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1

Origin of the polygons and underground structures in Southern layered deposits and Utopia Planitia on Mars  

NASA Astrophysics Data System (ADS)

Patterned ground is a common feature in the cold and/or arid regions of Earth, but similar features are also found on Mars. Polygons on the Martian surface have been classified into three different size classes: big (giant polygons, 1-20 km diameter), middle size (100-200 m diameter) and small size (5-20 m diameter). Many of small-scale polygons on the southern layered deposits near the South Pole possibly originated through thermal contraction as predicted by image analysis and statistical analysis, but many of the middle and small size polygons from Utopia Planitia may not be caused by thermal contraction. Polygons from southern layered deposits display characteristic shape factors, such as form factor, roundness, and aspect ratio, which are very similar to terrestrial frost polygons. Nearest-neighbor analyses of polygonal network distributions also yield comparable results with terrestrial polygonal networks. However, one significant difference is the spacing of the cracks, which is on the order of 5 - 10 times bigger than those on Earth. Polygon size provides some hints on the surface materials of the southern layered deposits. The polygonal patterns in Utopia Planitia have frequently been associated with collapsed features such as ancient subsurface channels (the width of the underground channel is estimated to be approximately 400-500 m) or a talik (unfrozen layer in the permafrost). These features also display linear structure, associated with lower surface albedo. The area of lower albedo has a higher density of polygonal patterns. These patterns potentially suggest that 1) the polygonal pattern is caused primarily by ground heaving and collapsing, 2) darker albedo materials had higher tensile strength and 3) liquid water or melt water (from ice rich materials) was running through the talik or near surface channel.

Yoshikawa, K.; Laderach, S.; Hinzman, L.

2001-12-01

2

Origins of Igneous Layering  

Microsoft Academic Search

Anyone who has ever seen a photo of a layered intrusion, let alone visited one first hand, or even seen a thin section from one, cannot help but be impressed by the stunning record of crystal growth and deposition. Such bodies stand as majestic monuments of undeniable evidence that intricate magmatic processes exist, processes that couple crystallization, convection, and crystal

Bruce Marsh

1988-01-01

3

Origins of Igneous Layering  

NASA Astrophysics Data System (ADS)

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

Marsh, Bruce

4

Origin of the polygons and underground structures in Southern layered deposits and Utopia Planitia on Mars  

Microsoft Academic Search

Patterned ground is a common feature in the cold and\\/or arid regions of Earth, but similar features are also found on Mars. Polygons on the Martian surface have been classified into three different size classes: big (giant polygons, 1-20 km diameter), middle size (100-200 m diameter) and small size (5-20 m diameter). Many of small-scale polygons on the southern layered

K. Yoshikawa; S. Laderach; L. Hinzman

2001-01-01

5

Origins and implications of soil layering  

NASA Astrophysics Data System (ADS)

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

Phillips, Jonathan D.; Lorz, Carsten

2008-08-01

6

Origin and evolution of asthenospheric layers  

NASA Astrophysics Data System (ADS)

The lithosphere is underlain by the asthenosphere. Traditionally, the boundary between the lithosphere and the asthenosphere (LAB) is defined by a difference in response to stress: the lithosphere remains elastic or brittle, while the asthenosphere deforms viscously and accommodates strain through plastic deformation. The reology of rocks depends on many factors: temperature, pressure, chemical composition, size of grains, etc. However, the basic differences of lithosphere and asthenosphere properties could be explained as a result of the temperature and pressure. The effective viscosity of mantle is proportional to C exp(A q), where q is the ratio (melting temperature/temperature), C and A are positive constants. The mantle is not molten, so q>1. If the temperature is close to the melting temperature then q is close to 1 and effective viscosity is low (e.g. 1018 Pa s). This situation is observed in asthenosphere. The lithosphere is a thermal boundary layer for the convection in the mantle. The temperature of the upper part is low (q is high) but the temperature gradient in the lithosphere is high and temperature is increasing fast. In the mantle below the lithosphere, the temperature gradient is low (could be close to the adiabatic one). The melting temperature is increasing with depth faster than true temperature. Hence, q and the viscosity reach minimum value just below LAB and are increasing with depth in the mantle below. It is a typical situation. The tectonic processes in subduction zones could change this picture. The one lithospheric plate could be placed in the mantle below another plate. Distribution q in such a case could have two minima, so two asthenospheric layers could be formed. Another important factor determining rheological properties is a stress tensor T. Generally viscosity is proportional to the power of the invariant of the stress tensor: I(T)^(1-n). For n=1 the viscosity does not depend on stress (i.e. Newtonian rheology), for true mantle n is probably in the range from 3 to 5. We investigate the processes of formation and evolution of low viscosity layers ("asthenospheric layers") in the upper mantle. The time scale of the temperature changes is of the order of 10 Myr. The characteristic time of stress changes could be much shorter depending on tectonic processes. Eventually processes of formation and vanishing of low viscosity layers is very dynamical. In a relatively short time (below 1 Myr) the pattern the viscosity distribution and velocity gradient could change substantially. Using results from deep seismic sounding and surface wave tomography we have found that below some regions there are structures in the mantle that could be a forming/vanishing low viscosity layers. Reflectors in the lower lithosphere are observed beneath Trans-European suture zone between Precambrian and Palaeozoic platforms. In a thick Baltic shield lithosphere (200 km or more) low velocity zones and seismic reflectors are observed in the depth range 60-100 km, which could be interpreted as mechanical low Vp velocity zones, in contrast to thermal velocity zone in deeper asthenosphere.

Czechowski, Leszek; Grad, Marek

2013-04-01

7

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

8

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

SciTech Connect

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

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

2011-08-04

9

Hydrothermal origin of mafic layers in alpine-type peridotites: Evidence from the seiad ultramafic complex, California, USA  

Microsoft Academic Search

Thin layers with simple mineralogical composition are found in alpine-type peridotite, zoned Alaskan intrusions, and basic layered intrusions. The following features suggest that an origin by hydrothermal processes should be considered for many of these layers: absence of cumulate structures, continuity of very thin layers, monominerallic banding, variety of juxtaposed layer compositions, and cross-cutting relationships that indicate a long history

Timothy P. Loomis; Richard R. Gottschalk

1981-01-01

10

Molecular origins of friction. The force on adsorbed layers  

NASA Astrophysics Data System (ADS)

Simulations and perturbation theory are used to study the molecular origins of an ideal model system, a layer of adsorbed molecules sliding over a substrate. These calculations reproduce several surprising features of experimental results. In most cases, the frictional force on a solid monolayer has a different form from that observed between macroscopic solids. No threshold force or static friction is needed to initiate sliding; instead, the velocity is proportional to the force. As in experiments, incommensurate solid layers actually slide more readily than fluid layers. A comparison of experiment, simulation, and analytic results shows that dissipation arises from anharmonic coupling between phonon modes and substrate-induced deformations in the adsorbate.

Cieplak, Marek; Smith, Elizabeth D.; Robbins, Mark O.

1994-08-01

11

Structural Origins of Silk Piezoelectricity  

PubMed Central

Uniaxially oriented, piezoelectric silk films were prepared by a two-step method that involved: (1) air drying aqueous, regenerated silk fibroin solutions into films, and (2) drawing the silk films to a desired draw ratio. The utility of two different drawing techniques, zone drawing and water immersion drawing were investigated for processing the silk for piezoelectric studies. Silk films zone drawn to a ratio of ?= 2.7 displayed relatively high dynamic shear piezoelectric coefficients of d14 = ?1.5 pC/N, corresponding to over two orders of magnitude increase in d14 due to film drawing. A strong correlation was observed between the increase in the silk II, ?-sheet content with increasing draw ratio measured by FTIR spectroscopy (C?? e2.5 ?), the concomitant increasing degree of orientation of ?-sheet crystals detected via WAXD (FWHM = 0.22° for ?= 2.7), and the improvement in silk piezoelectricity (d14? e2.4 ?). Water immersion drawing led to a predominantly silk I structure with a low degree of orientation (FWHM = 75°) and a much weaker piezoelectric response compared to zone drawing. Similarly, increasing the ?-sheet crystallinity without inducing crystal alignment, e.g. by methanol treatment, did not result in a significant enhancement of silk piezoelectricity. Overall, a combination of a high degree of silk II, ?-sheet crystallinity and crystalline orientation are prerequisites for a strong piezoelectric effect in silk. Further understanding of the structural origins of silk piezoelectricity will provide important options for future biotechnological and biomedical applications of this protein.

Yucel, Tuna; Cebe, Peggy

2012-01-01

12

Structural Origins of Silk Piezoelectricity.  

PubMed

Uniaxially oriented, piezoelectric silk films were prepared by a two-step method that involved: (1) air drying aqueous, regenerated silk fibroin solutions into films, and (2) drawing the silk films to a desired draw ratio. The utility of two different drawing techniques, zone drawing and water immersion drawing were investigated for processing the silk for piezoelectric studies. Silk films zone drawn to a ratio of ?= 2.7 displayed relatively high dynamic shear piezoelectric coefficients of d(14) = -1.5 pC/N, corresponding to over two orders of magnitude increase in d(14) due to film drawing. A strong correlation was observed between the increase in the silk II, ?-sheet content with increasing draw ratio measured by FTIR spectroscopy (C(?)? e(2.5) (?)), the concomitant increasing degree of orientation of ?-sheet crystals detected via WAXD (FWHM = 0.22° for ?= 2.7), and the improvement in silk piezoelectricity (d(14)? e(2.4) (?)). Water immersion drawing led to a predominantly silk I structure with a low degree of orientation (FWHM = 75°) and a much weaker piezoelectric response compared to zone drawing. Similarly, increasing the ?-sheet crystallinity without inducing crystal alignment, e.g. by methanol treatment, did not result in a significant enhancement of silk piezoelectricity. Overall, a combination of a high degree of silk II, ?-sheet crystallinity and crystalline orientation are prerequisites for a strong piezoelectric effect in silk. Further understanding of the structural origins of silk piezoelectricity will provide important options for future biotechnological and biomedical applications of this protein. PMID:23335872

Yucel, Tuna; Cebe, Peggy; Kaplan, David L

2011-01-13

13

Layered tektites - A multiple impact origin for the Australasian tektites  

NASA Astrophysics Data System (ADS)

The mechanisms proposed for the origin of tektites from the Australasian field are examined using neutron activation data for twenty layered tektites and six splash tektites of known and widely separated sites of a field greater than 1140 km in length. Evidence is presented indicating that the layered tektites formed as sheets or pools of melt. It is argued that their distribution across a field greater than 1140 km in length is inconsistent with their formation in a single crater, and that many impact craters are required to account for their distribution across such a large field.

Wasson, J. T.

1991-02-01

14

Analysis of arbitrary conducting periodic structures embedded in layered media  

Microsoft Academic Search

An analysis of arbitrary periodic conducting structures embedded in layered media has been performed using triangular patch basis functions and the mixed potential formulation implemented in the original PATCH code. Greens functions in layered media were used to develop closed-form expressions for the modified scalar and vector potentials due to an infinite array of arbitrarily oriented triangular patch basis functions

D. R. Wilton; N. W. Montgomery

1991-01-01

15

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

16

Magnetoplasmons in layered graphene structures  

Microsoft Academic Search

We calculate the dispersion equations for magnetoplasmons in a single layer, a pair of parallel layers, a graphite bilayer, and a superlattice of graphene layers in a perpendicular magnetic field. We demonstrate the feasibility of a drift-induced instability of magnetoplasmons. The magnetoplasmon instability in a superlattice is enhanced compared to a single graphene layer. The energies of the unstable magnetoplasmons

Oleg L. Berman; Godfrey Gumbs; Yurii E. Lozovik

2008-01-01

17

The origins of structural operational semantics  

Microsoft Academic Search

We review the origins of structural operational semantics. The main publication `A Structural Approach to Operational Semantics,' also known as the `Aarhus Notes,' appeared in 1981 [G.D. Plotkin, A structural approach to operational semantics, DAIMI FN-19, Computer Science Department, Aarhus University, 1981]. The development of the ideas dates back to the early 1970s, involving many people and building on previous

Gordon D. Plotkin

2004-01-01

18

Simulation of Sintering of Layered Structures.  

National Technical Information Service (NTIS)

An integrated approach, combining the continuum theory of sintering and Potts model based mesostructure evolution analysis, is used to solve the problem of bi-layered structure sintering. Two types of bi-layered structures are considered: layers of the sa...

Olevsky Tikare Garino Braginsky

2000-01-01

19

Magnetoplasmons in layered graphene structures  

Microsoft Academic Search

We calculate the dispersion equations for magnetoplasmons in a single layer,\\u000aa pair of parallel layers, a graphite bilayer and a superlattice of graphene\\u000alayers in a perpendicular magnetic field. We demonstrate the feasibility of a\\u000adrift-induced instability of magnetoplasmons. The magnetoplasmon instability in\\u000aa superlattice is enhanced compared to a single graphene layer. The energies of\\u000athe unstable magnetoplasmons

Oleg L. Berman; Godfrey Gumbs; Yurii E. Lozovik

2008-01-01

20

Simulation of Sintering of Layered Structures  

SciTech Connect

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

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

2000-11-22

21

The origin of large scale cosmic structure  

NASA Astrophysics Data System (ADS)

Problems and research on the origin of large-scale cosmic structure are discussed. The evolution of density perturbations is addressed, including the nonlinear regime and the relevant studies by Lifschitz (1946) and Bonnor (1974). The significance of the physics of the very early universe to these problems is taken into account. The clustering hierarchy of Gott and Rees (1975) is examined, and the statistics of random density fluctuations that led to galaxies and clusters of galaxies are briefly addressed. The spectrum of condensations and the resulting structures are analyzed, and evidence for biased galaxy formation is discussed. Finally, areas of future research are considered.

Jones, B. J. T.; Palmer, P. L.

22

The origin of the Drosophila subretinal pigment layer.  

PubMed

Optical insulation plays a critical role in the fine visual acuity of the Drosophila compound eye. Screening pigments expressed by a number of cell types contribute to this phenomenon. They provide optical insulation that prevents extraneous light rays from inappropriately activating the photoreceptors. This optical insulation can be divided into two categories; the insulation of the individual ommatidia, and the insulation of the compound eye as a whole. The whole-eye insulation is provided by two sources. The sides of the eye are optically insulated by the pigment rim, a band of pigment cells that circumscribes the eye. The base of the eye is insulated by the subretinal pigment layer; a thick layer of pigment that lies directly underneath the retina. How this subretinal pigment layer is generated has not been clearly described. Here, experiments that manipulate pigment expression during eye development suggest that the subretinal pigment layer is directly derived from pigment cells in the overlying retina. PMID:22684937

Tomlinson, Andrew

2012-08-15

23

The origin of layering of the Svecofennian crust  

Microsoft Academic Search

The FIRE1-3 seismic reflection sections display a frozen image of orogenic thickening followed by lateral spreading that took place during the Svecofennian Orogeny (2.0-1.8 Ga) in the Fennoscandian Shield. The decoupling of the upper, middle and lower crust during spreading resulted in the formation of layered superstructure-infrastructure of the crust. The FIRE profiles display three crustal layers with different reflection

A. Korja; P. J. Heikkinen

2009-01-01

24

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

25

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

Microsoft Academic Search

The discovery of layered deposits in the walls of a deep trough in Lunae Planum has implications for the origin of similar-appearing deposits in some canyons of Valles Marineris. Although layering is visible in the competent, cliff-forming upper walls of the canyons, the dissimilarity in appearance between canyon walls and soft rounded hills of layered deposits on canyon floors, as

David H. Scott

1993-01-01

26

On the origin of the high-latitude boundary layer  

Microsoft Academic Search

This paper presents a statistical study of the high-latitude boundary layer (HLBL) performed on 53 Interball-1 magnetopause crossings. In the study we verify if antiparallel merging is the main source of HLBL formation when the IMF is nearly horizontal. To provide such a study we designed a new coordinate system which allowed us to analyze HLBL under varied interplanetary conditions.

A. Fedorov; E. Budnik; J.-A. Sauvaud

2002-01-01

27

The Origins of Subsurface Layers below Tribological Contacts: A Historical Perspective on Research and Understanding  

SciTech Connect

Inspired by Sir George Beilby's research on polished surfaces in the 1920's, continuing progress in microscopy and surface probes has furthered understanding of tribo-formed layers. Known by various names, these highly-deformed and textured layers vary in thickness, defect arrangement, and uniformity. Their nature depends on the type of material being deformed and the type of wear process to which the surface is subjected. Under otherwise similar sliding conditions, different highly-deformed structures form in different materials because of the effects of stacking fault energy, the arrangement of phases, and the partition of frictional work into heat, fracture, and deformation. Third-body deposits originating from adhesive transfer and wear can shield the deformed layers, and the periodic growth and removal of plateaus can result in time-dependent variations in friction and wear. Combinations of tribo-contact modes, like impact with fretting, can also affect the nature of the near surface layers and their attendant effects on wear and friction.

Blau, Peter Julian [ORNL

2006-01-01

28

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

SciTech Connect

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

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

2011-10-01

29

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

30

On the origin of the high-latitude boundary layer  

NASA Astrophysics Data System (ADS)

This paper presents a statistical study of the high-latitude boundary layer (HLBL) performed on 53 Interball-1 magnetopause crossings. In the study we verify if antiparallel merging is the main source of HLBL formation when the IMF is nearly horizontal. To provide such a study we designed a new coordinate system which allowed us to analyze HLBL under varied interplanetary conditions. This coordinate system floats over the dayside magnetopause following the changes in the instant location of the reconnection site. Despite very different interplanetary conditions, the observed HLBL plasma regimes manifest systematic behavior in the "reconnection" frame of reference. We explain the observed pattern in terms of sporadic patchy reconnection in the high magnetic shear region of the magnetopause.

Fedorov, A.; Budnik, E.; Sauvaud, J.-A.

31

Ice Layers Origins in Icy Satellites and Icy Giants  

NASA Astrophysics Data System (ADS)

Icy giant planets such as Uranus and Neptune are believed to have differentiated into three primary sections: an atmosphere of helium, methane gas, and molecular hydrogen; an “icy” mantle of water, ammonia, and methane; and a core of rock and iron. Icy satellites of the gas giant planets Jupiter and Saturn are also thought to have layers of ices that include carbon monoxide and carbon dioxide, although at reduced pressures and temperatures. Here we investigate ammonium bicarbonate (NH4)HCO3, which degenerates to water, carbon dioxide and ammonia between 36 and 60 °C at room pressure. We performed quasi-hydrostatic high-pressure diamond-anvil cell (DAC) experiments up to 30 GPa over a range of temperatures (22 to 150 °C). Preliminary analysis shows that ammonium bicarbonate not only breaks down to its icy components with increased temperature, but also at increased pressures of ~2 GPa. The individual reaction components reformed into ammonium bicarbonate upon pressure quenching for unheated samples.

Panzik, J. E.; Lee, K. K.

2009-12-01

32

Electronic structure of bacterial surface protein layers  

NASA Astrophysics Data System (ADS)

We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer ( S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L.

2008-01-01

33

Electronic structure of bacterial surface protein layers  

SciTech Connect

We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer (S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L. [Martin-Luther-Universitaet Halle-Wittenberg, Fachbereich Physik, D-06099 Halle (Germany); Institut fuer Physikalische und Theoretische Chemie, Universitaet Bonn, D-53115 Bonn (Germany); Max-Bergmann-Zentrum fuer Biomaterialien, Technische Universitaet Dresden, D-01062 Dresden (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany)

2008-01-15

34

Thermal conductance of layer structure dichalcogenides  

Microsoft Academic Search

We have measured the thermal conductance in the temperature range 0.5–7 K of the layer structure compounds TaS1.6Se0.4 and TaS1.6Se0.4 (pyridine)1\\/2 parallel to the plane of the layers in both the normal and superconducting states. Our results indicate that the phonon contribution to the thermal conductivity, which varies approximately asT1.6 at low temperatures, dominates the electronic contribution in both the

E. K. Sichelt; B. Serin; J. F. Revelli

1974-01-01

35

Thermal conductance of layer structure dichalcogenides  

Microsoft Academic Search

We have measured the thermal conductance in the temperature range 0.5 7 K of the layer structure compounds TaS1.6Se0.4 and TaS1.6Se0.4 (pyridine)1\\/2 parallel to the plane of the layers in both the normal and superconducting states. Our results indicate that the phonon contribution to the thermal conductivity, which varies approximately as T 1.6 at low temperatures, dominates the electronic contribution

E. K. Sichel; B. Serin; J. F. Revelli

1974-01-01

36

On the Origin Of Three Dimensionality In Two-Dimensional Laminar Boundary Layer Separation  

NASA Astrophysics Data System (ADS)

The present experimental investigation aims to study the origin of three-dimensionality in a decelerating two-dimensional laminar boundary layer upstream of separation. The limiting surface streamline pattern is obtained from a standard visualization technique and is interpreted in terms of topological classification of critical points. Based on our experiments, the following hypothesis is proposed. Since the attached boundary layer upstream of separation is two-dimensional, one can naively expect the separation line also to be two-dimensional. However, from the perspective of critical point theory, a two-dimensional separation line would consist of an infinite sequence of saddle points; such a pattern is structurally unstable, thereby indicating that laminar separation as a two-dimensional phenomenon is untenable. Hence, a separation line, that is a finite sequence of saddle and nodal points along the span along which the flow is three-dimensional, develops. This inevitably makes the upstream boundary layer also three-dimensional in nature and the extent of upstream influence depends upon the "strength" of the critical points. At the critical points, the static pressure assumes either a local maximum or minimum value. This results in the generation of spanwise pressure gradients along as well as upstream of separation line and this is also corroborated by surface pressure measurements. Upstream of separation, the local spanwise pressure gradient can be expected to be a constant all across the height of the boundary layer (boundary layer assumption). Within the boundary layer, the resultant velocity continually increases away from the wall, and responds to the spanwise pressure gradient differently at different wall normal locations. This makes the flow field to skew with the streamline curvature being a maximum at the wall and nearly zero near the freestream. This skewed flow of the upstream boundary layer in turn alters the location of the separation line. This in turn alters the upstream flow and so forth. This feedback loop of upstream and downstream influence would eventually converge to a final configuration. It is surmised that this configuration is possibly similar to what is seen in the time-averaged surface flow visualisation pictures.

Diwan, Sourabh; Chetan, S. J.; Ramesh, O. N.

2004-11-01

37

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

38

View of hyphen stair hall between original abobe structure and ...  

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

View of hyphen stair hall between original abobe structure and wood frame addition (note original exterior siding now enclosed) - Zanetta House, San Juan Bautista State Historical Park, San Juan Bautista, San Benito County, CA

39

The origin and characterization of conformational heterogeneity in adsorbed polymer layers  

Microsoft Academic Search

The equilibration of polymer conformations tends to be sluggish in polymer layers adsorbed onto highly attractive substrates, so the structure of these layers must be understood in terms of the layer growth process rather than equilibrium theory. Initially adsorbed chains adopt a highly flattened configuration while the chains which arrive later must adapt their configurations to the increasingly limited space

Jack F. Douglas; Hildegard M. Schneider; Peter Frantz; Robert Lipman; Steve Granick

1997-01-01

40

Origins of interdiffusion, crystallization and layer exchange in crystalline Al/amorphous Si layer systems  

NASA Astrophysics Data System (ADS)

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/a-Si and a-Si/Al bilayers was studied upon annealing at low temperatures between 165 and 250 °C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer exchange in both types of bilayers. The change in bulk energy of the Al phase (release of macrostress and microstrain, increase of grain size) promotes the occurrence of layer exchange, whereas changes in surface and interface energies counteract the layer exchange.

He, D.; Wang, J. Y.; Mittemeijer, E. J.

2006-05-01

41

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

42

Origins of interdiffusion, crystallization and layer exchange in crystalline Al\\/amorphous Si layer systems  

Microsoft Academic Search

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al\\/a-Si and a-Si\\/Al bilayers was studied upon annealing at low temperatures between 165 and 250°C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer

D. He; J. Y. Wang; E. J. Mittemeijer

2006-01-01

43

Layered graphene structure of a hexagonal carbon  

NASA Astrophysics Data System (ADS)

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

Zhang, Bin

2013-06-01

44

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

45

Electroluminescence in organic films with three-layer structure  

Microsoft Academic Search

A stable organic electroluminescent (EL) device was successfully fabricated with a three-layer structure consisting of hole transport layer\\/emitting layer\\/electron transport layer. The EL device was prepared by vacuum evaporation. Efficient carrier double injection into the emitting layer was realized by the use of separate hole and electron transport layers. Bright EL emission was observed in a darkened room at the

Chihaya Adachi; Shizuo Tokito; Tetsuo Tsutsui; Shogo Saito

1988-01-01

46

Secondary Changes in the Strength of Clay Layers and the Origin of Sensitive Clays.  

National Technical Information Service (NTIS)

Knowledge of the origin of quick clay and of secondary changes in strength is of importance for construction purposes as well as for the prevention of landslides. A detailed study was made of adjacent clays in the same layer and of the same age - but with...

C. G. Wenner M. Pajuste O. A. Talme

1966-01-01

47

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

SciTech Connect

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

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

2012-08-06

48

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.

49

Structure of the surface layer of the methanogenic archaean Methanosarcina acetivorans.  

PubMed

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. PMID:22753492

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

2012-07-02

50

The Coriolis effect on coherent structures in planetary boundary layers  

Microsoft Academic Search

Coherent structures are often visible in atmospheric boundary layers as convective clouds and irregular fog. Large eddy simulations (LES) provide data to study the coherent structures by means of multivariate methods of statistical analysis. One of such methods is a proper orthogonal decomposition (POD). A POD can isolate most energetic three-dimensional structures in turbulent boundary layers. Coherent structures in planetary

Igor N Esau

2003-01-01

51

The Moon: Its structure, origin, and development  

NASA Astrophysics Data System (ADS)

Apollo program findings are summarized. The Moon is a differentiated body whose bulk major oxide composition is very similar to that of the terrestrial mantle, indicating a close genetic tie between the Earth and the Moon. The initial lunar differentiation produced a massive feldspathic crust which then underwent considerable tectonic, impact, chemical, and petrological modification, an olivine-rich mantle, and possibly a small Fe-FeS core. While the Moon is a simpler body than the Earth, the Moon has a very complex history and is petrologically and structurally complicated.

Binder, A. B.

1981-11-01

52

Superconductivity in Layered Structure Organometallic Crystals.  

National Technical Information Service (NTIS)

Superconductivity persists in several, layered, transition metal dichalcogenide superconductors when the layers are spread apart to accommodate organic molecules between them. These materials are of interest not only because of their two-dimensional chara...

F. R. Gamble F. J. DiSalvo R. A. Klemm T. H. Geballe

1970-01-01

53

The Origin of Epistemic Structures and Proto-Representations  

Microsoft Academic Search

Organisms across species use the strategy of generating structures in their environment to lower cognitive complexity. Examples include pheromones, markers, color codes, etc. We provide a model of how such structures originate, and present a simulation where organisms with only reactive behavior learn, within their lifetime, to add such structures to their world to lower cognitive load. This implementation is

Sanjay Chandrasekharan; Terrence C. Stewart

2007-01-01

54

Vertical columns originated in layers of depth hoar and near-surface faceted crystals  

NASA Astrophysics Data System (ADS)

Vertical columns originated in layers of depth hoar and near-surface faceted crystals Milena Kocianova (1), Nils Åke Andersson (2), Josef Harcarik (1) (1) Krkonose National Park Administration, Dobrovskeho 3, 54301 Vrchlabi, Czech republic (2)Abisko Scientific Research Station, Abisko, Sweden Within the winter subpolar climatic conditions, the deep layers of depth hoar crystals/sugar snow are common. In course of study snow profiles between Abisko and Kiruna (Northern Sweden) in March/April 2008, we have observed complexes of vertical columns composed of chain of depth hoar crystals repeatably. The height of columns reaches to 20 cm and about 5 cm in diameter, columns were formed in distance from several centimetres to some tens of centimetres between them. The best developed columns were formed by ice body inside. Within deeper snow profile (to 1 m) the columns formed two layers one above another. Earlier, in May 2006, similar layers of columns we were discovered inside continuous snowpack near Riksgransen and inside rest of snow patches in Abisko as well. Columns were formed by harder firn grains. Their origin should correspond to International classification for seasonal snow (Collbeck at al.1990), subclass. No 8b „Ice column". (Ice column from refreezing of draining meltwater within flow fingers). However, based on our knowledges from 2008, there should exist another way of their origin, e.g. temperature metamorphosis of depth hoar columns. Consequently, analogous vertical columns were found within layers of near-surface faceted crystals in subalpine and mountain areas of the Krkonose Mountains (Central Europe). We suppose the influence of space design of all three types of harder columns (originated in depth hoar, near-surface faceted crystals, refreezing of meltwater) and adjacent soft interspace as on the flux of air (gases) inside snowpack as on its stability. Photodocumentation of all forms is enclosed.

Kocianova, M.

2009-04-01

55

2. VIEW LOOKING WEST SHOWING STRUCTURE WHICH WAS ORIGINALLY A ...  

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

2. VIEW LOOKING WEST SHOWING STRUCTURE WHICH WAS ORIGINALLY A METHODIST CHURCH AND ONCE THE GARFIELD REFRACTORIES COMPANY OFFICE ON WASHINGTON STREET. - Town of Bolivar, Bolivar, Westmoreland County, PA

56

Structural Origins of Martian Pit Chains  

NASA Astrophysics Data System (ADS)

Pit craters are circular to elliptical depressions found in alignments (chains), which in many cases coalesce into linear troughs, and are common on the surface of Mars. Pit craters lack an elevated rim, ejecta deposits, or lava flows that are associated with impact craters or calderas. It is generally agreed that these features are formed by collapse into a subsurface cavity. Hypotheses regarding the formation of pit crater chains require development of a substantial subsurface void to accommodate collapse of the overlying sediments. Suggested mechanisms of formation include: collapsed lava tubes, dike swarms, collapsed magma chamber, karst dissolution, fissuring beneath loose material, and dilational faulting. The research described here is intended to constrain current interpretations of pit crater chain formation by analyzing their distribution and morphology. The western hemisphere of Mars was systematically mapped using Mars Orbiter Camera (MOC) images to generate ArcView Geographic Information System (GIS) coverages. All visible pit crater chains were mapped, including their orientations and associations with other structures. We found that pit chains commonly occur in areas that show regional extension or local fissuring. There is a strong correlation between pit chains and fault-bounded grabens. Frequently, there are transitions along strike from (i) visible faulting to (ii) faults and pits to (iii) pits alone. We performed a detailed quantitative analysis of pit crater morphology using MOC narrow angle images, Thermal Emission Imaging System (THEMIS) visual images and Mars Orbiter Laser Altimeter (MOLA) data. This allowed us to interpret a pattern of pit chain evolution and calculate pit depth, slope, and volume. The information collected in the study was then compared with non-Martian examples of pit chains and physical analog models. We evaluated the various mechanisms for pit chain development based on the data collected and conclude that dilational normal faulting and sub-vertical fissuring provide the simplest and most comprehensive mechanisms to explain the regional associations, detailed geometry, and progression of pit chain development.

Wyrick, D.; Ferrill, D. A.; Morris, A. P.; Colton, S. L.; Sims, D. W.

2003-12-01

57

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

58

New Evidence for the Origin of Layered Deposits in Valles Marineris  

Microsoft Academic Search

Results from CRISM, HiRISE, and CTX on MRO provide new insights into the origin of interior layered deposits (ILDs) in Valles Marineris. A well-exposed, thick sequence in western Candor Chasma has spectral properties consistent with basaltic sand mixed with nanophase iron oxide-rich dust, with the addition of sulfates and crystalline ferric oxides. Most of the deposit is dominated spectrally by

S. Murchie; F. Seelos; L. Roach; J. Mustard; R. Milliken; R. Arvidson; S. Wiseman; K. Lichtenberg; J. Andrews-Hanna; J. Bibring; J. Bishop; M. Parente; R. Morris

2008-01-01

59

Understanding the origins of the intrinsic dead layer effect in nanocapacitors  

NASA Astrophysics Data System (ADS)

Thin films of high-permittivity dielectrics are considered ideal candidates for realizing high charge-density nanosized capacitors for use in next generation energy storage and nanoelectronic applications. The experimentally observed capacitance of such film nanocapacitors is, however, 1 order of magnitude lower than expected. This dramatic drop in capacitance is attributed to the so-called “dead layer”—a low-permittivity layer at the metal-dielectric interface in series with the high-permittivity dielectric. The exact nature of the dead layer and the reasons for its origin still remain somewhat unclear. Based on insights gained from recently published ab initio work on SrRuO3/SrTiO3/SrRuO3 and our first-principles simulations on Au/MgO/Au and Pt/MgO/Pt nanocapacitors, we construct an analytical model that isolates the contributions of various physical mechanisms to the intrinsic dead layer. In particular we argue that strain-gradients automatically arise in very thin films even in absence of external strain inducers and, due to flexoelectric coupling, are dominant contributors to the dead layer effect. Our theoretical results compare well to existing as well as our own ab initio calculations and suggest that inclusion of flexoelectricity is necessary for qualitative reconciliation of atomistic results. Our results also hint at some remedies for mitigating the dead layer effect.

Majdoub, M. S.; Maranganti, R.; Sharma, P.

2009-03-01

60

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

61

Superconductivity in layered structure organometallic crystals.  

PubMed

Superconductivity persists in several, layered, transition metal dichalcogenide superconductors when the layers are spread apart to accommodate organic molecules between them. These materials are of interest not only because of their two-dimensional character but also because they may provide a means for examining hypotheses regarding organic molecules and superconductivity. PMID:17806773

Gamble, F R; Disalvo, F J; Klemm, R A; Geballe, T H

1970-05-01

62

Saturn's low-latitude boundary layer: 2. Electron structure  

Microsoft Academic Search

The boundary of a planetary magnetosphere is the site of mass, momentum, and energy transport. This transport produces a layer of mixed solar wind and magnetospheric plasma inside and adjacent to the boundary. In the case of Earth, the electron structure of this layer is distinctive, and has been explained by models of the layer on open magnetic field lines.

A. Masters; A. P. Walsh; A. N. Fazakerley; A. J. Coates; M. K. Dougherty

2011-01-01

63

The stratigraphy of Meridiani Planum, Mars, and implications for the layered deposits' origin  

NASA Astrophysics Data System (ADS)

Large exposures of water-altered layered deposits have recently been identified on the surface of Mars. The source materials, formation, and aqueous alteration history are presently poorly understood. The Mars Exploration Rover Opportunity has examined a tiny fraction of large-scale layered deposits in Meridiani Planum, and many questions remain about the origin and history of these widespread materials. Here we present the first detailed stratigraphic study of sulfate-bearing layers throughout the region. We used altimetry data to examine the three-dimensional disposition of twenty-two distinct stratigraphic horizons along their exposures. Our results show that most of these benchmark horizons: (1) are planar and coherent over at least a 100-km scale, and (2) have dip azimuth and magnitudes that are similar to the underlying regional slope, which was emplaced by 3.70 Ga. Nearby ancient river valleys, that appear to have been formed by precipitation-fed surface runoff, originally were incised at ~ 3.74 Ga and then reactivated near the Noachian-Hesperian boundary (3.70 Ga). Mapping relations with these valleys suggest that the Meridiani layers formed near and after this time and without significant volumetric contributions of material excavated from the valleys. Thermal infrared data and erosional expressions imply that significant physical compositional differences exist within the stratigraphy, and these likely reflect a changing paleodepositional environment and/or chemical alteration histories. Any hypothesis for the origin of these regional-scale materials must be consistent with all these observations. We conclude that the previously stated hypotheses of aeolian deposition cemented by a fluxing groundwater table and sulfur-rich volcanic processes are both viable possibilities, while other hypotheses are not supported by these observations.

Hynek, Brian M.; Phillips, Roger J.

2008-09-01

64

Electroluminescent apparatus having a structured luminescence conversion layer  

DOEpatents

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

Krummacher, Benjamin Claus (Sunnyvale, CA)

2008-09-02

65

Growth and Electronic Structure of Thin Epitaxial Metal Layers.  

National Technical Information Service (NTIS)

The thesis deals with the physics and chemistry of thin epitaxial metal layers. Various substrates are used to study the structure, morphology and electronic structure of thin epitaxial metal films. In the first part of the thesis, the author used layered...

H. H. Weitering

1991-01-01

66

Combinations of processes responsible for Martian impact crater “layered ejecta structures” emplacement  

Microsoft Academic Search

We utilized images and stereo-derived topographic data acquired by the High Resolution Stereo Camera (HRSC) and Thermal Emission Imaging System (THEMIS) images together with other data in order to study the geology of “layered ejecta structures” associated with relatively pristine Martian impact craters. The geomorphology and morphometric properties indicate their origin as complex combinations of a variety of impact processes.

Goro Komatsu; Gian Gabriele Ori; Stefano Di Lorenzo; Angelo Pio Rossi; Gerhard Neukum

2007-01-01

67

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

2010-03-18

68

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

69

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

70

Reaction-layer fatigue: understanding the limitations of structural silicon  

NASA Astrophysics Data System (ADS)

Previous research has attributed the fatigue susceptibility of silicon films to the sequential oxidation of the silicon and environmentally-assisted crack growth solely within the SiO2 surface layer. This "reaction-layer fatigue" mechanism is only significant in thin films where the critical crack size for catastrophic failure can be reached by a crack growing within the oxide layer. Fracture mechanics analyses can provide important insight into the limitations of structural silicon films. In this paper, our current understanding of the reaction-layer fatigue mechanism will be reviewed. Current results suggest that surface oxide layer thicknesses as low as 10-20 nm may induce reaction-layer fatigue when considering failure of the specimen for a crack reaching the silica/silicon interface. In contrast, 3-fold thicker surface oxide layers are required for failure due to a crack within the oxide layer.

Muhlstein, Christopher L.; Pierron, O. N.

2003-12-01

71

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

SciTech Connect

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. 46 references.

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

1987-06-01

72

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

73

Turbulent boundary layer structure, drag reduction  

Microsoft Academic Search

The research work has progressed along the following lines: (1) continuation of theoretical work on the effects of large-eddy breakup devices on turbulent eddies; (2) theoretical study of the role of pressures in the wall turbulence generation process; (3) application of a theoretical model for designing smart wall boundary layer control; (4) use of a new bursting model for predicting

Marten T. Landahl; Joseph H. Haritonidis

1986-01-01

74

Quantum-mechanical modeling of accumulation layers in MOS structure  

Microsoft Academic Search

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

J. Sune; P. Olivo; B. Ricco

1992-01-01

75

New Evidence for the Origin of Layered Deposits in Valles Marineris  

NASA Astrophysics Data System (ADS)

Results from CRISM, HiRISE, and CTX on MRO provide new insights into the origin of interior layered deposits (ILDs) in Valles Marineris. A well-exposed, thick sequence in western Candor Chasma has spectral properties consistent with basaltic sand mixed with nanophase iron oxide-rich dust, with the addition of sulfates and crystalline ferric oxides. Most of the deposit is dominated spectrally by the dust component. Monohydrated and polyhydrated sulfates are concentrated in separate, interbedded layers, which in some cases are traceable over tens of kilometers. Monhydrated sulfates dominate the lower part of the deposits whereas polyhydrated sulfates are more common in upper strata. The deposits are partially mantled by low- albedo eolian ripples that contain pyroxenes similar in composition to what is found on the surrounding plateau, plus sulfates predominantly in monohydrated form. The dark ripples originate from discrete, friable layers. Similar dark, erodible layers elsewhere on Mars have been interpreted as buried eolian sand. Crystalline ferric oxides are concentrated in the sulfate-rich layers, and mass wasting has accumulated them at the base of steep slopes to form the deposits of gray hematite detected by TES. The persistence of monohydrated sulfates in debris shows that alteration of monohydrated to polyhydrated sulfates, proposed as an important weathering process, takes long compared to formation of the thin layer that dominates reflectance properties. The observed stratification of sulfate compositions implies differences in the abundance of liquid water or brine chemistry during deposition or early chemical modification of sediments. Inferred mineralogy and compositional stratification are similar to what is observed in sulfate-rich sediments in the Meridiani and Aram Chaos regions. The Meridiani deposits were proposed to accumulate where evaporites formed in areas of groundwater discharge and cemented eolian sediments, in which coarse- grained hematite formed by diagenetic alteration. Modeling of the history of groundwater discharge in Valles Marineris shows that thick evaporite sequences are also expected within the chasmata, and could have similarly trapped eolian sediments. Areas with predicted thick accumulations enclose the major eroded remnants of the ILDs. Formation of the ILDs by lithification of eolian sediment by evaporites in areas of groundwater discharge links the spectrally and morphologically similar, sulfate- and ferric-oxide bearing deposits in Valles Marineris, Aram Chaos, and Meridiani to a common regional process.

Murchie, S.; Seelos, F.; Roach, L.; Mustard, J.; Milliken, R.; Arvidson, R.; Wiseman, S.; Lichtenberg, K.; Andrews-Hanna, J.; Bibring, J.; Bishop, J.; Parente, M.; Morris, R.

2008-12-01

76

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

77

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

78

Endohedral cage and layered structures of Al46  

NASA Astrophysics Data System (ADS)

First-principles calculations were performed to study the structure and stability of the Al46 cluster. The results suggest two competing structural motifs, the spherical endohedral cage and layer-stacking structures. It is shown that although medium-sized Al clusters tend to form layered structures (i.e., fcc fragments with a stacking fault), a spherical endohedral cage configuration is also an important structural motif for the magic Al46 cluster. Besides, the cluster ions were also studied, and the calculated PES of the Al46- isomer with the minimum of free energy is in better agreement with the experimental PES data.

Zhao, Li-Zhen; Lu, Wen-Cai; Qin, Wei; Zang, Qing-Jun; Wang, C. Z.; Ho, K. M.

2012-10-01

79

Nanoscale Structures and Dynamics of a Boundary Liquid Layer  

Microsoft Academic Search

Our long term scientific interest is the understanding of the interface properties of flowing liquids on a microscopic level. Various mechanisms have been introduced to explain the origin of slip at a solid-liquid interface like the formation of a thin depletion layer or a molecular ordering of the liquid near the interface. Reflectometry (using x-rays or neutrons) is a powerful

Marco Walz

2011-01-01

80

Elastic layer-structured metal organic frameworks (ELMs)  

Microsoft Academic Search

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

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

2009-01-01

81

Structure of sink flow turbulent boundary layers  

NASA Astrophysics Data System (ADS)

This paper reports on an investigation of the influence of sink flow pressure gradient on the structure of a fluid's turbulent flow. Experimental data (Jones 1998) of sink flow cases corresponding to three different strengths are brought into the picture for investigation. An attempt has been made to predict the structure of turbulence from experimental evidence. The result shows that like zero-pressure gradient flow, two different similarities, one in the inner region and the other in the wake region, are preserved.

Mandal, B. C.; Mazumdar, H. P.

2013-05-01

82

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

83

Saturn's low-latitude boundary layer: 2. Electron structure  

NASA Astrophysics Data System (ADS)

The boundary of a planetary magnetosphere is the site of mass, momentum, and energy transport. This transport produces a layer of mixed solar wind and magnetospheric plasma inside and adjacent to the boundary. In the case of Earth, the electron structure of this layer is distinctive, and has been explained by models of the layer on open magnetic field lines. In this paper we examine the electron structure of Saturn's low-latitude boundary layer (LLBL) using observations made by the Cassini spacecraft; the typical properties and variability of Saturn's LLBL are examined in a companion paper. By analyzing the relationship between the electron density and temperature measured during Cassini magnetopause crossings we demonstrate that the electron structure of Saturn's LLBL is highly variable. At some of the crossings the structure of Saturn's LLBL is similar to previously reported examples of the structure of Earth's LLBL, where the major changes in electron density and temperature clearly occur in different regions of the layer, producing a distinctive shape to the temperature-density distribution. However, at many crossings the structure of Saturn's LLBL is unlike the previously reported examples of the structure of Earth's LLBL, since they lack the same distinctive shape to the distribution. We discuss the possible explanations for these differences in the electron structure of Saturn's LLBL, and what these differences could tell us about how the solar wind interacts with a planetary magnetosphere.

Masters, A.; Walsh, A. P.; Fazakerley, A. N.; Coates, A. J.; Dougherty, M. K.

2011-06-01

84

Structural, compositional and optical properties of PECVD silicon nitride layers  

NASA Astrophysics Data System (ADS)

We have investigated the correlation between the various plasma-enhanced chemical vapour deposition (PECVD) process parameters on the structural, compositional and optical properties of SiNx layers. The investigated process parameters are gas composition, radio frequency power and its frequency and deposition temperature. We also investigated SiON and ammonia-free SiNx layers. Refractive index, thickness, residual stress, structure and composition of the dielectric layers were determined using interferometry, wafer bowing, scanning electron microscopy, Fourier transform infra-red and secondary ion mass spectrometry measurements. SiNx films can be deposited to be almost stress-free with relatively low concentration of hydrogen (10 to 19% of atomic H). SiNx layers have the potential to cover a wide range of refractive indices (1.8-2.1) with possible extension down to 1.40 through various SiON layers.

Karouta, Fouad; Vora, Kaushal; Tian, Jie; Jagadish, Chennupati

2012-11-01

85

Origins of large critical temperature variations in single-layer cuprates  

SciTech Connect

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

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

2008-08-26

86

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

SciTech Connect

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

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

2010-07-15

87

Multiple maternal origins and weak phylogeographic structure in domestic goats  

PubMed Central

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

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

2001-01-01

88

Prediction of replication origins by calculating DNA structural properties.  

PubMed

In this study, we introduced two DNA structural characteristics, namely, bendability and hydroxyl radical cleavage intensity to analyze origin of replication (ORI) in the Saccharomyces cerevisiae genome. We found that both DNA bendability and cleavage intensity in core replication regions were significantly lower than in the linker regions. By using these two DNA structural characteristics, we developed a computational model for ORI prediction and evaluated the model in a benchmark dataset. The predictive performance of the jackknife cross-validation indicates that DNA bendability and cleavage intensity have the ability to describe core replication regions and our model is effective in ORI prediction. PMID:22449982

Chen, Wei; Feng, Pengmian; Lin, Hao

2012-02-28

89

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

90

Structured Water Layers Adjacent to Biological Membranes  

Microsoft Academic Search

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,

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

2006-01-01

91

Electronic Structure of Graphene layers on SiO2  

NASA Astrophysics Data System (ADS)

Using ab initio density functional theory we investigate the electronic structures of single, double and triple layers of graphene on SiO2 surfaces terminated either with Si or with O. After performing full geometry relaxation, we find that the first graphene layer is chemically bonded to the substrate and does not show any grapheme-like electronic structure. The graphitic electronic character is somewhat recovered by putting second and third layers of graphene, although subtle differences are observed among different stacking configurations, such as AA, AB, and ABC, and so on. These effects can be seen both on Si- terminated and O- terminated substrates. These studies would provide fundamental understanding to gives control over the band structure of graphene layers on SiO2, and raises the potential application of graphene.

Shahbazian, J. H.; Choi, H. S.; Woo, S. J.; Kwon, Y.-K.

2008-10-01

92

Differences in the structure of a planetary magnetopause boundary layer  

NASA Astrophysics Data System (ADS)

The boundary of a planetary magnetosphere is known as a magnetopause, and is the site of energy, mass, and momentum transfer. The structure of internal boundary layers adjacent to these boundaries is intimately related to the processes responsible for this transport. We use thermal electron observations made by the Cassini spacecraft to examine the structure of Saturn’s low-latitude internal boundary layer. By analyzing the relationship between the electron density and temperature during the crossings we demonstrate that the structure of the layer is variable. At some of the crossings the major changes in electron density and temperature occur in distinct regions of the layer (as for previously reported examples at Earth), whereas at others the two quantities change over a similar region. We discuss the possible explanations for this phenomenon, and what this could tell us about how the solar wind interacts with a planetary magnetosphere.

Coates, A. J.; Masters, A.; Walsh, A. P.; Fazakerley, A. N.; Dougherty, M. K.

2010-12-01

93

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

94

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

95

A DNA structure is required for geminivirus replication origin function.  

PubMed Central

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

Orozco, B M; Hanley-Bowdoin, L

1996-01-01

96

A DNA structure is required for geminivirus replication origin function.  

PubMed

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

Orozco, B M; Hanley-Bowdoin, L

1996-01-01

97

Layer-by-layer microfluidics for biomimetic three-dimensional structures  

Microsoft Academic Search

Due to the complex structures of living systems, with size scales spanning from the micron to millimeter range, the use of microtechnology to recreate in vivo-like architecture has exciting potential applications. However, most microscale systems are two-dimensional, and few three-dimensional (3-D) systems are being explored. We have developed a versatile technique, combining surface engineering with layer-by-layer microfluidics technology, to create

Wei Tan; Tejal A. Desai

2004-01-01

98

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

99

Inner-Layer Structure of a Shear-Driven 3-D Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

An investigation of a planar, shear-driven 3-D turbulent boundary layer (3DTBL) was performed to examine the effects of variable skewing on the turbulence structure and flow physics of the non-equilibrium flow field. Particle image velocimetry (PIV) measurements were acquired in both the xy-plane (perpendicular to the wall) and the xz-plane (parallel to the wall) to examine modifications to the near-wall turbulence when subject to varying strengths of crossflow. These measurements reveal significant changes to the inner region of the boundary layer, particularly at higher shear rates. Increased spanwise shear leads to the breakup of larger organized flow structures into smaller structures that are displaced out from the near-wall region of the boundary layer, leading to increased transport and a thickening of the inner region of the boundary layer. The crossflow is also associated with increases in the (normal and shear) Reynolds stresses, particularly over the translating wall section. The discontinuity at the trailing edge of the translating wall results in an initial decrease of the streamwise normal stress, which subsequently recovers and increases above 2-D levels. Another effect of the crossflow is the disruption of the initial 2-D boundary layer spanwise vorticity layer, contributing to the increased momentum transfer in this region.

Kiesow, Robert; Plesniak, Michael

1999-11-01

100

The role of groundwater in the origin of the indurated layered deposits of Arabia Terra, Mars  

NASA Astrophysics Data System (ADS)

Indurated layered deposits of likely sedimentary origin are widely distributed across the Arabia Terra region of Mars. In situ observations by the MER Opportunity rover of one such deposit in Meridiani Planum have been interpreted to represent grains composed of dirty evaporites that have been extensively reworked by fluvial and aeolian processes in a playa environment and diagenetically modified by a fluctuating water table. Stratigraphic relationships, morphological similarities, and spectral evidence suggest a related origin for the many layered deposits throughout Arabia Terra. Isolated intra-crater deposits, erosional outliers, and pedestal craters suggest that the Arabia Terra deposits were once thicker and more widespread than their current extent. We investigate the origin of these sedimentary deposits using global and regional hydrological models, in which groundwater flow is driven by evaporation where the water table intersects the surface and redistribution of that water as low-latitude precipitation. These models predict focused groundwater upwelling and evaporation in Arabia Terra during the Late Noachian to Early Hesperian, driven by its unique topography relative to the adjacent southern highlands and northern lowlands. This hydrological cycle would have brought a steady flux of groundwater to the surface, which upon evaporation, would concentrate any dissolved solutes as a cementing salt that would indurate aeolian material and allow buildup of thick sedimentary deposits. Groundwater upwelling would first be limited to the large craters in the region, resulting in rapid sedimentary infilling by a combination of evaporites and evaporite-cemented clastic material. As the craters were filled, groundwater upwelling would spread out over broad regions of Arabia Terra, producing widespread deposits covering much of the inter-crater plains. The observed distribution and thickness of the deposits agrees with the predictions from the hydrological models. This work suggests that the extensive sedimentary deposits of Arabia Terra preserve the record of a Late Noachian-Early Hesperian global hydrological system, and a climate in which surface temperatures in the low latitudes were largely above the freezing point of water, allowing liquid precipitation to infiltrate the surface to recharge aquifers and drive continued groundwater flow.

Andrews-Hanna, J. C.; Wiseman, S. M.; Arvidson, R. E.

2008-12-01

101

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

SciTech Connect

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

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

1996-05-01

102

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

103

Energy dissipating structures in turbulent boundary layers  

NASA Astrophysics Data System (ADS)

We present numerical experiments of a dipole crashing into a wall, a generic event in two-dimensional incompressible flows with solid boundaries. The Reynolds number Re is varied from 985 to 7880, and no-slip boundary conditions are approximated by Navier boundary conditions with a slip length proportional to Re-1. Energy dissipation is shown to first set up within a vorticity sheet of thickness proportional to Re-1 in the neighborhood of the wall, and to continue as this sheet rolls up into a spiral and detaches from the wall. The energy dissipation rate integrated over these regions appears to converge towards Rey-independent values, indicating the existence of energy dissipating structures that persist in the vanishing viscosity limit. Details can be found in Nguyen van yen, Farge and Schneider, PRL, 106, 184502 (2011).

Farge, Marie; Nguyen van Yen, Romain; Schneider, Kai

2011-11-01

104

Combinations of processes responsible for Martian impact crater ``layered ejecta structures'' emplacement  

NASA Astrophysics Data System (ADS)

We utilized images and stereo-derived topographic data acquired by the High Resolution Stereo Camera (HRSC) and Thermal Emission Imaging System (THEMIS) images together with other data in order to study the geology of ``layered ejecta structures'' associated with relatively pristine Martian impact craters. The geomorphology and morphometric properties indicate their origin as complex combinations of a variety of impact processes. The studied (inner) layered ejecta structures often exhibit ground-hugging characteristics, and many of them do not have topographic profiles expected from simple ballistic emplacement. Such profiles include ones that are plateau-shaped or thickening outward. We think that water-rich fluidized flows driven by the momentum due to the impact and by gravity, together with ballistic emplacement and vortex produced by the atmosphere-ejecta curtain interaction, were essential to the (inner) layered ejecta structure formation. We hypothesize that the thinner outer layered ejecta structures were formed by various combinations of shockwave-induced liquefaction of water-rich near-surface sediments, ballistic emplacement of ejecta-entraining water, and strong winds (expanding vapor, vortex, base surge) related to the impact. The contribution of each proposed layered ejecta structure formation mechanism should have been variable depending on the condition of the impact.

Komatsu, Goro; Ori, Gian Gabriele; Di Lorenzo, Stefano; Rossi, Angelo Pio; Neukum, Gerhard

2007-06-01

105

Metastable structures of Dy layers adsorbed on Mo(112) and their transformations  

NASA Astrophysics Data System (ADS)

Ordering of dysprosium on Mo(112) up to 1.5 monolayers has been investigated by LEED and work function analysis after adsorption at 100 K and annealing between 200 and 1000 K. At low annealing temperatures (< 350-600 K) ordered structures are found, which are changed or even destroyed irreversibly by annealing steps to higher temperatures. At coverages, ?, up to 0.3 monolayer a (6×1) not strictly commensurate chain structure is seen, which coexists up to ? = 0.58 with a one-dimensionally incommensurate c( 1.56×2) structure. At higher coverages up to the physical monolayer at ? 0.77, incommensurate ( n×2) followed by oblique ( n×1) structures are seen with n continuously variable with coverage. The second layer forms a p (1.33×1) structure. Annealing to higher temperatures causes irreversible structural transitions with strongly coverage dependent properties. Up to ? = 0.58, only a glass-like disordered phase is formed, which cannot be ordered again. In contrast, the rectangular incommensurate structures between 0.58 < ? < 0.68 remain unchanged upon annealing, whereas the structures at higher coverages and those of the second layer are transformed into commensurate (s×1) structures with integer s. Geometrical models are presented for the non-annealed structures and possible origins for the two-dimensional concentration dependent vitrification of the Dy layers are discussed.

Fedorus, A.; Koval, V.; Naumovets, A.; Pfnür, H.

2001-12-01

106

Lactobacillus surface layer proteins: structure, function and applications.  

PubMed

Bacterial surface (S) layers are the outermost proteinaceous cell envelope structures found on members of nearly all taxonomic groups of bacteria and Archaea. They are composed of numerous identical subunits forming a symmetric, porous, lattice-like layer that completely covers the cell surface. The subunits are held together and attached to cell wall carbohydrates by non-covalent interactions, and they spontaneously reassemble in vitro by an entropy-driven process. Due to the low amino acid sequence similarity among S-layer proteins in general, verification of the presence of an S-layer on the bacterial cell surface usually requires electron microscopy. In lactobacilli, S-layer proteins have been detected on many but not all species. Lactobacillus S-layer proteins differ from those of other bacteria in their smaller size and high predicted pI. The positive charge in Lactobacillus S-layer proteins is concentrated in the more conserved cell wall binding domain, which can be either N- or C-terminal depending on the species. The more variable domain is responsible for the self-assembly of the monomers to a periodic structure. The biological functions of Lactobacillus S-layer proteins are poorly understood, but in some species S-layer proteins mediate bacterial adherence to host cells or extracellular matrix proteins or have protective or enzymatic functions. Lactobacillus S-layer proteins show potential for use as antigen carriers in live oral vaccine design because of their adhesive and immunomodulatory properties and the general non-pathogenicity of the species. PMID:23677442

Hynönen, Ulla; Palva, Airi

2013-05-16

107

Electronic origin of high-temperature superconductivity in single-layer FeSe superconductor  

NASA Astrophysics Data System (ADS)

The recent discovery of high-temperature superconductivity in iron-based compounds has attracted much attention. How to further increase the superconducting transition temperature (Tc) and how to understand the superconductivity mechanism are two prominent issues facing the current study of iron-based superconductors. The latest report of high-Tc superconductivity in a single-layer FeSe is therefore both surprising and significant. Here we present investigations of the electronic structure and superconducting gap of the single-layer FeSe superconductor. Its Fermi surface is distinct from other iron-based superconductors, consisting only of electron-like pockets near the zone corner without indication of any Fermi surface around the zone centre. Nearly isotropic superconducting gap is observed in this strictly two-dimensional system. The temperature dependence of the superconducting gap gives a transition temperature Tc~ 55 K. These results have established a clear case that such a simple electronic structure is compatible with high-Tc superconductivity in iron-based superconductors.

Liu, Defa; Zhang, Wenhao; Mou, Daixiang; He, Junfeng; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Zhao, Lin; He, Shaolong; Peng, Yingying; Liu, Xu; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Hu, Jiangping; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X. J.

2012-07-01

108

Boundary Layer Structure and Processes in Mid - Ocean Storms  

Microsoft Academic Search

Measurements taken during the Storm Transfer and Response Experiment (STREX) are used to analyze boundary layer structures and processes in the vicinity of North Pacific storms. Case studies are carried out for the pre -frontal, post-frontal, and frontal sectors of storms. The effects of sub-grid scale processes on the boundary layer and the overlying atmosphere receive special emphasis. The pre-frontal

Nicholas A. Bond

1986-01-01

109

Boundary Layer Structure and Dynamics in Outer Hurricane Rainbands.  

NASA Astrophysics Data System (ADS)

Results of hurricane boundary layer experiments conducted in outer rainbands of Hurricanes Josephine (1984) and Earl (1986) are presented. Comparisons of precipitation, kinematic, and thermodynamic structures in these storms and in Hurricane Floyd (1981) indicate that principal rainbands have common characteristic mesoscale and convective scale features in the boundary layer. The two-dimensional mesoscale structure suggests that rainbands are made up of a linear aggregate of cellular reflectivity elements (on the inner, upshear side of the band) and stratiform rain (on the outer downshear side). The band is oriented perpendicular to the shear above the boundary layer and cells move downband at about 80% of the maximum wind. Alongband and crossband wind maxima, and maximum equivalent potential temperatures are located on the outer side of the band axis, with minima 4-8 km to the inner side. Updrafts and downdrafts are preferentially located on the inner side of the band axis, along with maximum crossband convergence, cyclonic shear vorticity, and minimum equivalent potential temperatures. Downdraft transport of cool and dry air from middle levels on the inner side of the rainband was responsible for modifying mixed layer structure adjacent to the band on alongband scales of 100 km. An undisturbed mixed layer of 500 m was present on the outer side of the band while a variety of structures were observed on the inner side indicative of both disturbed and recovering mixed layers. Application of a mixed layer model to low level flow trajectories from the outer rainband to the eyewall indicates that under some conditions, the mixed layer may not recover sufficiently and low surface equivalent potential temperature air may reach the eyewall. These conditions are associated with suppressed flow in a region of positive divergence with moderate rainfall from a middle level anvil cloud. Incomplete recovery was most evident when a recovering mixed layer exhibited a negative jump in water vapor mixing ratio. Differential evaporation cooling over the transition layer drives entrainment of dry air from above which overcomes any evaporation moistening, resulting in a drier mixed layer (with lower surface equivalent potential temperature). Depending on the humidity profile and spatial scale of the initial disturbed mixed layer, the model results suggest that incomplete recovery may be responsible for transitional changes in hurricane intensity.

Powell, Mark Dillon

110

Enhanced columnar structure in CsI layer by substrate patterning  

SciTech Connect

Columnar structure in evaporated CsI layers can be controlled by patterning substrates as well as varying evaporation conditions. Mesh-patterned substrates with various dimensions were created by spin-coating polyimide on glass or amorphous silicon substrates and defining patterns with standard photolithography technique. CsI(Tl) layers 200--1000 {mu}m were evaporated. Scintillation properties of these evaporated layers, such as light yield and speed, were equivalent to those of the source materials. Spatial resolution of X-ray detectors consisting of these layers and a linear array of X-ray detectors consisting of these layers and a linear array of Si photodiodes was evaluated by exposing them to a 25{mu}m narrow beam of X-ray. The results obtained with 200{mu}m thick CsI layers coupled to a linear photodiode array with 20 dots/mm resolution showed that the spatial resolution of CsI(Tl) evaporated on patterned substrates was about 75 {mu}m FWHM, whereas that on CsI(Tl) on flat substrates was about 230 {mu}m FWHM. Micrographs taken by SEM revealed that these layers retained the well-defined columnar structure originating from substrate patterns. Adhesion and light transmission of CsI(Tl) were also improved by patterning the substrate.

Jing, T.; Cho, G.; Drewery, J.; Kaplan, S.N.; Mireshghi, A.; Perez-Mendez, V.; Wildermuth, D. (Lawrence Berkeley Lab., CA (United States)); Fujieda, I. (Xerox Palo Alto Research Center, CA (United States))

1991-10-01

111

The ferrite/superconductor layered structure for tunable microwave devices  

NASA Astrophysics Data System (ADS)

The ferrite/superconductor (FS) structure composed from the separate ferrite garnet Y3Fe5O12 epitaxial layers and superconducting films was used for development of such microwave devices as tunable pass-band filter, phase-shifter and delay line. Application of superconducting layer decreases the microwave losses and it provides new functions of magnetostatic waveguide FS structures. The central frequency of band-pass filter is tuned from 1.5 up to 3 GHz; bandwidth can be regulated by the geometry of antenna transducers (from 30 up to 300 MHz); band insertion loss is about 1.5-3 dB.

Bobyl, A.; Suris, R.; Karmanenko, S.; Semenov, A.; Melkov, A.; Konuhov, S.; Olshevski, A.

2002-08-01

112

Temperature Structure of Protoplanetary Disks Undergoing Layered Accretion  

NASA Astrophysics Data System (ADS)

We calculate the temperature structures of protoplanetary disks (PPDs) around T Tauri stars heated by both incident starlight and viscous dissipation. We present a new algorithm for calculating the temperatures in disks in hydrostatic and radiative equilibrium, based on Rybicki's method for iteratively calculating the vertical temperature structure within an annulus. At each iteration, the method solves for the temperature at all locations simultaneously, and converges rapidly even at high (Gt104) optical depth. The method retains the full frequency dependence of the radiation field. We use this algorithm to study for the first time disks evolving via the magnetorotational instability. Because PPD midplanes are weakly ionized, this instability operates preferentially in their surface layers, and disks will undergo layered accretion. We find that the midplane temperatures T mid are strongly affected by the column density ?a of the active layers, even for fixed mass accretion rate \\dot{M}. Models assuming uniform accretion predict midplane temperatures in the terrestrial planet forming region several × 102 K higher than our layered accretion models do. For \\dot{M} < 10^{-7} \\, M_{\\odot } \\, yr^{-1} and the column densities ?a < 10 g cm-2 associated with layered accretion, disk temperatures are indistinguishable from those of a passively heated disk. We find emergent spectra are insensitive to ?a, making it difficult to observationally identify disks undergoing layered versus uniform accretion.

Lesniak, M. V.; Desch, S. J.

2011-10-01

113

Structural optimization of MTJs with a composite free layer  

NASA Astrophysics Data System (ADS)

We investigate the switching statistics dependence on cell geometry by means of systematic micromagnetic simulations. We find that MTJs with a free layer composed of two ellipses with the axes a/2 and b inscribed into a rectangle a × b are characterized by the same switching speed and thermal stability as MTJs with a composite free layer (C-MTJs). As has been shown, the C-MTJs demonstrate a substantial decrease of the switching time and the switching current as compared to conventional MTJs with a monolithic free layer. Thus, while preserving all the advantages of the C-MTJs, the newly proposed structure does not require a narrow gap between the two parts of the composite layer and therefore can be easily fabricated.

Makarov, Alexander; Sverdlov, Viktor; Selberherr, Siegfried

2013-09-01

114

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

115

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

2012-11-01

116

Deep structure and origin of active volcanoes in China  

NASA Astrophysics Data System (ADS)

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

Zhao, D.

2010-12-01

117

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

118

Strained layer superlattice focal plane array having a planar structure  

SciTech Connect

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

119

Structure evolution of implanted polymers: Buried conductive layer formation  

NASA Astrophysics Data System (ADS)

The polarization, temperature and frequency dependence of the conductivity of polyethylene and polyamide-6 films implanted with B+ ions at 60-100keV to various fluences were investigated. The phenomenon of hysteresis was observed in the d.c. current-voltage dependence for the polymers implanted with moderate fluences. This effect was attributed to the aligning of electric dipoles (attributed to the carbon-rich clusters) in the implanted layer by the applied electric field. The possibility of fabrication of a sandwich structure insulator/conductive layer/insulator combining the ion implantation with the electrochemical deposition of dielectric polymer poly-ortho-phenylenediamine from solution was demonstrated. The spatial characteristics of this structure enable the control of the conductance of the concealed carbonaceous layer by applying an external electric field that opens the way for fabrication of a transistor-like electronic switch.

Popok, V. N.; Karpovich, I. A.; Odzhaev, V. B.; Sviridov, D. V.

1999-01-01

120

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

121

On the origin of strain relaxation in epitaxial CdZnO layers  

NASA Astrophysics Data System (ADS)

The origin of a double peak, detected by X-ray diffraction (XRD), in a wurtzite CdxZn1-xO (x=0.17) epilayer, is investigated using Rutherford backscattering spectrometry in channeling geometry (RBS/C). In-depth compositional characterization by RBS/C demonstrates that strain relaxation does not take place via compositional phase separation and does not cause any compositional pulling effects. On the contrary, RBS/C angular scans demonstrate that relaxation is a consequence of progressive structural changes during the heteroepitaxial growth of the film on MgZnO, likely due to the large distortion of the lattice induced by the high Cd content.

Redondo-Cubero, A.; Rodrigues, J.; Brandt, M.; Schäfer, P.; Henneberger, F.; Correia, M. R.; Monteiro, T.; Alves, E.; Lorenz, K.

2013-03-01

122

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

123

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

124

Vertical velocity structure of nonprecipitating continental boundary layer stratocumulus clouds  

Microsoft Academic Search

Continental boundary layer (BL) stratocumulus clouds affect the local weather by modulating the surface energy and moisture budgets and are also intimately tied to the diurnal cycle of the turbulence in the BL. Vertical velocity structure of these clouds is studied using data from the Atmospheric Radiation Measurement Program's Southern Great Plains observing facility located near Lamont, Oklahoma. Data from

Virendra P. Ghate; Bruce A. Albrecht; Pavlos Kollias

2010-01-01

125

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

126

Preparation and structural properties of Pd nanoparticles in layered silicate  

Microsoft Academic Search

Pd nanocrystals in the 5–15 nm ranges were prepared on pillared clay minerals (PILCs) as supports by immobilizing Pd nanoparticles in the interlamellar space of montmorillonite and saponite by pillaring with aluminium hydroxide cations. Pd nanoparticles were generated via reduction by ethanol of Pd acetate present in the adsorption layer at room temperature. The structure of Pd-PILC samples was characterized

Anna Sz?cs; Ferenc Berger; Imre Dékány

2000-01-01

127

The structure of the near neutral atmospheric surface layer as observed during the CASES'99 experiment  

NASA Astrophysics Data System (ADS)

Recent observational data obtained during the Cooperative Surface-Atmosphere Exchange Study field campaign in October 1999 (CASES'99), show evidence of layered structure of the near-neutral surface layer (SL): (i) the upper surface layer (USL) which corresponds to the upper part of the surface layer, where the mean velocity profile is logarithmic and the spectrum decays as k_1-5/3 (where k_1 is the longitudinal wavenumber); (ii) the Yaglom surface layer (YSL) which is an intermediate sublayer, where shear affects the isotropy of turbulence; (iii) the eddy surface layer (ESL) which is the lower sublayer where blocking of impinging eddies is the dominating mechanism. The origin of the eddies impinging from aloft (probably from the YSL) downto the ESL is preliminary addressed in this study, since the data show evidence of linear organized eddies imbedded in the surface layer (i.e. about 100 m vertical extent) and horizontally spaced by about 300 m. This is consistent with theories predicting that the primary mechanism of eddy motion in high Reynolds number wall layers is 'top-down'. The layered structure of the SL also has visible effect on vertical profiles of vertical velocity variance (overline{w^2}) and momentum transport. In the ESL, overline{w^2} scales as z2/3 while it is constant or slightly decreases within the YSL. Concerning, momentum transport, ejections contribute identically to the momentum flux than do sweeps in the ESL, whereas in the YSL, ejections give about 50 % higher relative contribution.

Drobinski, P.; Carlotti, P.; Newsom, R. K.; Banta, R. M.; Foster, R. C.; Redelsperger, J. L.

2003-04-01

128

Origins.  

PubMed

The farthest of the galaxies that can be seen through the large ground-based telescopes of modern astronomy, such as those on La Palma in the Canary Islands, are so far away that they appear as they did close to the time of the origin of the universe, perhaps some 10 billion years ago. Much has been learned, and much has still to be learned, about the young universe from optical and radio telescopes, but these instruments cannot be used to look directly at the universe in its first few hundred thousand years. Instead, they are used to search the relatively recent past for relics of much earlier times. Together with experiments planned for the next generation of elementary particle accelerators, astronomical observations should continue to extend what is known about the universe backward in time to the Big Bang and may eventually help to reveal the origins of the physical laws that govern the universe. PMID:17817144

Weinberg, S

1985-10-01

129

Terpenoid hydrocarbons in Hula peat: Structure and origins  

NASA Astrophysics Data System (ADS)

Tri- and tetracyclic diterpenoid and pentacyclic triterpenoid hydrocarbons have been identified in the lipid extracts of three peat samples from the Hula Basin, Israel. Tentative structures for the diterpenoids have been proposed based on mass spectral studies and on extrapolation of known mass spectral fragmentation patterns of most probable biological precursors. The identification of ent-kaurenes in one peat sample appears to be a unique observation. Kaurenes most likely originated from higher plant resins. The triterpenoids in the three samples consist mainly of 17?-hopanes and hopenes, derived from recent biogenic activity. The preponderance of the 17?(H)-hopanes indicates the geological immaturity of the samples and implies that they have undergone only a mild thermal history.

Venkatesan, M. I.; Ruth, E.; Kaplan, I. R.

1986-06-01

130

Origin and structure of the Galactic disc(s)  

NASA Astrophysics Data System (ADS)

We examine the chemical and dynamical structure in the solar neighbourhood of a model Galaxy that is the endpoint of a simulation of the chemical evolution of the Milky Way in the presence of radial mixing of stars and gas. Although the simulation's star formation rate declines monotonically from its unique peak and no merger or tidal event ever takes place, the model replicates all known properties of a thick disc, as well as matching special features of the local stellar population such as a metal-poor extension of the thin disc that has high rotational velocity. We divide the disc by chemistry and relate this dissection to observationally more convenient kinematic selection criteria. We conclude that the observed chemistry of the Galactic disc does not provide convincing evidence for a violent origin of the thick disc, as has been widely claimed.

Schönrich, Ralph; Binney, James

2009-11-01

131

The Synthesis, Structure, and Properties of Several New Layered Cuprates  

NASA Astrophysics Data System (ADS)

The compounds LaSrCuAlO_5 and LaSrCuGaO_5 have been investigated by powder neutron, single crystal X-ray, and powder X-ray diffraction. The structure of LaSrCuAlO_5 can be described as layers of square pyramidal copper oxygen polyhedra separated by aluminum oxygen tetrahedra. Resistivity measurements on polycrystalline sample indicate that the sample is a semiconductor with an activation energy of 11 meV. Attempts to dope the compound have proved unsuccessful. The gallium compound was found by X-ray single crystal structure analysis to be isostructural with the mineral brownmillerite, Ca_2FeAlO_5. The compound can be described as planes of octahedral copper and oxygen separated by tetrahedra of gallium and oxygen. In polycrystalline form, the compound was found to exist only in the small range La_{rm 1-x }Sr_{rm 1 + x} CuGaO_5 (0.10 < x < 0.15). Resistivity measurements on the two endmembers show that the compounds are semiconducting with activation energies of 28meV and 7meV respectively. The structures of the double layered cuprates, LnSr_2Cu_2GaO _7 and LaSr_2Cu _2AlO_7 have been determined. The new layered cuprate LnSr _2Cu_2GaO _7 (Ln = La-Yb, Y), was synthesized and characterized structurally by both powder neutron diffraction and X-ray single crystal analysis. The structure can be described as a layer of double copper oxygen square pyramids sharing an oxygen vacancy separated by a layer of gallium oxygen tetrahedra. Doping with calcium, Y_{ rm 1-x}Ca_{rm x}Sr_2Cu_2 GaO_7, was found, after proper annealing and heat treatment, to cause the compound to go from a semiconductor to a metal to a superconductor. The structure of LaSr_2Cu _2AlO_7 was determined by Rietveld analysis of powder neutron diffraction data. The compound was found to be composed of double copper oxygen layers, similar to the ones seen in LaSr _2Cu_2GaO _7, but with the tetrahedral layers constructed of aluminum-oxygen rings rather than chains. Doping studies have shown that the compound has a limited substitutional chemistry. Superconductivity has not been observed to date in any sample.

Vaughey, John Thomas

132

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

133

Spectroscopic analysis of ALD-coated 3D structures and origin of the Berreman effect  

NASA Astrophysics Data System (ADS)

The Berreman effect shed light on various phenomena in 2D systems. However, coatings of 3D systems in soft-lithography and photonic devices, or 3D fibers suggest that the Berreman effect in 3D structures could be different. Experimental and computational infrared spectroscopy studies of 3D structures conformally coated with Al2O3 and ZnO layers using atomic layer deposition support this conclusion. In 2D systems, defining ?0 the macroscopic incidence angle of the IR beam on a sample, the LO mode absorbance increases as [Sin(?0)]^4 when ?0 becomes grazing. On the other hand, in 3D systems a linear combination of [Sin(?0)]^4 with appropriate coefficients must be considered. Accounting for Snell's law in the simulation model is essential to explain these results and the origin of the Berreman effect. We conclude that sample geometry determines infrared absorbance of LO modes versus ? and vice-versa Our results promise a new tool to investigate topography of insulating ionic oxide layers.

Scarel, Giovanna; Na, Jeong-Seok; Hyde, Kevin; Parsons, Gregory

2009-03-01

134

Wave structure interaction problems in three-layer fluid  

NASA Astrophysics Data System (ADS)

Wave structure interaction problems in a three-layer fluid having an elastic plate covered free surface are studied in a three-dimensional fluid domain in both the cases of finite and infinite water depths. Wave characteristics are analyzed from the dispersion relation of the associated wave motion, and approximate results are derived in both the cases of deep water and shallow water waves. Further, the expansion formulae and the associated orthogonal mode-coupling relations are derived for the velocity potentials for the wave structure interaction problems in channels of finite and infinite depths. The utility of the expansion formulae is demonstrated by (1) deriving the source potentials associated with the wave structure interaction problems in a three-layer fluid medium of finite and infinite water depths and (2) analyzing the wave scattering by a partially frozen crack in a floating ice sheet in the three-layer fluid medium in a three-dimensional channel of finite water depth. Various results derived can be used to deal with acoustic wave interaction with flexible structures and other wave structure interaction problems of similar nature arising in different branches of physics and engineering.

Mondal, R.; Sahoo, T.

2013-10-01

135

Nonlinear Stability and Structure of the Compressible Reacting Mixing Layer  

NASA Astrophysics Data System (ADS)

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

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

1998-11-01

136

Hybrid transfer-matrix FDTD method for layered periodic structures.  

PubMed

A hybrid transfer-matrix finite-difference time-domain (FDTD) method is proposed for modeling the optical properties of finite-width planar periodic structures. This method can also be applied for calculation of the photonic bands in infinite photonic crystals. We describe the procedure of evaluating the transfer-matrix elements by a special numerical FDTD simulation. The accuracy of the new method is tested by comparing computed transmission spectra of a 32-layered photonic crystal composed of spherical or ellipsoidal scatterers with the results of direct FDTD and layer-multiple-scattering calculations. PMID:19282957

Deinega, Alexei; Belousov, Sergei; Valuev, Ilya

2009-03-15

137

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

138

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

139

The motor origins of human and avian song structure  

PubMed Central

Human song exhibits great structural diversity, yet certain aspects of melodic shape (how pitch is patterned over time) are widespread. These include a predominance of arch-shaped and descending melodic contours in musical phrases, a tendency for phrase-final notes to be relatively long, and a bias toward small pitch movements between adjacent notes in a melody [Huron D (2006) Sweet Anticipation: Music and the Psychology of Expectation (MIT Press, Cambridge, MA)]. What is the origin of these features? We hypothesize that they stem from motor constraints on song production (i.e., the energetic efficiency of their underlying motor actions) rather than being innately specified. One prediction of this hypothesis is that any animals subject to similar motor constraints on song will exhibit similar melodic shapes, no matter how distantly related those animals are to humans. Conversely, animals who do not share similar motor constraints on song will not exhibit convergent melodic shapes. Birds provide an ideal case for testing these predictions, because their peripheral mechanisms of song production have both notable similarities and differences from human vocal mechanisms [Riede T, Goller F (2010) Brain Lang 115:69–80]. We use these similarities and differences to make specific predictions about shared and distinct features of human and avian song structure and find that these predictions are confirmed by empirical analysis of diverse human and avian song samples.

Tierney, Adam T.; Russo, Frank A.; Patel, Aniruddh D.

2011-01-01

140

Effects of image charges on double layer structure and forces.  

PubMed

The study of the electrical double layer lies at the heart of soft matter physics and biophysics. Here, we address the effects of the image charges on the double layer structure and forces. For electrolyte solutions between two neutral plates, we show that depletion of the salt ions by the image charge repulsion results in short-range attractive and long-range repulsive forces. If cations and anions are of different valency, the asymmetric depletion leads to the formation of an induced electrical double layer. In comparison to a 1:1 electrolyte solution, both the attractive and the repulsive parts of the interaction are stronger for the 2:1 electrolyte solution. For two charged plates, the competition between the surface charge and the image charge effect can give rise to like-charge attraction and charge inversion. These results are in stark contrast with predictions from the Poisson-Boltzmann theory. PMID:24089790

Wang, Rui; Wang, Zhen-Gang

2013-09-28

141

Effects of image charges on double layer structure and forces  

NASA Astrophysics Data System (ADS)

The study of the electrical double layer lies at the heart of soft matter physics and biophysics. Here, we address the effects of the image charges on the double layer structure and forces. For electrolyte solutions between two neutral plates, we show that depletion of the salt ions by the image charge repulsion results in short-range attractive and long-range repulsive forces. If cations and anions are of different valency, the asymmetric depletion leads to the formation of an induced electrical double layer. In comparison to a 1:1 electrolyte solution, both the attractive and the repulsive parts of the interaction are stronger for the 2:1 electrolyte solution. For two charged plates, the competition between the surface charge and the image charge effect can give rise to like-charge attraction and charge inversion. These results are in stark contrast with predictions from the Poisson-Boltzmann theory.

Wang, Rui; Wang, Zhen-Gang

2013-09-01

142

Redox Active Layer-by-Layer Structures containing MnO2 Nanoparticles  

SciTech Connect

Nanoscale materials provide unique properties that will enable new technologies and enhance older ones. One area of intense activity in which nanoscale materials are being used is in the development of new functional materials for battery applications. This effort promises superior materials with properties that circumvent many of the problems associated with traditional battery materials. Previously we have worked on several approaches for using nanoscale materials for application as cathode materials in rechargeable Li batteries. Our recent work has focused on synthesizing MnO2 nanoparticles and using these in layer-by-layer (LbL) structures to probe the redox properties of the nanoparticles. We show that the aqueous colloidal nanoparticles produced by butanol reduction of tetramethylammonium permanganate can be trapped in thin films using a layer-by-layer deposition approach, and that these films are both redox active and exhibit kinetically facile electrochemical responses. We show cyclic voltammetry of MnO2 colloidal nanoparticles entrapped in a LbL thin film at an ITO electrode surface using poly(diallyldimethylammonium chloride) (PDDA). CV experiments demonstrate that Li+ insertion accompanies Mn(IV) reduction in LiClO4 supporting electrolytes, and that reduction is hindered in supporting electrolytes containing only tetrabutylammonium cations. We also show that electron propagation through multilayer films is facile, suggesting that electrons percolate through the films via electron exchange between nanoparticles.

Bazito, Fernanda; O'Brien, Robert; Buttry, Daniel A.

2005-02-01

143

Optical contrastivity of complicated materials: finite layered structures  

NASA Astrophysics Data System (ADS)

We define the intrinsic optical contrastivity of a complicated layered structure as the relative total gap taken inside the total internal reflection region over a chosen range of frequencies. The notion introduced for ordered 1D systems retains its meaning for 2D and 3D ordered optical systems, as well as for disordered structures. The parametric maps of contrastivity and sensitivity are calculated for 1D comb matrices based on glass, silicon, and microporous silicon with various fillings, comb sizes, and densities of a gaseous filling. The existence of areas on a parametric map which are highly sensitive to deviations in the contrastivity is shown for different materials. In the case of a gaseous filling of voids between the matrix material layers, the areas of a very high sensitivity are also found.

Glushko, E. Y.

2012-01-01

144

The origin of SH-wave resonance frequencies in sedimentary layers  

NASA Astrophysics Data System (ADS)

Resonance frequencies are often analysed in geo-engineering studies to evaluate seismic risk and microzonation in urban areas. The Nakamura technique constitutes a popular approach that computes the spectral ratio of horizontal-to-vertical ground motion in ambient noise recordings to reveal the existence of any site resonance frequencies. Its theoretical basis remains however unclear with some authors arguing that the method de-emphasizes any Rayleigh-wave contributions and that the resonance frequencies are solely caused by vertically incident SH waves. Other authors explain the same resonance frequencies by the ellipticity of the fundamental Rayleigh wave. Recent numerical simulations reveal that the magnitude of the peak frequency is proportional to the relative portion of Love waves present. This study demonstrates that Love waves alone can be responsible for any observed resonance frequencies in sedimentary layers. Yet sharp SH-wave resonance frequencies are only excited by a source in the bedrock. These resonance frequencies are caused by inhomogeneous waves excited by the bedrock source that tunnel through the high-velocity bedrock to emerge in the low-velocity sediments with a very reduced range of slownesses. The resulting SH waves are then free to interfere constructively thereby creating the observed resonance frequencies. This general trigger mechanism leads to resonances that are almost offset independent. The resulting resonance frequencies map onto points of maximum curvature in the Love-wave phase-velocity dispersion curves at or just beyond the critical horizontal slowness. They can be analysed with the quarter-wavelength law if a large velocity contrast exists between the unconsolidated sediments and the bedrock. A minor modification of the quarter-wavelength law provides more accurate predictions, also for smaller velocity contrasts. Multisource simulations show that site amplification factors as determined by horizontal-over-vertical (H/V) spectral ratios would not only depend on the relative portion of Love waves in the total wavefield but also on the depth distribution and the relative strength of the SH sources inside the bedrock compared with those in the sediments. An accurate interpretation of site amplification factors by means of H/V peak frequencies would thus require in-depth knowledge of the causes and origins of the local microseismic noise field.

van der Baan, Mirko

2009-09-01

145

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

146

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

147

Origin and Timing of Voltage-Sensitive Dye Signals within layers of the Turtle Cerebellar Cortex  

PubMed Central

Optical recording techniques were applied to the turtle cerebellum to localize synchronous responses to microstimulation of its cortical layers and reveal the cerebellum's three-dimensional processing. The in vitro yet intact cerebellum was first immersed in voltage–sensitive dye and its responses while intact were compared to those measured in thick cerebellar slices. Each slice is stained throughout its depth, even though the pial half appeared darker during epi-illumination and lighter during trans-illumination. Optical responses were shown to be mediated by the voltage–sensitive dye because the evoked signals had opposite polarity for 540- and 710-nm light, but no response to 850-nm light. Molecular layer stimulation of the intact cerebellum evoked slow transverse beams. Similar beams were observed in the molecular layer of thick transverse slices but not sagittal slices. With low currents, beams in transverse slices were restricted to sublayers within the molecular layer, conducting slowly away from the stimulus site. These excitatory beams were observed nearly all the way across the turtle cerebellum, distances of 4-6 mm. Microstimulation of the granule cell layer of both transverse or sagittal slices either evoked a local membrane depolarization restricted to a radial wedge, but these radial responses did not activate measurable molecular layer beams in transverse slices. White matter microstimulation in sagittal slices (near the ventricular surface of the turtle cerebellum) activated the granule cell and Purkinje cell layers, but not the molecular layer. These responses were nearly synchronous, were primarily caudal to the stimulation, and were blocked by cobalt ions. Therefore, synaptic responses in all cerebellar layers contribute to optical signals recorded in intact cerebellum in vitro (Brown and Ariel, 2009). Rapid radial signaling connects a sagittally-oriented, fast-conduction system of the deep layers with the transverse-oriented, slow-conducting molecular layer, thereby permitting complex temporal processing between two tangential but orthogonal paths in the cerebellar cortex.

Ariel, Michael; Brown, Michael E.

2010-01-01

148

The Turbulent Structure of Drag Reducing Boundary Layer Flows  

Microsoft Academic Search

The turbulent structure of wall-bounded drag reduced flow has been studied with particle image velocimetry (PIV) in a zero-pressure-gradient boundary layer. Drag reduction was achieved by injection of a concentrated polymer solution through a spanwise slot along the test wall at a distance approximately 2 m upstream of the PIV measurement station. For comparison, water was injected at the same

C. M. White; V. Somandepalli; M. G. Mungal

149

A model for periodic structures in turbulent boundary layers  

Microsoft Academic Search

Many experimental studies emphasize the importance of periodic recognizable flow patterns for the transport process in turbulent\\u000a flow. In this paper a model is formulated for the large scale part of the turbulent motion. The experimental observation that\\u000a the structures in the outer region run in phase with the bursting cycle in the wall layer forms the basis of the

A. Beljaars; K. Krishna Prasad

150

Mode-I crack problem for functionally graded layered structures  

Microsoft Academic Search

This paper deals with two bonded functionally graded finite strips with two collinear cracks. Different layers may have different\\u000a nonhomogeneity properties in the structure. A bi-parameter exponential function was introduced to simulate the continuous\\u000a variation of material properties. The problem is solved by using the integral transform, singular integral equation methods\\u000a and the theory of residues. Various internal cracks and

Sheng-Hu Ding; Xing Li

2011-01-01

151

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

152

Numerical analysis for three-dimensional transport structures of dust layer over Japan  

NASA Astrophysics Data System (ADS)

The origin and three-dimensional transport structures of dust layer over Japan during April 2001 were analyzed using the regional-scale aerosol transport model (CFORS). Simulated dust field was compared with the NCAR-C130 airborne measurements, and it was shown that CFORS captures many of the important observed features. The back trajectories of high dust levels over Japan show that dense dust layers within the boundary layer are mainly transported from northern and north eastern China, respectively, while one_fs at the upper level (3-6km) are mainly Taklimakan Desert (Tarim Basin) origin. It is also found that Taklimakan dust has higher transport altitude than Gobi dust. Further examination of dust transport within the Tarim Basin using the nesting CFORS results with the finer resolution clearly show that Taklimakan dust is uplifted to altitude of 4-5km when the cold air involving the strong northeasterly wind and north wind goes into the basin, and is transported by the westerlies. Finally, sensitivity simulation controlling dust emission for Gobi Desert and Taklimakan Desert were conducted, and we found that Gobi dust is mainly transported within the boundary layer between 40 degrees north and 45 degrees north, while Taklimakan dust is tend to transport at altitude level between 4km and 6km centered at 40 degrees north.

Satake, S.; Uno, I.; Hayasaka, T.

2005-12-01

153

Band structures of phononic-crystal plates in the form of a sandwich-layered structure.  

PubMed

This study investigates the propagation of Lamb waves in phononic-crystal plates in the form of a sandwich-layered structure. The composite plates are composed of periodic layers bilaterally deposited on both sides of the homogeneous core layer. Using the analyses of the band structures and the transmission spectra, it is revealed that the core layer may induce significant modulations to the lower-order Lamb modes. The modulations are ascribed to the reshaped particle displacement fields of the eigenmodes. Prominently, the core layer made of soft material (rubber) combines the identical eigenmodes of the periodic layers into a pair of asymmetric and symmetric modes in which case the periodic layers vibrate independently. However, the core layer made of hard material (tungsten) or medium hardness material (silicon) couples the periodic layers tightly, in which case the composites vibrate as a whole. In addition, it is found that the phononic band gaps are very sensitive to the thickness of the core layer; this could be indispensable to practical applications such as bandgap tuning. PMID:22087902

Cheng, Y; Liu, X J; Wu, D J

2011-11-01

154

Band Structures of Transition-Metal-Dichalcogenide Layer Compounds  

Microsoft Academic Search

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

L. F. Mattheiss

1973-01-01

155

Negative thermal expansion due to negative area compressibility in TlGaSe2 semiconductor with layered crystalline structure  

NASA Astrophysics Data System (ADS)

We conducted comparison of the original experimental data of the temperature dependences of thermal expansion in crystals with layered crystalline structure. It is shown that in most crystals with layered structure (graphite, boron nitride, GaSe, GaS, and InSe) the effect of negative thermal expansion can be explained by the specific character of the phonon spectra. It was shown, that in contrast to other crystals with layered structure, negative thermal expansion in the layers' plane of TlGaSe2 is the result of negative area compressibility. We demonstrate that the thermal expansion of TlGaSe2 crystals can be controlled by illumination, external electric field, and thermal annealing. The nature of observed effects and a special mechanism of the negative area compressibility in TlGaSe2 crystals are discussed.

Seyidov, Mirhasan Yu.; Suleymanov, Rauf A.

2010-09-01

156

Structural Changes in Individual Retinal Layers in Diabetic Macular Edema  

PubMed Central

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

Yoshimura, Nagahisa

2013-01-01

157

Layered structure of Asian dust and pollutants outbreak in spring  

NASA Astrophysics Data System (ADS)

Three-dimensional structures of Asian dust and anthropogenic pollutants transport occurring successively during May 2007 were clarified using results of space-borne backscatter lidar (NASA/CALIPSO), NIES ground lidar data and results simulated with a data-assimilated version of a dust transport model (RC4) and US EPA-CMAQ. First large scale outbreak occurred in May 7-9 was characterized by the elevated dust layer height at 2500-4000 m, and anthropogenic pollutants below the dust layer over the Japan, which indicates the dust and pollutants were transported in decoupled condition. Another large outbreak was occurred during May 25 - 28. In this case, we found that the dust and anthropogenic pollutants were mixed within the planetary boundary layer over the Japan. These transport characteristics of dust and pollutants were well simulated by RC4 and CMAQ, both in concentration level and horizontal/vertical scale. Based on CALIPSO and RC4/CMAQ, two significant transport mechanisms of Asian dust/pollutants in the PBL and free atmosphere were clarified: a low level dust outbreak within the dry slot region of a well developed low- pressure system, and formation of an elevated dust layer within the warm sector of a low-pressure system. We will also show clear 3D view of dust/pollutants transport based on CALIPSO and RC4/CMAQ model to help the understanding of large-scale outbreak of dust and pollutants.

Itahashi, S.; Uno, I.; Yumimoto, K.; Hara, Y.

2008-12-01

158

Structure of proteoglycans from different layers of human articular cartilage.  

PubMed Central

Full-depth plugs of adult human articular cartilage were cut into serial slices from the articular surface and analysed for their glycosaminoglycan content. The amount of chondroitin sulphate was highest in the mid-zone, whereas keratan sulphate increased progressively through the depth. Proteoglycans were isolated from each layer by extraction with 4M-guanidinium chloride followed by centrifugation in 0.4M-guanidinium chloride/CsCl at a starting density of 1.5 g/ml. The efficiency with which proteoglycans were extracted depended on slice thickness, and extraction was complete only when cartilage from each zone was sectioned at 20 microns or less. When thick sections (250 microns) were extracted, hyaluronic acid was retained in the tissue. Most of the proteoglycans, extracted from each layer under optimum conditions, could interact with hyaluronic acid to form aggregates, although the extent of aggregation was less in the deeper layers. Two pools of proteoglycan were identified in all layers by gel chromatography (Kav. 0.33 and 0.58). The smaller of these was rich in keratan sulphate and protein, and gradually increased in proportion through the cartilage depth. Chondroitin sulphate chain size was constant in all regions. The changes in composition and structure observed were consistent with the current model for hyaline-cartilage proteoglycans and were similar to those observed with increasing age in human articular cartilage. Images Fig. 9. Fig. 12.

Bayliss, M T; Venn, M; Maroudas, A; Ali, S Y

1983-01-01

159

Evaluating Satiated Copepod Behavioral Responses to Thin Layer Flow Structure  

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

160

Boundary layer structure during sea breeze conditions at Ahtopol, Bulgaria  

NASA Astrophysics Data System (ADS)

Continuous sodar (Scintec MFAS) and ultrasonic anemometer (Typhoon - Obninsk make) measurements were initiated in summer 2008 at the meteorological observatory of Ahtopol at the Black Sea coast (south-east Bulgaria) under a Bulgarian-Russian collaborative programme. These observations of high resolution form the basis for studies of the atmospheric boundary layer turbulence and vertical structure at a coastal site. This sodar is unique in Bulgaria and provides the first continuous high resolution data on the wind profile up to 400 - 500 m above the ground. In addition, the continuous turbulence parameters monitoring allows atmospheric boundary studies needed for different applications. The meteorological observatory at Ahtopol is under development as a background atmospheric composition station in coastal area and the wind data are essential for the studies of gases exchange under breeze conditions. The measurements revealed quite different sea breeze seasons during the years 2008 to 2011 and within the individual seasons, a number of different sea breeze types were identified depending on the interaction of local and larger-scale forcing. In this study we investigate the turbulence parameters and the vertical structure of the boundary layer related to only to sea breeze conditions. We also study the wind profile within the first 400 - 500 m above the ground. For the surface layer, we test the free convection theory against the sodar observations.

Barantiev, D.; Batchvarova, E.; Novitzky, M. A.

2012-04-01

161

Characterization of semiconductor layered structures by spectroscopic ellipsometry  

NASA Astrophysics Data System (ADS)

Spectroscopic ellipsometry (SE) is a non-destructive optical technique suitable for the characterization of materials. The measurement is based on the accurate determination of the change of polarization state of a polarized incident light beam after interaction with the specimen. In this work, a rotating analyzer type spectroscopic ellipsometer has been constructed and aligned for the non-destructive characterization of semiconductor materials in the wavelength range from UV to NIR. New results on the mathematical formulation for layers of gradually varying dielectric functions have been obtained and included in the software developed for the analysis of the experimental SE spectra. With these software programs, the interpretation of the measured SE spectra of complex structures becomes possible by using appropriate physical models and non-linear least-square fitting. The system is first tested by a few different types of material systems, such as thermally grown SiO2 on Si substrate and SIMOX structures. Then, it is applied to the study of a series of ion beam synthesized (IBS) material systems, such as SiC/Si heterostructures formed by carbon implantation into silicon, and CoSi2/Si layered structures formed by cobalt implantation into silicon. From the ellipsometric spectra of these samples, useful information on these material structures have been obtained and discussed.

Guo, Wensheng

1997-07-01

162

Ordered equilibrium structures of soft particles in thin layers  

NASA Astrophysics Data System (ADS)

Considering a system of Gaussian particles confined between two hard, parallel plates, we investigate at T = 0, ordered equilibrium configurations that the system forms as the distance D between the plates gradually increases. Using a very sensitive and reliable optimization technique that is based on ideas of genetic algorithms, we are able to identify the emerging sequences of the energetically most favorable structures. Although the resulting phase diagram is rather complex, its essential features can be reduced to the discussion of two archetypes of structural transitions: (i) a continuous transformation at a fixed number of layers, leading from a square to a centered rectangular and then to a hexagonal lattice; (ii) a discontinuous transition, transforming a hexagonal to a square lattice via complex intermediate structures, i.e., the so-called buckling transition, which is encountered as the system forms a new layer. Detailed Monte Carlo simulations are able to confirm the theoretical predictions on a semiquantitative level but are not able to grasp the tiny energetic differences between competing structures.

Kahn, Mario; Weis, Jean-Jacques; Kahl, Gerhard

2010-12-01

163

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

164

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

2013-05-01

165

Magnetic stratification and the internal structure of layered intrusions  

NASA Astrophysics Data System (ADS)

Magnetic methods can be used to investigate the internal structure and to constrain the magmatic history of mafic layered intrusions. Borehole cores provide a nearly continuous record of the vertical zonation of magnetic properties (i.e., magnetic stratification) across the compositional layering. Two intrusions with contrasting petrogenetic histories were investigated: the Insizwa sill (South Africa), an open system characterized by multiple magma pulses, and the Sonju Lake intrusion (Minnesota), a nearly perfect closed system. Both intrusions display vertical variations of their magnetic properties (magnetic susceptibility, AMS, degree of anisotropy, and shape factor). Magnetic units were initially defined based on magnetic susceptibility and its variability and were further refined using additional magnetic parameters. Magnetic stratification occurs at scales from a few meters to several 10's of meters and the boundaries between magnetic units range from gradual to abrupt. Petrologic and rock magnetic studies indicate that modal variations in primary magnetite/titanomagnetite and/or paramagnetic minerals (olivine, pyroxene) control the magnetic susceptibility. In the open system case (Insizwa), magnetic stratification correlates well with the prominent petrologic and geochemical layering. Within units appearing compositionally homogeneous (i.e., no visible macroscopic layering), magnetic stratification is also observed. The abrupt changes in susceptibility are interpreted to result from magma replenishment in a growing magma chamber. A magma recharge event could shift petrologic equilibrium and postpone magnetite crystallization, leading to a sudden decrease in susceptibility. In the closed system case (Sonju Lake), many layers are characterized by cyclical trends in susceptibility; an upward increase followed by an upward decrease. Cyclic trends may result from fractional crystallization, during which an initial upward increase in magnetic susceptibility is predicted due to the volumetric increase in Fe-silicates. At the onset of magnetite crystallization, a dramatic increase in magnetic susceptibility occurs followed by a gradual decrease due to a decreasing abundance of magnetite.

Maes, S. M.; Ferré, E. C.; Geissman, J.

2008-12-01

166

Hierarchical fractal structure of perfect single-layer graphene  

NASA Astrophysics Data System (ADS)

The atomic lattice structure of perfect singlelayer graphene that can actually be regarded as a kind of hierarchical fractal structure from the perspective of fractal geometry was studied for the first time. Three novel and special discoveries on hierarchical fractal structure and sets were unveiled upon examination of the regular crystal lattices of the single-layer graphene. The interior fractaltype structure was discovered to be the fifth space-filling curve from physical realm. Two efficient methods for calculating the fractal dimension of this fresh member was also provided. The outer boundary curve had a fractal dimension equal to one, and a multi-fractal structure from a naturally existing material was found for the first time. A series of strict self-similar hexagons comprised a rotating fractal set. These hexagons slewed at a constant counterclockwise angle ? of 19.1° when observed from one level to the next higher level. From the perspective of fractal geometry, these pioneering discoveries added three new members to the existing regular fractal structures and sets. A fundamental example of a multi-fractal structure was also presented.

Zhang, T.; Ding, K.

2013-10-01

167

Electrical breakdown of graphene and few-layer graphene structures  

NASA Astrophysics Data System (ADS)

The electrical breakdown of graphene and few-layer graphene (FLG) structures are investigated. To better understand the dynamics of these nano-scale thermal effects, we investigate graphene and FLG nanowires of various dimensions and find that significant joule heating occurs inducing the structures to evolve. A distinct change in the behavior during electrical stressing indicates that different mechanisms occur at the various stages of evolution. The results are compared to detailed thermal modeling of our structures and could have implications on the development of high current carrying nanoscale graphene devices. Supported in part by NSF Award No. DMR-0805136, the Kentucky NSF EPSCoR program, the University of Kentucky Center for Advanced Materials, and the University of Kentucky Center for Nanoscale Science and Engineering.

Sundararajan, Abhishek; Johnson, Stephen; Hunley, D. Patrick; Flores, Roel; Johnson, A. T. Charlie; Strachan, Douglas

2011-03-01

168

Electrical breakdown of graphene and few-layer graphene structures  

NASA Astrophysics Data System (ADS)

The electrical breakdown of graphene and few-layer graphene (FLG) structures are investigated. To better understand the dynamics of these nano-scale thermal effects, we investigate graphene and FLG structures of various dimensions and find that significant joule heating occurs inducing the structures to evolve. A distinct change in the behavior during electrical stressing indicates that different mechanisms and geometrical effects occur at the various stages of evolution. The results could have implications on the development of high current carrying nanoscale graphene devices. Supported in part by NSF Award No. DMR-0805136, the Kentucky NSF EPSCoR program through award EPS-0814194, and the University of Kentucky Center for Advanced Materials.

Sundararajan, Abhishek; Hunley, D. Patrick; Strachan, Douglas. R.

2012-02-01

169

Electroluminescent Device Comprising a Transparent Structured Electrode Layer Made From a Conductive Polymer  

Microsoft Academic Search

An electroluminescent (EL) device is (1) composed of polymeric LEDs comprising an active layer (7) of a conjugated polymer and a transparent polymeric electrode layer (5) having electroconductive areas (51) as electrodes. Like the active layer (7), the electrode layer (5) can be manufactured in a simple manner by spin coating. The electrode layer (5) is structured into conductive electrodes

Aemilianus G. J. Staring; David Braun

1998-01-01

170

Compressive failure of delamination-embedded layered structures  

NASA Astrophysics Data System (ADS)

Various failure mechanisms involving both local and global deformation mechanisms of layered structures, consisting of differently oriented orthotropic laminae, are investigated with a large deformation finite element analysis. The aim of this study is to identify the dominant mode which leads to the structural failure under a given boundary condition and geometrical shape. It is assumed that these structures contain initial interlaminar flaws represented by embedded delaminations. Such flaws can play a significant role in defining overall structural integrity and deformation mechanisms. The energy release rate, mixed-mode stress intensity factors and phase angle are computed to quantify the crack driving force and used to measure likelihood of delamination growth in two-dimensional and three- dimensional composite structures. In the first part, two composite structures with distinguished shapes, consisting of four laminae are considered in two-dimensional analysis. One is a flat panel under compressive load and the other structure is a cylindrical shell subjected to external pressure. In the flat panel model, two buckling modes, a global and a local ligament, are observed under quasi-static loading conditions. The interaction of these two modes produces an unstable post-buckling behavior. It is found that the energy release rate exceeds experimentally estimated fracture toughness values only after buckling occurs. In the cylindrical shell study, lower critical buckling loads are observed for models with longer interlaminar delamination as in the flat panel model. However, unlike the flat panel case, the energy release rate surpasses the critical toughness well before the applied pressure reaches the buckling load of the flawed cylindrical shell. This behavior implies that a shell containing an embedded defect along an interface can fail by delamination growth and therefore has a failure load lower than its critical buckling load. Also for thicker cylindrical shells, the compressive internal stress exceeds the predicted stress required for kink band formation prior to structural buckling. In the second part, the coupled local-global buckling behavior in laminated composite structures with embedded delamination and the associated failure mechanisms under compressive loading are critically examined by different geometrical effects. Whether the post-buckling behavior is stable or unstable depends not only on the delamination length and location but also the fiber stacking sequence and number of layers. An 'infinite layer model' is also constructed to simulate the mechanical behavior of laminated composites consisting of large number of layers. In the last part, we extend our computational procedures and models to the case of three-dimensional laminated composite structures with embedded penny-shaped delaminations. A new three-dimensional finite element model which combines shell elements in the region far-away from crack region and continuum elements in the crack front region is introduced and applied. (Abstract shortened by UMI.)

Wu, Li-Chun

1997-11-01

171

Graphene originated 3D structures grown on the assembled nickel particles  

NASA Astrophysics Data System (ADS)

Recently, the fabrication of various morphologies of graphene originated structures became very important due to the perspective of wide range of new applications. Particularly, free standing 3D structured graphene foams could be imperative in energy related areas. Here, we present the new approach of the CVD growth of 3D graphene network by using primarily sintered Ni particle's (˜40?m size) assembles as a template-catalyst via decomposition of low rate of CH4 at 1100^o C based on synthesis method described earlier [1]. SEM and Raman spectra analysis revealed the formation of graphene structure containing a single up to few layers grown on the sintered metal particles served as a catalyst-template. After etching the metal frame without using any support polymer, 3D free-standing graphene microporous structure was formed demonstrating high BET surface area. Two probe measurements of frame resistance were ˜2-8?. Our approach allows controllable tune the pore size and thereby the surface area of 3D graphene network through the variation of the template-catalyst particles size. [4pt] [1]. T. M. Paronyan et al. ACS Nano, 5, p. 9619 (2011)

Paronyan, Tereza; Harutyunyan, Avetik

2013-03-01

172

Magnetic properties of iron-doped layer-structure dichalcogenides  

Microsoft Academic Search

Magnetic-susceptibility measurements have been made on dilute excess Fe alloys of the layer-structure crystals TaSe2, NbSe2, and TaS2. The 2H selenides show local-moment formation and obey a Curie-Weiss law in the range 300-30 K with effective moments in the range (2.5-4.5)muB. For 2H-FexTaSe2 a strong susceptibility maximum is observed at low temperature and at low fields the maximum has a

S. J. Hillenius; R. V. Coleman; E. R. Domb; D. J. Sellmyer

1979-01-01

173

Inverting neutron reflectivity from layered film structures using polarized beams  

NASA Astrophysics Data System (ADS)

It has recently been discovered that the phase of neutrons specularly reflected from a film structure can be determined exactly, even in the dynamical scattering region at small wave vector transfer, by using polarized beams and a buried magnetic reference layer. This is possible for both magnetic and nonmagnetic material films of interest. Given the reflection amplitude as a function of wave vector transfer, the scattering potential can be uniquely obtained by direct inversion, without resort to fitting. A review of some of the theory is presented, and new experimental results are reported.

Majkrzak, C. F.; Berk, N. F.

1999-06-01

174

Free-Surface Boundary Layer and the Origin of Bow Vortices.  

National Technical Information Service (NTIS)

The boundary layer that exists due to the boundary conditions at a curved free surface of a viscous liquid ahead of a body in motion is analyzed. It is shown that surface tension and viscous effects are important and together explain the occurrence of vor...

C. J. Tang L. Landweber V. C. Patel

1984-01-01

175

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

176

Synthesis and structural characterization of three-layer Aurivillius ceramics  

NASA Astrophysics Data System (ADS)

The three layer Aurivillius crystal structure was investigated for use as an ionic conductor. Sample synthesis was investigated using high temperature x-ray diffraction (HTXRD) for a range of compounds, using solid state synthesis and the polymerized complex method. Isothermal Avrami type kinetics studies were performed on Bi4Ti3O12 using in situ HTXRD and quantitative analysis performed via Rietveld refinements using TOPAS. The kinetics analysis yielded Avrami exponents of approximately 0.54, which fell in the range of the diffusion controlled reaction mechanisms. The activation energy over a range of temperatures was calculated to be on the order of 140kJ/mol. Crystal structure refinements were performed on the Bi2Sr2-xAxNb2TiO12 (A = Ca,Ba, x = 0.5, 1) series using combined x-ray and neutron diffraction Rietveld refinements. Refinements indicated a static disorder between the Bi and A sites, and between the Nb and Ti sites. A-site lattice strain investigated via the bond valence method reveals a linear increase in strain with the size of the substituted alkaline earth cation. Furthermore, large isotropic thermal parameters for the O1 and O4 oxygen sites reveal possible oxygen vacancy formation as a result of unresolved strain between the A and Ti layers of the structure. Oxygen stoichiometry is found to decrease as the size of the a lattice parameter decreases. Synthesis of non-stoichiometric three-layer phases was accomplished by aliovalent substitution and via forced site-mixing. Neither method produced samples with conductivities greater than 10-3 Scm at 900°C. Non-stoichiometric compositions follow similar structural trends to those observed in the stoichiometric crystal structure refinements. Increased numbers of oxygen vacancies were recorded than anticipated from the dopants. The number of extra vacancies corresponds well with the amount shown in the stoichiometric compositions. Based on the conductivity and number of charge carriers, the mobilities of the charge carriers are very low, on the order of 10-7 to 10-10 cm2 Vsec at 1000°C.

Haluska, Michael Stephan

2003-07-01

177

Origins of threading dislocations in GaN epitaxial layers grown on sapphire by metalorganic chemical vapor deposition  

NASA Astrophysics Data System (ADS)

The origins of threading dislocations (TDs) in GaN epitaxial layers grown on (0001) sapphire have been investigated by examining different stages of high-temperature (HT) GaN growth on low-temperature GaN nucleation layers (NLs) by transmission electron microscopy. Results indicate that after 20 s of HT growth, GaN islands were free of TDs. After 75 and 120 s of growth, most of the islands contained pure screw (c type) and pure edge (a type) TDs with an interspersion of mixed (c+a type) TDs. Most of the TDs originated from faulted regions located within NLs. TDs move toward the island top surface (c type) or curve toward island side facets (a, c+a type). Coalescence of HT GaN islands did not give rise to either a, c, or c+a type TDs. After 240 s of growth, most TDs were predominantly of a type and could result from climb and glide of basal plane (BP) dislocations that form by the dissociation of Shockley partials located within the faulted regions. BP dislocations are also observed attached to the side facets of islands away from the faulted regions and their possible origins are discussed. c and c+a type TDs form primarily by the coalescence of Frank partials near the GaN/sapphire interface.

Narayanan, V.; Lorenz, K.; Kim, Wook; Mahajan, S.

2001-03-01

178

Bending vibration control of composite plate structures through intelligent constrained-layer treatments  

Microsoft Academic Search

This paper applies intelligent constrained layer (ICL) damping treatments to control bending vibration of composite plate structures. The ICL damping treatment consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be dampened. According to measured vibration response of the structure, a feedback controller regulates in-plane deformation of the piezoelectric layer to perform

I.-Yeu Shen

1994-01-01

179

Formation of multilayered structures in the layer by layer deposition of colloid particles  

Microsoft Academic Search

Theoretical calculations of particle film formation in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to twenty) was simulated for two kinds of particles of equal size. The

Zbigniew Adamczyk; Pawe? Wero?ski; Jakub Barbasz

2008-01-01

180

Giant magnetoresistance of manganese oxides with a layered perovskite structure  

NASA Astrophysics Data System (ADS)

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 needed in both the sensitivity and temperature dependence of the magnetoresistive response. One approach under consideration for optimizing these properties is chemical substitution10. Here we demonstrate an alternative strategy, in which we synthesize layered variants of the cubic perovskite parent compounds that have a controlled number of MnO2 sheets per unit cell. This strategy is structurally analogous to that employed for the systematic exploration of the high-transition-temperature copper oxide superconductors11. We find that the magneto-resistive properties of these materials depend sensitively on the dimensionality of the manganese oxide lattice. Although the properties of our materials are still far from optimal, further exploration of this series of layered perovskites may prove fruitful.

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

1996-03-01

181

Modeling of Sporadic Layers Meteoritic in Origin in the Mars' Ionosphere  

NASA Astrophysics Data System (ADS)

Recent measurements of the Martian ionosphere has revealed the existence of low altitude layers at altitudes ranging from 70 and 90 km, well below the main photoionospheric peak. These peaks were detected by radio science experiments both Mars Global Surveyor (in 71 of 56000 profiles, [1]) and Mars Express (in 75 of 465 profiles, [2]). The presence of these layers was not limited to specific times of the day, longitude or latitude. Previous theoretical models [3,4] predicted the existence of a constant low altitude layer, with a maximum density of the same order of magnitude compared with the recent observations. Long-live metallic ions coming from meteoroid particles can increase the concentration of electrons. However, the models are not able to explain the huge variability of the observations. Similar layers have been observed in the Earth's atmosphere, especially during strong meteor shower and it is well known that they contain metallic ions coming from the ablation of extraterrestrial dust. Here we present a model of the vertical density profile of metallic species (magnesium and iron) between 60 and 120 km altitude. The model includes ablation of meteoroids, metal diffusion in the atmosphere, photoionization of neutrals by ultraviolet photons, and the chemistry of ions and neutrals including charge exchange between neutrals and ions. We have found that the presence of Mg and Fe reduces the concentration of the most abundant atmospheric ions and also increase the concentration of electrons below 90 km of altitude. Model results are compared with some selected electron density profiles observed by Mars Express in order to understand the existence of this sporadic layer. We obtain that in some conditions a low altitude layer can be formed which compared relatively well with the observations, even under steady state scenarios. However dynamic models or high meteoroid fluxes, i.e. meteor showers, are required to explain fully the observations. [1] Withers et al. (2008), J. Geophys. Res. 113, A12314. [2] Patzold et al. (2005), Science 310, 837-838. [3] Pesnell et al. (2000), J. Geophys. Res.105, 1695. [4] Molina-Cuberos et al. (2003), Planet. and Space Sci. 51, 239

Molina-Cuberos, G. J.; Peter, K.; Witasse, O. G.; Nuñez, M. J.; Paetzold, M.

2011-12-01

182

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

183

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

184

Isotopic evidence on the origin of compositional layering in an epizonal magma body  

Microsoft Academic Search

A detailed isotopic study of the Oligocene age (36 Ma), alkaline composition Organ Needle pluton in south-central New Mexico was undertaken to test models for the generation of compositional layering in silicic, epizonal magma bodies. The pluton is isotopically heterogeneous with its alkali feldspar granite composition cap (73–76% SiO2) having lower initial ?Nd and higher 87Sr86Sr ratio than the underlying

P. L. Verplanck; G. L. Farmer; M. McCurry; S. Mertzman; L. W. Snee

1995-01-01

185

Isotopic evidence on the origin of compositional layering in an epizonal magma body  

Microsoft Academic Search

A detailed isotopic study of the Oligocene age (36 Ma), alkaline composition Organ Needle pluton in south-central New Mexico was undertaken to test models for the generation of compositional layering in silicic, epizonal magma bodies. The pluton is isotopically heterogeneous with its alkali feldspar granite composition cap (73-76% SiO 2 ) having lower initial Nd and higher ratio than the

P. L. Verplanck; G. L. Farmer; M. McCurry; S. Mertzman; L. W. Snee

1995-01-01

186

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

187

Electroluminescence of ZnSe enhanced by improved layered optimization structure  

Microsoft Academic Search

The electroluminescence thin-film device with layered optimization structure based on ZnSe emitting layer was deposited by electron-beam evaporation. Electroluminescence of ZnSe film, which has not appeared in device with traditional double insulator structure, was observed. According to this phenomenon, SiO2 ultra-thin layer was inserted into the middle of ZnSe layer and the device with this kind of improved layered optimization

W. W. Jiang; S. L. Zhao; F. J. Zhang; Z. Xu

188

The Electronic Structure of Single-Layer Graphene  

NASA Astrophysics Data System (ADS)

Single-layer graphene has been widely researched in recent years due to its perceived technological applicability and its scientific importance as a unique model system with relativistic Dirac Fermions. Because of its unique geometric and electronic structure, the properties of graphene can be tuned or manipulated in several ways. This tunability is important for technological applications in its own right, and it also allows us to study the fundamental properties of Dirac Fermions, including unique many-body interactions and the nature of the quasiparticles at half-filling. This thesis is a detailed examination of the electronic and structural properties of graphene, studied with angle-resolved photoemission spectroscopy (ARPES) and other surface science techniques like low-energy electron microscopy and diffraction. This thesis is organized as follows. Chapter 1 gives an introduction to the electronic and structural properties of single-layer graphene. It provides a brief historical overview of major theoretical and experimental milestones and sets the stage for the important theoretical and experimental questions that this thesis addresses. Chapters 2 and 3 describe the experimental setup. Chapter 2 discusses the experimental techniques used in this thesis with particular focus on the mechanics of ARPES. Chapter 3 discusses the different graphene growth techniques that were used to create our sample with particular focus on our characterization of epitaxial graphene on SiC(0001). Chapters 4 and 5 form the meat of this thesis: they provide a thorough discussion of the electronic properties of graphene as studied by ARPES. Chapter 4 describes how various perturbations can result in the manipulation of the bare electronic band structure, including the deposition of atomic or molecular species on top of an epitaxial graphene sheet as well as the interactions between graphene and its substrate. Chapter 5 describes the many-body physics in single-layer graphene. It begins with a discussion of the electron-electron interaction in undoped graphene, demonstrating that these interactions qualitatively differ from ordinary metals and semiconductors and depart from the standard Fermi liquid picture for quasiparticles; it then continues by describing how screening the electron-electron and electron-impurity interactions can impact the electronic properties of graphene. Chapter 5 ends with a discussion of the doping-dependent coupling strength of the electron-phonon interaction.

Siegel, David Alan

189

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

190

Thesaurus of Common Topics (TCT): Origin, Functions, Structure.  

ERIC Educational Resources Information Center

|Discusses origin, scope, objectives, term relationships, updating, and future of "Thesaurus of Common Topics," an interdisciplinary thesaurus being developed by the Polish Centre for Scientific, Technical, and Economic Information as a main source of terms for branch thesauri development for the Polish national System of Scientific, Technical and…

Scibor, Eugeniusz; Jabrzemska, Eleonora

1985-01-01

191

Preferential Origin and Layer Destination of GAD65GFP Cortical Interneurons  

Microsoft Academic Search

To identify the origin and track the migratory pathway of specific subpopulations of GABAergic interneurons, we studied tangential migration in a recently developed GAD65-GFP transgenic mouse strain. First, we used immunohistochemical methods to characterize the expression of specific neurochemical markers in the GAD65-GFP neurons. Then, organotypic cultures were used in combination with birth-dating studies to determine the time of generation,

Guillermina López-Bendito; Katherine Sturgess; Ferenc Erdélyi; Gábor Szabó; Zoltán Molnár; Ole Paulsen

192

Modified endoscopic submucosal dissection with enucleation for treatment of gastric subepithelial tumors originating from the muscularis propria layer  

PubMed Central

Background Gastric subepithelial tumors are usually asymptomatic and observed incidentally during endoscopic examination. Although most of these tumors are considered benign, some have a potential for malignant transformation, particularly those originating from the muscularis propria layer. For this type of tumor, surgical resection is the standard treatment of choice. With recent advent of endoscopic resection techniques and devices, endoscopic submucosal dissection (ESD) has been considered as an alternative way of treatment. The aim of this study is to demonstrate the feasibility of a modified ESD technique with enucleation for removal of gastric subepithelial tumors originating from the muscularis propria layer, and to evaluate its efficacy and safety. Methods From November 2009 to May 2011, a total of 16 patients received a modified ESD with enucleation for their subepithelial tumors. All tumors were smaller than 5?cm and originated from the muscularis propria layer of the stomach, as shown by endoscopic ultrasonography (EUS). The procedure was conducted with an insulated-tip knife 2. Patient’s demographics, tumor size and pathological diagnosis, procedure time, procedure-related complication, and treatment outcome were reviewed. Results Fifteen of the sixteen tumors were successful complete resection. The mean tumor size measured by EUS was 26.1?mm (range: 20–42?mm). The mean procedure time was 52?minutes (range: 30–120?minutes). Endoscopic features of the 4 tumors were pedunculated and 12 were sessile. Their immunohistochemical diagnosis was c-kit (+) stromal tumor in 14 patients and leiomyoma in 2 patients. There was no procedure-related perforation or overt bleeding. During a mean follow up duration of 14.8?months (range: 6–22?months), there was no tumor recurrence or metastasis. Conclusions Using a modified ESD with enucleation for treatment of gastric subepithelial tumors originating from the muscularis propria layer and larger than 2?cm, complete resection can be successfully performed without serious complication. It is a safe and effective alternative to surgical therapy for these tumors of 2 to 5?cm in size.

2012-01-01

193

On the Origin of Near-Surface Streaks in the Neutrally-Stratified Planetary Boundary Layer  

NASA Astrophysics Data System (ADS)

The dynamics of near-surface streak formation in the neutrallystratified, rotating planetary boundary layer areinvestigated. The purpose of this note is to compare large-eddysimulation results to theoretical predictions suggesting thatstreaks are associated with non-normal mode optimal perturbations.Streaks are regions near the surface of alternating high and lowspeed fluid organized into nearly linear bands, with horizontalspacing of several hundred metres, oriented up to 30° relativeto the geostrophic wind, that evolve through a continuous cycle ofgeneration, growth, decay and reformation. We find that the earlystages of streak formation and growth are consistent with thelinear theory.

Drobinski, Philippe; Foster, Ralph C.

194

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

195

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

196

Boundary Layer Height and Structure during the NATO LASIE Campaign  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

197

Identification of Lagrangian Coherent Structures in a Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

In this study, we identify Lagrangian coherent structures (LCS) in a flat plate turbulent boundary layer at Re? 0f 19:100. To detect the LCS, we compute direct Lyapunov exponents (DLE) (Haller, G., Physica D, vol 149, pp 248-277, 2001). Specifically we use the velocity field obtained from stereo PIV measurements to compute trajectories, x (t,t0,x 0), from initial positions, x0, at time t0. For fixed integration times, | t-t0|, we numerically differentiate the flow map, given by Ft0^t(x0) = x(t, t0, x0), and then compute the deformation gradient tensor field ?^tt0(x0) = [ ?Ft0^t(x0) ]^T [ ?Ft0^t(x0) ]. The DLE field is then found as DLEt0^t(x0) = ( ?max ( ?t0^t(x0) ) )/ (2| t-t0| ). Two dimensional gradient climbing is then used to find points on the locally maximizing, LCS surfaces of the field, DLEt0^t(x0). To determine whether these surfaces truly repel (attract) near by fluid particles, the hyperbolicity criterion is applied (Mathur et al., Phys. Rev. Lett., vol 98, pp 144502, 2007). In particular we compute normal strain rates, , to locate repelling surfaces ( t>>t0:and: >0) and attracting surfaces ( t<<0) within the boundary layer.

Wilson, Zachary; Tutkun, Murat; Bayoan Cal, Raul

2010-11-01

198

Bose-Einstein condensation in low dimensional layered structures  

NASA Astrophysics Data System (ADS)

Bose-Einstein condensation critical temperature, among other thermodynamic properties are reported for an ideal boson gas inside layered structures created by trapping potential of the Kronig-Penney type. We start with a big box where we introduce the Kronig-Penney potential in three directions to get a honey comb of cubes of side a size and walls of variable penetrability (P=mV0ab/^2), with bosons instead of bees. We are able to reduce the dimensions of the cubes to simulate bosons inside quantum dots. The critical temperature, starting from that of an ideal boson gas inside the big box, decreases as the small cube wall impenetrability increases arriving to a tiny but different from zero when the penetrability is zero (P-->?). We also calculate the internal energy and the specific heat, and compare them to the ones obtained for the case of the same Kronig-Penney potential in one direction (simulating layers), and two directions (nanotubes).

Salas, Patricia; Solis, M. A.

2008-03-01

199

Optimum designs for multi-layered film structures based on the knowledge on residual stresses  

Microsoft Academic Search

Residual stresses are inevitably generated within the multi-layered film structures due to the mismatches of material properties between the adjacent layers. Using the force and moment equilibrium conditions and beam bending theory, the residual stresses in each layer can be predicted and expressed as sigmai(z) = Ei[?' + K(z + delta)], where Ei is the elastic modulus of the layer,

X. C. Zhang; B. S. Xu; H. D. Wang; Y. X. Wu

2007-01-01

200

Structure of three-dimensional turbulent boundary layers  

NASA Astrophysics Data System (ADS)

The changes that occur in the Reynolds-stress-producing motion when a cross-stream pressure gradient is applied to an initially two-dimensional turbulent flow are discussed. Two examples are used: (1) a temporal simulation of a channel flow with crossflow applied by a spanwise pressure gradient for t is greater than 0; and (2) a spatial simulation of the boundary layer on an infinite swept wing. Evidence examined to date suggests that the structural changes in the two cases are similar, but the mechanisms may be significantly different, even if effects peculiar to the viscous wall region are ignored. The results from (2) are provisional, based on too short a time series for accurate statistical averages to be obtained. We treat turbulence 'statistics' (solutions of the Navier-Stokes equations in three space dimensions and time) in the same way as experiments: both have limitations of accuracy but both are acceptable representations of real fluid flows.

Bradshaw, P.; Sendstad, O.

1990-12-01

201

Structure function scaling in a Re? = 250 turbulent mixing layer  

NASA Astrophysics Data System (ADS)

A highly resolved Direct Numerical Simulation of a spatially developing turbulent mixing layer is presented. In the fully developed region, the flow achieves a turbulent Reynolds number Re? = 250, high enough for a clear separation between large and dissipative scales, so for the presence of an inertial range. Structure functions have been calculated in the self-similar region using velocity time series and Taylor's frozen turbulence hypothesis. The Extended Self-Similarity (ESS) concept has been employed to evaluate relative scaling exponents. A wide range of scales with scaling exponents and intermittency levels equal to homogeneous isotropic turbulence has been identified. Moreover an additional scaling range exists for larger scales; it is characterized by smaller exponents, similar to the values reported in the literature for flows with strong shear.

Attili, Antonio; Bisetti, Fabrizio

2011-12-01

202

On the Origin of Irregular Structure in Saturn's Rings  

Microsoft Academic Search

We suggest that the irregular structure in Saturn's B ring arises from the formation of shear-free ring particle assemblies of up to ~100 km in radial extent. The characteristic scale of the irregular structure is set by the competition between tidal forces and the yield stress of these assemblies; the required tensile strength of ~105 dyn cm-2 is consistent with

Scott Tremaine

2003-01-01

203

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.

204

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

205

The Youngest Stars: , Circumstellar Structure, Binarity and Origin of Jets  

NASA Astrophysics Data System (ADS)

We propose to obtain broadband 2.2 Mum images of the compact cavities illuminated by Herbig-Haro energy sources, and to obtain narrowband H_2 images to study how the HH jets originate at their sources. The sources that drive HH jets are among the youngest stars known, with ages of less than 1-2 * 10^5 yrs. These extremely young stars are deeply embedded, and therefore we will study them indirectly via their associated infrared reflection nebulae. It is not clear if these nebulae outline massive flaring disks, or are holes punched by the jets, or are cavities resulting from the envelope collapse process. The proposed NICMOS images of a statistically significant source sample will be used to determine characteristic features of the cavities at the highest achievable resolution so as to compare with model predictions. In order to interpret such images we need to know the location of the embedded source relative to the infrared reflection nebula far better than IRAS positions allow, so a key element here is that we have detected all the sources with the VLA, and therefore know their positions to a fraction of an arcsecond. The NICMOS images will also help reveal if some of the sources are binaries, as would be statistically expected. Finding such extremely young binaries is a first step towards understanding the origin of binaries and their role in outflow evolution. Finally, comparing the broadband continuum images with the narrowband H_2 images allows us to study the jet origin region at hitherto unprecedented resolution.

Reipurth, Bo

1997-12-01

206

Nanoparticles of layered compounds with hollow cage structures (inorganic fullerene-like structures)  

SciTech Connect

Using the paradigm of carbon fullerenes, it is shown that nanoparticles of inorganic compounds with a layered structure, like MoS{sub 2}, are unstable against bending and form hollow closed clusters, designated inorganic fullerene-like structures (IF). The analogy can be extended to similar nanostructures, like nanotubes (NT), nested fullerenes, fullerenes with negative curvature (Schwartzites), etc. Various synthetic routes are described to obtain isolated phases of IF. Pentagons and heptagons are expected to play a primodal role in the folding of these nanostructures but no direct evidence for their presence or their detailed structure exits so far. Depending on the structure of the unit cell of the layered compound, apexes of a different topology, like triangles or rectangles, are believed to be stable elements in IF. Applications of such nanoparticles as solid lubricants in mixtures with lubricating fluids are described.

Tenne, R.; Homyonfer, M.; Feldman, Y. [Weizmann Inst., Rehovot (Israel). Dept. of Materials and Interfaces

1998-11-01

207

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

Microsoft Academic Search

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

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

1981-01-01

208

Origin of chert layers associated with some Middle Ordovician K-bentonite beds from the southern Appalachians and the eastern mid-continent  

Microsoft Academic Search

Chert layers associated with the Middle Ordovician Deicke, Millibrig, and V-7 K-bentonite beds have been examined in thin-section to determine their origin. Textural evidence indicate that the chert layers are inorganic in origin. Complex diagenetic features include abundant chalcedony veinlets, replacement textures, and preservation of primary CO[sub 3] cements. The model the authors propose for the formation of these chert

M. P. S. Krekeler; D. E. McVey; W. D. Huff

1994-01-01

209

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

210

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

NASA Astrophysics Data System (ADS)

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

Hanley, Jacob; Adlakha, Erin

2013-04-01

211

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

212

50 GB Read Only Memory Disc with Dual Layer Structure  

NASA Astrophysics Data System (ADS)

We developed a 50 GB dual layer read only memory (ROM) disc made by electron beam recorder (EBR) recording. The practical recording velocity was realized by control of the recording pulse and the adjustment of the post exposure bake (PEB) condition of the chemically amplified resist. An applicable replication process of dual layer ROM disc to production was realized. The recording condition was optimized for each layer. A sufficient jitter value was obtained from each layer.

Tsukuda, Masahiko; Ito, Eiichi; Tomiyama, Morio; Abe, Shinya; Furumiya, Shigeru; Ohno, Eiji

2003-02-01

213

Impact of vertical transport processes on the tropospheric ozone layering above Europe. Part I: Study of air mass origin using multivariate analysis, clustering and trajectories  

Microsoft Academic Search

A new method is proposed to classify ozone-rich layers observed in tropospheric profiles in terms of their origin using multivariate analysis. We combine principal component and discriminant analyses to quantify the respective ability of 21 measured physical parameters to describe the layers. Agglomerative hierarchical clustering shows the existence of clusters of air masses with specific physical characteristics. Quadratic discriminant analysis

Augustin Colette; Gérard Ancellet; François Borchi

2005-01-01

214

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

215

Near-Origin Structure of the Hooke's Atoms  

NASA Astrophysics Data System (ADS)

The Hooke's atoms with two or more than two electrons give rise to an interesting quantum mechanical model with valuable practical applications. In this work, we study the electronic properties near the origin of the harmonic potential. It is seen that the spherically averaged density, ?¯, exhibits an interesting character — it has only even order terms in its small r expansion. The spherical average of the Hartree potential, v¯H, and the spherical average of the Kohn—Sham exchange-correlation potential, v¯xc, are also shown to have the same property — all odd order terms in their expansions vanish. Furthermore, the analysis and results extend also to the case of two-dimensional models. While only models interacting via. the Coulomb potential are primarily considered in the article, the results also extend to models interacting via. other potentials (viz. Van der Waals potential).

Wang, Xue-Mei

2012-12-01

216

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

217

Structure and properties of titanium oxide layers deposited by reactive plasma activated electron beam evaporation  

Microsoft Academic Search

Titanium oxide layers were deposited by reactive electron beam evaporation with and without additional plasma activation by spotless arc discharge. The influence of substrate temperature and plasma activation on structure and properties of TiO2 layers are presented. The layers were deposited with very high deposition rates between 40 and 70 nm\\/s.XRD investigations have revealed that structure of all layers deposited

T. Modes; B. Scheffel; Chr. Metzner; O. Zywitzki; E. Reinhold

2005-01-01

218

The structure of periglacial layers in the uplands of Rhineland-Palatinate (West Germany)  

NASA Astrophysics Data System (ADS)

The poster presents several examples taken from Taunus, Hunsrück and Westerwald Mts. (Rhenish Slate Massif), the Palatinate Forest (Bunter Sandstone) and the Donnersberg monolith (porphyry). Extended research activities during the last years were carried on to specify the well known differentiation of periglacial slope deposits into three layers: Basic layer, medium layer and main layer on the top. At several places the medium layer is missing but, at a few places the basic layer and where it occurs, also the medium layer can be divided in two or more sublayers. The typical sediment of the medium layer and the main layer is fine silt, originating from periglacial loess deposits. Typically, the medium layer is more silty than the main layer. Exclusively involved in the main layer is Laacher Bims tephra of different content. Several problems are under discussion, such as: The different ages of the basal and medium layers at various places and the existence of a top layer (Oberlage). Another problem is the distinction between the main layer and Holocene colluvia.

Stolz, Christian; Grunert, Jörg

2010-05-01

219

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.

220

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

221

Structure and Origin of the Columbia Hills, Gusev Crater, Mars  

NASA Astrophysics Data System (ADS)

The Mars Exploration Rover Spirit has yielded profound insights into features at millimeter to decimeter scales. However, the origin of the Columbia Hills has remained enigmatic given the traverse across one peak [1]. We present a geologic history of the Hills consistent with their morphology, bedding attitudes, and stratigraphy. The Columbia Hills form a triangle 4.2 by 2.3 km, are bounded by linear to slightly concave margins, lie near the center of Gusev Crater, and have peaks rising to 90 m. Bedding dips away from a NNE-SSW axis cutting the Tennessee Valley. Husband Hill dips (15-32°) are steeper than local topography ( 8-10°) and those on West Spur are conformable with greater scatter in strike and shallower dips (7-15°). Husband Hill is cored by volcaniclastic rocks and impact breccias altered to various extents (Wishstone, Watchtower and Descartes classes), ringed by ultramafic volcaniclastic rocks and sulfate-cemented sands (Algonquin and Peace classes), ringed by localized impact breccias and volcaniclastic deposits (West Spur and Home Plate) [2]. The Columbia Hills likely formed by (1) Uplift of the Gusev Crater central peak, raising the Hills to 3 km above the crater floor, assuming the Hills are deeply-rooted and subsequently buried. Uplift by overlapping crater rims is inconsistent with bedding attitudes, but may have modified the margins of the Hills. (2) Draping by impact and volcaniclastic rocks and sands with localized alteration and cementation. Fragile rocks (Peace) and in situ soils (Paso Robles) would not have survived Gusev Crater formation. (3) Mass wasting of the Tennessee Valley removed tens of meters from the peak of the Hills, exposing older units in the core, (4) Plains (Adirondack) basalts surrounded and embayed the Hills, and (5) Small impacts redistributed rocks. [1] Rice J.W. (2004) Fall AGU, #P23B-03. [2] Squyres S.W. et al. (2006) JGR 111, E02S11.

McCoy, Timothy; Sims, M.; Crumpler, L. S.; Cohen, B. A.; Blaney, D. L.; Schmidt, M. E.; Treguier, E.; d'Uston, C.; Rice, J. W.; Tornabene, L. L.; Squyres, S. W.; Arvidson, R. E.; Haldemann, A.

2007-10-01

222

Molecular analysis of neocortical layer structure in the ferret.  

PubMed

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, however, is unknown. To assess the conservation of layer markers more broadly, we isolated orthologs for 15 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 layers 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. PMID:20575059

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

2010-08-15

223

Multifractal Thermal Structure in the Western Philippine Sea Upper Layer  

NASA Astrophysics Data System (ADS)

Upper layer (above 140 m depth) temperature in the western Philippine Sea near Taiwan was sampled using a coastal monitoring buoy (CMB) with attached 15 thermistors during July 28 - August 7, 2005. The data were collected every 10 minutes at 1, 3, 5, 10, 15, and 20 m using the CMB sensors, and every 15 seconds at 15 different depths between 25 m and 140 m in order to observe turbulent thermal structure. Internal waves and solitons were also identified using the empirical orthogonal function analysis. Without the internal waves and solitons, the power spectra, structure functions, and singular measures (representing the intermittency) of temperature field satisfy the power law with multi-scale characteristics at all depths. Without the internal waves and solitons (turbulence-dominated type), the temperature fluctuation has maximum values at the surface, decreases with depth to mid-depths (60-65 m deep), and then increases with depth to 140 m deep. Such depth dependent (decreasing then increasing) pattern preserves during the internal wave propagation during 1000-1500 GMT July 29, 2005. However, this was altered during the internal soliton propagation to a pattern that increases with depth from the surface to 60 m deep, decreases with depth from 60 m deep to 100 m deep, and increases again with depth from 100 m to 140 m deep. The temperature fluctuation enhances with the internal wave and soliton propagation. Between the two, the internal solitons bring larger fluctuations. Three types of thermal variability are identified: IW-turbulence, IS-turbulence, and turbulence-dominated. The power spectra of temperature at all the depths have multi-scale characteristics. For the IW-turbulence type and turbulence-dominated type, the spectral exponent is in the range of (1, 2) and thus the temperature field is nonstationary with stationary increments. For the IS-turbulence type, the spectrum is quite different and the spectral exponent is less than 1 for the low wavenumber domain. The structure function satisfies the power law with multifractal characteristics for the IW-turbulence type and turbulence-dominated type, but not for the IS- turbulence type. The internal waves increase the power of the structure function especially for high moments. The internal solitons destroy the multifractal characteristics of the structure function. The power law is broken approximately at the lag of 8 min, which is nearly half period of the IS (with frequency of 4 CPH). The internal waves do not change the basic characteristics of the multifractal structure. However, the internal solitons change the power exponent of the power spectra drastically especially in the low wave number domain; break down the power law of the structure function; and increase the intermittency parameter. The physical mechanisms causing these different effects are also presented.

Chu, P. C.; Hsieh, C.

2009-05-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

225

Structural origin of circularly polarized iridescence in jeweled beetles.  

PubMed

The iridescent metallic green beetle, Chrysina gloriosa, which selectively reflects left circularly polarized light, possesses an exoskeleton decorated by hexagonal cells (approximately 10 microm) that coexist with pentagons and heptagons. The fraction of hexagons decreases with an increase in curvature. In bright field microscopy, each cell contains a bright yellow core, placed in a greenish cell with yellowish border, but the core disappears in dark field. With use of confocal microscopy, we observe that these cells consist of nearly concentric nested arcs that lie on the surface of a shallow cone. We infer that the patterns are structurally and optically analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal. These textures provide the basis for the morphogenesis as well as key insights for emulating the intricate optical response of the exoskeleton of scarab beetles. PMID:19628862

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

2009-07-24

226

Molluscan shell proteins: primary structure, origin, and evolution.  

PubMed

In the last few years, the field of molluscan biomineralization has known a tremendous mutation, regarding fundamental concepts on biomineralization regulation as well as regarding the methods of investigation. The most recent advances deal more particularly with the structure of shell biominerals at nanoscale and the identification of an increasing number of shell matrix protein components. Although the matrix is quantitatively a minor constituent in the shell of mollusks (less than 5% w/w), it is, however, the major component that controls different aspects of the shell formation processes: synthesis of transient amorphous minerals and evolution to crystalline phases, choice of the calcium carbonate polymorph (calcite vs aragonite), organization of crystallites in complex shell textures (microstructures). Until recently, the classical paradigm in molluscan shell biomineralization was to consider that the control of shell synthesis was performed primarily by two antagonistic mechanisms: crystal nucleation and growth inhibition. New concepts and emerging models try now to translate a more complex reality, which is remarkably illustrated by the wide variety of shell proteins, characterized since the mid-1990s, and described in this chapter. These proteins cover a broad spectrum of pI, from very acidic to very basic. The primary structure of a number of them is composed of different modules, suggesting that these proteins are multifunctional. Some of them exhibit enzymatic activities. Others may be involved in cell signaling. The oldness of shell proteins is discussed, in relation with the Cambrian appearance of the mollusks as a mineralizing phylum and with the Phanerozoic evolution of this group. Nowadays, the extracellular calcifying shell matrix appears as a whole integrated system, which regulates protein-mineral and protein-protein interactions as well as feedback interactions between the biominerals and the calcifying epithelium that synthesized them. Consequently, the molluscan shell matrix may be a source of bioactive molecules that would offer interesting perspectives in biomaterials and biomedical fields. PMID:17950376

Marin, Frédéric; Luquet, Gilles; Marie, Benjamin; Medakovic, Davorin

2008-01-01

227

Les Investigation of Coherent Structures in Boundary Layers and Wakes. Volume I: Investigation of Coherent Structure in an Attached Shear Layer.  

National Technical Information Service (NTIS)

Purpose of the present investigation was to assess the feasibility of simulating and studying coherent structures in turbulent shear layers, making use of Large Eddy Simulations (LES). The current investigation has been performed across a rather wide rang...

C. Benocci R. Giammanco

2002-01-01

228

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

229

Structured Analysis of a Layered Manufacturing Decision Support System  

Microsoft Academic Search

Layer manufacturing technologies produce 3D physical parts directly from CAD solid models. Since 3D Systems Inc. introduced the first rapid prototyping system (stereolithography, SL) in 1988, many system manufacturers have developed layer manufacturing technologies and techniques, with SL, selective laser sintering (SLS), fused deposition modelling (FDM), and 3D printing (3DP) being the most common. At start, these technologies were initially

M. M. Ghazy; K. W. Dalgarno

230

Effects of coastal forcing on turbulence and boundary- layer structure  

Microsoft Academic Search

Coastal mountains of significant elevation impose constraints for the surrounding flow. The aim of this study is to describe the modifications of the marine atmospheric boundary layer that occur offshore of the west coast of the United States. Aircraft measurements, up to 1000 km off the coast from two experiments, are used. This boundary layer is capped by a subsidence

Linda Maria Viktoria Strom

1999-01-01

231

Communication: Origin of the contributions to DNA structure in phages  

NASA Astrophysics Data System (ADS)

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

2013-02-01

232

Adhesion of a Metal Layer to a Substrate and Related Structures.  

National Technical Information Service (NTIS)

Methods and resulting structures are described in which a metal layer is adhered to a surface of a substrate. The methods involve applying a sacrificial acidic organic layer to the surface of the substrate prior to depositing the metal layer onto the subs...

J. J. Watkins Y. Zong

2005-01-01

233

Adhesion of a Metal Layer to a Substrate and Related Structures.  

National Technical Information Service (NTIS)

Methods and resulting structures are described in which a metal layer is adhered to a surface of a substrate. The methods involve applying a sacrificial acidic organic layer to the surface of the substrate prior to depositing the metal layer onto the subs...

J. J. Watkins Y. Zong

2006-01-01

234

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

235

Origin and evolution of protein fold designs inferred from phylogenomic analysis of CATH domain structures in proteomes.  

PubMed

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. PMID:23555236

Bukhari, Syed Abbas; Caetano-Anollés, Gustavo

2013-03-28

236

Composite magnetic recording structure having a metamagnetic layer with field induced transition to ferromagnetic state  

US Patent & Trademark Office Database

A magnetic recording medium having a composite magnetic recording structure comprising the combination of a hard magnetic layer and a metamagnetic layer that possesses a field induced metamagnetic transition characteristic at ambient operating temperature. Under an applied external magnetic field, the metamagnetic layer transitions from an antiferromagnetic state to a ferromagnetic state, and the magnetic field induces magnetization of the metamagnetic layer. The hard magnetic recording layer is magnetically exchange coupled to the magnetized metamagnetic layer. This results in the softening of the coercivity of the overall magnetic recording structure and reduction of the required switching field during data recording. Upon removal of the applied magnetic field, the metamagnetic layer experiences transition back to an antiferromagnetic state and the coercivity of the hard magnetic layer is restored. This restoration allows the written bit to be stored at a high thermostability ratio and thus, preventing magnetization thermal decay of the data bit.

2008-12-16

237

layer  

Microsoft Academic Search

This paper analyzes the propagation of a cohesive crack through a reinforcement layer and gives a solution that can be used for any specimen and loading condition. Here it faces the case of a reinforced prismatic beam loaded at three points. Reinforcement is represented by means of a free-slip bar bridging the cracked section, anchored at both sides of the

Gonzalo Ruiz

238

Structural changes to epitaxial (0001) holmium layers during hydrogen loading  

NASA Astrophysics Data System (ADS)

HoHy exhibits dramatic changes in both structural and optical properties as y is varied from zero to three by hydrogen loading. This work reports on the effect of such loading upon epitaxial single-crystal Ho films grown by molecular beam epitaxy on (110) Nbparallel (112-bar 0) Al2 O3 substrates. Upon loading, the film undergoes a structural transition from hcp metal (icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> -phase, H in solid solution) to the fcc dihydride (icons/Journals/Common/beta" ALT="beta" ALIGN="TOP"/> -phase). There is a further transformation between the dihydride phase and the hexagonal trihydride (icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/> -phase). Three films of HoHy , where, nominally, y = 0,2,3, were studied by XRD, AFM, UFM, SEM and TEM. Triangular networks of features of width ~300 nm and height ~20-30 nm that align with the [01-bar 1], [1-bar 01] and [11-bar 0] directions of the dihydride sample are seen on the surface of both the dihydride and the trihydride samples, but have a much greater density on the surface of the latter. Such features are not present on the as-grown metal layer. In situ controlled-environment transmission electron microscopy (CETEM) studied the effects of hydrogen loading within the dihydride phase, in cross sectional geometry. During loading, slip within the dihydride phase was observed. The hypothesis that the triangular features are due to the precipitation of the di- and trihydride compounds, with expanded lattices, on the slip planes within the icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> - or icons/Journals/Common/beta" ALT="beta" ALIGN="TOP"/> -phase host crystal is discussed.

Grier, E. J.; Kolosov, O.; Petford-Long, A. K.; Ward, R. C. C.; Wells, M. R.; Hjörvarsson, B.

2000-04-01

239

Optimum designs for multi-layered film structures based on the knowledge on residual stresses  

Microsoft Academic Search

Residual stresses are inevitably generated within the multi-layered film structures due to the mismatches of material properties between the adjacent layers. Using the force and moment equilibrium conditions and beam bending theory, the residual stresses in each layer can be predicted and expressed as ?i(z)=Ei[??+K(z+?)], where Ei is the elastic modulus of the layer, ?? the strain due to the

X. C. Zhang; B. S. Xu; H. D. Wang; Y. X. Wu

2007-01-01

240

Simulation of switching noise in multi-layer structures using generalized transmission line equation method  

Microsoft Academic Search

This paper discusses the use of the generalized transmission line equations (GTLE) for the simulation of switching noise distribution in multi-layered packaging structures. After a brief discussion on the formulation and its application to a simple dual trace transmission line, two-layered plane and two-layered plane with four drivers and traces, the method has been applied to a complicated fourteen layer

Lixi Wan; Madhavan Swaminathan; R. R. Turnmala

2002-01-01

241

The crystal and magnetic structures of the organic–inorganic layer compound phenylphosphonato-Mn(II)-hydrate: A synchrotron X-ray and neutron powder diffraction study  

Microsoft Academic Search

The crystal and magnetic structures of the organic–inorganic layer compound phenylphosphonato-Mn(II)-hydrate, C6D5PO3Mn?D2O, have been studied by powder diffraction using synchrotron X-rays and neutrons. The crystal structure is resolved by both techniques including orientational disorder of the phenyl-groups. Temperature-dependent neutron diffraction peaks below 12 K are identified as magnetic in origin; their indices show that the magnetic structure is closely similar

Simon G. Carling; Gail E. Fanucci; Daniel R. Talham; Dirk Visser; Peter Day

2006-01-01

242

Coherent Structure of a Turbulent Boundary Layer in a Convected Reference Frame.  

National Technical Information Service (NTIS)

This is an interim annual report for an ongoing research program studying coherent structure in turbulent boundary layers. The design and development of a water channel facility for use in flow visualization studies of coherent turbulent boundary structur...

C. R. Smith S. L. Huston J. J. Brown

1977-01-01

243

Resonant transparency of a two-layer plasma structure in a magnetic field.  

PubMed

Transparency of a two-layer plasma structure in an external steady-state magnetic field, perpendicular to the wave incidence plane, is studied. The case of the p-polarized electromagnetic wave is considered. The electromagnetic wave is obliquely incident on the two-layer structure and is evanescent in both layers. The conditions for total transparency of the two-layer structure are found. The parametric dependencies of the transparency coefficient on the plasma slab widths, the magnitude of the wave number component, as well on the magnetic field magnitude are obtained. PMID:21867322

Ivko, S; Smolyakov, A; Denysenko, I; Azarenkov, N A

2011-07-25

244

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

SciTech Connect

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

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

2011-11-15

245

Plasmon amplification by strong coupling in a layered structure  

NASA Astrophysics Data System (ADS)

A layered waveguide supported hybrid modes between a surface plasmon and a confined guided mode is studied. The condition for the strong coupling regime are described. The Green function is obtained and decomposed along the continuous and discrete spectrum.

Castanié, Aurore; Guizal, Brahim; Antezza, M.; Felbacq, Didier

2013-09-01

246

Structure of the Laminar Ablating Air-Teflon Boundary Layer.  

National Technical Information Service (NTIS)

Radiation profiles in an ablating flat plate air-teflon laminar boundary layer were studied both experimentally and theoretically. The experiments were conducted in a one atmosphere, 3000 - 6000K, subsonic free stream produced by an arc jet. Spatially res...

R. A. Greenberg N. H. Kemp K. L. Wray

1968-01-01

247

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

248

Structural and magnetic stabilization of edges of layered zigzag graphene nanoribbons  

Microsoft Academic Search

We report first-principle study on structural and magnetic stabilization of bilayer and trilayer zigzag graphene nanoribbons with two different edge alignments. Our results showed that (I) structural deformation only happens in layered ZGNRs with a- alignment edges; the ground state of the bi-layered ZGNR with a- alignment edges is nonmagnetic; while that of the tri-layered ZGNR with a-alignment edges is

Jun-Qiang Lu; Yanna Zhang; Xiao-Li Lu; Yongjin Jiang; Botao Teng

2010-01-01

249

Two structural intensity prediction methods in plates excited by turbulent boundary layers  

Microsoft Academic Search

Structural intensity (S-I) fields may be used to identify energy flow paths through a vibrating structure, as well as energy source and sink regions. Boundary layer excitation of structures occurs in numerous aerospace and underwater applications. This study describes two methods of predicting S-I fields in structures excited by turbulent boundary layers. The first prediction method combines well known multiple-input\\/multiple-output

Michael J. Daley; Stephen A. Hambric

2002-01-01

250

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

251

Decidability of the Theory of the Totally Unbounded omega-Layered Structure  

Microsoft Academic Search

In this paper, we address the decision problem for a sys- tem of monadic second-order logic interpreted over an!- layered temporal structure devoid of both a finest layer and a coarsest one (we call such a structure totally unbounded). We propose an automaton-theoretic method that solves the problem in two steps: first, we reduce the considered prob- lem to the

Angelo Montanari; Gabriele Puppis

2004-01-01

252

Measuring the atomic-scale structure of a Helmholtz `double layer'  

Microsoft Academic Search

We propose a powerful new technique to measure the structure of the Helmholtz `double layer' formed in an aqueous electrolyte in contact with a metal electrode. The critical innovation is to couple a structural probe which is specific to the environment of a particular atom species with a `tag' layer of metal atoms electrodeposited in underpotential conditions on an unlike-metal

T. M. Hayes; L. B. Lurio; J. Pant; L. Wang; T. E. Furtak

1997-01-01

253

THE THEORETICAL AND APPLICATION STUDY ON A DOUBLE LAYER MICROPERFORATED SOUND ABSORPTION STRUCTURE  

Microsoft Academic Search

The calculation of resonance and anti-resonance frequencies of a double layer microperforated sound absorption structure is studied, and simplified analytical formulae which will be very useful for the design and analysis of wide bandwidth double layer microperforated sound absorption structures are derived. The results obtained provide an effective method for the design of wide bandwidth microperforated panel silencers.

Z. M. Zhang; X. T. Gu

1998-01-01

254

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)  

NASA Astrophysics Data System (ADS)

A detailed mineralogical study is presented of the matrix of mudrocks sampled from spot coring at three key locations along the San Andreas Fault Observatory at depth (SAFOD) drill hole. The characteristics of authigenic illite-smectite (I-S) and chlorite-smectite (C-S) mixed-layer mineral clays indicate a deep diagenetic origin. A randomly ordered I-S mineral with ca. 20-25% smectite layers is one of the dominant authigenic clay species across the San Andreas Fault zone (sampled at 3,066 and 3,436 m measured depths/MD), whereas an authigenic illite with ca. 2-5% smectite layers is the dominant phase beneath the fault (sampled at 3,992 m MD). The most smectite-rich mixed-layered assemblage with the highest water content occurs in the actively deforming creep zone at ca. 3,300-3,353 m (true vertical depth of ca. 2.7 km), with I-S (70:30) and C-S (50:50). The matrix of all mudrock samples show extensive quartz and feldspar (both plagioclase and K-feldspar) dissolution associated with the crystallization of pore-filling clay minerals. However, the effect of rock deformation in the matrix appears only minor, with weak flattening fabrics defined largely by kinked and fractured mica grains. Adopting available kinetic models for the crystallization of I-S in burial sedimentary environments and the current borehole depths and thermal structure, the conditions and timing of I-S growth can be evaluated. Assuming a typical K+ concentration of 100-200 ppm for sedimentary brines, a present-day geothermal gradient of 35°C/km and a borehole temperature of ca. 112°C for the sampled depths, most of the I-S minerals can be predicted to have formed over the last 4-11 Ma and are probably still in equilibrium with circulating fluids. The exception to this simple burial pattern is the occurrence of the mixed layered phases with higher smectite content than predicted by the burial model. These minerals, which characterize the actively creeping section of the fault and local thin film clay coating on polished brittle slip surfaces, can be explained by the influence of either cooler fluids circulating along this segment of the fault or the flow of K+-depleted brines.

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

2009-02-01

255

Bureaucratic imperatives and policy outcomes: The origins of World Bank structural adjustment lending  

Microsoft Academic Search

Although the impact of World Bank and IMF structural adjustment loans on developing country borrowers has been the subject of considerable analysis, our understanding of the origins of these operations remains poor. This article rectifies this deficiency by providing an account of the genesis of the Bank's program of structural adjustment. Drawing on documents from the Bank's archives as well

Patrick Sharma

2012-01-01

256

Origin of the phase transition in IrTe2: structural modulation and local bonding instability  

SciTech Connect

We used X-ray/neutron diffraction to determine the low temperature (LT) structure of IrTe2. A structural modulation was observed with a wavevector of k =(1/5, 0, 1/5) below Ts285 K, accompanied by a structural transition from a trigonal to a triclinic lattice. We also performed the first principles calculations for high temperature (HT) and LT structures, which elucidate the nature of the phase transition and the LT structure. A local bonding instability associated with the Te 5p states is likely the origin of the structural phase transition in IrTe2.

Cao, Huibo [ORNL; Chakoumakos, Bryan C [ORNL; Yan, Jiaqiang [ORNL; Zhou, Haidong [ORNL; Custelcean, Radu [ORNL; Mandrus, D. [University of Tennessee (UTK) and Oak Ridge National Laboratory (ORNL); McGuire, Michael A [ORNL; Singh, David J [ORNL; Chen, Xin [ORNL; Yang, Hui [University of Tennessee, Knoxville (UTK)

2013-01-01

257

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

SciTech Connect

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

258

Fabrication of hierarchical hybrid structures using bio-enabled layer-by-layer self-assembly.  

PubMed

Development of versatile and flexible assembly systems for fabrication of functional hybrid nanomaterials with well-defined hierarchical and spatial organization is of a significant importance in practical nanobiotechnology applications. Here we demonstrate a bio-enabled self-assembly technique for fabrication of multi-layered protein and nanometallic assemblies utilizing a modular gold-binding (AuBP1) fusion tag. To accomplish the bottom-up assembly we first genetically fused the AuBP1 peptide sequence to the C'-terminus of maltose-binding protein (MBP) using two different linkers to produce MBP-AuBP1 hetero-functional constructs. Using various spectroscopic techniques, surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR), we verified the exceptional binding and self-assembly characteristics of AuBP1 peptide. The AuBP1 peptide tag can direct the organization of recombinant MBP protein on various gold surfaces through an efficient control of the organic-inorganic interface at the molecular level. Furthermore using a combination of soft-lithography, self-assembly techniques and advanced AuBP1 peptide tag technology, we produced spatially and hierarchically controlled protein multi-layered assemblies on gold nanoparticle arrays with high molecular packing density and pattering efficiency in simple, reproducible steps. This model system offers layer-by-layer assembly capability based on specific AuBP1 peptide tag and constitutes novel biological routes for biofabrication of various protein arrays, plasmon-active nanometallic assemblies and devices with controlled organization, packing density and architecture. PMID:22170333

Hnilova, Marketa; Karaca, Banu Taktak; Park, James; Jia, Carol; Wilson, Brandon R; Sarikaya, Mehmet; Tamerler, Candan

2011-12-26

259

Origin of ferroelectric polarization in spiral magnetic structure of MnWO4  

NASA Astrophysics Data System (ADS)

Magnetism and the origin of ferroelectricity in the multiferroic MnWO4 are studied using ab initio electronic-structure calculations, correctly reproducing the magnetic ground state. The calculated ferroelectric polarization is in good agreement with experiments. Our results reveal that spin-orbit interaction is necessary and sufficient to explain the observed ferroelectric polarization, establishing an entirely electronic origin of ferroelectricity in MnWO4 . The origin of spin-orbit interaction in this compound with a nominally d5L=0 orbitally quenched state is elucidated by analyzing results of x-ray absorption spectroscopy.

Shanavas, K. V.; Choudhury, Debraj; Dasgupta, I.; Sharma, Surinder M.; Sarma, D. D.

2010-06-01

260

Structural origin of perpendicular magnetic anisotropy in Ni-W thin films  

NASA Astrophysics Data System (ADS)

The magnetic properties and microstructure of electrodeposited Ni-W thin films (0-11.7at% W in composition) were studied. The film structures were divided into three regions: an FCC nanocrystalline phase (0-2at% W), a transition region from FCC nanocrystalline to amorphous phase (2-7at% W), and an amorphous phase (>7at% W). In the transition region, (4-5at% W) films with perpendicular magnetic anisotropy (PMA) were found. The saturation magnetization, magnetic anisotropy field, perpendicular magnetic anisotropy and perpendicular coercivity for a typical Ni-W film (4.5at% W) were 420kA/m, 451kA/m, 230kJ/m and 113kA/m, respectively. The microstructure of Ni-W films with PMA is composed of isolated columnar crystalline grains (27-36nm) with the FCC phase surrounded by the Ni-W amorphous phase. The appearance of the interface between the magnetic core of Ni crystalline grains and the Ni-W non-magnetic boundary layer seems to be the driving mechanism for the appearance of PMA. The origin of PMA in Ni-W films is mainly attributed to the magnetoelastic anisotropy associated with in-plane internal stress and positive magnetostriction. The secondary source of PMA is believed to be the magnetocrystalline anisotropy of <111> columnar grains and its shape magnetic anisotropy. It is concluded that Ni-W electrodeposited films (4-5at% W) may be applicable for perpendicular magnetic recording media.

Sulitanu, N.

2001-05-01

261

The critical layer number of epitaxially grown Cu and Ni films with strained structure  

Microsoft Academic Search

The thickness dependent structural transition of epitaxially grown thin films from a tetragonal structure to the corresponding bulk structure is thermodynamically considered. It is found that there exists a competition between elastic energy of the tetragonal structure and film–substrate interface energy. Equilibrium between these energies is present at a critical layer number nc. The predictions for nc are in agreement

J. C. Li; W. Liu; Q. Jiang

2005-01-01

262

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

NASA Astrophysics Data System (ADS)

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

Wang, Li; Lu, Xi-Yun

2011-03-01

263

Estimation of insulation layer conductance in MNOS structure  

Microsoft Academic Search

A method for estimating the conductance of each insulation layer of MNOS devices is described. In this method, the conductance values can be independently estimated using the frequency dependence of the capacitance and conductance versus gate voltage characteristics. The frequency dependence in the accumulation region can be explained by an equivalent circuit which considers the substrate resistance and the conductance

Yoshihiro Takahashi; Kazunori Ohnishi

1993-01-01

264

On the Asymmetric Structure of the Tropical Cyclone Outflow Layer.  

National Technical Information Service (NTIS)

ATS-III satellite data and conventional aerological data are used to construct detailed wind analyses of the outflow layer for four hurricanes and one tropical storm. Harmonic analysis of these data, and of the data for a mean Atlantic hurricane and a mea...

P. G. Black R. A. Anthes

1971-01-01

265

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

266

Magma mixing and the origin of layered cumulates: evidence from the Oman ophiolite (Bahla and Wuqbah massifs)  

NASA Astrophysics Data System (ADS)

Ultramafic cumulates, essentially wehrlitic, are an important component of the crustal section of the Oman ophiolite. They cannot be related to the most common gabbroic cumulates through simple fractional crystallization processes in anhydrous conditions. They occur frequently as intrusions post-dating the crystallization of the gabbros and, in such cases, are interpreted as "late intrusive" attributed to subduction or obduction related processes. Many authors have generalized this conclusion to all kinds of ultramafic cumulates, whatever their mode of occurrence, including those that are interlayered with the gabbros and that are supposed to be injected as sills between pre-existing gabbroic layers. In order to better constrain the origin of the ultramafic cumulates interlayered with gabbros, we have conducted a field, petrographic, and geochemical study of the lower crustal section of Bahla and Wuqbah massifs (westernmost part of the Oman ophiolite) where gabbroic and ultramafic cumulates occur in roughly equal proportions. We have performed detailed geochemical profiles with the SEM and with the LA-ICP-MS across the boundaries between gabbroic and ultramafic layers. In terms of modal composition, individual layers are quite homogeneous and the boundaries between layers are clear-cut down to the microscopic scale. In spite of the sharp nature of the lithological boundaries, the chemical composition in both major and trace elements defines progressive evolutions as they are approached. The thickness of these "cryptic transition zones" varies considerably according to the element and to the mineral considered. It ranges typically from a few mm to a few cm. By the same way, the shape of the geochemical profiles is curved (close to hyperbolic) for some elements (mostly major elements), but is almost linear for many other elements, especially some trace elements. These characteristics are inconsistent with solid-state intra-crystalline diffusion but call for diffusion in a liquid phase and/or for magma mixing. Mixing between either the parent melts of each cumulate suite or between intercumulus liquids percolating in the crystal mush may be envisioned. Whatever the details of the processes, our observations show that the crystallization of interlayered ultramafic and gabbroic cumulates are contemporary events. Both gabbroic and ultramafic rocks from these massifs are characterized by early crystallization of orthopyroxene, implying that their parent melts were significantly richer in SiO2 than MORB. Moreover, for a same degree of differentiation, their plagioclases are richer in An% and their Cpx are poorer in Al2O3 than MOR gabbros. These characteristics are reminiscent of boninitic-andesitic parent melts. However, Bahla and Wuqbah ultramafic and gabbroic cumulates do not present the extreme depletion in HFSE typical of supra subduction zone boninites. Their trace element signature implies that a MORB source was actually an important ingredient of their parent melts. The simplest way to account for these observations is to invoke mixing between N-MORB extracted from an asthenospheric upwelling and silica enriched melts produced by hydrated re-melting of the lithosphere in response to the deep penetration of hydrothermal fluids. Magma mixing may account for the coexistence of clear-cut mineralogical boundaries and of progressive geochemical transitions, the change in the nature of the cotectic assemblage occurring suddenly after a certain amount of mixing. We conclude that interlayered ultramafic and gabbroic cumulates characteristic of some cumulate sections in the Oman ophiolite bear witness of complex hybridization processes related to interaction between anhydrous and hydrous magmas.

Abily, Bénédicte; Ceuleneer, Georges; Gregoire, Michel; Benoit, Mathieu

2010-05-01

267

Fundamentals of layered nanoparticle covered pyramidal structures formed on nickel during femtosecond laser surface interactions  

NASA Astrophysics Data System (ADS)

The formation of nanoparticle covered pyramidal structures using femtosecond laser pulses with a fluence near the ablation threshold is reported for the first time. These unique structures form through a combination of preferential ablation of flat regions around the pyramids and redeposition of nanoparticles created during the ablation process. The structures are demonstrated on nickel and stainless steel 316. When produced by rastering Gaussian pulses across the sample, layers of nanoparticles join together by sintering to form unique layered shells.

Zuhlke, Craig A.; Anderson, Troy P.; Alexander, Dennis R.

2013-10-01

268

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

269

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

270

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

271

Theoretical Consideration of High-Sensitive Biosensor Using Shear Horizontal Acoustic Waves in Layered Structures  

NASA Astrophysics Data System (ADS)

Realization of high sensitive biosensors is required. As an acoustic wave based biosensor can detect immunoreactions, it is expected for applying the biosensor. In this paper, a shear horizontal (SH) acoustic wave in layered structures, namely Love wave, is discussed on the basis of numerical calculations. For generating the Love wave, a 36YX-LiTaO3 is chosen as a piezoelectric substrate. Also, SiO2, polymer, and gold are chosen as guiding layer materials. First, phase velocity and propagation loss are calculated as a function of layer thickness. Then, an additional mass layer is loaded on the guiding layer for simulating bio-layer deposition. The simulated results indicate that high sensitive biosensor is realized by using gold guiding layer.

Kondoh, Jun

272

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

PubMed Central

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. Images

MacLeod, F A; Guiot, S R; Costerton, J W

1990-01-01

273

Hierarchical structure formation in layered superconducting systems with multi-scale inter-vortex interactions.  

PubMed

We demonstrate the formation of hierarchical structures in two-dimensional systems with multiple length scales in the inter-particle interaction. These include states such as clusters of clusters, concentric rings, clusters inside a ring, and stripes in a cluster. We propose to realize such systems in vortex matter (where a vortex is mapped onto a particle with multi-scale interactions) in layered superconducting systems with varying inter-layer thicknesses and different layer materials. PMID:24061107

Varney, Christopher N; Sellin, Karl A H; Wang, Qing-Ze; Fangohr, Hans; Babaev, Egor

2013-09-24

274

Model for evolution of periodic layered structure in the SiO 2\\/Mg system  

Microsoft Academic Search

A mathematical model for the growth of MgO\\/Mg2Si periodic layered structure (PLS) is presented based on Fick's diffusion law and conservation of matter. The model explains the temporal evolution of the width of periodic layers at different temperatures, for layers distant enough from the Mg source. It is demonstrated that the difference in thickness of a pair of any two

I. Gutman; L. Klinger; I. Gotman; M. Shapiro

2009-01-01

275

Structure and properties of crystalline titanium oxide layers deposited by reactive pulse magnetron sputtering  

Microsoft Academic Search

Crystalline TiO2 layers could be deposited on glass and silicon substrates by reactive pulse magnetron sputtering without additional substrate heating using a long-term stable process with high deposition rate. XRD investigations have revealed that the variation of pulse mode between unipolar and bipolar allows the deposition of layers with anatase and rutile structures, respectively. The SEM micrographs of anatase layers

O. Zywitzki; T. Modes; H. Sahm; P. Frach; K. Goedicke; D. Glöß

2004-01-01

276

X-ray CT image segmentation: automatic sandwich structure layer separation using reduced dimension Hough transformation  

Microsoft Academic Search

Many structures in aerospace, semiconductor and precision engineering are multi-layer in nature. Examples include Low Temperature Co-Fire Ceramic (LTCC), PCBA, stacked IC, Through-Silicon-Via and composite materials for aircraft wings. Segmentation of each internal layer in any orientation is essential for layer alignment as well as delamination, disbond and warpage analysis. In this paper we propose a RDHT (Reduced Dimension Hough

J. Xu; T. Liu; R. Kakarala; X. M. Yin

2009-01-01

277

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

278

Hierarchical structure formation in layered superconducting systems with multi-scale inter-vortex interactions  

NASA Astrophysics Data System (ADS)

We demonstrate the formation of hierarchical structures in two-dimensional systems with multiple length scales in the inter-particle interaction. These include states such as clusters of clusters, concentric rings, clusters inside a ring, and stripes in a cluster. We propose to realize such systems in vortex matter (where a vortex is mapped onto a particle with multi-scale interactions) in layered superconducting systems with varying inter-layer thicknesses and different layer materials.

Varney, Christopher N.; Sellin, Karl A. H.; Wang, Qing-Ze; Fangohr, Hans; Babaev, Egor

2013-10-01

279

Positively and negatively large Goos-Hänchen lateral displacements from a single negative layered structure.  

PubMed

We study the electromagnetic beam reflection from layered structures that include the so-called ?-negative and the ?-negative materials, also called single negative materials. We predict that such structures can demonstrate a giant lateral Goos-Hänchen shift of the resonant excitation of surface waves at the interface between the conventional and single negative materials, as well as due to the excitation of leaky modes in the layered structures. Then we replace the conventional layer with a left-handed layer (a material with both ?<0 and ?<0). We show that the Goos-Hänchen shift can be positive and negative depending on the type of this layer (conventional or LH material), which can support TE or TM surface waves. PMID:23033017

Talebzadeh, Robabeh; Namdar, Abdolrahman

2012-09-20

280

The continuous wavelet transform used for the disclose of transitional boundary-layer structures  

NASA Astrophysics Data System (ADS)

Previous experiments on boundary layer transition have revealed that a laminar boundary layer subjected to high levels of free stream turbulence (FST) is dominated by low frequency oscillations with large amplitudes of streamwise velocity component. In this presentation we outline a wavelet procedure to reveal structures in transitional boundary-layers, subjected to a high FST level. The continuous wavelet transform is used to extract information in the time-frequency domain, and this information discloses the existence of temporally and spatially localized low-frequency structures, which indicates the presence of longitudinal structures in the flow. The results found are in good agreement with previous experimental observations on boundary layer transition at moderate and high FST levels. In particular, the wavelet method has been verified on artificial flat plate boundary layer disturbances.

Stein, Carl-Fredrik; Bergh, Jöran; Bakchinov, Andrey; Löfdahl, Lennart

1998-11-01

281

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

282

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 2n 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

2013-04-01

283

Effects of interfacial layer structures on crystal structural properties of ZnO films  

SciTech Connect

Single crystalline ZnO films were grown on Cr compound buffer layers on (0001) Al{sub 2}O{sub 3} substrates by plasma assisted molecular beam epitaxy. In terms of lattice misfit reduction between ZnO and substrate, the CrN and Cr{sub 2}O{sub 3}/CrN buffers are investigated. The structural and optical qualities of ZnO films suggest the feasibility of Cr compound buffers for high-quality ZnO films growth on (0001) Al{sub 2}O{sub 3} substrates. Moreover, the effects of interfacial structures on selective growth of different polar ZnO films are investigated. Zn-polar ZnO films are grown on the rocksalt CrN buffer and the formation of rhombohedral Cr{sub 2}O{sub 3} results in the growth of O-polar films. The possible mechanism of polarity conversion is proposed. By employing the simple patterning and regrowth procedures, a periodical polarity converted structure in lateral is fabricated. The periodical change of the polarity is clearly confirmed by the polarity sensitive piezo response microscope images and the opposite hysteretic characteristic of the piezo response curves, which are strict evidences for the validity of the polarity controlling method as well as the successful fabrication of the periodical polarity controlled ZnO structure.

Park, J. S.; Minegishi, T.; Lee, S. H.; Im, I. H.; Park, S. H.; Hanada, T.; Goto, T.; Cho, M. W.; Yao, T.; Hong, S. K.; Chang, J. H. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); School of Nanoscience and Technology, Chungnam National University, Daejeon 305-764 (Korea, Republic of); Major of Nano Semiconductor, Korea Maritime University, Youngdo-ku, Pusan 606-791 (Korea, Republic of)

2008-01-15

284

Structure characterization of adsorbed poly (ethylene oxide) layers on solid substrate  

NASA Astrophysics Data System (ADS)

In recent years, irreversibly adsorbed polymer layers formed on solid substrates have been received considerable interest since they can modify various properties of polymeric materials confined at the nanometer scale. In this thesis, I investigate the annealing time dependence of the poly (ethylene oxide) (PEO) adsorbed layer formed at the substrate interface. The detailed structures of the PEO adsorbed layer prepared were characterized by ellipsometry, atomic force microscopy (AFM), and x-ray reflectivity techniques. The total thickness of the PEO adsorbed layer is generally around 3 nm. Different from PS, the annealing time dependence of the PEO adsorbed layer simple show minor increase when annealing 2hr, then stay the same. ScCO2 and toluene rinse cycle can further reduce the thickness of PS adsorbed layer. For PEO, only toluene rinse is enough to obtain the final adsorbed layer. We discuss the model of the structure of the adsorbed layer, and estimate that there is no crystal structure formed in the PEO adsorbed layer.

Chen, Fen

285

Layered hydroxide nickel benzoates: hydrothermal synthesis, structure characterization, and exfoliation reaction.  

PubMed

This paper introduces two hydrothermally synthesized layered hydroxide nickel benzoates with the layered basic metal salt structures of basal spacings of 1.71 and 1.48 nm and their exfoliation reactions. These inorganic-organic hybrid layered compounds were characterized with XRD, FTIR, TG-DTA, SEM, SAED, and TEM. The 1.71 nm layered phase is a low temperature stable phase and has lattice parameters of a=0.7017(1)nm, b=0.3495(0)nm, c=1.763(7)nm, ?=?=90°, and ?=101.6(6)°. The 1.48 nm layered phase is a high temperature stable phase and has lattice parameters of a=0.6277(2)nm, b=0.3678(2)nm, c=1.514(1)nm, ?=?=90°, and ?=97.35(0)°. The benzoate anions in the interlayer space are coordinated to Ni(II) with unidentate and bidentate binding modes in the 1.71 nm layered phase, and with only bidentate binding mode in the 1.48 nm layered phase. These hybrid layered phases were exfoliated into their nanosheets in organic solvents, which gave a new category of inorganic-organic hybrid nanosheets. The exfoliation reactions are dependent on the structures and chemical compositions of the hybrid layered phases, as well as the molecule structures of the organic solvents used in the exfoliation. PMID:22897953

Xu, Yaohua; Kominami, Keichi; Ishikawa, Yoshie; Feng, Qi

2012-07-24

286

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

287

Influence of microshot peening on surface layer characteristics of structural steel  

Microsoft Academic Search

The influence of microshot peening on the surface layer characteristics of the structural steel was investigated. Shot peening is one of the surface treatments and it is a mechanical surface treatment widely used in automotive industry to enhance fatigue life and surface layer characteristics of mechanical parts. In this process, the surface is collided repeatedly with small spherical media called

Y. Harada; K. Fukaura; S. Haga

2007-01-01

288

An observational study of the structure of the nocturnal boundary layer  

Microsoft Academic Search

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

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

1979-01-01

289

Spin-transfer phenomena in layered magnetic structures: Physical phenomena and materials aspects  

Microsoft Academic Search

During the past 20 years, layered structures consisting of ferromagnetic layers and spacers of various material classes with a thickness of only a few nanometers have revealed a variety of exciting and potentially very useful phenomena not present in bulk material. Representing distinct manifestations of spin-transfer processes, these phenomena may be categorized into interlayer exchange coupling (IEC), giant magnetoresistance (GMR),

P. Grünberg; D. E. Bürgler; H. Dassow; A. D. Rata; C. M. Schneider

2007-01-01

290

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

291

Electromagnetic characteristics features of 1D periodic structures including layers with negative index of refraction  

Microsoft Academic Search

Propagation of plane electromagnetic waves in 1D periodic structures including the layers with both positive and negative refraction indexes is considered within the frame of the long wavelength approximation. The dependencies of the media effective characteristics (dielectric, magnetic, gyrotropic, electrooptic) on the corresponding properties and the relative thicknesses of the layers are investigated. These dependencies can have a resonant form

E. G. Starodubtsev

2005-01-01

292

Theory of thermal wave interference induced by laser action on a normally cut layered structure  

Microsoft Academic Search

The exact analytical solution for the thermal wave multiple reflections and interference in a normally cut layered structure is derived. The analysis predicts the existence of the new characteristic spatial scale in the considered phenomena—the length of thermal wave synchronism, which depends on the modulation frequency of the laser-induced heat flux and the thermal diffusivities of the alternating layers. Both

A. Kalinovskii; V. Gusev

1995-01-01

293

Theory of thermal wave interference induced by laser action on a normally cut layered structure  

Microsoft Academic Search

The exact analytical solution for the thermal wave multiple reflections and interference in a normally cut layered structure is derived. The analysis predicts the existence of the new characteristic spatial scale in the considered phenomena—the length of thermal wave synchronism, which depends on the modulation frequency of the laser-induced head flux and the thermal diffusivities of the alternating layers. Both

A. Kalinovskii; V. Gusev

1995-01-01

294

Temperature dependence of magnetoresistance in magnetic tunnel junctions with different free layer structures  

NASA Astrophysics Data System (ADS)

The temperature and bias voltage dependence of magnetoresistance and the resistance of two types of magnetic tunnel junction (MTJ) samples were studied. These two types of MTJ samples have different free layer structures, while having the same pinned layer structures and with the same material for free and reference layers. The layer structure for type 1 MTJs is 80Ru-8CoFeB-15Al2O3-50CoFeB-9Ru-54FeCo-350CrMnPt (in angstroms). The layer structure for type 2 MTJs is 80Ru-40CoFeB-50RuTa-40CoFeB-15Al2O3-50CoFeB-9Ru-54FeCo-350CrMnPt . The tunneling magnetoresistance (TMR) ratio [(RAP-RP)/RP] is about 26% and 69% at room temperature for type 1 and type 2 MTJs, respectively. A TMR as high as 107% has been observed for type 2 MTJ samples at 13K . By analysis of the voltage and temperature dependence of the resistance and magnetoresistance in these MTJs, we discuss the effects of the magnetic behavior of the free layers, barrier qualities, and barrier interfaces. The results clearly indicate that the micromagnetization orientation at the interface between the free layer and the barrier layer is one of the important factors that determines the TMR ratio.

Yuan, L.; Liou, S. H.; Wang, Dexin

2006-04-01

295

The structural origins of the stability of palladium-nickel-phosphorus bulk metallic glasses  

Microsoft Academic Search

The fundamental origins of the stability of the (Pd-Ni)80P 20 bulk metallic glasses (BMGs), a prototype for a whole class of BMG formers, were explored. While much of the properties of their BMGs have been characterized, their glass-stability have not been explained in terms of the atomic and electronic structure. The local structure around all three constituent atoms was obtained,

Faisal Muhammad Alamgir

2003-01-01

296

Effect of the original structure on softening of cold-worked steel during heating  

Microsoft Academic Search

1.The carbon content affects softening during subsequent heating of cold-worked steels. With increasing carbon concentrations the hardening effect is retained after heating to higher temperatures.2.During subsequent annealing, cold-worked steels retain the hardening effect up to ~ 10% deformation, which is due to polygonization and formation of a cellular structure.3.Softening of cold-worked steels depends on the original structure of the pearlite.

V. E. Pil'guk; M. S. Podgaiskii; V. I. Ikonnikov; R. P. Malova; V. A. Kharchenko

1979-01-01

297

Structural vs electronic origin of renormalized band widths in TTF-TCNQ: An angular dependent NEXAFS study  

SciTech Connect

We have performed angle-dependent near-edge x-ray absorption fine structure measurements in the Auger electron yield mode on the correlated quasi-one-dimensional organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) in order to determine the orientation of the molecules in the topmost surface layer. We find that the tilt angles of the molecules with respect to the one-dimensional axis are essentially the same as in the bulk. Thus, we can rule out surface relaxation as the origin of the renormalized band widths which were inferred from the analysis of photoemission data within the one-dimensional Hubbard model. Thereby, recent theoretical results are corroborated which invoke long-range Coulomb repulsion as alternative explanation to understand the spectral dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.

Sing, M.; Meyer, J.; Glawion, S.; Claessen, R. [Experimentelle Physik IV, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Hoinkis, M. [Experimentelle Physik IV, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Experimentalphysik II, Universitaet Augsburg, D-86135 Augsburg (Germany); Blaha, P. [Institute of Materials Chemistry, Vienna University of Technology, A-1060 Vienna (Austria); Gavrila, G. [Institut fuer Physik, Technische Universitaet Chemnitz, D-09107 Chemnitz (Germany); Jacobsen, C. S. [Department of Physics, Technical University of Denmark, DK-2800 Lyngby (Denmark)

2007-12-15

298

Origin, taxonomy and population structure of the allopolyploid peat moss Sphagnum majus  

Microsoft Academic Search

The polyploid peat mossSphagnum majus shows considerable phenotypic plasticity along ecological gradients in mires. It is considered taxonomically heterogeneous, and two subspecies have been described. Isozyme analyses were carried out on populations ofS. majus from Central Norway and from eastern coast of North America in order to assess the origin, taxonomy and population structure of this species. High levels of

S. M. Såstad; K. I. Flatberg; L. Hanssen

2000-01-01

299

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

300

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

301

Caseins of various origins and biologically active casein peptides and oligosaccharides: Structural and physiological aspects  

Microsoft Academic Search

The first part of the present review is focused on structural aspects concerning the so far studied casein fractions of various origins: they are compared to the four classical major bovine caseins (ssl-, ss2- ß- and ?). The calcium-sensitive casein fractions are always phosphorylated whereas ?-caseins are glycosylated. The study of the casein genes showed that the calcium-sensitive caseins diverged

Anne-Marie Fiat; Pierre Jollès

1989-01-01

302

The origin and structure of wooded permafrost mounds at the arctic treeline in eastern Canada  

Microsoft Academic Search

Background: Permafrost mounds covered by open or dense forests (or krummholz – stunted trees) correspond to the category of wooded palsas and wooded peat plateaux extensively distributed in wetlands of North America. Very few data exist on the origin and development of wooded palsas, in particular their inception during the Holocene and the structure and dynamics of their forest\\/krummholz cover

S. Cyr; S. Payette

2010-01-01

303

Hydrodynamical calculations towards steady state structures in boundary layers in accretion disks. 1: 1-D polytropic boundary layers  

NASA Astrophysics Data System (ADS)

We apply the one dimensional version of the multi-dimensional robust solver developed by Hujeirat & Rannacher (1994) to follow the viscous evolution of various models of polytropic boundary layers in accretion disks around a non-magnetic white dwarf. In this paper, we present the results of 13 different time-dependent hydrodynamical calculations. The results indicate that (1) no steady structure of the flow in the boundary layer is encountered. The solutions show that a quasi-standing shock is always present for very small alpha and high stellar rotation, (2) the rate of accreted angular momentum into the central object is much less than the corresponding Keplerian one, (3) the radial extent of the boundary layer (delta RBL) is much smaller than the vertical one as well as the radial extent of classical viscous boundary layers, (4) delta RBL increases with the rotational speed of the star, (5) an instability of the shock position is detected as well as quasi-periodic oscillations which are viscosity-dependent, (6) the polytropic equation of state with gamma = 2 yields unstable and chaotic behavior of the flow in the disk region.

Hujeirat, A.

1995-03-01

304

Wavevector filtering through single-layer and bilayer graphene with magnetic barrier structures  

Microsoft Academic Search

We show that the angular range of the transmission through magnetic barrier structures can be efficiently controlled in single-layer and bilayer graphenes and this renders the structure’s efficient wavevector filters. As the number of magnetic barriers increases, this range shrinks, the gaps in the transmission versus energy become wider, and the conductance oscillates with the Fermi energy.

M. Ramezani Masir; P. Vasilopoulos; F. M. Peeters

2008-01-01

305

Stability Effects on Coherent structures in the Unstable Atmospheric Surface Layer  

Microsoft Academic Search

Atmospheric stability effects on the characteristics of coherent structures such as ramp structures, ejections and sweeps, size, vorticity, and statistics associated with fluxes in the atmospheric surface layer are examined, with a specific focus on the dissimilarity between turbulent transport of momentum and scalar fluxes (e.g., water vapor flux and heat flux). It is found that coherent structures under close

D. Li; E. Bou-Zeid

2010-01-01

306

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

307

Electronic band structure and bonding in transition metal layered dichalcogenides by atomic orbital methods  

Microsoft Academic Search

It is shown that the main features of the electronic structure of transition metal layered dichalcogenides can be calculated in a simple ab initio atomic orbital framework. Examples from Groups IV, V and VI of the transition series are considered.

D. W. Bullett

1978-01-01

308

Numerical Simulation of Unsteady Three-Dimensional Turbulent Structures in Boundary Layer Flows.  

National Technical Information Service (NTIS)

The capabilities for numerical simulations of the dynamical effects of the underlying structures occurring in turbulent boundary layers have been developed. A mathematically operational model of hairpin vortex, which closely resembles the experimentally o...

N. S. Lui S. J. Shamroth H. McDonald

1985-01-01

309

Boundary layer structure over areas of heterogeneous heat fluxes  

SciTech Connect

In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moreover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discusses some initial findings from those campaigns.

Doran, J.C. (Pacific Northwest Lab., Richland, WA (United States)); Barnes, F.J. (Los Alamos National Lab., NM (United States)); Coulter, R.L. (Argonne National Lab., IL (United States)); Crawford, T.L. (National Oceanic and Atmospheric Administration, Oak Ridge, TN (United States). Air Resources Lab. Atmospheric Turbulence and Diffusion Div.)

1993-01-01

310

Boundary layer structure over areas of heterogeneous heat fluxes  

SciTech Connect

In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations within the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moveover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discuses some initial findings from those campaigns.

Doran, J.C. (Pacific Northwest Lab., Richland, WA (United States)); Barnes, F.J. (Los Alamos National Lab., NM (United States)); Coulter, R.L. (Argonne National Lab., IL (United States)); Crawford, T.L. (National Oceanic and Atmospheric Administration, Oak Ridge, TN (United States). Air Resources Lab. Atmospheric Turbulence and Diffusion Div.)

1993-01-01

311

Boundary layer structure over areas of heterogeneous heat fluxes  

SciTech Connect

In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moreover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations? To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discusses some initial findings from those campaigns.

Doran, J.C. [Pacific Northwest Lab., Richland, WA (United States); Barnes, F.J. [Los Alamos National Lab., NM (United States); Coulter, R.L. [Argonne National Lab., IL (United States); Crawford, T.L. [National Oceanic and Atmospheric Administration, Oak Ridge, TN (United States). Air Resources Lab. Atmospheric Turbulence and Diffusion Div.

1993-01-01

312

Boundary layer structure over areas of heterogeneous heat fluxes  

SciTech Connect

In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations within the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moveover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations? To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discuses some initial findings from those campaigns.

Doran, J.C. [Pacific Northwest Lab., Richland, WA (United States); Barnes, F.J. [Los Alamos National Lab., NM (United States); Coulter, R.L. [Argonne National Lab., IL (United States); Crawford, T.L. [National Oceanic and Atmospheric Administration, Oak Ridge, TN (United States). Air Resources Lab. Atmospheric Turbulence and Diffusion Div.

1993-04-01

313

Seasonal evolution of upper-ocean horizontal structure and the remnant mixed layer  

NASA Astrophysics Data System (ADS)

We discuss the seasonal evolution of upper-ocean thermohaline structure at small horizontal scales. The upper 350 m of a 1000 km long section in the subtropical North Pacific was observed in winter, spring, and summer with 3-14 km horizontal resolution. Four vertical regions had distinct density and salinity structure: the mixed layer, remnant mixed layer, high-stratification layer, and permanent thermocline. The remnant mixed layer consists of water from the winter mixed layer left over after restratification. The remnant mixed layer was most similar to the mixed layer in winter and spring, and most similar to the high-stratification layer below in summer. The high-stratification layer had elevated stratification that varied seasonally. The permanent thermocline varied little seasonally and was horizontally and vertically uniform in comparison. In all seasons, density ratios showed that mixed-layer ?-S differences tended to compensate in density with the strongest tendency toward compensation in winter. Density ratios were temperature dominated in the remnant mixed layer consistent with salt-fingering. Salinity anomalies were largest at the surface and decayed with depth in all seasons. Spectra of isopycnal depth and ?-S anomalies along isopycnals are compared between the three seasons and four vertical layers. Isopycnal depth variance at 30-46 km wavelengths decreased from winter to spring to summer by a factor of 2-10 in stratified regions. By treating salinity anomalies as a tracer, the effective isopycnal diffusivity in the remnant mixed layer was estimated to be 1.4 m2 s-1 over 30-46 km wavelengths.

Cole, Sylvia T.; Rudnick, Daniel L.; Colosi, John A.

2010-04-01

314

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

PubMed Central

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

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

1983-01-01

315

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

316

Dipole-exchange theory of hybrid electromagnetic-spin waves in layered film structures  

Microsoft Academic Search

A theory has been developed for normal mode electromagnetic-spin waves propagating in metal–dielectric-ferromagnetic-dielectric-metal film structures. Dipole and exchange interactions are taken into account. An arbitrary direction of the internal bias magnetic field is assumed. A dispersion equation for hybrid waves is derived. Effects of varying the dielectric constants of the dielectric layers and the geometry of the layered structure are

V. E. Demidov; B. A. Kalinikos; P. Edenhofer

2002-01-01

317

Dipole-exchange theory of hybrid electromagnetic-spin waves in layered film structures  

Microsoft Academic Search

A theory has been developed for normal mode electromagnetic-spin waves propagating in metal-dielectric-ferromagnetic-dielectric-metal film structures. Dipole and exchange interactions are taken into account. An arbitrary direction of the internal bias magnetic field is assumed. A dispersion equation for hybrid waves is derived. Effects of varying the dielectric constants of the dielectric layers and the geometry of the layered structure are

V. E. Demidov; B. A. Kalinikos; P. Edenhofer

2002-01-01

318

Structure and properties of an iron based self-lubricant wear-resistant gradient layer  

Microsoft Academic Search

The structure and properties of an iron based self-lubricant wear-resistant gradient layer, with spherical graphites as well as alloy-carbides on a surface of cast steel, were studied. From the outside in, the composition, structure and properties of the self-lubricant wear-resistant gradient layer with a thickness of 5–6 mm take on a gradient distribution and transform gradually into that of a

Yisan Wang; Wen Huang

1998-01-01

319

Surface polaritons and transmission in multi-layer structures containing anisotropic left-handed materials  

Microsoft Academic Search

We study the surface polaritons and optical transmission in multi-layer structures containing alternate anisotropic left-handed\\u000a materials and isotropic right-handed materials. By means of the transfer matrix method, the dispersive relations of the surface\\u000a polaritons are derived. In contrast to the single left-handed slab, the multi-layer structure is capable of supporting more\\u000a surface polaritons due to the existence of more interfaces

L. Gao; Y. Huang; C. Tang

2007-01-01

320

Layer structured graphite oxide as a novel adsorbent for humic acid removal from aqueous solution  

Microsoft Academic Search

Layer structured graphite oxide (GO) was prepared from graphite using the Hummers–Offeman method, characterised using N2 adsorption, XRD, XPS, SEM(TEM), and FT-IR, and tested for humic acid (HA) adsorption in aqueous solution. XRD, XPS, and FT-IR measurements indicate the formation of layered structure with strong functional groups of GO. It is also found that the GO exhibits strong and much

Tri Hartono; Shaobin Wang; Qing Ma; Zhonghua Zhu

2009-01-01

321

The origin of endothelial cells in novel structures, Bonghan ducts and Bonghan corpuscles determined using immunofluorescence.  

PubMed

Bonghan ducts (BHDs), and their associated Bonghan corpuscles (BHCs), which are novel threadlike structures, were recently observed in rats and rabbits by using various methods. As further support for the putative circulatory function of the novel threadlike structures (NTS), we investigated the presence and the origin of the endothelial cells within these structures. We immunostained the NTS with anti-CD146, an endothelial cell marker, and with anti-podoplanin, a lymphatic cell marker. Positive expression of CD146 in the BHDs was obtained, and the distribution of endothelial cells showed that the inner boundaries of the channels in the subducts branched from the BHDs and curled around, in a complicated manner, inside a BHCs. The negative expression of podoplanin implies that the endothelial cells in the BHDs are likely to be of vascular and not of lymphatic origin. PMID:20633491

Yi, Sun-Shin; Hwang, In-Koo; Kim, Min-Su; Soh, Kwang-Sup; Yoon, Yeo-Sung

2009-09-01

322

Plasmon resonance absorption in layered structures of silver with periodic corrugation  

SciTech Connect

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

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

1987-01-01

323

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

2013-04-01

324

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

325

Origin of chert layers associated with some Middle Ordovician K-bentonite beds from the southern Appalachians and the eastern mid-continent  

SciTech Connect

Chert layers associated with the Middle Ordovician Deicke, Millibrig, and V-7 K-bentonite beds have been examined in thin-section to determine their origin. Textural evidence indicate that the chert layers are inorganic in origin. Complex diagenetic features include abundant chalcedony veinlets, replacement textures, and preservation of primary CO[sub 3] cements. The model the authors propose for the formation of these chert layers incorporates both silica release associated with the devitrification of volcanic glass and silica precipitation from a migrating regional brine. Precipitation from a brine is the dominant mechanism of silicification based on stoichiometric calculations of silica release during illite/smectite (I/S) transformations, petrography of the chert layers, and work by previous authors. However, multiple generations of silica observed in the rock suggest that other contributing small scale sources of silica may also exist. Brine derived silica preferentially replaces low Mg calcite that has high surface area, such as micrite and fossil debris. Some dolomite rhombs preserved in the chert may have formed during primary sedimentary dolomitization yet textural comparisons indicate this is unlikely for most samples. Birdseye and brachiopod cements are typically well preserved in the cherts. Cherts that have been subjected to elevated burial temperatures (150--200 C) have significant amounts of authigenic clay minerals. Pyrite mineralization exhibits cross cutting relationships with chert and micrite. Clay and pyrite mineralization suggest the presence of significant porosity early in the history of formation of the chert layers.

Krekeler, M.P.S.; McVey, D.E.; Huff, W.D. (Univ. of Cincinnati, OH (United States). Dept. of Geology)

1994-03-01

326

Crystal structure of centrosymmetric 12-layer sodium-rich eudialyte  

SciTech Connect

The structure of a new representative of the eudialyte group with the formula (Na,Sr,K){sub 18}Ca{sub 6}Zr{sub 3}Fe[Si{sub 25}O{sub 72}](OH){sub 2}Cl . H{sub 2}O from the Lovozero massif (Kola Peninsula) was studied by X-ray diffraction. The trigonal unit-cell parameters are a = 14.226 A, c = 30.339 A, sp. gr. R3-barm; the R factor is 0.045 based on 990 reflections. This sample is of interest as a sodium-rich and iron-poor mineral having a rare centrosymmetric structure, in which the M(2) site is occupied predominantly by sodium atoms. The dependence of the formation of centrosymmetric and non-centrosymmetric structures on the composition of eudialyte-group minerals was analyzed.

Rozenberg, K. A.; Rastsvetaeva, R. K., E-mail: rast@ns.crys.ras.ru; Verin, I. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2009-05-15

327

Injection terahertz laser using the resonant inter-layer radiative transitions in double-graphene-layer structure  

NASA Astrophysics Data System (ADS)

We propose and substantiate the concept of terahertz (THz) laser enabled by the resonant electron radiative transitions between graphene layers (GLs) in double-GL structures. We estimate the THz gain for TM-mode exhibiting very low Drude absorption in GLs and show that the gain can exceed the losses in metal-metal waveguides at the low end of the THz range. The spectrum of the emitted photons can be tuned by the applied voltage. A weak temperature dependence of the THz gain promotes an effective operation at room temperature.

Ryzhii, V.; Dubinov, A. A.; Aleshkin, V. Ya.; Ryzhii, M.; Otsuji, T.

2013-10-01

328

Crystal Structure of the Simian Virus 40 Large T-Antigen Origin-Binding Domain  

SciTech Connect

The origins of replication of DNA tumor viruses have a highly conserved feature, namely, multiple binding sites for their respective initiator proteins arranged as inverted repeats. In the 1.45- Angstroms crystal structure of the simian virus 40 large T-antigen (T-ag) origin-binding domain (obd) reported herein, T-ag obd monomers form a left-handed spiral with an inner channel of 30 Angstroms having six monomers per turn. The inner surface of the spiral is positively charged and includes residues known to bind DNA. Residues implicated in hexamerization of full-length T-ag are located at the interface between adjacent T-ag obd monomers. These data provide a high-resolution model of the hexamer of origin-binding domains observed in electron microscopy studies and allow the obd's to be oriented relative to the hexamer of T-ag helicase domains to which they are connected.

Meinke,G.; Bullock, P.; Bohm, A.

2006-01-01

329

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

330

Optical characterization of the structure of SIPOS layers  

Microsoft Academic Search

Using IR spectroscopy, Rutherford back-scattering technique and optical microscopy the structure of SIPOS films produced by CVD method is investigated. The network of oxygen- doped silicon is shown to represent a mixture of Si-Oy-Si4-y complexes with 0 less than or equal to y less than or equal to 4 and micro-inclusions of strongly oxidized silicon. Contribution of these complexes is

I. P. Lisovskii; Vladimir G. Litovchenko; V. B. Lozinskii; E. V. Mischenko; Walter Fussel

1995-01-01

331

Structure and friction-reducing property of the sulfide layer produced by ion sulfuration  

SciTech Connect

Sulfide layers with a certain thickness were made on the surface of 1045 and 52100 steels by means of the low-temperature ion sulfuration technique. Metallography, scanning electron microscope (SEM) + energy-dispersive x-ray analysis (EDX), and x-ray diffraction (XRD) were adopted to analyze the structure of sulfide layers; the tribological properties of the layers lubricated by paraffin oil were also investigated on a reciprocating tester. The results showed that sulfide layer is porous, and its structure is mainly composed of FeS, FeS{sub 2}, and substrate phases. The sulfide layer possessed a remarkable friction-reducing effect; its friction coefficient was lower on average, by about 50%, than that of the surface without layer. With the increase of layer thickness, its friction coefficient was unchanged, and under low load conditions, its operational period was prolonged. Under the same experimental conditions, the operational period of sulfide layer on 52100 steel was longer than that on 1045 steel, and its friction coefficient was lower as well.

Ning, Z.; Da-Ming, Z.; Yan-Hua, W.; Jia-Jun, L.; Xiao-Dong, F.; Ming-Xi, G.

2000-04-01

332

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

333

Ion beam-based characterization of multicomponent oxide thin films and thin film layered structures  

SciTech Connect

Fabrication of thin film layered structures of multi-component materials such as high temperature superconductors, ferroelectric and electro-optic materials, and alloy semiconductors, and the development of hybrid materials requires understanding of film growth and interface properties. For High Temperature Superconductors, the superconducting coherence length is extremely short (5--15 [Angstrom]), and fabrication of reliable devices will require control of film properties at extremely sharp interfaces; it will be necessary to verify the integrity of thin layers and layered structure devices over thicknesses comparable to the atomic layer spacing. Analytical techniques which probe the first 1--2 atomic layers are therefore necessary for in-situ characterization of relevant thin film growth processes. However, most surface-analytical techniques are sensitive to a region within 10--40 [Angstrom] of the surface and are physically incompatible with thin film deposition and are typically restricted to ultra high vacuum conditions. A review of ion beam-based analytical methods for the characterization of thin film and multi-layered thin film structures incorporating layers of multicomponent oxides is presented. Particular attention will be paid to the use of time-of-flight techniques based on the use of 1- 15 key ion beams which show potential for use as nondestructive, real-time, in-situ surface diagnostics for the growth of multicomponent metal and metal oxide thin films.

Krauss, A.R.; Rangaswamy, M.; Lin, Yuping; Gruen, D.M. (Argonne National Lab., IL (United States)); Schultz, J.A. (Ionwerks, Inc., Houston, TX (United States)); Schmidt, H.K. (Schmidt Instruments, Inc., Houston, TX (United States)); Chang, R.P.H. (Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science)

1992-01-01

334

Ion beam-based characterization of multicomponent oxide thin films and thin film layered structures  

SciTech Connect

Fabrication of thin film layered structures of multi-component materials such as high temperature superconductors, ferroelectric and electro-optic materials, and alloy semiconductors, and the development of hybrid materials requires understanding of film growth and interface properties. For High Temperature Superconductors, the superconducting coherence length is extremely short (5--15 {Angstrom}), and fabrication of reliable devices will require control of film properties at extremely sharp interfaces; it will be necessary to verify the integrity of thin layers and layered structure devices over thicknesses comparable to the atomic layer spacing. Analytical techniques which probe the first 1--2 atomic layers are therefore necessary for in-situ characterization of relevant thin film growth processes. However, most surface-analytical techniques are sensitive to a region within 10--40 {Angstrom} of the surface and are physically incompatible with thin film deposition and are typically restricted to ultra high vacuum conditions. A review of ion beam-based analytical methods for the characterization of thin film and multi-layered thin film structures incorporating layers of multicomponent oxides is presented. Particular attention will be paid to the use of time-of-flight techniques based on the use of 1- 15 key ion beams which show potential for use as nondestructive, real-time, in-situ surface diagnostics for the growth of multicomponent metal and metal oxide thin films.

Krauss, A.R.; Rangaswamy, M.; Lin, Yuping; Gruen, D.M. [Argonne National Lab., IL (United States); Schultz, J.A. [Ionwerks, Inc., Houston, TX (United States); Schmidt, H.K. [Schmidt Instruments, Inc., Houston, TX (United States); Chang, R.P.H. [Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science

1992-11-01

335

Analysis of the possibility of the spin-orbit origin of surface state splitting in thin Mg(0001) layers on W(110) and Mo(110)  

Microsoft Academic Search

A set of magnesium films ranging in thickness from submonolayer to a few tens of atomic layers grown on single-crystal W(110)\\u000a has revealed film-thickness dependent splitting of states localized energywise close to the magnesium surface state. Literature\\u000a refers to several models describing the origin of this splitting; in one case, it is treated as substrate-induced spin-orbit\\u000a splitting, and in another,

A. M. Shikin; D. E. Marchenko; N. A. Vinogradov; G. V. Prudnikova; A. G. Rybkin; V. K. Adamchuk; O. Rader

2009-01-01

336

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

337

Structural investigations of a series of petrified woods of different origin  

NASA Astrophysics Data System (ADS)

Since the investigations on petrified wood performed so far have not proved the assumption that the ring structure is coupled to the changes in the crystalline form of silica, attention was paid to other possible reasons. Using small angle X-ray scattering methods we determined the Porod curves and pore size distributions for five different samples of petrified wood, of different origin. We observed clear porosity differences in different samples. In addition, the normal X-ray diffractometric measurements were carried out, which gave a totally uniform image of the crystallographic structure of all the samples. All of them were made of pure ?-quartz. The differentiation of rings in dark and bright zones should be put down to the changes in porosity rather than to other factors. The pores seem to be much more concentrated in those ring locations, which correspond to the original dark wood positions in living wood.

Kuczumow, A.; Pikus, S.; Un-Ro, C.; Sadowski, P.; Wajnberg, P.; Jurek, M.

2001-04-01

338

Computational methods in eddy current crack detection at fastener sites in multi-layer structures  

Microsoft Academic Search

Reliable detection of both surface and subsurface cracks around fastener sites continues to be a need for maintaining ageing aircraft structures. In this work, a comprehensive overview of both experimental and modelling work addressing eddy current crack detection around fastener holes in multi-layer structures is presented. This overview consists of a strategy for the application of computational methods along with

Jeremy S. Knopp; John C. Aldrin; Kumar V. Jata

2009-01-01

339

Wavevector filtering through single-layer and bilayer graphene with magnetic barrier structures  

Microsoft Academic Search

We show that the angular range of the transmission through magnetic barrier structures can be efficiently controlled in single-layer and bilayer graphenes and this renders the structure's efficient wavevector filters. As the number of magnetic barriers increases, this range shrinks, the gaps in the transmission versus energy become wider, and the conductance oscillates with the Fermi energy.

M. Ramezani Masir; P. Vasilopoulos; F. M. Peeters

2008-01-01

340

Layer type tungsten dichalcogenide compounds - Their preparation, structure, properties and uses  

Microsoft Academic Search

Tungsten dichalcogenides, which crystallize in layered structures, are applicable to catalysis, high temperature\\/pressure lubrication, and photoelectrochemical cell electrodes. They also exhibit superconducting behavior when intercalated with alkali or alkaline earth metals, and divalent rare earth metals. Attention is presently given to the preparation, crystal structure, and band models of these compounds. An attempt is also made to incorporate the physical,

S. K. Srivastava; B. N. Avasthi

1985-01-01

341

Long-time behavior of PML absorbing boundaries for layered periodic structures  

NASA Astrophysics Data System (ADS)

In this work we consider a special case of the Perfectly Matched Layer (PML) divergence which is observed by the simulation of the planar periodic structures such as photonic crystal slabs or antenna arrays. This divergence is caused by an excitation of long-living artefact evanescent waves in these structures by an incident external pulse. We study the application of the known remedies to this problem: increasing the distance between the structure and PML, employing the ? parameter, employing non-PML absorbers. We also suggest a new simple and effective solution, where the usual PML is backed by an additional absorbing layer.

Deinega, Alexei; Valuev, Ilya

2011-01-01

342

Quantum confinement in two dimensional layers of PbSe/ZnSe multiple quantum well structures  

NASA Astrophysics Data System (ADS)

The structural and optical properties of thermally evaporated PbSe/ZnSe multiple quantum well (MQW) structures as a function of the PbSe quantum well (QW) layer thickness in the range between 2.5 and 10 nm have been investigated. An ordered periodicity in the MQW structure was confirmed by transmission electron microscopy. The discrete linear resonances in the absorption spectra and the corresponding blue shift observed with decreasing well layer thickness unambiguously reflect the quantum confinement effect. The effective QW band gap is calculated from the infinite well approximation and compared to the experimentally observed value. The QW emission is identified and discussed.

Arivazhagan, V.; Manonmani Parvathi, M.; Rajesh, S.; Sæterli, Ragnhild; Holmestad, Randi

2013-06-01

343

Extrinsic origin of giant permittivity in hexagonal BaTiO3 single crystals: Contributions of interfacial layer and depletion layer  

Microsoft Academic Search

Three dielectric relaxations in hexagonal (h)-BaTiO3 single crystals exhibiting giant permittivity were detected in a frequency range of 100 Hz-3 GHz and analyzed by an equivalent circuit with three parallel RC elements. A best-fit result indicated that the three dielectric relaxations were the responses of bulk crystal with a capacitance of 1 pF, an interfacial layer with a capacitance of

Jianding Yu; Takehiko Ishikawa; Yasutomo Arai; Shinichi Yoda; Mitsuru Itoh; Yutaka Saita

2005-01-01

344

Structure and origin of insoluble and non-hydrolyzable, aliphatic organic matter in a forest soil  

Microsoft Academic Search

Insoluble, non-hydrolyzable, macromolecular organic matter was shown to occur in substantial amounts in the loamy, acid, forest soil found in Lacadée (South–west France). The chemical structure of resistant organic material isolated from the Lacadée soil was examined by a combination of spectroscopic (solid state 13C NMR, FTIR) and pyrolytic (Curie-point flash Py\\/GC\\/MS) methods. The origin of this non-hydrolyzable, aliphatic, material

Natacha Augris; Jerome Balesdent; Andre Mariotti; Sylvie Derenne; Claude Largeau

1998-01-01

345

Genetic Population Structure and Origin of Life History Types in Chinook Salmon in British Columbia, Canada  

Microsoft Academic Search

We used protein electrophoresis to examine genetic population structure and origin of life history types of chinook salmon Oncorhynchus tshawytscha in British Columbia, Canada. Among 31 allozyme loci resolved in 91 samples from 63 populations of chinook salmon in rivers and hatcheries throughout British Columbia, population heterozygosities averaged 0.084 (range 0.048–0.108) and were typical of values for populations in other

David J. Teel; George B. Milner; Gary A. Winans; W. Stewart Grant

2000-01-01

346

Identification of Persistent RNA-DNA Hybrid Structures within the Origin of Replication of Human Cytomegalovirus  

Microsoft Academic Search

Human cytomegalovirus (HCMV) lytic-phase DNA replication initiates at the cis-acting origin of replication, oriLyt. oriLyt is a structurally complex region containing repeat elements and transcription factor binding sites. We identified two site-specific alkali-labile regions within oriLyt which flank an alkali-resistant DNA segment. These alkali-sensitive regions were the result of the degradation of two RNA species embedded within oriLyt and covalently

MARK N. PRICHARD; SANJU JAIRATH; MARK E. T. PENFOLD; STEPHEN S. T. JEOR; MARLENE C. BOHLMAN; GREGORY S. PARI

347

Polar cap F layer patches: structure and dynamics  

SciTech Connect

Coordinated measurements of F-region plasma patches were conducted on February 3/4, 1984, from Thule and Sondrestrom, Greenland. Optical, ionsonde, amplitude scintillation, total electron content (TEC), and incoherent scatter radar measurements were combined to reveal several new aspects of the structure and transport of these localized regions of enhanced F region ionization. For the first time, these patches were directly tracked flowing in the antisunward direction over distances of 3000 km from the center of the polar cap to the poleward edge of the auroral oval. Quantative measurements of TEC show increases of 10-15 TEC units within the patches, above a background polar cap value of 5 TEC units. Amplitude scintillation measurements show the presence of ionospheric irregularities through the entire patch, with a weak indication of stronger scintillation on the trailing (or E x B unstable) edge.

Weber, E.J.; Klobuchar, J.A.; Buchau, J.; Carlson, H.C.; Livingston, R.C.

1986-11-01

348

The structure of nanoscale polaron correlations in the layered manganites  

NASA Astrophysics Data System (ADS)

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

Campbell, Branton

2002-03-01

349

New condensed cluster structure with triple metal layers: LaâINiâ and LaâICuâ. Synthesis, structure, and bonding  

Microsoft Academic Search

Syntheses of the title compounds result from appropriate reactions of the elements and LaIâ in sealed Nb or Ta containers at 800 C. These exhibit a new structural type with an unusual metal-rich layered structure, detailed for LaâINiâ by single-crystal X-ray diffraction. This is related to the GdâIFeâ-type structure known for LaâIZâ for Z = Fe, Co, and others. Both

Seung-Tae Hong; James D. Martin; John D. Corbett

1998-01-01

350

Raman spectroscopy study of rotated double-layer graphene: misorientation-angle dependence of electronic structure.  

PubMed

We present a systematic Raman study of unconventionally stacked double-layer graphene, and find that the spectrum strongly depends on the relative rotation angle between layers. Rotation-dependent trends in the position, width and intensity of graphene 2D and G peaks are experimentally established and accounted for theoretically. Our theoretical analysis reveals that changes in electronic band structure due to the interlayer interaction, such as rotational-angle dependent Van Hove singularities, are responsible for the observed spectral features. Our combined experimental and theoretical study provides a deeper understanding of the electronic band structure of rotated double-layer graphene, and leads to a practical way to identify and analyze rotation angles of misoriented double-layer graphene. PMID:23004295

Kim, Kwanpyo; Coh, Sinisa; Tan, Liang Z; Regan, William; Yuk, Jong Min; Chatterjee, Eric; Crommie, M F; Cohen, Marvin L; Louie, Steven G; Zettl, A

2012-06-14

351

Large GMR values of sputtered Co/Cu multilayer structures with Co-Cu buffer layers  

SciTech Connect

We demonstrate large giant magnetoresistance (GMR) values of Co/Cu multilayers (MLs) sputtered on combined Co18{angstrom}/Cu48{angstrom} buffer layer. GMR values at room temperature reach 62% at the first antiferromagnetically (AF) coupling peak and 33% at the 2nd AF coupled peak, which are very close to those found in Co/Cu MLs sputtered on a Fe buffer layer. The large GMR effect is attributed to the superior superlattice structure of these samples, as evidenced by the x-ray reflectivity data as well as the TEM micrographs. In particular, the role of thin Co initial layer deposited beneath the Cu buffer layer on improved ML structure has been clarified from cross-sectional micrographs of high-resolution TEM.

Huai, Y.; Vernon, S.P.; Stearns, D.G.; Cerjan, C.; Kania, D.R.

1996-02-29

352

Visualization of the structural response of a hypersonic turbulent boundary layer to convex curvature  

NASA Astrophysics Data System (ADS)

The effects of convex curvature on the outer structure of a Mach 4.9 turbulent boundary layer (Re? = 4.7 × 104) are investigated using condensate Rayleigh scattering and analyzed using spatial correlations, intermittency, and fractal theory. It is found that the post-expansion boundary layer structure morphology appears subtle, but certain features exhibit a more obvious response. The large-scale flow structures survive the initial expansion, appearing to maintain the same physical size. However, due to the nature of the expansion fan, a differential acceleration effect takes place across the flow structures, causing them to be reoriented, leaning farther away from the wall. The onset of intermittency moves closer towards the boundary layer edge and the region of intermittent flow decreases. It is likely that this reflects the less frequent penetration of outer irrotational fluid into the boundary layer, consistent with a boundary layer that is losing its ability to entrain freestream fluid. The fractal dimension of the turbulent/nonturbulent interface decreases with increasing favorable pressure gradient, indicating that the interface's irregularity decreases. Because fractal scale similarity does not encompass the largest scales, this suggests that the change in fractal dimension is due to the action of the smaller-scales, consistent with the idea that the small-scale flow structures are quenched during the expansion in response to bulk dilatation.

Humble, R. A.; Peltier, S. J.; Bowersox, R. D. W.

2012-10-01

353

An effective structure prediction method for layered materials based on 2D particle swarm optimization algorithm.  

PubMed

A structure prediction method for layered materials based on two-dimensional (2D) particle swarm optimization algorithm is developed. The relaxation of atoms in the perpendicular direction within a given range is allowed. Additional techniques including structural similarity determination, symmetry constraint enforcement, and discretization of structure constructions based on space gridding are implemented and demonstrated to significantly improve the global structural search efficiency. Our method is successful in predicting the structures of known 2D materials, including single layer and multi-layer graphene, 2D boron nitride (BN) compounds, and some quasi-2D group 6 metals(VIB) chalcogenides. Furthermore, by use of this method, we predict a new family of mono-layered boron nitride structures with different chemical compositions. The first-principles electronic structure calculations reveal that the band gap of these N-rich BN systems can be tuned from 5.40 eV to 2.20 eV by adjusting the composition. PMID:23248988

Wang, Yanchao; Miao, Maosheng; Lv, Jian; Zhu, Li; Yin, Ketao; Liu, Hanyu; Ma, Yanming

2012-12-14

354

An effective structure prediction method for layered materials based on 2D particle swarm optimization algorithm  

NASA Astrophysics Data System (ADS)

A structure prediction method for layered materials based on two-dimensional (2D) particle swarm optimization algorithm is developed. The relaxation of atoms in the perpendicular direction within a given range is allowed. Additional techniques including structural similarity determination, symmetry constraint enforcement, and discretization of structure constructions based on space gridding are implemented and demonstrated to significantly improve the global structural search efficiency. Our method is successful in predicting the structures of known 2D materials, including single layer and multi-layer graphene, 2D boron nitride (BN) compounds, and some quasi-2D group 6 metals(VIB) chalcogenides. Furthermore, by use of this method, we predict a new family of mono-layered boron nitride structures with different chemical compositions. The first-principles electronic structure calculations reveal that the band gap of these N-rich BN systems can be tuned from 5.40 eV to 2.20 eV by adjusting the composition.

Wang, Yanchao; Miao, Maosheng; Lv, Jian; Zhu, Li; Yin, Ketao; Liu, Hanyu; Ma, Yanming

2012-12-01

355

Band structure of Al\\/Si\\/n-type GaAs with a strained Si interfacial layer  

Microsoft Academic Search

The band structure of a coherently strained Si layer (<15 Å) on GaAs has been calculated using the empirical pseudopotential method. The pseudopotential form factor of the strained Si layer is derived by considering that the pseudopotential of the strained layer is slightly modified by a factor which is proportional to the volume change of the unit cell. The band-structure

Z. Chen; S. N. Mohammad; H. Morkoç

1996-01-01

356

Three-layered models of Ganymede and Callisto - Compositions, structures, and aspects of evolution  

Microsoft Academic Search

The structural models presently defined for Ganymede and Callisto, which encompass a pure-ice upper layer, a mixed ice\\/rock lower mantle, and a rock core, incorporate three alternative rock component candidates representing various degrees of silicate hydration and oxidation. The three-layered model facilitates close study of the radius increase required for the internal differentiation of an ice-rock satellite; such expansion is

Steve Mueller; William B. McKinnon

1988-01-01

357

Structure of Protein Layers in Polyelectrolyte Matrices Studied by Neutron Reflectivity  

SciTech Connect

Polyelectrolyte multilayer films obtained by localized incorporation of Green Fluorescent Protein (GFP) within electrostatically assembled matrices of poly(styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH) via spin-assisted layer-by-layer growth were discovered to be highly structured, with closely packed monomolecular layers of the protein within the bio-hybrid films. The structure of the films was evaluated in both vertical and lateral directions with neutron reflectometry, using deuterated GFP as a marker for neutron scattering contrast. Importantly, the GFP preserves its structural stability upon assembly as confirmed by circular dichroism (CD) and in situ attenuated total reflection Fourier Transform Infrared spectroscopy (ATR-FTIR). Atomic force microscopy was complimented with X-ray reflectometry to characterize the external roughness of the biohybrid films. Remarkably, films assembled with a single GFP layer confined at various distances from the substrate exhibit a strong localization of the GFP layer without intermixing into the LbL matrix. However, partial intermixing of the GFP layers with polymeric material is evidenced in multiple-GFP layer films with alternating protein-rich and protein-deficient regions. We hypothesize that the polymer-protein exchange observed in the multiple-GFP layer films suggests the existence of a critical protein concentration which can be accommodated by the multilayer matrix. Our results yield new insights into the mechanism of GFP interaction with a polyelectrolyte matrix and open opportunities for fabrication of bio-hybrid films with well-organized structure and controllable function, a crucial requirement for advanced sensing applications.

Kozlovskaya, Veronika [University of Alabama, Birmingham; Ankner, John Francis [ORNL; O'Neill, Hugh Michael [ORNL; Zhang, Qiu [ORNL; Kharlampieva, Eugenia [University of Alabama, Birmingham

2011-01-01

358

Modeling shared-via decoupling in a multi-layer structure using the CEMPIE approach  

Microsoft Academic Search

The CEMPIE approach, a circuit extraction technique based on a mixed-potential integral equation, has been applied to model multi-layer structures including power and signal layers. Power-bus noise mitigation effects due to a decoupling capacitor were studied for several cases with different spacing between the capacitor and an integrated circuit (IC). Modeling results indicate that the capacitor sharing a common via

Wei Cui; Jun Fan; Shaofeng Luan; J. L. Drewniak

2001-01-01

359

Synthesis of buried silicon oxynitride layers by ion implantation for silicon-on-insulator (SOI) structures  

Microsoft Academic Search

Silicon oxynitride (SixOyNz) buried insulating layers were synthesized by SIMNOX (separation by implanted nitrogen–oxygen) process by 14N+ and 16O+ ion implantation to high fluence levels 1×1017, 2.5×1017 and 5×1017ionscm?2 sequentially in the ratio 1:1 at 150keV into p-type (100) silicon wafers. The identification of structures and defects in the ion beam synthesized buried layers were carried out by FTIR, XRD

A. D. Yadav; Rucha H. Polji; Vibha Singh; S. K. Dubey; T. K. Gundu Rao

2006-01-01

360

Structural and Optoelectronic Properties of In-Zn-S sprayed Layers  

Microsoft Academic Search

In this work, In-Zn-S thin layers were prepared using the spray pyrolysis technique on glass substrates at 320ºC. The molar ratio between zinc and indium x=[Zn2+]\\/[In3+] was varied in 0-0.4 domain whereas [S2- ]\\/[In3+] one was taken constant equal to 2. The atomic composition was carried out with the atomic absorption. The structural study of all layers via X-ray diffraction

S. Lazzez; K. Boubaker; T. Ben; Nasrallah; M. Amlouk; S. Belgacem; M. Mnari; R. Chtourou

2008-01-01

361

A self-aligned retrograde twin-well structure with buried p+ -layer  

Microsoft Academic Search

A self-aligned retrograde twin-well structure with a buried p+-layer surrounding the n-well is presented. The retrograde twin well and buried p+-layer are fabricated by a single lithographic step using high-energy ion implantation. The retrograde n-well is self-aligned to the retrograde p-well regions, and the channel stop processes are eliminated by using tight spatial distributions of retrograde n- and p-wells. This

SHINJI ODANAKA; TOSHIKI YABU; NORISATO SHIMIZU; HIROYUKI UMIMOTO; TAKASHI OHZONE

1990-01-01

362

Far-Infrared investigation of the structural phase transitions of some two-dimensional layer compounds  

Microsoft Academic Search

The far-infrared spectra of the layer structure compounds of the type (CnH2n+1NH3)2MCl4, n = 1, 2, 3,…, M = Cu, Cd, have been measured in the region of 10–400 cm as a function of the temperature between 1 and 300 K. The rather involved spectra of the compounds investigated are due to the normal lattice modes of the layers alone.

J. Holvast; J. H. M. Stoelinga; P. Wyder

1976-01-01

363

Sh-matrices method as applied to scattering by particles with layered structure  

Microsoft Academic Search

We develop a modification of the T-matrix method that allows for fast calculations of light-scattering properties of non-spherical particles with layered structure. This modification uses the Sh-matrices that depend on the shape of particles only and do not depend on the particle size or optical constants. The matrices are obtained for any number of discrete layers of a particle with

D. Petrov; Yu. Shkuratov; E. Zubko; G. Videen

2007-01-01

364

Fine structures in Fe 3 Al alloy layer of a new hot dip aluminized steel  

Microsoft Academic Search

The fine structure in the Fe-Al alloy layer of a new hot dip aluminized steel (HDA) was examined by means of X-ray diffractometry\\u000a (XRD), electron diffraction technique, etc. The test results indicated that the Fe-Al alloy layer of the new aluminized steel\\u000a mainly composed of Fe3Al, FeAl and ?-Fe (Al) solid solution. There was no brittle phase containing higher aluminum

LI Yajiang; Wang Juan; Zhang Yonglan; X. Holly

2002-01-01

365

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

Microsoft Academic Search

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

R. E. Camley; J. Barnas

1989-01-01

366

An investigation of the structure and chemistry of a chromium-conversion surface layer on aluminum  

Microsoft Academic Search

X-ray absorption spectroscopy (XAS), Fourier transmission infra red spectroscopy (FTIR), X-ray photo-electron spectroscopy (XPS), Auger profiling and microscopy were used to characterize chemically and structurally the surface oxide layer created by the Alodine 1200S process on 2024 and 7075 aluminum alloys. The thickness of the layer was found to range from ~2000 Å to 1 ?m for processing times of

F. W. Lytle; R. B. Greegor; G. L. Bibbins; K. Y. Blohowiak; R. E. Smith; G. D. Tuss

1995-01-01

367

Structure of the turbulent boundary layer over a rod-roughened wall  

Microsoft Academic Search

Turbulent coherent structures near a rod-roughened wall are scrutinized by analyzing instantaneous flow fields obtained from direct numerical simulations (DNSs) of a turbulent boundary layer (TBL). The roughness elements used are periodically arranged two-dimensional spanwise rods, and the roughness height is k\\/?=0.05 where ? is the boundary layer thickness. The Reynolds number based on the momentum thickness is varied in

Jae Hwa Lee; Seung-Hyun Lee; Kyoungyoun Kim; Hyung Jin Sung

2009-01-01

368

Structure and stressed state of molybdenum layers in Mo\\/Si multilayers  

Microsoft Academic Search

Structure and stressed state of molybdenum layers in Mo\\/Si multilayer periodical compositions prepared by direct current magnetron sputtering have been investigated by methods of X-ray tensometry in grazing-incidence asymmetrical geometry, cross-sectional transmission electron microscopy and small-angle X-ray reflectometry. The level of symmetrical biaxial stresses depends non-monotonously on the thickness of Mo layers. Value and sign of stresses are defined by

V. I. Pinegyn; E. N. Zubarev; V. V. Kondratenko; V. A. Sevryukova; S. A. Yulin; T. Feigl; N. Kaiser

2008-01-01

369

Optical and structural characterization of AlInN layers for optoelectronic applications  

Microsoft Academic Search

Al1-xInxN layers with an indium content between x=10.5% and x=24% were grown by metal-organic vapor-phase epitaxy and characterized concerning their optical, structural and morphological properties with regard to the realization of optoelectronic devices. The indium content and the strain of these layers were measured by high resolution x-ray diffraction. Ellipsometric measurements were used to determine the optical constants [refractive index

T. Aschenbrenner; H. Dartsch; C. Kruse; M. Anastasescu; M. Stoica; M. Gartner; A. Pretorius; A. Rosenauer; Thomas Wagner; D. Hommel

2010-01-01

370

SH-SAW propagation in layered functionally graded piezoelectric material structures loaded with viscous liquid  

Microsoft Academic Search

We investigate the properties of shear horizontal surface acoustic wave propagation in layered functionally graded piezoelectric\\u000a material structures loaded with viscous liquid. The piezoelectric material is polarized in the z-direction and the material properties change gradually along the thickness of the layer. Interfacial mechanical conditions\\u000a are continuity of particle velocity and stress components at the interface. We here assume that

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

2010-01-01

371

Bi-layered calcium phosphate cement-based composite scaffold mimicking natural bone structure  

NASA Astrophysics Data System (ADS)

In this study, a core/shell bi-layered calcium phosphate cement (CPC)-based composite scaffold with adjustable compressive strength, which mimicked the structure of natural cortical/cancellous bone, was fabricated. The dense tubular CPC shell was prepared by isostatic pressing CPC powder with a specially designed mould. A porous CPC core with unidirectional lamellar pore structure was fabricated inside the cavity of dense tubular CPC shell by unidirectional freeze casting, followed by infiltration of poly(lactic-co-glycolic acid) and immobilization of collagen. The compressive strength of bi-layered CPC-based composite scaffold can be controlled by varying thickness ratio of dense layer to porous layer. Compared to the scaffold without dense shell, the pore interconnection of bi-layered scaffold was not obviously compromised because of its high unidirectional interconnectivity but poor three dimensional interconnectivity. The in vitro results showed that the rat bone marrow stromal cells attached and proliferated well on the bi-layered CPC-based composite scaffold. This novel bi-layered CPC-based composite scaffold is promising for bone repair.

He, Fupo; Ye, Jiandong

2013-08-01

372

Effect of layer stacking on the electronic structure of graphene nanoribbons.  

PubMed

The evolution of electronic structure of graphene nanoribbons (GNRs) as a function of the number of layers stacked together is investigated using 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 from interlayer interactions plays a crucial role in determining the magnetic polarization and the band structure. The antiferromagnetic (AF) interlayer coupling is more stable compared to the ferromagnetic (FM) interlayer coupling. ZGNRs with the AF in-layer and AF interlayer coupling have a finite band gap, while ZGNRs with the FM in-layer and AF interlayer coupling do not have a band gap. The ground state of the bilayer ZGNR is nonmagnetic with a small but finite band gap. The magnetic ordering is less stable in multilayer ZGNRs compared to that in single-layer ZGNRs. The quasiparticle GW corrections are smaller for bilayer GNRs compared to single-layer GNRs because of the reduced Coulomb effects in bilayer GNRs compared to single-layer GNRs. PMID:21766785

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

2011-07-20

373

Self-sustained localized structures in a boundary-layer flow.  

PubMed

When a boundary layer starts to develop spatially over a flat plate, only disturbances of sufficiently large amplitude survive and trigger turbulence subcritically. Direct numerical simulation of the Blasius boundary-layer flow is carried out to track the dynamics in the region of phase space separating transitional from relaminarizing trajectories. In this intermediate regime, the corresponding disturbance is fully localized and spreads slowly in space. This structure is dominated by a robust pair of low-speed streaks, whose convective instabilities spawn hairpin vortices evolving downstream into transient disturbances. A quasicyclic mechanism for the generation of offspring is unfolded using dynamical rescaling with the local boundary-layer thickness. PMID:22400847

Duguet, Yohann; Schlatter, Philipp; Henningson, Dan S; Eckhardt, Bruno

2012-01-25

374

Three-dimensional structure of the T-layer of Bacillus sphaericus P-1.  

PubMed Central

The three-dimensional structure of the regular surface layer of Bacillus sphaericus P-1 (T-layer) was determined to a resolution of ca. 2.5 nm by electron microscopy and image analysis. The T-layer has P4 symmetry, a lattice constant of 13 +/- 0.2 nm, and a thickness of ca. 8 nm. The reconstruction revealed three distinct domains: a major, a minor, and an arm domain. In the z-direction, the domains are arranged in two planes creating two different surface reliefs. Images

Lepault, J; Martin, N; Leonard, K

1986-01-01

375

Formation of thin ZrO2 layers for nanotransistor gate structures by electron beam evaporation  

Microsoft Academic Search

Zirconium oxide (ZrO2) films have been deposited on cleaned and heated p-type Si (100) substrates by electron-beam evaporation technique. It is shown that the intermediate SiO2 layer on ZrO2\\/Si interface is absence. The W\\/YSZ\\/Si and Mo\\/YSZ\\/Si structures with 3÷20-nm-thick dielectric layers were formed by electron-beam evaporation technique. The fixed charge densities in 3-nm-thick YSZ layers are 3x1010 - 3.7x1010cm2, leakage

D. G. Drozdov; I. A. Khorin; V. B. Kopylov; A. A. Orlikovsky; A. E. Rogozhin; A. G. Vasiliev

2008-01-01

376

Formation of thin ZrO2 layers for nanotransistor gate structures by electron beam evaporation  

NASA Astrophysics Data System (ADS)

Zirconium oxide (ZrO2) films have been deposited on cleaned and heated p-type Si (100) substrates by electron-beam evaporation technique. It is shown that the intermediate SiO2 layer on ZrO2/Si interface is absence. The W/YSZ/Si and Mo/YSZ/Si structures with 3÷20-nm-thick dielectric layers were formed by electron-beam evaporation technique. The fixed charge densities in 3-nm-thick YSZ layers are 3x1010 - 3.7x1010cm2, leakage current density at a voltage -1V achieves ~7,9•10-7?/cm2.

Drozdov, D. G.; Khorin, I. A.; Kopylov, V. B.; Orlikovsky, A. A.; Rogozhin, A. E.; Vasiliev, A. G.

2008-05-01

377

Total transparency of a two-moving-magnetized-plasma-layer structure  

NASA Astrophysics Data System (ADS)

In the present Letter the transparency of a two-moving-magnetized-plasma-layer structure irradiated by an electromagnetic wave is investigated theoretically and its resonant conditions are determined. Here, the direction of the external magnetic field is normal to the plasma surface and two layers move with different velocities parallel to the interface. The effects of the external magnetic field, speed of plasma layers and the magnitude of the wave number component on transparency are simulated. These investigations for S-polarized and P-polarized electromagnetic waves have been done separately.

Rahmani, Z.; Jazi, B.; Shokri, B.

2013-09-01

378

Local structures surrounding Zr in nanostructurally stabilized cubic zirconia: Structural origin of phase stability  

SciTech Connect

Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO{sub 2}) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO{sub 2} nanocrystal sample prepared by a sol-gel method. Variations in local structures due to thermal annealing were observed and analyzed. Most importantly, our x-ray results provide direct experimental evidence for the existence of oxygen vacancies arising from local disorder and distortion of the oxygen sublattice in nanocrystalline ZrO{sub 2}. These oxygen vacancies are regarded as the essential stabilizing factor for the nanostructurally stabilized cubic zirconia.

Soo, Y. L.; Chen, P. J.; Huang, S. H.; Shiu, T. J.; Tsai, T. Y.; Chow, Y. H.; Lin, Y. C.; Weng, S. C.; Chang, S. L. [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Wang, G.; Cheung, C. L. [Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 (United States); Sabirianov, R. F.; Mei, W. N. [Department of Physics, University of Nebraska at Omaha, Omaha, Nebraska 68182 (United States); Namavar, F.; Haider, H.; Garvin, K. L. [Department of Orthopaedics Surgery and Rehabilitation, University of Nebraska Medical Center, Omaha, Nebraska 68198 (United States); Lee, J. F. [National Synchrotron Radiation Research Center, Hsinchu 30013, Taiwan (China); Lee, H. Y.; Chu, P. P. [Department of Chemistry, National Central University, Jhongli 32001, Taiwan (China)

2008-12-01

379

Photophysical properties and electronic structure of highly donor doped (110) layered perovskite material  

Microsoft Academic Search

Sr2Nb2O7, a donor doped (110) layered perovskite material was synthesized by solid state reaction method and studied for its photo physical properties. The morphology, crystal structure and optical properties were characterized respectively by SEM, XRD and UV-DRS spectroscopies. We performed the electronic band structure calculations on orthorhombic crystal structure of Sr2Nb2O7, within the framework of density functional theory (DFT) by

E. D. Jeong; M. G. Ha; M. S. Won; H. G. Kim; H. K. Pak; P. H. Borse; S. M. Ji; J. S. Lee

2006-01-01

380

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

DOEpatents

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

Spahn, Olga B. (Albuquerque, NM); Lear, Kevin L. (Albuquerque, NM)

1998-01-01

381

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

PubMed Central

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

Grant, L M; Tiberg, F

2002-01-01

382

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

PubMed

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

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

2012-10-05

383

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

384

Cinematic visualization of coherent density structures in a supersonic turbulent boundary layer  

NASA Astrophysics Data System (ADS)

High speed schlieren photography was used in a cinematic investigation of coherent density structures in a high Reynolds number, zero pressure gradient, compressible, Mach 3 turbulent boundary layer. A high speed drum camera with a maximum framing rate of 38,000 frames per second was used to record the passage of both positive and negative density gradient events. The stronger and more coherent positive events appear on the images as straight, narrow structures attached to the wall and inclined to it at an angle of between 30 and 50 degrees. They nearly span the boundary layer. The negative events are weaker and less angular. Convection velocities for both varieties of structure are grouped around 0.9 U. Also, a model of a compressible outer-layer turbulent 'bulge' is proposed.

Smith, M. W.; Smits, A. J.

1988-01-01

385

Layer selective magnetometry in ultrathin magnetic structures by polarised neutron reflection  

NASA Astrophysics Data System (ADS)

We discuss the application of polarised neutron reflection to layer selective vector magnetometry measurements in thin magnetic films. To illustrate the application of PNR, we review recent measurements of the absolute moment in X/Fe/Ag(001) structures with X = Pd, Ag, Au and Cu and compare the results with the predictions based on theoretical calculations which take into account the measured interface roughness. For the case of strained fct Ni/Cu(001) structures we illustrate the use of PNR as a self-calibrating magnetometric technique in determining both the magnetic layer thickness and total sample moment for which a reduced moment per Ni atom is observed. Finally we present measurements of the layer dependent moments in FeNi/Cu/Co spin valve structures. We show that by comparing the PNR measurements with SQUID magnetometry measurements of the total sample moment we are able to determine the interface moments on an atomic scale.

Bland, J. A. C.; Lee, J.; Hope, S.; Lauhoff, G.; Penfold, J.; Bucknall, D.

1997-01-01

386

Measuring the atomic-scale structure of a Helmholtz `double layer'  

NASA Astrophysics Data System (ADS)

We propose a powerful new technique to measure the structure of the Helmholtz `double layer' formed in an aqueous electrolyte in contact with a metal electrode. The critical innovation is to couple a structural probe which is specific to the environment of a particular atom species with a `tag' layer of metal atoms electrodeposited in underpotential conditions on an unlike-metal electrode. The efficacy of our approach is illustrated through a measurement of the double layer in a dilute sulfuric acid electrolyte in contact with a Pt electrode decorated with Cu atoms, the surface structure of which we have studied extensively.( T E Furtak, L Wang, J Pant, K Pansewicz, and T M Hayes, J Electrochem Soc 141) 2369 (1994); L B Lurio, J Pant, T M Hayes, L Wang, and T E Furtak, Physica B 208 413 (1995)

Hayes, T. M.; Lurio, L. B.; Pant, J.; Wang, L.; Furtak, T. E.

1997-03-01

387

Structural origin of the nonlinear optical properties of lead niobium germanate film glasses  

NASA Astrophysics Data System (ADS)

The structural origin of the nonlinear optical susceptibility (/?(3)/) of lead-niobium-germanate film glasses with large Nb2O5 contents has been investigated. /?(3)/ shows a strong enhancement with the Nb content in the films with /?(3)/ values close to 2 × 10-11 esu at 800 nm for a Nb content as high as 0.71. Boling-Glass-Owyoung and Lines' semiempirical models predict accurately the values of /?(3)/ for transparent bulk glasses but not for film glasses. This discrepancy is related to the remarkable structural differences between them. Raman spectroscopy suggests the formation of a three-dimensional (3D) structure of [NbO6] octahedra in the case of film glasses having large Nb contents, while X-ray photoelectron spectroscopy shows that a significant fraction of these units contain Nb4+ ions. The combination of a 3D structure of [NbO6] with the presence of Nb4+ polarons and their migration through electron intervalence transfer is proposed as the origin of the observed enhancement of /?(3)/ in the film glasses.

Munoz-Martin, D.; de La Cruz, A. Ruiz; Fernandez-Navarro, J. M.; Domingo, C.; Solis, J.; Gonzalo, J.

2011-07-01

388

Constraining the Origin and Structure of the Zodiacal Dust Bands with the MSX Celestial Backgrounds Data  

NASA Astrophysics Data System (ADS)

In recent years much work has been done to establish the provenance of the zodiacal dust bands, near-ecliptic enhancements in the brightness of the zodiacal cloud. The bands represent the debris of collisional activity in the asteroid belt, thought to be occuring within the major asteroid families of Eos, Themis and Koronis. However, recent numerical evidence for relatively fresh collisions in the Karin cluster and the Veritas family, which are located at orbital inclinations matching the observed dust band structures, have provided an alternate theory for the origin of the bands. Here we plan to take advantage of the unique nature of the MSX Celestial Backgrounds data, which in contrast to previous IRAS and COBE measurements include observations over a wide range of solar elongation angle (25 to 180 degrees). This MSX data set therefore represents a powerful resource to reconstruct the full three-dimensional structure of the dust bands, to quantify the size-frequency distribution of the dust band structures as a function of heliocentric distance, and to provide a more concrete genetic relationship between the dust bands and putative parent bodies. Previous work has also demonstrated that the zodiacal cloud is predominantly asteroidal in origin, therefore this investigation also has direct relevance to the nature and structure of asteroidal exozodiacal clouds, which needs to be understood to help ensure the success of future extrasolar planet finding missions such as Terrestrial Planet Finder.

Grogan, K.; Price, S. D.

2003-12-01

389

Analysis of lattice-translocation disorder in the layered hexagonal structure of carboxysome shell protein CsoS1C  

SciTech Connect

Lattice-translocation or crystal order-disorder phenomena occur when some layers or groups of molecules in a crystal are randomly displaced relative to other groups of molecules by a discrete set of vectors. In previous work, the effects of lattice translocation on diffraction intensities have been corrected by considering that the observed intensities are the product of the intensities from an ideal crystal (lacking disorder) multiplied by the squared magnitude of the Fourier transform of the set of translocation vectors. Here, the structure determination is presented of carboxysome protein CsoS1C from Halothiobacillius neapolitanus in a crystal exhibiting a lattice translocation with unique features. The diffraction data are fully accounted for by a crystal unit cell composed of two layers of cyclic protein hexamers. The first layer is fully ordered (i.e. has one fixed position), while the second layer randomly takes one of three alternative positions whose displacements are related to each other by threefold symmetry. Remarkably, the highest symmetry present in the crystal is P3, yet the intensity data (and the Patterson map) obey 6/m instead of {bar 3} symmetry; the intensities exceed the symmetry expected from combining the crystal space group with an inversion center. The origin of this rare phenomenon, known as symmetry enhancement, is discussed and shown to be possible even for a perfectly ordered crystal. The lattice-translocation treatment described here may be useful in analyzing other cases of disorder in which layers or groups of molecules are shifted in multiple symmetry-related directions.

Tsai, Yingssu; Sawaya, Michael R.; Yeates, Todd O.; UCLA

2010-03-29

390

Polyoxometalate-based layered structures for charge transport control in molecular devices.  

PubMed

Hybrid organic-inorganic films consisted of molecular layers of a Keggin-structure polyoxometalate (POM: 12-tungstophosphoric acid, H(3)PW(12)O(40)) and 1,12-diaminododecane (DD) on 3-aminopropyl triethoxysilane (APTES)-modified silicon surface, fabricated via the layer-by-layer (LBL) self-assembly method are evaluated as molecular materials for electronic devices. The effect of the fabrication process parameters, including primarily compositions of deposition solutions, on the structural characteristics of the POM-based multilayers was studied extensively with a combination of spectroscopic methods (UV, FTIR, and XPS). Well-characterized POM-based films (both single-layers and multilayers) in a controlled and reproducible way were obtained. The conduction mechanisms in single-layered and multilayered structures were elucidated by the electrical characterization of the produced films supported by the appropriate theoretical analysis. Fowler-Nordheim (FN) tunneling and percolation mechanisms were encountered in good correlation with the structural characteristics of the films encouraging further investigation on the use of these materials in electronic and, in particular, in memory devices. PMID:19206605

Douvas, Antonios M; Makarona, Eleni; Glezos, Nikos; Argitis, Panagiotis; Mielczarski, Jerzy A; Mielczarski, Ela

2008-04-01

391

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

PubMed

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

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

2013-08-20

392

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

PubMed

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

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

2011-02-15

393

Structural Layers of Ex Vivo Rat Hippocampus at 7T MRI  

PubMed Central

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

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

2013-01-01

394

Layer-by-layer structured films of TiO2 nanoparticles and poly(acrylic acid) on electrospun nanofibres  

NASA Astrophysics Data System (ADS)

We report a new approach for fabricating layer-by-layer (LBL) structured ultrathin hybrid films on electrospun nanofibres. Oppositely charged anatase TiO2 nanoparticles and poly(acrylic acid) (PAA) were alternately deposited on the surface of negatively charged cellulose acetate (CA) nanofibres using the electrostatic LBL self-assembly technique. The fibrous mats were characterized by wide-angle x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller (BET) surface area techniques. The crystalline phase of anatase TiO2 remained unchanged in the resultant TiO2/PAA films coated on CA fibrous mats. Moreover, the TiO2/PAA film coated fibres showed rough surfaces with grains due to the deposition of aggregated TiO2 particles. The average diameter of the fibres increased from 344 to 584 nm and the BET surface area of the fibrous mats increased from 2.5 to 6.0 m2 g-1 after coating with five bilayers of TiO2/PAA films.

Ding, Bin; Kim, Jinho; Kimura, Eiji; Shiratori, Seimei

2004-08-01

395

Effects of plastic constraint on the cyclic and static fatigue behavior of metal\\/ceramic layered structures  

Microsoft Academic Search

The role of metal layer thickness and resultant plastic constraint in the metal layer during the failure of metal\\/ceramic layered structures is examined under cyclic and static loading conditions. Crack-growth experiments were conducted on sandwich specimens consisting of 99.999% pure aluminum layers bonded between 99.5% pure polycrystalline alumina with the metal layer thickness varying from 5 to 100 ?m. Under

J. J. Kruzic; J. M. McNaney; R. M. Cannon; R. O. Ritchie

2004-01-01

396

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 Zhang; Shi-Wun Tong; Chang-Yun Jiang; En-Tang Kang; Daniel S. H. Chan; Chunxiang Zhu

2010-01-01

397

Influence of the surface spin pinning parameter of a ferrite film on dispersion characteristics of layered ferrite-ferroelectric structures  

NASA Astrophysics Data System (ADS)

A theory has been constructed for rigorously describing a spectrum of hybrid electromagnetic-spin waves on an arbitrarily magnetized screened layered structure consisting of ferromagnetic, ferroelectric, and several dielectric layers with the inclusion of an arbitrary pinning of spins on the surface of a ferromagnetic film. The dependence of dispersion characteristics of the layered structure on the surface spin pinning parameter and on the permittivity of the ferroelectric layer has been investigated theoretically.

Grigoryeva, N. Yu.; Sultanov, R. A.; Kalinikos, B. A.

2011-05-01

398

Synthesis and structural transformations of colloidal 2D layered metal chalcogenide nanocrystals.  

PubMed

This review presents recent advances in synthetic methods and structural transformations of colloidal 2D layered metal chalcogenide nanocrystals. Planar 2D anisotropy and interlayer van der Waals gaps are the important characteristics of these nanocrystals for pristine disc, plate or sheet morphologies. These 2D nanocrystals undergo unique chemical transformations upon exposure to external chemical stimuli and newly obtained structures are 2D nanostructures with high complexity in their morphological geometries and chemical compositions. Finally, future opportunities and potential applications of 2D layered metal chalcogenide nanocrystals are briefly discussed. PMID:23212120

Han, Jae Hyo; Lee, Sujeong; Cheon, Jinwoo

2013-04-01

399

A structural role for ATP in the formation and stability of the human origin recognition complex.  

PubMed

The locally restricted recruitment of the multisubunit origin recognition complex (ORC) to eukaryotic chromosomes defines the position of origins of DNA replication. In budding yeast and metazoans the DNA binding activity of ORC is stimulated by ATP and requires an AAA+-type nucleotide binding domain in the largest subunit. Little else is known about the mechanisms behind the ATP requirement for ORC in its initiator function and, specifically, the relevance of nucleotide binding domains present on other subunits. Here we show that ATP is required for specific subunit interactions in the human ORC, with the Orc4 subunit playing a critical role in this dynamic process. ATP is essential for the maintenance of ORC integrity and facilitates complex formation. Thus, besides its previously identified role in DNA binding, ATP serves also as a structural cofactor for human ORC. PMID:16549788

Ranjan, Anand; Gossen, Manfred

2006-03-20

400

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

PubMed Central

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

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

2009-01-01

401

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

NASA Astrophysics Data System (ADS)

Identification of the origin of groundwater samples based on their geochemistry.Enhancement of a geochemical dataset featuring doubtful samples.Novel application of Random Forest (RF) machine learning technique in Hydrogeology.High discrimination capacity, beyond similar water types and heterogeneous dataset.Optimization of the classification model by assessing the most useful variables.

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

2013-08-01

402

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

NASA Astrophysics Data System (ADS)

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

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

403

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

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

404

The peri-albumen layer: a novel structure in the envelopes of an avian egg  

PubMed Central

The present paper describes a novel structure, termed the peri-albumen layer, in the egg-envelopes of the quail Coturnix japonica. It reacts with Alcian blue and exists between the egg white and the shell membrane. Ultrastructurally, it is of fine granular structure and forms a fenestrate sheet, the width of which is 190 nm or less. Isolated materials of the peri-albumen layer include an Alcian-blue-positive polysaccharide of 260 kDa, and three glycoproteins of 160, 108 and 52 kDa. The layer is supplied to an egg when it passes through the magnum–isthmus junction, the normalized length of which is 0.62–0.63 of the oviduct. The mucosa of the junction consists exclusively of a luminal epithelium. It is apparently distinct from the mucosa of the magnum and the isthmus, which consist of a luminal epithelium and tubular glands. The luminal epithelium of the magnum–isthmus junction stains prominently with Alcian blue and consists of alternately distributed ciliated cells and granular cells. Immunohistochemistry with an antiserum raised against the materials of the peri-albumen layer revealed the staining of the peri-albumen layer of the egg, and secretory cells of the luminal epithelium at the magnum–isthmus junction. It was concluded that the materials of the peri-albumen layer are produced by secretory cells at the magnum–isthmus junction of the oviduct.

Sultana, F; Yokoe, A; Ito, Y; Mao, KM; Yoshizaki, N

2003-01-01

405

The boundary layer structure in Rayleigh-B'enard convection in a cylindrical cell  

NASA Astrophysics Data System (ADS)

We report first results of our studies of the boundary layer structure in turbulent Rayleigh-B'enard convection in a cylindrical cell of aspect ratio one. They are based on three-dimensional direct numerical simulations (DNS) of the Boussinesq equations at Ra=3x10^9 and Pr=0.7. The study is motivated by two recent experiments: LDA measurements of the velocity boundary layer structure in the cylindrical Barrel of Ilmenau by du Puits et al. and PIV measurements in a slender rectangular convection cell by Xia et al. Both experiments detected deviations from the classical Blasius solution for time-averaged flow profiles. A rescaling by the instantaneous boundary layer thickness resulted however in a much better agreement with the Blasius profile in case of the rectangular cell. The DNS allow us to combine the analysis methods of both experiments. We confirm the significant deviation for the time-averaged profiles. Closer agreement with the Blasius solution is also reproduced for the fit with the instantaneous thickness. Our analysis is extended to the Pohlhausen solution in case of the thermal boundary layer. The flow profiles are also taken at different positions in the boundary layers. Further statistical properties in both boundary layers are reported.

Shi, Nan; Schumacher, Joerg

2010-11-01

406

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

407

Characterization of cake layer structure on the microfiltration membrane permeability by iron pre-coagulation.  

PubMed

A cake layer is formed by coagulation aggregates under certain transmembrane pressure in the coagulation-microfiltration (MF) process. The characteristics of humic acid aggregates coagulated by different iron-based coagulants, such as charge, size, fractal dimension and compressibility, have an effect on the cake layer structure. At the optimum iron dose of 0.6 to 0.8 mmol/L for ferric chloride (FC) and polymer ferric sulfate (PFS) pre-coagulation, at the point of charge neutralization for near zero zeta potential, the aggregate particles produced possess the greatest size and highest fractal dimension, which contributes to the cake layer being most loose with high porosity and low compressibility. Thus the membrane filterability is better. At a low or high iron dose of FC and PFS, a high negative or positive zeta potential with high charge repulsion results in so many small aggregate particles and low fractal dimension that the cake layer is compact with low porosity and high compressibility. Therefore the membrane fouling is accelerated and MF permeability becomes worse. The variation of cake layer structure as measured by scanning electric microscopy corresponds with the fact that the smaller the coagulation flocs size and fractal dimension are, the lower the porosity and the tighter the cake layer conformation. This also explains the MF membrane flux variation visually and accurately. PMID:23596951

Wang, Jin; Pan, Siru; Luo, Dongping

2013-02-01

408

Structure of the regular surface layer of Aquaspirillum serpens MW5.  

PubMed

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

Stewart, M; Murray, R G

1982-04-01

409

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

DOEpatents

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

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

1998-03-10

410

Turbulence structure and polymer drag reduction in adverse pressure gradient boundary layers  

NASA Astrophysics Data System (ADS)

One zero pressure gradient Newtonian boundary layer and two adverse pressure gradient equilibrium boundary layers in a water channel were examined. The momentum thickness Reynolds numbers, Re(sub theta), were in the range 1360 to 4980. The adverse pressure gradient boundary layers were characterized by equilibrium parameters, beta of 1.8 and 2.4. These boundary layers were modified by injecting a drag reducing polymer solution at 2.6 and 5.1 times the flow rate of the undisturbed flows inside of y(+) = 5. The sum of the viscous and Reynolds shear stresses was sometimes less than the total shear stress in the drag reduced boundary layer and in these cases the production of Reynolds shear and normal stresses was virtually eliminated. The mean streamwise velocity measurements in the drag reduced boundary layers showed that both parameters, kappa and B, of the logarithmic velocity profile changed. The slope parameter, kappa, varied directly with the percent drag reduction. The peak in the root-mean-square streamwise velocities remained essentially unchanged in the presence of polymer but its location moved away from the wall. The root-mean-square normal velocities and the Reynolds shear stress were reduced in the inner region of the boundary layer during drag reduction. The adverse pressure gradient boundary layers did not separate during drag reduction even when large amounts of polymer were injected. The influence of the polymer on the turbulent boundary layer structure was greatly reduced, but the effects of polymer were consistent with those in the zero pressure gradient boundary layer. The hypothesis that the extensional motions in the flow must be strong enough to stretch the polymer molecules so that stretched molecules will form an anisotropic viscosity that damps the small scales of the turbulence (Hinch, 1977) was supported by the present data. Walker's (1985) modified mixing length model correctly predicted the wall shear stress coefficient, c(sub f), in all the drag reduced boundary layers as long as the measured polymer concentration in the linear sublayer was within the range of concentrations for which the model was derived and the non-Newtonian shear stresses in the boundary layer were small. Mixed scaling of the average time between bursts best scaled the present zero and adverse pressure gradient Newtonian boundary layer data. The data was consistent with the hypothesis that the method of tripping the boundary layer affects the average burst period at very low Reynolds numbers.

Koskie, John Edward

1991-05-01

411

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

NASA Astrophysics Data System (ADS)

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

Abe, Hiroyuki; Mizobuchi, Yasuhiro; Matsuo, Yuichi

2011-11-01

412

Coherent Structures in the Atmospheric Surface Layer under Stable and Unstable Conditions  

NASA Astrophysics Data System (ADS)

Simultaneous measurements of the instantaneous values of absolute temperatureat seven heights within the lower 36 m of the atmospheric boundary layer underdifferent stability conditions were carried out, accompanied by measurements ofthe wind velocity components at two levels and of solar radiation flux at the surface.The data obtained allow one to investigate individual convective cells known ascoherent structures (CS). Outside the CS, i.e., during quiet periods, an instanttemperature profile is in close agreement with the dry-adiabatic lapse rate, butwithin CS the temperature changes much faster with height, and the shape ofthe profile varies significantly.A method was developed to transform temperature records from sensors atseveral heights into an other form, namely, into temporal variations of theheights of isothermal surfaces. Since coherent structures were found to advectwith the mean wind velocity, these temporal height variations may be transformedinto the spatial ones, i.e., into the xoz-plane section of the temperature field.In such a pictorial presentation coherent structures look like asymmetric columnsof heat, penetrating the whole atmospheric surface layer.Coherent structures also exist in the stable stratified surface layer, but they have aninverse asymmetry and occupy only the lower several metres. Wavelike activitydominates in the upper part of the stable surface layer.The characteristic time of surface-layer adjustment to the rapid changes of solarradiation (due to cloud shadows or cloud gaps) was found to be on the order ofone minute. Such a time interval is required for coherent structure to reach the topof surface layer.

Koprov, B. M.; Koprov, V. M.; Makarova, T. I.; et al.

413

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

414

Structure Analyses of Ti-Based Self-Formed Barrier Layers  

NASA Astrophysics Data System (ADS)

Self-formed Ti-based barrier layer using Cu(Ti) alloy seed applied to 45-nm-node dual-damascene interconnects was reported to have sufficient barrier strength to prevent Cu diffusion into dielectrics. The constituent Ti compounds in the self-formed Ti-based barrier layers and the barrier structures in Cu(Ti)/dielectric samples were identified by X-ray photoelectron spectroscopy (XPS) analyses. Two types of SiOC with low dielectric constants, SiO2, and SiCN were used as dielectrics. The Ti-based barrier layers consisted mainly of amorphous Ti oxides such as TiO2, Ti2O3, and TiO, regardless of the dielectric. In addition to Ti oxides, barrier layers containing TiC, TiSi, and TiN w