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Diffusion
Kinds of Diffusion Terms modified by Diffusion Selected AbstractsSPREADING DIFFUSION IN CRIMINOLOGYCRIMINOLOGY AND PUBLIC POLICY, Issue 3 2003DAVID A. KLINGER First page of article [source] THE NON-PENNSYLVANIA TOWN: DIFFUSION OF URBAN PLAN FORMS IN THE AMERICAN WEST,GEOGRAPHICAL REVIEW, Issue 2 2006MICHAEL P. CONZEN ABSTRACT. Wilbur Zelinsky's classic 1977 account of the Pennsylvania town as a cultural place type,the urban component of the nationally influential Pennsylvanian culture region,acknowledged that it was not exported intact across the successive western frontiers of the United States. But, aside from Edward Price's specialized study of courthouse squares, we know little that is systematic about how town-planning ideas diffused across the continent. This investigation offers evidence from the Willamette Valley in Oregon of the eventual variety and geographical distribution of town-platting conventions that developed in this Pacific Coast "destination' setting and the possible provenance in the Ohio Valley of certain early Oregonian town-plan features. The evidence raises questions about the resilience of town-planning conventions in light of the distance carried, cultural time lags, and changing ideas about best practice and local suitability. [source] A SIMPLE METHOD TO DETERMINE DIFFUSION OF SODIUM IN THE EPIDERMIS OF GREEN OLIVESJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2004CARLOS ALBERTO ZURITZ ABSTRACT The present study reports a simple method, both mathematical and experimental, to determine variable effective diffusion coefficients for sodium through the skins of olives. Skins removed from green olives, variety Arauco (also known as Criolla), were studied using a lye concentration of 2.25% (w/w) of NaOH at 20C. The diffusion of sodium was evaluated through fresh skins and previously alkali-treated skins. The measured values of effective diffusion coefficients for untreated (fresh) olive skins increased two orders of magnitude during the processing time, from 10,12 to 10,10 m2/s. Whereas, the effective diffusion coefficients determined for previously treated olive skins were of the order of 10,10 m2/s and increased very little with treatment time. [source] DETERMINATION OF VARIABLE DIFFUSION OF SODIUM DURING DEBITTERING OF GREEN OLIVESJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2004MARIELA BEATRIZ MALDONADO ABSTRACT Time-variable average effective diffusion coefficients of sodium in the skin and flesh were determined using Macroscopic Mass Balances from experimental data obtained during debittering of green olives, variety Arauco at temperatures of 15, 20 and 25C and lye concentrations of 1.50, 2.25 and 3.00% of NaOH. The effective diffusion coefficient of sodium increased with treatment time at both surfaces of the skin, while it varied very little within the flesh, and in many cases, remained almost constant during the debittering process. In general, the diffusion coefficients determined in the present study were within an order of magnitude of 10,10 m2/s for the flesh during most of the treatment time, while for the skin, they were of the order of 10,12 m2/s for the initial treatment times. Macroscopic mass balances are a simple mathematical method that can be used in lieu of more common numerical techniques, to evaluate variable diffusion coefficients providing accuracy and greater detail of the whole phenomena. [source] DIFFUSION OF BEET DYE DURING ELECTRICAL AND CONVENTIONAL HEATING AT STEADY-STATE TEMPERATURE,JOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2001MARYBETH LIMA ABSTRACT Ohmic heating has been shown to alter mass transfer properties of fruit and vegetable tissue. Diffusion of beet dye from beetroot tissue into a fluid was studied during conventional and ohmic heating as a function of steady-state temperature. The volume of beet dye diffusing into solution during ohmic heating was enhanced with respect to conventional heating at 42C and 58C, but not at 72C. This can be explained by examining the differences in electrical conductivity of beet tissue at these temperatures during conventional and ohmic heating. At 42 and 58C, the electrical conductivity of beet tissue heated ohmically is higher than the electrical conductivity of beet tissue heated conventionally. At 72C, the electrical conductivities of beet tissue during conventional and ohmic heating are equal. The extent of diffusion in the ohmic case is also positively correlated with applied voltage. These results suggest that food processes involving mass transfer can be enhanced by choosing conditions in which the electrical conductivity of a sample under ohmic conditions is maximized. [source] INCORPORATING TECHNOLOGY DIFFUSION, FACTOR MOBILITY AND STRUCTURAL CHANGE INTO CROSS-REGION GROWTH REGRESSION: AN APPLICATION TO CHINA,JOURNAL OF REGIONAL SCIENCE, Issue 3 2010Laixiang Sun ABSTRACT This paper advocates a spatial dynamic model that introduces technology diffusion, factor mobility, and structural change into the cross-region growth regression. The spatial setting is derived from theory rather than spatial statistical tests. An application of this model to the study of cross-province growth in China over the period 1980,2005 indicates that incomes are spatially correlated, which highlights the significance of technology diffusion and factor mobility. Furthermore, the integration of neoclassical growth empirics and the structural change perspective of development economics provide a much improved account of interprovincial variations in income levels and economic growth. [source] NON-SCALE EFFECTS OF INTERNATIONAL TECHNOLOGICAL-KNOWLEDGE DIFFUSION ON SOUTHERN GROWTH AND WAGESTHE JAPANESE ECONOMIC REVIEW, Issue 3 2010OSCAR AFONSO We develop a dynamic, general equilibrium non-scale endogenous growth model of North,South technological-knowledge diffusion by imitation. Countries differ in levels of exogenous productivity, human-capital levels and R&D capacity. Growth is driven by Northern innovative R&D and the South converges towards the North. Growth is also driven by human-capital accumulation, scale effects are removed, imitation is only feasible once a threshold distance to the frontier has been attained and is dependent on the South's relative level of employed human capital and on domestic policies promoting R&D. Imitation promotes partial convergence of inter-country wages and governs the path of intra-South wage inequality. [source] Deterministic Importance Sampling with Error DiffusionCOMPUTER GRAPHICS FORUM, Issue 4 2009László Szirmay-Kalos This paper proposes a deterministic importance sampling algorithm that is based on the recognition that delta-sigma modulation is equivalent to importance sampling. We propose a generalization for delta-sigma modulation in arbitrary dimensions, taking care of the curse of dimensionality as well. Unlike previous sampling techniques that transform low-discrepancy and highly stratified samples in the unit cube to the integration domain, our error diffusion sampler ensures the proper distribution and stratification directly in the integration domain. We also present applications, including environment mapping and global illumination rendering with virtual point sources. [source] Diffusion tensor magnetic resonance imaging in spinal cord injuryCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2008Benjamin M. Ellingson Abstract Noninvasive assessment of spinal cord integrity following injury is critical for precise diagnosis, prognosis, and surgical intervention strategies. Diffusion weighted imaging and diffusion tensor imaging are more sensitive to the underlying spinal cord microstructure than traditional imaging techniques. As a result, diffusion imaging is emerging as the clinical technique for imaging the spinal cord after trauma, surgery or during progressive degenerative diseases. This review describes the basic physics of diffusion imaging using magnetic resonance, techniques used to visualize diffusion measurements, and expected changes in diffusion measurements following spinal cord injury. © 2008 Wiley Periodicals, Inc.Concepts Magn Reson Part A 32A: 219,237, 2008. [source] Analysis of b -value calculations in diffusion weighted and diffusion tensor imagingCONCEPTS IN MAGNETIC RESONANCE, Issue 1 2005Daniel Güllmar Abstract Diffusion weighted imaging has opened new diagnostic possibilities by using microscopic diffusion of water molecules as a means of image contrast. The directional dependence of diffusion has led to the development of diffusion tensor imaging, which allows us to characterize microscopic tissue geometry. The link between the measured NMR signal and the self-diffusion tensor is established by the so-called b matrices that depend on the gradient's direction, strength, and timing. However, in the calculation of b -matrix elements, the influence of imaging gradients on each element of the b matrix is often neglected. This may cause errors, which in turn leads to an incorrect extraction of diffusion coefficients. In cases where the imaging gradients are high (high spatial resolution), these errors may be substantial. Using a generic pulsed gradient spin-echo (PGSE) imaging sequence, the effects of neglecting the imaging gradients on the b -matrix calculation are demonstrated. By measuring an isotropic phantom with this sequence it can be analytically as well as experimentally shown that large deviations in single b -matrix elements are generated. These deviations are obtained by applying the diffusion weighting in the readout direction of the imaging dimension in combination with relatively large imaging gradients. The systematic errors can be avoided by a full b -matrix calculation considering all the gradients of the sequence or by generating cross-term free signals using the geometric average of two diffusion weighted images with opposite polarity. The importance of calculating the exact b matrices by the proposed methods is based on the fact that more precise diffusion parameters are obtained for extracting correct property maps, such as fractional anisotropy, volume ratio, or conductivity tensor maps. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 25A: 53,66, 2005 [source] Diffusion induced segregation in the case of the ternary system sphalerite, chalcopyrite and cubaniteCRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2004T. Blesgen Abstract A mathematical model for describing natural and experimental diffusion induced segregation (DIS) in the case of a (Zn,Fe)S single crystal with three coexisting phases is derived. As main result, a new and quite general segregation principle for ternary systems is discovered where one phase has a flat free energy density and serves as catalyst for the segregation of the other two phases. The model includes also a stochastic noise term to represent fluctuations of the copper concentration. Numerical simulations in 2-d underline the physical significance of the model and allow to make quantitative predictions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Botulinum Toxin Type B (MYOBLOC) Versus Botulinum Toxin Type A (BOTOX) Frontalis Study: Rate of Onset and Radius of DiffusionDERMATOLOGIC SURGERY, Issue 5 2003Timothy Corcoran Flynn MD Background. Botulinum toxin types A and B can improve the appearance of facial wrinkles. Differences in the time until onset and the degree of diffusion have been observed anecdotally, but no direct comparative studies have been done. Objective. To compare the rate of onset and the radius of diffusion of botulinum toxin types A and B in the rhytides of the forehead. Methods. Adults with symmetrical moderate to severe forehead wrinkles at full contracture received botulinum toxin type A (BOTOX; 5 U) on one side of the forehead and type B (MYOBLOC; 500 U) on the other side. Photographs taken at rest and full frontalis contracture were analyzed by computer, and a time-lapse motion picture was created. Radius of diffusion and time until full effect were measured. Results. Botulinum toxin type B had a slightly faster onset of action than type A. All patients responded to type B quickly, whereas some had a delayed response to type A. A greater radius of diffusion was consistently observed with botulinum toxin type B, as measured by the greater area of wrinkle reduction at the doses used. Conclusions. In this comparative study of patients with symmetrical forehead wrinkles, botulinum toxin type B produced a greater area of diffusion and a more rapid onset of action than type A. [source] Fiber tracking using magnetic resonance diffusion tensor imaging and its applications to human brain developmentDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 3 2003Richard Watts Abstract Diffusion tensor imaging is unique in its ability to noninvasively visualize white matter fiber tracts in the human brain in vivo. Diffusion is the incoherent motion of water molecules on a microscopic scale. This motion is itself dependent on the micro-structural environment that restricts the movement of the water molecules. In white matter fibers there is a pronounced directional dependence on diffusion. With white matter fiber tracking or tractography, projections among brain regions can be detected in the three-dimensional diffusion tensor dataset according to the directionality of the fibers. Examples of developmental changes in diffusion, tracking of major fiber tracts, and examples of how diffusion tensor tractography and functional magnetic resonance imaging can be combined are provided. These techniques are complimentary and allow both the identification of the eloquent areas of the brain involved in specific functional tasks, and the connections between them. The noninvasive nature of magnetic resonance imaging will allow these techniques to be used in both longitudinal developmental and diagnostic studies. An overview of the technique and preliminary applications are presented, along with its current limitations. MRDD Research Reviews 2003;9:168,177. © 2003 Wiley-Liss, Inc. [source] Diffusion-based magnetic resonance imaging and tractography in epilepsyEPILEPSIA, Issue 2 2008Mahinda Yogarajah Summary Diffusion-based imaging is an advanced MRI technique that is sensitive to the movement of water molecules, providing additional information on the micro-structural arrangement of tissue. Qualitative and quantitative analysis of peri, post and interictal diffusion images can aid the localization of seizure foci. Diffusion tensor tractography is an extension of diffusion-based imaging, and can provide additional information about white matter pathways. Both techniques are able to increase understanding of the effects of epilepsy on the structural organization of the brain, and can be used to optimize presurgical planning of patients with epilepsy. This review focuses on the basis, applications, limitations, and future directions of diffusion imaging in epilepsy. Literature search strategy: We searched Pubmed using the terms "diffusion MRI or diffusion tensor MRI or tractography and epilepsy." [source] Prolonged Febrile Seizures Are Associated with Hippocampal Vasogenic Edema and Developmental ChangesEPILEPSIA, Issue 9 2006Rod C. Scott Summary:,Purpose: There is mounting evidence that a prolonged febrile seizure (PFS) can cause acute hippocampal edema although the nature of that edema remains uncertain. The principal aims of the current study were: (1) to use apparent diffusion coefficient (ADC) measurements to further characterize the hippocampal edema previously identified within 5 days of a PFS, and (2) to determine whether the age dependency of ADC in the hippocampus is different in patients when compared to a control population following a PFS. Methods: Diffusion weighted imaging was acquired in 23 children within 5 days of a PFS, and in 14 of these children a mean of 5.5 months later. Twenty-four control children were enrolled. Results: There was a reduction in ADC between the acute and follow-up investigations [mean reduction = 0.0072 mm2/s/month since PFS (95% confidence interval; 0.0001,0.014 mm2/s/month since PFS), p = 0.048] consistent with early vasogenic edema, followed by recovery in children investigated within 2 days of a PFS. In addition, the behavior of ADC with respect to age was different in patients when compared to control subjects [mean difference in slope =,0.155 mm2/s/log10 age (95% confidence interval; ,0.290,0.0203 mm2/s/log10 age), p = 0.029], in that the expected age dependence was observed only in the control subjects. Conclusion: We suggest that these latter findings are most consistent with a preexisting developmental hippocampal abnormality that may predispose individuals to having a PFS. [source] European Momentum Strategies, Information Diffusion, and Investor ConservatismEUROPEAN FINANCIAL MANAGEMENT, Issue 3 2005John A. Doukas G1; G11; G14 Abstract In this paper we conduct an out-of-sample test of two behavioural theories that have been proposed to explain momentum in stock returns. We test the gradual-information-diffusion model of Hong and Stein (1999) and the investor conservatism bias model of Barberis et al. (1998) in a sample of 13 European stock markets during the period 1988 to 2001. These two models predict that momentum comes from the (i) gradual dissemination of firm-specific information and (ii) investors' failure to update their beliefs sufficiently when they observe new public information. The findings of this study are consistent with the predictions of the behavioural models of Hong and Stein's (1999) and Barberis et al. (1998). The evidence shows that momentum is the result of the gradual diffusion of private information and investors' psychological conservatism reflected on the systematic errors they make in forming earnings expectations by not updating them adequately relative to their prior beliefs and by undervaluing the statistical weight of new information. [source] Plasticity and Grain Boundary Diffusion at Small Grain Sizes,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Gerhard Wilde Bulk nanostructured,or ultrafine-grained materials are often fabricated by severe plastic deformation to break down the grain size by dislocation accumulation. Underlying the often spectacular property enhancement that forms the basis for a wide range of potential applications is a modification of the volume fraction of the grain boundaries. Yet, along with the property enhancements, several important questions arise concerning the accommodation of external stresses if dislocation-based processes are not longer dominant at small grain sizes. One question concerns so-called "non-equilibrium" grain boundaries that have been postulated to form during severe deformation and that might be of importance not only for the property enhancement known already today, but also for spectacular applications in the context of, e.g., gas permeation or fast matter transport for self-repairing structures. This contribution addresses the underlying issues by combining quantitative microstructure analysis at high resolution with grain boundary diffusion measurements. [source] Biomimetic Carbonate,Hydroxyapatite Nanocrystals Prepared by Vapor Diffusion,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Michele Iafisco Abstract Biomimetic carbonate,hydroxyapatite (HA) nanocrystals have been synthesized by using the sitting drop vapor diffusion technique, for the first time. The method consists of diffusing vapors of an aqueous solution of NH4HCO3 through drops containing an aqueous mixture of (CH3COO)2Ca and (NH4)2HPO4 in order to increase slowly their pH. This synthesis has been performed in a crystallization mushroom, a glass device developed for protein and small molecules crystallization. The concentrations of the reagents, the final pH and the crystallization time have been optimized to produce pure carbonate,HA as a single phase. X-Ray diffraction, Fourier transformed infrared spectroscopy, and transmission electron microscopy have been utilized to characterize the synthesized carbonated substituted HA crystals which display nanometric dimensions, plate-like morphology, and low crystallinity degree, closely resembling the inorganic phase of bones, teeth, and many pathological calcifications. This novel method may prove to be suitable for the study of the interactions and/or the co-crystallization of hydroxyapatite with minute amounts of biomolecules, polymers, or drugs. [source] Modeling the Porosity Formation in Austenitic SGI Castings by Using a Physics-Based Material Model,ADVANCED ENGINEERING MATERIALS, Issue 3 2010B. Pustal Abstract On solidification, microsegregations build up in solid phases due to changes in solid concentrations with temperature. Diffusion, which is a kinetic process, usually reduces the occurrence of microsegregations. This work is aimed at modeling such kinetic effects on the solidification of austenitic cast iron, using a holistic approach. For this purpose, a microsegregation model is developed and validated. Moreover, this model is directly coupled to a commercial process-simulation tool and thermodynamic software. A series of GJSA-XNiCr 20-2 clamp-rings is cast by varying the inoculation state and the number of feeders. The composition of this cast alloy is analyzed and the microstructure characterized to provide input data for the microsegregation model. In order to validate the software, cooling curves are recorded; differential thermal analysis, electron dispersive X-ray analysis and electron probe micro analysis are carried out. Furthermore, the porosity within the casting is analyzed by X-ray. By performing coupled simulations, the different cooling characteristics within the casting lead to pronounced differences in phase fractions and solidification temperatures which are due to dendrite arm coarsening. The hot spot effect below the feeders is assisted by a shift towards lower solidification temperatures over the solidification time. This shift is a result of the local cooling characteristics, which can only be predicted when process simulation is directly coupled with material simulation. The porosity predictions and the porosity analysis exhibit good agreement. A comparison between experimental and virtual cooling curves closes, implying that the novel coupling concept and its implementation are valid. [source] Analysis of Tin Diffusion in Zircaloy-4 and Tin Redistribution after Steam Oxidation by Means of X-ray Fluorescence Measurements,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Mirco Grosse The temperature dependence of tin diffusion coefficients in the nuclear fuel rod cladding tube material Zircaloy-4 is determined in the range of 1,000,1,400,°C by means of X-ray fluorescence measurements. During oxidation at these temperatures, tin is redistributed, as shown in the figure. Due to tin diffusion in zirconium being much slower than the growing of the oxide layer, tin is segregated inside the oxide layer and at phase boundaries. [source] Diffusion of strongly sorbed solutes in soil: a dual-porosity model allowing for slow access to sorption sites and time-dependent sorption reactionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2010M. Ptashnyk We use homogenization techniques to derive a dual (or double) porosity model of solute diffusion and reaction in soil, allowing for slow access to sorption sites within micro-aggregates and time-dependent sorption reactions. We give a means for determining the conditions in which micro-scale concentration gradients affect macro-scale gradients and fluxes. We present equations for a unit volume of soil represented as a series of uniformly-spaced, porous spherical particles, containing and surrounded by solution through which solutes diffuse. The methods we use can, in principle, be applied to more complex geometries. We compare the model's predictions with those of the equivalent single porosity model for commonly used boundary conditions. We show that failure to allow for slow access to reaction sites can lead to seriously erroneous results. Slow access has the effect of decreasing the sorption of solute into soil from a source or desorption from soil to a sink. As a result of slow access, the diffusion coefficients of strongly-sorbed solutes measured at the macro-scale will be time-dependent and will depend on the method of measurement. We also show that slow access is more often likely to limit macro-scale diffusion than rates of slow chemical reactions per se. In principle, the unimportance of slow reactions except at periods longer than several weeks of diffusion simplifies modelling because, if slow access is correctly allowed for, sorption can be described with equilibrium relations with an understanding of speciation and rapid sorption-desorption reactions. [source] Roll-Bonded Titanium/Stainless-Steel Couples, Part 1: Diffusion and Interface-Layer InvestigationsADVANCED ENGINEERING MATERIALS, Issue 1-2 2009S. Dziallach A survey of the diffusion of the alloying elements Fe, Ni and Cr in a roll-bonded titanium/stainless-steel couple after an application-orientated heat treatment is presented. Diffusion profiles of the investigated elements by means of EPMA, and the diffusion coefficients and activation energies for application-oriented short annealing times up to 12,min in a temperature range of 750 to 950,°C are determined. The transformation of the hcp , -titanium into bcc , -titanium has a significant influence on the diffusion of the elements. The forming interface layers are characterised by LOM and SEM pictures. [source] Stress Corrosion Cracking and Hydrogen Diffusion in Magnesium,ADVANCED ENGINEERING MATERIALS, Issue 8 2006A. Atrens Evaluation of recent data for hydrogen (H) diffusion in magnesium (Mg) yielded a new equation for the diffusion coefficient of H in Mg. This indicates that there can be significant H transport ahead of a stress corrosion crack in Mg at ambient temperature and that H may be involved in the mechanism of stress corrosion cracking in Mg. [source] Diffusion in Nanocrystalline Metals and Alloys,A Status Report,ADVANCED ENGINEERING MATERIALS, Issue 5 2003R. Würschum Abstract Diffusion is a key property determining the suitability of nanocrystalline materials for use in numerous applications, and it is crucial to the assessment of the extent to which the interfaces in nanocrystalline samples differ from conventional grain boundaries. The present article offers an overview of diffusion in nanocrystalline metals and alloys. Emphasis is placed on the interfacial characteristics that affect diffusion in nanocrystalline materials, such as structural relaxation, grain growth, porosity, and the specific type of interface. In addition, the influence of intergranular amorphous phases and intergranular melting on diffusion is addressed, and the atomistic simulation of GB structures and diffusion is briefly summarized. On the basis of the available diffusion data, the diffusion-mediated processes of deformation and induced magnetic anisotropy are discussed. [source] Formation of Nickel Oxide Nanotubes with Uniform Wall Thickness by Low-Temperature Thermal Oxidation Through Understanding the Limiting Effect of Vacancy Diffusion and the Kirkendall PhenomenonADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Yi Ren Abstract In this work, the step-wise oxidation mechanism of nickel (Ni) nanowires is elucidated. Rapid vacancy diffusion plays a significant role at low temperatures in forming heterostructures of nickel oxide (NiO) nanotubes with Ni nanowires. Subsequent investigations of Ni nanowire oxidation at higher temperatures and faster temperature ramp rates show that it is difficult to bypass this rapid vacancy diffusion stage, which affects the formation of the final structure. Therefore, it is unlikely to form solid NiO nanowires or NiO nanotubes with uniform wall thickness through the conventional annealing/oxidation process of Ni nanowires. Instead, a step-wise oxidation process by combining low temperature oxidation with a chemical etching step is utilized to produce for the first time NiO nanotubes with uniform wall thickness from Ni nanowires. [source] WDX Studies on Ceramic Diffusion Barrier Layers of Metal Supported SOECsFUEL CELLS, Issue 6 2009D. Wiedenmann Abstract Solid oxide electrolyser cells (SOECs) have great potential for efficient and economical production of hydrogen fuel. Element diffusion between the Ni-cermet electrode and the metal substrate of metal supported cells (MSC) is a known problem in fuel cell and electrolysis technology. In order to hinder this unintentional mass transport, different ceramic diffusion barrier layers (DBLs) are included in recent cell design concepts. This paper is based on wavelength dispersive X-ray fluorescence investigations of different SOEC and focuses on Fe, Cr and Ni diffusion between the metal grains of the cathode and the metal substrate. Due to the low detection limits and therefore high analytical sensitivity, wavelength dispersive electron probe microanalysis (EPMA) provides a precise method to determine element distribution, absolute element concentration and changes between the reference material and aged cells on a microstructural level by element mappings and concentration profiles. The results of this work show considerable concentration gradients in the metal grains caused by mass exchange during cell operation. Diffusion can be inhibited significantly by integrating different ceramic DBLs of doped LaCrO3 -type or doped LaMnO3 -type perovskite, either by vacuum plasma spraying (VPS) or physical vapour deposition technique (PVD). [source] Study of Energy Transfer and Triplet Exciton Diffusion in Hole-Transporting Host MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Chao Wu Abstract A device structure is used in which the hole-transporting layer (HTL) of an OLED is doped with either fluorescent or phosphorescent emitters, that is, anode/HTL-host/hole blocker/electron-transporting layer/cathode. The HTL hosts have higher HOMO energy allowing holes to be transported without being trapped by dopant molecules, avoiding direct recombination on the dopant. The unconventional mismatch of HOMO energies between host and dopant allow for the study of energy transfer in these host/guest systems and triplet exciton diffusion in the HTL-host layers of OLED devices, without the complication of charge trapping at dopants. The host materials examined here are tetraaryl- p- phenylenediamines. Data shows that Förster energy transfer between these hosts and emissive dopant in devices is inefficient. Triplet exciton diffusion in these host materials is closely related to molecular structure and the degree of intermolecular interaction. Host materials that contain naphthyl groups demonstrate longer triplet exciton diffusion lengths than those with phenyl substituents, consistent with DFT calculations and photophysical measurements. [source] Hydrologic and geochemical controls on soluble benzene migration in sedimentary basinsGEOFLUIDS (ELECTRONIC), Issue 2 2005Y. ZHANG Abstract The effects of groundwater flow and biodegradation on the long-distance migration of petroleum-derived benzene in oil-bearing sedimentary basins are evaluated. Using an idealized basin representation, a coupled groundwater flow and heat transfer model computes the hydraulic head, stream function, and temperature in the basin. A coupled mass transport model simulates water washing of benzene from an oil reservoir and its miscible, advective/dispersive transport by groundwater. Benzene mass transfer at the oil,water contact is computed assuming equilibrium partitioning. A first-order rate constant is used to represent aqueous benzene biodegradation. A sensitivity study is used to evaluate the effect of the variation in aquifer/geochemical parameters and oil reservoir location on benzene transport. Our results indicate that in a basin with active hydrodynamics, miscible benzene transport is dominated by advection. Diffusion may dominate within the cap rock when its permeability is less than 10,19 m2. Miscible benzene transport can form surface anomalies, sometimes adjacent to oil fields. Biodegradation controls the distance of transport down-gradient from a reservoir. We conclude that benzene detected in exploration wells may indicate an oil reservoir that lies hydraulically up-gradient. Geochemical sampling of hydrocarbons from springs and exploration wells can be useful only when the oil reservoir is located within about 20 km. Benzene soil gas anomalies may form due to regional hydrodynamics rather than separate phase migration. Diffusion alone cannot explain the elevated benzene concentration observed in carrier beds several km away from oil fields. [source] Diffusion through time-dependent mediaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000M. Holschneider Summary In this theoretical paper we show how to solve a time-dependent diffusion equation by means of a perturbation series. This technique is applied to the case of diffusion of a liquid through a time-dependent porous matrix. We compute to first order the phase and amplitude relations between the small deformation of the transporting matrix and the corresponding variation of the saturation at the surface. In particular we show that, for a large frequency range, there is a constant phase shift of ,/2 between the matrix and the surface saturation variations. Since the conductivity is to first approximation proportional to the saturation at the surface, this might explain the observed phase relations observed in an experiment in a cave near Abaratsubo (Japan). [source] Nutrients Released by Gastric Epithelial Cells Enhance Helicobacter pylori GrowthHELICOBACTER, Issue 6 2004Karin Van Amsterdam ABSTRACT Background.,Helicobacter pylori survives and proliferates in the human gastric mucosa. In this niche, H. pylori adheres to the gastric epithelial cells near the tight junctions. In vitro, H. pylori proliferated well in tissue-culture medium near gastric epithelial cells. However, in the absence of epithelial cells, growth of H. pylori could only be established in tissue-culture medium when, prior to the experiment, it was preincubated near gastric epithelial cells. Therefore, we aimed to determine whether diffusion of nutrients derived from epithelial cells was required for H. pylori growth in Dulbecco's modified Eagle's minimal essential medium (DMEM) cell culture medium. Materials and Methods., Cell culture conditions essential for H. pylori growth in vitro were determined with gastric epithelial HM02 cells. Results., Deprivation of iron in cell-culture-conditioned DMEM resulted in a growth arrest of H. pylori. However, near gastric epithelial cells, growth of H. pylori was resistant to iron deprivation. Evidently, when residing close to epithelial cells, H. pylori was able to fulfil its iron requirements, even when the DMEM was deprived of iron. Nevertheless, supplementation with iron alone did not restore H. pylori growth in DMEM, hence other nutrients were deficient as well in the absence of epithelial cells. Growth of H. pylori in DMEM was restored when hypoxanthine, l -alanine and l -proline were added to the DMEM. Conclusions, Diffusion of (precursors of) these nutrients from the gastric epithelial cells is essential for H. pylori growth in vitro. We hypothesize that in vivo, H. pylori favors colonization near the tight junctions, to gain maximal access to the nutrient(s) released by gastric epithelial cells. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||