate that oxide heterointerfaces can lead to enhanced ionic conductivity, but these same reports cannot elucidate the origin of this enhancement, often vaguely referring to pipe diffusion at misfit dislocations as a potential explanation. However, this highlights the need to understand the role of misfit dislocation structure at semi-coherent oxide heterointerfaces in modifying carrier mobilities. Here, we use atomistic and kinetic Monte Carlo (KMC) simulations to develop a model of oxygen vacancy migration at SrTiO 3/MgOmore » interfaces, chosen because the misfit dislocation structure can be modified by changing the termination chemistry. We use atomistic simulations to determine the energetics of oxygen vacancies at both SrO and TiO 2 terminated interfaces, which are then used as the basis of the KMC simulations. While this model is approximate (as revealed by select nudged elastic band calculations), it highlights the role of the misfit dislocation structure in modifying the oxygen vacancy dynamics. We find that oxygen vacancy mobility is significantly reduced at either interface, with slight differences at each interface due to the differing misfit dislocation structure. Here, we conclude that if such semi-coherent oxide heterointerfaces induce enhanced ionic conductivity, it is not a consequence of higher carrier mobility.« less

Enhancement of activity of RuSex electrocatalyst by modification with nanostructured iridium towards more efficient reduction of oxygen

NASA Astrophysics Data System (ADS)

Dembinska, Beata; Kiliszek, Malgorzata; Elzanowska, Hanna; Pisarek, Marcin; Kulesza, Pawel J.

2013-12-01

Electrocatalytic activity of carbon (Vulcan XC-72) supported selenium-modified ruthenium, RuSex/C, nanoparticles for reduction of oxygen was enhanced through intentional decoration with iridium nanostructures (dimensions, 2-3 nm). The catalytic materials were characterized in oxygenated 0.5 mol dm-3 H2SO4 using cyclic and rotating ring disk voltammetric techniques as well as using transmission electron microscopy and scanning electron microscopy equipped with X-ray dispersive analyzer. Experiments utilizing gas diffusion electrode aimed at mimicking conditions existing in the low-temperature fuel cell. Upon application of our composite catalytic system, the reduction of oxygen proceeded at more positive potentials, and higher current densities were observed when compared to the behavior of the simple iridium-free system (RuSex/C) investigated under the analogous conditions. The enhancement effect was more pronounced than that one would expect from simple superposition of voltammetric responses for the oxygen reduction at RuSex/C and iridium nanostructures studied separately. Nanostructured iridium acted here as an example of a powerful catalyst for the reduction of H2O2 (rather than O2) and, when combined with such a moderate catalyst as ruthenium-selenium (for O2 reduction), it produced an integrated system of increased electrocatalytic activity in the oxygen reduction process. The proposed system retained its activity in the presence of methanol that could appear in a cathode compartment of alcohol fuel cell.

Density functional study on the mechanism for the highly active palladium monolayer supported on titanium carbide for the oxygen reduction reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Jianjun; Zhang, Yanxing; Chu, Xingli

2016-05-28

The adsorption, diffusion, and dissociation of O{sub 2} on the palladium monolayer supported on TiC(001) surface, MLPd/TiC(001), are investigated using ab initio density functional theory calculations. Strong adhesion of palladium monolayer to the TiC(001) support, accompanied by a modification of electronic structure of the supported palladium, is evidenced. Compared with Pt(111) surface, the MLPd/TiC(001) can enhance the adsorption of O{sub 2}, leading to comparable dissociation barrier and a smaller diffusion barrier of O{sub 2}. Whilst the adsorption strength of atomic O (the dissociation product of O{sub 2}) on MLPd/TiC(001) is similar to that on the Pt(111) surface, possessing high mobility,more » our theoretical results indicate that MLPd/TiC(001) may serve as a good catalyst for the oxygen reduction reaction.« less

Study on low intensity aeration oxygenation model and optimization for shallow water

NASA Astrophysics Data System (ADS)

Chen, Xiao; Ding, Zhibin; Ding, Jian; Wang, Yi

2018-02-01

Aeration/oxygenation is an effective measure to improve self-purification capacity in shallow water treatment while high energy consumption, high noise and expensive management refrain the development and the application of this process. Based on two-film theory, the theoretical model of the three-dimensional partial differential equation of aeration in shallow water is established. In order to simplify the equation, the basic assumptions of gas-liquid mass transfer in vertical direction and concentration diffusion in horizontal direction are proposed based on engineering practice and are tested by the simulation results of gas holdup which are obtained by simulating the gas-liquid two-phase flow in aeration tank under low-intensity condition. Based on the basic assumptions and the theory of shallow permeability, the model of three-dimensional partial differential equations is simplified and the calculation model of low-intensity aeration oxygenation is obtained. The model is verified through comparing the aeration experiment. Conclusions as follows: (1)The calculation model of gas-liquid mass transfer in vertical direction and concentration diffusion in horizontal direction can reflect the process of aeration well; (2) Under low-intensity conditions, the long-term aeration and oxygenation is theoretically feasible to enhance the self-purification capacity of water bodies; (3) In the case of the same total aeration intensity, the effect of multipoint distributed aeration on the diffusion of oxygen concentration in the horizontal direction is obvious; (4) In the shallow water treatment, reducing the volume of aeration equipment with the methods of miniaturization, array, low-intensity, mobilization to overcome the high energy consumption, large size, noise and other problems can provide a good reference.

Image-based 3D modeling study of the influence of vessel density and blood hemoglobin concentration on tumor oxygenation and response to irradiation.

PubMed

Lagerlöf, Jakob H; Kindblom, Jon; Cortez, Eliane; Pietras, Kristian; Bernhardt, Peter

2013-02-01

Hypoxia is one of the most important factors influencing clinical outcome after radiotherapy. Improved knowledge of factors affecting the levels and distribution of oxygen within a tumor is needed. The authors constructed a theoretical 3D model based on histological images to analyze the influence of vessel density and hemoglobin (Hb) concentration on the response to irradiation. The pancreases of a Rip-Tag2 mouse, a model of malignant insulinoma, were excised, cryosectioned, immunostained, and photographed. Vessels were identified by image thresholding and a 3D vessel matrix assembled. The matrix was reduced to functional vessel segments and enlarged by replication. The steady-state oxygen tension field of the tumor was calculated by iteratively employing Green's function method for diffusion and the Michaelis-Menten model for consumption. The impact of vessel density on the radiation response was studied by removing a number of randomly selected vessels. The impact of Hb concentration was studied by independently changing vessel oxygen partial pressure (pO(2)). For each oxygen distribution, the oxygen enhancement ratio (OER) was calculated and the mean absorbed dose at which the tumor control probability (TCP) was 0.99 (D(99)) was determined using the linear-quadratic cell survival model (LQ model). Decreased pO(2) shifted the oxygen distribution to lower values, whereas decreased vessel density caused the distribution to widen and shift to lower values. Combined scenarios caused lower-shifted distributions, emphasising log-normal characteristics. Vessel reduction combined with increased blood pO(2) caused the distribution to widen due to a lack of vessels. The most pronounced radiation effect of increased pO(2) occurred with tumor tissue with 50% of the maximum vessel density used in the simulations. A 51% decrease in D(99), from 123 to 60 Gy, was found between the lowest and highest pO(2) concentrations. Our results indicate that an intermediate vascular density region exists where enhanced blood oxygen concentration may be beneficial for radiation response. The results also suggest that it is possible to distinguish between diffusion-limited and anemic hypoxia from the characteristics of the pO(2) distribution.

Oxygen precipitation and bulk microdefects induced by the pre- and postepitaxial annealing in N/N + (100) silicon wafers

NASA Astrophysics Data System (ADS)

Wijaranakula, W.; Matlock, J. H.; Mollenkopf, H.

1987-12-01

Substrate wafers used for fabrication of epitaxial silicon wafers heavily doped with antimony at the concentration of 1020 atoms/cm3 were preannealed at a temperature between 500 and 900 °C prior to epitaxial deposition. Device fabrication thermal simulation was performed by heat treating the preannealed epitaxial wafers at 1050 °C in dry oxygen ambient for 16 h. Postepitaxial nucleation heat treatment at 750 °C for 4 h prior to the 1050 °C heat treament cycle was also applied on some epitaxial wafers for the purpose of enhancing the oxygen precipitation in silicon. It was observed that morphology and density of the bulk defects induced by the thermal treatment are affected by the preannealing temperature. The results also indicate that nucleation and growth kinetics of oxygen precipitates in preannealed n+ degenerate silicon substrate is strongly governed by oxygen and point defect diffusion.

Dopant-Modulating Mechanism of Lithium Adsorption and Diffusion at the Graphene /Li2S Interface

NASA Astrophysics Data System (ADS)

Guo, Lichao; Li, Jiajun; Wang, Huayu; Zhao, Naiqin; Shi, Chunsheng; Ma, Liying; He, Chunnian; He, Fang; Liu, Enzuo

2018-02-01

Graphene modification is one of the most effective routes to enhance the electrochemical properties of the transition-metal sulfide anode for Li-ion batteries and the Li2S cathode for Li-S batteries. Boron, nitrogen, oxygen, phosphorus, and sulfur doping greatly affect the electrochemical properties of Li2S /graphene . Here, we investigate the interfacial binding energy, lithium adsorption energy, interface diffusion barrier, and electronic structure by first-principles calculations to unveil the diverse effects of different dopants during interfacial lithiation reactions. The interfacial lithium storage follows the pseudocapacitylike mechanism with intercalation character. Two different mechanisms are revealed to enhance the interfacial lithium adsorption and diffusion, which are the electron-deficiency host doping and the vacancylike structure evolutions with bond breaking. The synergistic effect between different dopants with diverse doping effects is also proposed. The results give a theoretical basis for the materials design with doped graphene as advanced materials modification for energy storage.

Theoretical study of oxygen sorption and diffusion in the volume and on the surface of a γ-TiAl alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bakulin, A. V., E-mail: bakulin@ispms.tsc.ru; Kulkova, S. E.; Hu, Q. M.

2015-02-15

The oxygen sorption on the low-index (001), (100), and (110) surfaces of a γ-TiAl alloy is studied by the pseudopotential method with the generalized gradient approximation for the exchange-correlation functional. The most preferred sites for oxygen sorption in the bulk and on the surface of the alloy are determined. The titanium-rich octahedral site is shown to be preferred for oxygen sorption in the bulk material. The effect of the oxygen concentration on the atomic and electronic structures of the stoichiometric TiAl(100) surface is studied. It is shown that, at the first stage of oxidation, oxygen prefers to form bonds withmore » titanium. The energy barriers for oxygen diffusion on the stoichiometric (100) surface and in the bulk of the material are calculated. The energy barriers are shown to depend substantially on the local environments of oxygen and to increase during diffusion from titanium-rich sites. The most possible mechanism of oxygen diffusion from the (100) surface to the bulk of the material is oxygen migration through tetrahedral sites.« less

Effective optical path length for tandem diffuse cubic cavities as gas absorption cell

NASA Astrophysics Data System (ADS)

Yu, J.; Gao, Q.; Zhang, Y. G.; Zhang, Z. G.; Wu, S. H.

2014-12-01

Tandem diffuse cubic cavities designed by connecting two single diffuse cubic-shaped cavities, A and B, with an aperture (port fraction fap) in the middle of the connecting baffle was developed as a gas absorption cell. The effective optical path length (EOPL) was evaluated by comparing the oxygen absorption signal in the cavity and in air based on tunable diode laser absorption spectroscopy (TDLAS). Experimental results manifested an enhancement of EOPL for the tandem diffuse cubic cavities as the decrease of fap and can be expressed as the sum of EOPL of two single cubic cavities at fap < 0.01, which coincided well with theoretical analysis. The simulating EOPL was smaller than experimental results at fap > 0.01, which indicated that back scattering light from cavity B to cavity A cannot be ignored at this condition.

Pharmaceutical micelles featured with singlet oxygen-responsive cargo release and mitochondrial targeting for enhanced photodynamic therapy.

PubMed

Zhang, Xin; Yan, Qi; Mulatihan, Di Naer; Zhu, Jundong; Fan, Aiping; Wang, Zheng; Zhao, Yanjun

2018-06-22

The efficacy of nanoparticulate photodynamic therapy is often compromised by the short life time and limited diffusion radius of singlet oxygen as well as uncontrolled intracellular distribution of photosensitizer. It was hypothesized that rapid photosensitizer release upon nanoparticle internalization and its preferred accumulation in mitochondria would address the above problems. Hence, the aim of this study was to engineer a multifunctional micellar nanosystem featured with singlet oxygen-responsive cargo release and mitochondria-targeting. An imidazole-bearing amphiphilic copolymer was employed as the micelle building block to encapsulate triphenylphosphonium-pyropheophorbide a (TPP-PPa) conjugate or PPa. Upon laser irradiation, the singlet oxygen produced by TPP-PPa/PPa oxidized the imidazole moiety to produce hydrophilic urea, leading to micelle disassembly and rapid cargo release. The co-localization analysis showed that the TPP moiety significantly enhanced the photosensitizer uptake by mitochondria, improved mitochondria depolarization upon irradiation, and hence boosted the cytotoxicity in 4T1 cells. The targeting strategy also dramatically reduced the intracellular ATP concentration as a consequence of mitochondria injury. The mitochondria damage was accompanied with the activation of the apoptosis signals (caspase 3 and caspase 9), whose level was directly correlated to the apoptosis extent. The current work provides a facile and robust means to enhance the efficacy of photodynamic therapy.

Pharmaceutical micelles featured with singlet oxygen-responsive cargo release and mitochondrial targeting for enhanced photodynamic therapy

NASA Astrophysics Data System (ADS)

Zhang, Xin; Yan, Qi; Naer Mulatihan, Di; Zhu, Jundong; Fan, Aiping; Wang, Zheng; Zhao, Yanjun

2018-06-01

The efficacy of nanoparticulate photodynamic therapy is often compromised by the short life time and limited diffusion radius of singlet oxygen as well as uncontrolled intracellular distribution of photosensitizer. It was hypothesized that rapid photosensitizer release upon nanoparticle internalization and its preferred accumulation in mitochondria would address the above problems. Hence, the aim of this study was to engineer a multifunctional micellar nanosystem featured with singlet oxygen-responsive cargo release and mitochondria-targeting. An imidazole-bearing amphiphilic copolymer was employed as the micelle building block to encapsulate triphenylphosphonium-pyropheophorbide a (TPP-PPa) conjugate or PPa. Upon laser irradiation, the singlet oxygen produced by TPP-PPa/PPa oxidized the imidazole moiety to produce hydrophilic urea, leading to micelle disassembly and rapid cargo release. The co-localization analysis showed that the TPP moiety significantly enhanced the photosensitizer uptake by mitochondria, improved mitochondria depolarization upon irradiation, and hence boosted the cytotoxicity in 4T1 cells. The targeting strategy also dramatically reduced the intracellular ATP concentration as a consequence of mitochondria injury. The mitochondria damage was accompanied with the activation of the apoptosis signals (caspase 3 and caspase 9), whose level was directly correlated to the apoptosis extent. The current work provides a facile and robust means to enhance the efficacy of photodynamic therapy.

Influence of Cholesterol on the Oxygen Permeability of Membranes: Insight from Atomistic Simulations.

PubMed

Dotson, Rachel J; Smith, Casey R; Bueche, Kristina; Angles, Gary; Pias, Sally C

2017-06-06

Cholesterol is widely known to alter the physical properties and permeability of membranes. Several prior works have implicated cell membrane cholesterol as a barrier to tissue oxygenation, yet a good deal remains to be explained with regard to the mechanism and magnitude of the effect. We use molecular dynamics simulations to provide atomic-resolution insight into the influence of cholesterol on oxygen diffusion across and within the membrane. Our simulations show strong overall agreement with published experimental data, reproducing the shapes of experimental oximetry curves with high accuracy. We calculate the upper-limit transmembrane oxygen permeability of a 1-palmitoyl,2-oleoylphosphatidylcholine phospholipid bilayer to be 52 ± 2 cm/s, close to the permeability of a water layer of the same thickness. With addition of cholesterol, the permeability decreases somewhat, reaching 40 ± 2 cm/s at the near-saturating level of 62.5 mol % cholesterol and 10 ± 2 cm/s in a 100% cholesterol mimic of the experimentally observed noncrystalline cholesterol bilayer domain. These reductions in permeability can only be biologically consequential in contexts where the diffusional path of oxygen is not water dominated. In our simulations, cholesterol reduces the overall solubility of oxygen within the membrane but enhances the oxygen transport parameter (solubility-diffusion product) near the membrane center. Given relatively low barriers to passing from membrane to membrane, our findings support hydrophobic channeling within membranes as a means of cellular and tissue-level oxygen transport. In such a membrane-dominated diffusional scheme, the influence of cholesterol on oxygen permeability is large enough to warrant further attention. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Oxygen Pathways and Budget for the Eastern South Pacific Oxygen Minimum Zone

NASA Astrophysics Data System (ADS)

Llanillo, P. J.; Pelegrí, J. L.; Talley, L. D.; Peña-Izquierdo, J.; Cordero, R. R.

2018-03-01

Ventilation of the eastern South Pacific Oxygen Minimum Zone (ESP-OMZ) is quantified using climatological Argo and dissolved oxygen data, combined with reanalysis wind stress data. We (1) estimate all oxygen fluxes (advection and turbulent diffusion) ventilating this OMZ, (2) quantify for the first time the oxygen contribution from the subtropical versus the traditionally studied tropical-equatorial pathway, and (3) derive a refined annual-mean oxygen budget for the ESP-OMZ. In the upper OMZ layer, net oxygen supply is dominated by tropical-equatorial advection, with more than one-third of this supply upwelling into the Ekman layer through previously unevaluated vertical advection, within the overturning component of the regional Subtropical Cell (STC). Below the STC, at the OMZ's core, advection is weak and turbulent diffusion (isoneutral and dianeutral) accounts for 89% of the net oxygen supply, most of it coming from the oxygen-rich subtropical gyre. In the deep OMZ layer, net oxygen supply occurs only through turbulent diffusion and is dominated by the tropical-equatorial pathway. Considering the entire OMZ, net oxygen supply (3.84 ± 0.42 µmol kg-1 yr-1) is dominated by isoneutral turbulent diffusion (56.5%, split into 32.3% of tropical-equatorial origin and 24.2% of subtropical origin), followed by isoneutral advection (32.0%, split into 27.6% of tropical-equatorial origin and 4.4% of subtropical origin) and dianeutral diffusion (11.5%). One-quarter (25.8%) of the net oxygen input escapes through dianeutral advection (most of it upwelling) and, assuming steady state, biological consumption is responsible for most of the oxygen loss (74.2%).

Cuticular gas exchange by Antarctic sea spiders.

PubMed

Lane, Steven J; Moran, Amy L; Shishido, Caitlin M; Tobalske, Bret W; Woods, H Arthur

2018-04-25

Many marine organisms and life stages lack specialized respiratory structures, like gills, and rely instead on cutaneous respiration, which they facilitate by having thin integuments. This respiratory mode may limit body size, especially if the integument also functions in support or locomotion. Pycnogonids, or sea spiders, are marine arthropods that lack gills and rely on cutaneous respiration but still grow to large sizes. Their cuticle contains pores, which may play a role in gas exchange. Here, we examined alternative paths of gas exchange in sea spiders: (1) oxygen diffuses across pores in the cuticle, a common mechanism in terrestrial eggshells, (2) oxygen diffuses directly across the cuticle, a common mechanism in small aquatic insects, or (3) oxygen diffuses across both pores and cuticle. We examined these possibilities by modeling diffusive oxygen fluxes across all pores in the body of sea spiders and asking whether those fluxes differed from measured metabolic rates. We estimated fluxes across pores using Fick's law parameterized with measurements of pore morphology and oxygen gradients. Modeled oxygen fluxes through pores closely matched oxygen consumption across a range of body sizes, which means the pores facilitate oxygen diffusion. Furthermore, pore volume scaled hypermetrically with body size, which helps larger species facilitate greater diffusive oxygen fluxes across their cuticle. This likely presents a functional trade-off between gas exchange and structural support, in which the cuticle must be thick enough to prevent buckling due to external forces but porous enough to allow sufficient gas exchange. © 2018. Published by The Company of Biologists Ltd.

Selective electrocatalysts toward a prototype of the membraneless direct methanol fuel cell.

PubMed

Feng, Yan; Yang, Jinhua; Liu, Hui; Ye, Feng; Yang, Jun

2014-01-22

Mastery over the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the design and fabrication of Pt-based nanomaterials with enhanced catalytic activity and superior selectivity toward the reactions in direct methanol fuel cells (DMFCs) upon the deep understanding of the mechanisms of these electrochemical reactions. In particular, the ternary Au@Ag2S-Pt nanocomposites display superior methanol oxidation reaction (MOR) selectivity due to the electronic coupling effect among different domains of the nanocomposites, while the cage-bell structured Pt-Ru nanoparticles exhibit excellent methanol tolerance for oxygen reduction reaction (ORR) at the cathode because of the differential diffusion of methanol and oxygen in the porous Ru shell of the cage-bell nanoparticles. The good catalytic selectivity of these Pt-based nanomaterials via structural construction enables a DMFC to be built without a proton exchange membrane between the fuel electrode and the oxygen electrode.

Selective electrocatalysts toward a prototype of the membraneless direct methanol fuel cell

PubMed Central

Feng, Yan; Yang, Jinhua; Liu, Hui; Ye, Feng; Yang, Jun

2014-01-01

Mastery over the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the design and fabrication of Pt-based nanomaterials with enhanced catalytic activity and superior selectivity toward the reactions in direct methanol fuel cells (DMFCs) upon the deep understanding of the mechanisms of these electrochemical reactions. In particular, the ternary Au@Ag2S-Pt nanocomposites display superior methanol oxidation reaction (MOR) selectivity due to the electronic coupling effect among different domains of the nanocomposites, while the cage-bell structured Pt-Ru nanoparticles exhibit excellent methanol tolerance for oxygen reduction reaction (ORR) at the cathode because of the differential diffusion of methanol and oxygen in the porous Ru shell of the cage-bell nanoparticles. The good catalytic selectivity of these Pt-based nanomaterials via structural construction enables a DMFC to be built without a proton exchange membrane between the fuel electrode and the oxygen electrode. PMID:24448514

Bifunctional catalytic electrode

NASA Technical Reports Server (NTRS)

Cisar, Alan (Inventor); Murphy, Oliver J. (Inventor); Clarke, Eric (Inventor)

2005-01-01

The present invention relates to an oxygen electrode for a unitized regenerative hydrogen-oxygen fuel cell and the unitized regenerative fuel cell having the oxygen electrode. The oxygen electrode contains components electrocatalytically active for the evolution of oxygen from water and the reduction of oxygen to water, and has a structure that supports the flow of both water and gases between the catalytically active surface and a flow field or electrode chamber for bulk flow of the fluids. The electrode has an electrocatalyst layer and a diffusion backing layer interspersed with hydrophilic and hydrophobic regions. The diffusion backing layer consists of a metal core having gas diffusion structures bonded to the metal core.

Sulfur transformations at the hydrogen sulfide/oxygen interface in stratified waters and in cyanobacterial mats

NASA Technical Reports Server (NTRS)

Cohen, Y.

1985-01-01

Stratified water bodies allow the development of several microbial plates along the water column. The microbial plates develop in relation to nutrient availability, light penetration, and the distribution of oxygen and sulfide. Sulfide is initially produced in the sediment by sulfate-reducing bacteria. It diffuses along the water column creating a zone of hydrogen sulfide/oxygen interface. In the chemocline of Solar Lake oxygen and sulfide coexist in a 0 to 10 cm layer that moves up and down during a diurnal cycle. The microbial plate at the chemocline is exposed to oxygen and hydrogen sulfide, alternating on a diurnal basis. The cyanobacteria occupying the interface switch from anoxygenic photosynthesis in the morning to oxygenic photosynthesis during the rest of the day which results in a temporal build up of elemental sulfur during the day and disappears at night due to both oxidation to thiosulfate and sulfate by thiobacilli, and reduction to hydrogen sulfide by Desulfuromonas sp. and anaerobically respiring cyanobacteria. Sulfate reduction was enhanced in the light at the surface of the cyanobacterial mats. Microsulfate reduction measurements showed enhanced activity of sulfate reduction even under high oxygen concentrations of 300 to 800 micrometer. Apparent aerobic SO sub 4 reduction activity is explained by the co-occurrence of H sub 2. The physiology of this apparent sulfate reduction activity is studied.

Oxygen diffusion in monazite

NASA Astrophysics Data System (ADS)

Cherniak, D. J.; Zhang, X. Y.; Nakamura, M.; Watson, E. B.

2004-09-01

We report measurements of oxygen diffusion in natural monazites under both dry, 1-atm conditions and hydrothermal conditions. For dry experiments, 18O-enriched CePO4 powder and monazite crystals were sealed in Ag-Pd capsules with a solid buffer (to buffer at NNO) and annealed in 1-atm furnaces. Hydrothermal runs were conducted in cold-seal pressure vessels, where monazite grains were encapsulated with 18O-enriched water. Following the diffusion anneals, oxygen concentration profiles were measured with Nuclear Reaction Analysis (NRA) using the reaction 18O(p,α)15N. Over the temperature range 850-1100 °C, the Arrhenius relation determined for dry diffusion experiments on monazite is given by: Under wet conditions at 100 MPa water pressure, over the temperature range 700-880 °C, oxygen diffusion can be described by the Arrhenius relationship: Oxygen diffusion under hydrothermal conditions has a significantly lower activation energy for diffusion than under dry conditions, as has been found the case for many other minerals, both silicate and nonsilicate. Given these differences in activation energies, the differences between dry and wet diffusion rates increase with lower temperatures; for example, at 600 °C, dry diffusion will be more than 4 orders of magnitude slower than diffusion under hydrothermal conditions. These disparate diffusivities will result in pronounced differences in the degree of retentivity of oxygen isotope signatures. For instance, under dry conditions (presumably rare in the crust) and high lower-crustal temperatures (∼800 °C), monazite cores of 70-μm radii will preserve O isotope ratios for about 500,000 years; by comparison, they would be retained at this temperature under wet conditions for about 15,000 years.

Oxygen migration during resistance switching and failure of hafnium oxide memristors

DOE PAGES

Kumar, Suhas; Wang, Ziwen; Huang, Xiaopeng; ...

2017-03-06

While the recent establishment of the role of thermophoresis/diffusion-driven oxygen migration during resistance switching in metal oxide memristors provided critical insights required for memristor modeling, extended investigations of the role of oxygen migration during ageing and failure remain to be detailed. Such detailing will enable failure-tolerant design, which can lead to enhanced performance of memristor-based next-generation storage-class memory. Furthermore, we directly observed lateral oxygen migration using in-situ synchrotron x-ray absorption spectromicroscopy of HfO x memristors during initial resistance switching, wear over millions of switching cycles, and eventual failure, through which we determined potential physical causes of failure. Using this information,more » we reengineered devices to mitigate three failure mechanisms and demonstrated an improvement in endurance of about three orders of magnitude.« less

Growth of the 889 per cm infrared band in annealed electron-irradiated silicon

NASA Technical Reports Server (NTRS)

Svensson, B. G.; Lindstrom, J. L.; Corbett, J. W.

1985-01-01

Isothermal annealing of electron-irradiated Czochralski silicon has been studied at four different temperatures ranging from 304 to 350 C using infrared spectroscopy. At annealing temperatures above 300 C the irradiation-induced band at 830 per cm, usually attributed to a vacancy-oxygen complex (the A center), disappears and a new band at 889 per cm grows up. Within the experimental accuracy, the activation energy for the growth of this band is found to be identical with the value given by Stavola et al. for 'anomalous' oxygen diffusion in silicon. Also the frequency factors for the two processes are in reasonable agreement. The results show that a vacancy-assisted process may provide an explanation for enhanced motion of oxygen in silicon.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Suhas; Wang, Ziwen; Huang, Xiaopeng

While the recent establishment of the role of thermophoresis/diffusion-driven oxygen migration during resistance switching in metal oxide memristors provided critical insights required for memristor modeling, extended investigations of the role of oxygen migration during ageing and failure remain to be detailed. Such detailing will enable failure-tolerant design, which can lead to enhanced performance of memristor-based next-generation storage-class memory. Furthermore, we directly observed lateral oxygen migration using in-situ synchrotron x-ray absorption spectromicroscopy of HfO x memristors during initial resistance switching, wear over millions of switching cycles, and eventual failure, through which we determined potential physical causes of failure. Using this information,more » we reengineered devices to mitigate three failure mechanisms and demonstrated an improvement in endurance of about three orders of magnitude.« less

Thermophysical properties and oxygen transport in (Th x,Pu 1-x)O 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Th x,Pu 1–x)O 2 (0 ≤ x ≤ 1) between 300–3500 K. Specifically, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Th x,Pu 1–x)O 2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and themore » increase in oxygen diffusivity. The increase in oxygen diffusivity for (Th x,Pu 1–x)O 2 is explained in terms of lower oxygen defect formation enthalpies for (Th x,Pu 1–x)O 2 than PuO 2 and ThO 2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.« less

Thermophysical properties and oxygen transport in (Th x,Pu 1-x)O 2

DOE PAGES

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.; ...

2016-10-31

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Th x,Pu 1–x)O 2 (0 ≤ x ≤ 1) between 300–3500 K. Specifically, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Th x,Pu 1–x)O 2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and themore » increase in oxygen diffusivity. The increase in oxygen diffusivity for (Th x,Pu 1–x)O 2 is explained in terms of lower oxygen defect formation enthalpies for (Th x,Pu 1–x)O 2 than PuO 2 and ThO 2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.« less

Analytic Models of Oxygen and Nutrient Diffusion, Metabolism Dynamics, and Architecture Optimization in Three-Dimensional Tissue Constructs with Applications and Insights in Cerebral Organoids

PubMed Central

2016-01-01

Diffusion models are important in tissue engineering as they enable an understanding of gas, nutrient, and signaling molecule delivery to cells in cell cultures and tissue constructs. As three-dimensional (3D) tissue constructs become larger, more intricate, and more clinically applicable, it will be essential to understand internal dynamics and signaling molecule concentrations throughout the tissue and whether cells are receiving appropriate nutrient delivery. Diffusion characteristics present a significant limitation in many engineered tissues, particularly for avascular tissues and for cells whose viability, differentiation, or function are affected by concentrations of oxygen and nutrients. This article seeks to provide novel analytic solutions for certain cases of steady-state and nonsteady-state diffusion and metabolism in basic 3D construct designs (planar, cylindrical, and spherical forms), solutions that would otherwise require mathematical approximations achieved through numerical methods. This model is applied to cerebral organoids, where it is shown that limitations in diffusion and organoid size can be partially overcome by localizing metabolically active cells to an outer layer in a sphere, a regionalization process that is known to occur through neuroglial precursor migration both in organoids and in early brain development. The given prototypical solutions include a review of metabolic information for many cell types and can be broadly applied to many forms of tissue constructs. This work enables researchers to model oxygen and nutrient delivery to cells, predict cell viability, study dynamics of mass transport in 3D tissue constructs, design constructs with improved diffusion capabilities, and accurately control molecular concentrations in tissue constructs that may be used in studying models of development and disease or for conditioning cells to enhance survival after insults like ischemia or implantation into the body, thereby providing a framework for better understanding and exploring the characteristics and behaviors of engineered tissue constructs. PMID:26650970

Sediment diffusion method improves wastewater nitrogen removal in the receiving lake sediments.

PubMed

Aalto, Sanni L; Saarenheimo, Jatta; Ropponen, Janne; Juntunen, Janne; Rissanen, Antti J; Tiirola, Marja

2018-07-01

Sediment microbes have a great potential to transform reactive N to harmless N 2 , thus decreasing wastewater nitrogen load into aquatic ecosystems. Here, we examined if spatial allocation of the wastewater discharge by a specially constructed sediment diffuser pipe system enhanced the microbial nitrate reduction processes. Full-scale experiments were set on two Finnish lake sites, Keuruu and Petäjävesi, and effects on the nitrate removal processes were studied using the stable isotope pairing technique. All nitrate reduction rates followed nitrate concentrations, being highest at the wastewater-influenced sampling points. Complete denitrification with N 2 as an end-product was the main nitrate reduction process, indicating that the high nitrate and organic matter concentrations of wastewater did not promote nitrous oxide (N 2 O) production (truncated denitrification) or ammonification (dissimilatory nitrate reduction to ammonium; DNRA). Using 3D simulation, we demonstrated that the sediment diffusion method enhanced the contact time and amount of wastewater near the sediment surface especially in spring and in autumn, altering organic matter concentration and oxygen levels, and increasing the denitrification capacity of the sediment. We estimated that natural denitrification potentially removed 3-10% of discharged wastewater nitrate in the 33 ha study area of Keuruu, and the sediment diffusion method increased this areal denitrification capacity on average 45%. Overall, our results indicate that sediment diffusion method can supplement wastewater treatment plant (WWTP) nitrate removal without enhancing alternative harmful processes. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Twin-domain size and bulk oxygen in-diffusion kinetics of YBa 2Cu 3O 6+x studied by neutron powder diffraction and gas volumetry

NASA Astrophysics Data System (ADS)

Poulsen, H. F.; Andersen, N. H.; Lebech, B.

1991-02-01

We report experimental results of twin-domain size and bulk oxygen in-diffusion kinetics of YBa 2Cu 3O 6+ x, which supplement a previous and simultaneous study of the structural phase diagram and oxygen equilibrium partial pressure. Analysis of neutron powder diffraction peak broadening show features which are identified to result from temperature independent twin-domain formation in to different orthorhombic phases with domain sizes and 250 and 350Å, respectively. The oxygen in-diffusion flow shows simple relaxation type behaviour J=J 0 exp( {-t}/{τ}) despite a rather broad particle size distribution. At higher temperatures, τ is activated with activation energies 0.55 and 0.25 eV in the tetragonal and orthorhombic phases, respectively. Comparison between twin-domain sizes and bulk oxygen in-diffusion time constants indicates that the twin-domain boundaries may contribute to the effective bulk oxygen in-diffusion. All our results may be interpreted in terms of the 2D ASYNNNI model description of the oxygen basal plane ordering, and they suggest that recent first principles interaction parameters should be modified.

Kinetic Monte Carlo Simulation of Oxygen Diffusion in Ytterbium Disilicate

NASA Technical Reports Server (NTRS)

Good, Brian S.

2015-01-01

Ytterbium disilicate is of interest as a potential environmental barrier coating for aerospace applications, notably for use in next generation jet turbine engines. In such applications, the transport of oxygen and water vapor through these coatings to the ceramic substrate is undesirable if high temperature oxidation is to be avoided. In an effort to understand the diffusion process in these materials, we have performed kinetic Monte Carlo simulations of vacancy-mediated and interstitial oxygen diffusion in Ytterbium disilicate. Oxygen vacancy and interstitial site energies, vacancy and interstitial formation energies, and migration barrier energies were computed using Density Functional Theory. We have found that, in the case of vacancy-mediated diffusion, many potential diffusion paths involve large barrier energies, but some paths have barrier energies smaller than one electron volt. However, computed vacancy formation energies suggest that the intrinsic vacancy concentration is small. In the case of interstitial diffusion, migration barrier energies are typically around one electron volt, but the interstitial defect formation energies are positive, with the result that the disilicate is unlikely to exhibit experience significant oxygen permeability except at very high temperature.

Kinetic Monte Carlo Investigation of the Effects of Vacancy Pairing on Oxygen Diffusivity in Yttria-Stabilized Zirconia

NASA Technical Reports Server (NTRS)

Good, Brian S.

2011-01-01

Yttria-stabilized zirconia s high oxygen diffusivity and corresponding high ionic conductivity, and its structural stability over a broad range of temperatures, have made the material of interest for use in a number of applications, for example, as solid electrolytes in fuel cells. At low concentrations, the stabilizing yttria also serves to increase the oxygen diffusivity through the presence of corresponding oxygen vacancies, needed to maintain charge neutrality. At higher yttria concentration, however, diffusivity is impeded by the larger number of relatively high energy migration barriers associated with yttrium cations. In addition, there is evidence that oxygen vacancies preferentially occupy nearest-neighbor sites around either dopant or Zr cations, further affecting vacancy diffusion. We present the results of ab initio calculations that indicate that it is energetically favorable for oxygen vacancies to occupy nearest-neighbor sites adjacent to Y ions, and that the presence of vacancies near either species of cation lowers the migration barriers. Kinetic Monte Carlo results from simulations incorporating this effect are presented and compared with results from simulations in which the effect is not present.

Diffusion of oxygen interstitials in UO2+x using kinetic Monte Carlo simulations: Role of O/M ratio and sensitivity analysis

NASA Astrophysics Data System (ADS)

Behera, Rakesh K.; Watanabe, Taku; Andersson, David A.; Uberuaga, Blas P.; Deo, Chaitanya S.

2016-04-01

Oxygen interstitials in UO2+x significantly affect the thermophysical properties and microstructural evolution of the oxide nuclear fuel. In hyperstoichiometric Urania (UO2+x), these oxygen interstitials form different types of defect clusters, which have different migration behavior. In this study we have used kinetic Monte Carlo (kMC) to evaluate diffusivities of oxygen interstitials accounting for mono- and di-interstitial clusters. Our results indicate that the predicted diffusivities increase significantly at higher non-stoichiometry (x > 0.01) for di-interstitial clusters compared to a mono-interstitial only model. The diffusivities calculated at higher temperatures compare better with experimental values than at lower temperatures (< 973 K). We have discussed the resulting activation energies achieved for diffusion with all the mono- and di-interstitial models. We have carefully performed sensitivity analysis to estimate the effect of input di-interstitial binding energies on the predicted diffusivities and activation energies. While this article only discusses mono- and di-interstitials in evaluating oxygen diffusion response in UO2+x, future improvements to the model will primarily focus on including energetic definitions of larger stable interstitial clusters reported in the literature. The addition of larger clusters to the kMC model is expected to improve the comparison of oxygen transport in UO2+x with experiment.

Oxygen Delivery from Hyperbarically Loaded Microtanks Extends Cell Viability in Anoxic Environments

PubMed Central

Cook, Colin A.; Hahn, Kathryn C.; Morrissette-McAlmon, Justin B.F.; Grayson, Warren L.

2016-01-01

Oxygen diffusion limitations within nascent tissue engineered (TE) grafts lead to the development of hypoxic regions, cell death, and graft failure. Previous efforts have been made to deliver oxygen within TE scaffolds, including peroxide-doping, perfluorocarbons, and hyperbaric oxygen therapy, to mitigate these effects and help maintain post transplantation cell viability, but these have suffered from significant drawbacks. Here we present a novel approach utilizing polymeric hollow-core microspheres that can be hyperbarically loaded with oxygen and subsequently provide prolonged oxygen delivery. These oxygen carriers are termed, microtanks. With an interest in orthopedic applications, we combined microtanks within polycaprolactone to form solid phase constructs with oxygen delivery capabilities. The mathematical laws governing oxygen delivery from microtank-loaded constructs are developed along with empirical validation. Constructs achieved periods of oxygen delivery out to 6 days, which was shown to prolong the survival of human adipose derived stem cells (hASCs) and human umbilical vein endothelial cells (HUVECs) as well as to enhance their cellular morphology under anoxic conditions. The results of this study suggest the microtank approach may be a feasible means of maintaining cell viability in TE scaffolds during the critical period of vascularization in vivo. PMID:25818444

Oxygen diffusion in alpha-Al2O3. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Cawley, J. D.; Halloran, J. W.; Cooper, A. R.

1984-01-01

Oxygen self diffusion coefficients were determined in single crystal alpha-Al2O3 using the gas exchange technique. The samples were semi-infinite slabs cut from five different boules with varying background impurities. The diffusion direction was parallel to the c-axis. The tracer profiles were determined by two techniques, single spectrum proton activation and secondary ion mass spectrometry. The SIMS proved to be a more useful tool. The determined diffusion coefficients, which were insensitive to impurity levels and oxygen partial pressure, could be described by D = .00151 exp (-572kJ/RT) sq m/s. The insensitivities are discussed in terms of point defect clustering. Two independent models are consistent with the findings, the first considers the clusters as immobile point defect traps which buffer changes in the defect chemistry. The second considers clusters to be mobile and oxygen diffusion to be intrinsic behavior, the mechanism for oxygen transport involving neutral clusters of Schottky quintuplets.

DFT-based ab initio MD simulation of the ionic conduction in doped ZrO₂ systems under epitaxial strain.

PubMed

Oka, M; Kamisaka, H; Fukumura, T; Hasegawa, T

2015-11-21

The oxygen ionic conduction in ZrO2 systems under tensile epitaxial strain was investigated by performing ab initio molecular dynamics (MD) calculations based on density functional theory (DFT) to elucidate the essential factors in the colossal ionic conductivity observed in the yttria stabilized ZrO2 (YSZ)/SrTiO3 heterostructure. Three factors were evaluated: lattice strain, oxygen vacancies, and dopants. Phonon calculations based on density functional perturbation theory (DFPT) were used to obtain the most stable structure for nondoped ZrO2 under 7% tensile strain along the a- and b-axes. This structure has the space group Pbcn, which is entirely different from that of cubic ZrO2, suggesting that previous ab initio MD calculations assuming cubic ZrO2 may have overestimated the ionic conductivity due to relaxation from the initial structure to the stable structure (Pbcn). Our MD calculations revealed that the ionic conductivity is enhanced only when tensile strain and oxygen vacancies are incorporated, although the presently obtained diffusion constant is far below the range for the colossal ionic conduction experimentally observed. The enhanced ionic conductivity is due to the combined effects of oxygen sublattice formation induced by strain and deformation of this sublattice by oxygen vacancies.

Two-photon NADH imaging exposes boundaries of oxygen diffusion in cortical vascular supply regions

PubMed Central

Kasischke, Karl A; Lambert, Elton M; Panepento, Ben; Sun, Anita; Gelbard, Harris A; Burgess, Robert W; Foster, Thomas H; Nedergaard, Maiken

2011-01-01

Oxygen transport imposes a possible constraint on the brain's ability to sustain variable metabolic demands, but oxygen diffusion in the cerebral cortex has not yet been observed directly. We show that concurrent two-photon fluorescence imaging of endogenous nicotinamide adenine dinucleotide (NADH) and the cortical microcirculation exposes well-defined boundaries of tissue oxygen diffusion in the mouse cortex. The NADH fluorescence increases rapidly over a narrow, very low pO2 range with a p50 of 3.4±0.6 mm Hg, thereby establishing a nearly binary reporter of significant, metabolically limiting hypoxia. The transient cortical tissue boundaries of NADH fluorescence exhibit remarkably delineated geometrical patterns, which define the limits of tissue oxygen diffusion from the cortical microcirculation and bear a striking resemblance to the ideal Krogh tissue cylinder. The visualization of microvessels and their regional contribution to oxygen delivery establishes penetrating arterioles as major oxygen sources in addition to the capillary network and confirms the existence of cortical oxygen fields with steep microregional oxygen gradients. Thus, two-photon NADH imaging can be applied to expose vascular supply regions and to localize functionally relevant microregional cortical hypoxia with micrometer spatial resolution. PMID:20859293

Two-photon NADH imaging exposes boundaries of oxygen diffusion in cortical vascular supply regions.

PubMed

Kasischke, Karl A; Lambert, Elton M; Panepento, Ben; Sun, Anita; Gelbard, Harris A; Burgess, Robert W; Foster, Thomas H; Nedergaard, Maiken

2011-01-01

Oxygen transport imposes a possible constraint on the brain's ability to sustain variable metabolic demands, but oxygen diffusion in the cerebral cortex has not yet been observed directly. We show that concurrent two-photon fluorescence imaging of endogenous nicotinamide adenine dinucleotide (NADH) and the cortical microcirculation exposes well-defined boundaries of tissue oxygen diffusion in the mouse cortex. The NADH fluorescence increases rapidly over a narrow, very low pO(2) range with a p(50) of 3.4 ± 0.6 mm Hg, thereby establishing a nearly binary reporter of significant, metabolically limiting hypoxia. The transient cortical tissue boundaries of NADH fluorescence exhibit remarkably delineated geometrical patterns, which define the limits of tissue oxygen diffusion from the cortical microcirculation and bear a striking resemblance to the ideal Krogh tissue cylinder. The visualization of microvessels and their regional contribution to oxygen delivery establishes penetrating arterioles as major oxygen sources in addition to the capillary network and confirms the existence of cortical oxygen fields with steep microregional oxygen gradients. Thus, two-photon NADH imaging can be applied to expose vascular supply regions and to localize functionally relevant microregional cortical hypoxia with micrometer spatial resolution.

Kinetic Monte Carlo Simulations of Oxygen Diffusion in Environmental Barrier Coating Materials

NASA Technical Reports Server (NTRS)

Good, Brian S.

2017-01-01

Ceramic Matrix Composite (CMC) materials are of interest for use in next-generation turbine engine components, offering a number of significant advantages, including reduced weight and high operating temperatures. However, in the hot environment in which such components operate, the presence of water vapor can lead to corrosion and recession, limiting the useful life of the components. Such degradation can be reduced through the use of Environmental Barrier Coatings (EBCs) that limit the amount of oxygen and water vapor reaching the component. Candidate EBC materials include Yttrium and Ytterbium silicates. In this work we present results of kinetic Monte Carlo (kMC) simulations of oxygen diffusion, via the vacancy mechanism, in Yttrium and Ytterbium disilicates, along with a brief discussion of interstitial diffusion. An EBC system typically includes a bond coat located between the EBC and the component surface. Bond coat materials are generally chosen for properties other than low oxygen diffusivity, but low oxygen diffusivity is nevertheless a desirable characteristic, as the bond coat could provide some additional component protection, particularly in the case where cracks in the coating system provide a direct path from the environment to the bond coat interface. We have therefore performed similar kMC simulations of oxygen diffusion in this material.

Active diffusion and microtubule-based transport oppose myosin forces to position organelles in cells

PubMed Central

Lin, Congping; Schuster, Martin; Guimaraes, Sofia Cunha; Ashwin, Peter; Schrader, Michael; Metz, Jeremy; Hacker, Christian; Gurr, Sarah Jane; Steinberg, Gero

2016-01-01

Even distribution of peroxisomes (POs) and lipid droplets (LDs) is critical to their role in lipid and reactive oxygen species homeostasis. How even distribution is achieved remains elusive, but diffusive motion and directed motility may play a role. Here we show that in the fungus Ustilago maydis ∼95% of POs and LDs undergo diffusive motions. These movements require ATP and involve bidirectional early endosome motility, indicating that microtubule-associated membrane trafficking enhances diffusion of organelles. When early endosome transport is abolished, POs and LDs drift slowly towards the growing cell end. This pole-ward drift is facilitated by anterograde delivery of secretory cargo to the cell tip by myosin-5. Modelling reveals that microtubule-based directed transport and active diffusion support distribution, mobility and mixing of POs. In mammalian COS-7 cells, microtubules and F-actin also counteract each other to distribute POs. This highlights the importance of opposing cytoskeletal forces in organelle positioning in eukaryotes. PMID:27251117

Isopycnal diffusivity in the tropical North Atlantic oxygen minimum zone

NASA Astrophysics Data System (ADS)

Köllner, Manuela; Visbeck, Martin; Tanhua, Toste; Fischer, Tim

2017-04-01

Isopycnal diffusivity plays an important role in the ventilation of the Eastern Tropical North Atlantic (ETNA) Oxygen Minimum Zone (OMZ). Lateral tracer transport is described by isopycnal diffusivity and mean advection of the tracer (e.g. oxygen), together they account for up to 70% of the oxygen supply for the OMZ. One of the big challenges is to separate diffusivity from advection. Isopycnal diffusivity was estimated to be Ky=(500 ± 200) m2 s-1 and Kx=(1200 ± 600) m2 s-1 by Banyte et. al (2013) from a Tracer Release Experiment (TRE). Hahn et al. (2014) estimated a meridional eddy diffusivity of 1350 m2 s-1 at 100 m depth decaying to less than 300 m2 s-1 below 800 m depth from repeated ship sections of CTD and ADCP data in addition with hydrographic mooring data. Uncertainties of the estimated diffusivities were still large, thus the Oxygen Supply Tracer Release Experiment (OSTRE) was set up to estimate isopycnal diffusivity in the OMZ using a newly developed sampling strategy of a control volume. The tracer was released in 2012 in the core of the OMZ at approximately 410 m depth and mapped after 6, 15 and 29 months in a regular grid. In addition to the calculation of tracer column integrals from vertical tracer profiles a new sampling method was invented and tested during two of the mapping cruises. The mean eddy diffusivity during OSTRE was found to be about (300 ± 130) m2 s-1. Additionally, the tracer has been advected further to the east and west by zonal jets. We compare different analysis methods to estimate isopycnal diffusivity from tracer spreading and show the advantage of the control volume surveys and control box approach. From the control box approach we are estimating the strength of the zonal jets within the OMZ core integrated over the TRE time period. References: Banyte, D., Visbeck, M., Tanhua, T., Fischer, T., Krahmann, G.,Karstensen, J., 2013. Lateral Diffusivity from Tracer Release Experiments in the Tropical North Atlantic Thermocline. Journal of Geophysical Research 118. Hahn, J., Brandt, P., Greatbatch, R., Krahmann, G., Körtzinger, A., 2014. Oxygen variance and meridional oxygen supply in the Tropical North East Atlantic oxygen minimum zone. Climate Dynamics 43, 2999-3024.

Ultraviolet photodetection of flexible ZnO nanowire sheets in polydimethylsiloxane polymer

PubMed Central

Motta, Nunzio; Lee, Soonil

2012-01-01

Summary ZnO nanowires are normally exposed to an oxygen atmosphere to achieve high performance in UV photodetection. In this work we present results on a UV photodetector fabricated using a flexible ZnO nanowire sheet embedded in polydimethylsiloxane (PDMS), a gas-permeable polymer, showing reproducible UV photoresponse and enhanced photoconduction. PDMS coating results in a reduced response speed compared to that of a ZnO nanowire film in air. The rising speed is slightly reduced, while the decay time is prolonged by about a factor of four. We conclude that oxygen molecules diffusing in PDMS are responsible for the UV photoresponse. PMID:23016139

Ultraviolet photodetection of flexible ZnO nanowire sheets in polydimethylsiloxane polymer.

PubMed

Liu, Jinzhang; Motta, Nunzio; Lee, Soonil

2012-01-01

ZnO nanowires are normally exposed to an oxygen atmosphere to achieve high performance in UV photodetection. In this work we present results on a UV photodetector fabricated using a flexible ZnO nanowire sheet embedded in polydimethylsiloxane (PDMS), a gas-permeable polymer, showing reproducible UV photoresponse and enhanced photoconduction. PDMS coating results in a reduced response speed compared to that of a ZnO nanowire film in air. The rising speed is slightly reduced, while the decay time is prolonged by about a factor of four. We conclude that oxygen molecules diffusing in PDMS are responsible for the UV photoresponse.

Investigating the oxidation mechanism of tantalum nanoparticles at high heating rates

NASA Astrophysics Data System (ADS)

DeLisio, Jeffery B.; Wang, Xizheng; Wu, Tao; Egan, Garth C.; Jacob, Rohit J.; Zachariah, Michael R.

2017-12-01

Reduced diffusion length scales and increased specific surface areas of nanosized metal fuels have recently demonstrated increased reaction rates for these systems, increasing their relevance in a wide variety of applications. The most commonly employed metal fuel, aluminum, tends to oxidize rapidly near its melting point (660 °C) in addition to undergoing a phase change of the nascent oxide shell. To further expand on the understanding of nanosized metal fuel oxidation, tantalum nanoparticles were studied due to their high melting point (3017 °C) in comparison to aluminum. Both traditional slow heating rate and in-situ high heating rate techniques were used to probe the oxidation of tantalum nanoparticles in oxygen containing environments in addition to nanothermite mixtures. When oxidized by gas phase oxygen, the oxide shell of the tantalum nanoparticles rapidly crystallized creating cracks that may attribute to enhanced oxygen diffusion into the particle. In the case of tantalum based nanothermites, oxide shell crystallization was shown to induce reactive sintering with the metal oxide resulting in a narrow range of ignition temperatures independent of the metal oxide used. The oxidation mechanism was modeled using the Deal-Grove model to extract rate parameters, and theoretical burn times for tantalum based nanocomposites were calculated.

Annealing and anomalous high-energy electron irradiation effects in low-cost silicon N+P solar cells

NASA Technical Reports Server (NTRS)

Garlick, G. F. J.; Kachare, A. H.

1981-01-01

Silicon solar cells of N(+)P type were subjected to 1 MeV electron irradiation (up to 10 to the 16th electrons/sq cm) and then annealed at 450 C for 20 min or annealed with no electron irradiation. Electron irradiation resulted in a degradation of longer wavelength cell response, but produced a marked enhancement of response at shorter wavelengths with a peak change of 40% at 0.44 microns. Subsequent thermal anneal at 450 C reduced the long-wavelength degradation, but enhancement at shorter wavelengths persisted. Excitation at the shorter wavelengths was in the N(+)-diffused layer and in the junction region of the cell. Anneal of unirradiated cells produced shorter-wavelength enhancement with a similar peaking at 0.44 microns, but with a relative change of only 20%. More enhancement was produced in the longer wavelength region (up to 0.8 microns). These effects in the different cell regions are explained by a decrease in the interstitial oxygen-impurity complexes (deep recombination levels) and the formation of substantial oxygen-silicon vacancy centers (donors).

Imaging oxygen distribution in marine sediments. The importance of bioturbation and sediment heterogeneity.

PubMed

Pischedda, L; Poggiale, J C; Cuny, P; Gilbert, F

2008-06-01

The influence of sediment oxygen heterogeneity, due to bioturbation, on diffusive oxygen flux was investigated. Laboratory experiments were carried out with 3 macrobenthic species presenting different bioturbation behaviour patterns: the polychaetes Nereis diversicolor and Nereis virens, both constructing ventilated galleries in the sediment column, and the gastropod Cyclope neritea, a burrowing species which does not build any structure. Oxygen two-dimensional distribution in sediments was quantified by means of the optical planar optode technique. Diffusive oxygen fluxes (mean and integrated) and a variability index were calculated on the captured oxygen images. All species increased sediment oxygen heterogeneity compared to the controls without animals. This was particularly noticeable with the polychaetes because of the construction of more or less complex burrows. Integrated diffusive oxygen flux increased with oxygen heterogeneity due to the production of interface available for solute exchanges between overlying water and sediments. This work shows that sediment heterogeneity is an important feature of the control of oxygen exchanges at the sediment-water interface.

Diffusion coefficients of oxygen and hemoglobin measured by facilitated oxygen diffusion through hemoglobin solutions.

PubMed

Bouwer, S T; Hoofd, L; Kreuzer, F

1997-03-07

Diffusion coefficients of oxygen (DO2) and hemoglobin (DHb) were obtained from measuring the oxygen flux through thin layers of hemoglobin solutions at 20 degrees C. The liquid layers were supported by a membrane and not soaked in any filter material. Oxygen fluxes were measured from the changes in oxygen partial pressure in the gas phases at both sides of the layer. A mathematical treatment is presented for correct evaluation of the measurements. Measurements were done for bovine and for human hemoglobin. Hemoglobin concentrations (CHb) were between 11 and 42 g/dl, which covers the concentrations in the erythrocyte. Both DO2 and DHb could be fitted to the empirical equation D = D0(1-CHb/C1)10-CHb/C2. The following parameters were obtained: DO = 1.80 x 10(-9) m2/s, C1 = 100 g/dl, C2 = 119 g/dl, for oxygen and D0 = 7.00 x 10(-11) m2/s, C1 = 46 g/dl, C2 = 128 g/dl, for hemoglobin. No difference between the diffusion coefficients of bovine or human hemoglobin was found. The diffusion coefficients of hemoglobin were higher than most values reported in the literature, probably because in this study the mobility of hemoglobin was not hindered by surrounding filter material.

High-pressure injection of dissolved oxygen for hydrocarbon remediation in a fractured dolostone aquifer.

PubMed

Greer, K D; Molson, J W; Barker, J F; Thomson, N R; Donaldson, C R

2010-10-21

A field experiment was completed at a fractured dolomite aquifer in southwestern Ontario, Canada, to assess the delivery of supersaturated dissolved oxygen (supersaturated with respect to ambient conditions) for enhanced bioremediation of petroleum hydrocarbons in groundwater. The injection lasted for 1.5h using iTi's gPro® oxygen injection technology at pressures of up to 450 kPa and at concentrations of up to 34 mg O₂/L. A three-dimensional numerical model for advective-dispersive transport of dissolved oxygen within a discretely-fractured porous medium was calibrated to the observed field conditions under a conservative (no-consumption) scenario. The simulation demonstrated that oxygen rapidly filled the local intersecting fractures as well as the porous matrix surrounding the injection well. Following injection, the local fractures were rapidly flushed by the natural groundwater flow system but slow back-diffusion ensured a relatively longer residence time in the matrix. A sensitivity analysis showed significant changes in behaviour with varying fracture apertures and hydraulic gradients. Applying the calibrated model to a 7-day continuous injection scenario showed oxygen residence times (at the 3mg/L limit), within a radius of 2-4m from the injection well, of up to 100 days. This study has demonstrated that supersaturated dissolved oxygen can be effectively delivered to this type of a fractured and porous bedrock system at concentrations and residence times potentially sufficient for enhanced aerobic biodegradation. Copyright © 2010 Elsevier B.V. All rights reserved.

Oxygen, carbon, and nutrient exchanges at the sediment-water interface in the Mar Piccolo of Taranto (Ionian Sea, southern Italy).

PubMed

De Vittor, Cinzia; Relitti, Federica; Kralj, Martina; Covelli, Stefano; Emili, Andrea

2016-07-01

In the shallow environment, the nutrient and carbon exchanges at the sediment-water interface contribute significantly to determine the trophic status of the whole water column. The intensity of the allochthonous input in a coastal environment subjected to strong anthropogenic pressures determines an increase in the benthic oxygen demand leading to depressed oxygen levels in the bottom waters. Anoxic conditions resulting from organic enrichment can enhance the exchange of nutrients between sediments and the overlying water. In the present study, carbon and nutrient fluxes at the sediment-water interface were measured at two experimental sites, one highly and one moderately contaminated, as reference point. In situ benthic flux measurements of dissolved species (O2, DIC, DOC, N-NO3 (-), N-NO2 (-), N-NH4 (+), P-PO4 (3-), Si-Si(OH)4, H2S) were conducted using benthic chambers. Furthermore, undisturbed sediment cores were collected for analyses of total and organic C, total N, and biopolymeric carbon (carbohydrates, proteins, and lipids) as well as of dissolved species in porewaters and supernatant in order to calculate the diffusive fluxes. The sediments were characterized by suboxic to anoxic conditions with redox values more negative in the highly contaminated site, which was also characterized by higher biopolymeric carbon content (most of all lipids), lower C/N ratios and generally higher diffusive fluxes, which could result in a higher release of contaminants. A great difference was observed between diffusive and in situ benthic fluxes suggesting the enhancing of fluxes by bioturbation and the occurrence of biogeochemically important processes at the sediment-water interface. The multi-contamination of both inorganic and organic pollutants, in the sediments of the Mar Piccolo of Taranto (declared SIN in 1998), potentially transferable to the water column and to the aquatic trophic chain, is of serious concern for its ecological relevance, also considering the widespread fishing and mussel farming activities in the area.

Application of SR Methods for the Study of Nanocomposite Materials for Hydrogen Energy

NASA Astrophysics Data System (ADS)

Sadykov, V. A.; Pavlova, S. N.; Vinokurov, Z. S.; Shmakov, A. N.; Eremeev, N. F.; Fedorova, Yu. E.; Yakimchuk, E. P.; Kriventsov, V. V.; Bolotov, V. A.; Tanashev, Yu. Yu.; Sadovskaya, E. M.; Cherepanova, S. V.; Zolotarev, K. V.

This work summarizes results of synchrotron radiation (SR) studies of the real/defect structure of nanocrystalline/nanocomposite oxide materials, which determines their functional properties in hydrogen energy field as catalysts and mixed ionic electronic conductors (cathodes and anodes of solid oxide fuel cells, oxygen separation membranes). For nanocrystalline ceria-zirconia mixed oxide prepared via modified Pechini route using ethanol solution of reagents, a high spatial uniformity of cations distribution between domains along with the oxygen sublattice deficiency revealed by full-profile Rietveld refinement of SR diffraction data provide structure disordering enhancing oxygen mobility. For PrNi0.5Co0.5O3-δ - Ce0.9Y0.1O2-δ nanocomposite extensive transfer of Pr cations into fluorite domains generates a new path of fast oxygen diffusion along chains of Pr3+ - Pr4+ cations as directly proved by analysis of the unit cell relaxation after changing pO2 in perfect agreement with data obtained by oxygen isotope heteroexchange.

Ultrafast atomic layer-by-layer oxygen vacancy-exchange diffusion in double-perovskite LnBaCo2O5.5+δ thin films.

PubMed

Bao, Shanyong; Ma, Chunrui; Chen, Garry; Xu, Xing; Enriquez, Erik; Chen, Chonglin; Zhang, Yamei; Bettis, Jerry L; Whangbo, Myung-Hwan; Dong, Chuang; Zhang, Qingyu

2014-04-22

Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ (LnBCO) single-crystalline thin films (Ln = Er, Pr; -0.5 < δ < 0.5) by carefully monitoring the resistance changes under a switching flow of oxidizing gas (O2) and reducing gas (H2) in the temperature range of 250 ~ 800 °C. A giant resistance change ΔR by three to four orders of magnitude in less than 0.1 s was found with a fast oscillation behavior in the resistance change rates in the ΔR vs. t plots, suggesting that the oxygen vacancy exchange diffusion with oxygen/hydrogen atoms in the LnBCO thin films is taking the layer by layer oxygen-vacancy-exchange mechanism. The first principles density functional theory calculations indicate that hydrogen atoms are present in LnBCO as bound to oxygen forming O-H bonds. This unprecedented oscillation phenomenon provides the first direct experimental evidence of the layer by layer oxygen vacancy exchange diffusion mechanism.

Oxygen vacancy diffusion in bulk SrTiO3 from density functional theory calculations

DOE PAGES

Zhang, Lipeng; Liu, Bin; Zhuang, Houlong; ...

2016-04-01

Point defects and point defect diffusion contribute significantly to the properties of perovskite materials. However, even for the prototypical case of oxygen vacancies in SrTiO 3 (STO), predictions vary widely. Here we present a comprehensive and systematic study of the diffusion barriers for this material. We use density functional theory (DFT) and assess the role of different cell sizes, density functionals, and charge states. Our results show that vacancy-induced octahedral rotations, which are limited by the boundary conditions of the supercell, can significantly affect the computed oxygen vacancy diffusion energy barrier. The diffusion energy barrier of a charged oxygen vacancymore » is lower than that of a neutral one. Unexpectedly, we find that with increasing supercell size, the effects of the oxygen vacancy charge state, the type of DFT exchange and correlation functional on the energy barrier diminish, and the different DFT predictions asymptote to a value in the range of 0.39-0.49 eV. This work provides important insight and guidance that should be considered for investigations of point defect diffusion in other perovskite materials and in oxide superlattices.« less

Enhanced Biological Attenuation of Aircraft Deicing Fluid Runoff Using Constructed Wetlands

DTIC Science & Technology

2004-09-01

treatment wetlands have variable water column oxygen levels depending on several factors. Atmospheric diffusion, wind action, algae, and macrophytes ...visible to the unassisted eye are called macrophytes and include the vascular, herbaceous, and woody species common to wetland environments. Microbes are...of pH in treatment wetlands shows that typical operational pH levels range from 6.5 to 7.5 13. Rooted wetland macrophytes also actively transport

Remarkably stable amorphous metal oxide grown on Zr-Cu-Be metallic glass

PubMed Central

Lim, Ka Ram; Kim, Chang Eun; Yun, Young Su; Kim, Won Tae; Soon, Aloysius; Kim, Do Hyang

2015-01-01

In the present study, we investigated the role of an aliovalent dopant upon stabilizing the amorphous oxide film. We added beryllium into the Zr50Cu50 metallic glass system, and found that the amorphous oxide layer of Be-rich phase can be stabilized even at elevated temperature above Tg of the glass matrix. The thermal stability of the amorphous oxide layer is substantially enhanced due to Be addition. As confirmed by high-temperature cross-section HR-TEM, fully disordered Be-added amorphous layer is observed, while the rapid crystallization is observed without Be. To understand the role of Be, we employed ab-initio molecular dynamics to compare the mobility of ions with/without Be dopant, and propose a disordered model where Be dopant occupies Zr vacancy and induces structural disorder to the amorphous phase. We find that the oxygen mobility is slightly suppressed due to Be dopant, and Be mobility is unexpectedly lower than that of oxygen, which we attribute to the aliovalent nature of Be dopant whose diffusion always accompany multiple counter-diffusion of other ions. Here, we explain the origin of superior thermal stability of amorphous oxide film in terms of enhanced structural disorder and suppressed ionic mobility due to the aliovalent dopant. PMID:26658671

Remarkably stable amorphous metal oxide grown on Zr-Cu-Be metallic glass.

PubMed

Lim, Ka Ram; Kim, Chang Eun; Yun, Young Su; Kim, Won Tae; Soon, Aloysius; Kim, Do Hyang

2015-12-14

In the present study, we investigated the role of an aliovalent dopant upon stabilizing the amorphous oxide film. We added beryllium into the Zr50Cu50 metallic glass system, and found that the amorphous oxide layer of Be-rich phase can be stabilized even at elevated temperature above Tg of the glass matrix. The thermal stability of the amorphous oxide layer is substantially enhanced due to Be addition. As confirmed by high-temperature cross-section HR-TEM, fully disordered Be-added amorphous layer is observed, while the rapid crystallization is observed without Be. To understand the role of Be, we employed ab-initio molecular dynamics to compare the mobility of ions with/without Be dopant, and propose a disordered model where Be dopant occupies Zr vacancy and induces structural disorder to the amorphous phase. We find that the oxygen mobility is slightly suppressed due to Be dopant, and Be mobility is unexpectedly lower than that of oxygen, which we attribute to the aliovalent nature of Be dopant whose diffusion always accompany multiple counter-diffusion of other ions. Here, we explain the origin of superior thermal stability of amorphous oxide film in terms of enhanced structural disorder and suppressed ionic mobility due to the aliovalent dopant.

Effect of nickel diffusion and oxygen behavior on heterojunction Schottky diodes of Au/NiO/ZnO with a NiO interlayer prepared by radio-frequency magnetron sputtering

NASA Astrophysics Data System (ADS)

Hwang, Jun-Dar; Chen, Hsin-Yu; Chen, Yu-Huang; Ho, Ting-Hsiu

2018-07-01

The rectifying characteristic of Au/ZnO Schottky diodes (SDs) was remarkably improved by introducing a NiO layer in-between the Au and ZnO layers. Compared with the Au/ZnO SDs, the introduction of the NiO layer significantly enhanced the rectification ratio from 1.38 to 1300, and reduced the ideality factor from 5.78 to 2.14. The NiO and ZnO layers were deposited on an indium-tin-oxide/glass substrate by radio-frequency magnetron sputtering. Secondary ion mass spectroscopy showed that Ni atoms diffused from NiO to ZnO, leading to a graded distribution of Ni in ZnO. X-ray diffraction demonstrated that the diffusion of Ni atoms increased the grain size and electron concentration of ZnO. X-ray photoelectron spectroscopy showed that the interstitial oxygen (Oi) atoms in NiO and ZnO compensated the oxygen vacancies (OV) at the NiO/ZnO interface; the amount of OV was significantly reduced, while Oi vanished at the interface. The band diagram revealed a potential drop in the bulk ZnO, owing to the graded distribution of Ni in ZnO, which accelerated the carriers, collected by the outer circuit. The carriers at the NiO/ZnO interface easily crossed over the barrier height, instead of being recombined by OV, owing to the lower amount of OV at the interface.

Reflectance spectroscopy can quantify cutaneous haemoglobin oxygenation by oxygen uptake from the atmosphere after epidermal barrier disruption.

PubMed

Heise, H M; Lampen, P; Stücker, M

2003-11-01

The supply of oxygen to the viable skin tissue within the upper layers is not only secured by the cutaneous blood vascular system, but to a significant part also by oxygen diffusion from the atmosphere through the horny layer. The aim of this study was to examine whether changes in haemoglobin oxygenation can be observed within the isolated perfused bovine udder skin used as a skin model by removing the upper horny layer by adhesive tape stripping. Diffuse reflectance spectroscopy in the visible spectral range was used for non-invasive characterisation of haemoglobin oxygenation in skin under in vitro conditions. Mid-infrared attenuated total reflectance spectroscopy was employed for analysing the surface layer of the stratum corneum with respect to keratin, water and lipid components. Skin barrier disruption was achieved by repeated stripping of superficial corneocyte layers by adhesive tape. Significant changes in skin haemoglobin oxygenation were observed for skin areas with reduced lipid concentration and a reduced stratum corneum layer, as determined from the quantitative evaluation of the diffuse reflectance skin spectra. The result can be interpreted as an increase of oxygen diffusion after the removal of the upper horny layer.

About the Role of the Bottleneck/Cork Interface on Oxygen Transfer.

PubMed

Lagorce-Tachon, Aurélie; Karbowiak, Thomas; Paulin, Christian; Simon, Jean-Marc; Gougeon, Régis D; Bellat, Jean-Pierre

2016-09-07

The transfer of oxygen through a corked bottleneck was investigated using a manometric technique. First, the effect of cork compression on oxygen transfer was evaluated without considering the glass/cork interface. No significant effect of cork compression (at 23% strain, corresponding to the compression level of cork in a bottleneck for still wines) was noticeable on the effective diffusion coefficient of oxygen. The mean value of the effective diffusion coefficient is equal to 10(-8) m(2) s(-1), with a statistical distribution ranging from 10(-10) to 10(-7) m(2) s(-1), which is of the same order of magnitude as for the non-compressed cork. Then, oxygen transfer through cork compressed in a glass bottleneck was determined to assess the effect of the glass/cork interface. In the particular case of a gradient-imposed diffusion of oxygen through our model corked bottleneck system (dry cork without surface treatment; 200 and ∼0 hPa of oxygen on both sides of the sample), the mean effective diffusion coefficient is of 5 × 10(-7) m(2) s(-1), thus revealing the possible importance of the role of the glass/stopper interface in the oxygen transfer.

Titanium aluminide intermetallic alloys with improved wear resistance

DOEpatents

Qu, Jun; Lin, Hua-Tay; Blau, Peter J.; Sikka, Vinod K.

2014-07-08

The invention is directed to a method for producing a titanium aluminide intermetallic alloy composition having an improved wear resistance, the method comprising heating a titanium aluminide intermetallic alloy material in an oxygen-containing environment at a temperature and for a time sufficient to produce a top oxide layer and underlying oxygen-diffused layer, followed by removal of the top oxide layer such that the oxygen-diffused layer is exposed. The invention is also directed to the resulting oxygen-diffused titanium aluminide intermetallic alloy, as well as mechanical components or devices containing the improved alloy composition.

Oxygen gradients in the microcirculation.

PubMed

Pittman, R N

2011-07-01

Early in the last century August Krogh embarked on a series of seminal studies to understand the connection between tissue metabolism and mechanisms by which the cardiovascular system supplied oxygen to meet those needs. Krogh recognized that oxygen was supplied from blood to the tissues by passive diffusion and that the most likely site for oxygen exchange was the capillary network. Studies of tissue oxygen consumption and diffusion coefficient, coupled with anatomical studies of capillarity in various tissues, led him to formulate a model of oxygen diffusion from a single capillary. Fifty years after the publication of this work, new methods were developed which allowed the direct measurement of oxygen in and around microvessels. These direct measurements have confirmed the predictions by Krogh and have led to extensions of his ideas resulting in our current understanding of oxygenation within the microcirculation. Developments during the last 40 years are reviewed, including studies of oxygen gradients in arterioles, capillaries, venules, microvessel wall and surrounding tissue. These measurements were made possible by the development and use of new methods to investigate oxygen in the microcirculation, so mention is made of oxygen microelectrodes, microspectrophotometry of haemoglobin and phosphorescence quenching microscopy. Our understanding of oxygen transport from the perspective of the microcirculation has gone from a consideration of oxygen gradients in capillaries and tissue to the realization that oxygen has the ability to diffuse from any microvessel to another location under the conditions that there exists a large enough PO(2) gradient and that the permeability for oxygen along the intervening pathway is sufficient. © 2011 The Author. Acta Physiologica © 2011 Scandinavian Physiological Society.

Oxygen Gradients in the Microcirculation

PubMed Central

Pittman, Roland N.

2010-01-01

Early in the last century August Krogh embarked on a series of seminal studies to understand the connection between tissue metabolism and mechanisms by which the cardiovascular system supplied oxygen to meet those needs. Krogh recognized that oxygen was supplied from blood to the tissues by passive diffusion and that the most likely site for oxygen exchange was the capillary network. Studies of tissue oxygen consumption and diffusion coefficient, coupled with anatomical studies of capillarity in various tissues, led him to formulate a model of oxygen diffusion from a single capillary. Fifty years after the publication of this work, new methods were developed which allowed the direct measurement of oxygen in and around microvessels. These direct measurements have confirmed the predictions by Krogh and have led to extensions of his ideas resulting in our current understanding of oxygenation within the microcirculation. Developments during the last 40 years are reviewed, including studies of oxygen gradients in arterioles, capillaries, venules, microvessel wall and surrounding tissue. These measurements were made possible by the development and use of new methods to investigate oxygen in the microcirculation, so mention is made of oxygen microelectrodes, microspectrophotometry of haemoglobin and phosphorescence quenching microscopy. Our understanding of oxygen transport from the perspective of the microcirculation has gone from a consideration of oxygen gradients in capillaries and tissue to the realization that oxygen has the ability to diffuse from any microvessel to another location under the conditions that there exists a large enough PO2 gradient and that the permeability for oxygen along the intervening pathway is sufficient. PMID:21281453

Oxygen exchange at gas/oxide interfaces: how the apparent activation energy of the surface exchange coefficient depends on the kinetic regime.

PubMed

Fielitz, Peter; Borchardt, Günter

2016-08-10

In the dedicated literature the oxygen surface exchange coefficient KO and the equilibrium oxygen exchange rate [Fraktur R] are considered to be directly proportional to each other regardless of the experimental circumstances. Recent experimental observations, however, contradict the consequences of this assumption. Most surprising is the finding that the apparent activation energy of KO depends dramatically on the kinetic regime in which it has been determined, i.e. surface exchange controlled vs. mixed or diffusion controlled. This work demonstrates how the diffusion boundary condition at the gas/solid interface inevitably entails a correlation between the oxygen surface exchange coefficient KO and the oxygen self-diffusion coefficient DO in the bulk ("on top" of the correlation between KO and [Fraktur R] for the pure surface exchange regime). The model can thus quantitatively explain the range of apparent activation energies measured in the different regimes: in the surface exchange regime the apparent activation energy only contains the contribution of the equilibrium exchange rate, whereas in the mixed or in the diffusion controlled regime the contribution of the oxygen self-diffusivity has also to be taken into account, which may yield significantly higher apparent activation energies and simultaneously quantifies the correlation KO ∝ DO(1/2) observed for a large number of oxides in the mixed or diffusion controlled regime, respectively.

Is Subsurface Oxygen Necessary for the Electrochemical Reduction of CO 2 on Copper?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garza, Alejandro J.; Bell, Alexis T.; Head-Gordon, Martin

It has recently been proposed that subsurface oxygen is crucial for the adsorption and subsequent electroreduction of CO 2 on copper. Using density functional theory, we have studied the stability and diffusion of subsurface oxygen in single crystals of copper exposing (111) and (100) facets. Oxygen is at least 1.5 eV more stable on the surface than beneath it for both crystal orientations; interstitial sites are too small to accommodate oxygen. Here, the rate of atomic oxygen diffusion from one layer below a Cu(111) surface to the surface is 5 × 10 3 s –1. Oxygen can survive longer inmore » deeper layers, but it does not promote CO 2 adsorption there. Diffusion of subsurface oxygen is easier to the less-dense Cu(100) surface, even from lower layers (rate ≈ 1 × 107 s–1). Finally, once the applied voltage and dispersion forces are properly modeled, we find that subsurface oxygen is unnecessary for CO 2 adsorption on copper.« less

Is Subsurface Oxygen Necessary for the Electrochemical Reduction of CO 2 on Copper?

DOE PAGES

Garza, Alejandro J.; Bell, Alexis T.; Head-Gordon, Martin

2018-01-17

It has recently been proposed that subsurface oxygen is crucial for the adsorption and subsequent electroreduction of CO 2 on copper. Using density functional theory, we have studied the stability and diffusion of subsurface oxygen in single crystals of copper exposing (111) and (100) facets. Oxygen is at least 1.5 eV more stable on the surface than beneath it for both crystal orientations; interstitial sites are too small to accommodate oxygen. Here, the rate of atomic oxygen diffusion from one layer below a Cu(111) surface to the surface is 5 × 10 3 s –1. Oxygen can survive longer inmore » deeper layers, but it does not promote CO 2 adsorption there. Diffusion of subsurface oxygen is easier to the less-dense Cu(100) surface, even from lower layers (rate ≈ 1 × 107 s–1). Finally, once the applied voltage and dispersion forces are properly modeled, we find that subsurface oxygen is unnecessary for CO 2 adsorption on copper.« less

Ion-enhanced oxidation of aluminum as a fundamental surface process during target poisoning in reactive magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuschel, Thomas; Keudell, Achim von

2010-05-15

Plasma deposition of aluminum oxide by reactive magnetron sputtering (RMS) using an aluminum target and argon and oxygen as working gases is an important technological process. The undesired oxidation of the target itself, however, causes the so-called target poisoning, which leads to strong hysteresis effects during RMS operation. The oxidation occurs by chemisorption of oxygen atoms and molecules with a simultaneous ion bombardment being present. This heterogenous surface reaction is studied in a quantified particle beam experiment employing beams of oxygen molecules and argon ions impinging onto an aluminum-coated quartz microbalance. The oxidation and/or sputtering rates are measured with thismore » microbalance and the resulting oxide layers are analyzed by x-ray photoelectron spectroscopy. The sticking coefficient of oxygen molecules is determined to 0.015 in the zero coverage limit. The sputtering yields of pure aluminum by argon ions are determined to 0.4, 0.62, and 0.8 at 200, 300, and 400 eV. The variation in the effective sticking coefficient and sputtering yield during the combined impact of argon ions and oxygen molecules is modeled with a set of rate equations. A good agreement is achieved if one postulates an ion-induced surface activation process, which facilitates oxygen chemisorption. This process may be identified with knock-on implantation of surface-bonded oxygen, with an electric-field-driven in-diffusion of oxygen or with an ion-enhanced surface activation process. Based on these fundamental processes, a robust set of balance equations is proposed to describe target poisoning effects in RMS.« less

Magnetoresistance of oxygen concentration-modulated Co-Ti-O films

NASA Astrophysics Data System (ADS)

Nakano, Masatoshi; Wan, Fuxing; Wang, Jian; Sannomiya, Takumi; Muraishi, Shinji; Harumoto, Takashi; Nakamura, Yoshio; Shi, Ji

2018-06-01

Co-Ti-O films have been prepared by a sputtering method in an Ar- and O2-mixed atmosphere. The O2 flow rate was modulated during the deposition to optimize the oxygen concentration and the microstructure of the films. For the as-deposited film, negligible magnetization and magnetoresistance (MR) were observed. The structure of the layers with lower O2 flow rate is basically amorphous alloy with Ti-O and Co-Ti bonds. On the other hand, in the layers with high O2 flow rate, both Ti and Co are oxidized. Upon thermal annealing in a vacuum, significant enhancements in both magnetization and MR in Co-Ti-O films were observed. It is found that granular structure of Co particles embedded in insulating TiO2 matrix is formed due to the oxygen diffusion and further oxidization of Ti as a result of the heat treatment. The significantly enhanced magnetization and MR ratio have been ascribed to the formation of nano-sized Co particles and the tunneling conduction between these Co particles across the TiO2 interlayers, respectively.

Phase Stability and Transformations in Vanadium Oxide Nanocrystals

NASA Astrophysics Data System (ADS)

Bergerud, Amy Jo

Vanadium oxides are both fascinating and complex, due in part to the many compounds and phases that can be stabilized as well as the phase transformations which occur between them. The metal to insulator transitions (MITs) that take place in vanadium oxides are particularly interesting for both fundamental and applied study as they can be induced by a variety of stimuli ( i.e., temperature, pressure, doping) and utilized in many applications (i.e., smart windows, sensors, phase change memory). Nanocrystals also tend to demonstrate interesting phase behavior, due in part to the enhanced influence of surface energy on material thermodynamics. Vanadium oxide nanocrystals are thus expected to demonstrate very interesting properties in regard to phase stability and phase transformations, although synthesizing vanadium oxides in nanocrystal form remains a challenge. Vanadium sesquioxide (V2O3) is an example of a material that undergoes a MIT. For decades, the low temperature monoclinic phase and high temperature corundum phase were the only known crystal structures of V2O3. However, in 2011, a new metastable polymorph of V2O3 was reported with a cubic, bixbyite crystal structure. In Chapter 2, a colloidal route to bixbyite V2O 3 nanocrystals is presented. In addition to being one of the first reported observations of the bixbyite phase in V2O3, it is also one of the first successful colloidal syntheses of any of the vanadium oxides. The nanocrystals possess a flower-like morphology, the size and shape of which are dependent on synthesis time and temperature, respectively. An aminolysis reaction mechanism is determined from Fourier transform infrared spectroscopy data and the bixbyite crystal structure is confirmed by Rietveld refinement of X-ray diffraction (XRD) data. Phase stability is assessed in both air and inert environments, confirming the metastable nature of the material. Upon heating in an inert atmosphere above 700°C, the nanocrystals irreversibly transform to the bulk stable corundum phase of V2O3 with concurrent particle coarsening. This, in combination with the enhanced stability of the nanocrystals over bulk, suggests that the bixbyite phase may be stabilized due to surface energy effects, a well-known phenomenon in nanocrystal research. In Chapter 3, the reversible incorporation of oxygen in bixbyite V 2O3 is reported, which can be controlled by varying temperature and oxygen partial pressure. Based on XRD and thermogravimetric analysis, it is found that oxygen occupies interstitial sites in the bixbyite lattice. Two oxygen atoms per unit cell can be incorporated rapidly and with minimal changes to the structure while the addition of three or more oxygen atoms destabilizes the structure, resulting in a phase change that can be reversed upon oxygen removal. Density functional theory (DFT) supports the reversible occupation of interstitial sites in bixbyite by oxygen and the 1.1 eV barrier to oxygen diffusion predicted by DFT matches the activation energy of the oxidation process derived from observations by in situ XRD. The observed rapid oxidation kinetics are thus facilitated by short diffusion paths through the bixbyite nanocrystals. Due to the exceptionally low temperatures of oxidation and reduction, this material, made from earth-abundant atoms, is proposed for use in oxygen storage applications, where oxygen is reversibly stored and released. Further oxidation of bixbyite V2O3 under controlled oxygen partial pressure can lead to the formation of nanocrystalline vanadium dioxide (VO2), a material that is studied for its MIT that occurs at 68 C in the bulk. This transformation is accompanied by a change in crystal structure, from monoclinic to rutile phase, and a change in optical properties, from infrared transparent to infrared blocking. Because of this, VO2 is promising for thermochromic smart window applications, where optical properties vary with temperature. Recently, alternative stimuli have been utilized to trigger MITs in VO2, including electrochemical gating. Rather than inducing the expected monoclinic to rutile phase transition as originally proposed, electrochemical gating of the insulating phase was recently shown to induce oxygen vacancy formation in VO2, thereby inducing metallization, while the characteristic V-V dimerization of the monoclinic phase was retained. In Chapter 4, the preparation and electrochemical reduction of VO2 nanocrystal films is presented. The nanocrystalline morphology allows for the study of transformations under conditions that enhance the gating effect by creating a large VO2-electrolyte interfacial area and by reducing the path length for diffusion. The resulting transitions are observed optically, from insulator to metal to insulator and back, with in situ visible-near infrared spectroelectrochemistry and correlated with structural changes monitored by Raman and X-ray absorption spectroscopies. The never-before-seen transition to an insulating phase under progressive electrochemical reduction is attributed to an oxygen defect induced phase transition to a new phase. This is likely enabled by the nanocrystalline nature of the sample, which may enhance the kinetics of oxygen diffusion, support a higher degree of lattice expansion-induced strain, or simply alter the thermodynamics of the system.

The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT).

PubMed

Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

2016-11-22

The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La 3+ donor-doped, Fe 3+ acceptor-doped and La 3+ /Fe 3+ -co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT)

PubMed Central

Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

2016-01-01

The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT. PMID:28774067

Diffusion in cementitious materials. 2: Further investigations of chloride and oxygen diffusion in well-cured OPC and OPC/30%PFA pastes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ngala, V.T.; Page, C.L.; Parrott, L.J.

1995-05-01

Steady-state diffusion of dissolved oxygen and chloride ions in hydrated OPC and OPC/30%PFA pastes, hydrated for 2 weeks at 20 C and 10 weeks at 38 C, was studied at water/binder (w/s) ratios 0.4, 0.5, 0.6 and 0.7. Total porosity and a simple measure of capillary porosity, the volume fractions of the water lost in specimens from a saturated surface dry condition to a near-constant weight at 90.7% relative humidity, were also determined. The diffusion rate of chloride ions diminished markedly, to very low values, as the capillary porosity approached zero. For a given w/s ratio or capillary porosity themore » chloride ion diffusion coefficient for OPC/30%PFA pastes was about one order of magnitude smaller than that to OPC pastes. The rate of diffusion of dissolved oxygen also diminished as the capillary porosity reduced but it was still significant as the capillary porosity approached zero. For a given capillary porosity the oxygen diffusion coefficient for OPC/30%PFA pastes was about 30% smaller than that for OPC pastes. The results support the view that chloride ion diffusion in pastes of low capillary porosity is retarded by the surface charge of the hydrated cement gel. In contrast, the hydrated cement gel is much more permeable to the similarly-sized, neutral oxygen molecule.« less

Oxygen diffusion and consumption in extracellular matrix gels: implications for designing three-dimensional cultures.

PubMed

Colom, Adai; Galgoczy, Roland; Almendros, Isaac; Xaubet, Antonio; Farré, Ramon; Alcaraz, Jordi

2014-08-01

Three-dimensional (3D) cultures are increasingly used as tissue surrogates to study many physiopathological processes. However, to what extent current 3D culture protocols provide physiologic oxygen tension conditions remains ill defined. To address this limitation, oxygen tension was measured in a panel of acellular or cellularized extracellular matrix (ECM) gels with A549 cells, and analyzed in terms of oxygen diffusion and consumption. Gels included reconstituted basement membrane, fibrin and collagen. Oxygen diffusivity in acellular gels was up to 40% smaller than that of water, and the lower values were observed in the denser gels. In 3D cultures, physiologic oxygen tension was achieved after 2 days in dense (≥3 mg/mL) but not sparse gels, revealing that the latter gels are not suitable tissue surrogates in terms of oxygen distribution. In dense gels, we observed a dominant effect of ECM composition over density in oxygen consumption. All diffusion and consumption data were used in a simple model to estimate ranges for gel thickness, seeding density and time-window that may support physiologic oxygen tension. Thus, we identified critical variables for oxygen tension in ECM gels, and introduced a model to assess initial values of these variables, which may short-cut the optimization step of 3D culture studies. © 2013 Wiley Periodicals, Inc.

Excess oxygen limited diffusion and precipitation of iron in amorphous silicon dioxide

NASA Astrophysics Data System (ADS)

Leveneur, J.; Langlois, M.; Kennedy, J.; Metson, James B.

2017-10-01

In micro- and nano- electronic device fabrication, and particularly 3D designs, the diffusion of a metal into sublayers during annealing needs to be minimized as it is usually detrimental to device performance. Diffusion also causes the formation and growth of nanoprecipitates in solid matrices. In this paper, the diffusion behavior of low energy, low fluence, ion implanted iron into a thermally grown silicon oxide layer on silicon is investigated. Different ion beam analysis and imaging techniques were used. Magnetization measurements were also undertaken to provide evidence of nanocrystalline ordering. While standard vacuum furnace annealing and electron beam annealing lead to fast diffusion of the implanted species towards the Si/SiO2 interface, we show that furnace annealing in an oxygen rich atmosphere prevents the diffusion of iron that, in turn, limits the growth of the nanoparticles. The diffusion and particle growth is also greatly reduced when oxygen atoms are implanted in the SiO2 prior to Fe implantation, effectively acting as a diffusion barrier. The excess oxygen is hypothesized to trap Fe atoms and reduce their mean free path during the diffusion. Monte-Carlo simulations of the diffusion process which consider the random walk of Fe, Fick's diffusion of O atoms, Fe precipitation, and desorption of the SiO2 layer under the electron beam annealing were performed. Simulation results for the three preparation conditions are found in good agreement with the experimental data.

Perfluorocarbons enhance a T2*-based MRI technique for identifying the penumbra in a rat model of acute ischemic stroke

PubMed Central

Deuchar, Graeme A; Brennan, David; Griffiths, Hugh; Macrae, I  Mhairi; Santosh, Celestine

2013-01-01

Accurate imaging of ischemic penumbra is crucial for improving the management of acute stroke patients. T2* magnetic resonance imaging (MRI) combined with a T2*oxygen challenge (T2*OC) is being developed to detect penumbra based on changes in blood deoxyhemoglobin. Using 100% O2, T2*OC-defined penumbra exhibits ongoing glucose metabolism and tissue recovery on reperfusion. However, potential limitations in translating this technique include a sinus artefact in human scans with delivery of 100% OC and relatively small signal changes. Here we investigate whether an oxygen-carrying perfluorocarbon (PFC) emulsion can enhance the sensitivity of the technique, enabling penumbra detection with lower levels of inspired oxygen. Stroke was induced in male Sprague-Dawley rats (n=17) with ischemic injury and perfusion deficit determined by diffusion and perfusion MRI, respectively. T2* signal change was measured in regions of interest (ROIs) located within ischemic core, T2*OC-defined penumbra and equivalent contralateral areas during 40% O2±prior PFC injection. Region of interest analyses between groups showed that PFC significantly enhanced the T2* response to 40% O2 in T2*-defined penumbra (mean increase of 10.6±2.3% compared to 5.6±1.5% with 40% O2, P<0.001). This enhancement was specific to the penumbra ROI. Perfluorocarbon emulsions therefore enhances the translational potential of the T2*OC technique for identifying penumbra in acute stroke patients. PMID:23801243

Kinetic Monte Carlo Simulations of Diffusion in Environmental Barrier Coating Materials

NASA Technical Reports Server (NTRS)

Good, Brian

2017-01-01

Ceramic Matrix Components (CMC) components for use in turbine engines offer a number of advantages compared with current practice. However, such components are subject to degradation through a variety of mechanisms. In particular, in the hot environment inside a turbine in operation a considerable amount of water vapor is present, and this can lead to corrosion and recession. Environmental Barrier Coating (EBC) systems that limit the amount of oxygen and water reaching the component are required to reduce this degradation and extend component life. A number of silicate-based materials are under consideration for use in such coating systems, including Yttterbium and Yttrium di- and monosilicates. In this work, we present results of kinetic Monte Carlo computer simulations of oxygen diffusion in Yttrium disilicate, and compare with previous work on Yttterbium disilicate. Coatings may also exhibit cracking, and the cracks can provide a direct path for oxygen to reach the component. There is typically a bond coat between the coating and component surface, but the bond coat material is generally chosen for properties other than low oxygen diffusivity. Nevertheless, the degree to which the bond coat can inhibit oxygen diffusion is of interest, as it may form the final defense against oxygen impingement on the component. We have therefore performed similar simulations of oxygen diffusion through HfSiO4, a proposed bond coat material.

Oxygen self-diffusion in diopside with application to cooling rate determinations

NASA Astrophysics Data System (ADS)

Farver, John R.

1989-04-01

The kinetics of oxygen self-diffusion in a natural diopside have been measured over the temperature range 700-1250°C. Experiments were run under hydrothermal conditions using 18O-enriched water. Profiles of 18O/( 16O+ 18O) versus depth into the crystal were obtained using an ion microprobe. At 1000 bars (100 MPa) confining pressure, the Arrhenius relation for diffusion parallel to the c crystallographic direction yields a pre-exponential factor ( D0) = 1.5 × 10 -6 cm 2/s and an activation energy ( Q) = 54 ± 5 kcal/g-atom O (226 kJ/g-atom O) over the temperature range of the experiments. Diffusion coefficients parallel to the c crystallographic direction are ≈ 100 times greater than perpendicular to c. The oxygen self-diffusion coefficient obtained for diopside is ≈ 1000 times less than that for diffusion in feldspars, and ≈ 100 times less than that for quartz at 800°C, transport parallel to the c axis. Closure temperatures calculated for oxygen diffusional exchange in natural diopside are significantly higher than for quartz or feldspars. Measurable oxygen isotope exchange in diopside by diffusion would require geological settings with very high temperatures maintained for very long durations. The oxygen diffusional exchange kinetics in diopside presented in this paper find important applications in studies of meteoric hydrothermal circulation systems and the time-temperature history of high-grade regionally metamorphosed terrains. Examples considered include the Outer Unlayered Gabbro, Cuillins Gabbro Complex, Isle of Skye, Scotland, and the granulite-grade Turpentine Hill Metamorphics near Einasleigh, Queensland, Australia.

Oxygen depletion speeds and simplifies diffusion in HeLa cells.

PubMed

Edwald, Elin; Stone, Matthew B; Gray, Erin M; Wu, Jing; Veatch, Sarah L

2014-10-21

Many cell types undergo a hypoxic response in the presence of low oxygen, which can lead to transcriptional, metabolic, and structural changes within the cell. Many biophysical studies to probe the localization and dynamics of single fluorescently labeled molecules in live cells either require or benefit from low-oxygen conditions. In this study, we examine how low-oxygen conditions alter the mobility of a series of plasma membrane proteins with a range of anchoring motifs in HeLa cells at 37°C. Under high-oxygen conditions, diffusion of all proteins is heterogeneous and confined. When oxygen is reduced with an enzymatic oxygen-scavenging system for ≥ 15 min, diffusion rates increase by > 2-fold, motion becomes unconfined on the timescales and distance scales investigated, and distributions of diffusion coefficients are remarkably consistent with those expected from Brownian motion. More subtle changes in protein mobility are observed in several other laboratory cell lines examined under both high- and low-oxygen conditions. Morphological changes and actin remodeling are observed in HeLa cells placed in a low-oxygen environment for 30 min, but changes are less apparent in the other cell types investigated. This suggests that changes in actin structure are responsible for increased diffusion in hypoxic HeLa cells, although superresolution localization measurements in chemically fixed cells indicate that membrane proteins do not colocalize with F-actin under either experimental condition. These studies emphasize the importance of controls in single-molecule imaging measurements, and indicate that acute response to low oxygen in HeLa cells leads to dramatic changes in plasma membrane structure. It is possible that these changes are either a cause or consequence of phenotypic changes in solid tumor cells associated with increased drug resistance and malignancy.

Determination of kinetic data for soot oxidation: Modeling of competition between oxygen diffusion and reaction during thermogravimetric analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilot, P.; Bonnefoy, F.; Marcuccilli, F.

1993-10-01

Kinetic data concerning carbon black oxidation in the temperature range between 600 and 900 C have been obtained using thermogravimetric analysis. Modeling of diffusion in a boundary layer above the pan and inside the porous medium coupled to oxygen reaction with carbon black is necessary to obtain kinetic constants as a function of temperature. These calculations require the knowledge of the oxidation rate at a given constant temperature as a function of the initial mass loading m[sub o]. This oxidation rate, expressed in milligrams of soot consumed per second and per milligram of initial soot loading, decreases when m[sub o]more » increases, in agreement with a reaction in an intermediary regime where the kinetics and the oxygen diffusion operate. The equivalent diffusivity of oxygen inside the porous medium is evaluated assuming two degrees of porosity: between soot aggregates and inside each aggregate. Below 700 C an activation energy of about 103 kJ/mol can be related to a combustion reaction probably kinetically controlled. Beyond 700 C the activation energy of about 20 kJ/ mol corresponds to a reaction essentially controlled by oxygen diffusion leading to a constant density oxidation with oxygen consumption at or near the particle surface. To validate these data, they are used in the modeling of a Diesel particulate trap regeneration. In this particular case, the oxidizing flux is forced across the carbon black deposit, oxygen diffusion being insignificant. A good agreement between experimental results and model predictions is obtained, proving the rate constants validity.« less

Oxygen chemical diffusion in hypo-stoichiometric MOX

NASA Astrophysics Data System (ADS)

Kato, Masato; Morimoto, Kyoichi; Tamura, Tetsuya; Sunaoshi, Takeo; Konashi, Kenji; Aono, Shigenori; Kashimura, Motoaki

2009-06-01

Kinetics of the oxygen-to-metal ratio change in (U 0.8Pu 0.2)O 2-x and (U 0.7Pu 0.3)O 2-x was evaluated in the temperature range of 1523-1623 K using a thermo-gravimetric technique. The oxygen chemical diffusion coefficients were decided as a function of temperature from the kinetics of the reduction process under a hypo-stoichiometric composition. The diffusion coefficient of (U 0.7Pu 0.3)O 2-x was smaller than that of (U 0.8Pu 0.2)O 2-x. No strong dependence was observed for the diffusion coefficient on the O/M variation of samples.

Stability of nanoclusters in an oxide dispersion strengthened alloy under neutron irradiation

DOE PAGES

Liu, Xiang; Miao, Yinbin; Wu, Yaqiao; ...

2017-06-01

In this paper, we report atom probe tomography results of the nanoclusters in a neutron-irradiated oxide dispersion strengthened alloy. Following irradiation to 5 dpa at target temperatures of 300 °C and 450 °C, fewer large nanoclusters were found and the residual nanoclusters tend to reach an equilibrium Guinier radius of 1.8 nm. With increasing dose, evident decrease in peak oxygen and titanium (but not yttrium) concentrations in the nanoclusters was observed, which was explained by atomic weight, solubility, diffusivity, and chemical bonding arguments. Finally, the chemical modifications indicate the equilibrium size is indeed a balance of two competing processes: radiationmore » enhanced diffusion and collisional dissolution.« less

Theoretical analysis of oxygen diffusion at startup in an alkali metal heat pipe with gettered alloy walls

NASA Technical Reports Server (NTRS)

Tower, L. K.

1973-01-01

The diffusion of oxygen into, or out of, a gettered alloy exposed to oxygenated alkali liquid metal coolant, a situation arising in some high temperature heat transfer systems, was analyzed. The relation between the diffusion process and the thermochemistry of oxygen in the alloy and in the alkali metal was developed by making several simplifying assumptions. The treatment is therefore theoretical in nature. However, a practical example pertaining to the startup of a heat pipe with walls of T-111, a tantalum alloy, and lithium working fluid illustrates the use of the figures contained in the analysis.

Myocardial oxygen delivery after experimental hemorrhagic shock.

PubMed Central

Archie, J P; Mertz, W R

1978-01-01

The two components of myocardial oxygen delivery, coronary blood flow to capillaries and diffusion from capillaries to mitochondria, were studied in six dogs, (1) prior to shock, (2) after three hours of hemorrhage shock at a mean systemic arterial pressure of 40 torr, (3) after reinfusion of shed blood, and (4) during the irreversible late posttransfusion stage. There was a maldistribution of left ventricular coronary flow during late shock consistent with subendocardial ischemia. Cardiac performance was significantly impaired after resuscitation and all dogs became irreversible. Total and regional left ventricular coronary blood flow and myocardial oxygen delivery to capillaries were significantly greater than preshock values in (3) but not different from preshock values in (4). However, the myocardial oxygen diffusion area to distance ratio was significantly lower than preshock values in (3), and slightly lower in (4). These data suggest that myocardial oxygen diffusion may be impaired in the early post transfusion period, (3). Accordingly, the probable etiology of left ventricular dysfunction and possibly irreversibility after resuscitation from hemorrhagic shock is subendocardial ischemia during shock with either post-resuscitation impairment of myocardial oxygen diffusion, or in cellular oxygen utilization, or both. PMID:629622

A compartment model of alveolar-capillary oxygen diffusion with ventilation-perfusion gradient and dynamics of air transport through the respiratory tract.

PubMed

Jaworski, Jacek; Redlarski, Grzegorz

2014-08-01

This paper presents a model of alveolar-capillary oxygen diffusion with dynamics of air transport through the respiratory tract. For this purpose electrical model representing the respiratory tract mechanics and differential equations representing oxygen membrane diffusion are combined. Relevant thermodynamic relations describing the mass of oxygen transported into the human body are proposed as the connection between these models, as well as the influence of ventilation-perfusion mismatch on the oxygen diffusion. The model is verified based on simulation results of varying exercise intensities and statistical calculations of the results obtained during various clinical trials. The benefit of the approach proposed is its application in simulation-based research aimed to generate quantitative data of normal and pathological conditions. Based on the model presented, taking into account many essential physiological processes and air transport dynamics, comprehensive and combined studies of the respiratory efficiency can be performed. The impact of physical exercise, precise changes in respiratory tract mechanics and alterations in breathing pattern can be analyzed together with the impact of various changes in alveolar-capillary oxygen diffusion. This may be useful in simulation of effects of many severe medical conditions and increased activity level. Copyright © 2014 Elsevier Ltd. All rights reserved.

Enhancing the methanol tolerance of platinum nanoparticles for the cathode reaction of direct methanol fuel cells through a geometric design.

PubMed

Feng, Yan; Ye, Feng; Liu, Hui; Yang, Jun

2015-11-18

Mastery over the structure of nanoparticles might be an effective way to enhance their performance for a given application. Herein we demonstrate the design of cage-bell nanostructures to enhance the methanol tolerance of platinum (Pt) nanoparticles while remaining their catalytic activity for oxygen reduction reaction. This strategy starts with the synthesis of core-shell-shell nanoparticles with Pt and silver (Ag) residing respectively in the core and inner shell regions, which are then agitated with saturated sodium chloride (NaCl) solution to eliminate the Ag component from the inner shell region, leading to the formation of bimetallic nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a metal shell with nano-channels, which exhibit superior methanol-tolerant property in catalyzing oxygen reduction reaction due to the different diffusion behaviour of methanol and oxygen in the porous metal shell of cage-bell structured nanoparticles. In particular, the use of remarkably inexpensive chemical agent (NaCl) to promote the formation of cage-bell structured particles containing a wide spectrum of metal shells highlights its engineering merit to produce highly selective electrocatalysts on a large scale for the cathode reaction of direct methanol fuel cells.

Platinum-Coated Hollow Graphene Nanocages as Cathode Used in Lithium-Oxygen Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Feng; Xing, Yi; Zeng, Xiaoqiao

2016-08-31

One of the formidable challenges facing aprotic lithium-oxygen (Li-O-2) batteries is the high charge overpotential, which induces the formation of byproducts, loss in efficiency, and poor cycling performance. Herein, the synthesis of the ultrasmall Pt-coated hollow graphene nano cages as cathode in Li-O-2 batteries is reported. The charge voltage plateau can reduce to 3.2 V at the current density of 100 mA g(-1), even maintain below 3.5 V when the current density increased to 500 mA g(-1). The unique hollow graphene nanocages matrix can not only provide numerous nanoscale tri-phase regions as active sites for efficient oxygen reduction, but alsomore » offer sufficient amount of mesoscale pores for rapid oxygen diffusion. Furthermore, with strong atomic-level oxygen absorption into its subsurface, ultrasmall Pt catalytically serves as the nucleation site for Li2O2 growth. The Li2O2 is subsequently induced into a favorable form with small size and amorphous state, decomposed more easily during recharge. Meanwhile, the conductive hollow graphene substrate can enhance the catalytic activity of noble metal Pt catalysts due to the graphene-metal interfacial interaction. Benefiting from the above synergistic effects between the hollow graphene nanocages and the nanosized Pt catalysts, the ultrasmall Pt-decorated graphene nanocage cathode exhibits enhanced electrochemical performances.« less

Effect of Oxygen Enrichment in Propane Laminar Diffusion Flames under Microgravity and Earth Gravity Conditions

NASA Astrophysics Data System (ADS)

Bhatia, Pramod; Singh, Ravinder

2017-06-01

Diffusion flames are the most common type of flame which we see in our daily life such as candle flame and match-stick flame. Also, they are the most used flames in practical combustion system such as industrial burner (coal fired, gas fired or oil fired), diesel engines, gas turbines, and solid fuel rockets. In the present study, steady-state global chemistry calculations for 24 different flames were performed using an axisymmetric computational fluid dynamics code (UNICORN). Computation involved simulations of inverse and normal diffusion flames of propane in earth and microgravity condition with varying oxidizer compositions (21, 30, 50, 100 % O2, by mole, in N2). 2 cases were compared with the experimental result for validating the computational model. These flames were stabilized on a 5.5 mm diameter burner with 10 mm of burner length. The effect of oxygen enrichment and variation in gravity (earth gravity and microgravity) on shape and size of diffusion flames, flame temperature, flame velocity have been studied from the computational result obtained. Oxygen enrichment resulted in significant increase in flame temperature for both types of diffusion flames. Also, oxygen enrichment and gravity variation have significant effect on the flame configuration of normal diffusion flames in comparison with inverse diffusion flames. Microgravity normal diffusion flames are spherical in shape and much wider in comparison to earth gravity normal diffusion flames. In inverse diffusion flames, microgravity flames were wider than earth gravity flames. However, microgravity inverse flames were not spherical in shape.

Thermodynamic approach to oxygen delivery in vivo by natural and artificial oxygen carriers.

PubMed

Bucci, Enrico

2009-06-01

Oxygen is a toxic gas, still indispensable to aerobic life. This paper explores how normal physiology uses the physico-chemical and thermodynamic characteristics of oxygen for transforming a toxic gas into a non toxic indispensable metabolite. Plasma oxygen concentration is in the range of 10(-5) M, insufficient to sustain metabolism. Oxygen carriers, present in blood, release oxygen into plasma, thereby replacing consumed oxygen and buffering PO(2) near their P(50). They are the natural cell-bound carriers, like hemoglobin inside red cells, myoglobin inside myocytes, and artificial cell-free hemoglobin-based oxygen carriers (HBOC) dissolved in plasma. Metabolic oxygen replacement can be defined as cell-bound and cell-free delivery. Cell-bound delivery is retarded by the slow diffusion of oxygen in plasma and interstitial fluids. The 40% hematocrit of normal blood compensates for the delay, coping with the fast oxygen consumption by mitochondria. Facilitated oxygen diffusion by HBOCs corrects for the slow diffusion, making cell-free delivery relatively independent from P(50). At all oxygen affinities, HBOCs produce hyperoxygenations that are compensated by vasoconstrictions. There is a strict direct correlation between the rate of oxygen replacement and hemoglobin content of blood. The free energy loss of the gradient adds a relevant regulation of tissues oxygenation. Oxygen is retained intravascularly by the limited permeability to gases of vessel walls.

Constraints on oxygen fugacity within metal capsules

NASA Astrophysics Data System (ADS)

Faul, Ulrich H.; Cline, Christopher J., II; Berry, Andrew; Jackson, Ian; Garapić, Gordana

2018-06-01

Experiments were conducted with olivine encapsulated or wrapped in five different metals (Pt, Ni, Ni_{70}Fe_{30}, Fe, and Re) to determine the oxygen fugacity in the interior of large capsules used for deformation and seismic property experiments. Temperature (1200°C), pressure (300 MPa), and duration (24 h) were chosen to represent the most common conditions in these experiments. The oxygen fugacity was determined by analysing the Fe content of initially pure Pt particles that were mixed with the olivine powder prior to the experiments. Oxygen fugacities in the more oxidizing metal containers are substantially below their respective metal-oxide buffers, with the fO_2 of sol-gel olivine in Ni about 2.5 orders of magnitude below Ni-NiO. Analysis of olivine and metal blebs reveals three different length-, and hence diffusive time scales: (1) Fe loss to the capsule over ˜ 100 μ m, (2) fO_2 gradients at the sample-capsule interface up to 2 mm into the sample, and (3) constant interior fO_2 values with an ordering corresponding to the capsule material. The inferred diffusive processes are: Fe diffusion in olivine with a diffusivity ˜ 10^{-14} m^2/s, diffusion possibly of oxygen along grain boundaries with a diffusivity ˜ 10^{-12} m^2/s, and diffusion possibly involving pre-existing defects with a diffusivity ˜ 10^{-10} m^2/s. The latter, fast adjustment to changing fO_2 may consist of a rearrangement of pre-existing defects, representing a metastable equilibrium, analogous to decoration of pre-existing defects by hydrogen. Full adjustment to the external fO_2 requires atomic diffusion.

A method for modeling oxygen diffusion in an agent-based model with application to host-pathogen infection

DOE PAGES

Plimpton, Steven J.; Sershen, Cheryl L.; May, Elebeoba E.

2015-01-01

This paper describes a method for incorporating a diffusion field modeling oxygen usage and dispersion in a multi-scale model of Mycobacterium tuberculosis (Mtb) infection mediated granuloma formation. We implemented this method over a floating-point field to model oxygen dynamics in host tissue during chronic phase response and Mtb persistence. The method avoids the requirement of satisfying the Courant-Friedrichs-Lewy (CFL) condition, which is necessary in implementing the explicit version of the finite-difference method, but imposes an impractical bound on the time step. Instead, diffusion is modeled by a matrix-based, steady state approximate solution to the diffusion equation. Moreover, presented in figuremore » 1 is the evolution of the diffusion profiles of a containment granuloma over time.« less

Diffusive flux in a model of stochastically gated oxygen transport in insect respiration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berezhkovskii, Alexander M.; Shvartsman, Stanislav Y.

Oxygen delivery to insect tissues is controlled by transport through a branched tubular network that is connected to the atmosphere by valve-like gates, known as spiracles. In certain physiological regimes, the spiracles appear to be randomly switching between open and closed states. Quantitative analysis of this regime leads a reaction-diffusion problem with stochastically switching boundary condition. We derive an expression for the diffusive flux at long times in this problem. Our approach starts with the derivation of the passage probability for a single particle that diffuses between a stochastically gated boundary, which models the opening and closing spiracle, and themore » perfectly absorbing boundary, which models oxygen absorption by the tissue. This passage probability is then used to derive an expression giving the diffusive flux as a function of the geometric parameters of the tube and characteristic time scales of diffusion and gate dynamics.« less

Diffusive flux in a model of stochastically gated oxygen transport in insect respiration.

PubMed

Berezhkovskii, Alexander M; Shvartsman, Stanislav Y

2016-05-28

Oxygen delivery to insect tissues is controlled by transport through a branched tubular network that is connected to the atmosphere by valve-like gates, known as spiracles. In certain physiological regimes, the spiracles appear to be randomly switching between open and closed states. Quantitative analysis of this regime leads a reaction-diffusion problem with stochastically switching boundary condition. We derive an expression for the diffusive flux at long times in this problem. Our approach starts with the derivation of the passage probability for a single particle that diffuses between a stochastically gated boundary, which models the opening and closing spiracle, and the perfectly absorbing boundary, which models oxygen absorption by the tissue. This passage probability is then used to derive an expression giving the diffusive flux as a function of the geometric parameters of the tube and characteristic time scales of diffusion and gate dynamics.

Effect of ship locking on sediment oxygen uptake in impounded rivers

NASA Astrophysics Data System (ADS)

Lorke, A.; McGinnis, D. F.; Maeck, A.; Fischer, H.

2012-12-01

In the majority of large river systems, flow is regulated and/or otherwise affected by operational and management activities, such as ship locking. The effect of lock operation on sediment-water oxygen fluxes was studied within a 12.9 km long impoundment at the Saar River (Germany) using eddy-correlation flux measurements. The continuous observations cover a time period of nearly 5 days and 39 individual locking events. Ship locking is associated with the generation of surges propagating back and forth through the impoundment which causes strong variations of near-bed current velocity and turbulence. These wave-induced flow variations cause variations in sediment-water oxygen fluxes. While the mean flux during time periods without lock operation was 0.5 ± 0.1 g m-2 d-1, it increased by about a factor of 2 to 1.0 ± 0.5 g m-2 d-1within time periods with ship locking. Following the daily schedule of lock operations, fluxes are predominantly enhanced during daytime and follow a pronounced diurnal rhythm. The driving force for the increased flux is the enhancement of diffusive transport across the sediment-water interface by bottom-boundary layer turbulence and perhaps resuspension. Additional means by which the oxygen budget of the impoundment is affected by lock-induced flow variations are discussed.

Dislocations Accelerate Oxygen Ion Diffusion in La 0.8Sr 0.2MnO 3 Epitaxial Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Navickas, Edvinas; Chen, Yan; Lu, Qiyang

Revealing whether dislocations accelerate oxygen ion transport is important for providing abilities in tuning the ionic conductivity of ceramic materials. In this study, we report how dislocations affect oxygen ion diffusion in Sr-doped LaMnO 3 (LSM), a model perovskite oxide that serves in energy conversion technologies. LSM epitaxial thin films with thicknesses ranging from 10 nm to more than 100 nm were prepared by pulsed laser deposition on single-crystal LaAlO 3 and SrTiO 3 substrates. The lattice mismatch between the film and substrates induces compressive or tensile in-plane strain in the LSM layers. This lattice strain is partially reduced bymore » dislocations, especially in the LSM films on LaAlO 3. Oxygen isotope exchange measured by secondary ion mass spectrometry revealed the existence of at least two very different diffusion coefficients in the LSM films on LaAlO 3. In conclusion, the diffusion profiles can be quantitatively explained by the existence of fast oxygen ion diffusion along threading dislocations that is faster by up to 3 orders of magnitude compared to that in LSM bulk.« less

Dislocations Accelerate Oxygen Ion Diffusion in La0.8Sr0.2MnO3 Epitaxial Thin Films

PubMed Central

2017-01-01

Revealing whether dislocations accelerate oxygen ion transport is important for providing abilities in tuning the ionic conductivity of ceramic materials. In this study, we report how dislocations affect oxygen ion diffusion in Sr-doped LaMnO3 (LSM), a model perovskite oxide that serves in energy conversion technologies. LSM epitaxial thin films with thicknesses ranging from 10 nm to more than 100 nm were prepared by pulsed laser deposition on single-crystal LaAlO3 and SrTiO3 substrates. The lattice mismatch between the film and substrates induces compressive or tensile in-plane strain in the LSM layers. This lattice strain is partially reduced by dislocations, especially in the LSM films on LaAlO3. Oxygen isotope exchange measured by secondary ion mass spectrometry revealed the existence of at least two very different diffusion coefficients in the LSM films on LaAlO3. The diffusion profiles can be quantitatively explained by the existence of fast oxygen ion diffusion along threading dislocations that is faster by up to 3 orders of magnitude compared to that in LSM bulk. PMID:28981249

Dislocations Accelerate Oxygen Ion Diffusion in La 0.8Sr 0.2MnO 3 Epitaxial Thin Films

DOE PAGES

Navickas, Edvinas; Chen, Yan; Lu, Qiyang; ...

2017-10-05

Revealing whether dislocations accelerate oxygen ion transport is important for providing abilities in tuning the ionic conductivity of ceramic materials. In this study, we report how dislocations affect oxygen ion diffusion in Sr-doped LaMnO 3 (LSM), a model perovskite oxide that serves in energy conversion technologies. LSM epitaxial thin films with thicknesses ranging from 10 nm to more than 100 nm were prepared by pulsed laser deposition on single-crystal LaAlO 3 and SrTiO 3 substrates. The lattice mismatch between the film and substrates induces compressive or tensile in-plane strain in the LSM layers. This lattice strain is partially reduced bymore » dislocations, especially in the LSM films on LaAlO 3. Oxygen isotope exchange measured by secondary ion mass spectrometry revealed the existence of at least two very different diffusion coefficients in the LSM films on LaAlO 3. In conclusion, the diffusion profiles can be quantitatively explained by the existence of fast oxygen ion diffusion along threading dislocations that is faster by up to 3 orders of magnitude compared to that in LSM bulk.« less

Utilizing multiple state variables to improve the dynamic range of analog switching in a memristor

NASA Astrophysics Data System (ADS)

Jeong, YeonJoo; Kim, Sungho; Lu, Wei D.

2015-10-01

Memristors and memristive systems have been extensively studied for data storage and computing applications such as neuromorphic systems. To act as synapses in neuromorphic systems, the memristor needs to exhibit analog resistive switching (RS) behavior with incremental conductance change. In this study, we show that the dynamic range of the analog RS behavior can be significantly enhanced in a tantalum-oxide-based memristor. By controlling different state variables enabled by different physical effects during the RS process, the gradual filament expansion stage can be selectively enhanced without strongly affecting the abrupt filament length growth stage. Detailed physics-based modeling further verified the observed experimental effects and revealed the roles of oxygen vacancy drift and diffusion processes, and how the diffusion process can be selectively enhanced during the filament expansion stage. These findings lead to more desirable and reliable memristor behaviors for analog computing applications. Additionally, the ability to selectively control different internal physical processes demonstrated in the current study provides guidance for continued device optimization of memristor devices in general.

Oxygen-induced high diffusion rate of magnesium dopants in GaN/AlGaN based UV LED heterostructures.

PubMed

Michałowski, Paweł Piotr; Złotnik, Sebastian; Sitek, Jakub; Rosiński, Krzysztof; Rudziński, Mariusz

2018-05-23

Further development of GaN/AlGaN based optoelectronic devices requires optimization of the p-type material growth process. In particular, uncontrolled diffusion of Mg dopants may decrease the performance of a device. Thus it is meaningful to study the behavior of Mg and the origins of its diffusion in detail. In this work we have employed secondary ion mass spectrometry to study the diffusion of magnesium in GaN/AlGaN structures. We show that magnesium has a strong tendency to form Mg-H complexes which immobilize Mg atoms and restrain their diffusion. However, these complexes are not present in samples post-growth annealed in an oxygen atmosphere or Al-rich AlGaN structures which naturally have a high oxygen concentration. In these samples, more Mg atoms are free to diffuse and thus the average diffusion length is considerably larger than for a sample annealed in an inert atmosphere.

Hyperthermal atomic oxygen generator

NASA Technical Reports Server (NTRS)

Khandelwal, Govind S.; Wu, Dongchuan

1990-01-01

Characterization of the transport properties of oxygen through silver was continued. Specifically, experiments measuring the transport through Ag(111), Ag(110), Ag(100) single crystals and through Ag0.05 Zr alloy were completed. In addition, experiments using glow discharge excitation of oxygen to assist in the transport were completed. It was found that the permeability through the different orientations of single crystal Ag was the same, but significant differences existed in the diffusivity. The experimental ratio of diffusivities, however, was in reasonable agreement with theoretical estimates. Since the solubilities of orientations must be the same, this suggests some problems with the assumption K = DS. The glow discharge experiments show that there is a substantial increase in transport (factor of six) when the upstream pressure is dissociated to some fraction of atoms (which have a much higher sticking coefficient). These results indicate that there is a significant surface limitation because of dissociative adsorption of the molecules. Experiments with the Ag0.05 Zr alloy and its high-grain boundary and defect density show a permeability of greater than a factor of two over ordinary polycrystalline Ag, but it is unclear as to whether this is because of enhanced transport through these defects or whether the Zr and defects on the surface increased the sticking coefficient and therefore the transport.

Performance and microbial ecology of air-cathode microbial fuel cells with layered electrode assemblies.

PubMed

Butler, Caitlyn S; Nerenberg, Robert

2010-05-01

Microbial fuel cells (MFCs) can be built with layered electrode assemblies, where the anode, proton exchange membrane (PEM), and cathode are pressed into a single unit. We studied the performance and microbial community structure of MFCs with layered assemblies, addressing the effect of materials and oxygen crossover on the community structure. Four MFCs with layered assemblies were constructed using Nafion or Ultrex PEMs and a plain carbon cloth electrode or a cathode with an oxygen-resistant polytetrafluoroethylene diffusion layer. The MFC with Nafion PEM and cathode diffusion layer achieved the highest power density, 381 mW/m(2) (20 W/m(3)). The rates of oxygen diffusion from cathode to anode were three times higher in the MFCs with plain cathodes compared to those with diffusion-layer cathodes. Microsensor studies revealed little accumulation of oxygen within the anode cloth. However, the abundance of bacteria known to use oxygen as an electron acceptor, but not known to have exoelectrogenic activity, was greater in MFCs with plain cathodes. The MFCs with diffusion-layer cathodes had high abundance of exoelectrogenic bacteria within the genus Geobacter. This work suggests that cathode materials can significantly influence oxygen crossover and the relative abundance of exoelectrogenic bacteria on the anode, while PEM materials have little influence on anode community structure. Our results show that oxygen crossover can significantly decrease the performance of air-cathode MFCs with layered assemblies, and therefore limiting crossover may be of particular importance for these types of MFCs.

Phase separated membrane bioreactor: Results from model system studies

NASA Astrophysics Data System (ADS)

Petersen, G. R.; Seshan, P. K.; Dunlop, E. H.

The operation and evaluation of a bioreactor designed for high intensity oxygen transfer in a microgravity environment is described. The reactor itself consists of a zero headspace liquid phase separated from the air supply by a long length of silicone rubber tubing through which the oxygen diffuses in and the carbon dioxide diffuses out. Mass transfer studies show that the oxygen is film diffusion controlled both externally and internally to the tubing and not by diffusion across the tube walls. Methods of upgrading the design to eliminate these resistances are proposed. Cell growth was obtained in the fermenter using Saccharomyces cerevisiae showing that this concept is capable of sustaining cell growth in the terrestial simulation.

A novel method for effective diffusion coefficient measurement in gas diffusion media of polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Yang, Linlin; Sun, Hai; Fu, Xudong; Wang, Suli; Jiang, Luhua; Sun, Gongquan

2014-07-01

A novel method for measuring effective diffusion coefficient of porous materials is developed. The oxygen concentration gradient is established by an air-breathing proton exchange membrane fuel cell (PEMFC). The porous sample is set in a sample holder located in the cathode plate of the PEMFC. At a given oxygen flux, the effective diffusion coefficients are related to the difference of oxygen concentration across the samples, which can be correlated with the differences of the output voltage of the PEMFC with and without inserting the sample in the cathode plate. Compared to the conventional electrical conductivity method, this method is more reliable for measuring non-wetting samples.

Phase separated membrane bioreactor - Results from model system studies

NASA Technical Reports Server (NTRS)

Petersen, G. R.; Seshan, P. K.; Dunlop, E. H.

1989-01-01

The operation and evaluation of a bioreactor designed for high intensity oxygen transfer in a microgravity environment is described. The reactor itself consists of a zero headspace liquid phase separated from the air supply by a long length of silicone rubber tubing through which the oxygen diffuses in and the carbon dioxide diffuses out. Mass transfer studies show that the oxygen is film diffusion controlled both externally and internally to the tubing and not by diffusion across the tube walls. Methods of upgrading the design to eliminate these resistances are proposed. Cell growth was obtained in the fermenter using Saccharomyces cerevisiae showing that this concept is capable of sustaining cell growth in the terrestrial simulation.

Model system studies with a phase separated membrane bioreactor

NASA Technical Reports Server (NTRS)

Petersen, G. R.; Seshan, P. K.; Dunlop, Eric H.

1989-01-01

The operation and evaluation of a bioreactor designed for high intensity oxygen transfer in a microgravity environment is described. The reactor itself consists of a zero headspace liquid phase separated from the air supply by a long length of silicone rubber tubing through which the oxygen diffuses in and the carbon dioxide diffuses out. Mass transfer studies show that the oxygen is film diffusion controlled both externally and internally to the tubing and not by diffusion across the tube walls. Methods of upgrading the design to eliminate these resistances are proposed. Cell growth was obtained in the fermenter using Saccharomyces cerevisiae showing that this concept is capable of sustaining cell growth in the terrestial simulation.

Oxygenation level and hemoglobin concentration in experimental tumor estimated by diffuse optical spectroscopy

NASA Astrophysics Data System (ADS)

Orlova, A. G.; Kirillin, M. Yu.; Volovetsky, A. B.; Shilyagina, N. Yu.; Sergeeva, E. A.; Golubiatnikov, G. Yu.; Turchin, I. V.

2017-07-01

Using diffuse optical spectroscopy the level of oxygenation and hemoglobin concentration in experimental tumor in comparison with normal muscle tissue of mice have been studied. Subcutaneously growing SKBR-3 was used as a tumor model. Continuous wave fiber probe diffuse optical spectroscopy system was employed. Optical properties extraction approach was based on diffusion approximation. Decreased blood oxygen saturation level and increased total hemoglobin content were demonstrated in the neoplasm. The main reason of such differences between tumor and norm was significant elevation of deoxyhemoglobin concentration in SKBR-3. The method can be useful for diagnosis of tumors as well as for study of blood flow parameters of tumor models with different angiogenic properties.

Evaluation of Eu(II) -based positive contrast enhancement after intravenous, intraperitoneal, and subcutaneous injections.

PubMed

Ekanger, Levi A; Polin, Lisa A; Shen, Yimin; Haacke, E Mark; Allen, Matthew J

2016-07-01

Eu(II) -based contrast agents offer physiologically relevant, metal-based redox sensing that is unachievable with Gd(III) -based contrast agents. To evaluate the in vivo contrast enhancement of Eu(II) as a function of injection type, we performed intravenous, intraperitoneal, and subcutaneous injections in mice. Our data reveal a correlation between reported oxygen content and expected rates of diffusion with the persistence of Eu(II) -based contrast enhancement. Biodistribution studies revealed europium clearance through the liver and kidneys for intravenous and intraperitoneal injections, but no contrast enhancement was observed in organs associated with clearance. These data represent a step toward understanding the behavior of Eu(II) -based complexes in vivo. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Experimental determination of oxygen diffusion in liquid iron at high pressure

NASA Astrophysics Data System (ADS)

Posner, Esther S.; Rubie, David C.; Frost, Daniel J.; Steinle-Neumann, Gerd

2017-04-01

Oxygen diffusion experiments in liquid iron have been performed at 3-18 GPa and 1975-2643 K using a multi-anvil apparatus. Diffusion couples consisted of a pure iron rod and a sintered disk of Fe0.85O0.15 placed end-to-end in a vertical orientation. Images and chemical spot analyses were acquired along the full length of the quenched sample on lines perpendicular to the diffusion interface. Exsolution features that formed during quenching consist mostly of spherical oxide blobs of at least two size populations, as well as feathery dendritic textures in more oxygen-rich regions near the top of the samples. Diffusion during heating (i.e. prior to reaching the peak annealing temperature, Tf) is treated numerically to refine Arrhenian parameters from simultaneous least-squares fits to several concentration profiles obtained from experiments at constant pressure and variable Tf. Diffusion coefficients range from ∼ 6 ×10-9 to ∼ 2 ×10-8 m2s-1 over the P-T range of the study, with activation enthalpies of less than 100 kJ mol-1. We find a very weak effect of pressure on oxygen diffusion with an activation volume of 0.1 ± 0.1 cm3mol-1, in agreement with computational studies performed above 100 GPa. Arrhenian extrapolation of diffusion coefficients for oxygen to P-T conditions of the Earth's outer core yields faster average diffusion rates (∼ 3 ×10-8 m2s-1) than for Si or Fe in silicon-rich liquid iron alloys or pure liquid iron (∼ 5 ×10-9 m2s-1) reported previously. Oxygen diffusion data are used to constrain the maximum size of descending liquid metal droplets in a magma ocean that is required for chemical equilibration to be achieved. Our results indicate that if the Earth's core composition is representative of equilibrium chemical exchange with a silicate magma ocean, then it could only have been accomplished by large-scale break-up of impactor cores to liquid iron droplet sizes no larger than a few tens of centimeters.

Effect of nickel diffusion and oxygen behavior on heterojunction Schottky diodes of Au/NiO/ZnO with a NiO interlayer prepared by radio-frequency magnetron sputtering.

PubMed

Hwang, Jun-Dar; Chen, Hsin-Yu; Chen, Yu-Hung; Ho, Ting-Hsiu

2018-05-03

The rectifying characteristic of Au/ZnO Schottky diodes (SDs) was remarkably improved by introducing a NiO layer in-between the Au and ZnO layers. Compared with the Au/ZnO SDs, the introduction of the NiO layer significantly enhanced the rectification ratio from 1.38 to 1,300, and reduced the ideality factor from 5.78 to 2.14. The NiO and ZnO layers were deposited on an indium-tin-oxide/glass substrate by radio-frequency magnetron sputtering. Secondary ion mass spectroscopy showed that Ni atoms diffused from NiO to ZnO, leading to a graded distribution of Ni in ZnO. X-ray diffraction demonstrated that the diffusion of Ni atoms increased the grain size and electron concentration of ZnO. X-ray photoelectron spectroscopy showed that the interstitial oxygen (Oi) atoms in NiO and ZnO compensated the oxygen vacancies (OV) at the NiO/ZnO interface; the amount of OV was significantly reduced, while Oi vanished at the interface. The band diagram revealed a potential drop in the bulk ZnO, owing to the graded distribution of Ni in ZnO, which accelerated the carriers, collected by the outer circuit. The carriers at the NiO/ZnO interface easily crossed over the barrier height, instead of being recombined by OV, owing to the lower amount of OV at the interface. © 2018 IOP Publishing Ltd.

Diffusion of oxygen through cork stopper: is it a Knudsen or a Fickian mechanism?

PubMed

Lagorce-Tachon, Aurélie; Karbowiak, Thomas; Simon, Jean-Marc; Gougeon, Régis; Bellat, Jean-Pierre

2014-09-17

The aim of this work is to identify which law governs oxygen transfer through cork: Knudsen or Fickian mechanism. This is important to better understand wine oxidation during post-bottling aging. Oxygen transfer through cork wafers is measured at 298 K using a manometric permeation technique. Depending on the mechanism, we can extract the transport coefficients. Increasing the initial pressure of oxygen from 50 to 800 hPa leads to a change in the values of the transport coefficients. This implies that oxygen transport through cork does not obey the Knudsen law. From these results, we conclude that the limiting step of oxygen transport through cork occurs in the cell wall following Fickian law. From the diffusion dependence's coefficients with pressure, we also extract by applying transition state theory an apparent activation volume of 45 ± 4 nm(3). This high value indicates that oxygen molecules also diffuse from one site to another by passing through a gas phase.

Redox-stratification controlled biofilm (ReSCoBi) for completely autotrophic nitrogen removal: the effect of co- versus counter-diffusion on reactor performance.

PubMed

Terada, Akihiko; Lackner, Susanne; Tsuneda, Satoshi; Smets, Barth F

2007-05-01

A multi-population biofilm model for completely autotrophic nitrogen removal was developed and implemented in the simulation program AQUASIM to corroborate the concept of a redox-stratification controlled biofilm (ReSCoBi). The model considers both counter- and co-diffusion biofilm geometries. In the counter-diffusion biofilm, oxygen is supplied through a gas-permeable membrane that supports the biofilm while ammonia (NH(4)(+)) is supplied from the bulk liquid. On the contrary, in the co-diffusion biofilm, both oxygen and NH(4)(+) are supplied from the bulk liquid. Results of the model revealed a clear stratification of microbial activities in both of the biofilms, the resulting chemical profiles, and the obvious effect of the relative surface loadings of oxygen and NH(4)(+) (J(O(2))/J(NH(4)(+))) on the reactor performances. Steady-state biofilm thickness had a significant but different effect on T-N removal for co- and counter-diffusion biofilms: the removal efficiency in the counter-diffusion biofilm geometry was superior to that in the co-diffusion counterpart, within the range of 450-1,400 microm; however, the efficiency deteriorated with a further increase in biofilm thickness, probably because of diffusion limitation of NH(4)(+). Under conditions of oxygen excess (J(O(2))/J(NH(4)(+)) > 3.98), almost all NH(4)(+) was consumed by aerobic ammonia oxidation in the co-diffusion biofilm, leading to poor performance, while in the counter-diffusion biofilm, T-N removal efficiency was maintained because of the physical location of anaerobic ammonium oxidizers near the bulk liquid. These results clearly reveal that counter-diffusion biofilms have a wider application range for autotrophic T-N removal than co-diffusion biofilms. (c) 2006 Wiley Periodicals, Inc.

Increased sediment oxygen flux in lakes and reservoirs: The impact of hypolimnetic oxygenation

NASA Astrophysics Data System (ADS)

Bierlein, Kevin A.; Rezvani, Maryam; Socolofsky, Scott A.; Bryant, Lee D.; Wüest, Alfred; Little, John C.

2017-06-01

Hypolimnetic oxygenation is an increasingly common lake management strategy for mitigating hypoxia/anoxia and associated deleterious effects on water quality. A common effect of oxygenation is increased oxygen consumption in the hypolimnion and predicting the magnitude of this increase is the crux of effective oxygenation system design. Simultaneous measurements of sediment oxygen flux (JO2) and turbulence in the bottom boundary layer of two oxygenated lakes were used to investigate the impact of oxygenation on JO2. Oxygenation increased JO2 in both lakes by increasing the bulk oxygen concentration, which in turn steepens the diffusive gradient across the diffusive boundary layer. At high flow rates, the diffusive boundary layer thickness decreased as well. A transect along one of the lakes showed JO2 to be spatially quite variable, with near-field and far-field JO2 differing by a factor of 4. Using these in situ measurements, physical models of interfacial flux were compared to microprofile-derived JO2 to determine which models adequately predict JO2 in oxygenated lakes. Models based on friction velocity, turbulence dissipation rate, and the integral scale of turbulence agreed with microprofile-derived JO2 in both lakes. These models could potentially be used to predict oxygenation-induced oxygen flux and improve oxygenation system design methods for a broad range of reservoir systems.

Dynamics of oxygen species on reduced TiO2 (110) rutile

NASA Astrophysics Data System (ADS)

Wang, Yun; Pillay, Devina; Hwang, Gyeong S.

2004-11-01

Using density functional theory calculations, we have investigated the adsorption and diffusion of oxygen species on the reduced TiO2(110) surface. We have found that molecular O2 strongly binds not only to O vacancies, but also to Ti(5c) neighbors, due to delocalization of unpaired electrons arising from removal of neutral bridging oxygen. Our results show that molecular O2 can jump across an oxygen vacancy and diffuse along a Ti(5c) row with moderate barriers. On the other hand, atomic O diffusion along a Ti(5c) row is rather unlikely at low temperatures (<300K) , because of the relatively higher probability of O-O formation from interaction with an adjacent bridging O(2c) atom. Based on our calculation results, we discuss the diffusion and healing of O vacancies associated with O2 adsorption.

Operational Considerations for Oxygen Flammability Risks: Concentrated Oxygen Diffusion and Permeation Behaviors

NASA Technical Reports Server (NTRS)

Harper, Susana; Smith, Sarah; Juarez, Alfredo; Hirsch, David

2010-01-01

Increased human spaceflight operations utilize oxygen concentrations that are frequently varied with use of concentrations up to 100 percent oxygen. Even after exiting a higher percentage oxygen environment, high oxygen concentrations can still be maintained due to material saturation and oxygen entrapment between barrier materials. This paper examines the material flammability concerns that arise from changing oxygen environments during spaceflight operations. We examine the time required for common spacecraft and spacesuit materials exposed to oxygen to return to reduced ignitability and flammability once removed from the increased concentration. Various common spacecraft materials were considered: spacecraft cabin environment foams, Extra Vehicular Mobility Unit materials and foams, Advanced Crew Escape Suit materials, and other materials of interest such as Cotton, Nomex^ HT90-40, and Tiburon Surgical Drape. This paper presents calculated diffusion coefficients derived from experimentally obtained oxygen transmission rates for the tested materials and the analytically derived times necessary for reduced flammability to be achieved based on NASA flammability criteria. Oxygen material saturation and entrapment scenarios are examined. Experimental verification data on oxygen diffusion in saturation scenarios are also presented and discussed. We examine how to use obtained data to address flammability concerns during operational planning to reduce the likelihood of fires while improving efficiency for procedures.

Fuel cell tubes and method of making same

DOEpatents

Borglum, Brian P.

1999-11-30

A method of manufacturing porous ceramic tubes for fuel cells with improved properties and higher manufacturing yield is disclosed. The method involves extruding a closed end fuel cell tube, such as an air electrode of a solid oxide fuel cell, in which the closed end also functions as the sintering support. The resultant fuel cell tube has a superior porosity distribution which allows improved diffusion of oxygen at the closed end of the tube during operation of the fuel cell. Because this region has the highest current density, performance enhancement and improved reliability of the fuel cell tube result. Furthermore, the higher manufacturing yield associated with the present method decreases the overall fuel cell cost. A method of manufacturing porous ceramic tubes for fuel cells with improved properties and higher manufacturing yield is disclosed. The method involves extruding a closed end fuel cell tube, such as an air electrode of a solid oxide fuel cell, in which the closed end also functions as the sintering support. The resultant fuel cell tube has a superior porosity distribution which allows improved diffusion of oxygen at the closed end of the tube during operation of the fuel cell. Because this region has the highest current density, performance enhancement and improved reliability of the fuel cell tube result. Furthermore, the higher manufacturing yield associated with the present method decreases the overall fuel cell cost.

A modelling approach for the heterogeneous oxidation of elastomers

NASA Astrophysics Data System (ADS)

Herzig, A.; Sekerakova, L.; Johlitz, M.; Lion, A.

2017-09-01

The influence of oxygen on elastomers, known as oxidation, is one of the most important ageing processes and becomes more and more important for nowadays applications. The interaction with thermal effects as well as antioxidants makes oxidation of polymers a complex process. Based on the polymer chosen and environmental conditions, the ageing processes may behave completely different. In a lot of cases the influence of oxygen is limited to the surface layer of the samples, commonly referred to as diffusion-limited oxidation. For the lifetime prediction of elastomer components, it is essential to have detailed knowledge about the absorption and diffusion behaviour of oxygen molecules during thermo-oxidative ageing and how they react with the elastomer. Experimental investigations on industrially used elastomeric materials are executed in order to develop and fit models, which shall be capable of predicting the permeation and consumption of oxygen as well as changes in the mechanical properties. The latter are of prime importance for technical applications of rubber components. Oxidation does not occur homogeneously over the entire elastomeric component. Hence, material models which include ageing effects have to be amplified in order to consider heterogeneous ageing, which highly depends on the ageing temperature. The influence of elevated temperatures upon accelerated ageing has to be critically analysed, and influences on the permeation and diffusion coefficient have to be taken into account. This work presents phenomenological models which describe the oxygen uptake and the diffusion into elastomers based on an improved understanding of ongoing chemical processes and diffusion limiting modifications. On the one side, oxygen uptake is modelled by means of Henry's law in which solubility is a function of the temperature as well as the ageing progress. The latter is an irreversible process and described by an inner differential evolution equation. On the other side, further diffusion of oxygen into the material is described by a model based on Fick's law, which is modified by a reaction term. The evolved diffusion-reaction equation depends on the ageing temperature as well as on the progress of ageing and is able to describe diffusion-limited oxidation.

Buoyancy and Pressure Effects on Bulk Metal-Oxygen Reactions

NASA Technical Reports Server (NTRS)

Abbud-Madrid, A.; McKnight, C.; Branch, M. C.; Daily, J. W.; Friedman, R. (Technical Monitor)

1998-01-01

The combustion behavior of metal-oxygen reactions if a weakly buoyant environment is studied to understand the rate-controlling mechanisms in the homogeneous and heterogeneous combustion of bulk metals. Cylindrical titanium and magnesium specimens are ignited in pure-oxygen at pressures ranging from 0.1 to 4.0 atm. Reduced gravity is obtained from an aircraft flying parabolic trajectories. A weakly buoyant environment is generated at low pressures under normal gravity and also at 1 atm under reduced gravity (0.01g). The similarity between these two experimental conditions comes from the p(exp 2)g buoyancy scale extracted from the Grashof number. Lower propagation rates of the molten interface on titanium samples are found at progressively lower pressures at 1 g. These rates are compared to theoretical results from heat conduction analyses with a diffusion/convection controlled reaction. The close agreement found between experimental and theoretical values indicate the importance values indicate the importance of natural convection enhanced oxygen transport on combustion rates. For magnesium, progressively longer burning times are experienced at lower pressures and 1 g. Under reduced gravity conditions at 1 atm, a burning time twice as long as in 1 g is exhibited. However, in this case, the validity of the p(exp 2)g buoyancy scale remains untested due to the inability to obtain steady gas-phase burning of the magnesium sample at 0.1 atm. Nevertheless, longer burning times and larger flame standoff distance at low pressures and at low gravity points to a diffusion/convection controlled reaction.

Diffusion of oxygen in cork.

PubMed

Lequin, Sonia; Chassagne, David; Karbowiak, Thomas; Simon, Jean-Marc; Paulin, Christian; Bellat, Jean-Pierre

2012-04-04

This work reports measurements of effective oxygen diffusion coefficient in raw cork. Kinetics of oxygen transfer through cork is studied at 298 K thanks to a homemade manometric device composed of two gas compartments separated by a cork wafer sample. The first compartment contains oxygen, whereas the second one is kept under dynamic vacuum. The pressure decrease in the first compartment is recorded as a function of time. The effective diffusion coefficient D(eff) is obtained by applying Fick's law to transient state using a numerical method based on finite differences. An analytical model derived from Fick's law applied to steady state is also proposed. Results given by these two methods are in close agreement with each other. The harmonic average of the effective diffusion coefficients obtained from the distribution of 15 cork wafers of 3 mm thickness is 1.1 × 10(-9) m(2) s(-1) with a large distribution over four decades. The statistical analysis of the Gaussian distribution obtained on a 3 mm cork wafer is extrapolated to a 48 mm cork wafer, which length corresponds to a full cork stopper. In this case, the probability density distribution gives a mean value of D(eff) equal to 1.6 × 10(-9) m(2) s(-1). This result shows that it is possible to obtain the effective diffusion coefficient of oxygen through cork from short time (few days) measurements performed on a thin cork wafer, whereas months are required to obtain the diffusion coefficient for a full cork stopper. Permeability and oxygen transfer rate are also calculated for comparison with data from other studies.

Wyman's equation and oxygen flux through the red cell.

PubMed

McCabe, Michael; Maguire, David J

2007-01-01

Wyman's equation of 1966 describes the facilitation of flux of a reversibly bound substrate such as oxygen, consequent on the translational diffusion of the binding protein (the carrier). While Wyman's equation, or some modification of it such as that by Murray 2, may provide a realistic description of the flux of oxygen through a dilute solution of haemoglobin (see also Wittenburg), it is unlikely to be the complete explanation, nor even the basis, for oxygen transport through the intact red cell. The mature erythrocyte contains approximately 350 g/l haemoglobin, and while this suggests that only 35% of the available water volume is actually occupied by the protein, the remaining 65% is unavailable for protein translational diffusion due to the mutual exclusion of the haemoglobin molecules. For this reason we have examined other possible mechanisms whereby haemoglobin may facilitate the translational diffusion of oxygen within the erythrocyte. Possible alternatives include rotational diffusion by the haemoglobins, intracellular shuffling of haemoglobins due to shape changes by the erythrocyte, and haemoglobin rotations and oxygen exchange consequent on the charge change which accompanies substration and desubstration of the haemoglobin molecule. Finally the dipole interactions are shown to generate significant intermolecular attractions between adjacent haemoglobins.

Incorporating Geochemical And Microbial Kinetics In Reactive Transport Models For Generation Of Acid Rock Drainage

NASA Astrophysics Data System (ADS)

Andre, B. J.; Rajaram, H.; Silverstein, J.

2010-12-01

Acid mine drainage, AMD, results from the oxidation of metal sulfide minerals (e.g. pyrite), producing ferrous iron and sulfuric acid. Acidophilic autotrophic bacteria such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans obtain energy by oxidizing ferrous iron back to ferric iron, using oxygen as the electron acceptor. Most existing models of AMD do not account for microbial kinetics or iron geochemistry rigorously. Instead they assume that oxygen limitation controls pyrite oxidation and thus focus on oxygen transport. These models have been successfully used for simulating conditions where oxygen availability is a limiting factor (e.g. source prevention by capping), but have not been shown to effectively model acid generation and effluent chemistry under a wider range of conditions. The key reactions, oxidation of pyrite and oxidation of ferrous iron, are both slow kinetic processes. Despite being extensively studied for the last thirty years, there is still not a consensus in the literature about the basic mechanisms, limiting factors or rate expressions for microbially enhanced oxidation of metal sulfides. An indirect leaching mechanism (chemical oxidation of pyrite by ferric iron to produce ferrous iron, with regeneration of ferric iron by microbial oxidation of ferrous iron) is used as the foundation of a conceptual model for microbially enhanced oxidation of pyrite. Using literature data, a rate expression for microbial consumption of ferrous iron is developed that accounts for oxygen, ferrous iron and pH limitation. Reaction rate expressions for oxidation of pyrite and chemical oxidation of ferrous iron are selected from the literature. A completely mixed stirred tank reactor (CSTR) model is implemented coupling the kinetic rate expressions, speciation calculations and flow. The model simulates generation of AMD and effluent chemistry that qualitatively agrees with column reactor and single rock experiments. A one dimensional reaction diffusion model at the scale of a single rock is developed incorporating the proposed kinetic rate expressions. Simulations of initiation, washout and AMD flows are discussed to gain a better understanding of the role of porosity, effective diffusivity and reactive surface area in generating AMD. Simulations indicate that flow boundary conditions control generation of acid rock drainage as porosity increases.

Mannitol Improves Brain Tissue Oxygenation in a Model of Diffuse Traumatic Brain Injury.

PubMed

Schilte, Clotilde; Bouzat, Pierre; Millet, Anne; Boucheix, Perrine; Pernet-Gallay, Karin; Lemasson, Benjamin; Barbier, Emmanuel L; Payen, Jean-François

2015-10-01

Based on evidence supporting a potential relation between posttraumatic brain hypoxia and microcirculatory derangements with cell edema, we investigated the effects of the antiedematous agent mannitol on brain tissue oxygenation in a model of diffuse traumatic brain injury. Experimental study. Neurosciences and physiology laboratories. Adult male Wistar rats. Thirty minutes after diffuse traumatic brain injury (impact-acceleration model), rats were IV administered with either a saline solution (traumatic brain injury-saline group) or 20% mannitol (1 g/kg) (traumatic brain injury-mannitol group). Sham-saline and sham-mannitol groups received no insult. Two series of experiments were conducted 2 hours after traumatic brain injury (or equivalent) to investigate 1) the effect of mannitol on brain edema and oxygenation, using a multiparametric magnetic resonance-based approach (n = 10 rats per group) to measure the apparent diffusion coefficient, tissue oxygen saturation, mean transit time, and blood volume fraction in the cortex and caudoputamen; 2) the effect of mannitol on brain tissue PO2 and on venous oxygen saturation of the superior sagittal sinus (n = 5 rats per group); and 3) the cortical ultrastructural changes after treatment (n = 1 per group, taken from the first experiment). Compared with the sham-saline group, the traumatic brain injury-saline group had significantly lower tissue oxygen saturation, brain tissue PO2, and venous oxygen saturation of the superior sagittal sinus values concomitant with diffuse brain edema. These effects were associated with microcirculatory collapse due to astrocyte swelling. Treatment with mannitol after traumatic brain injury reversed all these effects. In the absence of traumatic brain injury, mannitol had no effect on brain oxygenation. Mean transit time and blood volume fraction were comparable between the four groups of rats. The development of posttraumatic brain edema can limit the oxygen utilization by brain tissue without evidence of brain ischemia. Our findings indicate that an antiedematous agent such as mannitol can improve brain tissue oxygenation, possibly by limiting astrocyte swelling and restoring capillary perfusion.

Integrating spatial and temporal oxygen data to improve the quantification of in situ petroleum biodegradation rates.

PubMed

Davis, Gregory B; Laslett, Dean; Patterson, Bradley M; Johnston, Colin D

2013-03-15

Accurate estimation of biodegradation rates during remediation of petroleum impacted soil and groundwater is critical to avoid excessive costs and to ensure remedial effectiveness. Oxygen depth profiles or oxygen consumption over time are often used separately to estimate the magnitude and timeframe for biodegradation of petroleum hydrocarbons in soil and subsurface environments. Each method has limitations. Here we integrate spatial and temporal oxygen concentration data from a field experiment to develop better estimates and more reliably quantify biodegradation rates. During a nine-month bioremediation trial, 84 sets of respiration rate data (where aeration was halted and oxygen consumption was measured over time) were collected from in situ oxygen sensors at multiple locations and depths across a diesel non-aqueous phase liquid (NAPL) contaminated subsurface. Additionally, detailed vertical soil moisture (air-filled porosity) and NAPL content profiles were determined. The spatial and temporal oxygen concentration (respiration) data were modeled assuming one-dimensional diffusion of oxygen through the soil profile which was open to the atmosphere. Point and vertically averaged biodegradation rates were determined, and compared to modeled data from a previous field trial. Point estimates of biodegradation rates assuming no diffusion ranged up to 58 mg kg(-1) day(-1) while rates accounting for diffusion ranged up to 87 mg kg(-1) day(-1). Typically, accounting for diffusion increased point biodegradation rate estimates by 15-75% and vertically averaged rates by 60-80% depending on the averaging method adopted. Importantly, ignoring diffusion led to overestimation of biodegradation rates where the location of measurement was outside the zone of NAPL contamination. Over or underestimation of biodegradation rate estimates leads to cost implications for successful remediation of petroleum impacted sites. Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.

The roles of resuspension, diffusion and biogeochemical processes on oxygen dynamics offshore of the Rhône River, France: a numerical modeling study

NASA Astrophysics Data System (ADS)

Moriarty, Julia M.; Harris, Courtney K.; Fennel, Katja; Friedrichs, Marjorie A. M.; Xu, Kehui; Rabouille, Christophe

2017-04-01

Observations indicate that resuspension and associated fluxes of organic material and porewater between the seabed and overlying water can alter biogeochemical dynamics in some environments, but measuring the role of sediment processes on oxygen and nutrient dynamics is challenging. A modeling approach offers a means of quantifying these fluxes for a range of conditions, but models have typically relied on simplifying assumptions regarding seabed-water-column interactions. Thus, to evaluate the role of resuspension on biogeochemical dynamics, we developed a coupled hydrodynamic, sediment transport, and biogeochemical model (HydroBioSed) within the Regional Ocean Modeling System (ROMS). This coupled model accounts for processes including the storage of particulate organic matter (POM) and dissolved nutrients within the seabed; fluxes of this material between the seabed and the water column via erosion, deposition, and diffusion at the sediment-water interface; and biogeochemical reactions within the seabed. A one-dimensional version of HydroBioSed was then implemented for the Rhône subaqueous delta in France. To isolate the role of resuspension on biogeochemical dynamics, this model implementation was run for a 2-month period that included three resuspension events; also, the supply of organic matter, oxygen, and nutrients to the model was held constant in time. Consistent with time series observations from the Rhône Delta, model results showed that erosion increased the diffusive flux of oxygen into the seabed by increasing the vertical gradient of oxygen at the seabed-water interface. This enhanced supply of oxygen to the seabed, as well as resuspension-induced increases in ammonium availability in surficial sediments, allowed seabed oxygen consumption to increase via nitrification. This increase in nitrification compensated for the decrease in seabed oxygen consumption due to aerobic remineralization that occurred as organic matter was entrained into the water column. Additionally, entrainment of POM into the water column during resuspension events, and the associated increase in remineralization there, also increased oxygen consumption in the region of the water column below the pycnocline. During these resuspension events, modeled rates of oxygen consumption increased by factors of up to ˜ 2 and ˜ 8 in the seabed and below the pycnocline, respectively. When averaged over 2 months, the intermittent cycles of erosion and deposition led to a ˜ 16 % increase of oxygen consumption in the seabed, as well as a larger increase of ˜ 140 % below the pycnocline. These results imply that observations collected during quiescent periods, and biogeochemical models that neglect resuspension or use typical parameterizations for resuspension, may underestimate net oxygen consumption at sites like the Rhône Delta. Local resuspension likely has the most pronounced effect on oxygen dynamics at study sites with a high oxygen concentration in bottom waters, only a thin seabed oxic layer, and abundant labile organic matter.

Reaction Kernel Structure of a Slot Jet Diffusion Flame in Microgravity

NASA Technical Reports Server (NTRS)

Takahashi, F.; Katta, V. R.

2001-01-01

Diffusion flame stabilization in normal earth gravity (1 g) has long been a fundamental research subject in combustion. Local flame-flow phenomena, including heat and species transport and chemical reactions, around the flame base in the vicinity of condensed surfaces control flame stabilization and fire spreading processes. Therefore, gravity plays an important role in the subject topic because buoyancy induces flow in the flame zone, thus increasing the convective (and diffusive) oxygen transport into the flame zone and, in turn, reaction rates. Recent computations show that a peak reactivity (heat-release or oxygen-consumption rate) spot, or reaction kernel, is formed in the flame base by back-diffusion and reactions of radical species in the incoming oxygen-abundant flow at relatively low temperatures (about 1550 K). Quasi-linear correlations were found between the peak heat-release or oxygen-consumption rate and the velocity at the reaction kernel for cases including both jet and flat-plate diffusion flames in airflow. The reaction kernel provides a stationary ignition source to incoming reactants, sustains combustion, and thus stabilizes the trailing diffusion flame. In a quiescent microgravity environment, no buoyancy-induced flow exits and thus purely diffusive transport controls the reaction rates. Flame stabilization mechanisms in such purely diffusion-controlled regime remain largely unstudied. Therefore, it will be a rigorous test for the reaction kernel correlation if it can be extended toward zero velocity conditions in the purely diffusion-controlled regime. The objectives of this study are to reveal the structure of the flame-stabilizing region of a two-dimensional (2D) laminar jet diffusion flame in microgravity and develop a unified diffusion flame stabilization mechanism. This paper reports the recent progress in the computation and experiment performed in microgravity.

The role of facilitated diffusion in oxygen transport by cell-free hemoglobins: implications for the design of hemoglobin-based oxygen carriers.

PubMed

McCarthy, M R; Vandegriff, K D; Winslow, R M

2001-08-30

We compared rates of oxygen transport in an in vitro capillary system using red blood cells (RBCs) and cell-free hemoglobins. The axial PO(2) drop down the capillary was calculated using finite-element analysis. RBCs, unmodified hemoglobin (HbA(0)), cross-linked hemoglobin (alpha alpha-Hb) and hemoglobin conjugated to polyethylene-glycol (PEG-Hb) were evaluated. According to their fractional saturation curves, PEG-Hb showed the least desaturation down the capillary, which most closely matched the RBCs; HbA(0) and alpha alpha-Hb showed much greater desaturation. A lumped diffusion parameter, K*, was calculated based on the Fick diffusion equation with a term for facilitated diffusion. The overall rates of oxygen transfer are consistent with hemoglobin diffusion rates according to the Stokes-Einstein Law and with previously measured blood pressure responses in rats. This study provides a conceptual framework for the design of a 'blood substitute' based on mimicking O(2) transport by RBCs to prevent autoregulatory changes in blood flow and pressure.

Variation in diffusion of gases through PDMS due to plasma surface treatment and storage conditions.

PubMed

Markov, Dmitry A; Lillie, Elizabeth M; Garbett, Shawn P; McCawley, Lisa J

2014-02-01

Polydimethylsiloxane (PDMS) is a commonly used polymer in the fabrication of microfluidic devices due to such features as transparency, gas permeability, and ease of patterning with soft lithography. The surface characteristics of PDMS can also be easily changed with oxygen or low pressure air plasma converting it from a hydrophobic to a hydrophilic state. As part of such a transformation, surface methyl groups are removed and replaced with hydroxyl groups making the exposed surface to resemble silica, a gas impermeable substance. We have utilized Platinum(II)-tetrakis(pentaflourophenyl)porphyrin immobilized within a thin (~1.5 um thick) polystyrene matrix as an oxygen sensor, Stern-Volmer relationship, and Fick's Law of simple diffusion to measure the effects of PDMS composition, treatment, and storage on oxygen diffusion through PDMS. Results indicate that freshly oxidized PDMS showed a significantly smaller diffusion coefficient, indicating that the SiO2 layer formed on the PDMS surface created an impeding barrier. This barrier disappeared after a 3-day storage in air, but remained significant for up to 3 weeks if PDMS was maintained in contact with water. Additionally, higher density PDMS formulation (5:1 ratio) showed similar diffusion characteristics as normal (10:1 ratio) formulation, but showed 60 % smaller diffusion coefficient after plasma treatment that never recovered to pre-treatment levels even after a 3-week storage in air. Understanding how plasma surface treatments contribute to oxygen diffusion will be useful in exploiting the gas permeability of PDMS to establish defined normoxic and hypoxic oxygen conditions within microfluidic bioreactor systems.

Variation in diffusion of gases through PDMS due to plasma surface treatment and storage conditions

PubMed Central

Markov, Dmitry A.; Lillie, Elizabeth M.; Garbett, Shawn P.; McCawley, Lisa J.

2013-01-01

Polydimethylsiloxane (PDMS) is a commonly used polymer in the fabrication of microfluidic devices due to such features as transparency, gas permeability, and ease of patterning with soft lithography. The surface characteristics of PDMS can also be easily changed with oxygen or low pressure air converting it from a hydrophobic to a hydrophilic state. As part of such a transformation, surface methyl groups are removed and replaced with hydroxyl groups making the exposed surface to resemble silica, a gas impermeable substance. We have utilized Platinum(II)-tetrakis(pentaflourophenyl)porphyrin immobilized within a thin (~1.5 um thick) polystyrene matrix as an oxygen sensor, Stern-Volmer relationship, and Fick's Law of simple diffusion to measure the effects of PDMS composition, treatment, and storage on oxygen diffusion through PDMS. Results show that freshly oxidized PDMS showed a significantly smaller diffusion coefficient, indicating that the SiO2 layer formed on the PDMS surface created an impeding barrier. This barrier disappeared after a three-day storage in air, but remained significant for up to three weeks if PDMS was maintained in contact with water. Additionally, higher density PDMS formulation (5:1 ratio) showed similar diffusion characteristics as normal (10:1 ratio) formulation, but showed 60% smaller diffusion coefficient after plasma treatment that never recovered to pre-treatment levels even after a three-week storage in air. Understanding how plasma surface treatments contribute to oxygen diffusion will be useful in exploiting the gas permeability of PDMS to establish defined normoxic and hypoxic oxygen conditions within microfluidic bioreactor systems. PMID:24065585

Oxygen potentials, oxygen diffusion coefficients and defect equilibria of nonstoichiometric (U,Pu)O2±x

NASA Astrophysics Data System (ADS)

Kato, Masato; Watanabe, Masashi; Matsumoto, Taku; Hirooka, Shun; Akashi, Masatoshi

2017-04-01

Oxygen potential of (U,Pu)O2±x was evaluated based on defect chemistry using an updated experimental data set. The relationship between oxygen partial pressure and deviation x in (U,Pu)O2±x was analyzed, and equilibrium constants of defect formation were determined as functions of Pu content and temperature. Brouwer's diagrams were constructed using the determined equilibrium constants, and a relational equation to determine O/M ratio was derived as functions of O/M ratio, Pu content and temperature. In addition, relationship between oxygen potential and oxygen diffusion coefficients were described.

Exploring the Diffusion of Molecular Oxygen in the Red Fluorescent Protein mCherry Using Explicit Oxygen Molecular Dynamics Simulations

PubMed Central

Regmi, Chola K.; Bhandari, Yuba R.; Gerstman, Bernard S.; Chapagain, Prem P.

2013-01-01

The development of fluorescent proteins (FPs) has revolutionized cell biology research. The monomeric variants of red fluorescent proteins (RFPs), known as mFruits, have been especially valuable for tagging and tracking cellular processes in vivo. Determining oxygen diffusion pathways in FPs can be important for improving photostability and for understanding maturation of the chromophore. We use molecular dynamics (MD) calculations to investigate the diffusion of molecular oxygen in one of the most useful monomeric RFPs, mCherry. We describe a pathway that allows oxygen molecules to enter from the solvent and travel through the protein barrel to the chromophore. We calculate the free-energy of an oxygen molecule at points along the path. The pathway contains several oxygen hosting pockets, which are identified by the amino acid residues that form the pocket. We also investigate an RFP variant known to be significantly less photostable than mCherry and find much easier oxygen access in this variant. The results provide a better understanding of the mechanism of molecular oxygen access into the fully folded mCherry protein barrel and provide insight into the photobleaching process in these proteins. PMID:23363049

Determination of oxygen diffusion kinetics during thin film ruthenium oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coloma Ribera, R., E-mail: r.colomaribera@utwente.nl; Kruijs, R. W. E. van de; Yakshin, A. E.

2015-08-07

In situ X-ray reflectivity was used to reveal oxygen diffusion kinetics for thermal oxidation of polycrystalline ruthenium thin films and accurate determination of activation energies for this process. Diffusion rates in nanometer thin RuO{sub 2} films were found to show Arrhenius behaviour. However, a gradual decrease in diffusion rates was observed with oxide growth, with the activation energy increasing from about 2.1 to 2.4 eV. Further exploration of the Arrhenius pre-exponential factor for diffusion process revealed that oxidation of polycrystalline ruthenium joins the class of materials that obey the Meyer-Neldel rule.

Relaxation and diffusion of perfluorocarbon gas mixtures with oxygen for lung MRI

NASA Astrophysics Data System (ADS)

Chang, Yulin V.; Conradi, Mark S.

2006-08-01

We report measurements of free diffusivity D0 and relaxation times T1 and T2 for pure C 2F 6 and C 3F 8 and their mixtures with oxygen. A simplified relaxation theory is presented and used to fit the data. The results enable spatially localized relaxation time measurements to determine the local gas concentration in lung MR images, so the free diffusivity D0 is then known. Comparison of the measured diffusion to D0 will express the extent of diffusion restriction and allow the local surface-to-volume ratio to be found.

Multifunctional Micelles Dually Responsive to Hypoxia and Singlet Oxygen: Enhanced Photodynamic Therapy via Interactively Triggered Photosensitizer Delivery.

PubMed

Li, Juanjuan; Meng, Xuan; Deng, Jian; Lu, Di; Zhang, Xin; Chen, Yanrui; Zhu, Jundong; Fan, Aiping; Ding, Dan; Kong, Deling; Wang, Zheng; Zhao, Yanjun

2018-05-23

Nanoparticulate antitumor photodynamic therapy (PDT) has been suffering from the limited dose accumulation in tumor. Herein, we report dually hypoxia- and singlet oxygen-responsive polymeric micelles to efficiently utilize the photosensitizer deposited in the disease site and hence facilely improve PDT's antitumor efficacy. Tailored methoxy poly(ethylene glycol)-azobenzene-poly(aspartic acid) copolymer conjugate with imidazole as the side chains was synthesized. The conjugate micelles (189 ± 19 nm) obtained by self-assembly could efficiently load a model photosensitizer, chlorin e6 (Ce6) with a loading of 4.1 ± 0.5% (w/w). The facilitated cellular uptake of micelles was achieved by the triggered azobenzene collapse that provoked poly(ethylene glycol) shedding; rapid Ce6 release was enabled by imidazole oxidation that induced micelle disassembly. In addition, the singlet oxygen-mediated cargo release not only addressed the limited diffusion range and short half-life of singlet oxygen but also decreased the oxygen level, which could in turn enhance internalization and increase the intracellular Ce6 concentration. The hypoxia-induced dePEGylation and singlet oxygen-triggered Ce6 release was demonstrated both in aqueous buffer and in Lewis lung carcinoma (LLC) cells. The cellular uptake study demonstrated that the dually responsive micelles could deliver significantly more Ce6 to the cells, which resulted in a substantially improved cytotoxicity. This concurred well with the superior in vivo antitumor ability of micelles in a LLC tumor-bearing mouse model. This study presented an intriguing nanoplatform to realize interactively triggered photosensitizer delivery and improved antitumor PDT efficacy.

Thermodynamic assessment of oxygen diffusion in non-stoichiometric UO2±x from experimental data and Frenkel pair modeling

NASA Astrophysics Data System (ADS)

Berthinier, C.; Rado, C.; Chatillon, C.; Hodaj, F.

2013-02-01

The self and chemical diffusion of oxygen in the non-stoichiometric domain of the UO2 compound is analyzed from the point of view of experimental determinations and modeling from Frenkel pair defects. The correlation between the self-diffusion and the chemical diffusion coefficients is analyzed using the Darken coefficient calculated from a thermodynamic description of the UO2±x phase. This description was obtained from an optimization of thermodynamic and phase diagram data and modeling with different point defects, including the Frenkel pair point defects. The proposed diffusion coefficients correspond to the 300-2300 K temperature range and to the full composition range of the non stoichiometric UO2 compound. These values will be used for the simulation of the oxidation and ignition of the uranium carbide in different oxygen atmospheres that starts at temperatures as low as 400 K.

Oxygen supply in aquatic ectotherms: partial pressure and solubility together explain biodiversity and size patterns.

PubMed

Verberk, Wilco C E P; Bilton, David T; Calosi, Piero; Spicer, John I

2011-08-01

Aquatic ectotherms face the continuous challenge of capturing sufficient oxygen from their environment as the diffusion rate of oxygen in water is 3 x 10(5) times lower than in air. Despite the recognized importance of oxygen in shaping aquatic communities, consensus on what drives environmental oxygen availability is lacking. Physiologists emphasize oxygen partial pressure, while ecologists emphasize oxygen solubility, traditionally expressing oxygen in terms of concentrations. To resolve the question of whether partial pressure or solubility limits oxygen supply in nature, we return to first principles and derive an index of oxygen supply from Fick's classic first law of diffusion. This oxygen supply index (OSI) incorporates both partial pressure and solubility. Our OSI successfully explains published patterns in body size and species across environmental clines linked to differences in oxygen partial pressure (altitude, organic pollution) or oxygen solubility (temperature and salinity). Moreover, the OSI was more accurately and consistently related to these ecological patterns than other measures of oxygen (oxygen saturation, dissolved oxygen concentration, biochemical oxygen demand concentrations) and similarly outperformed temperature and altitude, which covaried with these environmental clines. Intriguingly, by incorporating gas diffusion rates, it becomes clear that actually more oxygen is available to an organism in warmer habitats where lower oxygen concentrations would suggest the reverse. Under our model, the observed reductions in aerobic performance in warmer habitats do not arise from lower oxygen concentrations, but instead through organismal oxygen demand exceeding supply. This reappraisal of how organismal thermal physiology and oxygen demands together shape aerobic performance in aquatic ectotherms and the new insight of how these components change with temperature have broad implications for predicting the responses of aquatic communities to ongoing global climate shifts.

Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co2−xFexO5+δ

PubMed Central

Choi, Sihyuk; Yoo, Seonyoung; Kim, Jiyoun; Park, Seonhye; Jun, Areum; Sengodan, Sivaprakash; Kim, Junyoung; Shin, Jeeyoung; Jeong, Hu Young; Choi, YongMan; Kim, Guntae; Liu, Meilin

2013-01-01

Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co2−xFexO5+δ, which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm−2 at 600°C, representing an important step toward commercially viable SOFC technologies. PMID:23945630

Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ).

PubMed

Choi, Sihyuk; Yoo, Seonyoung; Kim, Jiyoun; Park, Seonhye; Jun, Areum; Sengodan, Sivaprakash; Kim, Junyoung; Shin, Jeeyoung; Jeong, Hu Young; Choi, YongMan; Kim, Guntae; Liu, Meilin

2013-01-01

Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ), which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm(-2) at 600°C, representing an important step toward commercially viable SOFC technologies.

Effect of non-Newtonian and pulsatile blood flow on mass transport in the human aorta.

PubMed

Liu, Xiao; Fan, Yubo; Deng, Xiaoyan; Zhan, Fan

2011-04-07

To investigate the effects of both non-Newtonian behavior and the pulsation of blood flow on the distributions of luminal surface LDL concentration and oxygen flux along the wall of the human aorta, we numerically compared a non-Newtonian model with the Newtonian one under both steady flow and in vivo pulsatile flow conditions using a human aorta model constructed from MRI images. The results showed that under steady flow conditions, although the shear thinning non-Newtonian nature of blood could elevate wall shear stress (WSS) in most regions of the aorta, especially areas with low WSS, it had little effect on luminal surface LDL concentration (c(w)) in most regions of the aorta. Nevertheless, it could significantly enhance c(w) in areas with high luminal surface LDL concentration through the shear dependent diffusivity of LDLs. For oxygen transport, the shear thinning non-Newtonian nature of blood could slightly reduce oxygen flux in most regions of the aorta, but this effect became much more apparent in areas with already low oxygen flux. The pulsation of blood flow could significantly reduce c(w) and enhance oxygen flux in these disturbed places. In most other regions of the aorta, the oxygen flux was also significantly higher than that for the steady flow simulation. In conclusion, the shear shining non-Newtonian nature of blood has little effect on LDL and oxygen transport in most regions of the aorta, but in the atherogenic-prone areas where luminal surface LDL concentration is high and oxygen flux is low, its effect is apparent. Similar is for the effect of pulsatile flow on the transport of LDLs. But, the pulsation of blood flow can apparently affect oxygen flux in the aorta, especially in areas with low oxygen flux. Copyright © 2011 Elsevier Ltd. All rights reserved.

Membrane culture and reduced oxygen tension enhances cartilage matrix formation from equine cord blood mesenchymal stromal cells in vitro.

PubMed

Co, C; Vickaryous, M K; Koch, T G

2014-03-01

Ongoing research is aimed at increasing cartilage tissue yield and quality from multipotent mesenchymal stromal cells (MSC) for the purpose of treating cartilage damage in horses. Low oxygen culture has been shown to enhance chondrogenesis, and novel membrane culture has been proposed to increase tissue yield and homogeneity. The objective of this study was to evaluate and compare the effect of reduced oxygen and membrane culture during in vitro chondrogenesis of equine cord blood (CB) MSC. CB-MSC (n = 5 foals) were expanded at 21% oxygen prior to 3-week differentiation in membrane or pellet culture at 5% and 21% oxygen. Assessment included histological examination (H&E, toluidine Blue, immunohistochemistry (IHC) for collagen type I and II), protein quantification by hydroxyproline assay and dimethylmethylene assay, and mRNA analysis for collagen IA1, collagen IIA1, collagen XA1, HIF1α and Sox9. Among treatment groups, 5% membrane culture produced neocartilage most closely resembling hyaline cartilage. Membrane culture resulted in increased wet mass, homogenous matrix morphology and an increase in total collagen content, while 5% oxygen culture resulted in higher GAG and type II collagen content. No significant differences were observed for mRNA analysis. Membrane culture at 5% oxygen produces a comparatively larger amount of higher quality neocartilage. Matrix homogeneity is attributed to a uniform diffusion gradient and reduced surface tension. Membrane culture holds promise for scale-up for therapeutic purposes, for cellular preconditioning prior to cytotherapeutic applications, and for modeling system for gas-dependent chondrogenic differentiation studies. Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.

Numerical investigation of oxygen transport by hemoglobin-based carriers through microvessels.

PubMed

Hyakutake, Toru; Kishimoto, Takumi

2017-12-01

The small size of hemoglobin-based oxygen carriers (HBOCs) may expand the realm of new treatment possibilities for various circulatory diseases. The parametric evaluation of HBOC performance for oxygen transport within tissue is essential for effectively characterizing its performance for each circulatory disease assessed. Thus, the overarching objective of this present study was to numerically investigate the reaction-diffusion phenomenon of oxygenated HBOCs and oxygen on tissues through microvessels. We considered dissociation rate coefficients, oxygen affinity, and diffusion coefficients due to Brownian motion as the biophysical parameters for estimating HBOC performance for oxygen transport. A two-dimensional computational domain, including vessel and tissue regions, was, therefore, accordingly assumed. It was observed that HBOC flows in a microvessel with a diameter of 25 μm and a length of 1 mm, and that the dissociated oxygen diffuses to the tissue region. The results indicated that oxyhemoglobin saturation and partial oxygen tension in a downstream region changed according to each biophysical parameter of HBOC. Moreover, the change in oxygen consumption rate in the tissue region had considerable influence on the oxyhemoglobin saturation level within the vessel. Comparison between simulation results and existing in vitro experimental data of actual HBOCs and RBC showed qualitatively good agreement. These results provide important information for the effective design of robust HBOCs in future.

Sealed glass coating of high temperature ceramic superconductors

DOEpatents

Wu, W.; Chu, C.Y.; Goretta, K.C.; Routbort, J.L.

1995-05-02

A method and article of manufacture of a lead oxide based glass coating on a high temperature superconductor is disclosed. The method includes preparing a dispersion of glass powders in a solution, applying the dispersion to the superconductor, drying the dispersion before applying another coating and heating the glass powder dispersion at temperatures below oxygen diffusion onset and above the glass melting point to form a continuous glass coating on the superconductor to establish compressive stresses which enhance the fracture strength of the superconductor. 8 figs.

Sealed glass coating of high temperature ceramic superconductors

DOEpatents

Wu, Weite; Chu, Cha Y.; Goretta, Kenneth C.; Routbort, Jules L.

1995-01-01

A method and article of manufacture of a lead oxide based glass coating on a high temperature superconductor. The method includes preparing a dispersion of glass powders in a solution, applying the dispersion to the superconductor, drying the dispersion before applying another coating and heating the glass powder dispersion at temperatures below oxygen diffusion onset and above the glass melting point to form a continuous glass coating on the superconductor to establish compressive stresses which enhance the fracture strength of the superconductor.

The diffusive boundary layer of sediments: oxygen microgradients over a microbial mat

NASA Technical Reports Server (NTRS)

Jorgensen, B. B.; Des Marais, D. J.

1990-01-01

Oxygen microelectrodes were used to analyze the distribution of the diffusive boundary layer (DBL) at the sediment-water interface in relation to surface topography and flow velocity. The sediment, collected from saline ponds, was covered by a microbial mat that had high oxygen consumption rate and well-defined surface structure. Diffusion through the DBL constituted an important rate limitation to the oxygen uptake of the sediment. The mean effective DBL thickness decreased from 0.59 to 0.16 mm as the flow velocity of the overlying water was increased from 0.3 to 7.7 cm s-1 (measured 1 cm above the mat). The oxygen uptake rate concurrently increased from 3.9 to 9.4 nmol cm-2 min-1. The effects of surface roughness and topography on the thickness and distribution of the DBL were studied by three-dimensional mapping of the sediment-water interface and the upper DBL boundary at 0.1-mm spatial resolution. The DBL boundary followed mat structures that had characteristic dimensions > 1/2 DBL thickness but the DBL had a dampened relief relative to the mat. The effective surface area of the sediment-water interface and of the upper DBL boundary were 31 and 14% larger, respectively, than a flat plane. Surface topography thereby increased the oxygen flux across the sediment-water interface by 49% relative to a one-dimensional diffusion flux calculated from the vertical oxygen microgradients.

Kinetic analysis of the interactions between calcium ferrite and coal char for chemical looping gasification applications: Identifying reduction routes and modes of oxygen transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riley, Jarrett; Siriwardane, Ranjani; Tian, Hanjing

Chemical Looping Gasification (CLG) is an emerging technology that shows promise for efficient coal gasification by eliminating the need for energy intensive gas separations to achieve a non-nitrogen diluted syngas stream. Oxygen from oxygen carriers, such as CaFe 2O 4, are used for coal gasification in place of conventionally produced gaseous oxygen from cryogenic separation of air. These oxygen carriers are unique for their ability to selectively oxidize coal to form syngas and show limited reactivity with syngas components (H 2, CO). To gain a deeper understanding of how these unique oxygen carriers perform and to offer a first attemptmore » at the reaction modeling of solid mediated interactions of this nature, this study was carried out to determine the kinetic parameters associated with the selective oxidation of coal derived char (Wyodak and Illinois #6) with a metal ferrite, CaFe 2O 4. Using thermogravimetric analysis (TGA) coupled with mass spectrometry, the selective oxygen release of metal ferrite in the presence of char by proximal contact was examined. The application of combinatory model fitting approaches was used to describe controlling resistances during oxygen release. A combination of the modified shrinking core model (SCM) with planar oxygen ion diffusion control and reaction order based models was used for kinetic parameter determination. CaFe 2O 4 particle size plays a major role in the prevailing mode of oxygen release. Particle sizes on the order of 40–50 μm tend to favor first order kinetically controlled regimes independent of geometric and diffusion controls. The probability for oxygen ion diffusion controlling regimes increased when the particle size range of the oxygen carrier was increased up to 350 μm. Char type also impacted the prevalence of the controlling regime. Higher ranked chars react in a slower manner, limiting the gradient for oxygen ion release from the oxygen carrier. Activation energies determined for this process range from 120–200kJ/mol and oxygen ion diffusion coefficients are on the order of 10-8 cm 2/s. It is suggested that oxygen ion movement is regulated by lattice diffusion out of partially reduced phases (Ca 2Fe 2O 5) and through reduced outer layers composed of CaO and Fe. The controlled movement of oxygen ions influences the rate of carbon oxidation in the char and therefore the selectivity towards partial oxidation products, which are desirable in CLG applications.« less

Kinetic analysis of the interactions between calcium ferrite and coal char for chemical looping gasification applications: Identifying reduction routes and modes of oxygen transfer

DOE PAGES

Riley, Jarrett; Siriwardane, Ranjani; Tian, Hanjing; ...

2017-05-20

Chemical Looping Gasification (CLG) is an emerging technology that shows promise for efficient coal gasification by eliminating the need for energy intensive gas separations to achieve a non-nitrogen diluted syngas stream. Oxygen from oxygen carriers, such as CaFe 2O 4, are used for coal gasification in place of conventionally produced gaseous oxygen from cryogenic separation of air. These oxygen carriers are unique for their ability to selectively oxidize coal to form syngas and show limited reactivity with syngas components (H 2, CO). To gain a deeper understanding of how these unique oxygen carriers perform and to offer a first attemptmore » at the reaction modeling of solid mediated interactions of this nature, this study was carried out to determine the kinetic parameters associated with the selective oxidation of coal derived char (Wyodak and Illinois #6) with a metal ferrite, CaFe 2O 4. Using thermogravimetric analysis (TGA) coupled with mass spectrometry, the selective oxygen release of metal ferrite in the presence of char by proximal contact was examined. The application of combinatory model fitting approaches was used to describe controlling resistances during oxygen release. A combination of the modified shrinking core model (SCM) with planar oxygen ion diffusion control and reaction order based models was used for kinetic parameter determination. CaFe 2O 4 particle size plays a major role in the prevailing mode of oxygen release. Particle sizes on the order of 40–50 μm tend to favor first order kinetically controlled regimes independent of geometric and diffusion controls. The probability for oxygen ion diffusion controlling regimes increased when the particle size range of the oxygen carrier was increased up to 350 μm. Char type also impacted the prevalence of the controlling regime. Higher ranked chars react in a slower manner, limiting the gradient for oxygen ion release from the oxygen carrier. Activation energies determined for this process range from 120–200kJ/mol and oxygen ion diffusion coefficients are on the order of 10-8 cm 2/s. It is suggested that oxygen ion movement is regulated by lattice diffusion out of partially reduced phases (Ca 2Fe 2O 5) and through reduced outer layers composed of CaO and Fe. The controlled movement of oxygen ions influences the rate of carbon oxidation in the char and therefore the selectivity towards partial oxidation products, which are desirable in CLG applications.« less

Diapycnal diffusivity in the core and oxycline of the tropical North Atlantic oxygen minimum zone

NASA Astrophysics Data System (ADS)

Köllner, Manuela; Visbeck, Martin; Tanhua, Toste; Fischer, Tim

2016-08-01

Diapycnal diffusivity estimates from two Tracer Release Experiments (TREs) and microstructure measurements in the oxycline and core of the oxygen minimum zone (OMZ) in the Eastern Tropical North Atlantic (ETNA) are compared. For the first time, two TREs within the same area at different depths were realized: the Guinea Upwelling Tracer Release Experiment (GUTRE) initiated in 2008 in the oxycline at approximately 320 m depth, and the Oxygen Supply Tracer Release Experiment (OSTRE) initiated in 2012 in the core of the OMZ at approximately 410 m depth. The mean diapycnal diffusivity Dz was found to be insignificantly smaller in the OMZ core with (1.06 ± 0.24) × 10- 5 m2 s- 1 compared to (1.11 ± 0.22) × 10- 5 m2 s- 1 90 m shallower in the oxycline. Unexpectedly, GUTRE tracer was detected during two of the OSTRE surveys which showed that the estimated diapycnal diffusivity from GUTRE over a time period of seven years was within the uncertainty of the previous estimates over a time period of three years. The results are consistent with the Dz estimates from microstructure measurements and demonstrate that Dz does not vary significantly vertically in the OMZ within the depth range of 200-600 m and does not change with time. The presence of a seamount chain in the vicinity of the GUTRE injection region did not cause enhanced Dz compared to the smoother bottom topography of the OSTRE injection region, although the analysis of vertical shear spectra from ship ADCP data showed elevated internal wave energy level in the seamount vicinity. However, the two tracer patches covered increasingly overlapping areas with time and thus spatially integrated increasingly similar fields of local diffusivity, as well as the difference in local stratification counteracted the influence of roughness on Dz. For both experiments no significant vertical displacements of the tracer were observed, thus diapycnal upwelling within the ETNA OMZ is below the uncertainty level of 5 m yr- 1.

Effect of annealing on structural changes and oxygen diffusion in amorphous HfO2 using classical molecular dynamics

NASA Astrophysics Data System (ADS)

Shen, Wenqing; Kumari, Niru; Gibson, Gary; Jeon, Yoocharn; Henze, Dick; Silverthorn, Sarah; Bash, Cullen; Kumar, Satish

2018-02-01

Non-volatile memory is a promising alternative to present memory technologies. Oxygen vacancy diffusion has been widely accepted as one of the reasons for the resistive switching mechanism of transition-metal-oxide based resistive random access memory. In this study, molecular dynamics simulation is applied to investigate the diffusion coefficient and activation energy of oxygen in amorphous hafnia. Two sets of empirical potential, Charge-Optimized Many-Body (COMB) and Morse-BKS (MBKS), were considered to investigate the structural and diffusion properties at different temperatures. COMB predicts the activation energy of 0.53 eV for the temperature range of 1000-2000 K, while MBKS predicts 2.2 eV at high temperature (1600-2000 K) and 0.36 eV at low temperature (1000-1600 K). Structural changes and appearance of nano-crystalline phases with increasing temperature might affect the activation energy of oxygen diffusion predicted by MBKS, which is evident from the change in coordination number distribution and radial distribution function. None of the potentials make predictions that are fully consistent with density functional theory simulations of both the structure and diffusion properties of HfO2. This suggests the necessity of developing a better multi-body potential that considers charge exchange.

Theoretical approach to oxygen atom degradation of silver

NASA Technical Reports Server (NTRS)

Fromhold, Albert T., Jr.; Noh, Seung; Beshears, Ronald; Whitaker, Ann F.; Little, Sally A.

1987-01-01

Based on available Rutherford backscattering spectrometry (RBS), proton induced X-ray emission (PIXE) and ellipsometry data obtained on silver specimens subjected to atomic oxygen attack in low Earth orbit STS flight 41-G, a theory was developed to model the oxygen atom degradation of silver. The diffusion of atomic oxygen in a microscopically nonuniform medium is an essential constituent of the theory. The driving force for diffusion is the macroscopic electrochemical potential gradient developed between the specimen surface exposed to the ambient and the bulk of the silver specimen. The longitudinal electric effect developed parallel to the gradient is modified by space charge of the diffusing charged species. Lateral electric fields and concentration differences also exist due to the nonuniform nature of the medium. The lateral concentration differences are found to be more important than the lateral electric fields in modifying the diffusion rate. The model was evaluated numerically. Qualitative agreement exists between the kinetics predicted by the theory and kinetic data taken in ground-based experiments utilizing a plasma asher.

Modeling oxygen transport in human placental terminal villi.

PubMed

Gill, J S; Salafia, C M; Grebenkov, D; Vvedensky, D D

2011-12-21

Oxygen transport from maternal blood to fetal blood is a primary function of the placenta. Quantifying the effectiveness of this exchange remains key in identifying healthy placentas because of the great variability in capillary number, caliber and position within the villus-even in placentas deemed clinically "normal". By considering villous membrane to capillary membrane transport, stationary oxygen diffusion can be numerically solved in terminal villi represented by digital photomicrographs. We aim to provide a method to determine whether and if so to what extent diffusional screening may operate in placental villi. Segmented digital photomicrographs of terminal villi from the Pregnancy, Infection and Nutrition study in North Carolina 2002 are used as a geometric basis for solving the stationary diffusion equation. Constant maternal villous oxygen concentration and perfect fetal capillary membrane absorption are assumed. System efficiency is defined as the ratio of oxygen flux into a villus and the sum of the capillary areas contained within. Diffusion screening is quantified by comparing numerical and theoretical maximum oxygen fluxes. A strong link between various measures of villous oxygen transport efficiency and the number of capillaries within a villus is established. The strength of diffusional screening is also related to the number of capillaries within a villus. Our measures of diffusional efficiency are shown to decrease as a function of the number of capillaries per villus. This low efficiency, high capillary number relationship supports our hypothesis that diffusional screening is present in this system. Oxygen transport per capillary is reduced when multiple capillaries compete for diffusing oxygen. A complete picture of oxygen fluxes, capillary and villus areas is obtainable and presents an opportunity for future work. Copyright © 2011 Elsevier Ltd. All rights reserved.

Effect of pore architecture on oxygen diffusion in 3D scaffolds for tissue engineering.

PubMed

Ahn, Geunseon; Park, Jeong Hun; Kang, Taeyun; Lee, Jin Woo; Kang, Hyun-Wook; Cho, Dong-Woo

2010-10-01

The aim of this study was to maximize oxygen diffusion within a three-dimensional scaffold in order to improve cell viability and proliferation. To evaluate the effect of pore architecture on oxygen diffusion, we designed a regular channel shape with uniform diameter, referred to as cylinder shaped, and a new channel shape with a channel diameter gradient, referred to as cone shaped. A numerical analysis predicted higher oxygen concentration in the cone-shaped channels than in the cylinder-shaped channels, throughout the scaffold. To confirm these numerical results, we examined cell proliferation and viability in 2D constructs and 3D scaffolds. Cell culture experiments revealed that cell proliferation and viability were superior in the constructs and scaffolds with cone-shaped channels.

High Rate Oxygen Reduction in Non-aqueous Electrolytes with the Addition of Perfluorinated Additives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y.; Yang, X.; Zheng, D.

2011-08-04

The discharge rate capability of Li-air batteries is substantially increased by using perfluorinated compounds as oxygen carriers. The solubility of oxygen in a non-aqueous electrolyte can be significantly increased by the introduction of such compounds, which leads to the increase in the diffusion-limited current of oxygen reduction on the gas diffusion electrode in a Li-air battery. The perfluorinated compound is found to be stable within the electrochemical window of the electrolyte. A powder microelectrode and a rotating disk electrode were used to study the gas diffusion-limited current together with a rotating disk electrode. A 5 mA cm{sup -2} discharge ratemore » is demonstrated in a lab Li-O{sub 2} cell.« less

Determining the inertial states of low Prandtl number fluids using electrochemical cells

NASA Astrophysics Data System (ADS)

Crunkleton, Daniel Wray

The quality of crystals grown from the melt is often deteriorated by the presence of buoyancy-induced convection, produced by temperature or concentration inhomogenities. It is, therefore, important to develop techniques to visualize such flows. In this study, a novel technique is developed that uses solid-state electrochemical cells to establish and measure dissolved oxygen boundary conditions. To visualize convection, a packet of oxygen is electrochemically introduced at a specific location in the melt. As the fluid convects, this oxygen packet follows the flow, acting as a tracer. Electrochemical sensors located along the enclosure then detect the oxygen as it passes. Over sufficiently long times, oxygen diffusion is important; consequently, the oxygen diffusivity in the fluid is measured. This diffusivity is determined using both transient and steady state experiments with tin and tin-lead alloys as model fluids. It is concluded that the presence of convection due to solutal gradients and/or tilt increases the measured diffusivity by one-half to one order of magnitude. The oxygen diffusivity in tin-lead alloys is measured and the results show that the alloy diffusivities are lower than those of the corresponding pure metals. This concentration functionality is explained with a multicomponent diffusion model and shows good agreement. Rayleigh-Benard convection was used to validate the electrochemical approach to flow visualization. Thus, a numerical characterization of the second critical Rayleigh numbers in liquid tin was conducted for a variety of Cartesian aspect ratios. The extremely low Prandtl number of tin represents the lowest value studied numerically. Additionally, flow field oscillations are visualized and the effect of tilt on convecting systems is quantified. Finally, experimental studies of the effect of convection in liquid tin are presented. Three geometries are studied: (1) double cell with vertical concentration gradients; (2) double cell with horizontal concentration gradients; and (3) multiple cell with vertical temperature gradients. The first critical Rayleigh number transition is detected with geometry (1) and it is concluded that current measurements are not as affected by convection as EMF measurements. The system is compared with numerical simulations in geometry (2), and oscillating convection is detected with geometry (3).

Hydroxylamine diffusion can enhance N₂O emissions in nitrifying biofilms: a modeling study.

PubMed

Sabba, Fabrizio; Picioreanu, Cristian; Pérez, Julio; Nerenberg, Robert

2015-02-03

Wastewater treatment plants can be significant sources of nitrous oxide (N2O), a potent greenhouse gas. However, little is known about N2O emissions from biofilm processes. We adapted an existing suspended-growth mathematical model to explore N2O emissions from nitrifying biofilms. The model included N2O formation by ammonia-oxidizing bacteria (AOB) via the hydroxylamine and the nitrifier denitrification pathways. Our model suggested that N2O emissions from nitrifying biofilms could be significantly greater than from suspended growth systems under similar conditions. The main cause was the formation and diffusion of hydroxylamine, an AOB nitrification intermediate, from the aerobic to the anoxic regions of the biofilm. In the anoxic regions, hydroxylamine oxidation by AOB provided reducing equivalents used solely for nitrite reduction to N2O, since there was no competition with oxygen. For a continuous system, very high and very low dissolved oxygen (DO) concentrations resulted in lower emissions, while intermediate values led to higher emissions. Higher bulk ammonia concentrations and greater biofilm thicknesses increased emissions. The model effectively predicted N2O emissions from an actual pilot-scale granular sludge reactor for sidestream nitritation, but significantly underestimated the emissions when the NH2OH diffusion coefficient was assumed to be minimal. This numerical study suggests an unexpected and important role of hydroxylamine in N2O emission in biofilms.

Oxygen-vacancy behavior in La2-xSrxCuO4-y by positron annihilation and oxygen diffusion

NASA Astrophysics Data System (ADS)

Smedskjaer, L. C.; Routbort, J. L.; Flandermeyer, B. K.; Rothman, S. J.; Legnini, D. G.; Baker, J. E.

1987-09-01

Oxygen-diffusion and positron-annihilation results for La2-xSrxCuO4-y compounds are reported. A qualitative explanation of the observed results is given on the basis of a model in which the oxygen-vacancy concentration in La2-xSrxCuO4-y is determined by Sr2+ ion clustering on the La sublattice. This model also leads to a maximum in the Cu3+ ion concentration as a function of the Sr2+ ion concentration.

Measurement of the oxygen mass transfer through the air-water interface.

PubMed

Mölder, Erik; Mashirin, Alelxei; Tenno, Toomas

2005-01-01

Gas mass transfer through the liquid-gas interface has enormous importance in various natural and industrial processes. Surfactants or insoluble compounds adsorbed onto an interface will inhibit the gas mass transfer through the liquid-gas surface. This study presents a technique for measuring the oxygen mass transfer through the air-water interface. Experimental data obtained with the measuring device were incorporated into a novel mathematical model, which allowed one to calculate diffusion conduction of liquid surface layer and oxygen mass transfer coefficient in the liquid surface layer. A special measurement cell was constructed. The most important part of the measurement cell is a chamber containing the electrochemical oxygen sensor inside it. Gas exchange between the volume of the chamber and the external environment takes place only through the investigated surface layer. Investigated liquid was deoxygenated, which triggers the oxygen mass transfer from the chamber through the liquid-air interface into the liquid phase. The decrease of oxygen concentration in the cell during time was measured. By using this data it is possible to calculate diffusional parameters of the water surface layer. Diffusion conduction of oxygen through the air-water surface layer of selected wastewaters was measured. The diffusion conduction of different wastewaters was about 3 to 6 times less than in the unpolluted water surface. It was observed that the dilution of wastewater does not have a significant impact on the oxygen diffusion conduction through the wastewater surface layer. This fact can be explained with the presence of the compounds with high surface activity in the wastewater. Surfactants achieved a maximum adsorption and, accordingly, the maximum decrease of oxygen permeability already at a very low concentration of surfactants in the solution. Oxygen mass transfer coefficient of the surface layer of the water is found to be Ds/ls = 0.13 x 10(-3) x cm/s. A simple technique for measuring oxygen diffusion parameters through the air-water solution surface has been developed. Derived equations enable the calculation of diffusion parameters of the surface layer at current conditions. These values of the parameters permit one to compare the resistances of the gas-liquid interface to oxygen mass transfer in the case of adsorption of different substances on the surface layer. This simple technique may be used for a determination of oxygen permeability of different water-solution surface layers. It enables one to measure the resistance to the oxygen permeability of all inflowing wastewater surface layers in the wastewater treatment plant, and to initiate a preliminary cleaning of this wastewater if required. Similarly, we can measure oxygen permeability of natural waterbodies. Especially in the case of pollution, it is important to know to what extent the oxygen permeability of the water surface layer has been decreased. Based on the tehnique presented in this research, fieldwork equipment will be developed.

Role of oxygen diffusion at Ni/Cr2O3 interface in intergranular oxidation of Ni-Cr alloy

NASA Astrophysics Data System (ADS)

Medasani, Bharat; Sushko, Maria; Schreiber, Daniel; Rosso, Kevin; Bruemmer, Stephen

Certain Ni-Cr alloys used in nuclear systems experience intergranular oxidation and stress corrosion cracking when exposed to high-temperature water leading to their degradation and unexpected failure. To develop a mechanistic understanding of grain boundary oxidation processes, we proposed a mesoscale metal alloy oxidation model that combines quantum Density Functional Theory (DFT) with mesoscopic Poisson-Nernst-Planck/classical DFT. This framework encompasses the chemical specificity of elementary diffusion processes and mesoscale reactive dynamics, and allows modeling oxidation processes on experimentally relevant length scales from first principles. As a proof of concept, a preliminary model was previously employed that limited oxygen diffusion pathways to those through the oxide phase and did not allow oxygen diffusion in the alloy or across oxide/alloy interfaces. In this work, we expand the model to include oxygen diffusion pathways along Ni/Cr2O3 interfaces and demonstrate the increasing importance of such pathways for intergranular oxidation of Ni-Cr alloys with high Cr content. This work is supported by the U.S. Dept. of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Simulations are performed using PNNL Institutional Computing facility.

Vortical ciliary flows actively enhance mass transport in reef corals.

PubMed

Shapiro, Orr H; Fernandez, Vicente I; Garren, Melissa; Guasto, Jeffrey S; Debaillon-Vesque, François P; Kramarsky-Winter, Esti; Vardi, Assaf; Stocker, Roman

2014-09-16

The exchange of nutrients and dissolved gasses between corals and their environment is a critical determinant of the growth of coral colonies and the productivity of coral reefs. To date, this exchange has been assumed to be limited by molecular diffusion through an unstirred boundary layer extending 1-2 mm from the coral surface, with corals relying solely on external flow to overcome this limitation. Here, we present direct microscopic evidence that, instead, corals can actively enhance mass transport through strong vortical flows driven by motile epidermal cilia covering their entire surface. Ciliary beating produces quasi-steady arrays of counterrotating vortices that vigorously stir a layer of water extending up to 2 mm from the coral surface. We show that, under low ambient flow velocities, these vortices, rather than molecular diffusion, control the exchange of nutrients and oxygen between the coral and its environment, enhancing mass transfer rates by up to 400%. This ability of corals to stir their boundary layer changes the way that we perceive the microenvironment of coral surfaces, revealing an active mechanism complementing the passive enhancement of transport by ambient flow. These findings extend our understanding of mass transport processes in reef corals and may shed new light on the evolutionary success of corals and coral reefs.

Interstitial photodynamic therapy and glioblastoma: light fractionation study on a preclinical model: preliminary results

NASA Astrophysics Data System (ADS)

Leroy, Henri-Arthur; Vermandel, Maximilien; Tétard, Marie-Charlotte; Lejeune, Jean-Paul; Mordon, Serge; Reyns, Nicolas

2015-03-01

Background Glioblastoma is a high-grade cerebral tumor with local recurrence and poor outcome. Photodynamic therapy (PDT) is a local treatment based on the light activation of a photosensitizer (PS) in the presence of oxygen to form cytotoxic species. Fractionation of light delivery may enhance treatment efficiency by restoring tissue oxygenation. Objectives To evaluate the efficiency of light fractionation using MRI imaging, including diffusion and perfusion, compared to histological data. Materials and Methods Thirty-nine "Nude" rats were grafted with human U87 cells into the right putamen. After PS precursor intake (5-ALA), an optic fiber was introduced into the tumor. The rats were randomized in three groups: without illumination, with monofractionated illumination and the third one with multifractionated light. Treatment effects were assessed with early MRI including diffusion and perfusion sequences. The animals were eventually sacrificed to perform brain histology. Results On MRI, we observed elevated diffusion values in the center of the tumor among treated animals, especially in multifractionated group. Perfusion decreased around the treatment site, all the more in the multifractionated group. Histology confirmed our MRI findings, with a more extensive necrosis and associated with a rarified angiogenic network in the treatment area, after multifractionated PDT. However, we observed more surrounding edema and neovascularization in the peripheral ring after multifractionated PDT. Conclusion Fractionated interstitial PDT induced specific tumoral lesions. The multifractionated scheme was more efficient, inducing increased tumoral necrosis, but it also caused significant peripheral edema and neovascularization. Diffusion and perfusion MRI imaging were able to predict the histological lesions.

Point-of-care instrument for monitoring tissue health during skin graft repair

NASA Astrophysics Data System (ADS)

Gurjar, R. S.; Seetamraju, M.; Zhang, J.; Feinberg, S. E.; Wolf, D. E.

2011-06-01

We have developed the necessary theoretical framework and the basic instrumental design parameters to enable mapping of subsurface blood dynamics and tissue oxygenation for patients undergoing skin graft procedures. This analysis forms the basis for developing a simple patch geometry, which can be used to map by diffuse optical techniques blood flow velocity and tissue oxygenation as a function of depth in subsurface tissue.skin graft, diffuse correlation analysis, oxygen saturation.

Enhanced mixing and spatial instability in concentrated bacterial suspensions

NASA Astrophysics Data System (ADS)

Sokolov, Andrey; Goldstein, Raymond E.; Feldchtein, Felix I.; Aranson, Igor S.

2009-09-01

High-resolution optical coherence tomography is used to study the onset of a large-scale convective motion in free-standing thin films of adjustable thickness containing suspensions of swimming aerobic bacteria. Clear evidence is found that beyond a threshold film thickness there exists a transition from quasi-two-dimensional collective swimming to three-dimensional turbulent behavior. The latter state, qualitatively different from bioconvection in dilute bacterial suspensions, is characterized by enhanced diffusivities of oxygen and bacteria. These results emphasize the impact of self-organized bacterial locomotion on the onset of three-dimensional dynamics, and suggest key ingredients necessary to extend standard models of bioconvection to incorporate effects of large-scale collective motion.

The dependence of nano-contact magnetoresistance on the bulk scattering spin asymmetry in CoFe alloys with oxidation impurities

NASA Astrophysics Data System (ADS)

Shiokawa, Yohei; Jung, JinWon; Otsuka, Takahiko; Sahashi, Masashi

2015-08-01

Nano-contact magnetoresistance (NCMR) spin-valves (SVs) using an AlOx nano-oxide-layer (NOL) have numerous nanocontacts in the thin AlOx oxide layer. The NCMR theoretically depends on the bulk scattering spin asymmetry ( β) of the ferromagnetic material in the nanocontacts. To determine the relationship between NCMR and β, we investigated the dependence of NCMR on the composition of the ferromagnetic material Co1-xFex. The samples were annealed at 270 °C and 380 °C to enhance the MR ratio. For both annealing temperatures, the magnetorsistance ratio in the low-resistance area product region at less than 1 Ω μm2 was maximized for Co0.5Fe0.5. To evaluate β exactly, we fabricated current-perpendicular-to-plane giant magnetoresistance SVs with Co1-xFex/Cu/Co1-xFex layers and used Valet and Fert's theory to solve the diffusion equation of the spin accumulation for a ferromagnetic layer/non-ferromagnetic layer of five layers with a finite diffusion length. The evaluated β for Co1-xFex was also maximized for Co0.5Fe0.5. Additionally, to determine the difference between the experimental MR ratio of NCMR SVs and the theoretical MR ratio, we fabricated Co0.5Fe0.5 with oxygen impurities and estimated the decrease in β with increasing oxygen impurity concentration. Our Co0.5Fe0.5 nano-contacts fabricated using ion-assisted oxidation may contain oxygen impurities, and the oxygen impurities might cause a decrease in β and the MR ratio.

Diffusive Transfer of Oxygen From Seamount Basaltic Crust Into Overlying Sediments: an Example From the Clarion-Clipperton Fracture Zone, Equatorial Pacific Ocean

NASA Astrophysics Data System (ADS)

Kasten, S.; Mewes, K.; Mogollón, J.; Picard, A.; Rühlemann, C.; Eisenhauer, A.; Kuhn, T.; Ziebis, W.

2015-12-01

Within the Clarion-Clipperton Fracture Zone (CCFZ) located in the equatorial Pacific Ocean numerous seamounts, with diameters ranging from 3 to 30 km and varying heights above the surrounding seafloor of up to 2500 m, occur throughout the deep-sea plain. There is evidence that these may serve as conduits for low-temperature hydrothermal circulation of seawater through the oceanic crust. During RV SONNE cruise SO205 in April/May 2010 and BIONOD cruise with RV ĹATALANTE in spring 2012 we took piston and gravity cores for geochemical analyses, as well as for high-resolution pore-water oxygen and nutrient measurements. Specifically, we took cores along a transect at three sites, located 400, 700 and 1000 m away from the foot of a 240 m high seamount, called 'Teddy Bare'. At all 3 sites oxygen penetrates the entire sediment column of the organic carbon-poor sediment. More importantly, oxygen concentrations initially decrease with sediment depth but increase again at depths of 3 m and 7 m above the basaltic basement, suggesting an upward diffusion of oxygen from seawater circulating within the seamount crust into the overlying basal sediments. This is the first time this has been shown for the deep subsurface in the Pacific Ocean. Mirroring the oxygen concentrations nitrate concentrations accumulate with sediment depth but decrease towards the basement. Transport-reaction modeling revealed that (1) the diffusive flux of oxygen from the basaltic basement exceeds the oxygen consumption through organic matter oxidation and nitrification in the basal sediments and (2) the nutrient exchange between the sediment and the underlying basaltic crust occurs at orders-of-magnitude lower rates than between the sediment surface and the overlying bottom water. We furthermore show that the upward diffusion of oxygen from the basaltic basement affects the preservation of organic compounds within the oxic sediment column at all 3 sites. Our investigations indicate that an upward diffusion of oxygen from the basalt into the overlying sediment may be a widespread phenomenon in this area of the Pacific Ocean that is characterized by numerous seamounts.

OXYGEN TRANSFER EFFICIENCY SURVEYS AT THE SOUTH SHORE WASTEWATER TREATMENT PLANT - 1985-1987

EPA Science Inventory

Ceramic plate diffusers were among the earliest forms of fine pore diffusers used for oxygen transfer in activated sludge treatment. They have been successfully used for over 60 years in the Jones Island West Plant of the Milwaukee Metropolitan Sewerage District and, since initi...

OXYGEN TRANSFER EFFICIENCY SURVEYS AT THE JONES ISLAND TREATMENT PLANTS - 1985-1988

EPA Science Inventory

Ceramic plate diffusers were among the earliest forms of fine pore diffusers used for oxygen transfer in activated sludge treatment. They have been successfully used for over 60 years in the Jones Island West Plant of the Milwaukee Metropolitan Sewerage District and, since initia...

Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations

DOE PAGES

Vathonne, Emerson; Andersson, David Ragnar Anders; Freyss, Michel; ...

2016-12-16

We present a study of the diffusion of krypton in UO 2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT + U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO 2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and themore » interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μ O or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO 2, migration is assisted by the bound Schottky defect and the charged uranium vacancy, V U 4–. Around stoichiometry, migration assisted by the charged uranium–oxygen divacancy (V UO 2–) and V U 4– is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two V U 4– dominates. Kr migration is enhanced at higher μ O, and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. Finally, the mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.« less

The Use Of Fluorescence Quenching To Measure Oxygen Concentration

NASA Astrophysics Data System (ADS)

Cox, M. E.; Dunn, B.

1986-01-01

The method of fluorescence quenching is used to measure the concentration of molecular oxygen. The method is rapid, reversible, and does not consume oxygen. The method may provide the basis for a unique biomedical sensor. The key to developing such a device lies in the choice of a fluorophor/polymer composite matrix having the desired optical and transport properties. Experimental results will be presented for certain parameters essential for assessing device development. The properties of interest include the kinetics of fluorescence quenching, the biomolecular rate constants, the temperature dependence of oxygen solubility and diffusivity in the composite matrix, and the oxygen diffusion coefficient. Poly(dimethyl siloxane) [PDMS] was chosen as the polymer host because it is biocompatible, hydrophobic, has a high diffusivity for the simple gases, and is easily bonded to fused silica. 9,10-diphenyl anthracene [9,10-D] was selected since it is readily soluble in a number of organic solvents, has an excitation spectrum in the near UV, an emission spectrum in the visible, a long fluorescence lifetime, and a high quantum yield. When incorporated into PDMS, the optical spectra of 9,10-D does not alter appreciably. The response time of the device is determined by the solution/diffusion kinetics of oxygen in PDMS. The solubility of oxygen in PDMS decreases with increasing temperature and an enthalpy of solution of off = -3.0 kcal/mole. (1) The diffusion of oxyzen in PDMS is found to obey an Arrhenius relation over the temperature range of 5'C to 450C with D = Do exp (-ED/RT) (2) where Do = 0.115 cm2/s (3) and ED = 4.77 kcal/mole. (4) Results of these studies indicate that an appropriate device, based on a fluorophor/polymer composite, for the measurement of oxygen concentration should be sensitive over those ranges which are important for physiological monitoring.

Unsteady Oxygen Transfer in Space-Filling Models of the Pulmonary Acinus

NASA Astrophysics Data System (ADS)

Hofemeier, Philipp; Shachar-Berman, Lihi; Filoche, Marcel; Sznitman, Josue

2014-11-01

Diffusional screening in the pulmonary acinus is a well-known physical phenomenon that results from the depletion of fresh oxygen in proximal acinar generations diffusing through the alveolar wall membranes and effectively creating a gradient in the oxygen partial pressure along the acinar airways. Until present, most studies have focused on steady-state oxygen diffusion in generic sub-acinar structures and discarded convective oxygen transport due to low Peclet numbers in this region. Such studies, however, fall typically short in capturing the complex morphology of acinar airways as well as the oscillatory nature of convecive acinar breathing. Here, we revisit this problem and solve the convective-diffusive transport equations in breathing 3D acinar structures, underlining the significance of convective flows in proximal acinar generations as well as recirculating alveolar flow patterns. In particular, to assess diffusional screening, we monitor time-dependent efficiencies of the acinus under cyclic breathing motion. Our study emphasizes the necessity of capturing both a dynamically breathing and anatomically-realistic model of the sub-acinus to characterize unsteady oxygen transport across the acinar walls.

A Highly Active Low Voltage Redox Mediator for Enhanced Rechargeability of Lithium-Oxygen Batteries.

PubMed

Kundu, Dipan; Black, Robert; Adams, Brian; Nazar, Linda F

2015-12-23

Owing to its high theoretical specific energy, the Li-oxygen battery is one of the fundamentally most promising energy storage systems, but also one of the most challenging. Poor rechargeability, involving the oxidation of insoluble and insulating lithium peroxide (Li2O2), has remained the "Achilles' heel" of this electrochemical energy storage system. We report here on a new redox mediator tris[4-(diethylamino)phenyl]amine (TDPA), that-at 3.1 V-exhibits the lowest and closest potential redox couple compared to the equilibrium voltage of the Li-oxygen cell of those reported to date, with a second couple also at a low potential of 3.5 V. We show it is a soluble "catalyst" capable of lowering the Li2O2 charging potential by >0.8 V without requiring direct electrical contact of the peroxide and that it also facilitates high discharge capacities. Its chemical and electrochemical stability, fast diffusion kinetics, and two dynamic redox potentials represent a significant advance in oxygen-evolution catalysis. It enables Li-O2 cells that can be recharged more than 100 cycles with average round-trip efficiencies >80%, opening a new avenue for practical Li-oxygen batteries.

Oxygen concentration sensor for an internal combustion engine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakajima, T.; Okada, Y.; Mieno, T.

1988-09-29

This patent describes an oxygen concentration sensor, comprising: an oxygen ion conductive solid electrolyte member forming a gas diffusion restricted region into which a measuring gas is introduced; a pair of electrodes sandwiching the solid electrolyte member; pump current supply means applying a pump voltage to the pair of electrodes through a current detection element to generate a pump current; and a heater element connected to the solid electrolyte member for heating the solid electrolyte member for heating the solid electrolyte member when a heater current is supplied from a heater current source; wherein the oxygen concentration sensor detects anmore » oxygen concentration in the measuring gas in terms of a current value of the pump current supplied through the current detection element and controls oxygen concentration in the gas diffusion restricted region by conducting oxygen ions through the solid electrolyte member in accordance to the flow of the pump current; and wherein the current detection element is connected to the electrode of the pair of electrodes facing the gas diffusion restricted region for insuring that the current value is representative of the pump current and possible leakage current from the heater current.« less

Large enhancement of perfusion contribution on fMRI signal

PubMed Central

Wang, Xiao; Zhu, Xiao-Hong; Zhang, Yi; Chen, Wei

2012-01-01

The perfusion contribution to the total functional magnetic resonance imaging (fMRI) signal was investigated using a rat model with mild hypercapnia at 9.4 T, and human subjects with visual stimulation at 4 T. It was found that the total fMRI signal change could be approximated as a linear superposition of ‘true' blood oxygenation level-dependent (BOLD; T2/T2*) effect and the blood flow-related (T1) effect. The latter effect was significantly enhanced by using short repetition time and large radiofrequency pulse flip angle and became comparable to the ‘true' BOLD signal in response to a mild hypercapnia in the rat brain, resulting in an improved contrast-to-noise ratio (CNR). Bipolar diffusion gradients suppressed the intravascular signals but had no significant effect on the flow-related signal. Similar results of enhanced fMRI signal were observed in the human study. The overall results suggest that the observed flow-related signal enhancement is likely originated from perfusion, and this enhancement can improve CNR and the spatial specificity for mapping brain activity and physiology changes. The nature of mixed BOLD and perfusion-related contributions in the total fMRI signal also has implication on BOLD quantification, in particular, the BOLD calibration model commonly used to estimate the change of cerebral metabolic rate of oxygen. PMID:22395206

Enhancing oxygen transport through Mixed-Ionic-and-Electronic-Conducting ceramic membranes

NASA Astrophysics Data System (ADS)

Yu, Anthony S.

Ceramic membranes based on Mixed-Ionic-and-Electronic-Conducting (MIEC) oxides are capable of separating oxygen from air in the presence of an oxygen partial-pressure gradient. These MIEC membranes show great promise for oxygen consuming industrial processes, such as the production of syngas from steam reforming of natural gas (SRM), as well as for electricity generation in Solid Oxide Fuel Cells (SOFC). For both applications, the overall performance is dictated by the rate of oxygen transport across the membrane. Oxygen transport across MIEC membranes is composed of a bulk oxygen-ion diffusion process and surface processes, such as surface reactions and adsorption/desorption of gaseous reactants/products. The main goal of this thesis was to determine which process is rate-limiting in order to significantly enhance the overall rate of oxygen transport in MIEC membrane systems. The rate-limiting step was determined by evaluating the total resistance to oxygen transfer, Rtot. Rtot is the sum of a bulk diffusion resistance in the membrane itself, Rb, and interfacial loss components, Rs. Rb is a function of the membrane's ionic conductivity and thickness, while Rs arises primarily from slow surface-exchange kinetics that cause the P(O2) at the surfaces of the membrane to differ from the P(O 2) in the adjacent gas phases. Rtot can be calculated from the Nernst potential across the membrane and the measured oxygen flux. The rate-limiting process can be determined by evaluating the relative contributions of the various losses, Rs and Rb, to Rtot. Using this method, this thesis demonstrates that for most membrane systems, Rs is the dominating factor. In the development of membrane systems with high oxygen transport rates, thin membranes with high ionic conductivities are required to achieve fast bulk oxygen-ion diffusion. However, as membrane thickness is decreased, surface reaction kinetics become more important in determining the overall transport rate. The two approaches to increase surface reaction kinetics and decrease Rs that were examined in this thesis involved modifying the surface microstructure, as well as adding both metallic (e.g. Pt) and oxide (e.g. CeO2, La0.8Sr0.2FeO3) catalysts to both membrane surfaces. These two approaches were investigated for single-phase MIEC membrane reactors (La0.9Ca0.1FeO3-delta ), as well as composite membrane reactors composed of an electronic conductor (La0.8Sr-0.2CrO3-delta) and an ionic conductor (YSZ). The use of catalysts and microstructure modifications to decrease interfacial losses is equally important for SOFCs. In this thesis, the electrochemical activity and microstructure of metallic catalysts formed by "ex-solving" metals from an oxide lattice, and oxide catalysts deposited by Atomic Layer Deposition (ALD) were investigated. It is shown that these methods for depositing catalysts resulted in very different effects on electrode performance when compared to the same catalysts deposited by wet impregnation. For example, when transition metals, such as Ni and Co, were "ex-solved" from a La0.8Sr0.2CrO3-delta anode lattice, these "ex-solved" metal particles not only exhibited great catalytic activity, they were also less prone to coking compared to their wet impregnated counterparts. On the cathode side, thin layers of various oxides (e.g. Al 2O3, CeOx, SrO) that were deposited using ALD also exhibited drastically different electrochemical activity compared to their wet impregnated counterparts. It was determined that differences in electrochemical activity could be attributed to a difference in the oxide morphology, showing that a catalyst's microstructure and morphology are very important in dictating its overall activity in SOFC electrodes.

Pressure dependence of the oxygen reduction reaction at the platinum microelectrode/nafion interface - Electrode kinetics and mass transport

NASA Technical Reports Server (NTRS)

Parthasarathy, Arvind; Srinivasan, Supramaniam; Appleby, A. J.; Martin, Charles R.

1992-01-01

The investigation of oxygen reduction kinetics at the platinum/Nafion interface is of great importance in the advancement of proton-exchange-membrane (PEM) fuel-cell technology. This study focuses on the dependence of the oxygen reduction kinetics on oxygen pressure. Conventional Tafel analysis of the data shows that the reaction order with respect to oxygen is unity at both high and low current densities. Chronoamperometric measurements of the transport parameters for oxygen in Nafion show that oxygen dissolution follows Henry's isotherm. The diffusion coefficient of oxygen is invariant with pressure; however, the diffusion coefficient for oxygen is lower when air is used as the equilibrating gas as compared to when oxygen is used for equilibration. These results are of value in understanding the influence of O2 partial pressure on the performance of PEM fuel cells and also in elucidating the mechanism of oxygen reduction at the platinum/Nafion interface.

Oxygen impurity effects at metal/silicide interfaces - Formation of silicon oxide and suboxides in the Ni/Si system

NASA Technical Reports Server (NTRS)

Grunthaner, P. J.; Grunthaner, F. J.; Scott, D. M.; Nicolet, M.-A.; Mayer, J. W.

1981-01-01

The effect of implanted oxygen impurities on the Ni/Ni2Si interface is investigated using X-ray photoelectron spectroscopy, He-4(+) backscattering and O(d, alpha)-16 N-14 nuclear reactions. Oxygen dosages corresponding to concentrations of 1, 2, and 3 atomic percent were implanted into Ni films evaporated on Si substrates. The oxygen, nickel, and silicon core lines were monitored as a function of time during in situ growth of the Ni silicide to determine the chemical nature of the diffusion barrier which forms in the presence of oxygen impurities. Analysis of the Ni, Si, and O core levels demonstrates that the formation of SiO2 is responsible for the Ni diffusion barrier rather than Ni oxide or mixed oxides, such as Ni2SiO4. It is determined that 2.2 x 10 to the 16th O/qu cm is sufficient to prevent Ni diffusion under UHV annealing conditions.

Investigation of the oxygen exchange mechanism on Pt|yttria stabilized zirconia at intermediate temperatures: Surface path versus bulk path

PubMed Central

Opitz, Alexander K.; Lutz, Alexander; Kubicek, Markus; Kubel, Frank; Hutter, Herbert; Fleig, Jürgen

2011-01-01

The oxygen exchange kinetics of platinum on yttria-stabilized zirconia (YSZ) was investigated by means of geometrically well-defined Pt microelectrodes. By variation of electrode size and temperature it was possible to separate two temperature regimes with different geometry dependencies of the polarization resistance. At higher temperatures (550–700 °C) an elementary step located close to the three phase boundary (TPB) with an activation energy of ∼1.6 eV was identified as rate limiting. At lower temperatures (300–400 °C) the rate limiting elementary step is related to the electrode area and exhibited a very low activation energy in the order of 0.2 eV. From these observations two parallel pathways for electrochemical oxygen exchange are concluded. The nature of these two elementary steps is discussed in terms of equivalent circuits. Two combinations of parallel rate limiting reaction steps are found to explain the observed geometry dependencies: (i) Diffusion through an impurity phase at the TPB in parallel to diffusion of oxygen through platinum – most likely along Pt grain boundaries – as area-related process. (ii) Co-limitation of oxygen diffusion along the Pt|YSZ interface and charge transfer at the interface with a short decay length of the corresponding transmission line (as TPB-related process) in parallel to oxygen diffusion through platinum. PMID:22210951

The diving paradox: new insights into the role of the dive response in air-breathing vertebrates.

PubMed

Davis, Randall W; Polasek, Lori; Watson, Rebecca; Fuson, Amanda; Williams, Terrie M; Kanatous, Shane B

2004-07-01

When aquatic reptiles, birds and mammals submerge, they typically exhibit a dive response in which breathing ceases, heart rate slows, and blood flow to peripheral tissues is reduced. The profound dive response that occurs during forced submergence sequesters blood oxygen for the brain and heart while allowing peripheral tissues to become anaerobic, thus protecting the animal from immediate asphyxiation. However, the decrease in peripheral blood flow is in direct conflict with the exercise response necessary for supporting muscle metabolism during submerged swimming. In free diving animals, a dive response still occurs, but it is less intense than during forced submergence, and whole-body metabolism remains aerobic. If blood oxygen is not sequestered for brain and heart metabolism during normal diving, then what is the purpose of the dive response? Here, we show that its primary role may be to regulate the degree of hypoxia in skeletal muscle so that blood and muscle oxygen stores can be efficiently used. Paradoxically, the muscles of diving vertebrates must become hypoxic to maximize aerobic dive duration. At the same time, morphological and enzymatic adaptations enhance intracellular oxygen diffusion at low partial pressures of oxygen. Optimizing the use of blood and muscle oxygen stores allows aquatic, air-breathing vertebrates to exercise for prolonged periods while holding their breath.

Cerebral blood flow and metabolism during exercise: implications for fatigue.

PubMed

Secher, Neils H; Seifert, Thomas; Van Lieshout, Johannes J

2008-01-01

During exercise: the Kety-Schmidt-determined cerebral blood flow (CBF) does not change because the jugular vein is collapsed in the upright position. In contrast, when CBF is evaluated by (133)Xe clearance, by flow in the internal carotid artery, or by flow velocity in basal cerebral arteries, a approximately 25% increase is detected with a parallel increase in metabolism. During activation, an increase in cerebral O(2) supply is required because there is no capillary recruitment within the brain and increased metabolism becomes dependent on an enhanced gradient for oxygen diffusion. During maximal whole body exercise, however, cerebral oxygenation decreases because of eventual arterial desaturation and marked hyperventilation-related hypocapnia of consequence for CBF. Reduced cerebral oxygenation affects recruitment of motor units, and supplemental O(2) enhances cerebral oxygenation and work capacity without effects on muscle oxygenation. Also, the work of breathing and the increasing temperature of the brain during exercise are of importance for the development of so-called central fatigue. During prolonged exercise, the perceived exertion is related to accumulation of ammonia in the brain, and data support the theory that glycogen depletion in astrocytes limits the ability of the brain to accelerate its metabolism during activation. The release of interleukin-6 from the brain when exercise is prolonged may represent a signaling pathway in matching the metabolic response of the brain. Preliminary data suggest a coupling between the circulatory and metabolic perturbations in the brain during strenuous exercise and the ability of the brain to access slow-twitch muscle fiber populations.

Kinetic Monte Carlo Simulation of Oxygen Diffusion in Ytterbium Disilicate

NASA Technical Reports Server (NTRS)

Good, Brian S.

2015-01-01

Silicon-based ceramic components for next-generation jet turbine engines offer potential weight savings, as well as higher operating temperatures, both of which lead to increased efficiency and lower fuel costs. Silicon carbide (SiC), in particular, offers low density, good strength at high temperatures, and good oxidation resistance in dry air. However, reaction of SiC with high-temperature water vapor, as found in the hot section of jet turbine engines in operation, can cause rapid surface recession, which limits the lifetime of such components. Environmental Barrier Coatings (EBCs) are therefore needed if long component lifetime is to be achieved. Rare earth silicates such as Yb2Si2O7 and Yb2SiO5 have been proposed for such applications; in an effort to better understand diffusion in such materials, we have performed kinetic Monte Carlo (kMC) simulations of oxygen diffusion in Ytterbium disilicate, Yb2- Si2O7. The diffusive process is assumed to take place via the thermally activated hopping of oxygen atoms among oxygen vacancy sites or among interstitial sites. Migration barrier energies are computed using density functional theory (DFT).

Study of tissue oxygen supply rate in a macroscopic photodynamic therapy singlet oxygen model

NASA Astrophysics Data System (ADS)

Zhu, Timothy C.; Liu, Baochang; Penjweini, Rozhin

2015-03-01

An appropriate expression for the oxygen supply rate (Γs) is required for the macroscopic modeling of the complex mechanisms of photodynamic therapy (PDT). It is unrealistic to model the actual heterogeneous tumor microvascular networks coupled with the PDT processes because of the large computational requirement. In this study, a theoretical microscopic model based on uniformly distributed Krogh cylinders is used to calculate Γs=g (1-[O]/[]0) that can replace the complex modeling of blood vasculature while maintaining a reasonable resemblance to reality; g is the maximum oxygen supply rate and [O]/[]0 is the volume-average tissue oxygen concentration normalized to its value prior to PDT. The model incorporates kinetic equations of oxygen diffusion and convection within capillaries and oxygen saturation from oxyhemoglobin. Oxygen supply to the tissue is via diffusion from the uniformly distributed blood vessels. Oxygen can also diffuse along the radius and the longitudinal axis of the cylinder within tissue. The relations of Γs to [3O2]/] are examined for a biologically reasonable range of the physiological parameters for the microvasculature and several light fluence rates (ϕ). The results show a linear relationship between Γs and [3O2]/], independent of ϕ and photochemical parameters; the obtained g ranges from 0.4 to 1390 μM/s.

Emergence of microstructure and oxygen diffusion in yttrium-stabilized cubic zirconia

NASA Astrophysics Data System (ADS)

Yang, C.; Trachenko, K.; Hull, S.; Todorov, I. T.; Dove, M. T.

2018-05-01

Large-scale molecular dynamics simulations have been used to study the microstructure in Y-doped ZrO2. From simulations performed as a function of composition the dependence of microstructure on composition is quantified, showing how it is formed from two coexisting phases, and the transformation to the stabilized cubic form is observed at higher concentrations of yttrium and higher temperatures. The effect of composition and temperature on oxygen diffusion is also studied, showing strong correlations between microstructure and diffusion.

Morphological Pulmonary Diffusion Capacity for Oxygen of Burmese Pythons (Python molurus): a Comparison of Animals in Healthy Condition and with Different Pulmonary Infections.

PubMed

Starck, J M; Weimer, I; Aupperle, H; Müller, K; Marschang, R E; Kiefer, I; Pees, M

2015-11-01

A qualitative and quantitative morphological study of the pulmonary exchange capacity of healthy and diseased Burmese pythons (Python molurus) was carried out in order to test the hypothesis that the high morphological excess capacity for oxygen exchange in the lungs of these snakes is one of the reasons why pathological processes extend throughout the lung parenchyma and impair major parts of the lungs before clinical signs of respiratory disease become apparent. Twenty-four Burmese pythons (12 healthy and 12 diseased) were included in the study. A stereology-based approach was used to quantify the lung parenchyma using computed tomography. Light microscopy was used to quantify tissue compartments and the respiratory exchange surface, and transmission electron microscopy was used to measure the thickness of the diffusion barrier. The morphological diffusion capacity for oxygen of the lungs and the anatomical diffusion factor were calculated. The calculated anatomical diffusion capacity was compared with published values for oxygen consumption of healthy snakes, and the degree to which the exchange capacity can be obstructed before normal physiological function is impaired was estimated. Heterogeneous pulmonary infections result in graded morphological transformations of pulmonary parenchyma involving lymphocyte migration into the connective tissue and thickening of the septal connective tissue, increasing thickness of the diffusion barrier and increasing transformation of the pulmonary epithelium into a columnar pseudostratified or stratified epithelium. The transformed epithelium developed by hyperplasia of ciliated cells arising from the tip of the faveolar septa and by hyperplasia of type II pneumocytes. These results support the idea that the lungs have a remarkable overcapacity for oxygen consumption and that the development of pulmonary disease continuously reduces the capacity for oxygen consumption. However, due to the overcapacity of the lungs, this reduction does not result in clinical signs and disease can progress unrecognized for an extended period. Copyright © 2015 Elsevier Ltd. All rights reserved.

Theoretical examination of effective oxygen diffusion coefficient and electrical conductivity of polymer electrolyte fuel cell porous components

NASA Astrophysics Data System (ADS)

Inoue, Gen; Yokoyama, Kouji; Ooyama, Junpei; Terao, Takeshi; Tokunaga, Tomomi; Kubo, Norio; Kawase, Motoaki

2016-09-01

The reduction of oxygen transfer resistance through porous components consisting of a gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas diffusion with a negative effect on performance. The relative diffusion coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative diffusion coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance.

Osmotic phenomena in application for hyperbaric oxygen treatment.

PubMed

Babchin, A; Levich, E; Melamed M D, Y; Sivashinsky, G

2011-03-01

Hyperbaric oxygen (HBO) treatment defines the medical procedure when the patient inhales pure oxygen at elevated pressure conditions. Many diseases and all injuries are associated with a lack of oxygen in tissues, known as hypoxia. HBO provides an effective method for fast oxygen delivery in medical practice. The exact mechanism of the oxygen transport under HBO conditions is not fully identified. The objective of this article is to extend the colloid and surface science basis for the oxygen transport in HBO conditions beyond the molecular diffusion transport mechanism. At a pressure in the hyperbaric chamber of two atmospheres, the partial pressure of oxygen in the blood plasma increases 10 times. The sharp increase of oxygen concentration in the blood plasma creates a considerable concentration gradient between the oxygen dissolved in the plasma and in the tissue. The concentration gradient of oxygen as a non-electrolyte solute causes an osmotic flow of blood plasma with dissolved oxygen. In other words, the molecular diffusion transport of oxygen is supplemented by the convective diffusion raised due to the osmotic flow, accelerating the oxygen delivery from blood to tissue. A non steady state equation for non-electrolyte osmosis is solved asymptotically. The solution clearly demonstrates two modes of osmotic flow: normal osmosis, directed from lower to higher solute concentrations, and anomalous osmosis, directed from higher to lower solute concentrations. The fast delivery of oxygen from blood to tissue is explained on the basis of the strong molecular interaction between the oxygen and the tissue, causing an influx of oxygen into the tissue by convective diffusion in the anomalous osmosis process. The transport of the second gas, nitrogen, dissolved in the blood plasma, is also taken into the consideration. As the patient does not inhale nitrogen during HBO treatment, but exhales it along with oxygen and carbon dioxide, the concentration of nitrogen in blood plasma drops and the nitrogen concentration gradient becomes directed from blood to tissue. On the assumption of weak interaction between the inert nitrogen and the human tissue, normal osmosis for the nitrogen transport takes place. Thus, the directions of anomalous osmotic flow caused by the oxygen concentration gradient coincide with the directions of normal osmotic flow, caused by the nitrogen concentration gradient. This leads to the conclusion that the presence of nitrogen in the human body promotes the oxygen delivery under HBO conditions, rendering the overall success of the hyperbaric oxygen treatment procedure. 2010 Elsevier B.V. All rights reserved.

Oxygen diffusion model of the mixed (U,Pu)O2 ± x: Assessment and application

NASA Astrophysics Data System (ADS)

Moore, Emily; Guéneau, Christine; Crocombette, Jean-Paul

2017-03-01

The uranium-plutonium (U,Pu)O2 ± x mixed oxide (MOX) is used as a nuclear fuel in some light water reactors and considered for future reactor generations. To gain insight into fuel restructuring, which occurs during the fuel lifetime as well as possible accident scenarios understanding of the thermodynamic and kinetic behavior is crucial. A comprehensive evaluation of thermo-kinetic properties is incorporated in a computational CALPHAD type model. The present DICTRA based model describes oxygen diffusion across the whole range of plutonium, uranium and oxygen compositions and temperatures by incorporating vacancy and interstitial migration pathways for oxygen. The self and chemical diffusion coefficients are assessed for the binary UO2 ± x and PuO2 - x systems and the description is extended to the ternary mixed oxide (U,Pu)O2 ± x by extrapolation. A simulation to validate the applicability of this model is considered.

Computation of the unsteady facilitated transport of oxygen in hemoglobin

NASA Technical Reports Server (NTRS)

Davis, Sanford

1990-01-01

The transport of a reacting permeant diffusing through a thin membrane is extended to more realistic dissociation models. A new nonlinear analysis of the reaction-diffusion equations, using implicit finite-difference methods and direct block solvers, is used to study the limits of linearized and equilibrium theories. Computed curves of molecular oxygen permeating through hemoglobin solution are used to illustrate higher-order reaction models, the effect of concentration boundary layers at the membrane interfaces, and the transient buildup of oxygen flux.

Oxygen diffusion in zircon

NASA Astrophysics Data System (ADS)

Watson, E. B.; Cherniak, D. J.

1997-05-01

Oxygen diffusion in natural, non-metamict zircon was characterized under both dry and water-present conditions at temperatures ranging from 765°C to 1500°C. Dry experiments were performed at atmospheric pressure by encapsulating polished zircon samples with a fine powder of 18O-enriched quartz and annealing the sealed capsules in air. Hydrothermal runs were conducted in cold-seal pressure vessels (7-70 MPa) or a piston cylinder apparatus (400-1000 MPa) on zircon samples encapsulated with both 18O-enriched quartz and 18O water. Diffusive-uptake profiles of 18O were measured in all samples with a particle accelerator, using the 18O(p, α) 15N reaction. For dry experimental conditions at 1100-1500°C, the resulting oxygen diffusivities (24 in all) are well described by: D dry (m 2/s) = 1.33 × 10 -4exp(-53920/T) There is no suggestion of diffusive anisotropy. Under wet conditions at 925°C, oxygen diffusion shows little or no dependence upon P H 2O in the range 7-1000 MPa, and is insensitive to total pressure as well. The results of 27 wet experiments at 767-1160°C and 7-1000 MPa can be described a single Arrhenius relationship: D wet (m 2/s) = 5.5 × 10 -12exp(-25280/T) The insensitivity of oxygen diffusion to P H 2O means that applications to geologic problems can be pursued knowing only whether the system of interest was 'wet' (i.e., P H 2O > 7MPa ) or 'dry'. Under dry conditions (presumably rare in the crust), zircons are extremely retentive of their oxygen isotopic signatures, to the extent that δ 18O would be perturbed at the center of a 200 μm zircon only during an extraordinarily hot and protracted event (e.g., 65 Ma at 900°C). Under wet conditions, δ 18O may or may not be retained in the central regions of individual crystals, cores or overgrowth rims, depending upon the specific thermal history of the system.

Terrestrial Fe-oxide Concretions and Mars Blueberries: Comparisons of Similar Advective and Diffusive Chemical Infiltration Reaction Mechanisms

NASA Astrophysics Data System (ADS)

Park, A. J.; Chan, M. A.

2006-12-01

Abundant iron oxide concretions occurring in Navajo Sandstone of southern Utah and those discovered at Meridiani Planum, Mars share many common observable physical traits such as their spheriodal shapes, occurrence, and distribution patterns in sediments. Terrestrial concretions are products of interaction between oxygen-rich aquifer water and basin-derived reducing (iron-rich) water. Water-rock interaction simulations show that diffusion of oxygen and iron supplied by slow-moving water is a reasonable mechanism for producing observed concretion patterns. In short, southern Utah iron oxide concretions are results of Liesegang-type diffusive infiltration reactions in sediments. We propose that the formation of blueberry hematite concretions in Mars sediments followed a similar diagenetic mechanism where iron was derived from the alteration of volcanic substrate and oxygen was provided by the early Martian atmosphere. Although the terrestrial analog differs in the original host rock composition, both the terrestrial and Mars iron-oxide precipitation mechanisms utilize iron and oxygen interactions in sedimentary host rock with diffusive infiltration of solutes from two opposite sources. For the terrestrial model, slow advection of iron-rich water is an important factor that allowed pervasive and in places massive precipitation of iron-oxide concretions. In Mars, evaporative flux of water at the top of the sediment column may have produced a slow advective mass-transfer mechanism that provided a steady source and the right quantity of iron. The similarities of the terrestrial and Martian systems are demonstrated using a water-rock interaction simulator Sym.8, initially in one-dimensional systems. Boundary conditions such as oxygen content of water, partial pressure of oxygen, and supply rate of iron were varied. The results demonstrate the importance of slow advection of water and diffusive processes for producing diagenetic iron oxide concretions.

White Matter Damage Relates to Oxygen Saturation in Children With Sickle Cell Anemia Without Silent Cerebral Infarcts.

PubMed

Kawadler, Jamie M; Kirkham, Fenella J; Clayden, Jonathan D; Hollocks, Matthew J; Seymour, Emma L; Edey, Rosanna; Telfer, Paul; Robins, Andrew; Wilkey, Olu; Barker, Simon; Cox, Tim C S; Clark, Chris A

2015-07-01

Sickle cell anemia is associated with compromised oxygen-carrying capability of hemoglobin and a high incidence of overt and silent stroke. However, in children with no evidence of cerebral infarction, there are changes in brain morphometry relative to healthy controls, which may be related to chronic anemia and oxygen desaturation. A whole-brain tract-based spatial statistics analysis was carried out in 25 children with sickle cell anemia with no evidence of abnormality on T2-weighted magnetic resonance imaging (13 male, age range: 8-18 years) and 14 age- and race-matched controls (7 male, age range: 10-19 years) to determine the extent of white matter injury. The hypotheses that white matter damage is related to daytime peripheral oxygen saturation and steady-state hemoglobin were tested. Fractional anisotropy was found to be significantly lower in patients in the subcortical white matter (corticospinal tract and cerebellum), whereas mean diffusivity and radial diffusivity were higher in patients in widespread areas. There was a significant negative relationship between radial diffusivity and oxygen saturation (P<0.05) in the anterior corpus callosum and a trend-level negative relationship between radial diffusivity and hemoglobin (P<0.1) in the midbody of the corpus callosum. These data show widespread white matter abnormalities in a sample of asymptomatic children with sickle cell anemia, and provides for the first time direct evidence of a relationship between brain microstructure and markers of disease severity (eg, peripheral oxygen saturation and steady-state hemoglobin). This study suggests that diffusion tensor imaging metrics may serve as a biomarker for future trials of reducing hypoxic exposure. © 2015 American Heart Association, Inc.

Determination of Sediment Oxygen Demand in the Ziya River Watershed, China: Based on Laboratory Core Incubation and Microelectrode Measurements

PubMed Central

Rong, Nan; Shan, Baoqing; Wang, Chao

2016-01-01

A study coupling sedimentcore incubation and microelectrode measurementwas performed to explore the sediment oxygen demand (SOD) at 16 stations in the Ziya River Watershed, a severely polluted and anoxic river system in the north of China. Total oxygen flux values in the range 0.19–1.41 g/(m2·d) with an average of 0.62 g/(m2·d) were obtained by core incubations, and diffusive oxygen flux values in the range 0.15–1.38 g/(m2·d) with an average of 0.51 g/(m2·d) were determined by microelectrodes. Total oxygen flux obviously correlated with diffusive oxygen flux (R2 = 0.842). The microelectrode method produced smaller results than the incubation method in 15 of 16 sites, and the diffusive oxygen flux was smaller than the total oxygen flux. Although the two sets of SOD values had significant difference accepted by the two methods via the Wilcoxon signed-rank test (p < 0.05), the microelectrode method was shown to produce results that were similar to those from the core incubation method. The microelectrode method, therefore, could be used as an alternative method for traditional core incubation method, or as a method to verify SOD rates measured by other methods. We consider that high potential sediment oxygen demand would occur in the Ziya River Watershed when the dissolved oxygen (DO) recovered in the overlying water. PMID:26907307

Dissolved oxygen and its response to eutrophication in a tropical black water river.

PubMed

Rixen, Tim; Baum, Antje; Sepryani, Harni; Pohlmann, Thomas; Jose, Christine; Samiaji, Joko

2010-08-01

The Siak is a typical, nutrient-poor, well-mixed, black water river in central Sumatra, Indonesia, which owes its brown color to dissolved organic matter (DOM) leached from surrounding, heavily disturbed peat soils. We measured dissolved organic carbon (DOC) and oxygen concentrations along the river, carried out a 36-h experiment in the province capital Pekanbaru and quantified organic matter and nutrient inputs from urban wastewater channels into the Siak. In order to consider the complex dynamic of oxygen in rivers, a box-diffusion model was used to interpret the measured data. The results suggest that the decomposition of soil derived DOM was the main factor influencing the oxygen concentration in the Siak which varied between approximately 100 and 140 micromol l(-1). Additional DOM input caused by wastewater discharges appeared to reduce the oxygen concentrations by approximately 20 micromol l(-1) during the peak-time in household water use in the early morning and in the early evening. Associated enhanced nutrient inputs appear to reduce the impact of the anthropogenic DOM by favoring the photosynthetic production of oxygen in the morning. A reduction of 20 micromol l(-1), which although perhaps not of great significance in Pekanbaru, has strong implications for wastewater management in the fast developing areas downstream Pekanbaru where oxygen concentrations rarely exceed 20 micromol l(-1). Copyright 2010 Elsevier Ltd. All rights reserved.

New Electrode and Electrolyte Configurations for Lithium-Oxygen Battery.

PubMed

Ulissi, Ulderico; Elia, Giuseppe Antonio; Jeong, Sangsik; Reiter, Jakub; Tsiouvaras, Nikolaos; Passerini, Stefano; Hassoun, Jusef

2018-03-02

Cathode configurations reported herein are alternative to the most diffused ones for application in lithium-oxygen batteries, using an ionic liquid-based electrolyte. The electrodes employ high surface area conductive carbon as the reaction host, and polytetrafluoroethylene as the binding agent to enhance the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) reversibility. Roll-pressed, self-standing electrodes (SSEs) and thinner, spray deposited electrodes (SDEs) are characterized in lithium-oxygen cells using an ionic liquid (IL) based electrolyte formed by mixing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethanesulfonyl)imide (DEMETFSI). The electrochemical results reveal reversible reactions for both electrode configurations, but improved electrochemical performance for the self-standing electrodes in lithium-oxygen cells. These electrodes show charge/discharge polarizations at 60 °C limited to 0.4 V, with capacity up to 1 mAh cm -2 and energy efficiency of about 88 %, while the spray deposited electrodes reveal, under the same conditions, a polarization of 0.6 V and energy efficiency of 80 %. The roll pressed electrode combined with the DEMETFSI-LiTFSI electrolyte and a composite Li x Sn-C alloy anode forms a full Li-ion oxygen cell showing extremely limited polarization, and remarkable energy efficiency. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stimulation of aerobic degradation of bentazone, mecoprop and dichlorprop by oxygen addition to aquifer sediment.

PubMed

Levi, S; Hybel, A-M; Bjerg, P L; Albrechtsen, H-J

2014-03-01

In order to investigate aerobic degradation potential for the herbicides bentazone, mecoprop and dichlorprop, anaerobic groundwater samples from two monitoring and three drinking water wells near a drinking water abstraction field in Nybølle, Denmark, were screened for their degradation potential for the herbicides. In the presence of oxygen (14)C-labelled bentazone and mecoprop were removed significantly from the two monitoring wells' groundwater samples. Oxygen was added to microcosms in order to investigate whether different oxygen concentrations stimulate the biodegradation of the three herbicides in microcosms using groundwater and sandy aquifer materials. To maintain a certain oxygen concentration this level was measured from the outside of the bottles with a fibre oxygen meter using oxygen-sensitive luminescent sensor foil mounted inside the microcosm, to which supplementary oxygen was added. The highest oxygen concentrations (corresponding to 4-11 mg L(-1)) stimulated degradation (a 14-27% increase for mecoprop, 3-9% for dichlorprop and 15-20% for bentazone) over an experimental period of 200 days. Oxygen was required to biodegrade the herbicides, since no degradation was observed under anaerobic conditions. This is the first time bentazone degradation has been observed in aquifer material at low oxygen concentrations (2 mg L(-1)). The sediment had substantial oxygen consumption (0.92-1.45O2 g(-1)dw over 200 days) and oxygen was depleted rapidly in most incubations soon after its addition, which might be due to the oxidation of organic matter and other reduced species such as Fe(2+), S(2-) and Mn in sediment before the biodegradation of herbicides takes place. This study suggests that oxygen enhancement around a drinking water abstraction field could stimulate the bioremediation of diffuse source contamination. Copyright © 2013. Published by Elsevier B.V.

Kinetic Monte Carlo Simulations of Oxygen Diffusion in Environmental Barrier Coating Materials

NASA Technical Reports Server (NTRS)

Good, Brian S.

2017-01-01

Ceramic Matrix Composite (CMC) materials are of interest for use in next-generation turbine engine components, offering a number of significant advantages, including reduced weight and high operating temperatures. However, in the hot environment in which such components operate, the presence of water vapor can lead to corrosion and recession, limiting the useful life of the components. Such degradation can be reduced through the use of Environmental Barrier Coatings (EBCs) that limit the amount of oxygen and water vapor reaching the component. Candidate EBC materials include Yttrium and Ytterbium silicates. In this work we present results of kinetic Monte Carlo (kMC) simulations of oxygen diffusion, via the vacancy mechanism, in Yttrium and Ytterbium disilicates, along with a brief discussion of interstitial diffusion.

Effect of Azospirillum brasilense and Burkholderia unamae Bacteria on Maize Photosynthetic Activity Evaluated Using the Photoacoustic Technique

NASA Astrophysics Data System (ADS)

Gordillo-Delgado, F.; Marín, E.; Calderón, A.

2016-09-01

In this work, the photosynthetic process of maize plants ( Zea mays), which were grown using seeds inoculated with plant growth promoting bacteria Azospirillum brasilense and Burkholderia unamae, was monitored. Photothermal and photobaric signals obtained by a time-resolved photoacoustic measurement configuration were used for measuring the oxygen evolution rate in situ. A frequency-resolved configuration of the method was utilized to determine the oxygen diffusion coefficient and the thermal diffusivity of the maize leaves. The latter parameters, which can be used as indicators of the photosynthetic activity of maize, are found to vary according to the plant-microbe interaction. Treatment with plant growth promoting bacteria induced a decrease in the oxygen diffusion coefficient of about 20 %.

Anomaly diffuse and dielectric relaxation in strontium doped lanthanum molybdate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiao; Fan, Huiqing, E-mail: hqfan3@163.com; Shi, Jing

2011-12-15

Highlights: Black-Right-Pointing-Pointer The anomaly diffuse and dielectric relaxation behaviors are fitted by the Cole-Cole approach. Black-Right-Pointing-Pointer The peak in the LSMO is corresponding to different oxygen ion diffusion process. Black-Right-Pointing-Pointer We first give better explanation about the strange conductivity change caused by doping. Black-Right-Pointing-Pointer The oxygen ion diffusion is due to a combination of the dipolar relaxation and the motion of ions. -- Abstract: The dielectric properties of the La{sub 2-x}Sr{sub x}Mo{sub 2}O{sub 9-{delta}} (x = 0-0.2) ceramics were investigated in the temperature range of 300-800 K. Dielectric measurement reveals that two dielectric anomalies, associated with the oxygen ion diffusion,more » exist in frequency spectrum with x = 0.5. The broad dielectric peaks in tan {delta}({omega}) can be well fitted by a modified Cole-Cole approach. When x = 0.1, only one dielectric relaxation peak is observed, corresponding to different oxygen ion diffusion processes, as distinct from the only relaxation peak in the pure La{sub 2}Mo{sub 2}O{sub 9}. The relaxation parameters {tau}{sub 0}, the dielectric relaxation strength {Delta}, and the activation energy E{sub a} were obtained. The result of this work shows that, the conductivity change caused by doping between the two phases is due to the combination of the dipolar effects and motion of ions.« less

A pseudo-three-dimensional model for quantification of oxygen diffusion from preglomerular arteries to renal tissue and renal venous blood.

PubMed

Lee, Chang-Joon; Ngo, Jennifer P; Kar, Saptarshi; Gardiner, Bruce S; Evans, Roger G; Smith, David W

2017-08-01

To assess the physiological significance of arterial-to-venous (AV) oxygen shunting, we generated a new pseudo-three-dimensional computational model of oxygen diffusion from intrarenal arteries to cortical tissue and veins. The model combines the 11 branching levels (known as "Strahler" orders) of the preglomerular renal vasculature in the rat, with an analysis of an extensive data set obtained using light microscopy to estimate oxygen mass transfer coefficients for each Strahler order. Furthermore, the AV shunting model is now set within a global oxygen transport model that includes transport from arteries, glomeruli, peritubular capillaries, and veins to tissue. While a number of lines of evidence suggest AV shunting is significant, most importantly, our AV oxygen shunting model predicts AV shunting is small under normal physiological conditions (~0.9% of total renal oxygen delivery; range 0.4-1.4%), but increases during renal ischemia, glomerular hyperfiltration (~2.1% of total renal oxygen delivery; range 0.84-3.36%), and some cardiovascular disease states (~3.0% of total renal oxygen delivery; range 1.2-4.8%). Under normal physiological conditions, blood Po 2 is predicted to fall by ~16 mmHg from the root of the renal artery to glomerular entry, with AV oxygen shunting contributing ~40% and oxygen diffusion from arteries to tissue contributing ~60% of this decline. Arterial Po 2 is predicted to fall most rapidly from Strahler order 4 , under normal physiological conditions. We conclude that AV oxygen shunting normally has only a small impact on renal oxygenation, but may exacerbate renal hypoxia during renal ischemia, hyperfiltration, and some cardiovascular disease states. Copyright © 2017 the American Physiological Society.

Multi-spectral imaging of oxygen saturation

NASA Astrophysics Data System (ADS)

Savelieva, Tatiana A.; Stratonnikov, Aleksander A.; Loschenov, Victor B.

2008-06-01

The system of multi-spectral imaging of oxygen saturation is an instrument that can record both spectral and spatial information about a sample. In this project, the spectral imaging technique is used for monitoring of oxygen saturation of hemoglobin in human tissues. This system can be used for monitoring spatial distribution of oxygen saturation in photodynamic therapy, surgery or sports medicine. Diffuse reflectance spectroscopy in the visible range is an effective and extensively used technique for the non-invasive study and characterization of various biological tissues. In this article, a short review of modeling techniques being currently in use for diffuse reflection from semi-infinite turbid media is presented. A simple and practical model for use with a real-time imaging system is proposed. This model is based on linear approximation of the dependence of the diffuse reflectance coefficient on relation between absorbance and reduced scattering coefficient. This dependence was obtained with the Monte Carlo simulation of photon propagation in turbid media. Spectra of the oxygenated and deoxygenated forms of hemoglobin differ mostly in the red area (520 - 600 nm) and have several characteristic points there. Thus four band-pass filters were used for multi-spectral imaging. After having measured the reflectance, the data obtained are used for fitting the concentration of oxygenated and free hemoglobin, and hemoglobin oxygen saturation.

Spin-labeled small unilamellar vesicles with the T1-sensitive saturation-recovery EPR display as an oxygen sensitive analyte for measurement of cellular respiration

PubMed Central

Mainali, Laxman; Vasquez-Vivar, Jeannette; Hyde, James S.; Subczynski, Witold K.

2015-01-01

This study validated the use of small unilamellar vesicles (SUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine with 1 mol% spin label of 1-palmitoyl-2-(16-doxylstearoyl)phosphatidylcholine (16-PC) as an oxygen sensitive analyte to study cellular respiration. In the analyte the hydrocarbon environment surrounds the nitroxide moiety of 16-PC. This ensures high oxygen concentration and oxygen diffusion at the location of the nitroxide as well as isolation of the nitroxide moiety from cellular reductants and paramagnetic ions that might interfere with spin-label oximetry measurements. The saturation-recovery EPR approach was applied in the analysis since this approach is the most direct method to carry out oximetric studies. It was shown that this display (spin-lattice relaxation rate) is linear in oxygen partial pressure up to 100% air (159 mmHg). Experiments using a neuronal cell line in suspension were carried out at X-band for closed chamber geometry. Oxygen consumption rates showed a linear dependence on the number of cells. Other significant benefits of the analyte are: the fast effective rotational diffusion and slow translational diffusion of the spin-probe is favorable for the measurements, and there is no cross reactivity between oxygen and paramagnetic ions in the lipid bilayer. PMID:26441482

Spin-labeled small unilamellar vesicles with the T1-sensitive saturation-recovery EPR display as an oxygen sensitive analyte for measurement of cellular respiration.

PubMed

Mainali, Laxman; Vasquez-Vivar, Jeannette; Hyde, James S; Subczynski, Witold K

2015-08-01

This study validated the use of small unilamellar vesicles (SUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine with 1 mol% spin label of 1-palmitoyl-2-(16-doxylstearoyl)phosphatidylcholine (16-PC) as an oxygen sensitive analyte to study cellular respiration. In the analyte the hydrocarbon environment surrounds the nitroxide moiety of 16-PC. This ensures high oxygen concentration and oxygen diffusion at the location of the nitroxide as well as isolation of the nitroxide moiety from cellular reductants and paramagnetic ions that might interfere with spin-label oximetry measurements. The saturation-recovery EPR approach was applied in the analysis since this approach is the most direct method to carry out oximetric studies. It was shown that this display (spin-lattice relaxation rate) is linear in oxygen partial pressure up to 100% air (159 mmHg). Experiments using a neuronal cell line in suspension were carried out at X-band for closed chamber geometry. Oxygen consumption rates showed a linear dependence on the number of cells. Other significant benefits of the analyte are: the fast effective rotational diffusion and slow translational diffusion of the spin-probe is favorable for the measurements, and there is no cross reactivity between oxygen and paramagnetic ions in the lipid bilayer.

A method for monitoring of oxygen saturation changes in brain tissue using diffuse reflectance spectroscopy.

PubMed

Rejmstad, Peter; Johansson, Johannes D; Haj-Hosseini, Neda; Wårdell, Karin

2017-03-01

Continuous measurement of local brain oxygen saturation (SO 2 ) can be used to monitor the status of brain trauma patients in the neurocritical care unit. Currently, micro-oxygen-electrodes are considered as the "gold standard" in measuring cerebral oxygen pressure (pO 2 ), which is closely related to SO 2 through the oxygen dissociation curve (ODC) of hemoglobin, but with the drawback of slow in response time. The present study suggests estimation of SO 2 in brain tissue using diffuse reflectance spectroscopy (DRS) for finding an analytical relation between measured spectra and the SO 2 for different blood concentrations. The P 3 diffusion approximation is used to generate a set of spectra simulating brain tissue for various levels of blood concentrations in order to estimate SO 2 . The algorithm is evaluated on optical phantoms mimicking white brain matter (blood volume of 0.5-2%) where pO 2 and temperature is controlled and on clinical data collected during brain surgery. The suggested method is capable of estimating the blood fraction and oxygen saturation changes from the spectroscopic signal and the hemoglobin absorption profile. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optical in situ monitoring of plasma-enhanced atomic layer deposition process

NASA Astrophysics Data System (ADS)

Zeeshan Arshad, Muhammad; Jo, Kyung Jae; Kim, Hyun Gi; Jeen Hong, Sang

2018-06-01

An optical in situ process monitoring method for the early detection of anomalies in plasma process equipment is presented. Cyclic process steps of precursor treatment and plasma reaction for the deposition of an angstrom-scale film increase their complexity to ensure the process quality. However, a small deviation in process parameters, for instance, gas flow rate, process temperature, or RF power, may jeopardize the deposited film quality. As a test vehicle for the process monitoring, we have investigated the aluminum-oxide (Al2O3) encapsulation process in plasma-enhanced atomic layer deposition (PEALD) to form a moisture and oxygen diffusion barrier in organic-light emitting diodes (OLEDs). By optical in situ monitoring, we successfully identified the reduction in oxygen flow rates in the reaction steps, which resulted in a 2.67 times increase in the water vapor transmission ratio (WVTR) of the deposited Al2O3 films. Therefore, we are convinced that the suggested in situ monitoring method is useful for the detection of process shifts or drifts that adversely affect PEALD film quality.

Pseudocapacitance of TiO2-x /CNT Anodes for High-Performance Quasi-Solid-State Li-Ion and Na-Ion Capacitors.

PubMed

Que, Lan-Fang; Yu, Fu-Da; Wang, Zhen-Bo; Gu, Da-Ming

2018-04-01

It is challenging for flexible solid-state hybrid capacitors to achieve high-energy-high-power densities in both Li-ion and Na-ion systems, and the kinetics discrepancy between the sluggish faradaic anode and the rapid capacitive cathode is the most critical issue needs to be addressed. To improve Li-ion/Na-ion diffusion kinetics, flexible oxygen-deficient TiO 2- x /CNT composite film with ultrafast electron/ion transport network is constructed as self-supported and light-weight anode for a quasi-solid-state hybrid capacitor. It is found that the designed porous yolk-shell structure endows large surface area and provides short diffusion length, the oxygen-deficient composite film can improve electrical conductivity, and enhance ion diffusion kinetic by introducing intercalation pseudocapacitance, therefore resulting in advance electrochemical properties. It exhibits high capacity, excellent rate performance, and long cycle life when utilized as self-supported anodes for Li-ion and Na-ion batteries. When assembled with activated carbon/carbon nanotube (AC/CNT) flexible cathode, using ion conducting gel polymer as the electrolyte, high energy densities of 104 and 109 Wh kg -1 are achieved at 250 W kg -1 in quasi-solid-state Li-ion and Na-ion capacitors (LICs and SICs), respectively. Still, energy densities of 32 and 36 Wh kg -1 can be maintained at high power densities of 5000 W kg -1 in LICs and SICs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The role of intraluminal thrombus on oxygen transport in abdominal aortic aneurysms

NASA Astrophysics Data System (ADS)

Madhavan, Sudharsan; Cherry Kemmerling, Erica

2017-11-01

Abdominal aortic aneurysm is ranked as the 13th leading cause of death in the United States. The presence of intraluminal thrombus is thought to cause hypoxia in the vessel wall eventually aggravating the condition. Our work investigates oxygen transport and consumption in a patient-specific model of an abdominal aortic aneurysm. The model includes intraluminal thrombus and consists of the abdominal aorta, renal arteries, and iliac arteries. Oxygen transport to and within the aortic wall layer was modeled, accounting for oxygen consumption and diffusion. Flow and transport in the lumen layer were modeled using coupled Navier-Stokes and scalar transport equations. The thrombus layer was assumed to be biomechanically inactive but permeable to oxygen transport in accordance with previously-measured diffusion coefficients. Plots of oxygen concentration through the layers illustrating reduced oxygen supply to the vessel walls in parts of the model that include thrombus will be presented.

Development of lithium diffused radiation resistant solar cells, part 2

NASA Technical Reports Server (NTRS)

Payne, P. R.; Somberg, H.

1971-01-01

The work performed to investigate the effect of various process parameters on the performance of lithium doped P/N solar cells is described. Effort was concentrated in four main areas: (1) the starting material, (2) the boron diffusion, (3) the lithium diffusion, and (4) the contact system. Investigation of starting material primarily involved comparison of crucible grown silicon (high oxygen content) and Lopex silicon (low oxygen content). In addition, the effect of varying growing parameters of crucible grown silicon on lithium cell output was also examined. The objective of the boron diffusion studies was to obtain a diffusion process which produced high efficiency cells with minimal silicon stressing and could be scaled up to process 100 or more cells per diffusion. Contact studies included investigating sintering of the TiAg contacts and evaluation of the contact integrity.

Ignition and Combustion of Bulk Metals in a Microgravity Environment

NASA Technical Reports Server (NTRS)

Branch, Melvyn C.; Daily, John W.; Abbud-Madrid, Angel

1999-01-01

Results of a study of heterogeneous and homogeneous combustion of metals in reduced gravity are presented. Cylindrical titanium and magnesium samples are radiatively ignited in pure-oxygen at 1 atm. Qualitative observations, propagation rates, and burning times are extracted from high-speed cinematography. Time-resolved emission spectra of gas-phase reactions are acquired with an imaging spectrograph. Lower propagation rates of the reacting mass on titanium and of ignition waves on magnesium are obtained at reduced gravity. These rates are compared to theoretical results from fire-spread analyses with a diffusion/convection controlled reaction. The close agreement found between experimental and theoretical propagation rates indicates the strong influence of natural-convection-enhanced oxygen transp6rt on burning rates. Lower oxygen flux and lack of condensed product removal appear to be responsible for longer burning times of magnesium gas-phase diffusion flames in reduced gravity. Spherically symmetric explosions in magnesium flames at reduced gravity (termed radiation-induced metal explosions, or RIME) may be driven by increased radiation heat transfer from accumulated condensed products to an evaporating metal core covered by a porous, flexible oxide coating. In titanium specimens, predominantly heterogeneous burning characterizes the initial steady propagation of the molten mass, while homogeneous gas-phase reactions are detected around particles ejected from the molten mixture. In magnesium specimens, band and line reversal of all the UV spectral systems of Mg and MgO are attributed to the interaction between small oxide particles and the principal gaseous emitters.

The response of the ionosphere to the injection of chemically reactive vapors

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.

1976-01-01

As a gas released in the ionosphere expands, it is rapidly cooled. When the vapor becomes sufficiently tenuous, it is reheated by collisions with the ambient atmosphere and its flow is then governed by diffusive expansion. As the injected gas becomes well mixed with the plasma, a hole is created by chemical processes. In the case of diatomic hydrogen release, depression of the electron concentrations is governed by the charge exchange reaction between oxygen ions and hydrogen, producing positive hydroxyl ions. Hydroxyl ions rapidly react with the electron gas to produce excited oxygen and hydrogen atoms. Enhanced airglow emissions result from the transition of the excited atoms to lower energy states. The electron temperature in the depleted region rises sharply causing a thermal expansion of the plasma and a further reduction in the local plasma concentration.

Concentrations and behavior of oxygen and oxide ion in melts of composition CaO.MgO.xSiO2

NASA Technical Reports Server (NTRS)

Semkow, K. W.; Haskin, L. A.

1985-01-01

The behavior of oxygen and oxide ion in silicate melts was investigated through their electrochemical reactions at a platinum electrode. Values are given for the diffusion coefficient for molecular oxygen in diopside melt and the activation energy of diffusion. It is shown that molecular oxygen dissociates prior to undergoing reduction and that oxide ion reacts quickly with silicate polymers when it is produced. The concentration of oxide ion is kept low by a buffering effect of the silicate, the exact level being dependent on the silicate composition. Data on the kinetics of reaction of the dissociation of molecular oxygen and on the buffering reactions are provided. It is demonstrated that the data on oxygen in these silicate melts are consistent with those for solid buffers.

Oxidation of Carbon Fibers in a Cracked Ceramic Matrix Composite Modeled as a Function of Temperature

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Cawley, James D.; Eckel, Andrew J.

2003-01-01

The oxidation model simulates the oxidation of the reinforcing carbon fibers within a ceramic matrix composite material containing as-fabricated microcracks. The physics-based oxidation model uses theoretically and experimentally determined variables as input for the model. The model simulates the ingress of oxygen through microcracks into a two-dimensional plane within the composite material. Model input includes temperature, oxygen concentration, the reaction rate constant, the diffusion coefficient, and the crack opening width as a function of the mechanical and thermal loads. The model is run in an iterative process for a two-dimensional grid system in which oxygen diffuses through the porous and cracked regions of the material and reacts with carbon in short time steps. The model allows the local oxygen concentrations and carbon volumes from the edge to the interior of the composite to be determined over time. Oxidation damage predicted by the model was compared with that observed from microstructural analysis of experimentally tested composite material to validate the model for two temperatures of interest. When the model is run for low-temperature conditions, the kinetics are reaction controlled. Carbon and oxygen reactions occur relatively slowly. Therefore, oxygen can bypass the carbon near the outer edge and diffuse into the interior so that it saturates the entire composite at relatively high concentrations. The kinetics are limited by the reaction rate between carbon and oxygen. This results in an interior that has high local concentrations of oxygen and a similar amount of consumed carbon throughout the cross section. When the model is run for high-temperature conditions, the kinetics are diffusion controlled. Carbon and oxygen reactions occur very quickly. The carbon consumes oxygen as soon as it is supplied. The kinetics are limited by the relatively slow rate at which oxygen is supplied in comparison to the relatively fast rate at which carbon and oxygen reactions occur. This results in a sharp gradient in oxygen concentration from the edge where it is supplied to the nearest source of carbon, which is where the oxygen is quickly consumed. A moving reaction front is seen in which the outlaying carbon is consumed before the next inner layer of carbon begins to react.

Thermite at the Nano-Scale

NASA Astrophysics Data System (ADS)

Mily, Edward Joseph, Jr.

Physical vapor deposition of thin film thermites allow for a clean avenue for probing fundamental properties of nanoenergetic materials that prove difficult for traditional powder processing. Precise control over diffusion dimensions, microstructure, and total amount of material are able to be realized with this fabrication technique and the testing of such materials provide valuable insight into how oxidation occurs. This thesis provides several examples of how existing PVD techniques can be coupled with thermite constituents to further the energetic community's understanding of how oxidation occurs in the solid state with the variation of geometric and chemical alterations. The goal of these investigations was to elucidate which material properties and mechanisms drive exothermic activity. The thermite thin films of Al/CuO, Zr/CuO, and Mg/Cuo with varied reducing metal constituents were tested under slow heating conditions. The trend of the metal variation demonstrated the importance of terminal oxide diffusion properties in either impeding or enhancing oxygen exchange. When the reducing metal forms a terminal oxide with limited oxygen diffusivity, exothermicity requires elevated activation energies to commence self-sustaining reaction. In addition to the effects of chemical variation, bilayer thicknesses were varied and found to decrease exothermic peak temperatures similar to the trends found in intermetallic thin film energetics and powder energetic materials. The thin film thermites were also subjected to extreme initiation methods via laser driven flyer plate impact ignition and high heating rate heat treatment (105 K/s). General insight into nano thermite behavior at environments characteristic of applications was sought, and similar trends discovered among slow vs rapid testing. Decreasing reaction dimensions yielded higher reactivity and diffusion barrier properties role in impacting exothermic behavior persist to into the microsecond regime. Ultimately through this work it has been shown that the process of thermite exothermicity proceeds through more than one pathway and more than the free energy of oxidation of reducing metals should be considered when describing how oxygen exchange occurs. It has been shown that these self-sustaining reactivity can be realized in the solid and.

Development and fabrication of lithium-doped solar cells

NASA Technical Reports Server (NTRS)

Iles, P. A.

1971-01-01

The application of contacts and coatings after lithium diffusion provides good electrical output and satisfactory contact adhesion by sintering for short times at temperatures less than the lithium diffusion temperature. High output and repeatability are obtainable from both oxygen-rich and oxygen-lean silicon. These fabrication sequence alterations have led to higher cell output, better appearance, and increased contact strength.

A novel (ex situ) method to quantify oxygen diffusion coefficient of polymer fuel cells backing and catalyst layers

NASA Astrophysics Data System (ADS)

Baricci, Andrea; Casalegno, Andrea

2016-09-01

Limiting current density of oxygen reduction reaction in polymer electrolyte fuel cells is determined by several mass transport resistances that lower the concentration of oxygen on the catalyst active site. Among them, diffusion across porous media plays a significant role. Despite the extensive experimental activity documented in PEMFC literature, only few efforts have been dedicated to the measurement of the effective transport properties in porous layers. In the present work, a methodology for ex situ measurement of the effective diffusion coefficient and Knudsen radius of porous layers for polymer electrolyte fuel cells (gas diffusion layer, micro porous layer and catalyst layer) is described and applied to high temperature polymer fuel cells State of Art materials. Regression of the measured quantities by means of a quasi 2D physical model is performed to quantify the Knudsen effect, which is reported to account, respectively, for 30% and 50% of the mass transport resistance in micro porous layer and catalyst layer. On the other side, the model reveals that pressure gradient consequent to permeation in porous layers of high temperature polymer fuel cells has a negligible effect on oxygen concentration in relevant operating conditions.

Quantitative confirmation of diffusion-limited oxidation theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gillen, K.T.; Clough, R.L.

1990-01-01

Diffusion-limited (heterogeneous) oxidation effects are often important for studies of polymer degradation. Such effects are common in polymers subjected to ionizing radiation at relatively high dose rate. To better understand the underlying oxidation processes and to aid in the planning of accelerated aging studies, it would be desirable to be able to monitor and quantitatively understand these effects. In this paper, we briefly review a theoretical diffusion approach which derives model profiles for oxygen surrounded sheets of material by combining oxygen permeation rates with kinetically based oxygen consumption expressions. The theory leads to a simple governing expression involving the oxygenmore » consumption and permeation rates together with two model parameters {alpha} and {beta}. To test the theory, gamma-initiated oxidation of a sheet of commercially formulated EPDM rubber was performed under conditions which led to diffusion-limited oxidation. Profile shapes from the theoretical treatments are shown to accurately fit experimentally derived oxidation profiles. In addition, direct measurements on the same EPDM material of the oxygen consumption and permeation rates, together with values of {alpha} and {beta} derived from the fitting procedure, allow us to quantitatively confirm for the first time the governing theoretical relationship. 17 refs., 3 figs.« less

OXYGEN TRANSPORT IN THE MICROCIRCULATION AND ITS REGULATION

PubMed Central

Pittman, Roland N.

2012-01-01

Cells require energy to carry out their functions and they typically use oxidative phosphorylation to generate the needed ATP. Thus, cells have a continuous need for oxygen which they receive by diffusion from the blood through the interstitial fluid. The circulatory system pumps oxygen-rich blood through a network of increasingly minute vessels, the microcirculation. The structure of the microcirculation is such that all cells have at least one nearby capillary for diffusive exchange of oxygen and red blood cells release the oxygen bound to hemoglobin as they traverse capillaries. This review focuses first on the historical development of techniques to measure oxygen at various sites in the microcirculation, including the blood, interstitium and cells. Next, approaches are described as to how these techniques have been employed to make discoveries about different aspects of oxygen transport. Finally, ways in which oxygen might participate in the regulation of blood flow toward matching oxygen supply to oxygen demand is discussed. Overall, the transport of oxygen to the cells of the body is one of the most critical functions of the cardiovascular system and it is in the microcirculation where the final local determinants of oxygen supply, oxygen demand and their regulation are decided. PMID:23025284

Oxygen concentration dependence of silicon oxide dynamical properties

NASA Astrophysics Data System (ADS)

Yajima, Yuji; Shiraishi, Kenji; Endoh, Tetsuo; Kageshima, Hiroyuki

2018-06-01

To understand oxidation in three-dimensional silicon, dynamic characteristics of a SiO x system with various stoichiometries were investigated. The calculated results show that the self-diffusion coefficient increases as oxygen density decreases, and the increase is large when the temperature is low. It also shows that the self-diffusion coefficient saturates, when the number of removed oxygen atoms is sufficiently large. Then, approximate analytical equations are derived from the calculated results, and the previously reported expression is confirmed in the extremely low-SiO-density range.

Tensile Lattice Strain Accelerates Oxygen Surface Exchange and Diffusion in La1–xSrxCoO3−δ Thin Films

PubMed Central

2013-01-01

The influence of lattice strain on the oxygen exchange kinetics and diffusion in oxides was investigated on (100) epitaxial La1–xSrxCoO3−δ (LSC) thin films grown by pulsed laser deposition. Planar tensile and compressively strained LSC films were obtained on single-crystalline SrTiO3 and LaAlO3. 18O isotope exchange depth profiling with ToF-SIMS was employed to simultaneously measure the tracer surface exchange coefficient k* and the tracer diffusion coefficient D* in the temperature range 280–475 °C. In accordance with recent theoretical findings, much faster surface exchange (∼4 times) and diffusion (∼10 times) were observed for the tensile strained films compared to the compressively strained films in the entire temperature range. The same strain effect—tensile strain leading to higher k* and D*—was found for different LSC compositions (x = 0.2 and x = 0.4) and for surface-etched films. The temperature dependence of k* and D* is discussed with respect to the contributions of strain states, formation enthalpy of oxygen vacancies, and vacancy mobility at different temperatures. Our findings point toward the control of oxygen surface exchange and diffusion kinetics by means of lattice strain in existing mixed conducting oxides for energy conversion applications. PMID:23527691

Calibrated imaging reveals altered grey matter metabolism related to white matter microstructure and symptom severity in multiple sclerosis.

PubMed

Hubbard, Nicholas A; Turner, Monroe P; Ouyang, Minhui; Himes, Lyndahl; Thomas, Binu P; Hutchison, Joanna L; Faghihahmadabadi, Shawheen; Davis, Scott L; Strain, Jeremy F; Spence, Jeffrey; Krawczyk, Daniel C; Huang, Hao; Lu, Hanzhang; Hart, John; Frohman, Teresa C; Frohman, Elliot M; Okuda, Darin T; Rypma, Bart

2017-11-01

Multiple sclerosis (MS) involves damage to white matter microstructures. This damage has been related to grey matter function as measured by standard, physiologically-nonspecific neuroimaging indices (i.e., blood-oxygen-level dependent signal [BOLD]). Here, we used calibrated functional magnetic resonance imaging and diffusion tensor imaging to examine the extent to which specific, evoked grey matter physiological processes were associated with white matter diffusion in MS. Evoked changes in BOLD, cerebral blood flow (CBF), and oxygen metabolism (CMRO 2 ) were measured in visual cortex. Individual differences in the diffusion tensor measure, radial diffusivity, within occipital tracts were strongly associated with MS patients' BOLD and CMRO 2 . However, these relationships were in opposite directions, complicating the interpretation of the relationship between BOLD and white matter microstructural damage in MS. CMRO 2 was strongly associated with individual differences in patients' fatigue and neurological disability, suggesting that alterations to evoked oxygen metabolic processes may be taken as a marker for primary symptoms of MS. This work demonstrates the first application of calibrated and diffusion imaging together and details the first application of calibrated functional MRI in a neurological population. Results lend support for neuroenergetic hypotheses of MS pathophysiology and provide an initial demonstration of the utility of evoked oxygen metabolism signals for neurology research. Hum Brain Mapp 38:5375-5390, 2017. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

[Function of alveoles as a result of evolutionary development of respiratory system in mammals].

PubMed

Ivanov, K P

2013-01-01

Reaction of hemoglobin oxygenation is known to occur for 40 femtoseconds (40 x 10(-15) s). However, the process of oxygen diffusion to hemoglobin under physiologic conditions decelerated this reaction approximately billion times. In mammalian lungs, blood is moving at a high rate and in a relatively high amount. The human lung mass is as low as 600 g, but the complete cardiac output approaches 6 1/min. In rat, from 20 to 40 ml of blood is passed for q min through the lung whose mass is about 1.5 g. Such blood flow rate is possible, as in lungs of high animals there exists a dense network of relatively large microvessels with diameter from 20 to 40 microm and more. In spite of a large volume and a high blood flow rate hampering oxygen diffusion, the complete blood oxygenation occurs in lung alveoli. This is due to peculiar mechanisms that facilitate markedly the oxygen diffusion and that developed in alveoli of mammals in the course of many million years of evolution of their respiratory system. Thus, alveolus is not a bubble with air, but a complex tool of fight with inertness of diffusion. It is interesting that in lungs of the low vertebrates, neither such system of blood vessels nor alveoli exist, and their blood flow rate is much lower than in mammals.

Germanium diffusion with vapor-phase GeAs and oxygen co-incorporation in GaAs

NASA Astrophysics Data System (ADS)

Wang, Wei-Fu; Cheng, Kai-Yuan; Hsieh, Kuang-Chien

2018-01-01

Vapor-phase germanium diffusion has been demonstrated in Zn-doped and semi-insulating GaAs in sealed ampoules with GeAs powders and excess arsenic. Secondary-ion-mass spectroscopy (SIMS) profiles indicate the presence of unintentional co-incorporation of oxygen in high densities (>1017/cm3) along with diffused germanium donors whose concentration (>>1018/cm3) determined by electro-chemical capacitance-voltage (ECV) profiler shows significant compensation near the surface. The source of oxygen mainly originates from the GeAs powder which contains Ge-O surface oxides. Variable-temperature photoluminescence (PL) shows that in GeAs-diffused samples, a broad peak ranging from 0.86-1.38 eV with the peak position around 1.1 eV predominates at low temperatures while the near band-edge luminescence quenches. The broad band is attributed to the GeGa-VGa self-activated (SA) centers possibly associated with nearby oxygen-related defect complex, and its luminescence persists up to 400 K. The configurational-coordinate modeling finds that the SA defect complex has a thermal activation energy of 150-180 meV and a vibrational energy 26.8 meV. The presence of oxygen does not much affect the SA emission intensity but may have influenced the peak position, vibration frequency and activation energy as compared to other common donor-VGa defects in GaAs.

Experimental Determination of Fe-Mg Interdiffusion Coefficients in Orthopyroxene Using Pulsed Laser Ablation and Nanoscale Thin Films

NASA Astrophysics Data System (ADS)

Ter Heege, J. H.; Dohmen, R.; Becker, H.; Chakraborty, S.

2006-12-01

Fe-Mg interdiffusion in silicate minerals is of interest in petrological studies for determining the closure temperature of geothermometers and for determining cooling rates from compositional profiles. It is also relevant for studies of the physical properties of silicates, such as rheology or electrical conductivity, because knowledge of its dependence on oxygen fugacity can aid in the understanding of point defect chemistry. Compositionally zoned orthopyroxenes are common in meteorites, mantle rocks, lower crustal rocks and a variety of plutonic and volcanic igneous rocks. However, experimental difficulties have precluded direct determination of Fe-Mg diffusion rates in orthopyroxenes so far and the available information comes from (1) Mg tracer diffusion coefficients obtained from isotope tracer studies using enriched ^{25}MgO films [1], (2) calculations of interdiffusion rates based on the (diffusion-controlled) order-disorder kinetics measured in orthopyroxene [2], and (3) indirect estimates from the comparison of diffusion widths in coexisting garnets and olivines, in which Fe-Mg diffusion rates are relatively well known [e.g., 3]. We have directly measured Fe-Mg interdiffusion coefficients parallel to the [001] direction in two natural orthopyroxene single crystals (approximately En95Fs5 and En90Fs10) using diffusion couples consisting of an olivine thin film (Fo30Fa70, typically 20 - 50 nm thick) deposited under vacuum on pre-heated, polished and oriented pyroxene single crystals using a pulsed laser ablation deposition technique. Samples were annealed for 4 - 337 hours at 800 - 1100 °C under atmospheric pressure in a continuous flow of CO + CO2 to control the oxygen fugacity between 10-16 and 10^{-12} bar within the stability field of pyroxene. Film thickness and compositional profiles were measured using Rutherford backscattering Spectroscopy (RBS) on reference and annealed samples, and Fe concentration depth profiles were extracted from the RBS spectra and fitted numerically. At an oxygen fugacity of 10-16 bar, Fe-Mg interdiffusion coefficients in the Fs richer orthopyroxene vary between 4.10^{-22} m2/s and 2.10^{-20} m2/s for temperatures between 800 and 1000°C. Diffusion coefficients decrease by a factor of ~ 4 with decreasing oxygen fugacity between 10^{-12} and 10-16 bar at 1000 °C. Comparison of our data with other Fe-Mg diffusion data shows that these diffusion coefficients are (1) similar to Mg tracer diffusion coefficients measured in orthopyroxene at somewhat more reducing (e.g. fO2 = 10-16 to 10^{-19} bar) conditions at the same temperatures [1], (2) similar to Mg tracer diffusion in garnets measured at higher pressures of 10 kbar at an oxygen fugacity corresponding to the C-O equilibrium in graphite present systems [4], and (3) slower than Fe-Mg diffusion rates in olivine by a factor of ~10 at the same oxygen fugacities [5]. Further experiments to quantify the dependence on composition, temperature and oxygen fugacity are in progress. References: [1] Schwandt et al. (1998), Contr. Mineral. Petrol. 130: 390-396; [2] Ganguly and Tazzoli (1994), Am. Mineral. 79: 930-937; [3] Smith and Barron (1991), Am. Mineral. 76: 1950-1963; [4] Ganguly et al. (1998), Contr. Mineral. Petrol. 131: 171-180; [5] Chakraborty (1997), J. Geoph. Res. 102: 12317-12331.

Activation volumes of oxygen self-diffusion in fluorite structured oxides

DOE PAGES

Christopoulos, S-R G.; Kordatos, A.; Cooper, Michael William D.; ...

2016-10-27

In this study, fluorite structured oxides are used in numerous applications and as such it is necessary to determine their materials properties over a range of conditions. In the present study we employ molecular dynamics calculations to calculate the elastic and expansivity data, which are then used in a thermodynamic model (the cBΩ model) to calculate the activation volumes of oxygen self-diffusion coefficient in ThO 2, UO 2 and PuO 2 fluorite structured oxides over a wide temperature range. We present relations to calculate the activation volumes of oxygen self-diffusion coefficient in ThO 2, UO 2 and PuO 2 formore » a wide range of temperature (300–1700 K) and pressure (–7.5 to 7.5 GPa).« less

Critical role for mesoscale eddy diffusion in supplying oxygen to hypoxic ocean waters

NASA Astrophysics Data System (ADS)

Gnanadesikan, Anand; Bianchi, Daniele; Pradal, Marie-Aude

2013-10-01

of the oceanic lateral eddy diffusion coefficient Aredi vary by more than an order of magnitude, ranging from less than a few hundred m2/s to thousands of m2/s. This uncertainty has first-order implications for the intensity of oceanic hypoxia, which is poorly simulated by the current generation of Earth System Models. Using satellite-based estimate of oxygen consumption in hypoxic waters to estimate the required diffusion coefficient for these waters gives a value of order 1000 m2/s. Varying Aredi across a suite of Earth System Models yields a broadly consistent result given a thermocline diapycnal diffusion coefficient of 1 × 10-5 m2/s.

Facile Aluminum Reduction Synthesis of Blue TiO2 with Oxygen Deficiency for Lithium-Ion Batteries.

PubMed

Zheng, Jing; Ji, Guangbin; Zhang, Peng; Cao, Xingzhong; Wang, Baoyi; Yu, Linghui; Xu, Zhichuan J

2015-12-07

An ultrafacile aluminum reduction method is reported herein for the preparation of blue TiO2 nanoparticles (donated as Al-TiO2 , anatase phase) with abundant oxygen deficiency for lithium-ion batteries. Under aluminum reduction, the morphology of the TiO2 nanosheets changes from well-defined rectangular into uniform round or oval nanoparticles and the particle size also decreases from 60 to 31 nm, which can aggressively accelerate the lithium-ion diffusion. Electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) results reveal that plentiful oxygen deficiencies relative to the Ti(3+) species were generated in blue Al-TiO2 ; this effectively enhances the electron conductivity of the TiO2 . X-ray photoelectron spectrometry (XPS) analysis indicates that a small peak is observed for the Al-O bond, which probably plays a very important role in the stabilization of the oxygen deficiencies/Ti(3+) species. As a result, the blue Al-TiO2 possesses significantly higher capacity, better rate performance, and a longer cycle life than the white pure TiO2 . Such improvements can be attributed to the decreased particle size, as well as the existence of the oxygen deficiencies/Ti(3+) species. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Energetics of defects formation and oxygen migration in pyrochlore compounds from first principles calculations

NASA Astrophysics Data System (ADS)

Li, Yan; Kowalski, Piotr M.

2018-07-01

In order to get better understanding of the selective order-disorder transition in pyrochlore compounds, using ab initio methods we calculated the formation energies of coupled cation anti-site and anion Frenkel pair defects and the energy barriers for the oxygen migration for number of families of A2B2 O7 pyrochlore-type compounds. While these parameters have been previously computed with force field-based methods, the ab initio results provide more reliable values that can be confidently used in subsequent analysis. We found a fairly good correlation between the formation energies of the coupled defects and the stability field of pyrochlores. In line with previous studies, the compounds that crystallize in defect fluorite structure are found to have smaller values of coupled defect formation energies than those crystallizing in the pyrochlore phase, although the correlation is not that sharp as in the case of isolated anion Frenkel pair defect. The investigation of the energy barriers for the oxygen migration shows that it is not a good, sole indicator of the tendency of the order-disorder phase transition in pyrochlores. However, we found that the oxygen migration barrier is reduced in the presence of the cation antisite defect. This points at disordering-induced enhancement of oxygen diffusion in pyrochlore compounds.

Heat transfer, diffusion, and evaporation

NASA Technical Reports Server (NTRS)

Nusselt, Wilhelm

1954-01-01

Although it has long been known that the differential equations of the heat-transfer and diffusion processes are identical, application to technical problems has only recently been made. In 1916 it was shown that the speed of oxidation of the carbon in iron ore depends upon the speed with which the oxygen of the combustion air diffuses through the core of gas surrounding the carbon surface. The identity previously referred to was then used to calculate the amount of oxygen diffusing to the carbon surface on the basis of the heat transfer between the gas stream and the carbon surface. Then in 1921, H. Thoma reversed that procedure; he used diffusion experiments to determine heat-transfer coefficients. Recently Lohrisch has extended this work by experiment. A technically very important application of the identity of heat transfer and diffusion is that of the cooling tower, since in this case both processes occur simultaneously.

General Solvent-dependent Strategy toward Enhanced Oxygen Reduction Reaction in Graphene/Metal Oxide Nanohybrids: Effects of Nitrogen-containing Solvent

NASA Astrophysics Data System (ADS)

Kao, Wei-Yao; Chen, Wei-Quan; Chiu, Yu-Hsiang; Ho, Yu-Hsuan; Chen, Chun-Hu

2016-11-01

A general solvent-dependent protocol directly influencing the oxygen reduction reaction (ORR) in metal oxide/graphene nanohybrids has been demonstrated. We conducted the two-step synthesis of cobalt oxide/N-doped graphene nanohybrids (CNG) with solvents of water, ethanol, and dimethylformamide (DMF), representing tree typical categories of aqueous, polar organic, and organic N-containing solvents commonly adopted for graphene nanocomposites preparation. The superior ORR performance of the DMF-hybrids can be attributed to the high nitrogen-doping, aggregation-free hybridization, and unique graphene porous structures. As DMF is the more effective N-source, the spectroscopic results support a catalytic nitrogenation potentially mediated by cobalt-DMF coordination complexes. The wide-distribution of porosity (covering micro-, meso-, to macro-pore) and micron-void assembly of graphene may further enhance the diffusion kinetics for ORR. As the results, CNG by DMF-synthesis exhibits the high ORR activities close to Pt/C (i.e. only 8 mV difference of half-wave potential with electron transfer number of 3.96) with the better durability in the alkaline condition. Additional graphene hybrids comprised of iron and manganese oxides also show the superior ORR activities by DMF-synthesis, confirming the general solvent-dependent protocol to achieve enhanced ORR activities.

General Solvent-dependent Strategy toward Enhanced Oxygen Reduction Reaction in Graphene/Metal Oxide Nanohybrids: Effects of Nitrogen-containing Solvent

PubMed Central

Kao, Wei-Yao; Chen, Wei-Quan; Chiu, Yu-Hsiang; Ho, Yu-Hsuan; Chen, Chun-Hu

2016-01-01

A general solvent-dependent protocol directly influencing the oxygen reduction reaction (ORR) in metal oxide/graphene nanohybrids has been demonstrated. We conducted the two-step synthesis of cobalt oxide/N-doped graphene nanohybrids (CNG) with solvents of water, ethanol, and dimethylformamide (DMF), representing tree typical categories of aqueous, polar organic, and organic N-containing solvents commonly adopted for graphene nanocomposites preparation. The superior ORR performance of the DMF-hybrids can be attributed to the high nitrogen-doping, aggregation-free hybridization, and unique graphene porous structures. As DMF is the more effective N-source, the spectroscopic results support a catalytic nitrogenation potentially mediated by cobalt-DMF coordination complexes. The wide-distribution of porosity (covering micro-, meso-, to macro-pore) and micron-void assembly of graphene may further enhance the diffusion kinetics for ORR. As the results, CNG by DMF-synthesis exhibits the high ORR activities close to Pt/C (i.e. only 8 mV difference of half-wave potential with electron transfer number of 3.96) with the better durability in the alkaline condition. Additional graphene hybrids comprised of iron and manganese oxides also show the superior ORR activities by DMF-synthesis, confirming the general solvent-dependent protocol to achieve enhanced ORR activities. PMID:27853187

Pore network modeling to explore the effects of compression on multiphase transport in polymer electrolyte membrane fuel cell gas diffusion layers

NASA Astrophysics Data System (ADS)

Fazeli, Mohammadreza; Hinebaugh, James; Fishman, Zachary; Tötzke, Christian; Lehnert, Werner; Manke, Ingo; Bazylak, Aimy

2016-12-01

Understanding how compression affects the distribution of liquid water and gaseous oxygen in the polymer electrolyte membrane fuel cell gas diffusion layer (GDL) is vital for informing the design of improved porous materials for effective water management strategies. Pore networks extracted from synchrotron-based micro-computed tomography images of compressed GDLs were employed to simulate liquid water transport in GDL materials over a range of compression pressures. The oxygen transport resistance was predicted for each sample under dry and partially saturated conditions. A favorable GDL compression value for a preferred liquid water distribution and oxygen diffusion was found for Toray TGP-H-090 (10%), yet an optimum compression value was not recognized for SGL Sigracet 25BC. SGL Sigracet 25BC exhibited lower transport resistance values compared to Toray TGP-H-090, and this is attributed to the additional diffusion pathways provided by the microporous layer (MPL), an effect that is particularly significant under partially saturated conditions.

Migration mechanisms and diffusion barriers of vacancies in Ga2O3

NASA Astrophysics Data System (ADS)

Kyrtsos, Alexandros; Matsubara, Masahiko; Bellotti, Enrico

2017-06-01

We employ the nudged elastic band and the dimer methods within the standard density functional theory (DFT) formalism to study the migration of the oxygen and gallium vacancies in the monoclinic structure of β -Ga2O3 . We identify all the first nearest neighbor paths and calculate the migration barriers for the diffusion of the oxygen and gallium vacancies. We also identify the metastable sites of the gallium vacancies which are critical for the diffusion of the gallium atoms. The migration barriers for the diffusion of the gallium vacancies are lower than the migration barriers for oxygen vacancies by 1 eV on average, suggesting that the gallium vacancies are mobile at lower temperatures. Using the calculated migration barriers we estimate the annealing temperature of these defects within the harmonic transition state theory formalism, finding excellent agreement with the observed experimental annealing temperatures. Finally, we suggest the existence of percolation paths which enable the migration of the species without utilizing all the migration paths of the crystal.

Porous boron doped diamonds as metal-free catalysts for the oxygen reduction reaction in alkaline solution

NASA Astrophysics Data System (ADS)

Suo, Ni; Huang, Hao; Wu, Aimin; Cao, Guozhong; Hou, Xiaoduo; Zhang, Guifeng

2018-05-01

Porous boron doped diamonds (BDDs) were obtained on foam nickel substrates with a porosity of 80%, 85%, 90% and 95% respectively by hot filament chemical vapor deposition (HFCVD) technology. Scanning electron microscopy (SEM) reveals that uniform and compact BDDs with a cauliflower-like morphology have covered the overall frame of the foam nickel substrates. Raman spectroscopy shows that the BDDs have a poor crystallinity due to heavily doping boron. X-ray photoelectron spectroscopy (XPS) analysis effectively demonstrates that boron atoms can be successfully incorporated into the crystal lattice of diamonds. Electrochemical measurements indicate that the oxygen reduction potential is unaffected by the specific surface area (SSA), and both the onset potential and the limiting diffusion current density are enhanced with increasing SSA. It is also found that the durability and methanol tolerance of the boron doped diamond catalysts are attenuated as the increasing of SSA. The SSA of the catalyst is directly proportional to the oxygen reduction activity and inversely to the durability and methanol resistance. These results provide a reference to the application of porous boron doped diamonds as potential cathodic catalysts for the oxygen reduction reaction in alkaline solution by adjusting the SSA.

Structural enhancement of ZnO on SiO2 for photonic applications

NASA Astrophysics Data System (ADS)

Ruth, Marcel; Meier, Cedrik

2013-07-01

Multi-layer thin films are often the basis of photonic devices. Zinc oxide (ZnO) with its excellent optoelectronic properties can serve as a high quality emitter in structures like microdisks or photonic crystals. Here, we present a detailed study on the enhancement of the structural properties of low-temperature MBE grown ZnO on silica (SiO2). By thermal annealing a grain coalescence of the initially polycrystalline layer leads to an enhancement of the electronic structure, indicated by a blue shift of the photoluminescence (PL) signal maximum. Oxygen atmosphere during the annealing process prevents the creation of intrinsic defects by out-diffusion. Pre-annealing deposited SiO2 capping layers instead obstruct the recrystallization and lead to less intense emission. While thin capping layers partially detach from the ZnO film at high temperatures and cause higher surface roughness and the weakest emission, thicker layers remain smoother and exhibit a significantly stronger photoluminescence.

The platinum microelectrode/Nafion interface - An electrochemical impedance spectroscopic analysis of oxygen reduction kinetics and Nafion characteristics

NASA Technical Reports Server (NTRS)

Parthasarathy, Arvind; Dave, Bhasker; Srinivasan, Supramaniam; Appleby, John A.; Martin, Charles R.

1992-01-01

The objectives of this study were to use electrochemical impedance spectroscopy (EIS) to study the oxygen-reduction reaction under lower humidification conditions than previously studied. The EIS technique permits the discrimination of electrode kinetics of oxygen reduction, mass transport of O2 in the membrane, and the electrical characteristics of the membrane. Electrode-kinetic parameters for the oxygen-reduction reaction, corrosion current densities for Pt, and double-layer capacitances were calculated. The production of water due to electrochemical reduction of oxygen greatly influenced the EIS response and the electrode kinetics at the Pt/Nafion interface. From the finite-length Warburg behavior, a measure of the diffusion coefficient of oxygen in Nafion and diffusion-layer thickness was obtained. An analysis of the EIS data in the high-frequency domain yielded membrane and interfacial characteristics such as ionic conductivity of the membrane, membrane grain-boundary capacitance and resistance, and uncompensated resistance.

Simulation study of pO2 distribution in induced tumour masses and normal tissues within a microcirculation environment.

PubMed

Li, Mao; Li, Yan; Wen, Peng Paul

2014-01-01

The biological microenvironment is interrupted when tumour masses are introduced because of the strong competition for oxygen. During the period of avascular growth of tumours, capillaries that existed play a crucial role in supplying oxygen to both tumourous and healthy cells. Due to limitations of oxygen supply from capillaries, healthy cells have to compete for oxygen with tumourous cells. In this study, an improved Krogh's cylinder model which is more realistic than the previously reported assumption that oxygen is homogeneously distributed in a microenvironment, is proposed to describe the process of the oxygen diffusion from a capillary to its surrounding environment. The capillary wall permeability is also taken into account. The simulation study is conducted and the results show that when tumour masses are implanted at the upstream part of a capillary and followed by normal tissues, the whole normal tissues suffer from hypoxia. In contrast, when normal tissues are ahead of tumour masses, their pO2 is sufficient. In both situations, the pO2 in the whole normal tissues drops significantly due to the axial diffusion at the interface of normal tissues and tumourous cells. As the existence of the axial oxygen diffusion cannot supply the whole tumour masses, only these tumourous cells that are near the interface can be partially supplied, and have a small chance to survive.

Preserve the (intraocular) environment: the importance of maintaining normal oxygen gradients in the eye.

PubMed

Beebe, David C; Shui, Ying-Bo; Siegfried, Carla J; Holekamp, Nancy M; Bai, Fang

2014-05-01

Oxygen levels in the eye are generally low and tightly regulated. Oxygen enters the eye largely by diffusion from retinal arterioles and through the cornea. In intact eyes, oxygen from the retinal arterioles diffuses into the vitreous body. There is a decreasing oxygen gradient from the retina to the lens, established by oxygen consumption by ascorbate in the vitreous fluid and lens metabolism. Age-related degeneration of the vitreous body or removal during vitrectomy exposes the posterior of the lens to increased oxygen, causing nuclear sclerotic cataracts. Lowering oxygen in the vitreous, as occurs in patients with ischemic diabetic retinopathy, protects against cataracts after vitrectomy. Vitrectomy and cataract surgery increase oxygen levels at the trabecular meshwork and with it the risk of open angle glaucoma. Two additional risk factors for glaucoma, African heritage and having a thinner cornea, are also associated with increased oxygen in the anterior chamber angle. Preservation of the vitreous body and the lens, two important oxygen consumers, would protect against nuclear sclerotic cataracts and open angle glaucoma. Delaying removal of the lens for as long as possible after vitrectomy would be an important step in delaying ocular hypertension and glaucoma progression.

Non-invasive measurements of tissue hemodynamics with hybrid diffuse optical methods

NASA Astrophysics Data System (ADS)

Durduran, Turgut

Diffuse optical techniques were used to measure hemodynamics of tissues non-invasively. Spectroscopy and tomography of the brain, muscle and implanted tumors were carried out in animal models and humans. Two qualitatively different methods, diffuse optical tomography and diffuse correlation tomography, were hybridized permitting simultaneous measurement of total hemoglobin concentration, blood oxygen saturation and blood flow. This combination of information was processed further to derive estimates of oxygen metabolism (e.g. CMRO 2) in tissue. The diffuse correlation measurements of blood flow were demonstrated in human tissues, for the first time, demonstrating continous, non-invasive imaging of oxygen metabolism in large tissue volumes several centimeters below the tissue surface. The bulk of these investigations focussed on cerebral hemodynamics. Extensive validation of this methodology was carried out in in vivo rat brain models. Three dimensional images of deep tissue hemodynamics in middle cerebral artery occlusion and cortical spreading depression (CSD) were obtained. CSD hemodynamics were found to depend strongly on partial pressure of carbon dioxide. The technique was then adapted for measurement of human brain. All optical spectroscopic measurements of CMRO2 during functional activation were obtained through intact human skull non-invasively. Finally, a high spatio-temporal resolution measurement of cerebral blood flow due to somatosensory cortex activation following electrical forepaw stimulation in rats was carried out with laser speckle flowmetry. New analysis methods were introduced for laser speckle flowmetry. In other organs, deep tissue hemodynamics were measured on human calf muscle during exercise and cuff-ischemia and were shown to have some clinical utility for peripheral vascular disease. In mice tumor models, the measured hemodynamics were shown to be predictive of photodynamic therapy efficacy, again suggesting promise of clinical utility. In total, the research has pioneered the development of diffuse optical measurements of blood flow, oxygenation and oxygen metabolism in a large range of research and clinical applications.

In vitro performance of a perfusion and oxygenation optical sensor using a unique liver phantom

NASA Astrophysics Data System (ADS)

Akl, Tony J.; King, Travis J.; Long, Ruiqi; Ericson, M. N.; Wilson, Mark A.; McShane, Michael J.; Coté, Gerard L.

2012-03-01

Between the years 1999 and 2008, on average 2,052 people died per year on the waiting list for liver transplants. Monitoring perfusion and oxygenation in transplanted organs in the 7 to 14 days period post-transplant can enhance graft and patient survival rates, and resultantly increase the availability of organs. In this work, we present in vitro results using a unique liver phantom that support the ability of our sensor to detect perfusion changes in the portal vein at low levels (50 mL/min . 4.5% of normal level). Our sensor measures diffuse reflection from three wavelengths (735, 805 and 940 nm) around the hemoglobin isobestic point (805 nm) to determine perfusion and oxygenation separately. To assess the sensitivity of our sensor to flow changes in the low range, we used two peristaltic pumps to pump a dye solution mimicking the optical properties of oxygenated blood, at various rates, through a PDMS based phantom mimicking the optical properties of liver tissue. The collected pulsatile signal increased by 120% (2.2X) for every 100 mL/min flow rise for all three wavelengths in the range 50 to 500 mL/min. In addition, we used different dye mixtures to mimic oxygenation changes at constant perfusion/flow levels. The optical properties of the dye mixtures mimic oxygen saturations ranging between 0 and 100%. The sensor was shown to be sensitive to changes in oxygen saturations above 50%.

Rotation driven translational diffusion of polyatomic ions in water: A novel mechanism for breakdown of Stokes-Einstein relation

NASA Astrophysics Data System (ADS)

Banerjee, Puja; Yashonath, Subramanian; Bagchi, Biman

2017-04-01

While most of the existing theoretical and simulation studies have focused on simple, spherical, halide and alkali ions, many chemically, biologically, and industrially relevant electrolytes involve complex non-spherical polyatomic ions like nitrate, chlorate, and sulfate to name only a few. Interestingly, some polyatomic ions in spite of being larger in size show anomalously high diffusivity and therefore cause a breakdown of the venerable Stokes-Einstein (S-E) relation between the size and diffusivity. Here we report a detailed analysis of the dynamics of anions in aqueous potassium nitrate (KNO3) and aqueous potassium acetate (CH3COOK) solutions. The two ions, nitrate (-NO3) and acetate (CH3-CO2 ), with their similar size show a large difference in diffusivity values. We present evidence that the translational motion of these polyatomic ions is coupled to the rotational motion of the ion. We show that unlike the acetate ion, nitrate ion with a symmetric charge distribution among all periphery oxygen atoms shows a faster rotational motion with large amplitude rotational jumps which enhances its translational motion due to translational-rotational coupling. By creating a family of modified-charge model systems, we have analysed the rotational motion of asymmetric polyatomic ions and the contribution of it to the translational motion. These model systems help clarifying and establishing the relative contribution of rotational motion in enhancing the diffusivity of the nitrate ion over the value predicted by the S-E relation and also over the other polyatomic ions having asymmetric charge distribution like the acetate ion. In the latter case, reduced rotational motion results in lower diffusivity values than those with symmetric charge distribution. We propose translational-rotational coupling as a general mechanism of the breakdown of the S-E relation in the case of polyatomic ions.

Rotation driven translational diffusion of polyatomic ions in water: A novel mechanism for breakdown of Stokes-Einstein relation.

PubMed

Banerjee, Puja; Yashonath, Subramanian; Bagchi, Biman

2017-04-28

While most of the existing theoretical and simulation studies have focused on simple, spherical, halide and alkali ions, many chemically, biologically, and industrially relevant electrolytes involve complex non-spherical polyatomic ions like nitrate, chlorate, and sulfate to name only a few. Interestingly, some polyatomic ions in spite of being larger in size show anomalously high diffusivity and therefore cause a breakdown of the venerable Stokes-Einstein (S-E) relation between the size and diffusivity. Here we report a detailed analysis of the dynamics of anions in aqueous potassium nitrate (KNO 3 ) and aqueous potassium acetate (CH 3 COOK) solutions. The two ions, nitrate (NO3-) and acetate (CH 3 CO2-), with their similar size show a large difference in diffusivity values. We present evidence that the translational motion of these polyatomic ions is coupled to the rotational motion of the ion. We show that unlike the acetate ion, nitrate ion with a symmetric charge distribution among all periphery oxygen atoms shows a faster rotational motion with large amplitude rotational jumps which enhances its translational motion due to translational-rotational coupling. By creating a family of modified-charge model systems, we have analysed the rotational motion of asymmetric polyatomic ions and the contribution of it to the translational motion. These model systems help clarifying and establishing the relative contribution of rotational motion in enhancing the diffusivity of the nitrate ion over the value predicted by the S-E relation and also over the other polyatomic ions having asymmetric charge distribution like the acetate ion. In the latter case, reduced rotational motion results in lower diffusivity values than those with symmetric charge distribution. We propose translational-rotational coupling as a general mechanism of the breakdown of the S-E relation in the case of polyatomic ions.

The origin of the residual conductivity of GaN films on ferroelectric materials

NASA Astrophysics Data System (ADS)

Lee, Kyoung-Keun; Cai, Zhuhua; Ziemer, Katherine; Doolittle, William Alan

2009-08-01

In this paper, the origin of the conductivity of GaN films grown on ferroelectric materials was investigated using XPS, AES, and XRD analysis tools. Depth profiles confirmed the existence of impurities in the GaN film originating from the substrates. Bonding energy analysis from XPS and AES verified that oxygen impurities from the substrates were the dominant origin of the conductivity of the GaN film. Furthermore, Ga-rich GaN films have a greater chance of enhancing diffusion of lithium oxide from the substrates, resulting in more substrate phase separation and a wider inter-mixed region confirmed by XRD. Therefore, the direct GaN film growth on ferroelectric materials causes impurity diffusion from the substrates, resulting in highly conductive GaN films. Future work needs to develop non-conductive buffer layers for impurity suppression in order to obtain highly resistive GaN films.

The growth of oscillating bubbles in an ultrasound field

NASA Astrophysics Data System (ADS)

Yamauchi, Risa; Yamashita, Tatsuya; Ando, Keita

2017-11-01

From our recent experiments to test particle removal by underwater ultrasound, dissolved gas supersaturation is found to play an important role in physical cleaning; cavitation bubble nucleation can be triggered easily by weak ultrasound under the supersaturation and mild motion of the bubbles contributes to efficient cleaning without erosion. The state of gas bubble nuclei in water is critical to the determination of a cavitation inception threshold. Under ultrasound forcing, the size of bubble nuclei is varied by the transfer of dissolved gas (i.e., rectified diffusion); the growth rate will be promoted by the supersaturation and is thus expected to contribute to cavitation activity enhancement. In the present work, we experimentally study rectified diffusion for bubbles attached at glass surfaces in an ultrasound field. We will present the evolution of bubble nuclei sizes with varying parameters such as dissolved oxygen supersaturation, and ultrasound intensity and frequency. the Research Grant of Keio Leading-edge Laboratory of Science & Technology.

Simultaneous measurement of deep tissue blood flow and oxygenation using noncontact diffuse correlation spectroscopy flow-oximeter

PubMed Central

Li, Ting; Lin, Yu; Shang, Yu; He, Lian; Huang, Chong; Szabunio, Margaret; Yu, Guoqiang

2013-01-01

We report a novel noncontact diffuse correlation spectroscopy flow-oximeter for simultaneous quantification of relative changes in tissue blood flow (rBF) and oxygenation (Δ[oxygenation]). The noncontact probe was compared against a contact probe in tissue-like phantoms and forearm muscles (n = 10), and the dynamic trends in both rBF and Δ[oxygenation] were found to be highly correlated. However, the magnitudes of Δ[oxygenation] measured by the two probes were significantly different. Monte Carlo simulations and phantom experiments revealed that the arm curvature resulted in a significant underestimation (~−20%) for the noncontact measurements in Δ[oxygenation], but not in rBF. Other factors that may cause the residual discrepancies between the contact and noncontact measurements were discussed, and further comparisons with other established technologies are needed to identify/quantify these factors. Our research paves the way for noncontact and simultaneous monitoring of blood flow and oxygenation in soft and vulnerable tissues without distorting tissue hemodynamics. PMID:23446991

UO(2) Oxidative Corrosion by Nonclassical Diffusion.

PubMed

Stubbs, Joanne E; Chaka, Anne M; Ilton, Eugene S; Biwer, Craig A; Engelhard, Mark H; Bargar, John R; Eng, Peter J

2015-06-19

Using x-ray scattering, spectroscopy, and density-functional theory, we determine the structure of the oxidation front when a UO(2) (111) surface is exposed to oxygen at ambient conditions. In contrast to classical diffusion and previously reported bulk UO(2+x) structures, we find oxygen interstitials order into a nanoscale superlattice with three-layer periodicity and uranium in three oxidation states: IV, V, and VI. This oscillatory diffusion profile is driven by the nature of the electron transfer process, and has implications for understanding the initial stages of oxidative corrosion in materials at the atomistic level.

Effect of dual-dielectric hydrogen-diffusion barrier layers on the performance of low-temperature processed transparent InGaZnO thin-film transistors

NASA Astrophysics Data System (ADS)

Tari, Alireza; Wong, William S.

2018-02-01

Dual-dielectric SiOx/SiNx thin-film layers were used as back-channel and gate-dielectric barrier layers for bottom-gate InGaZnO (IGZO) thin-film transistors (TFTs). The concentration profiles of hydrogen, indium, gallium, and zinc oxide were analyzed using secondary-ion mass spectroscopy characterization. By implementing an effective H-diffusion barrier, the hydrogen concentration and the creation of H-induced oxygen deficiency (H-Vo complex) defects during the processing of passivated flexible IGZO TFTs were minimized. A bilayer back-channel passivation layer, consisting of electron-beam deposited SiOx on plasma-enhanced chemical vapor-deposition (PECVD) SiNx films, effectively protected the TFT active region from plasma damage and minimized changes in the chemical composition of the semiconductor layer. A dual-dielectric PECVD SiOx/PECVD SiNx gate-dielectric, using SiOx as a barrier layer, also effectively prevented out-diffusion of hydrogen atoms from the PECVD SiNx-gate dielectric to the IGZO channel layer during the device fabrication.

Reaction products and oxide thickness formed by Ti out-diffusion and oxidization in poly-Pt/Ti/SiO 2/Si with oxide films deposited

NASA Astrophysics Data System (ADS)

Chen, Changhong; Huang, Dexiu; Zhu, Weiguang; Feng, Yi; Wu, Xigang

2006-08-01

In the paper, we present experimental results to enhance the understanding of Ti out-diffusion and oxidization in commercial poly-Pt/Ti/SiO 2/Si wafers with perovskite oxide films deposited when heat-treated in flowing oxygen ambient. It indicates that when heat-treated at 550 and 600 °C, PtTi 3+PtTi and PtTi are the reaction products from interfacial interaction, respectively; while heat-treated at 650 °C and above, the products become three layers of titanium oxides instead of the alloys. Confirmed to be rutile TiO 2, the first two layers spaced by 65 nm encapsulate the Pt surface by the first layer with 60 nm thick forming at its surface and by the next layer with 35 nm thick inserting its original layer. In addition, the next layer is formed as a barrier to block up continuous diffusion paths of Ti, and thus results in the last layer of TiO 2- x formed by the residual Ti oxidizing.

On optima: the case of myoglobin-facilitated oxygen diffusion.

PubMed

Wittenberg, Jonathan B

2007-08-15

The process of myoglobin/leghemoglobin-facilitated oxygen diffusion is adapted to function in different environments in diverse organisms. We enquire how the functional parameters of the process are optimized in particular organisms. The ligand-binding properties of the proteins, myoglobin and plant symbiotic hemoglobins, we discover, suggest that they have been adapted under genetic selection pressure for optimal performance. Since carrier-mediated oxygen transport has probably evolved independantly many times, adaptation of diverse proteins for a common functionality exemplifies the process of convergent evolution. The progenitor proteins may be built on the myoglobin scaffold or may be very different.

Modeling and simulation of a low-grade urinary bladder carcinoma.

PubMed

Bunimovich-Mendrazitsky, Svetlana; Pisarev, Vladimir; Kashdan, Eugene

2015-03-01

In this work, we present a mathematical model of the initiation and progression of a low-grade urinary bladder carcinoma. We simulate the crucial processes affecting tumor growth, such as oxygen diffusion, carcinogen penetration, and angiogenesis, within the framework of the urothelial cell dynamics. The cell dynamics are modeled using the discrete technique of cellular automata, while the continuous processes of carcinogen penetration and oxygen diffusion are described by nonlinear diffusion-absorption equations. As the availability of oxygen is necessary for tumor progression, processes of oxygen transport to the tumor growth site seem most important. Our model yields a theoretical insight into the main stages of development and growth of urinary bladder carcinoma with emphasis on the two most common types: bladder polyps and carcinoma in situ. Analysis of histological structure of bladder tumor is important to avoid misdiagnosis and wrong treatment. We expect our model to be a valuable tool in the study of bladder cancer progression due to the exposure to carcinogens and the oxygen dependent expression of genes promoting tumor growth. Our numerical simulations have good qualitative agreement with in vivo results reported in the corresponding medical literature. Copyright © 2015 Elsevier Ltd. All rights reserved.

Assessment of Microcirculatory Hemoglobin Levels in Normal and Diabetic Subjects using Diffuse Reflectance Spectroscopy in the Visible Region — a Pilot Study

NASA Astrophysics Data System (ADS)

Sujatha, N.; Anand, B. S. Suresh; Nivetha, K. Bala; Narayanamurthy, V. B.; Seshadri, V.; Poddar, R.

2015-07-01

Light-based diagnostic techniques provide a minimally invasive way for selective biomarker estimation when tissues transform from a normal to a malignant state. Spectroscopic techniques based on diffuse reflectance characterize the changes in tissue hemoglobin/oxygenation levels during the tissue transformation process. Recent clinical investigations have shown that changes in tissue oxygenation and microcirculation are observed in diabetic subjects in the initial and progressive stages. In this pilot study, we discuss the potential of diffuse reflectance spectroscopy (DRS) in the visible (Vis) range to differentiate the skin microcirculatory hemoglobin levels between normal and advanced diabetic subjects with and without neuropathy. Average concentration of hemoglobin as well as hemoglobin oxygen saturation within the probed tissue volume is estimated for a total of four different sites in the foot sole. The results indicate a statistically significant decrease in average total hemoglobin and increase in hemoglobin oxygen saturation levels for diabetic foot compared with a normal foot. The present study demonstrates the ability of reflectance spectroscopy in the Vis range to determine and differentiate the changes in tissue hemoglobin and hemoglobin oxygen saturation levels in normal and diabetic subjects.

Molecular Dynamics Simulations of Hydration Effects on Solvation, Diffusivity, and Permeability in Chitosan/Chitin Films.

PubMed

McDonnell, Marshall T; Greeley, Duncan A; Kit, Kevin M; Keffer, David J

2016-09-01

The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in sustainable, biodegradable chitosan/chitin food packaging films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane has a more homogeneous water distribution with the polymer chains being fully solvated. The diffusivity increased by a factor of 4 for oxygen molecules and by an order of magnitude for water with increasing the humidity. To calculate the Henry's constant and solubility of oxygen in the membranes with changing hydration, the excess chemical potential was calculated via free energy perturbation, thermodynamic integration and direct particle deletion methods. The simulations predicted a higher solubility and permeability for the lower humidity, in contradiction to experimental results. All three methods for calculating the solubility were in good agreement. It was found that the Coulombic interactions in the potential caused the oxygen to bind too strongly to the protonated amine group. Insight from this work will help guide molecular modeling of chitosan/chitin membranes, specifically permeability measurements for small solute molecules. Efforts to chemically tailor chitosan/chitin membranes to favor discrete as opposed to continuous aqueous domains could reduce oxygen permeability.

Oxygen in the deep-sea: The challenge of maintaining uptake rates in a changing ocean

NASA Astrophysics Data System (ADS)

Hofmann, A. F.; Peltzer, E. T.; Brewer, P. G.

2011-12-01

Although focused on recently, ocean acidification is not the only effect of anthropogenic CO2 emissions on the ocean. Ocean warming will reduce dissolved oxygen concentrations and at the hypoxic limit for a given species this can pose challenges to marine life. The limit is traditionally reported simply as the static mass concentration property [O2]; here we treat it as a dynamic gas exchange problem for the animal analogous to gas exchange at the sea surface. The diffusive limit and its relationship to water velocity is critical for the earliest stages of marine life (eggs, embryos), but the effect is present for all animals at all stages of life. We calculate the external limiting O2 conditions for several representative metabolic rates and their relationship to flow of the bulk fluid under different environmental conditions. Ocean O2 concentrations decline by ≈ 14 μmol kg-1 for a 2 °C rise in temperature. At standard 1000 m depth conditions in the Pacific, flow over the surface would have to increase by ≈ 60% from 2.0 to 3.2 cm s-1 to compensate for this change. The functions derived allow new calculations of depth profiles of limiting O2 concentrations, as well as maximal diffusively sustainable metabolic oxygen consumption rates at various places around the world. Our treatment shows that there is a large variability in the global ocean in terms of facilitating aerobic life. This variability is greater than the variability of the oxygen concentration alone. It becomes clear that temperature and pressure dependencies of diffusion and partial pressure create a region typically around 1000 m depth where a maximal [O2] is needed to sustain a given metabolic rate. This zone of greatest physical constriction on the diffusive transport in the boundary layer is broadly consistent with the oxygen minimum zone, i.e., the zone of least oxygen concentration supply, resulting in a pronounced minimum of maximal diffusively sustainable metabolic oxygen consumption rates. This least-favorable zone for aerobic respiration is bound to expand with further ocean warming.

Experimental thermal conductivity, thermal diffusivity, and specific heat values for mixtures of nitrogen, oxygen, and argon

NASA Technical Reports Server (NTRS)

Perkins, R. A.; Cieszkiewicz, M. T.

1991-01-01

Experimental measurements of thermal conductivity and thermal diffusivity obtained with a transient hot-wire apparatus are reported for three mixtures of nitrogen, oxygen, and argon. Values of the specific heat, Cp, are calculated from these measured values and the density calculated with an equation of state. The measurements were made at temperatures between 65 and 303 K with pressures between 0.1 and 70 MPa. The data cover the vapor, liquid, and supercritical gas phases for the three mixtures. The total reported points are 1066 for the air mixture (78.11 percent nitrogen, 20.97 percent oxygen, and 0.92 percent argon), 1058 for the 50 percent nitrogen, 50 percent oxygen mixture, and 864 for the 25 percent nitrogen, 75 oxygen mixture. Empirical thermal conductivity correlations are provided for the three mixtures.

Micro-Raman study of isotope substitution in YBa2Cu183O6.2 during local laser annealing

NASA Astrophysics Data System (ADS)

Ivanov, V. G.; Iliev, M. N.; Thomsen, C.

1995-11-01

The local laser heating of YBa2Cu183O6.2 in air was used to study the oxygen diffusion and oxygen ordering in sample volumes of the order of a few μm3. Raman microprobe at points corresponding to different annealing temperatures was applied to monitor both the stages of substitution of 16O for 18O at different oxygen sites and the structural changes in the basal [Cu(1)-O(1)] planes occurring during the oxygen in-diffusion. The population of the O(1) sites initially results in the formation of short Cu(1)-O(1) fragments which later conjunct into long chains. The results can be applied for a better understanding of oxygen reordering processes in YBa2Cu3O7-δ during thermal treatment.

Impact of oxygen diffusion on superconductivity in YBa2Cu3O7 -δ thin films studied by positron annihilation spectroscopy

NASA Astrophysics Data System (ADS)

Reiner, M.; Gigl, T.; Jany, R.; Hammerl, G.; Hugenschmidt, C.

2018-04-01

The oxygen deficiency δ in YBa2Cu3O7 -δ (YBCO) plays a crucial role for affecting high-temperature superconductivity. We apply (coincident) Doppler broadening spectroscopy of the electron-positron annihilation line to study in situ the temperature dependence of the oxygen concentration and its depth profile in single crystalline YBCO film grown on SrTiO3 (STO) substrates. The oxygen diffusion during tempering is found to lead to a distinct depth dependence of δ , which is not accessible using x-ray diffraction. A steady state reached within a few minutes is defined by both, the oxygen exchange at the surface and at the interface to the STO substrate. Moreover, we reveal the depth-dependent critical temperature Tc in the as prepared and tempered YBCO film.

Effect of nitrogen-doped carbon dots on the anticorrosion properties of waterborne epoxy coatings

NASA Astrophysics Data System (ADS)

Ren, Siming; Cui, Mingjun; Zhao, Haichao; Wang, Liping

2018-06-01

In this work, nitrogen-doped carbon dots (NCDs) are prepared by solvothermal method and the effect of NCDs on the anticorrosion property of waterborne epoxy (EP) is investigated. Scanning probe microscopy results show that the size of the NCDs is about 4–6 nm. In addition, the anticorrosion property of NCD-incorporated waterborne epoxy coatings is investigated via electrochemical techniques and scanning electron microscopy. Electrochemical results demonstrate that the impedance modulus of 2.0% NCDs/EP is 364 times higher than that of blank EP after 800 h of immersion, indicating significant enhancement in the anticorrosion property of waterborne epoxy coating. The reason is that NCDs with lots of surface functional groups can connect with waterborne epoxy to suppress enlargement of the pores, and reduce the diffusion of oxygen in the coating, thus cutting off the connection between the substrate and oxygen, and delaying corrosion of the substrate.

Radial transport of high-energy oxygen ions into the deep inner magnetosphere observed by Van Allen Probes

NASA Astrophysics Data System (ADS)

Mitani, K.; Seki, K.; Keika, K.; Gkioulidou, M.; Lanzerotti, L. J.; Mitchell, D. G.; Kletzing, C.

2017-12-01

It is known that proton is main contributor of the ring current and oxygen ions can make significant contribution during major magnetic storms. Ions are supplied to the ring current by radial transport from the plasma sheet. Convective transport of lower-energy protons and diffusive transport of higher-energy protons were reported to contribute to the storm-time and quiet-time ring current respectively [e.g., Gkioulidou et al., 2016]. However, supply mechanisms of the oxygen ions are not clear. To characterize the supply of oxygen ions to the ring current during magnetic storms, we studied the properties of energetic proton and oxygen ion phase space densities (PSDs) for specific magnetic moment (μ) during the April 23-25, 2013, geomagnetic storm observed by the Van Allen Probes mission. We here report on radial transport of high-energy (μ ≥ 0.5 keV/nT) oxygen ions into the deep inner magnetosphere during the late main phase of the magnetic storm. Since protons show little change during this period, this oxygen radial transport is inferred to cause the development of the late main phase. Enhancement of poloidal magnetic fluctuations is simultaneously observed. We estimated azimuthal mode number ≤5 by using cross wavelet analysis with ground-based observation of IMAGE ground magnetometers. The fluctuations can resonate with drift and bounce motions of the oxygen ions. The results suggest that combination of the drift and drift-bounce resonances is responsible for the radial transport of high-energy oxygen ions into the deep inner magnetosphere. We also report on the radial transport of the high-energy oxygen ions into the deep inner magnetosphere during other magnetic storms.

Approaching the evolutionary advantage of ancillary types of haemoglobin in Daphnia magna by simulation of oxygen supply.

PubMed

Moenickes, S; Richter, O; Pirow, R

2010-02-01

The planktonic crustacean Daphnia magna synthesizes haemoglobin (Hb) macromolecules of variant subunit composition and oxygen affinity. This is one of the strategies by which the animals cope with variations in environmental conditions such as ambient oxygen tension. The enrichment of high-affinity Hb molecules in the haemolymph of hypoxia-exposed animals is thought to reduce Hb synthesis costs due to an enhanced transport efficiency of these molecules in comparison to the low-affinity Hb molecules. How great this economic advantage is, and under which conditions this benefit disappears, is still not fully understood. Here we implemented a rigorously simplified model of the daphnid body and described the transport of oxygen from the environment via the haemolymph to the tissues in terms of the convection-diffusion-reaction equation. The model was validated by comparing various model predictions with experimental data. A sensitivity analysis was used to evaluate the influence of parameter uncertainties on the model predictions. Cost-benefit analysis revealed in which way at the system's level the increase in Hb oxygen affinity improves the oxygen loading at the respiratory surfaces and impairs the release of oxygen to the tissues. The benefit arising from the improved oxygen loading exceeds the disadvantage of impaired unloading only under conditions where the ambient oxygen tension is critically low and the Hb concentration is high. The low-affinity Hb, on the other hand, provides an advantage given that the Hb concentration is low and the ambient oxygen tension is well above the critical level. Computer-aided modelling and simulation therefore provide valuable mechanistic insights into the driving forces that could have shaped the evolution of globin genes in daphnids.

Comparative evaluation of diffusion hypoxia and psychomotor skills with or without postsedation oxygenation following administration of nitrous oxide in children undergoing dental procedures: A clinical study.

PubMed

Khinda, Vineet Inder Singh; Bhuria, Parvesh; Khinda, Paramjit; Kallar, Shiminder; Brar, Gurlal Singh

2016-01-01

Diffusion hypoxia is the most serious potential complication associated with nitrous oxide. It occurs during the recovery period. Hence, administration of 100% oxygen is mandatory as suggested by many authors. The aim of this study is to evaluate the occurrence/nonoccurrence of diffusion hypoxia in two groups of patients undergoing routine dental treatment under nitrous oxide sedation when one group is subjected to 7 min of postsedation oxygenation and the second group of the patients is made to breathe room air for the similar period. A total of sixty patients within the age group of 7-10 years requiring invasive dental procedures were randomly divided into two groups of 30 each using chit method. In the control group, patients were administered 100% oxygen postsedation, whereas, in the study group, patients were made to breathe room air postsedation. Various parameters (pulse rate, respiratory rate, blood pressure, and oxygen saturation [SpO2]) were recorded pre- and post-operatively. Data were collected and then sent for statistical analysis. The mean postoperative SpO2 at measurement times 1, 3, 5, and 7 min in both the groups was higher than the mean preoperative SpO2. This increase was statistically significant. No significant difference was found between the Trieger test scores. This study proves that clinical occurrence of diffusion hypoxia is not possible while following the routine procedure of nitrous oxide sedation.

A technique for measuring oxygen saturation in biological tissues based on diffuse optical spectroscopy

NASA Astrophysics Data System (ADS)

Kleshnin, Mikhail; Orlova, Anna; Kirillin, Mikhail; Golubiatnikov, German; Turchin, Ilya

2017-07-01

A new approach to optical measuring blood oxygen saturation was developed and implemented. This technique is based on an original three-stage algorithm for reconstructing the relative concentration of biological chromophores (hemoglobin, water, lipids) from the measured spectra of diffusely scattered light at different distances from the probing radiation source. The numerical experiments and approbation of the proposed technique on a biological phantom have shown the high reconstruction accuracy and the possibility of correct calculation of hemoglobin oxygenation in the presence of additive noise and calibration errors. The obtained results of animal studies have agreed with the previously published results of other research groups and demonstrated the possibility to apply the developed technique to monitor oxygen saturation in tumor tissue.

Chemistry of the metal-polymer interfacial region.

PubMed

Leidheiser, H; Deck, P D

1988-09-02

In many polymer-metal systems, chemical bonds are formed that involve metal-oxygen-carbon complexes. Infrared and Mössbauer spectroscopic studies indicate that carboxylate groups play an important role in some systems. The oxygen sources may be the polymer, the oxygen present in the oxide on the metal surface, or atmospheric oxygen. Diffusion of metal ions from the substrate into the polymer interphase may occur in some systems that are cured at elevated temperatures. It is unclear whether a similar, less extensive diffusion occurs over long time periods in systems maintained at room temperature. The interfacial region is dynamic, and chemical changes occur with aging at room temperature. Positron annihilation spectroscopy may have application to characterizing the voids at the metal-polymer interface.

Sources of oxygen flux in groundwater during induced bank filtration at a site in Berlin, Germany

NASA Astrophysics Data System (ADS)

Kohfahl, Claus; Massmann, Gudrun; Pekdeger, Asaf

2009-05-01

The microbial degradation of pharmaceuticals found in surface water used for artificial recharge is strongly dependent on redox conditions of the subsurface. Furthermore the durability of production wells may decrease considerably with the presence of oxygen and ferrous iron due to the precipitation of trivalent iron oxides and subsequent clogging. Field measurements are presented for oxygen at a bank filtration site in Berlin, Germany, along with simplified calculations of different oxygen pathways into the groundwater. For a two-dimensional vertical cross-section, oxygen input has been calculated for six scenarios related to different water management strategies. Calculations were carried out in order to assess the amount of oxygen input due to (1) the infiltration of oxic lake water, (2) air entrapment as a result of water table oscillations, (3) diffusive oxygen flux from soil air and (4) infiltrating rainwater. The results show that air entrapment and infiltrating lake water during winter constitute by far the most important mechanism of oxygen input. Oxygen input by percolating rainwater and by diffusive delivery of oxygen in the gas phase is negligible. The results exemplify the importance of well management as a determining factor for water oscillations and redox conditions during artificial recharge.

The influence of negative ions in helium-oxygen barrier discharges: III. Simulation of laser photodetachment and comparison with experiment

NASA Astrophysics Data System (ADS)

Nemschokmichal, Sebastian; Tschiersch, Robert; Meichsner, Jürgen

2017-11-01

The laser photodetachment experiment in a diffuse helium-oxygen barrier discharge is evaluated by a 1D fluid simulation. As in the experiment, the simulated discharge operates in helium with 400 {ppm} oxygen admixture at 500 {mbar} inside a discharge gap of 3 {mm}. The laser photodetachment is included by the interaction of negative ions with a temporally and spatially dependent photon flux. The simulation with the usually applied set of reactions and rate coefficients provides a much lower negative ion density than needed to explain the impact on the discharge characteristics in the experiment. Further processes for an enhanced negative ion formation and their capabilities of reproducing the experimental results are discussed. These further processes are additional attachment processes in the volume and the negative ion formation at the negatively charged dielectric. Both approaches are able to reproduce the measured laser photodetachment effect partially, but the best agreement with the experimental results is achieved with the formation of negative ions at the negatively charged dielectric.

Loss of Cystic Fibrosis Transmembrane Conductance Regulator Function Enhances Activation of p38 and ERK MAPKs, Increasing Interleukin-6 Synthesis in Airway Epithelial Cells Exposed to Pseudomonas aeruginosa*

PubMed Central

Bérubé, Julie; Roussel, Lucie; Nattagh, Leila; Rousseau, Simon

2010-01-01

In cystic fibrosis (CF), the absence of functional cystic fibrosis transmembrane conductance regulator (CFTR) translates into chronic bacterial infection, excessive inflammation, tissue damage, impaired lung function and eventual death. Understanding the mechanisms underlying this vicious circle of inflammation is important to design better therapies for CF. We found in CF lung biopsies increased immunoreactivity for p38 MAPK activity markers. Moreover, when compared with their non-CF counterpart, airway epithelial cells expressing the most common mutation in CF (CFTRΔF508) were more potent at inducing neutrophil chemotaxis through increased interleukin (IL)-6 synthesis when challenged with Pseudomonas aeruginosa diffusible material. We then discovered that in CFTRΔF508 cells, the p38 and ERK MAPKs are hyperactivated in response to P. aeruginosa diffusible material, leading to increased IL-6 mRNA expression and stability. Moreover, although TLR5 contributes to p38 MAPK activation upon P. aeruginosa challenge, it only played a weak role in IL-6 synthesis. Instead, we found that the production of reactive oxygen species is essential for IL-6 synthesis in response to P. aeruginosa diffusible material. Finally, we uncovered that in CFTRΔF508 cells, the extracellular glutathione levels are decreased, leading to a greater sensitivity to reactive oxygen species, providing an explanation for the hyperactivation of the p38 and ERK MAPKs and increased IL-6 synthesis. Taken together, our study has characterized a mechanism whereby the CFTRΔF508 mutation in airway epithelial cells contributes to increase inflammation of the airways. PMID:20460375

Rooting Responses of Three Oak Species to Low Oxygen Stress

Treesearch

Karel A. Jacobs; James D. MacDonald; Alison M. Berry; Laurence R. Costello

1997-01-01

Rooting characteristics were compared in blue (Q. douglasii), valley (Q. lobata), and cork oak (Q. suber) seedlings under hypoxic (low oxygen) conditions. A 50 percent reduction in root growth occurred in all species at an oxygen level of 4 percent, or an oxygen diffusion rate of 0.3 mg cm-2...

Microstructure design for fast oxygen conduction

DOE PAGES

Aidhy, Dilpuneet S.; Weber, William J.

2015-11-11

Research from the last decade has shown that in designing fast oxygen conducting materials for electrochemical applications has largely shifted to microstructural features, in contrast to material-bulk. In particular, understanding oxygen energetics in heterointerface materials is currently at the forefront, where interfacial tensile strain is being considered as the key parameter in lowering oxygen migration barriers. Nanocrystalline materials with high densities of grain boundaries have also gathered interest that could possibly allow leverage over excess volume at grain boundaries, providing fast oxygen diffusion channels similar to those previously observed in metals. In addition, near-interface phase transformations and misfit dislocations aremore » other microstructural phenomenon/features that are being explored to provide faster diffusion. In this review, the current understanding on oxygen energetics, i.e., thermodynamics and kinetics, originating from these microstructural features is discussed. Moreover, our experimental observations, theoretical predictions and novel atomistic mechanisms relevant to oxygen transport are highlighted. In addition, the interaction of dopants with oxygen vacancies in the presence of these new microstructural features, and their future role in the design of future fast-ion conductors, is outlined.« less

Phosphorescence Kinetics of Singlet Oxygen Produced by Photosensitization in Spherical Nanoparticles. Part I. Theory.

PubMed

Hovan, Andrej; Datta, Shubhashis; Kruglik, Sergei G; Jancura, Daniel; Miskovsky, Pavol; Bánó, Gregor

2018-05-24

The singlet oxygen produced by energy transfer between an excited photosensitizer (pts) and ground-state oxygen molecules plays a key role in photodynamic therapy. Different nanocarrier systems are extensively studied to promote targeted pts delivery in a host body. The phosphorescence kinetics of the singlet oxygen produced by the short laser pulse photosensitization of pts inside nanoparticles is influenced by singlet oxygen diffusion from the particles to the surrounding medium. Two theoretical models are presented in this work: a more complex numerical one and a simple analytical one. Both the models predict the time course of singlet oxygen concentration inside and outside of the spherical particles following short-pulse excitation of pts. On the basis of the comparison of the numerical and analytical results, a semiempirical analytical formula is derived to calculate the characteristic diffusion time of singlet oxygen from the nanoparticles to the surrounding solvent. The phosphorescence intensity of singlet oxygen produced in pts-loaded nanocarrier systems can be calculated as a linear combination of the two concentrations (inside and outside the particles), taking the different phosphorescence emission rate constants into account.

Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics

PubMed Central

Liu, Jianqiao; Gao, Yinglin; Wu, Xu; Jin, Guohua; Zhai, Zhaoxia; Liu, Huan

2017-01-01

The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width. PMID:28796167

Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics.

PubMed

Liu, Jianqiao; Gao, Yinglin; Wu, Xu; Jin, Guohua; Zhai, Zhaoxia; Liu, Huan

2017-08-10

The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.

Complementary methods for the determination of dissolved oxygen content in perfluorocarbon emulsions and other solutions.

PubMed

Fraker, Christopher A; Mendez, Armando J; Stabler, Cherie L

2011-09-08

Perfluorocarbons (PFCs) are compounds with increased oxygen solubility and effective diffusivity, making them ideal candidates for improving oxygen mass transfer in numerous biological applications. Historically, quantification of the mass transfer characteristics of these liquids has relied on the use of elaborate laboratory equipment and complicated methodologies, such as in-line gas chromatography coupled with temperature-controlled glass fritted diffusion cells. In this work, we present an alternative method for the determination of dissolved oxygen content in PFC emulsions and, by extrapolation, pure PFCs. We implemented a simple stirred oxygen consumption microchamber coupled with an enzymatic reaction for the quantitative determination of oxygen by optical density measurements. Chambers were also custom fitted with lifetime oxygen sensors to permit simultaneous measurement of internal chamber oxygen levels. Analyzing the consumption of oxygen during the enzymatic reaction via recorded oxygen depletion traces, we found a strong degree of correlation between the zero-order reaction rate and the total measured oxygen concentrations, relative to control solutions. The values obtained were in close agreement with published values in the literature, establishing the accuracy of this method. Overall, this method allows for easy, reliable, and reproducible measurements of oxygen content in aqueous solutions, including, but not limited to PFC emulsions.

Multichannel Porous TiO2 Hollow Nanofibers with Rich Oxygen Vacancies and High Grain Boundary Density Enabling Superior Sodium Storage Performance.

PubMed

Wu, Ying; Jiang, Yu; Shi, Jinan; Gu, Lin; Yu, Yan

2017-06-01

TiO 2 as an anode for sodium-ion batteries (NIBs) has attracted much recent attention, but poor cyclability and rate performance remain problematic owing to the intrinsic electronic conductivity and the sluggish diffusivity of Na ions in the TiO 2 matrix. Herein, a simple process is demonstrated to improve the sodium storage performance of TiO 2 by fabricating a 1D, multichannel, porous binary-phase anatase-TiO 2 -rutile-TiO 2 composite with oxygen-deficient and high grain-boundary density (denoted as a-TiO 2- x /r-TiO 2- x ) via electrospinning and subsequent vacuum treatment. The introduction of oxygen vacancies in the TiO 2 matrix enables enhanced intrinsic electronic conductivity and fast sodium-ion diffusion kinetics. The porous structure offers easy access of the liquid electrolyte and a short transport path of Na + through the pores toward the TiO 2 nanoparticle. Furthermore, the high density of grain boundaries between the anatase TiO 2 and rutile TiO 2 offer more interfaces for a novel interfacial storage. The a-TiO 2- x /r-TiO 2- x shows excellent long cycling stability (134 mAh g -1 at 10 C after 4500 cycles) and superior rate performance (93 mAh g -1 after 4500 cycles at 20 C) for sodium-ion batteries. This simple and effective process could serve as a model for the modification of other materials applied in energy storage systems and other fields. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Getting an Answer Right

NASA Astrophysics Data System (ADS)

Moore, John W.

1999-07-01

Maintaining the credibility and power of science requires knowledge and experience, healthy skepticism, constant vigilance, and a set of ethical standards. It also requires communication media and willingness on the part of members of the scientific community to discuss their ideas with others when their skepticism leads them to question oral, written, or electronically transmitted statements. Good examples of such discourse are provided in this issue. Parsons (1) suggests that an earlier paper on determining the volume fraction of oxygen in air was in error. He also provides calculations and arguments in support of his hypothesis regarding what really happens. Birk and Lawson (2) describe the long history of the idea that a burning candle in a closed container will not be extinguished until all the oxygen has been used up. Many published experiments for determining the fraction of oxygen in air depend on this hypothesis. Birk and Lawson's results, however, contradict it. A mouse confined with the burning candle remains active and unharmed after the candle goes out, showing no signs of oxygen deprivation. Quantitative measurement of the change in volume of the gas inside the container confirms that only part of the oxygen is consumed before the candle goes out. It is quite clear that we teachers can fool ourselves into thinking we have demonstrated a scientific principle or fact when we have not. Often we show students a captivating visual display of a phenomenon, but interpret it incorrectly. Another of the many examples that have appeared in these pages involves diffusion. Graham's law is usually derived and related to the kinetic-molecular theory based on the speeds of molecules. It was shown some time ago in JCE that molecular speeds are related to rates of effusion of gases into a vacuum through an orifice in a thin barrier (3). A different derivation is required (but a similar result is obtained) when gases at equal pressure diffuse into one another through a porous medium. Still another derivation is required (and a different result is obtained) when two gases diffuse into a third gas from opposite ends of a constant-volume container. Graham's law is typically demonstrated either by diffusion through a porous frit or by diffusion of HCl and NH3 into air from opposite ends of a glass tube. Neither of these involves experimental conditions that satisfy the assumptions of the derivation presented in most texts. Also misleading are demonstrations in which perfume released in one place becomes detectable throughout a room, or a crystal of KMnO4 dissolves and disperses to form a uniformly colored aqueous solution. Unless special precautions are taken, dispersion of a substance into a fluid depends more on convection than on diffusion (4). In one case a study of student misconceptions about diffusion was based on the researcher's misconception that dispersion of a dye in water during a period of only a few minutes was an illustration of diffusion (5). If we can convince ourselves that we have accurately determined an expected result or demonstrated a principle, even though the experiment or demonstration should not give that result, then most students are also likely to be convinced. It is important that they learn that skepticism and courteous, rational discourse are important components of scientific progress. Persistent misconceptions such as the two described above provide a golden opportunity to involve students in such discourse. We could, for example, demonstrate both a method that works and one that does not, compare results, and ask students to suggest additional experiments that might resolve the issue. (Steel wool and 0.25 M acetic acid can be used to achieve a reproducible and reasonably accurate determination of the fraction of oxygen in air [6]. Davis [4] reports that rates of diffusion in an agar gel, which minimizes convection, are essentially the same as in water, which provides a way of showing how slow diffusion really is.) Or we could ask students to make careful observations as an experiment is being carried out and then decide whether the proposed interpretation was correct. (If the only effect of burning a candle in a beaker inverted in a water bath is to use up the oxygen, then the water should rise slowly and steadily into the beaker as long as the candle burns; it does not.) Getting the right answer is not nearly as important as getting an answer right- exploring and experimenting to eliminate alternative hypotheses and finding the best-supported explanation. Diffusion and the fraction of oxygen in air can be studied with simple, inexpensive equipment, and it is easy for students to experiment with them. If we use them appropriately, these two subjects have great potential for enhancing students' skills in critical thinking and experimental design. Many other phenomena reported in these pages provide similar opportunities. Let's apply our ingenuity and effort to making the most of them. Literature Cited 1. Parsons, L. J. Chem. Educ. 1999, 76, 898. 2. Birk, J. P.; Lawson, A. E. J. Chem. Educ. 1999, 76, 914. 3. Mason, E. A.; Kronstadt, B. J. Chem. Educ. 1967, 44, 740. Kirk, A. D. J. Chem. Educ. 1967, 44, 745. 4. Davis, L. C. J. Chem. Educ. 1996, 73, 824. 5. Westbrook, S.; Marek, E. A. J. Res. Sci. Teach. 1991, 28, 649-660 6. Birk, J. P.; McGrath, L.; Gunter, S. K. J. Chem. Educ. 1981, 58, 804.

Using a high-flow nasal cannula provides superior results to OxyMask delivery in moderate to severe bronchiolitis: a randomized controlled study.

PubMed

Ergul, Ayse Betul; Calıskan, Emrah; Samsa, Hasan; Gokcek, Ikbal; Kaya, Ali; Zararsiz, Gozde Erturk; Torun, Yasemin Altuner

2018-06-18

The effectiveness of using a face mask with a small diffuser for oxygen delivery (OxyMask) was compared to use of a high-flow nasal cannula (HFNC) in patients with moderate or severe bronchiolitis.The study population in this open, phase 4, randomized controlled trial consisted of 60 patients aged 1-24 months diagnosed with moderate or severe bronchiolitis and admitted to an intensive care unit (ICU) for oxygen therapy. The patients were randomized into two groups according to the method of oxygen delivery: a diffuser mask group and an HFNC group.There were seven failures in the mask group and none in the HFNC group. The survival probability differed significantly between the two treatment methods (p = 0.009).Time to weaning off oxygen therapy was 56 h in the HFNC group and 96 h in the mask group (p < 0.001). HFNC use decreased the treatment failure rate and the duration of both oxygen therapy and ICU treatment compared to the diffuser mask, which implies that an HFNC should be the first choice for treating patients admitted to the ICU with severe bronchiolitis. What is known: • A high-flow nasal cannula (HFNC) does not significantly reduce the time on oxygen compared to standard therapy in children with moderate to severe bronchiolitis. Observational studies show that, since the introduction of HFNC, fewer children with bronchiolitis need intubation. For children with moderate to severe bronchiolitis there is no proof of its benefit. What Is New: • In children with moderate to severe bronchiolitis, HFNC provides faster and more effective improvement than can be achieved with a diffuser mask.

Complete suppression of boron transient-enhanced diffusion and oxidation-enhanced diffusion in silicon using localized substitutional carbon incorporation

NASA Astrophysics Data System (ADS)

Carroll, M. S.; Chang, C.-L.; Sturm, J. C.; Büyüklimanli, T.

1998-12-01

In this letter, we show the ability, through introduction of a thin Si1-x-yGexCy layer, to eliminate the enhancement of enhanced boron diffusion in silicon due to an oxidizing surface or ion implant damage. This reduction of diffusion is accomplished through a low-temperature-grown thin epitaxial Si1-x-yGexCy layer which completely filters out excess interstitials introduced by oxidation or ion implant damage. We also quantify the oxidation-enhanced diffusion (OED) and transient-enhanced diffusion (TED) dependence on substitutional carbon level, and further report both the observation of carbon TED and OED, and its dependence on carbon levels.

Acetone-Assisted Oxygen Vacancy Diffusion on TiO2(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, Yaobiao; Zhang, Bo; Ye, Jingyun

2012-10-18

We have studied the dynamic relationship between acetone and bridge-bonded oxygen (Ob) vacancy (VO) defect sites on the TiO2(110)-1 × 1 surface using scanning tunneling microscopy (STM) and density function theory (DFT) calculations. We report an adsorbate-assisted VO diffusion mechanism. The STM images taken at 300 K show that acetone preferably adsorbs on the VO site and is mobile. The sequential isothermal STM images directly show that the mobile acetone effectively migrates the position of VO by a combination of two acetone diffusion channels: one is the diffusion along the Ob row and moving as an alkyl group, which healsmore » the initial VO; another is the diffusion from the Ob row to the fivecoordinated Ti4+ row and then moving along the Ti4+ row as an acetone, which leaves a VO behind. The calculated acetone diffusion barriers for the two channels are comparable and agree with experimental results.« less

Compositional and Ionic-Size Controls on the Diffusion of Divalent Cations in Garnet: Insights from Atomistic Simulations

NASA Astrophysics Data System (ADS)

Carlson, W. D.

2012-12-01

Divalent cations in garnet (Mg, Fe, Mn, Ca) diffuse at rates that depend strongly on the host-crystal composition and on the ionic radius of the diffusant. Understanding of the nanoscale basis for these behaviors comes from atomistic simulations that calculate energies in the static limit for the defects and transition-state configurations associated with each diffusive step. Diffusion of divalent cations requires (a) creation of a cation-vacancy defect in a dodecahedral site and of a charge-compensating oxygen-vacancy defect that may or may not be in close spatial association; (b) except in the case of self-diffusion, creation of an impurity defect in which a foreign atom replaces the normal atom in a dodecahedral site adjacent to the vacancy; and (c) during the diffusive process, motion of the diffusing atom to a 'saddlepoint' position that represents the transition-state configuration. Comparisons of the system's energy in these various states, in structures of different composition and for ions of different ionic size, allows assessment of the nanoscale controls on diffusion kinetics. Molecular-statics calculations quantify defect energies and identify the transition-state configuration: the maximum energy along the diffusion path between two adjacent dodecahedral sites results when the diffusing ion is surrounded symmetrically by the six oxygen atoms that lie between the two sites. Across the range of end-member compositions, self-diffusion coefficients measured at identical conditions, and the tracer diffusivity of a single ion measured at identical conditions, can each vary by five orders of magnitude or more. Measured activation energies for these motions, however, are all equivalent to within ±6%. Calculated activation energies are in agreement with observations, in that they vary by only ±10%. Calculated vacancy-formation energies, on the other hand, are significantly larger in expanded structures; for example, that energy is greater for Prp than for Grs by ~ 470 kJ/mol. Thus in expanded structures, much higher vacancy concentrations can be produced at the same energetic cost, greatly enhancing rates of diffusion. The primary explanation for the more rapid diffusion of divalent cations in structures with larger cell dimensions therefore comes not from reduced saddlepoint strain energies in more compliant structures, but instead from the smaller energy required to create vacancy defects. Diffusivities of divalent cations exhibit a curious parabolic dependence on ionic size: for each structure, an optimally-sized ion exists, close in size to the dominant ion, that exhibits the fastest diffusion. Larger ions — and enigmatically, smaller ions — both diffuse more slowly. Calculated impurity-defect energies show that undersized impurity ions are bound more tightly in their sites, but the effects are too small in comparison to corresponding reductions in strain energy for the transition-state configuration to account for observed rate differences. Calculated vacancy-association energies reveal a slight tendency for vacancies to associate preferentially with larger impurity ions, but again the effect appears to be too small to provide a full explanation for observed behaviors.

Electrochemical Reduction of Dissolved Oxygen in Alkaline, Solid Polymer Electrolyte Films.

PubMed

Novitski, David; Kosakian, Aslan; Weissbach, Thomas; Secanell, Marc; Holdcroft, Steven

2016-11-30

Mass transport of oxygen through an ionomer contained within the cathode catalyst layer in an anion exchange membrane fuel cell is critical for a functioning fuel cell, yet is relatively unexplored. Moreover, because water is a reactant in the oxygen reduction reaction (ORR) in alkaline media, an adequate supply of water is required. In this work, ORR mass transport behavior is reported for methylated hexamethyl-p-terphenyl polymethylbenzimidazoles (HMT-PMBI), charge balanced by hydroxide ions (IEC from 2.1 to 2.5 mequiv/g), and commercial Fumatec FAA-3 membranes. Electrochemical mass transport parameters are determined by potential step chronoamperometry using a Pt microdisk solid-state electrochemical cell, in air at 60 °C, with relative humidity controlled between 70% and 98%. The oxygen diffusion coefficient (D bO2 ), oxygen concentration (c bO2 ), and oxygen permeability (D bO2 ·c bO2 ) were obtained by nonlinear curve fitting of the current transients using the Shoup-Szabo equation. Mass transport parameters are correlated to water content of the ionomer membrane. It is found that the oxygen diffusion coefficients decreased by 2 orders of magnitude upon reducing the water content of the ionomer membrane by lowering the relative humidity. The limitation of the Shoup-Szabo equation for extracting ORR mass transport parameters using thin ionomer films was evaluated by numerical modeling of the current transients, which revealed that a significant discrepancy (up to 29% under present conditions) was evident for highly hydrated membranes for which the oxygen diffusion coefficient was largest, and in which the oxygen depletion region reached the ionomer/gas interface during the chronoamperometric analysis.

STUDY OF THE OXIDATION OF NON-ALLOYED ZIRCONIUM AND OF OXYGEN DIFFUSION IN THE OXIDE FILM AND IN THE METAL (in French)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Debuigne, J.; Lehr, P.

1963-12-01

The oxidation processes of zirconium at 600-850 deg C were studied. A micrographic and radiocrystallographic analysis of the oxide layers formed at the surface of the metal was carried out. The kinetic results, weight gains as function nf time, were completed by the study of oxygen diffusion through the oxide layer formed and in the underlying metal. (auth)

Computational modeling of mediator oxidation by oxygen in an amperometric glucose biosensor.

PubMed

Simelevičius, Dainius; Petrauskas, Karolis; Baronas, Romas; Razumienė, Julija

2014-02-07

In this paper, an amperometric glucose biosensor is modeled numerically. The model is based on non-stationary reaction-diffusion type equations. The model consists of four layers. An enzyme layer lies directly on a working electrode surface. The enzyme layer is attached to an electrode by a polyvinyl alcohol (PVA) coated terylene membrane. This membrane is modeled as a PVA layer and a terylene layer, which have different diffusivities. The fourth layer of the model is the diffusion layer, which is modeled using the Nernst approach. The system of partial differential equations is solved numerically using the finite difference technique. The operation of the biosensor was analyzed computationally with special emphasis on the biosensor response sensitivity to oxygen when the experiment was carried out in aerobic conditions. Particularly, numerical experiments show that the overall biosensor response sensitivity to oxygen is insignificant. The simulation results qualitatively explain and confirm the experimentally observed biosensor behavior.

Computational Modeling of Mediator Oxidation by Oxygen in an Amperometric Glucose Biosensor

PubMed Central

Šimelevičius, Dainius; Petrauskas, Karolis; Baronas, Romas; Julija, Razumienė

2014-01-01

In this paper, an amperometric glucose biosensor is modeled numerically. The model is based on non-stationary reaction-diffusion type equations. The model consists of four layers. An enzyme layer lies directly on a working electrode surface. The enzyme layer is attached to an electrode by a polyvinyl alcohol (PVA) coated terylene membrane. This membrane is modeled as a PVA layer and a terylene layer, which have different diffusivities. The fourth layer of the model is the diffusion layer, which is modeled using the Nernst approach. The system of partial differential equations is solved numerically using the finite difference technique. The operation of the biosensor was analyzed computationally with special emphasis on the biosensor response sensitivity to oxygen when the experiment was carried out in aerobic conditions. Particularly, numerical experiments show that the overall biosensor response sensitivity to oxygen is insignificant. The simulation results qualitatively explain and confirm the experimentally observed biosensor behavior. PMID:24514882

Sulfur-doped porous reduced graphene oxide hollow nanosphere frameworks as metal-free electrocatalysts for oxygen reduction reaction and as supercapacitor electrode materials.

PubMed

Chen, Xi'an; Chen, Xiaohua; Xu, Xin; Yang, Zhi; Liu, Zheng; Zhang, Lijie; Xu, Xiangju; Chen, Ying; Huang, Shaoming

2014-11-21

Chemical doping with foreign atoms is an effective approach to significantly enhance the electrochemical performance of the carbon materials. Herein, sulfur-doped three-dimensional (3D) porous reduced graphene oxide (RGO) hollow nanosphere frameworks (S-PGHS) are fabricated by directly annealing graphene oxide (GO)-encapsulated amino-modified SiO2 nanoparticles with dibenzyl disulfide (DBDS), followed by hydrofluoric acid etching. The XPS and Raman spectra confirmed that sulfur atoms were successfully introduced into the PGHS framework via covalent bonds. The as-prepared S-PGHS has been demonstrated to be an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR) with the activity comparable to that of commercial Pt/C (40%) and much better methanol tolerance and durability, and to be a supercapacitor electrode material with a high specific capacitance of 343 F g(-1), good rate capability and excellent cycling stability in aqueous electrolytes. The impressive performance for ORR and supercapacitors is believed to be due to the synergistic effect caused by sulfur-doping enhancing the electrochemical activity and 3D porous hollow nanosphere framework structures facilitating ion diffusion and electronic transfer.

Imaging techniques in the management of chronic kidney disease: current developments and future perspectives.

PubMed

Herget-Rosenthal, Stefan

2011-05-01

The measurement of both renal function and structure is critical in clinical nephrology to detect, stage, and monitor chronic kidney disease (CKD). Current imaging modalities especially ultrasound (US), computed tomography, and magnetic resonance imaging (MRI) provide adequate information on structural changes but little on functional impairment in CKD. Although not yet considered first-line procedures for evaluating patients with renal disease, new US and MR imaging techniques may permit the assessment of renal function in the near future. Combined with established imaging techniques, contrast-enhanced US, dynamic contrast-enhanced MRI, blood oxygen level dependency MRI, or diffusion-weighted imaging may provide rapid, accurate, simultaneous, and noninvasive imaging of the structure of kidneys, macrovascular and microvascular renal perfusion, oxygenation, and glomerular filtration rate. Recent developments in molecular imaging indicate that pathophysiological pathways of renal diseases such as apoptosis, coagulation, fibrosis, and ischemia will be visualized at the tissue level. These major advances in imaging and developments in hardware and software could enable comprehensive imaging of renal structure and function in four dimensions (three dimensions plus time), and imaging is expected to play an increasing role in the management of CKD. Copyright © 2011 Elsevier Inc. All rights reserved.

Transport of oxygen ions in Er doped La2Mo2O9 oxide ion conductors: Correlation with microscopic length scales

NASA Astrophysics Data System (ADS)

Paul, T.; Ghosh, A.

2018-01-01

We report oxygen ion transport in La2-xErxMo2O9 (0.05 ≤ x ≤ 0.25) oxide ion conductors. We have measured conductivity and dielectric spectra at different temperatures in a wide frequency range. The mean square displacement and spatial extent of non-random sub-diffusive regions are estimated from the conductivity spectra and dielectric spectra, respectively, using linear response theory. The composition dependence of the conductivity is observed to be similar to that of the spatial extent of non-random sub-diffusive regions. The behavior of the composition dependence of the mean square displacement of oxygen ions is opposite to that of the conductivity. The attempt frequency estimated from the analysis of the electric modulus agrees well with that obtained from the Raman spectra analysis. The full Rietveld refinement of X-ray diffraction data of the samples is performed to estimate the distance between different oxygen lattice sites. The results obtained from such analysis confirm the ion hopping within the spatial extent of non-random sub-diffusive regions.

Model development and verification for mass transport to Escherichia coli cells in a turbulent flow

NASA Astrophysics Data System (ADS)

Hondzo, Miki; Al-Homoud, Amer

2007-08-01

Theoretical studies imply that fluid motion does not significantly increase the molecular diffusive mass flux toward and away from microscopic organisms. This study presents experimental and theoretical evidence that small-scale turbulence modulates enhanced mass transport to Escherichia coli cells in a turbulent flow. Using the technique of inner region and outer region expansions, a model for dissolved oxygen and glucose uptake by E. coli was developed. The mass transport to the E. coli was modeled by the Sherwood (Sh)-Péclet (Pe) number relationship with redefined characteristic length and velocity scales. The model Sh = (1 + Pe1/2 + Pe) agreed with the laboratory measurements well. The Péclet number that quantifies the role and function of small-scale turbulence on E. coli metabolism is defined by Pe = (?) where Ezz is the root mean square of fluid extension in the direction of local vorticity, ηK is the Kolmogorov length scale, Lc is the length scale of E. coli, and D is the molecular diffusion coefficient. An alternative formulation for the redefined Pe is given by Pe = (?) where ? = 0.5(ɛν)1/4 is the Kolmogorov velocity averaged over the Kolmogorov length scale, ɛ is dissipation of turbulent kinetic energy, and ν is the kinematic viscosity of fluid. The dissipation of turbulent kinetic energy was estimated directly from measured velocity gradients and was within the reported range in engineered and natural aquatic ecosytems. The specific growth of E. coli was up to 5 times larger in a turbulent flow in comparison to the still water controls. Dissolved oxygen and glucose uptake were enhanced with increased ɛ in the turbulent flow.

Coupled CaAl-NaSi diffusion in plagioclase feldspar: Experiments and applications to cooling rate speedometry

NASA Astrophysics Data System (ADS)

Grove, Timothy L.; Baker, Michael B.; Kinzler, Rosamond J.

1984-10-01

The rate of CaAl-NaSi interdiffusion in plagioclase feldspar was determined under 1 atm anhydrous conditions over the temperature range 1400° to 1000°C in calcic plagioclase (An 80-81) by homogenizing coherent exsolution lamellae. The dependence of the average interdiffusion coefficient on temperature is given by the expression: D˜ = 10.99 ( cm 2/sec) exp (-123.4( kcal/mol)/RT), (T in °K). This value is for diffusion perpendicular to the (03 1¯) interface of the lamellae. CaAl-NaSi interdiffusion is 4 to 5 orders of magnitude slower than oxygen diffusion in the temperature range 1400° to 1200°C and possibly 10 orders of magnitude slower at subsolidus temperatures. The large differences in diffusion rates explain the apparent contradiction posed by the plagioclases of large layered intrusions ( e.g., the Skaergaard), which retain delicate Ca, Na compositional zoning profiles on the micron scale, but have undergone complete oxygen isotopic exchange with heated meteoric groundwater from the surrounding wall rocks. CaAl-NaSi diffusion is slow, the closure temperature is high (within the solidus-liquidus interval), and Ca-Na zoning is preserved. Oxygen diffusion is faster, the closure temperature is lower (350°-400°C) and the feldspars exchange oxygen with the low-temperature hydrothermal fluids. The complex micron-scale oscillatory zones in plagioclase can also be used as cooling rate speedometers for volcanic and plutonic plagioclase. Cooling histories typical of large mafic intrusions ( e.g. the Stillwater) are slow, begin at high initial temperatures (1200°C) and result in homogenization of oscillatory zones on the scale of 10 microns. The oscillatory zones found in the plagioclase of granodioritic plutons are preserved because cooling is initiated at a lower temperature (1000°C) limiting diffusion to submicron length scales despite the slow cooling rate of the intrusion.

Quantifying the correlation between spatially defined oxygen gradients and cell fate in an engineered three-dimensional culture model.

PubMed

Ardakani, Amir G; Cheema, Umber; Brown, Robert A; Shipley, Rebecca J

2014-09-06

A challenge in three-dimensional tissue culture remains the lack of quantitative information linking nutrient delivery and cellular distribution. Both in vivo and in vitro, oxygen is delivered by diffusion from its source (blood vessel or the construct margins). The oxygen level at a defined distance from its source depends critically on the balance of diffusion and cellular metabolism. Cells may respond to this oxygen environment through proliferation, death and chemotaxis, resulting in spatially resolved gradients in cellular density. This study extracts novel spatially resolved and simultaneous data on tissue oxygenation, cellular proliferation, viability and chemotaxis in three-dimensional spiralled, cellular collagen constructs. Oxygen concentration gradients drove preferential cellular proliferation rates and viability in the higher oxygen zones and induced chemotaxis along the spiral of the collagen construct; an oxygen gradient of 1.03 mmHg mm(-1) in the spiral direction induced a mean migratory speed of 1015 μm day(-1). Although this movement was modest, it was effective in balancing the system to a stable cell density distribution, and provided insights into the natural cell mechanism for adapting cell number and activity to a prevailing oxygen regime.

Reversible control of magnetism in La 0.67Sr 0.33MnO 3 through chemically-induced oxygen migration

DOE PAGES

Grutter, A. J.; Gilbert, D. A.; Alaan, U. S.; ...

2016-02-22

We demonstrate reversible control of magnetization and anisotropy in La 0.67Sr 0.33MnO 3 films through interfacial oxygen migration. Gd metal capping layers deposited onto La 0.67Sr 0.33MnO 3 leach oxygen from the film through a solid-state redox reaction to form porous Gd 2O 3. X-ray absorption and polarized neutron reflectometry measurements show Mn valence alterations consistent with high oxygen vacancy concentrations, resulting in suppressed magnetization and increased coercive fields. Effects of the oxygen migration are observed both at the interface and also throughout the majority of a 40 nm thick film, suggesting extensive diffusion of oxygen vacancies. After Gd-capped Lamore » 0.67Sr 0.33MnO 3 is exposed to atmospheric oxygen for a prolonged period of time, oxygen diffuses through the Gd 2O 3 layer and the magnetization of the La 0.67Sr 0.33MnO 3 returns to the uncapped value. In conclusion, these findings showcase perovskite heterostructures as ideal candidates for developing functional interfaces through chemically-induced oxygen migration.« less

Cobalt porphyrin-mediated oxygen transport in a polymer membrane. Effect of the cobalt porphyrin structure on the oxygen-binding reaction, oxygen-diffusion constants, and oxygen-transport efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishide, Hiroyuki; Suzuki, Takayuki; Kawakami, Hiroyoshi

1994-05-12

New derivatives of (meso-[alpha],[alpha],[alpha],[alpha]-tetrakis(o-pivalamidophenyl)porphinato)cobalt (CoPs) were characterized by oxygen-binding equilibrium and rate constants of the cobalt centered in the porphyrins. They depended on the structure of the porphyrin; for example, the rate constants of oxygen binding and dissociation (k[sub on] and k[sub off]) for [alpha][sup 3][beta]-CoP[sub 4]P were 3 and 20 times as large as those for [alpha][sup 4]-CoB[sub 4]P, respectively. Oxygen transport through the polymer membranes containing CoPs as the fixed oxygen carriers was facilitated and was affected by the oxygen-binding character or the structure of CoPs. The logarithmically linear correlation of the oxygen-dissociation rate constant of CoPs (k[submore » off] = (3-66) x 10[sup 3] S[sup [minus]1]) with the diffusion constant of oxygen via CoPs fixed in the membranes (D[sub cc] = (3-140) x 10[sup [minus]9] cm[sup 2] s[sup [minus]1]) was given for those six CoP derivatives. 26 refs., 5 figs., 2 tabs.« less

Nanoscale metal-organic frameworks for photodynamic therapy and cancer immunotherapy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lin, Wenbin

2017-02-01

Photodynamic therapy (PDT) is an effective anticancer procedure that relies on tumor localization of a photosensitizer followed by light activation to generate cytotoxic reactive oxygen species. We recently reported the rational design of a Hf-porphyrin nanoscale metal-organic framework, DBP-UiO, as an exceptionally effective photosensitizer for PDT of resistant head and neck cancer. DBP-UiO efficiently generates singlet oxygen owing to site isolation of porphyrin ligands, enhanced intersystem crossing by heavy Hf centers, and facile singlet oxygen diffusion through porous DBP-UiO nanoplates. Consequently, DBP-UiO displayed greatly enhanced PDT efficacy both in vitro and in vivo, leading to complete tumor eradication in half of the mice receiving a single DBP-UiO dose and a single light exposure. The photophysical properties of DBP-UiO are however not optimum with the lowest energy absorption at 634 nm and a relatively small extinction coefficient of 2200 M-1·cm-1. We recently designed a chlorin-based NMOF, DBC-UiO, with much improved photophysical properties and PDT efficacy in two colon cancer mouse models. Reduction of the DBP ligands in DBP-UiO to the DBC ligands in DBC-UiO led to a 13 nm red-shift and an 11-fold extinction coefficient increase of the lowest energy Q-band. While inheriting the crystallinity, stability, porosity, and nanoplate morphology of DBP-UiO, DBC-UiO sensitizes more efficient singlet oxygen generation and exhibits much enhanced photodynamic therapy (PDT) efficacy on two colon cancer mouse models as a result of its improved photophysical properties. Both apoptosis and immunogenic cell death contributed to cancer cell-killing in DBC-UiO induced PDT. Our work has thus demonstrated that NMOFs represent a new class of highly potent PDT agents and hold great promise in treating resistant cancers in the clinic.

Investigation of Reaction Mechanism on the Lime-Free Roasting of Chromium-Containing Slag

NASA Astrophysics Data System (ADS)

Yu, Kai-ping; Zhang, Hong-ling; Chen, Bo; Xu, Hong-bin; Zhang, Yi

2015-12-01

The lime-free roasting process of trivalent chromium-containing slag was investigated. The effect of Fe and liquid phase on the conversion reaction of chromium was discussed. The oxidation of trivalent chromium depends greatly on the diffusion of Na+ and O2. Both the raw material Na2CO3 and the intermediate product NaFeO2 serve as the carriers of Na+. The Na+ diffusion is improved by the binary liquid phase of Na2CrO4-Na2CO3, whereas excess liquid phase results in a low conversion rate of chromium by hindering the diffusion of oxygen towards the reaction interface. With the increasing of liquid volume, the controlled step of chromium oxidation changes from Na+ diffusion to oxygen diffusion. The mechanism study showed that the volume of liquid phase increased while raising the reaction temperature or prolonging the reaction time. Based on the role of both liquid phase and Fe, the oxidation process of chromium was summarized as a three-stage model: the Na+ diffusion-controlled stage, the O2 diffusion-controlled stage, and the oxidation reaction halted stage.

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

NASA Astrophysics Data System (ADS)

Lui, E. W.; Palanisamy, S.; Dargusch, M. S.; Xia, K.

2017-12-01

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.

Will open ocean oxygen stress intensify under climate change?

NASA Astrophysics Data System (ADS)

Gnanadesikan, A.; Dunne, J. P.; John, J.

2011-07-01

Global warming is expected to reduce oxygen solubility and vertical exchange in the ocean, changes which would be expected to result in an increase in the volume of hypoxic waters. A simulation made with a full earth system model with dynamical atmosphere, ocean, sea ice and biogeochemical cycling shows that this holds true if the condition for hypoxia is set relatively high. However, the volume of the most hypoxic waters does not increase under global warming, as these waters actually become more oxygenated. We show that the rise in oxygen is associated with a drop in ventilation time. A term-by-term analysis within the least oxygenated waters shows an increased supply of oxygen due to lateral diffusion. compensating an increase in remineralization within these highly hypoxic waters. This lateral diffusive flux is the result of an increase of ventilation along the Chilean coast, as a drying of the region under global warming opens up a region of wintertime convection in our model.

Oxygen vacancies: The origin of n -type conductivity in ZnO

NASA Astrophysics Data System (ADS)

Liu, Lishu; Mei, Zengxia; Tang, Aihua; Azarov, Alexander; Kuznetsov, Andrej; Xue, Qi-Kun; Du, Xiaolong

2016-06-01

Oxygen vacancy (VO) is a common native point defect that plays crucial roles in determining the physical and chemical properties of metal oxides such as ZnO. However, fundamental understanding of VO is still very sparse. Specifically, whether VO is mainly responsible for the n -type conductivity in ZnO has been still unsettled in the past 50 years. Here, we report on a study of oxygen self-diffusion by conceiving and growing oxygen-isotope ZnO heterostructures with delicately controlled chemical potential and Fermi level. The diffusion process is found to be predominantly mediated by VO. We further demonstrate that, in contrast to the general belief of their neutral attribute, the oxygen vacancies in ZnO are actually +2 charged and thus responsible for the unintentional n -type conductivity as well as the nonstoichiometry of ZnO. The methodology can be extended to study oxygen-related point defects and their energetics in other technologically important oxide materials.

Method for facilitating catalyzed oxidation reactions, device for facilitating catalyzed oxidation reactions

DOEpatents

Beuhler, Robert J [East Moriches, NY; White, Michael G [Blue Point, NY; Hrbek, Jan [Rocky Point, NY

2006-08-15

A catalytic process for the oxidation of organic. Oxygen is loaded into a metal foil by heating the foil while in contact with an oxygen-containing fluid. After cooling the oxygen-activated foil to room temperature, oxygen diffuses through the foil and oxidizes reactants exposed to the other side of the foil.

Defect engineering of the oxygen-vacancy clusters formation in electron irradiated silicon by isovalent doping: An infrared perspective

NASA Astrophysics Data System (ADS)

Londos, C. A.; Sgourou, E. N.; Chroneos, A.

2012-12-01

Infrared spectroscopy was used to study the production and evolution of oxygen-vacancy (VOn for n = 1, 2, 3 and VmO for m = 1, 2, 3) clusters, in electron-irradiated Czochralski silicon (Cz-Si) samples, doped with isovalent dopants. It was determined that the production of the VO pair is enhanced in Ge-doped Si but is suppressed in Sn and Pb-doped Si. The phenomenon is discussed in terms of the competition between isovalent dopants and oxygen atoms in capturing vacancies in the course of irradiation. In the case of Ge, only transient GeV pairs form, leading finally to an increase of the VO production. Conversely, for Sn and Pb the corresponding pairs with vacancies are stable, having an opposite impact on the formation of VO pairs. Regarding V2O and V3O clusters, our measurements indicate that Ge doping enhances their formation, although Sn and Pb dopants suppress it. Similar arguments as those for the VO pair could be put forward, based on the effect of isovalent impurities on the availability of vacancies. Additionally, it was found that the conversion ratio of VO to VO2 decreases as the covalent radius of the isovalent dopant increases. These results are discussed in terms of the local strains introduced by the isovalent dopants in the Si lattice. These local strains affect the balance of the intrinsic defects created as a result of irradiation, as well as the balance between the two main reactions (VO + Oi → VO2 and VO + SiI → Oi) participating in the VO annealing, leading finally to a decrease of the VO2 production. The larger the covalent radius of the isovalent dopant (rGe < rSn < rPb), the larger the introduced strains in the lattice and then the less the VO2 formation in accordance with our experimental results. Interestingly, an opposite trend was observed for the conversion ratio of VO2 to VO3. The phenomenon is attributed to the enhanced diffusivity of oxygen impurity as a result of the presence of isovalent dopants, leading to an enhanced formation of the VO3 cluster. The results indicate that isovalent doping of Si is an effective way to control the formation of the deleterious oxygen-vacancy clustering that can affect Si-based devices.

Oxygen diffusion coefficient in isolated chicken red and white skeletal muscle fibers in ontogenesis.

PubMed

Baranov, V I; Belichenko, V M; Shoshenko, C A

2000-09-01

Oxygen diffusion from medium to cultured isolated muscle fibers from red gastrocnemius muscle (deep part) (RGM) and white pectoralis muscle (WPM) of embryonic and postnatal chickens (about 6 months) was explored. The intracellular effective O(2) diffusion coefficient (D(i)) in muscle fiber was calculated from a model of a cylindrical fiber with a uniform distribution of an oxygen sink based on these experimentally measured parameters: critical tension of O(2) (PO(2)) on the surface of a fiber, specific rate of O(2) consumption by a weight unit of muscle fibers (;VO(2)), and average diameter of muscle fibers. The results document the rapid hypertrophic growth of RGM fibers when compared to WPM fibers in the second half of the embryonic period and the higher values of;VO(2) and critical PO(2) during the ontogenetic period under study. The oxygen D(i) in RGM fibers of embryos and 1-day chickens was two to three times higher than observed for WPM fibers. For senior chickens, the oxygen D(i) value in RGM and WPM fibers does not differ. The D(i) of O(2) in both RGM and WPM fibers increased from 1.4-2.7 x 10(-8) to 90-95 x 10(-8) cm(2)/s with an ontogenetic increase in fiber diameter from 7. 5 to 67.0 microm. At all stages the oxygen D(i) values in RGM and WPM fibers are significantly lower than the O(2) diffusion coefficient in water: for 11-day embryos they are 889 and 1714 times lower and for adult individuals 25 and 27 times lower, respectively. Why oxygen D(i) values in RGM and WPM fibers are so low and why they are gradually increasing during the course of hypertrophic ontogenetic growth are still unclear. Copyright 2000 Academic Press.

A potentiostatic study of oxygen transport through poly(2-ethoxyethyl methacrylate-co-2,3-dihydroxypropylmethacrylate) hydrogel membranes.

PubMed

Compañ, Vicente; Tiemblo, Pilar; García, F; García, J M; Guzmán, Julio; Riande, Evaristo

2005-06-01

The oxygen permeability and diffusion coefficients of hydrogel membranes prepared with copolymers of 2-ethoxyethyl methacrylate (EEMA)/2,3-dihydroxypropylmethacrylate (MAG) with mole fraction of the second monomer in the range between 0 and 0.75 are described. Values of the permeability and diffusion coefficients of oxygen are determined by using electrochemical procedures involving the measurement of the steady-state current in membranes prepared by radical polymerization of the monomers. The results obtained for the transport properties were analyzed taking into account the fractional free volumes, the cohesive energy densities and the glass transition temperatures of the hydrogels.

Molecular Diffusion Coefficients: Experimental Determination and Demonstration.

ERIC Educational Resources Information Center

Fate, Gwendolyn; Lynn, David G.

1990-01-01

Presented are laboratory methods which allow the demonstration and determination of the diffusion coefficients of compounds ranging in size from water to small proteins. Included are the procedures involving the use of a spectrometer, UV cell, triterated agar, and oxygen diffusion. Results including quantification are described. (CW)

Electrochemical cell for obtaining oxygen from carbon dioxide atmospheres

NASA Technical Reports Server (NTRS)

Hooker, M. W.; Rast, H. E.; Rogers, D. K.

1989-01-01

For manned missions to Mars to become a reality, an efficient and reliable means of obtaining oxygen from the carbon dioxide-rich atmosphere will be required. Otherwise, the high cost of transporting the oxygen needed to sustain the astronauts will severely restrict the expedition to the martian surface. Recently, the use of electrochemical devices has been explored as a means of obtaining oxygen from the carbon dioxide-rich atmosphere. In these devices, oxygen ions diffuse through solid oxide membranes, thus, separating oxygen from the other gases presented. This phenomenon has only recently been explored as a means of obtaining large quantities of oxygen from toxic atmospheres, although first observed by Walter nernst in 1899. Nernst observed that stabilized zirconia will conduct oxygen ions when an electrical potential is applied across metallic electrodes applied to the ceramic membrane. Diatomic oxygen molecules are dissociated at the positive electrode/electrolyte interface. The oxygen ions enter the ceramic body due to the ion density gradient which is produced by the electrical potential across the electrolytic membrane. Once the ions have diffused through the membrane, they reform diatomic oxygen molecules at the anode. The separation of oxygen from carbon dioxide is achieved by the combination of thermal and electrochemical processes. The thermal decomposition of carbon dioxide (at 1000 C) results in the production of carbon monoxide and oxygen by the reaction.

Oxygen dynamics and transport in the Mediterranean sponge Aplysina aerophoba.

PubMed

Hoffmann, Friederike; Røy, Hans; Bayer, Kristina; Hentschel, Ute; Pfannkuchen, Martin; Brümmer, Franz; de Beer, Dirk

2008-01-01

The Mediterranean sponge Aplysina aerophoba kept in aquaria or cultivation tanks can stop pumping for several hours or even days. To investigate changes in the chemical microenvironments, we measured oxygen profiles over the surface and into the tissue of pumping and non-pumping A. aerophoba specimens with Clark-type oxygen microelectrodes (tip diameters 18-30 μm). Total oxygen consumption rates of whole sponges were measured in closed chambers. These rates were used to back-calculate the oxygen distribution in a finite-element model. Combining direct measurements with calculations of diffusive flux and modeling revealed that the tissue of non-pumping sponges turns anoxic within 15 min, with the exception of a 1 mm surface layer where oxygen intrudes due to molecular diffusion over the sponge surface. Molecular diffusion is the only transport mechanism for oxygen into non-pumping sponges, which allows total oxygen consumption rates of 6-12 μmol cm -3  sponge day -1 . Sponges of different sizes had similar diffusional uptake rates, which is explained by their similar surface/volume ratios. In pumping sponges, oxygen consumption rates were between 22 and 37 μmol cm -3  sponge day -1 , and the entire tissue was oxygenated. Combining different approaches of direct oxygen measurement in living sponges with a dynamic model, we can show that tissue anoxia is a direct function of the pumping behavior. The sponge-microbe system of A. aerophoba thus has the possibility to switch actively between aerobic and anaerobic metabolism by stopping the water flow for more than 15 min. These periods of anoxia will greatly influence physiological variety and activity of the sponge microbes. Detailed knowledge about the varying chemical microenvironments in sponges will help to develop protocols to cultivate sponge-associated microbial lineages and improve our understanding of the sponge-microbe-system.

Formation of Cr2O3 Diffusion Barrier Between Cr-Contained Stainless Steel and Cold-Sprayed Ni Coatings at High Temperature

NASA Astrophysics Data System (ADS)

Xu, Ya-Xin; Luo, Xiao-Tao; Li, Cheng-Xin; Yang, Guan-Jun; Li, Chang-Jiu

2016-02-01

A novel approach to prepare a coating system containing an in situ grown Cr2O3 diffusion barrier between a nickel top layer and 310SS was reported. Cold spraying was employed to deposit Ni(O) interlayer and top nickel coating on the Cr-contained stainless steel substrate. Ni(O) feedstock was prepared by mechanical alloying of pure nickel powders in ambient atmosphere, acting as an oxygen provider. The post-spray annealing was adopted to grow in situ Cr2O3 layer between the substrate and nickel coating. The results revealed that the diffusible oxygen can be introduced into nickel powders by mechanical alloying. The oxygen content increases to 3.25 wt.% with the increase of the ball milling duration to 8 h, while Ni(O) powders maintain a single phase of Ni. By annealing the sample in Ar atmosphere at 900 °C, a continuous Cr2O3 layer of 1-2 μm thick at the interface between 310SS and cold-sprayed Ni coating is formed. The diffusion barrier effect evaluation by thermal exposure at 750 °C shows that the Cr2O3 oxide layer effectively suppresses the outward diffusion of Fe and Cr in the substrate effectively.

Diffusivities of Redox-Sensitive Elements in Basalt vs. Oxygen Fugacity Determined by LA-ICP-MS

NASA Technical Reports Server (NTRS)

Szumila, Ian; Danielson, Lisa; Trail, Dustin

2017-01-01

Several diffusion experiments were conducted in a piston cylinder device across a range of oxygen fugacities (FMQ-3 FMQ-1.2, FMQ+6) at 1 GPa and 1300 C. This was done to explore the effects of oxygen fugacity (fO2) on diffusivity of redox sensitive trace elements. This allows investigation of how these elements diffuse across the fO2 range encountered in different reservoirs on planets and moons in our solar system. The University of Rochester LA-ICP-MS system was used for analysis of samples. Analyses were conducted using an Agilent 7900 quadrupole mass spectrometer connected to a Photon Machines 193 nm G2 laser ablation (LA) system equipped with a HelEx 2-volume sample chamber. Spots used were 35 micrometers circles spaced at 65 micrometers intervals. Laser fluence was 7.81 J/cm^2 with a rep rate of 10 Hz. The iolite software package was used to reduce data collected from laser ablation analysis of experiments with Si-29 used as the internal standard isotope. Iolite's global fit module was used to simultaneously fit elements' diffusivities in each experiment while keeping the Matano interface constant. Elements analysed include V, Nb, W, Mo, La, Ce, Pr, Sm, Eu, Gd, Ta, and W. Figures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Hao; Materials Science Program, University of Wisconsin, Madison, Wisconsin 53706; Stewart, Derek A., E-mail: derek.stewart@hgst.com

Metal oxide resistive memory devices based on Ta{sub 2}O{sub 5} have demonstrated high switching speed, long endurance, and low set voltage. However, the physical origin of this improved performance is still unclear. Ta{sub 2}O{sub 5} is an important archetype of a class of materials that possess an adaptive crystal structure that can respond easily to the presence of defects. Using first principles nudged elastic band calculations, we show that this adaptive crystal structure leads to low energy barriers for in-plane diffusion of oxygen vacancies in λ phase Ta{sub 2}O{sub 5}. Identified diffusion paths are associated with collective motion of neighboringmore » atoms. The overall vacancy diffusion is anisotropic with higher diffusion barriers found for oxygen vacancy movement between Ta-O planes. Coupled with the fact that oxygen vacancy formation energy in Ta{sub 2}O{sub 5} is relatively small, our calculated low diffusion barriers can help explain the low set voltage in Ta{sub 2}O{sub 5} based resistive memory devices. Our work shows that other oxides with adaptive crystal structures could serve as potential candidates for resistive random access memory devices. We also discuss some general characteristics for ideal resistive RAM oxides that could be used in future computational material searches.« less

Effect of cation ordering on oxygen vacancy diffusion pathways in double perovskites

DOE PAGES

Uberuaga, Blas Pedro; Pilania, Ghanshyam

2015-07-08

Perovskite structured oxides (ABO 3) are attractive for a number of technological applications, including as superionics because of the high oxygen conductivities they exhibit. Double perovskites (AA’BB’O 6) provide even more flexibility for tailoring properties. Using accelerated molecular dynamics, we examine the role of cation ordering on oxygen vacancy mobility in one model double perovskite SrLaTiAlO 6. We find that the mobility of the vacancy is very sensitive to the cation ordering, with a migration energy that varies from 0.6 to 2.7 eV. In the extreme cases, the mobility is both higher and lower than either of the two endmore » member single perovskites. Further, the nature of oxygen vacancy diffusion, whether one-dimensional, two-dimensional, or three-dimensional, also varies with cation ordering. We correlate the dependence of oxygen mobility on cation structure to the distribution of Ti 4+ cations, which provide unfavorable environments for the positively charged oxygen vacancy. The results demonstrate the potential of using tailored double perovskite structures to precisely control the behavior of oxygen vacancies in these materials.« less

Electric-field-enhanced nutrient consumption in dielectric biomaterials that contain anchorage-dependent cells.

PubMed

Belfiore, Laurence A; Floren, Michael L; Belfiore, Carol J

2012-02-01

This research contribution addresses electric-field stimulation of intra-tissue mass transfer and cell proliferation in viscoelastic biomaterials. The unsteady state reaction-diffusion equation is solved according to the von Kármán-Pohlhausen integral method of boundary layer analysis when nutrient consumption and tissue regeneration occur in response to harmonic electric potential differences across a parallel-plate capacitor in a dielectric-sandwich configuration. The partial differential mass balance with diffusion and electro-kinetic consumption contains the Damköhler (Λ(2)) and Deborah (De) numbers. Zero-field and electric-field-sensitive Damköhler numbers affect nutrient boundary layer growth. Diagonal elements of the 2nd-rank diffusion tensor are enhanced in the presence of weak electric fields, in agreement with the formalism of equilibrium and nonequilibrium thermodynamics. Induced dipole polarization density within viscoelastic biomaterials is calculated via the real and imaginary components of the complex dielectric constant, according to the Debye equation, to quantify electro-kinetic stimulation. Rates of nutrient consumption under zero-field conditions are described by third-order kinetics that include local mass densities of nutrients, oxygen, and attached cells. Thinner nutrient boundary layers are stabilized at shorter dimensionless diffusion times when the zero-field intra-tissue Damköhler number increases above its initial-condition-sensitive critical value [i.e., {Λ(2)(zero-field)}(critical)≥53, see Eq. (23)], such that the biomaterial core is starved of essential ingredients required for successful proliferation. When tissue regeneration occurs above the critical electric-field-sensitive intra-tissue Damköhler number, the electro-kinetic contribution to nutrient consumption cannot be neglected. The critical electric-field-sensitive intra-tissue Damköhler number is proportional to the Deborah number. Copyright © 2011 Elsevier B.V. All rights reserved.

Oxygen Permeability and Grain-Boundary Diffusion Applied to Alumina Scales

NASA Technical Reports Server (NTRS)

Smialek, James L.; Jacobson, Nathan S.; Gleeson, Brian; Hovis, David B.; Heuer, Arthur H.

2013-01-01

High-temperature oxygen permeability measurements had determined grain-boundary diffusivities (deltaD(sub gb)) in bulk polycrystalline alumina (Wada, Matsudaira, and Kitaoka). They predict that oxygen deltaD(sub gb,O) varies with oxygen pressure as P(O2)(sup -1/6) at low pressure whereas aluminum deltaD(sub gb),Al varies with P(O2)(sup +3/16) at high pressure. These relations were used to evaluate alumina scale growth in terms of diffusivity and grain size. A modified Wagner treatment for dominant inward oxygen growth produces the concise solution: ?(sub i) = k(sub p,i)×G(sub i) = 12 deltaD(sub gb,O,int), where ?(sub i) is a constant and k(sub p,i) and G(sub i) refer to instantaneous values of the scale parabolic growth constant and grain size, respectively. A commercial FeCrAl(Zr) alloy was oxidized at 1100 to 1400 degC to determine k(sub p,i), interfacial grain size, ?, and thus deltaD(sub gb,O,int). The deltaD(sub gb,O,int) values predicted from oxidation at (375 kJ/mole) were about 20 times less than those obtained above (at 298 kJ/mole), but closer than extrapolations from high-temperature bulk measurements. The experimental oxidation results agree with similar FeCrAl(X) studies, especially where both k(sub p,i) and G(sub i) were characterized. This complete approach accounts for temperature-sensitive oxidation effects of grain enlargement, equilibrium interface pressure variation, and grain-boundary diffusivity.

Axial oxygen diffusion in the Krogh model: modifications to account for myocardial oxygen tension in isolated perfused rat hearts measured by EPR oximetry.

PubMed

Grinberg, Oleg; Novozhilov, Boris; Grinberg, Stalina; Friedman, Bruce; Swartz, Harold M

2005-01-01

The cylindrical steady-state model developed by Krogh with Erlang has served as the basis of understanding oxygen supply in living tissue for over eighty years. Due to its simplicity and agreement with some observations, it has been extensively used and successfully extended to new fields, especially for situations such as drug diffusion, water transport, and ice formation in tissues. However, the applicability of the model to make even a qualitative prediction of the oxygen level of specific volumes of the tissue is still controversial. We recently have developed an approximate analytical solution of a steady-state diffusion equation for a Krogh cylinder, including oxygen concentration in the capillary. This model was used to explain our previous experimental data on myocardial pO2 in isolated perfused rat hearts measured by EPR oximetry. An acceptable agreement with the experimental data was obtained by assuming that a known limitation of the existing EPR methods--a tendency to over-weight low pO2 values--had resulted in an under-estimate of the pO2. These results are consistent with recent results of others, which stress the importance of taking into account the details of what is measured by various methods.

Quantitative Microplate-Based Respirometry with Correction for Oxygen Diffusion

PubMed Central

2009-01-01

Respirometry using modified cell culture microplates offers an increase in throughput and a decrease in biological material required for each assay. Plate based respirometers are susceptible to a range of diffusion phenomena; as O2 is consumed by the specimen, atmospheric O2 leaks into the measurement volume. Oxygen also dissolves in and diffuses passively through the polystyrene commonly used as a microplate material. Consequently the walls of such respirometer chambers are not just permeable to O2 but also store substantial amounts of gas. O2 flux between the walls and the measurement volume biases the measured oxygen consumption rate depending on the actual [O2] gradient. We describe a compartment model-based correction algorithm to deconvolute the biological oxygen consumption rate from the measured [O2]. We optimize the algorithm to work with the Seahorse XF24 extracellular flux analyzer. The correction algorithm is biologically validated using mouse cortical synaptosomes and liver mitochondria attached to XF24 V7 cell culture microplates, and by comparison to classical Clark electrode oxygraph measurements. The algorithm increases the useful range of oxygen consumption rates, the temporal resolution, and durations of measurements. The algorithm is presented in a general format and is therefore applicable to other respirometer systems. PMID:19555051

Effects of Fiber Type and Size on the Heterogeneity of Oxygen Distribution in Exercising Skeletal Muscle

PubMed Central

Liu, Gang; Mac Gabhann, Feilim; Popel, Aleksander S.

2012-01-01

The process of oxygen delivery from capillary to muscle fiber is essential for a tissue with variable oxygen demand, such as skeletal muscle. Oxygen distribution in exercising skeletal muscle is regulated by convective oxygen transport in the blood vessels, oxygen diffusion and consumption in the tissue. Spatial heterogeneities in oxygen supply, such as microvascular architecture and hemodynamic variables, had been observed experimentally and their marked effects on oxygen exchange had been confirmed using mathematical models. In this study, we investigate the effects of heterogeneities in oxygen demand on tissue oxygenation distribution using a multiscale oxygen transport model. Muscles are composed of different ratios of the various fiber types. Each fiber type has characteristic values of several parameters, including fiber size, oxygen consumption, myoglobin concentration, and oxygen diffusivity. Using experimentally measured parameters for different fiber types and applying them to the rat extensor digitorum longus muscle, we evaluated the effects of heterogeneous fiber size and fiber type properties on the oxygen distribution profile. Our simulation results suggest a marked increase in spatial heterogeneity of oxygen due to fiber size distribution in a mixed muscle. Our simulations also suggest that the combined effects of fiber type properties, except size, do not contribute significantly to the tissue oxygen spatial heterogeneity. However, the incorporation of the difference in oxygen consumption rates of different fiber types alone causes higher oxygen heterogeneity compared to control cases with uniform fiber properties. In contrast, incorporating variation in other fiber type-specific properties, such as myoglobin concentration, causes little change in spatial tissue oxygenation profiles. PMID:23028531

Reactivity and oxygen diffusion property of resistive barriers for Bi-2223/Ag tapes

NASA Astrophysics Data System (ADS)

Kováč, P.; Hušek, I.

2002-12-01

Reactivity of several oxide materials (OM) with BSCCO powder and oxygen diffusion through OM layer has been tested at temperature ≈840 °C in air. The OM (e.g.: BaZrO 3, SrCO 3, MgO and ZrO 2) showing the low or no reactivity with BSCCO have been mixed (10 wt.%) with precursor powder and used for single-core tapes. Bi-2223/Ag/OM/Ag single-core tapes with oxide barriers made of BaZrO 3, SrCO 3, ZrO 2 and Al 2O 3 have been also prepared by a standard powder-in-tube technique. The used OM in the direct contact with BSCCO influences the electrical properties of Bi-2223 phase differently. These is because the oxides react with BSCCO during the heat treatment and simultaneously affect the 2212→2223 phase transformation, the Bi-2223 grain growth and so also grain connectivity. SrCO 3 powder has been evaluated as the best material from the point of no destructive effect on 2223 phase transport current property. The oxide barrier controls the oxygen diffusion during the tape heat treatment and simultaneously the HTS phase formation kinetics, its purity and content within the superconducting core. For single-core Bi-2223/Ag/OM/Ag tapes, the highest current density was measured for Al 2O 3 due to only slightly reduced oxygen diffusion through the barrier.

Effects of Material Degradation on the Structural Integrity of Composite Materials: Experimental Investigation and Modeling of High Temperature Degradation Mechanisms

NASA Technical Reports Server (NTRS)

Cunningham, Ronan A.; McManus, Hugh L.

1996-01-01

It has previously been demonstrated that simple coupled reaction-diffusion models can approximate the aging behavior of PMR-15 resin subjected to different oxidative environments. Based on empirically observed phenomena, a model coupling chemical reactions, both thermal and oxidative, with diffusion of oxygen into the material bulk should allow simulation of the aging process. Through preliminary modeling techniques such as this it has become apparent that accurate analytical models cannot be created until the phenomena which cause the aging of these materials are quantified. An experimental program is currently underway to quantify all of the reaction/diffusion related mechanisms involved. The following contains a summary of the experimental data which has been collected through thermogravimetric analyses of neat PMR-15 resin, along with analytical predictions from models based on the empirical data. Thermogravimetric analyses were carried out in a number of different environments - nitrogen, air and oxygen. The nitrogen provides data for the purely thermal degradation mechanisms while those in air provide data for the coupled oxidative-thermal process. The intent here is to effectively subtract the nitrogen atmosphere data (assumed to represent only thermal reactions) from the air and oxygen atmosphere data to back-figure the purely oxidative reactions. Once purely oxidative (concentration dependent) reactions have been quantified it should then be possible to quantify the diffusion of oxygen into the material bulk.

An algorithm for sensing venous oxygenation using ultrasound-modulated light enhanced by microbubbles

NASA Astrophysics Data System (ADS)

Honeysett, Jack E.; Stride, Eleanor; Deng, Jing; Leung, Terence S.

2012-02-01

Near-infrared spectroscopy (NIRS) can provide an estimate of the mean oxygen saturation in tissue. This technique is limited by optical scattering, which reduces the spatial resolution of the measurement, and by absorption, which makes the measurement insensitive to oxygenation changes in larger deep blood vessels relative to that in the superficial tissue. Acousto-optic (AO) techniques which combine focused ultrasound (US) with diffuse light have been shown to improve the spatial resolution as a result of US-modulation of the light signal, however this technique still suffers from low signal-to-noise when detecting a signal from regions of high optical absorption. Combining an US contrast agent with this hybrid technique has been proposed to amplify an AO signal. Microbubbles are a clinical contrast agent used in diagnostic US for their ability to resonate in a sound field: in this work we also make use of their optical scattering properties (modelled using Mie theory). A perturbation Monte Carlo (pMC) model of light transport in a highly absorbing blood vessel containing microbubbles surrounded by tissue is used to calculate the AO signal detected on the top surface of the tissue. An algorithm based on the modified Beer-Lambert law is derived which expresses intravenous oxygen saturation in terms of an AO signal. This is used to determine the oxygen saturation in the blood vessel from a dual wavelength microbubble-contrast AO measurement. Applying this algorithm to the simulation data shows that the venous oxygen saturation is accurately recovered, and this measurement is robust to changes in the oxygenation of the superficial tissue layer.

Enhanced diffusion on oscillating surfaces through synchronization

NASA Astrophysics Data System (ADS)

Wang, Jin; Cao, Wei; Ma, Ming; Zheng, Quanshui

2018-02-01

The diffusion of molecules and clusters under nanoscale confinement or absorbed on surfaces is the key controlling factor in dynamical processes such as transport, chemical reaction, or filtration. Enhancing diffusion could benefit these processes by increasing their transport efficiency. Using a nonlinear Langevin equation with an extensive number of simulations, we find a large enhancement in diffusion through surface oscillation. For helium confined in a narrow carbon nanotube, the diffusion enhancement is estimated to be over three orders of magnitude. A synchronization mechanism between the kinetics of the particles and the oscillating surface is revealed. Interestingly, a highly nonlinear negative correlation between diffusion coefficient and temperature is predicted based on this mechanism, and further validated by simulations. Our results provide a general and efficient method for enhancing diffusion, especially at low temperatures.

Multicolor tunability and upconversion enhancement of fluoride nanoparticles by oxygen dopant

NASA Astrophysics Data System (ADS)

Niu, Wenbin; Wu, Suli; Zhang, Shufen; Su, Liap Tat; Tok, Alfred Iing Yoong

2013-08-01

The ability to manipulate the upconversion luminescence of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) is particularly important and highly desired due to their wide applications in color displays, multiplexing bioassays and multicolor imaging. Here, we developed a strategy for simultaneously tuning color output and enhancing upconversion emission of Yb/Er doped fluoride UCNPs, based on adjusting the oxygen doping level. The synthesis of multicolored multifunctional NaGdF4:Yb,Er UCNPs was used as the model host system to demonstrate this protocol. Ammonium nitrate (NH4NO3) was used as the oxygen source and added into the reaction system at the beginning stage of nucleation and growth process of fluoride UCNPs, which facilitates the formation of enough oxygen atoms and the diffusion of these into the fluoride host matrix. The results revealed that multicolour output and upconversion enhancement mainly resulted from the variation of phonon energy and crystal field symmetry of the host lattice, respectively. This strategy can be further expanded to other fluoride host matrices. As an example of an application, multicolored UCNPs were used as a color converter in light emitting diodes, which can effectively convert near-infrared light into visible light. It is expected that these multicolored UCNPs will be promising for applications in multiplexing biodetection, bioimaging (optical and magnetic resonance imaging) and other optical technologies, and the present method for the control of O2- doping may also be used in other functional nanomaterials.The ability to manipulate the upconversion luminescence of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) is particularly important and highly desired due to their wide applications in color displays, multiplexing bioassays and multicolor imaging. Here, we developed a strategy for simultaneously tuning color output and enhancing upconversion emission of Yb/Er doped fluoride UCNPs, based on adjusting the oxygen doping level. The synthesis of multicolored multifunctional NaGdF4:Yb,Er UCNPs was used as the model host system to demonstrate this protocol. Ammonium nitrate (NH4NO3) was used as the oxygen source and added into the reaction system at the beginning stage of nucleation and growth process of fluoride UCNPs, which facilitates the formation of enough oxygen atoms and the diffusion of these into the fluoride host matrix. The results revealed that multicolour output and upconversion enhancement mainly resulted from the variation of phonon energy and crystal field symmetry of the host lattice, respectively. This strategy can be further expanded to other fluoride host matrices. As an example of an application, multicolored UCNPs were used as a color converter in light emitting diodes, which can effectively convert near-infrared light into visible light. It is expected that these multicolored UCNPs will be promising for applications in multiplexing biodetection, bioimaging (optical and magnetic resonance imaging) and other optical technologies, and the present method for the control of O2- doping may also be used in other functional nanomaterials. Electronic supplementary information (ESI) available: Upconversion spectra of NaYF4:Yb,Er UCNPs prepared with various oxygen sources (trimethylamine N-oxide and ammonium carbonate, Fig. S1) and different addition temperatures of NH4NO3 (Fig. S2), enlarged XRD patterns (Fig. S3), the intensity ratios of green to red emissions of NaGdF4:Yb,Er UCNPs prepared with various amounts of NH4NO3 (Fig. S4), power dependence of upconversion spectra of NaGdF4:Yb,Er UCNPs prepared at 300 °C for 1 h (Fig. S5), upconversion spectra of the product after further reaction between as-prepared NaYF4:Yb,Er and 50 mg of NH4NO3 at 300 °C for 1 h (Fig. S6), XRD patterns of NaYF4:Yb,Er and NaLuF4:Yb,Er UCNPs prepared with various amounts of NH4NO3 (Fig. S7 and S8), the corresponding magnetization curves of NaGdF4:Yb,Er UCNPs (Fig. S9). See DOI: 10.1039/c3nr01612a

Dextran-shelled oxygen-loaded nanodroplets reestablish a normoxia-like pro-angiogenic phenotype and behavior in hypoxic human dermal microvascular endothelium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basilico, Nicoletta, E-mail: nicoletta.basilico@unimi.it; Magnetto, Chiara, E-mail: c.magnetto@inrim.it; D'Alessandro, Sarah, E-mail: sarah.dalessandro@unimi.it

In chronic wounds, hypoxia seriously undermines tissue repair processes by altering the balances between pro-angiogenic proteolytic enzymes (matrix metalloproteinases, MMPs) and their inhibitors (tissue inhibitors of metalloproteinases, TIMPs) released from surrounding cells. Recently, we have shown that in human monocytes hypoxia reduces MMP-9 and increases TIMP-1 without affecting TIMP-2 secretion, whereas in human keratinocytes it reduces MMP-2, MMP-9, and TIMP-2, without affecting TIMP-1 release. Provided that the phenotype of the cellular environment is better understood, chronic wounds might be targeted by new oxygenating compounds such as chitosan- or dextran-shelled and 2H,3H-decafluoropentane-cored oxygen-loaded nanodroplets (OLNs). Here, we investigated the effects ofmore » hypoxia and dextran-shelled OLNs on the pro-angiogenic phenotype and behavior of human dermal microvascular endothelium (HMEC-1 cell line), another cell population playing key roles during wound healing. Normoxic HMEC-1 constitutively released MMP-2, TIMP-1 and TIMP-2 proteins, but not MMP-9. Hypoxia enhanced MMP-2 and reduced TIMP-1 secretion, without affecting TIMP-2 levels, and compromised cell ability to migrate and invade the extracellular matrix. When taken up by HMEC-1, nontoxic OLNs abrogated the effects of hypoxia, restoring normoxic MMP/TIMP levels and promoting cell migration, matrix invasion, and formation of microvessels. These effects were specifically dependent on time-sustained oxygen diffusion from OLN core, since they were not achieved by oxygen-free nanodroplets or oxygen-saturated solution. Collectively, these data provide new information on the effects of hypoxia on dermal endothelium and support the hypothesis that OLNs might be used as effective adjuvant tools to promote chronic wound healing processes. - Highlights: • Hypoxia enhances MMP-2 and reduces TIMP-1 secretion by dermal HMEC-1 cell line. • Hypoxia compromises migration and matrix invasion abilities of HMEC-1. • Nontoxic dextran-shelled oxygen-loaded nanodroplets (OLNs) are uptaken by HMEC-1. • Dextran-shelled OLNs abrogate hypoxia effects on HMEC-1 pro-angiogenic phenotype. • Dextran-shelled OLNs abrogate hypoxia effects on HMEC-1 pro-angiogenic behavior.« less

Methane oxidation and formation of EPS in compost: effect of oxygen concentration.

PubMed

Wilshusen, J H; Hettiaratchi, J P A; De Visscher, A; Saint-Fort, R

2004-05-01

Oxygen concentration plays an important role in the regulation of methane oxidation and the microbial ecology of methanotrophs. However, this effect is still poorly quantified in soil and compost ecosystems. The effect of oxygen on the formation of exopolymeric substances (EPS) is as yet unknown. We studied the effect of oxygen on the evolution of methanotrophic activity. At both high and low oxygen concentrations, peak activity was observed twice within a period of 6 months. Phospholipid fatty acid analysis showed that there was a shift from type I to type II methanotrophs during this period. At high oxygen concentration, EPS production was about 250% of the amount at low oxygen concentration. It is hypothesized that EPS serves as a carbon cycling mechanism for type I methanotrophs when inorganic nitrogen is limiting. Simultaneously, EPS stimulates nitrogenase activity in type II methanotrophs by creating oxygen-depleted zones. The kinetic results were incorporated in a simulation model for gas transport and methane oxidation in a passively aerated biofilter. Comparison between the model and experimental data showed that, besides acting as a micro-scale diffusion barrier, EPS can act as a barrier to macro-scale diffusion, reducing the performance of such biofilters.

Full scale evaluation of diffuser ageing with clean water oxygen transfer tests.

PubMed

Krampe, J

2011-01-01

Aeration is a crucial part of the biological wastewater treatment in activated sludge systems and the main energy user of WWTPs. Approximately 50 to 60% of the total energy consumption of a WWTP can be attributed to the aeration system. The performance of the aeration system, and in the case of fine bubble diffused aeration the diffuser performance, has a significant impact on the overall plant efficiency. This paper seeks to isolate the changes of the diffuser performance over time by eliminating all other influencing parameters like sludge retention time, surfactants and reactor layout. To achieve this, different diffusers have been installed and tested in parallel treatment trains in two WWTPs. The diffusers have been performance tested in clean water tests under new conditions and after one year of operation. A set of material property tests describing the diffuser membrane quality was also performed. The results showed a significant drop in the performance of the EPDM diffuser in the first year which resulted in similar oxygen transfer efficiency around 16 g/m3/m for all tested systems. Even though the tested silicone diffusers did not show a drop in performance they had a low efficiency in the initial tests. The material properties indicate that the EPDM performance loss is partly due to the washout of additives.

Size dependent anomalous dielectric behavior in nanoparticle Gd2 O 3 : SiO2 glass composite system

NASA Astrophysics Data System (ADS)

Mukherjee, Sudip; Lin, Yu-Hsing; Kao, Ting-Hui; Chou, C. C.; Yang, H. D.

2011-03-01

Gd 2 O3 (0.5 mol%) nanoparticles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures of 700& circ; C and above. Compared with the parent material Si O2 , this nano-glass composite system shows enhancement of dielectric constant and diffuse phase transition along with magnetodielectric effect around room temperature. Observed conduction mechanism is found to be closely related to the thermally activated oxygen vacancies. Magnetodielectric behavior is strongly associated with magnetoresistance changes, depending on the nanoparticle size and separation. Such a material might be treated as a potential candidate for device miniaturization.

Contribution of aerial hyphae of Aspergillus oryzae to respiration in a model solid-state fermentation system.

PubMed

Rahardjo, Yovita S P; Weber, Frans J; le Comte, E Paul; Tramper, Johannes; Rinzema, Arjen

2002-06-05

Oxygen transfer is for two reasons a major concern in scale-up and process control in industrial application of aerobic fungal solid-state fermentation (SSF): 1) heat production is proportional to oxygen uptake and it is well known that heat removal is one of the main problems in scaled-up fermenters, and 2) oxygen supply to the mycelium on the surface of or inside the substrate particles may be hampered by diffusion limitation. This article gives the first experimental evidence that aerial hyphae are important for fungal respiration in SSF. In cultures of A. oryzae on a wheat-flour model substrate, aerial hyphae contributed up to 75% of the oxygen uptake rate by the fungus. This is due to the fact that A. oryzae forms very abundant aerial mycelium and diffusion of oxygen in the gas-filled pores of the aerial hyphae layer is rapid. It means that diffusion limitation in the densely packed mycelium layer that is formed closer to the substrate surface and that has liquid-filled pores is much less important for A. oryzae than was previously reported for R. oligosporus and C. minitans. It also means that the overall oxygen uptake rate for A. oryzae is much higher than the oxygen uptake rate that can be predicted in the densely packed mycelium layer for R. oligosporus and C. minitans. This would imply that cooling problems become more pronounced. Therefore, it is very important to clarify the physiological role of aerial hyphae in SSF. Copyright 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 539-544, 2002.

Enhanced Intrinsic Catalytic Activity of λ-MnO2 by Electrochemical Tuning and Oxygen Vacancy Generation.

PubMed

Lee, Sanghan; Nam, Gyutae; Sun, Jie; Lee, Jang-Soo; Lee, Hyun-Wook; Chen, Wei; Cho, Jaephil; Cui, Yi

2016-07-18

Chemically prepared λ-MnO2 has not been intensively studied as a material for metal-air batteries, fuel cells, or supercapacitors because of their relatively poor electrochemical properties compared to α- and δ-MnO2 . Herein, through the electrochemical removal of lithium from LiMn2 O4 , highly crystalline λ-MnO2 was prepared as an efficient electrocatalyst for the oxygen reduction reaction (ORR). The ORR activity of the material was further improved by introducing oxygen vacancies (OVs) that could be achieved by increasing the calcination temperature during LiMn2 O4 synthesis; a concentration of oxygen vacancies in LiMn2 O4 could be characterized by its voltage profile as the cathode in a lithiun-metal half-cell. λ-MnO2-z prepared with the highest OV exhibited the highest diffusion-limited ORR current (5.5 mA cm(-2) ) among a series of λ-MnO2-z electrocatalysts. Furthermore, the number of transferred electrons (n) involved in the ORR was >3.8, indicating a dominant quasi-4-electron pathway. Interestingly, the catalytic performances of the samples were not a function of their surface areas, and instead depended on the concentration of OVs, indicating enhancement in the intrinsic catalytic activity of λ-MnO2 by the generation of OVs. This study demonstrates that differences in the electrochemical behavior of λ-MnO2 depend on the preparation method and provides a mechanism for a unique catalytic behavior of cubic λ-MnO2 . © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Diffusion of Redox-Sensitive Elements in Basalt at Different Oxygen Fugacities

NASA Technical Reports Server (NTRS)

Szumila, I.; Trail, D.; Danielson, L. R.

2017-01-01

The terrestrial planets and moons of our solar system have differentiated over a range of oxygen fugacity conditions. Basalts formed from magmas on the Earth cover a range of more oxidized states (from approximately IW (iron wustite) plus 2 to approximately FMQ (fayalite-magnetite-quartz) plus 3) than crustal rocks from Mars (IW to approximately IW plus 3), and basalts from the Moon are more reduced than both, ranging from IW to IW minus 2. The small body Vesta differentiated around IW minus 4. Characterization of redox sensitive elements' diffusivities will offer insight into behavior of these elements as a function of f (fugacity of) O2 for these planetary bodies. Here, we report a systematic study of the diffusion of redox-sensitive elements in basaltic melts with varying oxygen fugacities (fO2) for trace elements, V, Nb, W, Mo, La, Ce, Pr, Sm, Eu, Gd, Ta, and W. Since fO2 is an intensive variable that is different for the reservoirs of various planets and moons in our solar system, it is important to characterize how changes in redox states will affect diffusion. We conducted experiments in a piston cylinder device at 1300 degrees Centigrade and 1 gigapascal, at the University of Rochester and NASA Johnson Space Center. We buffered some experiments at Ru-RuO2 (FMQ plus 6.00), and conducted other experiments within either a graphite or Mo capsule, which corresponds to fO2s of either FMQ minus1.2, or FMQ minus 3.00, respectively. Characterizing the diffusivities of redox sensitive elements at different fO2s is important because some elements, like Eu, have varying valence states, such as Eu (sup 2 plus) and Eu (sup 3 plus). Differences in charge and ion radii may lead to differences in diffusivities within silicate melts. This could, lead to formation of a Eu anomaly by diffusion, the magnitude of which may be controlled by the fO2. Characterization of trace element diffusion is also important in understanding trace element fractionation. We found, during the course of our investigation, that not only did the diffusivities of the redox sensitive elements change with fO2, but that the diffusivities of all other analyzed elements also changed. This indicates that not only do changes in valence influence trace elements diffusivities but that the structure of melt may have changed with varying oxygen fugacity, probably due to changes in the speciation of the major element Fe.

Oxygen Diffusion and Reaction Kinetics in Continuous Fiber Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Eckel, Andrew J.; Cawley, James D.

1999-01-01

Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 C to 1500 C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e. diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics.

Bubble Formation Modeling in IE-911

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fondeur, F.F.

2000-09-27

The author used diffusion modeling to determine the hydrogen and oxygen concentration inside IE-911. The study revealed gas bubble nucleation will not occur in the bulk solution inside the pore or on the pore wall. This finding results from the fast oxygen and hydrogen gas molecular diffusion and a very confined pore space. The net steady state concentration of these species inside the pore proves too low to drive bubble nucleation. This study did not investigate other gas bubble nucleating mechanism such as suspended particles in solution.

Rhenium-Oxygen Interactions at High Temperatures

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.; Myers, Dwight L.; Zhu, Dongming; Humphrey, Donald

2000-01-01

The reaction of pure rhenium metal with dilute oxygen/argon mixtures was studied from 600 to 1400 C. Temperature, oxygen pressure, and flow rates were systematically varied to determine the rate-controlling steps. At lower temperatures the oxygen/rhenium chemical reaction is rate limiting; at higher temperatures gas-phase diffusion of oxygen through the static boundary layer is rate limiting. At all temperatures post-reaction microstructures indicate preferential attack along certain crystallographic planes and defects.

Method of measuring blood oxygenation based on spectroscopy of diffusely scattered light

NASA Astrophysics Data System (ADS)

Kleshnin, M. S.; Orlova, A. G.; Kirillin, M. Yu.; Golubyatnikov, G. Yu.; Turchin, I. V.

2017-05-01

A new approach to the measurement of blood oxygenation is developed and implemented, based on an original two-step algorithm reconstructing the relative concentration of biological chromophores (haemoglobin, water, lipids) from the measured spectra of diffusely scattered light at different distances from the radiation source. The numerical experiments and approbation of the proposed approach using a biological phantom have shown the high accuracy of the reconstruction of optical properties of the object in question, as well as the possibility of correct calculation of the haemoglobin oxygenation in the presence of additive noises without calibration of the measuring device. The results of the experimental studies in animals agree with the previously published results obtained by other research groups and demonstrate the possibility of applying the developed method to the monitoring of blood oxygenation in tumour tissues.

Electric-Loading Enhanced Kinetics in Oxide Ceramics: Pore Migration, Sintering and Grain Growth: Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, I-Wei

Solid oxide fuel cells and solid oxide electrolysis cells rely on solid electrolytes in which a large ionic current dominates. This project was initiated to investigate microstructural changes in such devices under electrochemical forces, because nominally insignificant processes may couple to the large ionic current to yield non-equilibrium phenomena that alter the microstructure. Our studies had focused on yttria-stabilized cubic zirconia (YSZ) widely used in these devices. The experiments have revealed enhanced grain growth at higher temperatures, pore and gas bubble migration at all temperatures, and the latter also lead to enhanced sintering of highly porous ceramics into fully densemore » ceramics at unprecedentedly low temperatures. These results have shed light on kinetic processes that fall completely outside the realm of classical ceramic processing. Other fast-oxygen oxide ceramics closely related to, and often used in conjunction with zirconia ceramics, have also be investigated, as are closely related scientific problems in zirconia ceramics. These include crystal structures, defects, diffusion kinetics, oxygen potentials, low temperature sintering, flash sintering, and coarsening theory, and all have resulted in greater clarity in scientific understanding. The knowledge is leveraged to provide new insight to electrode kinetics and near-electrode mixed conductivity and to new materials. In the following areas, our research has resulted in completely new knowledge that defines the state-of-the-art of the field. (a) Electrical current driven non-equilibrium phenomena, (b) Enhanced grain growth under electrochemically reducing conditions, (c) Development of oxygen potential polarization in electrically loaded electrolyte, (d) Low temperature sintering and grain growth, and (e) Structure, defects and cation kinetics of fluorite-structured oxides. Our research has also contributed to synthesis of new energy-relevant electrochemical materials and new understanding of flash sintering, which is a rapid sintering process initiated by a large electrical loading.« less

Composition and method for polymer moderated catalytic water formation

DOEpatents

Shepodd, Timothy Jon

1999-01-01

A composition suitable for safely removing hydrogen from gaseous mixtures containing hydrogen and oxygen, particularly those mixtures wherein the hydrogen concentration is within the explosive range. The composition comprises a hydrogenation catalyst, preferably Pd dispersed on carbon, wherein the concentration of Pd is from about 1-10 wt %, dispersed in a polymeric material matrix. As well as serving as a matrix to contain the hydrogenation catalyst, the polymeric material, which is substantially unreactive to hydrogen, provides both a diffusion restriction to hydrogen and oxygen, thereby limiting the rate at which the reactants (hydrogen and oxygen) can diffuse to the catalyst surface and thus, the production of heat from the recombination reaction and as a heat sink.

Geochemical impacts of waste disposal on the abyssal seafloor

NASA Astrophysics Data System (ADS)

Jahnke, Richard A.

1998-05-01

The response of pore water oxygen, nitrate, sulfate, sulfide, ammonium and methane and particulate organic carbon distributions to the input of 8.5 million m 3 (3.8×10 12 g) of organic-rich waste materials is simulated. The deposit is assumed to be conical with a maximum thickness of approximately 20 m. Remineralization reactions within the deposit rapidly deplete any initially available pore water oxidants such as oxygen, nitrate and sulfate, and are subsequently dominated by fermentation reactions. Diffusion downward of reduced metabolites, sulfide, ammonium and methane, depletes the available oxidants in the pore waters below the waste pile, increasing the thickness of the anoxic layer. While the impacted region is limited to essentially the deposition site, recovery of the pore waters is estimated to be >10 4 years. The overall computational results are corroborated by the pore water distributions observed at turbidite boundaries. Numerous uncertainties in the parameterizations limit the overall accuracy of the calculations presented. The most significant of these are: (1) A quantitatively accurate assessment of the remineralization rate of the deposited organic matter including its rate of inoculation by abyssal microorganisms; (2) a detailed assessment of potential non-diffusive pore water transport processes including advection due to compaction and buoyancy-driven flows and enhanced exchange due to macrobenthic irrigation activities and (3) an assessment of the potential alteration of pore space and methane reactivity due to gas hydrate formation.

Measuring the viscosity of whole bovine lens using a fiber optic oxygen sensing system

PubMed Central

Thao, Mai T.; Perez, Daniel; Dillon, James

2014-01-01

Purpose To obtain a better understanding of oxygen and nutrient transport within the lens, the viscosity of whole lenses was investigated using a fiber optic oxygen sensor (optode). The diffusion coefficient of oxygen was calculated using the Stokes-Einstein equation at the slip boundary condition. Methods The optode was used to measure the oxygen decay signal in samples consisting of different glycerol/water solutions with known viscosities. The oxygen decay signal was fitted to a double exponential decay rate equation, and the lifetimes (tau) were calculated. It was determined that the tau-viscosity relationship is linear, which served as the standard curve. The same procedure was applied to fresh bovine lenses, and the unknown viscosity of the bovine lens was calculated from the tau-viscosity relationship. Results The average viscosity in a whole bovine lens was determined to be 5.74±0.88 cP by our method. Using the Stokes-Einstein equation at the slip boundary condition, the diffusion coefficient for oxygen was calculated to be 8.2 × 10−6 cm2/s. Conclusions These data indicate a higher resistance to flow for oxygen and nutrients in the lens than what is currently assumed in the literature. Overall, this study allows a better understanding of oxygen transport within the lens. PMID:24505211

Intramyocardial oxygen transport by quantitative diffuse reflectance spectroscopy in calves

NASA Astrophysics Data System (ADS)

Lindbergh, Tobias; Larsson, Marcus; Szabó, Zoltán; Casimir-Ahn, Henrik; Strömberg, Tomas

2010-03-01

Intramyocardial oxygen transport was assessed during open-chest surgery in calves by diffuse reflectance spectroscopy using a small intramuscular fiber-optic probe. The sum of hemo- and myoglobin tissue fraction and oxygen saturation, the tissue fraction and oxidation of cytochrome aa3, and the tissue fraction of methemoglobin were estimated using a calibrated empirical light transport model. Increasing the oxygen content in the inhaled gas, 21%-50%-100%, in five calves (group A) gave an increasing oxygen saturation of 19+/-4%, 24+/-5%, and 28+/-8% (p<0.001, ANOVA repeated measures design) and mean tissue fractions of 1.6% (cytochrome aa3) and 1.1% (hemo- and myoglobin). Cardiac arrest in two calves gave an oxygen saturation lower than 5%. In two calves (group B), a left ventricular assistive device (LVAD pump) was implanted. Oxygen saturation in group B animals increased with LVAD pump speed (p<0.001, ANOVA) and with oxygen content in inhaled gas (p<0.001, ANOVA). The cytochrome aa3 oxidation level was above 96% in both group A and group B calves, including the two cases involving cardiac arrest. In conclusion, the estimated tissue fractions and oxygenation/oxidation levels of the myocardial chromophores during respiratory and hemodynamic provocations were in agreement with previously presented results, demonstrating the potential of the method.

The effects of capillary transit time heterogeneity (CTH) on brain oxygenation

PubMed Central

Angleys, Hugo; Østergaard, Leif; Jespersen, Sune N

2015-01-01

We recently extended the classic flow–diffusion equation, which relates blood flow to tissue oxygenation, to take capillary transit time heterogeneity (CTH) into account. Realizing that cerebral oxygen availability depends on both cerebral blood flow (CBF) and capillary flow patterns, we have speculated that CTH may be actively regulated and that changes in the capillary morphology and function, as well as in blood rheology, may be involved in the pathogenesis of conditions such as dementia and ischemia-reperfusion injury. The first extended flow–diffusion equation involved simplifying assumptions which may not hold in tissue. Here, we explicitly incorporate the effects of oxygen metabolism on tissue oxygen tension and extraction efficacy, and assess the extent to which the type of capillary transit time distribution affects the overall effects of CTH on flow–metabolism coupling reported earlier. After incorporating tissue oxygen metabolism, our model predicts changes in oxygen consumption and tissue oxygen tension during functional activation in accordance with literature reports. We find that, for large CTH values, a blood flow increase fails to cause significant improvements in oxygen delivery, and can even decrease it; a condition of malignant CTH. These results are found to be largely insensitive to the choice of the transit time distribution. PMID:25669911

Numerical study of influence of molecular diffusion in the Mild combustion regime

NASA Astrophysics Data System (ADS)

Mardani, Amir; Tabejamaat, Sadegh; Ghamari, Mohsen

2010-09-01

In this paper, the importance of molecular diffusion versus turbulent transport in the moderate or intense low-oxygen dilution (Mild) combustion mode has been numerically studied. The experimental conditions of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147-1154] were used for modelling. The EDC model was used to describe the turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI 2.11 full mechanism were used to represent the chemical reactions of an H2/methane jet flame. The importance of molecular diffusion for various O2 levels, jet Reynolds numbers and H2 fuel contents was investigated. Results show that the molecular diffusion in Mild combustion cannot be ignored in comparison with the turbulent transport. Also, the method of inclusion of molecular diffusion in combustion modelling has a considerable effect on the accuracy of numerical modelling of Mild combustion. By decreasing the jet Reynolds number, decreasing the oxygen concentration in the airflow or increasing H2 in the fuel mixture, the influence of molecular diffusion on Mild combustion increases.

Diffuser Test

NASA Image and Video Library

2007-09-13

Tests begun at Stennis Space Center's E Complex Sept. 13 evaluated a liquid oxygen lead for engine start performance, part of the A-3 Test Facility Subscale Diffuser Risk Mitigation Project at SSC's E-3 Test Facility. Phase 1 of the subscale diffuser project, completed Sept. 24, was a series of 18 hot-fire tests using a 1,000-pound liquid oxygen and gaseous hydrogen thruster to verify maximum duration and repeatability for steam generation supporting the A-3 Test Stand project. The thruster is a stand-in for NASA's developing J-2X engine, to validate a 6 percent scale version of A-3's exhaust diffuser. Testing the J-2X at altitude conditions requires an enormous diffuser. Engineers will generate nearly 4,600 pounds per second of steam to reduce pressure inside A-3's test cell to simulate altitude conditions. A-3's exhaust diffuser has to be able to withstand regulated pressure, temperatures and the safe discharge of the steam produced during those tests. Before the real thing is built, engineers hope to work out any issues on the miniature version. Phase 2 testing is scheduled to begin this month.

Report on simulation of fission gas and fission product diffusion in UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersson, Anders David; Perriot, Romain Thibault; Pastore, Giovanni

2016-07-22

In UO 2 nuclear fuel, the retention and release of fission gas atoms such as xenon (Xe) are important for nuclear fuel performance by, for example, reducing the fuel thermal conductivity, causing fuel swelling that leads to mechanical interaction with the clad, increasing the plenum pressure and reducing the fuel–clad gap thermal conductivity. We use multi-­scale simulations to determine fission gas diffusion mechanisms as well as the corresponding rates in UO 2 under both intrinsic and irradiation conditions. In addition to Xe and Kr, the fission products Zr, Ru, Ce, Y, La, Sr and Ba have been investigated. Density functionalmore » theory (DFT) calculations are used to study formation, binding and migration energies of small clusters of Xe atoms and vacancies. Empirical potential calculations enable us to determine the corresponding entropies and attempt frequencies for migration as well as investigate the properties of large clusters or small fission gas bubbles. A continuum reaction-­diffusion model is developed for Xe and point defects based on the mechanisms and rates obtained from atomistic simulations. Effective fission gas diffusivities are then obtained by solving this set of equations for different chemical and irradiation conditions using the MARMOT phase field code. The predictions are compared to available experimental data. The importance of the large Xe U3O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and high binding energy. We find that the Xe U3O cluster gives Xe diffusion coefficients that are higher for intrinsic conditions than under irradiation over a wide range of temperatures. Under irradiation the fast-­moving Xe U3O cluster recombines quickly with irradiation-induced interstitial U ions, while this mechanism is less important for intrinsic conditions. The net result is higher concentration of the Xe U3O cluster for intrinsic conditions than under irradiation. We speculate that differences in the irradiation conditions and their impact on the Xe U3O cluster can explain the wide range of diffusivities reported in experimental studies. However, all vacancy-­mediated mechanisms underestimate the Xe diffusivity compared to the empirical radiation-­enhanced rate used in most fission gas release models. We investigate the possibility that diffusion of small fission gas bubbles or extended Xe-­vacancy clusters may give rise to the observed radiation-­enhanced diffusion coefficient. These studies highlight the importance of U divacancies and an octahedron coordination of uranium vacancies encompassing a Xe fission gas atom. The latter cluster can migrate via a multistep mechanism with a rather low effective barrier, which together with irradiation-induced clusters of uranium vacancies, gives rise to the irradiation-enhanced diffusion coefficient observed in experiments.« less

Structure, electronic properties, and oxygen incorporation/diffusion characteristics of the Σ 5 TiN(310)[001] tilt grain boundary

NASA Astrophysics Data System (ADS)

McKenna, Keith P.

2018-02-01

First principles calculations are employed to investigate the structure, electronic properties, and oxygen incorporation/diffusion characteristics of the Σ 5 TiN(310) tilt grain boundary with relevance to applications of polycrystalline TiN in microelectronics and protective coatings. We show that the grain boundary does not significantly modify electronic states near the Fermi energy but does induce an upward shift of up to 0.6 eV in a number of deeper occupied bands. We also show that oxygen is preferentially incorporated into the TiN grain boundary (GB) but must overcome relatively high activation energies for further diffusion. These predictions are consistent with the "stuffed barrier model" proposed to explain the good barrier characteristics of TiN. We also show that while the oxidizing power of TiN GBs is not sufficient to reduce HfO2 (a prototypical gate dielectric material), they can act as a scavenger for interstitial oxygen. Altogether, these results provide the much needed atomistic insights into the properties of a model GB in TiN and suggest a number of directions for future investigation.

Metal based gas diffusion layers for enhanced fuel cell performance at high current densities

NASA Astrophysics Data System (ADS)

Hussain, Nabeel; Van Steen, Eric; Tanaka, Shiro; Levecque, Pieter

2017-01-01

The gas diffusion layer strongly influences the performance and durability of polymer electrolyte fuel cells. A major drawback of current carbon fiber based GDLs is the non-controlled variation in porosity resulting in a random micro-structure. Moreover, when subjected to compression these materials show significant reduction in porosity and permeability leading to water management problems and mass transfer losses within the fuel cell. This study investigated the use of uniform perforated metal sheets as GDLs in conjunction with microchannel flowfields. A metal sheet design with a pitch of 110 μm and a hole diameter of 60 μm in combination with an MPL showed superior performance in the high current density region compared to a commercially available carbon paper based GDL in a single cell environment. Fuel cell testing with different oxidants (air, heliox and oxygen) indicate that the metal sheet offers both superior diffusion and reduced flooding in comparison to the carbon based GDL. The presence of the MPL has been found to be critical to the functionality of the metal sheet suggesting that the MPL design may represent an important optimisation parameter for further improvements in performance.

Electron kinetics dependence on gas pressure in laser-induced oxygen plasma experiment: Theoretical analysis

NASA Astrophysics Data System (ADS)

Gamal, Yosr E. E.-D.; Abdellatif, Galila

2017-08-01

A study is performed to investigate the dependency of threshold intensity on gas pressure observed in the measurements of the breakdown of molecular oxygen that carried out by Phuoc (2000) [1]. In this experiment, the breakdown was induced by 532 nm laser radiation of pulse width 5.5 ns and spot size of 8.5 μm, in oxygen over a wide pressure range (190-3000 Torr). The analysis aimed to explore the electron kinetic reliance on gas pressure for the separate contribution of each of the gain and loss processes encountered in this study. The investigation is based on an electron cascade model applied previously in Gamal and Omar (2001) [2] and Gaabour et al. (2013) [3]. This model solves numerically a differential equation designates the time evolution of the electron energy distribution, and a set of rate equations that describe the change of excited states population. The numerical examination of the electron energy distribution function and its parameters revealed that photo-ionization of the excited molecules plays a significant role in enhancing the electron density growth rate over the whole tested gas pressure range. This process is off set by diffusion of electrons out of the focal volume in the low-pressure regime. At atmospheric pressure electron, collisional processes dominate and act mainly to populate the excited states. Hence photo-ionization becomes efficient and compete with the encountered loss processes (electron diffusion, vibrational excitation of the ground state molecules as well as two body attachments). At high pressures ( 3000 Torr) three body attachments are found to be the primary cause of losses which deplete the electron density and hence results in the slow decrease of the threshold intensity.

Oxide nucleation on thin films of copper during in situ oxidation in an electron microscope

NASA Technical Reports Server (NTRS)

Heinemann, K.; Rao, D. B.; Douglass, D. L.

1975-01-01

Single-crystal copper thin films were oxidized at an isothermal temperature of 425 C and at an oxygen partial pressure of 0.005 torr. Specimens were prepared by epitaxial vapor deposition onto polished faces of rocksalt and were mounted in a hot stage inside the ultrahigh-vacuum chamber of a high-resolution electron microscope. An induction period of roughly 30 min was established which was independent of the film thickness but depended strongly on the oxygen partial pressure and to exposure to oxygen prior to oxidation. Neither stacking faults nor dislocations were found to be associated with the Cu2O nucleation sites. The experimental data, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving the formation of a surface charge layer, oxygen saturation of the metal with formation of a supersaturated zone near the surface, and nucleation followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

Smooth Interfacial Scavenging for Resistive Switching Oxide via the Formation of Highly Uniform Layers of Amorphous TaOx.

PubMed

Tsurumaki-Fukuchi, Atsushi; Nakagawa, Ryosuke; Arita, Masashi; Takahashi, Yasuo

2018-02-14

We demonstrate that the inclusion of a Ta interfacial layer is a remarkably effective strategy for forming interfacial oxygen defects at metal/oxide junctions. The insertion of an interfacial layer of a reactive metal, that is, a "scavenging" layer, has been recently proposed as a way to create a high concentration of oxygen defects at an interface in redox-based resistive switching devices, and growing interest has been given to the underlying mechanism. Through structural and chemical analyses of Pt/metal/SrTiO 3 /Pt structures, we reveal that the rate and amount of oxygen scavenging are not directly determined by the formation free energies in the oxidation reactions of the scavenging metal and unveil the important roles of oxygen diffusibility. Active oxygen scavenging and highly uniform oxidation via scavenging are revealed for a Ta interfacial layer with high oxygen diffusibility. In addition, the Ta scavenging layer is shown to exhibit a highly uniform structure and to form a very flat interface with SrTiO 3 , which are advantageous for the fabrication of a steep metal/oxide contact.

Impact of oxygen on the coexistence of nitrification, denitrification, and sulfate reduction in oxygen-based membrane aerated biofilm.

PubMed

Liu, Hong; Tan, Shuying; Sheng, Zhiya; Yu, Tong; Liu, Yang

2015-03-01

Membrane aerated biofilms (MABs) are subject to "counter diffusion" of oxygen and substrates. In a membrane aerated biofilm reactor, gases (e.g., oxygen) diffuse through the membrane into the MAB, and liquid substrates pass from the bulk liquid into the MAB. This behavior can result in a unique biofilm structure in terms of microbial composition, distribution, and community activity in the MAB. Previous studies have shown simultaneous aerobic oxidation, nitrification, and denitrification within a single MAB. Using molecular techniques, we investigated the growth of sulfate-reducing bacteria (SRB) in the oxygen-based MAB attached to a flat sheet membrane. Denaturing gradient gel electrophoresis of the amplified 16S rRNA gene fragments and functional gene fragments specific for ammonia-oxidizing bacteria (amoA), denitrifying bacteria (nirK), and SRB (dsrB) demonstrated the coexistence of nitrifiers, denitrifiers, and SRB communities within a single MAB. The functional diversities of SRB and denitrifiers decreased with an increase in the oxygen concentration in the bulk water of the reactor.

Observation of silicon self-diffusion enhanced by the strain originated from end-of-range defects using isotope multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isoda, Taiga; Uematsu, Masashi; Itoh, Kohei M., E-mail: kitoh@appi.keio.ac.jp

2015-09-21

Si self-diffusion in the presence of end-of-range (EOR) defects is investigated using {sup nat}Si/{sup 28}Si isotope multilayers. The isotope multilayers were amorphized by Ge ion implantation, and then annealed at 800–950 °C. The behavior of Si self-interstitials is investigated through the {sup 30}Si self-diffusion. The experimental {sup 30}Si profiles show further enhancement of Si self-diffusion at the EOR defect region, in addition to the transient enhanced diffusion via excess Si self-interstitials by EOR defects. To explain this additional enhanced diffusion, we propose a model which takes into account enhanced diffusion by tensile strain originated from EOR defects. The calculation results basedmore » on this model have well reproduced the experimental {sup 30}Si profiles.« less

Dynamics of Gas Exchange through the Fractal Architecture of the Human Lung, Modeled as an Exactly Solvable Hierarchical Tree

NASA Astrophysics Data System (ADS)

Mayo, Michael; Pfeifer, Peter; Gheorghiu, Stefan

2008-03-01

The acinar airways lie at the periphery of the human lung and are responsible for the transfer of oxygen from air to the blood during respiration. This transfer occurs by the diffusion-reaction of oxygen over the irregular surface of the alveolar membranes lining the acinar airways. We present an exactly solvable diffusion-reaction model on a hierarchically branched tree, allowing a quantitative prediction of the oxygen current over the entire system of acinar airways responsible for the gas exchange. We discuss the effect of diffusional screening, which is strongly coupled to oxygen transport in the human lung. We show that the oxygen current is insensitive to a loss of permeability of the alveolar membranes over a wide range of permeabilities, similar to a ``constant-current source'' in an electric network. Such fault tolerance has been observed in other treatments of the gas exchange in the lung and is obtained here as a fully analytical result.

Modified nondestructive colorimetric method to evaluate the variability of oxygen diffusion rate through wine bottle closures.

PubMed

Brotto, Laura; Battistutta, Franco; Tat, Lara; Comuzzo, Piergiorgio; Zironi, Roberto

2010-03-24

Some modifications to a previous nondestructive colorimetric method that permits evaluation of the oxygen diffusion rate through wine closures were proposed. The method is based on the reaction of indigo carmine solution with oxygen and the tristimulus measurement of the consequent color change. Simplified preparation and measurement procedures were set up, allowing the analysis of a large number of samples simultaneously. The method was applied to the evaluation of the variability within the lot of 20 different types of stoppers (synthetic, produced by molding, and natural cork). The closures were tested at a storage temperature of 26 degrees C. With regard to oxygen permeability, the natural cork stopper showed a low homogeneity within the lot, especially during the first month after bottling, whereas the synthetic closure showed a greater steadiness in the performance. The limits of the colorimetric method were also analyzed, and three possible causes of degradation of the indigo carmine solution were identified: oxygen, light, and heat.

Modification of molybdenum surface by low-energy oxygen implantation at room temperature

NASA Astrophysics Data System (ADS)

Kavre Piltaver, Ivna; Jelovica Badovinac, Ivana; Peter, Robert; Saric, Iva; Petravic, Mladen

2017-12-01

We have studied the initial stages of oxide formation on molybdenum surfaces under 1 keV O2+ ion bombardment at room temperature (RT), using x-ray photoelectron spectroscopy around Mo 3d or O 1s core-levels and the valence band photoemission. The results are compared with the oxidation mechanism of thermally oxidized Mo at RT. The thermal oxidation reveals the formation of a very thin MoO2 layer that prevents any further adsorption of oxygen at higher oxygen doses. Oxygen implantation is more efficient in creating thicker oxide films with the simultaneous formation of several oxide compounds. The oxidation rates of MoO2 and Mo2O5 follow the parabolic growth rate consistent with the mass transport driven by diffusion of either neutral or singly and doubly charged oxygen interstitials. The oxidation of MoO3, which occurs at a later oxidation stage, follows the logarithmic rate driven by the diffusion of cations in an electric field.

Atomic scale observation of oxygen delivery during silver–oxygen nanoparticle catalysed oxidation of carbon nanotubes

PubMed Central

Yue, Yonghai; Yuchi, Datong; Guan, Pengfei; Xu, Jia; Guo, Lin; Liu, Jingyue

2016-01-01

To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars–van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the silver nanoparticles to reach the silver/carbon interfaces and subsequently oxidize the carbon. The lattice distortion caused by oxygen concentration gradient within the silver nanoparticles provides the direct evidence for oxygen diffusion. Such direct observation of atomic scale dynamics provides an important general methodology for investigations of catalytic processes. PMID:27406595

Modeling of Diffusion Based Correlations Between Heart Rate Modulations and Respiration Pattern

DTIC Science & Technology

2001-10-25

1 of 4 MODELING OF DIFFUSION BASED CORRELATIONS BETWEEN HEART RATE MODULATIONS AND RESPIRATION PATTERN R.Langer,(1) Y.Smorzik,(2) S.Akselrod,(1...generations of the bronchial tree. The second stage describes the oxygen diffusion process from the pulmonary gas in the alveoli into the pulmonary...patterns (FRC, TV, rate). Keywords – Modeling, Diffusion , Heart Rate fluctuations I. INTRODUCTION Under a whole-body management perception, the

Effects of myocardial infarction on the distribution and transport of nutrients and oxygen in porcine myocardium.

PubMed

Davis, Bryce H; Morimoto, Yoshihisa; Sample, Chris; Olbrich, Kevin; Leddy, Holly A; Guilak, Farshid; Taylor, Doris A

2012-10-01

One of the primary limitations of cell therapy for myocardial infarction is the low survival of transplanted cells, with a loss of up to 80% of cells within 3 days of delivery. The aims of this study were to investigate the distribution of nutrients and oxygen in infarcted myocardium and to quantify how macromolecular transport properties might affect cell survival. Transmural myocardial infarction was created by controlled cryoablation in pigs. At 30 days post-infarction, oxygen and metabolite levels were measured in the peripheral skeletal muscle, normal myocardium, the infarct border zone, and the infarct interior. The diffusion coefficients of fluorescein or FITC-labeled dextran (0.3-70 kD) were measured in these tissues using fluorescence recovery after photobleaching. The vascular density was measured via endogenous alkaline phosphatase staining. To examine the influence of these infarct conditions on cells therapeutically used in vivo, skeletal myoblast survival and differentiation were studied in vitro under the oxygen and glucose concentrations measured in the infarct tissue. Glucose and oxygen concentrations, along with vascular density were significantly reduced in infarct when compared to the uninjured myocardium and infarct border zone, although the degree of decrease differed. The diffusivity of molecules smaller than 40 kD was significantly higher in infarct center and border zone as compared to uninjured heart. Skeletal myoblast differentiation and survival were decreased stepwise from control to hypoxia, starvation, and ischemia conditions. Although oxygen, glucose, and vascular density were significantly reduced in infarcted myocardium, the rate of macromolecular diffusion was significantly increased, suggesting that diffusive transport may not be inhibited in infarct tissue, and thus the supply of nutrients to transplanted cells may be possible. in vitro studies mimicking infarct conditions suggest that increasing nutrients available to transplanted cells may significantly increase their ability to survive in infarct.

Morphological respiratory diffusion capacity of the lungs of ball pythons (Python regius).

PubMed

Starck, J Matthias; Aupperle, Heike; Kiefer, Ingmar; Weimer, Isabel; Krautwald-Junghanns, Maria-Elisabeth; Pees, Michael

2012-08-01

This study aims at a functional and morphological characterization of the lung of a boid snake. In particular, we were interested to see if the python's lungs are designed with excess capacity as compared to resting and working oxygen demands. Therefore, the morphological respiratory diffusion capacity of ball pythons (Python regius) was examined following a stereological, hierarchically nested approach. The volume of the respiratory exchange tissue was determined using computed tomography. Tissue compartments were quantified using stereological methods on light microscopic images. The tissue diffusion barrier for oxygen transport was characterized and measured using transmission electron micrographs. We found a significant negative correlation between body mass and the volume of respiratory tissue; the lungs of larger snakes had relatively less respiratory tissue. Therefore, mass-specific respiratory tissue was calculated to exclude effects of body mass. The volume of the lung that contains parenchyma was 11.9±5.0mm(3)g(-1). The volume fraction, i.e., the actual pulmonary exchange tissue per lung parenchyma, was 63.22±7.3%; the total respiratory surface was, on average, 0.214±0.129m(2); it was significantly negatively correlated to body mass, with larger snakes having proportionally smaller respiratory surfaces. For the air-blood barrier, a harmonic mean of 0.78±0.05μm was found, with the epithelial layer representing the thickest part of the barrier. Based on these findings, a median diffusion capacity of the tissue barrier ( [Formula: see text] ) of 0.69±0.38ml O(2)min(-1)mmHg(-1) was calculated. Based on published values for blood oxygen concentration, a total oxygen uptake capacity of 61.16mlO(2)min(-1)kg(-1) can be assumed. This value exceeds the maximum demand for oxygen in ball pythons by a factor of 12. We conclude that healthy individuals of P. regius possess a considerable spare capacity for tissue oxygen exchange. Copyright © 2012 Elsevier GmbH. All rights reserved.

Solid state oxygen sensor

DOEpatents

Garzon, Fernando H.; Brosha, Eric L.

1997-01-01

A potentiometric oxygen sensor is formed having a logarithmic response to a differential oxygen concentration while operating as a Nernstian-type sensor. Very thin films of mixed conducting oxide materials form electrode services while permitting diffusional oxygen access to the interface between the zirconia electrolyte and the electrode. Diffusion of oxygen through the mixed oxide is not rate-limiting. Metal electrodes are not used so that morphological changes in the electrode structure do not occur during extended operation at elevated temperatures.

Solid state oxygen sensor

DOEpatents

Garzon, F.H.; Brosha, E.L.

1997-12-09

A potentiometric oxygen sensor is formed having a logarithmic response to a differential oxygen concentration while operating as a Nernstian-type sensor. Very thin films of mixed conducting oxide materials form electrode services while permitting diffusional oxygen access to the interface between the zirconia electrolyte and the electrode. Diffusion of oxygen through the mixed oxide is not rate-limiting. Metal electrodes are not used so that morphological changes in the electrode structure do not occur during extended operation at elevated temperatures. 6 figs.

Kinetics of oxygen reduction in perovskite cathodes for solid oxide fuel cells: A combined modeling and experimental approach

NASA Astrophysics Data System (ADS)

Miara, Lincoln James

Solid oxide fuel cells (SOFCs) have the potential to replace conventional stationary power generation technologies; however, there are major obstacles to commercialization, the most problematic of which is poor cathode performance. Commercialization of SOFCs will follow when the mechanisms occurring at the cathode are more thoroughly understood and adapted for market use. The catalytic reduction of oxygen occurring in SOFC cathodes consists of many elementary steps such as gas phase diffusion, chemical and/or electrochemical reactions which lead to the adsorption and dissociation of molecular oxygen onto the cathode surface, mass transport of oxygen species along the surface and/or through the bulk of the cathode, and full reduction and incorporation of the oxygen at the cathode/electrolyte two or three phase boundary. Electrochemical impedance spectroscopy (EIS) is the main technique used to identify the occurrence of these different processes, but when this technique is used without an explicit model describing the kinetics it is difficult to unravel the interdependence of each of these processes. The purpose of this dissertation is to identify the heterogeneous reactions occurring at the cathode of an SOFC by combining experimental EIS results with mathematical models describing the time dependent behavior of the system. This analysis is performed on two different systems. In the first case, experimental EIS results from patterned half cells composed of Ca-doped lanthanum manganite (LCM)| yttria-doped ZrO2 (YSZ) are modeled to investigate the temperature and partial pressure of oxygen, pO2, dependence of oxygen adsorption/dissociation onto the LCM surface, surface diffusion of atomic oxygen, and electrochemical reduction and incorporation of the oxygen into the electrolyte in the vicinity of the triple phase boundary (TPB). This model determines the time-independent state-space equations from which the Faradaic admittance transfer function is obtained. The unknown rate constants (kad, k des, k1, k1¯ ), and parameters (Ds, Q°, n) arising from the governing equations are estimated from a combination of experiments, mathematical analysis, and numerical data analysis. In the second system, dense patterned films of cathode with composition: La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF-6428) were fabricated on Ga-doped CeO2 coated YSZ substrates. These samples were analyzed by EIS over a temperature and pO 2 range of 600--800 °C and 10-3--1.00 atm, respectively. To understand the EIS results, a 2-dimensional model was developed which accounted for surface oxygen exchange, and both surface and bulk transport of oxygen to the electrolyte interface. The results were obtained by numerically solving a stationary partial differential equation describing the oxygen vacancy distribution in the cathode. From these results, the model impedance was derived and then fitted to the experimental EIS results. From the fitting results the contributions to the impedance from each of the processes were estimated. Also, the surface exchange rate was estimated over the experimental operating conditions. Finally, the results suggest that the surface diffusion occurred by an interstitial type mechanism in this material. The cathode surface is intimately involved in most of the oxygen reduction processes; however, the surface structure and chemistry is typically treated as an extension of the bulk without consideration of the actual surface properties. Recent evidence suggests that significant changes occur to the surface during operation which in turn leads to changes in electrochemical performance. To investigate these phenomena, well-oriented thin films (250 nm in thickness) of Sr-doped lanthanum manginite (LSM) films were grown on single crystals of YSZ (111). Films which were cathodically biased with a -1 V applied dc potential were compared to control samples. The cathodic bias results in both an enhancement in electrochemical performance and a change in surface chemistry. The changes in electrochemical performance were monitored by ES, while the surface changes were tracked with a combination of soft x-ray techniques such as x-ray photoemission spectroscopy and x-ray absorption spectroscopy. The soft x-ray results indicated that the removal of surface passivating phases (i.e., SrO and MnO) are correlated with improved performance. This work demonstrates the success of estimating fundamental parameters, such as diffusivity and surface coverage, from experimental EIS results using a physically realistic model without, as is commonly done, assuming a specific rate limiting step or using an ambiguous equivalent circuit. This allows researchers to fabricate designer cathodes by selecting materials with optimal kinetic properties such as rapid oxygen dissociation and rapid oxygen transport in (or on) the cathode, independent of geometry.

Relation of retinal blood flow and retinal oxygen extraction during stimulation with diffuse luminance flicker

PubMed Central

Palkovits, Stefan; Lasta, Michael; Told, Reinhard; Schmidl, Doreen; Werkmeister, René; Cherecheanu, Alina Popa; Garhöfer, Gerhard; Schmetterer, Leopold

2015-01-01

Cerebral and retinal blood flow are dependent on local neuronal activity. Several studies quantified the increase in cerebral blood flow and oxygen consumption during activity. In the present study we investigated the relation between changes in retinal blood flow and oxygen extraction during stimulation with diffuse luminance flicker and the influence of breathing gas mixtures with different fractions of O2 (FiO2; 100% 15% and 12%). Twenty-four healthy subjects were included. Retinal blood flow was studied by combining measurement of vessel diameters using the Dynamic Vessel Analyser with measurements of blood velocity using laser Doppler velocimetry. Oxygen saturation was measured using spectroscopic reflectometry and oxygen extraction was calculated. Flicker stimulation increased retinal blood flow (57.7 ± 17.8%) and oxygen extraction (34.6 ± 24.1%; p < 0.001 each). During 100% oxygen breathing the response of retinal blood flow and oxygen extraction was increased (p < 0.01 each). By contrast, breathing gas mixtures with 12% and 15% FiO2 did not alter flicker–induced retinal haemodynamic changes. The present study indicates that at a comparable increase in blood flow the increase in oxygen extraction in the retina is larger than in the brain. During systemic hyperoxia the blood flow and oxygen extraction responses to neural stimulation are augmented. The underlying mechanism is unknown. PMID:26672758

Metallated porphyrin based porous organic polymers as efficient electrocatalysts

NASA Astrophysics Data System (ADS)

Lu, Guolong; Zhu, Youlong; Xu, Kongliang; Jin, Yinghua; Ren, Zhiyong Jason; Liu, Zhenning; Zhang, Wei

2015-10-01

Developing efficient, stable and low-cost catalysts for Oxygen Reduction Reaction (ORR) is of great significance to many emerging technologies including fuel cells and metal-air batteries. Herein, we report the development of a cobalt(ii) porphyrin based porous organic polymer (CoPOP) and its pyrolyzed derivatives as highly active ORR catalysts. The as-synthesized CoPOP exhibits high porosity and excellent catalytic performance stability, retaining ~100% constant ORR current over 50 000 s in both alkaline and acidic media. Pyrolysis of CoPOP at various temperatures (600 °C, 800 °C, and 1000 °C) yields the materials consisting of graphitic carbon layers and cobalt nanoparticles, which show greatly enhanced catalytic activity compared to the as-synthesized CoPOP. Among them, CoPOP-800/C pyrolyzed at 800 °C shows the highest specific surface area and ORR activity, displaying the most positive half-wave potential (0.825 V vs. RHE) and the largest limited diffusion current density (5.35 mA cm-2) in an alkaline medium, which are comparable to those of commercial Pt/C (20 wt%) (half-wave potential 0.829 V vs. RHE, limited diffusion current density 5.10 mA cm-2). RDE and RRDE experiments indicate that CoPOP-800/C directly reduces molecular oxygen to water through a 4-e- pathway in both alkaline and acidic media. More importantly, CoPOP-800/C exhibits excellent durability and methanol-tolerance under acidic and alkaline conditions, which surpass the Pt/C (20 wt%) system.Developing efficient, stable and low-cost catalysts for Oxygen Reduction Reaction (ORR) is of great significance to many emerging technologies including fuel cells and metal-air batteries. Herein, we report the development of a cobalt(ii) porphyrin based porous organic polymer (CoPOP) and its pyrolyzed derivatives as highly active ORR catalysts. The as-synthesized CoPOP exhibits high porosity and excellent catalytic performance stability, retaining ~100% constant ORR current over 50 000 s in both alkaline and acidic media. Pyrolysis of CoPOP at various temperatures (600 °C, 800 °C, and 1000 °C) yields the materials consisting of graphitic carbon layers and cobalt nanoparticles, which show greatly enhanced catalytic activity compared to the as-synthesized CoPOP. Among them, CoPOP-800/C pyrolyzed at 800 °C shows the highest specific surface area and ORR activity, displaying the most positive half-wave potential (0.825 V vs. RHE) and the largest limited diffusion current density (5.35 mA cm-2) in an alkaline medium, which are comparable to those of commercial Pt/C (20 wt%) (half-wave potential 0.829 V vs. RHE, limited diffusion current density 5.10 mA cm-2). RDE and RRDE experiments indicate that CoPOP-800/C directly reduces molecular oxygen to water through a 4-e- pathway in both alkaline and acidic media. More importantly, CoPOP-800/C exhibits excellent durability and methanol-tolerance under acidic and alkaline conditions, which surpass the Pt/C (20 wt%) system. Electronic supplementary information (ESI) available: Details of the experimental section, powder X-ray diffraction (PXRD) data, scanning electron microscopy (FE-SEM) images, Fourier transform infrared spectroscopy (FT-IR) data, and additional electrochemical data. See DOI: 10.1039/c5nr05324b

Ethanol flame synthesis of carbon nanotubes in deficient oxygen environments

NASA Astrophysics Data System (ADS)

Hu, Wei-Chieh; Lin, Ta-Hui

2016-04-01

In this study, carbon nanotubes (CNTs) were synthesized using ethanol diffusion flames in a stagnation-flow system composed of an upper oxidizer duct and a lower liquid pool. In the experiments, a gaseous mixture of oxygen and nitrogen flowed from the upper oxidizer duct, and then impinged onto the vertically aligned ethanol pool to generate a planar and steady diffusion flame in a deficient oxygen environment. A nascent nickel mesh was used as the catalytic metal substrate to collect deposited materials. The effect of low oxygen concentration on the formation of CNTs was explored. The oxygen concentration significantly influenced the flame environment and thus the synthesized carbon products. Lowering the oxygen concentration increased the yield, diameter, and uniformity of CNTs. The optimal operating conditions for CNT synthesis were an oxygen concentration in the range of 15%-19%, a flame temperature in the range of 460 °C-870 °C, and a sampling position of 0.5-1 mm below the upper edge of the blue flame front. It is noteworthy that the concentration gradient of C2 species and CO governed the CNT growth directly. CNTs were successfully fabricated in regions with uniform C2 species and CO distributions.

Microscale measurements of oxygen concentration across the thickness of diffusion media in operating polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Epting, William K.; Litster, Shawn

2016-02-01

Although polymer electrolyte fuel cells (PEFCs) offer promise as efficient, low emission power sources, the large amount of platinum catalyst used for the cathode's oxygen reduction (ORR) results in high costs. One approach to using less Pt is to increase the oxygen concentration at the catalyst by reducing the oxygen transport resistances. An important resistance is that of the diffusion media (DM). The DM are highly heterogeneous porous carbon fiber substrates with a graded composition of additives across their thickness. In this work we use an oxygen microsensor with a micro-positioning system to measure the oxygen concentration and presence of liquid water in the pores at discrete points across the thickness of a commercial carbon felt DM in operating PEFCs. Under conditions with no liquid water, the DM accounts for 60% of the oxygen depletion, with 60-70% of that depletion being due to the thin microporous layer (MPL) on the catalyst layer (CL) side. Using concentration gradient data, we quantify the non-uniform local transport resistance across the DM and relate it to high resolution 3D X-ray computed tomography of the same DM.

Redox and fungicidal properties of phthalocyanine metal complexes as related to active oxygen.

PubMed

Vol'pin, M E; Novodarova, G N; Krainova NYu; Lapikova, V P; Aver'yanov, A A

2000-10-01

Some chemical and fungicidal effects of 20 phthalocyanines of Co, Fe, Cu, and Al were studied. Under dark conditions, these complexes reduced nitroblue tetrazolium in the presence of KCN, accelerated the autoxidation of ascorbate or hydroquinone and decomposed hydrogen peroxide. In the later reaction, hydroxyl radical was generated as evidenced with the deoxyribose assay. The inhibition by superoxide dismutase and catalase of catalyzed autoxidation of ascorbate suggests the participation of superoxide anion-radical and hydrogen peroxide in the reaction. Most complexes were toxic to the fungus Magnaporthe grisea which causes blast disease of rice. The toxicity was enhanced by light being diminished by antioxidant reagents sequestering active oxygen species. Some complexes (including nontoxic ones), after 1-day contact with a leaf surface of the disease-susceptible rice cultivar, induced the fungitoxicity of leaf diffusate. This toxicity was also light-activated and sensitive to antioxidant reagents. Several complexes, when added to inocula, decreased 2-3 times the frequency of the compatible symptoms of the blast. It is suggested that in planta, the dark redox activity of phthalocyanines along with their photosensitization promote the generation of active oxygen, which damages the parasite and, therefore, favors disease resistance.

Lateral diffusion contributes to FRET from lanthanide-tagged membrane proteins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lan, Tien-Hung; Wu, Guangyu; Lambert, Nevin A., E-mail: nelambert@gru.edu

2015-08-14

Diffusion can enhance Förster resonance energy transfer (FRET) when donors or acceptors diffuse distances that are similar to the distances separating them during the donor's excited state lifetime. Lanthanide donors remain in the excited state for milliseconds, which makes them useful for time-resolved FRET applications but also allows time for diffusion to enhance energy transfer. Here we show that diffusion dramatically enhances FRET between membrane proteins labeled with lanthanide donors. This phenomenon complicates interpretation of experiments that use long-lived donors to infer association or proximity of mobile membrane proteins, but also offers a method of monitoring diffusion in membrane domainsmore » in real time in living cells. - Highlights: • Diffusion enhances TR-FRET from membrane proteins labeled with lanthanide donors. • Diffusion-dependent FRET can overshadow FRET due to oligomerization or clustering. • FRET studies using lanthanide-tagged membrane proteins should consider diffusion. • FRET from lanthanide donors can be used to monitor membrane protein diffusion.« less

Diffusion of neon in white dwarf stars.

PubMed

Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

2010-12-01

Sedimentation of the neutron rich isotope 22Ne may be an important source of gravitational energy during the cooling of white dwarf stars. This depends on the diffusion constant for 22Ne in strongly coupled plasma mixtures. We calculate self-diffusion constants D(i) from molecular dynamics simulations of carbon, oxygen, and neon mixtures. We find that D(i) in a mixture does not differ greatly from earlier one component plasma results. For strong coupling (coulomb parameter Γ> few), D(i) has a modest dependence on the charge Z(i) of the ion species, D(i)∝Z(i)(-2/3). However, D(i) depends more strongly on Z(i) for weak coupling (smaller Γ). We conclude that the self-diffusion constant D(Ne) for 22Ne in carbon, oxygen, and neon plasma mixtures is accurately known so that uncertainties in D(Ne) should be unimportant for simulations of white dwarf cooling.

BIOLOGICALLY ENHANCED OXYGEN TRANSFER IN THE ACTIVATED SLUDGE PROCESS (JOURNAL)

EPA Science Inventory

Biologically enhanced oxgyen transfer has been a hypothesis to explain observed oxygen transfer rates in activated sludge systems that were well above that predicted from aerator clean-water testing. The enhanced oxygen transfer rates were based on tests using BOD bottle oxygen ...

Dielectric-barrier-discharge plasma-assisted hydrogen diffusion flame. Part 1: Temperature, oxygen, and fuel measurements by one-dimensional fs/ps rotational CARS imaging

DOE PAGES

Retter, Jonathan E.; Elliott, Gregory S.; Kearney, Sean P.

2018-02-21

One-dimensional hybrid fs/ps CARS imaging provides single-laser-shot measurements of temperature, oxygen, and hydrogen in a plasma-assisted hydrogen diffusion flame. The coaxial dielectric-barrier-discharge burner collapses the Re ~50 hydrogen diffusion flame to within ~5 mm of the burner surface at an applied AC potential of 8.75 kV at 18 kHz, coinciding nicely with the full spatial extent of the 1D CARS measurements. Translating the burner through the measurement volume allowed for measurements at numerous radial locations in increments of 1 mm with a resolution of 140 µm × 30 µm × 600 µm, sufficient to resolve spatial gradients in this unsteadymore » flame. Longer probe delays, required for improved dynamic range in regions of high temperature fluctuations, proved difficult to model as a result of a nontrivial decay in the O 2 Raman coherence arising from complexities associated with the triplet ground electronic state of the O 2 molecule. Oxygen linewidths were treated empirically using the observed O 2 coherence decay in spectra acquired from the product gases of lean, near-adiabatic H 2/air flames stabilized on a Hencken flat-flame burner. While still leading to errors up to 10% at worst, the empirically determined Raman linewidth factors eliminated any systematic error in the O 2/N 2 measurements with probe delay. Temperature measurements in the Hencken Burner flames proved to be insensitive to probe pulse delay, providing robust thermometry. Here, demonstration of this technique in both the canonical Hencken burner flames and a new DBD burner validates its effectiveness in producing multiple spatially resolved measurements in combustion environments. Measurements in the DBD burner revealed an unsteady, counterflow flattened flame structure near the fuel orifice which became unsteady as the reaction zone curves towards the surface for larger radial positions. Lastly, fluctuations in the fuel concentration were largest at the source, as the large, plasma-generated, unsteady external toroidal vortex that dominates the transport in this flame provides enhanced ventilation of the flame surface in close proximity to the fuel tube.« less

Dielectric-barrier-discharge plasma-assisted hydrogen diffusion flame. Part 1: Temperature, oxygen, and fuel measurements by one-dimensional fs/ps rotational CARS imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Retter, Jonathan E.; Elliott, Gregory S.; Kearney, Sean P.

One-dimensional hybrid fs/ps CARS imaging provides single-laser-shot measurements of temperature, oxygen, and hydrogen in a plasma-assisted hydrogen diffusion flame. The coaxial dielectric-barrier-discharge burner collapses the Re ~50 hydrogen diffusion flame to within ~5 mm of the burner surface at an applied AC potential of 8.75 kV at 18 kHz, coinciding nicely with the full spatial extent of the 1D CARS measurements. Translating the burner through the measurement volume allowed for measurements at numerous radial locations in increments of 1 mm with a resolution of 140 µm × 30 µm × 600 µm, sufficient to resolve spatial gradients in this unsteadymore » flame. Longer probe delays, required for improved dynamic range in regions of high temperature fluctuations, proved difficult to model as a result of a nontrivial decay in the O 2 Raman coherence arising from complexities associated with the triplet ground electronic state of the O 2 molecule. Oxygen linewidths were treated empirically using the observed O 2 coherence decay in spectra acquired from the product gases of lean, near-adiabatic H 2/air flames stabilized on a Hencken flat-flame burner. While still leading to errors up to 10% at worst, the empirically determined Raman linewidth factors eliminated any systematic error in the O 2/N 2 measurements with probe delay. Temperature measurements in the Hencken Burner flames proved to be insensitive to probe pulse delay, providing robust thermometry. Here, demonstration of this technique in both the canonical Hencken burner flames and a new DBD burner validates its effectiveness in producing multiple spatially resolved measurements in combustion environments. Measurements in the DBD burner revealed an unsteady, counterflow flattened flame structure near the fuel orifice which became unsteady as the reaction zone curves towards the surface for larger radial positions. Lastly, fluctuations in the fuel concentration were largest at the source, as the large, plasma-generated, unsteady external toroidal vortex that dominates the transport in this flame provides enhanced ventilation of the flame surface in close proximity to the fuel tube.« less

Cubic PdNP-based air-breathing cathodes integrated in glucose hybrid biofuel cells

NASA Astrophysics Data System (ADS)

Faggion Junior, D.; Haddad, R.; Giroud, F.; Holzinger, M.; Maduro de Campos, C. E.; Acuña, J. J. S.; Domingos, J. B.; Cosnier, S.

2016-05-01

Cubic Pd nanoparticles (PdNPs) were synthesized using ascorbic acid as a reducing agent and were evaluated for the catalytic oxygen reduction reaction. PdNPs were confined with multiwalled carbon nanotube (MWCNT) dispersions to form black suspensions and these inks were dropcast onto glassy carbon electrodes. Different nanoparticle sizes were synthesized and investigated upon oxygen reduction capacities (onset potential and electrocatalytic current densities) under O2 saturated conditions at varying pH values. Strong evidence of O2 diffusion limitation was demonstrated. In order to overcome oxygen concentration and diffusion limitations in solution, we used a gas diffusion layer to create a PdNP-based air-breathing cathode, which delivered -1.5 mA cm-2 at 0.0 V with an onset potential of 0.4 V. This air-breathing cathode was combined with a specially designed phenanthrolinequinone/glucose dehydrogenase-based anode to form a complete glucose/O2 hybrid bio-fuel cell providing an open circuit voltage of 0.554 V and delivering a maximal power output of 184 +/- 21 μW cm-2 at 0.19 V and pH 7.0.Cubic Pd nanoparticles (PdNPs) were synthesized using ascorbic acid as a reducing agent and were evaluated for the catalytic oxygen reduction reaction. PdNPs were confined with multiwalled carbon nanotube (MWCNT) dispersions to form black suspensions and these inks were dropcast onto glassy carbon electrodes. Different nanoparticle sizes were synthesized and investigated upon oxygen reduction capacities (onset potential and electrocatalytic current densities) under O2 saturated conditions at varying pH values. Strong evidence of O2 diffusion limitation was demonstrated. In order to overcome oxygen concentration and diffusion limitations in solution, we used a gas diffusion layer to create a PdNP-based air-breathing cathode, which delivered -1.5 mA cm-2 at 0.0 V with an onset potential of 0.4 V. This air-breathing cathode was combined with a specially designed phenanthrolinequinone/glucose dehydrogenase-based anode to form a complete glucose/O2 hybrid bio-fuel cell providing an open circuit voltage of 0.554 V and delivering a maximal power output of 184 +/- 21 μW cm-2 at 0.19 V and pH 7.0. Electronic supplementary information (ESI) available: Physical characterization, Fig. S1-S4 electrochemical experiments Fig. S5-S11. See DOI: 10.1039/c6nr01245k

Gas diffusion layers coated with a microporous layer containing hydrophilic carbon nanotubes for performance enhancement of polymer electrolyte fuel cells under both low and high humidity conditions

NASA Astrophysics Data System (ADS)

Kitahara, Tatsumi; Nakajima, Hironori; Okamura, Kosuke

2015-06-01

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) composed of carbon black and polytetrafluoroethylene (PTFE) have been commonly used to improve the water management characteristics of polymer electrolyte fuel cells (PEFCs). However, the hydrophobic MPL coated GDL designed to prevent dehydration of the membrane under low humidity conditions is generally inferior at reducing flooding under high humidity conditions. It is therefore important to develop a robust MPL coated GDL that can enhance the PEFC performance regardless of the humidity conditions. In the present study, a GDL coated with an MPL containing hydrophilic carbon nanotubes (CNTs) was developed. The less hydrophobic pores incorporating CNTs are effective at conserving the membrane humidity under low humidity conditions. The MPL with CNTs is also effective at expelling excess water from the catalyst layer while maintaining oxygen flow pathways from the GDL substrate, allowing the mean flow pore diameter to be decreased to 2 μm without reducing the ability of the MPL to prevent flooding under high humidity conditions. An MPL coated GDL with a CNT content of 4 mass% exhibits significantly higher performance under both low and high humidity conditions than a hydrophobic MPL coated GDL.

Fabrication of Polyimide Membrane Incorporated with Functional Graphene Oxide for CO2 Separation: The Effects of GO Surface Modification on Membrane Performance.

PubMed

Wang, Ting; Cheng, Cheng; Wu, Li-Guang; Shen, Jiang-Nan; Van der Bruggen, Bart; Chen, Qian; Chen, Di; Dong, Chun-Ying

2017-06-06

Two kinds of isocyanate were used to modify graphene oxide (GO) samples. Then, polyimide (PI) hybrid membranes containing GO and modified GO were prepared by in situ polymerization. The permeation of CO 2 and N 2 was studied using these novel membranes. The morphology experiments showed that the isocyanate groups were successfully grafted on the surface of GO by replacement of the oxygen-containing functional groups. After modification, the surface polarity of the GO increased, and more defect structures were introduced into the GO surface. This resulted in a good distribution of more modified GO samples in the PI polymer matrix. Thus, the PI hybrid membranes incorporated by modified GO samples showed a high gas permeability and ideal selectivity of membranes. In addition, enhancement of the selectivity due to the solubility of CO 2 played a major role in the increase in the separation performance of the hybrid membranes for CO 2 , although the diffusion coefficients for CO 2 also increased. Both the higher condensability and the strong affinity between CO 2 molecules and GO in the polymer matrix caused an enhancement of the solubility selectivity higher than the diffusion selectivity after GO surface modification.

Linear bubble plume model for hypolimnetic oxygenation: Full-scale validation and sensitivity analysis

NASA Astrophysics Data System (ADS)

Singleton, V. L.; Gantzer, P.; Little, J. C.

2007-02-01

An existing linear bubble plume model was improved, and data collected from a full-scale diffuser installed in Spring Hollow Reservoir, Virginia, were used to validate the model. The depth of maximum plume rise was simulated well for two of the three diffuser tests. Temperature predictions deviated from measured profiles near the maximum plume rise height, but predicted dissolved oxygen profiles compared very well with observations. A sensitivity analysis was performed. The gas flow rate had the greatest effect on predicted plume rise height and induced water flow rate, both of which were directly proportional to gas flow rate. Oxygen transfer within the hypolimnion was independent of all parameters except initial bubble radius and was inversely proportional for radii greater than approximately 1 mm. The results of this work suggest that plume dynamics and oxygen transfer can successfully be predicted for linear bubble plumes using the discrete-bubble approach.

Toward highly efficient electrocatalyst for Li–O 2 batteries using biphasic N-doping cobalt@graphene multiple-capsule heterostructures

DOE PAGES

Tan, Guoqiang; Chong, Lina; Amine, Rachid; ...

2017-04-12

To promote lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport, and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electro-active zones possible; furthermore, the colander-like porous electrode facilitates themore » oxygen diffusion, catalytic reaction, and stable deposition of discharge products. Finally, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.« less

Redistribution of oxygen ions in single crystal YBa2Cu3O7-x owing to external hydrostatic pressure

NASA Astrophysics Data System (ADS)

Boiko, Yu. I.; Bogdanov, V. V.; Vovk, R. V.; Khadzhai, G. Ya.; Savich, S. V.

2018-01-01

The effect of high hydrostatic pressure on the temperature dependences of the electrical resistance in the basal plane of single crystal YBa2Cu3O7-x with an oxygen deficit is studied. It is found that an external hydrostatic pressure P ≈ 7 kbar substantially intensifies the diffusive coalescence of oxygen clusters, i.e., causes an increase in their average size. This, in turn, produces an increased number of negative U-centers whose presence leads to the appearance of a phase capable of generating paired carriers of electrical charge and is, therefore, characterized by a higher transition temperature Tc. Changes in the form of the temperature and time dependences of the electrical resistivity under external hydrostatic pressure are discussed in terms of this same hypothesis regarding the mechanism of diffusive coalescence of oxygen clusters.

Toward Highly Efficient Electrocatalyst for Li–O 2 Batteries Using Biphasic N-Doping Cobalt@Graphene Multiple-Capsule Heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, Guoqiang; Chong, Lina; Amine, Rachid

For the promotion of lithium oxygen batteries available for :practical applications, the development of advanced cathode catalysts with low-high activity, and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@grapbene Multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium oxygen cells. 'The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electroactive zones possible; furthermore the colander-like porousmore » electrode facilitates the oxygen diffusion, catalytic reaction,and stable deposition of discharge products. As a result, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.« less

Toward highly efficient electrocatalyst for Li–O 2 batteries using biphasic N-doping cobalt@graphene multiple-capsule heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, Guoqiang; Chong, Lina; Amine, Rachid

To promote lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport, and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electro-active zones possible; furthermore, the colander-like porous electrode facilitates themore » oxygen diffusion, catalytic reaction, and stable deposition of discharge products. Finally, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.« less

Toward Highly Efficient Electrocatalyst for Li-O2 Batteries Using Biphasic N-Doping Cobalt@Graphene Multiple-Capsule Heterostructures.

PubMed

Tan, Guoqiang; Chong, Lina; Amine, Rachid; Lu, Jun; Liu, Cong; Yuan, Yifei; Wen, Jianguo; He, Kun; Bi, Xuanxuan; Guo, Yuanyuan; Wang, Hsien-Hau; Shahbazian-Yassar, Reza; Al Hallaj, Said; Miller, Dean J; Liu, Dijia; Amine, Khalil

2017-05-10

For the promotion of lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity, and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electroactive zones possible; furthermore, the colander-like porous electrode facilitates the oxygen diffusion, catalytic reaction, and stable deposition of discharge products. As a result, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.

Unipolar resistive switching behaviors and mechanisms in an annealed Ni/ZrO2/TaN memory device

NASA Astrophysics Data System (ADS)

Tsai, Tsung-Ling; Ho, Tsung-Han; Tseng, Tseung-Yuen

2015-01-01

The effects of Ni/ZrO2/TaN resistive switching memory devices without and with a 400 °C annealing process on switching properties are investigated. The devices exhibit unipolar resistive switching behaviors with low set and reset voltages because of a large amount of Ni diffusion with no reaction with ZrO2 after the annealing process, which is confirmed by ToF-SIMS and XPS analyses. A physical model based on a Ni filament is constructed to explain such phenomena. The device that undergoes the 400 °C annealing process exhibits an excellent endurance of more than 1.5  ×  104 cycles. The improvement can be attributed to the enhancement of oxygen ion migration along grain boundaries, which result in less oxygen ion consumption during the reset process. The device also performs good retention up to 105 s at 150 °C. Therefore, it has great potential for high-density nonvolatile memory applications.

Effect of Gas Pressure on Polarization of SOFC Cathode Prepared by Plasma Spray

NASA Astrophysics Data System (ADS)

Li, Cheng-Xin; Wang, Zhun-Zhun; Liu, Shuai; Li, Chang-Jiu

2013-06-01

A cermet-supported tubular SOFC was fabricated using thermal spray. The cell performance was investigated at temperatures from 750 to 900 °C and pressures from 0.1 to 0.5 MPa to examine the effect of operating gas pressure on the cell performance. The influence of gas pressure on the cathodic polarization was studied through the electrochemical impedance approach to examine the controlling electrochemical processes during cell operation. Results show that increasing the operating gas pressure improves the power output performance significantly. When the gas pressure is increased from 0.1 to 0.3 MPa, the maximum power density is increased by a factor of 32% at a temperature of 800 °C. The cathode polarization decreases significantly with the increase of the gas pressure. The electrochemical analysis shows that the main control processes of the cathode reaction are the oxygen species transfer at the three-phase boundary and oxygen diffusion on the surface or in the bulk of the cathode, which are enhanced with increasing gas pressure.

Miniaturized Planar Room Temperature Ionic Liquid Electrochemical Gas Sensor for Rapid Multiple Gas Pollutants Monitoring.

PubMed

Wan, Hao; Yin, Heyu; Lin, Lu; Zeng, Xiangqun; Mason, Andrew J

2018-02-01

The growing impact of airborne pollutants and explosive gases on human health and occupational safety has escalated the demand of sensors to monitor hazardous gases. This paper presents a new miniaturized planar electrochemical gas sensor for rapid measurement of multiple gaseous hazards. The gas sensor features a porous polytetrafluoroethylene substrate that enables fast gas diffusion and room temperature ionic liquid as the electrolyte. Metal sputtering was utilized for platinum electrodes fabrication to enhance adhesion between the electrodes and the substrate. Together with carefully selected electrochemical methods, the miniaturized gas sensor is capable of measuring multiple gases including oxygen, methane, ozone and sulfur dioxide that are important to human health and safety. Compared to its manually-assembled Clark-cell predecessor, this sensor provides better sensitivity, linearity and repeatability, as validated for oxygen monitoring. With solid performance, fast response and miniaturized size, this sensor is promising for deployment in wearable devices for real-time point-of-exposure gas pollutant monitoring.

Improvement of laser molecular beam epitaxy grown SrTiO3 thin film properties by temperature gradient modulation growth

NASA Astrophysics Data System (ADS)

Li, Jin Long; Hao, J. H.; Li, Y. R.

2007-09-01

Oxygen diffusion at the SrTiO3/Si interface was analyzed. A method called temperature gradient modulation growth was introduced to control oxygen diffusion at the interface of SrTiO3/Si. Nanoscale multilayers were grown at different temperatures at the initial growing stage of films. Continuous growth of SrTiO3 films was followed to deposit on the grown sacrificial layers. The interface and crystallinity of SrTiO3/Si were investigated by in situ reflection high energy electron diffraction and x-ray diffraction measurements. It has been shown that the modulated multilayers may help suppress the interfacial diffusion, and therefore improve SrTiO3 thin film properties.

Direct observation of localized radial oxygen migration in functioning tantalum oxide memristors

DOE PAGES

Kumar, Suhas; Graves, Catherine E.; Strachan, John Paul; ...

2016-02-02

Oxygen migration in tantalum oxide, a promising next-generation storage material, is studied using in operando x-ray absorption spectromicroscopy and is used to microphysically describe accelerated evolution of conduction channel and device failure. Furthermore, the resulting ring-like patterns of oxygen concentration are modeled using thermophoretic forces and Fick diffusion, establishing the critical role of temperature-activated oxygen migration that has been under question lately.

Strontium-free rare earth perovskite ferrites with fast oxygen exchange kinetics: Experiment and theory

NASA Astrophysics Data System (ADS)

Berger, Christian; Bucher, Edith; Windischbacher, Andreas; Boese, A. Daniel; Sitte, Werner

2018-03-01

The Sr-free mixed ionic electronic conducting perovskites La0.8Ca0.2FeO3-δ (LCF82) and Pr0.8Ca0.2FeO3-δ (PCF82) were synthesized via a glycine-nitrate process. Crystal structure, phase purity, and lattice constants were determined by XRD and Rietveld analysis. The oxygen exchange kinetics and the electronic conductivity were obtained from in-situ dc-conductivity relaxation experiments at 600-800 °C and 1×10-3≤pO2/bar≤0.1. Both LCF82 and PCF82 show exceptionally fast chemical surface exchange coefficients and chemical diffusion coefficients of oxygen. The oxygen nonstochiometry of LCF82 and PCF82 was determined by precision thermogravimetry. A point defect model was used to calculate the thermodynamic factors of oxygen and to estimate self-diffusion coefficients and ionic conductivities. Density Functional Theory (DFT) calculations on the crystal structure, oxygen vacancy formation as well as oxygen migration energies are in excellent agreement with the experimental values. Due to their favourable properties both LCF82 and PCF82 are of interest for applications in solid oxide fuel cell cathodes, solid oxide electrolyser cell anodes, oxygen separation membranes, catalysts, or electrochemical sensors.

Optical modeling toward optimizing monitoring of intestinal perfusion in trauma patients

NASA Astrophysics Data System (ADS)

Akl, Tony J.; Wilson, Mark A.; Ericson, M. N.; Coté, Gerard L.

2013-02-01

Trauma is the number one cause of death for people between the ages 1 and 44 years in the United States. In addition, according to the Centers of Disease Control and Prevention, injury results in over 31 million emergency department visits annually. Minimizing the resuscitation period in major abdominal injuries increases survival rates by correcting impaired tissue oxygen delivery. Optimization of resuscitation requires a monitoring method to determine sufficient tissue oxygenation. Oxygenation can be assessed by determining the adequacy of tissue perfusion. In this work, we present the design of a wireless perfusion and oxygenation sensor based on photoplethysmography. Through optical modeling, the benefit of using the visible wavelengths 470, 525 and 590nm (around the 525nm hemoglobin isobestic point) for intestinal perfusion monitoring is compared to the typical near infrared (NIR) wavelengths (805nm isobestic point) used in such sensors. Specifically, NIR wavelengths penetrate through the thin intestinal wall ( 4mm) leading to high background signals. However, these visible wavelengths have two times shorter penetration depth that the NIR wavelengths. Monte-Carlo simulations show that the transmittance of the three selected wavelengths is lower by 5 orders of magnitude depending on the perfusion state. Due to the high absorbance of hemoglobin in the visible range, the perfusion signal carried by diffusely reflected light is also enhanced by an order of magnitude while oxygenation signal levels are maintained. In addition, short source-detector separations proved to be beneficial for limiting the probing depth to the thickness of the intestinal wall.

Solubility and diffusion of oxygen in phospholipid membranes.

PubMed

Möller, Matías N; Li, Qian; Chinnaraj, Mathivanan; Cheung, Herbert C; Lancaster, Jack R; Denicola, Ana

2016-11-01

The transport of oxygen and other nonelectrolytes across lipid membranes is known to depend on both diffusion and solubility in the bilayer, and to be affected by changes in the physical state and by the lipid composition, especially the content of cholesterol and unsaturated fatty acids. However, it is not known how these factors affect diffusion and solubility separately. Herein we measured the partition coefficient of oxygen in liposome membranes of dilauroyl-, dimiristoyl- and dipalmitoylphosphatidylcholine in buffer at different temperatures using the equilibrium-shift method with electrochemical detection. The apparent diffusion coefficient was measured following the fluorescence quenching of 1-pyrenedodecanoate inserted in the liposome bilayers under the same conditions. The partition coefficient varied with the temperature and the physical state of the membrane, from below 1 in the gel state to above 2.8 in the liquid-crystalline state in DMPC and DPPC membranes. The partition coefficient was directly proportional to the partial molar volume and was then associated to the increase in free-volume in the membrane as a function of temperature. The apparent diffusion coefficients were corrected by the partition coefficients and found to be nearly the same, with a null dependence on viscosity and physical state of the membrane, probably because the pyrene is disturbing the surrounding lipids and thus becoming insensitive to changes in membrane viscosity. Combining our results with those of others, it is apparent that both solubility and diffusion increase when increasing the temperature or when comparing a membrane in the gel to one in the fluid state. Copyright © 2016 Elsevier B.V. All rights reserved.

Nitrogen-Doped Carbon Nanotube/Graphite Felts as Advanced Electrode Materials for Vanadium Redox Flow Batteries.

PubMed

Wang, Shuangyin; Zhao, Xinsheng; Cochell, Thomas; Manthiram, Arumugam

2012-08-16

Nitrogen-doped carbon nanotubes have been grown, for the first time, on graphite felt (N-CNT/GF) by a chemical vapor deposition approach and examined as an advanced electrode for vanadium redox flow batteries (VRFBs). The unique porous structure and nitrogen doping of N-CNT/GF with increased surface area enhances the battery performance significantly. The enriched porous structure of N-CNTs on graphite felt could potentially facilitate the diffusion of electrolyte, while the N-doping could significantly contribute to the enhanced electrode performance. Specifically, the N-doping (i) modifies the electronic properties of CNT and thereby alters the chemisorption characteristics of the vanadium ions, (ii) generates defect sites that are electrochemically more active, (iii) increases the oxygen species on CNT surface, which is a key factor influencing the VRFB performance, and (iv) makes the N-CNT electrochemically more accessible than the CNT.

Understanding and removing surface states limiting charge transport in TiO2 nanowire arrays for enhanced optoelectronic device performance.

PubMed

Sheng, Xia; Chen, Liping; Xu, Tao; Zhu, Kai; Feng, Xinjian

2016-03-01

Charge transport within electrode materials plays a key role in determining the optoelectronic device performance. Aligned single-crystal TiO 2 nanowire arrays offer an ideal electron transport path and are expected to have higher electron mobility. Unfortunately, their transport is found not to be superior to that in nanoparticle films. Here we show that the low electron transport in rutile TiO 2 nanowires is mainly caused by surface traps in relatively deep energy levels, which cannot be removed by conventional approaches, such as oxygen annealing treatment. Moreover, we demonstrate an effective wet-chemistry approach to minimize these trap states, leading to over 20-fold enhancement in electron diffusion coefficient and 62% improvement in solar cell performance. On the basis of our results, the potential of TiO 2 NWs can be developed and well-utilized, which is significantly important for their practical applications.

Structural basis of mitochondrial dysfunction in response to cytochrome c phosphorylation at tyrosine 48

PubMed Central

Moreno-Beltrán, Blas; Guerra-Castellano, Alejandra; Del Conte, Rebecca; García-Mauriño, Sofía M.; Díaz-Moreno, Sofía; González-Arzola, Katiuska; Santos-Ocaña, Carlos; Velázquez-Campoy, Adrián; De la Rosa, Miguel A.; Turano, Paola; Díaz-Moreno, Irene

2017-01-01

Regulation of mitochondrial activity allows cells to adapt to changing conditions and to control oxidative stress, and its dysfunction can lead to hypoxia-dependent pathologies such as ischemia and cancer. Although cytochrome c phosphorylation—in particular, at tyrosine 48—is a key modulator of mitochondrial signaling, its action and molecular basis remain unknown. Here we mimic phosphorylation of cytochrome c by replacing tyrosine 48 with p-carboxy-methyl-l-phenylalanine (pCMF). The NMR structure of the resulting mutant reveals significant conformational shifts and enhanced dynamics around pCMF that could explain changes observed in its functionality: The phosphomimetic mutation impairs cytochrome c diffusion between respiratory complexes, enhances hemeprotein peroxidase and reactive oxygen species scavenging activities, and hinders caspase-dependent apoptosis. Our findings provide a framework to further investigate the modulation of mitochondrial activity by phosphorylated cytochrome c and to develop novel therapeutic approaches based on its prosurvival effects. PMID:28348229

Method of producing improved microstructure and properties for ceramic superconductors

DOEpatents

Singh, Jitendra P.; Guttschow, Rob A.; Dusek, Joseph T.; Poeppel, Roger B.

1996-01-01

A ceramic superconductor is produced by close control of oxygen partial pressure during sintering of the material. The resulting microstructure of YBa.sub.2 Cu.sub.3 O.sub.x indicates that sintering kinetics are enhanced at reduced p(O.sub.2). The density of specimens sintered at 910.degree. C. increased from 79 to 94% theoretical when p(O.sub.2) was decreased from 0.1 to 0.0001 MPa. The increase in density with decrease in p(O.sub.2) derives from enhanced sintering kinetics, due to increased defect concentration and decreased activation energy of the rate-controlling species undergoing diffusion. Sintering at 910.degree. C. resulted in a fine-grain microstructure, with an average grain size of approximately 4 .mu.m. Such a microstructure results in reduced microcracking, strengths as high as 191 MPa and high critical current density capacity.

Method of producing improved microstructure and properties for ceramic superconductors

DOEpatents

Singh, J.P.; Guttschow, R.A.; Dusek, J.T.; Poeppel, R.B.

1996-06-11

A ceramic superconductor is produced by close control of oxygen partial pressure during sintering of the material. The resulting microstructure of YBa{sub 2}Cu{sub 3}O{sub x} indicates that sintering kinetics are enhanced at reduced p(O{sub 2}). The density of specimens sintered at 910 C increased from 79 to 94% theoretical when p(O{sub 2}) was decreased from 0.1 to 0.0001 MPa. The increase in density with decrease in p(O{sub 2}) derives from enhanced sintering kinetics, due to increased defect concentration and decreased activation energy of the rate-controlling species undergoing diffusion. Sintering at 910 C resulted in a fine-grain microstructure, with an average grain size of approximately 4 {micro}m. Such a microstructure results in reduced microcracking, strengths as high as 191 MPa and high critical current density capacity. 20 figs.

Effect of Sediment Gas Voids and Ebullition on Benthic Solute Exchange.

PubMed

Flury, Sabine; Glud, Ronnie N; Premke, Katrin; McGinnis, Daniel F

2015-09-01

The presence of free gas in sediments and ebullition events can enhance the pore water transport and solute exchange across the sediment-water interface. However, we experimentally and theoretically document that the presence of free gas in sediments can counteract this enhancement effect. The apparent diffusivities (Da) of Rhodamine WT and bromide in sediments containing 8-18% gas (Da,YE) were suppressed by 7-39% compared to the control (no gas) sediments (Da,C). The measured ratios of Da,YE:Da,C were well within the range of ratios predicted by a theoretical soil model for gas-bearing soils. Whereas gas voids in sediments reduce the Da for soluble species, they represent a shortcut for low-soluble species such as methane and oxygen. Therefore, the presence of even minor amounts of gas can increase the fluxes of low-soluble species (i.e., gases) by several factors, while simultaneously suppressing fluxes of dissolved species.

WE-FG-BRA-03: Oxygen Interplay in Hypofractionated Radiotherapy: A Hidden Opportunity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kissick, M; Campos, D; Desai, V

2016-06-15

Purpose: Local oxygen during a radiotherapy fraction has been shown to change over a full range of the oxygen enhancement ratio (OER) during the same time scale as the treatment fraction. Interplay with local oxygen is then likely a concern, especially for hypofractionation. Our experiments that show a strong role for metabolic dynamics suggesting one could manipulate this interplay for more efficacious treatments. Methods: Two published experiments are presented with the same human head and neck cancer cell line (UM-SCC-22B). One is a cell-specific in vitro prompt response to a 10 Gy dose of orthovotage radiation using fluorescence lifetime imagingmore » (FLIM), benchmarked with a Seahorse assay. The other in vivo study uses autocorrelation analysis with blood oxygen level dependent magnetic resonance imaging (MRI-BOLD) on xenografts. In vivo results are verified with diffuse optics using spectra fitting and photoacoustic measurements. All these measurements are at high time resolution: sampling is one per minute. Results: Interplay happens when the radiosensitivity modulates at the same time scale as the radiation. These results show dynamics at these time scales. 1. The dominant time scale of the acute hypoxia in cell line xenografts is shown to be on the order of minutes to tens of minutes: similar to a metabolic oscillation known as the ‘glycolytic oscillator.’ 2. The radiation dose itself alters metabolism within minutes to tens of minutes also. Conclusion: These results vary with cell type. There is a possibility that special timing and dose levels could be used for radiation. Gating could be used for maximal oxygen during treatment. There is an analogy to the interplay discussions with tumor motion, except that an oxygen interplay could more likely be patient-specific at a more fundamental level.« less

Point Defect Structure of Cr203

DTIC Science & Technology

1987-10-01

Calculation of Electron Hole Mobility ........................ 104 6.2.3 Construction of the Defect Concentration vs. Oxygen Pressure Diagram...1000’ to 16000C ............ 123 7.7 Calculated diffusion coefficient vs. oxygen partial pressure diagram for pure Cr203 at 1100 0 C...127 7.10 Calculated parabolic rate constant vs. oxygen partial pressure diagram for pure Cr203 at

Oxygen-Barrier Coating for Titanium

NASA Technical Reports Server (NTRS)

Clark, Ronald K.; Unnam, Jalaiah

1987-01-01

Oxygen-barrier coating for titanium developed to provide effective and low-cost means for protecting titanium alloys from oxygen in environment when alloys used in high-temperature mechanical or structural applications. Provides protective surface layer, which reduces extent of surface oxidation of alloy and forms barrier to diffusion of oxygen, limiting contamination of substrate alloy by oxygen. Consists of submicron layer of aluminum deposited on surface of titanium by electron-beam evaporation, with submicron layer of dioxide sputtered onto aluminum to form coat.

Simultaneous estimation of transcutaneous bilirubin, hemoglobin, and melanin based on diffuse reflectance spectroscopy

NASA Astrophysics Data System (ADS)

Nishidate, Izumi; Abdul, Wares MD.; Ohtsu, Mizuki; Nakano, Kazuya; Haneishi, Hideaki

2018-02-01

We propose a method to estimate transcutaneous bilirubin, hemoglobin, and melanin based on the diffuse reflectance spectroscopy. In the proposed method, the Monte Carlo simulation-based multiple regression analysis for an absorbance spectrum in the visible wavelength region (460-590 nm) is used to specify the concentrations of bilirubin (Cbil), oxygenated hemoglobin (Coh), deoxygenated hemoglobin (Cdh), and melanin (Cm). Using the absorbance spectrum calculated from the measured diffuse reflectance spectrum as a response variable and the extinction coefficients of bilirubin, oxygenated hemoglobin, deoxygenated hemoglobin, and melanin, as predictor variables, multiple regression analysis provides regression coefficients. Concentrations of bilirubin, oxygenated hemoglobin, deoxygenated hemoglobin, and melanin, are then determined from the regression coefficients using conversion vectors that are numerically deduced in advance by the Monte Carlo simulations for light transport in skin. Total hemoglobin concentration (Cth) and tissue oxygen saturation (StO2) are simply calculated from the oxygenated hemoglobin and deoxygenated hemoglobin. In vivo animal experiments with bile duct ligation in rats demonstrated that the estimated Cbil is increased after ligation of bile duct and reaches to around 20 mg/dl at 72 h after the onset of the ligation, which corresponds to the reference value of Cbil measured by a commercially available transcutaneous bilirubin meter. We also performed in vivo experiments with rats while varying the fraction of inspired oxygen (FiO2). Coh and Cdh decreased and increased, respectively, as FiO2 decreased. Consequently, StO2 was dramatically decreased. The results in this study indicate potential of the method for simultaneous evaluation of multiple chromophores in skin tissue.

Thermodynamic calculations of oxygen self-diffusion in mixed-oxide nuclear fuels

DOE PAGES

Parfitt, David C.; Cooper, Michael William; Rushton, Michael J.D.; ...

2016-07-29

Mixed-oxide fuels containing uranium with thorium and/or plutonium may play an important part in future nuclear fuel cycles. There are, however, significantly less data available for these materials than conventional uranium dioxide fuel. In the present study, we employ molecular dynamics calculations to simulate the elastic properties and thermal expansivity of a range of mixed oxide compositions. These are then used to support equations of state and oxygen self-diffusion models to provide a self-consistent prediction of the behaviour of these mixed oxide fuels at arbitrary compositions.

Evidence for Enhanced Matrix Diffusion in Geological Environment

NASA Astrophysics Data System (ADS)

Sato, Kiminori; Fujimoto, Koichiro; Nakata, Masataka; Shikazono, Naotatsu

2013-01-01

Molecular diffusion in rock matrix, called as matrix diffusion, has been appreciated as a static process for elemental migration in geological environment that has been acknowledged in the context of geological disposal of radioactive waste. However, incomprehensible enhancement of matrix diffusion has been reported at a number of field test sites. Here, the matrix diffusion of saline water at Horonobe, Hokkaido, Japan is highlighted directly probing angstrom-scale pores on a field scale up to 1 km by positron--positronium annihilation spectroscopy. The first application of positron--positronium annihilation spectroscopy to field-scale geophysical research reveals the slight variation of angstrom-scale pores influenced by saline water diffusion with complete accuracy. We found widely interconnected 3 Å pores, which offer the pathway of saline water diffusion with the highly enhanced effective matrix diffusion coefficient of 4× 10-6 cm2 s-1. The present findings provide unambiguous evidence that the angstrom-scale pores enhance effective matrix diffusion on a field scale in geological environment.

Decreases in maximal oxygen uptake following long-duration spaceflight: Role of convective and diffusive O2 transport mechanisms.

PubMed

Ade, C J; Broxterman, R M; Moore, A D; Barstow, T J

2017-04-01

We have previously predicted that the decrease in maximal oxygen uptake (V̇o 2max ) that accompanies time in microgravity reflects decrements in both convective and diffusive O 2 transport to the mitochondria of the contracting myocytes. The aim of this investigation was therefore to quantify the relative changes in convective O 2 transport (Q̇o 2 ) and O 2 diffusing capacity (Do 2 ) following long-duration spaceflight. In nine astronauts, resting hemoglobin concentration ([Hb]), V̇o 2max , maximal cardiac output (Q̇ Tmax ), and differences in arterial and venous O 2 contents ([Formula: see text]-[Formula: see text]) were obtained retrospectively for International Space Station Increments 19-33 (April 2009-November 2012). Q̇o 2 and Do 2 were calculated from these variables via integration of Fick's Principle of Mass Conservation and Fick's Law of Diffusion. V̇o 2max significantly decreased from pre- to postflight (-53.9 ± 45.5%, P = 0.008). The significant decrease in Q̇ Tmax (-7.8 ± 9.1%, P = 0.05), despite an unchanged [Hb], resulted in a significantly decreased Q̇o 2 (-11.4 ± 10.5%, P = 0.02). Do 2 significantly decreased from pre- to postflight by -27.5 ± 24.5% ( P = 0.04), as did the peak [Formula: see text]-[Formula: see text] (-9.2 ± 7.5%, P = 0.007). With the use of linear regression analysis, changes in V̇o 2max were significantly correlated with changes in Do 2 ( R 2  = 0.47; P = 0.04). These data suggest that spaceflight decreases both convective and diffusive O 2 transport. These results have practical implications for future long-duration space missions and highlight the need to resolve the specific mechanisms underlying these spaceflight-induced changes along the O 2 transport pathway. NEW & NOTEWORTHY Long-duration spaceflight elicited a significant decrease in maximal oxygen uptake. Given the adverse physiological adaptations to microgravity along the O 2 transport pathway that have been reported, an integrative approach to the determinants of postflight maximal oxygen uptake is needed. We demonstrate that both convective and diffusive oxygen transport are decreased following ~6 mo International Space Station missions. Copyright © 2017 the American Physiological Society.

Effects of temperature and oxygen on growth and differentiation of embryos of the ground skink, Scincella lateralis.

PubMed

Flewelling, Sarena; Parker, Scott L

2015-08-01

Development of reptile embryos is dependent upon adequate oxygen availability to meet embryonic metabolic demand. Metabolic rate of embryos is temperature dependent, with oxygen consumption increasing exponentially as a function of temperature. Because metabolic rate is more temperature sensitive than diffusion, developmental processes are predicted to be oxygen-limited at high temperatures. We tested the hypothesis that the amount of development lizard embryos achieve in the oviduct is dependent upon both temperature and oxygen availability. We evaluated the effect of temperature (23, 33°C) and oxygen concentration (9%, 15%, 21% O2 ) on survival and development of embryos of the oviparous skink Scincella lateralis. We predicted that incubation at 33°C under hypoxic conditions would result in higher embryo mortality due to mismatch between embryo oxygen demand and oxygen supply compared to eggs incubated at 23°C under hypoxic conditions. Embryo mortality was highest at 33°C/9% O2 (86%) compared to 23°C/9% O2 (14%), however, mortality did not differ among any other oxygen-temperature treatment combination. Both temperature and oxygen affected differentiation, but the interaction between temperature and oxygen was not significant. Embryo growth in mass and hatchling mass were affected by oxygen concentration independent of temperature treatment. Differing responses of growth and differentiation to temperature and oxygen treatments suggests that somatic growth may be more sensitive to oxygen availability than differentiation. Results indicate that embryo mortality can occur both via the direct effect of high temperature on cellular function as well as indirectly through thermally induced oxygen diffusion limitation. © 2015 Wiley Periodicals, Inc.

Ti diffusion in ion prebombarded MgO(100). I. A model for quantitative analysis

NASA Astrophysics Data System (ADS)

Lu, M.; Lupu, C.; Styve, V. J.; Lee, S. M.; Rabalais, J. W.

2002-01-01

Enhancement of Ti diffusion in MgO(100) prebombarded with 7 keV Ar+ has been observed. Diffusion was induced by annealing to 1000 °C following the prebombardment and Ti evaporation. Such a sample geometry and experimental procedure alleviates the continuous provision of freely mobile defects introduced by ion irradiation during annealing for diffusion, making diffusion proceed in a non-steady-state condition. Diffusion penetration profiles were obtained by using secondary ion mass spectrometry depth profiling techniques. A model that includes a depth-dependent diffusion coefficient was proposed, which successfully explains the observed non-steady-state radiation enhanced diffusion. The diffusion coefficients are of the order of 10-20 m2/s and are enhanced due to the defect structure inflected by the Ar+ prebombardment.

Oxygen content modulation by nanoscale chemical and electrical patterning in epitaxial SrCoO3-δ (0 < δ ≤ 0.5) thin films.

PubMed

Hu, S; Seidel, J

2016-08-12

Fast controllable redox reactions in solid materials at room temperature are a promising strategy for enhancing the overall performance and lifetime of many energy technology materials and devices. Easy control of oxygen content is a key concept for the realisation of fast catalysis and bulk diffusion at room temperature. Here, high quality epitaxial brownmillerite SrCoO2.5 thin films have been oxidised to perovskite (P) SrCoO3 with NaClO. X-ray diffraction, scanning probe microscopy and x-ray photoelectron spectroscopy measurements were performed to investigate the structural and electronic changes of the material. The oxidised thin films were found to exhibit distinct morphological changes from an atomically flat terrace structure to forming small nanosized islands with boundaries preferentially in [100] or [010] directions all over the surface, relaxing the in-plane strain imposed by the substrate. The conductivity, or oxygen content, of each single island is confined by these textures, which can be locally patterned even further with electric poling. The high charging level at the island boundaries indicates a magnified electric capacity of SCO thin films, which could be exploited in future device geometries. This finding represents a new way of oxygen modulation with associated self-assembled charge confinement to nanoscale boundaries, offering interesting prospects in nanotechnology applications.

Oxygen content modulation by nanoscale chemical and electrical patterning in epitaxial SrCoO3-δ (0 < δ ≤ 0.5) thin films

NASA Astrophysics Data System (ADS)

Hu, S.; Seidel, J.

2016-08-01

Fast controllable redox reactions in solid materials at room temperature are a promising strategy for enhancing the overall performance and lifetime of many energy technology materials and devices. Easy control of oxygen content is a key concept for the realisation of fast catalysis and bulk diffusion at room temperature. Here, high quality epitaxial brownmillerite SrCoO2.5 thin films have been oxidised to perovskite (P) SrCoO3 with NaClO. X-ray diffraction, scanning probe microscopy and x-ray photoelectron spectroscopy measurements were performed to investigate the structural and electronic changes of the material. The oxidised thin films were found to exhibit distinct morphological changes from an atomically flat terrace structure to forming small nanosized islands with boundaries preferentially in [100] or [010] directions all over the surface, relaxing the in-plane strain imposed by the substrate. The conductivity, or oxygen content, of each single island is confined by these textures, which can be locally patterned even further with electric poling. The high charging level at the island boundaries indicates a magnified electric capacity of SCO thin films, which could be exploited in future device geometries. This finding represents a new way of oxygen modulation with associated self-assembled charge confinement to nanoscale boundaries, offering interesting prospects in nanotechnology applications.

Effects of hypobaria and hypoxia on seed germination of six plant species

NASA Astrophysics Data System (ADS)

Tang, Yongkang; Gao, Feng; Guo, Shuangsheng; Li, Fang

2014-10-01

Hypobaria (low pressure) is typically associated with hypoxia (low oxygen partial pressure). There are several advantages of growing higher plants under hypobaria in the moon or mars habitat. The objectives of this research were to investigate the seed germination of six plant species under hypobaric and ambient total pressure conditions. Seeds were sown and germinated under three levels of total atmospheric pressure (101, 30 and 10 kPa) and three levels of oxygen partial pressures (21, 6 and 2 kPa) in an 8-day study. Hypoxia (6 or 2 kPa) significantly inhibited all seed germination under three levels of total atmospheric pressure by increasing the electrical conductivity and the optical density, decreasing the seed germination percentage and seed dehydrogenase activity and inhibiting the growth of the shoots and roots. Hypobaria (30 or 10 kPa) markedly improved seed germination and root growth by enhancing the oxygen diffusion rate under hypoxic conditions (6 or 2 kPa). The seeds of three dicot plants (lettuce, Chinese cabbage and cucumber) were more sensitive to hypoxia caused by hypobaria than were those of three monocot plants (maize, wheat and rice); lettuce and cucumber seeds had the highest sensitivity, whereas rice seeds had the lowest sensitivity. This research demonstrates that six experimental seeds can germinate normally under hypobaria (30 kPa), but the oxygen partial pressure should not be less than 6 kPa.

Effect of Anesthesia Carrier Gas on In-Vivo Circulation Times of Ultrasound Microbubble Contrast Agents in Rats

PubMed Central

Mullin, Lee; Gessner, Ryan; Kwan, James; Kaya, Mehmet; Borden, Mark A.; Dayton, Paul A.

2012-01-01

Purpose Microbubble contrast agents are currently implemented in a variety of both clinical and preclinical ultrasound imaging studies. The therapeutic and diagnostic capabilities of these contrast agents are limited by their short in-vivo lifetimes, and research to lengthen their circulation times is ongoing. In this manuscript, observations are presented from a controlled experiment performed to evaluate differences in circulation times for lipid shelled perfluorocarbon-filled contrast agents circulating within rodents as a function of inhaled anesthesia carrier gas. Methods The effects of two common anesthesia carrier gas selections - pure oxygen and medical air – were observed within five rats. Contrast agent persistence within the kidney was measured and compared for oxygen and air anesthesia carrier gas for six bolus contrast injections in each animal. Simulations were performed to examine microbubble behavior with changes in external environment gases. Results A statistically significant extension of contrast circulation time was observed for animals breathing medical air compared to breathing pure oxygen. Simulations support experimental observations and indicate that enhanced contrast persistence may be explained by reduced ventilation/perfusion mismatch and classical diffusion, in which nitrogen plays a key role by contributing to the volume and diluting other gas species in the microbubble gas core. Conclusion: Using medical air in place of oxygen as the carrier gas for isoflurane anesthesia can increase the circulation lifetime of ultrasound microbubble contrast agents. PMID:21246710

Oxygen and wound care: a review of current therapeutic modalities and future direction.

PubMed

Howard, Michael A; Asmis, Reto; Evans, Karen Kim; Mustoe, Thomas A

2013-01-01

While the importance of oxygen to the wound healing process is well accepted, research and technological advances continue in this field and efforts are ongoing to further utilize oxygen as a therapeutic modality. In this paper, the authors briefly review the role of oxygen in wound healing and discuss the distinct mechanism of action as well as the advantages and disadvantages of the three major oxygen-based therapies currently in clinical use (Hyperbaric Oxygen and Topical Oxygen and Continuous Diffusion of Oxygen), as well as review the existing literature regarding these distinct therapeutic modalities. © 2013 by the Wound Healing Society.

Anomalous dielectric behavior in nanoparticle Eu2O3 : SiO2 glass composite system

NASA Astrophysics Data System (ADS)

Mukherjee, S.; Chen, C. H.; Chou, C. C.; Yang, H. D.

2010-12-01

Eu2O3 (0.5 mol%) nanoparticles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures of 700 °C and above. Compared with the parent material SiO2, this nano-glass composite system shows enhancement of dielectric constant and diffuse phase transition along with magnetodielectric effect around room temperature (~270 K). The observed conduction mechanism is found to be closely related to the thermally activated oxygen vacancies. Magnetodielectric behavior is strongly associated with magnetoresistance changes, depending on the nanoparticle size and separation. Such a material might be treated as a potential candidate for device miniaturization.

ZnO:Gd nanocrystals for fluorescent applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Divya, N. K., E-mail: divyank90@gmail.com; Pradyumnan, P. P.

2016-05-23

Gadolinium doped ZnO crystals within the solubility limit of gadolinium in ZnO matrix were prepared by solid state reaction technique. The method is relatively less expense and enables the production in large scale. The samples were characterised by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), UV/Vis diffuse reflectance spectroscopy and photoluminescence techniques. Fluorescent property studies of gadolinium doped ZnO at room temperature show enhanced visible light emission due to the defects and oxygen vacancies produced via doping. This work reports the impact of gadolinium doping in the structural, optical and luminescent properties of ZnO inmore » detail.« less

High Field Small Animal Magnetic Resonance Oncology Studies

PubMed Central

Bokacheva, Louisa; Ackerstaff, Ellen; LeKaye, H. Carl; Zakian, Kristen; Koutcher, Jason A.

2014-01-01

This review focuses on the applications of high magnetic field magnetic resonance imaging (MRI) and spectroscopy (MRS) to cancer studies in small animals. High field MRI can provide information about tumor physiology, the microenvironment, metabolism, vascularity and cellularity. Such studies are invaluable for understanding tumor growth and proliferation, response to treatment and drug development. The MR techniques reviewed here include 1H, 31P, Chemical Exchange Saturation Transfer (CEST) imaging, and hyperpolarized 13C MR spectroscopy as well as diffusion-weighted, Blood Oxygen Level Dependent (BOLD) contrast imaging, and dynamic contrast-enhanced MR imaging. These methods have been proven effective in animal studies and are highly relevant to human clinical studies. PMID:24374985

A mechanistic investigation of the oxygen fixation hypothesis and oxygen enhancement ratio.

PubMed

Grimes, David Robert; Partridge, Mike

2015-12-04

The presence of oxygen in tumours has substantial impact on treatment outcome; relative to anoxic regions, well-oxygenated cells respond better to radiotherapy by a factor 2.5-3. This increased radio-response is known as the oxygen enhancement ratio. The oxygen effect is most commonly explained by the oxygen fixation hypothesis, which postulates that radical-induced DNA damage can be permanently 'fixed' by molecular oxygen, rendering DNA damage irreparable. While this oxygen effect is important in both existing therapy and for future modalities such a radiation dose-painting, the majority of existing mathematical models for oxygen enhancement are empirical rather than based on the underlying physics and radiochemistry. Here we propose a model of oxygen-enhanced damage from physical first principles, investigating factors that might influence the cell kill. This is fitted to a range of experimental oxygen curves from literature and shown to describe them well, yielding a single robust term for oxygen interaction obtained. The model also reveals a small thermal dependency exists but that this is unlikely to be exploitable.

Effect of porous structure of catalyst layer on effective oxygen diffusion coefficient in polymer electrolyte fuel cell

NASA Astrophysics Data System (ADS)

Inoue, Gen; Kawase, Motoaki

2016-09-01

It is important to reduce the oxygen diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas diffusion coefficient of CL is lower than MPL in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.

Origins and implications of the ordering of oxygen vacancies and localized electrons on partially reduced CeO 2(111)

DOE PAGES

Sutton, Jonathan E.; Beste, Ariana; Steven H. Overbury

2015-10-12

In this study, we use density functional theory to explain the preferred structure of partially reduced CeO 2(111). Low-energy ordered structures are formed when the vacancies are isolated (maximized intervacancy separation) and the size of the Ce 3+ ions is minimized. Both conditions help minimize disruptions to the lattice around the vacancy. The stability of the ordered structures suggests that isolated vacancies are adequate for modeling more complex (e.g., catalytic) systems. Oxygen diffusion barriers are predicted to be low enough that O diffusion between vacancies is thermodynamically controlled at room temperature. The O-diffusion-reaction energies and barriers are decreased when onemore » Ce f electron hops from a nearest-neighbor Ce cation to a next-nearest-neighbor Ce cation, with a barrier that has been estimated to be slightly less than the barrier to O diffusion in the absence of polaron hopping. In conculsion, this indicates that polaron hopping plays a key role in facilitating the overall O diffusion process, and depending on the relative magnitudes of the polaron hopping and O diffusion barriers, polaron hopping may be the kinetically limiting process.« less

An oxygen-vacancy-rich Z-scheme g-C3N4/Pd/TiO2 heterostructure for enhanced visible light photocatalytic performance

NASA Astrophysics Data System (ADS)

Guo, Yanru; Xiao, Limin; Zhang, Min; Li, Qiuye; Yang, Jianjun

2018-05-01

An oxygen-vacancy-rich Z-scheme g-C3N4/Pd/TiO2 ternary nanocomposite was fabricated using nanotubular titanic acid as precursors via a simple photo-deposition of Pd nanoparticles and calcination process. The prepared nanocomposites were investigated by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-visible diffuse reflectance spectroscopy, respectively. For g-C3N4/TiO2 binary nanocomposites, at the optimal content of g-C3N4 (2%), the apparent photocatalytic activity of 2%g-C3N4/TiO2 was 9 times higher than that of pure TiO2 under visible-light illumination. After deposition of Pd (1 wt%) at the contact interface between g-C3N4 and TiO2, the 2%g-C3N4/Pd/TiO2 ternary nanocomposites demonstrated the highest visible-light-driven photocatalytic activity for the degradation of gaseous propylene, which was 16- and 2-fold higher activities than pure TiO2 and 2%g-C3N4/TiO2, respectively. The mechanism for the enhanced photocatalytic performance of the g-C3N4/Pd/TiO2 photo-catalyst is proposed to be based on the efficient separation of photo-generated electron-hole pairs through Z-scheme system, in which uniform dispersity of Pd nanoparticles at contact interface between g-C3N4 and TiO2 and oxygen vacancies promote charge separation.

The effect of dissolved oxygen concentration (DO) on oxygen diffusion and bacterial community structure in moving bed sequencing batch reactor (MBSBR).

PubMed

Cao, Yongfeng; Zhang, Chaosheng; Rong, Hongwei; Zheng, Guilin; Zhao, Limin

2017-01-01

The effect of dissolved oxygen concentration (DO) on simultaneous nitrification and denitrification was studied in a moving bed sequencing batch reactor (MBSBR) by microelectrode measurements and by real-time PCR. In this system, the biofilm grew on polyurethane foam carriers used to treat municipal sewage at five DO concentrations (1.5, 2.5, 3.5, 4.5 and 5.5 mg/L). The results indicated that the MBSBR exhibited good removal of chemical oxygen demand (92.43%) and nitrogen (83.73%) when DO concentration was 2.5 mg/L. Increasing the oxygen concentration in the reactor was inhibitory to denitrification. Microelectrode measurements showed that the thickness of oxygen penetration increased from 1.2 to 2.6 mm when the DO concentration (from 1.5 mg/L to 5.5 mg/L) in the system increased. Oxygen diffusion was not significantly limited by the boundary layer surrounding the carrier and had the largest slope when DO concentration was 2.5 mg/L. The real-time PCR analysis indicated that the amount of the ammonia-oxidizing bacteria and nitrite-oxidizing bacteria increased slowly as DO concentration increased. The proportions of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, as a percentage of the total bacteria, were low with average values of 0.063% and 0.67%, respectively. When the DO concentration was 2.5 mg/L, oxygen diffusion was optimal and ensured the optimal bacterial community structure and activity; under these conditions, the MBSBR was efficient for total inorganic nitrogen removal. Changing the DO concentration could alter the aerobic zone and the bacterial community structure in the biofilm, directly influencing the simultaneous nitrification and denitrification activity in MBSBRs. Copyright © 2016 Elsevier Ltd. All rights reserved.

Adsorption of oxygen on low-index surfaces of the TiAl{sub 3} alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Latyshev, A. M.; Bakulin, A. V.; Kulkova, S. E., E-mail: kulkova@ms.tsc.ru

Method of the projector augmented waves in the plane-wave basis within the generalized-gradient approximation for the exchange-correlation functional has been used to study oxygen adsorption on (001), (100), and (110) low-index surfaces of the TiAl{sub 3} alloy. It has been established that the sites that are most energetically preferred for the adsorption of oxygen are hollow (H) positions on the (001) surface and bridge (B) positions on the (110) and (100) surfaces. Structural and electronic factors that define their energy preference have been discussed. Changes in the atomic and electronic structure of subsurface layers that occur as the oxygen concentrationmore » increases to three monolayers have been analyzed. It has been shown that the formation of chemical bonds of oxygen with both components of the alloy leads to the appearance of states that are split-off from the bottoms of their valence bands, which is accompanied by the formation of a forbidden gap at the Fermi level and by a weakening of the Ti–Al metallic bonds in the alloy. On the Al-terminated (001) and (110) surfaces, the oxidation of aluminum dominates over that of titanium. On the whole, the binding energy of oxygen on the low-index surfaces with a mixed termination is higher than that at the aluminum-terminated surface. The calculation of the diffusion of oxygen in the TiAl{sub 3} alloy has shown that the lowest barriers correspond to the diffusion between tetrahedral positions in the (001) plane; the diffusion of oxygen in the [001] direction occurs through octahedral and tetrahedral positions. An increase in the concentration of aluminum in the alloy favors a reduction in the height of the energy barriers as compared to the corresponding barriers in the γ-TiAl alloy.« less

TRANSIENT BIOGEOCHEMICAL CYCLING AND SEDIMENT OXYGEN DEMAND

EPA Science Inventory

Through this research, the effects of variable sediment accumulation and oxygen concentration on SOD and soluble chemical fluxes will be quantified. This study will enable correct estimates of “diffuser-induced” SOD to be made that will facilitate appropriate desig...

18O-tracer diffusion along nanoscaled Sc2O3/yttria stabilized zirconia (YSZ) multilayers: on the influence of strain.

PubMed

Aydin, Halit; Korte, Carsten; Janek, Jürgen

2013-06-01

The oxygen tracer diffusion coefficient describing transport along nano-/microscaled YSZ/Sc 2 O 3 multilayers as a function of the thick-ness of the ion-conducting YSZ layers has been measured by isotope exchange depth profiling (IEDP), using secondary ion mass spec-trometry (SIMS). The multilayer samples were prepared by pulsed laser deposition (PLD) on (0001) Al 2 O 3 single crystalline substrates. The values for the oxygen tracer diffusion coefficient were analyzed as a combination of contributions from bulk and interface contributions and compared with results from YSZ/Y 2 O 3 -multilayers with similar microstructure. Using the Nernst-Einstein equation as the relation between diffusivity and electrical conductivity we find very good agreement between conductivity and diffusion data, and we exclude substantial electronic conductivity in the multilayers. The effect of hetero-interface transport can be well explained by a simple interface strain model. As the multilayer samples consist of columnar film crystallites with a defined inter-face structure and texture, we also discuss the influence of this particular microstructure on the interfacial strain.

Membrane properties change in fine-pore aeration diffusers: full-scale variations of transfer efficiency and headloss.

PubMed

Rosso, Diego; Libra, Judy A; Wiehe, Wolfgang; Stenstrom, Michael K

2008-05-01

Fine-pore diffusers are the most common aeration system in municipal wastewater treatment. Punched polymeric membranes are often used in fine-pore aeration due to their advantageous initial performance. These membranes are subject to fouling and scaling, resulting in increased headloss and reduced oxygen transfer efficiency, both contributing to increased plant energy costs. This paper describes and discusses the change in material properties for polymeric fine-pore diffusers, comparing new and used membranes. Three different diffuser technologies were tested and sample diffusers from two wastewater treatment facilities were analysed. The polymeric membranes analysed in this paper were composed of ethylene-propylene-diene monomer (EPDM), polyurethane, and silicon. Transfer efficiency is usually lower with longer times in operation, as older, dilated orifices produce larger bubbles, which are unfavourable to mass transfer. At the same time, headloss increases with time in operation, since membranes increase in rigidity and hardness, and fouling and scaling phenomena occur at the orifice opening. Change in polymer properties and laboratory test results correlate with the decrease in oxygen transfer efficiency.

Nitrous Oxide Production in Co- Versus Counter-Diffusion Nitrifying Biofilms

NASA Astrophysics Data System (ADS)

Peng, Lai; Sun, Jing; Liu, Yiwen; Dai, Xiaohu; Ni, Bing-Jie

2016-06-01

For the application of biofilm processes, a better understanding of nitrous oxide (N2O) formation within the biofilm is essential for design and operation of biofilm reactors with minimized N2O emissions. In this work, a previously established N2O model incorporating both ammonia oxidizing bacteria (AOB) denitrification and hydroxylamine (NH2OH) oxidation pathways is applied in two structurally different biofilm systems to assess the effects of co- and counter-diffusion on N2O production. It is demonstrated that the diffusion of NH2OH and oxygen within both types of biofilms would form an anoxic layer with the presence of NH2OH and nitrite ( ), which would result in a high N2O production via AOB denitrification pathway. As a result, AOB denitrification pathway is dominant over NH2OH oxidation pathway within the co- and counter-diffusion biofilms. In comparison, the co-diffusion biofilm may generate substantially higher N2O than the counter-diffusion biofilm due to the higher accumulation of NH2OH in co-diffusion biofilm, especially under the condition of high-strength ammonium influent (500 mg N/L), thick biofilm depth (300 μm) and moderate oxygen loading (~1-~4 m3/d). The effect of co- and counter-diffusion on N2O production from the AOB biofilm is minimal when treating low-strength nitrogenous wastewater.

Nitrous Oxide Production in Co- Versus Counter-Diffusion Nitrifying Biofilms

PubMed Central

Peng, Lai; Sun, Jing; Liu, Yiwen; Dai, Xiaohu; Ni, Bing-Jie

2016-01-01

For the application of biofilm processes, a better understanding of nitrous oxide (N2O) formation within the biofilm is essential for design and operation of biofilm reactors with minimized N2O emissions. In this work, a previously established N2O model incorporating both ammonia oxidizing bacteria (AOB) denitrification and hydroxylamine (NH2OH) oxidation pathways is applied in two structurally different biofilm systems to assess the effects of co- and counter-diffusion on N2O production. It is demonstrated that the diffusion of NH2OH and oxygen within both types of biofilms would form an anoxic layer with the presence of NH2OH and nitrite ( ), which would result in a high N2O production via AOB denitrification pathway. As a result, AOB denitrification pathway is dominant over NH2OH oxidation pathway within the co- and counter-diffusion biofilms. In comparison, the co-diffusion biofilm may generate substantially higher N2O than the counter-diffusion biofilm due to the higher accumulation of NH2OH in co-diffusion biofilm, especially under the condition of high-strength ammonium influent (500 mg N/L), thick biofilm depth (300 μm) and moderate oxygen loading (~1–~4 m3/d). The effect of co- and counter-diffusion on N2O production from the AOB biofilm is minimal when treating low-strength nitrogenous wastewater. PMID:27353382