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1

Origins of Igneous Layering  

NASA Astrophysics Data System (ADS)

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.

Marsh, Bruce

2

Investigation of surface defect structure originating in dislocations in AlGaN/GaN epitaxial layer grown on a Si substrate  

NASA Astrophysics Data System (ADS)

Pit arrays forming a network structure were observed by an atomic force microscopy (AFM) on an AlGaN surface of AlGaN/GaN heterostructure on a Si(1 1 1) substrate. In order to clarify the origin of these pit arrays, AlGaN/GaN layers were investigated using a transmission electron microscopy (TEM). As a result, it was confirmed that pit arrays of the surface observed by an AFM represent the surface termination of edge dislocations formed at the small-angle boundaries of slightly misoriented crystal domains. The difference in buffer layer structures formed on Si substrates affected the surface pits arrangement. It was also confirmed that the optimization of a buffer structure on a Si substrate is very effective for the reduction of the pit density.

Sasaki, Hitoshi; Kato, Sadahiro; Matsuda, Takeyoshi; Sato, Yoshihiro; Iwami, Masayuki; Yoshida, Seikoh

2007-01-01

3

'Blueberry' Layers Indicate Watery Origins  

NASA Technical Reports Server (NTRS)

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.

2004-01-01

4

Structured luminescence conversion layer  

DOEpatents

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.

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

2012-12-11

5

Origins and implications of soil layering  

NASA Astrophysics Data System (ADS)

Layering is common in soils, due to a variety of pedologic and geologic processes, and has important consequences for the interpretation of soils and landscapes. Layering can derive from original sedimentary layering; depositional upbuilding; episodic surface erosion, deposition, and stability; soil production by weathering; vertical or lateral translocation; bioturbation; and various combinations of these. Complex and polygenetic models incorporate both geogenic and pedogenic processes, and allow for physical and biological processes, as well as both vertical and horizontal movements. We review these conceptual frameworks and synthesize them into a vertical contrast model (VCM) for interpreting layered surficial materials. The VCM incorporates a variety of geologic and pedologic processes which may create, destroy, enhance, or obscure vertical contrasts. The model is illustrated via application to sites in the Ouachita Mountains, USA, and northwest Saxonian Lowlands, Germany. The examples illustrate the importance of a comprehensive pedogeomorphic interpretation of layering, since neither standard stratigraphic or top-down pedogenetic principles necessarily apply. The examples also show that the same process can, sometimes contemporaneously, both create and destroy vertical contrasts.

Phillips, Jonathan D.; Lorz, Carsten

2008-08-01

6

Structural Origin of Overcharge-induced Thermal Instability of Ni-containing Layered-cathodes for High-energy-density Lithium Batteries  

SciTech Connect

Using a combination of time-resolved X-ray diffraction (XRD), in situ transmission electron microscopy (TEM), and first principles calculations, we explore the structural origin of the overcharge induced thermal instability of two cathode materials, LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} and LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2}, which exhibit significant difference in thermal stabilities. Detailed TEM analysis reveals, for the first time, a complex core-shell-surface structure of the particles in both materials that was not previously detected by XRD. Structural comparison indicates that the overcharged Li{sub x}Ni{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} (x < 0.15) particles consist of a rhombohedral core, a spinel shell, and a rock-salt structure at the surface, while the overcharged LixNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} consists of a similar core-shell-surface structure but a very different CdI{sub 2}-type surface structure. The thermal instability of LixNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} can be attributed to the release of oxygen because of the rapid growth of the rock-salt-type structure on the surface during heating. In contrast, the CdI{sub 2}-type surface structure of the overcharged LixNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} particles delays the oxygen-release reaction to a much higher temperature resulting in better stability. These results gave deep insight into the relationship between the local structural changes and the thermal stability of cathode materials, which is vital to the development of new cathode materials for the next generation of lithium-ion batteries.

L Wu; K Nam; X Wang; Y Zhou; J Zheng; X Yang; Y Zhu

2011-12-31

7

Structural Origin of Overcharge-Induced Thermal Instability of Ni-Containing Layered-Cathodes for High-Energy-Density Lithium Batteries  

SciTech Connect

Using a combination of time-resolved X-ray diffraction (XRD), in situ transmission electron microscopy (TEM), and first principles calculations, we explore the structural origin of the overcharge induced thermal instability of two cathode materials, LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} and LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2}, which exhibit significant difference in thermal stabilities. Detailed TEM analysis reveals, for the first time, a complex core-shell-surface structure of the particles in both materials that was not previously detected by XRD. Structural comparison indicates that the overcharged Li{sub x}Ni{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} (x < 0.15) particles consist of a rhombohedral core, a spinel shell, and a rock-salt structure at the surface, while the overcharged Li{sub x}Ni{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} consists of a similar core-shell-surface structure but a very different CdI{sub 2}-type surface structure. The thermal instability of Li{sub x}Ni{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} can be attributed to the release of oxygen because of the rapid growth of the rock-salt-type structure on the surface during heating. In contrast, the CdI{sub 2}-type surface structure of the overcharged Li{sub x}Ni{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} particles delays the oxygen-release reaction to a much higher temperature resulting in better stability. These results gave deep insight into the relationship between the local structural changes and the thermal stability of cathode materials, which is vital to the development of new cathode materials for the next generation of lithium-ion batteries.

Wu, L.; Nam, K.-W.; Wang, X.; Zhou, Y.; Zheng, J.-C.; Yang, X.-Q.; Zhu, Y.

2011-08-04

8

Layered tektites - A multiple impact origin for the Australasian tektites  

Microsoft Academic Search

The mechanisms proposed for the origin of tektites from the Australasian field are examined using neutron activation data for twenty layered tektites and six splash tektites of known and widely separated sites of a field greater than 1140 km in length. Evidence is presented indicating that the layered tektites formed as sheets or pools of melt. It is argued that

J. T. Wasson

1991-01-01

9

Planetary Origin Evolution and Structure  

NASA Technical Reports Server (NTRS)

This wide-ranging grant supported theoretical modeling on many aspects of the formation, evolution and structure of planets and satellites. Many topics were studied during this grant period, including the evolution of icy bodies; the origin of magnetic fields in Ganymede; the thermal histories of terrestrial planets; the nature of flow inside giant planets (especially the coupling to the magnetic field) and the dynamics of silicate/iron mixing during giant impacts and terrestrial planet core formation. Many of these activities are ongoing and have not reached completion. This is the nature of this kind of research.

Stevenson, David J.

2005-01-01

10

Natural layer-by-layer photonic structure in the squamae of Hoplia coerulea (Coleoptera)  

NASA Astrophysics Data System (ADS)

The microscopic structure of the hard external parts of the body of the iridescent blue-violet chaffer beetle Hoplia coerulea is studied using scanning electron microscopy. The blue iridescence is shown to originate from the structure of the squamae within scales covering the dorsal side of the beetle. The internal structure of the scales shows a stack of planar sheets, separated by a well-organized network of spacers, a structure which belongs to the family of the layer-by-layer photonic crystals. The blue iridescence is easily explained by a planar multilayer approximation model, deduced from the observed three-dimensional structure.

Vigneron, Jean Pol; Colomer, Jean-François; Vigneron, Nathalie; Lousse, Virginie

2005-12-01

11

Acoustic emissions from unsteady transitional boundary layer flow structures  

Microsoft Academic Search

The acoustic radiation contribution of boundary layer flow structures has long been the subject of debate. The research described critically examines the popular approaches to modeling the radiation mechanisms and attempts to bring some degree of closure to the physical and practical significance of noise and pseudo-noise originating in the laminar-to-turbulent transition zone within a natural boundary layer. This includes

Richard Chostner Marboe

2000-01-01

12

The origin of rhythmic layering in the Cape Neddick Plutonic Complex, Maine  

SciTech Connect

The Cape Neddick Plutonic Complex located along the southwestern coast of Maine is a small layered gabbroic body. It contains four concentric gabbros of differing composition, From the center to the exterior these are Cortlandtitic, Anorthositic, Normal, and Pegmatitic gabbros. They vary slightly in the proportion of essential minerals; plagioclase, clinopyroxene, hornblende, and biotite [+-] opaques and olivine. Rhythmic layering is seen in all four gabbros. This layering is also concentric around the center of the complex. The best exposure of the layering is along the coast where non-graded and graded rhythmic layering is seen extensively in the Normal gabbro. Only non-graded layering is seen in the Anorthositic gabbro. Non-graded layers were sampled at two localities. One locality is on Cape Nubble Island in the Normal gabbro. The second locality is in the Anorthositic gabbro along the northern coast. The layers are roughly 5--8 cm in width and are continuous around the complex. They are identified on weathered surfaces as alternating bands of felsic and mafic minerals. Layers are not obvious in hand sample. Approximately 15--20 layers were sampled perpendicular to layering. Petrographic and geochemical studies will help constrain the origin of rhythmic layering in the Cape Neddick Complex. Crystal settling or structural processes seem highly unlikely due to the small distance between the layers and the fact that they are not graded. Possible models include multiple pulses of magma within the same magma chamber, density currents, or in situ fractionation by a nucleation-diffusion process. Modal and chemical analysis of mineral phases within individual layers will allow comparison of the bulk composition of each layer. Analysis of coexisting pyroxene and plagioclase can be used to estimate compositional variations in the parent liquid.

Shipley, J. (Hartwick Coll., Oneonta, NY (United States). Dept. of Geology)

1993-03-01

13

Simulation of plasma double-layer structures  

NASA Technical Reports Server (NTRS)

Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2 dimensional particle in cell method. The investigation of planar double layers indicates that these one dimensional potential structures are susceptible to periodic disruption by instabilities in the low potential plasmas. Only a slight increase in the double layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double layer electric field alignment of accelerated particles and strong magnetization results in their magnetic field alignment. The numerical simulations of spatially periodic two dimensional double layers also exhibit cyclical instability. A morphological invariance in two dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron beam excited electrostatic electron cyclotron waves and (ion beam driven) solitary waves are present in the plasmas adjacent to the double layers.

Borovsky, J. E.; Joyce, G.

1982-01-01

14

Lattice Vibrations and Superconductivity in Layered Structures  

E-print Network

PHYSICAL REVIEW B VOLUME 2, NUMBER 7 1 OCTOB ER, 1970 Lattice Vibrations and Superconductivity in Layered Structures* B. E. Allen, G. P. Alldredge, and F. W. de bette DePartment of Physics, University of Texas, Austin, Texas 78712 (Received 18... May 1970) In order to estimate the influence of both surface and interface effects on phonon frequencies and superconducting transition temperatures in layered structures, we have calculated the vibrational modes of structures composed...

Allen, Roland E.; Alldredg, GP; WETTE, FWD.

1970-01-01

15

Original Article Structural Health Monitoring  

E-print Network

depth, seasonal thermal variations, and the geomechanical environment. Soil properties movements, or material het- erogeneities introduced during construction/repair affect the stability of the major causes of disorders in hydraulic structures and could lead to their failure.1 Consequently

Paris-Sud XI, Université de

16

The kinematics of turbulent boundary layer structure  

NASA Technical Reports Server (NTRS)

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.

Robinson, Stephen Kern

1991-01-01

17

A sporadic layer in the Venus lower ionosphere of meteoric origin M. Patzold,1  

E-print Network

A sporadic layer in the Venus lower ionosphere of meteoric origin M. Pa¨tzold,1 S. Tellmann,1 B. Ha meteor layer electron densities increase with decreasing solar zenith angle. Layer shapes are symmetric in the Venus lower ionosphere of meteoric origin, Geophys. Res. Lett., 36, L05203, doi:10.1029/ 2008GL035875. 1

Mendillo, Michael

18

ORIGINAL PAPER Vegetation structural and compositional heterogeneity  

E-print Network

ORIGINAL PAPER Vegetation structural and compositional heterogeneity as a key feature in Alpine April 2011 /Published online: 3 May 2011 # Springer-Verlag 2011 Abstract European Alpine landscapes are facing marked land-use changes. On the one hand, outdoor winter recreation is spreading, with ski

Richner, Heinz

19

Original article Structural features trigger capping  

E-print Network

already be closed by a cap- ping made of bee's wax, otherwise the lar- va will fall out and die. RecentlyOriginal article Structural features trigger capping of brood cells in honey bees B Goetz N- bee larva turns around in its comb cell and spins its cocoon. At this time the cell opening must

Paris-Sud XI, Université de

20

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

SciTech Connect

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.

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

2011-10-01

21

DNS Study for the origin of the flow Randomization in Late Boundary Layer Transition  

E-print Network

This paper is devoted to the investigation of the origin and mechanism of randomization in late boundary layer transition over a flat plate without pressure gradient. The flow randomization is a crucial phase before flow transition to the turbulent state. According to existing literatures, the randomization was caused by the big background noises and non-periodic spanwise boundary conditions. It was assumed that the large ring structure is affected by background noises first, and then the change of large ring structure affects the small length scales quickly, which directly leads to randomization and formation of turbulence. However, by careful analysis of our high order DNS results, we believe that the internal instability of multiple ring cycles structure is the main reason. What we observed is that randomization begins when the third cycle overlaps the first and second cycles. A significant asymmetric phenomenon is originated from the second cycle in the middle of both streamwise and spanwise directions. More technically, a visible asymmetric phenomenon in the middle vortex ring cycle starts at time step t=16.25T and x=838.9{\\delta}in where the top and bottom level rings are still completely symmetric. The non-symmetric structure of middle level ring affects the small length scale in boundary layer bottom quickly. The randomization phenomenon spreads to top level through ejections. Finally, the whole flow domain becomes randomized. A hypothesis of C- and K-types shift is given as a possible mechanism of flow randomization.

Manoj Thapa; Ping Lu; Chaoqun Liu

2014-02-25

22

Learning Layered Pictorial Structures from Video  

Microsoft Academic Search

We propose a new unsupervised learning method to ob- tain a layered pictorial structure (LPS) representation of an articulated object from video sequences. It will be seen that this is related in turn to methods for learning sprite based representations of an image. The method we describe in- volves a new generative model for performing segmentation on a set of

M. Pawan Kumar; Philip H. S. Torr; Andrew Zisserman

2004-01-01

23

Multi-Layer Laminated Thin Films for Inflatable Structures  

NASA Technical Reports Server (NTRS)

Special-purpose balloons and other inflatable structures would be constructed as flexible laminates of multiple thin polymeric films interspersed with layers of adhesive, according to a proposal. In the original intended application, the laminate would serve as the envelope of the Titan Aerobot a proposed robotic airship for exploring Titan (one of the moons of Saturn). Potential terrestrial applications for such flexible laminates could include blimps and sails. In the original application, the multi-layered laminate would contain six layers of 0.14-mil (0.0036-mm)-thick Mylar (or equivalent) polyethylene terephthalate film with a layer of adhesive between each layer of Mylar . The overall thickness and areal density of this laminate would be nearly the same as those of 1-mil (0.0254-mm)-thick monolayer polyethylene terephthalate sheet. However, the laminate would offer several advantages over the monolayer sheet, especially with respect to interrelated considerations of flexing properties, formation of pinholes, and difficulty or ease of handling, as discussed next. Most of the damage during flexing of the laminate would be localized in the outermost layers, where the radii of bending in a given bend would be the largest and, hence, the bending stress would be the greatest. The adverse effects of formation of pinholes would be nearly completely mitigated in the laminate because a pinhole in a given layer would not propagate to adjacent layers. Hence, the laminate would tend to remain effective as a barrier to retain gas. Similar arguments can be made regarding cracks: While a crack could form as a result of stress or a defect in the film material, a crack would not propagate into adjacent layers, and the adjacent layer(s) would even arrest propagation of the crack. In the case of the monolayer sheet, surface damage (scratches, dents, permanent folds, pinholes, and the like) caused by handling would constitute or give rise to defects that could propagate through the thickness as cracks or pinholes that would render the sheet less effective or ineffective as a barrier. In contrast, because damage incurred during handling of the laminate would ordinarily be limited to the outermost layers, the barrier properties of the laminate would be less likely to be adversely affected. Therefore, handling of the laminate would be easier because there would be less of a need to exercise care to ensure against surface damage.

Yavrouian, Andre; Plett, Gary; Mannella, Jerami

2005-01-01

24

Persistent Structures in the Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

Persistent structures in the turbulent boundary layer are located and analyzed. The data are taken from flight experiments on large commercial aircraft. An interval correlation technique is introduced which is able to locate the structures. The Morlet continuous wavelet is shown to not only locates persistent structures but has the added benefit that the pressure data are decomposed in time and frequency. To better understand how power is apportioned among these structures, a discrete Coiflet wavelet is used to decompose the pressure data into orthogonal frequency bands. Results indicate that some structures persist a great deal longer in the TBL than would be expected. These structure contain significant power and may be a primary source of vibration energy in the airframe.

Palumbo, Dan; Chabalko, Chris

2005-01-01

25

Origin of voltage decay in high-capacity layered oxide electrodes  

NASA Astrophysics Data System (ADS)

Although Li-rich layered oxides (Li1+xNiyCozMn1?x?y?zO2 > 250 mAh g?1) are attractive electrode materials providing energy densities more than 15% higher than today’s commercial Li-ion cells, they suffer from voltage decay on cycling. To elucidate the origin of this phenomenon, we employ chemical substitution in structurally related Li2RuO3 compounds. Li-rich layered Li2Ru1?yTiyO3 phases with capacities of ~240 mAh g?1 exhibit the characteristic voltage decay on cycling. A combination of transmission electron microscopy and X-ray photoelectron spectroscopy studies reveals that the migration of cations between metal layers and Li layers is an intrinsic feature of the charge–discharge process that increases the trapping of metal ions in interstitial tetrahedral sites. A correlation between these trapped ions and the voltage decay is established by expanding the study to both Li2Ru1?ySnyO3 and Li2RuO3; the slowest decay occurs for the cations with the largest ionic radii. This effect is robust, and the finding provides insights into new chemistry to be explored for developing high-capacity layered electrodes that evade voltage decay.

Sathiya, M.; Abakumov, A. M.; Foix, D.; Rousse, G.; Ramesha, K.; Saubanère, M.; Doublet, M. L.; Vezin, H.; Laisa, C. P.; Prakash, A. S.; Gonbeau, D.; Vantendeloo, G.; Tarascon, J.-M.

2015-02-01

26

Plane mixing layer vortical structure kinematics  

NASA Technical Reports Server (NTRS)

The objective of the current project was to experimentally investigate the structure and dynamics of the streamwise vorticity in a plane mixing layer. The first part of this research program was intended to clarify whether the observed decrease in mean streamwise vorticity in the far-field of mixing layers is due primarily to the 'smearing' caused by vortex meander or to diffusion. Two-point velocity correlation measurements have been used to show that there is little spanwise meander of the large-scale streamwise vortical structure. The correlation measurements also indicate a large degree of transverse meander of the streamwise vorticity which is not surprising since the streamwise vorticity exists in the inclined braid region between the spanwise vortex core regions. The streamwise convection of the braid region thereby introduces an apparent transverse meander into measurements using stationary probes. These results corroborated with estimated secondary velocity profiles in which the streamwise vorticity produces a signature which was tracked in time.

Leboeuf, Richard L.

1993-01-01

27

Ion transport and structure of layer-by-layer assemblies  

E-print Network

Layer-by-layer (LbL) films of various architectures were examined as potential solid state electrolytes for electrochemical systems (e.g. batteries and fuel cells). The relationship between materials properties and ion ...

Lutkenhaus, Jodie Lee

2007-01-01

28

Phase decorrelation of coherent structures in a free shear layer  

NASA Technical Reports Server (NTRS)

The vortices near the origin of an initially laminar mixing layer have a single frequency with a well-defined phase; i.e., there is little phase jitter. Further downstream, however, the phase jitter increases suddenly. Even when the flow is forced, this same transition is observed. The forcing partially loses its influence because of the decorrelation of the phase between the forcing signal and the passing coherent structures. In the present investigation, this phenomenon is documented and the physical mechanism responsible for the phase decorrelation is identified.

Ho, Chih-Ming; Zohar, Yitshak; Foss, Judith K.; Buell, Jeffrey C.

1991-01-01

29

Structural origin of light emission in germanium quantum dots  

NASA Astrophysics Data System (ADS)

We used a combination of optically-detected x-ray absorption spectroscopy with molecular dynamics simulations to explore the origins of light emission in small (5 nm to 9 nm) Ge nanoparticles. Two sets of nanoparticles were studied, with oxygen and hydrogen terminated surfaces. We show that optically-detected x-ray absorption spectroscopy shows sufficient sensitivity to reveal the different origins of light emission in these two sets of samples. We found that in oxygen terminated nanoparticles its the oxide-rich regions that are responsible for the light emission. In hydrogen terminated nanoparticles we established that structurally disordered Ge regions contribute to the luminescence. Using a combination of molecular dynamics simulations and optically-detected x-ray absorption spectroscopy we show that these disordered regions correspond to the disordered layer a few Å thick at the surface of the simulated nanoparticle.

Little, W.; Karatutlu, A.; Bolmatov, D.; Trachenko, K.; Sapelkin, A. V.; Cibin, G.; Taylor, R.; Mosselmans, F.; Dent, A. J.; Mountjoy, G.

2014-12-01

30

Structure of the Azotobacter vinelandii surface layer.  

PubMed Central

Electron microscopy of the Azotobacter vinelandii tetragonal surface array, negatively stained with ammonium molybdate in the presence of 1 mM calcium chloride, showed an apparent repeat frequency of 12 to 13 nm. Image processing showed dominant tetrad units alternating with low-contrast cruciform structures formed at the junction of slender linkers extending from corner macromolecules of four adjoining dominant units. The actual unit cell showed p4 symmetry, and a = b = 18.4 nm. Distilled water extraction of the surface array released a multimeric form of the single 60,000 molecular-weight protein (S protein) which constitutes the surface layer. The molecular weight of the multimer was estimated at 255,000 by gel filtration, indicating a tetrameric structure of four identical subunits and suggesting that this multimer was the morphological subunit of the S layer. Tetrameric S protein exhibited low intrinsic stability once released from the outer membrane, dissociating into monomers when incubated in a variety of buffers including those which served as the base for defined media used to cultivate A. vinelandii. The tetramer could not be stabilized in these buffers at any temperature between 4 and 30 degrees C, but the addition of 2 to 5 mM Ca2+ or Mg2+ completely prevented its dissociation into monomers. Circular dichroism measurements indicated that the secondary structure of the tetramer was dominated by aperiodic and beta-sheet conformations, and the addition of Ca2+ did not produce any gross changes in this structure. Only the tetrameric form of S protein was able to reassemble in vitro in the presence of divalent cations onto the surface of cells stripped of their native S layer. Images PMID:3804978

Bingle, W H; Whippey, P W; Doran, J L; Murray, R G; Page, W J

1987-01-01

31

Structure and origin of cometary nuclei  

NASA Technical Reports Server (NTRS)

There is strong evidence that a comet nucleus consists of a single object whose basic structure is Whipple's icy conglomerate. A number of cometary phenomena indicate that the nucleus is a low density, fragile object with a large degree of radial uniformity in structure and composition. Details of the ice-dust pattern are more uncertain. A working model is proposed which is based on theories of accumulation of larger objects from grains. This nucleus is a distorted spherical aggregate of a hierarchy of ice-dust cometesimals. These cometesimals retain some separate identity which lead to comet fragmentation when larger components break off. The outer layers of new comets were modified by cosmic ray irradiation in the Oort Cloud. The evidence for meteorite-comet association is steill controversial. Current dynamical studies do not seem to require a cometary source of meteorites.

Donn, B.; Rahe, J.

1981-01-01

32

Deep subwavelength plasmonic waveguide switch in double graphene layer structure  

E-print Network

Deep subwavelength plasmonic waveguide switch in double graphene layer structure Hideo Iizuka in double graphene layer structure Hideo Iizuka1,a) and Shanhui Fan2,b) 1 Toyota Central Research that in a deep subwavelength double graphene layer structure, graphene plasmons can be routed between two

Fan, Shanhui

33

Layered graphene structure of a hexagonal carbon  

NASA Astrophysics Data System (ADS)

Experiments show that there is a novel hexagonal carbon polymorph restricted to the space group of P-62c, but the detailed atomic structure is not determined. Here we set carbon atoms occupying P-62c 4f or P-62c 2c and 2d Wyckoff positions, and calculate the total energy of the different cell structures changing the internal parameter by first-principles calculations, which demonstrates that the stable structures in energy (at local minima) are hexagonal carbon (P-62c 2c and 2d) and hexagonal diamond (P-62c 4f, z=1/16). The calculated bulk modulus 437±16 GPa and interlayer distance 2.062 Å of the layered graphene structure P-62c 2c and 2d are in good agreement with those of the proposed new carbon, which indicates that P-62c 2c and 2d is a possible precursor or intermediate hard phase during the structural transformation of carbon.

Zhang, Bin

2013-06-01

34

Three layers of skyrmions in the magnetic triple-layer structure without the Dzyaloshinsky-Moriya interaction  

NASA Astrophysics Data System (ADS)

The skyrmionic state is an exciting realm of study and the skyrmions are being explored as the promising candidates of information carriers. In most systems, the skyrmions originate from the Dzyaloshinsky-Moriya interaction (DMI). However, in this work, it is demonstrated that in the triple-layer CoPt/Co/CoPt structure, the skyrmion-like state can be formed not only in the CoPt layers but also in the middle Co layer, without DMI. In this new structure, the skyrmion-like state in Co layer can exist in a large CoPt thickness range with thick Co. It can be very stable even against the external field from -500 to 200 mT along Z axis. The skyrmion number (S) in Co (SCo) can be as large as 0.9. These advanced properties make it high application potential for the future information-processing and storage devices.

Xie, Kaixuan; Sang, Hai

2014-12-01

35

Original article Tree canopy and herb layer transpiration in three Scots  

E-print Network

Original article Tree canopy and herb layer transpiration in three Scots pine stands with different-eastern Germany, we measured tree canopy and herb layer transpiration in three stands. Parameters of tree rate per needle area and tree canopy transpiration were least at the site dominated by the tall grass

Paris-Sud XI, Université de

36

Smectic Layer Structures in Complex Geometries—Modelling Complex Layer Structures in Smectic Liquid Crystals  

Microsoft Academic Search

In order to understand the operation of liquid crystal devices based on tilted smectic materials it is highly important to also understand the formation of the smectic liquid crystal layer structures. However, in many situations this is not easy to do. It is well established that in devices filled with materials that have an upper lying SmA phase a “chevron”

Steve J. Elston; Lesley A. Parry-Jones

2005-01-01

37

Structure of the surface layer of the methanogenic archaean Methanosarcina acetivorans  

SciTech Connect

Archaea have a self-assembling proteinaceous surface (S-) layer as the primary and outermost boundary of their cell envelopes. The S-layer maintains structural rigidity, protects the organism from adverse environmental elements, and yet provides access to all essential nutrients. We have determined the crystal structure of one of the two 'homologous' tandem polypeptide repeats that comprise the Methanosarcina acetivorans S-layer protein and propose a high-resolution model for a microbial S-layer. The molecular features of our hexameric S-layer model recapitulate those visualized by medium resolution electron microscopy studies of microbial S-layers and greatly expand our molecular view of S-layer dimensions, porosity, and symmetry. The S-layer model reveals a negatively charged molecular sieve that presents both a charge and size barrier to restrict access to the cell periplasmic-like space. The {beta}-sandwich folds of the S-layer protein are structurally homologous to eukaryotic virus envelope proteins, suggesting that Archaea and viruses have arrived at a common solution for protective envelope structures. These results provide insight into the evolutionary origins of primitive cell envelope structures, of which the S-layer is considered to be among the most primitive: it also provides a platform for the development of self-assembling nanomaterials with diverse functional and structural properties.

Arbing, Mark A.; Chan, Sum; Shin, Annie; Phan, Tung; Ahn, Christine J.; Rohlin, Lars; Gunsalus, Robert P. (UCLA)

2012-09-05

38

Are there double layers in solar coronal transition region that accelerate ions originating solar wind?  

NASA Astrophysics Data System (ADS)

Drawing from the physics of laser plasma expansion, laboratory experiments, magnetospheric observations on double layers (DLs), theory and simulations, we suggest that solar coronal transition region may contain randomly distributed numerous patches of double layers, which accelerate the ions from the upper chromosphere into the low corona. We expect the DLs to be distributed in a vertically thin layer while horizontally they are distributed widely. Such DLs provide a novel mechanism for the origin of the solar wind. The DL-based mechanism is based on expansion of dense cold chromospheric plasma consisting of cold ions, cold electrons with temperature Tc and a minor hot electron population with temperature Teh. Such plasma expansion naturally involves electric double layers, which are thin structures with vertical widths L much less than, say, about 100 plasma Debye lengths d. We envision that such double layers form in the upper chromosphere where charged particles collisions with neutral particles become rare at heights h > 1500 km above the photosphere and where ion-electron collision mean-free-path length S > L~ 10d. Such DLs are likely to form in magnetic flux tubes (coronal funnels) undergoing magnetic reconnection with magnetic fields in the chromospheric magnetic networks. Such reconnections produce the prerequisite hot electron population in the flux tube. The apparent vertical width of the coronal transition region (CTR) of the order of a few hundred kilometers is the consequence of the DLs vertically displaced in the plasma volume where the condition S > L ~ 10d is met. Since the magnetic reconnection and the DLs are dynamically evolving events, the CTR must be a highly dynamic region giving the observed zigzag boundary. The existence of the DLs in the CTR can be inferred from the outflow of ions from the chromosphere as beams, consisting of heavy and light ions, having the same energy before they are affected by other plasma processes and the solar gravity. The CTR double layers are analogous to the terrestrial auroral double layers that form at the zigzag transition between the dense ionospheric cold plasma and the hot plasma in the auroral density cavities. In the latter case, the hot electrons in the ionosphere result from backscattered hot electrons mirroring in the Earth's magnetic field. The mirroring of hot coronal electrons penetrating into the chromosphere may provide an additional source of the minor hot electron population in the upper chromosphere, in addition to the reconnection.

Singh, N.

2013-12-01

39

Origin of the outer layer of martian low-aspect ratio layered ejecta craters  

NASA Astrophysics Data System (ADS)

Low-aspect ratio layered ejecta (LARLE) craters are one of the most enigmatic types of martian layered ejecta craters. We propose that the extensive outer layer of these craters is produced through the same base surge mechanism as that which produced the base surge deposits generated by near-surface, buried nuclear and high-explosive detonations. However, the LARLE layers have higher aspect ratios compared with base surge deposits from explosion craters, a result of differences in thicknesses of these layers. This characteristics is probably caused by the addition of large amounts of small particles of dust and ice derived from climate-related mantles of snow, ice and dust in the areas where LARLE craters form. These deposits are likely to be quickly stabilized (order of a few days to a few years) from eolian erosion by formation of duricrust produced by diffusion of water vapor out of the deposits.

Boyce, Joseph M.; Wilson, Lionel; Barlow, Nadine G.

2015-01-01

40

Titan's planetary boundary layer structure at the Huygens landing site  

Microsoft Academic Search

Huygens Atmospheric Structure Instrument (HASI) for the first time performed an in situ measurement of the thermal structure in Titan's atmosphere with a vertical resolution sufficient to analyze the planetary boundary layer (PBL). The vertical potential temperature profile reveals the presence of a weakly convective PBL, with a surface layer thickness of 10 m and an outer layer with a

Tetsuya Tokano; Francesca Ferri; Giacomo Colombatti; Teemu Mäkinen; Marcello Fulchignoni

2006-01-01

41

Electroluminescence in organic films with three-layer structure  

NASA Astrophysics Data System (ADS)

A stable organic electroluminescent (EL) device was successfully fabricated with a three-layer structure consisting of hole transport layer/emitting layer/electron transport layer. The EL device was prepared by vacuum evaporation. Efficient carrier double injection into the emitting layer was realized by the use of separate hole and electron transport layers. Bright EL emission was observed in a darkened room at the dc bias voltage of 50 V. Stable emission lasted for more than five hours at this condition. The emission spectrum could be changed with variation of the organic material for the emitting layer.

Adachi, Chihaya; Tokito, Shizuo; Tsutsui, Tetsuo; Saito, Shogo

1988-02-01

42

Origins of microspherules from the Permian-Triassic boundary event layers in South China  

NASA Astrophysics Data System (ADS)

Volcanism and impact scenarios are two of the most plausible ways of interpreting the causes of the largest biological mass extinction at the end-Permian. Microspherules have previously been widely reported from tens of different Permian-Triassic boundary (PTB) sections in South China and some other regions. These microspherules have been interpreted as either the product of volcanic eruptions or an impact event. In order to test these scenarios, we collected 60 samples from 12 intensively-studied PTB sections in South China. In addition, four soil samples close to these PTB layers were also collected for comparison. Our investigation indicates that abundant microspherules with mosaic or dot shape crystals on rounded surface are present in the surface samples in the PTB layers at Meishan, Meili, and Shatian sections and most soil background samples in South China. Those microspherules consist of four different types based on their main chemical composition, surface features, and internal structure including iron, magnetite-silicate, glassy, pyrite microspherules and framboids. In contrast, microspherules have not been found in a few sections in remote areas such as the Selong Xishan section in Tibet and the Dalongkou section in Xinjiang, Northwest China, in the deeply-excavated samples at the Shangsi section and the hard tuff layers around the PTB at the Xiaochehe Section in Guiyang. Microspherules decrease in abundance with depth in PTB clay beds. All these microspherules except the pyrite microspherules and framboids are found in both the PTB layers and the nearby soil background samples. The iron microspherules are pure iron oxides such as magnetite, hematite or maghemite and contain low concentrations of nickel and chromium, and lack an Ni-Fe core and general extraterrestrial mineral wüstite. All these external and chemical characteristics suggest that most of iron microspherules previously reported from PTB sections in South China are modern industrial fly ashes. A low ratio of Fe3 +/FeTotal in crystals of magnetite-silicate microspherules and high ZnO contents can identify them as industrial contaminants. The pyrite microspherules and framboidal pyrite found from bed 24e and bed 26 at the Meishan sections are of depositional or/and diagenetic origins, and only the rounded quartz and the fragments containing extremely high SiO2 and TiO2 are possibly of volcanic origin.

Zhang, Hua; Shen, Shu-zhong; Cao, Chang-qun; Zheng, Quan-feng

2014-09-01

43

What is the Age and Origin of the Spherule Bearing Layer in some Ross Sea Cores?  

NASA Astrophysics Data System (ADS)

L.P. Khyranina (1985) was the first to suggest that there were two structures present on the Antarctic continental shelf beneath the Ross Sea. One was the ~100 km Bowers impact crater candidate. However, there was no solid evidence that proved an extraterrestrial impact produced the Bowers structure. Debate has ensued for decades on whether the Bowers structure was an impact crater. Now we have come close to finding an answer. We used core samples taken near the crater and sieved into four size fractions (>250,>125,>63,>38 ?m). Impact ejecta candidates were then picked from cores ELT 32-08, ELT 32-03, ELT 32-43, ELT 32-06, DSDP 273, DSDP 274, and NPB 95-01 39KC and were analyzed for chemical composition and physical features. All but DSDP site 274 contain pure SiO2 glasses that resemble tektites. We also found candidates for flow textured impact glass and shocked quartz. This led us to conclude that the origin of the spherule-bearing layer was from an impact. With the use of dated core NBP 95-01 39KC, we have constrained the age to lie between 7,305±80 BP and 11,150±95 BP (corrected radiocarbon ages) (Cunningham et al., 1999).

Yeh, C.; Abbott, D. H.; Anders, M. H.; Breger, D.

2012-12-01

44

1. Building #3, original structure and first addition, north side, ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. Building #3, original structure and first addition, north side, looking south. Photo shows (from left) the original 1911 structure, the 1939 infill addition, and the 1934 structure. - S. W. Shattuck Chemical Company, Incorporated, Building No. 3, 1805 South Bannock Street, Denver, Denver County, CO

45

The nature and origin of lateral composition modulations in short-period strained-layer superlattices  

SciTech Connect

The nature and origin of lateral composition modulations in (AlAs){sub m}(InAs){sub n} SPSs grown by MBE on InP substrates have been investigated by XRD, AFM, and TEM. Strong modulations were observed for growth temperatures between {approx} 540 and 560 C. The maximum strength of modulations was found for SPS samples with InAs mole fraction x (=n/(n+m)) close to {approx} 0.50 and when n {approx} m {approx} 2. The modulations were suppressed at both high and low values of x. For x >0.52 (global compression) the modulations were along the <100> directions in the (001) growth plane. For x < 0.52 (global tension) the modulations were along the two <310> directions rotated {approx} {+-} 27{degree} from [110] in the growth plane. The remarkably constant wavelength of the modulations, between {approx} 20--30 nm, and the different modulation directions observed, suggest that the origin of the modulations is due to surface roughening associated with the high misfit between the individual SPS layers and the InP substrate. Highly uniform unidirectional modulations have been grown, by control of the InAs mole fraction and growth on suitably offcut substrates, which show great promise for application in device structures.

NORMAN,A.G.; AHRENKIEL,S.P.; MOUTINHO,H.R.; BALLIF,C.; ALJASSIM,M.M.; MASCARENHAS,A.; FOLLSTAEDT,DAVID M.; LEE,STEPHEN R.; RENO,JOHN L.; JONES,ERIC D.; MIRECKI-MILLUNCHICK,J.; TWESTEN,R.D.

2000-01-27

46

Theoretical study on SAW characteristics of layered structures including a diamond layer  

Microsoft Academic Search

Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus can provide much advantage for fabrication of high frequency SAW devices when it is combined with a piezoelectric thin film. Basic SAW properties of layered structures consisting of a piezoelectric material layer, a diamond layer and a substrate were examined by theoretical calculation. Rayleigh mode SAW's

Hideaki Nakahata; Akihiro Hachigo; Kenjiro Higaki; Satoshi Fujii; Shin-ichi Shikata; Naoji Fujimori

1995-01-01

47

Boron-Based Layered Structures for Energy Storage  

SciTech Connect

Based on Density Functional Theory simulations, we have studied the boron-based graphite-like materials, i.e., LiBC and MgB2 for energy storage. First, when half of the Li-ions in the LiBC are removed, the BC layered structure is still preserved. The Li intercalation potential (equilibrium lithium-insertion voltage of 2.3-2.4 V relative to lithium metal) is significantly higher than that in graphite, allowing Li0.5BC to function as a cathode material. The reversible electrochemical reaction, LiBC = Li0.5BC + 0.5Li, enables a specific energy density of 1088 Wh/kg and a volumetric energy density of 2463 Wh/L. Second, 75% of the Mg ions in MgB2 can be removed and reversibly inserted with the layered boron structures being preserved through an in-plane topological transformation between the hexagonal lattice domains and triangular domains. The mechanism of such a charge-driven transformation originates from the versatile valence state of boron in its planar form.

Zhao, Y.; Wei, S. H.

2012-01-01

48

Shear-layer structures in near-wall turbulence  

NASA Technical Reports Server (NTRS)

The structure of internal shear layer observed in the near-wall region of turbulent flows is investigated by analyzing flow fields obtained from numerical simulations of channel and boundary-layer flows. It is found that the shear layer is an important contributor to the turbulence production. The conditionally averaged production at the center of the structure was almost twice as large as the long-time mean value. The shear-layer structure is also found to retain its coherence over streamwise distances on the order of a thousand viscous length units, and propagates with a constant velocity of about 10.6 u sub rho throughout the near wall region.

Johansson, A. V.; Alfredsson, P. H.; Kim, J.

1987-01-01

49

Electroluminescent apparatus having a structured luminescence conversion layer  

DOEpatents

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

Krummacher, Benjamin Claus (Sunnyvale, CA)

2008-09-02

50

Structure and morphology of submarine slab slides: clues to origin and behavior  

USGS Publications Warehouse

Geologic features suggest that some slab slides probably result from long-term strength degradation of weak layers deep in the homoclinal section. Time-dependent strain in clay-rich layers can create potential slide surfaces of low frictional strength. Competent layers are weak in tension and probably fragment in the first instance of, or even prior to, translation, and the allochthonous mass is readily transformed into a high-momentum debris flow. The structure and geomorphology of slab slides provide important clues to their origin and behavior. -from Author

O'Leary, D. W.

1991-01-01

51

Composite S-layer lipid structures  

PubMed Central

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

Schuster, Bernhard; Sleytr, Uwe B.

2010-01-01

52

Origin of chromitite layers in the Muskox intrusion and other stratiform intrusions: A new interpretation  

Microsoft Academic Search

A mechanism of origin for chromitite layers in stratiform intrusions is described, based on the same physicochemical principles as an earlier explanation but formulated in a geologically very different way. By this new mechanism, the concentrated chromite is precipitated from chromite-saturated picritic tholeiite liquid when this liquid is blended with earlier liquid of the same type that has differentiated to

T. N. Irvine

1977-01-01

53

Origin of ferromagnetism enhancement in bi-layer chromium-doped indium zinc oxides  

SciTech Connect

This work demonstrates that by controlling the rapid thermal annealing temperature, amorphous chromium-doped indium zinc oxide films develop an amorphous-crystalline bi-layer structure and show magnetization up to {approx}30 emu/cm{sup 3}. The crystalline layer arises from significant out-diffusion of Zn from surfaces, leading to a large difference in the Zn:In ratio in amorphous and crystalline layers. Doped Cr ions in amorphous and crystalline layers form different valence configurations, creating a charge reservoir which transfers electrons through amorphous-crystalline interfaces and in turn enhances ferromagnetism.

Hsu, C. Y. [Physics Department, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China)

2012-08-06

54

Mars: New evidence for origin of some Valles Marineris layered deposits  

NASA Technical Reports Server (NTRS)

The discovery of layered deposits in the walls of a deep trough in Lunae Planum has implications for the origin of similar-appearing deposits in some canyons of Valles Marineris. Although layering is visible in the competent, cliff-forming upper walls of the canyons, the dissimilarity in appearance between canyon walls and soft rounded hills of layered deposits on canyon floors, as well as their contrasting patterns of erosion, has been considered strong evidence that their modes of origin were different. Most workers agree that the wall rocks are volcanic flows derived from fissure vents and other volcanic sources in the region. However, several hypotheses have been advanced to account for the softer-appearing stratified floor deposits. Chief among them is the proposal that the floor deposits are waterlaid sediments that accumulated in large lakes within the canyons and include materials eroded from canyon walls, eolian deposits, and subaqueous volcanic eruptives.

Scott, David H.

1993-01-01

55

Hybrid inorganic–organic superlattice structures with atomic layer deposition/molecular layer deposition  

SciTech Connect

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.

Tynell, Tommi; Yamauchi, Hisao; Karppinen, Maarit, E-mail: maarit.karppinen@aalto.fi [Department of Chemistry, Aalto University, FI-00076 Aalto (Finland)

2014-01-15

56

Failure modes and materials design for biomechanical layer structures  

NASA Astrophysics Data System (ADS)

Ceramic materials are finding increasing usage in the area of biomechanical replacements---dental crowns, hip and bone implants, etc.---where strength, wear resistance, biocompatibility, chemical durability and even aesthetics are critical issues. Aesthetic ceramic crowns have been widely used in dentistry to replace damaged or missing teeth. However, the failure rates of ceramic crowns, especially all-ceramic crowns, can be 1%˜6% per year, which is not satisfactory to patients. The materials limitations and underlying fracture mechanisms of these prostheses are not well understood. In this thesis, fundamental fracture and damage mechanisms in model dental bilayer and trilayer structures are studied. Principle failure modes are identified from in situ experimentation and confirmed by fracture mechanics analysis. In bilayer structures of ceramic/polycarbonate (representative of ceramic crown/dentin structure), three major damage sources are identified: (i) top-surface cone cracks or (ii) quasiplasticity, dominating in thick ceramic bilayers; (iii) bottom-surface radial cracks, dominating in thin ceramic bilayers. Critical load P for each damage mode are measured in six dental ceramics: Y-TZP zirconia, glass-infiltrated zirconia and alumina (InCeram), glass-ceramic (Empress II), Porcelain (Mark II and Empress) bonded to polymer substrates, as a function of ceramic thickness d in the range of 100 mum to 10 mm. P is found independent of d for mode (i) and (ii), but has a d 2 relations for mode (iii)---bottom surface radial cracking. In trilayer structures of glass/core-ceramic/polycarbonate (representing veneer porcelain/core/dentin structures), three inner fracture origins are identified: radial cracks from the bottom surface in the (i) first and (ii) second layers; and (iii) quasiplasticity in core-ceramic layer. The role of relative veneer/core thickness, d1/d 2 and materials properties is investigated for three core materials with different modulus (114--270GPa) and strength (400--1400MPa): Y-TZP zirconia, InCeram alumina and Empress II glass-ceramic. Explicit relations for the critical loads P to produce these different damage modes in bilayer and trilayer structures are developed in terms of basic material properties (modulus E, strength, hardness H and toughness T) and geometrical variables (thickness d and contact sphere radius r). These experimentally validated relations are used to design of optimal material combinations for improved fracture resistance and to predict mechanical performance of current dental materials.

Deng, Yan

57

Geochemical evidence for an impact origin for a Late Archean spherule layer, Transvaal Supergroup, South Africa  

NASA Astrophysics Data System (ADS)

A Late Archean layer rich in sand-sized spherules of former silicate melt in the Monteville Formation (Transvaal Supergroup, South Africa) has Ir concentrations as high as 6.4 ppb and is clearly enriched in Ir relative to associated tuffs, carbonates, and shales. The Monteville spherule layer is also enriched in other siderophile elements, including the platinum group elements (PGEs). The PGEs in the spherule layer produce a flat (meteorite like) pattern when they are normalized to chondritic abundances. The abundances of Ir and other siderophile elements are similar to broadly contemporaneous spherule layers in the Hamersley basin of Western Australia. That the mineral compositions, textures, and sedimentary structures of the spherule layers in the Transvaal Supergroup and Hamersley basin are also very similar suggests that they were all formed by the same processes. We think that the best way to explain the high Ir concentrations and other characteristics of the Monteville spherule layer is that it represents distal impact ejecta. There are, however, significant differences between the Monteville spherule layer and Early Archean spherule layers in the Barberton greenstone belt, including much higher average and maximum concentrations of Ir in the latter. The data presented here clearly show that each Precambrian spherule layer is unique and needs to be characterized individually, as is true for the impact spherule layers of the Phanerozoic.

Simonson, Bruce M.; Koeberl, Christian; McDonald, Iain; Reimold, Wolf Uwe

2000-12-01

58

Quantum-mechanical modeling of accumulation layers in MOS structure  

Microsoft Academic Search

An original method is used for the quantum-mechanical modeling of n-type silicon accumulation layers. Unlike previous methods, which were only valid near 4.2 K, the approach is valid up to room temperature and beyond. The self-consistent results obtained are compared with those of the standard classical model for the accumulation layer, and the differences between them are found to be

J. Sune; P. Olivo; B. Ricco

1992-01-01

59

Origin and Structure of Dynamic Cooperative Networks  

PubMed Central

Societies are built on social interactions among individuals. Cooperation represents the simplest form of a social interaction: one individual provides a benefit to another one at a cost to itself. Social networks represent a dynamical abstraction of social interactions in a society. The behaviour of an individual towards others and of others towards the individual shape the individual's neighbourhood and hence the local structure of the social network. Here we propose a simple theoretical framework to model dynamic social networks by focussing on each individual's actions instead of interactions between individuals. This eliminates the traditional dichotomy between the strategy of individuals and the structure of the population and easily complements empirical studies. As a consequence, altruists, egoists and fair types are naturally determined by the local social structures, while globally egalitarian networks or stratified structures arise. Cooperative interactions drive the emergence and shape the structure of social networks. PMID:25030202

Wardil, Lucas; Hauert, Christoph

2014-01-01

60

Origin and Structure of Dynamic Cooperative Networks  

NASA Astrophysics Data System (ADS)

Societies are built on social interactions among individuals. Cooperation represents the simplest form of a social interaction: one individual provides a benefit to another one at a cost to itself. Social networks represent a dynamical abstraction of social interactions in a society. The behaviour of an individual towards others and of others towards the individual shape the individual's neighbourhood and hence the local structure of the social network. Here we propose a simple theoretical framework to model dynamic social networks by focussing on each individual's actions instead of interactions between individuals. This eliminates the traditional dichotomy between the strategy of individuals and the structure of the population and easily complements empirical studies. As a consequence, altruists, egoists and fair types are naturally determined by the local social structures, while globally egalitarian networks or stratified structures arise. Cooperative interactions drive the emergence and shape the structure of social networks.

Wardil, Lucas; Hauert, Christoph

2014-07-01

61

Elastodynamic behavior of the three dimensional layer-by-layer metamaterial structure  

NASA Astrophysics Data System (ADS)

In this work, we numerically investigate for the first time the elastodynamic behavior of a three dimensional layer-by-layer rod structure, which is easy to fabricate and has already proved to be very efficient as a photonic crystal. The Finite Difference Time Domain method was used for the numerical calculations. For the rods, several materials were examined and the effects of all the geometric parameters of the structure were also numerically investigated. Additionally, two modifications of the structure were included in our calculations. The results obtained here (for certain geometric parameters), exhibiting a high ratio of longitudinal over transverse sound velocity and therefore a close approach to ideal pentamode behavior over a frequency range, clearly show that the layer-by-layer rod structure, besides being an efficient photonic crystal, is a very serious contender as an elastodynamic metamaterial.

Aravantinos-Zafiris, N.; Sigalas, M. M.; Economou, E. N.

2014-10-01

62

Elastodynamic behavior of the three dimensional layer-by-layer metamaterial structure  

SciTech Connect

In this work, we numerically investigate for the first time the elastodynamic behavior of a three dimensional layer-by-layer rod structure, which is easy to fabricate and has already proved to be very efficient as a photonic crystal. The Finite Difference Time Domain method was used for the numerical calculations. For the rods, several materials were examined and the effects of all the geometric parameters of the structure were also numerically investigated. Additionally, two modifications of the structure were included in our calculations. The results obtained here (for certain geometric parameters), exhibiting a high ratio of longitudinal over transverse sound velocity and therefore a close approach to ideal pentamode behavior over a frequency range, clearly show that the layer-by-layer rod structure, besides being an efficient photonic crystal, is a very serious contender as an elastodynamic metamaterial.

Aravantinos-Zafiris, N.; Sigalas, M. M. [Department of Materials Science, University of Patras, 26504 Patras (Greece); Economou, E. N. [Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology—Hellas (FORTH), P.O. Box 1385, Heraklion GR-71110, Greece and Department of Physics, University of Crete, Heraklion GR-71003 (Greece)

2014-10-07

63

Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange  

Microsoft Academic Search

The electrical resistivity of Fe-Cr-Fe layers with antiferromagnetic interlayer exchange increases when the magnetizations of the Fe layers are aligned antiparallel. The effect is much stronger than the usual anisotropic magnetoresistance and further increases in structures with more than two Fe layers. It can be explained in terms of spin-flip scattering of conduction electrons caused by the antiparallel alignment of

G. Binasch; P. Grünberg; F. Saurenbach; W. Zinn

1989-01-01

64

Original Article Using Structured Decision Making to  

E-print Network

pneumonia in bighorn sheep (Ovis canadensis) as a case study for our approach, applying it to 2 populations, Ovis canadensis, proactive management, structured decision-making. Infectious diseases in wildlife

Mitchell, Mike

65

ORIGINAL PAPER Structural characteristics of rootfungus associations  

E-print Network

. (Duddridge and Read 1982; Dexheimer and Gérard 1993), Monotropa uniflora L. (Lutz and Sjolund 1973 and Massicotte 2004; Bidartondo 2005). Detailed structural studies have only involved Monotropa hypopitys L

Massicotte, Hugues

66

ORIGINAL PAPER Population genetic structure of the European kestrel  

E-print Network

ORIGINAL PAPER Population genetic structure of the European kestrel Falco tinnunculus in Central and population genetic structure (Rubin et al. 2001; Wood and Pullin 2002). These studies demonstrated September 2009 # Springer-Verlag 2009 Abstract We analysed the genetic structure of the European kestrel

Paris-Sud XI, Université de

67

Origin and evolution of the layered deposits in the Valles Marineris, Mars  

NASA Astrophysics Data System (ADS)

Four hypotheses are discussed concerning the origin of the layered deposits in the Martian Valles Marineris, whose individual thicknesses range from about 70 to 300 m. The hypothesized processes are: (1) aeolian deposition; (2) deposition of remnants of the material constituting the canyon walls; (3) deposition of volcanic eruptions; and (4) deposition in standing bodies of water. The last process is chosen as most consistent with the rhythm and lateral continuity of the layers, as well as their great thickness and stratigraphic relationship with other units in the canyons. Attention is given to ways in which the sediments could have entered an ice-covered lake; several geologically feasible mechanisms are identified.

Nedell, S. S.; Squyres, S. W.; Andersen, D. W.

1987-06-01

68

Tuning delamination of layered covalent organic frameworks through structural design.  

PubMed

Exfoliation of a family of polyacetylenic porous layered covalent organic frameworks by means of a simple sonication procedure results in the obtention of nanolayer structures as observed by AFM and TEM measurements. Systematic AFM analysis of the isolated nanostructures reveals that the degree of exfoliation depends on the polymer architecture, thinner layers being observed when the pore size decreases. PMID:22774002

Berlanga, Isadora; Mas-Ballesté, Rubén; Zamora, Felix

2012-08-18

69

5. Building #3, original structure, second addition, and first addition ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

5. Building #3, original structure, second addition, and first addition (from right to left), south and east sides, looking northwest. - S. W. Shattuck Chemical Company, Incorporated, Building No. 3, 1805 South Bannock Street, Denver, Denver County, CO

70

83. LOOKING NORTHWEST AT INTERSECTION OF ORIGINAL STRUCTURE AND 1885 ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

83. LOOKING NORTHWEST AT INTERSECTION OF ORIGINAL STRUCTURE AND 1885 FARM SHOP ADDITION. ROOF PEAK IN BACKGROUND IS 1905 ELEVATOR ADDITION. - Gruber Wagon Works, Pennsylvania Route 183 & State Hill Road at Red Bridge Park, Bernville, Berks County, PA

71

1. GENERAL VIEW OF FACTORY SHOWING ORIGINAL STRUCTURE (MANSARD ROOFED ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. GENERAL VIEW OF FACTORY SHOWING ORIGINAL STRUCTURE (MANSARD ROOFED PORTION AT CENTER), SOUTH ADDITION (LEFT) AND NORTH ADDITION (RIGHT). - Silver Lake Cordage Company, 308 Nevada Street, Newton, Middlesex County, MA

72

ORIGINAL PAPER Canopy structure analysis for estimating forest regeneration  

E-print Network

ORIGINAL PAPER Canopy structure analysis for estimating forest regeneration dynamics and growth systems applied in Nothofagus pumilio forests are based on opening the canopy to stimulate natural. pumilio along different forest canopy and solar radiation gradients. & Materials and methods Regeneration

Boyer, Edmond

73

Shielding and Radiation Characteristics of Cylindrical Layered Bianisotropic Structures  

Microsoft Academic Search

In this paper we propose an analytical study in the spectral domain of cylindrical layered structures filled with general bianisotropic media and fed by a 3D electric source. The integrated structure is characterized in terms of transmission matrices leading to an equivalent circuit representation of the whole multilayered structure. Within the framework of this two-port formalism, we present a new

Lucio VEGNI; Alessandro TOSCANO

74

Adsorption of copolymers aggregates: from kinetics to adsorbed layer structure.  

PubMed

We examined the adsorption, on hydrophobic and hydrophilic surfaces, of 4 rake-type poly(dimethyl siloxane) (PDMS) copolymers varying the amount of poly(ethylene glycol) (PEG) graft arms from 41 to 72%. The copolymers formed large aggregates in solution, complicating their adsorption kinetics and layer structures. We found the adsorption process always to be dominated by the adsorption of large aggregates, with strongly bound layers resistant to rinsing in adsorbing buffer. Adsorbed amounts were nearly independent of the substrate. However, subtleties in the adsorption kinetics suggested different layer structures for the different systems. On hydrophilic silica, aggregates adsorbed at the transport limited rate until surface saturation, and associated interfacial structures were likely retained. On the hydrophobic surface, a subset of the copolymers exhibited retarded late stage adsorption kinetics suggestive of brush formation. This work demonstrates how subtle differences in adsorption kinetics provide insight into potential interfacial layer structures. PMID:18436230

Zdyrko, Bogdan; Ofir, Pazit Bar-Yosef; Alb, Alina M; Reed, Wayne F; Santore, Maria M

2008-06-15

75

ORIGINAL PAPER Functional insights from structural genomics  

E-print Network

, USA E. Pichersky Department of Molecular, Cellular and Developmental Biology, University of Michigan of protein sequence [3]. While many of these are for proteins with known biological/biochemical functions of these proteins are annotated as `hypothetical' in the sequence database. As structure is more conserved than

Pichersky, Eran

76

Elastic layer-structured metal organic frameworks (ELMs)  

Microsoft Academic Search

Elastic layer-structured metal organic frameworks (ELMs) having flexible two-dimensional structure show a gate phenomenon in sorption\\/desorption of simple gas molecules. The gate phenomenon is accompanied by expansion\\/shrinkage of the layers. The gas sorption\\/desorption is not based on a physical adsorption, but on a chemical reaction, which includes high cooperativity. The cooperative reaction could be analyzed thermodynamically. The gate phenomenon showed

Hirofumi Kanoh; Atsushi Kondo; Hiroshi Noguchi; Hiroshi Kajiro; Aya Tohdoh; Yoshiyuki Hattori; Wei-Chun Xu; Mamoru Inoue; Tsutomu Sugiura; Kazuhiro Morita; Hideki Tanaka; Tomonori Ohba; Katsumi Kaneko

2009-01-01

77

Photothermal characterization of solid two-layer spherical structures  

NASA Astrophysics Data System (ADS)

A theoretical model for evaluating 2-layer solid spherical samples that are heated by a modulated light is presented using the Green function method. The specific Green's function corresponding to the composite structure has been derived. The characteristics of the thermal-wave field with respect to the thermophysical properties of the material and the geometrical factors are presented. Experimental results obtained with laser infrared photothermal radiometry show the capability of the model for characterizing the spherical layered structures.

Xie, Guangxi; Chen, Zhifeng; Wang, Chinhua; Mandelis, Andreas

2010-03-01

78

Structural origins of morphing in plant tissues  

NASA Astrophysics Data System (ADS)

Plant tissues are able to generate complex movements via shape modifications. These effects are tightly related to distinctive multi-scale composite architectures of the plant material, and can therefore largely be interpreted by composite mechanics principles. Here, we propose a generic framework for the analysis and prediction of the shape morphing of intricate biological composite materials, arising from changes in humidity. We have examined in depth the hierarchical structures of three types of seed pods for which we propose a theoretical scheme that is able to accurately simulate the relevant shape deformations. The validity and generality of this approach are confirmed by means of laboratory scale synthetic models with similar architectures leading to equivalent morphing patterns. Such synthetic configurations could pave the way to future morphing architectures of advanced materials and structures.

Bar-On, Benny; Sui, Xiaomeng; Livanov, Konstantin; Achrai, Ben; Kalfon-Cohen, Estelle; Wiesel, Erica; Daniel Wagner, H.

2014-07-01

79

The Origin of Structures in Generalized Gravity  

E-print Network

In a class of generalized gravity theories with general couplings between the scalar field and the scalar curvature in the Lagrangian, we can describe the quantum generation and the classical evolution of both the scalar and tensor structures in a simple and unified manner. An accelerated expansion phase based on the generalized gravity in the early universe drives microscopic quantum fluctuations inside a causal domain to expand into macroscopic ripples in the spacetime metric on scales larger than the local horizon. Following their generation from quantum fluctuations, the ripples in the metric spend a long period outside the causal domain. During this phase their evolution is characterized by their conserved amplitudes. The evolution of these fluctuations may lead to the observed large scale structures of the universe and anisotropies in the cosmic microwave background radiation.

J. Hwang

1997-11-21

80

Metal diphosphonates with double-layer and pillared layered structures based on N-cyclohexylaminomethanediphosphonate  

SciTech Connect

Based on N-cyclohexylaminomethanediphosphonic acid (cmdpH{sub 4}), four new metal diphosphonate compounds with formula M{sub 3}(cmdpH){sub 2}(H{sub 2}O){sub 2} [M=Zn(1), Co(2)] and M{sub 2}(cmdpH{sub 2}){sub 2}(4,4'-bipy){sub 0.5}(H{sub 2}O) [M=Co(3), Mn(4)] have been obtained and structurally determined. Compounds 1 and 2 are isostructural. Within the structure, the M(2)O{sub 6} octahedra are each corner-shared with four PO{sub 3}C tetrahedra to form a single layer containing 3- and 7-member rings. Neighboring single layers are pillared by M(1)O{sub 4} tetrahedra, resulting in a novel double-layer structure. The organic moieties of cmdpH{sup 3-} are grafted on the two sides of the double layer. Compounds 3 and 4 are also isostructural, displaying a pillared layered structure. Within the inorganic layer, the M(1)O{sub 5} tetragonal pyramids and M(2)NO{sub 5} octahedra are each linked by PO{sub 3}C tetrahedra through corner-sharing, forming a layer in the ab plane which contains 3- and 10-member rings. These layers are pillared by 4,4'-bipyridine via coordination with the M(2) atoms from the adjacent layers, leading to a three-dimensional open framework structure with channels generated along the a-axis. The organic groups of cmdpH{sub 2}{sup 2-} locate within the channels. Magnetic studies show that antiferromagnetic interactions are dominant in compounds 2-4. Field dependent magnetization reveals a spin flop behavior for 2. - Graphical abstract: Based on N-cyclohexylaminomethanediphosphonate (cmdp{sup 4-}), compounds Zn{sub 3}(cmdpH){sub 2}(H{sub 2}O){sub 2} (1) and Co{sub 3}(cmdpH){sub 2}(H{sub 2}O){sub 2} (2) with a double-layer structure and compounds Co{sub 2}(cmdpH{sub 2}){sub 2}(4,4'-bipy){sub 0.5}(H{sub 2}O) (3) and Mn{sub 2}(cmdpH{sub 2}){sub 2}(4,4'-bipy){sub 0.5}(H{sub 2}O) (4) with a pillared layered structure are reported in this paper. Dominant antiferromagnetic interactions are found in compounds 2-4 and an interesting spin flop behavior is observed in 2.

Su Yanhui; Cao Dengke; Duan Yan; Li Yizhi [State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China); Zheng Limin, E-mail: lmzheng@nju.edu.c [State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China)

2010-07-15

81

Perturbation of the Heat Lateral Diffusion by Interface Resistance in Layered Structures  

NASA Astrophysics Data System (ADS)

It is well established that interface resistances do usually exist in layered structures, and their values strongly depend on their origin. They may arise from different vibrational properties of the layers, nonharmonic processes at the interface, surface chemical contamination, interfacial defects, etc. Numerous studies have been published to evaluate their values, most of the time, in a perpendicular heat diffusion scheme. In this paper, the effect of interface resistances on the lateral modulated surface temperature of a layered structure for cylindrical symmetry heat diffusion is studied. The thermoreflectance microscope is a particularly convenient tool to record heat lateral diffusion from a surface modulated heated point and thus to evidence the presence of such resistance interfaces. In a first part, the theoretical model of heat diffusion in cylindrical symmetry, in a layered structure exhibiting an interface resistance between the layer and the substrate, is briefly described. In a second part, the C/I configuration (good conductive layer deposited on an insulating substrate, with an interface resistance) is investigated. Experimental results illustrate the theory. In the third part, the reverse case I/C (insulating layer deposited on a conductive substrate, with an interface resistance) is discussed. To conclude, all the cases and the ability of the lateral diffusion to recover interface thermal resistances are compared.

Frétigny, C.; Duquesne, J.-Y.; Fournier, D.

2014-07-01

82

Layered Structures in Magmatic Systems From Double-Diffusive Convection  

NASA Astrophysics Data System (ADS)

The evolution of magmatic systems is often influenced by the existence of discrete layers. Such layering can not be explained by gravitational settling and other dynamical mechanisms have been proposed. Double-diffusive convection is considered to be such a mechanism. In the diffusive regime, where the slowly diffusing component (e,g composition) acts to stabilize the system and the fast diffusing component /e.g. heat) provides the destabilizing force, the formation of layers has been observed. Most studies. however, concentrated on the properties of layers and not on the actual formation. In a series of two- and three dimensional numerical experiments, we have investigated the evolution of layers from non-layered initial states. Layer formation is found to depend on the ratio of thermal to compositional diffusivities (the Lewis number). The influence of the Lewis number has been systematically investigated by employing a field approach to monitor the evolution of the composition. Magmatic systems have a very high Lewis number which can hardly be realized with such an approach. We have therefore developed a tracer method, allowing to study the system in the limit of an infinite Lewis number. With both methods we obtain qualitative similar layered structures. In order to better understand layer formation in magmatic systems, we have included effects of temperature-and compositionaly dependent viscosity. Our results show that the viscosity has a strong influence on the temporal evolution of the system and on the resulting type of layering

Hansen, U.; Schmalzl, J.

2004-05-01

83

Cocured damped layers in composite structure  

SciTech Connect

A study was made on the feasibility of laminating and cocuring graphite fiber-epoxy prepreg with plies of commercially available damping materials for form beams and hat-stiffened panels. Experiments showed that cocuring did not adversely affect the damping materials and that excellent structural damping properties could be obtained. The construction of the hat-stiffened panels proved that complex parts containing damping materials could be fabricated. Dynamic testing of these components showed that internal architectural features could be designed to promote damping in primary structure.

Rotz, C.A. (Brigham Young Univ., Provo, UT (United States)); Barrett, D.J. (Naval Air Development Center, Warminster, PA (United States))

1992-01-01

84

ORIGINAL PAPER Linking canopy images to forest structural parameters  

E-print Network

ORIGINAL PAPER Linking canopy images to forest structural parameters: potential of a modeling structure can be inverted from RS data, we propose a modeling framework allowing to produce forest canopy appears as a valuable component for developing inversion methods from canopy images and studying

Paris-Sud XI, Université de

85

ORIGINAL PAPER Impacts of tree canopy structure on wind flows  

E-print Network

ORIGINAL PAPER Impacts of tree canopy structure on wind flows and fire propagation simulated heterogeneous spatial patterns of vegetation. However, the impact of the canopy structure on both wind flows behavior model, HIGRAD/FIRETEC, was used to investigate the effects of canopy treatment on wind field

Paris-Sud XI, Université de

86

Structural Origins of Aminoglycoside Specificity for Prokaryotic Ribosomes  

E-print Network

Structural Origins of Aminoglycoside Specificity for Prokaryotic Ribosomes Stephen R. Lynch of a prokaryotic decoding region A-site oligonucleotide free in solution and bound to the aminogly- cosides to the prokaryotic A-site-paromomycin structure. A con- formational change in three adenosine residues of an internal

Puglisi, Joseph

87

Manipulation by exchange coupling in layered magnetic structures  

SciTech Connect

Exchange coupling in magnetic heterostructures can be modified via introduction of additional magnetic spacer layers at the interfaces. The magnetic characteristics and the spacer layer thickness determine the functional properties of the whole system. We show that the hysteresis loop area of trilayer spring magnets with two different soft magnetic layers (s1, s2) and one hard magnetic layer (h) with the sequence s1/s2/h can be increased as compared to both bilayer structures s1/h and s2/h with the same total thickness of the soft layers and for definite thickness ratios of the soft layers and their sequences. For ferrimagnetic spin valves, the perpendicular exchange bias effect can be tuned via the thickness of non-magnetic spacer layers at the interface, which determine the exchange coupling between ferrimagnets. A simple quasi one-dimensional phenomenological model is able to describe the magnetic hysteresis of even complex layered structures and to predict optimal geometrical and magnetic parameters of such heterostructures.

Moskalenko, M. A. [St. Petersburg National Research University of Information Technologies, Mechanics and Optics, St. Petersburg 197101 (Russian Federation); Science Institute and Faculty of Science, VR-III, University of Iceland, 107 Reykjavík (Iceland); Uzdin, V. M. [St. Petersburg National Research University of Information Technologies, Mechanics and Optics, St. Petersburg 197101 (Russian Federation); St.-Petersburg State University, Ul'yanovskaya ul.1, Petrodvorets, St.-Petersburg 198904 (Russian Federation); Zabel, H. [Department of Physics and Astronomy, Ruhr-University Bochum, 44780 Bochum (Germany)

2014-02-07

88

Crystallization sequences in the Muskox intrusion and other layered intrusions--II. Origin of chromitite layers and similar deposits of other magmatic ores  

Microsoft Academic Search

A mechanism of origin for chromite-rich layers in stratiform ultramafic-gabbroic intrusions is proposed whereby the layers are precipitated on occasions when the basic parental magma of the intrusion is suddenly extensively contaminated with granitic liquid melted from salic roof rocks. It is inferred that the increase of silica and alkalies in the basic liquid should cause it to become more

T. N. Irvine

1975-01-01

89

Intermediate layers for tandem structure of bulk heterojunction photovoltaic cells  

NASA Astrophysics Data System (ADS)

For advanced organic thin film photovoltaic cell, stacked structure of single cells, tandem structure, would be a key issue. Many kinds of tandem structure have been already reported. When an appropriate intermediate layer was inserted between the single cells, open circuit voltage (Voc) can be doubled compared with the single cell. For small molecules, vacuum evaporation can be applicable for fabrication. Systematic investigations have been made to reveal the requirement for the intermediate materials. Quite thin, a few nm thick, metal layer can act as intermediate layer[1]. The metal cannot form continuous layer but island lake structure in such small amount. On the other hand, the combination of the metal oxide (such as ZnO, TiO2 and ITO) and PEDOT:PSS are used for the intermediate layer. We need to reveal minimum requirement for the intermediate materials for polymer based bulkhererojunction cells for low-cost high performance organic photovoltaic cells. We have developed a polymer thin film preparation technique, Evaporative Spray Deposition using Ultradilute Solution (ESDUS)[2]. This method has enabled fabricating organic thin films applicable to polymer light-emitting diodes, organic photovoltaics and organic field-effect transistors13 from highly diluted solutions of 1-10 ppm. Moreover, it has been exhibited that a successive polymer layer can be deposited without damaging the preceding polymer layer by use of a same solvent for each layer deposition. We conduct the systematic investigation of the intermediate materials. Onto the bottom cell/intermediate layer, top cell can be deposited by use of ESDUS.

Kawanami, Akito; Fujita, Katsuhiko

2012-09-01

90

Thermal and wind structure of the monsoon trough boundary layer  

Microsoft Academic Search

Radiosonde data from Jodhpur, taken at 0530, 1730 and around 1100 hr IST during MONTBLEX 1990, reveal that the distribution of virtual potential temperature 0 v below about 500 hPa has a structure characterized by up to three layers each of approximately constant gradient. We are thus led to introduce a characterization of the observed thermal structure through a sequence

G. Rajkumar; R. Narasimha; S. P. Singal; B. S. Gera

1996-01-01

91

Structural design of pavements with stabilized layers Animesh Das  

E-print Network

Structural design of pavements with stabilized layers Animesh Das Associate Professor, Department@iitk.ac.in The talk will primarily be divided in three parts, namely analysis of pavement structure, empirical design and composite pavements will be mentioned. The governing equations and the boundary conditions will be discussed

Das, Animesh

92

GPR determination of physical parameters of railway structural layers  

NASA Astrophysics Data System (ADS)

The paper studies the possibility of quantitative processing of the GPR data for determining the refractive index and conductivity of motor road and railway constructional layers. The main objective of the work is to develop a method of obtaining quantitative information on chosen physical properties of soil layers from regular GPR surveys. Theoretical study of plane electromagnetic wave propagation is made for the model of layered soil structure. As a result of the study appropriate equation systems are derived for the calculations of refractive index and conductivity of structural layers. Based on these equations the method of quantitative processing of radargrams is proposed. The method includes the GPR data processing algorithm and theoretical techniques for determination of refractive index and conductivity of the structural layers. The applicability of the proposed method was initially validated by lab experiments using radargrams of the soil samples with specified values of moisture and conductivity and reliable results were achieved. The methods were also successfully used while monitoring the long term seasonal changes in structural layers of several Russian railways sections. The contamination of ballast material is also evaluated by this method in addition to the refractive index and conductivity.

Khakiev, Zelimkhan; Shapovalov, Vladimir; Kruglikov, Alexander; Yavna, Victor

2014-07-01

93

Development of a dual layered dielectric-loaded accelerating structure.  

SciTech Connect

Due to the high magnetic field-induced surface currents on its conducting sleeve, a conventional single layer Dielectric-Loaded Accelerating (DLA) structure exhibits a relatively high RF loss. One possible way to solve this problem is to use multilayered DLA structures. In these devices, the RF power attenuation is reduced by making use of the Bragg Fiber concept: the EM fields are well confined by multiple reflections from multiple dielectric layers. This paper presents the design of an X-band dual layer DLA structure as well as the results of bench tests of the device. We will also present results on the design, numerical modeling, and fabrication of structures for coupling RF into multilayer DLAs such as a novel TM{sub 03} mode launcher and a TM{sub 01}-TM{sub 03} mode converter using dielectric-loaded corrugated waveguide.

Gai, W.; Liu, W.; Jing, C.; Kanareykin, A.; Antipov, S.; Nenasheva, E.; Schoessow, P.; High Energy Physics; Euclid Techlabs, LLC; Illinois Inst. of Tech.; KEK

2008-09-01

94

The simulation of coherent structures in a laminar boundary layer  

NASA Technical Reports Server (NTRS)

Coherent structures in turbulent shear flows were studied extensively by several techniques, including the VITA technique which selects rapidly accelerating or decelerating regions in the flow. The evolution of a localized disturbance in a laminar boundary layer shows strong similarity to the evolution of coherent structures in a turbulent-wall bounded flow. Starting from a liftup-sweep motion, a strong shear layer develops which shares many of the features seen in conditionally-sampled turbulent velocity fields. The structure of the shear layer, Reynolds stress distribution, and wall pressure footprint are qualitatively the same, indicating that the dynamics responsible for the structure's evolution are simple mechanisms dependent only on the presence of a high mean shear and a wall and independent of the effects of local random fluctuations and outer flow effects. As the disturbance progressed, the development of streak-like-high- and low-speed regions associated with the three-dimensionality.

Breuer, Kenny; Landahl, Marten T.; Spalart, Philippe R.

1987-01-01

95

Composite Structure of Plumes in Stratus-topped Boundary Layers  

Microsoft Academic Search

Knowledge of convective plumes within the clear convective boundary layer (CBL) is quite advanced owing to direct measurements, tank experiments, and large-eddy simulation studies. As a result, modeling of the CBL is relatively successful. Progress for the stratus-topped boundary layer (STBL), however, is slow. This study compares the plume structure of the surface-heated CBL with that of the cloud-top-cooled STBL

Chin-Hoh Moeng; Ulrich Schumann

1991-01-01

96

New aspects of turbulent boundary-layer structure  

Microsoft Academic Search

Using flow visualization techniques and hot wire measurements, the structure of the zero-pressure-gradient turbulent boundary-layer is studied over the Reynolds number range of 500 less than Re sub theta less than 17,500. A section of the turbulent layer, filled with smoke, is illuminated by an intense plane of light, and a low-speed wind tunnel with a very long working section

M. R. Head; P. Bandyopadhyay

1981-01-01

97

A New View on Origin, Role and Manipulation of Large Scales in Turbulent Boundary Layers  

NASA Technical Reports Server (NTRS)

The potential of passive 'manipulators' for altering the large scale turbulent structures in boundary layers was investigated. Utilizing smoke wire visualization and multisensor probes, the experiment verified that the outer scales could be suppressed by simple arrangements of parallel plates. As a result of suppressing the outer scales in turbulent layers, a decrease in the streamwise growth of the boundary layer thickness was achieved and was coupled with a 30 percent decrease in the local wall friction coefficient. After accounting for the drag on the manipulator plates, the net drag reduction reached a value of 20 percent within 55 boundary layer thicknesses downstream of the device. No evidence for the reoccurrence of the outer scales was present at this streamwise distance thereby suggesting that further reductions in the net drag are attainable. The frequency of occurrence of the wall events is simultaneously dependent on the two parameters, Re2 delta sub 2 and Re sub x. As a result of being able to independently control the inner and outer boundary layer characteristics with these manipulators, a different view of these layers emerged.

Corke, T. C.; Nagib, H. M.; Guezennec, Y. G.

1982-01-01

98

Electromagnetic normal modes and Casimir effects in layered structures  

NASA Astrophysics Data System (ADS)

We derive a general procedure for finding the electromagnetic normal modes in layered structures. We apply this procedure to planar, spherical, and cylindrical structures. These normal modes are important in a variety of applications. They are the only input needed in calculations of Casimir interactions. We present an explicit expression for the condition for modes and Casimir energy for a large number of specific geometries. The layers are allowed to be two-dimensional so graphene and graphenelike sheets as well as two-dimensional electron gases can be handled within the formalism. Also, forces on atoms in layered structures are obtained. One side result is the van der Waals and Casimir-Polder interaction between two atoms.

Sernelius, Bo E.

2014-10-01

99

Oblique along path toward structures at rear of parcel. Original ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Oblique along path toward structures at rear of parcel. Original skinny mosaic path along edge of structures was altered (delineation can be seen in concrete) path was widened with a newer mosaic to make access to the site safer. Structures (from right) edge of Round House (with "Spring Garden"), Pencil house, Shell House, School House, wood lattice is attached to chain-link fence along north (rear) property line. These structures were all damaged by the 1994 Northridge earthquake. Camera facing northeast. - Grandma Prisbrey's Bottle Village, 4595 Cochran Street, Simi Valley, Ventura County, CA

100

52. Humbug Creek Diversion Dam showing original masonry structure at ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

52. Humbug Creek Diversion Dam showing original masonry structure at right and concrete weir at left added later. Photographer James Eastwood, 1986. Source: Salt River Project. - Waddell Dam, On Agua Fria River, 35 miles northwest of Phoenix, Phoenix, Maricopa County, AZ

101

ORIGINAL ARTICLE Spatial genetic structure in the Laperrine's olive  

E-print Network

ORIGINAL ARTICLE Spatial genetic structure in the Laperrine's olive (Olea europaea subsp The Laperrine's olive (Olea europaea subsp. laperrinei) is an emblematic species of the Sahelo-Saharan Mountains.hdy.6801051 Keywords: conservation genetics; microsatellites; olive tree; plastid DNA; spatial autocorrelation

Alvarez, Nadir

102

Original article Structure and fractal dimensions of root systems  

E-print Network

Original article Structure and fractal dimensions of root systems of four co-occurring fruit tree, Bangor, Gwynedd LL57 2UW, UK (Received 1 February 1999; accepted 29 October 1999) Abstract ­ Coarse root-auto- matically digitized. Spatial distributions of root length were determined from the digitally

Paris-Sud XI, Université de

103

Original article Genetic structure of the Marseilles cat  

E-print Network

Original article Genetic structure of the Marseilles cat population: is there really a strong 4 February 1992; accepted 21 December 1993) Summary - In a previous study on the Marseilles cat population it was concluded that the small cat colonies were subject to a strong founder effect. A more

Paris-Sud XI, Université de

104

Origin of the F-Layer by ``Snowfall'' in the Earth's Core  

NASA Astrophysics Data System (ADS)

Recent seismological observations of phases reflecting (PKiKP), diffracting (PKPdiff), or going through the inner core (PKIKP) called for modification of PREM at the top of the Inner Core Boundary (ICB). Both the AK135 and PREM2 models proposed a flattened P-wave velocity gradient relative to PREM in the ~200 km region above the ICB, often referred to as the F-layer. This reduced velocity gradient implies density stratification, which may reflect a gradient in the light element concentration decreasing from the top of the F-layer to the ICB. Here we propose a mechanism to generate a chemical stratification in the F-layer through crystallization of solid iron “snow” at the top of the F-layer, which then precipitates, partially dissolves, and eventually accumulates at the ICB to produce the F-layer and contribute to the growth of the inner core. The formation of iron “snow” in the outer core (OC) requires that the core geotherm intercepts the FeX liquidus, where X is an alloying light element, to create a region of stability for solid iron at the base of the OC. This study examines two potential scenarios in which iron “snowfall” might occur in the F-layer. The first scenario involves the FeX liquidus gradient decreasing or even changing sign such that a region of solid stability is created at the top of the F-layer. This behavior is observed in the Fe-S binary system at lower pressures and has been proposed to cause “snowing” in the interiors of Mercury and Ganymede. In the second case, the outer core temperature may increase relative to the FeX liquidus near the ICB due to viscomagnetic heating. Results based on mineral physics calculations of an iron-sulfur binary system show that an F-layer composition ranging from 7.2 wt% S at the top of the F-layer to 5.7 wt% S at the ICB is sufficient to explain the Vp structure of the F-layer in AK135. In these calculations, the density and bulk modulus as a function of depth were determined using the 3rd order Birch-Murnaghan equation of state. Temperature was accounted for using the Mie-Grüneisen-Debye equation of state. Published experimental values for Fe-FeS solid and liquid end-members were used and those of intermediate compositions were determined using ideal solution theory. The crystal fraction was assumed to be small enough to allow approximation of a pure liquid composition in the F-layer. Comparison of our F-layer model to PREM results in a better fit to the observed travel time data. Comparison of normal mode eigenfrequencies from the two models shows subtle differences; therefore normal modes have been determined to be insensitive to the small-scale structure of the relatively thin F-layer

Hernlund, J. W.; Li, J.; Armentrout, M. M.; Buono, A. S.; Chen, B.; Durand, S.; Gaeman, J.; Pigott, J. S.; Waszek, L.; Zheng, Z.

2010-12-01

105

Strained layer superlattice focal plane array having a planar structure  

DOEpatents

An infrared focal plane array (FPA) is disclosed which utilizes a strained-layer superlattice (SLS) formed of alternating layers of InAs and In.sub.xGa.sub.1-xSb with 0.ltoreq.x.ltoreq.0.5 epitaxially grown on a GaSb substrate. The FPA avoids the use of a mesa structure to isolate each photodetector element and instead uses impurity-doped regions formed in or about each photodetector for electrical isolation. This results in a substantially-planar structure in which the SLS is unbroken across the entire width of a 2-D array of the photodetector elements which are capped with an epitaxially-grown passivation layer to reduce or eliminate surface recombination. The FPA has applications for use in the wavelength range of 3-25 .mu.m.

Kim, Jin K; Carroll, Malcolm S; Gin, Aaron; Marsh, Phillip F; Young, Erik W; Cich, Michael J

2012-10-23

106

Ternary metal-rich sulfide with a layered structure  

DOEpatents

A ternary Nb-Ta-S compound is provided having the atomic formula, Nb.sub.1.72 Ta.sub.3.28 S.sub.2, and exhibiting a layered structure in the sequence S-M3-M2-M1-M2-M3-S wherein S represents sulfur layers and M1, M2, and M3 represent Nb/Ta mixed metal layers. This sequence generates seven sheets stacked along the [001] direction of an approximate body centered cubic crystal structure with relatively weak sulfur-to-sulfur van der Waals type interactions between adjacent sulfur sheets and metal-to-metal bonding within and between adjacent mixed metal sheets.

Franzen, Hugo F. (Ames, IA); Yao, Xiaoqiang (Ames, IA)

1993-08-17

107

Origin of Martian Interior Layered Deposits (ILDs) by atmospherically driven processes  

NASA Astrophysics Data System (ADS)

Since the first photogeologic exploration of Mars, vast mounds of layered sediments found within the Valles Marineris canyon system (Interior Layered Deposits or ILDs) have remained unexplained. Recent spectroscopic results showing that these materials contain coarse-grained hematite [1] and sulfate [2-8] suggest that they are fundamentally similar to layered sulfate deposits seen elsewhere on Mars [3], and are therefore a key piece of Mars' global aqueous history. Layered sulfate deposits (including ILDs) are often considered to have formed in association with transient, wet surface environments caused by groundwater upwelling [9] in the Hesperian. Here, we use spectroscopic mapping along with geomorphic observations and mass balance calculations to demonstrate that the sulfate-bearing ILDs likely did not form due to groundwater upwelling or any similar playa-lacustrine scenario. Instead, the ILDs likely formed from atmospherically driven processes in a configuration similar to that observed today. We suggest that Hesperian layered sulfate deposits formed in response to massive amounts of pyroclastic volcanism and SO2-outgassing that peaked near 3.5-3.7 Ga in a Martian climate that was largely cold and dry. This origin for the ILDs is also applicable to other layered terrain of similar age and characteristics, including sulphate-bearing crater fill, chaos terrains, and the Meridiani Planum sediments. [1] Weitz, C. M., Lane, M. D., Staid, M. & Dobrea, E. N. Gray hematite distribution and formation in Ophir and Candor chasmata. Journal of Geophysical Research-Planets 113, doi:E02016 10.1029/2007je002930 (2008). [2] Wendt, L. et al. Sulfates and iron oxides in Ophir Chasma, Mars, based on OMEGA and CRISM observations. Icarus 213, 86-103, doi:10.1016/j.icarus.2011.02.013 (2011). [3] Murchie, S. et al. Evidence for the origin of layered deposits in Candor Chasma, Mars, from mineral composition and hydrologic modeling. Journal of Geophysical Research-Planets 114, doi:E00d05 10.1029/2009je003343 (2009). [4] Mangold, N. et al. Spectral and geological study of the sulfate-rich region of West Candor Chasma, Mars. Icarus 194, 519-543, doi:10.1016/j.icarus.2007.10.021 (2008). [5] Le Deit, L. et al. Morphology, stratigraphy, and mineralogical composition of a layered formation covering the plateaus around Valles Marineris, Mars: Implications for its geological history. Icarus 208, 684-703, doi:10.1016/j.icarus.2010.03.012 (2010). [6] Gendrin, A. et al. Suffates in martian layered terrains: the OMEGA/Mars Express view. Science 307, 1587-1591, doi:10.1126/science.1109087 (2005). [7] Bibring, J.-P. et al. Coupled Ferric Oxides and Sulfates on the Martian Surface. Science 317, 1206-1210, doi:10.1126/science.1144174 (2007). [8] Roach, L. H., Mustard, J. F., Lane, M. D., Bishop, J. L. & Murchie, S. L. Diagenetic haematite and sulfate assemblages in Valles Marineris. Icarus 207, 659-674, doi:10.1016/j.icarus.2009.11.029 (2010). [9] Andrews-Hanna, J. C. & Lewis, K. W. Early Mars hydrology: 2. Hydrological evolution in the Noachian and Hesperian epochs. Journal of Geophysical Research-Planets 116, doi:E02007 10.1029/2010je003709 (2011).

Michalski, J. R.; Niles, P. B.

2011-12-01

108

Original size of the Vredefort structure, South Africa  

NASA Technical Reports Server (NTRS)

The Vredefort structure is located approximately 120 km southwest of Johannesburg, South Africa, and is deeply eroded. Controversies remain on the origin of this structure with the most popular hypotheses being: (1) by impact cratering about 2.0 Ga; (2) as a cryptoexplosion structure about 2.0 Ga; and (3) by purely tectonic processes starting at about 3.0 Ga and ending with the Vredefort event at 2.0 Ga. In view of recent work in which the granophyre dikes are interpreted as the erosional remants of a more extensive impact melt sheet, injected downward into the underlying country rocks, the impact origin hypothesis for Vredefort is adopted. In order to estimate the original dimensions of the Vredefort impact structure, it is assumed that the structure was initially circular, that its predeformation center corresponds to the center of the granitic core, and that the pre-Vredefort geology of the area prior to approximately 2.0 Ga ago is as suggested by Fletcher and Reimold. The spatial relationship between shock metamorphic effects, the shock pressures they record, and the morphological features of the crater were established for a number of large terrestrial craters. The principles of crater formation at large complex impact structures comparable in size to Vredefort were also established, although many details remain unresolved. An important conclusion is that the transient crater, which is formed directly by excavation and displacement by the shock-induced cratering flow-field (i.e., the particle velocity flow field existing in the region of the transient crater but behind the initial outgoing shock front), is highly modified during the late stage processes. The original transient crater diameter lies well within the final rim of the crater, which is established by structural movements during late-stage cavity modification.

Therriault, A. M.; Reid, A. M.; Reimold, W. U.

1993-01-01

109

Electrical properties of double layer dielectric structures for space technology  

NASA Astrophysics Data System (ADS)

Polymeric films such as polyimide (PI) and polyethylene terephthalate (PET) are used in space technology as thermal blankets. Thin SiO2 and SiN coatings plasma deposited onto PI and PET surfaces were proposed to protect the blanket materials against the space environment. The electrical properties of this kind of dual layer dielectric structure were investigated to understand the mechanisms for suppressing charge accumulation and flashover. Bulk and surface electrical conductivities of thin single-layer PI and PET samples and of the dual layer SiO2 and SiN combinations with PI and PET were measured in a range of applied electrical fields. The capacitance voltage (CV) technique was used for analyzing charge transport and distribution in the structures. The electric current in the bulk of the SiO2/PI and SiN/PI samples was found to depend on the polarity of the electric field. Other samples did not exhibit any such polarity effect. The polarity dependence is attributed to charge trapping at the PI/plasma deposit interface. The CV characteristics of the Al-PI-SiO2-Si structure confirm that charges which can modify the local electric field can be trapped near the interface. A model is proposed to interpret the properties of the currents in dual layer structures. This model can semi-quantitatively explain all the observed results.

Lian, Anqing

1993-04-01

110

Layered Structure and Management in Internet of Things  

Microsoft Academic Search

The development for Internet of Things and RFID technology is described in this paper. A feasible scheme and layered structure is proposed for Internet of Things. Its management is presented according to the demand for Internet of Things in China. The general system contains two parts: computer information subsystem and RFID terminal subsystem, the latter of which is the main

Huansheng Ning; Na Ning; Shenfeng Qu; Yan Zhang; Huiping Yang

2007-01-01

111

Impact origin of the Sudbury structure: Evolution of a theory  

NASA Technical Reports Server (NTRS)

This paper reviews the origin, development, and present status of the widely accepted theory, proposed by Robert S. Dietz in 1962, that the Sudbury structure was formed by meteoritic or asteroidal impact. The impact theory for the origin of the Sudbury structure seems supported by a nearly conclusive body of evidence. However, even assuming an impact origin to be correct, at least three major questions require further study: (1) the original size and shape of the crater, before tectonic deformation and erosion; (2) the source of the melt now forming the Sudbury Igneous Complex; and (3) the degree, if any, to which the Ni-Cu-platinum group elements are meteoritic. The history of the impact theory illustrates several under-appreciated aspects of scientific research: (1) the importance of cross-fertilization between space research and terrestrial geology; (2) the role of the outsider in stimulating thinking by insiders; (3) the value of small science, at least in the initial stages of an investigation, Dietz's first field work having been at his own expense; and (4) the value of analogies (here, between the Sudbury Igneous Complex and the maria), which although incorrect in major aspects, may trigger research on totally new lines. Finally, the Sudbury story illustrates the totally unpredictable and, by implication, unplannable nature of basic research, in that insight to the origin of the world's then-greatest Ni deposit came from the study of tektites and the Moon.

Lowman, Paul D., Jr.

1992-01-01

112

Origins of unintentional incorporation of gallium in InAlN layers during epitaxial growth, part II: Effects of underlying layers and growth chamber conditions  

NASA Astrophysics Data System (ADS)

We systematically study the origins and mechanisms for unintentional incorporation of gallium (Ga) during epitaxial growth of ternary InAlN thin-film layers. The origins of auto-incorporation of Ga have been investigated by using different underlying layers, regrown layers, and growth chamber conditions. It is shown that Ga-containing deposition on a wafer susceptor/carrier and on surrounding surfaces of uncooled parts in a growth chamber can be responsible for Ga in the InAl(Ga)N layers, while a GaN underlying layer below an InAl(Ga)N layer does not contribute to the auto-incorporation of Ga in the InAl(Ga)N layers. Especially, the Ga-containing deposition on the surfaces inside the chamber is believed to be the dominant source of auto-incorporated Ga, possibly due to the high vapor pressure of a liquid phase as a result of eutectic system formation between indium (In) and Ga. The pressure of liquid-phase Ga, pGa=~3.67×10-4 Torr, can be significant as compared to precursor partial pressures with pTMAl=3.7×10-4 Torr and pTMIn=2.4×10-5 Torr. In addition, magnesium (Mg) or magnesium precursor (Cp2Mg) in the growth chamber is shown to promote the auto-incorporation of Ga in the InAl(Ga)N layers.

Kim, Jeomoh; Lochner, Zachary; Ji, Mi-Hee; Choi, Suk; Kim, Hee Jin; Kim, Jin Soo; Dupuis, Russell D.; Fischer, Alec M.; Juday, Reid; Huang, Yu; Li, Ti; Huang, Jingyi Y.; Ponce, Fernando A.; Ryou, Jae-Hyun

2014-02-01

113

Stable single-layer honeycomblike structure of silica.  

PubMed

Silica or SiO(2), the main constituent of Earth's rocks has several 3D complex crystalline and amorphous phases, but it does not have a graphitelike layered structure in 3D. Our theoretical analysis and numerical calculations from the first principles predict a single-layer honeycomblike allotrope, h? silica, which can be viewed to be derived from the oxidation of silicene and it has intriguing atomic structure with reentrant bond angles in hexagons. It is a wide band gap semiconductor, which attains remarkable electromechanical properties showing geometrical changes under an external electric field. In particular, it is an auxetic metamaterial with a negative Poisson's ratio and has a high piezoelectric coefficient. While it can form stable bilayer and multilayer structures, its nanoribbons can show metallic or semiconducting behavior depending on their chirality. Coverage of dangling Si orbitals by foreign adatoms can attribute new functionalities to h? silica. In particular, Si(2)O(5), where Si atoms are saturated by oxygen atoms from top and bottom sides alternatingly can undergo a structural transformation to make silicatene, another stable, single layer structure of silica. PMID:24996101

Özçelik, V Ongun; Cahangirov, S; Ciraci, S

2014-06-20

114

Structural attributes affecting peptide entrapment in PEO brush layers  

PubMed Central

A more quantitative understanding of peptide loading and release from polyethylene oxide (PEO) brush layers will provide direction for development of new strategies for drug storage and delivery. In this work we recorded selected effects of peptide structure and amphiphilicity on adsorption into PEO brush layers based on covalently stabilized Pluronic®F 108. Optical waveguide lightmode spectroscopy and circular dichroism measurements were used to characterize the adsorption of poly-L-glutamic acid, poly-L-lysine, and the cationic amphiphilic peptide WLBU2, to the brush layers. The structure of WLBU2 as well as that of the similarly-sized homopolymers was controlled between disordered and more ordered (helical) forms by varying solution conditions. Adsorption kinetic patterns were interpreted with reference to a simple model for protein adsorption, in order to evaluate rate constants for peptide adsorption and desorption from loosely and tightly bound states. While more ordered peptide structure apparently promoted faster adsorption and elution rates, resistance to elution while in the PEO layer was dependent on peptide amphiphilicity. The results presented here are compelling evidence of the potential to create anti-fouling surface coatings capable of storing and delivering therapeutics. PMID:23434695

Lampi, Marsha C.; Wu, Xiangming; Schilke, Karl F.; McGuire, Joseph

2013-01-01

115

Nonlinear Stability and Structure of the Compressible Reacting Mixing Layer  

NASA Astrophysics Data System (ADS)

The nonlinear stability of the compressible reacting mixing layer is investigated with a parabolized stability equation (PSE) technique. Single-step chemistry is implemented in the PSE approach to yield a low-cost but quantitatively accurate tool for investigating shear layer structure and mixing over a wide parameter space. A comparison of nonreacting PSE predictions to both linear stability and direct simulation results is presented. Building on parametric study results from a linear technique(Day, M.J., Mansour, N.N., Reynolds, W.C., ``The structure of the compressible reacting mixing layer: Insights from linear stability analysis'', Phys. Fluids, 10), 4 (1998)., this work investigates the nonlinear interaction of the three instability modes (central, fast and slow) in different regimes of the mixing layer. Specific interest is placed on conditions where two outer stability modes are equally amplified and a ``colayer'' forms; the mixing enhancement of this structure relative to the single-mode case is discussed. The effect of density and equivalence ratios on the single-mode mixing performance is also addressed.

Day, M. J.; Reynolds, W. C.; Mansour, N. N.

1998-11-01

116

Multi-functional layered structure having structural and radiation shielding attributes  

NASA Technical Reports Server (NTRS)

A cosmic and solar radiation shielding structure that also has structural attributes is comprised of three layers. The first layer is 30-42 percent by volume of ultra-high molecular weight (UHMW) polyethylene fibers, 18-30 percent by volume of graphite fibers, and a remaining percent by volume of an epoxy resin matrix. The second layer is approximately 68 percent by volume of UHMW polyethylene fibers and a remaining percent by volume of a polyethylene matrix. The third layer is a ceramic material.

Kaul, Raj K. (Inventor); Barghouty, Abdulnasser Fakhri (Inventor); Penn, Benjamin G. (Inventor); Hulcher, Anthony Bruce (Inventor)

2010-01-01

117

Identification of the Methanococcus voltae S-layer structural gene.  

PubMed Central

We have established that the gene which we had previously identified as encoding the Methanococcus voltae P-type ATPase is, in fact, the structural gene for the M. voltae S-layer protein. This conclusion is based on a comparison of the N-terminal sequence of S-layer protein prepared by two independent methods with that derived from the nucleotide sequence of the cloned gene. This conclusion was further supported by immunocytochemical localization of the antigen directed against the antibodies used in the cloning experiments. Images PMID:8132478

Konisky, J; Lynn, D; Hoppert, M; Mayer, F; Haney, P

1994-01-01

118

Origins of large critical temperature variations in single-layer cuprates  

SciTech Connect

We study the electronic structures of two single-layer superconducting cuprates, Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} (Tl2201) and (Bi{sub 1.35}Pb{sub 0.85}) (Sr{sub 1.47}La{sub 0.38}) CuO{sub 6+{delta}} (Bi2201) which have very different maximum critical temperatures (90 K and 35 K, respectively) using angular-resolved photoemission spectroscopy (ARPES). We are able to identify two main differences in their electronic properties. First, the shadow band that is present in double-layer and low T{sub c,max} single-layer cuprates is absent in Tl2201. Recent studies have linked the shadow band to structural distortions in the lattice and the absence of these in Tl2201 may be a contributing factor in its T{sub c,max}. Second, Tl2201's Fermi surface (FS) contains long straight parallel regions near the antinode, while in Bi2201 the antinodal region is much more rounded. Since the size of the superconducting gap is largest in the antinodal region, differences in the band dispersion at the antinode may play a significant role in the pairing and therefore affect the maximum transition temperature.

Palczewski, A.D.; Kondo, T.; Khasanov, R.; Kolesikov, N.N.; Timonina; Rotenberg, E.; Ohta, T.; Bendounan, A.; Sassa, Y.; Fedorov, A.; Paihes, S.; Santander-Syro, A.F.; Chang, J.; Shi, M.; Mesot, J.; Fretwell, H.M.; Kaminski, A.

2008-08-26

119

Intermediate and transisitonal scale structure in midlaitude sporadic E layers  

NASA Astrophysics Data System (ADS)

Irregular midlatitude sporadic E (Es) layers exhibit irregularities at large (~100 km), intermediate (~10 km), transitional (~1 km), and small (<< 1 lm) scales. This paper focuses on the causes of intermediate- and transitional-scale irregularities using analysis and observations from the Arecibo incoherent scatter radar and a 30 MHz coherent scatter radar imager located on St. Croix, USVI. We attribute the intermediate-scale structure we observe to shear instability in the neutral flow. Estimates of the time-varying vector neutral wind profiles in which the Es layers are embedded are analyzed and shown to be shear unstable in the Richardson number sense. In addition to the calculation of the Richardson number values, we present an eigenvalue analysis for the wind profiles. The calculated eigenmodes have dominant Kelvin-Helmholtz modes for the estimated flow that are propagating to the southwest with phase speeds near 50 m/s and horizontal wavelengths between 10--15 km. The growth times for the waves would have been as little as about 1 min. Transitional-scale fine structure is also apparent in incoherent scatter observations of Es layers from Arecibo. The fine structure is wavelike with predominant horizontal wavelengths as large as about 2--3 km. We attribute this structure to a drift wave instability operating in the collisional regime. A linear, local dispersion relation for the waves is described which predicts growth driven by polarization electric fields in the layers, a consequence of the intermediate-scale irregularities. A numerical simulation produces wave growth and other features consistent with the dispersion relation, including finite parallel wavenumbers. The kilometric irregularities are thought to be the primary waves from which secondary, small-scale waves in the layers can form.

Hysell, D. L.; Nossa, E.; Larsen, M.; Sulzer, M. P.; Gonzalez, S. A.

2012-12-01

120

Composition, structure, and properties of iron-rich nontronites of different origins  

SciTech Connect

The composition, structure, and properties of smectites of different origins have been studied by X-ray diffraction, IR spectroscopy, scanning electron microscopy, and microprobe analysis. The results showed that nontronites of different origins differ in composition, properties, morphology, and IR spectroscopic characteristics. Depending on the degree of structural order and the negative charge of iron-silicate layers in nontronites, the shift of the 001 reflection to smaller angles as a result of impregnation with ethylene glycol (this shift is characteristic of the smectite group) occurs differently. The calculated values of the parameter b (from 9.11 to 9.14A) are valid for the extreme terms of dioctahedral smectite representatives: nontronites.

Palchik, N. A., E-mail: nadezhda@igm.nsc.ru; Grigorieva, T. N.; Moroz, T. N. [Russian Academy of Sciences, Sobolev Institute of Geology and Mineralogy, Siberian Branch (Russian Federation)] [Russian Academy of Sciences, Sobolev Institute of Geology and Mineralogy, Siberian Branch (Russian Federation)

2013-03-15

121

Morphological and mechanical investigation of double layer reciprocal structures Cyril Douthe1  

E-print Network

1 Morphological and mechanical investigation of double layer reciprocal structures Cyril Douthe1 in the structure and/or modifying the structure into a double layer space structure. The proposed paper is thus: to introduce curvature and/or to increase the structural thickness. Various configurations of double layer

Boyer, Edmond

122

Origin of superconductivity in layered centrosymmetric LaNiGa{sub 2}  

SciTech Connect

We have examined the origin of superconductivity in layered centrosymmetric LaNiGa{sub 2} by employing a linear response approach based on the density functional perturbation theory. Our results indicate that this material is a conventional electron-phonon superconductor with intermediate level of coupling strength, with the electron-phonon coupling parameter of 0.70, and the superconducting critical temperature of 1.90?K in excellent accordance with experimental value of 1.97?K. The largest contribution to the electron-phonon coupling comes from the La d and Ga p electrons near the Fermi energy and the B{sub 3g} phonon branch resulting from vibrations of these atoms along the ?-Z symmetry line in the Brillouin zone.

Tütüncü, H. M. [Sakarya Üniversitesi, Fen-Edebiyat Fakültesi, Fizik Bölümü, 54187 Adapazar? (Turkey); Srivastava, G. P. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)

2014-01-13

123

Streamwise vortices originating from synthetic jet-turbulent boundary layer interaction  

NASA Astrophysics Data System (ADS)

The interaction between a flat plate turbulent boundary layer and a synthetic jet issuing from a rectangular slot slanted with respect to the free stream was studied experimentally using digital particle image velocimetry. Instantaneous flow fields were sampled in a cross-plane downstream of the slot. Results concerning the effects of varying the synthetic jet velocity ratio at fixed stroke length L0 and yaw angle, and the effects of varying the orifice yaw angle ? at a fixed frequency are presented. The formation of a pair of counter-rotating vortical structures, completely embedded in the boundary layer, was observed in the mean flow field when the slot was aligned with the cross-flow. As the slot yaw angle was increased, the leeward vortex intensified while the other became weaker. These vortical structures are the traces of streamwise vortices forming upstream, at the slot exit, during the blowing phases. As the jet velocity ratio and the slot yaw angle were increased the vortices grew in size and intensity. The vortex identification technique showed that these vortical structures are intermittently present in the instantaneous flow fields with a percentage growing with the frequency but not influenced by the yaw angle. Conditional averages showed that while the rotational core of the identified vortices is nearly unaffected, their outer region is greatly modified and grows in size and intensity as the jet velocity ratio and the yaw angle increases.

Lasagna, D.; Orazi, M.; Iuso, G.

2014-02-01

124

Nonlinear stability and structure of compressible reacting mixing layers  

NASA Astrophysics Data System (ADS)

The parabolized stability equations (PSE) are used to investigate issues of nonlinear flow development and mixing in compressible reacting shear layers, which are modelled with an infinitely fast-chemistry assumption. Particular emphasis is placed on investigating the change in flow structure that occurs when compressibility and heat release are added to the flow. These conditions allow the ‘outer’ instability modes one associated with each of the fast and slow streams to dominate over the ‘central’, Kelvin Helmholtz mode that exists unaccompanied in incompressible non-reacting mixing layers. Analysis of scalar probability density functions in flows with dominant outer modes demonstrates the ineffective, one-sided nature of mixing that accompanies these flow structures. Colayer conditions, where two modes have equal growth rate and the mixing layer is formed by two sets of vortices, offer some opportunity for mixing enhancement. Their extent, however, is found to be limited in the mixing layer's parameter space. Extensive validation of the PSE technique also provides a unique perspective on central-mode vortex pairing, further supporting the view that pairing is primarily governed by instability growth rates; mutual induction appears to be a secondary process. This perspective sheds light on how linear stability theory is able to provide such an accurate prediction of experimentally observed, fully nonlinear flow phenomenon.

Day, M. J.; Mansour, N. N.; Reynolds, W. C.

2001-11-01

125

Nonlinear Stability and Structure of Compressible Reacting Mixing Layers  

NASA Technical Reports Server (NTRS)

The parabolized stability equations (PSE) are used to investigate issues of nonlinear flow development and mixing in compressible reacting shear layers. Particular interest is placed on investigating the change in flow structure that occurs when compressibility and heat release are added to the flow. These conditions allow the 'outer' instability modes- one associated with each of the fast and slow streams-to dominate over the 'central', Kelvin-Helmholtz mode that unaccompanied in incompressible nonreacting mixing layers. Analysis of scalar probability density functions in flows with dominant outer modes demonstrates the ineffective, one-sided nature of mixing that accompany these flow structures. Colayer conditions, where two modes have equal growth rate and the mixing layer is formed by two sets of vortices, offer some opportunity for mixing enhancement. Their extent, however, is found to be limited in the mixing layer's parameter space. Extensive validation of the PSE technique also provides a unique perspective on central- mode vortex pairing, further supporting the view that pairing is primarily governed perspective sheds insight on how linear stability theory is able to provide such an accurate prediction of experimentally-observed, fully nonlinear flow phenomenon.

Day, M. J.; Mansour, N. N.; Reynolds, W. C.

2000-01-01

126

Multiple maternal origins and weak phylogeographic structure in domestic goats  

PubMed Central

Domestic animals have played a key role in human history. Despite their importance, however, the origins of most domestic species remain poorly understood. We assessed the phylogenetic history and population structure of domestic goats by sequencing a hypervariable segment (481 bp) of the mtDNA control region from 406 goats representing 88 breeds distributed across the Old World. Phylogeographic analysis revealed three highly divergent goat lineages (estimated divergence >200,000 years ago), with one lineage occurring only in eastern and southern Asia. A remarkably similar pattern exists in cattle, sheep, and pigs. These results, combined with recent archaeological findings, suggest that goats and other farm animals have multiple maternal origins with a possible center of origin in Asia, as well as in the Fertile Crescent. The pattern of goat mtDNA diversity suggests that all three lineages have undergone population expansions, but that the expansion was relatively recent for two of the lineages (including the Asian lineage). Goat populations are surprisingly less genetically structured than cattle populations. In goats only ?10% of the mtDNA variation is partitioned among continents. In cattle the amount is ?50%. This weak structuring suggests extensive intercontinental transportation of goats and has intriguing implications about the importance of goats in historical human migrations and commerce. PMID:11344314

Luikart, Gordon; Gielly, Ludovic; Excoffier, Laurent; Vigne, Jean-Denis; Bouvet, Jean; Taberlet, Pierre

2001-01-01

127

On the origin of information in epigenetic structures in metazoans.  

PubMed

Epigenetic inheritance implies the existence of epigenetic information. Great progress has been made in recent years in understanding the role of the changes in epigenetic structures (methylated DNA, histone acetylation/deacetylation and chromatin remodelling) as well as the role of miRNA (MIR) expression patterns in epigenetic processes. However, as of yet, we do not have a satisfactory understanding of the origin of epigenetic information stored in, and conveyed by, these structures. We do not know whether these structures are the ultimate source of the information or whether they are simply media for storing and transmitting epigenetic information for gene expression from upstream sources to the phenotype. Herein an attempt is made to ascertain the ultimate sources of the epigenetic information they contain and transmit by tracing back the causal chain leading to the changes in epigenetic structures. PMID:25037317

Cabej, Nelson R

2014-09-01

128

Electrical properties of double layer dielectric structures for space technology  

Microsoft Academic Search

Polymeric films such as polyimide (PI) and polyethylene terephthalate (PET) are used in space technology as thermal blankets. Thin SiO2 and SiN coatings plasma deposited onto PI and PET surfaces were proposed to protect the blanket materials against the space environment. The electrical properties of this kind of dual layer dielectric structure were investigated to understand the mechanisms for suppressing

Anqing Lian

1993-01-01

129

Characteristics of turbulent structures in the unstable atmospheric surface layer  

NASA Astrophysics Data System (ADS)

An atmospheric surface-layer (ASL) experiment conducted at a meteorological site in the Oostelijk-Flevoland polder of the Netherlands is described. Turbulent fluctuations of wind velocity, air temperature and static pressure were measured, using three 10 m towers. Simultaneous turbulent signals at several heights on the towers were used to investigate the properties of the turbulent structures which contribute most significantly to the turbulent vertical transports in the unstable ASL. These turbulent structures produce between 30 and 50% of the mean turbulent vertical transport of horizontal alongwind momentum and they contribute to between 40 and 50% of the mean turbulent vertical heat transport; in both cases this occurs during 15 to 20% of the total observation time. The translation speed of the turbulent structures equals the wind speed averaged over the depth of the ASL, which scales on the surface friction velocity. The inclination angle of the temperature interface at the upstream edge of the turbulent structures to the surface is significantly smaller than that of the internal shear layer, which is associated with the temperature interface. The turbulent structures in the unstable ASL are determined by a large-scale temperature field: Convective motions, which encompass the whole depth of the planetary boundary layer (PBL), penetrate into the ASL. The curvature of the vertical profile of mean horizontal alongwind velocity forces the alignment of the convective cells in the flow direction (Kuettner, 1971), which have an average length of several hundreds of metres and an average width of a few tens of metres. This mechanism leads to the formation of turbulent structures, which extend throughout the depth of the ASL.

Schols, J. L. J.; Jansen, A. E.; Krom, J. G.

1985-10-01

130

A DNA structure is required for geminivirus replication origin function.  

PubMed Central

The genome of the geminivirus tomato golden mosaic virus (TGMV) consists of two single-stranded circular DNAs, A and B, that replicate through a rolling-circle mechanism in nuclei of infected plant cells. The TGMV origin of replication is located in a conserved 5' intergenic region and includes at least two functional elements: the origin recognition site of the essential viral replication protein, AL1, and a sequence motif with the potential to form a hairpin or cruciform structure. To address the role of the hairpin motif during TGMV replication, we constructed a series of B-component mutants that resolved sequence changes from structural alterations of the motif. Only those mutant B DNAs that retained the capacity to form the hairpin structure replicated to wild-type levels in tobacco protoplasts when the viral replication proteins were provided in trans from a plant expression cassette. In contrast, the same B DNAs replicated to significantly lower levels in transient assays that included replicating, wild-type TGMV A DNA. These data established that the hairpin structure is essential for TGMV replication, whereas its sequence affects the efficiency of replication. We also showed that TGMV AL1 functions as a site-specific endonuclease in vitro and mapped the cleavage site to the loop of the hairpin. In vitro cleavage analysis of two TGMV B mutants with different replication phenotypes indicated that there is a correlation between the two assays for origin activity. These results suggest that the in vivo replication results may reflect structural and sequence requirements for DNA cleavage during initiation of rolling-circle replication. PMID:8523519

Orozco, B M; Hanley-Bowdoin, L

1996-01-01

131

Band Structures of Transition-Metal-Dichalcogenide Layer Compounds  

Microsoft Academic Search

The nonrelativistic augmented-plane-wave (APW) method is applied to calculate the electronic band structures of several transition-metal-dichalcogenide (TX2) layer compounds, including materials with the C 6 (1T-HfS2,1T-TaS2), C 27 (2H-TaS2,2H-NbSe2), and C 7 (2H-MoS2) structure types. These calculations involve crystal potentials that are derived from neutral-atom charge densities. The results of these calculations confirm that the group-IVB (1T-HfS2) and group-VIB (2H-MoS2)

L. F. Mattheiss

1973-01-01

132

Plasmon and exciton superconductivity mechanisms in layered structures  

NASA Technical Reports Server (NTRS)

Plasmon and exciton superconductivity mechanisms are discussed. Superconductivity in a three layer metal semiconductor metal and insulator semimetal insulator sandwich structure was described in terms of the temperature dependent Green function of the longitudinal (Coulomb) field. The dependences of the superconducting transition temperature on structure parameters were obtained. In a semiconducting film, as a result of interactions of degenerate free carriers with excitons, superconductivity exists only in a certain range of parameter values, and the corresponding critical temperature is much lower than in the plasmon mechanism of superconductivity.

Gabovich, A. M.; Pashitskiy, E. A.; Uvarova, S. K.

1977-01-01

133

Acoustic structure and propagation in highly porous, layered, fibrous materials  

NASA Technical Reports Server (NTRS)

The acoustic structure and propagation of sound in highly porous, layered, fine fiber materials is examined. Of particular interest is the utilization of the Kozeny number for determining the static flow resistance and the static structure factor based on flow permeability measurements. In this formulation the Kozeny number is a numerical constant independent of volume porosity at high porosities. The other essential parameters are then evaluated employing techniques developed earlier for open cell foams. The attenuation and progressive phase characteristics in bulk samples are measured and compared with predicted values. The agreements on the whole are very satisfactory.

Lambert, R. F.; Tesar, J. S.

1984-01-01

134

Hierarchical layered double hydroxide nanocomposites: structure, synthesis and applications.  

PubMed

Layered double hydroxide (LDH)-based nanocomposites, constructed by interacting LDH nanoparticles with other nanomaterials (e.g. silica nanoparticles and magnetic nanoparticles) or polymeric molecules (e.g. proteins), are an emerging yet active area in healthcare, environmental remediation, energy conversion and storage. Combining advantages of each component in the structure and functions, hierarchical LDH-based nanocomposites have shown great potential in biomedicine, water purification, and energy storage and conversion. This feature article summarises the recent advances in LDH-based nanocomposites, focusing on their synthesis, structure, and application in drug delivery, bio-imaging, water purification, supercapacitors, and catalysis. PMID:25562489

Gu, Zi; Atherton, John James; Xu, Zhi Ping

2015-02-01

135

Effect of layered composite meta-structures on the optical activity and ellipticity of structural biomolecules  

NASA Astrophysics Data System (ADS)

In this paper, we design layered composite meta-structures to investigate its' effect on the optical activity and circular dichroism (CD). The layered composite meta-structures consist of thin gammadion nanostructure with thickness ?/10, where ? is the incident wavelength. The layered meta-structures are alternate between a dielectric and gold (AU) material. Each layered composite meta-gammadion is arranged together in an array of pitch 700 nm. In the first case, 3 layers of meta-gammadion, with metal-insulator-metal (MIM) and insulator-metal-insulator (IMI) configuration are simulated with material properties from optical hand book. There are 3 modes in the CD spectrum, which can be characterized into Bloch CD mode and hybrid CD modes. Compared with the CD spectrum of whole structure of gammadion in gold with same total height, the CD of the MIM layered composite are larger. When the number layer increase to 5, it is observed that the CD is reduced by 30% and there is a red shift in the Bloch CD mode and a slight blue shift in the hybrid CD modes. By further increasing the number of layers to 7, we observed further CD increment and larger wavelength shift in the CD modes. The layered composite meta-gammadion is fabricated using template stripping method. Experimental results also show excellent agreement with the simulation results for CD and wavelength shift. We submerge the layered meta-gammadion into a solution of chiral molecules. The CD spectrum of the meta-gammadion shows a larger wavelength shift compared to pure metal structures. This indicate a more sensitive and robust detection of chiral molecules.

Khoo, E. H.; Hor, Y. Li; Leong, Eunice S. P.; Liu, Y. J.

2014-09-01

136

Impact origin of the Newporte structure, Williston basin, North Dakota  

SciTech Connect

The Newporte field is located just south of the United States-Canada border in Renville County, North Dakota, in the north-central portion of the Williston basin. Integration of seismic, well-log, and core data supports the interpretation of an impact origin for the Newporte structure. The structure involves both Precambrian basement and lower Paleozoic sedimentary units. Oil and gas production began in 1977 from brecciated basement rocks along the rim of the 3.2-km-diameter circular structure. Both well logs and seismic data were used to determine thickness changes of sedimentary units overlying the structure. Resulting isopach maps reveal a circular, bowl-shaped feature with a recognizable rim. Microscopic shock metamorphic features in quartz and feldspar are visible in basement clasts that form a mixed breccia with Cambrian Deadwood sandstone within the western rim of the structure. A Late Cambrian-Early Ordovician age is suggested for the structure because of the presence of flatlying Deadwood sandstone overlying mixed basement/sandstone breccia along portions of the rim. Identification of the Newporte structure as an impact crater adds to the growing base of evidence revealing the relevance of impact craters to petroleum exploration.

Forsman, N.F.; Gerlach, T.R. [Univ. of North Dakota, Grand Forks, ND (United States); Anderson, N.L. [Univ. of Missouri, Rolla, MO (United States)

1996-05-01

137

Evaluating Satiated Copepod Behavioral Responses to Thin Layer Flow Structure  

NASA Astrophysics Data System (ADS)

Zooplankton exploit a variety of chemical and fluid mechanical cues in foraging, mate-seeking, and habitat partitioning contexts. To examine the influence of environmental cues on zooplankton aggregations in coastal marine thin layers, a laboratory thin layer mimic was built. The apparatus uses a laminar, planar jet (the Bickley jet) to produce ecologically-relevant layers of chemical (beneficial and harmful phytoplankton) and fluid mechanical (shear strain rate) cues for zooplankton behavioral assays. Particle image velocimetry (PIV) and laser-induced fluorescence (LIF) were employed to fully quantify the spatial structure of the chemical and fluid mechanical cues, ensuring a close match to in situ conditions and allowing for investigations into threshold cue levels responsible for inducing behavioral responses. Evaluating the effect of hunger level on behavioral responses is particularly important for producing accurate individual-based simulations of zooplankton population dynamics. Behavioral assays with the calanoid copepod Temora longicornis have produced digitized trajectories and, subsequently, path kinematics. Observed behaviors include increased turn frequency and decreased relative swimming speed, which result in increased residence time in the free jet shear layer. Cue-induced individual behaviors have the potential to produce population-scale aggregations.

True, Aaron C.; Webster, Donald R.; Weissburg, Marc J.; Yen, Jeannette

2011-11-01

138

Structural Changes in Individual Retinal Layers in Diabetic Macular Edema  

PubMed Central

Optical coherence tomography (OCT) has enabled objective measurement of the total retinal thickness in diabetic macular edema (DME). The central retinal thickness is correlated modestly with visual impairment and changes paradoxically after treatments compared to the visual acuity. This suggests the clinical relevance of the central retinal thickness in DME and the presence of other factors that affect visual disturbance. Recent advances in spectral-domain (SD) OCT have provided better delineation of the structural changes and fine lesions in the individual retinal layers. Cystoid spaces in the inner nuclear layer and outer plexiform layer are related to quantitative and qualitative parameters in fluorescein angiography. OCT often shows vitreoretinal interface abnormalities in eyes with sponge-like retinal swelling. Serous retinal detachment is sometimes accompanied by hyperreflective foci in the subretinal fluid, which exacerbates the pathogenesis at the interface of the photoreceptors and retinal pigment epithelium. Photoreceptor damage at the fovea is thought to be represented by disruption of the external limiting membrane or the junction between the inner and outer segment lines and is correlated with visual impairment. Hyperreflective foci in the outer retinal layers on SD-OCT images, another marker of visual disturbance, are associated with foveal photoreceptor damage. PMID:24073417

Yoshimura, Nagahisa

2013-01-01

139

An experimental study on the preparation of tochilinite-originated intercalation compounds comprised of Fe 1-xS host layers and various kinds of guest layers  

NASA Astrophysics Data System (ADS)

Tochilinite represents a mineral group of ordered mixed-layer structures containing alternating Fe 1-xS layers with mackinawite-like structure and metal hydroxide layers with Mg(OH) 2-like structure. In this article, we report the preparation of a series of tochilinite-originated (or Fe 1-xS-based) intercalation compounds (ICs). According to their preparation procedures, these ICs can be divided into four kinds. The first kind of IC was sodium tochilinite (Na-tochilinite), which was prepared by the hydrothermal reaction of metallic Fe particles with concentrated Na 2S·9H 2O aqueous solutions. The hydroxide layer of the Na-tochilinite was a mixed hydroxide of Na + ions along with a certain amount of Fe 2+ ions. When the hydroxide layer of the Na-tochilinite completely dissolved in aqueous solutions, a Fe-deficient mackinawite-like phase Fe 1-xS was obtained, which was probably an electron-deficient p-type conductor. The second kind of ICs was prepared by 'low-temperature direct intercalation in aqueous solutions, using Na-tochilinite as a parental precursor. When the Na-tochilinite was ultrasonicated in aqueous solutions containing Lewis basic complexing agents (like NH 3, N 2H 4, 2,2'-bipyridine (bipy), and 1,10-phenanthroline (phen)), the Na + ions of the Na-tochilinite were removed and the Lewis basic complexing agents entered the hydroxide layer of the Na-tochilinite and became coordinated with the Fe 2+ ions, and the second kind of ICs was thus produced. The second kind of ICs includes NH 3 IC, N 2H 4 IC, N 2H 4-NH 3 IC, [Fe(bipy) 3] 2+-containing IC and [Fe(phen) 3] 2+-containing IC. The third kind of ICs, which includes NH 3 IC, N 2H 4-NH 3 IC and N 2H 4-LiOH (NaOH) IC, was prepared by the hydrothermal reaction of metallic Fe particles with (NH 4) 2S aqueous solution, S (elemental) + N 2H 4·H 2O aqueous solution, and S + N 2H 4·H 2O + LiOH (NaOH) aqueous solution, respectively. The third kind of ICs has a close relationship with the second kind of ICs both in composition and structure. The fourth kind of ICs was prepared by the oxidation and reduction of some of the N 2H 4-containing ICs mentioned above, which include N 2H 2 (diazene or diimide) IC, N 2 (dinitrogen) IC and NH 3 IC. The N 2H 2 IC was prepared by mild air oxidation of the N 2H 4-LiOH IC. The N 2 IC was prepared by strong air oxidation of the N 2H 4-LiOH IC, however, we have not been able to separate the pure phase N 2 IC. Hydrothermal reduction of the N 2H 4 IC made by the direct intercalation method in strong reducing environment by H 2S + Fe (metal) led to the production of the NH 3 IC of the fourth kind of ICs. The NH 3 ICs prepared by the three methods had similar compositions and structures. As almost all the ICs reported in this paper were extremely sensitive both to air and to the electron beam, they were mainly characterized by XRD. The properties and interrelationships (or mutual transformations) of the Fe 1-xS-based ICs revealed novel chemistry occurring in the sub-nanoscopic space between the micrometer- to nanometer-sized electron-deficient Fe 1-xS layers. An important finding of this novel chemistry was that the Fe 1-xS-based ICs tended to oxidize or reduce the intercalated species when the redox state of their environments varied. The results of our experiments potentially have many cosmochemical implications. The most important implication is that our experimental results, along with previous studies, strongly suggested that some of the ammonium salts, ammonia and carbonates existing in the matrix of the CM carbonaceous chondrites may have been formed by abiotic reactions employing molecular nitrogen as the nitrogen source and carbon monoxide as the carbon source and iron sulfide and/or iron hydroxide as catalysts.

Peng, Yiya; Xi, Guangcheng; Zhong, Chang; Wang, Linping; Lu, Jun; Sun, Ximeng; Zhu, Lu; Han, Qikun; Chen, Lin; Shi, Lei; Sun, Mei; Li, Qianrong; Yu, Min; Yin, Mingwen

2009-08-01

140

Electron microscopy analysis of the boundary layer structure of SrTiO3 semiconducting ceramic  

PubMed

In a boundary layer (BL) semiconducting SrTiO3-based ceramic condenser, the BL structure has been investigated using high-resolution field-emission scanning electron microscopy (FE-SEM) and field-emission (scanning) transmission electron microscopy (FE-(S)TEM). In an initial TEM observation, a double layered structure was observed at the grain boundary region. It consisted of a grain boundary (second phase) and a pair of the metal diffusion layers of up to several nanometres in width across the grain boundary where the change of the crystal lattice distance was undetected by the high-resolution TEM image. A facet structure was often observed on the grain boundaries. It was particularly formed on (020) plane of the grain crystal. High resolution SEM showed a jagged striped structure on the surface of the bulk material and on the inside grain as revealed by fracture. Using the similarity in shape and size, it can be identified to correspond to the facet boundary structure. Its formation mechanism can be explained as that during the reoxidization process when the oxide flux of the mixture of Bi2O3, PbO and CuO, painted on the bulk material, surfaces migrates into the ceramic along the grain boundary. The oxide corrodes the grain surfaces including the bulk surfaces. This corrosion particularly occurs on (020) plane of the grain so that the facet structure is produced. In this paper, by using the atomic scale high angle annular dark field STEM, it has been determined that Bi atoms preferentially replace Sr atoms on (020) in the diffusion layers. The atom position displacement was also detected at the grain surfaces and this altered atomic assignment can be determined as an origin of production of Sr2Bi4Ti5O18 at the grain boundary. Also, it was observed that the layer width of the metal diffusion layers was often different between the both grains and changed locally so that the ribbon of the diffusion layers meandered around the straight grain boundary. Its possible mechanism is also proposed. PMID:10791423

Kawasaki; Yoshioka; Sato; Nomura; Shiojiri

2000-01-01

141

Original Size and Shape of the Sudbury Structure  

NASA Technical Reports Server (NTRS)

This paper presents new evidence bearing on the original size and shape of the Sudbury impact structure. Current opinion is almost unanimous that the structure is a multiring basin with an original diameter of about 200 km and a circular shape that has since been shortened in a northwest-southeast direction by Penokean deformation Evidence for this interpretation, collected chiefly from north of the Sudbury Igneous Complex (SIC), includes supposed outer rings on Landsat imagery, distant occurrences of "Sudbury breccia" (generally defined as pseudotachylite), shatter cone occurrences, and outliers of Huronian sedimentary rock thought to be down-faulted rings. New data from imaging radar and field work north of the SIC, however, contradict this evidence. Radar imagery shows no signs of the supposed outer rings mapped by earlier workers on Landsat images. The most prominent ring has been found to be a chance alignment of two independent fracture sets. Radar imagery from the CCRS Convair 580, with look direction almost normal to the north rim of the SIC, shows no evidence of the rings despite strong look azimuth highlighting. Radar imagery has shown many unmapped diabase dikes north of the SIC. Several exposures of supposed Sudbury breccia are associated with these dikes or with Nipissing diabase intrusions, in some cases actually inside the dikes or directly continuous with them. They appear to be igneous intrusion breccias with no relation to impact. Shock-wave interaction at lithologic contacts cannot be invoked for most of these, because they are part of a northwest trending swarm cutting the SIC in the North Range, and hence too young for an impact origin. Similar diabase-related breccias and pseudotachylite-like veins have been found far outside the Sudbury area between Chapleau and Thessalon. Shatter cones north of the SIC are few and poorly developed, perhaps due to the coarse-grained Footwall rock, and cannot be considered a continuous zone analogous to their occurrence on the South Range in Huronian rocks. Supposed down-faulted outliers of Huronian rocks north of the SIC show no consistent relation to faulting, and the Huronian/Archean contact is locally erosional. Radar imagery and field-checking confirm Rousell's conclusion that the North Range has undergone little or no Penokean deformation. T'his implies that the plan view outline of the crater (floor of the SIC) is original. Extrapolation of the North Range as part of a circular arc leads to an impossibly great diameter. It is concluded that although Penokean deformation largely accounts for the structure's shape, the original crater was not circular and was much smaller than 200 km across.

Lowman, P. D., Jr.

1997-01-01

142

Magnetic structure of Tb-Fe films with an artificially layered structure  

SciTech Connect

The magnetic structure of Tb-Fe films with an artificially layered structure has been investigated by measuring the temperature dependence of the magnetization of the films. Ferrimagnetic coupling between Tb and Fe through the interface was explicitly observed up to about 9-A Tb and 10-A Fe layers. Films with thinner Tb and Fe layers than these thicknesses are composed of only ferrimagnetically coupled Tb-Fe regions. Films with thicker layers of Tb and Fe are composed of ferrimagnetically coupled Tb-Fe, ferromagnetic Fe, ferromagnetic Tb, and/or magnetically compensated Tb regions. The Tb-Fe films exhibit various temperature dependencies of the magnetization corresponding to these magnetic structures.

Yamauchi, K.; Habu, K.; Sato, N.

1988-11-15

143

3D spherical layer photonic band-gap structures in dichromate gelatin.  

E-print Network

??Three-dimensional spherical layer photonic band-gap structures were fabricated in dichromate gelatin (DCG) holographic emulsions by a holographic lithography technique. Five spherical layer structures with different… (more)

Hung, Jenny

2008-01-01

144

Changes in the turbulent boundary layer structure associated with net drag reduction by outer layer manipulators  

NASA Technical Reports Server (NTRS)

A specially designed wind tunnel was used to examine the effects of tandemly arranged parallel plate manipulators (TAPPMs) on a turbulent boundary-layer structure and the associated drag. Momentum balances, as well as measurements of the local shear stress from the velocity gradient near the wall, were used to obtain the net drag and local skin friction changes. Two TAPPMs, identical except for the thickness of their plates, were used in the study. Results with .003 inch plates were a maximum net drag reduction of 10 percent at 58 beta sub o (using a momentum balance). At 20 beta sub o, simultaneous laser sheet flow visualization and hot-wire anemometry data showed that the Reynolds stress in the large eddies was significantly reduced, as were the streamwise and normal velocity components. Using space-time correlations the reductions were again identified. Furthermore, quantitative flow visualization showed that the outward normal velocity of the inner region was also significantly decreased in the region around 20 beta sub o. However, throughout the first 130 beta sub o, the measured sublayer thickness with the TAPPMs in place was 15 to 20 percent greater. The data showed that the skin friction, as well as the structure of the turbulence, was strongly modified in the first 35 beta sub o, but that they both significantly relaxed toward unmanipulated boundary layer values by 50 beta sub o.

Rashidnia, N.; Falco, R. E.

1987-01-01

145

Origin of the significantly enhanced optical transitions in layered boron nitride  

NASA Astrophysics Data System (ADS)

It is normally expected that an excellent optical material should have p?s-like transitions at the absorption edge. This is because the strength of p?s-like transitions usually is much stronger than those of p?p transitions, especially in those ionic semiconductors where the electronic states are more localized and behave as atomic characters. Here, we demonstrate an exception that the luminescence intensity of hexagonal boron nitride (h-BN) could be at least two orders of magnitude greater than that of AlN, despite the dominated atomic p?p transitions at the absorption edge of h-BN. Using group theory analysis and first-principles calculations, we show that the strong optical transitions in h-BN originate from the unusually strong p?p-like transitions and its “two-dimensional” nature. As learned from h-BN, we demonstrate that one can dramatically increase the absorption or luminescence intensity at the fundamental absorption edge of an optical material by confining its thickness into a few layers, which is much more effective than the commonly used superlattice technology.

Huang, Bing; Cao, X. K.; Jiang, H. X.; Lin, J. Y.; Wei, Su-Huai

2012-10-01

146

Morphology and origins of sedimentary structures on submarine slopes.  

PubMed

Submarine slopes in deep water, such as continental slopes, are often indented by valleys or channels and made uneven by ridges or levees. The origins of many of these features are unknown or disputed. Morphologically, however, there is often great similarity between forms on deep slopes and forms on shallow slopes or on land. Structurally the slopes in deep water are less well explored, but several observations reveal features, such as lamination and crossbedding, that are known from shallow water also. Measurements of current indicate that periodically the movement of water near the bottom is fast enough to move particles of sediment from time to time. Morphology, fine structure, and currents suggest that internal waves and associated currents, as well as gravity, may control the shape of deep submarine slopes analogously to the shaping by surface waves of slopes in shallow water. PMID:17756512

Hulsemann, J

1968-07-01

147

Surface-plasmons lasing in double-graphene-layer structures  

SciTech Connect

We consider the concept of injection terahertz lasers based on double-graphene-layer (double-GL) structures with metal surface-plasmon waveguide and study the conditions of their operation. The laser under consideration exploits the resonant radiative transitions between GLs. This enables the double-GL laser room temperature operation and the possibility of voltage tuning of the emission spectrum. We compare the characteristics of the double-GL lasers with the metal surface-plasmon waveguides with those of such laser with the metal-metal waveguides.

Dubinov, A. A. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Institute for Physics of Microstructures of Russian Academy of Sciences, and Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Aleshkin, V. Ya. [Institute for Physics of Microstructures of Russian Academy of Sciences, and Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Ryzhii, V. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Center for Photonics and Infrared Engineering, Bauman Moscow State Technical University, Moscow 105005 (Russian Federation); Shur, M. S. [Department of Electrical, Electronics, and System Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Otsuji, T. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan)

2014-01-28

148

Intrinsic growth of layered structure GaS microtubes from banana-leaf like structures  

NASA Astrophysics Data System (ADS)

We report the growth of highly crystalline GaS tubular structures directly on Ga metal from banana-leaf like structures via a facile catalyst free physical vapor deposition process. GaS microtube arrays with 1.5-2 ?m length were synthesized by promoting the intrinsic layered crystal structure of GaS during thermal evaporation where the thermal stress and interlayer interactions are mostly dominant. We monitored the growth process systematically to build a proper understanding of the formed tubular structures in this layered material. Microstructural analyses indicate that the GaS microtubes start with the formation of ultra-long, uniform banana-leaf like morphology that eventually splits into thinner flakes and starts rolling in nanometer size diameters. Final realization of GaS microtubes happened by the expansion of these intermediate rolled-up layers in their outer diameter by minimizing the strain energy in the system in a self-catalytic growth process.

Datta, Anuja; Sinha, Godhuli; Panda, Subhendu K.

2013-04-01

149

Layers  

NASA Astrophysics Data System (ADS)

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 ?4( z), ?5( x), and ?5( y) to the conduction-band state ?1( 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 ?4( z), ?5( x), and ?5( 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.

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

2014-09-01

150

S4 : A free electromagnetic solver for layered periodic structures  

NASA Astrophysics Data System (ADS)

We describe S4, a free implementation of the Fourier modal method (FMM), which has also been commonly referred to as rigorous coupled wave analysis (RCWA), for simulating electromagnetic propagation through 3D structures with 2D periodicity. We detail design aspects that allow S4 to be a flexible platform for these types of simulations. In particular, we highlight the ability to select different FMM formulations, user scripting, and extensibility of program capabilities for eigenmode computations. Program summary Program title: S4 Catalogue identifier: AEMO_v1_0. Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEMO_v1_0..html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 2 No. of lines in distributed program, including test data, etc.: 56910 No. of bytes in distributed program, including test data, etc.: 433883 Distribution format: Programming language: C, C++. Computer: Any computer with a Unix-like environment and a C++ compiler. Developed on 2.3 GHz AMD Phenom 9600. Operating system: Any Unix-like environment; developed under MinGW32 on Windows 7. Has the code been vectorized or parallelized?: Yes. Parallelized using MPI. RAM: Problem dependent (linearly proportional to number of layers and quadratic in number of Fourier components). A single layer calculation with approximately 100 Fourier components uses approximately 10 MB. Classification: 10. Electrostatics and Electromagnetics. External routines: Lua [1] and optionally exploits additional free software packages: FFTW [2], CHOLMOD [3], MPI message-passing interface [4], LAPACK and BLAS linear-algebra software [5], and Kiss FFT [6]. Nature of problem: Time-harmonic electromagnetism in layered bi-periodic structures. Solution method: The Fourier modal method (rigorous coupled wave analysis) and the scattering matrix method. Running time: Problem dependent and highly dependent on quality of the BLAS implementation (linearly proportional to number of layers and cubic in number of Fourier components). A single layer calculation with approximately 100 Fourier components takes 4 s on the development machine using the reference BLAS.

Liu, Victor; Fan, Shanhui

2012-10-01

151

Layered manganites : magnetic structure at extreme doping levels.  

SciTech Connect

We report powder neutron diffraction results on the crystal and magnetic structures of the bilayer Ruddlesden-Popper phase Sr{sub 3}Mn{sub 2}O{sub 7{minus}{delta}} ({delta} = 0.0, 0.45) and correlate these structures with their magnetic and transport properties. The {delta} = 0.45 compound contains a large number of oxygen vacancies that are disordered in the MnO{sub 2} planes. As a result of this disordered vacancy structure, Sr{sub 3}Mn{sub 2}O{sub 6.55} is a nonmagnetic insulator. Sr{sub 3}Mn{sub 2}O{sub 7.0} ({delta} = 0) is an antiferromagnetic insulator whose magnetic structure is related to that of the SrMnO{sub 3} perovskite. Comparison of this end-member compound to its doped congeners in the La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} series highlights the extreme sensitivity of magnetic structure to dopant concentration in these layered materials.

Mitchell, J. F.

1998-09-11

152

Composite structure of plumes in stratus-topped boundary layers  

SciTech Connect

Knowledge of convective plumes within the clear convective boundary layer (CBL) is quite advanced owing to direct measurements, tank experiments, and large-eddy simulation studies. As a result, modeling of the CBL is relatively successful. Progress for the stratus-topped boundary layer (STBL), however, is slow. This study compares the plume structure of the surface-heated CBL with that of the cloud-top-cooled STBL in the hope of extending knowledge of the CBL to the STBL. A conditional sampling technique is applied to the STBL flow fields that are generated through large-eddy simulations, so that the structures of typical updrafts and downdrafts may be derived. For the purpose of comparing the surface-heated CBL and the cloud-top-cooled STBL, an idealized STBL, the compensating updrafts are nearly as strong as the top-cooling-generated downdrafts, and they contribute a significant amount to the heat, moisture, and momentum transports. This differs very much from the CBL, where the compensating downdrafts are much weaker than the surface-heating-generated updrafts and contribute much less to the transports. The mechanism that results in such an asymmetry between the CBL and STBL is examined, and suggestions on how the asymmetry affects the entrainment process are made. 25 refs., 26 figs.

Moeng, C.H. (National Center for Atmospheric Research, Boulder, CO (United States)); Schumann, U. (Institute of Atmospheric Physics, Oberpfaffenhofen (Germany))

1991-10-15

153

Radial transmission line analysis of multi-layer structures  

SciTech Connect

The analysis of multi-layer beam tubes is a standard problem and involves axially propagating waves. This treatment is ill suited to a short multi-layer structure such as the present example of a ferrite covered ceramic break in the beam tube at the ERL photo-cathode electron gun. This paper demonstrates that such structure can better be treated by radial wave propagation. The theoretical method is presented and numerical results are compared with measured network analyser data and Microwave Studio generated simulations. The results confirm the concept of radial transmission lines as a valid analytical method. An Energy Recovery Linac (ERL) is being constructed at this laboratory for the purpose of research towards an envisioned Electron Ion Collider. One of the pertinent topics is damping of Higher Order Modes (HOM). In this ERL, the damping is provided by ferrite absorbers in the beam tube. A modified version thereof, a ceramic break surrounded by ferrite, is planed for the superconducting electron gun. The damper here is located at room temperature just outside of the gun. If used in a cavity chain, the ceramic break is in the vacuum tube at helium temperature whereas the ferrite is moved into the cryostat insulating vacuum allowing higher temperatures. The general properties of the ferrite HOM dampers have been published but are more detailed in this paper.

Hahn, H.; Hammons, L.

2011-03-28

154

A new prediction strategy for long local protein structures using an original description  

E-print Network

- 1 - A new prediction strategy for long local protein structures using an original description Prediction Keywords: library of fragments, structural networks, local structure prediction, support vector approximation. A local structure prediction method was also proposed. Here, overlapping properties of local

Paris-Sud XI, Université de

155

Deep structure and origin of active volcanoes in China  

NASA Astrophysics Data System (ADS)

Recent geophysical studies have provided important constraints on the deep structure and origin of the active intraplate volcanoes in Mainland China. Magmatism in the western Pacific arc and back-arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab (e.g., Zhao et al., 2009a), while the intraplate magmatism in China has different origins. The active volcanoes in Northeast China (such as the Changbai and Wudalianchi) are caused by hot upwelling in the big mantle wedge (BMW) above the stagnant slab in the mantle transition zone and deep slab dehydration as well (Zhao et al., 2009b). The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate (or Indian plate) (Lei et al., 2009a). The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs' deep subduction in the east and Indian slab's deep subduction in the west down to the lower mantle (Lei et al., 2009b; Zhao, 2009). The stagnant slab finally collapses down to the bottom of the mantle, which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab-plume interactions (Zhao, 2009). References Lei, J., D. Zhao, Y. Su, 2009a. Insight into the origin of the Tengchong intraplate volcano and seismotectonics in southwest China from local and teleseismic data. J. Geophys. Res. 114, B05302. Lei, J., D. Zhao, B. Steinberger et al., 2009b. New seismic constraints on the upper mantle structure of the Hainan plume. Phys. Earth Planet. Inter. 173, 33-50. Zhao, D., 2009. Multiscale seismic tomography and mantle dynamics. Gondwana Res. 15, 297-323. Zhao, D., Z. Wang, N. Umino, A. Hasegawa, 2009a. Mapping the mantle wedge and interplate thrust zone of the northeast Japan arc. Tectonophysics 467, 89-106. Zhao, D., Y. Tian, J. Lei, L. Liu, 2009b. Seismic image and origin of the Changbai intraplate volcano in East Asia: Role of big mantle wedge above the stagnant Pacific slab. Phys. Earth Planet. Inter. 173, 197-206.

Zhao, D.

2010-12-01

156

Crystal structure of britvinite [Pb{sub 7}(OH){sub 3}F(BO{sub 3}){sub 2}(CO{sub 3})][Mg{sub 4.5}(OH){sub 3}(Si{sub 5}O{sub 14})]: A new layered silicate with an original type of silicon-oxygen networks  

SciTech Connect

The crystal structure of a new mineral britvinite Pb{sub 7.1}Mg{sub 4.5}(Si{sub 4.8}Al{sub 0.2}O{sub 14})(BO{sub 3})(CO{sub 3})[(BO{sub 3}){sub 0.7}(SiO{sub 4}){sub 0.3}]= (OH, F){sub 6.7} from the Langban iron-manganese skarn deposit (Vaermland, Sweden) is determined at T = 173 K using X-ray diffraction (Stoe IPDS diffractometer, {lambda}MoK{alpha}, graphite monochromator, 2{theta}{sub max} = 58.43{sup o}, R = 0.052 for 6262 reflections). The main crystal data are as follows: a = 9.3409(8) A, b = 9.3579(7) A, c = 18.8333(14) A, {alpha} = 80.365(6) deg., {beta} = 75.816(6) deg., {gamma} = 59.870(5) deg., V = 1378.7(2) A{sup 3}, space group P1, Z = 2, and {rho}{sub calcd} = 5.42 g/cm{sup 3}. The idealized structural formula of the mineral is represented as [Pb{sub 7}(OH){sub 3}F(BO{sub 3}){sub 2}(CO{sub 3})][Mg{sub 4.5}(OH){sub 3}(Si{sub 5}O{sub 14})]. It is demonstrated that the mineral britvinite is a new representative of the group of mica-like layered silicates with structures in which three-layer (2: 1) 'sandwiches' composed of tetrahedra and octahedra alternate with blocks of other compositions, such as oxide, oxide-carbonate, oxide-carbonate-sulfate, and other blocks. The tetrahedral networks (Si{sub 5}O{sub 14}){sub {infinity}}{sub {infinity}} consisting of twelve-membered rings are fragments of the britvinite structure. Similar networks also form crystal structures of the mineral zeophyllite and the synthetic phase Rb{sub 6}Si{sub 10}O{sub 23}. In the crystal structures under consideration, the tetrahedral networks differ in the rotation of tetrahedra with respect to the layer plane.

Yakubovich, O. V. [Lomonosov Moscow State University (Russian Federation)], E-mail: yakubol@geol.msu.ru; Massa, W. [Philipps-Universitaet Marburg (Germany); Chukanov, N. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2008-03-15

157

Turbulence structure of the surface layer Boun 2247-03D TURBULENCE STRUCTURE OF THE UNSTABLE ATMOSPHERIC  

E-print Network

ATMOSPHERIC SURFACE LAYER AND TRANSITION TO THE OUTER LAYER K.G. McNAUGHTON School of GeoSciences, University of Edinburgh, Scotland EH9 3JU. (Accepted by Boundary-Layer Meteorology, 3 Nov. 2003) Abstract. This paper presents a new model of the structure of turbulence in the unstable atmospheric surface layer

Moncrieff, John B.

158

The structural origin of second harmonic generation in fascia  

PubMed Central

Fascia tissue is rich in collagen type I proteins and can be imaged by second harmonic generation (SHG) microscopy. While identifying the overall alignment of the collagen fibrils is evident from those images, the tridimensional structural origin for the observation of SHG signal is more complex than it apparently seems. Those images reveal that the noncentrosymmetric (piezoelectric) structures are distributed heterogeneously on spatial dimensions inferior to the resolution provided by the nonlinear optical microscope (sub-micron). Using piezoresponse force microscopy (PFM), we show that an individual collagen fibril has a noncentrosymmetric structural organization. Fibrils are found to be arranged in nano-domains where the anisotropic axis is preserved along the fibrillar axis, while across the collagen sheets, the phase of the second order nonlinear susceptibility is changing by 180 degrees between adjacent nano-domains. This complex architecture of noncentrosymmetric nano-domains governs the coherent addition of 2? light within the focal volume and the observed features in the SHG images taken in fascia. PMID:21326632

Rivard, Maxime; Laliberté, Mathieu; Bertrand-Grenier, Antony; Harnagea, Catalin; Pfeffer, Christian P.; Vallières, Martin; St-Pierre, Yves; Pignolet, Alain; El Khakani, My Ali; Légaré, François

2011-01-01

159

Sound-insulation layers low-frequency modeling, using the fuzzy structure theory  

E-print Network

09NVC-0163 Sound-insulation layers low-frequency modeling, using the fuzzy structure theory Laurent [20,200] Hz, sound-insulation layer modeling remains a critical topic. Recent work allows- insulation layer. Nevertheless, such an approach requires a FE model of sound-insulation layer, which may

Boyer, Edmond

160

Boundary Layer Height and Structure during the NATO LASIE Campaign  

NASA Astrophysics Data System (ADS)

The NATO Ligurian Air-Sea Interaction Experiment (LASIE) took place in 2007, from 16 to 22 June, in the Mediterranean Sea. This filed campaign was organized under the auspices of the NATO Undersea Research Centre (NURC), located in La Spezia, Italy. The main scientific goal was to contribute to the evaluation and development of parameterizations of the oceanic and atmospheric boundary layers and their interactions. Extensive meteorological and oceanographic measurements were collected, on board the research vessels Leonardo, Planet, and Urania, and from the spar buoy ODAS Italia 1. In this study ceilometer (Vaisala CL31) and atmospheric radiosondes (Vaisala DigiCORA) measurements are used to assess the evolution of the marine atmospheric boundary layer (MABL) structure and height during the LASIE cruise. The ceilometer measured continuously the cloud height base, while the radiosondes, launched every 3 hours, recorded vertical profiles of wind speed, wind direction, potential temperature and relative humidity. Several methods available in the literature are used to determine the height of the MABL from observations. The results from these methods are compared with the MABL heights from the limited-area numeric weather prediction models WRF (Weather Research and Forecasting) and MM5 (Fifth-Generation Mesoscale Model).

Tomé, R.; Sempreviva, A. M.; Schiano, E.; Bozzano, R.; Miranda, P. M.; Pensieri, S.; Semedo, A.; Teixeira, J.

2009-09-01

161

Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides.  

PubMed

Interplay among various collective electronic states such as charge density wave and superconductivity is of tremendous significance in low-dimensional electron systems. However, the atomistic and physical nature of the electronic structures underlying the interplay of exotic states, which is critical to clarifying its effect on remarkable properties of the electron systems, remains elusive, limiting our understanding of the superconducting mechanism. Here, we show evidence that an ordering of selenium and sulphur atoms surrounding tantalum within star-of-David clusters can boost superconductivity in a layered chalcogenide 1T-TaS2-xSex, which undergoes a superconducting transition in the nearly commensurate charge density wave phase. Advanced electron microscopy investigations reveal that such an ordered superstructure forms only in the x area, where the superconductivity manifests, and is destructible to the occurrence of the Mott metal-insulator transition. The present findings provide a novel dimension in understanding the relationship between lattice and electronic degrees of freedom. PMID:25625438

Ang, R; Wang, Z C; Chen, C L; Tang, J; Liu, N; Liu, Y; Lu, W J; Sun, Y P; Mori, T; Ikuhara, Y

2015-01-01

162

AIP/123-QED Fuzzy structure theory modeling of sound-insulation layers in complex  

E-print Network

AIP/123-QED Fuzzy structure theory modeling of sound-insulation layers in complex vibroacoustic France (Dated: September 11, 2008) Fuzzy structure theory for sound-insulation layers 1 hal-00684495 is proposed in developing an elas- toacoustic element useful to model sound-insulation layers for compu

Paris-Sud XI, Université de

163

Ferrite-ferroelectric layered structures for electrically and magnetically tunable microwave resonators  

E-print Network

Ferrite-ferroelectric layered structures for electrically and magnetically tunable microwave It is demonstrated experimentally that a layered structure consisting of ferrite and ferroelectric thin films can constant , and a bias magnetic field to the ferrite layer. The resonator having central frequency f0 5 GHz

Demokritov, S.O.

164

Journal of the Atmospheric Sciences Comments on "Symmetric and Asymmetric Structures of Hurricane Boundary Layer in  

E-print Network

Boundary Layer in Coupled Atmosphere-Wave-Ocean Models and Observations" --Manuscript Draft-- Manuscript symmetric and asymmetric hurricane boundary-layer structures in a fully coupled atmosphere-28 wave Number: Full Title: Comments on "Symmetric and Asymmetric Structures of Hurricane Boundary Layer

Smith, Roger K.

165

Atmospheric sounding over the winter Kuroshio Extension: Effect of surface stability on atmospheric boundary layer structure  

E-print Network

: Effect of surface stability on atmospheric boundary layer structure, Geophys. Res. Lett., 33, L04703, doi the Pacific equatorial front [Hashizume et al., 2002] show marked changes in atmospheric boundary layer (ABL boundary layer structure Hiroki Tokinaga,1,2 Youichi Tanimoto,3,4 Masami Nonaka,5 Bunmei Taguchi,6 Tomohiro

Xie, Shang-Ping

166

Atmospheric boundary-layer structure from simultaneous SODAR, RASS, and ceilometer measurements  

Microsoft Academic Search

A comparison of the determination of boundary-layer structures by a SODAR, by a RASS, and by a ceilometer is presented. One important structure is the mixing-layer height (MLH). The comparison is focused on 3 days with an evolution of a convective boundary layer over a larger city in Germany. The three instruments give information that partly agree and partly complement

Stefan Emeis; Christoph Münkel; Siegfried Vogt; Wolfgang J Müller; Klaus Schäfer

2004-01-01

167

Structure of the Entrainment Zone Capping the Convective Atmospheric Boundary Layer  

Microsoft Academic Search

The authors use large-eddy simulation (LES) to investigate entrainment and structure of the inversion layer of a clear convectively driven planetary boundary layer (PBL) over a range of bulk Richardson numbers, Ri. The LES code uses a nested grid technique to achieve fine resolution in all three directions in the inversion layer.Extensive flow visualization is used to examine the structure

Peter P. Sullivan; Chin-Hoh Moeng; Bjorn Stevens; Donald H. Lenschow; Shane D. Mayor

1998-01-01

168

Microhardness and structural defects of GaSe layered semiconductor  

NASA Astrophysics Data System (ADS)

Microhardness of GaSe layered single crystals was studied. The dependences of Vickers microhardness on load and time under load were studied experimentally to find a range of these parameters acceptable for reliable measurements. A range of loads was found, where time under load had no significant effect on microhardness. Mechanisms of deformation under concentrated load are discussed. The GaSe crystals showed anisotropy of microhardness in the (0 0 0 1) plane; the coefficient of anisotropy is k= Hmax/ Hmin=1.4. Profiles of indentations and topography of the surface in the vicinity of an indentation were studied by atomic force microscopy (AFM). The experiment demonstrated good agreement between the calculated and the measured depths of indentation pits. AFM proved to be an informative technique for the description of a structure of the material after microindentation. Basal and non-basal dislocations were studied by optical microscopy and AFM.

Borisenko, E. B.; Kolesnikov, N. N.; Borisenko, D. N.; Bozhko, S. I.

2011-02-01

169

Electrical properties of magnetron sputtered amorphous carbon films with sequential sp3-rich/sp2-rich layered structure  

NASA Astrophysics Data System (ADS)

The electrical properties of thick amorphous carbon (a-C) films with sequential sp3-rich/sp2-rich layered structure, grown by magnetron sputtering on Si substrates at room temperature, were investigated. At low electric fields, the conduction is due to the variable range hopping mechanism. At high electric fields, thermally assisted band-to-band indirect tunneling is the dominant conduction mechanism, while the Arrhenius plots of the current show a deviation from straight lines in the form of continuous bending satisfying the Meyer-Nelder rule. Comparative studies of low-frequency noise in sp2-rich single layer and sp3-rich/sp2-rich layered a-C films indicate that the noise in the a-C layered originates from traps located mainly at the interfaces of the sp3-rich/sp2-rich bilayers.

Hastas, N. A.; Dimitriadis, C. A.; Tassis, D. H.; Panayiotatos, Y.; Logothetidis, S.; Papadimitriou, D.

2001-11-01

170

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique  

SciTech Connect

Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.

Kevin Jerome Sutherland

2001-05-01

171

Layered structure in the interaction of thin foil with two laser pulses  

SciTech Connect

An interesting layered structure of multiple high density layers are formed when two counter-propagating circularly polarized laser pulses with the same polarization direction irradiate on an ultra-thin foil. This structure changes periodically. For light atoms most of which electrons may be fully ionized, this layered structure can keep for dozens of laser periods after the laser-foil interaction. This interesting structure may have potential applications.

Yu, Yahong; Shen, Baifei, E-mail: bfshen@mail.shcnc.ac.cn, E-mail: jill@siom.ac.cn; Yu, Wei; Wang, Wenpeng; Zhang, Xiaomei; Ji, Liangliang, E-mail: bfshen@mail.shcnc.ac.cn, E-mail: jill@siom.ac.cn; Zhao, Xueyan; Wang, Xiaofeng; Yi, Longqing; Shi, Yin; Xu, Tongjun; Zhang, Lingang [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China)] [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Wen, Meng [Institute of Photonics and Photon-Technology, Northwest University, Xi'an 710069 (China)] [Institute of Photonics and Photon-Technology, Northwest University, Xi'an 710069 (China)

2014-02-15

172

Corrosion detection in multi-layered rotocraft structures  

SciTech Connect

Rotorcraft structures do not readily lend themselves to quantifiable inspection methods due to airframe construction techniques. Periodic visual inspections are a common practice for detecting corrosion. Unfortunately, when the telltale signs of corrosion appear visually, extensive repair or refurbishment is required. There is a need to nondestructively evaluate airframe structures in order to recognize and quantify corrosion before visual indications are present. Nondestructive evaluations of rotorcraft airframes face inherent problems different from those of the fixed wing industry. Most rotorcraft lap joints are very narrow, contain raised fastener heads, may possess distortion, and consist of thinner gage materials ({approximately}0.012--0.125 inches). In addition the structures involve stack-ups of two and three layers of thin gage skins that are separated by sealant of varying thickness. Industry lacks the necessary data techniques, and experience to adequately perform routine corrosion inspection of rotorcraft. In order to address these problems, a program is currently underway to validate the use of eddy current inspection on specific rotorcraft lap joints. Probability of detection (POD) specimens have been produced that simulate two lap joint configurations on a model TH-57/206 helicopter. The FAA's Airworthiness Assurance Center (AANC) at Sandia Labs and Bell Helicopter have applied single and dual frequency eddy current (EC) techniques to these test specimens. The test results showed enough promise to justify beta site testing of the eddy current methods evolved in this study. The technique allows users to distinguish between corrosion signals and those caused by varying gaps between the assembly of skins. Specific structural joints were defined as prime corrosion areas and a series of corrosion specimens were produced with 5--20% corrosion distributed among the layers of each joint. Complete helicopter test beds were used to validate the laboratory findings. This paper will present the laboratory and field results that quantify the EC technique's corrosion detection performance. Plans for beta site testing, adoption of the new inspection procedure into routine rotorcraft maintenance, and NDI training issues will also be discussed.

ROACH,DENNIS P.; WALKINGTON,PHILLIP D.; HOHMAN,ED; MARSHALL,GREG

2000-04-25

173

Structure Identification Within a Transitioning Swept-Wing Boundary Layer  

NASA Technical Reports Server (NTRS)

Extensive measurements are made in a transitioning swept-wing boundary layer using hot-film, hot-wire and cross-wire anemometry. The crossflow-dominated flow contains stationary vortices that breakdown near mid-chord. The most amplified vortex wavelength is forced by the use of artificial roughness elements near the leading edge. Two-component velocity and spanwise surface shear-stress correlation measurements are made at two constant chord locations, before and after transition. Streamwise surface shear stresses are also measured through the entire transition region. Correlation techniques are used to identify stationary structures in the laminar regime and coherent structures in the turbulent regime. Basic techniques include observation of the spatial correlations and the spatially distributed auto-spectra. The primary and secondary instability mechanisms are identified in the spectra in all measured fields. The primary mechanism is seen to grow, cause transition and produce large-scale turbulence. The secondary mechanism grows through the entire transition region and produces the small-scale turbulence. Advanced techniques use Linear Stochastic Estimation (LSE) and Proper Orthogonal Decomposition (POD) to identify the spatio-temporal evolutions of structures in the boundary layer. LSE is used to estimate the instantaneous velocity fields using temporal data from just two spatial locations and the spatial correlations. Reference locations are selected using maximum RMS values to provide the best available estimates. POD is used to objectively determine modes characteristic of the measured flow based on energy. The stationary vortices are identified in the first laminar modes of each velocity component and shear component. Experimental evidence suggests that neighboring vortices interact and produce large coherent structures with spanwise periodicity at double the stationary vortex wavelength. An objective transition region detection method is developed using streamwise spatial POD solutions which isolate the growth of the primary and secondary instability mechanisms in the first and second modes, respectively. Temporal evolutions of dominant POD modes in all measured fields are calculated. These scalar POD coefficients contain the integrated characteristics of the entire field, greatly reducing the amount of data to characterize the instantaneous field. These modes may then be used to train future flow control algorithms based on neural networks.

Chapman, Keith; Glauser, Mark

1996-01-01

174

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique  

SciTech Connect

Over the last ten years, photonic band gap (PBG) theory and technology have become an important area of research because of the numerous possible applications ranging from high-efficiency laser diodes to optical circuitry. This research concentrates on reducing the length scale in the fabrication of layered photonic band gap structures and developing procedures to improve processing consistency. Various procedures and materials have been used in the fabrication of layered PBG structures. This research focused on an economical micro transfer molding approach to create the final PBG structure. A poly dimethylsiloxane (PDMS) rubber mold was created from a silicon substrate. It was filled with epoxy and built layer-by-layer to create a 3-D epoxy structure. This structure was infiltrated with nanoparticle titania or a titania sol-gel, then fired to remove the polymer mold, leaving a monolithic ceramic inverse of the epoxy structure. The final result was a lattice of titania rolds that resembles a face-centered tetragonal structure. The original intent of this research was to miniaturize this process to a bar size small enough to create a photonic band gap for wavelengths of visible electro-magnetic radiation. The factor limiting progress was the absence of a silicon master mold of small enough dimensions. The Iowa State Microelectronics Research Center fabricated samples with periodicities of 2.5 and 1.0 microns with the existing technology, but a sample was needed on the order of 0.3 microns or less. A 0.4 micron sample was received from Sandia National Laboratory, which was made through an electron beam lithography process, but it contained several defects. The results of the work are primarily from the 2.5 and 1.0 micron samples. Most of the work focused on changing processing variables in order to optimize the infiltration procedure for the best results. Several critical parameters were identified, ranging from the ambient conditions to the specifics of the procedure. It is believed that most critical for fabrication of high quality samples is control of the temperature of the sample during and after infiltration, and the rate and amount of time spent applying epoxy to the PDMS.

Kevin Jerome Sutherland

2001-06-27

175

Origin and Significance of Magnetic Anisotropy in the Dufek Layered Intrusion  

NASA Astrophysics Data System (ADS)

Anisotropy of magnetic susceptibility (AMS) is commonly used as a rapid, precise and nondestructive measure of fabrics in igneous rocks. In mafic intrusions that lack cumulus magnetite, magnetic susceptibility is typically low and the anisotropy reflects the combined contribution from paramagnetic Fe-bearing silicates and trace amounts of silicate-hosted magnetite. The precise origin of the AMS signal may be difficult to ascertain and, consequently, inferences about magmatic processes may be limited. Here we illustrate that combined AMS, remanence anisotropy and silicate fabric data (from electron backscatter diffraction, EBSD) from large data sets allow the origin of the magnetic fabrics to be more clearly related to the silicate fabric. We collected approximately 800 cores (3600 specimens) from the lowermost 500m of the Jurassic Dufek layered intrusion in Antarctica. AMS for these specimens reveals moderate anisotropy (mean P' = 1.09) with dominantly oblate magnetic fabrics. We also determined anisotropy of thermoremanence (ATRM) for more than 500 specimens. Remanence anisotropy is much more pronounced, with an average anisotropy of P' = 2.1 (range 1.08-10.4) and dominantly prolate fabrics. AMS and ATRM reveal a consistent fabric, with subvertical minima approximating the pole to the magmatic foliation and subhorizontal maxima clustered in the northeast quadrant. EBSD results from 13 samples, spanning a range of magnetic fabric intensities and lithologies, indicate that statistically significant mineral lineations are absent in most samples. Because silicate-hosted magnetite is expected to be the dominant magnetic carrier in these cumulates (three quarters have susceptibility < 0.001 SI and no discrete magnetite grains are observed petrographically), the lack of detectable lineation in the silicates is apparently difficult to reconcile with the pronounced magnetic fabrics. However, when crystallographic data from all samples are combined, the substantial data set (n=135,735 for plagioclase, n=48,608 for orthopyroxene, n=14,365 for clinopyroxene) allows relatively unambiguous correlation of magnetic and silicate fabrics. Crystallographic c-axes for orthopyroxene show the highest degree of clustering (maximum eigenvalue 0.53) and have a mean direction (039°/09°) that is virtually indistiguishable from the ATRM maxima (031°/03°). Clinopyroxene and plagioclase c-axes show less pronounced clustering (maximum eigenvalues 0.41 and 0.37, respectively) with more easterly, subhorizontal directions (099°/03°). Orthopyroxene-hosted magnetite needles (elongate parallel to the c-axis) are presumably the dominant source of the magnetic lineation in both ATRM and AMS. These results provide compelling evidence that magnetic fabric data can provide a robust measure of, at least, the alignment of pyroxene in the Dufek intrusion. When corroborated by silicate fabric analysis, magnetic fabrics may be a sensitive indicator of silicate mineral alignment including subtle lineations that are otherwise difficult to discern.

Gee, J. S.; Lusk, M. W.; Cheadle, M. J.; Grimes, C. B.; Meurer, W. P.

2009-12-01

176

Characterization of the Turbulence Structure in Supersonic Boundary Layers using DNS Data  

E-print Network

Characterization of the Turbulence Structure in Supersonic Boundary Layers using DNS Data Matthew J parameters for the DNS database. In the outer layer, beyond the logarithmic region, the flow at moderate Mach

Martín, Pino

177

Towards a model for the in situ origin of PGE reefs in layered intrusions: insights from chromitite seams of the Rum Eastern Layered Intrusion, Scotland  

NASA Astrophysics Data System (ADS)

The current debate on the origin of platinum-group element (PGE) reefs in layered intrusions centres mostly on gravity settling of sulphide liquid from overlying magma versus its introduction with interstitial melt/fluids migrating upward from the underlying cumulate pile. Here, we show that PGE-rich chromitite seams of the Rum Eastern Layered Intrusion provide evidence for an alternative origin of such deposits in layered intrusions. These laterally extensive 2-mm-thick chromitite seams occur at the bases of several cyclic mafic-ultramafic units and show lithological and textural relationships suggesting in situ growth directly at a crystal-liquid interface. This follows from chromitite development along the edges of steeply inclined culminations and depressions at unit boundaries, even where these are vertically oriented or overhanging. High concentrations of PGE (up to 2-3 ppm Pd + Pt) are controlled by fine-grained base-metal sulphides, which are closely associated with chromitite seams. The following sequence of events explains the origin of the PGE-rich chromitite seams: (a) emplacement of picritic magma that caused thermal and mechanical erosion of underlying cumulate, followed by in situ growth of chromite against the base, (b) precipitation of sulphide droplets on chromite grains acting as favourable substrate or catalyst for sulphide nucleation, (c) the scavenging of PGE by sulphide droplets from fresh magma continuously brought towards the base by convection. Since the rate of magma convection is 105-107 times higher than that of the solidification (km/year to km/day versus 0.5-1.0 cm/year), the in situ formed sulphide droplets can equilibrate with picritic magma of thousands to million times their own volume. As a result, the sulphide-bearing rocks are able to reach economic concentrations of PGE (several ppm). We tentatively suggest that the basic principles of our model may be used to explain the origin of PGE-rich chromitites and classical PGE reefs in other layered mafic-ultramafic intrusions.

Latypov, Rais; O'Driscoll, Brian; Lavrenchuk, Andrey

2013-07-01

178

Controlling structure distortions in 3-layer ferroelectric Aurivillius oxides  

NASA Astrophysics Data System (ADS)

Combined Rietveld refinements of x-ray and neutron powder diffraction data were used to understand the subtle structure distortions in 3-layer Aurivillius oxides that yield off-centering displacements in ferroelectric and multiferroic compositions. Ferroelectric phases including Bi2A2Ti3O12 (A=La, Pr, Nd, La/Pr, La/Nd, Pr/Nd), Bi2A2TiNb2O12 (A=Ca/Sr, Sr, and Sr/Ba) and Bi2A2TiTa2O12 (A=Ca/Sr, and Sr/Ba) were studied to separate the effects of cation size and charge on the structure distortions and properties. A new approach to describing the local coordination around the Ti, Nb, and/or Ta ions is presented, where the oxygen octahedra are characterized as containing kinks in three dimensions. The kink angles follow trends with the A-site ionic radius and the ferroelectric polarization. The driving force for extensive cation site mixing between the Bi and A-site cations has been clearly established, with site mixing required to maintain interlayer bonding.

Nichols, Eric J.; Shi, Jiawanjun; Huq, Ashfia; Vogel, Sven C.; Misture, Scott T.

2013-01-01

179

Intercalation of cellulase enzyme into a hydrotalcite layer structure  

NASA Astrophysics Data System (ADS)

A new inorganic-organic hybrid material whereby cellulase enzyme is incorporated into a hydrotalcite type layered double hydroxide (LDH) structure is reported. The Mg2Al-cellulase-LDH was synthesized via co-precipitation from Mg/Al nitrate at pH=9.6. Characterization was performed using X-ray powder diffraction (XRD), small angle X-ray scattering (SAXS), elemental analysis, infrared spectroscopy (IR) and thermogravimetry (TG). From XRD and SAXS measurements, a d-value of ~5.0 nm was identified for the basal spacing of the Mg2Al-cellulase-LDH. Consequently, the cellulase enzyme (hydrodynamic diameter ~6.6 nm) attains a slightly compressed conformation when intercalated. Formation of the LDH hybrid was also confirmed via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mg2Al-cellulase-LDH phases appear as ~20 nm thin foils which are intergrown to flower-like aggregates. Activity of the enzyme was retained after deintercalation from the Mg2Al-LDH framework using anion exchange. Accordingly, cellulase is not denatured during the intercalation process, and LDH presents a suitable host structure for time-controlled release of the biomolecule.

Zou, N.; Plank, J.

2015-01-01

180

Substrate Structures For Growth Of Highly Oriented And/Or Epitaxial Layers Thereon  

DOEpatents

A composite substrate structure including a substrate, a layer of a crystalline metal oxide or crystalline metal oxynitride material upon the substrate, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the crystalline metal oxide or crystalline metal oxynitride material layer is provided together with additional layers such as one or more layers of a buffer material upon the oriented cubic oxide material layer. Jc's of 2.3×106 A/cm2 have been demonstrated with projected Ic's of 320 Amperes across a sample 1 cm wide for a superconducting article including a flexible polycrystalline metallic substrate, an inert oxide material layer upon the surface of the flexible polycrystalline metallic substrate, a layer of a crystalline metal oxide or crystalline metal oxynitride material upon the layer of the inert oxide material, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the crystalline metal oxide or crystalline metal oxynitride material layer, a layer of a buffer material upon the oriented cubic oxide material layer, and, a top-layer of a high temperature superconducting material upon the layer of a buffer material.

Arendt, Paul N. (Los Alamos, NM); Foltyn, Stephen R. (Los Alamos, NM); Groves, James R. (Los Alamos, NM); Jia, Quanxi (Los Alamos, NM)

2005-07-26

181

THE EFFECTS OF PERIODIC WAKE STRUCTURES ON TURBULENT BOUNDARY LAYERS  

Microsoft Academic Search

Compressor and turbine blade boundary layers in axial-flow turbomachines are subject to periodically disturbed flow. This study modelled these conditions in a wind tunnel with circular cylinders traversing in front of a flat plate. Turbulent boundary layer velocity profiles on the flat plate were measured with a hot-wire anemometer. The turbulence intensity in the boundary layer was found to be

R. M. Holland; R. L. Evans

1996-01-01

182

Enhancement of perpendicular magnetic anisotropy and transmission of spin-Hall-effect-induced spin currents by a Hf spacer layer in W/Hf/CoFeB/MgO layer structures  

SciTech Connect

We report that strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25?nm between the W and CoFeB layers. The Hf spacer also allows transmission of spin currents generated by an in-plane charge current in the W layer to apply strong spin torque on the CoFeB, thereby enabling current-driven magnetic switching. The antidamping-like and field-like components of the spin torque exerted on a 1?nm CoFeB layer are of comparable magnitudes in this geometry. Both components originate from the spin Hall effect in the underlying W layer.

Pai, Chi-Feng; Nguyen, Minh-Hai; Vilela-Leão, Luis Henrique; Buhrman, R. A., E-mail: rab8@cornell.edu [Cornell University, Ithaca, New York 14853 (United States); Belvin, Carina [Department of Physics, Wellesley College, Massachusetts 02481 (United States); Ralph, D. C. [Cornell University, Ithaca, New York 14853 (United States); Kavli Institute at Cornell, Ithaca, New York 14853 (United States)

2014-02-24

183

Thermoacoustic effects on layered structures for the evaluation of structural parameters  

NASA Astrophysics Data System (ADS)

The temperature dependent material characteristics of a layered panel are experimentally measured using a Thermal Mechanical Analysis (TMA) configuration. The temperature dependent wave dispersion characteristics of the panel are subsequently computed using a Wave Finite Element Method (WFEM). The WFEM predictions are eventually used within a wave context SEA approach in order to calculate the temperature dependent Sound Transmission Loss (STL) of the layered panel. Results on the STL for temperatures varying between -100 °C to 160 °C are computed for a structure operating at sea level. The importance of the glass transition region on the panel's vibroacoustic response is exhibited and discussed.

Bareille, Olivier A.; Chronopoulos, Dimitrios; Ichchou, Mohamed N.; Troclet, Bernard

2014-03-01

184

Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers  

SciTech Connect

The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

Yastrubchak, O., E-mail: yastrub@hektor.umcs.lublin.pl; Gluba, L.; ?uk, J. [Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin (Poland); Wosinski, T., E-mail: wosin@ifpan.edu.pl; Andrearczyk, T.; Domagala, J. Z. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Sadowski, J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); MAX-IV Laboratory, Lund University, 221 00 Lund (Sweden)

2014-01-07

185

On the Origin and Variability of CCN in the Remote Marine Boundary Layer  

NASA Astrophysics Data System (ADS)

The role of CCN and their complex influence upon cloud albedo, cloudiness, radiative transfer and precipitation has emerged as a key research issue in the past decade due to the large and uncertain influence they may have on global climate. Aerosol that activate at low supersaturation in the marine boundary layer (MBL) (i.e. below about 0.4% S (CCN0.4) with sizes near 60 nm diameter) can influence clouds over a dominant fraction of the globe, including extensive regions of marine stratus. Hence, greater efforts have recently been directed at understanding the CCN cycle in this environment. Advection of continental aerosol in the MBL can often account for most CCN0.4 near coastal regions until precipitation scavenging reduces their concentrations to low values. Away from such influences, the dominant sources of new CCN0.4 are from the ocean surface via bubble bursting, from the free troposphere (FT) via entrainment and possibly from nucleation and growth of new particles in the MBL. As the latter process generally appears weak and uncommon, the former two sources appear to dominate most regions. Surface sources via bubble bursting were long presumed to be larger sea-salt with sizes above several hundred nanometers and with production rates driven by white cap coverage that increased with wind speed. More recently, production of sizes smaller than 20 nm has been observed and other constituents including organic aerosol and polysaccharides have become recognized contributors. Growth of smaller sizes into the CCN0.4 range is evident via uptake of sulfate originating from DMS. However, long range transport and entrainment of aerosol from the FT has been identified as another important source of MBL CCN0.4 that may be either natural (eg. sulfuric acid formed in cloud outflow) or continental (eg. biomass burning aerosol). Hence; regional wind speeds, entrainment rates, FT transport, oceanic bio-chemistry and removal rates via precipitation etc. can modulate the nature and variability of CCN in the remote MBL. This modulation also involves various size-dependent processes that influence the CCN growth and removal. The relative importance of these aerosol sources and removal to the CCN0.4 budget varies regionally and temporally in ways that are complex and uncertain. We focus here on recent observations in the equatorial and lower latitudes (<30 deg) of the South Pacific and highlight examples of transport and entrainment of FT aerosol as well as the production of sea spray aerosol (SSA) and the processes influencing their relative importance on MBL CCN0.4. Entrainment was found to be a dominant source of CCN0.4 in the MBL with concentrations in quasi equilibrium with overlying FT concentrations on a scale of several days. SSA was a weaker secondary source in these environments with winds below 14 m s-1. Entrainment of CCN0.4 appeared most active in cloudy (stratus) regions and SSA appeared rapidly depleted by drizzle in regions of higher winds and cloudiness in spite of increased production. Because the response time for a change in the MBL concentrations in these regions to a surface and FT source is on the order of a day(s), addressing CCN0.4 variability requires understanding processes active in the MBL and FT well beyond conditions at the point of measurement.

Clarke, A. D.; Freitag, S.; Hudson, J.; Howell, S. G.; Blot, R.; Kapustin, V. N.

2012-12-01

186

Origin of the Mackenzie large igneous province and sourcing of flood basalts from layered intrusions  

NASA Astrophysics Data System (ADS)

The 1.27 Ga Coppermine continental flood basalt (CFB) in northern Canada represents the extrusive manifestation of the Mackenzie large igneous province (LIP) that includes the Mackenzie dyke swarm and the Muskox layered intrusion. New Re-Os isotope and highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundance data are reported together with whole-rock major- and trace-element abundances and Nd isotopes to examine the behaviour of the HSE during magmatic differentiation and to place constraints on the extent of crustal interaction with mantle-derived melts. Mineral-chemical data are also reported for an unusual andesite glass flow (4.9 wt.% MgO) found in proximity to newly recognised picrites (>20 wt.% MgO) in the lowermost stratigraphy of the Coppermine CFB. Compositions of mineral phases in the andesite are similar to equivalent phases found in Muskox Intrusion chromitites and the melt composition is identical to Muskox chromite melt inclusions. Elevated HSE contents (e.g., 3.8 ppb Os) and the mantle-like initial Os isotope composition of this andesitic glass contrast strongly with oxygen isotope and lithophile element evidence for extensive crustal contamination. These signatures implicate an origin for the glass as a magma mingling product formed within the Muskox Intrusion during chromitite genesis. The combination of crust and mantle signatures define roles for both these reservoirs in chromitite genesis, but the HSE appear to be dominantly mantle-sourced. Combined with Nd isotope data that places the feeder for lower Coppermine CFB picrites and basalts within the Muskox Intrusion, this provides the strongest evidence yet for direct processing of some CFB within upper-crustal magma chambers. Modeling of absolute and relative HSE abundances in CFB reveal that HSE concentrations decrease with increasing fractionation for melts with <8×1 wt.% MgO in the Coppermine CFB, with picrites (>13.5wt.% MgO) from CFB having higher Os abundances than ocean island basalt (OIB) equivalents. The differences between CFB and OIB picrite absolute Os abundances may result from higher degrees of partial melting to form CFB but may also reflect incorporation of trace sulphide in CFB picrites from magmas that reached S-saturation in shallow-level magma chambers. Significant inter-element fractionation between (Re+Pt+Pd)/(Os+Ir+Ru) are generated during magmatic differentiation in response to strongly contrasting partitioning of these two groups of elements into sulphides and/or HSE-rich alloys. Furthermore, fractional crystallization has a greater role on absolute and relative HSE abundances than crustal contamination under conditions of CFB petrogenesis due to the dilution effect of continental crust. The Coppermine CFB define a Re-Os isochron with an age of 1263 +16/-20 Ma and initial gamma Os = +2.2×0.8. Combined data for the basaltic and intrusive portions of the Mackenzie LIP indicate a mantle source broadly within the range of the primitive upper mantle. The majority of Archaean komatiites and Phanerozoic CFB also require mantle sources with primitive upper mantle to chondritic Re/Os evolution, with exceptions typically being from analyses of highly-fractionated MgO-poor basalts.

Day, J. M.; Pearson, D.

2013-12-01

187

Adsorption and structure of the adsorbed layer of ionic surfactants.  

PubMed

Our goal in this study was to investigate theoretically and experimentally the adsorption of ionic surfactants and the role of different factors in the mechanism of adsorption, the adsorption parameters and the structure of the adsorbed layer. We used available literature data for the interfacial tension, sigma, vs. concentration, C(s), for sodium dodecyl sulfate (SDS) in three representative systems with Air/Water (A/W), Oil/Water (O/W) and Oil/Water + 0.1 M NaCl (O/WE) interfaces. We derived 6 new adsorption isotherms and 6 new equations of state (EOS) based on the adsorption isotherms for non-ionic surfactants of Langmuir, Volmer and Helfand-Frisch-Lebowitz (HFL) with interaction term betatheta2/2 in the EOS, theta=alphaGamma being the degree of coverage, with Gamma--adsorption and alpha--minimum area per molecule. We applied Gouy equation for high surface potentials and modified it to account for partial penetration of the counterions in the adsorbed layer. The equations were written in terms of the effective concentration C=[C(s)(C(s)+C(el))](1/2), where C(s) and C(el) are, respectively concentrations of the surfactant and the electrolyte. We showed that the adsorption constant K was model independent and derived an equation for the effective thickness of the adsorbed layer, delta(s). We found also that the minimum area per molecule, alpha, is larger than the true area, alpha(0), which depends on the adsorption model and is a function of the adsorption Gamma. The interaction term betatheta2/2 in the Langmuir EOS was found to be exact for small beta<1, but for the Volmer EOS it turned out to be only a crude approximation. Semi-quantitative considerations about the interaction between adsorbed discrete charges revealed that at A/W interface part of the adsorbed surfactant molecules are partially immersed in water, which leads to decreased repulsion and increased adsorption Gamma. At O/W the larger adsorption energy keeps the surfactant molecules on the surface, so that the electrostatic repulsion is stronger, which translates into negative beta's, larger alpha's and smaller adsorption. The addition of electrolyte partly screens the repulsion at O/W, leading to decreased alpha and increased adsorption. We determined K, alpha and beta by a three-parameter fit. The constant K was found to be model independent and smaller for A/W than for O/W, because of the smaller adsorption energy. The values of alpha were larger for O/W than for A/W and decreased for O/W upon addition of electrolyte in agreement with the theory. For the Volmer model alpha was smaller than for Langmuir's model and both were found to increase with decreasing Gamma - again in agreement with the theoretical predictions. It turned out that theta never exceeds 0.5 i.e. the adsorbed layer is never saturated. We tried to determine which adsorption model gave better results by calculating theoretically the Gibbs elasticity, but it turned out that when the results were plotted vs. an experimental variable, say C, all curves collapsed in a single one, which coincided with the respective experimental curve. This means that it is impossible to determine the adsorption model by using only interfacial tension data. PMID:16860769

Ivanov, Ivan B; Ananthapadmanabhan, Kavssery P; Lips, Alex

2006-11-16

188

Layered magnetic structures: Evidence for antiferromagnetic coupling of Fe layers across Cr interlayers  

Microsoft Academic Search

We investigated exchange coupling of Fe layers across Au and Cr interlayers by means of light scattering from spin waves. For Au interlayers we find a continuous decrease of this coupling to zero as the Au thickness is increased from 0 to ~=20 Å. For Cr interlayers of prpoer thickness we find antiferromagnetic coupling of the Fe layers. In small

P. Grünberg; R. Schreiber; Y. Pang; M. B. Brodsky; H. Sowers

1986-01-01

189

Controlling structure distortions in 3-layer ferroelectric Aurivillius oxides  

SciTech Connect

Combined Rietveld refinements of x-ray and neutron powder diffraction data were used to understand the subtle structure distortions in 3-layer Aurivillius oxides that yield off-centering displacements in ferroelectric and multiferroic compositions. Ferroelectric phases including Bi{sub 2}A{sub 2}Ti{sub 3}O{sub 12} (A=La, Pr, Nd, La/Pr, La/Nd, Pr/Nd), Bi{sub 2}A{sub 2}TiNb{sub 2}O{sub 12} (A=Ca/Sr, Sr, and Sr/Ba) and Bi{sub 2}A{sub 2}TiTa{sub 2}O{sub 12} (A=Ca/Sr, and Sr/Ba) were studied to separate the effects of cation size and charge on the structure distortions and properties. A new approach to describing the local coordination around the Ti, Nb, and/or Ta ions is presented, where the oxygen octahedra are characterized as containing kinks in three dimensions. The kink angles follow trends with the A-site ionic radius and the ferroelectric polarization. The driving force for extensive cation site mixing between the Bi and A-site cations has been clearly established, with site mixing required to maintain interlayer bonding. - Graphical abstract: Distortion of the oxygen octahedra from planar geometries can be controlled via choice of the perovskite A-site cation, and the kink angle correlates with cation off-centering and ferroelectric polarization. Highlights: Black-Right-Pointing-Pointer A-site cations define the tilt and distortion of the octahedral. Black-Right-Pointing-Pointer Distortions of oxygen octahedra, ignoring the central cation, link to ferroelectric polarization. Black-Right-Pointing-Pointer Bi ion occupancy in the perovskite causes distortion of the oxygen sublattice. Black-Right-Pointing-Pointer We predict multiferroic behavior from off-centering caused by the Bi ion lone pair.

Nichols, Eric J.; Shi, Jiawanjun [Kazuo Inamori School of Engineering, Alfred University, Alfred, NY 14802 (United States); Huq, Ashfia [Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Vogel, Sven C. [Manuel Lujan Jr. Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Misture, Scott T., E-mail: misture@alfred.edu [Kazuo Inamori School of Engineering, Alfred University, Alfred, NY 14802 (United States)

2013-01-15

190

Crustal Structure of Salton Trough using Deformable Layer Tomography  

NASA Astrophysics Data System (ADS)

Salton Trough is an important geologic structure to understand the active rift between Imperial Fault and San Andreas Fault. To determine the underground geometry of Salton Trough and its nearby faults, we analyzed seismic phase data recorded by Southern California Earthquake Data Center (SCEDC). Both 2-D and 3-D models have been made to refine the velocity model so as to determine the basin and moho geometry beneath Salton Trough region. Here three inline and five cross-line velocity profiles were built by using 2D Deformable Layer Tomography (DLT) method. From these 2D profiles, we can see that the velocity gradient is very small in the low velocity zone. The low velocity anomaly can be detected beneath the axis of the Salton Trough around the depth of 19-21 km, and the relatively high velocity can be seen beneath the San Andreas faults. Within 100*150*40 km3 model volume, 90,180 P-wave and S-wave first arrival picks from 27,663 local events (from 2001 to 2012), which were obtained from 44 stations, were used to build 3D seismic velocity model of the crust. During the iterations of velocity updating, full 3-D ray tracing is implemented. From these 3-D velocity models with different sizes of grids, low velocity anomalies are present under the southwest of Salton Sea, while high velocity zone is present across Southern San Andreas Fault throughout all the depths. Profiles from 2-D velocity models compared to 3-D velocity models show similar geometry. 3-D crustal structure, which is determined from 3-D DLT, helps to better understand the divergent boundary between the North American and the Pacific tectonic plates

Yuan, F.

2012-12-01

191

Structure and Response to Flow of the Glycocalyx Layer  

PubMed Central

The glycocalyx is a sugar-rich layer located at the luminal part of the endothelial cells. It is involved in key metabolic processes and its malfunction is related to several diseases. To understand the function of the glycocalyx, a molecular level characterization is necessary. In this article, we present large-scale molecular-dynamics simulations that provide a comprehensive description of the structure and dynamics of the glycocalyx. We introduce the most detailed, to-date, all-atom glycocalyx model, composed of lipid bilayer, proteoglycan dimers, and heparan sulfate chains with realistic sequences. Our results reveal the folding of proteoglycan ectodomain and the extended conformation of heparan sulfate chains. Furthermore, we study the glycocalyx response under shear flow and its role as a flypaper for binding fibroblast growth factors (FGFs), which are involved in diverse functions related to cellular differentiation, including angiogenesis, morphogenesis, and wound healing. The simulations show that the glycocalyx increases the effective concentration of FGFs, leading to FGF oligomerization, and acts as a lever to transfer mechanical stimulus into the cytoplasmic side of endothelial cells. PMID:24411255

Cruz-Chu, Eduardo R.; Malafeev, Alexander; Pajarskas, Tautrimas; Pivkin, Igor V.; Koumoutsakos, Petros

2014-01-01

192

Plant Biomechanics Conference Cayenne, November 16 21, 2009 Origins of abnormal behaviors of gelatinous layer in tension wood  

E-print Network

of gelatinous layer in tension wood fiber - A micromechanical approach H. Yamamoto1 , J. Ruelle2 , Y. Arakawa1 Abstract The mechanism responsible for unusual mechanical properties of tension wood gelatinous fiber (G, and rapid increase of Young's modulus due to drying, in association with microscopic structure of gelatinous

Paris-Sud XI, Université de

193

Origins.  

ERIC Educational Resources Information Center

Provides an annotated list of resources dealing with the theme of origins of life, the universe, and traditions. Includes Web sites, videos, books, audio materials, and magazines with appropriate grade levels and/or subject disciplines indicated; professional resources; and learning activities. (LRW)

Online-Offline, 1999

1999-01-01

194

Nature and origin of layered deposits of the Martian polar regions  

NASA Technical Reports Server (NTRS)

Layered deposits in the Martian polar regions are interpreted as accumulations of dust derived from atmospheric suspensions. Depressed and eroded terrains of the equatorial region are considered to be the principal sources of dust. A depositional model based on polar precipitation of dust predicts the formation of a vast, dome-shaped, featureless plateau underlain by layered deposits and occupying most of the area of annual frost cover. The rates of accumulation of dust and water ice in the polar regions have been estimated on the basis of atmospheric conditions in the present era. The analysis indicates an accumulation time of about 500 x 1 million years for the layered deposits and the presence of significant quantities of water ice in the deposits beneath the perennial cap.

Cutts, J. A.

1973-01-01

195

STOCHASTIC COMPUTATIONAL DYNAMICAL MODEL OF UNCERTAIN STRUCTURE COUPLED WITH AN INSULATION LAYER  

E-print Network

STOCHASTIC COMPUTATIONAL DYNAMICAL MODEL OF UNCERTAIN STRUCTURE COUPLED WITH AN INSULATION LAYER the effect of insulation layers in complex dynamical systems for low- and medium-frequency ranges such as car booming noise analysis, one introduces a sim- plified stochastic model of insulation layers based

Boyer, Edmond

196

Cusp and Ytype Magnetic Structures and Velocity Fields at the Endpoint of the Reconnection Layer.  

E-print Network

Cusp and Y­type Magnetic Structures and Velocity Fields at the Endpoint of the Reconnection Layer Syrovatskii­type Y­point con­ figuration, with surface current concentrated only in the reconnection layer, it is necessary to understand the dynamic behavior of the plasma in thin layers. A closer examination

197

Geophysical characterization of two circular structures at Bajada del Diablo (Patagonia, Argentina): Indication of impact origin  

NASA Astrophysics Data System (ADS)

An impact origin has been proposed for the circular structures found in Bajada del Diablo, Patagonia, Argentina. Taking into account its extension and the number of impact structures, Bajada del Diablo would be the largest meteoritic impact areas known on Earth, being an extremely interesting area for the research of impact events and processes. Moreover, the global distribution of known impact structures shows a surprising asymmetry. Particularly, South America has only seven described areas. It is evident that this situation is an artifact, highlighting the importance of intensifying the research in the least studied areas such as Argentina. Circular structures in Bajada del Diablo have been identified on two rock types: the Quiñelaf eruptive complex and Pampa Sastre Formation. In the first case, circular structures are placed in olivine basalts. On the other hand, Pampa Sastre Formation (late Pliocene/early Pleistocene) corresponds to conglomerate layers with basalt clasts boulder and block in size in a coarse sandy matrix. With the aim of further the investigation of the proposed impact origin for these circular structures, we carried out detailed topographic, magnetic and electromagnetic ground surveys in two circular structures ("8" and "A") found in Pampa Sastre conglomerates. Both circular structures are simple, bowl-shaped with rim diameters of 300 m and maximum depths of 10 m. They have been partially filled in by debris flows from the rims and wind-blown sands. Two preliminary magnetic profiles have also been carried out in circular structure "G" found in Quiñelaf basalts. The magnetic anomalies show a circular pattern with a slightly negative and relatively flat signal in the circular structures' bases. Furthermore in the circular structures' rims, high-amplitude, conspicuous and localized (short wavelength) anomalies are observed. Such large amplitude and short wavelength anomalies are not detected outside the circular structures. For all used frequencies, the electromagnetic profiles show lower apparent electrical conductivities in the circular structures' base, while the rims present notably higher values. Curvature attributes, analytic signal, horizontal gradient and Euler solutions were calculated for the magnetic data. 2.5D magnetic models were developed across the studied circular structures. Our results suggest that in the circular structures' bases up to 12 m of Pampa Sastre conglomerate would have been removed. On the contrary, the circular structures' rims exhibit high-amplitude, localized magnetic anomalies and higher apparent electrical conductivities, which would be related to the anomalous accumulation of basalt boulders and blocks remanently magnetized. Such high-amplitude anomalies are not present outside the surveyed circular structures. The geomorphological, geological and geophysical features of the studied circular structures can only be explained by means of an extra-terrestrial projectile impact. We conclude that, considering the results obtained to date, Bajada del Diablo should be envisaged as a focus of further research, which could provide novel information about impact events, associated processes and their evidences. Particularly, the data produced in this study could represent one of the first documented geophysical signatures of the impact of a comet nucleus on Earth.

Prezzi, Claudia B.; Orgeira, María Julia; Acevedo, Rogelio D.; Ponce, Juan Federico; Martinez, Oscar; Rabassa, Jorge O.; Corbella, Hugo; Vásquez, Carlos; González-Guillot, Mauricio; Subías, Ignacio

2012-02-01

198

Stratigraphy, Structure, and Origin; A Geophysical Survey of the Mendeleev Ridge  

NASA Astrophysics Data System (ADS)

The Mendeleev Ridge is a broad, aseismic ridge that extends from the Siberian Shelf into the central Arctic Ocean. While it is continuous with the Alpha Ridge and is inferred to be an oceanic plateau, it may have had a distinct and separate history. The origin of the Mendeleev ridge has only rarely been visited and, as a result, understanding the history of this region has largely been based on the presumption of a common origin for both features. In late summer 2005, a geophysical survey was conducted from USCGC Healy over the Mendeleev Ridge as part of a trans-arctic crossing. During this survey ~730 km of seismic reflection data was recovered over the ridge along with co-registered gravity and bathymetry data and seismic refraction profiles. The seismic source was two 250 cu in G-guns. The streamer length was limited by ice conditions to 300 meters. Wear and tear caused by towing the streamer through the ice pack eliminated hydrophones, so the number of active channels ranged from 24 to as few as 11. The seismic reflection data requires significant trace editing to eliminate random electrical noise and frequency-wave number filtering to eliminate low velocity noise caused by the streamer traveling through heavy ice. After trace editing the data are stacked and migrated with constant water velocity. Stacking velocities are used as input into initial ray tracing models. Derived boundary velocities from ray tracing models will be reapplied to the migration of reflection data and are converted through empirical relationships into densities, and used as input into gravity models. Brute stacked reflection images of the Mendeleev Ridge reveal pervasive extensional faulting of the basement and lower sediment layers, and a continuous, undeformed pelagic sediment layer mantling the ridge, indicative of recent tectonic inactivity. The age of the unconformity underlying this layer should date the end of significant deformation of the Alpha and Mendeleev Ridges. Consistency of modeled seismic velocities from the upper basement will provide some insight into the nature of the crustal material. Upper basement velocities estimated from the sonobuoy data range from 3.7-5.0 km/s, suggestive of a heterogeneous upper crust. Initial gravity models suggest that much of the amplitude variation over the Mendeleev Ridge is accommodated by invoking a single, continuous density layer for the crust. Future work will include: developing a structural map of the Mendeleev ridge as well as the refining of both the ray-tracing and gravity modeling in an attempt to better understand the crustal style of the ridge.

Dove, D.; Coakley, B.; Hopper, J.

2006-12-01

199

Structure and growth of the mixing layer over the Amazonian rain forest  

NASA Technical Reports Server (NTRS)

The structure and growth of the atmospheric mixed layer over the Amazonian rain forest were examined using measurements obtained during the NASA Amazon Boundary Layer Experiment. Measurements of temperature, moisture, and horizontal wind were carried out in and above the mixed layer by means of a tethered balloon, rawinsonde, and aircraft; fluxes of sensible and latent heat were measured at the top of the canopy. It was found that the mixing layer grows rapidly, at 5-8 cm/sec, soon after sunrise to a mean maximum height of 1200 m by 1300 LT; during undisturbed conditions, mixed layer heights of 1000 are common between 1000 and 1600 LT. No horizontal inhomogeneities in the mixed layer structure or depth were found over large distances. A simple mixed layer model was applied to show how fluxes of species might be estimated using only quantities measured at the surface and prescribing an initial condition and boundary condition for the mixed layer.

Martin, Charles L.; Fitzjarrald, David; Garstang, Michael; Greco, Steve; Oliveira, Amauri P.; Browell, Edward

1988-01-01

200

Phase transitions between single-and double-layered smectic structures in binary mixtures of cyano-mesogens  

E-print Network

1583 Phase transitions between single- and double-layered smectic structures in binary mixtures respectively single-layered (A1), double layered (A2) and partially double layered (Ad) smectic phases show abrupt A2-A1 or A2-Ad transitions as a function of concentration. Double layered structures imply

Paris-Sud XI, Université de

201

Acoustic double layer structures in dense magnetized electron-positron-ion plasmas  

SciTech Connect

The acoustic double layer structures are studied using quantum hydrodynamic model in dense magnetized electron-positron-ion plasmas. The extended Korteweg-de Vries is derived using reductive perturbation method. It is found that increase in the ion concentration in dense magnetized electron-positron plasmas increases the amplitude as well as the steepness of the double layer structure. However, increase in the magnetic field strength and decrease in the obliqueness of the nonlinear acoustic wave enhances only the steepness of the double layer structures. The numerical results have also been shown by using the data of the outer layer regions of white dwarfs given in the literature.

Akhtar, N.; Mahmood, S. [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad 44000 (Pakistan); Department of Physics and Applied Mathematics, PIEAS, P. O. Nilore, Islamabad 44000 (Pakistan)

2011-11-15

202

Charge carrier transport properties in layer structured hexagonal boron nitride  

SciTech Connect

Due to its large in-plane thermal conductivity, high temperature and chemical stability, large energy band gap (~ 6.4 eV), hexagonal boron nitride (hBN) has emerged as an important material for applications in deep ultraviolet photonic devices. Among the members of the III-nitride material system, hBN is the least studied and understood. The study of the electrical transport properties of hBN is of utmost importance with a view to realizing practical device applications. Wafer-scale hBN epilayers have been successfully synthesized by metal organic chemical deposition and their electrical transport properties have been probed by variable temperature Hall effect measurements. The results demonstrate that undoped hBN is a semiconductor exhibiting weak p-type at high temperatures (> 700?°K). The measured acceptor energy level is about 0.68 eV above the valence band. In contrast to the electrical transport properties of traditional III-nitride wide bandgap semiconductors, the temperature dependence of the hole mobility in hBN can be described by the form of ? ? (T/T{sub 0}){sup ??} with ? = 3.02, satisfying the two-dimensional (2D) carrier transport limit dominated by the polar optical phonon scattering. This behavior is a direct consequence of the fact that hBN is a layer structured material. The optical phonon energy deduced from the temperature dependence of the hole mobility is ?? = 192 meV (or 1546 cm{sup -1}), which is consistent with values previously obtained using other techniques. The present results extend our understanding of the charge carrier transport properties beyond the traditional III-nitride semiconductors.

Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X., E-mail: hx.jiang@ttu.edu [Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)

2014-10-15

203

On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer  

SciTech Connect

In this work, the origin of electron blocking effect of n-type Al{sub 0.25}Ga{sub 0.75}N electron blocking layer (EBL) for c+ InGaN/GaN light-emitting diodes has been investigated through dual-wavelength emission method. It is found that the strong polarization induced electric field within the n-EBL reduces the thermal velocity and correspondingly the mean free path of the hot electrons. As a result, the electron capture efficiency of the multiple quantum wells is enhanced, which significantly reduces the electron overflow from the active region and increases the radiative recombination rate with holes.

Zhang, Zi-Hui; Ji, Yun; Liu, Wei; Tiam Tan, Swee; Kyaw, Zabu; Ju, Zhengang; Zhang, Xueliang; Hasanov, Namig; Lu, Shunpeng; Zhang, Yiping; Zhu, Binbin; Wei Sun, Xiao, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Volkan Demir, Hilmi, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Department of Electrical and Electronics, Department of Physics, and UNAM-Institute of Material Science and Nanotechnology, Bilkent University, TR-06800, Ankara (Turkey)

2014-02-17

204

Comparison of the structures of the hot-work tool steels laser modified surface layers  

Microsoft Academic Search

Investigations include comparison between structure and properties of remelting and alloying the X40CrMoV5-1 hot-work tool steel surface layer using the high power diode laser (HPDL). The tungsten carbide powder was used as an alloying material. The X40CrMoV5-1 conventionally heat treated steel was used as reference material. The structural mechanism was determined of surface layers development. Development of the surface layer

L. A. Dobrza?ski; M. Bonek; E. Hajduczek; A. Klimpel; A. Lisiecki

2005-01-01

205

Bifurcation Structure of a Wind-Driven Shallow Water Model with Layer-Outcropping  

E-print Network

Bifurcation Structure of a Wind-Driven Shallow Water Model with Layer-Outcropping Fran¸cois W of the double-gyre wind-driven ocean circu- lation is examined in a shallow water model where the upper layer structure had hitherto remained unexplored. Preprint submitted to Elsevier 26 October 2006 #12;Key words: 1

Newman, David

206

Spatial Variability of Atmospheric Boundary Layer Structure over the Eastern Equatorial Pacific  

Microsoft Academic Search

Variations in the atmospheric boundary layer structure over the eastern equatorial Pacific are analyzed using 916 soundings collected during the First Global Atmospheric Research Program Global Experiment. Unstable boundary layer structures are observed much more frequently in soundings north of the ocean front located near 2.5°N in the eastern equatorial Pacific than in soundings south of the front. An objective

Bingfan Yin; Bruce A. Albrecht

2000-01-01

207

The viscosity structure of the D00 layer of the Earth's mantle inferred  

E-print Network

The viscosity structure of the D00 layer of the Earth's mantle inferred from the analysis layer Core­mantle boundary Viscosity Maxwell body a b s t r a c t The viscosity structure of the D00-diurnal to 18.6 years tidal deformations combined with model viscosity­depth profiles corresponding to a range

208

Physical Structures of Lipid Layers X I A N G V . Z H A N G ,  

E-print Network

Physical Structures of Lipid Layers on Pyrite X I A N G V . Z H A N G , T R E A V O R A . K E N D at Stony Brook, Stony Brook, New York 11794 The physical structures of lipid layers on pyrite (FeS2 experimental observations show that this lipid formed bilayers on an atomically rough pyrite surface

209

The development of bone-shaped structures in initially segmented layers during layer-parallel extension: numerical modelling and parameter sensitivity analysis  

Microsoft Academic Search

In orogenic zones the geometric occurrence of specific tectonic structures can often be related to contrasting rheological properties of rock materials. One of such tectonic structures is layer-perpendicular naturally fractured layers with vein infill that underwent subsequent deformation. Internal deformation by coaxial extension of these segmented layers, with host-rock material less competent than the vein material, gives rise to the

I. Kenis; J. L. Urai; M. Sintubin

2006-01-01

210

Structure of the zero-pressure-gradient turbulent boundary layer.  

PubMed

A processing of recent experimental data by Nagib and Hites [Nagib, H. & Hites, M. (1995) AIAA paper 95-0786, Reno, NV) shows that the flow in a zero-pressure-gradient turbulent boundary layer, outside the viscous sublayer, consists of two self-similar regions, each described by a scaling law. The results concerning the Reynolds-number dependence of the coefficients of the wall-region scaling law are consistent with our previous results concerning pipe flow, if the proper definition of the boundary layer Reynolds number (or boundary layer thickness) is used. PMID:11038559

Barenblatt, G I; Chorin, A J; Hald, O H; Prostokishin, V M

1997-07-22

211

Structure of turbulence in three-dimensional boundary layers  

NASA Technical Reports Server (NTRS)

This report provides an overview of the three dimensional turbulent boundary layer concepts and of the currently available experimental information for their turbulence modeling. It is found that more reliable turbulence data, especially of the Reynolds stress transport terms, is needed to improve the existing modeling capabilities. An experiment is proposed to study the three dimensional boundary layer formed by a 'sink flow' in a fully developed two dimensional turbulent boundary layer. Also, the mean and turbulence field measurement procedure using a three component laser Doppler velocimeter is described.

Subramanian, Chelakara S.

1993-01-01

212

Fabrication of luminescent porous silicon with stain etches and evidence that luminescence originates in amorphous layers  

NASA Technical Reports Server (NTRS)

Simple immersion of Si in stain etches of HF:HNO3:H2O or NaNO2 in aqueous HF was used to produce films exhibiting luminescence in the visible similar to that of anodically-etched porous Si. All of the luminescent samples consist of amorphous porous Si in at least the near surface region. No evidence was found for small crystalline regions within these amorphous layers.

Fathauer, R. W.; George, T.; Ksendzov, A.; Lin, T. L.; Pike, W. T.; Vasquez, R. P.; Wu, Z.-C.

1992-01-01

213

Stratigraphy, mineralogy, and origin of layered deposits inside Terby crater, Mars  

NASA Astrophysics Data System (ADS)

The 174 km diameter Terby impact crater (28.0°S-74.1°E) located on the northern rim of the Hellas basin displays anomalous inner morphology, including a flat floor and light-toned layered deposits. An analysis of these deposits was performed using multiple datasets from Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter missions, with visible images for interpretation, near-infrared data for mineralogical mapping, and topography for geometry. The geometry of layered deposits was consistent with that of sediments that settled mainly in a sub-aqueous environment, during the Noachian period as determined by crater counts. To the north, the thickest sediments displayed sequences for fan deltas, as identified by 100 m to 1 km long clinoforms, as defined by horizontal beds passing to foreset beds dipping by 6-10° toward the center of the Terby crater. The identification of distinct sub-aqueous fan sequences, separated by unconformities and local wedges, showed the accumulation of sediments from prograding/onlapping depositional sequences, due to lake level and sediment supply variations. The mineralogy of several layers with hydrated minerals, including Fe/Mg phyllosilicates, supports this type of sedimentary environment. The volume of fan sediments was estimated as >5000 km 3 (a large amount considering classical martian fan deltas such as Eberswalde (6 km 3)) and requires sustained liquid water activity. Such a large sedimentary deposition in Terby crater is characteristic of the Noachian/Phyllosian period during which the environment favored the formation of phyllosilicates. The latter were detected by spectral data in the layered deposits of Terby crater in three distinct layer sequences. During the Hesperian period, the sediments experienced strong erosion, possibly enhanced by more acidic conditions, forming the current morphology with three mesas and closed depressions. Small fluvial valleys and alluvial fans formed subsequently, attesting to late fluvial processes dated as late Early to early Late Hesperian. After this late fluvial episode, the Terby impact crater was submitted to aeolian processes and permanent cold conditions with viscous flow features. Therefore, the Terby crater displays, in a single location, geologic features that characterize the three main periods of time on Mars, with the presence of one of the thickest sub-aqueous fan deposits reported on Mars. The filling of Terby impact crater is thus one potential "reference geologic cross-section" for Mars stratigraphy.

Ansan, V.; Loizeau, D.; Mangold, N.; Le Mouélic, S.; Carter, J.; Poulet, F.; Dromart, G.; Lucas, A.; Bibring, J.-P.; Gendrin, A.; Gondet, B.; Langevin, Y.; Masson, Ph.; Murchie, S.; Mustard, J. F.; Neukum, G.

2011-01-01

214

Polymer layered silicate nanocomposites: Structure, morphology, and properties  

Microsoft Academic Search

Layered silicates are important fillers for improving various mechanical, flame retardant, and barrier properties of polymers, which can be attributed to their sheet-like morphology. Layered silicates can be modified with organic surfactants to render them compatible with polymer matrices. Organically modified silicates (organoclays) having large surface areas are very cost-efficient non-toxic nanofillers effective at very low loads and are readily

Pranav Nawani

2008-01-01

215

Turbine airfoil with dual wall formed from inner and outer layers separated by a compliant structure  

DOEpatents

A turbine airfoil usable in a turbine engine with a cooling system and a compliant dual wall configuration configured to enable thermal expansion between inner and outer layers while eliminating stress formation is disclosed. The compliant dual wall configuration may be formed a dual wall formed from inner and outer layers separated by a compliant structure. The compliant structure may be configured such that the outer layer may thermally expand without limitation by the inner layer. The compliant structure may be formed from a plurality of pedestals positioned generally parallel with each other. The pedestals may include a first foot attached to a first end of the pedestal and extending in a first direction aligned with the outer layer, and may include a second foot attached to a second end of the pedestal and extending in a second direction aligned with the inner layer.

Campbell; Christian X. (Oviedo, FL), Morrison; Jay A. (Oviedo, FL)

2011-12-20

216

Nepheloid layers origin and development in the nazaré canyon eustrataform project  

NASA Astrophysics Data System (ADS)

In the frame of EUSTRATAFORM project was conducted a general hydrographic and nephelometric survey in the Nazaré canyon (Portuguese continental shelf), under winter conditions. Discrete measurements include CTD, turbidity, sampling of water-sediment interface, concentration of particles and estimation of grain-size distribution. A sampling grid throws the canyon axis and head was visited, allowing visualizing the nepheloid layers distribution. In this study the evaluation of optical and mineralogical proprieties of suspended matter and the interpretation of this variation in a physical and geological context will be presented.

Oliveira, A.; Vitorino, J.; Rodrigues, A.

2003-04-01

217

On the Origin of the Aflou Structure (Algeria)  

NASA Astrophysics Data System (ADS)

Here we report the results of our field observations in the Aflou structure (Algeria). This structure is interpreted as a Triassic diapir. The igneous rocks that outcrop in the area are Triassic/Jurassic ophites within the Triassic formation.

Chabou, M. C.; Laghouag, M. Y.

2014-09-01

218

The Levantine Basin—crustal structure and origin  

Microsoft Academic Search

The origin of the Levantine Basin in the Southeastern Mediterranean Sea is related to the opening of the Neo-Tethys. The nature of its crust has been debated for decades. Therefore, we conducted a geophysical experiment in the Levantine Basin. We recorded two refraction seismic lines with 19 and 20 ocean bottom hydrophones, respectively, and developed velocity models. Additional seismic reflection

G. L. Netzeband; K. Gohl; C. P. Hübscher; Z. Ben-Avraham; G. A. Dehghani; D. Gajewski; P. Liersch

2006-01-01

219

ORIGINAL ARTICLE Geographically structured host specificity is caused  

E-print Network

and Evolutionary Biology, FAS Center for Systems Biology, Harvard University, Cambridge, MA, USA The inability in a new range forms a functional symbiosis with a species it never encountered in its original range microbial mutualists are difficult to observe and the effects of mutualists on hosts are less apparent than

Pringle, Anne

220

Statistical Analysis of Coherent Vortical Structures in a Supersonic Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

Characteristics of coherent vortical structures in a compressible turbulent boundary layer are statistically analyzed by means of direct numerical simulation of the compressible Navier-Stokes equations for Mach number M=2 and Reynolds number Re? ? 1000 based on the inlet momentum thickness. It is found that a large variety of hairpin-like and cane-like vortical structures exist in the boundary layer and the most popular structure is the cane-like one. The injection and sweep events contribute a major proportion of the total Reynolds stress. This study indicates structural similarities with the incompressible case. Moreover, the length scales of coherent structures in the streamwise and spanwise directions increase with the distance from the wall. The inclination angle of coherent vortical structures with respect to the streamwise direction increases from the sublayer to the buffer layer and then decreases from the buffer layer to the wake region.

Wang, Li; Lu, Xi-Yun

2011-03-01

221

Controllable Nanocage Structure Derived from Cyclodextrin-Intercalated Layered Double Hydroxides and Its Inclusion Properties for Dodecylbenzene  

E-print Network

Controllable Nanocage Structure Derived from Cyclodextrin-Intercalated Layered Double Hydroxides carboxymethyl- -cyclodextrins (CMCDs) intercalated in layered double hydroxides (LDHs), whose gates can or large-sized guests within the "empty" core domain. Layered double hydroxides (LDHs, also known

Wang, Zhong L.

222

Influence of structural defects on carrier lifetime in 4H-SiC epitaxial layers: Optical lifetime mapping  

NASA Astrophysics Data System (ADS)

The influence of structural defects on carrier lifetime in 4H-SiC epilayers has been studied using high spatial resolution optically detected lifetime measurements. Full wafers mappings with 200 ?m spatial resolution revealed the carrier lifetime variations that can be associated with structural defects replicated from the substrate and variations in the epitaxial growth conditions due to the susceptor design. High resolution mappings over smaller regions with lateral step size down to 20 ?m, revealed local carrier lifetime reductions associated with different structural defects in the epitaxial layers. Identified defects that influence the carrier lifetime are the carrot defects and different types of in-grown stacking faults. Also clusters of threading screw dislocations in the epilayer probably originating from the dissociation of micropipe in the substrate are found to effectively reduce the carrier lifetime. Furthermore, optically detected lifetime mapping has been demonstrated as a nondestructive technique which allows nonvisible structural defects to be detected in as-grown epilayers.

Hassan, J.; Bergman, J. P.

2009-06-01

223

Hybrid structures and optical effects in Morpho scales with thin and thick coatings using an atomic layer deposition method  

NASA Astrophysics Data System (ADS)

Thin and thick Al2O3 coatings are deposited onto the surfaces of the cover and ground scales in the butterfly Morpho menelaus by low-temperature atomic layer deposition method. By spectral measurements and electronic microscopy, it is revealed that the morphologies of the hybrid structures encapsulated with thin coatings and thick coatings behave in a different way and thus the distinguishing color changes in both cover and ground scales. Theoretical analyses show that the coloration change can be attributed to the correlations of the naturally occurring photonic structures and the coating thicknesses. The different structural origins of the coloration in cover scales and ground scales lead to different optical performances as the coating increases its thicknesses in succession. The study presented offers an alternating route to produce desirable nanostructures such as nanolines and artificial photonic devices such as solar absorbers, and also the intact biotemplates an indirect analysis of structural characterizations and their optical effects.

Liu, Feng; Shi, Wangzhou; Hu, Xinhua; Dong, Biqin

2013-03-01

224

The Time-Dependent Structure of the Electron Reconnection Layer  

NASA Technical Reports Server (NTRS)

Collisionless magnetic reconnection is often associated with time-dependent behavior. Specifically, current layers in the diffusion region can become unstable to tearing-type instabilities on one hand, or to instabilities with current-aligned wave vectors on the other. In the former case, the growth of tearing instabilities typically leads to the production of magnetic islands, which potentially provide feedback on the reconnection process itself, as well as on the rate of reconnection. The second class of instabilities tend to modulate the current layer along the direction of the current flow, for instance generating kink-type perturbations, or smaller-scale turbulence with the potential to broaden the current layer. All of these processes contribute to rendering magnetic reconnection time-dependent. In this presentation, we will provide a summary of these effects, and a discussion of how much they contribute to the overall magnetic reconnection rate.

Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex

2009-01-01

225

Dichotomy of the electronic structure and superconductivity between single-layer and double-layer FeSe/SrTiO3 films.  

PubMed

The latest discovery of possible high-temperature superconductivity in the single-layer FeSe film grown on a SrTiO3 substrate has generated much attention. Initial work found that, while the single-layer FeSe/SrTiO3 film exhibits a clear signature of superconductivity, the double-layer film shows an insulating behaviour. Such a marked layer-dependent difference is surprising and the underlying origin remains unclear. Here we report a comparative angle-resolved photoemission study between the single-layer and double-layer FeSe/SrTiO3 films annealed in vacuum. We find that, different from the single-layer FeSe/SrTiO3 film, the double-layer FeSe/SrTiO3 film is hard to get doped and remains in the semiconducting/insulating state under an extensive annealing condition. Such a behaviour originates from the much reduced doping efficiency in the bottom FeSe layer of the double-layer FeSe/SrTiO3 film from the FeSe-SrTiO3 interface. These observations provide key insights in understanding the doping mechanism and the origin of superconductivity in the FeSe/SrTiO3 films. PMID:25248072

Liu, Xu; Liu, Defa; Zhang, Wenhao; He, Junfeng; Zhao, Lin; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

2014-01-01

226

Multiplatform observations of boundary layer structure in the outer rainbands of landfalling typhoons  

NASA Astrophysics Data System (ADS)

paper analyzes data collected from a new set of observational platforms in the coastal area of China, which consist of a mobile observation system, meteorological tower, automatic weather station, and Doppler radars, to investigate the mean and turbulent boundary layer structure and evolution during the landfall of typhoons. An example of these data is provided from Typhoon Morakot (2009). Vertical profiles of wind velocities and thermodynamic parameters from the observed data allow us to identify different boundary layer structures during and after landfall. These structures, sampled in regions of the outer core, are stratified into periods where convection is occurring (termed "convective") and periods where convection has recently (<2 h) occurred (termed "postconvective"). Data analyses show that the thermodynamic mixed-layer depth and inflow layer depth are higher during the convective period than the postconvective period. The mixed-layer depth is found to be within the strong inflow layer, but the height of the maximum tangential wind speed is above the inflow layer during both periods, contrary to recent observational studies of the boundary-layer structure of tropical cyclones over water. High-frequency wind data show that momentum flux, turbulent kinetic energy (TKE) and integral length scales of wind velocities are all much larger during the convective period than the postconvective period. The results suggest that convective downdrafts may play an important role in modulating turbulent flux, TKE, vertical mixing, and boundary layer recovery processes.

Ming, Jie; Zhang, Jun A.; Rogers, Robert F.; Marks, Frank D.; Wang, Yuan; Cai, Ninghao

2014-07-01

227

Origin of Structure in the Universe: Quantum Cosmology Reconsidered  

E-print Network

Based on a more careful canonical analysis, we motivate a reduced quantization of slightly inhomogeneous cosmology in place of the Dirac quantization in the existing literature, and provide it in the vacuum case. This is attained via consideration of configuration space geometries at various levels of reduction. Some of these have the good fortunate of being flat. Geometrically natural coordinates thereupon are interpreted in terms of the original redundant formulation's well-known mode expansion coefficients.

Anderson, Edward

2015-01-01

228

Origin of Structure in the Universe: Quantum Cosmology Reconsidered  

E-print Network

Based on a more careful canonical analysis, we motivate a reduced quantization of slightly inhomogeneous cosmology in place of the Dirac quantization in the existing literature, and provide it in the vacuum case. This is attained via consideration of configuration space geometries at various levels of reduction. Some of these have the good fortunate of being flat. Geometrically natural coordinates thereupon are interpreted in terms of the original redundant formulation's well-known mode expansion coefficients.

Edward Anderson

2015-01-11

229

Targeted structure modulation of "pillar-layered" metal-organic frameworks for CO? capture.  

PubMed

Two new zinc MOFs with similar "pillar-layered" framework structures based on 1,1'-biphenyl-2,2',6,6'-tetracarboxylic acid (H4bpta) and two different bipyridine pillar ligands, namely {[Zn4(bpta)2(4-pna)2(H2O)2]·4DMF·3H2O}n (1) and {[Zn2(bpta)(bpy-ea)(H2O)]·2DMF·H2O}n (2) (4-pna = N-(4-pyridyl)isonicotinamide and bpy-ea = 1,2-bis(4-pyridyl)ethane), have been synthesized and investigated with their CO2 adsorption properties. By analysis of the structure properties and the CO2 adsorption performances of these two MOFs, it was found that the introduction of polar acylamide groups via 4-pna resulted in 1 with enhanced CO2 capacity and CO2/CH4 selectivity at low pressure. In contrast, the framework of 2 shows flexible properties originating from the flexibility of the ethanediylidene group in the bpy-ea ligand, which benefits the sieve effect of pores to give higher CO2/CH4 selectivity at a relatively high pressure range. PMID:25127434

Xuan, Zhi-Hong; Zhang, Da-Shuai; Chang, Ze; Hu, Tong-Liang; Bu, Xian-He

2014-09-01

230

Multiple Layer Structure of Non-Abelian Vortex  

E-print Network

Bogomol'nyi-Prasad-Sommerfield (BPS) vortices in U(N) gauge theories have two layers corresponding to non-Abelian and Abelian fluxes, whose widths depend nontrivially on the ratio of U(1) and SU(N) gauge couplings. We find numerically and analytically that the widths differ significantly from the Compton lengths of lightest massive particles with the appropriate quantum number.

Minoru Eto; Toshiaki Fujimori; Takayuki Nagashima; Muneto Nitta; Keisuke Ohashi; Norisuke Sakai

2009-03-09

231

Improved structural/morphological durability for organic solar cells based on poly(3-hexylthiophene) fibers photoactive layers  

NASA Astrophysics Data System (ADS)

Organic photovoltaic (OPV) materials must meet some stringent technological requirements, to bear continuous operation under variable temperature conditions. Here, an original approach to control the degradation pathway associated to the active material morphological instability is proposed. We demonstrate, for the first time, that polymer-fullerene nanostructured films incorporating poly(3-hexylthiophene) nanofibers, obtained from concentrated solutions at room-temperature, are characterized by superior structural durability. This is obtained monitoring in situ the active layer bulk/interface morphological properties by joint energy dispersive X-ray and atomic force microscopy time-resolved techniques: the preservation of the nanoscale morphology of the pristine films is very promising for flexible OPV applications.

Paci, B.; Generosi, A.; Albertini, V. Rossi; de Bettignes, R.

2013-11-01

232

Revealing Multiple Layers of Hidden Community Structure in Networks  

E-print Network

We introduce a new conception of community structure, which we refer to as hidden community structure. Hidden community structure refers to a specific type of overlapping community structure, in which the detection of weak, but meaningful, communities is hindered by the presence of stronger communities. We present Hidden Community Detection HICODE, an algorithm template that identifies both the strong, dominant community structure as well as the weaker, hidden community structure in networks. HICODE begins by first applying an existing community detection algorithm to a network, and then removing the structure of the detected communities from the network. In this way, the structure of the weaker communities becomes visible. Through application of HICODE, we demonstrate that a wide variety of real networks from different domains contain many communities that, though meaningful, are not detected by any of the popular community detection algorithms that we consider. Additionally, on both real and synthetic netwo...

He, Kun; Cao, Xuezhi; Hopcroft, John; Huang, Menglong

2015-01-01

233

Solvent-free synthesis of new metal phosphites with double-layered, pillared-layered, and framework structures  

NASA Astrophysics Data System (ADS)

Three new metal phosphites, formulated as (H3O)2·Mn2(HPO3)3 (1), Co(bpy) (H2O) (HPO3) (2), and H2tmpda·Zn3(HPO3)4 (3), have been synthesized under solvent-free conditions, where bpy = 4,4?-bipyridine, and tmpda = N,N,N?,N?-tetramethyl-1,3-propanediamine. Compound 1 has a double-layered structure with a thickness of 5.68 Å. Compound 2 has an inorganic-organic hybrid framework with cobalt phosphite layers pillared by bpy ligands. Compound 3 has a three-dimensional open-framework structure containing 8-ring channels. The temperature dependence of the magnetic susceptibility of compounds 1 and 2 were also investigated.

Liu, Lin; Zhang, Wei; Shi, Zhonghua; Chen, Yaoqiang; Lin, Zhien

2014-12-01

234

Influence of alignment layer thickness on ferroelectric liquid-crystal structure  

NASA Astrophysics Data System (ADS)

We have investigated the influence of the thickness of polyvinyl alcohol alignment layer on azimuthal anchoring of ferroelectric liquid crystals by measuring the azimuthal angle of the chevron C2 structure. By varying not only the alignment but also the ferroelectric liquid-crystal layer thickness, we also studied the influence of the ions screening the polarization charge on the chevron layer structure. A simple model describing the free enthalpy of the system was used to calculate the anchoring coefficient from the azimuthal angle of the structure.

Petkovšek, Rok; ?opi?, Martin; Pirš, Janez

2006-02-01

235

Effect of Interlayer Interaction on the Structural, Electronic, and Thermal Properties of Layered MS2 (M=W, Mo) Structures  

NASA Astrophysics Data System (ADS)

Using density functional theory (DFT) supplemented with van der Waals interaction, we investigate the effect of interlayer interaction on the structural, electroinic, and thermal properties of transition-metal disulfides MS2, such as MoS2 and WS2. We calculate the relative stability of various layer-layer stacking configurations determined by considering relative positions and orientations between neighboring layers. We find that MS2 layers may slide over each other with a small sliding barrier. We explore the effect of layer stacking on the electronic structure, and find an intriguing coupling effect. We also calculate their thermal properties including thermal expansion behavior especially along the direction normal to the plane. Such thermal expansion behavior is considered for our study of Li-intercalation into layered MS2, which may become a fundamental understanding for future development of Li-ion battery. We evaluate thoroughly the diffusion paths and barriers in between layers and compare them with those on the surface. Interestingly we find that the diffusion barrier between layers is ˜100 meV smaller than that on a single layer, implying layered MS2 may be a good candidate for Li-ion battery electrodes.

Kang, Seoung-Hun; Park, Sora; Kwon, Young-Kyun

2012-02-01

236

ORIGINAL ARTICLE: Experimental Endoscopy EUS with CT improves efficiency and structure identification  

E-print Network

is a 3-dimensional (3D) anatomic model that tracks scope position; the sec- ond display is an oblique CT (variable contrast, dependence on boundary-layer reflections, and occlusion by sonically opa- que structures

237

The origin and significance of hypersaline magmatic volatiles in giant layered intrusions  

NASA Astrophysics Data System (ADS)

Fluid and melt inclusions are preserved within pegmatite bodies and cumulus minerals within mafic-ultramafic layered intrusions that host economic concentrations of the platinum-group elements (e.g., Bushveld Complex, South Africa; Stillwater Complex, Montana). The inclusions indicate that the earliest volatile phase to have exsolved from the crystallizing intrusions was a relatively anhydrous carbonic fluid (CO2-dominated). As crystallization proceeded, volatiles appear to have become increasingly water-rich and saline, consistent with the relative saturation limits of carbonic and aqueous fluids in mafic silicate liquids. However, the latest stage volatiles in the layered intrusions were unusual halide melts (only slightly hydrous molten salts) of relatively simply composition (NaCl±KCl, CaCl2) with salinities in excess of 90 wt% eq. NaCl or CaCl2. These volatiles were trapped at minimum temperatures of ~750-800oC, near the eutectic temperature for water-saturated felsic (very late, intercumulate) liquid. Heterogeneous entrapment of late-stage silicate melt and halide melt provides unambiguous evidence for the coexistence of both phases. However, experimental constraints on the nature of exsolved volatiles from mafic silicate liquids suggest that the halide melt phases cannot represent an exsolved phase from that coexisting silicate liquid, since this would require unrealistically high (initial) Cl:H2O ratios for the parental silicate liquid (> 9). Analysis of rhyodacitic silicate melt inclusions that coexist with the halide melt inclusions show that the coevally-trapped silicate melt had a Cl:H2O ratios of only ~ 0.1 to 0.2. Similarily, the salt melt phases could not have evolved via the crystallization of hydrous magmatic minerals (e.g., biotite, apatite) since their abundance in the intrusion are very low. The most plausible explanation for the halide melt phases involves the "dehydration" of an initially lower salinity aqueous fluid. This may have occurred by the reaction of the aqueous fluid with nominally-anhydrous minerals such as pyroxene, or by the late-stage alteration of cumulus minerals to hydrous mineral assemblages. Through the use of conventional hydrothermal experimental techniques, it can be shown that the reaction of a volumetrically-minor CaCl2-rich aqueous fluid (20 wt% eq. CaCl2) with the assemblage diopside-enstatite-quartz at near-solidus conditions (700oC, 0.4 kbar) results in the formation of tremolite by the reaction of H2O with the initially anhydrous mafic mineral assemblage. The resulting salinity of the saline phase, trapped as synthetic inclusions in quartz, was > 96 wt% eq. CaCl2, consistent with the water-poor nature of the salt melt inclusions observed in most layered intrusions globally.

Hanley, Jacob; Adlakha, Erin

2013-04-01

238

Structural molecular components of septate junctions in cnidarians point to the origin of epithelial junctions in eukaryotes.  

PubMed

Septate junctions (SJs) insure barrier properties and control paracellular diffusion of solutes across epithelia in invertebrates. However, the origin and evolution of their molecular constituents in Metazoa have not been firmly established. Here, we investigated the genomes of early branching metazoan representatives to reconstruct the phylogeny of the molecular components of SJs. Although Claudins and SJ cytoplasmic adaptor components appeared successively throughout metazoan evolution, the structural components of SJs arose at the time of Placozoa/Cnidaria/Bilateria radiation. We also show that in the scleractinian coral Stylophora pistillata, the structural SJ component Neurexin IV colocalizes with the cortical actin network at the apical border of the cells, at the place of SJs. We propose a model for SJ components in Cnidaria. Moreover, our study reveals an unanticipated diversity of SJ structural component variants in cnidarians. This diversity correlates with gene-specific expression in calcifying and noncalcifying tissues, suggesting specific paracellular pathways across the cell layers of these diploblastic animals. PMID:25246700

Ganot, Philippe; Zoccola, Didier; Tambutté, Eric; Voolstra, Christian R; Aranda, Manuel; Allemand, Denis; Tambutté, Sylvie

2015-01-01

239

Dimensionality of intermolecular interactions in layered crystals by electronic-structure theory and geometric analysis.  

PubMed

Two-dimensional (2D) and layered structures gained a lot of attention in the recent years ("post-graphene era"). The chalcogen cyanides S(CN)2 and Se(CN)2 offer themselves as interesting model systems to study layered inorganic crystal structures; both are built up from cyanide molecules connected by chalcogen bonds (ChBs). Here, we investigate ChBs and their cooperativity directly within the layers of the S(CN)2 and Se(CN)2 crystal structures and, furthermore, in putative O(CN)2 and Te(CN)2 crystal structures derived therefrom. Moreover, we determine the energetic contributions of ChBs within the layers to the overall stabilization energy. To compare these structures not only energetically but also geometrically, we derive a direction-dependent root mean square of the Cartesian displacement, a possible tool for further computational investigations of layered compounds. The molecular chains connected by ChBs are highly cooperative but do not influence each other when combined to layers: the ChBs are nearly orthogonal in terms of energy when connected to the same chalcogen acceptor atom. Layers built up from ChBs account for 41% to 79% of the overall interaction energy in the crystal. This provides new, fundamental insight into the meaning of ChBs, and therefore directed intermolecular interactions, for the stability of crystal structures. PMID:25363246

George, Janine; Deringer, Volker L; Dronskowski, Richard

2015-02-01

240

Large-Eddy Simulation of a Stratus-Topped Boundary Layer. Part I: Structure and Budgets  

Microsoft Academic Search

The structure of a stratus-topped boundary layer is observed through large-eddy simulation which includes the interaction of longwave radiation and turbulence processes. This simulated boundary layer has a relatively warm and dry overlying inversion, a weak surface buoyancy flux, no solar heating, and an insignificant wind shear across the cloud top. The cloud top height and the layer-averaged buoyancy flux

Chin-Hoh Moeng

1986-01-01

241

Direct Structure Determination of Multilayered Membrane-Type Systems Which Contain Fluid Layers  

PubMed Central

The theory of direct methods of structure analysis in the case of multilayered membrane-type systems which contain fluid layers is described. Diffraction formulas for this kind of analysis are derived. Deconvolution methods are used when the centrosymmetrical unit cells contain wide fluid layers. When the membrane systems contain narrow fluid layers, other direct methods are used. These direct methods involve computing either the Fourier series representations or the sampling theorem expressions. PMID:4704487

Worthington, C. R.; King, G. I.; McIntosh, T. J.

1973-01-01

242

Superfast fronts of impact ionization in initially unbiased layered semiconductor structures  

NASA Astrophysics Data System (ADS)

A mode of impact ionization breakdown of a p-n junction is suggested: We demonstrate that when a sufficiently sharp voltage ramp is applied in reverse direction to an initially unbiased equilibrium p+-n-n+ structure, after some delay the system will reach a high conductivity state via the propagation of a superfast impact ionization front. The front travels towards the anode with a velocity vf several times larger than the saturated drift velocity of electrons vs leaving a dense electron-hole plasma behind. The excitation of the superfast front corresponds to the transition from the common avalanche breakdown of a semiconductor structure to a collective mode of streamer-like breakdown. We propose that similar fronts can be excited not in layered structures but in plain bulk samples without p-n junctions. Our numerical simulations apply to a Si structure with typical thickness of Wapprox100 mum switched in series with a load Rapprox100 Omega, with a voltage ramp of A>1012 V/s applied to the whole system. Our simulations show that first there is a delay of about 1 ns during which the voltage reaches a value of several kilovolts. Then, as the front is triggered, the voltage abruptly breaks down to several hundreds of volts within approx100 ps. This provides a voltage ramp of up to approx2 x1013 V/s hence up to 10 times sharper than the externally applied ramp. We unravel the source of initial carriers which trigger the front, explain the origin of the time delay in triggering the front, and we identify the mechanism of front propagation.

Rodin, P.; Ebert, U.; Hundsdorfer, W.; Grekhov, I. V.

2002-08-01

243

On the Origin of Discrete Cosmic Structure Scales  

NASA Astrophysics Data System (ADS)

The phenomenon of discrete structure scales in the universe ranging from hadrons to galaxies and superclusters can be reproduced within a unique, quantized formalism. Restricted by a cosmological grouping condition a hierarchical clustering process determines systematically a sequence of inhomogeneities without referring to a specific force. Upon introducing gravity, a gravitational pressure balance condition arises as physical interpretation. Observed characteristics as mass, radius and mean distance of basic cosmic structures are obtained consistent with modern knowledge. Furthermore, Dirac's LNH and the ratio of strong to gravitational interaction appear as natural consequence within the concept of structure scale unification.

Leubner, M. P.

2002-12-01

244

Dynamics of coherent structures in a plane mixing layer  

NASA Technical Reports Server (NTRS)

An incompressible, time developing 3-D mixing layer with idealized initial conditions was simulated numerically. Consistent with the suggestions from experimental measurements, the braid region between the dominant spanwise vortices or rolls develops longitudinal vortices or ribs, which are aligned upstream and downstream of a roll and produce spanwise distortion of the rolls. The process by which this distortion occurs is explained by studying a variety of quantities of dynamic importance (e.g., production of enstrophy, vortex stretching). Other quantities of interest (dissipation, helicity density) are also computed and discussed. The currently available simulation only allows the study of the early evolution (before pairing) of the mixing layer. New simulations in progress will relieve this restriction.

Hussain, Fazle; Moser, R. D.; Colonius, T.; Moin, P.; Rogers, M. M.

1988-01-01

245

Three-dimensional structure of the regular tetragonal surface layer of Azotobacter vinelandii.  

PubMed Central

Fragments of the Azotobacter vinelandii tetragonal surface (S) layer, free of outer membrane material, were obtained by treating whole cells with 100 microM EDTA. The three-dimensional structure of the S layer was reconstructed from tilted-view electron micrographs of the S-layer fragments, after computer-assisted image processing by correlation averaging. At a resolution of 1.7 nm, the S layer exhibited funnel-shaped subunits situated at one fourfold-symmetry axis and interconnected at the other fourfold-symmetry axis to form prominent cruciform linking structures. These data, in conjunction with a relief reconstruction of the surface of freeze-etched whole cells, indicated that the apex of the funnel-shaped subunit was associated with the outer membrane, while the funnel "opening" faced the environment; the cruciform linking structures were formed at the outermost surface of the S layer. Electron microscopy and image enhancement were used to compare the structure of the outer membrane-associated S layer with that of fragments of the S layer dislodged from the outer membrane. This analysis revealed an increase in the lattice constant of the S layer from 12.5 to 13.6 nm and an alteration in the position of the cruciform linking structures in the z direction. These conformational changes resulted in a reduction in the thickness of the S layer (minimum estimate, 5 nm) and an apparent increase in the size of the gaps between the subunits. In terms of the porosity of the S layer, this gave the appearance of a transition from a closed to a more open structure. Images PMID:3667523

Bingle, W H; Engelhardt, H; Page, W J; Baumeister, W

1987-01-01

246

Origins of Structural Hole Traps in Hydrogenated Amorphous Silicon  

E-print Network

The inherently disordered nature of hydrogenated amorphous silicon (a-Si:H) obscures the influence of atomic features on the trapping of holes. To address this, we have created a set of over two thousand ab initio structures ...

Johlin, Eric Carl

247

Analysis of Coherent Structures Within the Atmospheric Boundary Layer  

Microsoft Academic Search

Large-eddy simulation has become an important tool for the study of the atmospheric boundary layer. However, since large-eddy\\u000a simulation does not simulate small scales, which do interact to some degree with large scales, and does not explicitly resolve\\u000a the viscous sublayer, it is reasonable to ask if these limitations affect significantly the ability of large-eddy simulation\\u000a to simulate large-scale coherent

J. Huang; M. Cassiani; J. D. Albertson

2009-01-01

248

Origin of the filamentary structure in space plasmas  

NASA Astrophysics Data System (ADS)

We propose a scenario that filamentary structure appears together with propagating waves on the scale of ion gyroradius. The method is based on two-dimensional ion particle-in-cell (or hybrid) simulation in low-beta plasmas. Coherent, filamentary structures in space plasmas are found as the zero-frequency mode in the wavenumber-frequency domain. The existence of the wave modes might be the key to understand filament formation in space plasmas.

Comi?el, Horia; Constantinescu, Vlad; Narita, Yasuhito

2014-12-01

249

The Structure and Origin of Solar Plumes: Network Plumes  

NASA Astrophysics Data System (ADS)

This study is based upon plumes seen close to the solar limb within coronal holes in the emission from ions formed in the temperature region of 1 MK, in particular, the band of Fe IX 171 Å from EIT on the Solar and Heliospheric Observatory. It is shown, using geometric arguments, that two distinct classes of structure contribute to apparently similar plume observations. Quasi-cylindrical structures are anchored in discrete regions of the solar surface (beam plumes), and faint extended structures require integration along the line of sight (LOS) in order to reproduce the observed brightness. This second category, sometimes called "curtains," are ubiquitous within the polar holes and are usually more abundant than the beam plumes, which depend more on the enhanced magnetic structures detected at their footpoints. It is here proposed that both phenomena are based on plasma structures in which emerging magnetic loops interact with ambient monopolar fields, involving reconnection. The important difference is in terms of physical scale. It is proposed that curtains are composed of a large number of microplumes, distributed along the LOS. The supergranule network provides the required spatial structure. It is shown by modeling that the observations can be reproduced if microplumes are concentrated within some 5 Mm of the cell boundaries. For this reason, we propose to call this second population "network plumes." The processes involved could represent a major contribution to the heating mechanism of the solar corona.

Gabriel, A.; Bely-Dubau, F.; Tison, E.; Wilhelm, K.

2009-07-01

250

A class of unsteady, three-dimensional flow structures in turbulent boundary layers  

NASA Technical Reports Server (NTRS)

A restricted class of mathematically admissible, unsteady, three dimensional flows was identified which may constitute part of the structure observed in turbulent boundary layers. The development of the model and some general results are discussed. The resulting solution has characteristics which suggest how upwelling low speed flow can trigger a downward jetting of irrotational high speed fluid into the boundary layer.

Ash, R. L.

1981-01-01

251

Identification of a sound-insulation layer modelled by fuzzy structure theory -Experimental validation  

E-print Network

Identification of a sound-insulation layer modelled by fuzzy structure theory - Experimental.fernandez@univ-paris-est.fr Abstract One proposes a novel approach to model sound-insulation layers based on the use of the fuzzy in computational models. The keypoint of the method is the construction of a mean elastoacoustic sound-insulation

Boyer, Edmond

252

Scaling structure of the velocity statistics in atmospheric boundary layers Susan Kurien,1,2  

E-print Network

Scaling structure of the velocity statistics in atmospheric boundary layers Susan Kurien,1,2 Victor. INTRODUCTION The atmospheric boundary layer is a natural laboratory of turbulence that is unique to be universal in the limit Re , are thus attracted to atmospheric measurements. On the other hand, the boundary

Kurien, Susan

253

Effect of Layer-Stacking on the Electronic Structure of Graphene Nanoribbons  

Microsoft Academic Search

The evolution of electronic structure of graphene nanoribbons (GNRs) as a function of the number of layers stacked together is investigated using \\\\textit{ab initio} density functional theory (DFT) including interlayer van der Waals interactions. Multilayer armchair GNRs (AGNRs), similar to single-layer AGNRs, exhibit three classes of band gaps depending on their width. In zigzag GNRs (ZGNRs), the geometry relaxation resulting

Neerav Kharche; Yu Zhou; Kevin P. O'Brien; Swastik Kar; Saroj K. Nayak

2011-01-01

254

An observational study of the structure of the nocturnal boundary layer  

Microsoft Academic Search

In an effort to describe the basic vertical structure of the nocturnal boundary layer, observations from four experiments are analyzed. During the night, the depth of significant cooling appears to increase with time while the depth of the turbulence and height of the low level wind maximum tend to remain constant or decrease with time. Since the inversion layer extends

L. Mahrt; R. C. Heald; D. H. Lenschow; B. B. Stankov; Ib Troen

1979-01-01

255

Analysis of a concentric coplanar capacitive sensor for nondestructive evaluation of multi-layered dielectric structures  

Microsoft Academic Search

A concentric coplanar capacitive sensor is analyzed for the quantitative characterization of material properties for multi-layered dielectrics. The sensor output signal, transcapacitance CT, is related to the thickness and dielectric constant of each layer of the material under test. Electrostatic Green¿s functions due to point charges over different dielectric structures are derived utilizing the Hankel transform given the cylindrical symmetry

Tianming Chen; Nicola Bowler

2010-01-01

256

Affine matching pattern-recognition analysis of eddy structures in a numerically simulated boundary layer  

Microsoft Academic Search

A method is introduced of educing coherent eddy structures from turbulent flows and quantifying the variation of the structures found. The method has been applied to conditionally sampled flow fields associated with ejection events in a numerical simulation of a turbulent boundary layer at very low Reynolds number. It is found that asymmetric streamwise vortical structures, reminiscent of those seen

Peter R. Voke; Surrey GU

1993-01-01

257

Average Transmission Decrease in One-Dimensional Photonic Structures by Widening the Random Layer Thickness Distribution  

E-print Network

In this work we have studied the optical properties of disordered photonic structures, in which we have controlled the distribution of the random layer thickness. Such structures are characterized by an alternation of high and low refractive index layers, but the layer thicknesses follow the aforementioned distributions. We have used two types of distribution: a distribution in which each thickness has the same probability to occur and one in which the thickness follows a Gaussian function. We have simulated the average transmission all over the spectrum for photonic structure characterized by a different width of the distribution. We have found that the choice of the distribution of the layer thickness is a control of the average transmission of a random photonic structure.

Scotognella, Francesco

2015-01-01

258

Bias-dependent molecular-level structure of electrical double layer in ionic liquid on graphite  

SciTech Connect

Bias-dependent structure of electrochemical double layers at liquid-solid interfaces underpin a multitude of phenomena in virtually all areas of scientific enquiry ranging from energy storage and conversion systems, biology, to geophysics and geochemistry. Here we report the bias-evolution of the electric double layer structure of an ionic liquid on highly ordered pyrolytic graphite as a model system for carbon-based electrodes for electrochemical supercapacitors measured by atomic force microscopy. Matching the observed structures to molecular dynamics simulations allows us to resolve steric effects due to cation and anion layers. We observe reconfiguration under applied bias and the orientational transitions in the Stern layer. The synergy between molecular dynamics simulation and experiment provides a comprehensive picture of structural phenomena and long- and short range interactions. This insight will improve understanding of the mechanism of charge storage in electrochemical capacitors on a molecular level which can be used to enhance their electrochemical performance.

Black, Jennifer M [ORNL] [ORNL; Walters, Deron [Asylum Research, Santa Barbara, CA] [Asylum Research, Santa Barbara, CA; Labuda, Aleksander [Asylum Research, Santa Barbara, CA] [Asylum Research, Santa Barbara, CA; Feng, Guang [ORNL] [ORNL; Hillesheim, Patrick C [ORNL] [ORNL; Dai, Sheng [ORNL] [ORNL; Cummings, Peter T [ORNL] [ORNL; Kalinin, Sergei V [ORNL] [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA] [Asylum Research, Santa Barbara, CA; Balke, Nina [ORNL] [ORNL

2013-01-01

259

A structural origin for the cantaloupe terrain of Triton  

NASA Technical Reports Server (NTRS)

Cantaloupe terrain is unique to Triton. It is Triton's oldest terrain and includes about 250,000 km sq. region displaying sparsely cratered, closely spaced, nearly circular dimples about 30-40 km across. This terrain is found on no other planet because, only on Triton the final major global thermal pulse (1) caused completed (or nearly) interior melting resulting in a cooling history where large thermal stresses shattered and contorted a thin, weak lithosphere, and (2) occurred after heavy bombardment so that the surface features were preserved. The cantaloupe terrain is composed of intersecting sets of structures (folds and/or faults) that have developed as a result of global compression generated by volumetric changes associated with cooling of Triton's interior. Further, it is proposed that these structures developed after the period of heavy bombardment, and resulted from the last major global thermal epoch in Triton's unique history (either caused by tidal or radio metric heating). Initially, as the body cooled and the structures formed, their surface topography was most likely modified by thermal relaxation of the warm surface ices. In other bodies like Mercury, thermal stresses generated from global cooling and contraction have resulted in widely spaced thrust faults, whereas on Triton, thermal stresses produced more closely-spaced folds and faults sets. This difference in structural style is probably due to differences in lithospheric properties (thickness, strength, etc.), the magnitude of stress (directly dependent on the thermal history), and when the structures formed, relative to the period of heavy bombardment.

Boyce, Joseph M.

1993-01-01

260

A structural origin for the cantaloupe terrain of Triton  

NASA Astrophysics Data System (ADS)

Cantaloupe terrain is unique to Triton. It is Triton's oldest terrain and includes about 250,000 km sq. region displaying sparsely cratered, closely spaced, nearly circular dimples about 30-40 km across. This terrain is found on no other planet because, only on Triton the final major global thermal pulse (1) caused completed (or nearly) interior melting resulting in a cooling history where large thermal stresses shattered and contorted a thin, weak lithosphere, and (2) occurred after heavy bombardment so that the surface features were preserved. The cantaloupe terrain is composed of intersecting sets of structures (folds and/or faults) that have developed as a result of global compression generated by volumetric changes associated with cooling of Triton's interior. Further, it is proposed that these structures developed after the period of heavy bombardment, and resulted from the last major global thermal epoch in Triton's unique history (either caused by tidal or radio metric heating). Initially, as the body cooled and the structures formed, their surface topography was most likely modified by thermal relaxation of the warm surface ices. In other bodies like Mercury, thermal stresses generated from global cooling and contraction have resulted in widely spaced thrust faults, whereas on Triton, thermal stresses produced more closely-spaced folds and faults sets. This difference in structural style is probably due to differences in lithospheric properties (thickness, strength, etc.), the magnitude of stress (directly dependent on the thermal history), and when the structures formed, relative to the period of heavy bombardment.

Boyce, Joseph M.

1993-03-01

261

Effects of physical processes on structure and transport of thin zooplankton layers in the coastal ocean  

USGS Publications Warehouse

Thin layers of plankton are recurrent features in a variety of coastal systems. These layers range in thickness from a few centimeters to a few meters. They can extend horizontally for kilometers and have been observed to persist for days. Densities of organisms found within thin layers are far greater than those above or below the layer, and as a result, thin layers may play an important role in the marine ecosystem. The paramount objective of this study was to understand the physical processes that govern the dynamics of thin layers of zooplankton in the coastal ocean. We deployed instruments to measure physical processes and zooplankton distribution in northern Monterey Bay; during an 11 d period of persistent upwelling-favorable winds, 7 thin zooplankton layers were observed. These zooplankton layers persisted throughout daylight hours, but were observed to dissipate during evening hours. These layers had an average vertical thickness of 1.01 m. No layers were found in regions where the Richardson number was <0.25. In general, when the Richardson number is <0.25 the water column is unstable, and incapable of supporting thin layers. Thin zooplankton layers were also located in regions of reduced flow. In addition, our observations show that the vertical depth distribution of thin zooplankton layers is modulated by high-frequency internal waves, with periods of 18 to 20 min. Results from this study clearly show an association between physical structure, physical processes and the presence of thin zooplankton layers in Monterey Bay. With this new understanding we may identify other coastal regions that have a high probability of supporting thin layers. ?? Inter-Research 2005.

McManus, M.A.; Cheriton, O.M.; Drake, P.J.; Holliday, D.V.; Storlazzi, C.D.; Donaghay, P.L.; Greenlaw, C.F.

2005-01-01

262

Origin of water layer multiple phases with anomalously high amplitude in near-seafloor wide-angle seismic recordings  

NASA Astrophysics Data System (ADS)

Water layer multiple seismic phases are recorded at ocean bottom seismometers and hydrophones as arrivals that correspond to the reflection of the primary phases at the sea-free air interface. In regions of low to moderate seabed relief, the shape of these phases mimics that of the primary phases with a traveltime delay that depends on the water layer thickness at the receiver location. Given their longer travel paths, multiple phases should have smaller amplitudes than their corresponding primary phases. However, depending on the geological context it can be relatively common to observe the opposite, which results in the identification of the multiple phases at longer offsets than the primary events. In this paper, we examine the origin of this apparently paradoxical phenomenon by analysing the combined effect of the major factors potentially involved: the source frequency content, the subsurface velocity distribution, the receiver-seafloor distance, the geometrical spreading and attenuation of sound waves and the ambient noise level. We use synthetic modelling to show that for certain combinations of these factors, the interference between the multiple and its reflection at the seafloor is constructive and has a higher amplitude than the primary wave. Our analysis indicates that in the most favourable cases the phases resulting from this interference can be observed at offsets some tens of kilometres longer than their corresponding primary phases, and thus they can provide useful information for velocity modelling.

Meléndez, Adrià; Sallarès, Valentí; Ranero, César R.; Kormann, Jean

2014-01-01

263

Beyond phonics: Integrated decoding and spelling instruction based on word origin and structure.  

PubMed

In this paper, the relevance of word structure knowledge to decoding and spelling instruction is discussed. An explicit, discussion oriented, direct approach to teaching decoding and spelling based on word origin and structure results in improved reading and spelling. This instruction leads students to a comparison and contrast of letter-sound correspondences, syllable patterns, and morpheme patterns in English words of Anglo-Saxon, Romance, and Greek origin. PMID:24235045

Henry, M K

1988-01-01

264

Three-dimensional structure of the regularly constructed surface layer from Synechocystis sp. strain CLII.  

PubMed Central

The isolated, outermost cell wall layer from Synechocystis sp. strain CLII is described using electron microscopy and Fourier reconstruction to study the three-dimensional structure of the proteins within the layer to a resolution of ca. 3 nm. This surface layer forms regular hexagonal arrays (a = b = 15.2 nm). The two-dimensional space group is p6. The monomer proteins form hexamers arranged around a central hollow cylinder. The linkers between the hexamers are of the delta type and are located approximately in the central section between the top and bottom of the protein layer. Images PMID:6417112

Karlsson, B; Vaara, T; Lounatmaa, K; Gyllenberg, H

1983-01-01

265

Differential PIXE for investigating the layer structure of paintings  

NASA Astrophysics Data System (ADS)

This paper reports an example of how the differential PIXE technique can be successfully applied to the investigation of wood or canvas paintings. The work analysed is a famous wood painting by Leonardo da Vinci, the "Madonna dei fusi" (ex-Reford version, 1501), chosen for a pilot study in a wide international project aimed at analysing Leonardo's works of art by means of non-destructive techniques. While illustrating the results obtained concerning the identification of pigments and the discrimination of the stratigraphy of layers, the merits and limits of differential PIXE in general are pointed out.

Mandò, P. A.; Fedi, M. E.; Grassi, N.; Migliori, A.

2005-09-01

266

Modern Structures in the 1906 Quake (Not from original site)  

NSDL National Science Digital Library

A series of QuickTime movies illustrating the deformation of modern Californian structures subjected to the 1906 earthquake. The deformation, exaggerated 100 times, is shown for the Golden Gate Bridge, the SF International Airport, and the San Francisco Marriot. Los Angeles City Hall is also simulated in order to show how buildings further from the epicenter were affected.

Computers & amp; amp; Structures, Inc.

267

Local structure of Cu2S/ZnS multi-layer films prepared using ALD  

NASA Astrophysics Data System (ADS)

We present local structure studies of ZnS, Cu2S, and ZnS/Cu2S composite films, using extended x-ray absorption fine structure (EXAFS) technique. The films were prepared using atomic layer deposition (ALD), which can in principle deposit films layer by layer and hence form mesoscopic structures. ZnS and Cu2S films prepared using ALD are very similar to the bulk material; the main difference is a reduced amplitude for the second neighbor Zn-Zn peak in ZnS, suggesting increased disorder within the film. Relative disorder in the films also increases with decreasing thickness as well as with decreasing deposition temperature. More importantly, multi-layer ZnS/Cu2S films prepared using the same parameters as for individual films do not produce the expected multi-layer for ˜1 nm thick layers. If there is some excess Zn, the multi-layer is predominately ZnS and the CuxS fraction is highly disordered, and may include some ZnS:Cu. In contrast if there is a little Cu excess, the film is nearly all Cu2S and the small Zn fraction is highly disordered ZnS with a shifted Zn-S distance. Consequences for multi-layer formation for solar cell applications will be discussed.

Bridges, Frank; Jewell, Leila; Short, Andrew; Alers, Glenn; Carter, Sue A.

2013-03-01

268

Effect of electron collecting metal oxide layer in normal and inverted structure polymer solar cells  

SciTech Connect

We performed a systematic study of the effect of electron collecting metal oxide layer on the performance of P3HT: PCBM solar cells. Zinc oxide (ZnO) or titanium dioxide (TiO{sub 2}) buffer layers were prepared by either e-beam evaporation or solution processing method. We also compared the photovoltaic performance of inserting the buffer layer between indium tin oxide (ITO) and the polymer layer for the inverted structure (ITO/ ZnO or TiO{sub 2}/P3HT:PCBM/V{sub 2}O{sub 5}/Au) as well as inserting the buffers layers between the polymer and the aluminum electrode for the conventional structure (ITO/V{sub 2}O{sub 5}/P3HT:PCBM/ZnO or TiO{sub 2}/Al). The results are shown in detail.

Ng, A.; Liu, X.; Sun, Y. C.; Djuriši?, A. B. [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. (China); Ng, A. M. C. [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China and Nanostructure Institute for Energy and Environmental Research, Division of Physical Sciences, South University of Science and Technology of China, Shenzhen (China); Chan, W. K. [Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. (China)

2013-12-04

269

Photo-Activity Research of Nano-Structured TiO2 Layers  

NASA Astrophysics Data System (ADS)

Titania with anatase structure is investigated due to its photo-active properties that can be used in the water photocatalysis applications and in the organic photovoltaic devices. In this work the anodization conditions are described to obtain stable thin film TiO2 layers formed from vertically oriented nanotubes with approximate height 358 nm, inner tube diameter 48 nm and wall thickness 20 nm, but centre to centre distance 100 nm. Annealed at 500°C TiO2 layer mostly consists from oxide with anatase structure, though XRD spectroscopy shows rutile impurities as well. Obtained nanotube layers are sensitive mostly to UV light.

Linitis, Janis; Kalis, Arturs; Grinberga, Liga; Kleperis, Janis

2011-06-01

270

Nonlinear layered lattice model and generalized solitary waves in imperfectly bonded structures  

NASA Astrophysics Data System (ADS)

We study nonlinear waves in a two-layered imperfectly bonded structure using a nonlinear lattice model. The key element of the model is an anharmonic chain of oscillating dipoles, which can be viewed as a basic lattice analog of a one-dimensional macroscopic waveguide. Long nonlinear longitudinal waves in a layered lattice with a soft middle (or bonding) layer are governed by a system of coupled Boussinesq-type equations. For this system we find conservation laws and show that pure solitary waves, which exist in a single equation and can exist in the coupled system in the symmetric case, are structurally unstable and are replaced with generalized solitary waves.

Khusnutdinova, Karima R.; Samsonov, Alexander M.; Zakharov, Alexey S.

2009-05-01

271

Plasmon resonance absorption in layered structures of silver with periodic corrugation  

SciTech Connect

Plasmon resonance absorption in periodically corrugated layered structures of silver was studied by the photoacoustic method. The layered structures were self-supporting and corrugated with a period of 1888 nm and amplitude varying from 6 to 12 nm, depending on the thickness. Experimental results of resonance absorption of 633-nm photons were analyzed in terms of the propagation and damping constants of coupled modes of surface plasmons. The coupling efficiency of incident photons to these modes was found to be strongly dependent on corrugation amplitude and layer thickness.

Arakawa, E.T.; Inagaki, T.; Goudonnet, J.P.

1987-01-01

272

4E-2 Theoretical and Experimental Study of the Differential Thermal Expansion Effect on the TCD of Layered SAW Temperature Sensors Application to Aluminum Nitride Based Layered Structures  

Microsoft Academic Search

In this paper, we show that the stress and strain fields induced in a layered SAW structure by the thermal expansion of the different layers must be taken into account to compute the global structure temperature coefficient of delay (TCD). Experimental and numerical results are provided. The numerical model is described. It is based at the same time on the

P. Nicolay; O. Elmazria; B. Assouar; F. Sarry; L. Lebrizoual

2007-01-01

273

Crustal structure and origin of the Cape Verde Rise  

Microsoft Academic Search

The Cape Verde Islands are located on a mid-plate topographic swell and are thought to have formed above a deep mantle plume. Wide-angle seismic data have been used to determine the crustal and uppermost mantle structure along a ~440 km long transect of the archipelago. Modelling shows that ‘normal’ oceanic crust, ~7 km in thickness, exists between the islands and is gently

J. Pim; C. Peirce; A. B. Watts; I. Grevemeyer; A. Krabbenhoeft

2008-01-01

274

The Origins of Magnetic Structure in the Corona and Wind  

NASA Technical Reports Server (NTRS)

One of the most important and most puzzling features of the coronal magnetic field is that it appears to have smooth magnetic structure with little evidence for non-potentiality except at two special locations: photospheric polarity inversions lines. (non-potentiality observed as a filament channel) and coronal hole boundaries, (observed as the slow solar wind). This characteristic feature of the closed-field corona is highly unexpected given that its magnetic field is continuously tangled by photospheric motions. Although reconnection can eliminate some of the injected structure, it cannot destroy the helicity, which should build up to produce observable complexity. I propose that an inverse cascade process transports the injected helicity from the interior of closed flux regions to their boundaries inversion lines and coronal holes, creating both filament channels and the slow wind. We describe how the helicity is injected and transported and calculate the relevant rates. I argue that one process, helicity transport, can explain both the observed lack and presence of structure in the coronal magnetic field. This work has been supported by the NASA HTP, SR&T, and LWS programs.

Antiochos, Spiro K.

2010-01-01

275

Unequal density effect on static structure factor of coupled electron layers  

SciTech Connect

In order to understand the ordered phase, if any, in a real coupled electron layers (CEL), there is a need to take into account the effect of unequal layer density. Such phase is confirmed by a strong peak in a static structure factor. With the aid of quantum/dynamical version of Singwi, Tosi, Land and Sjölander (so-called qSTLS) approximation, we have calculated the intra- and interlayer static structure factors, S{sub ll}(q) and S{sub 12}(q), over a wide range of density parameter r{sub sl} and interlayer spacing d. In our present study, the sharp peak in S{sub 22}(q) has been found at critical density with sufficiently lower interlayer spacing. Further, to find the resultant effect of unequal density on intra- and interlayer static structure factors, we have compared our results with that of the recent CEL system with equal layer density and isolated single electron layer.

Saini, L. K., E-mail: lks@ashd.svnit.ac.in; Nayak, Mukesh G., E-mail: lks@ashd.svnit.ac.in [Department of Applied Physics, S. V. National Institute of Technology, Surat - 395007, Gujarat (India)

2014-04-24

276

Two isostructural layered oxohalide compounds containing Mn2+, Te4+ and Si4+; crystal structure and magnetic susceptibility  

NASA Astrophysics Data System (ADS)

The new compounds Mn4(TeO3)(SiO4)X2 (X=Br, Cl) were synthesized by solid state reactions in sealed evacuated silica tubes. The compounds crystallize in the monoclinic space group P21/m with the unit cell parameters a=5.5463(3) Å (5.49434(7) Å), b=6.4893(4) Å (6.44184(9) Å), c=12.8709(7) Å (12.60451(18) Å), ?=93.559(5)° (94.1590(12)°) and Z=2 for the respective Br and Cl analogues. Manganese adopts various distorted coordination polyhedra; [MnO6] octahedra, [MnO5] tetragonal pyramids and [MnO2X2] tetrahedra. Other building blocks are [SiO4] tetrahedra and [TeO3] trigonal pyramids. The structure is made up from layers having no net charge that are connected via weak Van der Waal interactions. The layers that are parallel to (1 1 0) consist of two manganese oxide sheets which are separated by [SiO4] tetrahedra. On the outer sides of the sheets are the [MnO2X2] tetrahedra and the [TeO3] trigonal pyramids connected so that the halide ions and the stereochemically active lone pairs on the tellurium atoms protrude from the layers. Magnetic susceptibility measurements reveal a Curie law with a Weiss temperature of ?=-153(3) K for temperatures ?100 K and indicate antiferromagnetic ordering at TN ~4 K. Possible structural origins of the large frustration parameter of f=38 are discussed. The new compounds Mn4(TeO3)(SiO4)X2 (X=Br, Cl) are layered with weak Van der Waal interactions in between the layers. Manganese adopts various distorted coordination polyhedral, other building blocks are [SiO4] tetrahedra and [TeO3] trigonal pyramids. Magnetic susceptibility measurements indicate antiferromagnetic ordering at low temperatures and a large frustration parameter.

Zimmermann, Iwan; Kremer, Reinhard K.; Johnsson, Mats

2014-10-01

277

Bathymetry, controlled source seismic and gravity observations of the Mendeleev ridge; implications for ridge structure, origin, and regional tectonics  

NASA Astrophysics Data System (ADS)

Multichannel seismic (MCS), seismic refraction, and gravity data collected down the flank of the Chukchi Plateau, but predominantly over the Mendeleev Ridge have been processed and interpreted to describe the crustal style of the ridge, as well as the structural history. These results provide constraints on the origin of the ridge, and the tectonic evolution of the Amerasian Basin. MCS images reveal two primary sediment sequences separated by an unconformity that persists across the entire Mendeleev Ridge. The basement and lower sediment sequence exhibit pervasive normal faulting. The upper sequence is laterally conformable and not effected by faulting, thus the regional unconformity dividing the two sequences is interpreted to mark the end of extensional deformation. Modeling of sonobuoy seismic refraction data reveals upper crustal P-wave velocities ranging from 3.5 to 6.4kms-1 approximately 5km into the basement. The velocity structure of the Mendeleev Ridge is consistent with either a volcanic rifted continental margin, or an oceanic plateau origin. Observed gravity anomalies over the ridge are reproduced by a model consisting of bathymetry, sediment and basement horizons from the MCS data and a single crustal layer of 2.86gcm-3. This result is consistent with homogeneous, mafic crust. The similar velocity and density structures of the Mendeleev and Alpha ridges is consistent with a model where the two ridges are contiguous and share a common geological origin. Gravity modelling over the transition between the Chukchi Plateau and the Mendeleev Ridge suggests the two features have differing compositions and distinct emplacement histories. Three tectonic models are presented for the origin of the Alpha Mendeleev Ridge (AMR) that satisfy constraints set by this and previous studies: (1) a rifted volcanic continental margin, (2) an oceanic plateau formed at a spreading centre-perpendicular to the AMR and (3) an oceanic plateau formed at a spreading centre-parallel to the AMR.

Dove, Dayton; Coakley, Bernard; Hopper, John; Kristoffersen, Yngve

2010-11-01

278

Mirror instability and origin of morningside auroral structure  

NASA Technical Reports Server (NTRS)

Auroral optical imagery shows marked differences between auroral features of the evening and morning sectors: the separation between diffuse and discrete auroras in the evening sector is not distinct in the morning sector, which is dominated by auroral patches and multiple banded structures aligned along some direction. Plasma distribution function signatures also show marked differences: downward electron beams and inverted-V signatures prefer the evening sector, while the electron spectra on the morning sector are similar to the diffuse aurora. A theory of morningside auroras consistent with these features was constructed. The theory is based on modulation of the growth rates of electron cyclotron waves by the mirror instability, which is in turn driven by inward-convected ions that have become anisotropic. This modulation produces alternating bands of enhanced and reduced electron precipitation which approximate the observed multiple auroral bands and patches of the morning sector.

Chiu, Y. T.; Schulz, M.; Fennell, J. F.; Kishi, A. M.

1983-01-01

279

Structural Origin of Circularly Polarized Iridescence in Jeweled Beetles  

NASA Astrophysics Data System (ADS)

The iridescent metallic green beetle, Chrysina gloriosa, which selectively reflects left circularly polarized light, possesses an exoskeleton decorated by hexagonal cells (~10 ?m) that coexist with pentagons and heptagons. The fraction of hexagons decreases with an increase in curvature. In bright field microscopy, each cell contains a bright yellow core, placed in a greenish cell with yellowish border, but the core disappears in dark field. With use of confocal microscopy, we observe that these cells consist of nearly concentric nested arcs that lie on the surface of a shallow cone. We infer that the patterns are structurally and optically analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal. These textures provide the basis for the morphogenesis as well as key insights for emulating the intricate optical response of the exoskeleton of scarab beetles.

Sharma, Vivek; Crne, Matija; Park, Jung Ok; Srinivasarao, Mohan

2009-07-01

280

Structural origin of circularly polarized iridescence in jeweled beetles  

NASA Astrophysics Data System (ADS)

The iridescent metallic green beetle, Chrysina gloriosa, selectively reflects left circularly polarized light. The exoskeleton is decorated by hexagonal cells (˜10 micron) that coexist with pentagons and heptagons. We find that the fraction of hexagons decreases with an increase in curvature. In bright field microscopy, each cell contains a bright yellow core, placed in a greenish cell with yellowish border, but the core disappears in the dark field. Using confocal microscopy, we observe that these cells consist of nearly concentric, nested arcs that lie on surface of a shallow cone. We infer that the patterns are structurally and optically analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal. The microstructure provides the bases for the morphogenesis as well as key insights for emulating the intricate optical response the exoskeleton of scarab beetles.

Crne, Matija; Sharma, Vivek; Park, Jung O.; Srinivasarao, Mohan

2010-03-01

281

Structure prediction of an S-layer protein by the mean force method  

NASA Astrophysics Data System (ADS)

S-layer proteins have a wide range of application potential due to their characteristic features concerning self-assembling, assembling on various surfaces, and forming of isoporous structures with functional groups located on the surface in an identical position and orientation. Although considerable knowledge has been experimentally accumulated on the structure, biochemistry, assemble characteristics, and genetics of S-layer proteins, no structural model at atomic resolution has been available so far. Therefore, neither the overall folding of the S-layer proteins—their tertiary structure—nor the exact amino acid or domain allocations in the lattices are known. In this paper, we describe the tertiary structure prediction for the S-layer protein SbsB from Geobacillus stearothermophilus PV72/p2. This calculation was based on its amino acid sequence using the mean force method (MF method) achieved by performing molecular dynamic simulations. This method includes mainly the thermodynamic aspects of protein folding as well as steric constraints of the amino acids and is therefore independent of experimental structure analysis problems resulting from biochemical properties of the S-layer proteins. Molecular dynamic simulations were performed in vacuum using the simulation software NAMD. The obtained tertiary structure of SbsB was systematically analyzed by using the mean force method, whereas the verification of the structure is based on calculating the global free energy minimum of the whole system. This corresponds to the potential of mean force, which is the thermodynamically most favorable conformation of the protein. Finally, an S-layer lattice was modeled graphically using CINEMA4D and compared with scanning force microscopy data down to a resolution of 1nm. The results show that this approach leads to a thermodynamically favorable atomic model of the tertiary structure of the protein, which could be verified by both the MF Method and the lattice model.

Horejs, C.; Pum, D.; Sleytr, U. B.; Tscheliessnig, R.

2008-02-01

282

Amino acids equivalences within protein structures The original publication is available at www.springerlink.com  

E-print Network

Amino acids equivalences within protein structures 1 The original publication is available at www.springerlink.com A reduced amino acid alphabet for understanding and designing protein adaptation to mutation. C. Etchebest 1, 75251 Paris, France Short title: Amino acids equivalences within protein structures * Corresponding

Paris-Sud XI, Université de

283

ORIGINAL PAPER Evolution of growth but not structural or chemical defense  

E-print Network

ORIGINAL PAPER Evolution of growth but not structural or chemical defense in Verbascum thapsus of defense, as predicted by the influential evolution of increased competitive ability (EICA) hypothesis generalists. Thus, different types of defense (e.g., structural versus chemical) may evolve in different

Hufbauer, Ruth A.

284

ORIGINAL PAPER Evolution of growth but not structural or chemical defense  

E-print Network

ORIGINAL PAPER Evolution of growth but not structural or chemical defense in Verbascum thapsus- tently associated with a loss of defense, as predicted by the influential evolution of increased, they often do not escape attack from generalists. Thus, different types of defense (e.g., structural versus

Hufbauer, Ruth A.

285

Cusp and Y-type Magnetic Structures and Velocity Fields at the Endpoint of the Reconnection Layer.  

E-print Network

Cusp and Y-type Magnetic Structures and Velocity Fields at the Endpoint of the Reconnection Layer Syrovatskii-type Y-point con- #12;guration, with surface current concentrated only in the reconnection layer the dynamic behavior of the plasma in thin layers. A closer examination of these layers reveals

286

Structure and electronic properties of ionic nano-layers MBE-grown on IIIV semiconductors  

E-print Network

Structure and electronic properties of ionic nano-layers MBE-grown on III±V semiconductors MSb semiconductors by means of molecular beam epitaxy (MBE). Electronic and structural properties of the freshly on the AIIIBV semiconductor is arranged by the strong bond formed between the halogen ion and the AIII metallic

Korecki, Pawe³

287

Acoustic band-gap engineering using finite-size layered structures of multiple periodicity  

E-print Network

Acoustic band-gap engineering using finite-size layered structures of multiple periodicity Mingrong and also measured as a function of frequency. It was found that acoustic band gaps can be created using structure, very sharp passbands and very broad stopbands can be engineered for acoustic waves. Such acoustic

Cao, Wenwu

288

Origin of Permeability and Structure of Flows in Fractured Media  

NASA Astrophysics Data System (ADS)

After more than three decades of research, flows in fractured media have been shown to result from multi-scale geological structures. Flows result non-exclusively from the damage zone of the large faults, from the percolation within denser networks of smaller fractures, from the aperture heterogeneity within the fracture planes and from some remaining permeability within the matrix. While the effect of each of these causes has been studied independently, global assessments of the main determinisms is still needed. We propose a general approach to determine the geological structures responsible for flows, their permeability and their organization based on field data and numerical modeling [de Dreuzy et al., 2012b]. Multi-scale synthetic networks are reconstructed from field data and simplified mechanical modeling [Davy et al., 2010]. High-performance numerical methods are developed to comply with the specificities of the geometry and physical properties of the fractured media [Pichot et al., 2010; Pichot et al., 2012]. And, based on a large Monte-Carlo sampling, we determine the key determinisms of fractured permeability and flows (Figure). We illustrate our approach on the respective influence of fracture apertures and fracture correlation patterns at large scale. We show the potential role of fracture intersections, so far overlooked between the fracture and the network scales. We also demonstrate how fracture correlations reduce the bulk fracture permeability. Using this analysis, we highlight the need for more specific in-situ characterization of fracture flow structures. Fracture modeling and characterization are necessary to meet the new requirements of a growing number of applications where fractures appear both as potential advantages to enhance permeability and drawbacks for safety, e.g. in energy storage, stimulated geothermal energy and non-conventional gas productions. References Davy, P., et al. (2010), A likely universal model of fracture scaling and its consequence for crustal hydromechanics, Journal of Geophysical Research-Solid Earth, 115, 13. de Dreuzy, J.-R., et al. (2012a), Influence of fracture scale heterogeneity on the flow properties of three-dimensional Discrete Fracture Networks (DFN), J. Geophys. Res.-Earth Surf., 117(B11207), 21 PP. de Dreuzy, J.-R., et al. (2012b), Synthetic benchmark for modeling flow in 3D fractured media, Computers and Geosciences(0). Pichot, G., et al. (2010), A Mixed Hybrid Mortar Method for solving flow in Discrete Fracture Networks, Applicable Analysis, 89(10), 1729-1643. Pichot, G., et al. (2012), Flow simulation in 3D multi-scale fractured networks using non-matching meshes, SIAM Journal on Scientific Computing (SISC), 34(1). Figure: (a) Fracture network with a broad-range of fracture lengths. (b) Flows (log-scale) with homogeneous fractures. (c) Flows (log-scale) with heterogeneous fractures [de Dreuzy et al., 2012a]. The impact of the fracture apertures (c) is illustrated on the organization of flows.

De Dreuzy, J.; Darcel, C.; Davy, P.; Erhel, J.; Le Goc, R.; Maillot, J.; Meheust, Y.; Pichot, G.; Poirriez, B.

2013-12-01

289

Giant magnetoresistance of manganese oxides with a layered perovskite structure  

Microsoft Academic Search

MANGANESE oxides with the cubic perovskite structure (typified by LaMnO3) have stimulated considerable interest because of their magnetoresistive properties1-9 they exhibit extremely large changes in electrical resistance in response to applied magnetic fields, a property that is of technological relevance for the development of magnetic memory and switching devices. But for such applications to be viable, great improvements will be

Y. Moritomo; A. Asamitsu; H. Kuwahara; Y. Tokura

1996-01-01

290

Ferromagnetic GaAs structures with single Mn delta-layer fabricated using laser deposition.  

PubMed

The new technique combining metal-organic chemical vapor epitaxy with laser ablation of solid targets was used for fabrication of ferromagnetic GaAs structures with single Mn delta-doped layer. The structures demonstrated anomalous Hall effect, planar Hall effect, negative and anisotropic magnetoresistance in temperature range of 10-35 K. In GaAs structures with only single Mn delta-layer (without additional 2D hole gas channel or quantum well) ferromagnetism was observed for the first time. PMID:22905589

Danilov, Yuri A; Vikhrova, Olga V; Kudrin, Alexey V; Zvonkov, Boris N

2012-06-01

291

The origin of oil in the Cretaceous succession from the South Pars Oil Layer of the Persian Gulf  

NASA Astrophysics Data System (ADS)

The origin of the oil in Barremian-Hauterivian and Albian age source rock samples from two oil wells (SPO-2 and SPO-3) in the South Pars oil field has been investigated by analyzing the quantity of total organic carbon (TOC) and thermal maturity of organic matter (OM). The source rocks were found in the interval 1,000-1,044 m for the Kazhdumi Formation (Albian) and 1,157-1,230 m for the Gadvan Formation (Barremian-Hauterivian). Elemental analysis was carried out on 36 samples from the source rock candidates (Gadvan and Kazhdumi formations) of the Cretaceous succession of the South Pars Oil Layer (SPOL). This analysis indicated that the OM of the Barremian-Hauterivian and Albian samples in the SPOL was composed of kerogen Types II and II-III, respectively. The average TOC of analyzed samples is less than 1 wt%, suggesting that the Cretaceous source rocks are poor hydrocarbon (HC) producers. Thermal maturity and Ro values revealed that more than 90 % of oil samples are immature. The source of the analyzed samples taken from Gadvan and Kazhdumi formations most likely contained a content high in mixed plant and marine algal OM deposited under oxic to suboxic bottom water conditions. The Pristane/nC17 versus Phytane/nC18 diagram showed Type II-III kerogen of mixture environments for source rock samples from the SPOL. Burial history modeling indicates that at the end of the Cretaceous time, pre-Permian sediments remained immature in the Qatar Arch. Therefore, lateral migration of HC from the nearby Cretaceous source rock kitchens toward the north and south of the Qatar Arch is the most probable origin for the significant oils in the SPOL.

Rahmani, Omeid; Aali, Jafar; Junin, Radzuan; Mohseni, Hassan; Padmanabhan, Eswaran; Azdarpour, Amin; Zarza, Sahar; Moayyed, Mohsen; Ghazanfari, Parviz

2013-07-01

292

Structure in multilayer films of zinc sulfide and copper sulfide via atomic layer deposition  

SciTech Connect

Multilayer film stacks of ZnS and Cu{sub x}S (x???2) were made via atomic layer deposition. The precursors were bis(2,2,6,6-tetramethyl-3,5-heptanedionato)zinc, bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper, and H{sub 2}S generated in situ for sulfur. Samples were deposited at 200?°C, in layers ranging from approximately 2 to 20 nm thick, based on binary growth rates. The properties of the film stacks were studied with atomic force microscopy, ultraviolet–visible spectroscopy, and extended x-ray absorption fine structure. The results demonstrate that the structure of films with the thinnest layers is dominated by Cu{sub x}S, whereas in the thicker films, the structure is determined by whichever material is first deposited. This can be attributed to the crystal structure mismatch of ZnS and Cu{sub x}S.

Short, Andrew; Jewell, Leila; Bielecki, Anthony; Keiber, Trevor; Bridges, Frank; Carter, Sue; Alers, Glenn, E-mail: galers@ucsc.edu [Department of Physics, University of California at Santa Cruz, 1156 High Street, Santa Cruz, California 95064 (United States)

2014-01-15

293

Three-dimensional structure of the tetragonal surface layer of Sporosarcina ureae.  

PubMed Central

The three-dimensional structure of the regular surface layer of Sporosarcina ureae has been determined to a resolution of 1.7 nm by electron microscopy and image reconstruction. The S-layer has p4 symmetry, a lattice constant of 12.9 nm, and a minimum thickness of 6.6 nm. The reconstruction reveals a distinct domain structure: a massive core, arms connecting adjacent unit cells, and spurs which make contact at the subsidiary fourfold symmetry axes. In the z-direction the domains appear to be arranged in three planes, creating two entirely different surface reliefs. The S-layer has a complex pattern of pores and gaps that are 2 to 3 nm wide. In addition, the secondary-structure composition has been determined by infrared spectroscopy: about 35% of the polypeptide appears to have a beta-structure conformation. Images PMID:3759908

Engelhardt, H; Saxton, W O; Baumeister, W

1986-01-01

294

THE STRUCTURE, ORIGIN, AND EVOLUTION OF INTERSTELLAR HYDROCARBON GRAINS  

SciTech Connect

Many materials have been considered for the carrier of the hydrocarbon absorption bands observed in the diffuse interstellar medium (ISM). In order to refine the model for ISM hydrocarbon grains, we analyze the observed aromatic (3.28, 6.2 {mu}m) and aliphatic (3.4 {mu}m) hydrocarbon absorption features in the diffuse ISM along the line of sight toward the Galactic center Quintuplet Cluster. Observationally, sp {sup 2} bonds can be measured in astronomical spectra using the 6.2 {mu}m CC aromatic stretch feature, whereas the 3.4 {mu}m aliphatic feature can be used to quantify the fraction of sp {sup 3} bonds. The fractional abundance of these components allows us to place the Galactic diffuse ISM hydrocarbons on a ternary phase diagram. We conclude that the Galactic hydrocarbon dust has, on average, a low H/C ratio and sp {sup 3} content and is highly aromatic. We have placed the results of our analysis within the context of the evolution of carbon dust in the ISM. We argue that interstellar carbon dust consists of a large core of aromatic carbon surrounded by a thin mantle of hydrogenated amorphous carbon (a-C:H), a structure that is a natural consequence of the processing of stardust grains in the ISM.

Chiar, J. E.; Ricca, A. [SETI Institute, Carl Sagan Center, 189 Bernardo Avenue, Mountain View, CA 94043 (United States); Tielens, A. G. G. M. [Leiden Observatory, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Adamson, A. J., E-mail: jchiar@seti.org, E-mail: Alessandra.Ricca@1.nasa.gov, E-mail: tielens@strw.leidenuniv.nl, E-mail: aadamson@gemini.edu [Gemini Observatory, Northern Operations Center, 670 North A'ohoku Place, Hilo, HI 96729 (United States)

2013-06-10

295

Preparation of thermoelectric Si:B/SiGe multilayer structures on quartz glasses by RF-magnetron sputtering with layer-by-layer annealing methods  

NASA Astrophysics Data System (ADS)

We prepared boron-doped Si/Si0.8Ge0.2 (Si:B/SiGe) multilayers sputter-deposited on quartz glass substrates, and investigated their structural and thermoelectric properties. These samples were processed by using conventional whole-layer annealing and layer-by-layer annealing methods. Si:B/SiGe multilayer samples annealed layer-by-layer showed good periodicity with well-defined interfaces as compared with conventionally annealed samples (whole-layer annealing). However, Ge diffusion was observed at the interfaces near substrates since the SiGe layer near the substrates suffered a longer integrated annealing time during the layer-by-layer annealing process. It was found that the Si:B/SiGe multilayer annealed layer-by-layer showed thermally stable thermoelectric properties in a wide temperature range from 50 to 800 °C. The present experiment proved that the layer-by-layer-annealing method is an effective way of achieving stable and reliable thermoelectric properties in Si:B/SiGe multilayer micro-thermoelectric devices.

Ookura, Takuya; Toyota, Hideyuki; Takeda, Masatoshi; Kambayashi, Toshio; Uchitomi, Naotaka

2014-08-01

296

Turbulent Structures and Coherence in the Atmospheric Surface Layer  

NASA Astrophysics Data System (ADS)

Organized structures in turbulent flow fields are a well-known and still fascinating phenomenon. Although these so-called coherent structures are obvious from visual inspection, quantitative assessment is a challenge and many aspects e.g., formation mechanisms and contribution to turbulent fluxes, are discussed controversially. During the "High Definition Clouds and Precipitation for Advancing Climate Prediction" Observational Prototype Experiment (HOPE) from April to May 2013, an advanced dual Doppler lidar technique was used to image the horizontal wind field near the surface for approximately 300 h. A visual inspection method, as well as a two-dimensional integral length scale analysis, were performed to characterize the observations qualitatively and quantitatively. During situations with forcing due to shear, the wind fields showed characteristic patterns in the form of clearly bordered, elongated areas of enhanced or reduced wind speed, which can be associated with near-surface streaks. During calm situations with strong buoyancy forcing, open cell patterns in the horizontal divergence field were observed. The measurement technique used enables the calculation of integral length scales of both horizontal wind components in the streamwise and cross-stream directions. The individual length scales varied considerably during the observation period but were on average shorter during situations with compared to strongly stable situations. During unstable situations, which were dominated by wind fields with structures, the streamwise length scales increased with increasing wind speed, whereas the cross-stream length scales decreased. Consequently, the anisotropy increased from 1 for calm situations to values of 2-3 for wind speeds of 8-10. During neutral to stable situations, the eddies were on average quite isotropic in the horizontal plane.

Träumner, K.; Damian, Th.; Stawiarski, Ch.; Wieser, A.

2015-01-01

297

Cloud climatology at the Southern Great Plains and the layer structure, drizzle, and atmospheric modes of continental stratus  

E-print Network

Cloud climatology at the Southern Great Plains and the layer structure, drizzle, and atmospheric. Boundary layer clouds exhibit the strongest seasonal variability because of continental stratus associated at the Southern Great Plains and the layer structure, drizzle, and atmospheric modes of continental stratus, J

298

Love wave propagation in piezoelectric layered structure with dissipation Jianke Du a,b,*, Kai Xian a  

E-print Network

Love wave propagation in piezoelectric layered structure with dissipation Jianke Du a,b,*, Kai Xian October 2008 Keywords: Love waves Piezoelectric Viscous Dissipation Sensors a b s t r a c t We investigate characteristics of Love wave propagation in a layered structure, which involves a thin pie- zoelectric layer

Wang, Ji

299

Observation of double-layer-like structures at rocket altitudes  

NASA Technical Reports Server (NTRS)

Two hundred and thirty large amplitude electric field pulses in a rocket flight to an apogee of 585 km over an aurora have been observed. While the limitations of the instrumentation only allow limits to be set on the characteristics of these pulses, the limits are nevertheless significant. A typical lower limit on the potential jump of the pulses is about .4 volts. Many of the pulses show structure at a frequency very close (less than 2 percent) to the proton-cyclotron frequency.

Kellogg, P. J.; Monson, S. J.; Whalen, B. A.

1984-01-01

300

Structural inheritance from polycrystalline underlayers in the growth of double-layered aluminum films  

SciTech Connect

Experimental evidence of the inherited strong <111> orientation from the room-temperature-evaporated Al underlayer is presented for the Al upperlayers evaporated at temperatures higher than the Al recrystallization temperature, in the double-layered Al films. By contrast, Al films evaporated on an amorphous SiO{sub 2} substrate at high temperatures exhibit a remarkable weakening of the <111> fiber texture. Crystallographic characteristics of the Al films were evaluated by rocking curves in the x-ray diffraction measurement. Inheritance of the strong preferential orientation observed for the double-layered structures suggests that the Al upper-layers grow in a layer-by-layer process during the deposition at high temperatures through the surface migration of Al atoms. 19 refs., 9 figs.

Tsukada, Mitsuo; Ohfuji, Shin-ichi [NTT LSI Labs., Kanagawa (Japan)] [NTT LSI Labs., Kanagawa (Japan)

1993-03-01

301

Anomalous absorption of bulk shear sagittal acoustic waves in a layered structure with viscous fluid  

E-print Network

It is demonstrated theoretically that the absorptivity of bulk shear sagittal waves by an ultra-thin layer of viscous fluid between two different elastic media has a strong maximum (in some cases as good as 100%) at an optimal layer thickness. This thickness is usually much smaller than the penetration depths and lengths of transverse and longitudinal waves in the fluid. The angular dependencies of the absorptivity are demonstrated to have significant and unusual structure near critical angles of incidence. The effect of non-Newtonian properties and non-uniformities of the fluid layer on the absorptivity is also investigated. In particular, it is shown that the absorption in a thin layer of viscous fluid is much more sensitive to non-zero relaxation time(s) in the fluid layer than the absorption at an isolated solid-fluid interface.

Dmitri K. Gramotnev; Melissa L. Mather; Timo A. Nieminen

2005-09-05

302

Structural analysis of nitride layer formed on uranium metal by glow plasma surface nitriding  

NASA Astrophysics Data System (ADS)

The nitride layer was formed on uranium metal by a glow plasma surface nitriding method. The structure and composition of the layer were investigated by X-ray diffraction and Auger electron spectroscopy. The nitride layer mainly consisted of ?-phase U2N3 nanocrystals with an average grain size about 10-20 nm. Four zones were identified in the layer, which were the oxide surface zone, the nitride mainstay zone, the oxide-existence interface zone, and the nitrogen-diffusion matrix zone. The gradual decrease of binding energies of uranium revealed the transition from oxide to nitride to metal states with the layer depth, while the chemical states of nitrogen and oxygen showed small variation.

Liu, Kezhao; Bin, Ren; Xiao, Hong; Long, Zhong; Hong, Zhanglian; Yang, Hui; Wu, Sheng

2013-01-01

303

Resonance magnetoelectric interactions in an asymmetric ferromagnetic-ferroelectric layered structure  

NASA Astrophysics Data System (ADS)

Strain mediated magnetoelectric (ME) interactions have been investigated in a sample consisting of oppositely poled lead zirconate titanate (PZT) and asymmetric magnetostrictive layers. A thin layer of Ni with negative magnetostriction and amorphous ferromagnetic Metglas with positive magnetostriction are bonded to the PZT layers. It is shown that the magnetic layers facilitate effective excitation of bending oscillations in the structure, whereas the use of oppositely poled PZT layers results in an increase in the ME voltage at the bending resonance frequency, suppression of the voltage at the longitudinal electromechanical resonance frequency, and cancellation of thermal fluctuation in the voltage. The ME voltage coefficient at resonance is 18 V/(cm Oe); that is an order of magnitude higher than the value measured for a Ni-PZT bilayer of similar dimensions. Theoretical estimates of the ME voltage and resonance frequency are in good agreement with the data.

Fetisov, L. Y.; Perov, N. S.; Fetisov, Y. K.; Srinivasan, G.; Petrov, V. M.

2011-03-01

304

The stabilities and electronic structures of single-layer bismuth oxyhalides for photocatalytic water splitting.  

PubMed

The stabilities and electronic/band structures of single-layer bismuth oxyhalides have been investigated by employing first-principles calculations. The results indicate that the single-layer bismuth oxyhalide materials, except for BiOF, have robust energetic and dynamical stabilities because of their low formation energies and the absence of imaginary frequencies within the entire Brillouin zone. Furthermore, calculations of the electronic structures and optical absorptions indicate that single-layer BiOI possesses a favorable band gap, suitable band edge positions, different orbital characteristics and different effective masses at the valence band maximum (VBM) and conduction band minimum (CBM), thus presenting excellent photocatalytic activity for water splitting. Moreover, the resulting compressive strains can shift the band edge positions of the single-layer materials to more suitable places to enhance their photocatalytic activities. PMID:25354143

Zhang, Xue; Li, Baihai; Wang, Jianlin; Yuan, Yu; Zhang, Qiujie; Gao, Zhanzhong; Liu, Li-Min; Chen, Liang

2014-12-21

305

Synaptic deficits in layer 5 neurons precede overt structural decay in 5xFAD mice.  

PubMed

Synaptic decay and neurodegeneration are hallmarks of Alzheimer's disease that are thought to precede dementia. Recently, we have reported that the first signs of neuritic dystrophy in a new transgenic mouse model of familial Alzheimer's disease (FAD) called the "5xFAD" are axonal dystrophy followed by loss of spines on basal dendrites. The 5xFAD mouse has profound loss of layer 5 neurons by 12months, and these initial structural insults appear between 4 and 6months of age. Here, we test, for the first time, if synaptic failure of layer 5 neurons in the 5xFAD mouse precedes these structural changes. We used longitudinal, in vivo two-photon fluorescence imaging of bigenic 5xFAD/YFP mice to assess the overall structural stability of layer 5 neurons in young mice (age less than 14weeks). We found these neurons to be structurally and morphologically sound. In parallel, we used in vitro, whole-cell patch clamp electrophysiology of layer 5 pyramidal neurons, from mice aged 8-12weeks, to reveal significant pre- and postsynaptic defects in these cells. Thus our data suggest that layer 5 neurons in the 5xFAD mouse model have synaptic deficits at an early time point, before any overt structural dystrophy, and that such synaptic failure, with co-temporal biochemical changes, may be an early step in neuronal loss. PMID:24055684

Buskila, Y; Crowe, S E; Ellis-Davies, G C R

2013-12-19

306

Synaptic deficits in layer 5 neurons precede overt structural decay in 5xFAD mice  

PubMed Central

Synaptic decay and neurodegeneration are hallmarks of Alzheimer’s disease that are thought to precede dementia. Recently, we have reported that the first signs of neuritic dystrophy in a new transgenic mouse model of familial Alzheimer’s disease called the “5xFAD” are axonal dystrophy followed by loss of spines on basal dendrites. The 5xFAD mouse has profound loss of layer 5 neurons by 12 months, and these initial structural insults appear between 4 to 6 months of age. Here, we test, for the first time, if synaptic failure of layer 5 neurons in the 5xFAD mouse precedes these structural changes. We used longitudinal, in vivo two-photon fluorescence imaging of bigenic 5xFAD/YFP mice to assess the overall structural stability of layer 5 neurons in young mice (age less than 14 weeks). We found these neurons to be structurally and morphologically sound. In parallel, we used in vitro, whole-cell patch clamp electrophysiology of layer 5 pyramidal neurons, from mice aged 8-12 weeks, to reveal significant pre- and postsynaptic defects in these cells. Thus our data suggest that layer 5 neurons in the 5xFAD mouse model have synaptic deficits at an early time point, before any overt structural dystrophy, and that such synaptic failure, with co-temporal biochemical changes, may be an early step in neuronal loss. PMID:24055684

Buskila, Yossi; Crowe, Sarah E; Ellis-Davies, Graham C.R.

2014-01-01

307

Instantaneous Wavenumber Estimation for Damage Quantification in Layered Plate Structures  

NASA Technical Reports Server (NTRS)

This paper illustrates the application of instantaneous and local wavenumber damage quantification techniques for high frequency guided wave interrogation. The proposed methodologies can be considered as first steps towards a hybrid structural health monitoring/ nondestructive evaluation (SHM/NDE) approach for damage assessment in composites. The challenges and opportunities related to the considered type of interrogation and signal processing are explored through the analysis of numerical data obtained via EFIT simulations of damage in CRFP plates. Realistic damage configurations are modeled from x-ray CT scan data of plates subjected to actual impacts, in order to accurately predict wave-damage interactions in terms of scattering and mode conversions. Simulation data is utilized to enhance the information provided by instantaneous and local wavenumbers and mitigate the complexity related to the multi-modal content of the plate response. Signal processing strategies considered for this purpose include modal decoupling through filtering in the frequency/wavenumber domain, the combination of displacement components, and the exploitation of polarization information for the various modes as evaluated through the dispersion analysis of the considered laminate lay-up sequence. The results presented assess the effectiveness of the proposed wavefield processing techniques as a hybrid SHM/NDE technique for damage detection and quantification in composite, plate-like structures.

Mesnil, Olivier; Leckey, Cara A. C.; Ruzzene, Massimo

2014-01-01

308

Electromagnetic forces on the dielectric layers of the planar optical Bragg acceleration structure  

NASA Astrophysics Data System (ADS)

Optical Bragg acceleration structures are waveguides with a vacuum core and dielectric layers as a cladding, designed to guide laser light at the speed-of-light TM mode and accelerate charged particles. In this study, we analyze the electromagnetic forces exerted on the dielectric layers of a planar structure by both the guided laser light and the wake-field of moving charges. The distribution of the volume force densities, as well as the surface force densities, in the interfaces between the layers as a result of the laser propagation is given, and analytic scaling laws for the maximal values are obtained. Separation of the wake-field into the structure’s eigenmodes is essential in order to determine the different contributions of the wake-field to the total impulse that acts on the structure. It is shown that the impact of the wake-field on the structure results almost entirely from the fundamental TM mode. While the total force on the dielectric layers may be significantly stronger than the gravitational force, we show that for typical structures, the pressures that develop are orders of magnitude below the damage threshold.

Mizrahi, Amit; Schächter, Levi

2006-09-01

309

The origin of slow relaxation following photoexcitation of W7 in myoglobin and the dynamics of its hydration layer  

PubMed Central

Molecular dynamics simulations are used to calculate the time dependent Stokes shift following photoexcitation of Trp-7 (W7) in myoglobin. In agreement with experiment, a long time (~60ps) component is observed. Since the long time Stokes shift component is absent when we repeat the calculation with protein frozen at the instant of photoexcitation, we firmly establish that protein flexibility is required to observe slow Stokes shift dynamics in this case. A transition between sub-states near the middle of a 30ns ground state trajectory gave us an opportunity to compare solvation dynamics in two different environments. While some of the superficial features are different, we find that the underlying dynamics are shared by the two isomers. It is necessary to look beyond a decomposition of the Stokes shift into protein and water contributions, and probe the underlying dynamics of protein side groups, backbone, and water dynamics to obtain a full picture of the relaxation process. We analyze water residence times, diffusion, and reorientation dynamics in the hydration layer. We find slow components in each of these quantities, and critically examine their origin and how they affect the observed Stokes shift. PMID:19368022

Li, Tanping; Hassanali, Ali A.; Singer, Sherwin J.

2009-01-01

310

Theory of giant magnetoresistance effects in magnetic layered structures with antiferromagnetic coupling  

Microsoft Academic Search

We present a simple theoretical description of recently measured giant magnetoresistance effects in Fe\\/Cr layered structures. The resistivity is calculated by solving the Boltzmann transport equation with spin-dependent scattering at the interfaces. The magnitude of the effect depends on the ratio of the layer thickness to the mean free path and on the asymmetry in scattering for spin-up and spin-down

R. E. Camley; J. Barnas

1989-01-01

311

Multiscale Structure, Interfacial Cohesion, Adsorbed Layers, and Thermodynamics in Dense Polymer-Nanoparticle Mixtures  

NASA Astrophysics Data System (ADS)

We establish the existence and size of adsorbed polymer layers in miscible dense nanocomposites and their consequences on microstructure and the bulk modulus. Using contrast-matching small-angle neutron scattering to characterize all partial collective structure factors of polymers, particles, and their interface, we demonstrate qualitative failure of the random phase approximation, accuracy of the polymer reference site interaction model theory, ability to deduce the adsorbed polymer layer thickness, and high sensitivity of the nanocomposite bulk modulus to interfacial cohesion.

Kim, So Youn; Schweizer, Kenneth S.; Zukoski, Charles F.

2011-11-01

312

Very-large-scale coherent structures in the wall pressure field beneath a supersonic turbulent boundary layer.  

SciTech Connect

Previous wind tunnel experiments up to Mach 3 have provided fluctuating wall-pressure spectra beneath a supersonic turbulent boundary layer, which essentially are flat at low frequency and do not exhibit the theorized {psi}{sup 2} dependence. The flat portion of the spectrum extends over two orders of magnitude and represents structures reaching at least 100 {delta} in scale, raising questions about their physical origin. The spatial coherence required over these long lengths may arise from very-large-scale structures that have been detected in turbulent boundary layers due to groupings of hairpin vortices. To address this hypothesis, data have been acquired from a dense spanwise array of fluctuating wall pressure sensors, then invoking Taylor's Hypothesis and low-pass filtering the data allows the temporal signals to be converted into a spatial map of the wall pressure field. This reveals streaks of instantaneously correlated pressure fluctuations elongated in the streamwise direction and exhibiting spanwise alternation of positive and negative events that meander somewhat in tandem. As the low-pass filter cutoff is lowered, the fluctuating pressure magnitude of the coherent structures diminishes while their length increases.

Beresh, Steven Jay; Spillers, Russell Wayne; Henfling, John Francis; Pruett, Brian Owen Matthew

2010-11-01

313

Electronic band structure imaging of three layer twisted graphene on single crystal Cu(111)  

NASA Astrophysics Data System (ADS)

Few layer graphene (FLG) is grown on single crystal Cu(111) by Chemical Vapor Deposition, and the electronic valence band structure is imaged by Angle-Resolved Photo-Emission Spectroscopy. It is found that graphene essentially grows polycrystalline. Three nearly ideal Dirac cones are observed along the Cu ?¯K¯ direction in k-space, attributed to the presence of ˜4° twisted three layer graphene with negligible interlayer coupling. The number of layers and the stacking order are compatible with Raman data analysis demonstrating the complementarity of the two techniques for a more accurate characterization of FLG.

Marquez Velasco, J.; Kelaidis, N.; Xenogiannopoulou, E.; Raptis, Y. S.; Tsoutsou, D.; Tsipas, P.; Speliotis, Th.; Pilatos, G.; Likodimos, V.; Falaras, P.; Dimoulas, A.

2013-11-01

314

Electronic band structure imaging of three layer twisted graphene on single crystal Cu(111)  

SciTech Connect

Few layer graphene (FLG) is grown on single crystal Cu(111) by Chemical Vapor Deposition, and the electronic valence band structure is imaged by Angle-Resolved Photo-Emission Spectroscopy. It is found that graphene essentially grows polycrystalline. Three nearly ideal Dirac cones are observed along the Cu ?{sup ¯}K{sup ¯} direction in k-space, attributed to the presence of ?4° twisted three layer graphene with negligible interlayer coupling. The number of layers and the stacking order are compatible with Raman data analysis demonstrating the complementarity of the two techniques for a more accurate characterization of FLG.

Marquez Velasco, J. [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece) [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece); Department of Physics, National Technical University of Athens, Athens (Greece); Kelaidis, N.; Xenogiannopoulou, E.; Tsoutsou, D.; Tsipas, P.; Speliotis, Th.; Pilatos, G.; Likodimos, V.; Falaras, P.; Dimoulas, A., E-mail: dimoulas@ims.demokritos.gr [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece); Raptis, Y. S. [Department of Physics, National Technical University of Athens, Athens (Greece)] [Department of Physics, National Technical University of Athens, Athens (Greece)

2013-11-18

315

Effects of Earth's layered structure, gravity and curvature on coseismic deformation  

NASA Astrophysics Data System (ADS)

The effects of Earth's layered structure, gravity and curvature on coseismic deformation are systematically quantified for all fundamental point sources and some finite-fault sources, respectively. The point-source simulations show that the layering effect (about ?25 per cent) is significantly higher than the gravity effect (about ?11 per cent) and the curvature effect (about ?5 per cent). A case study on the 2011 Mw 9.0 Tohoku earthquake is made to quantify the uncertainties of the dislocation models of large earthquakes, in which the three different effects are neglected. Finally, it is investigated how geodetic finite-fault slip inversions are affected by neglecting the layering effect.

Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang

2014-12-01

316

Analysis of mixed-layer clay mineral structures  

USGS Publications Warehouse

Among the enormously abundant natural occurrences of clay minerals, many examples are encountered in which no single specific crystallization scheme extends through a single ultimate grain. The characterization of such assemblages becomes an analysis of the distribution of matter within such grains, rather than the simple identification of mineral species. It having become established that the particular coordination complex typified by mica is a common component of many natural subcrystalline assemblages, the opportunity is afforded to analyze scattering from random associations of these complexes with other structural units. Successful analyses have been made of mixed hydration states of montmorillonite, of montmorillonite with mica, of vermiculite with mica, and of montmorillonite with chlorite, all of which are variants of the mica complex, and of halloysite with hydrated halloysite.

Bradley, W.F.

1953-01-01

317

The structure of nanoscale polaron correlations in the layered manganites  

NASA Astrophysics Data System (ADS)

Recent x-ray and neutron scattering experiments have uncovered nanoscale polaron correlations that play an essential role in the colossal magnetoresistive (CMR) behavior of the perovskite manganites. Short-range polaronic order decreases the charge-carrier mobility of the high-temperature paramagnetic state, and subsequently becomes unstable at the ferromagnetic transition, contributing to a pronounced resistivity decrease at T_C. In the bilayered perovskite system La_2-2xSr_1+2xMn_2O7 (0.3 < x < 0.5), weak x-ray diffuse scattering maxima reveal a one-dimensional incommensurate structural modulation with wavevector q = (0.3, 0, ± 1) and a correlation length of 10 to 30 Angstroms. A crystallographic analysis of the diffuse satellite intensities yields a longitudinal Jahn-Teller stretch mode suggestive of charge-density-wave fluctuations. Within the correlated regions, polaronic eg electrons form a striped pattern of occupied d(3x^2-r^2) orbitals. Dynamic polaron correlations of the zig-zag orbital type are also observed above TC and exhibit distinctly glassy behavior. These structures provide unique insights into the nature of strongly correlated polaronic systems. Collaborators: R. Osborn, D.N. Argyriou, S. Rosenkranz, L. Vasiliu-Doloc, J.F. Mitchell, S.K. Sinha, J.W. Lynn, C.D. Ling, Z. Islam, U. Ruett, and A. Berger. This work was supported by the U.S. DOE Office of Science contract No. W-31-109-ENG-38.

Campbell, Branton

2002-03-01

318

Late-Stage Transitional Boundary-Layer Structures. Direct Numerical Simulation and Experiment  

Microsoft Academic Search

IntroductionA large number of experimental as well as numerical studies have been devotedto the study of the generation and development of specic structuresin the transitional boundary layer in order to investigate their relevance forlaminar-turbulent transition in wall-bounded ows, but the origins of turbulencevia the process of ow randomization are still not well understood. Forthis reason a detailed comparison of experimental

D. g. w. Meyer; U. Rist; V. i. Borodulin

1999-01-01

319

Structural-acoustic optimization of structures excited by turbulent boundary layer flow  

NASA Astrophysics Data System (ADS)

In order to reduce noise radiation of aircraft or marine panels, a general structural-acoustic optimization technique is presented. To compute the structural-acoustic response, a modal approach based on finite element / boundary element analysis is used which can easily incorporate fluid loading, added structures and static pre-loads. Simple deterministic or complex random forcing functions are included in the analysis by transforming their cross-spectral density matrices to modal space. Particular emphasis is placed in this dissertation on structures excited by the fluctuating pressures due to turbulent boundary layer (TBL) flow. An efficient frequency-spacing is also used to minimize evaluation time but ensure accuracy. The response from the structural-acoustic analysis is coupled to an evolutionary strategy with covariance matrix adaptation (CMA-ES) to find the best design for low noise and weight. CMA-ES, a stochastic optimizer with robust search properties, samples candidate solutions from a multi-variate normal distribution and adapts the covariance matrix to favor good solutions. The optimization procedure is validated by minimizing the sound radiated by a point-driven ribbed panel and comparing the optimization results to an exhaustive search of the design space. Structural-acoustic optimization is then performed on a curved marine panel with heavy fluid loading excited by slow TBL flow. A weighted combination of noise radiation and mass are minimized by changing the thickness of strips and patches of elements. An uncorrelated pressure approximation is used to estimate the modal force due to TBL flow thus reducing the evaluation time required to compute the objective function. The results show that the best noise reduction is achieved by minimizing the modal acceptance of energy by the panel. This is equivalent to pushing the structural modes away from the peak frequency range of the forcing function. Additionally, the Pareto trade-off curve between total sound power and panel mass is estimated to show the best designs which will simultaneously reduce both noise and weight. As a final case, the sound power radiated is minimized for a ribbed aircraft panel excited by TBL flow at typical cruise conditions. A static pressure load is applied to the panel to simulate cabin pressurization during flight and the rib locations and cross-sectional area are used as the design variables during optimization. Nearly 10 dB of reduction is achieved by pushing the ribs to the edge of the panel, thus lowering the modal amplitudes excited by the forcing function. The optimal configuration is also found for a higher speed and a larger downstream distance. The design variables are then separated, and the optimization is repeated to determine the coupling between the design variables. Finally, a static constraint is included in the procedure using a very low-frequency dynamic calculation to approximate a static response. The constraint limits the amount of reduction that can be achieved by the optimizer. Guidance for designing quiet aircraft panels is then presented.

Shepherd, Micah R.

320

Effect of layered structures on the location of emissive regions in organic electroluminescent devices  

NASA Astrophysics Data System (ADS)

Effect of layered structures on the location of emissive regions was studied in four types of organic electroluminescent (EL) devices: a single-layered (SL) device consisting only of an emissive layer (EML), two types of double-layered (DL-H and DL-E) devices in which a hole-transport layer (HTL) or an electron-transport layer (ETL) is attached to an EML, and a triple-layered (TL) device in which an EML is sandwiched between a HTL and an ETL. As EML, HTL and ETL material, 9, 10-bis[4-(diphenylamino)styryl]anthracene, 4,4'-bis[(3-methylphenyl)phenylamino]biphenyl and 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene, respectively, were used. Within EML layers, a thin sensing layer doped with a squarilium dye, 2,4-bis[4-diethylamino)-2- hydroxyphenyl]cycrobutenediylium-1,3-dioxide was inserted. The change in emission intensity from the dopant, when the location of the sensing layer was systematically varied, gave information on emissive regions in each type of EL device. The emissive region in the SL device extended through the EML, and that in the DL-H device resided near the HTL/EML boundary. On the contrary, those in the DL-E and TL devices were located within a 10-nm-wide region adjacent to the EML/ETL boundary. Moreover, the emission efficiencies of the DL-E and TL devices were found to be higher than those of the SL and DL-H devices. It was experimentally demonstrated that the carrier recombination within the narrow region adjacent to the EML/carrier transport layer boundary gave high emission efficiency.

Aminaka, Ei-ichiro; Tsutsui, Tetsuo; Saito, Shogo

1996-06-01

321

Fabrication and mechanical evaluation of anatomically-inspired quasilaminate hydrogel structures with layer-specific formulations.  

PubMed

A major tissue engineering challenge is the creation of multilaminate scaffolds with layer-specific mechanical properties representative of native tissues, such as heart valve leaflets, blood vessels, and cartilage. For this purpose, poly(ethylene glycol) diacrylate (PEGDA) hydrogels are attractive materials due to their tunable mechanical and biological properties. This study explored the fabrication of trilayer hydrogel quasilaminates. A novel sandwich method was devised to create quasilaminates with layers of varying stiffnesses. The trilayer structure was comprised of two "stiff" outer layers and one "soft" inner layer. Tensile testing of bilayer quasilaminates demonstrated that these scaffolds do not fail at the interface. Flexural testing showed that the bending modulus of acellular quasilaminates fell between the bending moduli of the "stiff" and "soft" hydrogel layers. The bending modulus and swelling of trilayer scaffolds with the same formulations were not significantly different than single layer gels of the same formulation. The encapsulation of cells and the addition of phenol red within the hydrogel layers decreased bending modulus of the trilayer scaffolds. The data presented demonstrates that this fabrication method can make quasilaminates with robust interfaces, integrating layers of different mechanical properties and biofunctionalization, and thus forming the foundation for a multilaminate scaffold that more accurately represents native tissue. PMID:23053300

Tseng, Hubert; Cuchiara, Maude L; Durst, Christopher A; Cuchiara, Michael P; Lin, Chris J; West, Jennifer L; Grande-Allen, K Jane

2013-02-01

322

Normal and lateral forces between lipid covered solids in solution: correlation with layer packing and structure.  

PubMed Central

We report on the normal and lateral forces between controlled-density mono- and bilayers of phospholipid co-adsorbed onto hydrophobic and hydrophilic solid supports, respectively. Interactions between 1,2-dioleoyl-sn-glycero-3-phosphocholine layers were measured using an atomic force microscope. Notable features of the normal force curves (barrier heights and widths) were found to correlate with the thickness and density of the supported lipid layers. The friction and normal force curves were also found interrelated. Thus, very low friction values were measured as long as the supported layer(s) resisted the normal pressure of the tip. However, as the applied load exceeded the critical value needed for puncturing the layers, the friction jumped to values close to those recorded between bare surfaces. The lipid layers were self-healing between measurements, but a significant hysteresis was observed in the force curves measured on approach and retraction, respectively. The study shows the potential of using atomic force microscopy for lipid layer characterization both with respect to structure and interactions. It further shows the strong lubricating effect of adsorbed lipid layers and how this varies with surface density of lipids. The findings may have important implications for the issue of joint lubrication. PMID:11867453

Grant, L M; Tiberg, F

2002-01-01

323

Origin of Degradation Phenomenon under Drain Bias Stress for Oxide Thin Film Transistors using IGZO and IGO Channel Layers.  

PubMed

Top-gate structured thin film transistors (TFTs) using In-Ga-Zn-O (IGZO) and In-Ga-O (IGO) channel compositions were investigated to reveal a feasible origin for degradation phenomenon under drain bias stress (DBS). DBS-driven instability in terms of VTH shift, deviation of the SS value, and increase in the on-state current were detected only for the IGZO-TFT, in contrast to the IGO-TFT, which did not demonstrate VTH shift. These behaviors were visually confirmed via nanoscale transmission electron microscopy and energy-dispersive x-ray spectroscopy observations. To understand the degradation mechanism, we performed ab initio molecular dynamic simulations on the liquid phases of IGZO and IGO. The diffusivities of Ga and In atoms were enhanced in IGZO, confirming the degradation mechanism to be increased atomic diffusion. PMID:25601183

Bak, Jun Yong; Kang, Youngho; Yang, Shinhyuk; Ryu, Ho-Jun; Hwang, Chi-Sun; Han, Seungwu; Yoon, Sung-Min

2015-01-01

324

Origin of Degradation Phenomenon under Drain Bias Stress for Oxide Thin Film Transistors using IGZO and IGO Channel Layers  

NASA Astrophysics Data System (ADS)

Top-gate structured thin film transistors (TFTs) using In-Ga-Zn-O (IGZO) and In-Ga-O (IGO) channel compositions were investigated to reveal a feasible origin for degradation phenomenon under drain bias stress (DBS). DBS-driven instability in terms of VTH shift, deviation of the SS value, and increase in the on-state current were detected only for the IGZO-TFT, in contrast to the IGO-TFT, which did not demonstrate VTH shift. These behaviors were visually confirmed via nanoscale transmission electron microscopy and energy-dispersive x-ray spectroscopy observations. To understand the degradation mechanism, we performed ab initio molecular dynamic simulations on the liquid phases of IGZO and IGO. The diffusivities of Ga and In atoms were enhanced in IGZO, confirming the degradation mechanism to be increased atomic diffusion.

Bak, Jun Yong; Kang, Youngho; Yang, Shinhyuk; Ryu, Ho-Jun; Hwang, Chi-Sun; Han, Seungwu; Yoon, Sung-Min

2015-01-01

325

Origin of Degradation Phenomenon under Drain Bias Stress for Oxide Thin Film Transistors using IGZO and IGO Channel Layers  

PubMed Central

Top-gate structured thin film transistors (TFTs) using In-Ga-Zn-O (IGZO) and In-Ga-O (IGO) channel compositions were investigated to reveal a feasible origin for degradation phenomenon under drain bias stress (DBS). DBS-driven instability in terms of VTH shift, deviation of the SS value, and increase in the on-state current were detected only for the IGZO-TFT, in contrast to the IGO-TFT, which did not demonstrate VTH shift. These behaviors were visually confirmed via nanoscale transmission electron microscopy and energy-dispersive x-ray spectroscopy observations. To understand the degradation mechanism, we performed ab initio molecular dynamic simulations on the liquid phases of IGZO and IGO. The diffusivities of Ga and In atoms were enhanced in IGZO, confirming the degradation mechanism to be increased atomic diffusion. PMID:25601183

Bak, Jun Yong; Kang, Youngho; Yang, Shinhyuk; Ryu, Ho-Jun; Hwang, Chi-Sun; Han, Seungwu; Yoon, Sung-Min

2015-01-01

326

Fabrication and atomic structure of size-selected, layered MoS2 clusters for catalysis.  

PubMed

Well defined MoS2 nanoparticles having a layered structure and abundant edges would be of considerable interest for applications including photocatalysis. We report the atomic structure of MoS2 size-selected clusters with mass in a range all the way from 50 to ?2000 MoS2 units. The clusters were prepared by magnetron sputtering and gas condensation prior to size selection and soft landing on carbon supports. Aberration-corrected scanning transmission electron microscopy (STEM) in high-angle annular dark-field (HAADF) mode reveals a layered structure and Mo-Mo spacing similar to the bulk material. The mean number of layers in these lamellar clusters increases from one to three with increasing mass, consistent with density functional theory calculations of the balance between edge energies and interlayer binding. PMID:25226541

Cuddy, Martin J; Arkill, Kenton P; Wang, Zhi Wei; Komsa, Hannu-Pekka; Krasheninnikov, Arkady V; Palmer, Richard E

2014-11-01

327

Electromagnetic forces on the dielectric layers of the planar optical Bragg acceleration structure  

SciTech Connect

Optical Bragg acceleration structures are waveguides with a vacuum core and dielectric layers as a cladding, designed to guide laser light at the speed-of-light TM mode and accelerate charged particles. In this study, we analyze the electromagnetic forces exerted on the dielectric layers of a planar structure by both the guided laser light and the wake-field of moving charges. The distribution of the volume force densities, as well as the surface force densities, in the interfaces between the layers as a result of the laser propagation is given, and analytic scaling laws for the maximal values are obtained. Separation of the wake-field into the structure's eigenmodes is essential in order to determine the different contributions of the wake-field to the total impulse that acts on the structure. It is shown that the impact of the wake-field on the structure results almost entirely from the fundamental TM mode. While the total force on the dielectric layers may be significantly stronger than the gravitational force, we show that for typical structures, the pressures that develop are orders of magnitude below the damage threshold.

Mizrahi, Amit; Schaechter, Levi [Department of Electrical Engineering, Technion--Israel Institute of Technology, Haifa 32000 (Israel)

2006-09-15

328

Structural and electronic properties of the transition layer at the SiO2/4H-SiC interface  

NASA Astrophysics Data System (ADS)

Using first-principles methods, we generate an amorphous SiO2/4H-SiC interface with a transition layer. Based this interface model, we investigate the structural and electronic properties of the interfacial transition layer. The calculated Si 2p core-level shifts for this interface are comparable to the experimental data, indicating that various SiCxOy species should be present in this interface transition layer. The analysis of the electronic structures reveals that the tetrahedral SiCxOy structures cannot introduce any of the defect states at the interface. Interestingly, our transition layer also includes a C-C=C trimer and SiO5 configurations, which lead to the generation of interface states. The accurate positions of Kohn-Sham energy levels associated with these defects are further calculated within the hybrid functional scheme. The Kohn-Sham energy levels of the carbon trimer and SiO5 configurations are located near the conduction and valence band of bulk 4H-SiC, respectively. The result indicates that the carbon trimer occurred in the transition layer may be a possible origin of near interface traps. These findings provide novel insight into the structural and electronic properties of the realistic SiO2/SiC interface.

Li, Wenbo; Zhao, Jijun; Wang, Dejun

2015-01-01

329

Structure and magnetism of new hybrid cobalt hydroxide materials built from decorated brucite layers.  

PubMed

The structure, synthesis and magnetic properties of three new complex cobalt hydroxyl oxalates are presented, showing a modification of the 2-D double layer hydroxide structure. Co(12)(OH)(18)(ox)(3)(pip) [ox = oxalate, C(2)O(4)(2-); pip = piperazine, C(4)N(2)H(10)] (1), is essentially built from brucite-like layers with a one ninth depletion of the octahedral sites and a preservation of a trigonal crystallographic symmetry. ACo(28)(OH)(43)(ox)(6)Br(2)(H(2)O)(2) [A = Na (2), K (3)] are similarly composed of a brucite-like layer with three nineteenths depletion of octahedral sites, again preserving a trigonal symmetry. Both 2 and 3 show a small degree of structural disorder within the framework. All of these compounds have alternating layers of a mineral-like metal hydroxide structure and a metal oxalate coordination network, with the depletion in the hydroxyl layers being templated by the coordination network. Magnetic studies of 1 reveal a metamagnetic character, with the onset of an antiferromagnetic phase below T(c) = 23.5 K (H = 0 G), and a first order antiferromagnet to metamagnet transition at H(c) = 500-1000 G (T = 20-6 K). Compound 3 shows a more conventional ferrimagnetic ordering below 33(±1) K with a small coercive field of 107(±5) G at 10 K. PMID:21327226

Keene, Tony D; Light, Mark E; Hursthouse, Michael B; Price, Daniel J

2011-03-28

330

Morphology and atomic-scale structure of single-layer WS2 nanoclusters.  

PubMed

Two-dimensional sheets of transition metal (Mo and W) sulfides are attracting strong attention due to the unique electronic and optical properties associated with the material in its single-layer form. The single-layer MoS2 and WS2 are already in widespread commercial use in catalytic applications as both hydrotreating and hydrocracking catalysts. Consequently, characterization of the morphology and atomic structure of such particles is of utmost importance for the understanding of the catalytic active phase. However, in comparison with the related MoS2 system only little is known about the fundamental properties of single-layer WS2 (tungstenite). Here, we use an interplay of atom-resolved Scanning Tunneling Microscopy (STM) studies of Au(111)-supported WS2 nanoparticles and calculated edge structures using Density Functional Theory (DFT) to reveal the equilibrium morphology and prevalent edge structures of single-layer WS2. The STM results reveal that the single layer S-W-S sheets adopt a triangular equilibrium shape under the sulfiding conditions of the synthesis, with fully sulfided edges. The predominant edge structures are determined to be the (101[combining macron]0) W-edge, but for the smallest nanoclusters also the (1[combining macron]010) S-edges become important. DFT calculations are used to construct phase diagrams of the WS2 edges, and describe their sulfur and hydrogen coordination under different conditions, and in this way shed light on the catalytic role of WS2 edges. PMID:23959329

Füchtbauer, Henrik G; Tuxen, Anders K; Moses, Poul G; Topsøe, Henrik; Besenbacher, Flemming; Lauritsen, Jeppe V

2013-10-14

331

Studies of Surface Electronic Structure Based on the Layer Kkr Method  

NASA Astrophysics Data System (ADS)

In this dissertation I apply the layer KKR (LKKR) formalism to study the electronic structure of various monolayers and thin films. I present energy band results for fcc (111) and bcc (110) palladium (Pd) monolayers, planes of (110) niobium (Nb) and (100) copper, and I give the spectrum from a (111) fcc layer involving atomic hydrogen. My thin film results include bands for: a plane of Pd commensurate with a (110) layer of Nb, three (111) planes of Pd, four layer films involving (111) Pd planes and a commensurate hydrogen layer placed immediately above and below the surface of the film, a structure with the same Pd arrangement but involving (2 x 2) coverage of hydrogen on the surface, and three (111) Pd planes with commensurate hydrogen layers placed on both sides of the central Pd plane. I use the results from calculations involving bcc (110) planes of Nb, Pd and Nb and Pd to analyze the experimentally observed near-surface electronic structure of thin Pd overlayers commensurate with a (110) Nb substrate. The remaining Pd monolayer calculation is used to model the electronic structure of the second incommensurate overlayer. I use the calculations involving films of (111) planes to model the near surface electronic structure of hydrogen near a (111) Pd surface, and, in particular, to explain the observed near-room-temperature disappearance of the lowest angle-resolved photoemission peak. I also present various extensions of the LKKR formalism, including: expressions for the normalized wave function and charge at all points in space, the modifications of Kambe's manylayer structure constants (which are appropriate for describing scattering states) that are necessary to make them suitable for the bound state problem, and the modifications of secular equation and wave function which occur when the energy falls below the muffin tin zero.

Chubb, Scott Robinson

332

Sensitivity of the structure of untripped mixing layers to small changes in initial conditions  

NASA Technical Reports Server (NTRS)

An experimental study was conducted concerning the influence of small changes in initial conditions on the near- and far-field evolution of the three-dimensional structure of a plan mixing layer. A two-stream mixing layer with a velocity ratio of 0.6 was generated with the initial boundary layers on the splitter plate laminar and was nominally two-dimensional. The initial conditions were changed slightly by interchanging the high- and low-speed sides of the wind tunnel, while maintaining the same velocities, and hence velocity ratio. This resulted in small changes in the initial boundary layer properties, and the perturbations present in the boundary layers were interchanged between the high- and low-speed sides for the two cases. The results indicate that, even with this relatively minor change in initial conditions, the near-field regions of the two cases differ significantly. The peak Reynolds stress levels in the near-field differ by up to 100 percent, and this is attributed to a difference in the location of the initial spanwise vortex roll-up. In addition, the positions and shapes of the individual streamwise vortical structures differ for the two cases, although the overall structures differ for the two cases, although the overall qualitative description of these structures is comparable. The subsequent reorganization and decay of the streamwise vortical structures is very similar for the two cases. As a result, in the far field, both mixing layers achieve similar structure, yielding comparable growth rates, Reynolds stress, distribution, and spectral content.

Plesniak, M. W.; Bell, J. H.; Mehta, R. D.

1992-01-01

333

SbsB structure and lattice reconstruction unveil Ca2+ triggered S-layer assembly.  

PubMed

S-layers are regular two-dimensional semipermeable protein layers that constitute a major cell-wall component in archaea and many bacteria. The nanoscale repeat structure of the S-layer lattices and their self-assembly from S-layer proteins (SLPs) have sparked interest in their use as patterning and display scaffolds for a range of nano-biotechnological applications. Despite their biological abundance and the technological interest in them, structural information about SLPs is limited to truncated and assembly-negative proteins. Here we report the X-ray structure of the SbsB SLP of Geobacillus stearothermophilus PV72/p2 by the use of nanobody-aided crystallization. SbsB consists of a seven-domain protein, formed by an amino-terminal cell-wall attachment domain and six consecutive immunoglobulin-like domains, that organize into a ?-shaped disk-like monomeric crystallization unit stabilized by interdomain Ca(2+) ion coordination. A Ca(2+)-dependent switch to the condensed SbsB quaternary structure pre-positions intermolecular contact zones and renders the protein competent for S-layer assembly. On the basis of crystal packing, chemical crosslinking data and cryo-electron microscopy projections, we present a model for the molecular organization of this SLP into a porous protein sheet inside the S-layer. The SbsB lattice represents a previously undescribed structural model for protein assemblies and may advance our understanding of SLP physiology and self-assembly, as well as the rational design of engineered higher-order structures for biotechnology. PMID:22722836

Baranova, Ekaterina; Fronzes, Rémi; Garcia-Pino, Abel; Van Gerven, Nani; Papapostolou, David; Péhau-Arnaudet, Gérard; Pardon, Els; Steyaert, Jan; Howorka, Stefan; Remaut, Han

2012-07-01

334

Structural Layers of Ex Vivo Rat Hippocampus at 7T MRI  

PubMed Central

Magnetic resonance imaging (MRI) applied to the hippocampus is challenging in studies of the neurophysiology of memory and the physiopathology of numerous diseases such as epilepsy, Alzheimer’s disease, ischemia, and depression. The hippocampus is a well-delineated cerebral structure with a multi-layered organization. Imaging of hippocampus layers is limited to a few studies and requires high magnetic field and gradient strength. We performed one conventional MRI sequence on a 7T MRI in order to visualize and to delineate the multi-layered hippocampal structure ex vivo in rat brains. We optimized a volumic three-dimensional T2 Rapid Acquisition Relaxation Enhancement (RARE) sequence and quantified the volume of the hippocampus and one of its thinnest layers, the stratum granulare of the dentate gyrus. Additionally, we tested passive staining by gadolinium with the aim of decreasing the acquisition time and increasing image contrast. Using appropriated settings, six discrete layers were differentiated within the hippocampus in rats. In the hippocampus proper or Ammon’s Horn (AH): the stratum oriens, the stratum pyramidale of, the stratum radiatum, and the stratum lacunosum moleculare of the CA1 were differentiated. In the dentate gyrus: the stratum moleculare and the stratum granulare layer were seen distinctly. Passive staining of one brain with gadolinium decreased the acquisition time by four and improved the differentiation between the layers. A conventional sequence optimized on a 7T MRI with a standard receiver surface coil will allow us to study structural layers (signal and volume) of hippocampus in various rat models of neuropathology (anxiety, epilepsia, neurodegeneration). PMID:24086700

Kamsu, Jeanine Manuella; Constans, Jean-Marc; Lamberton, Franck; Courtheoux, Patrick; Denise, Pierre; Philoxene, Bruno; Coquemont, Maelle; Besnard, Stephane

2013-01-01

335

Diverse and tunable electronic structures of single-layer metal phosphorus trichalcogenides for photocatalytic water splitting  

NASA Astrophysics Data System (ADS)

The family of bulk metal phosphorus trichalcogenides (APX3, A = MII, M_{0.5}^IM_{0.5}^{III}; X = S, Se; MI, MII, and MIII represent Group-I, Group-II, and Group-III metals, respectively) has attracted great attentions because such materials not only own magnetic and ferroelectric properties, but also exhibit excellent properties in hydrogen storage and lithium battery because of the layered structures. Many layered materials have been exfoliated into two-dimensional (2D) materials, and they show distinct electronic properties compared with their bulks. Here we present a systematical study of single-layer metal phosphorus trichalcogenides by density functional theory calculations. The results show that the single layer metal phosphorus trichalcogenides have very low formation energies, which indicates that the exfoliation of single layer APX3 should not be difficult. The family of single layer metal phosphorus trichalcogenides exhibits a large range of band gaps from 1.77 to 3.94 eV, and the electronic structures are greatly affected by the metal or the chalcogenide atoms. The calculated band edges of metal phosphorus trichalcogenides further reveal that single-layer ZnPSe3, CdPSe3, Ag0.5Sc0.5PSe3, and Ag0.5In0.5PX3 (X = S and Se) have both suitable band gaps for visible-light driving and sufficient over-potentials for water splitting. More fascinatingly, single-layer Ag0.5Sc0.5PSe3 is a direct band gap semiconductor, and the calculated optical absorption further convinces that such materials own outstanding properties for light absorption. Such results demonstrate that the single layer metal phosphorus trichalcogenides own high stability, versatile electronic properties, and high optical absorption, thus such materials have great chances to be high efficient photocatalysts for water-splitting.

Liu, Jian; Li, Xi-Bo; Wang, Da; Lau, Woon-Ming; Peng, Ping; Liu, Li-Min

2014-02-01

336

Diverse and tunable electronic structures of single-layer metal phosphorus trichalcogenides for photocatalytic water splitting.  

PubMed

The family of bulk metal phosphorus trichalcogenides (APX3, A = M(II), M(I)(0.5)M(III)(0.5); X = S, Se; M(I), M(II), and M(III) represent Group-I, Group-II, and Group-III metals, respectively) has attracted great attentions because such materials not only own magnetic and ferroelectric properties, but also exhibit excellent properties in hydrogen storage and lithium battery because of the layered structures. Many layered materials have been exfoliated into two-dimensional (2D) materials, and they show distinct electronic properties compared with their bulks. Here we present a systematical study of single-layer metal phosphorus trichalcogenides by density functional theory calculations. The results show that the single layer metal phosphorus trichalcogenides have very low formation energies, which indicates that the exfoliation of single layer APX3 should not be difficult. The family of single layer metal phosphorus trichalcogenides exhibits a large range of band gaps from 1.77 to 3.94 eV, and the electronic structures are greatly affected by the metal or the chalcogenide atoms. The calculated band edges of metal phosphorus trichalcogenides further reveal that single-layer ZnPSe3, CdPSe3, Ag0.5Sc0.5PSe3, and Ag0.5In0.5PX3 (X = S and Se) have both suitable band gaps for visible-light driving and sufficient over-potentials for water splitting. More fascinatingly, single-layer Ag0.5Sc0.5PSe3 is a direct band gap semiconductor, and the calculated optical absorption further convinces that such materials own outstanding properties for light absorption. Such results demonstrate that the single layer metal phosphorus trichalcogenides own high stability, versatile electronic properties, and high optical absorption, thus such materials have great chances to be high efficient photocatalysts for water-splitting. PMID:24511968

Liu, Jian; Li, Xi-Bo; Wang, Da; Lau, Woon-Ming; Peng, Ping; Liu, Li-Min

2014-02-01

337

Electronic structure of the ferroelectric layered perovskite SrBi{sub 2}Ta{sub 2}O{sub 9}  

SciTech Connect

The band structure of the layered perovskite SrBi{sub 2}Ta{sub 2}O{sub 9} (SBT) was calculated by tight binding and the valence band density of states was measured by x-ray photoemission spectroscopy. We find both the valence and conduction band edges to consist of states primarily derived from the Bi{endash}O layer rather than the perovskite Sr{endash}Ta{endash}O blocks. The valence band maximum arises from O {ital p} and some Bi {ital s} states, while the conduction band minimum consists of Bi {ital p} states, with a wide band gap of 5.1 eV. It is argued that the Bi{endash}O layers largely control the electronic response whereas the ferroelectric response originates mainly from the perovskite Sr{endash}Ta{endash}O block. Bi and Ta centered traps are calculated to be shallow, which may account in part for its excellent fatigue properties. {copyright} {ital 1996 American Institute of Physics.}

Robertson, J.; Chen, C.W. [Engineering Department, Cambridge University, Cambridge CB21PZ (United Kingdom)] [Engineering Department, Cambridge University, Cambridge CB21PZ (United Kingdom); Warren, W.L. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1349 (United States)] [Sandia National Laboratories, Albuquerque, New Mexico 87185-1349 (United States); Gutleben, C.D. [Sony Corporation Research Center, Hodogaya-ku, Yokohama-shi 240 (Japan)] [Sony Corporation Research Center, Hodogaya-ku, Yokohama-shi 240 (Japan)

1996-09-01

338

Pressure-induced phase transition of BiOF: novel two-dimensional layered structures.  

PubMed

Bismuth oxide haloids BiOXs (X = Cl, Br, I) have received attention as photocatalytic materials after TiO2 in recent years due to their unique layered structures. Using an ab initio evolutionary methodology structure search method, we systematically investigate the evolution of BiOF structures under pressure. It is found that BiOF can maintain its layered structure up to 300 GPa. Three stable new phases with Pnma, P3[combining macron]m1 and Cmcm structure at a pressure of 10, 66, and 286 GPa have been identified for the first time. All the newly found phases are two-dimensional layered structures characterized by Bi-O slabs interleaved with F(-) anion slabs. Moreover, all three phases are indirect semiconductors with wide band gaps. It is found that pressure can cause great change in the band gaps of BiOF. The band gaps of the high-pressure phases of BiOF vary nearly linearly with pressure but exhibit different pressure trends. The electronic structure, structural stability, phase transition mechanisms and evolution of the Bi-O slabs of BiOF under pressure are discussed. PMID:25578959

Zhou, Dawei; Pu, Chunying; He, Chaozheng; Zhang, Feiwu; Lu, Cheng; Bao, Gang

2015-01-28

339

Band structure and broadband compensation of absorption by amplification in layered optical metamaterials  

NASA Astrophysics Data System (ADS)

The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities.

Rozanov, N. N.; Fedorov, S. V.; Savel'ev, R. S.; Sukhorukov, A. A.; Kivshar, Yu. S.

2012-05-01

340

Monitoring thickness deviations in planar multi-layer elastic structures using impedance signatures.  

PubMed

In this letter, a low frequency ultrasonic resonance technique that operates in the 20-80-kHz regime is presented that demonstrates detection of thickness changes on the order of +/-10 mum. This measurement capability is a result of the direct correlation between the electrical impedance of an electro-acoustic transducer and the mechanical loading it experiences when placed in contact with a layered elastic structure. The relative frequency shifts of the resonances peaks can be estimated through a simple one-dimensional transmission model. Separate experimental measurements confirm this technique to be sensitive to subtle changes in the underlying layered elastic structure. PMID:18646950

Fisher, Karl A

2008-07-01

341

Finite element simulation of laser-induced guided wave in layered structure  

NASA Astrophysics Data System (ADS)

Ultrasonic field in layered structure excited by a nanosecond pulsed laser irradiation is numerically simulated by finite element method. Typical calculation is executed for a configuration of a zirconium nitride (ZrN) thin film with different thickness on a steel substrate. The waveforms of surface acoustic wave are presented and the dispersion properties of surface waves in two-layered structure are analyzed by the method of phase spectral analysis, and the results show that the surface wave is anomalous dispersive with the higher frequencies propagating fast than the lower frequencies, and that with the decrease of film thickness, the dispersion of surface wave becomes more serious.

Zhao, Yan; Xue, Liping

2014-11-01

342

Frequency separation of surface acoustic waves in layered structures with acoustic metamaterials  

NASA Astrophysics Data System (ADS)

We show theoretically that in elastic layered structures containing an upper layer of smoothly varied thickness and a substrate of a highly dispersive metametarial it is possible to significantly enhance spatial frequency separation of surface acoustic waves. Theory of Love surface acoustic waves propagation in waveguides with varied thickness, taking into account mutual modes coupling, is built. Appropriate structure of metamatererial with resonant frequency dependence of material parameters, making frequency separation effective, is provided. Efficiency of spatial frequency separation and modes coupling is calculated for various metamaterial parameters and wave frequencies.

Kalyabin, D.; Lisenkov, I.; Lee, Y. P.; Nikitov, S.

2014-06-01

343

Sperm yield after single layer centrifugation with Androcoll-E is related to the potential fertility of the original ejaculate.  

PubMed

Many attempts have been made to identify laboratory tests that are predictive of sperm fertility, both to improve the quality of stallion semen doses for artificial insemination (AI) and to identify potential breeding sires if no fertility data are available. Sperm quality at the stud is mostly evaluated by assessing subjective motility, although this parameter can be poorly indicative of fertility. Sperm morphology and chromatin integrity in Swedish stallions are correlated to pregnancy rate after AI. Because single layer centrifugation (SLC) selects for spermatozoa with normal morphology and good chromatin, retrospective analysis was carried out to investigate whether sperm yield after SLC is linked to potential fertility. Commercial semen doses for AI from 24 stallions (five stallions with four ejaculates each, 19 stallions with three ejaculates each; n = 77) obtained during the breeding season were cooled, and sent overnight to the Swedish University of Agricultural Sciences in an insulated box for evaluation, with other doses being sent to studs for commercial AI. On arrival at Swedish University of Agricultural Sciences, the semen was used for SLC and also for evaluation of sperm motility, membrane integrity, chromatin integrity, and morphology. The seasonal pregnancy rates for each stallion were available. The yield of progressively motile spermatozoa after SLC (calculated as a proportion of the initial load) was found to be highly correlated with pregnancy rate (r = 0.75; P < 0.001). Chromatin damage was highly negatively correlated with pregnancy rate (r = -0.69; P < 0.001). Pregnancy rate was also correlated with membrane integrity (r = 0.58; P < 0.01), progressive motility (r = 0.63; P < 0.01), and normal morphology (r = 0.45; P < 0.05). In conclusion, these preliminary results show that sperm yield after SLC is related to the potential fertility of the original ejaculate, and could be an alternative indicator of stallion fertility if breeding data are not available. Single layer centrifugation is fast (30 minutes) and does not require expensive equipment, whereas other assays require a flow cytometer and/or specialist skills. An additional option could be to transport semen doses to a laboratory for SLC if the stud personnel do not want to perform the procedure themselves. PMID:24582376

Morrell, J M; Stuhtmann, G; Meurling, S; Lundgren, A; Winblad, C; Macias Garcia, B; Johannisson, A

2014-05-01

344

Origin of the metallic conductivity in PdCoO 2 with delafossite structure  

Microsoft Academic Search

Valence state, valence band structure and specific heat of metallic oxide PdCoO2 with the delafossite structure, which has alternative layers of Pd, Co and O ions with a formation of each triangular lattice, are first investigated using polycrystalline samples by means of photoelectron spectroscopy and specific heat measurements. The lowest electrical resistivity in PdCoO2 among the whole conductive oxides is

Masayuki Tanaka; Masashi Hasegawa; Thoru Higuchi; Takeyo Tsukamoto; Yasuhisa Tezuka; Shik Shin; Humihiko Takei

1998-01-01

345

A Long-Lived Tracer Perspective on the Origin of Air in the Tropical Tropopause Layer during ATTREX  

NASA Astrophysics Data System (ADS)

The origin of air in the tropical tropopause layer (TTL) and the subsequent transport pathways of these air masses play a critical role in the delivery of trace gases, including ozone depleting substances and water vapor, to the stratosphere. The Airborne Tropical Tropopause Experiment (ATTREX) is designed to study this transport and processing in the TTL over the Pacific Ocean, including how dehydration occurs in this region and how trace gases involved in ozone depletion and climate reach the tropical lower stratosphere. For this mission, the NASA Global Hawk aircraft is carrying a suite of in situ and remote sensing instruments for trace gases, aerosols, radiation, and meteorology. Two deployments have occurred from NASA/Dryden Flight Research Center, with flights to the eastern and central tropical Pacific. Two more deployments, targeting the western equatorial Pacific, are planned for 2014 from Guam and one other location. Over 100 vertical profiles from about 14 to 18 km have now been obtained from the tropics to midlatitudes, as well as long sections at nearly constant altitude. Results are shown here from the UAS Chromatograph for Atmospheric Trace Species (UCATS) instrument and other sensors. UCATS was configured to measure the long-lived tracers N2O, SF6, H2, and CH4, as well as water vapor, CO, and ozone. Results thus far have shown a mix of midlatitude and tropical air in the tropical and subtropical lower stratosphere, particularly for flights in November 2011. Recent results from February 2013 indicate much more homogeneous air masses in the TTL during this period. This homogeneity may be related to fact that these flights occurred in the middle of (northern) winter rather than fall, or to the 'sudden stratospheric warming' in January 2013, with sinking motion in the Arctic polar region and a corresponding rising motion and cooling in the tropics. Data will be presented in the context of trajectory model calculations of the origin and fate of the air masses sampled. These findings are relevant for understanding the composition of air rising through the TTL and into the tropical stratosphere, one of the central goals of ATTREX.

Hintsa, E. J.; Moore, F.; Dutton, G. S.; Hall, B. D.; Nance, J. D.; Elkins, J. W.; Gao, R.; Rollins, D. W.; Thornberry, T. D.; Watts, L.; Fahey, D. W.; Daube, B. C.; Pittman, J. V.; Wofsy, S. C.; Atlas, E. L.; Navarro, M. A.; Dessler, A. E.; Mahoney, M.

2013-12-01

346

The internal structure of Jupiter family cometary nuclei from Deep Impact observations: The “talps” or “layered pile” model  

NASA Astrophysics Data System (ADS)

We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441-446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230-238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253-263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136-2160; 1999a. Astron. J. 118, 1101-1119; 1999b. Astrophys. J. 526, 465-470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255-1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220-229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670-1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193-204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or "layered pile" model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects.

Belton, Michael J. S.; Thomas, Peter; Veverka, J.; Schultz, Peter; A'Hearn, Michael F.; Feaga, Lori; Farnham, Tony; Groussin, Olivier; Li, Jian-Yang; Lisse, Casey; McFadden, Lucy; Sunshine, Jessica; Meech, Karen J.; Delamere, W. Alan; Kissel, Jochen

2007-03-01

347

The internal structure of Jupiter family cometary nuclei from Deep Impact observations: The “talps” or “layered pile” model  

NASA Astrophysics Data System (ADS)

We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441 446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230 238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253 263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136 2160; 1999a. Astron. J. 118, 1101 1119; 1999b. Astrophys. J. 526, 465 470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255 1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220 229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670 1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193 204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or “layered pile” model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects.

Belton, Michael J. S.; Thomas, Peter; Veverka, J.; Schultz, Peter; A'Hearn, Michael F.; Feaga, Lori; Farnham, Tony; Groussin, Olivier; Li, Jian-Yang; Lisse, Casey; McFadden, Lucy; Sunshine, Jessica; Meech, Karen J.; Delamere, W. Alan; Kissel, Jochen

348

Strong, macroporous, and in situ-setting calcium phosphate cement-layered structures  

PubMed Central

Calcium phosphate cement (CPC) is highly promising for clinical uses due to its in situ-setting ability, excellent osteoconductivity and bone-replacement capability. However, the low strength limits its use to non-load-bearing applications. The objectives of this study were to develop a layered CPC structure by combining a macroporous CPC layer with a strong CPC layer, and to investigate the effects of porosity and layer thickness ratios. The rationale was for the macroporous layer to accept tissue ingrowth, while the fiber-reinforced strong layer would provide the needed early-strength. A biopolymer chitosan was incorporated to strengthen both layers. Flexural strength, S (mean±sd; n = 6) of CPC-scaffold decreased from (9.7±1.2) to (1.8±0.3) MPa (p<0.05), when the porosity increased from 44.6% to 66.2%. However, with a strong-layer reinforcement, S increased to (25.2±6.7) and (10.0±1.4) MPa, respectively, at these two porosities. These strengths matched/exceeded the reported strengths of sintered porous hydroxyapatite implants and cancellous bone. Relationships were established between S and the ratio of strong layer thickness/specimen thickness, a/h:S = (17.6 a/h+3.2) MPa. The scaffold contained macropores with a macropore length (mean±sd; n = 147) of (183±73) ?m, suitable for cell infiltration and tissue ingrowth. Nano-sized hydroxyapatite crystals were observed to form the scaffold matrix of CPC with chitosan. In summary, a layered CPC implant, combining a macroporous CPC with a strong CPC, was developed. Mechanical strength and macroporosity are conflicting requirements. However, the novel functionally graded CPC enabled a relatively high strength and macroporosity to be simultaneously achieved. Such an in situ-hardening nano-apatite may be useful in moderate stress-bearing applications, with macroporosity to enhance tissue ingrowth and implant resorption. PMID:17574665

Xu, Hockin H.K.; Burguera, Elena F.; Carey, Lisa E.

2009-01-01

349

Effects of seed layers on structural, morphological, and optical properties of ZnO nanorods.  

PubMed

We studied the effects of seed layers on the structural and optical properties of ZnO nanorods. ZnO and Ag-doped ZnO (ZnO:Ag) seed layers were deposited on glass substrates by magnetron co-sputtering. ZnO nanorods were grown on these seed layers by the chemical bath deposition in an aqueous solution of Zn(NO3)2 and hexamethyltetramine. SEM micrographs clearly reveal that ZnO nanorods were successfully grown on both kinds of seed layers. The XRD patterns indicate that crystallization of ZnO nanorods is along the c-axis. Meanwhile, the packing density and the vertical alignment of the ZnO nanorods on the ZnO seed layer are better than those of the ZnO nanorods on ZnO:Ag. The enhanced growth of nanorods is thought to be due to the fact that the ZnO layer exhibits a higher crystalline quality than the ZnO:Ag layer. According to the low-temperature photoluminescence spectra, the ZnO nanorods on the ZnO seed layer show a narrow strong ultraviolet emission band centered at 369 nm, while those on ZnO:Ag exhibit multiple bands. These results are thought to be related with the crystallinity of ZnO nanorods, the morphologies of ZnO nanorods, and the reflectivities of seed layers. More detailed studies for clarification of the seed layer effect on the growth of ZnO nanorods are desirable. PMID:21446487

Lee, Geon Joon; Min, Soon-Ki; Oh, Cha-Hwan; Leel, YoungPak; Lim, Hyunjin; Cheong, Hyeonsik; Nam, Hyun Jung; Hwangbo, Chang Kwon; Min, Sun-Ki; Han, Sung-Hwan

2011-01-01

350

DNS study of large-scale structures in a separated turbulent boundary layer  

NASA Astrophysics Data System (ADS)

Direct numerical simulations (DNSs) of a separated flat-plate turbulent boundary layer have been carried out. The inlet data are prescribed by DNSs of a zero-pressure-gradient turbulent boundary layer with the rescaling-recycling method; blowing and suction are imposed at the upper boundary for producing a separation bubble. The Reynolds numbers at the inlet are set to be Re?=300, 600 and 900, where Re? is the Reynolds number based on the freestream velocity and the momentum thickness. Particular attention is given to large- scale structures existing in a separated region. Results indicate that large-scale organized structures of the streamwise velocity fluctuation appear in a detached shear layer when a large separated region is formed. The latter structures consist of positive and negative regions alternating in the spanwise direction with a spacing of about 2˜3 ?99 (?99 denotes the 99% boundary layer thickness at the inlet), which become more apparent with increasing Reynolds number. They are most likely associated with large-scale spanwise meandering of the separation line. There is also close relationship between the large-scale structures and vortical structures, the latter tending to form vortex clusters where hairpin-like vortices are also observed.

Abe, Hiroyuki; Mizobuchi, Yasuhiro; Matsuo, Yuichi

2011-11-01

351

Effect of compositional gradient on mechanical properties in aluminum/duralumin multi-layered clad structures  

NASA Astrophysics Data System (ADS)

This study aims to investigate the effect of compositional gradient on nano-, micro- and macro-mechanical properties in aluminum (A1050)/ duralumin (A2017) multi-layered clad structures fabricated by hot rolling. Such multilayered clad structures are possibly adopted to a new type of automobile crash boxes to effectively absorb the impact forces generated when automobiles having collisions. 2- and 6-layered clad structures with asymmetric lay-ups from one side of aluminum to another side of duralumin have been fabricated, which have been suffering three different heattreatments such as (1) as-rolled (no heat-treatment), (2) annealed at 400°C and (3) homogenized at 500°C followed by water quenching and aging (T4 heat treatment). For nano- and micro-scale mechanical properties proved by nanoindentation, higher hardness and elastic modulus correspond to higher Cu content at the interface in annealed and aged samples. For macro-scale mechanical properties, internal friction of 2-layered clad structures is higher than that of 6-layered clad structures in any heat-treatment samples. Deep drawing formability of annealed samples is considerably high compared to as-rolled and aged ones.

Tsukamoto, Hideaki; Komiya, Yoshiki; Sato, Hisashi; Watanabe, Yoshimi

2013-12-01

352

Monitoring of hidden damage in multi-layered aerospace structures using high-frequency guided waves  

NASA Astrophysics Data System (ADS)

Aerospace structures contain multi-layered components connected by fasteners, where fatigue cracks and disbonds or localized lack of sealant can develop due to cyclic loading conditions and stress concentration. High frequency guided waves propagating along such a structure allow for the efficient non-destructive testing of large components, such as aircraft wings. The type of multi-layered model structure investigated in this contribution consists of two aluminium plates adhesively bonded with an epoxy based sealant layer. Using commercially available transducer equipment, specific high frequency guided ultrasonic wave modes that penetrate through the complete thickness of the structure were excited. The wave propagation along the structure was measured experimentally using a laser interferometer. Two types of hidden damage were considered: a localized lack of sealant and small surface defects in the metallic layer facing the sealant. The detection sensitivity using standard pulse-echo measurement equipment has been quantified and the detection of small hidden defects from significant stand-off distances has been shown. Fatigue experiments were carried out and the potential of high frequency guided waves for the monitoring of fatigue crack growth at a fastener hole during cyclic loading was discussed.

Semoroz, A.; Masserey, B.; Fromme, P.

2011-04-01

353

Structure of the regular surface layer of Aquaspirillum serpens MW5.  

PubMed

The structure of the regular surface layer of Aquaspirillum serpens MW5 has been investigated by electon microscopy supplemented by computer image processing and least-squares analysis. The layer has a ribbed appearance, both on the bacterium and in isolated, negatively stained fragments. However, detailed analysis indicated that the layer was composed of two hexagonal sheets having p6mm symmetry and a = 16 nm. One sheet was staggered by one half repeat along a (1,0) line of the p6nm lattice relative to the second so that, in projection, the pattern of the composite layer was a translational moiré, characterized by a series of ribs spaced 16 nm apart. The ribbed layer had cmm symmetry with a = 32 nm and b = 18.5 nm. Analysis of this pattern indicated that the two p6nm hexagonal sheets were unevenly stained, and this was confirmed by using least-squares methods to simulate the observed pattern by combining two hexagonal patterns. The general structure of the layer was consistent with a role as a selective and protective barrier on the cell surface. PMID:7061396

Stewart, M; Murray, R G

1982-04-01

354

Electronic and thermoelectric transport in graphene double layer structures with boron nitride spacers  

NASA Astrophysics Data System (ADS)

Recently, much attention has been devoted to electrically isolated graphene-graphene double layers in which interaction-driven novel physics such as exciton condensation are predicted. We have used polyvinyl alcohol (PVA) based carrier films and a micro-manipulator to transfer mechanically exfoliated flakes onto desired locations with accuracy of ˜1 ?m. We have fabricated graphene/boron nitride (BN)/graphene stacking structures on BN substrates to study their electronic and thermoelectric transport properties. We observed the low temperature mobility of graphene as high as 75000 cm^2/V-s. We have performed Coulomb drag measurements and observed the sign and magnitude dependence of the drag resistivity on the carrier types and densities of both graphene layers, consistent with the previous reports. We also performed thermoelectric transport measurements in such graphene double layer structures, especially in the complementary doped regime (so called excitonic regime) with one layer of electrons and the other layer of holes. Our approach may be useful to probe exciton condensation and other novel physics driven by electron-electron interactions in graphene double layers.

Hu, Jiuning; Wu, Tailung; Tian, Jifa; Chen, Yong

2013-03-01

355

Semiconductor structures having electrically insulating and conducting portions formed from an AlSb-alloy layer  

DOEpatents

The semiconductor structure comprises a plurality of semiconductor layers formed on a substrate including at least one layer of a III-V compound semiconductor alloy comprising aluminum (Al) and antimony (Sb), with at least a part of the AlSb-alloy layer being chemically converted by an oxidation process to form superposed electrically insulating and electrically conducting portions. The electrically insulating portion formed from the AlSb-alloy layer comprises an oxide of aluminum (e.g., Al{sub 2}O{sub 3}), while the electrically conducting portion comprises Sb. A lateral oxidation process allows formation of the superposed insulating and conducting portions below monocrystalline semiconductor layers for forming many different types of semiconductor structures having particular utility for optoelectronic devices such as light-emitting diodes, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodetectors and optical modulators (waveguide and surface normal), and for electronic devices such as heterojunction bipolar transistors, field-effect transistors and quantum-effect devices. The invention is expected to be particularly useful for forming light-emitting devices for use in the 1.3--1.6 {mu}m wavelength range, with the AlSb-alloy layer acting to define an active region of the device and to effectively channel an electrical current therein for efficient light generation. 10 figs.

Spahn, O.B.; Lear, K.L.

1998-03-10

356

Thermal properties of composite two-layer systems with a fractal inclusion structure  

NASA Astrophysics Data System (ADS)

In this work, we study the thermal transport properties of platelike composite two-layer samples made of polyester resin and magnetite inclusions. By means of photoacoustic spectroscopy and thermal relaxation, their effective thermal diffusivity and conductivity were experimentally measured. The composite layers were prepared under the action of a static magnetic field, resulting in anisotropic (fractal) inclusion structures with the formation of chain-like magnetite aggregates parallel to the faces of the layers. In one kind of the bilayers, a composite layer was formed on top of a resin layer while their relative thickness was varied. These samples can be described by known models. In contrast, bilayers with the same concentration of inclusions and the same thickness on both sides, where only the angle between their inclusion structures was systematically varied, show a nontrivial behaviour of their thermal conductivity as a function of this angle. Through a multifractal and lacunarity analysis, we explain the observed thermal response in terms of the complexity of the interface between the layers.

Reyes-Salgado, J. J.; Dossetti, V.; Bonilla-Capilla, B.; Carrillo, J. L.

2015-01-01

357

Nonlinear instability research of longitudinal structure generated by roughness in unswept wing boundary layer  

NASA Astrophysics Data System (ADS)

The results of experimental study of a nonlinear varicose instability of the streaky structure generated by roughness element in unswept-wing boundary layer are presented. Features of the varicose breakdown of longitudinal steady streaky structure such as modulation of structure in transverse and streamwise directions by secondary disturbance, occurrence of the new streaky structures and A-structures downstream are shown. Spatio-temporal pictures of the hot-wire visualization of flow during spatial evolution of the streaky structures under influence of secondary high-frequency disturbance are discussed. Features of the adverse pressure gradient influence upon processes of the nonlinear varicose instability evolution and flow structure are revealed. Essential influence of the adverse pressure gradient on evolution of disturbances in shown. Comparison of varicose instability of the streaky structures generated in two different ways (the roughness element as in the given work, and continuous air blowing as in the earlier published work) is the carried out.

Chernorai, V. G.; Litvinenko, Yu. A.; Kozlov, V. V.; Grek, G. R.

2007-09-01

358

Structural Analysis and Evidence for Dynamic Emergence of Bacillus anthracis S-Layer Networks  

PubMed Central

Surface layers (S-layers), which form the outermost layers of many Bacteria and Archaea, consist of protein molecules arranged in two-dimensional crystalline arrays. Bacillus anthracis, a gram-positive, spore-forming bacterium, responsible for anthrax, synthesizes two abundant surface proteins: Sap and EA1. Regulatory studies showed that EA1 and Sap appear sequentially at the surface of the parental strain. Sap and EA1 can form arrays. The structural parameters of S-layers from mutant strains (EA1? and Sap?) were determined by computer image processing of electron micrographs of negatively stained regular S-layer fragments or deflated whole bacteria. Sap and EA1 projection maps were calculated on a p1 symmetry basis. The unit cell parameters of EA1 were a = 69 Å, b = 83 Å, and ? = 106°, while those of Sap were a = 184 Å, b = 81 Å, and ? = 84°. Freeze-etching experiments and the analysis of the peripheral regions of the cell suggested that the two S-layers have different settings. We characterized the settings of each network at different growth phases. Our data indicated that the scattered emergence of EA1 destabilizes the Sap S-layer. PMID:12426331

Couture-Tosi, Evelyne; Delacroix, Hervé; Mignot, TÂm; Mesnage, Stéphane; Chami, Mohamed; Fouet, Agnès; Mosser, Gervaise

2002-01-01

359

Damping characteristics of active-passive hybrid constrained-layer treated beam structures  

NASA Astrophysics Data System (ADS)

A new configuration of surface damping treatments, Active- Passive Hybrid Constrained Layer (HCL) damping, is analyzed and experimentally investigated. The purpose is to improve the performance of the current active constrained layer (ACL) and passive constrained layer (PCL) treatments by mixing passive and active materials in the constraining layer. In HCL, the viscoelastic material is constrained by an active-passive hybrid constraining layer -- the active part is made of PZT ceramics, and the passive part can be selected by the designer to meet different requirements, such as higher damping performance or lighter weight. The active and passive constraining parts are mechanically connected such that the displacement and force are continuous at the connecting surface, but are isolated electrically so the passive constraining part will not affect the function of its active counterpart. Following a generic study of the HCL concept by the authors earlier, the purpose of this paper is to illustrate and validate the HCL performance through both numerical and experimental investigations on a beam structure. The governing equations and boundary conditions of an HCL treated beam are derived and a finite element model is formulated. Tabletop tests with cantilever beam specimens are used for the experimental study. The new hybrid constrained layer is found to have the advantages of both ACL and PCL. By selecting a stiffer passive constraining material and an optimal active-to-passive length ratio, the HCL can achieve better closed-loop and open-loop performances than the treatment with a pure active constraining layer.

Liu, Yanning; Wang, Kon-Well

2000-04-01

360

Characteristic length scale of the intermediate structure in zero-pressure-gradient boundary layer flow.  

PubMed

In a turbulent boundary layer over a smooth flat plate with zero pressure gradient, the intermediate structure between the viscous sublayer and the free stream consists of two layers: one adjacent to the viscous sublayer and one adjacent to the free stream. When the level of turbulence in the free stream is low, the boundary between the two layers is sharp, and both have a self-similar structure described by Reynolds-number-dependent scaling (power) laws. This structure introduces two length scales: one-the wall-region thickness-determined by the sharp boundary between the two intermediate layers and the second determined by the condition that the velocity distribution in the first intermediate layer be the one common to all wall-bounded flows and in particular coincide with the scaling law previously determined for pipe flows. Using recent experimental data, we determine both these length scales and show that they are close. Our results disagree with the classical model of the "wake region." PMID:10760253

Barenblatt, G I; Chorin, A J; Prostokishin, V M

2000-04-11

361

Characterization of pore network structure in catalyst layers of polymer electrolyte fuel cells  

NASA Astrophysics Data System (ADS)

We model and validate the effect of ionomer content and Pt nanoparticles on nanoporous structure of catalyst layers in polymer electrolyte fuel cells. By employing Pore network modeling technique and analytical solutions, we analyze and reproduce experimental N2-adsorption isotherms of carbon, Pt/carbon and catalyst layers with various ionomer contents. The porous catalyst layer structures comprise of Ketjen Black carbon, Pt and Nafion ionomer. The experimental pore size distributions obtained by N2-adsorption are used as an input to generate porous media using the pore network approach. Subsequently, the simulated porous structures are used to produce simulated N2-adsorption isotherms, which are then compared to the experimentally measured isotherms. The results show a good agreement in the prediction of the effect of the ionomer content on the microstructure of catalyst layers. Moreover, the analysis of the isotherms confirms the hypothesis of ionomer distribution on the surface of agglomerates as well as the existence of different sorption regimes in primary and secondary pores of fuel cell catalyst layers.

El Hannach, Mohamed; Soboleva, Tatyana; Malek, Kourosh; Franco, Alejandro A.; Prat, Marc; Pauchet, Joël; Holdcroft, Steven

2014-02-01

362

Metal and semiconductor nanoparticles stabilized in ultrathin nanofilms and layer-structured materials  

NASA Astrophysics Data System (ADS)

The interlamellar space of layer structured materials, such as montmorillonite, kaolinite, graphite oxide can be regarded as a nanophase reactor, in which size-quantized semiconductor and noble metal particles can be prepared. Particle growth is sterically hindered in the interlamellar space between neighboring lamellae which favors the formation of 2-10 nm particles. These synthesis strategies were successfully applied for the preparation and incorporation of Pd and Ag metal and CdS, ZnO, SnO2 semiconductor nanoparticles. Layer-by-layer self-assembled nanofilms were prepared from aqueous suspensions of semiconductor nanoparticles and various clay mineral suspensions onto glass surface. The nanoparticles adsorb on the surface of the support wiht their protecting layers allwoing the preparation of semiconductor and noble metal nanocomposites by this method. The properties of these nanocomposites have been investigated by optical measurements, x-ray diffraction, small angle x-ray scattering, atomic force and transmission electron microscopy.

Dekany, Imre; Szabo, Tamas; Korosi, Laszlo

2003-04-01

363

A review of vortex structures and associated coherent motions in turbulent boundary layers  

NASA Technical Reports Server (NTRS)

The experimental and computational evidence for the existence and role of vortices in turbulent boundary layers is briefly reviewed. Quasi-streamwise and transverse vortices are considered, and various published conceptual models for horseshoe-like vortical structures are compared. The causes for upright and inverted horseshoe-shaped vorticity lines are discussed, and the distinction between vorticity lines and vortices is demonsrated. Finally, results from a numerically-simulated turbulent boundary layer are used to compute distributions of diameter, height, and strength for quasi-streamwise and spanwise vortices. These results confirm that quasi-streamwise vortices are clustered near the wall, while spanwise vortices are distributed throughout the layer. The variation of spanwise vortex core diameter with distance from the wall is found to be consistent with the mixing-length distribution for a boundary layer.

Robinson, Stephen K.

1990-01-01

364

Shrinkage anisotropy characteristics from soil structure and initial sample/layer size  

E-print Network

The objective of this work is a physical prediction of such soil shrinkage anisotropy characteristics as variation with drying of (i) different sample/layer sizes and (ii) the shrinkage geometry factor. With that, a new presentation of the shrinkage anisotropy concept is suggested through the sample/layer size ratios. The work objective is reached in two steps. First, the relations are derived between the indicated soil shrinkage anisotropy characteristics and three different shrinkage curves of a soil relating to: small samples (without cracking at shrinkage), sufficiently large samples (with internal cracking), and layers of similar thickness. Then, the results of a recent work with respect to the physical prediction of the three shrinkage curves are used. These results connect the shrinkage curves with the initial sample size/layer thickness as well as characteristics of soil texture and structure (both inter- and intra-aggregate) as physical parameters. The parameters determining the reference shrinkage c...

Chertkov, V Y

2014-01-01

365

Nanosized Structural Anti-Reflection Layer for Thin Film Solar Cells  

NASA Astrophysics Data System (ADS)

A nanosized pattern layer was formed on the front surface (glass side) of the thin film solar cell using nanoimprint lithography with a Ni based moth-eye imprint mold in order to increase the total conversion efficiency of the amorphous silicon based thin film solar cell. The imprinted pattern layer had nanosized protrusions, which suppressed the reflection of light on the glass surfaces. The nanopatterns were formed using a methacryloxypropyl terminated poly(dimethylsiloxane) (MPDMS) based hard polymeric resin. The reflectance of the thin film solar cell significantly decreased because of the nanosized structural anti-reflection layer, and the total conversion efficiency of the cell increased about 3% compared to the identical solar cell without the nanosized pattern layer. Moreover, the surface exhibited a hydrophobic nature because of the surface nanopatterns and the self-assembled monolayer coating, and this hydrophobicity provided the solar cell with a self-cleaning functionality.

Han, Kang-Soo; Shin, Ju-Hyeon; Kim, Kang-In; Lee, Heon

2011-02-01

366

A randomly nano-structured scattering layer for transparent organic light emitting diodes.  

PubMed

A random scattering layer (RSL) consisting of a random nano-structure (RNS) and a high refractive index planarization layer (HRI PL) is suggested and demonstrated as an efficient internal light-extracting layer for transparent organic light emitting diodes (TOLEDs). By introducing the RSL, a remarkable enhancement of 40% and 46% in external quantum efficiency (EQE) and luminous efficacy (LE) was achieved without causing deterioration in the transmittance. Additionally, with the use of the RSL, the viewing angle dependency of EL spectra was reduced to a marginal degree. The results were interpreted as the stronger influence of the scattering effect over the microcavity. The RSL can be applied widely in TOLEDs as an effective light-extracting layer for extracting the waveguide mode of confined light at the indium tin oxide (ITO)/OLED stack without introducing spectral changes in TOLEDs. PMID:25099663

Huh, Jin Woo; Shin, Jin-Wook; Cho, Doo-Hee; Moon, Jaehyun; Joo, Chul Woong; Park, Seung Koo; Hwang, Joohyun; Cho, Nam Sung; Lee, Jonghee; Han, Jun-Han; Chu, Hye Yong; Lee, Jeong-Ik

2014-09-21

367

Controlled gentamicin release from multi-layered electrospun nanofibrous structures of various thicknesses  

PubMed Central

Polyvinyl alcohol nanofibers incorporating the wide spectrum antibiotic gentamicin were prepared by Nanospider™ needleless technology. A polyvinyl alcohol layer, serving as a drug reservoir, was covered from both sides by polyurethane layers of various thicknesses. The multilayered structure of the nanofibers was observed using scanning electron microscopy, the porosity was characterized by mercury porosimetry, and nitrogen adsorption/desorption measurements were used to determine specific surface areas. The stability of the gentamicin released from the electrospun layers was proved by high-performance liquid chromatography (HPLC) and inhibition of bacterial growth. Drug release was investigated using in vitro experiments with HPLC/MS quantification, while the antimicrobial efficacy was evaluated on Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa. Both experiments proved that the released gentamicin retained its activity and showed that the retention of the drug in the nanofibers was prolonged with the increasing thickness of the covering layers. PMID:23071393

Sirc, Jakub; Kubinova, Sarka; Hobzova, Radka; Stranska, Denisa; Kozlik, Petr; Bosakova, Zuzana; Marekova, Dana; Holan, Vladimir; Sykova, Eva; Michalek, Jiri

2012-01-01

368

Origin of the Mt Ashmore structural dome, west Bonaparte Basin, Timor Sea  

Microsoft Academic Search

New insights into the 3D structure, composition and origin of the Mt Ashmore dome, west Bonaparte Basin, Timor Sea, are enabled by reprocessed seismic-reflection data and by optical microscopic, X-ray diffraction (XRD), scanning electron microscopy (SEM)\\/energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM) analyses of drill cuttings. The structural dome, located below a major pre-Oligocene post-Late Eocene unconformity and

A. Y. Glikson; D. Jablonski; S. Westlake

2010-01-01

369

A randomly nano-structured scattering layer for transparent organic light emitting diodes  

NASA Astrophysics Data System (ADS)

A random scattering layer (RSL) consisting of a random nano-structure (RNS) and a high refractive index planarization layer (HRI PL) is suggested and demonstrated as an efficient internal light-extracting layer for transparent organic light emitting diodes (TOLEDs). By introducing the RSL, a remarkable enhancement of 40% and 46% in external quantum efficiency (EQE) and luminous efficacy (LE) was achieved without causing deterioration in the transmittance. Additionally, with the use of the RSL, the viewing angle dependency of EL spectra was reduced to a marginal degree. The results were interpreted as the stronger influence of the scattering effect over the microcavity. The RSL can be applied widely in TOLEDs as an effective light-extracting layer for extracting the waveguide mode of confined light at the indium tin oxide (ITO)/OLED stack without introducing spectral changes in TOLEDs.A random scattering layer (RSL) consisting of a random nano-structure (RNS) and a high refractive index planarization layer (HRI PL) is suggested and demonstrated as an efficient internal light-extracting layer for transparent organic light emitting diodes (TOLEDs). By introducing the RSL, a remarkable enhancement of 40% and 46% in external quantum efficiency (EQE) and luminous efficacy (LE) was achieved without causing deterioration in the transmittance. Additionally, with the use of the RSL, the viewing angle dependency of EL spectra was reduced to a marginal degree. The results were interpreted as the stronger influence of the scattering effect over the microcavity. The RSL can be applied widely in TOLEDs as an effective light-extracting layer for extracting the waveguide mode of confined light at the indium tin oxide (ITO)/OLED stack without introducing spectral changes in TOLEDs. Electronic supplementary information (ESI) available: Simulation results of total (bottom and top) radiance of TOLEDs with the RSL depending on HTL and ETL thicknesses. See DOI: 10.1039/c4nr01520g

Huh, Jin Woo; Shin, Jin-Wook; Cho, Doo-Hee; Moon, Jaehyun; Joo, Chul Woong; Park, Seung Koo; Hwang, Joohyun; Cho, Nam Sung; Lee, Jonghee; Han, Jun-Han; Chu, Hye Yong; Lee, Jeong-Ik

2014-08-01

370

Origin of the 'dike-like' structure and transitions in eruptive styles at Colton Crater, northern Arizona: San Francisco Volcanic Field REU  

NASA Astrophysics Data System (ADS)

Colton Crater, located within the San Francisco Volcanic Field (SFVF) in northern Arizona, is one of over 600 scoria cones in the field. Unlike most other volcanoes in the SFVF, Colton Crater is characterized as a hybrid volcano that had Strombolian, Hawaiian, and Surtseyan explosions. Surtseyan explosions led to the excavation of the center of the volcano, creating a large 1.3-km-diameter crater with a 30-m post-phreatomagmatic scoria cone at its center. A vertical erosion-resistant feature along the northern rim of the crater, originally mapped as a dike, provides valuable information about the sequence and timing of the transition to phreatomagmatic eruptions because it disrupts the otherwise continuous spatter layers deposited just prior to that change. Stratigraphic sections and paleomagnetic analysis of Colton Crater reveal the origin and timing of emplacement of this vertical structure and its place in the transitional eruptive history. The prominent upper layers in the crater walls show some variation throughout the crater, but generally are composed of agglutinated spatter, welded scoria and bombs, and rootless lava flows. The uppermost portion of the outward-dipping spatter layers that lie between the two saddles on the northern rim closely match the layers observed in the vertical structure, revealing that the structure is a section of rotated spatter. The characteristic remanent magnetization (ChRM), identified using alternating field (AF) demagnetization, shows the timing of the displacement of sections of the agglutinated spatter and welded cinder. Sites along the vertical structure yield ChRMs statistically identical to non-rotated sites, which indicates that rotation of the vertical structure occurred before the ChRM had been set, i.e., the layers were above the Curie temperature during rotation. The eruption started as Strombolian and Hawaiian perhaps because the flux of magma overpowered the influx of water from local aquifer formations, creating a stable and sealed conduit. Lava flows associated with the Strombolian and Hawaiian activity breached the northern flank and destabilized the walls of the crater. Water may have been introduced to the magmatic system through conduit collapse beneath the water table or vent migration to a conduit location with greater water flux, leading to the Surtseyan explosions. As space was created on the northern rim, the destabilized spatter layers detached and rotated, creating the vertical structure. The eruption ended with a small Strombolian phase, forming the 30-m-high scoria cone in the bottom of the crater. The sequence of these events must have happened within a short time period because the rotated spatter layers of the vertical structure remained above 580 oC.

Witter, M. R.; Ort, M. H.; Leudemann, L. A.

2013-12-01

371

EXAFS Signatures of Structural Zn at Trace Levels in Layered Minerals  

SciTech Connect

Many in situ XAFS studies have shown that zinc incorporated in layered minerals is a major form of zinc in Zn-contaminated soils. Quantitative information on the local structural environment(s) and ordering of Zn in these minerals is required to better understand its behavior in soils. In this study, EXAFS spectroscopy was used to assess the structural environment of zinc incorporated at trace levels (40 ppm to 4,000 ppm) within the octahedral sheets of various natural and synthetic layered minerals. Results indicate that EXAFS data analyzed using ab initio FEFF calculations (FEFF 8.10) can unambiguously distinguish between zinc incorporation within the octahedral sheet of dioctahedral versus trioctahedral layered minerals and can determine the distribution (random or ordered) of zinc cations within the octahedral sheets of these minerals.

Juillot, Farid; Morin, Guillaume; /Paris U., VI-VII, LMCP; Hazemann, Jean-Louis; Proux, Olivier; /ESRF, Grenoble; Belin, Stephanie; Briois, Valerie; /ESRF, Grenoble; Brown,; /Stanford U., Geo. Environ. Sci. /SLAC, SSRL; Calas, Georges; /Paris U., VI-VII, LMCP

2006-12-13

372

Characterization of ion-implantation doping of strained-layer superlattices. I - Structural properties  

NASA Astrophysics Data System (ADS)

The effects of ion implantation and controlled-atmosphere annealing on the structure of Ga(AsP)/GaP strained-layer superlattices (SLSs) with layers of equal thickness are considered in detail. Damage and strain distributions within the implanted layers are examined by cantilever-beam bending measurements, double-crystal X-ray rocking curves, and a variety of ion-channeling techniques. The results indicate that appropriate structures can sustain a substantial amount of ion damage and still recover on annealing with no detectable loss of strain or other degradation. It is shown that the implantation technologies developed for the nearest binary semiconductor (GaP) can be successfully applied to the Ga(AsP)/GaP SLSs without modification.

Myers, D. R.; Picraux, S. T.; Doyle, B. L.; Arnold, G. W.; Biefeld, R. M.

1986-11-01

373

Formation of Structured Dayside Boundary Layers under Different Solar Wind Conditions: THEMIS Observations  

NASA Technical Reports Server (NTRS)

We have begun an investigation of the formation of the dayside low latitude boundary layer under different solar wind conditions using data from the THEMIS spacecraft. We present two cases of magnetopause/LLBL interface crossings made by the five spacecraft; one under long lasting northward IMF and a second for a period of southward IMF. All spacecraft during these observations traversed the dayside magnetosphere in a string-of-pearls configuration with the farthest distance between spacecraft less than approx.2 R(sub E). The sequence of observations from spacecraft, as they crossed the magnetopause, shows the development of a highly structured boundary layer regardless of the polarity of the IMF. We discuss possible scenarios for the development of such structured boundary layers, including low latitude reconnection under northward IMF as well as double reconnection in opposite hemispheres.

Avanov, Levon A.; Chandler, Michael O.

2008-01-01

374

Three-Layered Atmospheric Structure in Accretion Disks Around Stellar-Mass Black Holes  

NASA Technical Reports Server (NTRS)

Modeling of the x-ray spectra of the Galactic superluminal jet sources GRS 1915+105 and GRO J1655-40 reveals a three-layered atmospheric structure in the inner region of the inner accretion disks. Above the cold and optically thick disk with a temperature of 0.2 to 0.5 kiloelectron volts, there is a warm layer with a temperature of 1.0 to 1.5 kiloelectron volts and an optical depth around 10. Sometimes there is also a much hotter, optically thin corona above the warm layer, with a temperature of 100 kiloelectron volts or higher and an optical depth around unity. The structural similarity between the accretion disks and the solar atmosphere suggests that similar physical processes may be operating in these different systems.

Zhang, S. N.; Cui, Wei; Chen, Wan; Yao, Yangsen; Zhang, Xiaoling; Sun, Xuejun; Wu, Xue-Bing; Xu, Haiguang

2000-01-01

375

ORIGINAL ARTICLE Community structure and nutrition of deep methane-seep  

E-print Network

ORIGINAL ARTICLE Community structure and nutrition of deep methane-seep macrobenthos from the North Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA, USA Keywords Cold seep Methane seeps occur at depths extending to over 7000 m along the world's continental margins

Levin, Lisa

376

The structure and origin of magnetic clouds in the solar wind V. Bothmer1  

E-print Network

The structure and origin of magnetic clouds in the solar wind V. Bothmer1 * and R. Schwenn2 1 Space in the surrounding solar wind. Minimum variance analysis (MVA) showed that MCs can best be described as large- scale to be proportional to RÃ?2X4 , thus being stronger compared to the average solar wind. Four dierent magnetic con

Boyer, Edmond

377

ORIGINAL ARTICLE 3D crustal structure and long-period ground motions  

E-print Network

ORIGINAL ARTICLE 3D crustal structure and long-period ground motions from a M9.0 megathrust of the shaking up to 5 min, these long-period ground motions may inflict significant damage on the built-period ground motion . Megathrust earthquake 1 Introduction Around 9:00 P.M. local time, on January 26th, 1700

Olsen, Kim Bak

378

Structural and Tectonic Constraints on the Origin of Gold Deposits in the Ballarat  

E-print Network

* Structural and Tectonic Constraints on the Origin of Gold Deposits in the Ballarat Slate Belt). The vast proportion of this gold, much of which was recovered from Tertiary alluvial deposits gold deposition,re- gional deformation and granite genesis within the slate belt remain the subject

Sandiford, Mike

379

ORIGINAL PAPER Small-scale gold mining erodes fish assemblage structure  

E-print Network

operations, as the alluvial gold deposits are mined by washing the soils adjacent to the streams with highORIGINAL PAPER Small-scale gold mining erodes fish assemblage structure in small neotropical+Business Media B.V. 2011 Abstract The current gold rush experienced by the Guiana shield is profoundly dis

Grenouillet, Gael

380

Protein folding, protein structure and the origin of life: Theoretical methods and solutions of dynamical problems  

NASA Technical Reports Server (NTRS)

Theoretical methods and solutions of the dynamics of protein folding, protein aggregation, protein structure, and the origin of life are discussed. The elements of a dynamic model representing the initial stages of protein folding are presented. The calculation and experimental determination of the model parameters are discussed. The use of computer simulation for modeling protein folding is considered.

Weaver, D. L.

1982-01-01

381

A conceptual model for the origin of fault damage zone structures in high-porosity sandstone  

E-print Network

A conceptual model for the origin of fault damage zone structures in high-porosity sandstone Zoe K-porosity sandstones. Damage zone deformation has been particularly well constrained for two 4-km-long normal faults formed in the Navajo Sandstone of central Utah, USA. For these faults the width of the damage zone

Cowie, Patience

382

Origin, taxonomy and population structure of the allopolyploid peat moss Sphagnum majus  

Microsoft Academic Search

The polyploid peat mossSphagnum majus shows considerable phenotypic plasticity along ecological gradients in mires. It is considered taxonomically heterogeneous, and two subspecies have been described. Isozyme analyses were carried out on populations ofS. majus from Central Norway and from eastern coast of North America in order to assess the origin, taxonomy and population structure of this species. High levels of

S. M. Såstad; K. I. Flatberg; L. Hanssen

2000-01-01

383

Structure A, steel shelving. Drawing no. H3300. Original drawing by ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Structure A, steel shelving. Drawing no. H3-300. Original drawing by Black & Veatch, Consulting Engineers, Kansas City, Missouri, prepared for the U.S. Department of the Army, Office of Engineers, Military Construction Division, Washington D.C. dated November 5, 1951. - Travis Air Force Base, Building No. 925, W Street, Fairfield, Solano County, CA

384

Structure A, reinforcing details. Drawing No. H2302, as built, Original ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Structure A, reinforcing details. Drawing No. H2-302, as built, Original drawing by Black & Veatch, Consulting Engineers, Kansas City, Missouri, prepared for the U.S. Department of the Army, Office of Engineers, Military Construction Division, Washington, D.C. dated October 1, 1951. - Travis Air Force Base, Building No. 925, W Street, Fairfield, Solano County, CA

385

Population structure and origins of Purple Sandpipers Calidris maritima in north Norway during winter  

Microsoft Academic Search

Wintering Purple Sandpipers Calidris maritima were captured at Varangerfjorden, Finnmark, in March 1992, and compared with samples from Troms county in November 1988 to describe the population structure in north Norway in terms of age and sex classes, and to determine the origins of these wintering birds. The overall percentage of first?year birds was 35% at Varangerfjorden, higher than that

Ron W. Summers; Rab Rae

2006-01-01

386

Electrical Characteristics of Thin-Film Transistors with Double-Active-Layer Structure  

Microsoft Academic Search

Thin-film transistors (TFTs) with a double-active-layer (DAL) structure have been proposed and found to exhibit two kinds of special electrical characteristics. One is the improvement of current drivability and transconductance as compared to the traditional structure. The other is the double-switching characteristics caused by the bi-transistor action. By means of a buried oxide separating the conduction channel into two parts,

Meng-Jin Tsai; Ping-Wei Wang; Huan-Ping Su; Huang-Chung Cheng

1995-01-01

387

GMR sensing array technique validation study for the inspection of multi-layer metallic structures  

NASA Astrophysics Data System (ADS)

Giant Magnetoresistive (GMR) sensing arrays have been developed to detect fatigue cracks in thick, multi-layered metallic structures. As part of a program conducted by the U.S. Air Force Research Laboratory, fatigue crack specimens were fabricated to provide inspection targets for a GMR array. These specimens were mounted to simulate a wing structure and inspected using a Boeing Mobile Automated Scanner (MAUS). Probability of Detection (POD) from inspections and the results of capability studies are presented.

Motes, Doyle; Aldrin, John C.; Keiser, Mark; Steffes, Gary; Forsyth, David S.

2013-01-01

388

Thermal emission from layered structures containing a negative-zero-positive index metamaterial  

NASA Astrophysics Data System (ADS)

Motivated by the realization of the optical Dirac dispersion in the homogenous negative-zero-positive index (NZPI) material, we make a theoretical investigation on the properties of thermal emission in layered structures containing the NZPI medium. We find that when the thermal emission frequency is close to the Dirac point of the NZPI medium, the spectral hemispherical power of thermal emission in such a structure is strongly suppressed and the emission can become a high directional source with large spatial coherence.

Wang, Li-Gang; Li, Gao-Xiang; Zhu, Shi-Yao

2010-02-01

389

Mode manipulation and near-THz absorptions in binary grating-graphene layer structures  

PubMed Central

The excitation and absorption properties of grating coupled graphene surface plasmons were studied. It was found that whether a mode can be excited is mainly determined by the frequency of incident light and the duty ratio of gratings. In the structure consisting graphene bilayer, a blueshift of the excitation frequency existed when the distance between neighbor graphene layer were decreased gradually. In graphene-grating multilayer structures, a strong absorption (approximately 90% at maximum) was found in near-THz range. PMID:24559407

2014-01-01

390

Structure and chemical composition of layers adsorbed at interfaces with champagne.  

PubMed

The structure and the chemical composition of the layer adsorbed at interfaces involving champagne have been investigated using native champagne, as well as ultrafiltrate (UFch) and ultraconcentrate (UCch) obtained by ultrafiltration with a 10(4) nominal molar mass cutoff. The layer adsorbed at the air/liquid interface was examined by surface tension and ellipsometry kinetic measurements. Brewster angle microscopy demonstrated that the layer formed on polystyrene by adsorption or drop evaporation was heterogeneous, with a domain structure presenting similarities with the layer adsorbed at the air/liquid interface. The surface chemical composition of polystyrene with the adlayer was determined by X-ray photoelectron spectroscopy (XPS). The contribution of champagne constituents varied according to the liquid (native, UFch, and UCch) and to the procedure of adlayer formation (evaporation, adsorption, and adsorption + rinsing). However, their chemical composition was not significantly influenced either by ultrafiltration or by the procedure of deposition on polystyrene. Modeling this composition in terms of classes of model compounds gave approximately 35% (w/w) of proteins and 65% (w/w) of polysaccharides. In the adlayer, the carboxyl groups or esters represent about 18% of carbon due to nonpolypeptidic compounds, indicating the presence of either uronic acids in the complex structure of pectic polysaccharides or of polyphenolic esters. This structural and chemical information and its relationship with the experimental procedures indicate that proteins alone cannot be used as a realistic model for the macromolecules forming the adsorption layer of champagne. Polysaccharides, the other major macromolecular components of champagne wine, are assembled with proteins at the interfaces, in agreement with the heterogeneous character of the adsorbed layer at interfaces. PMID:19813745

Aguié-Béghin, V; Adriaensen, Y; Péron, N; Valade, M; Rouxhet, P; Douillard, R

2009-11-11

391

Synthesis and single crystal structure refinement of the one-layer hydrate of sodium brittle mica  

SciTech Connect

A sodium brittle mica with the ideal composition [Na{sub 4}]{sup inter}[Mg{sub 6}]{sup oct}[Si{sub 4}Al{sub 4}]{sup tet}O{sub 20}F{sub 4} was synthesized via melt synthesis in a gas tight crucible. This mica is unusual inasmuch as the known mica structure holds only room for two interlayer cations per unit cell and inasmuch as it readily hydrates despite the high layer charge while ordinary micas and brittle micas are non-swelling. The crystal structure of one-layer hydrate sodium brittle mica was determined and refined from single crystal X-ray data. Interlayer cations reside at the center of the distorted hexagonal cavities and are coordinated by the three inner basal oxygen atoms. The coordination of the interlayer cation is completed by three interlayer water molecules residing at the center of the interlayer region. The relative position of adjacent 2:1-layers thus is fixed by these octahedrally coordinated interlayer cations. Pseudo-symmetry leads to extensive twinning. In total five twin operations generate the same environment for the interlayer species and are energetically degenerate. - Graphical abstract: The sodium brittle mica has been successfully synthesized by melt synthesis and the crystal structure of the one-layer hydrate of sodium brittle mica was determined from single crystal X-ray diffraction data. Highlights: Black-Right-Pointing-Pointer Melt synthesis yielded coarse grained sodium brittle mica which showed little disorder. Black-Right-Pointing-Pointer Sodium brittle mica hydrated completely to the state of one-layer hydrate. Black-Right-Pointing-Pointer Structure of one-layer hydrate of sodium brittle mica could therefore be determined and refined. Black-Right-Pointing-Pointer Arrangement of upper and lower tetrahedral sheet encompassing interlayer cation were clarified.

Kalo, Hussein; Milius, Wolfgang [Lehrstuhl fuer Anorganische Chemie I, University of Bayreuth, D-95440 Bayreuth (Germany)] [Lehrstuhl fuer Anorganische Chemie I, University of Bayreuth, D-95440 Bayreuth (Germany); Braeu, Michael [BASF Construction Chemicals GmbH, 83308 Trostberg (Germany)] [BASF Construction Chemicals GmbH, 83308 Trostberg (Germany); Breu, Josef, E-mail: Josef.Breu@uni-bayreuth.de [Lehrstuhl fuer Anorganische Chemie I, University of Bayreuth, D-95440 Bayreuth (Germany)] [Lehrstuhl fuer Anorganische Chemie I, University of Bayreuth, D-95440 Bayreuth (Germany)

2013-02-15

392

Substructure and in vitro assembly of the outer, structured layer of Spirillum serpens.  

PubMed

Electron micrographs of disintegrating units of the outer, structured (HP) layer of Spirillum serpens and of the isolated protein obtained from the HP layer revealed V- and Y-shaped and linear profiles. Interpretation of these forms, influenced by the seemingly trimeric form of the isolated protein and by biochemical data, suggested that the protein subunits were identical and Y shaped. A model is proposed for the assembly of the Y-shaped subunits to form a hexagon composed of two triads (three Y-shaped subunits each). The isolated protein adsorbed to a template of wall fragments (basal layer) to the same degree (over 90%) in high concentrations of Na+, K+ (5 X 10(-2) M), Ca2+, Sr2+, and Mg2+ (10(-2) M). At a lower concentration (4 x 10(-5) M) of the cations there was differential adsorption of the protein. Adsorption to the template in the presence of each cation, followed by dilution, also led to differential release of the protein. The adsorption of the protein to the basal layer was correlated with reassembly of the HP layer on the template. The mechanisms seem to be: (i) an ionic strength-dependent reassembly, which results in an HP layer loosely attached to the template (this layer is easily dissociated by decreasing the ionic strength); and (ii) a cation-specific (Ca2+ or Sr2+, but not Mg2+, Na+, or K+) mechanism independent of ionic strength. In this latter case, the specific cations presumably form strong noncovalent "salt" linkages between triads and the basal layer, enabling stable hexagons and the HP layer to be formed. PMID:1245458

Buckmire, F L; Murray, R G

1976-01-01

393

Nanocomposites of layered clays and cadmium sulfide: Similarities and differences in formation, structure and properties  

Microsoft Academic Search

Four series of nanocomposites of layered clays and cadmium sulfide have been prepared from laponite, saponite, hectorite and montmorillonite. These nanocomposites have been characterized in terms of the sizes and morphologies of the sulfide species, their textural features, and light absorption properties. From this detailed study, the similarities and differences in structure and properties of the four types of composite

Zhaohui Han; Huaiyong Zhu; Kyle R. Ratinac; Simon P. Ringer; Jeffrey Shi; Jiangwen Liu

2008-01-01

394

Kinetic and Structural Study of the Interaction of Myelin Basic Protein with Dipalmitoylphosphatidylglycerol Layers  

Microsoft Academic Search

The interaction of myelin basic protein (MBP) with dipalmitoylphosphatidylglycerol films has been investigated by means of a microgravimetric gauge sensitive to the changes in load and structural modifications of the layer deposited onto its surface. Fourier transform infrared spectroscopy, circular dichroism, and x-ray diffraction have confirmed protein uptake by the lipid phase along with a global disordering effect onto the

P. Facci; P. Cavatorta; L. Cristofolini; M. P. Fontana; A. Fasano; Paolo Riccio

2000-01-01

395

A physical model of the turbulent boundary layer consonant with mean momentum balance structure  

Microsoft Academic Search

Recent studies by the present authors have empirically and analytically explored the properties and scaling behaviours of the Reynolds averaged momentum equation as applied to wall-bounded flows. The results from these efforts have yielded new perspectives regarding mean flow structure and dynamics, and thus provide a context for describing flow physics. A physical model of the turbulent boundary layer is

Joe Klewicki; Paul Fife; Tie Wei; Pat McMurtry

2007-01-01

396

Adhesive properties of laminated alginate gels for tissue engineering of layered structures  

E-print Network

Adhesive properties of laminated alginate gels for tissue engineering of layered structures Jason P: A significant challenge in tissue engineering is the creation of tissues with stratified morphology or em are commonly used in tissue engineer- ing, in part due to their ability to form solid con- structs

397

Flow structure around a finite circular cylinder embedded in various atmospheric boundary layers  

Microsoft Academic Search

The flow structure around the free end of a finite circular cylinder (FC) embedded in various atmospheric boundary layers (ABLs) was investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with various oncoming ABLs. A finite circular cylinder with an aspect ratio (L\\/D) of 6 was mounted vertically on a flat plate. The Reynolds number

Cheol-Woo Park; Sang-Joon Lee

2002-01-01

398

High-frequency permeability in double-layered structure of amorphous Co-Ta-Zr films  

SciTech Connect

The high-frequency permeability of amorphous Co-Ta-Zr films was studied and the frequency dependence was described in terms of the eddy-current-loss formula. For the double-layered structure intervened with SiO/sub 2/ film, the degradation of the permeability became apparent with the decrease of SiO/sub 2/ thickness.

Ochiai, Y.; Hayakawa, M.; Hayashi, K.; Aso, K.

1988-06-01

399

The Propagation of Rayleigh Waves in Layered Piezoelectric Structures with Viscosity  

E-print Network

The Propagation of Rayleigh Waves in Layered Piezoelectric Structures with Viscosity Jinxiang Shen propagation in resonators with viscosity of materials for solutions which can be used for the estimations of the viscosity, which usually is not the ideal value we can obtain from material testing. Not hard to imagine

Wang, Ji

400

SPATIAL VARIATION OF THE EVOLUTION AND STRUCTURE OF THE URBAN BOUNDARY LAYER  

EPA Science Inventory

The spatial variation of the nocturnal urban boundary layer structure and the time variation of the mixing height, the nocturnal inversion top and strength after sunrise are presented for urban sites located upwind, downwind, and near the center of the heat island and for upwind ...

401

Special aspects of structure formation of a multicomponent layer in vacuum-arc plasma  

NASA Astrophysics Data System (ADS)

A phase boundary is an energy barrier to diffusing atoms. To decrease the diffusion rate, densely packed multicomponent structures were used. The correlation between the methods of obtaining and properties of multicomponent coating formed in a single fabrication cycle upon step-by-step synthesis of carbide of a substrate material and sputter deposition of layers of zirconium and zirconium carbide was investigated.

Bystrov, Yu. A.; Vetrov, N. Z.; Lisenkov, A. A.

2013-10-01

402

(±)-2,2-Dimethyl-5-oxotetrahydrofuran-3-carboxylic acid (terebic acid): a racemic layered structure.  

PubMed

A racemic crystalline form of terebic acid, C(7)H(10)O(4), which is an important industrial chemical compound, is reported for the first time. The crystal structure is stabilized by O-H···O and C-H···O hydrogen bonds which form racemic double layers parallel to (001). PMID:22850854

Santos, L M; Legendre, A O; Villis, P C M; Viegas, C; Doriguetto, A C

2012-08-01

403

The atomic structure of a bare buffer layer on SiC(0001) chemically resolved.  

PubMed

A chemical-specific photoelectron diffraction structure determination of a carbon rich buffer layer on SiC is reported. In addition to the long-range ripple of this surface, a local buckling in the hexagonal sublattice, which breaks the local range order symmetry, was unraveled. PMID:25245167

de Lima, Luis Henrique; Handschak, Dominique; Schönbohm, Frank; Landers, Richard; Westphal, Carsten; de Siervo, Abner

2014-11-14

404

a Monte Carlo Study of Carbon Monoxide Layers Adsorbed on Ionic Substrates:. Structures and Phase Transitions  

NASA Astrophysics Data System (ADS)

We have studied the order-disorder phase transitions of carbon monoxide layers adsorbed on sodium chloride and lithium flouride substrates using the Metropolis Monte Carlo method. The simulations have been performed in the temperature range from 5 K to 60 K. At low temperature and monolayer coverage, both of these systems form ordered phases which disorder as the temperature is increased. The transition temperature (Tc) is between 30 K and 35 K for CO/NaCl, and from 40 K to 45 K for CO/LiF. Below Tc, both systems have an ordered p(2 × 1) type structure due to correlated azimuthal orientations. Above Tc, both systems undergo a phase transition to an azimuthally disordered p(1 × 1) structure, i.e. one with no preferred orientation in the surface plane. The heat capacity shows a characteristic divergence at the transition temperature. Coverages of less than a monolayer of the CO/NaCl system have also been studied. The CO molecules are found to aggregate and form islands with an ordered structure in the middle of the islands. These islands also undergo an order-disorder transition but at lower temperatures. Multilayer systems were found to destabilize the p(2 × 1) structure of the bottommost layer in favor of a p(1 × 1) structure with the upper layers adopting the bulk structure.

Vu, Ngoc-Thanh; Jack, David B.

405

Growth and surface structure analysis of a new SiON single layer on SiC(0001)  

NASA Astrophysics Data System (ADS)

A new silicon oxynitride layer was formed on a 6H-SiC(0001) surface by a nitrogen oxide treatment. The atomic structure of this single layer on the SiC(0001) substrate was determined by means of low-energy electron diffraction (LEED) analysis. The surface layer has a (?{3}×?{3}) R30° periodicity. Its LEED I(E) spectra are different from those of the previously reported silicon oxynitride layer which has a Si4O5N3 composition [Phys. Rev. Lett. 98 (2007) 136105]. The best-fit structure has a single layer of Si2ON3 composition terminated by O bridges. The Si-N layer of the determined structure has the same structure as that in the Si4O5N3 surface. The obtained Si2O3 structure would be useful for preparing an ideal SiC-insulator interfaces with a low interfacial density of states.

Kohmatsu, Ryo; Nakagawa, Takeshi; Mizuno, Seigi

2014-10-01

406

Improvement of pin-type amorphous silicon solar cell performance by employing double silicon-carbide p-layer structure  

E-print Network

Received 30 October 2003; accepted 18 November 2003 We investigated a double silicon-carbide p-layer-a-SiC:H window layer is an advantage of this double p-layer structure. We achieved a considerable initialImprovement of pin-type amorphous silicon solar cell performance by employing double silicon

Kim, Yong Jung

407

Structural and electronic properties of manganese-doped Bi2Te3 epitaxial layers  

NASA Astrophysics Data System (ADS)

We show that in manganese-doped topological insulator bismuth telluride layers, Mn atoms are incorporated predominantly as interstitials in the van der Waals gaps between the quintuple layers and not substitutionally on Bi sites within the quintuple layers. The structural properties of epitaxial layers with Mn concentration of up to 13% are studied by high-resolution x-ray diffraction, evidencing a shrinking of both the in-plane and out-of plane lattice parameters with increasing Mn content. Ferromagnetism sets in for Mn contents around 3% and the Curie temperatures rises up to 15 K for a Mn concentration of 9%. The easy magnetization axis is along the c-axis perpendicular to the (0001) epilayer plane. Angle-resolved photoemission spectroscopy reveals that the Fermi level is situated in the conduction band and no evidence for a gap opening at the topological surface state with the Dirac cone dispersion is found within the experimental resolution at temperatures close to the Curie temperature. From the detailed analysis of the extended x-ray absorption fine-structure experiments (EXAFS) performed at the MnK-edge, we demonstrate that the Mn atoms occupy interstitial positions within the van der Waals gap and are surrounded octahedrally by Te atoms of the adjacent quintuple layers.

R?ži?ka, J.; Caha, O.; Holý, V.; Steiner, H.; Volobuiev, V.; Ney, A.; Bauer, G.; Ducho?, T.; Veltruská, K.; Khalakhan, I.; Matolín, V.; Schwier, E. F.; Iwasawa, H.; Shimada, K.; Springholz, G.

2015-01-01

408

Observations of the Thermodynamic Structure and Cloud Structure of the Atmospheric Boundary Layer over the Southern Ocean (Invited)  

NASA Astrophysics Data System (ADS)

Much of the radiation bias displayed in climate models over the Southern Ocean has been attributed to the representation of low and mid-elevation clouds including those within the atmospheric boundary layer (ABL). Limited in-situ observations from the Aerosol Characterization Experiment I (ACE-1) (Russell et al, 1998) and the Southern Ocean Cloud Experiment II (SOCEX II) (Jensen et al, 2000) suggest that the boundary layer structure is highly complex with multiple layers in spite of strong wind shear. An understanding of the dynamics of the ABL and maintenance of the boundary layer clouds remains elusive as a consequence of the lack of observations. The historic meteorological observations from Macquarie Island (54.50°S, 158.94°E), specifically the upper air soundings, have been employed to develop a climatology of the thermodynamic structure including an analysis of the winds and wind shear. Consistent with the field observations, the climatology suggests that a decoupling is commonly observed in the ABL, often with strong wind shear present across the interface. In the words of Russell et al (1998) a 'buffer layer' can routinely be observed. Ekman turning in the ABL is also commonly observed in the lowest few hundred meters of the ABL, suggesting that the wind shear is an important process just above the ocean surface. This climatology is then employed to evaluate the ABL structure of the ERA-Interim reanalysis and the high resolution ECMWF analysis from the two years of the Year of Tropical Convection. Not surprisingly, the poor resolution of these analysis products smooths out the fine scale structure observed in the historic observations; both the winds and the wind shear are reduced throughout the ABL. The analysis also produces a stronger inversion at the top of the ABL. Ekman turning is observed over a greater depth. The upper air soundings are then employed to evaluate the COSMIC soundings over the SO commonly finding little consistency between these two methods.

Siems, S. T.; Hande, L.; Belusic, D.; Manton, M.

2013-12-01

409

Structural and chemical characterization of the S layer of a Pseudomonas-like bacterium.  

PubMed Central

Sections and freeze-fractured preparations showed an S layer on the surface of Pseudomonas-like strain EU2. Polyacrylamide gel electrophoresis of cell envelopes extracted with 1% sodium dodecyl sulfate (SDS) at room temperature showed three proteins (45K, 55K, and 110K). The 55K protein was identified as the S-layer protein. Incubation in 1.5 M guanidine hydrochloride removed the S layer from cell envelopes and dissociated the structure into subunits. The soluble 55K protein reassembled into planar sheets upon removal of the guanidine hydrochloride by dialysis. Electron microscopy and image processing indicated that these sheets had p4 symmetry in projection with a lattice constant of 13.2 +/- 0.1 nm (corresponding to 9.3 nm between adjacent fourfold axes). In some instances these reassemblies appeared to form small three-dimensional crystals which gave particularly clear views of the structure in projection because of the superimposition of information from a number of layers. A model is proposed with molecules having rounded lobes connected by a narrower linker region and joining at the lobes to form the fourfold axes of the array. The pattern superficially resembles those of other bacterial S layers, such as those of Aeromonas salmonicida, Aeromonas hydrophila, and Azotobacter vinelandii. Extraction of cell envelopes with 1% SDS at 50 degrees C released the 110K protein from the envelopes and removed an amorphous backing layer from the S layer. The 45K protein displayed heat-modifiable migration in SDS-polyacrylamide gel electrophoresis and was insoluble in SDS at 50 degrees C or in high concentrations of guanidine hydrochloride, suggesting that it was associated with the peptidoglycan. Images FIG. 1 FIG. 2 FIG. 3 FIG. 4 FIG. 5 FIG. 6 PMID:2298701

Austin, J W; Stewart, M; Murray, R G

1990-01-01

410

Behavior of Turbulent Structures within a Mach 5 Mechanically Distorted Boundary Layer  

E-print Network

...................................................... 145 6.7. Conditional Structure of Near-Wall Flow ........................................................... 157 6.8. Origin of Retrograde Vortices ............................................................................. 165 6.9. Summary... of retrograde swirling strength r ci ? . ................................ 155 Figure 6.26 Cross-correlation of prograde and retrograde swirling strength, indicating the position of retrograde events relative to a reference prograde vortex...

Peltier, Scott Jacob

2013-08-05

411

Remarkable transition from rocksalt/perovskite layered structure to fluorite/rocksalt layered structure in rapidly cooled Ln2CuO4  

PubMed Central

Lanthanide cuprates of formula Ln2CuO4 exist in two principal forms, T and T? which are renowned for their exhibition at low temperatures of hole and electronic types of superconductivity, respectively. These structures differ primarily in the arrangement of oxygen between the perovskite layers and also in nature of the copper oxygen planes. The Cu-O distance in the T structure (~1.90 Å) is much shorter than the T? (1.97Å), reflecting a transition between partial Cu+ and partial Cu3+ character. In seeking to find compositions that bridge these two structure/electron carrier types, we observed the transition from a T structure to a T? type structure, resulting in the metastable form T? with slightly larger volume but similar character to T?. This transition from T to T? is associated with 5% increase in a and a 5% decrease in c parameters of the tetragonal unit cells, which results in disintegration of ceramic bodies. PMID:23514849

Patabendige, Chami N. K.; Azad, Abul K.; Connor, Paul A.; Rolle, Aurélie; Irvine, John T. S.

2013-01-01

412

Structural Analysis and Direct Imaging of Rotational Stacking Faults in Few-Layer Graphene Synthesized from Solid Botanical Precursor  

NASA Astrophysics Data System (ADS)

Here, we report the structural analysis and rotational stacking faults of few-layer graphene sheets derived by the controlled pyrolysis of the solid botanical derivative camphor (C10H16O). The second-order Raman spectra of the sheets show that the graphene layers are more than one single layer, and the numbers of layers can be controlled by adjusting the amount of camphor pyrolyzed. Transmission electron microscopy images show a minimum of 3 layers for thinner graphene sheets and a maximum of 12 layers for thicker graphene sheets. Low-voltage aberration-corrected high-resolution transmission electron microscopy is also carried out to gain insight into the hexagonal structure and stacking of graphene layers. The transmission electron microscopy study showed the presence of moiré patterns with a relative rotation between graphene layers.

Kalita, Golap; Wakita, Koichi; Umeno, Masayoshi

2011-07-01

413

Effect of cation on the layer structure of fatty acid salt Langmuir-Blodgett films  

NASA Astrophysics Data System (ADS)

Using surface x-ray difraction, we have studied the growth of Langmuir-Blodgett films of fatty acid salts containing lead, cadmium and calcium ions. The first layer always has a hexagonal structure (19.5Åper molecule) with the molecules extended perpendicular to the substrate. Structure of subsequent layers is dependent on the cation being used. Lead stearate and cadmium stearate form a distorted hexagonal structure, whereas calcium arachitate forms a triclinic structure.The molecules are tilted by ~8^o with respect to surface normal in all cases. The structure normal to plane is also dependent on the cation. While the lead samples show positional correlation normal to the surface equal to the size of the sample, the correlation only extends to two monolayers in the cadmium samples. In the calcium samples there is no correlation between layers. 1) A.Malik, M.K.Durbin, A.G.Richter, K.Huang and P.Dutta, Phys. Rev. B 52 654 (1995). 2)A.Malik, M.K.Durbin, A.G.Richter, K.Huang and P.Dutta, Thin Solid Films in press.

Malik, A.; Durbin, M. K.; Richter, A. G.; Dutta, P.; Kurnaz, M. L.; Sikes, H. D.; Schwartz, D. K.; Lee, P.

1996-03-01

414

Response of rocky invertebrate diversity, structure and function to the vertical layering of vegetation  

NASA Astrophysics Data System (ADS)

Macroalgae comprise a prominent part of the rocky benthos where many invertebrates develop, and are believed to be undergoing severe declines worldwide. In order to investigate how the vegetation structure (crustose, basal and canopy layers) contributes to the diversity, structure and function of benthic invertebrates, a total of 31 subtidal transects were sampled along the northeast Atlantic coast of Spain. Significant positive relationships were found between the canopy layer and faunal abundance, taxonomic diversity and functional group diversity. Canopy forming algae were also related to epiphytic invertebrates, medium size forms, colonial strategy and suspensivores. By contrast, basal algae showed negative relationships with all variables tested except for detritivores. Multivariate multiple regression analyses (DISTLM) point to crustose as well as canopy layers as the best link between seaweeds and invertebrate assemblage structure. A close relationship was found between taxonomic and functional diversities. In general, low levels of taxonomic redundancy were detected for functional groups correlated with vegetation structure. A conceptual model based on the results is proposed, describing distinct stages of invertebrate assemblages in relation to the vertical structure of vegetation.

Bustamante, María; Tajadura, Javier; Gorostiaga, José María; Saiz-Salinas, José Ignacio

2014-06-01

415

Self-assembly Columnar Structure in Active Layer of Bulk Heterojunction Solar Cell  

NASA Astrophysics Data System (ADS)

Bulk Heterojunction (BHJ) polymer solar cells are an area of intense interest due to their flexibility and relatively low cost. However, due to the disordered inner structure in active layer, the power conversion efficiency of BHJ solar cell is relatively low. Our research provides the method to produce ordered self-assembly columnar structure within active layer of bulk heterojunction (BHJ) solar cell by introducing polystyrene (PS) into the active layer. The blend thin film of polystyrene, poly (3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) at different ratio are spin coated on substrate and annealed in vacuum oven for certain time. Atomic force microscopy (AFM) images show uniform phase segregation on the surface of polymer blend thin film and highly ordered columnar structure is then proven by etching the film with ion sputtering. TEM cross-section technology is also used to investigate the column structure. Neutron reflectometry was taken to establish the confinement of PCBM at the interface of PS and P3HT. The different morphological structures formed via phase segregation will be correlated with the performance of the PEV cells to be fabricated at the BNL-CFN.

Pan, Cheng; Segui, Jennifer; Yu, Yingjie; Li, Hongfei; Akgun, Bulent; Satijia, Sushil. K.; Gersappe, Dilip; Nam, Chang-Yong; Rafailovich, Miriam

2012-02-01

416

Three-dimensional cell manipulation and patterning using dielectrophoresis via a multi-layer scaffold structure.  

PubMed

Cell manipulation is imperative to the areas of cellular biology and tissue engineering, providing them a useful tool for patterning cells into cellular patterns for different analyses and applications. This paper presents a novel approach to perform three-dimensional (3D) cell manipulation and patterning with a multi-layer engineered scaffold. This scaffold structure employed dielectrophoresis as the non-contact mechanism to manipulate cells in the 3D domain. Through establishing electric fields via this multi-layer structure, the cells in the medium became polarized and were attracted towards the interior part of the structure, forming 3D cellular patterns. Experiments were conducted to evaluate the manipulation and the patterning processes with the proposed structure. Results show that with the presence of a voltage input, this multi-layer structure was capable of manipulating different types of biological cells examined through dielectrophoresis, enabling automatic cell patterning in the time-scale of minutes. The effects of the voltage input on the resultant cellular pattern were examined and discussed. Viability test was performed after the patterning operation and the results confirmed that majority of the cells remained viable. After 7 days of culture, 3D cellular patterns were observed through SEM. The results suggest that this scaffold and its automated dielectrophoresis-based patterning mechanism can be used to construct artificial tissues for various tissue engineering applications. PMID:25501324

Chu, H K; Huan, Z; Mills, J K; Yang, J; Sun, D

2015-01-22

417

Ultrasonic guided waves for the detection of defects and corrosion in multi-layer structures  

NASA Astrophysics Data System (ADS)

Ultrasonic guided waves have received considerable attention over the last decade from both a theoretical and experimental point of view. Emphasis is now on technology transfer to the field. Emphasis in this paper is focused on the inspection of aircraft components. Several problem descriptions and laboratory simulation studies will be presented. Reference to such basic topics as dispersion curves, wave structure and group velocity will be made. Sample inspection problems include fuselage wall thinning, lap splice, tear strap, composite patch repair, transverse cracking in helicopter blade assemblies, skin to core delamination in honeycomb structures, crack detection from bolt holes in the transmission beam of a helicopter, landing gear, cracks in the second layer, and hidden corrosion in multiple layer structures. Sample results will be presented along with aspects of test protocol development.

Soley, L. E.; Rose, J. L.

2000-05-01

418

Layer speciation and electronic structure investigation of freestanding hexagonal boron nitride nanosheets  

NASA Astrophysics Data System (ADS)

Chemical imaging, thickness mapping, layer speciation and polarization dependence have been performed on single and multilayered (up to three layers and trilayered nanosheets overlapping to form 6 and 9 layers) hexagonal boron nitride (hBN) nanosheets by scanning transmission X-ray microscopy. Spatially-resolved XANES directly from freestanding regions of different layers has been extracted and compared with sample normal and 30° tilted configurations. Notably a double feature ?* excitonic state and a stable high energy ?* state were observed at the boron site in addition to the intense ?* excitonic state. The boron projected ?* DOS, especially the first ?* exciton, is sensitive to surface modification, particularly in the single layered hBN nanosheet which shows more significant detectable contaminants and defects such as tri-coordinated boron/nitrogen oxide. The nitrogen site has shown very weak or no excitonic character. The distinct excitonic effect on boron and nitrogen was interpreted to the partly ionic state of hBN. Bulk XANES of hBN nanosheets was also measured to confirm the spectro-microscopic STXM result. Finally, the unoccupied electronic structures of hBN and graphene were compared.Chemical imaging, thickness mapping, layer speciation and polarization dependence have been performed on single and multilayered (up to three layers and trilayered nanosheets overlapping to form 6 and 9 layers) hexagonal boron nitride (hBN) nanosheets by scanning transmission X-ray microscopy. Spatially-resolved XANES directly from freestanding regions of different layers has been extracted and compared with sample normal and 30° tilted configurations. Notably a double feature ?* excitonic state and a stable high energy ?* state were observed at the boron site in addition to the intense ?* excitonic state. The boron projected ?* DOS, especially the first ?* exciton, is sensitive to surface modification, particularly in the single layered hBN nanosheet which shows more significant detectable contaminants and defects such as tri-coordinated boron/nitrogen oxide. The nitrogen site has shown very weak or no excitonic character. The distinct excitonic effect on boron and nitrogen was interpreted to the partly ionic state of hBN. Bulk XANES of hBN nanosheets was also measured to confirm the spectro-microscopic STXM result. Finally, the unoccupied electronic structures of hBN and graphene were compared. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr04445b

WangEqual Contribution To This Work., Jian; Wang, Zhiqiang; Cho, Hyunjin; Kim, Myung Jong; Sham, T. K.; Sun, Xuhui

2015-01-01

419

Upper layer structure and variability of the Antarctic Circumpolar Current in the Drake Passage  

NASA Astrophysics Data System (ADS)

The spatiotemporal variability of the Antarctic Circumpolar Current (ACC) structure in the upper 100-800 m layer is analyzed at two sections in the Drake Passage. The existence of the Subantarctic and Polar Current superjets, formed due to the confluence of a few jets together, is confirmed. Peak eddy activity at the periphery of all the ACC jets is revealed, which demonstates intensive meridional eddy exchange of properties across the Passage. The ACC jets are strongly coherent in the vertical direction. The ACC upper layer transport intensifies over bottom relief rises because of jet acceleration during their crossing.

Gladyshev, S. V.

2014-07-01

420

Mass Conservation in Modeling Moisture Diffusion in Multi-Layer Carbon Composite Structures  

NASA Technical Reports Server (NTRS)

Moisture diffusion in multi-layer carbon composite structures is difficult to model using finite difference methods due to the discontinuity in concentrations between adjacent layers of differing materials. Applying a mass conserving approach at these boundaries proved to be effective at accurately predicting moisture uptake for a sample exposed to a fixed temperature and relative humidity. Details of the model developed are presented and compared with actual moisture uptake data gathered over 130 days from a graphite epoxy composite sandwich coupon with a Rohacell foam core.

Nurge, Mark A.; Youngquist, Robert C.; Starr, Stanley O.

2009-01-01

421

Multiscale structure, interfacial cohesion, adsorbed layers, and thermodynamics in dense polymer-nanoparticle mixtures.  

PubMed

We establish the existence and size of adsorbed polymer layers in miscible dense nanocomposites and their consequences on microstructure and the bulk modulus. Using contrast-matching small-angle neutron scattering to characterize all partial collective structure factors of polymers, particles, and their interface, we demonstrate qualitative failure of the random phase approximation, accuracy of the polymer reference site interaction model theory, ability to deduce the adsorbed polymer layer thickness, and high sensitivity of the nanocomposite bulk modulus to interfacial cohesion. PMID:22182034

Kim, So Youn; Schweizer, Kenneth S; Zukoski, Charles F

2011-11-25

422

Layer-dependent electronic structure of an atomically heavy two-dimensional dichalcogenide  

NASA Astrophysics Data System (ADS)

We report angle-resolved photoemission spectroscopic measurements of the evolution of the thickness-dependent electronic band structure of the atomically heavy two-dimensional layered dichalcogenide, tungsten diselenide (WS e2 ). Our data, taken on mechanically exfoliated WS e2 single crystals, provide direct evidence for shifting of the valence-band maximum from ? ¯ (multilayer WS e2 ) to K ¯ (single-layer WS e2 ). Further, our measurements also set a lower bound on the energy of the direct band gap and provide direct measurement of the hole effective mass.

Yeh, Po-Chun; Jin, Wencan; Zaki, Nader; Zhang, Datong; Liou, Jonathan T.; Sadowski, Jerzy T.; Al-Mahboob, Abdullah; Dadap, Jerry I.; Herman, Irving P.; Sutter, Peter; Osgood, Richard M.

2015-01-01

423

Domain-wall guided nucleation of superconductivity in hybrid ferromagnet-superconductor-ferromagnet layered structures.  

PubMed

Domain-wall superconductivity is studied in a superconducting Nb film placed between two ferromagnetic Co/Pd multilayers with perpendicular magnetization. The parameters of top and bottom ferromagnetic films are chosen to provide different coercive fields, so that the magnetic domain structure of the ferromagnets can be selectively controlled. From the dependence of the critical temperature Tc on the applied magnetic field H, we have found evidence for domain-wall superconductivity in this three-layered F/S/F structure for different magnetic domain patterns. The phase boundary, calculated numerically for this structure from the linearized Ginzburg-Landau equation, is in good agreement with the experimental data. PMID:16384256

Gillijns, W; Aladyshkin, A Yu; Lange, M; Van Bael, M J; Moshchalkov, V V

2005-11-25

424

Adaptive nonlinear polynomial neural networks for control of boundary layer/structural interaction  

NASA Technical Reports Server (NTRS)

The acoustic pressures developed in a boundary layer can interact with an aircraft panel to induce significant vibration in the panel. Such vibration is undesirable due to the aerodynamic drag and structure-borne cabin noises that result. The overall objective of this work is to develop effective and practical feedback control strategies for actively reducing this flow-induced structural vibration. This report describes the results of initial evaluations using polynomial, neural network-based, feedback control to reduce flow induced vibration in aircraft panels due to turbulent boundary layer/structural interaction. Computer simulations are used to develop and analyze feedback control strategies to reduce vibration in a beam as a first step. The key differences between this work and that going on elsewhere are as follows: that turbulent and transitional boundary layers represent broadband excitation and thus present a more complex stochastic control scenario than that of narrow band (e.g., laminar boundary layer) excitation; and secondly, that the proposed controller structures are adaptive nonlinear infinite impulse response (IIR) polynomial neural network, as opposed to the traditional adaptive linear finite impulse response (FIR) filters used in most studies to date. The controllers implemented in this study achieved vibration attenuation of 27 to 60 dB depending on the type of boundary layer established by laminar, turbulent, and intermittent laminar-to-turbulent transitional flows. Application of multi-input, multi-output, adaptive, nonlinear feedback control of vibration in aircraft panels based on polynomial neural networks appears to be feasible today. Plans are outlined for Phase 2 of this study, which will include extending the theoretical investigation conducted in Phase 2 and verifying the results in a series of laboratory experiments involving both bum and plate models.

Parker, B. Eugene, Jr.; Cellucci, Richard L.; Abbott, Dean W.; Barron, Roger L.; Jordan, Paul R., III; Poor, H. Vincent

1993-01-01