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1

'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

2

Origin of the biomechanical properties of wood related to the fine structure of the multi-layered cell wall.  

PubMed

In this study, a basic model is introduced to describe the biomechanical properties of the wood from the viewpoint of the composite structure of its cell wall. First, the mechanical interaction between the cellulose microfibril (CMF) as a bundle framework and the lignin-hemicellulose as a matrix (MT) skeleton in the secondary wall is formulated based on "the two phase approximation." Thereafter, the origins of (1) tree growth stress, (2) shrinkage or swelling anisotropy of the wood, and (3) moisture dependency of the Young's modulus of wood along the grain were simulated using the newly introduced model. Through the model formulation; (1) the behavior of the cellulose microfibril (CMF) and the matrix substance (MT) during cell wall maturation was estimated; (2) the moisture reactivity of each cell wall constituent was investigated; and (3) a realistic model of the fine composite structure of the matured cell wall was proposed. Thus, it is expected that the fine structure and internal property of each cell wall constituent can be estimated through the analyses of the macroscopic behaviors of wood based on the two phase approximation. PMID:12188209

Yamamoto, H; Kojima, Y; Okuyama, T; Abasolo, W P; Gril, J

2002-08-01

3

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

4

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

Microsoft Academic Search

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}Oâ and LiNiââCoââMnââOâ, which exhibit significant difference in thermal stabilities. Detailed TEM analysis reveals, for the first time, a complex core-shell-surface structure of the

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

2011-01-01

5

The Investigation of the Structure of the Signal of Geophysical and Astrophysical Origin in the Electromagnetic Field of the Atmosphere Boundary Surface Layer  

NASA Astrophysics Data System (ADS)

There has been developed a program - analytical system for investigation the structure of the signal in the spectral and time ranges caused by geophysical processes. The main purpose of developing such system is - to investigate the structure of the signal in the spectral and time ranges, caused by geophysical and astrophysical magnetic field of the atmosphere boundary surface layer and to find under - noise periodical processes of geophysical nature. The analysis of the exposing efficiency in the time ranges of the components corresponding to the periods of the moon gravitational tides showed high efficiency of the eigen vectors, chosen according to the criterion MKK which provides very slight probably of the false alarm of omitting displayed signs at the level 10-4.

Grunskaya, L.; Isakevich, V.; Yefimov, V.; Zakirov, A.; Rubay, D.; Leshchev, I.

6

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

7

Bismuth oxyhalide nanomaterials: layered structures meet photocatalysis.  

PubMed

In recent years, layered bismuth oxyhalide nanomaterials have received more and more interest as promising photocatalysts because their unique layered structures endow them with fascinating physicochemical properties; thus, they have great potential photocatalytic applications for environment remediation and energy harvesting. In this article, we explore the synthesis strategies and growth mechanisms of layered bismuth oxyhalide nanomaterials, and propose design principles of tailoring a layered configuration to control the nanoarchitectures for high efficient photocatalysis. Subsequently, we focus on their layered structure dependent properties, including pH-related crystal facet exposure and phase transformation, facet-dependent photoactivity and molecular oxygen activation pathways, so as to clarify the origin of the layered structure dependent photoreactivity. Furthermore, we summarize various strategies for modulating the composition and arrangement of layered structures to enhance the photoactivity of nanostructured bismuth oxyhalides via internal electric field tuning, dehalogenation effect, surface functionalization, doping, plasmon modification, and heterojunction construction, which may offer efficient guidance for the design and construction of high-performance bismuth oxyhalide-based photocatalysis systems. Finally, we highlight some crucial issues in engineering the layered-structure mediated properties of bismuth oxyhalide photocatalysts and provide tentative suggestions for future research on increasing their photocatalytic performance. PMID:24975748

Li, Jie; Yu, Ying; Zhang, Lizhi

2014-07-10

8

New insert layer structure OLEDs  

NASA Astrophysics Data System (ADS)

An insert layer structure organic electroluminescent device(OLED) based on a new luminescent material (Zn(salen)) is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn(salen)/Liq/LiF/Al/CuPc/NPD/Zn(salen)/Liq/LiF/Al. Effective insert electrode layers comprising LiF(1 nm)/Al(5 nm) are used as a single semitransparent mirror, and bilayer cathode LiF(1 nm)/Al(100 nm) is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.

Gao, Zhi-Xiang; Hao, Yu-Ying; Lei, Jun-Feng; Ma, Cheng; Xu, Bing-She

2008-05-01

9

Tomographic reconstruction of layered tissue structures  

NASA Astrophysics Data System (ADS)

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

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

2001-11-01

10

Wavy structures in compressible mixing layers  

NASA Astrophysics Data System (ADS)

Semi-periodic structures namely inclined wavy structures (IWS) are experimentally observed in compressible mixing layers at two convective Mach numbers ( M c = 0.11 and 0.47). Flow structures are visualized by the laserinduced planar laser Mie scattering (PLMS) technique. Two methods are developed to investigate the spatial distribution and geometry of IWS: (1) the dominant mode extraction (DME) method, to extract the dominant modes of IWS from the streamwise gray-level fluctuation, and (2) the phase tracking (PT) method, to identify the shape of IWS. The results suggest that pressure perturbations account for the formation of IWS in the initialmixing region and the joint effect of dilatation and coherent vortices enhances IWS in the welldeveloped region. The large transverse (cross-flow) scale of the IWS and their relation to coherent vortices (CV) indicate that the disturbance originated from CV in the mixing center propagates far into the free streams. The DME and the PT method are shown to be the effective tools to study the geometrical features of wavy structures in compressible shear flows.

Chen, Jun; Shi, Xiao-Tian; Wang, Tie-Jin; She, Zhen-Su

2013-10-01

11

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

12

Origins of serotonin innervation of forebrain structures  

NASA Technical Reports Server (NTRS)

The tryptophan hydroxylase activity and high-affinity uptake of (3H) serotonin ((3H)5-HT) were measured in five discrete brain regions of rats following lesions of the dorsal or median raphe nuclei. Dorsal raphe lesions reduced enzyme and uptake activity in the striatum only. Median raphe lesions reduced activities in the hippocampus, septal area, frontal cortex, and, to a lesser extent, in the hypothalamus. These data are consistent with the suggestion that the dorsal and median raphe nuclei are the origins of two separate ascending serotonergic systems - one innervating striatal structures and the other mesolimbic structures, predominantly. In addition, the data suggest that measurements of high-affinity uptake of (3H)5-HT may be a more reliable index of innervation than either 5-HT content or tryptophan hydroxylase activity.

Kellar, K. J.; Brown, P. A.; Madrid, J.; Bernstein, M.; Vernikos-Danellis, J.; Mehler, W. R.

1977-01-01

13

Two layer structure for reinforcing pothole repair  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

14

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

15

Structure of a swirling turbulent mixing layer  

NASA Astrophysics Data System (ADS)

A single-stream swirling turbulent mixing layer was produced in which the angular momentum instability acts over most of the layer for most of its development length. The instability is associated with a large increase in the level of the conventional Reynolds stresses over those in an unswirled mixing layer. This paper presents measurements of the three-dimensionality of the mean flow at one axial location well downstream of the origin. The output of a fixed hot-wire probe was ensemble-averaged to produce an approximation to the mean flow field that would be seen by a rotating observer. The main goals of this study were to establish the presence or absence of Taylor-Goertler vortices found in unstable laminar boundary layers. The variations in the mean velocities and Reynolds stresses are generally consistent with a bodily 'wrinkling' of the mixing layer, without a significant variation in the layer thickness. The wrinkling is most probably a result of circumferential variations in the initial boundary layer, which in turn originate at the swirl generator.

Wood, D. H.; Mehta, R. D.; Koh, S. G.

1992-03-01

16

Structure of reconnection layers in the magnetosphere  

Microsoft Academic Search

Magnetic reconnection can lead to the formation of observed boundary layers at the dayside magnetopause and in the nightside plasma sheet of the earth's magnetosphere. In this paper, the structure of these reconnection layers is studied by solving the one-dimensional Riemann problem for the evolution of a current sheet. Analytical method, resistive MHD simulations, and hybrid simulations are used. Based

Yu. Lin; L. C. Lee

1993-01-01

17

Structural Aspects of Layered Double Hydroxides  

Microsoft Academic Search

Layered double hydroxides (LDHs) have been known for a considerable time and have been\\u000a widely studied. The basic features of their structure, involving positively charged brucite-like\\u000a layers together with charge-balancing anions and water in interlayer galleries are well understood,\\u000a but some detailed aspects of their structure have been the subject of controversy in the literature.\\u000a In this article we review the

David G. Evans; Robert C. T. Slade

18

Structure of the low latitude boundary layer  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

19

Fine structure in midlatitude sporadic E layers  

NASA Astrophysics Data System (ADS)

Fine structure in midlatitude sporadic E layer patches or "clouds" is apparent in incoherent scatter observations from the Arecibo Radio Telescope. The fine structure is wavelike with predominant horizontal wavelengths as large as about 2-3km. We attribute the 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 cloud. 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, meter-scale waves in the layers can form.

Hysell, D. L.; Nossa, E.; Aveiro, H. C.; Larsen, M. F.; Munro, J.; Sulzer, M. P.; González, S. A.

2013-10-01

20

Origin and effect of nonlocality in a layered composite.  

SciTech Connect

A simple demonstration of nonlocality in a heterogeneous material is presented. By analysis of the microscale deformation of a two-component layered medium, it is shown that nonlocal interactions necessarily appear in a homogenized model of the system. Explicit expressions for the nonlocal forces are determined. The way these nonlocal forces appear in various nonlocal elasticity theories is derived. The length scales that emerge involve the constituent material properties as well as their geometrical dimen- sions. A peridynamic material model for the smoothed displacement eld is derived. It is demonstrated by comparison with experimental data that the incorporation of non- locality in modeling dramatically improves the prediction of the stress concentration in an open hole tension test on a composite plate.

Silling, Stewart Andrew

2014-01-01

21

Energy gap structure of layered superconductors  

SciTech Connect

We report the energy gap structure and density-of-states (DOS) of a model layered superconductor with one superconducting layer and one normal layer in a unit cell along the c-axis. In the physically interesting parameter range where the interlayer hopping strengths of the quasiparticles are comparable to the critical temperature, the peaks in the DOS curve do not correspond to the order parameter (OP) of the superconducting layer, but depend on the OP and the band dispersion in the c-direction in a complex manner. In contrast to a BCS superconductor, the DOS of layered systems have logarithmic singularities. Our simulated tunneling characteristics bear close resemblance to experimental results.

Liu, S.H. [Oak Ridge National Lab., TN (United States); Klemm, R.A. [Argonne National Lab., IL (United States)

1993-12-01

22

Energy gap structure of layered superconductors  

SciTech Connect

We report the energy gap structure and density-of-states (DOS) of a model layered superconductor with one superconducting layer and one normal layer in a unit cell along the c-axis. In the physically interesting parameter range where the interlayer hopping strengths of the quasiparticles are comparable to the critical temperature, the peaks in the DOS curve do not correspond to the order parameter (OP) of the superconducting layer, but depend on the OP and the band dispersion in the c-direction in a complex manner. In contrast to a BCS superconductor, the DOS of layered systems have logarithmic singularities. Our simulated tunneling characteristics bear close resemblance to experimental results.

Liu, S.H. [Oak Ridge National Lab., TN (United States); Klemm, R.A. [Argonne National Lab., IL (United States)

1993-11-01

23

Conserved variable analysis of the convective boundary layer thermodynamic structure over the tropical oceans  

NASA Technical Reports Server (NTRS)

An analysis of FGGE dropwindsonde data using conserved thermodynamic variables shows mixing line structures for the convective boundary layer over the equatorial Pacific. Deeper boundary layers show a double structure. Reversals of the gradients of mixing ratio and equivalent potential temperature above the boundary-layer top are present in all the averages and suggest that the origin of the air sinking into the boundary layer needs further study.

Betts, Alan K.; Albrecht, Bruce A.

1987-01-01

24

Thermal analysis of multiple-layer structures  

Microsoft Academic Search

The response of temperature to dc and steady-state ac power inputs in multiple-layer rectangular structures has been derived by solving analytically the problem of heat flow in three dimensions. Attention is focused on electrothermal integrated circuit (IC) substrates consisting of a semiconductor, a thermal conductor, and a thermal insulator. The analysis applies as well to single-layer systems, such as conventional

A. G. Kokkas

1974-01-01

25

Shear deformation plate continua of large double layered space structures  

NASA Technical Reports Server (NTRS)

A simple method is presented to model large rigid-jointed lattice structures as continuous elastic media with couple stresses using energy equivalence. In the analysis, the transition from the discrete system to the continuous media is achieved by expanding the displacements and the rotations of the nodal points in a Taylor series about a suitable chosen origin. The strain energy of the continuous media with couple stresses is then specialized to obtain shear deformation plate continua. Equivalent continua for single layered grids, double layered grids, and three-dimensional lattices are then obtained.

Hefzy, Mohamed Samir; Nayfeh, Adnan H.

1986-01-01

26

On the origin of charge-density waves in select layered transition-metal dichalcogenides  

NASA Astrophysics Data System (ADS)

The occurrence of charge-density waves in three selected layered transition-metal dichalcogenides—1T-TaS2, 2H-TaSe2 and 1T-TiSe2—is discussed from an experimentalist's point of view with a particular focus on the implications of recent angle-resolved photoelectron spectroscopy results. The basic models behind charge-density-wave formation in low-dimensional solids are recapitulated, the experimental and theoretical results for the three selected compounds are reviewed, and their band structures and spectral weight distributions in the commensurate charge-density-wave phases are calculated using an empirical tight-binding model. It is explored whether the origin of charge-density waves in the layered transition-metal dichalcogenides can be understood in a unified way on the basis of a few measured and calculated parameters characterizing the interacting electron-lattice system. It is found that the predictions of the standard mean-field model agree only semi-quantitatively with the experimental data and that there is not one generally dominant factor driving charge-density-wave formation in this family of layer compounds. The need for further experimental and theoretical scrutiny is emphasized.

Rossnagel, K.

2011-06-01

27

DUAL ORIGIN OF AEROSOLS IN TITAN'S DETACHED HAZE LAYER  

SciTech Connect

We have analyzed scattered light profiles from the Cassini Imaging Science Subsystem, taken at the limb and at several large phase angles. We also used results from an occultation observed by Ultraviolet Imaging Spectrograph in the ultraviolet. We found that particles responsible for the scattering in the detached haze have an effective radius around 0.15 {mu}m and the aerosol size distribution follows a power law (exponent about -4.5). We discuss these results along with microphysical constraints and thermal equilibrium of the detached haze, and we conclude that only a strong interaction with atmospheric dynamics can explain such a structure.

Cours, T.; Burgalat, J.; Rannou, P. [Groupe de Spectrometrie Moleculaire et Atmospherique (GSMA), CNRS UMR-6089, Universite de Reims Champagne-Ardenne, 51687 Reims Cedex 2 (France); Rodriguez, S.; Brahic, A. [Laboratoire AIM, Universite Paris 7, CNRS UMR-7158, CEA-Saclay/DSM/IRFU/SAp, 91191 Gif/Yvette (France); West, R. A., E-mail: thibaud.cours@univ-reims.fr [Jet Propulsion Laboratory M/S 169-237, Pasadena, CA 91109 (United States)

2011-11-10

28

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

29

Structural Origins of Fibrin Clot Rheology  

Microsoft Academic Search

The origins of clot rheological behavior associated with network morphology and factor XIIIa-induced cross-linking were studied in fibrin clots. Network morphology was manipulated by varying the concentrations of fibrinogen, thrombin, and calcium ion, and cross-linking was controlled by a synthetic, active-center inhibitor of FXIIIa. Quantitative measurements of network features (fiber lengths, fiber diameters, and fiber and branching densities) were made

Esther A. Ryan; Lyle F. Mockros; John W. Weisel; Laszlo Lorand

1999-01-01

30

The elasticity of structured surface liquid layers  

Microsoft Academic Search

The notion of “elasticity of structured surface liquid layers” has been introduced and considered in detail for the first\\u000a time. It is shown to be reasonably connected with the thermodynamics of condensed matter, allowing the logical derivation\\u000a of the general equations for the surface tension of liquids and solids which had been impossible before.

V. A. Marichev

2011-01-01

31

Earth Structure: Layers of the Earth  

NSDL National Science Digital Library

This interactive Flash allows users to explore Earth's structure and processes that occur on Earth such as earthquakes and plate tectonics and how scientists know the composition and state of the Earth's layers. Interactive diagrams and animations with supplementary information make this a helpful overview or review for high school and undergraduate introductory-level courses in physical geology and Earth sciences.

Smoothstone; Mifflin, Houghton

32

Fission fragment tracks in semiconducting layer structures  

Microsoft Academic Search

Fission fragment irradiation of a number of semiconducting materials establishes that permanent tracks are formed only when the conductivity is ?2 × 10 (ohm-cm). The intermittent nature of particle tracks is a characteristic of layer structures and further analysis confirms that there is one ‘defect’ per sandwich plane crossed by the fission particle. The intermittency is ascribed to the reduced

D. Vernon Morgan; L. T. Chadderton

1968-01-01

33

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.

Wardil, Lucas; Hauert, Christoph

2014-01-01

34

THREE POSSIBLE ORIGINS FOR THE GAS LAYER ON GJ 1214b  

SciTech Connect

We present an analysis of the bulk composition of the MEarth transiting super-Earth exoplanet GJ 1214b using planet interior structure models. We consider three possible origins for the gas layer on GJ 1214b: direct accretion of gas from the protoplanetary nebula, sublimation of ices, and outgassing from rocky material. Armed only with measurements of the planet mass (M{sub p} = 6.55 {+-} 0.98 M{sub +}), radius (R{sub p} = 2.678 {+-} 0.13 R{sub +}), and stellar irradiation level, our main conclusion is that we cannot infer a unique composition. A diverse range of planet interiors fits the measured planet properties. Nonetheless, GJ 1214b's relatively low average density ({rho}{sub p} = 1870 {+-} 400 kg m{sup -3}) means that it almost certainly has a significant gas component. Our second major conclusion is that under most conditions we consider GJ 1214b would not have liquid water. Even if the outer envelope is predominantly sublimated water ice, the envelope will likely consist of a super-fluid layer sandwiched between vapor above and plasma (electrically conductive fluid) below at greater depths. In our models, a low intrinsic planet luminosity ({approx_lt}2TW) is needed for a water envelope on GJ 1214b to pass through the liquid phase.

Rogers, L. A.; Seager, S. [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

2010-06-20

35

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

36

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

37

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

38

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

39

Phonon engineering in nanoscale layered structures  

NASA Astrophysics Data System (ADS)

Thermal conductivity in GaN/AlGaN heterostructures is investigated by solving the steady-state phonon Boltzman equation in the relaxation-time approximation using phonon density of state, average group velocity and phonon relaxation time. In this paper dispersion curves, group velocity, density of states of energy, relaxation time of phonon and finally thermal conduction of several types of symmetric and asymmetric nanostructures are simulated. It has been concluded that proper selection of layer widths yields minimum thermal conduction in the considered structure. Also, making the structure asymmetric, affects the thermal conduction.

Rostami, A.; Alizade, A.; Bagban, H.; Alizade, T.; Balazadeh Bahar, H.

2010-12-01

40

Modelling apparent low thermal inertia by layered structure  

NASA Astrophysics Data System (ADS)

Thermal inertia of planetary surface is a physical property that controls the diurnal and seasonal cycles in the surface temperature. At the same time it provides a unique window into geologic structure of the surface and the nature of geologic processes that shapes the planetary surface. Especially on Mars, it has been extensively derived from spacecraft remote-sensing observations. It shows existence of the area with very low thermal inertia in the equatorial and middle latitudes, which at the same time display complicated heterogeneous characteristics(Putzig and Mellon, 2007). This is one of the enigma about the surface state of Mars. Physical interpretation about the origin of this heterogeneous nature of the thermal inertia is needed. In this study, we discuss a possibility of apparent low thermal inertia when there exists a layered structure having contrasting thermal conductivities based on laboratory experiments. The layered structure we examined in the experiments are an acrylic plate(3.2mm , 5mm , 10mm in thickness) on top of Polystyrene foam block or vesiculated particle layer. In both cases the lower layer has lower thermal conductivity. They are heated periodically by a infrared lump from above(period from 10 to 600 sec.). We measured the temperature at the surface, bottom of the acrylic plate and inside the lower Polystyrene foam and the granular layer using the thermocouples and infrared thermometer. From amplitude of temperature variation, we estimated the thermal inertia. The important controlling factor in this experimental design is a thermal relaxation time of the surface layer, which is controlled by period of the applied heating cycle and the thickness. At the fixed layer thickness thermal structure changes drastically between the periods below and above the relaxation time. We estimated variation of apparent thermal inertia with period. In a homogeneous semi-infinite layer the amplitude of variation of the surface temperature induced by periodic heating under controlled situation is proportional to square root of the period and inversely proportional to the thermal inertia(Wang et al 2010). We utilized their formula to determine apparent thermal inertia. At the periods below thermal relaxation time unique value for thermal inertia was obtained while above the relaxation time it decreases even below the value of the lower layer. This is caused by the effect of finite layer thickness,which reduces thermal gradient in the surface layer. This leads to apparent low thermal inertia value. In our experiments we can demonstrate a simple layered structure; a thin layer having higher thermal conductivity on top of a layer with low thermal conductivity can produce apparent low thermal inertia. In the martian situation the thermal inertia is obtained mostly by diurnal heating cycle, which has a penetration depth(Thermal relaxation depth) of several to 10 cm. We discuss several geological processes to produce layered structure in this depth range in the presentation.

Yoshida, Akari; Toyota, Takenori; Kurita, Kei

2013-04-01

41

Origin and population structure of the Icelanders.  

PubMed

The Norse and Celtic contributions to the founding population of Iceland have been estimated previously on a pan-Icelandic basis using gene frequency data for the entire island. Accounts of the settlement of Iceland, however, suggest that different regions received different proportions of Norse and Celtic settlers, indicating the need to incorporate geographic variation into Icelandic admixture studies. A formal likelihood ratio test rejects the null hypothesis of regional homogeneity in admixture proportions. Here, regional admixture estimates for Iceland are reported; they are in agreement with the settlement pattern inferred from historical accounts. The western, northern, and southern regions of Iceland exhibit a moderate Celtic component, consistent with historical indications that these regions were settled by Norse Vikings from the British Isles, accompanied by Celtic wives and slaves. Eastern Iceland, believed to have been settled chiefly by Vikings from Scandinavia, is characterized by a large Norse component of admixture. The northwestern peninsula is also found to be predominantly Norse. Regional genetic data are used to elucidate the contemporary population structure of Iceland. The observed structure correlates well with patterns of Icelandic geography, history, economy, marriage, urbanization, and internal migration. The northeastern region is strongly isolated, the urbanized areas of the north and southwest are representative of the overall population, and the remaining regions exhibit small-scale variation about the genetic central tendency. A high level of genetic homogeneity is indicated (RST = 0.0005), consistent with the high internal migration rate of the Icelanders. A regression of mean per-locus heterozygosity on distance from the gene frequency centroid reveals a greater than average external gene flow into the eastern region, whereas the northwestern peninsula has received less than average external gene flow. Iceland is compared with possible founding populations and was found to have diverged markedly from other northern European countries. PMID:8449480

Williams, J T

1993-04-01

42

Critical layer structure in transitional Couette flows  

NASA Astrophysics Data System (ADS)

A recent theoretical/numerical investigation (Hall & Sherwin 2010) demonstrates that vortex-wave interaction in the critical layer of a roll-streak system provides a driving mechanism that will maintain the coupled flow system in near-equilibrium. In addition the predictions made for the variation in the strength of the roll-wave system with Reynolds number asymptotically match those for the lower-branch states observed by Wang et al. (2007) in the Couette system. We use DNS of transitional Couette flows to examine two key predictions made by the theory. First, for fixed spanwise periodic wavelength, we examine the maximum streamwise periodic wavelength for which the flow does not relaminarize, since the theory suggests a wavelength below which equilibrium cannot be maintained. Second, we extract Reynolds stresses in the critical layer, and examine their relationship to observed roll structures, since the theory predicts that rolls are maintained by tangential gradients of Reynolds stress within the critical layer. Hall P & Sherwin SJ (2010), Streamwise vortices in shear flows: harbingers of transition and the skeleton of coherent structures, J Fluid Mech. In press. Wang J, Gibson J & Waleffe F (2007), Lower branch coheremt states in shear flows: transition and control, Phys Rev Let 98, 204501.

Blackburn, Hugh; Hall, Philip; Sherwin, Spencer

2010-11-01

43

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

NASA Astrophysics Data System (ADS)

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 ~30 emu/cm3. 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.

2012-08-01

44

A challenging interpretation of a hexagonally layered protein structure.  

PubMed

The carboxysome is a giant protein complex that acts as a metabolic organelle in cyanobacteria and some chemoautotrophs. Its outer structure is formed by the assembly of thousands of copies of hexameric shell protein subunits into a molecular layer. The structure determination of a CcmK1 shell protein mutant (L11K) from the ?-carboxysome of the cyanobacterium Synechocystis PCC6803 led to challenges in structure determination. Twinning, noncrystallographic symmetry and packing of hexameric units in a special arrangement led to initial difficulties in space-group assignment. The correct space group was clarified after initial model refinement revealed additional symmetry. This study provides an instructive example in which broken symmetry requires a new choice of unit-cell origin in order to identify the highest symmetry space group. An additional observation related to the packing arrangement of molecules in this crystal suggests that these hexameric shell proteins might have lower internal symmetry than previously believed. PMID:24419393

Thompson, Michael C; Yeates, Todd O

2014-01-01

45

Unstable flow structures in the Blasius boundary layer.  

PubMed

Finite amplitude coherent structures with a reflection symmetry in the spanwise direction of a parallel boundary layer flow are reported together with a preliminary analysis of their stability. The search for the solutions is based on the self-sustaining process originally described by Waleffe (Phys. Fluids 9, 883 (1997)). This requires adding a body force to the Navier-Stokes equations; to locate a relevant nonlinear solution it is necessary to perform a continuation in the nonlinear regime and parameter space in order to render the body force of vanishing amplitude. Some states computed display a spanwise spacing between streaks of the same length scale as turbulence flow structures observed in experiments (S.K. Robinson, Ann. Rev. Fluid Mech. 23, 601 (1991)), and are found to be situated within the buffer layer. The exact coherent structures are unstable to small amplitude perturbations and thus may be part of a set of unstable nonlinear states of possible use to describe the turbulent transition. The nonlinear solutions survive down to a displacement thickness Reynolds number Re * = 496 , displaying a 4-vortex structure and an amplitude of the streamwise root-mean-square velocity of 6% scaled with the free-stream velocity. At this Re* the exact coherent structure bifurcates supercritically and this is the point where the laminar Blasius flow starts to cohabit the phase space with alternative simple exact solutions of the Navier-Stokes equations. PMID:24771239

Wedin, H; Bottaro, A; Hanifi, A; Zampogna, G

2014-04-01

46

Structural properties of replication origins in yeast DNA sequences  

NASA Astrophysics Data System (ADS)

Sequence-dependent DNA flexibility is an important structural property originating from the DNA 3D structure. In this paper, we investigate the DNA flexibility of the budding yeast (S. Cerevisiae) replication origins on a genome-wide scale using flexibility parameters from two different models, the trinucleotide and the tetranucleotide models. Based on analyzing average flexibility profiles of 270 replication origins, we find that yeast replication origins are significantly rigid compared with their surrounding genomic regions. To further understand the highly distinctive property of replication origins, we compare the flexibility patterns between yeast replication origins and promoters, and find that they both contain significantly rigid DNAs. Our results suggest that DNA flexibility is an important factor that helps proteins recognize and bind the target sites in order to initiate DNA replication. Inspired by the role of the rigid region in promoters, we speculate that the rigid replication origins may facilitate binding of proteins, including the origin recognition complex (ORC), Cdc6, Cdt1 and the MCM2-7 complex.

Cao, Xiao-Qin; Zeng, Jia; Yan, Hong

2008-09-01

47

Investigating the origin of intense photoluminescence in Si capping layer on Ge1-xSnx nanodots by transmission electron microscopy  

NASA Astrophysics Data System (ADS)

The authors investigated the annealing effects on atomic structures and elemental compositions in a stacking structure, Si capping layer on Ge1-xSnx nanodots on Si substrate covered with ultrathin SiO2 film, to clarify the origin of intense photoluminescence at ~0.8 eV from the structure, using transmission electron microscopy. After the annealing, it was found that decay of Ge1-xSnx nanodots, formation of SiOx precipitates embedded in Si-rich Si1-xGex layer at the Si cap/Si substrate interface, formation of SnO2 nanoparticles on the oxidized surface of the Si capping layer, and morphological change of dislocations in the Si capping layer occur. Reaction products that appear as a result of the movement of dislocations can be related to the origin of intense photoluminescence.

Kikkawa, Jun; Nakamura, Yoshiaki; Fujinoki, Norihito; Ichikawa, Masakazu

2013-02-01

48

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

Microsoft Academic Search

The crystal structure of a new mineral britvinite Pb7.1Mg4.5(Si4.8Al0.2O14)(BO3)(CO3)[(BO3)0.7(SiO4)0.3](OH, F)6.7 from the Lángban iron-manganese skarn deposit (Värmland, Sweden) is determined at T = 173 K using X-ray diffraction (Stoe IPDS diffractometer, ?MoK?, graphite monochromator, 2?max = 58.43°, R = 0.052 for 6262 reflections). The main crystal data are as follows: a = 9.3409(8) Å, b = 9.3579(7) Å, c =

O. V. Yakubovich; W. Massa; N. V. Chukanov

2008-01-01

49

Structured Water Layers Adjacent to Biological Membranes  

PubMed Central

Water amid the restricted space of crowded biological macromolecules and at membrane interfaces is essential for cell function, though the structure and function of this “biological water” itself remains poorly defined. The force required to remove strongly bound water is referred to as the hydration force and due to its widespread importance, it has been studied in numerous systems. Here, by using a highly sensitive dynamic atomic force microscope technique in conjunction with a carbon nanotube probe, we reveal a hydration force with an oscillatory profile that reflects the removal of up to five structured water layers from between the probe and biological membrane surface. Further, we find that the hydration force can be modified by changing the membrane fluidity. For 1,2-dipalmitoyl-sn-glycero-3-phosphocholine gel (L?) phase bilayers, each oscillation in the force profile indicates the force required to displace a single layer of water molecules from between the probe and bilayer. In contrast, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine fluid (L?) phase bilayers at 60°C and 1,2-dioleoyl-sn-glycero-3-phosphocholine fluid (L?) phase bilayers at 24°C seriously disrupt the molecular ordering of the water and result predominantly in a monotonic force profile.

Higgins, Michael J.; Polcik, Martin; Fukuma, Takeshi; Sader, John E.; Nakayama, Yoshikazu; Jarvis, Suzanne P.

2006-01-01

50

Structured water layers adjacent to biological membranes.  

PubMed

Water amid the restricted space of crowded biological macromolecules and at membrane interfaces is essential for cell function, though the structure and function of this "biological water" itself remains poorly defined. The force required to remove strongly bound water is referred to as the hydration force and due to its widespread importance, it has been studied in numerous systems. Here, by using a highly sensitive dynamic atomic force microscope technique in conjunction with a carbon nanotube probe, we reveal a hydration force with an oscillatory profile that reflects the removal of up to five structured water layers from between the probe and biological membrane surface. Further, we find that the hydration force can be modified by changing the membrane fluidity. For 1,2-dipalmitoyl-sn-glycero-3-phosphocholine gel (Lbeta) phase bilayers, each oscillation in the force profile indicates the force required to displace a single layer of water molecules from between the probe and bilayer. In contrast, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine fluid (Lalpha) phase bilayers at 60 degrees C and 1,2-dioleoyl-sn-glycero-3-phosphocholine fluid (Lalpha) phase bilayers at 24 degrees C seriously disrupt the molecular ordering of the water and result predominantly in a monotonic force profile. PMID:16798815

Higgins, Michael J; Polcik, Martin; Fukuma, Takeshi; Sader, John E; Nakayama, Yoshikazu; Jarvis, Suzanne P

2006-10-01

51

Characteristic Lifelength of Coherent Structure in the Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

A characteristic lifelength is defined by which a Gaussian distribution is fit to data correlated over a 3 sensor array sampling streamwise sidewall pressure. The data were acquired at subsonic, transonic and supersonic speeds aboard a Tu-144. Lifelengths are estimated using the cross spectrum and are shown to compare favorably with Efimtsov's prediction of correlation space scales. Lifelength distributions are computed in the time/frequency domain using an interval correlation technique on the continuous wavelet transform of the original time data. The median values of the lifelength distributions are found to be very close to the frequency averaged result. The interval correlation technique is shown to allow the retrieval and inspection of the original time data of each event in the lifelength distribution, thus providing a means to locate and study the nature of the coherent structure in the turbulent boundary layer. The lifelength data can be converted to lifetimes using the convection velocity. The lifetime of events in the time/frequency domain are displayed in Lifetime Maps. The primary purpose of the paper is to validate these new analysis techniques so that they can be used with confidence to further characterize coherent structure in the turbulent boundary layer.

Palumbo, Daniel L.

2006-01-01

52

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

53

The origin, evolution and structure of the protein world.  

PubMed

Contemporary protein architectures can be regarded as molecular fossils, historical imprints that mark important milestones in the history of life. Whereas sequences change at a considerable pace, higher-order structures are constrained by the energetic landscape of protein folding, the exploration of sequence and structure space, and complex interactions mediated by the proteostasis and proteolytic machineries of the cell. The survey of architectures in the living world that was fuelled by recent structural genomic initiatives has been summarized in protein classification schemes, and the overall structure of fold space explored with novel bioinformatic approaches. However, metrics of general structural comparison have not yet unified architectural complexity using the 'shared and derived' tenet of evolutionary analysis. In contrast, a shift of focus from molecules to proteomes and a census of protein structure in fully sequenced genomes were able to uncover global evolutionary patterns in the structure of proteins. Timelines of discovery of architectures and functions unfolded episodes of specialization, reductive evolutionary tendencies of architectural repertoires in proteomes and the rise of modularity in the protein world. They revealed a biologically complex ancestral proteome and the early origin of the archaeal lineage. Studies also identified an origin of the protein world in enzymes of nucleotide metabolism harbouring the P-loop-containing triphosphate hydrolase fold and the explosive discovery of metabolic functions that recapitulated well-defined prebiotic shells and involved the recruitment of structures and functions. These observations have important implications for origins of modern biochemistry and diversification of life. PMID:19133840

Caetano-Anollés, Gustavo; Wang, Minglei; Caetano-Anollés, Derek; Mittenthal, Jay E

2009-02-01

54

Mercury: Remote Estimation of Surface Layer Structure  

NASA Astrophysics Data System (ADS)

Results of the optical observations of Mercury and the Moon confirm the close simi- larity of photometric properties of the bodies. Experience of lunar studies shows that space weathering processes on the Mercury (such as micrometeorite bombardment, solar wind ion bombardment etc.) can form properties of the upper layer of regolith. The amount of fused glassy particles and others agglutinates in the lunar upper layer is the direct index of the soil reworking caused be the micrometeorite bombardment. Besides, this micrometeorite bombardment is also responsible for the mechanical pro- cess through which the large particles are broken down into smaller ones. For lunar re- golith was showed that increasingly mature soils become progressively finer-grained, better-sorted, and composed of a greater proportion of agglutinates. The increasing rate of the fused glassy fragments, of agglutinates, and of fine size fraction in the regolith during its space weathering affects the polarization of the light reflected by an exposed lunar or Mercurian soil. Therefore, polarimetric properties of the regolith may be modified by the soil reworking process in the course of time. Comparison of the lunar and Mercurian optic observations confirms the remarkable similarity of the polarimetric properties of Mercury and the Moon. From of summary of polarization measurements of whole disk of Mercury it is possible to conclude that maturity of the soil on the Mercurian surface in scale of whole disk is similar to one in large old craters on the lunar highland. Comparison of the lunar and Mercurian disk-integrated photometric functions indicates the likeness of the surface layer structures of the bod- ies. Analysis of the phase curve inclination and magnitude of the opposition effect shows that Mercurian relief in scale of meter details is smoother than lunar one. It was measured brightness of number of small plots (10x10 cm) on the lunar surface (Luna-13 data). The range of phase angles was from 68 to 75 deg. These values close correlate with corresponding part of the Mercurian disk-integrated phase function. ItSs possible if Mercurian phase function received from Earth-based telescopes and lunar one received in cm-scale is coincided the structures of regolith may be similar in both cases. These conclusions may be used for planning BepiColombo mission. This work was supported by INTAS-ESA grant No. 99-00403.

Shevchenko, V. V.

55

Structure of the surface layer of the methanogenic archaean Methanosarcina acetivorans  

PubMed Central

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 ?-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.

2012-01-01

56

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

57

Acoustic emissions from unsteady transitional boundary layer flow structures  

NASA Astrophysics Data System (ADS)

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 improving models to include recent computational and experimental statistics, evaluation of model sensitivities to input parameters, and applicability to situations of engineering relevance. Prior efforts to model wall pressure fluctuation statistics resulting from boundary layer transition zone flow structures allow further development of direct radiation prediction codes. Several refinements were made to theoretical models for directly radiated noise based upon the Liepmann analogy for fluctuating displacement thickness including the incorporation of a semi- empirically derived space-time correlation function for the intermittency indicator. A similar two-fluids model uses a Lighthill acoustic analogy. Radiation by vortex structures and direct numerical simulation methods are reviewed to help define their useful role in predicting sound radiation from transition. The role of pressure gradient in axisymmetric body flows, flat plate flows, and over hydrofoils is investigated. A quiet airflow facility was developed to measure the direct acoustic radiation from a naturally transitioning boundary layer. Real-time acoustic intensity measurement instrumentation was developed if measurements of isolated spots in otherwise laminar flow had been necessary. This technique uses a hot film signal from the transition structure to obtain the coherent output intensity (COI). Model predictions are compared to the measured acoustic radiation from a naturally transitioning boundary layer. Radiated noise measurements isolating the direct transition zone radiation demonstrated similar dependence with axial location within the transition zone as previous wall pressure measurements. The measurements suggest that radiation from transition flow structures is multipolar and has low radiation efficiency. Transition noise per unit area is greater than TBL noise per unit area. Thus, the contribution to overall directly radiated flow noise from the transition zone in typical engineering applications is negligible compared to the radiation from the much larger area of fully turbulent flow.

Marboe, Richard Chostner

58

The origins of planar magnetic structures in the solar wind  

NASA Technical Reports Server (NTRS)

It is shown that the solar-wind settings of planar magnetic structures (PMSs) are generally inconsistent with their interpretation by Nakagawa et al. (1989) as magnetic loops or tongues resulting from newly emerging magnetic flux in the photosphere. It is suggested that PMS events have two origins: (1) compression and/or draping of preexisting magnetic structures on the leading edge of high-speed streams, especially ahead of coronal mass ejections; and (2) discontinuities near the heliospheric current sheet.

Neugebauer, M.; Clay, D. R.; Gosling, J. T.

1993-01-01

59

On the physical origin of conical bubble structure under an ultrasonic horn.  

PubMed

The cavitation field generated by an ultrasonic horn at low frequency and high power is known to self-organize into a conical bubble structure. The physical mechanism at the origin of this bubble structure is investigated using numerical simulations and acoustic pressure measurements. The thin bubbly layer lying at horn surface is shown to act as a nonlinear thickness resonator that amplifies acoustic pressure and distorts acoustic waveform. This mechanism explains the self-stabilization of the conical bubble structure as well as the generation of shock wave and the focusing at very short distance. PMID:20371200

Dubus, Bertrand; Vanhille, Christian; Campos-Pozuelo, Cleofé; Granger, Christian

2010-06-01

60

Dynamic failure characteristics in layered materials and structures  

Microsoft Academic Search

Systematic investigations were carried out to understand the general nature of dynamic failure mechanisms in layered materials and structures. A series of impact experiments on model-layered specimens were conducted using high-speed photography and dynamic photoelasticity. For the first time, the sequence and interaction of two major dynamic failure modes in layered materials-inter-layer cracking and intra-layer cracking were revealed in real

Luoyu Roy Xu

2002-01-01

61

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

62

Structural failure of two-density-layer cohesionless biaxial ellipsoids  

NASA Astrophysics Data System (ADS)

This paper quantitatively evaluates structural failure of biaxial cohesionless ellipsoids that have a two-density-layer distribution. The internal density layer is modeled as a sphere, while the external density layer is the rest of the part. The density is supposed to be constant in each layer. The present study derives averaged stresses over the whole volume of these bodies and uses limit analysis to determine their global failure. The upper bound of global failure is considered in terms of the size of the internal layer and the aspect ratio of the shape. The result shows that the two-density-layer causes the body to have different strength against structural failure.

Hirabayashi, Masatoshi

2014-07-01

63

Divergent fate and origin of neurosphere-like bodies from different layers of the gut.  

PubMed

Enteric neural stem cells (ENSCs) are a population of neural crest-derived multipotent stem cells present in postnatal gut that may play an important role in regeneration of the enteric nervous system. In most studies, these cells have been isolated from the layer of the gut containing the myenteric plexus. However, a recent report demonstrated that neurosphere-like bodies (NLBs) containing ENSCs could be isolated from mucosal biopsy specimens from children, suggesting that ENSCs are present in multiple layers of the gut. The aim of our study was to assess whether NLBs isolated from layers of gut containing either myenteric or submucosal plexus are equivalent. We divided the mouse small intestine into two layers, one containing myenteric plexus and the other submucosal plexus, and assessed for NLB formation. Differences in NLB density, proliferation, apoptosis, neural crest origin, and phenotype were investigated. NLBs isolated from the myenteric plexus layer were present at a higher density and demonstrated greater proliferation, lower apoptosis, and higher expression of nestin, p75, Sox10, and Ret than those from submucosal plexus. Additionally, they contained a higher percentage of neural crest-derived cells (99.4 ± 1.5 vs. 0.7 ± 1.19% of Wnt1-cre:tdTomato cells; P < 0.0001) and produced more neurons and glial cells than those from submucosal plexus. NLBs from the submucosal plexus layer expressed higher CD34 and produced more smooth muscle-like cells. NLBs from the myenteric plexus layer contain more neural crest-derived ENSCs while those from submucosal plexus appear more heterogeneous, likely containing a population of mesenchymal stem cells. PMID:22361728

Becker, Laren; Kulkarni, Subhash; Tiwari, Gunjan; Micci, Maria-Adelaide; Pasricha, Pankaj Jay

2012-05-01

64

Guided Wave Inspection of Multi-Layered Structures  

NASA Astrophysics Data System (ADS)

This study investigates the utilization of guided waves for inspecting structures that consist of multiple layers. Advances have been made in recent years using guided waves to inspect single layer structures, such as pipes, tubes, and aircraft structures. Multi-layered structures present many new aspects to guided wave propagation. A theoretical understanding of what modes exist, how do the modes behave, and what factors influence them needs to be acquired for many applications. Experiments must be carried out to evaluate potential for practical applications. Examples of practical applications include coated pipes, composites, diffusion bonded aircraft structures, and microelectronic structures. This work is a fundamental study of ultrasonic guided waves in multi-layered plates. Experiments were conducted on multi-layered plates to demonstrate defect detection in layer of interest of a multi-layered structure by preferentially exciting modes with sufficient energy in that layer. Analysis of the dispersion curves show that some modes are more attractive candidates than others based on their displacements and energy distribution across the structure. Experimental results show that sweeping frequency and phase velocity can be performed to find suitable modes for inspecting a layer of interest for a given multi-layered structure.

Quarry, M. J.

2004-02-01

65

Structural origins of dynamical heterogeneity in colloidal gels  

NASA Astrophysics Data System (ADS)

We show by resolving single-particle dynamics as a function of contact number that dynamical heterogeneity in depletion colloidal gels must have more than one structural origin. Although the magnitude of dynamical heterogeneity of weak gels with cluster structure and strong gels with string structure is similar, the dependence of particle localization on contact number differs significantly in each. The observed transition between contact number dependent and independent dynamics for the weak and strong gels is abrupt. The results suggest that spatially heterogeneous dynamics cannot be a complete explanation of the dynamical heterogeneity of colloidal gels.

Dibble, Clare J.; Kogan, Michael; Solomon, Michael J.

2008-05-01

66

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

67

Experimental study of vortex structure in a plane mixing layer  

Microsoft Academic Search

Entrainment and mixing in shear layers are results of the behavior of large coherent structures that are formed in these flows. Therefore, an understanding of the structure of these large vortices is fundamental to the understanding and predictions of these flows. In this study, coherent structures in a plane shear layer were investigated. A new technique for cine flow visualization

Sanjay Vinayak Sherikar

1987-01-01

68

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

69

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers  

PubMed Central

La0.7Sr0.3MnO3 is a conducting ferromagnet at room temperature. Combined with thin SrTiO3 layers, the resulting heterostructures could be used as highly spin-polarized magnetic-tunnel-junction memories. However, when shrunk to dimensions below an apparent critical thickness, the structures become insulating and ferromagnetic ordering is suppressed. Interface spin and charge modulations are thought to create an interfacial dead layer, thus fundamentally limiting the use of this material in atomic-scale devices. The thickness of this dead layer, and whether it is intrinsic, is still controversial. Here we use atomic-resolution electron spectroscopy to demonstrate that the degradation of the magnetic and transport properties of La0.7Sr0.3MnO3/SrTiO3 multilayers correlates with atomic intermixing at the interfaces, and the presence of extended two-dimensional cation defects in the La0.7Sr0.3MnO3 layers (in contrast to three-dimensional precipitates in thick films). When these extrinsic defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in five-unit-cell-thick manganite layers in superlattices, placing the upper limit for any intrinsic dead layer at two unit cells per interface.

Kourkoutis, L. Fitting; Song, J. H.; Hwang, H. Y.; Muller, D. A.

2010-01-01

70

An origin of marginal reversal of the Fongen-Hyllingen layered intrusion by prolonged magma emplacement  

NASA Astrophysics Data System (ADS)

The ~100 m thick marginal zone of the Fongen-Hyllingen Intrusion (FHI) consists of nonlayered, highly iron-enriched ferrodiorites that are overlain by a ~6 km thick layered sequence of gabbroic to dioritic rocks of the Layered Series. From the base upwards the marginal zone become more primitive as exemplified by a significant increase in whole-rock MgO, Mg-number, and normative An. The reverse trends are also evident from an upward increase in An-content of plagioclase (from ~30 to ~43 at.%) and Mg-number of amphibole (from ~9 to ~23 at.%) and clinopyroxene (from ~23 to ~37 at.%). The marginal zone is abruptly terminated at the contact with the overlying Layered Series as is evident from a step-like increase in Mg-number of mafic minerals and An-content of plagioclase, as well as a sharp increase in whole-rock MgO and Mg-number in overlying olivine gabbronorites of the Layered Series. Based on these features the marginal zone of the FHI can be interpreted as an aborted marginal reversal. Reverse trends in whole-rock and mineral compositions, as well as a sharp break in these parameters are indicative of its formation in an open system with the involvement of the prolonged emplacement of magma that became increasingly more primitive. Such development of the marginal reversal was interrupted by the emplacement of a major influx of more primitive magma that produced the Layered Series. The open system evolution of a basaltic magma chamber may represent a general mechanism for the origin of marginal reversals in mafic sills and layered intrusions.

Egorova, V.; Latypov, R.

2012-04-01

71

The origin ofsubdural neomembranes. II. Fine structural of neomembranes.  

PubMed Central

A comparison of the fine structure of subdural neomembranes with the fine structural organization of the normal human dura-arachnoid interface discloses that neomembranes are not de novo proliferations of tissue from a smooth inner dural surface. Rather, a neomembrane is the result of proliferation and excessive thickening of the normal layer of dural border cells. On proliferation, the dural border cells form multilayered tiers and clusters of cells, transfixed by capillaries, with collagen fibrils and elastic fibers between them. Capillaries and collagen fibrils are absent from the normal interface layer. Pathogenetic concepts of chronic subdural hematoma need to be revised. Any pathologic condition inducing cleavage of tissue within the dural border layer at dura-arachnoid interface will be followed by proliferation of fural border cells with production of a neomembrane. There is no compelling reason to postulate that proliferation of the border cell layer is always secondary to traumatic hemorrhage. Images Figure 10 Figure 11 Figure 4 Figure 5 Figure 7 Figure 8 Figure 9 Figure 12 Figure 13 Figure 14 Figure 1 Figure 2 Figure 3 Figure 6

Friede, R. L.; Schachenmayr, W.

1978-01-01

72

Dynamic rolling process of tires as layered structures  

Microsoft Academic Search

Due to inner pressure the tire is a prestressed system of cord layers. The cord layers are covered by rubber layers. The whole structure is coated by a wear-resistive thread and a soft side wall coating. Serving as a boundary condition at the cord ends is a steel ring at both sides of the wheel rim. To stiffen the thread

F. Böhm

1996-01-01

73

Dynamic response and failure in layered structures and composites  

Microsoft Academic Search

Layered structures or media and their constituent materials—composite laminates have been studied. Topics discussed include attenuation of stress wave propagation in periodically layered elastic media, pre-stress effect on layered plates consisting of a hard and brittle phase (glass) and a soft phase (aluminum) subjected to dynamic contact loading, simulation of the conic fracture in the brittle phase and investigation of

Chenghua Han

2000-01-01

74

Porous-layer capillary gas chromatography columns with a hybrid structured sorbent based on alkyltriethoxysilane  

NASA Astrophysics Data System (ADS)

Porous-layer capillary columns with a hybrid organic-inorganic sorbent based on structured silica are described. Properties of the prepared columns are discussed. Examples of separating C1-C4 hydrocarbons and a mixture of solvents on the obtained columns are presented. It is shown that changes in the organic component content of the original sol make it possible to control the selectivity of porous-layer columns.

Patrushev, Yu. V.; Sidelnikov, V. N.

2013-04-01

75

Origin of chaotic structures on New World Island, Newfoundland  

SciTech Connect

Previous workers interpreted complex folds in Upper Ordovician turbiditic sandstone at Farmer Head, southwestern New World Island, to result from slumping in unlithified sediments. This interpretation is based on (1) the presence of various outcrop-scale ductile structures combined with the absence of brittle structures, (2) the presence of welded contacts, (3) the apparent disharmonic and chaotic nature of the folds, and (4) the absence of tectonic cleavage. However, recent investigations indicate that the folds are tectonic in origin. Ductile deformation structures are common, but they are not diagnostic of penecontemporaneous deformation. Moreover, brittle deformation structures associated with folding are visible in thin section. The folds on Farmer Head are not disharmonic, and the complex outcrop patterns can be explained in terms of noncoaxial overprinting of two fold generations that both fold an older tectonic cleavage. These folds can be correlated with F/sub 3/ and F/sub 4/ folds in adjacent areas. F/sub 1/ folds on New World Island probably formed in unlithified sediments, but where they are associated with olistostromal horizons, they are probably tectonic in origin. Elsewhere, F/sub 1/ folds may be slump structures; however, because of at least three subsequent stages of tectonic deformation, F/sub 1/ folds are difficult, if not impossible, to distinguish from tectonic folds.

Elliott, C.G.

1986-05-01

76

Structural synthesis of fast two-layer neural networks  

Microsoft Academic Search

Methods of construction of structural models of fast two-layer neural networks are considered. The methods are based on the\\u000a criteria of minimum computing operations and maximum degrees of freedom. Optimal structural models of two-layer neural networks\\u000a are constructed. Illustrative examples are given.

A. Yu. Dorogov

2000-01-01

77

FEM modelling of surface acoustic wave in diamond layered structure  

Microsoft Academic Search

This paper describes a general finite element method (FEM) for the AC steady state analysis of two-dimensional piezoelectric devices. The method is applied to a diamond based surface acoustic wave (SAW) layered structure. We determined the penetration depth of the elastic waves corresponding to ZnO layer of 1 mum thick and spatial periodicity of 4 mum. The structure admittance response

L. Le Brizoual; F. Sarry; F. Moreira; O. Elmazria

2006-01-01

78

Multi-layer laminate structure and manufacturing method  

DOEpatents

The present invention is premised upon a multi-layer laminate structure and method of manufacture, more particularly to a method of constructing the multi-layer laminate structure utilizing a laminate frame and at least one energy activated flowable polymer.

Keenihan, James R.; Cleereman, Robert J.; Eurich, Gerald; Graham, Andrew T.; Langmaid, Joe A.

2013-01-29

79

Multi-layer laminate structure and manufacturing method  

DOEpatents

The present invention is premised upon a multi-layer laminate structure and method of manufacture, more particularly to a method of constructing the multi-layer laminate structure utilizing a laminate frame and at least one energy activated flowable polymer.

Keenihan, James R. (Midland, MI); Cleereman, Robert J. (Midland, MI); Eurich, Gerald (Merrill, MI); Graham, Andrew T. (Midland, MI); Langmaid, Joe A. (Caro, MI)

2012-04-24

80

Origin of perpendicular magnetic anisotropy in Co/Ni multilayers on Ti layer  

NASA Astrophysics Data System (ADS)

Magnetic materials in which their magnetic moment direction is oriented perpendicular to the plane of the magnetic layers in thin film heterostructures have been much studied for their potential application to spintronic devices. In particular, theories of current induced excitation, via the phenomenon of spin torque transfer, show that perpendicularly magnetized layers can be more easily excited or their magnetization direction switched than in-plane magnetized layers. In particular, Co/Ni multilayers are promising due to high spin polarization and small Gilbert damping compared to Co/Pt or Fe/Pt. However, their perpendicular magnetic anisotropy (PMA) is highly sensitive to the underlayer that is critical in device performance because, for instance, the current shunting can substantially reduce the spin transfer torque in magnetic racetrack memory. We observed an excellent PMA in annealed Co/Ni on Ti underlayer whose resistance is significantly greater than those of Co/Ni, thereby minimizing the current shunting. It is found that the PMA does not simply originate from magneto-crystalline effect (spin-orbit interaction) but mainly from magnetoelastic effect caused by compressive strain along (111) direction. We will present systematic results and quantitative analyses.

Yang, See-Hun; Thoms, Kuei-Hung; Thomas, Luc; Parkin, Stuart

2012-02-01

81

Revisiting the origin of anomalous structures in liquid Ga  

NASA Astrophysics Data System (ADS)

By using an interatomic pair potential, which consists of a ledge-shape repulsive core and long-range Friedel oscillations, we investigate again the origin for the anomalous structures of liquid Ga, which is well known for a shoulder on the high-q side of the first peak in its static structure factor. We first examine our model by calculating dynamic properties and comparing with experimental data. Then, the liquid structures generated by MD simulations with our model at T=323K are analyzed. Though indeed found in our simulations, dimers with short bond-lengths are excluded as the possibility for the origin of the high-q shoulder. Instead, our results indicate that the high-q shoulder is resulted from some medium-range order, which is related to the structures beyond the first shell of the radial distribution function. The medium range order is caused by a cooperation between the ledge-shape repulsive core and the Friedel oscillations within a range of nanoscale.

Wu, Ten-Ming

2013-02-01

82

The origin recognition complex: a biochemical and structural view  

PubMed Central

The origin recognition complex (ORC) was first discovered in the baker’s yeast in 1992. Identification of ORC opened up a path for subsequent molecular level investigations on how eukaryotic cells initiate and control genome duplication each cell cycle. Twenty years after the first biochemical isolation, ORC is now taking on a three-dimensional shape, although a very blurry shape at the moment, thanks to the recent electron microscopy and image reconstruction efforts. In this chapter, we outline the current biochemical knowledge about ORC from several eukaryotic systems, with emphasis on the most recent structural and biochemical studies. Despite many species-specific properties, an emerging consensus is that ORC is a ATP-dependent machine that recruits other key proteins to form pre-Replicative Complexes (pre-RCs) at many origins of DNA replication, enabling the subsequent initiation of DNA replication in S phase.

Li, Huilin; Stillman, Bruce

2013-01-01

83

Properties of Love waves in a piezoelectric layered structure with a viscoelastic guiding layer  

NASA Astrophysics Data System (ADS)

A theoretical method is developed for analyzing Love waves in a structure with a viscoelastic guiding layer bounded on a piezoelectric substrate. The dispersion equation previously derived for piezoelectric Love waves propagating in the layered structure with an elastic layer is adopted for analyzing a structure with a viscoelastic layer. A Maxwell–Weichert model is introduced to describe the shear stiffness of a polymeric material. Newton’s method is employed for the numerical calculation. The dispersion equation for piezoelectric–elastic Love waves is proved suitable for solving a structure with a viscoelastic layer on a piezoelectric substrate. The theoretical results indicate that the propagation velocity of the Love wave is mainly decided by the shear stiffness of the guiding layer, whereas the propagation loss is approximately proportional to its viscosity. A detailed experimental study was conducted on a Love wave delay line fabricated on an ST-90° X quartz substrate and overlaid with various thicknesses of SU-8 guiding layers. A tail-raising caused by the viscosity of the guiding layer existed in both the calculated and the measured propagation velocities. The calculated insertion loss of the Love wave delay lines was in good agreement with the measured results. The method and the results presented in this paper are beneficial to the design of Love wave sensors with a viscoelastic guiding layer.

Liu, Jiansheng; Wang, Lijun; Lu, Yanyan; He, Shitang

2013-12-01

84

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

NASA Astrophysics Data System (ADS)

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 9.14Å) are valid for the extreme terms of dioctahedral smectite representatives: nontronites.

Palchik, N. A.; Grigorieva, T. N.; Moroz, T. N.

2013-03-01

85

Mean Structure of the Nocturnal Boundary Layer under Strong and Weak Wind Conditions: EPRI Case Study.  

NASA Astrophysics Data System (ADS)

The major objective of this study was to analyze the mean structure and evolution of the nocturnal boundary layer (NBL) under strong and weak wind conditions. Meteorological data collected during the plume-validation experiment conducted by the Electric Power Research Institute (EPRI) over a flat homogeneous terrain at Kincaid, Illinois (39°35N, 89°25W), were utilized. A one-dimensional meteorological boundary layer model originally developed by R. A. Pielke, modified with turbulent kinetic energy mixing-length closure, a layer-by-layer emissivity-based radiation scheme, and nonlinear nondimensional temperature and wind profiles in the surface layer, was used. In the four cases that were considered, ranging from strong to weak geostrophic forcing, the model reproduced the observed mean profiles, their evolutions in the NBL, and the inertial oscillations reasonably well. The NBL developed into three layers wherein 1) very close to the surface, radiative cooling dominated over turbulence cooling; 2) a layer above, turbulent cooling was the dominant mechanism; and 3) near the top of the turbulent layer and above, clear-air radiative cooling was the dominating mechanism. However, depending on the geostrophic wind, the structure of these layers varied from one situation to another. The wind maximum, which was at least above 200 m of altitude under windy conditions, was located at an altitude of less than 100 m for the weak-wind case, probably because of weaker diffusion in the boundary layer during transition.

Krishna, T. B. P. S. Rama V.; Sharan, Maithili; Gopalakrishnan, S. G.; Aditi

2003-07-01

86

A Dynamic Explanation For The Origin Of The Western Mediterranean Organic Rich Layers  

NASA Astrophysics Data System (ADS)

The eastern Mediterranean sapropels are amongst the most intensively investigated phenomena in the palaeoceanographic record , but relatively little has been written regarding the origin of the equivalent of the sapropels in the western Mediterranean, the Organic Rich Layers (ORL's). ORL's are recognised as sediment layers containing enhanced Total Organic Carbon that extend throughout the deep basins of the Western Mediterranean, and are associated with enhanced total barium concentration and a reduced diversity (dysoxic but not anoxic) benthic foraminiferal assemblage. Consequently, it has been suggested that ORL's represent periods of enhanced productivity coupled with reduced deep ventilation, presumably related to increased continental runoff, in close analogy to the sapropels. We demonstrate that despite their superficial similarity, the timing of the deposition of the most recent ORL in the Alboran Sea is different to that of the approximately coincident sapropel, indicating that there are important differences between their modes of formation. We go on to demonstrate, through physical arguments, that a likely explanation for the origin of the Alboran ORLs lies in the response of the Western Mediterranean basin to a strong reduction in surface water density and a shoaling of the interface between intermediate and deep water during the deglacial period. This moves the emphasis for forcing deep convection collapse in the western basins away from atmospheric forcing and towards changes in the residence time of water in the Mediterranean Sea (i.e. oceanic forcing). Furthermore, we provide evidence that deep convection had already slowed by the time of Heinrich Event 1, and explore this event as a potential agent for preconditioning deep convection collapse. Important differences between Heinrich-like and deglacial-like influences are highlighted, giving insight into the response of the western Mediterranean system to external forcing.

Rogerson, M.; Cacho, I.; Jimenez-Espejo, F.; Reguera, I.; Sierro, F.; Martinez-Ruiz, F.; Frigola, J.

2007-12-01

87

A dynamic explanation for the origin of the western Mediterranean organic-rich layers  

NASA Astrophysics Data System (ADS)

The eastern Mediterranean sapropels are among the most intensively investigated phenomena in the paleoceanographic record, but relatively little has been written regarding the origin of the equivalent of the sapropels in the western Mediterranean, the organic-rich layers (ORLs). ORLs are recognized as sediment layers containing enhanced total organic carbon that extend throughout the deep basins of the western Mediterranean and are associated with enhanced total barium concentration and a reduced diversity (dysoxic but not anoxic) benthic foraminiferal assemblage. Consequently, it has been suggested that ORLs represent periods of enhanced productivity coupled with reduced deep ventilation, presumably related to increased continental runoff, in close analogy to the sapropels. We demonstrate that despite their superficial similarity, the timing of the deposition of the most recent ORL in the Alboran Sea is different than that of the approximately coincident sapropel, indicating that there are important differences between their modes of formation. We go on to demonstrate, through physical arguments, that a likely explanation for the origin of the Alboran ORLs lies in the response of the western Mediterranean basin to a strong reduction in surface water density and a shoaling of the interface between intermediate and deep water during the deglacial period. Furthermore, we provide evidence that deep convection had already slowed by the time of Heinrich Event 1 and explore this event as a potential agent for preconditioning deep convection collapse. Important differences between Heinrich-like and deglacial-like influences are highlighted, giving new insights into the response of the western Mediterranean system to external forcing.

Rogerson, M.; Cacho, I.; Jimenez-Espejo, F.; Reguera, M. I.; Sierro, F. J.; Martinez-Ruiz, F.; Frigola, J.; Canals, M.

2008-07-01

88

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

89

Characteristics of surface layer structure formation during laser boriding  

NASA Astrophysics Data System (ADS)

The surface layers of a mild steel and steels 40 and U8 were studied metallographically following a laser boriding treatment. In particular, the structure and properties of the borided layer were investigated as a function of the irradiation rate and the thickness of the coating compound. It is shown that laser boriding produces a sharp increase in the hardness of the steels and leads to the formation of hardened layers that are as thick as those produced by diffusion boriding treatments.

Tananko, I. A.; Levchenko, A. A.; Guiva, R. T.; Guiva, V. A.; Sittsevaia, E. Iu.

1989-08-01

90

Boundary-layer wind structure in a landfalling tropical cyclone  

Microsoft Academic Search

In this study, a slab boundary layer model with a constant depth is used to analyze the boundary-layer wind structure in a\\u000a landfalling tropical cyclone. Asymmetry is found in both the tangential and radial components of horizontal wind in the tropical\\u000a cyclone boundary layer at landfall. For a steady tropical cyclone on a straight coastline at landfall, the magnitude of

Xiaodong Tang; Zhemin Tan

2006-01-01

91

Origin of weak layer contraction in de Vries smectic liquid crystals.  

PubMed

Structural investigations of the de Vries smectic-A (SmA) and smectic-C (SmC) phases of four mesogens containing a trisiloxane end segment reveal a linear molecular conformation in the SmA phase and a bent conformation resembling a hockey stick in the SmC phase. The siloxane and the hydrocarbon parts of the molecule tilt at different angles relative to the smectic layer normal and are oriented along different directions. For the compounds investigated, the shape of orientational distribution function (ODF) is found to be sugarloaf shaped and not the widely expected volcano like with positive orientational order parameters: ?P2? = 0.53-0.78, ?P4? = 0.14-0.45, and ?P6??0.10. The increase in the effective molecular length, and consequently in the smectic layer spacing caused by reduced fluctuations and the corresponding narrowing of the ODF, counteracts the effect of molecular tilt and significantly reduces the SmC layer contraction. Maximum tilt of the hydrocarbon part of the molecule lies between approximately 18° and 25° and between 6° and 12° for the siloxane part. The critical exponent of the tilt order parameter, ??0.25, is in agreement with tricritical behavior at the SmA-SmC transition for two compounds and has lower value for first-order transition in the other compounds with finite enthalpy of transition. PMID:24730863

Agra-Kooijman, Dena M; Yoon, HyungGuen; Dey, Sonal; Kumar, Satyendra

2014-03-01

92

Humidity sensors using porous silicon layer with mesa structure  

Microsoft Academic Search

A capacitance-type humidity sensor in which a porous silicon layer is used as a humidity-sensing material was developed. This sensor was fabricated monolithically to be compatible with the typical IC process technology except for the formation of porous silicon layer. As the sensor is made as a mesa structure, the correct measurement of capacitance is expected because it can remove

Seong-Jeen Kim; Jae-Yoon Park; Sang-Hoon Lee; Seung-Hwan Yi

2000-01-01

93

Structure of the steady state SGEMP boundary layer  

Microsoft Academic Search

When X-rays illuminate a material surface, they eject electrons backwards which then congregate in a relatively thin layer near the surface. The structure of this layer is studied in the steady-state limit in the cases in which the electron emission angular distribution is proportional to the cosine of the emission angle measured from normal, and when the electron energy distribution

N. J. Carron; C. L. Longmire

1976-01-01

94

Structure of the Steady State SGEMP Boundary Layer  

Microsoft Academic Search

When X rays illuminate a material surface they eject electrons backwards which then congregate in a relatively thin layer near the surface. We study the structure of this layer in the steady state limit in the cases in which the electron emission angular distribution is proportional to cos¿, where ¿ is the emission angle measured from normal, and when the

N. J. Carron; C. L. Longmire

1976-01-01

95

Optimal design of structures with active constrained-layer damping  

Microsoft Academic Search

A piezoelectric element and a constrained layer damping element are combined to allow for an active constrained layer damping treatment. The development of these elements is reviewed and results are compared with the literature to insure that the elements work together. A procedure for placing patches damping treatments or other material anomalies on structures is introduced. The patch placement process

Duane E. Veley; S. S. Rao

1995-01-01

96

Reliability of multi-layer aluminum capped copper interconnect structures  

Microsoft Academic Search

Driven for further silicon reduction, wireless applications utilize copper interconnection and increase metal layer count from three to five layers. More aggressive ESD structures placed under the bond pads offer a significant opportunity for additional die area and cost reduction. Capping copper bond pads with aluminum was selected as the primary approach for probing and wire bonding of copper devices.

Lei Mercado; Robert Radke; Matthew Ruston; Tu Anh Tran; B. Williams; L. Yong; A. Chen; S. Chen

2000-01-01

97

Layer selective control of the lattice structure in oxide superlattices.  

PubMed

A combined synchrotron X-ray diffraction and transmission electron microscopy study reveals a structural phase transition controlled by the overall thickness of epitaxial nickelate-aluminate superlattices. The transition between uniform and twin-domain states is confined to the nickelate layers and leaves the aluminate layers unaffected. PMID:24155253

Frano, Alex; Benckiser, Eva; Lu, Yi; Wu, Meng; Castro-Colin, Miguel; Reehuis, Manfred; Boris, Alexander V; Detemple, Eric; Sigle, Wilfried; van Aken, Peter; Cristiani, Georg; Logvenov, Gennady; Habermeier, Hanns-Ulrich; Wochner, Peter; Keimer, Bernhard; Hinkov, Vladimir

2014-01-15

98

Plane electromagnetic waves in layered periodic dielectric structures  

NASA Astrophysics Data System (ADS)

Several analytic methods are used to derive and discuss analytic expressions for electromagnetic wave fields in finite one-dimensional layered structures. A new modification is obtained for the so-called multiple reflection method. Special attention is given to layered periodic dielectric structures. The systematic dependence of the reflection coefficient on the parameters characterizing this type of structure is studied in detail, using the two-layered periodic dielectric structure as a typical example. A general method for the construction of the Green's function for finite one-dimensional layered structures is developed. The sum of the total Neumann (Born) series is calculated for sufficiently simple cases of perturbations in the profile of the refractive index. Using the Green's function, the influence of fluctuations of the width of the basic layers on the reflection and transmission of electromagnetic waves propagating through the two-layered periodic dielectric structure is investigated. The results are applied to the design of optical switching systems with periodic dielectric structures as the operating medium.

Morozov, Gregory V.

2001-07-01

99

The Origin of Mercury's Magnetic Field and Its Multipolar Structure  

NASA Astrophysics Data System (ADS)

The origin of Mercury's planetary magnetic field is still unclear and likely to remain an unsolved problem at least until the currently planned space missions, BepiColombo and Messenger perform a full magnetic mapping of the planet. However, the likely generation mechanisms have a common feature. It is unlikely that the planetary field is dominated by the dipolar term; multipolar terms (quadrupole, octupole and higher order terms) are probably more important, when compared to the dipole, than in the case of the Earth. The main reason for this is that the location of the generation mech- anism, at the vicinity of the core-mantle boundary, is much closer to the surface of the planet, due to the large size of the core, than at the Earth. Whether the field is generated by a hydrodynamic dynamo in a molten outer layer of the core, or by a thermoelec- tric dynamo at the core-mantle boundary, the mechanisms yield relatively significant higher order multipolar terms. Following a brief review of these models and the way the multipoles can be generated, we present examples of quantitative modelling of simple cases of magnetic field generation that provide a first insight into the relative importance of these terms.

Balogh, A.; Giampieri, G.

100

Field grading of multi-layered insulation structures  

NASA Astrophysics Data System (ADS)

A field grading technique is proposed which introduces conducting films between the insulating layers of a mutilayered structure, causing the capacitance and electric stress to be more uniformly distributed between the layers. Application of the technique to conventional multilayered insulation systems results in some improvment in breakdown voltage. The present data indicate that field-graded multilayered insulation structures which are either one-polymer or composite have particular application to devices where high energy density per unit weight is required.

Cygan, S.; Laghari, J. R.

101

Multiple reflection method for electromagnetic waves in layered dielectric structures  

SciTech Connect

Reflection and transmission of a plane electromagnetic wave propagating in a layered dielectric structure with an arbitrary number of layers of various thicknesses are investigated. For the general case of oblique incidence of the wave on this structure, the reflection and transmission coefficients are calculated for both TE and TM waves using a multiple reflection method. An algorithm to apply the obtained formulas for numerical and analytical calculations is suggested. (physical foundations of quantum electronics)

Morozov, G V; Maev, R G; Drake, G W F [Department of Physics, University of Windsor (Canada)

2001-09-30

102

Review of methods for analyzing constrained-layer damped structures  

Microsoft Academic Search

This paper reviews and examines different numerical approaches for modeling and analyzing the behavior of structures having constrained-layer damping. Specific topics that are addressed included: modeling of the material behavior, implementation of structural damping and constrained-layer damping into two- and three-dimensional finite elements, and assessment of the different analysis methods for calculating the damped response and estimation of the damping

J. B. Kosmatka; S. L. Liguore

1993-01-01

103

Dynamic characteristics of specialty composite structures with embedded damping layers  

NASA Technical Reports Server (NTRS)

Damping mechanics for simulating the damped dynamic characteristics in specialty composite structures with compliant interlaminar damping layers are presented. Finite-element based mechanics incorporating a discrete layer (or layer-wise) laminate damping theory are utilized to represent general laminate configurations in terms of lay-up and fiber orientation angles, cross-sectional thickness, shape, and boundary conditions. Evaluations of the method with exact solutions and experimental data illustrate the accuracy of the method. Additional applications investigate the potential for significant damping enhancement in angle-ply composite laminates with cocured interlaminar damping layers.

Saravanos, D. A.; Chamis, C. C.

1993-01-01

104

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.

Rivard, Maxime; Laliberte, Mathieu; Bertrand-Grenier, Antony; Harnagea, Catalin; Pfeffer, Christian P.; Vallieres, Martin; St-Pierre, Yves; Pignolet, Alain; El Khakani, My Ali; Legare, Francois

2011-01-01

105

Lactobacillus helveticus MIMLh5-Specific Antibodies for Detection of S-Layer Protein in Grana Padano Protected-Designation-of-Origin Cheese  

PubMed Central

Single-chain variable-fragment antibodies (scFvs) have considerable potential in immunological detection and localization of bacterial surface structures. In this study, synthetic phage-displayed antibody libraries were used to select scFvs against immunologically active S-layer protein of Lactobacillus helveticus MIMLh5. After three rounds of panning, five relevant phage clones were obtained, of which four were specific for the S-layer protein of L. helveticus MIMLh5 and one was also capable of binding to the S-layer protein of L. helveticus ATCC 15009. All five anti-S-layer scFvs were expressed in Escherichia coli XL1-Blue, and their specificity profiles were characterized by Western blotting. The anti-S-layer scFv PolyH4, with the highest specificity for the S-layer protein of L. helveticus MIMLh5, was used to detect the S-layer protein in Grana Padano protected-designation-of-origin (PDO) cheese extracts by Western blotting. These results showed promising applications of this monoclonal antibody for the detection of immunomodulatory S-layer protein in dairy (and dairy-based) foods.

Brockmann, Eeva-Christine; Huovinen, Tuomas; Guglielmetti, Simone; Mora, Diego; Taverniti, Valentina; Arioli, Stefania; De Noni, Ivano; Lamminmaki, Urpo

2014-01-01

106

Studies in the origin of large-scale structure  

NASA Astrophysics Data System (ADS)

Observations of the large-scale structure of the universe provide important tests of cosmology. I explore two ways how such observations can be compared with cosmological models, and look at some of the theoretical questions underlying the formation of large-scale structure. The first approach uses the evolution of the number density of galaxy clusters with time, which strongly depends on the density and other parameters of the universe. The optimum observation strategy for X-ray telescopes (Chandra and XMM) is determined which yields the largest number of clusters at high redshifts. The cluster numbers are large enough to differentiate between various inflation-based cosmological scenarios if redshifts are established by follow-up observations. Since these predictions are based on cosmological simulations, I compare different ways how clusters are identified in simulations and which one gives the most reliable results. The second approach looks at the geometry of large-scale structure in redshift surveys. I use a statistic which quantifies its degree of linearity, planarity, and sphericity. The presence of linear (fingers of God) and planar (the Great Wall) structures is detected in the CfA2 survey. There are no systematic differences between mock surveys constructed from simulations and the CfA2 survey. Different realizations of mock surveys from the same simulation show variations which are larger than the differences between the cosmological models. It appears that the CfA2 survey has not reached the scale of homogeneity. At a more theoretical level is the question when the different structures emerged from the initial density perturbations. In the cosmic web hypothesis, spherical structures appear first with filaments growing between them, followed by walls connecting the filaments. By using the structure functions to trace the evolution of the geometry of large-scale structure in simulations, I find that this picture is not correct, and that instead filaments and sheets grow simultaneously. In the theory of the origin and evolution of density perturbations, a criticism of the gauge-invariant approach has been put forward. I point out a mistake in the criticism, and construct a counterexample to its claims.

Gotz, Martin

107

Novel nanoscroll structures from carbon nitride layers.  

PubMed

Nanoscrolls (papyrus-like nanostructures) are very attractive structures for a variety of applications, owing to their tunable diameter and large accessible surface area. They have been successfully synthesized from different materials. In this work, we investigate, through fully atomistic molecular dynamics simulations, the dynamics of scroll formation for a series of graphene-like carbon nitride (CN) two-dimensional systems: g-CN, triazine-based g-C3 N4 , and heptazine-based g-C3 N4 . Our results show that stable nanoscrolls can be formed for each of these structures. Possible synthetic routes to produce these nanostructures are also addressed. PMID:24819427

Perim, Eric; Galvao, Douglas S

2014-08-01

108

Structural and optical properties of InGaN/GaN layers close to the critical layer thickness  

NASA Astrophysics Data System (ADS)

In this work, we investigate structural and optical properties of metalorganic chemical vapor deposition grown wurtzite InxGa1-xN/GaN epitaxial layers with thicknesses that are close to the critical layer thickness (CLT) for strain relaxation. CLT for InxGa1-xN/GaN structures was calculated as a function of the InN content, x, using the energy balance model proposed by People and Bean [Appl. Phys. Lett. 47, 322 (1985)]. Experimentally determined CLT are in good agreement with these calculations. The occurrence of discontinuous strain relaxation (DSR), when the CLT is exceeded, is revealed in the case of a 120 nm thick In0.19Ga0.89N layer by x-ray reciprocal space mapping of an asymmetrical reflection. The effect of DSR on the luminescence of this layer is clear: The luminescence spectrum shows two peaks centered at approx2.50 and approx2.67 eV, respectively. These two components of the luminescence of the sample originate in regions of different strain, as discriminated by depth-resolving cathodoluminescence spectroscopy. DSR leads directly to the emergence of the second, lower-energy, peak. Based on this experimental evidence, it is argued that the appearance of luminescence doublets in InGaN is not evidence of "quantum dotlike In-rich" or "phase separated" regions, as commonly proposed.

Pereira, S.; Correia, M. R.; Pereira, E.; Trager-Cowan, C.; Sweeney, F.; O'Donnell, K. P.; Alves, E.; Franco, N.; Sequeira, A. D.

2002-08-01

109

Semi analytical numerical analysis of plasmonic structures in layered geometries  

NASA Astrophysics Data System (ADS)

An upgrade for the efficiency proven electromagnetic simulation tool, Multiple Multipole Program (MMP) is proposed, in order to efficiently analyze plasmonic structures in layered geometries. In this upgrade, a new expansion set, the layered media Green's function, is included in the open source EM simulation package Open- MaX, which contains the latest version of MMP. By this upgrade the advantages of both the MMP and layered media Green's functions are combined and an efficient and robust simulation tool for the analysis of structures in layered geometries in optical range of the spectrum is obtained. In this paper, the fundamentals of MMP and the derivation of layered media Green's functions will be discussed. Numerical results will also be included in order to demonstrate the efficiency of the upgraded method.

Alparslan, Aytac; Hafner, Christian

2011-09-01

110

Kaolmite layer structure: relaxation by dehydroxylation.  

PubMed

Single-crystal electron-diffraction data reveal features of metakaolin. The basal plane parameters increase 2.2 percent in formation of metakaolin produced by heating kaolinite in air at 700 degrees C for 12 hours. This increase results from removal of the distortion of sheet structure (relaxation). PMID:17752638

Brindley, G W; Gibbon, D L

1968-12-20

111

The Coherent Structure of Turbulent Mixing Layers. I. Similarity of the Primary Vortex Structure. II. Secondary Streamwise Vortex Structure.  

National Technical Information Service (NTIS)

The primary spanwise organized vortex structure and the secondary streamwise vortex structure of turbulent mixing layers have been investigated. Flow visualization motion pictures of a constant density mixing layer were used to measure the properties of t...

L. P. Bernal

1981-01-01

112

Framework structures of interconnected layers in calcium iron arsenides.  

PubMed

The new calcium iron arsenide compounds Can(n+1)/2(Fe1-xMx)(2+3n)M'n(n-1)/2As(n+1)(n+2)/2 (n = 1-3; M = Nb, Pd, Pt; M' = ?, Pd, Pt) were synthesized and their crystal structures determined by single-crystal X-ray diffraction. The series demonstrates the structural flexibility of iron arsenide materials, which otherwise prefer layered structures, as is known from the family of iron-based superconductors. In the new compounds, iron arsenide tetrahedral layers are bridged by iron-centered pyramids, giving rise to so far unknown frameworks of interconnected FeAs layers. Channels within the structures are occupied with calcium and palladium or platinum, respectively. Common basic building blocks are identified that lead to a better understanding of the building principles of these structures and their relation to CaFe4As3. PMID:24884132

Stürzer, Tobias; Hieke, Christine; Löhnert, Catrin; Nitsche, Fabian; Stahl, Juliane; Maak, Christian; Pobel, Roman; Johrendt, Dirk

2014-06-16

113

Superconducting structure with layers of niobium nitride and aluminum nitride  

DOEpatents

A superconducting structure is formed by depositing alternate layers of aluminum nitride and niobium nitride on a substrate. Deposition methods include dc magnetron reactive sputtering, rf magnetron reactive sputtering, thin-film diffusion, chemical vapor deposition, and ion-beam deposition. Structures have been built with layers of niobium nitride and aluminum nitride having thicknesses in a range of 20 to 350 Angstroms. Best results have been achieved with films of niobium nitride deposited to a thickness of approximately 70 Angstroms and aluminum nitride deposited to a thickness of approximately 20 Angstroms. Such films of niobium nitride separated by a single layer of aluminum nitride are useful in forming Josephson junctions. Structures of 30 or more alternating layers of niobium nitride and aluminum nitride are useful when deposited on fixed substrates or flexible strips to form bulk superconductors for carrying electric current. They are also adaptable as voltage-controlled microwave energy sources.

Murduck, James M. (Lisle, IL); Lepetre, Yves J. (Lauris, FR); Schuller, Ivan K. (Woodridge, IL); Ketterson, John B. (Evanston, IL)

1989-01-01

114

Superconducting structure with layers of niobium nitride and aluminum nitride  

DOEpatents

A superconducting structure is formed by depositing alternate layers of aluminum nitride and niobium nitride on a substrate. Deposition methods include dc magnetron reactive sputtering, rf magnetron reactive sputtering, thin-film diffusion, chemical vapor deposition, and ion-beam deposition. Structures have been built with layers of niobium nitride and aluminum nitride having thicknesses in a range of 20 to 350 Angstroms. Best results have been achieved with films of niobium nitride deposited to a thickness of approximately 70 Angstroms and aluminum nitride deposited to a thickness of approximately 20 Angstroms. Such films of niobium nitride separated by a single layer of aluminum nitride are useful in forming Josephson junctions. Structures of 30 or more alternating layers of niobium nitride and aluminum nitride are useful when deposited on fixed substrates or flexible strips to form bulk superconductors for carrying electric current. They are also adaptable as voltage-controlled microwave energy sources. 8 figs.

Murduck, J.M.; Lepetre, Y.J.; Schuller, I.K.; Ketterson, J.B.

1989-07-04

115

Integrated characterization of multilayer periodic systems with nanosized layers as applied to Mo/Si structures  

NASA Astrophysics Data System (ADS)

The potential inherent in integrated characterization of multilayer periodic systems employed in development of extreme-ultraviolet mirrors was demonstrated using the example of Mo/Si structures grown by magnetron sputtering in different technological regimes. An integrated study provided mutually consistent data on the thicknesses and crystal structure of the layers, as well as on the quality of the interfaces. Measurements by atomic force microscopy permitted a comparison of surface roughness of the substrates and the multilayer systems grown on them. An analysis of the power spectral density functions revealed that low-frequency roughness is replicated from the substrate, whereas the high-frequency one can become smoothed out in the course of growth. X-ray diffractometry performed in the thin film mode showed that the Mo layers in the samples studied have different crystal structures, from the amorphous and polycrystalline to the [110]-textured one. An analysis of the transmission electron microscopy data confirmed that there is a difference in the degrees of crystallinity of Mo layers. The thicknesses of individual layers, the period, and the irreproducibility of the thicknesses and the period were determined using X-ray reflectometry. The root-mean-square roughness amplitude of the interfaces was estimated, and the existence of transition layers originating primarily from the Si layer was demonstrated. The study was used to formulate a proper strategy for the analysis of multilayer periodic systems with nanosized layers.

Valkovskiy, G. A.; Baidakova, M. V.; Brunkov, P. N.; Konnikov, S. G.; Sitnikova, A. A.; Yagovkina, M. A.; Zadiranov, Yu. M.

2013-03-01

116

Origin of the large scale structures of the universe  

SciTech Connect

We revise the statistical properties of the primordial cosmological density anisotropies that, at the time of matter-radiation equality, seeded the gravitational development of large scale structures in the otherwise homogeneous and isotropic Friedmann-Robertson-Walker flat universe. Our analysis shows that random fluctuations of the density field at the same instant of equality and with comoving wavelength shorter than the causal horizon at that time can naturally account, when globally constrained to conserve the total mass (energy) of the system, for the observed scale invariance of the anisotropies over cosmologically large comoving volumes. Statistical systems with similar features are generically known as glasslike or latticelike. Obviously, these conclusions conflict with the widely accepted understanding of the primordial structures reported in the literature, which requires an epoch of inflationary cosmology to precede the standard expansion of the universe. The origin of the conflict must be found in the widespread, but unjustified, claim that scale invariant mass (energy) anisotropies at the instant of equality over comoving volumes of cosmological size, larger than the causal horizon at the time, must be generated by fluctuations in the density field with comparably large comoving wavelength.

Oaknin, David H. [Department of Physics and Astronomy, University of British Columbia, Vancouver V6T 1Z1 (Canada)

2004-11-15

117

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

118

Narrowband ultrasonic spectroscopy for NDE of layered structures  

Microsoft Academic Search

NDE of airspace sandwich structures is often performed using a simple resonant transducer sensing the information in the frequency domain obtained due to the constructive and destructive interference of elastic waves. Application field of ultrasonic narrowband ultrasonic spectroscopy (NBUS) is likely to increase rapidly with the growing application of layered structures in modern aircraft, for example, GLARE. The aim of

T. Stepinski; M. Jonsson

2005-01-01

119

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

120

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

121

Structural origin of the colored reflections from the black-billed magpie feathers  

NASA Astrophysics Data System (ADS)

The structural origin of the weak iridescence on some of the dark feathers of the black-billed magpie, Pica pica (Corvidae), is found in the structure of the ribbon-shaped barbules. The cortex of these barbules contains cylindrical holes distributed as the nodes of an hexagonal lattice in the hard layer cross section. The cortex optical properties are described starting from a photonic-crystal film theory. The yellowish-green coloration of the bird’s tail can be explained by the appearance of a reflection band related to the photonic-crystal lowest-lying gap. The bluish reflections from the wings are produced by a more complicated mechanism, involving the presence of a cortex second gap.”

Pol Vigneron, Jean; Colomer, Jean-François; Rassart, Marie; Ingram, Abigail L.; Lousse, Virginie

2006-02-01

122

Love wave propagation in piezoelectric layered structure with dissipation.  

PubMed

We investigate analytically the effect of the viscous dissipation of piezoelectric material on the dispersive and attenuated characteristics of Love wave propagation in a layered structure, which involves a thin piezoelectric layer bonded perfectly to an unbounded elastic substrate. The effects of the viscous coefficient on the phase velocity of Love waves and attenuation are presented and discussed in detail. The analytical method and the results can be useful for the design of the resonators and sensors. PMID:19022465

Du, Jianke; Xian, Kai; Wang, Ji; Yong, Yook-Kong

2009-02-01

123

Toward the origin of exciton electronic structure in phycobiliproteins  

NASA Astrophysics Data System (ADS)

Femtosecond laser spectroscopies are used to examine the electronic structures of two proteins found in the phycobilisome antenna of cyanobacteria, allophycocyanin (APC) and C-phycocyanin (CPC). The wave function composition involving the pairs of phycocyanobilin pigments (i.e., dimers) found in both proteins is the primary focus of this investigation. Despite their similar geometries, earlier experimental studies conducted in our laboratory and elsewhere observe clear signatures of exciton electronic structure in APC but not CPC. This issue is further investigated here using new experiments. Transient grating (TG) experiments employing broadband quasicontinuum probe pulses find a redshift in the signal spectrum of APC, which is almost twice that of CPC. Dynamics in the TG signal spectra suggest that the sub-100 fs dynamics in APC and CPC are respectively dominated by internal conversion and nuclear relaxation. A specialized technique, intraband electronic coherence spectroscopy (IECS), photoexcites electronic and nuclear coherences with nearly full suppression of signals corresponding to electronic populations. The main conclusion drawn by IECS is that dephasing of intraband electronic coherences in APC occurs in less than 25 fs. This result rules out correlated pigment fluctuations as the mechanism enabling exciton formation in APC and leads us to propose that the large Franck-Condon factors of APC promote wave function delocalization in the vibronic basis. For illustration, we compute the Hamiltonian matrix elements involving the electronic origin of the ?84 pigment and the first excited vibronic level of the ?84 pigment associated with a hydrogen out-of-plane wagging mode at 800 cm-1. For this pair of vibronic states, the -51 cm-1 coupling is larger than the 40 cm-1 energy gap, thereby making wave function delocalization a feasible prospect. By contrast, CPC possesses no pair of vibronic levels for which the intermolecular coupling is larger than the energy gap between vibronic states. This study of APC and CPC may be important for understanding the photophysics of other phycobiliproteins, which generally possess large vibronic couplings.

Womick, Jordan M.; Miller, Stephen A.; Moran, Andrew M.

2010-07-01

124

Atomic and electronic-structure study on the layers of 4Hb-TaS2 prepared by a layer-by-layer etching technique  

Microsoft Academic Search

We have studied the atomic and electronic structures of 4Hb-TaS2, which has alternating layers of the 1T and 1H type, at room temperature and 77 K, using a scanning tunneling microscope. Using a layer-by-layer etching technique, we fabricated staircases with alternating layers of the 1T and 1H type. The T-type layers showed the typical &surd;13×&surd;13 charge-density-wave structures, whereas the H-type

Ju-Jin Kim; H. Olin

1995-01-01

125

Manipulation of the structure of a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

The manipulation of a turbulent boundary layer for the purpose of net drag reduction is an attractive topic for research, because even modest success will result in large energy savings. The focus is on passive manipulation, one of the simplest manipulation techniques. The most promising manipulator is the so-called BLADE device, consisting of two thin ribbons or foils suspended in the outer portion of the boundary layer. When the research was begun, there was significant controversy over the magnitude of the net drag reduction possible (20 percent) and the maximum skin friction reduction obtainable (50 percent). Accurate local skin-friction measurements were made using sublayer fences in a perturbed boundary layer. By comparing the direct measurements with those obtained by indirect methods, it was determined that the degree of drag reduction obtained depends on the method used to calculate the combined device drag and skin friction drag. Using auto and two-point correlation measurements as well as space-time correlations, the effects of BLADE were investigated on the turbulent structures in the boundary layer, comparing them with wire devices, which are not known to produce a net reduction in drag. The space-time correlation revealed that the most significant effect of the BLADE device was on the large structures (the dominant structures in the outer region of the boundary layer). The inner layer devices consisting of sublayer wires were also investigated. The results from both the inner and outer layer manipulations suggest that the effective alteration of a turbulent boundary layer depends on the scaling of the device.

Lynn, Theodore Brooks

126

Bending a periodically layered structure for transformation acoustics  

NASA Astrophysics Data System (ADS)

Anisotropic acoustic metamaterials have been proved very useful for their high potential in guiding and manipulating sound energy. In this letter, we further develop the idea by using periodically layered structures for transformational acoustics. Such a simple scheme periodically inserts identically bent solid plates in a background fluid. It forms a metamaterial with high refractive index normal to the curved plates and an index near to one along the plates. We show that the periodically layered structure, combined with transformation approach, can be cut into particular device shapes for acoustic cloaking and illusion.

Liang, Zixian; Li, Jensen

2011-06-01

127

Origin of micro-layering in a deep magma chamber: Evidence from two ultramafic mafic layered xenoliths from Puy Beaunit (French Massif Central)  

NASA Astrophysics Data System (ADS)

The origin of magmatic layering is still hotly debated. To try to shed some light on this problem, two ultramafic-mafic layered xenoliths from Puy Beaunit (French Massif Central) were investigated in detail. The nodules belong to a stratiform intrusion emplaced in the deep crust during the Permian (257 ± 6 Ma; Féménias, O., Coussaert, N., Bingen, B., Whitehouse, M., Mercier, J.-C., Demaiffe, D., 2003. A Permian underplating event in late- to post-orogenic tectonic setting. Evidence from the mafic-ultramafic layered xenoliths from Beaunit (French Massif Central). Chem. Geol. 199 293-315.). The 3 to 5 cm thick nodules have, in common, a central orthopyroxenite layer; the succession of layers is, respectively, norite-orthopyroxenite-norite (PBN 00-01) and norite-orthopyroxenite-harzburgite (PBN 00-03). The variations of both major (by electron microprobe) and trace, essentially the RE, elements (by LA-ICP-MS) were measured in major mineral phases (orthopyroxene, clinopyroxene, plagioclase, spinel) along cross-section perpendicular to the layering. Strong grain size, chemical and textural variations occur along these sections: they can be continuous or discontinuous, symmetrical or asymmetrical. Such complex variations cannot be solely related to a single magmatic history (fractional crystallisation, mineral sorting). Other processes such as element enrichment by residual liquid channelling along layer boundaries and/or sub-solidus recrystallisation and element redistribution must be invoked. It appears, in particular, that element distribution in the central orthopyroxenite layer could result from the injection of micro-sills of orthopyroxene-rich liquid between previously consolidated layers.

Féménias, Olivier; Ohnenstetter, Daniel; Coussaert, Nicolas; Berger, Julien; Demaiffe, Daniel

2005-08-01

128

Influence of Bowen Ratio on Boundary-Layer Cloud Structure.  

NASA Astrophysics Data System (ADS)

An investigation of the influence of the ratio of surface sensible heat flux to latent heat flux, the Bowen ratio. on the structure of boundary-layer clouds is carried out utilizing numerical large eddy simulations (LES). The role of cloud-top radiational cooling, cloud-top temperature and moisture jump conditions, and wind shear are included in a secondary way. Although no detailed comparisons have been made, the LES results appear to be qualitatively consistent with the Atlantic Stratocumulus Transition Experiment, the recent field study on marine boundary-layer cloud structure. Some conclusions that follow from an examination of these LES results are the following: First, there is a highly bimodal character to the cloud ceiling frequency within a very low Bowen ratio boundary layer. The updrafts tend to produce a lower cloud ceiling than the surrounding environment with its weak downdrafts. Second, a very low Bowen ratio with the aid of some boundary-layer shear makes the development of persistent microcell cloud circulations possible within the boundary layer. Third, when the surface latent heat flux is the dominant factor in the dynamics of the boundary layer, the approach to a conditionally stable lapse rate results in the potential for subsequent decoupling. Last, the maximum partial cloud fraction is very well represented by the relation suggested by Sommeria and Deardorff for a Gaussian probability distribution for the range of conditions studied.

Lewellen, D. C.; Lewellen, W. S.; Yoh, S.

1996-01-01

129

Evolution and structure of sink-flow turbulent boundary layers  

NASA Astrophysics Data System (ADS)

An experimental and theoretical investigation of turbulent boundary layers developing in a sink-flow pressure gradient was undertaken. Three flow cases were studied, corresponding to different acceleration strengths. Mean-flow measurements were taken for all three cases, while Reynolds stresses and spectra measurements were made for two of the flow cases. In this study attention was focused on the evolution of the layers to an equilibrium turbulent state. All the layers were found to attain a state very close to precise equilibrium. This gave equilibrium sink flow data at higher Reynolds numbers than in previous experiments. The mean velocity profiles were found to collapse onto the conventional logarithmic law of the wall. However, for profiles measured with the Pitot tube, a slight ‘kick-up’ from the logarithmic law was observed near the buffer region, whereas the mean velocity profiles measured with a normal hot wire did not exhibit this deviation from the logarithmic law. As the layers approached equilibrium, the mean velocity profiles were found to approach the pure wall profile and for the highest level of acceleration [Pi] was very close to zero, where [Pi] is the Coles wake factor. This supports the proposition of Coles (1957), that the equilibrium sink flow corresponds to pure wall flow. Particular interest was also given to the evolutionary stages of the boundary layers, in order to test and further develop the closure hypothesis of Perry, Marusic & Li (1994). Improved quantitative agreement with the experimental results was found after slight modification of their original closure equation.

Jones, M. B.; Marusic, Ivan; Perry, A. E.

2001-02-01

130

Toward the origin of exciton electronic structure in phycobiliproteins.  

PubMed

Femtosecond laser spectroscopies are used to examine the electronic structures of two proteins found in the phycobilisome antenna of cyanobacteria, allophycocyanin (APC) and C-phycocyanin (CPC). The wave function composition involving the pairs of phycocyanobilin pigments (i.e., dimers) found in both proteins is the primary focus of this investigation. Despite their similar geometries, earlier experimental studies conducted in our laboratory and elsewhere observe clear signatures of exciton electronic structure in APC but not CPC. This issue is further investigated here using new experiments. Transient grating (TG) experiments employing broadband quasicontinuum probe pulses find a redshift in the signal spectrum of APC, which is almost twice that of CPC. Dynamics in the TG signal spectra suggest that the sub-100 fs dynamics in APC and CPC are respectively dominated by internal conversion and nuclear relaxation. A specialized technique, intraband electronic coherence spectroscopy (IECS), photoexcites electronic and nuclear coherences with nearly full suppression of signals corresponding to electronic populations. The main conclusion drawn by IECS is that dephasing of intraband electronic coherences in APC occurs in less than 25 fs. This result rules out correlated pigment fluctuations as the mechanism enabling exciton formation in APC and leads us to propose that the large Franck-Condon factors of APC promote wave function delocalization in the vibronic basis. For illustration, we compute the Hamiltonian matrix elements involving the electronic origin of the alpha84 pigment and the first excited vibronic level of the beta84 pigment associated with a hydrogen out-of-plane wagging mode at 800 cm(-1). For this pair of vibronic states, the -51 cm(-1) coupling is larger than the 40 cm(-1) energy gap, thereby making wave function delocalization a feasible prospect. By contrast, CPC possesses no pair of vibronic levels for which the intermolecular coupling is larger than the energy gap between vibronic states. This study of APC and CPC may be important for understanding the photophysics of other phycobiliproteins, which generally possess large vibronic couplings. PMID:20632763

Womick, Jordan M; Miller, Stephen A; Moran, Andrew M

2010-07-14

131

Structure Inclination Angles in the Convective Atmospheric Surface Layer  

NASA Astrophysics Data System (ADS)

Two-point correlations of the fluctuating streamwise velocity are examined in the atmospheric surface layer over the salt flats of Utah's western desert, and corresponding structure inclination angles are obtained for neutral, stable and unstable conditions. The neutral surface-layer results supplement evidence for the invariance of the inclination angle given in Marusic and Heuer (Phys Rev Lett 99:114504, 2007). In an extension of those results it is found that the inclination angle changes drastically under different stability conditions in the surface layer, varying systematically with the Monin-Obukhov stability parameter in the unstable regime. The variation is parametrized and subsequently can be used to improve existing near-wall models in the large-eddy simulation of the atmospheric surface layer.

Chauhan, Kapil; Hutchins, Nicholas; Monty, Jason; Marusic, Ivan

2013-04-01

132

Coherent structures in compressible free-shear-layer flows  

SciTech Connect

Large scale coherent structures are intrinsic fluid mechanical characteristics of all free-shear flows, from incompressible to compressible, and laminar to fully turbulent. These quasi-periodic fluid structures, eddies of size comparable to the thickness of the shear layer, dominate the mixing process at the free-shear interface. As a result, large scale coherent structures greatly influence the operation and efficiency of many important commercial and defense technologies. Large scale coherent structures have been studied here in a research program that combines a synergistic blend of experiment, direct numerical simulation, and analysis. This report summarizes the work completed for this Sandia Laboratory-Directed Research and Development (LDRD) project.

Aeschliman, D.P.; Baty, R.S. [Sandia National Labs., Albuquerque, NM (United States). Engineering Sciences Center; Kennedy, C.A.; Chen, J.H. [Sandia National Labs., Livermore, CA (United States). Combustion and Physical Sciences Center

1997-08-01

133

Structure of the magnetopause current layer at the subsolar point  

SciTech Connect

A one-dimensional electromagnetic particle simulation model developed for the magnetopause current layer between the shocked solar wind and the dipole magnetic field at the subsolar point has been extended to include the interplanetary magnetic field (IMF) in the solar wind. Interaction of the solar wind with the vacuum dipole field as well as the dipole field filled with a low-density magnetospheric plasma are studied. It is found that the width and the structure of the magnetopause current layer differ markedly depending on the direction of the IMF. When the IMF is pointing southward, the current layer between the solar wind and the dipole field is narrow, and the magnetic field has a single ramp structure caused by the reflection of the solar wind at that point. The current layer becomes several times wider and the magnetic field develops a multiple ramp structure when the IMF is northward. This broadening of the current layer is caused by the multiple reflection of the solar wind by the magnetic field. For the northward IMF the magnetic field does not change its sign across the current layer, so that the E {times} B drift of the solar wind electrons remains the same direction, while for the southward IMF is reverses the sign. This results in a single reflection of the solar wind for the southward IMF and multiple reflections for the northward IMF. When a low-density magnetospheric plasma is present in the dipole magnetic field beyond the reflection point of the solar wind electrons. The width of the ion current layer is of the order of the solar wind ion gyroradius; however, the current associated with the ions remains much smaller than the electron current so long as the density of the magnetospheric plasma is much smaller than the density of the solar wind.

Okuda, H. (Princeton Univ., NJ (United States))

1992-02-01

134

Novel layer-by-layer structured nanofibrous mats coated by protein films for dermal regeneration.  

PubMed

Layer-by-layer coating technique is effective in modifying the surface of nanofibrous mats, but overmuch film-coating makes the mats less porous to hardly suit the condition for tissue engineering. We developed novel nanofibrous mats layer-by-layer coated by silk fibroin and lysozyme on the cellulose electrospun template via electrostatic interaction. The film-coating assembled on the mats was not excessive because the charge of the proteins varied in the coating process due to different pH value. In addition, pure nature materials made the mats nontoxic, biodegradable and low-cost. The morphology and composition variation during layer-by-layer coating process was investigated and the results showed that the structure and thickness of film-coatings could be well-controlled. The antibacterial assay and in vitro cell experiments indicated that the mats could actively inhibit bacteria and exhibit excellent biocompatibility. In vivo implant assay further verified the mats cultured with human epidermal cells could promote wound healing and avoid wound infection. Therefore, these mats showed promising prospects when performed for dermal reconstruction. PMID:24734533

Xin, Shangjing; Li, Xueyong; Wang, Qun; Huang, Rong; Xu, Xiaoli; Lei, Zhanjun; Deng, Hongbing

2014-05-01

135

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

136

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

137

Structural reinforcement of microvascular networks using electrostatic layer-by-layer assembly with halloysite nanotubes.  

PubMed

We demonstrate a method for tailoring local mechanical properties near channel surfaces of vascular structural polymers in order to achieve high structural performance in microvascular systems. While synthetic vascularized materials have been created by a variety of manufacturing techniques, unreinforced microchannels act as stress concentrators and lead to the initiation of premature failure. Taking inspiration from biological tissues such as dentin and bone, these mechanical deficiencies can be mitigated by complex hierarchical structural features near to channel surfaces. By employing electrostatic layer-by-layer assembly (ELbL) to deposit films containing halloysite nanotubes onto scaffold surfaces followed by matrix infiltration and scaffold removal, we are able to controllably deposit nanoscale reinforcement onto 200 micron diameter channel surface interiors in microvascular networks. High resolution strain measurements on reinforced networks under load verify that the halloysite reduces strain concentrations and improves mechanical performance. PMID:24652338

Olugebefola, Solar C; Hamilton, Andrew R; Fairfield, Daniel J; Sottos, Nancy R; White, Scott R

2014-01-28

138

Improvement in photoconductor film properties by changing dielectric layer structures  

NASA Astrophysics Data System (ADS)

In recent times, digital X-ray detectors have been actively applied to the medical field; for example, digital radiography offers the potential of improved image quality and provides opportunities for advances in medical image management, computer-aided diagnosis and teleradiology. In this study, two candidate materials (HgI2 and PbI2) have been employed to study the influence of the dielectric structure on the performance of fabricated X-ray photoconducting films. Parylene C with high permittivity was deposited as a dielectric layer using a parylene deposition system (PDS 2060). The structural and morphological properties of the samples were evaluated field emission scanning electron microscopy and X-ray diffraction. Further, to investigate improvements in the electrical characteristics, a dark current in the dark room and sensitivity to X-ray exposure in the energy range of general radiography diagnosis were measured across the range of the operating voltage. The electric signals varied with the dielectric layer structure of the X-ray films. The PbI2 film with a bottom dielectric layer showed optimized electric properties. On the other hand, in the case of HgI2, the film with a top dielectric layer showed superior electric characteristics. Further, although the sensitivity of the film decreased, the total electrical efficiency of the film improved as a result of the decrease in dark current. When a dielectric layer is deposited on a photoconductor, the properties of the photoconductor, such as hole-electron mobility, should be considered to improve the image quality in digital medical imaging application. In this study, we have thus demonstrated that the use of dielectric layer structures improves the performance of photoconductors.

Kim, S.; Oh, K.; Lee, Y.; Jung, J.; Cho, G.; Jang, G.; Cha, B.; Park, J.; Nam, S.

2011-01-01

139

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 Degree-Sign , R = 0.052 for 6262 reflections). The main crystal data are as follows: a = 9.3409(8) Angstrom-Sign , b = 9.3579(7) Angstrom-Sign , c = 18.8333(14) Angstrom-Sign , {alpha} = 80.365(6) Degree-Sign , {beta} = 75.816(6) Degree-Sign , {gamma} = 59.870(5) Degree-Sign , V = 1378.7(2) Angstrom-Sign {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}{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., E-mail: yakubol@geol.msu.ru [Lomonosov Moscow State University (Russian Federation); Massa, W. [Philipps-Universitaet Marburg (Germany); Chukanov, N. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2008-03-15

140

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

141

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

142

Bending a periodically layered structure for transformation acoustics  

Microsoft Academic Search

Anisotropic acoustic metamaterials have been proved very useful for their high potential in guiding and manipulating sound energy. In this letter, we further develop the idea by using periodically layered structures for transformational acoustics. Such a simple scheme periodically inserts identically bent solid plates in a background fluid. It forms a metamaterial with high refractive index normal to the curved

Zixian Liang; Jensen Li

2011-01-01

143

Structure of spherical electric double layers: A density functional approach  

Microsoft Academic Search

A density functional theory is presented for the structure of spherical electric double layers within the restricted primitive model, where the macroion is considered as a hard sphere having uniform surface charge density, the small ions as charged hard spheres, and the solvent is taken as a dielectric continuum. The theory is partially perturbative as the hard-sphere contribution to the

Teena Goel; Chandra N. Patra

2007-01-01

144

Using Layer-Cake Geology to Illustrate Structural Topographic Relationships.  

ERIC Educational Resources Information Center

Discusses some of the difficulties of visualizing underlying geologic structural patterns by using maps or wooden blocks. Suggests the use of a modified layer cake to show dipping beds, folds, faults and differential erosion, as well as the relationships of stream valleys to outcrop patterns. (TW)

Wagner, John Robert

1987-01-01

145

Electron-Phonon Interaction in Semiconducting Layer Structures  

Microsoft Academic Search

A new electron-phonon interaction characteristic of layer structures is described. Depending on the strength of the coupling between electron and lattice, this interaction, which involves short-range forces, leads to free or self-trapped charge carriers. The theoretical findings are compared with the experimentally determined charge-carrier mobilities in GaSe and MoS2.

R. Fivaz; E. Mooser

1964-01-01

146

Scattering of X-Rays by Layered Structures.  

National Technical Information Service (NTIS)

The diffraction of X-rays by perfect layered crystal structures is analyzed, with particular attention given to both the incidence of plane waves and collimated beams on a crystal plate of finite breadth set for Laue diffraction (or substantial transmissi...

W. R. Jones

1966-01-01

147

Optical Detection Using Four-Layer Semiconductor Structures.  

National Technical Information Service (NTIS)

The application of a thyristor (a four-layer P1-N1-P2-N2 semiconductor structure) as an optical detector is explored. Based on laboratory experiments which demonstrated that this device produces a pulse- mode output to incident light, the thyristor is inv...

D. A. Moore

2005-01-01

148

Thermal and wind structure of the monsoon trough boundary layer  

NASA Astrophysics Data System (ADS)

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 of the symbols N, S and U, standing respectively for neutral, stable or unstable conditions in the different layers, beginning with the one closest to the ground. It is found that, of the 29 combinations possible, only the seven classes, S, SS', SNS', NS, NSS', USS' and UNS are observed, where S' stands for a stable layer with a different gradient of 0 r. than in the layer S. It is also found that, in 90% of the launches at 0530 hr, 48% of the launches at 1730 hr and 69% of the launches around 1100 hr, the first radiosonde layer near the ground is stable; the classical mixed layer was found in only 11 % of the data set analysed, and, if present on other occasions, must have been less than 250 m in height, the first level at which radiosonde data are available. Supplementing the above data, sodar echograms, available during 82% of the time between June and August 1990, suggest a stable layer up to a few tens of metres 48% of the time. A comparative study of the radiosonde data at Ranchi shows that the frequent prevalence of stability near the surface at Jodhpur cannot be attributed entirely to the large scale subsidence known to be characteristic of the Rajasthan area. Further, data at Jodhpur reveal a weak low level jet at heights generally ranging from 400 to 900 m with wind speeds of 6 to 15 m/s. Based on these results, it is conjectured that the lowest layers in the atmosphere during the monsoons, especially with heavy clouding or rain, may frequently be closer to the classical nocturnal boundary layer than to the standard convective mixed layer, although often with shallow plumes that penetrate such a stable layer during daytime.

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

1996-09-01

149

A model for a shear-free convective boundary layer with parameterized capping inversion structure  

NASA Astrophysics Data System (ADS)

The paper extends Deardorff's general structure parameterization for a shear-free convective boundary layer. The model suggested employs the mixed layer hypothesis that the buoyancy (which is defined as b = g(rho(sub 0) - rho/rho(sub 0) where rho is the density, rho(sub 0) is the reference density, and g is the acceleration due to gravity) is constant with height within the mixed layer. The buoyancy flux zero-crossing height is taken as the mixed layer. The buoyancy flux zero-crossing height is taken as the mixed layer depth. The vertical buoyancy profile within the capping inversion, where the buoyancy flux is negative due to entrainment, is made dimensionless, using the buoyancy difference across the inversion and its thickness as appropiate scales. The auhtors examine the idea against the data from atmospheric measurements, laboratory experiments with buoyancy-agitated turbulence, and large-eddy simulations. The rate equations for the mixed layer and inversion layer depths are derived using the turbulent kinetic energy equation and Deardorff's scaling hypothesis refined to account for the inversion layer structure. The constants of the model are evaluated from the data of atmospheric, oceanic, and laboratory measurements, and large-eddy simulations. The causes of divergence of the estimates based on data of different origin are discussed. The model is applied to simulate convective entrainment in laboratory experiments. A reasonable explanation for ambiguous behavior of the entrainment zone in the experiments with a two-layer fluid is suggested. The model simulates transition regimes of convective entrainment in multilayer fluid strongly affected by the nonstationary of the entrainment zone.

Fedorovich, E. E.; Mironov, D. V.

1995-01-01

150

Electronic Structure Properties of Graphene/Boron Nitride Layered Systems  

NASA Astrophysics Data System (ADS)

We explore the properties of systems composed of two or three layers of graphene and hexagonal boron nitride (hBN) using the Vienna Ab-Initio Simulation Package (VASP), a software package for performing first principles simulations based on density functional theory (DFT). Particular attention is given to the contribution of inter-layer dispersion interactions, which are modeled within VASP by the ``DFT-D2'' method of Grimme. We obtain the binding and van der Waals energies, and inter-layer separations for the most stable stacking configurations of each of the following systems: hBN/graphene, graphene/hBN/graphene, hBN/graphene/hBN, hBN/hBN/graphene, and graphene/graphene/hBN. We observe that the addition of hBN layers to graphene structures induces a band gap, ranging from 0.024 eV, for the graphene/hBN/graphene arrangement, to 0.16 eV, for the hBN/graphene/hBN arrangement. These results, specifically band gaps on the same order as those of silicon and germanium, indicate that graphene/hBN layered structures may have applications in electronics.

Petulante, Max; Le, Nam; Woods, Lilia

2012-02-01

151

In situ processing of silicon carbide layer structures  

SciTech Connect

A novel route to low-cost processing of silicon carbide (SiC) layer structures is described. The processing involves pressureless liquid-phase cosintering of compacted powder layers of SiC, containing alumina (Al{sub 2}O{sub 3}) and yttria (Y{sub 2}O{sub 3}) sintering additives to yield a yttrium aluminum garnet (YAG) second phase. By adjusting the {beta}:{alpha} SiC phase ratios in the individual starting powders, alternate layers with distinctly different microstructures are produced: (i) homogeneous microstructures, with fine equiaxed SiC grains, designed for high strength; and (ii) heterogeneous microstructures with coarse and elongate SiC grains, designed for high toughness. By virtue of the common SiC and YAG phases, the interlayer interfaces are chemically compatible and strongly bonded. Exploratory Hertzian indentation tests across a bilayer interface confirm the capacity of the tough heterogeneous layer to inhibit potentially dangerous cracks propagating through the homogeneous layer. The potential for application of this novel processing approach to other layer architectures and other ceramic systems is considered.

Padture, N.P.; Pender, D.C. [Univ. of Connecticut, Storrs, CT (United States); Wuttiphan, S.; Lawn, B.R. [National Inst. of Standards and Technology, Gaithersburg, MD (United States). Materials Science and Engineering Lab.

1995-11-01

152

Magnetic layered structure for the production of polarized neutron microbeams  

NASA Astrophysics Data System (ADS)

A neutron waveguide is a three-layer structure in which a guiding layer with low optical potential is placed between two cladding layers with high optical potential. Under proper operation conditions, the neutron density is resonantly enhanced inside the guiding layer. In our experimental scheme, the neutron beam enters through the surface of the top layer at glancing angle and goes out from the edge of the guiding layer, with an angular distribution corresponding to Fraunhofer diffraction from a narrow slit. The incident neutron beam is relatively wide (0.1 mm) and highly collimated (0.01°). The outgoing sub-micron beam is extremely narrow at the outlet (0.1 ?m) and more divergent (0.1°). So far only the production of unpolarized sub-micron neutron beams has been reported. Here we present first experiments on polarized sub-micron neutron beams. For these studies a polarized incident beam was used and two types of magnetic waveguides were investigated: a polarizing magnetic waveguide Fe(20 nm)/Cu(140 nm)/Fe(50 nm)//glass and a non-polarizing magnetic waveguide Py(10 nm)/Al(140 nm)/Py(50 nm)//glass (Py is permalloy). The waveguide samples were characterized by polarized neutron reflectometry.

Kozhevnikov, S. V.; Rühm, A.; Ott, F.; Pleshanov, N. K.; Major, J.

2011-06-01

153

Stable Single-Layer Honeycomblike Structure of Silica  

NASA Astrophysics Data System (ADS)

Silica or SiO2, 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, Si2O5, 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.

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

2014-06-01

154

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

Ozçelik, V Ongun; Cahangirov, S; Ciraci, S

2014-06-20

155

Structural characterisation of a layered double hydroxide nanosheet.  

PubMed

We report the atomic-scale structure of a Zn2Al-borate layered double hydroxide (LDH) nanosheet, as determined by reverse Monte Carlo (RMC) modelling of X-ray total scattering data. This study involves the extension of the RMC method to enable structural refinement of two-dimensional nanomaterials. The refined LDH models show the intra-layer geometry in this highly-exfoliated phase to be consistent with that observed in crystalline analogues, with the reciprocal-space scattering data suggesting a disordered arrangement of the Zn(2+) and Al(3+) cations within the nanosheet. The approach we develop is generalisable and so offers a method of characterising the structures of arbitrary nanosheet phases, including systems that support complex forms of disorder within the nanosheets themselves. PMID:24906206

Funnell, Nicholas P; Wang, Qiang; Connor, Leigh; Tucker, Matthew G; O'Hare, Dermot; Goodwin, Andrew L

2014-06-26

156

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.

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

2013-01-01

157

Structural attributes affecting peptide entrapment in PEO brush layers.  

PubMed

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

2013-06-01

158

Deep Crack Detection around Fastener Holes in Airplane Multi-Layered Structures Using GMR-Based Eddy Current Probes  

NASA Astrophysics Data System (ADS)

Rotational and linearly scanned eddy current probes based on giant magnetoresistive (GMR) sensors have been developed for detecting buried cracks and flaws emanating from fastener holes. The use of shaped excitation coils, the original positioning and orientation of the magnetic sensors enhance the sensitivity of these probes to buried defects while reducing the influence of fastener holes edge. Corner cracks of 2.5 mm in length were detected in the second layer of a 13 mm thick two-layer structure.

Dogaru, T.; Smith, C. H.; Schneider, R. W.; Smith, S. T.

2004-02-01

159

Electronic structure of misfit-layered calcium cobaltite  

Microsoft Academic Search

We have performed the first-principles calculations on (Ca2CoO3)4(CoO2)6 to understand electronic structures of the misfit-layered calcium cobaltite, (Ca2CoO3)xCoO2, within the generalized gradient approximation. The optimized structure, consisting of a triple rocksalt-type Ca2CoO3 subsystem and a CdI2-type CoO2 subsystem in which their respective octahedra are significantly distorted, shows good agreement with recent experiment. The calculated electronic structures include two-dimensionally dispersive eg

Ryoji Asahi; Jun Sugiyama; Toshihiko Tani

2002-01-01

160

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

161

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

162

Fabrication of three-dimensional polymer quadratic nonlinear grating structures by layer-by-layer direct laser writing technique  

NASA Astrophysics Data System (ADS)

We demonstrate the fabrication of a three-dimensional (3D) polymer quadratic nonlinear (?(2)) grating structure. By performing layer-by-layer direct laser writing (DLW) and spin-coating approaches, desired photobleached grating patterns were embedded in the guest--host dispersed-red-1/poly(methylmethacrylate) (DR1/PMMA) active layers of an active-passive alternative multilayer structure through photobleaching of DR1 molecules. Polyvinyl-alcohol and SU8 thin films were deposited between DR1/PMMA layers serving as a passive layer to separate DR1/PMMA active layers. After applying the corona electric field poling to the multilayer structure, nonbleached DR1 molecules in the active layers formed polar distribution, and a 3D ?(2) grating structure was obtained. The ?(2) grating structures at different DR1/PMMA nonlinear layers were mapped by laser scanning second harmonic (SH) microscopy, and no cross talk was observed between SH images obtained from neighboring nonlinear layers. The layer-by-layer DLW technique is favorable to fabricating hierarchical 3D polymer nonlinear structures for optoelectronic applications with flexible structural design.

Bich Do, Danh; Lin, Jian Hung; Diep Lai, Ngoc; Kan, Hung-Chih; Hsu, Chia Chen

2011-08-01

163

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

164

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

165

Crystallographic structure and superconductive properties of Nb-Ti films with an artificially layered structure  

SciTech Connect

Artificially layered niobium-titanium (Nb-Ti) films with various thickness ratios (3/1--1/3) and periodicities (2--100 A) are made in an argon or in a mixed argon/nitrogen atmosphere by a dc magnetron sputtering method. Films with small periodicities (less than 30 A) have an artificial superlattice structure (ASL) with crystallographic coherence between constituent layers, where Nb and Ti grow epitaxially on the closest planes. The crystallographic structures of films are bcc with the (110) plane parallel to the film for films with the same or a thicker Nb layer than a Ti layer, and hcp with the (001) plane parallel to the film for films with a thinner Nb layer than a Ti layer. Films with large periodicities have an artificial superstructure (ASS) with only periodic stacking of constituent layers. Films deposited in the Ar/N atmosphere also have the artificially layered structures of ASL or ASS. The artificially layered structure is thermally stable at temperatures up to 500 {degree}C. The superconducting properties of the films depend strongly on the periodicity and thickness ratio of Nb and Ti layers. The dependence of the transition temperature on the periodicity and thickness ratio is qualitatively explained by a proximity effect with a three-region model. Films with periodicities less than 20 A, composed of the same or a thicker Nb layer than a Ti layer, show high transition temperatures (above 9.3 K). The highest {ital T}{sub {ital c}} of about 13.6 K is obtained in the film composed of monatomic layers of constituents deposited in an Ar atmosphere including 30 vol % N.

Sato, N. (SONY Corporation, Research Center, 7-35 Kitashinagawa-6, Shinagawa-ku, Tokyo 141, Japan (JP))

1990-06-15

166

The Origin of Mercury's Magnetic Field and Its Multipolar Structure  

Microsoft Academic Search

The origin of Mercury's planetary magnetic field is still unclear and likely to remain an unsolved problem at least until the currently planned space missions, BepiColombo and Messenger perform a full magnetic mapping of the planet. However, the likely generation mechanisms have a common feature. It is unlikely that the planetary field is dominated by the dipolar term; multipolar terms

A. Balogh; G. Giampieri

2002-01-01

167

Polymer layered silicate nanocomposites: Structure, morphology, and properties  

NASA Astrophysics Data System (ADS)

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 available. Upon amalgamation of organoclays with polymer matrix nanocomposites, polymer chains can penetrate in between the silicate layers and result in an intercalated structure where the clay stack remains intact but the interlayer spacing is increased. When penetration becomes more severe, disintegration of clay stacks can occur, resulting in an exfoliated structure. It has often been observed that exfoliation is not complete down to the level of isolated silicate layers; rather, the large clay stacks are broken up into shorter stacks termed 'tactoids' together with a few individual silicate layers, resulting in a kind of mixed intercalated-exfoliated structure. Organoclay particles are mostly intercalated, having a preferred orientation with the clay gallery planes being preferentially parallel to the plane of the pressed film. Preferential orientation of organoclays affects the barrier properties of polymer membranes. Additional fillers like carbon black can induce a change in the orientation of organoclays. The effect of carbon black on the orientation of organoclays was elucidated and a relationship between orientation and permeability of air through such membranes was established. We have also investigated the flammability properties of a series of polymer nanocomposites, containing various Transition Metal Ion (TMI) modified organoclays. The improved fire retardation in nanocomposites with TMI-modified organoclays can be attributed to enhanced carbonaceous char formation during combustion, i.e., charring promoted by the presence of catalytically active TMI. Polymer nanocomposite materials depend not only on the properties of individual components but also on their morphology and interfacial interactions. In polymer nanocomposites, the interfacial interactions are maximized due to the large surface area of the filler particles exposed to the polymer matrix, resulting in unique anisotropic properties. Thus, it will be of great importance to achieve exfoliation of the lamellar stacks prior to mixing with the polymer matrix, in the dry powder state or in a solution state. In layered silicates the lamellar stacks are held by electrostatic interactions between the basal charges and ions present within the basal spacing. Lamellar stacks of layered silicates can be exfoliated if the amount of energy gained by them is higher than the electrostatic energy required to hold the lamellar stacks together. Using 'Microwave radiation', exfoliation of organoclays was achieved. Various characterization techniques were used to evaluate structure, morphology and properties of fillers and polymer nanocomposites.

Nawani, Pranav

168

Influence of Coulomb collisions on the structure of reconnection layers  

SciTech Connect

The influence of Coulomb collisions on the structure of reconnection layers is examined in neutral sheet geometry using fully kinetic simulations with a Monte Carlo treatment of the Fokker-Planck operator. The algorithm is first carefully benchmarked against key predictions from transport theory, including the parallel and perpendicular resistivities as well as the thermal force. The results demonstrate that the collisionality is accurately specified, thus allowing the initial Lundquist number to be chosen as desired. For modest Lundquist numbers S < or approx. 1000, the classic Sweet-Parker solution is recovered. Furthermore, a distinct transition to a faster kinetic regime is observed when the thickness of the resistive layer {delta}{sub SP} falls below the ion inertial length d{sub i}. For higher Lundquist numbers S > or approx. 1000, plasmoids (secondary islands) are observed within the elongated resistive layers. These plasmoids give rise to a measurable increase in the reconnection rate and for certain cases induce a transition to kinetic regimes sooner than expected from the {delta}{sub SP}{approx_equal}d{sub i} condition. During this transition, the reconnection electric field exceeds the runaway limit, leading to electron scale current layers in which the nonideal electric field is supported predominantly by off-diagonal components in the electron pressure tensor, along with a residual contribution from electron-ion momentum exchange. These weakly collisional electron layers are also unstable to the formation of new plasmoids.

Daughton, W.; Roytershteyn, V.; Albright, B. J.; Yin, L.; Bowers, Kevin J. [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Karimabadi, H. [University of California, San Diego, La Jolla, California 92093 (United States)

2009-07-15

169

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

170

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

171

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

172

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

173

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

174

Structural simplicity and complexity of compressed calcium: electronic origin.  

PubMed

A simple cubic structure with one atom in the unit cell found in compressed calcium is counterintuitive to the traditional view of a tendency towards densely packed structures with an increase in pressure. To understand this unusual transformation it is necessary to assume electron transfer from the outer core band to the valence band, and an increase of valence electron number for calcium from 2 to ??3.5. This assumption is supported by the Fermi sphere-Brillouin zone interaction model that increases under compression. The recently found structure of Ca-VII with a tetragonal cell containing 32 atoms (tI32) is similar to that in the intermetallic compound In5Bi3 with 3.75 valence electrons per atom. Structural relations are analyzed in terms of electronic structure resemblance. Correlations of structure and physical properties of Ca are discussed. PMID:24892588

Degtyareva, Valentina F

2014-06-01

175

Thermal structure in the Venus middle cloud layer  

NASA Technical Reports Server (NTRS)

Thermal structure measurements obtained by the two Vega balloons show the Venus atmosphere in the middle cloud layer to be near-adiabatic, on the whole; but discrete air masses are present that differ slightly from one another in potential temperature and entropy. The Vega 1 temperatures are 6.5 K warmer than measured by Vega 2 at given pressures. Measurements taken by the Vega 2 lander on descent through these levels agree with the Vega 2 balloon data.

Linkin, V. M.; Lipatov, A. N.; Shurupov, A. A.; Ignatova, S. P.; Frank, G. A.; Seiff, A.; Ragent, B.; Young, R. E.; Elson, L. S.; Preston, R. A.

1986-01-01

176

Mobility of Charge Carriers in Semiconducting Layer Structures  

Microsoft Academic Search

The electrical resistivities and the Hall constants of the compound semiconductors GaSe, MoS2, MoSe2, and WSe2, which crystallize in layer structures, have been measured at temperatures ranging from 100 to 700°K. The Hall mobilities derived from these measurements are all of the order of 100 cm2\\/V sec at room temperature, and they exhibit a temperature dependence of the form mu~(TT0)-n,

R. Fivaz; E. Mooser

1967-01-01

177

Aliphatic structure of humic acids; a clue to their origin  

USGS Publications Warehouse

Nuclear magnetic resonance spectra (both 1H and 13C) of humic acids from diverse depositional environments indicate the presence of aromatic chemical structures, most likely derived from lignin of vascular plants, and complex, paraffinic structures, most likely derived from algal or microbial sources. The latter components account for a major fraction of humic acid structures in both terrestrial and aquatic environments, suggesting that algae or microbes play a large role in humification of organic remains from both systems. ?? 1981.

Hatcher, P. G.; Maciel, G. E.; Dennis, L. W.

1981-01-01

178

Structure of the magnetopause current layer at the subsolar point  

SciTech Connect

A one-dimensional electromagnetic particle simulation model developed for the magnetopause current layer between the shocked solar wind and the dipole magnetic field at the subsolar point has been extended to include the interplanetary magnetic field (IMF) in the solar wind. Interaction of the solar wind with the vacuum dipole field as well as the dipole field filled with a low density magnetospheric plasma are studied. It is found that the width and the structure of the magnetopause current layer differ markedly depending on the direction of the IMF. When the IMF is pointing southward, the current layer between the solar wind and the dipole field is narrow and the magnetic field has a single ramp structure caused by the reflection of the solar wind at that point. The current layer becomes several times wider and the magnetic field developes a multiple ramp structure when the IMF is northward. This broadening of the current layer is caused by the multiple reflection of the solar wind by the magnetic field. For the northward IMF, the magnetic field does not change its sign across the current layer so that the E {times} B drift of the solar wind electrons remains the same direction while for the southward IMF, it reverses the sign. This results in a single reflection of the solar wind for the southward IMF and multiple reflections for the northward IMF. When a low density mangetospheric plasma is present in the dipole magnetic field, a small fraction of the solar wind ions are found to penetrate into the dipole magnetic field beyond the reflection point of the solar wind electrons. The width of the ion current layer is of the order of the solar wind ion gyroradius, however, the current associated with the ions remains much smaller than the electron current so long as the density of the magnetospheric plasma is much smaller than the density of the solar wind. Comparisons of our simulation results with the magnetopause crossing near the subsolar point are provided.

Okuda, H.

1991-12-01

179

Identifying the origin of groundwater samples in a multi-layer aquifer system with Random Forest classification  

NASA Astrophysics Data System (ADS)

Accurate identification of the origin of groundwater samples is not always possible in complex multilayered aquifers. This poses a major difficulty for a reliable interpretation of geochemical results. The problem is especially severe when the information on the tubewells design is hard to obtain. This paper shows a supervised classification method based on the Random Forest (RF) machine learning technique to identify the layer from where groundwater samples were extracted. The classification rules were based on the major ion composition of the samples. We applied this method to the Campo de Cartagena multi-layer aquifer system, in southeastern Spain. A large amount of hydrogeochemical data was available, but only a limited fraction of the sampled tubewells included a reliable determination of the borehole design and, consequently, of the aquifer layer being exploited. Added difficulty was the very similar compositions of water samples extracted from different aquifer layers. Moreover, not all groundwater samples included the same geochemical variables. Despite of the difficulty of such a background, the Random Forest classification reached accuracies over 90%. These results were much better than the Linear Discriminant Analysis (LDA) and Decision Trees (CART) supervised classification methods. From a total of 1549 samples, 805 proceeded from one unique identified aquifer, 409 proceeded from a possible blend of waters from several aquifers and 335 were of unknown origin. Only 468 of the 805 unique-aquifer samples included all the chemical variables needed to calibrate and validate the models. Finally, 107 of the groundwater samples of unknown origin could be classified. Most unclassified samples did not feature a complete dataset. The uncertainty on the identification of training samples was taken in account to enhance the model. Most of the samples that could not be identified had an incomplete dataset.

Baudron, Paul; Alonso-Sarría, Francisco; García-Aróstegui, José Luís; Cánovas-García, Fulgencio; Martínez-Vicente, David; Moreno-Brotóns, Jesús

2013-08-01

180

Structural Investigation of Layered Niobates by DFT Calculations  

NASA Astrophysics Data System (ADS)

Layered forms of inorganic niobates have been used for various applications, such as charge transport and storage, photo-catalysis, solid acids, magnetic materials, superconductors, magneto-resistors and photo-luminescence devices. The layered niobates exists in different geometrical forms and composition with variation in the packing of oxide lattice by the constituting monovalent, divalent/trivalent and pentavalent cations. Four different types of lamellar niobates are studied in this research by theoretical methods, namely the all-electron full-potential DFT method using plane wave and periodic boundary conditions. A common feature of all the layered niobates is that the basic building block, NbO6 octahedral units are shared with each other at the corners and edges forming a covalent network and that the sharing is terminated in a particular direction. These octahedral units get modulated along with the geometry of interlayer interface with the change in the composition of the material. The macroscopic structure change is reflected by the alteration of the unit cell axes whereas the local change at various sites in the structure is revealed by the variation of the atomic distances and angles/tilt. The different properties of the layered compounds are a function of these structural variations and thus understanding the mechanism and the characteristics requires atomic level analysis. Calculations reveal the local bonding details and the bulk geometry of a material and can be compared to that obtained from powder diffraction methods. The EFG tensor which is a sensitive probe of the electronic environment around a quadrupolar nucleus can be used to monitor the minor changes in the bond lengths and angles in various structures. Among the configurations lying in the minima of the potential energy surfaces, the one representing the real material would be the one matching with the EFG tensor calculated from DFT methods with that determined from the SSNMR experiments. The main aims of this research work are summarized as follows- 1. Calculation of the crystal structure of layered material and comparison with the published ones for the refinement. 2. Proposition of the crystal structure of acid forms of the layered materials and of the nanosheets. 3. Elucidation of the distortion of NbO6 building blocks, tilting along various axes, stacking sequences of the adjacent slabs, rearrangement of the interlayer gallery and location of protons; comparison of the results with those obtained from powder diffraction methods in case of availability. 4. Calculation of the EFG tensors at various sites (93Nb, 2H and 87Rb) in the lattice; comparison of the results with those obtained from SSNMR experiments in case of availability. 5. Using quadrupolar coupling as a guide for atomic level details for modeling the crystal structure of layered niobates and nanosheets with unknown geometry. 6. Establishing a correlation between a structure parameter and the quadrupolar coupling of various 93Nb sites in the structure.

Adhikari Subin, Jhashanath

181

Accurate characterization of a thick multilayer structure using the marking-layer-based scanning electron microscopy method  

NASA Astrophysics Data System (ADS)

A multilayer Laue lens (MLL) is a promising optics to advance the focusing resolution of hard x-rays to below 10 nm with high efficiency. It consists of a thickness-graded multilayer with hundreds or thousands of layers. To realize this nano-focusing optics, a high-precision characterization method is needed to measure the position and thickness of each layer. Scanning electron microscopy (SEM) combined with a marking layer method is illustrated in this paper. By inserting WSi2 layers as marking layers in the original MLL structure, the layer positions in different areas can be determined. All the SEM images can be stitched seamlessly and the thickness-graded multilayer is characterized more precisely compared with the conventional method. This new method can help in depositing a more accurate MLL to achieve near-theoretical focusing performance.

Huang, Qiushi; Li, Haochuan; Zhu, Jingtao; Wang, Zhanshan; Chen, Hong

2013-07-01

182

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

183

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

184

Local structure determination in strained-layer semiconductors  

NASA Astrophysics Data System (ADS)

The theory of elasticity accurately describes the deformations of macroscopic bodies under the action of applied stress [1]. In this review, we examine the internal mechanisms of elasticity for strained-layer semiconductor heterostructures. In particular, we present extended x-ray-absorption fine structure (EXAFS) and x-ray diffraction (XRD) measurements to show how the bond lengths and bond angles in semiconductor thin-alloy films change with strain when they are grown coherently on substrates with different lattice constants. The structural distortions measured by experiment are compared to valence-force field (VFF) calculations and other theoretical models. Atomic switching and interfacial strain at buried interfaces are also discussed.

Woicik, Joseph C.

2014-03-01

185

Synthesis and structural characterization of layered cuprates containing a lead halide separating layer  

SciTech Connect

A series of layered cuprates of the general formula Pb{sub y}(Ba/Sr){sub 4{minus}y}Cu{sub 2}MO{sub 8}X, where M = Nb, Ta, and Sb; X = Br and Cl; and y = 2, 3, have been synthesized. The detailed structural characterization of these materials has been performed using Rietveld refinement of high-resolution PND data. The compounds crystallize with a tetragonal unit cell, space group P4/mmm; cell parameters in the range a = 3.8982(2)--3.9732(2) {angstrom} and c = 15.3886(8)-15.8689(11) {angstrom}. The structure of the materials consists of two CuO{sub 5} square pyramids connected by a (Ba/Sr)MO{sub 3} perovskite layer, a unit also present in the widely studied Ln-1212 phases, with an interleaving Pb{sub 2}X layer. The material Pb{sub 2}Sr{sub 2}Cu{sub 2}SbO{sub 8}Cl has the shortest Cu-O in plane bond length of 1.9570(5) {angstrom}, which lies close to the length required for the observation of superconductivity. However, preliminary investigation of the electronic properties of these materials show that they exhibit semiconducting behavior down to 4 K.

Crooks, R.J.; Knee, C.S.; Weller, M.T. [Univ. of Southampton (United Kingdom). Dept. of Chemistry] [Univ. of Southampton (United Kingdom). Dept. of Chemistry

1998-12-01

186

Propagation of waves in layered structures viewed as number recognition  

NASA Astrophysics Data System (ADS)

We propose to consider multilayer spatial structures as numbers. An arbitrary finite sequence of layers with N values of a material parameter which determines the speed of wave propagation is considered as a number written in the numeration system with base N. Within the framework of this approach propagation of classical waves and quantum particles can be treated as number recognition. A problem is formulated of identification of a type among spatial sequences featuring unique spectral portraits versus spatial structure. It is shown possible to perform certain arithmetic operations by means of sequential propagation of waves through several structures. Using fractal Cantor structures as a representative example, spectral properties of waves are shown to reproduce certain properties of the corresponding numbers. A possibility is outlined to use the above approach for data storage. If a set of numbers possessing unique spectral portraits forms a complete set, then compact coding of arbitrary numbers will become possible.

Gaponenko, S. V.; Zhukovsky, S. V.; Lavrinenko, A. V.; Sandomirskii, K. S.

2002-04-01

187

Chemical and physical evolution of the ‘lower layered sequence’ from the nepheline syenitic Ilímaussaq intrusion, South Greenland: Implications for the origin of magmatic layering in peralkaline felsic liquids  

NASA Astrophysics Data System (ADS)

The Mid-Proterozoic composite Ilímaussaq complex, South Greenland, is a classic locality to study magmatic layering in evolved peralkaline magmas. Most of the rock units show magmatic layering to differing extents, but 'kakortokites' - generally medium-grained agpaitic nepheline syenites - show a spectacular recurrence of black, red and white layers, which is due to regular changes in the modal contents of arfvedsonitic amphibole, eudialyte (sensu lato), alkali feldspar and nepheline, respectively. These three-layer units are found in the lower part of the intrusion and recur 29 times before grading into the overlying lujavrites (melanocratic agpaitic nepheline syenites), which are generally fine-grained and fissile with less-developed layering. The compositional trends observed in amphibole and eudialyte throughout the stratigraphic sequence reflect various processes including the chemical evolution of the melt by crystal fractionation, changes in the crystallising mineral assemblage and sub-solidus alteration. Eudialyte is the first mineral to crystallise in the investigated sequence and is therefore appropriate for recording evolution trends within the melt. Amphibole, on the other hand, always crystallises later and is therefore affected by other crystallising minerals. A detailed microprobe study of both minerals through the whole kakortokite stratigraphy displays surprisingly little change in mineral compositions within the kakortokites, but strong fractionation trends in the overlying lujavrites. Although various models have been proposed to explain the recurrence of the 29 rhythmic units, the origin of this prominent magmatic layering in the kakortokites and the lack of mineralogical and strong mineral chemical changes has not been quantitatively explained. We propose, that in the kakortokites, minerals were probably separated from each other as a result of their different densities. The interior cooled, resulting in crystallization but only a very small proportion of crystals (0.1-0.3% for each of the four minerals) could remain suspended in the melt before gravity forced them to settle down in a stagnant layer of reduced convection. A combination of volatile pressure variations caused by eruptive activity and repeated replenishment can explain the oscillating liquidus temperature, the small changes in mineral compositions and such a process would produce enough crystals to form the 29 layers.

Pfaff, Katharina; Krumrei, Thomas; Marks, Michael; Wenzel, Thomas; Rudolf, Tina; Markl, Gregor

2008-12-01

188

Nepheloid Layers: Origin and Development In A Narrow Continental Shelf (nw Portugal)  

NASA Astrophysics Data System (ADS)

A general hydrographic, nephelometric and sedimentological surveying of the NW Portuguese continental shelf and slope was undertaken, under winter and spring con- ditions in order to elaborate a conceptual model of suspended sediments (nepheloid layer) dynamics. Two major situations were found: 1) Spring/Summer - with northerly winds (upwelling) and low energetic wave regime that favour the deposition of sedi- ments. The northerly winds promote offshore transport in the surface nepheloid layer (SNL) and the establishment of a seasonal thermocline allow the expansion of the SNL to the west. The SNL can reach or even cross the shelf-break (?50 km from coastline). Particulate organic carbon (POC) content in this layer highlights the higher contribution of biogenic particles (average concentration of 22%); 2) Winter, with southerly winds (downwelling) and high energetic wave regime that favour mid- shelf sediments resuspension and offshore transport in the bottom nepheloid layer (BNL). In the shelf-break the BNL detached to form intermediate nepheloid layers (INL). The SNL is restricted to the inner shelf. The effect of southerly winds gener- ates shoreward Ekman transport and detains the offshore westward extension of this layer even during high river run-off periods. The POC content indicates a dominance of litogenic particles in suspension (average concentration of 8%). Over the mid- and inner-shelf the dominant resuspension mechanism is associated with surface waves (Vitorino et al., 2002). Estimates based on wave measurements at mid-shelf (86m depth) suggested that, in winter, the wave shear velocity frequently exceeds 1 cm/s, assumed as the critical shear velocity for the resuspension of the fine grained sedi- ments (34?m) of the bottom cover. Storm events, such as the one observed in November 1996 easily increase the wave shear velocities over 3 cm/s, leading to the increase of the BNL thickness (20-30m) (Vitorino et al., 2002; Oliveira et al., 2002). Low-frequency currents (periods longer than about 2 days) and internal waves can also lead to the resuspension of fine bottom sediments. Shelf morphology (outer shelf re- lieves and Porto submarine canyon) and sedimentary cover can also affect both spatial and vertical development of BNL.

Oliveira, A.; Vitorino, J.; Rodrigues, A.; Jouanneau, J. M.; Weber, O.; Dias, J. A.

189

Do The Concentrations Of Platinum Group Elements In The Younger Dryas Black Layer Really Support An Extraterrestrial Origin?  

NASA Astrophysics Data System (ADS)

An enigmatic carbon-rich black layer, of possible worldwide occurrence, is interpreted to indicate an extraterrestrial impact around 12.9 ka, a period coeval with the Younger Dryas (YD) environmental changes (Firestone et al. 2007, PNAS 104). This interpretation is based on the possible identification of a series of markers postulated to be of impact origin, such as magnetic grains and microspherules, charcoal, soot, C- spherules, nanodiamonds, fullerenes with extraterrestrial He and elevated concentrations of Ir. Among these markers, only the elevated Ir concentration is a non-ambiguous impact indicator. In early 2007, one of us (PC) measured the concentration of platinum group elements (including Ir) in 4 samples of this black layer. Allen West provided the samples along with their Ir concentrations. The samples originated from Howard Bay, NC (level HB-11D2) and Blackwater Draw, NM (levels BW-DT, D/C and BW-B/A), and were supposed to contain 15 ng/g Ir (<150 micron magnetic fraction), 2.0 ng/g Ir (bulk sediment), 2.25 ng/g Ir (bulk sediment) and <0.1 ng/g Ir (bulk sediment) respectively. In Table 1 of Firestone et al. (2007) the Blackwater Draw sample contains 2.3 ng/g Ir, and the separated magnetic fraction rises up 24 ng/g. The obtained results showed that none of the 4 samples yielded PGE concentrations above 0.5 ng/g. Considering the attention the claim of a possible YD impact has generated in the last year, we are currently reanalyzing these 4 samples of the black layer using high precision NiS fire-assay preconcentration combined with ICP-MS analyses. On proven crater melt rocks or impact layers, the quantitation limits reach: 0.06 ng/g Ru, 0.01 ng/g Rh, 0.14 ng/g Pd, 0.06 ng/g Ir, and 0.1 ng/g Pt, far below the Ir values claimed by Firestone et al. (2007). In addition, these 4 samples are being analyzed for Os isotopes, known to be most sensitive for the detection of minute amounts of extraterrestrial components (%<%%<%0.05 wt%) in impact layers. The results of these new analyses will confirm or not the extraterrestrial origin of the Younger Dryas C-rich black layer.

Claeys, P.; Paquay, F.; Goderis, S.; Vanhaecke, F.

2008-12-01

190

Microstructure Analysis. Volume I. The Origin of Ocean Fine Structure.  

National Technical Information Service (NTIS)

The horizontal and vertical length scales of ocean fine structure appear to correlate to the corresponding wavelengths of inertial waves (internal waves whose motion is dominated by Coriolis forces). A priori, there are four possible non-linear mechanisms...

G. A. Simons

1975-01-01

191

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

192

Using in situ isotopic analyses of crystals to investigate the origins of layered intrusions  

NASA Astrophysics Data System (ADS)

An important conclusion from recent detailed textural and geochemical work on many volcanic rocks is that the crystals they contain are largely allochtonous. Isotopic work in particular has shown that crystals grew largely from magmatic reservoirs different from the host in which they are erupted. The term “antecryst” has been adopted to describe such crystals - associated with the magma system in space and time, perhaps cumulates from earlier episodes, but not directly grown from the magma in which they are entrained. Given that layered intrusions are formed entirely from crystals we should surely ask to what degree to the crystals represent a common magma source, or to what degree are they the accumulated record of recycled earlier episodes? The Rum layered intrusion, NW Scotland, has been sampled across a unit boundary (9/10) over which large changes in bulk rock initial Sr isotope ratio had been recorded. Analyses were performed using a microdrill and analysing Sr isotopes following column chemistry. This approach gives superior precision and spatial resolution. Sr isotopic heterogeneity was recovered at mineral and even intra-mineral scale. The isotopic variations coincide with observed grain boundaries and are therefore considered primary. A similar exercise for the Ferrar Dais layered intrusion of the Dry Valleys in Antarctica also showed inter-mineral isotopic heterogeneity. These results indicate that the crystals in each case have grown in isotopically different magmas and mechanically aggregated subsequently. The isotopic heterogeneity suggests that diffusive re-equilibration did not take place and the intrusions must have cooled relatively quickly (closure to Sr diffusion in <1000 years). In principle, isotopic variations over small (crystal-scale) distances can be used to constrain not only the crystal ancestry, but also the cooling histories of layered intrusions.

Davidson, J. P.; Tepley, F. J.; Font, L.

2009-12-01

193

Acoustic properties of the film/plate layered structure.  

PubMed

A new propagation medium-a layered structure composed of a film and a plate-is suggested and studied, using c-oriented ZnO and AlN films on (001), {100}-Si plate, as two opposite examples of slow-on-fast and fast-on-slow material combinations. For both structures, the modes belonging to Lamb, quasi-longitudinal (QL), and Anisimkin Jr.' (AN) families are found. For each family, the velocities v(n), displacement profiles, and electromechanical coupling coefficients K(n)2 for 4 electrode configurations are numerically calculated by the matrix method as a function of the mode order n = 0 to 8, plate thickness H/? = 0 to 2.0, and film thickness h/? = 0.02 to 0.04 (H and h are thicknesses; ? is the wavelength). Some high-order modes in the structure have K(n)2 = 0 for any H/?, h/?, and electrode configuration. Other modes possess variable K(n) 2 with a maximum value larger than the coupling coefficient for the Rayleigh SAWs in ZnO and AlN single crystals or layered structures using the same films and semi-infinite silicon substrate. There are also QL-modes having high velocity v(n), large K(n)2, and low propagation loss caused by liquid loading. These modes are well suited for liquid sensors. PMID:21429848

Anisimkin, Vladimir; Voronova, Natalia

2011-03-01

194

Characteristics and Origin of Martian Low-Aspect-Ratio Layered Ejecta (LARLE) Craters  

NASA Astrophysics Data System (ADS)

An unusual crater morphology is found primarily at high latitudes on Mars. These craters display an extensive outer deposit beyond the normal layered ejecta blanket. This outer deposit extends up to 20 crater radii from the rim, terminates in a sinuous flame-like edge, and is extremely thin, leading to a low aspect ratio (A = thickness/length). These craters are thus called Low-Aspect-Ratio Layered Ejecta (LARLE) craters. We have conducted a survey of all LARLE craters 1-km-diameter and larger on Mars. We find 139 LARLE craters ranging in diameter from 1.0 to 12.2 km with a median of 2.8 km. Most (97%) are found poleward of 35N and 40S, with the remainder primarily found in the equatorial Medusae Fossae Formation. The surfaces of the freshest LARLE layers commonly exhibit radial, curvilinear ridges and dune-like landforms, and the LARLE deposit typically drapes over pre-existing terrain. We propose that the LARLE deposit is formed by a different mechanism than that responsible for the normal layered ejecta patterns. We suggest that impact into relatively-thick fine-grained ice-rich mantles enhances the formation of a base surge that is deposited after formation of the inner layered ejecta deposits. This base surge is similar to the density-driven, turbulent cloud of suspended fine-grained particles produced by impact erosion and mobilization of the surrounding surface material by ejecta from shallow-depth-of-burst nuclear and high-explosion craters. We have applied a base surge equation developed for terrestrial explosive events to two fresh LARLE craters. After adjustment of the equation for Martian conditions, it predicts runout distances that are within 99% of the observed values. All Martian craters likely produce a base surge during formation, but the presence of the obvious LARLE deposit is attributed to crater formation in thick, fine-grained, sedimentary deposits. These sediments are the source of the extra particulate debris incorporated into and deposited by the base surge.

Barlow, Nadine G.; Boyce, J. M.

2013-10-01

195

Structural and texture evolution with temperature of layered double hydroxides intercalated with paramolybdate anions.  

PubMed

Paramolybdate-LDHs with MgAl or ZnAl cations within the layers have been prepared by the ion-exchange method from hydrotalcites with different interlayer anions (OH-, NO3(-), and terephthalate). The samples and the oxides obtained after their calcination were characterized by element chemical analysis, PXRD, FT-Raman spectroscopy, thermal analysis (TG/DTA), N2 adsorption at -196 degrees C, and SEM. The results show that layered solids with hydrotalcite-type structure were obtained in which the interlayer space is occupied by heptamolybdate with a small amount of MoO4(2-) units formed through hydrolysis of the polyanion; both oxomolybdenum species undergo a progressive distortion of the octahedral units from 50 degrees C but are roughly stable up to 250 degrees C as a consequence of the interaction between the polyanion and the brucite-like layers. This distortion is responsible for the observed decrease in the height of the gallery for samples heated in the temperature range, 50-250 degrees C, with respect to the original samples. Rehydration of the calcined solids allows recovering of their original structures and the initial values for the gallery heights. Calcination between 300 and 400 degrees C gives rise to a collapse of the layered structure, and amorphous phases are formed, in which molybdenum is both octahedrally and tetrahedrally coordinated. Crystalline magnesium and zinc molybdates (MgMoO4 and ZnMoO4) are formed at 450 and 600 degrees C, respectively. All solids have some microporosity, which decreases with increasing the calcination temperature. PMID:16441136

Carriazo, D; Domingo, C; Martín, C; Rives, V

2006-02-01

196

Structural origin of bulk molecular hydrogen in hydrogenated amorphous silicon  

SciTech Connect

The elastic anomaly observed previously at the triple point of bulk molecular hydrogen in hydrogenated amorphous silicon films prepared by hot-wire chemical-vapor deposition has also been observed in deuterated films at the triple point of D{sub 2}. The origin of this anomaly has now been traced to bubbles formed at the crystalline-amorphous interface. An upper limit of the pressure in these bubbles at their formation temperature, 440 C, has been estimated to be 11 MPa, and is suggested to be a measure of the bonding strength between film and substrate at that temperature. Bubble formation after heat treatment at 400 C has also been observed in films prepared by plasma-enhanced chemical-vapor deposition. The internal friction anomalies resemble those observed previously in cold-worked hydrogenated iron where they have been interpreted through plastic deformation of solid hydrogen in voids.

Liu, X.; Pohl, R.O.; Crandall, R.S.

1999-07-01

197

On the origin of photoluminescence in indium oxide octahedron structures  

NASA Astrophysics Data System (ADS)

A sixfold decrease in photoluminescence signal intensity at 590 nm with increase in deposition time from 3 to 12 h has been observed in single crystalline indium oxide octahedron structures grown by vapor-phase evaporation method. Electron paramagnetic resonance and energy dispersive x-ray analysis confirm that the concentration of oxygen vacancies increases with deposition time. These results are contrary to the previous reports where oxygen vacancies were shown to be responsible for photoluminescence in indium oxide structures. Our results indicate that indium interstitials and their associated complex defects other than oxygen vacancies are responsible for the photoluminescence in In2O3 microstructures.

Kumar, Mukesh; Singh, V. N.; Singh, F.; Lakshmi, K. V.; Mehta, B. R.; Singh, J. P.

2008-04-01

198

Vortical structure in a forced plane mixing layer  

NASA Technical Reports Server (NTRS)

The objective of this phase of an ongoing study is to obtain detailed three dimensional phase-averaged measurements of forced mixing layer vorticity development and evolution. Acoustic forcing is being used to phase-lock the initial development and subsequent pairing of the span wise vortical structures. Phase averaged measurements of the three velocity components will permit the study of three dimensional vorticity distributions without invoking Taylor's hypothesis which is known to introduce uncertainty. Currently two sine waves, one at the fundamental roll-up frequency and the second, its subharmonic, are being used to force the initial roll-up and first pairing of the span wise rollers. The two dimensional measurements described in this report were obtained in order to determine the best operating conditions for the detailed three dimensional study of the mixing layer undergoing pairing via various pairing mechanisms.

Leboeuf, Richard L.

1993-01-01

199

Flexural strength and failure modes of layered ceramic structures  

PubMed Central

Objective to evaluate the effect of the specimen design on the flexural strength (?f) and failure mode of ceramic structures, testing the hypothesis that the ceramic material under tension controls the mechanical performance of the structure. Methods Three ceramics used as framework materials for fixed partial dentures (YZ - Vita In-Ceram YZ; IZ - Vita In-Ceram Zirconia; AL - Vita In-Ceram AL) and two veneering porcelains (VM7 and VM9) were studied. Bar-shaped specimens were produced in three different designs (n=10): monolithic, two layers (porcelain-framework) and three layers (TRI) (porcelain-framework-porcelain). Specimens were tested for three-point flexural strength at 1 MPa/s in 37°C artificial saliva. For bi-layered design, the specimens were tested in both conditions: with porcelain (PT) or framework ceramic (FT) layer under tension. Fracture surfaces were analyzed using stereomicroscope and scanning electron microscopy (SEM). Young’s modulus (E) and Poisson’s ratio (?) were determined using ultrasonic pulse-echo method. Results were statistically analyzed by Kruskal-Wallis and Student-Newman-Keuls tests. Results Except for VM7 and VM9, significant differences were observed for E values among the materials. YZ showed the highest ? value followed by IZ and AL. YZ presented the highest ?f. There was no statistical difference in the ?f value between IZ and IZ-FT and between AL and AL-FT. ?f values for YZ-PT, IZ-PT, IZ-TRI, AL-PT, AL-TRI were similar to the results obtained for VM7 and VM9. Two types of fracture mode were identified: total and partial failure. Significance The mechanical performance of the specimens was determined by the material under tension during testing, confirming the study hypothesis.

Borba, Marcia; de Araujo, Maico D.; de Lima, Erick; Yoshimura, Humberto N.; Cesar, Paulo F.; Griggs, Jason A.; Bona, Alvaro Della

2011-01-01

200

Satellited Y chromosomes: Structure, origin, and clinical significance  

Microsoft Academic Search

Three cases of inherited satellited Y chromosomes (Yqs) were analysed using several cytogenetic techniques. The cytogenetic data of the 14 cases of Yqs chromosomes described to date were reviewed. All Yqs chromosomes carry an active nucleolus organizer region (NOR) in their long arm and must have developed from translocations involving the short arms of the acrocentric autosomes. The structure of

M. Schmid; T. Haaf; Eva Solleder; W. Schempp; M. Leipoldt; H. Heilbronner

1984-01-01

201

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; Structures, Inc.

202

On the origin of charge-density waves in select layered transition-metal dichalcogenides  

Microsoft Academic Search

The occurrence of charge-density waves in three selected layered transition-metal dichalcogenides---1T-TaS2, 2H-TaSe2 and 1T-TiSe2---is discussed from an experimentalist's point of view with a particular focus on the implications of recent angle-resolved photoelectron spectroscopy results. The basic models behind charge-density-wave formation in low-dimensional solids are recapitulated, the experimental and theoretical results for the three selected compounds are reviewed, and their band

K. Rossnagel

2011-01-01

203

The origin of the distortion product otoacoustic emission fine structure  

NASA Astrophysics Data System (ADS)

Distortion-product otoacoustic emissions (DPOAEs) are sounds detected in the ear canal which are generated by the nonlinear processes in the inner ear (cochlea) in response to the external stimulation of two or more tones (primaries). Their generation region in the cochlea can be systematically changed by varying the primary frequencies, and they are currently being evaluated for possible clinical use in screening for hearing defects. The phase and amplitude of various orders of DPOAEs of frequencies, f/sb [dp]=f1-n(f2-f1),/ (n=1,2,/...), were measured in human subjects for two- tone stimuli of frequencies f1 and f2 (>f1). A number of experimental paradigms (fixed primary ratio f2/f1, fixed f1, fixed f2, and fixed f/sb [dp]) were used to investigate the nature of peaks and valleys (fine structure) of DPOAEs in their phase and amplitude dependence on the primary frequencies. This fine structure must be taken into account in any potential clinical applications of DPOAEs. The experimental results largely support a model in which the fine structure stems from interference at the base of the cochlea between distortion product (DP) components coming from the primary DPOAE source region (around the f2 tonotopic place) and components coming from the DP tonotopic place (via reflection of an apically moving DP wave). The spectral periodicity of the fine structures for several orders of apical DPOAEs corresponds to a tonotopic displacement of about 0.4 mm along the basilar membrane (BM) (0.4 bark). In agreement with the reaction model, this spectral spacing is also characteristic of synchronous evoked and spontaneous otoacoustic emission spectra as well as the microstructure of the hearing threshold. Approximate analytic expressions for the mechanisms which are responsible for the fine structure are used to interpret the data.

Piskorski, Pawel

204

Structural Origins of Oxacillinase Specificity in Class D ?-Lactamases  

PubMed Central

Since the discovery and use of penicillin, the increase of antibiotic resistance among bacterial pathogens has become a major health concern. The most prevalent resistance mechanism in Gram-negative bacteria is due to ?-lactamase expression. Class D ?-lactamases are of particular importance due to their presence in multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa. The class D enzymes were initially characterized by their ability to efficiently hydrolyze isoxazolyl-type ?-lactams like oxacillin. Due to this substrate preference, these enzymes are traditionally referred to as oxacillinases or OXAs. However, this class is comprised of subfamilies characterized by diverse activities that include oxacillinase, carbapenemase, or cephalosporinase substrate specificity. OXA-1 represents one subtype of class D enzyme that efficiently hydrolyzes oxacillin, and OXA-24/40 represents another with weak oxacillinase, but increased carbapenemase, activity. To examine the structural basis for the substrate selectivity differences between OXA-1 and OXA-24/40, the X-ray crystal structures of deacylation-deficient mutants of these enzymes (Lys70Asp for OXA-1; Lys84Asp for OXA-24) in complexes with oxacillin were determined to 1.4 ? and 2.4 ?, respectively. In the OXA-24/40/oxacillin structure, the hydrophobic R1 side chain of oxacillin disrupts the bridge between Tyr112 and Met223 present in the apo OXA-24/40 structure, causing the main chain of the Met223-containing loop to adopt a completely different conformation. In contrast, in the OXA-1/oxacillin structure, a hydrophobic pocket consisting of Trp102, Met99, Phe217, Leu161, and Leu255 nicely complements oxacillin's nonpolar R1 side chain. Comparison of the OXA-1/oxacillin and OXA-24/40/oxacillin complexes provides novel insight on how substrate selectivity is achieved among subtypes of class D ?-lactamases. By elucidating important active site interactions, these findings can also inform the design of novel antibiotics and inhibitors.

June, Cynthia M.; Vallier, Beth C.; Bonomo, Robert A.; Leonard, David A.

2014-01-01

205

On the origin of ion bombardment induced exchange bias modifications in polycrystalline layers  

NASA Astrophysics Data System (ADS)

A model for the modifications of the exchange bias (EB) field \\overrightarrow{H}_eb of antiferromagnet (AF)/ferromagnet (F) bilayers with a polycrystalline or multidomain AF layer induced by ion bombardment (IB) in an external magnetic field is proposed. The model is based on a known two-energy level model for an antiferromagnetic grain or domain in contact with a ferromagnet where two free energy minima are separated by an energy barrier. The model explains the as yet unexplained increase of \\overrightarrow{H}_eb upon IB on the basis of the grain/domain size and magnetic anisotropy constants distributions in the antiferromagnetic layer after its deposition and on the basis of a twofold effect of the IB on the antiferromagnetic grains/domains: (1) IB acts like local hyperthermal heating leading to an almost immediate increase of the sample's EB. (2) Defects induced by IB in the antiferromagnetic grains/domains lead to a decrease of the energy barrier between the two minima, resulting in a slow additional increase of \\overrightarrow{H}_eb with time (with temperature T as a parameter) after the bombardment. The model is tested by experiments on the time dependence of the EB and coercive fields after the IB of NiO/NiFe bilayers.

Ehresmann, A.; Junk, D.; Engel, D.; Paetzold, A.; Röll, K.

2005-03-01

206

Unexpected strong magnetism of Cu doped single-layer MoS? and its origin.  

PubMed

The magnetism of the 3d transition-metal (TM) doped single-layer (1L) MoS2, where the Mo atom is partially replaced by the 3d TM atom, is investigated using the first-principles density functional calculations. In a series of 3d TM doped 1L-MoS2's, the induced spin polarizations are negligible for Sc, Ti, and Cr dopings, while the induced spin polarizations are confirmed for V, Mn, Fe, Co, Ni, Cu, and Zn dopings and the systems become magnetic. Especially, the Cu doped system shows unexpectedly strong magnetism although Cu is nonmagnetic in its bulk state. The driving force is found to be a strong hybridization between Cu 3d states and 3p states of neighboring S, which results in an extreme unbalanced spin-population in the spin-split impurity bands near the Fermi level. Finally, we also discuss further issues of the Cu induced magnetism of 1L-MoS2 such as investigation of additional charge states, the Cu doping at the S site instead of the Mo site, and the Cu adatom on the layer (i.e., 1L-MoS2). PMID:24695769

Yun, Won Seok; Lee, J D

2014-05-21

207

The Origins of Magnetic Structure in the Corona and Wind  

Microsoft Academic Search

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

Spiro K. Antiochos

2009-01-01

208

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

209

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

210

Deep subwavelength plasmonic waveguide switch in double graphene layer structure  

NASA Astrophysics Data System (ADS)

Graphene provides excellent prospects of the dynamic tunability, low propagation loss, and extreme mode confinement for plasmonic excitations in the infra-red and terahertz frequencies. We show that in a deep subwavelength double graphene layer structure, graphene plasmons can be routed between two different graphene waveguides by relatively small chemical potential tuning. We develop a coupled mode theory that completely accounts for the switching behavior observed in numerical simulations. Such a deep subwavelength 1 × 2 device is a crucial enabling component towards large-scale integrated deep-subwavelength electromagnetic circuits.

Iizuka, Hideo; Fan, Shanhui

2013-12-01

211

Plasma resonant terahertz photomixers based on double graphene layer structures  

NASA Astrophysics Data System (ADS)

We propose terahertz (THz) photomixers based on double graphene layer (DGL) structures, utilizing the interband absorption of modulated optical radiation, tunneling or thermionic inter-GL transitions, and resonant excitation of plasma oscillations. Using the developed device model, we substantiate the operation of the photomixers and calculate their characteristics. We demonstrate that the output frequency-dependent power of THz radiation exhibits pronounced resonant peaks at the plasmonic resonant frequencies. The proposed THz photomixer can surpass the pertinent devices based on the standard heterostructures.

Ryzhii, Maxim; Shur, Michael S.; Mitin, Vladimir; Satou, Akira; Ryzhii, Victor; Otsuji, Taiichi

2014-03-01

212

On the origins of the mitotic shift in proliferating cell layers  

PubMed Central

Background During plant and animal development, monolayer cell sheets display a stereotyped distribution of polygonal cell shapes. In interphase cells these shapes range from quadrilaterals to decagons, with a robust average of six sides per cell. In contrast, the subset of cells in mitosis exhibits a distinct distribution with an average of seven sides. It remains unclear whether this ‘mitotic shift’ reflects a causal relationship between increased polygonal sidedness and increased division likelihood, or alternatively, a passive effect of local proliferation on cell shape. Methods We use a combination of probabilistic analysis and mathematical modeling to predict the geometry of mitotic polygonal cells in a proliferating cell layer. To test these predictions experimentally, we use Flp-Out stochastic labeling in the Drosophila wing disc to induce single cell clones, and confocal imaging to quantify the polygonal topologies of these clones as a function of cellular age. For a more generic test in an idealized cell layer, we model epithelial sheet proliferation in a finite element framework, which yields a computationally robust, emergent prediction of the mitotic cell shape distribution. Results Using both mathematical and experimental approaches, we show that the mitotic shift derives primarily from passive, non-autonomous effects of mitoses in neighboring cells on each cell’s geometry over the course of the cell cycle. Computationally, we predict that interphase cells should passively gain sides over time, such that cells at more advanced stages of the cell cycle will tend to have a larger number of neighbors than those at earlier stages. Validating this prediction, experimental analysis of randomly labeled epithelial cells in the Drosophila wing disc demonstrates that labeled cells exhibit an age-dependent increase in polygonal sidedness. Reinforcing these data, finite element simulations of epithelial sheet proliferation demonstrate in a generic framework that passive side-gaining is sufficient to generate a mitotic shift. Conclusions Taken together, our results strongly suggest that the mitotic shift reflects a time-dependent accumulation of shared cellular interfaces over the course of the cell cycle. These results uncover fundamental constraints on the relationship between cell shape and cell division that should be general in adherent, polarized cell layers.

2014-01-01

213

Perpendicular magnetic anisotropy in FePt/AlN layered structure  

NASA Astrophysics Data System (ADS)

FePt/AlN layered structures were deposited onto fused quartz substrate by magnetron sputtering method and found to show in-plane anisotropy. However, annealing of the films leads to a transition of magnetic anisotropy from in-plane to perpendicular direction, and the perpendicular anisotropy gets stronger as the annealing temperature increases. Structural analysis shows that the FePt and AlN layers are textured with (111) and (002) orientations, respectively, along the film normal, and no ordering transformation is found for FePt alloy. To study the origin of the developed anisotropy, stress condition was analyzed with an equal biaxial stress model using X-ray diffraction 2?-? scan method and interface quality was evaluated by X-ray reflectivity measurement and transmission electron microscopy observation. The results reveal that perpendicular magnetic anisotropy of the annealed FePt/AlN layered structure can be attributed to the enhanced interface anisotropy, which is due to flattening of the interfaces through annealing.

Zhang, Cong; Sannomiya, Takumi; Muraishi, Shinji; Shi, Ji; Nakamura, Yoshio

2014-02-01

214

Structural or pigmentary? Origin of the distinctive white stripe on the blue wing of a Morpho butterfly  

PubMed Central

A few species of Morpho butterflies have a distinctive white stripe pattern on their structurally coloured blue wings. Since the colour pattern of a butterfly wing is formed as a mosaic of differently coloured scales, several questions naturally arise: are the microstructures the same between the blue and white scales? How is the distinctive whiteness produced, structurally or by means of pigmentation? To answer these questions, we have performed structural and optical investigations of the stripe pattern of a butterfly, Morpho cypris. It is found that besides the dorsal and ventral scale layers, the wing substrate also has the corresponding stripe pattern. Quantitative optical measurements and analysis using a simple model for the wing structure reveal the origin of the higher reflectance which makes the white stripe brighter.

Yoshioka, Shinya; Kinoshita, Shuichi

2005-01-01

215

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

216

Anatomy of the auditory thalamocortical system in the mongolian gerbil: Nuclear origins and cortical field-, layer-, and frequency-specificities.  

PubMed

Knowledge of the anatomical organization of the auditory thalamocortical (TC) system is fundamental for the understanding of auditory information processing in the brain. In the Mongolian gerbil (Meriones unguiculatus), a valuable model species in auditory research, the detailed anatomy of this system has not yet been worked out in detail. Here, we investigated the projections from the three subnuclei of the medial geniculate body (MGB), namely, its ventral (MGv), dorsal (MGd), and medial (MGm) divisions, as well as from several of their subdivisions (MGv: pars lateralis [LV], pars ovoidea [OV], rostral pole [RP]; MGd: deep dorsal nucleus [DD]), to the auditory cortex (AC) by stereotaxic pressure injections and electrophysiologically guided iontophoretic injections of the anterograde tract tracer biocytin. Our data reveal highly specific features of the TC connections regarding their nuclear origin in the subdivisions of the MGB and their termination patterns in the auditory cortical fields and layers. In addition to tonotopically organized projections, primarily of the LV, OV, and DD to the AC, a large number of axons diverge across the tonotopic gradient. These originate mainly from the RP, MGd (proper), and MGm. In particular, neurons of the MGm project in a columnar fashion to several auditory fields, forming small- and medium-sized boutons, and also hitherto unknown giant terminals. The distinctive layer-specific distribution of axonal endings within the AC indicates that each of the TC connectivity systems has a specific function in auditory cortical processing. J. Comp. Neurol. 522:2397-2430, 2014. © 2014 Wiley Periodicals, Inc. PMID:24435884

Saldeitis, Katja; Happel, Max F K; Ohl, Frank W; Scheich, Henning; Budinger, Eike

2014-07-01

217

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

218

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

219

Structures of turbulent boundary layers with adverse pressure gradients  

NASA Astrophysics Data System (ADS)

Turbulent structures in spanwise/wall-normal plane of the turbulent boundary layers (TBLs) subjected to adverse pressure gradients (APGs) were investigated by analyzing the DNS database of Lee & Sung (2009). Probability density functions of the strength of the vortex cores normalized by their r.m.s. values displayed that strong swirling motions are frequently observed on the APG TBLs than zero pressure gradient TBLs. Influence of APGs on the population trends of spanwise vortex cores showed that those have a local maximum at the outer region for APG TBLs which might be due to the maximum Reynolds shear stress. Moreover, two-point correlations and linear stochastic estimations were scrutinized to provide statistical evidence for hairpin packet motions in the vertical plane of the TBLs with APGs. We found that wall-normal extent of the contours is elongated vertically owing to the strong swirling motion of the individual vortex located in the wake region or wake-type detached structures.

Lee, Jin; Sung, Hyung Jin

2009-11-01

220

Origin of spatial genetic structure in an expanding oak population.  

PubMed

Spatial genetic structure (SGS) results from the interplay of several demographical processes that are difficult to tease apart. In this study, we explore the specific effects of seed and pollen dispersal and of early postdispersal mortality on the SGS of a seedling cohort (N = 786) recruiting within and around an expanding pedunculate oak (Quercus robur) stand. Using data on dispersal (derived from parentage analysis) and mortality (monitored in the field through two growing seasons), we decompose the overall SGS of the cohort into its components by contrasting the SGS of dispersed (i.e. growing away from their mother tree) vs. nondispersed (i.e. growing beneath their mother tree) and initial vs. surviving seedlings. Patterns differ strongly between nondispersed and dispersed seedlings. Nondispersed seedlings are largely responsible for the positive kinship values observed at short distances in the studied population, whereas dispersed seedlings determine the overall SGS at distances beyond c. 30 m. The paternal alleles of nondispersed seedlings show weak yet significantly positive kinships up to c. 15 m, indicating some limitations in pollen flow that should further promote pedigree structures at short distances. Seedling mortality does not alter SGS, except for a slight increase in the nondispersed group. Field data reveal that mortality in this group is negatively density-dependent, probably because of small-scale variation in light conditions. Finally, we observe a remarkable similarity between the SGS of the dispersed seedlings and that of the adults, which probably reflects dispersal processes during the initial expansion of the population. Overall, this study demonstrates that incorporating individual-level complementary information into analyses can greatly improve the detail and confidence of ecological inferences drawn from SGS. PMID:20070522

Hampe, Arndt; El Masri, Leila; Petit, Rémy J

2010-02-01

221

A Turbulent Origin for Flocculent Spiral Structure in Galaxies  

NASA Astrophysics Data System (ADS)

The flocculent structure of star formation in galaxies has a Fourier transform power spectrum for azimuthal intensity scans with a power-law slope that increases systematically from about -1 at large scales to about -5/3 at small scales. This is the same pattern as in the power spectra for azimuthal scans of H I emission in the Large Magellanic Clouds and for flocculent dust clouds in galactic nuclei. The steep part also corresponds to the slope of about -3 for two-dimensional power spectra that have been observed in atomic and molecular gas surveys of the Milky Way and the Large and Small Magellanic Clouds. The power-law structure for star formation in galaxies arises in both flocculent and grand-design disks, which implies that star formation is the same in each and most likely related to turbulence. The characteristic scale that separates these two slopes corresponds to several tens of pixels or several hundred parsecs in most galaxies, which is comparable to the scale height, the inverse of the Jeans wavenumber, and the size of the largest star complexes. We suggest that the power spectrum of optical light is the result of turbulence and that the large-scale turbulent motions are generated by sheared gravitational instabilities that make flocculent spiral arms first and then cascade to form clouds and clusters on smaller scales. Stellar energy sources presumably contribute to this turbulence by driving smaller scale motions and by replacing the gravitational binding energy that is released during spiral arm collapse. The spiral wave mode in the image of M81 is removed by reconstructing the Fourier transforms without the lowest 10 wavenumbers. The result shows the underlying flocculent spirals and reverse-shear spirals of star formation that are normally overwhelmed by the density wave.

Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Leitner, Samuel N.

2003-06-01

222

Wintertime Boundary Layer Structure in the Grand Canyon.  

NASA Astrophysics Data System (ADS)

Wintertime temperature profiles in the Grand Canyon exhibit a neutral to isothermal stratification during both daytime and nighttime, with only rare instances of actual temperature inversions. The canyon warms during daytime and cools during nighttime more or less uniformly through the canyon's entire depth. This weak stability and temperature structure evolution differ from other Rocky Mountain valleys, which develop strong nocturnal inversions and exhibit convective and stable boundary layers that grow upward from the valley floor. Mechanisms that may be responsible for the different behavior of the Grand Canyon are discussed, including the possibility that the canyon atmosphere is frequently mixed to near-neutral stratification when cold air drains into the top of the canyon from the nearby snow-covered Kaibab Plateau. Another feature of canyon temperature profiles is the sharp inversions that often form near the canyon rims. These are generally produced when warm air is advected over the canyon in advance of passing synoptic-scale ridges.Wintertime winds in the main canyon are not classical diurnal along-valley wind systems. Rather, they are driven along the canyon axis by the horizontal synoptic-scale pressure gradient that is superimposed along the canyon's axis by passing synoptic-scale weather disturbances. They may thus bring winds into the canyon from either end at any time of day.The implications of the observed canyon boundary layer structure for air pollution dispersion are discussed.

Whiteman, C. David; Zhong, Shiyuan; Bian, Xindi

1999-08-01

223

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

224

Communication: Origin of the contributions to DNA structure in phages  

PubMed Central

Cryo electron microscopy (cryo-EM) data of the interior of phages show ordering of the interior DNA that has been interpreted as a nearly perfectly ordered polymer. We show surface-induced correlations, excluded volume, and electrostatic forces are sufficient to predict most of the major features of the current structural data for DNA packaged within viral capsids without additional ordering due to elastic bending forces for the polymer. Current models assume highly-ordered, even spooled, hexagonally packed conformations based on interpretation of cryo-EM density maps. We show herein that the surface induced packing of short (6mer), unconnected DNA polymer segments is the only necessary ingredient in creating ringed densities consistent with experimental density maps. This implies the ensemble of possible conformations of polymeric DNA within the capsid that are consistent with cryo-EM data may be much larger than implied by traditional interpretations where such rings can only result from highly-ordered spool-like conformations. This opens the possibility of a more disordered, entropically-driven view of phage packaging thermodynamics. We also show the electrostatics of the DNA contributes a large portion of the internal hydrostatic and osmotic pressures of a phage virion, suggesting that nonlinear elastic anomalies might reduce the overall elastic bending enthalpy of more disordered conformations to have allowable free energies.

Myers, Christopher G.; Pettitt, B. Montgomery

2013-01-01

225

The Omeonga Structure, Democratic Republic of Congo: Geological and Petrographical Results, and Implications for its Origin  

NASA Astrophysics Data System (ADS)

For the first time, the origin of the ~38-km-diameter Omeonga structure, located in the Democratic Republic of Congo, is discussed using geological field observations and petrographic investigations on samples from our July 2011 field campaign.

Ferrière, L.; Kaseti, P. K.; Lubala, F. R. T.; Koeberl, C.

2012-03-01

226

Protein Folding, Protein Structure and the Origin of Life: Theoretical Methods and Solutions of Dynamical Problems.  

National Technical Information Service (NTIS)

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 calcu...

D. L. Weaver

1982-01-01

227

The double-layered chemical structure in DB white dwarfs  

NASA Astrophysics Data System (ADS)

The purpose of this work is to study the structure and evolution of white dwarf stars with helium-rich atmospheres (DB) in a self-consistent way with the predictions of time-dependent element diffusion. Specifically, we have considered white dwarf models with stellar masses in the range 0.60-0.85 M? and helium envelopes with masses from 10-2 to 10-4 M*. Our treatment of diffusion, appropriate for multicomponent gases, includes gravitational settling and chemical and thermal diffusion. OPAL radiative opacities for arbitrary metallicity and carbon-and oxygen-rich compositions are employed. Emphasis is placed on the evolution of the diffusion-modeled double-layered chemical structure. This structure, which is characterized by a pure helium envelope atop an intermediate remnant shell rich in helium, carbon and oxygen, is expected for pulsating DB white dwarfs, assuming that they are descendants of hydrogen-deficient PG 1159 post-AGB stars. We find that, depending on the stellar mass, if DB white dwarf progenitors are formed with a helium content smaller than ?10-3 M*, a single-layered configuration is expected to emerge during the DB pulsation instability strip. We also explore the consequences of diffusively evolving chemical stratifications on the adiabatic pulsational properties of our DB white dwarf models. In this context, we find that the evolving shape of the chemical profile translates into a distinct behaviour of the theoretical period distribution as compared with the case in which the shape of the profile is assumed to be fixed during the evolution across the instability strip. In particular, we find that the presence of a double-layered structure causes the period spacing diagrams to exhibit mode-trapping substructures. Finally, we extend the scope of the calculations to the domain of the helium-rich carbon-contaminated DQ white dwarfs. In particular, we speculate that DQ white dwarfs with low detected carbon abundances would not be descendants of the PG 1159 stars.

Althaus, L. G.; Córsico, A. H.

2004-04-01

228

Electronic structure, adsorption geometry, and photoswitchability of azobenzene layers adsorbed on layered crystals.  

PubMed

Mono- and multilayers of the molecular photoswitch azobenzene were adsorbed on two layered transition-metal dichalcogenides, semiconducting HfS2 and metallic TiTe2, at temperatures of 80-120 K and investigated in situ using valence-band and core-level photoelectron spectroscopy as well as near-edge X-ray absorption fine structure spectroscopy. The spectroscopic results indicate similar growth modes on the two substrates. In the monolayer systems, the azobenzene molecules tend to lie flat on the surface with average tilt angles of <15°, whereas the multilayer systems show a larger average tilt angle of 35-45°, depending on substrate surface conditions. The chemical environment of azobenzene, as investigated by XPS, does not change significantly from mono- to multilayers suggesting weak adsorbate-substrate coupling for the molecular layer that forms the interface with the substrate. Irradiation with ultraviolet light with a wavelength of 365 nm leads to a partial rearrangement of the adsorbed azobenzene molecules with a trans-to-cis conversion of up to 35%. PMID:24166534

Ludwig, Eric; Strunskus, Thomas; Hellmann, Stefan; Nefedov, Alexei; Wöll, Christof; Kipp, Lutz; Rossnagel, Kai

2013-12-14

229

Super-hydrophobic surfaces of layer-by-layer structured film-coated electrospun nanofibrous membranes  

NASA Astrophysics Data System (ADS)

We have recently fabricated super-hydrophobic membrane surfaces based on the inspiration of self-cleaning silver ragwort leaves. This biomimetic super-hydrophobic surface was composed of fluoroalkylsilane (FAS)-modified layer-by-layer (LBL) structured film-coated electrospun nanofibrous membranes. The rough fibre surface caused by the electrostatic LBL coating of TiO2 nanoparticles and poly(acrylic acid) (PAA) was used to imitate the rough surface of nanosized grooves along the silver ragwort leaf fibre axis. The results showed that the FAS modification was the key process for increasing the surface hydrophobicity of the fibrous membranes. Additionally, the dependence of the hydrophobicity of the membrane surfaces upon the number of LBL coating bilayers was affected by the membrane surface roughness. Moreover, x-ray photoelectron spectroscopy (XPS) results further indicated that the surface of LBL film-coated fibres absorbed more fluoro groups than the fibre surface without the LBL coating. A (TiO2/PAA)10 film-coated cellulose acetate nanofibrous membrane with FAS surface modification showed the highest water contact angle of 162° and lowest water-roll angle of 2°.

Ogawa, Tasuku; Ding, Bin; Sone, Yuji; Shiratori, Seimei

2007-04-01

230

Development of a single-layer finite element and a simplified finite element modeling approach for constrained layer damped structures  

Microsoft Academic Search

A new finite element (FE) is formulated based on an extension of previous FE models for studying constrained layer damping (CLD) in beams. Most existing CLD FE models are based on the assumption that the shear deformation in the core layer is the only source of damping in the structure. However, previous research has shown that other types of deformation

Zhengchao Xie; W. Steve Shepard Jr.

2009-01-01

231

Filamentary Structures in U-Shaped Double Layers  

NASA Astrophysics Data System (ADS)

Observations from the Polar and FAST satellites have revealed a host of intriguing features of the auroral accelerations processes in the upward current region (UCR). These features include: (i) large-amplitude parallel and perpendicular fluctuating as well as quasi-static electric fields in density cavities, (ii) fairly large-amplitude unipolar parallel electric fields like in a strong double layer (DL), (iii) variety of wave modes, (iv) counter-streaming of upward going ion beams and downward accelerated electrons, (v) horizontally corrugated bottom region of the potential structures (PS), in which electron and ion accelerations occur, (vi) filamentary ion beams in the corrugated PS, and (vii) both upward and downward moving narrow regions of parallel electric fields, inferred from the frequency drifts of the auroral kilometric radiations. Numerical simulations of U-shaped potential structures reveal that such observed features of the UCR are integral parts of dynamically evolving auroral U-shaped potential structures. Using a 2.5-D particle-in-cell (PIC) code we simulate a U-shaped broad potential structure (USBPS). The dynamical behavior revealed by the simulation includes: (i) recurring redistribution of the parallel potential drop (PPD) in the PS, (ii) its up and downward motion, (iii) formation of filaments in the potential and density structures, and (iv) creation of filamentary as well as broad extended density cavities. The formation of the filamentary structures is initiated by an ion-beam driven instability of an oblique ion mode trapped inside a broad cavity, when it becomes sufficiently thin in height. The filaments of the PS create filamentary electron beams, which generate waves at frequencies above the lower hybrid frequency, affecting plasma heating. This results in plasma evacuation and formation of a cavity extended in height. The waves associated with filamentary electron beams also evolve into electron holes. The transverse and parallel scale lengths of the regions with large E Parallel and E Perpendicular as well as their magnitudes are compared with satellite data.

Deverapalli, C. M.; Singh, N.; Khazanov, I.

2005-12-01

232

Origin of n-type conduction at the interface between epitaxial-grown layer and InP substrate and its suppression by heating in phosphine atmosphere  

Microsoft Academic Search

The origin of unintentionally introduced n-type conduction at the interface of epitaxially grown layer-InP substrate is identified. From the relation between the sheet carrier concentration and the etching depth, an n-type conducting layer was found at the epitaxial layer-substrate interface. The sheet carrier concentration and the sheet Si concentration at the surface of the InP substrate, which was obtained by

Hideto Ishikawa; Shiro Miwa; Toshiyuki Maruyama; Mikio Kamada

1992-01-01

233

Neutron diffraction studies of organic and magnetic layered structures  

NASA Astrophysics Data System (ADS)

Two different neutron diffraction experiments on layered structures have been carried out at the University of Missouri Research Reactor Center. In the first project, the structure of lipid model membranes, consisting of phosphatidylcholine (PC) and cholesterol, and the effect of introducing various alkanes, such as hexane, decane, and toluene, was investigated. The experiments were conducted using PC's with 10 to 20 carbon atoms in the polymethylene chains. By replacing hydrogen with deuterium on parts of the molecules (deuterium labeling) and comparing the scattering amplitude density profiles for the labeled and unlabeled bilayers, it was possible to resolve the spatial arrangement within the bilayer. It was found that the alkanes are localized in a narrow band in the hydrophobic region of the bilayer and that the orientation of their long axis was within the plane of the bilayer. Also, the change of position of the cholesterol molecule as a function of the polymethylene chain length was studied and lead to the unexpected result that it neither aligns itself with the PC head group nor with the end of the polymethylene chains. Additionally, the Debye-Waller factor for the labels on the PC and the cholesterol was determined, and for cholesterol it was found that the disorder (thermal and static) of the cholesterol molecules decreases with increasing temperature. The second project involved the study of the magnetic properties of Dy/Y superlattices with the surface normal between the (1-102) and (1-103) direction. Thus, the c-axis, the propagation direction of the helimagnetic spiral is at an angle of about 35sp° to the surface normal. Neutron diffraction scans showed that the 200nm thick Dy film and the (Dysb{239}|Ysb5rbracksb6 superlattice sample behaves like bulk dysprosiun, i.e., having a helimagnetic to ferromagnetic phase transition at Tsb{C} = 85K. The other Dy/Y superlattice samples showed a coexistence of helimagnetic and ferromagnetic phase from low temperatures up to even above Tsb{C}. This was the first time that ferromagnetism was observed in Dy/Y superlattices. This coexistence can be attributed to the faceted structure of the samples which consists of two distinct domains, i.e., two mesoscopic superlattices. For all the samples investigated, the magnetic moment, the turnangle of the helimagnetic spiral, and the coherence length as a function of temperature were determined. Also, an attempt was made to model the nuclear scattering, i.e., structure factor calculation. Thus, both experiments focused on layered structures and utilized the neutrons unique capabilities as a probe to study the properties of these thin samples.

Hamacher, Klaus Antonius

234

Structure of the nocturnal boundary layer over a complex terrain  

SciTech Connect

The complex nature of the nocturnal boundary layer (NBL) has been shown extensively in the literature Project STABLE was conducted in 1988 to study NBL turbulence and diffusion over the complex terrain of the Savannah River Site (SRS) near Augusta, Georgia. The third night of the study was particularly interesting because of the unusual phenomena observed in the structure of the NBL. Further analyses of microscale and mesoscale data from this night are presented using data from SRS network of eight 61 m towers over 900 km{sup 2}, from six launches of an instrumented tethersonde, from permanent SRL meteorological instrumentation at seven levels of the 304 m (1,000 ft) WJBF-TV tower near SRS, and additional data collected at 36 m (CC) by North Carolina State University (NCSU) including a one dimensional sonic anemometer, fine wire thermocouple, and a three dimensional propeller anemometer. Also, data from the nearby Plant Vogtle nuclear power plant observation tower and the National Weather Service at Augusta`s Bush Field (AGS) are presented. The passage of a mesoscale phenomenon, defined as a microfront (with an explanation of the nomenclature used), and a vertical composite schematic of the NBL which shows dual low level wind maxima, dual inversions, and a persistent, elevated turbulent layer over a complex terrain are described.

Parker, M.J. [Westinghouse Savannah River Co., Aiken, SC (United States); Raman, S. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Marine, Earth and Atmospheric Sciences

1992-08-01

235

Structure of the nocturnal boundary layer over a complex terrain  

SciTech Connect

The complex nature of the nocturnal boundary layer (NBL) has been shown extensively in the literature Project STABLE was conducted in 1988 to study NBL turbulence and diffusion over the complex terrain of the Savannah River Site (SRS) near Augusta, Georgia. The third night of the study was particularly interesting because of the unusual phenomena observed in the structure of the NBL. Further analyses of microscale and mesoscale data from this night are presented using data from SRS network of eight 61 m towers over 900 km{sup 2}, from six launches of an instrumented tethersonde, from permanent SRL meteorological instrumentation at seven levels of the 304 m (1,000 ft) WJBF-TV tower near SRS, and additional data collected at 36 m (CC) by North Carolina State University (NCSU) including a one dimensional sonic anemometer, fine wire thermocouple, and a three dimensional propeller anemometer. Also, data from the nearby Plant Vogtle nuclear power plant observation tower and the National Weather Service at Augusta's Bush Field (AGS) are presented. The passage of a mesoscale phenomenon, defined as a microfront (with an explanation of the nomenclature used), and a vertical composite schematic of the NBL which shows dual low level wind maxima, dual inversions, and a persistent, elevated turbulent layer over a complex terrain are described.

Parker, M.J. (Westinghouse Savannah River Co., Aiken, SC (United States)); Raman, S. (North Carolina State Univ., Raleigh, NC (United States). Dept. of Marine, Earth and Atmospheric Sciences)

1992-01-01

236

Structure of temperature fluctuations in turbulent convective boundary layers  

NASA Astrophysics Data System (ADS)

The Large-Eddy Simulation technique is exploited to investigate statistics of temperature fluctuations, ?r?, in Atmospheric Boundary Layers (ABLs) with different degrees of convection. We found statistical characterizations for both strong and weak fluctuations. In terms of probability density functions (pdfs) of ?r?, weak and strong fluctuations reflect themselves in different rescaling properties of pdf cores and tails, respectively. For the cores, the observed rescaling is P(?r?) = r-?(?r?/r?); while for the tails, data are compatible with P(?r?)? r??. Such two rescaling properties are equivalent to saying <|?r?|p>˜ r?p, with ?p = ? p for small p's and ?p = ?? = constant for large p's. Both ? and ?? turn out to be z-independent within the mixed layer and, more importantly, they do not appreciably vary by changing the degree of convection in the ABL. We also address the question related to the geometrical structure of temperature jumps contributing to large |?r?|. Finally, the possible relevance of our results to the long-standing problem of subgrid scale parameterizations is discussed.

Antonelli, M.; Martins Afonso, M.; Mazzino, A.; Rizza, U.

237

Investigation of turbulent boundary layer structures using Tomographic PIV  

NASA Astrophysics Data System (ADS)

Tomographic particle image velocimetry (TPIV) data were acquired in the logarithmic region of a zero pressure gradient turbulent boundary layer flow at friction Reynolds number Re? = 1160. Experiments were conducted in a suction type wind tunnel seeded with olive oil particles of diameter ˜ 1?m. The volume of interest was illuminated by two Nd:YAG laser beams expanded with appropriate optics into sheets of 8mm thickness in the wall-normal direction (z). Images were acquired by four 2k x 2k pixel cameras, and correlation of reconstructed fields provided the full velocity gradient tensor in a volume of 0.7? x 0.7? x 0.07?, which resolved the region z^+ = 70-150 in the log layer. Various vortex identification techniques, such as Galilean decomposition and iso-surfaces of two- and three-dimensional swirl, were utilized to visualize and analyze the eddy structures present in instantaneous fields. The results of the present study will be compared to results from earlier experimental studies that relied on planar PIV data only to identify vortices and vortex packets as well as from a direct numerical simulation of fully developed channel flow at comparable Re?.

Saikrishnan, Neelakantan; Longmire, Ellen; Wieneke, Bernd

2008-11-01

238

Magnetic structures inside boundary layers of magnetic clouds  

NASA Astrophysics Data System (ADS)

We analyze 23 magnetic cloud boundary layers (BLs) in Feb. 1995-Oct. 1998 and find that: (1) the distribution functions of fluctuations in the southward field component inside the boundary layer, ?BzL, is very different from ?BzS in the background solar wind and ?BzM inside the cloud, with the enhancement in the fluctuation amplitude and the variation of the magnitude and direction of the average field. (2) in the maximum variance plane (MVP) composed of the maximum and medium variance directions, the walk of the tips of the magnetic field vectors in the BL could be classified into two types based on: (a) field vectors vibrate along a circle arc, which is possibly related with Alfven fluctuations inside the BL; (b) field vectors walk randomly in the MVP, which could be correlated with the turbulence inside the BL. (3) In the ?-? plane, fields inside the BL exhibits a `U' or inverse `U' shape with a spacing of about 180 degree in the azimuthal angle, which indicate the existence of a field reverse region and are often associated with the Alfvenic fluctuations. The results above suggest that the cloud's BL owns the magnetic structure different from that in the solar wind and cloud body, which is a manifestation for the interaction of the magnetic cloud (MC) with the solar wind (SW).

Wei, Fengsi; Liu, Rui; Feng, Xueshang; Zhong, Dingkun; Yang, Fang

2003-12-01

239

Origin and Evolution of Protein Fold Designs Inferred from Phylogenomic Analysis of CATH Domain Structures in Proteomes  

PubMed Central

The spatial arrangements of secondary structures in proteins, irrespective of their connectivity, depict the overall shape and organization of protein domains. These features have been used in the CATH and SCOP classifications to hierarchically partition fold space and define the architectural make up of proteins. Here we use phylogenomic methods and a census of CATH structures in hundreds of genomes to study the origin and diversification of protein architectures (A) and their associated topologies (T) and superfamilies (H). Phylogenies that describe the evolution of domain structures and proteomes were reconstructed from the structural census and used to generate timelines of domain discovery. Phylogenies of CATH domains at T and H levels of structural abstraction and associated chronologies revealed patterns of reductive evolution, the early rise of Archaea, three epochs in the evolution of the protein world, and patterns of structural sharing between superkingdoms. Phylogenies of proteomes confirmed the early appearance of Archaea. While these findings are in agreement with previous phylogenomic studies based on the SCOP classification, phylogenies unveiled sharing patterns between Archaea and Eukarya that are recent and can explain the canonical bacterial rooting typically recovered from sequence analysis. Phylogenies of CATH domains at A level uncovered general patterns of architectural origin and diversification. The tree of A structures showed that ancient structural designs such as the 3-layer (???) sandwich (3.40) or the orthogonal bundle (1.10) are comparatively simpler in their makeup and are involved in basic cellular functions. In contrast, modern structural designs such as prisms, propellers, 2-solenoid, super-roll, clam, trefoil and box are not widely distributed and were probably adopted to perform specialized functions. Our timelines therefore uncover a universal tendency towards protein structural complexity that is remarkable.

Bukhari, Syed Abbas; Caetano-Anolles, Gustavo

2013-01-01

240

Origins and evolution of stress development in sol-gel derived thin layers and multideposited coatings of lead titanate  

SciTech Connect

Stress development in thin layers of lead titanate prepared by sol-gel processing was monitored by {ital in situ} laser reflectance measurements. Layers were spin coated onto silicon substrates and thermally cycled to 500{degree}C. The shrinkage normal to the rigid substrate was determined by {ital in situ} ellipsometry. Changes that occurred on drying and firing, which related to densification and stress development, are reported. The observed changes were explained in terms of evaporation and solvent/polymeric network interactions at lower temperatures, and thermal expansion mismatch between the substrate and the coating after formation of the dense oxide. Crystallization into the perovskite structure occurred only in thicker or multideposited coatings, altering the state of stress from tensile, to progressively more compressive, on cooling. The importance of the choice of substrate material, deposition method and heat treatment conditions, in relation to stress development and dependent electrical properties, are discussed. {copyright} {ital 1998 American Institute of Physics.}

Sengupta, S.S.; Park, S.M.; Payne, D.A.; Allen, L.H. [Department of Materials Science and Engineering, Seitz Materials Research Laboratory, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Materials Science and Engineering, Seitz Materials Research Laboratory, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

1998-02-01

241

Origins and evolution of stress development in sol-gel derived thin layers and multideposited coatings of lead titanate  

NASA Astrophysics Data System (ADS)

Stress development in thin layers of lead titanate prepared by sol-gel processing was monitored by in situ laser reflectance measurements. Layers were spin coated onto silicon substrates and thermally cycled to 500 °C. The shrinkage normal to the rigid substrate was determined by in situ ellipsometry. Changes that occurred on drying and firing, which related to densification and stress development, are reported. The observed changes were explained in terms of evaporation and solvent/polymeric network interactions at lower temperatures, and thermal expansion mismatch between the substrate and the coating after formation of the dense oxide. Crystallization into the perovskite structure occurred only in thicker or multideposited coatings, altering the state of stress from tensile, to progressively more compressive, on cooling. The importance of the choice of substrate material, deposition method and heat treatment conditions, in relation to stress development and dependent electrical properties, are discussed.

Sengupta, S. S.; Park, S. M.; Payne, D. A.; Allen, L. H.

1998-02-01

242

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

243

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

244

Remote estimation of the Mercury surface layer structure  

NASA Astrophysics Data System (ADS)

Results of the optical observations of Mercury and the Moon confirm the close similarity of photometric properties of the bodies. Experience of lunar studies shows that space weathering processes on the Mercury (such as micrometeorite bombardment, solar wind ion bombardment etc.) can form properties of the upper layer of regolith. The amount of fused glassy particles and others agglutinates in the lunar upper layer is the direct index of the soil reworking caused be the micrometeorite bombardment. Besides, this micrometeorite bombardment is also responsible for the mechanical process through which the large particles are broken down into smaller ones. For lunar regolith was showed that increasingly mature soils become progressively finer-grained, better-sorted, and composed of a greater proportion of agglutinates. The increasing rate of the fused glassy fragments, of agglutinates, and of fine size fraction in the regolith during its space weathering affects the polarization of the light reflected by an exposed lunar or Mercurian soil. Therefore, polarimetric properties of the regolith may be modified by the soil reworking process in the course of time. Comparison of the lunar and Mercurian optic observations confirms the remarkable similarity of the polarimetric properties of Mercury and the Moon. From of summary of polarization measurements of whole disk of Mercury it is possible to conclude that maturity of the soil on the Mercurian surface in scale of whole disk is similar to one in large old craters on the lunar highland. Comparison of the lunar and Mercurian disk-integrated photometric functions indicates the likeness of the surface layer structures of the bodies. Analysis of the phase curve inclination and magnitude of the opposition effect shows that Mercurian relief in scale of meter details is smoother than lunar one. It was measured brightness of number of small plots (10x10 cm) on the lunar surface (Luna-13 data). The range of phase angles was from 68 to 75 deg. These values close correlate with corresponding part of the Mercurian disk-integrated phase function. ItSs possible if Mercurian phase function received from Earth-based telescopes and lunar one received in cm-scale is coincided the structures of regolith may be similar in both cases. These conclusions may be used for planning BepiColombo mission. This work was supported by INTAS-ESA grant No. 99-00403.

Shevchenko, V.

245

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

246

The mixing layer: Deterministic models of a turbulent flow. II - The origin of the three-dimensional motion  

NASA Astrophysics Data System (ADS)

Nonlinear calculations of the two-dimensional motion of the turbulent shear flow are performed and this flow is simultaneously used as the time-dependent flow upon which the linearized three-dimensional perturbations grow. This leads to the development of second-order motion, and the dynamical effect of the new motion on the first-order flow is not considerable. The layer becomes segregated into a region in which the kinetic energy of the secondary flow is quite weak (though the value of the streamwise vorticity may reach a maximum) and a region of intense magnitude and production rate of three-dimensional kinetic energy. The first region, preferentially two-dimensional, is the sequential pairing instability, giving rise to the growth of the layer by the coalescence of spanwise vortices. The second region is expected to grow side by side with the pairing instability. It is likely that the strong streamwise vorticity that appears in the central part of the braids is caused initially by the original three-dimensional shear instability.

Corcos, G. M.; Lin, S. J.

1984-02-01

247

Differential Chromatin Structure Encompassing Replication Origins in Transformed and Normal Cells  

PubMed Central

This study examines the chromatin structure encompassing replication origins in transformed and normal cells. Analysis of the global levels of histone H3 acetylated at K9&14 (open chromatin) and histone H3 trimethylated at K9 (closed chromatin) revealed a higher ratio of open to closed chromatin in the transformed cells. Also, the trithorax and polycomb group proteins, Brg-1 and Bmi-1, respectively, were overexpressed and more abundantly bound to chromatin in the transformed cells. Quantitative comparative analyses of episomal and in situ chromosomal replication origin activity as well as chromatin immunoprecipitation (ChIP) assays, using specific antibodies targeting members of the pre-replication complex (pre-RC) as well as open/closed chromatin markers encompassing both episomal and chromosomal origins, revealed that episomal origins had similar levels of in vivo activity, nascent DNA abundance, pre-RC protein association, and elevated open chromatin structure at the origin in both cell types. In contrast, the chromosomal origins corresponding to 20mer1, 20mer2, and c-myc displayed a 2- to 3-fold higher activity and pre-RC protein abundance as well as higher ratios of open to closed chromatin and of Brg-1 to Bmi-1 in the transformed cells, whereas the origin associated with the housekeeping lamin B2 gene exhibited similar levels of activity, pre-RC protein abundance, and higher ratios of open to closed chromatin and of Brg-1 to Bmi-1 in both cell types. Nucleosomal positioning analysis, using an MNase-Southern blot assay, showed that all the origin regions examined were situated within regions of inconsistently positioned nucleosomes, with the nucleosomes being spaced farther apart from each other prior to the onset of S phase in both cell types. Overall, the results indicate that cellular transformation is associated with differential epigenetic regulation, whereby chromatin structure is more open, rendering replication origins more accessible to initiator proteins, thus allowing increased origin activity.

Di Paola, Domenic; Rampakakis, Emmanouil; Chan, Man Kid

2012-01-01

248

Applications of Electro-Rheological Fluids for Constrained Layer Damping Treatment of Structures  

Microsoft Academic Search

Constrained layer damping (CLD) technique employs solid viscoelastic materials for controlling the vibration characteristics of structures. The effectiveness of the CLD treatment depends on the dynamic mechanical properties and geometrical dimensions of the viscoelastic and constraining layers. It also depends on the percentage coverage of the structure by the viscoelastic and constraining layers. Since the complex dynamic properties of electro-rheological

S. O. Oyadiji

1996-01-01

249

Structural Analysis and Lifetime Distribution of Electric Carriers in CdSe Epitaxial Layers  

Microsoft Academic Search

X-ray diffraction and scanning microscopy were used to analyze the structure of CdSe epitaxial layers. The structural data indicate the growth from CdSe layers of crystallites corresponding to the hexagonal modification. The lifetime distribution of electric carriers investigated by photoconductive frequency-resolved spectroscopy allows for the appreciation of the carrier kinetics in the studied semiconducting layers.

G. Cerbanic; I. Burda; Gh. Borodi; I. Chicinas; I. Vida Simitti; S. Simon

2003-01-01

250

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

251

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

252

Self-organization of local magnetoplasma structures in the upper layers of the solar convection zone  

NASA Astrophysics Data System (ADS)

Self-organization and evolution of magnetoplasma structures in the upper layers of the solar convection zone are discussed as a process of diffuse aggregation of magnetic flux tubes. Equations describing the tube motion under the action of magnetic interaction forces, hydrodynamic forces, and random forces are written explicitly. The process of aggregation of magnetic flux tubes into magnetic flux clusters of different shapes and dimensions is simulated numerically. The obtained structures are compared with the observed morphological types of sunspot groups. The quantitative comparison with the observational data was performed by comparing the fractal dimensions of the photospheric magnetic structures observed in solar active regions with those of structures obtained in the numerical experiment. The model has the following free parameters: the numbers of magnetic flux tubes with opposite polarities on the considered area element ( Nn and Ns), the average radius of the cross section of the magnetic flux tube ( a), its effective length ( l), the twist factor of the tube field ( k), and the absolute value of the average velocity of chaotic tube displacements ( d). Variations in these parameters in physically reasonable limits leads to the formation of structures (tube clusters of different morphological types) having different fractal dimensions. Using the NOAA 10488 active region, which appeared and developed into a complicated configuration near the central meridian, as an example, it is shown that good quantitative agreement between the fractal dimensions is achieved at the following parameters of the model: Nn = Ns = 250 ± 50; a = 150 ± 50 km; l ˜ 5000 km, and d = 80 ± 10 m/s. These results do not contradict the observational data and theoretical estimates obtained in the framework of the Parker "spaghetti" model and provide new information on the physical processes resulting in the origin and evolution of local magnetic plasma structures in the near-photospheric layers of the solar convection zone.

Chumak, O. V.

2013-08-01

253

Self-organization of local magnetoplasma structures in the upper layers of the solar convection zone  

SciTech Connect

Self-organization and evolution of magnetoplasma structures in the upper layers of the solar convection zone are discussed as a process of diffuse aggregation of magnetic flux tubes. Equations describing the tube motion under the action of magnetic interaction forces, hydrodynamic forces, and random forces are written explicitly. The process of aggregation of magnetic flux tubes into magnetic flux clusters of different shapes and dimensions is simulated numerically. The obtained structures are compared with the observed morphological types of sunspot groups. The quantitative comparison with the observational data was performed by comparing the fractal dimensions of the photospheric magnetic structures observed in solar active regions with those of structures obtained in the numerical experiment. The model has the following free parameters: the numbers of magnetic flux tubes with opposite polarities on the considered area element (Nn and Ns), the average radius of the cross section of the magnetic flux tube (a), its effective length (l), the twist factor of the tube field (k), and the absolute value of the average velocity of chaotic tube displacements (d). Variations in these parameters in physically reasonable limits leads to the formation of structures (tube clusters of different morphological types) having different fractal dimensions. Using the NOAA 10488 active region, which appeared and developed into a complicated configuration near the central meridian, as an example, it is shown that good quantitative agreement between the fractal dimensions is achieved at the following parameters of the model: Nn = Ns = 250 ± 50; a = 150 ± 50 km; l ? 5000 km, and d = 80 ± 10 m/s. These results do not contradict the observational data and theoretical estimates obtained in the framework of the Parker “spaghetti” model and provide new information on the physical processes resulting in the origin and evolution of local magnetic plasma structures in the near-photospheric layers of the solar convection zone.

Chumak, O. V., E-mail: chuo@yandex.ru [Moscow State University, Sternberg Astronomical Institute (Russian Federation)

2013-08-15

254

The Origin and Evolution of tRNA Inferred from Phylogenetic Analysis of Structure  

Microsoft Academic Search

The evolutionary history of the two structural and functional domains of tRNA is controversial but harbors the secrets of\\u000a early translation and the genetic code. To explore the origin and evolution of tRNA, we reconstructed phylogenetic trees directly\\u000a from molecular structure. Forty-two structural characters describing the geometry of 571 tRNAs and three statistical parameters\\u000a describing thermodynamic and mechanical features of

Feng-Jie Sun; Gustavo Caetano-Anollés

2008-01-01

255

Structural Defects and the Origin of the Second Length Scale in SrTiO3  

Microsoft Academic Search

To understand the origin of the second long-length scale in SrTiO 3, we studied structural defects in Verneuil-grown single crystals by transmission electron microscopy. The density of the dislocations was observed to decrease with increasing depth from the original cut surface of the crystals. The high density of dislocations in the skin region is most likely responsible for the second

Renhui Wang; Yimei Zhu; S. M. Shapiro

1998-01-01

256

Noise and vibration level reduction by covering metal structures with layers of damping materials. [considering viscoelastic insulation layers  

NASA Technical Reports Server (NTRS)

One of the most important methods of reducing the noise and vibration level is the damping of the secondary sources, such as metal plates, often used in vehicle structures, by means of covering materials with high internal viscosity. Damping layers are chosen at an optimum thickness corresponding to the frequency and temperature range in which a certain structure works. The structure's response corresponding to various real situations is analyzed by means of a measuring chain including electroacoustical or electromechanical transducers. The experimental results provide the dependence of the loss factor and damping transmission coefficient as a function of the damping layer thickness or of the frequency for various viscoelastic covering materials.

Rugina, I.; Paven, H. T. O.

1974-01-01

257

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

258

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

259

Preparation of Epitaxial SrCuOX Thin Films with an Infinite-Layer Structure  

NASA Astrophysics Data System (ADS)

The authors successfully prepared epitaxially-grown SrCuOX films with an infinite-layer structure by stacking atomic layers of SrOX and CuOX alternately, using a shutter-controlled sputtering method. High-resolution electron microscopy (HREM) observation indicated that the films had an infinite-layer structure and were epitaxially grown. It was considered that in order to prepare epitaxial SrCuOX films with an infinite-layer structure, the CuOX layers had to be CuO, not Cu2O or Cu.

Terashima, Yoshiaki; Sato, Rie; Takeno, Shiro; Nakamura, Shin-ichi; Miura, Tadao

1993-01-01

260

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

261

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

262

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

263

Electric Double Layer Structures near Rough Surfaces: Molecular Dynamics Simulation  

NASA Astrophysics Data System (ADS)

S. S. Dukhin in Surface and Colloid Science (1974) mentioned both the possibility of increase in zeta potential due to surface roughness and the possibility of decrease, depending on Debye length relative to surface roughness. In this work we report our results of molecular dynamic (MD) simulations on electric double layer structures near solid surfaces having roughness with the order of magnitude of Debye length. For computational simplicity only counter-ions are present. We computed static and dynamics properties including density profiles of water and ions, electrostatic potential distributions due to ions, polarization density profiles and self-diffusivities of water and ions. We also performed nonequilibrium MD to simulate electroosmotic flows. From electrostatic potential distributions and slip plane locations, we computed zeta potential and found that it decreases with surface roughness. It also showed a dependency on the spatial frequency of surface roughness. For comparison we used the Helmholtz-Smoluchowski relation and found the same trend. Currently we are studying pressure-driven flows, a computational counterpart to streaming current experiments. One of the purposes is to find more exact locations of slip planes by fitting to Poiseuille flow solutions. We are also simulating model systems with co-ions to investigate the possibility of charge inversion and other effects.

Kim, Daejoong; Darve, Eric

2006-03-01

264

Experimental Study of a Silver Layer on an Antireflection Subwavelength-Structured Surface  

Microsoft Academic Search

The optical characteristics of a silver layer deposited on an antireflection subwavelength-structured surface are investigated. The experimental results of the reflectance and the transmittance of several different thicknesses of silver layer on the subwavelength-structured surface are carried out. A subwavelength structure with the spatial period and diameter of about 230 nm and height of about 150 nm on polyethylene terphthalate

Chia-Jen Ting; Chi-Feng Chen; C. P. Chou

2008-01-01

265

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

NASA Astrophysics Data System (ADS)

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.; Wosinski, T.; Gluba, L.; Andrearczyk, T.; Domagala, J. Z.; ?uk, J.; Sadowski, J.

2014-01-01

266

Dispersion relations for SH-wave propagation in periodic piezoelectric composite layered structures  

Microsoft Academic Search

Propagation behavior of horizontally polarized shear waves (SH-waves) in a periodic piezoelectric–polymeric layered structure is taken into account. The layered structures are consisted of piezoelectric thin films bonded perfectly with polymeric thin films alternately. The phase velocity equations of SH-waves propagation in the periodic layered piezoelectric structure are obtained for the cases of wave propagation in the direction normal to

Zhenghua Qian; Feng Jin; Zikun Wang; Kikuo Kishimoto

2004-01-01

267

Molecular analysis of neocortical layer structure in the ferret  

PubMed Central

Molecular markers that distinguish specific layers of rodent neocortex are increasingly employed to study cortical development and the physiology of cortical circuits. The extent to which these markers represent general features of neocortical cell type identity across mammals is, however, unknown. To assess the conservation of layer markers more broadly, we isolated orthologs for fifteen layer-enriched genes in the ferret, a carnivore with a large, gyrencephalic brain, and analyzed their patterns of neocortical gene expression. Our major findings are: (1) Many but not all layer markers tested show similar patterns of layer-specific gene expression between mouse and ferret cortex, supporting the view that layer-specific cell type identity is conserved at a molecular level across mammalian superorders; (2) Our panel of deep layer markers (ER81/ETV1, SULF2, PCP4, FEZF2/ZNF312, CACNA1H, KCNN2/SK2, SYT6, FOXP2, CTGF) provides molecular evidence that the specific stratifications of layer 5 and 6 into 5a, 5b, 6a and 6b are also conserved between rodents and carnivores. (3) Variations in layer-specific gene expression are more pronounced across areas of ferret cortex than between homologous areas of mouse and ferret cortex; (4) This variation of area gene expression was clearest with the superficial layer markers studied (SERPINE2, MDGA1, CUX1, UNC5D, RORB/NR1F2, EAG2/KCNH5). Most dramatically, the layer 4 markers RORB and EAG2 disclosed a molecular sublamination to ferret visual cortex and demonstrated a molecular dissociation among the so-called agranular areas of the neocortex. Our findings establish molecular markers as a powerful complement to cytoarchitecture for neocortical layer and cell-type comparisons across mammals.

Rowell, Joanna J.; Mallik, Atul K.; Dugas-Ford, Jennifer; Ragsdale, Clifton W.

2010-01-01

268

Antireflection efficiency comparison of single- and double-layered structures for photovoltaic glass covers.  

PubMed

For single-layer antireflection (AR) on glass, a low refractive index (n) AR layer is required to achieve high AR efficiency, which limits the selection of materials. The double-layered AR structure has a lower requirement on materials' n but is typically used for narrow waveband AR, and photovoltaic glass covers require broadband AR to increase the whole-spectrum solar energy transmittance. With the help of a multilayered optical simulation, we optimized the n and thickness of the single and double layered AR structure and found that, for broadband AR, double-layered structure only showed AR efficiency advantages in very high or low top layers' n compared to single AR layer structure. For a n=1.45 top layer of the double layer structure, the optimized reflectance is 2.57% (single side), while the optimized reflectance of a single AR layer with n=1.45 is 2.87%, which is a negligible AR efficiency advantage (0.30%) when considering production costs. Moreover, in our experiment, using SiO2 and SiO2 and TiO2 composite layers, the absorption of short wavelengths by TiO2 ostensibly cancelled this advantage out (92.87% compare to the single layer's 92.98% for single side AR). PMID:24921132

Chen, Zhang; Gao, Yanfeng

2014-06-10

269

Tunable Photonic Devices in Ferroelectric-Based Layered Structures  

NASA Astrophysics Data System (ADS)

This thesis presents the studies on the optical properties of perovskite ferroelectric thin films, as well as the preparation and applications of ferroelectrics in tunable photonic devices. Ba(Zr,Ti)O3 (BZT) thin films with different Zr concentration were grown on MgO substrates by pulsed laser deposition, and their structural and optical properties in the visible range were systematically characterized, including the out-of-plane lattice constant, grain size, refractive index, optical band gap energy, electro-optic coefficient, optical loss and absorption coefficient. The obtained results provide information for the design of BZT thin film-based optical devices. One-dimensional photonic crystal filter working in the terahertz (THz) range was studied. The transmission properties of SrTiO3 (STO) crystals were first characterized by THz time-domain spectroscopy. Si/STO multilayers with different STO defect thicknesses were designed by the transfer matrix method and then constructed by polishing and stacking. The shift of defect mode was observed and comparable with the calculations. Two-dimensional photonic structures in the optical and infra-red range were then attempted. A combination of nanoimprint lithography and inductively coupled plasma etching were investigated on (Ba,Sr)TiO3 thin films. Then, in order to simplify the nanoimprint process and allow thick metal sacrificial layer deposition for high aspect-ratio etching, a transfer imprint lithography technique was developed. Finally, surface plasmon resonance (SPR) tuning via thermally-induced refractive index changes in ferroelectrics was investigated. Ag stripes with periodicity 750 nm were fabricated on flat BST surface by nanoimprint lithography and subsequent lift-off. (-1), (2) and (-2) SP modes from Ag/BST interface were observed in visible range. Red shift of the modes up to 3.9 nm was obtained with increasing temperature. Then continuous Au film on corrugated BST surface with periodicity of 1 mum was obtained by nanoimprint lithography and subsequent dry etching. Thermal tuning of the (-1) SP mode from Au/BST interface by 1 nm was observed in the near infrared range. All the measurement results were comparable with the calculation by Rigorous coupled wave analysis and a simple analytical model. These results indicated the feasibility of active modulation in SPR in solid-state structures.

Xin, Jianzhuo

270

Surface electromagnetic waves in thin-layer biaxial structure in a magnetic field  

NASA Astrophysics Data System (ADS)

The conditions for the existence of surface electromagnetic waves at the planar interface between a homogeneous medium (vacuum) and a thin-layer periodic structure consisting of alternating semiconductor and dielectric layers in an external magnetic field have been investigated. This structure represents an optically biaxial crystal with the effective permittivity tensor components dependent both on the geometric parameters of the structure and on the physical characteristics (magnetic field strength, frequency, and thicknesses of the layers). It has been shown that the propagation of surface electromagnetic waves localized near the interface can occur in the thin-layer biaxial structure within specific ranges of frequencies and external magnetic field strengths.

Bulgakov, A. A.; Fedorin, I. V.

2012-08-01

271

Towards a unified model of passive drug permeation I: origins of the unstirred water layer with applications to ionic permeation.  

PubMed

In this work, we provide a unified theoretical framework describing how drug molecules can permeate across membranes in neutral and ionized forms for unstirred in vitro systems. The analysis provides a self-consistent basis for the origin of the unstirred water layer (UWL) within the Nernst-Planck framework in the fully unstirred limit and further provides an accounting mechanism based simply on the bulk aqueous solvent diffusion constant of the drug molecule. Our framework makes no new assumptions about the underlying physics of molecular permeation. We hold simply that Nernst-Planck is a reasonable approximation at low concentrations and all physical systems must conserve mass. The applicability of the derived framework has been examined both with respect to the effect of stirring and externally applied voltages to measured permeability. The analysis contains data for 9 compounds extracted from the literature representing a range of permeabilities and aqueous diffusion coefficients. Applicability with respect to ionized permeation is examined using literature data for the permanently charged cation, crystal violet, providing a basis for the underlying mechanism for ionized drug permeation for this molecule as being due to mobile counter-current flow. PMID:24211511

Ghosh, Avijit; Scott, Dennis O; Maurer, Tristan S

2014-02-14

272

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.

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

2009-01-01

273

A spatial interaction model with spatially structured origin and destination effects  

NASA Astrophysics Data System (ADS)

We introduce a Bayesian hierarchical regression model that extends the traditional least-squares regression model used to estimate gravity or spatial interaction relations involving origin-destination flows. Spatial interaction models attempt to explain variation in flows from n origin regions to n destination regions resulting in a sample of N = n 2 observations that reflect an n by n flow matrix converted to a vector. Explanatory variables typically include origin and destination characteristics as well as distance between each region and all other regions. Our extension introduces latent spatial effects parameters structured to follow a spatial autoregressive process. Individual effects parameters are included in the model to reflect latent or unobservable influences at work that are unique to each region treated as an origin and destination. That is, we estimate 2 n individual effects parameters using the sample of N = n 2 observations. We illustrate the method using a sample of commodity flows between 18 Spanish regions during the 2002 period.

LeSage, James P.; Llano, Carlos

2013-07-01

274

Autonomous Sensing of Layered Structures in Hawaiian Waters.  

National Technical Information Service (NTIS)

Our long-term goals are (1) to determine the spatial and temporal scales of thin layers, (2) to identify the processes responsible for the formation, maintenance and dissipation of vertically thin layers, and (3) to develop the capability to predict thin ...

M. A. McManus

2008-01-01

275

A method to calculate the laser heating of layered structures  

Microsoft Academic Search

This work describes a method to calculate the heating that occurs when a Gaussian laser beam is scanned across the surface of a flat object which may be coated with one or more layers of differing materials. The laser beam is characterized by its power, radius, and scan velocity. Each layer of the object is characterized by its thickness, density,

Roger J. Anderson

1988-01-01

276

Interlayer structure of iodide intercalated layered double hydroxides (LDHs)  

Microsoft Academic Search

The iodide-containing layered double hydroxides (LDHs) of Mg and Zn with Al crystallize by the inclusion of extensive positional disorder of I? ions in the interlayer region. I? ion given its poor charge to size ratio can neither screen effectively the positive charge nor participate in H-bonding with the metal hydroxide layers. Thereby the I? ions are not stabilized in

S. V. Prasanna; P. Vishnu Kamath; C. Shivakumara

2010-01-01

277

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

278

Layer-by-layer structured polysaccharides film-coated cellulose nanofibrous mats for cell culture  

Microsoft Academic Search

For the first time, a novel fibrous polysaccharide scaffold for cell culture was fabricated by the combination of electrospinning and electrostatic layer-by-layer (LBL) self-assembly technique. Oppositely charged chitosan (CS) and alginate (ALG) in aqueous media were alternatively deposited onto the negatively charged cellulose nanofibrous mats which hydrolyzed from electrospun cellulose acetate mats. The morphology and biocompatibility of the resultant scaffolds

Hongbing Deng; Xue Zhou; Xiaoying Wang; Chunyan Zhang; Bin Ding; Qiuhua Zhang; Yumin Du

2010-01-01

279

Observed Boundary Layer Wind Structure and Balance in the Hurricane Core. Part I: Hurricane Georges  

Microsoft Academic Search

The GPS dropsonde allows observations at unprecedentedly high horizontal and vertical resolution, and of very high accuracy, within the tropical cyclone boundary layer. These data are used to document the boundary layer wind field of the core of Hurricane Georges (1998) when it was close to its maximum intensity. The spatial variability of the boundary layer wind structure is found

Jeffrey D. Kepert

2006-01-01

280

Structure of the carbon layer deposited on the steel surface after low pressure carburizing  

Microsoft Academic Search

During low pressure carburizing a carbon layer precipitates on the surface of steel parts. The structure of the carbon layer was tested by means of optical and electron microscopy and Raman spectroscopy as well. It was found out that the carbon layer is composed of fine-crystalline graphite. A sample was carburized (boost step), and was subsequently observed with an optical

R. Gorockiewicz; A. ?api?ski

2010-01-01

281

Small scale structure in circumstellar envelopes and the origin of globules in planetary nebulae  

Microsoft Academic Search

We analyze the small scale structure in the circumstellar envelopes of NGC 7027 and IRC+10216, using high resolution optical images in dust scattered light. We use the observations to test the proposal that globules in planetary nebulae, typified by globules in the Helix nebula, originate in high density contrast proto-globules in the atmosphere of the progenitor AGB star and are

P. J. Huggins; N. Mauron

2002-01-01

282

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

283

Genetic origins of the Japanese: A partial support for the dual structure hypothesis  

Microsoft Academic Search

Based on the morphological characteristics of the skull and teeth, Hanihara ((1991) Japan Review 2:1-33) proposed the ''dual structure model'' for the formation of modern Japanese populations. We examine this model by dividing it into two independent hypotheses: 1) the Upper Paleo- lithic population of Japan that gave rise to the Neolithic Jomon people was of southeast Asian origin, and

Keiichi Omoto; Naruya Saitou

1997-01-01

284

NASA Strategic Roadmap: Origin, Evolution, Structure, and Destiny of the Universe.  

National Technical Information Service (NTIS)

The NASA strategic roadmap on the Origin, Evolution, Structure and Destiny of the Universe is one of 13 roadmaps that outline NASA's approach to implement the vision for space exploration. The roadmap outlines a program to address the questions: What powe...

N. E. White

2005-01-01

285

Understanding origins of present-day genetic structure in marine fish: biologically or historically driven patterns?  

Microsoft Academic Search

Determining the origin of genetic structure is of wide interest because of its use in stock discrimination in marine organisms. Schematically, genetic differentiation can result from historical patterns maintained over geological time or from present-day isolation attributable to biological characteristics of the species. We used a comparative approach to population genetic analysis based on allozyme polymorphism to determine the impact

C. Fauvelot; S. Planes

2002-01-01

286

The Structure of Catalyst Layers and Cell Performance in Proton Exchange Membrane Fuel Cells  

NASA Astrophysics Data System (ADS)

A catalyst layer is one of the key elements in polymer electrolyte membrane fuel cells (PEMFC). Improvements in the performance of a membrane electrode assembly (MEA) for PEMFC are much influenced by an electrochemically active surface area in a catalyst layer. But the relation between the structure of a catalyst layer and the cell performance has not been clarified yet. In the present study, catalyst layers with different structure and composition were fabricated, and the structural properties of catalyst layers, such as thickness and roughness, and the polarization curves were measured. The experimental results suggested that there is an optimum mass ratio of electrolyte in a catalyst layer for the cell performance, and the thickness and roughness of a catalyst layer change significantly at the optimum mass ratio.

Inoue, Hiroyuki; Daiguji, Hirofumi; Hihara, Eiji

287

Electronic structure of the structural components of a surface layer obtained by laser alloying  

NASA Astrophysics Data System (ADS)

It has been shown with the help of x-ray researches that the electronic structure of structural components formed in a surface layer of steel during laser alloying differs form that of similar structural components formed in equilibrium conditions. Saturation of a solid solution beyond the limit solubilities during laser alloying leads to some increase of electron localization on atoms. The analysis of distribution of electronic density in an elementary cell of a solid solution shows that some part of atoms of boron is dissolved in a solid solution on the basis of iron by replacement. The nonequilibrium process of cooling after crystallization leads to appreciable change of an electronic structure of boron iron Fe2B. The comparison of boron iron, formed in equilibrium conditions, with boron iron form a laser alloyed layer shows that in an elementary cell of latter the distribution of electronic density is more dim, that allows to speak about some decrease of a degree of electron localization on atoms.

Postnikov, V. S.

1999-01-01

288

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

289

Structure of the magnetopause current layer at the subsolar point.  

National Technical Information Service (NTIS)

A one-dimensional electromagnetic particle simulation model developed for the magnetopause current layer between the shocked solar wind and the dipole magnetic field at the subsolar point has been extended to include the interplanetary magnetic field (IMF...

H. Okuda

1991-01-01

290

Structure of surface reaction layer of poly-Si etched by fluorocarbon plasma  

SciTech Connect

A structure of surface reaction layer of poly-Si substrate during fluorocarbon plasma etching was studied by using a plasma beam irradiation apparatus and a quasi-in situ x-ray photoelectron spectroscopy. A fluorinated silicon (SiF) layer was formed under a fluorocarbon (CF) layer. It was found that the thickness of the SiF layer linearly increased with the etch yield of poly-Si regardless of the change of the CF layer thickness. The average ratio of the number of Si to that of F in the SiF layer did not strongly depend on the etch yield. The carbon-rich region of the CF layer was formed just above the SiF layer due to the consumption of fluorine for the formation of SiF layer.

Kurihara, Kazuaki; Egami, Akihiko; Nakamura, Moritaka [Corporate Research and Development Center, Toshiba Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8522 (Japan); Environmentally Benign Etching Technology Laboratory, Association of Super-Advanced Electronics Technologies (ASET), 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198 (Japan)

2006-03-15

291

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

NASA Astrophysics Data System (ADS)

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.

2011-11-01

292

High frequency intravascular photoacoustic (IVPA) imaging for differentiating arterial wall layered structures  

NASA Astrophysics Data System (ADS)

Arterial wall is composed of three layers: intima, media and adventitia. Intima-media thickness (IMT) is an important prognostic indicator of atherosclerotic diseases. Although intravascular ultrasound (IVUS) imaging is a commonly used method for delineation of the layered structures, it is inferior to the optical absorption contrast offered by intravascular photoacoustic (IVPA) imaging. We introduce an integrated miniature probe that combines the capabilities of IVUS and IVPA imaging for the evaluation of arterial wall layered structures. Healthy rabbit aorta was imaged ex vivo. IVPA results showed superior contrast over IVUS in identifying the layered structures of arterial wall.

Li, Xiang; Wei, Wei; Zhou, Qifa; Shung, K. Kirk; Chen, Zhongping

2012-02-01

293

Detection of Disbonds in Multi-layer Structures by Laser-Based Ultrasonic Technique  

Microsoft Academic Search

Adhesively bonded multi-layer structures are frequently used, mostly in the aerospace industry, for their structural efficiency. Nondestructive evaluation of bond integrity in these types of structures, both after manufacturing and for periodic inspection during service, is extremely important.A laser-based ultrasonic technique has been evaluated for non-contact detection of disbonds in aluminum multi-layer structures. Two configurations have been used to detect

D. Cerniglia; N. Montinaro; V. Nigrelli

2008-01-01

294

Dynamic Instability of Solidification Fronts and Formation of Transverse Layered Structures  

NASA Technical Reports Server (NTRS)

A plane front of crystallization in a unidirectional process of solidification of a binary melt or a solution is shown to be unstable with respect to virtual perturbations of the front velocity within some region of physical and operating parameters. This dynamic instability has nothing in common with morphological instability of the front also possible under certain conditions. It gives rise to the origination of a self-oscillating regime of solidification. The oscillations of the front velocity are accompanied by oscillations of other relevant variables, such as the melt concentration and temperature at the front. What is most important is that this provides for a natural explanation of phenomena of the formation of ordered striations commonly observed when producing alloys and withdrawing crystals. A theory of nonlinear instability of the solidification front is developed which also allows for properties of both self-oscillating regimes of solidification and transverse layered structures it allows to be described in an explicit form, without introducing any additional hypotheses and empirical parameters. Apart from other things, the properties are strongly dependent on convective transport originated in consequence of a difference between the densities of the liquid melt and solid alloy. The theory results in a remarkably good agreement with experimental evidence on crystal withdrawal obtained in normal gravity and under space flight conditions. The problem of interplay between modes of the dynamic and morphological types of instability is also discussed. There are parametric regions in which either only one of these types occurs or both of them arise simultaneously.

Buyevich, Yu A.; Mansurov, Valery V.; Webbon, Bruce W. (Technical Monitor)

1995-01-01

295

Cation Effects on the Layer Structure of Biogenic Mn-Oxides  

Microsoft Academic Search

Biologically catalyzed Mn(II) oxidation produces biogenic Mn-oxides (BioMnO) and may serve as one of the major formation pathways for layered Mn-oxides in soils and sediments. The structure of Mn octahedral layers in layered Mn-oxides controls its metal sequestration properties, photochemistry, oxidizing ability, and topotactic transformation to tunneled structures. This study investigates the impacts of cations (H{sup +}, Ni(II), Na{sup +},

Mengqiang Zhu; Matthew Ginder-Vogel; Sanjai J. Parikh; Xiong-Han Feng; Donald L. Sparks

2010-01-01

296

Graphenelike surface boron layer: Structural phases on transition-metal diborides (0001)  

NASA Astrophysics Data System (ADS)

We have identified two structure phases for a surface boron layer on transition-metal diborides ZrB2(0001) and NbB2(0001) using first-principles calculations. Surface-formation free-energy calculations of various surface structures combined with preliminary molecular-dynamics simulations revealed that, in a boron-rich condition, the well-known 1×1 graphitic boron layer (boraphene) and 3×3(R±30°)(3) boraphene are, respectively, thermodynamically more favorable surfaces than the 1×1 metal-terminated surfaces of NbB2(0001) and ZrB2(0001) . The origin of the 3 and 1×1 boraphene surface stability is discussed herein from the electronic-structure perspective. Full-phonon calculations based on the density-functional perturbation theory for these surfaces as well as for ZrB2 , NbB2 , ?-B , Zr, and Nb bulk crystals were also performed. The calculated phonon dispersions of the 3 and 1×1 boraphenes show excellent agreement with the experimental surface-phonon dispersions. Using phonon energy and electronic density of states of these surface and bulk systems with the harmonic approximation and the Sommerfeld theory, we obtained stable phases of the ZrB2(0001) and NbB2(0001) surfaces at each temperature. The calculated phase diagrams show that the thermodynamically favorable region of the boraphene surfaces slightly extends with increasing temperature in these transition-metal diboride surfaces.

Suehara, Shigeru; Aizawa, Takashi; Sasaki, Taizo

2010-02-01

297

Radiation and thermal effects on porous and layer structured materials as getters of radionuclides  

Microsoft Academic Search

The long term radiation and thermal effects on porous and layer structured materials that may function as getters for radionuclides have been evaluated using accelerated laboratory experiments including energetic electron, ion or neutron irradiation, as well as high-temperature thermal annealing. The materials studied include: zeolites, layered silicates (mica and smectite clays), open framework structured apatite and crystalline silicotitanate (CST) which

L. M. Wang; J. Chen; R. C. Ewing

2004-01-01

298

Tectonic control on the origin and orientation of igneous layering: An example from the Greendale Complex,Antigonish Highlands, Nova Scotia, Canada  

NASA Astrophysics Data System (ADS)

Layering in appinites (hornblende-rich gabbros) of the ca. 610 Ma Greendale Complex, Antigonish Highlands, Nova Scotia, is defined by variations in texture and modal abundances of hornblede and plagioclase, and ranges in width from 5 to 50 cm. Regional studies indicate that the complex was probably emplaced during late Precambrian dextral shear on northeast-trending faults by brittle failure at the roof of the magma chameber. The origin and orientation of the layers may have been controlled by the regional tectonic setting. The layering is steep to vertically dipping and varies in strike from 080° to 180° (clockwise) with concentrations at 090° and 160°. The 090° layers are dilational and are thought to have developed perpendicular to north-south extension along the extensional plane of the instantaneous strain ellipsoid associated with progressive dextral shear. The 160° layers commonly display boudinage. They may have rotated clockwise from an original 090° attitude toward the plane of flattening (and hence into a stretching field) during progressive dextral shear. Late-stage cogenetic felsic veins fill conjugate shear fractures consistent with a dextral shear regime. This study emphasizes the potential importance of considering regional tectonic setting when analyzing the origin and orientation of igneous fabrics.

Brendan Murphy, J.; Hynes, Andrew J.

1990-05-01

299

The elasticity of lawsonite at high pressure and the origin of low velocity layers in subduction zones  

NASA Astrophysics Data System (ADS)

Subduction zones exhibit faster seismic wave velocities compared to the surrounding mantle due to the recycling of relatively cold oceanic lithosphere. In certain subduction zones, however, a 5-10 km thick low velocity layer (LVL) has been inferred to exist along the top surface of the subducting slab at depths of up to 250 km. Shear-wave velocities, in particular, within these layers have been estimated as up to 10% slower than the surrounding mantle. We have conducted high-pressure ultrasonic interferometric measurements to gain insight into the elastic properties of lawsonite [CaAl2(Si2O7)(OH)2·H2O], a hydrous mineral phase stabilized under cold subduction zone conditions. In addition, we have computed the full elastic constant tensor at elevated pressures and temperature, using static electronic structure calculations and molecular dynamics simulations. The bulk and shear modulus obtained from theory and experiments are in good agreement. We find that lawsonite has an unusually low shear modulus at high pressure and its formation in subducted oceanic crust can explain some seismic evidence for LVL at depths exceeding 100 km. To approach estimated LVL velocities requires lawsonite to form in the subducting crust as a result of a fluid influx due to the breakdown of other hydrous minerals such as serpentine. The formation of lawsonite additionally lowers seismic velocities because it forms at the expense of garnet, a mineral with relatively fast seismic velocities. LVL observations may therefore be used to place constraints on the amount of H2O subducted into the deep mantle.

Chantel, Julien; Mookherjee, Mainak; Frost, Daniel J.

2012-10-01

300

The coherent structure of turbulent mixing layers. 1: Similarity of the primary vortex structure. 2: Secondary streamwise vortex structure  

NASA Astrophysics Data System (ADS)

The primary spanwise organized vortex structure and the secondary streamwise vortex structure of turbulent mixing layers have been investigated. Flow visualization motion pictures of a constant density mixing layer were used to measure the properties of the large scale vortices. It was found that after an initial transition region mean properties of the large scale vortices reach the expected linear growth with downstream distance required by similarity. In the self-similar region, the vortex core area and visual thickness increase continuously during its life-span. A theoretical model of probability distribution function for the large-scale vortex circulation was developed. This distribution is found to be lognormal and to have a standard deviation, normalized with the mean of 0.28. From this model the mean life-span of the vortices could also be obtained and was found to be 0.67 times the mean life-span position. The streamwise streak pattern observed by Konrad (1976) and Breidenthal (1978) in plan-view pictures of the mixing layer was investigated, using flow visualization and spanwise concentration measurements. It was confirmed that this pattern is the results of a secondary vortex structure dominated by streamwise, counter-rotating vortices. A detailed description of its spatial relation to the primary, spanwise vortex structure is presented. From time average flow pictures, the onset position and initial scale of the secondary structures were determined.

Bernal, L. P.

1981-06-01

301

Multi-layer metal/shape memory polymer roll-up wing structures for fitment-constrained air vehicles  

US Patent & Trademark Office Database

A laminated wing structure includes at least one layer of metal material and at least one layer of a shape memory polymer (SMP) material. The SMP is heated to a temperature in its glass transition band Tg to roll the wing around the air vehicle into a stored position. The metal layer(s) must be thin enough to remain below its yield point when rolled up. In preparation for launch, the SMP material is thermally activated allowing the strain energy stored in the layer of metal material to return the wing to its deployed position at launch. Once deployed, the SMP cools to its glassy state. The SMP material may be reinforced with fiber to form a polymer matrix composite (PMC). SMP may be used to provide shear strain relief for multiple metal layers. By offloading the motive force required to return the wing to its original deployed position from the SMP to the metal, the polymer does not acquire a permanent set and the wing may be deployed accurately.

2013-09-10

302

Two-silicon-nanocrystal layer memory structure with improved retention characteristics.  

PubMed

It was demonstrated in the literature that the use of self-aligned doubly-stacked Si dots improves retention characteristics of a nanocrystal memory. In this paper, we show that a similar effect may be obtained by using two distinct layers of silicon nanocrystals within the gate dielectric of the MOS structure, if the nanocrystal density in each layer is high enough (above 10(12) dots/cm2) so as to get an average effect of at least one smaller dot underneath each larger one. The relative distance of the layers and their position from the silicon substrate and the gate metal are critical for optimum memory operation. Two different double-nanocrystal-layer structures were investigated. In the first structure the two nanocrystal layers were close together and they were composed of dots of different size (lower layer: 3 nm, upper layer: 5 nm), while in the second structure the dot layers were composed of dots of equal diameter (d = 3 nm) and their inter-distance was much larger. In both cases, the retention characteristics of the structure were improved compared with a single dot layer structure. In the second case this improvement was significantly larger than in the first case. Extrapolation of the data to ten years memory operation, showed that the charge loss after this time was only approximately 12%. PMID:17455506

Nassiopoulou, A G; Salonidou, A

2007-01-01

303

Origin of the structure and planform of small impact craters in fractured targets: Endurance Crater at Meridiani Planum, Mars  

NASA Astrophysics Data System (ADS)

We present observations and models that together explain many hallmarks of the structure and growth of small impact craters forming in targets with aligned fractures. Endurance Crater at Meridiani Planum on Mars (diameter ? 150 m) formed in horizontally-layered aeolian sandstones with a prominent set of wide, orthogonal joints. A structural model of Endurance Crater is assembled and used to estimate the transient crater planform. The model is based on observations from the Mars Exploration Rover Opportunity: (a) bedding plane orientations and layer thicknesses measured from stereo image pairs; (b) a digital elevation model of the whole crater at 0.3 m resolution; and (c) color image panoramas of the upper crater walls. This model implies that the crater's current shape was mostly determined by highly asymmetric excavation rather than long-term wind-mediated erosion. We show that modal azimuths of conjugate fractures in the surrounding rocks are aligned with the square component of the present-day crater planform, suggesting excavation was carried farther in the direction of fracture alignments. This was previously observed at Barringer Crater in Arizona and we show the same relationship also holds for Tswaing Crater in South Africa. We present models of crater growth in which excavation creates a "stellate" transient cavity that is concave-cuspate in planform. These models reproduce the "lenticular-crescentic" layering pattern in the walls of some polygonal impact craters such as Endurance and Barringer Craters, and suggest a common origin for tear faults and some crater rays. We also demonstrate a method for detailed error analysis of stereogrammetric measurements of bedding plane orientations.

Watters, Wesley A.; Grotzinger, John P.; Bell, James; Grant, John; Hayes, Alex G.; Li, Rongxing; Squyres, Steven W.; Zuber, Maria T.

2011-01-01

304

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

305

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

306

Defect structure of InAlAs\\/InP layers  

Microsoft Academic Search

InxAl1?xAs layers on InP substrate can be subjected to compressive as well as tensile strain due to lattice parameter differences induced by suitable alloy composition changes. The 2?m thick InxAl1?xAs (0.50?x?0.53) layers were grown on the (001) oriented InP substrates by molecular beam epitaxy (MBE). They were investigated using X-ray diffraction and chemical etching. X-ray studies were performed applying high-resolution

A. Shalimov; J. Bak-Misiuk; J. Kaniewski; J. Trela; W. Wierzchowski; K. Wieteska; W. Graeff

2005-01-01

307

The ancient history of the structure of ribonuclease P and the early origins of Archaea  

PubMed Central

Background Ribonuclease P is an ancient endonuclease that cleaves precursor tRNA and generally consists of a catalytic RNA subunit (RPR) and one or more proteins (RPPs). It represents an important macromolecular complex and model system that is universally distributed in life. Its putative origins have inspired fundamental hypotheses, including the proposal of an ancient RNA world. Results To study the evolution of this complex, we constructed rooted phylogenetic trees of RPR molecules and substructures and estimated RPP age using a cladistic method that embeds structure directly into phylogenetic analysis. The general approach was used previously to study the evolution of tRNA, SINE RNA and 5S rRNA, the origins of metabolism, and the evolution and complexity of the protein world, and revealed here remarkable evolutionary patterns. Trees of molecules uncovered the tripartite nature of life and the early origin of archaeal RPRs. Trees of substructures showed molecules originated in stem P12 and were accessorized with a catalytic P1-P4 core structure before the first substructure was lost in Archaea. This core currently interacts with RPPs and ancient segments of the tRNA molecule. Finally, a census of protein domain structure in hundreds of genomes established RPPs appeared after the rise of metabolic enzymes at the onset of the protein world. Conclusions The study provides a detailed account of the history and early diversification of a fundamental ribonucleoprotein and offers further evidence in support of the existence of a tripartite organismal world that originated by the segregation of archaeal lineages from an ancient community of primordial organisms.

2010-01-01

308

Radiation Effects in Strained-Layer Superlattice (SLS) Structures.  

National Technical Information Service (NTIS)

The effects of gamma and neutron irradiation on GaP/GaAsP strained-layer superlattices (SLS's) have been studied and compared with results on similar non-SLS alloys. The carrier removal rate was significantly greater in the non-SLS samples for both types ...

C. E. Barnes G. A. Samara R. M. Biefeld T. E. Zipperian G. C. Osbourn

1984-01-01

309

Wire bonding of aluminum\\/polyimide multi-layer structures  

Microsoft Academic Search

Gold thermosonic wire bonding of aluminum pads located on thick polyimide films has been studied. Bond pull and bond shear studies indicated that the weld between the wire and pad was very poor, resulting in unacceptable failure strengths and failure modes. The incorporation of a thin Ti layer between the aluminum and polyimide was found to improve the weld quality

V. Murali; M. Gasparek; A. Bhansali; S. H. Chen; R. Dias

1992-01-01

310

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

311

Thermodynamic structure of the monsoon boundary layer under the influence of a large-scale depression  

NASA Astrophysics Data System (ADS)

Using data from the MONsoon Trough Boundary Layer EXperiment (MONTBLEX), the thermodynamic structure of the atmospheric boundary layer (ABL) under the influence of a monsoon depression has been studied. When the depression was in the vicinity of the observing station, the soundings showed an increase in potential temperature, the sub-cloud layer was well mixed, the wind speed increased to 35 m/s, and the monsoon boundary layer was convectively more unstable at night than in the daytime. Cloud-top processes, which lead to an apparent breakdown of the boundary layer, seem to explain this.

Rajkumar, G.; Saraswat, R. S.; Chakravarty, B.

1994-02-01

312

Origin of Blue Hole Structures in Coral Reefs: Houtman Abrolhos, Western Australia  

Microsoft Academic Search

WYRWOLL, K.-H.; ZHU, R.Z.; COLLINS, L.B., and HATCHER, B.G., 2006. Origin of blue hole structures in coral reefs: Houtman Abrolhos, Western Australia. Journal of Coastal Research, 22(1), 202-208. West Palm Beach (Florida), ISSN 0749-0208. The distinctive blue hole terrains of the Houtman Abrolhos reef complex have been previously interpreted as the result of karst processes controlling Holocene reef growth and

Karl-Heinz Wyrwoll; Zhong Rong Zhu; Lindsay B. Collins; Bruce G. Hatcher

2006-01-01

313

Sacrificial adhesion promotion layers for copper metallization of device structures.  

PubMed

The adhesion of copper films to adjacent device layers including TiN, Ta, and TaN diffusion barriers is a crucial reliability issue for integrated circuits. We report that ultrathin layers of poly(acrylic acid) (PAA) prepared on barrier surfaces or on the native oxide of Si wafers dramatically increase the interfacial adhesion of Cu films deposited by the H2 assisted reduction of bis(2,2,7-trimethyloctane-3,5-dionato)copper in supercritical carbon dioxide. Similar improvements were achieved on Si wafers using a simple vapor phase exposure of the substrate to acrylic acid prior to metallization. The deposited films and the substrate/Cu interfaces were analyzed by X-ray photoelectron spectroscopy (XPS), electron microscopy, atomic force microscopy, and variable-angle spectroscopic ellipsometry. No trace of the adhesion layer was detected at the interface, indicating it was sacrificial at the deposition conditions used. Moreover, the presence and subsequent decomposition of the PAA layer during deposition substantially reduced or eliminated metal oxides at the substrate interface. For depositions on PAA-treated Si wafers, copper was present primarily as Cu0 at the interface and Si was present only as Si0. On PAA-treated Ta substrates, XPS analysis indicated Ta was present primarily as Ta0 at the metallized interface whereas Ta2O5 dominated the interface of samples prepared without the adhesion layers. The technique can be extended to patterned substrates using adsorption of acrylic acid or thermal/UV polymerization of acrylic acid. PMID:15461508

Zong, Yinfeng; Shan, Xiaoying; Watkins, James J

2004-10-12

314

Electronic structure of superconducting layered zirconium and hafnium nitride  

Microsoft Academic Search

The electronic energy-band structures for beta-ZrNCl and beta-HfNCl, which can be superconducting by intercalation, have been calculated by using the scalar-relativistic full-potential linearized augmented-plane-wave method within the local-density approximation. For beta-ZrNCl, we have calculated the electronic structure for the four proposed crystal structures, and obtained two kinds of qualitatively different energy bands. For the first two structures, the calculations show

Izumi Hase; Yoshikazu Nishihara

1999-01-01

315

On the origin of a band gap in compounds of diamond-like structures.  

PubMed

Electronic structure calculations were performed to examine the origin of a band gap present in most 18-electron half-Heusler compounds and its absence in NaTl. In these compounds of diamond-like structures, the presence or absence of a band gap is controlled by the sigma antibonding between the valence s orbitals, and the bonding characteristics of the late-main-group elements depend on the extent of their ns/np hybridization. Implications of these observations on the formal oxidation state and the covalent bonding of the transition-metal atoms in 18-electron half-Heusler and related compounds were discussed. PMID:17290986

Köhler, Jürgen; Deng, Shuiquan; Lee, Changhoon; Whangbo, Myung-Hwan

2007-03-19

316

Structural Origins of the Excellent Glass Forming Ability of Pd40Ni40P20  

NASA Astrophysics Data System (ADS)

We report a hybrid atomic packing scheme comprised of a covalent-bond-mediated “stereochemical” structure and a densely packed icosahedron in a bulk metallic glass Pd40Ni40P20. The coexistence of two atomic packing models can simultaneously satisfy the criteria for both the charge saturation of the metalloid element and the densest atomic packing of the metallic elements. The hybrid packing scheme uncovers the structural origins of the excellent glass forming ability of Pd40Ni40P20 and has important implications in understanding the bulk metallic glass formation of metal-metalloid alloys.

Guan, P. F.; Fujita, T.; Hirata, A.; Liu, Y. H.; Chen, M. W.

2012-04-01

317

Tangling Turbulence and Semi-Organized Structures in Convective Boundary Layers  

NASA Astrophysics Data System (ADS)

A new mean-field theory of turbulent convection is developed based on the idea that only the small-scale region of the spectrum is considered as turbulence, whereas its large-scale part, including both regular and semi-organized motions, is treated as the mean flow. In the shear-free regime, this theory predicts the convective wind instability, which causes the formation of large-scale semi-organized motions in the form of cells. In the presence of wind shear, the theory predicts another type of instability, which causes the formation of large-scale semi-organized structures in the form of rolls and the generation of convective-shear waves propagating perpendicular to the convective rolls. The spatial characteristics of these structures, such as the minimum size of the growing perturbations and the size of perturbations with the maximum growth rate, are determined. This theory might be useful for understanding the origin of large-scale cells and rolls observed in the convective boundary layer and laboratory turbulent convection

Elperin, T.; Kleeorin, N.; Rogachevskii, I.; Zilitinkevich, S. S.

2006-06-01

318

The coherent structure of turbulent mixing layers. I. Similarity of the primary vortex structure. II. Secondary streamwise vortex structure  

NASA Astrophysics Data System (ADS)

The primary spanwise organized vortex structure and the secondary streamwise vortex structure of turbulent mixing layers have been investigated. Flow visualization motion pictures of a constant density mixing layer were used to measure the properties of the large scale vortices. It was found that after an initial transition region mean properties of the large scale vortices reach the expected linear growth with downstream distance required by similarity. In the self-similar region, the vortex core area and visual thickness increase continuously during its life-span. A theoretical model of probability distribution function for the large-scale vortex circulation was developed. This distribution is found to be lognormal and to have a standard deviation, normalized with the mean of 0.28. From this model the mean life-span of the vortices could also be obtained and was found to be 0.67 times the mean life-span position. The streamwise streak pattern observed by Konrad (1976) and Breidenthal (1978) in plan-view pictures of the mixing layer was investigated, using flow visualization and spanwise concentration measurements. It was confirmed that this pattern is the result of a secondary vortex structure dominated by streamwise, counterrotating vortices. A detailed description of its spatial relation to the primary, spanwise vortex structure is presented. From time average flow pictures, the onset position and initial scale of the secondary structures were determined. From concentration measurements, spanwise variations in mean properties, resulting from the secondary structure, were found. This also showed an increase of the spanwise scale with downstream distance and the existence of the streamwise vortices in the fully developed turbulent region. In this region the mean spacing is found approximately equal to the vorticity thickness.

Bernal, Luis Paulino

319

The origin and evolution of tRNA inferred from phylogenetic analysis of structure.  

PubMed

The evolutionary history of the two structural and functional domains of tRNA is controversial but harbors the secrets of early translation and the genetic code. To explore the origin and evolution of tRNA, we reconstructed phylogenetic trees directly from molecular structure. Forty-two structural characters describing the geometry of 571 tRNAs and three statistical parameters describing thermodynamic and mechanical features of molecules quantitatively were used to derive phylogenetic trees of molecules and molecular substructures. Trees of molecules failed to group tRNA according to amino acid specificity and did not reveal the tripartite nature of life, probably due to loss of phylogenetic signal or because tRNA diversification predated organismal diversification. Trees of substructures derived from both structural and statistical characters support the origin of tRNA in the acceptor arm and the hypothesis that the top half domain composed of acceptor and pseudouridine (TPsiC) arms is more ancient than the bottom half domain composed of dihydrouridine (DHU) and anticodon arms. This constitutes the cornerstone of the genomic tag hypothesis that postulates tRNAs were ancient telomeres in the RNA world. The trees of substructures suggest a model for the evolution of the major functional and structural components of tRNA. In this model, short RNA hairpins with stems homologous to the acceptor arm of present day tRNAs were extended with regions homologous to TPsiC and anticodon arms. The DHU arm was then incorporated into the resulting three-stemmed structure to form a proto-cloverleaf structure. The variable region was the last structural addition to the molecular repertoire of evolving tRNA substructures. PMID:18058157

Sun, Feng-Jie; Caetano-Anollés, Gustavo

2008-01-01

320

Structure investigations of nonpolar GaN layers.  

PubMed

The microstructure of nonpolar m-plane (1100) oriented GaN layers deposited on (100)gamma-LiAlO(2) was analysed by transmission electron microscopy. This study shows that the films contain a large number of defects. The most dominant defects in the m-plane GaN are intrinsic I(1) basal plane stacking faults (approximately 10(4) cm(-1)), threading dislocations (approximately 10(9) cm(-2)) as well as a complex defect network consisting of planar defects located on prismatic {1010} GaN and differently inclined pyramidal planes. A large number of the stacking faults nucleate at the GaN/LiAlO(2) interface. Furthermore, the inclined planar defects act as additional nucleation sites for the basal plane stacking faults. A decreasing crystal quality with an increasing layer thickness can be explained by this defect formation mechanism. PMID:20500386

Neumann, W; Mogilatenko, A; Wernicke, T; Richter, E; Weyers, M; Kneissl, M

2010-03-01

321

Structure analysis of surface layer on passivated magnesium powders  

Microsoft Academic Search

The combustion-time of the passivated magnesium powders as desulfurizer was determined to be about 15.7 s, much higher than that of non-passivated magnesium powders. The surface layer of the passivated magnesium powders was studied by using SEM, XRD and AES. It is uniform and compact and no obvious holes or cracks have been found from the SEM micrographs. The result of

Junlin Huang; Jianfeng F. Wan; Chaoying Xie; Jinsong Chen; Chuanjiang Long

2007-01-01

322

Structure and Properties of Epoxy?Based Layered Silicate Nanocomposites  

Microsoft Academic Search

Epoxy?based layered silicate nanocomposites of various compositions were synthesized and their physical and water vapor diffusion properties studied. Mixtures of an epoxide monomer, diglycidyl ether of bisphenol A, with nonmodified sodium montmorillonite (NaMMT) or organophilically modified montmorillonites were prepared and cross?polarized optical microscopy, oscillatory shear rheological measurements, transmission electron microscopy (TEM), and X?ray diffraction (XRD) studies were used to assess

Darwin P. R. Kint; Gordon Seeley; Andrew N. Burgess

2005-01-01

323

Long-range effects in layered spin structures  

Microsoft Academic Search

We study theoretically layered spin systems where long-range dipolar interactions play a relevant role. By choosing a specific sample shape, we are able to reduce the complex Hamiltonian of the system to that of a much simpler coupled rotator model with short-range and mean-field interactions. This latter model has been studied in the past because of its interesting dynamical and

Alessandro Campa; Ramaz Khomeriki; David Mukamel; Stefano Ruffo

2007-01-01

324

Sliding Contact Fatigue Damage in Layered Ceramic Structures  

Microsoft Academic Search

Porcelain-veneered restorations often chip and fracture from repeated occlusal loading, making fatigue studies relevant. Most fatigue studies are limited to uni-axial loading without sliding motion. We hypothesized that bi-axial loading (contact-load-slide-liftoff, simulating a masticatory cycle), as compared with uni-axial loading, accelerates the fatigue of layered ceramics. Monolithic glass plates were epoxy-joined to polycarbonate substrates as a transparent model for an

J.-W. Kim; J.-H. Kim; V. P. Thompson; Y. Zhang

2007-01-01

325

Ultrasonic plate waves for fatigue crack detection in multi-layered metallic structures  

NASA Astrophysics Data System (ADS)

A representative area of concern for fatigue crack growth in aircraft occurs in multi-layered metallic structures. Ultrasonic plate waves are currently being investigated by multiple initiatives to detect these types of flaws with a minimal number of sensors to enable Structural Health Monitoring (SHM). Previous work has focused on structures with one or two layers, coupled with modeling of the wave propagation within these representative samples. However, it is common for multi-layered structures to have more than two layers in many areas of interest. Therefore, this study investigates ultrasonic wave propagation and flaw detection in a multi-layered sample consisting of 2 to 4 total layers with fatigue cracks located in only one layer. The samples contain fastener holes configured as would be expected to find on typical aircraft structure. The flaws in this study are represented by electric discharge machined (EDM) notches. Preliminary measurements show that EDM notches can be detected by the guided ultrasonic waves, but that the sensitivity to EDM notch location is dependent on the boundary conditions of each layer. The boundary conditions are changed by applying various loads on the surface of each layer by tightening and loosening the fasteners that hold the sample together. This variation depicts representative conditions found of aircraft. The experimental results are supplemented by modeling of the guided wave propagation within the structure using the Finite Element Method. The primary parameter studied in the modeling effort is the effect of the changes in the boundary condition on the mode and amplitude of the guided wave. The results of this investigation establish some guidelines for the use of guided waves in multi-layered structures, plus challenges that exist for their use in SHM applications and strategies to address these challenges.

Lindgren, Eric; Aldrin, John C.; Jata, Kumar; Scholes, Brett; Knopp, Jeremy

2007-05-01

326

On the origin of mixed-layered clay minerals from the San Andreas Fault at 2.5–3 km vertical depth (SAFOD drillhole at Parkfield, California)  

Microsoft Academic Search

A detailed mineralogical study is presented of the matrix of mudrocks sampled from spot coring at three key locations along\\u000a the San Andreas Fault Observatory at depth (SAFOD) drill hole. The characteristics of authigenic illite–smectite (I–S) and\\u000a chlorite–smectite (C–S) mixed-layer mineral clays indicate a deep diagenetic origin. A randomly ordered I–S mineral with ca.\\u000a 20–25% smectite layers is one of

A. M. Schleicher; L. N. Warr; B. A. van der Pluijm

2009-01-01

327

The effect of adhesive layers on the fracture of laminated structures  

NASA Technical Reports Server (NTRS)

The effect of the thickness and the elastic properties of the adhesive layers in laminated structures is considered. The structure is assumed to consist of two sets of periodically arranged dissimilar layers which may contain cracks perpendicular to the interfaces. The crack problem is solved under the assumption of plane strain or generalized plane stress and by using two different models for the adhesive layers. In the first model the adhesive layer is approximated by a combination of tensile and shear springs. In the second the adhesive layer is considered to be an elastic continuum, hence involving no approximating assumptions. The results regarding the stress intensity and stress concentration factors obtained from these two models and that found by ignoring the adhesive layers are presented and some comparisons are made.

Gecit, M. R.; Erdogan, F.

1978-01-01

328

Crystal structure, luminescence, and photoelectrochemistry of thin electroplated Cd-chalcogenide layers  

SciTech Connect

The relationship between crystal structure, photoluminescence spectrum and photoelectrochemical behavior of CdSe /SUB x/ Te /SUB 1-x/ alloy layers has been investigated. Layers having the hexagonal wurzite structure are strongly luminescent both in the red (at a photon energy corresponding to the direct bandgap of the alloy) and in the near infrared. Much weaker luminescence is shown by the layers with cubic zincblende structure. Annealing is responsible for recrystallization and cubic-to-hexagonal phase transformation (CdSe-rich alloys), being beneficial to the efficiency both of photoluminescence an of photoelectrochemical solar energy conversion.

Abramovich, M.; Brash, M.J.P.; Decker, F.; Moro, J.R.; Motisuke, P.; Muller-st., N.; Salvador, P.

1985-08-01

329

Deriving Lifetime Maps in the Time/Frequency Domain of Coherent Structures in the Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

The lifetimes of coherent structures are derived from data correlated over a 3 sensor array sampling streamwise sidewall pressure at high Reynolds number (> 10(exp 8)). The data were acquired at subsonic, transonic and supersonic speeds aboard a Tupolev Tu-144. The lifetimes are computed from a variant of the correlation length termed the lifelength. Characteristic lifelengths are estimated by fitting a Gaussian distribution to the sensors cross spectra and are shown to compare favorably with Efimtsov s prediction of correlation space scales. Lifelength distributions are computed in the time/frequency domain using an interval correlation technique on the continuous wavelet transform of the original time data. The median values of the lifelength distributions are found to be very close to the frequency averaged result. The interval correlation technique is shown to allow the retrieval and inspection of the original time data of each event in the lifelength distributions, thus providing a means to locate and study the nature of the coherent structure in the turbulent boundary layer. The lifelength data are converted to lifetimes using the convection velocity. The lifetime of events in the time/frequency domain are displayed in Lifetime Maps. The primary purpose of the paper is to validate these new analysis techniques so that they can be used with confidence to further characterize the behavior of coherent structures in the turbulent boundary layer.

Palumbo, Dan

2008-01-01

330

Origin and Impact of 3-D Structural Effects in the Radiative Signature of Vegetation  

NASA Astrophysics Data System (ADS)

Vegetation canopies are inherently 3-D, with various levels of clumping occuring at different scales: the within-crown, the tree, and the canopy level. As such their reflectance anisotropy in the optical domain is not accurately simulated by adopting a purely turbid medium representation. For example, the local reflection maximum in the retro-reflection direction - known as the 'hot spot' - is precisely due to the finite size of the scatterers in the canopy layer, as well as the spectral contrast with the underlying background. Structurally homogeneous canopy representations (i.e., plane-parallel vegetation layers containing uniformly distributed finite-sized scatterers with specified distributions of their orientation: 1-D') thus constitute the simplest canopy representation capable of matching multi-spectral space borne reflectance measurements under almost any view and illumination geometry. In actual situations where a hierarchy of scales related to vegetation clumpiness exists the structural information of a given surface target is exposed through multi-directional reflectance measurements. This presentation will address the aptitude of 1-D' canopy repesentations to match multi-angular and multi-spectral reflectance observations over 3-D target surfaces, for a variety of spatial resolutions and structural target characteristics. A variety of arguments will be presented as to the causes of the spatial resolution dependent divergences between the radiation fields of 1-D' and 3-D canopy representations, including: sensor footprint location, structural target characteristics, and horizontal photon migration.

Widlowski, J.; Pinty, B.; Gobron, N.; Verstraete, M. M.

2004-05-01

331

The adenovirus terminal protein influences binding of replication proteins and changes the origin structure.  

PubMed Central

The adenovirus terminal protein (TP) is covalently linked to the 5' ends of the adenovirus genome and enhances DNA replication in vitro by increasing template activity. To study the effect of TP in more detail we isolated short origin fragments containing functional TP using anion exchange chromatography. These fragments were highly active as templates for DNA replication in a reconstituted system. Employing band-shift assays we found that the affinity of the precursor terminal protein-DNA polymerase complex for the TP-containing origin was increased 2 to 3-fold. Binding affinities of two other replication stimulating proteins, NFI and Oct-1, were not influenced by the terminal protein. Upon DNaseI footprinting we observed, unexpectedly, that the breakdown pattern had changed at various positions in the origin, notably in the area 3-6 and 41-51 by the presence of TP. Some differences in the footprint pattern of NFI and Oct-1 were also found. Our results indicate that TP induces subtle changes in the origin structure that influence the interaction of other replication proteins. Images

Pronk, R; van der Vliet, P C

1993-01-01

332

Two-dimensional complete photonic gaps from layered periodic structures containing anisotropic left-handed metamaterials  

Microsoft Academic Search

We demonstrate that a two-dimensional complete photonic band-gap (PBG) can be realized in a layered periodic structure with a double-layer unit cell containing an anisotropic left-handed metamaterial layer. A set of criteria is derived for the geometric and material parameters to realize a two-dimensional complete PBG in such systems, and a detailed phase diagram is given. We discuss the underlying

Shulin Sun; Xueqin Huang; Lei Zhou

2007-01-01

333

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

334

Role of indenter material and size in veneer failure of brittle layer structures  

Microsoft Academic Search

The roles of indenter material and size in the failure of brittle veneer layers in all- ceramic crown-like structures are studied. Glass veneer layers 1 mm thick bonded to alumina layers 0.5 mm thick on polycarbonate bases (representative of porcelain\\/ceramic-core\\/dentin) are subject to cyclic contact loading with spherical indenters in water (representative of occlusal biting environment). Two indenter materials—glass and

Sanjit Bhowmick; Juan José Meléndez-Martínez; Ilja Hermann; Yu Zhang; Brian R. Lawn

2007-01-01

335

Layered structure of bacterial aggregates produced in an upflow anaerobic sludge bed and filter reactor  

SciTech Connect

The ultrastructure of bacterial granules that were maintained in an upflow anaerobic sludge bed and filter reactor was examined. The reactor was fed a sucrose medium, and it was operated at 35{degrees}C. Scanning and transmission electron microscopy revealed that the granular aggregates were three-layered structures. The exterior layer of the granule contained a very heterogeneous population that included rods, cocci, and filaments of various sizes. The middle layer consisted of a slightly less heterogeneous population than the exterior layer. A more ordered arrangement, made up predominantly of bacterial rods, was evident in this second layer. The third layer formed the internal core of the granules. It consisted of large numbers of Methanothrix-like cells. Large cavities, indicative of vigorous gas production, were evident in the third layer. On the basis of these ultrastructural results, a model that presents a possible explanation of granule development is offered.

MacLeod, F.A.; Guiot, S.R.; Costerton, J.W. (National Research Council of Canada, Montreal, Quebec (Canada))

1990-06-01

336

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures  

NASA Technical Reports Server (NTRS)

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are documented through flow visualization and hot wire measurements. The boundary layer manipulator was designed to manage the large scale structures of turbulence leading to a reduction in surface drag. The differences in the turbulent structure of the boundary layer are summarized to demonstrate differences in various flow properties. The manipulator inhibited the intermittent large scale structure of the turbulent boundary layer for at least 70 boundary layer thicknesses downstream. With the removal of the large scale, the streamwise turbulence intensity levels near the wall were reduced. The downstream distribution of the skin friction was also altered by the introduction of the manipulator.

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

1981-01-01

337

Layered manganites: magnetic structure at extreme doping levels.  

National Technical Information Service (NTIS)

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 prop...

J. F. Mitchell

1998-01-01

338

Defects and Impurities in 4H- and 6H-SiC Homoepitaxial Layers: Identification, Origin, Effect on Properties of Ohmic Contacts and Insulating Layers and Reduction.  

National Technical Information Service (NTIS)

The two most important materials related problems affecting the performance of all SiC devices and their associated components (e.g., contacts) are the defects and the undesired impurities which become incorporated in the homoepitaxial SiC layers in which...

R. F. Davis M. O. Aboelfotoh B. J. Baliga R. J. Nemanich

1995-01-01

339

Surface damping effect of anchored constrained viscoelastic layers on the flexural response of simply supported structures  

NASA Astrophysics Data System (ADS)

Viscoelastic (VE) materials are commonly used to control vibration-induced fatigue in airframes and to suppress general vibration in various structures. This study investigates the effects of anchored constrained VE layers on the flexural response of simply supported Euler beams or plate strips under base excitations. Emphasis is placed on the development of two surface damping treatments: one VE layer anchored at one end, and two VE layers anchored at their different ends. Each anchorage is realized with a thin stiff layer in tension, such as a fiber reinforced polymer sheet, bonded to the surface of a VE layer and anchored to one end of the beam for maximum shear deformation in the constrained VE layer. Non-uniform shear deformation in VE layers is taken into account in the new solution formulation. Sensitivity analyses are performed to understand and quantify the effects of various parameters on flexural responses of the structures. The minimum thickness of VE layers is mainly bounded by the relative stiffness between the VE layers and the constraining face layer. The performances of various configurations are compared and the two-end anchored configuration is found most effective in vibration suppression.

Karim, K. R.; Chen, G. D.

2012-02-01

340

On the origin and highly likely completeness of single-domain protein structures.  

PubMed

The size and origin of the protein fold universe is of fundamental and practical importance. Analyzing randomly generated, compact sticky homopolypeptide conformations constructed in generic simplified and all-atom protein models, all have similar folds in the library of solved structures, the Protein Data Bank, and conversely, all compact, single-domain protein structures in the Protein Data Bank have structural analogues in the compact model set. Thus, both sets are highly likely complete, with the protein fold universe arising from compact conformations of hydrogen-bonded, secondary structures. Because side chains are represented by their Cbeta atoms, these results also suggest that the observed protein folds are insensitive to the details of side-chain packing. Sequence specificity enters both in fine-tuning the structure and thermodynamically stabilizing a given fold with respect to the set of alternatives. Scanning the models against a three-dimensional active-site library, close geometric matches are frequently found. Thus, the presence of active-site-like geometries also seems to be a consequence of the packing of compact, secondary structural elements. These results have significant implications for the evolution of protein structure and function. PMID:16478803

Zhang, Yang; Hubner, Isaac A; Arakaki, Adrian K; Shakhnovich, Eugene; Skolnick, Jeffrey

2006-02-21

341

New states of surface waves in a linear layered structure  

NASA Astrophysics Data System (ADS)

The existence of hyperbolic surface waves in a linear carrier layer, which are associated with the presence of a superlattice and have an N-shaped spectrum, is demonstrated. It is further shown that, for each fixed frequency, there exist three independent modes with different propagation constants. The descending branches of this spectrum are characterized by a negative group velocity and are similar to the decay parts of the spectrum. Experimentally, a breakdown of the waveguide propagation mode should be expected in this frequency and wave vector range.

Bolshinskii, L. G.; Lomtev, A. I.

1987-01-01

342

On the period of the coherent structure in boundary layers at large Reynolds numbers  

NASA Technical Reports Server (NTRS)

The period of the large coherent structure in a subsonic, compressible, turbulent boundary layer was determined using the autocorrelation of the velocity and pressure fluctuations for Reynolds numbers between 5,000 and 35,000. In low Reynolds number flows the overall correlation period scaled with the outer variables - namely, the free stream velocity and the boundary layer thickness.

Narayanan, M. A. B.; Marvin, J. G.

1978-01-01

343

A model of the excitation of orderly structures in a shear layer  

NASA Technical Reports Server (NTRS)

The artificial excitation of shear layers is investigated theoretically and experimentally. The present paper describes quantitatively the coupling between exciting sound field and shear layer fluctuations. The mathematical model is restricted to low Strouhal numbers at which large scale structures are occurring. The theory does not contain any empirical constants and it is confirmed by the experiments in the expected validity range.

Bechert, D. W.

1984-01-01

344

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

345

Layer type tungsten dichalcogenide compounds: their preparation, structure, properties and uses  

Microsoft Academic Search

Tungsten dichalcogenides constitute a well defined family of compounds which crystallize in a layer type structure. These compounds find a wide range of applications in the field of catalysis and as a lubricant at high temperatures and pressures. They have also been investigated successfully as cathode and anode materials in photoelectrochemical cells for solar energy conversion. The layered tungsten dichalcogenides

S. K. Srivastava; B. N. Avasthi

1985-01-01

346

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

347

A structural framework for replication origin opening by AAA? initiation factors  

PubMed Central

ATP-dependent initiation factors help process replication origins and coordinate replisome assembly to control the onset of DNA synthesis. Although the specific properties and regulatory mechanisms of initiator proteins can vary greatly between different organisms, certain nucleotide-binding elements and assembly patterns appear preserved not only within the three domains of cellular life (bacteria, archaea, and eukaryotes), but also with certain classes of double-stranded DNA viruses. Structural studies of replication initiation proteins, both as higher-order oligomers and in complex with cognate DNA substrates, are revealing how an evolutionarily-related ATPase fold can support different modes of macromolecular assembly and function. Comparative studies between initiation systems in turn provide clues as to how duplex origin regions may be melted during initiation events.

Duderstadt, Karl E.; Berger, James M.

2012-01-01

348

Structural origins of Johari-Goldstein relaxation in a metallic glass.  

PubMed

Johari-Goldstein or ? relaxation, persisting down to glassy state from a supercooled liquid, is a universal phenomenon of glassy dynamics. Nevertheless, the underlying micromechanisms leading to the relaxation are still in debate despite great efforts devoted to this problem for decades. Here we report experimental evidence on the structural origins of Johari-Goldstein relaxation in an ultra-quenched metallic glass. The measured activation energy of the relaxation (~26 times of the product of gas constant and glass transition temperature) is consistent with the dynamic characteristics of Johari-Goldstein relaxation. Synchrotron X-ray investigations demonstrate that the relaxation originates from short-range collective rearrangements of large solvent atoms, which can be realized by local cooperative bonding switch. Our observations provide experimental insights into the atomic mechanisms of Johari-Goldstein relaxation and will be helpful in understanding the low-temperature dynamics and properties of metallic glasses. PMID:24488115

Liu, Y H; Fujita, T; Aji, D P B; Matsuura, M; Chen, M W

2014-01-01

349

General circulation model study on the green Sahara during the mid-Holocene: An impact of convection originating above boundary layer  

Microsoft Academic Search

The mechanism maintaining widespread vegetation over the Sahara, 6000 years before present (6kBP), is investigated with an atmospheric general circulation model (GCM) focusing on an impact of convection originating above the planetary boundary layer (PBL). The multiple cloud base Arakawa-Schubert scheme (MCB) is implemented in the GCM, and it is shown that MCB significantly strengthens the impact of vegetation over

M. Chikira; A. Abe-Ouchi; A. Sumi

2006-01-01

350

Local structure of the convective boundary layer measured by a volume-imaging radar  

Microsoft Academic Search

For over 30 years, radars have examined the structure of the convective boundary layer (CBL). Those studies have consisted either of the three dimensional structure of km-scale features, or of the vertical structure of local, 1 to 100 m-scale features. A new instrument, the Turbulent Eddy Profiler (TEP), images the local, three dimensional character of the CBL with the 10

Brian David Pollard

1998-01-01

351

First-principles based semi-classical model for transport in magnetic layered structures  

Microsoft Academic Search

We present a first principles based semiclassical model for transport in an inhomogeneous magnetic layered structure. The approach solves the Boltzmann transport equation using the band structure, Bloch wave velocities and scattering matrices, describing the reflection and transmission of Bloch waves from interfaces, derived from ab-initio local spin density electronic structure calculations. The model has been tested for thick Co

W. H. Butler; X.-G. Zhang; J. M. MacLaren

1998-01-01

352

Genetic Structure and Natal Origins of Immature Hawksbill Turtles (Eretmochelys imbricata) in Brazilian Waters  

PubMed Central

Understanding the connections between sea turtle populations is fundamental for their effective conservation. Brazil hosts important hawksbill feeding areas, but few studies have focused on how they connect with nesting populations in the Atlantic. Here, we (1) characterized mitochondrial DNA control region haplotypes of immature hawksbills feeding along the coast of Brazil (five areas ranging from equatorial to temperate latitudes, 157 skin samples), (2) analyzed genetic structure among Atlantic hawksbill feeding populations, and (3) inferred natal origins of hawksbills in Brazilian waters using genetic, oceanographic, and population size information. We report ten haplotypes for the sampled Brazilian sites, most of which were previously observed at other Atlantic feeding grounds and rookeries. Genetic profiles of Brazilian feeding areas were significantly different from those in other regions (Caribbean and Africa), and a significant structure was observed between Brazilian feeding grounds grouped into areas influenced by the South Equatorial/North Brazil Current and those influenced by the Brazil Current. Our genetic analysis estimates that the studied Brazilian feeding aggregations are mostly composed of animals originating from the domestic rookeries Bahia and Pipa, but some contributions from African and Caribbean rookeries were also observed. Oceanographic data corroborated the local origins, but showed higher connection with West Africa and none with the Caribbean. High correlation was observed between origins estimated through genetics/rookery size and oceanographic/rookery size data, demonstrating that ocean currents and population sizes influence haplotype distribution of Brazil's hawksbill populations. The information presented here highlights the importance of national conservation strategies and international cooperation for the recovery of endangered hawksbill turtle populations.

Proietti, Maira C.; Reisser, Julia; Marins, Luis Fernando; Rodriguez-Zarate, Clara; Marcovaldi, Maria A.; Monteiro, Danielle S.; Pattiaratchi, Charitha; Secchi, Eduardo R.

2014-01-01

353

Shear Induced Structures in Lamellar Systems ---From Layers to Onions to Onions and Layers---  

NASA Astrophysics Data System (ADS)

Shear flow induces the formation of multilamellar vesicles (MLV, also termed ``onions") in the lamellar phase of the nonionic surfactant C_{10}E_{3} in water. Depending on the applied shear rate, one can reach a state of polydisperse MLV (at intermediate shear rates) or densely packed monodisperse MLV at high shear rates. In this contribution we investigated the structure evolution when the shear rate is reduced by means of rheo-microscopy as well as rheo-small angle light and neutron scattering (SALS, SANS). Different shear quenches within the MLV structure region of 40 wt% C_{10}E_{3} reveal two different MLV size growth mechanisms: (i) a continuous and (ii) a discontinuous MLV size growth. In the later case, a part of the initial MLV structure transforms into planar lamellar domains leading to shear thinning. The lamellar domains perform a re-orientation process from parallel oriented lamellae into MLV in coexistence with the initial MLV structure. The pathway of the transformation of the parallel lamellae to MLV is the same as in start-up experiments, i.e. from a homeotropically aligned lamellar phase.

Koschoreck, S.; Fujii, S.; Richtering, W.

354

Anisotropic electrical properties in bismuth layer structured dielectrics with natural super lattice structure  

NASA Astrophysics Data System (ADS)

Dielectric property of epitaxial SrBi4Ti4O15 thin films with (001)-, (1110)-, (105)/(015)-, and (100)/(010)-orientations was investigated as a function of film thickness. As the tilting angle of c-axis from the surface normal is smaller, the relative dielectric constant begins to degrade at thinner thickness; eventually, the (001)-oriented films for which the c-axis is vertical to the substrate do not show noticeable degradation. The leakage current density also strongly depends of the tilting angle of the c-axis. The results indicate that the layer structure of SrBi4Ti4O15 exhibits a small size effect with high insulation performance.

Kojima, Takashi; Kimura, Junichi; Suzuki, Muneyasu; Takahashi, Kenji; Oikawa, Takahiro; Sakashita, Yukio; Kato, Kazumi; Watanabe, Takayuki; Takenaka, Tadashi; Yamada, Tomoaki; Funakubo, Hiroshi

2012-07-01

355

The Evolutionary Origin of Man Can Be Traced in the Layers of Defunct Ancestral Alpha Satellites Flanking the Active Centromeres of Human Chromosomes  

PubMed Central

Alpha satellite domains that currently function as centromeres of human chromosomes are flanked by layers of older alpha satellite, thought to contain dead centromeres of primate progenitors, which lost their function and the ability to homogenize satellite repeats, upon appearance of a new centromere. Using cladistic analysis of alpha satellite monomers, we elucidated complete layer patterns on chromosomes 8, 17, and X and related them to each other and to primate alpha satellites. We show that discrete and chronologically ordered alpha satellite layers are partially symmetrical around an active centromere and their succession is partially shared in non-homologous chromosomes. The layer structure forms a visual representation of the human evolutionary lineage with layers corresponding to ancestors of living primates and to entirely fossil taxa. Surprisingly, phylogenetic comparisons suggest that alpha satellite arrays went through periods of unusual hypermutability after they became “dead” centromeres. The layer structure supports a model of centromere evolution where new variants of a satellite repeat expanded periodically in the genome by rounds of inter-chromosomal transfer/amplification. Each wave of expansion covered all or many chromosomes and corresponded to a new primate taxon. Complete elucidation of the alpha satellite phylogenetic record would give a unique opportunity to number and locate the positions of major extinct taxa in relation to human ancestors shared with extant primates. If applicable to other satellites in non-primate taxa, analysis of centromeric layers could become an invaluable tool for phylogenetic studies.

Shepelev, Valery A.; Alexandrov, Alexander A.; Yurov, Yuri B.; Alexandrov, Ivan A.

2009-01-01

356

Addendum: Improvement in photoconductor film properties by changing dielectric layer structures Addendum: Improvement in photoconductor film properties by changing dielectric layer structures  

NASA Astrophysics Data System (ADS)

In recent times, digital X-ray detectors have been actively applied to the medical field; for example, digital radiography offers the potential of improved image quality and provides opportunities for advances in medical image management, computer-aided diagnosis and teleradiology. In this study, two candidate materials (HgI2 and PbI2) have been employed to study the influence of the dielectric structure on the performance of fabricated X-ray photoconducting films. Parylene C with high permittivity was deposited as a dielectric layer using a parylene deposition system (PDS 2060). The structural and morphological properties of the samples were evaluated field emission scanning electron microscopy and X-ray diffraction. Further, to investigate improvements in the electrical characteristics, a dark current in the dark room and sensitivity to X-ray exposure in the energy range of general radiography diagnosis were measured across the range of the operating voltage. The electric signals varied with the dielectric layer structure of the X-ray films. The PbI2 film with a bottom dielectric layer showed optimized electric properties. On the other hand, in the case of HgI2, the film with a top dielectric layer showed superior electric characteristics. Further, although the sensitivity of the film decreased, the total electrical efficiency of the film improved as a result of the decrease in dark current. When a dielectric layer is deposited on a photoconductor, the properties of the photoconductor, such as hole-electron mobility, should be considered to improve the image quality in digital medical imaging application. In this study, we have thus demonstrated that the use of dielectric layer structures improves the performance of photoconductors

Kim, S.; Oh, K.; Lee, Y.; Jung, J.; Cho, G.; Jang, G.; Cha, B.; Park, J.; Nam, S.

2011-02-01

357

Three-dimensional visualization of large structures in the turbulent boundary layer  

NASA Astrophysics Data System (ADS)

A new method of visualizing the coherent structures in the boundary layer is used to develop insight into how these structures form and to provide information on the relative frequency of typical shapes noticed in the near-wall flow. These results were achieved in a water channel using a recently developed tracer which remains as a moving dye streak while conforming to the convoluted motions in the boundary layer. The tracer is formulated from a surfactant-polymer-emulsion mixture which retains its capabilities as a marker of evolving flow motions in the boundary layer for a meter or more before eventually dispersing. Three-dimensional, continuous visualization of the structures can be obtained as they move along a flat plate. Photos and video frames demonstrate the evolution and properties of the most widely discussed boundary-layer structure, the Theodorsen (horseshoe) vortex.

Hoyt, J. W.; Sellin, R. H. J.

358

Impact Energy Absorbing Surface Layers for Protection of Composite Aircraft Structures.  

National Technical Information Service (NTIS)

In the framework of a European Defense Research Program the NLR investigated how the tolerance behavior of carbon/epoxy composite aircraft structures can be improved by application of impact energy absorbing surface layers. A promising concept of protecti...

W. G. J. Hart L. C. Ubels

1998-01-01

359

Shear-horizontal surface waves in a layered structure of piezoelectric ceramics.  

PubMed

A new existence condition for shear-horizontal (SH) surface waves in a layered structure of piezoelectric ceramics is give. The discussed SH surface wave is not a stiffened Love wave, but a new type surface wave. PMID:18263171

Hanhua, F; Xingjiao, L

1993-01-01

360

The effects of alloying material on regrowth-layer structure in silicon power devices  

Microsoft Academic Search

The effects on silicon regrowth-layer structure of pure aluminium are compared with those of aluminium-silicon alloy of eutectic composition when these are used as alloying material in joining silicon discs to metal contacts.

F. M. Roberts; E. L. G. Wilkinson

1971-01-01

361

Combined SnS@SnS2 double layers: charge transfer and electronic structure  

NASA Astrophysics Data System (ADS)

The present paper focuses on the interactions between single SnS and SnS2 monolayers and the properties of the combined SnS@SnS2 double-layer system. These materials occur as structural elements in inorganic nanotubes. We have employed density-functional theory-based methods to calculate structural, energetic, and electronic properties of these structures. Thereby, we have put emphasis on the difference between the two single layers and the double-layer system with special consideration of an occurring charge transfer from SnS2 to SnS. We will show that the interlayer interplay is beyond a simple non-bonding van-der-Waals interaction, which contrasts the properties of many other layered structures and makes combined SnS@SnS2 a unique material.

Lorenz, Tommy; Joswig, Jan-Ole; Seifert, Gotthard

2014-06-01

362

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

363

Structural Changes and Their Effects upon the Magnetic Properties of Ultrathin Iron Layers  

NASA Astrophysics Data System (ADS)

Ultrathin Fe/Si, Fe/Mo, Fe/V and Fe/Cr metallic multilayers have been prepared with a UHV sputtering system. The individual layer thickness is between 3 monolayers(ML) and 40 ML. Sputtered Si is amorphous while the lattice parameter mismatches between bulk crystalline constituents are 9%, 5% and 0.6% in Fe/Mo, Fe/V and Fe/Cr respectively. Standard reflection X-ray diffraction(XRD), transmission electron diffraction(TED) and limited EXAFS data were used for structural studies. Fe layers in Fe/Si are structurally isolated(non-coherent). For layer thickness of <=10A, amorphous Fe layers were observed in Fe/Si and these amorphous Fe layers were non-magnetic. Fe/Mo, Fe/V and Fe/Cr systems form coherent structures with a perpendicular coherence length of at about ~ 200A. Strained layer superlattices(SLS) have been directly observed in Fe/V and Fe/Mo for the first time using TED. The double BCC to single BCC transition in the layer planes occurred at bilayer thickness ~32ML in Fe/V and ~16ML in Fe/Mo. XRD data were consistent with TED data but suggested that the strain was uniaxial. The saturation magnetizations of Fe multilayers at thin layer thicknesses were closely related to the lattice mismatches. Fe/Mo lost its magnetism abruptly at a layer thickness between 3ML and 6ML while the reduction in Fe/V was gradual. Fe/Cr retained bulk-like magnetism over all the thickness range indicating little structural change in the Fe layers. Anomalously large saturation fields and magnetic anisotropy have been observed in Fe/Cr. The antiferromagnetic coupling between magnetic Fe layers, known to exist in Fe/Cr, is believed to be responsible for these large saturation fields and anisotropy.

Sung, Heekyung

364

Graphene oxide. Origin of acidity, its instability in water, and a new dynamic structural model.  

PubMed

The existing structural models of graphene oxide (GO) contradict each other and cannot adequately explain the acidity of its aqueous solutions. Inadequate understanding of chemical structure can lead to a misinterpretation of observed experimental phenomena. Understanding the chemistry and structure of GO should enable new functionalization protocols while explaining GO's limitations due to its water instability. Here we propose an unconventional view of GO chemistry and develop the corresponding "dynamic structural model" (DSM). In contrast to previously proposed models, the DSM considers GO as a system, constantly changing its chemical structure due to interaction with water. Using potentiometric titration, (13)C NMR, FTIR, UV-vis, X-ray photoelectron microscopy, thermogravimetric analysis, and scanning electron microscopy we show that GO does not contain any significant quantity of preexisting acidic functional groups, but gradually generates them through interaction with water. The reaction with water results in C-C bond cleavage, formation of vinylogous carboxylic acids, and the generation of protons. An electrical double layer formed at the GO interface in aqueous solutions plays an important role in the observed GO chemistry. Prolonged exposure to water gradually degrades GO flakes converting them into humic acid-like structures. The proposed DSM provides an explanation for the acidity of GO aqueous solutions and accounts for most of the known spectroscopic and experimental data. PMID:23215236

Dimiev, Ayrat M; Alemany, Lawrence B; Tour, James M

2013-01-22

365

Grain Oriented Perovskite Layer Structure Ceramics for High-Temperature Piezoelectric Applications  

Microsoft Academic Search

The perovskite layer structure (PLS) compounds have the general formula (A^{2+}) _2(B^{5+})_2 O_7, or (A^ {3+})_2(B^{4+ })_2O_7, and crystallize in a very anisotropic layered structure consisting of parallel slabs made up of perovskite units. Several of these compounds possess the highest Curie temperatures (T_{rm c} ) of any known ferroelectrics. Two examples are Sr_2Nb_2O _7 with T_{rm c} of 1342^circC,

Paul Anton Fuierer

1991-01-01

366

Ni(II) Sorption on Biogenic Mn-Oxides with Varying Mn Octahedral Layer Structure  

Microsoft Academic Search

Biogenic Mn-oxides (BioMnO), produced by microorganisms, possess an extraordinary ability to sequester metals. BioMnO are generally layered structures containing varying amounts of Mn(III) and vacant sites in the Mn layers. However the relationship between the varying structure of BioMnO and metal sorption properties remains unclear. In this study, BioMnO produced by Pseudomonas putida strain GB-1 was synthesized at either pH

Mengqiang Zhu; Matthew Ginder-Vogel; Donald L. Sparks

2010-01-01

367

Electronic structures of single- and multi-layer epitaxial graphene on SiC (0001)  

Microsoft Academic Search

The electronic structures of single- and multi-layered epitaxial graphene on silicon carbide (0001) surface are studied theoretically. To calculate energy bands of the systems, we construct the simple Hamiltonian with tight-binding approximations. We confirm that the present simple model do give identical electronic structure to the previous ab-initio study on the single layer case [1]. We extend the model up

Seungchul Kim; Jisoon Ihm; Young-Woo Son

2009-01-01

368

Effects of heat release on the large-scale structure in turbulent mixing layers  

NASA Technical Reports Server (NTRS)

The effects of chemical heat release on the large-scale structure in a chemically reacting turbulent mixing layer have been studied using three-dimensional time-dependent simulations. Moderate heat release is found to slow the development of the large-scale structures and to shift their wavelengths to larger scales. The results suggest that previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers may be the result of vorticity generation by baroclinic torques.

Mcmurtry, P. A.; Riley, J. J.; Metcalfe, R. W.

1989-01-01

369

Design maps for failure of all-ceramic layer structures in concentrated cyclic loading  

Microsoft Academic Search

A study is made of the competition between failure modes in ceramic-based bilayer structures joined to polymer-based substrates, in simulation of dental crown-like structures with a functional but weak “veneer” layer bonded onto a strong “core” layer. Cyclic contact fatigue tests are conducted in water on model flat systems consisting of glass plates joined to glass, sapphire, alumina or zirconia

Sanjit Bhowmick; Juan José Meléndez-Martínez; Yu Zhang; Brian R. Lawn

2007-01-01

370

Fabrication of multi-layered absorption structure for high quantum efficiency photon detectors  

SciTech Connect

We report on some efforts to improve a quantum efficiency of titanium-based optical superconducting transition edge sensors using the multi-layered absorption structure for maximizing photon absorption in the Ti layer. Using complex refractive index values of each film measured by a Spectroscopic Ellipsometry, we designed and optimized by a simulation code. An absorption measurement of fabricated structure was in good agreement with the design and was higher than 99% at optimized wavelength of 1550 nm.

Fujii, Go [National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8563 (Japan); Institute of Quantum Science, Nihon University, 1-8 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8303 (Japan); Fukuda, Daiji; Numata, Takayuki; Yoshizawa, Akio; Tsuchida, Hidemi; Fujino, Hidetoshi; Ishii, Hiroyuki; Itatani, Taro; Zama, Tatsuya [National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8563 (Japan); Inoue, Shuichiro [Institute of Quantum Science, Nihon University, 1-8 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8303 (Japan)

2009-12-16

371

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

PubMed

Here we report the bias-evolution of the electrical double layer structure of an ionic liquid on highly ordered pyrolytic graphite measured by atomic force microscopy. 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, which improves our understanding of the mechanism of charge storage on a molecular level. PMID:24215396

Black, Jennifer M; Walters, Deron; Labuda, Aleksander; Feng, Guang; Hillesheim, Patrick C; Dai, Sheng; Cummings, Peter T; Kalinin, Sergei V; Proksch, Roger; Balke, Nina

2013-12-11

372

Terahertz and infrared photodetection using p-i-n multiple-graphene-layer structures  

Microsoft Academic Search

We propose to utilize multiple-graphene-layer structures with lateral p-i-n junctions for terahertz and infrared (IR) photodetection and substantiate the operation of photodetectors based on these structures. Using the developed device model, we calculate the detector dc responsivity and detectivity as functions of the number of graphene layers and geometrical parameters and show that the dc responsivity and detectivity can be

V. Ryzhii; M. Ryzhii; V. Mitin; T. Otsuji

2010-01-01

373

Terahertz and Infrared Photodetection using p-i-n Multiple-Graphene-Layer Structures  

Microsoft Academic Search

We propose to utilize multiple-graphene-layer structures with lateral p-i-n\\u000ajunctions for terahertz (THz) and infrared (IR) photodetection and substantiate\\u000athe operation of photodetectors based on these structures. Using the developed\\u000adevice model, we calculate the detector dc responsivity and detectivity as\\u000afunctions of the number of graphene layers and geometrical parameters and show\\u000athat the dc responsivity and detectivity can

V. Ryzhiiand; M. Ryzhii; V. Mitin; T. Otsuji

2009-01-01

374

Endogenous and nonimpact origin of the Arkenu circular structures (al-Kufrah basin—SE Libya)  

NASA Astrophysics Data System (ADS)

The twin Arkenu circular structures (ACS), located in the al-Kufrah basin in southeastern Libya, were previously considered as double impact craters (the "Arkenu craters"). The ACS consist of a NE (Arkenu 1) and a SW structure (Arkenu 2), with approximate diameters of about 10 km. They are characterized by two shallow depressions surrounded by concentric circular ridges and silica-impregnated sedimentary dikes cut by local faults. Our field, petrographic, and textural observations exclude that the ACS have an impact origin. In fact, we did not observe any evidence of shock metamorphism, such as planar deformation features in the quartz grains of the collected samples, and the previously reported "shatter cones" are wind-erosion features in sandstones (ventifacts). Conversely, the ACS should be regarded as a "paired" intrusion of porphyritic stocks of syenitic composition that inject the Nubia Formation and form a rather simple and eroded ring dike complex. Stock emplacement was followed by hydrothermal activity that involved the deposition of massive magnetite-hematite horizons (typical of iron oxide copper-gold deposits). Their origin was nearly coeval with the development of silicified dikes in the surroundings. Plugs of tephritic-phonolitic rocks and lamprophyres (monchiquites) inject the Nubian sandstone along conjugate fracture zones, trending NNW-SSE and NE-SW, that crosscut the structural axis of the basin.

Cigolini, Corrado; di Martino, Mario; Laiolo, Marco; Coppola, Diego; Rossetti, Piergiorgio; Morelli, Marco

2012-11-01

375

Clonal population structure of Pseudomonas avellanae strains of different origin based on multilocus enzyme electrophoresis.  

PubMed

To assess the genetic diversity and genetic relationships of Pseudomonas avellanae, the causative agent of hazelnut decline, a total of 102 strains, obtained from central Italy (provinces of Viterbo and Rome) and northern Greece, were studied using multilocus enzyme electrophoresis (MLEE). Their allelic variation in 10 loci was determined. All loci were polymorphic and 53 electrophoretic types (ETs) were identified from the total sample. The mean genetic diversity (H) was 0.65 and this value ranged from 0.37 for the least polymorphic to 0.82 for the most polymorphic locus. The dendrogram originated from MLEE data indicated two main groups of ETs, A and B. The groups do not appear to be correlated to the geographic origin of the strains, although all the ETs from northern Greece clustered into subgroup B1. Pseudomonas syringae pv. actinidiae and P. syringae pv. theae, included in the analysis as outgroups, clustered apart. The index of association (I(A)) for P. avellanae was 0.90. The I(A) values were always significantly different from zero for the population subsets studied and no epidemic structure was found. These results would indicate that the population structure of P. avellanae is clonal either in northern Greece or in central Italy. The recent outbreaks of the bacterium in new areas of hazelnut cultivation would explain the current clonal structure that is persisting over decades. PMID:14523121

Scortichini, Marco; Natalini, Emanuela; Angelucci, Luca

2003-10-01

376

Fuselage Structure Response to Boundary Layer, Tonal Sound, and Jet Noise  

NASA Technical Reports Server (NTRS)

Experiments have been conducted to study the response of curved aluminum and graphite-epoxy fuselage structures to flow and sound loads from turbulent boundary layer, tonal sound, and jet noise. Both structures were the same size. The aluminum structure was reinforced with tear stoppers, while the graphite-epoxy structure was not. The graphite-epoxy structure weighed half as much as the aluminum structure. Spatiotemporal intermittence and chaotic behavior of the structural response was observed, as jet noise and tonal sound interacted with the turbulent boundary layer. The fundamental tone distributed energy to other components via wave interaction with the turbulent boundary layer. The added broadband sound from the jet, with or without a shock, influenced the responses over a wider range of frequencies. Instantaneous spatial correlation indicates small localized spatiotemporal regions of convected waves, while uncorrelated patterns dominate the larger portion of the space. By modifying the geometry of the tear stoppers between panels and frame, the transmitted and reflected waves of the aluminum panels were significantly reduced. The response level of the graphite-epoxy structure was higher, but the noise transmitted was nearly equal to that of the aluminum structure. The fundamental shock mode is between 80 deg and 150 deg and the first harmonic is between 20 deg and 80 deg for the underexpanded supersonic jet impinging on the turbulent boundary layer influencing the structural response. The response of the graphite-epoxy structure due to the fundamental mode of the shock impingement was stabilized by an externally fixed oscillator.

Maestrello, L.

2004-01-01

377

Paralogous Radiations of PIN Proteins with Multiple Origins of Noncanonical PIN Structure  

PubMed Central

The plant hormone auxin is a conserved regulator of development which has been implicated in the generation of morphological novelty. PIN-FORMED1 (PIN) auxin efflux carriers are central to auxin function by regulating its distribution. PIN family members have divergent structures and cellular localizations, but the origin and evolutionary significance of this variation is unresolved. To characterize PIN family evolution, we have undertaken phylogenetic and structural analyses with a massive increase in taxon sampling over previous studies. Our phylogeny shows that following the divergence of the bryophyte and lycophyte lineages, two deep duplication events gave rise to three distinct lineages of PIN proteins in euphyllophytes. Subsequent independent radiations within each of these lineages were taxonomically asymmetric, giving rise to at least 21 clades of PIN proteins, of which 15 are revealed here for the first time. Although most PIN protein clades share a conserved canonical structure with a modular central loop domain, a small number of noncanonical clades dispersed across the phylogeny have highly divergent protein structure. We propose that PIN proteins underwent sub- and neofunctionalization with substantial modification to protein structure throughout plant evolution. Our results have important implications for plant evolution as they suggest that structurally divergent PIN proteins that arose in paralogous radiations contributed to the convergent evolution of organ systems in different land plant lineages.

Bennett, Tom; Brockington, Samuel F.; Rothfels, Carl; Graham, Sean W.; Stevenson, Dennis; Kutchan, Toni; Rolf, Megan; Thomas, Philip; Wong, Gane Ka-Shu; Leyser, Ottoline; Glover, Beverley J.; Harrison, C. Jill

2014-01-01

378

Paralogous Radiations of PIN Proteins with Multiple Origins of Noncanonical PIN Structure.  

PubMed

The plant hormone auxin is a conserved regulator of development which has been implicated in the generation of morphological novelty. PIN-FORMED1 (PIN) auxin efflux carriers are central to auxin function by regulating its distribution. PIN family members have divergent structures and cellular localizations, but the origin and evolutionary significance of this variation is unresolved. To characterize PIN family evolution, we have undertaken phylogenetic and structural analyses with a massive increase in taxon sampling over previous studies. Our phylogeny shows that following the divergence of the bryophyte and lycophyte lineages, two deep duplication events gave rise to three distinct lineages of PIN proteins in euphyllophytes. Subsequent independent radiations within each of these lineages were taxonomically asymmetric, giving rise to at least 21 clades of PIN proteins, of which 15 are revealed here for the first time. Although most PIN protein clades share a conserved canonical structure with a modular central loop domain, a small number of noncanonical clades dispersed across the phylogeny have highly divergent protein structure. We propose that PIN proteins underwent sub- and neofunctionalization with substantial modification to protein structure throughout plant evolution. Our results have important implications for plant evolution as they suggest that structurally divergent PIN proteins that arose in paralogous radiations contributed to the convergent evolution of organ systems in different land plant lineages. PMID:24758777

Bennett, Tom; Brockington, Samuel F; Rothfels, Carl; Graham, Sean W; Stevenson, Dennis; Kutchan, Toni; Rolf, Megan; Thomas, Philip; Wong, Gane Ka-Shu; Leyser, Ottoline; Glover, Beverley J; Harrison, C Jill

2014-08-01

379

Simulating photonic structures in layered geometries by the Multiple Multipole Program  

NASA Astrophysics Data System (ADS)

Layered media Green's functions are introduced as an additional expansion set for the Multiple Multipole Program (MMP). By using these new expansions, the necessity of matching the boundary conditions along the infinite boundaries in the layered geometry is eliminated. As the result, OpenMaX, the open-source platform that includes the latest version of MMP, becomes more user friendly and robust when handling photonic structures in layered media. A description of both MMP and the layered media Green's functions, together with various numerical examples are introduced to demonstrate the efficiency of the method.

Alparslan, Aytac; Hafner, Christian

2011-05-01

380

A perspective on coherent structures and conceptual models for turbulent boundary layer physics  

NASA Technical Reports Server (NTRS)

Direct numerical simulations of turbulent boundary layers have been analyzed to develop a unified conceptual model for the kinematics of coherent motions in low Reynolds number canonical turbulent boundary layers. All classes of coherent motions are considered in the model, including low-speed streaks, ejections and sweeps, vortical structures, near-wall and outer-region shear layers, sublayer pockets, and large-scale outer-region eddies. The model reflects the conclusions from the study of the simulated boundary layer that vortical structures are directly associated with the production of turbulent shear stresses, entrainment, dissipation of turbulence kinetic energy, and the fluctuating pressure field. These results, when viewed from the perspective of the large body of published work on the subject of coherent motions, confirm that vortical structures may be considered the central dynamic element in the maintenance of turbulence in the canonical boundary layer. Vortical structures serve as a framework on which to construct a unified picture of boundary layer structure, providing a means to relate the many known structural elements in a consistent way.

Robinson, Stephen K.

1990-01-01

381

The structure of protostellar accretion disks and the origin of bipolar flows  

NASA Technical Reports Server (NTRS)

Equations are obtained which govern the disk-wind structure and identify the physical parameters relevant to circumstellar disks. The system of equations is analyzed in the thin-disk approximation, and it is shown that the system can be consistently reduced to a set of ordinary differential equations in z. Representative solutions are presented, and it is shown that the apparent paradox discussed by Shu (1991) is resolved when the finite thickness of the disk is taken into account. Implications of the results for the origin of bipolar flows in young stellar objects and possible application to active galactic nuclei are discussed.

Wardle, Mark; Koenigl, Arieh

1993-01-01

382

Structural Analysis of the Evolutionary Origins of Influenza Virus Hemagglutinin and Other Viral Lectins  

PubMed Central

Influenza virus and other viruses use host cell surface sugars as receptors. Here we show that the sugar-binding domains in influenza virus hemagglutinin and other viral lectins share the same structural fold as human galectins (host lectins). Unlike the easily accessible sugar-binding sites in human galectins, the sugar-binding sites in viral lectins are hidden in cavities. We propose that these viral lectins originated from host lectins but have evolved to use hidden sugar-binding sites to evade host immune attacks.

Chen, Lang

2013-01-01

383

Domain structure of the Acetogenium kivui surface layer revealed by electron crystallography and sequence analysis.  

PubMed Central

The three-dimensional structure of the Acetogenium kivui surface layer (S-layer) has been determined to a resolution of 1.7 nm by electron crystallographic techniques. Two independent reconstructions were made from layers negatively stained with uranyl acetate and Na-phosphotungstate. The S-layer has p6 symmetry with a center-to-center spacing of approximately 19 nm. Within the layer, six monomers combine to form a ring-shaped core surrounded by a fenestrated rim and six spokes that point towards the axis of threefold symmetry and provide lateral connectivity to other hexamers in the layer. The structure of the A. kivui S-layer protein is very similar to that of the Bacillus brevis middle wall protein, with which it shares an N-terminal domain of homology. This domain is found in several other extracellular proteins, including the S-layer proteins from Bacillus sphaericus and Thermus thermophilus, Omp alpha from Thermotoga maritima, an alkaline cellulase from Bacillus strain KSM-635, and xylanases from Clostridium thermocellum and Thermoanaerobacter saccharolyticum, and may serve to anchor these proteins to the peptidoglycan. To our knowledge, this is the first example of a domain conserved in several S-layer proteins. Images

Lupas, A; Engelhardt, H; Peters, J; Santarius, U; Volker, S; Baumeister, W

1994-01-01

384

Instantaneous wavenumber estimation for damage quantification in layered plate structures  

NASA Astrophysics Data System (ADS)

Guided wavefield detection is at the basis of a number of promising techniques for the identification and the characterization of damage in plate structures. Among the processing techniques proposed, the estimation of instantaneous and local wavenumbers can lead to effective metrics that quantify the extent of delaminations in composite plates. 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 approach for damage assessment in composites.

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

2014-03-01

385

The growth and electronic structure of azobenzene-based functional molecules on layered crystals  

NASA Astrophysics Data System (ADS)

In situ ultraviolet photoelectron spectroscopy is used to study the growth of ultrathin films of azobenzene-based functional molecules (azobenzene, Disperse Orange 3 and a triazatriangulenium platform with an attached functional azo-group) on the layered metal TiTe2 and on the layered semiconductor HfS2 at liquid nitrogen temperatures. Effects of intermolecular interactions, of the substrate electronic structure, and of the thermal energy of the sublimated molecules on the growth process and on the adsorbate electronic structure are identified and discussed. A weak adsorbate-substrate interaction is particularly observed for the layered semiconducting substrate, holding the promise of efficient molecular photoswitching.

Iwicki, J.; Ludwig, E.; Buck, J.; Kalläne, M.; Köhler, F.; Herges, R.; Kipp, L.; Rossnagel, K.

2012-10-01

386

Influence of bias electric field on elastic waves propagation in piezoelectric layered structures.  

PubMed

Theoretical and computer investigations of acoustic wave propagation in piezoelectric layered structures, subjected to the dc electric field influence have been fulfilled. Analysis of the dispersive parameters of elastic waves propagation in the BGO/fused silica and fused silica/LiNbO3 piezoelectric layered structures for a number of variants of dc electric field application has been executed. Transformation of bulk acoustic wave into SAW type mode under the dc electric field influence has been found. Possibility to control the permission or prohibition of the wave propagation by the dc electric field application and the appropriate choice of the layer and substrate materials has been discussed. PMID:23601967

Burkov, S I; Zolotova, O P; Sorokin, B P

2013-08-01

387

GMR enhancement in spin valves structures with nano-semiconducting layer  

Microsoft Academic Search

We report on the giant magnetoresistance enhancement in Co\\/Ru\\/Co-based spin valve structures with nano-semiconducting layer. The films were grown by ion beam sputtering on glass substrate at room temperature. The soft layer is composed of Fe\\/Co bilayers, while the hard layer is ensured by the Co\\/Ru\\/Co artificial antiferromagnetic subsystem (AAF) as follows: Fe5nm\\/Co0.5nm\\/Cu3nm\\/Co3nm\\/Ru0.5nm\\/Co3nm\\/Cu2nm\\/Cr2nm. This structure shows a giant magnetoresistance (GMR)

A. Dinia; M. Guth; S. Colis; G. Schmerber; C. Ulhacq; H. Errahmani; A. Berrada

2002-01-01

388

The growth and electronic structure of azobenzene-based functional molecules on layered crystals.  

PubMed

In situ ultraviolet photoelectron spectroscopy is used to study the growth of ultrathin films of azobenzene-based functional molecules (azobenzene, Disperse Orange 3 and a triazatriangulenium platform with an attached functional azo-group) on the layered metal TiTe(2) and on the layered semiconductor HfS(2) at liquid nitrogen temperatures. Effects of intermolecular interactions, of the substrate electronic structure, and of the thermal energy of the sublimated molecules on the growth process and on the adsorbate electronic structure are identified and discussed. A weak adsorbate-substrate interaction is particularly observed for the layered semiconducting substrate, holding the promise of efficient molecular photoswitching. PMID:22964419

Iwicki, J; Ludwig, E; Buck, J; Kalläne, M; Köhler, F; Herges, R; Kipp, L; Rossnagel, K

2012-10-01

389

Polarization-dependent plasmonic coupling in dual-layer metallic structures at terahertz frequencies.  

PubMed

Dual-layer metallic wire-hole structures were fabricated and their terahertz transmission properties were measured. They exhibit polarization-dependent transmittance with large extinction ratios. Simulation and experimental results on structures with different wire-to-hole orientations provide strong evidence that the resonance peaks are caused by plasmonic coupling between the two metallic layers. A simplified LC-circuit model is proposed to explain the coupling mechanism and to estimate the peak frequencies. Our results suggest that specific electromagnetic response can be achieved by appropriate design of the geometrical patterns on the two metallic layers and a suitable polarization of the incident wave. PMID:21369100

Zhang, Zhong Xiang; Chan, Kam Tai

2011-01-31

390

The multi-layered structure of Dps with a novel di-nuclear ferroxidase center.  

PubMed

The crystallization of cellular components represents a unique survival strategy for bacterial cells under stressed conditions. A highly ordered, layered structure is often formed in such a process, which may involve one or more than one type of bio-macromolecules. The main advantage of biocrystallization has been attributed to the fact that it is a physical process and thus is independent of energy consumption. Dps is a protein that crystallizes to form a multi-layered structure in starved cells in order to protect DNA against oxidative damage and other detrimental factors. The multi-layered crystal structure of a Dps protein from Bacillus brevis has been revealed for the first time at atomic resolution in the absence of DNA. Inspection of the structure provides the first direct evidence for the existence of a di-nuclear ferroxidase center, which possesses unique features among all the di-iron proteins identified so far. It constitutes the structural basis for the ferroxidase activity of Dps in the crystalline state as well as in solution. This finding proves that the enzymatic process of detoxification of metal ions, which may cause severe oxidative damage to DNA, is the other important aspect of the defense mechanism performed by Dps. In the multi-layered structure, Dps dodecamers are organized in a highly ordered manner. They adopt the classic form of hexagonal packing in each layer of the structure. Such arrangement results in reinforced structural features that would facilitate the attraction and absorption of metal ions from the environment. The highly ordered layered structure may provide an ideal basis for the accommodation of DNA between the layers so that it can be isolated and protected from harmful factors under stress conditions. PMID:12767829

Ren, Bin; Tibbelin, Gudrun; Kajino, Tsutomu; Asami, Osamu; Ladenstein, Rudolf

2003-06-01

391

Geographic population structure analysis of worldwide human populations infers their biogeographical origins.  

PubMed

The search for a method that utilizes biological information to predict humans' place of origin has occupied scientists for millennia. Over the past four decades, scientists have employed genetic data in an effort to achieve this goal but with limited success. While biogeographical algorithms using next-generation sequencing data have achieved an accuracy of 700 km in Europe, they were inaccurate elsewhere. Here we describe the Geographic Population Structure (GPS) algorithm and demonstrate its accuracy with three data sets using 40,000-130,000 SNPs. GPS placed 83% of worldwide individuals in their country of origin. Applied to over 200 Sardinians villagers, GPS placed a quarter of them in their villages and most of the rest within 50 km of their villages. GPS's accuracy and power to infer the biogeography of worldwide individuals down to their country or, in some cases, village, of origin, underscores the promise of admixture-based methods for biogeography and has ramifications for genetic ancestry testing. PMID:24781250

Elhaik, Eran; Tatarinova, Tatiana; Chebotarev, Dmitri; Piras, Ignazio S; Maria Calò, Carla; De Montis, Antonella; Atzori, Manuela; Marini, Monica; Tofanelli, Sergio; Francalacci, Paolo; Pagani, Luca; Tyler-Smith, Chris; Xue, Yali; Cucca, Francesco; Schurr, Theodore G; Gaieski, Jill B; Melendez, Carlalynne; Vilar, Miguel G; Owings, Amanda C; Gómez, Rocío; Fujita, Ricardo; Santos, Fabrício R; Comas, David; Balanovsky, Oleg; Balanovska, Elena; Zalloua, Pierre; Soodyall, Himla; Pitchappan, Ramasamy; Ganeshprasad, Arunkumar; Hammer, Michael; Matisoo-Smith, Lisa; Wells, R Spencer

2014-01-01

392

Geographic population structure analysis of worldwide human populations infers their biogeographical origins  

PubMed Central

The search for a method that utilizes biological information to predict humans’ place of origin has occupied scientists for millennia. Over the past four decades, scientists have employed genetic data in an effort to achieve this goal but with limited success. While biogeographical algorithms using next-generation sequencing data have achieved an accuracy of 700?km in Europe, they were inaccurate elsewhere. Here we describe the Geographic Population Structure (GPS) algorithm and demonstrate its accuracy with three data sets using 40,000–130,000 SNPs. GPS placed 83% of worldwide individuals in their country of origin. Applied to over 200 Sardinians villagers, GPS placed a quarter of them in their villages and most of the rest within 50?km of their villages. GPS’s accuracy and power to infer the biogeography of worldwide individuals down to their country or, in some cases, village, of origin, underscores the promise of admixture-based methods for biogeography and has ramifications for genetic ancestry testing.

Elhaik, Eran; Tatarinova, Tatiana; Chebotarev, Dmitri; Piras, Ignazio S.; Maria Calo, Carla; De Montis, Antonella; Atzori, Manuela; Marini, Monica; Tofanelli, Sergio; Francalacci, Paolo; Pagani, Luca; Tyler-Smith, Chris; Xue, Yali; Cucca, Francesco; Schurr, Theodore G.; Gaieski, Jill B.; Melendez, Carlalynne; Vilar, Miguel G.; Owings, Amanda C.; Gomez, Rocio; Fujita, Ricardo; Santos, Fabricio R.; Comas, David; Balanovsky, Oleg; Balanovska, Elena; Zalloua, Pierre; Soodyall, Himla; Pitchappan, Ramasamy; GaneshPrasad, ArunKumar; Hammer, Michael; Matisoo-Smith, Lisa; Wells, R. Spencer; Acosta, Oscar; Adhikarla, Syama; Adler, Christina J.; Bertranpetit, Jaume; Clarke, Andrew C.; Cooper, Alan; Der Sarkissian, Clio S. I.; Haak, Wolfgang; Haber, Marc; Jin, Li; Kaplan, Matthew E.; Li, Hui; Li, Shilin; Martínez-Cruz, Begoña; Merchant, Nirav C.; Mitchell, John R.; Parida, Laxmi; Platt, Daniel E.; Quintana-Murci, Lluis; Renfrew, Colin; Lacerda, Daniela R.; Royyuru, Ajay K.; Sandoval, Jose Raul; Santhakumari, Arun Varatharajan; Soria Hernanz, David F.; Swamikrishnan, Pandikumar; Ziegle, Janet S.

2014-01-01

393

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

394

Origin of the energy level alignment at organic/organic interfaces: The role of structural defects  

NASA Astrophysics Data System (ADS)

In this paper, the electronic properties of as-deposited and N2-exposedCuPc/F16CuPc interface, a prototype system for organic photovoltaic applications, are investigated by using ultralow background, high-sensitivity photoemission spectroscopy. It is found that (i) N2 exposure significantly modifies the energy level alignment (ELA) at the interface between CuPc and F16CuPc layer and (ii) the direction of the N2-induced energy level shift of the CuPc depends on the position of the Fermi level (EF) in the CuPc highest occupied molecular orbital-lowest unoccupied molecular orbital gap of the as-deposited film. These observations are related to the changes in the density of gap states (DOGS) produced by structural imperfections in the molecular packing geometry, as introduced by the N2 penetration into the CuPc layer. This result demonstrates the key role of structure-induced DOGS in controlling the ELA at organic/organic interfaces.

Bussolotti, Fabio; Yang, Jinpeng; Hinderhofer, Alexander; Huang, Yuli; Chen, Wei; Kera, Satoshi; Wee, Andrew T. S.; Ueno, Nobuo

2014-03-01

395

A review of quasi-coherent structures in a numerically simulated turbulent boundary layer  

NASA Technical Reports Server (NTRS)

Preliminary results of a comprehensive study of the structural aspects of a numerically simulated number turbulent boundary layer are presented. A direct Navier-Stokes simulation of a flat-plate, zero pressure gradient boundary layer at Re0 = 670 was used. Most of the known nonrandom, coherent features of turbulent boundary layers are confirmed in the simulation, and several new aspects of their spatial character are reported. The spatial relationships between many of the various structures are described, forming the basis for a more complete kinematical picture of boundary layer physics than has been previously known. In particular, the importance of vortex structures of various forms to the generation of Reynolds shear stress is investigated.

Robinson, S. K.; Kline, S. J.; Spalart, P. R.

1989-01-01

396

Unequal density effect on static structure factor of coupled electron layers  

NASA Astrophysics Data System (ADS)

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, Sll(q) and S12(q), over a wide range of density parameter rsl and interlayer spacing d. In our present study, the sharp peak in S22(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.; Nayak, Mukesh G.

2014-04-01

397

Sliding contact fatigue damage in layered ceramic structures.  

PubMed

Porcelain-veneered restorations often chip and fracture from repeated occlusal loading, making fatigue studies relevant. Most fatigue studies are limited to uni-axial loading without sliding motion. We hypothesized that bi-axial loading (contact-load-slide-liftoff, simulating a masticatory cycle), as compared with uni-axial loading, accelerates the fatigue of layered ceramics. Monolithic glass plates were epoxy-joined to polycarbonate substrates as a transparent model for an all-ceramic crown on dentin. Uni-and bi-axial cyclic contact was applied through a hard sphere in water, by means of a mouth-motion simulator apparatus. The uni-axial (contact-load-hold-liftoff) and traditional R-ratio fatigue (indenter never leaves the specimen surface) produced similar lifespans, while bi-axial fatigue was more severe. The accelerated crack growth rate in bi-axial fatigue is attributed to enhanced tensile stresses at the trailing edges of a moving indenter. Fracture mechanics descriptions for damage evolution in brittle materials loaded repeatedly with a sliding sphere are provided. Clinical relevance is addressed. PMID:17959894

Kim, J-W; Kim, J-H; Thompson, V P; Zhang, Y

2007-11-01

398

Unattended automatic monitoring of boundary layer structures with cost effective lidar ceilometers  

NASA Astrophysics Data System (ADS)

The vertical temperature and moisture distribution affect the layering of the atmospheric boundary layer and the existence of inversions within this layer or on the top of it. These layers have a strong influence on the development of episodes of high concentrations of air pollutants which might be harmful to people and ecosystems. The height of the mixing layer is defined as the height up to which due to the thermal structure of the boundary layer vertical dispersion by turbulent mixing of air pollutants takes place. Most of the aerosol particles in an atmospheric column are usually confined to atmospheric layers below this height, the knowledge on the mixing layer height can thus be employed to convert column-mean optical depths measured from satellites into near-surface air quality information. Eye-safe lidar ceilometers are reliable tools for unattended boundary layer structure monitoring around the clock up to heights exceeding 2500 m. Comparison to temperature, humidity, and wind profiles reported by RASS, sodar, radio soundings, and weather mast in-situ sensors has confirmed their ability to detect convective or residual layers. In addition, ceilometers with a single lens optical design enable precise assessment of inversion layers and nocturnal stable layers below 200 m. This design has been chosen for the Vaisala Ceilometer CL31, the standard cloud height indicator for the Automated Surface Observing System of the US National Weather Service (NWS). During a two years evaluation period, the NWS permanently collected backscatter profiles from at least three ceilometers at its test site in Sterling, VA. Based on these and on data from units running at the Vaisala test sites in Vantaa, Finland, and Hamburg, Germany, an automatic algorithm for online retrieval of aerosol layer heights within the boundary layer has been developed that covers not only ideal boundary layer diurnal evolution, but all situations involving clouds, fog, and precipitation. This algorithm is part of the Vaisala boundary layer reporting and analysis tool BL-VIEW. The algorithm is based on the gradient method looking for gradient minima of the backscatter intensity to mark upper edges of aerosol layers. Main additional features of the novel automatic algorithm are a cloud, fog and precipitation filter designed to avoid false hits, a noise and range dependant averaging scheme, and a variable detection threshold. Examples covering a variety of meteorological situations in all seasons will be presented that demonstrate the quality of the algorithm and its application in the field of air quality forecasting.

Münkel, Christoph; Roininen, Reijo

2010-05-01

399

Quantum processes of propagation of electron waves in layered structures  

Microsoft Academic Search

The interaction of electron waves with (001) heteroboundaries in GaAs\\/AlAs systems is considered using the scattering matrix and pseudopotential methods. The different transmision channels of electrons through one boundary and a two-barrier structure are analyzed. It is shown that the matching matrix contains a 3×3 block of strongly interacting Gamma1, X1, and X3 states. Hence a three-trough model is proposed

G. F. Karavaev; S. N. Grinyaev; V. N. Chernyshov

1992-01-01

400

Quantum processes of propagation of electron waves in layered structures  

Microsoft Academic Search

The interaction of electron waves with (001) heteroboundaries in GaAs\\/AlAs systems is considered using the scattering matrix and pseudopotential methods. The different transmision channels of electrons through one boundary and a two-barrier structure are analyzed. It is shown that the matching matrix contains a 3×3 block of strongly interacting G1, X1, and X3 states. Hence a three-trough model is proposed

G. F. Karavaev; S. N. Grinyaev; V. N. Chernyshov

1992-01-01

401

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

402

Origin of Different Dependences of Open-Circuit Voltage on the Electrodes in Layered and Bulk Heterojunction Organic Photovoltaic Cells  

Microsoft Academic Search

Experimental results show that the V OC of layered heterojunction (HJ) organic photovoltaic (PV) cells behaves with a very weak dependence on the electrodes. However, the V OC of bulk HJ PV cells behaves with a strong dependence on the electrodes. In this paper, an explanation for the different behaviors of V OC on the electrodes is proposed. It is

Chunfu Zha