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

Reactive diffusion in the presence of a diffusion barrier: Experiment and model

NASA Astrophysics Data System (ADS)

Mangelinck, D.; Luo, T.; Girardeaux, C.

2018-05-01

Reactions in thin films and diffusion barriers are important for applications such as protective coatings, electrical contact, and interconnections. In this work, the effect of a barrier on the kinetics of the formation for a single phase by reactive diffusion is investigated from both experimental and modeling point of views. Two types of diffusion barriers are studied: (i) a thin layer of W deposited between a Ni film and Si substrate and (ii) Ni alloy films, Ni(1%W) and Ni(5%Pt), that form a diffusion barrier during the reaction with the Si substrate. The effect of the barriers on the kinetics of δ-Ni2Si formation is determined by in situ X ray diffraction and compared to models that explain the kinetic slowdown induced by both types of barrier. A linear parabolic growth is found for the deposited barrier with an increasing linear contribution for increasing barrier thickness. On the contrary, the growth is mainly parabolic for the barrier formed by the reaction between an alloy film and the substrate. The permeability of the two types of barrier is determined and discussed. The developed models fit well with the dedicated model experiments, leading to a better understanding of the barrier effect on the reactive diffusion and allowing us to predict the barrier behaviour in various applications.

Diffusion barriers

NASA Technical Reports Server (NTRS)

Nicolet, M. A.

1983-01-01

The choice of the metallic film for the contact to a semiconductor device is discussed. One way to try to stabilize a contact is by interposing a thin film of a material that has low diffusivity for the atoms in question. This thin film application is known as a diffusion barrier. Three types of barriers can be distinguished. The stuffed barrier derives its low atomic diffusivity to impurities that concentrate along the extended defects of a polycrystalline layer. Sacrificial barriers exploit the fact that some (elemental) thin films react in a laterally uniform and reproducible fashion. Sacrificial barriers have the advantage that the point of their failure is predictable. Passive barriers are those most closely approximating an ideal barrier. The most-studied case is that of sputtered TiN films. Stuffed barriers may be viewed as passive barriers whose low diffusivity material extends along the defects of the polycrystalline host.

Diffusion chamber system for testing of collagen-based cell migration barriers for separation of ligament enthesis zones in tissue-engineered ACL constructs.

PubMed

Hahner, J; Hoyer, M; Hillig, S; Schulze-Tanzil, G; Meyer, M; Schröpfer, M; Lohan, A; Garbe, L-A; Heinrich, G; Breier, A

2015-01-01

A temporary barrier separating scaffold zones seeded with different cell types prevents faster growing cells from overgrowing co-cultured cells within the same construct. This barrier should allow sufficient nutrient diffusion through the scaffold. The aim of this study was to test the effect of two variants of collagen-based barriers on macromolecule diffusion, viability, and the spreading efficiency of primary ligament cells on embroidered scaffolds. Two collagen barriers, a thread consisting of a twisted film tape and a sponge, were integrated into embroidered poly(lactic-co-caprolactone) and polypropylene scaffolds, which had the dimension of lapine anterior cruciate ligaments (ACL). A diffusion chamber system was designed and established to monitor nutrient diffusion using fluorescein isothiocyanate-labeled dextran of different molecular weights (20, 40, 150, 500 kDa). Vitality of primary lapine ACL cells was tested at days 7 and 14 after seeding using fluorescein diacetate and ethidium bromide staining. Cell spreading on the scaffold surface was measured using histomorphometry. Nuclei staining of the cross-sectioned scaffolds revealed the penetration of ligament cells through both barrier types. The diffusion chamber was suitable to characterize the diffusivity of dextran molecules through embroidered scaffolds with or without integrated collagen barriers. The diffusion coefficients were generally significantly lower in scaffolds with barriers compared to those without barriers. No significant differences between diffusion coefficients of both barrier types were detected. Both barriers were cyto-compatible and prevented most of the ACL cells from crossing the barrier, whereby the collagen thread was easier to handle and allowed a higher rate of cell spreading.

Enhancement of tunneling magnetoresistance by inserting a diffusion barrier in L10-FePd perpendicular magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Zhang, De-Lin; Schliep, Karl B.; Wu, Ryan J.; Quarterman, P.; Reifsnyder Hickey, Danielle; Lv, Yang; Chao, Xiaohui; Li, Hongshi; Chen, Jun-Yang; Zhao, Zhengyang; Jamali, Mahdi; Mkhoyan, K. Andre; Wang, Jian-Ping

2018-04-01

We studied the tunnel magnetoresistance (TMR) of L10-FePd perpendicular magnetic tunnel junctions (p-MTJs) with an FePd free layer and an inserted diffusion barrier. The diffusion barriers studied here (Ta and W) were shown to enhance the TMR ratio of the p-MTJs formed using high-temperature annealing, which are necessary for the formation of high quality L10-FePd films and MgO barriers. The L10-FePd p-MTJ stack was developed with an FePd free layer with a stack of FePd/X/Co20Fe60B20, where X is the diffusion barrier, and patterned into micron-sized MTJ pillars. The addition of the diffusion barrier was found to greatly enhance the magneto-transport behavior of the L10-FePd p-MTJ pillars such that those without a diffusion barrier exhibited negligible TMR ratios (<1.0%), whereas those with a Ta (W) diffusion barrier exhibited TMR ratios of 8.0% (7.0%) at room temperature and 35.0% (46.0%) at 10 K after post-annealing at 350 °C. These results indicate that diffusion barriers could play a crucial role in realizing high TMR ratios in bulk p-MTJs such as those based on FePd and Mn-based perpendicular magnetic anisotropy materials for spintronic applications.

Molecular dynamics simulation of the evolution of hydrophobic defects in one monolayer of a phosphatidylcholine bilayer: relevance for membrane fusion mechanisms.

PubMed Central

Tieleman, D Peter; Bentz, Joe

2002-01-01

The spontaneous formation of the phospholipid bilayer underlies the permeability barrier function of the biological membrane. Tears or defects that expose water to the acyl chains are spontaneously healed by lipid lateral diffusion. However, mechanical barriers, e.g., protein aggregates held in place, could sustain hydrophobic defects. Such defects have been postulated to occur in processes such as membrane fusion. This gives rise to a new question in bilayer structure: What do the lipids do in the absence of lipid lateral diffusion to minimize the free energy of a hydrophobic defect? As a first step to understand this rather fundamental question about bilayer structure, we performed molecular dynamic simulations of up to 10 ns of a planar bilayer from which lipids have been deleted randomly from one monolayer. In one set of simulations, approximately one-half of the lipids in the defect monolayer were restrained to form a mechanical barrier. In the second set, lipids were free to diffuse around. The question was simply whether the defects caused by removing a lipid would aggregate together, forming a large hydrophobic cavity, or whether the membrane would adjust in another way. When there are no mechanical barriers, the lipids in the defect monolayer simply spread out and thin with little effect on the other intact monolayer. In the presence of a mechanical barrier, the behavior of the lipids depends on the size of the defect. When 3 of 64 lipids are removed, the remaining lipids adjust the lower one-half of their chains, but the headgroup structure changes little and the intact monolayer is unaffected. When 6 to 12 lipids are removed, the defect monolayer thins, lipid disorder increases, and lipids from the intact monolayer move toward the defect monolayer. Whereas this is a highly simplified model of a fusion site, this engagement of the intact monolayer into the fusion defect is strikingly consistent with recent results for influenza hemagglutinin mediated fusion. PMID:12202375

Visualizing Molecular Diffusion through Passive Permeability Barriers in Cells: Conventional and Novel Approaches

PubMed Central

Lin, Yu-Chun; Phua, Siew Cheng; Lin, Benjamin; Inoue, Takanari

2013-01-01

Diffusion barriers are universal solutions for cells to achieve distinct organizations, compositions, and activities within a limited space. The influence of diffusion barriers on the spatiotemporal dynamics of signaling molecules often determines cellular physiology and functions. Over the years, the passive permeability barriers in various subcellular locales have been characterized using elaborate analytical techniques. In this review, we will summarize the current state of knowledge on the various passive permeability barriers present in mammalian cells. We will conclude with a description of several conventional techniques and one new approach based on chemically-inducible diffusion trap (C-IDT) for probing permeable barriers. PMID:23731778

Temperature dependence of copper diffusion in different thickness amorphous tungsten/tungsten nitride layer

NASA Astrophysics Data System (ADS)

Asgary, Somayeh; Hantehzadeh, Mohammad Reza; Ghoranneviss, Mahmood

2017-11-01

The amorphous W/WN films with various thickness (10, 30 and 40 nm) and excellent thermal stability were successfully prepared on SiO2/Si substrate with evaporation and reactive evaporation method. The W/WN bilayer has technological importance because of its low resistivity, high melting point, and good diffusion barrier properties between Cu and Si. The thermal stability was evaluated by X-ray diffractometer (XRD) and Scanning Electron Microscope (SEM). In annealing process, the amorphous W/WN barrier crystallized and this phenomenon is supposed to be the start of Cu atoms diffusion through W/WN barrier into Si. With occurrence of the high-resistive Cu3Si phase, the W/WN loses its function as a diffusion barrier. The primary mode of Cu diffusion is the diffusion through grain boundaries that form during heat treatments. The amorphous structure with optimum thickness is the key factor to achieve a superior diffusion barrier characteristic. The results show that the failure temperature increased by increasing the W/WN film thickness from 10 to 30 nm but it did not change by increasing the W/WN film thickness from 30 to 40 nm. It is found that the 10 and 40 nm W/WN films are good diffusion barriers at least up to 800°C while the 30 nm W/WN film shows superior properties as a diffusion barrier, but loses its function as a diffusion barrier at about 900°C (that is 100°C higher than for 10 and 40 nm W/WN films).

[Diffusion and diffusion-osmosis models of the charged macromolecule transfer in barriers of biosystems].

PubMed

Varakin, A I; Mazur, V V; Arkhipova, N V; Serianov, Iu V

2009-01-01

Mathematical models of the transfer of charged macromolecules have been constructed on the basis of the classical equations of electromigration diffusion of Helmholtz-Smolukhovskii, Goldman, and Goldman-Hodgkin-Katz. It was shown that ion transfer in placental (mimicking lipid-protein barriers) and muscle barriers occurs by different mechanisms. In placental barriers, the electromigration diffusion occurs along lipid-protein channels formed due to the conformational deformation of phospholipid and protein molecules with the coefficients of diffusion D = (2.6-3.6) x 10(-8) cm2/s. The transfer in muscle barriers is due to the migration across charged interfibrillar channels with the negative diffusion activation energy, which is explained by changes in the structure of muscle fibers and expenditures of thermal energy for the extrusion of Cl- from channel walls with the diffusion coefficient D = (6.0-10.0) x 10(-6) cm2/s.

Barriers to the widespread adoption of health data standards: an exploratory qualitative study in tertiary healthcare organizations in Saudi Arabia.

PubMed

Alkraiji, Abdullah; Jackson, Thomas; Murray, Ian

2013-04-01

Although health data standards are perceived to be the essential solution for interoperability barriers within medical IT systems, the level of adoption of those standards still remains frustratingly low. Little is known about the barriers facing their adoption within the healthcare organizations context. In addressing this gap in the literature, based on IT related standards adoption theories such as Diffusion of Innovation Theory and the theories surrounding the Economics of Standards, a qualitative multiple-case study was undertaken in Saudi Arabia to investigate those barriers. The results exposed that few standards were adopted because of four broad reasons, managerial, technical, educational and governmental. While some of the findings can be rooted to those related standards theories, others can be underpinned through the normative literature. Core barriers are the lack of a national regulator and a data exchange plan, and the lack of an adequate policy regarding medical IT systems and information management and national healthcare system; also important are technical barriers and the switching costs to the standards. The outcome of this study can be used in forming effective interventions when planning to use health data standards and, in particular those in developing countries.

Interdiffusion and reactions between U-Mo and Zr at 650 °C as a function of time

NASA Astrophysics Data System (ADS)

Park, Y.; Keiser, D. D.; Sohn, Y. H.

2015-01-01

Development of monolithic U-Mo alloy fuel (typically U-10 wt.%Mo) for the Reduced Enrichment for Research and Test Reactors (RERTR) program entails a use of Zr diffusion barrier to eliminate the interdiffusion-reactions between the fuel alloy and Al-alloy cladding. The application of Zr barrier to the U-Mo fuel system requires a co-rolling process that utilizes a soaking temperature of 650 °C, which represents the highest temperature the fuel system is exposed to during both fuel manufacturing and reactor application. Therefore, in this study, development of phase constituents, microstructure and diffusion kinetics of U-10 wt.%Mo and Zr was examined using solid-to-solid diffusion couples annealed at 650 °C for 240, 480 and 720 h. Phase constituents and microstructural development were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Concentration profiles were mapped as diffusion paths on the isothermal ternary phase diagram. Within the diffusion zone, single-phase layers of β-Zr and β-U were observed along with a discontinuous layer of Mo2Zr between the β-Zr and β-U layers. In the vicinity of Mo2Zr phase, islands of α-Zr phases were also found. In addition, acicular α-Zr and U6Zr3Mo phases were observed within the γ-U(Mo) terminal alloy. Growth rate of the interdiffusion-reaction zone was determined to be 7.75 (± 5.84) × 10-16 m2/s at 650 °C, however with an assumption of a certain incubation period.

Visualizing molecular diffusion through passive permeability barriers in cells: conventional and novel approaches.

PubMed

Lin, Yu-Chun; Phua, Siew Cheng; Lin, Benjamin; Inoue, Takanari

2013-08-01

Diffusion barriers are universal solutions for cells to achieve distinct organizations, compositions, and activities within a limited space. The influence of diffusion barriers on the spatiotemporal dynamics of signaling molecules often determines cellular physiology and functions. Over the years, the passive permeability barriers in various subcellular locales have been characterized using elaborate analytical techniques. In this review, we will summarize the current state of knowledge on the various passive permeability barriers present in mammalian cells. We will conclude with a description of several conventional techniques and one new approach based on chemically inducible diffusion trap (CIDT) for probing permeable barriers. Copyright © 2013 Elsevier Ltd. All rights reserved.

Feasibility study of tungsten as a diffusion barrier between nickel-chromium-aluminum and Gamma/Gamma prime - Delta eutectic alloys

NASA Technical Reports Server (NTRS)

Young, S. G.; Zellars, G. R.

1978-01-01

Coating systems proposed for potential use on eutectic alloy components in high-temperature gas turbine engines were studied with emphasis on deterioration of such systems by diffusion. A 1-mil thick W sheet was placed between eutectic alloys and a NiCrAl layer. Layered test specimens were aged at 1100 C for as long as long as 500 hours. Without the W barrier, the delta phase of the eutectic deteriorated by diffusion of Nb into the NiCrAl. Insertion of the W barrier stopped the diffusion of Nb from delta. Chromium diffusion from the NiCrAl into the gamma/gamma prime phase of the eutectic was greatly reduced by the barrier. However, the barrier thickness decreased with time; and W diffused into both the NiCrAl and the eutectic. When the delta platelets were alined parallel to the NiCrAl layer, rather than perpendicular, diffusion into the eutectic was reduced.

Diffusion properties of molecules at the blood-brain interface: potential contributions of astrocyte endfeet to diffusion barrier functions.

PubMed

Nuriya, Mutsuo; Shinotsuka, Takanori; Yasui, Masato

2013-09-01

Molecular diffusion in the extracellular space (ECS) plays a key role in determining tissue physiology and pharmacology. The blood-brain barrier regulates the exchange of substances between the brain and the blood, but the diffusion properties of molecules at this blood-brain interface, particularly around the astrocyte endfeet, are poorly characterized. In this study, we used 2-photon microscopy and acute brain slices of mouse neocortex and directly assessed the diffusion patterns of fluorescent molecules. By observing the diffusion of unconjugated and 10-kDa dextran-conjugated Alexa Fluor 488 from the ECS of the brain parenchyma to the blood vessels, we find various degrees of diffusion barriers at the endfeet: Some allow the invasion of dye inside the endfoot network while others completely block it. Detailed analyses of the time course for dye clearance support the existence of a tight endfoot network capable of acting as a diffusion barrier. Finally, we show that this diffusion pattern collapses under pathological conditions. These data demonstrate the heterogeneous nature of molecular diffusion dynamics around the endfeet and suggest that these structures can serve as the diffusion barrier. Therefore, astrocyte endfeet may add another layer of regulation to the exchange of molecules between blood vessels and brain parenchyma.

Lifetime of Major Histocompatibility Complex Class-I Membrane Clusters Is Controlled by the Actin Cytoskeleton

PubMed Central

Lavi, Yael; Gov, Nir; Edidin, Michael; Gheber, Levi A.

2012-01-01

Lateral heterogeneity of cell membranes has been demonstrated in numerous studies showing anomalous diffusion of membrane proteins; it has been explained by models and experiments suggesting dynamic barriers to free diffusion, that temporarily confine membrane proteins into microscopic patches. This picture, however, comes short of explaining a steady-state patchy distribution of proteins, in face of the transient opening of the barriers. In our previous work we directly imaged persistent clusters of MHC-I, a type I transmembrane protein, and proposed a model of a dynamic equilibrium between proteins newly delivered to the cell surface by vesicle traffic, temporary confinement by dynamic barriers to lateral diffusion, and dispersion of the clusters by diffusion over the dynamic barriers. Our model predicted that the clusters are dynamic, appearing when an exocytic vesicle fuses with the plasma membrane and dispersing with a typical lifetime that depends on lateral diffusion and the dynamics of barriers. In a subsequent work, we showed this to be the case. Here we test another prediction of the model, and show that changing the stability of actin barriers to lateral diffusion changes cluster lifetimes. We also develop a model for the distribution of cluster lifetimes, consistent with the function of barriers to lateral diffusion in maintaining MHC-I clusters. PMID:22500754

Polymeric hydrogen diffusion barrier, high-pressure storage tank so equipped, method of fabricating a storage tank and method of preventing hydrogen diffusion

DOEpatents

Lessing, Paul A [Idaho Falls, ID

2008-07-22

An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.

Polymeric hydrogen diffusion barrier, high-pressure storage tank so equipped, method of fabricating a storage tank and method of preventing hydrogen diffusion

DOEpatents

Lessing, Paul A.

2004-09-07

An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.

Restricted ADP movement in cardiomyocytes: Cytosolic diffusion obstacles are complemented with a small number of open mitochondrial voltage-dependent anion channels.

PubMed

Simson, Päivo; Jepihhina, Natalja; Laasmaa, Martin; Peterson, Pearu; Birkedal, Rikke; Vendelin, Marko

2016-08-01

Adequate intracellular energy transfer is crucial for proper cardiac function. In energy starved failing hearts, partial restoration of energy transfer can rescue mechanical performance. There are two types of diffusion obstacles that interfere with energy transfer from mitochondria to ATPases: mitochondrial outer membrane (MOM) with voltage-dependent anion channel (VDAC) permeable to small hydrophilic molecules and cytoplasmatic diffusion barriers grouping ATP-producers and -consumers. So far, there is no method developed to clearly distinguish the contributions of cytoplasmatic barriers and MOM to the overall diffusion restriction. Furthermore, the number of open VDACs in vivo remains unknown. The aim of this work was to establish the partitioning of intracellular diffusion obstacles in cardiomyocytes. We studied the response of mitochondrial oxidative phosphorylation of permeabilized rat cardiomyocytes to changes in extracellular ADP by recording 3D image stacks of NADH autofluorescence. Using cell-specific mathematical models, we determined the permeability of MOM and cytoplasmatic barriers. We found that only ~2% of VDACs are accessible to cytosolic ADP and cytoplasmatic diffusion barriers reduce the apparent diffusion coefficient by 6-10×. In cardiomyocytes, diffusion barriers in the cytoplasm and by the MOM restrict ADP/ATP diffusion to similar extents suggesting a major role of both barriers in energy transfer and other intracellular processes. Copyright © 2016 Elsevier Ltd. All rights reserved.

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.

Lithium diffusion at Si-C interfaces in silicon-graphene composites

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

Odbadrakh, Khorgolkhuu; McNutt, N. W.; Nicholson, D. M.

2014-08-04

Models of intercalated Li and its diffusion in Si-Graphene interfaces are investigated using density functional theory. Results suggest that the presence of interfaces alters the energetics of Li binding and diffusion significantly compared to bare Si or Graphene surfaces. Our results show that cavities along reconstructed Si surface provide diffusion paths for Li. Diffusion barriers calculated along these cavities are significantly lower than penetration barriers to bulk Si. Interaction with Si surface results in graphene defects, creating Li diffusion paths that are confined along the cavities but have still lower barrier than in bulk Si.

Effect of SiN x diffusion barrier thickness on the structural properties and photocatalytic activity of TiO2 films obtained by sol-gel dip coating and reactive magnetron sputtering.

PubMed

Ghazzal, Mohamed Nawfal; Aubry, Eric; Chaoui, Nouari; Robert, Didier

2015-01-01

We investigate the effect of the thickness of the silicon nitride (SiN x ) diffusion barrier on the structural and photocatalytic efficiency of TiO2 films obtained with different processes. We show that the structural and photocatalytic efficiency of TiO2 films produced using soft chemistry (sol-gel) and physical methods (reactive sputtering) are affected differentially by the intercalating SiN x diffusion barrier. Increasing the thickness of the SiN x diffusion barrier induced a gradual decrease of the crystallite size of TiO2 films obtained by the sol-gel process. However, TiO2 obtained using the reactive sputtering method showed no dependence on the thickness of the SiN x barrier diffusion. The SiN x barrier diffusion showed a beneficial effect on the photocatalytic efficiency of TiO2 films regardless of the synthesis method used. The proposed mechanism leading to the improvement in the photocatalytic efficiency of the TiO2 films obtained by each process was discussed.

The effects of sulfur mustard exposure and freezing on transdermal penetration of tritiated water through ex vivo pig skin.

PubMed

Payne, O J; Graham, S J; Dalton, C H; Spencer, P M; Mansson, R; Jenner, J; Azeke, J; Braue, E

2013-02-01

The percutaneous absorption of tritiated water ((3)H(2)O) through sulfur mustard (SM) exposed abdominal pig skin was measured using in vitro Franz-type static diffusion cells. The barrier function to water permeation following exposure to liquid SM for 8 min and excision 3h later did not change significantly. A small, but statistically significant difference (P<0.05) in steady state penetration (Jss), permeability coefficient (Kp) and lag time (t(L)) of (3)H(2)O was observed between fresh skin and skin stored frozen (-20 °C) for up to two weeks. Steady-state penetration and Kp values were significantly higher (P < 0.05) in skin stored frozen compared with fresh skin. Fresh naïve skin had an average Kp of 1.65 × 10(-3) cm h(-1), whereas frozen naïve skin was 2.04 × 10(-3) cm h(-1). Fresh SM exposed skin had a mean Kp of 1.72 × 10(-3) cm h(-1), whereas frozen SM exposed skin was 2.31 × 10(-3) cm h(-1). Lag times were also shorter (P<0.05) in skin that had been stored frozen. Frozen, SM-exposed porcine abdominal skin may be used for in vitro penetration studies, but effects of treatment and storage on the barrier layer should be taken into account. Copyright © 2012 Elsevier Ltd. All rights reserved.

Diffusion Barriers to Increase the Oxidative Life of Overlay Coatings

NASA Technical Reports Server (NTRS)

Nesbitt, James A.; Lei, Jih-Fen

1999-01-01

Currently, most blades and vanes in the hottest section of aero gas turbine engines require some type of coating for oxidation protection. Newly developed single crystal superalloys have the mechanical potential to operate at increasingly higher component temperatures. However, at these elevated temperatures, coating/substrate interdiffusion can shorten the protective life of the coating. Diffusion barriers between overlay coatings and substrates are being examined to extend the protective life of the coating. A previously- developed finite-difference diffusion model has been modified to predict the oxidative life enhancement due to use of a diffusion barrier. The original diffusion model, designated COSIM, simulates Al diffusion in the coating to the growing oxide scale as well as Al diffusion into the substrate. The COSIM model incorporates an oxide growth and spalling model to provide the rate of Al consumption during cyclic oxidation. Coating failure is predicted when the Al concentration at the coating surface drops to a defined critical level. The modified COSIM model predicts the oxidative life of an overlay coating when a diffusion barrier is present eliminating diffusion of Al from the coating into the substrate. Both the original and the modified diffusion models have been used to predict the effectiveness of a diffusion barrier in extending the protective life of a NiCrAl overlay coating undergoing cyclic oxidation at 1100 C.

A network model of successive partitioning-limited solute diffusion through the stratum corneum.

PubMed

Schumm, Phillip; Scoglio, Caterina M; van der Merwe, Deon

2010-02-07

As the most exposed point of contact with the external environment, the skin is an important barrier to many chemical exposures, including medications, potentially toxic chemicals and cosmetics. Traditional dermal absorption models treat the stratum corneum lipids as a homogenous medium through which solutes diffuse according to Fick's first law of diffusion. This approach does not explain non-linear absorption and irregular distribution patterns within the stratum corneum lipids as observed in experimental data. A network model, based on successive partitioning-limited solute diffusion through the stratum corneum, where the lipid structure is represented by a large, sparse, and regular network where nodes have variable characteristics, offers an alternative, efficient, and flexible approach to dermal absorption modeling that simulates non-linear absorption data patterns. Four model versions are presented: two linear models, which have unlimited node capacities, and two non-linear models, which have limited node capacities. The non-linear model outputs produce absorption to dose relationships that can be best characterized quantitatively by using power equations, similar to the equations used to describe non-linear experimental data.

A sphingolipid-dependent diffusion barrier confines ER stress to the yeast mother cell

PubMed Central

Clay, Lori; Caudron, Fabrice; Denoth-Lippuner, Annina; Boettcher, Barbara; Buvelot Frei, Stéphanie; Snapp, Erik Lee; Barral, Yves

2014-01-01

In many cell types, lateral diffusion barriers compartmentalize the plasma membrane and, at least in budding yeast, the endoplasmic reticulum (ER). However, the molecular nature of these barriers, their mode of action and their cellular functions are unclear. Here, we show that misfolded proteins of the ER remain confined into the mother compartment of budding yeast cells. Confinement required the formation of a lateral diffusion barrier in the form of a distinct domain of the ER-membrane at the bud neck, in a septin-, Bud1 GTPase- and sphingolipid-dependent manner. The sphingolipids, but not Bud1, also contributed to barrier formation in the outer membrane of the dividing nucleus. Barrier-dependent confinement of ER stress into the mother cell promoted aging. Together, our data clarify the physical nature of lateral diffusion barriers in the ER and establish the role of such barriers in the asymmetric segregation of proteotoxic misfolded proteins during cell division and aging. DOI: http://dx.doi.org/10.7554/eLife.01883.001 PMID:24843009

CO Diffusion and Desorption Kinetics in CO2 Ices

NASA Astrophysics Data System (ADS)

Cooke, Ilsa R.; Öberg, Karin I.; Fayolle, Edith C.; Peeler, Zoe; Bergner, Jennifer B.

2018-01-01

The diffusion of species in icy dust grain mantles is a fundamental process that shapes the chemistry of interstellar regions; yet, measurements of diffusion in interstellar ice analogs are scarce. Here we present measurements of CO diffusion into CO2 ice at low temperatures (T = 11–23 K) using CO2 longitudinal optical phonon modes to monitor the level of mixing of initially layered ices. We model the diffusion kinetics using Fick’s second law and find that the temperature-dependent diffusion coefficients are well fit by an Arrhenius equation, giving a diffusion barrier of 300 ± 40 K. The low barrier along with the diffusion kinetics through isotopically labeled layers suggest that CO diffuses through CO2 along pore surfaces rather than through bulk diffusion. In complementary experiments, we measure the desorption energy of CO from CO2 ices deposited at 11–50 K by temperature programmed desorption and find that the desorption barrier ranges from 1240 ± 90 K to 1410 ± 70 K depending on the CO2 deposition temperature and resultant ice porosity. The measured CO–CO2 desorption barriers demonstrate that CO binds equally well to CO2 and H2O ices when both are compact. The CO–CO2 diffusion–desorption barrier ratio ranges from 0.21 to 0.24 dependent on the binding environment during diffusion. The diffusion–desorption ratio is consistent with the above hypothesis that the observed diffusion is a surface process and adds to previous experimental evidence on diffusion in water ice that suggests surface diffusion is important to the mobility of molecules within interstellar ices.

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.

Approximation of effective moisture-diffusion coefficient to characterize performance of a barrier coating

NASA Astrophysics Data System (ADS)

Nagai, Shingo

2013-11-01

We report estimation of the effective diffusion coefficient of moisture through a barrier coating to develop an encapsulation technology for the thin-film electronics industry. This investigation targeted a silicon oxide (SiOx) film that was deposited on a plastic substrate by a large-process-area web coater. Using the finite difference method based on diffusion theory, our estimation of the effective diffusion coefficient of a SiOx film corresponded to that of bulk glass that was previously reported. This result suggested that the low diffusivities of barrier films can be obtained on a mass-production level in the factory. In this investigation, experimental observations and mathematical confirmation revealed the limit of the water vapor transmission rate on the single barrier coating.

How thin barrier metal can be used to prevent Co diffusion in the modern integrated circuits?

NASA Astrophysics Data System (ADS)

Dixit, Hemant; Konar, Aniruddha; Pandey, Rajan; Ethirajan, Tamilmani

2017-11-01

In modern integrated circuits (ICs), billions of transistors are connected to each other via thin metal layers (e.g. copper, cobalt, etc) known as interconnects. At elevated process temperatures, inter-diffusion of atomic species can occur among these metal layers, causing sub-optimal performance of interconnects, which may lead to the failure of an IC. Thus, typically a thin barrier metal layer is used to prevent the inter-diffusion of atomic species within interconnects. For ICs with sub-10 nm transistors (10 nm technology node), the design rule (thickness scaling) demands the thinnest possible barrier layer. Therefore, here we investigate the critical thickness of a titanium-nitride (TiN) barrier that can prevent the cobalt diffusion using multi-scale modeling and simulations. First, we compute the Co diffusion barrier in crystalline and amorphous TiN with the nudged elastic band method within first-principles density functional theory simulations. Later, using the calculated activation energy barriers, we quantify the Co diffusion length in the TiN metal layer with the help of kinetic Monte Carlo simulations. Such a multi-scale modelling approach yields an exact critical thickness of the metal layer sufficient to prevent the Co diffusion in IC interconnects. We obtain a diffusion length of a maximum of 2 nm for a typical process of thermal annealing at 400 °C for 30 min. Our study thus provides useful physical insights for the Co diffusion in the TiN layer and further quantifies the critical thickness (~2 nm) to which the metal barrier layer can be thinned down for sub-10 nm ICs.

CO Diffusion into Amorphous H2O Ices

NASA Astrophysics Data System (ADS)

Lauck, Trish; Karssemeijer, Leendertjan; Shulenberger, Katherine; Rajappan, Mahesh; Öberg, Karin I.; Cuppen, Herma M.

2015-03-01

The mobility of atoms, molecules, and radicals in icy grain mantles regulates ice restructuring, desorption, and chemistry in astrophysical environments. Interstellar ices are dominated by H2O, and diffusion on external and internal (pore) surfaces of H2O-rich ices is therefore a key process to constrain. This study aims to quantify the diffusion kinetics and barrier of the abundant ice constituent CO into H2O-dominated ices at low temperatures (15-23 K), by measuring the mixing rate of initially layered H2O(:CO2)/CO ices. The mixed fraction of CO as a function of time is determined by monitoring the shape of the infrared CO stretching band. Mixing is observed at all investigated temperatures on minute timescales and can be ascribed to CO diffusion in H2O ice pores. The diffusion coefficient and final mixed fraction depend on ice temperature, porosity, thickness, and composition. The experiments are analyzed by applying Fick’s diffusion equation under the assumption that mixing is due to CO diffusion into an immobile H2O ice. The extracted energy barrier for CO diffusion into amorphous H2O ice is ˜160 K. This is effectively a surface diffusion barrier. The derived barrier is low compared to current surface diffusion barriers in use in astrochemical models. Its adoption may significantly change the expected timescales for different ice processes in interstellar environments.

Reduction of diffusion barriers in isolated rat islets improves survival, but not insulin secretion or transplantation outcome

PubMed Central

Janette Williams, S; Huang, Han-Hung; Kover, Karen; Moore, Wayne; Berkland, Cory; Singh, Milind; Smirnova, Irina V; MacGregor, Ronal

2010-01-01

For people with type 1 diabetes and severe hypoglycemic unawareness, islet transplants offer hope for improving the quality of life. However, islet cell death occurs quickly during or after transplantation, requiring large quantities of islets per transplant. The purpose of this study was to determine whether poor function demonstrated in large islets was a result of diffusion barriers and if removing those barriers could improve function and transplantation outcomes. Islets were isolated from male DA rats and measured for cell viability, islet survival, glucose diffusion and insulin secretion. Modeling of diffusion barriers was completed using dynamic partial differential equations for a sphere. Core cell death occurred in 100% of the large islets (diameter >150 µm), resulting in poor survival within 7 days after isolation. In contrast, small islets (diameter <100 µm) exhibited good survival rates in culture (91%). Glucose diffusion into islets was tracked with 2-NBDG; 4.2 µm/min in small islets and 2.8 µm/min in large islets. 2-NBDG never permeated to the core cells of islets larger than 150 µm diameter. Reducing the diffusion barrier in large islets improved their immediate and long-term viability in culture. However, reduction of the diffusion barrier in large islets failed to improve their inferior in vitro insulin secretion compared to small islets, and did not return glucose control to diabetic animals following transplantation. Thus, diffusion barriers lead to low viability and poor survival for large islets, but are not solely responsible for the inferior insulin secretion or poor transplantation outcomes of large versus small islets. PMID:20885858

The Long and Viscous Road: Uncovering Nuclear Diffusion Barriers in Closed Mitosis

PubMed Central

Zavala, Eder; Marquez-Lago, Tatiana T.

2014-01-01

Diffusion barriers are effective means for constraining protein lateral exchange in cellular membranes. In Saccharomyces cerevisiae, they have been shown to sustain parental identity through asymmetric segregation of ageing factors during closed mitosis. Even though barriers have been extensively studied in the plasma membrane, their identity and organization within the nucleus remains poorly understood. Based on different lines of experimental evidence, we present a model of the composition and structural organization of a nuclear diffusion barrier during anaphase. By means of spatial stochastic simulations, we propose how specialised lipid domains, protein rings, and morphological changes of the nucleus may coordinate to restrict protein exchange between mother and daughter nuclear lobes. We explore distinct, plausible configurations of these diffusion barriers and offer testable predictions regarding their protein exclusion properties and the diffusion regimes they generate. Our model predicts that, while a specialised lipid domain and an immobile protein ring at the bud neck can compartmentalize the nucleus during early anaphase; a specialised lipid domain spanning the elongated bridge between lobes would be entirely sufficient during late anaphase. Our work shows how complex nuclear diffusion barriers in closed mitosis may arise from simple nanoscale biophysical interactions. PMID:25032937

First-principles study of transition-metal nitrides as diffusion barriers against Al

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

Mei, Zhi-Gang; Yacout, Abdellatif M.; Kim, Yeon Soo

2016-04-01

Using density-functional theory based first-principles calculations we provided a comparative study of the diffusion barrier properties of TiN, ZrN, and HfN against Al for U-Mo dispersion fuel applications. We firstly examined the thermodynamic stability of these transition-metal nitrides with Al. The calculated heats of reaction show that both TiN and ZrN are thermodynamically unstable diffusion barrier materials, which might be decomposed by Al at relatively high temperatures. As a comparison, HfN is a stable diffusion barrier material for Al. To evaluate the kinetic stability of these nitride systems against Al diffusion, we investigated the diffusion mechanisms of Al in TiN,more » ZrN and HfN using atomic scale simulations. The effect of non-stoichiometry on the defect formation and Al migration was systematically studied. (C) 2015 ELSEVIER B.V. All rights reserved« less

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

Enzyme localization, crowding, and buffers collectively modulate diffusion-influenced signal transduction: Insights from continuum diffusion modeling

PubMed Central

Kekenes-Huskey, Peter M.; Eun, Changsun; McCammon, J. A.

2015-01-01

Biochemical reaction networks consisting of coupled enzymes connect substrate signaling events with biological function. Substrates involved in these reactions can be strongly influenced by diffusion “barriers” arising from impenetrable cellular structures and macromolecules, as well as interactions with biomolecules, especially within crowded environments. For diffusion-influenced reactions, the spatial organization of diffusion barriers arising from intracellular structures, non-specific crowders, and specific-binders (buffers) strongly controls the temporal and spatial reaction kinetics. In this study, we use two prototypical biochemical reactions, a Goodwin oscillator, and a reaction with a periodic source/sink term to examine how a diffusion barrier that partitions substrates controls reaction behavior. Namely, we examine how conditions representative of a densely packed cytosol, including reduced accessible volume fraction, non-specific interactions, and buffers, impede diffusion over nanometer length-scales. We find that diffusion barriers can modulate the frequencies and amplitudes of coupled diffusion-influenced reaction networks, as well as give rise to “compartments” of decoupled reactant populations. These effects appear to be intensified in the presence of buffers localized to the diffusion barrier. These findings have strong implications for the role of the cellular environment in tuning the dynamics of signaling pathways. PMID:26342355

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.

Review of Graphene as a Solid State Diffusion Barrier.

PubMed

Morrow, Wayne K; Pearton, Stephen J; Ren, Fan

2016-01-06

Conventional thin-film diffusion barriers consist of 3D bulk films with high chemical and thermal stability. The purpose of the barrier material is to prevent intermixing or penetration from the two materials that encase it. Adhesion to both top and bottom materials is critical to the success of the barrier. Here, the effectiveness of a single atomic layer of graphene as a solid-state diffusion barrier for common metal schemes used in microelectronics is reviewed, and specific examples are discussed. Initial studies of electrical contacts to graphene show a distinct separation in behavior between metallic groups that strongly or weakly bond to it. The two basic classes of metal reactions with graphene are either physisorbed metals, which bond weakly with graphene, or chemisorbed metals, which bond strongly to graphene. For graphene diffusion barrier testing on Si substrates, an effective barrier can be achieved through the formation of a carbide layer with metals that are chemisorbed. For physisorbed metals, the barrier failure mechanism is loss of adhesion at the metal–graphene interface. A graphene layer encased between two metal layers, in certain cases, can increase the binding energy of both films with graphene, however, certain combinations of metal films are detrimental to the bonding with graphene. While the prospects for graphene's future as a solid-state diffusion barrier are positive, there are open questions, and areas for future research are discussed. A better understanding of the mechanisms which influence graphene's ability to be an effective diffusion barrier in microelectronic applications is required, and additional experiments are needed on a broader range of metals, as well as common metal stack contact structures used in microelectronic applications. The role of defects in the graphene is also a key area, since they will probably influence the barrier properties. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acceleration of metal-atom diffusion in electric field at metal/insulator interfaces: First-principles study

NASA Astrophysics Data System (ADS)

Nagasawa, Riki; Asayama, Yoshihiro; Nakayama, Takashi

2018-04-01

Metal-atom diffusion from metal electrodes into SiO2 in electric fields was studied using first-principles calculations. It was shown in the case without electric field that the diffusion barrier of a metal atom is mainly made of the cohesive energy of bulk metal layers, while the shape of the diffusion potential reflects the hybridization of the metal-atom state with metal-induced gap states (MIGSs) and the electron transfer between the metal atom and the electrode. We found that the metal-atom diffusion is markedly accelerated by the applied electric field, such that the diffusion barrier ϕB(E) decreases almost linearly with increasing electric field strength E. By analyzing the physical origins of the metal-atom diffusion, we derived the universal formula to estimate the diffusion barrier in the electric field, which is closely related to MIGSs.

Protective coatings for sensitive materials

DOEpatents

Egert, Charles M.

1997-01-01

An enhanced protective coating to prevent interaction between constituents of the environment and devices that can be damaged by those constituents. This coating is provided by applying a synergistic combination of diffusion barrier and physical barrier materials. These materials can be, for example, in the form of a plurality of layers of a diffusion barrier and a physical barrier, with these barrier layers being alternated. Further protection in certain instances is provided by including at least one layer of a getter material to actually react with one or more of the deleterious constituents. The coating is illustrated by using alternating layers of an organic coating (such as Parylene-C.TM.) as the diffusion barrier, and a metal coating (such as aluminum) as the physical barrier. For best results there needs to be more than one of at least one of the constituent layers.

A novel method for calculating the energy barriers for carbon diffusion in ferrite under heterogeneous stress

NASA Astrophysics Data System (ADS)

Tchitchekova, Deyana S.; Morthomas, Julien; Ribeiro, Fabienne; Ducher, Roland; Perez, Michel

2014-07-01

A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ˜3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.

A novel method for calculating the energy barriers for carbon diffusion in ferrite under heterogeneous stress.

PubMed

Tchitchekova, Deyana S; Morthomas, Julien; Ribeiro, Fabienne; Ducher, Roland; Perez, Michel

2014-07-21

A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ∼3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.

Contamination and UV ageing of diffuser targets used in satellite inflight and ground reference test site calibrations

NASA Astrophysics Data System (ADS)

Vaskuri, Anna; Greenwell, Claire; Hessey, Isabel; Tompkins, Jordan; Woolliams, Emma

2018-02-01

Diffuser reflectance targets are key components in in-orbit calibrations and for verifying ground reference test sites. In this work, Spectralon, Diffusil, and Heraeus diffusers were exposed to exhaust gases and ultraviolet (UV) radiation in the ambient air conditions and their degradations were monitored by measuring changes in spectral reflectances. Spectralon is a state-of-the-art diffuser made of polytetrafluoroethylene, and Diffusil and Heraeus diffusers are made of fused silica with gas bubbles inside. Based on the contamination tests, Spectralon degrades faster than fused silica diffusers. For the samples exposed to contamination for 20 minutes, the 250 nm - 400 nm total diffuse spectral reflectance of Spectralon degraded 3-5 times more when exposed to petrol-like emission and 16-23 times more when exposed to diesel-like emission, compared with Diffusil. When the reflectance changes of Spectralon were compared with those of Heraeus, Spectralon degraded 3-4 times more when exposed to petrol-like emission for 20 minutes and 5-7 times more when exposed to diesel-like emission for 7.5 minutes. When the samples contaminated were exposed to UV radiation in the ambient air, their reflectance gradually restored back to the original level. In conclusion, fused silica diffusers are more resistant to hydrocarbon contaminants present in ground reference test sites, and thus more stable under UV radiation in the air.

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

Axial diffusion barriers in near-infrared nanopillar LEDs.

PubMed

Scofield, Adam C; Lin, Andrew; Haddad, Michael; Huffaker, Diana L

2014-11-12

The growth of GaAs/GaAsP axial heterostructures is demonstrated and implemented as diffusion current barriers in nanopillar light-emitting diodes at near-infrared wavelengths. The nanopillar light-emitting diodes utilize an n-GaAs/i-InGaAs/p-GaAs axial heterostructure for current injection. Axial GaAsP segments are inserted into the n- and p-GaAs portions of the nanopillars surrounding the InGaAs emitter region, acting as diffusion barriers to provide enhanced carrier confinement. Detailed characterization of growth of the GaAsP inserts and electronic band-offset measurements are used to effectively implement the GaAsP inserts as diffusion barriers. The implementation of these barriers in nanopillar light-emitting diodes provides a 5-fold increase in output intensity, making this a promising approach to high-efficiency pillar-based emitters in the near-infrared wavelength range.

Mesoscale elucidation of laser-assisted chemical deposition of Sn nanostructured electrodes

NASA Astrophysics Data System (ADS)

Liu, Zhixiao; Deng, Biwei; Cheng, Gary J.; Deng, Huiqiu; Mukherjee, Partha P.

2015-06-01

Nanostructured tin (Sn) is a promising high-capacity electrode for improved performance in lithium-ion batteries for electric vehicles. In this work, Sn nanoisland growth for nanostructured electrodes assisted by the pulse laser irradiation has been investigated based on a mesoscale modeling formalism. The influence of pertinent processing conditions, such as pulse duration, heating/cooling rates, and atom flux, on the Sn nanostructure formation is specifically considered. The interaction between the adsorbed atom and the substrate, represented by the adatom diffusion barrier, is carefully studied. It is found that the diffusion barrier predominantly affects the distribution of Sn atoms. For both α-Sn and β-Sn, the averaged coordination number is larger than 3 when the diffusion barrier equals to 0.15 eV. The averaged coordination number decreases as the diffusion barrier increases. The substrate temperature, which is determined by heating/cooling rates and pulse duration, can also affect the formation of Sn nanoislands. For α-Sn, when applied low heating/cooling rates, nanoislands cannot form if the diffusion barrier is larger than 0.35 eV.

Protective coatings for sensitive materials

DOEpatents

Egert, C.M.

1997-08-05

An enhanced protective coating is disclosed to prevent interaction between constituents of the environment and devices that can be damaged by those constituents. This coating is provided by applying a synergistic combination of diffusion barrier and physical barrier materials. These materials can be, for example, in the form of a plurality of layers of a diffusion barrier and a physical barrier, with these barrier layers being alternated. Further protection in certain instances is provided by including at least one layer of a getter material to actually react with one or more of the deleterious constituents. The coating is illustrated by using alternating layers of an organic coating (such as Parylene-C{trademark}) as the diffusion barrier, and a metal coating (such as aluminum) as the physical barrier. For best results there needs to be more than one of at least one of the constituent layers. 4 figs.

First-principles investigation of point defect and atomic diffusion in Al2Ca

NASA Astrophysics Data System (ADS)

Tian, Xiao; Wang, Jia-Ning; Wang, Ya-Ping; Shi, Xue-Feng; Tang, Bi-Yu

2017-04-01

Point defects and atomic diffusion in Al2Ca have been studied from first-principles calculations within density functional framework. After formation energy and relative stability of point defects are investigated, several predominant diffusion processes in Al2Ca are studied, including sublattice one-step mechanism, 3-jump vacancy cycles and antistructure sublattice mechanism. The associated energy profiles are calculated with climbing image nudged elastic band (CI-NEB) method, then the saddle points and activation barriers during atomic diffusion are further determined. The resulted activation barriers show that both Al and Ca can diffuse mainly mediated by neighbor vacancy on their own sublattice. 3-jump cycle mechanism mediated by VCa may make some contribution to the overall Al diffusion. And antistructure (AS) sublattice mechanism can also play an important role in Ca atomic diffusion owing to the moderate activation barrier.

Multilayer Regulation of Atomic Boron Nitride Films to Improve Oxidation and Corrosion Resistance of Cu.

PubMed

Ren, Siming; Cui, Mingjun; Pu, Jibin; Xue, Qunji; Wang, Liping

2017-08-16

The boron nitride (BN) monolayer (1L) with high impermeability and resistivity seems to hold promise as a long-term corrosion barrier for Cu under ambient condition, which is supported by recent researches. Here, we perform a complete study of the alternating temperature tests (the sample is exposed in air for 30 days and subsequently heated at 200 °C for 2 h) and electrochemical measurements on 1L and multilayer BN-coated Cu foils. Results imply that the BN-coated Cu foils are less oxidized than uncoated Cu foils after alternating temperature tests, regardless of the layers of BN. Particularly, the oxidation process proceeds slowly in multilayers because most of the underlying defects are covered with BN layers to suppress the oxygen diffusion in the vertical direction and the oxidation mainly occurs on the wrinkled region of BN films. Electrochemical analyses reveal that the BN layers provide an effective physical barrier against the corrosive medium and inhibit the electron diffusion because of their high electrical insulating behavior and the corrosion resistance of the samples increases with increasing BN layers. These findings indicate that BN films with adequate layers are good candidates for oxidation and corrosion protection at the atomic level, which is vital to many industrial and academic applications.

Investigation of microstructure and properties of ultrathin graded ZrNx self-assembled diffusion barrier in deep nano-vias prepared by plasma ion immersion implantation

NASA Astrophysics Data System (ADS)

Zou, Jianxiong; Liu, Bo; Lin, Liwei; Lu, Yuanfu; Dong, Yuming; Jiao, Guohua; Ma, Fei; Li, Qiran

2018-01-01

Ultrathin graded ZrNx self-assembled diffusion barriers with controllable stoichiometry was prepared in Cu/p-SiOC:H interfaces by plasma immersion ion implantation (PIII) with dynamic regulation of implantation fluence. The fundamental relationship between the implantation fluence of N+ and the stoichiometry and thereby the electrical properties of the ZrNx barrier was established. The optimized fluence of a graded ZrN thin film with gradually decreased Zr valence was obtained with the best electrical performance as well. The Cu/p-SiOC:H integration is thermally stable up to 500 °C due to the synergistic effect of Cu3Ge and ZrNx layers. Accordingly, the PIII process was verified in a 100-nm-thick Cu dual-damascene interconnect, in which the ZrNx diffusion barrier of 1 nm thick was successfully self-assembled on the sidewall without barrier layer on the via bottom. In this case, the via resistance was reduced by approximately 50% in comparison with Ta/TaN barrier. Considering the results in this study, ultrathin ZrNx conformal diffusion barrier can be adopted in the sub-14 nm technology node.

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.

Alloyed coatings for dispersion strengthened alloys

NASA Technical Reports Server (NTRS)

Wermuth, F. R.; Stetson, A. R.

1971-01-01

Processing techniques were developed for applying several diffusion barriers to TD-Ni and TD-NiCr. Barrier coated specimens of both substrates were clad with Ni-Cr-Al and Fe-Cr-Al alloys and diffusion annealed in argon. Measurement of the aluminum distribution after annealing showed that, of the readily applicable diffusion barriers, a slurry applied tungsten barrier most effectively inhibited the diffusion of aluminum from the Ni-Cr-Al clad into the TD-alloy substrates. No barrier effectively limited interdiffusion of the Fe-Cr-Al clad with the substrates. A duplex process was then developed for applying Ni-Cr-Al coating compositions to the tungsten barrier coated substrates. A Ni-(16 to 32)Cr-3Si modifier was applied by slurry spraying and firing in vacuum, and was then aluminized by a fusion slurry process. Cyclic oxidation tests at 2300 F resulted in early coating failure due to inadequate edge coverage and areas of coating porosity. EMP analysis showed that oxidation had consumed 70 to 80 percent of the aluminum in the coating in less than 50 hours.

TiO2 as diffusion barrier at Co/Alq3 interface studied by x-ray standing wave technique

NASA Astrophysics Data System (ADS)

Phatak Londhe, Vaishali; Gupta, A.; Ponpandian, N.; Kumar, D.; Reddy, V. R.

2018-06-01

Nano-scale diffusion at the interfaces in organic spin valve thin films plays a vital role in controlling the performance of magneto-electronic devices. In the present work, it is shown that a thin layer of titanium dioxide at the interface of Co/Alq3 can act as a good diffusion barrier. The buried interfaces of Co/Alq3/Co organic spin valve thin film has been studied using x-ray standing waves technique. A planar waveguide is formed with Alq3 layer forming the cavity and Co layers as the walls of the waveguide. Precise information about diffusion of Co into Alq3 is obtained through excitation of the waveguide modes. It is found that the top Co layer diffuses deep into the Alq3 resulting in incorporation of 3.1% Co in the Alq3 layer. Insertion of a 1.7 nm thick barrier layer of TiO2 at Co/Alq3 interface results in a drastic reduction in the diffusion of Co into Alq3 to a value of only 0.4%. This suggests a better performance of organic spin valve with diffusion barrier of TiO2.

Analysis and experimental study on formation conditions of large-scale barrier-free diffuse atmospheric pressure air plasmas in repetitive pulse mode

NASA Astrophysics Data System (ADS)

Li, Lee; Liu, Lun; Liu, Yun-Long; Bin, Yu; Ge, Ya-Feng; Lin, Fo-Chang

2014-01-01

Atmospheric air diffuse plasmas have enormous application potential in various fields of science and technology. Without dielectric barrier, generating large-scale air diffuse plasmas is always a challenging issue. This paper discusses and analyses the formation mechanism of cold homogenous plasma. It is proposed that generating stable diffuse atmospheric plasmas in open air should meet the three conditions: high transient power with low average power, excitation in low average E-field with locally high E-field region, and multiple overlapping electron avalanches. Accordingly, an experimental configuration of generating large-scale barrier-free diffuse air plasmas is designed. Based on runaway electron theory, a low duty-ratio, high voltage repetitive nanosecond pulse generator is chosen as a discharge excitation source. Using the wire-electrodes with small curvature radius, the gaps with highly non-uniform E-field are structured. Experimental results show that the volume-scaleable, barrier-free, homogeneous air non-thermal plasmas have been obtained between the gap spacing with the copper-wire electrodes. The area of air cold plasmas has been up to hundreds of square centimeters. The proposed formation conditions of large-scale barrier-free diffuse air plasmas are proved to be reasonable and feasible.

Suppression of Lateral Diffusion and Surface Leakage Currents in nBn Photodetectors Using an Inverted Design

NASA Astrophysics Data System (ADS)

Du, X.; Savich, G. R.; Marozas, B. T.; Wicks, G. W.

2018-02-01

Surface leakage and lateral diffusion currents in InAs-based nBn photodetectors have been investigated. Devices fabricated using a shallow etch processing scheme that etches through the top contact and stops at the barrier exhibited large lateral diffusion current but undetectably low surface leakage. Such large lateral diffusion current significantly increased the dark current, especially in small devices, and causes pixel-to-pixel crosstalk in detector arrays. To eliminate the lateral diffusion current, two different approaches were examined. The conventional solution utilized a deep etch process, which etches through the top contact, barrier, and absorber. This deep etch processing scheme eliminated lateral diffusion, but introduced high surface current along the device mesa sidewalls, increasing the dark current. High device failure rate was also observed in deep-etched nBn structures. An alternative approach to limit lateral diffusion used an inverted nBn structure that has its absorber grown above the barrier. Like the shallow etch process on conventional nBn structures, the inverted nBn devices were fabricated with a processing scheme that only etches the top layer (the absorber, in this case) but avoids etching through the barrier. The results show that inverted nBn devices have the advantage of eliminating the lateral diffusion current without introducing elevated surface current.

Plasma Spray and Pack Cementation Process Optimization and Oxidation Behaviour of Novel Multilayered Coatings

NASA Astrophysics Data System (ADS)

Gao, Feng

The hot section components in gas turbines are subjected to a harsh environment with the temperature being increased continuously. The higher temperature has directly resulted in severe oxidation of these components. Monolithic coatings such as MCrAIY and aluminide have been traditionally used to protect the components from oxidation; however, increased operating temperature quickly deteriorates the coatings due to accelerated diffusion of aluminum in the coatings. To improve the oxidation resistance a group of multilayered coatings are developed in this study. The multilayered coatings consist of a Cr-Si co-deposited layer as the diffusion barrier, a plasma sprayed NiCrA1Y coating as the middle layer and an aluminized top layer. The Cr-Si and aluminized layers are fabricated using pack cementation processes and the NiCrA1Y coatings are produced using the Mettech Axial III(TM) System. All of the coating processes are optimized using the methodology of Design of Experiments (DOE) and the results are analyzed using statistical method. The optimal processes are adopted to fabricate the multilayered coatings for oxidation tests. The coatings are exposed in air at 1050°C and 1150°C for 1000 hr. The results indicate that a Cr layer and a silicon-rich barrier layer have formed on the interface between the Cr-Si coating and the NiCrA1Y coating. This barrier layer not only prevents aluminum and chromium from diffusing into the substrate, but also impedes the diffusion of other elements from the substrate into the coating. The results also reveal that, for optimal oxidation resistance at 1050°C, the top layer in a multilayered coating should have at least Al/Ni ratio of one; whereas the multilayered coating with the All Ni ratio of two in the top layer exhibits the best oxidation resistance at 1150°C. The DOE methodology provides an excellent means for process optimization and the selection of oxidation test matrix, and also offers a more thorough understanding of the effects of process parameters on the coating microstructure, and the effects of layers and their interactions on the oxidation behavior of the multilayered coatings.

Dynamic surface tension and adsorption mechanism of surfactin biosurfactant at the air-water interface.

PubMed

Onaizi, Sagheer A

2018-03-01

The dynamic adsorption of the anionic biosurfactant, surfactin, at the air-water interface has been investigated in this work and compared to those of two synthetic surfactants: the anionic sodium dodecylbenzenesulfonate (SDBS) and the nonionic octaethylene glycol monotetradecyl ether (C 14 E 8 ). The results revealed that surfactin adsorption at the air-water interface is purely controlled by diffusion mechanism at the initial stage of the adsorption process (i.e., [Formula: see text]), but shifts towards a mixed diffusion-barrier mechanism when surface tension approaches equilibrium (i.e., [Formula: see text]) due to the development of an energy barrier for adsorption. Such energy barrier has been found to be a function of the surfactin bulk concentration (increases with increasing surfactin concentration) and it is estimated to be in the range of 1.8-9.5 kJ/mol. Interestingly, such a trend (pure diffusion-controlled mechanism at [Formula: see text] and mixed diffusion-barrier mechanism at [Formula: see text]) has been also observed for the nonionic C 14 E 8 surfactant. Unlike the pure diffusion-controlled mechanism of the initial surfactin adsorption, which was the case in the presence and the absence of the sodium ion (Na + ), SDBS showed a mixed diffusion-barrier controlled at both short and long time, with an energy barrier of 3.0-9.0 and 3.8-18.0 kJ/mol, respectively. Such finding highlights the nonionic-like adsorption mechanism of surfactin despite its negative charge.

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.

The role of the Ti and Mo barrier layer in Ti/Al metallization to AlGaN/GaN heterostructures at identical process conditions: a structural and chemical characterization

NASA Astrophysics Data System (ADS)

Chandran, Narendraraj; Kolakieva, Lilyana; Kakanakov, Roumen; Polychroniadis, E. K.

2015-11-01

The composition and structure of TiAl-based metallizations have been investigated depending on the Ti and Mo barriers. The lowest contact resistivity of 4 × 10-6 Ω.cm2 for a Ti barrier and 7 × 10-6 Ω.cm2 for a Mo barrier is obtained at a Ti/Al ratio of 0.43 after annealing at 800 °C. The scanning transmission electron microscope (STEM) and energy dispersive spectroscopy (EDS) analyses reveal that Mo is not an effective barrier for the Au in-diffusion and Al out of diffusion during annealing. The intensive diffusion processes lead to the formation of the semimetal TiN compound at the interface and intermetallic phases of Au, Al, and Ti, the structure and composition of which depend on the barrier metal.

Material Barriers to Diffusive Mixing

NASA Astrophysics Data System (ADS)

Haller, George; Karrasch, Daniel

2017-11-01

Transport barriers, as zero-flux surfaces, are ill-defined in purely advective mixing in which the flux of any passive scalar is zero through all material surfaces. For this reason, Lagrangian Coherent Structures (LCSs) have been argued to play the role of mixing barriers as most repelling, attracting or shearing material lines. These three kinematic concepts, however, can also be defined in different ways, both within rigorous mathematical treatments and within the realm of heuristic diagnostics. This has lead to a an ever-growing number of different LCS methods, each generally identifying different objects as transport barriers. In this talk, we examine which of these methods have actual relevance for diffusive transport barriers. The latter barriers are arguably the practically relevant inhibitors in the mixing of physically relevant tracers, such as temperature, salinity, vorticity or potential vorticity. We demonstrate the role of the most effective diffusion barriers in analytical examples and observational data. Supported in part by the DFG Priority Program on Turbulent Superstructures.

Oxidation Resistant Ti-Al-Fe Diffusion Barrier for FeCrAlY Coatings on Titanium Aluminides

NASA Technical Reports Server (NTRS)

Brady, Michael P. (Inventor); Smialke, James L. (Inventor); Brindley, William J. (Inventor)

1996-01-01

A diffusion barrier to help protect titanium aluminide alloys, including the coated alloys of the TiAl gamma + Ti3Al (alpha2) class, from oxidative attack and interstitial embrittlement at temperatures up to at least 1000 C is disclosed. The coating may comprise FeCrAlX alloys. The diffusion barrier comprises titanium, aluminum, and iron in the following approximate atomic percent: Ti-(50-55)Al-(9-20)Fe. This alloy is also suitable as an oxidative or structural coating for such substrates.

Rotation and diffusion of naphthalene on Pt(111)

NASA Astrophysics Data System (ADS)

Kolsbjerg, E. L.; Goubert, G.; McBreen, P. H.; Hammer, B.

2018-03-01

The behavior of naphthalene on Pt(111) surfaces is studied by combining insight from scanning tunneling microscopy (STM) and van der Waals enabled density functional theory. Adsorption, diffusion, and rotation are investigated by a series of variable temperature STM experiments revealing naphthalene ability to rotate on-site with ease with a rotational barrier of 0.69 eV. Diffusion to neighbouring sites is found to be more difficult. The experimental results are in good agreement with the theoretical investigations which confirm that the barrier for diffusion is slightly higher than the one for rotation. The theoretical barriers for rotation and translation are found to be 0.75 and 0.78 eV, respectively. An automatic mapping of the possible diffusion pathways reveals very detailed diffusion paths with many small local minima that would have been practically impossible to find manually. This automated procedure provides detailed insight into the preferred diffusion pathways that are important for our understanding of molecule-substrate interactions.

Ethyl cellulose nanocarriers and nanocrystals differentially deliver dexamethasone into intact, tape-stripped or sodium lauryl sulfate-exposed ex vivo human skin - assessment by intradermal microdialysis and extraction from the different skin layers.

PubMed

Döge, Nadine; Hönzke, Stefan; Schumacher, Fabian; Balzus, Benjamin; Colombo, Miriam; Hadam, Sabrina; Rancan, Fiorenza; Blume-Peytavi, Ulrike; Schäfer-Korting, Monika; Schindler, Anke; Rühl, Eckart; Skov, Per Stahl; Church, Martin K; Hedtrich, Sarah; Kleuser, Burkhard; Bodmeier, Roland; Vogt, Annika

2016-11-28

Understanding penetration not only in intact, but also in lesional skin with impaired skin barrier function is important, in order to explore the surplus value of nanoparticle-based drug delivery for anti-inflammatory dermatotherapy. Herein, short-term ex vivo cultures of (i) intact human skin, (ii) skin pretreated with tape-strippings and (iii) skin pre-exposed to sodium lauryl sulfate (SLS) were used to assess the penetration of dexamethasone (Dex). Intradermal microdialysis was utilized for up to 24h after drug application as commercial cream, nanocrystals or ethyl cellulose nanocarriers applied at the therapeutic concentration of 0.05%, respectively. In addition, Dex was assessed in culture media and extracts from stratum corneum, epidermis and dermis after 24h, and the results were compared to those in heat-separated split skin from studies in Franz diffusion cells. Providing fast drug release, nanocrystals significantly accelerated the penetration of Dex. In contrast to the application of cream and ethyl cellulose nanocarriers, Dex was already detectable in eluates after 6h when applying nanocrystals on intact skin. Disruption of the skin barrier further accelerated and enhanced the penetration. Encapsulation in ethyl cellulose nanocarriers delayed Dex penetration. Interestingly, for all formulations highly increased concentrations in the dialysate were observed in tape-stripped skin, whereas the extent of enhancement was less in SLS-exposed skin. The results were confirmed in tissue extracts and were in line with the predictions made by in vitro release studies and ex vivo Franz diffusion cell experiments. The use of 45kDa probes further enabled the collection of inflammatory cytokines. However, the estimation of glucocorticoid efficacy by Interleukin (IL)-6 and IL-8 analysis was limited due to the trauma induced by the probe insertion. Ex vivo intradermal microdialysis combined with culture media analysis provides an effective, skin-sparing method for preclinical assessment of novel drug delivery systems at therapeutic doses in models of diseased skin. Copyright © 2016 Elsevier B.V. All rights reserved.

The effect of environment on thermal barrier coating lifetime

DOE PAGES

Pint, Bruce A.; Unocic, Kinga A.; Haynes, James Allen

2016-03-15

While the water vapor content of the combustion gas in natural gas-fired land-based turbines is ~10%, it can be 20–85% with coal-derived (syngas or H 2) fuels or innovative turbine concepts for more efficient carbon capture. Additional concepts envisage working fluids with high CO 2 contents to facilitate carbon capture and sequestration. To investigate the effects of changes in the gas composition on thermal barrier coating (TBC) lifetime, furnace cycling tests (1-h and 100-h cycles) were performed in air with 10, 50, and 90 vol. % water vapor and CO 2-10% H 2O and compared to prior results in drymore » air or O 2. Two types of TBCs were investigated: (1) diffusion bond coatings (Pt-diffusion or Pt-modified aluminide) with commercial electron-beam physical vapor-deposited yttria-stabilized zirconia (YSZ) top coatings on second-generation superalloy N5 and N515 substrates and (2) high-velocity oxygen fuel (HVOF) sprayed MCrAlYHfSi bond coatings with air plasma-sprayed YSZ top coatings on superalloys X4, 1483, or 247 substrates. For both types of coatings exposed in 1-h cycles, the addition of water vapor resulted in a decrease in coating lifetime, except for Pt-diffusion coatings which were unaffected by the environment. In 100-h cycles, environment was less critical, perhaps because coating failure was chemical (i.e., due to interdiffusion) rather than mechanical. As a result, in both 1-h and 100-h cycles, CO 2 did not appear to have any negative effect on coating lifetime.« less

The Drosophila blood-brain barrier: development and function of a glial endothelium.

PubMed

Limmer, Stefanie; Weiler, Astrid; Volkenhoff, Anne; Babatz, Felix; Klämbt, Christian

2014-01-01

The efficacy of neuronal function requires a well-balanced extracellular ion homeostasis and a steady supply with nutrients and metabolites. Therefore, all organisms equipped with a complex nervous system developed a so-called blood-brain barrier, protecting it from an uncontrolled entry of solutes, metabolites or pathogens. In higher vertebrates, this diffusion barrier is established by polarized endothelial cells that form extensive tight junctions, whereas in lower vertebrates and invertebrates the blood-brain barrier is exclusively formed by glial cells. Here, we review the development and function of the glial blood-brain barrier of Drosophila melanogaster. In the Drosophila nervous system, at least seven morphologically distinct glial cell classes can be distinguished. Two of these glial classes form the blood-brain barrier. Perineurial glial cells participate in nutrient uptake and establish a first diffusion barrier. The subperineurial glial (SPG) cells form septate junctions, which block paracellular diffusion and thus seal the nervous system from the hemolymph. We summarize the molecular basis of septate junction formation and address the different transport systems expressed by the blood-brain barrier forming glial cells.

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

Copper diffusion in Ti Si N layers formed by inductively coupled plasma implantation

NASA Astrophysics Data System (ADS)

Ee, Y. C.; Chen, Z.; Law, S. B.; Xu, S.; Yakovlev, N. L.; Lai, M. Y.

2006-11-01

Ternary Ti-Si-N refractory barrier films of 15 nm thick was prepared by low frequency, high density, inductively coupled plasma implantation of N into TixSiy substrate. This leads to the formation of Ti-N and Si-N compounds in the ternary film. Diffusion of copper in the barrier layer after annealing treatment at various temperatures was investigated using time-of-flight secondary ion mass spectrometer (ToF-SIMS) depth profiling, X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and sheet resistance measurement. The current study found that barrier failure did not occur until 650 °C annealing for 30 min. The failure occurs by the diffusion of copper into the Ti-Si-N film to form Cu-Ti and Cu-N compounds. FESEM surface morphology and EDX show that copper compounds were formed on the ridge areas of the Ti-Si-N film. The sheet resistance verifies the diffusion of Cu into the Ti-Si-N film; there is a sudden drop in the resistance with Cu compound formation. This finding provides a simple and effective method of monitoring Cu diffusion in TiN-based diffusion barriers.

Deterioration of reflecting coatings by intermetallic diffusion.

PubMed

Hunter, W R; Mikes, T L; Hass, G

1972-07-01

Gold diffraction gratings overcoated with Al + MgF(2) to increase their efficiency in the vacuum ultraviolet suffered a severe loss in efficiency within six months to a year after coating; for example, from 50% to 2% at lambda1216 A. The cause of this loss was assumed to be interdiffusion of Au and Al; therefore, a more complete study of Au-Al film combinations was performed. The coatings were aged at room and elevated temperatures. Reflectance measurements were made in the visible and vacuum ultraviolet spectral regions. For wavelengths longer than lambda900 A, the measurements show very little change until the diffusion boundary reaches the penetration depth of the radiation. If Al is the first surface layer, however, reflectance measurements at lambda584 A permit measuring the progress of the diffusion boundary toward the Al surface because of the low absorptance of Al at this wavelength. Interdiffusion can be effectively eliminated by the use of thin dielectric layers uch as SiO and the natural oxide of Al. Such protected coatings have been exposed for one week at a temperature of 170 degrees C with no visible sign of diffusion, whereas a similar coating without the barrier layer would become useless in less than 1 h. Some preliminary studies have been made with Pt-Al film combinations.

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.

Self-learning kinetic Monte Carlo simulations of diffusion in ferromagnetic α -Fe–Si alloys

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

Nandipati, Giridhar; Jiang, Xiujuan; Vemuri, Rama S.

Diffusion in α-Fe-Si alloys is studied using AKSOME, an on-lattice self-learning KMC code, in the ferromagnetic state. Si diffusivity in the α-Fe matrix were obtained with and without the magnetic disorder in various temperature ranges. In addition we studied vacancy diffusivity in ferromagnetic α-Fe at various Si concentrations up to 12.5at.% in the temperature range of 350–550 K. The results were compared with available experimental and theoretical values in the literature. Local Si-atom dependent activation energies for vacancy hops were calculated using a broken-model and were stored in a database. The migration barrier and prefactors for Si-diffusivity were found tomore » be in reasonable agreement with available modeling results in the literature. Magnetic disorder has a larger effect on the prefactor than on the migration barrier. Prefactor was approximately an order of magnitude and the migration barrier a tenth of an electron-volt higher with magnetic disorder when compared to a fully ferromagnetic ordered state. In addition, the correlation between various have a larger effect on the Si-diffusivity extracted in various temperature range than the magnetic disorder. In the case of vacancy diffusivity, the migration barrier more or less remained constant while the prefactor decreased with increasing Si concentration in the disordered or A2-phase of Fe-Si alloy. Important vacancy-Si/Fe atom exchange processes and their activation barriers were also identified and discuss the effect of energetics on the formation of ordered phases in Fe-Si alloys.« less

Investigation of heavy-ion fusion with deformed surface diffuseness: Actinide and lanthanide targets

NASA Astrophysics Data System (ADS)

Alavi, S. A.; Dehghani, V.

2017-05-01

By using a deformed Broglia-Winther nuclear interaction potential in the framework of the WKB method, the near- and above-barrier heavy-ion-fusion cross sections of 16O with some lanthanides and actinides have been calculated. The effect of deformed surface diffuseness on the nuclear interaction potential, the effective interaction potential at distinct angle, barrier position, barrier height, cross section at each angles, and fusion cross sections of 16O+147Sm,150Nd,154Sm , and 166Er and 16O+232Th,238U,237Np , and 248Cm have been studied. The differences between the results obtained by using deformed surface diffuseness and those obtained by using constant surface diffuseness were noticeable. Good agreement between experimental data and theoretical calculation with deformed surface diffuseness were observed for 16O+147Sm,154Sm,166Er,238U,237Np , and 248Cm reactions. It has been observed that deformed surface diffuseness plays a significant role in heavy-ion-fusion studies.

In Situ Ramp Anneal X-ray Diffraction Study of Atomic Layer Deposited Ultrathin TaN and Ta 1-x Al x N y Films for Cu Diffusion Barrier Applications

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

Consiglio, S.; Dey, S.; Yu, K.

2016-01-01

Ultrathin TaN and Ta 1-xAl xN y films with x = 0.21 to 0.88 were deposited by atomic layer deposition (ALD) and evaluated for Cu diffusion barrier effectiveness compared to physical vapor deposition (PVD) grown TaN. Cu diffusion barrier effectiveness was investigated using in-situ ramp anneal synchrotron X-ray diffraction (XRD) on Cu/1.8 nm barrier/Si stacks. A Kissinger-like analysis was used to assess the kinetics of Cu 3Si formation and determine the effective activation energy (E a) for Cu silicidation. Compared to the stack with a PVD TaN barrier, the stacks with the ALD films exhibited a higher crystallization temperature (Tmore » c) for Cu silicidation. The Ea values of Cu 3Si formation for stacks with the ALD films were close to the reported value for grain boundary diffusion of Cu whereas the Ea of Cu 3Si formation for the stack with PVD TaN is closer to the reported value for lattice diffusion. For 3 nm films, grazing incidence in-plane XRD showed evidence of nanocrystallites in an amorphous matrix with broad peaks corresponding to high density cubic phase for the ALD grown films and lower density hexagonal phase for the PVD grown film further elucidating the difference in initial failure mechanisms due to differences in barrier crystallinity and associated phase.« less

How air pollution alters brain development: the role of neuroinflammation.

PubMed

Brockmeyer, Sam; D'Angiulli, Amedeo

2016-01-01

The present review synthesizes lines of emerging evidence showing how several samples of children populations living in large cities around the world suffer to some degree neural, behavioral and cognitive changes associated with air pollution exposure. The breakdown of natural barriers warding against the entry of toxic particles, including the nasal, gut and lung epithelial barriers, as well as widespread breakdown of the blood-brain barrier facilitatethe passage of airborne pollutants into the body of young urban residents. Extensive neuroinflammation contributes to cell loss within the central nervous system, and likely is a crucial mechanism by which cognitive deficits may arise. Although subtle, neurocognitive effects of air pollution are substantial, apparent across all populations, and potentially clinically relevant as early evidence of evolving neurodegenerative changes. The diffuse nature of the neuroinflammation risk suggests an integrated neuroscientific approach incorporating current clinical, cognitive, neurophysiological, radiological and epidemiologic research. Neuropediatric air pollution research requires extensive multidisciplinary collaborations to accomplish the goal of protecting exposed children through multidimensional interventions having both broad impact and reach. While intervening by improving environmental quality at a global scale is imperative, we also need to devise efficient strategies on how the neurocognitive effects on local pediatric populations should be monitored.

How air pollution alters brain development: the role of neuroinflammation

PubMed Central

Brockmeyer, Sam

2016-01-01

Abstract The present review synthesizes lines of emerging evidence showing how several samples of children populations living in large cities around the world suffer to some degree neural, behavioral and cognitive changes associated with air pollution exposure. The breakdown of natural barriers warding against the entry of toxic particles, including the nasal, gut and lung epithelial barriers, as well as widespread breakdown of the blood-brain barrier facilitatethe passage of airborne pollutants into the body of young urban residents. Extensive neuroinflammation contributes to cell loss within the central nervous system, and likely is a crucial mechanism by which cognitive deficits may arise. Although subtle, neurocognitive effects of air pollution are substantial, apparent across all populations, and potentially clinically relevant as early evidence of evolving neurodegenerative changes. The diffuse nature of the neuroinflammation risk suggests an integrated neuroscientific approach incorporating current clinical, cognitive, neurophysiological, radiological and epidemiologic research. Neuropediatric air pollution research requires extensive multidisciplinary collaborations to accomplish the goal of protecting exposed children through multidimensional interventions having both broad impact and reach. While intervening by improving environmental quality at a global scale is imperative, we also need to devise efficient strategies on how the neurocognitive effects on local pediatric populations should be monitored. PMID:28123818

SC lipid model membranes designed for studying impact of ceramide species on drug diffusion and permeation--part II: diffusion and permeation of model drugs.

PubMed

Ochalek, M; Podhaisky, H; Ruettinger, H-H; Wohlrab, J; Neubert, R H H

2012-10-01

The barrier function of two quaternary stratum corneum (SC) lipid model membranes, which were previously characterized with regard to the lipid organization, was investigated based on diffusion studies of model drugs with varying lipophilicities. Diffusion experiments of a hydrophilic drug, urea, and more lipophilic drugs than urea (i.e. caffeine, diclofenac sodium) were conducted using Franz-type diffusion cells. The amount of permeated drug was analyzed using either HPLC or CE technique. The subjects of interest in the present study were the investigation of the influence of physicochemical properties of model drugs on their diffusion and permeation through SC lipid model membranes, as well as the study of the impact of the constituents of these artificial systems (particularly ceramide species) on their barrier properties. The diffusion through both SC lipid model membranes and the human SC of the most hydrophilic model drug, urea, was faster than the permeation of the more lipophilic drugs. The slowest rate of permeation through SC lipid systems occurred in the case of caffeine. The composition of SC lipid model membranes has a significant impact on their barrier function. Model drugs diffused and permeated faster through Membrane II (presence of Cer [EOS]). In terms of the barrier properties, Membrane II is much more similar to the human SC than Membrane I. Copyright © 2012 Elsevier B.V. All rights reserved.

Modeling the Impenetrable Barrier to Inward Transport of Ultra-relativistic Radiation Belt Electrons

NASA Astrophysics Data System (ADS)

Tu, W.; Cunningham, G.; Chen, Y.; Baker, D. N.; Henderson, M. G.; Reeves, G. D.

2014-12-01

It has long been considered that the inner edge of the Earth's outer radiation belt is closely correlated with the minimum plasmapause location. However, recent discoveries by Baker et al. [1] show that it is not the case for ultra-relativistic electrons (2-10 MeV) in the radiation belt. Based on almost two years of Van Allen Probes/REPT data, they find that the inner edge of highly relativistic electrons is rarely collocated with the plasmapause; and more interestingly, there is a clear, persistent, and nearly impenetrable barrier to inward transport of high energy electrons, observed to locate at L~2.8. The presence of such an impenetrable barrier at this very specific location poses a significant puzzle. Using our DREAM3D diffusion model, which includes radial, pitch angle, and momentum diffusion, we are able to simulate the observed impenetrable barrier of ultra-relativistic electrons. The simulation demonstrates that during strong geomagnetic storms the plasmapause can be compressed to very low L region (sometimes as low as L~3), then strong chorus waves just outside the plasmapause can locally accelerate electrons up to multiple-MeV; when storm recovers, plasmapause moves back to large L, while the highly-relativistic electrons generated at low L continue to diffuse inward and slow decay by pitch angle diffusion from plasmaspheric hiss. The delicate balance between slow inward radial diffusion and weak pitch angle scattering creates a fixed inner boundary or barrier for ultra-relativistic electrons. The barrier is found to locate at a fixed L location, independent of the initial penetration depth of electrons that is correlated with the plasmapause location. Our simulation results quantitatively reproduce the evolution of the flux versus L profile, the L location of the barrier, and the decay rate of highly energetic electrons right outside the barrier. 1Baker, D. N., et al. (2014), Nearly Impenetrable Barrier to Inward Ultra-relativistic Magnetospheric Electron Transport, submitted to Nature.

Bio-Fluid Dynamics in a Centimeter-Scale Diagnostics Incubator with Integrated Perfusion

NASA Astrophysics Data System (ADS)

Vukasinovic, J.; Cullen, D. K.; Glezer, A.; Laplaca, M. C.

2006-11-01

Growing demands for long-term incubation of biologically faithful, three-dimensional neuronal and other cultures during extended physiological studies require efficient perfusion platforms with functional vasculatures that mimic the in vivo condition in a thermally regulated environment. While thermostatically controlled incubation baths with capillary action perfusion are available, their use is confined to specific experimental conditions. The interstitial nutrient and gas delivery remains diffusion limited over the long term and cultures decay metabolically. To overcome these problems, we describe simple fabrication and experimental characterization of a compact, diagnostics incubator that allows in situ monitoring of culture activity with a superior control of critical biological functions using convectively enhanced heat and mass transport. To overcome intercellular diffusion barriers culture is exposed to a direct flow of media issuing from an array of micro-nozzles that are directed normal to the substrate upholding the culture, and further improved by 3-D convection induced by jet interactions and biased, peripheral perfusate extraction through an array of microchannels as demonstrated by microPIV measurements.

Air pollution and detrimental effects on children's brain. The need for a multidisciplinary approach to the issue complexity and challenges.

PubMed

Calderón-Garcidueñas, Lilian; Torres-Jardón, Ricardo; Kulesza, Randy J; Park, Su-Bin; D'Angiulli, Amedeo

2014-01-01

Millions of children in polluted cities are showing brain detrimental effects. Urban children exhibit brain structural and volumetric abnormalities, systemic inflammation, olfactory, auditory, vestibular and cognitive deficits v low-pollution controls. Neuroinflammation and blood-brain-barrier (BBB) breakdown target the olfactory bulb, prefrontal cortex and brainstem, but are diffusely present throughout the brain. Urban adolescent Apolipoprotein E4 carriers significantly accelerate Alzheimer pathology. Neurocognitive effects of air pollution are substantial, apparent across all populations, and potentially clinically relevant as early evidence of evolving neurodegenerative changes. The diffuse nature of the neuroinflammation and neurodegeneration forces to employ a weight of evidence approach incorporating current clinical, cognitive, neurophysiological, radiological and epidemiological research. Pediatric air pollution research requires extensive multidisciplinary collaborations to accomplish a critical goal: to protect exposed children through multidimensional interventions having both broad impact and reach. Protecting children and teens from neural effects of air pollution should be of pressing importance for public health.

Air pollution and detrimental effects on children’s brain. The need for a multidisciplinary approach to the issue complexity and challenges

PubMed Central

Calderón-Garcidueñas, Lilian; Torres-Jardón, Ricardo; Kulesza, Randy J.; Park, Su-Bin; D’Angiulli, Amedeo

2014-01-01

Millions of children in polluted cities are showing brain detrimental effects. Urban children exhibit brain structural and volumetric abnormalities, systemic inflammation, olfactory, auditory, vestibular and cognitive deficits v low-pollution controls. Neuroinflammation and blood-brain-barrier (BBB) breakdown target the olfactory bulb, prefrontal cortex and brainstem, but are diffusely present throughout the brain. Urban adolescent Apolipoprotein E4 carriers significantly accelerate Alzheimer pathology. Neurocognitive effects of air pollution are substantial, apparent across all populations, and potentially clinically relevant as early evidence of evolving neurodegenerative changes. The diffuse nature of the neuroinflammation and neurodegeneration forces to employ a weight of evidence approach incorporating current clinical, cognitive, neurophysiological, radiological and epidemiological research. Pediatric air pollution research requires extensive multidisciplinary collaborations to accomplish a critical goal: to protect exposed children through multidimensional interventions having both broad impact and reach. Protecting children and teens from neural effects of air pollution should be of pressing importance for public health. PMID:25161617

Self-learning kinetic Monte Carlo simulations of diffusion in ferromagnetic α-Fe-Si alloys

NASA Astrophysics Data System (ADS)

Nandipati, Giridhar; Jiang, Xiujuan; Vemuri, Rama S.; Mathaudhu, Suveen; Rohatgi, Aashish

2018-01-01

Diffusion of Si atom and vacancy in the A2-phase of α-Fe-Si alloys in the ferromagnetic state, with and without magnetic order and in various temperature ranges, are studied using AKSOME, an on-lattice self-learning KMC code. Diffusion of the Si atom and the vacancy are studied in the dilute limit and up to 12 at.% Si, respectively, in the temperature range 350-700 K. Local Si neighborhood dependent activation energies for vacancy hops were calculated on-the-fly using a broken-bond model based on pairwise interaction. The migration barrier and prefactor for the Si diffusion in the dilute limit were obtained and found to agree with published data within the limits of uncertainty. Simulations results show that the prefactor and the migration barrier for the Si diffusion are approximately an order of magnitude higher, and a tenth of an electron-volt higher, respectively, in the magnetic disordered state than in the fully ordered state. However, the net result is that magnetic disorder does not have a significant effect on Si diffusivity within the range of parameters studied in this work. Nevertheless, with increasing temperature, the magnetic disorder increases and its effect on the Si diffusivity also increases. In the case of vacancy diffusion, with increasing Si concentration, its diffusion prefactor decreases while the migration barrier more or less remained constant and the effect of magnetic disorder increases with Si concentration. Important vacancy-Si/Fe atom exchange processes and their activation barriers were identified, and the effect of energetics on ordered phase formation in Fe-Si alloys are discussed.

Corrosion resistant coatings suitable for elevated temperature application

DOEpatents

Chan, Kwai S [San Antonio, TX; Cheruvu, Narayana Sastry [San Antonio, TX; Liang, Wuwei [Austin, TX

2012-07-31

The present invention relates to corrosion resistance coatings suitable for elevated temperature applications, which employ compositions of iron (Fe), chromium (Cr), nickel (Ni) and/or aluminum (Al). The compositions may be configured to regulate the diffusion of metals between a coating and a substrate, which may then influence coating performance, via the formation of an inter-diffusion barrier layer. The inter-diffusion barrier layer may comprise a face-centered cubic phase.

Kinetic Monte Carlo Simulation of Cation Diffusion in Low-K Ceramics

NASA Technical Reports Server (NTRS)

Good, Brian

2013-01-01

Low thermal conductivity (low-K) ceramic materials are of interest to the aerospace community for use as the thermal barrier component of coating systems for turbine engine components. In particular, zirconia-based materials exhibit both low thermal conductivity and structural stability at high temperature, making them suitable for such applications. Because creep is one of the potential failure modes, and because diffusion is a mechanism by which creep takes place, we have performed computer simulations of cation diffusion in a variety of zirconia-based low-K materials. The kinetic Monte Carlo simulation method is an alternative to the more widely known molecular dynamics (MD) method. It is designed to study "infrequent-event" processes, such as diffusion, for which MD simulation can be highly inefficient. We describe the results of kinetic Monte Carlo computer simulations of cation diffusion in several zirconia-based materials, specifically, zirconia doped with Y, Gd, Nb and Yb. Diffusion paths are identified, and migration energy barriers are obtained from density functional calculations and from the literature. We present results on the temperature dependence of the diffusivity, and on the effects of the presence of oxygen vacancies in cation diffusion barrier complexes as well.

Production of atmospheric pressure diffuse nanosecond pulsed dielectric barrier discharge using the array needles-plate electrode in air

NASA Astrophysics Data System (ADS)

Yang, De-zheng; Wang, Wen-chun; Jia, Li; Nie, Dong-xia; Shi, Heng-chao

2011-04-01

In this paper, a bidirectional high pulse voltage with 20 ns rising time is employed to generate an atmospheric pressure diffuse dielectric barrier discharge using the array needles-plate electrode configuration. Both double needle and multiple needle electrode configurations nanosecond pulsed dielectric barrier discharges are investigated. It is found that a diffuse discharge plasma with low gas temperature can be obtained, and the plasma volume increases with the increase of the pulse peak voltage, but remains almost constant with the increase of the pulse repetition rate. In addition to showing the potential application on a topographically nonuniform surface treatment of the discharge, the multiple needle-plate electrode configuration with different needle-plate electrode gaps are also employed to generate diffuse discharge plasma.

DNA damage in nasal and brain tissues of canines exposed to air pollutants is associated with evidence of chronic brain inflammation and neurodegeneration.

PubMed

Calderón-Garcidueñas, Lilian; Maronpot, Robert R; Torres-Jardon, Ricardo; Henríquez-Roldán, Carlos; Schoonhoven, Robert; Acuña-Ayala, Hilda; Villarreal-Calderón, Anna; Nakamura, Jun; Fernando, Reshan; Reed, William; Azzarelli, Biagio; Swenberg, James A

2003-01-01

Acute, subchronic, or chronic exposures to particulate matter (PM) and pollutant gases affect people in urban areas and those exposed to fires, disasters, and wars. Respiratory tract inflammation, production of mediators of inflammation capable of reaching the brain, systemic circulation of PM, and disruption of the nasal respiratory and olfactory barriers are likely in these populations. DNA damage is crucial in aging and in age-associated diseases such as Alzheimer's disease. We evaluated apurinic/apyrimidinic (AP) sites in nasal and brain genomic DNA, and explored by immunohistochemistry the expression of nuclear factor NFkappaB p65, inducible nitric oxide synthase (iNOS), cyclo-oxygenase 2 (COX2), metallothionein I and II, apolipoprotein E, amyloid precursor protein (APP), and beta-amyloid(1-42) in healthy dogs naturally exposed to urban pollution in Mexico City. Nickel (Ni) and vanadium (V) were measured by inductively coupled plasma mass spectrometry (ICP-MS). Forty mongrel dogs, ages 7 days-10 years were studied (14 controls from Tlaxcala and 26 exposed to urban pollution in South West Metropolitan Mexico City (SWMMC)). Nasal respiratory and olfactory epithelium were found to be early pollutant targets. Olfactory bulb and hippocampal AP sites were significantly higher in exposed than in control age matched animals. Ni and V were present in a gradient from olfactory mucosa > olfactory bulb > frontal cortex. Exposed dogs had (a) nuclear neuronal NFkappaB p65, (b) endothelial, glial and neuronal iNOS, (c) endothelial and glial COX2, (d) ApoE in neuronal, glial and vascular cells, and (e) APP and beta amyloid(1-42) in neurons, diffuse plaques (the earliest at age 11 months), and in subarachnoid blood vessels. Increased AP sites and the inflammatory and stress protein brain responses were early and significant in dogs exposed to urban pollution. Oil combustion PM-associated metals Ni and V were detected in the brain. There was an acceleration of Alzheimer's-type pathology in dogs chronically exposed to air pollutants. Respiratory tract inflammation and deteriorating olfactory and respiratory barriers may play a role in the observed neuropathology. These data suggest that Alzheimer's disease may be the sequela of air pollutant exposures and the resulting systemic inflammation.

The Diffusion Process of Patient Education in Dutch Community Pharmacy: An Exploration.

ERIC Educational Resources Information Center

Pronk, M. C. M.; Blom, A. Th. G.; Van Burg, A.; Jonkers, R.

2001-01-01

Identifies barriers and facilitators to the implementation of patient education in community pharmacies and classifies these barriers and facilitators into the diffusion stages of Rogers'"Innovations in Organizations" model. Discusses the implementation of patient education activities that require individual and organizational change in…

Effects of humidified and dry air on corneal endothelial cells during vitreal fluid-air exchange.

PubMed

Cekiç, Osman; Ohji, Masahito; Hayashi, Atsushi; Fang, Xiao Y; Kusaka, Shunji; Tano, Yasuo

2002-07-01

To report the immediate anatomic and functional alterations in corneal endothelial cells following use of humidified air and dry air during vitreal fluid-air exchange in rabbits. Experimental study. Rabbits undergoing pars plana vitrectomy and lensectomy were perfused with either dry or humidified air during fluid-air exchange for designated durations. Three different experiments were performed. First, control and experimental corneas were examined by scanning electron microscopy (SEM). Second, corneas were stained with Phalloidin-FITC and examined by fluorescein microscopy. Finally, third, transendothelial permeability for carboxyfluorescein was determined using a diffusion chamber. While different from the corneal endothelial cells, those cells exposed to humidified air were less stressed than cells exposed to dry air by SEM. Actin cytoskeleton was found highly disorganized with dry air exposure. Humidified air maintained the normal actin cytoskeleton throughout the 20 minutes of fluid-air exchange. Paracellular carboxyfluorescein leakage was significantly higher in dry air insufflated eyes compared with that of the humidified air after 5, 10, and 20 minutes of fluid-air exchange (P =.002, P =.004, and P =.002, respectively). Dry air stress during fluid-air exchange causes significant immediate alterations in monolayer appearance, actin cytoskeleton, and barrier function of corneal endothelium in aphakic rabbit eyes. Use of humidified air largely prevents the alterations in monolayer appearance, actin cytoskeleton, and barrier function of corneal endothelial cells.

Theory and simulation of ion conduction in the pentameric GLIC channel.

PubMed

Zhu, Fangqiang; Hummer, Gerhard

2012-10-09

GLIC is a bacterial member of the large family of pentameric ligand-gated ion channels. To study ion conduction through GLIC and other membrane channels, we combine the one-dimensional potential of mean force for ion passage with a Smoluchowski diffusion model, making it possible to calculate single-channel conductance in the regime of low ion concentrations from all-atom molecular dynamics (MD) simulations. We then perform MD simulations to examine sodium ion conduction through the GLIC transmembrane pore in two systems with different bulk ion concentrations. The ion potentials of mean force, calculated from umbrella sampling simulations with Hamiltonian replica exchange, reveal a major barrier at the hydrophobic constriction of the pore. The relevance of this barrier for ion transport is confirmed by a committor function that rises sharply in the barrier region. From the free evolution of Na(+) ions starting at the barrier top, we estimate the effective diffusion coefficient in the barrier region, and subsequently calculate the conductance of the pore. The resulting diffusivity compares well with the position-dependent ion diffusion coefficient obtained from restrained simulations. The ion conductance obtained from the diffusion model agrees with the value determined via a reactive-flux rate calculation. Our results show that the conformation in the GLIC crystal structure, with an estimated conductance of ~1 picosiemens at 140 mM ion concentration, is consistent with a physiologically open state of the channel.

TC-99 Decontaminant from heat treated gaseous diffusion membrane -Phase I, Part B

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

Oji, L.; Restivo, M.; Duignan, M.

2017-11-01

Uranium gaseous diffusion cascades represent a significant environmental challenge to dismantle, containerize and dispose as low-level radioactive waste. Baseline technologies rely on manual manipulations involving direct access to technetium-contaminated piping and materials. There is a potential to utilize novel decontamination technologies to remove the technetium and allow for on-site disposal of the very large uranium converters. Technetium entered these gaseous diffusion cascades as a hexafluoride complex in the same fashion as uranium. Technetium, as the isotope Tc-99, is an impurity that follows uranium in the first cycle of the Plutonium and Uranium Extraction (PUREX) process. The technetium speciation or exactmore » form in the gaseous diffusion cascades is not well defined. Several forms of Tc-99 compounds, mostly the fluorinated technetium compounds with varying degrees of volatility have been speculated by the scientific community to be present in these cascades. Therefore, there may be a possibility of using thermal or leaching desorption, which is independent of the technetium oxidation states, to perform an insitu removal of the technetium as a volatile species and trap the radionuclide on sorbent traps which could be disposed as low-level waste. Based on the positive results of the first part of this work1 the use of steam as a thermal decontamination agent was further explored with a second piece of used barrier material from a different location. This new series of tests included exposing more of the material surface to the flow of high temperature steam through the change in the reactor design, subjecting it to alternating periods of stream and vacuum, as well as determining if a lower temperature steam, i.e., 121°C (250°F) would be effective, too. Along with these methods, one other simpler method involving the leaching of the Tc-99 contaminated barrier material with a 1.0 M aqueous solution of ammonium carbonate, with and without sonication, was evaluated.« less

Amorphous-Metal-Film Diffusion Barriers

NASA Technical Reports Server (NTRS)

Nicolet, M. A.

1987-01-01

Incorporation of N into Ni/W films reduces reactivity with Si substrate. Paper describes reactions between Si substrates and deposited amorphous Ni/W or Ni/N/W films. Thermal stability of amorphous Ni/W films as diffusion barriers in Si markedly improved by introduction of N into Ni/W films during deposition.

Effect of stratum corneum heterogeneity, anisotropy, asymmetry and follicular pathway on transdermal penetration.

PubMed

Barbero, Ana M; Frasch, H Frederick

2017-08-28

The impact of the complex structure of the stratum corneum on transdermal penetration is not yet fully described by existing models. A quantitative and thorough study of skin permeation is essential for chemical exposure assessment and transdermal delivery of drugs. The objective of this study is to analyze the effects of heterogeneity, anisotropy, asymmetry, follicular diffusion, and location of the main barrier of diffusion on percutaneous permeation. In the current study, the solution of the transient diffusion through a two-dimensional-anisotropic brick-and-mortar geometry of the stratum corneum is obtained using the commercial finite element program COMSOL Multiphysics. First, analytical solutions of an equivalent multilayer geometry are used to determine whether the lipids or corneocytes constitute the main permeation barrier. Also these analytical solutions are applied for validations of the finite element solutions. Three illustrative compounds are analyzed in these sections: diethyl phthalate, caffeine and nicotine. Then, asymmetry with depth and follicular diffusion are studied using caffeine as an illustrative compound. The following findings are drawn from this study: the main permeation barrier is located in the lipid layers; the flux and lag time of diffusion through a brick-and-mortar geometry are almost identical to the values corresponding to a multilayer geometry; the flux and lag time are affected when the lipid transbilayer diffusivity or the partition coefficients vary with depth, but are not affected by depth-dependent corneocyte diffusivity; and the follicular contribution has significance for low transbilayer lipid diffusivity, especially when flux between the follicle and the surrounding stratum corneum is involved. This study demonstrates that the diffusion is primarily transcellular and the main barrier is located in the lipid layers. Published by Elsevier B.V.

Transport of Organic Compounds Through Porous Systems Containing Humic Acids.

PubMed

Smilek, Jiri; Sedlacek, Petr; Lastuvkova, Marcela; Kalina, Michal; Klucakova, Martina

2017-03-01

Soil pollution by the presence of different contaminants (e.g. heavy metal ions or pesticides) is one of the biggest problems worldwide. The positive affinity of natural humic acids towards these contaminants might contribute to the soil and ground water protection; therefore it is necessary to study the reactivity and barrier properties of humic acids. An original reactivity-mapping tool based on diffusion techniques designed to study the reactivity and barrier properties of polyelectrolytes was developed and tested on humic acids. The results of diffusion experiments demonstrate that the electrostatic interactions between humic acids functioning as a polyelectrolyte interpenetrated in a supporting hydrogel matrix (agarose) and cationic dye (methylene blue) as a model solute have a crucial impact on the rate of diffusion processes and on the barrier properties of hydrogels. The intensity of interactions was evaluated by fundamental diffusion parameters (effective diffusion coefficients and breakthrough time). The impact of modification of humic acids was also studied by means of diffusion experiments conducted on two types of standard humic acids (Leonardite 1S104H) and humic acids with selectively methylated carboxylic groups.

Communication: Surface-to-bulk diffusion of isolated versus interacting C atoms in Ni(111) and Cu(111) substrates: A first principle investigation.

PubMed

Harpale, Abhilash; Panesi, Marco; Chew, Huck Beng

2015-02-14

Using first principle calculations, we study the surface-to-bulk diffusion of C atoms in Ni(111) and Cu(111) substrates, and compare the barrier energies associated with the diffusion of an isolated C atom versus multiple interacting C atoms. We find that the preferential Ni-C bonding over C-C bonding induces a repulsive interaction between C atoms located at diagonal octahedral voids in Ni substrates. This C-C interaction accelerates C atom diffusion in Ni with a reduced barrier energy of ∼1 eV, compared to ∼1.4-1.6 eV for the diffusion of isolated C atoms. The diffusion barrier energy of isolated C atoms in Cu is lower than in Ni. However, bulk diffusion of interacting C atoms in Cu is not possible due to the preferential C-C bonding over C-Cu bonding, which results in C-C dimer pair formation near the surface. The dramatically different C-C interaction effects within the different substrates explain the contrasting growth mechanisms of graphene on Ni(111) and Cu(111) during chemical vapor deposition.

Illitization of Potassium, Cesium, and Ammonium Exchanged Smectite

NASA Astrophysics Data System (ADS)

Mills, M. M.; Wang, Y.; Payne, C.; Sanchez, A. C.; Boisvert, L.; Matteo, E. N.

2017-12-01

Bentonite clay is a primary choice for engineered barrier systems within geologic repositories for disposal of radioactive wastes due to its low permeability at saturated states, warranting diffusion as the dominant transport mechanism, and large swelling pressures that promote sealing. In order to predict how well the barrier will function over time at repository relevant temperatures, it is important to understand thermal alteration effects on montmorillonite, better known as smectite, a main constituent of bentonite. One type of thermal alteration is the conversion to illite, when exposed to elevated temperatures and a sufficient amount of potassium ions, thereby weakening barrier functions. To facilitate the conversion of smectite to illite and examine the influence of interlayer cations, illitization experiments on cation exchanged smectite were performed within hydrothermal reaction vessels over one week timescales. The <2um fraction of a Na-rich smectite clay was first exchanged with 1M Cs, K, and NH4 salt solutions and further exposed to hydrous pyrolysis using a 1M KCl solution with various solid to liquid ratios at 200°C. Multiple analysis techniques were used to characterize the altered clay and identify extent of conversion, such as XRD, cation exchange capacity, and morphology changes by SEM. The pore-water chemistry was also analyzed by ICP-OES to detect any dissolved products and silica content. Results suggest the conversion rate is relatively fast, occurring within days, and is dependent on not only the amount of K, but also dissolved silica concentration related to total solid in solution. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. SAND2017-7856A

Structural and Thermodynamic Factors of Suppressed Interdiffusion Kinetics in Multi-component High-entropy Materials

PubMed Central

Chang, Shou-Yi; Li, Chen-En; Huang, Yi-Chung; Hsu, Hsun-Feng; Yeh, Jien-Wei; Lin, Su-Jien

2014-01-01

We report multi-component high-entropy materials as extraordinarily robust diffusion barriers and clarify the highly suppressed interdiffusion kinetics in the multi-component materials from structural and thermodynamic perspectives. The failures of six alloy barriers with different numbers of elements, from unitary Ti to senary TiTaCrZrAlRu, against the interdiffusion of Cu and Si were characterized, and experimental results indicated that, with more elements incorporated, the failure temperature of the barriers increased from 550 to 900°C. The activation energy of Cu diffusion through the alloy barriers was determined to increase from 110 to 163 kJ/mole. Mechanistic analyses suggest that, structurally, severe lattice distortion strains and a high packing density caused by different atom sizes, and, thermodynamically, a strengthened cohesion provide a total increase of 55 kJ/mole in the activation energy of substitutional Cu diffusion, and are believed to be the dominant factors of suppressed interdiffusion kinetics through the multi-component barrier materials. PMID:24561911

Diffusion behavior of Cu/Ta heterogeneous interface under high temperature and high strain: An atomistic investigation

NASA Astrophysics Data System (ADS)

Li, Ganglong; Wu, Houya; Luo, Honglong; Chen, Zhuo; Tay, Andrew A. O.; Zhu, Wenhui

2017-09-01

Three-dimensional (3D) integration technology using Cu interconnections has emerged as a promising solution to improve the performance of silicon microelectronic devices. However, Cu diffuses into SiO2 and requires a barrier layer such as Ta to ensure acceptable reliability. In this paper, the effects of temperature and strain normal to the interface on the inter-diffusion of Cu and Ta at annealing conditions are investigated using a molecular dynamics (MD) technique with embedded atomic method (EAM) potentials. Under thermal annealing conditions without strain, it is found that a Cu-rich diffusion region approximately 2 nm thick is formed at 1000 K after 10 ns of annealing. Ta is capable of diffusing into the interior of Cu but Cu hardly diffuses into the inner lattice of Ta. At the Cu side near the interface an amorphous structure is formed due to the process of diffusion. The diffusion activation energy of Cu and Ta are found to be 0.9769 and 0.586 eV, respectively. However, when a strain is applied, a large number of crystal defects are generated in the sample. As the strain is increased, extrinsic stacking faults (ESFs) and lots of Shockley partial dislocations appear. The density of the dislocations and the diffusion channels increase, promoting the diffusion of Cu atoms into the inner lattice of Ta. The thickness of the diffusion layer increases to 4 times the value when only a temperature load of 700 K is applied. The MD simulations demonstrated that Ta is very effective as a barrier layer under thermal loading only, and its effectiveness is impaired by tensile strain at the Cu/Ta interface. The simulations also clarified the mechanism that caused the impairment. The methodology and approach described in this paper can be followed further to study the effectiveness of barrier layers under various annealing and strain conditions, and to determine the minimum thickness of barrier layers required for a particular application.

High-Performance Ink-Synthesized Cu-Gate Thin-Film Transistor with Diffusion Barrier Formation

NASA Astrophysics Data System (ADS)

Woo, Whang Je; Nam, Taewook; Oh, Il-Kwon; Maeng, Wanjoo; Kim, Hyungjun

2018-02-01

The improved electrical properties of Cu-gate thin-film transistors (TFTs) using an ink-synthesizing process were studied; this technology enables a low-cost and large area process for the display industry. We investigated the film properties and the effects of the ink-synthesized Cu layer in detail with respect to device characteristics. The mobility and reliability of the devices were significantly improved by applying a diffusion barrier at the interface between the Cu gate and the gate insulator. By using a TaN diffusion barrier layer, considerably improved and stabilized ink-Cu gated TFTs could be realized, comparable to sputtered-Cu gated TFTs under positive bias temperature stress measurements.

High-Performance Ink-Synthesized Cu-Gate Thin-Film Transistor with Diffusion Barrier Formation

NASA Astrophysics Data System (ADS)

Woo, Whang Je; Nam, Taewook; Oh, Il-Kwon; Maeng, Wanjoo; Kim, Hyungjun

2018-05-01

The improved electrical properties of Cu-gate thin-film transistors (TFTs) using an ink-synthesizing process were studied; this technology enables a low-cost and large area process for the display industry. We investigated the film properties and the effects of the ink-synthesized Cu layer in detail with respect to device characteristics. The mobility and reliability of the devices were significantly improved by applying a diffusion barrier at the interface between the Cu gate and the gate insulator. By using a TaN diffusion barrier layer, considerably improved and stabilized ink-Cu gated TFTs could be realized, comparable to sputtered-Cu gated TFTs under positive bias temperature stress measurements.

Metal diffusion barriers for GaAs solar cells.

PubMed

van Leest, R H; Mulder, P; Bauhuis, G J; Cheun, H; Lee, H; Yoon, W; van der Heijden, R; Bongers, E; Vlieg, E; Schermer, J J

2017-03-15

In this study accelerated ageing testing (AAT), J-V characterization and TEM imaging in combination with phase diagram data from literature are used to assess the potential of Ti, Ni, Pd and Pt as diffusion barriers for Au/Cu-based metallization of III-V solar cells. Ni barriers show the largest potential as at an AAT temperature of 250 °C both cells with 10 and 100 nm thick Ni barriers show significantly better performance compared to Au/Cu cells, with the cells with 10 nm Ni barriers even showing virtually no degradation after 7.5 days at 250 °C (equivalent to 10 years at 100 °C at an E a of 0.70 eV). Detailed investigation shows that Ni does not act as a barrier in the classical sense, i.e. preventing diffusion of Cu and Au across the barrier. Instead Ni modifies or slows down the interactions taking place during device degradation and thus effectively acts as an 'interaction' barrier. Different interactions occur at temperatures below and above 250 °C and for thin (10 nm) and thick (100 nm) barriers. The results of this study indicate that 10-100 nm thick Ni intermediate layers in the Cu/Au based metallization of III-V solar cells may be beneficial to improve the device stability upon exposure to elevated temperatures.

Assessing the permeability of the rat sciatic nerve epineural sheath against compounds with local anesthetic activity: an ex vivo electrophysiological study.

PubMed

Kagiava, Alexia; Theophilidis, George

2013-10-01

Abstract Studies have shown that the sciatic nerve epineural sheath acts as a barrier and has a delaying effect on the diffusion of local anesthetics into the nerve fibers and endoneurium. The purpose of this work is to assess and to quantify the permeability of the epineural sheath. For this purpose, we isolated the rat sciatic nerve in a three-chamber recording bath that allowed us to monitor the constant in amplitude evoked nerve compound action potential (nCAP) for over 24 h. For nerves exposed to the compounds under investigation, we estimated the IT50 the time required to inhibit the nCAP to 50% of its initial value. For desheathed nerves, the half-vitality time was denoted as IT50(-) and for the ensheath normal nerves as IT50(+). There was no significant difference between the IT50 of desheathed and ensheathed nerves exposed to normal saline. The IT50(-) for nerves exposed to 40 mM lidocaine was 12.1 ± 0.95 s (n=14) and the IT50(+) was 341.4 ± 2.49 s (n=6). The permeability (P) coefficient of the epineural sheath was defined as the ratio IT50(+)/IT50(-). The P coefficient for 40 mM lidocaine and linalool was 28.2 and 3.48, correspondingly, and for 30 mM 2-heptanone was 4.87. This is an indication that the epineural sheath provided a stronger barrier against lidocaine, compared to natural local anesthetics, linalool and 2-heptanone. The methodology presented here is a useful tool for studying epineural sheath permeability to compounds with local anesthetic properties.

Different approach to the modeling of nonfree particle diffusion

NASA Astrophysics Data System (ADS)

Buhl, Niels

2018-03-01

A new approach to the modeling of nonfree particle diffusion is presented. The approach uses a general setup based on geometric graphs (networks of curves), which means that particle diffusion in anything from arrays of barriers and pore networks to general geometric domains can be considered and that the (free random walk) central limit theorem can be generalized to cover also the nonfree case. The latter gives rise to a continuum-limit description of the diffusive motion where the effect of partially absorbing barriers is accounted for in a natural and non-Markovian way that, in contrast to the traditional approach, quantifies the absorptivity of a barrier in terms of a dimensionless parameter in the range 0 to 1. The generalized theorem gives two general analytic expressions for the continuum-limit propagator: an infinite sum of Gaussians and an infinite sum of plane waves. These expressions entail the known method-of-images and Laplace eigenfunction expansions as special cases and show how the presence of partially absorbing barriers can lead to phenomena such as line splitting and band gap formation in the plane wave wave-number spectrum.

Multiple Diffusion Mechanisms Due to Nanostructuring in Crowded Environments

PubMed Central

Sanabria, Hugo; Kubota, Yoshihisa; Waxham, M. Neal

2007-01-01

One of the key questions regarding intracellular diffusion is how the environment affects molecular mobility. Mostly, intracellular diffusion has been described as hindered, and the physical reasons for this behavior are: immobile barriers, molecular crowding, and binding interactions with immobile or mobile molecules. Using results from multi-photon fluorescence correlation spectroscopy, we describe how immobile barriers and crowding agents affect translational mobility. To study the hindrance produced by immobile barriers, we used sol-gels (silica nanostructures) that consist of a continuous solid phase and aqueous phase in which fluorescently tagged molecules diffuse. In the case of molecular crowding, translational mobility was assessed in increasing concentrations of 500 kDa dextran solutions. Diffusion of fluorescent tracers in both sol-gels and dextran solutions shows clear evidence of anomalous subdiffusion. In addition, data from the autocorrelation function were analyzed using the maximum entropy method as adapted to fluorescence correlation spectroscopy data and compared with the standard model that incorporates anomalous diffusion. The maximum entropy method revealed evidence of different diffusion mechanisms that had not been revealed using the anomalous diffusion model. These mechanisms likely correspond to nanostructuring in crowded environments and to the relative dimensions of the crowding agent with respect to the tracer molecule. Analysis with the maximum entropy method also revealed information about the degree of heterogeneity in the environment as reported by the behavior of diffusive molecules. PMID:17040979

Volatility of Common Protective Oxides in High-Temperature Water Vapor: Current Understanding and Unanswered Questions

NASA Technical Reports Server (NTRS)

Opila, Elizabeth J.

2004-01-01

Many structural materials rely on the formation of chromia, silica or alumina as a protective layer when exposed in high temperature oxidizing environments. The presence of these oxide layers provides a protective diffusion barrier which slows down further oxidation. In atmospheres containing water vapor, however, reactions to form volatile hydroxide species occur which remove the surface oxide, thus, lowering the protective capability of the oxide scale. This paper summarizes the current understanding of volatility of chromia, silica and alumina in water vapor containing combustion environments. In addition unanswered questions in each system are discussed. Th current paper represents an update on the considerable information learned in the past five years for these systems.

Field comparison of several commercially available radon detectors.

PubMed Central

Field, R W; Kross, B C

1990-01-01

To determine the accuracy and precision of commercially available radon detectors in a field setting, 15 detectors from six companies were exposed to radon and compared to a reference radon level. The detectors from companies that had already passed National Radon Measurement Proficiency Program testing had better precision and accuracy than those detectors awaiting proficiency testing. Charcoal adsorption detectors and diffusion barrier charcoal adsorption detectors performed very well, and the latter detectors displayed excellent time averaging ability. Alternatively, charcoal liquid scintillation detectors exhibited acceptable accuracy but poor precision, and bare alpha registration detectors showed both poor accuracy and precision. The mean radon level reported by the bare alpha registration detectors was 68 percent lower than the radon reference level. PMID:2368851

General Protein Diffusion Barriers create Compartments within Bacterial Cells

PubMed Central

Schlimpert, Susan; Klein, Eric A.; Briegel, Ariane; Hughes, Velocity; Kahnt, Jörg; Bolte, Kathrin; Maier, Uwe G.; Brun, Yves V.; Jensen, Grant J.; Gitai, Zemer; Thanbichler, Martin

2013-01-01

SUMMARY In eukaryotes, the differentiation of cellular extensions such as cilia or neuronal axons depends on the partitioning of proteins to distinct plasma membrane domains by specialized diffusion barriers. However, examples of this compartmentalization strategy are still missing for prokaryotes, although complex cellular architectures are widespread among this group of organisms. This study reveals the existence of a protein-mediated membrane diffusion barrier in the stalked bacterium Caulobacter crescentus. We show that the Caulobacter cell envelope is compartmentalized by macromolecular complexes that prevent the exchange of both membrane and soluble proteins between the polar stalk extension and the cell body. The barrier structures span the cross-sectional area of the stalk and comprise at least four proteins that assemble in a cell cycle-dependent manner. Their presence is critical for cellular fitness, as they minimize the effective cell volume, allowing faster adaptation to environmental changes that require de novo synthesis of envelope proteins. PMID:23201141

Theoretical analysis of nBn infrared photodetectors

NASA Astrophysics Data System (ADS)

Ting, David Z.; Soibel, Alexander; Khoshakhlagh, Arezou; Gunapala, Sarath D.

2017-09-01

The depletion and surface leakage dark current suppression properties of unipolar barrier device architectures such as the nBn have been highly beneficial for III-V semiconductor-based infrared detectors. Using a one-dimensional drift-diffusion model, we theoretically examine the effects of contact doping, minority carrier lifetime, and absorber doping on the dark current characteristics of nBn detectors to explore some basic aspects of their operation. We found that in a properly designed nBn detector with highly doped excluding contacts the minority carriers are extracted to nonequilibrium levels under reverse bias in the same manner as the high operating temperature (HOT) detector structure. Longer absorber Shockley-Read-Hall (SRH) lifetimes result in lower diffusion and depletion dark currents. Higher absorber doping can also lead to lower diffusion and depletion dark currents, but the benefit should be weighted against the possibility of reduced diffusion length due to shortened SRH lifetime. We also briefly examined nBn structures with unintended minority carrier blocking barriers due to excessive n-doping in the unipolar electron barrier, or due to a positive valence band offset between the barrier and the absorber. Both types of hole blocking structures lead to higher turn-on bias, although barrier n-doping could help suppress depletion dark current.

Large size self-assembled quantum rings: quantum size effect and modulation on the surface diffusion.

PubMed

Tong, Cunzhu; Yoon, Soon Fatt; Wang, Lijun

2012-09-24

We demonstrate experimentally the submicron size self-assembled (SA) GaAs quantum rings (QRs) by quantum size effect (QSE). An ultrathin In0.1 Ga0.9As layer with different thickness is deposited on the GaAs to modulate the surface nucleus diffusion barrier, and then the SA QRs are grown. It is found that the density of QRs is affected significantly by the thickness of inserted In0.1 Ga0.9As, and the diffusion barrier modulation reflects mainly on the first five monolayer . The physical mechanism behind is discussed. The further analysis shows that about 160 meV decrease in diffusion barrier can be achieved, which allows the SA QRs with density of as low as one QR per 6 μm2. Finally, the QRs with diameters of 438 nm and outer diameters of 736 nm are fabricated using QSE.

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.

Diffusion barriers in modified air brazes

DOEpatents

Weil, Kenneth Scott; Hardy, John S; Kim, Jin Yong; Choi, Jung-Pyung

2013-04-23

A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

Diffusion barriers in modified air brazes

DOEpatents

Weil, Kenneth Scott [Richland, WA; Hardy, John S [Richland, WA; Kim, Jin Yong [Richland, WA; Choi, Jung-Pyung [Richland, WA

2010-04-06

A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

The Ponseti method in Latin America: initial impact and barriers to its diffusion and implementation.

PubMed

Boardman, Allison; Jayawardena, Asitha; Oprescu, Florin; Cook, Thomas; Morcuende, Jose A

2011-01-01

The Ponseti method for correcting clubfoot is a safe, effective, and minimally invasive treatment that has recently been implemented in Latin America. This study evaluates the initial impact and unique barriers to the diffusion of the Ponseti method throughout this region. Structured interviews were conducted with 30 physicians practicing the Ponseti method in three socioeconomically diverse countries: Chile, Peru and Guatemala. Since learning the Ponseti method, these physicians have treated approximately 1,740 clubfoot patients, with an estimated 1,705 (98%) patients treated using the Ponseti method, and 35 (2%) patients treated using surgical techniques. The barriers were classified into the following themes: physician education, health care system of the country, culture and beliefs of patients, physical distance and transport, financial barriers for patients, and parental compliance with the method. The results yielded several common barriers throughout Latin America including lack of physician education, physical distance to the treatment centers, and financial barriers for patients. Information from this study can be used to inform, and to implement and evaluate specific strategies to improve the diffusion of the Ponseti method for treating clubfoot throughout Latin America.

Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped MgAl2O4

NASA Astrophysics Data System (ADS)

O'Rourke, Conn; Morgan, Benjamin J.

2018-04-01

The (Li,Al)-codoped magnesium spinel (LixMg1 -2 xAl2 +xO4 ) is a solid lithium-ion electrolyte with potential use in all-solid-state lithium-ion batteries. The spinel structure means that interfaces with spinel electrodes, such as LiyMn2O4 and Li4 +3 zTi5O12 , may be lattice matched, with potentially low interfacial resistances. Small lattice parameter differences across a lattice-matched interface are unavoidable, causing residual epitaxial strain. This strain potentially modifies lithium diffusion near the electrolyte-electrode interface, contributing to interfacial resistance. Here, we report a density functional theory study of strain effects on lithium diffusion pathways for (Li,Al)-codoped magnesium spinel, for xLi=0.25 and xLi=0.5 . We have calculated diffusion profiles for the unstrained materials, and for isotropic and biaxial tensile strains of up to 6 % , corresponding to {100 } epitaxial interfaces with LiyMn2O4 and Li4 +3 zTi5O12 . We find that isotropic tensile strain reduces lithium diffusion barriers by as much as 0.32 eV , with typical barriers reduced by ˜0.1 eV. This effect is associated with increased volumes of transitional octahedral sites, and broadly follows qualitative changes in local electrostatic potentials. For biaxial (epitaxial) strain, which more closely approximates strain at a lattice-matched electrolyte-electrode interface, changes in octahedral site volumes and in lithium diffusion barriers are much smaller than under isotropic strain. Typical barriers are reduced by only ˜0.05 eV. Individual effects, however, depend on the pathway considered and the relative strain orientation. These results predict that isotropic strain strongly affects ionic conductivities in (Li,Al)-codoped magnesium spinel electrolytes, and that tensile strain is a potential route to enhanced lithium transport. For a lattice-matched interface with candidate spinel-structured electrodes, however, epitaxial strain has a small, but complex, effect on lithium diffusion barriers.

[Cerebral metabolism and permeability of the hemato-encephalic barrier in an experimental model for brain radiotherapy].

PubMed

Cicciarello, R; Russi, E; Albiero, F; Mesiti, M; Torre, E; D'Aquino, A; Raffaele, L; Bertolani, S; D'Avella, D

1990-11-01

Whole brain irradiation (WBR) can produce acute and chronic neurological adverse effects, which are usually divided into acute, early delayed and late delayed reactions according to the time of onset. To assess the impact of WBR on brain functional parameters during the early-delayed phase, we employed the [14C]-2-deoxyglucose (2-DG) and the [14C]-alfa-aminoisobutyric (AIB) acid quantitative autoradiographic techniques to study local cerebral glucose utilization and blood-brain barrier permeability, respectively. Sprague-Dowley albino rats were exposed to conventional fractionation (200 Gy/day 5 days a week) for a total dose of 4000 Gy. Experiments were made 3 weeks after completion of the radiation exposure. In comparison with control and sham-irradiated animals, cerebral metabolic activity was diffusely decreased following irradiation. As a rule, brain areas with the highest basal metabolic rates showed the highest percentage drop in glucose utilization. Changes in blood-brain barrier function, as assessed by an increased transcapillary transport of AIB, were also demonstrated in specific brain regions. This study illustrates how moderate doses of WBR induce well-defined changes in brain metabolism and BBB function, which are possibly involved in the pathogenesis of the early-delayed radiation-induced cerebral dysfunction in humans.

Molecular dynamics simulations of substitutional diffusion

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

Zhou, Xiaowang; Jones, Reese E.; Gruber, Jacob

2016-12-18

In atomistic simulations, diffusion energy barriers are usually calculated for each atomic jump path using a nudged elastic band method. Practical materials often involve thousands of distinct atomic jump paths that are not known a priori. Hence, it is often preferred to determine an overall diffusion energy barrier and an overall pre-exponential factor from the Arrhenius equation constructed through molecular dynamics simulations of mean square displacement of the diffusion species at different temperatures. This approach has been well established for interstitial diffusion, but not for substitutional diffusion at the same confidence. Using In 0.1 Ga 0.9 N as an example,more » we have identified conditions where molecular dynamics simulations can be used to calculate highly converged Arrhenius plots for substitutional alloys. As a result, this may enable many complex diffusion problems to be easily and reliably studied in the future using molecular dynamics, provided that moderate computing resources are available.« less

Temperature- and composition-dependent hydrogen diffusivity in palladium from statistically-averaged molecular dynamics

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

Zhou, Xiaowang; Heo, Tae Wook; Wood, Brandon C.

Solid-state hydrogen storage materials undergo complex phase transformations whose kinetics is often limited by hydrogen diffusion. Among metal hydrides, palladium hydride undergoes a diffusional phase transformation upon hydrogen uptake, during which the hydrogen diffusivity varies with hydrogen composition and temperature. Here we perform robust statistically-averaged molecular dynamics simulations to obtain a well-converged analytical expression for hydrogen diffusivity in bulk palladium that is valid throughout all stages of the reaction. Our studies confirm significant dependence of the diffusivity on composition and temperature that elucidate key trends in the available experimental measurements. Whereas at low hydrogen compositions, a single process dominates, atmore » high hydrogen compositions, diffusion is found to exhibit behavior consistent with multiple hopping barriers. Further analysis, supported by nudged elastic band computations, suggests that the multi-barrier diffusion can be interpreted as two distinct mechanisms corresponding to hydrogen-rich and hydrogen-poor local environments.« less

Temperature- and composition-dependent hydrogen diffusivity in palladium from statistically-averaged molecular dynamics

DOE PAGES

Zhou, Xiaowang; Heo, Tae Wook; Wood, Brandon C.; ...

2018-03-09

Solid-state hydrogen storage materials undergo complex phase transformations whose kinetics is often limited by hydrogen diffusion. Among metal hydrides, palladium hydride undergoes a diffusional phase transformation upon hydrogen uptake, during which the hydrogen diffusivity varies with hydrogen composition and temperature. Here we perform robust statistically-averaged molecular dynamics simulations to obtain a well-converged analytical expression for hydrogen diffusivity in bulk palladium that is valid throughout all stages of the reaction. Our studies confirm significant dependence of the diffusivity on composition and temperature that elucidate key trends in the available experimental measurements. Whereas at low hydrogen compositions, a single process dominates, atmore » high hydrogen compositions, diffusion is found to exhibit behavior consistent with multiple hopping barriers. Further analysis, supported by nudged elastic band computations, suggests that the multi-barrier diffusion can be interpreted as two distinct mechanisms corresponding to hydrogen-rich and hydrogen-poor local environments.« less

Diffusion barrier properties of single- and multilayered quasi-amorphous tantalum nitride thin films against copper penetration

NASA Astrophysics Data System (ADS)

Chen, G. S.; Chen, S. T.

2000-06-01

Tantalum-related thin films containing different amounts of nitrogen are sputter deposited at different argon-to-nitrogen flow rate ratios on (100) silicon substrates. Using x-ray diffractometry, transmission electron microscopy, composition and resistivity analyses, and bending-beam stress measurement technique, this work examines the impact of varying the nitrogen flow rate, particularly on the crystal structure, composition, resistivity, and residual intrinsic stress of the deposited Ta2N thin films. With an adequate amount of controlled, reactive nitrogen in the sputtering gas, thin films of the tantalum nitride of nominal formula Ta2N are predominantly amorphous and can exist over a range of nitrogen concentrations slightly deviated from stoichiometry. The single-layered quasi-amorphous Ta2N (a-Ta2N) thin films yield intrinsic compressive stresses in the range 3-5 GPa. In addition, the use of the 40-nm-thick a-Ta2N thin films with different nitrogen atomic concentrations (33% and 36%) and layering designs as diffusion barriers between silicon and copper are also evaluated. When subjected to high-temperature annealing, the single-layered a-Ta2N barrier layers degrade primarily by an amorphous-to-crystalline transition of the barrier layers. Crystallization of the single-layered stoichiometric a-Ta2N (Ta67N33) diffusion barriers occurs at temperatures as low as 450 °C. Doing so allows copper to preferentially penetrate through the grain boundaries or thermal-induced microcracks of the crystallized barriers and react with silicon, sequentially forming {111}-facetted pyramidal Cu3Si precipitates and TaSi2 Overdoping nitrogen into the amorphous matrix can dramatically increase the crystallization temperature to 600 °C. This temperature increase slows down the inward diffusion of copper and delays the formation of both silicides. The nitrogen overdoped Ta2N (Ta64N36) diffusion barriers can thus be significantly enhanced so as to yield a failure temperature 100 °C greater than that of the Ta67N33 diffusion barriers. Moreover, multilayered films, formed by alternately stacking the Ta67N33 and Ta64N36 layers with an optimized bilayer thickness (λ) of 10 nm, can dramatically reduce the intrinsic compressive stress to only 0.7 GPa and undergo high-temperature annealing without crystallization. Therefore, the Ta67N33/Ta64N36 multilayered films exhibit a much better barrier performance than the highly crystallization-resistant Ta64N36 single-layered films.

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.

Effects of sodium and potassium on the photovoltaic performance of CIGS solar cells

DOE PAGES

Raguse, John M.; Muzzillo, Christopher P.; Sites, James R.; ...

2016-11-17

Here, the deliberate introduction of K and Na into Cu(In, Ga)Se 2 (CIGS) absorbers was investigated by varying a combination of an SiO 2 diffusion barrier, coevaporation of KF with the CIGS absorber, and a KF postdeposition treatment (PDT). Devices made with no diffusion barrier and KF coevaporation treatment exhibited the highest photovoltaic conversion efficiency with the smallest overall distribution in key current density-voltage (J-V) performance metrics. Out-diffusion of Na and K from the substrate, KF coevaporation, and KF PDT all increased carrier concentration, open-circuit voltage, fill factor, and power conversion efficiency. Quantum-efficiency analysis of devices highlighted the greatest lossmore » in the short-circuit current density due to incomplete absorption and collection. Secondary ion mass spectrometry illustrated the efficacy of the SiO 2 film as a sodium and potassium diffusion barrier, as well as their relative concentration in the absorber. Introduction of KF appeared to enhance diffusion of Na from the substrate, in agreement with previous studies.« less

Chromium oxide as a metal diffusion barrier layer: An x-ray absorption fine structure spectroscopy study

NASA Astrophysics Data System (ADS)

Ahamad Mohiddon, Md.; Lakshun Naidu, K.; Ghanashyam Krishna, M.; Dalba, G.; Ahmed, S. I.; Rocca, F.

2014-01-01

The interaction at the interface between chromium and amorphous Silicon (a-Si) films in the presence of a sandwich layer of chromium oxide is investigated using X-ray absorption fine structure (XAFS) spectroscopy. The oxidized interface was created, in situ, prior to the deposition of a 400 nm tick a-Si layer over a 50 nm tick Cr layer. The entire stack of substrate/metallic Cr/Cr2O3/a-Si was then annealed at temperatures from 300 up to 700 °C. Analysis of the near edge and extended regions of each XAFS spectrum shows that only a small fraction of Cr is able to diffuse through the oxide layer up to 500 °C, while the remaining fraction is buried under the oxide layer in the form of metallic Cr. At higher temperatures, diffusion through the oxide layer is enhanced and the diffused metallic Cr reacts with a-Si to form CrSi2. At 700 °C, the film contains Cr2O3 and CrSi2 without evidence of unreacted metallic Cr. The activation energy and diffusion coefficient of Cr are quantitatively determined in the two temperature regions, one where the oxide acts as diffusion barrier and another where it is transparent to Cr diffusion. It is thus demonstrated that chromium oxide can be used as a diffusion barrier to prevent metal diffusion into a-Si.

Characteristics of WN{sub x}C{sub y} films deposited using remote plasma atomic layer deposition with ({sup Me}Cp)W(CO){sub 2}(NO) for Cu diffusion barrier

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

Kim, Hyunjung; Park, Jingyu; Jeon, Heeyoung

Diffusion barrier characteristics of tungsten–nitride–carbide (WN{sub x}C{sub y}) thin films interposed between Cu and SiO{sub 2} layers were studied. The WN{sub x}C{sub y} films were deposited by remote plasma atomic layer deposition (RPALD) using a metal organic source, ({sup Me}Cp)W(CO){sub 2}(NO), and ammonia. Auger electron spectroscopy analysis indicated the WN{sub x}C{sub y} films consisted of tungsten, nitrogen, carbon, and oxygen. X-ray diffraction (XRD) analysis showed that the film deposited at 350 °C was nanocrystalline. The resistivity of WN{sub x}C{sub y} film deposited by RPALD was very low compared to that in previous research because of the lower nitrogen content and differentmore » crystal structures of the WN{sub x}C{sub y}. To verify the diffusion barrier characteristics of the WN{sub x}C{sub y} film, Cu films were deposited by physical vapor deposition after WN{sub x}C{sub y} film was formed by RPALD on Si substrate. The Cu/WN{sub x}C{sub y}/Si film stack was annealed in a vacuum by rapid thermal annealing at 500 °C. Cu diffusion through the barrier layer was verified by XRD. Stable film properties were observed up to 500 °C, confirming that WN{sub x}C{sub y} film is suitable as a Cu diffusion barrier in microelectronic circuits.« less

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.

Alterations of apparent diffusion coefficient (ADC) in the brain of rats chronically exposed to lead acetate.

PubMed

López-Larrubia, Pilar; Cauli, Omar

2011-03-15

Diffusion-weighted imaging (DWI) allows the assessment of the water apparent diffusion coefficient (ADC), a measure of tissue water diffusivity which is altered during different pathological conditions such as cerebral oedema. By means of DWI, we repeatedly measured in the same rats apparent diffusion coefficient ADC in different brain areas (motor cortex (MCx), somato-sensory cortex (SCx), caudate-putamen (CPu), hippocampus (Hip), mesencephalic reticular formation (RF), corpus callosum (CC) and cerebellum (Cb)) after 1 week, 4 and 12 weeks of lead acetate exposure via drinking water (50 or 500 ppm). After 12 weeks of lead exposure rats received albumin-Evans blue complex administration and were sacrificed 1h later. Blood-brain barrier permeability and water tissue content were determined in order to evaluate their relationship with ADC changes. Chronic exposure to lead acetate (500 ppm) for 4 weeks increased ADC values in Hip, RF and Cb but no in other brain areas. After 12 weeks of lead acetate exposure at 500 ppm ADC is significantly increased also in CPu and CC. Brain areas displaying high ADC values after lead exposure showed also an increased water content and increased BBB permeability to Evans blue-albumin complex. Exposure to 50 ppm for 12 weeks increased ADC values and BBB permeability in the RF and Cb. In summary, chronic lead exposure induces cerebral oedema in the adult brain depending on the brain area and the dose of exposure. RF and Cb appeared the most sensitive brain areas whereas cerebral cortex appears resistant to lead-induced cerebral oedema. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

Physical barrier effect of geopolymeric waste form on diffusivity of cesium and strontium.

PubMed

Jang, J G; Park, S M; Lee, H K

2016-11-15

The present study investigates the physical barrier effect of geopolymeric waste form on leaching behavior of cesium and strontium. Fly ash-based geopolymers and slag-blended geopolymers were used as solidification agents. The leaching behavior of cesium and strontium from geopolymers was evaluated in accordance with ANSI/ANS-16.1. The diffusivity of cesium and strontium in a fly ash-based geopolymer was lower than that in Portland cement by a factor of 10(3) and 10(4), respectively, showing significantly improved immobilization performance. The leaching resistance of fly ash-based geopolymer was relatively constant regardless of the type of fly ash. The diffusivity of water-soluble cesium and strontium ions were highly correlated with the critical pore diameter of the binder. The critical pore diameter of the fly ash-based geopolymer was remarkably smaller than those of Portland cement and slag-blended geopolymer; consequently, its ability physically to retard the diffusion of nuclides (physical barrier effect) was superior. Copyright © 2016 Elsevier B.V. All rights reserved.

Diffusion Tensor Imaging of Frontal White Matter and Executive Functioning in Cocaine-Exposed Children

PubMed Central

Warner, Tamara Duckworth; Behnke, Marylou; Eyler, Fonda Davis; Padgett, Kyle; Leonard, Christiana; Hou, Wei; Garvan, Cynthia Wilson; Schmalfuss, Ilona M.; Blackband, Stephen J.

2011-01-01

BACKGROUND Although animal studies have demonstrated frontal white matter and behavioral changes resulting from prenatal cocaine exposure, no human studies have associated neuropsychological deficits in attention and inhibition with brain structure. We used diffusion tensor imaging to investigate frontal white matter integrity and executive functioning in cocaine-exposed children. METHODS Six direction diffusion tensor images were acquired using a Siemens 3T scanner with a spin-echo echo-planar imaging pulse sequence on right-handed cocaine-exposed (n = 28) and sociodemographically similar non-exposed children (n = 25; mean age: 10.6 years) drawn from a prospective, longitudinal study. Average diffusion and fractional anisotropy were measured in the left and right frontal callosal and frontal projection fibers. Executive functioning was assessed using two well-validated neuropsychological tests (Stroop color-word test and Trail Making Test). RESULTS Cocaine-exposed children showed significantly higher average diffusion in the left frontal callosal and right frontal projection fibers. Cocaine-exposed children were also significantly slower on a visual-motor set-shifting task with a trend toward lower scores on a verbal inhibition task. Controlling for gender and intelligence, average diffusion in the left frontal callosal fibers was related to prenatal exposure to alcohol and marijuana and an interaction between cocaine and marijuana exposure. Performance on the visual-motor set-shifting task was related to prenatal cocaine exposure and an interaction between cocaine and tobacco exposure. Significant correlations were found between test performance and fractional anisotropy in areas of the frontal white matter. CONCLUSIONS Prenatal cocaine exposure, alone and in combination with exposure to other drugs, is associated with slightly poorer executive functioning and subtle microstructural changes suggesting less mature development of frontal white matter pathways. The relative contribution of postnatal environmental factors, including characteristics of the caregiving environment and stressors associated with poverty and out-of-home placement, on brain development and behavioral functioning in polydrug-exposed children awaits further research. PMID:17079574

Diffusion tensor imaging of frontal white matter and executive functioning in cocaine-exposed children.

PubMed

Warner, Tamara Duckworth; Behnke, Marylou; Eyler, Fonda Davis; Padgett, Kyle; Leonard, Christiana; Hou, Wei; Garvan, Cynthia Wilson; Schmalfuss, Ilona M; Blackband, Stephen J

2006-11-01

Although animal studies have demonstrated frontal white matter and behavioral changes resulting from prenatal cocaine exposure, no human studies have associated neuropsychological deficits in attention and inhibition with brain structure. We used diffusion tensor imaging to investigate frontal white matter integrity and executive functioning in cocaine-exposed children. Six direction diffusion tensor images were acquired using a Siemens 3T scanner with a spin-echo echo-planar imaging pulse sequence on right-handed cocaine-exposed (n = 28) and sociodemographically similar non-exposed children (n = 25; mean age: 10.6 years) drawn from a prospective, longitudinal study. Average diffusion and fractional anisotropy were measured in the left and right frontal callosal and frontal projection fibers. Executive functioning was assessed using two well-validated neuropsychological tests (Stroop color-word test and Trail Making Test). Cocaine-exposed children showed significantly higher average diffusion in the left frontal callosal and right frontal projection fibers. Cocaine-exposed children were also significantly slower on a visual-motor set-shifting task with a trend toward lower scores on a verbal inhibition task. Controlling for gender and intelligence, average diffusion in the left frontal callosal fibers was related to prenatal exposure to alcohol and marijuana and an interaction between cocaine and marijuana exposure. Performance on the visual-motor set-shifting task was related to prenatal cocaine exposure and an interaction between cocaine and tobacco exposure. Significant correlations were found between test performance and fractional anisotropy in areas of the frontal white matter. Prenatal cocaine exposure, alone and in combination with exposure to other drugs, is associated with slightly poorer executive functioning and subtle microstructural changes suggesting less mature development of frontal white matter pathways. The relative contribution of postnatal environmental factors, including characteristics of the caregiving environment and stressors associated with poverty and out-of-home placement, on brain development and behavioral functioning in polydrug-exposed children awaits further research.

Purposeful exposure of a polylactic acid barrier to achieve socket preservation for placement of dental implants: case series report.

PubMed

Rosen, Paul S; Rosen, Adam D

2013-01-01

This retrospective case series reports on the use of a polylactic acid barrier that was left exposed in the process of socket preparation for the placement of dental implants. A retrospective chart review found 43 patients with 48 extraction sockets that were treated in this manner. Teeth were removed and the sockets were thoroughly debrided, with 40 of them receiving a bone replacement graft covered by the polylactic acid barrier and the additional 8 receiving the membrane alone. Suturing left the barrier exposed, and the sites were re-entered on average at 23 weeks for the placement of a dental implant. All sites were able to receive a dental implant, demonstrating the ability to leave a polylactic acid barrier exposed and achieve successful guided bone regeneration (GBR) results. This ultimately helped avoid some of the negative sequelae of trying to achieve primary closure of the flaps at the time of tooth extraction.

Diffusion and interactions of interstitials in hard-sphere interstitial solid solutions

NASA Astrophysics Data System (ADS)

van der Meer, Berend; Lathouwers, Emma; Smallenburg, Frank; Filion, Laura

2017-12-01

Using computer simulations, we study the dynamics and interactions of interstitial particles in hard-sphere interstitial solid solutions. We calculate the free-energy barriers associated with their diffusion for a range of size ratios and densities. By applying classical transition state theory to these free-energy barriers, we predict the diffusion coefficients, which we find to be in good agreement with diffusion coefficients as measured using event-driven molecular dynamics simulations. These results highlight that transition state theory can capture the interstitial dynamics in the hard-sphere model system. Additionally, we quantify the interactions between the interstitials. We find that, apart from excluded volume interactions, the interstitial-interstitial interactions are almost ideal in our system. Lastly, we show that the interstitial diffusivity can be inferred from the large-particle fluctuations alone, thus providing an empirical relationship between the large-particle fluctuations and the interstitial diffusivity.

Influence of cell shape, inhomogeneities and diffusion barriers in cell polarization models

NASA Astrophysics Data System (ADS)

Giese, Wolfgang; Eigel, Martin; Westerheide, Sebastian; Engwer, Christian; Klipp, Edda

2015-12-01

In silico experiments bear the potential for further understanding of biological transport processes by allowing a systematic modification of any spatial property and providing immediate simulation results. Cell polarization and spatial reorganization of membrane proteins are fundamental for cell division, chemotaxis and morphogenesis. We chose the yeast Saccharomyces cerevisiae as an exemplary model system which entails the shuttling of small Rho GTPases such as Cdc42 and Rho, between an active membrane-bound form and an inactive cytosolic form. We used partial differential equations to describe the membrane-cytosol shuttling of proteins. In this study, a consistent extension of a class of 1D reaction-diffusion systems into higher space dimensions is suggested. The membrane is modeled as a thin layer to allow for lateral diffusion and the cytosol is modeled as an enclosed volume. Two well-known polarization mechanisms were considered. One shows the classical Turing-instability patterns, the other exhibits wave-pinning dynamics. For both models, we investigated how cell shape and diffusion barriers like septin structures or bud scars influence the formation of signaling molecule clusters and subsequent polarization. An extensive set of in silico experiments with different modeling hypotheses illustrated the dependence of cell polarization models on local membrane curvature, cell size and inhomogeneities on the membrane and in the cytosol. In particular, the results of our computer simulations suggested that for both mechanisms, local diffusion barriers on the membrane facilitate Rho GTPase aggregation, while diffusion barriers in the cytosol and cell protrusions limit spontaneous molecule aggregations of active Rho GTPase locally.

Silica-sol-based spin-coating barrier layer against phosphorous diffusion for crystalline silicon solar cells

PubMed Central

2014-01-01

The phosphorus barrier layers at the doping procedure of silicon wafers were fabricated using a spin-coating method with a mixture of silica-sol and tetramethylammonium hydroxide, which can be formed at the rear surface prior to the front phosphorus spin-on-demand (SOD) diffusion and directly annealed simultaneously with the front phosphorus layer. The optimization of coating thickness was obtained by changing the applied spin-coating speed; from 2,000 to 8,000 rpm. The CZ-Si p-type silicon solar cells were fabricated with/without using the rear silica-sol layer after taking the sheet resistance measurements, SIMS analysis, and SEM measurements of the silica-sol material evaluations into consideration. For the fabrication of solar cells, a spin-coating phosphorus source was used to form the n+ emitter and was then diffused at 930°C for 35 min. The out-gas diffusion of phosphorus could be completely prevented by spin-coated silica-sol film placed on the rear side of the wafers coated prior to the diffusion process. A roughly 2% improvement in the conversion efficiency was observed when silica-sol was utilized during the phosphorus diffusion step. These results can suggest that the silica-sol material can be an attractive candidate for low-cost and easily applicable spin-coating barrier for any masking purpose involving phosphorus diffusion. PMID:25520602

Silica-sol-based spin-coating barrier layer against phosphorous diffusion for crystalline silicon solar cells.

PubMed

Uzum, Abdullah; Fukatsu, Ken; Kanda, Hiroyuki; Kimura, Yutaka; Tanimoto, Kenji; Yoshinaga, Seiya; Jiang, Yunjian; Ishikawa, Yasuaki; Uraoka, Yukiharu; Ito, Seigo

2014-01-01

The phosphorus barrier layers at the doping procedure of silicon wafers were fabricated using a spin-coating method with a mixture of silica-sol and tetramethylammonium hydroxide, which can be formed at the rear surface prior to the front phosphorus spin-on-demand (SOD) diffusion and directly annealed simultaneously with the front phosphorus layer. The optimization of coating thickness was obtained by changing the applied spin-coating speed; from 2,000 to 8,000 rpm. The CZ-Si p-type silicon solar cells were fabricated with/without using the rear silica-sol layer after taking the sheet resistance measurements, SIMS analysis, and SEM measurements of the silica-sol material evaluations into consideration. For the fabrication of solar cells, a spin-coating phosphorus source was used to form the n(+) emitter and was then diffused at 930°C for 35 min. The out-gas diffusion of phosphorus could be completely prevented by spin-coated silica-sol film placed on the rear side of the wafers coated prior to the diffusion process. A roughly 2% improvement in the conversion efficiency was observed when silica-sol was utilized during the phosphorus diffusion step. These results can suggest that the silica-sol material can be an attractive candidate for low-cost and easily applicable spin-coating barrier for any masking purpose involving phosphorus diffusion.

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.

Evaluation of Electroplated Co-P Film as Diffusion Barrier Between In-48Sn Solder and SiC-Dispersed Bi2Te3 Thermoelectric Material

NASA Astrophysics Data System (ADS)

Li, Siyang; Yang, Donghua; Tan, Qing; Li, Liangliang

2015-06-01

The diffusion barrier property of Co-P film as a buffer layer between SiC-dispersed Bi2Te3 bulk material and In-48Sn solder was investigated. A Co-P film with thickness of ~6 µm was electroplated on SiC-dispersed Bi2Te3 substrate, joined with In-48Sn solder by a reflow process, and annealed at 100°C for up to 625 h. The formation and growth kinetics of intermetallic compounds (IMCs) at the interface between the In-48Sn and substrate were studied using transmission electron microscopy and scanning electron microscopy with energy-dispersive x-ray spectroscopy. The results showed that crystalline Co(In,Sn)3 formed as an irregular layer adjacent to the solder side at the solder/Co-P interface due to diffusion of Co towards the solder, and a small amount of amorphous Co45P13In12Sn30 appeared at the Co-P side because of diffusion of In and Sn into Co-P. The growth of Co(In,Sn)3 and Co45P13In12Sn30 during solid-state aging was slow, being controlled by interfacial reaction and diffusion, respectively. For comparison, In-48Sn/Bi2Te3-SiC joints were prepared and the IMCs in the joints analyzed. Without a diffusion barrier, In penetrated rapidly into the substrate, which led to the formation of amorphous In x Bi y phase in crystalline In4Te3 matrix. These IMCs grew quickly with prolongation of the annealing time, and their growth was governed by volume diffusion of elements. The experimental data demonstrate that electroplated Co-P film is an effective diffusion barrier for use in Bi2Te3-based thermoelectric modules.

Computational characterization of lightweight multilayer MXene Li-ion battery anodes

NASA Astrophysics Data System (ADS)

Ashton, Michael; Hennig, Richard G.; Sinnott, Susan B.

2016-01-01

MXenes, a class of two-dimensional transition metal carbides and nitrides, have shown promise experimentally and computationally for use in energy storage applications. In particular, the most lightweight members of the monolayer MXene family (M = Sc, Ti, V, or Cr) are predicted to have gravimetric capacities above 400 mAh/g, higher than graphite. Additionally, intercalation of ions into multilayer MXenes can be accomplished at low voltages, and low diffusion barriers exist for Li diffusing across monolayer MXenes. However, large discrepancies have been observed between the calculated and experimental reversible capacities of MXenes. Here, dispersion-corrected density functional theory calculations are employed to predict reversible capacities and other battery-related properties for six of the most promising members of the MXene family (O-functionalized Ti- and V-based carbide MXenes) as bilayer structures. The calculated reversible capacities of the V2CO2 and Ti2CO2 bilayers agree more closely with experiment than do previous calculations for monolayers. Additionally, the minimum energy paths and corresponding energy barriers along the in-plane [1000] and [0100] directions for Li travelling between neighboring MXene layers are determined. V4C3O2 exhibits the lowest diffusion barrier of the compositions considered, at 0.42 eV, but its reversible capacity (148 mAh/g) is dragged down by its heavy formula unit. Conversely, the V2CO2 MXene shows good reversible capacity (276 mAh/g), but a high diffusion barrier (0.82 eV). We show that the diffusion barriers of all bilayer structures are significantly higher than those calculated for the corresponding monolayers, advocating the use of dispersed monolayer MXenes instead of multilayers in high performance anodes.

Diffusion of One-Dimensional Crystals in Channels of Single-Walled Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Zhigalina, V. G.; Kumskov, A. S.; Falaleev, N. S.; Vasiliev, A. L.; Kiselev, N. A.

2018-05-01

The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10-21 m2/s, which corresponds to an activation-barrier height of 1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene.

Self-learning kinetic Monte Carlo simulations of Al diffusion in Mg

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

Nandipati, Giridhar; Govind, Niranjan; Andersen, Amity

2016-03-16

Atomistic on-lattice self-learning kinetic Monte Carlo (SLKMC) method was used to examine the vacancy-mediated diffusion of an Al atom in pure hcp Mg. Local atomic environment dependent activation barriers for vacancy-atom exchange processes were calculated on-the-fly using climbing image nudged-elastic band method (CI-NEB) and using a Mg-Al binary modified embedded-atom method (MEAM) interatomic potential. Diffusivities of vacancy and Al atom in pure Mg were obtained from SLKMC simulations and are compared with values available in the literature that are obtained from experiments and first-principle calculations. Al Diffusivities obtained from SLKMC simulations are lower, due to larger activation barriers and lowermore » diffusivity prefactors, than those available in the literature but have same order of magnitude. We present all vacancy-Mg and vacancy-Al atom exchange processes and their activation barriers that were identified in SLKMC simulations. We will describe a simple mapping scheme to map a hcp lattice on to a simple cubic lattice that would enable hcp lattices to be simulated in an on-lattice KMC framework. We also present the pattern recognition scheme used in SLKMC simulations.« less

Electronic Devices With Diffusion Barrier and Process for Making Same

DTIC Science & Technology

2000-05-03

components. Diffusion is also a problem with other high 10 conductivity metallization materials such as gold , silver, and platinum. As can be...those of subgroup IB of the Periodic Table (i.e., copper, silver, gold ), as well as platinum. These metals are highly attractive 10 for...the metal halide molecules of the desired thickness, is formed upon the monolayer portion of the barrier -7- material. The monolayer ( monoatomic

Effects of GSM modulated radio-frequency electromagnetic radiation on permeability of blood-brain barrier in male & female rats.

PubMed

Sırav, Bahriye; Seyhan, Nesrin

2016-09-01

With the increased use of mobile phones, their biological and health effects have become more important. Usage of mobile phones near the head increases the possibility of effects on brain tissue. This study was designed to investigate the possible effects of pulse modulated 900MHz and 1800MHz radio-frequency radiation on the permeability of blood-brain barrier of rats. Study was performed with 6 groups of young adult male and female wistar albino rats. The permeability of blood-brain barrier to intravenously injected evans blue dye was quantitatively examined for both control and radio-frequency radiarion exposed groups. For male groups; Evans blue content in the whole brain was found to be 0.08±0.01mg% in the control, 0.13±0.03mg% in 900MHz exposed and 0.26±0.05mg% in 1800MHz exposed animals. In both male radio-frequency radiation exposed groups, the permeability of blood-brain barrier found to be increased with respect to the controls (p<0.01). 1800MHz pulse modulated radio-frequency radiation exposure was found more effective on the male animals (p<0.01). For female groups; dye contents in the whole brains were 0.14±0.01mg% in the control, 0.24±0.03mg% in 900MHz exposed and 0.14±0.02mg% in 1800MHz exposed animals. No statistical variance found between the control and 1800MHz exposed animals (p>0.01). However 900MHz pulse modulated radio-frequency exposure was found effective on the permeability of blood-brain barrier of female animals. Results have shown that 20min pulse modulated radio-frequency radiation exposure of 900MHz and 1800MHz induces an effect and increases the permeability of blood-brain barrier of male rats. For females, 900MHz was found effective and it could be concluded that this result may due to the physiological differences between female and male animals. The results of this study suggest that mobile phone radation could lead to increase the permeability of blood-brain barrier under non-thermal exposure levels. More studies are needed to demonstrate the mechanisms of that breakdown. Copyright © 2015 Elsevier B.V. All rights reserved.

Principles of diffusion kurtosis imaging and its role in early diagnosis of neurodegenerative disorders.

PubMed

Arab, Anas; Wojna-Pelczar, Anna; Khairnar, Amit; Szabó, Nikoletta; Ruda-Kucerova, Jana

2018-05-01

Pathology of neurodegenerative diseases can be correlated with intra-neuronal as well as extracellular changes which lead to neuronal degeneration. The central nervous system (CNS) is a complex structure comprising of many biological barriers. These microstructural barriers might be affected by a variety of pathological processes. Specifically, changes in the brain tissue's microstructure affect the diffusion of water which can be assessed non-invasively by diffusion weighted (DW) magnetic resonance imaging (MRI) techniques. Diffusion tensor imaging (DTI) is a diffusion MRI technique that considers diffusivity as a Gaussian process, i.e. does not account for any diffusion hindrance. However, environment of the brain tissues is characterized by a non-Gaussian diffusion. Therefore, diffusion kurtosis imaging (DKI) was developed as an extension of DTI method in order to quantify the non-Gaussian distribution of water diffusion. This technique represents a promising approach for early diagnosis of neurodegenerative diseases when the neurodegenerative process starts. Hence, the purpose of this article is to summarize the ongoing clinical and preclinical research on Parkinson's, Alzheimer's and Huntington diseases, using DKI and to discuss the role of this technique as an early stage biomarker of neurodegenerative conditions. Copyright © 2018 Elsevier Inc. All rights reserved.

Understanding the anisotropic strain effects on lithium diffusion in graphite anodes: A first-principles study

NASA Astrophysics Data System (ADS)

Ji, Xiang; Wang, Yang; Zhang, Junqian

2018-06-01

The lithium diffusion in graphite anode, which is the most widely used commercial electrode material today, affects the charge/discharge performance of lithium-ion batteries. In this study, the anisotropic strain effects on lithium diffusion in graphite anodes are systematically investigated using first-principles calculations based on density functional theory (DFT) with van der Waals corrections. It is found that the effects of external applied strains along various directions of LixC6 (i.e., perpendicular or parallel to the basal planes of the graphite host) on lithium diffusivity are different. Along the direction perpendicular to the graphite planes, the tensile strain facilitates in-plane Li diffusion by reducing the energy barrier, and the compressive strain hinders in-plane Li diffusion by raising the energy barrier. In contrast, the in-plane biaxial tensile strain (parallel to the graphite planes) hinders in-plane Li diffusion, and the in-plane biaxial compressive strain facilitates in-plane Li diffusion. Furthermore, both in-plane and transverse shear strains slightly influence Li diffusion in graphite anodes. A discussion is presented to explain the anisotropic strain dependence of lithium diffusion. This research provides data for the continuum modelling of the electrodes in the lithium-ion batteries.

Giant Acceleration of Diffusion Observed in a Single-Molecule Experiment on F(1)-ATPase.

PubMed

Hayashi, Ryunosuke; Sasaki, Kazuo; Nakamura, Shuichi; Kudo, Seishi; Inoue, Yuichi; Noji, Hiroyuki; Hayashi, Kumiko

2015-06-19

The giant acceleration (GA) of diffusion is a universal phenomenon predicted by the theoretical analysis given by Reimann et al. [Phys. Rev. Lett. 87, 010602 (2001)]. Here we apply the theory of the GA of diffusion to a single-molecule experiment on a rotary motor protein, F(1), which is a component of F(o)F(1) adenosine triphosphate synthase. We discuss the energetic properties of F(1) and identify a high energy barrier of the rotary potential to be 20k(B)T, with the condition that the adenosine diphosphates are tightly bound to the F(1) catalytic sites. To conclude, the GA of diffusion is useful for measuring energy barriers in nonequilibrium and single-molecule experiments.

Giant Acceleration of Diffusion Observed in a Single-Molecule Experiment on F1-ATPase

NASA Astrophysics Data System (ADS)

Hayashi, Ryunosuke; Sasaki, Kazuo; Nakamura, Shuichi; Kudo, Seishi; Inoue, Yuichi; Noji, Hiroyuki; Hayashi, Kumiko

2015-06-01

The giant acceleration (GA) of diffusion is a universal phenomenon predicted by the theoretical analysis given by Reimann et al. [Phys. Rev. Lett. 87, 010602 (2001)]. Here we apply the theory of the GA of diffusion to a single-molecule experiment on a rotary motor protein, F1 , which is a component of Fo F1 adenosine triphosphate synthase. We discuss the energetic properties of F1 and identify a high energy barrier of the rotary potential to be 20 kBT , with the condition that the adenosine diphosphates are tightly bound to the F1 catalytic sites. To conclude, the GA of diffusion is useful for measuring energy barriers in nonequilibrium and single-molecule experiments.

Analysis of Molecular Movement Reveals Latticelike Obstructions to Diffusion in Heart Muscle Cells

PubMed Central

Illaste, Ardo; Laasmaa, Martin; Peterson, Pearu; Vendelin, Marko

2012-01-01

Intracellular diffusion in muscle cells is known to be restricted. Although characteristics and localization of these restrictions is yet to be elucidated, it has been established that ischemia-reperfusion injury reduces the overall diffusion restriction. Here we apply an extended version of raster image correlation spectroscopy to determine directional anisotropy and coefficients of diffusion in rat cardiomyocytes. Our experimental results indicate that diffusion of a smaller molecule (1127 MW fluorescently labeled ATTO633-ATP) is restricted more than that of a larger one (10,000 MW Alexa647-dextran), when comparing diffusion in cardiomyocytes to that in solution. We attempt to provide a resolution to this counterintuitive result by applying a quantitative stochastic model of diffusion. Modeling results suggest the presence of periodic intracellular barriers situated ∼1 μm apart having very low permeabilities and a small effect of molecular crowding in volumes between the barriers. Such intracellular structuring could restrict diffusion of molecules of energy metabolism, reactive oxygen species, and apoptotic signals, enacting a significant role in normally functioning cardiomyocytes as well as in pathological conditions of the heart. PMID:22385844

Infant feeding practices among HIV-exposed infants less than 6 months of age in Bomet County, Kenya: an in-depth qualitative study of feeding choices.

PubMed

Lang'at, Purity Chepkorir; Ogada, Irene; Steenbeek, Audrey; MacDonald, Noni E; Ochola, Sophie; Bor, Wesley; Odinga, Godfrey

2018-05-01

In children, HIV can be acquired from the mother during pregnancy, delivery and through breast milk. The WHO recommends exclusive breast feeding or exclusive replacement feeding for the first 6 months after birth for HIV-exposed infants. Barriers such as HIV-related stigma, inadequate resources, lack of access to safe water and negative cultural beliefs have been shown to influence infant feeding among HIV-exposed infants in some settings. In Kenya, there is limited literature on the barriers. The purpose of this study was to identify barriers to optimal feeding among HIV-exposed infants 0-5 months of age attending a mission hospital in Bomet County, Kenya. A cross-sectional qualitative study was conducted at a referral mission hospital in Bomet County, Southwest Kenya. Four focused group discussions were conducted among mothers/caregivers of HIV-exposed infants aged 0-5 months in accordance with their infant feeding practices, while two key informant interviews were also held with healthcare workers. All sessions were audio recorded and later transcribed verbatim. Content analysis was performed, and conclusions were made based on identified themes. Factors influencing the infant feeding choices were: financial constraints, cultural beliefs and practices, HIV-related stigma and conflicting knowledge among mothers/caregivers and healthcare workers on the recommendations for feeding HIV-exposed infants 0-5 months of age. Health worker retraining in and reinforcement of WHO guidance on feeding HIV exposed/infected infants will clarify misconceptions around feeding HIV exposed/infected infants, though there remain social and economic barriers to full implementation. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Fast diffusion of native defects and impurities in perovskite solar cell material CH 3NH 3PbI 3

DOE PAGES

Yang, Dongwen; Ming, Wenmei; Shi, Hongliang; ...

2016-06-01

CH 3NH 3PbI 3-based solar cells have shown remarkable progress in recent years but have also suffered from structural, electrical, and chemical instabilities related to the soft lattices and the chemistry of these halides. One of the instabilities is ion migration, which may cause current–voltage hysteresis in CH 3NH 3PbI 3 solar cells. Significant ion diffusion and ionic conductivity in CH 3NH 3PbI 3 have been reported; their nature, however, remain controversial. In the literature, the use of different experimental techniques leads to the observation of different diffusing ions (either iodine or CH 3NH 3 ion); the calculated diffusion barriersmore » for native defects scatter in a wide range; the calculated defect formation energies also differ qualitatively. These controversies hinder the understanding and the control of the ion migration in CH 3NH 3PbI 3. In this paper, we show density functional theory calculations of both the diffusion barriers and the formation energies for native defects (V I +, MA i +, V MA –, and I i –) and the Au impurity in CH 3NH 3PbI 3. V I + is found to be the dominant diffusing defect due to its low formation energy and the low diffusion barrier. I i – and MA i + also have low diffusion barriers but their formation energies are relatively high. The hopping rate of V I + is further calculated taking into account the contribution of the vibrational entropy, confirming V I + as a fast diffuser. We discuss approaches for managing defect population and migration and suggest that chemically modifying surfaces, interfaces, and grain boundaries may be effective in controlling the population of the iodine vacancy and the device polarization. We further show that the formation energy and the diffusion barrier of Au interstitial in CH 3NH 3PbI 3 are both low. As a result, it is thus possible that Au can diffuse into CH3NH3PbI3 under bias in devices (e.g., solar cell, photodetector) with Au/CH 3NH 3PbI 3 interfaces and modify the electronic properties of CH 3NH 3PbI 3.« less

Fast diffusion of native defects and impurities in perovskite solar cell material CH 3NH 3PbI 3

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

Yang, Dongwen; Ming, Wenmei; Shi, Hongliang

CH 3NH 3PbI 3-based solar cells have shown remarkable progress in recent years but have also suffered from structural, electrical, and chemical instabilities related to the soft lattices and the chemistry of these halides. One of the instabilities is ion migration, which may cause current–voltage hysteresis in CH 3NH 3PbI 3 solar cells. Significant ion diffusion and ionic conductivity in CH 3NH 3PbI 3 have been reported; their nature, however, remain controversial. In the literature, the use of different experimental techniques leads to the observation of different diffusing ions (either iodine or CH 3NH 3 ion); the calculated diffusion barriersmore » for native defects scatter in a wide range; the calculated defect formation energies also differ qualitatively. These controversies hinder the understanding and the control of the ion migration in CH 3NH 3PbI 3. In this paper, we show density functional theory calculations of both the diffusion barriers and the formation energies for native defects (V I +, MA i +, V MA –, and I i –) and the Au impurity in CH 3NH 3PbI 3. V I + is found to be the dominant diffusing defect due to its low formation energy and the low diffusion barrier. I i – and MA i + also have low diffusion barriers but their formation energies are relatively high. The hopping rate of V I + is further calculated taking into account the contribution of the vibrational entropy, confirming V I + as a fast diffuser. We discuss approaches for managing defect population and migration and suggest that chemically modifying surfaces, interfaces, and grain boundaries may be effective in controlling the population of the iodine vacancy and the device polarization. We further show that the formation energy and the diffusion barrier of Au interstitial in CH 3NH 3PbI 3 are both low. As a result, it is thus possible that Au can diffuse into CH3NH3PbI3 under bias in devices (e.g., solar cell, photodetector) with Au/CH 3NH 3PbI 3 interfaces and modify the electronic properties of CH 3NH 3PbI 3.« less

Influence of Structural Heterogeneity on Diffusion of CH4 and CO2 in Silicon Carbide-Derived Nanoporous Carbon

PubMed Central

2015-01-01

We investigate the influence of structural heterogeneity on the transport properties of simple gases in a Hybrid Reverse Monte Carlo (HRMC) constructed model of silicon carbide-derived carbon (SiC-DC). The energy landscape of the system is determined based on free energy analysis of the atomistic model. The overall energy barriers of the system for different gases are computed along with important properties, such as Henry constant and differential enthalpy of adsorption at infinite dilution, and indicate hydrophobicity of the SiC-DC structure and its affinity for CO2 and CH4 adsorption. We also study the effect of molecular geometry, pore structure and energy heterogeneity considering different hopping scenarios for diffusion of CO2 and CH4 through ultramicropores using the Nudged Elastic Band (NEB) method. It is shown that the energy barrier of a hopping molecule is very sensitive to the shape of the pore entry. We provide evidence for the influence of structural heterogeneity on self-diffusivity of methane and carbon dioxide using molecular dynamics simulation, based on a maximum in the variation of self-diffusivity with loading. A comparison of the MD simulation results with self-diffusivities from quasi-elastic neutron scattering (QENS) measurements and, with macroscopic uptake-based low-density transport coefficients, reveals the existence of internal barriers not captured in MD simulation and QENS experiments. Nevertheless, the simulation and macroscopic uptake-based diffusion coefficients agree within a factor of 2–3, indicating that our HRMC model structure captures most of the important energy barriers affecting the transport of CH4 in the nanostructure of SiC-DC. PMID:24932319

Influence of Structural Heterogeneity on Diffusion of CH4 and CO2 in Silicon Carbide-Derived Nanoporous Carbon.

PubMed

Farmahini, Amir H; Shahtalebi, Ali; Jobic, Hervé; Bhatia, Suresh K

2014-06-05

We investigate the influence of structural heterogeneity on the transport properties of simple gases in a Hybrid Reverse Monte Carlo (HRMC) constructed model of silicon carbide-derived carbon (SiC-DC). The energy landscape of the system is determined based on free energy analysis of the atomistic model. The overall energy barriers of the system for different gases are computed along with important properties, such as Henry constant and differential enthalpy of adsorption at infinite dilution, and indicate hydrophobicity of the SiC-DC structure and its affinity for CO 2 and CH 4 adsorption. We also study the effect of molecular geometry, pore structure and energy heterogeneity considering different hopping scenarios for diffusion of CO 2 and CH 4 through ultramicropores using the Nudged Elastic Band (NEB) method. It is shown that the energy barrier of a hopping molecule is very sensitive to the shape of the pore entry. We provide evidence for the influence of structural heterogeneity on self-diffusivity of methane and carbon dioxide using molecular dynamics simulation, based on a maximum in the variation of self-diffusivity with loading. A comparison of the MD simulation results with self-diffusivities from quasi-elastic neutron scattering (QENS) measurements and, with macroscopic uptake-based low-density transport coefficients, reveals the existence of internal barriers not captured in MD simulation and QENS experiments. Nevertheless, the simulation and macroscopic uptake-based diffusion coefficients agree within a factor of 2-3, indicating that our HRMC model structure captures most of the important energy barriers affecting the transport of CH 4 in the nanostructure of SiC-DC.

Measurements of Effective Schottky Barrier in Inverse Extraordinary Optoconductance Structures

NASA Astrophysics Data System (ADS)

Tran, L. C.; Werner, F. M.; Solin, S. A.; Gilbertson, Adam; Cohen, L. F.

2013-03-01

Individually addressable optical sensors with dimensions as low as 250nm, fabricated from metal semiconductor hybrid structures (MSH) of AuTi-GaAs Schottky interfaces, display a transition from resistance decreasing with intensity in micron-scale sensors (Extraordinary Optoconductance, EOC) to resistance increasing with intensity in nano-scale sensors (Inverse Extraordinary Optoconductance I-EOC). I-EOC is attributed to a ballistic to diffusive crossover with the introduction of photo-induced carriers and gives rise to resistance changes of up to 9462% in 250nm devices. We characterize the photo-dependence of the effective Schottky barrier in EOC/I-EOC structures by the open circuit voltage and reverse bias resistance. Under illumination by a 5 mW, 632.8 nm HeNe laser, the barrier is negligible and the Ti-GaAs interface becomes Ohmic. Comparing the behavior of two devices, one with leads exposed, another with leads covered by an opaque epoxy, the variation in Voc with the position of the laser can be attributed to a photovoltaic effect of the lead metal and bulk GaAs. The resistance is unaffected by the photovoltaic offset of the leads, as indicated by the radial symmetry of 2-D resistance maps obtained by rastering a laser across EOC/IEOC devices. SAS has a financial interest in PixelEXX, a start-up company whose mission is to market imaging arrays.

[Effect of infrasound on ultrastructure and permeability of rat's blood-retinal barrier].

PubMed

Qiu, Ping; Zhang, Zuoming; Jiang, Yong; Gou, Qun; Wang, Bing; Gou, Lin; Chen, Jingzao

2002-08-01

To investigate the possible effect of infrasound on the ultra-structure and permeability of rat's blood-retinal barrier (BRB). Ultra-structural changes of BRB were observed through the injection of lanthanum nitrate (La), which was used as a tracer to demonstrate the breakdown of the BRB, into blood vessels. Fifteen mature male rats divided into 5 groups were exposed to infrasound at a 8 Hz frequency, 130 dB sound pressure level in a pressure chamber especially designed for the experiment for 0, 1, 7, 14, 21 days, respectively. Under the action of infrasound, along with the prolongation of exposure, the damage of BRB was severer and severer. On the 1st day, there was no significant change in La leakage. On the 7th day, La diffused in the interphotoreceptor space at nuclear level. On the 14th day, La granules could be seen in the space of nervous cells. Finally, on the 21st day, La was found between synapses, synapses and nerve cells, as well as between the nerve cells and supporting cells, then sometimes reached vitreous body. Under the electron microscope, there were no significant morphological changes, but changes related to metabolism, such as edematous mitochondria, dilated rough endoplasmic reticula, precipitation of glycogen grandules, widening of perinuclear space, etc. The results thus suggest that the exposure to infrasound cause the breakdown of rat's blood-retinal barrier and visual impairment.

Efficacy of Tantalum Tungsten Alloys for Diffusion Barrier Applications

NASA Astrophysics Data System (ADS)

Smathers, D. B.; Aimone, P. R.

2017-12-01

Traditionally either Niobium, Tantalum or a combination of both have been used as diffusion barriers in Nb3Sn Multi-filament wire. Vanadium has also been used successfully but the ultimate RRR of the copper is limited unless an external shell of Niobium is included. Niobium is preferred over Tantalum when alternating current losses are not an issue as the Niobium will react to form Nb3Sn. Pure Tantalum tends to deform irregularly requiring extra starting thickness to ensure good barrier qualities. Our evaluations showed Tantalum lightly alloyed with 3 wt% Tungsten is compatible with the wire drawing process while deforming as well as or better than pure Niobium. Ta3wt%W has been processed as a single barrier and as a distributed barrier to fine dimensions. In addition, the higher modulus and strength of the Tantalum Tungsten alloy improves the overall tensile properties of the wire.

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.

Ion Exchange Method - Diffusion Barrier Investigations

NASA Astrophysics Data System (ADS)

Pielak, G.; Szustakowski, M.; Kiezun, A.

1990-01-01

Ion exchange method is used to GRIN-rod lenses manufacturing. In this process the ion exchange occurs between bulk glass (rod) and a molten salt. It was find that diffusion barrier exists on a border of glass surface and molten salt. The investigations of this barrier show that it value varies with ion exchange time and process temperature. It was find that in the case when thalium glass rod was treated in KNO3, bath, the minimum of the potential after 24 h was in temperature of 407°C, after 48 h in 422°C, after 72 h in 438°C and so on. So there are the possibility to keep the minimum of diffusion barrier by changing the temperature of the process and then the effectiveness of ion exchange process is the most effective. The time needed to obtain suitable refractive index distribution in a process when temperature was linearly changed from 400°C to 460°C was shorter of about 30% compare with the process in which temperature was constant and equal 450°C.

Superconducting MgB2 wires with vanadium diffusion barrier

NASA Astrophysics Data System (ADS)

Hušek, I.; Kováč, P.; Melišek, T.; Kulich, M.; Rosová, A.; Kopera, L.; Szundiová, B.

2017-10-01

Single-core MgB2 wires with a vanadium barrier and Cu stabilization have been made by the in situ powder-in-tube (PIT) and internal magnesium diffusion (IMD) into boron processes. Heat treatment of PIT wires was done at the temperature range of 650 °C-850 °C/30 min. Critical currents of differently treated MgB2/V/Cu wires have been measured and related with the structure of MgB2. It was found that critical current density of MgB2/V wire annealed above 700 °C decreases rapidly. The obtained results clearly show that vanadium is a well formable metal and can be applied as an effective diffusion barrier for MgB2 wires heat-treated at temperatures ≤700 °C. This temperature limit is well applicable for MgB2 wires with high current densities made by PIT and also by the IMD process.

Application of diffusion barriers to the refractory fibers of tungsten, columbium, carbon and aluminum oxide

NASA Technical Reports Server (NTRS)

Douglas, F. C.; Paradis, E. L.; Veltri, R. D.

1973-01-01

A radio frequency powered ion-plating system was used to plate protective layers of refractory oxides and carbide onto high strength fiber substrates. Subsequent overplating of these combinations with nickel and titanium was made to determine the effectiveness of such barrier layers in preventing diffusion of the overcoat metal into the fibers with consequent loss of fiber strength. Four substrates, five coatings, and two metal matrix materials were employed for a total of forty material combinations. The substrates were tungsten, niobium, NASA-Hough carbon, and Tyco sapphire. The diffusion-barrier coatings were aluminum oxide, yttrium oxide, titanium carbide, tungsten carbide with 14% cobalt addition, and zirconium carbide. The metal matrix materials were IN 600 nickel and Ti 6/4 titanium. Adhesion of the coatings to all substrates was good except for the NASA-Hough carbon, where flaking off of the oxide coatings in particular was observed.

Hydrogenated amorphous carbon coatings on implants drastically reduce biofilm formation and water permeation

NASA Astrophysics Data System (ADS)

Bernsmann, Falk; Laube, Norbert; Baldsiefen, Gerhard; Castellucci, Mattia

2014-11-01

Inflammations and crystalline bacterial biofilms (encrustations) remain a major complication in long-term artificial urinary tract drainage. To solve this problem we present urological implants with coatings made of amorphous hydrogenated carbon (a-C:H) that show excellent protection from encrustation in-vitro as well as in-vivo. Part of the success of a-C:H coatings is attributed to their ability to act as a diffusion barrier between an implant and the body, which prevents leaching of solvents from polymeric implants. To further enhance their barrier properties a-C:H coatings are combined with parylene coatings to develop diffusion-barrier multilayer coatings with a total thickness between 0.2 μm and 0.8 μm. The combination of the two types of coatings leads to a reduction of water diffusion by a factor of up to ten with respect to uncoated 25 μm thick polyimide sub-strates. The diffusion of water vapour from a controlled atmospheric pressure chamber through coated foils to a vacuum chamber is measured in a custom-built device.

Nanoscopic compartmentalization of membrane protein motion at the axon initial segment.

PubMed

Albrecht, David; Winterflood, Christian M; Sadeghi, Mohsen; Tschager, Thomas; Noé, Frank; Ewers, Helge

2016-10-10

The axon initial segment (AIS) is enriched in specific adaptor, cytoskeletal, and transmembrane molecules. During AIS establishment, a membrane diffusion barrier is formed between the axonal and somatodendritic domains. Recently, an axonal periodic pattern of actin, spectrin, and ankyrin forming 190-nm-spaced, ring-like structures has been discovered. However, whether this structure is related to the diffusion barrier function is unclear. Here, we performed single-particle tracking time-course experiments on hippocampal neurons during AIS development. We analyzed the mobility of lipid-anchored molecules by high-speed single-particle tracking and correlated positions of membrane molecules with the nanoscopic organization of the AIS cytoskeleton. We observe a strong reduction in mobility early in AIS development. Membrane protein motion in the AIS plasma membrane is confined to a repetitive pattern of ∼190-nm-spaced segments along the AIS axis as early as day in vitro 4, and this pattern alternates with actin rings. Mathematical modeling shows that diffusion barriers between the segments significantly reduce lateral diffusion along the axon. © 2016 Albrecht et al.

Blocking germanium diffusion inside silicon dioxide using a co-implanted silicon barrier

NASA Astrophysics Data System (ADS)

Barba, D.; Wang, C.; Nélis, A.; Terwagne, G.; Rosei, F.

2018-04-01

We investigate the effect of co-implanting a silicon sublayer on the thermal diffusion of germanium ions implanted into SiO2 and the growth of Ge nanocrystals (Ge-ncs). High-resolution imaging obtained by transmission electron microscopy and energy dispersive spectroscopy measurements supported by Monte-Carlo calculations shows that the Si-enriched region acts as a diffusion barrier for Ge atoms. This barrier prevents Ge outgassing during thermal annealing at 1100 °C. Both the localization and the reduced size of Ge-ncs formed within the sample region co-implanted with Si are observed, as well as the nucleation of mixed Ge/Si nanocrystals containing structural point defects and stacking faults. Although it was found that the Si co-implantation affects the crystallinity of the formed Ge-ncs, this technique can be implemented to produce size-selective and depth-ordered nanostructured systems by controlling the spatial distribution of diffusing Ge. We illustrate this feature for Ge-ncs embedded within a single SiO2 monolayer, whose diameters were gradually increased from 1 nm to 5 nm over a depth of 100 nm.

Hole Polaron Diffusion in the Final Discharge Product of Lithium–Sulfur Batteries

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

Liu, Zhixiao; Balbuena, Perla B.; Mukherjee, Partha P.

Poor electronic conductivity of bulk lithium sulfide (Li 2S) is a critical challenge for the debilitating performance of the lithium–sulfur battery. In this study we focus on investigating the thermodynamic and kinetic properties of native defects in Li 2S based on a first-principles approach. It is found that the hole polaron p + can form in Li 2S by removing a 3p electron from an S 2– anion. The p + diffusion barrier is only 90 meV, which is much lower than the Li vacancy (V Li –) diffusion barrier. Hence p + has the potential to serve as amore » charge carrier in the discharge product. Once the vacancy–polaron complex (V Li -––2p +) forms, the charge transport will be hindered due to the relatively higher diffusion barrier of the complex. Heteroatom dopants, which can decrease the p + formation energy and increase V Li – formation energy, are expected to be introduced to the discharge product to improve the electronic conductivity.« less

Global diffusive fluxes of methane in marine sediments

NASA Astrophysics Data System (ADS)

Egger, Matthias; Riedinger, Natascha; Mogollón, José M.; Jørgensen, Bo Barker

2018-06-01

Anaerobic oxidation of methane provides a globally important, yet poorly constrained barrier for the vast amounts of methane produced in the subseafloor. Here we provide a global map and budget of the methane flux and degradation in diffusion-controlled marine sediments in relation to the depth of the methane oxidation barrier. Our new budget suggests that 45-61 Tg of methane are oxidized with sulfate annually, with approximately 80% of this oxidation occurring in continental shelf sediments (<200 m water depth). Using anaerobic oxidation as a nearly quantitative sink for methane in steady-state diffusive sediments, we calculate that 3-4% of the global organic carbon flux to the seafloor is converted to methane. We further report a global imbalance of diffusive methane and sulfate fluxes into the sulfate-methane transition with no clear trend with respect to the corresponding depth of the methane oxidation barrier. The observed global mean net flux ratio between sulfate and methane of 1.4:1 indicates that, on average, the methane flux to the sulfate-methane transition accounts for only 70% of the sulfate consumption in the sulfate-methane transition zone of marine sediments.

Hole Polaron Diffusion in the Final Discharge Product of Lithium–Sulfur Batteries

DOE PAGES

Liu, Zhixiao; Balbuena, Perla B.; Mukherjee, Partha P.

2017-07-24

Poor electronic conductivity of bulk lithium sulfide (Li 2S) is a critical challenge for the debilitating performance of the lithium–sulfur battery. In this study we focus on investigating the thermodynamic and kinetic properties of native defects in Li 2S based on a first-principles approach. It is found that the hole polaron p + can form in Li 2S by removing a 3p electron from an S 2– anion. The p + diffusion barrier is only 90 meV, which is much lower than the Li vacancy (V Li –) diffusion barrier. Hence p + has the potential to serve as amore » charge carrier in the discharge product. Once the vacancy–polaron complex (V Li -––2p +) forms, the charge transport will be hindered due to the relatively higher diffusion barrier of the complex. Heteroatom dopants, which can decrease the p + formation energy and increase V Li – formation energy, are expected to be introduced to the discharge product to improve the electronic conductivity.« less

Ultrathin Cr added Ru film as a seedless Cu diffusion barrier for advanced Cu interconnects

NASA Astrophysics Data System (ADS)

Hsu, Kuo-Chung; Perng, Dung-Ching; Yeh, Jia-Bin; Wang, Yi-Chun

2012-07-01

A 5 nm thick Cr added Ru film has been extensively investigated as a seedless Cu diffusion barrier. High-resolution transmission electron microscopy micrograph, X-ray diffraction (XRD) pattern and Fourier transform-electron diffraction pattern reveal that a Cr contained Ru (RuCr) film has a glassy microstructure and is an amorphous-like film. XRD patterns and sheet resistance data show that the RuCr film is stable up to 650 °C, which is approximately a 200 °C improvement in thermal stability as compared to that of the pure Ru film. X-ray photoelectron spectroscopy depth profiles show that the RuCr film can successfully block Cu diffusion, even after a 30-min 650 °C annealing. The leakage current of the Cu/5 nm RuCr/porous SiOCH/Si stacked structure is about two orders of magnitude lower than that of a pristine Ru sample for electric field below 1 MV/cm. The RuCr film can be a promising Cu diffusion barrier for advanced Cu metallization.

Atmospheric pressure synthesis of photoluminescent hybrid materials by sequential organometallic vapor infiltration into polyethylene terephthalate fibers

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

Akyildiz, Halil I.; Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695; Mousa, Moataz Bellah M.

Exposing a polymer to sequential organometallic vapor infiltration (SVI) under low pressure conditions can significantly modify the polymer's chemical, mechanical, and optical properties. We demonstrate that SVI of trimethylaluminum into polyethylene terephthalate (PET) can also proceed readily at atmospheric pressure, and at 60 °C the extent of reaction determined by mass uptake is independent of pressure between 2.5 Torr and 760 Torr. At 120 °C, however, the mass gain is 50% larger at 2.5 Torr relative to that at 760 Torr, indicating that the precursor diffusion in the chamber and fiber matrix decreases at higher source pressure. Mass gain decreases, in general, as the SVI processmore » temperature increases both at 2.5 Torr and 760 Torr attributed to the faster reaction kinetics forming a barrier layer, which prevents further diffusion of the reactive species. The resulting PET/Al-O{sub x} product shows high photoluminescence compared to untreated fibers. A physical mask on the polymer during infiltration at 760 Torr is replicated in the underlying polymer, producing an image in the polymer that is visible under UV illumination. Because of the reduced precursor diffusivity during exposure at 760 Torr, the image shows improved resolution compared to SVI performed under typical 2.5 Torr conditions.« less

Diffusion of gas mixtures in the sI hydrate structure

NASA Astrophysics Data System (ADS)

Waage, Magnus H.; Trinh, Thuat T.; van Erp, Titus S.

2018-06-01

Replacing methane with carbon dioxide in gas hydrates has been suggested as a way of harvesting methane, while at the same time storing carbon dioxide. Experimental evidence suggests that this process is facilitated if gas mixtures are used instead of pure carbon dioxide. We studied the free energy barriers for diffusion of methane, carbon dioxide, nitrogen, and hydrogen in the sI hydrate structure using molecular simulation techniques. Cage hops between neighboring cages were considered with and without a water vacancy and with a potential inclusion of an additional gas molecule in either the initial or final cage. Our results give little evidence for enhanced methane and carbon dioxide diffusion if nitrogen is present as well. However, the inclusion of hydrogen seems to have a substantial effect as it diffuses rapidly and can easily enter occupied cages, which reduces the barriers of diffusion for the gas molecules that co-occupy a cage with hydrogen.

Method for improving the performance of oxidizable ceramic materials in oxidizing environments

NASA Technical Reports Server (NTRS)

Nagaraj, Bangalore A. (Inventor)

2002-01-01

Improved adhesion of thermal barrier coatings to nonmetallic substrates using a dense layer of ceramic on an underlying nonmetallic substrate that includes at least one oxidizable component. The improved adhesion occurs because the application of the dense ceramic layer forms a diffusion barrier for oxygen. This diffusion barrier prevents the oxidizable component of the substrate from decomposing. The present invention applies ceramic by a process that deposits a relatively thick and dense ceramic layer on the underlying substrate. The formation of the dense layer of ceramic avoids the problem of void formation associated with ceramic formation by most prior art thermal decomposition processes. The formation of voids has been associated with premature spalling of thermal barrier layers and other protective layers applied to substrates.

Stability diagrams for the surface patterns of GaN(0001bar) as a function of Schwoebel barrier height

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.

2017-01-01

Height and type of Schwoebel barriers (direct or inverse) decides about the character of the surface instability. Different surface morphologies are presented. Step bunches, double steps, meanders, mounds and irregular patterns emerge at the surface as a result of step (Schwoebel) barriers at some temperature or miscut values. The study was carried out on the two-component kinetic Monte Carlo (kMC) model of GaN(0001bar) surface grown in nitrogen rich conditions. Diffusion of gallium adatoms over N-polar surface is slow and nitrogen adatoms are almost immobile. We show that in such conditions surfaces remain smooth when gallium adatoms diffuse in the presence of low inverse Schwoebel barrier. It is illustrated by adequate stability diagrams for surface morphologies.

Barriers to the free diffusion of proteins and lipids in the plasma membrane

PubMed Central

Trimble, William S.

2015-01-01

Biological membranes segregate into specialized functional domains of distinct composition, which can persist for the entire life of the cell. How separation of their lipid and (glyco)protein components is generated and maintained is not well understood, but the existence of diffusional barriers has been proposed. Remarkably, the physical nature of such barriers and the manner whereby they impede the free diffusion of molecules in the plane of the membrane has rarely been studied in depth. Moreover, alternative mechanisms capable of generating membrane inhomogeneity are often disregarded. Here we describe prototypical biological systems where membrane segregation has been amply documented and discuss the role of diffusional barriers and other processes in the generation and maintenance of their structural and functional compartmentalization. PMID:25646084

Barriers to the free diffusion of proteins and lipids in the plasma membrane.

PubMed

Trimble, William S; Grinstein, Sergio

2015-02-02

Biological membranes segregate into specialized functional domains of distinct composition, which can persist for the entire life of the cell. How separation of their lipid and (glyco)protein components is generated and maintained is not well understood, but the existence of diffusional barriers has been proposed. Remarkably, the physical nature of such barriers and the manner whereby they impede the free diffusion of molecules in the plane of the membrane has rarely been studied in depth. Moreover, alternative mechanisms capable of generating membrane inhomogeneity are often disregarded. Here we describe prototypical biological systems where membrane segregation has been amply documented and discuss the role of diffusional barriers and other processes in the generation and maintenance of their structural and functional compartmentalization. © 2015 Trimble and Grinstein.

Pulsed laser diffusion of thin hole-barrier contacts in high purity germanium for gamma radiation detectors

NASA Astrophysics Data System (ADS)

Maggioni, G.; Carturan, S.; Raniero, W.; Riccetto, S.; Sgarbossa, F.; Boldrini, V.; Milazzo, R.; Napoli, D. R.; Scarpa, D.; Andrighetto, A.; Napolitani, E.; De Salvador, D.

2018-03-01

A new method for the formation of hole-barrier contacts in high purity germanium (HPGe) is described, which consists in the sputter deposition of a Sb film on HPGe, followed by Sb diffusion produced through laser annealing of the Ge surface in the melting regime. This process gives rise to a very thin ( ≤ 100 nm) n-doped layer, as determined by SIMS measurement, while preserving the defect-free morphology of HPGe surface. A small prototype of gamma ray detector with a Sb laser-diffused contact was produced and characterized, showing low leakage currents and good spectroscopy data with different gamma ray sources.

Fast self-diffusion of ions in CH 3 NH 3 PbI 3 : the interstiticaly mechanism versus vacancy-assisted mechanism

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

Yang, Ji-Hui; Yin, Wan-Jian; Park, Ji-Sang

2016-01-01

The stability of organic-inorganic halide perovskites is a major challenge for their applications and has been extensively studied. Among the possible underlying reasons, ion self-diffusion has been inferred to play important roles. While theoretical studies congruously support that iodine is more mobile, experimental studies only observe the direct diffusion of the MA ion and possible diffusion of iodine. The discrepancy may result from the incomplete understanding of ion diffusion mechanisms. With the help of first-principles calculations, we studied ion diffusion in CH3NH3PbI3 (MAPbI3) through not only the vacancy-assisted mechanisms presumed in previous theoretical studies, but also the neglected interstiticaly mechanisms.more » We found that compared to the diffusion through the vacancy-assisted mechanism, MA ion diffusion through the interstiticaly mechanism has a much smaller barrier which could explain experimental observations. For iodine diffusion, both mechanisms can yield relatively small barriers. Depending on the growth conditions, defect densities of vacancies and interstitials can vary and so do the diffusion species as well as diffusion mechanisms. Our work thus supports that both MA and iodine ion diffusion could contribute to the performance instability of MAPbI3. While being congruous with experimental results, our work fills the research gap by providing a full understanding of ion diffusion in halide perovskites.« less

Electronic Devices with Strontium Barrier Film and Process for Making Same

DTIC Science & Technology

1998-08-20

structure of the barrier film on an atomic level where the barrier film is comprised of a plurality of contiguous monolayers, while FIG. 7B shows another...another embodiment where the barrier film is comprised of a plurality of contiguous monolayers in which different monolayers thereof are formed of...High Energy Electron 10 Diffraction (RHEED) diagnostic system directed toward the substrate 26. A diffusion barrier precursor compound effusion

Electronic Devices with Composite Atomic Barrier Film and Process for Making Same

DTIC Science & Technology

1998-08-20

structure of the barrier film on an atomic level where the barrier film is comprised of a plurality of contiguous monolayers, while FIG. 7B shows...another embodiment where the barrier film is comprised of a plurality of contiguous monolayers in which different monolayers thereof are formed of...High Energy Electron 10 Diffraction (RHEED) diagnostic system directed toward the substrate 26. A diffusion barrier precursor compound effusion

Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

DOE PAGES

Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

2016-04-08

Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessedmore » as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.« less

Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

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

Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessedmore » as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.« less

[Gloves: some unknowns].

PubMed

Checchi, L; D'Achille, C; Conti, S

1991-01-01

The diffusion of transmissible diseases such as the Acquired Immunodeficiency Syndrome, well known as AIDS, has induced in the population a great sensibility to the problem of disease transmission. Dentists and patients, because of peculiar features of oral environment and dental procedures, are very exposed to these risks. For this reason every technique which reduces the risk of cross-infections patient to patient and patient to dentist to patient are absolutely necessary. From this point of view the use of gloves is very important to protect dental operator and patients. The aim of this study is: a) to stress the importance of mechanical barriers, like gloves, in dentistry in order to sensitize dental practitioners to the use of gloves; b) to underline that the quality of dental gloves in Italy is lower than in other countries which have a quality standard.

A C-terminal cyclic 8-13 neurotensin fragment analog appears less exposed to neprilysin when it crosses the blood-brain barrier than the cerebrospinal fluid-brain barrier in mice.

PubMed

Van Kemmel, F M; Dubuc, I; Bourdel, E; Fehrentz, J A; Martinez, J; Costentin, J

1996-10-11

A C-terminal cyclic 8-13 neurotensin fragment analog. JMV 1193, a direct agonist of central neurotensin receptors, is able to cross both the cerebrospinal fluid-brain barrier and the blood-brain barrier. When administered intracerebroventricularly (i.c.v.), its hypothermic effect was potentiated by the enkephalinase inhibition induced either by thiorphan (simultaneous intracerebroventricular administration of 10 micrograms) or by the thiorphan prodrug. acetorphan (intravenous (i.v.) administration of 10 mg/kg). Such a potentiation was not observed when both JMV 1193 and acetorphan were administered intravenously. Therefore it appears that the sensitivity of JMV 1193 to enkephalinase depends on its route of administration. It is exposed to this peptidase after i.c.v. injection (when crossing the cerebrospinal fluid-brain barrier), while it is not after i.v. administration (when crossing the blood-brain barrier).

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.

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

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.

Analysis of molecular movement reveals latticelike obstructions to diffusion in heart muscle cells.

PubMed

Illaste, Ardo; Laasmaa, Martin; Peterson, Pearu; Vendelin, Marko

2012-02-22

Intracellular diffusion in muscle cells is known to be restricted. Although characteristics and localization of these restrictions is yet to be elucidated, it has been established that ischemia-reperfusion injury reduces the overall diffusion restriction. Here we apply an extended version of raster image correlation spectroscopy to determine directional anisotropy and coefficients of diffusion in rat cardiomyocytes. Our experimental results indicate that diffusion of a smaller molecule (1127 MW fluorescently labeled ATTO633-ATP) is restricted more than that of a larger one (10,000 MW Alexa647-dextran), when comparing diffusion in cardiomyocytes to that in solution. We attempt to provide a resolution to this counterintuitive result by applying a quantitative stochastic model of diffusion. Modeling results suggest the presence of periodic intracellular barriers situated ∼1 μm apart having very low permeabilities and a small effect of molecular crowding in volumes between the barriers. Such intracellular structuring could restrict diffusion of molecules of energy metabolism, reactive oxygen species, and apoptotic signals, enacting a significant role in normally functioning cardiomyocytes as well as in pathological conditions of the heart. Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Method of manufacturing lightweight thermo-barrier material

NASA Technical Reports Server (NTRS)

Blair, Winford (Inventor)

1987-01-01

A method of manufacturing thermal barrier structures comprising at least three dimpled cores separated by flat plate material with the outer surface of the flat plate material joined together by diffusion bonding.

Molecular dynamics simulations of hydrogen diffusion in aluminum

DOE PAGES

Zhou, X. W.; El Gabaly, F.; Stavila, V.; ...

2016-03-23

In this study, hydrogen diffusion impacts the performance of solid-state hydrogen storage materials and contributes to the embrittlement of structural materials under hydrogen-containing environments. In atomistic simulations, the diffusion energy barriers are usually calculated using molecular statics simulations where a nudged elastic band method is used to constrain a path connecting the two end points of an atomic jump. This approach requires prior knowledge of the “end points”. For alloy and defective systems, the number of possible atomic jumps with respect to local atomic configurations is tremendous. Even when these jumps can be exhaustively studied, it is still unclear howmore » they can be combined to give an overall diffusion behavior seen in experiments. Here we describe the use of molecular dynamics simulations to determine the overall diffusion energy barrier from the Arrhenius equation. This method does not require information about atomic jumps, and it has additional advantages, such as the ability to incorporate finite temperature effects and to determine the pre-exponential factor. As a test case for a generic method, we focus on hydrogen diffusion in bulk aluminum. We find that the challenge of this method is the statistical variation of the results. However, highly converged energy barriers can be achieved by an appropriate set of temperatures, output time intervals (for tracking hydrogen positions), and a long total simulation time. Our results help elucidate the inconsistencies of the experimental diffusion data published in the literature. The robust approach developed here may also open up future molecular dynamics simulations to rapidly study diffusion properties of complex material systems in multidimensional spaces involving composition and defects.« less

Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization

NASA Astrophysics Data System (ADS)

Kumm, J.; Samadi, H.; Chacko, R. V.; Hartmann, P.; Wolf, A.

2016-07-01

An evaporated Al layer is known as an excellent rear metallization for highly efficient solar cells, but suffers from incompatibility with a common solder process. To enable solar cell-interconnection and module integration, in this work the Al layer is complemented with a solder stack of TiN/Ti/Ag or TiN/NiV/Ag, in which the TiN layer acts as an Al diffusion barrier. X-ray photoelectron spectroscopy measurements prove that diffusion of Al through the stack and the formation of an Al2O3 layer on the stack's surface are responsible for a loss of solderability after a strong post-metallization anneal, which is often mandatory to improve contact resistance and passivation quality. An optimization of the reactive TiN sputter process results in a densification of the TiN layer, which improves its barrier quality against Al diffusion. However, measurements with X-ray diffraction and scanning electron microscopy show that small grains with vertical grain boundaries persist, which still offer fast diffusion paths. Therefore, the concept of stuffing is introduced. By incorporating oxygen into the grain boundaries of the sputtered TiN layer, Al diffusion is strongly reduced as confirmed by secondary ion mass spectroscopy profiles. A quantitative analysis reveals a one order of magnitude lower Al diffusion coefficient for stuffed TiN layers. This metallization system maintains its solderability even after strong post-metallization annealing at 425 °C for 15 min. This paper thus presents an industrially feasible, conventionally solderable, and long-term stable metallization scheme for highly efficient silicon solar cells.

Cu diffusion in single-crystal and polycrystalline TiN barrier layers: A high-resolution experimental study supported by first-principles calculations

NASA Astrophysics Data System (ADS)

Mühlbacher, Marlene; Bochkarev, Anton S.; Mendez-Martin, Francisca; Sartory, Bernhard; Chitu, Livia; Popov, Maxim N.; Puschnig, Peter; Spitaler, Jürgen; Ding, Hong; Schalk, Nina; Lu, Jun; Hultman, Lars; Mitterer, Christian

2015-08-01

Dense single-crystal and polycrystalline TiN/Cu stacks were prepared by unbalanced DC magnetron sputter deposition at a substrate temperature of 700 °C and a pulsed bias potential of -100 V. The microstructural variation was achieved by using two different substrate materials, MgO(001) and thermally oxidized Si(001), respectively. Subsequently, the stacks were subjected to isothermal annealing treatments at 900 °C for 1 h in high vacuum to induce the diffusion of Cu into the TiN. The performance of the TiN diffusion barrier layers was evaluated by cross-sectional transmission electron microscopy in combination with energy-dispersive X-ray spectrometry mapping and atom probe tomography. No Cu penetration was evident in the single-crystal stack up to annealing temperatures of 900 °C, due to the low density of line and planar defects in single-crystal TiN. However, at higher annealing temperatures when diffusion becomes more prominent, density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N sublattice for the experimental N/Ti ratio. In comparison, localized diffusion of Cu along grain boundaries in the columnar polycrystalline TiN barriers was detected after the annealing treatment. The maximum observed diffusion length was approximately 30 nm, yielding a grain boundary diffusion coefficient of the order of 10-16 cm2 s-1 at 900 °C. This is 10 to 100 times less than for comparable underdense polycrystalline TiN coatings deposited without external substrate heating or bias potential. The combined numerical and experimental approach presented in this paper enables the contrasting juxtaposition of diffusion phenomena and mechanisms in two TiN coatings, which differ from each other only in the presence of grain boundaries.

Electrochemical evidences and consequences of significant differences in ions diffusion rate in polyacrylate-based ion-selective membranes.

PubMed

Woźnica, Emilia; Mieczkowski, Józef; Michalska, Agata

2011-11-21

The origin and effect of surface accumulation of primary ions within the ion-selective poly(n-butyl acrylate)-based membrane, obtained by thermal polymerization, is discussed. Using a new method, based on the relation between the shape of a potentiometric plot and preconditioning time, the diffusion of copper ions in the membrane was found to be slow (the diffusion coefficient estimated to be close to 10(-11) cm(2) s(-1)), especially when compared to ion-exchanger counter ions--sodium cations diffusion (a diffusion coefficient above 10(-9) cm(2) s(-1)). The higher mobility of sodium ions than those of the copper-ionophore complex results in exposed ion-exchanger role leading to undesirably exposed sensitivity to sodium or potassium ions.

Anti-collimation of ballistic electrons by a potential barrier

NASA Astrophysics Data System (ADS)

Coleridge, P. T.; Taylor, R. P.; Sachrajda, A. S.; Adams, J. A.

1994-03-01

A pair of Quantum Point Contacts separated by a continuous barrier have been fabricated using the surface gate technique. Transport measurements for each component of this system and for various combinations have shown both additive and non-additive behaviour. The results are explained by a combination of reflection by the barrier of electrons collimated by the Quantum Point Contacts and transport by diffusion across the barrier.

Determination of Time Required for Materials Exposed to Oxygen to Return to Reduced Flammability

NASA Technical Reports Server (NTRS)

Harper, Susana; Hirsch, David; Smith, Sarah

2009-01-01

Increased material flammability due to exposure to high oxygen concentrations is a concern from both a safety and operational perspective. Localized, high oxygen concentrations can occur when exiting a higher oxygen concentration environment due to material saturation, as well as oxygen entrapment between barrier materials. Understanding of oxygen diffusion and permeation and its correlation to flammability risks can reduce the likelihood of fires while improving procedures as NASA moves to longer missions with increased extravehicular activities in both spacecraft and off-Earth habitats. This paper examines the time required for common spacecraft materials exposed to oxygen to return to reduced flammability after removal from the increased oxygen concentration environment. Specifically, NASA-STD-6001A maximum oxygen concentration testing and ASTM F-1927 permeability testing were performed on Nomex 4 HT90-40, Tiburon 5 Surgical Drape, Cotton, Extravehicular Mobility Unit (EMU) Liquid-Cooled Ventilation Garment, EMU Thermal Comfort Undergarment, EMU Mosite Foam with Spandex Covering, Advanced Crew Escape Suit (ACES) Outer Cross-section, ACES Liquid Cooled Garment (LCG), ACES O2 Hose Material, Minicel 6 Polyethylene Foam, Minicel Polyethylene Foam with Nomex Covering, Pyrell Polyurethane Foam, and Zotek 7 F-30 Foam.

Adsorption and diffusion of lithium in a graphene/blue-phosphorus heterostructure and the effect of an external electric field.

PubMed

Fan, Kaimin; Tang, Jing; Wu, Shiyun; Yang, Chengfu; Hao, Jiabo

2016-12-21

The adsorption and diffusion behaviors of lithium (Li) in a graphene/blue-phosphorus (G/BP) heterostructure have been investigated using a first principles method based on density functional theory (DFT). The effect of an external electric field on the adsorption and diffusion behaviors has also been investigated. The results show that the adsorption energy of Li on the graphene side of the G/BP heterostructure is higher than that on monolayer graphene, and Li adsorption on the BP side of the G/BP/Li system is slightly stronger than that on monolayer BP (BP/Li). The adsorption energy of Li reaches 2.47 eV, however, the energy barriers of Li diffusion decrease in the interlayer of the G/BP heterostructure. The results mentioned above suggest that the rate performance of the G/BP heterostructure is better than that of monolayer graphene. Furthermore, the adsorption energies of Li atoms in the three different most stable sites, i.e., H G , T P and H 1 sites, increase by about 0.49 eV, 0.26 eV, and 0.13 eV, respectively, as the electric field intensity reaches 0.6 V Å -1 . The diffusion energy barrier is significantly decreased by an external electric field. It is demonstrated that the external electric field can not only enhance the adsorption but can also modulate the diffusion barriers of Li atoms in the G/BP heterostructure.

3-D Observation of dopant distribution at NAND flash memory floating gate using Atom probe tomography

NASA Astrophysics Data System (ADS)

Lee, Ji-hyun; Chae, Byeong-Kyu; Kim, Joong-Jeong; Lee, Sun Young; Park, Chan Gyung

2015-01-01

Dopant control becomes more difficult and critical as silicon devices become smaller. We observed the dopant distribution in a thermally annealed polysilicon gate using Transmission Electron Microscopy (TEM) and Atom probe tomography (APT). Phosphorus was doped at the silicon-nitride-diffusion-barrier-layer-covered polycrystalline silicon gate. Carbon also incorporated at the gate for the enhancement of operation uniformity. The impurity distribution was observed using atom probe tomography. The carbon atoms had segregated at grain boundaries and suppressed silicon grain growth. Phosphorus atoms, on the other hand, tended to pile-up at the interface. A 1-nm-thick diffusion barrier effectively blocked P atom out-diffusion. [Figure not available: see fulltext.

Modeling the migration of platinum nanoparticles on surfaces using a kinetic Monte Carlo approach

DOE PAGES

Li, Lin; Plessow, Philipp N.; Rieger, Michael; ...

2017-02-15

We propose a kinetic Monte Carlo (kMC) model for simulating the movement of platinum particles on supports, based on atom-by-atom diffusion on the surface of the particle. The proposed model was able to reproduce equilibrium cluster shapes predicted using Wulff-construction. The diffusivity of platinum particles was simulated both purely based on random motion and assisted using an external field that causes a drift velocity. The overall particle diffusivity increases with temperature; however, the extracted activation barrier appears to be temperature independent. Additionally, this barrier was found to increase with particle size, as well as, with the adhesion between the particlemore » and the support.« less

An Ab Initio and Kinetic Monte Carlo Simulation Study of Lithium Ion Diffusion on Graphene

PubMed Central

Zhong, Kehua; Yang, Yanmin; Xu, Guigui; Zhang, Jian-Min; Huang, Zhigao

2017-01-01

The Li+ diffusion coefficients in Li+-adsorbed graphene systems were determined by combining first-principle calculations based on density functional theory with Kinetic Monte Carlo simulations. The calculated results indicate that the interactions between Li ions have a very important influence on lithium diffusion. Based on energy barriers directly obtained from first-principle calculations for single-Li+ and two-Li+ adsorbed systems, a new equation predicting energy barriers with more than two Li ions was deduced. Furthermore, it is found that the temperature dependence of Li+ diffusion coefficients fits well to the Arrhenius equation, rather than meeting the equation from electrochemical impedance spectroscopy applied to estimate experimental diffusion coefficients. Moreover, the calculated results also reveal that Li+ concentration dependence of diffusion coefficients roughly fits to the equation from electrochemical impedance spectroscopy in a low concentration region; however, it seriously deviates from the equation in a high concentration region. So, the equation from electrochemical impedance spectroscopy technique could not be simply used to estimate the Li+ diffusion coefficient for all Li+-adsorbed graphene systems with various Li+ concentrations. Our work suggests that interactions between Li ions, and among Li ion and host atoms will influence the Li+ diffusion, which determines that the Li+ intercalation dependence of Li+ diffusion coefficient should be changed and complex. PMID:28773122

A reaction-diffusion model of the Darien Gap Sterile Insect Release Method

NASA Astrophysics Data System (ADS)

Alford, John G.

2015-05-01

The Sterile Insect Release Method (SIRM) is used as a biological control for invasive insect species. SIRM involves introducing large quantities of sterilized male insects into a wild population of invading insects. A fertile/sterile mating produces offspring that are not viable and the wild insect population will eventually be eradicated. A U.S. government program maintains a permanent sterile fly barrier zone in the Darien Gap between Panama and Columbia to control the screwworm fly (Cochliomyia Hominivorax), an insect that feeds off of living tissue in mammals and has devastating effects on livestock. This barrier zone is maintained by regular releases of massive quantities of sterilized male screwworm flies from aircraft. We analyze a reaction-diffusion model of the Darien Gap barrier zone. Simulations of the model equations yield two types of spatially inhomogeneous steady-state solutions representing a sterile fly barrier that does not prevent invasion and a barrier that does prevent invasion. We investigate steady-state solutions using both phase plane methods and monotone iteration methods and describe how barrier width and the sterile fly release rate affects steady-state behavior.

Morphometric partitioning of the respiratory surface area and diffusion capacity of the gills and swim bladder in juvenile Amazonian air-breathing fish, Arapaima gigas.

PubMed

Fernandes, Marisa Narciso; da Cruz, André Luis; da Costa, Oscar Tadeu Ferreira; Perry, Steven Franklin

2012-09-01

The gills and the respiratory swim bladders of juvenile specimens (mean body mass 100g) of the basal teleost Arapaima gigas (Cuvier 1829) were evaluated using stereological methods in vertical sections. The surface areas, harmonic mean barrier thicknesses and morphometric diffusing capacities for oxygen and carbon dioxide were estimated. The average respiratory surface area of the swim bladder (2173 cm² kg⁻¹) exceeded that of the gills (780 cm² kg⁻¹) by a factor of 2.79. Due to the extremely thin air-blood barrier in the swim bladder (harmonic mean 0.22 μm) and the much thicker water-blood barrier of the gills (9.61 μm), the morphometric diffusing capacity for oxygen and carbon dioxide was 88 times greater in the swim bladder than in the gills. These data clearly indicate the importance of the swim bladder, even in juvenile A. gigas that still engage in aquatic respiration. Because of the much greater diffusion constant of CO₂ than O₂ in water, the gills also remain important for CO₂ release. Copyright © 2012 Elsevier Ltd. All rights reserved.

Hybrid functional studies of stability and diffusion of hydrogen in Mg-doped GaN

NASA Astrophysics Data System (ADS)

Park, Ji-Sang; Chang, K. J.

2012-02-01

Nitride semiconductors are known to suffer from low p-type doping efficiency due to the high activation energy of Mg acceptors and the compensation of hole carriers. To enhance hole carrier concentration, the hydrogen co-doping method is widely used, in which hydrogen is intentionally doped with Mg dopants and removed by subsequent thermal annealing. In this work, we perform first-principles density functional calculations to study the stability and diffusion of hydrogen in Mg-doped GaN. For the exchange-correlation potential, we employ both the generalized gradient approximation (GGA) proposed by Perdew, Burke, and Ernzerhof and the hybrid density functional of Heyd, Scuseria, and Ernzerhof. We examine the diffusion pathways and dissociation barriers of H from the Mg-H complex using the nudged elastic band and dimer methods. We compare the results of the GGA and hybrid density functional calculations for the stability of various H interstitial configurations and the migration barriers for H diffusion. Finally, using the calculated migration barriers as inputs, we perform kinetic Monte Carlo simulations for the dissociation of the Mg-H complex and find that the Mg acceptors are activated by thermal annealing up to 700-800 ^oC, in good agreement with experiments.

Transparent, Ultrahigh-Gas-Barrier Films with a Brick-Mortar-Sand Structure.

PubMed

Dou, Yibo; Pan, Ting; Xu, Simin; Yan, Hong; Han, Jingbin; Wei, Min; Evans, David G; Duan, Xue

2015-08-10

Transparent and flexible gas-barrier materials have shown broad applications in electronics, food, and pharmaceutical preservation. Herein, we report ultrahigh-gas-barrier films with a brick-mortar-sand structure fabricated by layer-by-layer (LBL) assembly of XAl-layered double hydroxide (LDH, X=Mg, Ni, Zn, Co) nanoplatelets and polyacrylic acid (PAA) followed by CO2 infilling, denoted as (XAl-LDH/PAA)n-CO2. The near-perfectly parallel orientation of the LDH "brick" creates a long diffusion length to hinder the transmission of gas molecules in the PAA "mortar". Most significantly, both the experimental studies and theoretical simulations reveal that the chemically adsorbed CO2 acts like "sand" to fill the free volume at the organic-inorganic interface, which further depresses the diffusion of permeating gas. The strategy presented here provides a new insight into the perception of barrier mechanism, and the (XAl-LDH/PAA)n-CO2 film is among the best gas barrier films ever reported. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Submersed sensing electrode used in fuel-cell type hydrogen detector

NASA Technical Reports Server (NTRS)

Niedrach, L. W.; Rudek, F. P.; Rutkoneski, M. D.

1971-01-01

Electrode has silicone rubber diffusion barrier with fixed permeation constant for hydrogen. Barrier controls flow of hydrogen to anode and Faraday relationship establishes upper limit for current through cell. Electrode fabrication is described.

10 CFR Appendix C to Part 110 - Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components Under NRC...

Code of Federal Regulations, 2011 CFR

2011-01-01

... welds with substantial amounts of repetition of layout. The equipment, components and piping systems are... fully fluorinated hydrocarbon polymers. 1. Assemblies and components especially designed or prepared for use in gaseous diffusion enrichment. 1.1 Gaseous Diffusion Barriers Especially designed or prepared...

10 CFR Appendix C to Part 110 - Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components Under NRC...

Code of Federal Regulations, 2012 CFR

2012-01-01

... welds with substantial amounts of repetition of layout. The equipment, components and piping systems are... fully fluorinated hydrocarbon polymers. 1. Assemblies and components especially designed or prepared for use in gaseous diffusion enrichment. 1.1 Gaseous Diffusion Barriers Especially designed or prepared...

10 CFR Appendix C to Part 110 - Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components Under NRC...

Code of Federal Regulations, 2014 CFR

2014-01-01

... welds with substantial amounts of repetition of layout. The equipment, components and piping systems are... fully fluorinated hydrocarbon polymers. 1. Assemblies and components especially designed or prepared for use in gaseous diffusion enrichment. 1.1 Gaseous Diffusion Barriers Especially designed or prepared...

10 CFR Appendix C to Part 110 - Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components Under NRC...

Code of Federal Regulations, 2013 CFR

2013-01-01

... welds with substantial amounts of repetition of layout. The equipment, components and piping systems are... fully fluorinated hydrocarbon polymers. 1. Assemblies and components especially designed or prepared for use in gaseous diffusion enrichment. 1.1 Gaseous Diffusion Barriers Especially designed or prepared...

Ag out-surface diffusion in crystalline SiC with an effective SiO 2 diffusion barrier

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

Xue, H.; Xiao, H. Y.; Zhu, Z.

2015-05-07

For applications of tristructural isotropic (TRISO) fuel particles in high temperature reactors, release of radioactive Ag isotope ( 110mAg) through the SiC coating layer is a safety concern. In order to understand the diffusion mechanism, Ag ion implantations near the surface and in the bulk were performed by utilizing different ion energies and energy-degrader foils. High temperature annealing was carried out on the as-irradiated samples to study the possible out-surface diffusion. Before and after annealing, Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS) measurements were employed to obtain the elemental profiles of the implanted samples. Our results suggestmore » little migration of buried Ag in the bulk, and an out-diffusion of the implanted Ag in the near-surface region of single crystal SiC. It is also found that a SiO 2 layer, which was formed during annealing, may serve as an effective barrier to reduce or prevent Ag out diffusion through the SiC coating layer.« less

Ag Out-surface Diffusion In Crystalline SiC With An Effective SiO2 Diffusion Barrier

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

Xue, H.; Xiao, Haiyan Y.; Zhu, Zihua

2015-09-01

For applications of tristructural isotropic (TRISO) fuel particles in high temperature reactors, release of radioactive Ag isotope (110mAg) through the SiC coating layer is a safety concern. To understand the diffusion mechanism, Ag ion implantations near the surface and in the bulk were performed by utilizing different ion energies and energy-degrader foils. High temperature annealing was carried out on the as-irradiated samples to study the possible out-surface diffusion. Before and after annealing, Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS) measurements were employed to obtain the elemental profiles of the implanted samples. The results suggest little migration ofmore » buried Ag in the bulk, and an out-diffusion of the implanted Ag in the near-surface region of single crystal SiC. It is also found that a SiO2 layer, which was formed during annealing, may serve as an effective barrier to reduce or prevent Ag out diffusion through the SiC coating layer.« less

Structural Stability of Diffusion Barriers in Cu/Ru/MgO/Ta/Si

PubMed Central

Hsieh, Shu-Huei; Chen, Wen Jauh; Chien, Chu-Mo

2015-01-01

Various structures of Cu (50 nm)/Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm)/Si were prepared by sputtering and electroplating techniques, in which the ultra-thin trilayer of Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm) is used as the diffusion barrier against the interdiffusion between Cu film and Si substrate. The various structures of Cu/Ru/MgO/Ta/Si were characterized by four-point probes for their sheet resistances, by X-ray diffractometers for their crystal structures, by scanning electron microscopes for their surface morphologies, and by transmission electron microscopes for their cross-section and high resolution views. The results showed that the ultra-thin tri-layer of Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm) is an effective diffusion barrier against the interdiffusion between Cu film and Si substrate. The MgO, and Ta layers as deposited are amorphous. The mechanism for the failure of the diffusion barrier is that the Ru layer first became discontinuous at a high temperature and the Ta layer sequentially become discontinuous at a higher temperature, the Cu atoms then diffuse through the MgO layer and to the substrate at the discontinuities, and the Cu3Si phases finally form. The maximum temperature at which the structures of Cu (50 nm)/Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm)/Si are annealed and still have low sheet resistance is from 550 to 750 °C for the annealing time of 5 min and from 500 to 700 °C for the annealing time of 30 min. PMID:28347099

Diffusion Barrier Selection from Refractory Metals (Zr, Mo and Nb) via Interdiffusion Investigation for U-Mo RERTR Fuel Alloy

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

K. Huang; C. Kammerer; D. D. Keiser, Jr.

2014-04-01

U-Mo alloys are being developed as low enrichment monolithic fuel under the Reduced Enrichment for Research and Test Reactor (RERTR) Program. Diffusional interactions between the U-Mo fuel alloy and Al-alloy cladding within the monolithic fuel plate construct necessitate incorporation of a barrier layer. Fundamentally, a diffusion barrier candidate must have good thermal conductivity, high melting point, minimal metallurgical interaction, and good irradiation performance. Refractory metals, Zr, Mo, and Nb are considered based on their physical properties, and the diffusion behavior must be carefully examined first with U-Mo fuel alloy. Solid-to-solid U-10wt.%Mo vs. Mo, Zr, or Nb diffusion couples were assembledmore » and annealed at 600, 700, 800, 900 and 1000 degrees C for various times. The interdiffusion microstructures and chemical composition were examined via scanning electron microscopy and electron probe microanalysis, respectively. For all three systems, the growth rate of interdiffusion zone were calculated at 1000, 900 and 800 degrees C under the assumption of parabolic growth, and calculated for lower temperature of 700, 600 and 500 degrees C according to Arrhenius relationship. The growth rate was determined to be about 10 3 times slower for Zr, 10 5 times slower for Mo and 10 6 times slower for Nb, than the growth rates reported for the interaction between the U-Mo fuel alloy and pure Al or Al-Si cladding alloys. Zr, however was selected as the barrier metal due to a concern for thermo- mechanical behavior of UMo/Nb interface observed from diffusion couples, and for ductile-to-brittle transition of Mo near room temperature.« less

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

Custer, Jonathan S.; Fleming, James G.; Roherty-Osmun, Elizabeth

Refractory ternary nitride films for diffusion barriers in microelectronics have been grown using chemical vapor deposition. Thin films of titanium-silicon-nitride, tungsten-boron-nitride, and tungsten-silicon-nitride of various compositions have been deposited on 150 mm Si wafers. The microstructure of the films are either fully amorphous for the tungsten based films, or nauocrystalline TiN in an amorphous matrix for titanium-silicon-nitride. All films exhibit step coverages suitable for use in future microelectronics generations. Selected films have been tested as diffusion barriers between copper and silicon, and generally perform extremely weH. These fiIms are promising candidates for advanced diffusion barriers for microelectronics applications. The manufacturingmore » of silicon wafers into integrated circuits uses many different process and materials. The manufacturing process is usually divided into two parts: the front end of line (FEOL) and the back end of line (BEOL). In the FEOL the individual transistors that are the heart of an integrated circuit are made on the silicon wafer. The responsibility of the BEOL is to wire all the transistors together to make a complete circuit. The transistors are fabricated in the silicon itself. The wiring is made out of metal, currently aluminum and tungsten, insulated by silicon dioxide, see Figure 1. Unfortunately, silicon will diffuse into aluminum, causing aluminum spiking of junctions, killing transistors. Similarly, during chemical vapor deposition (CVD) of tungsten from ~fj, the reactivity of the fluorine can cause "worn-holes" in the silicon, also destroying transistors. The solution to these problems is a so-called diffusion barrier, which will allow current to pass from the transistors to the wiring, but will prevent reactions between silicon and the metal.« less

Barrier mechanism of multilayers graphene coated copper against atomic oxygen irradiation

NASA Astrophysics Data System (ADS)

Zhang, Haijing; Ren, Siming; Pu, Jibin; Xue, Qunji

2018-06-01

Graphene has been demonstrated as a protective coating for Cu under ambient condition because of its high impermeability and light-weight oxidation barrier. However, it lacks the research of graphene as a protective coating in space environment. Here, we experimentally and theoretically study the oxidation behavior of graphene-coated Cu in vacuum atomic oxygen (AO) condition. After AO irradiation, the experimental results show multilayer graphene has better anti-oxidation than monolayer graphene. Meanwhile, the calculation results show the oxidation appeared on the graphene's grain boundaries or the film's vacancy defects for the monolayer graphene coated Cu foil. Moreover, the calculation results show the oxidation process proceeds slowly in multilayers because of the matched defects overlaps each other to form a steric hindrance to suppress the O atom diffusion in the vertical direction, and the mismatched defects generates potential energy barriers for interlayer to suppress the O atom diffusion in the horizontal direction. Hence, multilayer graphene films could serve as protection coatings to prevent diffusion of O atom.

Study of Diffusion Barrier for Solder/ n-Type Bi2Te3 and Bonding Strength for p- and n-Type Thermoelectric Modules

NASA Astrophysics Data System (ADS)

Lin, Wen-Chih; Li, Ying-Sih; Wu, Albert T.

2018-01-01

This paper investigates the interfacial reaction between Sn and Sn3Ag0.5Cu (SAC305) solder on n-type Bi2Te3 thermoelectric material. An electroless Ni-P layer successfully suppressed the formation of porous SnTe intermetallic compound at the interface. The formation of the layers between Bi2Te3 and Ni-P indicates that Te is the dominant diffusing species. Shear tests were conducted on both Sn and SAC305 solder on n- and p-type Bi2Te3 with and without a Ni-P barrier layer. Without a Ni-P layer, porous SnTe would result in a more brittle fracture. A comparison of joint strength for n- and p-type thermoelectric modules is evaluated by the shear test. Adding a diffusion barrier increases the mechanical strength by 19.4% in n-type and 74.0% in p-type thermoelectric modules.

Preparation and Bond Properties of Thermal Barrier Coatings on Mg Alloy with Sprayed Al or Diffused Mg-Al Intermetallic Interlayer

NASA Astrophysics Data System (ADS)

Fan, Xizhi; Wang, Ying; Zou, Binglin; Gu, Lijian; Huang, Wenzhi; Cao, Xueqiang

2014-02-01

Sprayed Al or diffused Mg-Al layer was designed as interlayer between the thermal barrier coatings (TBCs) and Mg alloy substrate. The effects of the interlayer on the bond properties of the coats were investigated. Al layers were prepared by arc spraying and atmospheric plasma spraying (APS), respectively. Mg-Al diffused layer was obtained after the heat treatment of the sprayed sample (Mg alloy with APS Al coat) at 400 °C. The results show that sprayed Al interlayer does not improve the bond stability of TBCs. The failure of the TBCs on Mg alloy with Al interlayer occurs mainly due to the low strength of Al layer. Mg-Al diffused layer improves corrosion resistance of substrate and the bond interface. The TBCs on Mg alloy with Mg-Al diffused interlayer shows better bond stability than the sample of which the TBCs is directly sprayed on Mg alloy substrate by APS.

Vacancy–Vacancy Interaction Induced Oxygen Diffusivity Enhancement in Undoped Nonstoichiometric Ceria

DOE PAGES

Yuan, Fenglin; Zhang, Yanwen; Weber, William J.

2015-05-19

In this paper, molecular dynamics simulations and molecular static calculations have been used to systematically study oxygen vacancy transport in undoped nonstoichiometric ceria. A strong oxygen diffusivity enhancement appears in the vacancy concentration range of 2–4% over the temperature range from 1000 to 2000 K. An Arrhenius ion diffusion mechanism by vacancy hopping along the (100) direction is unambiguously identified, and an increasing trend of both the oxygen migration barrier and the prefactor with increasing vacancy concentration is observed. Within the framework of classical diffusion theory, a weak concentration dependence of the prefactor in oxygen vacancy migration is shown tomore » be crucial for explaining the unusual fast oxygen ion migration in the low concentration range and consequently the appearance of a maximum in oxygen diffusivity. Finally, a representative (100) direction interaction model is constructed to identify long-range vacancy–vacancy interaction as the structural origin of the positive correlation between oxygen migration barrier and vacancy concentration.« less

Chemically-inducible diffusion trap at cilia (C-IDTc) reveals molecular sieve-like barrier

PubMed Central

Lin, Yu-Chun; Phua, Siew Cheng; Jiao, John; Levchenko, Andre; Inoue, Takafumi; Rohatgi, Rajat; Inoue, Takanari

2013-01-01

Primary cilia function as specialized compartments for signal transduction. The stereotyped structure and signaling function of cilia inextricably depend on the selective segregation of molecules in cilia. However, the fundamental principles governing the access of soluble proteins to primary cilia remain unresolved. We developed a methodology termed Chemically-Inducible Diffusion Trap at Cilia (C-IDTc) to visualize the diffusion process of a series of fluorescent proteins ranging in size from 3.2 to 7.9 nm into primary cilia. We found that the interior of the cilium was accessible to proteins as large as 7.9 nm. The kinetics of ciliary accumulation of this panel of proteins was exponentially limited by their Stokes radii. Quantitative modeling suggests that the diffusion barrier operates as a molecular sieve at the base of cilia. Our study presents a set of powerful, generally applicable tools for the quantitative monitoring of ciliary protein diffusion under both physiological and pathological conditions. PMID:23666116

First-principles study of fission gas incorporation and migration in zirconium nitride

DOE PAGES

Mei, Zhi-Gang; Liang, Linyun; Yacout, Abdellatif M.

2017-03-24

To evaluate the effectiveness of ZrN as a diffusion barrier against fission gases, we investigate in this paper the incorporation and migration of fission gas atoms, with a focus on Xe, in ZrN by first-principles calculations. The formations of point defects in ZrN, including vacancies, interstitials, divacancies, Frenkel pairs, and Schottky defects, are first studied. Among all the defects, the Schottky defect with two vacancies as first nearest neighbor is predicted to be the most favorable incorporation site for fission gas Xe in ZrN. The migration of Xe gas atom in ZrN is investigated through two diffusion mechanisms, i.e., interstitialmore » and vacancy-assisted diffusions. The migration barrier of Xe gas atom through the intrinsic interstitials in ZrN is considerably lower than that through vacancies. Finally, therefore, at low temperatures fission gas Xe atoms diffuse mainly through interstitials in single crystal ZrN, whereas at high temperatures Xe may diffuse in ZrN assisted by vacancies.« less

Diffusion of point defects in crystalline silicon using the kinetic activation-relaxation technique method

DOE PAGES

Trochet, Mickaël; Béland, Laurent Karim; Joly, Jean -François; ...

2015-06-16

We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Weber potential. We focus more particularly on the evolution of crystalline cells with one to four vacancies and one to four interstitials in order to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for those systems that diffuse. Additionally, we characterize diffusion pathsmore » and special configurations such as dumbbell complex, di-interstitial (IV-pair+2I) superdiffuser, tetrahedral vacancy complex, and more. In conclusion, this study points to an unsuspected dynamical richness even for this apparently simple system that can only be uncovered by exhaustive and systematic approaches such as the kinetic activation-relaxation technique.« less

Simple rules for passive diffusion through the nuclear pore complex

PubMed Central

Mironska, Roxana; Kim, Seung Joong

2016-01-01

Passive macromolecular diffusion through nuclear pore complexes (NPCs) is thought to decrease dramatically beyond a 30–60-kD size threshold. Using thousands of independent time-resolved fluorescence microscopy measurements in vivo, we show that the NPC lacks such a firm size threshold; instead, it forms a soft barrier to passive diffusion that intensifies gradually with increasing molecular mass in both the wild-type and mutant strains with various subsets of phenylalanine-glycine (FG) domains and different levels of baseline passive permeability. Brownian dynamics simulations replicate these findings and indicate that the soft barrier results from the highly dynamic FG repeat domains and the diffusing macromolecules mutually constraining and competing for available volume in the interior of the NPC, setting up entropic repulsion forces. We found that FG domains with exceptionally high net charge and low hydropathy near the cytoplasmic end of the central channel contribute more strongly to obstruction of passive diffusion than to facilitated transport, revealing a compartmentalized functional arrangement within the NPC. PMID:27697925

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

Batal, Mohamed; Département de Toxicologie et Risques Chimiques, Unité de Brûlure Chimique, Institut de Recherche Biomédicale des Armées, Antenne de La Tronche, BP87, F-38702 La Tronche Cedex; Boudry, Isabelle

Sulphur mustard (SM) is a chemical warfare agent that attacks mainly skin, eye and lungs. Due to its lipophilic properties, SM is also able to diffuse through the skin and reach internal organs. DNA represents one of the most critical molecular targets of this powerful alkylating agent which modifies DNA structure by forming monoadducts and biadducts. These DNA lesions are involved in the acute toxicity of SM as well as its long-term carcinogenicity. In the present work we studied the formation and persistence of guanine and adenine monoadducts and guanine biadducts in the DNA of brain, lungs, kidneys, spleen, andmore » liver of SKH-1 mice cutaneously exposed to 2, 6 and 60 mg/kg of SM. SM-DNA adducts were detected in all studied organs, except in liver at the two lowest doses. Brain and lungs were the organs with the highest level of SM-DNA adducts, followed by kidney, spleen and liver. Monitoring the level of adducts for three weeks after cutaneous exposure showed that the lifetime of adducts were not the same in all organs, lungs being the organ with the longest persistence. Diffusion from skin to internal organs was much more efficient at the highest compared to the lowest dose investigated as the result of the loss of the skin barrier function. These data provide novel information on the distribution of SM in tissues following cutaneous exposures and indicate that brain is an important target. - Highlights: • Sulphur mustard reaches internal organs after skin exposure • Adducts are detected in the DNA of internal organs • Brain is the organ with the highest level of DNA damage • The barrier function of skin is lost at high dose of sulphur mustard • DNA adducts persist in organs for 2 or 3 weeks.« less

Integration of amorphous tantalum silicon nitride (TaSiN) films as diffusion barriers in a Cu/SiLK(TM) metallization scheme

NASA Astrophysics Data System (ADS)

Padiyar, Sumant Devdas

2003-09-01

Current and future performance requirements for high- speed integrated circuit (IC) devices have placed great emphasis on the introduction of novel materials, deposition techniques and improved metrology techniques. The introduction of copper interconnects and more currently low-k dielectric materials in IC fabrication are two such examples. This introduction necessitates research on the compatibility of these materials and process techniques with adjacent diffusion barrier materials. One candidate, which has attracted significant attention is tantalum-silicon-nitride (TaSiN) on account of its superior diffusion barrier performance and high recrystallization temperature1. The subject of this dissertation is an investigation of the integration compatibility and performance of TaSiN barrier layers with a low-k dielectric polymer (SiLK ®2). A plasma- enhanced chemical vapor deposition (PECVD) approach is taken for growth of TaSiN films in this work due to potential advantages in conformal film coverage compared to more conventional physical vapor deposition methods. A Design of Experiment (DOE) methodology was introduced for PECVD of TaSiN on SiLK to optimize film properties such as film composition, resistivity, growth rate and film roughness with respect to the predictors viz. substrate temperature, precursor gas flow and plasma power. The first pass study determined the response window for optimized TaSiN film composition, growth rate and low halide contamination and the compatibility of the process with an organic polymer substrate, i.e. SiLK. Second-pass studies were carried out to deposit ultra- thin (10nm) films on: (a)blanket SiLK to investigate the performance of TaSiN films against copper diffusion, and (b)patterned SiLK to evaluate step coverage and conformality. All TaSiN depositions were carried out on SiO2 substrates for baseline comparisons. A second purpose of the diffusion barrier in IC processing is to improve interfacial adhesion between the barrier and the adjacent dielectric material; especially important for an organic polymer like SiLK. Hence, a detailed study was undertaken to evaluate the interfacial adhesion of TaSiN with SiLK and SiO2 and study the dependence of the adhesion with the film composition. The results of diffusion barrier performance studies, conformality studies, and interfacial adhesion studies of TaSiN films are discussed in relation to the elemental compositions of the films. 1J. S. Reid, M. Nicolet, J. Appl. Phys. 79 (2) p. 1109 (1996). 2SiLK is a low-k dielectric candidate registered by Dow Chemical Company, MI.

Modelisation de la diffusion sur les surfaces metalliques: De l'adatome aux processus de croissance

NASA Astrophysics Data System (ADS)

Boisvert, Ghyslain

Cette these est consacree a l'etude des processus de diffusion en surface dans le but ultime de comprendre, et de modeliser, la croissance d'une couche mince. L'importance de bien mai triser la croissance est primordiale compte tenu de son role dans la miniaturisation des circuits electroniques. Nous etudions ici les surface des metaux nobles et de ceux de la fin de la serie de transition. Dans un premier temps, nous nous interessons a la diffusion d'un simple adatome sur une surface metallique. Nous avons, entre autres, mis en evidence l'apparition d'une correlation entre evenements successifs lorsque la temperature est comparable a la barriere de diffusion, i.e., la diffusion ne peut pas etre associee a une marche aleatoire. Nous proposons un modele phenomenologique simple qui reproduit bien les resultats des simulations. Ces calculs nous ont aussi permis de montrer que la diffusion obeit a la loi de Meyer-Neldel. Cette loi stipule que, pour un processus active, le prefacteur augmente exponentiellement avec la barriere. En plus, ce travail permet de clarifier l'origine physique de cette loi. En comparant les resultats dynamiques aux resultats statiques, on se rend compte que la barriere extraite des calculs dynamiques est essentiellement la meme que celle obtenue par une approche statique, beaucoup plus simple. On peut donc obtenir cette barriere a l'aide de methodes plus precises, i.e., ab initio, comme la theorie de la fonctionnelle de la densite, qui sont aussi malheureusement beaucoup plus lourdes. C'est ce que nous avons fait pour plusieurs systemes metalliques. Nos resultats avec cette derniere approche se comparent tres bien aux resultats experimentaux. Nous nous sommes attardes plus longuement a la surface (111) du platine. Cette surface regorge de particularites interessantes, comme la forme d'equilibre non-hexagonale des i lots et deux sites d'adsorption differents pour l'adatome. De plus, des calculs ab initio precedents n'ont pas reussi a confirmer la forme d'equilibre et surestiment grandement la barriere. Nos calculs, plus complets et dans un formalisme mieux adapte a ce genre de probleme, predisent correctement la forme d'equilibre, qui est en fait due a un relachement different du stress de surface aux deux types de marches qui forment les cotes des i lots. Notre valeur pour la barriere est aussi fortement diminuee lorsqu'on relaxe les forces sur les atomes de la surface, amenant le resultat theorique beaucoup plus pres de la valeur experimentale. Nos calculs pour le cuivre demontre en effet que la diffusion de petits i lots pendant la croissance ne peut pas etre negligee dans ce cas, mettant en doute la valeur des interpretations des mesures experimentales. (Abstract shortened by UMI.)

Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization

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

Kumm, J.; Samadi, H.; Chacko, R. V.

An evaporated Al layer is known as an excellent rear metallization for highly efficient solar cells, but suffers from incompatibility with a common solder process. To enable solar cell-interconnection and module integration, in this work the Al layer is complemented with a solder stack of TiN/Ti/Ag or TiN/NiV/Ag, in which the TiN layer acts as an Al diffusion barrier. X-ray photoelectron spectroscopy measurements prove that diffusion of Al through the stack and the formation of an Al{sub 2}O{sub 3} layer on the stack's surface are responsible for a loss of solderability after a strong post-metallization anneal, which is often mandatorymore » to improve contact resistance and passivation quality. An optimization of the reactive TiN sputter process results in a densification of the TiN layer, which improves its barrier quality against Al diffusion. However, measurements with X-ray diffraction and scanning electron microscopy show that small grains with vertical grain boundaries persist, which still offer fast diffusion paths. Therefore, the concept of stuffing is introduced. By incorporating oxygen into the grain boundaries of the sputtered TiN layer, Al diffusion is strongly reduced as confirmed by secondary ion mass spectroscopy profiles. A quantitative analysis reveals a one order of magnitude lower Al diffusion coefficient for stuffed TiN layers. This metallization system maintains its solderability even after strong post-metallization annealing at 425 °C for 15 min. This paper thus presents an industrially feasible, conventionally solderable, and long-term stable metallization scheme for highly efficient silicon solar cells.« less

Tungsten nitride coatings obtained by HiPIMS as plasma facing materials for fusion applications

NASA Astrophysics Data System (ADS)

Tiron, Vasile; Velicu, Ioana-Laura; Porosnicu, Corneliu; Burducea, Ion; Dinca, Paul; Malinský, Petr

2017-09-01

In this work, tungsten nitride coatings with nitrogen content in the range of 19-50 at% were prepared by reactive multi-pulse high power impulse magnetron sputtering as a function of the argon and nitrogen mixture and further exposed to a deuterium plasma jet. The elemental composition, morphological properties and physical structure of the samples were investigated by Rutherford backscattering spectrometry, atomic force microscopy and X-ray diffraction. Deuterium implantation was performed using a deuterium plasma jet and its retention in nitrogen containing tungsten films was investigated using thermal desorption spectrometry. Deuterium retention and release behaviour strongly depend on the nitrogen content in the coatings and the films microstructure. All nitride coatings have a polycrystalline structure and retain a lower deuterium level than the pure tungsten sample. Nitrogen content in the films acts as a diffusion barrier for deuterium and leads to a higher desorption temperature, therefore to a higher binding energy.

Gauge calibration by diffusion

NASA Technical Reports Server (NTRS)

Brock, F. J.; Feakes, F. (Inventor)

1968-01-01

Vacuum gage calibration by diffusing a known quantity of gas through a heated barrier into a gauge is examined. The gas flow raises the pressure in the gauge to known level and is then compared with the gauge's pressure reading.

Field Testing of an Unvented Roof with Fibrous Insulation, Tiles, and Vapor Diffusion Venting

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

Ueno, K.; Lstiburek, J. W.

This research is a test implementation of an unvented tile roof assembly in a hot-humid climate (Orlando, FL; Zone 2A), insulated with air permeable insulation (netted and blown fiberglass). Given the localized moisture accumulation and failures seen in previous unvented roof field work, it was theorized that a 'diffusion vent' (water vapor open, but air barrier 'closed') at the highest points in the roof assembly might allow for the wintertime release of moisture, to safe levels. The 'diffusion vent' is an open slot at the ridge and hips, covered with a water-resistant but vapor open (500+ perm) air barrier membrane.more » As a control comparison, one portion of the roof was constructed as a typical unvented roof (self-adhered membrane at ridge). The data collected to date indicate that the diffusion vent roof shows greater moisture safety than the conventional, unvented roof design.« less

Hypomyelination, memory impairment, and blood-brain barrier permeability in a model of sleep apnea.

PubMed

Kim, Lenise Jihe; Martinez, Denis; Fiori, Cintia Zappe; Baronio, Diego; Kretzmann, Nélson Alexandre; Barros, Helena Maria Tannhauser

2015-02-09

We investigated the effect of intermittent hypoxia, mimicking sleep apnea, on axonal integrity, blood-brain barrier permeability, and cognitive function of mice. Forty-seven C57BL mice were exposed to intermittent or sham hypoxia, alternating 30s of progressive hypoxia and 30s of reoxigenation, during 8h/day. The axonal integrity in cerebellum was evaluated by transmission electron microscopy. Short- and long-term memories were assessed by novel object recognition test. The levels of endothelin-1 were measured by ELISA. Blood-brain barrier permeability was quantified by Evans Blue dye. After 14 days, animals exposed to intermittent hypoxia showed hypomyelination in cerebellum white matter and higher serum levels of endothelin-1. The short and long-term memories in novel object recognition test was impaired in the group exposed to intermittent hypoxia as compared to controls. Blood-brain barrier permeability was similar between the groups. These results indicated that hypomyelination and impairment of short- and long-term working memories occurred in C57BL mice after 14 days of intermittent hypoxia mimicking sleep apnea. Copyright © 2014 Elsevier B.V. All rights reserved.

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.

High Temperature Characteristics of Pt/TaSi2/Pt/W and Pt/Ti/W Diffusion Barrier Systems for Ohmic Contacts to 4H-SiC

NASA Technical Reports Server (NTRS)

Okojie, Robert S.; Lukco, Dorothy

2017-01-01

The degradation of ohmic contacts to 4H-SiC pressure sensors over time at high temperature is primarily due to two failure mechanisms: migrating bond pad Au and atmospheric O toward the ohmic contact SiC interface and the inter-metallic mixing between diffusion barrier systems (DBS) and the underlying ohmic contact metallization. We investigated the effectiveness of Pt/TaSi2/Pt/W (DBS-A) and Pt/Ti/W (DBS-B) in preventing Au and O diffusion through the underlying binary Ti/W or alloyed W50:Ni50 ohmic contacts to 4H-SiC and the DBS ohmic contact intermixing at temperature up to 700 C.

Bacterial lipopolysaccharide-induced systemic inflammation alters perfusion of white matter-rich regions without altering flow in brain-irrigating arteries: Relationship to blood-brain barrier breakdown?

PubMed

Dhaya, Ibtihel; Griton, Marion; Raffard, Gérard; Amri, Mohamed; Hiba, Bassem; Konsman, Jan Pieter

2018-01-15

To better understand brain dysfunction during sepsis, cerebral arterial blood flow was assessed with Phase Contrast Magnetic Resonance Imaging, perfusion with Arterial Spin Labeling and structure with diffusion-weighted Magnetic Resonance Imaging in rats after intraperitoneal administration of bacterial lipopolysaccharides. Although cerebral arterial flow was not altered, perfusion of the corpus callosum region and diffusion parallel to its fibers were higher after lipopolysaccharide administration as compared to saline injection. In parallel, lipopolysaccharide induced perivascular immunoglobulin-immunoreactivity in white matter. These findings indicate that systemic inflammation can result in increased perfusion, blood-brain barrier breakdown and altered water diffusion in white matter. Copyright © 2017 Elsevier B.V. All rights reserved.

Comparisons of Force Measurement Methods for DBD Plasma Actuators in Quiescent Air

NASA Technical Reports Server (NTRS)

Hoskinson, Alan R.; Hershkowitz, Noah; Ashpis, David E.

2009-01-01

We have performed measurements of the force induced by both single (one electrode insulated) and double (both electrodes insulated) dielectric barrier discharge plasma actuators in quiescent air. We have shown that, for single barrier actuators with cylindrical exposed electrodes, as the electrode diameter decrease the force efficiencies increase much faster than a previously reported linear trend. This behavior has been experimentally verified using two different measurement techniques: stagnation probe measurements of the induced flow velocity and direct measurement of the force using an electronic balance. Actuators with rectangular cross-section exposed electrodes do not show the same rapid increase at small thicknesses. We have also shown that the induced force is independent of the material used for the exposed electrode. The same techniques have shown that the induced force of a double barrier actuator increases with decreasing narrow electrode diameter.

Adsorption and diffusion of Ru adatoms on Ru(0001)-supported graphene: Large-scale first-principles calculations

DOE PAGES

Han, Yong; Evans, James W.

2015-10-27

Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moiré cell, there are three distinct regions: fcc, hcp, and mound, in which the C6-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atom inmore » the fcc region, next strongest in the hcp region, then the fcc-hcp boundary (ridge) between these regions, and the weakest binding in the mound region. Behavior is similar to that observed from small-unit-cell calculations of Habenicht et al. [Top. Catal. 57, 69 (2014)], which differ from previous large-scale calculations. We determine the minimum-energy path for local diffusion near the center of the fcc region and obtain a local diffusion barrier of ~0.48 eV. We also estimate a significantly lower local diffusion barrier in the ridge region. These barriers and information on the adsorption energy variation facilitate development of a realistic model for the global potential energy surface for Ru adatoms. Furthermore, this in turn enables simulation studies elucidating diffusion-mediated directed-assembly of Ru nanoclusters during deposition of Ru on G/Ru(0001).« less

Density Functional Theory Investigation of Proton Diffusion in Tungsten Oxide And Its Hydrates

NASA Astrophysics Data System (ADS)

Lin, Hao

Fast proton conduction mechanism is of key importance for achieving high performance in fuel cell membranes, batteries, supercapacitors, and electrochromic materials. Enhanced proton diffusion is often observed in hydrated materials where it is thought to occur via the famous Grotthuss mechanism through pathways formed by structural water. Using first-principles calculations, we demonstrate that proton diffusion in tungsten oxide dihydrate (WO3·2H 2O), a known good proton conductor, takes place within the layers of corner-sharing WO6 octahedra without direct involvement of structural water. The calculated proton migration barrier in WO3·2H 2O is in good agreement with the experimental value inferred from the temperature dependence of conductivity. The preferred proton diffusion path in WO3·2H2O is essentially the same as in gamma-WO 3. In contrast to the small intercalation voltages calculated for WO 3 and WO3·2H2O, we find that proton absorption in the monohydrate WO3·H2O is energetically highly favorable. However, strong proton-proton repulsion limits the equilibrium H content at zero voltage. We find a fast one-dimensional diffusion channel in WO3·H2O at dilute proton concentrations, but much higher barriers are expected at near-equilibrium concentrations due to strong repulsive interactions with other protons. Our results illustrate that low proton diffusion barriers and low insertion voltages both contribute to fast proton transport in bulk WO3·2H2O and gamma-WO 3.

Adsorption and diffusion of Ru adatoms on Ru(0001)-supported graphene: Large-scale first-principles calculations

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

Han, Yong; Evans, James W.

2015-10-28

Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moiré cell, there are three distinct regions: fcc, hcp, and mound, in which the C{sub 6}-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atommore » in the fcc region, next strongest in the hcp region, then the fcc-hcp boundary (ridge) between these regions, and the weakest binding in the mound region. Behavior is similar to that observed from small-unit-cell calculations of Habenicht et al. [Top. Catal. 57, 69 (2014)], which differ from previous large-scale calculations. We determine the minimum-energy path for local diffusion near the center of the fcc region and obtain a local diffusion barrier of ∼0.48 eV. We also estimate a significantly lower local diffusion barrier in the ridge region. These barriers and information on the adsorption energy variation facilitate development of a realistic model for the global potential energy surface for Ru adatoms. This in turn enables simulation studies elucidating diffusion-mediated directed-assembly of Ru nanoclusters during deposition of Ru on G/Ru(0001)« less

Influence of dislocation strain fields on the diffusion of interstitial iron impurities in silicon

NASA Astrophysics Data System (ADS)

Ziebarth, Benedikt; Mrovec, Matous; Elsässer, Christian; Gumbsch, Peter

2015-09-01

The efficiency of silicon (Si)-based solar cells is strongly affected by crystal defects and impurities. Metallic impurities, in particular interstitial iron (Fe) atoms, cause large electric losses because they act as recombination centers for photogenerated charge carriers. Here, we present a systematic first-principles density functional theory (DFT) study focusing on the influence of hydrostatic, uniaxial, and shear strains on the thermodynamic stability and the diffusivity of Fe impurities in crystalline Si. Our calculations show that the formation energy of neutral Fe interstitials in tetrahedral interstitial sites is almost unaffected by uniform deformations of the Si crystal up to strains of 5%. In contrast, the migration barrier varies significantly with strain, especially for hydrostatic deformation. In order to determine effective diffusion coefficients for different strain states, a kinetic Monte Carlo (kMC) model was set up based on the activation energy barriers and frequency factors obtained from the DFT simulations. By using the strain dependence of the migration barrier, we examined the migration of Fe interstitials in the vicinity of perfect 1 /2 <110 > screw and 60∘ mixed dislocations, and 1 /6 <112 > 90∘ and 30∘ partial dislocations. While the strain field of the perfect screw dislocation always enhances the local Fe diffusion, the existence of tensile and compressive regions around the 60∘ mixed dislocation results in a strong anisotropic diffusion profile with significantly faster and slower diffusivities on its tensile and compressive sides. The influences of the partial dislocations are qualitatively similar to that of the 60∘ mixed dislocation.

Loss of Endothelial Barrier in Marfan Mice (mgR/mgR) Results in Severe Inflammation after Adenoviral Gene Therapy

PubMed Central

Weymann, Alexander; Arif, Rawa; Weber, Antje; Zaradzki, Marcin; Richter, Karsten; Ensminger, Stephan; Robinson, Peter Nicholas; Wagner, Andreas H.; Karck, Matthias; Kallenbach, Klaus

2016-01-01

Objectives Marfan syndrome is an autosomal dominant inherited disorder of connective tissue. The vascular complications of Marfan syndrome have the biggest impact on life expectancy. The aorta of Marfan patients reveals degradation of elastin layers caused by increased proteolytic activity of matrix metalloproteinases (MMPs). In this study we performed adenoviral gene transfer of human tissue inhibitor of matrix metalloproteinases-1 (hTIMP-1) in aortic grafts of fibrillin-1 deficient Marfan mice (mgR/mgR) in order to reduce elastolysis. Methods We performed heterotopic infrarenal transplantation of the thoracic aorta in female mice (n = 7 per group). Before implantation, mgR/mgR and wild-type aortas (WT, C57BL/6) were transduced ex vivo with an adenoviral vector coding for human TIMP-1 (Ad.hTIMP-1) or β-galactosidase (Ad.β-Gal). As control mgR/mgR and wild-type aortas received no gene therapy. Thirty days after surgery, overexpression of the transgene was assessed by immunohistochemistry (IHC) and collagen in situ zymography. Histologic staining was performed to investigate inflammation, the neointimal index (NI), and elastin breaks. Endothelial barrier function of native not virus-exposed aortas was evaluated by perfusion of fluorescent albumin and examinations of virus-exposed tissue were performed by transmission electron microscopy (TEM). Results IHC and ISZ revealed sufficient expression of the transgene. Severe cellular inflammation and intima hyperplasia were seen only in adenovirus treated mgR/mgR aortas (Ad.β-Gal, Ad.hTIMP-1 NI: 0.23; 0.43), but not in native and Ad.hTIMP-1 treated WT (NI: 0.01; 0.00). Compared to native mgR/mgR and Ad.hTIMP-1 treated WT aorta, the NI is highly significant greater in Ad.hTIMP-1 transduced mgR/mgR aorta (p = 0.001; p = 0.001). As expected, untreated Marfan grafts showed significant more elastolysis compared to WT (p = 0.001). However, elastolysis in Marfan aortas was not reduced by adenoviral overexpression of hTIMP-1 (compared to untreated Marfan aorta: Ad.hTIMP-1 p = 0.902; control Ad.β-Gal. p = 0.165). The virus-untreated and not transplanted mgR/mgR aorta revealed a significant increase of albumin diffusion through the endothelial barrier (p = 0.037). TEM analysis of adenovirus-exposed mgR/mgR aortas displayed disruption of the basement membrane and basolateral space. Conclusions Murine Marfan aortic grafts developed severe inflammation after adenoviral contact. We demonstrated that fibrillin-1 deficiency is associated with relevant dysfunction of the endothelial barrier that enables adenovirus to induce vessel-harming inflammation. Endothelial dysfunction may play a pivotal role in the development of the vascular phenotype of Marfan syndrome. PMID:26840980

Implementation of a Non-Metallic Barrier in an Electric Motor

NASA Technical Reports Server (NTRS)

M'Sadoques, George A. (Inventor); Carra, Michael R. (Inventor); Beringer, Durwood M. (Inventor)

2013-01-01

A motor for use in a volatile environment includes a rotor exposed to the volatile environment, electronics for rotating the rotor, an impervious ceramic barrier separating the electronics and the rotor, and a flexible seal for preventing the volatile environment from contacting the electronics and for minimizing vibratory and twisting loads upon the barrier to minimize damage to the barrier.

Communication barriers to applying federal research in support of land management in the United States

Treesearch

Vita Wright

2007-01-01

Barriers to effective communication between researchers and managers can ultimately result in barriers to the application of scientific knowledge and technology for land management. Both individual and organizational barriers are important in terms of how they affect the first three stages of the innovation-decision process: 1) knowledge, where an individual is exposed...

Electronic Devices with Rubidium Barrier Film and Process for Making Same

DTIC Science & Technology

1998-08-20

barrier film is comprised of a plurality of contiguous monolayers, while FIG. 7B shows another embodiment of the 20 invention where the barrier film is... plurality of contiguous monolayers in which different monolayers thereof are formed of different types of metal atoms. -10- FIG. 8 is a schematic...system directed toward the substrate 26. A diffusion barrier precursor compound effusion cell, for example a barium fluoride, strontium fluoride or the

Encapsulation of organic light emitting diodes

NASA Astrophysics Data System (ADS)

Visweswaran, Bhadri

Organic Light Emitting Diodes (OLEDs) are extremely attractive candidates for flexible display and lighting panels due to their high contrast ratio, light weight and flexible nature. However, the materials in an OLED get oxidized by extremely small quantities of atmospheric moisture and oxygen. To obtain a flexible OLED device, a flexible thin-film barrier encapsulation with low permeability for water is necessary. Water permeates through a thin-film barrier by 4 modes: microcracks, contaminant particles, along interfaces, and through the bulk of the material. We have developed a flexible barrier film made by Plasma Enhanced Chemical Vapor Deposition (PECVD) that is devoid of any microcracks. In this work we have systematically reduced the permeation from the other three modes to come up with a barrier film design for an operating lifetime of over 10 years. To provide quantitative feedback during barrier material development, techniques for measuring low diffusion coefficient and solubility of water in a barrier material have been developed. The mechanism of water diffusion in the barrier has been identified. From the measurements, we have created a model for predicting the operating lifetime from accelerated tests when the lifetime is limited by bulk diffusion. To prevent the particle induced water permeation, we have encapsulated artificial particles and have studied their cross section. A three layer thin-film that can coat a particle at thicknesses smaller than the particle diameter is identified. It is demonstrated to protect a bottom emission OLED device that was contaminated with standard sized glass beads. The photoresist and the organic layers below the barrier film causes sideways permeation that can reduce the lifetime set by permeation through the bulk of the barrier. To prevent the sideways permeation, an impermeable inorganic grid made of the same barrier material is designed. The reduction in sideways permeation due to the impermeable inorganic grid is demonstrated in an encapsulated OLED. In this work, we have dealt with three permeation mechanisms and shown solution to each of them. These steps give us reliable flexible encapsulation that has a lifetime of greater than 10 years.

High-throughput ab-initio dilute solute diffusion database.

PubMed

Wu, Henry; Mayeshiba, Tam; Morgan, Dane

2016-07-19

We demonstrate automated generation of diffusion databases from high-throughput density functional theory (DFT) calculations. A total of more than 230 dilute solute diffusion systems in Mg, Al, Cu, Ni, Pd, and Pt host lattices have been determined using multi-frequency diffusion models. We apply a correction method for solute diffusion in alloys using experimental and simulated values of host self-diffusivity. We find good agreement with experimental solute diffusion data, obtaining a weighted activation barrier RMS error of 0.176 eV when excluding magnetic solutes in non-magnetic alloys. The compiled database is the largest collection of consistently calculated ab-initio solute diffusion data in the world.

Atomistic Modeling of Cation Diffusion in Transition Metal Perovskites La1-xSrxMnO3+/-δfor Solid Oxide Fuel Cell Cathodes Applications

NASA Astrophysics Data System (ADS)

Lee, Yueh-Lin; Duan, Yuhua; Morgan, Dane; Sorescu, Dan; Abernathy, Harry

Cation diffusion in La1-xSrxMnO3+/-δ (LSM) and in related perovskite materials play an important role in controlling long term performance and stability of solid oxide fuel cell (SOFCs) cathodes. Due to sluggish rates of cation diffusion and complex coupling between defect chemistry and cation diffusion pathways, currently there is still lack of quantitative theoretical model predictions on cation diffusivity vs. T and P(O2) to describe experimental cation tracer diffusivities. In this work, based on ab initio modeling of LSM defect chemistry and migration barriers of the possible cation diffusion pathways, we assess the rates of A-site and B-site cation diffusion in a wide range of T and P(O2) at x =0.0 and 0.2 for SOFC applications. We demonstrate the active cation diffusion pathways in LSM involve cation defect clusters as cation transport carriers, where reduction in the cation migration barriers, which are governed by the steric effect associated with the metal-oxygen cage in the perovskite lattice, is much greater than the penalty of repulsive interaction in the A-site and B-site cation vacancy clusters, leading to higher cation diffusion rates as compared to those of single cation vacancy hopping mechanisms. The predicted Mn and La/Sr cation self-diffusion coefficients of LSM at at x =0.0 and 0.2 along with their 1/T and P(O2) dependences, are in good agreement with the experimental tracer diffusion coefficients.

Simultaneous cell death and desquamation of the embryonic diffusion barrier during epidermal development.

PubMed

Saathoff, Manuela; Blum, Barbara; Quast, Thomas; Kirfel, Gregor; Herzog, Volker

2004-10-01

The periderm is an epithelial layer covering the emerging epidermis in early embryogenesis of vertebrates. In the chicken embryo, an additional cellular layer, the subperiderm, occurs at later embryonic stages underneath the periderm. The questions arose what is the function of both epithelial layers and, as they are transitory structures, by which mechanism are they removed. By immunocytochemistry, the tight junction (TJ) proteins occludin and claudin-1 were localized in the periderm and in the subperiderm, and sites of close contact between adjacent cells were detected by electron microscopy. Using horseradish peroxidase (HRP) as tracer, these contacts were identified as tight junctions involved in the formation of the embryonic diffusion barrier. This barrier was lost by desquamation at the end of the embryonic period, when the cornified envelope of the emerging epidermis was formed. By TUNEL and DNA ladder assays, we detected simultaneous cell death in the periderm and the subperiderm shortly before hatching. The absence of caspases-3, -6, and -7 activity, key enzymes of apoptosis, and the lack of typical morphological criteria of apoptosis such as cell fragmentation or membrane blebbing point to a special form of programmed cell death (PCD) leading to the desquamation of the embryonic diffusion barrier. Copyright 2004 Elsevier Inc.

Correlative study of functional and structural regeneration of urothelium after chitosan-induced injury.

PubMed

Erman, Andreja; Kerec Kos, Mojca; Žakelj, Simon; Resnik, Nataša; Romih, Rok; Veranič, Peter

2013-11-01

High transepithelial electrical resistance (TEER) demonstrates a functional permeability barrier of the normal urothelium, which is maintained by a layer of highly differentiated superficial cells. When the barrier is challenged, a quick regeneration is induced. We used side-by-side diffusion chambers as an ex vivo system to determine the time course of functional and structural urothelial regeneration after chitosan-induced injury. The exposure of the urothelium to chitosan caused a 60 % decrease in TEER, the exposure of undifferentiated urothelial cells to the luminal surface and leaky tight junctions. During the regeneration period (350 min), TEER recovered to control values after approximately 200 min, while structural regeneration continued until 350 min after injury. The tight junctions are the earliest and predominant component of the barrier to appear, while complete barrier regeneration is achieved by delayed superficial cell terminal differentiation. The barrier function and the structure of untreated urothelium were unaffected in side-by-side diffusion chambers for at least 6 h. The urinary bladder tissue excised from an animal thus retains the ability to maintain and restore the transepithelial barrier and cellular ultrastructure for a sufficient period to allow for studies of regeneration in ex vivo conditions.

Strain effect on the adsorption, diffusion, and molecular dissociation of hydrogen on Mg (0001) surface

NASA Astrophysics Data System (ADS)

Lei, Huaping; Wang, Caizhuang; Yao, Yongxin; Wang, Yangang; Hupalo, Myron; McDougall, Dan; Tringides, Michael; Ho, Kaiming

2013-12-01

The adsorption, diffusion, and molecular dissociation of hydrogen on the biaxially strained Mg (0001) surface have been systematically investigated by the first principle calculations based on density functional theory. When the strain changes from the compressive to tensile state, the adsorption energy of H atom linearly increases while its diffusion barrier linearly decreases oppositely. The dissociation barrier of H2 molecule linearly reduces in the tensile strain region. Through the chemical bonding analysis including the charge density difference, the projected density of states and the Mulliken population, the mechanism of the strain effect on the adsorption of H atom and the dissociation of H2 molecule has been elucidated by an s-p charge transfer model. With the reduction of the orbital overlap between the surface Mg atoms upon the lattice expansion, the charge transfers from p to s states of Mg atoms, which enhances the hybridization of H s and Mg s orbitals. Therefore, the bonding interaction of H with Mg surface is strengthened and then the atomic diffusion and molecular dissociation barriers of hydrogen decrease accordingly. Our works will be helpful to understand and to estimate the influence of the lattice deformation on the performance of Mg-containing hydrogen storage materials.

Tin-phthalocyanine adsorption and diffusion on Cu and Au (111) surfaces: A density functional theory study

NASA Astrophysics Data System (ADS)

Qin, Dan; Ge, Xu-Jin; Lü, Jing-Tao

2018-05-01

Through density functional theory based calculations, we study the adsorption and diffusion of tin phthalocyanine (SnPc) molecule on Au(111) and Cu(111) surfaces. SnPc has two conformers with Sn pointing to the vacuum (Sn-up) and substrate (Sn-down), respectively. The binding energies of the two conformers with different adsorption sites on the two surfaces, including top, bridge, fcc, hcp, are calculated and compared. It is found that the SnPc molecule binds stronger on Cu(111) surface, with binding energy about 1 eV larger than that on Au(111). Only the bridge and top adsorption sites are stable on Cu(111), while all the four adsorption sites are stable on Au(111), with small diffusion barriers between them. Moreover, the flipping barrier from Sn-up to Sn-down conformer is of the same magnitude on the two metal surfaces. These results are consistent with a recent experiment [Zhang, et al., Angew. Chem., 56, 11769 (2017)], which shows that conformation change from Sn-up to Sn-down on Cu(111) surface can be induced by a C60-functionalized STM tip, while similar change is difficult to realize on Au(111), due to smaller diffusion barrier on Au(111).

Silicon based substrate with calcium aluminosilicate/thermal barrier layer

NASA Technical Reports Server (NTRS)

Eaton, Jr., Harry Edwin (Inventor); Allen, William Patrick (Inventor); Miller, Robert Alden (Inventor); Jacobson, Nathan S. (Inventor); Smialek, James L. (Inventor); Opila, Elizabeth J. (Inventor); Lee, Kang N. (Inventor); Nagaraj, Bangalore A. (Inventor); Wang, Hongyu (Inventor); Meschter, Peter Joel (Inventor)

2001-01-01

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a calcium alumino silicate.

Silicon based substrate with environmental/thermal barrier layer

NASA Technical Reports Server (NTRS)

Eaton, Jr., Harry Edwin (Inventor); Allen, William Patrick (Inventor); Jacobson, Nathan S. (Inventor); Bansal, Narottam P. (Inventor); Opila, Elizabeth J. (Inventor); Smialek, James L. (Inventor); Lee, Kang N. (Inventor); Spitsberg, Irene T. (Inventor); Wang, Hongyu (Inventor); Meschter, Peter Joel (Inventor)

2002-01-01

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a barium-strontium alumino silicate.

Silicon based substrate with environmental/ thermal barrier layer

NASA Technical Reports Server (NTRS)

Eaton, Jr., Harry Edwin (Inventor); Allen, William Patrick (Inventor); Jacobson, Nathan S. (Inventor); Bansal, Nanottam P. (Inventor); Opila, Elizabeth J. (Inventor); Smialek, James L. (Inventor); Lee, Kang N. (Inventor); Spitsberg, Irene T. (Inventor); Wang, Hongyu (Inventor); Meschter, Peter Joel (Inventor)

2002-01-01

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a barium-strontium alumino silicate.

Pulmonary function abnormalities in never-smoking flight attendants exposed to secondhand tobacco smoke in the aircraft cabin.

PubMed

Arjomandi, Mehrdad; Haight, Thaddeus; Redberg, Rita; Gold, Warren M

2009-06-01

To determine whether the flight attendants who were exposed to secondhand tobacco smoke in the aircraft cabin have abnormal pulmonary function. We administered questionnaires and performed pulmonary function testing in 61 never-smoking female flight attendants who worked in active air crews before the smoking ban on commercial aircraft (preban). Although the preban flight attendants had normal FVC, FEV1, and FEV1/FVC ratio, they had significantly decreased flow at mid- and low-lung volumes, curvilinear flow-volume curves, and evidence of air trapping. Furthermore, the flight attendants had significantly decreased diffusing capacity (77.5% +/- 11.2% predicted normal) with 51% having a diffusing capacity below their 95% normal prediction limit. This cohort of healthy never-smoking flight attendants who were exposed to secondhand tobacco smoke in the aircraft cabin showed pulmonary function abnormalities suggestive of airway obstruction and impaired diffusion.

Corneal critical barrier against the penetration of dexamethasone and lomefloxacin hydrochloride: evaluation by the activation energy for drug partition and diffusion in cornea.

PubMed

Yasueda, Shin-ichi; Higashiyama, Masayo; Yamaguchi, Masazumi; Isowaki, Akiharu; Ohtori, Akira

2007-08-01

The cornea is a solid barrier against drug permeation. We searched the critical barrier of corneal drug permeation using a hydrophobic drug, dexamethasone (DM), and a hydrophilic drug, lomefloxacin hydrochloride (LFLX). The activation energies for permeability of DM and LFLX across the intact cornea were 88.0 and 42.1 kJ/mol, respectively. Their activation energies for permeability across the cornea without epithelium decreased to 33.1 and 16.6 kJ/mol, respectively. The results show that epithelium is the critical barrier on the cornea against the permeation of a hydrophobic drug of DM as well as a hydrophilic drug of LFLX. The activation energy of partition for DM (66.8 kJ/mol) was approximately 3-fold larger than that of diffusion (21.2 kJ/mol). The results indicate that the partition for the hydrophobic drug of DM to the corneal epithelium is the primary barrier. Thermodynamic evaluation of activation energy for the drug permeation parameters is a good approach to investigate the mechanism of drug permeability.

Predicting First Traversal Times for Virions and Nanoparticles in Mucus with Slowed Diffusion

PubMed Central

Erickson, Austen M.; Henry, Bruce I.; Murray, John M.; Klasse, Per Johan; Angstmann, Christopher N.

2015-01-01

Particle-tracking experiments focusing on virions or nanoparticles in mucus have measured mean-square displacements and reported diffusion coefficients that are orders of magnitude smaller than the diffusion coefficients of such particles in water. Accurate description of this subdiffusion is important to properly estimate the likelihood of virions traversing the mucus boundary layer and infecting cells in the epithelium. However, there are several candidate models for diffusion that can fit experimental measurements of mean-square displacements. We show that these models yield very different estimates for the time taken for subdiffusive virions to traverse through a mucus layer. We explain why fits of subdiffusive mean-square displacements to standard diffusion models may be misleading. Relevant to human immunodeficiency virus infection, using computational methods for fractional subdiffusion, we show that subdiffusion in normal acidic mucus provides a more effective barrier against infection than previously thought. By contrast, the neutralization of the mucus by alkaline semen, after sexual intercourse, allows virions to cross the mucus layer and reach the epithelium in a short timeframe. The computed barrier protection from fractional subdiffusion is some orders of magnitude greater than that derived by fitting standard models of diffusion to subdiffusive data. PMID:26153713

Bicarbonate diffusion through mucus.

PubMed

Livingston, E H; Miller, J; Engel, E

1995-09-01

The mucus layer overlying duodenal epithelium maintains a pH gradient against high luminal acid concentrations. Despite these adverse conditions, epithelial surface pH remains close to neutrality. The exact nature of the gradient-forming barrier remains unknown. The barrier consists of mucus into which HCO3- is secreted. Quantification of the ability of HCO3- to establish and maintain the gradient depends on accurate measurement of this ion's diffusion coefficient through mucus. We describe new experimental and mathematical methods for diffusion measurement and report diffusion coefficients for HCO3- diffusion through saline, 5% mucin solutions, and rat duodenal mucus. The diffusion coefficients were 20.2 +/- 0.10, 3.02 +/- 0.31, and 1.81 +/- 0.12 x 10(-6) cm2/s, respectively. Modeling of the mucobicarbonate layer with this latter value suggests that for conditions of high luminal acid strength the neutralization of acid by HCO3- occurs just above the epithelial surface. Under these conditions the model predicts that fluid convection toward the lumen could be important in maintaining the pH gradient. In support of this hypothesis we were able to demonstrate a net luminal fluid flux of 5 microliters.min-1.cm-2 after perfusion of 0.15 N HCl in the rat duodenum.

Quantitative SIMS depth profiling of diffusion barrier gate-oxynitride structures in TFT-LCDs.

PubMed

Dreer, Sabine; Wilhartitz, Peter; Piplits, Kurt; Mayerhofer, Karl; Foisner, Johann; Hutter, Herbert

2004-06-01

Gate oxynitride structures of TFT-LCDs were investigated by SIMS, and successful solutions are demonstrated to overcome difficulties arising due to the charging effects of the multilayer systems, the matrix effect of the method, and the small pattern sizes of the samples. Because of the excellent reproducibility achieved by applying exponential relative sensitivity functions for quantitative analysis, minor differences in the barrier gate-oxynitride composition deposited on molybdenum capped aluminium-neodymium metallisation electrodes were determined between the centre and the edge of the TFT-LCD substrates. No differences were found for molybdenum-tungsten metallisations. Furthermore, at the edge of the glass substrates, aluminium, neodymium, and molybdenum SIMS depth profiles show an exponential trend. With TEM micrographs an inhomogeneous thickness of the molybdenum capping is revealed as the source of this effect, which influences the electrical behaviour of the device. The production process was improved after these results and the aging behaviour of TFT-LCDs was investigated in order to explain the change in control voltage occurring during the lifetime of the displays. SIMS and TEM show an enrichment of neodymium at the interface to the molybdenum layer, confirming good diffusion protection of the molybdenum barrier during accelerated aging. The reason for the shift of the control voltage was finally located by semi-quantitative depth profiling of the sodium diffusion originating from the glass substrate. Molybdenum-tungsten was a much better buffer for the highly-mobile charge carriers than aluminium-neodymium. Best results were achieved with PVD silicon oxynitride as diffusion barrier and gate insulator deposited on aluminium-neodymium metallisation layers.

Advanced study of thermal behaviour of CSZ comparing with the classic YSZ coating

NASA Astrophysics Data System (ADS)

Dragomirescu, A.; Constantin, N.; Ştefan, A.; Manoliu, V.; Truşcă, R.

2017-01-01

Thermal barrier coatings (TBC) are advanced materials typically applied to metal surfaces subjected to extreme temperatures to protect them and increase their lifetime. Ceria stabilized zirconia ceramic layer (CSZ) is increasingly used as an alternative improved as replace for classical TBC system - yttria stabilized zirconia - thanks to superior properties, including mechanical and high resistance to thermal corrosion. The paper describes the thermal shock testing of two types of thermal barrier coatings used to protect a nickel super alloy. For the experimental procedure, it was used plate samples from nickel super alloy with a bond coat and a ceramic top coat. The top coat was different: on some samples, it was used YSZ and on others CSZ. Ni based super alloys have good corrosion resistance in reducing environments action, but poor in oxidizing conditions. Extreme environments can lead to loss of material by oxidation / corrosion, along with decreased mechanical properties of the substrate due to damaging elements which diffuses into the substrate at high temperatures. Using laboratory equipment, the TBC systems were exposed repeatedly to extreme high temperatures for a short time and then cooled. After the thermal shock tests, the samples were morph-structured characterized using electronic microscopy to analyze the changes. The experimental results were compared to rank the TBC systems in order of performance.

Impact of eliminating fracture intersection nodes in multiphase compositional flow simulation

NASA Astrophysics Data System (ADS)

Walton, Kenneth M.; Unger, Andre J. A.; Ioannidis, Marios A.; Parker, Beth L.

2017-04-01

Algebraic elimination of nodes at discrete fracture intersections via the star-delta technique has proven to be a valuable tool for making multiphase numerical simulations more tractable and efficient. This study examines the assumptions of the star-delta technique and exposes its effects in a 3-D, multiphase context for advective and dispersive/diffusive fluxes. Key issues of relative permeability-saturation-capillary pressure (kr-S-Pc) and capillary barriers at fracture-fracture intersections are discussed. This study uses a multiphase compositional, finite difference numerical model in discrete fracture network (DFN) and discrete fracture-matrix (DFM) modes. It verifies that the numerical model replicates analytical solutions and performs adequately in convergence exercises (conservative and decaying tracer, one and two-phase flow, DFM and DFN domains). The study culminates in simulations of a two-phase laboratory experiment in which a fluid invades a simple fracture intersection. The experiment and simulations evoke different invading fluid flow paths by varying fracture apertures as oil invades water-filled fractures and as water invades air-filled fractures. Results indicate that the node elimination technique as implemented in numerical model correctly reproduces the long-term flow path of the invading fluid, but that short-term temporal effects of the capillary traps and barriers arising from the intersection node are lost.

Pediatric respiratory and systemic effects of chronic air pollution exposure: nose, lung, heart, and brain pathology.

PubMed

Calderón-Garcidueñas, Lilian; Franco-Lira, Maricela; Torres-Jardón, Ricardo; Henriquez-Roldán, Carlos; Barragán-Mejía, Gerardo; Valencia-Salazar, Gildardo; González-Maciel, Angelica; Reynoso-Robles, Rafael; Villarreal-Calderón, Rafael; Reed, William

2007-01-01

Exposures to particulate matter and gaseous air pollutants have been associated with respiratory tract inflammation, disruption of the nasal respiratory and olfactory barriers, systemic inflammation, production of mediators of inflammation capable of reaching the brain and systemic circulation of particulate matter. Mexico City (MC) residents are exposed to significant amounts of ozone, particulate matter and associated lipopolysaccharides. MC dogs exhibit brain inflammation and an acceleration of Alzheimer's-like pathology, suggesting that the brain is adversely affected by air pollutants. MC children, adolescents and adults have a significant upregulation of cyclooxygenase-2 (COX2) and interleukin-1beta (IL-1beta) in olfactory bulb and frontal cortex, as well as neuronal and astrocytic accumulation of the 42 amino acid form of beta -amyloid peptide (Abeta 42), including diffuse amyloid plaques in frontal cortex. The pathogenesis of Alzheimer's disease (AD) is characterized by brain inflammation and the accumulation of Abeta 42, which precede the appearance of neuritic plaques and neurofibrillary tangles, the pathological hallmarks of AD. Our findings of nasal barrier disruption, systemic inflammation, and the upregulation of COX2 and IL-1beta expression and Abeta 42 accumulation in brain suggests that sustained exposures to significant concentrations of air pollutants such as particulate matter could be a risk factor for AD and other neurodegenerative diseases.

Evaluation of evaporation coefficient for micro-droplets exposed to low pressure: A semi-analytical approach

NASA Astrophysics Data System (ADS)

Chakraborty, Prodyut R.; Hiremath, Kirankumar R.; Sharma, Manvendra

2017-02-01

Evaporation rate of water is strongly influenced by energy barrier due to molecular collision and heat transfer limitations. The evaporation coefficient, defined as the ratio of experimentally measured evaporation rate to that maximum possible theoretical limit, varies over a conflicting three orders of magnitude. In the present work, a semi-analytical transient heat diffusion model of droplet evaporation is developed considering the effect of change in droplet size due to evaporation from its surface, when the droplet is injected into vacuum. Negligible effect of droplet size reduction due to evaporation on cooling rate is found to be true. However, the evaporation coefficient is found to approach theoretical limit of unity, when the droplet radius is less than that of mean free path of vapor molecules on droplet surface contrary to the reported theoretical predictions. Evaporation coefficient was found to reduce rapidly when the droplet under consideration has a radius larger than the mean free path of evaporating molecules, confirming the molecular collision barrier to evaporation rate. The trend of change in evaporation coefficient with increasing droplet size predicted by the proposed model will facilitate obtaining functional relation of evaporation coefficient with droplet size, and can be used for benchmarking the interaction between multiple droplets during evaporation in vacuum.

Strategies of dissolved inorganic carbon use in macroalgae across a gradient of terrestrial influence: implications for the Great Barrier Reef in the context of ocean acidification

NASA Astrophysics Data System (ADS)

Diaz-Pulido, Guillermo; Cornwall, Christopher; Gartrell, Patrick; Hurd, Catriona; Tran, Dien V.

2016-12-01

Macroalgae are generally used as indicators of coral reef status; thus, understanding the drivers and mechanisms leading to increased macroalgal abundance are of critical importance. Ocean acidification (OA) due to elevated carbon dioxide (CO2) concentrations has been suggested to stimulate macroalgal growth and abundance on reefs. However, little is known about the physiological mechanisms by which reef macroalgae use CO2 from the bulk seawater for photosynthesis [i.e., (1) direct uptake of bicarbonate (HCO3 -) and/or CO2 by means of carbon concentrating mechanisms (CCM) and (2) the diffusive uptake of CO2], which species could benefit from increased CO2 or which habitats may be more susceptible to acidification-induced algal proliferations. Here, we provide the first quantitative examination of CO2-use strategies in coral reef macroalgae and provide information on how the proportion of species and the proportional abundance of species utilising each of the carbon acquisition strategies varies across a gradient of terrestrial influence (from inshore to offshore reefs) in the Great Barrier Reef (GBR). Four macroalgal groups were identified based on their carbon uptake strategies: (1) CCM-only (HCO3 - only users); (2) CCM-HCO3 -/CO2 (active uptake HCO3 - and/or CO2 use); (3) Non-CCM species (those relying on diffusive CO2 uptake); and (4) Calcifiers. δ13C values of macroalgae, confirmed by pH drift assays, show that diffusive CO2 use is more prevalent in deeper waters, possibly due to low light availability that limits activity of CCMs. Inshore shallow reefs had a higher proportion of CCM-only species, while reefs further away from terrestrial influence and exposed to better water quality had a higher number of non-CCM species than inshore and mid-shelf reefs. As non-CCM macroalgae are more responsive to increased seawater CO2 and OA, reef slopes of the outer reefs are probably the habitats most vulnerable to the impacts of OA. Our results suggest a potentially important role of carbon physiology in structuring macroalgal communities in the GBR.

Density functional theory study of lithium diffusion at the interface between olivine-type LiFePO4 and LiMnPO4

NASA Astrophysics Data System (ADS)

Shi, Jianjian; Wang, Zhiguo; Qing Fu, Yong

2016-12-01

Coating LiMnPO4 with a thin layer of LiFePO4 shows a better electrochemical performance than the pure LiFePO4 and LiMnPO4, thus it is critical to understand Li diffusion at their interfaces to improve the performance of electrode materials. Li diffusion at the (1 0 0)\\text{LiFeP{{\\text{O}}4}} //(1 0 0)\\text{LiMnP{{\\text{O}}4}} , (0 1 0)\\text{LiFeP{{\\text{O}}4}} //(0 1 0)\\text{LiMnP{{\\text{O}}4}} , and (0 0 1)\\text{LiFeP{{\\text{O}}4}} //(0 0 1)\\text{LiMnP{{\\text{O}}4}} interfaces between LiFePO4 and LiMnPO4 was investigated using density functional theory. The calculated diffusion energy barriers are 0.55 eV for Li to diffuse along the (0 0 1) interface, 0.44 and 0.49 eV for the Li diffusion inside the LiMnPO4 and along the (1 0 0) interface, respectively. When Li diffuses from the LiFePO4 to LiMnPO4 by passing through the (0 1 0) interfaces, the diffusion barriers are 0.45 and 0.60 eV for the Li diffusions in both sides. The diffusion barriers for Li to diffuse in LiMnPO4 near the interfaces decrease compared with those in the pure LiMnPO4. The calculated diffusion coefficient of Li along the (1 0 0) interface is in the range of 3.65  ×  10-11-5.28  ×  10-12 cm2 s-1, which is larger than that in the pure LiMnPO4 with a value of 7.5  ×  10-14 cm2 s-1. Therefore, the charging/discharging rate performance of the LiMnPO4 can be improved by surface coating with the LiFePO4.

Silicon based substrate with calcium aluminosilicate environmental/thermal barrier layer

NASA Technical Reports Server (NTRS)

Eaton, Jr., Harry Edwin (Inventor); Allen, William Patrick (Inventor); Miller, Robert Alden (Inventor); Jacobson, Nathan S. (Inventor); Smialek, James L. (Inventor); Opila, Elizabeth J. (Inventor); Lee, Kang N. (Inventor); Nagaraj, Bangalore A. (Inventor); Wang, Hongyu (Inventor); Meschter, Peter Joel (Inventor)

2001-01-01

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a calcium alumino silicate.

Barriers to front propagation in laminar, three-dimensional fluid flows

NASA Astrophysics Data System (ADS)

Doan, Minh; Simons, J. J.; Lilienthal, Katherine; Solomon, Tom; Mitchell, Kevin A.

2018-03-01

We present experiments on one-way barriers that block reaction fronts in a fully three-dimensional (3D) fluid flow. Fluorescent Belousov-Zhabotinsky reaction fronts are imaged with laser-scanning in a laminar, overlapping vortex flow. The barriers are analyzed with a 3D extension to burning invariant manifold (BIM) theory that was previously applied to two-dimensional advection-reaction-diffusion processes. We discover tube and sheet barriers that guide the front evolution. The experimentally determined barriers are explained by BIMs calculated from a model of the flow.

Stuffed MO layer as a diffusion barrier in metallizations for high temperature electronics

NASA Technical Reports Server (NTRS)

Boah, J. K.; Russell, V.; Smith, D. P.

1981-01-01

Auger electron spectroscopy was employed to characterize the diffusion barrier properties of molybdenum in the CrSi2/Mo/Au metallization system. The barrier action of Mo was demonstrated to persist even after 2000 hours annealing time at 300 C in a nitrogen ambient. At 340 C annealing temperature, however, rapid interdiffusion was observed to have occurred between the various metal layers after only 261 hours. The presence of controlled amounts of oxygen in the Mo layer is believed to be responsible for suppressing the short circuit interdiffusion between the thin film layers. Above 340 C, its is believed that the increase in the oxygen mobility led to deterioration of its stuffing action, resulting in the rapid interdiffusion of the thin film layers along grain boundaries.

Measuring the continuity of diffusion barriers on porous films using γ-ray energy spectra of escaping positronium

NASA Astrophysics Data System (ADS)

Xu, Jun; Mills, Allen P.; Case, Carlye

2005-08-01

Diffusion barriers for capping porous low dielectric constant films are important for preventing metal migration into a semiconductor circuit. Using the fact that positrons implanted into a porous dielectric form ortho-positronium (o-Ps) copiously, Gidley et al. [D. W. Gidley, W. F. Frieze, T. L. Dull, J. Sun, A. F. Yee, C. V. Nguyen, and D. Y. Yoon, Appl. Phys. Lett. 76, 1282 (2000)], have been able to measure open area fractions as low as 10-5 in porous dielectric film barrier layers from the increase in the ortho-positronium lifetime and intensity associated with positronium escape into vacuum. We demonstrate that it is possible to obtain comparable sensitivities by measuring the gamma-ray energy spectrum of the escaping positronium.

Fractional Brownian motion with a reflecting wall

NASA Astrophysics Data System (ADS)

Wada, Alexander H. O.; Vojta, Thomas

2018-02-01

Fractional Brownian motion, a stochastic process with long-time correlations between its increments, is a prototypical model for anomalous diffusion. We analyze fractional Brownian motion in the presence of a reflecting wall by means of Monte Carlo simulations. Whereas the mean-square displacement of the particle shows the expected anomalous diffusion behavior ˜tα , the interplay between the geometric confinement and the long-time memory leads to a highly non-Gaussian probability density function with a power-law singularity at the barrier. In the superdiffusive case α >1 , the particles accumulate at the barrier leading to a divergence of the probability density. For subdiffusion α <1 , in contrast, the probability density is depleted close to the barrier. We discuss implications of these findings, in particular, for applications that are dominated by rare events.

Electrostatic Estimation of Intercalant Jump-Diffusion Barriers Using Finite-Size Ion Models.

PubMed

Zimmermann, Nils E R; Hannah, Daniel C; Rong, Ziqin; Liu, Miao; Ceder, Gerbrand; Haranczyk, Maciej; Persson, Kristin A

2018-02-01

We report on a scheme for estimating intercalant jump-diffusion barriers that are typically obtained from demanding density functional theory-nudged elastic band calculations. The key idea is to relax a chain of states in the field of the electrostatic potential that is averaged over a spherical volume using different finite-size ion models. For magnesium migrating in typical intercalation materials such as transition-metal oxides, we find that the optimal model is a relatively large shell. This data-driven result parallels typical assumptions made in models based on Onsager's reaction field theory to quantitatively estimate electrostatic solvent effects. Because of its efficiency, our potential of electrostatics-finite ion size (PfEFIS) barrier estimation scheme will enable rapid identification of materials with good ionic mobility.

Nonlocal transport in the presence of transport barriers

NASA Astrophysics Data System (ADS)

Del-Castillo-Negrete, D.

2013-10-01

There is experimental, numerical, and theoretical evidence that transport in plasmas can, under certain circumstances, depart from the standard local, diffusive description. Examples include fast pulse propagation phenomena in perturbative experiments, non-diffusive scaling in L-mode plasmas, and non-Gaussian statistics of fluctuations. From the theoretical perspective, non-diffusive transport descriptions follow from the relaxation of the restrictive assumptions (locality, scale separation, and Gaussian/Markovian statistics) at the foundation of diffusive models. We discuss an alternative class of models able to capture some of the observed non-diffusive transport phenomenology. The models are based on a class of nonlocal, integro-differential operators that provide a unifying framework to describe non- Fickian scale-free transport, and non-Markovian (memory) effects. We study the interplay between nonlocality and internal transport barriers (ITBs) in perturbative transport including cold edge pulses and power modulation. Of particular interest in the nonlocal ``tunnelling'' of perturbations through ITBs. Also, flux-gradient diagrams are discussed as diagnostics to detect nonlocal transport processes in numerical simulations and experiments. Work supported by the US Department of Energy.

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.

Hydrogen-permeable composite metal membrane and uses thereof

DOEpatents

Edlund, D.J.; Friesen, D.T.

1993-06-08

Various hydrogen production and hydrogen sulfide decomposition processes are disclosed that utilize composite metal membranes that contain an intermetallic diffusion barrier separating a hydrogen-permeable base metal and a hydrogen-permeable coating metal. The barrier is a thermally stable inorganic proton conductor.

Fibrous gypsum veins as diffuse features and within fault zones: the case study of the Pisco Basin (Ica desert, southern Peru)

NASA Astrophysics Data System (ADS)

Rustichelli, Andrea; Di Celma, Claudio; Tondi, Emanuele; Baud, Patrick; Vinciguerra, Sergio

2016-04-01

New knowledge on patterns of fibrous gypsum veins, their genetic mechanisms, deformation style and weathering are provided by a field- and laboratory-based study carried out on the Neogene to Quaternary Pisco Basin sedimentary strata (porous sandstones, siltstones and diatomites) exposed in the Ica desert, southern Peru. Gypsum veins vary considerably in dimensions, attitudes and timing and can develop in layered and moderately fractured rocks also in the absence of evaporitic layers. Veins occur both as diffuse features, confined to certain stratigraphic levels, and localised within fault zones. Arrays formed by layer-bounded, mutually orthogonal sets of steeply-dipping gypsum veins are reported for the first time. Vein length, height and spacing depend on the thickness of the bed packages in which they are confined. Within fault zones, veins are partly a product of faulting but also inherited layer-bounded features along which faults are superimposed. Due to the different petrophysical properties with respect to the parent rocks and their susceptibility to textural and mineralogical modifications, water dissolution and rupture, gypsum veins may have a significant role in geofluid management. Depending on their patterns and grade of physical and chemical alteration, veins may influence geofluid circulation and storage, acting as barriers to flow and possibly also as conduits.

Submonolayer Ag films on Fe(100): A first-principles analysis of energetics controlling adlayer thermodynamics and kinetics

DOE PAGES

Li, Wei; Huang, Li; Evans, James W.; ...

2016-04-11

Epitaxial growth of Ag on Fe(100) and postdeposition relaxation have been studied in several experiments. We provide a first-principles density functional theory analysis of key adatom interaction energies and diffusion barriers controlling growth and relaxation kinetics for the submonolayer regime, as these have not been assessed previously. A cluster expansion approach is used to obtain an extensive set of conventional lateral interactions between adatoms on fourfold hollow adsorption sites. We find robust oscillatory decay of pair interactions with increasing separation, and of trio interactions with increasing perimeter length. First- and second-nearest-neighbor pair interactions, as well as compact linear and bentmore » trio interactions, dominate. The adatom terrace diffusion barrier is estimated to be E d ≈ 0.39 eV. We also provide a limited analysis of unconventional interactions for which one adatom is at the bridge-site transition state for hopping and one or more others are at fourfold hollow sites. Furthermore, energy barriers for diffusion along island edges can be determined with the aid of both conventional and unconventional interactions.« less

Fabrication of fine-grain tantalum diffusion barrier tube for Nb3Sn conductors

NASA Astrophysics Data System (ADS)

Hartwig, K. T.; Balachandran, S.; Mezyenski, R.; Seymour, N.; Robinson, J.; Barber, R. E.

2014-01-01

Diffusion barriers used in Nb3Sn wire are often fabricated by wrapping Ta sheet into a tube with an overlap seam. A common result of such practice is non-uniform deformation in the Ta sheet as it thins by wire drawing because of non-uniform grain size and texture in the original Ta sheet. Seamless Ta tube with a fine-grain and uniform microstructure would be much better for the diffusion barrier application, but such material is expensive and difficult to manufacture. This report presents results on a new fabrication strategy for Ta tube that shows promise for manufacture of less costly tube with an improved microstructure. The fabrication method begins with seam-welded tube but gives a fine-grain uniform microstructure with little difference between the longitudinal seam weld region and the parent metal after post-weld processing. Severe plastic deformation processing (SPD) applied by area reduction extrusion and tube equal channel angular extrusion (tECAE) are used to refine and homogenize the microstructure. Microstructure and mechanical property results are presented for Ta tubes fabricated by this new processing strategy.

Integration of perovskite oxide dielectrics into complementary metal-oxide-semiconductor capacitor structures using amorphous TaSiN as oxygen diffusion barrier

NASA Astrophysics Data System (ADS)

Mešić, Biljana; Schroeder, Herbert

2011-09-01

The high permittivity perovskite oxides have been intensively investigated for their possible application as dielectric materials for stacked capacitors in dynamic random access memory circuits. For the integration of such oxide materials into the CMOS world, a conductive diffusion barrier is indispensable. An optimized stack p++-Si/Pt/Ta21Si57N21/Ir was developed and used as the bottom electrode for the oxide dielectric. The amorphous TaSiN film as oxygen diffusion barrier showed excellent conductive properties and a good thermal stability up to 700 °C in oxygen ambient. The additional protective iridium layer improved the surface roughness after annealing. A 100-nm-thick (Ba,Sr)TiO3 film was deposited using pulsed laser deposition at 550 °C, showing very promising properties for application; the maximum relative dielectric constant at zero field is κ ≈ 470, and the leakage current density is below 10-6 A/cm2 for fields lower then ± 200 kV/cm, corresponding to an applied voltage of ± 2 V.

Ab initio calculation of diffusion barriers for Cu adatom hopping on Cu(1 0 0) surface and evolution of atomic configurations

NASA Astrophysics Data System (ADS)

Zhang, Wei; Gan, Jie; Li, Qian; Gao, Kun; Sun, Jian; Xu, Ning; Ying, Zhifeng; Wu, Jiada

2011-06-01

The self-diffusion dynamics of Cu adatoms on Cu(1 0 0) surface has been studied based on the calculation of the energy barriers for various hopping events using lattice-gas based approach and a modified model. To simplify the description of the interactions and the calculation of the energy barrier, a three-tier hierarchy of description of atomic configurations was conceived in which the active adatom and its nearest atoms were chosen to constitute basic configuration and taken as a whole to study many-body interactions of the atoms in various atomic configurations, whereas the impacts of the next nearest atoms on the diffusion of the active adatom were considered as multi-site interactions. Besides the simple hopping of single adatoms, the movements of dimers and trimers as the results of multiple hopping events have also been examined. Taking into account the hopping events of all adatoms, the stability of atomic configurations has been examined and the evolution of atomic configurations has also been analyzed.

Performance of two differently designed permeable reactive barriers with sulfate and zinc solutions.

PubMed

Pérez, Norma; Schwarz, Alex O; Barahona, Esteban; Sanhueza, Pamela; Diaz, Isabel; Urrutia, Homero

2018-06-18

For the first time, this laboratory-scale study evaluates the feasibility of incorporating diffusive exchange in permeable reactive barriers. In order to do this, the performance of two permeable reactive barriers (PRB) with different internal substrate arrangements were compared during the administration of a sulfate solution without metals (for 163 days) and with metals (for 60 days), simulating groundwater contaminated with acid mine drainage (AMD). In order to simulate a traditional PRB, a homogeneous distribution was implemented in the first reactor and the other PRB reactor utilized diffusion-active technology (DAPRB). In the DAPRB, the distribution of the reactive material was interspersed with the conductive material. The measurements in the internal ports showed that transverse gradients of sulfide formed in the DAPRB, causing the diffusion of sulfide from the substrate toward the layer interface, which is where the sulfide reacts by forming complexes with the metal. The DAPRB prevents the microorganisms from direct contact with AMD. This protection caused greater activity (sulfide production). Copyright © 2018 Elsevier B.V. All rights reserved.

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.

Retention and diffusion of H, He, O, C impurities in Be

NASA Astrophysics Data System (ADS)

Zhang, Pengbo; Zhao, Jijun; Wen, Bin

2012-04-01

We report the energetics and diffusion behavior of H, He, O, and C impurities in beryllium as fusion materials from first-principles calculations. Among the six interstitial sites in Be, the basal tetrahedral one is most stable for H, He, O, while C prefers to occupy an octahedral site. Solution of O impurity in Be is an exothermic process with solution energy of -2.37 eV, whereas solution of H, C and He is an endothermic process (solution energy: 1.55 eV, 2.46 eV, and 5.70 eV, respectively). Overall speaking, these impurities prefer to diffuse along longer paths. The H and O impurities share the same out-of-plane diffusion path via basal tetrahedral sites, while the He and C impurities in Be mainly diffuse via basal tetrahedral and octahedral sites along the (0 0 1) plane. Diffusion of He in Be is easiest with a lowest barrier of 0.14 eV; whereas H diffusion in Be is also rather fast with migration energies of 0.4 eV. On the contrary, diffusion of C and O impurities is more difficult because of strong bonding with lattice atoms and high energy barriers of 0.42 and 1.63 eV, respectively. Our theoretical results provide the fundamental parameters for understanding the impurity aggregation and bubble formation in early stage of irradiation damage.

High-throughput ab-initio dilute solute diffusion database

PubMed Central

Wu, Henry; Mayeshiba, Tam; Morgan, Dane

2016-01-01

We demonstrate automated generation of diffusion databases from high-throughput density functional theory (DFT) calculations. A total of more than 230 dilute solute diffusion systems in Mg, Al, Cu, Ni, Pd, and Pt host lattices have been determined using multi-frequency diffusion models. We apply a correction method for solute diffusion in alloys using experimental and simulated values of host self-diffusivity. We find good agreement with experimental solute diffusion data, obtaining a weighted activation barrier RMS error of 0.176 eV when excluding magnetic solutes in non-magnetic alloys. The compiled database is the largest collection of consistently calculated ab-initio solute diffusion data in the world. PMID:27434308

Real-time ab initio KMC simulation of the self-assembly and sintering of bimetallic epitaxial nanoclusters: Au + Ag on Ag(100).

PubMed

Han, Yong; Liu, Da-Jiang; Evans, James W

2014-08-13

Far-from-equilibrium shape and structure evolution during formation and post-assembly sintering of bimetallic nanoclusters is extremely sensitive to the periphery diffusion and intermixing kinetics. Precise characterization of the many distinct local-environment-dependent diffusion barriers is achieved for epitaxial nanoclusters using density functional theory to assess interaction energies both with atoms at adsorption sites and at transition states. Kinetic Monte Carlo simulation incorporating these barriers then captures structure evolution on the appropriate time scale for two-dimensional core-ring and intermixed Au-Ag nanoclusters on Ag(100).

Real-Time Ab Initio KMC Simulation of the Self-Assembly and Sintering of Bimetallic Epitaxial Nanoclusters: Au + Ag on Ag(100)

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

Han, Yong; Liu, Da-Jiang; Evans, James W

2014-08-13

Far-from-equilibrium shape and structure evolution during formation and post-assembly sintering of bimetallic nanoclusters is extremely sensitive to the periphery diffusion and intermixing kinetics. Precise characterization of the many distinct local-environment-dependent diffusion barriers is achieved for epitaxial nanoclusters using density functional theory to assess interaction energies both with atoms at adsorption sites and at transition states. Kinetic Monte Carlo simulation incorporating these barriers then captures structure evolution on the appropriate time scale for two-dimensional core-ring and intermixed Au-Ag nanoclusters on Ag(100).

Surface-structure dependence of healing radiation-damage mechanism in nanoporous tungsten

NASA Astrophysics Data System (ADS)

Duan, Guohua; Li, Xiangyan; Sun, Jingjing; Hao, Congyu; Xu, Yichun; Zhang, Yange; Liu, Wei; Liu, C. S.

2018-01-01

Under nuclear fusion environments, displacement damage in tungsten (W) is usually caused by neutrons irradiation through producing large quantities of vacancies (Vs) and self-interstitial atoms (SIAs). These defects not only affect the mechanical properties of W, but also act as the trap sites for implanted hydrogen isotopes and helium. Nano-porous (NP) W with a high fraction of free surfaces has been developed to mitigate the radiation damage. However, the mechanism of the surface reducing defects accumulation is not well understood. By using multi-scale simulation methods, we investigated the interaction of the SIA and V with different surfaces on across length and time scales. We found that, at a typical operation temperature of 1000 K, surface (1 1 0) preferentially heals radiation damage of W compared with surface (1 0 0) and boundary (3 1 0). On surface (1 1 0), the diffusion barrier for the SIA is only 0.68 eV. The annihilation of the SIA-V happens via the coupled motion of the V segregation towards the surface from the bulk and the two-dimensional diffusion of the SIA on the surface. Such mechanism makes the surface (1 1 0) owe better healing capability. On surface (1 0 0), the diffusion energy barrier for the SIA is 2.48 eV, higher than the diffusion energy barrier of the V in bulk. The annihilation of the SIA-V occurs via the V segregation and recombination. The SIA was found to migrate one-dimensionally along a boundary (3 1 0) with a barrier of 0.21 eV, leading to a lower healing efficiency in the boundary. This study suggested that the on-surface process plays an important role in healing radiation damage of NP W in addition to surface-enhanced diffusion and annihilation near the surface. A certain surface structure renders nano-structured W more radiation-tolerant.

Effects of epitaxial structure and processing on electrical characteristics of InAs-based nBn infrared detectors

NASA Astrophysics Data System (ADS)

Du, X.; Savich, G. R.; Marozas, B. T.; Wicks, G. W.

2017-02-01

The conventional processing of the III-V nBn photodetectors defines mesa devices by etching the contact n-layer and stopping immediately above the barrier, i.e., a shallow etch. This processing enables great suppression of surface leakage currents without having to explore surface passivation techniques. However, devices that are made with this processing scheme are subject to lateral diffusion currents. To address the lateral diffusion current, we compare the effects of different processing approaches and epitaxial structures of nBn detectors. The conventional solution for eliminating lateral diffusion current, a deep etch through the barrier and the absorber, creates increased dark currents and an increased device failure rate. To avoid deep etch processing, a new device structure is proposed, the inverted-nBn structure. By comparing with the conventional nBn structure, the results show that the lateral diffusion current is effectively eliminated in the inverted-nBn structure without elevating the dark currents.

An in vitro assay for entry into cilia reveals unique properties of the soluble diffusion barrier

PubMed Central

Breslow, David K.; Koslover, Elena F.; Seydel, Federica; Spakowitz, Andrew J.

2013-01-01

Specific proteins are concentrated within primary cilia, whereas others remain excluded. To understand the mechanistic basis of entry into cilia, we developed an in vitro assay using cells in which the plasma membrane was permeabilized, but the ciliary membrane was left intact. Using a diffusion-to-capture system and quantitative analysis, we find that proteins >9 nm in diameter (∼100 kD) are restricted from entering cilia, and we confirm these findings in vivo. Interference with the nuclear pore complex (NPC) or the actin cytoskeleton in permeabilized cells demonstrated that the ciliary diffusion barrier is mechanistically distinct from those of the NPC or the axon initial segment. Moreover, applying a mass transport model to this system revealed diffusion coefficients for soluble and membrane proteins within cilia that are compatible with rapid exploration of the ciliary space in the absence of active transport. Our results indicate that large proteins require active transport for entry into cilia but not necessarily for movement inside cilia. PMID:24100294

Inter-diffusion analysis of joint interface of tungsten-rhenium couple

NASA Astrophysics Data System (ADS)

Hua, Y. F.; Li, Z. X.; Zhang, X.; Du, J. H.; Huang, C. L.; Du, M. H.

2011-09-01

The tungsten-rhenium couple was prepared by using glow plasma physical vapor deposition (PVD) on the isotropic fine grained graphite (IG) substrates. Diffusion anneals of the tungsten-rhenium couple were conducted at the temperature from 1100 °C to 1400 °C to investigate the inter-diffusion behaviors. The results showed that the thickness of the inter-diffusion zone increased with increasing annealing temperature. The relationship between the inter-diffusion coefficient and the annealing temperature accorded with the Arrhenius manner. The value of inter-diffusion activation energies was 189 kJ/mole (1.96 eV). The service time of tungsten-rhenium multilayer diffusion barrier was limited by the inter-diffusion for rhenium and tungsten rather than the diffusion of carbon in rhenium.

Preoperative care of Polypoid exposed mucosal template in bladder exstrophy: the role of high-barrier plastic wraps in reducing inflammation and polyp size.

PubMed

Sabetkish, Nastaran; Sabetkish, Shabnam; Kajbafzadeh, Abdol-Mohammad

2018-01-26

To assess the role of high-barrier plastic wrap in reducing the number and size of polyps, as well as decreasing the inflammation and allergic reactions in exstrophy cases, and to compare the results with the application of low-barrier wrap. Eight patients with bladder exstrophy-epispadias complex (BEEC) that had used a low density polyethylene (LDPE) wrap for coverage of the exposed polypoid bladder in preoperative care management were referred. The main complaint of their parents was increase in size and number of polyps. After a period of 2 months using the same wrap and observing the increasing pattern in size of polyps, these patients were recommended to use a high-barrier wrap which is made of polyvinylidene chloride (PVdC), until closure. Patients were monitored for the number and size of polyps before and after the change of barriers. The incidence of para-exstrophy skin infection/inflammation and skin allergy were assessed. Biopsies were taken from the polyps to identify histopathological characteristics of the exposed polyps. The high barrier wrap was applied for a mean ± SD duration of 12±2.1 months. Polyps' size and number decreased after 12 months. No allergic reaction was detected in patients after the usage of PVdC; three patients suffered from low-grade skin allergy when LDPE was applied. Also, pre-malignant changes were observed in none of the patients in histopathological examination after the application of PVdC. Polyps' size and number and skin allergy may significantly decrease with the use of a high-barrier wrap. Certain PVdC wraps with more integrity and less evaporative permeability may be more "exstrophy-friendly". Copyright® by the International Brazilian Journal of Urology.

Fractional Brownian motion with a reflecting wall.

PubMed

Wada, Alexander H O; Vojta, Thomas

2018-02-01

Fractional Brownian motion, a stochastic process with long-time correlations between its increments, is a prototypical model for anomalous diffusion. We analyze fractional Brownian motion in the presence of a reflecting wall by means of Monte Carlo simulations. Whereas the mean-square displacement of the particle shows the expected anomalous diffusion behavior 〈x^{2}〉∼t^{α}, the interplay between the geometric confinement and the long-time memory leads to a highly non-Gaussian probability density function with a power-law singularity at the barrier. In the superdiffusive case α>1, the particles accumulate at the barrier leading to a divergence of the probability density. For subdiffusion α<1, in contrast, the probability density is depleted close to the barrier. We discuss implications of these findings, in particular, for applications that are dominated by rare events.

Measuring the continuity of diffusion barriers on porous films using {gamma}-ray energy spectra of escaping positronium

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

Xu Jun; Mills, Allen P. Jr.; Case, Carlye

2005-08-01

Diffusion barriers for capping porous low dielectric constant films are important for preventing metal migration into a semiconductor circuit. Using the fact that positrons implanted into a porous dielectric form ortho-positronium (o-Ps) copiously, Gidley et al. [D. W. Gidley, W. F. Frieze, T. L. Dull, J. Sun, A. F. Yee, C. V. Nguyen, and D. Y. Yoon, Appl. Phys. Lett. 76, 1282 (2000)], have been able to measure open area fractions as low as 10{sup -5} in porous dielectric film barrier layers from the increase in the ortho-positronium lifetime and intensity associated with positronium escape into vacuum. We demonstrate thatmore » it is possible to obtain comparable sensitivities by measuring the gamma-ray energy spectrum of the escaping positronium.« less

Ab initio and kinetic Monte Carlo study of lithium diffusion in LiSi, Li12Si7, Li13Si5 and Li15Si4

NASA Astrophysics Data System (ADS)

Moon, Janghyuk; Lee, Byeongchan; Cho, Maenghyo; Cho, Kyeongjae

2016-10-01

The kinetics of lithium atoms in various Li-Si binary compounds are investigated using density functional theory calculations and kinetic Monte Carlo calculations. The values of the Li migration energy barriers are identified by NEB calculations with vacancy-mediated, interstitial and exchange migration mechanisms in crystalline LiSi, Li12Si7, Li13Si4, and Li15Si4. A comparison of these NEB results shows that the vacancy-mediated Li migration is identified as the dominant diffusion mechanisms in Li-Si compounds. The diffusion coefficients of Li in Li-Si compounds at room temperature are determined by KMC simulation. From the KMC results, the recalculated migration energy barriers in LiSi, Li12Si7, Li13Si4, and Li15Si4 correspond to 0.306, 0.301, 0.367 and 0.320 eV, respectively. Compared to the Li migration energy barrier of 0.6 eV in crystalline Si, the drastic reduction in the Li migration energy barriers in the lithiated silicon indicates that the initial lithiation of the Si anode is the rate-limiting step. Furthermore, it is also found that Si migration is possible in Li-rich configurations. On the basis of these findings, the underlying mechanisms of kinetics on the atomic scale details are elucidated.

Memory effects in funnel ratchet of self-propelled particles

NASA Astrophysics Data System (ADS)

Hu, Cai-Tian; Wu, Jian-Chun; Ai, Bao-Quan

2017-05-01

The transport of self-propelled particles with memory effects is investigated in a two-dimensional periodic channel. Funnel-shaped barriers are regularly arrayed in the channel. Due to the asymmetry of the barriers, the self-propelled particles can be rectified. It is found that the memory effects of the rotational diffusion can strongly affect the rectified transport. The memory effects do not always break the rectified transport, and there exists an optimal finite value of correlation time at which the rectified efficiency takes its maximal value. We also find that the optimal values of parameters (the self-propulsion speed, the translocation diffusion coefficient, the rotational noise intensity, and the self-rotational diffusion coefficient) can facilitate the rectified transport. When introducing a finite load, particles with different self-propulsion speeds move to different directions and can be separated.

Electronic Devices with Diffusion Barrier and Process for Making Same

DTIC Science & Technology

2001-05-09

conductivity metallization materials such as gold , silver, and platinum. As can be appreciated from the foregoing, a barrier film is needed which... gold ), as well as platinum. These metals are highly attractive 10 for interconnect strategies on account of there intrinsic low resistivity and...the monolayer portion of the barrier -7- material. The monolayer ( monoatomic ) layer of metal atoms and the homoepitaxial film of metal halide

Profiling of barrier capacitance and spreading resistance using a transient linearly increasing voltage technique.

PubMed

Gaubas, E; Ceponis, T; Kusakovskij, J

2011-08-01

A technique for the combined measurement of barrier capacitance and spreading resistance profiles using a linearly increasing voltage pulse is presented. The technique is based on the measurement and analysis of current transients, due to the barrier and diffusion capacitance, and the spreading resistance, between a needle probe and sample. To control the impact of deep traps in the barrier capacitance, a steady state bias illumination with infrared light was employed. Measurements of the spreading resistance and barrier capacitance profiles using a stepwise positioned probe on cross sectioned silicon pin diodes and pnp structures are presented.

A study of dynamical evolution of small two-dimensional Copper islands’ diffusion on Ag(111) surface and observed surface effects

NASA Astrophysics Data System (ADS)

Hayat, Sardar Sikandar; Rehman, Zakirur; Shah, Zulfiqar Ali

2017-11-01

We study the diffusion of two-dimensional Cun(1 ≤ n ≤ 9) islands on Ag(111) surface using molecular dynamics (MD) simulations. The work is the extension of calculations of monomer and dimer Hayat et al. [Phys. Rev. B 82 (2010) 085411] and trimer results Shah et al. [Phys. Lett. A 378 (2014) 1732]. Simulations carried out at three different temperatures — 300, 500, and 700 K — show the concerted motion to be dominant for the smaller islands (2- to 4-atoms), while the shape-changing multiple-atom processes are responsible for the diffusion of larger islands. Arrhenius plots of the diffusion coefficients reveal that the effective energy barrier is less than 260 ± 5 meV for the largest island size of Cu/Ag(111). There is a scaling of the effective energy barrier with size to some extent, but most notably it remains constant for islands with 4- to 6-atoms. The diffusion coefficient increases within a factor of 10 at the three temperatures 300, 500, and 700 K. The observed anharmonic features of the Cun adislands (breakage and pop-up) at Ag(111) surface as well as the surface anharmonicity of the Ag-substrate (fissures, dislocations, vacancy generation, and atomic exchange), are also presented. These findings can serve as an input for kinetic Monte Carlo (KMC) simulations. For the smaller sized islands the variation in the effective energy barrier with the island size is in good agreement with the experimental findings.

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.

Development of an optical thermal history coating sensor based on the oxidation of a divalent rare earth ion phosphor

NASA Astrophysics Data System (ADS)

Yáñez-González, Álvaro; Ruiz-Trejo, Enrique; van Wachem, Berend; Skinner, Stephen; Beyrau, Frank; Heyes, Andrew

2016-11-01

The measurement of temperatures in gas turbines, boilers, heat exchangers and other components exposed to hot gases is essential to design energy efficient systems and improve maintenance procedures. When on-line measurements, such as those performed with thermocouples and pyrometers, are not possible or inconvenient, the maximum temperatures of operation can be recorded and measured off-line after operation. Although thermal paints have been used for many years for this purpose, a novel technique based on irreversible changes in the optical properties of thermographic phosphors, can overcome some of the disadvantages of previous methods. In particular, oxidation of the divalent rare earth ion phosphor BaMgAl10O17:Eu (BAM:Eu) has shown great potential for temperature sensing between 700 °C and 1200 °C. The emission spectra of this phosphor change with temperature, which permits to define an intensity ratio between different lines in the spectra that can be used as a measurand of the temperature. In this paper, the study of the sensing capabilities of a sensor coating based on BAM:Eu phosphor material is addressed for the first time. The sensitivity of the intensity ratio is investigated in the temperature range from 800 °C to 1100 °C, and is proved to be affected by ionic diffusion of transition metals from the substrate. The use of an interlayer made of zirconia proves efficient in reducing ionic diffusion and coatings with this diffusion barrier present sensitivity comparable to that of the powder material.

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.

Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy.

PubMed

Perrotta, Alberto; García, Santiago J; Michels, Jasper J; Andringa, Anne-Marije; Creatore, Mariadriana

2015-07-29

Water permeation in inorganic moisture permeation barriers occurs through macroscale defects/pinholes and nanopores, the latter with size approaching the water kinetic diameter (0.27 nm). Both permeation paths can be identified by the calcium test, i.e., a time-consuming and expensive optical method for determining the water vapor transmission rate (WVTR) through barrier layers. Recently, we have shown that ellipsometric porosimetry (i.e., a combination of spectroscopic ellipsometry and isothermal adsorption studies) is a valid method to classify and quantify the nanoporosity and correlate it with the WVTR values. Nevertheless, no information is obtained about the macroscale defects or the kinetics of water permeation through the barrier, both essential in assessing the quality of the barrier layer. In this study, electrochemical impedance spectroscopy (EIS) is shown as a sensitive and versatile method to obtain information on nanoporosity and macroscale defects, water permeation, and diffusivity of moisture barrier layers, complementing the barrier property characterization obtained by means of EP and calcium test. EIS is performed on thin SiO2 barrier layers deposited by plasma enhanced-CVD. It allows the determination of the relative water uptake in the SiO2 layers, found to be in agreement with the nanoporosity content inferred by EP. Furthermore, the kinetics of water permeation is followed by EIS, and the diffusivity (D) is determined and found to be in accordance with literature values. Moreover, differently from EP, EIS data are shown to be sensitive to the presence of local macrodefects, correlated with the barrier failure during the calcium test.

[Blood cerebrospinal fluid barrier damage of rats induced by lead acetate or nano-lead exposure].

PubMed

Feng, P P; Zhai, F J; Jiang, S F; Wu, J Z; Xue, L; Zheng, M M; Zhou, L L; Meng, C Y; Cao, M Y; Zhang, Y S

2016-05-20

To investigate the damage of blood-cerebrospinal fluid barrier (BCB) of rats induced by lead and nano-lead exposure in order to provide the basis for mechanism study of lead neurotoxicity. 39 male rats were randomly divided into control group, lead acetate exposed group and nano-lead exposed group. Rats in lead acetate exposed group and nano-lead exposed group were given 20 mg/kg lead acetate or nano-lead by oral gavage and rats in control groups were given the same amount saline for 9 weeks.Morris maze was used to test the learning function, serum albumin and CSF albumin were determined by ELISA. Confocal laser scanning microscope was applied to detect ZO-1 and Occludin protein expression in choroid plexus, real time-PCR was used to test the expression of ZO-1 and Occludin mRNA expression. Pathological changes of choroid plexus cells were observed by the electron microscopy. Compared with the control group, the escape latency of rats in lead acetate or nano-lead exposure group were longer and times of across platform were less. The levels of CSF albumin and the CSF albumin index in lead acetate or nano-lead exposed rats were obviously higher, and the fluorescence intensity of ZO-1, Occludin as well as mRNA expressions were lower than those in control group(P<0.05). Compared with lead acetate exposed group, the levels of CSF albumin and the CSF albumin index in nano-lead exposure group were higher. The fluorescence intensity and mRNA expressions of ZO-1, Occludin in nano-lead exposure group were than those in lead acetate group(P<0.05). Electron microscopy revealed that lead acetate or nano-lead exposure could induce shorter microvillus of choroid plexus epithelial cells, mitochondrion destruction and partial disconnection in intracellular junctions between two adjacent epithelial cells. Lead acetate and nano-lead exposed can result in the blood-cerebrospinal fluid barrier damage, which may involve in the process of lead induced neurotoxicity. Meanwhile, nano-lead exposure can induced in more worse damage in terms of blood-results in blood-cerebrospinal fluid barrier function.

Effect of Si in reactively sputtered Ti-Si-N films on structure and diffusion barrier performance

NASA Astrophysics Data System (ADS)

Sun, X.; Kolawa, E.; Im, S.; Garland, C.; Nicolet, M.-A.

Two ternary films about 100 nm thick, Ti34Si23N43 (b3) and Ti35Si13N52 (c3), are synthesized by reactively sputtering a Ti5Si3 or a Ti3Si target, respectively. The silicon-lean film (c3) has a columnar structure closely resembling that of TiN. As a diffusion barrier between a shallow Si n+p junction diode and a Cu overlayer, this material is effective up to 700 °C for 30 min annealing in vacuum, a performance similar to that for TiN. The silicon-rich (b3) film contains nanocrystals of TiN, randomly oriented and embedded in an amorphous matrix. A film of (b3) maintains the stability of the same diode structure up to 850 °C for 30 min in vacuum. This film (b3) is clearly superior to TiN or to (c3). Similar experiments performed with Al instead of Cu overlayers highlight the importance of the thermodynamic stability of a barrier layer and demonstrate convincingly that for stable barriers the microstructure is a parameter that directly determines the barrier performance.

What is the most efficient respiratory organ for the loricariid air-breathing fish Pterygoplichthys anisitsi, gills or stomach? A quantitative morphological study.

PubMed

da Cruz, André Luis; Fernandes, Marisa Narciso

2016-12-01

The purpose of the present study was to evaluate the morphometric respiratory potential of gills compared to the stomach in obtaining oxygen for aerobic metabolism in Pterygoplichthys anisitsi, a facultative air-breathing fish. The measurements were done using stereological methods. The gills showed greater total volume, volume-to-body mass ratio, potential surface area, and surface-to-volume ratio than the stomach. The water-blood diffusion barrier of the gills is thicker than the air-blood diffusion barrier of the stomach. Taken together, the surface area, the surface-to-volume ratio and the diffusion distance for O 2 transfer from the respiratory medium to blood yield a greater diffusing capacity for gills than for the stomach, suggesting greater importance of aquatic respiration in this species. On the other hand, water breathing is energetically more expensive than breathing air. Under severe hypoxic conditions, O 2 uptake by the stomach is more efficient than by the gills, although the stomach has a much lower diffusing capacity. Thus, P. anisitsi uses gills under normoxic conditions but the stomach may also support aerobic metabolism depending on environmental conditions. Copyright © 2016 Elsevier GmbH. All rights reserved.

Host Status of Different Potato (Solanum tuberosum) Varieties and Hatching in Root Diffusates of Globodera ellingtonae

PubMed Central

Zasada, Inga A.; Peetz, Amy; Wade, Nadine; Navarre, Roy A.; Ingham, Russ E.

2013-01-01

Globodera ellingtonae was detected in Oregon in 2008. In order to make decisions regarding the regulation of this nematode, knowledge of its biology is required. We determined the host status of a diversity of potato (Solanum tuberosum) varieties in soil-based experiments and identified hatching stimulants in in vitro hatching assays. ‘Russet Burbank,’ ‘Desiree,’ ‘Modac,’ ‘Norland,’ ‘Umatilla,’ and ‘Yukon Gold’ were good hosts (RF > 14) for G. ellingtonae. Potato varieties ‘Maris Piper,’ ‘Atlantic,’ and ‘Satina,’ all which contain the Ro1 gene that confers resistance to G. rostochiensis, were not hosts for G. ellingtonae. In in vitro hatching assays, G. ellingtonae hatched readily in the presence of diffusates from potato (PRD) and tomato (Solanum lycopersicum; TRD). Egg hatch occurred in an average of between 87% and 90% of exposed cysts, with an average of between 144 and 164 juveniles emerging per cyst, from PRD- and TRD-treated cysts, respectively. This nematode hatched rapidly in the presence of PRD and TRD, with at least 66% of total hatch occurring by day 3 of exposure. There was no dose-response of egg hatch to concentrations of PRD or TRD ranging from 1:5 to 1:100 diffusate to water. When G. ellingtonae was exposed to root diffusates from 21 different plants, hatch occurred in 0% to 70% of exposed cysts, with an average of between 0 to 27 juveniles emerging per cyst. When root diffusate-exposed cysts were subsequently transferred to PRD to test viability, root diffusates from arugula (Eruca sativa), sudangrass (Sorghum bicolor subsp. drummondii), and common vetch (Vicia sativa) continued to inhibit egg hatch compared with the other root diffusates or water in which hatch occurred readily (60 to 182 juveniles emerging per cyst). Previously known hatching stimulants of G. rostochiensis and G. pallida, sodium metavanadate, sodium orthovanadate, and sodium thiocyanate, stimulated some egg hatch. Although, Globodera ellingtonae hatched readily in PRD and TRD and reproduced on potato, the pathogenicity of this nematode on potato remains to be determined. PMID:24115784

Host Status of Different Potato (Solanum tuberosum) Varieties and Hatching in Root Diffusates of Globodera ellingtonae.

PubMed

Zasada, Inga A; Peetz, Amy; Wade, Nadine; Navarre, Roy A; Ingham, Russ E

2013-09-01

Globodera ellingtonae was detected in Oregon in 2008. In order to make decisions regarding the regulation of this nematode, knowledge of its biology is required. We determined the host status of a diversity of potato (Solanum tuberosum) varieties in soil-based experiments and identified hatching stimulants in in vitro hatching assays. 'Russet Burbank,' 'Desiree,' 'Modac,' 'Norland,' 'Umatilla,' and 'Yukon Gold' were good hosts (RF > 14) for G. ellingtonae. Potato varieties 'Maris Piper,' 'Atlantic,' and 'Satina,' all which contain the Ro1 gene that confers resistance to G. rostochiensis, were not hosts for G. ellingtonae. In in vitro hatching assays, G. ellingtonae hatched readily in the presence of diffusates from potato (PRD) and tomato (Solanum lycopersicum; TRD). Egg hatch occurred in an average of between 87% and 90% of exposed cysts, with an average of between 144 and 164 juveniles emerging per cyst, from PRD- and TRD-treated cysts, respectively. This nematode hatched rapidly in the presence of PRD and TRD, with at least 66% of total hatch occurring by day 3 of exposure. There was no dose-response of egg hatch to concentrations of PRD or TRD ranging from 1:5 to 1:100 diffusate to water. When G. ellingtonae was exposed to root diffusates from 21 different plants, hatch occurred in 0% to 70% of exposed cysts, with an average of between 0 to 27 juveniles emerging per cyst. When root diffusate-exposed cysts were subsequently transferred to PRD to test viability, root diffusates from arugula (Eruca sativa), sudangrass (Sorghum bicolor subsp. drummondii), and common vetch (Vicia sativa) continued to inhibit egg hatch compared with the other root diffusates or water in which hatch occurred readily (60 to 182 juveniles emerging per cyst). Previously known hatching stimulants of G. rostochiensis and G. pallida, sodium metavanadate, sodium orthovanadate, and sodium thiocyanate, stimulated some egg hatch. Although, Globodera ellingtonae hatched readily in PRD and TRD and reproduced on potato, the pathogenicity of this nematode on potato remains to be determined.

Unconfined lateral diffusion and an estimate of pericellular matrix viscosity revealed by measuring the mobility of gold-tagged lipids

PubMed Central

1993-01-01

Nanovid (video-enhanced) microscopy was used to determine whether lateral diffusion in the plasma membrane of colloidal gold-tagged lipid molecules is confined or is unrestricted. Confinement could be produced by domains within the plane of the plasma membrane or by filamentous barriers within the pericellular matrix. Fluorescein- phosphatidylethanolamine (F1-PE), incorporated into the plasma membranes of cultured fibroblasts, epithelial cells and keratocytes, was labeled with 30-nm colloidal gold conjugated to anti-fluorescein (anti-F1). The trajectories of the gold-labeled lipids were used to compute diffusion coefficients (DG) and to test for restricted motion. On the cell lamella, the gold-labeled lipids diffused freely in the plasma membrane. Since the gold must move through the pericellular matrix as the attached lipid diffuses in the plasma membrane, this result suggests that any extensive filamentous barriers in the pericellular matrix are at least 40 nm from the plasma membrane surface. The average diffusion coefficients ranged from 1.1 to 1.7 x 10(-9) cm2/s. These values were lower than the average diffusion coefficients (DF) (5.4 to 9.5 x 10(-9) cm2/s) obtained by FRAP. The lower DG is partially due to the pericellular matrix as demonstrated by the result that heparinase treatment of keratocytes significantly increased DG to 2.8 x 10(-9) cm2/s, but did not affect DF. Pericellular matrix viscosity was estimated from the frictional coefficients computed from DG and DF and ranged from 0.5 to 0.9 poise for untreated cells. Heparinase treatment of keratocytes decreased the apparent viscosity to approximately 0.1 poise. To evaluate the presence of domains or barriers, the trajectories and corresponding mean square displacement (MSD) plots of gold-labeled lipids were compared to the trajectories and MSD plots resulting from computer simulations of random walks within corrals. Based on these comparisons, we conclude that, if there are domains limiting the diffusion of F1-PE, most are larger than 5 microns in diameter. PMID:8416991

[The mechanism of the transport of organophosphorus compounds across the histo-hematic barriers].

PubMed

Miroshkina, V N; Kosmachev, A B; Salova, L S

1999-01-01

It was demonstrated in experiments on mice [correction of rats] that the transport of organophosphorus compounds (OPC) through membranes of the histohematic barriers (HHB) of the organism occurs by means of diffusion. The rate of this process depends on the interaction of OPC with the specific sites of binding with the tissues, among which the enzyme carboxylesterase plays an important part. It is suggested that both the rate and direction of OPC diffusion are determined by the relationship between the values of affinity of the ligands for the sites of their specific binding found on both sides of the HHB.

Electron-Beam-Induced Deposition as a Technique for Analysis of Precursor Molecule Diffusion Barriers and Prefactors.

PubMed

Cullen, Jared; Lobo, Charlene J; Ford, Michael J; Toth, Milos

2015-09-30

Electron-beam-induced deposition (EBID) is a direct-write chemical vapor deposition technique in which an electron beam is used for precursor dissociation. Here we show that Arrhenius analysis of the deposition rates of nanostructures grown by EBID can be used to deduce the diffusion energies and corresponding preexponential factors of EBID precursor molecules. We explain the limitations of this approach, define growth conditions needed to minimize errors, and explain why the errors increase systematically as EBID parameters diverge from ideal growth conditions. Under suitable deposition conditions, EBID can be used as a localized technique for analysis of adsorption barriers and prefactors.

Study of Nickel Silicide as a Copper Diffusion Barrier in Monocrystalline Silicon Solar Cells

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

Kale, Abhijit; Beese, Emily; Saenz, Theresa

NiSi as a conductive diffusion barrier to silicon has been studied. We demonstrate that the NiSi films formed using the single step annealing process are as good as the two step process using XRD and Raman. Quality of NiSi films formed using e-beam Ni and electroless Ni process has been compared. Incomplete surface coverage and presence of constituents other than Ni are the main challenges with electroless Ni. We also demonstrate that Cu reduces the thermal stability of NiSi films. The detection of Cu has proven to be difficult due to temperature limitations.

Information and communication technology: students' health education in 1st- to 6th-grade South Korea elementary schools.

PubMed

Lee, Eunjoo; Park, Hyejin; Whyte, James; Jeong, Eunhoe

2013-09-01

The purposes of this study were to (1) identify school nurses' awareness of information and communication technology (ICT) use in students' health education and (2) explore the barriers or reasons for the adoption of ICT in school nursing practice, while (3) presenting strategies to speed ICT diffusion and dissemination into practice. For data collection, 209 primary school nurses in K province of Korea were selected and e-mailed the questionnaires. Collected data were analyzed as frequency, percentages, and chi-square tests. The major reasons to adopt ICT were increasing school nurses' confidence in providing health education and improving teaching methods using diverse multimedia. The major barriers to utilization of ICT were lack of time for preparation of educational materials, lack of software availability, and lack of computer skills of school nurses and students. Several strategies were suggested to speed the diffusion of ICT into students' health education, such as integrating a health education course into regular curriculum. It is important to identify barriers and reasons for adoption of ICT in school nursing. In addition, strategies should be emphasized that result in more rapid diffusion of these technologies in school nursing practice. © 2013, American School Health Association.

Controlled release of betamethasone from vitamin E-loaded silicone-based soft contact lenses.

PubMed

Rad, Maryam Shayani; Sajadi Tabassi, Sayyed Abolghasem; Moghadam, Maryam Hassanpour; Mohajeri, Seyed Ahmad

2016-11-01

Betamethasone (BMZ) is an effective drug which is commonly used as an eye drop for the management of ophthalmic inflammations. Due to low ocular bioavailability, it is necessary to prepare and optimize an ocular drug delivery system for BMZ. In this study we tried to use vitamin E diffusion barrier for sustaining BMZ release. Three commercial contact lenses were soaked in vitamin E solutions and swelling percentage, diameter, transmittance, binding capacity and release amount and time were evaluated in comparison with non-vitamin E-loaded pure lenses. The results showed that vitamin E significantly decreased water content of contact lenses whereas, increased the lens diameter in both dry and wet states. It effectively blocked UV radiation which is harmful for the eye surface while had no significant effect on visible transmittance. BMZ loading capacity enhanced and release rate remarkably decreased after using vitamin E as a hydrophobic diffusion barrier. This study revealed that vitamin E can be applied as a hydrophobic diffusion barrier for controlling and sustaining BMZ release from silicone-based soft contact lenses into the lachrymal fluid. It can also protect eye tissues as an antioxidant by blocking the UV radiation.

Low-Resistance Spin Injection into Silicon Using Graphene Tunnel Barriers

DTIC Science & Technology

2012-11-01

compromise spin injection/transport/detection. Ferromagnetic metals readily form silicides even at room tempera- ture19, and diffusion of the ferromagnetic... metal /tunnel barrier/Si contacts using 2 nm SiO2 (triangles), 1.5 nm Al2O3 (diamond) and monolayer graphene (circles) tunnel barriers prepared from...and B. T. Jonker* Spin manipulation in a semiconductor offers a new paradigm for device operation beyond Moore’s law. Ferromagnetic metals are ideal

Integrating diffusion maps with umbrella sampling: Application to alanine dipeptide

NASA Astrophysics Data System (ADS)

Ferguson, Andrew L.; Panagiotopoulos, Athanassios Z.; Debenedetti, Pablo G.; Kevrekidis, Ioannis G.

2011-04-01

Nonlinear dimensionality reduction techniques can be applied to molecular simulation trajectories to systematically extract a small number of variables with which to parametrize the important dynamical motions of the system. For molecular systems exhibiting free energy barriers exceeding a few kBT, inadequate sampling of the barrier regions between stable or metastable basins can lead to a poor global characterization of the free energy landscape. We present an adaptation of a nonlinear dimensionality reduction technique known as the diffusion map that extends its applicability to biased umbrella sampling simulation trajectories in which restraining potentials are employed to drive the system into high free energy regions and improve sampling of phase space. We then propose a bootstrapped approach to iteratively discover good low-dimensional parametrizations by interleaving successive rounds of umbrella sampling and diffusion mapping, and we illustrate the technique through a study of alanine dipeptide in explicit solvent.

A diffuse argon plume generated by a longitudinal slit jet equipped with a quadri-electrode barrier discharge

NASA Astrophysics Data System (ADS)

Li, Xuechen; Chu, Jingdi; Zhang, Qi; Zhang, Panpan; Jia, Pengying; Dong, Lifang

2018-04-01

A diffuse argon plume at atmospheric pressure is generated downstream of a longitudinal slit jet equipped with a dielectric barrier discharge in a quadri-electrode configuration. Results indicate that both the plume length and the spectral line intensities increase with the increase in the peak voltage. With fast photography it is found that there is a clear difference for discharges with different polarities. The positive discharge is composed of nonuniform branching filaments; however, it is fairly uniform for the negative discharge. Due to the charge overflow of the intra-electrode discharge, the streamer mechanism is involved in the plume discharge. In fact, the positive discharge and the negative one correspond to a cathode-directed streamer and an anode-directed streamer, respectively. The formation mechanisms of the branching filaments and the diffuse background are discussed at last.

Performance of temporary concrete traffic barriers during the widening of I-95.

DOT National Transportation Integrated Search

1982-01-01

This research effort was initiated at the request of officials of the Virginia Department of Highways and Transportation to obtain information on the performance of the precast concrete traffic barrier (PCTB) when exposed to heavy vehicles. The PCTB ...

Ammonia Released by Streptomyces aburaviensis Induces Droplet Formation in Streptomyces violaceoruber.

PubMed

Schmidt, Kathrin; Spiteller, Dieter

2017-08-01

Streptomyces violaceoruber grown in co-culture with Streptomyces aburaviensis produces an about 17-fold higher volume of droplets on its aerial mycelium than in single-culture. Physical separation of the Streptomyces strains by either a plastic barrier or by a dialysis membrane, which allowed communication only by the exchange of volatile compounds or diffusible compounds in the medium, respectively, still resulted in enhanced droplet formation. The application of molecular sieves to bioassays resulted in the attenuation of the droplet-inducing effect of S. aburaviensis indicating the absorption of the compound. 1 H-NMR analysis of molecular-sieve extracts and the selective indophenol-blue reaction revealed that the volatile droplet-inducing compound is ammonia. The external supply of ammonia in biologically relevant concentrations of ≥8 mM enhanced droplet formation in S. violaceoruber in a similar way to S. aburaviensis. Ammonia appears to trigger droplet production in many Streptomyces strains because four out of six Streptomyces strains exposed to ammonia exhibited induced droplet production.

Liquid-Like, Self-Healing Aluminum Oxide during Deformation at Room Temperature.

PubMed

Yang, Yang; Kushima, Akihiro; Han, Weizhong; Xin, Huolin; Li, Ju

2018-04-11

Effective protection from environmental degradation relies on the integrity of oxide as diffusion barriers. Ideally, the passivation layer can repair its own breaches quickly under deformation. While studies suggest that the native aluminum oxide may manifest such properties, it has yet to be experimentally proven because direct observations of the air-environmental deformation of aluminum oxide and its initial formation at room temperature are challenging. Here, we report in situ experiments to stretch pure aluminum nanotips under O 2 gas environments in a transmission electron microscope (TEM). We discovered that aluminum oxide indeed deforms like liquid and can match the deformation of Al without any cracks/spallation at moderate strain rate. At higher strain rate, we exposed fresh metal surface, and visualized the self-healing process of aluminum oxide at atomic resolution. Unlike traditional thin-film growth or nanoglass consolidation processes, we observe seamless coalescence of new oxide islands without forming any glass-glass interface or surface grooves, indicating greatly accelerated glass kinetics at the surface compared to the bulk.

Multi-scale kinetics of a field-directed colloidal phase transition.

PubMed

Swan, James W; Vasquez, Paula A; Whitson, Peggy A; Fincke, E Michael; Wakata, Koichi; Magnus, Sandra H; De Winne, Frank; Barratt, Michael R; Agui, Juan H; Green, Robert D; Hall, Nancy R; Bohman, Donna Y; Bunnell, Charles T; Gast, Alice P; Furst, Eric M

2012-10-02

Polarizable colloids are expected to form crystalline equilibrium phases when exposed to a steady, uniform field. However, when colloids become localized this field-induced phase transition arrests and the suspension persists indefinitely as a kinetically trapped, percolated structure. We anneal such gels formed from magneto-rheological fluids by toggling the field strength at varied frequencies. This processing allows the arrested structure to relax periodically to equilibrium--colloid-rich, cylindrical columns. Two distinct growth regimes are observed: one in which particle domains ripen through diffusive relaxation of the gel, and the other where the system-spanning structure collapses and columnar domains coalesce apparently through field-driven interactions. There is a stark boundary as a function of magnetic field strength and toggle frequency distinguishing the two regimes. These results demonstrate how kinetic barriers to a colloidal phase transition are subverted through measured, periodic variation of driving forces. Such directed assembly may be harnessed to create unique materials from dispersions of colloids.

Molecular assemblies as protective barriers and adhesion promotion interlayer

DOEpatents

King, David E.; Czanderna, Alvin W.; Kennedy, Cheryl E.

1996-01-01

A protective diffusion barrier having adhesive qualifies for metalized surfaces is provided by a passivating agent having the formula HS--(CH.sub.2).sub.11 --COOH Which forms a very dense, transparent organized molecular assembly or layer that is impervious to water, alkali, and other impurities and corrosive substances that typically attack metal surfaces.

Spin Transfer Torque in Graphene

NASA Astrophysics Data System (ADS)

Lin, Chia-Ching; Chen, Zhihong

2014-03-01

Graphene is an idea channel material for spin transport due to its long spin diffusion length. To develop graphene based spin logic, it is important to demonstrate spin transfer torque in graphene. Here, we report the experimental measurement of spin transfer torque in graphene nonlocal spin valve devices. Assisted by a small external in-plane magnetic field, the magnetization reversal of the receiving magnet is induced by pure spin diffusion currents from the injector magnet. The magnetization switching is reversible between parallel and antiparallel configurations by controlling the polarity of the applied charged currents. Current induced heating and Oersted field from the nonlocal charge flow have also been excluded in this study. Next, we further enhance the spin angular momentum absorption at the interface of the receiving magnet and graphene channel by removing the tunneling barrier in the receiving magnet. The device with a tunneling barrier only at the injector magnet shows a comparable nonlocal spin valve signal but lower electrical noise. Moreover, in the same preset condition, the critical charge current density for spin torque in the single tunneling barrier device shows a substantial reduction if compared to the double tunneling barrier device.

Probabilistic migration modelling focused on functional barrier efficiency and low migration concepts in support of risk assessment.

PubMed

Brandsch, Rainer

2017-10-01

Migration modelling provides reliable migration estimates from food-contact materials (FCM) to food or food simulants based on mass-transfer parameters like diffusion and partition coefficients related to individual materials. In most cases, mass-transfer parameters are not readily available from the literature and for this reason are estimated with a given uncertainty. Historically, uncertainty was accounted for by introducing upper limit concepts first, turning out to be of limited applicability due to highly overestimated migration results. Probabilistic migration modelling gives the possibility to consider uncertainty of the mass-transfer parameters as well as other model inputs. With respect to a functional barrier, the most important parameters among others are the diffusion properties of the functional barrier and its thickness. A software tool that accepts distribution as inputs and is capable of applying Monte Carlo methods, i.e., random sampling from the input distributions of the relevant parameters (i.e., diffusion coefficient and layer thickness), predicts migration results with related uncertainty and confidence intervals. The capabilities of probabilistic migration modelling are presented in the view of three case studies (1) sensitivity analysis, (2) functional barrier efficiency and (3) validation by experimental testing. Based on the predicted migration by probabilistic migration modelling and related exposure estimates, safety evaluation of new materials in the context of existing or new packaging concepts is possible. Identifying associated migration risk and potential safety concerns in the early stage of packaging development is possible. Furthermore, dedicated material selection exhibiting required functional barrier efficiency under application conditions becomes feasible. Validation of the migration risk assessment by probabilistic migration modelling through a minimum of dedicated experimental testing is strongly recommended.

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).

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

Morphology Effect on Proton Dynamics in Nafion® 117 and Sulfonated Polyether Ether Ketone

NASA Astrophysics Data System (ADS)

Leong, Jun Xing; Diño, Wilson Agerico; Ahmad, Azizan; Daud, Wan Ramli Wan; Kasai, Hideaki

2016-09-01

We report results of our experimental and theoretical studies on the dynamics of proton conductivity in Nafion® 117 and self-fabricated sulfonated polyether ether ketone (SPEEK) membranes. Knowing that the presence of water molecules in the diffusion process results in a lower energy barrier, we determined the diffusion barriers and corresponding tunneling probabilities of Nafion® 117 and SPEEK system using a simple theoretical model that excludes the medium (water molecules) in the initial calculations. We then propose an equation that relates the membrane conductivity to the tunneling probability. We recover the effect of the medium by introducing a correction term into the proposed equation, which takes into account the effect of the proton diffusion distance and the hydration level. We have also experimentally verified that the proposed equation correctly explain the difference in conductivity between Nafion® 117 and SPEEK. We found that membranes that are to be operated in low hydration environments (high temperatures) need to be designed with short diffusion distances to enhance and maintain high conductivity.

Stigma and Barriers to Care: Caring for Those Exposed to War, Disaster and Terrorism. Executive Summary and Recommendations

DTIC Science & Technology

2012-03-06

Proceedings Executive Summary 3. DATES COVERED (From - To) 3/25/2010-3/26/2010 4. TITLE AND SUBTITLE Stigma and Barriers To Care: Caring for Those...Health and National Security, directed to addressing stigma and barriers to care, brought together a diverse group of leaders in order to expand our...researchers and health care planners across mental health, health care systems, military and disaster care and the specific issues of stigma and barriers

Carrier-Mediated Cocaine Transport at the Blood-Brain Barrier as a Putative Mechanism in Addiction Liability

PubMed Central

Chapy, Hélène; Smirnova, Maria; André, Pascal; Schlatter, Joël; Chiadmi, Fouad; Couraud, Pierre-Olivier; Scherrmann, Jean-Michel; Declèves, Xavier

2015-01-01

Background: The rate of entry of cocaine into the brain is a critical factor that influences neuronal plasticity and the development of cocaine addiction. Until now, passive diffusion has been considered the unique mechanism known by which cocaine crosses the blood-brain barrier. Methods: We reassessed mechanisms of transport of cocaine at the blood-brain barrier using a human cerebral capillary endothelial cell line (hCMEC/D3) and in situ mouse carotid perfusion. Results: Both in vivo and in vitro cocaine transport studies demonstrated the coexistence of a carrier-mediated process with passive diffusion. At pharmacological exposure level, passive diffusion of cocaine accounted for only 22.5% of the total cocaine influx in mice and 5.9% in hCMEC/D3 cells, whereas the carrier-mediated influx rate was 3.4 times greater than its passive diffusion rate in vivo. The functional identification of this carrier-mediated transport demonstrated the involvement of a proton antiporter that shared the properties of the previously characterized clonidine and nicotine transporter. The functionnal characterization suggests that the solute carrier (SLC) transporters Oct (Slc22a1-3), Mate (Slc47a1) and Octn (Slc22a4-5) are not involved in the cocaine transport in vivo and in vitro. Diphenhydramine, heroin, tramadol, cocaethylene, and norcocaine all strongly inhibited cocaine transport, unlike benzoylecgonine. Trans-stimulation studies indicated that diphenhydramine, nicotine, 3,4-methylenedioxyamphetamine (ecstasy) and the cathinone compound 3,4-methylenedioxypyrovalerone (MDPV) were also substrates of the cocaine transporter. Conclusions: Cocaine transport at the BBB involves a proton-antiporter flux that is quantitatively much more important than its passive diffusion. The molecular identification and characterization of this transporter will provide new tools to understand its role in addictive mechanisms. PMID:25539501

Impact of homogeneous strain on uranium vacancy diffusion in uranium dioxide

DOE PAGES

Goyal, Anuj; Phillpot, Simon R.; Subramanian, Gopinath; ...

2015-03-03

We present a detailed mechanism of, and the effect of homogeneous strains on, the migration of uranium vacancies in UO 2. Vacancy migration pathways and barriers are identified using density functional theory and the effect of uniform strain fields are accounted for using the dipole tensor approach. We report complex migration pathways and noncubic symmetry associated with the uranium vacancy in UO 2 and show that these complexities need to be carefully accounted for to predict the correct diffusion behavior of uranium vacancies. We show that under homogeneous strain fields, only the dipole tensor of the saddle with respect tomore » the minimum is required to correctly predict the change in the energy barrier between the strained and the unstrained case. Diffusivities are computed using kinetic Monte Carlo simulations for both neutral and fully charged state of uranium single and divacancies. We calculate the effect of strain on migration barriers in the temperature range 800–1800 K for both vacancy types. Homogeneous strains as small as 2% have a considerable effect on diffusivity of both single and divacancies of uranium, with the effect of strain being more pronounced for single vacancies than divacancies. In contrast, the response of a given defect to strain is less sensitive to changes in the charge state of the defect. Further, strain leads to anisotropies in the mobility of the vacancy and the degree of anisotropy is very sensitive to the nature of the applied strain field for strain of equal magnitude. Our results indicate that the influence of strain on vacancy diffusivity will be significantly greater when single vacancies dominate the defect structure, such as sintering, while the effects will be much less substantial under irradiation conditions where divacancies dominate.« less

Radon Diffusion Measurement in Polyethylene based on Alpha Detection

NASA Astrophysics Data System (ADS)

Rau, Wolfgang

2011-04-01

We present a method to measure the diffusion of Radon in solid materials based on the alpha decay of the radon daughter products. In contrast to usual diffusion measurements which detect the radon that penetrates a thin barrier, we let the radon diffuse into the material and then measure the alpha decays of the radon daughter products in the material. We applied this method to regular and ultra high molecular weight poly ethylene and find diffusion lengths of order of mm as expected. However, the preliminary analysis shows significant differences between two different approaches we have chosen. These differences may be explained by the different experimental conditions.

Kinetics of Ta ions penetration into porous low-k dielectrics under bias-temperature stress

NASA Astrophysics Data System (ADS)

He, Ming; Ou, Ya; Wang, Pei-I.; Lu, Toh-Ming

2010-05-01

It is known that Ta, a popular diffusion barrier material, can itself penetrate into low-k dielectrics under bias-temperature stress. In this work, we derived a model which directly correlates the diffusivity of Ta ions to the rate of flatband voltage shift (FBS) of the Ta/methyl silsesquixane (MSQ)/Si capacitors. From our experimentally measured constant FBS rate, the Ta diffusivity and activation energy were determined. It appears that an increase in the porosity of MSQ film enhances the Ta diffusivity but does not affect the associated activation energy. This suggests the Ta ion diffusion is mainly through interconnected pore surfaces.

Surface charge- and space-dependent transport of proteins in crowded environments of nanotailored posts.

PubMed

Choi, Chang Kyoung; Fowlkes, Jason D; Retterer, Scott T; Siuti, Piro; Iyer, Sukanya; Doktycz, Mitchel J

2010-06-22

The reaction and diffusion of molecules across barriers and through crowded environments is integral to biological system function and to separation technologies. Ordered, microfabricated post arrays are a promising route to creating synthetic barriers with controlled chemical and physical characteristics. They can be used to create crowded environments, to mimic aspects of cellular membranes, and to serve as engineered replacements of polymer-based separation media. Here, the translational diffusion of fluorescein isothiocyante and various forms of green fluorescent protein (GFP), including "supercharged" variants, are examined in a silicon-based post array environment. The technique of fluorescence recovery after photobleaching (FRAP) is combined with analytical approximations and numerical simulations to assess the relative effects of reaction and diffusion on molecular transport, respectively. FRAP experiments were conducted for 64 different cases where the molecular species, the density of the posts, and the chemical surface charge of the posts were varied. In all cases, the dense packing of the posts hindered the diffusive transport of the fluorescent species. The supercharged GFPs strongly interacted with oppositely charged surfaces. With similar molecular and surface charges, transport is primarily limited by hindered diffusion. For conventional, enhanced GFP in a positively charged surface environment, transport was limited by the coupled action of hindered diffusion and surface interaction with the posts. Quantification of the size-, space-, time-, and charge-dependent translational diffusion in the post array environments can provide insight into natural processes and guide the design and development of selective membrane systems.

Side chain variations radically alter the diffusion of poly(2-alkyl-2-oxazoline) functionalised nanoparticles through a mucosal barrier.

PubMed

Mansfield, Edward D H; de la Rosa, Victor R; Kowalczyk, Radoslaw M; Grillo, Isabelle; Hoogenboom, Richard; Sillence, Katy; Hole, Patrick; Williams, Adrian C; Khutoryanskiy, Vitaliy V

2016-08-16

Functionalised nanomaterials are gaining popularity for use as drug delivery vehicles and, in particular, mucus penetrating nanoparticles may improve drug bioavailability via the oral route. To date, few polymers have been investigated for their muco-penetration, and the effects of systematic structural changes to polymer architectures on the penetration and diffusion of functionalised nanomaterials through mucosal tissue have not been reported. We investigated the influence of poly(2-oxazoline) alkyl side chain length on nanoparticle diffusion; poly(2-methyl-2-oxazoline), poly(2-ethyl-2-oxazoline), and poly(2-n-propyl-2-oxazoline) were grafted onto the surface of thiolated silica nanoparticles and characterised by FT-IR, Raman and NMR spectroscopy, thermogravimetric analysis, and small angle neutron scattering. Diffusion coefficients were determined in water and in a mucin dispersion (using Nanoparticle Tracking Analysis), and penetration through a mucosal barrier was assessed using an ex vivo fluorescence technique. The addition of a single methylene group in the side chain significantly altered the penetration and diffusion of the materials in both mucin dispersions and mucosal tissue. Nanoparticles functionalised with poly(2-methyl-2-oxazoline) were significantly more diffusive than particles with poly(2-ethyl-2-oxazoline) while particles with poly(2-n-propyl-2-oxazoline) showed no significant increase compared to the unfunctionalised particles. These data show that variations in the polymer structure can radically alter their diffusive properties with clear implications for the future design of mucus penetrating systems.

The diffusion dynamics of PEGylated liposomes in the intact vitreous of the ex vivo porcine eye: A fluorescence correlation spectroscopy and biodistribution study.

PubMed

Eriksen, Anne Z; Brewer, Jonathan; Andresen, Thomas L; Urquhart, Andrew J

2017-04-30

The diffusion dynamics of nanocarriers in the vitreous and the influence of nanocarrier physicochemical properties on these dynamics is an important aspect of the efficacy of intravitreal administered nanomedicines for the treatment of posterior segment eye diseases. Here we use fluorescence correlation spectroscopy (FCS) to determine liposome diffusion coefficients in the intact vitreous (D Vit ) of ex vivo porcine eyes using a modified Miyake-Apple technique to minimize the disruption of the vitreous fine structure. We chose to investigate whether the zeta potential of polyethylene glycol functionalized (i.e. PEGylated) liposomes altered liposome in situ diffusion dynamics in the vitreous. Non-PEGylated cationic nanocarriers have previously shown little to no diffusion in the vitreous, whilst neutral and anionic have shown diffusion. The liposomes investigated had diameters below 150nm and zeta potentials ranging from -20 to +12mV. We observed that PEGylated cationic liposomes had significantly lower D Vit values (1.14μm 2 s -1 ) than PEGylated neutral and anionic liposomes (2.78 and 2.87μm 2 s -1 ). However, PEGylated cationic liposomes had a similar biodistribution profile across the vitreous to the other systems. These results show that PEGylated cationic liposomes with limited cationic charge can diffuse across the vitreous and indicate that the vitreous as a barrier to nanocarriers (Ø<500nm) is more complicated than simply an electrostatic barrier as previously suggested. Copyright © 2017 Elsevier B.V. All rights reserved.

Anisotropic Thermal Diffusivities of Plasma-Sprayed Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Akoshima, Megumi; Takahashi, Satoru

2017-09-01

Thermal barrier coatings (TBCs) are used to shield the blades of gas turbines from heat and wear. There is a pressing need to evaluate the thermal conductivity of TBCs in the thermal design of advanced gas turbines with high energy efficiency. These TBCs consist of a ceramic-based top coat and a bond coat on a superalloy substrate. Usually, the focus is on the thermal conductivity in the thickness direction of the TBC because heat tends to diffuse from the surface of the top coat to the substrate. However, the in-plane thermal conductivity is also important in the thermal design of gas turbines because the temperature distribution within the turbine cannot be ignored. Accordingly, a method is developed in this study for measuring the in-plane thermal diffusivity of the top coat. Yttria-stabilized zirconia top coats are prepared by thermal spraying under different conditions. The in-plane and cross-plane thermal diffusivities of the top coats are measured by the flash method to investigate the anisotropy of thermal conduction in a TBC. It is found that the in-plane thermal diffusivity is higher than the cross-plane one for each top coat and that the top coats have significantly anisotropic thermal diffusivity. The cross-sectional and in-plane microstructures of the top coats are observed, from which their porosities are evaluated. The thermal diffusivity and its anisotropy are discussed in detail in relation to microstructure and porosity.

First Principles Study for Proton Transport and Diffusion Behavior in Hydrous Hexagonal WO3

NASA Astrophysics Data System (ADS)

Liu, Chi-Ping; Zhou, Fei; Ozolins, Vidvuds; QPAM Team

2013-03-01

Proton transport is of great importance in biological species and energy storage and conversion systems. Previous studies have shown fast proton conduction in liquids and polymers but seldom in inorganic materials. In this work, first principles density functional theory (DFT) reveals that the formation of hydronium and water chains inside the hexagonal channels plays the key roles for the anomalously fast proton transport, by following modified Grotthuss mechanism. Our DFT study shows the detailed microscopic proton diffusion mechanism along the channel in hydrous WO3 with 50% water composition, which is proper for water chain formation. The water chain in the channel serves as a possible diffusion media for hydronium (H3O +) . With the continuous formation and cleavage of hydrogen bonds in the channel, the hydronium diffuses by hydrogen bonds exchange between water molecules. This mechanism is very similar with Grotthuss relay mechanism for proton transport in liquid. The possible proton diffusion were studied for hydronium is either far away from the water chain bond defect or next to H2O defect at the end of water chain. The diffusion barriers for both conditions are around 150 meV to 200 meV, and water defects reorganization in the chain is the rate-limited step for proton diffusion. These small diffusion barriers could explain the fast 1-D proton transport in hydrous WO3 channel. Further studies about fast proton transport in other inorganic materials could be an important topic in not only biochemistry but also clean energy applications like fuel cell applications.

First-Principles Study of MoO3/Graphene Composite as Cathode Material for High-Performance Lithium-Ion Batteries

NASA Astrophysics Data System (ADS)

Cui, Yanhua; Zhao, Yu; Chen, Hong; Wei, Kaiyuan; Ni, Shuang; Cui, Yixiu; Shi, Siqi

2018-03-01

Using first-principles calculations, we have systematically investigated the adsorption and diffusion behavior of Li in MoO3 bulk, on MoO3 (010) surface and in MoO3/graphene composite. Our results indicate that, in case of MoO3 bulk, Li diffusion barriers in the interlayer and intralayer spaces are 0.55 eV and 0.58 eV respectively, which are too high to warrant fast Lithium-ion charge/discharge processes. While on MoO3 (010) surface, Li exhibits a diffusion barrier as low as 0.07 eV which guarantees an extremely fast Li diffusion rate during charge/discharge cycling. However, in MoO3/graphene monolayer, Li diffusion barrier is at the same level as that on MoO3 (010) surface, which also ensures a very rapid Li charge/discharge rate. The rapid Li charge/discharge rate in this system originates from the removal of the upper dangling O1 atoms which hinder the Li diffusion on the lower MoO3 layer. Besides this, due to the interaction between Li and graphene, the Li average binding energy increases to 0.14 eV compared to its value on MoO3 (010) surface which contributes to a higher voltage. Additionally, the increased ratio of surface area provides more space for Li storage and the capacity of MoO3/graphene composite increases up to 279.2 mAhg-1. The last but not the least, due to the high conductivity of graphene, the conductivity of MoO3/graphene composite enhances greatly which is beneficial for electrode materials. In the light of present results, MoO3/graphene composite exhibits higher voltage, good conductivity, large Li capacity and very rapid Li charge/discharge rate, which prove it as a promising cathode material for high-performance lithium-ion batteries (LIBs).

Posttraumatic Stress Symptom Severity and Cognitive-Based Smoking Processes Among Trauma-Exposed Treatment-Seeking Smokers: The Role of Perceived Stress

PubMed Central

Garey, Lorra; Bakhshaie, Jafar; Vujanovic, Anka A.; Reitzel, Lorraine R.; Schmidt, Norman B.; Zvolensky, Michael J.

2016-01-01

Trauma exposure and smoking co-occur at an alarmingly high rate. However, there is little understanding of the mechanisms underlying this clinically significant relation. The present study examined perceived stress as an explanatory mechanism linking posttraumatic stress symptom severity and smoking-specific avoidance/inflexibility, perceived barriers to smoking cessation, and negative affect reduction/negative reinforcement expectancies from smoking among trauma-exposed smokers. Participants were trauma-exposed, treatment-seeking daily cigarette smokers (n = 179; 48.0% female; Mage = 41.17; SD = 12.55). Results indicated that posttraumatic stress symptom severity had an indirect significant effect on each of the dependent variables via perceived stress. The present results provide empirical support that perceived stress may be an underlying mechanism that indirectly explains posttraumatic symptoms relation to smoking-specific avoidance/inflexibility, perceived barriers to smoking cessation, and negative affect reduction/negative reinforcement expectancies among trauma-exposed smokers. These findings suggest that there may be clinical utility in targeting perceived stress among trauma-exposed smokers via stress management psychoeducation and skills training. PMID:27100473

Fusion cross sections for reactions involving medium and heavy nucleus-nucleus systems

NASA Astrophysics Data System (ADS)

Atta, Debasis; Basu, D. N.

2014-12-01

Existing data on near-barrier fusion excitation functions of medium and heavy nucleus-nucleus systems have been analyzed by using a simple diffused-barrier formula derived assuming the Gaussian shape of the barrier-height distributions. The fusion cross section is obtained by folding the Gaussian barrier distribution with the classical expression for the fusion cross section for a fixed barrier. The energy dependence of the fusion cross section, thus obtained, provides good description to the existing data on near-barrier fusion and capture excitation functions for medium and heavy nucleus-nucleus systems. The theoretical values for the parameters of the barrier distribution are estimated which can be used for fusion or capture cross-section predictions that are especially important for planning experiments for synthesizing new superheavy elements.

Sex-Specific Alterations of White Matter Developmental Trajectories in Infants With Prenatal Exposure to Methamphetamine and Tobacco.

PubMed

Chang, Linda; Oishi, Kenichi; Skranes, Jon; Buchthal, Steven; Cunningham, Eric; Yamakawa, Robyn; Hayama, Sara; Jiang, Caroline S; Alicata, Daniel; Hernandez, Antonette; Cloak, Christine; Wright, Tricia; Ernst, Thomas

2016-12-01

Methamphetamine is a common illicit drug used worldwide. Methamphetamine and/or tobacco use by pregnant women remains prevalent. However, little is known about the effect of comorbid methamphetamine and tobacco use on human fetal brain development. To investigate whether microstructural brain abnormalities reported in children with prenatal methamphetamine and/or tobacco exposure are present at birth before childhood environmental influences. A prospective, longitudinal study was conducted between September 17, 2008, and February 28, 2015, at an ambulatory academic medical center. A total of 752 infant-mother dyads were screened and 139 of 195 qualified neonates were evaluated (36 methamphetamine/tobacco exposed, 32 tobacco exposed, and 71 unexposed controls). They were recruited consecutively from the community. Prenatal methamphetamine and/or tobacco exposure. Quantitative neurologic examination and diffusion tensor imaging performed 1 to 3 times through age 4 months; diffusivities and fractional anisotropy (FA) assessed in 7 white matter tracts and 4 subcortical brain regions using an automated atlas-based method. Of the 139 infants evaluated, 72 were female (51.8%); the mean (SE) postmenstrual age at baseline was 41.5 (0.27) weeks. Methamphetamine/tobacco-exposed infants showed delayed developmental trajectories on active muscle tone (group × age, P < .001) and total neurologic scores (group × age, P = .01) that normalized by ages 3 to 4 months. Only methamphetamine/tobacco-exposed boys had lower FA (group × age, P = .02) and higher diffusivities in superior (SCR) and posterior corona radiatae (PCR) (group × age × sex, P = .002; group × age × sex, P = .01) at baseline that normalized by age 3 months. Only methamphetamine/tobacco- and tobacco-exposed girls showed persistently lower FA in anterior corona radiata (ACR) (group, P = .04; group × age × sex, P = .01). Tobacco-exposed infants showed persistently lower axial diffusion in the thalamus and internal capsule across groups (P = .02). Prenatal methamphetamine/tobacco exposure may lead to delays in motor development, with less coherent fibers and less myelination in SCR and PCR only in male infants, but these abnormalities may normalize by ages 3 to 4 months after cessation of stimulant exposure. In contrast, persistently less coherent ACR fibers were observed in methamphetamine/tobacco- and tobacco-exposed girls, possibly from increased dendritic branching or spine density due to epigenetic influences. Persistently lower diffusivity in the thalamus and internal capsule of all tobacco-exposed infants suggests aberrant axonal development. Collectively, prenatal methamphetamine and/or tobacco exposure may lead to delayed motor development and white matter maturation in sex- and regional-specific manners.

The impact of aging on epithelial barriers.

PubMed

Parrish, Alan R

2017-10-02

The epithelium has many critical roles in homeostasis, including an essential responsibility in establishing tissue barriers. In addition to the fundamental role in separating internal from external environment, epithelial barriers maintain nutrient, fluid, electrolyte and metabolic waste balance in multiple organs. While, by definition, barrier function is conserved, the structure of the epithelium varies across organs. For example, the skin barrier is a squamous layer of cells with distinct structural features, while the lung barrier is composed of a very thin single cell to minimize diffusion space. With the increased focus on age-dependent alterations in organ structure and function, there is an emerging interest in the impact of age on epithelial barriers. This review will focus on the impact of aging on the epithelial barrier of several organs, including the skin, lung, gastrointestinal tract and the kidney, at a structural and functional level.

Matrix Metalloproteinase-Mediated Blood-Brain Barrier Dysfunction in Epilepsy.

PubMed

Rempe, Ralf G; Hartz, Anika M S; Soldner, Emma L B; Sokola, Brent S; Alluri, Satya R; Abner, Erin L; Kryscio, Richard J; Pekcec, Anton; Schlichtiger, Juli; Bauer, Björn

2018-05-02

The blood-brain barrier is dysfunctional in epilepsy, thereby contributing to seizure genesis and resistance to antiseizure drugs. Previously, several groups reported that seizures increase brain glutamate levels, which leads to barrier dysfunction. One critical component of barrier dysfunction is brain capillary leakage. Based on our preliminary data, we hypothesized that glutamate released during seizures mediates an increase in matrix-metalloproteinase (MMP) expression and activity levels, thereby contributing to barrier leakage. To test this hypothesis, we exposed isolated brain capillaries from male Sprague Dawley rats to glutamate ex vivo and used an in vivo / ex vivo approach of isolated brain capillaries from female Wistar rats that experienced status epilepticus as an acute seizure model. We found that exposing isolated rat brain capillaries to glutamate increased MMP-2 and MMP-9 protein and activity levels, and decreased tight junction protein levels, which resulted in barrier leakage. We confirmed these findings in vivo in rats after status epilepticus and in brain capillaries from male mice lacking cytosolic phospholipase A 2 Together, our data support the hypothesis that glutamate released during seizures signals an increase in MMP-2 and MMP-9 protein expression and activity levels, resulting in blood-brain barrier leakage. SIGNIFICANCE STATEMENT The mechanism leading to seizure-mediated blood-brain barrier dysfunction in epilepsy is poorly understood. In the present study, we focused on defining this mechanism in the brain capillary endothelium. We demonstrate that seizures trigger a pathway that involves glutamate signaling through cytosolic phospholipase A 2 , which increases MMP levels and decreases tight junction protein expression levels, resulting in barrier leakage. These findings may provide potential therapeutic avenues within the blood-brain barrier to limit barrier dysfunction in epilepsy and decrease seizure burden. Copyright © 2018 the authors 0270-6474/18/384301-15$15.00/0.

Microvillar Ca++ signaling: a new view of an old problem.

PubMed

Lange, K

1999-07-01

Proceeding from the recent finding that the main components of the Ca++ signal pathway are located in small membrane protrusions on the surface of differentiated cells, called microvilli, a novel concept of cellular Ca++ signaling was developed. The main features of this concept can be summarized as follows: Microvilli are formed on the cell surface of differentiating or resting cells from exocytic membrane domains, growing out from the cell surface by elongation of an internal bundle of actin filaments. The microvillar tip membranes contain all functional important proteins synthesized such as ion channels and transporters for energy-providing substrates and structural components, which are, in rapidly growing undifferentiated cells, distributed over the whole cell surface by lateral diffusion. The microvillar shaft structure, a bundle of actin filaments, forms a dense cytoskeletal matrix tightly covered by the microvillar lipid membrane and represents an effective diffusion barrier separating the microvillar tip compartment (entrance compartment) from the cytoplasm. This diffusion barrier prevents the passage of low molecular components such as Ca++ glucose and other relevant substrates from the entrance compartment into the cytoplasm. The effectiveness of the actin-based diffusion barrier is modulated by various signal pathways and effectors, most importantly, by the actin-depolymerizing/reorganizing activity of the phospholipase C (PLC)-coupled Ca++ signaling. Moreover, the microvillar bundle of actin filaments plays a dual role in Ca++ signaling. It combines the function of a diffusion barrier, preventing Ca++ influx into the resting cell, with that of a high-affinity, ATP-dependent, and IP3-sensitive Ca++ store. Activation of Ca++ signaling via PLC-coupled receptors simultaneously empties Ca++ stores and activates the influx of external Ca++. The presented concept of Ca++ signaling is compatible with all established data on Ca++ signaling. Properties of Ca++ signaling, that could not be reconciled with the basic principles of the current hypothesis, are intrinsic properties of the new concept. Quantal Ca++ release, Ca(++)-induced Ca++ release (CICR), the coupling phenomen between the filling state of the Ca++ store and the activity of the Ca++ influx pathway, as well as the various yet unexplained complex kinetics of Ca++ uptake and release can be explained on a common mechanistic basis.

Intracellular tortuosity underlies slow cAMP diffusion in adult ventricular myocytes.

PubMed

Richards, Mark; Lomas, Oliver; Jalink, Kees; Ford, Kerrie L; Vaughan-Jones, Richard D; Lefkimmiatis, Konstantinos; Swietach, Pawel

2016-06-01

3',5'-Cyclic adenosine monophosphate (cAMP) signals in the heart are often confined to concentration microdomains shaped by cAMP diffusion and enzymatic degradation. While the importance of phosphodiesterases (degradative enzymes) in sculpting cAMP microdomains is well established in cardiomyocytes, less is known about cAMP diffusivity (DcAMP) and factors affecting it. Many earlier studies have reported fast diffusivity, which argues against sharply defined microdomains. [cAMP] dynamics in the cytoplasm of adult rat ventricular myocytes were imaged using a fourth generation genetically encoded FRET-based sensor. The [cAMP]-response to the addition and removal of isoproterenol (β-adrenoceptor agonist) quantified the rates of cAMP synthesis and degradation. To obtain a read out of DcAMP, a stable [cAMP] gradient was generated using a microfluidic device which delivered agonist to one half of the myocyte only. After accounting for phosphodiesterase activity, DcAMP was calculated to be 32 µm(2)/s; an order of magnitude lower than in water. Diffusivity was independent of the amount of cAMP produced. Saturating cAMP-binding sites with the analogue 6-Bnz-cAMP did not accelerate DcAMP, arguing against a role of buffering in restricting cAMP mobility. cAMP diffused at a comparable rate to chemically unrelated but similar sized molecules, arguing for a common physical cause of restricted diffusivity. Lower mitochondrial density and order in neonatal cardiac myocytes allowed for faster diffusion, demonstrating the importance of mitochondria as physical barriers to cAMP mobility. In adult cardiac myocytes, tortuosity due to physical barriers, notably mitochondria, restricts cAMP diffusion to levels that are more compatible with microdomain signalling. © The Author 2016. Published by Oxford University Press on behalf of the European Society of Cardiology.

Effects of fluorine incorporation into β-Ga2O3

NASA Astrophysics Data System (ADS)

Yang, Jiangcheng; Fares, Chaker; Ren, F.; Sharma, Ribhu; Patrick, Erin; Law, Mark E.; Pearton, S. J.; Kuramata, Akito

2018-04-01

β-Ga2O3 rectifiers fabricated on lightly doped epitaxial layers on bulk substrates were exposed to CF4 plasmas. This produced a significant decrease in Schottky barrier height relative to unexposed control diodes (0.68 eV compared to 1.22 eV) and degradation in ideality factor (2.95 versus 1.01 for the control diodes). High levels of F (>1022 cm-3) were detected in the near-surface region by Secondary Ion Mass Spectrometry. The diffusion of fluorine into the Ga2O3 was thermally activated with an activation energy of 1.24 eV. Subsequent annealing in the range 350-400 °C brought recovery of the diode characteristics and an increase in barrier height to a value larger than in the unexposed control diodes (1.36 eV). Approximately 70% of the initial F was removed from the Ga2O3 by 400 °C, with the surface outgas rate also being thermally activated with an activation energy of 1.23 eV. Very good fits to the experimental data were obtained by integrating physics of the outdiffusion mechanisms into the Florida Object Oriented Process Simulator code and assuming that the outgas rate from the surface was mediated through fluorine molecule formation. The fluorine molecule forward reaction rate had an activation energy of 1.24 eV, while the reversal rate of this reaction had an activation energy of 0.34 eV. The net carrier density in the drift region of the rectifiers decreased after CF4 exposure and annealing at 400 °C. The data are consistent with a model in which near-surface plasma-induced damage creates degraded Schottky barrier characteristics, but as the samples are annealed, this damage is removed, leaving the compensation effect of Si donors by F- ions. The barrier lowering and then enhancement are due to the interplay between surface defects and the chemical effects of the fluorine.

Thermionic emission current in a single barrier varactor

NASA Technical Reports Server (NTRS)

Hjelmgren, Hans; East, Jack; Kollberg, Erik

1992-01-01

From I-V measurements on Single Barrier Varactors (SBV) at different temperatures we concluded that thermionic emission across the barrier of the actual device is mainly due to transport through the X band. The same structure was also modeled with a one-dimensional drift-diffusion model, including a 'boundary condition' for thermionic emission across the heterojunction interface. By including thermionic field emission through the top of the triangular barrier of a biased diode and the effect of a non-abrupt interface at the heterojunction, we obtained good agreement between the modeled and measured I-V characteristics.

Molecular assemblies as protective barriers and adhesion promotion interlayer

DOEpatents

King, D.E.; Czanderna, A.W.; Kennedy, C.E.

1996-01-30

A protective diffusion barrier having adhesive qualities for metalized surfaces is provided by a passivating agent having the formula HS--(CH{sub 2}){sub 11}--COOH which forms a very dense, transparent organized molecular assembly or layer that is impervious to water, alkali, and other impurities and corrosive substances that typically attack metal surfaces. 8 figs.

A stepwise mechanism for the permeation of phloretin through a lipid bilayer

PubMed Central

1982-01-01

The thermodynamics of interactions between phloretin and a phosphatidylcholine (PC) vesicle membrane are characterized using equilibrium spectrophotometric titration, stopped-flow, and temperature- jump techniques. Binding of phloretin to a PC vesicle membrane is diffusion limited, with an association rate constant greater than 10(8) M-1s-1, and an interfacial activation free energy of less than 2 kcal/mol. Equilibrium binding of phloretin to a vesicle membrane is characterized by a single class of high-affinity (8 micro M), noninteracting sites. Binding is enthalpy driven (delta H = -4.9 kcal/mol) at 23 degrees C. Analysis of amplitudes of kinetic processes shows that 66 +/- 3% of total phloretin binding sites are exposed at the external vesicle surface. The rate of phloretin movement between binding sites located near the external and internal interfaces is proportional to the concentration of un-ionized phloretin, with a rate constant of 5.7 X 10(4) M-1s-1 at 23 degrees C. The rate of this process is limited by a large enthalpic (9 kcal/mol) and entropic (-31 entropy units) barrier. An analysis of the concentration dependence of the rate of transmembrane movement suggests the presence of multiple intramembrane potential barriers. Permeation of phloretin through a lipid bilayer is modeled quantitatively in terms of discrete steps: binding to a membrane surface, translocation across a series of intramembrane barriers, and dissociation from the opposite membrane surface. The permeability coefficient for phloretin is calculated as 1.9 X 10(-3) cm/s on the basis of the model presented. Structure- function relationships are examined for a number of phloretin analogues. PMID:7142954

Thermal conductivity of zirconia thermal barrier coatings

NASA Technical Reports Server (NTRS)

Dinwiddie, R. B.; Beecher, S. C.; Nagaraj, B. A.; Moore, C. S.

1995-01-01

Thermal barrier coatings (TBC's) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBC's is of primary importance. Physical vapor description (PVD) and plasma spraying (PS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The PS coatings were applied with either standard power or hollow sphere particles. The hollow sphere particles yielded a lower density and lower thermal conductivity coating. The thermal conductivity of both fully and partially stabilized zirconia, before and after thermal aging, will be compared. The thermal conductivity of the coatings permanently increase upon being exposed to high temperatures. These increases are attributed to microstructural changes within the coatings. Sintering of the as fabricated plasma sprayed lamellar structure is observed by scanning electron microscopy of coatings isothermally heat treated at temperatures greater than 1100 C. During this sintering process the planar porosity between lamella is converted to a series of small spherical pores. The change in pore morphology is the primary reason for the observed increase in thermal conductivity. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the PVD coatings are less susceptible to thermal aging effects, preliminary results suggest that they have a higher thermal conductivity than PS coatings, both before and after thermal aging. The increases in thermal conductivity due to thermal aging for partially stabilized plasma sprayed zirconia have been found to be less than for fully stabilized plasma sprayed zirconia coatings. The high temperature thermal diffusivity data indicates that if these coatings reach a temperature above 1100 C during operation, they will begin to lose their effectiveness as a thermal barrier.

Thermal conductivity of zirconia thermal barrier coatings

NASA Technical Reports Server (NTRS)

Dinwiddie, R. B.; Beecher, S. C.; Nagaraj, B. A.; Moore, C. S.

1995-01-01

Thermal barrier coatings (TBC's) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBC's is of primary importance. Physical vapor deposition (PVD) and plasma spraying (PS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The PS coatings were applied with either standard powder or hollow sphere particles. The hollow sphere particles yielded a lower density and lower thermal conductivity coating. The thermal conductivity of both fully and partially stabilized zirconia, before and after thermal aging, will be compared. The thermal conductivity of the coatings permanently increases upon exposed to high temperatures. These increases are attributed to microstructural changes within the coatings. Sintering of the as-fabricated plasma sprayed lamellar structure is observed by scanning electron microscopy of coatings isothermally heat treated at temperatures greater than 1100 C. During this sintering process the planar porosity between lamella is converted to a series of small spherical pores. The change in pore morphology is the primary reason for the observed increase in thermal conductivity. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the PVD coatings are less susceptible to thermal aging effects, preliminary results suggest that they have a higher thermal conductivity than PS coatings, both before and after thermal aging. The increases in thermal conductivity due to thermal aging for partially stabilized plasma sprayed zirconia have been found to be less than for fully stabilized plasma sprayed zirconia coatings. The high temperature thermal diffusivity data indicate that if these coatings reach a temperature above 1100 C during operation, they will begin to lose their effectiveness as a thermal barrier.

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.

Diffusion anisotropy of poor metal solute atoms in hcp-Ti

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

Scotti, Lucia, E-mail: lxs234@bham.ac.uk; Mottura, Alessandro, E-mail: a.mottura@bham.ac.uk

2015-05-28

Atom migration mechanisms influence a wide range of phenomena: solidification kinetics, phase equilibria, oxidation kinetics, precipitation of phases, and high-temperature deformation. In particular, solute diffusion mechanisms in α-Ti alloys can help explain their excellent high-temperature behaviour. The purpose of this work is to study self- and solute diffusion in hexagonal close-packed (hcp)-Ti, and its anisotropy, from first-principles using the 8-frequency model. The calculated diffusion coefficients show that diffusion energy barriers depend more on bonding characteristics of the solute rather than the size misfit with the host, while the extreme diffusion anisotropy of some solute elements in hcp-Ti is a resultmore » of the bond angle distortion.« less

Nanolaminates with Novel Properties Fabricated Using Atomic Layer Deposition Techniques

DTIC Science & Technology

2006-07-01

Enhance X-Ray Reflectivity of Polysilicon Micro-Mirrors at 1.54 A Wavelength", Proceedings of SPIE 5720, 241-251 (2005). 20. D.C. Miller, C.F...diodes ( OLEDs ). This project has demonstrated that the A120 3 ALD gas diffusion barrier helps to prevent H20 and 02 gases from diffusing through the

Measurement of N-Type 6H SiC Minority-Carrier Diffusion Lengths by Electron Bombardment of Schottky Barriers

NASA Technical Reports Server (NTRS)

Hubbard, S. M.; Tabib-Azar, M.; Balley, S.; Rybickid, G.; Neudeck, P.; Raffaelle, R.

2004-01-01

Minority-Carrier diffusion lengths of n-type 6H-SiC were measured using the electron-beam induced current (EBIC) technique. Experimental values of primary beam current, EBIC, and beam voltage were obtained for a variety of SIC samples. This data was used to calculate experimental diode efficiency vs. beam voltage curves. These curves were fit to theoretically calculated efficiency curves, and the diffusion length and metal layer thickness were extracted. The hole diffusion length in n-6H SiC ranged from 0.93 +/- 0.15 microns.

Fibroblast Growth Factor-Peptide Improves Barrier Function and Proliferation in Human Keratinocytes After Radiation

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

Zhang Kunzhong; Tian Yeping; Yin Liangjie

2011-09-01

Purpose: Epidermal keratinocytes, which can be severely damaged after ionizing radiation (IR), are rapid turnover cells that function as a barrier, protecting the host from pathogenic invasion and fluid loss. We tested fibroblast growth factor-peptide (FGF-P), a small peptide derived from the receptor-binding domain of FGF-2, as a potential mitigator of radiation effects via proliferation and the barrier function of keratinocytes. Methods and Materials: Keratinocytes isolated from neonatal foreskin were grown on transwells. After being exposed to 0, 5, or 10 Gy IR, the cells were treated with a vehicle or FGF-P. The permeability of IR cells was assessed bymore » using transepithelial electrical resistance (TEER) and a paracellular tracer flux of fluorescein isothiocyanate-conjugated bovine serum albumin (FITC-BSA) with Ussing chambers. The cell proliferation was measured with yellow tetrazolium salt (MTT) and tritiated thymidine ([{sup 3}H]-TdR) assays. The phosphorylation of extracellular signal-regulated kinases (ERK) was measured in an enzyme-linked immunosorbent (ELISA)-like assay, and the proteins related to tight junctions (TJ) and adherens junctions (AJ) were examined with Western blotting. We used a mouse model to assess the ability of FGF-P to promote the healing of skin {beta} burns created with a strontium applicator. Results: We found (1) FGF-P reduced the permeability of irradiated keratinocytes, as evidenced by increased TEER and decreased diffusion of FITC-BSA, both associated with the regulation of different proteins and levels of TJ and AJ; and (2) FGF-P enhanced the proliferation of irradiated keratinocytes, as evidenced by increased MTT activity and [{sup 3}H]-TdR incorporation, which was associated with activation of the ERK pathway; and (3) FGF-P promoted the healing of skin {beta} burns. Conclusions: FGF-P enhances the barrier function, including up-regulation of TJ proteins, increases proliferation of human keratinocytes, and accelerates the healing of skin {beta} burns. FGF-P is a promising mitigator that improves the proliferation and barrier function of keratinocytes after IR.« less

Outer-membrane translocation of bulky small molecules by passive diffusion

PubMed Central

van den Berg, Bert; Prathyusha Bhamidimarri, Satya; Dahyabhai Prajapati, Jigneshkumar; Kleinekathöfer, Ulrich; Winterhalter, Mathias

2015-01-01

The outer membrane (OM) of gram-negative bacteria forms a protective layer around the cell that serves as a permeability barrier to prevent unrestricted access of noxious substances. The permeability barrier of the OM results partly from the limited pore diameters of OM diffusion channels. As a consequence, there is an “OM size-exclusion limit,” and the uptake of bulky molecules with molecular masses of more than ∼600 Da is thought to be mediated by TonB-dependent, active transporters. Intriguingly, the OM protein CymA from Klebsiella oxytoca does not depend on TonB but nevertheless mediates efficient OM passage of cyclodextrins with diameters of up to ∼15 Å. Here we show, by using X-ray crystallography, molecular dynamics simulations, and single-channel electrophysiology, that CymA forms a monomeric 14-stranded β-barrel with a large pore that is occluded on the periplasmic side by the N-terminal 15 residues of the protein. Representing a previously unidentified paradigm in OM transport, CymA mediates the passive diffusion of bulky molecules via an elegant transport mechanism in which a mobile element formed by the N terminus acts as a ligand-expelled gate to preserve the permeability barrier of the OM. PMID:26015567

Cell based metabolic barriers to glucose diffusion: macrophages and continuous glucose monitoring.

PubMed

Klueh, Ulrike; Frailey, Jackman T; Qiao, Yi; Antar, Omar; Kreutzer, Donald L

2014-03-01

It is assumed that MQ are central to glucose sensor bio-fouling and therefore have a major negative impact on continuous glucose monitoring (CGM) performance in vivo. However to our knowledge there is no data in the literature to directly support or refute this assumption. Since glucose and oxygen (O2) are key to glucose sensor function in vivo, understanding and controlling glucose and O2 metabolic activity of MQ is likely key to successful glucose sensor performance. We hypothesized that the accumulation of MQ at the glucose sensor-tissue interface will act as "Cell Based Metabolic Barriers" (CBMB) to glucose diffusing from the interstitial tissue compartment to the implanted glucose sensor and as such creating an artificially low sensor output, thereby compromising sensor function and CGM. Our studies demonstrated that 1) direct injections of MQ at in vivo sensor implantation sites dramatically decreased sensor output (measured in nA), 2) addition of MQ to glucose sensors in vitro resulted in a rapid and dramatic fall in sensor output and 3) lymphocytes did not affect sensor function in vitro or in vivo. These data support our hypothesis that MQ can act as metabolic barriers to glucose and O2 diffusion in vivo and in vitro. Copyright © 2014 Elsevier Ltd. All rights reserved.

Containing diffusion: the tobacco industry's multipronged trade strategy to block tobacco standardised packaging.

PubMed

Crosbie, Eric; Eckford, Robert; Bialous, Stella

2018-04-21

To analyse the tobacco industry's strategy of using trade and investment agreements to prevent the global diffusion of standardised packaging (SP) of tobacco products. Review of tobacco industry documents, relevant government documents and media items. The data were triangulated and thematically analysed. Internal tobacco industry documents reveal that during the early 1990s, tobacco companies developed a multipronged trade strategy to prevent the global diffusion of progressive tobacco packaging and labelling proposals, including SP. This strategy consisted of (1) framing the health issue in terms of trade and investment, (2) detailing alleged legal violations concerning trade barriers, intellectual property and investment rights, (3) threatening legal suits and reputational damage, and (4) garnering third-party support. These efforts helped delay SP until 2010 when Australia became the first country to reintroduce SP proposals, followed by governments in the UK and New Zealand in 2012, Ireland in 2013 and France in 2014. Review of government documents and media sources in each of the five countries indicate the industry continues to employ this multipronged strategy throughout the SP policy's progression. Although this strategy is tailored towards each domestic context, the overall tobacco industry's trade strategy remains consistently focused on shifting the attention away from public health and towards the realm of trade and investment with more corporate-friendly allies. Governments seeking to implement SP need to be prepared to resist and counter the industry's multipronged trade strategy by avoiding trade diversions, exposing false industry legal and reputational claims, and monitoring third-party support. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Diminished Mercury Emission From Water Surfaces by Duckweed (Lemna minor)

NASA Astrophysics Data System (ADS)

Wollenberg, J. L.; Peters, S. C.

2007-12-01

Aquatic plants of the family Lemnaceae (generally referred to as duckweeds) are a widely distributed type of floating vegetation in freshwater systems. Under suitable conditions, duckweeds form a dense vegetative mat on the water surface, which reduces light penetration into the water column and decreases the amount of exposed water surface. These two factors would be expected to reduce mercury emission by limiting a) direct photoreduction of Hg(II), b) indirect reduction via coupled DOC photooxidation-Hg(II) reduction, and c) gas diffusion across the water-air interface. Conversely, previous studies have demonstrated transpiration of Hg(0) by plants, so it is therefore possible that the floating vegetative mat would enhance emission via transpiration of mercury vapor. The purpose of this experiment was to determine whether duckweed limits mercury flux to the atmosphere by shading and the formation of a physical barrier to diffusion, or whether it enhances emission from aquatic systems via transpiration of Hg(0). Deionized water was amended with mercury to achieve a final concentration of approximately 35 ng/L and allowed to equilibrate prior to the experiment. Experiments were conducted in rectangular polystyrene flux chambers with measured UV-B transmittance greater than 60% (spectral cutoff approximately 290 nm). Light was able to penetrate the flux chamber from the sides as well as the top throughout the experiment, limiting the effect of shading by duckweed on the water surface. Flux chambers contained 8L of water with varying percent duckweed cover, and perforated plastic sheeting was used as an abiotic control. Exposures were conducted outside on days with little to no cloud cover. Real time mercury flux was measured using atomic absorption (Mercury Instruments UT-3000). Total solar and ultraviolet radiation, as well as a suite of meteorological parameters, were also measured. Results indicate that duckweed diminishes mercury emission from the water surface as compared to open water controls. Decreases in emission rate varied linearly with percent duckweed cover, with lower fluxes occurring at higher percent cover. Mercury flux in the duckweed treatments as compared to open water treatments decreased from 17% in the lowest percent cover treatment to 67% in the highest percent cover treatment. The observed decrease in mercury emission suggests that duckweed limits emission via the formation of a physical barrier to diffusion.

The Effects of Vegetation Barriers on Near-road Ultrafine Particle Number and Carbon Monoxide Concentrations

EPA Science Inventory

Numerous studies have shown that people living in near-roadway communities (within 100 m of the road) are exposed to high ultrafine particle (UFP) number concentrations, which may be associated with adverse health effects. Vegetation barriers have been shown to affect pollutant t...

Barriers to Physical Activity for People with Long-Term Neurological Conditions: A Review Study

ERIC Educational Resources Information Center

Mulligan, Hilda F.; Hale, Leigh A.; Whitehead, Lisa; Baxter, G. David

2012-01-01

People with disability are insufficiently physically active for health. This study identified the volume, quality, and findings of research that exposes environmental and personal barriers of physical activity participation for people with neurological conditions. CINAHL, Sport Discus, EMBASE, Medline, and AMED were systematically searched between…

Vocal Fold Epithelial Barrier in Health and Injury: A Research Review

ERIC Educational Resources Information Center

Levendoski, Elizabeth Erickson; Leydon, Ciara; Thibeault, Susan L.

2014-01-01

Purpose: Vocal fold epithelium is composed of layers of individual epithelial cells joined by junctional complexes constituting a unique interface with the external environment. This barrier provides structural stability to the vocal folds and protects underlying connective tissue from injury while being nearly continuously exposed to potentially…

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.

The NASA/DOD aerospace knowledge diffusion research project: A research agenda

NASA Technical Reports Server (NTRS)

Pinelli, Thomas E.; Kennedy, John M.

1990-01-01

The project has both immediate and long term purposes. In the first instance it provides a practical and pragmatic basis for understanding how the results of NASA/DoD research diffuse into the aerospace R and D process. Over the long term it provides an empirical basis for understanding the aerospace knowledge diffusion process itself, and its implications at the individual, organizational, national, and international levels. The project is studying the major barriers to effective knowledge diffusion. This project will provide descriptive and analytical data regarding the flow of scientific and technical information (STI). It will examine both channels used to communicate information and the social system of the aerospace knowledge diffusion process.

Lung injury induced by secondhand smoke exposure detected with hyperpolarized helium-3 diffusion MR.

PubMed

Wang, Chengbo; Mugler, John P; de Lange, Eduard E; Patrie, James T; Mata, Jaime F; Altes, Talissa A

2014-01-01

To determine whether helium-3 diffusion MR can detect the changes in the lungs of healthy nonsmoking individuals who were regularly exposed to secondhand smoke. Three groups were studied (age: 59 ± 9 years): 23 smokers, 37 exposure-to-secondhand-smoke subjects, and 29 control subjects. We measured helium-3 diffusion values at diffusion times from 0.23 to 1.97 s. One-way analysis of variance revealed that the mean area under the helium-3 diffusion curves (ADC AUC) of the smokers was significantly elevated compared with the controls and to the exposure-to-secondhand-smoke subjects (P < 0.001 both). No difference between the mean ADC AUC of the exposure-to-secondhand-smoke subjects and that of the controls was found (P = 0.115). However, application of a receiver operator characteristic-derived rule to classify subjects as either a "control" or a "smoker," based on ADC AUC, revealed that 30% (11/37) of the exposure-to-secondhand subjects were classified as "smokers" indicating an elevation of the ADC AUC. Using helium-3 diffusion MR, elevated ADC values were detected in 30% of nonsmoking healthy subjects who had been regularly exposed to secondhand smoke, supporting the concept that, in susceptible individuals, secondhand smoke causes mild lung damage. Copyright © 2013 Wiley Periodicals, Inc.

High Interfacial Barriers at Narrow Carbon Nanotube-Water Interfaces.

PubMed

Varanasi, Srinivasa Rao; Subramanian, Yashonath; Bhatia, Suresh K

2018-06-26

Water displays anomalous fast diffusion in narrow carbon nanotubes (CNTs), a behavior that has been reproduced in both experimental and simulation studies. However, little is reported on the effect of bulk water-CNT interfaces, which is critical to exploiting the fast transport of water across narrow carbon nanotubes in actual applications. Using molecular dynamics simulations, we investigate here the effect of such interfaces on the transport of water across arm-chair CNTs of different diameters. Our results demonstrate that diffusion of water is significantly retarded in narrow CNTs due to bulk regions near the pore entrance. The slowdown of dynamics can be attributed to the presence of large energy barriers at bulk water-CNT interfaces. The presence of such intense barriers at the bulk-CNT interface arises due to the entropy contrast between the bulk and confined regions, with water molecules undergoing high translational and rotational entropy gain on entering from the bulk to the CNT interior. The intensity of such energy barriers decreases with increase in CNT diameter. These results are very important for emerging technological applications of CNTs and other nanoscale materials, such as in nanofluidics, water purification, nanofiltration, and desalination, as well as for biological transport processes.

Barrier Coatings for Refractory Metals and Superalloys

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

SM Sabol; BT Randall; JD Edington

2006-02-23

In the closed working fluid loop of the proposed Prometheus space nuclear power plant (SNPP), there is the potential for reaction of core and plant structural materials with gas phase impurities and gas phase transport of interstitial elements between superalloy and refractory metal alloy components during service. Primary concerns are surface oxidation, interstitial embrittlement of refractory metals and decarburization of superalloys. In parallel with kinetic investigations, this letter evaluates the ability of potential coatings to prevent or impede communication between reactor and plant components. Key coating requirements are identified and current technology coating materials are reviewed relative to these requirements.more » Candidate coatings are identified for future evaluation based on current knowledge of design parameters and anticipated environment. Coatings were identified for superalloys and refractory metals to provide diffusion barriers to interstitial transport and act as reactive barriers to potential oxidation. Due to their high stability at low oxygen potential, alumina formers are most promising for oxidation protection given the anticipated coolant gas chemistry. A sublayer of iridium is recommended to provide inherent diffusion resistance to interstitials. Based on specific base metal selection, a thin film substrate--coating interdiffusion barrier layer may be necessary to meet mission life.« less

Effect of polyethyleneimine modified graphene on the mechanical and water vapor barrier properties of methyl cellulose composite films.

PubMed

Liu, Hongyu; Liu, Cuiyun; Peng, Shuge; Pan, Bingli; Lu, Chang

2018-02-15

A series of novel methyl cellulose (MC) composite films were prepared using polyethyleneimine reduced graphene oxide (PEI-RGO) as an effective filler for water vapor barrier application. The as-prepared PEI-RGO/MC composites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, tensile test and scanning electron microscopy. The experimental and theoretical results exhibited that PEI-RGO was uniformly dispersed in the MC matrix without aggregation and formed an aligned dispersion. The addition of PEI-RGO resulted in an enhanced surface hydrophobicity and a tortuous diffusion pathway for water molecules. Water vapor permeability of PEI-RGO/MC with loading of 3.0% of surface modified graphene was as low as 5.98×10 -11 gmm -2 s -1 Pa -1 . The synergistic effects of enhanced surface hydrophobicity and tortuous diffusion pathway were accounted for the improved water vapor barrier performance of the PEI-RGO/MC composite films. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tunneling-Magnetoresistance Ratio Comparison of MgO-Based Perpendicular-Magnetic-Tunneling-Junction Spin Valve Between Top and Bottom Co2Fe6B2 Free Layer Structure.

PubMed

Lee, Du-Yeong; Lee, Seung-Eun; Shim, Tae-Hun; Park, Jea-Gun

2016-12-01

For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.

Analytical investigation of thermal barrier coatings for advanced power generation combustion turbines

NASA Technical Reports Server (NTRS)

Amos, D. J.

1977-01-01

An analytical evaluation was conducted to determine quantitatively the improvement potential in cycle efficiency and cost of electricity made possible by the introduction of thermal barrier coatings to power generation combustion turbine systems. The thermal barrier system, a metallic bond coat and yttria stabilized zirconia outer layer applied by plasma spray techniques, acts as a heat insulator to provide substantial metal temperature reductions below that of the exposed thermal barrier surface. The study results show the thermal barrier to be a potentially attractive means for improving performance and reducing cost of electricity for the simple, recuperated, and combined cycles evaluated.

Technical and Economical Aspects of Current Thermal Barrier Coating Systems for Gas Turbine Engines by Thermal Spray and EBPVD: A Review

NASA Astrophysics Data System (ADS)

Feuerstein, Albert; Knapp, James; Taylor, Thomas; Ashary, Adil; Bolcavage, Ann; Hitchman, Neil

2008-06-01

The most advanced thermal barrier coating (TBC) systems for aircraft engine and power generation hot section components consist of electron beam physical vapor deposition (EBPVD) applied yttria-stabilized zirconia and platinum modified diffusion aluminide bond coating. Thermally sprayed ceramic and MCrAlY bond coatings, however, are still used extensively for combustors and power generation blades and vanes. This article highlights the key features of plasma spray and HVOF, diffusion aluminizing, and EBPVD coating processes. The coating characteristics of thermally sprayed MCrAlY bond coat as well as low density and dense vertically cracked (DVC) Zircoat TBC are described. Essential features of a typical EBPVD TBC coating system, consisting of a diffusion aluminide and a columnar TBC, are also presented. The major coating cost elements such as material, equipment and processing are explained for the different technologies, with a performance and cost comparison given for selected examples.

Escape rate of Brownian particles from a metastable potential well under time derivative Ornstein-Uhlenbeck noise

NASA Astrophysics Data System (ADS)

Bai, Zhan-Wu; Wang, Ping

2016-03-01

We investigate the escape rate of Brownian particles that move in a cubic metastable potential subjected to an internal time derivative Ornstein-Uhlenbeck noise (DOUN). This noise can induce the ballistic diffusion of force-free Brownian particles. Some new features are found. The escape rate for DOUN shows qualitative different dependence on potential well width compared with OUN which induces normal diffusion. As the potential barrier height decreases, the escape rate of DOUN deviates from Arrhenius law considerably earlier than that of Ornstein-Uhlenbeck noise (OUN). The Brownian particles escape faster under DOUN than that under OUN. A quasi-periodic oscillation occurs in transient state. A solvable case is presented to demonstrate the significant cancellation behavior in the barrier region that governs most of these phenomena. The physical mechanism of the findings can be clarified by the noise features. These characteristics should be common for internal noises that induce superdiffusion, especially the ballistic diffusion.

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.

Effects of Stereotypes about Feminists on Feminist Self-Identification

ERIC Educational Resources Information Center

Roy, Robin E.; Weibust, Kristin S.; Miller, Carol T.

2007-01-01

This study examined whether negative stereotypes about feminists serve as a barrier to self-identifying as a feminist. College women were exposed to positive stereotypes about feminists, negative stereotypes about feminists, or were not exposed to stereotypes about feminists (control condition) in a between-participants design. Women who read a…

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.

Pyridine adsorption and diffusion on Pt(111) investigated with density functional theory

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

Kolsbjerg, Esben L.; Groves, Michael N.; Hammer, Bjørk, E-mail: hammer@phys.au.dk

2016-04-28

The adsorption, diffusion, and dissociation of pyridine, C{sub 5}H{sub 5}N, on Pt(111) are investigated with van der Waals-corrected density functional theory. An elaborate search for local minima in the adsorption potential energy landscape reveals that the intact pyridine adsorbs with the aromatic ring parallel to the surface. Piecewise interconnections of the local minima in the energy landscape reveal that the most favourable diffusion path for pyridine has a barrier of 0.53 eV. In the preferred path, the pyridine remains parallel to the surface while performing small single rotational steps with a carbon-carbon double bond hinged above a single Pt atom.more » The origin of the diffusion pathway is discussed in terms of the C{sub 2}–Pt π-bond being stronger than the corresponding CN–Pt π-bond. The energy barrier and reaction enthalpy for dehydrogenation of adsorbed pyridine into an adsorbed, upright bound α-pyridyl species are calculated to 0.71 eV and 0.18 eV, respectively (both zero-point energy corrected). The calculations are used to rationalize previous experimental observations from the literature for pyridine on Pt(111).« less

Ab initio study of novel carbon nanofoam structure as an anode material for Li secondary battery

NASA Astrophysics Data System (ADS)

Park, Hanjin; Park, Sora; Kang, Seoung-Hun; Kwon, Young-Kyun

2014-03-01

Using ab inito density functional theory, we investigate the adsorption and diffusion properties of Li atoms on a new carbon nanostructure, which may be used as an anode of Li secondary battery. We focus on a special carbon nanofoam structure consisting of Schwarzite structures with negative Gaussian curvature as core parts, which are interconnected through (4,4) CNT segments. Considering the symmetry of the nanofoam structure, we find various Li adsorption sites exhibiting relatively large binding energies (>= 2 . 00 eV). Based on these adsorption sites, we identify several diffusion paths on the outside or inside surface of the nanofoam structure and examine the diffusion barriers along the paths. Our results show that Li atom can diffuse almost freely due to its low energy barriers on both outside and inside surfaces. Finally, we also evaluate the energy gain tendency and the volume expansion as well as the average binding energy while adding Li atoms to estimate the Li-capacity and recyclability of the system, which are important characterisitics for anode materials. We conclude that the carbon nanofoam structure would be better as an anode material than graphite in Li capacity and volume expansion.

Transition from diffuse to self-organized discharge in a high frequency dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Belinger, Antoine; Naudé, Nicolas; Gherardi, Nicolas

2017-05-01

Depending on the operating conditions, different regimes can be obtained in a dielectric barrier discharge (DBD): filamentary, diffuse (also called homogeneous) or self-organized. For a plane-to-plane DBD operated at high frequency (160 kHz) and at atmospheric pressure in helium gas, we show that the addition of a small amount of nitrogen induces a transition from the diffuse regime to a self-organized regime characterized by the appearance of filaments at the exit of the discharge. In this paper, we detail mechanisms that could be responsible of the transition from diffuse mode to this self-organized mode. We point out the critical role of the power supply and the importance of the gas memory effect from one discharge to the following one on the transition to the self-organised mode. The self-organized mode is usually attributed to a surface memory effect. In this work, we show an additional involvement of the gas memory effect on the self-organized mode. Contribution to the topical issue "The 15th International Symposium on High Pressure Low Temperature Plasma Chemistry (HAKONE XV)", edited by Nicolas Gherardi and Tomáš Hoder

Bond lifetime and diffusion coefficient in colloids with short-range interactions.

PubMed

Ndong Mintsa, E; Germain, Ph; Amokrane, S

2015-03-01

We use molecular dynamics simulations to study the influence of short-range structures in the interaction potential between hard-sphere-like colloidal particles. Starting from model potentials and effective potentials in binary mixtures computed from the Ornstein-Zernike equations, we investigate the influence of the range and strength of a possible tail beyond the usual core repulsion or the presence of repulsive barriers. The diffusion coefficient and mean "bond" lifetimes are used as indicators of the effect of this structure on the dynamics. The existence of correlations between the variations of these quantities with the physical parameters is discussed to assess the interpretation of dynamics slowing down in terms of long-lived bonds. We also discuss the question of a universal behaviour determined by the second virial coefficient B ((2)) and the interplay of attraction and repulsion. While the diffusion coefficient follows the B ((2)) law for purely attractive tails, this is no longer true in the presence of repulsive barriers. Furthermore, the bond lifetime shows a dependence on the physical parameters that differs from that of the diffusion coefficient. This raises the question of the precise role of bonds on the dynamics slowing down in colloidal gels.

Classification Order of Surface-Confined Intermixing at Epitaxial Interface

NASA Astrophysics Data System (ADS)

Michailov, M.

The self-organization phenomena at epitaxial interface hold special attention in contemporary material science. Being relevant to the fundamental physical problem of competing, long-range and short-range atomic interactions in systems with reduced dimensionality, these phenomena have found exacting academic interest. They are also of great technological importance for their ability to bring spontaneous formation of regular nanoscale surface patterns and superlattices with exotic properties. The basic phenomenon involved in this process is surface diffusion. That is the motivation behind the present study which deals with important details of diffusion scenarios that control the fine atomic structure of epitaxial interface. Consisting surface imperfections (terraces, steps, kinks, and vacancies), the interface offers variety of barriers for surface diffusion. Therefore, the adatoms and clusters need a certain critical energy to overcome the corresponding diffusion barriers. In the most general case the critical energies can be attained by variation of the system temperature. Hence, their values define temperature limits of system energy gaps associated with different diffusion scenarios. This systematization imply classification order of surface alloying: blocked, incomplete, and complete. On that background, two diffusion problems, related to the atomic-scale surface morphology, will be discussed. The first problem deals with diffusion of atomic clusters on atomically smooth interface. On flat domains, far from terraces and steps, we analyzed the impact of size, shape, and cluster/substrate lattice misfit on the diffusion behavior of atomic clusters (islands). We found that the lattice constant of small clusters depends on the number N of building atoms at 1 < N ≤ 10. In heteroepitaxy, this effect of variable lattice constant originates from the enhanced charge transfer and the strong influence of the surface potential on cluster atomic arrangement. At constant temperature, the variation of the lattice constant leads to variable misfit which affects the island migration. The cluster/substrate commensurability influences the oscillation behavior of the diffusion coefficient caused by variation in the cluster shape. We discuss the results in a physical model that implies cluster diffusion with size-dependent cluster/substrate misfit. The second problem is devoted to diffusion phenomena in the vicinity of atomic terraces on stepped or vicinal surfaces. Here, we develop a computational model that refines important details of diffusion behavior of adatoms accounting for the energy barriers at specific atomic sites (smooth domains, terraces, and steps) located on the crystal surface. The dynamic competition between energy gained by mixing and substrate strain energy results in diffusion scenario where adatoms form alloyed islands and alloyed stripes in the vicinity of terrace edges. Being in agreement with recent experimental findings, the observed effect of stripe and island alloy formation opens up a way regular surface patterns to be configured at different atomic levels on the crystal surface. The complete surface alloying of the entire interface layer is also briefly discussed with critical analysis and classification of experimental findings and simulation data.

COATED CARBON ELEMENT FOR USE IN NUCLEAR REACTORS AND THE PROCESS OF MAKING THE ELEMENT

DOEpatents

Pyle, R.J.; Allen, G.L.

1963-01-15

S>This patent relates to a carbide-nitride-carbide coating for carbon bodies that are to be subjected to a high temperature nuclear reactor atmosphere, and a method of applying the same. This coating is a highly efficient diffusion barrier and protects the C body from corrosion and erosion by the reactor atmosphere. Preferably, the innermost coating is Zr carbide, the middle coatlng is Zr nitride, and the outermost coating is a mixture of Zr and Nb carbide. The nitride coating acts as a diffusion barrier, while the innermost carbide bonds the nitride to the C body and prevents deleterious reaction between the nitride and C body. The outermost carbide coating protects the nitride coating from the reactor atmosphere. (AEC)

Convective diffusion of nanoparticles from the epithelial barrier toward regional lymph nodes.

PubMed

Dukhin, Stanislav S; Labib, Mohamed E

2013-11-01

Drug delivery using nanoparticles as drug carriers has recently attracted the attention of many investigators. Targeted delivery of nanoparticles to the lymph nodes is especially important to prevent cancer metastasis or infection, and to diagnose disease stage. However, systemic injection of nanoparticles often results in organ toxicity because they reach and accumulate in all the lymph nodes in the body. An attractive strategy would be to deliver the drug-loaded nanoparticles to a subset of draining lymph nodes corresponding to a specific site or organ to minimize systemic toxicity. In this respect, mucosal delivery of nanoparticles to regional draining lymph nodes of a selected site creates a new opportunity to accomplish this task with minimal toxicity. One example is the delivery of nanoparticles from the vaginal lumen to draining lymph nodes to prevent the transmission of HIV in women. Other known examples include mucosal delivery of vaccines to induce immunity. In all cases, molecular and particle transport by means of diffusion and convective diffusion play a major role. The corresponding transport processes have common inherent regularities and are addressed in this review. Here we use nanoparticle delivery from the vaginal lumen to the lymph nodes as an example to address the many aspects of associated transport processes. In this case, nanoparticles penetrate the epithelial barrier and move through the interstitium (tissue) to the initial lymphatics until they finally reach the lymph nodes. Since the movement of interstitial liquid near the epithelial barrier is retarded, nanoparticle transport was found to take place through special foci present in the epithelium. Immediately after nanoparticles emerge from the foci, they move through the interstitium due to diffusion affected by convection (convective diffusion). Specifically, the convective transport of nanoparticles occurs due to their convection together with interstitial fluid through the interstitium toward the initial lymph capillaries. Afterwards, nanoparticles move together with the lymph flow along the initial lymph capillaries and then enter the afferent lymphatics and ultimately reach the lymph node. As the liquid moves through the interstitium toward the initial lymph capillaries due to the axial movement of lymph along the lymphatics, the theory for coupling between lymph flow and concomitant flow through the interstitium is developed to describe this general case. The developed theory is applied to interpret the large uptake of Qdots by lymph nodes during inflammation, which is induced by pre-treating mouse vagina with the surfactant Nonoxynol-9 prior to instilling the Qdots. Inflammation is viewed here to cause broadening of the pores within the interstitium with the concomitant formation of transport channels which function as conduits to transport the nanoparticles to the initial lymph capillaries. We introduced the term "effective channels" to denote those channels which interconnect with foci present in the epithelial barrier and which function to transport nanoparticles to initial lymph capillaries. The time of transport toward the lymph node, predicated by the theory, increases rapidly with increasing the distance y0 between the epithelial barrier and the initial lymph capillaries. Transport time is only a few hours, when y0 is small, about some R (where R is the initial lymph capillary radius), due to the predomination of a rather rapid convection in this case. This transport time to the lymph nodes may be tens of hours (or longer) when y0 is essentially larger and the slow diffusion controls the transport rate in a zone not far from the epithelial barrier, where convection is weak at large y0. Accounting for transport by diffusion only, which is mainly considered in many relevant publications, is not sufficient to explain our nanoparticle uptake kinetics because the possibility of fast transport due to convection is overlooked. Our systematic investigations have revealed that the information about the main transport conditions, namely, y0 and the pore broadening up to the dimension of the interstitial transport channels, is necessary to create the quantitative model of enhanced transport during inflammation with the use of the proposed model as a prerequisite. The modeling for convective diffusion of nanoparticles from the epithelial barrier to the lymph node has been mainly accomplished here, while the diffusion only scenario is accounted for in other studies. This first modeling is a semi-quantitative one. A more rigorous mathematical approach is almost impossible at this stage because the transport properties of the model are introduced here for the first time. These properties include: discovery of foci in the epithelium, formation of transport channels, definition of channels interconnecting with foci (effective foci and channels), generation of flow in the interstitium toward the initial lymph capillaries due to axial flow within afferent lymphatics, deformation of this flow due to hydrodynamic impermeability of the squamous layer with the formation of the hydrodynamic stagnation zone near the epithelial barrier, predomination of slow diffusion transport within the above zone, and predomination of fast convection of nanoparticles near the initial lymph capillaries. Copyright © 2013 Elsevier B.V. All rights reserved.

Convective diffusion of nanoparticles from the epithelial barrier towards regional lymph nodes

PubMed Central

Dukhin, Stanislav S; Labib, Mohamed E.

2013-01-01

Drug delivery using nanoparticles as drug carriers has recently attracted the attention of many investigators. Targeted delivery of nanoparticles to lymph nodes is especially important to prevent cancer metastasis or infection, and to diagnose disease stage. However, systemic injection of nanoparticles often results in organ toxicity because they reach and accumulate in all the lymph nodes in the body. An attractive strategy would be to deliver the drug-loaded nanoparticles to a subset of draining lymph nodes corresponding to a specific site or organ to minimize systemic toxicity. In this respect, mucosal delivery of nanoparticles to regional draining lymph nodes of a selected site creates a new opportunity to accomplish this task with minimal toxicity. One example is the delivery of nanoparticles from the vaginal lumen to draining lymph nodes to prevent the transmission of HIV in women. Other known examples include mucosal delivery of vaccines to induce immunity. In all cases, molecular and particle transport by means of diffusion and convective diffusion play a major role. The corresponding transport processes have common inherent regularities and are addressed in this review. Here we use nanoparticles delivery from the vaginal lumen to lymph nodes as an example to address the many aspects of associated transport processes. In this case, nanoparticles penetrate the epithelial barrier and move through the interstitium (tissue) to the initial lymphatics until they finally reach the lymph nodes. Since the movement of interstitial liquid near the epithelial barrier is retarded, nanoparticles transport was found to take place through special foci present in the epithelium. Immediately after nanoparticles emerge from the foci, they move through the interstitium due to diffusion affected by convection (convective diffusion). Specifically, the convective transport of nanoparticles occurs due to their convection together with interstitial fluid through the interstitium towards the initial lymph capillaries. Afterwards, nanoparticles move together with the lymph flow along the initial lymph capillaries and then enter the afferent lymphatics and ultimately reach the lymph node. As the liquid moves through the interstitium towards the initial lymph capillaries due to the axial movement of lymph along the lymphatics, the theory for coupling between lymph flow and concomitant flow through the interstitium is developed to describe this general case. The developed theory is applied to interpret the large uptake of Qdots by lymph nodes during inflammation, which is induced by pre-treating mouse vagina with the surfactant Nonoxynol-9 prior to instilling the Qdots. Inflammation is viewed here to cause broadening of the pores within the interstitium with the concomitant formation of transport channels which function as conduits to transport the nanoparticles to the initial lymph capillaries. We introduced the term “effective channels” to denote those channels which interconnect with foci present in the epithelial barrier and which function to transport nanoparticles to initial lymph capillaries. The time of transport towards the lymph node, predicated by the theory, increases rapidly with increasing the distance y0 between the epithelial barrier and the initial lymph capillaries. Transport time is only a few hours, when y0 is small, about some R (where R is the initial lymph capillary radius), due to the predomination of a rather rapid convection in this case. This transport time to lymph nodes may be tens of hours (or longer) when y0 is essentially larger and the slow diffusion controls the transport rate in a zone not far from the epithelial barrier, where convection is weak at large y0. Accounting for transport by diffusion only, which is mainly considered in many relevant publications, is not sufficient to explain our nanoparticles uptake kinetics because the possibility of fast transport due to convection is overlooked. Our systematic investigations have revealed that the information about the main transport conditions, namely, y0 and the pore broadening up to the dimension of the interstitial transport channels, is necessary to create the quantitative model of enhanced transport during inflammation with the use of the proposed model as a prerequisite. The modeling for convective diffusion of nanoparticles from the epithelial barrier to the lymph node has been mainly accomplished here, while the diffusion only scenario is accounted for in other studies. This first modeling is a semi-quantitative one. A more rigorous mathematical approach is almost impossible at this stage because the transport properties of the model are introduced here for the first time. These properties include: discovery of foci in the epithelium, formation of transport channels, definition of channels interconnecting with foci (effective foci and channels), generation of flow in the interstitium towards the initial lymph capillaries due to axial flow within afferent lymphatics, deformation of this flow due to hydrodynamic impermeability of the squamous layer with the formation of the hydrodynamic stagnation zone near the epithelial barrier, predomination of slow diffusion transport within the above zone, and predomination of fast convection of nanoparticles near the initial lymph capillaries. PMID:23859221

Universal time-dependent dispersion properties for diffusion in a one-dimensional critically tilted potential

NASA Astrophysics Data System (ADS)

Guérin, T.; Dean, D. S.

2017-01-01

We consider the time-dependent dispersion properties of overdamped tracer particles diffusing in a one-dimensional periodic potential under the influence of an additional constant tilting force F . The system is studied in the region where the force is close to the critical value Fc at which the barriers separating neighboring potential wells disappear. We show that, when F crosses the critical value, the shape of the mean-square displacement (MSD) curves is strongly modified. We identify a diffusive regime at intermediate-time scales with an effective diffusion coefficient which is much larger than the late-time diffusion coefficient for F >Fc , whereas for F

Mechanisms involved in the blood-testis barrier increased permeability induced by EMP.

PubMed

Wang, Xiao-Wu; Ding, Gui-Rong; Shi, Chang-Hong; Zeng, Li-Hua; Liu, Jun-Ye; Li, Jing; Zhao, Tao; Chen, Yong-Bin; Guo, Guo-Zhen

2010-09-30

The blood-testis barrier (BTB) plays an important role in male reproductive system. Lots of environmental stimulations can increase the permeability of BTB and then result in antisperm antibody (AsAb) generation, which is a key step in male immune infertility. Here we reported the results of male mice exposed to electromagnetic pulse (EMP) by measuring the expression of tight-junction-associated proteins (ZO-1 and Occludin), vimentin microfilaments, and transforming growth factor-beta (TGF-beta3) as well as AsAb level in serum. Male BALB/c mice were sham exposed or exposed to EMP at two different intensities (200kV/m and 400kV/m) for 200 pulses. The testes were collected at different time points after EMP exposure. Immunofluorescence histocytochemistry, western blotting, laser confocal microscopy and RT-PCR were used in this study. Compared with sham group, the expression of ZO-1 and TGF-beta3 significantly decreased accompanied with unevenly stained vimentin microfilaments and increased serum AsAb levels in EMP-exposed mice. These results suggest a potential BTB injury and immune infertility in male mice exposed to a certain intensity of EMP. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.

Surface transport mechanisms in molecular glasses probed by the exposure of nano-particles

NASA Astrophysics Data System (ADS)

Ruan, Shigang; Musumeci, Daniele; Zhang, Wei; Gujral, Ankit; Ediger, M. D.; Yu, Lian

2017-05-01

For a glass-forming liquid, the mechanism by which its surface contour evolves can change from bulk viscous flow at high temperatures to surface diffusion at low temperatures. We show that this mechanistic change can be conveniently detected by the exposure of nano-particles native in the material. Despite its high chemical purity, the often-studied molecular glass indomethacin contains low-concentration particles approximately 100 nm in size and 0.3% in volume fraction. Similar particles are present in polystyrene, another often-used model. In the surface-diffusion regime, particles are gradually exposed in regions vacated by host molecules, for example, the peak of a surface grating and the depletion zone near a surface crystal. In the viscous-flow regime, particle exposure is not observed. The surface contour around an exposed particle widens over time in a self-similar manner as 3 (Bt)1/4, where B is a surface mobility constant and the same constant obtained by surface grating decay. This work suggests that in a binary system composed of slow- and fast-diffusing molecules, slow-diffusing molecules can be stranded in surface regions vacated by fast-diffusing molecules, effectively leading to phase separation.

Redefining Authentic Research Experiences in Introductory Biology Laboratories and Barriers to Their Implementation

ERIC Educational Resources Information Center

Spell, Rachelle M.; Guinan, Judith A.; Miller, Kristen R.; Beck, Christopher W.

2014-01-01

Incorporating authentic research experiences in introductory biology laboratory classes would greatly expand the number of students exposed to the excitement of discovery and the rigor of the scientific process. However, the essential components of an authentic research experience and the barriers to their implementation in laboratory classes are…

Method of making dense, conformal, ultra-thin cap layers for nanoporous low-k ILD by plasma assisted atomic layer deposition

DOEpatents

Jiang, Ying-Bing [Albuquerque, NM; Cecchi, Joseph L [Albuquerque, NM; Brinker, C Jeffrey [Albuquerque, NM

2011-05-24

Barrier layers and methods for forming barrier layers on a porous layer are provided. The methods can include chemically adsorbing a plurality of first molecules on a surface of the porous layer in a chamber and forming a first layer of the first molecules on the surface of the porous layer. A plasma can then be used to react a plurality of second molecules with the first layer of first molecules to form a first layer of a barrier layer. The barrier layers can seal the pores of the porous material, function as a diffusion barrier, be conformal, and/or have a negligible impact on the overall ILD k value of the porous material.

Transport of the moving barrier driven by chiral active particles

NASA Astrophysics Data System (ADS)

Liao, Jing-jing; Huang, Xiao-qun; Ai, Bao-quan

2018-03-01

Transport of a moving V-shaped barrier exposed to a bath of chiral active particles is investigated in a two-dimensional channel. Due to the chirality of active particles and the transversal asymmetry of the barrier position, active particles can power and steer the directed transport of the barrier in the longitudinal direction. The transport of the barrier is determined by the chirality of active particles. The moving barrier and active particles move in the opposite directions. The average velocity of the barrier is much larger than that of active particles. There exist optimal parameters (the chirality, the self-propulsion speed, the packing fraction, and the channel width) at which the average velocity of the barrier takes its maximal value. In particular, tailoring the geometry of the barrier and the active concentration provides novel strategies to control the transport properties of micro-objects or cargoes in an active medium.

Numerical analysis of similarity of barrier discharges in the 0.95 Ne/0.05 Xe mixture

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

Avtaeva, S. V.; Kulumbaev, E. B.

2009-04-15

Established dynamic regimes of similar (with a scale factor of 10) barrier discharges in the 0.95 Ne/0.05 Xe mixture are simulated in a one-dimensional drift-diffusion model. The similarity is examined of barrier discharges excited in gaps of lengths 0.4 and 4 mm at gas pressures of 350 and 35 Torr and dielectric layer thicknesses of 0.2 and 2 mm, the frequencies of the 400-V ac voltage applied to the discharge electrodes being 100 and 10 kHz, respectively.

A computational ab initio study of surface diffusion of sulfur on the CdTe (111) surface

NASA Astrophysics Data System (ADS)

Naderi, Ebadollah; Ghaisas, S. V.

2016-08-01

In order to discern the formation of epitaxial growth of CdS shell over CdTe nanocrystals, kinetics related to the initial stages of the growth of CdS on CdTe is investigated using ab-initio methods. We report diffusion of sulfur adatom on the CdTe (111) A-type (Cd-terminated) and B-type (Te-terminated) surfaces within the density functional theory (DFT). The barriers are computed by applying the climbing Nudge Elastic Band (c-NEB) method. From the results surface hopping emerges as the major mode of diffusion. In addition, there is a distinct contribution from kick-out type diffusion in which a CdTe surface atom is kicked out from its position and is replaced by the diffusing sulfur atom. Also, surface vacancy substitution contributes to the concomitant dynamics. There are sites on the B- type surface that are competitively close in terms of the binding energy to the lowest energy site of epitaxy on the surface. The kick-out process is more likely for B-type surface where a Te atom of the surface is displaced by a sulfur adatom. Further, on the B-type surface, subsurface migration of sulfur is indicated. Furthermore, the binding energies of S on CdTe reveal that on the A-type surface, epitaxial sites provide relatively higher binding energies and barriers than on B-type.

A computational ab initio study of surface diffusion of sulfur on the CdTe (111) surface

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

Naderi, Ebadollah, E-mail: enaderi42@gmail.com; Ghaisas, S. V.

2016-08-15

In order to discern the formation of epitaxial growth of CdS shell over CdTe nanocrystals, kinetics related to the initial stages of the growth of CdS on CdTe is investigated using ab-initio methods. We report diffusion of sulfur adatom on the CdTe (111) A-type (Cd-terminated) and B-type (Te-terminated) surfaces within the density functional theory (DFT). The barriers are computed by applying the climbing Nudge Elastic Band (c-NEB) method. From the results surface hopping emerges as the major mode of diffusion. In addition, there is a distinct contribution from kick-out type diffusion in which a CdTe surface atom is kicked outmore » from its position and is replaced by the diffusing sulfur atom. Also, surface vacancy substitution contributes to the concomitant dynamics. There are sites on the B- type surface that are competitively close in terms of the binding energy to the lowest energy site of epitaxy on the surface. The kick-out process is more likely for B-type surface where a Te atom of the surface is displaced by a sulfur adatom. Further, on the B-type surface, subsurface migration of sulfur is indicated. Furthermore, the binding energies of S on CdTe reveal that on the A-type surface, epitaxial sites provide relatively higher binding energies and barriers than on B-type.« less

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.

Diffusion of anthracene derivatives on Cu(111) studied by STM and DFT

NASA Astrophysics Data System (ADS)

Wyrick, Jonathan; Bartels, Ludwig; Einstein, Theodore

2014-03-01

Substituted anthracenes have drawn attention due to their ability to diffuse uniaxially on a Cu(111) surface. We compare anthracene to three of its derivatives whose 9,10 hydrogens are replaced by elements of the chalcogen group that act as linkers binding the molecules to a Cu(111) substrate. DFT calculations shed light on STM imaging and diffusion studies on the three substituted species. We present an analysis of the DFT results in which energetic contributions to the diffusion barriers are partitioned among the Kohn-Sham orbitals, allowing us to make assignments as to how each orbital affects diffusion for each species and draw comparisons between them. Present address: Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD.

Simulation of atomic diffusion in the Fcc NiAl system: A kinetic Monte Carlo study

DOE PAGES

Alfonso, Dominic R.; Tafen, De Nyago

2015-04-28

The atomic diffusion in fcc NiAl binary alloys was studied by kinetic Monte Carlo simulation. The environment dependent hopping barriers were computed using a pair interaction model whose parameters were fitted to relevant data derived from electronic structure calculations. Long time diffusivities were calculated and the effect of composition change on the tracer diffusion coefficients was analyzed. These results indicate that this variation has noticeable impact on the atomic diffusivities. A reduction in the mobility of both Ni and Al is demonstrated with increasing Al content. As a result, examination of the pair interaction between atoms was carried out formore » the purpose of understanding the predicted trends.« less

Analysis and estimation of service life of corrosion prevention materials using diffusion, resistivity and accelerated curing for new bridge structures : [summary].

DOT National Transportation Integrated Search

2014-01-01

Much infrastructure on Floridas coasts relies : on steel-reinforced concrete that is exposed : to seawater. Corrosion of steel reinforcing bars : (rebar) in concrete exposed to seawater has : been documented as a major cause of bridge : deteriorat...

Observations of Ag diffusion in ion implanted SiC

DOE PAGES

Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; ...

2015-03-17

The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature gas-cooled nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500–1625°C, were investigated in this study by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated,more » including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Lastly, estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.« less

Carrier-mediated cocaine transport at the blood-brain barrier as a putative mechanism in addiction liability.

PubMed

Chapy, Hélène; Smirnova, Maria; André, Pascal; Schlatter, Joël; Chiadmi, Fouad; Couraud, Pierre-Olivier; Scherrmann, Jean-Michel; Declèves, Xavier; Cisternino, Salvatore

2014-10-31

The rate of entry of cocaine into the brain is a critical factor that influences neuronal plasticity and the development of cocaine addiction. Until now, passive diffusion has been considered the unique mechanism known by which cocaine crosses the blood-brain barrier. We reassessed mechanisms of transport of cocaine at the blood-brain barrier using a human cerebral capillary endothelial cell line (hCMEC/D3) and in situ mouse carotid perfusion. Both in vivo and in vitro cocaine transport studies demonstrated the coexistence of a carrier-mediated process with passive diffusion. At pharmacological exposure level, passive diffusion of cocaine accounted for only 22.5% of the total cocaine influx in mice and 5.9% in hCMEC/D3 cells, whereas the carrier-mediated influx rate was 3.4 times greater than its passive diffusion rate in vivo. The functional identification of this carrier-mediated transport demonstrated the involvement of a proton antiporter that shared the properties of the previously characterized clonidine and nicotine transporter. The functionnal characterization suggests that the solute carrier (SLC) transporters Oct (Slc22a1-3), Mate (Slc47a1) and Octn (Slc22a4-5) are not involved in the cocaine transport in vivo and in vitro. Diphenhydramine, heroin, tramadol, cocaethylene, and norcocaine all strongly inhibited cocaine transport, unlike benzoylecgonine. Trans-stimulation studies indicated that diphenhydramine, nicotine, 3,4-methylenedioxyamphetamine (ecstasy) and the cathinone compound 3,4-methylenedioxypyrovalerone (MDPV) were also substrates of the cocaine transporter. Cocaine transport at the BBB involves a proton-antiporter flux that is quantitatively much more important than its passive diffusion. The molecular identification and characterization of this transporter will provide new tools to understand its role in addictive mechanisms. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Diffusion Dominant Solute Transport Modelling In Deep Repository Under The Effect of Emplacement Media Degradation - 13285

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

Kwong, S.; Jivkov, A.P.

2013-07-01

Deep geologic disposal of high activity and long-lived radioactive waste is being actively considered and pursued in many countries, where low permeability geological formations are used to provide long term waste contaminant with minimum impact to the environment and risk to the biosphere. A multi-barrier approach that makes use of both engineered and natural barriers (i.e. geological formations) is often used to further enhance the containment performance of the repository. As the deep repository system subjects to a variety of thermo-hydro-chemo-mechanical (THCM) effects over its long 'operational' lifespan (e.g. 0.1 to 1.0 million years, the integrity of the barrier systemmore » will decrease over time (e.g. fracturing in rock or clay)). This is broadly referred as media degradation in the present study. This modelling study examines the effects of media degradation on diffusion dominant solute transport in fractured media that are typical of deep geological environment. In particular, reactive solute transport through fractured media is studied using a 2-D model, that considers advection and diffusion, to explore the coupled effects of kinetic and equilibrium chemical processes, while the effects of degradation is studied using a pore network model that considers the media diffusivity and network changes. Model results are presented to demonstrate the use of a 3D pore-network model, using a novel architecture, to calculate macroscopic properties of the medium such as diffusivity, subject to pore space changes as the media degrade. Results from a reactive transport model of a representative geological waste disposal package are also presented to demonstrate the effect of media property change on the solute migration behaviour, illustrating the complex interplay between kinetic biogeochemical processes and diffusion dominant transport. The initial modelling results demonstrate the feasibility of a coupled modelling approach (using pore-network model and reactive transport model) to examine the long term behaviour of deep geological repositories with media property change under complex geochemical conditions. (authors)« less

Multi-scale simulation of lithium diffusion in the presence of a 30° partial dislocation and stacking fault in Si

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

Wang, Chao-Ying; Li, Chen-liang; Wu, Guo-Xun

The multi-scale simulation method is employed to investigate how defects affect the performances of Li-ion batteries (LIBs). The stable positions, binding energies and dynamics properties of Li impurity in Si with a 30° partial dislocation and stacking fault (SF) have been studied in comparison with the ideal crystal. It is found that the most table position is the tetrahedral (T{sub d}) site and the diffusion barrier is 0.63 eV in bulk Si. In the 30° partial dislocation core and SF region, the most stable positions are at the centers of the octagons (Oct-A and Oct-B) and pentahedron (site S), respectively. Inmore » addition, Li dopant may tend to congregate in these defects. The motion of Li along the dislocation core are carried out by the transport among the Oct-A (Oct-B) sites with the barrier of 1.93 eV (1.12 eV). In the SF region, the diffusion barrier of Li is 0.91 eV. These two types of defects may retard the fast migration of Li dopant that is finally trapped by them. Thus, the presence of the 30° partial dislocation and SF may deactivate the Li impurity and lead to low rate capability of LIB.« less

First principles calculations of ceramics surfaces and interfaces: Examples from beta-silicon nitride and alpha-alumina

NASA Astrophysics Data System (ADS)

Dunn, Jennifer Synowczynski

The goal of this thesis was to use first principles calculations to provide a fundamental understanding at the atomistic level of the mechanisms (e.g. structural relaxations of ceramic surfaces/interfaces, charge transfer reactions, adsorption and dissociation phenomena, localized debonding) behind macroscopic behavior in ceramics (e.g. fracture toughness, corrosion, catalysis). This thesis includes the results from three independent Density Functional Theory (DFT) studies of beta-Si3N4 and alpha-Al2O 3. Due to the computational complexity of first principles calculations, the models in this thesis do not consider temperature or pressure effects and are limited to describing the behavior of systems containing less than 200 atoms. In future studies, these calculations can be used to train a reactive molecular dynamics force field (REAXFF) so that larger scale phenomena including temperature effects can be explicitly simulated. In the first study, the effect of over 30 dopants on the stability of the interface between beta-Si3N4 grains and the intergranular glassy SiON film (IGF) was investigated. The dopants chosen not only represented commonly known glass modifiers and sintering aides but also enabled us to search for dependencies based on atomic size and electronic orbital configuration. To ensure that the approximations used in our model captured the key physical phenomena occurring on the beta-Si3N4 (100) surface and at the Si3N4/ IGF interface, we compared to experimental data (i.e. High Angle Annual Dark Field-Scanning Transmission Electron Microscopy atomic positions and fracture toughness values (Mikijelj B., 2009)). We identified a computational metric (the interfacial stability factor S) which correlates with experimentally measured fracture toughness values. The interfacial stability factor S is defined as the binding energy of the doped system minus the binding energy of the undoped system, where the binding energy is the total energy of the system minus the sum of the energies of the constituent atoms. In the second study, we performed constrained geometry barrier calculations of the interaction of CO with the (001) beta-Si3N4 surface to answer the following questions: (1) Does the CO combustion product interact with the Si3N4 surface and if so, what is the mechanism? (2) Once adsorbed, can CO further dissociate into isolated surface active C and O species? (3) Is it more energetically favorable for C to diffuse into the bulk beta-Si3N4 or along its surface? and (4) What is the barrier to C diffusing into an amorphous SiO2 intergranular film? Our calculations indicated that CO spontaneously adsorbs to the (001) beta-Si 3N4 surface. However, at ambient temperatures, further dissociation into isolated surface adsorbed C and O species was not thermodynamically or kinetically feasible. The barrier to C diffusing interstitially 1A and 5A into the bulk crystalline lattice is 2.12 and 4.42 eV respectively for a defect free, clean surface. However, the barrier for C surface diffusion is much smaller, ˜ 0.87 eV. Therefore, we concluded that surface is rich in C which can diffuse to the Si3N4/SiO2 interface and contribute to chemical erosion near the grain boundary interface. In the final study, we created a DFT model to investigate the 'inverse spillover effect' that occurs during hydrogen combustion on catalytically active Pt clusters supported by alpha-Al2O3. Our results indicated that the dissociation of O2 was not thermodynamically favored on the alpha-Al2O3 surface. However, both H2 and H2O dissociated, forming hydroxyls with oxygen atoms in the second atomic layer. Once dissociated, the oxygen species could diffuse locally but encountered a large barrier to long-range surface diffusion in the absence of defects or other species. In contrast, the barrier to the long-range surface diffusion of hydrogen was modest under ideal conditions. We also identified several adsorption and dissociation products for Pt, Pt-O [ads] Pt3, O, H, O2, H2, and H 2O on the alpha-Al2O3 (0001) surface and described how these structures changed the surface reconstruction. Specifically, we concluded that the adsorption of molecular H2O, atomic Pt, and Pt trimers changed the termination for the alpha-Al2O3 (0001) surface from aluminum to oxygen terminated in the vicinity of the adsorption products. This should have a dramatic affect on catalytic activity and surface diffusion. We confirmed this for O surface diffusion near surface Al where the presence of atomic Pt decreased the diffusion barrier from 1.17 to 0.22 eV.

Folic Acid Promotion for Hispanic Women in Florida: A Vitamin Diary Study

ERIC Educational Resources Information Center

Thomas, Kamilah B.; Hauser, Kimberlea; Rodriguez, Nydia Y.; Quinn, Gwendolyn P.

2010-01-01

Objective: To assess the barriers and benefits of taking multivitamins among Hispanic women exposed to a folic acid social marketing campaign in Florida, USA. Design and setting: Evaluation of non-pregnant women aged 18-35 from multiple Hispanic subgroups. Method: For 6 months, participants exposed to social marketing campaign educational…

Subliminal mere exposure: specific, general, and diffuse effects.

PubMed

Monahan, J L; Murphy, S T; Zajonc, R B

2000-11-01

The present research examined the possibility that repeated exposure may simultaneously produce specific and diffuse effects. In Study 1, participants were presented with 5-ms exposures of 25 stimuli each shown once (single-exposure condition) or with five repetitions of 5 stimuli (repeated-exposure condition). Participants in the repeated-exposure condition subsequently rated their own mood more positively than those in the single-exposure condition. Study 2 examined whether affect generated by subliminal repeated exposures transfers to unrelated stimuli. After a subliminal exposure phase, affective reactions to previously exposed stimuli, to new but similar stimuli, and to stimuli from a different category were obtained. Previously exposed stimuli were rated most positively and novel different stimuli least positively. All stimuli were rated more positively in the repeated-exposure condition than in the single-exposure condition. These findings suggest that affect generated by subliminal repeated exposure is sufficiently diffuse to influence ratings of unrelated stimuli and mood.

Electrochemical monitoring of native catalase activity in skin using skin covered oxygen electrode.

PubMed

Nocchi, Sarah; Björklund, Sebastian; Svensson, Birgitta; Engblom, Johan; Ruzgas, Tautgirdas

2017-07-15

A skin covered oxygen electrode, SCOE, was constructed with the aim to study the enzyme catalase, which is part of the biological antioxidative system present in skin. The electrode was exposed to different concentrations of H 2 O 2 and the amperometric current response was recorded. The observed current is due to H 2 O 2 penetration through the outermost skin barrier (referred to as the stratum corneum, SC) and subsequent catalytic generation of O 2 by catalase present in the underlying viable epidermis and dermis. By tape-stripping the outermost skin layers we demonstrate that SC is a considerable diffusion barrier for H 2 O 2 penetration. Our experiments also indicate that skin contains a substantial amount of catalase, which is sufficient to detoxify H 2 O 2 that reaches the viable epidermis after exposure of skin to high concentrations of peroxide (0.5-1mM H 2 O 2 ). Further, we demonstrate that the catalase activity is reduced at acidic pH, as compared with the activity at pH 7.4. Finally, experiments with often used penetration enhancer thymol shows that this compound interferes with the catalase reaction. Health aspect of this is briefly discussed. Summarizing, the results of this work show that the SCOE can be utilized to study a broad spectrum of issues involving the function of skin catalase in particular, and the native biological antioxidative system in skin in general. Copyright © 2017 Elsevier B.V. All rights reserved.

Balanced improvement of high performance concrete material properties with modified graphite nanomaterials

NASA Astrophysics Data System (ADS)

Peyvandi, Amirpasha

Graphite nanomaterials offer distinct features for effective reinforcement of cementitious matrices in the pre-crack and post-crack ranges of behavior. Thoroughly dispersed and well-bonded nanomaterials provide for effective control of the size and propagation of defects (microcracks) in matrix, and also act as closely spaced barriers against diffusion of moisture and aggressive solutions into concrete. Modified graphite nanomaterials can play multi-faceted roles towards enhancing the mechanical, physical and functional attributes of concrete materials. Graphite nanoplatelets (GP) and carbon nanofibers (CNF) were chosen for use in cementitious materials. Experimental results highlighted the balanced gains in diverse engineering properties of high-performance concrete realized by introduction of graphite nanomaterials. Nuclear Magnetic Resonance (NMR) spectroscopy was used in order to gain further insight into the effects of nanomaterials on the hydration process and structure of cement hydrates. NMR exploits the magnetic properties of certain atomic nuclei, and the sensitivity of these properties to local environments to generate data which enables determination of the internal structure, reaction state, and chemical environment of molecules and bulk materials. 27 Al and 29Si NMR spectroscopy techniques were employed in order to evaluate the effects of graphite nanoplatelets on the structure of cement hydrates, and their resistance to alkali-silica reaction (ASR), chloride ion diffusion, and sulfate attack. Results of 29Si NMR spectroscopy indicated that the percent condensation of C-S-H in cementitious paste was lowered in the presence of nanoplatelets at the same age. The extent of chloride diffusion was assessed indirectly by detecting Friedel's salt as a reaction product of chloride ions with aluminum-bearing cement hydrates. Graphite nanoplatelets were found to significantly reduce the concentration of Friedel's salt at different depths after various periods of exposure to chloride solutions, pointing at the benefits of nanoplatelets towards enhancement of concrete resistance to chloride ion diffusion. It was also found that the intensity of Thaumasite, a key species marking sulfate attack on cement hydrates, was lowered with the addition of graphite nanoplatelets in concrete exposed to sulfate solutions. Experimental evaluations were conducted on scaled-up production of concrete nanocomposite in precast concrete plants. Full-scale reinforced concrete pipes and beams were produced using concrete nanocomposites. Durability and structural tests indicated that the use of graphite nanoplatelets, alone or in combination with synthetic (PVA) fibers, produced significant gains in the durability characteristics, and also benefited the structural performance of precast reinforced concrete products. The material and scaled-up structural investigations conducted in the project concluded that lower-cost graphite nanomaterials (e.g., graphite nanoplatelets) offer significant potentials as multi-functional additives capable of enhancing the barrier, durability and mechanical performance of concrete materials. The benefits of graphite nanomaterials tend to be more pronounced in higher-performance concrete materials.

DNA damage in internal organs after cutaneous exposure to sulphur mustard.

PubMed

Batal, Mohamed; Boudry, Isabelle; Mouret, Stéphane; Cléry-Barraud, Cécile; Wartelle, Julien; Bérard, Izabel; Douki, Thierry

2014-07-01

Sulphur mustard (SM) is a chemical warfare agent that attacks mainly skin, eye and lungs. Due to its lipophilic properties, SM is also able to diffuse through the skin and reach internal organs. DNA represents one of the most critical molecular targets of this powerful alkylating agent which modifies DNA structure by forming monoadducts and biadducts. These DNA lesions are involved in the acute toxicity of SM as well as its long-term carcinogenicity. In the present work we studied the formation and persistence of guanine and adenine monoadducts and guanine biadducts in the DNA of brain, lungs, kidneys, spleen, and liver of SKH-1 mice cutaneously exposed to 2, 6 and 60mg/kg of SM. SM-DNA adducts were detected in all studied organs, except in liver at the two lowest doses. Brain and lungs were the organs with the highest level of SM-DNA adducts, followed by kidney, spleen and liver. Monitoring the level of adducts for three weeks after cutaneous exposure showed that the lifetime of adducts were not the same in all organs, lungs being the organ with the longest persistence. Diffusion from skin to internal organs was much more efficient at the highest compared to the lowest dose investigated as the result of the loss of the skin barrier function. These data provide novel information on the distribution of SM in tissues following cutaneous exposures and indicate that brain is an important target. Copyright © 2014 Elsevier Inc. All rights reserved.

Carbon diffusion paths and segregation at high-angle tilt grain boundaries in α-Fe studied by using a kinetic activation-relation technique

NASA Astrophysics Data System (ADS)

Restrepo, Oscar A.; Mousseau, Normand; Trochet, Mickaël; El-Mellouhi, Fedwa; Bouhali, Othmane; Becquart, Charlotte S.

2018-02-01

Carbon diffusion and segregation in iron is fundamental to steel production but is also associated with corrosion. Using the kinetic activation-relaxation technique (k-ART), a kinetic Monte Carlo (KMC) algorithm with an on-the-fly catalog that allows to obtain diffusion properties over large time scales taking into account long-range elastic effects coupled with an EAM force field, we study the motion of a carbon impurity in four Fe systems with high-angle grain boundaries (GB), focusing on the impact of these extended defects on the long-time diffusion of C. Short and long-time stability of the various GBs is first analyzed, which allows us to conclude that the Σ 3 (1 1 1 ) θ =109 .53∘<110 > GB is unstable, with Fe migration barriers of ˜0.1 eV or less, and C acts as a pinning center. Focusing on three stable GBs, in all cases, these extended defects trap C in energy states lower than found in the crystal. Yet, contrary to general understanding, we show, through simulations extending to 0.1 s, that even tough C diffusion takes place predominantly in the GB, it is not necessarily faster than in the bulk and can even be slower by one to two orders of magnitude depending on the GB type. Analysis of the energy landscape provided by k-ART also shows that the free cavity volume around the impurity is not a strong predictor of diffusion barrier height. Overall, results show rather complex diffusion kinetics intimately dependent on the local environment.

Adsorption and diffusion of Au atoms on the (001) surface of Ti, Zr, Hf, V, Nb, Ta, and Mo carbides.

PubMed

Florez, Elizabeth; Viñes, Francesc; Rodriguez, Jose A; Illas, Francesc

2009-06-28

The adsorption of atomic Au on the (001) surface of TiC, ZrC, HfC, VC, NbC, TaC, and delta-MoC and the mechanism of diffusion of this adatom through the surface have been studied in terms of a periodic density functional theory based approach. In all the cases, the Au adsorption energies are in the range of 1.90-2.35 eV. The moderately large adsorption energies allow the Au diffusion before desorption could take place. For TiC(001), ZrC(001), and HfC(001), atomic Au is adsorbed directly on top of C atoms and diffusion takes place along the diagonal of the squares formed by M-C-M-C atoms with the transition state located above the hollow sites. For the rest of transition metal carbides the situation is less simple with the appearance of more than one stable adsorption site, as for NbC and TaC, of a small energy barrier for diffusion around the most stable adsorption site and of a more complex diffusion pathway. The small energy barrier for diffusion around the most stable site will result in a highly mobile Au species which could be observed in scanning tunnel microscope experiments. After depositing Au on metal-carbide surfaces, there is a noticeable charge transfer from the substrate to the adsorbed Au atom. The electronic perturbations on Au increase when going from TiC to ZrC or TaC. Our results indicate that metal carbides should be better supports for the chemical activation of Au than metal oxides.

How to Motivate Military Veterans to Participate in the GI Bill

ERIC Educational Resources Information Center

Baskas, Richard S.

2012-01-01

Over the years, some military veterans have been influenced by barriers, preventing them from using their educational benefits. Any active duty member or military veteran could have been exposed to and influenced by these barriers and become unmotivated and not use or discontinue using these benefits. If veterans do not use their educational…

Universal time-dependent dispersion properties for diffusion in a one-dimensional critically tilted potential.

PubMed

Guérin, T; Dean, D S

2017-01-01

We consider the time-dependent dispersion properties of overdamped tracer particles diffusing in a one-dimensional periodic potential under the influence of an additional constant tilting force F. The system is studied in the region where the force is close to the critical value F_{c} at which the barriers separating neighboring potential wells disappear. We show that, when F crosses the critical value, the shape of the mean-square displacement (MSD) curves is strongly modified. We identify a diffusive regime at intermediate-time scales with an effective diffusion coefficient which is much larger than the late-time diffusion coefficient for F>F_{c}, whereas for F

Macromolecule diffusion and confinement in prokaryotic cells.

PubMed

Mika, Jacek T; Poolman, Bert

2011-02-01

We review recent observations on the mobility of macromolecules and their spatial organization in live bacterial cells. We outline the major fluorescence microscopy-based methods to determine the mobility and thus the diffusion coefficients (D) of molecules, which is not trivial in small cells. The extremely high macromolecule crowding of prokaryotes is used to rationalize the reported lower diffusion coefficients as compared to eukaryotes, and we speculate on the nature of the barriers for diffusion observed for proteins (and mRNAs) in vivo. Building on in vitro experiments and modeling studies, we evaluate the size dependence of diffusion coefficients for macromolecules in vivo, in case of both water-soluble and integral membrane proteins. We comment on the possibilities of anomalous diffusion and provide examples where the macromolecule mobility may be limiting biological processes. Copyright © 2010 Elsevier Ltd. All rights reserved.

[Simulation on contamination forecast and control of groundwater in a certain hazardous waste landfill].

PubMed

Ma, Zhi-Fei; An, Da; Jiang, Yong-Hai; Xi, Bei-Dou; Li, Ding-Long; Zhang, Jin-Bao; Yang, Yu

2012-01-01

On the basis of site investigation and data collection of a certain hazardous waste landfill, the groundwater flow and solute transport coupled models were established by applying Visual Modflow software, which was used to conduct a numerical simulation that forecast the transport process of Cr6+ in groundwater and the effects of three control measures (ground-harden, leakage-proof barriers and drainage ditches) of contaminants transport after leachate leakage happened in impermeable layer of the landfill. The results show that the contamination plume of Cr6+ transports with groundwater flow direction, the contamination rang would reach the pool's boundary in 10 years, and the distance of contamination transport is 1 450 m. But the diffusion range of contamination plume would not be obviously expanded between 10 and 20 years. While the ground is hardened, the contamination plume would not reach the pool's boundary in 20 years. When the leakage-proof barrier is set in the bottom of water table aquifer, the concentration of Cr6+ is higher than that the leakage-proof barrier is unset, but the result is just opposite when setting the leakage-proof barrier in the bottom of underlying aquifer. The range of contamination plume is effectively controlled by setting drainage ditches that water discharge is 2 642 m3 x d(-1), which makes the monitoring wells would not be contaminated in 20 years. Moreover, combining the ground-harden with drainage ditches can get the best effect in controlling contaminants diffusion, and meanwhile, the drainage ditches' daily discharge is reduced to 1 878 m3 x d(-1). Therefore, it is suggested that the control measure combining the ground-harden with drainage ditches should apply to prevent contamination diffusion in groundwater when leachate leakage have happened in impermeable layer of the landfill.

Impact of volume and surface processes on the pre-ionization of dielectric barrier discharges: advanced diagnostics and fluid modeling

NASA Astrophysics Data System (ADS)

Nemschokmichal, Sebastian; Tschiersch, Robert; Höft, Hans; Wild, Robert; Bogaczyk, Marc; Becker, Markus M.; Loffhagen, Detlef; Stollenwerk, Lars; Kettlitz, Manfred; Brandenburg, Ronny; Meichsner, Jürgen

2018-05-01

The phenomenology and breakdown mechanism of dielectric barrier discharges are strongly determined by volume and surface memory effects. In particular, the pre-ionization provided by residual species in the volume or surface charges on the dielectrics influences the breakdown behavior of filamentary and diffuse discharges. This was investigated by advanced diagnostics such as streak camera imaging, laser photodetachment of negative ions and laser photodesorption of electrons from dielectric surfaces in correlation with 1D fluid modeling. The streak camera images show that an increasing number of residual charges in the volume changes the microdischarge breakdown in air-like gas mixtures from a cathode-directed streamer to a simultaneous propagation of cathode- and anode-directed streamers. In contrast, seed electrons are important for the pre-ionization if the density of residual charges in the volume is low. One source of seed electrons are negative ions, whose density exceeds the electron density during the pre-phase of diffuse helium-oxygen barrier discharges as indicated by the laser photodetachment experiments. Electrons desorbed from the cathodic dielectric have an even larger influence. They induce a transition from the glow-like to the Townsend-like discharge mode in nominally pure helium. Apart from analyzing the importance of the pre-ionization for the breakdown mechanism, the opportunities for manipulating the lateral structure and discharge modes are discussed. For this purpose, the intensity and diameter of a diffuse discharge in helium are controlled by an illuminated semiconducting barrier. Contribution to the Topical Issue "Fundamentals of Complex Plasmas", edited by Jürgen Meichsner, Michael Bonitz, Holger Fehske, Alexander Piel.

Release from the cone ribbon synapse under bright light conditions can be controlled by the opening of only a few Ca2+ channels

PubMed Central

Bartoletti, Theodore M.; Jackman, Skyler L.; Babai, Norbert; Mercer, Aaron J.; Kramer, Richard H.

2011-01-01

Light hyperpolarizes cone photoreceptors, causing synaptic voltage-gated Ca2+ channels to open infrequently. To understand neurotransmission under these conditions, we determined the number of L-type Ca2+ channel openings necessary for vesicle fusion at the cone ribbon synapse. Ca2+ currents (ICa) were activated in voltage-clamped cones, and excitatory postsynaptic currents (EPSCs) were recorded from horizontal cells in the salamander retina slice preparation. Ca2+ channel number and single-channel current amplitude were calculated by mean-variance analysis of ICa. Two different comparisons—one comparing average numbers of release events to average ICa amplitude and the other involving deconvolution of both EPSCs and simultaneously recorded cone ICa—suggested that fewer than three Ca2+ channel openings accompanied fusion of each vesicle at the peak of release during the first few milliseconds of stimulation. Opening fewer Ca2+ channels did not enhance fusion efficiency, suggesting that few unnecessary channel openings occurred during strong depolarization. We simulated release at the cone synapse, using empirically determined synaptic dimensions, vesicle pool size, Ca2+ dependence of release, Ca2+ channel number, and Ca2+ channel properties. The model replicated observations when a barrier was added to slow Ca2+ diffusion. Consistent with the presence of a diffusion barrier, dialyzing cones with diffusible Ca2+ buffers did not affect release efficiency. The tight clustering of Ca2+ channels, along with a high-Ca2+ affinity release mechanism and diffusion barrier, promotes a linear coupling between Ca2+ influx and vesicle fusion. This may improve detection of small light decrements when cones are hyperpolarized by bright light. PMID:21880934

Knowledge barriers to PACS adoption and implementation in hospitals.

PubMed

Paré, Guy; Trudel, Marie-Claude

2007-01-01

Drawing on the classical theory of diffusion of innovations advanced by Rogers [E.M. Rogers, Diffusion of Innovations, 4th ed., Free Press, New York, NY, 1995] and on the theory of barriers to innovation [P. Attewell, Technology diffusion and organizational learning: the case of business computing. Organ. Sci. 3 (1992) 1-19; H. Tanriverdi, C.S. Iacono, Knowledge barriers to diffusion of telemedicine. Proceedings of the 20th International Conference on Information Systems, Charlotte, NC, 1999, pp. 39-50; S. Nambisan, Y.-M. Wang, Roadblocks to web technology adoption? Commun. ACM, 42 (1) (1999) 98-101], this study seeks a better understanding of challenges faced in PACS implementations in hospitals and of the strategies required to ensure their success. To attain this objective, we describe and analyze the process used to adopt and implement PACS at two Canadian hospitals. Our findings clearly demonstrate the importance of treating any PACS deployment not simply as a rollout of new technology but as a project that will transform the organization. Proponents of these projects must not lose sight of the fact that, even if technological complexity represents a significant issue, it must not garner all the project team's attention. This situation is even more dangerous, inasmuch as the greatest risk to the implementation often lies elsewhere. It would also appear to be crucial to anticipate and address organizational and behavioral challenges from the very first phase of the innovation process, in order to ensure that all participants will be committed to the project. In order to maximize the likelihood of PACS success, it appears crucial to adopt a proactive implementation strategy, one that takes into consideration all the technical, economic, organizational, and human factors, and does so from the first phase of the innovation process.

Release from the cone ribbon synapse under bright light conditions can be controlled by the opening of only a few Ca(2+) channels.

PubMed

Bartoletti, Theodore M; Jackman, Skyler L; Babai, Norbert; Mercer, Aaron J; Kramer, Richard H; Thoreson, Wallace B

2011-12-01

Light hyperpolarizes cone photoreceptors, causing synaptic voltage-gated Ca(2+) channels to open infrequently. To understand neurotransmission under these conditions, we determined the number of L-type Ca(2+) channel openings necessary for vesicle fusion at the cone ribbon synapse. Ca(2+) currents (I(Ca)) were activated in voltage-clamped cones, and excitatory postsynaptic currents (EPSCs) were recorded from horizontal cells in the salamander retina slice preparation. Ca(2+) channel number and single-channel current amplitude were calculated by mean-variance analysis of I(Ca). Two different comparisons-one comparing average numbers of release events to average I(Ca) amplitude and the other involving deconvolution of both EPSCs and simultaneously recorded cone I(Ca)-suggested that fewer than three Ca(2+) channel openings accompanied fusion of each vesicle at the peak of release during the first few milliseconds of stimulation. Opening fewer Ca(2+) channels did not enhance fusion efficiency, suggesting that few unnecessary channel openings occurred during strong depolarization. We simulated release at the cone synapse, using empirically determined synaptic dimensions, vesicle pool size, Ca(2+) dependence of release, Ca(2+) channel number, and Ca(2+) channel properties. The model replicated observations when a barrier was added to slow Ca(2+) diffusion. Consistent with the presence of a diffusion barrier, dialyzing cones with diffusible Ca(2+) buffers did not affect release efficiency. The tight clustering of Ca(2+) channels, along with a high-Ca(2+) affinity release mechanism and diffusion barrier, promotes a linear coupling between Ca(2+) influx and vesicle fusion. This may improve detection of small light decrements when cones are hyperpolarized by bright light.

Investigation of nanosecond pulsed dielectric barrier discharge using plate-to-plate electrode with asymmetric dielectric arrangement in airflow

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

Qi, Haicheng; School of Physics Science and Technology, Anshan Normal University, Anshan 114005; Fan, Zhihui

Atmospheric pressure dielectric barrier discharge plasma is produced in airflow by applying nanosecond high voltage pulses with peak voltage about 35 kV and rising time about 40 ns on a plate-to-plate electrode arrangement. The effects of airflow rate (0–50 m/s) on the discharge characteristics are investigated under different barrier conditions (the bare anode case and the bare cathode case). For both cases, the breakdown voltage and the time lag increase distinctly and the discharge intensity decreases sharply when the airflow rate increases from 0 to 30 m/s, and then keep almost constant until the airflow rate is further increased to 50 m/s. For the baremore » anode case (the cathode is covered by dielectric plate), the discharge mode transforms gradually from filamentary to diffuse discharge with the increasing airflow rate. While for the bare cathode case, some micro-discharge channels are still excited, though the discharge becomes more diffuse when the airflow rate is higher than 30 m/s. By acquiring the time-resolved images of the discharge, it is proved that it is the primary discharge which becomes diffuse when airflow is introduced and the following two discharges of the same voltage pulse occur principally at the positions where the primary discharge is more intense. And in both cases, the plasma temperatures are reduced, but the degree is different. All the phenomena can be explained mainly by the variation of the space charge distribution when the airflow is introduced into the discharge gap. And it is indicated that the bare anode case has an advantage in obtaining diffuse discharge.« less

Influence of La/W ratio on electrical conductivity of lanthanum tungstate with high La/W ratio

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

Kojo, Gen; Shono, Yohei; Ushiyama, Hiroshi

The proton-conducting properties of lanthanum tungstates (LWOs) with high La/W ratios were investigated using electrochemical measurements and quantum chemical calculations. Single phases of LWOs with high La/W ratios (6.3≤La/W≤6.7) were synthesized by high-temperature sintering at around 1700 °C. The electrical conductivity of LWO increased with increasing La/W ratio in the single-phase region. The LWO synthesized at the optimum sintering temperature and time, and with the optimum La/W ratio gave the maximum conductivity, i.e., 2.7×10{sup −3} S cm{sup −1} with La/W=6.7 at 500 °C. Density functional theory calculations, using the nudged elastic band method, were performed to investigate the proton diffusionmore » barrier. The results suggest that the proton diffusion paths around La sites have the lowest proton diffusion barrier. These findings improve our understanding of LWO synthesis and the proton-conducting mechanism and provide a strategy for improving proton conduction in LWOs. - Graphical abstract: The LWOs with high La/W ratios were synthesized for the first time. The optimum La/W ratio gave the maximum conductivity with La/W=6.7 at 500 °C. The proton diffusion paths were also considered with density functional theory calculations. - Highlights: • The proton-conducting properties of lanthanum tungstates (LWOs) were investigated. • Single phase LWOs with high La/W ratios (6.3≤La/W≤6.7) were synthesized successfully. • LWOs with the high La/W ratios showed high proton conductivity. • The DFT calculation suggested the lowest proton diffusion barrier in the path around La sites.« less

Nerve cell damage in mammalian brain after exposure to microwaves from GSM mobile phones.

PubMed

Salford, Leif G; Brun, Arne E; Eberhardt, Jacob L; Malmgren, Lars; Persson, Bertil R R

2003-06-01

The possible risks of radio-frequency electromagnetic fields for the human body is a growing concern for our society. We have previously shown that weak pulsed microwaves give rise to a significant leakage of albumin through the blood-brain barrier. In this study we investigated whether a pathologic leakage across the blood-brain barrier might be combined with damage to the neurons. Three groups each of eight rats were exposed for 2 hr to Global System for Mobile Communications (GSM) mobile phone electromagnetic fields of different strengths. We found highly significant (p< 0.002) evidence for neuronal damage in the cortex, hippocampus, and basal ganglia in the brains of exposed rats.

Performance of WCN diffusion barrier for Cu multilevel interconnects

NASA Astrophysics Data System (ADS)

Lee, Seung Yeon; Ju, Byeong-Kwon; Kim, Yong Tae

2018-04-01

The electrical and thermal properties of a WCN diffusion barrier have been studied for Cu multilevel interconnects. The WCN has been prepared using an atomic layer deposition system with WF6-CH4-NH3-H2 gases and has a very low resistivity of 100 µΩ cm and 96.9% step coverage on the high-aspect-ratio vias. The thermally stable WCN maintains an amorphous state at 800 °C and Cu/WCN contact resistance remains within a 10% deviation from the initial value after 700 °C. The mean time to failure suggests that the Cu/WCN interconnects have a longer lifetime than Cu/TaN and Cu/WN interconnects because WCN prevents Cu migration owing to the stress evolution from tensile to compressive.

Novel Fabrication of Biodegradable Superabsorbent Microspheres with Diffusion Barrier through Thermo-Chemical Modification and Their Potential Agriculture Applications for Water Holding and Sustained Release of Fertilizer.

PubMed

Feng, Diejing; Bai, Bo; Wang, Honglun; Suo, Yourui

2017-07-26

Synergistic utilization of water and fertilizer has vital contribution to the modern production of agriculture. This work reports on a simple and facile strategy to prepare biodegradable yeast/sodium alginate/poly(vinyl alcohol) superabsorbent microspheres with a diffusion barrier merit by thermo-chemical modification route. The integrated performances, including water absorbency, water retention, water evaporation ratio, leaching loss control, sustained-release behaviors, and degradation in soil, were systematically investigated. The results revealed that the modified microspheres were a triumphant water and fertilizer manager to effectively hold water and control the unexpected leakage of fertilizer for sustained release. Therefore, this work provides a promising approach to ameliorate the utilization efficiency of water and fertilizer in potential agriculture applications.

Preliminary study of a solar selective coating system using black cobalt oxide for high temperature solar collectors

NASA Technical Reports Server (NTRS)

Mcdonald, G.

1980-01-01

Black cobalt oxide coatings (high solar absorptance layer) were deposited on thin layers of silver or gold (low emittance layer) which had been previously deposited on oxidized (diffusion barrier layer) stainless steel substrates. The reflectance properties of these coatings were measured at various thicknesses of cobalt for integrated values of the solar and infrared spectrum. The values of absorptance and emittance were calculated from the measured reflectance values, before and after exposure in air at 650 C for approximately 1000 hours. Absorptance and emittance were interdependent functions of the weight of cobalt oxide. Also, these cobalt oxide/noble metal/oxide diffusion barrier coatings have absorptances greater than 0.90 and emittances of approximately 0.20 even after about 1000 hours at 650 C.

Nano-Nucleation Characteristic of Cu-Ag Alloy Directly Electrodeposited on W Diffusion Barrier for Microelectronic Device Interconnect.

PubMed

Kim, Kang O; Kim, Sunjung

2016-05-01

Cu-Ag alloy interconnect is promising for ultra-large-scale integration (ULSI) microelectronic system of which device dimension keeps shrinking. In this study, seedless electrodeposition of Cu-Ag alloy directly on W diffusion barrier as interconnect technology is presented in respect of nano-nucleation control. Chemical equilibrium state of electrolyte was fundamentally investigated according to the pH of electrolyte because direct nano-nucleation of Cu-Ag alloy on W surface is challenging. Chelation behavior of Cu2+ and Ag+ ions with citrate (Cit) and ammonia ligands was dependent on the pH of electrolyte. The amount and kind of Cu- and Ag-based complexes determine the deposition rate, size, elemental composition, and surface morphology of Cu-Ag alloy nano-nuclei formed on W surface.

Fast Mg2+ diffusion in Mo3(PO4)3O for Mg batteries.

PubMed

Rong, Ziqin; Xiao, Penghao; Liu, Miao; Huang, Wenxuan; Hannah, Daniel C; Scullin, William; Persson, Kristin A; Ceder, Gerbrand

2017-07-13

In this work, we identify a new potential Mg battery cathode structure Mo 3 (PO 4 ) 3 O, which is predicted to exhibit ultra-fast Mg 2+ diffusion and relatively high voltage based on first-principles density functional theory calculations. Nudged elastic band calculations reveal that the migration barrier of the percolation channel is only ∼80 meV, which is remarkably low, and comparable to the best Li-ion conductors. This low barrier is verified by ab initio molecular dynamics and kinetic Monte Carlo simulations. The voltage and specific energy are predicted to be ∼1.98 V and ∼173 W h kg -1 , respectively. If confirmed by experiments, this material would have the highest known Mg mobility among inorganic compounds.

Characterisation of Ceramic-Coated 316LN Stainless Steel Exposed to High-Temperature Thermite Melt and Molten Sodium

NASA Astrophysics Data System (ADS)

Ravi Shankar, A.; Vetrivendan, E.; Shukla, Prabhat Kumar; Das, Sanjay Kumar; Hemanth Rao, E.; Murthy, S. S.; Lydia, G.; Nashine, B. K.; Mallika, C.; Selvaraj, P.; Kamachi Mudali, U.

2017-11-01

Currently, stainless steel grade 316LN is the material of construction widely used for core catcher of sodium-cooled fast reactors. Design philosophy for core catcher demands its capability to withstand corium loading from whole core melt accidents. Towards this, two ceramic coatings were investigated for its application as a layer of sacrificial material on the top of core catcher to enhance its capability. Plasma-sprayed thermal barrier layer of alumina and partially stabilised zirconia (PSZ) with an intermediate bond coat of NiCrAlY are selected as candidate material and deposited over 316LN SS substrates and were tested for their suitability as thermal barrier layer for core catcher. Coated specimens were exposed to high-temperature thermite melt to simulate impingement of molten corium. Sodium compatibility of alumina and PSZ coatings were also investigated by exposing samples to molten sodium at 400 °C for 500 h. The surface morphology of high-temperature thermite melt-exposed samples and sodium-exposed samples was examined using scanning electron microscope. Phase identification of the exposed samples was carried out by x-ray diffraction technique. Observation from sodium exposure tests indicated that alumina coating offers better protection compared to PSZ coating. However, PSZ coating provided better protection against high-temperature melt exposure, as confirmed during thermite melt exposure test.

All-Diamond Microelectrodes as Solid State Probes for Localized Electrochemical Sensing.

PubMed

Silva, Eduardo L; Gouvêa, Cristol P; Quevedo, Marcela C; Neto, Miguel A; Archanjo, Braulio S; Fernandes, António J S; Achete, Carlos A; Silva, Rui F; Zheludkevich, Mikhail L; Oliveira, Filipe J

2015-07-07

The fabrication of an all-diamond microprobe is demonstrated for the first time. This ME (microelectrode) assembly consists of an inner boron doped diamond (BDD) layer and an outer undoped diamond layer. Both layers were grown on a sharp tungsten tip by chemical vapor deposition (CVD) in a stepwise manner within a single deposition run. BDD is a material with proven potential as an electrochemical sensor. Undoped CVD diamond is an insulating material with superior chemical stability in comparison to conventional insulators. Focused ion beam (FIB) cutting of the apex of the ME was used to expose an electroactive BDD disk. By cyclic voltammetry, the redox reaction of ferrocenemethanol was shown to take place at the BDD microdisk surface. In order to ensure that the outer layer was nonelectrically conductive, a diffusion barrier for boron atoms was established seeking the formation of boron-hydrogen complexes at the interface between the doped and the undoped diamond layers. The applicability of the microelectrodes in localized corrosion was demonstrated by scanning amperometric measurements of oxygen distribution above an Al-Cu-CFRP (Carbon Fiber Reinforced Polymer) galvanic corrosion cell.

Liquid-Like, Self-Healing Aluminum Oxide during Deformation at Room Temperature

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

Yang, Yang; Kushima, Akihiro; Han, Weizhong

Effective protection from environmental degradation relies on the integrity of oxide as diffusion barriers. Ideally, the passivation layer can repair its own breaches quickly under deformation. While studies suggest that the native aluminum oxide may manifest such properties, it has yet to be experimentally proven because direct observations of the air-environmental deformation of aluminum oxide and its initial formation at room temperature are challenging. In this letter, we report in situ experiments to stretch pure aluminum nanotips under O 2 gas environments in a transmission electron microscope (TEM). We discovered that aluminum oxide indeed deforms like liquid and can matchmore » the deformation of Al without any cracks/spallation at moderate strain rate. At higher strain rate, we exposed fresh metal surface, and visualized the self-healing process of aluminum oxide at atomic resolution. Unlike traditional thin-film growth or nanoglass consolidation processes, we observe seamless coalescence of new oxide islands without forming any glass–glass interface or surface grooves, indicating greatly accelerated glass kinetics at the surface compared to the bulk.« less

Liquid-Like, Self-Healing Aluminum Oxide during Deformation at Room Temperature

DOE PAGES

Yang, Yang; Kushima, Akihiro; Han, Weizhong; ...

2018-02-28

Effective protection from environmental degradation relies on the integrity of oxide as diffusion barriers. Ideally, the passivation layer can repair its own breaches quickly under deformation. While studies suggest that the native aluminum oxide may manifest such properties, it has yet to be experimentally proven because direct observations of the air-environmental deformation of aluminum oxide and its initial formation at room temperature are challenging. In this letter, we report in situ experiments to stretch pure aluminum nanotips under O 2 gas environments in a transmission electron microscope (TEM). We discovered that aluminum oxide indeed deforms like liquid and can matchmore » the deformation of Al without any cracks/spallation at moderate strain rate. At higher strain rate, we exposed fresh metal surface, and visualized the self-healing process of aluminum oxide at atomic resolution. Unlike traditional thin-film growth or nanoglass consolidation processes, we observe seamless coalescence of new oxide islands without forming any glass–glass interface or surface grooves, indicating greatly accelerated glass kinetics at the surface compared to the bulk.« less

Diffusion of Messages from an Electronic Cigarette Brand to Potential Users through Twitter

PubMed Central

Chu, Kar-Hai; Unger, Jennifer B.; Allem, Jon-Patrick; Pattarroyo, Monica; Soto, Daniel; Cruz, Tess Boley; Yang, Haodong; Jiang, Ling; Yang, Christopher C.

2015-01-01

Objective This study explores the presence and actions of an electronic cigarette (e-cigarette) brand, Blu, on Twitter to observe how marketing messages are sent and diffused through the retweet (i.e., message forwarding) functionality. Retweet networks enable messages to reach additional Twitter users beyond the sender’s local network. We follow messages from their origin through multiple retweets to identify which messages have more reach, and the different users who are exposed. Methods We collected three months of publicly available data from Twitter. A combination of techniques in social network analysis and content analysis were applied to determine the various networks of users who are exposed to e-cigarette messages and how the retweet network can affect which messages spread. Results The Blu retweet network expanded during the study period. Analysis of user profiles combined with network cluster analysis showed that messages of certain topics were only circulated within a community of e-cigarette supporters, while other topics spread further, reaching more general Twitter users who may not support or use e-cigarettes. Conclusions Retweet networks can serve as proxy filters for marketing messages, as Twitter users decide which messages they will continue to diffuse among their followers. As certain e-cigarette messages extend beyond their point of origin, the audience being exposed expands beyond the e-cigarette community. Potential implications for health education campaigns include utilizing Twitter and targeting important gatekeepers or hubs that would maximize message diffusion. PMID:26684746

Structural and kinetic mapping of side-chain exposure onto the protein energy landscape.

PubMed

Bernstein, Rachel; Schmidt, Kierstin L; Harbury, Pehr B; Marqusee, Susan

2011-06-28

Identification and characterization of structural fluctuations that occur under native conditions is crucial for understanding protein folding and function, but such fluctuations are often rare and transient, making them difficult to study. Native-state hydrogen exchange (NSHX) has been a powerful tool for identifying such rarely populated conformations, but it generally reveals no information about the placement of these species along the folding reaction coordinate or the barriers separating them from the folded state and provides little insight into side-chain packing. To complement such studies, we have performed native-state alkyl-proton exchange, a method analogous to NSHX that monitors cysteine modification rather than backbone amide exchange, to examine the folding landscape of Escherichia coli ribonuclease H, a protein well characterized by hydrogen exchange. We have chosen experimental conditions such that the rate-limiting barrier acts as a kinetic partition: residues that become exposed only upon crossing the unfolding barrier are modified in the EX1 regime (alkylation rates report on the rate of unfolding), while those exposed on the native side of the barrier are modified predominantly in the EX2 regime (alkylation rates report on equilibrium populations). This kinetic partitioning allows for identification and placement of partially unfolded forms along the reaction coordinate. Using this approach we detect previously unidentified, rarely populated conformations residing on the native side of the barrier and identify side chains that are modified only upon crossing the unfolding barrier. Thus, in a single experiment under native conditions, both sides of the rate-limiting barrier are investigated.

Structural and kinetic mapping of side-chain exposure onto the protein energy landscape

PubMed Central

Bernstein, Rachel; Schmidt, Kierstin L.; Harbury, Pehr B.; Marqusee, Susan

2011-01-01

Identification and characterization of structural fluctuations that occur under native conditions is crucial for understanding protein folding and function, but such fluctuations are often rare and transient, making them difficult to study. Native-state hydrogen exchange (NSHX) has been a powerful tool for identifying such rarely populated conformations, but it generally reveals no information about the placement of these species along the folding reaction coordinate or the barriers separating them from the folded state and provides little insight into side-chain packing. To complement such studies, we have performed native-state alkyl-proton exchange, a method analogous to NSHX that monitors cysteine modification rather than backbone amide exchange, to examine the folding landscape of Escherichia coli ribonuclease H, a protein well characterized by hydrogen exchange. We have chosen experimental conditions such that the rate-limiting barrier acts as a kinetic partition: residues that become exposed only upon crossing the unfolding barrier are modified in the EX1 regime (alkylation rates report on the rate of unfolding), while those exposed on the native side of the barrier are modified predominantly in the EX2 regime (alkylation rates report on equilibrium populations). This kinetic partitioning allows for identification and placement of partially unfolded forms along the reaction coordinate. Using this approach we detect previously unidentified, rarely populated conformations residing on the native side of the barrier and identify side chains that are modified only upon crossing the unfolding barrier. Thus, in a single experiment under native conditions, both sides of the rate-limiting barrier are investigated. PMID:21670244

Thermal stability, adhesion and electrical studies on (Ti,Zr)N x thin films as low resistive diffusion barriers between Cu and Si

NASA Astrophysics Data System (ADS)

Huang, Cheng-Lin; Lai, Chih-Huang; Tsai, Po-Hao; Kuo, Yu-Lin; Lin, Jing-Cheng; Lee, Chiapyng

2014-05-01

In this study, we investigated the thermal stability, wettability, adhesion and reliability of (Ti,Zr)N x films used as the diffusion barrier between Cu and Si. (Ti,Zr)N x films were prepared by DC reactive magnetron sputtering from a Ti-5 at. % Zr alloy target in N2/Ar gas mixtures. A minimum film resistivity of 59.3 µω cm was obtained at an N2/Ar flow ratio of 2.75, which corresponds to the near stoichiometric composition (N/(Ti,Zr) ratio ˜0.95). The sheet resistance of Cu/(Ti,Zr)N0.95/Si was not significantly increased until annealing above 750°C, indicating good thermal stability. On the other hand, the adhesion energy between Cu and the (Ti,Zr)Nx film was reduced as the N/Ti ratio was increased. To obtain reliable performance on stress-induced-voiding (SIV) and electromigration (EM) tests, we proposed to use (Ti,Zr)/(Ti,Zr)N x /(Ti,Zr) tri-layers. We suggest that the interfacial adhesion between barrier and Cu plays an important role in reliability. The proposed tri-layer structure may be a promising candidate for a barrier, as it exhibits excellent reliability without increasing resistance.

Microstructural analysis of as-processed U-10 wt.%Mo monolithic fuel plate in AA6061 matrix with Zr diffusion barrier

NASA Astrophysics Data System (ADS)

Perez, E.; Yao, B.; Keiser, D. D., Jr.; Sohn, Y. H.

2010-07-01

For higher U-loading in low-enriched U-10 wt.%Mo fuels, monolithic fuel plate clad in AA6061 is being developed as a part of Reduced Enrichment for Research and Test Reactor (RERTR) program. This paper reports the first characterization results from a monolithic U-10 wt.%Mo fuel plate with a Zr diffusion barrier that was fabricated as part of a plate fabrication campaign for irradiation testing in the Advanced Test Reactor (ATR). Both scanning and transmission electron microscopy (SEM and TEM) were employed for analysis. At the interface between the Zr barrier and U-10 wt.%Mo, going from Zr to U(Mo), UZr 2, γ-UZr, Zr solid-solution and Mo 2Zr phases were observed. The interface between AA6061 cladding and Zr barrier plate consisted of four layers, going from Al to Zr, (Al, Si) 2Zr, (Al, Si)Zr 3 (Al, Si) 3Zr, and AlSi 4Zr 5. Irradiation behavior of these intermetallic phases is discussed based on their constituents. Characterization of as-fabricated phase constituents and microstructure would help understand the irradiation behavior of these fuel plates, interpret post-irradiation examination, and optimize the processing parameters of monolithic fuel system.

Activated dynamics in dense fluids of attractive nonspherical particles. II. Elasticity, barriers, relaxation, fragility, and self-diffusion

NASA Astrophysics Data System (ADS)

Tripathy, Mukta; Schweizer, Kenneth S.

2011-04-01

In paper II of this series we apply the center-of-mass version of Nonlinear Langevin Equation theory to study how short-range attractive interactions influence the elastic shear modulus, transient localization length, activated dynamics, and kinetic arrest of a variety of nonspherical particle dense fluids (and the spherical analog) as a function of volume fraction and attraction strength. The activation barrier (roughly the natural logarithm of the dimensionless relaxation time) is predicted to be a rich function of particle shape, volume fraction, and attraction strength, and the dynamic fragility varies significantly with particle shape. At fixed volume fraction, the barrier grows in a parabolic manner with inverse temperature nondimensionalized by an onset value, analogous to what has been established for thermal glass-forming liquids. Kinetic arrest boundaries lie at significantly higher volume fractions and attraction strengths relative to their dynamic crossover analogs, but their particle shape dependence remains the same. A limited universality of barrier heights is found based on the concept of an effective mean-square confining force. The mean hopping time and self-diffusion constant in the attractive glass region of the nonequilibrium phase diagram is predicted to vary nonmonotonically with attraction strength or inverse temperature, qualitatively consistent with recent computer simulations and colloid experiments.

Role of constant value of surface diffuseness in alpha decay half-lives of superheavy nuclei

NASA Astrophysics Data System (ADS)

Dehghani, V.; Alavi, S. A.; Benam, Kh.

2018-05-01

By using WKB method and considering deformed Woods-Saxon nuclear potential, deformed Coulomb potential, and centrifugal potential, the alpha decay half-lives of 68 superheavy alpha emitters have been calculated. The effect of the constant value of surface diffuseness parameter in the range of 0.1 ≤ a ≤ 0.9 (fm) on the potential barrier, tunneling probability, assault frequency, and alpha decay half-lives has been investigated. Significant differences were observed for alpha decay half-lives and decay quantities in this range of surface diffuseness. Good agreement between calculated half-lives with fitted surface diffuseness parameter a = 0.54 (fm) and experiment was observed.

ICP-MS measurement of iodine diffusion in IG-110 graphite for HTGR/VHTR

NASA Astrophysics Data System (ADS)

Carter, L. M.; Brockman, J. D.; Robertson, J. D.; Loyalka, S. K.

2016-05-01

Graphite functions as a structural material and as a barrier to fission product release in HTGR/VHTR designs, and elucidation of transport parameters for fission products in reactor-grade graphite is thus required for reactor source terms calculations. We measured iodine diffusion in spheres of IG-110 graphite using a release method based on Fickain diffusion kinetics. Two sources of iodine were loaded into the graphite spheres; molecular iodine (I2) and cesium iodide (CsI). Measurements of the diffusion coefficient were made over a temperature range of 873-1293 K. We have obtained the following Arrhenius expressions for iodine diffusion:DI , CsI infused =(6 ×10-12 2/s) exp(30,000 J/mol RT) And,DI , I2 infused =(4 ×10-10 m2/s) exp(-11,000 J/mol RT ) The results indicate that iodine diffusion in IG-110 graphite is not well-described by Fickan diffusion kinetics. To our knowledge, these are the first measurements of iodine diffusion in IG-110 graphite.

Enhancing Cation Diffusion and Suppressing Anion Diffusion via Lewis-Acidic Polymer Electrolytes.

PubMed

Savoie, Brett M; Webb, Michael A; Miller, Thomas F

2017-02-02

Solid polymer electrolytes (SPEs) have the potential to increase both the energy density and stability of lithium-based batteries, but low Li + conductivity remains a barrier to technological viability. SPEs are designed to maximize Li + diffusivity relative to the anion while maintaining sufficient salt solubility. It is thus remarkable that poly(ethylene oxide) (PEO), the most widely used SPE, exhibits Li + diffusivity that is an order of magnitude smaller than that of typical counterions at moderate salt concentrations. We show that Lewis-basic polymers like PEO favor slow cation and rapid anion diffusion, while this relationship can be reversed in Lewis-acidic polymers. Using molecular dynamics, polyboranes are identified that achieve up to 10-fold increases in Li + diffusivities and significant decreases in anion diffusivities, relative to PEO in the dilute-ion regime. These results illustrate a general principle for increasing Li + diffusivity and transference number with chemistries that exhibit weaker cation and stronger anion coordination.

Oxygen uptake rate in alginate producer (algU+) and nonproducer (algU-) strains of Azotobacter vinelandii under nitrogen-fixation conditions.

PubMed

Castillo, T; López, I; Flores, C; Segura, D; García, A; Galindo, E; Peña, C

2018-07-01

The sigma E (AlgU) in Azotobacter vinelandii has been shown to control the expression of cydR gene, a repressor of genes of the alternative respiratory chain, and alginate has been considered a barrier for oxygen diffusion. Therefore, the aim of the present study was to compare the respiratory activity of an alginate nonproducing strain, lacking the sigma factor E (algU-), and polymer-producing strains (algU+) of A. vinelandii under diazotrophic conditions at different aeration conditions. Our results reveal that under diazotrophic and high aeration conditions, A. vinelandii strain OP (algU-) had a specific oxygen consumption rate higher (30 and 54%) than those observed in the OP algU+-complemented strain, named OPAlgU+, and the ATCC 9046 respectively. However, the specific growth rate and biomass yields (based on oxygen and sucrose) were lower for OP cultivations as compared to the algU+ strains. These differences were partially explained by an increase in 1·5-fold of cydA relative expression in the OP strain, as compared to that obtained in the isogenic OPAlgU+ strain. Overall, our results confirm the important role of algU gene on the regulation of respiratory metabolism under diazotrophic growth when A. vinelandii is exposed to high aeration. This study highlights the role of AlgU to control respiration of A. vinelandii when exposed to diazotrophy. © 2018 The Society for Applied Microbiology.

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

Capurro, O. A.; Niello, J. O. Fernandez; Pacheco, A. J.

We have investigated experimental quasielastic cross sections measured at backward angles and at deep sub-barrier energies for the {sup 35}Cl+{sup 105,106,110}Pd and {sup 32}S+{sup 110}Pd systems. Since coupling effects are almost negligible at very low bombarding energies, the quasielastic data allow one to determine the diffuseness parameter of the ion-ion potential. For the analyzed reactions we have obtained a surface diffuseness parameter value around 0.58{+-}0.04 fm.

Impact of diffusion barriers to small cytotoxic molecules on the efficacy of immunotherapy in breast cancer.

PubMed

Das, Hiranmoy; Wang, Zhihui; Niazi, M Khalid Khan; Aggarwal, Reeva; Lu, Jingwei; Kanji, Suman; Das, Manjusri; Joseph, Matthew; Gurcan, Metin; Cristini, Vittorio

2013-01-01

Molecular-focused cancer therapies, e.g., molecularly targeted therapy and immunotherapy, so far demonstrate only limited efficacy in cancer patients. We hypothesize that underestimating the role of biophysical factors that impact the delivery of drugs or cytotoxic cells to the target sites (for associated preferential cytotoxicity or cell signaling modulation) may be responsible for the poor clinical outcome. Therefore, instead of focusing exclusively on the investigation of molecular mechanisms in cancer cells, convection-diffusion of cytotoxic molecules and migration of cancer-killing cells within tumor tissue should be taken into account to improve therapeutic effectiveness. To test this hypothesis, we have developed a mathematical model of the interstitial diffusion and uptake of small cytotoxic molecules secreted by T-cells, which is capable of predicting breast cancer growth inhibition as measured both in vitro and in vivo. Our analysis shows that diffusion barriers of cytotoxic molecules conspire with γδ T-cell scarcity in tissue to limit the inhibitory effects of γδ T-cells on cancer cells. This may increase the necessary ratios of γδ T-cells to cancer cells within tissue to unrealistic values for having an intended therapeutic effect, and decrease the effectiveness of the immunotherapeutic treatment.

Diffusion in quasi-one-dimensional channels: A small system n, p, T, transition state theory for hopping times.

PubMed

Ahmadi, Sheida; Bowles, Richard K

2017-04-21

Particles confined to a single file, in a narrow quasi-one-dimensional channel, exhibit a dynamic crossover from single file diffusion to Fickian diffusion as the channel radius increases and the particles begin to pass each other. The long time diffusion coefficient for a system in the crossover regime can be described in terms of a hopping time, which measures the time it takes for a particle to escape the cage formed by its neighbours. In this paper, we develop a transition state theory approach to the calculation of the hopping time, using the small system isobaric-isothermal ensemble to rigorously account for the volume fluctuations associated with the size of the cage. We also describe a Monte Carlo simulation scheme that can be used to calculate the free energy barrier for particle hopping. The theory and simulation method correctly predict the hopping times for a two-dimensional confined ideal gas system and a system of confined hard discs over a range of channel radii, but the method breaks down for wide channels in the hard discs' case, underestimating the height of the hopping barrier due to the neglect of interactions between the small system and its surroundings.

Anomalous diffusion of brain metabolites evidenced by diffusion-weighted magnetic resonance spectroscopy in vivo

PubMed Central

Marchadour, Charlotte; Brouillet, Emmanuel; Hantraye, Philippe; Lebon, Vincent; Valette, Julien

2012-01-01

Translational displacement of molecules within cells is a key process in cellular biology. Molecular motion potentially depends on many factors, including active transport, cytosol viscosity and molecular crowding, tortuosity resulting from cytoskeleton and organelles, and restriction barriers. However, the relative contribution of these factors to molecular motion in the cytoplasm remains poorly understood. In this work, we designed an original diffusion-weighted magnetic resonance spectroscopy strategy to probe molecular motion at subcellular scales in vivo. This led to the first observation of anomalous diffusion, that is, dependence of the apparent diffusion coefficient (ADC) on the diffusion time, for endogenous intracellular metabolites in the brain. The observed increase of the ADC at short diffusion time yields evidence that metabolite motion is characteristic of hindered random diffusion rather than active transport, for time scales up to the dozen milliseconds. Armed with this knowledge, data modeling based on geometrically constrained diffusion was performed. Results suggest that metabolite diffusion occurs in a low-viscosity cytosol hindered by ∼2-μm structures, which is consistent with known intracellular organization. PMID:22929443

Integrin-based diffusion barrier separates membrane domains enabling the formation of microbiostatic frustrated phagosomes

PubMed Central

Maxson, Michelle E; Naj, Xenia; O'Meara, Teresa R; Plumb, Jonathan D; Cowen, Leah E

2018-01-01

Candida albicans hyphae can reach enormous lengths, precluding their internalization by phagocytes. Nevertheless, macrophages engulf a portion of the hypha, generating incompletely sealed tubular phagosomes. These frustrated phagosomes are stabilized by a thick cuff of F-actin that polymerizes in response to non-canonical activation of integrins by fungal glycan. Despite their continuity, the surface and invaginating phagosomal membranes retain a strikingly distinct lipid composition. PtdIns(4,5)P2 is present at the plasmalemma but is not detectable in the phagosomal membrane, while PtdIns(3)P and PtdIns(3,4,5)P3 co-exist in the phagosomes yet are absent from the surface membrane. Moreover, endo-lysosomal proteins are present only in the phagosomal membrane. Fluorescence recovery after photobleaching revealed the presence of a diffusion barrier that maintains the identity of the open tubular phagosome separate from the plasmalemma. Formation of this barrier depends on Syk, Pyk2/Fak and formin-dependent actin assembly. Antimicrobial mechanisms can thereby be deployed, limiting the growth of the hyphae. PMID:29553370

Method and apparatus for operating an improved thermocline storage unit

DOEpatents

Copeland, R.J.

1982-09-30

A method and apparatus for operating a thermocline storage unit in which an insulated barrier member is provided substantially at the interface region between the hot and cold liquids in the storage tank. The barrier member physically and thermally separates the hot and cold liquids substantially preventing any diffusing or mixing between them and substantially preventing any heat transfer there between. The barrier member follows the rise and fall of the interface region between the liquids as the tank is charged and discharged. Two methods of maintaining it in the interface region are disclosed. With the structure and operation of the present invention and in particular the significant reduction in diffusing or mixing between the hot and cold liquids as well as the significant reduction in the thermal heat transfer between them, the performance of the storage tank is improved. More specifically, the stability of the interface region or thermocline is enhanced and the thickness of the thermocline is reduced producing a corresponding increase in the steepness of the temperature gradient across the thermocline and a more efficiently operating thermocline storage unit.

Method and apparatus for operating an improved thermocline storage unit

DOEpatents

Copeland, Robert J.

1985-01-01

A method and apparatus for operating a thermocline storage unit in which an insulated barrier member is provided substantially at the interface region between the hot and cold liquids in the storage tank. The barrier member physically and thermally separates the hot and cold liquids substantially preventing any diffusing or mixing between them and substantially preventing any heat transfer therebetween. The barrier member follows the rise and fall of the interface region between the liquids as the tank is charged and discharged. Two methods of maintaining it in the interface region are disclosed. With the structure and operation of the present invention and in particular the significant reduction in diffusing or mixing between the hot and cold liquids as well as the significant reduction in the thermal heat transfer between them, the performance of the storage tank is improved. More specifically, the stability of the interface region or thermocline is enhanced and the thickness of the thermocline is reduced producing a corresponding increase in the steepness of the temperature gradient across the thermocline and a more efficiently operating thermocline storage unit.

Corrosion Properties of Dissimilar Friction Stir Welded 6061 Aluminum and HT590 Steel

NASA Astrophysics Data System (ADS)

Seo, Bosung; Song, Kuk Hyun; Park, Kwangsuk

2018-05-01

Corrosion properties of dissimilar friction stir welded 6061 aluminum and HT590 steel were investigated to understand effects of galvanic corrosion. As cathode when coupled, HT590 was cathodically protected. However, the passivation of AA6061 made the aluminum alloy cathode temporarily, which leaded to corrosion of HT590. From the EIS analysis showing Warburg diffusion plot in Nyquist plots, it can be inferred that the stable passivation layer was formed on AA6061. However, the weld as well as HT590 did not show Warburg diffusion plot in Nyquist plots, suggesting that there was no barrier for corrosion or even if it exists, the barrier had no function for preventing and/or retarding charge transport through the passivation layer. The open circuit potential measurements showed that the potential of the weld was similar to that of HT590, which lied in the pitting region for AA6061, making the aluminum alloy part of the weld keep corrosion state. That resulted in the cracked oxide film on AA6061 of the weld, which could not play a role of corrosion barrier.

Influence of ion transport on discharge propagation of nanosecond dielectric barrier discharge plasma actuator

NASA Astrophysics Data System (ADS)

Hua, Weizhuo; Koji, Fukagata

2017-11-01

A numerical study has been conducted to understand the streamer formation and propagation of nanosecond pulsed surface dielectric barrier discharge of positive polarity. First we compared the result of different grid configuration to investigate the influence of x and y direction grid spacing on the streamer propagation. The streamer propagation is sensitive to y grid spacing especially at the dielectric surface. The streamer propagation velocity can reach 0.2 cm/ns when the voltage magnitude is 12 kV. A narrow gap was found between the streamer and dielectric barrier, where the plasma density is several orders of magnitude smaller than the streamer region. Analyses on the ion transport in the gap and streamer regions show the different ion transport mechanisms in the two different region. In the gap region, the diffusion of electron toward the dielectric layer decreases the seed electron in the beginning of voltage pulse, resulting that ionization avalanche does not occur. The streamer region is not significantly affected by the diffusion flux toward the dielectric layer, so that ionization avalanche takes place and leads to dramatic increase of plasma density.

Tight junctions and the modulation of barrier function in disease

PubMed Central

2008-01-01

Tight junctions create a paracellular barrier in epithelial and endothelial cells protecting them from the external environment. Two different classes of integral membrane proteins constitute the tight junction strands in epithelial cells and endothelial cells, occludin and members of the claudin protein family. In addition, cytoplasmic scaffolding molecules associated with these junctions regulate diverse physiological processes like proliferation, cell polarity and regulated diffusion. In many diseases, disruption of this regulated barrier occurs. This review will briefly describe the molecular composition of the tight junctions and then present evidence of the link between tight junction dysfunction and disease. PMID:18415116

Microstructural characterization of a thin film ZrN diffusion barrier in an As-fabricated U-7Mo/Al matrix dispersion fuel plate

NASA Astrophysics Data System (ADS)

Keiser, Dennis D.; Perez, Emmanuel; Wiencek, Tom; Leenaers, Ann; Van den Berghe, Sven

2015-03-01

The United States High Performance Research Reactor Fuel Development program is developing low enriched uranium fuels for application in research and test reactors. One concept utilizes U-7 wt.% Mo (U-7Mo) fuel particles dispersed in Al matrix, where the fuel particles are coated with a 1 μm-thick ZrN coating. The ZrN serves as a diffusion barrier to eliminate a deleterious reaction that can occur between U-7Mo and Al when a dispersion fuel is irradiated under aggressive reactor conditions. To investigate the final microstructure of a physically-vapor-deposited ZrN coating in a dispersion fuel plate after it was fabricated using a rolling process, characterization samples were taken from a fuel plate that was fabricated at 500 °C using ZrN-coated U-7Mo particles, Al matrix and AA6061 cladding. Scanning electron and transmission electron microscopy analysis were performed. Data from these analyses will be used to support future microstructural examinations of irradiated fuel plates, in terms of understanding the effects of irradiation on the ZrN microstructure, and to determine the role of diffusion barrier microstructure in eliminating fuel/matrix interactions during irradiation. The as-fabricated coating was determined to be cubic-ZrN (cF8) phase. It exhibited a columnar microstructure comprised of nanometer-sized grains and a region of relatively high porosity, mainly near the Al matrix. Small impurity-containing phases were observed at the U-7Mo/ZrN interface, and no interaction zone was observed at the ZrN/Al interface. The bonding between the U-7Mo and ZrN appeared to be mechanical in nature. A relatively high level of oxygen was observed in the ZrN coating, extending from the Al matrix in the ZrN coating in decreasing concentration. The above microstructural characteristics are discussed in terms of what may be most optimal for a diffusion barrier in a dispersion fuel plate application.

Influence of interface inhomogeneities in thin-film Schottky diodes

NASA Astrophysics Data System (ADS)

Wilson, Joshua; Zhang, Jiawei; Li, Yunpeng; Wang, Yiming; Xin, Qian; Song, Aimin

2017-11-01

The scalability of thin-film transistors has been well documented, but there have been very few investigations into the effects of device scalability in Schottky diodes. Indium-gallium-zinc-oxide (IGZO) Schottky diodes were fabricated with IGZO thicknesses of 50, 150, and 250 nm. Despite the same IGZO-Pt interface and Schottky barrier being formed in all devices, reducing the IGZO thickness caused a dramatic deterioration of the current-voltage characteristics, most notably increasing the reverse current by nearly five orders of magnitude. Furthermore, the forward characteristics display an increase in the ideality factor and a reduction in the barrier height. The origins of this phenomenon have been elucidated using device simulations. First, when the semiconductor layer is fully depleted, the electric field increases with the reducing thickness, leading to an increased diffusion current. However, the effects of diffusion only offer a small contribution to the huge variations in reverse current seen in the experiments. To fully explain this effect, the role of inhomogeneities in the Schottky barrier height has been considered. Contributions from lower barrier regions (LBRs) are found to dominate the reverse current. The conduction band minimum below these LBRs is strongly dependent upon thickness and bias, leading to reverse current variations as large as several orders of magnitude. Finally, it is demonstrated that the thickness dependence of the reverse current is exacerbated as the magnitude of the inhomogeneities is increased and alleviated in the limit where the LBRs are large enough not to be influenced by the adjacent higher barrier regions.

Defining the Interaction of HIV-1 with the Mucosal Barriers of the Female Reproductive Tract

PubMed Central

Carias, Ann M.; McCoombe, Scott; McRaven, Michael; Anderson, Meegan; Galloway, Nicole; Vandergrift, Nathan; Fought, Angela J.; Lurain, John; Duplantis, Maurice; Veazey, Ronald S.

2013-01-01

Worldwide, HIV-1 infects millions of people annually, the majority of whom are women. To establish infection in the female reproductive tract (FRT), HIV-1 in male ejaculate must overcome numerous innate and adaptive immune factors, traverse the genital epithelium, and establish infection in underlying CD4+ target cells. How the virus achieves this remains poorly defined. By utilizing a new technique, we define how HIV-1 interacts with different tissues of the FRT using human cervical explants and in vivo exposure in the rhesus macaque vaginal transmission model. Despite previous claims of the squamous epithelium being an efficient barrier to virus entry, we reveal that HIV-1 can penetrate both intact columnar and squamous epithelial barriers to depths where the virus can encounter potential target cells. In the squamous epithelium, we identify virus entry occurring through diffusive percolation, penetrating areas where cell junctions are absent. In the columnar epithelium, we illustrate that virus does not transverse barriers as well as previously thought due to mucus impediment. We also show a statistically significant correlation between the viral load of inocula and the ability of HIV-1 to pervade the squamous barrier. Overall, our results suggest a diffusive percolation mechanism for the initial events of HIV-1 entry. With these data, we also mathematically extrapolate the number of HIV-1 particles that penetrate the mucosa per coital act, providing a biological description of the mechanism for HIV-1 transmission during the acute and chronic stages of infection. PMID:23966398

Tribological properties of ceramic-(Ti3Al-Nb) sliding couples for use as candidate seal materials to 700 C

NASA Technical Reports Server (NTRS)

Dellacorte, Christhopher; Steinetz, Bruce M.; Brindley, Pamela K.

1990-01-01

Tribological properties of Ti3Al-Nb intermetallic disks sliding against alumina-boria-silicate fabric were ascertained in air at temperatures from 25 to 700 C. These materials are candidates for sliding seal applications for the National AeroSpace Plane. The tests were done using a pin on disk tribometer. Sliding was unidirectional at 0.27 m/sec under a nominal contact stress of 340 kPa. Gold sputter or ion plating deposited films were used to reduce friction and wear. Rhodium and palladium films were used beneath the gold lubricating films to prevent diffusion of the substrate into the gold at high temperature. The friction and wear of the unlubricated specimens was unacceptable. Friction coefficients were generally greater than 1.0. The ion plated gold films, when used with a rhodium diffusion barrier reduced friction by almost a factor of 2. Wear was also substantially reduced. The sputter deposited films were not adherent unless the substrate was sputter cleaned immediately prior to film deposition. Palladium did not function as a diffusion barrier.

Diffusion of multiwall carbon nanotubes (MWCNTs) through a high density polyethylene (HDPE) geomembrane.

PubMed

Saheli, P T; Rowe, R K; Petersen, E J; O'Carroll, D M

2017-05-01

The new applications for carbon nanotubes (CNTs) in various fields and consequently their greater production volume have increased their potential release to the environment. Landfills are one of the major locations where carbon nanotubes are expected to be disposed and it is important to ensure that they can limit the release of CNTs. Diffusion of multiwall carbon nanotubes (MWCNTs) dispersed in an aqueous media through a high-density polyethylene (HDPE) geomembrane (as a part of the landfill barrier system) was examined. Based on the laboratory tests, the permeation coefficient was estimated to be less than 5.1×10 -15 m 2 /s. The potential performance of a HDPE geomembrane and geosynthetic clay liner (GCL) as parts of a composite liner in containing MWCNTs was modelled for six different scenarios. The results suggest that the low value of permeation coefficient of an HDPE geomembrane makes it an effective diffusive barrier for MWCNTs and by keeping the geomembrane defects to minimum during the construction (e.g., number of holes and length of wrinkles) a composite liner commonly used in municipal solid waste landfills will effectively contain MWCNTs.

Tribological properties of ceramic/Ti3Al-Nb sliding couples for use as candidate seal materials to 700 deg C

NASA Technical Reports Server (NTRS)

Dellacorte, Christopher; Steinetz, Bruce M.; Brindley, Pamela K.

1989-01-01

Tribological properties of Ti3Al-Nb intermetallic disks sliding against alumina-boria-silicate fabric were ascertained in air at temperatures from 25 to 700 C. These materials are candidates for sliding seal applications for the National AeroSpace Plane. The tests were done using a pin on disk tribometer. Sliding was unidirectional at 0.27 m/sec under a nominal contact stress of 340 kPa. Gold sputter or ion plating deposited films were used to reduce friction and wear. Rhodium and palladium films were used beneath the gold lubricating films to prevent diffusion of the substrate into the gold at high temperature. The friction and wear of the unlubricated specimens was unacceptable. Friction coefficients were generally greater than 1.0. The ion plated gold films, when used with a rhodium diffusion barrier reduced friction by almost a factor of 2. Wear was also substantially reduced. The sputter deposited films were not adherent unless the substrate was sputter cleaned immediately prior to film deposition. Palladium did not function as a diffusion barrier.

Markov Chain Monte Carlo in the Analysis of Single-Molecule Experimental Data

NASA Astrophysics Data System (ADS)

Kou, S. C.; Xie, X. Sunney; Liu, Jun S.

2003-11-01

This article provides a Bayesian analysis of the single-molecule fluorescence lifetime experiment designed to probe the conformational dynamics of a single DNA hairpin molecule. The DNA hairpin's conformational change is initially modeled as a two-state Markov chain, which is not observable and has to be indirectly inferred. The Brownian diffusion of the single molecule, in addition to the hidden Markov structure, further complicates the matter. We show that the analytical form of the likelihood function can be obtained in the simplest case and a Metropolis-Hastings algorithm can be designed to sample from the posterior distribution of the parameters of interest and to compute desired estiamtes. To cope with the molecular diffusion process and the potentially oscillating energy barrier between the two states of the DNA hairpin, we introduce a data augmentation technique to handle both the Brownian diffusion and the hidden Ornstein-Uhlenbeck process associated with the fluctuating energy barrier, and design a more sophisticated Metropolis-type algorithm. Our method not only increases the estimating resolution by several folds but also proves to be successful for model discrimination.

Nitriding of super alloys for enhancing physical properties

DOEpatents

Purohit, A.

1984-06-25

The invention teaches the improvement of certain super alloys by exposing the alloy to an atmosphere of elemental nitrogen at elevated temperatures in excess of 750/sup 0/C but less than 1150/sup 0/C for an extended duration, viz., by nitriding the surface of the alloy, to establish barrier nitrides of the order of 25 to 100 micrometers thickness. These barrier

Hot chemistry in the diffuse medium: spectral signature in the H2 rotational lines

NASA Astrophysics Data System (ADS)

Verstraete, L.; Falgarone, E.; Pineau des Forets, G.; Flower, D.; Puget, J. L.

1999-03-01

Most of the diffuse interstellar medium is cold, but it must harbor pockets of hot gas to explain the large observed abundances of molecules like CH+ and HCO+. Because they dissipate locally large amounts of kinetic energy, MHD shocks and coherent vortices in turbulence can drive endothermic chemical reactions or reactions with large activation barriers. We predict the spectroscopic signatures in the H2 rotational lines of MHD shocks and vortices and compare them to those observed with the ISO-SWS along a line of sight through the Galaxy which samples 20 magnitudes of mostly diffuse gas.

Removing the barrier to the calculation of activation energies: Diffusion coefficients and reorientation times in liquid water.

PubMed

Piskulich, Zeke A; Mesele, Oluwaseun O; Thompson, Ward H

2017-10-07

General approaches for directly calculating the temperature dependence of dynamical quantities from simulations at a single temperature are presented. The method is demonstrated for self-diffusion and OH reorientation in liquid water. For quantities which possess an activation energy, e.g., the diffusion coefficient and the reorientation time, the results from the direct calculation are in excellent agreement with those obtained from an Arrhenius plot. However, additional information is obtained, including the decomposition of the contributions to the activation energy. These results are discussed along with prospects for additional applications of the direct approach.

Local Versus Long-Range Diffusion Effects of Photoexcited States on Radiative Recombination in Organic-Inorganic Lead Halide Perovskites.

PubMed

Vrućinić, Milan; Matthiesen, Clemens; Sadhanala, Aditya; Divitini, Giorgio; Cacovich, Stefania; Dutton, Sian E; Ducati, Caterina; Atatüre, Mete; Snaith, Henry; Friend, Richard H; Sirringhaus, Henning; Deschler, Felix

2015-09-01

Radiative recombination in thin films of the archetypical, high-performing perovskites CH 3 NH 3 PbBr 3 and CH 3 NH 3 PbI 3 shows localized regions of increased emission with dimensions ≈500 nm. Maps of the spectral emission line shape show narrower emission lines in high emission regions, which can be attributed to increased order. Excited states do not diffuse out of high emission regions before they decay, but are decoupled from nearby regions, either by slow diffusion rates or energetic barriers.

First-principles-based kinetic Monte Carlo studies of diffusion of hydrogen in Ni–Al and Ni–Fe binary alloys

DOE PAGES

Tafen, De Nyago

2015-02-14

The diffusion of dilute hydrogen in fcc Ni–Al and Ni–Fe binary alloys was examined using kinetic Monte Carlo method with input kinetic parameters obtained from first-principles density functional theory. The simulation involves the implementation of computationally efficient energy barrier model that describes the configuration dependence of the hydrogen hopping. The predicted hydrogen diffusion coefficients in Ni and Ni 89.4Fe 10.6 are compared well with the available experimental data. In Ni–Al, the model predicts lower hydrogen diffusivity compared to that in Ni. Overall, diffusion prefactors and the effective activation energies of H in Ni–Fe and Ni–Al are concentration dependent of themore » alloying element. Furthermore, the changes in their values are the results of the short-range order (nearest-neighbor) effect on the interstitial diffusion of hydrogen in fcc Ni-based alloys.« less

Surface diffusion on SrTiO3 (100): A temperature accelerated dynamics and first principles study

NASA Astrophysics Data System (ADS)

Hong, Minki; Wohlwend, Jennifer L.; Behera, Rakesh K.; Phillpot, Simon R.; Sinnott, Susan B.; Uberuaga, Blas P.

2013-11-01

Temperature accelerated dynamics (TAD) with an empirical potential is used to predict diffusion mechanisms and energy barriers associated with surface diffusion of adatoms and surface vacancies on (100) SrTiO3 (STO). Specifically, Sr, O, and Ti adatoms and vacancies are investigated on each termination - SrO and TiO2 - of the SrTiO3 surface. We find that the empirical potential predicts different surface mobility of adatoms depending on the surface termination: they are mobile with relatively low diffusion barriers on the SrO-terminated surface, whereas they are largely immobile on the TiO2-terminated surface. One important finding is that, of the two binding sites on the SrO-terminated surface, one is typically very close in energy to the saddle point. Thus, one of the two sites is a good estimator of the migration energy of the adatom, a conclusion supported by select density functional theory (DFT) calculations. Motivated by this result, we calculate the migration energies for a number of metal elements on the SrO-terminated surface: Ti, Ba, La, and Al. The DFT results also reveal that the details of the migration mechanism depend on the charge state of the diffusing species and that the ability of the empirical potential to properly estimate the migration mechanism depends on the magnitude and variability of the charge transfer between the adatom and the surface.

Multiscale modeling of transdermal drug delivery

NASA Astrophysics Data System (ADS)

Rim, Jee Eun

2006-04-01

This study addresses the modeling of transdermal diffusion of drugs, to better understand the permeation of molecules through the skin, and especially the stratum corneum, which forms the main permeation barrier of the skin. In transdermal delivery of systemic drugs, the drugs diffuse from a patch placed on the skin through the epidermis to the underlying blood vessels. The epidermis is the outermost layer of the skin and can be further divided into the stratum corneum (SC) and the viable epidermis layers. The SC consists of keratinous cells (corneocytes) embedded in the lipid multi-bilayers of the intercellular space. It is widely accepted that the barrier properties of the skin mostly arises from the ordered structure of the lipid bilayers. The diffusion path, at least for lipophilic molecules, seems to be mainly through the lipid bilayers. Despite the advantages of transdermal drug delivery compared to other drug delivery routes such as oral dosing and injections, the low percutaneous permeability of most compounds is a major difficulty in the wide application of transdermal drug delivery. In fact, many transdermal drug formulations include one or more permeation enhancers that increase the permeation of the drug significantly. During the last two decades, many researchers have studied percutaneous absorption of drugs both experimentally and theoretically. However, many are based on pharmacokinetic compartmental models, in which steady or pseudo-steady state conditions are assumed, with constant diffusivity and partitioning for single component systems. This study presents a framework for studying the multi-component diffusion of drugs coupled with enhancers through the skin by considering the microstructure of the stratum corneum (SC). A multiscale framework of modeling the transdermal diffusion of molecules is presented, by first calculating the microscopic diffusion coefficient in the lipid bilayers of the SC using molecular dynamics (MD). Then a homogenization procedure is performed over a model unit cell of the heterogeneous SC, resulting in effective diffusion parameters. These effective parameters are the macroscopic diffusion coefficients for the homogeneous medium that is "equivalent" to the heterogeneous SC, and thus can be used in finite element simulations of the macroscopic diffusion process.

Collective phenomena in volume and surface barrier discharges

NASA Astrophysics Data System (ADS)

Kogelschatz, U.

2010-11-01

Barrier discharges are increasingly used as a cost-effective configuration to produce non-equilibrium plasmas at atmospheric pressure. This way, copious amounts of electrons, ions, free radicals and excited species can be generated without significant heating of the background gas. In most applications the barrier is made of dielectric material. Major applications utilizing mainly dielectric barriers include ozone generation, surface cleaning and modification, polymer and textile treatment, sterilization, pollution control, CO2 lasers, excimer lamps, plasma display panels (flat TV screens). More recent research efforts are devoted to biomedical applications and to plasma actuators for flow control. Sinusoidal feeding voltages at various frequencies as well as pulsed excitation schemes are used. Volume as well as surface barrier discharges can exist in the form of filamentary, regularly patterned or diffuse, laterally homogeneous discharges. The physical effects leading to collective phenomena in volume and surface barrier discharges are discussed in detail. Special attention is paid to self-organization of current filaments and pattern formation. Major similarities of the two types of barrier discharges are elaborated.

Regenerative switching CMOS system

DOEpatents

Welch, James D.

1998-01-01

Complementary Metal Oxide Semiconductor (CMOS) Schottky barrier Field Effect Transistor systems, which are a seriesed combination of N and P-Channel MOSFETS, in which Source Schottky barrier junctions of the N and P-Channel Schottky barrier MOSFETS are electically interconnected, (rather than the Drains as in conventional diffused junction CMOS), which Schottky barrier MOSFET system demonstrates Regenerative Inverting Switching Characteristics in use are disclosed. Both the N and P-Channel Schottky barrier MOSFET devices are unique in that they provide operational Drain Current vs. Drain to Source voltage as a function of Gate voltage only where the polarities of the Drain voltage and Gate voltage are opposite, referenced to the Source as a common terminal, and where the polarity of the voltage applied to the Gate is appropriate to cause Channel inversion. Experimentally derived results which demonstrate and verify the operation of N and P-Channel Schottky barrier MOSFETS actually fabricated on P and N-type Silicon respectively, by a common procedure using vacuum deposited Chromium as a Schottky barrier forming metal, are also provided.

Regenerative switching CMOS system

DOEpatents

Welch, J.D.

1998-06-02

Complementary Metal Oxide Semiconductor (CMOS) Schottky barrier Field Effect Transistor systems, which are a series combination of N and P-Channel MOSFETS, in which Source Schottky barrier junctions of the N and P-Channel Schottky barrier MOSFETS are electrically interconnected, (rather than the Drains as in conventional diffused junction CMOS), which Schottky barrier MOSFET system demonstrates Regenerative Inverting Switching Characteristics in use are disclosed. Both the N and P-Channel Schottky barrier MOSFET devices are unique in that they provide operational Drain Current vs. Drain to Source voltage as a function of Gate voltage only where the polarities of the Drain voltage and Gate voltage are opposite, referenced to the Source as a common terminal, and where the polarity of the voltage applied to the Gate is appropriate to cause Channel inversion. Experimentally derived results which demonstrate and verify the operation of N and P-Channel Schottky barrier MOSFETS actually fabricated on P and N-type Silicon respectively, by a common procedure using vacuum deposited Chromium as a Schottky barrier forming metal, are also provided. 14 figs.

Textural break foundation wall construction modules

DOEpatents

Phillips, Steven J.

1990-01-01

Below-grade, textural-break foundation wall structures are provided for inhibiting diffusion and advection of liquids and gases into and out from a surrounding hydrogeologic environment. The foundation wall structure includes a foundation wall having an interior and exterior surface and a porous medium disposed around a portion of the exterior surface. The structure further includes a modular barrier disposed around a portion of the porous medium. The modular barrier is substantially removable from the hydrogeologic environment.

Microstructural Changes to the Brain of Mice after Methamphetamine Exposure as Identified with Diffusion Tensor Imaging

PubMed Central

McKenna, Benjamin S.; Brown, Gregory G.; Archibald, Sarah; Scadeng, Miriam; Bussell, Robert; Kesby, James P.; Markou, Athina; Soontornniyomkij, Virawudh; Achim, Cristian; Semenova, Svetlana

2016-01-01

Methamphetamine (METH) is an addictive psychostimulant inducing neurotoxicity. Human magnetic resonance imaging and diffusion tensor imaging (DTI) of METH-dependent participants find various structural abnormities. Animal studies demonstrate immunohistochemical changes in multiple cellular pathways after METH exposure. Here, we characterized the long-term effects of METH on brain microstructure in mice exposed to an escalating METH binge regimen using in vivo DTI, a methodology directly translatable across species. Results revealed four patterns of differential fractional anisotropy (FA) and mean diffusivity (MD) response when comparing METH-exposed (n=14) to saline-treated mice (n=13). Compared to the saline group, METH-exposed mice demonstrated: 1) decreased FA with no change in MD [corpus callosum (posterior forceps), internal capsule (left), thalamus (medial aspects), midbrain], 2) increased MD with no change in FA [posterior isocortical regions, caudate-putamen, hypothalamus, cerebral peduncle, internal capsule (right)], 3) increased FA with decreased MD [frontal isocortex, corpus callosum (genu)], and 4) increased FA with no change or increased MD [hippocampi, amygdala, lateral thalamus]. MD was negatively associated with calbindin-1 in hippocampi and positively with dopamine transporter in caudate-putamen. These findings highlight distributed and differential METH effects within the brain suggesting several distinct mechanisms. Such mechanisms likely change brain tissue differentially dependent upon neural location. PMID:27000304

Improving the light output power of DUV-LED by introducing an intrinsic last quantum barrier interlayer on the high-quality AlN template

NASA Astrophysics Data System (ADS)

Tsai, Chia-Lung; Liu, Hsueh-Hsing; Chen, Jun-Wei; Lu, Chien-Pin; Ikenaga, Kazutada; Tabuchi, Toshiya; Matsumoto, Koh; Fu, Yi-Keng

2017-12-01

We demonstrate that the light output power of deep ultraviolet light-emitting diodes (DUV-LEDs) can be improved by introducing an intrinsic last quantum barrier interlayer to a high quality AlN template. The light output power of the DUV-LEDs can be doubled by substituting the last quantum barrier with an intrinsic last quantum barrier (u-LQB)/Mg-doped LQB for only pure u-LQB in the same thickness with a 35 A/cm2 injection current. It is believed that the improved performance of the DUV LED could be attributed to the decreased diffusion of Mg tunneling into MQW and the reduction of sub-band parasitic emissions.

Periodontal and peri-implant bone regeneration: clinical and histologic observations.

PubMed

Artzi, Z; Zohar, R; Tal, H

1997-02-01

The principle of guided tissue regeneration by barrier membranes to restore lost periodontal tissue around natural teeth has also been used around osseointegrated implants in an attempt to restore alveolar ridge defects. While most periodontal procedures in the literature describe root coverage by mucogingival surgery, which achieves healing through soft tissue attachment, regeneration of denuded root surfaces is performed by guided tissue regeneration using expanded polytetrafluoroethylene barrier membranes and demineralized freeze-dried bone allografts as inductive/conductive materials. In this study the technique is applied in two partially exposed cylindrical hydroxyapatite-coated implants in extraction sites in one patient. Surgical reentry in both sites is presented, with histologic examination revealing new bone formation on the exposed root surface and the hydroxyapatite-coated implants.

Evaluation of hot corrosion behavior of thermal barrier coatings

NASA Technical Reports Server (NTRS)

Hodge, P. E.; Miller, R. A.; Gedwill, M. A.

1980-01-01

Calcium silicate and yttria stabilized zirconia/MCrAlY thermal barrier coating systems on air-cooled specimens were exposed to sodium plus vanadium doped Mach 0.3 combustion gases. Thermal barrier coating endurance was determined to be a strong inverse function of ceramic coating thickness. Coating system durability was increased through the use of higher Cr + Al NiCrAl and CoCrAlY bond coatings. Chemical and electron microprobe analyses supported the predictions of condensate compositions and the determination of their roles in causing spalling of the ceramic coatings.

Simulation of stationary glow patterns in dielectric barrier discharges at atmospheric pressure

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

Liu, Fucheng, E-mail: hdlfc@hbu.cn; He, Yafeng; Dong, Lifang

2014-12-15

Self-organized stationary patterns in dielectric barrier discharges operating in glow regime at atmospheric pressure are investigated by a self-consistent two-dimensional fluid model. The simulation results show that two different modes, namely, the diffuse mode and the static patterned mode, can be formed in different ranges of the driving frequency. The discharge operates in Townsend regime in the diffuse mode, while it operates in a glow regime inside the filaments and in a Townsend regime outside the filaments in the stable pattered mode. The forming process of the stationary filaments can be divided into three stages, namely, destabilizing stage, self-assembling stage,more » and stable stage. The space charge associated with residual electron density and surface charge is responsible for the formation of these stationary glow patterns.« less

An entropic barriers diffusion theory of decision-making in multiple alternative tasks

PubMed Central

Sigman, Mariano; Cecchi, Guillermo A.

2018-01-01

We present a theory of decision-making in the presence of multiple choices that departs from traditional approaches by explicitly incorporating entropic barriers in a stochastic search process. We analyze response time data from an on-line repository of 15 million blitz chess games, and show that our model fits not just the mean and variance, but the entire response time distribution (over several response-time orders of magnitude) at every stage of the game. We apply the model to show that (a) higher cognitive expertise corresponds to the exploration of more complex solution spaces, and (b) reaction times of users at an on-line buying website can be similarly explained. Our model can be seen as a synergy between diffusion models used to model simple two-choice decision-making and planning agents in complex problem solving. PMID:29499036

Lithium and sodium adsorption properties of two-dimensional aluminum nitride

NASA Astrophysics Data System (ADS)

Sengupta, Amretashis

2018-09-01

In this work the lithiation and sodiation properties of 2-dimensional (2D) AlN sheets are studied from density functional theory (DFT) simulations. 2D AlN showed theoretical specific capacity of 500.8 and 385.3 mA h g-1, maximum open circuit voltage of 1.49 and 1.86 V and diffusion barriers 0.40 and 0.15 eV, for Li and Na adsorption respectively. The calculations show 2D AlN as a possible alternative as anode material in Li-ion and Na-ion batteries. Further the high specific capacity and small diffusion barriers for Na atoms can make 2D AlN useful in supercapacitors. The change in carrier transport properties due to Li/Na adsorption on monolayer AlN can also be useful in chemical/bio-sensors and nanoelectronics devices.

Minority carrier diffusion length and edge surface-recombination velocity in InP

NASA Technical Reports Server (NTRS)

Hakimzadeh, Roshanak; Bailey, Sheila G.

1993-01-01

A scanning electron microscope was used to obtain the electron-beam-induced current (EBIC) profiles in InP specimens containing a Schottky barrier perpendicular to the scanned (edge) surface. An independent technique was used to measure the edge surface-recombination velocity. These values were used in a fit of the experimental EBIC data with a theoretical expression for normalized EBIC (Donolato, 1982) to obtain the electron (minority carrier) diffusion length.

Magnetic resonance imaging of blood-brain barrier permeability in ischemic stroke using diffusion-weighted arterial spin labeling in rats.

PubMed

Tiwari, Yash V; Lu, Jianfei; Shen, Qiang; Cerqueira, Bianca; Duong, Timothy Q

2017-08-01

Diffusion-weighted arterial spin labeling magnetic resonance imaging has recently been proposed to quantify the rate of water exchange (K w ) across the blood-brain barrier in humans. This study aimed to evaluate the blood-brain barrier disruption in transient (60 min) ischemic stroke using K w magnetic resonance imaging with cross-validation by dynamic contrast-enhanced magnetic resonance imaging and Evans blue histology in the same rats. The major findings were: (i) at 90 min after stroke (30 min after reperfusion), group K w magnetic resonance imaging data showed no significant blood-brain barrier permeability changes, although a few animals showed slightly abnormal K w . Dynamic contrast-enhanced magnetic resonance imaging confirmed this finding in the same animals. (ii) At two days after stroke, K w magnetic resonance imaging revealed significant blood-brain barrier disruption. Regions with abnormal K w showed substantial overlap with regions of hyperintense T 2 (vasogenic edema) and hyperperfusion. Dynamic contrast-enhanced magnetic resonance imaging and Evans blue histology confirmed these findings in the same animals. The K w values in the normal contralesional hemisphere and the ipsilesional ischemic core two days after stroke were: 363 ± 17 and 261 ± 18 min -1 , respectively (P < 0.05, n = 9). K w magnetic resonance imaging is sensitive to blood-brain barrier permeability changes in stroke, consistent with dynamic contrast-enhanced magnetic resonance imaging and Evans blue extravasation. K w magnetic resonance imaging offers advantages over existing techniques because contrast agent is not needed and repeated measurements can be made for longitudinal monitoring or averaging.

Microimaging of transient guest profiles to monitor mass transfer in nanoporous materials

NASA Astrophysics Data System (ADS)

Kärger, Jörg; Binder, Tomas; Chmelik, Christian; Hibbe, Florian; Krautscheid, Harald; Krishna, Rajamani; Weitkamp, Jens

2014-04-01

The intense interactions of guest molecules with the pore walls of nanoporous materials is the subject of continued fundamental research. Stimulated by their thermal energy, the guest molecules in these materials are subject to a continuous, irregular motion, referred to as diffusion. Diffusion, which is omnipresent in nature, influences the efficacy of nanoporous materials in reaction and separation processes. The recently introduced techniques of microimaging by interference and infrared microscopy provide us with a wealth of information on diffusion, hitherto inaccessible from commonly used techniques. Examples include the determination of surface barriers and the sticking coefficient's analogue, namely the probability that, on colliding with the particle surface, a molecule may continue its diffusion path into the interior. Microimaging is further seen to open new vistas in multicomponent guest diffusion (including the detection of a reversal in the preferred diffusion pathways), in guest-induced phase transitions in nanoporous materials and in matching the results of diffusion studies under equilibrium and non-equilibrium conditions.

First-principles investigation of diffusion and defect properties of Fe and Ni in Cr2O3

NASA Astrophysics Data System (ADS)

Rak, Zs.; Brenner, D. W.

2018-04-01

Diffusion of Fe and Ni and the energetics of Fe- and Ni-related defects in chromium oxide (α-Cr2O3) are investigated using first-principles Density Functional Theory calculations in combination with the climbing-image nudged elastic band method. The orientations of the spin magnetic moments of the migrating ions are taken into account and their effects on migration barriers are examined. Several possible diffusion pathways were explored through interstitial and vacancy mechanisms, and it was found that the principal mode of ion transport in Cr2O3 is via vacancies. Both interstitial- and vacancy-mediated diffusions are anisotropic, with diffusion being faster in the z-direction. The energetics of defect formation indicates that the Ni-related defects are less stable than the Fe-related ones. This is consistent with Ni-diffusion being faster than Fe-diffusion. The results are compared with previous theoretical and experimental data and possible implications in corrosion control are discussed.

Influence of deformed surface diffuseness on alpha decay half-lives of actinides and lanthanides

NASA Astrophysics Data System (ADS)

Dahmardeh, S.; Alavi, S. A.; Dehghani, V.

2017-07-01

By using semiclassical WKB method and taking into account the Bohr-Sommerfeld quantization condition, the alpha decay half-lives of some deformed lanthanide (with 151 ≤ A ≤ 160 and 66 ≤ Z ≤ 73) and rare-earth nuclei (with 217 ≤ A ≤ 261 and 92 ≤ Z ≤ 104) have been calculated. The effective potential has been considered as sum of deformed Woods-Saxon nuclear potential, deformed Coulomb potential, and centrifugal potential. The influence of deformed surface diffuseness on the potential barrier, transmission coefficient at each angle, assault frequency, and alpha decay half-lives has been investigated. Good agreement between calculated half-lives with deformed surface diffuseness and experiment is observed. Relative differences between calculated half-lives with deformed surface diffuseness and with constant surface diffuseness were significant.

Hetero-diffusion of Au epitaxy on stepped Ag(110) surface: Study of the jump rate and diffusion coefficient

NASA Astrophysics Data System (ADS)

Benlattar, M.; El koraychy, E.; Kotri, A.; Mazroui, M.

2017-12-01

We have used molecular dynamics simulations combined with an interatomic potential derived from the embedded atom method, to investigate the hetero-diffusion of Au adatom near a stepped Ag(110) surface with the height of one monoatomic layer. The activation energies for different diffusion processes, which occur on the terrace and near the step edge, are calculated both by molecular statics and molecular dynamics simulations. Static energies are found by the drag method, whereas the dynamic barriers are computed at high temperature from the Arrhenius plots. Our numerical results reveal that the jump process requires very high activation energy compared to the exchange process either on the terrace or near the step edge. In this work, other processes, such as upward and downward diffusion at step edges, have also been discussed.

Multiple relaxations of the cluster surface diffusion in a homoepitaxial SrTiO3 layer

NASA Astrophysics Data System (ADS)

Woo, Chang-Su; Chu, Kanghyun; Song, Jong-Hyun; Yang, Chan-Ho

2018-03-01

We examine the surface diffusion process of adatomic clusters on a (001)-oriented SrTiO3 single crystal using reflection high energy electron diffraction (RHEED). We find that the recovery curve of the RHEED intensity acquired after a homoepitaxial half-layer growth can be accurately fit into a double exponential function, indicating the existence of two dominant relaxation mechanisms. The characteristic relaxation times at selected growth temperatures are investigated to determine the diffusion activation barriers of 0.67 eV and 0.91 eV, respectively. The Monte Carlo simulation of the cluster hopping model suggests that the decrease in the number of dimeric and trimeric clusters during surface diffusion is the origin of the observed relaxation phenomena.

Diffusion Tensor Analysis by Two-Dimensional Pair Correlation of Fluorescence Fluctuations in Cells.

PubMed

Di Rienzo, Carmine; Cardarelli, Francesco; Di Luca, Mariagrazia; Beltram, Fabio; Gratton, Enrico

2016-08-23

In a living cell, the movement of biomolecules is highly regulated by the cellular organization into subcompartments that impose barriers to diffusion, can locally break the spatial isotropy, and ultimately guide these molecules to their targets. Despite the pivotal role of these processes, experimental tools to fully probe the complex connectivity (and accessibility) of the cell interior with adequate spatiotemporal resolution are still lacking. Here, we show how the heterogeneity of molecular dynamics and the location of barriers to molecular motion can be mapped in live cells by exploiting a two-dimensional (2D) extension of the pair correlation function (pCF) analysis. Starting from a time series of images collected for the same field of view, the resulting 2D pCF is calculated in the proximity of each point for each time delay and allows us to probe the spatial distribution of the molecules that started from a given pixel. This 2D pCF yields an accurate description of the preferential diffusive routes. Furthermore, we combine this analysis with the image-derived mean-square displacement approach and gain information on the average nanoscopic molecular displacements in different directions. Through these quantities, we build a fluorescence-fluctuation-based diffusion tensor that contains information on speed and directionality of the local dynamical processes. Contrary to classical fluorescence correlation spectroscopy and related methods, this combined approach can distinguish between isotropic and anisotropic local diffusion. We argue that the measurement of this iMSD tensor will contribute to advance our understanding of the role played by the intracellular environment in the regulation of molecular diffusion at the nanoscale. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

A Comparison of Perceptions of Barriers to Academic Success among High-Ability Students from High- and Low-Income Groups: Exposing Poverty of a Different Kind

ERIC Educational Resources Information Center

Cross, Jennifer Riedl; Frazier, Andrea Dawn; Kim, Mihyeon; Cross, Tracy L.

2018-01-01

In 14 focus group interviews, sixth- to eighth-grade high-ability students from high- (n = 36) and low-income (n = 45) families were asked to describe the barriers they perceived to their academic success. Three themes were identified through the qualitative analysis: "Constraining Environments, Integration versus Isolation," and…

Nested barriers to low-carbon infrastructure investment

NASA Astrophysics Data System (ADS)

Granoff, Ilmi; Hogarth, J. Ryan; Miller, Alan

2016-12-01

Low-carbon, 'green' economic growth is necessary to simultaneously improve human welfare and avoid the worst impacts of climate change and environmental degradation. Infrastructure choices underpin both the growth and the carbon intensity of the economy. This Perspective explores the barriers to investing in low-carbon infrastructure and some of the policy levers available to overcome them. The barriers to decarbonizing infrastructure 'nest' within a set of barriers to infrastructure development more generally that cause spending on infrastructure--low-carbon or not--to fall more than 70% short of optimal levels. Developing countries face additional barriers such as currency and political risks that increase the investment gap. Low-carbon alternatives face further barriers, such as commercialization risk and financial and public institutions designed for different investment needs. While the broader barriers to infrastructure investment are discussed in other streams of literature, they are often disregarded in literature on renewable energy diffusion or climate finance, which tends to focus narrowly on the project costs of low- versus high-carbon options. We discuss how to overcome the barriers specific to low-carbon infrastructure within the context of the broader infrastructure gap.

“You Shall Not Pass”—tight junctions of the blood brain barrier

PubMed Central

Bauer, Hans-Christian; Krizbai, István A.; Bauer, Hannelore; Traweger, Andreas

2014-01-01

The structure and function of the barrier layers restricting the free diffusion of substances between the central nervous system (brain and spinal cord) and the systemic circulation is of great medical interest as various pathological conditions often lead to their impairment. Excessive leakage of blood-borne molecules into the parenchyma and the concomitant fluctuations in the microenvironment following a transient breakdown of the blood-brain barrier (BBB) during ischemic/hypoxic conditions or because of an autoimmune disease are detrimental to the physiological functioning of nervous tissue. On the other hand, the treatment of neurological disorders is often hampered as only minimal amounts of therapeutic agents are able to penetrate a fully functional BBB or blood cerebrospinal fluid barrier. An in-depth understanding of the molecular machinery governing the establishment and maintenance of these barriers is necessary to develop rational strategies allowing a controlled delivery of appropriate drugs to the CNS. At the basis of such tissue barriers are intimate cell-cell contacts (zonulae occludentes, tight junctions) which are present in all polarized epithelia and endothelia. By creating a paracellular diffusion constraint TJs enable the vectorial transport across cell monolayers. More recent findings indicate that functional barriers are already established during development, protecting the fetal brain. As an understanding of the biogenesis of TJs might reveal the underlying mechanisms of barrier formation during ontogenic development numerous in vitro systems have been developed to study the assembly and disassembly of TJs. In addition, monitoring the stage-specific expression of TJ-associated proteins during development has brought much insight into the “developmental tightening” of tissue barriers. Over the last two decades a detailed molecular map of transmembrane and cytoplasmic TJ-proteins has been identified. These proteins not only form a cell-cell adhesion structure, but integrate various signaling pathways, thereby directly or indirectly impacting upon processes such as cell-cell adhesion, cytoskeletal rearrangement, and transcriptional control. This review will provide a brief overview on the establishment of the BBB during embryonic development in mammals and a detailed description of the ultrastructure, biogenesis, and molecular composition of epithelial and endothelial TJs will be given. PMID:25520612

The Halo mass function from Excursion Set Theory. II. The Diffusing Barrier

NASA Astrophysics Data System (ADS)

Maggiore, Michele; Riotto, Antonio

2010-07-01

In excursion set theory, the computation of the halo mass function is mapped into a first-passage time process in the presence of a barrier, which in the spherical collapse model is a constant and in the ellipsoidal collapse model is a fixed function of the variance of the smoothed density field. However, N-body simulations show that dark matter halos grow through a mixture of smooth accretion, violent encounters, and fragmentations, and modeling halo collapse as spherical, or even as ellipsoidal, is a significant oversimplification. In addition, the very definition of what is a dark matter halo, both in N-body simulations and observationally, is a difficult problem. We propose that some of the physical complications inherent to a realistic description of halo formation can be included in the excursion set theory framework, at least at an effective level, by taking into account that the critical value for collapse is not a fixed constant δ c , as in the spherical collapse model, nor a fixed function of the variance σ of the smoothed density field, as in the ellipsoidal collapse model, but rather is itself a stochastic variable, whose scatter reflects a number of complicated aspects of the underlying dynamics. Solving the first-passage time problem in the presence of a diffusing barrier we find that the exponential factor in the Press-Schechter mass function changes from exp{-δ2 c /2σ2} to exp{-aδ2 c /2σ2}, where a = 1/(1 + DB ) and DB is the diffusion coefficient of the barrier. The numerical value of DB , and therefore the corresponding value of a, depends among other things on the algorithm used for identifying halos. We discuss the physical origin of the stochasticity of the barrier and, from recent N-body simulations that studied the properties of the collapse barrier, we deduce a value DB ~= 0.25. Our model then predicts a ~= 0.80, in excellent agreement with the exponential fall off of the mass function found in N-body simulations, for the same halo definition. Combining this result with the non-Markovian corrections computed in Paper I of this series, we derive an analytic expression for the halo mass function for Gaussian fluctuations and we compare it with N-body simulations.

Evaluation of genotoxic effects of lead in pottery-glaze workers using micronucleus assay, alkaline comet assay and DNA diffusion assay.

PubMed

Kašuba, V; Rozgaj, R; Milić, M; Zelježić, D; Kopjar, N; Pizent, A; Kljaković-Gašpić, Z; Jazbec, A

2012-10-01

We investigated genotoxic effects of occupational exposure to lead acetate in pottery-glaze ceramic workers. The study was carried out in 30 exposed workers and 30 matched controls, to whom several biochemical parameters-the blood lead (B-Pb; range: exposed, 41.68-404.77; controls, 12-52) and cadmium (B-Cd) level, the activity of delta-aminolevulinic acid dehydratase (ALAD), erythrocyte protoporphyrin (EP), the level of vitamin B(12) and folate in serum-were measured. The genotoxic effects were evaluated by the alkaline comet assay, the DNA diffusion assay and micronucleus test in peripheral blood lymphocytes. Subjects exposed to lead had significantly higher B-Pb level and, consequently, increased values of tail intensity (TI), frequency of apoptotic and necrotic cells, and frequency of micronuclei (MN). In contrast, their activity of ALAD, the level of vitamin B(12) and folate in serum were significantly lower compared to controls. Poisson regression analysis showed a significant correlation of profession, duration of exposure, smoking, level of cadmium in blood, ALAD and EP with primary DNA damage. A majority of primary damage repairs in a short period after exposure to a genotoxic agent. In addition, the influence of gender and level of vitamin B(12) and folate in serum MN frequency in exposed group was observed. In this study, DNA diffusion and micronucleus test showed higher influence of tested parameters to DNA damage. The results indicate a need for concomitant use of at least two different biomarkers of exposure when estimating a genetic risk of lead exposure.

Multichannel fiber-based diffuse reflectance spectroscopy for the rat brain exposed to a laser-induced shock wave: comparison between ipsi- and contralateral hemispheres

NASA Astrophysics Data System (ADS)

Miyaki, Mai; Kawauchi, Satoko; Okuda, Wataru; Nawashiro, Hiroshi; Takemura, Toshiya; Sato, Shunichi; Nishidate, Izumi

2015-03-01

Due to considerable increase in the terrorism using explosive devices, blast-induced traumatic brain injury (bTBI) receives much attention worldwide. However, little is known about the pathology and mechanism of bTBI. In our previous study, we found that cortical spreading depolarization (CSD) occurred in the hemisphere exposed to a laser- induced shock wave (LISW), which was followed by long-lasting hypoxemia-oligemia. However, there is no information on the events occurred in the contralateral hemisphere. In this study, we performed multichannel fiber-based diffuse reflectance spectroscopy for the rat brain exposed to an LISW and compared the results for the ipsilateral and contralateral hemispheres. A pair of optical fibers was put on the both exposed right and left parietal bone; white light was delivered to the brain through source fibers and diffuse reflectance signals were collected with detection fibers for both hemispheres. An LISW was applied to the left (ipsilateral) hemisphere. By analyzing reflectance signals, we evaluated occurrence of CSD, blood volume and oxygen saturation for both hemispheres. In the ipsilateral hemispheres, we observed the occurrence of CSD and long-lasting hypoxemia-oligemia in all rats examined (n=8), as observed in our previous study. In the contralateral hemisphere, on the other hand, no occurrence of CSD was observed, but we observed oligemia in 7 of 8 rats and hypoxemia in 1 of 8 rats, suggesting a mechanism to cause hypoxemia or oligemia or both that is (are) not directly associated with CSD in the contralateral hemisphere.

Modeling and sensitivity analysis of mass transfer in active multilayer polymeric film for food applications

NASA Astrophysics Data System (ADS)

Bedane, T.; Di Maio, L.; Scarfato, P.; Incarnato, L.; Marra, F.

2015-12-01

The barrier performance of multilayer polymeric films for food applications has been significantly improved by incorporating oxygen scavenging materials. The scavenging activity depends on parameters such as diffusion coefficient, solubility, concentration of scavenger loaded and the number of available reactive sites. These parameters influence the barrier performance of the film in different ways. Virtualization of the process is useful to characterize, design and optimize the barrier performance based on physical configuration of the films. Also, the knowledge of values of parameters is important to predict the performances. Inverse modeling and sensitivity analysis are sole way to find reasonable values of poorly defined, unmeasured parameters and to analyze the most influencing parameters. Thus, the objective of this work was to develop a model to predict barrier properties of multilayer film incorporated with reactive layers and to analyze and characterize their performances. Polymeric film based on three layers of Polyethylene terephthalate (PET), with a core reactive layer, at different thickness configurations was considered in the model. A one dimensional diffusion equation with reaction was solved numerically to predict the concentration of oxygen diffused into the polymer taking into account the reactive ability of the core layer. The model was solved using commercial software for different film layer configurations and sensitivity analysis based on inverse modeling was carried out to understand the effect of physical parameters. The results have shown that the use of sensitivity analysis can provide physical understanding of the parameters which highly affect the gas permeation into the film. Solubility and the number of available reactive sites were the factors mainly influencing the barrier performance of three layered polymeric film. Multilayer films slightly modified the steady transport properties in comparison to net PET, giving a small reduction in the permeability and oxygen transfer rate values. Scavenging capacity of the multilayer film increased linearly with the increase of the reactive layer thickness and the oxygen absorption reaction at short times decreased proportionally with the thickness of the external PET layer.

Modeling and sensitivity analysis of mass transfer in active multilayer polymeric film for food applications

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

Bedane, T.; Di Maio, L.; Scarfato, P.

The barrier performance of multilayer polymeric films for food applications has been significantly improved by incorporating oxygen scavenging materials. The scavenging activity depends on parameters such as diffusion coefficient, solubility, concentration of scavenger loaded and the number of available reactive sites. These parameters influence the barrier performance of the film in different ways. Virtualization of the process is useful to characterize, design and optimize the barrier performance based on physical configuration of the films. Also, the knowledge of values of parameters is important to predict the performances. Inverse modeling and sensitivity analysis are sole way to find reasonable values ofmore » poorly defined, unmeasured parameters and to analyze the most influencing parameters. Thus, the objective of this work was to develop a model to predict barrier properties of multilayer film incorporated with reactive layers and to analyze and characterize their performances. Polymeric film based on three layers of Polyethylene terephthalate (PET), with a core reactive layer, at different thickness configurations was considered in the model. A one dimensional diffusion equation with reaction was solved numerically to predict the concentration of oxygen diffused into the polymer taking into account the reactive ability of the core layer. The model was solved using commercial software for different film layer configurations and sensitivity analysis based on inverse modeling was carried out to understand the effect of physical parameters. The results have shown that the use of sensitivity analysis can provide physical understanding of the parameters which highly affect the gas permeation into the film. Solubility and the number of available reactive sites were the factors mainly influencing the barrier performance of three layered polymeric film. Multilayer films slightly modified the steady transport properties in comparison to net PET, giving a small reduction in the permeability and oxygen transfer rate values. Scavenging capacity of the multilayer film increased linearly with the increase of the reactive layer thickness and the oxygen absorption reaction at short times decreased proportionally with the thickness of the external PET layer.« less

Barriers to Uptake of Climate-Smart Agriculture Practices at the Farm Level: A Case Study of Dano and Ouahigouya Farmers, Burkina Faso

NASA Astrophysics Data System (ADS)

Thomas, Y. B.

2016-12-01

Smallholder farmers in Burkina Faso, which are already bearing the brunt of climate vagaries, are among the most exposed to the risks associated to climate change. Supporting these farmers in adoption of climate-smart agriculture (CSA) practices would help to increase farm productivity and incomes, improve their resilience to climate risks, and mitigate climate change by reducing GHG emissions. CSA is neither a new agricultural system nor a set of practice, but is a new approach, a way to guide the needed changes of agricultural systems, given the necessity to jointly address food security and climate change. Integrating statistics and visualization analysis, this paper identifies and analyzes the key barriers to farmers' effective adoption of CSA practices in Dano and Ouahigouya areas, Burkina Faso. The data used in this study were collected, in May 2016, from 147 households in the two different agro-ecological zones; these data were supplemented by information from focus group discussion (FGD), interview with institutions, and direct observation. It come out from this study that a better adoption of CSA practices requires a strong understanding of barriers and mechanisms (appropriate policies, strategies and actions) that may facilitate these practices by all actors involved in the diffusion, transfer and implementation process. The study revealed that farmers' adoption was influenced by several factors. The inaccessibility of inputs, credit constraints, water shortage, uncertainty in market condition, and climate risk appeared to be among factors that hindered farmers' ability and willingness to adopt CSA practices. Therefore mechanisms (such as index based crop insurance and property and procedural rights frameworks) that protect farmers from these hazards and shocks could encourage them (especially, risk-averse farmers) to take on more risky and more technologies that have high potential to maximize their profit.

Finite-time barriers to reaction front propagation

NASA Astrophysics Data System (ADS)

Locke, Rory; Mahoney, John; Mitchell, Kevin

2015-11-01

Front propagation in advection-reaction-diffusion systems gives rise to rich geometric patterns. It has been shown for time-independent and time-periodic fluid flows that invariant manifolds, termed burning invariant manifolds (BIMs), serve as one-sided dynamical barriers to the propagation of reaction front. More recently, theoretical work has suggested that one-sided barriers, termed burning Lagrangian Coherent structures (bLCSs), exist for fluid velocity data prescribed over a finite time interval, with no assumption on the time-dependence of the flow. In this presentation, we use a time-varying fluid ``wind'' in a double-vortex channel flow to demonstrate that bLCSs form the (locally) most attracting or repelling fronts.

Longitudinal Hierarchy Co3O4 Mesocrystals with High-dense Exposure Facets and Anisotropic Interfaces for Direct-Ethanol Fuel Cells.

PubMed

Hassen, Diab; El-Safty, Sherif A; Tsuchiya, Koichi; Chatterjee, Abhijit; Elmarakbi, Ahmed; Shenashen, Mohamed A; Sakai, Masaru

2016-04-14

Novel electrodes are needed for direct ethanol fuel cells with improved quality. Hierarchical engineering can produce catalysts composed of mesocrystals with many exposed active planes and multi-diffused voids. Here we report a simple, one-pot, hydrothermal method for fabricating Co3O4/carbon/substrate electrodes that provides control over the catalyst mesocrystal morphology (i.e., corn tubercle pellets or banana clusters oriented along nanotube domains, or layered lamina or multiple cantilevered sheets). These morphologies afforded catalysts with a high density of exposed active facets, a diverse range of mesopores in the cage interior, a window architecture, and vertical alignment to the substrate, which improved efficiency in an ethanol electrooxidation reaction compared with a conventional platinum/carbon electrode. On the atomic scale, the longitudinally aligned architecture of the Co3O4 mesocrystals resulted in exposed low- and high-index single and interface surfaces that had improved electron transport and diffusion compared with currently used electrodes.

Longitudinal Hierarchy Co3O4 Mesocrystals with High-dense Exposure Facets and Anisotropic Interfaces for Direct-Ethanol Fuel Cells

NASA Astrophysics Data System (ADS)

Hassen, Diab; El-Safty, Sherif A.; Tsuchiya, Koichi; Chatterjee, Abhijit; Elmarakbi, Ahmed; Shenashen, Mohamed. A.; Sakai, Masaru

2016-04-01

Novel electrodes are needed for direct ethanol fuel cells with improved quality. Hierarchical engineering can produce catalysts composed of mesocrystals with many exposed active planes and multi-diffused voids. Here we report a simple, one-pot, hydrothermal method for fabricating Co3O4/carbon/substrate electrodes that provides control over the catalyst mesocrystal morphology (i.e., corn tubercle pellets or banana clusters oriented along nanotube domains, or layered lamina or multiple cantilevered sheets). These morphologies afforded catalysts with a high density of exposed active facets, a diverse range of mesopores in the cage interior, a window architecture, and vertical alignment to the substrate, which improved efficiency in an ethanol electrooxidation reaction compared with a conventional platinum/carbon electrode. On the atomic scale, the longitudinally aligned architecture of the Co3O4 mesocrystals resulted in exposed low- and high-index single and interface surfaces that had improved electron transport and diffusion compared with currently used electrodes.