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Sample records for 6h-sic homoepitaxial layers

  1. Extended defects in 4H-silicon carbide homoepitaxial layers

    NASA Astrophysics Data System (ADS)

    Zhang, Xuan

    The purpose of this thesis is to study the structure of extended defects in 4H-SIC homoepitaxial layers, and to identify their nucleation mechanisms. Characteristics of basal plane dislocations in 4H-SiC epilayers were investigated in a comprehensive manner, including their morphologies, Burgers' vectors, positions, and correlation with the extended defects propagating from the substrate. Plan-view transmission x-ray topography was the major characterization technique used in this study. Complementary data was obtained by KOH etching and optical microscopy. Trace of glide was detected on every basal plane dislocation in the entire 3-inch epilayer. In the center area of the epi-wafer, the glide can extend to macroscopic distance and form edge-type dislocations at the epilayer/surface interface. During the motion, dislocation half loop arrays were found to nucleate at the growth front. The magnitude of the resolved shear stress was estimated based on the radius of curvature of the dislocation lines. It surpassed the critical resolved shear stress at the epitaxial growth temperature. The stress was identified to be compressive in the epilayer. Its origin was studied. Nitrogen-doping-difference-induced misfit strain was excluded as the source of the stress. The structures of two morphological defects, 'carrots' and 'arrows', were studied. Cross-section x-ray topography was used to image the structure of carrot defect in whole. The defect was found to nucleate at the epilayer/substrate interface on a threading screw dislocation propagating from the substrate. Its structure was mainly composed of a prismatic stacking fault and a Frank-type basal plane stacking fault. The arrow defect was found to be produced by a spheroid shape inclusion in the volume of the epilayer. Zone axis diffraction pattern under transmission electron microscope identified the nature of the inclusion as 3C-SIC. It was determined to nucleate at the substrate surface contaminations.

  2. Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

    NASA Astrophysics Data System (ADS)

    Choudhary, B. S.; Singh, A.; Tanwar, S.; Tyagi, P. K.; Kumar, M. Senthil; Kushvaha, S. S.

    2016-04-01

    We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surface with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.

  3. Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

    DOE PAGES

    Zhang, Lihua; Su, Dong; Kisslinger, Kim; Stach, Eric; Chung, Gil; Zhang, Jie; Thomas, Bernd; Sanchez, Edward K; Mueller, Stephan G.; Hansen, Darren; et al

    2014-12-04

    Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted regionmore » with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.« less

  4. Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

    SciTech Connect

    Zhang, Lihua; Su, Dong; Kisslinger, Kim; Stach, Eric; Chung, Gil; Zhang, Jie; Thomas, Bernd; Sanchez, Edward K; Mueller, Stephan G.; Hansen, Darren; Loboda, Mark J.; Wu, Fangzhen; Wang, Huanhuan; Raghothamachar, Balaji; Dudley, Michael

    2014-12-04

    Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted region with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.

  5. DEFECT SELECTIVE ETCHING OF THICK ALN LAYERS GROWN ON 6H-SIC SEEDS - A TRANSMISSION ELECTRON MICROSCOPY STUDY

    SciTech Connect

    Nyakiti, Luke; Chaudhari, Jharna; Kenik, Edward A; Lu, Peng; Edgar, J H

    2008-01-01

    In the present study, the type and densities of defects in AlN crystals grown on 6H-SiC seeds by the sublimation-recombination method were assessed. The positions of the defects in AlN were first identified by defect selective etching (DSE) in molten NaOH-KOH at 400 C for 2 minutes. Etching produced pits of three different sizes: 1.77 m, 2.35 m , and 2.86 m. The etch pits were either aligned together forming a sub-grain boundary or randomly distributed. The smaller etch pits were either isolated or associated with larger etch pits. After preparing crosssections of the pits by the focused ion beam (FIB) technique, transmission electron microscopy (TEM) was performed to determine which dislocation type (edge, mixed or screw) produced a specific etch pit sizes. Preliminary TEM bright field and dark field study using different zone axes and diffraction vectors indicates an edge dislocation with a Burgers vector 1/3[1120] is associated with the smallest etch pit size.

  6. Low-temperature photoluminescence of 8H-SiC homoepitaxial layer

    NASA Astrophysics Data System (ADS)

    Hatayama, Tomoaki; Henry, Anne; Yano, Hiroshi; Fuyuki, Takashi

    2016-02-01

    Low-temperature photoluminescence of a nitrogen-doped 8H-SiC epilayer homoepitaxially grown by a chemical vapor deposition method is reported. The polytype and stacking sequence of the epilayers were confirmed by transmission electron microscopy analyses. The identification of emission lines is discussed in terms of the temperature dependence of the luminescence spectra. Luminescence related to the free excitons and the nitrogen-bound excitons is observed, which allows the determination of the excitonic bandgap of the 8H-SiC polytype. In addition, the low binding energies found for the nitrogen-bound excitons imply shallow levels for the nitrogen donors.

  7. TOPICAL REVIEW: Properties of the state of the art of bulk III-V nitride substrates and homoepitaxial layers

    NASA Astrophysics Data System (ADS)

    Freitas, Jaime A., Jr.

    2010-02-01

    The technological importance of III-V nitride semiconductors relies on their variety of applications, which cover optical, optoelectronic and electronic devices capable of operating under extreme values of current, voltage and temperature. The major roadblock for full realization of the potential of nitride semiconductors is still the availability of affordable large-area and high-quality native substrates with controlled electrical properties. Despite the impressive accomplishments recently achieved by techniques such as hydride vapour phase epitaxy and ammonothermal for GaN and sublimation for AlN, much more must be attained before establishing a bulk growth technique of choice to grow these materials. A brief review of the structural, optical and electronic properties of the state of the art of bulk and thick-film (quasi-bulk) nitride substrates and homoepitaxial films is presented, and a few device applications are also highlighted.

  8. Properties of YBCO on LaMnO3-capped IBAD MgO-templates without Homo-epitaxial MgO layer.

    SciTech Connect

    Aytug, Tolga; Paranthaman, Mariappan Parans; Kim, Kyunghoon; Zhang, Yifei; Cantoni, Claudia; Zuev, Yuri L; Goyal, Amit; Thompson, James R; Christen, David K

    2009-01-01

    Previously, it has been well established that in an IBAD architecture for coated conductors, (1) LaMnO3 (LMO) buffer layers are structurally and chemically compatible with an underlying homo-epitaxial MgO layer and (2) high current density YBCO films can be grown on these LMO templates. In the present work, the homo-epi MgO layer has been successfully eliminated and a LMO cap layer was grown directly on the IBAD (MgO) template. The performance of the LMO/IBAD (MgO) samples has been qualified by depositing 1 m-thick YBCO coatings by pulsed laser deposition. Electrical transport measurements of YBCO films on the standard (with homo-epi MgO) and simplified (without homo-epi MgO) IBAD architectures were carried out. The angular dependencies of critical current density (Jc) are similar for both IBAD architectures. XRD measurements indicate good, c-axis aligned YBCO films. Transmission electron microscopy (TEM) images reveal that microstructures of YBCO/LMO/IBAD (MgO) and YBCO/LMO/homo-epi MgO/IBAD (MgO) templates are similar. These results demonstrate the strong potential of using LMO as a single cap layer directly on IBAD (MgO) for the development of a simplified IBAD architecture.

  9. Homoepitaxial graphene tunnel barriers for spin transport (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Friedman, Adam L.

    2015-09-01

    Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions (magnetic field, temperature, etc.) usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. Here, we demonstrate homoepitaxial tunnel barrier devices in which graphene serves as both the tunnel barrier and the high mobility transport channel. Beginning with multilayer graphene, we fluorinate or hydrogenate the top layer to decouple it from the bottom layer, so that it serves as a single monolayer tunnel barrier for both charge and spin injection into the lower graphene transport channel. We demonstrate successful tunneling by measuring non-linear IV curves, and a weakly temperature dependent zero bias resistance. We perform lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the non-local Hanle effect to be commensurate with previous studies (~200 ps). However, we also demonstrate the highest spin polarization efficiencies (~45%) yet measured in graphene-based spin devices [1]. [1] A.L. Friedman, et al., Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport, Nat. Comm. 5, 3161 (2014).

  10. The effect of surface treatment on the electrical properties of metal contacts to boron-doped homoepitaxial diamond film

    SciTech Connect

    Grot, S.A.; Gildenblat, G.S.; Hatfield, C.W.; Wronski, C.R. . Dept. of Electrical Engineering); Badzian, A.R.; Badzian, T.; Messier, R. . Materials Research Lab.)

    1990-02-01

    Both doped and undoped homoepitaxial diamond films were fabricated using microwave plasma-enhanced chemical vapor deposition (CVD). The conductivity of the diamond film is strongly affected by the surface treatment. In particular, exposure of film surface to a hydrogen plasma results in the formation of a conductive layer which can be used to obtain linear (ohmic) {ital I-V} characteristics of the Au/diamond contacts, regardless of the doping level. The proper chemical cleaning of the boron-doped homoepitaxial diamond surface allows the fabrication of Au-gate Schottky diodes with excellent rectifying characteristics at temperatures of at least 400{degrees}C.

  11. Optical functions of silicon from reflectance and ellipsometry on silicon-on-insulator and homoepitaxial samples

    SciTech Connect

    Humlíček, J.

    2015-11-21

    The optical properties of silicon have been determined from 0.2 to 6.5 eV at room temperature, using reflectance spectra of silicon-on-insulator (SOI) and ellipsometric spectra of homoepitaxial samples. Optimized Fabry-Perot-type SOI resonators exhibit high finesse even in near ultraviolet. Very high precision values of the real part of the refractive index are obtained in infrared up to a photon energy of 1.3 eV. The spectra of the extinction coefficient, based on observations of light attenuation, extend to 3.2 eV due to measurements on SOI layers as thin as 87 nm. These results allowed us to correct spectroellipsometric data on homoepitaxial samples for the presence of reduced and stabilized surface layers.

  12. Homoepitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C-H; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; McCarty, P.; George, M. A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    ZnO films have high potential for many applications, such as surface acoustic wave filters, UV detectors, and light emitting devices due to its structural, electrical, and optical properties. High quality epitaxial films are required for these applications. The Al2O3 substrate is commonly used for ZnO heteroepitaxial growth. Recently, high quality ZnO single crystals are available for grow homoepitaxial films. Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films were also deposited on (0001) Al2O3 substrates. It was found that the two polar ZnO surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which strongly influence the epitaxial film growth. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  13. Lattice parameters of AlN bulk, homoepitaxial and heteroepitaxial material

    NASA Astrophysics Data System (ADS)

    Nilsson, D.; Janzén, E.; Kakanakova-Georgieva, A.

    2016-05-01

    Homoepitaxial layers of AlN and heteroepitaxial layers of AlN on 4H-SiC substrates were grown by metalorganic chemical vapor deposition at high temperatures up to 1400 °C, and with various thicknesses. From high resolution x-ray diffraction measurements of a set of homoepitaxial layers of high structural quality, the following mean value of the lattice constants was determined: a  =  3.111 31  ±  0.000 16 Å, and c  =  4.980 79  ±  0.000 11 Å. The structural quality of the heteroepitaxial layers was demonstrated, for example, by extracting the full width at a half maximum of the (0002) and (10-12) rocking curves of 25 arcsec and 372 arcsec, respectively, associated with a crack-free heteroepitaxial layer with a thickness of 1.3 μm grown at 1240 °C. From measuring a set of AlN heteroepitaxial layers, the following value of the biaxial strain relaxation coefficient was determined: R B  =  -0.556.

  14. InAs homoepitaxy and InAs/AlSb/GaSb resonant interband tunneling diodes on InAs substrate

    NASA Astrophysics Data System (ADS)

    Xiang, Wei; Wang, Guowei; Hao, Hongyue; Liao, Yongping; Han, Xi; Zhang, Lichun; Xu, Yingqiang; Ren, Zhengwei; Ni, Haiqiao; He, Zhenhong; Niu, Zhichuan

    2016-06-01

    In this paper, the optimal conditions for growth of homoepitaxial InAs layer on InAs (001) substrate by molecular beam epitaxy were investigated over wide growth temperatures and As/In flux ratios. The oxide remove process is important and both the As/In flux ratio and growth temperature is in narrow range for InAs homoepitaxy. The high quality homoepitaxy has an RMS surface roughness of 0.26 nm measured by atomic force microscopy. High quality lattice matched InAs/AlSb/GaSb/InAs/AlSb/InAs double barrier resonant interband tunneling diodes was grown on InAs (001) substrate on the optimal condition. It shows high peak-valley current ratios of 105 at 77 K and 15 at room temperature.

  15. Homoepitaxial growth of gallium nitride and aluminum nitride and its effects on device properties

    NASA Astrophysics Data System (ADS)

    Grandusky, James R.

    Lattice and thermal mismatch between epitaxial layers and substrates have long been the major challenge in obtaining high quality devices in the III-Nitride material system due to the lack of availability of native substrates. Recently methods for obtaining high quality free standing native substrates have been achieved and these products are beginning to enter the commercial market. However the quality of these substrates is significantly lower than those in traditional substrates such as Si and GaAs and the high cost and low availability makes it difficult to study the homoepitaxial growth. In order to use these substrates for epitaxial growth, one first must understand what features are needed for the substrates to be epi ready. In addition, one must understand what features in the substrates impact optoelectronic device performances most significantly. Initial homoepitaxial growth was carried out on both AIN and GaN substrates. On AIN substrates it was found that annealing the sample prior to growth was very important to obtain improved surface morphologies for the homoepitaxial layers. Similar annealing steps were attempted on GaN substrates, however annealing under hydrogen left large Ga droplets on the surface. For homoepitaxy on HVPE GaN substrates, the substrate characteristics, such as bowing, surface morphology, structural properties, and optical properties were found to have a large influence on growth and device performance. Even with a reduced dislocation density, substrates with poor characteristics performed worse than devices on GaN/sapphire. The effect of polishing process on the substrates was found to be very important and substrates with subsurface damage led to poor growth, even though the starting surface was very smooth. Optimization of a thin GaN layer and a multiple quantum well structure revealed very different optimum growth conditions for the HVPE substrates and the GaN/sapphire templates. Theoretical modeling using density functional

  16. Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport.

    PubMed

    Friedman, Adam L; van 't Erve, Olaf M J; Li, Connie H; Robinson, Jeremy T; Jonker, Berend T

    2014-01-01

    The coupled imperatives for reduced heat dissipation and power consumption in high-density electronics have rekindled interest in devices based on tunnelling. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, layer uniformity, interface stability and electronic states that severely complicate fabrication and compromise performance. Two-dimensional materials such as graphene obviate these issues and offer a new paradigm for tunnel barriers. Here we demonstrate a homoepitaxial tunnel barrier structure in which graphene serves as both the tunnel barrier and the high-mobility transport channel. We fluorinate the top layer of a graphene bilayer to decouple it from the bottom layer, so that it serves as a single-monolayer tunnel barrier for both charge and spin injection into the lower graphene channel. We demonstrate high spin injection efficiency with a tunnelling spin polarization >60%, lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the Hanle effect.

  17. Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport.

    PubMed

    Friedman, Adam L; van 't Erve, Olaf M J; Li, Connie H; Robinson, Jeremy T; Jonker, Berend T

    2014-01-01

    The coupled imperatives for reduced heat dissipation and power consumption in high-density electronics have rekindled interest in devices based on tunnelling. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, layer uniformity, interface stability and electronic states that severely complicate fabrication and compromise performance. Two-dimensional materials such as graphene obviate these issues and offer a new paradigm for tunnel barriers. Here we demonstrate a homoepitaxial tunnel barrier structure in which graphene serves as both the tunnel barrier and the high-mobility transport channel. We fluorinate the top layer of a graphene bilayer to decouple it from the bottom layer, so that it serves as a single-monolayer tunnel barrier for both charge and spin injection into the lower graphene channel. We demonstrate high spin injection efficiency with a tunnelling spin polarization >60%, lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the Hanle effect. PMID:24445349

  18. HVPE homoepitaxial growth of high quality bulk GaN using acid wet etching method and its mechanism analysis

    NASA Astrophysics Data System (ADS)

    Liu, Nanliu; Cheng, Yutian; Wu, Jiejun; Li, Xingbin; Yu, Tongjun; Xiong, Huan; Li, Wenhui; Chen, Jiao; Zhang, Guoyi

    2016-11-01

    In this paper, crack-free 2-inch bulk GaN wafer with the thickness up to 3 mm was obtained by HVPE homoepitaxy. A new method of acid wet etching was used to pre-treat GaN substrate before re-growth. The formation of the mesh-like subsurface crack and interface layer were found to be suppressed between the re-growth layer and as-grown GaN substrate. EDS and time varied contact angle measurement proved that chemical etching would decrease the oxygen related surface adsorption and increase atoms diffusion length during HVPE homoepitaxial growth. Moreover, Morphology, Low temperature photoluminescence measurements indicated a reduction in stress of wet etching treated as-grown GaN substrate due to etching effect on its N face. High quality bulk GaN with the dislocation density of 1×106 cm-2 was achieved by using wet etching and HVPE multiple re-growth. It would offer a simple method to obtain bulk GaN with thicker layer and high quality.

  19. Homoepitaxial graphene tunnel barriers for spin transport

    NASA Astrophysics Data System (ADS)

    Friedman, Adam

    Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions (magnetic field, temperature, etc.) usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. We demonstrate successful tunneling, charge, and spin transport with a fluorinated graphene tunnel barrier on a graphene channel. We show that while spin transport stops short of room temperature, spin polarization efficiency values are the highest of any graphene spin devices. We also demonstrate that hydrogenation of graphene can also be used to create a tunnel barrier. We begin with a four-layer stack of graphene and hydrogenate the top few layers to decouple them from the graphene transport channel beneath. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the non-local Hanle effect to be commensurate with previous studies. The measured spin polarization efficiencies for hydrogenated graphene are higher than most oxide tunnel barriers on graphene, but not as high as with fluorinated graphene tunnel barriers. However, here we show that spin transport persists up to room temperature. Our results for the hydrogenated graphene tunnel barriers are compared with fluorinated tunnel barriers and we discuss the

  20. Homoepitaxial graphene tunnel barriers for spin transport

    NASA Astrophysics Data System (ADS)

    Friedman, Adam L.; van't Erve, Olaf M. J.; Robinson, Jeremy T.; Whitener, Keith E.; Jonker, Berend T.

    2016-05-01

    Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. Here, we demonstrate that hydrogenation or fluorination of graphene can be used to create a tunnel barrier. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures, and determine spin lifetimes with the non-local Hanle effect. We compare the results for hydrogenated and fluorinated tunnel and we discuss the possibility that ferromagnetic moments in the hydrogenated graphene tunnel barrier affect the spin transport of our devices.

  1. Process for the homoepitaxial growth of single-crystal silicon carbide films on silicon carbide wafers

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony (Inventor)

    1993-01-01

    The invention is a method for growing homoepitaxial films of SiC on low tilt angle vicinal (0001) SiC wafers. The invention proposes and teaches a new theoretical model for the homoepitaxial growth of SiC films on (0001) SiC substrates. The inventive method consists of preparing the growth surface of SiC wafers slightly off-axis (from less the 0.1 to 6 deg) from the (0001) plane, subjecting the growth surface to a suitable etch, and then growing the homoepitaxial film using conventional SiC growth techniques.

  2. Surface nanopattern formation due to current-induced homoepitaxial nanowire edge instability

    NASA Astrophysics Data System (ADS)

    Kumar, Ashish; Dasgupta, Dwaipayan; Maroudas, Dimitrios

    2016-09-01

    Physical nanopatterning based on a precise control of macroscopic forcing is an essential tool of nanoscale science and technology. Using an externally applied electric field as the macroscopic force, we report here a computational study on the formation of surface nanopatterns consisting of single-layer homoepitaxial islands as a result of a morphological instability that can occur under edge electromigration conditions on the straight edge of a single-layer nanowire grown epitaxially on a crystalline substrate. Direct dynamical simulations based on a model that has been validated experimentally for the Ag/Ag system show that the current-induced nanowire edge instability causes the breakup of the nanowire and leads to the formation of uniformly distributed islands, arranged in linear or V-shaped arrays, which are uniformly sized with nanoscale dimensions. The simulation results are supported by linear stability theory and demonstrate that the geometrical features of the island patterns and the island sizes can be controlled precisely by controlling the electric field direction with respect to the nanowire axis and the electric field strength. Our findings have important implications for developing physical nanopatterning approaches toward enabling future nanofabrication technologies.

  3. Evolution of Mound Morphology in Reversible Homoepitaxy on Cu(100)

    SciTech Connect

    Zuo, J.; Wendelken, J.

    1997-04-01

    Evolution of mound morphology in reversible homoepitaxy on Cu(100) was studied via spot-profile-analysis (SPA) LEED and scanning tunneling microscopy. The mound separation shows coarsening vs growth time with L(t){approximately}t{sup 1/4}, in support of theory based on capillarity between mounds. The growth ultimately reaches a steady state characterized by a selected mound angle of {approximately}5.6{degree}. We suggest that this results from a downhill current driven by step edge line tension in balance with an uphill current due to the Schwoebel barrier effect. Also, we have clarified the interpretation for the evolution of the SPA-LEED profile from a ring structure to a single time-invariant peak. {copyright} {ital 1997} {ital The American Physical Society}

  4. Growth of Homoepitaxial ZnO Semiconducting Films

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; George, M. A.; McCarty, P.

    1999-01-01

    As a high temperature wide-band-gap (3.3 eV at room temperature) semiconductor, ZnO has been used for many applications such as wave-guides, solar cells, and surface acoustic wave devices, Since ZnO has a 60 meV excitonic binding energy that makes it possible to produce excitonic lasing at room temperature, a recent surge of interest is to synthesize ZnO films for UV/blue/green laser diodes. These applications require films with a smooth surface, good crystal quality, and low defect density. Thus, homoepitaxial film growth is the best choice. Homoepitaxial films have been studied in terms of morphology, crystal structure, and electrical and optical properties. ZnO single crystal substrates grown by the hydrothermal method are mechanically polished and annealed in air for four hours before the films are deposited. The annealing temperature-dependence on ZnO substrate morphology and electrical properties is investigated. Films are synthesized by off-axis reactive sputtering deposition. This produces films that have very smooth surfaces with roughness less than or equal to 5 nm on a 5 microns x 5 microns area. The full width at half maximum of film theta rocking curves measured by the x-ray diffraction is slightly larger than that of the crystal substrate. Films are also characterized by measuring resistivity, optical transmittance, and photoluminescence. The properties of ZnO films grown on (0001) ZnO and (0001) sapphire substrates will also be compared and discussed.

  5. Interface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin films

    PubMed Central

    Molatta, Sebastian; Haindl, Silvia; Trommler, Sascha; Schulze, Michael; Wurmehl, Sabine; Hühne, Ruben

    2015-01-01

    Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties, and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1−xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1−xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1−xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1−xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1−xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C–320 °C) on MgO using PLD. This offers a broad scope of various applications. PMID:26548645

  6. Self-organized homo-epitaxial growth of (001) vanadium assisted by oxygen surface reconstruction

    NASA Astrophysics Data System (ADS)

    Andrieu, S.; Turban, P.; Kierren, B.

    2016-09-01

    In this paper the effect of oxygen on the vanadium homoepitaxial growth process is analyzed by using Auger spectroscopy, electron diffraction and scanning tunneling microscopy. As the oxygen induced 1 × 5 surface structure got a lattice spacing 6% different from the pure V lattice, relaxation is observed by electron diffraction during the growth. The average in-plane lattice spacing is thus shown to be proportional to the oxygen surface concentration. The surface lattice relaxation is observed to exponentially vary with the number of deposited atomic planes. A kinetic model is proposed and allows us to explain these observations. Furthermore, it helps us to distinguish two regimes depending on growth temperature. At high temperature, the oxygen surface concentration during growth is due to oxygen upward diffusion from the underneath V layer. For lower temperature however, this upward diffusion is not efficient and another source of oxygen contamination is evidenced. When the oxygen surface concentration is sufficient, a spectacular self-organization is observed at the surface by surface microscopy. Ribbons shape islands are observed and are tentatively explained as a consequence of oxygen surface concentration and stress induced by the surface reconstruction.

  7. Interface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin films

    NASA Astrophysics Data System (ADS)

    Molatta, Sebastian; Haindl, Silvia; Trommler, Sascha; Schulze, Michael; Wurmehl, Sabine; Hühne, Ruben

    2015-11-01

    Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties, and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1-xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1-xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1-xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1-xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1-xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C-320 °C) on MgO using PLD. This offers a broad scope of various applications.

  8. Homoepitaxial Boron Doped Diamond Anvils as Heating Elements in a Diamond Anvil Cell

    NASA Astrophysics Data System (ADS)

    Montgomery, Jeffrey; Samudrala, Gopi; Smith, Spencer; Tsoi, Georgiy; Vohra, Yogesh; Weir, Samuel

    2013-03-01

    Recent advances in designer-diamond technology have allowed for the use of electrically and thermally conducting homoepitaxially-grown layers of boron-doped diamond (grown at 1200 °C with a 2% mixture of CH4 in H, resulting in extremely high doping levels ~ 1020/cm3) to be used as heating elements in a diamond anvil cell (DAC). These diamonds allow for precise control of the temperature inside of the diamond anvil itself, particularly when coupled with a cryostat. Furthermore, the unmatched thermally conducting nature of diamond ensures that no significant lateral gradient in temperature occurs across the culet area. Since a thermocouple can easily be attached anywhere on the diamond surface, we can also measure diamond temperatures directly. With two such heaters, one can raise sample temperatures uniformly, or with any desired gradient along the pressure axis while preserving optical access. In our continuing set of benchmark experiments, we use two newly created matching heater anvils with 500 μm culets to analyze the various fluorescence emission lines of ruby microspheres, which show more complicated behavior than traditional ruby chips. We also report on the temperature dependence of the high-pressure Raman modes of paracetamol (C8H9NO2) up to 20 GPa.

  9. Growth of Homoepitaxial ZnO Semiconducting Films

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, Ching-Hua; Lehoczky, S. L.; Harris, M. T.; George, Michael A.; McCarty, P.

    1999-01-01

    As a high temperature semiconductor, ZnO has been used for many applications such as wave-guide, solar cells, and surface acoustic wave devices. Since the ZnO material has an energy gap of 3.3 eV at room temperature and an excitonic binding energy (60 meV) that is possible to make excitonic lasering at room temperature a recent surge of interest is to synthesize ZnO films for electro-optical devices. These applications require films with a smooth surface, good crystal quality, and low defect density. Homoepitaxial films have been studied in terms of morphology, crystal structure, and electrical and optical properties. ZnO single crystals are grown by the hydrothermal method. Substrates are mechanically polished and annealed in air for four hours before deposited films. The annealing temperature-dependence of ZnO substrates is studied. Films are synthesized by the off-axis reactive sputtering deposition. The films have very smooth surface with a roughness

  10. Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD

    NASA Astrophysics Data System (ADS)

    Guoguo, Yan; Feng, Zhang; Yingxi, Niu; Fei, Yang; Xingfang, Liu; Lei, Wang; Wanshun, Zhao; Guosheng, Sun; Yiping, Zeng

    2016-06-01

    Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition (CVD) system using H2‑SiH4‑C2H4‑HCl. The effect of the SiH4/H2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively. The growth rate increase in proportion to the SiH4/H2 ratio and the influence mechanism of chlorine has been investigated. With the reactor pressure increasing from 40 to 100 Torr, the growth rate increased to 52 μm/hand then decreased to 47 μm/h, which is due to the joint effect of H2 and HCl etching as well as the formation of Si clusters at higher reactor pressure. The surface root mean square (RMS) roughness keeps around 1 nm with the growth rate increasing to 49 μm/h. The scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved. These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy. Project supported by the National High Technology R&D Program of China (No. 2014AA041402), the National Natural Science Foundation of China (Nos. 61474113, 61274007, 61574140), the Beijing Natural Science Foundation of China (Nos. 4132076, 4132074), the Program of State Grid Smart Grid Research Institute (No. SGRI-WD-71-14-004), and the Youth Innovation Promotion Association of CAS.

  11. Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD

    NASA Astrophysics Data System (ADS)

    Guoguo, Yan; Feng, Zhang; Yingxi, Niu; Fei, Yang; Xingfang, Liu; Lei, Wang; Wanshun, Zhao; Guosheng, Sun; Yiping, Zeng

    2016-06-01

    Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition (CVD) system using H2-SiH4-C2H4-HCl. The effect of the SiH4/H2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively. The growth rate increase in proportion to the SiH4/H2 ratio and the influence mechanism of chlorine has been investigated. With the reactor pressure increasing from 40 to 100 Torr, the growth rate increased to 52 μm/hand then decreased to 47 μm/h, which is due to the joint effect of H2 and HCl etching as well as the formation of Si clusters at higher reactor pressure. The surface root mean square (RMS) roughness keeps around 1 nm with the growth rate increasing to 49 μm/h. The scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved. These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy. Project supported by the National High Technology R&D Program of China (No. 2014AA041402), the National Natural Science Foundation of China (Nos. 61474113, 61274007, 61574140), the Beijing Natural Science Foundation of China (Nos. 4132076, 4132074), the Program of State Grid Smart Grid Research Institute (No. SGRI-WD-71-14-004), and the Youth Innovation Promotion Association of CAS.

  12. Tuning thermal conductivity in homoepitaxial SrTiO{sub 3} films via defects

    SciTech Connect

    Brooks, Charles M.; Wilson, Richard B.; Cahill, David G.; Schäfer, Anna; Schubert, Jürgen; Mundy, Julia A.; Holtz, Megan E.; Muller, David A.; Schlom, Darrell G.

    2015-08-03

    We demonstrate the ability to tune the thermal conductivity of homoepitaxial SrTiO{sub 3} films deposited by reactive molecular-beam epitaxy by varying growth temperature, oxidation environment, and cation stoichiometry. Both point defects and planar defects decrease the longitudinal thermal conductivity (k{sub 33}), with the greatest decrease in films of the same composition observed for films containing planar defects oriented perpendicular to the direction of heat flow. The longitudinal thermal conductivity can be modified by as much as 80%—from 11.5 W m{sup −1}K{sup −1} for stoichiometric homoepitaxial SrTiO{sub 3} to 2 W m{sup −1}K{sup −1} for strontium-rich homoepitaxial Sr{sub 1+δ}TiO{sub x} films—by incorporating (SrO){sub 2} Ruddlesden-Popper planar defects.

  13. Homoepitaxial branching: an unusual polymorph of zinc oxide derived from seeded solution growth.

    PubMed

    Kozhummal, Rajeevan; Yang, Yang; Güder, Firat; Hartel, Andreas; Lu, Xiaoli; Küçükbayrak, Umut M; Mateo-Alonso, Aurelio; Elwenspoek, Miko; Zacharias, Margit

    2012-08-28

    The development of hydrothermal synthesis has greatly promoted bottom-up nanoscience for the rational growth of diverse zinc oxide (ZnO) nanostructures. In comparison with normal ZnO nanowires, ZnO nanostructures with a larger surface area, for instance, branched nanowires, are more attractive in the application fields of catalysis, sensing, dye-sensitized solar cells etc. So far the ZnO branched nanowires achieved by either one-step or multistep growth always present a boundary-governed nonepitaxial branch/stem interface. In this report, seeded growth of single-crystalline ZnO hexabranched nanostructures was achieved by selecting polyethylene glycol (PEG) as capping agent based on a low-temperature, laterally epitaxial solution growth strategy. We investigated the generality of this PEG-assisted growth process using different ZnO seed layers including continuous film, patterned dots, and vertically aligned nanowire arrays. It was revealed that PEG is a distinctive c-direction inhibitor responsible for the lateral growth and subsequent branching of ZnO due to its nonionic and nonacidic feature and weak reactivity in the solution system. All the obtained branched nanostructures are of single crystallinity in nature, which is methodologically determined by the homoepitaxial growth mode. This PEG-assisted process is versatile for diameter tuning and branch formation of ZnO nanowires by secondary growth. Our proof-of-concept experiments demonstrated that the ZnO hexabranched nanostructures presented superior photocatalytic efficiency for dye degradation relative to the normal ZnO nanowires. PMID:22849328

  14. Homoepitaxial SrTiO3(111) Film with High Dielectric Performance and Atomically Well-Defined Surface

    PubMed Central

    Liang, Yan; Li, Wentao; Zhang, Shuyuan; Lin, Chaojing; Li, Chao; Yao, Yuan; Li, Yongqing; Yang, Hao; Guo, Jiandong

    2015-01-01

    The six-fold symmetry possessed by the (111) surfaces of perovskite oxides allows the epitaxial growth of novel quantum materials such as topological insulators. The dielectric SrTiO3(111) thin film is an ideal buffer layer, providing the readily tunability of charge density in gate-controlled structures. But the high-quality film growth is challenging due to its strong surface polarity as well as the difficulty of obtaining the chemical stoichiometry. Here we show that the layer-by-layer growth of homoepitaxial SrTiO3(111) thin films can be achieved in molecular beam epitaxy method by keeping the growing surface reconstructed. And the cation stoichiometry is optimized precisely with the reflective high energy electron diffraction as the feedback signal that changes sensitively to the variation of metal concentration during growth. With atomically well-defined surfaces, the SrTiO3(111) films show high dielectric performance with the charge density modulated in the range of 2 × 1013/cm2 with the back gate voltage lower than 0.2 V. Methods of further broadening the range are also discussed. PMID:26073468

  15. Microscopic mechanism of the homoepitaxy on Si (111 )7 ×7

    NASA Astrophysics Data System (ADS)

    Shimada, Wataru; Sato, Tomoshige; Tochihara, Hiroshi

    2016-07-01

    Very initial stages of the homoepitaxy on the Si (111 )7 ×7 surface are studied at 310, 356, and 366° by in situ continuous observation using high-temperature scanning tunneling microscopy (HTSTM) at the atomic scale during Si deposition under a slow rate of 0.02 bilayer (BL ) min-1 . The substrate surface is reconstructed to the well-established dimer-adatom-stacking fault (DAS) structure with the 7 ×7 unit cell consisting of two triangular half unit cells (HUCs): a stacking faulted (F)-HUC and a normally stacked one. It is expected that the complex, large unit cell compels the initial homoepitaxy to proceed in a quite different manner from that on unreconstructed surfaces. Formation and growth of various adsorbed clusters are pursued by the continuous observation of the same narrow areas during the deposition, avoiding the tip-shadow effect. The most anomalous finding is a quasiliquid cluster (QLC) spreading to plural HUCs (spread QLC) on the 7 ×7 DAS substrate. This appears as a result of the difficulty of the F-HUC to be transformed into the normally stacked BL, being essential for the homoepitaxy. After the transformation, the spread QLC undergoes the following structural changes with an increase of the Si deposition: crystallization to a small epitaxial BL → surface reconstruction to the DAS structure. Validity and reasons of the transitional formation of the spread QLC are discussed. The spread QLC mediated homoepitaxy mechanism is concluded and is a new mode in the crystal growth. Real in situ HTSTM observations of the same areas on the nanoscale during Si deposition are indispensable to explore for the dynamic atomistic mechanism of the homoepitaxial growth on the Si (111 )7 ×7 .

  16. Depth-resolved cathodoluminescence of a homoepitaxial AlN thin film

    NASA Astrophysics Data System (ADS)

    Silveira, E.; Freitas, J. A.; Slack, G. A.; Schowalter, L. J.; Kneissl, M.; Treat, D. W.; Johnson, N. M.

    2005-07-01

    In the present work we will report on the optical properties of an AlN film homoepitaxially grown on a high-quality large bulk AlN single crystal. The latter was grown by a sublimation-recondensation technique, while the film was grown by organometallic vapor-phase epitaxy. Cathodoluminescence measurements were performed using electron beam energies between 2 and 10 keV in order to excite the sample and so to probe different sample depths, making it possible to differentiate between different features which originate in the AlN homoepitaxial film. The penetration depth has been determined through the calculation of the Bohr-Bethe maximum range of excitation using the approximation to the Everhart-Hoff expression for the energy loss within a solid.

  17. Gallium arsenide homoepitaxy employing [ital in]-[ital situ] generated arsine radicals

    SciTech Connect

    Pihlstrom, B.G.; Thompson, L.R.; Shaw, D.M.; Simone, A.D.; Sheng, T.Y.; Lurkins, J. ); Collins, G.J. )

    1992-12-01

    Removed from the deposition region, an upstream hydrogen microwave plasma generates arsenic hydrides by etching the surface of solid arsenic. The hydrides are transported to the deposition region and mixed with trimethylgallium to achieve low temperature (350--400 [degree]C) and low pressure (750 mTorr) homoepitaxial GaAs films. Low precursor V/III ratios are used to achieve homoepitaxial films with high levels of carbon dopants (10[sup 19] to mid 10[sup 20] cm[sup [minus]3]). No active or afterglow plasma exists in the growth region. The observed homoepitaxial growth activation energies of 54 kcal/mole and 66 kcal/mole for films deposited with V/III ratios of 1/1 and 1/4, respectively, are in the range of those reported for the heterogeneous decomposition of trimethylgallium in the absence of arsine. The majority carriers are holes and have hole concentrations which correlate to the carbon doping, as determined by room temperature Hall effect measurements and secondary ion mass spectroscopy. Carrier mobility versus carbon concentration is also presented.

  18. Properties of homoepitaxial 4H-SiC and characteristics of Ti/4H-SiC Schottky barrier diodes

    NASA Astrophysics Data System (ADS)

    Chen, G.; Li, Z. Y.; Bai, S.; Han, P.

    2008-02-01

    This paper describes the properties of the homoepitaxial 4H-SiC layer, the fabrication and electrical parameters of Ti/4H-SiC Schottky barrier diode (SBD). The 4H-SiC epitaxial layers, grown on the commercially available 8°off-oriented Si-face(0001) single-crystal 4H-SiC wafers, have been performed at 1550~1600°C by using the step controlled epitaxy with low pressure chemical vapor deposition. X-ray diffraction measurement result indicates the single crystal nature of the epilayer, and Raman spectrum shows the typical 4H-SiC feature peaks. When the off-oriented angle of substrate is 8°, the epitaxial growth perfectly replicates the substrate's polytype. High quality 4H-SiC epilayer has been generated on the 4H-SiC substrate. Ti/4H-SiC SBDs with blocking voltage 1kV have been made on an undoped epilayer with 12um in thick and 3×10 15cm -3 in carrier density. The ideality factor n=1.16 and the effective barrier height φ e=0.9V of the Ti/4H-SiC SBDs are measured with method of forward density-voltage (J-V). The diode rectification ratio of forward to reverse (defined at +/-1V) is over 10 7 at room temperature. By using B + implantation, an amorphous layer as the edge termination is formed. The SBDs have on-state current density of 200A/cm2 at a forward voltage drop of about 2V. The specific on-resistance for the rectifier is found to be as 6.6mΩ•cm2.

  19. High-quality and high-purity homoepitaxial diamond (100) film growth under high oxygen concentration condition

    SciTech Connect

    Teraji, Tokuyuki

    2015-09-21

    Defect formation during diamond homoepitaxial growth was sufficiently inhibited by adding oxygen simultaneously in the growth ambient with high concentration of 2%. A 30-μm thick diamond films with surface roughness of <2 nm were homoepitaxially deposited on the (100) diamond single crystal substrates with reasonable growth rate of approximately 3 μm h{sup −1} under the conditions of higher methane concentration of 10%, higher substrate temperature of ∼1000 °C, and higher microwave power density condition of >100 W cm{sup −3}. Surface characteristic patterns moved to an identical direction with growth thickness, indicating that lateral growth was dominant growth mode. High chemical purity represented by low nitrogen concentration of less than 1 ppb and the highest {sup 12}C isotopic ratio of 99.998% of the obtained homoepitaxial diamond (100) films suggest that the proposed growth condition has high ability of impurity control.

  20. Submonolayer nucleation and growth and the initial stage of multilayer kinetic roughening during Ag/Ag (100) homoepitaxy

    SciTech Connect

    Zhang, C.

    1996-08-01

    A comprehensive Scanning Tunneling Microscopy (STM) study of submonolayer nucleation and growth of 2D islands in Ag/Ag(100) homoepitaxy for temperature between 295K and 370K is presented. The initial stages of multilayer kinetic roughening is also studied. Analysis of an appropriate model for metal (100) homoepitaxy, produces estimates of 350 meV for the terrace diffusion barrier, 400 meV for the adatom bond energy, and 25 meV for the additional Ehrlich-Schwoebel step-edge barrier.

  1. Hydrogenated Graphene as a Homoepitaxial Tunnel Barrier for Spin and Charge Transport in Graphene.

    PubMed

    Friedman, Adam L; van 't Erve, Olaf M J; Robinson, Jeremy T; Whitener, Keith E; Jonker, Berend T

    2015-07-28

    We demonstrate that hydrogenated graphene performs as a homoepitaxial tunnel barrier on a graphene charge/spin channel. We examine the tunneling behavior through measuring the IV curves and zero bias resistance. We also fabricate hydrogenated graphene/graphene nonlocal spin valves and measure the spin lifetimes using the Hanle effect, with spintronic nonlocal spin valve operation demonstrated up to room temperature. We show that while hydrogenated graphene indeed allows for spin transport in graphene and has many advantages over oxide tunnel barriers, it does not perform as well as similar fluorinated graphene/graphene devices, possibly due to the presence of magnetic moments in the hydrogenated graphene that act as spin scatterers.

  2. Homoepitaxy of ZnO and MgZnO Films at 90 °C

    SciTech Connect

    Ehrentraut, Dirk; Goh, Gregory K.L.; Fujii, Katsushi; Ooi, Chin Chun; Quang, Le Hong; Fukuda, Tsuguo; Kano, Masataka; Zhang, Yuantao; Matsuoka, Takashi

    2014-06-01

    The aqueous synthesis of uniform single crystalline homoepitaxial zinc oxide, ZnO, and magnesium zinc oxide, Mg{sub x}Zn{sub 1−x}O, films under very low temperature conditions at T=90 °C and ambient pressure has been explored. A maximum Mg content of 1 mol% was recorded by energy dispersive spectroscopy. The growth on the polar (0 0 0 1) and (0 0 0 1¯) faces resulted in films that are strongly different in their structural and optical quality as evidenced by high-resolution X-ray diffraction, secondary electron microscopy, and photoluminescence. This is a result of the chemistry and temperature of the solution dictating the stability range of growth-governing metastable species. The use of trisodium citrate, Na{sub 3}C{sub 6}H{sub 5}O{sub 7}, yielded coalesced, mirror-like homoepitaxial films whereas adding magnesium nitrate hexahydrate, Mg(NO{sub 3}){sub 2}·6H{sub 2}O, favors the growth of films with pronounced faceting. - Graphical abstract: Homoepitaxial ZnO films grown from aqueous solution below boiling point of water on a ZnO substrate with off-orientation reveal parallel grooves that are characterized by (1 0 1{sup ¯} 1) facets. Adding trisodium citrate yields closed, single-crystalline ZnO films, which can further be functionalized. Alloying with MgO yields MgZnO films with low Mg content only. - Highlights: • A simple method to synthesize uniform single crystalline homoepitaxial ZnO and MgZnO films. • ZnO growth on (0 0 0 1) and (0 0 0 1{sup ¯}) face resulted in films that are strongly different in their structural and optical quality. • Single crystalline MgZnO film was fabricated under mild conditions (90 °C and ambient pressure). • Mg incorporation of nearly 1 mol% was obtained while maintaining single phase wurtzite structure.

  3. Radiation and temperature effects in heteroepitaxial and homoepitaxial InP cells

    NASA Technical Reports Server (NTRS)

    Weinberg, I.; Curtis, H. B.; Swartz, C. K.; Brinker, D. J.; Jenkins, P. P.; Faur, M.

    1991-01-01

    Heteroepitaxial (InP/GaAs) and homo-epitaxial (InP/InP) cells were irradiated by 1-MeV electrons and their performance, temperature dependencies and carrier removal rates determined. The radiation resistances of the InP/GaAs cells were significantly higher than that of the InP/InP cells. This was attributed to the high dislocation density present in the heteroepitaxial cells. In addition, the effects of dislocations in these latter cells were dominant in determining the temperature dependence of open-circuit voltage.

  4. Homoepitaxial meso- and microscale crystal co-orientation and organic matrix network structure in Mytilus edulis nacre and calcite.

    PubMed

    Griesshaber, Erika; Schmahl, Wolfgang W; Ubhi, Harbinder Singh; Huber, Julia; Nindiyasari, Fitriana; Maier, Bernd; Ziegler, Andreas

    2013-12-01

    New developments in high-resolution, low accelaration voltage electron backscatter diffraction (EBSD) enable us to resolve and quantify the co-orientation of nanocrystals constituting biological carbonate crystals with a scan step resolution of 125 nm. This allows the investigation of internal structures in carbonate tablets and tower biocrystals in the nacre of mollusc shells, and it provides details on the calcite-aragonite polymorph interface in bivalves. Within the aragonite tablets of Mytilus edulis nacre we find a mesoscale crystallographic mosaic structure with a misorientation distribution of 2° full width at half maximum. Selective etching techniques with critical point drying reveal an organic matrix network inside the nacre tablets. The size scales of the visible aragonite tablet subunits and nanoparticles correspond to those of the open pore system in the organic matrix network. We further observe by EBSD that crystal co-orientation spans over tablet boundaries and forms composite crystal units of up to 20 stacked co-oriented tablets (tower crystals). Statistical evaluation of the misorientation data gives a probability distribution of grain boundary misorientations with two maxima: a dominant peak for very-small-angle grain boundaries and a small maximum near 64°, the latter corresponding to {110} twinning orientations. However, the related twin boundaries are typically the membrane-lined {001} flat faces of the tablets and not {110} twin walls within tablets. We attribute this specific pattern of misorientation distribution to growth by particle accretion and subsequent semicoherent homoepitaxial crystallization. The semicoherent crystallization percolates between the tablets through mineral bridges and across matrix membranes surrounding the tablets. In the "prismatic" calcite layer crystallographic co-orientation of the prisms reaches over more than 50 micrometers. PMID:23896564

  5. Homoepitaxial meso- and microscale crystal co-orientation and organic matrix network structure in Mytilus edulis nacre and calcite.

    PubMed

    Griesshaber, Erika; Schmahl, Wolfgang W; Ubhi, Harbinder Singh; Huber, Julia; Nindiyasari, Fitriana; Maier, Bernd; Ziegler, Andreas

    2013-12-01

    New developments in high-resolution, low accelaration voltage electron backscatter diffraction (EBSD) enable us to resolve and quantify the co-orientation of nanocrystals constituting biological carbonate crystals with a scan step resolution of 125 nm. This allows the investigation of internal structures in carbonate tablets and tower biocrystals in the nacre of mollusc shells, and it provides details on the calcite-aragonite polymorph interface in bivalves. Within the aragonite tablets of Mytilus edulis nacre we find a mesoscale crystallographic mosaic structure with a misorientation distribution of 2° full width at half maximum. Selective etching techniques with critical point drying reveal an organic matrix network inside the nacre tablets. The size scales of the visible aragonite tablet subunits and nanoparticles correspond to those of the open pore system in the organic matrix network. We further observe by EBSD that crystal co-orientation spans over tablet boundaries and forms composite crystal units of up to 20 stacked co-oriented tablets (tower crystals). Statistical evaluation of the misorientation data gives a probability distribution of grain boundary misorientations with two maxima: a dominant peak for very-small-angle grain boundaries and a small maximum near 64°, the latter corresponding to {110} twinning orientations. However, the related twin boundaries are typically the membrane-lined {001} flat faces of the tablets and not {110} twin walls within tablets. We attribute this specific pattern of misorientation distribution to growth by particle accretion and subsequent semicoherent homoepitaxial crystallization. The semicoherent crystallization percolates between the tablets through mineral bridges and across matrix membranes surrounding the tablets. In the "prismatic" calcite layer crystallographic co-orientation of the prisms reaches over more than 50 micrometers.

  6. Effect of substrate orientation on CdS homoepitaxy by molecular dynamics

    DOE PAGES

    Almeida, S.; Chavez, J. J.; Zhou, X. W.; Zubia, D.

    2016-02-10

    CdS homoepitaxy growth was performed by molecular dynamics using different substrate orientations and structures in order to analyze the CdS crystallinity. As anticipated from thermodynamics of homoepitaxy, highly crystalline films with only point defects were obtained on substrates with rectangular surface geometries, including View the MathML source[112¯] zinc blende (ZB), [101¯0] wurtzite (WZ), [112¯0] WZ, [110][110] ZB, [010][010] ZB, and View the MathML source[1101110] ZB. In contrast, films grown on substrates with hexagonal surface geometries, corresponding to the [0001][0001] WZ and [111][111] ZB growth directions, showed structures with a large number of defects including; anti-sites, vacancies, stacking faults, twinning, andmore » polytypism. WZ and ZB transitions and grain boundaries are identified using a lattice identification algorithm and represented graphically in a structural map. A dislocation analysis was performed to detect, identify, and quantify linear defects within the atomistic data. Systematic simulations using different temperatures, deposition rates, and substrate polarities were perform to analyze the trends of dislocation densities on [0001][0001] WZ direction and showed persistent polytypism. As a result, the polytypism observed in the films grown on the substrates with hexagonal surface geometry is attributed to the similar formation energies of the WZ and ZB phases.« less

  7. Effect of substrate orientation on CdS homoepitaxy by molecular dynamics

    NASA Astrophysics Data System (ADS)

    Almeida, S.; Chavez, J. J.; Zhou, X. W.; Zubia, D.

    2016-05-01

    CdS homoepitaxy growth was performed by molecular dynamics using different substrate orientations and structures in order to analyze the CdS crystallinity. As anticipated from thermodynamics of homoepitaxy, highly crystalline films with only point defects were obtained on substrates with rectangular surface geometries, including [ 11 2 bar ] zinc blende (ZB), [ 10 1 bar 0 ] wurtzite (WZ), [ 11 2 bar 0 ] WZ, [ 110 ] ZB, [ 010 ] ZB, and [1/10 1 1/10 ] ZB. In contrast, films grown on substrates with hexagonal surface geometries, corresponding to the [ 0001 ] WZ and [ 111 ] ZB growth directions, showed structures with a large number of defects including; anti-sites, vacancies, stacking faults, twinning, and polytypism. WZ and ZB transitions and grain boundaries are identified using a lattice identification algorithm and represented graphically in a structural map. A dislocation analysis was performed to detect, identify, and quantify linear defects within the atomistic data. Systematic simulations using different temperatures, deposition rates, and substrate polarities were perform to analyze the trends of dislocation densities on [ 0001 ] WZ direction and showed persistent polytypism. The polytypism observed in the films grown on the substrates with hexagonal surface geometry is attributed to the similar formation energies of the WZ and ZB phases.

  8. In situ growth and density-functional-theory study of polarity-dependent homo-epitaxial ZnO microwires

    SciTech Connect

    Zhu, Rui; Xu, Jun; Gao, Jingyun; Zhang, Jingmin; Zhu, Wenguang; Xu, Hongjun; Sun, Yanghui; Fu, Qiang; Chen, Li; Du, Dapeng

    2012-01-01

    Polarity-dependent homo-epitaxy on (0001)-Zn and (0001)-O surfaces of cleaved ZnO microwires was investigated by in situ growth in ESEMand DFT simulations. ZnO monomers adsorption, adatoms desorption and chemisorption were simulated to understand the explicit mechanism.

  9. Hydrogenated Graphene as a Homoepitaxial Tunnel Barrier for Spin and Charge Transport in Graphene.

    PubMed

    Friedman, Adam L; van 't Erve, Olaf M J; Robinson, Jeremy T; Whitener, Keith E; Jonker, Berend T

    2015-07-28

    We demonstrate that hydrogenated graphene performs as a homoepitaxial tunnel barrier on a graphene charge/spin channel. We examine the tunneling behavior through measuring the IV curves and zero bias resistance. We also fabricate hydrogenated graphene/graphene nonlocal spin valves and measure the spin lifetimes using the Hanle effect, with spintronic nonlocal spin valve operation demonstrated up to room temperature. We show that while hydrogenated graphene indeed allows for spin transport in graphene and has many advantages over oxide tunnel barriers, it does not perform as well as similar fluorinated graphene/graphene devices, possibly due to the presence of magnetic moments in the hydrogenated graphene that act as spin scatterers. PMID:26047069

  10. Surface preparation and homoepitaxial deposition of AlN on (0001)-oriented AlN substrates by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Rice, A.; Collazo, R.; Tweedie, J.; Dalmau, R.; Mita, S.; Xie, J.; Sitar, Z.

    2010-08-01

    Chemical surface treatments were conducted on mechanically polished (MP) and chemomechanically polished (CMP) (0001)-oriented single crystalline aluminum nitride (AlN) substrates to determine a surface preparation procedure for the homoepitaxial deposition of AlN epitaxial layers by metalorganic chemical vapor deposition. MP AlN substrates characterized by atomic force microscopy exhibited 0.5 nm rms roughness and polishing scratches, while CMP AlN substrates exhibited 0.1 nm rms roughness and were scratch-free. X-ray photoelectron spectroscopy analysis of MP and CMP AlN substrates indicated the presence of a surface hydroxide layer composed of mixed aluminum oxide hydroxide and aluminum trihydroxide. Wet etching with sulfuric and phosphoric acid mixtures reduced the amount of surface hydroxide. Ammonia annealing at 1250 °C converted the substrate hydroxide layer to AlN and increased the rms roughness of MP and CMP AlN substrates to 2.2 nm and 0.2 nm, respectively. AlN epitaxial layers were deposited at 1100-1250 °C under 20 Torr total pressure with a V/III ratio of 180-300 in either N2 or H2 diluent. High-resolution x-ray diffraction measurements revealed that AlN epitaxial layers deposited on MP substrates were strained due to nucleation and coalescence of AlN grains on the mechanically damaged surfaces. AlN deposited on CMP substrates was epitaxial and strain-free. Thermodynamic models for nitridation and AlN deposition were also proposed and evaluated.

  11. Precise control of photoluminescence of silicon-vacancy color centers in homoepitaxial single-crystal diamond: evaluation of efficiency of Si doping from gas phase

    NASA Astrophysics Data System (ADS)

    Ralchenko, Victor; Sedov, Vadim; Saraykin, Vladimir; Bolshakov, Andrey; Zavedeev, Evgeny; Ashkinazi, Evgeny; Khomich, Andrew

    2016-09-01

    Ability to precisely control the Si-related color center abundance in diamond is important for the use of silicon-vacancy (SiV) defects with bright photoluminescence (PL) in quantum information technologies and optical biomarkers. Here, we evaluated the efficiency of Si incorporation in (100) plane of homoepitaxial diamond layers upon in situ doping by adding silane SiH4 in the course of diamond chemical vapor deposition in microwave plasma using CH4-H2 mixtures. Both the Si concentration in the doped samples, as determined by secondary ion mass spectrometry, and PL intensity of SiV centers at 738 nm wavelength, measured at excitation wavelength of 473 nm, demonstrate a linear increase with silane content in feed gas in the range. The incorporation efficiency f, defined as the ratio of Si concentration in diamond to that in gas, f = [Si/C]dia/[Si/C]gas is found to be (1.1 ± 0.5) × 10-3 for the silane concentrations explored, [SiH4/CH4] < 0.7 %; thus, the Si atoms are accommodated in (100) diamond face easier than nitrogen and phosphorus, but more difficult than boron. This finding allows a tailoring of the Si content and photoluminescence intensity of SiV centers in in situ doped CVD diamond.

  12. Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor.

    PubMed

    Pérez-Tomás, A; Catalàn, G; Fontserè, A; Iglesias, V; Chen, H; Gammon, P M; Jennings, M R; Thomas, M; Fisher, C A; Sharma, Y K; Placidi, M; Chmielowska, M; Chenot, S; Porti, M; Nafría, M; Cordier, Y

    2015-03-20

    The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

  13. On the Phase Shift of RHEED Intensity Oscillation during Homoepitaxy by MBE

    NASA Astrophysics Data System (ADS)

    Shin, B.; Leonard, J. P.; McCamy, J. W.; Aziz, M. J.

    2006-03-01

    Despite the widespread usage of RHEED over many years, there still remain fundamental questions unanswered with regard to the interpretation of RHEED measurements. One of these issues is the phase shift of the RHEED intensity oscillations upon changing the incidence angle of electron beams. Therefore, we have conducted a systematic investigation of the phase shift of the RHEED intensity oscillations during homoepitaxy of Ge(001) by MBE for a wide range of diffraction conditions. Our results show that for small incidence angles with a beam azimuth several degrees away from crystallographic symmetry directions, the phase stays the same; it starts to shift once the (004) Kikuchi line appears in the RHEED pattern. Moreover, under some conditions we observe the oscillations from only the Kikuchi feature and not from the specular spot, and the oscillatory behavior of the Kikuchi feature is almost out of phase with that of the specular spot. All these results convincingly demonstrate that the phase shift is caused by the interference of the specular spot by the Kikuchi features. The lesson that can be learned from our study is that in order to use the RHEED specular intensity oscillation to learn about surface morphology, one must be extremely careful that the RHEED measurements be conducted under conditions where the influence of the Kikuchi features is minimal.

  14. Layers

    NASA Astrophysics Data System (ADS)

    Hong, K. J.; Jeong, T. S.; Youn, C. J.

    2014-09-01

    The temperature-dependent photoresponse characteristics of MnAl2S4 layers have been investigated, for the first time, by use of photocurrent (PC) spectroscopy. Three peaks were observed at all temperatures. The electronic origin of these peaks was associated with band-to-band transitions from the valence-band states Γ4( z), Γ5( x), and Γ5( y) to the conduction-band state Γ1( s). On the basis of the relationship between PC-peak energy and temperature, the optical band gap could be well expressed by the expression E g( T) = E g(0) - 2.80 × 10-4 T 2/(287 + T), where E g(0) was estimated to be 3.7920 eV, 3.7955 eV, and 3.8354 eV for the valence-band states Γ4( z), Γ5( x), and Γ5( y), respectively. Results from PC spectroscopy revealed the crystal-field and spin-orbit splitting were 3.5 meV and 39.9 meV. The gradual decrease of PC intensity with decreasing temperature can be explained on the basis of trapping centers associated with native defects in the MnAl2S4 layers. Plots of log J ph, the PC current density, against 1/ T, revealed a dominant trap level in the high-temperature region. By comparing PC and the Hall effect results, we confirmed that this trap level is a shallow donor 18.9 meV below the conduction band.

  15. Buffer layer effect on ZnO nanorods growth alignment

    NASA Astrophysics Data System (ADS)

    Zhao, Dongxu; Andreazza, Caroline; Andreazza, Pascal; Ma, Jiangang; Liu, Yichun; Shen, Dezhen

    2005-06-01

    Vertical aligned ZnO nanorods array was fabricated on Si with introducing a ZnO thin film as a buffer layer. Two different nucleation mechanisms were found in growth process. With using Au catalyst, Zn vapor could diffuse into Au nanoclusters with forming a solid solution. Then the ZnO nucleation site is mainly on the catalyst by oxidation of Au/Zn alloy. Without catalyst, nucleation could occur directly on the surface of buffer layer by homoepitaxy. The density and the size of ZnO nanorods could be governed by morphological character of catalyst and buffer layer. The nanorods growth is followed by vapor-solid mechanism.

  16. Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions

    NASA Astrophysics Data System (ADS)

    Aseev, P.; Gačević, Ž.; Torres-Pardo, A.; González-Calbet, J. M.; Calleja, E.

    2016-06-01

    Series of GaN nanowires (NW) with controlled diameters (160-500 nm) and heights (420-1100 nm) were homoepitaxially grown on three different templates: GaN/Si(111), GaN/AlN/Si(111), and GaN/sapphire(0001). Transmission electron microscopy reveals a strong influence of the NW diameter on dislocation filtering effect, whereas photoluminescence measurements further relate this effect to the GaN NWs near-bandgap emission efficiency. Although the templates' quality has some effects on the GaN NWs optical and structural properties, the NW diameter reduction drives the dislocation filtering effect to the point where a poor GaN template quality becomes negligible. Thus, by a proper optimization of the homoepitaxial GaN NWs growth, the propagation of dislocations into the NWs can be greatly prevented, leading to an exceptional crystal quality and a total dominance of the near-bandgap emission over sub-bandgap, defect-related lines, such as basal stacking faults and so called unknown exciton (UX) emission. In addition, a correlation between the presence of polarity inversion domain boundaries and the UX emission lines around 3.45 eV is established.

  17. Homoepitaxial and Heteroepitaxial Growth on Step-Free SiC Mesas

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony

    2004-01-01

    This article describes the initial discovery and development of new approaches to SiC homoepitaxial and heteroepitaxial growth. These approaches are based upon the previously unanticipated ability to effectively supress two-dimensional nucleation of 3C-SiC on large basal plane terraces that form between growth steps when epitaxy is carried out on 4H- and 6H-SiC nearly on-axis substrates. After subdividing the growth surface into mesa regions, pure stepflow homoeptixay with no terrace nucleation was then used to grow all existing surface steps off the edges of screw-dislocation-free mesas, leaving behind perfectly on-axis (0001) basal plane mesa surfaces completely free of atomic-scale steps. Step-free mesa surfaces as large as 0.4 mm x 0.4 mm were experimentally realized, with the yield and size of step-free mesas being initally limited by substrate screw dislocations. Continued epitaxial growth following step-free surface formation leads to the formation of thin lateral cantilevers that extend the step-free surface area from the top edge of the mesa sidewalls. By selecting a proper pre-growth mesa shape and crystallographic orientation, the rate of cantilever growth can be greatly enhanced in a web growth process that has been used to (1) enlarge step-free surface areas and (2) overgrow and laterally relocate micropipes and screw dislocations. A new growth process, named step-free surface heteroepitaxy, has been developed to achieve 3C-SiC films on 4H- and 6H-SiC substrate mesas completely free of double positioning boundary and stacking fault defects. The process is based upon the controlled terrace nucleation and lateral expansion of a single island of 3C-SiC across a step-free mesa surface. Experimental results indicate that substrateepilayer lattice mismatch is at least partially relieved parallel to the interface without dislocations that undesirably thread through the thickness of the epilayer. These results should enable realization of improved Si

  18. Growth of Defect-Free 3C-Sic on 4H- and 6H-SIC Mesas Using Step-Free Surface Heteroepitaxy

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew J.; Huang, Xianrong R.; Dudley, Michael

    2002-01-01

    A new growth process, herein named step-free surface heteroepitaxy, has achieved 3C-SiC films completely free of double positioning boundaries and stacking faults on 4H-SiC and 6H-SiC substrate mesas. The process is based upon the initial 2-dimensional nucleation and lateral expansion of a single island of 3C-SiC on a 4H- or 6H-SiC mesa surface that is completely free of bilayer surface steps. Our experimental results indicate that substrate-epilayer in-plane lattice mismatch (Delta/a = 0.0854% for 3C/4H) is at least partially relieved parallel to the interface in the initial bilayers of the heterofilm, producing an at least partially relaxed 3C-SiC film without dislocations that undesirably thread through the thickness of the epilayer. This result should enable realization of improved 3C-SiC devices.

  19. Interplay of point defects, biaxial strain, and thermal conductivity in homoepitaxial SrTiO{sub 3} thin films

    SciTech Connect

    Wiedigen, S.; Kramer, T.; Knorr, I.; Nee, N.; Hoffmann, J.; Volkert, C. A.; Jooss, Ch.; Feuchter, M.; Kamlah, M.

    2012-02-06

    Separating out effects of point defects and lattice strain on thermal conductivity is essential for improvement of thermoelectric properties of SrTiO{sub 3}. We study relations between defects generated during deposition, induced lattice strain, and their impact on thermal conductivity {kappa} in homoepitaxial SrTiO{sub 3} films prepared by ion-beam sputtering. Lowering the deposition temperature gives rise to lattice expansion by enhancement of point defect density which increases the hardness of the films. Due to a fully coherent substrate-film interface, the lattice misfit induces a large biaxial strain. However, we can show that the temperature dependence of {kappa} is mainly sensitive on the defect concentration.

  20. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  1. Seed layer technique for high quality epitaxial manganite films

    NASA Astrophysics Data System (ADS)

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O'Shea, K.; MacLaren, D. A.; Riminucci, A.; Bergenti, I.; Fugattini, S.; Prezioso, M.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  2. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived. PMID:27648371

  3. Thermal conductivity as a metric for the crystalline quality of SrTiO{sub 3} epitaxial layers

    SciTech Connect

    Oh, Dong-Wook; Ravichandran, Jayakanth; Liang, Chen-Wei; Martin, Lane W.; Cahill, David G.; Siemons, Wolter; Jalan, Bharat; Stemmer, Susanne; Brooks, Charles M.; Schlom, Darrell G.; Huijben, Mark; Majumdar, Arun; Ramesh, Ramamoorthy

    2011-05-30

    Measurements of thermal conductivity {Lambda} by time-domain thermoreflectance in the temperature range 100layers of a prototypical oxide, SrTiO{sub 3}. Twenty samples from five institutions using two growth techniques, molecular beam epitaxy and pulsed laser deposition (PLD), were analyzed. Optimized growth conditions produce layers with {Lambda} comparable to bulk single crystals. Many PLD layers, particularly those that use ceramics as the target material, show surprisingly low {Lambda}. For homoepitaxial layers, the decrease in {Lambda} created by point defects correlates well with the expansion of the lattice parameter in the direction normal to the surface.

  4. Thermal conductivity as a metric for the crystalline quality of SrTiO3 epitaxial layers

    SciTech Connect

    Oh, Dong-Wook; Ravichandran, Jayakanth; Liang, Chen-Wei; Siemons, Wolter; Jalan, Bharat; Brooks, Charles M.; Huijben, Mark; Schlom, Darrell G.; Stemmer, Susanne; Martin, Lane W.; Majumdar, Arun; Ramesh, Ramamoorthy; Cahill, David G.

    2011-01-01

    Measurements of thermal conductivity Λ by time-domain thermoreflectance in the temperature range 100 < T < 300 K are used to characterize the crystalline quality of epitaxial layers of a prototypical oxide, SrTiO₃. Twenty samples from five institutions using two growth techniques, molecular beam epitaxy and pulsed laser deposition (PLD), were analyzed. Optimized growth conditions produce layers with Λ comparable to bulk single crystals. Many PLD layers, particularly those that use ceramics as the target material, show surprisingly low Λ. For homoepitaxial layers, the decrease in Λ created by point defects correlates well with the expansion of the lattice parameter in the direction normal to the surface.

  5. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

    DOE PAGES

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; Rouleau, Christopher M.

    2016-01-29

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on singlemore » crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Thus, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but it expands the utility of pulsed laser epitaxy of other materials as well.₃« less

  6. Light polarization sensitive photodetectors with m- and r-plane homoepitaxial ZnO/ZnMgO quantum wells

    SciTech Connect

    Tabares, G.; Hierro, A. Lopez-Ponce, M.; Muñoz, E.

    2015-02-09

    Homoepitaxial ZnO/(Zn,Mg)O multiple quantum wells (MQWs) grown with m- and r-plane orientations are used to demonstrate Schottky photodiodes sensitive to the polarization state of light. In both orientations, the spectral photoresponse of the MQW photodiodes shows a sharp excitonic absorption edge at 3.48 eV with a very low Urbach tail, allowing the observation of the absorption from the A, B and C excitonic transitions. The absorption edge energy is shifted by ∼30 and ∼15 meV for the m- and r-plane MQW photodiodes, respectively, in full agreement with the calculated polarization of the A, B, and C excitonic transitions. The best figures of merit are obtained for the m-plane photodiodes, which present a quantum efficiency of ∼11%, and a specific detectivity D* of ∼6.4 × 10{sup 10} cm Hz{sup 1/2}/W. In these photodiodes, the absorption polarization sensitivity contrast between the two orthogonal in-plane axes yields a maximum value of (R{sub ⊥}/R{sub ||}){sub max} ∼ 9.9 with a narrow bandwidth of ∼33 meV.

  7. Analytic formulations for one-dimensional decay of rectangular homoepitaxial islands during coarsening on anisotropic fcc (110) surfaces

    SciTech Connect

    Wang, Chi-Jen; Han, Yong; Walen, Holly; Russell, Selena M.; Thiel, Patricia A.; Evans, James W.

    2013-10-01

    Submonolayer homoepitaxial fcc (110) systems display behavior reflecting strong anisotropy at lower temperatures, including one-dimensional decay during Ostwald ripening of rectangular islands maintaining constant width in the (001) direction. To appropriately describe this behavior, we first develop a refined continuum Burton-Cabrera-Frank formalism, which accounts for a lack of equilibration of island shape and importantly also for inhibited incorporation of adatoms at almost-faceted (1¯10) island edges through effective kinetic coefficients. This formalism is shown to describe accurately the adatom diffusion fluxes between islands and thus island evolution for a complex experimental island configuration, as confirmed by matching results from realistic atomistic simulations for this configuration. This approach also elucidates basic dependencies of flux on island geometry and temperature. Second, a further refinement is presented incorporating separate terrace and edge adatom density fields either in a continuum setting or alternatively in a spatially discrete diffusion equation setting. The second approach allows more flexibility and accuracy in accounting for edge-diffusion kinetics including corner rounding, a lack of equilibration of the edge adatom density at (1¯10) island edges, and the effect of rare kinks on (1¯10) island edges. Finally and significantly, it suggests facile two-way corner rounding at the island periphery during island decay, contrasting the previous picture.

  8. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum.

    PubMed

    Lee, Ho Nyung; Ambrose Seo, Sung S; Choi, Woo Seok; Rouleau, Christopher M

    2016-01-29

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well.

  9. Comparison of morphology evolution of Ge(001) homoepitaxial films grown by pulsed laser deposition and molecular-beam epitaxy

    SciTech Connect

    Shin Byungha; Leonard, John P.; McCamy, James W.; Aziz, Michael J.

    2005-10-31

    Using a dual molecular-beam epitaxy (MBE)-pulsed laser deposition (PLD) ultrahigh vacuum chamber, we have conducted the first experiments under identical thermal, background, and surface preparation conditions to compare Ge(001) homoepitaxial growth morphology in PLD and MBE. We find that in PLD with low kinetic energy and in MBE the film morphology evolves in a similar fashion: initially irregularly shaped mounds form, followed by pyramidal mounds with edges of the square-base along the <100> directions; the film roughness and mound separation increase with film thickness. In PLD with high kinetic energy, well-defined pyramidal mounds are not observed and the morphology rather resembles that of an ion-etched Ge(001) surface. The areal feature density is higher for PLD films than for MBE films grown at the same average growth rate and temperature. Furthermore, the dependence upon film thickness of roughness and feature separation differ for PLD and MBE. We attribute these differences to the higher yield of defect generation by energetic species in PLD.

  10. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

    NASA Astrophysics Data System (ADS)

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; Rouleau, Christopher M.

    2016-01-01

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well.

  11. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

    PubMed Central

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; Rouleau, Christopher M.

    2016-01-01

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well. PMID:26823119

  12. Analytic formulations for one-dimensional decay of rectangular homoepitaxial islands during coarsening on anisotropic fcc (110) surfaces

    NASA Astrophysics Data System (ADS)

    Wang, Chi-Jen; Han, Yong; Walen, Holly; Russell, Selena M.; Thiel, Patricia A.; Evans, James W.

    2013-10-01

    Submonolayer homoepitaxial fcc (110) systems display behavior reflecting strong anisotropy at lower temperatures, including one-dimensional decay during Ostwald ripening of rectangular islands maintaining constant width in the <001> direction. To appropriately describe this behavior, we first develop a refined continuum Burton-Cabrera-Frank formalism, which accounts for a lack of equilibration of island shape and importantly also for inhibited incorporation of adatoms at almost-faceted <1¯10> island edges through effective kinetic coefficients. This formalism is shown to describe accurately the adatom diffusion fluxes between islands and thus island evolution for a complex experimental island configuration, as confirmed by matching results from realistic atomistic simulations for this configuration. This approach also elucidates basic dependencies of flux on island geometry and temperature. Second, a further refinement is presented incorporating separate terrace and edge adatom density fields either in a continuum setting or alternatively in a spatially discrete diffusion equation setting. The second approach allows more flexibility and accuracy in accounting for edge-diffusion kinetics including corner rounding, a lack of equilibration of the edge adatom density at <1¯10> island edges, and the effect of rare kinks on <1¯10> island edges. Significantly, it suggests facile two-way corner rounding at the island periphery during island decay, contrasting the previous picture.

  13. Spectroscopic ellipsometry of homoepitaxial diamond multilayers and delta-doped structures

    SciTech Connect

    Bousquet, J.; Chicot, G.; Eon, D.; Bustarret, E.

    2014-01-13

    The optimization of diamond-based unipolar electronic devices such as pseudo-vertical Schottky diodes or delta-doped field effect transistors relies in part on the sequential growth of nominally undoped (p{sup –}) and heavily boron doped (p{sup ++}) layers with well-controlled thicknesses and steep interfaces. Optical ellipsometry offers a swift and contactless method to characterize the thickness, roughness, and electronic properties of semiconducting and metallic diamond layers. We report ellipsometric studies carried out on delta-doped structures and other epitaxial multilayers with various boron concentrations and thicknesses (down to the nanometer range). The results are compared with Secondary Ion Mass Spectroscopy and transport measurements.

  14. Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy

    SciTech Connect

    Corrion, A. L.; Wu, F.; Speck, J. S.

    2012-09-01

    c-plane GaN films were grown by ammonia molecular beam epitaxy on metal-organic chemical vapor deposition templates for a wide range of NH{sub 3}:Ga flux ratios and growth temperatures, and the resulting films were characterized using atomic force microscopy, reflection high-energy electron diffraction, and transmission electron microscopy. Three distinct nitrogen-rich growth regimes - unstable layer-by-layer, quasi-stable step flow, and dislocation-mediated pitting - were identified based on the growth mode and film properties. In addition, step flow growth was observed under conditions of gallium droplet accumulation. The results indicate the existence of two regimes for step-flow growth of GaN by ammonia MBE - both gallium-rich and nitrogen-rich. Growth mode instabilities and mound formation were observed and are discussed in the context of a step-edge energy barrier to adatom diffusion over a terrace.

  15. AlN homoepitaxial growth on sublimation-AlN substrate by low-pressure HVPE

    NASA Astrophysics Data System (ADS)

    Nomura, Takuya; Okumura, Kenta; Miyake, Hideto; Hiramatsu, Kazumasa; Eryu, Osamu; Yamada, Yoichi

    2012-07-01

    Crack-free thick AlN layers with low impurity concentrations were grown on free-standing AlN substrates fabricated by a sublimation method. Cracks due to tensile stresses were generated in the overgrowth layer when using on-axis AlN (0 0 0 1) substrates, as indicated by Raman scattering spectroscopy. In contrast, cracks were not generated when using 5° off-angle AlN (0 0 0 1) substrates. High crystalline quality was indicated by X-ray rocking curve (XRC) analysis. The full width at half maximum (FWHM) values of the (0 0 0 2) and (1 0-1 0) diffractions were 277 and 306 arcsec, respectively. Secondary ion mass spectrometry (SIMS) measurements indicated that the Si and C impurity concentrations were reduced to half of those in the sublimation-grown AlN substrates.

  16. 4H-SiC homoepitaxy on nearly on-axis substrates using TFS-towards high quality epitaxial growth

    NASA Astrophysics Data System (ADS)

    Balachandran, Anusha; Song, Haizheng; Sudarshan, T. S.; Chandrashekhar, M. V. S.

    2016-08-01

    We report high quality homoepitaxial growth on nearly on-axis (± 0.5 °) 4H-SiC substrates by chemical vapor deposition (CVD) using Tetrafluorosilane and Propane as Si and C-precursors, respectively. N-type unintentional doping (1017-1014 cm-3) was obtained for 0.62.0, a linear dependence on C-flow is established, with a return to step-mediated growth, shown by the surface morphology (RMS roughness ∼1 nm), and high polytype uniformity from Raman at high Rg- 14 μm/h. These two behaviors were ascribed to a decrease in the etch rate of SiC by SiF4 with increasing C/Si due to C-aided decomposition of SiF4, both of which make available a greater amount of elemental Si at the surface, thereby suppressing spiral growth. Use of on-axis or near on-axis substrates can eliminate/reduce basal plane dislocations which limit the performance of SiC bipolar electronic devices.

  17. Enlargement of Step-Free SiC Surfaces by Homoepitaxial Web-Growth of Thin SiC Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Beheim, Glenn M.; Benavage, Emye L.; Abel, Phillip B.; Trunek, Andrew J.; Spry, David J.; Dudley, Michael; Vetter, William M.

    2002-01-01

    Lateral homoepitaxial growth of thin cantilevers emanating from mesa patterns that were reactive ion etched into on-axis commercial SiC substrates prior to growth is reported. The thin cantilevers form after pure stepflow growth removes almost all atomic steps from the top surface of a mesa, after which additional adatoms collected by the large step-free surface migrate to the mesa sidewall where they rapidly incorporate into the crystal near the top of the mesa sidewall. The lateral propagation of the step-free cantilevered surface is significantly affected by pregrowth mesa shape and orientation, with the highest lateral expansion rates observed at the inside concave comers of V-shaped pregrowth mesas with arms lengthwise oriented along the {1100} direction. Complete spanning of the interiors of V's and other mesa shapes with concave comers by webbed cantilevers was accomplished. Optical microscopy, synchrotron white beam x-ray topography and atomic force microscopy analysis of webbed regions formed over a micropipe and closed-core screw dislocations show that c-axis propagation of these defects is terminated by the webbing. Despite the nonoptimized process employed in this initial study, webbed surfaces as large as 1.4 x 10(exp -3) square centimeters, more than four times the pregrowth mesa area, were grown. However, the largest webbed surfaces were not completely free of bilayer steps, due to unintentional growth of 3C-SiC that occurred in the nonoptimized process. Further process optimization should enable larger step-free webs to be realized.

  18. Studies of large scale unstable growth formed during GaAs(001) homoepitaxy

    NASA Astrophysics Data System (ADS)

    Orme, C.; Johnson, M. D.; Leung, K.-T.; Orr, B. G.; Smilauer, P.; Vvedensky, D.

    1995-05-01

    Atomic force and scanning tunneling microscopy studies have been performed on GaAs(001) films grown by molecular beam epitaxy. Multilayered mounds are seen to evolve when the growth conditions favor island nucleation. As the epilayer thickness is increased, these features grow in all dimensions but the angle of inclination remains approximately constant at 1°. The mounding does not occur on surfaces grown in step-flow. We propose that the multi-layered features are due to an unstable growth mode which relies on island nucleation and the presence of a step edge barrier.

  19. Morphological switching in synchrotron-radiation-excited Ge homoepitaxy: Transition from kinetic roughening to smoothing

    SciTech Connect

    Akazawa, Housei

    2005-05-15

    The surface morphology of Ge films during GeH{sub 4}-source molecular beam epitaxy on a Ge(100) substrate is dramatically changed through irradiation with synchrotron radiation (h{nu}>100 eV). At temperatures below 300 deg. C, a two-dimensionally flat film continues to grow with the surface tightly passivated by a GeH{sub x} hydride layer. At temperatures above 350 deg. C, dangling bonds are partially terminated with hydrogen atoms while Ge adatoms are highly mobile, resulting in a nonuniform nucleation that creates the islands. Small islands merge into a few-hundred-nanometer-tall islands surrounded by the (113)-face sidewalls. This kinetic roughening continues until the nucleation on the (001) plane ceases due to the buildup of the GeH{sub x} layer. Once the surface free energy is minimized by the hydrogen termination, flattening of the islands proceeds to reduce the chemical potential of the system. The valleys between the islands are preferentially filled, and the film is eventually converted into a smooth epilayer with no memory of the initial roughening.

  20. Mutual relation among lattice distortion, Hall effect property and band edge cathodoluminescence of heavily-boron-doped microwave-plasma CVD diamond films homoepitaxially grown on vicinal (001) high-pressure/high-temperature-synthesized Ib substrates

    NASA Astrophysics Data System (ADS)

    Mori, Reona; Maida, Osamu; Ito, Toshimichi

    2015-04-01

    We have investigated properties of heavily-B-doped diamond (HBD) films homoepitaxially grown with boron-to-carbon (B/C) mole ratios ranging from 1000 to 5000 ppm in the source gas mainly by using X-Ray diffraction (XRD), cathodoluminescence (CL), and Hall effect measurements. Each HBD layer was deposited on a vicinal (001) substrate of high-pressure/high-temperature synthesized Ib-type diamond with 5° misorientation angle by means of high-power-density microwave-plasma chemical-vapor-deposition method with a source gas composed of 4% CH4 in H2 and H2-diluted B(CH3)3. XRD data indicated that the lattice constant of the B-doped layer slightly decreased for the B/C ratios≤3000 ppm while slightly increasing for that of 5000 ppm, suggesting that for the latter HBD sample a part of the incorporated B atoms behaved differently from the remaining other B atoms. By contrast the Hall data indicated that all the HBD samples had a degenerate feature only at temperatures well below room temperature (RT), above which a semiconducting feature was evident, and that the density of the degenerate holes steeply increased from 1.3×1019 to 1.2×1021 cm-3 with increases in the incorporated B density, [B], from 1.2×1020 to 5.9×1020 cm-3. This drastic change in the hole density strongly suggested the presence of a [B]-dependent impurity band. Their evident near-band-edge CL spectra taken at RT and 85 K demonstrated that radiative transition features in the HBD layers considerably varied for the B/C ratios studied. The CL peaks were consistently assigned by assuming both the presence of an impurity band and a slight bandgap shrinkage. These observed features are discussed in relation to the energy separation between the low-mobility impurity band assumed and the valence band in the high-quality HBD layer which are not merged in energy.

  1. When is one layer complete? Using simultaneous in-situ RHEED and x-ray reflectivity to map layer-by-layer thin-film oxide growth

    NASA Astrophysics Data System (ADS)

    Sullivan, M. C.; Ward, M. J.; Joress, H.; Gutierrez-Llorente, A.; White, A. E.; Woll, A.; Brock, J. D.

    2014-03-01

    The most popular tool for characterizing in situ layer-by-layer growth is Reflection High-Energy Electron Diffraction (RHEED). X-ray reflectivity can also be used to study layer-by-layer growth, as long as the incident angle of the x-rays is far from a Bragg peak. During layer-by-layer homoepitaxial growth, both the RHEED intensity and the reflected x-ray intensity will oscillate, and each complete oscillation indicates the addition of one layer of material. However, it is well documented, but not well understood, that the maxima in the RHEED intensity oscillations do not necessarily occur at the completion of a layer. In contrast, the maxima in the x-ray intensity oscillations do occur at the completion of a layer, thus the RHEED and x-ray oscillations are rarely in phase. We present our results on simultaneous in situ x-ray reflectivity and RHEED during layer-by-layer growth of SrTiO3 and discuss how to determine the completion of a layer for RHEED oscillations independent of the phase of the RHEED oscillation. Supported by DOE Office of Basic Energy Sciences Award DE-SC0001086, CHESS is supported by the NSF & NIH/NIGMS via NSF award DMR-0936384.

  2. Homoepitaxial seeding and growth of bulk AlN by sublimation

    NASA Astrophysics Data System (ADS)

    Hartmann, Carsten; Wollweber, Jürgen; Seitz, Christoph; Albrecht, Martin; Fornari, Roberto

    2008-03-01

    AlN boules, 35 mm in diameter and up to 25-mm long, were grown on TaC crucible lid in an inductively heated reactor. The growth rates range between 100 and 300 μm/h. The boules grown on TaC show a columnar structure mostly composed of <0 0 0 1> grains. The largest grains (4-5 mm in diameter) were sliced and used for subsequent growth runs. Successful epitaxial seeding and growth on the starting AlN wafer was demonstrated and confirmed by electron back-scatter diffraction (EBSD) measurements. Crystals were grown on both Al and N surfaces of the seeds up to a maximum diameter of about 9 mm so far. Formation of oxy-nitride layers, very detrimental to the further AlN deposition, could be avoided when starting from pre-sintered source powder. Secondary ion mass spectroscopy (SIMS) measurements on axial cuts revealed a relatively low oxygen content, with variable distribution along the growth direction (290 ppm near seed, 100 ppm near external surface).

  3. Formation of complex wedding-cake morphologies during homoepitaxial film growth of Ag on Ag(111): atomistic, step-dynamics, and continuum modeling

    NASA Astrophysics Data System (ADS)

    Li, Maozhi; Han, Yong; Thiel, P. A.; Evans, J. W.

    2009-02-01

    An atomistic lattice-gas model is developed which successfully describes all key features of the complex mounded morphologies which develop during deposition of Ag films on Ag(111) surfaces. We focus on this homoepitaxial thin film growth process below 200 K. The unstable multilayer growth mode derives from the presence of a large Ehrlich-Schwoebel step-edge barrier, for which we characterize both the step-orientation dependence and the magnitude. Step-dynamics modeling is applied to further characterize and elucidate the evolution of the vertical profiles of these wedding-cake-like mounds. Suitable coarse-graining of these step-dynamics equations leads to instructive continuum formulations for mound evolution.

  4. Observations of Screw Dislocation Driven Growth and Faceting During CVD Homoepitaxy on 4H-SiC On-Axis Mesa Arrays

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Trunek, Andrew J.; Powell, J. Anthony; Picard, Yoosuf N.; Twigg, Mark E.

    2009-01-01

    Previous studies of (0001) homoepitaxial growth carried out on arrays of small-area mesas etched into on-axis silicon-face 4H-SiC wafers have demonstrated that spiral growth emanating from at least one screw dislocation threading the mesa is necessary in order for a mesa to grow taller in the <0001> (c-axis vertical) direction while maintaining 4H stacking sequence [1]. However, even amongst mesas containing the screw dislocation step source necessary for vertical c-axis growth, we have observed striking differences in the height and faceting that evolve during prolonged homoepitaxial growths. This paper summarizes Atomic Force Microscopy (AFM), Electron Channeling Contrast Imaging (ECCI), Scanning Electron Microscopy (SEM), and optical microscopy observations of this phenomenon. These observations support our initially proposed model [2] that the observed large variation (for mesas where 3C-SiC nucleation has not occurred) is related to the lateral positioning of a screw dislocation step source within each etched mesa. When the screw dislocation step source is located close enough to the developing edge/sidewall facet of a mesa, the c-axis growth rate and facet angle are affected by the resulting interaction. In particular, the intersection (or near intersection) of the inward-sloping mesa sidewall facet with the screw dislocation appears to impede the rate at which the spiral provides new steps required for c-axis growth. Also, the inward slope of the sidewall facet during growth (relative to other sidewalls of the same mesa not near the screw dislocation) seems to be impeded by the screw dislocation. In contrast, mesas whose screw dislocations are centrally located grow vertically, but inward sloping sidewall facets shrink the area of the top (0001) growth surface almost to the point of vanishing.

  5. Boron concentration profiling by high angle annular dark field-scanning transmission electron microscopy in homoepitaxial δ-doped diamond layers

    SciTech Connect

    Araújo, D.; Alegre, M. P.; Piñero, J. C.; Fiori, A.; Bustarret, E.; Jomard, F.

    2013-07-22

    To develop further diamond related devices, the concentration and spatial location of dopants should be controlled down to the nanometer scale. Scanning transmission electron microscopy using the high angle annular dark field mode is shown to be sensitive to boron doping in diamond epilayers. An analytical procedure is described, whereby local boron concentrations above 10{sup 20} cm{sup −3} were quantitatively derived down to nanometer resolution from the signal dependence on thickness and boron content. Experimental boron local doping profiles measured on diamond p{sup −}/p{sup ++}/p{sup −} multilayers are compared to macroscopic profiles obtained by secondary ion mass spectrometry, avoiding reported artefacts.

  6. Self-organized homo-epitaxial growth in nonlinear optical BaAlBO3F2 crystal crossing lines patterned by laser in glass

    NASA Astrophysics Data System (ADS)

    Shinozaki, K.; Abe, S.; Honma, T.; Komatsu, T.

    2015-11-01

    Crystallization processing of glasses is important as a novel technique for the development of new optical materials, and laser-induced crystallization provides a new challenge in science and technology of materials. Nonlinear optical BaAlBO3F2 crystal lines with crossing, bending, and spiral shapes were patterned at the surface of 2NiO-49BaF2-24.5Al2O3-24.5B2O3 (mol%) and 2.9NiO-48.5BaF2-24.3Al2O3-24.3B2O3 (mol%) glasses by laser irradiation (Yb:YVO4 laser with a wavelength of 1080 nm) and the orientation state of BaAlBO3F2 crystals was examined from birefringence image observations. The birefringence images indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows along the laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of BaAlBO3F2 crystals changes gradually at the crossing and bending points. The model of "self-organized homo-epitaxial growth" is proposed for the crystal orientation at the crossing and bending points, as a new crystal growth science and engineering beyond the wise providence of nature.

  7. Narrow growth window for stoichiometric, layer-by-layer growth of LaAlO3 thin films using pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Golalikhani, M.; Lei, Q. Y.; Wolak, M. A.; Davidson, B. A.; Xi, X. X.

    2016-06-01

    We study the structure and surface morphology of the 100 nm homoepitaxial LaAlO3 films grown by pulsed laser deposition in a broad range of growth parameters. We show that there is a narrow window of growth conditions in which the stoichiometric, bulk-like structure is obtained while maintaining a 2-dimensional (2D) layer-by-layer growth mode. In our system, these optimum growth conditions are 100 mTorr background pressure with laser energy density 1.5-2 J/cm2. The sensitivity to growth conditions of the stoichiometry and structure of LaAlO3 films can have a crucial role in the 2-D electron gas formed at the LaAlO3/SrTiO3 interface.

  8. Geometric modeling of homoepitaxial CVD diamond growth: I. The {1 0 0}{1 1 1}{1 1 0}{1 1 3} system

    NASA Astrophysics Data System (ADS)

    Silva, F.; Bonnin, X.; Achard, J.; Brinza, O.; Michau, A.; Gicquel, A.

    2008-01-01

    Plasma-assisted CVD homoepitaxial diamond growth is a process that must satisfy many stringent requirements to meet industrial applications, particularly in high-power electronics. Purity control and crystalline quality of the obtained samples are of paramount importance and their optimization is a subject of active research. In the process of such studies, we have obtained high purity CVD diamond monocrystals with unusual morphologies, namely with apparent {1 1 3} stable faces. This phenomenon has led us to examine the process of CVD diamond growth and build up a 3D geometrical model, presented here, describing the film growth as a function of time. The model has been able to successfully describe the morphology of our obtained crystals and can be used as a predictive tool to predetermine the shape and size of a diamond crystal grown in a given process configuration. This renders accessible control of desirable properties such as largest usable diamond surface area and/or film thickness, before the cutting and polishing manufacture steps take place. The two latter steps are more sensitive to the geometry of the growth sectors, which will be addressed in a companion paper. Our model, applicable to the growth of any cubic lattice material, establishes a complete mapping of the final morphology state of growing diamond, as a function of the growth rates of the crystalline planes considered, namely {1 0 0}, {1 1 1}, {1 1 0}, and {1 1 3} planes, all of which have been observed experimentally in diamond films. The model makes no claim as to the stability of the obtained faces, such as the occurrence of non-epitaxial crystallites or twinning. It is also possible to deduce transient behavior of the crystal morphology as growth time is increased. The model conclusions are presented in the form of a series of diagrams, which trace the existence (and dominance) boundaries of each face type, in presence of the others, and where each boundary crossing represent a topology

  9. Influence of silicon dioxide capping layers on pore characteristics in nanocrystalline silicon membranes.

    PubMed

    Qi, Chengzhu; Striemer, Christopher C; Gaborski, Thomas R; McGrath, James L; Fauchet, Philippe M

    2015-02-01

    Porous nanocrystalline silicon (pnc-Si) membranes are a new class of membrane material with promising applications in biological separations. Pores are formed in a silicon film sandwiched between nm thick silicon dioxide layers during rapid thermal annealing. Controlling pore size is critical in the size-dependent separation applications. In this work, we systematically studied the influence of the silicon dioxide capping layers on pnc-Si membranes. Even a single nm thick top oxide layer is enough to switch from agglomeration to pore formation after annealing. Both the pore size and porosity increase with the thickness of the top oxide, but quickly reach a plateau after 10 nm of oxide. The bottom oxide layer acts as a barrier layer to prevent the a-Si film from undergoing homo-epitaxial growth during annealing. Both the pore size and porosity decrease as the thickness of the bottom oxide layer increases to 100 nm. The decrease of the pore size and porosity is correlated with the increased roughness of the bottom oxide layer, which hinders nanocrystal nucleation and nanopore formation.

  10. Boundary Layer

    NASA Technical Reports Server (NTRS)

    Loitsianskii. L. G.

    1956-01-01

    The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.

  11. Calibration of an isotopically enriched carbon-13 layer pressure sensor to 156 GPa in a diamond anvil cell

    SciTech Connect

    Qiu,W.; Baker, P.; Velisavljevic, N.; Vohra, Y.; Weir, S.

    2006-01-01

    An isotopically enriched {sup 13}C homoepitaxial diamond layer of 6{+-}1 {mu}m thickness was grown on top of a brilliant cut diamond anvil by a microwave plasma chemical vapor deposition process for application as a pressure sensor. This isotopically enriched diamond tip was then used in conjunction with a natural isotopic abundance diamond anvil to generate high pressure on the sample. We provide a calibration for the {sup 13}C Raman mode of this extremely thin epitaxial layer to 156 GPa using ruby fluorescence and the equation of state of copper as secondary pressure standards. The nonlinear calibration of the {sup 13}C Raman mode pressure sensor is compared with similar calibrations of {sup 12}C Raman edge and a good agreement is obtained. The Raman signal from the {sup 13}C epitaxial layer remained a distinct singlet to 156 GPa, and pressure calibration is independent of sample mechanical strength or the diamond anvil geometry. The use of even thinner layer would allow calibration further into ultrahigh pressure regime where the use of other optical sensors has proven to be difficult.

  12. Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum

    NASA Astrophysics Data System (ADS)

    Jokubavicius, Valdas; Sun, Jianwu; Liu, Xinyu; Yazdi, Gholamreza; Ivanov, Ivan. G.; Yakimova, Rositsa; Syväjärvi, Mikael

    2016-08-01

    We demonstrate growth of thick SiC layers (100-200 μm) on nominally on-axis hexagonal substrates using sublimation epitaxy in vacuum (10-5 mbar) at temperatures varying from 1700 to 1975 °C with growth rates up to 270 μm/h and 70 μm/h for 6H- and 4H-SiC, respectively. The stability of hexagonal polytypes are related to process growth parameters and temperature profile which can be engineered using different thermal insulation materials and adjustment of the induction coil position with respect to the graphite crucible. We show that there exists a range of growth rates for which single-hexagonal polytype free of foreign polytype inclusions can be maintained. Further on, foreign polytypes like 3C-SiC can be stabilized by moving out of the process window. The applicability of on-axis growth is demonstrated by growing a 200 μm thick homoepitaxial 6H-SiC layer co-doped with nitrogen and boron in a range of 1018 cm-3 at a growth rate of about 270 μm/h. Such layers are of interest as a near UV to visible light converters in a monolithic white light emitting diode concept, where subsequent nitride-stack growth benefits from the on-axis orientation of the SiC layer.

  13. Spallanzani Layers

    NASA Technical Reports Server (NTRS)

    2006-01-01

    31 March 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a layered, light-toned mesa among other layered materials exposed in a mound that covers much of the floor of Spallanzani Crater.

    Location near: 58.3oS, 273.9oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

  14. Polar Layers

    NASA Technical Reports Server (NTRS)

    2005-01-01

    12 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a slope upon which are exposed some of the layered materials that underlie the south polar cap of Mars. The layers are generally considered to be sediments--perhaps dust--that may have been cemented by water ice.

    Location near: 84.1oS, 343.9oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  15. Layered materials

    NASA Astrophysics Data System (ADS)

    Johnson, David; Clarke, Simon; Wiley, John; Koumoto, Kunihito

    2014-06-01

    Layered compounds, materials with a large anisotropy to their bonding, electrical and/or magnetic properties, have been important in the development of solid state chemistry, physics and engineering applications. Layered materials were the initial test bed where chemists developed intercalation chemistry that evolved into the field of topochemical reactions where researchers are able to perform sequential steps to arrive at kinetically stable products that cannot be directly prepared by other approaches. Physicists have used layered compounds to discover and understand novel phenomena made more apparent through reduced dimensionality. The discovery of charge and spin density waves and more recently the remarkable discovery in condensed matter physics of the two-dimensional topological insulating state were discovered in two-dimensional materials. The understanding developed in two-dimensional materials enabled subsequent extension of these and other phenomena into three-dimensional materials. Layered compounds have also been used in many technologies as engineers and scientists used their unique properties to solve challenging technical problems (low temperature ion conduction for batteries, easy shear planes for lubrication in vacuum, edge decorated catalyst sites for catalytic removal of sulfur from oil, etc). The articles that are published in this issue provide an excellent overview of the spectrum of activities that are being pursued, as well as an introduction to some of the most established achievements in the field. Clusters of papers discussing thermoelectric properties, electronic structure and transport properties, growth of single two-dimensional layers, intercalation and more extensive topochemical reactions and the interleaving of two structures to form new materials highlight the breadth of current research in this area. These papers will hopefully serve as a useful guideline for the interested reader to different important aspects in this field and

  16. Polytype stability, microstructural evolution, and impurities at the interface of homoepitaxial 4H-silicon carbide(1120) thin films grown via hot-wall chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Bishop, Seann M. G.

    The electronic properties of 4H-SiC make it a leading semiconductor material for high-power applications. Despite advances in SiC crystal growth, devices fabricated in 4H-SiC(0001) continue to be limited by defects like micropipes, dislocations and stacking faults. Investigations performed here on non-basal 4H-SiC have demonstrated micropipe-free, 4H-SiC(112¯0) films comparable with conventional 4H-SiC(0001). Improved device performance has been achieved for p-i-n rectifiers fabricated in 4H-SiC(112¯0). Hot-wall chemical vapor deposition (CVD) is the most widely used growth process employed to meet the material demands for 4H-SiC-based high-power electronics; however, the suitability of this technique for the growth of thin films (<10 mum) is not well established. A detailed analysis of the epitaxial growth of 4H-SiC(112¯0) thin films by vertical, hot-wall CVD has been performed in this work. Two growth regimes were identified and termed sublimation growth and precursor growth. In the former, the SiC coating decomposes and results in the in-situ (sublimation) growth of epitaxial SiC films. It is proposed that in-situ layer aids in subsequent thin film growth from reactant gases. Transmission electron microscopy revealed areas without observable defects and an indistinguishable interface between the substrate and sublimation grown layer. Aluminum impurity concentrations to 3x10 18 cm-3 were identified near the interface with the substrate. The influence of these impurities on the cathodoluminescence spectrum of 4H-SiC was studied. A model based on boundary layer theory was developed to explain the origin and the profile of the aluminum impurities. Secondary ion mass spectrometry revealed the SiC coating to be the major source of aluminum impurities. An argon diluent reduced the concentration of aluminum at the interface to 2x1017 cm-3. Films deposited via precursor growth exhibited specular surfaces. Optical and structural characterization showed the films

  17. Polar Layers

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA02153 Polar Layers

    This image of the south polar region shows layered material. It is not known if the layers are formed yearly or if they form over the period of 10s to 100s of years or more.

    Image information: VIS instrument. Latitude -80.3N, Longitude 296.2E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  18. Double Layers in Astrophysics

    NASA Technical Reports Server (NTRS)

    Williams, Alton C. (Editor); Moorehead, Tauna W. (Editor)

    1987-01-01

    Topics addressed include: laboratory double layers; ion-acoustic double layers; pumping potential wells; ion phase-space vortices; weak double layers; electric fields and double layers in plasmas; auroral double layers; double layer formation in a plasma; beamed emission from gamma-ray burst source; double layers and extragalactic jets; and electric potential between plasma sheet clouds.

  19. Polar Layers

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03581 Polar Layers

    This image shows just one example of the bright and dark markings that appear during summer time. The marks are related to the polar layers. If you happen to see a wild-eyed guy sticking his tongue out at you, you'll know why this image qualifies for the old 'art' category of THEMIS releases.

    Image information: VIS instrument. Latitude 80.6S, Longitude 34.1E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  20. Layered Fan

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA03692 Layered Fan

    This beautiful fan deposit is located at the end of a mega-gully that empties into the southern trough of Coprates Chasma.

    Image information: VIS instrument. Latitude -14.9N, Longitude 299.8E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  1. Core layering

    NASA Astrophysics Data System (ADS)

    Jacobson, S. A.; Rubie, D. C.; Hernlund, J. W.; Morbidelli, A.

    2015-12-01

    We have created a planetary accretion and differentiation model that self-consistently builds and evolves Earth's core. From this model, we show that the core grows stably stratified as the result of rising metal-silicate equilibration temperatures and pressures, which increases the concentrations of light element impurities into each newer core addition. This stable stratification would naturally resist convection and frustrate the onset of a geodynamo, however, late giant impacts could mechanically mix the distinct accreted core layers creating large homogenous regions. Within these regions, a geodynamo may operate. From this model, we interpret the difference between the planetary magnetic fields of Earth and Venus as a difference in giant impact histories. Our planetary accretion model is a numerical N-body integration of the Grand Tack scenario [1]—the most successful terrestrial planet formation model to date [2,3]. Then, we take the accretion histories of Earth-like and Venus-like planets from this model and post-process the growth of each terrestrial planet according to a well-tested planetary differentiation model [4,5]. This model fits Earth's mantle by modifying the oxygen content of the pre-cursor planetesimals and embryos as well as the conditions of metal-silicate equilibration. Other non-volatile major, minor and trace elements included in the model are assumed to be in CI chondrite proportions. The results from this model across many simulated terrestrial planet growth histories are robust. If the kinetic energy delivered by larger impacts is neglected, the core of each planet grows with a strong stable stratification that would significantly impede convection. However, if giant impact mixing is very efficient or if the impact history delivers large impacts late, than the stable stratification can be removed. [1] Walsh et al. Nature 475 (2011) [2] O'Brien et al. Icarus 223 (2014) [3] Jacobson & Morbidelli PTRSA 372 (2014) [4] Rubie et al. EPSL 301

  2. High Performance Green LEDs by Homoepitaxial

    SciTech Connect

    Wetzel, Christian; Schubert, E Fred

    2009-11-22

    This work's objective was the development of processes to double or triple the light output power from green and deep green (525 - 555 nm) AlGaInN light emitting diode (LED) dies within 3 years in reference to the Lumileds Luxeon II. The project paid particular effort to all aspects of the internal generation efficiency of light. LEDs in this spectral region show the highest potential for significant performance boosts and enable the realization of phosphor-free white LEDs comprised by red-green-blue LED modules. Such modules will perform at and outperform the efficacy target projections for white-light LED systems in the Department of Energy's accelerated roadmap of the SSL initiative.

  3. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    PubMed Central

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-01-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate. PMID:27756906

  4. Burning Graphene Layer-by-Layer.

    PubMed

    Ermakov, Victor A; Alaferdov, Andrei V; Vaz, Alfredo R; Perim, Eric; Autreto, Pedro A S; Paupitz, Ricardo; Galvao, Douglas S; Moshkalev, Stanislav A

    2015-01-01

    Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material.

  5. Burning Graphene Layer-by-Layer.

    PubMed

    Ermakov, Victor A; Alaferdov, Andrei V; Vaz, Alfredo R; Perim, Eric; Autreto, Pedro A S; Paupitz, Ricardo; Galvao, Douglas S; Moshkalev, Stanislav A

    2015-01-01

    Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material. PMID:26100466

  6. Modelling Layer parallel stylolites

    NASA Astrophysics Data System (ADS)

    Koehn, Daniel; Pataki Rood, Daisy; Beaudoin, Nicolas

    2016-04-01

    We modeled the geometrical roughening of mainly layer-dominated stylolites in order to understand their structural evolution, to present an advanced classification of stylolite shapes and to relate this classification to chemical compaction and stylolite sealing capabilities. Our simulations show that layer-dominated stylolites can grow in three distinct stages, an initial slow nucleation, a fast layer-pinning phase and a final freezing stage if the layer dissolves completely during growth. Dissolution of the pinning layer and thus destruction of the compaction tracking capabilities is a function of the background noise in the rock and the dissolution rate of the layer itself. Low background noise needs a slower dissolving layer for pinning to be successful but produces flatter teeth than higher background noise. We present an advanced classification based on our simulations and separate stylolites into four classes: rectangular layer type, seismogram pinning type, suture/sharp peak type and simple wave-like type.

  7. Photonic layered media

    DOEpatents

    Fleming, James G.; Lin, Shawn-Yu

    2002-01-01

    A new class of structured dielectric media which exhibit significant photonic bandstructure has been invented. The new structures, called photonic layered media, are easy to fabricate using existing layer-by-layer growth techniques, and offer the ability to significantly extend our practical ability to tailor the properties of such optical materials.

  8. Scintillator reflective layer coextrusion

    DOEpatents

    Yun, Jae-Chul; Para, Adam

    2001-01-01

    A polymeric scintillator has a reflective layer adhered to the exterior surface thereof. The reflective layer comprises a reflective pigment and an adhesive binder. The adhesive binder includes polymeric material from which the scintillator is formed. A method of forming the polymeric scintillator having a reflective layer adhered to the exterior surface thereof is also provided. The method includes the steps of (a) extruding an inner core member from a first amount of polymeric scintillator material, and (b) coextruding an outer reflective layer on the exterior surface of the inner core member. The outer reflective layer comprises a reflective pigment and a second amount of the polymeric scintillator material.

  9. Piezoelectric Resonator with Two Layers

    NASA Technical Reports Server (NTRS)

    Stephanou, Philip J. (Inventor); Black, Justin P. (Inventor)

    2013-01-01

    A piezoelectric resonator device includes: a top electrode layer with a patterned structure, a top piezoelectric layer adjacent to the top layer, a middle metal layer adjacent to the top piezoelectric layer opposite the top layer, a bottom piezoelectric layer adjacent to the middle layer opposite the top piezoelectric layer, and a bottom electrode layer with a patterned structure and adjacent to the bottom piezoelectric layer opposite the middle layer. The top layer includes a first plurality of electrodes inter-digitated with a second plurality of electrodes. A first one of the electrodes in the top layer and a first one of the electrodes in the bottom layer are coupled to a first contact, and a second one of the electrodes in the top layer and a second one of the electrodes in the bottom layer are coupled to a second contact.

  10. Layered plasma polymer composite membranes

    DOEpatents

    Babcock, W.C.

    1994-10-11

    Layered plasma polymer composite fluid separation membranes are disclosed, which comprise alternating selective and permeable layers for a total of at least 2n layers, where n is [>=]2 and is the number of selective layers. 2 figs.

  11. Layers and Erosion and more Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 4 November 2003

    This image is located within a set of eroded layered rocks known as the Medusae Fossae Formation. Careful inspection of this image reveals four separate layers. Starting at the bottom of the image, as well as the bottom of the sequence of layers, is a somewhat hilly, cratered plain. Above that is a mud or lava flow with a lobate edge that is characteristic of fluid flow. Above that is a layer with a spectacular rayed crater. This layer shows linear erosional patterns that are probably caused by persistent wind abrasion, typical of rocks in this area. And finally, a more blocky unit lies on top, mostly eroded away.

    Image information: VIS instrument. Latitude 3.6, Longitude 218.6 East (141.4 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  12. Multiple density layered insulator

    DOEpatents

    Alger, Terry W.

    1994-01-01

    A multiple density layered insulator for use with a laser is disclosed wh provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation.

  13. Multiple density layered insulator

    DOEpatents

    Alger, T.W.

    1994-09-06

    A multiple density layered insulator for use with a laser is disclosed which provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation. 4 figs.

  14. The Atmospheric Boundary Layer

    ERIC Educational Resources Information Center

    Tennekes, Hendrik

    1974-01-01

    Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

  15. Multiple layer insulation cover

    DOEpatents

    Farrell, James J.; Donohoe, Anthony J.

    1981-11-03

    A multiple layer insulation cover for preventing heat loss in, for example, a greenhouse, is disclosed. The cover is comprised of spaced layers of thin foil covered fabric separated from each other by air spaces. The spacing is accomplished by the inflation of spaced air bladders which are integrally formed in the cover and to which the layers of the cover are secured. The bladders are inflated after the cover has been deployed in its intended use to separate the layers of the foil material. The sizes of the material layers are selected to compensate for sagging across the width of the cover so that the desired spacing is uniformly maintained when the cover has been deployed. The bladders are deflated as the cover is stored thereby expediting the storage process and reducing the amount of storage space required.

  16. Anomalous Fe diffusion in Si-ion-implanted β-Ga2O3 and its suppression in Ga2O3 transistor structures through highly resistive buffer layers

    NASA Astrophysics Data System (ADS)

    Wong, Man Hoi; Sasaki, Kohei; Kuramata, Akito; Yamakoshi, Shigenobu; Higashiwaki, Masataka

    2015-01-01

    The thermal behavior of Fe as a compensating acceptor impurity in β-Ga2O3 (010) was studied in view of growing interests in semi-insulating Fe-doped Ga2O3 substrates for the realization of high-performance Ga2O3 field-effect transistors (FETs). An anomalous redistribution of Fe beyond the extent of intrinsic thermal diffusion was revealed by secondary ion mass spectroscopy in device-relevant structures where Ga2O3 grown homoepitaxially on Fe-doped substrates was doped by Si ion (Si+) implantation and annealed at high temperatures. The enhanced Fe diffusion was attributed to an athermal process involving intrinsic defects from the region of implantation damage. An undoped Ga2O3 buffer between the Si+-implanted layer and the Fe-doped substrate effectively suppressed Fe outdiffusion by protecting the substrate against unintentional ion damage or defects from a remote source, thereby preserving the electrical integrity of the Si-doped material. Temperature-dependent current-voltage measurements indicated that the undoped Ga2O3 buffer was highly resistive with inter-device leakage attributable to surface conduction via a variable-range hopping mechanism. The buffer scheme, together with dielectric passivation to eliminate surface leakage, was proposed to constitute an integral process module for future lateral Ga2O3 FET devices.

  17. Concentric layer ramjet fuel

    SciTech Connect

    Burdette, G.W.; Francis, J.P.

    1988-03-08

    This patent describes a solid fuel ramjet grain comprising concentric layers of solid ramjet fuel having a perforation therethrough along the center axis of the grain. The performation is connected to a combustion after-chamber. The solid ramjet fuel layers comprises a pure hydroxyl-terminated polybutadiene hydrocarbon fuel or a mixture of a hydroxyl-terminated polybutadiene hydrocarbon fuel and from about 5 to about 60 percent by weight of an additive to increase the fuel regression rate selected from the group consisting of magnesium, boron carbide, aluminum, and zirconium such that, when buried in the operation of the ramjet, each fuel layer produces a different level of thrust.

  18. Compliant layer chucking surface

    DOEpatents

    Blaedel, Kenneth L.; Spence, Paul A.; Thompson, Samuel L.

    2004-12-28

    A method and apparatus are described wherein a thin layer of complaint material is deposited on the surface of a chuck to mitigate the deformation that an entrapped particle might cause in the part, such as a mask or a wafer, that is clamped to the chuck. The harder particle will embed into the softer layer as the clamping pressure is applied. The material composing the thin layer could be a metal or a polymer for vacuum or electrostatic chucks. It may be deposited in various patterns to affect an interrupted surface, such as that of a "pin" chuck, thereby reducing the probability of entrapping a particle.

  19. Multi-layer coatings

    DOEpatents

    Maghsoodi, Sina; Brophy, Brenor L.; Abrams, Ze'ev R.; Gonsalves, Peter R.

    2016-06-28

    Disclosed herein are coating materials and methods for applying a top-layer coating that is durable, abrasion resistant, highly transparent, hydrophobic, low-friction, moisture-sealing, anti-soiling, and self-cleaning to an existing conventional high temperature anti-reflective coating. The top coat imparts superior durability performance and new properties to the under-laying conventional high temperature anti-reflective coating without reducing the anti-reflectiveness of the coating. Methods and data for optimizing the relative thickness of the under-layer high temperature anti-reflective coating and the top-layer thickness for optimizing optical performance are also disclosed.

  20. The Application of Layer Theory to Design: The Control Layer

    ERIC Educational Resources Information Center

    Gibbons, Andrew S.; Langton, Matthew B.

    2016-01-01

    A theory of design layers proposed by Gibbons ("An Architectural Approach to Instructional Design." Routledge, New York, 2014) asserts that each layer of an instructional design is related to a body of theory closely associated with the concerns of that particular layer. This study focuses on one layer, the control layer, examining…

  1. Terby's Layered Rocks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    14 March 2004 Layered rock outcrops are common all across Mars, and the Mars rover, Opportunity, has recently investigated some layered rocks in Meridiani Planum. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layered sedimentary rocks in northern Terby Crater, located just north of the giant Hellas Basin near 27.5oS, 285.8oW. Hundreds of layers are exposed in a deposit several kilometers thick within Terby. A history of events that shaped the northern Hellas region is recorded in these rocks, just waiting for a person or robot to investigate. The picture covers an area 3 km (1.9 mi) across. Sunlight illuminates the scene from the left.

  2. North Polar Layers, Mars

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This view shows the basal layers of Mars' north polar layered deposits. The floor of Chasma Boreale is at the bottom of the image. This is a sub-image of a larger view imaged by the High Resolution Imaging Science Experiment (HiRISE) on NASA's Mars Reconnaissance Orbiter on Oct. 1, 2006. The resolution is 64 centimeters (25 inches) per pixel, and the scene is 568 meters (621 yards) wide.

  3. Boundary Layer Relaminarization Device

    NASA Technical Reports Server (NTRS)

    Creel, Theodore R. (Inventor)

    1993-01-01

    Relamination of a boundary layer formed in supersonic flow over the leading edge of a swept airfoil is accomplished using at least one band, especially a quadrangular band, and most preferably a square band. Each band conforms to the leading edge and the upper and lower surfaces of the airfoil as an integral part thereof and extends perpendicularly from the leading edge. Each band has a height of about two times the thickness of the maximum expected boundary layer.

  4. Structured luminescence conversion layer

    DOEpatents

    Berben, Dirk; Antoniadis, Homer; Jermann, Frank; Krummacher, Benjamin Claus; Von Malm, Norwin; Zachau, Martin

    2012-12-11

    An apparatus device such as a light source is disclosed which has an OLED device and a structured luminescence conversion layer deposited on the substrate or transparent electrode of said OLED device and on the exterior of said OLED device. The structured luminescence conversion layer contains regions such as color-changing and non-color-changing regions with particular shapes arranged in a particular pattern.

  5. Tests on Double Layer Metalization

    NASA Technical Reports Server (NTRS)

    Woo, D. S.

    1983-01-01

    28 page report describes experiments in fabrication of integrated circuits with double-layer metalization. Double-layer metalization requires much less silicon "real estate" and allows more flexibility in placement of circuit elements than does single-layer metalization.

  6. South Polar Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    2 July 2004 Beneath the ice caps of both martian poles lies extensive deposits of layered material. Whether the material includes ice is unknown. In the north polar region, some of the layers contain dark sand, others may consist of dust cemented by ice. The south polar layers are a little bit more challenging to understand. In most places, they have been covered by thin mantles of debris that mask the true nature of the layered material. This is the case, even in the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shown here. South polar layers were eroded to provide this spectacular view, but later the materials were almost uniformly covered with a material that, when the image is viewed at full resolution (click on image, above), has become cracked. This picture is located near 82.0oS, 72.4oW, and covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the upper left.

  7. Layered electrode for electrochemical cells

    DOEpatents

    Swathirajan, Swathy; Mikhail, Youssef M.

    2001-01-01

    There is provided an electrode structure comprising a current collector sheet and first and second layers of electrode material. Together, the layers improve catalyst utilization and water management.

  8. Layers in Terby Crater

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-407, 30 June 2003

    Whether on Earth or Mars, sedimentary rocks provide a record of past environments. Of course, it is difficult to read that record without being able to visit the site. However, the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) has revealed hundreds of locales on Mars at which sedimentary rocks are exposed at the surface. Terby Crater exhibits hundreds of layers of similar thickness and physical properties--some have speculated these may be the record of an ancient lake or sea. This MOC image shows some of the layer outcrops in Terby Crater. Fans of debris have eroded from the steep, layered slopes in some places. This picture covers an area 3 km (1.9 mi) wide near 27.5oS, 285.7oW. The image is illuminated from the upper left and was obtained in June 2003.

  9. Frosty North Polar Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-349, 3 May 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image is a springtime view of frost-covered layers revealed by an eroded scarp in the martian north polar cap. The layers are thought to consist of a mixture of dust, ice, and possibly sand. Some layers are known to be a source for dark sand that occurs in nearby dunes. During the summer, this surface would be considerably darker because most of the bright frost sublimes away during the spring season. The picture covers an area about 3 km (1.9 mi) wide near 85.2oN, 4.4oW. Sunlight illuminates the scene from the lower left.

  10. North Polar Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    3 December 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an exposure of finely-detailed layers in the martian north polar region. The polar ice cap, which is made up of frozen water (whereas the south polar cap is mostly frozen carbon dioxide), is underlain by a thick sequence of layers. Some have speculated that these layers may record the history of changes in martian climate during the past few hundreds of millions of years. This picture is located near 86.0oN, 30.2oW, and covers an area approximately 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.

  11. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

    1989-01-01

    Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

  12. Layered Systems Engineering Engines

    NASA Technical Reports Server (NTRS)

    Breidenthal, Julian C.; Overman, Marvin J.

    2009-01-01

    A notation is described for depicting the relationships between multiple, contemporaneous systems engineering efforts undertaken within a multi-layer system-of-systems hierarchy. We combined the concepts of remoteness of activity from the end customer, depiction of activity on a timeline, and data flow to create a new kind of diagram which we call a "Layered Vee Diagram." This notation is an advance over previous notations because it is able to be simultaneously precise about activity, level of granularity, product exchanges, and timing; these advances provide systems engineering managers a significantly improved ability to express and understand the relationships between many systems engineering efforts. Using the new notation, we obtain a key insight into the relationship between project duration and the strategy selected for chaining the systems engineering effort between layers, as well as insights into the costs, opportunities, and risks associated with alternate chaining strategies.

  13. Layered semiconductor neutron detectors

    DOEpatents

    Mao, Samuel S; Perry, Dale L

    2013-12-10

    Room temperature operating solid state hand held neutron detectors integrate one or more relatively thin layers of a high neutron interaction cross-section element or materials with semiconductor detectors. The high neutron interaction cross-section element (e.g., Gd, B or Li) or materials comprising at least one high neutron interaction cross-section element can be in the form of unstructured layers or micro- or nano-structured arrays. Such architecture provides high efficiency neutron detector devices by capturing substantially more carriers produced from high energy .alpha.-particles or .gamma.-photons generated by neutron interaction.

  14. Layers and Streaks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    6 December 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an outcrop of light-toned layered rock and a plethora of dark streaks on the floor of a crater in southern Noachis Terra. The streaks were created by dozens of dust devils which disrupted and perhaps removed some of the thin layer of dust that coats the surface. This view is located near 55.5oS, 333.4oW. The scene is illuminated by sunlight from the lower right. The 500 meter scale bar is approximately 547 yards long.

  15. North Polar Layer Exposure

    NASA Technical Reports Server (NTRS)

    2004-01-01

    20 November 2004 Both the north and south polar ice caps overlie a thick accumulation of layered material. For more than three decades, these deposits have been assumed to consist of a mixture of dust and ice. This October 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows some of the north polar layers exposed on a slope located near 79.1oN, 348.4oW. The image covers an area approximately 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  16. Sedimentary Rock Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    27 January 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layers of sedimentary rock in a crater in western Arabia Terra. Layered rock records the history of a place, but an orbiter image alone cannot tell the entire story. These materials record some past episodes of deposition of fine-grained material in an impact crater that is much larger than the image shown here. The picture is located near 3.4oN, 358.7oW, and covers an area 3 km (1.9 mi.) wide. Sunlight illuminates the scene from the lower left.

  17. Layers in Melas Chasma

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Click on image for larger annotated version

    This scene of layered deposits is from Melas Chasma, part of the Valles Marineris valley network. The area consists of a series of plateaus and cliffs that form a step-like terrain similar to the Grand Staircase-Escalante region of southwest Utah. The upper-right half of the image covers the highest plateau, and lower cliffs and plateaus step down in elevation toward the lower left of the image. Dunes of dark sand commonly cover the flat plateaus and distinct layers of bedrock are exposed in the cliffs. The orientations of these layers may help scientists to understand how the layers formed and the kind of environment that the layers formed in. Black rectangles on the left side of the image are areas where the image data was lost during transmission from Mars Reconnaissance Orbiter to Earth. This subscene [above] shows a series of boulder tracks on the left side of the image. The boulders fell from the cliffs above and left behind a series of small depressions. Each depression was made as the boulder bounced and rolled along the surface. In many cases, the tracks can be followed to the specific boulder that made them. Also visible in this subscene are cross-sections through the layered bedrock. This bedrock likely formed through settling of sand-sized particles out of the air or out of a body of water that has since drained away. These layers are 'cross-bedded', which means that subsequent layers are not parallel to each other but are instead oriented at an angle to other layers. The fact that these layers are cross-bedded indicates that the sand-sized particles were moved horizontally along the surface as they settled, just like sand dunes or ripples at the bottom of a stream. The size and shape of these cross-beds may help scientists to determine if the layers formed underwater or on land.

    Image PSP_001377_1685 was taken by the High Resolution Imaging

  18. Layered pavement systems

    NASA Astrophysics Data System (ADS)

    Numerous aspects of the mechanical and structural response of layered pavement systems are discussed. Subgrade moduli for soil that exhibits nonlinear behavior are predicted. The use of a pressure meter test to predict modulus is discussed. Load equivalency factors of triaxial loading for flexible pavements is discussed, as well as a constitutive equation for the permanent strain of sand subjected to cyclic loading.

  19. Layer-Cake Earth

    ERIC Educational Resources Information Center

    Tedford, Rebecca; Warny, Sophie

    2006-01-01

    In this article, the authors offer a safe, fun, effective way to introduce geology concepts to elementary school children of all ages: "coring" layer cakes. This activity introduces the concepts and challenges that geologists face and at the same time strengthens students' inferential, observational, and problem-solving skills. It also addresses…

  20. Martian Meteor Ionization Layers

    NASA Technical Reports Server (NTRS)

    Grebowsky, J. M.; Pesnell, W. D.

    1999-01-01

    Small interplanetary grains bombard Mars, like all the solar system planets, and, like all the planets with atmospheres, meteoric ion and atom layers form in the upper atmosphere. We have developed a comprehensive one-dimensional model of the Martian meteoric ionization layer including a full chemical scheme. A persistent layer of magnesium ions should exist around an altitude of 70 km. Unlike the terrestrial case, where the metallic ions are formed via charge-exchange with the ambient ions, Mg(+) in the Martian atmosphere is produced by photoionization. Nevertheless, the predicted metal layer peak densities for Earth and Mars are similar. Diffusion solutions, such as those presented here, should be a good approximation of the metallic ions in regions where the magnetic field is negligible and may provide a significant contribution to the nightside ionosphere. The low ultraviolet absorption of the Martian atmosphere may make Mars an excellent laboratory in which to study meteoric ablation. Resonance lines not seen in the spectra of terrestrial meteors may be visible to a surface observatory in the Martian highlands.

  1. Teaching the Double Layer.

    ERIC Educational Resources Information Center

    Bockris, J. O'M.

    1983-01-01

    Suggests various methods for teaching the double layer in electrochemistry courses. Topics addressed include measuring change in absolute potential difference (PD) at interphase, conventional electrode potential scale, analyzing absolute PD, metal-metal and overlap electron PDs, accumulation of material at interphase, thermodynamics of electrified…

  2. MITRE sensor layer prototype

    NASA Astrophysics Data System (ADS)

    Duff, Francis; McGarry, Donald; Zasada, David; Foote, Scott

    2009-05-01

    The MITRE Sensor Layer Prototype is an initial design effort to enable every sensor to help create new capabilities through collaborative data sharing. By making both upstream (raw) and downstream (processed) sensor data visible, users can access the specific level, type, and quantities of data needed to create new data products that were never anticipated by the original designers of the individual sensors. The major characteristic that sets sensor data services apart from typical enterprise services is the volume (on the order of multiple terabytes) of raw data that can be generated by most sensors. Traditional tightly coupled processing approaches extract pre-determined information from the incoming raw sensor data, format it, and send it to predetermined users. The community is rapidly reaching the conclusion that tightly coupled sensor processing loses too much potentially critical information.1 Hence upstream (raw and partially processed) data must be extracted, rapidly archived, and advertised to the enterprise for unanticipated uses. The authors believe layered sensing net-centric integration can be achieved through a standardize-encapsulate-syndicateaggregate- manipulate-process paradigm. The Sensor Layer Prototype's technical approach focuses on implementing this proof of concept framework to make sensor data visible, accessible and useful to the enterprise. To achieve this, a "raw" data tap between physical transducers associated with sensor arrays and the embedded sensor signal processing hardware and software has been exploited. Second, we encapsulate and expose both raw and partially processed data to the enterprise within the context of a service-oriented architecture. Third, we advertise the presence of multiple types, and multiple layers of data through geographic-enabled Really Simple Syndication (GeoRSS) services. These GeoRSS feeds are aggregated, manipulated, and filtered by a feed aggregator. After filtering these feeds to bring just the type

  3. Boundary layer transition studies

    NASA Technical Reports Server (NTRS)

    Watmuff, Jonathan H.

    1995-01-01

    A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated

  4. Peeling Back the Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    NASA's Mars Exploration Rover Spirit took this panoramic camera image of the rock target named 'Mazatzal' on sol 77 (March 22, 2004). It is a close-up look at the rock face and the targets that will be brushed and ground by the rock abrasion tool in upcoming sols.

    Mazatzal, like most rocks on Earth and Mars, has layers of material near its surface that provide clues about the history of the rock. Scientists believe that the top layer of Mazatzal is actually a coating of dust and possibly even salts. Under this light coating may be a more solid portion of the rock that has been chemically altered by weathering. Past this layer is the unaltered rock, which may give scientists the best information about how Mazatzal was formed.

    Because each layer reveals information about the formation and subsequent history of Mazatzal, it is important that scientists get a look at each of them. For this reason, they have developed a multi-part strategy to use the rock abrasion tool to systematically peel back Mazatzal's layers and analyze what's underneath with the rover's microscopic imager, and its Moessbauer and alpha particle X-ray spectrometers.

    The strategy began on sol 77 when scientists used the microscopic imager to get a closer look at targets on Mazatzal named 'New York,' 'Illinois' and 'Arizona.' These rock areas were targeted because they posed the best opportunity for successfully using the rock abrasion tool; Arizona also allowed for a close-up look at a range of tones. On sol 78, Spirit's rock abrasion tool will do a light brushing on the Illinois target to preserve some of the surface layers. Then, a brushing of the New York target should remove the top coating of any dust and salts and perhaps reveal the chemically altered rock underneath. Finally, on sol 79, the rock abrasion tool will be commanded to grind into the New York target, which will give scientists the best chance of observing Mazatzal's interior.

    The Mazatzal targets were named

  5. Layers in Oudemans

    NASA Technical Reports Server (NTRS)

    2004-01-01

    24 July 2004 The central peak of Oudemans Crater, located near 10.0oS, 92.1oW, contains light-toned, layered rock that has been uplifted and severely tilted. When seen from overhead, as in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, the dipping layered rocks form a banded pattern on the landscape. These rocks were once in the ground beneath the present floor of Oudemans Crater. The impact which produced the crater brought these rocks to the surface. They are light-toned and very similar to some of the varieties of sedimentary rock outcrops found in portions of the vast Valles Marineris trough system. Oudemans Crater sits on the edge of the Valles Marineris, near the intersection of the Labyrinthus Noctis and Ius Chasma. The image is illuminated by sunlight from the left/upper left. The 180 meter scale bar is equal to about 197 yards.

  6. Crack layer theory

    NASA Technical Reports Server (NTRS)

    Chudnovsky, A.

    1984-01-01

    A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

  7. Layered seal for turbomachinery

    DOEpatents

    Sarawate, Neelesh Nandkumar; Morgan, Victor John; Weber, David Wayne

    2015-11-20

    The present application provides seal assemblies for reducing leakages between adjacent components of turbomachinery. The seal assemblies may include outer shims, and at least a portion of the outer shims may be substantially impervious. At least one of the outer shims may be configured for sealing engagement with seal slots of the adjacent components. The seal assemblies may also include at least one of an inner shim and a filler layer positioned between the outer shims. The at least one inner shim may be substantially solid and the at least one filler layer may be relatively porous. The seal assemblies may be sufficiently flexible to account for misalignment between the adjacent components, sufficiently stiff to meet assembly requirements, and sufficiently robust to operating meet requirements associated with turbomachinery.

  8. Layered Composite Analysis Capability

    NASA Technical Reports Server (NTRS)

    Narayanaswami, R.; Cole, J. G.

    1985-01-01

    Laminated composite material construction is gaining popularity within industry as an attractive alternative to metallic designs where high strength at reduced weights is of prime consideration. This has necessitated the development of an effective analysis capability for the static, dynamic and buckling analyses of structural components constructed of layered composites. Theoretical and user aspects of layered composite analysis and its incorporation into CSA/NASTRAN are discussed. The availability of stress and strain based failure criteria is described which aids the user in reviewing the voluminous output normally produced in such analyses. Simple strategies to obtain minimum weight designs of composite structures are discussed. Several example problems are presented to demonstrate the accuracy and user convenient features of the capability.

  9. North Polar Layers

    NASA Technical Reports Server (NTRS)

    2006-01-01

    13 January 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a slope on which layered materials are exposed by erosion in the north polar region of Mars. Wind streaks are also evident in this summertime scene. The layers that make up the material beneath the ice of the north polar residual cap are typically considered to be a mixture of some amount of dust and ice, but the proportions of these constituents are not known.

    Location near: 82.6oN, 298.1oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Summer

  10. Layered Rocks in Crater

    NASA Technical Reports Server (NTRS)

    2004-01-01

    19 June 2004 Exposures of layered, sedimentary rock are common on Mars. From the rock outcrops examined by the Mars Exploration Rover, Opportunity, in Meridiani Planum to the sequence in Gale Crater's central mound that is twice the thickness of of the sedimentary rocks exposed by Arizona's Grand Canyon, Mars presents a world of sediment to study. This unusual example, imaged by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), shows eroded layer outcrops in a crater in Terra Tyrrhena near 15.4oS, 270.5oW. Sedimentary rocks provide a record of past climates and events. Perhaps someday the story told by the rocks in this image will be known via careful field work. The image covers an area about 3 km (1.9 mi) wide and is illuminated by sunlight from the left.

  11. Sedimentary Rock Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-348, 2 May 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image acquired in March 2003 shows dozens of repeated layers of sedimentary rock in a western Arabia Terra crater at 8oN, 7oW. Wind has sculpted the layered forms into hills somewhat elongated toward the lower left (southwest). The dark patches at the bottom (south) end of the image are drifts of windblown sand. These sedimentary rocks might indicate that the crater was once the site of a lake--or they may result from deposition by wind in a completely dry, desert environment. Either way, these rocks have something important to say about the geologic history of Mars. The area shown is about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the left.

  12. Layered Rock Ahead

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Now that solar conjunction is over so that communication between Earth and Mars is no longer blocked by the Sun, NASA's Mars Exploration Rover Spirit is continuing its trek through the 'Columbia Hills' in Gusev Crater. Straight ahead, in the foreground of this image, is a horizontally layered rock dubbed 'Tetl,' which scientists hope to investigate. Layering can be either volcanic or sedimentary in origin; researchers aim to determine which of these processes created this rock. If for some reason this particular rock is not favorably positioned for grinding and examination by the toolbox of instruments on the rover's robotic arm, Spirit will be within short reach of another similar rock, dubbed 'Coba,' just to the right, toward the middle of this image. Spirit took this image with its navigation camera on its 263rd martian day, or sol (Sept. 28, 2004).

  13. Origins of Igneous Layering

    NASA Astrophysics Data System (ADS)

    Marsh, Bruce

    Anyone who has ever seen a photo of a layered intrusion, let alone visited one first hand, or even seen a thin section from one, cannot help but be impressed by the stunning record of crystal growth and deposition. Such bodies stand as majestic monuments of undeniable evidence that intricate magmatic processes exist, processes that couple crystallization, convection, and crystal sorting to form rocks so highly ordered and beautiful that they are a wonder to behold. These are the altars to which petrologists must carry their conceived petrologic processes for approval.Although significant in number, the best layered intrusions seem to be found almost always in remote places. Their names, Bushveld, Muskox, Kiglapait, Stillwater, Duke Island, Skaergaard, Rhum, ring through igneous petrology almost as historic military battles (Saratoga, Antietam, Bull Run, Manassas, Gettysburg) do through American history. People who have worked on such bodies are almost folk heros: Wager, Deer, Brown, Jackson, Hess, Irvine, McBirney, Morse; these names are petrologic household words. Yet with all this fanfare and reverence, layered instrusions are nearly thought of as period pieces, extreme examples of what can happen, but not generally what does. This is now all changing with the increasing realization that these bodies are perhaps highly representative of all magmatic bodies. They are simply more dynamically complete, containing more of the full range of interactions, and of course, exposing a more complete record. They are one end of a spectrum containing lava flows, lava lakes, large sills, plutons, and layered intrusions. This book uniquely covers this range with an abundance of first-hand field observations and a good dose of process conceptualization, magma physics, and crystal growth kinetics.

  14. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

    1984-01-01

    High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.

  15. Tropical tropopause layer

    NASA Astrophysics Data System (ADS)

    Fueglistaler, S.; Dessler, A. E.; Dunkerton, T. J.; Folkins, I.; Fu, Q.; Mote, P. W.

    2009-03-01

    Observations of temperature, winds, and atmospheric trace gases suggest that the transition from troposphere to stratosphere occurs in a layer, rather than at a sharp "tropopause." In the tropics, this layer is often called the "tropical tropopause layer" (TTL). We present an overview of observations in the TTL and discuss the radiative, dynamical, and chemical processes that lead to its time-varying, three-dimensional structure. We present a synthesis definition with a bottom at 150 hPa, 355 K, 14 km (pressure, potential temperature, and altitude) and a top at 70 hPa, 425 K, 18.5 km. Laterally, the TTL is bounded by the position of the subtropical jets. We highlight recent progress in understanding of the TTL but emphasize that a number of processes, notably deep, possibly overshooting convection, remain not well understood. The TTL acts in many ways as a "gate" to the stratosphere, and understanding all relevant processes is of great importance for reliable predictions of future stratospheric ozone and climate.

  16. Multifunctional layered magnetic composites.

    PubMed

    Siglreitmeier, Maria; Wu, Baohu; Kollmann, Tina; Neubauer, Martin; Nagy, Gergely; Schwahn, Dietmar; Pipich, Vitaliy; Faivre, Damien; Zahn, Dirk; Fery, Andreas; Cölfen, Helmut

    2015-01-01

    A fabrication method of a multifunctional hybrid material is achieved by using the insoluble organic nacre matrix of the Haliotis laevigata shell infiltrated with gelatin as a confined reaction environment. Inside this organic scaffold magnetite nanoparticles (MNPs) are synthesized. The amount of MNPs can be controlled through the synthesis protocol therefore mineral loadings starting from 15 wt % up to 65 wt % can be realized. The demineralized organic nacre matrix is characterized by small-angle and very-small-angle neutron scattering (SANS and VSANS) showing an unchanged organic matrix structure after demineralization compared to the original mineralized nacre reference. Light microscopy and confocal laser scanning microscopy studies of stained samples show the presence of insoluble proteins at the chitin surface but not between the chitin layers. Successful and homogeneous gelatin infiltration in between the chitin layers can be shown. The hybrid material is characterized by TEM and shows a layered structure filled with MNPs with a size of around 10 nm. Magnetic analysis of the material demonstrates superparamagnetic behavior as characteristic for the particle size. Simulation studies show the potential of collagen and chitin to act as nucleators, where there is a slight preference of chitin over collagen as a nucleator for magnetite. Colloidal-probe AFM measurements demonstrate that introduction of a ferrogel into the chitin matrix leads to a certain increase in the stiffness of the composite material. PMID:25671158

  17. Multifunctional layered magnetic composites

    PubMed Central

    Siglreitmeier, Maria; Wu, Baohu; Kollmann, Tina; Neubauer, Martin; Nagy, Gergely; Schwahn, Dietmar; Pipich, Vitaliy; Faivre, Damien; Zahn, Dirk; Fery, Andreas

    2015-01-01

    Summary A fabrication method of a multifunctional hybrid material is achieved by using the insoluble organic nacre matrix of the Haliotis laevigata shell infiltrated with gelatin as a confined reaction environment. Inside this organic scaffold magnetite nanoparticles (MNPs) are synthesized. The amount of MNPs can be controlled through the synthesis protocol therefore mineral loadings starting from 15 wt % up to 65 wt % can be realized. The demineralized organic nacre matrix is characterized by small-angle and very-small-angle neutron scattering (SANS and VSANS) showing an unchanged organic matrix structure after demineralization compared to the original mineralized nacre reference. Light microscopy and confocal laser scanning microscopy studies of stained samples show the presence of insoluble proteins at the chitin surface but not between the chitin layers. Successful and homogeneous gelatin infiltration in between the chitin layers can be shown. The hybrid material is characterized by TEM and shows a layered structure filled with MNPs with a size of around 10 nm. Magnetic analysis of the material demonstrates superparamagnetic behavior as characteristic for the particle size. Simulation studies show the potential of collagen and chitin to act as nucleators, where there is a slight preference of chitin over collagen as a nucleator for magnetite. Colloidal-probe AFM measurements demonstrate that introduction of a ferrogel into the chitin matrix leads to a certain increase in the stiffness of the composite material. PMID:25671158

  18. Modern Thin-Layer Chromatography.

    ERIC Educational Resources Information Center

    Poole, Colin F.; Poole, Salwa K.

    1989-01-01

    Some of the important modern developments of thin-layer chromatography are introduced. Discussed are the theory and instrumentation of thin-layer chromatography including multidimensional and multimodal techniques. Lists 53 references. (CW)

  19. Protecting the ozone layer.

    PubMed

    Munasinghe, M; King, K

    1992-06-01

    Stratospheric ozone layer depletion has been recognized as a problem by the Vienna Convention for the Protection of the Ozone Layer and the 1987 Montreal Protocol (MP). The ozone layer shields the earth from harmful ultraviolet radiation (UV-B), which is more pronounced at the poles and around the equator. Industrialized countries have contributed significantly to the problem by releasing chlorofluorocarbons (CFCs) and halons into the atmosphere. The effect of these chemicals, which were known for their inertness, nonflammability, and nontoxicity, was discovered in 1874. Action to deal with the effects of CFCs and halons was initiated in 1985 in a 49-nation UN meeting. 21 nations signed a protocol limiting ozone depleting substances (ODS): CFCs and halons. Schedules were set based on each country's use in 1986; the target phaseout was set for the year 2000. The MP restricts trade in ODSs and weights the impact of substances to reflect the extent of damage; i.e., halons are 10 times more damaging than CFCs. ODS requirements for developing countries were eased to accommodate scarce resources and the small fraction of ODS emissions. An Interim Multilateral Fund under the Montreal Protocol (IMFMP) was established to provide loans to finance the costs to developing countries in meeting global environmental requirements. The IMFMP is administered by the World Bank, the UN Environmental Program, and the UN Development Program. Financing is available to eligible countries who use .3 kg of ODS/person/year. Rapid phaseout in developed countries has occurred due to strong support from industry and a lower than expected cost. Although there are clear advantages to rapid phaseout, there were no incentives included in the MP for rapid phaseout. Some of the difficulties occur because the schedules set minimum targets at the lowest possible cost. Also, costs cannot be minimized by a country-specific and ODS-specific process. The ways to improve implementation in scheduling and

  20. The Keck keyword layer

    NASA Technical Reports Server (NTRS)

    Conrad, A. R.; Lupton, W. F.

    1992-01-01

    Each Keck instrument presents a consistent software view to the user interface programmer. The view consists of a small library of functions, which are identical for all instruments, and a large set of keywords, that vary from instrument to instrument. All knowledge of the underlying task structure is hidden from the application programmer by the keyword layer. Image capture software uses the same function library to collect data for the image header. Because the image capture software and the instrument control software are built on top of the same keyword layer, a given observation can be 'replayed' by extracting keyword-value pairs from the image header and passing them back to the control system. The keyword layer features non-blocking as well as blocking I/O. A non-blocking keyword write operation (such as setting a filter position) specifies a callback to be invoked when the operation is complete. A non-blocking keyword read operation specifies a callback to be invoked whenever the keyword changes state. The keyword-callback style meshes well with the widget-callback style commonly used in X window programs. The first keyword library was built for the two Keck optical instruments. More recently, keyword libraries have been developed for the infrared instruments and for telescope control. Although the underlying mechanisms used for inter-process communication by each of these systems vary widely (Lick MUSIC, Sun RPC, and direct socket I/O, respectively), a basic user interface has been written that can be used with any of these systems. Since the keyword libraries are bound to user interface programs dynamically at run time, only a single set of user interface executables is needed. For example, the same program, 'xshow', can be used to display continuously the telescope's position, the time left in an instrument's exposure, or both values simultaneously. Less generic tools that operate on specific keywords, for example an X display that controls optical

  1. Cooperating systems: Layered MAS

    NASA Technical Reports Server (NTRS)

    Rochowiak, Daniel

    1990-01-01

    Distributed intelligent systems can be distinguished by the models that they use. The model developed focuses on layered multiagent system conceived of as a bureaucracy in which a distributed data base serves as a central means of communication. The various generic bureaus of such a system is described and a basic vocabulary for such systems is presented. In presenting the bureaus and vocabularies, special attention is given to the sorts of reasonings that are appropriate. A bureaucratic model has a hierarchy of master system and work group that organizes E agents and B agents. The master system provides the administrative services and support facilities for the work groups.

  2. Layered kagome spin ice

    NASA Astrophysics Data System (ADS)

    Hamp, James; Dutton, Sian; Mourigal, Martin; Mukherjee, Paromita; Paddison, Joseph; Ong, Harapan; Castelnovo, Claudio

    Spin ice materials provide a rare instance of emergent gauge symmetry and fractionalisation in three dimensions: the effective degrees of freedom of the system are emergent magnetic monopoles, and the extensively many `ice rule' ground states are those devoid of monopole excitations. Two-dimensional (kagome) analogues of spin ice have also been shown to display a similarly rich behaviour. In kagome ice however the ground-state `ice rule' condition implies the presence everywhere of magnetic charges. As temperature is lowered, an Ising transition occurs to a charge-ordered state, which can be mapped to a dimer covering of the dual honeycomb lattice. A second transition, of Kosterlitz-Thouless or three-state Potts type, occurs to a spin-ordered state at yet lower temperatures, due to small residual energy differences between charge-ordered states. Inspired by recent experimental capabilities in growing spin ice samples with selective (layered) substitution of non-magnetic ions, in this work we investigate the fate of the two ordering transitions when individual kagome layers are brought together to form a three-dimensional pyrochlore structure coupled by long range dipolar interactions. We also consider the response to substitutional disorder and applied magnetic fields.

  3. Turbulent boundary layer heat

    NASA Astrophysics Data System (ADS)

    Finson, M. L.; Clarke, A. S.; Wu, P. K. S.

    1981-01-01

    A Reynolds stress model for turbulent boundary layers is used to study surface roughness effects on skin friction and heat transfer. The issues of primary interest are the influence of roughness character (element shape and spacing) and the nature of roughness effects at high Mach numbers. Computations based on the model compare satisfactorily with measurements from experiments involving variations in roughness character, in low speed and modestly supersonic conditions. The more limited data base at hypersonic Mach numbers is also examined with reasonable success, although no quantitative explanation is offered for the reduction of heat transfer with increasing roughness observed by Holden at Me -9.4. The present calculations indicate that the mean velocity is approximately uniform over much of the height range below the tops of the elements, y less than or equal to k. With this constant (roughness velocity,) it is simple to estimate the form drag on the elements. This roughness velocity has been investigated by systematically exercising the present model over ranges of potential parameters. The roughness velocity is found to be primarily a function of the projected element frontal area per unit surface area, thus providing a new and simple method for predicting roughness character effects. The model further suggests that increased boundary layer temperatures should be generated by roughness at high edge Mach numbers, which would tend to reduce skin friction and heat transfer, perhaps below smooth wall levels.

  4. The Boundary Layer Radiometer

    NASA Astrophysics Data System (ADS)

    Irshad, Ranah; Bowles, N. E.; Calcutt, S. B.; Hurley, J.

    2010-10-01

    The Boundary Layer Radiometer is a small, low mass (<1kg) radiometer with only a single moving part - a scan/calibration mirror. The instrument consists of a three mirror telescope system incorporating an intermediate focus for use with miniature infrared and visible filters. It also has an integrated low power blackbody calibration target to provide long-term calibration stability The instrument may be used as an upward looking boundary layer radiometer for both the terrestrial and Martian atmospheres with appropriate filters for the mid-infrared carbon dioxide band, as well as a visible channel for the detection of aerosol components such as dust. The scan mirror may be used to step through different positions from the local horizon to the zenith, allowing the vertical temperature profile of the atmosphere to be retrieved. The radiometer uses miniature infrared filter assemblies developed for previous space-based instruments by Oxford, Cardiff and Reading Universities. The intermediate focus allows for the use of upstream blocking filters and baffles, which not only simplifies the design of the filters and focal plane assembly, but also reduces the risk of problems due to stray light. Combined with the calibration target this means it has significant advantages over previous generations of small radiometers.

  5. Buried oxide layer in silicon

    DOEpatents

    Sadana, Devendra Kumar; Holland, Orin Wayne

    2001-01-01

    A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.

  6. Metal deposition using seed layers

    DOEpatents

    Feng, Hsein-Ping; Chen, Gang; Bo, Yu; Ren, Zhifeng; Chen, Shuo; Poudel, Bed

    2013-11-12

    Methods of forming a conductive metal layers on substrates are disclosed which employ a seed layer to enhance bonding, especially to smooth, low-roughness or hydrophobic substrates. In one aspect of the invention, the seed layer can be formed by applying nanoparticles onto a surface of the substrate; and the metallization is achieved by electroplating an electrically conducting metal onto the seed layer, whereby the nanoparticles serve as nucleation sites for metal deposition. In another approach, the seed layer can be formed by a self-assembling linker material, such as a sulfur-containing silane material.

  7. Adsorbate Effects on Film Evolution: Homoepitaxy on Ag(100)

    NASA Astrophysics Data System (ADS)

    Layson, A. R.; Thiel, P. A.

    2000-03-01

    We report the effects of various gases on the nucleation, and subsequent coarsening, of Ag islands on Ag(100). Both of these processes-nucleation and coarsening-are ultimately controlled by atomic-scale diffusional processes, and have been studied extensively for the clean surface [1]. Comparative study of these processes with and without background gases provides indirect evidence regarding their effect on atomic-scale diffusional processes. These UHV experiments were performed using High-Resolution Low Energy Electron Diffraction. Submonolayer films of Ag were deposited, with the sample held at 180 K and simultaneously exposed to the gas of choice, while subsequent coarsening was monitored after evacuation of the gas. Spot profile analysis shows the nucleation of islands is unaffected in the presence of oxygen, but the rate of subsequent coarsening is enhanced. Conversely, the presence of water vapor during deposition results in a decrease in the initial island density (indicating enhanced mobility), but shows no affect on subsequent coarsening. Exposure to CO had no effect on either nucleation density or coarsening. [1] P.A. Thiel and J.W. Evans, J. Phys. Chem. B 104 (2000) Feb.24

  8. On the kinetic barriers of graphene homo-epitaxy

    SciTech Connect

    Zhang, Wei; Yu, Xinke; Xie, Ya-Hong; Cahyadi, Erica; Ratsch, Christian

    2014-12-01

    The diffusion processes and kinetic barriers of individual carbon adatoms and clusters on graphene surfaces are investigated to provide fundamental understanding of the physics governing epitaxial growth of multilayer graphene. It is found that individual carbon adatoms form bonds with the underlying graphene whereas the interaction between graphene and carbon clusters, consisting of 6 atoms or more, is very weak being van der Waals in nature. Therefore, small carbon clusters are quite mobile on the graphene surfaces and the diffusion barrier is negligibly small (∼6 meV). This suggests the feasibility of high-quality graphene epitaxial growth at very low growth temperatures with small carbon clusters (e.g., hexagons) as carbon source. We propose that the growth mode is totally different from 3-dimensional bulk materials with the surface mobility of carbon hexagons being the highest over graphene surfaces that gradually decreases with further increase in cluster size.

  9. Homoepitaxial regrowth habits of ZnO nanowire arrays

    PubMed Central

    2011-01-01

    Synthetic regrowth of ZnO nanowires [NWs] under a similar chemical vapor transport and condensation [CVTC] process can produce abundant ZnO nanostructures which are not possible by a single CVTC step. In this work, we report three different regrowth modes of ZnO NWs: axial growth, radial growth, and both directions. The different growth modes seem to be determined by the properties of initial ZnO NW templates. By varying the growth parameters in the first-step CVTC process, ZnO nanostructures (e.g., nanoantenna) with drastically different morphologies can be obtained with distinct photoluminescence properties. The results have implications in guiding the rational synthesis of various ZnO NW heterostructures. PMID:22151820

  10. Liquefaction mechanism for layered soils

    SciTech Connect

    Fiegel, G.L.; Kutter, B.L. . Dept. of Civil and Environmental Engineering)

    1994-04-01

    Results from four centrifuge model tests are presented. Three of the model tests involve layered soil deposits subject to base shaking; one model test involves a uniform soil deposit of sand subject to base shaking. The layered soil models consisted of fine sand overlain by a layer of relatively impermeable silica flour (silt). Pore-water pressures, accelerations, and settlements were measured during all four tests. Results from the model tests involving layered soils suggest that during liquefaction a water interlayer or very loose zone of soil may develop at the sand-silt interface due to the difference in permeabilities. In each layered model test, boils were observed on the surface of the silt layer. These boils were concentrated in the thinnest zones of the overlying silt layer and provided a vent for the excess pore-water pressure generated in the fine sand.

  11. Double layer secure sketch

    NASA Astrophysics Data System (ADS)

    Li, Cai

    2012-09-01

    Secure sketch has been applied successfully in a wide variety of applications like cryptography, biometric authentication systems and so on. All of these secure sketches have properties in common namely error-tolerance and small entropy loss. The former ensures an input set w' can unlock the system if w' is substantially overlapped with a template set w while the latter means it is hard for an adversary to get the information of w even with the knowledge of s, which is produced by w and stored in the system publicly. In their constructions, they all consider w as a set of atomic elements. However, in the real word, it is very likely the elements in the template set are sets as well. In this paper, we propose a double layer secure sketch to address this issue.

  12. Layer Outcrops and Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-561, 1 December 2003

    This October 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows dark, windblown sand dunes amid outcrops of light-toned, sedimentary rock in a crater in western Arabia Terra. The darkest material in the scene is windblown sand; the steep slopes--the slip faces--of the dunes face toward the southwest (lower left), indicating that wind transport of sand has been from the northeast (upper right). The layered mounds are the remains of sedimentary rock that were once more extensive across this crater floor. The image is located near 8.9oN, 1.2oW, and covers an area 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  13. Templated, layered manganese phosphate

    DOEpatents

    Thoma, Steven G.; Bonhomme, Francois R.

    2004-08-17

    A new crystalline maganese phosphate composition having an empirical formula: O). The compound was determined to crystallize in the trigonal space group P-3c1 with a=8.8706(4) .ANG., c=26.1580(2) .ANG., and V (volume)=1783 .ANG..sup.3. The structure consists of sheets of corner sharing Mn(II)O.sub.4 and PO.sub.4 tetrahedra with layers of (H.sub.3 NCH.sub.2 CH.sub.2).sub.3 N and water molecules in-between. The pronated (H.sub.3 NCH.sub.2 CH.sub.2).sub.3 N molecules provide charge balancing for the inorganic sheets. A network of hydrogen bonds between water molecules and the inorganic sheets holds the structure together.

  14. Layers in Tithonium

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-570, 10 December 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows eroded layered bedrock outcrops in the upper walls of one of the depressions in the Tithonium Chasma trough system. Tithonium Chasma is one of the canyons of the Valles Marineris, a vast gouge that--if it occurred on Earth-would span the distance from Los Angeles, California, to New York City. The Valles Marineris canyons were not carved by running water, instead they formed mostly by the combined forces of faulting and mass movement (landslides) as gravity eroded materials from the walls. This image is located near 4.2oS, 85.1oW. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated from the lower left.

  15. Ozone Layer Observations

    NASA Technical Reports Server (NTRS)

    McPeters, Richard; Bhartia, P. K. (Technical Monitor)

    2002-01-01

    The US National Aeronautics and Space Administration (NASA) has been monitoring the ozone layer from space using optical remote sensing techniques since 1970. With concern over catalytic destruction of ozone (mid-1970s) and the development of the Antarctic ozone hole (mid-1980s), long term ozone monitoring has become the primary focus of NASA's series of ozone measuring instruments. A series of TOMS (Total Ozone Mapping Spectrometer) and SBUV (Solar Backscatter Ultraviolet) instruments has produced a nearly continuous record of global ozone from 1979 to the present. These instruments infer ozone by measuring sunlight backscattered from the atmosphere in the ultraviolet through differential absorption. These measurements have documented a 15 Dobson Unit drop in global average ozone since 1980, and the declines in ozone in the antarctic each October have been far more dramatic. Instruments that measure the ozone vertical distribution, the SBUV and SAGE (Stratospheric Aerosol and Gas Experiment) instruments for example, show that the largest changes are occurring in the lower stratosphere and upper troposphere. The goal of ozone measurement in the next decades will be to document the predicted recovery of the ozone layer as CFC (chlorofluorocarbon) levels decline. This will require a continuation of global measurements of total column ozone on a global basis, but using data from successor instruments to TOMS. Hyperspectral instruments capable of measuring in the UV will be needed for this purpose. Establishing the relative roles of chemistry and dynamics will require instruments to measure ozone in the troposphere and in the stratosphere with good vertical resolution. Instruments that can measure other chemicals important to ozone formation and destruction will also be needed.

  16. ZnO layers deposited by Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Pécz, B.; Baji, Zs; Lábadi, Z.; Kovács, A.

    2013-11-01

    The structure of 40 nm thick epitaxial ZnO layers grown on single crystalline sapphire and GaN substrates by atomic layer deposition has been studied using transmission electron microscopy. The growth is carried out between 150°C and 300°C without any buffer layer using di-ethyl zinc and water precursors. The ZnO layer on sapphire is found to be polycrystalline, which is probably due to the large misfit (~15 %) and the relatively low deposition temperature. However, the small misfit (~1.8 %) between the ZnO layer that is deposited on GaN at 300°C resulted in a high quality single crystalline layer.

  17. Processes for multi-layer devices utilizing layer transfer

    DOEpatents

    Nielson, Gregory N; Sanchez, Carlos Anthony; Tauke-Pedretti, Anna; Kim, Bongsang; Cederberg, Jeffrey; Okandan, Murat; Cruz-Campa, Jose Luis; Resnick, Paul J

    2015-02-03

    A method includes forming a release layer over a donor substrate. A plurality of devices made of a first semiconductor material are formed over the release layer. A first dielectric layer is formed over the plurality of devices such that all exposed surfaces of the plurality of devices are covered by the first dielectric layer. The plurality of devices are chemically attached to a receiving device made of a second semiconductor material different than the first semiconductor material, the receiving device having a receiving substrate attached to a surface of the receiving device opposite the plurality of devices. The release layer is etched to release the donor substrate from the plurality of devices. A second dielectric layer is applied over the plurality of devices and the receiving device to mechanically attach the plurality of devices to the receiving device.

  18. Inter-layer synchronization in multiplex networks of identical layers.

    PubMed

    Sevilla-Escoboza, R; Sendiña-Nadal, I; Leyva, I; Gutiérrez, R; Buldú, J M; Boccaletti, S

    2016-06-01

    Inter-layer synchronization is a distinctive process of multiplex networks whereby each node in a given layer evolves synchronously with all its replicas in other layers, irrespective of whether or not it is synchronized with the other units of the same layer. We analytically derive the necessary conditions for the existence and stability of such a state, and verify numerically the analytical predictions in several cases where such a state emerges. We further inspect its robustness against a progressive de-multiplexing of the network, and provide experimental evidence by means of multiplexes of nonlinear electronic circuits affected by intrinsic noise and parameter mismatch. PMID:27368794

  19. Boundary-Layer & health

    NASA Astrophysics Data System (ADS)

    Costigliola, V.

    2010-09-01

    It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate

  20. Excited waves in shear layers

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.

    1982-01-01

    The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.

  1. Nanostructure Neutron Converter Layer Development

    NASA Technical Reports Server (NTRS)

    Park, Cheol (Inventor); Sauti, Godfrey (Inventor); Kang, Jin Ho (Inventor); Lowther, Sharon E. (Inventor); Thibeault, Sheila A. (Inventor); Bryant, Robert G. (Inventor)

    2016-01-01

    Methods for making a neutron converter layer are provided. The various embodiment methods enable the formation of a single layer neutron converter material. The single layer neutron converter material formed according to the various embodiments may have a high neutron absorption cross section, tailored resistivity providing a good electric field penetration with submicron particles, and a high secondary electron emission coefficient. In an embodiment method a neutron converter layer may be formed by sequential supercritical fluid metallization of a porous nanostructure aerogel or polyimide film. In another embodiment method a neutron converter layer may be formed by simultaneous supercritical fluid metallization of a porous nanostructure aerogel or polyimide film. In a further embodiment method a neutron converter layer may be formed by in-situ metalized aerogel nanostructure development.

  2. Oxygen-reducing catalyst layer

    DOEpatents

    O'Brien, Dennis P.; Schmoeckel, Alison K.; Vernstrom, George D.; Atanasoski, Radoslav; Wood, Thomas E.; Yang, Ruizhi; Easton, E. Bradley; Dahn, Jeffrey R.; O'Neill, David G.

    2011-03-22

    An oxygen-reducing catalyst layer, and a method of making the oxygen-reducing catalyst layer, where the oxygen-reducing catalyst layer includes a catalytic material film disposed on a substrate with the use of physical vapor deposition and thermal treatment. The catalytic material film includes a transition metal that is substantially free of platinum. At least one of the physical vapor deposition and the thermal treatment is performed in a processing environment comprising a nitrogen-containing gas.

  3. A POROUS, LAYERED HELIOPAUSE

    SciTech Connect

    Swisdak, M.; Drake, J. F.; Opher, M. E-mail: drake@umd.edu

    2013-09-01

    The picture of the heliopause (HP)-the boundary between the domains of the Sun and the local interstellar medium (LISM)-as a pristine interface with a large rotation in the magnetic field fails to describe recent Voyager 1 (V1) data. Magnetohydrodynamic (MHD) simulations of the global heliosphere reveal that the rotation angle of the magnetic field across the HP at V1 is small. Particle-in-cell simulations, based on cuts through the MHD model at V1's location, suggest that the sectored region of the heliosheath (HS) produces large-scale magnetic islands that reconnect with the interstellar magnetic field while mixing LISM and HS plasma. Cuts across the simulation reveal multiple, anti-correlated jumps in the number densities of LISM and HS particles, similar to those observed, at the magnetic separatrices. A model is presented, based on both the observations and simulations, of the HP as a porous, multi-layered structure threaded by magnetic fields. This model further suggests that contrary to the conclusions of recent papers, V1 has already crossed the HP.

  4. The Martian surface layer

    NASA Technical Reports Server (NTRS)

    Christensen, Philip R.; Moore, Henry J.

    1992-01-01

    The global characteristics of the Martian surface layer are discussed on the basis of thermal, albedo, color, and radar data for the region between approximately 60 deg S and 60 deg N. Thermal data reveal the presence of large low- and high-inertia regions of the northern hemisphere, with much of the south covered by material of moderate inertia. There is a strong anticorrelation between inertia and albedo, a correlation between inertia and rock abundance, and, over much of the planet, a correlation of radar-derived density with inertia. Viking Orbiter color data indicate the presence of three major surface materials: low-inertia, bright-red material that is presumably dust; high-inertia, dark-grey material interpreted to be lithic material mixed with palagonitelike dust; and moderate-inertia, dark-red material that is rough at subpixel scales and interpreted to be indurated. Observations from the Viking landing sites show rocks, fines of varying cohesion and crusts. These sites have indications of aeolian erosion and deposition in the recent past.

  5. Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height

    NASA Astrophysics Data System (ADS)

    Allaerts, Dries; Meyers, Johan

    2015-11-01

    In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer layer effects on wind-farm boundary layers. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.

  6. Midlatitude sporadic-E layers

    NASA Technical Reports Server (NTRS)

    Smith, L. G.; Miller, K. L.

    1981-01-01

    Rocket borne probes and incoherent scatter radar were demonstrated to be effective methods of studying the structure of midlatitude sporadic E layers. Layers are formed when metal ions are converged vertically in a wind shear to produce a local enhancement of electron density. Rocket and radar observations show that the layers may occassionally have complex structure produced by an unstable wind shear. The partial transparency to radio waves of sporadic E layers is shown to be due to localized regions of high electron density.

  7. Secondary polymer layered impregnated tile

    NASA Technical Reports Server (NTRS)

    Tran, Huy K. (Inventor); Rasky, Daniel J. (Inventor); Szalai, Christine E. (Inventor); Carroll, Joseph A. (Inventor); Hsu, Ming-ta S. (Inventor)

    2005-01-01

    A low density organic polymer impregnated preformed fibrous ceramic article includes a plurality of layers. A front layer includes ceramic fibers or carbon fibers or combinations of ceramic fibers and carbon fibers, and is impregnated with an effective amount of at least one organic polymer. A middle layer includes polymer impregnated ceramic fibers. A back layer includes ceramic fibers or carbon fibers or combinations of ceramic fibers and carbon fibers, and is impregnated with an effective amount of at least one low temperature pyrolyzing organic polymer capable of decomposing without depositing residues.

  8. Layer Control of WSe2 via Selective Surface Layer Oxidation.

    PubMed

    Li, Zhen; Yang, Sisi; Dhall, Rohan; Kosmowska, Ewa; Shi, Haotian; Chatzakis, Ioannis; Cronin, Stephen B

    2016-07-26

    We report Raman and photoluminescence spectra of mono- and few-layer WSe2 and MoSe2 taken before and after exposure to a remote oxygen plasma. For bilayer and trilayer WSe2, we observe an increase in the photoluminescence intensity and a blue shift of the photoluminescence peak positions after oxygen plasma treatment. The photoluminescence spectra of trilayer WSe2 exhibit features of a bilayer after oxygen plasma treatment. Bilayer WSe2 exhibits features of a monolayer, and the photoluminescence of monolayer WSe2 is completely absent after the oxygen plasma treatment. These changes are observed consistently in more than 20 flakes. The mechanism of the changes observed in the photoluminescence spectra of WSe2 is due to the selective oxidation of the topmost layer. As a result, N-layer WSe2 is reduced to N-1 layers. Raman spectra and AFM images taken from the WSe2 flakes before and after the oxygen treatment corroborate these findings. Because of the low kinetic energy of the oxygen radicals in the remote oxygen plasma, the oxidation is self-limiting. By varying the process duration from 1 to 10 min, we confirmed that the oxidation will only affect the topmost layer of the WSe2 flakes. X-ray photoelectron spectroscopy shows that the surface layer WOx of the sample can be removed by a quick dip in KOH solution. Therefore, this technique provides a promising way of controlling the thickness of WSe2 layer by layer. PMID:27391161

  9. Layer-layer competition in multiplex complex networks.

    PubMed

    Gómez-Gardeñes, J; de Domenico, M; Gutiérrez, G; Arenas, A; Gómez, S

    2015-12-13

    The coexistence of multiple types of interactions within social, technological and biological networks has moved the focus of the physics of complex systems towards a multiplex description of the interactions between their constituents. This novel approach has unveiled that the multiplex nature of complex systems has strong influence in the emergence of collective states and their critical properties. Here we address an important issue that is intrinsic to the coexistence of multiple means of interactions within a network: their competition. To this aim, we study a two-layer multiplex in which the activity of users can be localized in each of the layers or shared between them, favouring that neighbouring nodes within a layer focus their activity on the same layer. This framework mimics the coexistence and competition of multiple communication channels, in a way that the prevalence of a particular communication platform emerges as a result of the localization of user activity in one single interaction layer. Our results indicate that there is a transition from localization (use of a preferred layer) to delocalization (combined usage of both layers) and that the prevalence of a particular layer (in the localized state) depends on the structural properties.

  10. Layer-layer competition in multiplex complex networks.

    PubMed

    Gómez-Gardeñes, J; de Domenico, M; Gutiérrez, G; Arenas, A; Gómez, S

    2015-12-13

    The coexistence of multiple types of interactions within social, technological and biological networks has moved the focus of the physics of complex systems towards a multiplex description of the interactions between their constituents. This novel approach has unveiled that the multiplex nature of complex systems has strong influence in the emergence of collective states and their critical properties. Here we address an important issue that is intrinsic to the coexistence of multiple means of interactions within a network: their competition. To this aim, we study a two-layer multiplex in which the activity of users can be localized in each of the layers or shared between them, favouring that neighbouring nodes within a layer focus their activity on the same layer. This framework mimics the coexistence and competition of multiple communication channels, in a way that the prevalence of a particular communication platform emerges as a result of the localization of user activity in one single interaction layer. Our results indicate that there is a transition from localization (use of a preferred layer) to delocalization (combined usage of both layers) and that the prevalence of a particular layer (in the localized state) depends on the structural properties. PMID:26527811

  11. Layer-by-Layer Proteomic Analysis of Mytilus galloprovincialis Shell

    PubMed Central

    Wang, Xin-xing; Bao, Lin-fei; Fan, Mei-hua; Li, Xiao-min; Wu, Chang-wen; Xia, Shu-wei

    2015-01-01

    Bivalve shell is a biomineralized tissue with various layers/microstructures and excellent mechanical properties. Shell matrix proteins (SMPs) pervade and envelop the mineral crystals and play essential roles in biomineralization. Despite that Mytilus is an economically important bivalve, only few proteomic studies have been performed for the shell, and current knowledge of the SMP set responsible for different shell layers of Mytilus remains largely patchy. In this study, we observed that Mytilus galloprovincialis shell contained three layers, including nacre, fibrous prism, and myostracum that is involved in shell-muscle attachment. A parallel proteomic analysis was performed for these three layers. By combining LC-MS/MS analysis with Mytilus EST database interrogations, a whole set of 113 proteins was identified, and the distribution of these proteins in different shell layers followed a mosaic pattern. For each layer, about a half of identified proteins are unique and the others are shared by two or all of three layers. This is the first description of the protein set exclusive to nacre, myostracum, and fibrous prism in Mytilus shell. Moreover, most of identified proteins in the present study are novel SMPs, which greatly extended biomineralization-related protein data of Mytilus. These results are useful, on one hand, for understanding the roles of SMPs in the deposition of different shell layers. On the other hand, the identified protein set of myostracum provides candidates for further exploring the mechanism of adductor muscle-shell attachment. PMID:26218932

  12. Layer-by-Layer Proteomic Analysis of Mytilus galloprovincialis Shell.

    PubMed

    Gao, Peng; Liao, Zhi; Wang, Xin-Xing; Bao, Lin-Fei; Fan, Mei-Hua; Li, Xiao-Min; Wu, Chang-Wen; Xia, Shu-Wei

    2015-01-01

    Bivalve shell is a biomineralized tissue with various layers/microstructures and excellent mechanical properties. Shell matrix proteins (SMPs) pervade and envelop the mineral crystals and play essential roles in biomineralization. Despite that Mytilus is an economically important bivalve, only few proteomic studies have been performed for the shell, and current knowledge of the SMP set responsible for different shell layers of Mytilus remains largely patchy. In this study, we observed that Mytilus galloprovincialis shell contained three layers, including nacre, fibrous prism, and myostracum that is involved in shell-muscle attachment. A parallel proteomic analysis was performed for these three layers. By combining LC-MS/MS analysis with Mytilus EST database interrogations, a whole set of 113 proteins was identified, and the distribution of these proteins in different shell layers followed a mosaic pattern. For each layer, about a half of identified proteins are unique and the others are shared by two or all of three layers. This is the first description of the protein set exclusive to nacre, myostracum, and fibrous prism in Mytilus shell. Moreover, most of identified proteins in the present study are novel SMPs, which greatly extended biomineralization-related protein data of Mytilus. These results are useful, on one hand, for understanding the roles of SMPs in the deposition of different shell layers. On the other hand, the identified protein set of myostracum provides candidates for further exploring the mechanism of adductor muscle-shell attachment.

  13. Natural melanin composites by layer-by-layer assembly

    NASA Astrophysics Data System (ADS)

    Eom, Taesik; Shim, Bong Sub

    2015-04-01

    Melanin is an electrically conductive and biocompatible material, because their conjugated backbone structures provide conducting pathways from human skin, eyes, brain, and beyond. So there is a potential of using as materials for the neural interfaces and the implantable devices. Extracted from Sepia officinalis ink, our natural melanin was uniformly dispersed in mostly polar solvents such as water and alcohols. Then, the dispersed melanin was further fabricated to nano-thin layered composites by the layer-by-layer (LBL) assembly technique. Combined with polyvinyl alcohol (PVA), the melanin nanoparticles behave as an LBL counterpart to from finely tuned nanostructured films. The LBL process can adjust the smart performances of the composites by varying the layering conditions and sandwich thickness. We further demonstrated the melanin loading degree of stacked layers, combination nanostructures, electrical properties, and biocompatibility of the resulting composites by UV-vis spectrophotometer, scanning electron microscope (SEM), multimeter, and in-vitro cell test of PC12, respectively.

  14. Layer-by-Layer Assembly of Enzymes on Carbon Nanotubes

    SciTech Connect

    Wang, Jun; Liu, Guodong; Lin, Yuehe

    2008-06-01

    The use of Layer-by-layer techniques for immobilizing several types of enzymes, e.g. glucose oxidase (GOx), horse radish oxidases(HRP), and choline oxidase(CHO) on carbon nanotubes and their applications for biosenseing are presented. The enzyme is immobilized on the negatively charged CNT surface by alternatively assembling a cationic polydiallyldimethyl-ammonium chloride (PDDA) layer and a enzyme layer. The sandwich-like layer structure (PDDA/enzyme/PDDA/CNT) formed by electrostatic assembling provides a favorable microenvironment to keep the bioactivity of enzyme and to prevent enzyme molecule leakage. The morphologies and electrocatalytic acitivity of the resulted enzyme film were characterized using TEM and electrochemical techniques, respectively. It was found that these enzyme-based biosensors are very sensitive, selective for detection of biomolecules, e.g. glucose, choline.

  15. On the equatorial Ekman layer

    NASA Astrophysics Data System (ADS)

    Marcotte, Florence; Dormy, Emmanuel; Soward, Andrew

    2016-09-01

    The steady incompressible viscous flow in the wide gap between spheres rotating about a common axis at slightly different rates (small Ekman number E) has a long and celebrated history. The problem is relevant to the dynamics of geophysical and planetary core flows, for which, in the case of electrically conducting fluids, the possible operation of a dynamo is of considerable interest. A comprehensive asymptotic study, in the limit E<<1, was undertaken by Stewartson (J. Fluid Mech. 1966, vol. 26, pp. 131-144). The mainstream flow, exterior to the E^{1/2} Ekman layers on the inner/outer boundaries and the shear layer on the inner sphere tangent cylinder C, is geostrophic. Stewartson identified a complicated nested layer structure on C, which comprises relatively thick quasi-geostrophic E^{2/7} (inside C) and E^{1/4} (outside C) layers. They embed a thinner E^{1/3} ageostrophic shear layer (on C), which merges with the inner sphere Ekman layer to form the E^{2/5} Equatorial Ekman layer of axial length E^{1/5}. Under appropriate scaling, this $E^{2/5}$--layer problem may be formulated, correct to leading order, independent of E. Accordingly, the Ekman boundary layer and ageostrophic shear layer become features of the far-field (as identified by the large value of the scaled axial co-ordinate z) solution. We present a numerical solution, which uses a non-local integral boundary condition at finite $z$ to account for the far-field behaviour. Adopting z^{-1} as a small parameter we extend Stewartson's similarity solution for the ageostrophic shear layer to higher orders. This far-field solution agrees well with that obtained from our numerical model.

  16. Advanced double layer capacitors

    NASA Technical Reports Server (NTRS)

    Sarangapani, S.; Lessner, P.; Forchione, J.; Laconti, A. B.

    1989-01-01

    There is a need for large amounts of power to be delivered rapidly in a number of airborne and space systems. Conventional, portable power sources, such as batteries, are not suited to delivering high peak power pulses. The charge stored at the electrode-electrolyte double layer is, however, much more assessible on a short time scale. Devices exploiting this concept were fabricated using carbon and metal oxides (Pinnacle Research) as the electrodes and sulfuric acid as the electrolyte. The approach reported, replaces the liquid sulfuric acid electrolyte with a solid ionomer electrolyte. The challenge is to form a solid electrode-solid ionomer electrolyte composite which has a high capacitance per geometric area. The approach to maximize contact between the electrode particles and the ionomer was to impregnate the electrode particles using a liquid ionomer solution and to bond the solvent-free structure to a solid ionomer membrane. Ruthenium dioxide is the electrode material used. Three strategies are being pursued to provide for a high area electrode-ionomer contact: mixing of the RuOx with a small volume of ionomer solution followed by filtration to remove the solvent, and impregnation of the ionomer into an already formed RuOx electrode. RuOx powder and electrodes were examined by non-electrochemical techniques. X-ray diffraction has shown that the material is almost pure RuO2. The electrode structure depends on the processing technique used to introduce the Nafion. Impregnated electrodes have Nafion concentrated near the surface. Electrodes prepared by the evaporation method show large aggregates of crystals surrounded by Nafion.

  17. Midlatitude sporadic-E layers

    NASA Technical Reports Server (NTRS)

    Miller, K. L.; Smith, L. G.

    1976-01-01

    The partially transparent echo from midlatitude sporadic E layers was recorded by ionosondes between the blanketing frequency and the maximum frequency. The theory that the midlatitude sporadic E layers are not uniform in the horizontal plane but contain localized regions of high electron density was evaluated using data obtained by incoherent scatter radar and found to provide a satisfactory explanation. The main features of midlatitude sporadic E layers are consistent with the convergence of metallic ions as described by the wind shear theory applied to gravity waves and tides. The interference of gravity waves with other gravity waves and tides can be recognized in the altitudes of occurrence and the structure of the layers. Small scale horizontal irregularities are attributed in some cases to critical level effects and in others to fluid instabilities. The convergence of a meteor trail can, under some circumstances, account for localized enhancement of the electron density in the layer.

  18. Fragmentation of drying paint layers

    NASA Astrophysics Data System (ADS)

    Bakos, Katinka; Dombi, András; Járai-Szabó, Ferenc; Néda, Zoltán

    2013-11-01

    Fragmentation of thin layers of drying granular materials on a frictional surface are studied both by experiments and computer simulations. Besides a qualitative description of the fragmentation phenomenon, the dependence of the average fragment size as a function of the layer thickness is thoroughly investigated. Experiments are done using a special nail polish, which forms characteristic crack structures during drying. In order to control the layer thickness, we diluted the nail polish in acetone and evaporated in a controlled manner different volumes of this solution on glass surfaces. During the evaporation process we managed to get an instable paint layer, which formed cracks as it dried out. In order to understand the obtained structures a previously developed spring-block model was implemented in a three-dimensional version. The experimental and simulation results proved to be in excellent qualitative and quantitative agreement. An earlier suggested scaling relation between the average fragment size and the layer thickness is reconfirmed.

  19. Lear jet boundary layer/shear layer laser propagation experiments

    NASA Technical Reports Server (NTRS)

    Gilbert, K.

    1980-01-01

    Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.

  20. Charged layer with undulated surface: configuration of electrical double layer.

    PubMed

    Lin, Sung-Hwa

    2010-06-15

    A charged layer with undulated surface exists commonly in natural entities (for example the biological membrane layer and the surface of charged colloid) and in artificial fabrications (for example the peripheral surface of ion-exchange membrane pores). When the micro- or nano-scale charged layer systems are concerned, the effect of undulation of charged layer surface on the electrical phenomenon may become great significant. In this work, using the perturbation method, the significance of undulated surface on a charged layer in the electrical phenomenon is investigated. Under assumptions that the undulation amplitude is small and that the Debye-Huckel approximation is applicable, the electrical potential field in three regions is solved simultaneously. Based on the analytical results it is found that, if compared with that in condition of flat surface, the undulation of charged layer surface decreases/increases the magnitude of electrical potential field near the wave crest/trough, due to the curvature of undulated surface. In addition, the surface potential on the undulated surface shows a wavelike distribution. The analytical results also show that, the significance of undulated surface is determined by the physical parameters, including the geometry of undulated surface, the amplitude and the period of undulation, and the fixed charge density in charged layer.

  1. Layers Exposed at Polar Canyon

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This false-color subframe of an image from the High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter shows the north polar layered deposits at top and darker materials at bottom, exposed in a scarp at the head of Chasma Boreale, a large canyon eroded into the layered deposits.

    The polar layered deposits appear red because of dust mixed within them, but are ice-rich as indicated by previous observations. Water ice in the layered deposits is probably responsible for the pattern of fractures seen near the top of the scarp. The darker material below the layered deposits may have been deposited as sand dunes, as indicated by the crossbedding (truncation of curved lines) seen near the middle of the scarp. It appears that brighter, ice-rich layers were deposited between the dark dunes in places. Exposures such as these are useful in understanding recent climate variations that are likely recorded in the polar layered deposits.

    NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace and Technology Corp., Boulder, Colo.

  2. Temperature synchronized molecular layer epitaxy

    NASA Astrophysics Data System (ADS)

    Kurabayashi, T.; Nishizawa, J.

    1994-12-01

    This paper reports the first results on a modified molecular layer epitaxy (MLE) technique to deposit epitaxial GaAs films by changing the substrate temperature for alternate TEG (or TMG) and AsH 3 injection. This method of temperature synchronized molecular layer epitaxy (TSMLE) is a new concept for MLE and atomic layer epitaxy (ALE). The growth rates and the doping phenomena showed different characteristics to the conventional methods which were performed at a constant temperature. This method was effective not only for the study of monolayer growth, but also for device application, especially for the heavily doped p-type layer of which carrier concentration is 10 20 cm -3 order. Carbon doped p-type layer was achieved by TMG-AsH 3 TSMLE. The carbon concentration increased by decreasing the temperature during AsH 3 injection and by increasing the temperature during TMG injection. Zn-doped layer was achieved by TEG-AsH 3 TSMLE using DEZn as a dopant gas for p-type layer fabrication. To doped heavily, DEZn injected after AsH 3 injection and the temperature during AsH 3 injection had a suitable value at 393°C.

  3. D0 layer 0 innermost layer of silicon microstrip tracker

    SciTech Connect

    Hanagaki, K.; /Fermilab

    2006-01-01

    A new inner layer silicon strip detector has been built and will be installed in the existing silicon microstrip tracker in D0. They report on the motivation, design, and performance of this new detector.

  4. The role of nonlinear critical layers in boundary layer transition

    NASA Technical Reports Server (NTRS)

    Goldstein, M.E.

    1995-01-01

    Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.

  5. Layer-by-layer-assembled healable antifouling films.

    PubMed

    Chen, Dongdong; Wu, Mingda; Li, Bochao; Ren, Kefeng; Cheng, Zhongkai; Ji, Jian; Li, Yang; Sun, Junqi

    2015-10-21

    Healable antifouling films are fabricated by the exponential layer-by-layer assembly of PEGylated branched poly(ethylenimine) and hyaluronic acid followed by post-crosslinking. The antifouling function originates from the grafted PEG and the extremely soft nature of the films. The rapid and multiple healing of damaged antifouling functions caused by cuts and scratches can be readily achieved by immersing the films in normal saline solution. PMID:26455733

  6. DNA release dynamics from bioreducible layer-by-layer films

    PubMed Central

    Blacklock, Jenifer; Mao, Guangzhao; Oupický, David; Möhwald, Helmuth

    2010-01-01

    DNA release dynamics from layer-by-layer (LbL) films is an important aspect to consider with regards to localized gene delivery systems. The rate of DNA release and the condensation state of DNA during release are of particular interest in the field of gene delivery. A hyperbranched poly(amido amine) (RHB) containing bioreducible disulfide bonds is used to form interpolyelectrolyte complexes with DNA during LbL film assembly. During films disassembly, DNA is released in physiologic conditions due to the reducing nature of the RHB. Uncondensed DNA deposited on the surface was compared to DNA condensed by RHB in polyplex form by using two types of LbL films, RHB/DNA/RHB and polyplex terminated films, RHB/DNA/polyplex. LbL films with up to three layers are used in order to facilitate high-resolution AFM imaging. X-ray reflectivity, ellipsometry, and Fourier transform infrared spectroscopy are also used. The film disassembly, rearrangement and release of molecules from the surface due to thiol-disulfide exchange is conducted in reducing dithiothreitol (DTT) solutions. Salt is found to accelerate the overall rate of film disassembly. Additionally, it was found that the polyplex layer disassembles faster than the DNA layer. The predominant intermediate structure is the toroid structure for the polyplex layer and the fiber bundle structure for the DNA layer during film disassembly. This study offers a simple means to modulate DNA release from LbL films by utilizing both condensed and uncondensed DNA in different layers. The study highlights nanostructures, toroids and bundles, as dominant intermediate DNA structures during the DNA release from LbL films. PMID:20131916

  7. On Multiple-Layered Vortices

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.

    2011-01-01

    As part of an ongoing effort to find ways to make vortex flow fields decompose more quickly, photographs and observations are presented of vortex flow fields that indicate the presence of multiple layers of fluid rotating about a common axis. A survey of the literature indicates that multiple-layered vortices form in waterspouts, tornadoes and lift-generated vortices of aircraft. An explanation for the appearance of multiple-layered structures in vortices is suggested. The observations and data presented are intended to improve the understanding of the formation and persistence of vortex flow fields.

  8. On the origin of rhythmic layering in layered gabbros

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Zhang, J.

    2015-12-01

    Rhythmic layering of silicates (plagioclase, pyroxene and olivine), ilmenite and magnitite is a common feature in mafic-ultramafic intrusions. The origin of rhythmic layering has been hotly debated in the literatures. Proposed mechanisms include gravity differentiation, double-diffusive convection, oscillatory crystallization of magma, repeated injection and supplement of magma, etc. Here we provide detailed FTIR and EBSD studies on the water content and deformation microstructure of gabbros from the Panzhihua intrusion and experimentally deformed synthetic gabrros and magnetite aggregates with a volume ratio of 6:4. The FTIR analyses revealed a significant amount of hydroxyls in both clinopyroxene (411-775 ppm) and plagioclase (328-716 ppm), suggesting a high water content mantle plume source. The EBSD analyses show similar fabrics in constitutent minerals of natural and experimental specimens: a weak clinopyroxene fabric of (100) parallel to foliation and [001] parallel to lineation; a strong plagioclase fabric of (010) parallel to foliation and [100] parallel to lineation, a weak ilmenite fabric of (001) parallel to foliation and [hk0] parallel to lieantion; and a near random magnitite fabric. There is an obvious rhythmic layering in sheared gabrros and magnetite aggregates similar to natural observations. Our results revealed strong layer-parallel shearing deformation during the formation of the Panxi layered intructions. There is a significant strength contrast between gabbro and Fe-Ti oxides. We propose that the formation of the rhythmic layering in mafic-ultramafic intrusions is caused mainly by rheological stratification of Fe-Ti oxides and gabbros.

  9. Inversion layer MOS solar cells

    NASA Technical Reports Server (NTRS)

    Ho, Fat Duen

    1986-01-01

    Inversion layer (IL) Metal Oxide Semiconductor (MOS) solar cells were fabricated. The fabrication technique and problems are discussed. A plan for modeling IL cells is presented. Future work in this area is addressed.

  10. Boundary Layer Control on Airfoils.

    ERIC Educational Resources Information Center

    Gerhab, George; Eastlake, Charles

    1991-01-01

    A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)

  11. Intermetallic Layers in Soldered Joints

    1998-12-10

    ILAG solves the one-dimensional partial differential equations describing the multiphase, multicomponent, solid-state diffusion-controlled growth of intermetallic layers in soldered joints. This software provides an analysis capability for materials researchers to examine intermetallic growth mechanisms in a wide variety of defense and commercial applications involving both traditional and advanced materials. ILAG calculates the interface positions of the layers, as well as the spatial distribution of constituent mass fractions, and outputs the results at user-prescribed simulation times.

  12. Removing Boundary Layer by Suction

    NASA Technical Reports Server (NTRS)

    Ackeret, J

    1927-01-01

    Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl boundary-layer theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the boundary layer into the inside of a body through a slot or slots in its surface.

  13. Modeling the urban boundary layer

    NASA Technical Reports Server (NTRS)

    Bergstrom, R. W., Jr.

    1976-01-01

    A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

  14. Simulation of auroral double layers

    NASA Technical Reports Server (NTRS)

    Hubbard, R. F.; Joyce, G.

    1979-01-01

    Some basic properties of plasma double layers are deduced from a particle-in-cell computer simulation and related to parallel electric-field structures above the auroral regions. The simulation results on the processes leading to double-layer formation are examined, particularly in relation to the transient stage and double-layer structure and stability. It is concluded that: (1) a large potential difference applied to a finite-length plasma will be concentrated in a shocklike localized region instead of occurring over the entire length of the system; (2) the initial stage in double-layer formation is dominated by a large-potential pulse propagating in the direction of the induced electrostatic drift; (3) the entire potential is dropped over a specific scale length once the double layer has formed; and (4) this scale length is expected to be of the order of 1 km for a double layer above a discrete auroral arc with a potential of 10 kV and the electric-field vector parallel to the magnetic-field vector.

  15. Double layers above the aurora

    NASA Technical Reports Server (NTRS)

    Temerin, M.; Mozer, F. S.

    1987-01-01

    Two different kinds of double layers were found in association with auroral precipitation. One of these is the so-called electrostatic shock, which is oriented at an oblique angle to the magnetic field in such a way that the perpendicular electric field is much larger than the parallel electric field. This type of double layer is often found at the edges of regions of upflowing ion beams and the direction of the electric fields in the shock points toward the ion beam. The potential drop through the shock can be several kV and is comparable to the total potential needed to produce auroral acceleration. Instabilities associated with the shock may generate obliquely propagating Alfven waves, which may accelerate electrons to produce flickering auroras. The flickering aurora provides evidence that the electrostatic shock may have large temporal fluctuations. The other kind of double layer is the small-amplitude double layer found in regions of upward flowing in beams, often in association with electrostatic ion cyclotron waves. The parallel and perpendicular electric fields in these structures are comparable in magnitude. The associated potentials are a few eV. Since many such double layers are found in regions of upward flowing ion beams, the combined potential drop through a set of these double layers can be substantial.

  16. Hybrid window layer for photovoltaic cells

    DOEpatents

    Deng, Xunming; Liao, Xianbo; Du, Wenhui

    2011-10-04

    A novel photovoltaic solar cell and method of making the same are disclosed. The solar cell includes: at least one absorber layer which could either be a lightly doped layer or an undoped layer, and at least a doped window-layers which comprise at least two sub-window-layers. The first sub-window-layer, which is next to the absorber-layer, is deposited to form desirable junction with the absorber-layer. The second sub-window-layer, which is next to the first sub-window-layer, but not in direct contact with the absorber-layer, is deposited in order to have transmission higher than the first-sub-window-layer.

  17. Hybrid window layer for photovoltaic cells

    DOEpatents

    Deng, Xunming; Liao, Xianbo; Du, Wenhui

    2011-02-01

    A novel photovoltaic solar cell and method of making the same are disclosed. The solar cell includes: at least one absorber layer which could either be a lightly doped layer or an undoped layer, and at least a doped window-layers which comprise at least two sub-window-layers. The first sub-window-layer, which is next to the absorber-layer, is deposited to form desirable junction with the absorber-layer. The second sub-window-layer, which is next to the first sub-window-layer, but not in direct contact with the absorber-layer, is deposited in order to have transmission higher than the first-sub-window-layer.

  18. Hybrid window layer for photovoltaic cells

    DOEpatents

    Deng, Xunming

    2010-02-23

    A novel photovoltaic solar cell and method of making the same are disclosed. The solar cell includes: at least one absorber layer which could either be a lightly doped layer or an undoped layer, and at least a doped window-layers which comprise at least two sub-window-layers. The first sub-window-layer, which is next to the absorber-layer, is deposited to form desirable junction with the absorber-layer. The second sub-window-layer, which is next to the first sub-window-layer, but not in direct contact with the absorber-layer, is deposited in order to have transmission higher than the first-sub-window-layer.

  19. Layer-by-layer assembly of vertically conducting graphene devices.

    PubMed

    Chen, Jing-Jing; Meng, Jie; Zhou, Yang-Bo; Wu, Han-Chun; Bie, Ya-Qing; Liao, Zhi-Min; Yu, Da-Peng

    2013-01-01

    Graphene has various potential applications owing to its unique electronic, optical, mechanical and chemical properties, which are primarily based on its two-dimensional nature. Graphene-based vertical devices can extend the investigations and potential applications range to three dimensions, while interfacial properties are crucial for the function and performance of such graphene vertical devices. Here we report a general method to construct graphene vertical devices with controllable functions via choosing different interfaces between graphene and other materials. Two types of vertically conducting devices are demonstrated: graphene stacks sandwiched between two Au micro-strips, and between two Co layers. The Au|graphene|Au junctions exhibit large magnetoresistance with ratios up to 400% at room temperature, which have potential applications in magnetic field sensors. The Co|graphene|Co junctions display a robust spin valve effect at room temperature. The layer-by-layer assembly of graphene offers a new route for graphene vertical structures. PMID:23715280

  20. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.

    1995-01-01

    This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.

  1. 'Blueberry' Layers Indicate Watery Origins

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This microscopic image, taken at the outcrop region dubbed 'El Capitan' near the Mars Exploration Rover Opportunity's landing site, reveals millimeter-scale (.04 inch-scale) layers in the lower portion. This same layering is hinted at by the fine notches that run horizontally across the sphere-like grain or 'blueberry' in the center left. The thin layers do not appear to deform around the blueberry, indicating that these geologic features are concretions and not impact spherules or ejected volcanic material called lapilli. Concretions are balls of minerals that form in pre-existing wet sediments. This image was taken by the rover's microscopic imager on the 29th martian day, or sol, of its mission. The observed area is about 3 centimeters (1.2 inches) across.

  2. North Polar Layers in Summer

    NASA Technical Reports Server (NTRS)

    2004-01-01

    15 October 2004 It is now early summer in the northern hemisphere on Mars, and this means that the ices of the north polar cap are in full retreat. Exposed from beneath seasonal frost are the eroded layers of what Mars scientists suspect are composed of a mixture of dust and ice (and in some layers, sand). This October 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows some of the north polar layers exposed on a moderately-dipping slope. The bright material at the top of the image is water ice frost; the triangular features are thought to be caused by wind erosion of the frost. This image is located near 87.1oN, 267.4oW, and covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  3. Lidar study of K layer

    NASA Astrophysics Data System (ADS)

    Jiao, Jing

    2016-07-01

    A double-laser-beam lidar was successfully developed in 2010 to measure the K layer over Yanqing County, Beijing (40.5°N, 116.2°E). Comprehensive statistical analyses of sporadic K (Ks) layer parameters were conducted using two years of lidar data, and the parameters of the Ks layers and their distribution obtained by the analyses are described. The seasonal distribution of Ks occurrence was obtained, with two maxima observed in January and July, respectively. The seasonal distributions of sporadic E (Es) occurrence over Beijing differ from those of Ks occurrence. However, good correlations between Es and Ks in case by case study were found. We also found that four Ks events with peak altitudes lower than 90 km were associated with large and sharp temperature increases in five comparative examples.

  4. Layered Rocks in 'Columbia Hills'

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This black-and-white image shows the first layered rocks scientists have seen close up in Gusev Crater, where NASA's Mars Exploration Rover Spirit landed Jan. 4, 2004. While Spirit's twin rover, Opportunity, reached the stadium-size Endurance Crater on the other side of Mars and began exploring its many layered outcrops in early May, Spirit traveled more than 3.5 kilometers (2.2 miles) to get to this layered bedrock in the 'Columbia Hills.' Scientists are planning to conduct a study of these rocks to determine if they are volcanic or sedimentary in origin, and if they have been chemically altered. Spirit's panoramic camera took this image on sol 217 (Aug. 13, 2004).

  5. Unsteady turbulent boundary layer analysis

    NASA Technical Reports Server (NTRS)

    Singleton, R. E.; Nash, J. F.; Carl, L. W.; Patel, V. C.

    1973-01-01

    The governing equations for an unsteady turbulent boundary layer on a swept infinite cylinder, composed of a continuity equation, a pair of momentum equations and a pair of turbulent energy equations which include upstream history efforts, are solved numerically. An explicit finite difference analog to the partial differential equations is formulated and developed into a computer program. Calculations were made for a variety of unsteady flows in both two and three dimensions but primarily for two dimensional flow fields in order to first understand some of the fundamental physical aspects of unsteady turbulent boundary layers. Oscillating free stream flows without pressure gradient, oscillating retarded free stream flows and monotonically time-varying flows have all been studied for a wide frequency range. It was found that to the lowest frequency considered, the lower frequency bound being determined by economic considerations (machine time), there were significant unsteady effects on the turbulent boundary layer.

  6. Controlled Layer-by-Layer Etching of MoS₂.

    PubMed

    Lin, TaiZhe; Kang, BaoTao; Jeon, MinHwan; Huffman, Craig; Jeon, JeaHoo; Lee, SungJoo; Han, Wei; Lee, JinYong; Lee, SeHan; Yeom, GeunYoung; Kim, KyongNam

    2015-07-29

    Two-dimensional (2D) metal dichalcogenides like molybdenum disulfide (MoS2) may provide a pathway to high-mobility channel materials that are needed for beyond-complementary metal-oxide-semiconductor (CMOS) devices. Controlling the thickness of these materials at the atomic level will be a key factor in the future development of MoS2 devices. In this study, we propose a layer-by-layer removal of MoS2 using the atomic layer etching (ALET) that is composed of the cyclic processing of chlorine (Cl)-radical adsorption and argon (Ar)(+) ion-beam desorption. MoS2 etching was not observed with only the Cl-radical adsorption or low-energy (<20 eV) Ar(+) ion-beam desorption steps; however, the use of sequential etching that is composed of the Cl-radical adsorption step and a subsequent Ar(+) ion-beam desorption step resulted in the complete etching of one monolayer of MoS2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) indicated the removal of one monolayer of MoS2 with each ALET cycle; therefore, the number of MoS2 layers could be precisely controlled by using this cyclical etch method. In addition, no noticeable damage or etch residue was observed on the exposed MoS2.

  7. The Entrainment Interface Layer of Stratocumulus-topped Boundary Layers

    NASA Astrophysics Data System (ADS)

    Krueger, S.; Hill, S.

    2010-09-01

    The entrainment interface layer (EIL) is the layer between cloud top and the free atmosphere. It contains mixtures of air from the cloud layer and the free atmosphere. In addition to turbulent mixing, phase changes and radiative heating or ccoling also affect the thermodynamic properties of air in the EIL. Eventually, air from the EIL is entrained into the cloud layer. How do processes in the EIL affect the entrainment rate? What is the structure of the EIL? Is cloud-top an interface (a region of high gradients), or simply an iso-surface? We are using airborne measuurements taken in the EIL during POST (Physics of Stratocumulus Top), which took place during July and August 2008 near Monterey, California, USA, to address these questions. High-rate measurements of temperature and liquid water content made just 0.5 m apart allow us to perform a high-resolution analysis of a conserved variable (liquid water potential temperature). When combined with lower-rate measurements of water vapor, they also allow us to perform a mixture fraction analysis following vanZanten and Duynkerke (2002).

  8. Operating System Abstraction Layer (OSAL)

    NASA Technical Reports Server (NTRS)

    Yanchik, Nicholas J.

    2007-01-01

    This viewgraph presentation reviews the concept of the Operating System Abstraction Layer (OSAL) and its benefits. The OSAL is A small layer of software that allows programs to run on many different operating systems and hardware platforms It runs independent of the underlying OS & hardware and it is self-contained. The benefits of OSAL are that it removes dependencies from any one operating system, promotes portable, reusable flight software. It allows for Core Flight software (FSW) to be built for multiple processors and operating systems. The presentation discusses the functionality, the various OSAL releases, and describes the specifications.

  9. Step Free Surface Heteroepitaxy of 3C-SiC Layers on Patterned 4H/6H-SiC Mesas and Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew J.; Spry, David J.

    2003-01-01

    Most SiC devices are implemented in homoepitaxial films grown on 4H/6H-SiC wafers with surfaces 3 degrees to 8 degrees off-axis from the (0001) basal plane. This approach has not prevented many substrate crystal defects from propagating into SiC epilayers, and does not permit the realization of SiC heteropolytype devices. This presentation describes recent advances in SiC epitaxial growth that begun to overcome the above shortcomings for arrays of mesas patterned into on-axis 4H/6H-SiC wafers. First, we demonstrated that atomic-scale surface steps can be completely eliminated from 4H/6H-SiC mesas via on-axis homoepitaxial step-flow growth, forming (0001) basal plane surfaces (up to 0.4 mm x 0.4 mm) for larger than previously thought possible. Step-free surface areas were then extended by growth fo thin lateral cantilevers from the mesa tops. These lateral cantilevers enabled substrate defects to be reduced and relocated in homoepitaxial films in a manner not possible with off-axis SiC growth. Finally, growth of vastly improved 3C-SiC heterofilms was achieved on 4H/6H-SiC mesas using the recently develop step-free surface heteroepitaxy process. These epitaxial growth developments should enable improved homojunction and heterojunction silicon carbide prototype devices.

  10. Thin bacteria/Layered Double Hydroxide films using a layer-by-layer approach.

    PubMed

    Halma, Matilte; Khenifi, Aicha; Sancelme, Martine; Besse-Hoggan, Pascale; Bussière, Pierre-Olivier; Prévot, Vanessa; Mousty, Christine

    2016-07-15

    This paper reports the design of thin bacteria/Layered Double Hydroxides (LDH) films in which bacterial cells of Pseudomonas sp. strain ADP were assembled alternatively with Mg2Al-NO3 LDH nanosheets by a layer-by-layer deposition method. The UV-Vis spectroscopy was used to monitor the assembly process, showing a progressive increase in immobilized bacteria amount upon deposited cycles. The {ADP/LDH}n film was characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy and atomic force microscopy. The metabolic activity of immobilized bacteria was determined using chronoamperometry by measuring the biochemical oxygen demand in presence of glucose using an artificial electron acceptor (Fe(CN)6(3-)) at 0.5V/Ag-AgCl. A steady current of 0.250μAcm(-2) was reached in about 30s after the addition of 5mM glucose. PMID:27124809

  11. Layering Literacies and Contemporary Learning

    ERIC Educational Resources Information Center

    Abrams, Sandra Schamroth; Russo, Michael P.

    2015-01-01

    This article explores how adolescents layer literacies in and outside school. Findings from a longitudinal study of gaming in a public library, as well as data related to the use of Portal 2 in a New York City middle school classroom, reveal how the students created, showcased, analyzed, and experimented with online and offline artifacts and…

  12. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

    The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles can be…

  13. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, I. H.

    1993-01-01

    The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.

  14. High Performance Thin Layer Chromatography.

    ERIC Educational Resources Information Center

    Costanzo, Samuel J.

    1984-01-01

    Clarifies where in the scheme of modern chromatography high performance thin layer chromatography (TLC) fits and why in some situations it is a viable alternative to gas and high performance liquid chromatography. New TLC plates, sample applications, plate development, and instrumental techniques are considered. (JN)

  15. Single-Layer, Multicolor Electroluminescent Phosphors

    NASA Technical Reports Server (NTRS)

    Robertson, James B.

    1988-01-01

    Etching eliminated in producing phosphor layers for displays. New process enables production of single-layer, two-color phosphor layer without etching. Method of construction, beginning with glass substrate with electrode and insulator layers, involves deposition of green phosphor masking with metal mask or photoresist; diffusion or ion implantation of manganese through mask to produce red phosphor and removal of mask.

  16. Doped LZO buffer layers for laminated conductors

    DOEpatents

    Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

    2010-03-23

    A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

  17. nBn and pBp infrared detectors with graded barrier layer, graded absorption layer, or chirped strained layer super lattice absorption layer

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath D. (Inventor); Ting, David Z. (Inventor); Hill, Cory J. (Inventor); Bandara, Sumith V. (Inventor)

    2010-01-01

    An nBn detector is described where for some embodiments the barrier layer has a concentration gradient, for some embodiments the absorption layer has a concentration gradient, and for some embodiments the absorption layer is a chirped strained layer super lattice. The use of a graded barrier or absorption layer, or the use of a chirped strained layer super lattice for the absorption layer, allows for design of the energy bands so that the valence band may be aligned across the device. Other embodiments are described and claimed.

  18. Organic photovoltaic cells utilizing ultrathin sensitizing layer

    DOEpatents

    Rand, Barry P.; Forrest, Stephen R.

    2011-05-24

    A photosensitive device includes a series of organic photoactive layers disposed between two electrodes. Each layer in the series is in direct contact with a next layer in the series. The series is arranged to form at least one donor-acceptor heterojunction, and includes a first organic photoactive layer comprising a first host material serving as a donor, a thin second organic photoactive layer comprising a second host material disposed between the first and a third organic photoactive layer, and the third organic photoactive layer comprising a third host material serving as an acceptor. The first, second, and third host materials are different. The thin second layer serves as an acceptor relative to the first layer or as a donor relative to the third layer.

  19. Rapid Prototyping Of Layered Composite Parts

    NASA Technical Reports Server (NTRS)

    Wolff, Edwin D.

    1992-01-01

    Numerically controlled cutting accelerates fabrication of layers. Proposed method derived from stereoscopic lithography. CATIA or CAEDS computer program used to generate three-dimensional mathematical model of prototype part. In model, geometry of part specified in layers, as in stereoscopic lithography. Model data for each layer fed to computer-numerically-controlled ultrasonic cutting machine. Sheet of prepreg (uncured composite material) of specified layer thickness placed in machine and cut, under control of model data, to specified shape of layer.

  20. Chemical solution seed layer for rabits tapes

    SciTech Connect

    Goyal, Amit; Paranthaman, Mariappan; Wee, Sung-Hun

    2014-06-10

    A method for making a superconducting article includes the steps of providing a biaxially textured substrate. A seed layer is then deposited. The seed layer includes a double perovskite of the formula A.sub.2B'B''O.sub.6, where A is rare earth or alkaline earth metal and B' and B'' are different rare earth or transition metal cations. A superconductor layer is grown epitaxially such that the superconductor layer is supported by the seed layer.

  1. Buffer layer for thin film structures

    DOEpatents

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

    2010-06-15

    A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

  2. Buffer layer for thin film structures

    DOEpatents

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

    2006-10-31

    A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

  3. Fluidized bed layer-by-layer microcapsule formation.

    PubMed

    Richardson, Joseph J; Teng, Darwin; Björnmalm, Mattias; Gunawan, Sylvia T; Guo, Junling; Cui, Jiwei; Franks, George V; Caruso, Frank

    2014-08-26

    Polymer microcapsules can be used as bioreactors and artificial cells; however, preparation methods for cell-like microcapsules are typically time-consuming, low yielding, and/or involve custom microfluidics. Here, we introduce a rapid (∼30 min per batch, eight layers), scalable (up to 500 mg of templates), and efficient (98% yield) microcapsule preparation technique utilizing a fluidized bed for the layer-by-layer (LbL) assembly of polymers, and we investigate the parameters that govern the formation of robust capsules. Fluidization in water was possible for particles of comparable diameter to mammalian cells (>5 μm), with the experimental flow rates necessary for fluidization matching well with the theoretical values. Important variables for polymer film deposition and capsule formation were the concentration of polymer solution and the molecular weight of the polymer, while the volume of the polymer solution had a negligible impact. In combination, increasing the polymer molecular weight and polymer solution concentration resulted in improved film deposition and the formation of robust microcapsules. The resultant polymer microcapsules had a thickness of ∼5.5 nm per bilayer, which is in close agreement with conventionally prepared (quiescent (nonflow) adsorption/centrifugation/wash) LbL capsules. The technique reported herein provides a new way to rapidly generate microcapsules (approximately 8 times quicker than the conventional means), while being also amenable to scale-up and mass production. PMID:25113552

  4. Fluidized bed layer-by-layer microcapsule formation.

    PubMed

    Richardson, Joseph J; Teng, Darwin; Björnmalm, Mattias; Gunawan, Sylvia T; Guo, Junling; Cui, Jiwei; Franks, George V; Caruso, Frank

    2014-08-26

    Polymer microcapsules can be used as bioreactors and artificial cells; however, preparation methods for cell-like microcapsules are typically time-consuming, low yielding, and/or involve custom microfluidics. Here, we introduce a rapid (∼30 min per batch, eight layers), scalable (up to 500 mg of templates), and efficient (98% yield) microcapsule preparation technique utilizing a fluidized bed for the layer-by-layer (LbL) assembly of polymers, and we investigate the parameters that govern the formation of robust capsules. Fluidization in water was possible for particles of comparable diameter to mammalian cells (>5 μm), with the experimental flow rates necessary for fluidization matching well with the theoretical values. Important variables for polymer film deposition and capsule formation were the concentration of polymer solution and the molecular weight of the polymer, while the volume of the polymer solution had a negligible impact. In combination, increasing the polymer molecular weight and polymer solution concentration resulted in improved film deposition and the formation of robust microcapsules. The resultant polymer microcapsules had a thickness of ∼5.5 nm per bilayer, which is in close agreement with conventionally prepared (quiescent (nonflow) adsorption/centrifugation/wash) LbL capsules. The technique reported herein provides a new way to rapidly generate microcapsules (approximately 8 times quicker than the conventional means), while being also amenable to scale-up and mass production.

  5. Deep layer malt drying modelling

    SciTech Connect

    Lopez, A.; Virseda, P.; Martinez, G.; Llorca, M.

    1997-05-01

    In malt production drying operation plays an important role in the total processing cost, however there are not many studies on malt drying modeling and optimization. In this paper a deep layer malt drying mathematical model in the form of four partial differential equations is presented. To determine drying constants, malt thin layer drying experiments at several air temperatures and relative humidities were made. The model were validated at industrial scale. The greatest energy savings, approximately 5.5% in fuel and 7.5% in electric energy, were obtained by an additional (and increased) air recirculation, which is carried out during the last 6 hours of the drying process and a significant decrease of air flow-rate during the last 6 hours of the drying process.

  6. Fluctuation phenomena in layered superconductors

    SciTech Connect

    Klemm, R.A.

    1996-10-01

    Gaussian fluctuations in layered superconductors have been the subject of study for many years. Although the FD was studied in detail long ago, the FC (fluctuation conductivity) was studied only recently, since the MT and DOS diagrams were previously neglected. Recent comparisons with experiment on YBCO have shown that the DOS diagrams are important and can lead to qualitatively different behaviors for the FC parallel and perpendicular to the layers. In both cases, Gaussian fluctuations fit the data above {Tc} very well, even for YBCO. To date, nearly all calculations of fluctuation quantities were for B{parallel}{cflx c}. Nevertheless, it should be possible to treat an arbitrary B, but the evaluation of the required matrix elements for the fluctuation quantities will be more complicated.

  7. Jupiter's deep magnetotail boundary layer

    NASA Astrophysics Data System (ADS)

    Nicolaou, G.; McComas, D. J.; Bagenal, F.; Elliott, H. A.; Ebert, R. W.

    2015-06-01

    In 2007 the New Horizons (NH) spacecraft flew by Jupiter for a gravity assist en route to Pluto. After closest approach on day of year (DOY) 58, 2007, NH followed a tailward trajectory that provided a unique opportunity to explore the deep jovian magnetotail and the surrounding magnetosheath. After DOY 132, 16 magnetopause crossings were observed between 1654 and 2429 Jupiter radii (Rj) along the dusk flank tailward of the planet. In some cases the crossings were identified as rapid transitions from the magnetotail to the magnetosheath and vice versa. In other cases a boundary layer was observed just inside the magnetopause. Solar Wind Around Pluto (SWAP) is an instrument on board NH that obtained spectra of low energy ions during the flyby period. We use a forward model including the SWAP instrument response to derive plasma parameters (density, temperature and velocity) which best reproduce the observations. We also vary the plasma parameters in our model in order to fit the observations more accurately on occasions where the measurements exhibit significant variability. We compare the properties of the plasma in the boundary layer with those of the magnetosheath plasma derived in our earlier work. We attempt to estimate the magnetic field in the boundary layer assuming pressure balance between it and the magnetosheath. Finally, we investigate several possible scenarios to assess if magnetopause movement and structure could cause the variations seen in the data.

  8. Angled Layers in Super Resolution

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Researchers used a special imaging technique with the panoramic camera on NASA's Mars Exploration Rover Opportunity to get as detailed a look as possible at a target region near eastern foot of 'Burns Cliff.' The intervening terrain was too difficult for driving the rover closer. The target is the boundary between two sections of layered rock. The layers in lower section (left) run at a marked angle to the layers in next higher section (right).

    This view is the product of a technique called super resolution. It was generated from data acquired on sol 288 of Opportunity's mission (Nov. 14, 2004) from a position along the southeast wall of 'Endurance Crater.' Resolution slightly higher than normal for the panoramic camera was synthesized for this view by combining 17 separate images of this scene, each one 'dithered' or pointed slightly differently from the previous one. Computer manipulation of the individual images was then used to generate a new synthetic view of the scene in a process known mathematically as iterative deconvolution, but referred to informally as super resolution. Similar methods have been used to enhance the resolution of images from the Mars Pathfinder mission and the Hubble Space Telescope.

  9. CFCS and the ozone layer.

    PubMed

    Hayman, G D

    1997-05-01

    Ozone is an important constituent of the atmosphere. Ozone forms a distinct layer in the lower stratosphere known as the ozone layer. The ozone layer acts as a fragile shield because it protects man and other life forms from exposure to harmful short-wavelength ultraviolet (UV) radiation. The agents, particularly chemical, which affect the amount of ozone present in the atmosphere have been a source of concern for more than 20 years. This has been reinforced by the dramatic decline of stratospheric ozone levels first measured in Antarctica and now apparent worldwide. The combination of routine measurements of ozone depletion, careful laboratory studies and mathematical modelling of ozone in the atmosphere, has demonstrated that the reactive fragments produced when chlorofluorocarbons (CFCs), halons and other halogenated compounds break down in the stratosphere are responsible for the ozone loss. As CFCs have widespread and sometimes apparently essential uses in modern society, there has been an intense effort to develop safe, effective replacements which have a negligible or much smaller impact on the environment. The Montreal Protocol, signed by over 140 nations, has been implemented to control and phase out the chemical compounds responsible for ozone loss.

  10. Mixed Layers and Satellite Retrievals

    NASA Technical Reports Server (NTRS)

    Boers, R.

    1984-01-01

    As part of the process to determine whether it is possible to retrieve boundary layer structure with the current sounding techniques, temperature retievals were performed for radiosonde profiles that showed temperature inversions. It was found that when temperature inversions exceed 8 to 10 C a retrieval will indeed show a temperature increase with height over a limited vertical distance. For weaker inversions retrieved temperatures are generally smoothly decreasing with height. It is, however, impossible to determine the actual mixed layer height from the retrievals. Whether the water vapor channels could be used in observing mixed layer structure was investigated. Temperature inversions are accompanied by significant drops in relative humidity. While this effect is very pronounced in parts of the trade wind regimes with relative humidity drops of up to 60%, it is widespread in other areas of the ocean as well. A simulation experiment was performed in which brightness temperatures were computed for smooth temperature and humidity profiles and compared with those computed from inversion profiles.

  11. Optimized capping layers for EUV multilayers

    DOEpatents

    Bajt, Sasa; Folta, James A.; Spiller, Eberhard A.

    2004-08-24

    A new capping multilayer structure for EUV-reflective Mo/Si multilayers consists of two layers: A top layer that protects the multilayer structure from the environment and a bottom layer that acts as a diffusion barrier between the top layer and the structure beneath. One embodiment combines a first layer of Ru with a second layer of B.sub.4 C. Another embodiment combines a first layer of Ru with a second layer of Mo. These embodiments have the additional advantage that the reflectivity is also enhanced. Ru has the best oxidation resistance of all materials investigated so far. B.sub.4 C is an excellent barrier against silicide formation while the silicide layer formed at the Si boundary is well controlled.

  12. Boundary layer receptivity and control

    NASA Technical Reports Server (NTRS)

    Hill, D. C.

    1993-01-01

    Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three

  13. Tomographic reconstruction of layered tissue structures

    NASA Astrophysics Data System (ADS)

    Hielscher, Andreas H.; Azeez-Jan, Mohideen; Bartel, Sebastian

    2001-11-01

    In recent years the interest in the determination of optical properties of layered tissue structure has resurfaced. Applications include, for example, studies on layered skin tissue and underlying muscles, imaging of the brain underneath layers of skin, skull, and meninges, and imaging of the fetal head in utero beneath the layered structures of the maternal abdomen. In this work we approach the problem of layered structures in the framework of model-based iterative image reconstruction schemes. These schemes are currently developed to determine the optical properties inside tissue from measurement on the surface. If applied to layered structure these techniques yield substantial improvements over currently available semi-analytical approaches.

  14. Subsurface plankton layers in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Churnside, James H.; Marchbanks, Richard D.

    2015-06-01

    The first synoptic measurements of subsurface plankton layers were made in the western Arctic Ocean in July 2014 using airborne lidar. Layers were detected in open water and in pack ice where up to 90% of the surface was covered by ice. Layers under the ice were less prevalent, weaker, and shallower than those in open water. Layers were more prevalent in the Chukchi Sea than in the Beaufort Sea. Three quarters of the layers observed were thinner than 5 m. The presence of these layers, which are not adequately captured in satellite data, will influence primary productivity, secondary productivity, fisheries recruitment, and carbon export to the benthos.

  15. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable, and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable, and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam, and the beam plasma discharge is ignited.

  16. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the 'beam plasma discharge' is ignited.

  17. Sparse coding for layered neural networks

    NASA Astrophysics Data System (ADS)

    Katayama, Katsuki; Sakata, Yasuo; Horiguchi, Tsuyoshi

    2002-07-01

    We investigate storage capacity of two types of fully connected layered neural networks with sparse coding when binary patterns are embedded into the networks by a Hebbian learning rule. One of them is a layered network, in which a transfer function of even layers is different from that of odd layers. The other is a layered network with intra-layer connections, in which the transfer function of inter-layer is different from that of intra-layer, and inter-layered neurons and intra-layered neurons are updated alternately. We derive recursion relations for order parameters by means of the signal-to-noise ratio method, and then apply the self-control threshold method proposed by Dominguez and Bollé to both layered networks with monotonic transfer functions. We find that a critical value αC of storage capacity is about 0.11|a ln a| -1 ( a≪1) for both layered networks, where a is a neuronal activity. It turns out that the basin of attraction is larger for both layered networks when the self-control threshold method is applied.

  18. Layer-by-layer nanoencapsulation of camptothecin with improved activity.

    PubMed

    Parekh, Gaurav; Pattekari, Pravin; Joshi, Chaitanya; Shutava, Tatsiana; DeCoster, Mark; Levchenko, Tatyana; Torchilin, Vladimir; Lvov, Yuri

    2014-04-25

    160 nm nanocapsules containing up to 60% of camptothecin in the core and 7-8 polyelectrolyte bilayers in the shell were produced by washless layer-by-layer assembly of heparin and block-copolymer of poly-l-lysine and polyethylene glycol. The outer surface of the nanocapsules was additionally modified with polyethylene glycol of 5 kDa or 20 kDa molecular weight to attain protein resistant properties, colloidal stability in serum and prolonged release of the drug from the capsules. An advantage of the LbL coated capsules is the preservation of camptothecin lactone form with the shell assembly starting at acidic pH and improved chemical stability of encapsulated drug at neutral and basic pH, especially in the presence of albumin that makes such formulation more active than free camptothecin. LbL nanocapsules preserve the camptothecin lactone form at pH 7.4 resulting in triple activity of the drug toward CRL2303 glioblastoma cell. PMID:24508806

  19. Layer-by-layer assemblies for cancer treatment and diagnosis

    PubMed Central

    Liu, Xi Qiu; Picart, Catherine

    2016-01-01

    The layer-by-layer (LbL) technique was introduced in the early 90s by Profs Moehwald, Lvov and Decher. Since then, it has undergone a series of technological developments, making it possible to engineer various theranostic platforms such as films and capsules, with precise control at the nanometer and micrometer scales. This Research News article highlights recent progress in the applications of LbL assemblies in the field of cancer therapy, diagnosis and fundamental biology study. The potentials of LbL-based systems as drug carriers are discussed, especially with regard to the engineering of innovative stimuli-responsive systems, and their advantageous multifunctionality in the development of new therapeutic tools. Then, the diagnostic functions of LbL assemblies are illustrated for detection and capture of rare cancer cells. Finally, LbL mimicking extracellular environments demonstrate the emerging potential for the study of cancer cell behaviors in vitro. We conclude by highlighting the advantages of LbL systems, important challenges that need to be overcome, and future perspectives in clinical practice. PMID:26390356

  20. Layer-by-layer nanoencapsulation of camptothecin with improved activity

    PubMed Central

    Parekh, Gaurav; Pattekari, Pravin; Joshi, Chaitanya; Shutava, Tatsiana; DeCoster, Mark; Levchenko, Tatyana; Torchilin, Vladimir; Lvov, Yuri

    2014-01-01

    160 nm nanocapsules containing up to 60% of camptothecin in the core and 7–8 polyelectrolyte bilayers in the shell were produced by washless layer-by-layer assembly of heparin and block-copolymer of poly-L-lysine and polyethylene glycol. The outer surface of the nanocapsules was additionally modified with polyethylene glycol of 5 kDa or 20 kDa molecular weight to attain protein resistant properties, colloidal stability in serum and prolonged release of the drug from the capsules. An advantage of the LbL coated capsules is the preservation of camptothecin lactone form with the shell assembly starting at acidic pH and improved chemical stability of encapsulated drug at neutral and basic pH, especially in the presence of albumin that makes such formulation more active than free camptothecin. LbL nanocapsules preserve the camptothecin lactone form at pH 7.4 resulting in triple activity of the drug toward CRL2303 glioblastoma cell. PMID:24508806

  1. Inkjet Deposition of Layer-by-Layer Assembled Films

    SciTech Connect

    Andres, C. M.; Kotov, Nicholas A.

    2010-09-23

    Layer-by-layer assembly (LBL) can create advanced composites with exceptional properties unavailable by other means, but the laborious deposition process and multiple dipping cycles hamper their utilization in microtechnologies and electronics. Multiple rinse steps provide both structural control and thermodynamic stability to LBL multilayers, but they significantly limit their practical applications and contribute significantly to the processing time and waste. Here we demonstrate that by employing inkjet technology one can deliver the necessary quantities of LBL components required for film buildup without excess, eliminating the need for repetitive rinsing steps. This feature differentiates this approach from all other recognized LBL modalities. Using a model system of negatively charged gold nanoparticles and positively charged poly(diallyldimethylammonium) chloride, the material stability, nanoscale control over thickness, and particle coverage offered by the inkjet LBL technique are shown to be equal or better than the case of multilayers made with traditional dipping cycles. The opportunity for fast deposition of complex metallic patterns using a simple inkjet printer is also shown. The additive nature of LBL deposition based on the formation of insoluble nanoparticle-polyelectrolyte complexes of various compositions provides an excellent opportunity for versatile, multicomponent, and noncontact patterning for the simple production of stratified patterns that are much needed in advanced devices.

  2. Inkjet Deposition of Layer by Layer Assembled Films

    PubMed Central

    Andres, Christine M.; Kotov, Nicholas A.

    2010-01-01

    Layer-by-layer assembly (LBL) can create advanced composites with exceptional properties unavailable by other means, but the laborious deposition process and multiple dipping cycles hamper their utilization in microtechnologies and electronics. Multiple rinse steps provide both structural control and thermodynamic stability to LBL multilayers but they significantly limit their practical applications and contribute significantly to the processing time and waste. Here we demonstrate that by employing inkjet technology one can deliver the necessary quantities of LBL components required for film build-up without excess, eliminating the need for repetitive rinsing steps. This feature differentiates this approach from all other recognized LBL modalities. Using a model system of negatively charged gold nanoparticles and positively charged poly(diallyldimethylammonium) chloride, the material stability, nanoscale control over thickness and particle coverage offered by the inkjet LBL technique are shown to be equal or better than the multilayers made with traditional dipping cycles. The opportunity for fast deposition of complex metallic patterns using a simple inkjet printer was also shown. The additive nature of LBL deposition based on the formation of insoluble nanoparticle-polyelectrolyte complexes of various compositions provides an excellent opportunity for versatile, multi-component, and non-contact patterning for the simple production of stratified patterns that are much needed in advanced devices. PMID:20863114

  3. Layer-by-Layer Assemblies for Cancer Treatment and Diagnosis.

    PubMed

    Liu, Xi Qiu; Picart, Catherine

    2016-02-10

    The layer-by-layer (LbL) technique was introduced in the early 1990s. Since then, it has undergone a series of technological developments, making it possible to engineer various theranostic platforms, such as films and capsules, with precise control at the nanometer and micrometer scales. Recent progress in the applications of LbL assemblies in the field of cancer therapy, diagnosis, and fundamental biological study are highlighted here. The potential of LbL-based systems as drug carriers is discussed, especially with regard to the engineering of innovative stimuli-responsive systems, and their advantageous multifunctionality in the development of new therapeutic tools. Then, the diagnostic functions of LbL assemblies are illustrated for detection and capture of rare cancer cells. Finally, LbL-mimicking extracellular environments demonstrate the emerging potential for the study of cancer cell behavior in vitro. The advantages of LbL systems, important challenges that need to be overcome, and future perspectives in clinical practice are then highlighted.

  4. Geodynamics: Layer cake or plum pudding?

    NASA Astrophysics Data System (ADS)

    Tackley, Paul J.

    2008-03-01

    Whether convection in the Earth's mantle extends through its entire depth or if the mantle is layered has long been debated. Recent research suggests that spatially and temporally intermittent or partial layering is the most likely solution.

  5. Layered Yardangs in Henry Crater

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-389, 12 June 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows wind-sculpted remnants of layered sedimentary rock that once completely covered the northwestern floor of Henry Crater, an ancient impact basin located at 11.7oN, 336.4oW. These landforms, shaped somewhat like inverted boat hulls, are 'textbook examples' of a wind erosion form known as a yardang. The image covers an area 2.3 km (1.4 mi) wide; sunlight illuminates the scene from the left.

  6. Ground Layer Laser Seeing Meter

    NASA Astrophysics Data System (ADS)

    Cavazzani, S.; Rodeghiero, G.; Capraro, I.; Ortolani, S.; Barbieri, C.; Zitelli, V.

    2014-03-01

    The seeing calculation and its evolution during the night is a key point for the operation of telescopes and adaptive optics systems. Currently, there are various instruments able to measure the seeing, for example, the DIMM (differential image motion monitor) and the MASS (multi aperture scintillation sensor). This paper describes a new tool for the local ground layer seeing measurement. In particular, we want to derive the Fried parameter r0 through a laser beam horizontal propagation. This is a new method for the experimental study of low-altitude atmospheric turbulence. Finally, we sketch an experimental setup for the Asiago Ekar Observatory and its possible applications.

  7. Bursts in inclined layer convection

    NASA Astrophysics Data System (ADS)

    Busse, F. H.; Clever, R. M.

    2000-08-01

    A new instability of longitudinal rolls in an inclined fluid layer heated from below is analyzed in the case of the Prandtl number P=0.71. The instability assumes the form of subharmonic undulations and evolves into a spatially chaotic pattern when the angle of inclination is of the order of 20°. The chaotic state rapidly decays and longitudinal rolls recover until the next burst of chaotic convection occurs. The theoretical findings closely correspond to recent experimental observations by Daniels et al. [Phys. Rev. Lett. (to be published)].

  8. Computer Program Re-layers Engineering Drawings

    NASA Technical Reports Server (NTRS)

    Crosby, Dewey C., III

    1990-01-01

    RULCHK computer program aids in structuring layers of information pertaining to part or assembly designed with software described in article "Software for Drawing Design Details Concurrently" (MFS-28444). Checks and optionally updates structure of layers for part. Enables designer to construct model and annotate its documentation without burden of manually layering part to conform to standards at design time.

  9. Outline of research on oscillating boundary layers

    NASA Technical Reports Server (NTRS)

    Cousteix, J.

    1979-01-01

    The state of the art in the field of unsteady boundary layers is outlined with emphasis on turbulent boundary layers. The unsteady flows considered are mainly periodic with the external velocity varying around a zero or nonzero mean time value. The principal results obtained on laminar boundary layers are also presented.

  10. Microscopy of single-layer carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Wang, Su; Zhou, Dan

    1994-07-01

    Single-layer carbon nanotubes produced with yttrium carbide as catalyst have been studied with high-resolution transmission electron microscopy (HRTEM). The morphology, condition of iamging and the method of measurement to determine the actual diameter of a single-layer carbon nanotube have been detailed and the growth mechanism of single-layer carbon nanotubes has been discussed in this research.

  11. Turbulent boundary layer of an airfoil

    NASA Technical Reports Server (NTRS)

    Fediaevsky, K

    1937-01-01

    A need has arisen for a new determination of the velocity profiles in the boundary layer. Assuming that the character of the velocity distribution depends to a large extent on the character of the shear distribution across the boundary layer, we shall consider the nature of the shear distribution for a boundary layer with a pressure gradient.

  12. The Hole in the Ozone Layer.

    ERIC Educational Resources Information Center

    Hamers, Jeanne S.; Jacob, Anthony T.

    This document contains information on the hole in the ozone layer. Topics discussed include properties of ozone, ozone in the atmosphere, chlorofluorocarbons, stratospheric ozone depletion, effects of ozone depletion on life, regulation of substances that deplete the ozone layer, alternatives to CFCs and Halons, and the future of the ozone layer.…

  13. Biaxially textured metal substrate with palladium layer

    DOEpatents

    Robbins, William B [Maplewood, MN

    2002-12-31

    Described is an article comprising a biaxially textured metal substrate and a layer of palladium deposited on at least one major surface of the metal substrate; wherein the palladium layer has desired in-plane and out-of-plane crystallographic orientations, which allow subsequent layers that are applied on the article to also have the desired orientations.

  14. Compressible turbulent boundary layer interaction experiments

    NASA Technical Reports Server (NTRS)

    Settles, G. S.; Bogdonoff, S. M.

    1981-01-01

    Four phases of research results are reported: (1) experiments on the compressible turbulent boundary layer flow in a streamwise corner; (2) the two dimensional (2D) interaction of incident shock waves with a compressible turbulent boundary layer; (3) three dimensional (3D) shock/boundary layer interactions; and (4) cooperative experiments at Princeton and numerical computations at NASA-Ames.

  15. Equilibrium states of pancake vortices in layered superconductors: coupling of inter-layer ordering and in-layer ordering

    NASA Astrophysics Data System (ADS)

    Wu, Wenjuan; Zhao, H. J.; Zhou, Wei; Shi, Z. X.

    2016-10-01

    We numerically study the static configurations of pancake vortices in layered superconductors. We analyze how disordering induced by random pinning centers competes with inter-layer ordering and in-layer ordering. In general, for inter-layer ordering, 3D states composed of coupled vortex lines are formed for strong inter-layer coupling strength and weak pinning strength. In contrast, 2D states composed of decoupled individual pancake vortices are formed for weak inter-layer coupling strength and strong pinning strength. For in-layer ordering, with increasing pinning forces, the in-layer structure evolves from crystals to Bragg glasses (BGs), vortex glasses (VGs), and liquid-like structures. Changing the vortex density, an initially fast disordering, then slow ordering procedure is found for both in-layer and inter-layer ordering, which is a possible clue to second peak effect (SPE). The reason behind this non-monotonic behavior is discussed. Our results are summarized in a phase diagram in the plane of ‘inter-layer coupling strength s m versus pinning strength f p.

  16. Modelling the transitional boundary layer

    NASA Technical Reports Server (NTRS)

    Narasimha, R.

    1990-01-01

    Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.

  17. Multilayer article having stabilized zirconia outer layer and chemical barrier layer

    NASA Technical Reports Server (NTRS)

    Lee, Kang N. (Inventor); Bansal, Narottam P. (Inventor)

    2004-01-01

    A multilayer article includes a substrate that includes at least one of a ceramic compound and a Si-containing metal alloy. An outer layer includes stabilized zirconia. Intermediate layers are located between the outer layer and the substrate and include a mullite-containing layer and a chemical barrier layer. The mullite-containing layer includes 1) mullite or 2) mullite and an alkaline earth metal aluminosilicate. The chemical barrier layer is located between the mullite-containing layer and the outer layer. The chemical barrier layer includes at least one of mullite, hafnia, hafnium silicate and rare earth silicate (e.g., at least one of RE.sub.2 SiO.sub.5 and RE.sub.2 Si.sub.2 O.sub.7 where RE is Sc or Yb). The multilayer article is characterized by the combination of the chemical barrier layer and by its lack of a layer consisting essentially of barium strontium aluminosilicate between the mullite-containing layer and the chemical barrier layer. Such a barium strontium aluminosilicate layer may undesirably lead to the formation of a low melting glass or unnecessarily increase the layer thickness with concomitant reduced durability of the multilayer article. In particular, the chemical barrier layer may include at least one of hafnia, hafnium silicate and rare earth silicate.

  18. Rocket observations of sporadic-E layers.

    NASA Technical Reports Server (NTRS)

    Smith, L. G.; Mechtly, E. A.

    1972-01-01

    The characteristics of midlatitude sporadic-E layers are observed using rocket payloads incorporating a probe and a propagation experiment. Layers below 120 km show evidence of preferred altitudes. The slopes of layers are within 1 deg of horizontal. The horizontal dimensions are deduced to be several hundred kilometers. Individual profiles of daytime layers show a range of shapes ranging from triangular to rectangular. The plasma frequency derived from the peak electron density in the layer is found to agree with the blanketing frequency given by the local ionosphere sounder.

  19. Dense, layered membranes for hydrogen separation

    DOEpatents

    Roark, Shane E.; MacKay, Richard; Mundschau, Michael V.

    2006-02-21

    This invention provides hydrogen-permeable membranes for separation of hydrogen from hydrogen-containing gases. The membranes are multi-layer having a central hydrogen-permeable layer with one or more catalyst layers, barrier layers, and/or protective layers. The invention also relates to membrane reactors employing the hydrogen-permeable membranes of the invention and to methods for separation of hydrogen from a hydrogen-containing gas using the membranes and reactors. The reactors of this invention can be combined with additional reactor systems for direct use of the separated hydrogen.

  20. Solar cell with silicon oxynitride dielectric layer

    SciTech Connect

    Shepherd, Michael; Smith, David D

    2015-04-28

    Solar cells with silicon oxynitride dielectric layers and methods of forming silicon oxynitride dielectric layers for solar cell fabrication are described. For example, an emitter region of a solar cell includes a portion of a substrate having a back surface opposite a light receiving surface. A silicon oxynitride (SiO.sub.xN.sub.y, 0layer is disposed on the back surface of the portion of the substrate. A semiconductor layer is disposed on the silicon oxynitride dielectric layer.

  1. Holographic recording medium employing a photoconductive layer and a low molecular weight microcrystalline polymeric layer

    NASA Technical Reports Server (NTRS)

    Gange, Robert Allen (Inventor)

    1977-01-01

    A holographic recording medium comprising a conductive substrate, a photoconductive layer and an electrically alterable layer of a linear, low molecular weight hydrocarbon polymer has improved fatigue resistance. An acrylic barrier layer can be interposed between the photoconductive and electrically alterable layers.

  2. Two layer structure for reinforcing pothole repair

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Yuan, Kuo-Yao; Zou, Linhua; Yang, Jenn-Ming; Ju, Jiann-Wen; Kao, Wei; Carlson, Larry

    2013-04-01

    We have applied dicyclopentadiene (DCPD) resin for reinforcing pothole patch materials due to its unique properties - low cost, low viscosity at beginning and ultra-toughness after curing, chemical compatibility with tar, tunable curing profile through catalyst design. In this paper, we have designed a two layer structure - well compacted base layer and DCPD reinforced 1-1.5" top layer - for pothole repair. By choosing two graded asphalt mixes, a porous top layer and fully compacted base layer was prepared after compaction and ready for DCPD resin infiltration. The DCPD curing and infiltration profile within this porous top layer was measured with thermocouples. The rutting resistance was tested with home-made wheel rutter. The cage effect due to the p-DCPD wrapping was characterized with wheel penetration test. The results showed that this two layer structure pothole repair has greatly improved properties and can be used for pothole repair to increase the service life.

  3. S-layers: principles and applications

    PubMed Central

    Sleytr, Uwe B; Schuster, Bernhard; Egelseer, Eva-Maria; Pum, Dietmar

    2014-01-01

    Monomolecular arrays of protein or glycoprotein subunits forming surface layers (S-layers) are one of the most commonly observed prokaryotic cell envelope components. S-layers are generally the most abundantly expressed proteins, have been observed in species of nearly every taxonomical group of walled bacteria, and represent an almost universal feature of archaeal envelopes. The isoporous lattices completely covering the cell surface provide organisms with various selection advantages including functioning as protective coats, molecular sieves and ion traps, as structures involved in surface recognition and cell adhesion, and as antifouling layers. S-layers are also identified to contribute to virulence when present as a structural component of pathogens. In Archaea, most of which possess S-layers as exclusive wall component, they are involved in determining cell shape and cell division. Studies on structure, chemistry, genetics, assembly, function, and evolutionary relationship of S-layers revealed considerable application potential in (nano)biotechnology, biomimetics, biomedicine, and synthetic biology. PMID:24483139

  4. Three layered framework for automatic service composition

    NASA Astrophysics Data System (ADS)

    Liu, Xinqiong; Xia, Ping; Wan, Junli

    2009-10-01

    For automatic service composition, a planning based framework MOCIS is proposed. Planning is based on two major techniques, service reasoning and constraint satisfaction. Constraint satisfaction can be divided into quality constraint satisfaction and quantity constraint satisfaction. Contrary to traditional methods realizing upon techniques by interleaving activity, message and provider, the novelty of the framework is dividing these concerns into three layers, with activity layer majoring service reasoning, message layer for quality constraint and provider layer for quantity constraint. The layered architecture makes automatic web service composition possible for activity tree that abstract BPEL list and concrete BPEL list are achieved automatically with each layer, and users can selection proper abstract BPEL or BPEL to satisfy their request. And E-traveling composition cases have been tested, demonstrating that complex service can be achieved through three layers compositing automatically.

  5. Vortex boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1986-01-01

    Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.

  6. Multi Layer Contaminant Migration Model

    1999-07-28

    This computer software augments and enhances certain calculation included in the previously copyrighted Vadose Zone Contaminant Migration Model. The computational method used in this model recognizes the heterogenous nature of the soils and attempts to account for the variability by using four separate layers to simulate the flow of water through the vadose zone. Therefore, the pore-water velocity calculated by the code will be different than the previous model because it accounts for a widermore » variety of soil properties encountered in the vadose zone. This model also performs an additional screening step than in the previous model. In this model the higher value of two different types of Soil Screening Levels are compared to soil concentrations of contaminants. If the contaminant concentration exceeds the highest of two SSLs, then that contaminant is listed. This is consistent with USEPA's Soil Screening Guidance.« less

  7. NDAS Hardware Translation Layer Development

    NASA Technical Reports Server (NTRS)

    Nazaretian, Ryan N.; Holladay, Wendy T.

    2011-01-01

    The NASA Data Acquisition System (NDAS) project is aimed to replace all DAS software for NASA s Rocket Testing Facilities. There must be a software-hardware translation layer so the software can properly talk to the hardware. Since the hardware from each test stand varies, drivers for each stand have to be made. These drivers will act more like plugins for the software. If the software is being used in E3, then the software should point to the E3 driver package. If the software is being used at B2, then the software should point to the B2 driver package. The driver packages should also be filled with hardware drivers that are universal to the DAS system. For example, since A1, A2, and B2 all use the Preston 8300AU signal conditioners, then the driver for those three stands should be the same and updated collectively.

  8. Tracer diffusion inside fibrinogen layers.

    PubMed

    Cieśla, Michał; Gudowska-Nowak, Ewa; Sagués, Francesc; Sokolov, Igor M

    2014-01-28

    We investigate the obstructed motion of tracer (test) particles in crowded environments by carrying simulations of two-dimensional Gaussian random walk in model fibrinogen monolayers of different orientational ordering. The fibrinogen molecules are significantly anisotropic and therefore they can form structures where orientational ordering, similar to the one observed in nematic liquid crystals, appears. The work focuses on the dependence between level of the orientational order (degree of environmental crowding) of fibrinogen molecules inside a layer and non-Fickian character of the diffusion process of spherical tracer particles moving within the domain. It is shown that in general particles motion is subdiffusive and strongly anisotropic, and its characteristic features significantly change with the orientational order parameter, concentration of fibrinogens, and radius of a diffusing probe. PMID:25669566

  9. Process Conditions of Forming the Surface Layer of Aluminum Powder Product by Layer-by-layer Laser Sintering

    NASA Astrophysics Data System (ADS)

    Saprykina, N. A.; Saprykin, A. A.; Ibragimov, E. A.; Arkhipova, D. A.

    2016-07-01

    The paper presents data on state of the art in selective laser sintering of products. Layer-by-layer sintering is shown to be a future-oriented technology, making it possible to synthesize products of metal powder materials. Factors, influencing the quality of a sintered product, are revealed in the paper. It presents outcomes of experiments, focused on the dependence of surface layer thickness of sintered aluminum powder PA-4 on laser processing conditions. Basic factors, influencing the quality of a sintered surface layer include laser power, speeds of scanning and moving the laser beam on the layer of powder. Thickness of the sintered layer varies from 0.74 to 1.55 mm, as the result of changing the laser processing conditions.

  10. Instabilities in Time Dependent Boundary Layers

    NASA Astrophysics Data System (ADS)

    Otto, Stephen Robert

    Available from UMI in association with The British Library. The work in this thesis is concerned with instabilities known to occur in boundary layers. The boundary layers considered herein are of a temporal nature; that is they are time dependent. In Chapter 1 a general overview of the subject is given. In Chapter 2, we consider two Stokes layers found to occur on a sphere. Firstly, the case where the sphere oscillates along a radius, referred to as transverse oscillations, and secondly where the sphere oscillates about its axis, referred to as torsional oscillations. We also consider the oscillations to be of such an amplitude and frequency so that the resulting boundary layer is thin compared to the sphere's radius. Chapter 3, is concerned with the development of vortices in a temporally growing boundary layer occurring on an infinite flat plate, the fluid above which is started to move impulsively. Here we take account of the fact that the boundary layer is growing with time, in a similar manner as has been used for the Blasius layer to grow with a downstream coordinate. In Chapter 4, we consider a boundary layer found to occur outside a cylinder, which at a certain instant has a torsional velocity imparted to it, this layer grows with time. The development of vortices in considered in this layer, and certain parameter regimes are investigated namely those appropriate to the right hand branch of the neutral curve, and those appropriate to the development of inviscid Gortler modes.

  11. Dynamical aspects of electrostatic double layers

    NASA Astrophysics Data System (ADS)

    Raadu, Michael A.; Rasmussen, J. Juul

    1988-05-01

    Electrostatic double layers have been proposed as an acceleration mechanism in solar flares and other astrophysical objects. They have been extensively studied in the laboratory and by means of computer simulations. The theory of steady-state double layers implies several existence criteria, in particular the Bohm criteria, restricting the conditions under which double layers may form. In the present paper several already published theoretical models of different types of double layers are discussed. It is shown that the existence conditions often imply current-driven instabilities in the ambient plasma, at least for strong double layers, and it is argued that such conditions must be used with care when applied to real plasmas. Laboratory double layers, and by implication those arising in astrophysical plasmas, often produce instabilities in the surrounding plasma and are generally time-dependent structures. Naturally occurring double layers should therefore, be far more common than the restrictions deduced from idealized time-independent models would imply. In particular it is necessary to understand more fully the time-dependent behavior of double layers. In the present paper the dynamics of weak double layers is discussed. Also a model for moving a strong double layer, where an associated potential minimum plays a significant role, is presented.

  12. Nanomanufacturing : nano-structured materials made layer-by-layer.

    SciTech Connect

    Cox, James V.; Cheng, Shengfeng; Grest, Gary Stephen; Tjiptowidjojo, Kristianto; Reedy, Earl David, Jr.; Fan, Hongyou; Schunk, Peter Randall; Chandross, Michael Evan; Roberts, Scott A.

    2011-10-01

    Large-scale, high-throughput production of nano-structured materials (i.e. nanomanufacturing) is a strategic area in manufacturing, with markets projected to exceed $1T by 2015. Nanomanufacturing is still in its infancy; process/product developments are costly and only touch on potential opportunities enabled by growing nanoscience discoveries. The greatest promise for high-volume manufacturing lies in age-old coating and imprinting operations. For materials with tailored nm-scale structure, imprinting/embossing must be achieved at high speeds (roll-to-roll) and/or over large areas (batch operation) with feature sizes less than 100 nm. Dispersion coatings with nanoparticles can also tailor structure through self- or directed-assembly. Layering films structured with these processes have tremendous potential for efficient manufacturing of microelectronics, photovoltaics and other topical nano-structured devices. This project is designed to perform the requisite R and D to bring Sandia's technology base in computational mechanics to bear on this scale-up problem. Project focus is enforced by addressing a promising imprinting process currently being commercialized.

  13. S-layer nanoglycobiology of bacteria

    PubMed Central

    Messner, Paul; Steiner, Kerstin; Zarschler, Kristof; Schäffer, Christina

    2015-01-01

    Cell surface layers (S-layers) are common structures of the bacterial cell envelope with a lattice-like appearance that are formed by a self-assembly process. Frequently, the constituting S-layer proteins are modified with covalently linked glycan chains facing the extracellular environment. S-layer glycoproteins from organisms of the Bacillaceae family possess long, O-glycosidically linked glycans that are composed of a great variety of sugar constituents. The observed variations already exceed the display found in eukaryotic glycoproteins. Recent investigations of the S-layer protein glycosylation process at the molecular level, which has lagged behind the structural studies due to the lack of suitable molecular tools, indicated that the S-layer glycoprotein glycan biosynthesis pathway utilizes different modules of the well-known biosynthesis routes of lipopolysaccharide O-antigens. The genetic information for S-layer glycan biosynthesis is usually present in S-layer glycosylation (slg) gene clusters acting in concert with housekeeping genes. To account for the nanometer-scale cell surface display feature of bacterial S-layer glycosylation, we have coined the neologism ‘nanoglycobiology’. It includes structural and biochemical aspects of S-layer glycans as well as molecular data on the machinery underlying the glycosylation event. A key aspect for the full potency of S-layer nanoglycobiology is the unique self-assembly feature of the S-layer protein matrix. Being aware that in many cases the glycan structures associated with a protein are the key to protein function, S-layer protein glycosylation will add a new and valuable component to an ‘S-layer based molecular construction kit’. In our long-term research strategy, S-layer nanoglycobiology shall converge with other functional glycosylation systems to produce ‘functional’ S-layer neoglycoproteins for diverse applications in the fields of nanobiotechnology and vaccine technology. Recent advances in

  14. S-layer nanoglycobiology of bacteria.

    PubMed

    Messner, Paul; Steiner, Kerstin; Zarschler, Kristof; Schäffer, Christina

    2008-08-11

    Cell surface layers (S-layers) are common structures of the bacterial cell envelope with a lattice-like appearance that are formed by a self-assembly process. Frequently, the constituting S-layer proteins are modified with covalently linked glycan chains facing the extracellular environment. S-layer glycoproteins from organisms of the Bacillaceae family possess long, O-glycosidically linked glycans that are composed of a great variety of sugar constituents. The observed variations already exceed the display found in eukaryotic glycoproteins. Recent investigations of the S-layer protein glycosylation process at the molecular level, which has lagged behind the structural studies due to the lack of suitable molecular tools, indicated that the S-layer glycoprotein glycan biosynthesis pathway utilizes different modules of the well-known biosynthesis routes of lipopolysaccharide O-antigens. The genetic information for S-layer glycan biosynthesis is usually present in S-layer glycosylation (slg) gene clusters acting in concert with housekeeping genes. To account for the nanometer-scale cell surface display feature of bacterial S-layer glycosylation, we have coined the neologism 'nanoglycobiology'. It includes structural and biochemical aspects of S-layer glycans as well as molecular data on the machinery underlying the glycosylation event. A key aspect for the full potency of S-layer nanoglycobiology is the unique self-assembly feature of the S-layer protein matrix. Being aware that in many cases the glycan structures associated with a protein are the key to protein function, S-layer protein glycosylation will add a new and valuable component to an 'S-layer based molecular construction kit'. In our long-term research strategy, S-layer nanoglycobiology shall converge with other functional glycosylation systems to produce 'functional' S-layer neoglycoproteins for diverse applications in the fields of nanobiotechnology and vaccine technology. Recent advances in the field of

  15. Microgravity Effects on Plant Boundary Layers

    NASA Technical Reports Server (NTRS)

    Stutte, Gary; Monje, Oscar

    2005-01-01

    The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

  16. Simulation of Sintering of Layered Structures

    SciTech Connect

    OLEVSKY,EUGENE; TIKARE,VEENA; GARINO,TERRY J.; BRAGINSKY,MICHAEL V.

    2000-11-22

    An integrated approach, combining the continuum theory of sintering and Potts model based mesostructure evolution analysis, is used to solve the problem of bi-layered structure sintering. Two types of bi-layered structures are considered: layers of the same material with different initial porosity, and layers of two different materials. The effective sintering stress for the bi-layer powder sintering is derived, both at the meso- and the macroscopic levels. Macroscopic shape distortions and spatial distributions of porosity are determined as functions of the dimensionless specific time of sintering. The effect of the thickness of the layers on shrinkage, warpage, and pore-grain structure is studied. Ceramic ZnO powders are employed as a model experimental system to assess the model predictions.

  17. LDV measurements of turbulent baroclinic boundary layers

    SciTech Connect

    Neuwald, P.; Reichenbach, H.; Kuhl, A.L.

    1993-07-01

    Described here are shock tube experiments of nonsteady, turbulent boundary layers with large density variations. A dense-gas layer was created by injecting Freon through the porous floor of the shock tube. As the shock front propagated along the layer, vorticity was created at the air-Freon interface by an inviscid, baroclinic mechanism. Shadow-schlieren photography was used to visualize the turbulent mixing in this baroclinic boundary layer. Laser-Doppler-Velocimetry (LDV) was used to measure the streamwise velocity histories at 14 heights. After transition, the boundary layer profiles may be approximated by a power-law function u {approximately} u{sup {alpha}} where {alpha} {approx_equal} 3/8. This value lies between the clean flat plate value ({alpha} = 1/7) and the dusty boundary layer value ({alpha} {approx_equal} 0.7), and is controlled by the gas density near the wall.

  18. Layer-by-layer all-transfer-based organic solar cells.

    PubMed

    Kim, Jung Kyu; Kim, Wanjung; Wang, Dong Hwan; Lee, Haksoo; Cho, Sung M; Choi, Dae-Geun; Park, Jong Hyeok

    2013-04-30

    For the first time, we describe a novel cost- and time-effective vacuum-free process to fabricate bulk-heterojunction (BHJ) organic photovoltaics (OPVs) via layer-by-layer selective stamping transfer of all layers. By controlling the surface properties of polyurethane acrylate (PUA) stamping molds with ultraviolet (UV)-ozone (UVO) exposure, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS), BHJ layer, and metal cathode were uniformly transferred layer by layer onto each of the bottom layers. Among several interfaces between each layer, we found that the interface between the active layer and metal cathode is a critical factor in obtaining conventional device-like efficiency. To enhance the interfacial connectivity between the BHJ layer and metal cathode and increase electron extraction from the BHJ layer, a titanium oxide (TiOx) interlayer was introduced. Cell performance was optimized by controlling the concentration of TiOx solution. The poly(3-hexylthiophene-2,5-diyl)/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PC60BM) BHJ device fabricated by transferring PEDOT/PSS, TiOx/active layer, and Al cathode showed 2.01% power conversion efficiency. This efficiency is not comparable to those of conventional OPVs, but our approach shows the possibility of fabricating OPVs via the layer-by-layer transfer method for the first time.

  19. Method to fabricate layered material compositions

    DOEpatents

    Fleming, James G.; Lin, Shawn-Yu

    2002-01-01

    A new class of processes suited to the fabrication of layered material compositions is disclosed. Layered material compositions are typically three-dimensional structures which can be decomposed into a stack of structured layers. The best known examples are the photonic lattices. The present invention combines the characteristic features of photolithography and chemical-mechanical polishing to permit the direct and facile fabrication of, e.g., photonic lattices having photonic bandgaps in the 0.1-20.mu. spectral range.

  20. Method to fabricate layered material compositions

    SciTech Connect

    Fleming, James G.; Lin, Shawn-Yu

    2004-11-02

    A new class of processes suited to the fabrication of layered material compositions is disclosed. Layered material compositions are typically three-dimensional structures which can be decomposed into a stack of structured layers. The best known examples are the photonic lattices. The present invention combines the characteristic features of photolithography and chemical-mechanical polishing to permit the direct and facile fabrication of, e.g., photonic lattices having photonic bandgaps in the 0.1-20.mu. spectral range.

  1. Turbulent boundary layers with secondary flow

    NASA Technical Reports Server (NTRS)

    Grushwitz, E.

    1984-01-01

    An experimental analysis of the boundary layer on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.

  2. Superconductive articles including cerium oxide layer

    DOEpatents

    Wu, Xin D.; Muenchausen, Ross E.

    1993-01-01

    A ceramic superconductor comprising a metal oxide substrate, a ceramic high temperature superconductive material, and a intermediate layer of a material having a cubic crystal structure, said layer situated between the substrate and the superconductive material is provided, and a structure for supporting a ceramic superconducting material is provided, said structure comprising a metal oxide substrate, and a layer situated over the surface of the substrate to substantially inhibit interdiffusion between the substrate and a ceramic superconducting material deposited upon said structure.

  3. Multi-layer seal for electrochemical devices

    DOEpatents

    Chou, Yeong-Shyung [Richland, WA; Meinhardt, Kerry D [Kennewick, WA; Stevenson, Jeffry W [Richland, WA

    2010-11-16

    Multi-layer seals are provided that find advantageous use for reducing leakage of gases between adjacent components of electrochemical devices. Multi-layer seals of the invention include a gasket body defining first and second opposing surfaces and a compliant interlayer positioned adjacent each of the first and second surfaces. Also provided are methods for making and using the multi-layer seals, and electrochemical devices including said seals.

  4. Multi-layer seal for electrochemical devices

    DOEpatents

    Chou, Yeong-Shyung [Richland, WA; Meinhardt, Kerry D [Kennewick, WA; Stevenson, Jeffry W [Richland, WA

    2010-09-14

    Multi-layer seals are provided that find advantageous use for reducing leakage of gases between adjacent components of electrochemical devices. Multi-layer seals of the invention include a gasket body defining first and second opposing surfaces and a compliant interlayer positioned adjacent each of the first and second surfaces. Also provided are methods for making and using the multi-layer seals, and electrochemical devices including said seals.

  5. Size distributions of boundary-layer clouds

    SciTech Connect

    Stull, R.; Berg, L.; Modzelewski, H.

    1996-04-01

    Scattered fair-weather clouds are triggered by thermals rising from the surface layer. Not all surface layer air is buoyant enough to rise. Also, each thermal has different humidities and temperatures, resulting in interthermal variability of their lifting condensation levels (LCL). For each air parcel in the surface layer, it`s virtual potential temperature and it`s LCL height can be computed.

  6. Nonequilibrium chemistry boundary layer integral matrix procedure

    NASA Technical Reports Server (NTRS)

    Tong, H.; Buckingham, A. C.; Morse, H. L.

    1973-01-01

    The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.

  7. Manganese containing layer for magnetic recording media

    DOEpatents

    Lambeth, David N.; Lee, Li-Lien; Laughlin, David E.

    1999-01-01

    The present invention provides for a magnetic recording media incorporating Mn-containing layers between a substrate and a magnetic layer to provide media having increased coercivity and lower noise. The Mn-containing layer can be incorporated in a rotating, translating or stationary recording media to operate in conjunction with magnetic transducing heads for recording and reading of magnetic data, as well as other applications. The magnetic recording medium of the invention preferably includes a Co or Co alloy film magnetic layer, and Mn-containing layer, preferably comprised of VMn, TiMn, MnZn, CrMnMo, CrMnW, CrMnV, and CrMnTi, and most preferably a CrMn alloy, disposed between the substrate and the magnetic layer to promote an epitaxial crystalline structure in the magnetic layer. The medium can further include seed layers, preferably polycrystalline MgO for longitudinal media, underlayers, and intermediate layers. Underlayers and intermediate layers are comprised of materials having either an A2 structure or a B2-ordered crystalline structure disposed between the seed layer and the magnetic layer. Materials having an A2 structure are preferably Cr or Cr alloys, such as CrV, CrMo, CrW and CrTi. Materials having a B2-ordered structure having a lattice constant that is substantially comparable to that of Cr, such as those preferably selected from the group consisting of NiAl, AILCo, FeAl, FeTi, CoFe, CoTi, CoHf, CoZr, NiTi, CuBe, CuZn, A-LMn, AlRe, AgMg, and Al.sub.2 FeMn.sub.2, and is most preferably FeAl or NiAl.

  8. Hydrogen in magnesium palladium thin layer structures

    NASA Astrophysics Data System (ADS)

    Kruijtzer, G. L.

    2008-02-01

    In this thesis, the study of hydrogen storage, absorption and desorption in magnesium layers is described. The magnesium layers have a thickness of 50-500 nm and are covered by a palladium layer which acts as a hydrogen dissociation/association catalyst. The study was preformed under ultra high vacuum conditions to avoid oxygen contamination. The main analysis techniques were RBS, ERD and TDS.

  9. Control of Separated Boundary Layers

    NASA Astrophysics Data System (ADS)

    Huang, Shao-Ching; Kim, John

    2003-11-01

    The control of separated boundary layers are numerically investigated. Two types of flow geometry are considered. The first case is flow separation on a flat plate caused by an imposed adverse pressure gradient. The second case is flow separation downstream of a curved leading edge. These cases represent laminar separation with turbulent reattachment with and without curvature effects. Open-loop control, with distributed surface blowing and suction as control input, is first applied to establish base-line cases. We then use a system identification approach to construct approximate system models for design of closed-loop control. The models are based on the input-output relationship obtained from numerical simulations. The linear quadratic Gaussian (LQG) control synthesis is applied to the models to produce feedback control laws. The distributed sensors and actuators are confined to the walls. The efficacy of the controllers are quantified by pressure distribution, separation bubble size and Reynolds stresses. Visualization of the controlled and uncontrolled flow fields will also be presented.

  10. Hollow glass for insulating layers

    NASA Astrophysics Data System (ADS)

    Merticaru, Andreea R.; Moagar-Poladian, Gabriel

    1999-03-01

    Common porous materials, some of which will be considered in the chapters of this book, include concrete, paper, ceramics, clays, porous semiconductors, chromotography materials, and natural materials like coral, bone, sponges, rocks and shells. Porous materials can also be reactive, such as in charcoal gasification, acid rock dissolution, catalyst deactivation and concrete. This study continues the investigations about the properties of, so-called, hollow glass. In this paper is presented a computer simulation approach in which the thermo-mechanical behavior of a 3D microstructure is directly computed. In this paper a computer modeling approach of porous glass is presented. One way to test the accuracy of the reconstructed microstructures is to computed their physical properties and compare to experimental measurement on equivalent systems. In this view, we imagine a new type of porous type of glass designed as buffer layer in multilayered printed boards in ICs. Our glass is a variable material with a variable pore size and surface area. The porosity could be tailored early from the deposition phases that permitting us to keep in a reasonable balance the dielectric constant and thermal conductivity.

  11. Modeling cathode boundary layer discharges

    NASA Astrophysics Data System (ADS)

    Munoz-Serrano, E.; Boeuf, J. P.; Pitchford, L. C.

    2009-10-01

    A Cathode Boundary Layer Discharge or CBL (Schoenbach, et al Plasma Sources Sci. Technol. 13, 177,2004) is an electrode/dielectric/electrode sandwich with a central hole pierced through the dielectric and one of the electrodes (the anode). Thus, the cathode surface area available to the discharge is limited by the annular dielectric, and the discharge operates in an abnormal glow mode with a positive V-I characteristic at higher current. Using a two-dimensional fluid model, we have studied the electrical properties of CBLs in argon at 100 and 400 torr pressure. The spatial profiles of charged particle and metastable densities, potential, and gas temperature, as well as calculated V-I characteristics will be shown for a range of conditions for a 800 micron hole diameter. One interesting result (anticipated in the work of Belostotskiy, et al, Plasma Sources Sci. Technol 17, 045018, 2008) is that there is a sharp increase in the slope of the V-I characteristic when gas heating is taken into account. This current limiting effect is not observed when the discharge is able to expand on the outer surface of the cathode as in the case of the MicroHollow Cathode Discharge (MHCD) configuration, for example.

  12. Radioluminescent nuclear batteries with different phosphor layers

    NASA Astrophysics Data System (ADS)

    Hong, Liang; Tang, Xiao-Bin; Xu, Zhi-Heng; Liu, Yun-Peng; Chen, Da

    2014-11-01

    A radioluminescent nuclear battery based on the beta radioluminescence of phosphors is presented, and which consists of 147Pm radioisotope, phosphor layers, and GaAs photovoltaic cell. ZnS:Cu and Y2O2S:Eu phosphor layers for various thickness were fabricated. To investigate the effect of phosphor layer parameters on the battery, the electrical properties were measured. Results indicate that the optimal thickness ranges for the ZnS:Cu and Y2O2S:Eu phosphor layers are 12 mg cm-2 to 14 mg cm-2 and 17 mg cm-2 to 21 mg cm-2, respectively. ZnS:Cu phosphor layer exhibits higher fluorescence efficiency compared with the Y2O2S:Eu phosphor layer. Its spectrum properly matches the spectral response of GaAs photovoltaic cell. As a result, the battery with ZnS:Cu phosphor layer indicates higher energy conversion efficiency than that with Y2O2S:Eu phosphor layer. Additionally, the mechanism of the phosphor layer parameters that influence the output performance of the battery is discussed through the Monte Carlo method and transmissivity test.

  13. Organic photovoltaic cells utilizing ultrathin sensitizing layer

    DOEpatents

    Forrest, Stephen R.; Yang, Fan; Rand, Barry P.

    2011-09-06

    A photosensitive device includes a plurality of organic photoconductive materials disposed in a stack between a first electrode and a second electrode, including a first continuous layer of donor host material, a second continuous layer of acceptor host material, and at least one other organic photoconductive material disposed as a plurality of discontinuous islands between the first continuous layer and the second continuous layer. Each of these other photoconductive materials has an absorption spectra different from the donor host material and the acceptor host material. Preferably, each of the discontinuous islands consists essentially of a crystallite of the respective organic photoconductive material, and more preferably, the crystallites are nanocrystals.

  14. Electromechanics and Electrical Breakdown of Particulate Layers

    NASA Astrophysics Data System (ADS)

    Moslehi, Bizhan G. R.

    A comprehensive theory of the electromechanics and electrical breakdown of a current-carrying particulate layer is developed, which takes into account its inhomogeneous nature and mode of compaction. The theory treates the general case of combined surface and volume conduction and takes account of self-compression of the layer due to electrical forces. The electromechanical theory predicts the existence of a remarkably large electrical cohesive stress in the layer due to a strong field enhancement in and around the contact regions. Furthermore, it shows a decrease in the apparent resistivity of the layer with increasing electric field as a result of self-compression. The analysis of electrical breakdown of current -carrying particulate layer predicts the onset of breakdown of the layer in the form of intermittent microsparks in the gap between the contacting particles when the electric field at the contact or in the surrounding gap exceeds the threshold breakdown value. An analysis of the behavior of the layer after breakdown in terms of a simplified equivalent lumped circuit predicts increases of sparking frequency and average current as the applied average field exceeds the threshold average field for the onset of breakdown. The results of measurements on layers of glass beads and fly-ash in a standard resistivity cell are in good agreement with the theoretical predictions for the field-dependent resistivity characteristics. The work has particular significance for electrostatic precipitation and addresses the phenomenon of backdischarge and the questions of the retention, rapping, and reentrainment of precipitation ash layers.

  15. Electrostatic Separation Of Layers In Thermal Insulation

    NASA Technical Reports Server (NTRS)

    Bhandari, Pradeep

    1995-01-01

    Layers in multilayer insulation charged to keep them separated by electrostatic repulsion, eliminating need for spacer nets. Removal of spacer nets reduces conduction of heat between layers. Insulation in question type used to slow leakage of heat into Dewar flasks containing liquid helium. Proposal originally applied to insulation in cryogenic cooling subsystems of infrared-detector systems in outer space, also appears applicable to small panels of insulation for terrestrial cryogenic equipment, provided layers contained in evacuated spaces and weight of each layer small fraction of electrostatic force upon it.

  16. Enhanced Densification of SDC Barrier Layers

    SciTech Connect

    Hardy, John S.; Templeton, Jared W.; Lu, Zigui; Stevenson, Jeffry W.

    2011-09-12

    This technical report explores the Enhanced Densification of SCD Barrier Layers A samaria-doped ceria (SDC) barrier layer separates the lanthanum strontium cobalt ferrite (LSCF) cathode from the yttria-stabilized zirconia (YSZ) electrolyte in a solid oxide fuel cell (SOFC) to prevent the formation of electrically resistive interfacial SrZrO{sub 3} layers that arise from the reaction of Sr from the LSCF with Zr from the YSZ. However, the sintering temperature of this SDC layer must be limited to {approx}1200 C to avoid extensive interdiffusion between SDC and YSZ to form a resistive CeO{sub 2}-ZrO{sub 2} solid solution. Therefore, the conventional SDC layer is often porous and therefore not as impervious to Sr-diffusion as would be desired. In the pursuit of improved SOFC performance, efforts have been directed toward increasing the density of the SDC barrier layer without increasing the sintering temperature. The density of the SDC barrier layer can be greatly increased through small amounts of Cu-doping of the SDC powder together with increased solids loading and use of an appropriate binder system in the screen print ink. However, the resulting performance of cells with these barrier layers did not exhibit the expected increase in accordance with that achieved with the prototypical PLD SDC layer. It was determined by XRD that increased sinterability of the SDC also results in increased interdiffusivity between the SDC and YSZ, resulting in formation of a highly resistive solid solution.

  17. Structure of the low latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. O.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.

    1980-01-01

    Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more.

  18. Kinetics of Initial Layer-by-Layer Oxidation of Si(001) Surfaces

    NASA Astrophysics Data System (ADS)

    Watanabe, Heiji; Kato, Koichi; Uda, Tsuyoshi; Fujita, Ken; Ichikawa, Masakazu; Kawamura, Takaaki; Terakura, Kiyoyuki

    1998-01-01

    Layer-by-layer oxidation of Si(001) surfaces has been studied by scanning reflection electron microscopy (SREM). The oxidation kinetics of the top and second layers were independently investigated from the change in oxygen Auger peak intensity calibrated from the SREM observation. A barrierless oxidation of the first subsurface layer, as well as oxygen chemisorption onto the top layer, occurs at room temperature. The energy barrier of the second-layer oxidation was found to be 0.3 eV. The initial oxidation kinetics are discussed based on first-principles calculations.

  19. Spray Layer-by-Layer Assembled Clay Composite Thin Films as Selective Layers in Reverse Osmosis Membranes.

    PubMed

    Kovacs, Jason R; Liu, Chaoyang; Hammond, Paula T

    2015-06-24

    Spray layer-by-layer assembled thin films containing laponite (LAP) clay exhibit effective salt barrier and water permeability properties when applied as selective layers in reverse osmosis (RO) membranes. Negatively charged LAP platelets were layered with poly(diallyldimethylammonium) (PDAC), poly(allylamine) (PAH), and poly(acrylic acid) (PAA) in bilayer and tetralayer film architectures to generate uniform films on the order of 100 nm thick that bridge a porous poly(ether sulfone) support to form novel RO membranes. Nanostructures were formed of clay layers intercalated in a polymeric matrix that introduced size-exclusion transport mechanisms into the selective layer. Thermal cross-linking of the polymeric matrix was used to increase the mechanical stability of the films and improve salt rejection by constraining swelling during operation. Maximum salt rejection of 89% was observed for the tetralayer film architecture, with an order of magnitude increase in water permeability compared to commercially available TFC-HR membranes. These clay composite thin films could serve as a high-flux alternative to current polymeric RO membranes for wastewater and brackish water treatment as well as potentially for forward osmosis applications. In general, we illustrate that by investigating the composite systems accessed using alternating layer-by-layer assembly in conjunction with complementary covalent cross-linking, it is possible to design thin film membranes with tunable transport properties for water purification applications.

  20. Mesoporous layer-by-layer ordered nanohybrids of layered double hydroxide and layered metal oxide: highly active visible light photocatalysts with improved chemical stability.

    PubMed

    Gunjakar, Jayavant L; Kim, Tae Woo; Kim, Hyo Na; Kim, In Young; Hwang, Seong-Ju

    2011-09-28

    Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O(2) generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn-Cr-layered double hydroxide (Zn-Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn-Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O(2) generation with a rate of ∼1.18 mmol h(-1) g(-1), which is higher than the O(2) production rate (∼0.67 mmol h(-1) g(-1)) by the pristine Zn-Cr-LDH material, that is, one of the most effective visible light photocatalysts for O(2) production, under the same experimental condition. This result highlights an excellent functionality of the Zn-Cr-LDH-layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn-Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical

  1. Modeling the summertime Arctic cloudy boundary layer

    SciTech Connect

    Curry, J.A.; Pinto, J.O.; McInnes, K.L.

    1996-04-01

    Global climate models have particular difficulty in simulating the low-level clouds during the Arctic summer. Model problems are exacerbated in the polar regions by the complicated vertical structure of the Arctic boundary layer. The presence of multiple cloud layers, a humidity inversion above cloud top, and vertical fluxes in the cloud that are decoupled from the surface fluxes, identified in Curry et al. (1988), suggest that models containing sophisticated physical parameterizations would be required to accurately model this region. Accurate modeling of the vertical structure of multiple cloud layers in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the layered structure of the Arctic summertime boundary-layer clouds and in particular, the representation of the more complex boundary layer type consisting of a stable foggy surface layer surmounted by a cloud-topped mixed layer. A hierarchical modeling/diagnosis approach is used. A case study from the summertime Arctic Stratus Experiment is examined. A high-resolution, one-dimensional model of turbulence and radiation is tested against the observations and is then used in sensitivity studies to infer the optimal conditions for maintaining two separate layers in the Arctic summertime boundary layer. A three-dimensional mesoscale atmospheric model is then used to simulate the interaction of this cloud deck with the large-scale atmospheric dynamics. An assessment of the improvements needed to the parameterizations of the boundary layer, cloud microphysics, and radiation in the 3-D model is made.

  2. Stable water layers on solid surfaces.

    PubMed

    Hong, Ying-Jhan; Tai, Lin-Ai; Chen, Hung-Jen; Chang, Pin; Yang, Chung-Shi; Yew, Tri-Rung

    2016-02-17

    Liquid layers adhered to solid surfaces and that are in equilibrium with the vapor phase are common in printing, coating, and washing processes as well as in alveoli in lungs and in stomata in leaves. For such a liquid layer in equilibrium with the vapor it faces, it has been generally believed that, aside from liquid lumps, only a very thin layer of the liquid, i.e., with a thickness of only a few nanometers, is held onto the surface of the solid, and that this adhesion is due to van der Waals forces. A similar layer of water can remain on the surface of a wall of a microchannel after evaporation of bulk water creates a void in the channel, but the thickness of such a water layer has not yet been well characterized. Herein we showed such a water layer adhered to a microchannel wall to be 100 to 170 nm thick and stable against surface tension. The water layer thickness was measured using electron energy loss spectroscopy (EELS), and the water layer structure was characterized by using a quantitative nanoparticle counting technique. This thickness was found for channel gap heights ranging from 1 to 5 μm. Once formed, the water layers in the microchannel, when sealed, were stable for at least one week without any special care. Our results indicate that the water layer forms naturally and is closely associated only with the surface to which it adheres. Our study of naturally formed, stable water layers may shed light on topics from gas exchange in alveoli in biology to the post-wet-process control in the semiconductor industry. We anticipate our report to be a starting point for more detailed research and understanding of the microfluidics, mechanisms and applications of gas-liquid-solid systems. PMID:26856872

  3. An ultra-thin buffer layer for Ge epitaxial layers on Si

    SciTech Connect

    Kawano, M.; Yamada, S.; Tanikawa, K.; Miyao, M.; Hamaya, K.; Sawano, K.

    2013-03-25

    Using an Fe{sub 3}Si insertion layer, we study epitaxial growth of Ge layers on a Si substrate by a low-temperature molecular beam epitaxy technique. When we insert only a 10-nm-thick Fe{sub 3}Si layer in between Si and Ge, epitaxial Ge layers can be obtained on Si. The detailed structural characterizations reveal that a large lattice mismatch of {approx}4% is completely relaxed in the Fe{sub 3}Si layer. This means that the Fe{sub 3}Si layers can become ultra-thin buffer layers for Ge on Si. This method will give a way to realize a universal buffer layer for Ge, GaAs, and related devices on a Si platform.

  4. Multi-Layer E-Textile Circuits

    NASA Technical Reports Server (NTRS)

    Dunne, Lucy E.; Bibeau, Kaila; Mulligan, Lucie; Frith, Ashton; Simon, Cory

    2012-01-01

    Stitched e-textile circuits facilitate wearable, flexible, comfortable wearable technology. However, while stitched methods of e-textile circuits are common, multi-layer circuit creation remains a challenge. Here, we present methods of stitched multi-layer circuit creation using accessible tools and techniques.

  5. Paracrystalline surface layers of dairy propionibacteria.

    PubMed Central

    Lortal, S; Rouault, A; Cesselin, B; Sleytr, U B

    1993-01-01

    We examined 70 dairy propionibacteria and detected a crystalline surface layer (S-layer) in only 2 organisms (Propionibacterium freudenreichii CNRZ 722 and Propionibacterium jensenii CNRZ 87) by freeze-etching and sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE). Both S-layers exhibited oblique (p2) symmetry (a = 9.9 nm; b = 5.4 nm; gamma = 80 degrees) and completely covered the cell surface. Treatment for 15 min at the ambient temperature with 5 M guanidine hydrochloride or acidic conditions (250 mM ammonium acetate, pH 2.7) efficiently extracted the S-layer protein from intact cells of strain CNRZ 722, whereas treatment with 5 M guanidine hydrochloride at 100 degrees C for 15 min was necessary to isolate the S-layer protein of strain CNRZ 87. The precipitates obtained after dialysis of the extracting agents produced no regular patterns. The molecular masses of the two S-layer proteins, as estimated by SDS-PAGE, were 58.5 kDa for the strain CNRZ 722 and 67.3 kDa for the strain CNRZ 87. Mass spectrometry of the isolated S-layer protein of strain CNRZ 722 gave a molecular mass value close to the expected value (56,533 Da). The N-terminal sequences of the two purified S-layer proteins differed, as did their amino acid compositions, except that the same high hydrophobic amino acid content (52%) was observed. Images PMID:8304753

  6. OSI Upper Layers Support for Applications.

    ERIC Educational Resources Information Center

    Davison, Wayne

    1990-01-01

    Discusses how various Open Systems Interconnection (OSI) application layer protocols can be used together, along with the Presentation and Session protocols, to support the interconnection requirements of applications. Application layer protocol standards that are currently available or under development are reviewed, and the File, Transfer,…

  7. Reassembly of S-layer proteins

    NASA Astrophysics Data System (ADS)

    Pum, Dietmar; Sleytr, Uwe B.

    2014-08-01

    Crystalline bacterial cell surface layers (S-layers) represent the outermost cell envelope component in a broad range of bacteria and archaea. They are monomolecular arrays composed of a single protein or glycoprotein species and represent the simplest biological membranes developed during evolution. They are highly porous protein mesh works with unit cell sizes in the range of 3 to 30 nm, and pore sizes of 2 to 8 nm. S-layers are usually 5 to 20 nm thick (in archaea, up to 70 nm). S-layer proteins are one of the most abundant biopolymers on earth. One of their key features, and the focus of this review, is the intrinsic capability of isolated native and recombinant S-layer proteins to form self-assembled mono- or double layers in suspension, at solid supports, the air-water interface, planar lipid films, liposomes, nanocapsules, and nanoparticles. The reassembly is entropy-driven and a fascinating example of matrix assembly following a multistage, non-classical pathway in which the process of S-layer protein folding is directly linked with assembly into extended clusters. Moreover, basic research on the structure, synthesis, genetics, assembly, and function of S-layer proteins laid the foundation for their application in novel approaches in biotechnology, biomimetics, synthetic biology, and nanotechnology.

  8. Rotational Atherectomy of Three Overlapping Stent Layers.

    PubMed

    Frisoli, Tiberio M; Friedman, Harold; O'Neill, William W

    2016-09-01

    A patient was referred to us for Canadian Cardiovascular Society class III refractory angina. He was found to have in-stent restenosis within three layers of underexpanded stents implanted in 2004, 2011, and 2014. Rotational atherectomy safely yielded stent strut ablation (reduced to one layer), lesion expansion, and very good angiographic and physiologic results. PMID:27591692

  9. Double sodium layers observation over Beijing, China

    NASA Astrophysics Data System (ADS)

    Wang, Jihong; Yang, Yong; Cheng, Xuewu; Yang, Guotao; Song, Shalei; Gong, Shunsheng

    2012-08-01

    The altitude of the sodium layer in the mesosphere and lower thermosphere is usually from 80 km to 105 km. In this paper, we report a set of double sodium layer (DSL) events observed by sodium lidar over Beijing, China. In these DSL events, the normal sodium layer and secondary sodium layer (SeSL) present separately. There were about 17 DSL events occurred in 319 observation nights during 2009˜2011. All DSL events were observed in spring and summer. The SeSL appeared independently within the altitude range from 105 km to 130 km. The density of the SeSL is very high. The maximum ratio of peak density and the ratio of column density for the SeSL to the normal sodium layer are up to ˜60% and ˜47%, respectively. The SeSL lasted several hours, and then merged into the normal sodium layer. After the SeSL, a sporadic sodium layer occurred in the normal sodium layer.

  10. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, Hannes

    1986-01-01

    As the rate of energy release in a double layer with voltage delta V is P approx I delta V, a double layer must be treated as a part of a circuit which delivers the current I. As neither double layer nor circuit can be derived from magnetofluid models of a plasma, such models are useless for treating energy transfer by means of double layers. They must be replaced by particle models and circuit theory. A simple circuit is suggested which is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object (one example is the double radio sources). It is tentatively suggested in X-ray and Gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). A study of how a number of the most used textbooks in astrophysics treat important concepts like double layers, critical velocity, pinch effects and circuits is made.

  11. Double layers and circuits in astrophysics

    SciTech Connect

    Alfven, H.

    1986-12-01

    As the rate of energy release in a double layer with voltage ..delta..V is P approx. = I..delta..V, a double layer must be treated as a part of a circuit which delivers the current I. As neither double layer nor circuit can be derived from magnetofluid models of a plasma, such models are useless for treating energy transfer by means of double layers. They must be replaced by particle models and circuit theory. A simple circuit is suggested which is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object (one example is the double radio sources). It is tentatively suggested that X-ray and ..gamma..-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). A study of how a number of the most used textbooks in astrophysics treat important concepts such as double layers, critical velocity, pinch effects, and circuits is made.

  12. Cyclone separator having boundary layer turbulence control

    DOEpatents

    Krishna, Coimbatore R.; Milau, Julius S.

    1985-01-01

    A cyclone separator including boundary layer turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the boundary layer of the vortical fluid flow through the separator.

  13. Method of designing layered sound absorbing materials

    NASA Astrophysics Data System (ADS)

    Atalla, Youssef; Panneton, Raymond

    2002-11-01

    A widely used model for describing sound propagation in porous materials is the Johnson-Champoux-Allard model. This rigid frame model is based on five geometrical properties of the porous medium: resistivity, porosity, tortuosity, and viscous and thermal characteristic lengths. Using this model and with the knowledge of such properties for different absorbing materials, the design of a multiple layered system can be optimized efficiently and rapidly. The overall impedance of the layered systems can be calculated by the repeated application of single layer impedance equation. The knowledge of the properties of the materials involved in the layered system and their physical meaning, allows to perform by computer a systematic evaluation of potential layer combinations rather than do it experimentally which is time consuming and always not efficient. The final design of layered materials can then be confirmed by suitable measurements. A method of designing the overall acoustic absorption of multiple layered porous materials is presented. Some aspects based on the material properties, for designing a flat layered absorbing system are considered. Good agreement between measured and computed sound absorption coefficients has been obtained for the studied configurations. [Work supported by N.S.E.R.C. Canada, F.C.A.R. Quebec, and Bombardier Aerospace.

  14. The Layered Nature of Planetary Mantle

    NASA Astrophysics Data System (ADS)

    Dude, S.; Hansen, U.

    2015-12-01

    The formation of layered structures is a common feature within many natural system and occur on various scales (planets, Earth's oceans, magma chambers, etc.). Since the knowledge of slab stagnation in the transitions zone of the Earth's mantle the question whether the mantle is or at least has been layered to some degree is still under debate. On this basis we address two important features that lead to layered mantle convection and may affect each other and with this the thermal evolution of the mantle and the evolving heterogeneities. On the one hand we examine a double-diffusive system that is capable of the self-organised formation of layers from a previously non-layered state and on the other hand we incorporate a phase transition. In oder to determine the interaction of double-diffusive layers with a phase transition we carried out numerical simulations ranging from exothermic to endothermic conditions. Taking into account a depth and temperature dependence of the phase transition the results show that on the one hand double-diffusive layering is strongly affected by the presence of phase transition but on the other hand the equilibrium position of the phase transition is shifted depending on the properties of the considered transition. In addition to that we incorporate the chemical dependence of the phase change and determine the influence on the layer growth and the overall dynamics.

  15. Dynamic Layer Formation in Planetary Interiors

    NASA Astrophysics Data System (ADS)

    Hansen, U.

    2009-12-01

    The thermal history of Earth an other planets, their chemical differentiation and reaction of the interior with the atmosphere are largely determined by convective processes. Convection does not always tend to homogenize the interior. Convection can rather establish structures and as such reservoirs which can stay intact for geological significant times. We employ. numerical models, ranging from simple 2D scenarios to fully 3D configurations with strongly temperature , pressure and compositionally dependent rheology , to explore the formation of such reservoirs. Layer formation plays a special role in the pattern formation process. . It will be shown that distinct convective layers can form as self-organized structures from non-layered states, without pre-existing density jumps., once effects of thermal - and compositional contributions to the density are taken into account. A stable compositional gradient, hearted from below and/or cooled from above resembles one reasonable scenario for the Earth-mantle after core formation. In this configuration a layered mantle structure emerges. The individual layers display different stabilities. The intermittent breakdown of individual layers leads to a strong episodicity in the thermal and chemical evolution. We also investigate the scenario of an initially unstably stratified mantle. After an initial overturn through a Rayleigh Taylor instability we observe again layer generation. Our results indicate the distinct layers in planetary mantles are formed by dynamics fractionation and are thus likely to appear as generic features of planets

  16. Electron temperature differences and double layers

    NASA Technical Reports Server (NTRS)

    Chan, C.; Hershkowitz, N.; Lonngren, K. E.

    1983-01-01

    Electron temperature differences across plasma double layers are studied experimentally. It is shown that the temperature differences across a double layer can be varied and are not a result of thermalization of the bump-on-tail distribution. The implications of these results for electron thermal energy transport in laser-pellet and tandem-mirror experiments are also discussed.

  17. Martian Mixed Layer during Pathfinder Mission

    NASA Astrophysics Data System (ADS)

    Martinez, G. M.; Valero, F.; Vazquez, L.

    2008-09-01

    In situ measurements of the Martian Planetary Boundary Layer (MPBL) encompass only the sur- face layer. Therefore, in order to fully address the MPBL, it becomes necessary to simulate somehow the behaviour of the martian mixed layer. The small-scale processes that happen in the MPBL cause GCM's ([1], [2]) to describe only partially the turbulent statistics, height, convective scales, etc, of the surface layer and the mixed layer. For this reason, 2D and 3D martian mesoscale models ([4], [5]), and large eddy simulations ([4], [6], [7], [8]) have been designed in the last years. Although they are expected to simulate more accurately the MPBL, they take an extremely expensive compu- tational time. Alternatively, we have derived the main turbu- lent characteristics of the martian mixed layer by using surface layer and mixed layer similarity ([9], [10]). From in situ temperature and wind speed measurements, together with quality-tested simu- lated ground temperature [11], we have character- ized the martian mixed layer during the convective hours of Pathfinder mission Sol 25. Mean mixed layer turbulent statistics like tem- perature variance < σ? >, horizontal wind speed variance < σu,v >, vertical wind speed variance < σw >, viscous dissipation rate < ǫ >, and turbu- lent kinetic energy < e > have been calculated, as well as the mixed layer height zi, and the convective scales of wind w? and temperature θ?. Our values, obtained with negligible time cost, match quite well with some previously obtained results via LES's ([4] and [8]). A comparisson between the above obtained mar- tian values and the typical Earth values are shown in Table 1. Convective velocity scale w doubles its counterpart terrestrial typical value, as it does the mean wind speed variances < σu,v > and < σw >. On the other hand, the temperature scale θ? and the mean temperature variance < σ > are virtually around one order higher on Mars. The limitations of these results concern the va- lidity

  18. Structure of relaminarizing turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Ramesh, O.; Patwardhan, Saurabh

    2014-11-01

    Relaminarization of a turbulent boundary layer in a strongly accelerated flow has received a great attention in recent times. It has been found that such relaminarization is a general and regularly occurring phenomenon in the leading-edge region of a swept wing of an airplane (van Dam et al., 1993). In this work, we investigate the effect of initial Reynolds number on the process of relaminarization in turbulent boundary layers. The experimental and numerical investigation of relaminarizing turbulent boundary layers undergoing same history reveals that the boundary layer with higher initial Reynolds number relaminarizes at a lower pressure gradient value compared to the one with lower Reynolds number. This effect can be explained on the inviscid theory proposed earlier in the literature. Further, various parameter criteria proposed to predict relaminarization, are assessed and the structure of relaminarizing boundary layers is investigated. A mechanism for stabilization of near-wall low speed streaks is proposed.

  19. Epitaxial growth of silicon for layer transfer

    DOEpatents

    Teplin, Charles; Branz, Howard M

    2015-03-24

    Methods of preparing a thin crystalline silicon film for transfer and devices utilizing a transferred crystalline silicon film are disclosed. The methods include preparing a silicon growth substrate which has an interface defining substance associated with an exterior surface. The methods further include depositing an epitaxial layer of silicon on the silicon growth substrate at the surface and separating the epitaxial layer from the substrate substantially along the plane or other surface defined by the interface defining substance. The epitaxial layer may be utilized as a thin film of crystalline silicon in any type of semiconductor device which requires a crystalline silicon layer. In use, the epitaxial transfer layer may be associated with a secondary substrate.

  20. Benthic boundary layer - IOS modelling programme

    NASA Astrophysics Data System (ADS)

    Richards, K. J.

    1983-04-01

    Factors which control the height of the benthic boundary layer in the deep ocean and the residence time of fluid and a tracer within it, were modeled numerically. In one model, the effects of steady and unsteady currents and variations in fluid density are examined. In conditions similar to those observed in the abyssal regions of the E.N. Atlantic the model predicts an average bottom layer height close to the value observed. A second model examines the effects of spatial variations in currents. Due to convergences and divergences produced by these variations, the height of the bottom mixed layer is distorted. Where thinning is large, mixing results in warm patches flanked by benthic fronts. It is proposed that within the warm regions, the bottom mixed layer is exchanged within the ocean above. The residence time of a tracer released within the bottom mixed layer, average value 100 days, is predicted to vary between 20 and 800 days.

  1. Lidar observation of marine mixed layer

    NASA Technical Reports Server (NTRS)

    Yamagishi, Susumu; Yamanouchi, Hiroshi; Tsuchiya, Masayuki

    1992-01-01

    Marine mixed layer is known to play an important role in the transportation of pollution exiting ship funnels. The application of a diffusion model is critically dependent upon a reliable estimate of a lid. However, the processes that form lids are not well understood, though considerable progress toward marine boundary layer has been achieved. This report describes observations of the marine mixed layer from the course Ise-wan to Nii-jima with the intention of gaining a better understanding of their structure by a shipboard lidar. These observations were made in the summer of 1991. One interesting feature of the observations was that the multiple layers of aerosols, which is rarely numerically modeled, was encountered. No attempt is yet made to present a systematic analysis of all the data collected. Instead we focus on observations that seem to be directly relevant to the structure of the mixed layer.

  2. Shear layer excitation, experiment versus theory

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.; Stahl, B.

    1984-01-01

    The acoustical excitation of shear layers is investigated. Acoustical excitation causes the so-called orderly structures in shear layers and jets. Also, the deviations in the spreading rate between different shear layer experiments are due to the same excitation mechanism. Measurements in the linear interaction region close to the edge from which the shear layer is shed are examined. Two sets of experiments (Houston 1981 and Berlin 1983/84) are discussed. The measurements were carried out with shear layers in air using hot wire anemometers and microphones. The agreement between these measurements and the theory is good. Even details of the fluctuating flow field correspond to theoretical predictions, such as the local occurrence of negative phase speeds.

  3. Boundary Layers of Air Adjacent to Cylinders

    PubMed Central

    Nobel, Park S.

    1974-01-01

    Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for νwindd between 200 and 30,000 cm2/second (where νwind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855

  4. Shear-Layer Effects on Trailing Vortices

    NASA Technical Reports Server (NTRS)

    Zheng, Z. C.; Baek, K.

    1998-01-01

    Crosswind shear can influence the trailing vortex trajectories significantly, according to both field measurement and numerical simulations. Point vortex models are used in this paper to study the fluid dynamic mechanism in the interactions between trailing vortex pair and shear layers. It has been shown that the shear-layer deformation causes the vortex descent history difference in the two vortices of the vortex pair. When a shear layer is below the vortex pair with the same sign as the left vortex, the right vortex descends less than the left vortex. When the same shear layer is above the vortex pair, the right vortex descends more. The descent altitudes of the two vortices are the same when they go through a constant, non-deformed shear layer. Those trends are in agreement with Navier-Stokes simulations.

  5. Instability limits for spontaneous double layer formation

    SciTech Connect

    Carr, J. Jr.; Galante, M. E.; McCarren, D.; Scime, E. E.; Sears, S.; VanDervort, R. W.; Magee, R. M.; Reynolds, E.

    2013-11-15

    We present time-resolved measurements that demonstrate that large amplitude electrostatic instabilities appear in pulsed, expanding helicon plasmas at the same time as particularly strong double layers appear in the expansion region. A significant cross-correlation between the electrostatic fluctuations and fluctuations in the number of ions accelerated by the double layer electric field is observed. No correlation is observed between the electrostatic fluctuations and ions that have not passed through the double layer. These measurements confirm that the simultaneous appearance of the electrostatic fluctuations and the double layer is not simple coincidence. In fact, the accelerated ion population is responsible for the growth of the instability. The double layer strength, and therefore, the velocity of the accelerated ions, is limited by the appearance of the electrostatic instability.

  6. Boundary layers of the earth's outer magnetosphere

    NASA Technical Reports Server (NTRS)

    Eastman, T. E.; Frank, L. A.

    1984-01-01

    The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.

  7. Subsurface Raman analysis of thin painted layers.

    PubMed

    Conti, Claudia; Colombo, Chiara; Realini, Marco; Zerbi, Giuseppe; Matousek, Pavel

    2014-01-01

    Here we present, for the first time, an extension of spatially offset Raman spectroscopy to thin (tens of micrometers thick), highly turbid stratified media such as those encountered in paintings. The method permits the non-destructive interrogation of painted layers in situations where conventional Raman microscopy is not applicable due to high turbidity of the top layer(s). The concept is demonstrated by recovering the pure Raman spectra of paint sub-layers that are completely obscured by paint over-layers. Potential application areas include the analysis of paintings in art preservation and restoration avoiding the cross-sectional analysis used currently with this type of samples. The technique also holds promise for the development as a non-destructive subsurface tool for in situ analysis using portable instruments.

  8. Intra-layer synchronization in multiplex networks

    NASA Astrophysics Data System (ADS)

    Gambuzza, L. V.; Frasca, M.; Gómez-Gardeñes, J.

    2015-04-01

    We study synchronization of N oscillators indirectly coupled through a medium which is inhomogeneous and has its own dynamics. The system is formalized in terms of a multilayer network, where the top layer is made of disconnected oscillators and the bottom one, modeling the medium, consists of oscillators coupled according to a given topology. The different dynamics of the medium and the top layer is accounted for by including a frequency mismatch between them. We show a novel regime of synchronization as intra-layer coherence does not necessarily require inter-layer coherence. This regime appears under mild conditions on the bottom layer: arbitrary topologies may be considered, provided that they support synchronization of the oscillators of the medium. The existence of a density-dependent threshold as in quorum-sensing phenomena is also demonstrated.

  9. Amorphous silicon Schottky barrier solar cells incorporating a thin insulating layer and a thin doped layer

    DOEpatents

    Carlson, David E.

    1980-01-01

    Amorphous silicon Schottky barrier solar cells which incorporate a thin insulating layer and a thin doped layer adjacent to the junction forming metal layer exhibit increased open circuit voltages compared to standard rectifying junction metal devices, i.e., Schottky barrier devices, and rectifying junction metal insulating silicon devices, i.e., MIS devices.

  10. Thermoelectric material including conformal oxide layers and method of making the same using atomic layer deposition

    DOEpatents

    Cho, Jung Young; Ahn, Dongjoon; Salvador, James R.; Meisner, Gregory P.

    2016-06-07

    A thermoelectric material includes a substrate particle and a plurality of conformal oxide layers formed on the substrate particle. The plurality of conformal oxide layers has a total oxide layer thickness ranging from about 2 nm to about 20 nm. The thermoelectric material excludes oxide nanoparticles. A method of making the thermoelectric material is also disclosed herein.

  11. Channel cracks in atomic-layer and molecular-layer deposited multilayer thin film coatings

    SciTech Connect

    Long, Rong; Dunn, Martin L.

    2014-06-21

    Metal oxide thin film coatings produced by atomic layer deposition have been shown to be an effective permeation barrier. The primary failure mode of such coatings under tensile loads is the propagation of channel cracks that penetrate vertically into the coating films. Recently, multi-layer structures that combine the metal oxide material with relatively soft polymeric layers produced by molecular layer deposition have been proposed to create composite thin films with desired properties, including potentially enhanced resistance to fracture. In this paper, we study the effects of layer geometry and material properties on the critical strain for channel crack propagation in the multi-layer composite films. Using finite element simulations and a thin-film fracture mechanics formalism, we show that if the fracture energy of the polymeric layer is lower than that of the metal oxide layer, the channel crack tends to penetrate through the entire composite film, and dividing the metal oxide and polymeric materials into thinner layers leads to a smaller critical strain. However, if the fracture energy of the polymeric material is high so that cracks only run through the metal oxide layers, more layers can result in a larger critical strain. For intermediate fracture energy of the polymer material, we developed a design map that identifies the optimal structure for given fracture energies and thicknesses of the metal oxide and polymeric layers. These results can facilitate the design of mechanically robust permeation barriers, an important component for the development of flexible electronics.

  12. Part I. Layered Double Hydroxides

    NASA Astrophysics Data System (ADS)

    Dimotakis, Emmanuel Dimitrios

    A new general method for the preparation of well -ordered layered double hydroxides (LDHs), (Mg_ {rm 1-x}Al_{ rm x} (OH)_2) (X^{rm n-}) _{rm n/x}{cdot}yH _2O, interlayered by organic anions has been developed. It is based on the reaction of meixnerite, (Mg_3Al(OH)_8) (OH) cdot2H_2O, with the free acid form of the desired anion--using glycerol as a swelling agent--to yield single crystalline products that are not readily available by conventional synthetic methods. The (Mg_3Al(OH) _8) -adipate and -p-toluenesulfonate derivatives undergo facile ion exchange reactions with Keggin-type (XM_{12}O_ {40}) ^{rm n -} or lacunary (XM_{11 }O_{39}) ^{rm m-} polyoxometalates (POMs) to form well-ordered, microporous pillared derivatives with the highest N_2 BET surface areas reported to date, namely 107 and 155 m^2 /g, respectively. Meixnerite, (Mg_3Al(OH) _8) (OH) cdot2H _2O, has unexpectedly been found to undergo similar ion exchange reactions, in a topotactic way, with retention of the structure of the intercalated POMs. The meixnerite was conveniently prepared for the first time from calcination of (Mg_3Al(OH) _8) (CO_3) _{0.5}{cdot}2H _2O and aqueous hydrolysis of the resulting NaCl-type solid solution. Metal carbonyl clusters have also been examined for ion-exchange (i.e., { (Pt _3(CO)_6) _{rm n}}^ {2-}) in these LDH-precursors. This chemistry is compared with the surface chemistry of (Mg_3 Al(OH)_8) (X^ {rm n-}) _{ rm 1/n}{cdot}2H _2O (X = CO_3^{2 -} or OH^{-}). It has been shown that the surface hydrolysis reaction: CO _3^{2-} + H _2O longrightarrow HCO_3^{-} + OH ^-, causes reductive condensation reactions of neutral carbonyl clusters with the LDH. The reactions were as efficient as with Na metal in solution. In part II of this work, Li-fluorohectorite, has been pillared with titanium polyoxocations derived from the acidic hydrolysis of TiCl_4 or Ti(i-OC_3H_7) _4. Raman spectroscopy of the product indicates that the pillars have a structure analogous to TiO_2(B) phase

  13. Constrained Deformable-Layer Tomography

    NASA Astrophysics Data System (ADS)

    Zhou, H.

    2006-12-01

    The improvement on traveltime tomography depends on improving data coverage and tomographic methodology. The data coverage depends on the spatial distribution of sources and stations, as well as the extent of lateral velocity variation that may alter the raypaths locally. A reliable tomographic image requires large enough ray hit count and wide enough angular range between traversing rays over the targeted anomalies. Recent years have witnessed the advancement of traveltime tomography in two aspects. One is the use of finite frequency kernels, and the other is the improvement on model parameterization, particularly that allows the use of a priori constraints. A new way of model parameterization is the deformable-layer tomography (DLT), which directly inverts for the geometry of velocity interfaces by varying the depths of grid points to achieve a best traveltime fit. In contrast, conventional grid or cell tomography seeks to determine velocity values of a mesh of fixed-in-space grids or cells. In this study, the DLT is used to map crustal P-wave velocities with first arrival data from local earthquakes and two LARSE active surveys in southern California. The DLT solutions along three profiles are constrained using known depth ranges of the Moho discontinuity at 21 sites from a previous receiver function study. The DLT solutions are generally well resolved according to restoration resolution tests. The patterns of 2D DLT models of different profiles match well at their intersection locations. In comparison with existing 3D cell tomography models in southern California, the new DLT models significantly improve the data fitness. In comparison with the multi-scale cell tomography conducted for the same data, while the data fitting levels of the DLT and the multi-scale cell tomography models are compatible, the DLT provides much higher vertical resolution and more realistic description of the undulation of velocity discontinuities. The constraints on the Moho depth

  14. Uncertainties in Surface Layer Modeling

    NASA Astrophysics Data System (ADS)

    Pendergrass, W.

    2015-12-01

    A central problem for micrometeorologists has been the relationship of air-surface exchange rates of momentum and heat to quantities that can be predicted with confidence. The flux-gradient profile developed through Monin-Obukhov Similarity Theory (MOST) provides an integration of the dimensionless wind shear expression where is an empirically derived expression for stable and unstable atmospheric conditions. Empirically derived expressions are far from universally accepted (Garratt, 1992, Table A5). Regardless of what form of these relationships might be used, their significance over any short period of time is questionable since all of these relationships between fluxes and gradients apply to averages that might rarely occur. It is well accepted that the assumption of stationarity and homogeneity do not reflect the true chaotic nature of the processes that control the variables considered in these relationships, with the net consequence that the levels of predictability theoretically attainable might never be realized in practice. This matter is of direct relevance to modern prognostic models which construct forecasts by assuming the universal applicability of relationships among averages for the lower atmosphere, which rarely maintains an average state. Under a Cooperative research and Development Agreement between NOAA and Duke Energy Generation, NOAA/ATDD conducted atmospheric boundary layer (ABL) research using Duke renewable energy sites as research testbeds. One aspect of this research has been the evaluation of legacy flux-gradient formulations (the ϕ functions, see Monin and Obukhov, 1954) for the exchange of heat and momentum. At the Duke Energy Ocotillo site, NOAA/ATDD installed sonic anemometers reporting wind and temperature fluctuations at 10Hz at eight elevations. From these observations, ϕM and ϕH were derived from a two-year database of mean and turbulent wind and temperature observations. From this extensive measurement database, using a

  15. Band diagrams of layered plasmonic metamaterials

    NASA Astrophysics Data System (ADS)

    Al Shakhs, Mohammed H.; Ott, Peter; Chau, Kenneth J.

    2014-11-01

    We introduce a method to map the band diagrams, or equipotential contours (EPCs), of any layered plasmonic metamaterial using a general expression for the Poynting vector in a lossy layered medium of finite extent under plane-wave illumination. Unlike conventional methods to get band diagrams by solving the Helmholtz equation using the Floquet-Bloch theorem (an approach restricted to infinite, periodic, lossless media), our method adopts a bottom-up philosophy based on spatial-frequency decomposition of the electric and magnetic fields (an approach applicable to finite, lossy media). Equipotential contours are used to visualize phase and group velocities in a wide range of layered plasmonic systems, including the basic building block of a thin metallic layer and more complex multi-layers with unique optical properties such as negative phase velocity, super-resolution imaging, canalization, and far-field imaging. We show that a thin metallic layer can mimic a left-handed electromagnetic response at the surface plasmon resonance and that stacks of metal and dielectric layers can do the same provided that the dielectric layer is sufficiently thin. We also use EPCs to estimate resolution limits of both Pendry's silver slab lens and the Veselago lens and show that the image location and lateral image resolution of metal-dielectric layered flat lenses can be described (and tailored) by the concavity and spectral reach of the dominant band in their EPCs. Homogenization methods for describing the effective optical properties of various layered systems are validated by the extent to which they accurately mimic features in their EPCs.

  16. Oxygen inhibition layer of composite resins: effects of layer thickness and surface layer treatment on the interlayer bond strength.

    PubMed

    Bijelic-Donova, Jasmina; Garoushi, Sufyan; Lassila, Lippo V J; Vallittu, Pekka K

    2015-02-01

    An oxygen inhibition layer develops on surfaces exposed to air during polymerization of particulate filling composite. This study assessed the thickness of the oxygen inhibition layer of short-fiber-reinforced composite in comparison with conventional particulate filling composites. The effect of an oxygen inhibition layer on the shear bond strength of incrementally placed particulate filling composite layers was also evaluated. Four different restorative composites were selected: everX Posterior (a short-fiber-reinforced composite), Z250, SupremeXT, and Silorane. All composites were evaluated regarding the thickness of the oxygen inhibition layer and for shear bond strength. An equal amount of each composite was polymerized in air between two glass plates and the thickness of the oxygen inhibition layer was measured using a stereomicroscope. Cylindrical-shaped specimens were prepared for measurement of shear bond strength by placing incrementally two layers of the same composite material. Before applying the second composite layer, the first increment's bonding site was treated as follows: grinding with 1,000-grit silicon-carbide (SiC) abrasive paper, or treatment with ethanol or with water-spray. The inhibition depth was lowest (11.6 μm) for water-sprayed Silorane and greatest (22.9 μm) for the water-sprayed short-fiber-reinforced composite. The shear bond strength ranged from 5.8 MPa (ground Silorane) to 36.4 MPa (water-sprayed SupremeXT). The presence of an oxygen inhibition layer enhanced the interlayer shear bond strength of all investigated materials, but its absence resulted in cohesive and mixed failures only with the short-fiber-reinforced composite. Thus, more durable adhesion with short-fiber-reinforced composite is expected.

  17. Electronic energy loss spectra from mono-layer to few layers of phosphorene

    NASA Astrophysics Data System (ADS)

    Mohan, Brij; Thakur, Rajesh; Ahluwalia, P. K.

    2016-05-01

    Using first principles calculations, electronic and optical properties of few-layers phosphorene has been investigated. Electronic band structure show a moderate band gap of 0.9 eV in monolayer phosphorene which decreases with increasing number of layers. Optical properties of few-layers of phosphorene in infrared and visible region shows tunability with number of layers. Electron energy loss function has been plotted and huge red shift in plasmonic behaviours is found. These tunable electronic and optical properties of few-layers of phosphorene can be useful for the applications of optoelectronic devices.

  18. Simulation of the layer-by-layer synthesis of articles with an electron beam

    NASA Astrophysics Data System (ADS)

    Rudskoi, A. I.; Kondrat'ev, S. Yu.; Sokolov, Yu. A.; Kopaev, V. N.

    2015-11-01

    The production of powder articles by layer-by-layer electron-beam synthesis is simulated. The following types of spatial distribution of the specific beam power over the surface of a powder layer are analyzed: truncated Gaussian distribution and β distribution. The mathematical description of the layer-by-layer electron- beam synthesis of articles includes a model for the interaction of a scanning electron beam with an article and a model for the heat-and-mass transfer processes that occur during the formation of an article.

  19. Error Control with Perfectly Matched Layer or Damping Layer Treatments for Computational Aeroacoustics with Jet Flows

    NASA Technical Reports Server (NTRS)

    Goodrich, John W.

    2009-01-01

    In this paper we show by means of numerical experiments that the error introduced in a numerical domain because of a Perfectly Matched Layer or Damping Layer boundary treatment can be controlled. These experimental demonstrations are for acoustic propagation with the Linearized Euler Equations with both uniform and steady jet flows. The propagating signal is driven by a time harmonic pressure source. Combinations of Perfectly Matched and Damping Layers are used with different damping profiles. These layer and profile combinations allow the relative error introduced by a layer to be kept as small as desired, in principle. Tradeoffs between error and cost are explored.

  20. Layer-by-Layer Assembly Onto Gold Nanoparticles of Various Size

    NASA Astrophysics Data System (ADS)

    Kilroy, Andrew; Kessler, Sarah; Dobbins, Tabbetha

    This research focuses on the potential applications of coated gold nanoparticles in medicine. By coating gold nanoparticles in layers of polyelectrolytes, with a final layer of antibodies which targets chemicals uniquely exhibited by cancer cells, we eventually hope to selectively attach the nanoparticles to the cancer cells. The coated nanoparticles are assembled through layer-by-layer coulombic attraction due to the passive zeta potential of the particle and the charged nature of the polyelectrolytes. This poster will explore the potential usefulness of variously sized nanoparticles with various thickness of polyelectrolyte layers.

  1. Instrument platforms for thin-layer chromatography.

    PubMed

    Bernard-Savary, Pierre; Poole, Colin F

    2015-11-20

    High performance column and thin-layer chromatography are both instrumental techniques but differ in that column chromatography requires a fully integrated instrument platform with high pressure capability while for thin-layer chromatography separate devices are used for each unit operation, usually at or close to atmospheric pressure, and afford higher flexibility supporting on-line or off-line operation. The unit operations of thin-layer chromatography are defined as sample application, development and evaluation with derivatization as an optional step. The diversity of equipment for each operation contributes to the flexibility of analysis by thin-layer chromatography and supports manual, semi-automated or full-automation of the separation process. Instrument platforms are more than a convenience as they affect performance, repeatability, sample detectability, and time management. The current trend in thin-layer chromatography is to make the unit operations independent of the user so that analysts can perform other tasks while each step is performed. In addition, in thin-layer chromatography it is general practice to separate several samples simultaneously, and instrument platforms are required to accommodate this feature. In this article, we review contemporary instrumentation employed in thin-layer chromatography for sample application, development, derivatization, photodocumentation, densitometric evaluation, and hyphenation with spectroscopic detectors with an emphasis on the variety and performance of commercially available systems. Some suggestions for best practices and avoidance of common mistakes are included.

  2. Electric fields and double layers in plasmas

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Thiemann, H.; Schunk, R. W.

    1987-01-01

    Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamical features of the double layers are discussed. These features, as seen in simulations, laboratory experiments, and theory, indicate that double layers and the currents through them undergo slow oscillations which are determined by the ion transit time across an effective length of the system in which double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations were considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields and double layers in an expanding plasma is discussed.

  3. Confined water between two graphene layers

    NASA Astrophysics Data System (ADS)

    Peeters, Francois; Sobrino Fernandez, Mario; Neek-Amal, Mehdi; Condensed Matter Theory Team

    Water confined between two layers with a separation of a few Angstrom forms a layered two- dimensional ice structure. Using large scale molecular dynamics simulations with the adoptable ReaxFF interatomic potential we found that monolayer ice with a rhombic-square structure nucleates between graphene layers which is non-polar and non-ferroelectric. We provide different energetic considerations and H-bonding results that explain the inter-layer and intra-layer properties of two-dimensional ice. The controversional AA-stacking found experimentally is consistent with our minimum energy crystal structure of bilayer ice. Furthermore, we predict that odd-number of layers of ice has the same lattice structure as monolayer ice, while even number of ice layers exhibit the square ice AA-stacking of bilayer ice.We predict that an inplane electric field polarizes the water molecules resulting in distinct-ferroelectricity. Electrical hysteresis in the response of the total dipole moment of monolayer ice is found

  4. Assessing Layered Materials in Gale Crater

    NASA Technical Reports Server (NTRS)

    Bridges, N. T.

    2001-01-01

    The recent analysis of high resolution Mars Orbiter Camera (MOC) images of layered outcrops in equatorial regions reinforces two important ideas, which will probably eventually become paradigms, about Mars: 1) It has had a long, complex geologic history marked by change, as manifested in the different layers observed, and 2) Standing bodies of water existed for substantial lengths of time, indicating clement conditions possibly conducive to life. Although observations of layering and evidence for lakes and oceans has been reported for years based on Mariner 9 and Viking data, the MOC data show that this layering is much more pervasive and complex than previously thought. These layered sites are ideal for studying the geologic, and possibly biologic, history of Mars. Here, a layered site within Gale Crater is advocated as a Mars Exploration Rover (MER) target. This is one of the few layered areas within closed depressions (e.g., other craters and Vallis Marineris) that meets the landing site constraints and is accessible to both MER A and B.

  5. Quantum key distribution networks layer model

    NASA Astrophysics Data System (ADS)

    Wen, Hao; Han, Zheng-fu; Hong, Pei-lin; Guo, Guang-can

    2008-03-01

    Quantum Key Distribution (QKD) networks allow multiple users to generate and share secret quantum keys with unconditional security. Although many schemes of QKD networks have been presented, they are only concentrated on the system realization and physical implementations. For the complete practical quantum network, a succinct theoretic model that systematically describes the working processes from physical schemes to key process protocols, from network topology to key management, and from quantum communication to classical communication is still absent. One would hope that research and experience have shown that there are certain succinct model in the design of communication network. With demonstration of the different QKD links and the four primary types of quantum networks including probability multiplexing, wavelength multiplexing, time multiplexing and quantum multiplexing, we suggest a layer model for QKD networks which will be compatible with different implementations and protocols. We divide it into four main layers by their functional independency while defining each layer's services and responsibilities in detail, orderly named quantum links layer, quantum networks layer, quantum key distribution protocols process layer, and keys management layer. It will be helpful for the systematic design and construction of real QKD networks.

  6. The neutral surface layer above rough surfaces

    NASA Astrophysics Data System (ADS)

    Smedman, Ann-Sofi; Sahlee, Erik

    2014-05-01

    It is generally accepted that turbulent fluxes (momentum and scalar fluxes) are approx. constant with height above horizontal surfaces with low roughness. But what will happen when the roughness sub-layer is large as found over cities, forests and rough seas? In a study of the kinematic structure of the near neutral atmospheric surface layer, Högström, Hunt and Smedman, 2002, it was demonstrated that a model with detached eddies from above the surface layer impinging on to the surface (Hunt and Morison, 2000) could explain some of the observed features in the neutral atmospheric boundary layer. Thus the detached eddy model proved successful in explaining the dynamic structure of the near neutral atmospheric surface layer, especially the shape of the spectra of the wind components and scalars and corresponding fluxes. Here we make the hypothesis that the detached-eddy model can also be used to explain the experimental results related to the 3-dimensional turbulence structure above rough surfaces. Measurements are taken both over land (grass and forest) and over sea (Baltic Sea and hurricane Fabian in the Atlantic) above the roughness sub-layer. Analysis of the turbulence structure shows a striking similarity between the different sites. Hunt, J.C.R and Morrison, J.F., 2000: Eddy structure in turbulent boundary layers, Euro. J. Mech. B-Fluids, 19, 673-694. Högström, U., Hunt, J.C.R., and Smedman, A., 2002: Theory and measurements for turbulence spectra and variances in the atmospheric neutral surface layer, Bound.-Layer Meteorol., 103,101-124.

  7. Layer-dependent Band Alignment and Work Function of Few-Layer Phosphorene

    PubMed Central

    Cai, Yongqing; Zhang, Gang; Zhang, Yong-Wei

    2014-01-01

    Using first-principles calculations, we study the electronic properties of few-layer phosphorene focusing on layer-dependent behavior of band gap, work function band alignment and carrier effective mass. It is found that few-layer phosphorene shows a robust direct band gap character, and its band gap decreases with the number of layers following a power law. The work function decreases rapidly from monolayer (5.16 eV) to trilayer (4.56 eV), and then slowly upon further increasing the layer number. Compared to monolayer phosphorene, there is a drastic decrease of hole effective mass along the ridge (zigzag) direction for bilayer phosphorene, indicating a strong interlayer coupling and screening effect. Our study suggests that 1). Few-layer phosphorene with a layer-dependent band gap and a robust direct band gap character is promising for efficient solar energy harvest. 2). Few-layer phosphorene outperforms monolayer counterpart in terms of a lighter carrier effective mass, a higher carrier density and a weaker scattering due to enhanced screening. 3). The layer-dependent band edges and work functions of few-layer phosphorene allow for modification of Schottky barrier with enhanced carrier injection efficiency. It is expected that few-layer phosphorene will present abundant opportunities for a plethora of new electronic applications. PMID:25327586

  8. Layer-dependent band alignment and work function of few-layer phosphorene.

    PubMed

    Cai, Yongqing; Zhang, Gang; Zhang, Yong-Wei

    2014-10-20

    Using first-principles calculations, we study the electronic properties of few-layer phosphorene focusing on layer-dependent behavior of band gap, work function band alignment and carrier effective mass. It is found that few-layer phosphorene shows a robust direct band gap character, and its band gap decreases with the number of layers following a power law. The work function decreases rapidly from monolayer (5.16 eV) to trilayer (4.56 eV), and then slowly upon further increasing the layer number. Compared to monolayer phosphorene, there is a drastic decrease of hole effective mass along the ridge (zigzag) direction for bilayer phosphorene, indicating a strong interlayer coupling and screening effect. Our study suggests that 1). Few-layer phosphorene with a layer-dependent band gap and a robust direct band gap character is promising for efficient solar energy harvest. 2). Few-layer phosphorene outperforms monolayer counterpart in terms of a lighter carrier effective mass, a higher carrier density and a weaker scattering due to enhanced screening. 3). The layer-dependent band edges and work functions of few-layer phosphorene allow for modification of Schottky barrier with enhanced carrier injection efficiency. It is expected that few-layer phosphorene will present abundant opportunities for a plethora of new electronic applications.

  9. A highly crystalline layered silicate with three-dimensionally microporous layers

    NASA Astrophysics Data System (ADS)

    Jeong, Hae-Kwon; Nair, Sankar; Vogt, Thomas; Dickinson, L. Charles; Tsapatsis, Michael

    2003-01-01

    Layered silicates with three-dimensional microporosity within the layers have the potential to enable new applications in catalysis, adsorption and ion-exchange. Until now no such materials have been reported. However, here we present the synthesis and structure of AMH-3, a silicate with three-dimensionally microporous layers, obtained in high purity and crystallinity. AMH-3 is composed of silicate layers containing eight-membered rings in all three principal crystal directions, and spaced by strontium cations, sodium cations and water molecules. Because of its three-dimensional pore structure, acid and thermal stability, this layered material could find applications in polymer-silicate composites for membrane applications, for synthesis of combined microporous-mesoporous materials, and for the formation of new zeolites and microporous films. Its existence also opens new possibilities for the synthesis of other layered silicates with multidimensional microporous framework layers.

  10. Enforced Layer-by-Layer Stacking of Energetic Salts towards High-Performance Insensitive Energetic Materials.

    PubMed

    Zhang, Jiaheng; Mitchell, Lauren A; Parrish, Damon A; Shreeve, Jean'ne M

    2015-08-26

    Development of modern high-performance insensitive energetic materials is significant because of the increasing demands for both military and civilian applications. Here we propose a rapid and facile strategy called the "layer hydrogen bonding pairing approach" to organize energetic molecules via layer-by-layer stacking, which grants access to tunable energetic materials with targeted properties. Using this strategy, an unusual energetic salt, hydroxylammonium 4-amino-furazan-3-yl-tetrazol-1-olate, with good detonation performances and excellent sensitivities, was designed, synthesized, and fully characterized. In addition, the expected unique layer-by-layer structure with a high crystal packing coefficient was confirmed by single-crystal X-ray crystallography. Calculations indicate that the layer-stacking structure of this material can absorb the mechanical stimuli-induced kinetic energy by converting it to layer sliding, which results in low sensitivity.

  11. Method for forming a barrier layer

    DOEpatents

    Weihs, Timothy P.; Barbee, Jr., Troy W.

    2002-01-01

    Cubic or metastable cubic refractory metal carbides act as barrier layers to isolate, adhere, and passivate copper in semiconductor fabrication. One or more barrier layers of the metal carbide are deposited in conjunction with copper metallizations to form a multilayer characterized by a cubic crystal structure with a strong (100) texture. Suitable barrier layer materials include refractory transition metal carbides such as vanadium carbide (VC), niobium carbide (NbC), tantalum carbide (TaC), chromium carbide (Cr.sub.3 C.sub.2), tungsten carbide (WC), and molybdenum carbide (MoC).

  12. Calculation methods for compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

    1976-01-01

    Calculation procedures for non-reacting compressible two- and three-dimensional turbulent boundary layers were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete boundary layer equations summarized. Alternative numerical solution procedures were examined, and both mean field and mean turbulence field closure models were considered. Physics and related calculation problems peculiar to compressible turbulent boundary layers are described. A catalog of available solution procedures of the finite difference, finite element, and method of weighted residuals genre is included. Influence of compressibility, low Reynolds number, wall blowing, and pressure gradient upon mean field closure constants are reported.

  13. Growth Layers on Ammonium Dihydrogen Phosphate.

    PubMed

    Torgesen, J L; Jackson, R W

    1965-05-14

    Microscopic observations of growth layers and etch pits on ammonium dihydrogen phosphate crystals reveal screw dislocations on the {100} face generating elliptical spirals that change rapidly but reversibly to rectangular shape when chromium-ion impurity is added. The effects of the impurity on crystal habit are judged to be secondary to changes in the morphology of the growth layers. No sources of growth are observed on the {101} faces; the layers spread inward from the edges and at times are mutually annihilating so that, temporarily, no steps are observed. Similar behavior is recorded for the {1011} faces of NaNO(3).

  14. Double layers on auroral field lines

    NASA Technical Reports Server (NTRS)

    Hudson, M. K.; Lotko, W.; Witt, E.

    1982-01-01

    Time-stationary solutions to the Vlasov-Poisson equation for ion holes and double layers were examined along with particle simulations which pertain to recent observations of small amplitude (e phi)/t sub e approx. 1 electric field structures on auroral field lines. Both the time-stationary analysis and the simulations suggest that double layers evolve from holes in ion phase space when their amplitude reaches (e phi)/t sub e approx. 1. Multiple small amplitude double layers which are seen in long simulation systems and are seen to propagate past spacecraft may account for the acceleration of plasma sheet electrons to produce the discrete aurora.

  15. Energy transport using natural convection boundary layers

    SciTech Connect

    Anderson, R

    1986-04-01

    Natural convection is one of the major modes of energy transport in passive solar buildings. There are two primary mechanisms for natural convection heat transport through an aperture between building zones: (1) bulk density differences created by temperature differences between zones; and (2) thermosyphon pumping created by natural convection boundary layers. The primary objective of the present study is to compare the characteristics of bulk density driven and boundary layer driven flow, and discuss some of the advantages associated with the use of natural convection boundary layers to transport energy in solar building applications.

  16. Strained layer Fabry-Perot device

    DOEpatents

    Brennan, Thomas M.; Fritz, Ian J.; Hammons, Burrell E.

    1994-01-01

    An asymmetric Fabry-Perot reflectance modulator (AFPM) consists of an active region between top and bottom mirrors, the bottom mirror being affixed to a substrate by a buffer layer. The active region comprises a strained-layer region having a bandgap and thickness chosen for resonance at the Fabry-Perot frequency. The mirrors are lattice matched to the active region, and the buffer layer is lattice matched to the mirror at the interface. The device operates at wavelengths of commercially available semiconductor lasers.

  17. Boundary-layer linear stability theory

    NASA Technical Reports Server (NTRS)

    Mack, L. M.

    1984-01-01

    Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of boundary layer instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius boundary layer, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a boundary layer, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer

  18. Boundary-layer linear stability theory

    NASA Astrophysics Data System (ADS)

    Mack, L. M.

    1984-06-01

    Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of boundary layer instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius boundary layer, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a boundary layer, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer

  19. Single layer multi-color luminescent display

    NASA Technical Reports Server (NTRS)

    Robertson, James B. (Inventor)

    1991-01-01

    The invention is a multi-color luminescent display comprising an insulator substrate and a single layer of host material which may be a phosphor deposited thereon that hosts one or more differential impurities, therein forming a pattern of selected and distinctly colored phosphors such as blue, green, and red phosphors in a single layer of host material. Transparent electrical conductor means may be provided for subjecting selected portions of the pattern of colored phosphors to an electric field thereby forming a multi-color, single layer electroluminescent display.

  20. Infrared Heating of Hydrogen Layers in Hohlraums

    SciTech Connect

    Kozioziemski, B J; McEachern, R L; London, R A; Bitter, D N

    2001-08-15

    The authors report results of modeling and experiments on infrared heated deuterium-hydride (HD) layers in hohlraums. A 2 mm diameter, 40 {micro}m thick shell with 100-400 {micro}m thick HD ice inside a NIF scale-1 gold hohlraum with 1-3 {micro}m rms surface roughness is heated by pumping the HD vibrational bands. Models indicate control of the low-mode layer shape by adjusting the infrared distribution along the hohlraum walls. They have experimentally demonstrated control of the layer symmetry perpendicular to the hohlraum axis.

  1. Parallel field penetration in a layered superconductor

    NASA Astrophysics Data System (ADS)

    Buzdin, A.; Feinberg, D.

    1992-05-01

    The Bean-Livingston entrance field Hs for vortex penetration at the surface is calculated for layered superconductors with Josephson interlayer coupling and field parallel to the layers. Two regimes must be distinguished: close to Tc, one can use the anisotropic London theory, so Hs is of the order of Hc, the thermodynamic critical field, and is the same as for a field normal to the layers. On the opposite, when the transverse coherence length ξ c is smaller than the interlayer distance d, Hs becomes smaller than Hc and is of the order of ( {ξ c}/{d})H c. Contrary to the entrance field for pure Josephson vortices (fluxons) in junctions, this field is still much larger than the first critical field Hc1∥. This behaviour is a consequence of the specific structure of the vortex core in a layered superconductor and results in a crossover from a linear to a square root temperature dependence as the temperature is lowered.

  2. Multi-layer waste containment barrier

    DOEpatents

    Smith, Ann Marie; Gardner, Bradley M.; Nickelson, David F.

    1999-01-01

    An apparatus for constructing an underground containment barrier for containing an in-situ portion of earth. The apparatus includes an excavating device for simultaneously (i) excavating earthen material from beside the in-situ portion of earth without removing the in-situ portion and thereby forming an open side trench defined by opposing earthen sidewalls, and (ii) excavating earthen material from beneath the in-situ portion of earth without removing the in-situ portion and thereby forming a generally horizontal underground trench beneath the in-situ portion defined by opposing earthen sidewalls. The apparatus further includes a barrier-forming device attached to the excavating device for simultaneously forming a side barrier within the open trench and a generally horizontal, multi-layer barrier within the generally horizontal trench. The multi-layer barrier includes at least a first layer and a second layer.

  3. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, H.

    1986-01-01

    A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

  4. Modeling of Intellite 3 Layer Deformable Mirror

    SciTech Connect

    Papavasiliou, A

    2002-04-15

    This is a report on modeling of the Intellite three layer membrane mirror design. The goal of this project was to provide Intellite with a model that will allow them to design a mirror with confidence.

  5. Josephson vortex lattice in layered superconductors

    SciTech Connect

    Koshelev, A. E.; Dodgson, M. J. W.

    2013-09-15

    Many superconducting materials are composed of weakly coupled conducting layers. Such a layered structure has a very strong influence on the properties of vortex matter in a magnetic field. This review focuses on the properties of the Josephson vortex lattice generated by the magnetic field applied in the direction of the layers. The theoretical description is based on the Lawrence-Doniach model in the London limit, which takes only the phase degree of freedom of the superconducting order parameter into account. In spite of its simplicity, this model leads to an amazingly rich set of phenomena. We review in detail the structure of an isolated vortex line and various properties of the vortex lattice, in both dilute and dense limits. In particular, we extensively discuss the influence of the layered structure and thermal fluctuations on the selection of lattice configurations at different magnetic fields.

  6. Layer resolved capacitive probing of graphene bilayers

    NASA Astrophysics Data System (ADS)

    Zibrov, Alexander; Parmentier, François; Li, Jia; Wang, Lei; Hunt, Benjamin; Dean, Cory; Hone, James; Taniguchi, Takashi; Watanabe, Kenji; Young, Andrea

    Compared to single layer graphene, graphene bilayers have an additional ``which-layer'' degree of freedom that can be controlled by an external electric field in a dual-gated device geometry. We describe capacitance measurements capable of directly probing this degree of freedom. By performing top gate, bottom gate, and penetration field capacitance measurements, we directly extract layer polarization of both Bernal and twisted bilayers. We will present measurements of hBN encapsulated bilayers at both zero and high magnetic field, focusing on the physics of the highly degenerate zero-energy Landau level in the high magnetic field limit where spin, valley, and layer degeneracy are all lifted by electronic interactions.

  7. Dynamics of Josephson pancakes in layered superconductors

    SciTech Connect

    Mints, R.G.; Snapiro, I.B.

    1994-03-01

    We consider a pointlike vortex in a layered superconductor with linear defects in the superconducting layers. We treat these defects as Josephson junctions with high critical current density. We consider the electrodynamics of these junctions within the framework of nonlocal Josephson electrodynamics. We show that Josephson current through a linear defect in a superconducting layer results in a pointlike vortex with a superconducting core residing in this layer (Josephson pancake). We find the mobility of a Josephson pancake. We consider a small amplitude wave in a Josephson junction with nonlocal electrodynamics. We treat a bending wave for an infinite stack of Josephson pancakes. We find the dispersion relation for these waves. We show that their velocities tend to a certain finite limit when the wavelength tends to infinity.

  8. Microwave-cut silicon layer transfer

    SciTech Connect

    Thompson, D.C.; Alford, T.L.; Mayer, J.W.; Hochbauer, T.; Nastasi, M.; Lau, S.S.; Theodore, N. David; Henttinen, K.; Suni, Ilkka; Chu, Paul K.

    2005-11-28

    Microwave heating is used to initiate exfoliation of silicon layers in conjunction with the ion-cut process for transfer of silicon layers onto insulator or heterogeneous layered substrates. Samples were processed inside a 2.45 GHz, 1300 W cavity applicator microwave system for time durations as low as 12 s. This is a significant decrease in exfoliation incubation times. Sample temperatures measured by pyrometry were within previous published ranges. Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy were used to determine layer thickness and crystallinity. Surface quality was measured by using atomic force microscopy. Hall measurements were used to characterize electrical properties as a function of postcut anneal time and temperature.

  9. Layered solid sorbents for carbon dioxide capture

    SciTech Connect

    Li, Bingyun; Jiang, Bingbing; Gray, McMahan L; Fauth, Daniel J; Pennline, Henry W; Richards, George A

    2014-11-18

    A solid sorbent for the capture and the transport of carbon dioxide gas is provided having at least one first layer of a positively charged material that is polyethylenimine or poly(allylamine hydrochloride), that captures at least a portion of the gas, and at least one second layer of a negatively charged material that is polystyrenesulfonate or poly(acryclic acid), that transports the gas, wherein the second layer of material is in juxtaposition to, attached to, or crosslinked with the first layer for forming at least one bilayer, and a solid substrate support having a porous surface, wherein one or more of the bilayers is/are deposited on the surface of and/or within the solid substrate. A method of preparing and using the solid sorbent is provided.

  10. Hydrothermal regimes of the dry active layer

    NASA Astrophysics Data System (ADS)

    Ishikawa, Mamoru; Zhang, Yinsheng; Kadota, Tsutomu; Ohata, Tetsuo

    2006-04-01

    Evaporation and condensation in the soil column clearly influence year-round nonconductive heat transfer dynamics in the dry active layer underlying semiarid permafrost regions. We deduced this from heat flux components quantified using state-of-the-art micrometeorological data sets obtained in dry and moist summers and in winters with various snow cover depths. Vapor moves easily through large pores, some of which connect to the atmosphere, allowing (1) considerable active layer warming driven by pipe-like snowmelt infiltration, and (2) direct vapor linkage between atmosphere and deeper soils. Because of strong adhesive forces, water in the dry active layer evaporates with great difficulty. The fraction of latent heat to total soil heat storage ranged from 26 to 45% in dry and moist summers, respectively. These values are not negligible, despite being smaller than those of arctic wet active layer, in which only freezing and thawing were considered.

  11. Complex oxides: Creative tension in layered crystals

    NASA Astrophysics Data System (ADS)

    Gopalan, Venkatraman; Engel-Herbert, Roman

    2016-09-01

    New findings suggest that the mechanical stretching of layered crystals can transform them from a polar to a nonpolar state. This could spur the design of multifunctional materials controlled by an electric field.

  12. Composite S-layer lipid structures

    PubMed Central

    Schuster, Bernhard; Sleytr, Uwe B.

    2010-01-01

    Designing and utilization of biomimetic membrane systems generated by bottom-up processes is a rapidly growing scientific and engineering field. Elucidation of the supramolecular construction principle of archaeal cell envelopes composed of S-layer stabilized lipid membranes led to new strategies for generating highly stable functional lipid membranes at meso- and macroscopic scale. In this review, we provide a state of the art survey how S-layer proteins, lipids, and polysaccharides may be used as basic building blocks for the assembly of S-layer supported lipid membranes. These biomimetic membrane systems are distinguished by a nanopatterned fluidity, enhanced stability and longevity and thus, provide a dedicated reconstitution matrix for membrane-active peptides and transmembrane proteins. Exciting areas for application of composite S-layer membrane systems concern sensor systems involving specific membrane functions. PMID:19303933

  13. Smog Layer Over Upstate New York

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The STS-92 Space Shuttle astronauts photographed upstate New York at sunset on October 21, 2000. Water bodies (Lake Ontario, Lake Erie, the Finger Lakes, the St. Lawrence and Niagara Rivers) are highlighted by sunglint (sun reflecting off the water surface), making for a dramatic and unusual regional view. The photograph was taken looking toward the southwest from southern Canada, and captures a regional smog layer extending across central New York, western Lake Erie and Ohio, and further west. The layer of atmospheric pollution layer is capped by an atmospheric inversion, which is marked by the layer of clouds at the top of the photograph. The astronauts were able to document this smog event from a variety of vantage points as they orbited over the northeastern U.S. and southern Canada. Image #STS092-713-32 Image provided by the Earth Science and Image Analysis Laboratory, Johnson Space Center

  14. Double layers and circuits in astrophysics

    SciTech Connect

    Alfven, H.

    1986-05-01

    A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object. It is suggested that x-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

  15. Cloaking with optimized homogeneous anisotropic layers

    NASA Astrophysics Data System (ADS)

    Popa, Bogdan-Ioan; Cummer, Steven A.

    2009-02-01

    We present a method to reduce the scattering from arbitrary objects by surrounding them with shells composed of several layers of homogeneous anisotropic materials. An optimization procedure is used to find the material parameters for each layer, the starting point of which is a discretized approximation of a coordinate transformation cloaking shell. We show that an optimized, three-layer shell can reduce the maximum scattering of an object by as much as 15dB more than a 100-layer realization of a coordinate transformation cloaking shell. Moreover, using an optimization procedure can yield high-performance cloaking shell solutions that also meet external constraints, such as the maximum value of permittivity or permeability. This design approach can substantially simplify the fabrication of moderate-size cloaking shells.

  16. Cryogenic target system for hydrogen layering

    SciTech Connect

    Parham, T.; Kozioziemski, B.; Atkinson, D.; Baisden, P.; Bertolini, L.; Boehm, K; Chernov, A.; Coffee, K.; Coffield, F.; Dylla-Spears, R.; Edwards, O.; Fair, J.; Fedorov, M.; Fry, J.; Gibson, C.; Haid, B.; Holunga, D.; Kohut, T.; Lewis, T.; Malsbury, T.; Mapoles, E.; Sater, J.; Skulina, K.; Trummer, D.; Walters, C.

    2015-11-24

    Here, a cryogenic target positioning system was designed and installed on the National Ignition Facility (NIF) target chamber. This instrument incorporates the ability to fill, form, and characterize the NIF targets with hydrogen isotopes needed for ignition experiments inside the NIF target bay then transport and position them in the target chamber. This effort brought to fruition years of research in growing and metrologizing high-quality hydrogen fuel layers and landed it in an especially demanding operations environment in the NIF facility. D-T (deuterium-tritium) layers for NIF ignition experiments have extremely tight specifications and must be grown in a very highly constrained environment: a NIF ignition target inside a cryogenic target positioner inside the NIF target bay. Exquisite control of temperature, pressure, contaminant level, and thermal uniformity are necessary throughout seed formation and layer growth to create an essentially-groove-free single crystal layer.

  17. Boundary-layer control for drag reduction

    NASA Technical Reports Server (NTRS)

    Harvey, William D.

    1988-01-01

    Although the number of possible applications of boundary-layer control is large, a discussion is given only of those that have received the most attention recently at NASA Langley Research Center to improve airfoil drag characteristics. This research concerns stabilizing the laminar boundary layer through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (laminar flow control, LFC) either through discrete slots or a perforated surface. At low Reynolds numbers, a combination of shaping and forced transition has been used to achieve the desired run of laminar flow and control of laminar separation. In the design of both natural laminar flow and laminar flow control airfoils and wings, boundary layer stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.

  18. Free Vibration of Curved Layered Composite Beams

    NASA Astrophysics Data System (ADS)

    Yavuz, Mustafa; Ergzgüven, M. Ertaç

    In practice, fibrous and layered composite beams have periodically and locally curved layers because of the design considerations and manufacturing processes. In this study, the effect of these curvatures and composite material properties to the natural frequencies of the beams is investigated. The periodically curved layered composite material of the considered beam is modelled with the use of the continuum theory proposed by Akbarov and Guz. The free vibration problems are solved by employing the finite element method. Obtained natural frequencies of the beams are presented for the different parameters of the curvature, modulus of elasticity and support condition of the beams. For the case that the ratio of the modulus of elasticity of the layers equals to one and the parameter of the curvature equals to zero, the results converge to natural frequencies of a classical Euler-Bernoulli beam. Results are in good agreement with the literature.

  19. Cryogenic target system for hydrogen layering

    DOE PAGES

    Parham, T.; Kozioziemski, B.; Atkinson, D.; Baisden, P.; Bertolini, L.; Boehm, K; Chernov, A.; Coffee, K.; Coffield, F.; Dylla-Spears, R.; et al

    2015-11-24

    Here, a cryogenic target positioning system was designed and installed on the National Ignition Facility (NIF) target chamber. This instrument incorporates the ability to fill, form, and characterize the NIF targets with hydrogen isotopes needed for ignition experiments inside the NIF target bay then transport and position them in the target chamber. This effort brought to fruition years of research in growing and metrologizing high-quality hydrogen fuel layers and landed it in an especially demanding operations environment in the NIF facility. D-T (deuterium-tritium) layers for NIF ignition experiments have extremely tight specifications and must be grown in a very highlymore » constrained environment: a NIF ignition target inside a cryogenic target positioner inside the NIF target bay. Exquisite control of temperature, pressure, contaminant level, and thermal uniformity are necessary throughout seed formation and layer growth to create an essentially-groove-free single crystal layer.« less

  20. A new hydrodynamic analysis of double layers

    NASA Technical Reports Server (NTRS)

    Hora, Heinrich

    1987-01-01

    A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic (not necessarily static) electric fields and double layers inside of plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitous and inverted double layers in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. Results are the rotation of plasmas in magnetic fields and a new second harmonic resonance, explanation of the measured inverted double layers, explanation of the observed density-independent, second harmonics emission from laser-produced plasmas, and a laser acceleration scheme by the very high fields of the double layers.

  1. Toward parameterization of the stable boundary layer

    NASA Technical Reports Server (NTRS)

    Wetzel, P. J.

    1982-01-01

    Wangara data is used to examine the depth of the nocturnal boundary layer (NBL) and the height to which surface-linked turbulence extends. It is noted that a linearity of virtual temperature profiles has been found to extend up to a significant portion of the NBL, and then diverge where the wind shear rides over the surface-induced turbulence. A series of Richardson numbers are examined for varying degrees of turbulence and the significant cooling region is observed to have greater depth than the depth of the linear relationship layer. A three-layer parameterization of the thermodynamic structure of the NBL is developed so that a system of five equations must be solved when the wind velocity profile and the temperature at the surface are known. A correlation between the bulk Richardson number and the depth of the linear layer was found to be 0.89.

  2. High index top layer for multimaterial coatings

    NASA Astrophysics Data System (ADS)

    Steinlechner, Jessica; Martin, Iain W.

    2016-05-01

    For application in future cryogenically cooled gravitational wave detectors, the thermal noise of low absorbing mirror coatings has to be reduced. The development of low mechanical and optical loss materials is challenging, but thermal noise reduction can be significantly supported by using a multimaterial coating design. We analyze the possible improvement of the total (optical and mechanical) loss of a three-material based coating obtained by optimizing the properties of the top layer of the coating stack. A top-layer material with sufficiently high refractive index could have a significantly higher optical and mechanical loss than currently used tantala, while still enabling reduction of the total coating loss. Restrictions on possible top-layer material properties are made, and the option of a crystalline top layer is discussed.

  3. High strain rate deformation of layered nanocomposites.

    PubMed

    Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A; Thomas, Edwin L

    2012-01-01

    Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers. PMID:23132014

  4. Observations of the magnetopause current layer: Cases with no boundary layer and tests of recent models

    NASA Technical Reports Server (NTRS)

    Eastman, Timothy E.

    1995-01-01

    Evidence for the probable existence of magnetospheric boundary layers was first presented by Hones, et al. (1972), based on VELA satellite plasma observations (no magnetic field measurements were obtained). This magnetotail boundary layer is now known to be the tailward extension of the high-latitude boundary layer or plasma mantle (first uniquely identified using HEOS 2 plasma and field observations by Rosenbauer et al., 1975) and the low-latitude boundary layer (first uniquely identified using IMP 6 plasma and field observations by Eastman et al., 1976). The magnetospheric boundary layer is the region of magnetosheath-like plasma located Earthward of, but generally contiguous with the magnetopause. This boundary layer is typically identified by comparing low-energy (less than 10 keV) ion spectra across the magnetopause. Low-energy electron measurements are also useful for identifying the boundary layer because the shocked solar wind or magnetosheath has a characteristic spectral signature for electrons as well. However, there are magnetopause crossings where low-energy electrons might suggest a depletion layer outside the magnetopause even though the traditional field-rotation signature indicates that this same region is a boundary layer Earthward of the current layer. Our analyses avoided crossings which exhibit such ambiguities. Pristine magnetopause crossings are magnetopause crossings for which the current layer is well defined and for which there is no adjoining magnetospheric boundary layer as defined above. Although most magnetopause models to date apply to such crossings, few comparisons between such theory and observations of pristine magnetopause crossings have been made because most crossings have an associated magnetospheric boundary layer which significantly affects the applicable boundary conditions for the magnetopause current layer. Furthermore, almost no observational studies of magnetopause microstructure have been done even though key

  5. Perovskite thin films via atomic layer deposition.

    PubMed

    Sutherland, Brandon R; Hoogland, Sjoerd; Adachi, Michael M; Kanjanaboos, Pongsakorn; Wong, Chris T O; McDowell, Jeffrey J; Xu, Jixian; Voznyy, Oleksandr; Ning, Zhijun; Houtepen, Arjan J; Sargent, Edward H

    2015-01-01

    A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI2 and subsequently CH3 NH3 PbI3 perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm(-1) .

  6. Axisymmetric vibrations of layered tapered plates

    NASA Astrophysics Data System (ADS)

    Navaneethakrishnan, P. V.; Chandrasekaran, K.; Ravisrinivas, N.

    1992-12-01

    The study of Navaneethakrishnan and Chandrasekaran (1989) on axisymmetric free vibrations of layered annular plates is extended to the vibrations of layered annular plates whose thickness can vary as the radial distance from the arbitrary concentric circle. Numerical results are presented, showing the relationship between the circular frequency of the plate vibration and the ratio between the inner and the outer radii of the plate.

  7. Boundary-layer stability and airfoil design

    NASA Technical Reports Server (NTRS)

    Viken, Jeffrey K.

    1986-01-01

    Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar boundary layer using linear stability codes. The NLF airfoils analyzed come from three different design conditions: incompressible; compressible with no sweep; and compressible with sweep. Some of the design problems are discussed, concentrating on those problems associated with keeping the boundary layer laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.

  8. Boundary-layer theory for blast waves

    NASA Technical Reports Server (NTRS)

    Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.

    1975-01-01

    It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.

  9. Layer Engineering of 2D Semiconductor Junctions.

    PubMed

    He, Yongmin; Sobhani, Ali; Lei, Sidong; Zhang, Zhuhua; Gong, Yongji; Jin, Zehua; Zhou, Wu; Yang, Yingchao; Zhang, Yuan; Wang, Xifan; Yakobson, Boris; Vajtai, Robert; Halas, Naomi J; Li, Bo; Xie, Erqing; Ajayan, Pulickel

    2016-07-01

    A new concept for junction fabrication by connecting multiple regions with varying layer thicknesses, based on the thickness dependence, is demonstrated. This type of junction is only possible in super-thin-layered 2D materials, and exhibits similar characteristics as p-n junctions. Rectification and photovoltaic effects are observed in chemically homogeneous MoSe2 junctions between domains of different thicknesses. PMID:27136275

  10. Symmetry Breaking in Few Layer Graphene Films

    SciTech Connect

    Bostwick, A.; Ohta, T.; McChesney, J.L.; Emtsev, K.; Seyller,Th.; Horn, K.; Rotenberg, E.

    2007-05-25

    Recently, it was demonstrated that the quasiparticledynamics, the layer-dependent charge and potential, and the c-axisscreening coefficient could be extracted from measurements of thespectral function of few layer graphene films grown epitaxially on SiCusing angle-resolved photoemission spectroscopy (ARPES). In this articlewe review these findings, and present detailed methodology for extractingsuch parameters from ARPES. We also present detailed arguments againstthe possibility of an energy gap at the Dirac crossing ED.

  11. Anaesthetic agents and the ozone layer.

    PubMed

    Westhorpe, R; Blutstein, H

    1990-02-01

    There is an important relationship between the stratospheric ozone layer and the absorption of potentially harmful ultraviolet-B radiation from the sun. Chlorofluorocarbons and halogenated hydrocarbons are commonly used chemicals which are implicated in the depletion of the ozone layer. Of the anaesthetic agents, halothane has the greatest potential for depleting ozone although, when compared with the global use of other chlorofluorocarbons and halogenated hydrocarbons, its current contribution to the problem is relatively small.

  12. Optical devices featuring textured semiconductor layers

    DOEpatents

    Moustakas, Theodore D.; Cabalu, Jasper S.

    2011-10-11

    A semiconductor sensor, solar cell or emitter, or a precursor therefor, has a substrate and one or more textured semiconductor layers deposited onto the substrate. The textured layers enhance light extraction or absorption. Texturing in the region of multiple quantum wells greatly enhances internal quantum efficiency if the semiconductor is polar and the quantum wells are grown along the polar direction. Electroluminescence of LEDs of the invention is dichromatic, and results in variable color LEDs, including white LEDs, without the use of phosphor.

  13. Optical devices featuring nonpolar textured semiconductor layers

    DOEpatents

    Moustakas, Theodore D; Moldawer, Adam; Bhattacharyya, Anirban; Abell, Joshua

    2013-11-26

    A semiconductor emitter, or precursor therefor, has a substrate and one or more textured semiconductor layers deposited onto the substrate in a nonpolar orientation. The textured layers enhance light extraction, and the use of nonpolar orientation greatly enhances internal quantum efficiency compared to conventional devices. Both the internal and external quantum efficiencies of emitters of the invention can be 70-80% or higher. The invention provides highly efficient light emitting diodes suitable for solid state lighting.

  14. Optical devices featuring textured semiconductor layers

    DOEpatents

    Moustakas, Theodore D.; Cabalu, Jasper S.

    2012-08-07

    A semiconductor sensor, solar cell or emitter, or a precursor therefor, has a substrate and one or more textured semiconductor layers deposited onto the substrate. The textured layers enhance light extraction or absorption. Texturing in the region of multiple quantum wells greatly enhances internal quantum efficiency if the semiconductor is polar and the quantum wells are grown along the polar direction. Electroluminescence of LEDs of the invention is dichromatic, and results in variable color LEDs, including white LEDs, without the use of phosphor.

  15. Push It to the Max! Thinking in Layers

    ERIC Educational Resources Information Center

    Winters, Laurel

    2009-01-01

    In this article, the author describes a project using acetate sheets. This project was to have at least two layers: (1) the first layer is a more detailed front layer of the acetate sheet; and (2) the second layer is a piece of painted paper behind the acetate. This lesson presents an opportunity to help students think in "layers," which will be…

  16. Surface layer effects on waste glass corrosion

    SciTech Connect

    Feng, X.

    1993-12-31

    Water contact subjects waste glass to chemical attack that results in the formation of surface alteration layers. Two principal hypotheses have been advanced concerning the effect of surface alteration layers on continued glass corrosion: (1) they act as a mass transport barrier and (2) they influence the chemical affinity of the glass reaction. In general, transport barrier effects have been found to be less important than affinity effects in the corrosion of most high-level nuclear waste glasses. However, they can be important under some circumstances, for example, in a very alkaline solution, in leachants containing Mg ions, or under conditions where the matrix dissolution rate is very low. The latter suggests that physical barrier effect may affect the long-term glass dissolution rate. Surface layers influence glass reaction affinity through the effects of the altered glass and secondary phases on the solution chemistry. The reaction affinity may be controlled by various precipitates and crystalline phases, amorphous silica phases, gel layer, or all the components of the glass. The surface alteration layers influence radionuclide release mainly through colloid formation, crystalline phase incorporation, and gel layer retention. This paper reviews current understanding and uncertainties.

  17. Evidence for Bulk Ripplocations in Layered Solids.

    PubMed

    Gruber, Jacob; Lang, Andrew C; Griggs, Justin; Taheri, Mitra L; Tucker, Garritt J; Barsoum, Michel W

    2016-09-19

    Plastically anisotropic/layered solids are ubiquitous in nature and understanding how they deform is crucial in geology, nuclear engineering, microelectronics, among other fields. Recently, a new defect termed a ripplocation-best described as an atomic scale ripple-was proposed to explain deformation in two-dimensional solids. Herein, we leverage atomistic simulations of graphite to extend the ripplocation idea to bulk layered solids, and confirm that it is essentially a buckling phenomenon. In contrast to dislocations, bulk ripplocations have no Burgers vector and no polarity. In graphite, ripplocations are attracted to other ripplocations, both within the same, and on adjacent layers, the latter resulting in kink boundaries. Furthermore, we present transmission electron microscopy evidence consistent with the existence of bulk ripplocations in Ti3SiC2. Ripplocations are a topological imperative, as they allow atomic layers to glide relative to each other without breaking the in-plane bonds. A more complete understanding of their mechanics and behavior is critically important, and could profoundly influence our current understanding of how graphite, layered silicates, the MAX phases, and many other plastically anisotropic/layered solids, deform and accommodate strain.

  18. Evidence for Bulk Ripplocations in Layered Solids

    NASA Astrophysics Data System (ADS)

    Gruber, Jacob; Lang, Andrew C.; Griggs, Justin; Taheri, Mitra L.; Tucker, Garritt J.; Barsoum, Michel W.

    2016-09-01

    Plastically anisotropic/layered solids are ubiquitous in nature and understanding how they deform is crucial in geology, nuclear engineering, microelectronics, among other fields. Recently, a new defect termed a ripplocation–best described as an atomic scale ripple–was proposed to explain deformation in two-dimensional solids. Herein, we leverage atomistic simulations of graphite to extend the ripplocation idea to bulk layered solids, and confirm that it is essentially a buckling phenomenon. In contrast to dislocations, bulk ripplocations have no Burgers vector and no polarity. In graphite, ripplocations are attracted to other ripplocations, both within the same, and on adjacent layers, the latter resulting in kink boundaries. Furthermore, we present transmission electron microscopy evidence consistent with the existence of bulk ripplocations in Ti3SiC2. Ripplocations are a topological imperative, as they allow atomic layers to glide relative to each other without breaking the in-plane bonds. A more complete understanding of their mechanics and behavior is critically important, and could profoundly influence our current understanding of how graphite, layered silicates, the MAX phases, and many other plastically anisotropic/layered solids, deform and accommodate strain.

  19. Multiple Field of View Layer Oriented

    NASA Astrophysics Data System (ADS)

    Ragazzoni, Roberto; Diolaiti, Emiliano; Farinato, Jacopo; Fedrigo, Enrico; Marchetti, Enrico; Tordi, Massimiliano.; Kirkman, David

    In layer oriented MCAO the same number of detectors and Deformable Mirrors are conjugated to a specific layer on the sky and collect light from a number of references, coadding them simultaneously and in an optical way. The correction achieved is perfect for the conjugated layer and it is limited to the smaller spatial frequencies for the layers within the DMs, approaching the optimum when a certain Field of View is considered. Here we introduce a further step, namely the use of different Field of View for the different DMs. In this way stars from an anulus are taken to correct for the ground layer, while stars within a certain patch are used to correct for the high altitude layers and for the residuals due to the not perfect correction on the ground volume (because of the large FoV used there). We show, along with an optomechanical design of such an approach, that in this way one can easily reach 30% of sky coverage near the Galactic Poles WITHOUT using any sort of gain introduced by the use of pyramid wavefront sensor, limiting the number of stars to the 20 brightest and assuming an overall efficiency of the order of 10%. The result in term of Sthrel is of the order of 0.2 at 800nm over an average continuum Cn2 profile distribution at Paranal (as devised from literature data). Extension to 100m class telescopes or the use of pyramid WFS are briefly discussed.

  20. Evidence for Bulk Ripplocations in Layered Solids.

    PubMed

    Gruber, Jacob; Lang, Andrew C; Griggs, Justin; Taheri, Mitra L; Tucker, Garritt J; Barsoum, Michel W

    2016-01-01

    Plastically anisotropic/layered solids are ubiquitous in nature and understanding how they deform is crucial in geology, nuclear engineering, microelectronics, among other fields. Recently, a new defect termed a ripplocation-best described as an atomic scale ripple-was proposed to explain deformation in two-dimensional solids. Herein, we leverage atomistic simulations of graphite to extend the ripplocation idea to bulk layered solids, and confirm that it is essentially a buckling phenomenon. In contrast to dislocations, bulk ripplocations have no Burgers vector and no polarity. In graphite, ripplocations are attracted to other ripplocations, both within the same, and on adjacent layers, the latter resulting in kink boundaries. Furthermore, we present transmission electron microscopy evidence consistent with the existence of bulk ripplocations in Ti3SiC2. Ripplocations are a topological imperative, as they allow atomic layers to glide relative to each other without breaking the in-plane bonds. A more complete understanding of their mechanics and behavior is critically important, and could profoundly influence our current understanding of how graphite, layered silicates, the MAX phases, and many other plastically anisotropic/layered solids, deform and accommodate strain. PMID:27640724

  1. Boundary Layers in Laminar Vortex Flows.

    NASA Astrophysics Data System (ADS)

    Baker, Glenn Leslie

    A detailed experimental study of the flow in an intense, laminar, axisymmetric vortex has been conducted in the Purdue Tornado Vortex Simulator. The complicated nature of the flow in the boundary layer of laboratory vortices and presumably on that encountered in full-scale tornadoes has been examined. After completing a number of modifications to the existing facility to improve the quality of the flow in the simulator, hot-film anemometry was employed for making velocity-component and turbulence-intensity measurements of both the free-stream and boundary layer portions of the flow. The measurements represent the first experimental boundary layer investigation of a well-defined vortex flow to appear in the literature. These results were compared with recent theoretical work by Burggraf, Stewartson and Belcher (1971) and with an exact similarity solution for line-sink boundary layers developed by the author. A comparison is also made with the numerical simulation of Wilson (1981) in which the boundary conditions were matched to those of the present experimental investigation. Expressions for the vortex core radius, the maximum tangential velocity and the maximum pressure drop are given in terms of dimensionless modeling parameters. References. Burggraf, O. R., K. Stewartson and R. Belcher, Boundary layer. induced by a potential vortex. Phys. Fluids 14, 1821-1833 (1971). Wilson, T., M. S. thesis, Vortex Boundary Layer Dynamics, Univ. Calif. Davis (1981).

  2. Evidence for Bulk Ripplocations in Layered Solids

    PubMed Central

    Gruber, Jacob; Lang, Andrew C.; Griggs, Justin; Taheri, Mitra L.; Tucker, Garritt J.; Barsoum, Michel W.

    2016-01-01

    Plastically anisotropic/layered solids are ubiquitous in nature and understanding how they deform is crucial in geology, nuclear engineering, microelectronics, among other fields. Recently, a new defect termed a ripplocation–best described as an atomic scale ripple–was proposed to explain deformation in two-dimensional solids. Herein, we leverage atomistic simulations of graphite to extend the ripplocation idea to bulk layered solids, and confirm that it is essentially a buckling phenomenon. In contrast to dislocations, bulk ripplocations have no Burgers vector and no polarity. In graphite, ripplocations are attracted to other ripplocations, both within the same, and on adjacent layers, the latter resulting in kink boundaries. Furthermore, we present transmission electron microscopy evidence consistent with the existence of bulk ripplocations in Ti3SiC2. Ripplocations are a topological imperative, as they allow atomic layers to glide relative to each other without breaking the in-plane bonds. A more complete understanding of their mechanics and behavior is critically important, and could profoundly influence our current understanding of how graphite, layered silicates, the MAX phases, and many other plastically anisotropic/layered solids, deform and accommodate strain. PMID:27640724

  3. Temperature structure in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Smedman, Ann-Sofi

    2010-05-01

    Temperature structure in the atmospheric boundary layer It is well established from experimental and theoretical studies that the temperature structure in the atmospheric boundary layer is depends on stability. During free convection conditions the flow is dominated by circular thermals but when stratification is becoming slightly unstable longitudinal roll structures that extend vertically throughout the entire boundary layer will be present. In close to neutral conditions on the unstable side (the UVCN regime) when the Obukhov length is much greater than the surface layer depth, it is observed that the structure of the surface layer turbulence does not accord with standard similarity theory. In particular the efficiency of the turbulent exchange of sensible and latent heat is observed to be more strongly enhanced than is consistent with the standard model. Also the profiles of dissipation of turbulent kinetic energy and temperature fluctuation variance are found to depend on the structure of the whole boundary layer (i.e. are non-local), indicating that a large-scale transport process is at work. At the same time, co-spectral analysis shows how the large scale eddy motions that determine the heat transport process near the surface are typically 1/5 of the surface layer depth. All these features are found to be similar in measurements at two marine sites, in the Baltic Sea and in Lake Ontario respectively and at several flat land sites ( around Uppsala and at the Island of Gotland), indicating that they are determined by the dynamics of the whole boundary layer rather than being simply dependent on the surface boundary conditions. The observed structures can also be interpreted as possible manifestations of a bifurcation of the large scale eddy structure towards a state in which there are quasi-steady longitudinal rolls and, on a smaller scale, unsteady detached eddies. Our interpretation of the results from the measurements is that, in the UVCN regime, the latter

  4. Multi-gradient hydrogels produced layer by layer with capillary flow and crosslinking in open microchannels.

    PubMed

    Piraino, Francesco; Camci-Unal, Gulden; Hancock, Matthew J; Rasponi, Marco; Khademhosseini, Ali

    2012-02-01

    This technical note describes a new bench-top method for producing anisotropic hydrogels composed of gradient layers of soluble factors, particles, polymer concentrations or material properties. Each gradient layer was produced by a previous gradient method in which a droplet of one precursor solution was added to a thin layer of a second solution. The ensuing rapid capillary flow along the open channel generated a gradient precursor solution, which was then crosslinked to form a gradient gel. Repeating these steps allowed a layered gel to be iteratively constructed with as many gradient layers as desired. This technique renders the synthesis of multi-layered gradient gels accessible to virtually any researcher and should help simplify the production of more biologically relevant cellular microenvironments.

  5. Learning layer-specific edges for segmenting retinal layers with large deformations.

    PubMed

    Karri, S P K; Chakraborthi, Debjani; Chatterjee, Jyotirmoy

    2016-07-01

    We present an algorithm for layer-specific edge detection in retinal optical coherence tomography images through a structured learning algorithm to reinforce traditional graph-based retinal layer segmentation. The proposed algorithm simultaneously identifies individual layers and their corresponding edges, resulting in the computation of layer-specific edges in 1 second. These edges augment classical dynamic programming based segmentation under layer deformation, shadow artifacts noise, and without heuristics or prior knowledge. We considered Duke's online data set containing 110 B-scans of 10 diabetic macular edema subjects with 8 retinal layers annotated by two experts for experimentation, and achieved a mean distance error of 1.38 pixels whereas that of the state-of-the-art was 1.68 pixels. PMID:27446714

  6. Discrete Layer-by-Layer Magnetic Switching in Fe /MgO (001 ) Superlattices

    NASA Astrophysics Data System (ADS)

    Moubah, R.; Magnus, F.; Warnatz, T.; Palsson, G. K.; Kapaklis, V.; Ukleev, V.; Devishvili, A.; Palisaitis, J.; Persson, P. O. Å.; Hjörvarsson, B.

    2016-04-01

    We report on a discrete layer-by-layer magnetic switching in Fe /MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90° and 180° periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe /MgO /Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.

  7. Learning layer-specific edges for segmenting retinal layers with large deformations

    PubMed Central

    Karri, S. P. K.; Chakraborthi, Debjani; Chatterjee, Jyotirmoy

    2016-01-01

    We present an algorithm for layer-specific edge detection in retinal optical coherence tomography images through a structured learning algorithm to reinforce traditional graph-based retinal layer segmentation. The proposed algorithm simultaneously identifies individual layers and their corresponding edges, resulting in the computation of layer-specific edges in 1 second. These edges augment classical dynamic programming based segmentation under layer deformation, shadow artifacts noise, and without heuristics or prior knowledge. We considered Duke’s online data set containing 110 B-scans of 10 diabetic macular edema subjects with 8 retinal layers annotated by two experts for experimentation, and achieved a mean distance error of 1.38 pixels whereas that of the state-of-the-art was 1.68 pixels. PMID:27446714

  8. Multilayer assembly. Technology-driven layer-by-layer assembly of nanofilms.

    PubMed

    Richardson, Joseph J; Björnmalm, Mattias; Caruso, Frank

    2015-04-24

    Multilayer thin films have garnered intense scientific interest due to their potential application in diverse fields such as catalysis, optics, energy, membranes, and biomedicine. Here we review the current technologies for multilayer thin-film deposition using layer-by-layer assembly, and we discuss the different properties and applications arising from the technologies. We highlight five distinct routes of assembly—immersive, spin, spray, electromagnetic, and fluidic assembly—each of which offers material and processing advantages for assembling layer-by-layer films. Each technology encompasses numerous innovations for automating and improving layering, which is important for research and industrial applications. Furthermore, we discuss how judicious choice of the assembly technology enables the engineering of thin films with tailor-made physicochemical properties, such as distinct-layer stratification, controlled roughness, and highly ordered packing. PMID:25908826

  9. Hybrid inorganic–organic superlattice structures with atomic layer deposition/molecular layer deposition

    SciTech Connect

    Tynell, Tommi; Yamauchi, Hisao; Karppinen, Maarit

    2014-01-15

    A combination of the atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques is successfully employed to fabricate thin films incorporating superlattice structures that consist of single layers of organic molecules between thicker layers of ZnO. Diethyl zinc and water are used as precursors for the deposition of ZnO by ALD, while three different organic precursors are investigated for the MLD part: hydroquinone, 4-aminophenol and 4,4′-oxydianiline. The successful superlattice formation with all the organic precursors is verified through x-ray reflectivity studies. The effects of the interspersed organic layers/superlattice structure on the electrical and thermoelectric properties of ZnO are investigated through resistivity and Seebeck coefficient measurements at room temperature. The results suggest an increase in carrier concentration for small concentrations of organic layers, while higher concentrations seem to lead to rather large reductions in carrier concentration.

  10. Lidar observations of mixed layer dynamics - Tests of parameterized entrainment models of mixed layer growth rate

    NASA Technical Reports Server (NTRS)

    Boers, R.; Eloranta, E. W.; Coulter, R. L.

    1984-01-01

    Ground based lidar measurements of the atmospheric mixed layer depth, the entrainment zone depth and the wind speed and wind direction were used to test various parameterized entrainment models of mixed layer growth rate. Six case studies under clear air convective conditions over flat terrain in central Illinois are presented. It is shown that surface heating alone accounts for a major portion of the rise of the mixed layer on all days. A new set of entrainment model constants was determined which optimized height predictions for the dataset. Under convective conditions, the shape of the mixed layer height prediction curves closely resembled the observed shapes. Under conditions when significant wind shear was present, the shape of the height prediction curve departed from the data suggesting deficiencies in the parameterization of shear production. Development of small cumulus clouds on top of the layer is shown to affect mixed layer depths in the afternoon growth phase.

  11. Selective layer disordering in III-nitrides with a capping layer

    DOEpatents

    Wierer, Jr., Jonathan J.; Allerman, Andrew A.

    2016-06-14

    Selective layer disordering in a doped III-nitride superlattice can be achieved by depositing a dielectric capping layer on a portion of the surface of the superlattice and annealing the superlattice to induce disorder of the layer interfaces under the uncapped portion and suppress disorder of the interfaces under the capped portion. The method can be used to create devices, such as optical waveguides, light-emitting diodes, photodetectors, solar cells, modulators, laser, and amplifiers.

  12. Sandwich-like layer-by-layer assembly of gold nanoparticles with tunable SERS properties

    PubMed Central

    Bai, Lu; Zhao, Guizhe

    2016-01-01

    Summary Sandwich-like layer-by-layer thin films consisting of polyelectrolytes and gold nanoparticles were utilized to construct surface-enhanced Raman scattering (SERS) substrates with tunable SERS properties. It is found that both the size of the nanoparticles in the layers and the interlayer distance significantly influence the SERS performance of the multilayered thin film. These simple, low-cost, easily processable and controllable SERS substrates have a promising future in the field of molecular sensing. PMID:27547620

  13. Sandwich-like layer-by-layer assembly of gold nanoparticles with tunable SERS properties.

    PubMed

    Liu, Zhicheng; Bai, Lu; Zhao, Guizhe; Liu, Yaqing

    2016-01-01

    Sandwich-like layer-by-layer thin films consisting of polyelectrolytes and gold nanoparticles were utilized to construct surface-enhanced Raman scattering (SERS) substrates with tunable SERS properties. It is found that both the size of the nanoparticles in the layers and the interlayer distance significantly influence the SERS performance of the multilayered thin film. These simple, low-cost, easily processable and controllable SERS substrates have a promising future in the field of molecular sensing. PMID:27547620

  14. Electronic and thermoelectric properties of nanograting layers

    NASA Astrophysics Data System (ADS)

    Tavkhelidze, A.

    2014-06-01

    Recently, new quantum features have been observed and studied in the area of nanostructured layers. Nanograting (NG) on the surface of the thin layer imposes additional boundary conditions on electron wave function and forbids some quantum states. Electrons, rejected from the forbidden quantum states, have to occupy states with higher energy. In the case of semiconductor materials, electrons rejected from the valence band have to occupy empty quantum states in the conduction band. Such increase in conduction band electron concentration n can be termed as geometry-induced doping or G-doping. G-doping is equivalent to donor doping from the point of view of the increase in n. However, there are no ionized impurities. This preserves charge carrier scattering to the intrinsic semiconductor level and increases carrier mobility. G-doping involves electron confinement to NG layer. Here, we investigate the system of multiple NG layers forming a series of homo junctions. Si and GaAs homojunctions were studied and G-doping levels of 1018-1019 cm-3 were obtained. We also study a system composed of NG layer and an additional top layer forming periodic series of p-n junctions. In such system, charge depletion region develops inside the NG and its effective depth reduces, becoming a rather strong function of temperature T. Consequently, T-dependence of chemical potential magnifies and Seebeck coefficient S increases. We investigate S in the system of semiconductor NG layer having abrupt p-n junctions on the top of the grating. Analysis made on the basis of Boltzmann transport equations shows dramatic increase in S. At the same time, other transport coefficients remain unaffected by the junctions. Calculations show one order of magnitude increase in the thermoelectric figure of merit ZT relative to bulk material.

  15. Laboratory Experiments of Radar-Detected Layering in Ice

    NASA Astrophysics Data System (ADS)

    Carter, L. M.; Koenig, L. S.; Courville, Z. R.; Ghent, R. R.; Koutnik, M. R.

    2016-09-01

    In a cold room at the Cold Regions Research and Engineering Laboratory, we constructed layered ice with a variety of layer types and thicknesses to investigate how the layers appear to ground-penetrating radar at a variety of frequencies.

  16. INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT

    EPA Science Inventory

    Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...

  17. Conserved S-Layer-Associated Proteins Revealed by Exoproteomic Survey of S-Layer-Forming Lactobacilli

    PubMed Central

    Johnson, Brant R.; Hymes, Jeffrey; Sanozky-Dawes, Rosemary; Henriksen, Emily DeCrescenzo

    2015-01-01

    The Lactobacillus acidophilus homology group comprises Gram-positive species that include L. acidophilus, L. helveticus, L. crispatus, L. amylovorus, L. gallinarum, L. delbrueckii subsp. bulgaricus, L. gasseri, and L. johnsonii. While these bacteria are closely related, they have varied ecological lifestyles as dairy and food fermenters, allochthonous probiotics, or autochthonous commensals of the host gastrointestinal tract. Bacterial cell surface components play a critical role in the molecular dialogue between bacteria and interaction signaling with the intestinal mucosa. Notably, the L. acidophilus complex is distinguished in two clades by the presence or absence of S-layers, which are semiporous crystalline arrays of self-assembling proteinaceous subunits found as the outermost layer of the bacterial cell wall. In this study, S-layer-associated proteins (SLAPs) in the exoproteomes of various S-layer-forming Lactobacillus species were proteomically identified, genomically compared, and transcriptionally analyzed. Four gene regions encoding six putative SLAPs were conserved in the S-layer-forming Lactobacillus species but not identified in the extracts of the closely related progenitor, L. delbrueckii subsp. bulgaricus, which does not produce an S-layer. Therefore, the presence or absence of an S-layer has a clear impact on the exoproteomic composition of Lactobacillus species. This proteomic complexity and differences in the cell surface properties between S-layer- and non-S-layer-forming lactobacilli reveal the potential for SLAPs to mediate intimate probiotic interactions and signaling with the host intestinal mucosa. PMID:26475115

  18. Layer-by-layer assembly of nanowires for three-dimensional, multifunctional electronics.

    PubMed

    Javey, Ali; Nam, SungWoo; Friedman, Robin S; Yan, Hao; Lieber, Charles M

    2007-03-01

    We report a general approach for three-dimensional (3D) multifunctional electronics based on the layer-by-layer assembly of nanowire (NW) building blocks. Using germanium/silicon (Ge/Si) core/shell NWs as a representative example, ten vertically stacked layers of multi-NW field-effect transistors (FETs) were fabricated. Transport measurements demonstrate that the Ge/Si NW FETs have reproducible high-performance device characteristics within a given device layer, that the FET characteristics are not affected by sequential stacking, and importantly, that uniform performance is achieved in sequential layers 1 through 10 of the 3D structure. Five-layer single-NW FET structures were also prepared by printing Ge/Si NWs from lower density growth substrates, and transport measurements showed similar high-performance characteristics for the FETs in layers 1 and 5. In addition, 3D multifunctional circuitry was demonstrated on plastic substrates with sequential layers of inverter logical gates and floating gate memory elements. Notably, electrical characterization studies show stable writing and erasing of the NW floating gate memory elements and demonstrate signal inversion with larger than unity gain for frequencies up to at least 50 MHz. The ability to assemble reproducibly sequential layers of distinct types of NW-based devices coupled with the breadth of NW building blocks should enable the assembly of increasing complex multilayer and multifunctional 3D electronics in the future.

  19. Development of new layered selenide oxides with perovskite-type oxide layers

    NASA Astrophysics Data System (ADS)

    Ushiyama, Koichi; Ogino, Hiraku; Kishio, Kohji; Shimoyama, Jun-Ichi

    2010-03-01

    Several Fe-based superconductors with perovskite-type oxide layers, such as Sr2ScFePO3 (Tc ˜ 17 K)^[1], were discovered in our previous study. These compounds are composed of alternate stacking of superconducting layers with antifluorite structure and perovskite-type blocking layers. Since both layers are flexible in terms of chemical composition, development of various new functional materials can be expected from this family. In the present study, we have attempted to synthesize new layered selenide oxides with CuSe layers and discovered more than ten compounds, such as Sr2MCu2Se2O2 (M = Mn, Co, Ni, Cu, Zn) and Sr2MCuSeO3 (M = Sc, Cr, Mn, Fe, Ga, In), thus far. These indicated that the CuSe layer can accommodate various types of blocking layers, which may lead various functions. Among them, Sr2Cu3Se2O2 has a potential as for the mother compound of superconductor, if appropriate concentration of carrier is introduced to the CuO2 layer. Crystal structure and physical properties of these newly found compounds will be reported. [1] H. Ogino et al., Supercond. Sci. Technol. 22 (2009) 075008

  20. Selective growth of graphene in layer-by-layer via chemical vapor deposition.

    PubMed

    Park, Jaehyun; An, Hyosub; Choi, Dong-Chul; Hussain, Sajjad; Song, Wooseok; An, Ki-Seok; Lee, Won-Jun; Lee, Naesung; Lee, Wan-Gyu; Jung, Jongwan

    2016-08-14

    Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene on a specific position. The key idea is to deposit a thin Cu layer (∼40 nm thick) on pre-grown monolayer graphene and to apply additional growth. The thin Cu atop the graphene/Cu substrate acts as a catalyst to decompose methane (CH4) gas during the additional growth. The adlayer is grown selectively on the pre-grown graphene, and the thin Cu is removed through evaporation during CVD, eventually forming large-area and uniform double layer graphene. With this technology, highly uniform graphene films with precise thicknesses of 1 to 5 layers and graphene check patterns with 1 to 3 layers were successfully demonstrated. This method provides precise LBL growth for a uniform graphene film and a technique for the design of new graphene devices. PMID:27436358

  1. Excitatory Synaptic Feedback from the Motor Layer to the Sensory Layers of the Superior Colliculus

    PubMed Central

    Ghitani, Nima; Bayguinov, Peter O.; Vokoun, Corinne R.; McMahon, Shane

    2014-01-01

    Neural circuits that translate sensory information into motor commands are organized in a feedforward manner converting sensory information into motor output. The superior colliculus (SC) follows this pattern as it plays a role in converting visual information from the retina and visual cortex into motor commands for rapid eye movements (saccades). Feedback from movement to sensory regions is hypothesized to play critical roles in attention, visual image stability, and saccadic suppression, but in contrast to feedforward pathways, motor feedback to sensory regions has received much less attention. The present study used voltage imaging and patch-clamp recording in slices of rat SC to test the hypothesis of an excitatory synaptic pathway from the motor layers of the SC back to the sensory superficial layers. Voltage imaging revealed an extensive depolarization of the superficial layers evoked by electrical stimulation of the motor layers. A pharmacologically isolated excitatory synaptic potential in the superficial layers depended on stimulus strength in the motor layers in a manner consistent with orthodromic excitation. Patch-clamp recording from neurons in the sensory layers revealed excitatory synaptic potentials in response to glutamate application in the motor layers. The location, size, and morphology of responsive neurons indicated they were likely to be narrow-field vertical cells. This excitatory projection from motor to sensory layers adds an important element to the circuitry of the SC and reveals a novel feedback pathway that could play a role in enhancing sensory responses to attended targets as well as visual image stabilization. PMID:24828636

  2. Characterization of CZTSSe photovoltaic device with an atomic layer-deposited passivation layer

    SciTech Connect

    Wu, Wei Cao, Yanyan; Caspar, Jonathan V.; Guo, Qijie; Johnson, Lynda K.; Mclean, Robert S.; Malajovich, Irina; Choudhury, Kaushik Roy

    2014-07-28

    We describe a CZTSSe (Cu{sub 2}ZnSn(S{sub 1−x},Se{sub x}){sub 4}) photovoltaic (PV) device with an ALD (atomic layer deposition) coated buffer dielectric layer for CZTSSe surface passivation. An ALD buffer layer, such as TiO{sub 2}, can be applied in order to reduce the interface recombination and improve the device's open-circuit voltage. Detailed characterization data including current-voltage, admittance spectroscopy, and capacitance profiling are presented in order to compare the performance of PV devices with and without the ALD layer.

  3. Automated segmentation of intraretinal layers from spectral-domain macular OCT: reproducibility of layer thickness measurements

    NASA Astrophysics Data System (ADS)

    Lee, Kyungmoo; Abràmoff, Michael D.; Sonka, Milan; Garvin, Mona K.

    2011-03-01

    Changes in intraretinal layer thickness occur in a variety of diseases such as glaucoma, macular edema and diabetes. To segment the intraretinal layers from macular spectral-domain OCT (SD-OCT) scans, we previously introduced an automated multiscale 3-D graph search method and validated its performance by computing unsigned border positioning differences when compared with human expert tracings. However, it is also important to study the reproducibility of resulting layer thickness measurements, as layer thickness is a commonly used clinical parameter. In this work, twenty eight (14 x 2) repeated macular OCT volumes were acquired from the right eyes of 14 normal subjects using two Zeiss-Cirrus SD-OCT scanners. After segmentation of 10 intraretinal layers and rigid registration of layer thickness maps from the repeated OCT scans, the thickness difference of each layer was calculated. The overall mean global and regional thickness differences of 10 intraretinal layers were 0.46 +/- 0.25 μm (1.70 +/- 0.72 %) and 1.16 +/- 0.84 μm (4.03 +/- 2.05 %), respectively. No specific local region showed a consistent thickness difference across the layers.

  4. Conserved S-Layer-Associated Proteins Revealed by Exoproteomic Survey of S-Layer-Forming Lactobacilli.

    PubMed

    Johnson, Brant R; Hymes, Jeffrey; Sanozky-Dawes, Rosemary; Henriksen, Emily DeCrescenzo; Barrangou, Rodolphe; Klaenhammer, Todd R

    2015-10-16

    The Lactobacillus acidophilus homology group comprises Gram-positive species that include L. acidophilus, L. helveticus, L. crispatus, L. amylovorus, L. gallinarum, L. delbrueckii subsp. bulgaricus, L. gasseri, and L. johnsonii. While these bacteria are closely related, they have varied ecological lifestyles as dairy and food fermenters, allochthonous probiotics, or autochthonous commensals of the host gastrointestinal tract. Bacterial cell surface components play a critical role in the molecular dialogue between bacteria and interaction signaling with the intestinal mucosa. Notably, the L. acidophilus complex is distinguished in two clades by the presence or absence of S-layers, which are semiporous crystalline arrays of self-assembling proteinaceous subunits found as the outermost layer of the bacterial cell wall. In this study, S-layer-associated proteins (SLAPs) in the exoproteomes of various S-layer-forming Lactobacillus species were proteomically identified, genomically compared, and transcriptionally analyzed. Four gene regions encoding six putative SLAPs were conserved in the S-layer-forming Lactobacillus species but not identified in the extracts of the closely related progenitor, L. delbrueckii subsp. bulgaricus, which does not produce an S-layer. Therefore, the presence or absence of an S-layer has a clear impact on the exoproteomic composition of Lactobacillus species. This proteomic complexity and differences in the cell surface properties between S-layer- and non-S-layer-forming lactobacilli reveal the potential for SLAPs to mediate intimate probiotic interactions and signaling with the host intestinal mucosa.

  5. Thin layer composite unimorph ferroelectric driver and sensor

    NASA Technical Reports Server (NTRS)

    Hellbaum, Richard F. (Inventor); Bryant, Robert G. (Inventor); Fox, Robert L. (Inventor); Jalink, Jr., Antony (Inventor); Rohrbach, Wayne W. (Inventor); Simpson, Joycelyn O. (Inventor)

    2004-01-01

    A method for forming ferroelectric wafers is provided. A prestress layer is placed on the desired mold. A ferroelectric wafer is placed on top of the prestress layer. The layers are heated and then cooled, causing the ferroelectric wafer to become prestressed. The prestress layer may include reinforcing material and the ferroelectric wafer may include electrodes or electrode layers may be placed on either side of the ferroelectric layer. Wafers produced using this method have greatly improved output motion.

  6. Three step double layers in the laboratory. [plasma physics

    NASA Technical Reports Server (NTRS)

    Bailey, Andrew, III; Hershkowitz, Noah

    1988-01-01

    A new class of stationary double layer structure, with three or more distinct steps, is demonstrated in the laboratory. A large monotonic potential increase results from a series of smaller double layers. In many respects, these double layer structures resemble those inferred from satellite measurements of auroral double layers. This new class of double layer appears to depend on turbulence for its existence and to be a hybrid structure, intermediate between anomalous resistivity and BGK double layers.

  7. Thin Layer Composite Unimorph Ferroelectric Driver and Sensor

    NASA Technical Reports Server (NTRS)

    Helbaum, Richard F. (Inventor); Bryant, Robert G. (Inventor); Fox, Robert L. (Inventor); Jalink, Antony, Jr. (Inventor); Rohrbach, Wayne W. (Inventor); Simpson, Joycelyn O. (Inventor)

    1995-01-01

    A method for forming ferroelectric wafers is provided. A prestress layer is placed on the desired mold. A ferroelectric wafer is placed on top of the prestress layer. The layers are heated and then cooled, causing the ferroelectric wafer to become prestressed. The prestress layer may include reinforcing material and the ferroelectric wafer may include electrodes or electrode layers may be placed on either side of the ferroelectric layer. Wafers produced using this method have greatly improved output motion.

  8. Thin Layer Composite Unimorph Ferroelectric Driver and Sensor

    NASA Technical Reports Server (NTRS)

    Hellbaum, Richard F. (Inventor); Bryant, Robert G. (Inventor); Fox, Robert L. (Inventor)

    1997-01-01

    A method for forming ferroelectric wafers is provided. A prestress layer is placed on the desired mold. A ferroelectric wafer is placed on top of the prestress layer. The layers are heated and then cooled causing the ferroelectric wafer to become prestressed. The prestress layer may include reinforcing material and the ferroelectric wafer may include electrodes or electrode layers may be placed on either side of the ferroelectric layer. Wafers produced using this method have greatly improved output motion.

  9. Layered Outcrops of Far West Candor Chasma

    NASA Technical Reports Server (NTRS)

    2000-01-01

    [figure removed for brevity, see original site]

    Images from Mariner 9 in 1972 revealed that some of the mesas and mounds found within the chasms of the martian 'Grand Canyon'--the Valles Marineris--have layers in them. Speculations as to the origin of these interior layered materials ranged from volcanic ash deposits to sediments laid down in lakes that could have partially filled the Vallis Marineris troughs, much as lakes now occupy portions of the rift valleys of eastern Africa. The proposal that the Valles Marineris once hosted deep martian lakes led to additional speculation as to the prospects for finding fossil evidence of martian life.

    Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images have ten or more times better resolution than the Mariner 9 and Viking orbiter images taken in the 1970s. MOC images have indeed confirmed the presence of layered outcrops within the Valles Marineris. They have also shown places previously not suspected to have layered rock, and they have shown that these materials might not have formed in the Valles Marineris, but were instead deposited in craters that were subsequently buried long before the chasms opened up (see discussion below). The layered rock is now visible because of faulting and erosion.

    The high resolution picture shown here (B, above right) was the first image received by MOC scientists that began to hint at a larger story of layered sedimentary rock on Mars. The picture shows a 1.5 km by 2.9 km (0.9 mi by 1.8 mi) area in far southwestern Candor Chasma (A, above left) that was--based on Mariner 9 and Viking orbiter images--not previously expected to exhibit layers. The MOC image reveals that the floor of western Candor Chasma at this location is indeed layered. What is most striking about the picture is the large number and uniformity of the layers, or beds. There are over 100 beds in this area, and each has about the same thickness (estimated to be about 10 meters (11 yards) thick). Each layer

  10. Tailoring polymer properties with layered silicates

    NASA Astrophysics Data System (ADS)

    Xu, Liang

    Polymer layered silicate nanocomposites have found widespread applications in areas such as plastics, oil and gas production, biomedical, automotive and information storage, but their successful commercialization critically depends on consistent control over issues such as complete dispersion of layered silicate into the host polymer and optimal interaction between the layered silicates and the polymers. Polypropylene is a commercially important polymer but usually forms intercalated structures with organically modified layered silicate upon mixing, even it is pre-treated with compatibilizing agent such as maleic anhydride. In this work, layered silicate is well dispersed in ammonium modified polypropylene but does not provide sufficient reinforcement to the host polymer due to poor interactions. On the other hand, interactions between maleic anhydride modified polypropylene and layered silicate are fine tuned by using a small amount of maleic anhydride and mechanical strength of the resultant nanocomposites are significantly enhanced. In particular, the melt rheological properties of layered silicate nanocomposites with maleic anhydride functionalized polypropylene are contrasted to those based on ammonium-terminated polypropylene. While the maleic anhydride treated polypropylene based nanocomposites exhibit solid-like linear dynamic behavior, consistent with the formation of a long-lived percolated nanoparticle network, the single-end ammonium functionalized polypropylene based nanocomposites demonstrated liquid-like behavior at comparable montmorillonite concentrations. The differences in the linear viscoelasticity are attributed to the presence of bridging interaction in maleic anhydride functionalized nanocomposites, which facilitates formation of a long-lived silicate network mediated by physisorbed polymer chains. Further, the transient shear stress of the maleic anhydride functionalized nanocomposites in start-up of steady shear is a function of the shear

  11. Inspection of additive-manufactured layered components.

    PubMed

    Cerniglia, D; Scafidi, M; Pantano, A; Rudlin, J

    2015-09-01

    Laser powder deposition (LPD) is a rapid additive manufacturing process to produce, layer upon layer, 3D geometries or to repair high-value components. Currently there is no nondestructive technique that can guarantee absence of flaws in LPD products during manufacturing. In this paper a laser ultrasonic technique for in-line inspection of LPD components is proposed. Reference samples were manufactured from Inconel and machined flaws were created to establish the sensitivity of the technique. Numerical models of laser-generated ultrasonic waves have been created to gain a deeper understanding of physics, to optimize the set-up and to verify the experimental measurements. Results obtained on two sets of reference samples are shown. A proof-of-concept prototype has been demonstrated on some specific deposition samples with induced flaws, that were confirmed by an ultra-high sensitivity X-ray technique. Experimental outcomes prove that typical micro-defects due to the layer-by-layer deposition process, such as near-surface and surface flaws in a single layer deposit, can be detected.

  12. An asymptotic model of the F layer

    NASA Astrophysics Data System (ADS)

    Oliver, W. L.

    2012-01-01

    A model of the F layer of the ionosphere is presented that consists of a bottomside asymptote that ignores transport and a topside asymptote that ignores chemistry. The asymptotes connect at the balance height dividing the chemistry and transport regimes. A combination of these two asymptotes produces a good approximation to the true F layer. Analogously, a model of F layer response to an applied vertical drift is presented that consists of two asymptotic responses, one that ignores transport and one that ignores chemistry. The combination of these asymptotic responses produces a good approximation to the response of the true F layer. This latter response is identical to the “servo” response of Rishbeth et al. (1978), derived from the continuity equation. The asymptotic approach bypasses the continuity equation in favor of “force balance” arguments and so replaces a differential equation with simpler algebraic equations. This new approach provides a convenient and intuitive mean for first-order estimates of the change in F layer peak height and density in terms of changes in neutral density, composition, temperature, winds, and electric fields. It is applicable at midlatitudes and at magnetically quiet times at high latitudes. Forensic inverse relations are possible but are not unique. The validity of the asymptotic relations is shown through numerical simulation.

  13. Soils and cultural layers in Velikii Novgorod

    NASA Astrophysics Data System (ADS)

    Dolgikh, A. V.; Aleksandrovskii, A. L.

    2010-05-01

    Urban pedosediments (cultural layers) dating back to the 10th-11th centuries AD and soddypodzolic soils buried under them were studied in two archaeological excavations in Velikii Novgorod. Stages of their development were described. It was found that the buried soddy-podzolic soils at the latest stages of their development were cultivated or were formed under meadow vegetation. Weakly developed garden soils were described in the thickness of urban pedosediments. The lowermost organic cultural layers in Velikii Novgorod were waterlogged and represented peatlike mass with well-preserved wood remains. The oxidation of organic matter, gleyzation, and vivianite formation were described in them. The upper mineral layers were enriched in brick debris and building lime. The processes of organic matter mineralization, alkalization, calcification, zoogenic turbation, and biogenic structuring were clearly manifested in this part. Soil solutions infiltrated from the cultural layers caused some alkalization of the buried soddy-podzolic soil. Diagenetic carbonates and vivianite appeared in some loci within the eluvial and the upper part of the illuvial horizon of this soil. The entire cultural layer was subjected to contamination with heavy metals.

  14. High enthalpy hypersonic boundary layer flow

    NASA Technical Reports Server (NTRS)

    Yanow, G.

    1972-01-01

    A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.

  15. Inducing electric polarization in ultrathin insulating layers

    NASA Astrophysics Data System (ADS)

    Martinez-Castro, Jose; Piantek, Marten; Persson, Mats; Serrate, David; Hirjibehedin, Cyrus F.

    Studies of ultrathin polar oxide films have attracted the interest of researchers for a long time due to their different properties compared to bulk materials. However they present several challenges such as the difficulty in the stabilization of the polar surfaces and the limited success in tailoring their properties. Moreover, recently developed Van der Waals materials have shown that the stacking of 2D-layers trigger new collective states thanks to the interaction between layers. Similarly, interface phenomena emerge in polar oxides, like induced ferroelectricity. This represents a promising way for the creation of new materials with customized properties that differ from those of the isolated layers. Here we present a new approach for the fabrication and study of atomically thin insulating films. We show that the properties of insulating polar layers of sodium chloride (NaCl) can be engineered when they are placed on top of a charge modulated template of copper nitride (Cu2N). STM studies carried out in ultra-high vacuum and at low temperatures over NaCl/Cu2N/Cu(001) show that we are able to build up and stabilize interfaces of polar surface at the limit of one atomic layer showing new properties not present before at the atomic scale.

  16. Inorganic dual-layer microporous supported membranes

    DOEpatents

    Brinker, C. Jeffrey; Tsai, Chung-Yi; Lu, Yungfeng

    2003-03-25

    The present invention provides for a dual-layer inorganic microporous membrane capable of molecular sieving, and methods for production of the membranes. The inorganic microporous supported membrane includes a porous substrate which supports a first inorganic porous membrane having an average pore size of less than about 25 .ANG. and a second inorganic porous membrane coating the first inorganic membrane having an average pore size of less than about 6 .ANG.. The dual-layered membrane is produced by contacting the porous substrate with a surfactant-template polymeric sol, resulting in a surfactant sol coated membrane support. The surfactant sol coated membrane support is dried, producing a surfactant-templated polymer-coated substrate which is calcined to produce an intermediate layer surfactant-templated membrane. The intermediate layer surfactant-templated membrane is then contacted with a second polymeric sol producing a polymeric sol coated substrate which is dried producing an inorganic polymeric coated substrate. The inorganic polymeric coated substrate is then calcined producing an inorganic dual-layered microporous supported membrane in accordance with the present invention.

  17. The Kinematics of Turbulent Boundary Layer Structure

    NASA Technical Reports Server (NTRS)

    Robinson, Stephen Kern

    1991-01-01

    The long history of research into the internal structure of turbulent boundary layers has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of boundary layer structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.

  18. Boundary-Layer-Ingesting Inlet Flow Control

    NASA Technical Reports Server (NTRS)

    Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

    2008-01-01

    An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.

  19. Thin Layer Samples Controlled by Dynamic Electrochemistry.

    PubMed

    Cuartero, Maria; Crespo, Gastón A; Bakker, Eric

    2015-01-01

    We summarize here recent advancements on thin layer samples controlled by dynamic electrochemistry techniques for determining different ions that include potassium, calcium, protamine, nitrate, nitrite and halides in diverse environmental and clinical samples. Generally, a thin layer liquid (less than 100 μm in thickness) is confined between a working electrode and an ion-selective membrane. Once an external electrical perturbation (i.e. constant potential) is applied to the system, an exhaustive ion transfer process is imposed in the entire thin layer solution. As a result, the observed charge (integration of the current decay) is proportional to the depleted ion concentration. Other electrochemical protocols such as linear sweep voltammetry were also explored aiming at the discrimination of several ions presented in the thin layer. One of the most attractive examples involves the detection of a mixture of three halides (iodide, bromide and chloride), which can be well resolved at moderated scan rates (10 mV.s(-1)). Paper-based coulometric sensing on thin layers defined by cellulose papers are being developed in view of translating these new concepts into a reliable and low cost sensing platform.

  20. Boundary Layer Cloudiness Parameterizations Using ARM Observations

    SciTech Connect

    Bruce Albrecht

    2004-09-15

    This study used DOE ARM data and facilities to: (1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, (2) develop a scientific basis for understanding the processes responsible for the formation of boundary layer clouds using ARM observations in conjunction with simple parametric models and LES, and (3) evaluate cumulus cloud characteristics retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of boundary layer clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer cloud studies, (2) evaluate the capability and limitations of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low- signal-to-noise conditions associated with weak no n-precipitating clouds, (3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of boundary layer clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.

  1. Natural instability of free shear layers

    NASA Technical Reports Server (NTRS)

    Husain, Z. D.; Hussain, A. K. M. F.

    1983-01-01

    Under controlled small-amplitude excitation, an initially laminar free shear layer experiences maximum growth rate at a Strouhal number St(theta) of 0.017 (consistent with theory) and maximum growth at St(theta) = 0.011, while the natural instability frequency St(theta-n) (of an unexcited shear layer) is found to have an intermediate value. Investigations in both axisymmetric and plane shear layers in a number of independent facilities reveal that the St(theta-n) value falls in the range 0.0125-0.0155, depending on the exit boundary-layer fluctuation level and the spanwise radius of curvature. The St(theta-n) value decreases with increasing jet diameter or exit boundary-layer fluctuation level, but is not a direct function of the exit momentum thickness Reynolds number. For a given facility, the instability details are found to be independent of whether the entrainment at the lip is parallel to the stream or orthogonal (due to the addition of an end plate). The steamwise evolutions of the amplitudes at the fundamental frequency and its harmonics and subharmonics are unique functions of the downstream distance nondimensionalized by the exit momentum thickness, but their details remain functions of the flow geometry (i.e., axisymmetric or plane).

  2. Layered farming for Marsupenaeus japonicus Bate

    NASA Astrophysics Data System (ADS)

    Li, Yuquan; Jiang, Lingxu; Wang, Renjie

    2014-05-01

    Marsupenaeus japonicus Bate is one of the most valuable cultured shrimp species in China and outdoor earthen pond farming is the most common method of culturing this organism. The need to increase soil usage efficiency in aquaculture has been recognized and a great deal of research effort has been directed toward development of super-intensive farming systems. However, current research and development in this field is largely devoted to Litopenaeus vannamei Boone, while to M. japonicus Bate it has been neglected. In this study, a layered farming system was designed and a 66-day study was conducted in M. japonicus Bate culture. The system comprised bracket and sand layers that divided a shrimp tank filled to a depth of 1.2 m into four water layers. Conventional tank culture (unlayered) was used as a control. The results show that survival rate, feed conversion efficiency and production of M. japonicus Bate in the layered farming system were 68%, 18%, and 0.59 kg/m2, respectively, all of which are significantly higher than in the unlayered farming system ( P <0.01). These findings confirmed the possibility of using a layered system to culture M. japonicus Bate.

  3. Smectic layer instabilities in liquid crystals.

    PubMed

    Dierking, Ingo; Mitov, Michel; Osipov, Mikhail A

    2015-02-01

    Scientists aspire to understand the underlying physics behind the formation of instabilities in soft matter and how to manipulate them for diverse investigations, while engineers aim to design materials that inhibit or impede the nucleation and growth of these instabilities in critical applications. The present paper reviews the field-induced rotational instabilities which may occur in chiral smectic liquid-crystalline layers when subjected to an asymmetric electric field. Such instabilities destroy the so-named bookshelf geometry (in which the smectic layers are normal to the cell surfaces) and have a detrimental effect on all applications of ferroelectric liquid crystals as optical materials. The transformation of the bookshelf geometry into horizontal chevron structures (in which each layer is in a V-shaped structure), and the reorientation dynamics of these chevrons, are discussed in details with respect to the electric field conditions, the material properties and the boundary conditions. Particular attention is given to the polymer-stabilisation of smectic phases as a way to forbid the occurrence of instabilities and the decline of related electro-optical performances. It is also shown which benefit may be gained from layer instabilities to enhance the alignment of the liquid-crystalline geometry in practical devices, such as optical recording by ferroelectric liquid crystals. Finally, the theoretical background of layer instabilities is given and discussed in relation to the experimental data.

  4. Thin Layer Samples Controlled by Dynamic Electrochemistry.

    PubMed

    Cuartero, Maria; Crespo, Gastón A; Bakker, Eric

    2015-01-01

    We summarize here recent advancements on thin layer samples controlled by dynamic electrochemistry techniques for determining different ions that include potassium, calcium, protamine, nitrate, nitrite and halides in diverse environmental and clinical samples. Generally, a thin layer liquid (less than 100 μm in thickness) is confined between a working electrode and an ion-selective membrane. Once an external electrical perturbation (i.e. constant potential) is applied to the system, an exhaustive ion transfer process is imposed in the entire thin layer solution. As a result, the observed charge (integration of the current decay) is proportional to the depleted ion concentration. Other electrochemical protocols such as linear sweep voltammetry were also explored aiming at the discrimination of several ions presented in the thin layer. One of the most attractive examples involves the detection of a mixture of three halides (iodide, bromide and chloride), which can be well resolved at moderated scan rates (10 mV.s(-1)). Paper-based coulometric sensing on thin layers defined by cellulose papers are being developed in view of translating these new concepts into a reliable and low cost sensing platform. PMID:26668939

  5. Intermolecular dimerization with pillared layered clay templates.

    SciTech Connect

    Wiederrecht, G. P.; Sandi, G.; Carrado, K. A.; Seifert, S.; Chemistry

    2001-11-19

    Solutions of pyrene in the presence of a pillared, layered montmorillonite clay produce hybrid organic-inorganic materials with substantial molecular loading in the gallery regions between the clay layers. The results are in sharp contrast to other aromatics, such as benzene, naphthalene, or perylene, which show minimal incorporation of the molecules into the gallery regions of the clay. We present evidence that the unusual affinity for pyrene to form intermolecular dimers is the reason for the high loading. Pyrene monomers are easily introduced to the layers. Through steric hindrance, subsequent intermolecular dimer formation is allowed, and they are captured by the pillared, layered structure. CW and time-resolved emission spectra strongly indicate the presence of face-to-face intermolecular dimers (excimers) within the clay galleries. The combination of the ease of high molecular loading into an inorganic, high aspect ratio template and the collective optical properties of the organic layer may be useful as a new means to create hybrid structures.

  6. Membrane catalyst layer for fuel cells

    DOEpatents

    Wilson, Mahlon S.

    1993-01-01

    A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

  7. Two-dimensional inter-layer debonding in deposited multi-layers

    SciTech Connect

    Beuth, J.L.; Narayan, S.H.

    1996-12-31

    Two-dimensional problems of residual stress-driven inter-layer debonding or delamination in successively deposited isotropic multi-layers are studied, with direct applications to the modeling of delamination in multi-layered coatings and films. Planar and axisymmetric configurations of a delamination crack extending from a free edge are considered. The term successively deposited is used to designate that each layer experiences a free thermal contraction relative to the layers below it. Results for energy release rates as a function of crack length are presented from fracture mechanics models of planar and axisymmetric multi-layer geometries. In planar problems, energy release rates reach a constant value for crack lengths greater than one or two debond thicknesses and maintain this value until the multi-layer is almost completely debonded. In axisymmetric problems, energy release rates increase steadily with increasing crack length, reaching a maximum just before the multi-layer separates into two pieces. These observed energy release rate behaviors are explained qualitatively. Methods are outlined for quantitatively predicting the steady-state energy release rate for planar debonding problems. Methods are also outlined for determining a conservative upper bound for the maximum energy release rate for an axisymmetrically extending delamination crack. Both methods are based on potential energy calculations from a residual stress model for an uncracked multi-layer. These easily-calculated energy release rate quantities for planar and axisymmetric delamination problems can be used to guide the specification of layer thicknesses, stacking sequences and other characteristics of multi-layered coatings and films.

  8. Issues in designing transport layer multicast facilities

    NASA Technical Reports Server (NTRS)

    Dempsey, Bert J.; Weaver, Alfred C.

    1990-01-01

    Multicasting denotes a facility in a communications system for providing efficient delivery from a message's source to some well-defined set of locations using a single logical address. While modem network hardware supports multidestination delivery, first generation Transport Layer protocols (e.g., the DoD Transmission Control Protocol (TCP) (15) and ISO TP-4 (41)) did not anticipate the changes over the past decade in underlying network hardware, transmission speeds, and communication patterns that have enabled and driven the interest in reliable multicast. Much recent research has focused on integrating the underlying hardware multicast capability with the reliable services of Transport Layer protocols. Here, we explore the communication issues surrounding the design of such a reliable multicast mechanism. Approaches and solutions from the literature are discussed, and four experimental Transport Layer protocols that incorporate reliable multicast are examined.

  9. Eclogites, pyroxene geotherm, and layered mantle convection.

    PubMed

    Basu, A R; Ongley, J S; Macgregor, I D

    1986-09-19

    Temperatures of equilibration for the majority (81 percent) of the eclogite xenoliths of the Roberts Victor kimberlite pipe in South Africa range between 1000 degrees and 1250 degrees C, falling essentially on the gap of the lower limb of the subcontinental inflected geotherm derived from garnet peridotite xenoliths. In view of the Archean age (>2.6 x 10(9) years) of these eclogites and their stratigraphic position on the geotherm, it is proposed that the inflected part of the geotherm represents the convective boundary layer beneath the conductive lid of the lithospheric plate. The gradient of 8 Celsius degrees per kilometer for the inflection is characteristic of a double thermal boundary layer and suggests layered convection rather than whole mantle convection for the earth. PMID:17843357

  10. Ground observations of magnetospheric boundary layer phenomena

    NASA Technical Reports Server (NTRS)

    Mchenry, Mark A.; Clauer, C. Robert; Friis-Christensen, Eigil; Newell, Patrick T.; Kelly, J. D.

    1990-01-01

    Several classes of traveling vortices in the dayside ionosphere convection have been detected and tracked using the Greenland magnetometer chain (Friis-Christensen et al., 1988, McHenry et al., 1989). One class observed during quiet times consists of a continuous series of vortices moving generally antisunward for several hours at a time. The vortices' strength is seen to be approximately steady and neighboring vortices rotate in opposite directions. Sondrestrom radar observations show that the vortices are located at the ionospheric convection reversal boundary. Low altitude DMSP observations indicate the vortices are on field lines which map to the inner edge of the low latitude boundary layer. Because the vortices are conjugate to the boundary layer, repeat in a regular fashion and travel antisunward, it is argued that this class of vortices is caused by the Kelvin-Helmholtz instability of the inner edge of the magnetospheric boundary layer.

  11. Layered classification techniques for remote sensing applications

    NASA Technical Reports Server (NTRS)

    Swain, P. H.; Wu, C. L.; Landgrebe, D. A.; Hauska, H.

    1975-01-01

    The single-stage method of pattern classification utilizes all available features in a single test which assigns the unknown to a category according to a specific decision strategy (such as the maximum likelihood strategy). The layered classifier classifies the unknown through a sequence of tests, each of which may be dependent on the outcome of previous tests. Although the layered classifier was originally investigated as a means of improving classification accuracy and efficiency, it was found that in the context of remote sensing data analysis, other advantages also accrue due to many of the special characteristics of both the data and the applications pursued. The layered classifier method and several of the diverse applications of this approach are discussed.

  12. Progress of simulations for reacting shear layers

    NASA Technical Reports Server (NTRS)

    Yu, Sheng-Tao

    1991-01-01

    An attempt was made to develop a high speed, chemically reactive shear layer test rig. The purpose of the experiment was to study the mixing of oxidizer and fuel streams in reacting shear layers for various density, velocity, and Mach number. The primary goal was to understand the effects of the compressibility upon mixing and combustion in a fundamental way. Therefore, a two-dimensional shear layer is highly desirable for its simplicity to quantify the compressibility effects. The RPLUS 2D code is used to calculate the flow fields of different sections of the test rig. The emphasis was on the supersonic nozzle design, the vitiation process for the hot air stream and the overall thermodynamic conditions of the test matrix. The k-epsilon turbulence model with wall function was successfully implemented in the RPLUS code. The k and epsilon equations are solved simultaneously and the LU scheme is used to make it compatible with the flow solver.

  13. Streamline curvature in supersonic shear layers

    NASA Technical Reports Server (NTRS)

    Kibens, V.

    1992-01-01

    Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.

  14. Polyethylene oxide hydration in grafted layers

    NASA Astrophysics Data System (ADS)

    Dormidontova, Elena; Wang, Zilu

    Hydration of water soluble polymers is one of the key-factors defining their conformation and properties, similar to biopolymers. Polyethylene oxide (PEO) is one of the most important biomedical-applications polymers and is known for its reverse temperature solubility due to hydrogen bonding with water. As in many practical applications PEO chains are grafted to surfaces, e.g. of nanoparticles or planar surfaces, it is important to understand PEO hydration in such grafted layers. Using atomistic molecular dynamic simulations we investigate the details of molecular conformation and hydration of PEO end-grafted to gold surfaces. We analyze polymer and water density distribution as a function of distance from the surface for different grafting densities. Based on a detailed analysis of hydrogen bonding between polymer and water in grafted PEO layers, we will discuss the extent of PEO hydration and its implication for polymer conformation, mobility and layer properties. This research is supported by NSF (DMR-1410928).

  15. Opportunity View of 'Gilbert' Layer (False Color)

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This view from NASA's Mars Exploration Rover Opportunity shows bedock within a stratigraphic layer informally named 'Gilbert,' which is the rover's next target after completing an examination of three stratigtaphic layers forming a bright band around the inside of Victoria Crater. The rover will descend deeper into the crater to reach the Gilbert layer.

    Opportunity used its panoramic camera (Pancam) to capture this image with low-sun angle at a local solar time of 3:30 p.m. during the rover's 1,429th Martian day, of sol (Jan. 31, 2008).

    This view combines separate images taken through the Pancam filters centered on wavelengths of 753 nanometers, 535 nanometers and 432 nanometers. It is presented in a false-color stretch to bring out subtle color differences in the scene.

  16. Automated retinal layer segmentation and characterization

    NASA Astrophysics Data System (ADS)

    Luisi, Jonathan; Briley, David; Boretsky, Adam; Motamedi, Massoud

    2014-05-01

    Spectral Domain Optical Coherence Tomography (SD-OCT) is a valuable diagnostic tool in both clinical and research settings. The depth-resolved intensity profiles generated by light backscattered from discrete layers of the retina provide a non-invasive method of investigating progressive diseases and injury within the eye. This study demonstrates the application of steerable convolution filters capable of automatically separating gradient orientations to identify edges and delineate tissue boundaries. The edge maps were recombined to measure thickness of individual retinal layers. This technique was successfully applied to longitudinally monitor changes in retinal morphology in a mouse model of laser-induced choroidal neovascularization (CNV) and human data from age-related macular degeneration patients. The steerable filters allow for direct segmentation of noisy images, while novel recombination of weaker segmentations allow for denoising post-segmentation. The segmentation before denoising strategy allows the rapid detection of thin retinal layers even under suboptimal imaging conditions.

  17. Process for depositing Cr-bearing layer

    DOEpatents

    Ellis, Timothy W.; Lograsso, Thomas A.; Eshelman, Mark A.

    1995-05-09

    A method of applying a Cr-bearing layer to a substrate, comprises introducing an organometallic compound, in vapor or solid powder form entrained in a carrier gas to a plasma of an inductively coupled plasma torch or device to thermally decompose the organometallic compound and contacting the plasma and the substrate to be coated so as to deposit the Cr-bearing layer on the substrate. A metallic Cr, Cr alloy or Cr compound such as chromium oxide, nitride and carbide can be provided on the substrate. Typically, the organometallic compound is introduced to an inductively coupled plasma torch that is disposed in ambient air so to thermally decompose the organometallic compound in the plasma. The plasma is directed at the substrate to deposit the Cr-bearing layer or coating on the substrate.

  18. Coronary tree extraction using motion layer separation.

    PubMed

    Zhang, Wei; Ling, Haibin; Prummer, Simone; Zhou, Kevin Shaohua; Ostermeier, Martin; Comaniciu, Dorin

    2009-01-01

    Fluoroscopic images contain useful information that is difficult to comprehend due to the collapse of the 3D information into 2D space. Extracting the informative layers and analyzing them separately could significantly improve the task of understanding the image content. Traditional Digital Subtraction Angiography (DSA) is not applicable for coronary angiography because of heart beat and breathing motion. In this work, we propose a layer extraction method for separating transparent motion layers in fluoroscopic image sequences, so that coronary tree can be better visualized.. The method is based on the fact that different anatomical structures possess different motion patterns, e.g., heart is beating fast, while lung is breathing slower. A multiscale implementation is used to further improve the efficiency and accuracy. The proposed approach helps to enhance the visibility of the vessel tree, both visually and quantitatively.

  19. Permafrost Active Layer Seismic Interferometry Experiment (PALSIE).

    SciTech Connect

    Abbott, Robert; Knox, Hunter Anne; James, Stephanie; Lee, Rebekah; Cole, Chris

    2016-01-01

    We present findings from a novel field experiment conducted at Poker Flat Research Range in Fairbanks, Alaska that was designed to monitor changes in active layer thickness in real time. Results are derived primarily from seismic data streaming from seven Nanometric Trillium Posthole seismometers directly buried in the upper section of the permafrost. The data were evaluated using two analysis methods: Horizontal to Vertical Spectral Ratio (HVSR) and ambient noise seismic interferometry. Results from the HVSR conclusively illustrated the method's effectiveness at determining the active layer's thickness with a single station. Investigations with the multi-station method (ambient noise seismic interferometry) are continuing at the University of Florida and have not yet conclusively determined active layer thickness changes. Further work continues with the Bureau of Land Management (BLM) to determine if the ground based measurements can constrain satellite imagery, which provide measurements on a much larger spatial scale.

  20. Ceramic with preferential oxygen reactive layer

    NASA Technical Reports Server (NTRS)

    Wang, Hongyu (Inventor); Luthra, Krishan Lal (Inventor)

    2001-01-01

    An article comprises a silicon-containing substrate and an external environmental/thermal barrier coating. The external environmental/thermal barrier coating is permeable to diffusion of an environmental oxidant and the silicon-containing substrate is oxidizable by reaction with oxidant to form at least one gaseous product. The article comprises an intermediate layer/coating between the silicon-containing substrate and the environmental/thermal barrier coating that is oxidizable to a nongaseous product by reaction with the oxidant in preference to reaction of the silicon-containing substrate with the oxidant. A method of forming an article, comprises forming a silicon-based substrate that is oxidizable by reaction with oxidant to at least one gaseous product and applying an intermediate layer/coating onto the substrate, wherein the intermediate layer/coating is oxidizable to a nongaseous product by reaction with the oxidant in preference to reaction of the silicon-containing substrate with the oxidant.

  1. Fixed-rate layered multicast congestion control

    NASA Astrophysics Data System (ADS)

    Bing, Zhang; Bing, Yuan; Zengji, Liu

    2006-10-01

    A new fixed-rate layered multicast congestion control algorithm called FLMCC is proposed. The sender of a multicast session transmits data packets at a fixed rate on each layer, while receivers each obtain different throughput by cumulatively subscribing to deferent number of layers based on their expected rates. In order to provide TCP-friendliness and estimate the expected rate accurately, a window-based mechanism implemented at receivers is presented. To achieve this, each receiver maintains a congestion window, adjusts it based on the GAIMD algorithm, and from the congestion window an expected rate is calculated. To measure RTT, a new method is presented which combines an accurate measurement with a rough estimation. A feedback suppression based on a random timer mechanism is given to avoid feedback implosion in the accurate measurement. The protocol is simple in its implementation. Simulations indicate that FLMCC shows good TCP-friendliness, responsiveness as well as intra-protocol fairness, and provides high link utilization.

  2. Process for depositing Cr-bearing layer

    DOEpatents

    Ellis, T.W.; Lograsso, T.A.; Eshelman, M.A.

    1995-05-09

    A method of applying a Cr-bearing layer to a substrate, comprises introducing an organometallic compound, in vapor or solid powder form entrained in a carrier gas to a plasma of an inductively coupled plasma torch or device to thermally decompose the organometallic compound and contacting the plasma and the substrate to be coated so as to deposit the Cr-bearing layer on the substrate. A metallic Cr, Cr alloy or Cr compound such as chromium oxide, nitride and carbide can be provided on the substrate. Typically, the organometallic compound is introduced to an inductively coupled plasma torch that is disposed in ambient air so to thermally decompose the organometallic compound in the plasma. The plasma is directed at the substrate to deposit the Cr-bearing layer or coating on the substrate. 7 figs.

  3. Flow through a charged biopolymer layer

    NASA Astrophysics Data System (ADS)

    Mokady, A. J.; Mestel, A. J.; Winlove, C. P.

    1999-03-01

    The polyelectrolyte layer coating mammalian cells, known as the glycocalyx, is important in communicating flow information to the cell. In this paper, the layer is modelled as a semi-infinite, doubly periodic array of parallel charged cylinders. The electric potential and ion distributions surrounding such an array are found using the Poisson Boltzmann equation and an iterative domain decomposition technique. Similar methods are used to calculate Stokes flows, driven either by a shear at infinity or by an electric field, parallel or transverse to the cylinders. The resulting electric streaming currents due to flow over endothelial cells, and the electrophoretic mobilities of red blood cells are deduced as functions of polymer concentration and electrolyte molarity. It is shown that only the top portion of the layer is important in these effects.

  4. Iodine Sequestration Using Delafossites and Layered Hydroxides

    SciTech Connect

    J.D. Pless; J.B. Chwirka; J.L. Krumhansl

    2006-03-28

    The objective of this document is to report on early success for sequestering {sup 129}I. Sorption coefficients (K{sub d}) for I{sup -} and IO{sub 3}{sup -} onto delafossites, spinels and layered metal hydroxides were measured in order to compare their applicability for sequestering {sup 129}I. The studies were performed using a dilute fluid composition representative of groundwater indigenous to the Yucca mountain area. Delafossites generally exhibited relatively poor sorption coefficients (< 10{sup 1.7} mL/g). In contrast, the composition of the layered hydroxides significantly affects their ability to sorb I. Cu/Al and Cu/Cr layered hydroxide samples exhibit K{sub d}'s greater than 10{sup 3} mL/g for both I{sup -} and IO{sub 3}{sup -}.

  5. Lithium transport through nanosized amorphous silicon layers.

    PubMed

    Hüger, Erwin; Dörrer, Lars; Rahn, Johanna; Panzner, Tobias; Stahn, Jochen; Lilienkamp, Gerhard; Schmidt, Harald

    2013-03-13

    Lithium migration in nanostructured electrode materials is important for an understanding and improvement of high energy density lithium batteries. An approach to measure lithium transport through nanometer thin layers of relevant electrochemical materials is presented using amorphous silicon as a model system. A multilayer consisting of a repetition of five [(6)LiNbO3(15 nm)/Si (10 nm)/(nat)LiNbO3 (15 nm)/Si (10 nm)] units is used for analysis, where LiNbO3 is a Li tracer reservoir. It is shown that the change of the relative (6)Li/(7)Li isotope fraction in the LiNbO3 layers by lithium diffusion through the nanosized silicon layers can be monitored nondestructively by neutron reflectometry. The results can be used to calculate transport parameters.

  6. Eclogites, pyroxene geotherm, and layered mantle convection.

    PubMed

    Basu, A R; Ongley, J S; Macgregor, I D

    1986-09-19

    Temperatures of equilibration for the majority (81 percent) of the eclogite xenoliths of the Roberts Victor kimberlite pipe in South Africa range between 1000 degrees and 1250 degrees C, falling essentially on the gap of the lower limb of the subcontinental inflected geotherm derived from garnet peridotite xenoliths. In view of the Archean age (>2.6 x 10(9) years) of these eclogites and their stratigraphic position on the geotherm, it is proposed that the inflected part of the geotherm represents the convective boundary layer beneath the conductive lid of the lithospheric plate. The gradient of 8 Celsius degrees per kilometer for the inflection is characteristic of a double thermal boundary layer and suggests layered convection rather than whole mantle convection for the earth.

  7. Excess Oxygen Defects in Layered Cuprates

    DOE R&D Accomplishments Database

    Lightfoot, P.; Pei, S. Y.; Jorgensen, J. D.; Manthiram, A.; Tang, X. X.; Goodenough, J. B.

    1990-09-01

    Neutron powder diffraction has been used to study the oxygen defect chemistry of two non-superconducting layered cuprates, La{sub 1. 25}Dy{sub 0.75}Cu{sub 3.75}F{sub 0.5}, having a T{sup {asterisk}}- related structure, and La{sub 1.85}Sr{sub 1.15}Cu{sub 2}O{sub 6.25}, having a structure related to that of the newly discovered double-layer superconductor La{sub 2-x}Sr{sub x}CaCu{sub 2}O{sub 6}. The role played by oxygen defects in determining the superconducting properties of layered cuprates is discussed.

  8. Growth of oxide exchange bias layers

    DOEpatents

    Chaiken, A.; Michel, R.P.

    1998-07-21

    An oxide (NiO, CoO, NiCoO) antiferromagnetic exchange bias layer produced by ion beam sputtering of an oxide target in pure argon (Ar) sputtering gas, with no oxygen gas introduced into the system. Antiferromagnetic oxide layers are used, for example, in magnetoresistive readback heads to shift the hysteresis loops of ferromagnetic films away from the zero field axis. For example, NiO exchange bias layers have been fabricated using ion beam sputtering of an NiO target using Ar ions, with the substrate temperature at 200 C, the ion beam voltage at 1000V and the beam current at 20 mA, with a deposition rate of about 0.2 {angstrom}/sec. The resulting NiO film was amorphous. 4 figs.

  9. Growth of oxide exchange bias layers

    DOEpatents

    Chaiken, Alison; Michel, Richard P.

    1998-01-01

    An oxide (NiO, CoO, NiCoO) antiferromagnetic exchange bias layer produced by ion beam sputtering of an oxide target in pure argon (Ar) sputtering gas, with no oxygen gas introduced into the system. Antiferromagnetic oxide layers are used, for example, in magnetoresistive readback heads to shift the hysteresis loops of ferromagnetic films away from the zero field axis. For example, NiO exchange bia layers have been fabricated using ion beam sputtering of an NiO target using Ar ions, with the substrate temperature at 200.degree. C., the ion beam voltage at 1000V and the beam current at 20 mA, with a deposition rate of about 0.2 .ANG./sec. The resulting NiO film was amorphous.

  10. Roles of Titanium-Intermetallic Compound Layer

    NASA Astrophysics Data System (ADS)

    Lee, Chii-Chang

    Four different configurations have been tested: Al-Cu, Ti/Al-Cu, Al-Cu/Ti, and Ti/Al-Cu/Ti to evaluate the possible contributions of Ti-intermetallic compound layer(s) to enhancement of the lifetime to failure. Basically, the proposed mechanisms can be classified into two groups: shunting effect and effects limited to changes in Al-Cu conducting layer(s). A resistance monitoring technique was adopted to supplement lifetime measurement to separate these two effects. By correlating the first resistance jump (spike) to the happening of a complete open across Al-Cu layer, it was found that the shunting effect contributes to enhancement of the lifetime by 4 times in Ti/Al-Cu, 2 times in Al-Cu/Ti, and 2 times in Ti/Al-Cu/Ti. A Ti underlayer was found to contribute mainly the shunting effect. However, from drift velocity measurements and failure mode analysis, it is possible to deduce that a Ti overlayer contributes not only the shunting effect but also another effect that acts to diminish the grain boundary mass transport rate by a factor of about 76. It is believed that the latter effect is a consequence of the high compressive yield stength conferred by the Ti-intermetallic compound overlayer to the Al-Cu layer. Finally, an important non-destructive technique, based on the characteristic x-rays generated by energetic electrons, to characterize the mass divergences in multilayer interconnects, was developed in this research, called SMEISIS, representing Simultaneous Multiple Elements Intensity Scanning of Interconnecting Stripes. This technique was proved to be capable of revealing detail about the shapes, nature, and location of mass divergence that cannot be revealed by thermal wave image technique and that requires time consuming multiple sectioning in TEM and SEM methods.

  11. Critical Layers and Protoplanetary Disk Turbulence

    NASA Astrophysics Data System (ADS)

    Umurhan, Orkan M.; Shariff, Karim; Cuzzi, Jeffrey N.

    2016-10-01

    A linear analysis of the zombie vortex instability (ZVI) is performed in a stratified shearing sheet setting for three model barotropic shear flows. The linear analysis is done by utilizing a Green’s function formulation to resolve the critical layers of the associated normal-mode problem. The instability is the result of a resonant interaction between a Rossby wave and a gravity wave that we refer to as Z-modes. The associated critical layer is the location where the Doppler-shifted frequency of a distant Rossby wave equals the local Brunt–Väisälä frequency. The minimum required Rossby number for instability, {\\mathtt{Ro}}=0.2, is confirmed for parameter values reported in the literature. It is also found that the shear layer supports the instability in the limit where stratification vanishes. The ZVI is examined in a jet model, finding that the instability can occur for {\\mathtt{Ro}}=0.05. Nonlinear vorticity forcing due to unstable Z-modes is shown to result in the creation of a jet flow at the critical layer emerging as the result of the competition between the vertical lifting of perturbation radial vorticity and the radial transport of perturbation vertical vorticity. We find that the picture of this instability leading to a form of nonlinearly driven self-replicating pattern of creation and destruction is warranted: a parent jet spawns a growing child jet at associated critical layers. A mature child jet creates a next generation of child jets at associated critical layers of the former while simultaneously contributing to its own destruction via the Rossby wave instability.

  12. Boundary layer emission in luminous LMXBs

    NASA Astrophysics Data System (ADS)

    Gilfanov, M.; Revnivtsev, M.

    We show that aperiodic and quasiperiodic variability of bright LMXBs -- atoll and Z- sources on sim sec -- msec time scales is caused primarily by variations of the luminosity of the boundary layer The kHz QPOs have the same origin as variability at lower frequencies i e independent of the nature of the clock the actual luminosity modulation takes place on the neutron star surface The boundary layer spectrum remains nearly constant in the course of the luminosity variations and is represented to certain accuracy by the Fourier frequency resolved spectrum In the investigated range of dot M sim 0 1-1 dot MEdd it depends weakly on the global mass accretion rate and in the limit dot M sim dot MEdd is close to Wien spectrum with kT sim 2 4 keV Its independence on the global value of dot M lends support to the theoretical suggestion by Inogamov Sunyaev 1999 that the boundary layer is radiation pressure supported Based on the knowledge of the boundary layer spectrum we attempt to relate the motion along the Z-track to changes of physically meaningful parameters Our results suggest that the contribution of the boundary layer to the observed emission decreases along the Z-track from conventional sim 50 on the horizontal branch to a rather small number on the normal branch This decrease can be caused for example by obscuration of the boundary layer by the geometrically thickened accretion disk at dot M sim dot MEdd Alternatively this can indicate significant change of

  13. Template-free synthesis and encapsulation technique for layer-by-layer polymer nanocarrier fabrication.

    PubMed

    Qi, Aisha; Chan, Peggy; Ho, Jenny; Rajapaksa, Anushi; Friend, James; Yeo, Leslie

    2011-12-27

    The encapsulation of therapeutic molecules within multiple layers of biocompatible and biodegradable polymeric excipients allows exquisite design of their release profile, to the extent the drug can be selectively delivered to a specific target location in vivo. Here, we develop a novel technique for the assembly of multilayer polyelectrolyte nanocarriers based on surface acoustic wave atomization as a rapid and efficient alternative to conventional layer-by-layer assembly, which requires the use of a sacrificial colloidal template over which consecutive polyelectrolyte layers are deposited. Polymer nanocarriers are synthesized by atomizing a polymer solution and suspending them within a complementary polymer solution of opposite charge subsequent to their solidification in-flight as the solvent evaporates; reatomizing this suspension produces nanocarriers with a layer of the second polymer deposited over the initial polymer core. Successive atomization-suspension layering steps can then be repeated to produce as many additional layers as desired. Specifically, we synthesize nanocarriers comprising two and three, and up to eight, alternating layers of chitosan (or polyethyleneimine) and carboxymethyl cellulose within which plasmid DNA is encapsulated and show in vitro DNA release profiles over several days. Evidence that the plasmid's viability is preserved and hence the potential of the technique for gene delivery is illustrated through efficient in vitro transfection of the encapsulated plasmid in human mesenchymal progenitor and COS-7 cells.

  14. Adaptation technology between IP layer and optical layer in optical Internet

    NASA Astrophysics Data System (ADS)

    Ji, Yuefeng; Li, Hua; Sun, Yongmei

    2001-10-01

    Wavelength division multiplexing (WDM) optical network provides a platform with high bandwidth capacity and is supposed to be the backbone infrastructure supporting the next-generation high-speed multi-service networks (ATM, IP, etc.). In the foreseeable future, IP will be the predominant data traffic, to make fully use of the bandwidth of the WDM optical network, many attentions have been focused on IP over WDM, which has been proposed as the most promising technology for new kind of network, so-called Optical Internet. According to OSI model, IP is in the 3rd layer (network layer) and optical network is in the 1st layer (physical layer), so the key issue is what adaptation technology should be used in the 2nd layer (data link layer). In this paper, firstly, we analyze and compare the current adaptation technologies used in backbone network nowadays. Secondly, aiming at the drawbacks of above technologies, we present a novel adaptation protocol (DONA) between IP layer and optical layer in Optical Internet and describe it in details. Thirdly, the gigabit transmission adapter (GTA) we accomplished based on the novel protocol is described. Finally, we set up an experiment platform to apply and verify the DONA and GTA, the results and conclusions of the experiment are given.

  15. Innovative layer-by-layer processing for flame retardant behavior of cotton fabric

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Flame retardant behavior has been prepared by the layer-by layer assemblies of kaolin/casein with inorganic chemicals on cotton fabrics. Three different kinds of cotton fabrics (print cloth, mercerized print cloth, and mercerized twill fabric) were prepared with solutions of mixture of BPEI, urea, ...

  16. Molecular layer-by-layer assembled thin-film composite membranes for water desalination.

    PubMed

    Gu, Joung-Eun; Lee, Seunghye; Stafford, Christopher M; Lee, Jong Suk; Choi, Wansuk; Kim, Bo-Young; Baek, Kyung-Youl; Chan, Edwin P; Chung, Jun Young; Bang, Joona; Lee, Jung-Hyun

    2013-09-14

    Molecular layer-by-layer (mLbL) assembled thin-film composite membranes fabricated by alternating deposition of reactive monomers on porous supports exhibit both improved salt rejection and enhanced water flux compared to traditional reverse osmosis membranes prepared by interfacial polymerization. Additionally, the well-controlled structures achieved by mLbL deposition further lead to improved antifouling performance.

  17. Coupling electrodeposition with layer-by-layer assembly to address proteins within microfluidic channels.

    PubMed

    Wang, Yifeng; Liu, Yi; Cheng, Yi; Kim, Eunkyoung; Rubloff, Gary W; Bentley, William E; Payne, Gregory F

    2011-12-22

    Two thin-film assembly methods are coupled to address proteins. Electrodeposition confers programmability and generates a template for layer-by-layer (LbL) assembly. LbL enables precise control of film thickness and the incorporation of labile biological components. The capabilities are demonstrated using glucose oxidase (GOx) based electrochemical biosensing within a microfabricated fluidic device.

  18. Stratified assemblies of magnetite nanoparticles and montmorillonite prepared by the layer-by-layer assembly

    SciTech Connect

    Mamedov, A.; Ostrander, J.; Aliev, F.; Kotov, N.A.

    2000-04-18

    Hybrid thin films are prepared from 8 to 10 nm Fe{sub 3}O{sub 4} nanoparticles and exfoliated montmorillonite clay by using layer-by-layer assembly on poly(diallyldimethylammonium bromide), PDDA. Distinct stratification of the Fe{sub 3}O{sub 4}/PDDA/clay films is obtained due to the sheetlike structure of the clay particles. This feature distinguishes these assemblies from their polyelectrolyte-polyelectrolyte analogues, where the layers of individual polyelectrolytes are strongly interdigitated. Being adsorbed on PDDA strictly parallel to the substrate surface, montmorillonite produces a dense layer of overlapping alumosilicate sheets, which virtually flawlessly separates one magnetite layer from another. The difference in magnetic properties between assemblies of various architectures is attributed to the insulation effect of clay layers inserted between magnetic layers. The montmorillonite sheets disrupt the electron exchange interactions between the magnetite nanoparticles in adjacent layers, thereby limiting the magnetization reversal to two dimensions. Some optical properties of Fe{sub 3}O{sub 4}/PDDA films are investigated as well. When they are deposited on thin plastic substrate, oscillations of optical density were observed in the red part of the UV-vis spectrum. This effect, which has never been observed for conventional, thick substrates such as glass slides, stems from the interference of the light beams passed through and reflected off of the assembled film.

  19. Sub-layers inside the entrainment zone of a dry, shear-free convective boundary layer

    NASA Astrophysics Data System (ADS)

    Garcia, Jade Rachele; Mellado, Juan Pedro

    2013-11-01

    The entrainment zone of a dry, shear-free convective boundary layer growing into a homogeneously stably-stratified fluid is studied using direct numerical simulation. Based on the self-similar analysis of the mean and variance buoyancy profiles, we identify two sub-layers within the entrainment zone, defined as the region of negative buoyancy flux: i) an upper sub-layer with a thickness comparable to the penetrative length scale based on the convective velocity and the buoyancy frequency of the free troposphere and ii) a lower sub-layer acting as a transition towards the mixed layer, with a thickness equal to a constant fraction of the boundary layer height. The capping region of the penetrative thermals belongs to the upper sub-layer of the entrainment zone, and the troughs between the penetrating thermals belong to the lower sub-layer of the entrainment zone. Correspondingly, different buoyancy scales are identified in the different regions; parametrizations thereof are provided and explained. This multiplicity of characteristic scales inside the entrainment zone helps to explain the uncertainty associated with previous analysis of entrainment zone properties and the difficulty to parametrize them based on a single length scale and a single buoyancy scale. Juelich Research Centre for the computing time.

  20. Layer-by-Layer Assembly of a pH-Responsive and Electrochromic Thin Film

    ERIC Educational Resources Information Center

    Schmidt, Daniel J.; Pridgen, Eric M.; Hammond, Paula T.; Love, J. Christopher

    2010-01-01

    This article summarizes an experiment on thin-film fabrication with layer-by-layer assembly that is appropriate for undergraduate laboratory courses. The purpose of this experiment is to teach students about self-assembly in the context of thin films and to expose students to the concepts of functional polymeric coatings. Students dip coat…