Dependence of the photovoltaic performance of pseudomorphic InGaN/GaN multiple-quantum-well solar cells on the active region thickness

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

Mukhtarova, Anna; Valdueza-Felip, Sirona; Redaelli, Luca

2016-04-18

We investigate the photovoltaic performance of pseudomorphic In{sub 0.1}Ga{sub 0.9}N/GaN multiple-quantum well (MQW) solar cells as a function of the total active region thickness. An increase in the number of wells from 5 to 40 improves the short-circuit current and the open-circuit voltage, resulting in a 10-fold enhancement of the overall conversion efficiency. Further increasing the number of wells leads to carrier collection losses due to an incomplete depletion of the active region. Capacitance-voltage measurements point to a hole diffusion length of 48 nm in the MQW region.

A Diffuse Interface Model with Immiscibility Preservation

PubMed Central

Tiwari, Arpit; Freund, Jonathan B.; Pantano, Carlos

2013-01-01

A new, simple, and computationally efficient interface capturing scheme based on a diffuse interface approach is presented for simulation of compressible multiphase flows. Multi-fluid interfaces are represented using field variables (interface functions) with associated transport equations that are augmented, with respect to an established formulation, to enforce a selected interface thickness. The resulting interface region can be set just thick enough to be resolved by the underlying mesh and numerical method, yet thin enough to provide an efficient model for dynamics of well-resolved scales. A key advance in the present method is that the interface regularization is asymptotically compatible with the thermodynamic mixture laws of the mixture model upon which it is constructed. It incorporates first-order pressure and velocity non-equilibrium effects while preserving interface conditions for equilibrium flows, even within the thin diffused mixture region. We first quantify the improved convergence of this formulation in some widely used one-dimensional configurations, then show that it enables fundamentally better simulations of bubble dynamics. Demonstrations include both a spherical bubble collapse, which is shown to maintain excellent symmetry despite the Cartesian mesh, and a jetting bubble collapse adjacent a wall. Comparisons show that without the new formulation the jet is suppressed by numerical diffusion leading to qualitatively incorrect results. PMID:24058207

Unravelling Photocarrier Dynamics beyond the Space Charge Region for Photoelectrochemical Water Splitting

DOE PAGES

Zhang, Wenrui; Yan, Danhua; Appavoo, Kannatassen; ...

2017-04-18

Semiconductor photoelectrodes for photoelectrochemical (PEC) water splitting require efficient carrier generation, separation, and transport at and beyond the space charge region (SCR) formed at the aqueous interface. The trade-off between photon collection and minority carrier delivery governs the photoelectrode design and implies maximum water splitting efficiency at an electrode thickness equivalent to the light absorption depth. Here, using planar ZnO thin films as a model system, we identify the photocarriers beyond the SCR as another significant source to substantially enhance the PEC performance. The high-quality ZnO films synthesized by pulsed laser deposition feature very few deep trap states and supportmore » a long photocarrier lifetime. Combined with photoelectrochemical characterization, ultrafast spectroscopy, and numerical calculations, it is revealed that engineering the exciton concentration gradient by film thickness facilitates the inward diffusion of photocarriers from the neighboring illuminated region to the SCR and, therefore, achieves a record high quantum efficiency over 80% at a thickness far beyond its light absorption depth and the SCR width. Furthermore, these results elucidate the important role of the photocarriers beyond SCR for the PEC process and provide new insight into exploring the full potential for efficient photoelectrode materials with large exciton diffusivity.« less

Asymptotic radiance and polarization in optically thick media: ocean and clouds.

PubMed

Kattawar, G W; Plass, G N

1976-12-01

Deep in a homogeneous medium that both scatters and absorbs photons, such as a cloud, the ocean, or a thick planetary atmosphere, the radiance decreases exponentially with depth, while the angular dependence of the radiance and polarization is independent of depth. In this diffusion region, the asymptotic radiance and polarization are also independent of the incident distribution of radiation at the upper surface of the medium. An exact expression is derived for the asymptotic radiance and polarization for Rayleigh scattering. The approximate expression for the asymptotic radiance derived from the scalar theory is shown to be in error by as much as 16.4%. An exact expression is also derived for the relation between the diffusion exponent k and the single scattering albedo. A method is developed for the numerical calculation of the asymptotic radiance and polarization for any scattering matrix. Results are given for scattering from the haze L and cloud C3 distributions for a wide range of single scattering albedos. When the absorption is large, the polarization in the diffusion region approaches the values obtained for single scattered photons, while the radiance approaches the value calculated from the expression: phase function divided by (1 + kmicro), where micro is the cosine of the zenith angle. The asymptotic distribution of the radiation is of interest since it depends only on the inherent optical properties of the medium. It is, however, difficult to observe when the absorption is large because of the very low radiance values in the diffusion region.

Control of a Normal Shock Boundary Layer Interaction with Ramped Vanes of Various Sizes

NASA Astrophysics Data System (ADS)

Lee, Sang; Loth, Eric

2017-11-01

A novel vortex generator design positioned upstream of a normal shock and a subsequent diffuser was investigated using large eddy simulations. In particular, ``ramped-vane'' flow control devices with three difference heights relative to the incoming boundary layer thickness (0.34 δ 0.52 δ and 0.75 δ were placed in a supersonic boundary layer with a freestream Mach number of 1.3 and a Reynolds number of 2,400 based on momentum thickness. These devices are similar to subsonic vanes but are designed to be more mechanically robust while having low wave drag. The devices generated strong streamwise vortices that entrained high momentum fluid to the near-wall region and increased turbulent mixing. The devices also decreased shock-induced flow separation, which resulted in a higher downstream skin friction in the diffuser. In general, the largest ramped-vane (0.75 δ) produced the largest reductions in flow separation, shape factor and overall unsteadiness. However, the medium-sized ramped vane (0.52 δ) was able to also reduce both the separation area and the diffuser displacement thickness. The smallest device (0.34 δ) had a weak impact of the flow in the diffuser, though a 10% reduction in the shape factor was achieved.

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.

Formation of precise 2D Au particle arrays via thermally induced dewetting on pre-patterned substrates

PubMed Central

Ji, Ran

2011-01-01

Summary The fabrication of precise 2D Au nanoparticle arrays over a large area is presented. The technique was based on pre-patterning of the substrate before the deposition of a thin Au film, and the creation of periodic particle arrays by subsequent dewetting induced by annealing. Two types of pre-patterned substrates were used: The first comprised an array of pyramidal pits and the second an array of circular holes. For the dewetting of Au films on the pyramidal pit substrate, the structural curvature-driven diffusion cooperates with capillarity-driven diffusion, resulting in the formation of precise 2D particle arrays for films within a structure dependent thickness-window. For the dewetting of Au films on the circular hole substrate, the periodic discontinuities in the films, induced by the deposition, can limit the diffusion paths and lead to the formation of one particle per individual separated region (holes or mesas between holes), and thus, result in the evolution of precise 2D particle arrays. The influence of the pre-patterned structures and the film thickness is analyzed and discussed. For both types of pre-patterned substrate, the Au film thickness had to be adjusted in a certain thickness-window in order to achieve the precise 2D particle arrays. PMID:21977445

Threshold for ion movements in wood cell walls below fiber saturation observed by X-ray fluorescence microscopy (XFM)

Treesearch

Samuel L. Zelinka; Sophie-Charlotte Gleber; Stefan Vogt; Gabriela M. Rodriguez Lopez; Joseph E. Jakes

2015-01-01

Diffusion of chemicals and ions through the wood cell wall plays an important role in wood damage mechanisms. In the present work, free diffusion of ions through wood secondary walls and middle lamellae has been investigated as a function of moisture content (MC) and anatomical direction. Various ions (K, Cl, Zn, Cu) were injected into selected regions of 2 ìm thick...

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.

Sexual dimorphism of volume reduction but not cognitive deficit in fetal alcohol spectrum disorders: A combined diffusion tensor imaging, cortical thickness and brain volume study.

PubMed

Treit, Sarah; Chen, Zhang; Zhou, Dongming; Baugh, Lauren; Rasmussen, Carmen; Andrew, Gail; Pei, Jacqueline; Beaulieu, Christian

2017-01-01

Quantitative magnetic resonance imaging (MRI) has revealed abnormalities in brain volumes, cortical thickness and white matter microstructure in fetal alcohol spectrum disorders (FASD); however, no study has reported all three measures within the same cohort to assess the relative magnitude of deficits, and few studies have examined sex differences. Participants with FASD (n = 70; 30 females; 5-32 years) and healthy controls (n = 74; 35 females; 5-32 years) underwent cognitive testing and MRI to assess cortical thickness, regional brain volumes and fractional anisotropy (FA)/mean diffusivity (MD) of white matter tracts. A significant effect of group, age-by-group, or sex-by-group was found for 9/9 volumes, 7/39 cortical thickness regions, 3/9 white matter tracts, and 9/10 cognitive tests, indicating group differences that in some cases differ by age or sex. Volume reductions for several structures were larger in males than females, despite similar deficits of cognition in both sexes. Correlations between brain structure and cognitive scores were found in females of both groups, but were notably absent in males. Correlations within a given MRI modality (e.g. total brain volume and caudate volume) were prevalent in both the control and FASD groups, and were more numerous than correlations between measurement types (e.g. volumes and diffusion tensor imaging) in either cohort. This multi-modal MRI study finds widespread differences of brain structure in participants with prenatal alcohol exposure, and to a greater extent in males than females which may suggest attenuation of the expected process of sexual dimorphism of brain structure during typical development.

Determination of carrier diffusion length in GaN

NASA Astrophysics Data System (ADS)

Hafiz, Shopan; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit; Metzner, Sebastian; Bertram, Frank; Christen, Jürgen; Gil, Bernard

2015-01-01

Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) and cross-sectional cathodoluminescence (CL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p-GaN or 1500 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photo-generation near the surface region by above bandgap excitation. Taking into consideration the absorption in the top GaN layer as well as active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be 93 ± 7 nm and 70 ± 7 nm for Mg-doped p-type GaN and 432 ± 30 nm and 316 ± 30 nm for unintentionally doped n-type GaN, respectively, at photogenerated carrier densities of 4.2 × 1018 cm-3 using PL spectroscopy. CL measurements of the unintentionally doped n-type GaN layer at much lower carrier densities of 1017 cm-3 revealed a longer diffusion length of 525 ± 11 nm at 6 K.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, expressions provide the temperature distribution and heat flow for a diffusing medium with a continually varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, the analytical expressions provide the temperature distribution and heat flow for a diffusing medium with a continuously varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Transmitting and reflecting diffuser. [for ultraviolet light

NASA Technical Reports Server (NTRS)

Keafer, L. S., Jr.; Burcher, E. E.; Kopia, L. P. (Inventor)

1973-01-01

A near-Lambertian diffuser is described which transmits and reflects ultraviolet light. An ultraviolet grade fused silica substrate is coated with vaporized fuse silica. The coating thickness is controlled, one thickness causing ultraviolet light to diffuse and another thickness causing ultraviolet light to reflect a near Lambertian pattern.

Impact of pentacene film thickness on the photoresponse spectra: Determination of the photocarrier generation mechanism

NASA Astrophysics Data System (ADS)

Gorgolis, S.; Giannopoulou, A.; Anastassopoulos, D.; Kounavis, P.

2012-07-01

Photocurrent response, optical absorption, and x-ray diffraction (XRD) measurements in pentacene films grown on glass substrates are performed in order to obtain an insight into the mobile photocarriers generation mechanism. For film thickness of the order of 50 nm and lower, the photocurrent response spectra are found to follow the optical absorption spectra demonstrating the so-called symbatic response. Upon increasing the film thickness, the photoresponse demonstrates a transition to the so-called antibatic response, which is characterized by a maximum and minimum photocurrent for photon energies of minimum and maximum optical absorption, respectively. The experimental results are not in accordance with the model of important surface recombination rate. By taking into account the XRD patterns, the experimental photoresponse spectra can be reproduced by model simulations assuming efficient exciton dissociation at a narrow layer of the order of 20 nm near the pentacene-substrate interface. The simulated spectra are found sensitive to the film thickness, the absolute optical absorption coefficient, and the diffusion exciton length. By comparing the experimental with the simulated spectra, it is deduced that the excitons, which are created by optical excitation in the spectral region of 1.7-2.2 eV, diffuse with a diffusion length of the order of 10-80 nm to the pentacene-substrate interface where efficiently dissociate into mobile charge carriers.

Aerosols and their influence on radiation partitioning and savanna productivity in northern Australia

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

Kanniah, K. D.; Beringer, J.; Tapper, N. J.

2010-05-01

We investigated the effect of aerosols and clouds on the Net Ecosystem Productivity (NEP) of savannas in northern Australia using aerosol optical depth, clouds and radiation data from the Atmospheric Radiation Measurement (ARM) site in Darwin and carbon flux data measured from eddy covariance techniques from a site at Howard Springs, 35km southeast of Darwin. Generally we found that the concentration of aerosols in this region was relatively low than observed at other sites, therefore the proportion of diffuse radiation reaching the earths surface was only ~ 30%. As a result, we observed only a modest change in carbon uptakemore » under aerosol laden skies and there was no significant difference for dry season Radiation Use Efficiency (RUE) between clear sky, aerosols or thin clouds. On the other hand thick clouds in the wet season produce much more diffuse radiation than aerosols or thin clouds and therefore the initial canopy quantum efficiency was seen to increase 45 and 2.5 times more than under thin clouds and aerosols respectively. The normalized carbon uptake under thick clouds is 57% and 50% higher than under aerosols and thin clouds respectively even though the total irradiance received under thick clouds was reduced 59% and 50% than under aerosols and thin clouds respectively. However, reduction in total irradiance decreases the mean absolute carbon uptake as much as 22% under heavy cloud cover compared to thin clouds or aerosols. Thus, any increase in aerosol concentration or cloud cover that can enhance the diffuse component may have large impacts on productivity in this region.« less

Reduced-thickness backlighter for autostereoscopic display and display using the backlighter

NASA Technical Reports Server (NTRS)

Eichenlaub, Jesse B (Inventor); Gruhlke, Russell W (Inventor)

1999-01-01

A reduced-thickness backlighter for an autostereoscopic display is disclosed having a lightguide and at least one light source parallel to an edge of the lightguide so as to be substantially coplanar with the lightguide. The lightguide is provided with a first surface which has a plurality of reflective linear regions, such as elongated grooves or glossy lines, parallel to the illuminated edge of the lightguide. Preferably the lightguide further has a second surface which has a plurality of lenticular lenses for reimaging the reflected light from the linear regions into a series of thin vertical lines outside the guide. Because of the reduced thickness of the backlighter system, autostereoscopic viewing is enabled in applications requiring thin backlighter systems. In addition to taking up less space, the reduced-thickness backlighter uses less lamps and less power. For accommodating 2-D applications, a 2-D diffuser plate or a 2-D lightguide parallel to the 3-D backlighter is disclosed for switching back and forth between 3-D viewing and 2-D viewing.

Propagation and transmission of optical vortex beams through turbid scattering wall with orbital angular momentums

NASA Astrophysics Data System (ADS)

Wang, W. B.; Gozali, Richard; Nguyen, Thien An; Alfano, R. R.

2015-03-01

Light scattering and transmission of optical Laguerre Gaussian (LG) vortex beams with different orbital angular momentum (OAM) states in turbid scattering media were investigated in comparison with Gaussian (G) beam. The scattering media used in the experiments consist of various sizes and concentrations of latex beads in water solutions. The LG beams were generated using a spatial light modulator in reflection mode. The ballistic transmissions of LG and G beams were measured with different ratios of thickness of samples (z) to scattering mean free path (ls) of the turbid media, z/ls. The results show that in the ballistic region where z/ls is small, the LG and G beams show no significant difference, while in the diffusive region where z/ls is large, LG beams show higher transmission than Gaussian beam. In the diffusive region, the LG beams with higher orbital angular momentum L values show higher transmission than the beams with lower L values. The transition points from ballistic to diffusive regions for different scattering media were studied and determined.

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

Wujcik, Kevin H.; Wang, Dunyang Rita; Pascal, Tod A.

Lithium sulfur (Li-S) batteries are well known for their high theoretical specific capacities, but are plagued with scientific obstacles that make practical implementation of the technology impossible. The success of Li-S batteries will likely necessitate the use of thick sulfur cathodes that enable high specific energy densities. However, little is known about the fundamental reaction mechanisms and chemical processes that take place in thick cathodes, as most research has focused on studying thinner cathodes that enable high performance. In this study, in situ X-ray absorption spectroscopy at the sulfur K-edge is used to examine the back of a 115 μmmore » thick Li-S cathode during discharge. Our results show that in such systems, where electrochemical reactions between sulfur and lithium are likely to proceed preferentially toward the front of the cathode, lithium polysulfide dianions formed in this region diffuse to the back of the cathode during discharge. We show that high conversion of elemental sulfur is achieved by chemical reactions between elemental sulfur and polysulfide dianions of intermediate chain length (Li 2S x, 4 ≤ x ≤ 6). Our work suggests that controlling the formation and diffusion of intermediate chain length polysulfide dianions is crucial for insuring full utilization of thick sulfur cathodes.« less

Determination of pollutant diffusion coefficients in naturally formed biofilms using a single tube extractive membrane bioreactor

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

Zhang, S.F.; Splendiani, A.; Freitas dos Santos, L.M.

A novel technique has been used to determine the effective diffusion coefficients for 1,1,2-trichloroethane (TCE), a nonreacting tracer, in biofilms growing on the external surface of a silicone rubber membrane tube during degradation of 1,2-dichloroethane (DCE) by Xanthobacter autotrophicus GJ10 and monochlorobenzene (MCB) by Pseudomonas JS150. Experiments were carried out in a single tube extractive membrane bioreactor (STEMB), whose configuration makes it possible to measure the transmembrane flux of substrates. A video imaging technique (VIT) was employed for in situ biofilm thickness measurement and recording. Diffusion coefficients of TCE in the biofilms and TCE mass transfer coefficients in the liquidmore » films adjacent to the biofilms were determined simultaneously using a resistances-in-series diffusion model. It was found that the flux and overall mass transfer coefficient of TCE decrease with increasing biofilm thickness, showing the importance of biofilm diffusion on the mass transfer process. Similar fluxes were observed for the nonreacting tracer (TCE) and the reactive substrates (MCB or DCE), suggesting that membrane-attached biofilm systems can be rate controlled primarily by substrate diffusion. The TCE diffusion coefficient in the JS150 biofilm appeared to be dependent on biofilm thickness, decreasing markedly for biofilm thicknesses of >1 mm. The values of the TCE diffusion coefficients in the JS150 biofilms <1-mm thick are approximately twice those in water and fall to around 30% of the water value for biofilms >1-mm thick.« less

Elimination of resistive losses in large-area LEDs by new diffusion-driven devices

NASA Astrophysics Data System (ADS)

Kivisaari, Pyry; Kim, Iurii; Suihkonen, Sami; Oksanen, Jani

2017-02-01

High-power operation of conventional GaN-based light-emitting diodes (LEDs) is severely limited by current crowding, which increases the bias voltage of the LED, concentrates light emission close to the p-type contact edge, and aggravates the efficiency droop. Fabricating LEDs on thick n-GaN substrates alleviates current crowding but requires the use of expensive bulk GaN substrates and fairly large n-contacts, which take away a large part of the active region (AR). In this work, we demonstrate through comparative simulations how the recently introduced diffusion-driven charge transport (DDCT) concept can be used to realize lateral heterojunction (LHJ) structures, which eliminate most of the lateral current crowding. Specifically in this work, we analyze how using a single-side graded AR can both facilitate electron and hole diffusion in DDCT and increase the effective AR thickness. Our simulations show that the increased effective AR thickness allows a substantial reduction in the efficiency droop at large currents, and that unlike conventional 2D LEDs, the LHJ structure shows practically no added efficiency loss or differential resistance due to current crowding. Furthermore, as both electrons and holes enter the AR from the same side without any notable potential barriers in the LHJ structure, the LHJ structure shows an additional wall-plug efficiency gain over the conventional structures under comparison. This injection from the same side is expected to be even more interesting in multiple quantum well structures, where carriers typically need to surpass several potential barriers in conventional LEDs before recombining. In addition to simulations, we also demonstrate selective-area growth of a finger structure suitable for operation as an LHJ device with 2µm distance between n- and p-GaN regions.

Computational investigation of longitudinal diffusion, eddy dispersion, and trans-particle mass transfer in bulk, random packings of core-shell particles with varied shell thickness and shell diffusion coefficient.

PubMed

Daneyko, Anton; Hlushkou, Dzmitry; Baranau, Vasili; Khirevich, Siarhei; Seidel-Morgenstern, Andreas; Tallarek, Ulrich

2015-08-14

In recent years, chromatographic columns packed with core-shell particles have been widely used for efficient and fast separations at comparatively low operating pressure. However, the influence of the porous shell properties on the mass transfer kinetics in core-shell packings is still not fully understood. We report on results obtained with a modeling approach to simulate three-dimensional advective-diffusive transport in bulk random packings of monosized core-shell particles, covering a range of reduced mobile phase flow velocities from 0.5 up to 1000. The impact of the effective diffusivity of analyte molecules in the porous shell and the shell thickness on the resulting plate height was investigated. An extension of Giddings' theory of coupled eddy dispersion to account for retention of analyte molecules due to stagnant regions in porous shells with zero mobile phase flow velocity is presented. The plate height equation involving a modified eddy dispersion term excellently describes simulated data obtained for particle-packings with varied shell thickness and shell diffusion coefficient. It is confirmed that the model of trans-particle mass transfer resistance of core-shell particles by Kaczmarski and Guiochon [42] is applicable up to a constant factor. We analyze individual contributions to the plate height from different mass transfer mechanisms in dependence of the shell parameters. The simulations demonstrate that a reduction of plate height in packings of core-shell relative to fully porous particles arises mainly due to reduced trans-particle mass transfer resistance and transchannel eddy dispersion. Copyright © 2015 Elsevier B.V. All rights reserved.

Diffusion of macromolecules through sclera.

PubMed

Miao, Heng; Wu, Bi-Dong; Tao, Yong; Li, Xiao-Xin

2013-02-01

To quantify the in vitro permeability coefficient over different topographical locations of porcine sclera to macromolecules with different molecular weight. Fresh equatorial and posterior superotemporal porcine sclera was mounted in a two-chamber diffusion apparatus, and its permeability to fluorescein isothiocyanate (FITC)-conjugated dextrans ranging in molecular weight from 40 kDa to 150 kDa was determined by fluorescence spectrophotometry. The sclera was processed as frozen sections and viewed with a fluorescence microscope. The thickness of the area and the thickness that macromolecules enriched in the surface of sclera were measured. The permeability coefficient (Pc) of porcine sclera to macromolecules was significantly higher (40 kDa, p = 0.028; 70 kDa, p = 0.033; 150 kDa, p = 0.007) in equatorial region than posterior, which could be attributed to the significant difference of thickness (p < 0.001, Kruskal-Wallis) between them. Moreover, linear regression indicated a significant negative relationship (40 kDa, p < 0.001; 70 kDa, p = 0.015; 150 kDa, p < 0.001) between scleral permeability coefficient and thickness. Also, Pc declined significantly with increasing molecular weight (MW, p < 0.001, Kruskal-Wallis). The area that the macromolecules enriched in the scleral surface was thicker for those with larger MW (p < 0.001, Kruskal-Wallis). The maximum MW and size for equatorial and posterior superotemporal scleral tissue were 185.01 KDa and 180.42 KDa, 9.92 nm and 9.67 nm, respectively. The permeability coefficient of porcine sclera has a significant negative relationship with scleral thickness and MW of macromolecules. Larger macromolecules are more likely to accumulate in scleral surface. The difference between topographical locations may have pharmacokinetic implications when considering transscleral diffusion of macromolecules. © 2012 The Authors. Acta Ophthalmologica © 2012 Acta Ophthalmologica Scandinavica Foundation.

Study of fluorescence quenching due to 2, 3, 5, 6-tetrafluoro-7, 7', 8, 8'-tetracyano quinodimethane and its solid state diffusion analysis using photoluminescence spectroscopy.

PubMed

Tyagi, Priyanka; Tuli, Suneet; Srivastava, Ritu

2015-02-07

In this work, we have studied the fluorescence quenching and solid state diffusion of 2, 3, 5, 6-tetrafluoro-7,  7',  8,  8'-tetracyano quinodimethane (F4-TCNQ) using photoluminescence (PL) spectroscopy. Quenching studies were performed with tris (8-hydroxyquinolinato) aluminum (Alq3) in solid state samples. Thickness of F4-TCNQ was varied in order to realize different concentrations and study the effect of concentration. PL intensity has reduced with the increase in F4-TCNQ thicknesses. Stern-Volmer and bimolecular quenching constants were evaluated to be 13.8 M(-1) and 8.7 × 10(8) M(-1) s(-1), respectively. The quenching mechanism was found to be of static type, which was inferred by the independent nature of excited state life time from the F4-TCNQ thickness. Further, solid state diffusion of F4-TCNQ was studied by placing a spacing layer of α-NPD between F4-TCNQ and Alq3, and its thickness was varied to probe the diffusion length. PL intensity was found to increase with the increase in this thickness. Quenching efficiency was evaluated as a function of distance between F4-TCNQ and Alq3. These studies were performed for the samples having 1, 2.5, and 5.5 nm thicknesses of F4-TCNQ to study the thickness dependence of diffusion length. Diffusion lengths were evaluated to be 12.5, 15, and 20 nm for 1, 2.5, and 5.5 nm thicknesses of F4-TCNQ. These diffusion lengths were found to be very close to that of determined by secondary ion mass spectroscopy technique.

Fabrication of Ternary AgPdAu Alloy Nanoparticles on c-Plane Sapphire by the Systematical Control of Film Thickness and Deposition Sequence

NASA Astrophysics Data System (ADS)

Kunwar, Sundar; Pandey, Puran; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-06-01

In this work, a systematic study on the fabrication of ternary AgPdAu alloy nanoparticles (NPs) on c-plane sapphire (0001) is presented and the corresponding structural and optical characteristics are demonstrated. The metallic trilayers of various thicknesses and deposition orders are annealed in a controlled manner (400 °C to 900 °C) to induce the solid-state dewetting that yields the various structural configurations of AgPdAu alloy NPs. The dewetting of relatively thicker trilayers (15 nm) is gradually progressed with void nucleation, growth, and coalescence, isolated NP formation, and shape transformation, along with the temperature control. For 6 nm thickness, owing to the sufficient dewetting of trilayers along with enhanced diffusion, dense and small spherical alloy NPs are fabricated. Depending on the specific growth condition, the surface diffusion and interdiffusion of metal atoms, surface and interface energy minimization, Rayleigh instability, and equilibrium configuration are correlated to describe the fabrication of ternary alloy NPs. Ternary alloy NPs exhibit morphology-dependent ultraviolet-visible-near infrared (UV-VIS-NIR) reflectance properties such as the inverse relationship of average reflectance with the surface coverage, absorption enhancement in specific regions, and reflectance maxima in UV and NIR regions. In addition, Raman spectra depict the six active phonon modes of sapphires and their intensity and position modulation by the alloy NPs.

An integrated platform for surface forces measurements and fluorescence correlation spectroscopy

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Ashis; Zhao, Jiang; Bae, Sung Chul; Granick, Steve

2003-06-01

We describe an apparatus to measure the diffusion of dilute fluorophores in molecularly thin liquid films within a surface forces apparatus (SFA). The design is a significant modification of the traditional SFA in that it allows one to combine nanorheology with the single-molecule sensitive technique of fluorescence correlation spectroscopy. The primary enabling idea was to place a miniaturized SFA onto the stage of an optical microscope equipped with a long working distance objective and illuminated by a femtosecond laser. A secondary enabling idea was that the silver coating on the backside of mica, normally used in the traditional SFA design for interferometric measurements of the film thickness, was replaced by multilayer dielectric coatings that allowed simultaneous interferometry and fluorescence measurements in different regions of the optical spectrum. To illustrate the utility of this instrument, we contrast the translational diffusion of rhodamine dye molecules (in the solvent, 1,2-propane diol), in the unconfined bulk state and confined between mica sheets to the thickness 2.5 nm. The diffusion coefficient is found to decrease by 2 orders of magnitude under confinement.

Residual fields from extinct dynamos

NASA Astrophysics Data System (ADS)

Parker, E. N.

The generation of magnetic fields in convective zones of declining vigor and/or thickness is considered, the goal being to explain the magnetic fields observed in A-stars. The investigation is restricted to kinematical dynamos in order to show some of the many possibilities, which depend on the assumed conditions of decline of the convection. The examples illustrate the quantitative detail required to describe the convection in order to extract any firm conclusions concerning specific stars. The first example treats the basic problem of diffusion from a layer of declining thickness. The second has a buoyant rise added to the field in the layer. The third deals with plane dynamo waves in a region with declining eddy diffusivity, dynamo coefficient, and large-scale shear. It is noted that the dynamo number may increase or decrease with declining convection, with an increase expected if the large-scale shear does not decline as rapidly as the eddy diffusivity. It is shown that one of the components of the field may increase without bound even when the dynamo number declines to zero.

LATERAL HEAT FLOW INFRARED THERMOGRAPHY FOR THICKNESS INDEPENDENT DETERMINATION OF THERMAL DIFFUSIVITY IN CFRP

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

Tralshawala, Nilesh; Howard, Don; Knight, Bryon

2008-02-28

In conventional infrared thermography, determination of thermal diffusivity requires thickness information. Recently GE has been experimenting with the use of lateral heat flow to determine thermal diffusivity without thickness information. This work builds on previous work at NASA Langley and Wayne State University but we incorporate thermal time of flight (tof) analysis rather than curve fitting to obtain quantitative information. We have developed appropriate theoretical models and a tof based data analysis framework to experimentally determine all components of thermal diffusivity from the time-temperature measurements. Initial validation was carried out using finite difference simulations. Experimental validation was done using anisotropicmore » carbon fiber reinforced polymer (CFRP) composites. We found that in the CFRP samples used, the in-plane component of diffusivity is about eight times larger than the through-thickness component.« less

Effect of catalyst film thickness on carbon nanotube growth by selective area chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wei, Y. Y.; Eres, Gyula; Merkulov, V. I.; Lowndes, D. H.

2001-03-01

The correlation between prepatterned catalyst film thickness and carbon nanotube (CNT) growth by selective area chemical vapor deposition (CVD) was studied using Fe and Ni as catalyst. To eliminate sample-to-sample variations and create a growth environment in which the film thickness is the sole variable, samples with continuously changing catalyst film thickness from 0 to 60 nm were fabricated by electron-gun evaporation. Using thermal CVD CNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature. There appears to be no strong correlation between the film thickness and the diameter of the tubes. In contrast, using plasma enhanced CVD with Ni as catalyst, vertically oriented CNTs grow in the entire range of catalyst film thickness. The diameter of these CNTs shows a strong correlation with the catalyst film thickness. The significance of these experimental trends is discussed within the framework of the diffusion model for CNT growth.

In Situ X-ray Absorption Spectroscopy Studies of Discharge Reactions in a Thick Cathode of a Lithium Sulfur Battery

DOE PAGES

Wujcik, Kevin H.; Wang, Dunyang Rita; Pascal, Tod A.; ...

2016-12-01

Lithium sulfur (Li-S) batteries are well known for their high theoretical specific capacities, but are plagued with scientific obstacles that make practical implementation of the technology impossible. The success of Li-S batteries will likely necessitate the use of thick sulfur cathodes that enable high specific energy densities. However, little is known about the fundamental reaction mechanisms and chemical processes that take place in thick cathodes, as most research has focused on studying thinner cathodes that enable high performance. In this study, in situ X-ray absorption spectroscopy at the sulfur K-edge is used to examine the back of a 115 μmmore » thick Li-S cathode during discharge. Our results show that in such systems, where electrochemical reactions between sulfur and lithium are likely to proceed preferentially toward the front of the cathode, lithium polysulfide dianions formed in this region diffuse to the back of the cathode during discharge. We show that high conversion of elemental sulfur is achieved by chemical reactions between elemental sulfur and polysulfide dianions of intermediate chain length (Li 2S x, 4 ≤ x ≤ 6). Our work suggests that controlling the formation and diffusion of intermediate chain length polysulfide dianions is crucial for insuring full utilization of thick sulfur cathodes.« less

Optical vortex beam transmission with different OAM in scattering beads and brain tissue media

NASA Astrophysics Data System (ADS)

Wang, W. B.; Shi, Lingyan; Lindwasser, Lukas; Marque, Paulo; Lavery, M. P. J.; Alfano, R. R.

2016-03-01

Light transmission of Laguerre Gaussian (LG) vortex beams with different orbital angular momentum (OAM) values (L) in scattering beads and mouse brain tissue media were experimentally investigated for the first time in comparison with Gaussian (G) beams. The LG beams with different OAM were generated using a spatial light modulator (SLM) in reflection mode. The scattering beads media consist of various sizes and concentrations of latex beads in water solutions. The transmissions of LG and G beams through scattering beads and brain tissue media were measured with different ratios of sample thicknesses (z) to scattering mean free path (ls) of the turbid media, z/ls. The results indicate that within the ballistic region where z/ls is small, the LG and G beams show no significant difference, while in the diffusive region where z/ls is higher, the vortex beams show higher transmission than G beams. In the diffusive region, the LG beams with higher L values show higher transmission than the beams with lower L values due to the eigen channels in the media. The transition points from the ballistic to diffusive regions for different scattering beads and brain tissue media were studied.

Mapping anatomical correlations across cerebral cortex (MACACC) using cortical thickness from MRI.

PubMed

Lerch, Jason P; Worsley, Keith; Shaw, W Philip; Greenstein, Deanna K; Lenroot, Rhoshel K; Giedd, Jay; Evans, Alan C

2006-07-01

We introduce MACACC-Mapping Anatomical Correlations Across Cerebral Cortex-to study correlated changes within and across different cortical networks. The principal topic of investigation is whether the thickness of one area of the cortex changes in a statistically correlated fashion with changes in thickness of other cortical regions. We further extend these methods by introducing techniques to test whether different population groupings exhibit significantly varying MACACC patterns. The methods are described in detail and applied to a normal childhood development population (n = 292), and show that association cortices have the highest correlation strengths. Taking Brodmann Area (BA) 44 as a seed region revealed MACACC patterns strikingly similar to tractography maps obtained from diffusion tensor imaging. Furthermore, the MACACC map of BA 44 changed with age, older subjects featuring tighter correlations with BA 44 in the anterior portions of the superior temporal gyri. Lastly, IQ-dependent MACACC differences were investigated, revealing steeper correlations between BA 44 and multiple frontal and parietal regions for the higher IQ group, most significantly (t = 4.0) in the anterior cingulate.

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).

On the meaning of the diffusion layer thickness for slow electrode reactions.

PubMed

Molina, A; González, J; Laborda, E; Compton, R G

2013-02-21

A key concept underpinning electrochemical science is that of the diffusion layer - the zone of depletion around an electrode accompanying electrolysis. The size of this zone can be found either from the simulated or measured concentration profiles (yielding the 'true' diffusion layer thickness) or, in the case of the Nernst ('linear') diffusion layer by extrapolating the concentration gradient at the electrode surface to the distance at which the concentration takes its bulk value. The latter concept is very well developed in the case of fast (so-called reversible) electrode processes, however the study of the linear diffusion layer has received scant attention in the case of slow charge transfer processes, despite its study being of great interest in the analysis of the influence of different experimental variables which determine the electrochemical response. Analytical explicit solutions for the concentration profiles, surface concentrations and real and linear diffusion layers corresponding to the application of a potential step to a slow charge transfer process are presented. From these expressions the dependence of the diffusion layer thickness on the potential, pulse time, heterogeneous rate constant and ratio of bulk concentrations of electroactive species and of diffusion coefficients is quantified. A profound influence of the reversibility degree of the charge transfer on the diffusion layer thickness is clear, showing that for non-reversible processes the real and linear diffusion layers reveal a minimum thickness which coincides with the equilibrium potential of the redox couple in the former case and with the reversible half-wave potential in the latter one.

Lithium-ions diffusion kinetic in LiFePO4/carbon nanoparticles synthesized by microwave plasma chemical vapor deposition for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Gao, Chao; Zhou, Jian; Liu, Guizhen; Wang, Lin

2018-03-01

Olivine structure LiFePO4/carbon nanoparticles are synthesized successfully using a microwave plasma chemical vapor deposition (MPCVD) method. Microwave is an effective method to synthesize nanomaterials, the LiFePO4/carbon nanoparticles with high crystallinity can shorten diffusion routes for ionic transfer and electron tunneling. Meanwhile, a high quality, complete and homogenous carbon layer with appropriate thickness coating on the surface of LiFePO4 particles during in situ chemical vapor deposition process, which can ensure that electrons are able to transfer fast enough from all sides. Electrochemical impedance spectroscopy (EIS) is carried out to collect information about the kinetic behavior of lithium diffusion in LiFePO4/carbon nanoparticles during the charging and discharging processes. The chemical diffusion coefficients of lithium ions, DLi, are calculated in the range of 10-15-10-9 cm2s-1. Nanoscale LiFePO4/carbon particles show the longer regions of the faster solid-solution diffusion, and corresponding to the narrower region of the slower two-phase diffusion during the insertion/exaction of lithium ions. The CV and galvanostatic charge-discharge measurements show that the LiFePO4/carbon nanoparticles perform an excellent electrochemical performance, especially the high rate capacity and cycle life.

A new Monte Carlo code for light transport in biological tissue.

PubMed

Torres-García, Eugenio; Oros-Pantoja, Rigoberto; Aranda-Lara, Liliana; Vieyra-Reyes, Patricia

2018-04-01

The aim of this work was to develop an event-by-event Monte Carlo code for light transport (called MCLTmx) to identify and quantify ballistic, diffuse, and absorbed photons, as well as their interaction coordinates inside the biological tissue. The mean free path length was computed between two interactions for scattering or absorption processes, and if necessary scatter angles were calculated, until the photon disappeared or went out of region of interest. A three-layer array (air-tissue-air) was used, forming a semi-infinite sandwich. The light source was placed at (0,0,0), emitting towards (0,0,1). The input data were: refractive indices, target thickness (0.02, 0.05, 0.1, 0.5, and 1 cm), number of particle histories, and λ from which the code calculated: anisotropy, scattering, and absorption coefficients. Validation presents differences less than 0.1% compared with that reported in the literature. The MCLTmx code discriminates between ballistic and diffuse photons, and inside of biological tissue, it calculates: specular reflection, diffuse reflection, ballistics transmission, diffuse transmission and absorption, and all parameters dependent on wavelength and thickness. The MCLTmx code can be useful for light transport inside any medium by changing the parameters that describe the new medium: anisotropy, dispersion and attenuation coefficients, and refractive indices for specific wavelength.

Subsurface Growth of CoSi2 by Deposition of Co on Si-Capped CoSi2 Seed Regions

NASA Technical Reports Server (NTRS)

Fathauer, R. W.; George, T.; Pike, W. T.

1991-01-01

At a growth temperature of 800 C, Co deposited on Si(111) diffuses through a Si cap and exhibits oriented growth on buried CoSi2 grains, a process referred to as endotaxy. This occurs preferentially to surface nucleation of CoSi2 provided the thickness of the Si cap is less than a critical value between 100 and 200 nm for a deposition rate of 0.01 nm/s. Steady-state endotaxy is modeled under the assumption that the process is controlled by Co diffusion.

Inverse design of centrifugal compressor vaned diffusers in inlet shear flows

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

Zangeneh, M.

1996-04-01

A three-dimensional inverse design method in which the blade (or vane) geometry is designed for specified distributions of circulation and blade thickness is applied to the design of centrifugal compressor vaned diffusers. Two generic diffusers are designed, one with uniform inlet flow (equivalent to a conventional design) and the other with a sheared inlet flow. The inlet shear flow effects are modeled in the design method by using the so-called ``Secondary Flow Approximation`` in which the Bernoulli surfaces are convected by the tangentially mean inviscid flow field. The difference between the vane geometry of the uniform inlet flow and nonuniformmore » inlet flow diffusers is found to be most significant from 50 percent chord to the trailing edge region. The flows through both diffusers are computed by using Denton`s three-dimensional inviscid Euler solver and Dawes` three-dimensional Navier-Stokes solver under sheared in-flow conditions. The predictions indicate improved pressure recovery and internal flow field for the diffuser designed for shear inlet flow conditions.« less

Characterization of Atomic-Layer-Deposited (ALD) Al2O3-Passivated Sub-50-μm-thick Kerf-less Si Wafers by Controlled Spalling

NASA Astrophysics Data System (ADS)

Lee, Yong Hwan; Cha, Hamchorom; Choi, Sunho; Chang, Hyo Sik; Jang, Boyun; Oh, Jihun

2018-05-01

A systematic characterization of sub-50-μm-thick, kerf-less monocrystalline Si wafers fabricated by a controlled fracture method is presented. The spalling process introduces various defects on the Si surface, which result in high surface roughness levels, residual stress, and low effective minority carrier lifetimes. In addition, metals used to induce fracturing in Si diffuse in the Si at room temperature and degrade the effective minority carrier lifetime. Selective removal of these defected Si regions improves the residual stress and effective lifetimes of spalled Si wafers.

General solution for diffusion-controlled dissolution of spherical particles. 1. Theory.

PubMed

Wang, J; Flanagan, D R

1999-07-01

Three classical particle dissolution rate expressions are commonly used to interpret particle dissolution rate phenomena. Our analysis shows that an assumption used in the derivation of the traditional cube-root law may not be accurate under all conditions for diffusion-controlled particle dissolution. Mathematical analysis shows that the three classical particle dissolution rate expressions are approximate solutions to a general diffusion layer model. The cube-root law is most appropriate when particle size is much larger than the diffusion layer thickness, the two-thirds-root expression applies when the particle size is much smaller than the diffusion layer thickness. The square-root expression is intermediate between these two models. A general solution to the diffusion layer model for monodispersed spherical particles dissolution was derived for sink and nonsink conditions. Constant diffusion layer thickness was assumed in the derivation. Simulated dissolution data showed that the ratio between particle size and diffusion layer thickness (a0/h) is an important factor in controlling the shape of particle dissolution profiles. A new semiempirical general particle dissolution equation is also discussed which encompasses the three classical particle dissolution expressions. The success of the general equation in explaining limitations of traditional particle dissolution expressions demonstrates the usefulness of the general diffusion layer model.

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.

Interface morphology of Mo/Si multilayer systems with varying Mo layer thickness studied by EUV diffuse scattering.

PubMed

Haase, Anton; Soltwisch, Victor; Braun, Stefan; Laubis, Christian; Scholze, Frank

2017-06-26

We investigate the influence of the Mo-layer thickness on the EUV reflectance of Mo/Si mirrors with a set of unpolished and interface-polished Mo/Si/C multilayer mirrors. The Mo-layer thickness is varied in the range from 1.7 nm to 3.05 nm. We use a novel combination of specular and diffuse intensity measurements to determine the interface roughness throughout the multilayer stack and do not rely on scanning probe measurements at the surface only. The combination of EUV and X-ray reflectivity measurements and near-normal incidence EUV diffuse scattering allows to reconstruct the Mo layer thicknesses and to determine the interface roughness power spectral density. The data analysis is conducted by applying a matrix method for the specular reflection and the distorted-wave Born approximation for diffuse scattering. We introduce the Markov-chain Monte Carlo method into the field in order to determine the respective confidence intervals for all reconstructed parameters. We unambiguously detect a threshold thickness for Mo in both sample sets where the specular reflectance goes through a local minimum correlated with a distinct increase in diffuse scatter. We attribute that to the known appearance of an amorphous-to-crystallization transition at a certain thickness threshold which is altered in our sample system by the polishing.

Threshold thickness for applying diffusion equation in thin tissue optical imaging

NASA Astrophysics Data System (ADS)

Zhang, Yunyao; Zhu, Jingping; Cui, Weiwen; Nie, Wei; Li, Jie; Xu, Zhenghong

2014-08-01

We investigated the suitability of the semi-infinite model of the diffusion equation when using diffuse optical imaging (DOI) to image thin tissues with double boundaries. Both diffuse approximation and Monte Carlo methods were applied to simulate light propagation in the thin tissue model with variable optical parameters and tissue thicknesses. A threshold value of the tissue thickness was defined as the minimum thickness in which the semi-infinite model exhibits the same reflected intensity as that from the double-boundary model and was generated as the final result. In contrast to our initial hypothesis that all optical properties would affect the threshold thickness, our results show that only absorption coefficient is the dominant parameter and the others are negligible. The threshold thickness decreases from 1 cm to 4 mm as the absorption coefficient grows from 0.01 mm-1 to 0.2 mm-1. A look-up curve was derived to guide the selection of the appropriate model during the optical diagnosis of thin tissue cancers. These results are useful in guiding the development of the endoscopic DOI for esophageal, cervical and colorectal cancers, among others.

Glial activation colocalizes with structural abnormalities in amyotrophic lateral sclerosis.

PubMed

Alshikho, Mohamad J; Zürcher, Nicole R; Loggia, Marco L; Cernasov, Paul; Chonde, Daniel B; Izquierdo Garcia, David; Yasek, Julia E; Akeju, Oluwaseun; Catana, Ciprian; Rosen, Bruce R; Cudkowicz, Merit E; Hooker, Jacob M; Atassi, Nazem

2016-12-13

In this cross-sectional study, we aimed to evaluate brain structural abnormalities in relation to glial activation in the same cohort of participants. Ten individuals with amyotrophic lateral sclerosis (ALS) and 10 matched healthy controls underwent brain imaging using integrated MR/PET and the radioligand [ 11 C]-PBR28. Diagnosis history and clinical assessments including Upper Motor Neuron Burden Scale (UMNB) were obtained from patients with ALS. Diffusion tensor imaging (DTI) analyses including tract-based spatial statistics and tractography were applied. DTI metrics including fractional anisotropy (FA) and diffusivities (mean, axial, and radial) were measured in regions of interest. Cortical thickness was assessed using surface-based analysis. The locations of structural changes, measured by DTI and the areas of cortical thinning, were compared to regional glial activation measured by relative [ 11 C]-PBR28 uptake. In this cohort of individuals with ALS, reduced FA and cortical thinning colocalized with regions demonstrating higher radioligand binding. [ 11 C]-PBR28 binding in the left motor cortex was correlated with FA (r = -0.68, p < 0.05) and cortical thickness (r = -0.75, p < 0.05). UMNB was correlated with glial activation (r = +0.75, p < 0.05), FA (r = -0.77, p < 0.05), and cortical thickness (r = -0.75, p < 0.05) in the motor cortex. Increased uptake of the glial marker [ 11 C]-PBR28 colocalizes with changes in FA and cortical thinning. This suggests a link between disease mechanisms (gliosis and inflammation) and structural changes (cortical thinning and white and gray matter changes). In this multimodal neuroimaging work, we provide an in vivo model to investigate the pathogenesis of ALS. © 2016 American Academy of Neurology.

Glial activation colocalizes with structural abnormalities in amyotrophic lateral sclerosis

PubMed Central

Alshikho, Mohamad J.; Zürcher, Nicole R.; Loggia, Marco L.; Cernasov, Paul; Chonde, Daniel B.; Izquierdo Garcia, David; Yasek, Julia E.; Akeju, Oluwaseun; Catana, Ciprian; Rosen, Bruce R.; Cudkowicz, Merit E.

2016-01-01

Objective: In this cross-sectional study, we aimed to evaluate brain structural abnormalities in relation to glial activation in the same cohort of participants. Methods: Ten individuals with amyotrophic lateral sclerosis (ALS) and 10 matched healthy controls underwent brain imaging using integrated MR/PET and the radioligand [11C]-PBR28. Diagnosis history and clinical assessments including Upper Motor Neuron Burden Scale (UMNB) were obtained from patients with ALS. Diffusion tensor imaging (DTI) analyses including tract-based spatial statistics and tractography were applied. DTI metrics including fractional anisotropy (FA) and diffusivities (mean, axial, and radial) were measured in regions of interest. Cortical thickness was assessed using surface-based analysis. The locations of structural changes, measured by DTI and the areas of cortical thinning, were compared to regional glial activation measured by relative [11C]-PBR28 uptake. Results: In this cohort of individuals with ALS, reduced FA and cortical thinning colocalized with regions demonstrating higher radioligand binding. [11C]-PBR28 binding in the left motor cortex was correlated with FA (r = −0.68, p < 0.05) and cortical thickness (r = −0.75, p < 0.05). UMNB was correlated with glial activation (r = +0.75, p < 0.05), FA (r = −0.77, p < 0.05), and cortical thickness (r = −0.75, p < 0.05) in the motor cortex. Conclusions: Increased uptake of the glial marker [11C]-PBR28 colocalizes with changes in FA and cortical thinning. This suggests a link between disease mechanisms (gliosis and inflammation) and structural changes (cortical thinning and white and gray matter changes). In this multimodal neuroimaging work, we provide an in vivo model to investigate the pathogenesis of ALS. PMID:27837005

Transport methods for probing the barrier domain of lipid bilayer membranes.

PubMed Central

Xiang, T X; Chen, X; Anderson, B D

1992-01-01

Two experimental techniques have been utilized to explore the barrier properties of lecithin/decane bilayer membranes with the aim of determining the contributions of various domains within the bilayer to the overall barrier. The thickness of lecithin/decane bilayers was systematically varied by modulating the chemical potential of decane in the annulus surrounding the bilayer using different mole fractions of squalene in decane. The dependence of permeability of a model permeant (acetamide) on the thickness of the solvent-filled region of the bilayer was assessed in these bilayers to determine the contribution of this region to the overall barrier. The flux of acetamide was found to vary linearly with bilayer area with Pm = (2.9 +/- 0.3) x 10(-4) cm s-1, after correcting for diffusion through unstirred water layers. The ratio between the overall membrane permeability coefficient and that calculated for diffusion through the hydrocarbon core in membranes having maximum thickness was 0.24, suggesting that the solvent domain contributes only slightly to the overall barrier properties. Consistent with these results, the permeability of acetamide was found to be independent of bilayer thickness. The relative contributions of the bilayer interface and ordered hydrocarbon regions to the transport barrier may be evaluated qualitatively by exploring the effective chemical nature of the barrier microenvironment. This may be probed by comparing functional group contributions to transport with those obtained for partitioning between water and various model bulk solvents ranging in polarity or hydrogen-bonding potential. A novel approach is described for obtaining group contributions to transport using ionizable permeants and pH adjustment. Using this approach, bilayer permeability coefficients of p-toluic acid and p-hydroxymethyl benzoic acid were determined to be 1.1 +/- 0.2 cm s-1 and (1.6 +/- 0.4) x 10(-3) cm s-1, respectively. From these values, the -OH group contribution to bilayer transport [delta(delta G0-OH)] was found to be 3.9 kcal/mol. This result suggests that the barrier region of the bilayer does not resemble the hydrogen-bonding environment found in octanol, but is somewhat less selective (more polar) than a hydrocarbon solvent. PMID:1420875

A study of the polyethylene membrane used in diffusion chambers for radon gas concentration measurements

NASA Astrophysics Data System (ADS)

Leung, S. Y. Y.; Nikezic, D.; Leung, J. K. C.; Yu, K. N.

2007-10-01

Solid-state nuclear track detectors (SSNTDs) in diffusion chambers have been routinely used for long-term measurements of radon gas concentrations. In usual practice, a filter is added across the top of the diffusion chamber to stop the progeny from entering. Thoron can also be deterred from entering the diffusion chamber by using a polyethylene (PE) membrane. However, the thickness of the PE membrane is rarely specified in the literature. In this paper, we will present our experimental results for a radon exposure that the number of alpha-particle tracks registered by the LR 115 SSNTD in a Karlsruhe diffusion chamber covered with one layer of PE membrane is actually enhanced. This is explained by enhanced deposition of radon progeny on the outside surface of the PE membrane and the insufficient thickness of the PE membrane to stop the alpha particles emitted from these deposited radon progeny to reach the SSNTD. We will present the PE thickness which can stop the alpha particles emitted from the deposited radon or thoron progeny. For the "twin diffusion chambers method", one of the diffusion chambers is covered with PE membranes. The optimal number of thickness of PE membranes will be determined, which allows the largest amount of radon gas to diffuse into the diffusion chamber while at the same time screening out the largest amount of thoron gas.

Decay of the zincate concentration gradient at an alkaline zinc cathode after charging

NASA Technical Reports Server (NTRS)

Kautz, H. E.; May, C. E.

1979-01-01

The study was carried out by observing the decay of the zincate concentration gradient at a horizontal zinc cathode after charging. This decay was found to approximate first order kinetics as expected from a proposed boundary layer model. The decay half life was shown to be a linear function of the thickness of porous zinc deposit on the cathode indicating a very rapid transport of zincate through porous zinc metal. The rapid transport is attributed to an electrochemical mechanism. The data also indicated a relatively sharp transition between the diffusion and convection transport regions. The diffusion of zincate ion through asbestos submerged in alkaline electrolyte was shown to be comparable with that predicted from the bulk diffusion coefficient of the zincate ion in alkali.

Moderate temperature detector development

NASA Technical Reports Server (NTRS)

Marciniec, J. W.; Briggs, R. J.; Sood, A. K.

1981-01-01

P-side backside reflecting constant, photodiode characterization, and photodiode diffusion and G-R currents were investigated in an effort to develop an 8 m to 12 m infrared quantum detector using mercury cadmium telluride. Anodization, phosphorus implantation, and the graded band gap concept were approaches considered for backside formation. Variable thickness diodes were fabricated with a back surface anodic oxide to investigate the effect of this surface preparation on the diffusion limited zero bias impedance. A modeling technique was refined to thoroughly model diode characteristics. Values for the surface recombination velocity in the depletion region were obtained. These values were improved by implementing better surface damage removal techniques.

Vertical Structure of NGC 4631

NASA Astrophysics Data System (ADS)

Ann, Hong Bae; Seo, Mira Seo; Baek, Su-Ja

2011-02-01

We present a deep CCD imaging in B and V bands which allows us to analyze the vertical structure of NGC 4631. We derive the scale heights of the thin and thick disks at a variety of positions along the major axis of the disk. The scale heights of the thin disk are nearly constant while those of the thick disk tend to increase with increasing galactocentric distance. The mean scale heights of the thin disk derived from B and V images are similar to each other (˜450 pc). Instead, those of the thick disk show a strong east-west asymmetry which is caused by the diffuse stellar emission that is most prominent in the north west regions above the disk plane. The ratio of scale heights (z_{thick}/z_{thin}) is about 2.5 in the east side of the disk. However, this ratio is greater than 4 for the thick disk above the disk plane in the west side of the galaxy.

Fluorescence Diffusion in the Presence of Optically Clear Tissues in a Mouse Head Model.

PubMed

Ancora, Daniele; Zacharopoulos, Athanasios; Ripoll, Jorge; Zacharakis, Giannis

2017-05-01

Diffuse Optical Tomography commonly neglects or assumes as insignificant the presence of optically clear regions in biological tissues, estimating their contribution as a small perturbation to light transport. The inaccuracy introduced by this practice is examined in detail in the context of a complete, based on realistic geometry, virtual fluorescence Diffuse Optical Tomography experiment where a mouse head is imaged in the presence of cerebral spinal fluid. Despite the small thickness of such layer, we point out that an error is introduced when neglecting it from the model with possibly reduction in the accuracy of the reconstruction and localization of the fluorescence distribution within the brain. The results obtained in the extensive study presented here suggest that fluorescence diffuse neuroimaging studies can be improved in terms of quantitative and qualitative reconstruction by accurately taking into account optically transparent regions especially in the cases where the reconstruction is aided by the prior knowledge of the structural geometry of the specimen. Thus, this has only recently become an affordable choice, thanks to novel computation paradigms that allow to run Monte Carlo photon propagation on a simple graphic card, hence speeding up the process a thousand folds compared to CPU-based solutions.

Fractional derivatives in the diffusion process in heterogeneous systems: The case of transdermal patches.

PubMed

Caputo, Michele; Cametti, Cesare

2017-09-01

In this note, we present a simple mathematical model of drug delivery through transdermal patches by introducing a memory formalism in the classical Fick diffusion equation based on the fractional derivative. This approach is developed in the case of a medicated adhesive patch placed on the skin to deliver a time released dose of medication through the skin towards the bloodstream.The main resistance to drug transport across the skin resides in the diffusion through its outermost layer (the stratum corneum). Due to the complicated architecture of this region, a model based on a constant diffusivity in a steady-state condition results in too simplistic assumptions and more refined models are required.The introduction of a memory formalism in the diffusion process, where diffusion parameters depend at a certain time or position on what happens at preceeding times, meets this requirement and allows a significantly better description of the experimental results.The present model may be useful not only for analyzing the rate of skin permeation but also for predicting the drug concentration after transdermal drug delivery depending on the diffusion characteristics of the patch (its thickness and pseudo-diffusion coefficient). Copyright © 2017 Elsevier Inc. All rights reserved.

Assessing White Matter Microstructure in Brain Regions with Different Myelin Architecture Using MRI.

PubMed

Groeschel, Samuel; Hagberg, Gisela E; Schultz, Thomas; Balla, Dávid Z; Klose, Uwe; Hauser, Till-Karsten; Nägele, Thomas; Bieri, Oliver; Prasloski, Thomas; MacKay, Alex L; Krägeloh-Mann, Ingeborg; Scheffler, Klaus

2016-01-01

We investigate how known differences in myelin architecture between regions along the cortico-spinal tract and frontal white matter (WM) in 19 healthy adolescents are reflected in several quantitative MRI parameters that have been proposed to non-invasively probe WM microstructure. In a clinically feasible scan time, both conventional imaging sequences as well as microstructural MRI parameters were assessed in order to quantitatively characterise WM regions that are known to differ in the thickness of their myelin sheaths, and in the presence of crossing or parallel fibre organisation. We found that diffusion imaging, MR spectroscopy (MRS), myelin water fraction (MWF), Magnetization Transfer Imaging, and Quantitative Susceptibility Mapping were myelin-sensitive in different ways, giving complementary information for characterising WM microstructure with different underlying fibre architecture. From the diffusion parameters, neurite density (NODDI) was found to be more sensitive than fractional anisotropy (FA), underlining the limitation of FA in WM crossing fibre regions. In terms of sensitivity to different myelin content, we found that MWF, the mean diffusivity and chemical-shift imaging based MRS yielded the best discrimination between areas. Multimodal assessment of WM microstructure was possible within clinically feasible scan times using a broad combination of quantitative microstructural MRI sequences. By assessing new microstructural WM parameters we were able to provide normative data and discuss their interpretation in regions with different myelin architecture, as well as their possible application as biomarker for WM disorders.

The Relationship between the Dense Neutral and Diffuse Ionized Gas in the Thick Disks of Two Edge-on Spiral Galaxies

NASA Astrophysics Data System (ADS)

Rueff, Katherine M.; Howk, J. Christopher; Pitterle, Marissa; Hirschauer, Alec S.; Fox, Andrew J.; Savage, Blair D.

2013-03-01

We present high-resolution, optical images (BVI + Hα) of the multiphase interstellar medium (ISM) in the thick disks of the edge-on spiral galaxies NGC 4013 and NGC 4302. Our images from the Hubble Space Telescope (HST), Large Binocular Telescope, and WIYN 3.5 m telescope reveal an extensive population of filamentary dust absorption seen to z ~2-2.5 kpc. Many of these dusty thick disk structures have characteristics reminiscent of molecular clouds found in the Milky Way disk. Our Hα images show that the extraplanar diffuse ionized gas (DIG) in these galaxies is dominated by a smooth, diffuse component. The strongly filamentary morphologies of the dust absorption have no counterpart in the smoothly distributed Hα emission. We argue that the thick disk DIG and dust-bearing filaments trace physically distinct phases of the thick disk ISM, the latter tracing a dense, warm or cold neutral medium. The dense, dusty matter in the thick disks of spiral galaxies is largely tracing matter ejected from the thin disk via energetic feedback from massive stars. The high densities of the gas may be a result of converging gas flows. This dense material fuels some thick disk star formation, as evidenced by the presence of thick disk H II regions. Based on observations obtained with the NASA/ESA Hubble Space Telescope operated at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Also, based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the US, Italy, and Germany. LBT Corporation partners are the University of Arizona, on behalf of the Arizona University System; Instituto Nazionale do Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute of Potsdam, and Heidelberg University; Ohio State University, and the Research Corporation, on behalf of the University of Notre Dame, the University of Minnesota, and the University of Virginia. Also, based on observations obtained by the WIYN Observatory which is a joint facility of the University of Wisconsin-Madison, Yale University, Indiana University, and the National Optical Astronomy Observatories.

Impact of a boron rich layer on minority carrier lifetime degradation in boron spin-on dopant diffused n-type crystalline silicon solar cells

NASA Astrophysics Data System (ADS)

Singha, Bandana; Singh Solanki, Chetan

2016-03-01

In the production of n-type crystalline silicon solar cells with boron diffused emitters, the formation of a boron rich layer (BRL) is a common phenomenon and is largely responsible for bulk lifetime degradation. The phenomenon of BRL formation during diffusion of boron spin-on dopant and its impact on bulk lifetime degradation are investigated in this work. The BRL formed beneath the borosilicate glass layer has thicknesses varying from 10 nm-150 nm depending on the diffusion conditions. The effective and bulk minority carrier lifetimes, measured with Al2O3 deposited layers and a quinhydron-methanol solution, show that carrier lifetime degradation is proportional to the BRL thicknesses and their surface recombination velocities. The controlled diffusion processes and different oxidation techniques used in this work can partially reduce the BRL thickness and improve carrier lifetime by more than 10%. But for BRL thicknesses higher than 50 nm, different etching techniques further lower the carrier lifetime and the degradation in the device cannot be recovered.

3D Radiative Hydrodynamics Simulations of Protoplanetary Disks: A Comparison Between Two Radiative Cooling Algorithms

NASA Astrophysics Data System (ADS)

Lord, Jesse W.; Boley, A. C.; Durisen, R. H.

2006-12-01

We present a comparison between two three-dimensional radiative hydrodynamics simulations of a gravitationally unstable 0.07 Msun protoplanetary disk around a 0.5 Msun star. The first simulation is the radiatively cooled disk described in Boley et al. (2006, ApJ, 651). This simulation employed an algorithm that uses 3D flux-limited diffusion wherever the vertical Rosseland optical depth is greater than 2/3, which defines the optically thick region. The optically thin atmosphere of the disk, which cools according to its emissivity, is coupled to the optically thick region through an Eddington-like boundary condition. The second simulation employed an algorithm that uses a combination of solving the radiative transfer equation along rays in the z direction and flux limited diffusion in the r and phi directions on a cylindrical grid. We compare the following characteristics of the disk simulations: the mass transport and torques induced by gravitational instabilities, the effective temperature profiles of the disks, the gravitational and Reynolds stresses measured in the disk and those expected in an alpha-disk, and the amplitudes of the Fourier modes. This work has been supported by the National Science Foundation through grant AST-0452975 (astronomy REU program to Indiana University).

Enhancement of Water Evaporation on Solid Surfaces with Nanoscale Hydrophobic-Hydrophilic Patterns.

PubMed

Wan, Rongzheng; Wang, Chunlei; Lei, Xiaoling; Zhou, Guoquan; Fang, Haiping

2015-11-06

Using molecular dynamics simulations, we show that the evaporation of nanoscale water on hydrophobic-hydrophilic patterned surfaces is unexpectedly faster than that on any surfaces with uniform wettability. The key to this phenomenon is that, on the patterned surface, the evaporation rate from the hydrophilic region only slightly decreases due to the correspondingly increased water thickness; meanwhile, a considerable number of water molecules evaporate from the hydrophobic region despite the lack of water film. Most of the evaporated water from the hydrophobic region originates from the hydrophilic region by diffusing across the contact lines. Further analysis shows that the evaporation rate from the hydrophobic region is approximately proportional to the total length of the contact lines.

Effect of the Platinum Electroplated Layer Thickness on the Coatings' Microstructure

NASA Astrophysics Data System (ADS)

Zagula-Yavorska, Maryana; Gancarczyk, Kamil; Sieniawski, Jan

2017-03-01

CMSX 4 and Inconel 625 superalloys were coated by platinum layers (3 and 7 μm thick) in the electroplating process. The heat treatment of platinum layers (at 1,050 ˚C for 2 h) was performed to increase platinum adherence to the superalloys substrate. The diffusion zone obtained on CMSX 4 superalloy (3 and 7 μm platinum thick before heat treatment) consisted of two phases: γ-Ni(Al, Cr) and (Al0.25Pt0.75)Ni3. The diffusion zone obtained on Inconel 625 superalloy (3 μm platinum thick before heat treatment) consisted of the α-Pt(Ni, Cr, Al) phase. Moreover, γ-Ni(Cr, Al) phase was identified. The X-ray diffraction (XRD) results revealed the presence of platinum in the diffusion zone of the heat-treated coating (7 μm platinum thick) on Inconel 625 superalloy. The surface roughness parameter Ra of heat-treated coatings increased with the increase of platinum layers thickness. This was due to the unequal mass flow of platinum and nickel.

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.

Topologically dissociable patterns of development of the human cerebral cortex.

PubMed

Vandekar, Simon N; Shinohara, Russell T; Raznahan, Armin; Roalf, David R; Ross, Michelle; DeLeo, Nicholas; Ruparel, Kosha; Verma, Ragini; Wolf, Daniel H; Gur, Ruben C; Gur, Raquel E; Satterthwaite, Theodore D

2015-01-14

Over 90 years ago, anatomists noted the cortex is thinner in sulci than gyri, suggesting that development may occur on a fine scale driven by local topology. However, studies of brain development in youth have focused on describing how cortical thickness varies over large-scale functional and anatomic regions. How the relationship between thickness and local sulcal topology arises in development is still not well understood. Here, we investigated the spatial relationships between cortical thickness, folding, and underlying white matter organization to elucidate the influence of local topology on human brain development. Our approach included using both T1-weighted imaging and diffusion tensor imaging (DTI) in a cross-sectional sample of 932 youths ages 8-21 studied as part of the Philadelphia Neurodevelopmental Cohort. Principal components analysis revealed separable development-related processes of regionally specific nonlinear cortical thickening (from ages 8-14) and widespread linear cortical thinning that have dissociable relationships with cortical topology. Whereas cortical thinning was most prominent in the depths of the sulci, early cortical thickening was present on the gyri. Furthermore, decline in mean diffusivity calculated from DTI in underlying white matter was correlated with cortical thinning, suggesting that cortical thinning is spatially associated with white matter development. Spatial permutation tests were used to assess the significance of these relationships. Together, these data demonstrate that cortical remodeling during youth occurs on a local topological scale and is associated with changes in white matter beneath the cortical surface. Copyright © 2015 the authors 0270-6474/15/350599-11$15.00/0.

Spatial variability of the Arctic Ocean's double-diffusive staircase

NASA Astrophysics Data System (ADS)

Shibley, N. C.; Timmermans, M.-L.; Carpenter, J. R.; Toole, J. M.

2017-02-01

The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure overlying the Atlantic Water Layer that can be attributed to the diffusive form of double-diffusive convection. The staircase consists of multiple layers of O(1) m in thickness separated by sharp interfaces, across which temperature and salinity change abruptly. Through a detailed analysis of Ice-Tethered Profiler measurements from 2004 to 2013, the double-diffusive staircase structure is characterized across the entire Arctic Ocean. We demonstrate how the large-scale Arctic Ocean circulation influences the small-scale staircase properties. These staircase properties (layer thicknesses and temperature and salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio spanning the staircase stratification. We show that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (approximately 3-4) on the Eurasian side and higher density ratio (approximately 6-7) on the Canadian side. We find that the Eurasian Basin staircase is characterized by fewer, thinner layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin layers and the absence of a well-defined staircase. A double-diffusive 4/3 flux law parametrization is used to estimate vertical heat fluxes in the Canadian Basin to be O(0.1) W m-2. It is shown that the 4/3 flux law may not be an appropriate representation of heat fluxes through the Eurasian Basin staircase. Here molecular heat fluxes are estimated to be between O(0.01) and O(0.1) W m-2. However, many uncertainties remain about the exact nature of these fluxes.

Structural and Diffusion Property Alterations in Unaffected Siblings of Patients with Obsessive-Compulsive Disorder

PubMed Central

Shi, Changzheng; Miao, Guodong; Yang, Qiong; Gao, Wei; Wolff, Jason J.; Chan, Raymond C. K.; Shen, Dinggang

2014-01-01

Disrupted white matter integrity and abnormal cortical thickness are widely reported in the pathophysiology of obsessive-compulsive disorder (OCD). However, the relationship between alterations in white matter connectivity and cortical thickness in OCD is unclear. In addition, the heritability of this relationship is poorly understood. To investigate the relationship of white matter microstructure with cortical thickness, we measure fractional anisotropy (FA) of white matter in 30 OCD patients, 19 unaffected siblings and 30 matched healthy controls. Then, we take those regions of significantly altered FA in OCD patients compared with healthy controls to perform fiber tracking. Next, we calculate the fiber quantity in the same tracts. Lastly, we compare cortical thickness in the target regions of those tracts. Patients with OCD exhibited decreased FA in cingulum, arcuate fibers near the superior parietal lobule, inferior longitudinal fasciculus near the right superior temporal gyrus and uncinate fasciculus. Siblings showed reduced FA in arcuate fibers near the superior parietal lobule and anterior limb of internal capsule. Significant reductions in both fiber quantities and cortical thickness in OCD patients and their unaffected siblings were also observed in the projected brain areas when using the arcuate fibers near the left superior parietal lobule as the starting points. Reduced FA in the left superior parietal lobule was observed not only in patients with OCD but also in their unaffected siblings. Originated from the superior parietal lobule, the number of fibers was also found to be decreased and the corresponding cortical regions were thinner relative to controls. The linkage between disrupted white matter integrity and the abnormal cortical thickness may be a vulnerability marker for OCD. PMID:24489665

Differential microstructural and morphological abnormalities in mild cognitive impairment and Alzheimer's disease: Evidence from cortical and deep gray matter.

PubMed

Gong, Nan-Jie; Chan, Chun-Chung; Leung, Lam-Ming; Wong, Chun-Sing; Dibb, Russell; Liu, Chunlei

2017-05-01

One aim of this study is to use non-Gaussian diffusion kurtosis imaging (DKI) for capturing microstructural abnormalities in gray matter of Alzheimer's disease (AD). The other aim is to compare DKI metrics against thickness of cortical gray matter and volume of deep gray matter, respectively. A cohort of 18 patients with AD, 18 patients with amnestic mild cognitive impairment (MCI), and 18 normal controls underwent morphological and DKI MR imaging. Images were investigated using regions-of-interest-based analyses for deep gray matter and vertex-wise analyses for cortical gray matter. In deep gray matter, more regions showed DKI parametric abnormalities than atrophies at the early MCI stage. Mean kurtosis (MK) exhibited the largest number of significant abnormalities among all DKI metrics. At the later AD stage, diffusional abnormalities were observed in fewer regions than atrophies. In cortical gray matter, abnormalities in thickness were mainly in the medial and lateral temporal lobes, which fit the locations of known early pathological changes. Microstructural abnormalities were predominantly in the parietal and even frontal lobes, which fit the locations of known late pathological changes. In conclusion, MK can complement conventional diffusion metrics for detecting microstructural changes, especially in deep gray matter. This study also provides evidence supporting the notion that microstructural changes predate morphological changes. Hum Brain Mapp 38:2495-2508, 2017. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Effects of convergent diffusion and charge transfer kinetics on the diffusion layer thickness of spherical micro- and nanoelectrodes.

PubMed

Molina, A; Laborda, E; González, J; Compton, R G

2013-05-21

Nuances of the linear diffusion layer approximation are examined for slow charge transfer reactions at (hemi)spherical micro- and nanoelectrodes. This approximation is widely employed in Electrochemistry to evaluate the extent of electrolyte solution perturbed by the electrode process, which is essential to the understanding of the effects arising from thin-layer diffusion, convergent diffusion, convection, coupled chemical reactions and the double layer. The concept was well established for fast charge transfer processes at macroelectrodes, but remains unclear under other conditions such that a thorough assessment of its meaning was necessary. In a previous publication [A. Molina, J. González, E. Laborda and R. G. Compton, Phys. Chem. Chem. Phys., 2013, 15, 2381-2388] we shed some light on the influence of the reversibility degree. In the present work, the meaning of the diffusion layer thickness is investigated when very small electrodes are employed and so the contribution of convergent diffusion to the mass transport is very important. An analytical expression is given to calculate the linear diffusion layer thickness at (hemi)spherical electrodes and its behaviour is studied for a wide range of conditions of reversibility (from reversible to fully-irreversible processes) and electrode size (from macro- to nano-electrodes). Rigorous analytical solutions are deduced for true concentration profiles, surface concentrations, linear diffusion layer thickness and current densities when a potential pulse is applied at (hemi)spherical electrodes. The expressions for the magnitudes mentioned above are valid for electrodes of any size (including (hemi)spherical nanoelectrodes) and for any degree of reversibility, provided that mass transport occurs exclusively via diffusion. The variation of the above with the electrode size, applied potential and charge transfer kinetics is studied.

Diffusion and sorption of organic micropollutants in biofilms with varying thicknesses.

PubMed

Torresi, Elena; Polesel, Fabio; Bester, Kai; Christensson, Magnus; Smets, Barth F; Trapp, Stefan; Andersen, Henrik R; Plósz, Benedek Gy

2017-10-15

Solid-liquid partitioning is one of the main fate processes determining the removal of micropollutants in wastewater. Little is known on the sorption of micropollutants in biofilms, where molecular diffusion may significantly influence partitioning kinetics. In this study, the diffusion and the sorption of 23 micropollutants were investigated in novel moving bed biofilm reactor (MBBR) carriers with controlled biofilm thickness (50, 200 and 500 μm) using targeted batch experiments (initial concentration = 1 μg L -1 , for X-ray contrast media 15 μg L -1 ) and mathematical modelling. We assessed the influence of biofilm thickness and density on the dimensionless effective diffusivity coefficient f (equal to the biofilm-to-aqueous diffusivity ratio) and the distribution coefficient K d,eq (L g -1 ). Sorption was significant only for eight positively charged micropollutants (atenolol, metoprolol, propranolol, citalopram, venlafaxine, erythromycin, clarithromycin and roxithromycin), revealing the importance of electrostatic interactions with solids. Sorption equilibria were likely not reached within the duration of batch experiments (4 h), particularly for the thickest biofilm, requiring the calculation of the distribution coefficient K d,eq based on the approximation of the asymptotic equilibrium concentration (t > 4 h). K d,eq values increased with increasing biofilm thickness for all sorptive micropollutants (except atenolol), possibly due to higher porosity and accessible surface area in the thickest biofilm. Positive correlations between K d,eq and micropollutant properties (polarity and molecular size descriptors) were identified but not for all biofilm thicknesses, thus confirming the challenge of improving predictive sorption models for positively charged compounds. A diffusion-sorption model was developed and calibrated against experimental data, and estimated f values also increased with increasing biofilm thickness. This indicates that diffusion in thin biofilms may be strongly limited (f ≪ 0.1) by the high biomass density (reduced porosity). Copyright © 2017 Elsevier Ltd. All rights reserved.

Transient Infrared Emission Spectroscopy

NASA Astrophysics Data System (ADS)

Jones, Roger W.; McClelland, John F.

1989-12-01

Transient Infrared Emission Spectroscopy (TIRES) is a new technique that reduces the occurrence of self-absorption in optically thick solid samples so that analytically useful emission spectra may be observed. Conventional emission spectroscopy, in which the sample is held at an elevated, uniform temperature, is practical only for optically thin samples. In thick samples the emission from deep layers of the material is partially absorbed by overlying layers.1 This self-absorption results in emission spectra from most optically thick samples that closely resemble black-body spectra. The characteristic discrete emission bands are severely truncated and altered in shape. TIRES bypasses this difficulty by using a laser to heat only an optically thin surface layer. The increased temperature of the layer is transient since the layer will rapidly cool and thicken by thermal diffusion; hence the emission collection must be correlated with the laser heating. TIRES may be done with both pulsed and cw lasers.2,3 When a pulsed laser is used, the spectrometer sampling must be synchronized with the laser pulsing so that only emission during and immediately after each laser pulse is observed.3 If a cw laser is used, the sample must move rapidly through the beam. The hot, transient layer is then in the beam track on the sample at and immediately behind the beam position, so the spectrometer field of view must be limited to this region near the beam position.2 How much self-absorption the observed emission suffers depends on how thick the heated layer has grown by thermal diffusion when the spectrometer samples the emission. Use of a pulsed laser synchronized with the spectrometer sampling readily permits reduction of the time available for heat diffusion to about 100 acs .3 When a cw laser is used, the heat-diffusion time is controlled by how small the spectrometer field of view is and by how rapidly the sample moves past within this field. Both a very small field of view and a very high sample speed would be required to attain a diffusion time of 100 μs. Accordingly, pulsed-laser TIRES generally produces spectra suffering from less self-absorption than cw-laser TIRES does, but the cw-laser technique is technically much simpler since no synchronization is required.

Radionuclide Transport in Fracture-Granite Interface Zones

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

Hu, Q; Mori, A

In situ radionuclide migration experiments, followed by excavation and sample characterization, were conducted in a water-conducting shear zone at the Grimsel Test Site (GTS) in Switzerland to study diffusion paths of radionuclides in fractured granite. In this work, we employed a micro-scale mapping technique that interfaces laser ablation sampling with inductively coupled plasma-mass spectrometry (LA/ICP-MS) to measure the fine-scale (micron-range) distribution of actinides ({sup 234}U, {sup 235}U, and {sup 237}Np) in the fracture-granite interface zones. Long-lived {sup 234}U, {sup 235}U, and {sup 237}Np were detected in flow channels, as well as in the adjacent rock matrix, using the sensitive, feature-basedmore » mapping of the LA/ICP-MS technique. The injected sorbing actinides are mainly located within the advective flowing fractures and the immediately adjacent regions. The water-conducting fracture studied in this work is bounded on one side by mylonite and the other by granitic matrix regions. These actinides did not penetrate into the mylonite side as much as the relatively higher-porosity granite matrix, most likely due to the low porosity, hydraulic conductivity, and diffusivity of the fracture wall (a thickness of about 0.4 mm separates the mylonite region from the fracture) and the mylonite region itself. Overall, the maximum penetration depth detected with this technique for the more diffusive {sup 237}Np over the field experimental time scale of about 60 days was about 10 mm in the granitic matrix, illustrating the importance of matrix diffusion in retarding radionuclide transport from the advective fractures. Laboratory tests and numerical modeling of radionuclide diffusion into granitic matrix was conducted to complement and help interpret the field results. Measured apparent diffusivity of multiple tracers in granite provided consistent predictions for radionuclide transport in the fractured granitic rock.« less

Gaseous templates in ant nests.

PubMed

Cox, M D; Blanchard, G B

2000-05-21

We apply a diffusion model to the atmosphere of ant nests. With particular reference to carbon dioxide (CO2), we explore analytically and numerically the spatial and temporal patterns of brood- or worker-produced gases in nests. The maximum concentration within a typical one-chamber ant nest with approximately 200 ants can reach 12.5 times atmospheric concentration, reaching 95% of equilibrium concentrations within 15 min. Maximum concentration increases with increasing number of ants in the nest (or production rate of the gas), distance between the centre of the nest ants and the nest entrance, entrance length, wall thickness, and with decreasing entrance width, wall permeability and diffusion coefficient. The nest can be divided into three qualitatively distinct regions according to the shape of the gradient: a plateau of high concentration in the back half of the nest; an intermediate region of increasingly steep gradient towards the entrance; and a steep linear gradient in the entrance tunnel. These regions are robust to changes in gas concentrations, but vary with changes in nest architecture. The pattern of diffusing gases contains information about position and orientation relative to gas sources and sinks, and about colony state, including colony size, activity state and aspects of nest architecture. We discuss how this diffusion pattern may act as a "dynamic template", providing local cues which trigger behavioural acts appropriate to colony needs, which in turn may feed back to changes in the gas template. In particular, wall building occurs along lines of similar concentration for a variety of nest geometries; there is surprising convergence between the period of cycles of synchronously active ants and the time taken for CO2 levels to equilibrate; and the qualitatively distinct regions of the "dynamic template" correspond to regions occupied by different groups of ants.

Imaging Effects of Neurotrophic Factor Genes on Brain Plasticity and Repair in Multiple Sclerosis

DTIC Science & Technology

2011-07-01

focal and diffuse effects in brain (including cortical thickness and subcortical volume measures, lesion volumetry , and voxel-based morphometry and...to both focal and diffuse effects in gray and white matter, including cortical thickness and subcortical volume measures, lesion volumetry , and

In vivo burn diagnosis by camera-phone diffuse reflectance laser speckle detection.

PubMed

Ragol, S; Remer, I; Shoham, Y; Hazan, S; Willenz, U; Sinelnikov, I; Dronov, V; Rosenberg, L; Bilenca, A

2016-01-01

Burn diagnosis using laser speckle light typically employs widefield illumination of the burn region to produce two-dimensional speckle patterns from light backscattered from the entire irradiated tissue volume. Analysis of speckle contrast in these time-integrated patterns can then provide information on burn severity. Here, by contrast, we use point illumination to generate diffuse reflectance laser speckle patterns of the burn. By examining spatiotemporal fluctuations in these time-integrated patterns along the radial direction from the incident point beam, we show the ability to distinguish partial-thickness burns in a porcine model in vivo within the first 24 hours post-burn. Furthermore, our findings suggest that time-integrated diffuse reflectance laser speckle can be useful for monitoring burn healing over time post-burn. Unlike conventional diffuse reflectance laser speckle detection systems that utilize scientific or industrial-grade cameras, our system is designed with a camera-phone, demonstrating the potential for burn diagnosis with a simple imager.

In vivo burn diagnosis by camera-phone diffuse reflectance laser speckle detection

PubMed Central

Ragol, S.; Remer, I.; Shoham, Y.; Hazan, S.; Willenz, U.; Sinelnikov, I.; Dronov, V.; Rosenberg, L.; Bilenca, A.

2015-01-01

Burn diagnosis using laser speckle light typically employs widefield illumination of the burn region to produce two-dimensional speckle patterns from light backscattered from the entire irradiated tissue volume. Analysis of speckle contrast in these time-integrated patterns can then provide information on burn severity. Here, by contrast, we use point illumination to generate diffuse reflectance laser speckle patterns of the burn. By examining spatiotemporal fluctuations in these time-integrated patterns along the radial direction from the incident point beam, we show the ability to distinguish partial-thickness burns in a porcine model in vivo within the first 24 hours post-burn. Furthermore, our findings suggest that time-integrated diffuse reflectance laser speckle can be useful for monitoring burn healing over time post-burn. Unlike conventional diffuse reflectance laser speckle detection systems that utilize scientific or industrial-grade cameras, our system is designed with a camera-phone, demonstrating the potential for burn diagnosis with a simple imager. PMID:26819831

Adsorption, Desorption, and Diffusion of Nitrogen in a Model Nanoporous Material: II. Diffusion Limited Kinetics in Amorphous Solid Water

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

Zubkov, Tykhon; Smith, R. Scott; Engstrom, Todd R.

2007-11-14

Tykhon Zubkov, R. Scott Smith, Todd R. Engstrom, and Bruce D. Kay The adsorption, desorption, and diffusion kinetics of N2 on thick (up to ~9 mm) porous films of amorphous solid water (ASW) films were studied using molecular beam techniques and temperature programmed desorption (TPD). Porous ASW films were grown on Pt(111) at low temperature (<30 K) from a collimated H2O beam at glancing incident angles. In thin films (<1 mm), the desorption kinetics are well described by a model that assumes rapid and uniform N2 distribution throughout the film. In thicker films, (>1 mm), N2 adsorption at 27 Kmore » results in a non-uniform distribution where most of N2 is trapped in the outer region of the film. Redistribution of N2 can be induced by thermal annealing. The apparent activation energy for this process is ~7 kJ/mol, which is approximately half of the desorption activation energy at the corresponding coverage. Blocking adsorption sites near the film surface facilitates transport into the film. Despite the onset of limited diffusion, the adsorption kinetics are efficient, precursor-mediated and independent of film thickness. An adsorption mechanism is proposed, in which a high-coverage N2 front propagates into a pore by the rapid transport of physisorbed 2nd layer N2 species on top of the 1st layer chemisorbed layer.« less

VBM-DTI correlates of verbal intelligence: a potential link to Broca's area.

PubMed

Konrad, Andreas; Vucurevic, Goran; Musso, Francesco; Winterer, Georg

2012-04-01

Human brain lesion studies first investigated the biological roots of cognitive functions including language in the late 1800s. Neuroimaging studies have reported correlation findings with general intelligence predominantly in fronto-parietal cortical areas. However, there is still little evidence about the relationship between verbal intelligence and structural properties of the brain. We predicted that verbal performance is related to language regions of Broca's and Wernicke's areas. Verbal intelligence quotient (vIQ) was assessed in 30 healthy young subjects. T1-weighted MRI and diffusion tensor imaging data sets were acquired. Voxel-wise regression analyses were used to correlate fractional anisotropy (FA) and mean diffusivity values with vIQ. Moreover, regression analyses of regional brain volume with vIQ were performed adopting voxel-based morphometry (VBM) and ROI methodology. Our analyses revealed a significant negative correlation between vIQ and FA and a significant positive correlation between vIQ and mean diffusivity in the left-hemispheric Broca's area. VBM regression analyses did not show significant results, whereas a subsequent ROI analysis of Broca's area FA peak cluster demonstrated a positive correlation of gray matter volume and vIQ. These findings suggest that cortical thickness in Broca's area contributes to verbal intelligence. Diffusion parameters predicted gray matter ratio in Broca's area more sensitive than VBM methodology.

Understanding the Thickness-Dependent Performance of Organic Bulk Heterojunction Solar Cells: The Influence of Mobility, Lifetime, and Space Charge.

PubMed

Kirchartz, Thomas; Agostinelli, Tiziano; Campoy-Quiles, Mariano; Gong, Wei; Nelson, Jenny

2012-12-06

We investigate the reasons for the dependence of photovoltaic performance on the absorber thickness of organic solar cells using experiments and drift-diffusion simulations. The main trend in photocurrent and fill factor versus thickness is determined by mobility and lifetime of the charge carriers. In addition, space charge becomes more and more important the thicker the device is because it creates field free regions with low collection efficiency. The two main sources of space-charge effects are doping and asymmetric mobilities. We show that for our experimental results on Si-PCPDTBT:PC71BM (poly[(4,40-bis(2-ethylhexyl)dithieno[3,2-b:20,30-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,50-diyl]:[6,6]-phenyl C71-butyric acid methyl ester) solar cells, the influence of doping is most likely the dominant influence on the space charge and has an important effect on the thickness dependence of performance.

General Model of Hindered Diffusion.

PubMed

Eloul, Shaltiel; Compton, Richard G

2016-11-03

The diffusion of a particle from bulk solution is slowed as it moves close to an adsorbing surface. A general model is reported that is easily applied by theoreticians and experimentalists. Specifically, it is shown here that in general and regardless of the space size, the magnitude of the effect of hindered diffusion on the flux is a property of the diffusion layer thickness. We explain and approximate the effect. Predictions of concentration profiles show that a "hindered diffusion layer" is formed near the adsorbing surface within the diffusion layer, observed even when the particle radius is just a 0.1% of the diffusion layer thickness. In particular, we focus on modern electrochemistry processes involving with impact of particles with either ultrasmall electrodes or particles in convective systems. The concept of the "hindered diffusion layer" is generally important for example in recent biophysical models of particles diffusion to small targets.

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.

Imaging Effects of Neurotrophic Factor Genes on Brain Plasticity and Repair in Multiple Sclerosis

DTIC Science & Technology

2012-07-01

sensitive to focal and diffuse changes in brain tissue (including cortical thickness and subcortical volume measures, lesion volumetry , and voxel-based...sensitive to both focal and diffuse effects in gray and white matter, including cortical thickness and subcortical volume measures, lesion volumetry , and

New Layer Thickness Parameterization of Diffusive Convection

NASA Astrophysics Data System (ADS)

Zhou, Sheng-Qi; Lu, Yuan-Zheng; Guo, Shuang-Xi; Song, Xue-Long; Qu, Ling; Cen, Xian-Rong; Fer, Ilker

2017-11-01

Double-diffusion convection is one of the most important non-mechanically driven mixing processes. Its importance has been particular recognized in oceanography, material science, geology, and planetary physics. Double-diffusion occurs in a fluid in which there are gradients of two (or more) properties with different molecular diffusivities and of opposing effects on the vertical density distribution. It has two primary modes: salt finger and diffusive convection. Recently, the importance of diffusive convection has aroused more interest due to its impact to the diapycnal mixing in the interior ocean and the ice and the ice-melting in the Arctic and Antarctic Oceans. In our recent work, we constructed a length scale of energy-containing eddy and proposed a new layer thickness parameterization of diffusive convection by using the laboratory experiment and in situ observations in the lakes and oceans. The new parameterization can well describe the laboratory convecting layer thicknesses (0.01 0.1 m) and those observed in oceans and lakes (0.1 1000 m). This work was supported by China NSF Grants (41476167,41406035 and 41176027), NSF of Guangdong Province, China (2016A030311042) and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA11030302).

On the thermo-chemical origin of the stratified region at the top of the Earth's core

NASA Astrophysics Data System (ADS)

Nakagawa, Takashi

2018-03-01

I developed a combined model of the thermal and chemical evolution of the Earth's core and investigated its influence on a thermochemically stable region beneath the core-mantle boundary (CMB). The chemical effects of the growing stable region are caused by the equilibrium chemical reaction between silicate and the metallic core. The thermal effects can be characterized by the growth of the sub-isentropic shell, which may have a rapid growth rate compared to that of the chemically stable region. When the present-day CMB heat flow was varied, the origin of the stable region changed from chemical to thermochemical to purely thermal because the rapid growth of the sub-isentropic shell can replace the chemically stable region. Physically reasonable values of the present-day CMB heat flow that can maintain the geodynamo action over 4 billion years should be between 8 and 11 TW. To constrain the thickness of the thermochemically stable region beneath the CMB, the chemical diffusivity is important and should be ∼O(10-8) m2/s to obtain a thickness of the thermochemically stable region beneath the CMB consistent with that inferred from geomagnetic secular variations (140 km). However, the strength of the stable region found in this study is too high to be consistent with the constraint on the stability of the stable region inferred from geomagnetic secular variations.

Effects of Refractive Index and Diffuse or Specular Boundaries on a Radiating Isothermal Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1994-01-01

Equilibrium temperatures of an absorbing-emitting layer were obtained for exposure to incident radiation and with the layer boundaries either specular or diffuse. For high refractive indices the surface condition can influence the radiative heat balance if the layer optical thickness is small. Hence for a spectrally varying absorption coefficient the layer temperature is affected if there is significant radiative energy in the spectral range with a small absorption coefficient. Similar behavior was obtained for transient radiative cooling of a layer where the results are affected by the initial temperature and hence the fraction of energy radiated in the short wavelength region where the absorption coefficient is small. The results are a layer without internal scattering. If internal scattering is significant, the radiation reaching the internal surface of a boundary is diffused and the effect of the two different surface conditions would become small.

Effect of diffuser vane shape on the performance of a centrifugal compressor stage

NASA Astrophysics Data System (ADS)

Reddy, T. Ch Siva; Ramana Murty, G. V.; Prasad, M. V. S. S. S. M.

2014-04-01

The present paper reports the results of experimental investigations on the effect of diffuser vane shape on the performance of a centrifugal compressor stage. These studies were conducted on the chosen stage having a backward curved impeller of 500 mm tip diameter and 24.5 mm width and its design flow coefficient is ϕd=0.0535. Three different low solidity diffuser vane shapes namely uncambered aerofoil, constant thickness flat plate and circular arc cambered constant thickness plate were chosen as the variants for diffuser vane shape and all the three shapes have the same thickness to chord ratio (t/c=0.1). Flow coefficient, polytropic efficiency, total head coefficient, power coefficient and static pressure recovery coefficient were chosen as the parameters for evaluating the effect of diffuser vane shape on the stage performance. The results show that there is reasonable improvement in stage efficiency and total head coefficient with the use of the chosen diffuser vane shapes as compared to conventional vaneless diffuser. It is also noticed that the aero foil shaped LSD has shown better performance when compared to flat plate and circular arc profiles. The aerofoil vane shape of the diffuser blade is seen to be tolerant over a considerable range of incidence.

Estimating the spin diffusion length and the spin Hall angle from spin pumping induced inverse spin Hall voltages

NASA Astrophysics Data System (ADS)

Roy, Kuntal

2017-11-01

There exists considerable confusion in estimating the spin diffusion length of materials with high spin-orbit coupling from spin pumping experiments. For designing functional devices, it is important to determine the spin diffusion length with sufficient accuracy from experimental results. An inaccurate estimation of spin diffusion length also affects the estimation of other parameters (e.g., spin mixing conductance, spin Hall angle) concomitantly. The spin diffusion length for platinum (Pt) has been reported in the literature in a wide range of 0.5-14 nm, and in particular it is a constant value independent of Pt's thickness. Here, the key reasonings behind such a wide range of reported values of spin diffusion length have been identified comprehensively. In particular, it is shown here that a thickness-dependent conductivity and spin diffusion length is necessary to simultaneously match the experimental results of effective spin mixing conductance and inverse spin Hall voltage due to spin pumping. Such a thickness-dependent spin diffusion length is tantamount to the Elliott-Yafet spin relaxation mechanism, which bodes well for transitional metals. This conclusion is not altered even when there is significant interfacial spin memory loss. Furthermore, the variations in the estimated parameters are also studied, which is important for technological applications.

Thin silicon solar cell performance characteristics

NASA Technical Reports Server (NTRS)

Gay, C. F.

1978-01-01

Refined techniques for surface texturizing, back surface field and back surface reflector formation were evaluated for use with shallow junction, single-crystal silicon solar cells. Each process was characterized individually and collectively as a function of device thickness and bulk resistivity. Among the variables measured and reported are open circuit voltage, short circuit current and spectral response. Substantial improvements were obtained by the utilization of a low cost aluminum paste process to simultaneously remove the unwanted n(+) diffused region, form the back surface field and produce an ohmic contact metallization. The highly effective BSF which results from applying this process has allowed fabrication of cells 0.05 mm thick with initial outputs as high as 79.5 mW/4 sq cm (28 C, AM0) and superior electron radiation tolerance. Cells of 0.02 mm to 0.04 mm thickness have been fabricated with power to mass ratios well in excess of 2 watts per gram.

Controlling the optical parameters of self-assembled silver films with wetting layers and annealing

NASA Astrophysics Data System (ADS)

Ciesielski, Arkadiusz; Skowronski, Lukasz; Trzcinski, Marek; Szoplik, Tomasz

2017-11-01

We investigated the influence of presence of Ni and Ge wetting layers as well as annealing on the permittivity of Ag films with thicknesses of 20, 35 and 65 nm. Most of the research on thin silver films deals with very small (<20 nm) or relatively large (≥50 nm) thicknesses. We studied the transition region (around 30 nm) from charge percolation pathways to fully continuous films and compared the values of optical parameters among silver layers with at least one fixed attribute (thickness, wetting and capping material, post-process annealing). Our study, based on atomic force microscopy, ellipsometric and X-ray photoelectron spectroscopy measurements, shows that utilizing a wetting layer is comparable to increasing the thickness of the silver film. Both operations decrease the roughness-to-thickness ratio, thus decreasing the scattering losses and both narrow the Lorentz-shaped interband transition peak. However, while increasing silver thickness increases absorption on the free carriers, the use of wetting layers influences the self-assembled internal structure of silver films in such a way, that the free carrier absorption decreases. Wetting layers also introduce additional contributions from effects like segregation or diffusion, which evolve in time and due to annealing.

Effect of clamping pressure on ohmic resistance and compression of gas diffusion layers for polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Mason, Thomas J.; Millichamp, Jason; Neville, Tobias P.; El-kharouf, Ahmad; Pollet, Bruno G.; Brett, Daniel J. L.

2012-12-01

This paper describes the use of an in situ analytical technique based on simultaneous displacement and resistance measurement of gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs), when exposed to varying compaction pressure. In terms of the losses within fuel cells, the ohmic loss makes up a significant portion. Of this loss, the contact resistance between the GDL and the bipolar plate (BPP) is an important constituent. By analysing the change in thickness and ohmic resistance of GDLs under compression, important mechanical and electrical properties are obtained. Derived parameters such as the 'displacement factor' are used to characterise a representative range of commercial GDLs. Increasing compaction pressure leads to a non-linear decrease in resistance for all GDLs. For Toray paper, compaction becomes more irreversible with pressure with no elastic region observed. Different GDLs have different intrinsic resistance; however, all GDLs of the same class share a common compaction profile (change in resistance with pressure). Cyclic compression of Toray GDL leads to progressive improvement in resistance and reduction in thickness that stabilises after ∼10 cycles.

Materials science in pre-plated leadframes for electronic packages

NASA Astrophysics Data System (ADS)

Liu, Lilin

Au/Pd/Ni pre-plated leadframes (PPF) are high performance frames for accommodating high-end electronic packages. Cost and reliability are major concerns in their wide application. The present work, from a materials science point view, deepens the understanding of PPFs, optimizes the conventional PPFs, develops a novel PPF architecture and models the residual stress relaxation in heteroepitaxial thin films. The wire pull test, the solderability test, and High-Resolution Transmission Electron Microscopy (HRTEM) were employed to characterize the PPFs in order to understand the relationship between performance and microstructure. We optimized the electroplating profiles and determined the minimum thickness of the Pd layer with the PPF performance satisfying the industry standards. Further increasing the Pd layer thickness beyond the critical thickness will not enhance the performance more, but increase the product cost. With the optimized electroplating profile, the electroplated Au layer is epitaxially deposited on the Pd layer, and so does the Pd layer on the Ni layer. Misfit dislocations and nanotwins are present at the interface between the Pd and Ni layers, which are generated to release the about 10.4% misfit strain between the Pd and Ni lattices. This work demonstrates that the electro-deposition technique can electroplate epitaxy-like Pd films on the highly (200) textured Ni films, which are grown on the Cu substrates. A novel technique for impeding Cu out-diffusion in Cu alloy based pre-plated leadframes was developed by electroplating a 3-4 nm thick Sn layer on a Cu alloy base prior to electroplating a Ni layer. A 10-14 nm thick epitaxy-like and dense (Cu,Ni)3Sn intermetallic compound (IMC) layer is automatically formed en route of diffuse reaction, which leads to a drastic reduction in Cu out-diffusion and hence improves significantly the protection of the leadframes against oxidation and corrosion attack. The oxidation behaviours were quantified by Electron Diffraction X-ray (EX) incorporated in Scanning Electron Microscopy (SEM) in the present work, which is a good complementary to the traditional weight gain test by a balance. A diffusion/oxidation model was developed to estimate the effective diffusion coefficient of Cu in the formed IMC nanolayers. The estimated Cu diffusion coefficient in the IMC interlayer is about 1.6x10 -22m2/s at 250°C, which is around 7~11 orders lower than the interdiffusion coefficients for eta- Cu6Sn5 and epsilon- Cu3Sn phases at corresponding temperatures. Based on the dislocation theory of twinning, analytical solutions by using the hybrid superposition and Fourier transformation approach were derived for the calculation of various energies involved in the misfit twinning process. For a given epilayer thickness and lattice mismatch strain, the twin formation energy should reach its minimum to determine the twin width and a zero minimum formation energy determines the critical thickness for misfit twinning. The effect of elastic mismatch between the epilayer and the substrate on the critical thickness was studied comprehensively, revealing that an elastically soft epilayer has a large critical thickness. Moreover, a misfit-twin-and-perfect-dislocation predominance chart is constructed to predict the predominant regions of misfit twinning and perfect dislocation in the mismatch strain and the specific twin boundary energy domain. Multiple misfit twins in epilayer/substrate systems were studied by summing up the stress and displacement fields of individual twins. In principle, the energy minimization approach can be applied to multiple misfit twins, although only periodic arrays of parallel and alternating twins were investigated here in detail. The equilibrium twin width and equilibrium twin spacing of a periodic array of twins represent the misfit twin morphology. The theoretical results indicate that the difference in elastic constants between an epilayer and its substrate has great effects on the morphology of equilibrium twins. The theoretical predictions agree with experimental observations.

Using Directional Diffusion Coefficients for Nonlinear Diffusion Acceleration of the First Order SN Equations in Near-Void Regions

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

Schunert, Sebastian; Hammer, Hans; Lou, Jijie

2016-11-01

The common definition of the diffusion coeffcient as the inverse of three times the transport cross section is not compat- ible with voids. Morel introduced a non-local tensor diffusion coeffcient that remains finite in voids[1]. It can be obtained by solving an auxiliary transport problem without scattering or fission. Larsen and Trahan successfully applied this diffusion coeffcient for enhancing the accuracy of diffusion solutions of very high temperature reactor (VHTR) problems that feature large, optically thin channels in the z-direction [2]. It is demonstrated that a significant reduction of error can be achieved in particular in the optically thin region.more » Along the same line of thought, non-local diffusion tensors are applied modeling the TREAT reactor confirming the findings of Larsen and Trahan [3]. Previous work of the authors have introduced a flexible Nonlinear-Diffusion Acceleration (NDA) method for the first order S N equations discretized with the discontinuous finite element method (DFEM), [4], [5], [6]. This NDA method uses a scalar diffusion coeffcient in the low-order system that is obtained as the flux weighted average of the inverse transport cross section. Hence, it su?ers from very large and potentially unbounded diffusion coeffcients in the low order problem. However, it was noted that the choice of the diffusion coeffcient does not influence consistency of the method at convergence and hence the di?usion coeffcient is essentially a free parameter. The choice of the di?usion coeffcient does, however, affect the convergence behavior of the nonlinear di?usion iterations. Within this work we use Morel’s non-local di?usion coef- ficient in the aforementioned NDA formulation in lieu of the flux weighted inverse of three times the transport cross section. The goal of this paper is to demonstrate that significant en- hancement of the spectral properties of NDA can be achieved in near void regions. For testing the spectral properties of the NDA with non-local diffusion coeffcients, the periodical horizontal interface problem is used [7]. This problem consists of alternating stripes of optically thin and thick materials both of which feature scattering ratios close to unity.« less

Modeling of adsorption dynamics at air-liquid interfaces using statistical rate theory (SRT).

PubMed

Biswas, M E; Chatzis, I; Ioannidis, M A; Chen, P

2005-06-01

A large number of natural and technological processes involve mass transfer at interfaces. Interfacial properties, e.g., adsorption, play a key role in such applications as wetting, foaming, coating, and stabilizing of liquid films. The mechanistic understanding of surface adsorption often assumes molecular diffusion in the bulk liquid and subsequent adsorption at the interface. Diffusion is well described by Fick's law, while adsorption kinetics is less understood and is commonly described using Langmuir-type empirical equations. In this study, a general theoretical model for adsorption kinetics/dynamics at the air-liquid interface is developed; in particular, a new kinetic equation based on the statistical rate theory (SRT) is derived. Similar to many reported kinetic equations, the new kinetic equation also involves a number of parameters, but all these parameters are theoretically obtainable. In the present model, the adsorption dynamics is governed by three dimensionless numbers: psi (ratio of adsorption thickness to diffusion length), lambda (ratio of square of the adsorption thickness to the ratio of adsorption to desorption rate constant), and Nk (ratio of the adsorption rate constant to the product of diffusion coefficient and bulk concentration). Numerical simulations for surface adsorption using the proposed model are carried out and verified. The difference in surface adsorption between the general and the diffusion controlled model is estimated and presented graphically as contours of deviation. Three different regions of adsorption dynamics are identified: diffusion controlled (deviation less than 10%), mixed diffusion and transfer controlled (deviation in the range of 10-90%), and transfer controlled (deviation more than 90%). These three different modes predominantly depend on the value of Nk. The corresponding ranges of Nk for the studied values of psi (10(-2)

Molecular-Beam-Epitaxy Program

NASA Technical Reports Server (NTRS)

Sparks, Patricia D.

1988-01-01

Molecular Beam Epitaxy (MBE) computer program developed to aid in design of single- and double-junction cascade cells made of silicon. Cascade cell has efficiency 1 or 2 percent higher than single cell, with twice the open-circuit voltage. Input parameters include doping density, diffusion lengths, thicknesses of regions, solar spectrum, absorption coefficients of silicon (data included for 101 wavelengths), and surface recombination velocities. Results include maximum power, short-circuit current, and open-circuit voltage. Program written in FORTRAN IV.

A multidimensional unified gas-kinetic scheme for radiative transfer equations on unstructured mesh

NASA Astrophysics Data System (ADS)

Sun, Wenjun; Jiang, Song; Xu, Kun

2017-12-01

In order to extend the unified gas kinetic scheme (UGKS) to solve radiative transfer equations in a complex geometry, a multidimensional asymptotic preserving implicit method on unstructured mesh is constructed in this paper. With an implicit formulation, the CFL condition for the determination of the time step in UGKS can be much relaxed, and a large time step is used in simulations. Differently from previous direction-by-direction UGKS on orthogonal structured mesh, on unstructured mesh the interface flux transport takes into account multi-dimensional effect, where gradients of radiation intensity and material temperature in both normal and tangential directions of a cell interface are included in the flux evaluation. The multiple scale nature makes the UGKS be able to capture the solutions in both optically thin and thick regions seamlessly. In the optically thick region the condition of cell size being less than photon's mean free path is fully removed, and the UGKS recovers a solver for diffusion equation in such a limit on unstructured mesh. For a distorted quadrilateral mesh, the UGKS goes to a nine-point scheme for the diffusion equation, and it naturally reduces to the standard five-point scheme for a orthogonal quadrilateral mesh. Numerical computations covering a wide range of transport regimes on unstructured and distorted quadrilateral meshes will be presented to validate the current approach.

Quantitative MRI of the spinal cord and brain in adrenomyeloneuropathy: in vivo assessment of structural changes.

PubMed

Castellano, Antonella; Papinutto, Nico; Cadioli, Marcello; Brugnara, Gianluca; Iadanza, Antonella; Scigliuolo, Graziana; Pareyson, Davide; Uziel, Graziella; Köhler, Wolfgang; Aubourg, Patrick; Falini, Andrea; Henry, Roland G; Politi, Letterio S; Salsano, Ettore

2016-06-01

Adrenomyeloneuropathy is the late-onset form of X-linked adrenoleukodystrophy, and is considered the most frequent metabolic hereditary spastic paraplegia. In adrenomyeloneuropathy the spinal cord is the main site of pathology. Differently from quantitative magnetic resonance imaging of the brain, little is known about the feasibility and utility of advanced neuroimaging in quantifying the spinal cord abnormalities in hereditary diseases. Moreover, little is known about the subtle pathological changes that can characterize the brain of adrenomyeloneuropathy subjects in the early stages of the disease. We performed a cross-sectional study on 13 patients with adrenomyeloneuropathy and 12 age-matched healthy control subjects who underwent quantitative magnetic resonance imaging to assess the structural changes of the upper spinal cord and brain. Total cord areas from C2-3 to T2-3 level were measured, and diffusion tensor imaging metrics, i.e. fractional anisotropy, mean, axial and radial diffusivity values were calculated in both grey and white matter of spinal cord. In the brain, grey matter regions were parcellated with Freesurfer and average volume and thickness, and mean diffusivity and fractional anisotropy from co-registered diffusion maps were calculated in each region. Brain white matter diffusion tensor imaging metrics were assessed using whole-brain tract-based spatial statistics, and tractography-based analysis on corticospinal tracts. Correlations among clinical, structural and diffusion tensor imaging measures were calculated. In patients total cord area was reduced by 26.3% to 40.2% at all tested levels (P < 0.0001). A mean 16% reduction of spinal cord white matter fractional anisotropy (P ≤ 0.0003) with a concomitant 9.7% axial diffusivity reduction (P < 0.009) and 34.5% radial diffusivity increase (P < 0.009) was observed, suggesting co-presence of axonal degeneration and demyelination. Brain tract-based spatial statistics showed a marked reduction of fractional anisotropy, increase of radial diffusivity (P < 0.001) and no axial diffusivity changes in several white matter tracts, including corticospinal tracts and optic radiations, indicating predominant demyelination. Tractography-based analysis confirmed the results within corticospinal tracts. No significant cortical volume and thickness reduction or grey matter diffusion tensor imaging values alterations were observed in patients. A correlation between radial diffusivity and disease duration along the corticospinal tracts (r = 0.806, P < 0.01) was found. In conclusion, in adrenomyeloneuropathy patients quantitative magnetic resonance imaging-derived measures identify and quantify structural changes in the upper spinal cord and brain which agree with the expected histopathology, and suggest that the disease could be primarily caused by a demyelination rather than a primitive axonal damage. The results of this study may also encourage the employment of quantitative magnetic resonance imaging in other hereditary diseases with spinal cord involvement. © The Author (2016). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Innovative coating of nanostructured vanadium carbide on the F/M cladding tube inner surface for mitigating the fuel cladding chemical interactions

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

Yang, Yong; Phillpot, Simon

Fuel cladding chemical interactions (FCCI) have been acknowledged as a critical issue in a metallic fuel/steel cladding system due to the formation of low melting intermetallic eutectic compounds between the fuel and cladding steel, resulting in reduction in cladding wall thickness as well as a formation of eutectic compounds that can initiate melting in the fuel at lower temperature. In order to mitigate FCCI, diffusion barrier coatings on the cladding inner surface have been considered. In order to generate the required coating techniques, pack cementation, electroplating, and electrophoretic deposition have been investigated. However, these methods require a high processing temperaturemore » of above 700 oC, resulting in decarburization and decomposition of the martensites in a ferritic/martensitic (F/M) cladding steel. Alternatively, organometallic chemical vapor deposition (OMCVD) can be a promising process due to its low processing temperature of below 600 oC. The aim of the project is to conduct applied and fundamental research towards the development of diffusion barrier coatings on the inner surface of F/M fuel cladding tubes. Advanced cladding steels such as T91, HT9 and NF616 have been developed and extensively studied as advanced cladding materials due to their excellent irradiation and corrosion resistance. However, the FCCI accelerated by the elevated temperature and high neutron exposure anticipated in fast reactors, can have severe detrimental effects on the cladding steels through the diffusion of Fe into fuel and lanthanides towards into the claddings. To test the functionality of developed coating layer, the diffusion couple experiments were focused on using T91 as cladding and Ce as a surrogate lanthanum fission product. By using the customized OMCVD coating equipment, thin and compact layers with a few micron between 1.5 µm and 8 µm thick and average grain size of 200 nm and 5 µm were successfully obtained at the specimen coated between 300oC and 500 oC, respectively. The coating layer contains both carbon and vanadium elements as quantified by WED, and the phases mainly consist of a mixture of V2C and VC, which was confirmed using X-ray diffraction patterns. In addition, the ratio between V and C varies with processing temperature, and it was observed that a higher temperature promotes the carbon adsorption and increases thickness of the coating. With optimized deposition conditions, we can apply the coating technique toward the actual T91 cladding materials, and provide the possibilities for the real application in sodium-cooled fast reactors (SFRs). Diffusion couple experiments were performed at both 550 oC and 690 oC, which corresponds to normal and aggressive operating temperatures, respectively. The results show that vanadium carbide coating with wider thickness (8 µm) and lower carbon concentration (27 at.%) reduced the width of the inter diffusion region, indicating that vanadium carbide coating can mitigate FCCI effectively. In specific, inter-diffusion between Fe and Ce was prohibited over most area, but Ce diffusion occurred toward the coating and the Fe substrate through thinner coating layer, which needs further optimization in terms of uniform coating thickness. Overall, it is concluded that this coating process can be successfully applied onto the inner surface of HT9 cladding tubes and the FCCI can be effectively mitigated if not totally eliminated.« less

Semiconductor laser devices having lateral refractive index tailoring

DOEpatents

Ashby, Carol I. H.; Hadley, G. Ronald; Hohimer, John P.; Owyoung, Adelbert

1990-01-01

A broad-area semiconductor laser diode includes an active lasing region interposed between an upper and a lower cladding layer, the laser diode further comprising structure for controllably varying a lateral refractive index profile of the diode to substantially compensate for an effect of junction heating during operation. In embodiments disclosed the controlling structure comprises resistive heating strips or non-radiative linear junctions disposed parallel to the active region. Another embodiment discloses a multi-layered upper cladding region selectively disordered by implanted or diffused dopant impurities. Still another embodiment discloses an upper cladding layer of variable thickness that is convex in shape and symmetrically disposed about a central axis of the active region. The teaching of the invention is also shown to be applicable to arrays of semiconductor laser diodes.

Positron annihilation studies in the field induced depletion regions of metal-oxide-semiconductor structures

NASA Astrophysics Data System (ADS)

Asoka-Kumar, P.; Leung, T. C.; Lynn, K. G.; Nielsen, B.; Forcier, M. P.; Weinberg, Z. A.; Rubloff, G. W.

1992-06-01

The centroid shifts of positron annihilation spectra are reported from the depletion regions of metal-oxide-semiconductor (MOS) capacitors at room temperature and at 35 K. The centroid shift measurement can be explained using the variation of the electric field strength and depletion layer thickness as a function of the applied gate bias. An estimate for the relevant MOS quantities is obtained by fitting the centroid shift versus beam energy data with a steady-state diffusion-annihilation equation and a derivative-gaussian positron implantation profile. Inadequacy of the present analysis scheme is evident from the derived quantities and alternate methods are required for better predictions.

Computational Analysis on Performance of Thermal Energy Storage (TES) Diffuser

NASA Astrophysics Data System (ADS)

Adib, M. A. H. M.; Adnan, F.; Ismail, A. R.; Kardigama, K.; Salaam, H. A.; Ahmad, Z.; Johari, N. H.; Anuar, Z.; Azmi, N. S. N.

2012-09-01

Application of thermal energy storage (TES) system reduces cost and energy consumption. The performance of the overall operation is affected by diffuser design. In this study, computational analysis is used to determine the thermocline thickness. Three dimensional simulations with different tank height-to-diameter ratio (HD), diffuser opening and the effect of difference number of diffuser holes are investigated. Medium HD tanks simulations with double ring octagonal diffuser show good thermocline behavior and clear distinction between warm and cold water. The result show, the best performance of thermocline thickness during 50% time charging occur in medium tank with height-to-diameter ratio of 4.0 and double ring octagonal diffuser with 48 holes (9mm opening ~ 60%) acceptable compared to diffuser with 6mm ~ 40% and 12mm ~ 80% opening. The conclusion is computational analysis method are very useful in the study on performance of thermal energy storage (TES).

Uptake of divalent ions (Mn+2 and Ca+2) by heat-set whey protein gels.

PubMed

Oztop, Mecit H; McCarthy, Kathryn L; McCarthy, Michael J; Rosenberg, Moshe

2012-02-01

Divalent salts are used commonly for gelation of polymer molecules. Calcium, Ca(+2), is one of the most common divalent ions that is used in whey protein gels. Manganese, Mn(+2), is also divalent, but paramagnetic, enhancing relaxation decay rates in magnetic resonance imaging (MRI) and can be used as a probe to understand the behavior of Ca(+2) in whey protein gels. The objective of this study was to investigate the diffusion of Ca(+2) and Mn(+2) ions in heat-set whey protein gels by using MRI and nuclear magnetic resonance (NMR) relaxometry. Whey protein gels were immersed in solutions containing MnCl(2) and CaCl(2) at neutral pH. Images obtained with gels immersed in MnCl(2) solution revealed a relaxation sink region in the gel's surface and the thickness of the region increased with time. These "no signal" regions in the MR images were attributed to uptake of Mn(+2) by the gel. Results obtained with CaCl(2) solution indicated that since Ca(+2) did not have the paramagnetic effect, the regions where Ca(+2) diffused into the gel exhibited a slight decrease in signal intensity. The relaxation spectrums exhibited 3 populations of protons, for gels immersed in MnCl(2) solution, and 2 populations for gels in CaCl(2) solution. No significant change in T(2) distributions was observed for the gels immersed in CaCl(2) solution. The results demonstrated that MRI and NMR relaxometry can be used to understand the diffusion of ions into the whey protein gel, which is useful for designing gels of different physical properties for controlled release applications. Design of food systems for delivery of bioactive compounds requires knowledge of diffusion rates and structure. Utilizing magnetic resonance imaging the diffusion rates of ions can be measured. Relaxation spectra could yield information concerning molecular interactions. © 2012 Institute of Food Technologists®

Permeation of halide anions through phospholipid bilayers occurs by the solubility-diffusion mechanism

NASA Technical Reports Server (NTRS)

Paula, S.; Volkov, A. G.; Deamer, D. W.

1998-01-01

Two alternative mechanisms are frequently used to describe ionic permeation of lipid bilayers. In the first, ions partition into the hydrophobic phase and then diffuse across (the solubility-diffusion mechanism). The second mechanism assumes that ions traverse the bilayer through transient hydrophilic defects caused by thermal fluctuations (the pore mechanism). The theoretical predictions made by both models were tested for halide anions by measuring the permeability coefficients for chloride, bromide, and iodide as a function of bilayer thickness, ionic radius, and sign of charge. To vary the bilayer thickness systematically, liposomes were prepared from monounsaturated phosphatidylcholines (PC) with chain lengths between 16 and 24 carbon atoms. The fluorescent dye MQAE (N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide) served as an indicator for halide concentration inside the liposomes and was used to follow the kinetics of halide flux across the bilayer membranes. The observed permeability coefficients ranged from 10(-9) to 10(-7) cm/s and increased as the bilayer thickness was reduced. Bromide was found to permeate approximately six times faster than chloride through bilayers of identical thickness, and iodide permeated three to four times faster than bromide. The dependence of the halide permeability coefficients on bilayer thickness and on ionic size were consistent with permeation of hydrated ions by a solubility-diffusion mechanism rather than through transient pores. Halide permeation therefore differs from that of a monovalent cation such as potassium, which has been accounted for by a combination of the two mechanisms depending on bilayer thickness.

Interior radiances in optically deep absorbing media. III Scattering from Haze L

NASA Technical Reports Server (NTRS)

Kattawar, G. W.; Plass, G. N.

1975-01-01

The interior radiances are calculated within an optically deep absorbing medium scattering according to the Haze L phase function. The dependence on the solar zenith angle, the single scattering albedo, and the optical depth within the medium is calculated by the matrix operator method. The development of the asymptotic angular distribution of the radiance in the diffusion region is illustrated through a number of examples; it depends only on the single scattering albedo and on the phase function for single scattering. The exact values of the radiance in the diffusion region are compared with values calculated from the approximate equations proposed by Van de Hulst. The variation of the radiance near the lower boundary of an optically thick medium is illustrated with examples. The attenuation length is calculated for various single scattering albedos and compared with the corresponding values for Rayleigh scattering. The ratio of the upward to the downward flux is found to be remarkably constant within the medium.

Numerical Evaluation of Lateral Diffusion Inside Diffusive Gradients in Thin Films Samplers

PubMed Central

2015-01-01

Using numerical simulation of diffusion inside diffusive gradients in thin films (DGT) samplers, we show that the effect of lateral diffusion inside the sampler on the solute flux into the sampler is a nonlinear function of the diffusion layer thickness and the physical sampling window size. In contrast, earlier work concluded that this effect was constant irrespective of parameters of the sampler geometry. The flux increase caused by lateral diffusion inside the sampler was determined to be ∼8.8% for standard samplers, which is considerably lower than the previous estimate of ∼20%. Lateral diffusion is also propagated to the diffusive boundary layer (DBL), where it leads to a slightly stronger decrease in the mass uptake than suggested by the common 1D diffusion model that is applied for evaluating DGT results. We introduce a simple correction procedure for lateral diffusion and demonstrate how the effect of lateral diffusion on diffusion in the DBL can be accounted for. These corrections often result in better estimates of the DBL thickness (δ) and the DGT-measured concentration than earlier approaches and will contribute to more accurate concentration measurements in solute monitoring in waters. PMID:25877251

Depletion of solar wind plasma near a planetary boundary

NASA Technical Reports Server (NTRS)

Zwan, B. J.; Wolf, R. A.

1976-01-01

A mathematical model is presented that describes the squeezing of solar wind plasma out along interplanetary magnetic field lines in the region between the bow shock and the effective planetary boundary (in the case of the earth, the magnetopause). In the absence of local magnetic merging the squeezing process should create a 'depletion layer', a region of very low plasma density just outside the magnetopause. Numerical solutions are obtained for the dimensionless magnetohydrodynamic equations describing this depletion process for the case where the solar wind magnetic field is perpendicular to the solar wind flow direction. For the case of the earth, the theory predicts that the density should be reduced by a factor exceeding 2 in a layer about 700-1300 km thick if the Alfven Mach number in the solar wind, is equal to 8. Scaling of the model calculations to Venus and Mars suggests layer thicknesses about 1/10 and 1/15 those of the earth, respectively, neglecting diffusion and ionospheric effects.

Analysis of epitaxial drift field N on P silicon solar cells

NASA Technical Reports Server (NTRS)

Baraona, C. R.; Brandhorst, H. W., Jr.

1976-01-01

The performance of epitaxial drift field silicon solar cell structures having a variety of impurity profiles was calculated. These structures consist of a uniformly doped P-type substrate layer, and a P-type epitaxial drift field layer with a variety of field strengths. Several N-layer structures were modeled. A four layer solar cell model was used to calculate efficiency, open circuit voltage and short circuit current. The effect on performance of layer thickness, doping level, and diffusion length was determined. The results show that peak initial efficiency of 18.1% occurs for a drift field thickness of about 30 micron with the doping rising from 10 to the 17th power atoms/cu cm at the edge of the depletion region to 10 to the 18th power atoms/cu cm in the substrate. Stronger drift fields (narrow field regions) allowed very high performance (17% efficiency) even after irradiation to 3x10 to the 14th power 1 MeV electrons/sq cm.

Methane Hydrate Formation in Thick Sand Reservoirs: Long-range Gas Transport or Short-range Methane Diffusion?

NASA Astrophysics Data System (ADS)

You, K.; Flemings, P. B.

2016-12-01

We developed two 2-D numerical models to simulate hydrate formation by long range methane gas transport and short-range methane diffusion. We interpret that methane hydrates in thick sands are most likely formed by long range gas transport where methane gas is transported upward into the hydrate stability zone (HSZ) under buoyancy and locally forms hydrate to its stability limit. In short-range methane diffusion, methane is generated locally by biodegradation of organic matter in mud and diffused into bounding sands where it forms hydrate. We could not simulate enough methane transport by diffusion to account for its observed concentration in thick sands. In our models, we include the capillary effect on dissolved methane solubility and on the hydrate phase boundary, sedimentation and different compaction in sand and mud, fracture generation as well as the fully coupled multiphase flow and multicomponent transport. We apply our models to a 12 meter-thick hydrate-bearing sand layer at Walker Ridge 313, Northern Gulf of Mexico. With the long-range gas transport, hydrate saturation is greater than 90% and salinity is increased from seawater to about 8 wt.% through the entire sand. With short-range diffusion, hydrate saturation is more than 90% at the sand base and is less than 10% in the overlying section; salinity is close to seawater when sand is deposited to 800 meter below seafloor by short-range methane diffusion. With short-range diffusion, the amount of hydrate formed is much less than that interpreted from the well log data. Two transient gas layers separated by a hydrate layer are formed from short-range diffusion caused by capillary effect. This could be interpreted as a double bottom simulating reflector. This study provides further insights into different hydrate formation mechanisms, and could serve as a base to confirm the hydrate formation mechanism in fields.

Systemic inflammation is associated with myocardial fibrosis, diastolic dysfunction, and cardiac hypertrophy in patients with hypertrophic cardiomyopathy

PubMed Central

Fang, Lu; Ellims, Andris H; Beale, Anna L; Taylor, Andrew J; Murphy, Andrew; Dart, Anthony M

2017-01-01

Background: Regional or diffuse fibrosis is an early feature of hypertrophic cardiomyopathy (HCM) and is related to poor prognosis. Previous studies have documented low-grade inflammation in HCM. The aim of this study was to examine the relationships between circulating inflammatory markers and myocardial fibrosis, systolic and diastolic dysfunction, and the degree of cardiac hypertrophy in HCM patients. Methods and results: Fifty HCM patients were recruited while 20 healthy subjects served as the control group. Seventeen inflammatory cytokines/chemokines were measured in plasma. Cardiac magnetic resonance imaging and echocardiography were used to assess cardiac phenotypes. Tumour necrosis factor (TNF)-α, interleukin (IL)-6 and serum amyloid P (SAP) were significantly increased in HCM patients compared to controls. IL-6, IL-4, and monocyte chemotactic protein (MCP)-1 were correlated with regional fibrosis while stromal cell-derived factor-1 and MCP-1 were correlated with diffuse fibrosis. Fractalkine and interferon-γ were associated with left ventricular wall thickness. The above associations remained significant in a linear regression model including age, gender, body mass index and family history. TNF-α, IL-6, SAP, MCP-1 and IL-10 were associated with parameters of diastolic dysfunction. White blood cells were also increased in HCM patients and correlated with diffuse fibrosis and diastolic dysfunction. However the associations between parameters of systemic inflammation and diastolic dysfunction were weakened in the linear regression analysis. Conclusions: Systemic inflammation is associated with parameters of the disease severity of HCM patients, particularly regional and diffuse fibrosis. Modifying inflammation may reduce myocardial fibrosis in HCM patients. PMID:29218105

Thick tissue diffusion model with binding to optimize topical staining in fluorescence breast cancer margin imaging

NASA Astrophysics Data System (ADS)

Xu, Xiaochun; Kang, Soyoung; Navarro-Comes, Eric; Wang, Yu; Liu, Jonathan T. C.; Tichauer, Kenneth M.

2018-03-01

Intraoperative tumor/surgical margin assessment is required to achieve higher tumor resection rate in breast-conserving surgery. Though current histology provides incomparable accuracy in margin assessment, thin tissue sectioning and the limited field of view of microscopy makes histology too time-consuming for intraoperative applications. If thick tissue, wide-field imaging can provide an acceptable assessment of tumor cells at the surface of resected tissues, an intraoperative protocol can be developed to guide the surgery and provide immediate feedback for surgeons. Topical staining of margins with cancer-targeted molecular imaging agents has the potential to provide the sensitivity needed to see microscopic cancer on a wide-field image; however, diffusion and nonspecific retention of imaging agents in thick tissue can significantly diminish tumor contrast with conventional methods. Here, we present a mathematical model to accurately simulate nonspecific retention, binding, and diffusion of imaging agents in thick tissue topical staining to guide and optimize future thick tissue staining and imaging protocol. In order to verify the accuracy and applicability of the model, diffusion profiles of cancer targeted and untargeted (control) nanoparticles at different staining times in A431 tumor xenografts were acquired for model comparison and tuning. The initial findings suggest the existence of nonspecific retention in the tissue, especially at the tissue surface. The simulator can be used to compare the effect of nonspecific retention, receptor binding and diffusion under various conditions (tissue type, imaging agent) and provides optimal staining and imaging protocols for targeted and control imaging agent.

Ultrafast demagnetization by hot electrons: Diffusion or super-diffusion?

PubMed

Salvatella, G; Gort, R; Bühlmann, K; Däster, S; Vaterlaus, A; Acremann, Y

2016-09-01

Ultrafast demagnetization of ferromagnetic metals can be achieved by a heat pulse propagating in the electron gas of a non-magnetic metal layer, which absorbs a pump laser pulse. Demagnetization by electronic heating is investigated on samples with different thicknesses of the absorber layer on nickel. This allows us to separate the contribution of thermalized hot electrons compared to non-thermal electrons. An analytical model describes the demagnetization amplitude as a function of the absorber thickness. The observed change of demagnetization time can be reproduced by diffusive heat transport through the absorber layer.

Regional MRI Diffusion, White-Matter Hyperintensities, and Cognitive Function in Alzheimer's Disease and Vascular Dementia

PubMed Central

Scrascia, Federica; Quattrocchi, Carlo Cosimo; Errante, Yuri; Gangemi, Emma; Curcio, Giuseppe; Ursini, Francesca; Silvestrini, Mauro; Maggio, Paola; Beomonte Zobel, Bruno; Rossini, Paolo Maria; Pasqualetti, Patrizio; Falsetti, Lorenzo; Vernieri, Fabrizio

2016-01-01

Background and Purpose An increase in brain water diffusivity as measured using magnetic resonance imaging (MRI) has been recently reported in normal-appearing white matter (NAWM) in patients affected by cognitive impairment. However, it remains to be clarified if this reflects an overt neuronal tissue disruption that leads to degenerative or microvascular lesions. This question was addressed by comparing the regional MRI apparent diffusion coefficients (ADCs) of NAWM in patients affected by Alzheimer's disease (AD) or vascular dementia (VaD). The relationships of ADCs with the white-matter hyperintensity (WMH) burden, carotid atherosclerosis, and cognitive performance were also investigated. Methods Forty-nine AD and 31 VaD patients underwent brain MRI to assess the WMH volume and regional NAWM ADCs, neuropsychological evaluations, and carotid ultrasound to assess the plaque severity and intima-media thickness (IMT). Results Regional ADCs in NAWM did not differ between VaD and AD patients, while the WMH volume was greater in VaD than in AD patients. The ADC in the anterior corpus callosum was related to the WMH volume, while a greater carotid IMT was positively correlated with the temporal ADC and WMH volume. The memory performance was worse in patients with higher temporal ADCs. Constructional praxis scores were related to ADCs in the frontal, and occipital lobes, in the anterior and posterior corpus callosum as well as to the WMH volume. Abstract reasoning was related to frontal, parietal, and temporal ADCs. Conclusions Our data show that higher regional ADCs in NAWM are associated with microcirculatory impairment, as depicted by the WMH volume. Moreover, regional ADCs in NAWM are differently associated with the neuropsychological performances in memory, constructional praxia, and abstract reasoning domains. PMID:27074295

Synchronous Changes of Cortical Thickness and Corresponding White Matter Microstructure During Brain Development Accessed by Diffusion MRI Tractography from Parcellated Cortex

PubMed Central

Jeon, Tina; Mishra, Virendra; Ouyang, Minhui; Chen, Min; Huang, Hao

2015-01-01

Cortical thickness (CT) changes during normal brain development is associated with complicated cellular and molecular processes including synaptic pruning and apoptosis. In parallel, the microstructural enhancement of developmental white matter (WM) axons with their neuronal bodies in the cerebral cortex has been widely reported with measurements of metrics derived from diffusion tensor imaging (DTI), especially fractional anisotropy (FA). We hypothesized that the changes of CT and microstructural enhancement of corresponding axons are highly interacted during development. DTI and T1-weighted images of 50 healthy children and adolescents between the ages of 7 and 25 years were acquired. With the parcellated cortical gyri transformed from T1-weighted images to DTI space as the tractography seeds, probabilistic tracking was performed to delineate the WM fibers traced from specific parcellated cortical regions. CT was measured at certain cortical regions and FA was measured from the WM fibers traced from same cortical regions. The CT of all frontal cortical gyri, including Brodmann areas 4, 6, 8, 9, 10, 11, 44, 45, 46, and 47, decreased significantly and heterogeneously; concurrently, significant, and heterogeneous increases of FA of WM traced from corresponding regions were found. We further revealed significant correlation between the slopes of the CT decrease and the slopes of corresponding WM FA increase in all frontal cortical gyri, suggesting coherent cortical pruning and corresponding WM microstructural enhancement. Such correlation was not found in cortical regions other than frontal cortex. The molecular and cellular mechanisms of these synchronous changes may be associated with overlapping signaling pathways of axonal guidance, synaptic pruning, neuronal apoptosis, and more prevalent interstitial neurons in the prefrontal cortex. Revealing the coherence of cortical and WM structural changes during development may open a new window for understanding the underlying mechanisms of developing brain circuits and structural abnormality associated with mental disorders. PMID:26696839

X-ray and Electrochemical Impedance Spectroscopy Diagnostic Investigations of Liquid Water in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers

NASA Astrophysics Data System (ADS)

Antonacci, Patrick

In this thesis, electrochemical impedance spectroscopy (EIS) and synchrotron x-ray radiography were utilized to characterize the impact of liquid water distributions in polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs) on fuel cell performance. These diagnostic techniques were used to quantify the effects of liquid water visualized on equivalent resistances measured through EIS. The effects of varying the thickness of the microporous layer (MPL) of GDLs were studied using these diagnostic techniques. In a first study on the feasibility of this methodology, two fuel cell cases with a 100 microm-thick and a 150 microm-thick MPL were compared under constant current density operation. In a second study with 10, 30, 50, and 100 microm-thick MPLs, the liquid water in the cathode substrate was demonstrated to affect mass transport resistance, while the liquid water content in the anode (from back diffusion) affected membrane hydration, evidenced through ohmic resistance measurements.

Maskless direct laser writing with visible light: Breaking through the optical resolving limit with cooperative manipulations of nonlinear reverse saturation absorption and thermal diffusion

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

Wei, Jingsong, E-mail: weijingsong@siom.ac.cn; Wang, Rui; University of Chinese Academy of Sciences, Beijing 100049

In this work, the resolving limit of maskless direct laser writing is overcome by cooperative manipulation from nonlinear reverse saturation absorption and thermal diffusion, where the nonlinear reverse saturation absorption can induce the formation of below diffraction-limited energy absorption spot, and the thermal diffusion manipulation can make the heat quantity at the central region of energy absorption spot propagate along the thin film thickness direction. The temperature at the central region of energy absorption spot transiently reaches up to melting point and realizes nanolithography. The sample “glass substrate/AgInSbTe” is prepared, where AgInSbTe is taken as nonlinear reverse saturation absorption thinmore » film. The below diffraction-limited energy absorption spot is simulated theoretically and verified experimentally by near-field spot scanning method. The “glass substrate/Al/AgInSbTe” sample is prepared, where the Al is used as thermal conductive layer to manipulate the thermal diffusion channel because the thermal diffusivity coefficient of Al is much larger than that of AgInSbTe. The direct laser writing is conducted by a setup with a laser wavelength of 650 nm and a converging lens of NA=0.85, the lithographic marks with a size of about 100 nm are obtained, and the size is only about 1/10 the incident focused spot. The experimental results indicate that the cooperative manipulation from nonlinear reverse saturation absorption and thermal diffusion is a good method to realize nanolithography in maskless direct laser writing with visible light.« less

Body mass scaling of passive oxygen diffusion in endotherms and ectotherms

PubMed Central

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

2016-01-01

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

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

PubMed

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

2016-05-10

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

Understanding Diffusion in Hierarchical Zeolites with House-of-Cards Nanosheets.

PubMed

Bai, Peng; Haldoupis, Emmanuel; Dauenhauer, Paul J; Tsapatsis, Michael; Siepmann, J Ilja

2016-08-23

Introducing mesoporosity to conventional microporous sorbents or catalysts is often proposed as a solution to enhance their mass transport rates. Here, we show that diffusion in these hierarchical materials is more complex and exhibits non-monotonic dependence on sorbate loading. Our atomistic simulations of n-hexane in a model system containing microporous nanosheets and mesopore channels indicate that diffusivity can be smaller than in a conventional zeolite with the same micropore structure, and this observation holds true even if we confine the analysis to molecules completely inside the microporous nanosheets. Only at high sorbate loadings or elevated temperatures, when the mesopores begin to be sufficiently populated, does the overall diffusion in the hierarchical material exceed that in conventional microporous zeolites. Our model system is free of structural defects, such as pore blocking or surface disorder, that are typically invoked to explain slower-than-expected diffusion phenomena in experimental measurements. Examination of free energy profiles and visualization of molecular diffusion pathways demonstrates that the large free energy cost (mostly enthalpic in origin) for escaping from the microporous region into the mesopores leads to more tortuous diffusion paths and causes this unusual transport behavior in hierarchical nanoporous materials. This knowledge allows us to re-examine zero-length-column chromatography data and show that these experimental measurements are consistent with the simulation data when the crystallite size instead of the nanosheet thickness is used for the nominal diffusional length.

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 length measurements of thin GaAs solar cells by means of energetic electrons

NASA Technical Reports Server (NTRS)

Vonross, O.

1980-01-01

A calculation of the short circuit current density (j sub sc) of a thin GaAs solar cell induced by fast electrons is presented. It is shown that in spite of the disparity in thickness between the N-type portion of the junction and the P-type portion of the junction, the measurement of the bulk diffusion length L sub p of the N-type part of the junction is seriously hampered due to the presence of a sizable contribution to the j sub sc from the P-type region of the junction. Corrections of up to 50% had to be made in order to interpret the data correctly. Since these corrections were not amenable to direct measurements it is concluded that the electron beam method for the determination of the bulk minority carrier diffusion length, which works so well for Si solar cells, is a poor method when applied to thin GaAs cells.

Investigation of the annealing temperature dependence of the spin pumping in Co20Fe60B20/Pt systems

NASA Astrophysics Data System (ADS)

Belmeguenai, M.; Aitoukaci, K.; Zighem, F.; Gabor, M. S.; Petrisor, T.; Mos, R. B.; Tiusan, C.

2018-03-01

Co20Fe60B20/Pt systems with variable thicknesses of Co20Fe60B20 and of Pt have been sputtered and then annealed at various temperatures (Ta) up to 300 °C. Microstrip line ferromagnetic resonance (MS-FMR) has been used to investigate Co20Fe60B20 and Pt thickness dependencies of the magnetic damping enhancement due to the spin pumping. Using diffusion and ballistic models for spin pumping, the spin mixing conductance and the spin diffusion length have been deduced from the Co20Fe60B20 and the Pt thickness dependencies of the Gilbert damping parameter α of the Co20Fe60B20/Pt heterostructures, respectively. Within the ballistic simple model, both the spin mixing conductance at the CoFeB/Pt interface and the spin-diffusion length of Pt increase with the increasing annealing temperature and show a strong enhancement at 300 °C annealing temperature. In contrast, the spin mixing conductance, which increases with Ta, shows a different trend to the spin diffusion length when using the diffusion model. Moreover, MS-FMR measurements revealed that the effective magnetization varies linearly with the Co20Fe60B20 inverse thickness due to the perpendicular interface anisotropy, which is found to decrease as the annealing temperature increases. It also revealed that the angular dependence of the resonance field is governed by small uniaxial anisotropy which is found to vary linearly with the Co20Fe60B20 inverse thickness of the annealed films, in contrast to that of the as grown ones.

Diffusion capacity and CT measures of emphysema and airway wall thickness - relation to arterial oxygen tension in COPD patients.

PubMed

Saure, Eirunn Waatevik; Bakke, Per Sigvald; Lind Eagan, Tomas Mikal; Aanerud, Marianne; Jensen, Robert Leroy; Grydeland, Thomas Blix; Johannessen, Ane; Nilsen, Roy Miodini; Thorsen, Einar; Hardie, Jon Andrew

2016-01-01

Decreased diffusing capacity of the lung for carbon monoxide (DLCO) is associated with emphysema. DLCO is also related to decreased arterial oxygen tension (PaO2), but there are limited data on associations between PaO2 and computed tomography (CT) derived measures of emphysema and airway wall thickness. To examine whether CT measures of emphysema and airway wall thickness are associated with level of arterial oxygen tension beyond that provided by measurements of diffusion capacity and spirometry. The study sample consisted of 271 smoking or ex-smoking COPD patients from the Bergen COPD Cohort Study examined in 2007-2008. Emphysema was assessed as percent of low-attenuation areas<-950 Hounsfield units (%LAA), and airway wall thickness as standardised measure at an internal perimeter of 10 mm (AWT-Pi10). Multiple linear regression models were fitted with PaO2 as the outcome variable, and %LAA, AWT-Pi10, DLCO and carbon monoxide transfer coefficient (KCO) as main explanatory variables. The models were adjusted for sex, age, smoking status, and haemoglobin concentration, as well as forced expiratory volume in one second (FEV1). Sixty two per cent of the subjects were men, mean (SD) age was 64 (7) years, mean (SD) FEV1 in percent predicted was 50 (15)%, and mean PaO2 (SD) was 9.3 (1.1) kPa. The adjusted regression coefficient (CI) for PaO2 was -0.32 (-0.04-(-0.019)) per 10% increase in %LAA (p<0.01). When diffusion capacity and FEV1 were added to the model, respectively, the association lost its statistical significance. No relationship between airway wall thickness and PaO2 was found. CT assessment of airway wall thickness is not associated with arterial oxygen tension in COPD patients. Emphysema score measured by chest CT, is related to decreased PaO2, but cannot replace measurements of diffusion capacity in the clinical evaluation of hypoxaemia.

High-Resolution Imaging of the Multiphase Interstellar Thick Disk in Two Edge-On Spiral Galaxies

NASA Astrophysics Data System (ADS)

Howk, J. Christopher; Rueff, K.

2009-01-01

We present broadband and narrow-band images, acquired from Hubble Space Telescope WFPC2 and WIYN 3.5 m telescope respectively, of two edge-on spiral galaxies, NGC 4302 and NGC 4013. These high-resolution images (BVI + H-alpha) provide a detailed view of the thick disk interstellar medium (ISM) in these galaxies. Both galaxies show prominent extraplanar dust-bearing clouds viewed in absorption against the background stellar light. Individual clouds are found to z 2 kpc in each galaxy. These clouds each contain >10^4 to >10^5 solar masses of gas. Both galaxies have extraplanar diffuse ionized gas (DIG), as seen in our H-alpha images and earlier work. In addition to the DIG, discrete H II regions are found at heights up to 1 kpc from both galaxies. We compare the morphologies of the dusty clouds with the DIG in these galaxies and discuss the relationship between these components of the thick disk ISM.

Polarization of Rayleigh scattered Lyα in active galactic nuclei

NASA Astrophysics Data System (ADS)

Chang, Seok-Jun; Lee, Hee-Won; Yang, Yujin

2017-02-01

The unification scheme of active galactic nuclei invokes an optically thick molecular torus component hiding the broad emission line region. Assuming the presence of a thick neutral component in the molecular torus characterized by a H I column density >1022 cm-2, we propose that far-UV radiation around Lyα can be significantly polarized through Rayleigh scattering. Adopting a Monte Carlo technique, we compute polarization of Rayleigh scattered radiation near Lyα in a thick neutral region in the shape of a slab and a cylindrical shell. It is found that radiation near Lyα Rayleigh reflected from a very thick slab can be significantly polarized in a fairly large range of wavelength Δλ ˜ 50 Å exhibiting a flux profile similar to the incident one. Rayleigh transmitted radiation in a slab is characterized by the central dip with a complicated polarization behaviour. The optically thick part near Lyα centre is polarized in the direction perpendicular to the slab normal, which is in contrast to weakly polarized wing parts in the direction parallel to the slab normal. A similar polarization flip phenomenon is also found in the case of a tall cylindrical shell, in which the spatial diffusion along the vertical direction near the inner cylinder wall for core photons leads to a tendency of the electric field aligned to the direction perpendicular to the vertical axis. Observational implications are briefly discussed including spectropolarimetry of the quasar PG 1630+377 by Koratkar et al. in 1990 where Lyα is strongly polarized with no other emission lines polarized.

Measuring and Overcoming Limits of the Saffman-Delbrück Model for Soap Film Viscosities

PubMed Central

Vivek, Skanda; Weeks, Eric R.

2015-01-01

We observe tracer particles diffusing in soap films to measure the two-dimensional (2D) viscous properties of the films. Saffman-Delbrück type models relate the single-particle diffusivity to parameters of the film (such as thickness h) for thin films, but the relation breaks down for thicker films. Notably, the diffusivity is faster than expected for thicker films, with the crossover at h/d = 5.2 ± 0.9 using the tracer particle diameter d. This indicates a crossover from purely 2D diffusion to diffusion that is more three-dimensional. We demonstrate that measuring the correlations of particle pairs as a function of their separation overcomes the limitations of the Saffman-Delbrück model and allows one to measure the viscosity of a soap film for any thickness. PMID:25822262

Measuring and overcoming limits of the Saffman-Delbrück model for soap film viscosities.

PubMed

Vivek, Skanda; Weeks, Eric R

2015-01-01

We observe tracer particles diffusing in soap films to measure the two-dimensional (2D) viscous properties of the films. Saffman-Delbrück type models relate the single-particle diffusivity to parameters of the film (such as thickness h) for thin films, but the relation breaks down for thicker films. Notably, the diffusivity is faster than expected for thicker films, with the crossover at h/d = 5.2 ± 0.9 using the tracer particle diameter d. This indicates a crossover from purely 2D diffusion to diffusion that is more three-dimensional. We demonstrate that measuring the correlations of particle pairs as a function of their separation overcomes the limitations of the Saffman-Delbrück model and allows one to measure the viscosity of a soap film for any thickness.

Monitoring the injured brain: registered, patient specific atlas models to improve accuracy of recovered brain saturation values

NASA Astrophysics Data System (ADS)

Clancy, Michael; Belli, Antonio; Davies, David; Lucas, Samuel J. E.; Su, Zhangjie; Dehghani, Hamid

2015-07-01

The subject of superficial contamination and signal origins remains a widely debated topic in the field of Near Infrared Spectroscopy (NIRS), yet the concept of using the technology to monitor an injured brain, in a clinical setting, poses additional challenges concerning the quantitative accuracy of recovered parameters. Using high density diffuse optical tomography probes, quantitatively accurate parameters from different layers (skin, bone and brain) can be recovered from subject specific reconstruction models. This study assesses the use of registered atlas models for situations where subject specific models are not available. Data simulated from subject specific models were reconstructed using the 8 registered atlas models implementing a regional (layered) parameter recovery in NIRFAST. A 3-region recovery based on the atlas model yielded recovered brain saturation values which were accurate to within 4.6% (percentage error) of the simulated values, validating the technique. The recovered saturations in the superficial regions were not quantitatively accurate. These findings highlight differences in superficial (skin and bone) layer thickness between the subject and atlas models. This layer thickness mismatch was propagated through the reconstruction process decreasing the parameter accuracy.

Nanostructures and dynamics of macromolecules bound to attractive filler surfaces

NASA Astrophysics Data System (ADS)

Koga, Tad; Barkley, Deborah; Jiang, Naisheng; Endoh, Maya; Masui, Tomomi; Kishimoto, Hiroyuki; Nagao, Michihiro; Satija, Sushil; Taniguchi, Takashi

We report in-situ nanostructures and dynamics of polybutadiene (PB) chains bound to carbon black (CB) fillers (the so-called ``bound polymer layer (BPL)'') in a good solvent. The BPL on the CB fillers were extracted by solvent leaching of a CB-filled PB compound and subsequently dispersed in deuterated toluene to label the BPL for small-angle neutron scattering and neutron spin echo techniques. Intriguingly, the results demonstrate that the BPL is composed of two regions regardless of molecular weights of PB: the inner unswollen region of ~ 0.5 nm thick and outer swollen region where the polymer chains display a parabolic profile with a diffuse tail. This two-layer formation on the filler surface is similar to that reported for polymer chains adsorbed on planar substrates from melts. In addition, the results show that the dynamics of the swollen bound chains can be explained by the so-called ``breathing mode'' and is generalized with the thickness of the swollen BPL. Furthermore, we will discuss how the breathing collective dynamics is affected by the presence of polymer chains in a matrix solution. We acknowledge the financial support from NSF Grant No. CMMI-1332499.

Competitive separation of di- vs. mono-valent cations in electrodialysis: effects of the boundary layer properties.

PubMed

Kim, Younggy; Walker, W Shane; Lawler, Desmond F

2012-05-01

In electrodialysis desalination, the boundary layer near ion-exchange membranes is the limiting region for the overall rate of ionic separation due to concentration polarization over tens of micrometers in that layer. Under high current conditions, this sharp concentration gradient, creating substantial ionic diffusion, can drive a preferential separation for certain ions depending on their concentration and diffusivity in the solution. Thus, this study tested a hypothesis that the boundary layer affects the competitive transport between di- and mono-valent cations, which is known to be governed primarily by the partitioning with cation-exchange membranes. A laboratory-scale electrodialyzer was operated at steady state with a mixture of 10mM KCl and 10mM CaCl(2) at various flow rates. Increased flows increased the relative calcium transport. A two-dimensional model was built with analytical solutions of the Nernst-Planck equation. In the model, the boundary layer thickness was considered as a random variable defined with three statistical parameters: mean, standard deviation, and correlation coefficient between the thicknesses of the two boundary layers facing across a spacer. Model simulations with the Monte Carlo method found that a greater calcium separation was achieved with a smaller mean, greater standard deviation, or more negative correlation coefficient. The model and experimental results were compared for the cationic transport number as well as the current and potential relationship. The mean boundary layer thickness was found to decrease from 40 to less than 10 μm as the superficial water velocity increased from 1.06 to 4.24 cm/s. The standard deviation was greater than the mean thickness at slower water velocities and smaller at faster water velocities. Copyright © 2012 Elsevier Ltd. All rights reserved.

Quantitative, depth-resolved determination of particle motion using multi-exposure, spatial frequency domain laser speckle imaging.

PubMed

Rice, Tyler B; Kwan, Elliott; Hayakawa, Carole K; Durkin, Anthony J; Choi, Bernard; Tromberg, Bruce J

2013-01-01

Laser Speckle Imaging (LSI) is a simple, noninvasive technique for rapid imaging of particle motion in scattering media such as biological tissue. LSI is generally used to derive a qualitative index of relative blood flow due to unknown impact from several variables that affect speckle contrast. These variables may include optical absorption and scattering coefficients, multi-layer dynamics including static, non-ergodic regions, and systematic effects such as laser coherence length. In order to account for these effects and move toward quantitative, depth-resolved LSI, we have developed a method that combines Monte Carlo modeling, multi-exposure speckle imaging (MESI), spatial frequency domain imaging (SFDI), and careful instrument calibration. Monte Carlo models were used to generate total and layer-specific fractional momentum transfer distributions. This information was used to predict speckle contrast as a function of exposure time, spatial frequency, layer thickness, and layer dynamics. To verify with experimental data, controlled phantom experiments with characteristic tissue optical properties were performed using a structured light speckle imaging system. Three main geometries were explored: 1) diffusive dynamic layer beneath a static layer, 2) static layer beneath a diffuse dynamic layer, and 3) directed flow (tube) submerged in a dynamic scattering layer. Data fits were performed using the Monte Carlo model, which accurately reconstructed the type of particle flow (diffusive or directed) in each layer, the layer thickness, and absolute flow speeds to within 15% or better.

Effects of annealing temperature and duration on the morphological and optical evolution of self-assembled Pt nanostructures on c-plane sapphire.

PubMed

Sui, Mao; Li, Ming-Yu; Kunwar, Sundar; Pandey, Puran; Zhang, Quanzhen; Lee, Jihoon

2017-01-01

Metallic nanostructures (NSs) have been widely adapted in various applications and their physical, chemical, optical and catalytic properties are strongly dependent on their surface morphologies. In this work, the morphological and optical evolution of self-assembled Pt nanostructures on c-plane sapphire (0001) is demonstrated by the control of annealing temperature and dwelling duration with the distinct thickness of Pt films. The formation of Pt NSs is led by the surface diffusion, agglomeration and surface and interface energy minimization of Pt thin films, which relies on the growth parameters such as system temperature, film thickness and annealing duration. The Pt layer of 10 nm shows the formation of overlaying NPs below 650°C and isolated Pt nanoparticles above 700°C based on the enhanced surface diffusion and Volmer-Weber growth model whereas larger wiggly nanostructures are formed with 20 nm thick Pt layers based on the coalescence growth model. The morphologies of Pt nanostructures demonstrate a sharp distinction depending on the growth parameters applied. By the control of dwelling duration, the gradual transition from dense Pt nanoparticles to networks-like and large clusters is observed as correlated to the Rayleigh instability and Ostwald ripening. The various Pt NSs show a significant distinction in the reflectance spectra depending on the morphology evolution: i.e. the enhancement in UV-visible and NIR regions and the related optical properties are discussed in conjunction with the Pt NSs morphology and the surface coverage.

A novel method for computing effective diffusivity: Application to helium implanted α-Fe thin films

NASA Astrophysics Data System (ADS)

Dunn, Aaron; Agudo-Merida, Laura; Martin-Bragado, Ignacio; McPhie, Mathieu; Cherkaoui, Mohammed; Capolungo, Laurent

2014-05-01

The effective diffusivity of helium in thin iron films is quantified using spatially resolved stochastic cluster dynamics and object kinetic Monte Carlo simulations. The roles of total displacement dose (in DPA), damage rate, helium to DPA ratio, layer thickness, and damage type (cascade damage vs Frenkel pair implantation) on effective He diffusivity are investigated. Helium diffusivity is found to decrease with increasing total damage and decreasing damage rate. Arrhenius plots show strongly increased helium diffusivity at high temperatures, high total implantation, and low implantation rates due to decreased vacancy and vacancy cluster concentrations. At low temperatures, effective diffusivity is weakly dependent on foil thickness while at high temperatures, narrower foils prevent defect accumulation by releasing all defects at the free surfaces. Helium to DPA ratio is not shown to strongly change helium diffusivity in the range of irradiation conditions simulated. Frenkel pair implantation is shown to cause higher effective diffusivity and more complex diffusion mechanisms than cascade implantation. The results of these simulations indicate that the differences in damage rates between implantation experiments and fission or fusion environments may result in differences in the final microstructure.

Red blood cell thickness is evolutionarily constrained by slow, hemoglobin-restricted diffusion in cytoplasm.

PubMed

Richardson, Sarah L; Swietach, Pawel

2016-10-25

During capillary transit, red blood cells (RBCs) must exchange large quantities of CO 2 and O 2 in typically less than one second, but the degree to which this is rate-limited by diffusion through cytoplasm is not known. Gas diffusivity is intuitively assumed to be fast and this would imply that the intracellular path-length, defined by RBC shape, is not a factor that could meaningfully compromise physiology. Here, we evaluated CO 2 diffusivity (D CO2 ) in RBCs and related our results to cell shape. D CO2 inside RBCs was determined by fluorescence imaging of [H + ] dynamics in cells under superfusion. This method is based on the principle that H + diffusion is facilitated by CO 2 /HCO 3 - buffer and thus provides a read-out of D CO2 . By imaging the spread of H + ions from a photochemically-activated source (6-nitroveratraldehyde), D CO2 in human RBCs was calculated to be only 5% of the rate in water. Measurements on RBCs containing different hemoglobin concentrations demonstrated a halving of D CO2 with every 75 g/L increase in mean corpuscular hemoglobin concentration (MCHC). Thus, to compensate for highly-restricted cytoplasmic diffusion, RBC thickness must be reduced as appropriate for its MCHC. This can explain the inverse relationship between MCHC and RBC thickness determined from >250 animal species.

Red blood cell thickness is evolutionarily constrained by slow, hemoglobin-restricted diffusion in cytoplasm

PubMed Central

Richardson, Sarah L.; Swietach, Pawel

2016-01-01

During capillary transit, red blood cells (RBCs) must exchange large quantities of CO2 and O2 in typically less than one second, but the degree to which this is rate-limited by diffusion through cytoplasm is not known. Gas diffusivity is intuitively assumed to be fast and this would imply that the intracellular path-length, defined by RBC shape, is not a factor that could meaningfully compromise physiology. Here, we evaluated CO2 diffusivity (DCO2) in RBCs and related our results to cell shape. DCO2 inside RBCs was determined by fluorescence imaging of [H+] dynamics in cells under superfusion. This method is based on the principle that H+ diffusion is facilitated by CO2/HCO3− buffer and thus provides a read-out of DCO2. By imaging the spread of H+ ions from a photochemically-activated source (6-nitroveratraldehyde), DCO2 in human RBCs was calculated to be only 5% of the rate in water. Measurements on RBCs containing different hemoglobin concentrations demonstrated a halving of DCO2 with every 75 g/L increase in mean corpuscular hemoglobin concentration (MCHC). Thus, to compensate for highly-restricted cytoplasmic diffusion, RBC thickness must be reduced as appropriate for its MCHC. This can explain the inverse relationship between MCHC and RBC thickness determined from >250 animal species. PMID:27777410

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

Streza, M.; Dadarlat, D.; Strzałkowski, K.

An accurate determination of thermophysical properties such as thermal diffusivity, thermal effusivity and thermal conductivity is extremely important for characterization and quality assurance of semiconductors. Thermal diffusivity and effusivity of some binary semiconductors have been investigated. Two experimental techniques were used: a contact technique (PPE calorimetry) and a non contact technique (lock-in thermography). When working with PPE, in the back (BPPE) configuration and in the thermally thick regim of the pyroelectric sensor, we can get the thermal diffusivity of the sample by performing a scanning of the excitation frequency of radiation. Thermal effusivity is obtained in front configuration (sensor directlymore » irradiated and sample in back position) by performing a thickness scan of a coupling fluid. By using the lock-in thermography technique, the thermal diffusivity of the sample is obtained from the phase image. The results obtained by the two techniques are in good agreement. Nevertheless, for the determination of thermal diffusivity, lock-in thermography is preferred.« less

Influence of earlobe thickness on near infrared spectroscopy

NASA Astrophysics Data System (ADS)

Jiang, Jingying; Wang, Tianpei; Li, Si; Li, Lin; Liu, Jiajia; Xu, Kexin

2017-03-01

Near-infrared spectroscopy has been recognized as a potential technology for noninvasive blood glucose sensing. However, the detected spectral signal is unstable mainly because of (1) the weak light absorption of glucose itself within NIR range, (2) the influence of temperature and individual differences of biotissue. Our previous results demonstrated that the synergistic effect of both transmittance and reflectance could enhance the strength of the detection signal. In this talk, we design a set of experiments to analyze the effect of earlobe thickness on Near Infrared spectroscopic measurement by using home-made optical fiber probe within the wavelength of 1000-1600nm. Firstly, we made a MC simulation of single-layer skin model and five-layer skin model to get the diffused transmittance spectra and diffused reflectance spectra under different optaical path lengths. And then we obtain the spectra of the earlobes from different volunteers by the same way. The experimental results showed that with the increase of the thickness,the light intensity of diffused transmittance decreases, and the light intensity of diffused reflectance remaines substantially unchanged.

Coercivity enhancement of Dy-coated Nd-Fe-B flakes by crystallization

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

Fukunaga, H.; Sugimoto, Y.; Nakano, M.

2011-04-01

The coercivity of isotropic Dy-coated Nd-Fe-B flakes was enhanced by crystallization and simultaneous diffusion of Dy from their surfaces. Amorphous Dy-coated Nd-Fe-B flakes were crystallized by heating them to 923 K 2over a 2 min period followed by rapid cooling. During crystallization, the Dy on the surface diffused into the flakes. This low-temperature rapid annealing produced flakes with fine grains and the Dy diffusion enhanced their coercivity. The coercivity after crystallization increased with increasing Dy layer thickness, although the remanence decreased when the layer thickness exceeded 3 {mu}m. Thick coatings of over 6 {mu}m resulted in the formation of DyFe{submore » 2}, which degraded the magnetic properties of the crystallized flakes. Flakes with a 3-{mu}m-thick coating exhibited excellent magnetic properties after annealing: They had a coercivity of 1880 kA/m and a remanence of 78 emu/g. This coercivity is approximately 500 kA/m higher than that of uncoated flakes, whereas the remanence is comparable to that of uncoated flakes.« less

Focused fluorescence excitation with time-reversed ultrasonically encoded light and imaging in thick scattering media

NASA Astrophysics Data System (ADS)

Lai, Puxiang; Suzuki, Yuta; Xu, Xiao; Wang, Lihong V.

2013-07-01

Scattering dominates light propagation in biological tissue, and therefore restricts both resolution and penetration depth in optical imaging within thick tissue. As photons travel into the diffusive regime, typically 1 mm beneath human skin, their trajectories transition from ballistic to diffusive due to the increased number of scattering events, which makes it impossible to focus, much less track, photon paths. Consequently, imaging methods that rely on controlled light illumination are ineffective in deep tissue. This problem has recently been addressed by a novel method capable of dynamically focusing light in thick scattering media via time reversal of ultrasonically encoded (TRUE) diffused light. Here, using photorefractive materials as phase conjugate mirrors, we show a direct visualization and dynamic control of optical focusing with this light delivery method, and demonstrate its application for focused fluorescence excitation and imaging in thick turbid media. These abilities are increasingly critical for understanding the dynamic interactions of light with biological matter and processes at different system levels, as well as their applications for biomedical diagnosis and therapy.

Mathematical analysis of the Photovoltage Decay (PVD) method for minority carrier lifetime measurements

NASA Technical Reports Server (NTRS)

Vonroos, O. H.

1982-01-01

When the diffusion length of minority carriers becomes comparable with or larger than the thickness of a p-n junction solar cell, the characteristic decay of the photon-generated voltage results from a mixture of contributions with different time constants. The minority carrier recombination lifetime tau and the time constant l(2)/D, where l is essentially the thickness of the cell and D the minority carrier diffusion length, determine the signal as a function of time. It is shown that for ordinary solar cells (n(+)-p junctions), particularly when the diffusion length L of the minority carriers is larger than the cell thickness l, the excess carrier density decays according to exp (-t/tau-pi(2)Dt/4l(2)), tau being the lifetime. Therefore, tau can be readily determined by the photovoltage decay method once D and L are known.

Theoretical investigation of discharge parameters in magnetized radio frequency excited CO2 lasers

NASA Astrophysics Data System (ADS)

Tavassoli, H.; Sohbatzadeh, F.; Latifi, H.

2003-06-01

In the present paper the magnetic field effects on discharge parameters in rf excited CO2 lasers are calculated. A rf generated plasma imbedded in an external, constant, and homogeneous magnetic field is considered. The continuity equation is used to derive the electron density. Quasineutrality condition and ambipolar diffusion are used. Electron attachment coefficient is neglected. Local electric field, local electron density, and thickness of charge layers are derived as a function of distance from the electrodes and magnetic field. The thickness of charge layers in the presence of magnetic field is always smaller than one without the magnetic field. When the magnetic field increases, the electron density increases in all regions of discharge, and the electric field reduces in the charge layers but increases in the middle part of discharge.

Surface and allied studies in silicon solar cells

NASA Technical Reports Server (NTRS)

Lindholm, F. A.

1984-01-01

Measuring small-signal admittance versus frequency and forward bias voltage together with a new transient measurement apparently provides the most reliable and flexible method available for determining back surface recombination velocity and low-injection lifetime of the quasineutral base region of silicon solar cells. The new transient measurement reported here is called short-circuit-current decay (SCCD). In this method, forward voltage equal to about the open-circuit or the maximum power voltage establishes excess holes and electrons in the junction transition region and in the quasineutral regions. The sudden application of a short circuit causes an exiting of the excess holes and electrons in the transition region within about ten picoseconds. From observing the slope and intercept of the subsequent current decay, the base lifetime and surface recombination velocity can be determined. The admittance measurement previously mentioned then enters to increase accuracy particularly for devices for which the diffusion length exceeds the base thickness.

An experimental evaluation of S-duct inlet-diffuser configurations for turboprop offset gearbox applications

NASA Technical Reports Server (NTRS)

Mcdill, Paul L.

1986-01-01

A test program, utilizing a large scale model, was run in the NASA Lewis Research Center 10- by 10-ft wind tunnel to examine the influence on performance of design parameters of turboprop S-duct inlet/diffuser systems. The parametric test program investigated inlet lip thickness, inlet/diffuser cross-sectional geometry, throat design Mach number, and shaft fairing shape. The test program was run at angles of attack to 15 deg and tunnel Mach numbers to 0.35. Results of the program indicate that current design techniques can be used to design inlet/diffuser systems with acceptable total pressure recovery, but several of the design parameters, notably lip thickness (contraction ratio) and shaft fairing cross section, must be optimized to prevent excessive distortion at the compressor face.

A comparative study of p(+)n and n(+)p InP solar cells made by a closed ampoule diffusion

NASA Technical Reports Server (NTRS)

Faur, M.; Faur, M.; Flood, D. J.; Weinberg, I.; Brinker, D. J.; Goradia, C.; Fatemi, N.; Goradia, M.; Thesling, W.

1991-01-01

The purpose was to demonstrate the possibility of fabricating thermally diffused p(+)n InP solar cells having high open-circuit voltage without sacrificing the short circuit current. The p(+)n junctions were formed by closed-ampoule diffusion of Cd through a 3 to 5 nm thick anodic or chemical phosphorus-rich oxide cap layer grown on n-InP:S Czochralski LEC grown substrates. For solar cells made by thermal diffusion the p(+)n configuration is expected to have a higher efficiency than the n(+)p configuration. It is predicted that the AM0, BOL efficiencies approaching 19 percent should be readily achieved providing that good ohmic front contacts could be realized on the p(+) emitters of thickness lower than 1 micron.

Comparative study of silver nanoparticle permeation using Side-Bi-Side and Franz diffusion cells

NASA Astrophysics Data System (ADS)

Trbojevich, Raul A.; Fernandez, Avelina; Watanabe, Fumiya; Mustafa, Thikra; Bryant, Matthew S.

2016-03-01

Better understanding the mechanisms of nanoparticle permeation through membranes and packaging polymers has important implications for the evaluation of drug transdermal uptake, in food safety and the environmental implications of nanotechnology. In this study, permeation of 21 nm diameter silver nanoparticles (AgNPs) was tested using Side-Bi-Side and Franz static diffusion cells through hydrophilic 0.1 and 0.05 µm pore diameter 125 µm thick synthetic cellulose membranes, and 16 and 120 µm thick low-density polyethylene (LDPE) films. Experiments performed with LDPE films discarded permeation of AgNPs or Ag ions over the investigated time-frame in both diffusion systems. But controlled release of AgNPs has been quantified using semipermeable hydrophilic membranes. The permeation followed a quasi-linear time-dependent model during the experimental time-frame, which represents surface reaction-limited permeation. Diffusive flux, diffusion coefficients, and membrane permeability were determined as a function of pore size and diffusion model. Concentration gradient and pore size were key to understand mass transfer phenomena in the diffusion systems.

Cadmium-free junction fabrication process for CuInSe.sub.2 thin film solar cells

DOEpatents

Ramanathan, Kannan V.; Contreras, Miguel A.; Bhattacharya, Raghu N.; Keane, James; Noufi, Rommel

1999-01-01

The present invention provides an economical, simple, dry and controllable semiconductor layer junction forming process to make cadmium free high efficiency photovoltaic cells having a first layer comprised primarily of copper indium diselenide having a thin doped copper indium diselenide n-type region, generated by thermal diffusion with a group II(b) element such as zinc, and a halide, such as chlorine, and a second layer comprised of a conventional zinc oxide bilayer. A photovoltaic device according the present invention includes a first thin film layer of semiconductor material formed primarily from copper indium diselenide. Doping of the copper indium diselenide with zinc chloride is accomplished using either a zinc chloride solution or a solid zinc chloride material. Thermal diffusion of zinc chloride into the copper indium diselenide upper region creates the thin n-type copper indium diselenide surface. A second thin film layer of semiconductor material comprising zinc oxide is then applied in two layers. The first layer comprises a thin layer of high resistivity zinc oxide. The second relatively thick layer of zinc oxide is doped to exhibit low resistivity.

X-ray Study of the Electric Double Layer at the n-Hexane/Nanocolloidal Silica Interface

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

Tikhonov,A.

The spatial structure of the transition region between an insulator and an electrolyte solution was studied with x-ray scattering. The electron-density profile across the n-hexane/silica sol interface (solutions with 5, 7, and 12 nm colloidal particles) agrees with the theory of the electrical double layer and shows separation of positive and negative charges. The interface consists of three layers, i.e., a compact layer of Na{sup +}, a loose monolayer of nanocolloidal particles as part of a thick diffuse layer, and a low-density layer sandwiched between them. Its structure is described by a model in which the potential gradient at themore » interface reflects the difference in the potentials of 'image forces' between the cationic Na{sup +} and anionic nanoparticles and the specific adsorption of surface charge. The density of water in the large electric field ({approx}10{sup 9}-10{sup 10} V/m) of the transition region and the layering of silica in the diffuse layer is discussed.« less

Experimental investigation on the caries characteristic of dental tissues by photothermal radiometry scanning imaging

NASA Astrophysics Data System (ADS)

Wang, Fei; Liu, Jun-yan; Wang, Xiao-chun; Wang, Yang

2018-03-01

In this paper, a one-dimensional (1D) thermal-wave model coupled diffuse-photon-density-wave for three-layer dental tissues using modulated laser stimulation was employed to illustrate the relationship between dental caries characteristic (i.e. caries layer thickness, optical absorption coefficient and optical scattering coefficient) and photothermal radiometry (PTR) signal. Experimental investigation of artificial caries was carried out using PTR scanning imaging. The PTR amplitude and phase delay were increased with dental demineralized treatment. The local caries characteristic parameters were obtained by the best-fitting method based on the 1D thermal-wave model. The PTR scanning imaging measurements illustrated that the optical absorption coefficient and scattering coefficient of caries region were much higher than those of the healthy enamel area. The demineralization thickness of caries region was measured by PTR scanning imaging and its average value shows in good agreement with the digital microscope. Experimental results show that PTR scanning imaging has the merits of high contrast for local inhomogeneity of dental caries; furthermore, this method is an allowance to provide a flexibility for non-contact quantitative evaluation of dental caries.

Potential energy landscape of an interstitial O2 molecule in a SiO2 film near the SiO2/Si(001) interface

NASA Astrophysics Data System (ADS)

Ohta, Hiromichi; Watanabe, Takanobu; Ohdomari, Iwao

2008-10-01

Potential energy distribution of interstitial O2 molecule in the vicinity of SiO2/Si(001) interface is investigated by means of classical molecular simulation. A 4-nm-thick SiO2 film model is built by oxidizing a Si(001) substrate, and the potential energy of an O2 molecule is calculated at Cartesian grid points with an interval of 0.05 nm in the SiO2 film region. The result shows that the potential energy of the interstitial site gradually rises with approaching the interface. The potential gradient is localized in the region within about 1 nm from the interface, which coincides with the experimental thickness of the interfacial strained layer. The potential energy is increased by about 0.62 eV at the SiO2/Si interface. The result agrees with a recently proposed kinetic model for dry oxidation of silicon [Phys. Rev. Lett. 96, 196102 (2006)], which argues that the oxidation rate is fully limited by the oxidant diffusion.

Flow field and performance characteristics of combustor diffusers: A basic study

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

Hestermann, R.; Kim, S.; Ben Khaled, A.

1995-10-01

Results of a detailed study concerning the influence of geometric as well as fluid mechanic parameters o the performance of a plane model combustor diffuser in cold flow are presented. For a qualitative insight into the complex flow field inside the prediffuser, the sudden expansion region, and the flow field around the flame tube dome, results of a flow visualization study with the hydrogen bubble method as well as with the ink jet method are presented for different opening angles of the prediffuser and for different flame tube distances. Also, quantitative data from detailed measurements with LDV and conventional pressuremore » probes in a geometrically similar air-driven setup are presented. These data clearly demonstrate the effect of boundary layer thickness as well as the influence of different turbulence levels at the entry of the prediffuser on the performance characteristics of combustor diffusers. The possibility of getting an unseparated flow field inside the prediffuser even at large opening angles by appropriately matching the diffuser`s opening angle and the flame tube distance is demonstrated. Also, for flows with an increased turbulence level at the entrance--all other conditions held constant--an increased opening angle can be realized without experiencing flow separation. The comparison of the experimental data with predictions utilizing a finite-volume-code based on a body-fitted coordinate system for diffusers with an included total opening angle less than 18 deg demonstrates the capability of describing the flow field in combustor diffusers with reasonable accuracy.« less

Thermal Diffusivity of High-Density Polyethylene Samples of Different Crystallinity Evaluated by Indirect Transmission Photoacoustics

NASA Astrophysics Data System (ADS)

Nesic, M.; Popovic, M.; Rabasovic, M.; Milicevic, D.; Suljovrujic, E.; Markushev, D.; Stojanovic, Z.

2018-02-01

In this work, thermal diffusivity of crystalline high-density polyethylene samples of various thickness, and prepared using different procedures, was evaluated by transmission gas-microphone frequency photoacoustics. The samples' composition analysis and their degree of crystallinity were determined from the wide-angle X-ray diffraction, which confirmed that high-density polyethylene samples, obtained by slow and fast cooling, were equivalent in composition but with different degrees of crystallinity. Structural analysis, performed by differential scanning calorimetry, demonstrated that all of the used samples had different levels of crystallinity, depending not only on the preparing procedure, but also on sample thickness. Therefore, in order to evaluate the samples' thermal diffusivity, it was necessary to modify standard photoacoustic fitting procedures (based on the normalization of photoacoustic amplitude and phase characteristics on two thickness levels) for the interpretation of photoacoustic measurements. The calculated values of thermal diffusivity were in the range of the expected literature values. Besides that, the obtained results indicate the unexpected correlation between the values of thermal diffusivity and thermal conductivity with the degree of crystallinity of the investigated geometrically thin samples. The results indicate the necessity of additional investigation of energy transport in macromolecular systems, as well as the possible employment of the photoacoustic techniques in order to clarify its mechanism.

Permeation of protons, potassium ions, and small polar molecules through phospholipid bilayers as a function of membrane thickness.

PubMed Central

Paula, S; Volkov, A G; Van Hoek, A N; Haines, T H; Deamer, D W

1996-01-01

Two mechanisms have been proposed to account for solute permeation of lipid bilayers. Partitioning into the hydrophobic phase of the bilayer, followed by diffusion, is accepted by many for the permeation of water and other small neutral solutes, but transient pores have also been proposed to account for both water and ionic solute permeation. These two mechanisms make distinctively different predictions about the permeability coefficient as a function of bilayer thickness. Whereas the solubility-diffusion mechanism predicts only a modest variation related to bilayer thickness, the pore model predicts an exponential relationship. To test these models, we measured the permeability of phospholipid bilayers to protons, potassium ions, water, urea, and glycerol. Bilayers were prepared as liposomes, and thickness was varied systematically by using unsaturated lipids with chain lengths ranging from 14 to 24 carbon atoms. The permeability coefficient of water and neutral polar solutes displayed a modest dependence on bilayer thickness, with an approximately linear fivefold decrease as the carbon number varied from 14 to 24 atoms. In contrast, the permeability to protons and potassium ions decreased sharply by two orders of magnitude between 14 and 18 carbon atoms, and leveled off, when the chain length was further extended to 24 carbon atoms. The results for water and the neutral permeating solutes are best explained by the solubility-diffusion mechanism. The results for protons and potassium ions in shorter-chain lipids are consistent with the transient pore model, but better fit the theoretical line predicted by the solubility-diffusion model at longer chain lengths. PMID:8770210

Permeation of protons, potassium ions, and small polar molecules through phospholipid bilayers as a function of membrane thickness

NASA Technical Reports Server (NTRS)

Paula, S.; Volkov, A. G.; Van Hoek, A. N.; Haines, T. H.; Deamer, D. W.

1996-01-01

Two mechanisms have been proposed to account for solute permeation of lipid bilayers. Partitioning into the hydrophobic phase of the bilayer, followed by diffusion, is accepted by many for the permeation of water and other small neutral solutes, but transient pores have also been proposed to account for both water and ionic solute permeation. These two mechanisms make distinctively different predictions about the permeability coefficient as a function of bilayer thickness. Whereas the solubility-diffusion mechanism predicts only a modest variation related to bilayer thickness, the pore model predicts an exponential relationship. To test these models, we measured the permeability of phospholipid bilayers to protons, potassium ions, water, urea, and glycerol. Bilayers were prepared as liposomes, and thickness was varied systematically by using unsaturated lipids with chain lengths ranging from 14 to 24 carbon atoms. The permeability coefficient of water and neutral polar solutes displayed a modest dependence on bilayer thickness, with an approximately linear fivefold decrease as the carbon number varied from 14 to 24 atoms. In contrast, the permeability to protons and potassium ions decreased sharply by two orders of magnitude between 14 and 18 carbon atoms, and leveled off, when the chain length was further extended to 24 carbon atoms. The results for water and the neutral permeating solutes are best explained by the solubility-diffusion mechanism. The results for protons and potassium ions in shorter-chain lipids are consistent with the transient pore model, but better fit the theoretical line predicted by the solubility-diffusion model at longer chain lengths.

Modulation of Morphology and Optical Property of Multi-Metallic PdAuAg and PdAg Alloy Nanostructures.

PubMed

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-05-16

In this work, the evolution of PdAg and PdAuAg alloy nanostructures is demonstrated on sapphire (0001) via the solid-state dewetting of multi-metallic thin films. Various surface configurations, size, and arrangements of bi- and tri-metallic alloy nanostructures are fabricated as a function of annealing temperature, annealing duration, film thickness, and deposition arrangements such as bi-layers (Pd/Ag), tri-layers (Pd/Au/Ag), and multi-layers (Pd/Au/Ag × 5). Specifically, the tri-layers film shows the gradual evolution of over-grown NPs, voids, wiggly nanostructures, and isolated PdAuAg alloy nanoparticles (NPs) along with the increased annealing temperature. In contrast, the multi-layers film with same thickness show the enhanced dewetting rate, which results in the formation of voids at relatively lower temperature, wider spacing, and structural regularity of alloy NPs at higher temperature. The dewetting enhancement is attributed to the increased number of interfaces and reduced individual layer thickness, which aid the inter-diffusion process at the initial stage. In addition, the time evolution of the Pd 150 nm /Ag 80 nm bi-layer films at constant temperature show the wiggly-connected and isolated PdAg alloy NPs. The overall evolution of alloy NPs is discussed based on the solid-state dewetting mechanism in conjunction with the diffusion, inter-diffusion, alloying, sublimation, Rayleigh instability, and surface energy minimization. Depending upon their surface morphologies, the bi- and tri-metallic alloy nanostructures exhibit the dynamic reflectance spectra, which show the formation of dipolar (above 700 nm) and quadrupolar resonance peaks (~ 380 nm) and wide dips in the visible region as correlated to the localized surface plasmon resonance (LSPR) effect. An absorption dip is readily shifted from ~ 510 to ~ 475 nm along with the decreased average size of alloy nanostructures.

Modulation of Morphology and Optical Property of Multi-Metallic PdAuAg and PdAg Alloy Nanostructures

NASA Astrophysics Data System (ADS)

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-05-01

In this work, the evolution of PdAg and PdAuAg alloy nanostructures is demonstrated on sapphire (0001) via the solid-state dewetting of multi-metallic thin films. Various surface configurations, size, and arrangements of bi- and tri-metallic alloy nanostructures are fabricated as a function of annealing temperature, annealing duration, film thickness, and deposition arrangements such as bi-layers (Pd/Ag), tri-layers (Pd/Au/Ag), and multi-layers (Pd/Au/Ag × 5). Specifically, the tri-layers film shows the gradual evolution of over-grown NPs, voids, wiggly nanostructures, and isolated PdAuAg alloy nanoparticles (NPs) along with the increased annealing temperature. In contrast, the multi-layers film with same thickness show the enhanced dewetting rate, which results in the formation of voids at relatively lower temperature, wider spacing, and structural regularity of alloy NPs at higher temperature. The dewetting enhancement is attributed to the increased number of interfaces and reduced individual layer thickness, which aid the inter-diffusion process at the initial stage. In addition, the time evolution of the Pd150 nm/Ag80 nm bi-layer films at constant temperature show the wiggly-connected and isolated PdAg alloy NPs. The overall evolution of alloy NPs is discussed based on the solid-state dewetting mechanism in conjunction with the diffusion, inter-diffusion, alloying, sublimation, Rayleigh instability, and surface energy minimization. Depending upon their surface morphologies, the bi- and tri-metallic alloy nanostructures exhibit the dynamic reflectance spectra, which show the formation of dipolar (above 700 nm) and quadrupolar resonance peaks ( 380 nm) and wide dips in the visible region as correlated to the localized surface plasmon resonance (LSPR) effect. An absorption dip is readily shifted from 510 to 475 nm along with the decreased average size of alloy nanostructures.

Photonic Devices Based on Surface and Composition-Engineered Infrared Colloidal Nanocrystals

DTIC Science & Technology

2012-01-27

NQD/P3HT solar cells , the need for submicron-phase-separated polymer-NQD blends is therefore expressed by the limiting exciton diffusion length ...P3HT:PbSe are very critical in designing the PM-HJ solar cells : The thickness of P3HT should approximate to the thickness of exciton diffuse length in... cells , luminescent solar concentrators, light emitting diodes, lasers, photonic crystals, CdSe, PbSe, Germanium Jian Xu Pennsylvania State University

Thinner retinal layers are associated with changes in the visual pathway: A population-based study.

PubMed

Mutlu, Unal; Ikram, Mohammad K; Roshchupkin, Gennady V; Bonnemaijer, Pieter W M; Colijn, Johanna M; Vingerling, Johannes R; Niessen, Wiro J; Ikram, Mohammad A; Klaver, Caroline C W; Vernooij, Meike W

2018-06-23

Increasing evidence shows that thinner retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL), assessed on optical coherence tomography (OCT), are reflecting global brain atrophy. Yet, little is known on the relation of these layers with specific brain regions. Using voxel-based analysis, we aimed to unravel specific brain regions associated with these retinal layers. We included 2,235 persons (mean age: 67.3 years, 55% women) from the Rotterdam Study (2007-2012) who had gradable retinal OCT images and brain magnetic resonance imaging (MRI) scans, including diffusion tensor (DT) imaging. Thicknesses of peripapillary RNFL and perimacular GCL were measured using an automated segmentation algorithm. Voxel-based morphometry protocols were applied to process DT-MRI data. We investigated the association between retinal layer thickness with voxel-wise gray matter density and white matter microstructure by performing linear regression models. We found that thinner RNFL and GCL were associated with lower gray matter density in the visual cortex, and with lower fractional anisotropy and higher mean diffusivity in white matter tracts that are part of the optic radiation. Furthermore, thinner GCL was associated with lower gray matter density of the thalamus. Thinner RNFL and GCL are associated with gray and white matter changes in the visual pathway suggesting that retinal thinning on OCT may be specifically associated with changes in the visual pathway rather than with changes in the global brain. These findings may serve as a basis for understanding visual symptoms in elderly patients, patients with Alzheimer's disease, or patients with posterior cortical atrophy. © 2018 Wiley Periodicals, Inc.

A Gas-Kinetic Method for Hyperbolic-Elliptic Equations and Its Application in Two-Phase Fluid Flow

NASA Technical Reports Server (NTRS)

Xu, Kun

1999-01-01

A gas-kinetic method for the hyperbolic-elliptic equations is presented in this paper. In the mixed type system, the co-existence and the phase transition between liquid and gas are described by the van der Waals-type equation of state (EOS). Due to the unstable mechanism for a fluid in the elliptic region, interface between the liquid and gas can be kept sharp through the condensation and evaporation process to remove the "averaged" numerical fluid away from the elliptic region, and the interface thickness depends on the numerical diffusion and stiffness of the phase change. A few examples are presented in this paper for both phase transition and multifluid interface problems.

Ultra-diffuse hydrothermal venting supports Fe-oxidizing bacteria and massive umber deposition at 5000 m off Hawaii

PubMed Central

Edwards, Katrina J; Glazer, B T; Rouxel, O J; Bach, W; Emerson, D; Davis, R E; Toner, B M; Chan, C S; Tebo, B M; Staudigel, H; Moyer, C L

2011-01-01

A novel hydrothermal field has been discovered at the base of Lōihi Seamount, Hawaii, at 5000 mbsl. Geochemical analyses demonstrate that ‘FeMO Deep', while only 0.2 °C above ambient seawater temperature, derives from a distal, ultra-diffuse hydrothermal source. FeMO Deep is expressed as regional seafloor seepage of gelatinous iron- and silica-rich deposits, pooling between and over basalt pillows, in places over a meter thick. The system is capped by mm to cm thick hydrothermally derived iron-oxyhydroxide- and manganese-oxide-layered crusts. We use molecular analyses (16S rDNA-based) of extant communities combined with fluorescent in situ hybridizations to demonstrate that FeMO Deep deposits contain living iron-oxidizing Zetaproteobacteria related to the recently isolated strain Mariprofundus ferroxydans. Bioenergetic calculations, based on in-situ electrochemical measurements and cell counts, indicate that reactions between iron and oxygen are important in supporting chemosynthesis in the mats, which we infer forms a trophic base of the mat ecosystem. We suggest that the biogenic FeMO Deep hydrothermal deposit represents a modern analog for one class of geological iron deposits known as ‘umbers' (for example, Troodos ophilolites, Cyprus) because of striking similarities in size, setting and internal structures. PMID:21544100

Second harmonic generation microscopy differentiates collagen type I and type III in COPD

NASA Astrophysics Data System (ADS)

Suzuki, Masaru; Kayra, Damian; Elliott, W. Mark; Hogg, James C.; Abraham, Thomas

2012-03-01

The structural remodeling of extracellular matrix proteins in peripheral lung region is an important feature in chronic obstructive pulmonary disease (COPD). Multiphoton microscopy is capable of inducing specific second harmonic generation (SHG) signal from non-centrosymmetric structural proteins such as fibrillar collagens. In this study, SHG microscopy was used to examine structural remodeling of the fibrillar collagens in human lungs undergoing emphysematous destruction (n=2). The SHG signals originating from these diseased lung thin sections from base to apex (n=16) were captured simultaneously in both forward and backward directions. We found that the SHG images detected in the forward direction showed well-developed and well-structured thick collagen fibers while the SHG images detected in the backward direction showed striking different morphological features which included the diffused pattern of forward detected structures plus other forms of collagen structures. Comparison of these images with the wellestablished immunohistochemical staining indicated that the structures detected in the forward direction are primarily the thick collagen type I fibers and the structures identified in the backward direction are diffusive structures of forward detected collagen type I plus collagen type III. In conclusion, we here demonstrate the feasibility of SHG microscopy in differentiating fibrillar collagen subtypes and understanding their remodeling in diseased lung tissues.

Influence of ground level SO2 on the diffuse to direct irradiance ratio in the middle ultraviolet

NASA Technical Reports Server (NTRS)

Klenk, K. F.; Green, A. E. S.

1977-01-01

The dependence of the ratio of the diffuse to direct irradiances at the ground were examined for a wavelength of 315.1 nm. A passive remote sensing method based on ratio measurements for obtaining the optical thickness of SO2 in the vertical column was proposed. If, in addition to the ratio measurements, the SO2 density at the ground is determining using an appropriate point-sampling technique then some inference on the vertical extent of SO2 can be drawn. An analytic representation is presented of the ratio for a wide range of SO2 and aerosol optical thicknesses and solar zenith angles which can be inverted algebraically to give the SO2 optical thickness in terms of the measured ratio, aerosol optical thickness and solar zenith angle.

Multiple modality biomarker prediction of cognitive impairment in prospectively followed de novo Parkinson disease.

PubMed

Caspell-Garcia, Chelsea; Simuni, Tanya; Tosun-Turgut, Duygu; Wu, I-Wei; Zhang, Yu; Nalls, Mike; Singleton, Andrew; Shaw, Leslie A; Kang, Ju-Hee; Trojanowski, John Q; Siderowf, Andrew; Coffey, Christopher; Lasch, Shirley; Aarsland, Dag; Burn, David; Chahine, Lana M; Espay, Alberto J; Foster, Eric D; Hawkins, Keith A; Litvan, Irene; Richard, Irene; Weintraub, Daniel

2017-01-01

To assess the neurobiological substrate of initial cognitive decline in Parkinson's disease (PD) to inform patient management, clinical trial design, and development of treatments. We longitudinally assessed, up to 3 years, 423 newly diagnosed patients with idiopathic PD, untreated at baseline, from 33 international movement disorder centers. Study outcomes were four determinations of cognitive impairment or decline, and biomarker predictors were baseline dopamine transporter (DAT) single photon emission computed tomography (SPECT) scan, structural magnetic resonance imaging (MRI; volume and thickness), diffusion tensor imaging (mean diffusivity and fractional anisotropy), cerebrospinal fluid (CSF; amyloid beta [Aβ], tau and alpha synuclein), and 11 single nucleotide polymorphisms (SNPs) previously associated with PD cognition. Additionally, longitudinal structural MRI and DAT scan data were included. Univariate analyses were run initially, with false discovery rate = 0.2, to select biomarker variables for inclusion in multivariable longitudinal mixed-effect models. By year 3, cognitive impairment was diagnosed in 15-38% participants depending on the criteria applied. Biomarkers, some longitudinal, predicting cognitive impairment in multivariable models were: (1) dopamine deficiency (decreased caudate and putamen DAT availability); (2) diffuse, cortical decreased brain volume or thickness (frontal, temporal, parietal, and occipital lobe regions); (3) co-morbid Alzheimer's disease Aβ amyloid pathology (lower CSF Aβ 1-42); and (4) genes (COMT val/val and BDNF val/val genotypes). Cognitive impairment in PD increases in frequency 50-200% in the first several years of disease, and is independently predicted by biomarker changes related to nigrostriatal or cortical dopaminergic deficits, global atrophy due to possible widespread effects of neurodegenerative disease, co-morbid Alzheimer's disease plaque pathology, and genetic factors.

Thermal and Surface Evaluation on The Process of Forming a Cu2O/CuO Semiconductor Photocatalyst on a Thin Copper Plate

NASA Astrophysics Data System (ADS)

Zainul, R.; Oktavia, B.; Dewata, I.; Efendi, J.

2018-04-01

This research aims to investigate the process of forming a multi-scale copper oxide semiconductor (CuO/Cu2O) through a process of calcining a copper plate. The changes that occur during the formation of the oxide are thermally and surface evaluated. Evaluation using Differential Thermal Analysis (DTA) obtained by surface change of copper plate happened at temperature 380°C. Calcination of oxide formation was carried out at temperature 380°C for 1 hour. Surface evaluation process by using Scanning Electron Microscope (SEM) surface and cross-section, to determine diffusion of oxide formation on copper plate. The material composition is monitored by XRF and XRD to explain the process of structural and physical changes of the copper oxide plate formed during the heating process. The thickness of Cu plates used is 200-250 μm. SEM analysis results, the oxygen atom interruption region is in the range of 20-30 μm, and diffuses deeper during thermal oxidation process. The maximum diffusion depth of oxygen atoms reaches 129 μm.

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

PubMed

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

2015-02-03

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

Preparation of TiO2/Ag/TiO2 (TAT) multilayer films with optical and electrical properties enhanced by using Cr-added Ag film

NASA Astrophysics Data System (ADS)

Loka, Chadrasekhar; Lee, Kee-Sun

2017-09-01

The dielectric-metal-dielectric tri-layer films have attracted much attention by virtue of their low-cost and high quality device performance as a transparent conductive electrode. Here, we report the deposition of Cr doped Ag films sandwiched between thin TiO2 layers and investigation on the surface microstructure, optical and electrical properties depending on the thickness of the Ag(Cr). The activation energy (1.18 eV) for grain growth of Ag was calculated from the Arrhenius plot using the law Dn -D0n = kt , which was comparable to the bulk diffusion of Ag. This result indicated the grain growth of Ag was effectively retarded by the Cr addition, which was presumed to related with blocking the surface and grain boundary diffusion due to Cr segregation. Based on thermal stability of Cr added Ag film, we deposited TiO2/Ag(Cr)/TiO2 (TAT) multilayer thin films and with a 10 nm thick Ag(Cr), the TAT films showed high optical transmittance in the visible region (94.2%), low electrical resistivity (8.66 × 10-5 Ω cm), and hence the high figure of merit 57.15 × 10-3 Ω-1 was achieved. The high transmittance of the TAT film was believed to be attributed to the low optical loss due to a reduction in the Ag layer thickness, the surface plasmon effect, and the electron scattering reduced by the Ag layer with a low electrical resistivity.

Space-time modeling of the photon diffusion in a three-layered model: application to the study of muscular oxygenation

NASA Astrophysics Data System (ADS)

Mansouri, C.; L'Huillier, J. P.; Piron, V.

2007-07-01

This work presents results on the modeling of the photon diffusion in a three-layered model, (skin, fat and muscle). The Finite Element method was performed in order to calculate the temporal response of the above-mentioned structure. The thickness of the fat layer was varied from 1 to 15 mm to investigate the effects of increasing fat thickness on the muscle layer absorption coefficient measurements for a source-detector spacing of 30 mm. The simulated time-resolved reflectance data, at different wavelengths, were fitted to the diffusion model to yield the scattering and absorption coefficients of muscle. The errors in estimating muscle absorption coefficients μ α depend on the thickness of the fat layer and its optical properties. In addition, it was shown that it is possible to recover with a good precision (~2.6 % of error) the absorption coefficient of muscle and this up to a thickness of the fat layer not exceeding 4mm. Beyond this limit a correction is proposed in order to make measurements coherent. The muscle-corrected absorption coefficient can be then used to calculate hemoglobin oxygenation.

Mesoscale simulations of confined Nafion thin films.

PubMed

Vanya, P; Sharman, J; Elliott, J A

2017-12-07

The morphology and transport properties of thin films of the ionomer Nafion, with thicknesses on the order of the bulk cluster size, have been investigated as a model system to explain the anomalous behaviour of catalyst/electrode-polymer interfaces in membrane electrode assemblies. We have employed dissipative particle dynamics (DPD) to investigate the interaction of water and fluorocarbon chains, with carbon and quartz as confining materials, for a wide range of operational water contents and film thicknesses. We found confinement-induced clustering of water perpendicular to the thin film. Hydrophobic carbon forms a water depletion zone near the film interface, whereas hydrophilic quartz results in a zone with excess water. There are, on average, oscillating water-rich and fluorocarbon-rich regions, in agreement with experimental results from neutron reflectometry. Water diffusivity shows increasing directional anisotropy of up to 30% with decreasing film thickness, depending on the hydrophilicity of the confining material. A percolation analysis revealed significant differences in water clustering and connectivity with the confining material. These findings indicate the fundamentally different nature of ionomer thin films, compared to membranes, and suggest explanations for increased ionic resistances observed in the catalyst layer.

Light-attenuating effect of dentin on the polymerization of light-activated restorative resins.

PubMed

Arikawa, Hiroyuki; Kanie, Takahito; Fujii, Koichi; Ban, Seiji; Takahashi, Hideo

2004-12-01

The light-attenuating effect of dentin on the mechanical properties of light-activated composite resins was evaluated using a simple experimental filter. The filter was designed to simulate the light transmittance and light diffusion characteristics of 1.0-mm thick dentin. The depth of cure, surface hardness, and flexural strength for 13 shades of three light-activated restorative resins were examined. These resins were cured either using direct irradiation with a light source, or indirect irradiation through the filter. The attenuation of light intensity by 1.0-mm thick dentin reached 85-90% in the 400-550 nm wavelength region. For all materials, the values of depth of cure, surface hardness on the top and bottom surfaces, and flexural strength of specimens irradiated indirectly through the simulated 1.0-mm thick dentin filter decreased by 37-60%, 16-55%, 50-83%, and 44-82% in comparison with those by direct irradiation, respectively. Recovery from mechanical properties' reduction was achieved when materials were irradiated 1.5-4 times longer than the standard irradiation time.

Mesoscale simulations of confined Nafion thin films

NASA Astrophysics Data System (ADS)

Vanya, P.; Sharman, J.; Elliott, J. A.

2017-12-01

The morphology and transport properties of thin films of the ionomer Nafion, with thicknesses on the order of the bulk cluster size, have been investigated as a model system to explain the anomalous behaviour of catalyst/electrode-polymer interfaces in membrane electrode assemblies. We have employed dissipative particle dynamics (DPD) to investigate the interaction of water and fluorocarbon chains, with carbon and quartz as confining materials, for a wide range of operational water contents and film thicknesses. We found confinement-induced clustering of water perpendicular to the thin film. Hydrophobic carbon forms a water depletion zone near the film interface, whereas hydrophilic quartz results in a zone with excess water. There are, on average, oscillating water-rich and fluorocarbon-rich regions, in agreement with experimental results from neutron reflectometry. Water diffusivity shows increasing directional anisotropy of up to 30% with decreasing film thickness, depending on the hydrophilicity of the confining material. A percolation analysis revealed significant differences in water clustering and connectivity with the confining material. These findings indicate the fundamentally different nature of ionomer thin films, compared to membranes, and suggest explanations for increased ionic resistances observed in the catalyst layer.

Energetic electron precipitation characteristics observed from Antarctica during a flux dropout event

NASA Astrophysics Data System (ADS)

Clilverd, Mark A.; Cobbett, Neil; Rodger, Craig J.; Brundell, James B.; Denton, Michael H.; Hartley, David P.; Rodriguez, Juan V.; Danskin, Donald; Raita, Tero; Spanswick, Emma L.

2013-11-01

from two autonomous VLF radio receiver systems installed in a remote region of the Antarctic in 2012 is used to take advantage of the juxtaposition of the L = 4.6 contour, and the Hawaii-Halley, Antarctica, great circle path as it passes over thick Antarctic ice shelf. The ice sheet conductivity leads to high sensitivity to changing D region conditions, and the quasi constant L shell highlights outer radiation belt processes. The ground-based instruments observed several energetic electron precipitation events over a moderately active 24 h period, during which the outer radiation belt electron flux declined at most energies and subsequently recovered. Combining the ground-based data with low and geosynchronous orbiting satellite observations on 27 February 2012, different driving mechanisms were observed for three precipitation events with clear signatures in phase space density and electron anisotropy. Comparison between flux measurements made by Polar-orbiting Operational Environmental Satellites (POES) in low Earth orbit and by the Antarctic instrumentation provides evidence of different cases of weak and strong diffusion into the bounce loss cone, helping to understand the physical mechanisms controlling the precipitation of energetic electrons into the atmosphere. Strong diffusion events occurred as the <600 keV fluxes began to recover as a result of adiabatic transport of electrons. One event appeared to have a factor of about 10 to 100 times more flux than was reported by POES, consistent with weak diffusion into the bounce loss cone. Two events had a factor of about 3 to 10 times more >30 keV flux than was reported by POES, more consistent with strong diffusion conditions.

Interface Defect States and Charge Transport Properties in Low-Cost Photovoltaic Devices made from Scalable Deposition Methods

NASA Astrophysics Data System (ADS)

Marin, Andrew; Munoz-Rojas, David; Iza, Diana; Gershon, Talia; MacManus-Driscoll, Judith

2011-03-01

In-plane (parallel to the substrate) polymer diffusion at and near interfaces has significant implications for polymeric surfactants used in tertiary oil recovery, exfoliation of clay sheets in polymer nano-composites, and several other high technology applications. Here, we report a study on the in-plane diffusion of whole polymer chains confined between interfaces using fluorescence recovery after photobleaching. Adapted from quantitative biology, FRAP provides a platform to independently study the effect of temperature, molecular weight, and film thickness on in-plane diffusion of polymers confined between interfaces. Fluorescently labeled polymers were synthesized, spin coated onto quartz substrates and the self-diffusion coefficient was measured by irreversibly photobleaching fluorophores in a pre-defined pattern and monitoring recovery of fluorescence over time. Preliminary results indicate that for thick films the diffusion coefficient is consistent with bulk values. The authors would like to thank the Gates-Cambridge Trust and the International Copper Association.

Anatomical basis of variation in mesophyll resistance in eastern Australian sclerophylls: news of a long and winding path

PubMed Central

Tosens, Tiina

2012-01-01

In sclerophylls, photosynthesis is particularly strongly limited by mesophyll diffusion resistance from substomatal cavities to chloroplasts (r m), but the controls on diffusion limits by integral leaf variables such as leaf thickness, density, and dry mass per unit area and by the individual steps along the diffusion pathway are imperfectly understood. To gain insight into the determinants of r m in leaves with varying structure, the full CO2 physical diffusion pathway was analysed in 32 Australian species sampled from sites contrasting in soil nutrients and rainfall, and having leaf structures from mesophytic to strongly sclerophyllous. r m was estimated based on combined measurements of gas exchange and chlorophyll fluorescence. In addition, r m was modelled on the basis of detailed anatomical measurements to separate the importance of different serial resistances affecting CO2 diffusion into chloroplasts. The strongest sources of variation in r m were S c/S, the exposed surface area of chloroplasts per unit leaf area, and mesophyll cell wall thickness, t cw. The strong correlation of r m with t cw could not be explained by cell wall thickness alone, and most likely arose from a further effect of cell wall porosity. The CO2 drawdown from intercellular spaces to chloroplasts was positively correlated with t cw, suggesting enhanced diffusional limitations in leaves with thicker cell walls. Leaf thickness and density were poorly correlated with S c/S, indicating that widely varying combinations of leaf anatomical traits occur at given values of leaf integrated traits, and suggesting that detailed anatomical studies are needed to predict r m for any given species. PMID:22888123

Volcanic glasses, their origins and alteration processes

USGS Publications Warehouse

Friedman, I.; Long, W.

1984-01-01

Natural glass can be formed by volcanic processes, lightning (fulgarites) burning coal, and by meteorite impact. By far the most common process is volcanic - basically the glass is rapidly chilled molten rock. All natural glasses are thermodynamically unstable and tend to alter chemically or to crystallize. The rate of these processes is determined by the chemical composition of the magma. The hot and fluid basaltic melts have a structure that allows for rapid crystal growth, and seldom forms glass selvages greater than a few centimeters thick, even when the melt is rapidly cooled by extrusion in the deep sea. In contrast the cooler and very viscous rhyolitic magmas can yield bodies of glass that are tens of meters thick. These highly polymerized magmas have a high silica content - often 71-77% SiO2. Their high viscosity inhibits diffusive crystal growth. Basalt glass in sea water forms an alteration zone called palagonite whose thickness increases linearly with time. The rate of diffusion of water into rhyolitic glass, which follows the relationship - thickness = k (time) 1 2, has been determined as a function of the glass composition and temperature. Increased SiO2 increases the rate, whereas increased CaO, MgO and H2O decrease the rate. The activation energy of water diffusion varies from about 19 to 22 kcal/mol. for the glasses studied. The diffusion of alkali out of rhyolite glass occurs simultaneously with water diffusion into the glass. The rate of devitrification of rhyolitic glass is a function of the glass viscosity, which in turn is a function of water content and temperature. Although all of the aforementioned processes tend to destroy natural glasses, the slow rates of these processes, particularly for rhyolitic glass, has allowed samples of glass to persist for 60 million years. ?? 1984.

Peripapillary choroidal thickness in healthy controls and patients with focal, diffuse, and sclerotic glaucomatous optic disc damage.

PubMed

Roberts, Kenneth F; Artes, Paul H; O'Leary, Neil; Reis, Alexandre S C; Sharpe, Glen P; Hutchison, Donna M; Chauhan, Balwantray C; Nicolela, Marcelo T

2012-08-01

To examine peripapillary choroidal thickness in healthy controls and in patients with glaucoma who have focal, diffuse, and sclerotic optic disc damage. Healthy controls (n=92) and patients with glaucoma who have focal (n=34), diffuse (n=35), and sclerotic (n=34) optic disc damage were imaged with spectral-domain optical coherence tomography (12° circular scan protocol centered on optic nerve head). Peripapillary choroidal thickness was measured as the distance between the automatically segmented retinal pigment epithelium/Bruch's membrane and the manually outlined interface between the posterior choroid and the anterior border of the sclera in eyes in which the anterior scleral border was visible over more than 85% of the scan circumference. The anterior scleral border was visible in 76 controls (83%) and 89 patients (86%). Peripapillary choroidal thickness in healthy controls decreased linearly with age (-11 μm/decade; P.001; r2=0.16), with a predicted value of 137 μm at age 70 years (95% prediction interval, 62-212 μm). While this value was similar in patients with focal and diffuse optic disc damage (126 and 130 μm, respectively; P=.22 compared with controls), it was approximately 30% lower in patients with sclerotic optic disc damage (96 μm; P.001 compared with controls). The peripapillary choroid of patients with glaucoma who have sclerotic optic disc damage was approximately 25% to 30% thinner compared with that in patients with focal and diffuse optic disc damage and with that in healthy controls. The role of the choroid in the pathophysiology of sclerotic glaucomatous optic disc damage needs further investigation.

Interpreting measurements obtained with the cloud absorption radiometer

NASA Technical Reports Server (NTRS)

1988-01-01

The software developed for the analysis of data from the Cloud Absorption Radiometer (CAR) is discussed. The CAR is a multichannel radiometer designed to measure the radiation field in the middle of an optically thick cloud (the diffusion domain). It can also measure the surface albedo and escape function. The instrument currently flies on a C-131A aircraft operated by the University of Washington. Most of this data was collected during the First International satellite cloud climatology project Regional Experiment (FIRE) Marine Stratocumulus Intensive Field Observation program off San Diego during July 1987. Earlier flights of the CAR have also been studied.

Annual Progress Report of Research Activities that Occured in the Coordinated Science Laboratory for July 1, 1982 through Jun 30, 1983,

DTIC Science & Technology

1983-08-01

particular fabrication concerns, both the emitter and collector region were made of Al„ -Ga0 5As wide gap material. Devices with emitter area of 10 x 60...im and collector area of 50 x 60 (im exhi- bited current gains of 500 for a base doping of 10 cm and thickness of 500 A, and 1700 for a base...spreading over a large enough distance, it is usually necessary to heat the surface to a temperature at which not just diffusion, but also

Monte Carlo Simulations of the Photospheric Emission in Gamma-Ray Bursts

NASA Astrophysics Data System (ADS)

Bégué, D.; Siutsou, I. A.; Vereshchagin, G. V.

2013-04-01

We studied the decoupling of photons from ultra-relativistic spherically symmetric outflows expanding with constant velocity by means of Monte Carlo simulations. For outflows with finite widths we confirm the existence of two regimes: photon-thick and photon-thin, introduced recently by Ruffini et al. (RSV). The probability density function of the last scattering of photons is shown to be very different in these two cases. We also obtained spectra as well as light curves. In the photon-thick case, the time-integrated spectrum is much broader than the Planck function and its shape is well described by the fuzzy photosphere approximation introduced by RSV. In the photon-thin case, we confirm the crucial role of photon diffusion, hence the probability density of decoupling has a maximum near the diffusion radius well below the photosphere. The time-integrated spectrum of the photon-thin case has a Band shape that is produced when the outflow is optically thick and its peak is formed at the diffusion radius.

MONTE CARLO SIMULATIONS OF THE PHOTOSPHERIC EMISSION IN GAMMA-RAY BURSTS

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

Begue, D.; Siutsou, I. A.; Vereshchagin, G. V.

2013-04-20

We studied the decoupling of photons from ultra-relativistic spherically symmetric outflows expanding with constant velocity by means of Monte Carlo simulations. For outflows with finite widths we confirm the existence of two regimes: photon-thick and photon-thin, introduced recently by Ruffini et al. (RSV). The probability density function of the last scattering of photons is shown to be very different in these two cases. We also obtained spectra as well as light curves. In the photon-thick case, the time-integrated spectrum is much broader than the Planck function and its shape is well described by the fuzzy photosphere approximation introduced by RSV.more » In the photon-thin case, we confirm the crucial role of photon diffusion, hence the probability density of decoupling has a maximum near the diffusion radius well below the photosphere. The time-integrated spectrum of the photon-thin case has a Band shape that is produced when the outflow is optically thick and its peak is formed at the diffusion radius.« less

Fabrication and Characterization of Diffusion Bonds for Silicon Carbide

NASA Technical Reports Server (NTRS)

Halbig, Michael; Singh, Mrityunjay; Martin, Richard E.; Cosgriff, Laura M.

2007-01-01

Diffusion bonds of silicon carbide (SiC) were fabricated using several different types of titanium (Ti) based interlayers between the SiC substrates. The interlayers were an alloyed Ti foil, a pure Ti foil, and a physically vapor deposited (PVD) Ti coating. Microscopy was conducted to evaluate the cross-sections of the resulting bonds. Microprobe analysis identified reaction formed phases in the diffusion bonded region. Uniform and well adhered bonds were formed between the SiC substrates. In the case where the alloyed Ti foil or a thick Ti coating (i.e. 20 micron) was used as the interlayer, microcracks and several phases were present in the diffusion bonds. When a thinner interlayer was used (i.e. 10 micron PVD Ti), no microcracks were observed and only two reaction formed phases were present. The two phases were preferred and fully reacted phases that did not introduce thermal stresses or microcracks during the cool-down stage after processing. Diffusion bonded samples were evaluated with the non-destructive evaluation (NDE) methods of pulsed thermography and immersion ultrasonic testing. Joined SiC substrates that were fully bonded and that had simulated bond flaws in the interlayer were also evaluated using immersion ultrasound. Pull testing was conducted on the bonds to determine the tensile strength. To demonstrate the joining approach for a complex multilayered component for a low NOx injector application, the diffusion bonding approach was used to join three 4" diameter SiC discs that contained complex fuel and air flow channels.

Comparison and analysis of theoretical models for diffusion-controlled dissolution.

PubMed

Wang, Yanxing; Abrahamsson, Bertil; Lindfors, Lennart; Brasseur, James G

2012-05-07

Dissolution models require, at their core, an accurate diffusion model. The accuracy of the model for diffusion-dominated dissolution is particularly important with the trend toward micro- and nanoscale drug particles. Often such models are based on the concept of a "diffusion layer." Here a framework is developed for diffusion-dominated dissolution models, and we discuss the inadequacy of classical models that are based on an unphysical constant diffusion layer thickness assumption, or do not correctly modify dissolution rate due to "confinement effects": (1) the increase in bulk concentration from confinement of the dissolution process, (2) the modification of the flux model (the Sherwood number) by confinement. We derive the exact mathematical solution for a spherical particle in a confined fluid with impermeable boundaries. Using this solution, we analyze the accuracy of a time-dependent "infinite domain model" (IDM) and "quasi steady-state model" (QSM), both formally derived for infinite domains but which can be applied in approximate fashion to confined dissolution with proper adjustment of a concentration parameter. We show that dissolution rate is sensitive to the degree of confinement or, equivalently, to the total concentration C(tot). The most practical model, the QSM, is shown to be very accurate for most applications and, consequently, can be used with confidence in design-level dissolution models so long as confinement is accurately treated. The QSM predicts the ratio of diffusion layer thickness to particle radius (the Sherwood number) as a constant plus a correction that depends on the degree of confinement. The QSM also predicts that the time required for complete saturation or dissolution in diffusion-controlled dissolution experiments is singular (i.e., infinite) when total concentration equals the solubility. Using the QSM, we show that measured differences in dissolution rate in a diffusion-controlled dissolution experiment are a result of differences in the degree of confinement on the increase in bulk concentration independent of container geometry and polydisperse vs single particle dissolution. We conclude that the constant diffusion-layer thickness assumption is incorrect in principle and should be replaced by the QSM with accurate treatment of confinement in models of diffusion-controlled dissolution.

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.

Physical properties and application in the confined geometrical systems

NASA Astrophysics Data System (ADS)

Pak, Hunkyun

Surface viscoelasticity of a vitamin E modified polyethylene glycol (vitamin E-TPGS) monolayers at the air/water interface is deduced by the surface light scattering method and Wilhelmy plate method. It was found that the viscoelasticity of vitamin E-TPGS monolayer is similar to that of PEO monolayer at the surface pressure lower than the collapse pressure of the polyethylene oxide (PEO). However, at higher surface pressure than the collapse pressure of PEO, it deviates from the viscoelastic behavior of PEO. Lateral diffusion constants of a probe lipid (NBD-PC) in a binary monolayer of L-a-dilauroylphosphatidylcholine (DLPC) and poly-(di-isobutylene-alt-maleic acid) (PDIBMA) were determined by the fluorescence recovery after photobleaching (FRAP) method at the air/pH 7 buffer interface as a function of composition. The diffusion constant is found to retard down to less than one hundredth to that at pure DLPC monolayers as the mole fraction of PDIBMA increased. The free area model was used to interpret the probe diffusion retardation. Translational diffusion constants of a probe molecule, 4-octadecylamino-7-nitrobenzo-2-oxa-1,3-diazole (C18-NBD), in thin polyisoprene (PI) and polydimethyl siloxane (PDMS) films, spin coated on methylated and propylyaminated silicon wafers, are studied by the FRAP method as a function of film thickness. Reduction of the diffusion constant is observed as thickness of the films is decreased. Two empirical models, the two-layer model and the continuous layer model are proposed to account for the diffusion constant dependence on the film thickness vs. thickness. It was observed that the diffusion profiles in the films are dependet on the nature of the substrate surfaces. Self-assembled patterns of magnetic particles were made and fixed by applying magnetic field on the particles dispersed at the air/liquid interface, followed by gelling of the liquid subphase. With this method, the large patterns with controllable lattice constant can be made. The fixation of the subphase enhances the stability of the patterns. Further, three-dimensional self-assembled patterns can be made by this method when the fixation process is incorporated.

THOR: Cloud Thickness from Off beam Lidar Returns

NASA Technical Reports Server (NTRS)

Cahalan, Robert F.; McGill, Matthew; Kolasinski, John; Varnai, Tamas; Yetzer, Ken

2004-01-01

Conventional wisdom is that lidar pulses do not significantly penetrate clouds having optical thickness exceeding about tau = 2, and that no returns are detectable from more than a shallow skin depth. Yet optically thicker clouds of tau much greater than 2 reflect a larger fraction of visible photons, and account for much of Earth s global average albedo. As cloud layer thickness grows, an increasing fraction of reflected photons are scattered multiple times within the cloud, and return from a diffuse concentric halo that grows around the incident pulse, increasing in horizontal area with layer physical thickness. The reflected halo is largely undetected by narrow field-of-view (FoV) receivers commonly used in lidar applications. THOR - Thickness from Off-beam Returns - is an airborne wide-angle detection system with multiple FoVs, capable of observing the diffuse halo, detecting wide-angle signal from which physical thickness of optically thick clouds can be retrieved. In this paper we describe the THOR system, demonstrate that the halo signal is stronger for thicker clouds, and validate physical thickness retrievals for clouds having z > 20, from NASA P-3B flights over the Department of Energy/Atmospheric Radiation Measurement/Southern Great Plains site, using the lidar, radar and other ancillary ground-based data.

Thermal Effusivity Determination of Metallic Films of Nanometric Thickness by the Electrical Micropulse Method

NASA Astrophysics Data System (ADS)

Lugo, J. M.; Oliva, A. I.

2017-02-01

The thermal effusivity of gold, aluminum, and copper thin films of nanometric thickness (20 nm to 200 nm) was investigated in terms of the films' thickness. The metallic thin films were deposited onto glass substrates by thermal evaporation, and the thermal effusivity was estimated by using experimental parameters such as the specific heat, thermal conductivity, and thermal diffusivity values obtained at room conditions. The specific heat, thermal conductivity, and thermal diffusivity values of the metallic thin films are determined with a methodology based on the behavior of the thermal profiles of the films when electrical pulses of few microseconds are applied at room conditions. For all the investigated materials, the thermal effusivity decreases with decreased thickness. The thermal effusivity values estimated by the presented methodology are consistent with other reported values obtained under vacuum conditions and more elaborated methodologies.

The optimal thickness of a transmission-mode GaN photocathode

NASA Astrophysics Data System (ADS)

Wang, Xiao-Hui; Shi, Feng; Guo, Hui; Hu, Cang-Lu; Cheng, Hong-Chang; Chang, Ben-Kang; Ren, Ling; Du, Yu-Jie; Zhang, Jun-Ju

2012-08-01

A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6 × 1017 cm-3 is activated by Cs/O in an ultrahigh vacuum chamber, and a quantum efficiency (QE) curve of the negative electron affinity transmission-mode (t-mode) of the GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5 × 104 cm·s-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.

Using satellite-derived optical thickness to assess the influence of clouds on terrestrial carbon uptake

Treesearch

S.J. Cheng; A.L. Steiner; D.Y. Hollinger; G. Bohrer; K.J. Nadelhoffer

2016-01-01

Clouds scatter direct solar radiation, generating diffuse radiation and altering the ratio of direct to diffuse light. If diffuse light increases plant canopy CO2 uptake, clouds may indirectly influence climate by altering the terrestrial carbon cycle. However, past research primarily uses proxies or qualitative categories of clouds to connect...

An inverse moisture diffusion algorithm for the determination of diffusion coefficient

Treesearch

Jen Y. Liu; William T. Simpson; Steve P. Verrill

2000-01-01

The finite difference approximation is applied to estimate the moisture-dependent diffusion coefficient by utilizing test data of isothermal moisture desorption in northern red oak (Quercus rubra). The test data contain moisture distributions at discrete locations across the thickness of specimens, which coincides with the radial direction of northern red oak, and at...

An inverse moisture diffusion algorithm for the determination of diffusion coefficient

Treesearch

Jen Y. Liu; William T. Simpson; Steve P. Verrill

2001-01-01

The finite difference approximation is applied to estimate the moisture-dependent diffusion coefficient by utilizing test data of isothermal moisture desorption in northern red oak (Quercus rubra). The test data contain moisture distributions at discrete locations across the thickness of specimens, which coincides with the radial direction of northern red oak, and at...

Association of Optic Radiation Integrity with Cortical Thickness in Children with Anisometropic Amblyopia.

PubMed

Qi, Shun; Mu, Yun-Feng; Cui, Long-Biao; Li, Rong; Shi, Mei; Liu, Ying; Xu, Jun-Qing; Zhang, Jian; Yang, Jian; Yin, Hong

2016-02-01

Previous studies have indicated regional abnormalities of both gray and white matter in amblyopia. However, alterations of cortical thickness associated with changes in white matter integrity have rarely been reported. In this study, structural magnetic resonance imaging and diffusion tensor imaging (DTI) data were obtained from 15 children with anisometropic amblyopia and 15 age- and gender-matched children with normal sight. Combining DTI and surface-based morphometry, we examined a potential linkage between disrupted white matter integrity and altered cortical thickness. The fractional anisotropy (FA) values in the optic radiations (ORs) of children with anisometropic amblyopia were lower than in controls (P < 0.05). The cortical thickness in amblyopic children was lower than controls in the following subregions: lingual cortex, lateral occipitotemporal gyrus, cuneus, occipital lobe, inferior parietal lobe, and temporal lobe (P < 0.05, corrected), but was higher in the calcarine gyrus (P < 0.05, corrected). Node-by-node correlation analysis of changes in cortical thickness revealed a significant association between a lower FA value in the OR and diminished cortical thickness in the following subregions: medial lingual cortex, lateral occipitotemporal gyrus, lateral, superior, and medial occipital cortex, and lunate cortex. We also found a relationship between changes of cortical thickness and white matter OR integrity in amblyopia. These findings indicate that developmental changes occur simultaneously in the OR and visual cortex in amblyopia, and provide key information on complex damage of brain networks in anisometropic amblyopia. Our results also support the hypothesis that the pathogenesis of anisometropic amblyopia is neurodevelopmental.

Phototransformation Rate Constants of PAHs Associated with Soot Particles

PubMed Central

Kim, Daekyun; Young, Thomas M.; Anastasio, Cort

2013-01-01

Photodegradation is a key process governing the residence time and fate of polycyclic aromatic hydrocarbons (PAHs) in particles, both in the atmosphere and after deposition. We have measured photodegradation rate constants of PAHs in bulk deposits of soot particles illuminated with simulated sunlight. The photodegradation rate constants at the surface (k0p), the effective diffusion coefficients (Deff), and the light penetration depths (z0.5) for PAHs on soot layers of variable thickness were determined by fitting experimental data with a model of coupled photolysis and diffusion. The overall disappearance rates of irradiated low molecular weight PAHs (with 2-3 rings) on soot particles were influenced by fast photodegradation and fast diffusion kinetics, while those of high molecular weight PAHs (with 4 or more rings) were apparently controlled by either the combination of slow photodegradation and slow diffusion kinetics or by very slow diffusion kinetics alone. The value of z0.5 is more sensitive to the soot layer thickness than the k0p value. As the thickness of the soot layer increases, the z0.5 values increase, but the k0p values are almost constant. The effective diffusion coefficients calculated from dark experiments are generally higher than those from the model fitting method for illumination experiments. Due to the correlation between k0p and z0.5 in thinner layers, Deff should be estimated by an independent method for better accuracy. Despite some limitations of the model used in this study, the fitted parameters were useful for describing empirical results of photodegradation of soot-associated PAHs. PMID:23247292

A Basin-Wide Examination of the Arctic Ocean's Double-Diffusive Staircase

NASA Astrophysics Data System (ADS)

Shibley, N.; Timmermans, M. L.; Carpenter, J. R.; Toole, J. M.

2016-02-01

The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure above the Atlantic Water Layer consisting of multiple mixed layers of order 1-m in height separated by sharp interfaces. This double-diffusive staircase structure is characterized across the entire Arctic Ocean through a detailed analysis of Ice-Tethered Profiler measurements acquired between 2004 and 2013. Staircase properties (mixed layer thicknesses and temperature-salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio for 50-m spanning the staircase stratification. It is shown that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (on the Eurasian side) and higher density ratio (on the Canadian side). We find that the diffusive staircase in the Eurasian Basin is characterized by fewer, thinner mixed layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin staircase mixed layers. Using a double-diffusive 4/3 flux law parameterization, the distribution of vertical heat fluxes through the staircase is estimated across the Arctic; it is found that heat fluxes in the Eurasian Basin [O(1) W/m^2] are generally an order of magnitude larger than those in the Canadian Basin [O(0.1) W/m^2].

Cortical geometry may influence placement of interface between Par protein domains in early Caenorhabditis elegans embryos.

PubMed

Dawes, Adriana T; Iron, David

2013-09-21

During polarization, proteins and other polarity determinants segregate to the opposite ends of the cell (the poles) creating biochemically and dynamically distinct regions. Embryos of the nematode worm Caenorhabditis elegans (C. elegans) polarize shortly after fertilization, creating distinct regions of Par protein family members. These regions are maintained through to first cleavage when the embryo divides along the plane specified by the interface between regions, creating daughter cells with different protein content. In wild type single cell embryos the interface between these Par protein regions is reliably positioned at approximately 60% egg length, however, it is not known what mechanisms are responsible for specifying the position of the interface. In this investigation, we use two mathematical models to investigate the movement and positioning of the interface: a biologically based reaction-diffusion model of Par protein dynamics, and the analytically tractable perturbed Allen-Cahn equation. When we numerically simulate the models on a static 2D domain with constant thickness, both models exhibit a persistently moving interface that specifies the boundary between distinct regions. When we modify the simulation domain geometry, movement halts and the interface is stably positioned where the domain thickness increases. Using asymptotic analysis with the perturbed Allen-Cahn equation, we show that interface movement depends explicitly on domain geometry. Using a combination of analytic and numeric techniques, we demonstrate that domain geometry, a historically overlooked aspect of cellular simulations, may play a significant role in spatial protein patterning during polarization. Copyright © 2013 Elsevier Ltd. All rights reserved.

Comparison of Single-Shot Echo-Planar and Line Scan Protocols for Diffusion Tensor Imaging1

PubMed Central

Kubicki, Marek; Maier, Stephan E.; Westin, Carl-Frederik; Mamata, Hatsuho; Ersner-Hershfield, Hal; Estepar, Raul; Kikinis, Ron; Jolesz, Ferenc A.

2009-01-01

Rationale and Objectives Both single-shot diffusion-weighted echo-planar imaging (EPI) and line scan diffusion imaging (LSDI) can be used to obtain magnetic resonance diffusion tensor data and to calculate directionally invariant diffusion anisotropy indices, ie, indirect measures of the organization and coherence of white matter fibers in the brain. To date, there has been no comparison of EPI and LSDI. Because EPI is the most commonly used technique for acquiring diffusion tensor data, it is important to understand the limitations and advantages of LSDI relative to EPI. Materials and Methods Five healthy volunteers underwent EPI and LSDI diffusion on a 1.5 Tesla magnet (General Electric Medical Systems, Milwaukee, WI). Four-mm thick coronal sections, covering the entire brain, were obtained. In addition, one subject was tested with both sequences over four sessions. For each image voxel, eigenvectors and eigenvalues of the diffusion tensor were calculated, and fractional anisotropy (FA) was derived. Several regions of interest were delineated, and for each, mean FA and estimated mean standard deviation were calculated and compared. Results Results showed no significant differences between EPI and LSDI for mean FA for the five subjects. When inter-session reproducibility for one subject was evaluated, there was a significant difference between EPI and LSDI in FA for the corpus callosum and the right uncinate fasciculus. Moreover, errors associated with each FA measure were larger for EPI than for LSDI. Conclusion Results indicate that both EPI- and LSDI-derived FA measures are sufficiently robust. However, when higher accuracy is needed, LSDI provides smaller error and smaller inter-subject and inter-session variability than EPI. PMID:14974598

Molecular dynamics simulations of lithium silicate/vanadium pentoxide interfacial lithium ion diffusion in thin film lithium ion-conducting devices

NASA Astrophysics Data System (ADS)

Li, Weiqun

The lithium ion diffusion behavior and mechanism in the glassy electrolyte and the electrolyte/cathode interface during the initial stage of lithium ion diffusing from electrolyte into cathode were investigated using Molecular Dynamics simulation technique. Lithium aluminosilicate glass electrolytes with different R (ratio of the concentration of Al to Li) were simulated. The structural features of the simulated glasses are analyzed using Radial Distribution Function (RDF) and Pair Distribution Function (PDF). The diffusion coefficient and activation energy of lithium ion diffusion in simulated lithium aluminosilicate glasses were calculated and the values are consistent with those in experimental glasses. The behavior of lithium ion diffusion from the glassy electrolyte into a polycrystalline layered intercalation cathode has been studied. The solid electrolyte was a model lithium silicate glass while the cathode was a nanocrystalline vanadia with amorphous V2O5 intergranular films (IGF) between the V2O5 crystals. Two different orientations between the V2O5 crystal planes are presented for lithium ion intercalation via the amorphous vanadia IGF. A series of polycrystalline vanadia cathodes with 1.3, 1.9, 2.9 and 4.4 nm thickness IGFs were simulated to examine the effects of the IGF thickness on lithium ion transport in the polycrystalline vanadia cathodes. The simulated results showed that the lithium ions diffused from the glassy electrolyte into the IGF of the polycrystalline vanadia cathode and then part of those lithium ions diffused into the crystalline V2O5 from the IGF. The simulated results also showed an ordering of the vanadium ion structure in the IGF near the IGF/V2 O5 interface. The ordering structure still existed with glass former silica additive in IGF. Additionally, 2.9 run is suggested to be the optimal thickness of the IGF, which is neither too thick to decrease the capacity of the cathode nor too thin to impede the transport of lithium from glassy electrolyte into the cathode. Parallel molecular dynamic simulation technique was also used for a larger electrolyte/cathode interface system, which include more atoms and more complicated microstructures. Simulation results from larger electrolyte/cathode interface system prove that there is no size effect on simulation of smaller electrolyte/cathode interface system from statistical point of view.

Plasma diffusion at the magnetopause - The case of lower hybrid drift waves

NASA Technical Reports Server (NTRS)

Treumann, R. A.; Labelle, J.; Pottelette, R.

1991-01-01

The diffusion expected from the quasi-linear theory of the lower hybrid drift instability at the earth's magnetopause is recalculated. The resulting diffusion coefficient is marginally large enough to explain the thickness of the boundary layer under quiet conditions, based on observational upper limits for the wave intensities. Thus, one possible model for the boundary layer could involve equilibrium between the diffusion arising from lower hybrid waves and various loss processes.

The effects of inlet temperature and turbulence characteristics on the flow development inside a gas turbine exhaust diffuser

NASA Astrophysics Data System (ADS)

Bomela, Christian Loangola

The overall industrial gas turbine efficiency is known to be influenced by the pressure recovery in the exhaust system. The design and, subsequently, the performance of an industrial gas turbine exhaust diffuser largely depend on its inflow conditions dictated by the turbine last stage exit flow state and the restraints of the diffuser internal geometry. Recent advances in Computational Fluid Dynamics (CFD) tools and the availability of computer hardware at an affordable cost made the virtual tool a very attractive one for the analysis of fluid flow through devices like a diffuser. In this backdrop, CFD analyses of a typical industrial gas turbine hybrid exhaust diffuser, consisting of an annular diffuser followed by a conical portion, have been carried out with the purpose of improving the performance of these thermal devices using an open-source CFD code "OpenFOAM". The first phase in the research involved the validation of the CFD approach using OpenFOAM by comparing CFD results against published benchmark experimental data. The numerical results closely captured the flow reversal and the separated boundary layer at the shroud wall where a steep velocity gradient has been observed. The standard k --epsilon turbulence model slightly over-predicted the mean velocity profile in the casing boundary layer while slightly under-predicted it in the reversed flow region. A reliable prediction of flow characteristics in this region is very important as the presence of the annular diffuser inclined wall has the most dominant effect on the downstream flow development. The core flow region and the presence of the hub wall have only a minor influence as reported by earlier experimental studies. Additional simulations were carried out in the second phase to test the veracity of other turbulence models; these include RNG k--epsilon, the SST k--o, and the Spalart-Allmaras turbulence models. It was found that a high resolution case with 47.5 million cells using the SST k--o turbulence model produced a mean flow velocity profile at the middle of the annular diffuser portion that had the best overall match with the experiment. The RNG k --epsilon, however, better predicted the diffuser performance along the exhaust diffuser length by means of the pressure recovery coefficient. These results were obtained using uniform inflow conditions and steady-state simulations. As such, the last phase of our investigations involved varying the inflow parameters like the turbulence intensity, the inlet flow temperature, and the flow angularity, which constitute important characteristics of the turbine blade wake, to investigate their impact on the diffuser design and performance. These isothermal CFD simulations revealed that by changing the flow temperature from 15 to 427°C, the pressure recovery coefficient significantly increased. However, it has been shown that the increase of temperature had no effects on the size of the reversed flow region and the thickness of the separated casing boundary layer, although the flow appears to be more turbulent. Furthermore, it has been established that an optimum turbulence intensity of about 4% produced comparable diffuser performance as the experiment. We also found that a velocity angle of about 2.5° at the last turbine stage will ensure a better exhaust diffuser performance.

The thickness effect of pre-deposited catalyst film on carbon nanotube growth by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wei, Y. Y.; Eres, Gyula; Lowndes, Douglas H.

2001-03-01

Chemical vapor deposition (CVD) of multi wall carbon nanotubes (MWCNTs) was realized on a substrate with a layer of iron film used as a catalyst. The catalyst film was pre-deposited in an electron-gun evaporator equipped with a movable shutter which partially blocks the beam during the evaporation process to produce a catalyst film with a continuously changing thickness from 0 to 60 nm. This technique creates a growth environment in which the film thickness is the only variable and eliminates sample-to-sample variations, enabling a systematic study of the thickness effect of the catalyst film on CNT growth. After the deposition of the catalyst film, the sample was immediately transferred into a CVD chamber where CNT growth was performed. Using Acetylene (C_2H_2) as a carbon-source gas, at the substrate temperature of around 700^oC, MWCNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature from 640^oC to 800^oC. There appears to be no strong correlation between the film thickness and the diameter of the tubes. At the substrate temperature of over 900^oC, the deposited carbon formed graphite sheets surrounding the catalyst particles and no CNTs were observed. A plot of the critical thickness of the catalyst film where CNTs start to grow as a function of the substrate temperature has obtained, which can be served as a reference for selecting the growth parameter in MWCNT growth. The significance of these experimental trends is discussed within the framework of the diffusion model for MWCNT growth.

Interior radiances in optically deep absorbing media. 3: Scattering from Haze L

NASA Technical Reports Server (NTRS)

Kattawar, G. W.; Plass, G. N.

1974-01-01

The interior radiances are calculated within an optically deep absorbing medium scattering according to the Haze L phase function. The dependence on the solar zenith angle, the single scattering albedo, and the optical depth within the medium is calculated by the matrix operator method. The development of the asymptotic angular distribution of the radiance in the diffusion region is illustrated through a number of examples; it depends only on the single scattering albedo and on the phase function for single scattering. The exact values of the radiance in the diffusion region are compared with values calculated from the approximate equations proposed by Van de Hulst. The variation of the radiance near the lower boundary of an optically thick medium is illustrated with examples. The attenuation length is calculated for various single scattering albedos and compared with the corresponding values for Rayleigh scattering. The ratio of the upward to the downward flux is found to be remarkably constant within the medium. The heating rate is calculated and found to have a maximum value at an optical depth of two within a Haze L layer when the sun is at the zenith.

Airfoil for a turbine of a gas turbine engine

DOEpatents

Liang, George

2010-12-21

An airfoil for a turbine of a gas turbine engine is provided. The airfoil comprises a main body comprising a wall structure defining an inner cavity adapted to receive a cooling air. The wall structure includes a first diffusion region and at least one first metering opening extending from the inner cavity to the first diffusion region. The wall structure further comprises at least one cooling circuit comprising a second diffusion region and at least one second metering opening extending from the first diffusion region to the second diffusion region. The at least one cooling circuit may further comprise at least one third metering opening, at least one third diffusion region and a fourth diffusion region.

Comparison with CLPX II airborne data using DMRT model

USGS Publications Warehouse

Xu, X.; Liang, D.; Andreadis, K.M.; Tsang, L.; Josberger, E.G.

2009-01-01

In this paper, we considered a physical-based model which use numerical solution of Maxwell Equations in three-dimensional simulations and apply into Dense Media Radiative Theory (DMRT). The model is validated in two specific dataset from the second Cold Land Processes Experiment (CLPX II) at Alaska and Colorado. The data were all obtain by the Ku-band (13.95GHz) observations using airborne imaging polarimetric scatterometer (POLSCAT). Snow is a densely packed media. To take into account the collective scattering and incoherent scattering, analytical Quasi-Crystalline Approximation (QCA) and Numerical Maxwell Equation Method of 3-D simulation (NMM3D) are used to calculate the extinction coefficient and phase matrix. DMRT equations were solved by iterative solution up to 2nd order for the case of small optical thickness and full multiple scattering solution by decomposing the diffuse intensities into Fourier series was used when optical thickness exceed unity. It was shown that the model predictions agree with the field experiment not only co-polarization but also cross-polarization. For Alaska region, the input snow structure data was obtain by the in situ ground observations, while for Colorado region, we combined the VIC model to get the snow profile. ??2009 IEEE.

Quantitative diffusion and swelling kinetic measurements using large-angle interferometric refractometry.

PubMed

Saunders, John E; Chen, Hao; Brauer, Chris; Clayton, McGregor; Chen, Weijian; Barnes, Jack A; Loock, Hans-Peter

2015-12-07

The uptake and release of sorbates into films and coatings is typically accompanied by changes of the films' refractive index and thickness. We provide a comprehensive model to calculate the concentration of the sorbate from the average refractive index and the film thickness, and validate the model experimentally. The mass fraction of the analyte partitioned into a film is described quantitatively by the Lorentz-Lorenz equation and the Clausius-Mosotti equation. To validate the model, the uptake kinetics of water and other solvents into SU-8 films (d = 40-45 μm) were explored. Large-angle interferometric refractometry measurements can be used to characterize films that are between 15 μm to 150 μm thick and, Fourier analysis, is used to determine independently the thickness, the average refractive index and the refractive index at the film-substrate interface at one-second time intervals. From these values the mass fraction of water in SU-8 was calculated. The kinetics were best described by two independent uptake processes having different rates. Each process followed one-dimensional Fickian diffusion kinetics with diffusion coefficients for water into SU-8 photoresist film of 5.67 × 10(-9) cm(2) s(-1) and 61.2 × 10(-9) cm(2) s(-1).

A Fast Hyperspectral Vector Radiative Transfer Model in UV to IR spectral bands

NASA Astrophysics Data System (ADS)

Ding, J.; Yang, P.; Sun, B.; Kattawar, G. W.; Platnick, S. E.; Meyer, K.; Wang, C.

2016-12-01

We develop a fast hyperspectral vector radiative transfer model with a spectral range from UV to IR with 5 nm resolutions. This model can simulate top of the atmosphere (TOA) diffuse radiance and polarized reflectance by considering gas absorption, Rayleigh scattering, and aerosol and cloud scattering. The absorption component considers several major atmospheric absorbers such as water vapor, CO2, O3, and O2 including both line and continuum absorptions. A regression-based method is used to parameterize the layer effective optical thickness for each gas, which substantially increases the computation efficiency for absorption while maintaining high accuracy. This method is over 500 times faster than the existing line-by-line method. The scattering component uses the successive order of scattering (SOS) method. For Rayleigh scattering, convergence is fast due to the small optical thickness of atmospheric gases. For cloud and aerosol layers, a small-angle approximation method is used in SOS calculations. The scattering process is divided into two parts, a forward part and a diffuse part. The scattering in the small-angle range in the forward direction is approximated as forward scattering. A cloud or aerosol layer is divided into thin layers. As the ray propagates through each thin layer, a portion diverges as diffuse radiation, while the remainder continues propagating in forward direction. The computed diffuse radiance is the sum of all of the diffuse parts. The small-angle approximation makes the SOS calculation converge rapidly even in a thick cloud layer.

Radiative transfer model of snow for bare ice regions

NASA Astrophysics Data System (ADS)

Tanikawa, T.; Aoki, T.; Niwano, M.; Hosaka, M.; Shimada, R.; Hori, M.; Yamaguchi, S.

2016-12-01

Modeling a radiative transfer (RT) for coupled atmosphere-snow-bare ice systems is of fundamental importance for remote sensing applications to monitor snow and bare ice regions in the Greenland ice sheet and for accurate climate change predictions by regional and global climate models. Recently, the RT model for atmosphere-snow system was implemented for our regional and global climate models. However, the bare ice region where recently it has been expanded on the Greenland ice sheet due to the global warming, has not been implemented for these models, implying that this region leads miscalculations in these climate models. Thus, the RT model of snow for bare ice regions is needed for accurate climate change predictions. We developed the RT model for coupled atmosphere-snow-bare ice systems, and conducted a sensitivity analysis of the RT model to know the effect of snow, bare ice and geometry parameters on the spectral radiant quantities. The RT model considers snow and bare-ice inherent optical properties (IOPs), including snow grain size, air bubble size and its concentration and bare ice thickness. The conventional light scattering theory, Mie theory, was used for IOP calculations. Monte Carlo method was used for the multiple scattering. The sensitivity analyses showed that spectral albedo for the bare ice increased with increasing the concentration of the air bubble in the bare ice for visible wavelengths because the air bubble is scatterer with no absorption. For near infrared wavelengths, spectral albedo has no dependence on the air bubble due to the strong light absorption by ice. When increasing solar zenith angle, the spectral albedo were increased for all wavelengths. This is the similar trend with spectral snow albedo. Cloud cover influenced the bare ice spectral albedo by covering direct radiation into diffuse radiation. The purely diffuse radiation has an effective solar zenith angle near 50°. Converting direct into diffuse radiation reduces the effective solar zenith angle, resulting in reducing the spectral albedo. This is also the similar trend with spectral snow albedo. Further work should focus on the validation of the RT model using in situ measurement data through field and laboratory experiments.

Lagrangian statistics across the turbulent-nonturbulent interface in a turbulent plane jet.

PubMed

Taveira, Rodrigo R; Diogo, José S; Lopes, Diogo C; da Silva, Carlos B

2013-10-01

Lagrangian statistics from millions of particles are used to study the turbulent entrainment mechanism in a direct numerical simulation of a turbulent plane jet at Re(λ) ≈ 110. The particles (tracers) are initially seeded at the irrotational region of the jet near the turbulent shear layer and are followed as they are drawn into the turbulent region across the turbulent-nonturbulent interface (TNTI), allowing the study of the enstrophy buildup and thereby characterizing the turbulent entrainment mechanism in the jet. The use of Lagrangian statistics following fluid particles gives a more correct description of the entrainment mechanism than in previous works since the statistics in relation to the TNTI position involve data from the trajectories of the entraining fluid particles. The Lagrangian statistics for the particles show the existence of a velocity jump and a characteristic vorticity jump (with a thickness which is one order of magnitude greater than the Kolmogorov microscale), in agreement with previous results using Eulerian statistics. The particles initially acquire enstrophy by viscous diffusion and later by enstrophy production, which becomes "active" only deep inside the turbulent region. Both enstrophy diffusion and production near the TNTI differ substantially from inside the turbulent region. Only about 1% of all particles find their way into pockets of irrotational flow engulfed into the turbulent shear layer region, indicating that "engulfment" is not significant for the present flow, indirectly suggesting that the entrainment is largely due to "nibbling" small-scale mechanisms acting along the entire TNTI surface. Probability density functions of particle positions suggests that the particles spend more time crossing the region near the TNTI than traveling inside the turbulent region, consistent with the particles moving tangent to the interface around the time they cross it.

The influence of radiation-induced vacancy on the formation of thin-film of compound layer during a reactive diffusion process

NASA Astrophysics Data System (ADS)

Akintunde, S. O.; Selyshchev, P. A.

2016-05-01

A theoretical approach is developed that describes the formation of a thin-film of AB-compound layer under the influence of radiation-induced vacancy. The AB-compound layer is formed as a result of a chemical reaction between the atomic species of A and B immiscible layers. The two layers are irradiated with a beam of energetic particles and this process leads to several vacant lattice sites creation in both layers due to the displacement of lattice atoms by irradiating particles. A- and B-atoms diffuse via these lattice sites by means of a vacancy mechanism in considerable amount to reaction interfaces A/AB and AB/B. The reaction interfaces increase in thickness as a result of chemical transformation between the diffusing species and surface atoms (near both layers). The compound layer formation occurs in two stages. The first stage begins as an interfacial reaction controlled process, and the second as a diffusion controlled process. The critical thickness and time are determined at a transition point between the two stages. The influence of radiation-induced vacancy on layer thickness, speed of growth, and reaction rate is investigated under irradiation within the framework of the model presented here. The result obtained shows that the layer thickness, speed of growth, and reaction rate increase strongly as the defect generation rate rises in the irradiated layers. It also shows the feasibility of producing a compound layer (especially in near-noble metal silicide considered in this study) at a temperature below their normal formation temperature under the influence of radiation.

18O-tracer diffusion along nanoscaled Sc2O3/yttria stabilized zirconia (YSZ) multilayers: on the influence of strain.

PubMed

Aydin, Halit; Korte, Carsten; Janek, Jürgen

2013-06-01

The oxygen tracer diffusion coefficient describing transport along nano-/microscaled YSZ/Sc 2 O 3 multilayers as a function of the thick-ness of the ion-conducting YSZ layers has been measured by isotope exchange depth profiling (IEDP), using secondary ion mass spec-trometry (SIMS). The multilayer samples were prepared by pulsed laser deposition (PLD) on (0001) Al 2 O 3 single crystalline substrates. The values for the oxygen tracer diffusion coefficient were analyzed as a combination of contributions from bulk and interface contributions and compared with results from YSZ/Y 2 O 3 -multilayers with similar microstructure. Using the Nernst-Einstein equation as the relation between diffusivity and electrical conductivity we find very good agreement between conductivity and diffusion data, and we exclude substantial electronic conductivity in the multilayers. The effect of hetero-interface transport can be well explained by a simple interface strain model. As the multilayer samples consist of columnar film crystallites with a defined inter-face structure and texture, we also discuss the influence of this particular microstructure on the interfacial strain.

Cu-Zn binary phase diagram and diffusion couples

NASA Technical Reports Server (NTRS)

Mccoy, Robert A.

1992-01-01

The objectives of this paper are to learn: (1) what information a binary phase diagram can yield; (2) how to construct and heat treat a simple diffusion couple; (3) how to prepare a metallographic sample; (4) how to operate a metallograph; (5) how to correlate phases found in the diffusion couple with phases predicted by the phase diagram; (6) how diffusion couples held at various temperatures could be used to construct a phase diagram; (7) the relation between the thickness of an intermetallic phase layer and the diffusion time; and (8) the effect of one species of atoms diffusing faster than another species in a diffusion couple.

Diffusion of Sites versus Polymers in Polyelectrolyte Complexes and Multilayers.

PubMed

Fares, Hadi M; Schlenoff, Joseph B

2017-10-18

It has long been assumed that the spontaneous formation of materials such as complexes and multilayers from charged polymers depends on (inter)diffusion of these polyelectrolytes. Here, we separately examine the mass transport of polymer molecules and extrinsic sites-charged polyelectrolyte repeat units balanced by counterions-within thin films of polyelectrolyte complex, PEC, using sensitive isotopic labeling techniques. The apparent diffusion coefficients of these sites within PEC films of poly(diallyldimethylammonium), PDADMA, and poly(styrenesulfonate), PSS, are at least 2 orders of magnitude faster than the diffusion of polyelectrolytes themselves. This is because site diffusion requires only local rearrangements of polyelectrolyte repeat units, placing far fewer kinetic limitations on the assembly of polyelectrolyte complexes in all of their forms. Site diffusion strongly depends on the salt concentration (ionic strength) of the environment, and diffusion of PDADMA sites is faster than that of PSS sites, accounting for the asymmetric nature of multilayer growth. Site diffusion is responsible for multilayer growth in the linear and into the exponential regimes, which explains how PDADMA can mysteriously "pass through" layers of PSS. Using quantitative relationships between site diffusion coefficient and salt concentration, conditions were identified that allowed the diffusion length to always exceed the film thickness, leading to full exponential growth over 3 orders of magnitude thickness. Both site and polymer diffusion were independent of molecular weight, suggesting that ion pairing density is a limiting factor. Polyelectrolyte complexes are examples of a broader class of dynamic bulk polymeric materials that (self-) assemble via the transport of cross-links or defects rather than actual molecules.

Multiple modality biomarker prediction of cognitive impairment in prospectively followed de novo Parkinson disease

PubMed Central

Caspell-Garcia, Chelsea; Simuni, Tanya; Tosun-Turgut, Duygu; Wu, I-Wei; Zhang, Yu; Nalls, Mike; Singleton, Andrew; Shaw, Leslie A.; Kang, Ju-Hee; Trojanowski, John Q.; Siderowf, Andrew; Coffey, Christopher; Lasch, Shirley; Aarsland, Dag; Burn, David; Chahine, Lana M.; Espay, Alberto J.; Foster, Eric D.; Hawkins, Keith A.; Litvan, Irene; Richard, Irene; Weintraub, Daniel

2017-01-01

Objectives To assess the neurobiological substrate of initial cognitive decline in Parkinson’s disease (PD) to inform patient management, clinical trial design, and development of treatments. Methods We longitudinally assessed, up to 3 years, 423 newly diagnosed patients with idiopathic PD, untreated at baseline, from 33 international movement disorder centers. Study outcomes were four determinations of cognitive impairment or decline, and biomarker predictors were baseline dopamine transporter (DAT) single photon emission computed tomography (SPECT) scan, structural magnetic resonance imaging (MRI; volume and thickness), diffusion tensor imaging (mean diffusivity and fractional anisotropy), cerebrospinal fluid (CSF; amyloid beta [Aβ], tau and alpha synuclein), and 11 single nucleotide polymorphisms (SNPs) previously associated with PD cognition. Additionally, longitudinal structural MRI and DAT scan data were included. Univariate analyses were run initially, with false discovery rate = 0.2, to select biomarker variables for inclusion in multivariable longitudinal mixed-effect models. Results By year 3, cognitive impairment was diagnosed in 15–38% participants depending on the criteria applied. Biomarkers, some longitudinal, predicting cognitive impairment in multivariable models were: (1) dopamine deficiency (decreased caudate and putamen DAT availability); (2) diffuse, cortical decreased brain volume or thickness (frontal, temporal, parietal, and occipital lobe regions); (3) co-morbid Alzheimer’s disease Aβ amyloid pathology (lower CSF Aβ 1–42); and (4) genes (COMT val/val and BDNF val/val genotypes). Conclusions Cognitive impairment in PD increases in frequency 50–200% in the first several years of disease, and is independently predicted by biomarker changes related to nigrostriatal or cortical dopaminergic deficits, global atrophy due to possible widespread effects of neurodegenerative disease, co-morbid Alzheimer’s disease plaque pathology, and genetic factors. PMID:28520803

Thickness limitations in carbon nanotube reinforced silicon nitride coatings synthesized by vapor infiltration

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

Eres, Gyula

Chemical vapor infiltration is a convenient method for synthesizing carbon nanotube (CNT)-reinforced ceramic coatings. The thickness over which infiltration is relatively uniform is limited by gas phase diffusion in the pore structure. These effects were investigated in two types of silicon nitride matrix composites. With CNTs that were distributed uniformly on the substrate surface dense coatings were limited to thicknesses of several microns. With dual structured CNT arrays produced by photolithography coatings up to 400 gm thick were obtained with minimal residual porosity. Gas transport into these dual structured materials was facilitated by creating micron sized channels between "CNT pillars"more » (i.e. each pillar consisted of a large number of individual CNTs). The experimental results are consistent with basic comparisons between the rates of gas diffusion and silicon nitride growth in porous structures. This analysis also provides a general insight into optimizing infiltration conditions during the fabrication of thick CNT-reinforced composite coatings. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.« less

Effect of sample thickness on the extracted near-infrared bulk optical properties of Bacillus subtilis in liquid culture.

PubMed

Dzhongova, Elitsa; Harwood, Colin R; Thennadil, Suresh N

2011-11-01

In order to determine the bulk optical properties of a Bacillus subtilis culture during growth phase we investigated the effect of sample thickness on measurements taken with different measurement configurations, namely total diffuse reflectance and total diffuse transmittance. The bulk optical properties were extracted by inverting the measurements using the radiative transfer theory. While the relationship between reflectance and biomass changes with sample thickness and the intensity (absorbance) levels vary significantly for both reflectance and transmittance measurements, the extracted optical properties show consistent behavior in terms of both the relationship with biomass and magnitude. This observation indicates the potential of bulk optical properties for building models that could be more easily transferable compared to those built using raw measurements.

Analytical Description of Degradation-Relaxation Transformations in Nanoinhomogeneous Spinel Ceramics.

PubMed

Shpotyuk, O; Brunner, M; Hadzaman, I; Balitska, V; Klym, H

2016-12-01

Mathematical models of degradation-relaxation kinetics are considered for jammed thick-film systems composed of screen-printed spinel Cu 0.1 Ni 0.1 Co 1.6 Mn 1.2 O 4 and conductive Ag or Ag-Pd alloys. Structurally intrinsic nanoinhomogeneous ceramics due to Ag and Ag-Pd diffusing agents embedded in a spinel phase environment are shown to define governing kinetics of thermally induced degradation under 170 °C obeying an obvious non-exponential behavior in a negative relative resistance drift. The characteristic stretched-to-compressed exponential crossover is detected for degradation-relaxation kinetics in thick-film systems with conductive contacts made of Ag-Pd and Ag alloys. Under essential migration of a conductive phase, Ag penetrates thick-film spinel ceramics via a considerable two-step diffusing process.

Geochemical impacts of waste disposal on the abyssal seafloor

NASA Astrophysics Data System (ADS)

Jahnke, Richard A.

1998-05-01

The response of pore water oxygen, nitrate, sulfate, sulfide, ammonium and methane and particulate organic carbon distributions to the input of 8.5 million m 3 (3.8×10 12 g) of organic-rich waste materials is simulated. The deposit is assumed to be conical with a maximum thickness of approximately 20 m. Remineralization reactions within the deposit rapidly deplete any initially available pore water oxidants such as oxygen, nitrate and sulfate, and are subsequently dominated by fermentation reactions. Diffusion downward of reduced metabolites, sulfide, ammonium and methane, depletes the available oxidants in the pore waters below the waste pile, increasing the thickness of the anoxic layer. While the impacted region is limited to essentially the deposition site, recovery of the pore waters is estimated to be >10 4 years. The overall computational results are corroborated by the pore water distributions observed at turbidite boundaries. Numerous uncertainties in the parameterizations limit the overall accuracy of the calculations presented. The most significant of these are: (1) A quantitatively accurate assessment of the remineralization rate of the deposited organic matter including its rate of inoculation by abyssal microorganisms; (2) a detailed assessment of potential non-diffusive pore water transport processes including advection due to compaction and buoyancy-driven flows and enhanced exchange due to macrobenthic irrigation activities and (3) an assessment of the potential alteration of pore space and methane reactivity due to gas hydrate formation.

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

NASA Astrophysics Data System (ADS)

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

2006-08-01

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

Experimental analysis of two-layered dissimilar metals by roll bonding

NASA Astrophysics Data System (ADS)

Zhao, Guanghui; Li, Yugui; Li, Juan; Huang, Qingxue; Ma, Lifeng

2018-02-01

Rolling reduction and base layers thickness have important implications for rolling compounding. A two-layered 304 stainless steel/Q345R low alloyed steel was roll bonded. The roll bonding was performed at the three thickness reductions of 25%, 40% and 55% with base layers of various thicknesses (Q345R). The microstructures of the composite were investigated by the ultra-deep microscope (OM) and scanning electron microscope (SEM) and Transmission electron microscope (TEM). Simultaneously, the mechanical properties of the composite were experimentally measured and the tensile fracture surfaces were observed by SEM. The interfaces were successfully bonded without any cracking or voids, which indicated a good fabrication of the 304/Q345R composite. The rolling reduction rate and thinning increase of the substrate contributed to the bonding effects appearance of the roll bonded sheet. The Cr and Ni enriched diffusion layer was formed by the interface elements diffusion. The Cr and Ni diffusion led to the formation of ˜10 μm wide Cr and Ni layers on the carbon steel side.

Spin-scattering rates in metallic thin films measured by ferromagnetic resonance damping enhanced by spin-pumping

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

Boone, C. T.; Shaw, J. M.; Nembach, H. T.

2015-06-14

We determined the spin-transport properties of Pd and Pt thin films by measuring the increase in ferromagnetic resonance damping due to spin-pumping in ferromagnetic (FM)-nonferromagnetic metal (NM) multilayers with varying NM thicknesses. The increase in damping with NM thickness depends strongly on both the spin- and charge-transport properties of the NM, as modeled by diffusion equations that include both momentum- and spin-scattering parameters. We use the analytical solution to the spin-diffusion equations to obtain spin-diffusion lengths for Pt and Pd. By measuring the dependence of conductivity on NM thickness, we correlate the charge- and spin-transport parameters, and validate the applicabilitymore » of various models for momentum-scattering and spin-scattering rates in these systems: constant, inverse-proportional (Dyakanov-Perel), and linear-proportional (Elliot-Yafet). We confirm previous reports that the spin-scattering time appears to be shorter than the momentum scattering time in Pt, and the Dyakanov-Perel-like model is the best fit to the data.« less

Thermal Transport Characteristics of Human Skin Measured In Vivo Using Ultrathin Conformal Arrays of Thermal Sensors and Actuators

PubMed Central

Webb, R. Chad; Pielak, Rafal M.; Bastien, Philippe; Ayers, Joshua; Niittynen, Juha; Kurniawan, Jonas; Manco, Megan; Lin, Athena; Cho, Nam Heon; Malyrchuk, Viktor; Balooch, Guive; Rogers, John A.

2015-01-01

Measurements of the thermal transport properties of the skin can reveal changes in physical and chemical states of relevance to dermatological health, skin structure and activity, thermoregulation and other aspects of human physiology. Existing methods for in vivo evaluations demand complex systems for laser heating and infrared thermography, or they require rigid, invasive probes; neither can apply to arbitrary regions of the body, offers modes for rapid spatial mapping, or enables continuous monitoring outside of laboratory settings. Here we describe human clinical studies using mechanically soft arrays of thermal actuators and sensors that laminate onto the skin to provide rapid, quantitative in vivo determination of both the thermal conductivity and thermal diffusivity, in a completely non-invasive manner. Comprehensive analysis of measurements on six different body locations of each of twenty-five human subjects reveal systematic variations and directional anisotropies in the characteristics, with correlations to the thicknesses of the epidermis (EP) and stratum corneum (SC) determined by optical coherence tomography, and to the water content assessed by electrical impedance based measurements. Multivariate statistical analysis establishes four distinct locations across the body that exhibit different physical properties: heel, cheek, palm, and wrist/volar forearm/dorsal forearm. The data also demonstrate that thermal transport correlates negatively with SC and EP thickness and positively with water content, with a strength of correlation that varies from region to region, e.g., stronger in the palmar than in the follicular regions. PMID:25658947

Thermal transport characteristics of human skin measured in vivo using ultrathin conformal arrays of thermal sensors and actuators.

PubMed

Webb, R Chad; Pielak, Rafal M; Bastien, Philippe; Ayers, Joshua; Niittynen, Juha; Kurniawan, Jonas; Manco, Megan; Lin, Athena; Cho, Nam Heon; Malyrchuk, Viktor; Balooch, Guive; Rogers, John A

2015-01-01

Measurements of the thermal transport properties of the skin can reveal changes in physical and chemical states of relevance to dermatological health, skin structure and activity, thermoregulation and other aspects of human physiology. Existing methods for in vivo evaluations demand complex systems for laser heating and infrared thermography, or they require rigid, invasive probes; neither can apply to arbitrary regions of the body, offers modes for rapid spatial mapping, or enables continuous monitoring outside of laboratory settings. Here we describe human clinical studies using mechanically soft arrays of thermal actuators and sensors that laminate onto the skin to provide rapid, quantitative in vivo determination of both the thermal conductivity and thermal diffusivity, in a completely non-invasive manner. Comprehensive analysis of measurements on six different body locations of each of twenty-five human subjects reveal systematic variations and directional anisotropies in the characteristics, with correlations to the thicknesses of the epidermis (EP) and stratum corneum (SC) determined by optical coherence tomography, and to the water content assessed by electrical impedance based measurements. Multivariate statistical analysis establishes four distinct locations across the body that exhibit different physical properties: heel, cheek, palm, and wrist/volar forearm/dorsal forearm. The data also demonstrate that thermal transport correlates negatively with SC and EP thickness and positively with water content, with a strength of correlation that varies from region to region, e.g., stronger in the palmar than in the follicular regions.

A Numerical Method for Obtaining Monoenergetic Neutron Flux Distributions and Transmissions in Multiple-Region Slabs

NASA Technical Reports Server (NTRS)

Schneider, Harold

1959-01-01

This method is investigated for semi-infinite multiple-slab configurations of arbitrary width, composition, and source distribution. Isotropic scattering in the laboratory system is assumed. Isotropic scattering implies that the fraction of neutrons scattered in the i(sup th) volume element or subregion that will make their next collision in the j(sup th) volume element or subregion is the same for all collisions. These so-called "transfer probabilities" between subregions are calculated and used to obtain successive-collision densities from which the flux and transmission probabilities directly follow. For a thick slab with little or no absorption, a successive-collisions technique proves impractical because an unreasonably large number of collisions must be followed in order to obtain the flux. Here the appropriate integral equation is converted into a set of linear simultaneous algebraic equations that are solved for the average total flux in each subregion. When ordinary diffusion theory applies with satisfactory precision in a portion of the multiple-slab configuration, the problem is solved by ordinary diffusion theory, but the flux is plotted only in the region of validity. The angular distribution of neutrons entering the remaining portion is determined from the known diffusion flux and the remaining region is solved by higher order theory. Several procedures for applying the numerical method are presented and discussed. To illustrate the calculational procedure, a symmetrical slab ia vacuum is worked by the numerical, Monte Carlo, and P(sub 3) spherical harmonics methods. In addition, an unsymmetrical double-slab problem is solved by the numerical and Monte Carlo methods. The numerical approach proved faster and more accurate in these examples. Adaptation of the method to anisotropic scattering in slabs is indicated, although no example is included in this paper.

H ATOM IRRADIATION OF CARBON GRAINS UNDER SIMULATED DENSE INTERSTELLAR MEDIUM CONDITIONS: THE EVOLUTION OF ORGANICS FROM DIFFUSE INTERSTELLAR CLOUDS TO THE SOLAR SYSTEM

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

Mennella, Vito, E-mail: mennella@na.astro.i

2010-08-01

We present the results of experiments aimed at studying the interaction of hydrogen atoms at 80 K with carbon grains covered with a water ice layer at 12 K. The effects of H processing have been analyzed, using IR spectroscopy, as a function of the water ice layer. The results confirm that exposure of the samples to H atoms induces the activation of the band at 3.47 {mu}m with no evidence for the formation of aromatic and aliphatic C-H bonds in the CH{sub 2} and CH{sub 3} functional groups. The formation cross section of the 3.47 {mu}m band has beenmore » estimated from the increase of its integrated optical depth as a function of the H atom fluence. The cross section decreases with increasing thickness of the water ice layer, indicating an increase of adsorption of H atoms in the water ice layer. A penetration depth of 100 nm has been estimated for H atoms in the porous water ice covering carbon grains. Sample warm-up at room temperature causes the activation of the IR features due to the vibrations of the CH{sub 2} and CH{sub 3} aliphatic functional groups. The evolution of the 3.47 {mu}m band carrier has been evaluated for dense and diffuse interstellar clouds, using the estimated formation cross section and assuming that the destruction cross section by energetic processing is the same as that derived for the 3.4 {mu}m band. In both environments, the presence of the 3.47 {mu}m band carrier is compatible with the evolutionary timescale limit imposed by fast cycling of materials between dense and diffuse regions of the interstellar medium. In diffuse regions the formation of the CH{sub 2} and CH{sub 3} aliphatic bands, inhibited in dense regions, takes place, masking the 3.47 {mu}m band. The activation of the CH{sub 2} and CH{sub 3} aliphatic vibrational modes at the end of H processing after sample warm-up represents the first experimental evidence supporting an evolutionary connection between the interstellar carbon grain population, which is responsible for the 3.4 {mu}m band (diffuse regions) and contributes to the absorption at 3.47 {mu}m (dense regions), and the organics observed in interplanetary dust particles and cometary Stardust grains.« less

Phototransformation rate constants of PAHs associated with soot particles.

PubMed

Kim, Daekyun; Young, Thomas M; Anastasio, Cort

2013-01-15

Photodegradation is a key process governing the residence time and fate of polycyclic aromatic hydrocarbons (PAHs) in particles, both in the atmosphere and after deposition. We have measured photodegradation rate constants of PAHs in bulk deposits of soot particles illuminated with simulated sunlight. The photodegradation rate constants at the surface (k(p)(0)), the effective diffusion coefficients (D(eff)), and the light penetration depths (z(0.5)) for PAHs on soot layers of variable thickness were determined by fitting experimental data with a model of coupled photolysis and diffusion. The overall disappearance rates of irradiated low molecular weight PAHs (with 2-3 rings) on soot particles were influenced by fast photodegradation and fast diffusion kinetics, while those of high molecular weight PAHs (with 4 or more rings) were apparently controlled by either the combination of slow photodegradation and slow diffusion kinetics or by very slow diffusion kinetics alone. The value of z(0.5) is more sensitive to the soot layer thickness than the k(p)(0) value. As the thickness of the soot layer increases, the z(0.5) values increase, but the k(p)(0) values are almost constant. The effective diffusion coefficients calculated from dark experiments are generally higher than those from the model fitting method for illumination experiments. Due to the correlation between k(p)(0) and z(0.5) in thinner layers, D(eff) should be estimated by an independent method for better accuracy. Despite some limitations of the model used in this study, the fitted parameters were useful for describing empirical results of photodegradation of soot-associated PAHs. Copyright © 2012 Elsevier B.V. All rights reserved.

Detailed magnetic resonance imaging features of a case series of primary gliosarcoma.

PubMed

Sampaio, Luísa; Linhares, Paulo; Fonseca, José

2017-12-01

Objective We aimed to characterise the magnetic resonance imaging (MRI) features of a case series of primary gliosarcoma, with the inclusion of diffusion-weighted imaging and perfusion imaging with dynamic susceptibility contrast MRI. Materials and methods We conducted a retrospective study of cases of primary gliosarcoma from the Pathology Department database from January 2006 to December 2014. Clinical and demographic data were obtained. Two neuroradiologists, blinded to diagnosis, assessed tumour location, signal intensity in T1 and T2-weighted images, pattern of enhancement, diffusion-weighted imaging and dynamic susceptibility contrast MRI studies on preoperative MRI. Results Seventeen patients with primary gliosarcomas had preoperative MRI study: seven men and 10 women, with a mean age of 59 years (range 27-74). All lesions were well demarcated, supratentorial and solitary (frontal n = 5, temporal n = 4, parietal n = 3); 13 tumours abutted the dural surface (8/13 with dural enhancement); T1 and T2-weighted imaging patterns were heterogeneous and the majority of lesions (12/17) showed a rim-like enhancement pattern with focal nodularities/irregular thickness. Restricted diffusion (mean apparent diffusion coefficient values 0.64 × 10 -3 mm 2 /s) in the more solid/thick components was present in eight out of 11 patients with diffusion-weighted imaging study. Dynamic susceptibility contrast MRI study ( n = 8) consistently showed hyperperfusion in non-necrotic/cystic components on relative cerebral volume maps. Conclusions The main distinguishing features of primary gliosarcoma are supratentorial and peripheral location, well-defined boundaries and a rim-like pattern of enhancement with an irregular thick wall. Diffusion-weighted imaging and relative cerebral volume map analysis paralleled primary gliosarcoma with high-grade gliomas, thus proving helpful in differential diagnosis.

Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS

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

Nole, Michael; Daigle, Hugh; Cook, Ann E.

The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1 to 20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two- dimensional and basin-scalemore » three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.« less

Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS

DOE PAGES

Nole, Michael; Daigle, Hugh; Cook, Ann E.; ...

2017-02-01

The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1 to 20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two- dimensional and basin-scalemore » three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.« less

Development of processing procedures for advanced silicon solar cells. [antireflection coatings and short circuit currents

NASA Technical Reports Server (NTRS)

Scott-Monck, J. A.; Stella, P. M.; Avery, J. E.

1975-01-01

Ten ohm-cm silicon solar cells, 0.2 mm thick, were produced with short circuit current efficiencies up to thirteen percent and using a combination of recent technical advances. The cells were fabricated in conventional and wraparound contact configurations. Improvement in cell collection efficiency from both the short and long wavelengths region of the solar spectrum was obtained by coupling a shallow junction and an optically transparent antireflection coating with back surface field technology. Both boron diffusion and aluminum alloying techniques were evaluated for forming back surface field cells. The latter method is less complicated and is compatible with wraparound cell processing.

Coordination of Leaf Photosynthesis, Transpiration, and Structural Traits in Rice and Wild Relatives (Genus Oryza).

PubMed

Giuliani, Rita; Koteyeva, Nuria; Voznesenskaya, Elena; Evans, Marc A; Cousins, Asaph B; Edwards, Gerald E

2013-07-01

The genus Oryza, which includes rice (Oryza sativa and Oryza glaberrima) and wild relatives, is a useful genus to study leaf properties in order to identify structural features that control CO(2) access to chloroplasts, photosynthesis, water use efficiency, and drought tolerance. Traits, 26 structural and 17 functional, associated with photosynthesis and transpiration were quantified on 24 accessions (representatives of 17 species and eight genomes). Hypotheses of associations within, and between, structure, photosynthesis, and transpiration were tested. Two main clusters of positively interrelated leaf traits were identified: in the first cluster were structural features, leaf thickness (Thick(leaf)), mesophyll (M) cell surface area exposed to intercellular air space per unit of leaf surface area (S(mes)), and M cell size; a second group included functional traits, net photosynthetic rate, transpiration rate, M conductance to CO(2) diffusion (g(m)), stomatal conductance to gas diffusion (g(s)), and the g(m)/g(s) ratio.While net photosynthetic rate was positively correlated with gm, neither was significantly linked with any individual structural traits. The results suggest that changes in gm depend on covariations of multiple leaf (S(mes)) and M cell (including cell wall thickness) structural traits. There was an inverse relationship between Thick(leaf) and transpiration rate and a significant positive association between Thick(leaf) and leaf transpiration efficiency. Interestingly, high g(m) together with high g(m)/g(s) and a low S(mes)/g(m) ratio (M resistance to CO(2) diffusion per unit of cell surface area exposed to intercellular air space) appear to be ideal for supporting leaf photosynthesis while preserving water; in addition, thick M cell walls may be beneficial for plant drought tolerance.

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.

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

PubMed

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

2007-05-01

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

Flash Diffusivity Technique Applied to Individual Fibers

NASA Technical Reports Server (NTRS)

Mayeaux, Brian; Yowell, Leonard; Wang, Hsin

2007-01-01

A variant of the flash diffusivity technique has been devised for determining the thermal diffusivities, and thus the thermal conductivities, of individual aligned fibers. The technique is intended especially for application to nanocomposite fibers, made from narrower fibers of polyphenylene benzobisthiazole (PBZT) and carbon nanotubes. These highly aligned nanocomposite fibers could exploit the high thermal conductivities of carbon nanotubes for thermal-management applications. In the flash diffusivity technique as practiced heretofore, one or more heat pulse(s) is (are) applied to the front face of a plate or disk material specimen and the resulting time-varying temperature on the rear face is measured. Usually, the heat pulse is generated by use of a xenon flash lamp, and the variation of temperature on the rear face is measured by use of an infrared detector. The flash energy is made large enough to produce a usefully high temperature rise on the rear face, but not so large as to significantly alter the specimen material. Once the measurement has been completed, the thermal diffusivity of the specimen is computed from the thickness of the specimen and the time dependence of the temperature variation on the rear face. Heretofore, the infrared detector used in the flash diffusivity technique has been a single-point detector, which responds to a spatial average of the thermal radiation from the rear specimen surface. Such a detector cannot distinguish among regions of differing diffusivity within the specimen. Moreover, two basic assumptions of the thermaldiffusivity technique as practiced heretofore are that the specimen is homogeneous and that heat flows one-dimensionally from the front to the rear face. These assumptions are not valid for an inhomogeneous (composite) material.

Comment on: Diffusion through a slab

NASA Astrophysics Data System (ADS)

Gieseler, U. D. J.; Kirk, J. G.

1997-05-01

Mahan [J. Math. Phys. 36, 6758 (1995)] has calculated the transmission coefficient and angular distribution of particles which enter a thick slab at normal incidence and which diffuse in the slab with linear anisotropic, non-absorbing, scattering. Using orthogonality relations derived by McCormick and Kuščer [J. Math. Phys. 6, 1939 (1965); 7, 2036 (1966)] for the eigenfunctions of the problem, this calculation is generalized to a boundary condition with particle input at arbitrary angles. It is also shown how to use the orthogonality relations to relax in a simple way the restriction to a thick slab.

Refractive-index profile and physical process determination in thick gratings in electrooptic crystals

NASA Technical Reports Server (NTRS)

Su, S. F.; Gaylord, T. K.

1976-01-01

A method for determining the refractive index profile of thick phase gratings in linear electrooptic crystals is presented. This method also determines the effective photovoltaic electric field and the relative contributions of diffusion and drift during hologram recording. The method requires only a knowledge of the modulation ratio during hologram recording and the fundamental and the higher-order diffraction efficiencies of the grating. As an illustration of the method, the refractive index profile, the effective photovoltaic field, and the relative contributions of diffusion and drift are determined from experimental measurements for a lithium niobate holographic grating.

Imaging Effects of Neurotrophic Factor Genes on Brain Plasticity and Repair in Multiple Sclerosis

DTIC Science & Technology

2010-07-01

cortical thickness and subcortical volume measures, lesion volumetry , and voxel-based morphometry and diffusion imaging. We are continuing to...th ickness and subcortical volume measures, lesion volumetry , and voxel-based morphometry and diffusion imaging. Regressio n and symbolic modeling

The spectral energy distribution of the scattered light from dark clouds

NASA Technical Reports Server (NTRS)

Mattila, Kalevi; Schnur, G. F. O.

1989-01-01

A dark cloud is exposed to the ambient radiation field of integrated starlight in the Galaxy. Scattering of starlight by the dust particles gives rise to a diffuse surface brightness of the dark nebula. The intensity and the spectrum of this diffuse radiation can be used to investigate, e.g., the scattering parameters of the dust, the optical thickness of the cloud, and as a probe of the ambient radiation field at the location of the cloud. An understanding of the scattering process is also a prerequisite for the isolation of broad spectral features due to fluorescence or to any other non-scattering origin of the diffuse light. Model calculations are presented for multiple scattering in a spherical cloud. These calculations show that the different spectral shapes of the observed diffuse light can be reproduced with standard dust parameters. The possibility to use the observed spectrum as a diagnostic tool for analyzing the thickness of the cloud and the dust particle is discussed.

Numerical Analysis of Transient Temperature Response of Soap Film

NASA Astrophysics Data System (ADS)

Tanaka, Seiichi; Tatesaku, Akihiro; Dantsuka, Yuki; Fujiwara, Seiji; Kunimine, Kanji

2015-11-01

Measurements of thermophysical properties of thin liquid films are important to understand interfacial phenomena due to film structures composed of amphiphilic molecules in soap film, phospholipid bilayer of biological cell and emulsion. A transient hot-wire technique for liquid films less than 1 \\upmu m thick such as soap film has been proposed to measure the thermal conductivity and diffusivity simultaneously. Two-dimensional heat conduction equations for a solid cylinder with a liquid film have been solved numerically. The temperature of a thin wire with liquid film increases steeply with its own heat generation. The feasibility of this technique is verified through numerical experiments for various thermal conductivities, diffusivities, and film thicknesses. Calculated results indicate that the increase in the volumetric average temperature of the thin wire sufficiently varies with the change of thermal conductivity and diffusivity of the soap film. Therefore, the temperature characteristics could be utilized to evaluate both the thermal conductivity and diffusivity using the Gauss-Newton method.

VALIDATION OF THE CORONAL THICK TARGET SOURCE MODEL

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

Fleishman, Gregory D.; Xu, Yan; Nita, Gelu N.

2016-01-10

We present detailed 3D modeling of a dense, coronal thick-target X-ray flare using the GX Simulator tool, photospheric magnetic measurements, and microwave imaging and spectroscopy data. The developed model offers a remarkable agreement between the synthesized and observed spectra and images in both X-ray and microwave domains, which validates the entire model. The flaring loop parameters are chosen to reproduce the emission measure, temperature, and the nonthermal electron distribution at low energies derived from the X-ray spectral fit, while the remaining parameters, unconstrained by the X-ray data, are selected such as to match the microwave images and total power spectra.more » The modeling suggests that the accelerated electrons are trapped in the coronal part of the flaring loop, but away from where the magnetic field is minimal, and, thus, demonstrates that the data are clearly inconsistent with electron magnetic trapping in the weak diffusion regime mediated by the Coulomb collisions. Thus, the modeling supports the interpretation of the coronal thick-target sources as sites of electron acceleration in flares and supplies us with a realistic 3D model with physical parameters of the acceleration region and flaring loop.« less

Grey matter abnormalities in social anxiety disorder: a pilot study.

PubMed

Syal, Supriya; Hattingh, Coenraad J; Fouché, Jean-Paul; Spottiswoode, Bruce; Carey, Paul D; Lochner, Christine; Stein, Dan J

2012-09-01

While a number of studies have explored the functional neuroanatomy of social anxiety disorder (SAD), data on grey matter integrity are lacking. We conducted structural MRI scans to examine the cortical thickness of grey matter in individuals with SAD. 13 unmedicated adult patients with a primary diagnosis of generalized social anxiety disorder and 13 demographically (age, gender and education) matched healthy controls underwent 3T structural magnetic resonance imaging. Cortical thickness and subcortical volumes were estimated using an automated algorithm (Freesurfer Version 4.5). Compared to controls, social anxiety disorder patients showed significant bilateral cortical thinning in the fusiform and post central regions. Additionally, right hemisphere specific thinning was found in the frontal, temporal, parietal and insular cortices of individuals with social anxiety disorder. Although uncorrected cortical grey matter volumes were significantly lower in individuals with SAD, we did not detect volumetric differences in corrected amygdala, hippocampal or cortical grey matter volumes across study groups. Structural differences in grey matter thickness between SAD patients and controls highlight the diffuse neuroanatomical networks involved in both social anxiety and social behavior. Additional work is needed to investigate the causal mechanisms involved in such structural abnormalities in SAD.

Sharp at any Age: Moho boundary thickness estimates along a trans-sect through 2 Ga of tectonic history.

NASA Astrophysics Data System (ADS)

Servali, A.; Levin, V. L.; VanTongeren, J. A.

2015-12-01

In this study we evaluate crustal thickness and Moho sharpness beneath seismic stations in three different tectonic units of the North American continent: the Archean Superior Province, the Proterozoic Grenville Province, and the Paleozoic Appalachian Orogen. Our analysis involves two steps. First, for each site, we produce P-to-S receiver functions (RFs) organized by backazimuth and epicentral distance, and use them to identify the phase most likely representing a conversion from the Moho. Second, we construct averaged RFs for groups of telesismic events located in a similar geographic region, which we employ to examine shapes of Moho P-to-S converted phases in time series with maximum frequencies increasing from 0.25Hz to 2-3 Hz. At some sites we observe a progressive narrowing of a simple Moho converted phase with an increase in frequency, typical of a vertically instantaneous boundary, while at others the converted phase becomes progressively more complex, typical of a diffuse Moho. Thus, we adopt this difference in converted wave shape dependence on increasing frequency as a measure of Moho thickness. Our estimates of Moho thickness range from less than 300 m to over 2 km, with some locations showing evidence for multiple converting boundaries in the 35-50 km depth range. In this study we define "sharp" Moho at those sites where its vertical thickness is less than 1 km. Our results show that sharp Moho is universal in the Archean terranes regardless of surface lithology, likely due to higher Moho temperatures facilitating wide-spread delamination of dense lower crustal rocks. While a sharp Moho is not unique to the Superior Province, all Grenville and Appalachians sites where we find sharp Moho are in regions of granitic plutonism, suggesting a possible general association with reworking and density sorting of the crustal material (e.g. volcanic arc).

On N. Park's Analytical solution for steady state density- and mixing regime—dependent solute transport in a vertical soil column

NASA Astrophysics Data System (ADS)

Thiele, Michael

1998-04-01

Recently, Park [1996] presented an analytical solution for stationary one-dimensional solute transport in a variable-density fluid flow through a vertical soil column. He used the widespread Bear-Scheidegger dispersion model describing solute mixing as a sum of molecular diffusion and velocity-proportional mechanical dispersion effects. His closed-form implicit concentration and pressure distributions thus allow for a discussion of the combined impact of molecular diffusion and mechanical dispersion in a variable-density environment. Whereas Park only considered the example of vanishing molecular diffusion in detail, both phenomena are taken into account simultaneously in the present study in order to elucidate their different influences on concentration distribution characteristics. The boundary value problem dealt with herein is based on an upward inflow of high-density fluid of constant solute concentration and corresponding outflow of a lower constant concentration fluid at the upper end of the column when dispersivity does not change along the flow path. The thickness of the transition zone between the two fluids appeared to strongly depend on the prevailing share of the molecular diffusion and mechanical dispersion mechanisms. The latter can be characterized by a molecular Peclet number Pe, which here is defined as the ratio of the column outflow velocity multiplied by a characteristic pore size and the molecular diffusion coefficient. For very small values of Pe, when molecular diffusion represents the exclusive mixing process, density differences have no impact on transition zone thicknesses. A relative density-;dependent thickness increases with flow velocities (increasing Pe values) very rapidly compared to the density-independent case, and after having passed a maximum decreases asymptotically to a constant value for the large Peclet number limit when mechanical dispersion is the only mixing mechanism. Hence the special transport problem analyzed gives further evidence for the importance of simultaneously considering molecular diffusion and mechanical dispersion in gravity-affected solute transport in porous media.

Simulation of the Impact of Si Shell Thickness on the Performance of Si-Coated Vertically Aligned Carbon Nanofiber as Li-Ion Battery Anode

PubMed Central

Das, Susobhan; Li, Jun; Hui, Rongqing

2015-01-01

Micro- and nano-structured electrodes have the potential to improve the performance of Li-ion batteries by increasing the surface area of the electrode and reducing the diffusion distance required by the charged carriers. We report the numerical simulation of Lithium-ion batteries with the anode made of core-shell heterostructures of silicon-coated carbon nanofibers. We show that the energy capacity can be significantly improved by reducing the thickness of the silicon anode to the dimension comparable or less than the Li-ion diffusion length inside silicon. The results of simulation indicate that the contraction of the silicon electrode thickness during the battery discharge process commonly found in experiments also plays a major role in the increase of the energy capacity. PMID:28347120

Impact of molybdenum out diffusion and interface quality on the performance of sputter grown CZTS based solar cells.

PubMed

Dalapati, Goutam Kumar; Zhuk, Siarhei; Masudy-Panah, Saeid; Kushwaha, Ajay; Seng, Hwee Leng; Chellappan, Vijila; Suresh, Vignesh; Su, Zhenghua; Batabyal, Sudip Kumar; Tan, Cheng Cheh; Guchhait, Asim; Wong, Lydia Helena; Wong, Terence Kin Shun; Tripathy, Sudhiranjan

2017-05-02

We have investigated the impact of Cu 2 ZnSnS 4 -Molybdenum (Mo) interface quality on the performance of sputter-grown Cu 2 ZnSnS 4 (CZTS) solar cell. Thin film CZTS was deposited by sputter deposition technique using stoichiometry quaternary CZTS target. Formation of molybdenum sulphide (MoS x ) interfacial layer is observed in sputter grown CZTS films after sulphurization. Thickness of MoS x layer is found ~142 nm when CZTS layer (550 nm thick) is sulphurized at 600 °C. Thickness of MoS x layer significantly increased to ~240 nm in case of thicker CZTS layer (650 nm) under similar sulphurization condition. We also observe that high temperature (600 °C) annealing suppress the elemental impurities (Cu, Zn, Sn) at interfacial layer. The amount of out-diffused Mo significantly varies with the change in sulphurization temperature. The out-diffused Mo into CZTS layer and reconstructed interfacial layer remarkably decreases series resistance and increases shunt resistance of the solar cell. The overall efficiency of the solar cell is improved by nearly five times when 600 °C sulphurized CZTS layer is applied in place of 500 °C sulphurized layer. Molybdenum and sulphur diffusion reconstruct the interface layer during heat treatment and play the major role in charge carrier dynamics of a photovoltaic device.

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

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

Growth of crack-free GaN films on Si(111) substrate by using Al-rich AlN buffer layer

NASA Astrophysics Data System (ADS)

Lu, Yuan; Cong, Guangwei; Liu, Xianglin; Lu, Da-Cheng; Zhu, Qinsheng; Wang, Xiaohui; Wu, Jiejun; Wang, Zhanguo

2004-11-01

GaN epilayers were grown on Si(111) substrate by metalorganic chemical vapor deposition. By using the Al-rich AlN buffer which contains Al beyond stoichiometry, crack-free GaN epilayers with 1 μm thickness were obtained. Through x-ray diffraction (XRD) and secondary ion mass spectroscopy analyses, it was found that a lot of Al atoms have diffused into the under part of the GaN epilayer from the Al-rich AlN buffer, which results in the formation of an AlxGa1-xN layer at least with 300 nm thickness in the 1 μm thick GaN epilayer. The Al fraction x was estimated by XRD to be about 2.5%. X-ray photoelectron spectroscopy depth analysis was also applied to investigate the stoichiometry in the Al-rich buffer before GaN growth. It is suggested that the underlayer AlxGa1-xN originated from Al diffusion probably provides a compressive stress to the upper part of the GaN epilayer, which counterbalances a part of tensile stress in the GaN epilayer during cooling down and consequently reduces the cracks of the film effectively. The method using the Al diffusion effect to form a thick AlGaN layer is really feasible to achieve the crack-free GaN films and obtain a high crystal quality simultaneously.

Extracting Information about the Electronic Quality of Organic Solar-Cell Absorbers from Fill Factor and Thickness

NASA Astrophysics Data System (ADS)

Kaienburg, Pascal; Rau, Uwe; Kirchartz, Thomas

2016-08-01

Understanding the fill factor in organic solar cells remains challenging due to its complex dependence on a multitude of parameters. By means of drift-diffusion simulations, we thoroughly analyze the fill factor of such low-mobility systems and demonstrate its dependence on a collection coefficient defined in this work. We systematically discuss the effect of different recombination mechanisms, space-charge regions, and contact properties. Based on these findings, we are able to interpret the thickness dependence of the fill factor for different experimental studies from the literature. The presented model provides a facile method to extract the photoactive layer's electronic quality which is of particular importance for the fill factor. We illustrate that over the past 15 years, the electronic quality has not been continuously improved, although organic solar-cell efficiencies increased steadily over the same period of time. Only recent reports show the synthesis of polymers for semiconducting films of high electronic quality that are able to produce new efficiency records.

Flow visualization of discrete hole film cooling for gas turbine applications

NASA Technical Reports Server (NTRS)

Colladay, R. S.; Russell, L. M.

1975-01-01

Film injection from discrete holes in a three row staggered array with 5-diameter spacing is studied for three different hole angles: (1) normal, (2) slanted 30 deg to the surface in the direction of the mainstream, and (3) slanted 30 deg to the surface and 45 deg laterally to the mainstream. The boundary layer thickness-to-hole diameter ratio and Reynolds number are typical of gas turbine film cooling applications. Two different injection locations are studied to evaluate the effect of boundary layer thickness on film penetration and mixing. Detailed streaklines showing the turbulent motion of the injected air are obtained by photographing very small neutrally buoyant helium filled 'soap' bubbles which follow the flow field. Unlike smoke, which diffuses rapidly in the high turbulent mixing region associated with discrete hole blowing, the bubble streaklines passing downstream injection locations are clearly identifiable and can be traced back to their origin. Visualization of surface temperature patterns obtained from infrared photographs of a similar film cooled surface are also included.

Development of a unique laboratory standard: Indium gallium arsenide detector for the 500-1700 nm spectral region

NASA Technical Reports Server (NTRS)

1987-01-01

A planar (5 mm diameter) indium gallium arsenide detector having a high (greater than 50 pct) quantum efficiency from the visible into the infrared spectrum (500 to 1700 nm) was fabricated. Quantum efficiencies as high as 37 pct at 510 nm, 58 pct at 820 nm and 62 pct at 1300 nm and 1550 nm were measured. A planar InP/InGaAs detector structure was also fabricated using vapor phase epitaxy to grow device structures with 0, 0.2, 0.4 and 0.6 micrometer thick InP caps. Quantum efficiency was studied as a function of cap thickness. Conventional detector structures were also used by completely etching off the InP cap after zinc diffusion. Calibrated quantum efficiencies were measured. Best results were obtained with devices whose caps were completely removed by etching. Certain problems still remain with these detectors including non-uniform shunt resistance, reproducibility, contact resistance and narrow band anti-reflection coatings.

Sinusoidal current and stress evolutions in lithium-ion batteries

NASA Astrophysics Data System (ADS)

Yang, Xiao-Guang; Bauer, Christoph; Wang, Chao-Yang

2016-09-01

Mechanical breakdown of graphite materials due to diffusion-induced stress (DIS) is a key aging mechanism of lithium-ion batteries. In this work, electrochemical-thermal coupled model along with a DIS model is developed to study the DIS distribution across the anode thickness. Special attention is paid to the evolution behavior of surface tangential stress (STS) in the discharge process for graphite at different locations of the anode. For the first time, we report that the evolution of STS, as well as local current, at all locations of the anode, evolve like sinusoidal waves in the discharge process with several crests and troughs. The staging behavior of graphite active material, in particular the sharp change of open-circuit potential (OCP) of graphite in the region between two plateaus, is found to be the root cause for the sinusoidal patterns of current and stress evolution. Furthermore, the effects of various parameters, such as starting state of charge, discharge C-rate and electrode thickness on the current and stress evolutions are investigated.

Paper plant effluent revisited-southern Lake Champlain, Vermont and New York

USGS Publications Warehouse

Haupt, R.S.; Folger, D.W.

1993-01-01

We used geologic and geochemical techniques to document the change with time of the distribution and concentration of contaminated bottom sediments in southern Lake Champlain near an International Paper Company plant. Our work, initiated in 1972, was expanded on behalf of Vermont citizens in a class-action suit against the International Paper Company. To update our 1972-1973 results, we collected nine cores in 1988 upstream and downstream from the paper plant effluent diffuser. Water content, volatile solids, organic carbon, and three ratios, Al/Si, Cl/Si, and S/Si, in addition to megascopic and microscopic observations, were evaluated to identify and trace the distribution of effluent and to measure the thickness of sediment affected by or containing components of effluent. Analyses were carried out on samples from the cores as well as from effluent collected directly from the plant's waste treatment facility. In 1973, two years after the plant opened, we cored near the diffuser; sediment contaminated with effluent was 4.5 cm thick. In 1988, in the same area, sediment contaminated with effluent was 17 cm thick. In 15 years, water content increased from 72 to 85 percent, volatile solids from 7 to 20 percent, and organic carbon from 2 to 12 percent. Cl/Si and S/Si were high only near the diffuser and were zero elsewhere. In the area of the diffuser, contaminated sediment appears to be accumulating at a rate of about 1 cm/yr. At a control location 22 km upstream (south) from the plant, the top, poorly consoli-dated layer was only 1 cm or less thick both in 1973 and in 1988. The class-action suit was settled in favor of the plaintiffs for $5 million. ?? 1993 Springer-Verlag.

Ion Diffusion Within Water Films in Unsaturated Porous Media.

PubMed

Tokunaga, Tetsu K; Finsterle, Stefan; Kim, Yongman; Wan, Jiamin; Lanzirotti, Antonio; Newville, Matthew

2017-04-18

Diffusion is important in controlling local solute transport and reactions in unsaturated soils and geologic formations. Although it is commonly assumed that thinning of water films controls solute diffusion at low water contents, transport under these conditions is not well understood. We conducted experiments in quartz sands at low volumetric water contents (θ) to quantify ion diffusion within adsorbed films. At the lowest water contents, we employed fixed relative humidities to control water films at nm thicknesses. Diffusion profiles for Rb + and Br - in unsaturated sand packs were measured with a synchrotron X-ray microprobe, and inverse modeling was used to determine effective diffusion coefficients, D e, as low as ∼9 × 10 -15 m 2 s -1 at θ = 1.0 × 10 -4 m 3 m -3 , where the film thickness = 0.9 nm. Given that the diffusion coefficients (D o ) of Rb + and Br - in bulk water (30 °C) are both ∼2.4 × 10 -9 m 2 s -1 , we found the impedance factor f = D e /(θD o ) is equal to 0.03 ± 0.02 at this very low saturation, in agreement with the predicted influence of interface tortuosity (τ a ) for diffusion along grain surfaces. Thus, reduced cross-sectional area (θ) and tortuosity largely accounted for the more than 5 orders of magnitude decrease in D e relative to D o as desaturation progressed down to nanoscale films.

Textural evidence of microbial activity in seafloor and subseafloor basalt: A comparison

NASA Astrophysics Data System (ADS)

Thorseth, I. H.; Pedersen, R. B.; Christie, D. M.

2003-04-01

SEM observations of alteration rims in basaltic glasses dredged from 0 -- 2.5 Ma seafloor and drilled from 18 -- 28 Ma ocean crust in the Australian-Antarctic Discordance (AAD) document the presence of endolithic microbes in altered basalt glass. In very young AAD lavas ˜10 μm thick alteration rims are developed along intersecting fractures and cracks. The altered glass contains numerous spherical, rod-shaped and star-shaped, partially fossilised microbial cells, similar to those from the Arctic Ridges (Thorseth et al., 2001). In 2.5 Ma basalt glasses, altered rims are up to 250 μm thick and zeolite (phillipsite) is present within the fractures. Spherical cells are observed both in porous zones in the outer part of alteration rims and on zeolite surfaces within central fractures, indicating that microbial activity persist in the region for at least 2.5 Ma. Mn-rich cell-encrustations suggest that Mn is used in an energy yielding metabolic process. Combined with recent results from the Arctic ridges the results from this study demonstrate that endolithic microbial growth is a general feature of mid-ocean spreading ridges. In glasses from ODP cores, ˜1mm thick alteration rims are developed along wide fractures lined with Mn(Fe)-oxyhydroxides and clay and filled by zeolite and calcite. Most common however are <10--200 μm thick rims developed along zeolite filled, more narrow fractures and cracks. Zeolite filled fractures with only minor to no alteration, indicate several episodes of fracturing followed by relatively fast sealing. There is no age progression in alteration thickness along fractures or other characteristics, suggesting that alteration is essentially completed between 2.5 and 18 Ma. A comparison of alteration in the 2.5 Ma glass with that in the ODP samples indicates that a significant part of the altered glass in the drilled samples developed at the surface stage. However, diffuse and highly irregular alteration fronts that are only observed in the ODP samples, most likely developed after burial. These diffuse alteration fronts are caused by partially dissolution and alteration of the glass into minute globules, 0.05 -- 0.2 μm in diameter, with no associated microbial morphologies. Fossilised, Mn-rich cells do occur within zeolite filled fractures, possibly indicating that microbial activity continued in the fractures for as long as circulation continued. The apparent non-biological origin of diffuse, irregular alteration fronts in buried AAD glasses indicates that these textural features are not reliable as diagnostic criteria for the existence of a deep biosphere in the volcanic ocean crust. Reference: Thorseth, I. H., Torsvik, T., Torsvik, V., Daae, F. L., Pedersen, R. B. & Keldysh -- 98 Scientific party (2001). Diversity of life in ocean floor basalt. Earth Planet. Sci. Lett., 194: 31-37.

Cost effective flat plate photovoltaic modules using light trapping

NASA Technical Reports Server (NTRS)

Bain, C. N.; Gordon, B. A.; Knasel, T. M.; Malinowski, R. L.

1981-01-01

Work in optical trapping in 'thick films' is described to form a design guide for photovoltaic engineers. A thick optical film can trap light by diffusive reflection and total internal reflection. Light can be propagated reasonably long distances compared with layer thicknesses by this technique. This makes it possible to conduct light from inter-cell and intra-cell areas now not used in photovoltaic modules onto active cell areas.

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

Gelles, D. S.; Browning, James Frederick; Snow, Clark Sheldon

Er(D,T){sub 2-x} {sup 3}He{sub x}, erbium di-tritide, films of thicknesses 500 nm, 400 nm, 300 nm, 200 nm, and 100 nm were grown and analyzed by Transmission Electron Microscopy, X-Ray Diffraction, and Ion Beam Analysis to determine variations in film microstructure as a function of film thickness and age, due to the time-dependent build-up of {sup 3}He in the film from the radioactive decay of tritium. Several interesting features were observed: One, the amount of helium released as a function of film thickness is relatively constant. This suggests that the helium is being released only from the near surface regionmore » and that the helium is not diffusing to the surface from the bulk of the film. Two, lenticular helium bubbles are observed as a result of the radioactive decay of tritium into {sup 3}He. These bubbles grow along the [111] crystallographic direction. Three, a helium bubble free zone, or 'denuded zone' is observed near the surface. The size of this region is independent of film thickness. Four, an analysis of secondary diffraction spots in the Transmission Electron Microscopy study indicate that small erbium oxide precipitates, 5-10 nm in size, exist throughout the film. Further, all of the films had large erbium oxide inclusions, in many cases these inclusions span the depth of the film.« less

Effect of capping layer on spin-orbit torques

NASA Astrophysics Data System (ADS)

Sun, Chi; Siu, Zhuo Bin; Tan, Seng Ghee; Yang, Hyunsoo; Jalil, Mansoor B. A.

2018-04-01

In order to enhance the magnitude of spin-orbit torque (SOT), considerable experimental works have been devoted to studying the thickness dependence of the different layers in multilayers consisting of heavy metal (HM), ferromagnet (FM), and capping layers. Here, we present a theoretical model based on the spin-drift-diffusion formalism to investigate the effect of the capping layer properties such as its thickness on the SOT observed in experiments. It is found that the spin Hall-induced SOT can be significantly enhanced by incorporating a capping layer with an opposite spin Hall angle to that of the HM layer. The spin Hall torque can be maximized by tuning the capping layer thickness. However, in the absence of the spin Hall effect (SHE) in the capping layer, the torque decreases monotonically with the capping layer thickness. Conversely, the spin Hall torque is found to decrease monotonically with the FM layer thickness, irrespective of the presence or absence of the SHE in the capping layer. All these trends are in correspondence with experimental observations. Finally, our model suggests that capping layers with a long spin diffusion length and high resistivity would also enhance the spin Hall torque.

Measuring joint cartilage thickness using reflectance spectroscopy non-invasively and in real-time

NASA Astrophysics Data System (ADS)

Canpolat, Murat; Denkceken, Tuba; Karagol, Cosar; Aydin, Ahmet T.

2011-03-01

Joint cartilage thickness has been estimated using spatially resolved steady-state reflectance spectroscopy noninvasively and in-real time. The system consists of a miniature UV-VIS spectrometer, a halogen tungsten light source, and an optical fiber probe with six 400 um diameter fibers. The first fiber was used to deliver the light to the cartilage and the other five were used to detect back-reflected diffused light. Distances from the detector fibers to the source fiber were 0.8 mm, 1.6 mm, 2.4 mm, 3.2 mm and 4 mm. Spectra of back-reflected diffused light were taken on 40 bovine patella cartilages. The samples were grouped into four; the first group was the control group with undamaged cartilages, in the 2nd, 3rd and 4th groups cartilage thickness was reduced approximately 25%, 50% and 100%, respectively. A correlation between cartilage thicknesses and hemoglobin absorption of light in the wavelength range of 500 nm- 600 nm for source-detector pairs was found. The proposed system with an optical fiber probe less than 4 mm in diameter has the potential for cartilage thickness assessment through an arthroscopy channel in real-time without damaging the cartilage.

Effects of short-term variability of meteorological variables on soil temperature in permafrost regions

NASA Astrophysics Data System (ADS)

Beer, Christian; Porada, Philipp; Ekici, Altug; Brakebusch, Matthias

2018-03-01

Effects of the short-term temporal variability of meteorological variables on soil temperature in northern high-latitude regions have been investigated. For this, a process-oriented land surface model has been driven using an artificially manipulated climate dataset. Short-term climate variability mainly impacts snow depth, and the thermal diffusivity of lichens and bryophytes. These impacts of climate variability on insulating surface layers together substantially alter the heat exchange between atmosphere and soil. As a result, soil temperature is 0.1 to 0.8 °C higher when climate variability is reduced. Earth system models project warming of the Arctic region but also increasing variability of meteorological variables and more often extreme meteorological events. Therefore, our results show that projected future increases in permafrost temperature and active-layer thickness in response to climate change will be lower (i) when taking into account future changes in short-term variability of meteorological variables and (ii) when representing dynamic snow and lichen and bryophyte functions in land surface models.

Effect of low temperature oxidation (LTO) in reducing boron skin in boron spin on dopant diffused emitter

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

Singha, Bandana; Solanki, Chetan Singh

Formation of boron skin is an unavoidable phenomenon in p-type emitter formation with boron dopant source. The boron skin thickness is generally less than 100 nm and difficult to remove by chemical and physical means. Low temperature oxidation (LTO) used in this work is useful in removing boron skin thickness up to 30 nm and improves the emitter performance. The effective minority carrier lifetime gets improved by more than 30% after using LTO and leakage current of the emitter gets lowered by 100 times thereby showing the importance of low temperature oxidation in boron spin on dopant diffused emitters.

Intermetallic Compound Growth and Stress Development in Al-Cu Diffusion Couple

NASA Astrophysics Data System (ADS)

Mishler, M.; Ouvarov-Bancalero, V.; Chae, Seung H.; Nguyen, Luu; Kim, Choong-Un

2018-01-01

This paper reports experimental observations evidencing that the intermetallic compound phase interfaced with Cu in the Al-Cu diffusion couple is most likely α2-Cu3Al phase, not γ-Cu9Al4 phase as previously assumed, and that its growth to a critical thickness may result in interface failure by stress-driven fracture. These conclusions are made based on an interdiffusion study of a diffusion couple made of a thick Cu plate coated with ˜ 2- μm-thick Al thin film. The interface microstructure and lattice parameter were characterized using scanning electron microscopy and x-ray diffraction analysis. Specimens aged at temperature between 623 K (350°C) and 723 K (450°C) for various hours produced consistent results supporting the main conclusions. It is found that disordered α2-Cu3Al phase grows in a similar manner to solid-state epitaxy, probably owing to its structural similarity to the Cu lattice. The increase in the interface strain that accompanies the α2-Cu3Al phase growth ultimately leads to interface fracture proceeding from crack initiation and growth along the interface. This mechanism provides the most consistent explanation for interface failures observed in other studies.

In-situ observation of impurity diffusion boundary layer in silicon Czochralski growth

NASA Astrophysics Data System (ADS)

Kakimoto, Koichi; Eguchi, Minoru; Watanabe, Hisao; Hibiya, Taketoshi

1990-01-01

In-situ observation of the impurity diffusion boundary layer during single crystal growth of indium-doped silicon was carried out by X-ray radiography. The difference in the transmitted X-ray image compared with molten silicon just beneath the crystal-melt interface was attributed to the concentration of indium impurities having a larger absorption coefficient. The intensity profile of the transmitted X-ray can be reproduced by a transmittance calculation that considers the meniscus shape and impurity distribution. The impurity distribution profile near the crystal-melt interface was estimated using the Burton-Prim-Slichter (BPS) equation. The observed impurity diffusion boundary layer thickness was about 0.5 mm. It was found that the boundary layer thickness was not constant in the radial direction, which cannot be explained by the BPS theory, since it is based on a one-dimensional calculation.

Reaction layer formation at the graphite/copper-chromium alloy interface

NASA Technical Reports Server (NTRS)

Devincent, Sandra M.; Michal, Gary M.

1992-01-01

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, auger electron spectroscopy, and x ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Numerical Study of Pressure Influence on Methane-Oxygen Laminar Counterflow Diffusion Flames

NASA Astrophysics Data System (ADS)

Iino, Kimio; Akamatsu, Fumiteru; Katsuki, Masashi

We carried out numerical studies on methane/oxygen diffusion flames of counter-flow configuration to elucidate the influence of pressure on flame structure, heat release rate and reaction mechanisms. The chemistry in gas-phase was based on GRI-Mech 3.0 database. The thickness of diffusion flame became thinner with increasing strain rate a , with its characteristic flame thickness varying inversely with √a, especially its relation became significant with increasing pressure. Flame temperature increased with increasing pressure. Enhanced H2O production reactions, especially chain terminal reactions for H2O production, were found to be important in determining the flame temperature at high pressures. The small reduction in the flame temperature with increasing strain rate at high pressures, compared to the atmospheric pressure, is caused by the capacitor effect of product dissociation. From QRPDs, the third body dependent reactions were enhanced in high pressure conditions, hence C2 pathway was enhanced.

Reaction layer formation at the graphite/copper-chromium alloy interface

NASA Technical Reports Server (NTRS)

Devincent, Sandra M.; Michal, Gary M.

1993-01-01

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Reconnection in Compressible Plasmas: Extended Conversion Region

NASA Technical Reports Server (NTRS)

Birn, J.; Hesse, M.; Zenitani, S.

2011-01-01

The classical Sweet-Parker approach to steady-state magnetic reconnection is extended into the regime of large resistivity (small magnetic Reynolds or Lundquist number) when the aspect ratio between the outflow and inflow scale, delta = d/L, approaches unity. In a previous paper the vicinity of the dissipation site ("diffusion region") was investigated. In this paper, the approach is extended to cover larger sites, in which the energy transfer and conversion is not confined to the diffusion region. Consistent with the results of Paper I, we find that increasing aspect ratio delta is associated with increasing compression, increasing reconnect ion rate for low Beta, but slightly decreasing rate for higher Beta, decreasing outflow speed, and increasing outflow magnetic field. These trends are stronger for lower Beta. Deviations from the traditional Sweet-Parker limit delta approaches 0 become significant for R(sub m) approx < 10, where R(sub m) is the magnetic Reynolds number (Lundquist number) based on the half-thickness of the current layer responsible for the Ohmic dissipation. They are also more significant for small gamma, that is, for increasing compressibility. In contrast to the results of Paper I, but consistent with earlier results for delta much < 1,nu(sub A) we find that in this limit the outflow speed is given by the Alfven speed nu(sub A) in the inflow region and the energy conversion is given by an even split of Poynting flux into enthalpy flux and bulk kinetic energy flux. However, with increasing delta the conversion to enthalpy flux becomes more and more dominant.

String-like collective motion and diffusion in the interfacial region of ice

NASA Astrophysics Data System (ADS)

Wang, Xinyi; Tong, Xuhang; Zhang, Hao; Douglas, Jack F.

2017-11-01

We investigate collective molecular motion and the self-diffusion coefficient Ds of water molecules in the mobile interfacial layer of the secondary prismatic plane (11 2 ¯ 0 ) of hexagonal ice by molecular dynamics simulation based on the TIP4P/2005 water potential and a metrology of collective motion drawn from the field of glass-forming liquids. The width ξ of the mobile interfacial layer varies from a monolayer to a few nm as the temperature is increased towards the melting temperature Tm, in accordance with recent simulations and many experimental studies, although different experimental methods have differed in their precise estimates of the thickness of this layer. We also find that the dynamics within this mobile interfacial ice layer is "dynamically heterogeneous" in a fashion that has many features in common with glass-forming liquids and the interfacial dynamics of crystalline Ni over the same reduced temperature range, 2/3 < T/Tm < 1. In addition to exhibiting non-Gaussian diffusive transport, decoupling between mass diffusion and the structural relaxation time, and stretched exponential relaxation, we find string-like collective molecular exchange motion in the interfacial zone within the ice interfacial layer and colored noise fluctuations in the mean square molecular atomic displacement 〈u2〉 after a "caging time" of 1 ps, i.e., the Debye-Waller factor. However, while the heterogeneous dynamics of ice is clearly similar in many ways to molecular and colloidal glass-forming materials, we find distinct trends between the diffusion coefficient activation energy Ea for diffusion Ds and the interfacial width ξ from the scale of collective string-like motion L than those found in glass-forming liquids.

Fluxless eutectic bonding of GaAs-on-Si by using Ag/Sn solder

NASA Astrophysics Data System (ADS)

Eo, Sung-Hwa; Kim, Dae-Seon; Jeong, Ho-Jung; Jang, Jae-Hyung

2013-11-01

Fluxless GaAs-on-Si wafer bonding using Ag/Sn solder was investigated to realize uniform and void-free heterogeneous material integration. The effects of the diffusion barrier, Ag/Sn thickness, and Ar plasma treatment were studied to achieve the optimal fluxless bonding process. Pt on a GaAs wafer and Mo on a Si wafer act as diffusion barriers by preventing the flow of Ag/Sn solder into both the wafers. The bonding strength is closely related to the Ag/Sn thickness and Ar plasma treatment. A shear strength test was carried out to investigate the bonding strength. Under identical bonding conditions, the Ag/Sn thickness was optimized to achieve higher bonding strength and to avoid the formation of voids due to thermal stress. An Ar plasma pretreatment process improved the bonding strength because the Ar plasma removed carbon contaminants and metal-oxide bonds from the metal surface.

Refractive Index Effects on Radiation in an Absorbing, Emitting, and Scattering Laminated Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting temperature radiative energy flow in a two-region semitransparent laminated layer in the limit of zero heat conduction. The composite is heated on its two sides by unequal amounts of incident radiation. The two layers of the composite have different refractive indices, and each material absorbs, emits, and isotropically scatters radiation. The interfaces are diffuse, and all interface reflections are included. To illustrate the thermal behavior that is readily calculated from the equations, typical results an given for various optical thicknesses and refractive indices of the layers. Internal reflections have a substantial effect on the temperature distribution and radiative heat flow.

Freshwater lake to salt-water sea causing widespread hydrate dissociation in the Black Sea.

PubMed

Riboulot, Vincent; Ker, Stephan; Sultan, Nabil; Thomas, Yannick; Marsset, Bruno; Scalabrin, Carla; Ruffine, Livio; Boulart, Cédric; Ion, Gabriel

2018-01-09

Gas hydrates, a solid established by water and gas molecules, are widespread along the continental margins of the world. Their dynamics have mainly been regarded through the lens of temperature-pressure conditions. A fluctuation in one of these parameters may cause destabilization of gas hydrate-bearing sediments below the seafloor with implications in ocean acidification and eventually in global warming. Here we show throughout an example of the Black Sea, the world's most isolated sea, evidence that extensive gas hydrate dissociation may occur in the future due to recent salinity changes of the sea water. Recent and forthcoming salt diffusion within the sediment will destabilize gas hydrates by reducing the extension and thickness of their thermodynamic stability zone in a region covering at least 2800 square kilometers which focus seepages at the observed sites. We suspect this process to occur in other world regions (e.g., Caspian Sea, Sea of Marmara).

Evaluation of laminated aluminum plate for shuttle applications

NASA Technical Reports Server (NTRS)

Martin, M. J.

1973-01-01

Flaw growth behavior in roll diffusion bonded and adhesive bonded 2219-T87 aluminum alloy was compared to that in monolothic 2219-T87. Based on tests at 40 KSI cyclic stress, for equivalent cyclic life, a .004 interlayer laminate can tolerate a surface flaw twice as wide as in monolithic material, or provide an 8% weight saving by operating at higher stress for the same initial flaw. Roll diffusion bonded material with three structural plies of 2219-T87 and two interlayers of 1100 aluminum was prepared with interlayer thicknesses of .004, .007 and .010 in. Total laminate thickness was .130 in. The .004 interlayer laminate was most effective and gave better results than monolithic material at 40 and 48 ksi. Adhesive bonded specimens were fabricated of three sheets of 2219-T87 aluminum alloy bonded with METLBOND 329 adhesive. Adhesive bonded specimens gave longer lives to failure than diffusion bonded specimens at 40 ksi the diffusion bonded material was superior. Flaws initiated in one ply of the laminate grew to the edges of the specimen in that ply but did not propagate into adjacent plies.

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.

Lamination and mixing in laminar flows driven by Lorentz body forces

NASA Astrophysics Data System (ADS)

Rossi, L.; Doorly, D.; Kustrin, D.

2012-01-01

We present a new approach to the design of mixers. This approach relies on a sequence of tailored flows coupled with a new procedure to quantify the local degree of striation, called lamination. Lamination translates to the distance over which the molecular diffusion needs to act to finalise mixing. A novel in situ mixing is achieved by the tailored sequence of flows. This sequence is shown with the property that material lines and lamination grow exponentially, according to processes akin to the well-known baker's map. The degree of mixing (stirring coefficient) likewise shows exponential growth before the saturation of the stirring rate. Such saturation happens when the typical striations' thickness is smaller than the diffusion's length scale. Moreover, without molecular diffusion, the predicted striations' thickness would be smaller than the size of an atom of hydrogen within 40 flow turnover times. In fact, we conclude that about 3 minutes, i.e. 15 turnover times, are sufficient to mix species with very low diffusivities, e.g. suspensions of virus, bacteria, human cells, and DNA.

Investigations of surface coatings to reduce memory effect in plastic scintillator detectors used for radioxenon detection

NASA Astrophysics Data System (ADS)

Bläckberg, L.; Fay, A.; Jõgi, I.; Biegalski, S.; Boman, M.; Elmgren, K.; Fritioff, T.; Johansson, A.; Mårtensson, L.; Nielsen, F.; Ringbom, A.; Rooth, M.; Sjöstrand, H.; Klintenberg, M.

2011-11-01

In this work Al2O3 and SiO2 coatings are tested as Xe diffusion barriers on plastic scintillator substrates. The motivation is improved beta-gamma coincidence detection systems, used to measure atmospheric radioxenon within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. One major drawback with the current setup of these systems is that the radioxenon tends to diffuse into the plastic scintillator material responsible for the beta detection, resulting in an unwanted memory effect. Here, coatings with thicknesses between 20 and 900 nm have been deposited onto plastic scintillators, and investigated using two different experimental techniques. The results show that all tested coatings reduce the Xe diffusion into the plastic. The reduction is observed to increase with coating thickness for both coating materials. The 425 nm Al2O3 coating is the most successful one, presenting a diffusion reduction of a factor 100, compared to uncoated plastic. In terms of memory effect reduction this coating is thus a viable solution to the problem in question.

Intravitreal bevacizumab (Avastin) treatment of diffuse diabetic macular edema in an Indian population

PubMed Central

Sinha, Subijay

2007-01-01

Background: To report the anatomic and visual acuity response after intravitreal bevacizumab (Avastin) in patients with diffuse diabetic macular edema. Design: Prospective, interventional case series study. Materials and Methods: This study included 20 eyes of metabolically stable diabetes mellitus with diffuse diabetic macular edema with a mean age of 59 years who were treated with two intravitreal injections of bevacizumab 1.25 mg in 0.05 ml six weeks apart. Main outcome measures were 1) early treatment diabetic retinopathy study visual acuity, 2) central macular thickness by optical coherence tomography imaging. Each was evaluated at baseline and follow-up visits. Results: All the eyes had received some form of laser photocoagulation before (not less than six months ago), but all of these patients had persistent diffuse macular edema with no improvement in visual acuity. All the patients received two injections of bevacizumab at an interval of six weeks per eye. No adverse events were observed, including endophthalmitis, inflammation and increased intraocular pressure or thromboembolic events in any patient. The mean baseline acuity was 20/494 (log Mar=1.338±0.455) and the mean acuity at three months following the second intravitreal injection was 20/295 (log Mar=1.094±0.254), a difference that was highly significant ( P =0.008). The mean central macular thickness at baseline was 492 µm which decreased to 369 µm ( P =0.001) at the end of six months. Conclusions: Initial treatment results of patients with diffuse diabetic macular edema not responding to previous photocoagulation did not reveal any short-term safety concerns. Intravitreal bevacizumab resulted in a significant decrease in macular thickness and improvement in visual acuity at three months but the effect was somewhat blunted, though still statistically significant at the end of six months. PMID:17951903

Linear diffusion into a Faraday cage.

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

Warne, Larry Kevin; Lin, Yau Tang; Merewether, Kimball O.

2011-11-01

Linear lightning diffusion into a Faraday cage is studied. An early-time integral valid for large ratios of enclosure size to enclosure thickness and small relative permeability ({mu}/{mu}{sub 0} {le} 10) is used for this study. Existing solutions for nearby lightning impulse responses of electrically thick-wall enclosures are refined and extended to calculate the nearby lightning magnetic field (H) and time-derivative magnetic field (HDOT) inside enclosures of varying thickness caused by a decaying exponential excitation. For a direct strike scenario, the early-time integral for a worst-case line source outside the enclosure caused by an impulse is simplified and numerically integrated tomore » give the interior H and HDOT at the location closest to the source as well as a function of distance from the source. H and HDOT enclosure response functions for decaying exponentials are considered for an enclosure wall of any thickness. Simple formulas are derived to provide a description of enclosure interior H and HDOT as well. Direct strike voltage and current bounds for a single-turn optimally-coupled loop for all three waveforms are also given.« less

Alcohols enhance the rate of acetic acid diffusion in S. cerevisiae: biophysical mechanisms and implications for acetic acid tolerance.

PubMed

Lindahl, Lina; Genheden, Samuel; Faria-Oliveira, Fábio; Allard, Stefan; Eriksson, Leif A; Olsson, Lisbeth; Bettiga, Maurizio

2017-12-01

Microbial cell factories with the ability to maintain high productivity in the presence of weak organic acids, such as acetic acid, are required in many industrial processes. For example, fermentation media derived from lignocellulosic biomass are rich in acetic acid and other weak acids. The rate of diffusional entry of acetic acid is one parameter determining the ability of microorganisms to tolerance the acid. The present study demonstrates that the rate of acetic acid diffusion in S. cerevisiae is strongly affected by the alcohols ethanol and n-butanol. Ethanol of 40 g/L and n-butanol of 8 g/L both caused a 65% increase in the rate of acetic acid diffusion, and higher alcohol concentrations caused even greater increases. Molecular dynamics simulations of membrane dynamics in the presence of alcohols demonstrated that the partitioning of alcohols to the head group region of the lipid bilayer causes a considerable increase in the membrane area, together with reduced membrane thickness and lipid order. These changes in physiochemical membrane properties lead to an increased number of water molecules in the membrane interior, providing biophysical mechanisms for the alcohol-induced increase in acetic acid diffusion rate. n-butanol affected S. cerevisiae and the cell membrane properties at lower concentrations than ethanol, due to greater and deeper partitioning in the membrane. This study demonstrates that the rate of acetic acid diffusion can be strongly affected by compounds that partition into the cell membrane, and highlights the need for considering interaction effects between compounds in the design of microbial processes.

Alcohols enhance the rate of acetic acid diffusion in S. cerevisiae: biophysical mechanisms and implications for acetic acid tolerance

PubMed Central

Lindahl, Lina; Genheden, Samuel; Faria-Oliveira, Fábio; Allard, Stefan; Eriksson, Leif A.; Olsson, Lisbeth; Bettiga, Maurizio

2017-01-01

Microbial cell factories with the ability to maintain high productivity in the presence of weak organic acids, such as acetic acid, are required in many industrial processes. For example, fermentation media derived from lignocellulosic biomass are rich in acetic acid and other weak acids. The rate of diffusional entry of acetic acid is one parameter determining the ability of microorganisms to tolerance the acid. The present study demonstrates that the rate of acetic acid diffusion in S. cerevisiae is strongly affected by the alcohols ethanol and n-butanol. Ethanol of 40 g/L and n-butanol of 8 g/L both caused a 65% increase in the rate of acetic acid diffusion, and higher alcohol concentrations caused even greater increases. Molecular dynamics simulations of membrane dynamics in the presence of alcohols demonstrated that the partitioning of alcohols to the head group region of the lipid bilayer causes a considerable increase in the membrane area, together with reduced membrane thickness and lipid order. These changes in physiochemical membrane properties lead to an increased number of water molecules in the membrane interior, providing biophysical mechanisms for the alcohol-induced increase in acetic acid diffusion rate. n-butanol affected S. cerevisiae and the cell membrane properties at lower concentrations than ethanol, due to greater and deeper partitioning in the membrane. This study demonstrates that the rate of acetic acid diffusion can be strongly affected by compounds that partition into the cell membrane, and highlights the need for considering interaction effects between compounds in the design of microbial processes. PMID:29354649

Thin-film metallic glass: an effective diffusion barrier for Se-doped AgSbTe2 thermoelectric modules

PubMed Central

Yu, Chia-Chi; Wu, Hsin-jay; Deng, Ping-Yuan; Agne, Matthias T.; Snyder, G. Jeffrey; Chu, Jinn P.

2017-01-01

The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8–360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick’s second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10−20–10−23(m2/s), which is 106~107 and 1012~1013 times smaller than those of Ni [10−14–10−17(m2/s)] and Cu [10−8–10−11(m2/s)] in Bi2Te3, respectively. PMID:28327655

Molecular simulation of structure and diffusion at smectite-water interfaces: Using expanded clay interlayers as model nanopores

DOE PAGES

Greathouse, Jeffery A.; Hart, David; Bowers, Geoffrey M.; ...

2015-07-20

In geologic settings relevant to a number of extraction and potential sequestration processes, nanopores bounded by clay mineral surfaces play a critical role in the transport of aqueous species. Solution structure and dynamics at clay–water interfaces are quite different from their bulk values, and the spatial extent of this disruption remains a topic of current interest. We have used molecular dynamics simulations to investigate the structure and diffusion of aqueous solutions in clay nanopores approximately 6 nm thick, comparing the effect of clay composition with model Na-hectorite and Na-montmorillonite surfaces. In addition to structural properties at the interface, water andmore » ion diffusion coefficients were calculated within each aqueous layer at the interface, as well as in the central bulk-like region of the nanopore. The results show similar solution structure and diffusion properties at each surface, with subtle differences in sodium adsorption complexes and water structure in the first adsorbed layer due to different arrangements of layer hydroxyl groups in the two clay models. Interestingly, the extent of surface disruption on bulk-like solution structure and diffusion extends to only a few water layers. Additionally, a comparison of sodium ion residence times confirms similar behavior of inner-sphere and outer-sphere surface complexes at each clay surface, but ~1% of sodium ions adsorb in ditrigonal cavities on the hectorite surface. Thus, the presence of these anhydrous ions is consistent with highly immobile anhydrous ions seen in previous nuclear magnetic resonance spectroscopic measurements of hectorite pastes.« less

Chemical reaction of atomic oxygen with evaporated films of copper, part 4

NASA Technical Reports Server (NTRS)

Fromhold, A. T.; Williams, J. R.

1990-01-01

Evaporated copper films were exposed to an atomic oxygen flux of 1.4 x 10(exp 17) atoms/sq cm per sec at temperatures in the range 285 to 375 F (140 to 191 C) for time intervals between 2 and 50 minutes. Rutherford backscattering spectroscopy (RBS) was used to determine the thickness of the oxide layers formed and the ratio of the number of copper to oxygen atoms in the layers. Oxide film thicknesses ranged from 50 to 3000 A (0.005 to 0.3 microns, or equivalently, 5 x 10(exp -9) to 3 x 10(exp -7); it was determined that the primary oxide phase was Cu2O. The growth law was found to be parabolic (L(t) varies as t(exp 1/2)), in which the oxide thickness L(t) increases as the square root of the exposure time t. The analysis of the data is consistent with either of the two parabolic growth laws. (The thin-film parabolic growth law is based on the assumption that the process is diffusion controlled, with the space charge within the growing oxide layer being negligible. The thick-film parabolic growth law is also based on a diffusion controlled process, but space-charge neutrality prevails locally within very thick oxides.) In the absence of a voltage measurement across the growing oxide, a distinction between the two mechanisms cannot be made, nor can growth by the diffusion of neutral atomic oxygen be entirely ruled out. The activation energy for the reaction is on the order of 1.1 eV (1.76 x 10(exp -19) joule, or equivalently, 25.3 kcal/mole).

Diffusion weighted whole body imaging with background body signal suppression (DWIBS): technical improvement using free breathing, STIR and high resolution 3D display.

PubMed

Takahara, Taro; Imai, Yutaka; Yamashita, Tomohiro; Yasuda, Seiei; Nasu, Seiji; Van Cauteren, Marc

2004-01-01

To examine a new way of body diffusion weighted imaging (DWI) using the short TI inversion recovery-echo planar imaging (STIR-EPI) sequence and free breathing scanning (diffusion weighted whole body imaging with background body signal suppression; DWIBS) to obtain three-dimensional displays. 1) Apparent contrast-to-noise ratios (AppCNR) between lymph nodes and surrounding fat tissue were compared in three types of DWI with and without breath-holding, with variable lengths of scan time and slice thickness. 2) The STIR-EPI sequence and spin echo-echo planar imaging (SE-EPI) sequence with chemical shift selective (CHESS) pulse were compared in terms of their degree of fat suppression. 3) Eleven patients with neck, chest, and abdominal malignancy were scanned with DWIBS for evaluation of feasibility. Whole body imaging was done in a later stage of the study using the peripheral vascular coil. The AppCNR of 8 mm slice thickness images reconstructed from 4 mm slice thickness source images obtained in a free breathing scan of 430 sec were much better than 9 mm slice thickness breath-hold scans obtained in 25 sec. High resolution multi-planar reformat (MPR) and maximum intensity projection (MIP) images could be made from the data set of 4 mm slice thickness images. Fat suppression was much better in the STIR-EPI sequence than SE-EPI with CHESS pulse. The feasibility of DWIBS was showed in clinical scans of 11 patients. Whole body images were successfully obtained with adequate fat suppression. Three-dimensional DWIBS can be obtained with this technique, which may allow us to screen for malignancies in the whole body.

Gas diffusion in and out of super-hydrophobic surface in transitional and turbulent boundary layers

NASA Astrophysics Data System (ADS)

Ling, Hangjian; Fu, Matthew; Hultmark, Marcus; Katz, Joseph

2017-11-01

The rate of gas diffusion in and out of a super-hydrophobic surface (SHS) located in boundary layers is investigated at varying Reynolds numbers and ambient pressures. The hierarchical SHS consists of nano-textured, 100 μm wide spanwise grooves. The boundary layers over the SHS under the Cassie-Baxter and Wenzel states as well as a smooth wall at same conditions are characterized by particle image velocimetry. The Reynolds number based on momentum thickness of the smooth wall, ReΘ0, ranges from 518 to 2088, covering transitional and turbulent boundary layer regimes. The mass diffusion rate is estimated by using microscopy to measure the time-evolution of plastron shape and volume. The data is used for calculating the Sherwood number based on smooth wall momentum thickness, ShΘ0. As expected, the diffusion rate increases linearly with the under- or super-saturation level, i.e., ShΘ0 is independent of ambient pressure. For the turbulent boundary layers, the data collapses onto ShΘ0 = 0.47ReΘ00.77 . For the transitional boundary layer, ShΘ0 is lower than the turbulent power law. When ShΘ0 is plotted against the friction Reynolds number (Reτ0) , both the transitional and turbulent boundary layer data collapse onto a single power law, ShΘ0 = 0.34Reτ00.913 . Results scaled based on Wenzel state momentum thickness show very similar trends. Sponsored by ONR.

Self-assembly of bimetallic AuxPd1-x alloy nanoparticles via dewetting of bilayers through the systematic control of temperature, thickness, composition and stacking sequence

NASA Astrophysics Data System (ADS)

Kunwar, Sundar; Pandey, Puran; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-03-01

Bimetallic alloy nanoparticles (NPs) are attractive materials for various applications with their morphology and elemental composition dependent optical, electronic, magnetic and catalytic properties. This work demonstrates the evolution of AuxPd1-x alloy nanostructures by the solid-state dewetting of sequentially deposited bilayers of Au and Pd on sapphire (0001). Various shape, size and configuration of AuxPd1‑x alloy NPs are fabricated by the systematic control of annealing temperature, deposition thickness, composition as well as stacking sequence. The evolution of alloy nanostructures is attributed to the surface diffusion, interface diffusion between bilayers, surface and interface energy minimization, Volmer-Weber growth model and equilibrium configuration. Depending upon the temperature, the surface morphologies evolve with the formation of pits, grains and voids and gradually develop into isolated semi-spherical alloy NPs by the expansion of voids and agglomeration of Au and Pd adatoms. On the other hand, small isolated to enlarged elongated and over-grown layer-like alloy nanostructures are fabricated due to the coalescence, partial diffusion and inter-diffusion with the increased bilayer thickness. In addition, the composition and stacking sequence of bilayers remarkably affect the final geometry of AuxPd1‑x nanostructures due to the variation in the dewetting process. The optical analysis based on the UV–vis-NIR reflectance spectra reveals the surface morphology dependent plasmonic resonance, scattering, reflection and absorption properties of AuxPd1‑x alloy nanostructures.

Resonant thickening of self-gravitating discs: imposed or self-induced orbital diffusion in the tightly wound limit

NASA Astrophysics Data System (ADS)

Fouvry, Jean-Baptiste; Pichon, Christophe; Chavanis, Pierre-Henri; Monk, Laura

2017-11-01

The secular thickening of a self-gravitating stellar galactic disc is investigated using the dressed collisionless Fokker-Planck equation and the inhomogeneous multicomponent Balescu-Lenard equation. The thick WKB limits for the diffusion fluxes are found using the epicyclic approximation, while assuming that only radially tightly wound transient spirals are sustained by the disc. This yields simple quadratures for the drift and diffusion coefficients, providing a clear understanding of the positions of maximum vertical orbital diffusion within the disc, induced by fluctuations either external or due to the finite number of particles. These thick limits also offer a consistent derivation of a thick disc Toomre parameter, which is shown to be exponentially boosted by the ratio of the vertical to radial scaleheights. Dressed potential fluctuations within the disc statistically induce a vertical bending of a subset of resonant orbits, triggering the corresponding increase in vertical velocity dispersion. When applied to a tepid stable tapered disc perturbed by shot noise, these two frameworks reproduce qualitatively the formation of ridges of resonant orbits towards larger vertical actions, as found in direct numerical simulations, but overestimates the time-scale involved in their appearance. Swing amplification is likely needed to resolve this discrepancy, as demonstrated in the case of razor-thin discs. Other sources of thickening are also investigated, such as fading sequences of slowing bars, or the joint evolution of a population of giant molecular clouds within the disc.

INTRAVITREAL DEXAMETHASONE IMPLANTATION IN PATIENTS WITH DIFFERENT MORPHOLOGICAL DIABETIC MACULAR EDEMA HAVING INSUFFICIENT RESPONSE TO RANIBIZUMAB.

PubMed

Kaldırım, Havva; Yazgan, Serpil; Atalay, Kursat; Gurez, Ceren; Savur, Fatma

2018-05-01

To evaluate the effectiveness of a single intravitreal injection of dexamethasone implant in resistant diabetic macular edema that have different morphological types. In this retrospective study, 31 patients (35 eyes) with persistent diabetic macular edema, who underwent a single injection of dexamethasone implant, were evaluated. Diabetic macular edema was classified into three types: diffuse retinal thickening (n = 10), cystoid macular edema (n = 13), and serous retinal detachment (n = 12). Primary outcome measures were best corrected visual acuity, and central macular thickness. The three subgroups were similar in terms of age and gender (P > 0.05). Total duration of diabetes was significantly less in the serous retinal detachment subgroup (P = 0.01). There were no differences in the best corrected visual acuity between the three subgroups until the sixth month. However, the best corrected visual acuity was significantly better in the diffuse retinal thickness subgroup at the sixth month (P = 0.008). Regarding the central macular thickness values, it was statistically better in serous retinal detachment than in diffuse retinal thickening and cystoid macular edema subgroups till the sixth month (P = 0.001). However, at the sixth month, there was not any statistical difference between subgroups regarding central macular thickness values. Antiglaucomatous agents were required in 4 (11.4%) patients throughout the study. Treatment algorithms should differ according to the morphology of diabetic macular edema; however, more data is needed to give specific recommendations.

Gravity Effects in Diffusive Coarsening of Bubble Lattices: von Neumann's Law

NASA Technical Reports Server (NTRS)

Noever, David A.

2000-01-01

von Neumann modelled the evolution of two-dimensional soap froths as a purely diffusive phenomenon; the area growth of a given cell was found to depend only on the geometry of the bubble lattice. In the model, hexagons are stable, pentagons shrink and heptagons grow. The simplest equivalent to the area growth law is / approximately t(sub beta). The result depends on assuming (1) an incompressible gas; (2) bubble walls which meet at 120 deg and (3) constant wall thickness and curvature. Each assumption is borne out in experiments except the last one: bubble wall thickness between connecting cells varies in unit gravity because of gravity drainage. The bottom part of the soap membrane is thickened, the top part is thinned, such that gas diffusion across the membrane shows a complex dependence on gravity. As a result, experimental tests of von Neumann's law have been influenced by effects of gravity; fluid behavior along cell borders can give non-uniform wall thicknesses and thus alter the effective area and gas diffusion rates between adjacent bubbles. For area plotted as a function of time, Glazier (J.A. Glazier, S.P. Gross, and I. Stavans, Phys. Rev. A. 36, 306 (1987); J. Stavans, J.A, Glazier, Phys. Rev. Lett. 62, 1318 (1989).) suggest that in some cases their failure to observe von Neumann's predicted growth exponent ((sup beta)theor(sup =1; beta)exp(sup =0.70 + 0.10)) may have been the result of such "fluid drainage onto the lower glass plate". Additional experiments which varied plate spacing gave different beta exponents in a fashion consistent with this suggestion. During preliminary long duration experiments (approximately 100 h) aboard Spacelab-J, a low-gravity test of froth coarsening has examined (1) power law scaling of von Neumann's law (beta values) in the appropriate diffusive limits; (2) new bubble lattice dynamics such as greater fluid wetting behavior on froth membranes in low gravity; and (3) explicit relations for the gravity dependence of the second moment (or disorder parameter) governing the geometric spread in cell-sidedness around the mean of perfect hexagonal filling. By reducing the gravity-induced distortion in lattice wall thickness, the diffusion-limited regime of bubble coarsening becomes available for performing critical tests of network dynamics.

Circulating inflammatory biomarkers in relation to brain structural measurements in a non-demented elderly population.

PubMed

Gu, Yian; Vorburger, Robert; Scarmeas, Nikolaos; Luchsinger, José A; Manly, Jennifer J; Schupf, Nicole; Mayeux, Richard; Brickman, Adam M

2017-10-01

The aim of this investigation was to determine whether circulating inflammatory biomarkers c-reactive protein (CRP), interleukin-6 (IL6), and alpha 1-antichymotrypsin (ACT) were related to structural brain measures assessed by magnetic resonance imaging (MRI). High-resolution structural MRI was collected on 680 non-demented elderly (mean age 80.1years) participants of a community-based, multiethnic cohort. Approximately three quarters of these participants also had peripheral inflammatory biomarkers (CRP, IL6, and ACT) measured using ELISA. Structural measures including brain volumes and cortical thickness (with both global and regional measures) were derived from MRI scans, and repeated MRI measures were obtained after 4.5years. Mean fractional anisotropy was used as the indicator of white matter integrity assessed with diffusion tensor imaging. We examined the association of inflammatory biomarkers with brain volume, cortical thickness, and white matter integrity using regression models adjusted for age, gender, ethnicity, education, APOE genotype, and intracranial volume. A doubling in CRP (b=-2.48, p=0.002) was associated with a smaller total gray matter volume, equivalent to approximately 1.5years of aging. A doubling in IL6 was associated with smaller total brain volume (b=-14.96, p<0.0001), equivalent to approximately 9years of aging. Higher IL6 was also associated with smaller gray matter (b=-6.52, p=0.002) and white matter volumes (b=-7.47, p=0.004). The volumes of most cortical regions including frontal, occipital, parietal, temporal, as well as subcortical regions including pallidum and thalamus were associated with IL6. In a model additionally adjusted for depression, vascular factors, BMI, and smoking status, the association between IL6 and brain volumes remained, and a doubling in ACT was marginally associated with 0.054 (p=0.001) millimeter thinner mean cortical thickness, equivalent to that of approximately 2.7years of aging. None of the biomarkers was associated with mean fractional anisotropy or longitudinal change of brain volumes and thickness. Among older adults, increased circulating inflammatory biomarkers were associated with smaller brain volume and cortical thickness but not the white matter tract integrity. Our preliminary findings suggest that peripheral inflammatory processes may be involved in the brain atrophy in the elderly. Copyright © 2017 Elsevier Inc. All rights reserved.

Stereological estimation of the surface area and oxygen diffusing capacity of the respiratory stomach of the air-breathing armored catfish Pterygoplichthys anisitsi (Teleostei: Loricariidae).

PubMed

da Cruz, André Luis; Pedretti, Ana Carolina Elias; Fernandes, Marisa Narciso

2009-05-01

The stomach of Pterygoplichthys anisitsi has a thin, translucent wall and a simple squamous epithelium with an underlying dense capillary network. In the cardiac and pyloric regions, most cells have short microvilli distributed throughout the cell surface and their edges are characterized by short, densely packed microvilli. The mucosal layer of the stomach has two types of pavement epithelial cells that are similar to those in the aerial respiratory organs. Type 1 pavement epithelial cells, resembling the Type I pneumocyte in mammal lungs, are flat, with a large nucleus, and extend a thin sheet of cytoplasm on the underlying capillary. Type 2 cells, resembling the Type II pneumocyte, possess numerous mitochondria, a well-developed Golgi complex, rough endoplasmic reticulum, and numerous lamellar bodies in different stages of maturation. The gastric glands, distributed throughout the mucosal layer, also have several cells with many lamellar bodies. The total volume (air + tissue), tissue, and air capacity of the stomach when inflated, increase along with body mass. The surface-to-tissue-volume ratio of stomach varies from 108 cm(-1) in the smallest fish (0.084 kg) to 59 cm(-1) in the largest fish (0.60 kg). The total stomach surface area shows a low correlation to body mass. Nevertheless, the body-mass-specific surface area varied from 281.40 cm(2) kg(-1) in the smallest fish to 68.08 cm(2) kg(-1) in the largest fish, indicating a negative correlation to body mass (b = -0.76). The arithmetic mean barrier thickness between air and blood was 1.52 +/- 0.07 microm, whereas the harmonic mean thickness (tau(h)) of the diffusion barrier ranged from 0.40 to 0.74 microm. The anatomical diffusion factor (ADF = cm(2) microm(-1) kg(-1)) and the morphological O(2) diffusion capacity (D(morphol)O(2) = cm(3) min(-1) mmHg(-1) kg(-1)) are higher in the smallest specimen and lower in the largest one. In conclusion, the structure and morphometric data of P. anisitsi stomach indicate that this organ is adapted for oxygen uptake from air. (c) 2008 Wiley-Liss, Inc.

WATER STABILITY OF FILLED ELASTOMERS,

DTIC Science & Technology

ELECTRICAL INSULATION, *BUTYL RUBBER , ELASTOMERS, STABILITY, STABILITY, HYDROLYSIS, CURING AGENTS, ADDITIVES, WATER, ABSORPTION, THICKNESS, ELECTRICAL RESISTANCE, LEAKAGE(ELECTRICAL), DIFFUSION, TALC, ELECTRIC CABLES.

Multiscale solutions of radiative heat transfer by the discrete unified gas kinetic scheme

NASA Astrophysics Data System (ADS)

Luo, Xiao-Ping; Wang, Cun-Hai; Zhang, Yong; Yi, Hong-Liang; Tan, He-Ping

2018-06-01

The radiative transfer equation (RTE) has two asymptotic regimes characterized by the optical thickness, namely, optically thin and optically thick regimes. In the optically thin regime, a ballistic or kinetic transport is dominant. In the optically thick regime, energy transport is totally dominated by multiple collisions between photons; that is, the photons propagate by means of diffusion. To obtain convergent solutions to the RTE, conventional numerical schemes have a strong dependence on the number of spatial grids, which leads to a serious computational inefficiency in the regime where the diffusion is predominant. In this work, a discrete unified gas kinetic scheme (DUGKS) is developed to predict radiative heat transfer in participating media. Numerical performances of the DUGKS are compared in detail with conventional methods through three cases including one-dimensional transient radiative heat transfer, two-dimensional steady radiative heat transfer, and three-dimensional multiscale radiative heat transfer. Due to the asymptotic preserving property, the present method with relatively coarse grids gives accurate and reliable numerical solutions for large, small, and in-between values of optical thickness, and, especially in the optically thick regime, the DUGKS demonstrates a pronounced computational efficiency advantage over the conventional numerical models. In addition, the DUGKS has a promising potential in the study of multiscale radiative heat transfer inside the participating medium with a transition from optically thin to optically thick regimes.

Evaluation of oxide-coated iridium-rhenium chambers

NASA Astrophysics Data System (ADS)

Reed, Brian D.

1994-03-01

Iridium-coated rhenium (Ir-Re) provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase Ir-Re rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated Ir-Re, 22-N rocket chambers were tested with gaseous hydrogen/gaseous oxygen (GHz/G02) propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia (HfO2) or zirconia (ZrO2). Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of ZrO2 infiltrated with sol gel HfO2. The other chamber had a coating composed of an Ir-oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. Testing the Ir-oxide composite-coated chamber included over 29 min at mixture ratio 16. The thicker walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner walled coatings did not experience the macrocracking and chipping of the chambers that was seen with the thick, monolithic coatings. However, burn-throughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stoichiometric. The burn-throughs were probably the result of oxygen diffusion through the oxide coating that allowed the underlying Ir and Re layers to be oxidized. The results of this test program indicated that the thin-walled oxide coatings are better suited for repeated thermal cycling than the thick-walled coating, while thicker coatings may be required for operation in aggressively oxidizing environments.

MODFLOW-2000 Ground-Water Model?User Guide to the Subsidence and Aquifer-System Compaction (SUB) Package

USGS Publications Warehouse

Hoffmann, Jörn; Leake, S.A.; Galloway, D.L.; Wilson, Alicia M.

2003-01-01

This report documents a computer program, the Subsidence and Aquifer-System Compaction (SUB) Package, to simulate aquifer-system compaction and land subsidence using the U.S. Geological Survey modular finite-difference ground-water flow model, MODFLOW-2000. The SUB Package simulates elastic (recoverable) compaction and expansion, and inelastic (permanent) compaction of compressible fine-grained beds (interbeds) within the aquifers. The deformation of the interbeds is caused by head or pore-pressure changes, and thus by changes in effective stress, within the interbeds. If the stress is less than the preconsolidation stress of the sediments, the deformation is elastic; if the stress is greater than the preconsolidation stress, the deformation is inelastic. The propagation of head changes within the interbeds is defined by a transient, one-dimensional (vertical) diffusion equation. This equation accounts for delayed release of water from storage or uptake of water into storage in the interbeds. Properties that control the timing of the storage changes are vertical hydraulic diffusivity and interbed thickness. The SUB Package supersedes the Interbed Storage Package (IBS1) for MODFLOW, which assumes that water is released from or taken into storage with changes in head in the aquifer within a single model time step and, therefore, can be reasonably used to simulate only thin interbeds. The SUB Package relaxes this assumption and can be used to simulate time-dependent drainage and compaction of thick interbeds and confining units. The time-dependent drainage can be turned off, in which case the SUB Package gives results identical to those from IBS1. Three sample problems illustrate the usefulness of the SUB Package. One sample problem verifies that the package works correctly. This sample problem simulates the drainage of a thick interbed in response to a step change in head in the adjacent aquifer and closely matches the analytical solution. A second sample problem illustrates the effects of seasonally varying discharge and recharge to an aquifer system with a thick interbed. A third sample problem simulates a multilayered regional ground-water basin. Model input files for the third sample problem are included in the appendix.

Evaluation of oxide-coated iridium-rhenium chambers

NASA Technical Reports Server (NTRS)

Reed, Brian D.

1994-01-01

Iridium-coated rhenium (Ir-Re) provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase Ir-Re rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated Ir-Re, 22-N rocket chambers were tested with gaseous hydrogen/gaseous oxygen (GHz/G02) propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia (HfO2) or zirconia (ZrO2). Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of ZrO2 infiltrated with sol gel HfO2. The other chamber had a coating composed of an Ir-oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. Testing the Ir-oxide composite-coated chamber included over 29 min at mixture ratio 16. The thicker walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner walled coatings did not experience the macrocracking and chipping of the chambers that was seen with the thick, monolithic coatings. However, burn-throughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stoichiometric. The burn-throughs were probably the result of oxygen diffusion through the oxide coating that allowed the underlying Ir and Re layers to be oxidized. The results of this test program indicated that the thin-walled oxide coatings are better suited for repeated thermal cycling than the thick-walled coating, while thicker coatings may be required for operation in aggressively oxidizing environments.

Testing and evaluation of oxide-coated iridium/rhenium chambers

NASA Technical Reports Server (NTRS)

Reed, Brian D.

1993-01-01

Iridium-coated rhenium provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase iridium/rhenium rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated iridium/rhenium, 22 N rocket chambers were tested on gaseous hydrogen/gaseous oxygen propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia or zirconia. Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of zirconia infiltrated with sol gel hafnia. The other chamber had a coating composed of an iridium/oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. The iridium/oxide composite coated chamber included testing for over 29 minutes at mixture ratio 16. The thicker-walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner-walled coatings did not experience the macrocracking and chipping of the chambers seen with the thick, monolithic coatings. However, burnthroughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stochiometric. The burn-throughs were probably the result of oxygen-diffusion through the oxide coating that allowed the underlying iridium and rhenium layers to be oxidized. The results of this test program indicated that the thin-walled oxide coatings are better suited for repeated thermal cycling than the thick-walled coating, while thicker coatings may be required for operation in aggressively oxidizing environments.

Giant Steps in Cefalù

NASA Astrophysics Data System (ADS)

Jeffery, David J.; Mazzali, Paolo A.

2007-08-01

Giant steps is a technique to accelerate Monte Carlo radiative transfer in optically-thick cells (which are isotropic and homogeneous in matter properties and into which astrophysical atmospheres are divided) by greatly reducing the number of Monte Carlo steps needed to propagate photon packets through such cells. In an optically-thick cell, packets starting from any point (which can be regarded a point source) well away from the cell wall act essentially as packets diffusing from the point source in an infinite, isotropic, homogeneous atmosphere. One can replace many ordinary Monte Carlo steps that a packet diffusing from the point source takes by a randomly directed giant step whose length is slightly less than the distance to the nearest cell wall point from the point source. The giant step is assigned a time duration equal to the time for the RMS radius for a burst of packets diffusing from the point source to have reached the giant step length. We call assigning giant-step time durations this way RMS-radius (RMSR) synchronization. Propagating packets by series of giant steps in giant-steps random walks in the interiors of optically-thick cells constitutes the technique of giant steps. Giant steps effectively replaces the exact diffusion treatment of ordinary Monte Carlo radiative transfer in optically-thick cells by an approximate diffusion treatment. In this paper, we describe the basic idea of giant steps and report demonstration giant-steps flux calculations for the grey atmosphere. Speed-up factors of order 100 are obtained relative to ordinary Monte Carlo radiative transfer. In practical applications, speed-up factors of order ten and perhaps more are possible. The speed-up factor is likely to be significantly application-dependent and there is a trade-off between speed-up and accuracy. This paper and past work suggest that giant-steps error can probably be kept to a few percent by using sufficiently large boundary-layer optical depths while still maintaining large speed-up factors. Thus, giant steps can be characterized as a moderate accuracy radiative transfer technique. For many applications, the loss of some accuracy may be a tolerable price to pay for the speed-ups gained by using giant steps.

Biexponential characterization of prostate tissue water diffusion decay curves over an extended b-factor range.

PubMed

Mulkern, Robert V; Barnes, Agnieszka Szot; Haker, Steven J; Hung, Yin P; Rybicki, Frank J; Maier, Stephan E; Tempany, Clare M C

2006-06-01

Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging examinations at 1.5 T, a single 10-mm-thick axial slice was scanned with a line scan diffusion imaging sequence in which 14 equally spaced b factors from 5 to 3,500 s/mm(2) were sampled along three orthogonal diffusion sensitization directions in 6 min. Due to the combination of long scan time and limited volume coverage associated with the multi-b-factor, multidirectional sampling, the slice was chosen online from the available T2-weighted axial images with the specific goal of enabling the sampling of presumed noncancerous regions of interest (ROIs) within the central gland (CG) and peripheral zone (PZ). Histology from prescan biopsy (n=9) and postsurgical resection (n=4) was subsequently employed to help confirm that the ROIs sampled were noncancerous. The CG ROIs were characterized from the T2-weighted images as primarily mixtures of glandular and stromal benign prostatic hyperplasia, which is prevalent in this population. The water signal decays with b factor from all ROIs were clearly non-monoexponential and better served with bi- vs. monoexponential fits, as tested using chi(2)-based F test analyses. Fits to biexponential decay functions yielded intersubject fast diffusion component fractions in the order of 0.73+/-0.08 for both CG and PZ ROIs, fast diffusion coefficients of 2.68+/-0.39 and 2.52+/-0.38 microm(2)/ms and slow diffusion coefficients of 0.44+/-0.16 and 0.23+/-0.16 um(2)/ms for CG and PZ ROIs, respectively. The difference between the slow diffusion coefficients within CG and PZ was statistically significant as assessed with a Mann-Whitney nonparametric test (P<.05). We conclude that a monoexponential model for water diffusion decay in prostate tissue is inadequate when a large range of b factors is sampled and that biexponential analyses are better suited for characterizing prostate diffusion decay curves.

Time-dependent, optically thick accretion onto a black hole

NASA Technical Reports Server (NTRS)

Gilden, D. L.; Wheeler, J. C.

1980-01-01

A fully relativistic hydrodynamics code which incorporates diffusive radiation transport is used to study time-dependent, spherically symmetric, optically thick accretion onto a black hole. It is found that matter free-falls into the hole regardless of whether the diffusion time scale is longer or shorter than the dynamical time. Nonadiabatic heating due to magnetic field reconnection is included. The internal energy thus generated affects the flow in a purely relativistic way, again ensuring free-fall collapse of the inflowing matter. Any matter enveloping a black hole will thus be swallowed on a dynamical time scale with relatively small net release of energy. The inclusion of angular momentum will not necessarily affect this conclusion.

Investigating Thermal Parameters of PVDF Sensor in the Front Pyroelectric Configuration

NASA Astrophysics Data System (ADS)

Noroozi, Monir; Zakaria, Azmi; Husin, Mohd Shahril; Moksin, Mohd Maarof; Wahab, Zaidan Abd

2013-11-01

A metalized PVDF pyroelectric (PE) sensor was used as an optically opaque sensor and in a thermally thick regime for both sensor and sample, instead of a very thick sensor in the conventional front PE configuration. From the frequency dependence measurements, the normalized amplitude and phase signal were independently analyzed to obtain the thermal effusivity of the sensor. The differential normalized amplitude measured with water as a substrate was analyzed to determine the sensor thermal diffusivity. The PVDF thermal diffusivity and thermal effusivity agree with literature values. Then, from the known thermal parameters of the sensor, the thermal effusivity of a standard liquid sample, glycerol, and other liquids were obtained by the similar procedure.

Modeling solute clustering in the diffusion layer around a growing crystal.

PubMed

Shiau, Lie-Ding; Lu, Yung-Fang

2009-03-07

The mechanism of crystal growth from solution is often thought to consist of a mass transfer diffusion step followed by a surface reaction step. Solute molecules might form clusters in the diffusion step before incorporating into the crystal lattice. A model is proposed in this work to simulate the evolution of the cluster size distribution due to the simultaneous aggregation and breakage of solute molecules in the diffusion layer around a growing crystal in the stirred solution. The crystallization of KAl(SO(4))(2)12H(2)O from aqueous solution is studied to illustrate the effect of supersaturation and diffusion layer thickness on the number-average degree of clustering and the size distribution of solute clusters in the diffusion layer.

Effect of Ru thickness on spin pumping in Ru/Py bilayer

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

Behera, Nilamani; Singh, M. Sanjoy; Chaudhary, Sujeet

2015-05-07

We report the effect of Ru thickness (t{sub Ru}) on ferromagnetic resonance (FMR) line-width of Ru(t{sub Ru})/Py(23 nm) bilayer samples grown on Si(100)/SiO{sub 2} substrates at room temperature by magnetron sputtering. The FMR line-width is found to vary linearly with frequency for all thicknesses of Ru, indicating intrinsic origin of damping. For Ru thicknesses below 15 nm, Gilbert-damping parameter, α is almost constant. We ascribe this behavior to spin back flow that is operative for Ru thicknesses lower than the spin diffusion length in Ru, λ{sub sd}. For thicknesses >15 nm (>λ{sub sd}), the damping constant increases with Ru thickness, indicating spin pumpingmore » from Py into Ru.« less

Demonstrating the feasibility of monitoring the molecular-level structures of moving polymer/silane interfaces during silane diffusion using SFG.

PubMed

Chen, Chunyan; Wang, Jie; Loch, Cheryl L; Ahn, Dongchan; Chen, Zhan

2004-02-04

In this paper, the feasibility of monitoring molecular structures at a moving polymer/liquid interface by sum frequency generation (SFG) vibrational spectroscopy has been demonstrated. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane (AATM, NH2(CH2)2NH(CH2)3Si(OCH3)3) has been brought into contact with a deuterated poly(methyl methacrylate) (d-PMMA) film, and the interfacial silane structure has been monitored using SFG. Upon initial contact, the SFG spectra can be detected, but as time progresses, the spectral intensity changes and finally disappears. Additional experiments indicate that these silane molecules can diffuse into the polymer film and the detected SFG signals are actually from the moving polymer/silane interface. Our results show that the molecular order of the polymer/silane interface exists during the entire diffusion process and is lost when the silane molecules traverse through the thickness of the d-PMMA film. The loss of the SFG signal is due to the formation of a new disordered substrate/silane interface, which contributes no detectable SFG signal. The kinetics of the diffusion of the silane into the polymer have been deduced from the time-dependent SFG signals detected from the AATM molecules as they diffuse through polymer films of different thickness.

Probing Exciton Diffusion and Dissociation in Single-Walled Carbon Nanotube-C60 Heterojunctions

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

Dowgiallo, Anne-Marie; Mistry, Kevin S.; Johnson, Justin C.

The efficiency of thin-film organic photovoltaic (OPV) devices relies heavily upon the transport of excitons to type-II heterojunction interfaces, where there is sufficient driving force for exciton dissociation and ultimately the formation of charge carriers. Semiconducting single-walled carbon nanotubes (SWCNTs) are strong near-infrared absorbers that form type-II heterojunctions with fullerenes such as C60. Although the efficiencies of SWCNT-fullerene OPV devices have climbed over the past few years, questions remain regarding the fundamental factors that currently limit their performance. In this study, we determine the exciton diffusion length in the C60 layer of SWCNT-C60 bilayer active layers using femtosecond transient absorptionmore » measurements. We demonstrate that hole transfer from photoexcited C60 molecules to SWCNTs can be tracked by the growth of narrow spectroscopic signatures of holes in the SWCNT 'reporter layer'. In bilayers with thick C60 layers, the SWCNT charge-related signatures display a slow rise over hundreds of picoseconds, reflecting exciton diffusion through the C60 layer to the interface. A model based on exciton diffusion with a Beer-Lambert excitation profile, as well as Monte Carlo simulations, gives the best fit to the data as a function of C60 layer thickness using an exciton diffusion length of approximately 5 nm.« less

Probing Exciton Diffusion and Dissociation in Single-Walled Carbon Nanotube-C(60) Heterojunctions.

PubMed

Dowgiallo, Anne-Marie; Mistry, Kevin S; Johnson, Justin C; Reid, Obadiah G; Blackburn, Jeffrey L

2016-05-19

The efficiency of thin-film organic photovoltaic (OPV) devices relies heavily upon the transport of excitons to type-II heterojunction interfaces, where there is sufficient driving force for exciton dissociation and ultimately the formation of charge carriers. Semiconducting single-walled carbon nanotubes (SWCNTs) are strong near-infrared absorbers that form type-II heterojunctions with fullerenes such as C60. Although the efficiencies of SWCNT-fullerene OPV devices have climbed over the past few years, questions remain regarding the fundamental factors that currently limit their performance. In this study, we determine the exciton diffusion length in the C60 layer of SWCNT-C60 bilayer active layers using femtosecond transient absorption measurements. We demonstrate that hole transfer from photoexcited C60 molecules to SWCNTs can be tracked by the growth of narrow spectroscopic signatures of holes in the SWCNT "reporter layer". In bilayers with thick C60 layers, the SWCNT charge-related signatures display a slow rise over hundreds of picoseconds, reflecting exciton diffusion through the C60 layer to the interface. A model based on exciton diffusion with a Beer-Lambert excitation profile, as well as Monte Carlo simulations, gives the best fit to the data as a function of C60 layer thickness using an exciton diffusion length of approximately 5 nm.

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.

Enhancement of Sn-Bi-Ag Solder Joints with ENEPIG Surface Finish for Low-Temperature Interconnection

NASA Astrophysics Data System (ADS)

Pun, Kelvin P. L.; Islam, M. N.; Rotanson, Jason; Cheung, Chee-wah; Chan, Alan H. S.

2018-05-01

Low-temperature soldering constitutes a promising solution in interconnect technology with the increasing trend of heat-sensitive materials in integrated circuit packaging. Experimental work was carried out to investigate the effect of electroless Ni/electroless Pd/immersion gold (ENEPIG) layer thicknesses on Sn-Bi-Ag solder joint integrity during extended reflow at peak temperatures as low as 175°C. Optimizations are proposed to obtain reliable solder joints through analysis of interfacial microstructure with the resulting joint integrity under extended reflow time. A thin Ni(P) layer with thin Pd led to diffusion of Cu onto the interface resulting in Ni3Sn4 intermetallic compound (IMC) spalling with the formation of thin interfacial (Ni,Cu)3Sn4 IMCs which enhance the robustness of the solder after extended reflow, while thick Ni(P) with thin Pd resulted in weakened solder joints with reflow time due to thick interfacial Ni3Sn4 IMCs with the entrapped brittle Bi-phase. With a suitable thin Ni(P), the Pd thickness has to be optimized to prevent excessive Ni-P consumption and early Cu outward diffusion to enhance the solder joint during extended reflow. Based on these findings, suitable Ni(P) and Pd thicknesses of ENEPIG are recommended for the formation of robust low-temperature solder joints.

Diffusion of Mg dopant in metal-organic vapor-phase epitaxy grown GaN and AlxGa1-xN

NASA Astrophysics Data System (ADS)

Köhler, K.; Gutt, R.; Wiegert, J.; Kirste, L.

2013-02-01

Diffusion of the p-type dopant Mg in GaN and AlxGa1-xN which is accompanied by segregation and affected by transient effects in metal-organic vapor-phase epitaxy reactors is investigated. We have grown 110 nm thick Mg doped GaN and Al0.1Ga0.9N layers on top of undoped GaN and Al0.1Ga0.9N layers, respectively, in a temperature range between 925 °C and 1050 °C where we placed special emphasis on the lower temperature limit without diffusion to allow separation of Mg transients, diffusion, and segregation. Hereby, AlxGa1-xN layers enable monitoring of the resolution limit by secondary ion mass spectrometry analyses for the respective samples; therefore, thin AlxGa1-xN marker layers are incorporated in the thick GaN layers. We found an upper limit of 1.25 × 1019 cm-3 for diffusing Mg atoms in both sample types. Owing to the marked influence of Mg segregation in Al0.1Ga0.9N, diffusion is only seen by using a GaN cap on top of the Al0.1Ga0.9N layer sequence. Diffusion in Al0.1Ga0.9N is shown to be increased by about 25%-30% compared to GaN. Post growth annealing experiments under conditions equivalent to those used for growth of the Mg doped samples showed negligible diffusion. Comparing the results to well established findings on other doped III-V compounds, diffusion is explained by an interstitial-substitutional mechanism with a diffusion coefficient, which is concentration dependent. Analysis of the temperature dependent diffusivity revealed an activation energy of 5.0 eV for GaN:Mg and 5.2 eV for Al0.1Ga0.9N:Mg.

The heavy ion diffusion region in magnetic reconnection in the Earth's magnetotail

NASA Astrophysics Data System (ADS)

Liu, Y. H.; Mouikis, C. G.; Kistler, L. M.; Wang, S.; Roytershteyn, V.; Karimabadi, H.

2015-05-01

While the plasma in the Earth's magnetotail predominantly consists of protons and electrons, there are times when a significant amount of oxygen is present. When magnetic reconnection occurs, the behavior of these heavy ions can be significantly different from that of the protons, due to their larger gyroradius. In this study, we investigate the heavy ion distribution functions in the reconnection ion diffusion region from a 2.5D three-species particle-in-cell numerical simulation and compare those with Cluster observations from the near-Earth magnetotail. From the simulation results, we find that the heavy ions are demagnetized and accelerated in a larger diffusion region, the heavy ion diffusion region. The ion velocity distribution functions show that, inside the heavy ion diffusion region, heavy ions appear as counterstreaming beams along z in the GSM x-z plane, while drifting in y, carrying cross-tail current. We compare this result with Cluster observations in the vicinity of reconnection regions in the near-Earth magnetotail and find that the simulation predictions are consistent with the observed ion distribution functions in the ion diffusion region, as well as the inflow, exhaust, and separatrix regions. Based on the simulation and observation results, the presence of a multiscale diffusion region model, for O+ abundant reconnection events in the Earth's magnetotail, is demonstrated. A test particle simulation shows that in the diffusion region, the H+ gains energy mainly through Ex, while the O+ energy gain comes equally from Ex and Ey.

Surface-based brain morphometry and diffusion tensor imaging in schizoaffective disorder.

PubMed

Landin-Romero, Ramón; Canales-Rodríguez, Erick J; Kumfor, Fiona; Moreno-Alcázar, Ana; Madre, Mercè; Maristany, Teresa; Pomarol-Clotet, Edith; Amann, Benedikt L

2017-01-01

The profile of grey matter abnormalities and related white-matter pathology in schizoaffective disorder has only been studied to a limited extent. The aim of this study was to identify grey- and white-matter abnormalities in patients with schizoaffective disorder using complementary structural imaging techniques. Forty-five patients meeting Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition criteria and Research Diagnostic Criteria for schizoaffective disorder and 45 matched healthy controls underwent structural-T1 and diffusion magnetic resonance imaging to enable surface-based brain morphometry and diffusion tensor imaging analyses. Analyses were conducted to determine group differences in cortical volume, cortical thickness and surface area, as well as in fractional anisotropy and mean diffusivity. At a threshold of p = 0.05 corrected, all measures revealed significant differences between patients and controls at the group level. Spatial overlap of abnormalities was observed across the various structural neuroimaging measures. In grey matter, patients with schizoaffective disorder showed abnormalities in the frontal and temporal lobes, striatum, fusiform, cuneus, precuneus, lingual and limbic regions. White-matter abnormalities were identified in tracts connecting these areas, including the corpus callosum, superior and inferior longitudinal fasciculi, anterior thalamic radiation, uncinate fasciculus and cingulum bundle. The spatial overlap of abnormalities across the different imaging techniques suggests widespread and consistent brain pathology in schizoaffective disorder. The abnormalities were mainly detected in areas that have commonly been reported to be abnormal in schizophrenia, and to some extent in bipolar disorder, which may explain the clinical and aetiological overlap in these disorders.

Diffusion mechanism in molten salt baths during the production of carbide coatings via thermal reactive diffusion

NASA Astrophysics Data System (ADS)

Ghadi, Aliakbar; Saghafian, Hassan; Soltanieh, Mansour; Yang, Zhi-gang

2017-12-01

The diffusion mechanism of carbide-forming elements from a molten salt bath to a substrate surface was studied in this research, with particular focus on the processes occurring in the molten bath at the time of coating. Metal, oxide, and metal-oxide baths were investigated, and the coating process was performed on H13 steel substrates. Scanning electron microscopy and electron-probe microanalysis were used to study the coated samples and the quenched salt bath. The thickness of the carbide coating layer was 6.5 ± 0.5, 5.2 ± 0.5, or 5.7 ± 0.5 μm depending on whether it was deposited in a metal, oxide, or metal-oxide bath, respectively. The phase distribution of vanadium-rich regions was 63%, 57%, and 74% of the total coating deposited in metal, oxide, and metal-oxide baths, respectively. The results obtained using the metal bath indicated that undissolved suspended metal particles deposited onto the substrate surface. Then, carbon subsequently diffused to the substrate surface and reacted with the metal particles to form the carbides. In the oxide bath, oxide powders dissolved in the bath with or without binding to the oxidative structure (Na2O) of borax; they were then reduced by aluminum and converted into metal particles. We concluded that, in the metal and oxide baths, the deposition of metal particles onto the sample surface is an important step in the formation of the coating.

Fineblanking, Diffusion Bonding, and Testing of Fluidic Laminates.

DTIC Science & Technology

1980-07-01

AD-AU69 347 TRITEC INC COLUMBIA ND F/$ 13/7 FINEBLANKING, DIFFUSION BONDING, AND TESTING OF FLUIDIC LAMINAT --ETCIU) JUL 80 L K PECAN OAAK21-79-C-0074...amplifier assembly. The effects of die roll and burrs can be minimized by secondary operations *such as abrasive machining , but this adds to the expense...clad material. Experience has shown that a clad thickness of 0.038 + 0.008 mm is required for the semi-solid diffusion bonding process. The composition

Transfer matrix method for four-flux radiative transfer.

PubMed

Slovick, Brian; Flom, Zachary; Zipp, Lucas; Krishnamurthy, Srini

2017-07-20

We develop a transfer matrix method for four-flux radiative transfer, which is ideally suited for studying transport through multiple scattering layers. The model predicts the specular and diffuse reflection and transmission of multilayer composite films, including interface reflections, for diffuse or collimated incidence. For spherical particles in the diffusion approximation, we derive closed-form expressions for the matrix coefficients and show remarkable agreement with numerical Monte Carlo simulations for a range of absorption values and film thicknesses, and for an example multilayer slab.

Modeling uptake of hydrophobic organic contaminants into polyethylene passive samplers.

PubMed

Thompson, Jay M; Hsieh, Ching-Hong; Luthy, Richard G

2015-02-17

Single-phase passive samplers are gaining acceptance as a method to measure hydrophobic organic contaminant (HOC) concentration in water. Although the relationship between the HOC concentration in water and passive sampler is linear at equilibrium, mass transfer models are needed for nonequilibrium conditions. We report measurements of organochlorine pesticide diffusion and partition coefficients with respect to polyethylene (PE), and present a Fickian approach to modeling HOC uptake by PE in aqueous systems. The model is an analytic solution to Fick's second law applied through an aqueous diffusive boundary layer and a polyethylene layer. Comparisons of the model with existing methods indicate agreement at appropriate boundary conditions. Laboratory release experiments on the organochlorine pesticides DDT, DDE, DDD, and chlordane in well-mixed slurries support the model's applicability to aqueous systems. In general, the advantage of the model is its application in the cases of well-agitated systems, low values of polyethylene-water partioning coefficients, thick polyethylene relative to the boundary layer thickness, and/or short exposure times. Another significant advantage is the ability to estimate, or at least bound, the needed exposure time to reach a desired CPE without empirical model inputs. A further finding of this work is that polyethylene diffusivity does not vary by transport direction through the sampler thickness.

Rates of weathering rind formation on Costa Rican basalt

NASA Astrophysics Data System (ADS)

Sak, Peter B.; Fisher, Donald M.; Gardner, Thomas W.; Murphy, Katherine; Brantley, Susan L.

2004-04-01

Weathering rind thicknesses were measured on ∼ 200 basaltic clasts collected from three regionally extensive alluvial fill terraces (Qt 1, Qt 2, and Qt 3) preserved along the Pacific coast of Costa Rica. Mass balance calculations suggest that conversion of unweathered basaltic core minerals (plagioclase and augite) to authigenic minerals in the porous rind (kaolinite, allophane, gibbsite, Fe oxyhydroxides) is iso-volumetric and Ti and Zr are relatively immobile. The hierarchy of cation mobility (Ca ≈ Na > K ≈ Mg > Si > Al > Fe ≈ P) is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering (anorthite > albite ≈ hypersthene > orthoclase ≫ apatite). Alteration profiles across the cm-thick rinds document dissolution of plagioclase and augite and the growth of kaolinite, with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age. The rate of weathering rind advance is evaluated using a diffusion-limited model which predicts a parabolic rate law for weathering rind thickness, rr, as a function of time, t(rr =κt), and an interface-limited model which predicts a linear rate law for weathering rind thickness as a function of time (rr = kappt). In these rate laws, κ is a diffusion parameter and kapp is an apparent rate constant. The rate of advance is best fit by the interface model. Terrace exposures are confined to the lower reaches of streams draining the Pacific slope near the coast where the stream gradient is less than ∼3 m/km, and terrace deposition is influenced by eustatic sea level fluctuations. Geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest. Assigning the most weathered regionally extensive terrace Qt 1 (mean rind thickness 6.9 ± 0. 6cm) to oxygen isotope stage (OIS) 7 (ca. 240 ka), and assuming that at time = 0 rind thickness = 0, it is inferred that terrace Qt 2 (rr = 2.9 ± 0.1 cm) is coincident with stage 5e (ca. 125 ka) and that Qt 3 (rr = 0.9 ± 0.1 cm) is consistent with OIS 3 (ca. 37 ka). These assignments yield a value of kapp of 8.6 × 10-13 cm s-1 (R2 = 0.99). Only this value satisfies both the existing age controls and yields ages coincident with sea level maxima. Using this value, elemental weathering release fluxes across a weathering rind from Qt 2 range from 6.0 × 10-9 mol Si m-2 s-1 to 2.5 × 10-11 mol K m-2 s-1. The rate of rind advance for the Costa Rican terraces is 2.8 × 10-7 m yr-1. Basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface-controlled weathering with an apparent activation energy of about 50 kJ mol-1. Rates of rind formation in Costa Rica are an order of magnitude slower than reported for global averages of soil formation rates.

Modeling on the cathodoluminescence properties of the thin film phosphors for field emission flat panel displays

NASA Astrophysics Data System (ADS)

Cho, Kyu-Gong

2000-12-01

In order to investigate the effects of the film roughness with the fundamental luminance parameters of thin film phosphors, Y2 O3:Eu films with different thickness and roughness values were deposited on various substrate materials using a pulsed laser deposition technique under a controlled experimental procedure. The best luminous efficiency was observed from the Y2O3:Eu films on quartz substrates due to the smaller refractive index and low absorption characteristics of the quartz substrates which produce a larger amount of total internal reflection in the film and low loss of light intensity during the multiple internal reflections. The trapped light inside the film can escape the film more easily due to rougher film surface. The better epitaxial growth capability of the Y2O 3:Eu films with the LaAlO3 substrates resulted in higher luminous efficiency in the small surface roughness region. Higher luminous efficiency was observed in reflection mode than in transmission mode due to the contribution of diffusely scattered light at the air-film interface. A new theoretical model based on the diffraction scattering theory of light, the steady-state diffusion condition of carriers and the Kanaya-Okayama's electron- beam-solid interaction range satisfactorily explains all the experimental results mentioned above. The model also provides solid understandings on the cathodoluminescence properties of the thin film phosphors with the effects of other single or multiple luminance parameters. The parameters encountered for the model are surface roughness, electron-beam-solid interaction, surface recombination rate of carriers, charge carrier diffusion properties, multiple scattering at the interfaces (air- film, film-substrate, and substrate-air), optical properties of the material, film thickness, and substrate type. The model supplies a general solution in both qualitative and quantitative ways to estimate the luminance properties of the thin film phosphors and it can be utilized to optimize the thin film phosphor properties for the application of field emission flat panel displays.

Two-dimensional and 3-D images of thick tissue using time-constrained times-of-flight and absorbance spectrophotometry

NASA Astrophysics Data System (ADS)

Benaron, David A.; Lennox, M.; Stevenson, David K.

1992-05-01

Reconstructing deep-tissue images in real time using spectrophotometric data from optically diffusing thick tissues has been problematic. Continuous wave applications (e.g., pulse oximetry, regional cerebral saturation) ignore both the multiple paths traveled by the photons through the tissue and the effects of scattering, allowing scalar measurements but only under limited conditions; interferometry works poorly in thick, highly-scattering media; frequency- modulated approaches may not allow full deconvolution of scattering and absorbance; and pulsed-light techniques allow for preservation of information regarding the multiple paths taken by light through the tissue, but reconstruction is both computation intensive and limited by the relative surface area available for detection of photons. We have developed a picosecond times-of-flight and absorbance (TOFA) optical system, time-constrained to measure only photons with a narrow range of path lengths and arriving within a narrow angel of the emitter-detector axis. The delay until arrival of the earliest arriving photons is a function of both the scattering and absorbance of the tissues in a direct line between the emitter and detector, reducing the influence of surrounding tissues. Measurement using a variety of emitter and detector locations produces spatial information which can be analyzed in a standard 2-D grid, or subject to computer reconstruction to produce tomographic images representing 3-D structure. Using such a technique, we have been able to demonstrate the principles of tc-TOFA, detect and localize diffusive and/or absorptive objects suspended in highly scattering media (such as blood admixed with yeast), and perform simple 3-D reconstructions using phantom objects. We are now attempting to obtain images in vivo. Potential future applications include use as a research tool, and as a continuous, noninvasive, nondestructive monitor in diagnostic imaging, fetal monitoring, neurologic and cardiac assessment. The technique may lead to real-time optical imaging and quantitation of tissues oxygen delivery.

Effects of nitrogen incorporation in HfO(2) grown on InP by atomic layer deposition: an evolution in structural, chemical, and electrical characteristics.

PubMed

Kang, Yu-Seon; Kim, Dae-Kyoung; Kang, Hang-Kyu; Jeong, Kwang-Sik; Cho, Mann-Ho; Ko, Dae-Hong; Kim, Hyoungsub; Seo, Jung-Hye; Kim, Dong-Chan

2014-03-26

We investigated the effects of postnitridation on the structural characteristics and interfacial reactions of HfO2 thin films grown on InP by atomic layer deposition (ALD) as a function of film thickness. By postdeposition annealing under NH3 vapor (PDN) at 600 °C, an InN layer formed at the HfO2/InP interface, and ionized NHx was incorporated in the HfO2 film. We demonstrate that structural changes resulting from nitridation of HfO2/InP depend on the film thickness (i.e., a single-crystal interfacial layer of h-InN formed at thin (2 nm) HfO2/InP interfaces, whereas an amorphous InN layer formed at thick (>6 nm) HfO2/InP interfaces). Consequently, the tetragonal structure of HfO2 transformed into a mixture structure of tetragonal and monoclinic because the interfacial InN layer relieved interfacial strain between HfO2 and InP. During postdeposition annealing (PDA) in HfO2/InP at 600 °C, large numbers of oxidation states were generated as a result of interfacial reactions between interdiffused oxygen impurities and out-diffused InP substrate elements. However, in the case of the PDN of HfO2/InP structures at 600 °C, nitrogen incorporation in the HfO2 film effectively blocked the out-diffusion of atomic In and P, thus suppressing the formation of oxidation states. Accordingly, the number of interfacial defect states (Dit) within the band gap of InP was significantly reduced, which was also supported by DFT calculations. Interfacial InN in HfO2/InP increased the electron-barrier height to ∼0.6 eV, which led to low-leakage-current density in the gate voltage region over 2 V.

Kinetics of Isothermal Reactive Diffusion Between Solid Cu and Liquid Sn

NASA Astrophysics Data System (ADS)

O, M.; Suzuki, T.; Kajihara, M.

2018-01-01

The Cu/Sn system is one of the most fundamental and important metallic systems for solder joints in electric devices. To realize reliable solder joints, information on reactive diffusion at the solder joint is very important. In the present study, we experimentally investigated the kinetics of the reactive diffusion between solid Cu and liquid Sn using semi-infinite Cu/Sn diffusion couples prepared by an isothermal bonding technique. Isothermal annealing of the diffusion couple was conducted in the temperature range of 533-603 K for various times up to 172.8 ks (48 h). Using annealing, an intermetallic layer composed of Cu6Sn5 with scallop morphology and Cu3Sn with rather uniform thickness is formed at the original Cu/Sn interface in the diffusion couple. The growth of the Cu6Sn5 scallop occurs much more quickly than that of the Cu3Sn layer and thus predominates in the overall growth of the intermetallic layer. This tendency becomes more remarkable at lower annealing temperatures. The total thickness of the intermetallic layer is proportional to a power function of the annealing time, and the exponent of the power function is close to unity at all the annealing temperatures. This means that volume diffusion controls the intermetallic growth and the morphology of the Cu6Sn5/Sn interface influences the rate-controlling process. Adopting a mean value of 0.99 for the exponent, we obtain a value of 26 kJ/mol for the activation enthalpy of the intermetallic growth.

The Dorsal Rather than Ventral Pathway Better Reflects Individual Syntactic Abilities in Second Language

PubMed Central

Yamamoto, Kayako; Sakai, Kuniyoshi L.

2016-01-01

The left inferior frontal gyrus (IFG) has been reported to be critically involved in syntactic processing, not only in first language (L1), but in second language (L2). Indeed, the leftward lateralization of the IFG has been shown to be correlated with the performance of a syntactic task in L2. Given that posterior language-related regions are systematically connected with the left IFG, the next question is which of the dorsal and ventral pathways is more critical to the individual syntactic abilities in L2. Here we used diffusion magnetic resonance imaging (MRI) and tractography with newly developed semi-automatic methods of defining seeds and selecting regions of interest (ROIs). We calculated mean thickness and fractional anisotropy (FA) in each ROI for the arcuate fasciculus (Arcuate) of the dorsal pathway, as well as for the inferior fronto-occipital fasciculus (IFOF) of the ventral pathway. In Experiment I, we performed partial correlation analyses between FA and the accuracy of the syntactic task, removing the effects of the accuracy of a spelling task, gender, and handedness. Among the two pathways in each hemisphere, only FA of the left Arcuate was significantly correlated with individual accuracy of the syntactic task. In Experiment II, we recruited monozygotic twins and examined to what extent their L2 abilities and their structural properties were similar. Within twin pairs, the highest significant correlation was observed for reaction times of the spelling task, while the correlation for the accuracy of the syntactic task was marginal; these two correlation coefficients were significantly different. Moreover, the thickness of the left Arcuate was highly correlated within pairs, while its FA, as well as the thickness/FA in the ventral pathways, was not significantly correlated. The correlation coefficient for the thickness of the left Arcuate was significantly larger than that of the left IFOF. These results suggest that the thickness of the left Arcuate is more associated with the shared genetic/environmental factors, whereas both of mutually correlated FA in the left Arcuate and individual syntactic abilities in L2 may be less prone to these shared factors. PMID:27378889

High spatial resolution of the mid-infrared emission of the Compton-thick type 2 Seyfert galaxy, Markarian 3

NASA Astrophysics Data System (ADS)

Sales, Dinalva A.; Ruschel-Dutra, D.; Pastoriza, M. G.; Riffel, R.; Winge, Cláudia

2014-06-01

The mid-infrared (MIR) spectra observed with Gemini/Michelle have been used to study the nuclear region of the Compton-thick type 2 Seyfert galaxy, Markarian 3 (Mrk 3), at a spatial resolution of ˜200 pc. No polycyclic aromatic hydrocarbon emission bands were detected in the N-band spectrum of Mrk 3. However, intense [Ar III] 8.99 μm, [S IV] 10.5 μm and [Ne II] 12.8 μm ionic emission lines, as well as a silicate absorption feature at 9.7 μm, have been found in the nuclear extraction (˜200 pc). We also present a subarcsecond-resolution Michelle N-band image of Mrk 3, which resolves its circumnuclear region. This diffuse MIR emission shows up as a wing towards the east-west direction, closely aligned with the S-shape of the narrow-line region observed in the optical [O III] λ5007Å image from the Faint Object Camera onboard the Hubble Space Telescope. The nuclear continuum spectrum can be well represented by a theoretical torus spectral energy distribution, suggesting that the nucleus of Mrk 3 might host a dusty toroidal structure, as predicted by the unified model of an active galactic nucleus (AGN). In addition, the hydrogen column density (N_H= 4.8^{+3.3}_{-3.1}× 10^{23} cm-2) estimated with a torus model for Mrk 3 is consistent with the value derived from X-ray spectroscopy. The torus model geometry of Mrk 3 is similar to that of NGC 3281 (both are Compton-thick galaxies), confirmed through fitting the 9.7-μm silicate band profile. These results might provide further evidence that silicate-rich dust can be associated with the AGN torus and might also be responsible for the absorption observed at X-ray wavelengths in those galaxies.

High mobility, dual layer, c-axis aligned crystalline/amorphous IGZO thin film transistor

NASA Astrophysics Data System (ADS)

Chung, Chen-Yang; Zhu, Bin; Greene, Raymond G.; Thompson, Michael O.; Ast, Dieter G.

2015-11-01

We demonstrate a dual layer IGZO thin film transistor (TFT) consisting of a 310 °C deposited c-axis aligned crystal (CAAC) 20 nm thick channel layer capped by a second, 30 nm thick, 260 °C deposited amorphous IGZO layer. The TFT exhibits a saturation field-effect mobility of ˜20 cm2/V s, exceeding the mobility of 50 nm thick single layer reference TFTs fabricated with either material. The deposition temperature of the second layer influences the mobility of the underlying transport layer. When the cap layer is deposited at room temperature (RT), the mobility in the 310 °C deposited CAAC layer is initially low (6.7 cm2/V s), but rises continuously with time over 58 days to 20.5 cm2/V s, i.e., to the same value as when the second layer is deposited at 260 °C. This observation indicates that the two layers equilibrate at RT with a time constant on the order of 5 × 106 s. An analysis based on diffusive transport indicates that the room temperature diffusivity must be of the order of 1 × 10-18 cm2 s-1 with an activation enthalpy EA < 0.2 eV for the mobility limiting species. The findings are consistent with a hypothesis that the amorphous layer deposited on top of the CAAC has a higher solubility for impurities and/or structural defects than the underlying nanocrystalline transport layer, and that the equilibration of the mobility limiting species is rate limited by hydrogen diffusion, whose known diffusivity fits these estimates.

Kinetic Plasma and Turbulent Mix Studies using DT Plastic-shell Implosions with Shell-thickness and Pressure Variations

NASA Astrophysics Data System (ADS)

Kim, Y.; Herrmann, H. W.; Hoffman, N. M.; Schmitt, M. J.; Bradley, P. A.; Kagan, G.; Gales, S.; Horsfield, C. J.; Rubery, M.; Leatherland, A.; Gatu Johnson, M.; Glebov, V.; Seka, W.; Marshall, F.; Stoeckl, C.; Church, J.

2014-10-01

Kinetic plasma and turbulent mix effects on inertial confinement fusion have been studied using a series of DT-filled plastic-shell implosions at the OMEGA laser facility. Plastic capsules of 4 different shell thicknesses (7.4, 15, 20, 29 micron) were shot at 2 different fill pressures in order to vary the ion mean free path compared to the size of fuel region (i.e., Knudsen number). We varied the empirical Knudsen number by a factor of 25. Measurements were obtained from the burn-averaged ion temperature and fuel areal density. Preliminary results indicate that as the empirical Knudsen number increases, fusion performances (e.g., neutron yield) increasingly deviate from hydrodynamic simulations unless turbulent mix and ion kinetic terms (e.g., enhanced ion diffusion, viscosity, thermal conduction, as well as Knudsen-layer fusion reactivity reduction) are considered. We are developing two separate simulations: one is a reduced-ion-kinetics model and the other is turbulent mix model. Two simulation results will be compared with the experimental observables.

Contribution of CT quantified emphysema, air trapping and airway wall thickness on pulmonary function in male smokers with and without COPD.

PubMed

Mohamed Hoesein, Firdaus A A; de Jong, Pim A; Lammers, Jan-Willem J; Mali, Willem P Th M; Mets, Onno M; Schmidt, Michael; de Koning, Harry J; Aalst, Carlijn van der; Oudkerk, Matthijs; Vliegenthart, Rozemarijn; Ginneken, Bram van; van Rikxoort, Eva M; Zanen, Pieter

2014-09-01

Emphysema, airway wall thickening and air trapping are associated with chronic obstructive pulmonary disease (COPD). All three can be quantified by computed tomography (CT) of the chest. The goal of the current study is to determine the relative contribution of CT derived parameters on spirometry, lung volume and lung diffusion testing. Emphysema, airway wall thickening and air trapping were quantified automatically on CT in 1,138 male smokers with and without COPD. Emphysema was quantified by the percentage of voxels below -950 Hounsfield Units (HU), airway wall thickness by the square root of wall area for a theoretical airway with 10 mm lumen perimeter (Pi10) and air trapping by the ratio of mean lung density at expiration and inspiration (E/I-ratio). Spirometry, residual volume to total lung capacity (RV/TLC) and diffusion capacity (Kco) were obtained. Standardized regression coefficients (β) were used to analyze the relative contribution of CT changes to pulmonary function measures. The independent contribution of the three CT measures differed per lung function parameter. For the FEV1 airway wall thickness was the most contributing structural lung change (β = -0.46), while for the FEV1/FVC this was emphysema (β = -0.55). For the residual volume (RV) air trapping was most contributing (β = -0.35). Lung diffusion capacity was most influenced by emphysema (β = -0.42). In a cohort of smokers with and without COPD the effect of different CT changes varies per lung function measure and therefore emphysema, airway wall thickness and air trapping need to be taken in account.

Diffusion of progestogens through Silastic rubber implants.

PubMed

Lifchez, A S; Scommegna, A

1970-05-01

Silastic rubber capsules in 2 thicknesses (.42 mm and .80 mm) and 3 lengths (9, 14, and 19 mm) were filled with progesterone, Provera, Norgestrel, or chlormadinone acetate and implanted under the skin of rats, and the amount of steroid released was measured after 1, 2, 4, and 8 weeks. The amount of steroid released was also measured from progesterone-filled capsules .42 mm thick and varying from 19-32 mm long inserted in the uterus of 16 women volunteers for 1-7 days. The rate of release of each steroid in the rats was found to be proportionate to the length of the capsule and related, but not proportional to the thickness of the capsule. The release rate of progesterone was 3-20 times greater than that of the other steroids, while Norgestrel diffused at the lowest rate. The influence of thickness of capsule was greater for the steroids with the highest diffusion rate, progesterone and chlormadinone acetate. The release rates of all except chlormadinone acetate were higher in the 1st week. The release rates of the synthetic progestins, unlike that of progesterone, were relatively constant after the 1st week. The release rate of progesterone tended to be related to the amount remaining in the capsule when the amount became small. The measured amount of progesterone released each day from each intrauterine capsule was also proportional to its length. It appears that Norgestrel, Provera, and chlormadinone acetate are all released slowly enough and have enough biologic activity at low concentrations to have a contraceptive effect for well over 1 year when administered in a 30 mm intrauterine capsule.

Approximate Solution Methods for Spectral Radiative Transfer in High Refractive Index Layers

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1994-01-01

Some ceramic materials for high temperature applications are partially transparent for radiative transfer. The refractive indices of these materials can be substantially greater than one which influences internal radiative emission and reflections. Heat transfer behavior of single and laminated layers has been obtained in the literature by numerical solutions of the radiative transfer equations coupled with heat conduction and heating at the boundaries by convection and radiation. Two-flux and diffusion methods are investigated here to obtain approximate solutions using a simpler formulation than required for exact numerical solutions. Isotropic scattering is included. The two-flux method for a single layer yields excellent results for gray and two band spectral calculations. The diffusion method yields a good approximation for spectral behavior in laminated multiple layers if the overall optical thickness is larger than about ten. A hybrid spectral model is developed using the two-flux method in the optically thin bands, and radiative diffusion in bands that are optically thick.

Diffusion analysis of one photosensitizer in bovine teeth using fluorescence optical imaging

NASA Astrophysics Data System (ADS)

Montanha, S.; Pratavieira, S.; Jacomassi, D. P.; Rastelli, A. N. S.; Bagnato, V. S.

2012-01-01

Some photosensitizers (PSs) used for PACT (Antimicrobial Photodynamic Therapy) show an affinity for bacterial walls and can be photo-activated to cause the desired damage. However, on dentine bacterias may be less susceptible to PACT as a result of limited penetration of the PS. The aim of this study was to evaluate the diffusion of one PS based on hematoporphyrin on dentine structures. Twelve bovine incisors were used. Class III cavities (3 x 3 x 1mm) were prepared on the mesial or distal surfaces using a diamond bur. Photogem® solution at 1 mg/mL (10 uL for each cavity) was used. The experimental Groups were divided according to thickness of dentine remaining and etched or no-etched before the PS application. The fluorescence excitation source was a VelScope® system. For image capture a scientific CCD color camera PixelFly® was coupled to VelScope. For image acquisition and processing, a computational routine was developed at Matlab®. Fick's Law was used to obtain the average diffusion coefficient of PS. Differences were found between all Groups. The longitudinal temporal diffusion was influenced by the different times, thickness and acid etching.

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.

Quantitative characterization of turbidity by radiative transfer based reflectance imaging

PubMed Central

Tian, Peng; Chen, Cheng; Jin, Jiahong; Hong, Heng; Lu, Jun Q.; Hu, Xin-Hua

2018-01-01

A new and noncontact approach of multispectral reflectance imaging has been developed to inversely determine the absorption coefficient of μa, the scattering coefficient of μs and the anisotropy factor g of a turbid target from one measured reflectance image. The incident beam was profiled with a diffuse reflectance standard for deriving both measured and calculated reflectance images. A GPU implemented Monte Carlo code was developed to determine the parameters with a conjugate gradient descent algorithm and the existence of unique solutions was shown. We noninvasively determined embedded region thickness in heterogeneous targets and estimated in vivo optical parameters of nevi from 4 patients between 500 and 950nm for melanoma diagnosis to demonstrate the potentials of quantitative reflectance imaging. PMID:29760971

Matrix operator theory of radiative transfer. 2: scattering from maritime haze.

PubMed

Kattawar, G W; Plass, G N; Catchings, F E

1973-05-01

Matrix operator theory is used to calculate the reflected and transmitted radiance of photons that have interacted with plane-parallel maritime haze layers. The results are presented for three solar zenith angles, three values of the surface albedo, and a range of optical thicknesses from very thin to very thick. The diffuse flux at the lower boundary and the cloud albedo are tabulated. The forward peak and other features in the single scattered phase function cause the radiance in many cases to be very different from that for Rayleigh scattering. In particular the variation of the radiance with both the zenith or nadir angle and the azimuthal angle is more marked and the relative limb darkening under very thick layers is greater for haze M than for Rayleigh scattering. The downward diffuse flux at the lower boundary for A = 0 is always greater and the cloud albedo is always less for haze M than for Rayleigh layers.

Optical properties of paint-on resins for shade modification of crown and bridge resins--light transmittance characteristics--.

PubMed

Arikawa, Hiroyuki; Kanie, Takahito; Fujii, Koichi; Homma, Tetsuya; Takahashi, Hideo; Ban, Seiji

2003-09-01

The purpose of this study was to examine the light transmittance characteristics of the paint-on resins for shade modification. Three shades of paint-on resin, one crown and bridge resin, and human enamel were used. Specimens with four different thicknesses (75-150 microm) were prepared. The light transmittances including its wavelength distribution and diffusion characteristics were measured. The color values and the color differences among thicknesses of specimens were also determined. The light transmittance values of the paint-on resins ranged from 60.3% to 88.3% at 100 microm thickness, which were lower or nearly equal in comparison with the crown and bridge resin and enamel. Although differences in the wavelength distribution of transmittance among materials were found at lower wavelengths, all materials showed similar diffusion characteristics. The thin layer of paint-on resin effectively changed the color of restorative resin. The paint-on resin may be an effective material for the modification of the color appearance matching required.

Microstructural Study on Oxidation Resistance of Nonmodified and Platinum Modified Aluminide Coating

NASA Astrophysics Data System (ADS)

Zagula-Yavorska, Maryana; Sieniawski, Jan

2014-03-01

Platinum electroplating layers (3 and 7 μm thick) were deposited on the surface of the Inconel 713 LC, CMSX 4, and Inconel 625 Ni-base superalloys. Diffusion treatment at 1050°C for 2 h under argon atmosphere was performed after electroplating. Diffusion treated samples were aluminized according to the low activity CVD process at 1050°C for 8 h. The nonmodified aluminide coatings consist of NiAl phase. Platinum modification let to obtain the (Ni,Pt)Al phase in coatings. The coated samples were subjected to cyclic oxidation testing at 1100°C. It was discovered that increase of the platinum electroplating thickness from 3 to 7 μm provides the improvement of oxidation resistance of aluminide coatings. Increase of the platinum thickness causes decreases in weight change and decreases in parabolic constant during oxidation. The platinum provides the pure Al2O3 oxide formation, slow growth oxide layer, and delay the oxide spalling during heating-cooling thermal cycles.

Static and hydrodynamic studies of the conformation of adsorbed macromolecules at the solid/liquid interface

NASA Astrophysics Data System (ADS)

Yavorsky, D. P.

1981-08-01

The structure of an adsorbed macromolecular layer at the solid/liquid interface under both stationary and flow conditions is examined. The conformation of adsorbed bovine serum albumin (BSA) is deduced from the thickness of surface layers formed on the pore walls of track etched (mica) membranes. Changes in membrane permeability due to protein adsorption are related directly to a net reduction in pore size or an equivalent adsorbed layer thickness. Complementary permeability measurements using electrolyte conduction, tracer diffusion, and pressure driven flow have verified the unique structural qualities of the track etched membrane and collectively demonstrate an ability to determine bare pore size with an accuracy of + or - 2A. The average static thickness of an adsorbed BSA layer, as derived from electrolyte conduction and tracer diffusion, was 43 + or - 3A independent of pore size. In comparison with the known BSA solution dimensions, this measured thickness is consistent with a monolayer of structurally unperturbed protein molecules each oriented in a "side-on" position. Pronounced conformational changes in adsorbed BSA layers were observed under conditions of shear flow. Electrostatic interactions were also shown to significantly affect adsorbed protein conformation through changes in solution ionic strength and surface charge.

Water Absorption and Thickness Swelling Behavior of Polypropylene Reinforced with Hybrid Recycled Newspaper and Glass Fiber

NASA Astrophysics Data System (ADS)

Shakeri, Alireza; Ghasemian, Ali

2010-04-01

This study aims to investigate the moisture absorption of recycled newspaper fiber and recycled newspaper-glass fiber hybrid reinforced polypropylene composites to study their suitability in outdoor applications. In this work composite materials were made from E-glass fiber (G), recycled newspaper (NP) and polypropylene (PP), by using internal mixing and hot-pressing molding. Long-term water absorption (WA) and thickness swelling (TS) kinetics of the composites was investigated with water immersion. It was found that the WA and TS increase with NP content in composite and water immersion time before an equilibrium condition was reached. Composites made from the NP show comparable results as those made of the hybrid fiber. The results suggest that the water absorption and thickness swelling composite decrease with increasing glass fiber contents in hybrid fiber composite. It is interesting to find that the WA and TS can be reduced significantly with incorporation of a coupling agent (maleated polypropylene) in the composite formulation. Further studies were conducted to model the water diffusion and thickness swelling of the composites. Diffusion coefficients and swelling rate parameters in the models were obtained by fitting the model predictions with the experimental data.

Optimizing ZnS/6LiF scintillators for wavelength-shifting-fiber neutron detectors

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

Crow, Lowell; Funk, Loren L; Hannan, Bruce W

2016-01-01

In this paper we compare the performance of grooved and flat ZnS/6LiF scintillators in a wavelength shifting-fiber (WLSF) detector. Flat ZnS/6LiF scintillators with the thickness L=0.2-0.8 mm were characterized using photon counting and pulse-height analysis and compared to a grooved scintillator of approximately 0.8 mm thick. While a grooved scintillator considerably increases the apparent thickness of the scintillator to neutrons for a given coating thickness, we find that the flat scintillators perform better than the grooved scintillators in terms of both light yield and neutron detection efficiency. The flat 0.8-mm-thick scintillator has the highest light output, and it is 52%more » higher compared with a grooved scintillator of same thickness. The lower light output of the grooved scintillator as compared to the flat scintillator is consistent with the greater scintillator-WLSF separation and the much larger average emission angle of the grooved scintillator. We also find that the average light cone width, or photon travel-length as measured using time-of-flight powder diffraction of diamond and vanadium, decreases with increasing L in the range of L=0.6-0.8 mm. This result contrasts with the traditional Swank diffusion model for micro-composite scintillators, and could be explained by a decrease in photon diffusion-coefficient or an increase in micro-particle content in the flat scintillator matrix for the thicker scintillators.« less

Measurement of diffusion coefficient of propylene glycol in skin tissue

NASA Astrophysics Data System (ADS)

Genin, Vadim D.; Bashkatov, Alexey N.; Genina, Elina A.; Tuchin, Valery V.

2015-03-01

Optical clearing of the rat skin under the action of propylene glycol was studied ex vivo. It was found that collimated transmittance of skin samples increased, whereas weight and thickness of the samples decreased during propylene glycol penetration in skin tissue. A mechanism of the optical clearing under the action of propylene glycol is discussed. Diffusion coefficient of propylene glycol in skin tissue ex vivo has been estimated as (1.35±0.95)×10-7 cm2/s with the taking into account of kinetics of both weight and thickness of skin samples. The presented results can be useful for enhancement of many methods of laser therapy and optical diagnostics of skin diseases and localization of subcutaneous neoplasms.

Highly efficient single-junction GaAs thin-film solar cell on flexible substrate.

PubMed

Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

2016-07-20

There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination.

Atomically thin p-n junctions with van der Waals heterointerfaces.

PubMed

Lee, Chul-Ho; Lee, Gwan-Hyoung; van der Zande, Arend M; Chen, Wenchao; Li, Yilei; Han, Minyong; Cui, Xu; Arefe, Ghidewon; Nuckolls, Colin; Heinz, Tony F; Guo, Jing; Hone, James; Kim, Philip

2014-09-01

Semiconductor p-n junctions are essential building blocks for electronic and optoelectronic devices. In conventional p-n junctions, regions depleted of free charge carriers form on either side of the junction, generating built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p-n junction at the ultimate thickness limit. Van der Waals junctions composed of p- and n-type semiconductors--each just one unit cell thick--are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p-n heterojunctions fabricated using van der Waals assembly of transition-metal dichalcogenides. We observe gate-tunable diode-like current rectification and a photovoltaic response across the p-n interface. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p-n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p-n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.

Fractal dimension brain morphometry: a novel approach to quantify white matter in traumatic brain injury.

PubMed

Rajagopalan, Venkateswaran; Das, Abhijit; Zhang, Luduan; Hillary, Frank; Wylie, Glenn R; Yue, Guang H

2018-06-16

Traumatic brain injury (TBI) is the main cause of disability in people younger than 35 in the United States. The mechanisms of TBI are complex resulting in both focal and diffuse brain damage. Fractal dimension (FD) is a measure that can characterize morphometric complexity and variability of brain structure especially white matter (WM) structure and may provide novel insights into the injuries evident following TBI. FD-based brain morphometry may provide information on WM structural changes after TBI that is more sensitive to subtle structural changes post injury compared to conventional MRI measurements. Anatomical and diffusion tensor imaging (DTI) data were obtained using a 3 T MRI scanner in subjects with moderate to severe TBI and in healthy controls (HC). Whole brain WM volume, grey matter volume, cortical thickness, cortical area, FD and DTI metrics were evaluated globally and for the left and right hemispheres separately. A neuropsychological test battery sensitive to cognitive impairment associated with traumatic brain injury was performed. TBI group showed lower structural complexity (FD) bilaterally (p < 0.05). No significant difference in either grey matter volume, cortical thickness or cortical area was observed in any of the brain regions between TBI and healthy controls. No significant differences in whole brain WM volume or DTI metrics between TBI and HC groups were observed. Behavioral data analysis revealed that WM FD accounted for a significant amount of variance in executive functioning and processing speed beyond demographic and DTI variables. FD therefore, may serve as a sensitive marker of injury and may play a role in outcome prediction in TBI.

Direct Collapse to Supermassive Black Hole Seeds with Radiative Transfer: Isolated Halos

NASA Astrophysics Data System (ADS)

Luo, Yang; Ardaneh, Kazem; Shlosman, Isaac; Nagamine, Kentaro; Wise, John H.; Begelman, Mitchell C.

2018-05-01

Direct collapse within dark matter haloes is a promising path to form supermassive black hole seeds at high redshifts. The outer part of this collapse remains optically thin. However, the innermost region of the collapse is expected to become optically thick and requires to follow the radiation field in order to understand its evolution. So far, the adiabatic approximation has been used exclusively for this purpose. We apply radiative transfer in the flux-limited diffusion (FLD) approximation to solve the evolution of coupled gas and radiation for isolated haloes. We find that (1) the photosphere forms at 10-6 pc and rapidly expands outwards. (2) A central core forms, with a mass of 1 M⊙, supported by gas pressure gradients and rotation. (3) Growing gas and radiation pressure gradients dissolve it. (4) This process is associated with a strong anisotropic outflow; another core forms nearby and grows rapidly. (5) Typical radiation luminosity emerging from the photosphere is 5 × 1037-5 × 1038 erg s-1, of the order the Eddington luminosity. (6) Two variability time-scales are associated with this process: a long one, which is related to the accretion flow within the central 10-4-10-3 pc, and 0.1 yr, related to radiation diffusion. (7) Adiabatic models evolution differs profoundly from that of the FLD models, by forming a geometrically thick disc. Overall, an adiabatic equation of state is not a good approximation to the advanced stage of direct collapse, because the radiation is capable of escaping due to anisotropy in the optical depth and associated gradients.

Using HT and DT gamma rays to diagnose mix in Omega capsule implosions

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

Schmitt, M. J.; Herrmann, H. W.; Kim, Y. H.

Experimental evidence [1] indicates that shell material can be driven into the core of Omega capsule implosions on the same time scale as the initial convergent shock. It has been hypothesized that shock-generated temperatures at the fuel/shell interface in thin exploding pusher capsules diffusively drives shell material into the gas core between the time of shock passage and bang time. Here, we propose a method to temporally resolve and observe the evolution of shell material into the capsule core as a function of fuel/shell interface temperature (which can be varied by varying the capsule shell thickness). Our proposed method usesmore » a CD plastic capsule filled with 50/50 HT gas and diagnosed using gas Cherenkov detection (GCD) to temporally resolve both the HT "clean" and DT "mix" gamma ray burn histories. Simulations using Hydra [2] for an Omega CD-lined capsule with a sub-micron layer of the inside surface of the shell pre-mixed into a fraction of the gas region produce gamma reaction history profiles that are sensitive to the depth to which this material is mixed. Furthermore, we observe these differences as a function of capsule shell thickness is proposed to determine if interface mixing is consistent with thermal diffusion λ ii~T 2/Z 2ρ at the gas/shell interface. Finally, since hydrodynamic mixing from shell perturbations, such as the mounting stalk and glue, could complicate these types of capsule-averaged temporal measurements, simulations including their effects also have been performed showing minimal perturbation of the hot spot geometry.« less

Color discrimination deficits in Parkinson's disease are related to cognitive impairment and white-matter alterations.

PubMed

Bertrand, Josie-Anne; Bedetti, Christophe; Postuma, Ronald B; Monchi, Oury; Génier Marchand, Daphné; Jubault, Thomas; Gagnon, Jean-François

2012-12-01

Color discrimination deficit is a common nonmotor manifestation of Parkinson's disease (PD). However, the pathophysiology of this dysfunction remains poorly understood. Although retinal structure changes found in PD have been suggested to cause color discrimination deficits, the impact of cognitive impairment and cortical alterations remains to be determined. We investigated the contribution of cognitive impairment to color discrimination deficits in PD and correlated them with cortical anomalies. Sixty-six PD patients without dementia and 20 healthy controls performed the Farnsworth-Munsell 100 hue test and underwent a comprehensive neuropsychological assessment for mild cognitive impairment diagnosis. In a subgroup of 26 PD patients, we also used high-definition neuroanatomical magnetic resonance imaging for cortical thickness and diffusion tensor analysis. PD patients with mild cognitive impairment performed poorly on the Farnsworth-Munsell 100 hue test compared with PD patients without mild cognitive impairment and controls. In PD patients, performance on the Farnsworth-Munsell 100 hue test was correlated with measures of visuospatial abilities and executive functions. Neuroimaging analysis revealed higher mean and radial diffusivity values in right posterior white-matter structures that correlated with poor performance on the Farnsworth-Munsell 100 hue test. No cortical thickness correlation reached significance. This study showed that cognitive impairment makes a major contribution to the color discrimination deficits reported in PD. Thus, performance on the Farnsworth-Munsell 100 hue test may reflect cognitive impairment more than color discrimination deficits in PD. Poor performance on the Farnsworth-Munsell 100 hue test was also associated with white-matter alterations in right posterior brain regions. Copyright © 2012 Movement Disorder Society.

Using HT and DT gamma rays to diagnose mix in Omega capsule implosions

DOE PAGES

Schmitt, M. J.; Herrmann, H. W.; Kim, Y. H.; ...

2016-05-26

Experimental evidence [1] indicates that shell material can be driven into the core of Omega capsule implosions on the same time scale as the initial convergent shock. It has been hypothesized that shock-generated temperatures at the fuel/shell interface in thin exploding pusher capsules diffusively drives shell material into the gas core between the time of shock passage and bang time. Here, we propose a method to temporally resolve and observe the evolution of shell material into the capsule core as a function of fuel/shell interface temperature (which can be varied by varying the capsule shell thickness). Our proposed method usesmore » a CD plastic capsule filled with 50/50 HT gas and diagnosed using gas Cherenkov detection (GCD) to temporally resolve both the HT "clean" and DT "mix" gamma ray burn histories. Simulations using Hydra [2] for an Omega CD-lined capsule with a sub-micron layer of the inside surface of the shell pre-mixed into a fraction of the gas region produce gamma reaction history profiles that are sensitive to the depth to which this material is mixed. Furthermore, we observe these differences as a function of capsule shell thickness is proposed to determine if interface mixing is consistent with thermal diffusion λ ii~T 2/Z 2ρ at the gas/shell interface. Finally, since hydrodynamic mixing from shell perturbations, such as the mounting stalk and glue, could complicate these types of capsule-averaged temporal measurements, simulations including their effects also have been performed showing minimal perturbation of the hot spot geometry.« less

Using HT and DT gamma rays to diagnose mix in Omega capsule implosions

NASA Astrophysics Data System (ADS)

Schmitt, M. J.; Herrmann, H. W.; Kim, Y. H.; McEvoy, A. M.; Zylstra, A.; Hammel, B. A.; Sepke, S. M.; Leatherland, A.; Gales, S.

2016-05-01

Experimental evidence [1] indicates that shell material can be driven into the core of Omega capsule implosions on the same time scale as the initial convergent shock. It has been hypothesized that shock-generated temperatures at the fuel/shell interface in thin exploding pusher capsules diffusively drives shell material into the gas core between the time of shock passage and bang time. We propose a method to temporally resolve and observe the evolution of shell material into the capsule core as a function of fuel/shell interface temperature (which can be varied by varying the capsule shell thickness). Our proposed method uses a CD plastic capsule filled with 50/50 HT gas and diagnosed using gas Cherenkov detection (GCD) to temporally resolve both the HT “clean” and DT “mix” gamma ray burn histories. Simulations using Hydra [2] for an Omega CD-lined capsule with a sub-micron layer of the inside surface of the shell pre-mixed into a fraction of the gas region produce gamma reaction history profiles that are sensitive to the depth to which this material is mixed. An experiment to observe these differences as a function of capsule shell thickness is proposed to determine if interface mixing is consistent with thermal diffusion λii∼T2/Z2ρ at the gas/shell interface. Since hydrodynamic mixing from shell perturbations, such as the mounting stalk and glue, could complicate these types of capsule-averaged temporal measurements, simulations including their effects also have been performed showing minimal perturbation of the hot spot geometry.

Linear single-step image reconstruction in the presence of nonscattering regions.

PubMed

Dehghani, H; Delpy, D T

2002-06-01

There is growing interest in the use of near-infrared spectroscopy for the noninvasive determination of the oxygenation level within biological tissue. Stemming from this application, there has been further research in using this technique for obtaining tomographic images of the neonatal head, with the view of determining the level of oxygenated and deoxygenated blood within the brain. Because of computational complexity, methods used for numerical modeling of photon transfer within tissue have usually been limited to the diffusion approximation of the Boltzmann transport equation. The diffusion approximation, however, is not valid in regions of low scatter, such as the cerebrospinal fluid. Methods have been proposed for dealing with nonscattering regions within diffusing materials through the use of a radiosity-diffusion model. Currently, this new model assumes prior knowledge of the void region; therefore it is instructive to examine the errors introduced in applying a simple diffusion-based reconstruction scheme in cases where a nonscattering region exists. We present reconstructed images, using linear algorithms, of models that contain a nonscattering region within a diffusing material. The forward data are calculated by using the radiosity-diffusion model, and the inverse problem is solved by using either the radiosity-diffusion model or the diffusion-only model. When using data from a model containing a clear layer and reconstructing with the correct model, one can reconstruct the anomaly, but the qualitative accuracy and the position of the reconstructed anomaly depend on the size and the position of the clear regions. If the inverse model has no information about the clear regions (i.e., it is a purely diffusing model), an anomaly can be reconstructed, but the resulting image has very poor qualitative accuracy and poor localization of the anomaly. The errors in quantitative and localization accuracies depend on the size and location of the clear regions.

Linear single-step image reconstruction in the presence of nonscattering regions

NASA Astrophysics Data System (ADS)

Dehghani, H.; Delpy, D. T.

2002-06-01

There is growing interest in the use of near-infrared spectroscopy for the noninvasive determination of the oxygenation level within biological tissue. Stemming from this application, there has been further research in using this technique for obtaining tomographic images of the neonatal head, with the view of determining the level of oxygenated and deoxygenated blood within the brain. Because of computational complexity, methods used for numerical modeling of photon transfer within tissue have usually been limited to the diffusion approximation of the Boltzmann transport equation. The diffusion approximation, however, is not valid in regions of low scatter, such as the cerebrospinal fluid. Methods have been proposed for dealing with nonscattering regions within diffusing materials through the use of a radiosity-diffusion model. Currently, this new model assumes prior knowledge of the void region; therefore it is instructive to examine the errors introduced in applying a simple diffusion-based reconstruction scheme in cases where a nonscattering region exists. We present reconstructed images, using linear algorithms, of models that contain a nonscattering region within a diffusing material. The forward data are calculated by using the radiosity-diffusion model, and the inverse problem is solved by using either the radiosity-diffusion model or the diffusion-only model. When using data from a model containing a clear layer and reconstructing with the correct model, one can reconstruct the anomaly, but the qualitative accuracy and the position of the reconstructed anomaly depend on the size and the position of the clear regions. If the inverse model has no information about the clear regions (i.e., it is a purely diffusing model), an anomaly can be reconstructed, but the resulting image has very poor qualitative accuracy and poor localization of the anomaly. The errors in quantitative and localization accuracies depend on the size and location of the clear regions.

Specific compartmental analysis of cartilage status in double-bundle ACL reconstruction patients: a comparative study using pre- and postoperative MR images.

PubMed

Lee, Yong Seuk; Jeong, Yu Mi; Sim, Jae Ang; Kwak, Ji Hoon; Kim, Kwang Hee; Nam, Shin Woo; Lee, Beom Koo

2013-03-01

The purpose of this study was to evaluate the changes in the site-specific cartilage status after a double-bundle ACL reconstruction using preoperative and follow-up MR images. Thirty-six knees that underwent a double-bundle ACL reconstruction from 2001 to 2009 with the available preoperative and follow-up magnetic resonance imaging were included. Patients with a meniscal injury were compared with those without a meniscal injury. The cartilage morphology was classified using a 6-grade scale [from 0 = normal thickness and signal, to 6 = diffuse full-thickness loss (>75 % of the region)]. The changes in cartilage status were evaluated at 14 sites. Cartilage changes were observed in all sites and were classified according to the site and degree of change. The majority of changes were grade 0 and 1, which accounted for 68 and 16.8 % of changes, respectively. The patella medial facet and anterolateral and centromedial femoral regions showed significantly more cartilage loss than the posteromedial, centrolateral, anterolateral, and anteromedial tibial regions. No significance was observed between the knees with or without combined injuries (n.s.). On the other hand, knees with or without combined injuries showed a different pattern of cartilage change, as demonstrated by different levels of grade change at sites. The change in cartilage status was minimal after a double-bundle ACL reconstruction. The patella medial facet, lateral femur anterior region, and medial femur central region showed significantly more cartilage loss than the medial tibia posterior, lateral tibia central, lateral tibia anterior, and medial tibia anterior regions. The presence of a combined injury did not affect the cartilage status changes, even though it was underpowered and too short term to assess the influence of the meniscal injury. Case series, Level IV.

Limiting diffusion current at rotating disk electrode with dense particle layer.

PubMed

Weroński, P; Nosek, M; Batys, P

2013-09-28

Exploiting the concept of diffusion permeability of multilayer gel membrane and porous multilayer we have derived a simple analytical equation for the limiting diffusion current at rotating disk electrode (RDE) covered by a thin layer with variable tortuosity and porosity, under the assumption of negligible convection in the porous film. The variation of limiting diffusion current with the porosity and tortuosity of the film can be described in terms of the equivalent thickness of stagnant solution layer, i.e., the average ratio of squared tortuosity to porosity. In case of monolayer of monodisperse spherical particles, the equivalent layer thickness is an algebraic function of the surface coverage. Thus, by means of cyclic voltammetry of RDE with a deposited particle monolayer we can determine the monolayer surface coverage. The effect of particle layer adsorbed on the surface of RDE increases non-linearly with surface coverage. We have tested our theoretical results experimentally by means of cyclic voltammetry measurements of limiting diffusion current at the glassy carbon RDE covered with a monolayer of 3 μm silica particles. The theoretical and experimental results are in a good agreement at the surface coverage higher than 0.7. This result suggests that convection in a monolayer of 3 μm monodisperse spherical particles is negligibly small, in the context of the coverage determination, in the range of very dense particle layers.

Serial Diffusion Tensor Imaging of the Optic Radiations after Acute Optic Neuritis.

PubMed

Kolbe, Scott C; van der Walt, Anneke; Butzkueven, Helmut; Klistorner, Alexander; Egan, Gary F; Kilpatrick, Trevor J

2016-01-01

Previous studies have reported diffusion tensor imaging (DTI) changes within the optic radiations of patients after optic neuritis (ON). We aimed to study optic radiation DTI changes over 12 months following acute ON and to study correlations between DTI parameters and damage to the optic nerve and primary visual cortex (V1). We measured DTI parameters [fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD)] from the optic radiations of 38 acute ON patients at presentation and 6 and 12 months after acute ON. In addition, we measured retinal nerve fibre layer thickness, visual evoked potential amplitude, optic radiation lesion load, and V1 thickness. At baseline, FA was reduced and RD and MD were increased compared to control. Over 12 months, FA reduced in patients at an average rate of -2.6% per annum (control = -0.51%; p = 0.006). Change in FA, RD, and MD correlated with V1 thinning over 12 months (FA: R = 0.450, p = 0.006; RD: R = -0.428, p = 0.009; MD: R = -0.365, p = 0.029). In patients with no optic radiation lesions, AD significantly correlated with RNFL thinning at 12 months (R = 0.489, p = 0.039). In conclusion, DTI can detect optic radiation changes over 12 months following acute ON that correlate with optic nerve and V1 damage.

Serial Diffusion Tensor Imaging of the Optic Radiations after Acute Optic Neuritis

PubMed Central

van der Walt, Anneke; Butzkueven, Helmut; Klistorner, Alexander; Egan, Gary F.; Kilpatrick, Trevor J.

2016-01-01

Previous studies have reported diffusion tensor imaging (DTI) changes within the optic radiations of patients after optic neuritis (ON). We aimed to study optic radiation DTI changes over 12 months following acute ON and to study correlations between DTI parameters and damage to the optic nerve and primary visual cortex (V1). We measured DTI parameters [fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD)] from the optic radiations of 38 acute ON patients at presentation and 6 and 12 months after acute ON. In addition, we measured retinal nerve fibre layer thickness, visual evoked potential amplitude, optic radiation lesion load, and V1 thickness. At baseline, FA was reduced and RD and MD were increased compared to control. Over 12 months, FA reduced in patients at an average rate of −2.6% per annum (control = −0.51%; p = 0.006). Change in FA, RD, and MD correlated with V1 thinning over 12 months (FA: R = 0.450, p = 0.006; RD: R = −0.428, p = 0.009; MD: R = −0.365, p = 0.029). In patients with no optic radiation lesions, AD significantly correlated with RNFL thinning at 12 months (R = 0.489, p = 0.039). In conclusion, DTI can detect optic radiation changes over 12 months following acute ON that correlate with optic nerve and V1 damage. PMID:27555964

The role of advection and diffusion in waste disposal by sea urchin embryos

NASA Astrophysics Data System (ADS)

Clark, Aaron; Licata, Nicholas

2014-03-01

We determine the first passage probability for the absorption of waste molecules released from the microvilli of sea urchin embryos. We calculate a perturbative solution of the advection-diffusion equation for a linear shear profile similar to the fluid environment which the embryos inhabit. Rapid rotation of the embryo results in a concentration boundary layer of comparable thickness to the length of the microvilli. A comparison of the results to the regime of diffusion limited transport indicates that fluid flow is advantageous for efficient waste disposal.

Low thermal diffusivity measurements of thin films using mirage technique

NASA Astrophysics Data System (ADS)

Wong, P. K.; Fung, P. C. W.; Tam, H. L.

1998-12-01

Mirage technique is proved to be powerful in measurements of thermal diffusivity. Its contactless nature makes it suitable for delicate samples such as thin films and single crystals. However, as the damping of the thermal wave profile increases progressively upon the decrease in thermal diffusivity of the medium, mirage technique becomes more difficult to be applied to low thermal diffusivity measurements. Moreover influences from substrate signals make analysis difficult when the samples are thermally thin. Recently a thermal-wave-coupling method for mirage signal analysis [P. K. Wong, P. C. W. Fung, H. L. Tam, and J. Gao, Phys. Rev. B 51, 523 (1995)] was reported for thermal diffusivity measurements of thin film down to 60 nm thick. In this article we apply the thermal-wave-coupling method to thin films of low thermal diffusivity, especially polymer films. A new lower limit of thermal diffusivity measurable by mirage technique has been reached.

Diffusion impact on atmospheric moisture transport

NASA Astrophysics Data System (ADS)

Moseley, C.; Haerter, J.; Göttel, H.; Hagemann, S.; Jacob, D.

2009-04-01

To ensure numerical stability, many global and regional climate models employ numerical diffusion to dampen short wavelength modes. Terrain following sigma diffusion is known to cause unphysical effects near the surface in orographically structured regions. They can be reduced by applying z-diffusion on geopotential height levels. We investigate the effect of the diffusion scheme on atmospheric moisture transport and precipitation formation at different resolutions in the European region. With respect to a better understanding of diffusion in current and future grid-space global models, current day regional models may serve as the appropriate tool for studies of the impact of diffusion schemes: Results can easily be constrained to a small test region and checked against reliable observations, which often are unavailable on a global scale. Special attention is drawn to the Alps - a region of strong topographic gradients and good observational coverage. Our study is further motivated by the appearance of the "summer drying problem" in South Eastern Europe. This too warm and too dry simulation of climate is common to many regional climate models and also to some global climate models, and remains a permanent unsolved problem in the community. We perform a systematic comparison of the two diffusion-schemes with respect to the hydrological cycle. In particular, we investigate how local meteorological quantities - such as the atmospheric moisture in the region east of the Alps - depend on the spatial model resolution. Higher model resolution would lead to a more accurate representation of the topography and entail larger gradients in the Alps. This could lead to consecutively stronger transport of moisture along the slopes in the case of sigma-diffusion with subsequent orographic precipitation, whereas the effect could be qualitatively different in the case of z-diffusion. For our study, we analyse a sequence of simulations of the regional climate model REMO employing the different diffusion methods over Europe. For these simulations, REMO was forced at the lateral boundaries with ERA40 reanalysis data for a five year period. For our higher resolution simulations we employ the double nesting technique.

Bipolar plate/diffuser for a proton exchange membrane fuel cell

DOEpatents

Besmann, Theodore M.; Burchell, Timothy D.

2001-01-01

A combination bipolar plate/diffuser fuel cell component includes an electrically conducting solid material having: a porous region having a porous surface; and a hermetic region, the hermetic region defining at least a portion of at least one coolant channel, the porous region defining at least a portion of at least one reactant channel, the porous region defining a flow field medium for diffusing the reactant to the porous surface.

Bipolar plate/diffuser for a proton exchange membrane fuel cell

DOEpatents

Besmann, Theodore M.; Burchell, Timothy D.

2000-01-01

A combination bipolar plate/diffuser fuel cell component includes an electrically conducting solid material having: a porous region having a porous surface; and a hermetic region, the hermetic region defining at least a portion of at least one coolant channel, the porous region defining at least a portion of at least one reactant channel, the porous region defining a flow field medium for diffusing the reactant to the porous surface.

Inert-Gas Diffuser For Plasma Or Arc Welding

NASA Technical Reports Server (NTRS)

Gilbert, Jeffrey L.; Spencer, Carl N.; Hosking, Timothy J.

1994-01-01

Inert-gas diffuser provides protective gas cover for weld bead as it cools. Follows welding torch, maintaining continuous flow of argon over newly formed joint and prevents it from oxidizing. Helps to ensure welds of consistently high quality. Devised for plasma arc keyhole welding of plates of 0.25-in. or greater thickness, also used in tungsten/inert-gas and other plasma or arc welding processes.

Automated array assembly task, phase 1

NASA Technical Reports Server (NTRS)

Carbajal, B. G.

1977-01-01

Various aspects of a sensitivity analysis, in particular, the impact of variations in metal sheet resistivity, metal line width, diffused layer sheet resistance, junction depth, base layer lifetime, optical coating thickness and optical coating refractive index and on process reproducibility for A's diffusion from a polymer dopant source and on module fabrication were studied. Model calculations show that acceptable process windows exist for each of these parameters.

Surface modification of an amorphous Si thin film crystallized by a linearly polarized Nd:YAG pulse laser beam

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

Horita, Susumu; Kaki, Hirokazu; Nishioka, Kensuke

2007-07-01

Amorphous Si films of 60 and 10 nm thick on glass substrates were irradiated by a linearly polarized Nd:YAG pulse laser with the wavelength {lambda}=532 nm at the incident angle {theta}{sub i}=0. The surface of the irradiated 60-nm-thick film had both periodic ridges perpendicular to the electric field vector E and aperiodic ridges roughly parallel to E, where the spatial period of the periodic ridges was almost {lambda}. From the continuous 10-nm-thick film, the separate rectangular Si islands were formed with a periodic distance of {lambda}, with the edges parallel or perpendicular to E. When {theta}{sub i} was increased frommore » normal incidence of the s-polarized beam for a 60-nm-thick film, the aperiodic ridges were reduced while the periodic ridges were still formed. For a 10-nm-thick film, the Si stripes were formed perpendicular to E, using the s-polarized beam at {theta}{sub i}=12 deg. In order to investigate the mechanisms of the surface modifications of, in particular, aperiodic ridges, islands, and stripes, we improved the previous theoretical model of the periodic distribution of the beam energy density (periodic E-D) generated by irradiation of the linearly polarized laser beam, taking account of the multireflection effect in the Si film which is semitransparent for {lambda}. Further, the calculated E-D was corrected with respect to the thermal diffusion in the irradiated Si film. The calculation results show that the two-dimensional E-D consists of a constant or a dc term and a sinusoidal or an ac term which contains various spatial periods. The multireflection effect strongly influences the amplitude and phase of every ac term, which means that the amplitude and phase depend on the film thickness. The thermal diffusion during the heating of the irradiated film greatly reduces the amplitudes of the ac terms with periods below the thermal diffusion length. The theoretical calculation showed that, by increasing {theta}{sub i}, the temperature distribution in the irradiated Si film was changed from two-dimensional toward one-dimensional, which can explain the above experimental results reasonably.« less

Diffusive transport of several hundred keV electrons in the Earth's slot region

NASA Astrophysics Data System (ADS)

Ma, Q.; Li, W.; Thorne, R. M.; Bortnik, J.

2017-12-01

We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of 200-600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10-day non-disturbed period following the storm, the peak of electron fluxes gradually moved from L 2.7 to L 2.4, and the flux levels decreased by a factor of 2-4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a 3-dimentional diffusion code, which reproduced the energy-dependent transport of electrons from 100 keV to 1 MeV in the slot region. At energies of 100-200 keV, the electrons experience fast transport across the slot region due to the dominance of radial diffusion; at energies of 200-600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable radial diffusion rate and pitch angle scattering rate by plasmaspheric hiss; at energies of E > 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF waves can cause the loss of high pitch angle electrons, relaxing the sharp `top-hat' shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of radial diffusion and pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.

Diffusive Transport of Several Hundred keV Electrons in the Earth's Slot Region

NASA Astrophysics Data System (ADS)

Ma, Q.; Li, W.; Thorne, R. M.; Bortnik, J.; Reeves, G. D.; Spence, H. E.; Turner, D. L.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Baker, D. N.

2017-10-01

We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of 200-600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10 day nondisturbed period following the storm, the peak of electron fluxes gradually moved from L 2.7 to L 2.4, and the flux levels decreased by a factor of 2-4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a three-dimensional diffusion code, which reproduced the energy-dependent transport of electrons from 100 keV to 1 MeV in the slot region. At energies of 100-200 keV, the electrons experience fast transport across the slot region due to the dominance of radial diffusion; at energies of 200-600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of radial diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E > 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp "top-hat" shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between radial diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.

Opening the closed box: lattice diffusion in zircon?

NASA Astrophysics Data System (ADS)

Wheeler, J.; MacDonald, J.; Goodenough, K. M.; Crowley, Q.; Harley, S.; Mariani, E.

2015-12-01

In principle, any radiogenic parent or daughter element can diffuse through any crystalline lattice. Given improved analytic techniques and mathematical models, geochronology is beginning to take such diffusion into account in a quantitative fashion. Whilst lattice diffusion compromises simple interpretation of radiometric data, it can, when combined with spatially resolved data, provide more detailed insight into thermal histories. In regions that have experienced particularly high temperatures diffusion may become significant in minerals normally thought to be reliably closed. We have modelled Pb diffusion in zircon, building on earlier work on Ar diffusion in micas - the mathematics being basically the same. We are motivated by some challenging isotope data from zircon in the Lewisian Complex of NW Scotland (a TTG region with a long Archaean and Proterozoic history). For example we have grains with old rims and younger cores. Whilst other explanations are possible, we show how lattice diffusion of Pb is plausible, using experimental diffusion data together with estimates of ultra-high temperatures from the region. We have modified a previous model for Ar diffusion ("Diffarg") to include variations in parent isotope concentration, so we can understand the consequences of U zonation within zircon grains during prolonged thermal histories. This is also relevant to asking why Pb has apparently not diffused in zircon from other UHT regions - or has it?

Preferential flow, diffuse flow, and perching in an interbedded fractured-rock unsaturated zone

NASA Astrophysics Data System (ADS)

Nimmo, John R.; Creasey, Kaitlyn M.; Perkins, Kim S.; Mirus, Benjamin B.

2017-03-01

Layers of strong geologic contrast within the unsaturated zone can control recharge and contaminant transport to underlying aquifers. Slow diffuse flow in certain geologic layers, and rapid preferential flow in others, complicates the prediction of vertical and lateral fluxes. A simple model is presented, designed to use limited geological site information to predict these critical subsurface processes in response to a sustained infiltration source. The model is developed and tested using site-specific information from the Idaho National Laboratory in the Eastern Snake River Plain (ESRP), USA, where there are natural and anthropogenic sources of high-volume infiltration from floods, spills, leaks, wastewater disposal, retention ponds, and hydrologic field experiments. The thick unsaturated zone overlying the ESRP aquifer is a good example of a sharply stratified unsaturated zone. Sedimentary interbeds are interspersed between massive and fractured basalt units. The combination of surficial sediments, basalts, and interbeds determines the water fluxes through the variably saturated subsurface. Interbeds are generally less conductive, sometimes causing perched water to collect above them. The model successfully predicts the volume and extent of perching and approximates vertical travel times during events that generate high fluxes from the land surface. These developments are applicable to sites having a thick, geologically complex unsaturated zone of substantial thickness in which preferential and diffuse flow, and perching of percolated water, are important to contaminant transport or aquifer recharge.

The Nature of Electrochemical Delithiation of Li-Mg Alloy Electrodes: Neutron Computed Tomography and Modeling of Li Diffusion and Delithiation Phenomenon

DOE PAGES

Zhang, Yuxuan; Chandran, K.S. Ravi; Jagannathan, M.; ...

2016-12-05

Li-Mg alloys are promising as positive electrodes (anodes) for Li-ion batteries due to the high Li storage capacity and the relatively lower volume change during the lithiation/delithiation process. They also present a unique opportunity to image the Li distribution through the electrode thickness at various delithiation states. In this work, spatial distributions of Li in electrochemically delithiated Li-Mg alloy electrodes have been quantitatively determined using neutron tomography. Specifically, the Li concentration profiles along thickness direction are determined. A rigorous analytical model to quantify the diffusion-controlled delithiation, accompanied by phase transition and boundary movement, has also been developed to explain themore » delithiation mechanism. The analytical modeling scheme successfully predicted the Li concentration profiles which agreed well with the experimental data. It is demonstrated that during discharge Li is removed by diffusion through the solid solution Li-Mg phases and this proceeds with β→α phase transition and the associated phase boundary movement through the thickness of the electrode. This is also accompanied by electrode thinning due to the change in molar volume during delithiation. In conclusion, following the approaches developed here, one can develop a rigorous and quantitative understanding of electrochemical delithiation in electrodes of electrochemical cells, similar to that in the present Li-Mg electrodes.« less

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.

Preferential flow, diffuse flow, and perching in an interbedded fractured-rock unsaturated zone

USGS Publications Warehouse

Nimmo, John R.; Creasey, Kaitlyn M; Perkins, Kimberlie; Mirus, Benjamin B.

2017-01-01

Layers of strong geologic contrast within the unsaturated zone can control recharge and contaminant transport to underlying aquifers. Slow diffuse flow in certain geologic layers, and rapid preferential flow in others, complicates the prediction of vertical and lateral fluxes. A simple model is presented, designed to use limited geological site information to predict these critical subsurface processes in response to a sustained infiltration source. The model is developed and tested using site-specific information from the Idaho National Laboratory in the Eastern Snake River Plain (ESRP), USA, where there are natural and anthropogenic sources of high-volume infiltration from floods, spills, leaks, wastewater disposal, retention ponds, and hydrologic field experiments. The thick unsaturated zone overlying the ESRP aquifer is a good example of a sharply stratified unsaturated zone. Sedimentary interbeds are interspersed between massive and fractured basalt units. The combination of surficial sediments, basalts, and interbeds determines the water fluxes through the variably saturated subsurface. Interbeds are generally less conductive, sometimes causing perched water to collect above them. The model successfully predicts the volume and extent of perching and approximates vertical travel times during events that generate high fluxes from the land surface. These developments are applicable to sites having a thick, geologically complex unsaturated zone of substantial thickness in which preferential and diffuse flow, and perching of percolated water, are important to contaminant transport or aquifer recharge.

The Nature of Electrochemical Delithiation of Li-Mg Alloy Electrodes: Neutron Computed Tomography and Modeling of Li Diffusion and Delithiation Phenomenon

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

Zhang, Yuxuan; Chandran, K.S. Ravi; Jagannathan, M.

Li-Mg alloys are promising as positive electrodes (anodes) for Li-ion batteries due to the high Li storage capacity and the relatively lower volume change during the lithiation/delithiation process. They also present a unique opportunity to image the Li distribution through the electrode thickness at various delithiation states. In this work, spatial distributions of Li in electrochemically delithiated Li-Mg alloy electrodes have been quantitatively determined using neutron tomography. Specifically, the Li concentration profiles along thickness direction are determined. A rigorous analytical model to quantify the diffusion-controlled delithiation, accompanied by phase transition and boundary movement, has also been developed to explain themore » delithiation mechanism. The analytical modeling scheme successfully predicted the Li concentration profiles which agreed well with the experimental data. It is demonstrated that during discharge Li is removed by diffusion through the solid solution Li-Mg phases and this proceeds with β→α phase transition and the associated phase boundary movement through the thickness of the electrode. This is also accompanied by electrode thinning due to the change in molar volume during delithiation. In conclusion, following the approaches developed here, one can develop a rigorous and quantitative understanding of electrochemical delithiation in electrodes of electrochemical cells, similar to that in the present Li-Mg electrodes.« less

Rarefaction-driven Rayleigh–Taylor instability. Part 1. Diffuse-interface linear stability measurements and theory

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

Morgan, R. V.; Likhachev, O. A.; Jacobs, J. W.

Theory and experiments are reported that explore the behaviour of the Rayleigh–Taylor instability initiated with a diffuse interface. Experiments are performed in which an interface between two gases of differing density is made unstable by acceleration generated by a rarefaction wave. Well-controlled, diffuse, two-dimensional and three-dimensional, single-mode perturbations are generated by oscillating the gases either side to side, or vertically for the three-dimensional perturbations. The puncturing of a diaphragm separating a vacuum tank beneath the test section generates a rarefaction wave that travels upwards and accelerates the interface downwards. This rarefaction wave generates a large, but non-constant, acceleration of the order ofmore » $$1000g_{0}$$, where$$g_{0}$$is the acceleration due to gravity. Initial interface thicknesses are measured using a Rayleigh scattering diagnostic and the instability is visualized using planar laser-induced Mie scattering. Growth rates agree well with theoretical values, and with the inviscid, dynamic diffusion model of Duffet al. (Phys. Fluids, vol. 5, 1962, pp. 417–425) when diffusion thickness is accounted for, and the acceleration is weighted using inviscid Rayleigh–Taylor theory. The linear stability formulation of Chandrasekhar (Proc. Camb. Phil. Soc., vol. 51, 1955, pp. 162–178) is solved numerically with an error function diffusion profile using the Riccati method. This technique exhibits good agreement with the dynamic diffusion model of Duffet al. for small wavenumbers, but produces larger growth rates for large-wavenumber perturbations. Asymptotic analysis shows a$$1/k^{2}$$decay in growth rates as$$k\\rightarrow \\infty$$for large-wavenumber perturbations.« less

Rarefaction-driven Rayleigh–Taylor instability. Part 1. Diffuse-interface linear stability measurements and theory

DOE PAGES

Morgan, R. V.; Likhachev, O. A.; Jacobs, J. W.

2016-02-15

Theory and experiments are reported that explore the behaviour of the Rayleigh–Taylor instability initiated with a diffuse interface. Experiments are performed in which an interface between two gases of differing density is made unstable by acceleration generated by a rarefaction wave. Well-controlled, diffuse, two-dimensional and three-dimensional, single-mode perturbations are generated by oscillating the gases either side to side, or vertically for the three-dimensional perturbations. The puncturing of a diaphragm separating a vacuum tank beneath the test section generates a rarefaction wave that travels upwards and accelerates the interface downwards. This rarefaction wave generates a large, but non-constant, acceleration of the order ofmore » $$1000g_{0}$$, where$$g_{0}$$is the acceleration due to gravity. Initial interface thicknesses are measured using a Rayleigh scattering diagnostic and the instability is visualized using planar laser-induced Mie scattering. Growth rates agree well with theoretical values, and with the inviscid, dynamic diffusion model of Duffet al. (Phys. Fluids, vol. 5, 1962, pp. 417–425) when diffusion thickness is accounted for, and the acceleration is weighted using inviscid Rayleigh–Taylor theory. The linear stability formulation of Chandrasekhar (Proc. Camb. Phil. Soc., vol. 51, 1955, pp. 162–178) is solved numerically with an error function diffusion profile using the Riccati method. This technique exhibits good agreement with the dynamic diffusion model of Duffet al. for small wavenumbers, but produces larger growth rates for large-wavenumber perturbations. Asymptotic analysis shows a$$1/k^{2}$$decay in growth rates as$$k\\rightarrow \\infty$$for large-wavenumber perturbations.« less

Distributed modeling of diffusive solute transport in peritoneal dialysis.

PubMed

Waniewski, Jacek

2002-01-01

The diffusive transport between blood and an ex-tissue medium (dialysis fluid) is evaluated using a mathematical model that takes into account the (quasicontinuous) distribution of capillaries within the tissue at various distances from the tissue surface, and includes diffusive-convective transport through the capillary wall and lymphatic absorption from the tissue. General formulas for solute penetration depth, lambda, and for the diffusive mass transport coefficient for the transport between blood and dialysis fluid, K(BD), are provided in terms of local transport coefficients for capillary wall, tissue, and lymphatic absorption. For pure diffusive transport between blood and dialysis fluid and thick tissue layers (i.e., if the solute penetration depth is much lower than the tissue thickness) these formulas yield previously known expressions. It is shown that apparent tissue layers, with widths lambdaTBL and lambdaT, respectively, may be defined according to the values of local transport parameters in such a way that K(BD) is equal to the solute clearance K(TBL) from the tissue by blood and lymph for a layer with width lambdaTBL or to the solute clearance K(T) from blood to dialysate by diffusion through the tissue layer with width lambdaT. For tissue layers with width much higher than the penetration depth: lambdaT approximately = lambdaTBL approximately = lambda. These characteristic width lengths depend on the transport parameters (and thus on the size) of solutes. Effective blood flow, which may be related to the exchange of the solute between blood and dialysate, is defined using an analogy to the extraction/absorption coefficients for blood-tissue exchange. Various approximations for the distributed model formula for diffusive mass transport coefficient (K(BD)) are possible. The appropriate range for their application is obtained from the general formula.

Age Differences in Prefrontal Surface Area and Thickness in Middle Aged to Older Adults.

PubMed

Dotson, Vonetta M; Szymkowicz, Sarah M; Sozda, Christopher N; Kirton, Joshua W; Green, Mackenzie L; O'Shea, Andrew; McLaren, Molly E; Anton, Stephen D; Manini, Todd M; Woods, Adam J

2015-01-01

Age is associated with reductions in surface area and cortical thickness, particularly in prefrontal regions. There is also evidence of greater thickness in some regions at older ages. Non-linear age effects in some studies suggest that age may continue to impact brain structure in later decades of life, but relatively few studies have examined the impact of age on brain structure within middle-aged to older adults. We investigated age differences in prefrontal surface area and cortical thickness in healthy adults between the ages of 51 and 81 years. Participants received a structural 3-Tesla magnetic resonance imaging scan. Based on a priori hypotheses, primary analyses focused on surface area and cortical thickness in the dorsolateral prefrontal cortex, anterior cingulate cortex, and orbitofrontal cortex. We also performed exploratory vertex-wise analyses of surface area and cortical thickness across the entire cortex. We found that older age was associated with smaller surface area in the dorsolateral prefrontal and orbitofrontal cortices but greater cortical thickness in the dorsolateral prefrontal and anterior cingulate cortices. Vertex-wise analyses revealed smaller surface area in primarily frontal regions at older ages, but no age effects were found for cortical thickness. Results suggest age is associated with reduced surface area but greater cortical thickness in prefrontal regions during later decades of life, and highlight the differential effects age has on regional surface area and cortical thickness.

Llama VHH antibody fragments against GFAP: better diffusion in fixed tissues than classical monoclonal antibodies.

PubMed

Perruchini, Claire; Pecorari, Frederic; Bourgeois, Jean-Pierre; Duyckaerts, Charles; Rougeon, François; Lafaye, Pierre

2009-11-01

Camelids produce antibodies made of homodimeric heavy chains, and the antigen-binding region being composed of a single domain called VHH. These VHHs are much smaller than complete IgG. They are also more thermostable and more soluble in water; they should, therefore, diffuse more readily in the tissues. VHHs, expressed in bacteria, are easier to produce than conventional monoclonal antibodies. Because of these special characteristics, these antibody fragments could have interesting developments in immunohistochemistry and in the development of biomarkers. To test the possibility of their use in immunohistochemistry (IHC), we selected the glial fibrillary acidic protein (GFAP), a well-known marker of astrocytes. One alpaca (Lama pacos) was immunized against GFAP. Lymphocytes were isolated; the DNA was extracted; the VHH-coding sequences were selectively amplified. Three VHHs with a high affinity for GFAP and their corresponding mRNA were selected by ribosome display. Large quantities of the recombinant VHHs coupled with different tags were harvested from transfected bacteria. One of them was shown to immunolabel strongly and specifically to GFAP of human astrocytes in tissue sections. The quality of the IHC was comparable or, in some aspects, superior to the quality obtained with conventional IgG. The VHH was shown to diffuse on a longer distance than conventional monoclonal antibodies in fixed cortical tissue: a property that may be useful in immunolabeling of thick sections.

Quasi-two-layer morphodynamic model for bedload-dominated problems: bed slope-induced morphological diffusion

NASA Astrophysics Data System (ADS)

Maldonado, Sergio; Borthwick, Alistair G. L.

2018-02-01

We derive a two-layer depth-averaged model of sediment transport and morphological evolution for application to bedload-dominated problems. The near-bed transport region is represented by the lower (bedload) layer which has an arbitrarily constant, vanishing thickness (of approx. 10 times the sediment particle diameter), and whose average sediment concentration is free to vary. Sediment is allowed to enter the upper layer, and hence the total load may also be simulated, provided that concentrations of suspended sediment remain low. The model conforms with established theories of bedload, and is validated satisfactorily against empirical expressions for sediment transport rates and the morphodynamic experiment of a migrating mining pit by Lee et al. (1993 J. Hydraul. Eng. 119, 64-80 (doi:10.1061/(ASCE)0733-9429(1993)119:1(64))). Investigation into the effect of a local bed gradient on bedload leads to derivation of an analytical, physically meaningful expression for morphological diffusion induced by a non-zero local bed slope. Incorporation of the proposed morphological diffusion into a conventional morphodynamic model (defined as a coupling between the shallow water equations, Exner equation and an empirical formula for bedload) improves model predictions when applied to the evolution of a mining pit, without the need either to resort to special numerical treatment of the equations or to use additional tuning parameters.

Quasi-two-layer morphodynamic model for bedload-dominated problems: bed slope-induced morphological diffusion.

PubMed

Maldonado, Sergio; Borthwick, Alistair G L

2018-02-01

We derive a two-layer depth-averaged model of sediment transport and morphological evolution for application to bedload-dominated problems. The near-bed transport region is represented by the lower (bedload) layer which has an arbitrarily constant, vanishing thickness (of approx. 10 times the sediment particle diameter), and whose average sediment concentration is free to vary. Sediment is allowed to enter the upper layer, and hence the total load may also be simulated, provided that concentrations of suspended sediment remain low. The model conforms with established theories of bedload, and is validated satisfactorily against empirical expressions for sediment transport rates and the morphodynamic experiment of a migrating mining pit by Lee et al. (1993 J. Hydraul. Eng. 119 , 64-80 (doi:10.1061/(ASCE)0733-9429(1993)119:1(64))). Investigation into the effect of a local bed gradient on bedload leads to derivation of an analytical, physically meaningful expression for morphological diffusion induced by a non-zero local bed slope. Incorporation of the proposed morphological diffusion into a conventional morphodynamic model (defined as a coupling between the shallow water equations, Exner equation and an empirical formula for bedload) improves model predictions when applied to the evolution of a mining pit, without the need either to resort to special numerical treatment of the equations or to use additional tuning parameters.

The Role of Nongyrotropy in Balancing the Reconnection Diffusion Region

NASA Astrophysics Data System (ADS)

Hesse, M.; Liu, Y. H.; Chen, L. J.; Bessho, N.; Wang, S.; Burch, J. L.; Moretto, T.; Genestreti, K.; Phan, T.; Tenfjord, P.

2017-12-01

The structure of the reconnection diffusion region is, to a large degree, determined by the requirement to balance both the current flow and its dissipation processes, and the forces exerted onto the current layer by the inflow magnetic pressure. These balances are critical: without resupply processes, the transport of accelerated and current-carrying particles away from the diffusion region would generate a current density depletion, which, in principle, could lead to a mismatch with the curl of the magnetic field. Similarly, without heating processes, the convection of hot plasma away from the diffusion region would generate a force imbalance with the ambient magnetic field. The fact that neither of these imbalances occur is a consequence of the reconnection electric field, which is therefore not only required to facilitate magnetic flux transport, but also to provide the energization required to maintain balance in the diffusion region. In this presentation, we will use particle-in-cell simulations to analyze these balance conditions. We will furthermore show that nongyrotropic particle dynamics plays a key role both as current dissipation mechanism, and as overall heating mechanism in the diffusion region current layer.

Triplet energy transfer and triplet exciton recycling in singlet fission sensitized organic heterojunctions

NASA Astrophysics Data System (ADS)

Hamid, Tasnuva; Yambem, Soniya D.; Crawford, Ross; Roberts, Jonathan; Pandey, Ajay K.

2017-08-01

Singlet exciton fission is a process where an excited singlet state splits into two triplets, thus leading to generation of multiple excitons per absorbed photon in organic semiconductors. Herein, we report a detailed exciton management approach for multiexciton harvesting over a broadband region of the solar spectrum in singlet fission sensitized organic photodiodes. Through systematic studies on the model cascade of pentacene/rubrene/C60, we found that efficient photocurrent generation from pentacene can still occur despite the presence of a >10nm thick interlayer of rubrene in between the pentacene/C60 heterojunction. Our results show that thin rubrene interlayers of thickness < 5 nm are effective in maintaining the delicate balance between two free charge generation channels that progress independently via the electron and hole transfer routes. The contribution to photocurrent from pentacene despite having a reasonably thick rubrene interlayer, that too with higher triplet energy (T1=1.12 eV) than pentacene (T1= 0.86 eV), makes its operation a rather interesting result. We discuss the role of rubrene interlayer film discontinuity, triplet exciton reflection from rubrene interlayer and triplet energy transfer from rubrene to pentacene layer followed by diffusion of triplet excitons through rubrene as plausible mechanisms that would enable triplet excitons from pentacene to generate significant photocurrent in a multilayer organic heterojunction.

Photospheric Magnetic Diffusion by Measuring Moments of Active Regions

NASA Astrophysics Data System (ADS)

Engell, Alexander; Longcope, D.

2013-07-01

Photospheric magnetic surface diffusion is an important constraint for the solar dynamo. The HMI Active Region Patches (HARPs) program automatically identify all magnetic regions above a certain flux. In our study we measure the moments of ARs that are no longer actively emerging and can thereby give us good statistical constraints on photospheric diffusion. We also present the diffusion properties as a function of latitude, flux density, and single polarity (leading or following) within each HARP.

Momentum transport process in the quasi self-similar region of free shear mixing layer

NASA Astrophysics Data System (ADS)

Takamure, K.; Ito, Y.; Sakai, Y.; Iwano, K.; Hayase, T.

2018-01-01

In this study, we performed a direct numerical simulation (DNS) of a spatially developing shear mixing layer covering both developing and developed regions. The aim of this study is to clarify the driving mechanism and the vortical structure of the partial counter-gradient momentum transport (CGMT) appearing in the quasi self-similar region. In the present DNS, the self-similarity is confirmed in x/L ≥ 0.67 (x/δU0 ≥ 137), where L and δU0 are the vertical length of the computational domain and the initial momentum thickness, respectively. However, the trend of CGMT is observed at around kδU = 0.075 and 0.15, where k is the wavenumber, δU is the normalized momentum thickness at x/L = 0.78 (x/δU0 = 160), and kδU = 0.075 corresponds to the distance between the vortical/stretching regions of the coherent structure. The budget analysis for the Reynolds shear stress reveals that it is caused by the pressure diffusion term at the off-central region and by -p (∂ u /∂ y ) ¯ in the pressure-strain correlation term at the central region. As the flow moves toward the downstream direction, the appearance of those terms becomes random and the unique trend of CGMT at the specific wavenumber bands disappears. Furthermore, we investigated the relationship between the CGMT and vorticity distribution in the vortex region of the mixing layer, in association with the spatial development. In the upstream location, the high-vorticity region appears in the boundary between the areas of gradient momentum transport and CGMT, although the high-vorticity region is not actively producing turbulence. The negative production area gradually spreads by flowing toward the downstream direction, and subsequently, the fluid mass with high-vorticity is transported from the forehead stretching region toward the counter-gradient direction. In this location, the velocity fluctuation in the high-vorticity region is large and turbulence is actively produced. In view of this, the trend of negative production appears in the flow where the turbulence production and non-turbulent regions mix. Then, the non-turbulent region and CGMT almost simultaneously disappear in the fully developed region.

Diffusion model validation and interpretation of stable isotopes in river and lake ice

USGS Publications Warehouse

Ferrick, M.G.; Calkins, D.J.; Perron, N.M.; Cragin, J.H.; Kendall, C.

2002-01-01

The stable isotope stratigraphy of river- and lake-ice archives winter hydroclimatic conditions, and can potentially be used to identify changing water sources or to provide important insights into ice formation processes and growth rates. However, accurate interpretations rely on known isotopic fractionation during ice growth. A one-dimensional diffusion model of the liquid boundary layer adjacent to an advancing solid interface, originally developed to simulate solute rejection by growing crystals, has been used without verification to describe non-equilibrium fractionation during congelation ice growth. Results are not in agreement, suggesting the presence of important uncertainties. In this paper we seek validation of the diffusion model for this application using large-scale laboratory experiments with controlled freezing rates and frequent sampling. We obtained consistent, almost constant, isotopic boundary layer thicknesses over a representative range of ice growth rates on both quiescent and well-mixed water. With the 18O boundary layer thickness from the laboratory, the model successfully quantified reduced river-ice growth rates relative to those of a nearby lake. These results were more representative and easier to obtain than those of a conventional thermal ice-growth model. This diffusion model validation and boundary layer thickness determination provide a powerful tool for interpreting the stable isotope stratigraphy of floating ice. The laboratory experiment also replicated successive fractionation events in response to a freeze-thaw-refreeze cycle, providing a mechanism for apparent ice fractionation that exceeds equilibrium. Analysis of the composition of snow ice and frazil ice in river and lake cores indicated surprising similarities between these ice forms. Published in 2002 by John Wiley & Sons, Ltd.

Slow positron beam production by a 14 MeV C.W. electron accelerator

NASA Astrophysics Data System (ADS)

Begemann, M.; Gräff, G.; Herminghaus, H.; Kalinowsky, H.; Ley, R.

1982-10-01

A 14 MeV c.w. electron accelerator is used for pair production in a tungsten target of 0.7 radiation lengths thickness. A small fraction of the positrons is thermalized and diffuses out of the surface ofsurface of a well annealed tungsten foil coated with MgO which is positioned immediately behind the target. The slow positrons are extracted from the target region and magnetically guided over a distance of 10 m onto a channelplate multiplier at the end of an S-shaped solenoid. The positrons are identified by their annihilation radiation using two NaI-detectors. The intensity of the slow positrons is proportional to the accelerator electron beam current. The maximum intensity of 2.2 × 10 5 slow positrons per second reaching thedetector at an accelerator current of 15 μA was limited by the power deposited in the uncooled target. The energy of the positrons is concentrated in a small region at about 1 eV and clearly demonstrates the emission of thermal positrons.

Improvements to Zirconia Thick-Film Oxygen Sensors

NASA Astrophysics Data System (ADS)

Maskell, William C.; Brett, Daniel J. L.; Brandon, Nigel P.

2013-06-01

Thick-film zirconia gas sensors are normally screen-printed onto a planar substrate. A sandwich of electrode-electrolyte-electrode is fired at a temperature sufficient to instigate sintering of the zirconia electrolyte. The resulting porous zirconia film acts as both the electrolyte and as the diffusion barrier through which oxygen diffuses. The high sintering temperature results in de-activation of the electrodes so that sensors must be operated at around 800 °C for measurements in the percentage range of oxygen concentration. This work shows that the use of cobalt oxide as a sintering aid allows reduction of the sensor operating temperature by 100-200 °C with clear benefits. Furthermore, an interesting and new technique is presented for the investigation of the influence of dopants and of the through-porosity of ionically-conducting materials.

The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions

NASA Astrophysics Data System (ADS)

Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

2013-12-01

During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, σ, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (≈ 2 -5 μm grain size) form next to calcite and elongated palisade-shaped grains (1-6 μm diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 μm thick granular dolomite layer and a 7 μm thick palisade-shaped layer evolve. At similar conditions and a differential stress of 30 MPa, the rim thickness remains similar; consequently the effect of non-isostatic stress on dolomite rim growth is negligible. Platinum markers show that the initial calcite-magnesite interface is located between granular and palisade-forming dolomite, indicating that rim growth occurs by counter diffusion of MgO and CaO. Diffusion of MgO across the dolomite reaction rim into calcite forms additionally magnesio-calcite grains with diameters of ≈ 13 - 46 μm, depending on the experimental conditions and increasing with increasing distance to the dolomite boundary. At T = 750°C, t = 29 hours, the thickness of the magnesio-calcite layer is 32 μm (isostatic) - 35 μm (σ = 30 MPa). The experiments indicate that solid-state reaction rim growth of dolomite between calcite and magnesite is primarily controlled by diffusion of MgO and CaO, forming layers with different microstructures during growth into the educt phases. The kinetics of the reaction in the carbonate system are not significantly changed by differential stresses up to 40 MPa. We suggest that volume diffusion is the dominant transport mechanism, which is presumably less affected by non-isostatic stresses than grain boundary diffusion.

Biexponential Characterization of Prostate Tissue Water Diffusion Decay Curves Over an Extended b-factor Range

PubMed Central

Mulkern, Robert V.; Barnes, Agnieszka Szot; Haker, Steven J.; Hung, Yin P.; Rybicki, Frank J.; Maier, Stephan E.; Tempany, Clare M.C.

2006-01-01

Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging exams at 1.5 T, a single 10 mm thick axial slice was scanned with a line scan diffusion imaging (LSDI) sequence in which 14 equally spaced b- factors from 5 to 3500 s/mm2 were sampled along three orthogonal diffusion sensitization directions in 6 minutes. Due to the combination of long scan time and limited volume coverage associated with the multi-b- factor, multi-directional sampling, the slice was chosen online from the available T2-weighted axial images with the specific goal of enabling the sampling of presumed non-cancerous regions of interest (ROI’s) within the central gland (CG) and peripheral zone (PZ). Histology from pre-scan biopsy (N = 9) and post-surgical resection (N = 4) was subsequently employed to help confirm that the ROIs sampled were non-cancerous. The CG ROIs were characterized from the T2-weighted images as primarily mixtures of glandular and stromal benign prostatic hyperplasia (BPH) which is prevalent in this population. The water signal decays with b- factor from all ROI’s were clearly non-monoexponential and better served with bi- vs monoexponential fits, as tested using λ2 based F-test analyses. Fits to biexponential decay functions yielded inter-subject fast diffusion component fractions on the order of 0.73 ± 0.08 for both CG and PZ ROIs, fast diffusion coefficients of 2.68 ± 0.39 and 2.52 ± 0.38 μm2/ms and slow diffusion coefficients of 0.44 ± 0.16 and 0.23 ± 0.16 um2/ms for CG and PZ ROI’s, respectively. The difference between the slow diffusion coefficients within CG and PZ was statistically significant as assessed with a Mann-Whitney non-parametric test (P < 0.05). We conclude that a monoexponential model for water diffusion decay in prostate tissue is inadequate when a large range of b- factors is sampled and that biexponential analyses are better suited for characterizing prostate diffusion decay curves. PMID:16735177

Apparent diffusion coefficient evaluation for secondary changes in the cerebellum of rats after middle cerebral artery occlusion

PubMed Central

Yang, Yunjun; Gao, Lingyun; Fu, Jun; Zhang, Jun; Li, Yuxin; Yin, Bo; Chen, Weijian; Geng, Daoying

2013-01-01

Supratentorial cerebral infarction can cause functional inhibition of remote regions such as the cerebellum, which may be relevant to diaschisis. This phenomenon is often analyzed using positron emission tomography and single photon emission CT. However, these methods are expensive and radioactive. Thus, the present study quantified the changes of infarction core and remote regions after unilateral middle cerebral artery occlusion using apparent diffusion coefficient values. Diffusion-weighted imaging showed that the area of infarction core gradually increased to involve the cerebral cortex with increasing infarction time. Diffusion weighted imaging signals were initially increased and then stabilized by 24 hours. With increasing infarction time, the apparent diffusion coefficient value in the infarction core and remote bilateral cerebellum both gradually decreased, and then slightly increased 3–24 hours after infarction. Apparent diffusion coefficient values at remote regions (cerebellum) varied along with the change of supratentorial infarction core, suggesting that the phenomenon of diaschisis existed at the remote regions. Thus, apparent diffusion coefficient values and diffusion weighted imaging can be used to detect early diaschisis. PMID:25206615

Dependence of growth of the phases of multiphase binary systems on the diffusion parameters

NASA Astrophysics Data System (ADS)

Molokhina, L. A.; Rogalin, V. E.; Filin, S. A.; Kaplunov, I. A.

2017-12-01

A mathematical model of the diffusion interaction of a binary system with several phases on the equilibrium phase diagram is presented. The theoretical and calculated dependences of the layer thickness of each phase in the multiphase diffusion zone on the isothermal annealing time and the ratio of the diffusion parameters in the neighboring phases with an unlimited supply of both components were constructed. The phase formation and growth in the diffusion zone during "reactive" diffusion corresponds to the equilibrium state diagram for two components, and the order of their appearance in the diffusion zone depends only on the ratio of the diffusion parameters in the phases themselves and on the duration of the incubation periods. The dependence of phase appearance on the incubation periods, annealing time, and difference in the movement rates of the components across the interface boundaries was obtained. An example of the application of the model for processing the experimental data on phase growth in a two-component three-phase system was given.

Retinal Thickening and Photoreceptor Loss in HIV Eyes without Retinitis.

PubMed

Arcinue, Cheryl A; Bartsch, Dirk-Uwe; El-Emam, Sharif Y; Ma, Feiyan; Doede, Aubrey; Sharpsten, Lucie; Gomez, Maria Laura; Freeman, William R

2015-01-01

To determine the presence of structural changes in HIV retinae (i.e., photoreceptor density and retinal thickness in the macula) compared with age-matched HIV-negative controls. Cohort of patients with known HIV under CART (combination Antiretroviral Therapy) treatment were examined with a flood-illuminated retinal AO camera to assess the cone photoreceptor mosaic and spectral-domain optical coherence tomography (SD-OCT) to assess retinal layers and retinal thickness. Twenty-four eyes of 12 patients (n = 6 HIV-positive and 6 HIV-negative) were imaged with the adaptive optics camera. In each of the regions of interest studied (nasal, temporal, superior, inferior), the HIV group had significantly less mean cone photoreceptor density compared with age-matched controls (difference range, 4,308-6,872 cones/mm2). A different subset of forty eyes of 20 patients (n = 10 HIV-positive and 10 HIV-negative) was included in the retinal thickness measurements and retinal layer segmentation with the SD-OCT. We observed significant thickening in HIV positive eyes in the total retinal thickness at the foveal center, and in each of the three horizontal B-scans (through the macular center, superior, and inferior to the fovea). We also noted that the inner retina (combined thickness from ILM through RNFL to GCL layer) was also significantly thickened in all the different locations scanned compared with HIV-negative controls. Our present study shows that the cone photoreceptor density is significantly reduced in HIV retinae compared with age-matched controls. HIV retinae also have increased macular retinal thickness that may be caused by inner retinal edema secondary to retinovascular disease in HIV. The interaction of photoreceptors with the aging RPE, as well as possible low-grade ocular inflammation causing diffuse inner retinal edema, may be the key to the progressive vision changes in HIV-positive patients without overt retinitis.

A mixed-order nonlinear diffusion compressed sensing MR image reconstruction.

PubMed

Joy, Ajin; Paul, Joseph Suresh

2018-03-07

Avoid formation of staircase artifacts in nonlinear diffusion-based MR image reconstruction without compromising computational speed. Whereas second-order diffusion encourages the evolution of pixel neighborhood with uniform intensities, fourth-order diffusion considers smooth region to be not necessarily a uniform intensity region but also a planar region. Therefore, a controlled application of fourth-order diffusivity function is used to encourage second-order diffusion to reconstruct the smooth regions of the image as a plane rather than a group of blocks, while not being strong enough to introduce the undesirable speckle effect. Proposed method is compared with second- and fourth-order nonlinear diffusion reconstruction, total variation (TV), total generalized variation, and higher degree TV using in vivo data sets for different undersampling levels with application to dictionary learning-based reconstruction. It is observed that the proposed technique preserves sharp boundaries in the image while preventing the formation of staircase artifacts in the regions of smoothly varying pixel intensities. It also shows reduced error measures compared with second-order nonlinear diffusion reconstruction or TV and converges faster than TV-based methods. Because nonlinear diffusion is known to be an effective alternative to TV for edge-preserving reconstruction, the crucial aspect of staircase artifact removal is addressed. Reconstruction is found to be stable for the experimentally determined range of fourth-order regularization parameter, and therefore not does not introduce a parameter search. Hence, the computational simplicity of second-order diffusion is retained. © 2018 International Society for Magnetic Resonance in Medicine.

Application of TRIZ Methodology in Diffusion Welding System Optimization

NASA Astrophysics Data System (ADS)

Ravinder Reddy, N.; Satyanarayana, V. V.; Prashanthi, M.; Suguna, N.

2017-12-01

Welding is tremendously used in metal joining processes in the manufacturing process. In recent years, diffusion welding method has significantly increased the quality of a weld. Nevertheless, diffusion welding has some extent short research and application progress. Therefore, diffusion welding has a lack of relevant information, concerned with the joining of thick and thin materials with or without interlayers, on welding design such as fixture, parameters selection and integrated design. This article intends to combine innovative methods in the application of diffusion welding design. This will help to decrease trial and error or failure risks in the welding process being guided by the theory of inventive problem solving (TRIZ) design method. This article hopes to provide welding design personnel with innovative design ideas under research and for practical application.

Influence of tantalum underlayer on magnetization dynamics in Ni{sub 81}Fe{sub 19} films

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

Kwon, Jae Hyun; Deorani, Praveen; Yoon, Jungbum

2015-07-13

The effect of tantalum (Ta) underlayer is investigated in Ni{sub 81}Fe{sub 19} thin films for magnetization dynamics. The damping parameters extracted from spin wave measurements increase systematically with increasing Ta thickness, whereas the damping parameters from ferromagnetic resonance measurements are found to be weakly dependent on the Ta thickness. The difference is attributed to propagating properties of spin wave and short spin diffusion length in Ta. The group velocity of spin waves is found to be constant for different Ta thicknesses, and nonreciprocity of spin waves is not affected by the Ta thickness. The experimental observations are supported by micromagneticmore » simulations.« less

Solvent annealing of perovskite-induced crystal growth for photovoltaic-device efficiency enhancement

DOE PAGES

Xiao, Zhengguo; Dong, Qingfeng; Bi, Cheng; ...

2014-08-26

Solvent-annealing is found to be an effective method to increase the grain size and carrier diffusion lengths of trihalide perovskite materials. Thus, the carrier diffusion length of MAPbI 3 is increased to over 1 μm. The efficiency remains above 14.5% when the MAPbI 3 thickness changes from 250 nm to 1 μm, with the highest efficiency reaching 15.6%.

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

Fabrication of a Biologically-Implantable, Multiplexed, Multielectrode Array of JFETS for Cortical Implantation.

DTIC Science & Technology

1984-12-01

which could be implanted at the surface of the brain. Electrodes of microfine dimensions I-1 . ..6...to check the operation of the diffusion furnace oxidation tube by comparing measured thicknesses of the oxide against calculated values. Oxide Growth...faster rate than that of Eq ), (11-2). Initial adjustments made prior to using the diffusion furnace included: (1) profiling the oxidation tube to

Diffusive Transport of Several Hundred keV Electrons in the Earth's Slot Region

DOE PAGES

Ma, Q.; Li, W.; Thorne, R. M.; ...

2017-09-29

Here, we investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of ~200–600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10 day nondisturbed period following the storm, the peak of electron fluxes gradually moved from L ~ 2.7 to L ~ 2.4, and the flux levels decreased by a factor of ~2–4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a three–dimensional diffusion code,more » which reproduced the energy–dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100–200 keV, the electrons experience fast transport across the slot region due to the dominance of radial diffusion; at energies of 200–600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of radial diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E > 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp “top–hat” shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between radial diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.« less

Thermal transport in suspended silicon membranes measured by laser-induced transient gratings

DOE PAGES

Vega-Flick, A.; Duncan, R. A.; Eliason, J. K.; ...

2016-12-05

Studying thermal transport at the nanoscale poses formidable experimental challenges due both to the physics of the measurement process and to the issues of accuracy and reproducibility. The laser-induced transient thermal grating (TTG) technique permits non-contact measurements on nanostructured samples without a need for metal heaters or any other extraneous structures, offering the advantage of inherently high absolute accuracy. We present a review of recent studies of thermal transport in nanoscale silicon membranes using the TTG technique. An overview of the methodology, including an analysis of measurements errors, is followed by a discussion of new findings obtained from measurements onmore » both “solid” and nanopatterned membranes. The most important results have been a direct observation of non-diffusive phonon-mediated transport at room temperature and measurements of thickness-dependent thermal conductivity of suspended membranes across a wide thickness range, showing good agreement with first-principles-based theory assuming diffuse scattering at the boundaries. Measurements on a membrane with a periodic pattern of nanosized holes (135nm) indicated fully diffusive transport and yielded thermal diffusivity values in agreement with Monte Carlo simulations. Based on the results obtained to-date, we conclude that room-temperature thermal transport in membrane-based silicon nanostructures is now reasonably well understood.« less

TEM Observation of the Ti Interlayer Between SiC Substrates During Diffusion Bonding

NASA Technical Reports Server (NTRS)

Tsuda, Hiroshi; Mori, Shigeo; Halbig, Michael C.; Singh, Mori

2012-01-01

Diffusion bonding was carried out to join SiC to SiC substrates using titanium interlayers. In this study, 10 m and 20 m thick physical vapor deposited (PVD) Ti surface coatings, and 10 and 20 m thick Ti foils were used. Diffusion bonding was performed at 1250 C for PVD Ti coatings and 1200 C for Ti foil. This study investigates the microstructures of the phases formed during diffusion bonding through TEM and selected-area diffraction analysis of a sample prepared with an FIB, which allows samples to be taken from the reacted area. In all samples, Ti3SiC2, Ti5Si3Cx and TiSi2 phases were identified. In addition, TiC and unknown phases also appeared in the samples in which Ti foils were used as interlayers. Furthermore, Ti3SiC2 phases show high concentration and Ti5Si3Cx formed less when samples were processed at a higher temperature and thinner interlayer samples were used. It appears that the formation of microcracks is caused by the presence of intermediate phase Ti5Si3Cx, which has anisotropic thermal expansion, and by the presence of an unidentified Ti-Si-C ternary phase with relatively low Si content.

Magnetic Resonance Characterization of Axonal Response to Spinal Cord Injury

DTIC Science & Technology

2012-10-01

frequency direction, phase FOV = 0.5, slice thickness = 10 mm. Spatial saturation bands were placed anterior and posterior to the slice of interest to...thickness = 10 mm, with spatial saturation bands placed anterior and posterior to the slice and diffusion sensitization in the right-to-left...the center frequency, and can be extracted by applying MT saturation pulses with alternating (positive/negative) off-resonance frequencies. The goal

Effect of pectin charge density on formation of multilayer films with chitosan.

PubMed

Kamburova, Kamelia; Milkova, Viktoria; Petkanchin, Ivana; Radeva, Tsetska

2008-04-01

The effect of pectin charge density on the formation of multilayer films with chitosan (PEC/CHI) is studied by means of electro-optics. Pectins of low (21%) and high (71%) degrees of esterification, which are inversely proportional to the pectin charge density, are used to form films on colloidal beta-FeOOH particles at pH 4.0 when the CHI is fully ionized. We find that, after deposition of the first 3-4 layers, the film thickness increases linearly with the number of adsorbed layers. However, the increase in the film thickness is larger when the film is terminated with CHI. Irregular increase of the film thickness is more marked for the PEC with higher density of charge. Oscillation in the electrical polarizability of the film-coated particles with the number of deposited layers is also registered in the PEC/CHI films. The charge balance of the multilayers, calculated from electrical polarizability of the film-coated particles, is positive, with larger excess of positive charge within the film constructed from CHI and less charged PEC. This is attributed to the ability of CHI to diffuse into the film at each deposition step. Despite the CHI diffusion, the film thickness increases linearly due to the dissolution of unstable PEC/CHI complexes from the film surface.

Theoretical models for the combustion of alloyable materials

NASA Astrophysics Data System (ADS)

Armstrong, Robert

1992-09-01

The purpose of this work is to extend a theoretical model of layered (laminar) media for SHS combustion presented in an earlier article [1] to explore possible mechanisms for after-burning in SHS ( i.e., gasless) combustion. As before, our particular interest is how the microscopic geometry of the solid reactants is reflected in the combustion wave and in the reaction product. The model is constructed from alternating lamina of two pure reactants that interdiffuse exothermically to form a product. Here, the laminar model is extended to contain layers of differing thicknesses. Using asymptotic theory, it was found that under certain conditions, the combustion wave can become “detached,” and an initial thin flame propagates through the media, leaving a slower, thicker flame following behind ( i.e., afterburning). Thin laminae are consumed in the initial flame and are thick in the secondary. The thin flame has a width determined by the inverse of the activation energy of diffusion, as found previously. The width of the afterburning zone, however, is determined by the absolute time of diffusion for the thicker laminae. Naturally, when the laminae are all the same thickness, there is only one thin flame. The condition for the appearance of afterburning is found to be contingent on the square of the ratio of smallestto-largest thicknesses being considerably less than unity.

Ex Vivo Diffusion Tensor Imaging of Spinal Cord Injury in Rats of Varying Degrees of Severity

PubMed Central

Jirjis, Michael B.; Kurpad, Shekar N.

2013-01-01

Abstract The aim of this study was to characterize magnetic resonance diffusion tensor imaging (DTI) in proximal regions of the spinal cord following a thoracic spinal cord injury (SCI). Sprague–Dawley rats (n=40) were administered a control, mild, moderate, or severe contusion injury at the T8 vertebral level. Six direction diffusion weighted images (DWIs) were collected ex vivo along the length of the spinal cord, with an echo/repetition time of 31.6 ms/14 sec and b=500 sec/mm2. Diffusion metrics were correlated to hindlimb motor function. Significant differences were found for whole cord region of interest (ROI) drawings for fractional anisotropy (FA), mean diffusivity (MD), longitudinal diffusion coefficient (LD), and radial diffusion coefficient (RD) at each of the cervical levels (p<0.01). Motor function correlated with MD in the cervical segments of the spinal cord (r2=0.80). The diffusivity of water significantly decreased throughout “uninjured” portions of the spinal cord following a contusion injury (p<0.05). Diffusivity metrics were found to be altered following SCI in both white and gray matter regions. Injury severity was associated with diffusion changes over the entire length of the cord. This study demonstrates that DTI is sensitive to SCI in regions remote from injury, suggesting that the diffusion metrics may be used as a biomarker for severity of injury. PMID:23782233

The iterative thermal emission method: A more implicit modification of IMC

DOE PAGES

Long, A. R.; Gentile, N. A.; Palmer, T. S.

2014-08-19

For over 40 years, the Implicit Monte Carlo (IMC) method has been used to solve challenging problems in thermal radiative transfer. These problems typically contain regions that are optically thick and diffusive, as a consequence of the high degree of “pseudo-scattering” introduced to model the absorption and reemission of photons from a tightly-coupled, radiating material. IMC has several well-known features that could be improved: a) it can be prohibitively computationally expensive, b) it introduces statistical noise into the material and radiation temperatures, which may be problematic in multiphysics simulations, and c) under certain conditions, solutions can be nonphysical, in thatmore » they violate a maximum principle, where IMC-calculated temperatures can be greater than the maximum temperature used to drive the problem.« less

Microfabrication Techniques for Plastic Microelectromechanical Systems (MEMS)

DTIC Science & Technology

2003-07-01

micromachining techniques were investigated. Surface micromachining techniques include deposition of thin and thick polymer films using vacuum and spin ...1 2.0 Introduction ...100 4.3.1 Nozzle-diffuser pumps theory

Molecular Diagnostics of Diffusive Boundary Layers

NASA Astrophysics Data System (ADS)

Rawlings, J. M. C.; Hartquist, T. W.

1995-11-01

We have assessed the role of diffusion in determining chemical abundances in molecular interface regions. Chemical models have been developed which include the appropriate diffusion terms and that are appropriate to a narrow diffusion region (˜0.01pc) that may exist at the interface between a dark core and a hot, shocked T-Tauri wind. We have assumed pressure balance throughout and have calculated the chemical abundances as functions of time and position through the interface. The results show that significant enhancements of detectable molecules/transitions are expected (e.g. CO J=6→5, OH and CH). Using a realistic value of the diffusion coefficient a diffusive region of dimension 0.01pc may be established within about 104 years. In general it seems likely that diffusion processes are highly significant on these and smaller lengthscales.

Enceladus' tidal dissipation revisited

NASA Astrophysics Data System (ADS)

Tobie, Gabriel; Behounkova, Marie; Choblet, Gael; Cadek, Ondrej; Soucek, Ondrej

2016-10-01

A series of chemical and physical evidence indicates that the intense activity at Enceladus' South Pole is related to a subsurface salty water reservoir underneath the tectonically active ice shell. The detection of a significant libration implies that this water reservoir is global and that the average ice shell thickness is about 20-25km (Thomas et al. 2016). The interpretation of gravity and topography data further predicts large variations in ice shell thickness, resulting in a shell potentially thinner than 5 km in the South Polar Terrain (SPT) (Cadek et al. 2016). Such an ice shell structure requires a very strong heat source in the interior, with a focusing mechanism at the SPT. Thermal diffusion through the ice shell implies that at least 25-30 GW is lost into space by passive diffusion, implying a very efficient dissipation mechanism in Enceladus' interior to maintain such an ocean/ice configuration thermally stable.In order to determine in which conditions such a large dissipation power may be generated, we model the tidal response of Enceladus including variable ice shell thickness. For the rock core, we consider a wide range of rheological parameters representative of water-saturated porous rock materials. We demonstrate that the thinning toward the South Pole leads to a strong increase in heat production in the ice shell, with a optimal thickness obtained between 1.5 and 3 km, depending on the assumed ice viscosity. Our results imply that the heat production in the ice shell within the SPT may be sufficient to counterbalance the heat loss by diffusion and to power eruption activity. However, outside the SPT, a strong dissipation in the porous core is required to counterbalance the diffusive heat loss. We show that about 20 GW can be generated in the core, for an effective viscosity of 1012 Pa.s, which is comparable to the effective viscosity estimated in water-saturated glacial tills on Earth. We will discuss the implications of this revisited tidal budget for the activity of Enceladus and the long-term evolution of its interior.

Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films

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

Mirigian, Stephen, E-mail: kschweiz@illinois.edu, E-mail: smirigian@gmail.com; Schweizer, Kenneth S., E-mail: kschweiz@illinois.edu, E-mail: smirigian@gmail.com

2015-12-28

We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made formore » how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.« less

Large Enhancement of Thermal Conductivity and Lorenz Number in Topological Insulator Thin Films.

PubMed

Luo, Zhe; Tian, Jifa; Huang, Shouyuan; Srinivasan, Mithun; Maassen, Jesse; Chen, Yong P; Xu, Xianfan

2018-02-27

Topological insulators (TI) have attracted extensive research effort due to their insulating bulk states but conducting surface states. However, investigation and understanding of thermal transport in topological insulators, particularly the effect of surface states, are lacking. In this work, we studied thickness-dependent in-plane thermal and electrical conductivity of Bi 2 Te 2 Se TI thin films. A large enhancement in both thermal and electrical conductivity was observed for films with thicknesses below 20 nm, which is attributed to the surface states and bulk-insulating nature of these films. Moreover, a surface Lorenz number much larger than the Sommerfeld value was found. Systematic transport measurements indicated that the Fermi surface is located near the charge neutrality point (CNP) when the film thickness is below 20 nm. Possible reasons for the large Lorenz number include electrical and thermal current decoupling in the surface state Dirac fluid, and bipolar diffusion transport. A simple computational model indicates that the surface states and bipolar diffusion indeed can lead to enhanced electrical and thermal transport and a large Lorenz number.

Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films.

PubMed

Mirigian, Stephen; Schweizer, Kenneth S

2015-12-28

We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made for how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.

Nitrogen-doped carbonaceous catalysts for gas-diffusion cathodes for alkaline aluminum-air batteries

NASA Astrophysics Data System (ADS)

Davydova, E. S.; Atamanyuk, I. N.; Ilyukhin, A. S.; Shkolnikov, E. I.; Zhuk, A. Z.

2016-02-01

Cobalt tetramethoxyphenyl porphyrin and polyacrylonitrile - based catalysts for oxygen reduction reaction were synthesized and characterized by means of SEM, TEM, XPS, BET, limited evaporation method, rotating disc and rotating ring-disc electrode methods. Half-cell and Al-air cell tests were carried out to determine the characteristics of gas-diffusion cathodes. Effect of active layer thickness and its composition on the characteristics of the gas-diffusion cathodes was investigated. Power density of 300 mW cm-2 was achieved for alkaline Al-air cell with an air-breathing polyacrylonitrile-based cathode.

Ischaemia-reperfusion injury in central retinal artery occlusion.

PubMed

Saxena, Sandeep; Mishra, Nibha; Meyer, Carsten H; Akduman, Levent

2013-10-21

A 53-year-old man presented with sudden painless diminution of vision in his right eye for 3 days. His fundus examination showed diffuse whitening of the retina with a cherry red spot at the fovea with cilioretinal artery sparing. On fluorescein angiography delayed arteriovenous transit was observed. Three-dimensional spectral domain optical coherence tomography was used to assess retinal nerve fibre layer thickness and average macular central subfield thickness on days 3, 7, 30 and 90. Marked retinal oedema due to ischaemia was observed on day 3 of occurrence of central retinal artery occlusion. On day 7, significant decrease in retinal nerve fibre thickness and macular thickness was noted suggestive of acute reperfusion injury. Retinal nerve fibre layer thickness and macular thickness returned to near normal on day 30 due to restoration of blood supply with wash out of stress mediators. Retinal atrophy was observed on day 90.

Ischaemia-reperfusion injury in central retinal artery occlusion

PubMed Central

Saxena, Sandeep; Mishra, Nibha; Meyer, Carsten H; Akduman, Levent

2013-01-01

A 53-year-old man presented with sudden painless diminution of vision in his right eye for 3 days. His fundus examination showed diffuse whitening of the retina with a cherry red spot at the fovea with cilioretinal artery sparing. On fluorescein angiography delayed arteriovenous transit was observed. Three-dimensional spectral domain optical coherence tomography was used to assess retinal nerve fibre layer thickness and average macular central subfield thickness on days 3, 7, 30 and 90. Marked retinal oedema due to ischaemia was observed on day 3 of occurrence of central retinal artery occlusion. On day 7, significant decrease in retinal nerve fibre thickness and macular thickness was noted suggestive of acute reperfusion injury. Retinal nerve fibre layer thickness and macular thickness returned to near normal on day 30 due to restoration of blood supply with wash out of stress mediators. Retinal atrophy was observed on day 90. PMID:24145508

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

Lyon, B.F.

The United States Department of Energy (DOE) currently manages the UF, Cylinder Project. The project was formed to maintain and safely manage depleted uranium hexafluoride (UF{sub 6}) stored in approximately 50,000 carbon steel cylinders. The cylinders located at three DOE sites: the K-25 site at Oak Ridge, Tennessee (K-25); the Paducah Gaseous Diffusion Plant in Paducah, Kentucky (PGDP), and the Portsmouth Gaseous Diffusion Plant (PORTS) in Portsmouth, Ohio. The System Requirements Document (SRD) (LMES 1997a) delineates the requirements of the project. The appropriate actions needed to fulfill these requirements are then specified within the System Engineering Management Plan (SEMP) (LMESmore » 1997b). The report presented herein documents activities that in whole or in part satisfy specific requirements and actions stated in the UF{sub 6} Cylinder Project SRD and SEMP with respect to forecasting cylinder conditions. The wall thickness projections made in this report are based on the assumption that the corrosion trends noted will continue. Some activities planned may substantially reduce the rate of corrosion, in which case the results presented here are conservative. The results presented here are intended to supercede and enlarge the scope of those presented previously (Lyon 1995,1996, 1997). In particular, projections are made for thin-walled cylinders (nominal initial thickness 312.5 mils) and thick-walled cylinders (nominal initial thickness 625 mils). In addition, a preliminary analysis is conducted for the minimum thickness at the head/skirt interface for skirted cylinders.« less

Practical and adequate approach to modeling light propagation in an adult head with low-scattering regions by use of diffusion theory.

PubMed

Koyama, Tatsuya; Iwasaki, Atsushi; Ogoshi, Yosuke; Okada, Eiji

2005-04-10

A practical and adequate approach to modeling light propagation in an adult head with a low-scattering cerebrospinal fluid (CSF) region by use of diffusion theory was investigated. The diffusion approximation does not hold in a nonscattering or low-scattering regions. The hybrid radiosity-diffusion method was adopted to model the light propagation in the head with a nonscattering region. In the hybrid method the geometry of the nonscattering region is acquired as a priori information. In reality, low-level scattering occurs in the CSF region and may reduce the error caused by the diffusion approximation. The partial optical path length and the spatial sensitivity profile calculated by the finite-element method agree well with those calculated by the Monte Carlo method in the case in which the transport scattering coefficient of the CSF layer is greater than 0.3 mm(-1). Because it is feasible to assume that the transport scattering coefficient of a CSF layer is 0.3 mm(-1), it is practical to adopt diffusion theory to the modeling of light propagation in an adult head as an alternative to the hybrid method.

Practical and adequate approach to modeling light propagation in an adult head with low-scattering regions by use of diffusion theory

NASA Astrophysics Data System (ADS)

Koyama, Tatsuya; Iwasaki, Atsushi; Ogoshi, Yosuke; Okada, Eiji

2005-04-01

A practical and adequate approach to modeling light propagation in an adult head with a low-scattering cerebrospinal fluid (CSF) region by use of diffusion theory was investigated. The diffusion approximation does not hold in a nonscattering or low-scattering regions. The hybrid radiosity-diffusion method was adopted to model the light propagation in the head with a nonscattering region. In the hybrid method the geometry of the nonscattering region is acquired as a priori information. In reality, low-level scattering occurs in the CSF region and may reduce the error caused by the diffusion approximation. The partial optical path length and the spatial sensitivity profile calculated by the finite-element method agree well with those calculated by the Monte Carlo method in the case in which the transport scattering coefficient of the CSF layer is greater than 0.3 mm^-1. Because it is feasible to assume that the transport scattering coefficient of a CSF layer is 0.3 mm^-1, it is practical to adopt diffusion theory to the modeling of light propagation in an adult head as an alternative to the hybrid method.

THEMIS Observations of the Magnetopause Electron Diffusion Region: Large Amplitude Waves and Heated Electrons

NASA Technical Reports Server (NTRS)

Tang, Xiangwei; Cattell, Cynthia; Dombeck, John; Dai, Lei; Wilson, Lynn B. III; Breneman, Aaron; Hupack, Adam

2013-01-01

We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by Scudder et al at the subsolar magnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (approx. 30 keV) within the electron diffusion region have anisotropic distributions with T(sub e(right angle))/T(sub e(parallel)) > 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the "X-line" along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.

Effect of Static Compressive Strain, Anisotropy, and Tissue Region on the Diffusion of Glucose in Meniscus Fibrocartilage.

PubMed

Kleinhans, Kelsey L; Jaworski, Lukas M; Schneiderbauer, Michaela M; Jackson, Alicia R

2015-10-01

Osteoarthritis (OA) is a significant socio-economic concern, affecting millions of individuals each year. Degeneration of the meniscus of the knee is often associated with OA, yet the relationship between the two is not well understood. As a nearly avascular tissue, the meniscus must rely on diffusive transport for nutritional supply to cells. Therefore, quantifying structure-function relations for transport properties in meniscus fibrocartilage is an important task. The purpose of the present study was to determine how mechanical loading, tissue anisotropy, and tissue region affect glucose diffusion in meniscus fibrocartilage. A one-dimensional (1D) diffusion experiment was used to measure the diffusion coefficient of glucose in porcine meniscus tissues. Results show that glucose diffusion is strain-dependent, decreasing significantly with increased levels of compression. It was also determined that glucose diffusion in meniscus tissues is anisotropic, with the diffusion coefficient in the circumferential direction being significantly higher than that in the axial direction. Finally, the effect of tissue region was not statistically significant, comparing axial diffusion in the central and horn regions of the tissue. This study is important for better understanding the transport and nutrition-related mechanisms of meniscal degeneration and related OA in the knee.

Narrow groove welding gas diffuser assembly and welding torch

DOEpatents

Rooney, Stephen J.

2001-01-01

A diffuser assembly is provided for narrow groove welding using an automatic gas tungsten arc welding torch. The diffuser assembly includes a manifold adapted for adjustable mounting on the welding torch which is received in a central opening in the manifold. Laterally extending manifold sections communicate with a shield gas inlet such that shield gas supplied to the inlet passes to gas passages of the manifold sections. First and second tapered diffusers are respectively connected to the manifold sections in fluid communication with the gas passages thereof. The diffusers extend downwardly along the torch electrode on opposite sides thereof so as to release shield gas along the length of the electrode and at the distal tip of the electrode. The diffusers are of a transverse width which is on the order of the thickness of the electrode so that the diffusers can, in use, be inserted into a narrow welding groove before and after the electrode in the direction of the weld operation.

Water Saturation Relations and Their Diffusion-Limited Equilibration in Gas Shale: Implications for Gas Flow in Unconventional Reservoirs

NASA Astrophysics Data System (ADS)

Tokunaga, Tetsu K.; Shen, Weijun; Wan, Jiamin; Kim, Yongman; Cihan, Abdullah; Zhang, Yingqi; Finsterle, Stefan

2017-11-01

Large volumes of water are used for hydraulic fracturing of low permeability shale reservoirs to stimulate gas production, with most of the water remaining unrecovered and distributed in a poorly understood manner within stimulated regions. Because water partitioning into shale pores controls gas release, we measured the water saturation dependence on relative humidity (rh) and capillary pressure (Pc) for imbibition (adsorption) as well as drainage (desorption) on samples of Woodford Shale. Experiments and modeling of water vapor adsorption into shale laminae at rh = 0.31 demonstrated that long times are needed to characterize equilibrium in larger (5 mm thick) pieces of shales, and yielded effective diffusion coefficients from 9 × 10-9 to 3 × 10-8 m2 s-1, similar in magnitude to the literature values for typical low porosity and low permeability rocks. Most of the experiments, conducted at 50°C on crushed shale grains in order to facilitate rapid equilibration, showed significant saturation hysteresis, and that very large Pc (˜1 MPa) are required to drain the shales. These results quantify the severity of the water blocking problem, and suggest that gas production from unconventional reservoirs is largely associated with stimulated regions that have had little or no exposure to injected water. Gravity drainage of water from fractures residing above horizontal wells reconciles gas production in the presence of largely unrecovered injected water, and is discussed in the broader context of unsaturated flow in fractures.

Apparatus and method for suppressing sound in a gas turbine engine powerplant

NASA Technical Reports Server (NTRS)

Wynosky, Thomas A. (Inventor); Mischke, Robert J. (Inventor)

1992-01-01

A method and apparatus for suppressing jet noise in a gas turbine engine powerplant 10 is disclosed. Various construction details are developed for providing sound suppression at sea level take-off operative conditions and not providing sound suppression at cruise operative conditions. In one embodiment, the powerplant 10 has a lobed mixer 152 between a primary flowpath 44 and a second flowpath 46, a diffusion region downstream of the lobed mixer region (first mixing region 76), and a deployable ejector/mixer 176 in the diffusion region which forms a second mixing region 78 having a diffusion flowpath 72 downstream of the ejector/mixer and sound absorbing structure 18 bounding the flowpath throughout the diffusion region. The method includes deploying the ejector/mixer 176 at take-off and stowing the ejector/mixer at cruise.

Optimization and design of pigments for heat-insulating coatings

NASA Astrophysics Data System (ADS)

Wang, Guang-Hai; Zhang, Yue

2010-12-01

This paper reports that heat insulating property of infrared reflective coatings is obtained through the use of pigments which diffuse near-infrared thermal radiation. Suitable structure and size distribution of pigments would attain maximum diffuse infrared radiation and reduce the pigment volume concentration required. The optimum structure and size range of pigments for reflective infrared coatings are studied by using Kubelka—Munk theory, Mie model and independent scattering approximation. Taking titania particle as the pigment embedded in an inorganic coating, the computational results show that core-shell particles present excellent scattering ability, more so than solid and hollow spherical particles. The optimum radius range of core-shell particles is around 0.3 ~ 1.6 μm. Furthermore, the influence of shell thickness on optical parameters of the coating is also obvious and the optimal thickness of shell is 100-300 nm.

Threshold for ion movements in wood cell walls below fiber saturation observed by X-ray fluorescence microscopy (XFM)

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

Zelinka, Samuel L.; Gleber, Sophie-Charlotte; Vogt, Stefan

Diffusion of chemicals and ions through the wood cell wall plays an important role in wood damage mechanisms. In the present work, free diffusion of ions through wood secondary walls and middle lamellae has been investigated as a function of moisture content (MC) and anatomical direction. Various ions (K, Cl, Zn, Cu) were injected into selected regions of 2 mu m thick wood sections with a microinjector and then the ion distribution was mapped by means of X-ray fluorescence microscopy with submicron spatial resolution. The MC of the wood was controlled in situ by means of climatic chamber with controlledmore » relative humidity (RH). For all ions investigated, there was a threshold RH below which the concentration profiles did not change. The threshold RH depended upon ionic species, cell wall layer, and wood anatomical orientation. Above the threshold RH, differences in mobility among ions were observed and the mobility depended upon anatomical direction and cell wall layer. These observations support a recently proposed percolation model of electrical conduction in wood. The results contribute to understanding the mechanisms of fungal decay and fastener corrosion that occur below the fiber saturation point.« less

Multilayer material characterization using thermographic signal reconstruction

NASA Astrophysics Data System (ADS)

Shepard, Steven M.; Beemer, Maria Frendberg

2016-02-01

Active-thermography has become a well-established Nondestructive Testing (NDT) method for detection of subsurface flaws. In its simplest form, flaw detection is based on visual identification of contrast between a flaw and local intact regions in an IR image sequence of the surface temperature as the sample responds to thermal stimulation. However, additional information and insight can be obtained from the sequence, even in the absence of a flaw, through analysis of the logarithmic derivatives of individual pixel time histories using the Thermographic Signal Reconstruction (TSR) method. For example, the response of a flaw-free multilayer sample to thermal stimulation can be viewed as a simple transition between the responses of infinitely thick samples of the individual constituent layers over the lifetime of the thermal diffusion process. The transition is represented compactly and uniquely by the logarithmic derivatives, based on the ratio of thermal effusivities of the layers. A spectrum of derivative responses relative to thermal effusivity ratios allows prediction of the time scale and detectability of the interface, and measurement of the thermophysical properties of one layer if the properties of the other are known. A similar transition between steady diffusion states occurs for flat bottom holes, based on the hole aspect ratio.

Flow control in a diffusing S-Duct

NASA Technical Reports Server (NTRS)

Vakili, A. D.; Wu, J. M.; Liver, P.; Bhat, M. K.

1985-01-01

Accurate measurements have been made of secondary flow in a 1.51 area ratio diffusing 30 deg - 30 deg S-Duct with circulair cross section. Turbulent flow was entering the duct at Mach number of 0.6, the boundary layer thickness at the duct entrance was ten percent of the duct inlet diameter. Through measurements made, local flow velocity vector as well as static and total pressures mapping of the flow at several stations were obtained. Strong secondary flow was measured in the first bend which continued into the second bend with new vorticity produced in there in the opposite direction. Surface oil flow visualization and wall pressures indicated a region of separated flow starting at theta approximately equal to 22 deg on the inside of the first bend up to theta approximately equal to 44 deg on the outside of the second bend. The flow separated in 'cyclone' form and never reattached in the duct. As a result of the secondary flow and the flow separation, significant total pressure distortion was observed at the exit of the duct. Using flow control devices the separation was eliminated while the exit distortion was improved.

Effect of Backing Plate Thermal Property on Friction Stir Welding of 25-mm-Thick AA6061

NASA Astrophysics Data System (ADS)

Upadhyay, Piyush; Reynolds, Anthony

2014-04-01

By using backing plates made out of materials with widely varying thermal diffusivity this work seeks to elucidate the effects of the root side thermal boundary condition on weld process variables and resulting joint properties. Welds were made in 25.4-mm-thick AA6061 using ceramic, titanium, steel, and aluminum as backing plate (BP) material. Welds were also made using a "composite backing plate" consisting of longitudinal narrow strip of low diffusivity material at the center and two side plates of high diffusivity aluminum. Stir zone temperature during the welding was measured using two thermocouples spot welded at the core of the probe: one at the midplane height and another near the tip of the probe corresponding to the root of the weld. Steady state midplane probe temperatures for all the BPs used were found to be very similar. Near root peak temperature, however, varied significantly among weld made with different BPs all other things being equal. Whereas the near root and midplane temperature were the same in the case of ceramic backing plate, the root peak temperature was 318 K (45 °C) less than the midplane temperature in the case of aluminum BP. The trends of nugget hardness and grain size in through thickness direction were in agreement with the measured probe temperatures. Hardness and tensile test results show that the use of composite BP results in stronger joint compared to monolithic steel BP.

Comparison and reproducibility of ADC measurements in breathhold, respiratory triggered, and free-breathing diffusion-weighted MR imaging of the liver.

PubMed

Kwee, Thomas C; Takahara, Taro; Koh, Dow-Mu; Nievelstein, Rutger A J; Luijten, Peter R

2008-11-01

To compare and determine the reproducibility of apparent diffusion coefficient (ADC) measurements of the normal liver parenchyma in breathhold, respiratory triggered, and free-breathing diffusion-weighted magnetic resonance imaging (DWI). Eleven healthy volunteers underwent three series of DWI. Each DWI series consisted of one breathhold, one respiratory triggered, and two free-breathing (thick and thin slice acquisition) scans of the liver, at b-values of 0 and 500 s/mm2. ADCs of the liver parenchyma were compared by using nonparametric tests. Reproducibility was assessed by the Bland-Altman method. Mean ADCs (in 10(-3) mm2/sec) in respiratory triggered DWI (2.07-2.27) were significantly higher than mean ADCs in breathhold DWI (1.57-1.62), thick slice free-breathing DWI (1.62-1.65), and thin slice free-breathing DWI (1.57-1.66) (P<0.005). Ranges of mean difference in ADC measurement+/-limits of agreement between two scans were -0.02-0.05+/-0.16-0.24 in breathhold DWI, -0.14-0.20+/-0.59-0.60 in respiratory triggered DWI, -0.03-0.03+/-0.20-0.29 in thick slice free-breathing DWI, and -0.01-0.09+/-0.21-0.29 in thin slice free-breathing DWI. ADC measurements of the normal liver parenchyma in respiratory triggered DWI are significantly higher and less reproducible than in breathhold and free-breathing DWI. Copyright (c) 2008 Wiley-Liss, Inc.

Optothermal in vitro diffusion measurements through silicone membranes

NASA Astrophysics Data System (ADS)

Cowen, J. A.; Liu, H.; Xiao, P.; Imhof, R. E.

2003-01-01

We report the development of a new method for measuring diffusion rates of surface-applied chemicals through polymer membranes such as polydimethylsiloxane (PDMS). An important feature of the approach is the use of optothermal transient emission radiometry to sense diffusant concentration in a noncontacting, noninvasive way. This allows the method to be adapted to perform similar measurements on human skin in vivo, thus providing a way of cross-verifying in vivo and in vitro measurements. The correlation between in vitro and in vivo diffusion measurements is also important for developing credible alternatives to in vivo testing, for use with toxic chemicals or animal substitution. We present the results of experiments with several polyols diffusing through PDMS membranes of thickness 125 or 250 μm, describing the experimental details, the measurement protocol, the data analysis methods, and a study of measurement errors.

Effect of Annealing Process on the Properties of Ni(55%)Cr(40%)Si(5%) Thin-Film Resistors

PubMed Central

Cheng, Huan-Yi; Chen, Ying-Chung; Li, Pei-Jou; Yang, Cheng-Fu; Huang, Hong-Hsin

2015-01-01

Resistors in integrated circuits (ICs) are implemented using diffused methods fabricated in the base and emitter regions of bipolar transistor or in source/drain regions of CMOS. Deposition of thin films on the wafer surface is another choice to fabricate the thin-film resistors in ICs’ applications. In this study, Ni(55%)Cr(40%)Si(5%) (abbreviated as NiCrSi) in wt % was used as the target and the sputtering method was used to deposit the thin-film resistors on Al2O3 substrates. NiCrSi thin-film resistors with different thicknesses of 30.8 nm~334.7 nm were obtained by controlling deposition time. After deposition, the thin-film resistors were annealed at 400 °C under different durations in N2 atmosphere using the rapid thermal annealing (RTA) process. The sheet resistance of NiCrSi thin-film resistors was measured using the four-point-probe method from 25 °C to 125 °C, then the temperature coefficient of resistance could be obtained. We aim to show that resistivity of NiCrSi thin-film resistors decreased with increasing deposition time (thickness) and the annealing process had apparent effect on the sheet resistance and temperature coefficient of resistance. We also aim to show that the annealed NiCrSi thin-film resistors had a low temperature coefficient of resistance (TCR) between 0 ppm/°C and +50 ppm/°C. PMID:28793598

Effect of Annealing Process on the Properties of Ni(55%)Cr(40%)Si(5%) Thin-Film Resistors.

PubMed

Cheng, Huan-Yi; Chen, Ying-Chung; Li, Pei-Jou; Yang, Cheng-Fu; Huang, Hong-Hsin

2015-10-02

Resistors in integrated circuits (ICs) are implemented using diffused methods fabricated in the base and emitter regions of bipolar transistor or in source/drain regions of CMOS. Deposition of thin films on the wafer surface is another choice to fabricate the thin-film resistors in ICs' applications. In this study, Ni(55%)Cr(40%)Si(5%) (abbreviated as NiCrSi) in wt % was used as the target and the sputtering method was used to deposit the thin-film resistors on Al2O3 substrates. NiCrSi thin-film resistors with different thicknesses of 30.8 nm~334.7 nm were obtained by controlling deposition time. After deposition, the thin-film resistors were annealed at 400 °C under different durations in N₂ atmosphere using the rapid thermal annealing (RTA) process. The sheet resistance of NiCrSi thin-film resistors was measured using the four-point-probe method from 25 °C to 125 °C, then the temperature coefficient of resistance could be obtained. We aim to show that resistivity of NiCrSi thin-film resistors decreased with increasing deposition time (thickness) and the annealing process had apparent effect on the sheet resistance and temperature coefficient of resistance. We also aim to show that the annealed NiCrSi thin-film resistors had a low temperature coefficient of resistance (TCR) between 0 ppm/°C and +50 ppm/°C.

Performance Simulation of Unipolar InAs/InAs1-x Sb x Type-II Superlattice Photodetector

NASA Astrophysics Data System (ADS)

Singh, Anand; Pal, Ravinder

2018-05-01

This paper reports performance simulation of a unipolar tunable band gap InAs-InAsSb type-II superlattice (T2SL) infrared photodetector. The generation-recombination and surface leakage currents limit the performance of T2SL photodiodes. Unipolar nBn device design incorporating a suitable barrier layer in the diode structure is taken to suppress the Auger recombination and tunneling currents. At low reverse bias, the generation-recombination current is negligible in the absence of a depletion region, but the dark current is dominated by the diffusion current at higher operation temperatures. The composition, band alignment, barrier width, doping level and thickness of the absorber region are optimized here to achieve low dark current and high quantum efficiency at elevated operating temperatures. Thin unipolar T2SL absorbers are placed in a resonant cavity to enhance photon-material interaction, thus allowing complete absorption in a thinner detector element. It leads to the reduction in the detector volume for lower dark current without affecting the quantum efficiency. It shows an improvement in the quantum efficiency and reduction in the dark current. Dark current density ˜ 10-5 A/cm2 is achievable with low absorber thickness of 2 μm and effective lifetime of 250 ns in the InAs/InAs0.6Sb0.4/B-AlAs1-x Sb x long wave length T2SL detector at 110 K.

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

NASA Astrophysics Data System (ADS)

Giri, Ashutosh; Niemelä, Janne-Petteri; Tynell, Tommi; Gaskins, John T.; Donovan, Brian F.; Karppinen, Maarit; Hopkins, Patrick E.

2016-03-01

Nanomaterial interfaces and concomitant thermal resistances are generally considered as atomic-scale planes that scatter the fundamental energy carriers. Given that the nanoscale structural and chemical properties of solid interfaces can strongly influence this thermal boundary conductance, the ballistic and diffusive nature of phonon transport along with the corresponding phonon wavelengths can affect how energy is scattered and transmitted across an interfacial region between two materials. In hybrid composites composed of atomic layer building blocks of inorganic and organic constituents, the varying interaction between the phononic spectrum in the inorganic crystals and vibronic modes in the molecular films can provide a new avenue to manipulate the energy exchange between the fundamental vibrational energy carriers across interfaces. Here, we systematically study the heat transfer mechanisms in hybrid superlattices of atomic- and molecular-layer-grown zinc oxide and hydroquinone with varying thicknesses of the inorganic and organic layers in the superlattices. We demonstrate ballistic energy transfer of phonons in the zinc oxide that is limited by scattering at the zinc oxide/hydroquinone interface for superlattices with a single monolayer of hydroquinone separating the thicker inorganic layers. The concomitant thermal boundary conductance across the zinc oxide interfacial region approaches the maximal thermal boundary conductance of a zinc oxide phonon flux, indicative of the contribution of long wavelength vibrations across the aromatic molecular monolayers in transmitting energy across the interface. This transmission of energy across the molecular interface decreases considerably as the thickness of the organic layers are increased.

Turbulent diffusion of chemically reacting flows: Theory and numerical simulations

NASA Astrophysics Data System (ADS)

Elperin, T.; Kleeorin, N.; Liberman, M.; Lipatnikov, A. N.; Rogachevskii, I.; Yu, R.

2017-11-01

The theory of turbulent diffusion of chemically reacting gaseous admixtures developed previously [T. Elperin et al., Phys. Rev. E 90, 053001 (2014), 10.1103/PhysRevE.90.053001] is generalized for large yet finite Reynolds numbers and the dependence of turbulent diffusion coefficient on two parameters, the Reynolds number and Damköhler number (which characterizes a ratio of turbulent and reaction time scales), is obtained. Three-dimensional direct numerical simulations (DNSs) of a finite-thickness reaction wave for the first-order chemical reactions propagating in forced, homogeneous, isotropic, and incompressible turbulence are performed to validate the theoretically predicted effect of chemical reactions on turbulent diffusion. It is shown that the obtained DNS results are in good agreement with the developed theory.

Effect of the Microstructure on Diffusion Bonded AA5083, AA6082 and AA7075 Aluminium Alloys

NASA Astrophysics Data System (ADS)

Venugopal, S.; Mahendran, G.

2018-05-01

Rolled plates of aluminium alloys AA5083, AA6082 and AA7075 of 5 mm thickness are joined by diffusion bonding at varied parameters. The microstructure evolution of AA5083, AA6082 and AA7075 aluminium alloys is characterized by Transmission Electron Microscopy (TEM). Metallurgical investigations and mechanical tests are also performed to correlate the results of the TEM investigations with the mechanical properties of the produced diffusion bonded joints. It is observed that the bonding and shear strength of the alloys increase with the increase in bonding temperature, due to the diffusion of micro-constituents in the interface. High temperature enhances the uniform distribution of secondary phase particles and reduces pore formation/defects in the bonded joints.

Turbulent diffusion of chemically reacting flows: Theory and numerical simulations.

PubMed

Elperin, T; Kleeorin, N; Liberman, M; Lipatnikov, A N; Rogachevskii, I; Yu, R

2017-11-01

The theory of turbulent diffusion of chemically reacting gaseous admixtures developed previously [T. Elperin et al., Phys. Rev. E 90, 053001 (2014)PLEEE81539-375510.1103/PhysRevE.90.053001] is generalized for large yet finite Reynolds numbers and the dependence of turbulent diffusion coefficient on two parameters, the Reynolds number and Damköhler number (which characterizes a ratio of turbulent and reaction time scales), is obtained. Three-dimensional direct numerical simulations (DNSs) of a finite-thickness reaction wave for the first-order chemical reactions propagating in forced, homogeneous, isotropic, and incompressible turbulence are performed to validate the theoretically predicted effect of chemical reactions on turbulent diffusion. It is shown that the obtained DNS results are in good agreement with the developed theory.

Estimating the thickness of diffusive solid electrolyte interface

NASA Astrophysics Data System (ADS)

Wang, XiaoHe; Shen, WenHao; Huang, XianFu; Zang, JinLiang; Zhao, YaPu

2017-06-01

The solid electrolyte interface (SEI) is a hierarchical structure formed in the transition zone between the electrode and the electrolyte. The properties of lithium-ion (Li-ion) battery, such as cycle life, irreversible capacity loss, self-discharge rate, electrode corrosion and safety are usually ascribed to the quality of the SEI, which are highly dependent on the thickness. Thus, understanding the formation mechanism and the SEI thickness is of prime interest. First, we apply dimensional analysis to obtain an explicit relation between the thickness and the number density in this study. Then the SEI thickness in the initial charge-discharge cycle is analyzed and estimated for the first time using the Cahn-Hilliard phase-field model. In addition, the SEI thickness by molecular dynamics simulation validates the theoretical results. It has been shown that the established model and the simulation in this paper estimate the SEI thickness concisely within order-of-magnitude of nanometers. Our results may help in evaluating the performance of SEI and assist the future design of Li-ion battery.

Progress in low light-level InAs detectors- towards Geiger-mode detection

NASA Astrophysics Data System (ADS)

Tan, Chee Hing; Ng, Jo Shien; Zhou, Xinxin; David, John; Zhang, Shiyong; Krysa, Andrey

2017-05-01

InAs avalanche photodiodes (APDs) can be designed such that only electrons are allowed to initiate impact ionization, leading to the lowest possible excess noise factor. Optimization of wet chemical etching and surface passivation produced mesa APDs with bulk dominated dark current and responsivity that are comparable and higher, respectively, than a commercial InAs detector. Our InAs electron-APDs also show high stability with fluctuation of 0.1% when operated at a gain of 11.2 over 60 s. These InAs APDs can detect very weak signal down to 35 photons per pulse. Fabrication of planar InAs by Be implantation produced planar APDs with bulk dominated dark current. Annealing at 550 °C was necessary to remove implantation damage and to activate Be dopants. Due to minimal diffusion of Be, thick depletion of 8 μm was achieved. Since the avalanche gain increases exponentially with the thickness of avalanche region, our planar APD achieved high gain > 300 at 200 K. Our work suggest that both mesa and planar InAs APDs can exhibit high gain. When combined with a suitable preamplifier, single photon detection using InAs electron-APDs could be achieved.

Cell fiber-based three-dimensional culture system for highly efficient expansion of human induced pluripotent stem cells.

PubMed

Ikeda, Kazuhiro; Nagata, Shogo; Okitsu, Teru; Takeuchi, Shoji

2017-06-06

Human pluripotent stem cells are a potentially powerful cellular resource for application in regenerative medicine. Because such applications require large numbers of human pluripotent stem cell-derived cells, a scalable culture system of human pluripotent stem cell needs to be developed. Several suspension culture systems for human pluripotent stem cell expansion exist; however, it is difficult to control the thickness of cell aggregations in these systems, leading to increased cell death likely caused by limited diffusion of gases and nutrients into the aggregations. Here, we describe a scalable culture system using the cell fiber technology for the expansion of human induced pluripotent stem (iPS) cells. The cells were encapsulated and cultured within the core region of core-shell hydrogel microfibers, resulting in the formation of rod-shaped or fiber-shaped cell aggregations with sustained thickness and high viability. By encapsulating the cells with type I collagen, we demonstrated a long-term culture of the cells by serial passaging at a high expansion rate (14-fold in four days) while retaining its pluripotency. Therefore, our culture system could be used for large-scale expansion of human pluripotent stem cells for use in regenerative medicine.

Optical studies of carriers’ vertical transport in the alternately-strained ZnS{sub 0.4}Se{sub 0.6}/CdSe superlattice

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

Evropeytsev, E. A., E-mail: evropeitsev@beam.ioffe.ru; Sorokin, S. V.; Gronin, S. V.

2015-03-15

We present the results of theoretical modelling and experimental optical studies of the alternatively-strained CdSe/ZnS{sub y}Se{sub 1−y} (y = 0.4) superlattice (SL) with effective band-gap E{sub g}{sup eff} ∼ 2.580 eV and a thickness of ∼300 nm, which was grown by molecular-beam epitaxy on a GaAs substrate. The thicknesses and composition of the layers of the superlattice are determined on the basis of the SL minibands parameters calculated implying both full lattice matching of the SL as a whole to a GaAs substrate and high efficiency of photoexcited carriers transport along the growth axis. Photoluminescence studies of the transport propertiesmore » of the structure (including a superlattice with one enlarged quantum well) show that the characteristic time of the diffusion of charge carriers at 300 K is shorter than the times defined by recombination processes. Such superlattices seem to be promising for the formation of a wide-gap photoactive region in a multijunction solar cell, which includes both III–V and II–VI compounds.« less

Drug release from slabs and the effects of surface roughness.

PubMed

Kalosakas, George; Martini, Dimitra

2015-12-30

We discuss diffusion-controlled drug release from slabs or thin films. Analytical and numerical results are presented for slabs with flat surfaces, having a uniform thickness. Then, considering slabs with rough surfaces, the influence of a non-uniform slab thickness on release kinetics is numerically investigated. The numerical release profiles are obtained using Monte Carlo simulations. Release kinetics is quantified through the stretched exponential (or Weibull) function and the resulting dependence of the two parameters of this function on the thickness of the slab, for flat surfaces, and the amplitude of surface fluctuations (or the degree of thickness variability) in case of roughness. We find that a higher surface roughness leads to a faster drug release. Copyright © 2015 Elsevier B.V. All rights reserved.

Structural, transport and microwave properties of 123/sapphire films: Thickness effect

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

Predtechensky, MR.; Smal, A.N.; Varlamov, Y.D.

1994-12-31

The effect of thickness and growth conditions on the structure and microwave properties has been investigated for the 123/sapphire films. It has been shown that in the conditions of epitaxial growth and Al atoms do not diffuse from substrate into the film and the films with thickness up to 100nm exhibit the excellent DC properties. The increase of thickness of GdBaCuO films causes the formation of extended line-mesh defects and the increase of the surface resistance (R{sub S}). The low value of surface resistance R{sub S}(75GHz,77K)=20 mOhm has been obtained for the two layer YBaCuO/CdBaCuO/sapphire films.

[Multiplayer white organic light-emitting diodes with different order and thickness of emission layers].

PubMed

Xu, Wei; Lu, Fu-Han; Cao, Jin; Zhu, Wen-Qing; Jiang, Xue-Yin; Zhang, Zhi-Lin; Xu, Shao-Hong

2008-02-01

In multilayer OLED devices, the order and thickness of the emission layers have great effect on their spectrum. Based on the three basic colours of red, blue and green, a series of white organic light-emitting diodes(WOLEDS)with the structure of ITO/CuPc(12 nm)/NPB(50 nm)/EML/LiF(1 nm)/Al(100 nm) and a variety of emission layer's orders and thicknesses were fabricated. The blue emission material: 2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN) doped with p-bis(p-N, N-diphenyl-amono-styryl)benzene(DSA-Ph), the green emission material: tris-[8-hydroxyquinoline]aluminum(Alq3) doped with C545, and the red emission material: tris-[8-hydroxyquinoline]aluminum( Alq3) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) were used. By adjusting the order and thickness of each emission layer in the RBG structure, we got a white OLED with current efficiency of 5.60 cd x A(-1) and Commission Internationale De L'Eclairage (CIE) coordinates of (0. 34, 0.34) at 200 mA x cm(-2). Its maximum luminance reached 20 700 cd x m(-2) at current density of 400 mA x cm(-2). The results were analyzed on the basis of the theory of excitons' generation and diffusion. According to the theory, an equation was set up which relates EL spectra to the luminance efficiency, the thickness of each layer and the exciton diffusion length. In addition, in RBG structure with different thickness of red layer, the ratio of th e spectral intensity of red to that of blue was calculated. It was found that the experimental results are in agreement with the theoretical values.

Method for producing small hollow spheres

DOEpatents

Rosencwaig, Allen; Koo, Jackson C.; Dressler, John L.

1981-01-01

A method for producing small hollow spheres of glass having an outer diameter ranging from about 100.mu. to about 500.mu. with a substantially uniform wall thickness in the range of about 0.5-20.mu.. The method involves introducing aqueous droplets of a glass-forming solution into a long vertical drop oven or furnace having varying temperature regions. In one embodiment, one of the temperature regions is lower than both the preceeding region and the subsequent region. One region utilizes a temperature of at least 200.degree. C. higher than the melting point of the glass-forming material in the solution and, for example, may be at least 3 times higher than the temperature of the preceeding region. In addition, there is a sharp temperature gradient between these regions. As each droplet of solution passes through a first region it forms into a gel membrane having a spherical shape and encapsulates the rest of the drop retained in the elastic outer surface and the water entrapped within diffuses rapidly through the thin gel membrane which causes more of the glass-forming material to go out of solution and is incorporated into the gel membrane causing it to grow in size and become hollow. thus produced hollow glass sphere has a sphericity, concentricity, and wall uniformity of better than 5%. The sphere is capable of retaining material of up to at least 100 atmospheres therein over long periods of time. In one embodiment.

Lateral mobility of plasma membrane proteins in dividing eggs of the loach (Misgurnus fossilis): Regional differences and changes during the cell cycle.

PubMed

Bozhkova, V P; Budayova, M; Kvasnicka, P; Cigankova, N; Chorvat, D

1994-12-01

Regional differences in lateral diffusion rates of fluorescence-labeled proteins have been studied in the plasma membrane of dividing eggs of the loach (Misgurnus fossilis) by fluorescence recovery after photobleaching (FRAP). Apparent animal-vegetal differences in fluorescence intensity, lateral diffusion coefficients, and fractions of mobile proteins have been found, with all these quantities being higher in the animal pole region than in the yolk region. Cyclic changes in protein diffusion coefficients and mobile fractions during the first few cell cycles have also been recorded. Soon after the end of a cleavage, the diffusion coefficient reaches its minimal value and increases rapidly before the next cleavage.

The mysteries of the diffusion region in asymmetric systems

NASA Astrophysics Data System (ADS)

Hesse, M.; Aunai, N.; Zenitani, S.; Kuznetsova, M. M.; Birn, J.

2013-12-01

Unlike in symmetric systems, where symmetry dictates a comparatively simple structure of the reconnection region, asymmetric systems offer a surprising, much more complex, structure of the diffusion region. Beyond the well-known lack of colocation of flow stagnation and magnetic null, the physical mechanism underpinning the reconnection electric field also appears to be considerably more complex. In this presentation, we will perform a detailed analysis of the reconnection diffusion region in an asymmetric system. We will show that, unlike in symmetric systems, the immediate reconnection electric field is not given by electron pressure tensor nongyrotropies, but by electron inertial contributions. We will further discuss the role of pressure nongyrotropies, and we will study the origin of the complex structures of electron distributions in the central part of the diffusion region.

Evaluation of Bone Thickness and Density in the Lower Incisors' Region in Adults with Different Types of Skeletal Malocclusion using Cone-beam Computed Tomography.

PubMed

Al-Masri, Maram M N; Ajaj, Mowaffak A; Hajeer, Mohammad Y; Al-Eed, Muataz S

2015-08-01

To evaluate the bone thickness and density in the lower incisors' region in orthodontically untreated adults, and to examine any possible relationship between thickness and density in different skeletal patterns using cone-beam computed tomography (CBCT). The CBCT records of 48 patients were obtained from the archive of orthodontic department comprising three groups of malocclusion (class I, II and III) with 16 patients in each group. Using OnDemand 3D software, sagittal sections were made for each lower incisor. Thicknesses and densities were measured at three levels of the root (cervical, middle and apical regions) from the labial and lingual sides. Accuracy and reliability tests were undertaken to assess the intraobserver reliability and to detect systematic error. Pearson correlation coefficients were calculated and one-way analysis of variance (ANOVA) was employed to detect significant differences among the three groups of skeletal malocclusion. Apical buccal thickness (ABT) in the four incisors was higher in class II and I patients than in class III patients (p < 0.05). There were significant differences between buccal and lingual surfaces at the apical and middle regions only in class II and III patients. Statistical differences were found between class I and II patients for the cervical buccal density (CBD) and between class II and III patients for apical buccal density (ABD). Relationship between bone thickness and density values ranged from strong at the cervical regions to weak at the apical regions. Sagittal skeletal patterns affect apical bone thickness and density at buccal surfaces of the four lower incisors' roots. Alveolar bone thickness and density increased from the cervical to the apical regions.

Initiation of a Low-Angle Normal Fault Active Across the Upper Brittle-Plastic Transition, Chemehuevi Mountains, CA

NASA Astrophysics Data System (ADS)

LaForge, J.; John, B. E.; Grimes, C. B.; Stunitz, H.; Heilbronner, R.

2016-12-01

The Chemehuevi detachment fault system, part of the regionally developed Colorado River extensional corridor, hosts exceptional exposures of a denuded fault system related to Miocene extension. Here, we characterize the early history of extension associated with a small slip (1-2 km) low-angle normal fault, the Mohave Wash fault (MWF), initially active across the brittle-plastic transition. Strain localized in three principal ways across the 23-km down-dip exposure (T <150° to >400°C): a brittle fault zone, localized, disseminated quartz mylonites, and syntectonic dikes hosting mylonitic fabrics. Brittle deformation in these crystalline rocks was concentrated into a 10-62-m thick brittle fault zone hosting localized, unmineralized to chlorite-epidote-quartz mineralized zones of cataclasite series fault rocks ≤3 m thick and rare pseudotachylite. Mylonitic deformation played an increased role in deformation down dip (NE), with mylonites increasing in quantity and average thickness. At shallow structural levels, footwall mylonites are absent; at 9-18 km down dip, cm-scale quartz mylonites are common; ≥18 km down dip, meter-scale syntectonic intermediate-felsic dikes are mylonitic, are attenuated into parallelism with the MWF, and host well-developed L-S fabric; 23 km down dip, the footwall hosts meter-thick zones of disseminated mylonitic quartz of varying intensities. These mylonites host microstructures that record progressively higher deformation temperature down dip, with dislocation-creep in quartz indicative of T of 280-400°C to ≥500°C, and diffusion creep with grain boundary sliding in dikes suggestive of even higher T deformation. Dike emplacement in the system is syntectonic with MWF slip; mafic-intermediate composition dikes intruded damage zone fractures and cataclasites, and were in turn fractured; Pb/U zircon ages of intermediate-felsic dikes range from ca. 1.5 ± 1 Ma to 3.8 ± 1 Ma after the onset of regional extension, but predate rapid slip. Cross cutting relations and absolute dating suggest the early history of the MWF evolved in two distinct phases: 1) seismogenic rupture with contemporaneous localized footwall mylonitization, followed by 2) additional cataclasis, episodic localized and magmatism, mylonitization and fluid-flow.

Multimodal Imaging of Brain Connectivity Using the MIBCA Toolbox: Preliminary Application to Alzheimer's Disease

NASA Astrophysics Data System (ADS)

Ribeiro, André Santos; Lacerda, Luís Miguel; Silva, Nuno André da; Ferreira, Hugo Alexandre

2015-06-01

The Multimodal Imaging Brain Connectivity Analysis (MIBCA) toolbox is a fully automated all-in-one connectivity analysis toolbox that offers both pre-processing, connectivity, and graph theory analysis of multimodal images such as anatomical, diffusion, and functional MRI, and PET. In this work, the MIBCA functionalities were used to study Alzheimer's Disease (AD) in a multimodal MR/PET approach. Materials and Methods: Data from 12 healthy controls, and 36 patients with EMCI, LMCI and AD (12 patients for each group) were obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database (adni.loni.usc.edu), including T1-weighted (T1-w), Diffusion Tensor Imaging (DTI) data, and 18F-AV-45 (florbetapir) dynamic PET data from 40-60 min post injection (4x5 min). Both MR and PET data were automatically pre-processed for all subjects using MIBCA. T1-w data was parcellated into cortical and subcortical regions-of-interest (ROIs), and the corresponding thicknesses and volumes were calculated. DTI data was used to compute structural connectivity matrices based on fibers connecting pairs of ROIs. Lastly, dynamic PET images were summed, and the relative Standard Uptake Values calculated for each ROI. Results: An overall higher uptake of 18F-AV-45, consistent with an increased deposition of beta-amyloid, was observed for the AD group. Additionally, patients showed significant cortical atrophy (thickness and volume) especially in the entorhinal cortex and temporal areas, and a significant increase in Mean Diffusivity (MD) in the hippocampus, amygdala and temporal areas. Furthermore, patients showed a reduction of fiber connectivity with the progression of the disease, especially for intra-hemispherical connections. Conclusion: This work shows the potential of the MIBCA toolbox for the study of AD, as findings were shown to be in agreement with the literature. Here, only structural changes and beta-amyloid accumulation were considered. Yet, MIBCA is further able to process fMRI and different radiotracers, thus leading to integration of functional information, and supporting the research for new multimodal biomarkers for AD and other neurodegenerative diseases.

Cryotherapy for conjunctival primary acquired melanosis and malignant melanoma. Experience with 62 cases.

PubMed

Jakobiec, F A; Rini, F J; Fraunfelder, F T; Brownstein, S

1988-08-01

Sixty-two patients were treated by some combination of cryotherapy and surgery with an average follow-up of 3.3 years for one of the following diseases: focal or diffuse flat conjunctival primary acquired melanosis (PAM) with atypia but without a nodule of melanoma (10 cases); unifocal malignant melanoma with or without focal or diffuse PAM (30 cases); and multinodular/multicentric melanoma with and without PAM (22 cases). Of the ten patients who had PAM with atypia, invasive nodules of malignant melanoma did not develop. A second treatment was required to control the disease in four of the ten patients with extensive or diffuse lesions, and one has mild persistent disease. Of the 30 patients with unifocal nodules of malignant melanoma, 27 remained free of recurrence after one treatment, and 2 are asymptomatic after two treatments. One patient with a thick nodule at presentation required a parotidectomy and radical neck dissection for cervical metastases after recurrence in the conjunctival sac. In the group of 22 patients with multinodular malignant melanoma, only two did not have recurrent disease after one treatment. Of those who received multiple therapies, seven remained free of recurrence for at least 2 years after the last treatment; regional or distant metastases developed in nine; four required exenteration; and eight died. Conjunctival adjunctive cryotherapy avoids exenteration in extensive lesions of pure PAM and in unifocal melanoma, but even after multiple therapies, multinodular malignant melanoma had a 45% rate of metastasis. Metastasis was related to the presence of PAM sine pigmento in four patients (microscopically but not clinically detectable PAM); to the location of the nodules (9 of 10 patients who experienced metastases had forniceal, palpebral, and/or caruncular nodules); to the thickness or depth of invasion of the nodules (greater than 2 mm); and to the development of intralymphatic spread ("in-transit" local metastasis) within the conjunctival sac in six patients. No metastases were encountered among patients with strictly limbal nodules and among five patients with invasive nodules composed of spindle cells in part or in toto. Therapeutic success in this spectrum of melanocytic proliferations is closely correlated with the clinical extent of the disease when initiating definitive therapy.

Investigation of olivine and orthopyroxene grain boundaries by atom probe tomography

NASA Astrophysics Data System (ADS)

Krawczynski, M.; Skemer, P. A.; Bachhav, M.; Dong, Y.; Marquis, E. A.

2016-12-01

Accurate chemical analysis at grain boundaries is challenging by traditional microscopic techniques, especially for poor conducting geological samples. Atom probe tomography (APT) is a unique technique that can elucidate chemistry and 3-D distribution of elements within a sample volume at the sub-nanometer length scale. With advances in laser and sample preparation techniques in the last decade, APT is now successfully applied to a wide range of poor conducting materials like metal oxides, ceramics, and biological minerals. In this study, we apply the APT technique to investigate the grain boundary chemistry of orthopyroxene (opx) and olivine. These minerals are the most abundant in the upper mantle and their grain boundaries may be important geochemical reservoirs in Earth. Moreover, physical properties such as grain boundary diffusivity, conductivity, and mobility, are likely influenced by the presence or absence of impurities. Single crystals of opx and olivine grains, separated from a San Carlos xenolith, were deformed at 1 GPa and 1500 K. Plastic deformation promoted dynamic recrystallization, creating new grain boundaries within a chemically homogeneous medium. Needle shaped specimens of opx-opx and olivine-olivine grain boundaries were prepared using standard lift out techniques and a dual beam focused ion beam (FIB). APT analyses were performed in laser mode with laser energy of 50 pJ/pulse, repetition rate of 200 kHz, and detection rate of 1%. A 3-D distribution of elements was reconstructed and 1-D profiles across the grain boundary have been calculated. Fe, Al, and Ca show enrichments at the grain boundaries for both phases, consistent with previous studies that used STEM/EDX or EPMA techniques. Although qualitatively similar, the spatial resolution of the APT method is significantly better than other methods, and our data show that the grain-boundary enrichment of minor elements in both olivine and pyroxene compositions is limited to a region no greater than 2-4 nm thick. These new data place constraints on the thickness of the grain boundary zone with unparalleled precision, allowing more accurate calculation of partition coefficients as well as diffusion coefficients from experimental studies of grain boundary diffusion.

Nanostructures and nanosecond dynamics at the polymer/filler interface

NASA Astrophysics Data System (ADS)

Koga, Tad; Barkley, Deborah; Endoh, Maya; Masui, Tomomi; Kishimoto, Hiroyuki; Nagao, Michihiro; Taniguchi, Takashi

We report in-situ nanostructures and nanosecond dynamics of polybutadiene (PB) chains bound to carbon black (CB) fillers (the so-called ``bound polymer layer (BPL)'') in polymer solutions (from dilute to concentrated solutions). The BPL on the CB fillers were extracted by solvent leaching of a CB-filled PB compound and subsequently dispersed in deuterated toluene (a good solvent) to label the BPL for ``contrast-matching'' small-angle neutron scattering (SANS) and neutron spin echo (NSE) techniques. The SANS results demonstrate that the BPL is composed of two regions regardless of molecular weights of PB: the inner unswollen region of 0.5 nm thick and outer swollen region where the polymer chains display a parabolic profile with a diffuse tail. In addition, the NSE results show that the dynamics of the swollen bound chains in the polymer solutions can be explained by the collective dynamics, the so-called ``breathing mode''. Intriguingly, it was also indicative that the collective dynamics is independent of the polymer concentrations and is much faster than that predicted from the solution viscosity. We will discuss the mechanism at the bound polymer-free polymer interface at the nanometer scale. T.K. acknowledges the financial support from NSF Grant (CMMI-1332499).

Analysis of Nb 3Sn surface layers for superconducting radio frequency cavity applications

DOE PAGES

Becker, Chaoyue; Posen, Sam; Groll, Nickolas; ...

2015-02-23

Here, we present an analysis of Nb 3Sn surface layers grown on a bulk Nb coupon prepared at the same time and by the same vapor diffusion process used to make Nb 3Sn coatings on 1.3 GHz Nb cavities. Tunneling spectroscopy reveal a well developed, homogeneous superconducting density of states at the surface with a gap value distribution centered around 2.7 ± 0.4 meV and superconducting critical temperature's (T c) up to 16.3K. Transmission electron microscopy (TEM) performed on cross sections of the sample's surface shows a ~ 2 microns thick Nb 3Sn surface layer. The elemental composition map exhibitsmore » a Nb:Sn ratio of 3:1 with buried substoichiometric regions with a ratio of 5:1. Synchrotron diffraction experiments indicate a polycrystalline Nb 3Sn film and confirm the presence of Nb rich regions that occupies about a third of the coating volume. These low T c regions could play an important role in the dissipation mechanisms occurring during RF tests of Nb 3Sn -coated Nb cavities and open the way for further improving a very promising alternative to pure Nb cavities for particle accelerators.« less

A Review of the Status of Brain Structure Research in Transsexualism.

PubMed

Guillamon, Antonio; Junque, Carme; Gómez-Gil, Esther

2016-10-01

The present review focuses on the brain structure of male-to-female (MtF) and female-to-male (FtM) homosexual transsexuals before and after cross-sex hormone treatment as shown by in vivo neuroimaging techniques. Cortical thickness and diffusion tensor imaging studies suggest that the brain of MtFs presents complex mixtures of masculine, feminine, and demasculinized regions, while FtMs show feminine, masculine, and defeminized regions. Consequently, the specific brain phenotypes proposed for MtFs and FtMs differ from those of both heterosexual males and females. These phenotypes have theoretical implications for brain intersexuality, asymmetry, and body perception in transsexuals as well as for Blanchard's hypothesis on sexual orientation in homosexual MtFs. Falling within the aegis of the neurohormonal theory of sex differences, we hypothesize that cortical differences between homosexual MtFs and FtMs and male and female controls are due to differently timed cortical thinning in different regions for each group. Cross-sex hormone studies have reported marked effects of the treatment on MtF and FtM brains. Their results are used to discuss the early postmortem histological studies of the MtF brain.

Comparison of orbital chemistry with crustal thickness and lunar sample chemistry

NASA Technical Reports Server (NTRS)

Schonfeld, E.

1977-01-01

A correlation between orbital chemistry (FeO, Al2O3, Mg/Al, MgO/FeO, Th) and the lunar crustal thickness is examined. The correlation suggests either lack of complete homogenization by lateral or vertical mixing, or lateral variation in the differentiation process. In addition, links between orbital chemistry and lunar sample chemistry are investigated. In regions with crustal thickness between 100 and 110 km, gabbroic anorthosites are very abundant, while in regions with crustal thickness of about 80 km anorthositic gabbros are frequent. Special attention is given to the distribution of low-potassium Fra Mauro basalt, found in high concentrations in regions with 50 to 60 km crustal thickness.

Correlations between the MR Diffusion-weighted Image (DWI) and the bone mineral density (BMD) as a function of the soft tissue thickness-focus on phantom and patient

NASA Astrophysics Data System (ADS)

Kim, Myung-Sam; Cho, Jae-Hwan; Lee, Hae-Kag; Lee, Sang-Jeong; Park, Cheol-Soo; Dong, Kyung-Rae; Park, Yong-Soon; Chung, Woon-Kwan; Lee, Jong-Woong; Kim, Ho-Sung; Kim, Eun-Hye; Kweon, Dae Cheol; Yeo, Hwa-Yeon

2013-02-01

In this study we used lumbar phantoms to determine if the BMD (bone mineral density) changes when only the thickness of soft tissue is increased. Second, we targeted osteoporosis patients to analyze the dependences of the changes in the SNR (signal-to-noise ratio) and the ADC (apparent diffusion coefficient) on changes in T-score. We used a bone mineral densitometer, phantoms such as an aluminum spine phantom (ASP), a Hologic spine phantom (HSP), and a European spine phantom (ESP), five sheets of acrylic panel, and a water bath to study the effects of changes in the thickness of soft tissue. First, we measured the ASP, the HSP and the ESP. For the measurement of the ASP, we filled it with water to increase the height by 0.5 cm starting from the baseline height. We then did three measurements for each height. For the measurements of the HSP and the ESP, we placed an acrylic panel on the phantom and then did three measurements at each height. We used the ASP to calculate the degree of precision of the standard mode and the thick mode at the maximum height of the water bath. To assess the degree of precision in the measurements of the three types of phantoms, we calculated precision errors and analyzed the correlation between the change in the thickness of soft tissue and the variables of the BMD. Using DWIs (diffusion weighted images), we targeted 30 healthy persons without osteoporosis and 30 patients with a finding of osteoporosis and measured the T-scores for the L1 — L4 (lumbar spine) segments of by the spine using the dual-energy X-ray absorptiometry (DXA) before classifying the measurement at each part of the spine as osteopenia or osteoporosis. We measured the signal intensity on all four parts of L1-L4 in the DWIs obtained using a 1.5T MR scanner and measured the ADC in the ADC map image. We compared changes in the SNR and the ADC for each group. The study results confirmed that an increase in the thickness of the soft tissue had a significant correlation with the BMD and that the SNR and the ADC decreased as the T-score in the DWI went down.

Diffusive leakage of brine from aquifers during CO2 geological storage

NASA Astrophysics Data System (ADS)

Dejam, Morteza; Hassanzadeh, Hassan

2018-01-01

The area of investigation in this study is designed around an improved understanding of fundamentals of the diffusive leakage of brine from a storage aquifer into overlying and underlying low permeability layers during geosequestration of carbon dioxide (CO2) through development of a theoretical model. Here, we consider a two-dimensional domain in cylindrical coordinates, comprised of an aquifer and an overburden, where the interaction between the two media is handled by imposing the continuities of pressures and fluid fluxes at the aquifer-overburden interface. This coupled problem is solved by successive implementation of the Laplace and finite Hankel transforms. The developed solutions can be used to analyze diffusive leakage of brine from the aquifer into overburden and generate type curves for average pressures in the aquifer and overburden during injection and post injection periods. The results show that the leakage rate at early times is scaled with t1/2 while it remains constant at late times. It is also shown that the average pressure in the aquifer is scaled with t for short and long times. Moreover, the average pressure in the overburden is scaled with t at late times while it is scaled with t3/2 at early times. In addition, the results reveal that factors affecting diffusive leakage rate through intact overburden during CO2 storage are, in decreasing order of significance, thickness of overburden, thickness of aquifer, aquifer to overburden permeability ratio, and aquifer to overburden porosity ratio. However, thickness of aquifer has minimal effect on diffusive leakage of brine within post injection period. To evaluate the theoretical model, case studies for two potential sites in United Kingdom, one in Lincolnshire and the other one in the Firth of Forth, are conducted. The field studies show that the diffusive leakage from the aquifer into the overburden diminishes ∼40 years after the injection has ceased for Lincolnshire while it stops after ∼12 years for Firth of Forth. The average amount of the brine leaked from the aquifers per standard cubic meter (Sm3) of the injected CO2 through diffusive leakage was found to be 6.28 × 10-4 m3 of brine (or 0.330 kg of brine/kg of CO2) over ∼70 years for Lincolnshire and 4.59 × 10-4 m3 of brine (or 0.242 kg of brine/kg of CO2) over ∼42 years for Firth of Forth.

Deep Chandra Observations of ESO 428-G014. II. Spectral Properties and Morphology of the Large-scale Extended X-Ray Emission

NASA Astrophysics Data System (ADS)

Fabbiano, G.; Paggi, A.; Karovska, M.; Elvis, M.; Maksym, W. P.; Risaliti, G.; Wang, Junfeng

2018-03-01

We present a deep Chandra spectral and spatial study of the kpc-scale diffuse X-ray emission of the Compton-thick (CT) active galactic nucleus (AGN) ESO 428-G014. The entire spectrum is best fit with composite photoionization + thermal models. The diffuse emission is more extended at lower energies (<3 keV). The smaller extent of the hard continuum and Fe Kα profiles implies that the optically thicker clouds responsible for this scattering may be relatively more prevalent closer to the nucleus. These clouds must not prevent soft ionizing X-rays from the AGN escaping to larger radii, in order to have photoionized ISM at larger radii. This suggests that at smaller radii, there may be a larger population of molecular clouds to scatter the hard X-rays, as in the Milky Way. The diffuse emission is also significantly extended in the cross-cone direction, where the AGN emission would be mostly obscured by the torus in the standard AGN model. Our results suggest that the transmission of the obscuring region in the cross-cone direction is ∼10% of that in the cone direction. In the 0.3–1.5 keV band, the ratio of cross-cone to cone photons increases to ∼84%, suggesting an additional soft diffuse emission component disjoint from the AGN. This could be due to hot ISM trapped in the potential of the galaxy. The luminosity of this component, ∼5 × 1038 erg s‑1, is roughly consistent with the thermal component suggested by the spectral fits in the 170–900 pc annulus.

Thickness engineering of atomic layer deposited Al2O3 films to suppress interfacial reaction and diffusion of Ni/Au gate metal in AlGaN/GaN HEMTs up to 600 °C in air

NASA Astrophysics Data System (ADS)

Suria, Ateeq J.; Yalamarthy, Ananth Saran; Heuser, Thomas A.; Bruefach, Alexandra; Chapin, Caitlin A.; So, Hongyun; Senesky, Debbie G.

2017-06-01

In this paper, we describe the use of 50 nm atomic layer deposited (ALD) Al2O3 to suppress the interfacial reaction and inter-diffusion between the gate metal and semiconductor interface, to extend the operation limit up to 600 °C in air. Suppression of diffusion is verified through Auger electron spectroscopy (AES) depth profiling and X-ray diffraction (XRD) and is further supported with electrical characterization. An ALD Al2O3 thin film (10 nm and 50 nm), which functions as a dielectric layer, was inserted between the gate metal (Ni/Au) and heterostructure-based semiconductor material (AlGaN/GaN) to form a metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). This extended the 50 nm ALD Al2O3 MIS-HEMT (50-MIS) current-voltage (Ids-Vds) and gate leakage (Ig,leakage) characteristics up to 600 °C. Both, the 10 nm ALD Al2O3 MIS-HEMT (10-MIS) and HEMT, failed above 350 °C, as evidenced by a sudden increase of approximately 50 times and 5.3 × 106 times in Ig,leakage, respectively. AES on the HEMT revealed the formation of a Ni-Au alloy and Ni present in the active region. Additionally, XRD showed existence of metal gallides in the HEMT. The 50-MIS enables the operation of AlGaN/GaN based electronics in oxidizing high-temperature environments, by suppressing interfacial reaction and inter-diffusion of the gate metal with the semiconductor.

Epilepsy in multiple sclerosis: The role of temporal lobe damage.

PubMed

Calabrese, M; Castellaro, M; Bertoldo, A; De Luca, A; Pizzini, F B; Ricciardi, G K; Pitteri, M; Zimatore, S; Magliozzi, R; Benedetti, M D; Manganotti, P; Montemezzi, S; Reynolds, R; Gajofatto, A; Monaco, S

2017-03-01

Although temporal lobe pathology may explain some of the symptoms of multiple sclerosis (MS), its role in the pathogenesis of seizures has not been clarified yet. To investigate the role of temporal lobe damage in MS patients suffering from epilepsy, by the application of advanced multimodal 3T magnetic resonance imaging (MRI) analysis. A total of 23 relapsing remitting MS patients who had epileptic seizures (RRMS/E) and 23 disease duration matched RRMS patients without any history of seizures were enrolled. Each patient underwent advanced 3T MRI protocol specifically conceived to evaluate grey matter (GM) damage. This includes grey matter lesions (GMLs) identification, evaluation of regional cortical thickness and indices derived from the Neurite Orientation Dispersion and Density Imaging model. Regional analysis revealed that in RRMS/E, the regions most affected by GMLs were the hippocampus (14.2%), the lateral temporal lobe (13.5%), the cingulate (10.0%) and the insula (8.4%). Cortical thinning and alteration of diffusion metrics were observed in several regions of temporal lobe, in insular cortex and in cingulate gyrus of RRMS/E compared to RRMS ( p< 0.05 for all comparisons). Compared to RRMS, RRMS/E showed more severe damage of temporal lobe, which exceeds what would be expected on the basis of the global GM damage observed.

Functional Significance of Atypical Cortical Organization in Spina Bifida Myelomeningocele: Relations of Cortical Thickness and Gyrification with IQ and Fine Motor Dexterity

PubMed Central

Treble, Amery; Juranek, Jenifer; Stuebing, Karla K.; Dennis, Maureen; Fletcher, Jack M.

2013-01-01

The cortex in spina bifida myelomeningocele (SBM) is atypically organized, but it is not known how specific features of atypical cortical organization promote or disrupt cognitive and motor function. Relations of deviant cortical thickness and gyrification with IQ and fine motor dexterity were investigated in 64 individuals with SBM and 26 typically developing (TD) individuals, aged 8–28 years. Cortical thickness and 3D local gyrification index (LGI) were quantified from 33 cortical regions per hemisphere using FreeSurfer. Results replicated previous findings, showing regions of higher and lower cortical thickness and LGI in SBM relative to the TD comparison individuals. Cortical thickness and LGI were negatively associated in most cortical regions, though less consistently in the TD group. Whereas cortical thickness and LGI tended to be negatively associated with IQ and fine motor outcomes in regions that were thicker or more gyrified in SBM, associations tended to be positive in regions that were thinner or less gyrified in SBM. The more deviant the levels of cortical thickness and LGI—whether higher or lower relative to the TD group—the more impaired the IQ and fine motor outcomes, suggesting that these cortical atypicalities in SBM are functionally maladaptive, rather than adaptive. PMID:22875857

Using Diffusion Bonding in Making Piezoelectric Actuators

NASA Technical Reports Server (NTRS)

Sager, Frank E.

2003-01-01

A technique for the fabrication of piezoelectric actuators that generate acceptably large forces and deflections at relatively low applied voltages involves the stacking and diffusion bonding of multiple thin piezoelectric layers coated with film electrodes. The present technique stands in contrast to an older technique in which the layers are bonded chemically, by use of urethane or epoxy agents. The older chemical-bonding technique entails several disadvantages, including the following: It is difficult to apply the bonding agents to the piezoelectric layers. It is difficult to position the layers accurately and without making mistakes. There is a problem of disposal of hazardous urethane and epoxy wastes. The urethane and epoxy agents are nonpiezoelectric materials. As such, they contribute to the thickness of a piezoelectric laminate without contributing to its performance; conversely, for a given total thickness, the performance of the laminate is below that of a unitary piezoelectric plate of the same thickness. The figure depicts some aspects of the fabrication of a laminated piezoelectric actuator by the present diffusion- bonding technique. First, stock sheets of the piezoelectric material are inspected and tested. Next, the hole pattern shown in the figure is punched into the sheets. Alternatively, if the piezoelectric material is not a polymer, then the holes are punched in thermoplastic films. Then both faces of each punched piezoelectric sheet or thermoplastic film are coated with a silver-ink electrode material by use of a silkscreen printer. The electrode and hole patterns are designed for minimal complexity and minimal waste of material. After a final electrical test, all the coated piezoelectric layers (or piezoelectric layers and coated thermoplastic films) are stacked in an alignment jig, which, in turn, is placed in a curved press for the diffusion-bonding process. In this process, the stack is pressed and heated at a specified curing temperature and pressure for a specified curing time. The pressure, temperature, and time depend on the piezoelectric material selected. At the end of the diffusion-bonding process, the resulting laminated piezoelectric actuator is tested to verify the adequacy of the mechanical output as a function of an applied DC voltage.

The surface diffusion coefficient for an arbitrarily curved fluid-fluid interface. (I). General expression

NASA Astrophysics Data System (ADS)

M. C. Sagis, Leonard

2001-03-01

In this paper, we develop a theory for the calculation of the surface diffusion coefficient for an arbitrarily curved fluid-fluid interface. The theory is valid for systems in hydrodynamic equilibrium, with zero mass-averaged velocities in the bulk and interfacial regions. We restrict our attention to systems with isotropic bulk phases, and an interfacial region that is isotropic in the plane parallel to the dividing surface. The dividing surface is assumed to be a simple interface, without memory effects or yield stresses. We derive an expression for the surface diffusion coefficient in terms of two parameters of the interfacial region: the coefficient for plane-parallel diffusion D (AB)aa(ξ) , and the driving force d(B)I||(ξ) . This driving force is the parallel component of the driving force for diffusion in the interfacial region. We derive an expression for this driving force using the entropy balance.

Position-Dependent Dynamics Explain Pore-Averaged Diffusion in Strongly Attractive Adsorptive Systems.

PubMed

Krekelberg, William P; Siderius, Daniel W; Shen, Vincent K; Truskett, Thomas M; Errington, Jeffrey R

2017-12-12

Using molecular simulations, we investigate the relationship between the pore-averaged and position-dependent self-diffusivity of a fluid adsorbed in a strongly attractive pore as a function of loading. Previous work (Krekelberg, W. P.; Siderius, D. W.; Shen, V. K.; Truskett, T. M.; Errington, J. R. Connection between thermodynamics and dynamics of simple fluids in highly attractive pores. Langmuir 2013, 29, 14527-14535, doi: 10.1021/la4037327) established that pore-averaged self-diffusivity in the multilayer adsorption regime, where the fluid exhibits a dense film at the pore surface and a lower density interior pore region, is nearly constant as a function of loading. Here we show that this puzzling behavior can be understood in terms of how loading affects the fraction of particles that reside in the film and interior pore regions as well as their distinct dynamics. Specifically, the insensitivity of pore-averaged diffusivity to loading arises from the approximate cancellation of two factors: an increase in the fraction of particles in the higher diffusivity interior pore region with loading and a corresponding decrease in the particle diffusivity in that region. We also find that the position-dependent self-diffusivities scale with the position-dependent density. We present a model for predicting the pore-average self-diffusivity based on the position-dependent self-diffusivity, which captures the unusual characteristics of pore-averaged self-diffusivity in strongly attractive pores over several orders of magnitude.

Comparison of Antarctic Crustal Thickness from Gravity Inversion and Seismology: Evidence for Mantle Dynamic Uplift under Marie Byrd Land

NASA Astrophysics Data System (ADS)

Ferraccioli, F.; Kusznir, N. J.; Jordan, T. A.

2017-12-01

Using gravity anomaly inversion, we produce comprehensive regional maps of crustal thickness and oceanic lithosphere distribution for Antarctica and the Southern Ocean. Antarctic crustal thicknesses derived from gravity inversion are compared with seismic estimates from Baranov (2011) and An et al. (2015). We determine Moho depth, crustal basement thickness, continental lithosphere thinning (1-1/) and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir 2008). Data used in the gravity inversion are elevation and bathymetry, free-air gravity anomaly, the Bedmap 2 ice thickness and bedrock topography compilation south of 60 degrees south and relatively sparse constraints on sediment thickness. Our gravity inversion study predicts thick crust (> 45 km) under interior East Antarctica, which is penetrated by narrow continental rifts featuring relatively thinner crust. The largest crustal thicknesses predicted from gravity inversion lie in the region of the Gamburtsev Subglacial Mountains, and are consistent with seismic estimates. The East Antarctic Rift System (EARS), a major Permian to Cretaceous age rift system, is imaged by our inversion and appears to extend from the continental margin at the Lambert Rift (LR) to the South Pole region, a distance of 2500 km. Thin crust is predicted under the Ross Sea and beneath the West Antarctic Ice Sheet and delineates the regional extent of the broad West Antarctic Rift System (WARS). Substantial regional uplift is required under Marie Byrd Land to reconcile gravity and seismic estimates. A mantle dynamic uplift origin of the uplift is preferred to a thermal anomaly from a very young rift. The new crustal thickness map produced by this gravity inversion study support the hypothesis that one branch of the WARS links through to the De Gerlache sea-mounts (DG) and Peter I Island (PI) in the Bellingshausen Sea region, while another branch may link to the George V Sound Rift in the Antarctic Peninsula region.

Record Charge Carrier Diffusion Length in Colloidal Quantum Dot Solids via Mutual Dot-To-Dot Surface Passivation.

PubMed

Carey, Graham H; Levina, Larissa; Comin, Riccardo; Voznyy, Oleksandr; Sargent, Edward H

2015-06-03

Through a combination of chemical and mutual dot-to-dot surface passivation, high-quality colloidal quantum dot solids are fabricated. The joint passivation techniques lead to a record diffusion length for colloidal quantum dots of 230 ± 20 nm. The technique is applied to create thick photovoltaic devices that exhibit high current density without losing fill factor. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced Atom Mobility on the Surface of a Metastable Film

NASA Astrophysics Data System (ADS)

Picone, A.; Riva, M.; Fratesi, G.; Brambilla, A.; Bussetti, G.; Finazzi, M.; Duò, L.; Ciccacci, F.

2014-07-01

A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization.

Enhanced atom mobility on the surface of a metastable film.

PubMed

Picone, A; Riva, M; Fratesi, G; Brambilla, A; Bussetti, G; Finazzi, M; Duò, L; Ciccacci, F

2014-07-25

A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization.

Determination of diffusion coefficients in polypyrrole thin films using a current pulse relaxation method

NASA Technical Reports Server (NTRS)

Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.

1987-01-01

The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.

Effect of Al-diffusion-induced positive flatband voltage shift on the electrical characteristics of Al-incorporated high-k metal-oxide-semiconductor field-effective transistor

NASA Astrophysics Data System (ADS)

Wang, Wenwu; Akiyama, Koji; Mizubayashi, Wataru; Nabatame, Toshihide; Ota, Hiroyuki; Toriumi, Akira

2009-03-01

We systematically studied what effect Al diffusion from high-k dielectrics had on the flatband voltage (Vfb) of Al-incorporated high-k gate stacks. An anomalous positive shift fin Vfb with the decreasing equivalent oxide thickness (EOT) of high-k gate stacks is reported. As the SiO2 interfacial layer is aggressively thinned in Al-incorporated HfxAl1-xOy gate stacks with a metal-gate electrode, the Vfb first lies on the well known linear Vfb-EOT plot and deviates toward the positive-voltage direction (Vfb roll-up), followed by shifting toward negative voltage (Vfb roll-off). We demonstrated that the Vfb roll-up behavior remarkably decreases the threshold voltage (Vth) of p-type metal-oxide-semiconductor field-effect transistors (p-MOSFETs), and does not cause severe degradation in the characteristics of hole mobility. The Vfb roll-up behavior, which is independent of gate materials but strongly dependent on high-k dielectrics, was ascribed to variations in fixed charges near the SiO2/Si interface, which are caused by Al diffusion from HfxAl1-xOy through SiO2 to the SiO2/Si interface. These results indicate that anomalous positive shift in Vfb, i.e., Vfb roll-up, should be taken into consideration in quantitatively adjusting Vfb in thin EOT regions and that it could be used to further tune Vth in p-MOSFETs.

Observations of O VI Emission from the Diffuse Interstellar Medium

NASA Technical Reports Server (NTRS)

Shelton, R. L.; Kruk, J. W.; Murphy, E. M.; Andersson, B. G.; Blair, W. P.; Dixon, W. V.; Edelstein, J.; Fullerton, A. W.; Gry, C.; Howk, J. C.;

Diffusion or advection? Mass transfer and complex boundary layer landscapes of the brown alga Fucus vesiculosus.

PubMed

Lichtenberg, Mads; Nørregaard, Rasmus Dyrmose; Kühl, Michael

2017-03-01

The role of hyaline hairs on the thallus of brown algae in the genus Fucus is long debated and several functions have been proposed. We used a novel motorized set-up for two-dimensional and three-dimensional mapping with O 2 microsensors to investigate the spatial heterogeneity of the diffusive boundary layer (DBL) and O 2 flux around single and multiple tufts of hyaline hairs on the thallus of Fucus vesiculosus. Flow was a major determinant of DBL thickness, where higher flow decreased DBL thickness and increased O 2 flux between the algal thallus and the surrounding seawater. However, the topography of the DBL varied and did not directly follow the contour of the underlying thallus. Areas around single tufts of hyaline hairs exhibited a more complex mass-transfer boundary layer, showing both increased and decreased thickness when compared with areas over smooth thallus surfaces. Over thallus areas with several hyaline hair tufts, the overall effect was an apparent increase in the boundary layer thickness. We also found indications for advective O 2 transport driven by pressure gradients or vortex shedding downstream from dense tufts of hyaline hairs that could alleviate local mass-transfer resistances. Mass-transfer dynamics around hyaline hair tufts are thus more complex than hitherto assumed and may have important implications for algal physiology and plant-microbe interactions. © 2017 The Author(s).

Diffusion or advection? Mass transfer and complex boundary layer landscapes of the brown alga Fucus vesiculosus

PubMed Central

Nørregaard, Rasmus Dyrmose

2017-01-01

The role of hyaline hairs on the thallus of brown algae in the genus Fucus is long debated and several functions have been proposed. We used a novel motorized set-up for two-dimensional and three-dimensional mapping with O2 microsensors to investigate the spatial heterogeneity of the diffusive boundary layer (DBL) and O2 flux around single and multiple tufts of hyaline hairs on the thallus of Fucus vesiculosus. Flow was a major determinant of DBL thickness, where higher flow decreased DBL thickness and increased O2 flux between the algal thallus and the surrounding seawater. However, the topography of the DBL varied and did not directly follow the contour of the underlying thallus. Areas around single tufts of hyaline hairs exhibited a more complex mass-transfer boundary layer, showing both increased and decreased thickness when compared with areas over smooth thallus surfaces. Over thallus areas with several hyaline hair tufts, the overall effect was an apparent increase in the boundary layer thickness. We also found indications for advective O2 transport driven by pressure gradients or vortex shedding downstream from dense tufts of hyaline hairs that could alleviate local mass-transfer resistances. Mass-transfer dynamics around hyaline hair tufts are thus more complex than hitherto assumed and may have important implications for algal physiology and plant–microbe interactions. PMID:28330986

Polypeptide multilayer films on colloidal particles: an in situ electro-optical study.

PubMed

Radeva, Tsetska; Kamburova, Kamelia

2007-04-15

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on beta-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse "in" and "out" of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.

Region of Interest Correction Factors Improve Reliability of Diffusion Imaging Measures Within and Across Scanners and Field Strengths

PubMed Central

Venkatraman, Vijay K; Gonzalez, Christopher E.; Landman, Bennett; Goh, Joshua; Reiter, David A.; An, Yang; Resnick, Susan M.

2017-01-01

Diffusion tensor imaging (DTI) measures are commonly used as imaging markers to investigate individual differences in relation to behavioral and health-related characteristics. However, the ability to detect reliable associations in cross-sectional or longitudinal studies is limited by the reliability of the diffusion measures. Several studies have examined reliability of diffusion measures within (i.e. intra-site) and across (i.e. inter-site) scanners with mixed results. Our study compares the test-retest reliability of diffusion measures within and across scanners and field strengths in cognitively normal older adults with a follow-up interval less than 2.25 years. Intra-class correlation (ICC) and coefficient of variation (CoV) of fractional anisotropy (FA) and mean diffusivity (MD) were evaluated in sixteen white matter and twenty-six gray matter bilateral regions. The ICC for intra-site reliability (0.32 to 0.96 for FA and 0.18 to 0.95 for MD in white matter regions; 0.27 to 0.89 for MD and 0.03 to 0.79 for FA in gray matter regions) and inter-site reliability (0.28 to 0.95 for FA in white matter regions, 0.02 to 0.86 for MD in gray matter regions) with longer follow-up intervals were similar to earlier studies using shorter follow-up intervals. The reliability of across field strengths comparisons was lower than intra- and inter-site reliability. Within and across scanner comparisons showed that diffusion measures were more stable in larger white matter regions (> 1500 mm3). For gray matter regions, the MD measure showed stability in specific regions and was not dependent on region size. Linear correction factor estimated from cross-sectional or longitudinal data improved the reliability across field strengths. Our findings indicate that investigations relating diffusion measures to external variables must consider variable reliability across the distinct regions of interest and that correction factors can be used to improve consistency of measurement across field strengths. An important result of this work is that inter-scanner and field strength effects can be partially mitigated with linear correction factors specific to regions of interest. These data-driven linear correction techniques can be applied in cross-sectional or longitudinal studies. PMID:26146196

Cortical thickness in symptomatic and asymptomatic bipolar offspring.

PubMed

Hanford, Lindsay C; Sassi, Roberto B; Minuzzi, Luciano; Hall, Geoffrey B

2016-05-30

Children of parents diagnosed with bipolar disorder are at greater risk for developing a variety of psychiatric disorders, however, the reasons remain unknown. The present study aimed to investigate gray matter integrity in high-risk bipolar offspring (HRO) and healthy offspring (HCO) using cortical thickness techniques. Here we examined healthy control offspring (HCO; n=20) and HRO with (n=17) or without (n=13) psychiatric symptoms. T1-weighted images were collected from all offspring, and cortical thickness and age-cortical thickness correlations were compared. HRO showed cortical thinning in superior and inferior temporal regions, supramarginal, and caudal and rostral middle frontal regions compared to HCO. When comparing HRO with and without psychiatric symptoms, we found cortical thinning in symptomatic offspring in the superior frontal and somatosensory related cortices. Age-thickness correlations showed a relatively consistent negative relationship in most regions in HCO, while the reverse was true for the HRO. These regions included parahippocampal, lateral orbitofrontal, and inferior temporal regions. Our study provides evidence of cortical thickness reductions among symptomatic and asymptomatic high-risk offspring during youth. Some of these alterations, found in regions of emotion processing and regulation, are evident only when associated with the presence of psychiatric symptoms. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Escape of Resonantly Scattered Lyβ and Hα from Hot and Optically Thick Media

NASA Astrophysics Data System (ADS)

Chang, Seok-Jun; Lee, Hee-Won; Ahn, Sang-Hyeon; Lee, Hogyu; Angeloni, Rodolfo; Palma, Tali; Di Mille, Francesco

2018-02-01

We investigate the escape of Lyβ from emission nebulae with a significant population of excited hydrogen atoms in the level n=2, rendering them optically thick in Hα. The transfer of Lyβ line photons in these optically thick regions is complicated by the presence of another scattering channel leading to re-emission of Hα, alternating their identities between Lyβ and Hα. In this work, we develop a Monte Carlo code to simulate the transfer of Lyβ line photons incorporating the scattering channel into Hα. Both Hα and Lyβ lines are formed through diffusion in frequency space, where a line photon enters the wing regime after a fairly large number of resonance scatterings with hydrogen atoms. Various line profiles of Hα and Lyβ emergent from our model nebulae are presented. It is argued that the electron temperature is a critical parameter which controls the flux ratio of emergent Lyβ and Hα. Specifically for T=3 × 10^4{K} and Hα line center optical depth τ_α=10, the number flux ratio of emergent Lyβ and Hα is ˜ 49 percent, which is quite significant. We propose that the leaking Lyβ can be an interesting source for the formation of Hα wings observed in many symbiotic stars and active galactic nuclei. Similar broad Hα wings are also expected in Lyα emitting halos found in the early universe, which can be potentially probed by the James Webb Telescope in the future.

Scaling oxygen microprofiles at the sediment interface of deep stratified waters

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Cubic zirconia as a species permeable coating for zinc diffusion in gallium arsenide

NASA Astrophysics Data System (ADS)

Bisberg, J. E.; Dabkowski, F. P.; Chin, A. K.

1988-10-01

Diffusion of zinc into GaAs through an yttria-stabilized cubic zirconia (YSZ) passivation layer has been demonstrated with an open-tube diffusion method. Pure zinc or GaAs/Zn2As3 sources produced high quality planar p-n junctions. The YSZ layer protects the GaAs surface from excessive loss of arsenic, yet is permeable to zinc, allowing its diffusion into the semiconductor. The YSZ films, deposited by electron beam evaporation, were typically 2000 Å thick. Zinc diffusion coefficients (DT) at 650 °C in the YSZ passivated GaAs ranged from 3.6×10-10 cm2/min for the GaAs/Zn2As3 source to 1.9×10-9 cm2/min for the pure zinc source. Doping concentrations for both YSZ passivated and uncapped samples were approximately 5×1019 cm-3.

Rapid fabrication of surface-relief plastic diffusers by ultrasonic embossing

NASA Astrophysics Data System (ADS)

Liu, Shih-Jung; Huang, Yu-Chin; Yang, Sen-Yeu; Hsieh, Kuo-Huang

2010-07-01

This paper discusses an innovative and effective ultrasonic embossing process, which enables the rapid fabrication of surface-relief plastic diffusers. The metallic mold bearing the microstructures is fabricated using a tungsten carbide turning machine. A 1500-W ultrasonic vibrator with an output frequency of 20 kHz was used to replicate the microstructure onto 1-mm-thick PMMA plates in the experiments. During ultrasonic embossing, the ultrasonic energy is converted into heat through intermolecular friction at the master mold/plastic plate interface due to asperities to melt the thermoplastic at the interface and thereby to replicate the microstructure. Under the proper processing conditions, high-performance plastic diffusers have been successfully fabricated. The cycle time required to successfully fabricate a diffuser is less than 2 s. The experimental results suggest that ultrasonic embossing could provide an effective way of fabricating high-performance plastic diffusers with a high throughput.

Diffusion Bonding of Silicon Carbide for MEMS-LDI Applications

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, J. Douglas

2007-01-01

A robust joining approach is critically needed for a Micro-Electro-Mechanical Systems-Lean Direct Injector (MEMS-LDI) application which requires leak free joints with high temperature mechanical capability. Diffusion bonding is well suited for the MEMS-LDI application. Diffusion bonds were fabricated using titanium interlayers between silicon carbide substrates during hot pressing. The interlayers consisted of either alloyed titanium foil or physically vapor deposited (PVD) titanium coatings. Microscopy shows that well adhered, crack free diffusion bonds are formed under optimal conditions. Under less than optimal conditions, microcracks are present in the bond layer due to the formation of intermetallic phases. Electron microprobe analysis was used to identify the reaction formed phases in the diffusion bond. Various compatibility issues among the phases in the interlayer and substrate are discussed. Also, the effects of temperature, pressure, time, silicon carbide substrate type, and type of titanium interlayer and thickness on the microstructure and composition of joints are discussed.

Porosity Measurement in Laminated Composites by Thermography and FEA

NASA Technical Reports Server (NTRS)

Chu, Tsuchin Philip; Russell, Samuel S.; Walker, James L.; Munafo, Paul M. (Technical Monitor)

2001-01-01

This paper presents the correlation between the through-thickness thermal diffusivity and the porosity of composites. Finite element analysis (FEA) was used to determine the transient thermal response of composites that were subjected to laser heating. A series of finite element models were built and thermal responses for isotropic and orthographic materials with various thermal diffusivities subjected to different heating conditions were investigated. Experiments were conducted to verify the models and to estimate the unknown parameters such as the amount of heat flux. The analysis and experimental results show good correlation between thermal diffusivity and porosity in the composite materials. They also show that both laser and flash heating can be used effectively to obtain thermal diffusivity. The current infrared thermography system is developed for use with flash heating. The laser heating models and the FEA results can provide useful tools to develop practical thermal diffusivity measurement scheme using laser heat.

Advanced Ceramic Matrix Composites with Multifunctional and Hybrid Structures

NASA Technical Reports Server (NTRS)

Singh, Mrityunjay; Morscher, Gregory N.

2004-01-01

Ceramic matrix composites are leading candidate materials for a number of applications in aeronautics, space, energy, and nuclear industries. Potential composite applications differ in their requirements for thickness. For example, many space applications such as "nozzle ramps" or "heat exchangers" require very thin (< 1 mm) structures whereas turbine blades would require very thick parts (> or = 1 cm). Little is known about the effect of thickness on stress-strain behavior or the elevated temperature tensile properties controlled by oxidation diffusion. In this study, composites consisting of woven Hi-Nicalon (trademark) fibers a carbon interphase and CVI SiC matrix were fabricated with different numbers of plies and thicknesses. The effect of thickness on matrix crack formation, matrix crack growth and diffusion kinetics will be discussed. In another approach, hybrid fiber-lay up concepts have been utilized to "alloy" desirable properties of different fiber types for mechanical properties, thermal stress management, and oxidation resistance. Such an approach has potential for the C(sub I)-SiC and SiC(sub f)-SiC composite systems. CVI SiC matrix composites with different stacking sequences of woven C fiber (T300) layers and woven SiC fiber (Hi-Nicalon (trademark)) layers were fabricated. The results will be compared to standard C fiber reinforced CVI SiC matrix and Hi-Nicalon reinforced CVI SiC matrix composites. In addition, shear properties of these composites at different temperatures will also be presented. Other design and implementation issues will be discussed along with advantages and benefits of using these materials for various components in high temperature applications.

Morphology, topography, and hardness of diffusion bonded sialon to AISI 420 at different bonding time

NASA Astrophysics Data System (ADS)

Ibrahim, Nor Nurulhuda Md.; Hussain, Patthi; Awang, Mokhtar

2015-07-01

Sialon and AISI 420 martensitic stainless steel were diffusion bonded in order to study the effect of bonding time on reaction layer's growth. Joining of these materials was conducted at 1200°C under a uniaxial pressure of 17 MPa in a vacuum ranging from 5.0 to 8.0×10-6 Torr with bonding time varied for 0.5, 2, and 3 h. Thicker reaction layer was formed in longer bonded sample since the elements from sialon could diffuse further into the steel. Sialon retained its microstructure but it was affected at the initial contact with the steel to form the new interface layer. Diffusion layer grew toward the steel and it was segregated with the parent steel as a result of the difference in properties between these regions. The segregation formed a stream-like structure and its depth decreased when the bonding time was increased. The microstructure of the steel transformed into large grain size with precipitates. Prolonging the bonding time produced more precipitates in the steel and reduced the steel thickness as well. Interdiffusions of elements occurred between the joined materials and the concentrations were decreasing toward the steel and vice versa. Silicon easily diffused into the steel because it possessed lower ionization potential compared to nitrogen. Formation of silicide and other compounds such as carbides were detected in the interface layer and steel grain boundary, respectively. These compounds were harmful due to silicide brittleness and precipitation of carbides in the grain boundary might cause intergranular corrosion cracking. Sialon retained its hardness but it dropped very low at the interface layer. The absence of crack at the joint in all samples could be contributed from the ductility characteristic of the reaction layer which compensated the residual stress that was formed upon the cooling process.

ON THE ORIGINS OF THE DIFFUSE H{alpha} EMISSION: IONIZED GAS OR DUST-SCATTERED H{alpha} HALOS?

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

Seon, Kwang-Il; Witt, Adolf N., E-mail: kiseon@kasi.re.kr

2012-10-20

It is known that the diffuse H{alpha} emission outside of bright H II regions not only are very extended, but also can occur in distinct patches or filaments far from H II regions, and the line ratios of [S II] {lambda}6716/H{alpha} and [N II] {lambda}6583/H{alpha} observed far from bright H II regions are generally higher than those in the H II regions. These observations have been regarded as evidence against the dust-scattering origin of the diffuse H{alpha} emission (including other optical lines), and the effect of dust scattering has been neglected in studies on the diffuse H{alpha} emission. In thismore » paper, we reexamine the arguments against dust scattering and find that the dust-scattering origin of the diffuse H{alpha} emission cannot be ruled out. As opposed to the previous contention, the expected dust-scattered H{alpha} halos surrounding H II regions are, in fact, in good agreement with the observed H{alpha} morphology. We calculate an extensive set of photoionization models by varying elemental abundances, ionizing stellar types, and clumpiness of the interstellar medium (ISM) and find that the observed line ratios of [S II]/H{alpha}, [N II]/H{alpha}, and He I {lambda}5876/H{alpha} in the diffuse ISM accord well with the dust-scattered halos around H II regions, which are photoionized by late O- and/or early B-type stars. We also demonstrate that the H{alpha} absorption feature in the underlying continuum from the dust-scattered starlight ({sup d}iffuse galactic light{sup )} and unresolved stars is able to substantially increase the [S II]/H{alpha} and [N II]/H{alpha} line ratios in the diffuse ISM.« less

The layer boundary effect on multi-layer mesoporous TiO 2 film based dye sensitized solar cells

DOE PAGES

Xu, Feng; Zhu, Kai; Zhao, Yixin

2016-10-10

Multi-layer mesoporous TiO 2 prepared by screen printing is widely used for fabrication of high-efficiency dye-sensitized solar cells (DSSCs). Here, we compare the three types of ~10 um thick mesoporous TiO 2 films, which were screen printed as 1-, 2- and 4-layers using the same TiO 2 nanocrystal paste. The layer boundary of the multi-layer mesoporous TiO 2 films was observed in the cross-section SEM. The existence of a layer boundary could reduce the photoelectron diffusion length with the increase of layer number. However, the photoelectron diffusion lengths of the Z907 dye sensitized solar cells based on these different layeredmore » mesoporous TiO 2 films are all longer than the film thickness. Consequently, the photovoltaic performance seems to have little dependence on the layer number of the multi-layer TiO 2 based DSSCs.« less

Probing molecular orientation of P3HT nanofibers in fiber-based organic solar cells

NASA Astrophysics Data System (ADS)

Yoon, Sangcheol; Han, Yaeeun; Hwang, Inchan

2018-01-01

Molecular orientation of conjugated polymers plays a key role in exciton generation/separation and charge transport, and thus significantly influence photovoltaic devices. Herein, we fabricated fiber-based organic solar cells and investigated the photovoltaic parameters with different diameters of fibers and PCBM diffusion. The open-circuit voltage that varies with molecular orientation whether it is face-on or edge-on was observed to differ. The investigation of the open-circuit voltage dependence reveals that thick fibers have core/shell like structures with different orientations. Thick fibers have face-on in the core and edge-on orientations in the shell. The face-on orientations are not preferentially formed in thin fibers, but the PCBM diffusion can induce face-on orientations that exist within the intermixed phase. Our results may shed a light on better understanding on fiber-based solar cells and suggest a way toward improving photovoltaic efficiency. [Figure not available: see fulltext.

Interdiffusion behavior between NiAlHf coating and Ni-based single crystal superalloy with different crystal orientations

NASA Astrophysics Data System (ADS)

Wang, Ruili; Gong, Xueyuan; Peng, Hui; Ma, Yue; Guo, Hongbo

2015-01-01

NiAlHf coatings were deposited onto Ni-based single crystal (SC) superalloy with different crystal orientations by electron beam physical vapor deposition (EB-PVD). The effects of the crystal orientations of the superalloy substrate on inter-diffusion behavior between the substrate and the NiAlHf coating were investigated. Substrate diffusion zone (SDZ) containing needle-like μ phases and interdiffusion zone (IDZ) mainly consisting of the ellipsoidal and rod-like μ phases were formed in the SC alloy after heat-treatment 10 h at 1100 °C. The thickness of secondary reaction zone (SRZ) formed in the SC alloy with (0 1 1) crystal orientation is about 14 μm after 50 h heat-treatment at 1100 °C, which is relatively thicker than that in the SC alloy with (0 0 1) crystal orientation, whereas the IDZ revealed similar thickness.

The layer boundary effect on multi-layer mesoporous TiO 2 film based dye sensitized solar cells

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

Xu, Feng; Zhu, Kai; Zhao, Yixin

Multi-layer mesoporous TiO 2 prepared by screen printing is widely used for fabrication of high-efficiency dye-sensitized solar cells (DSSCs). Here, we compare the three types of ~10 um thick mesoporous TiO 2 films, which were screen printed as 1-, 2- and 4-layers using the same TiO 2 nanocrystal paste. The layer boundary of the multi-layer mesoporous TiO 2 films was observed in the cross-section SEM. The existence of a layer boundary could reduce the photoelectron diffusion length with the increase of layer number. However, the photoelectron diffusion lengths of the Z907 dye sensitized solar cells based on these different layeredmore » mesoporous TiO 2 films are all longer than the film thickness. Consequently, the photovoltaic performance seems to have little dependence on the layer number of the multi-layer TiO 2 based DSSCs.« less

Magnetic resonance imaging of mass transport and structure inside a phototrophic biofilm.

PubMed

Ramanan, Baheerathan; Holmes, William M; Sloan, William T; Phoenix, Vernon R

2013-05-01

The aim of this study was to utilize magnetic resonance imaging (MRI) to image structural heterogeneity and mass transport inside a biofilm which was too thick for photon based imaging. MRI was used to map water diffusion and image the transport of the paramagnetically tagged macromolecule, Gd-DTPA, inside a 2.5 mm thick cyanobacterial biofilm. The structural heterogeneity of the biofilm was imaged at resolutions down to 22 × 22 μm, enabling the impact of biofilm architecture on the mass transport of both water and Gd-DTPA to be investigated. Higher density areas of the biofilm correlated with areas exhibiting lower relative water diffusion coefficients and slower transport of Gd-DTPA, highlighting the impact of biofilm structure on mass transport phenomena. This approach has potential for shedding light on heterogeneous mass transport of a range of molecular mass molecules in biofilms.

Thickness-dependent metal-to-insulator transition in epitaxial VO2 films

NASA Astrophysics Data System (ADS)

Zhi, Bowen; Gao, Guanyin; Tan, Xuelian; Chen, Pingfan; Wang, Lingfei; Jin, Shaowei; Wu, Wenbin

2014-12-01

The metal-to-insulator transition (MIT) of VO2 films with a thickness of 3-100 nm on TiO2(001) substrates has been investigated. When varying the film thickness from 10 to 100 nm, the MIT temperature was first kept at 290 K in the range of 10-14 nm, and then increased with thickness increasing due to the strain relaxation. The origin of the suppressed transition in VO2 films thinner than 6 nm was also investigated. When prolonging the in situ annealing time, the sharpness, amplitude and width of the transition for 4 nm thick films were all increased, suggesting improved crystallinity rather than Ti diffusion from the substrates. In addition, the MIT was suppressed when the VO2 films were covered by a TiO2 layer, indicating that the interface effect via the confinement of the dimerization of the V atoms should be the main reason.

What is the copper thin film thickness effect on thermal properties of NiTi/Cu bi-layer?

NASA Astrophysics Data System (ADS)

Fazeli, Sara; Vahedpour, Morteza; Khatiboleslam Sadrnezhaad, Sayed

2017-02-01

Molecular dynamics (MD) simulation was used to study of thermal properties of NiTi/Cu. Embedded atom method (EAM) potentials for describing of inter-atomic interaction and Nose-Hoover thermostat and barostat are employed. The melting of the bi-layers was considered by studying the temperature dependence of the cohesive energy and mean square displacement. To highlight the differences between bi-layers with various copper layer thickness, the effect of copper film thickness on thermal properties containing the cohesive energy, melting point, isobaric heat capacity and latent heat of fusion was estimated. The results show that thermal properties of bi-layer systems are higher than that of their corresponding of pure NiTi. But, these properties of bi-layer systems approximately are independent of copper film thicknesses. The mean square displacement (MSD) results show that, the diffusion coefficients enhance upon increasing of copper film thickness in a linear performance.

Spectral ellipsometry as a method for characterization of nanosized films with ferromagnetic layers

NASA Astrophysics Data System (ADS)

Hashim, H.; Singkh, S. P.; Panina, L. V.; Pudonin, F. A.; Sherstnev, I. A.; Podgornaya, S. V.; Shpetnyi, I. A.; Beklemisheva, A. V.

2017-11-01

Nanosized films with ferromagnetic layers are widely used in nanoelectronics, sensor systems and telecommunications. Their properties may strongly differ from those of bulk materials that is on account of interfaces, intermediate layers and diffusion. In the present work, spectral ellipsometry and magnetooptical methods are adapted for characterization of the optical parameters and magnetization processes in two- and three-layer Cr/NiFe, Al/NiFe and Cr(Al)/Ge/NiFe films onto a sitall substrate for various thicknesses of Cr and Al layers. At a layer thickness below 20 nm, the complex refractive coefficients depend pronouncedly on the thickness. In two-layer films, remagnetization changes weakly over a thickness of the top layer, but the coercive force in three-layer films increases by more than twice upon remagnetization, while increasing the top layer thickness from 4 to 20 nm.

Investigation on uric acid biosensor model for enzyme layer thickness for the application of arthritis disease diagnosis.

PubMed

Parthasarathy, P; Vivekanandan, S

2018-12-01

Uric acid biosensors for arthritis disease has been developed for the specific selection of uricase enzyme film thickness coated over the TiO 2 -CeO 2 nano-composite matrix is modelled mathematically. This model is purely based on R-diffusion conditions with irreversible first-order catalytic reactions. By arithmetical method, the impact of the thickness of enzyme layer on the current response of the biosensor was explored. This article displays a structure for choice of the enzyme layer thickness, guaranteeing the adequately stable sensitivity of a biosensor in a required extent of the maximal enzymatic rate. The numerical outcomes showed subjective and sensible quantitative information for oxidation current due to uric acid also shows the maximum change in the biosensor current response due to the change in membrane thickness, which will be more suitable for uric acid biosensor for the application of arthritis disease diagnosis.

Study of Diffusion Bonding of 45 Steel through the Compacted Nickel Powder Layer

NASA Astrophysics Data System (ADS)

Zeer, G. M.; Zelenkova, E. G.; Temnykh, V. I.; Tokmin, A. M.; Shubin, A. A.; Koroleva, Yu. P.; Mikheev, A. A.

2018-02-01

The microstructure of the transition zone and powder spacer, the concentration distribution of chemical elements over the width of the diffusion-bonded joint, and microhardness of 45 steel-compacted Ni powder spacer-45 steel layered composites formed by diffusion bonding have been investigated. It has been shown that the relative spacer thickness χ < 0.06 is optimal for obtaining a high-quality joint has been formed under a compacting pressure of 500 MPa. The solid-state diffusion bonding is accompanied by sintering the nickel powder spacer and the formation of the transition zone between the spacer and steel. The transition zone consists of solid solution of nickel in the α-Fe phase and ordered solid solution of iron in nickel (FeNi3).

Neutron Reflectivity Measurement for Polymer Dynamics near Graphene Oxide Monolayers

NASA Astrophysics Data System (ADS)

Koo, Jaseung

We investigated the diffusion dynamics of polymer chains confined between graphene oxide layers using neutron reflectivity (NR). The bilayers of polymethylmetacrylate (PMMA)/ deuterated PMMA (d-PMMA) films and polystyrene (PS)/d-PS films with various film thickness sandwiched between Langmuir-Blodgett (LB) monolayers of graphene oxide (GO) were prepared. From the NR results, we found that PMMA diffusion dynamics was reduced near the GO surface while the PS diffusion was not significantly changed. This is due to the different strength of GO-polymer interaction. In this talk, these diffusion results will be compared with dewetting dynamics of polymer thin films on the GO monolayers. This has given us the basis for development of graphene-based nanoelectronics with high efficiency, such as heterojunction devices for polymer photovoltaic (OPV) applications.

A Computational Investigation of Sooting Limits of Spherical Diffusion Flames

NASA Technical Reports Server (NTRS)

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

2007-01-01

Limiting conditions for soot particle inception in spherical diffusion flames were investigated numerically. The flames were modeled using a one-dimensional, time accurate diffusion flame code with detailed chemistry and transport and an optically thick radiation model. Seventeen normal and inverse flames were considered, covering a wide range of stoichiometric mixture fraction, adiabatic flame temperature, and residence time. These flames were previously observed to reach their sooting limits after 2 s of microgravity. Sooting-limit diffusion flames with residence times longer than 200 ms were found to have temperatures near 1190 K where C/O = 0.6, whereas flames with shorter residence times required increased temperatures. Acetylene was found to be a reasonable surrogate for soot precursor species in these flames, having peak mole fractions of about 0.01.

Effects of C/O Ratio and Temperature on Sooting Limits of Spherical Diffusion Flames

NASA Technical Reports Server (NTRS)

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

2008-01-01

Limiting conditions for soot particle inception in spherical diffusion flames were investigated numerically. The flames were modeled using a one-dimensional, time accurate diffusion flame code with detailed chemistry and transport and an optically thick radiation model. Seventeen normal and inverse flames were considered, covering a wide range of stoichiometric mixture fraction, adiabatic flame temperature, residence time and scalar dissipation rate. These flames were previously observed to reach their sooting limits after 2 s of microgravity. Sooting-limit diffusion flames with scalar dissipation rate lower than 2/s were found to have temperatures near 1400 K where C/O = 0.51, whereas flames with greater scalar dissipation rate required increased temperatures. This finding was valid across a broad range of fuel and oxidizer compositions and convection directions.