Plasmonic eigenmodes in individual and bow-tie graphene nanotriangles

NASA Astrophysics Data System (ADS)

Wang, Weihua; Christensen, Thomas; Jauho, Antti-Pekka; Thygesen, Kristian S.; Wubs, Martijn; Mortensen, N. Asger

2015-04-01

In classical electrodynamics, nanostructured graphene is commonly modeled by the computationally demanding problem of a three-dimensional conducting film of atomic-scale thickness. Here, we propose an efficient alternative two-dimensional electrostatic approach where all calculation procedures are restricted to the graphene sheet. Furthermore, to explore possible quantum effects, we perform tight-binding calculations, adopting a random-phase approximation. We investigate multiple plasmon modes in 20 nm equilateral triangles of graphene, treating the optical response classically as well as quantum mechanically. Compared to the classical plasmonic spectrum which is ``blind'' to the edge termination, we find that the quantum plasmon frequencies exhibit blueshifts in the case of armchair edge termination of the underlying atomic lattice, while redshifts are found for zigzag edges. Furthermore, we find spectral features in the zigzag case which are associated with electronic edge states not present for armchair termination. Merging pairs of triangles into dimers, plasmon hybridization leads to energy splitting that appears strongest in classical calculations while splitting is lower for armchair edges and even more reduced for zigzag edges. Our various results illustrate a surprising phenomenon: Even 20 nm large graphene structures clearly exhibit quantum plasmonic features due to atomic-scale details in the edge termination.

Tungsten dust impact on ITER-like plasma edge

DOE PAGES

Smirnov, R. D.; Krasheninnikov, S. I.; Pigarov, A. Yu.; ...

2015-01-12

The impact of tungsten dust originating from divertor plates on the performance of edge plasma in ITER-like discharge is evaluated using computer modeling with the coupled dust-plasma transport code DUSTT-UEDGE. Different dust injection parameters, including dust size and mass injection rates, are surveyed. It is found that tungsten dust injection with rates as low as a few mg/s can lead to dangerously high tungsten impurity concentrations in the plasma core. Dust injections with rates of a few tens of mg/s are shown to have a significant effect on edge plasma parameters and dynamics in ITER scale tokamaks. The large impactmore » of certain phenomena, such as dust shielding by an ablation cloud and the thermal force on tungsten ions, on dust/impurity transport in edge plasma and consequently on core tungsten contamination level is demonstrated. Lastly, it is also found that high-Z impurities provided by dust can induce macroscopic self-sustained plasma oscillations in plasma edge leading to large temporal variations of edge plasma parameters and heat load to divertor target plates.« less

Low-speed aerodynamic characteristics from wind-tunnel tests of a large-scale advanced arrow-wing supersonic-cruise transport concept

NASA Technical Reports Server (NTRS)

Smith, P. M.

1978-01-01

Tests have been conducted to extend the existing low speed aerodynamic data base of advanced supersonic-cruise arrow wing configurations. Principle configuration variables included wing leading-edge flap deflection, wing trailing-edge flap deflection, horizontal tail effectiveness, and fuselage forebody strakes. A limited investigation was also conducted to determine the low speed aerodynamic effects due to slotted training-edge flaps. Results of this investigation demonstrate that deflecting the wing leading-edge flaps downward to suppress the wing apex vortices provides improved static longitudinal stability; however, it also results in significantly reduced static directional stability. The use of a selected fuselage forebody strakes is found to be effective in increasing the level of positive static directional stability. Drooping the fuselage nose, which is required for low-speed pilot vision, significantly improves the later-directional trim characteristics.

Vortex interaction with a leading-edge of finite thickness

NASA Technical Reports Server (NTRS)

Sohn, D.; Rockwell, Donald

1987-01-01

Vortex interaction with a thick elliptical leading-edge at zero relative offset produces a pronounced secondary vortes of opposite sense that travels with the same phase speed as the primaty vortex along the lower surface of the edge. The edge thickness (scale) relative to the incident vorticity field has a strong effect on the distortion of the incident primary vortex during the impingement processs. When the thickness is sufficiently small, there is a definite severing of the incident vortex and the portion of the incident vortex that travels along the upper part of the elliptical surface has a considerably larger phase speed than that along the lower surface; this suggests that the integrated loading along the upper surface is more strongly correlated. When the thickness becomes too large, then most, if not all, of the incident vortex passes below the leading-edge. On the other hand, the relative tranverse offset of the edge with respect to the center of the incident vortex has a significant effect on the secondary vortex formation.

High-uniformity centimeter-wide Si etching method for MEMS devices with large opening elements

NASA Astrophysics Data System (ADS)

Okamoto, Yuki; Tohyama, Yukiya; Inagaki, Shunsuke; Takiguchi, Mikio; Ono, Tomoki; Lebrasseur, Eric; Mita, Yoshio

2018-04-01

We propose a compensated mesh pattern filling method to achieve highly uniform wafer depth etching (over hundreds of microns) with a large-area opening (over centimeter). The mesh opening diameter is gradually changed between the center and the edge of a large etching area. Using such a design, the etching depth distribution depending on sidewall distance (known as the local loading effect) inversely compensates for the over-centimeter-scale etching depth distribution, known as the global or within-die(chip)-scale loading effect. Only a single DRIE with test structure patterns provides a micro-electromechanical systems (MEMS) designer with the etched depth dependence on the mesh opening size as well as on the distance from the chip edge, and the designer only has to set the opening size so as to obtain a uniform etching depth over the entire chip. This method is useful when process optimization cannot be performed, such as in the cases of using standard conditions for a foundry service and of short turn-around-time prototyping. To demonstrate, a large MEMS mirror that needed over 1 cm2 of backside etching was successfully fabricated using as-is-provided DRIE conditions.

Electronic structure and aromaticity of large-scale hexagonal graphene nanoflakes.

PubMed

Hu, Wei; Lin, Lin; Yang, Chao; Yang, Jinlong

2014-12-07

With the help of the recently developed SIESTA-pole (Spanish Initiative for Electronic Simulations with Thousands of Atoms) - PEXSI (pole expansion and selected inversion) method [L. Lin, A. García, G. Huhs, and C. Yang, J. Phys.: Condens. Matter 26, 305503 (2014)], we perform Kohn-Sham density functional theory calculations to study the stability and electronic structure of hydrogen passivated hexagonal graphene nanoflakes (GNFs) with up to 11,700 atoms. We find the electronic properties of GNFs, including their cohesive energy, edge formation energy, highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap, edge states, and aromaticity, depend sensitively on the type of edges (armchair graphene nanoflakes (ACGNFs) and zigzag graphene nanoflakes (ZZGNFs)), size and the number of electrons. We observe that, due to the edge-induced strain effect in ACGNFs, large-scale ACGNFs' edge formation energy decreases as their size increases. This trend does not hold for ZZGNFs due to the presence of many edge states in ZZGNFs. We find that the energy gaps E(g) of GNFs all decay with respect to 1/L, where L is the size of the GNF, in a linear fashion. But as their size increases, ZZGNFs exhibit more localized edge states. We believe the presence of these states makes their gap decrease more rapidly. In particular, when L is larger than 6.40 nm, we find that ZZGNFs exhibit metallic characteristics. Furthermore, we find that the aromatic structures of GNFs appear to depend only on whether the system has 4N or 4N + 2 electrons, where N is an integer.

Some factors influencing radiation of sound from flow interaction with edges of finite surfaces

NASA Technical Reports Server (NTRS)

Hayden, R. E.; Fox, H. L.; Chanaud, R. C.

1976-01-01

Edges of surfaces which are exposed to unsteady flow cause both strictly acoustic effects and hydrodynamic effects, in the form of generation of new hydrodynamic sources in the immediate vicinity of the edge. An analytical model is presented which develops the explicit sound-generation role of the velocity and Mach number of the eddy convection past the edge, and the importance of relative scale lengths of the turbulence, as well as the relative intensity of pressure fluctuations. The Mach number (velocity) effects show that the important paramater is the convection Mach number of the eddies. The effects of turbulence scale lengths, isotropy, and spatial density (separation) are shown to be important in determining the level and spectrum of edge sound radiated for the edge dipole mechanism. Experimental data is presented which provides support for the dipole edge noise model in terms of Mach number (velocity) scaling, parametric dependence on flow field parameter, directivity, and edge diffraction effects.

Making Sense in the Edge of Chaos: A Framework for Effective Initial Response Efforts to Large-Scale Incidents

DTIC Science & Technology

2010-09-01

working with equally experienced partners who can, cumulatively, help each other make sense of chaotic situations. “Human brains collect, organize...but a process reinforced by years of Fire Department training. No matter what we do, even an optimally functioning human brain will prepare for...trick or reorganize the brain of those who will be first responding incident commanders to an edge-of-chaos event into creatively making sense of

[Scale effect of Nanjing urban green infrastructure network pattern and connectivity analysis.

PubMed

Yu, Ya Ping; Yin, Hai Wei; Kong, Fan Hua; Wang, Jing Jing; Xu, Wen Bin

2016-07-01

Based on ArcGIS, Erdas, GuidosToolbox, Conefor and other software platforms, using morphological spatial pattern analysis (MSPA) and landscape connectivity analysis methods, this paper quantitatively analysed the scale effect, edge effect and distance effect of the Nanjing urban green infrastructure network pattern in 2013 by setting different pixel sizes (P) and edge widths in MSPA analysis, and setting different dispersal distance thresholds in landscape connectivity analysis. The results showed that the type of landscape acquired based on the MSPA had a clear scale effect and edge effect, and scale effects only slightly affected landscape types, whereas edge effects were more obvious. Different dispersal distances had a great impact on the landscape connectivity, 2 km or 2.5 km dispersal distance was a critical threshold for Nanjing. When selecting the pixel size 30 m of the input data and the edge wide 30 m used in the morphological model, we could get more detailed landscape information of Nanjing UGI network. Based on MSPA and landscape connectivity, analysis of the scale effect, edge effect, and distance effect on the landscape types of the urban green infrastructure (UGI) network was helpful for selecting the appropriate size, edge width, and dispersal distance when developing these networks, and for better understanding the spatial pattern of UGI networks and the effects of scale and distance on the ecology of a UGI network. This would facilitate a more scientifically valid set of design parameters for UGI network spatiotemporal pattern analysis. The results of this study provided an important reference for Nanjing UGI networks and a basis for the analysis of the spatial and temporal patterns of medium-scale UGI landscape networks in other regions.

Performance of an Achromatic Focal Plane Mask for Exoplanet Imaging Coronagraphy

NASA Technical Reports Server (NTRS)

Newman, Kevin; Belikov, Ruslan; Pluzhnik, Eugene; Balasubramanian, Kunjithapatham; Wilson, Dan

2014-01-01

Coronagraph technology combined with wavefront control is close to achieving the contrast and inner working angle requirements in the lab necessary to observe the faint signal of an Earth-like exoplanet in monochromatic light. An important remaining technological challenge is to achieve high contrast in broadband light. Coronagraph bandwidth is largely limited by chromaticity of the focal plane mask, which is responsible for blocking the stellar PSF. The size of a stellar PSF scales linearly with wavelength; ideally, the size of the focal plane mask would also scale with wavelength. A conventional hard-edge focal plane mask has a fixed size, normally sized for the longest wavelength in the observational band to avoid starlight leakage. The conventional mask is oversized for shorter wavelengths and blocks useful discovery space. Recently we presented a solution to the size chromaticity challenge with a focal plane mask designed to scale its effective size with wavelength. In this paper, we analyze performance of the achromatic size-scaling focal plane mask within a Phase Induced Amplitude Apodization (PIAA) coronagraph. We present results from wavefront control around the achromatic focal plane mask, and demonstrate the size-scaling effect of the mask with wavelength. The edge of the dark zone, and therefore the inner working angle of the coronagraph, scale with wavelength. The achromatic mask enables operation in a wider band of wavelengths compared with a conventional hard-edge occulter.

Stress transfer mechanisms at the submicron level for graphene/polymer systems.

PubMed

Anagnostopoulos, George; Androulidakis, Charalampos; Koukaras, Emmanuel N; Tsoukleri, Georgia; Polyzos, Ioannis; Parthenios, John; Papagelis, Konstantinos; Galiotis, Costas

2015-02-25

The stress transfer mechanism from a polymer substrate to a nanoinclusion, such as a graphene flake, is of extreme interest for the production of effective nanocomposites. Previous work conducted mainly at the micron scale has shown that the intrinsic mechanism of stress transfer is shear at the interface. However, since the interfacial shear takes its maximum value at the very edge of the nanoinclusion it is of extreme interest to assess the effect of edge integrity upon axial stress transfer at the submicron scale. Here, we conduct a detailed Raman line mapping near the edges of a monolayer graphene flake that is simply supported onto an epoxy-based photoresist (SU8)/poly(methyl methacrylate) matrix at steps as small as 100 nm. We show for the first time that the distribution of axial strain (stress) along the flake deviates somewhat from the classical shear-lag prediction for a region of ∼ 2 μm from the edge. This behavior is mainly attributed to the presence of residual stresses, unintentional doping, and/or edge effects (deviation from the equilibrium values of bond lengths and angles, as well as different edge chiralities). By considering a simple balance of shear-to-normal stresses at the interface we are able to directly convert the strain (stress) gradient to values of interfacial shear stress for all the applied tensile levels without assuming classical shear-lag behavior. For large flakes a maximum value of interfacial shear stress of 0.4 MPa is obtained prior to flake slipping.

Edge of polar cap patches

NASA Astrophysics Data System (ADS)

Hosokawa, K.; Taguchi, S.; Ogawa, Y.

2016-04-01

On the night of 4 December 2013, a sequence of polar cap patches was captured by an all-sky airglow imager (ASI) in Longyearbyen, Norway (78.1°N, 15.5°E). The 630.0 nm airglow images from the ASI of 4 second exposure time, oversampled the emission of natural lifetime (with quenching) of at least ˜30 sec, introduce no observational blurring effects. By using such high-quality ASI images, we succeeded in visualizing an asymmetry in the gradients between the leading/trailing edges of the patches in a 2-D fashion. The gradient in the leading edge was found to be 2-3 times steeper than that in the trailing edge. We also identified fingerlike structures, appearing only along the trailing edge of the patches, whose horizontal scale size ranged from 55 to 210 km. These fingers are considered to be manifestations of plasma structuring through the gradient-drift instability (GDI), which is known to occur only along the trailing edge of patches. That is, the current 2-D observations visualized, for the first time, how GDI stirs the patch plasma and such a mixing process makes the trailing edge more gradual. This result strongly implies a close connection between the GDI-driven plasma stirring and the asymmetry in the large-scale shape of patches and then suggests that the fingerlike structures can be used as markers to estimate the fine-scale structure in the plasma flow within patches.

Quantifying the effect of hydrogen on dislocation dynamics: A three-dimensional discrete dislocation dynamics framework

NASA Astrophysics Data System (ADS)

Gu, Yejun; El-Awady, Jaafar A.

2018-03-01

We present a new framework to quantify the effect of hydrogen on dislocations using large scale three-dimensional (3D) discrete dislocation dynamics (DDD) simulations. In this model, the first order elastic interaction energy associated with the hydrogen-induced volume change is accounted for. The three-dimensional stress tensor induced by hydrogen concentration, which is in equilibrium with respect to the dislocation stress field, is derived using the Eshelby inclusion model, while the hydrogen bulk diffusion is treated as a continuum process. This newly developed framework is utilized to quantify the effect of different hydrogen concentrations on the dynamics of a glide dislocation in the absence of an applied stress field as well as on the spacing between dislocations in an array of parallel edge dislocations. A shielding effect is observed for materials having a large hydrogen diffusion coefficient, with the shield effect leading to the homogenization of the shrinkage process leading to the glide loop maintaining its circular shape, as well as resulting in a decrease in dislocation separation distances in the array of parallel edge dislocations. On the other hand, for materials having a small hydrogen diffusion coefficient, the high hydrogen concentrations around the edge characters of the dislocations act to pin them. Higher stresses are required to be able to unpin the dislocations from the hydrogen clouds surrounding them. Finally, this new framework can open the door for further large scale studies on the effect of hydrogen on the different aspects of dislocation-mediated plasticity in metals. With minor modifications of the current formulations, the framework can also be extended to account for general inclusion-induced stress field in discrete dislocation dynamics simulations.

Evaluation of Test Methods for Triaxially Braided Composites using a Meso-Scale Finite Element Model

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

Zhang, Chao

The characterization of triaxially braided composite is complicate due to the nonuniformity of deformation within the unit cell as well as the possibility of the freeedge effect related to the large size of the unit cell. Extensive experimental investigation has been conducted to develop more accurate test approaches in characterizing the actual mechanical properties of the material we are studying. In this work, a meso-scale finite element model is utilized to simulate two complex specimens: notched tensile specimen and tube tensile specimen, which are designed to avoid the free-edge effect and free-edge effect induced premature edge damage. The full fieldmore » strain data is predicted numerically and compared with experimental data obtained by Digit Image Correlation. The numerically predicted tensile strength values are compared with experimentally measured results. The discrepancy between numerically predicted and experimentally measured data, the capability of different test approaches are analyzed and discussed. The presented numerical model could serve as assistance to the evaluation of different test methods, and is especially useful in identifying potential local damage events.« less

Local and landscape scale factors influencing edge effects on woodland salamanders.

PubMed

Moseley, Kurtis R; Ford, W Mark; Edwards, John W

2009-04-01

We examined local and landscape-scale variable influence on the depth and magnitude of edge effects on woodland salamanders in mature mixed mesophytic and northern hardwood forest adjacent to natural gas well sites maintained as wildlife openings. We surveyed woodland salamander occurrence from June-August 2006 at 33 gas well sites in the Monongahela National Forest, West Virginia. We used an information-theoretic approach to test nine a priori models explaining landscape-scale effects on woodland salamander capture proportion within 20 m of field edge. Salamander capture proportion was greater within 0-60 m than 61-100 m of field edges. Similarly, available coarse woody debris proportion was greater within 0-60 m than 61-100 m of field edge. Our ASPECT model, that incorporated the single variable aspect, received the strongest support for explaining landscape-scale effects on salamander capture proportion within 20 m of opening edge. The ASPECT model indicated that fewer salamanders occurred within 20 m of opening edges on drier, hotter southwestern aspects than in moister, cooler northeastern aspects. Our results suggest that forest habitat adjacent to maintained edges and with sufficient cover still can provide suitable habitat for woodland salamander species in central Appalachian mixed mesophytic and northern hardwood forests. Additionally, our modeling results support the contention that edge effects are more severe on southwesterly aspects. These results underscore the importance of distinguishing among different edge types as well as placing survey locations within a landscape context when investigating edge impacts on woodland salamanders.

Controllable Edge Oxidation and Bubbling Exfoliation Enable the Fabrication of High Quality Water Dispersible Graphene

PubMed Central

Tian, Suyun; Sun, Jing; Yang, Siwei; He, Peng; Wang, Gang; Di, Zengfeng; Ding, Guqiao; Xie, Xiaoming; Jiang, Mianheng

2016-01-01

Despite significant progresses made on mass production of chemically exfoliated graphene, the quality, cost and environmental friendliness remain major challenges for its market penetration. Here, we present a fast and green exfoliation strategy for large scale production of high quality water dispersible few layer graphene through a controllable edge oxidation and localized gas bubbling process. Mild edge oxidation guarantees that the pristine sp2 lattice is largely intact and the edges are functionalized with hydrophilic groups, giving rise to high conductivity and good water dispersibility at the same time. The aqueous concentration can be as high as 5.0 mg mL−1, which is an order of magnitude higher than previously reports. The water soluble graphene can be directly spray-coated on various substrates, and the back-gated field effect transistor give hole and electron mobility of ~496 and ~676 cm2 V−1 s−1, respectively. These results achieved are expected to expedite various applications of graphene. PMID:27666869

Controllable Edge Oxidation and Bubbling Exfoliation Enable the Fabrication of High Quality Water Dispersible Graphene.

PubMed

Tian, Suyun; Sun, Jing; Yang, Siwei; He, Peng; Wang, Gang; Di, Zengfeng; Ding, Guqiao; Xie, Xiaoming; Jiang, Mianheng

2016-09-26

Despite significant progresses made on mass production of chemically exfoliated graphene, the quality, cost and environmental friendliness remain major challenges for its market penetration. Here, we present a fast and green exfoliation strategy for large scale production of high quality water dispersible few layer graphene through a controllable edge oxidation and localized gas bubbling process. Mild edge oxidation guarantees that the pristine sp 2 lattice is largely intact and the edges are functionalized with hydrophilic groups, giving rise to high conductivity and good water dispersibility at the same time. The aqueous concentration can be as high as 5.0 mg mL -1 , which is an order of magnitude higher than previously reports. The water soluble graphene can be directly spray-coated on various substrates, and the back-gated field effect transistor give hole and electron mobility of ~496 and ~676 cm 2 V -1 s -1 , respectively. These results achieved are expected to expedite various applications of graphene.

Controllable Edge Oxidation and Bubbling Exfoliation Enable the Fabrication of High Quality Water Dispersible Graphene

NASA Astrophysics Data System (ADS)

Tian, Suyun; Sun, Jing; Yang, Siwei; He, Peng; Wang, Gang; di, Zengfeng; Ding, Guqiao; Xie, Xiaoming; Jiang, Mianheng

2016-09-01

Despite significant progresses made on mass production of chemically exfoliated graphene, the quality, cost and environmental friendliness remain major challenges for its market penetration. Here, we present a fast and green exfoliation strategy for large scale production of high quality water dispersible few layer graphene through a controllable edge oxidation and localized gas bubbling process. Mild edge oxidation guarantees that the pristine sp2 lattice is largely intact and the edges are functionalized with hydrophilic groups, giving rise to high conductivity and good water dispersibility at the same time. The aqueous concentration can be as high as 5.0 mg mL-1, which is an order of magnitude higher than previously reports. The water soluble graphene can be directly spray-coated on various substrates, and the back-gated field effect transistor give hole and electron mobility of ~496 and ~676 cm2 V-1 s-1, respectively. These results achieved are expected to expedite various applications of graphene.

Streakline flow visualization study of a horseshoe vortex in a large-scale, two-dimensional turbine stator cascade

NASA Technical Reports Server (NTRS)

Gaugler, R. E.; Russell, L. M.

1980-01-01

Neutrally buoyant helium-filled bubbles were observed as they followed the streamlines in a horseshoe vortex system around the vane leading edge in a large-scale, two-dimensional, turbine stator cascade. Bubbles were introduced into the endwall boundary layer through a slot upstream of the vane leading edge. The paths of the bubbles were recorded photographically as streaklines on 16-mm movie film. Individual frames from the film have been selected, and overlayed to show the details of the horseshoe vortex around the leading edge. The transport of the vortex across the passage near the leading edge is clearly seen when compared to the streaks formed by bubbles carried in the main stream. Limiting streamlines on the endwall surface were traced by the flow of oil drops.

Acoustic testing of a 1.5 pressure ratio low tip speed fan with a serrated rotor (QEP fan B scale model). [reduction of engine noise

NASA Technical Reports Server (NTRS)

Kazin, S. B.; Paas, J. E.; Minzner, W. R.

1973-01-01

A scale model of the bypass flow region of a 1.5 pressure ratio, single stage, low tip speed fan was tested with a serrated rotor leading edge to determine its effects on noise generation. The serrated rotor was produced by cutting teeth into the leading edge of the nominal rotor blades. The effects of speed and exhaust nozzle area on the scale models noise characteristics were investigated with both the nominal rotor and serrated rotor. Acoustic results indicate the serrations reduced front quadrant PNL's at takeoff power. In particular, the 200 foot (61.0 m) sideline noise was reduced from 3 to 4 PNdb at 40 deg for nominal and large nozzle operation. However, the rear quadrant maximum sideline PNL's were increased 1.5 to 3 PNdb at approach thust and up to 2 PNdb at takeoff thust with these serrated rotor blades. The configuration with the serrated rotor produced the lowest maximum 200 foot (61.0 m) sideline PNL for any given thust when the large nozzle (116% of design area) was employed.

Edge detection based on adaptive threshold b-spline wavelet for optical sub-aperture measuring

NASA Astrophysics Data System (ADS)

Zhang, Shiqi; Hui, Mei; Liu, Ming; Zhao, Zhu; Dong, Liquan; Liu, Xiaohua; Zhao, Yuejin

2015-08-01

In the research of optical synthetic aperture imaging system, phase congruency is the main problem and it is necessary to detect sub-aperture phase. The edge of the sub-aperture system is more complex than that in the traditional optical imaging system. And with the existence of steep slope for large-aperture optical component, interference fringe may be quite dense when interference imaging. Deep phase gradient may cause a loss of phase information. Therefore, it's urgent to search for an efficient edge detection method. Wavelet analysis as a powerful tool is widely used in the fields of image processing. Based on its properties of multi-scale transform, edge region is detected with high precision in small scale. Longing with the increase of scale, noise is reduced in contrary. So it has a certain suppression effect on noise. Otherwise, adaptive threshold method which sets different thresholds in various regions can detect edge points from noise. Firstly, fringe pattern is obtained and cubic b-spline wavelet is adopted as the smoothing function. After the multi-scale wavelet decomposition of the whole image, we figure out the local modulus maxima in gradient directions. However, it also contains noise, and thus adaptive threshold method is used to select the modulus maxima. The point which greater than threshold value is boundary point. Finally, we use corrosion and expansion deal with the resulting image to get the consecutive boundary of image.

Grid-Enabled Quantitative Analysis of Breast Cancer

DTIC Science & Technology

2009-10-01

large-scale, multi-modality computerized image analysis . The central hypothesis of this research is that large-scale image analysis for breast cancer...pilot study to utilize large scale parallel Grid computing to harness the nationwide cluster infrastructure for optimization of medical image ... analysis parameters. Additionally, we investigated the use of cutting edge dataanalysis/ mining techniques as applied to Ultrasound, FFDM, and DCE-MRI Breast

Stress Transfer Mechanisms at the Submicron Level for Graphene/Polymer Systems

PubMed Central

2015-01-01

The stress transfer mechanism from a polymer substrate to a nanoinclusion, such as a graphene flake, is of extreme interest for the production of effective nanocomposites. Previous work conducted mainly at the micron scale has shown that the intrinsic mechanism of stress transfer is shear at the interface. However, since the interfacial shear takes its maximum value at the very edge of the nanoinclusion it is of extreme interest to assess the effect of edge integrity upon axial stress transfer at the submicron scale. Here, we conduct a detailed Raman line mapping near the edges of a monolayer graphene flake that is simply supported onto an epoxy-based photoresist (SU8)/poly(methyl methacrylate) matrix at steps as small as 100 nm. We show for the first time that the distribution of axial strain (stress) along the flake deviates somewhat from the classical shear-lag prediction for a region of ∼2 μm from the edge. This behavior is mainly attributed to the presence of residual stresses, unintentional doping, and/or edge effects (deviation from the equilibrium values of bond lengths and angles, as well as different edge chiralities). By considering a simple balance of shear-to-normal stresses at the interface we are able to directly convert the strain (stress) gradient to values of interfacial shear stress for all the applied tensile levels without assuming classical shear-lag behavior. For large flakes a maximum value of interfacial shear stress of 0.4 MPa is obtained prior to flake slipping. PMID:25644121

Large-Scale Outflows in Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Colbert, E. J. M.; Baum, S. A.

1995-12-01

\\catcode`\\@=11 \\ialign{m @th#1hfil ##hfil \\crcr#2\\crcr\\sim\\crcr}}} \\catcode`\\@=12 Highly collimated outflows extend out to Mpc scales in many radio-loud active galaxies. In Seyfert galaxies, which are radio-quiet, the outflows extend out to kpc scales and do not appear to be as highly collimated. In order to study the nature of large-scale (>~1 kpc) outflows in Seyferts, we have conducted optical, radio and X-ray surveys of a distance-limited sample of 22 edge-on Seyfert galaxies. Results of the optical emission-line imaging and spectroscopic survey imply that large-scale outflows are present in >~{{1} /{4}} of all Seyferts. The radio (VLA) and X-ray (ROSAT) surveys show that large-scale radio and X-ray emission is present at about the same frequency. Kinetic luminosities of the outflows in Seyferts are comparable to those in starburst-driven superwinds. Large-scale radio sources in Seyferts appear diffuse, but do not resemble radio halos found in some edge-on starburst galaxies (e.g. M82). We discuss the feasibility of the outflows being powered by the active nucleus (e.g. a jet) or a circumnuclear starburst.

Enhancing the transmission efficiency by edge deletion in scale-free networks

NASA Astrophysics Data System (ADS)

Zhang, Guo-Qing; Wang, Di; Li, Guo-Jie

2007-07-01

How to improve the transmission efficiency of Internet-like packet switching networks is one of the most important problems in complex networks as well as for the Internet research community. In this paper we propose a convenient method to enhance the transmission efficiency of scale-free networks dramatically by kicking out the edges linking to nodes with large betweenness, which we called the “black sheep.” The advantages of our method are of facility and practical importance. Since the black sheep edges are very costly due to their large bandwidth, our method could decrease the cost as well as gain higher throughput of networks. Moreover, we analyze the curve of the largest betweenness on deleting more and more black sheep edges and find that there is a sharp transition at the critical point where the average degree of the nodes ⟨k⟩→2 .

Streakline flow visualization study of a horseshoe vortex in a large-scale, two-dimensional turbine stator cascade

NASA Technical Reports Server (NTRS)

Gaugler, R. E.; Russell, L. M.

1979-01-01

Neutrally bouyant helium-filled bubbles were observed as they followed the streamlines in a horseshoe vortex system around the vane leading edge in a large scale, two dimensional, turbine stator cascade. Inlet Reynolds number, based on true chord, ranged between 100,000 to 300,000. Bubbles were introduced into the endwall boundary layer through a slot upstream of the vane leading edge. The paths of the bubbles were recorded photographically as streaklines on 16 mm movie film. Individual frames from the film were selected, and overlayed to show the details of the horseshoe vortex around the leading edge. The transport of the vortex across the passage near the leading edge is clearly seen when compared to the streaks formed by bubbles carried in the main stream. Limiting streamlines on the endwall surface were traced by the flow of oil drops.

How large is large enough for insects? Forest fragmentation effects at three spatial scales

NASA Astrophysics Data System (ADS)

Ribas, C. R.; Sobrinho, T. G.; Schoereder, J. H.; Sperber, C. F.; Lopes-Andrade, C.; Soares, S. M.

2005-02-01

Several mechanisms may lead to species loss in fragmented habitats, such as edge and shape effects, loss of habitat and heterogeneity. Ants and crickets were sampled in 18 forest remnants in south-eastern Brazil, to test whether a group of small remnants maintains the same insect species richness as similar sized large remnants, at three spatial scales. We tested hypotheses about alpha and gamma diversity to explain the results. Groups of remnants conserve as many species of ants as a single one. Crickets, however, showed a scale-dependent pattern: at small scales there was no significant or important difference between groups of remnants and a single one, while at the larger scale the group of remnants maintained more species. Alpha diversity (local species richness) was similar in a group of remnants and in a single one, at the three spatial scales, both for ants and crickets. Gamma diversity, however, varied both with taxa (ants and crickets) and spatial scale, which may be linked to insect mobility, remnant isolation, and habitat heterogeneity. Biological characteristics of the organisms involved have to be considered when studying fragmentation effects, as well as spatial scale at which it operates. Mobility of the organisms influences fragmentation effects, and consequently conservation strategies.

Zooming in and out: Scale dependence of extrinsic and intrinsic factors affecting salt marsh erosion

NASA Astrophysics Data System (ADS)

Wang, Heng; van der Wal, Daphne; Li, Xiangyu; van Belzen, Jim; Herman, Peter M. J.; Hu, Zhan; Ge, Zhenming; Zhang, Liquan; Bouma, Tjeerd J.

2017-07-01

Salt marshes are valuable ecosystems that provide important ecosystem services. Given the global scale of marsh loss due to climate change and coastal squeeze, there is a pressing need to identify the critical extrinsic (wind exposure and foreshore morphology) and intrinsic factors (soil and vegetation properties) affecting the erosion of salt marsh edges. In this study, we quantified rates of cliff lateral retreat (i.e., the eroding edge of a salt marsh plateau) using a time series of aerial photographs taken over four salt marsh sites in the Westerschelde estuary, the Netherlands. In addition, we experimentally quantified the erodibility of sediment cores collected from the marsh edge of these four marshes using wave tanks. Our results revealed the following: (i) at the large scale, wind exposure and the presence of pioneer vegetation in front of the cliff were the key factors governing cliff retreat rates; (ii) at the intermediate scale, foreshore morphology was partially related to cliff retreat; (iii) at the local scale, the erodibility of the sediment itself at the marsh edge played a large role in determining the cliff retreat rate; and (iv) at the mesocosm scale, cliff erodibility was determined by soil properties and belowground root biomass. Thus, both extrinsic and intrinsic factors determined the fate of the salt marsh but at different scales. Our study highlights the importance of understanding the scale dependence of the factors driving the evolution of salt marsh landscapes.

Role of Edges in Complex Network Epidemiology

NASA Astrophysics Data System (ADS)

Zhang, Hao; Jiang, Zhi-Hong; Wang, Hui; Xie, Fei; Chen, Chao

2012-09-01

In complex network epidemiology, diseases spread along contacting edges between individuals and different edges may play different roles in epidemic outbreaks. Quantifying the efficiency of edges is an important step towards arresting epidemics. In this paper, we study the efficiency of edges in general susceptible-infected-recovered models, and introduce the transmission capability to measure the efficiency of edges. Results show that deleting edges with the highest transmission capability will greatly decrease epidemics on scale-free networks. Basing on the message passing approach, we get exact mathematical solution on configuration model networks with edge deletion in the large size limit.

The Snowmastodon Project: cutting-edge science on the blade of a bulldozer

USGS Publications Warehouse

Pigati, Jeffery S.; Miller, Ian M.; Johnson, Kirk R.

2015-01-01

Cutting-edge science happens at a variety of scales, from the individual and intimate to the large-scale and collaborative. The publication of a special issue of Quaternary Research in Nov. 2014 dedicated to the scientific findings of the “Snowmastodon Project” highlights what can be done when natural history museums, governmental agencies, and academic institutions work toward a common goal.

An experimental study of heat transfer in a large-scale turbine rotor passage

NASA Astrophysics Data System (ADS)

Blair, Michael F.

1992-06-01

An experimental study of the heat transfer distribution in a turbine rotor passage was conducted in a large-scale, ambient temperature, rotating turbine model. Heat transfer was measured for both the full-span suction and pressure surfaces of the airfoil as well as for the hub endwall surface. The objective of this program was to document the effects of flow three-dimensionality on the heat transfer in a rotating blade row (vs a stationary cascade). Of particular interest were the effects of the hub and tip secondary flows, tip leakage and the leading-edge horseshoe vortex system. The effect of surface roughness on the passage heat transfer was also investigated. Midspan results are compared with both smooth-wall and rough-wall finite-difference two-dimensional heat transfer predictions. Contour maps of Stanton number for both the rotor airfoil and endwall surfaces revealed numerous regions of high heat transfer produced by the three-dimensional flows within the rotor passage. Of particular importance are regions of local enhancement (as much as 100 percent over midspan values) produced on the airfoil suction surface by the secondary flows and tip-leakage vortices and on the hub endwall by the leading-edge horseshoe vortex system.

Can dispersal mode predict corridor effects on plant parasites?

PubMed

Sullivan, Lauren L; Johnson, Brenda L; Brudvig, Lars A; Haddad, Nick M

2011-08-01

Habitat corridors, a common management strategy for increasing connectivity in fragmented landscapes, have experimentally validated positive influences on species movement and diversity. However, long-standing concerns that corridors could negatively impact native species by spreading antagonists, such as disease, remain largely untested. Using a large-scale, replicated experiment, we evaluated whether corridors increase the incidence of plant parasites. We found that corridor impacts varied with parasite dispersal mode. Connectivity provided by corridors increased incidence of biotically dispersed parasites (galls on Solidago odora) but not of abiotically dispersed parasites (foliar fungi on S. odora and three Lespedeza spp.). Both biotically and abiotically dispersed parasites responded to edge effects, but the direction of responses varied across species. Although our results require additional tests for generality to other species and landscapes, they suggest that, when establishing conservation corridors, managers should focus on mitigating two potential negative effects: the indirect effects of narrow corridors in creating edges and direct effects of corridors in enhancing connectivity of biotically dispersed parasites.

High-order multipole radiation from quantum Hall states in Dirac materials

NASA Astrophysics Data System (ADS)

Gullans, Michael J.; Taylor, Jacob M.; Imamoǧlu, Ataç; Ghaemi, Pouyan; Hafezi, Mohammad

2017-06-01

We investigate the optical response of strongly disordered quantum Hall states in two-dimensional Dirac materials and find qualitatively different effects in the radiation properties of the bulk versus the edge. We show that the far-field radiation from the edge is characterized by large multipole moments (>50 ) due to the efficient transfer of angular momentum from the electrons into the scattered light. The maximum multipole transition moment is a direct measure of the coherence length of the edge states. Accessing these multipole transitions would provide new tools for optical spectroscopy and control of quantum Hall edge states. On the other hand, the far-field radiation from the bulk appears as random dipole emission with spectral properties that vary with the local disorder potential. We determine the conditions under which this bulk radiation can be used to image the disorder landscape. Such optical measurements can probe submicron-length scales over large areas and provide complementary information to scanning probe techniques. Spatially resolving this bulk radiation would serve as a novel probe of the percolation transition near half filling.

Thermal properties of composite materials : effective conductivity tensor and edge effects

NASA Astrophysics Data System (ADS)

Matine, A.; Boyard, N.; Cartraud, P.; Legrain, G.; Jarny, Y.

2012-11-01

The homogenization theory is a powerful approach to determine the effective thermal conductivity tensor of heterogeneous materials such as composites, including thermoset matrix and fibres. Once the effective properties are calculated, they can be used to solve a heat conduction problem on the composite structure at the macroscopic scale. This approach leads to good approximations of both the heat flux and temperature in the interior zone of the structure, however edge effects occur in the vicinity of the domain boundaries. In this paper, following the approach proposed in [10] for elasticity, it is shown how these edge effects can be corrected. Thus an additional asymptotic expansion is introduced, which plays the role of a edge effect term. This expansion tends to zero far from the boundary, and is assumed to decrease exponentially. Moreover, the length of the edge effect region can be determined from the solution of an eigenvalue problem. Numerical examples are considered for a standard multilayered material. The homogenized solutions computed with a finite element software, and corrected with the edge effect terms, are compared to a heterogeneous finite element solution at the microscopic scale. The influences of the thermal contrast and scale factor are illustrated for different kind of boundary conditions.

Habitat edges have weak effects on duck nest survival at local spatial scales

USGS Publications Warehouse

Raquel, Amelia J; Ringelman, Kevin M.; Ackerman, Joshua T.; Eadie, John M.

2015-01-01

Edge effects on nesting success have been documented in breeding birds in a variety of contexts, but there is still uncertainty in how edge type and spatial scale determine the magnitude and detectability of edge effects. Habitat edges are often viewed as predator corridors that surround or penetrate core habitat and increase the risk of predation for nearby nests. We studied the effects of three different types of potential predator corridors (main perimeter roads, field boundaries, and ATV trails within fields) on waterfowl nest survival in California. We measured the distance from duck nests to the nearest edge of each type, and used distance as a covariate in a logistic exposure analysis of nest survival. We found only weak evidence for edge effects due to predation. The best supported model of nest survival included all three distance categories, and while all coefficient estimates were positive (indicating that survival increased with distance from edge), 85% coefficient confidence intervals approached or bounded zero indicating an overall weak effect of habitat edges on nest success. We suggest that given the configuration of edges at our site, there may be few areas far enough from hard edges to be considered ‘core’ habitat, making edge effects on nest survival particularly difficult to detect.

Adiabatic Edge Channel Transport in a Nanowire Quantum Point Contact Register.

PubMed

Heedt, S; Manolescu, A; Nemnes, G A; Prost, W; Schubert, J; Grützmacher, D; Schäpers, Th

2016-07-13

We report on a prototype device geometry where a number of quantum point contacts are connected in series in a single quasi-ballistic InAs nanowire. At finite magnetic field the backscattering length is increased up to the micron-scale and the quantum point contacts are connected adiabatically. Hence, several input gates can control the outcome of a ballistic logic operation. The absence of backscattering is explained in terms of selective population of spatially separated edge channels. Evidence is provided by regular Aharonov-Bohm-type conductance oscillations in transverse magnetic fields, in agreement with magnetoconductance calculations. The observation of the Shubnikov-de Haas effect at large magnetic fields corroborates the existence of spatially separated edge channels and provides a new means for nanowire characterization.

Large-Scale Wind-Tunnel Tests of an Airplane Model with an Unswept, Tilt Wing of Aspect Ratio 5.5, and with Four Propellers and Blowing Flaps

NASA Technical Reports Server (NTRS)

Weiberg, James A.; Holzhauser, Curt A.

1961-01-01

Tests were made of a large-scale tilt-wing deflected-slipstream VTOL airplane with blowing-type BLC trailing-edge flaps. The model was tested with flap deflections of 0 deg. without BLC, 50 deg. with and without BLC, and 80 deg. with BLC for wing-tilt angles of 0, 30, and 50 deg. Included are results of tests of the model equipped with a leading-edge flap and the results of tests of the model in the presence of a ground plane.

Prevalence, Features, and Prognostic Importance of Edge Dissection After Drug-Eluting Stent Implantation: An ADAPT-DES Intravascular Ultrasound Substudy.

PubMed

Kobayashi, Nobuaki; Mintz, Gary S; Witzenbichler, Bernhard; Metzger, D Christopher; Rinaldi, Michael J; Duffy, Peter L; Weisz, Giora; Stuckey, Thomas D; Brodie, Bruce R; Parvataneni, Rupa; Kirtane, Ajay J; Stone, Gregg W; Maehara, Akiko

2016-07-01

Intravascular ultrasound detects stent edge dissections after percutaneous coronary intervention that are not seen angiographically. This study investigated the association between stent edge dissections and clinical outcomes. ADAPT-DES (Assessment of Dual Antiplatelet Therapy With Drug-Eluting Stents) was a large-scale, prospective, multicenter study of patients undergoing drug-eluting stent implantation. In this prospective substudy, 2062 patients (2433 lesions) were evaluated with intravascular ultrasound to characterize the morphological features and clinical outcomes of stent edge dissection after percutaneous coronary intervention. The prevalence of post-percutaneous coronary intervention stent edge dissection was 6.6% per lesion (161 of 2433). Calcified plaque at the proximal stent edge (relative risk [RR]=1.72; P=0.04) and proximal stent edge expansion (RR=1.18; P=0.004) were predictors for proximal dissection; attenuated plaque at the distal stent edge (RR=3.52; P=0.004), distal reference plaque burden (RR=1.56; P<0.0001), and distal edge stent expansion (RR=1.11; P=0.02) were predictors for distal dissection. At 1-year follow-up, target lesion revascularization was more common in lesions with versus without dissection (5.2% versus 2.7%; P=0.04). Multivariable analysis indicated that residual dissection was associated with target lesion revascularization at 1-year follow-up (RR=2.67; P=0.02). Among lesions with dissection, smaller effective lumen area increased the risk of target lesion revascularization at 1-year follow-up (cutoff value of 5.1 mm(2); P=0.05). Greater stent expansion and the presence of large, calcified, and/or attenuated plaques were independent predictors of stent edge dissection. Residual stent edge dissection, especially with a smaller effective lumen area, was associated with target lesion revascularization during 1-year follow-up after drug-eluting stent implantation. URL: http://www.clinicaltrials.gov. Unique identifier: NCT00638794. © 2016 American Heart Association, Inc.

Toward a first-principles integrated simulation of tokamak edge plasmas

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

Chang, C S; Klasky, Scott A; Cummings, Julian

2008-01-01

Performance of the ITER is anticipated to be highly sensitive to the edge plasma condition. The edge pedestal in ITER needs to be predicted from an integrated simulation of the necessary firstprinciples, multi-scale physics codes. The mission of the SciDAC Fusion Simulation Project (FSP) Prototype Center for Plasma Edge Simulation (CPES) is to deliver such a code integration framework by (1) building new kinetic codes XGC0 and XGC1, which can simulate the edge pedestal buildup; (2) using and improving the existing MHD codes ELITE, M3D-OMP, M3D-MPP and NIMROD, for study of large-scale edge instabilities called Edge Localized Modes (ELMs); andmore » (3) integrating the codes into a framework using cutting-edge computer science technology. Collaborative effort among physics, computer science, and applied mathematics within CPES has created the first working version of the End-to-end Framework for Fusion Integrated Simulation (EFFIS), which can be used to study the pedestal-ELM cycles.« less

The former Iron Curtain still drives biodiversity-profit trade-offs in German agriculture.

PubMed

Batáry, Péter; Gallé, Róbert; Riesch, Friederike; Fischer, Christina; Dormann, Carsten F; Mußhoff, Oliver; Császár, Péter; Fusaro, Silvia; Gayer, Christoph; Happe, Anne-Kathrin; Kurucz, Kornélia; Molnár, Dorottya; Rösch, Verena; Wietzke, Alexander; Tscharntke, Teja

2017-09-01

Agricultural intensification drives biodiversity loss and shapes farmers' profit, but the role of legacy effects and detailed quantification of ecological-economic trade-offs are largely unknown. In Europe during the 1950s, the Eastern communist bloc switched to large-scale farming by forced collectivization of small farms, while the West kept small-scale private farming. Here we show that large-scale agriculture in East Germany reduced biodiversity, which has been maintained in West Germany due to >70% longer field edges than those in the East. In contrast, profit per farmland area in the East was 50% higher than that in the West, despite similar yield levels. In both regions, switching from conventional to organic farming increased biodiversity and halved yield levels, but doubled farmers' profits. In conclusion, European Union policy should acknowledge the surprisingly high biodiversity benefits of small-scale agriculture, which are on a par with conversion to organic agriculture.

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

Sullivan, Lauren, L.; Johnson, Brenda, L.; Brudvig, Lars, A.

Habitat corridors, a common management strategy for increasing connectivity in fragmented landscapes, have experimentally validated positive influences on species movement and diversity. However, long-standing concerns that corridors could negatively impact native species by spreading antagonists, such as disease, remain largely untested. Using a large-scale, replicated experiment, we evaluated whether corridors increase the incidence of plant parasites. We found that corridor impacts varied with parasite dispersal mode. Connectivity provided by corridors increased incidence of biotically dispersed parasites (galls on Solidago odora) but not of abiotically dispersed parasites (foliar fungi on S. odora and three Lespedeza spp.). Both biotically and abiotically dispersedmore » parasites responded to edge effects, but the direction of responses varied across species. Although our results require additional tests for generality to other species and landscapes, they suggest that, when establishing conservation corridors, managers should focus on mitigating two potential negative effects: the indirect effects of narrow corridors in creating edges and direct effects of corridors in enhancing connectivity of biotically dispersed parasites.« less

Variation in Local-Scale Edge Effects: Mechanisms and landscape Context

Treesearch

Therese M. Donovan; Peter W. Jones; Elizabeth M. Annand; Frank R. Thompson III

1997-01-01

Ecological processes near habitat edges often differ from processes away from edges. Yet, the generality of "edge effects" has been hotly debated because results vary tremendously. To understand the factors responsible for this variation, we described nest predation and cowbird distribution patterns in forest edge and forest core habitats on 36 randomly...

Unconventional Current Scaling and Edge Effects for Charge Transport through Molecular Clusters

PubMed Central

2017-01-01

Metal–molecule–metal junctions are the key components of molecular electronics circuits. Gaining a microscopic understanding of their conducting properties is central to advancing the field. In the present contribution, we highlight the fundamental differences between single-molecule and ensemble junctions focusing on the fundamentals of transport through molecular clusters. In this way, we elucidate the collective behavior of parallel molecular wires, bridging the gap between single molecule and large-area monolayer electronics, where even in the latter case transport is usually dominated by finite-size islands. On the basis of first-principles charge-transport simulations, we explain why the scaling of the conductivity of a junction has to be distinctly nonlinear in the number of molecules it contains. Moreover, transport through molecular clusters is found to be highly inhomogeneous with pronounced edge effects determined by molecules in locally different electrostatic environments. These effects are most pronounced for comparably small clusters, but electrostatic considerations show that they prevail also for more extended systems. PMID:29043825

Solute effects on edge dislocation pinning in complex alpha-Fe alloys

NASA Astrophysics Data System (ADS)

Pascuet, M. I.; Martínez, E.; Monnet, G.; Malerba, L.

2017-10-01

Reactor pressure vessel steels are well-known to harden and embrittle under neutron irradiation, mainly because of the formation of obstacles to the motion of dislocations, in particular, precipitates and clusters composed of Cu, Ni, Mn, Si and P. In this paper, we employ two complementary atomistic modelling techniques to study the heterogeneous precipitation and segregation of these elements and their effects on the edge dislocations in BCC iron. We use a special and highly computationally efficient Monte Carlo algorithm in a constrained semi-grand canonical ensemble to compute the equilibrium configurations for solute clusters around the dislocation core. Next, we use standard molecular dynamics to predict and analyze the effect of this segregation on the dislocation mobility. Consistently with expectations our results confirm that the required stress for dislocation unpinning from the precipitates formed on top of it is quite large. The identification of the precipitate resistance allows a quantitative treatment of atomistic results, enabling scale transition towards larger scale simulations, such as dislocation dynamics or phase field.

Edge effects and geometric constraints: a landscape-level empirical test.

PubMed

Ribeiro, Suzy E; Prevedello, Jayme A; Delciellos, Ana Cláudia; Vieira, Marcus Vinícius

2016-01-01

Edge effects are pervasive in landscapes yet their causal mechanisms are still poorly understood. Traditionally, edge effects have been attributed to differences in habitat quality along the edge-interior gradient of habitat patches, under the assumption that no edge effects would occur if habitat quality was uniform. This assumption was questioned recently after the recognition that geometric constraints tend to reduce population abundances near the edges of habitat patches, the so-called geometric edge effect (GEE). Here, we present the first empirical, landscape-level evaluation of the importance of the GEE in shaping abundance patterns in fragmented landscapes. Using a data set on the distribution of small mammals across 18 forest fragments, we assessed whether the incorporation of the GEE into the analysis changes the interpretation of edge effects and the degree to which predictions based on the GEE match observed responses. Quantitative predictions were generated for each fragment using simulations that took into account home range, density and matrix use for each species. The incorporation of the GEE into the analysis changed substantially the interpretation of overall observed edge responses at the landscape scale. Observed abundances alone would lead to the conclusion that the small mammals as a group have no consistent preference for forest edges or interiors and that the black-eared opossum Didelphis aurita (a numerically dominant species in the community) has on average a preference for forest interiors. In contrast, incorporation of the GEE suggested that the small mammal community as a whole has a preference for forest edges, whereas D. aurita has no preference for forest edges or interiors. Unexplained variance in edge responses was reduced by the incorporation of GEE, but remained large, varying greatly on a fragment-by-fragment basis. This study demonstrates how to model and incorporate the GEE in analyses of edge effects and that this incorporation is necessary to properly interpret edge effects in landscapes. It also suggests that geometric constraints alone are unlikely to explain the variability in edge responses of a same species among different areas, highlighting the need to incorporate other ecological factors into explanatory models of edge effects. © 2015 The Authors. Journal of Animal Ecology © 2015 British Ecological Society.

Morphology and variability of the Titan ringlet and Huygens ringlet edges

NASA Astrophysics Data System (ADS)

Jerousek, Richard G.; Colwell, Joshua E.; Esposito, Larry W.

2011-11-01

We present a forward modeling approach for determining, in part, the ring particle spatial distribution in the vicinity of sharp ring or ringlet edges. Synthetic edge occultation profiles are computed based on a two-parameter particle spatial distribution model. One parameter, h, characterizes the vertical extent of the ring and the other, δ, characterizes the radial scale over which the ring optical depth transitions from the background ring value to zero. We compare our synthetic occultation profiles to high resolution stellar occultation light curves observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS) High Speed Photometer (HSP) for occultations by the Titan ringlet and Huygens ringlet edges. More than 100 stellar occultations of the Huygens ringlet and Titan ringlet edges were studied, comprising 343 independent occultation cuts of the edges of these two ringlets. In 237 of these profiles the measured light-curve was fit well with our two-parameter edge model. Of the remaining edge occultations, 69 contained structure that could only be fit with extremely large values of the ring-plane vertical thickness ( h > 1 km) or by adopting a different model for the radial profile of the ring optical depth. An additional 37 could not be fit by our two-parameter model. Certain occultations at low ring-plane incidence angles as well as occultations nearly tangent to the ring edge allow the direct measurement of the radial scale over which the particle packing varies at the edge of the ringlet. In 24 occultations with these particular viewing geometries, we find a wide variation in the radial scale of the edge. We are able to constrain the vertical extent of the rings at the edge to less than ˜300 m in the 70% of the occultations with appropriate viewing geometry, however tighter constraints could not be placed on h due to the weaker sensitivity of the occultation profile to vertical thickness compared to its sensitivity to δ. Many occultations of a single edge could not be fit to a single value of δ, indicating large temporal or azimuthal variability, although the azimuthal variation in δ with respect to the longitudes of various moons in the system did not show any discernible pattern.

How Did Urban Land Expand in China between 1992 and 2015? A Multi-Scale Landscape Analysis.

PubMed

Xu, Min; He, Chunyang; Liu, Zhifeng; Dou, Yinyin

2016-01-01

Effective and timely quantification of the spatiotemporal pattern of urban expansion in China is important for the assessment of its environmental effects. However, the dynamics of the most recent urban expansions in China since 2012 have not yet been adequately explained due to a lack of current information. In this paper, our objective was to quantify spatiotemporal patterns of urban expansion in China between 1992 and 2015. First, we extracted information on urban expansion in China between 1992 and 2015 by integrating nighttime light data, vegetation index data, and land surface temperature data. Then we analyzed the spatiotemporal patterns of urban expansion at the national and regional scales, as well as at that of urban agglomerations. We found that China experienced a rapid and large-scale process of urban expansion between 1992 and 2015, with urban land increasing from 1.22 × 104 km2 to 7.29 × 104 km2, increasing in size nearly fivefold and with an average annual growth rate of 8.10%, almost 2.5 times as rapid as the global average. We also found that urban land in China expanded mainly by occupying 3.31 × 104 km2 of cropland, which comprised 54.67% of the total area of expanded urban land. Among the three modes of growth-infilling, edge expansion, and leapfrog-edge expansion was the main cause of cropland loss. Cropland loss resulting from edge expansion of urban land totalled 2.51 × 104 km2, accounting for over 75% of total cropland loss. We suggest that effective future management with respect to edge expansion of urban land is needed to protect cropland in China.

How Did Urban Land Expand in China between 1992 and 2015? A Multi-Scale Landscape Analysis

PubMed Central

Xu, Min; He, Chunyang; Liu, Zhifeng; Dou, Yinyin

2016-01-01

Effective and timely quantification of the spatiotemporal pattern of urban expansion in China is important for the assessment of its environmental effects. However, the dynamics of the most recent urban expansions in China since 2012 have not yet been adequately explained due to a lack of current information. In this paper, our objective was to quantify spatiotemporal patterns of urban expansion in China between 1992 and 2015. First, we extracted information on urban expansion in China between 1992 and 2015 by integrating nighttime light data, vegetation index data, and land surface temperature data. Then we analyzed the spatiotemporal patterns of urban expansion at the national and regional scales, as well as at that of urban agglomerations. We found that China experienced a rapid and large-scale process of urban expansion between 1992 and 2015, with urban land increasing from 1.22 × 104 km2 to 7.29 × 104 km2, increasing in size nearly fivefold and with an average annual growth rate of 8.10%, almost 2.5 times as rapid as the global average. We also found that urban land in China expanded mainly by occupying 3.31 × 104 km2 of cropland, which comprised 54.67% of the total area of expanded urban land. Among the three modes of growth—infilling, edge expansion, and leapfrog—edge expansion was the main cause of cropland loss. Cropland loss resulting from edge expansion of urban land totalled 2.51 × 104 km2, accounting for over 75% of total cropland loss. We suggest that effective future management with respect to edge expansion of urban land is needed to protect cropland in China. PMID:27144589

Emerging Roles: Key Insights from Librarians in a Massive Open Online Course

ERIC Educational Resources Information Center

Stephens, Michael; Jones, Kyle M. L.

2015-01-01

From the cutting edge of innovations in online education comes the MOOC (Massive Open Online Course), a potentially disruptive and transformational mechanism for large-scale learning. What's the role of librarians in a MOOC? What can librarians learn from participating in a large-scale professional development opportunity delivered in an open…

The crack detection algorithm of pavement image based on edge information

NASA Astrophysics Data System (ADS)

Yang, Chunde; Geng, Mingyue

2018-05-01

As the images of pavement cracks are affected by a large amount of complicated noises, such as uneven illumination and water stains, the detected cracks are discontinuous and the main body information at the edge of the cracks is easily lost. In order to solve the problem, a crack detection algorithm in pavement image based on edge information is proposed. Firstly, the image is pre-processed by the nonlinear gray-scale transform function and reconstruction filter to enhance the linear characteristic of the crack. At the same time, an adaptive thresholding method is designed to coarsely extract the cracks edge according to the gray-scale gradient feature and obtain the crack gradient information map. Secondly, the candidate edge points are obtained according to the gradient information, and the edge is detected based on the single pixel percolation processing, which is improved by using the local difference between pixels in the fixed region. Finally, complete crack is obtained by filling the crack edge. Experimental results show that the proposed method can accurately detect pavement cracks and preserve edge information.

Effectiveness and tolerability of second-line therapy with vildagliptin vs. other oral agents in type 2 diabetes: A real-life worldwide observational study (EDGE)

PubMed Central

Mathieu, C; Barnett, A H; Brath, H; Conget, I; de Castro, J J; Göke, R; Márquez Rodriguez, E; Nilsson, P M; Pagkalos, E; Penfornis, A; Schaper, NC; Wangnoo, S K; Kothny, W; Bader, G

2013-01-01

Aim Real-life studies are needed to confirm the clinical relevance of findings from randomised controlled trials (RCTs). This study aimed to assess the effectiveness and tolerability of vildagliptin add-on vs. other oral antihyperglycaemic drugs (OADs) added to OAD monotherapy in a real-life setting, and to explore the advantages and limitations of large-scale ‘pragmatic’ trials. Methods EDGE was a prospective, 1-year, worldwide, real-life observational study in which 2957 physicians reported on the effects of second-line OADs in 45,868 patients with T2DM not reaching glycaemic targets with monotherapy. Physicians could add any OAD, and patients entered either vildagliptin or (pooled) comparator cohort. The primary effectiveness and tolerability end-point (PEP) evaluated proportions of patients decreasing HbA1c > 0.3%, without hypoglycaemia, weight gain, peripheral oedema or gastrointestinal side effects. The most clinically relevant secondary end-point (SEP 3) was attainment of end-point HbA1c < 7% without hypoglycaemia or ≥ 3% increase in body weight. Results In this large group of T2DM patients, a second OAD was added at mean HbA1c of 8.2 ± 1.3%, with no baseline HbA1c difference between cohorts. Second-line OAD therapy attained the PEP in the majority of patients, with higher attainment in those prescribed a vildagliptin-based regimen. The adjusted odds ratio was 1.49 (95% CI: 1.42, 1.55; p < 0.001). In patients with baseline HbA1c ≥ 7%, SEP 3 was achieved by 35% of patients on a vildagliptin-based combination and by 23% of those receiving comparator combinations. The adjusted odds ratio was 1.96 (95% CI: 1.85, 2.07; p < 0.001). Safety events were reported infrequently and safety profiles of vildagliptin and other OADs were consistent with previous data. Conclusion EDGE demonstrates that in a ‘real-life’ setting, vildagliptin as second OAD can lower HbA1c to target without well-recognised OAD side effects, more frequently than comparator OADs. In addition, EDGE illustrates that conducting large-scale, prospective, real-life studies poses challenges but yields valuable clinical information complementary to RCTs. PMID:23961850

Growth dominates choice in network percolation

NASA Astrophysics Data System (ADS)

Vijayaraghavan, Vikram S.; Noël, Pierre-André; Waagen, Alex; D'Souza, Raissa M.

2013-09-01

The onset of large-scale connectivity in a network (i.e., percolation) often has a major impact on the function of the system. Traditionally, graph percolation is analyzed by adding edges to a fixed set of initially isolated nodes. Several years ago, it was shown that adding nodes as well as edges to the graph can yield an infinite order transition, which is much smoother than the traditional second-order transition. More recently, it was shown that adding edges via a competitive process to a fixed set of initially isolated nodes can lead to a delayed, extremely abrupt percolation transition with a significant jump in large but finite systems. Here we analyze a process that combines both node arrival and edge competition. If started from a small collection of seed nodes, we show that the impact of node arrival dominates: although we can significantly delay percolation, the transition is of infinite order. Thus, node arrival can mitigate the trade-off between delay and abruptness that is characteristic of explosive percolation transitions. This realization may inspire new design rules where network growth can temper the effects of delay, creating opportunities for network intervention and control.

Low-speed wind-tunnel investigation of a large scale advanced arrow-wing supersonic transport configuration with engines mounted above wing for upper-surface blowing

NASA Technical Reports Server (NTRS)

Shivers, J. P.; Mclemore, H. C.; Coe, P. L., Jr.

1976-01-01

Tests have been conducted in a full scale tunnel to determine the low speed aerodynamic characteristics of a large scale advanced arrow wing supersonic transport configuration with engines mounted above the wing for upper surface blowing. Tests were made over an angle of attack range of -10 deg to 32 deg, sideslip angles of + or - 5 deg, and a Reynolds number range of 3,530,000 to 7,330,000. Configuration variables included trailing edge flap deflection, engine jet nozzle angle, engine thrust coefficient, engine out operation, and asymmetrical trailing edge boundary layer control for providing roll trim. Downwash measurements at the tail were obtained for different thrust coefficients, tail heights, and at two fuselage stations.

Variations of mesoscale and large-scale sea ice morphology in the 1984 Marginal Ice Zone Experiment as observed by microwave remote sensing

NASA Technical Reports Server (NTRS)

Campbell, W. J.; Josberger, E. G.; Gloersen, P.; Johannessen, O. M.; Guest, P. S.

1987-01-01

The data acquired during the summer 1984 Marginal Ice Zone Experiment in the Fram Strait-Greenland Sea marginal ice zone, using airborne active and passive microwave sensors and the Nimbus 7 SMMR, were analyzed to compile a sequential description of the mesoscale and large-scale ice morphology variations during the period of June 6 - July 16, 1984. Throughout the experiment, the long ice edge between northwest Svalbard and central Greenland meandered; eddies were repeatedly formed, moved, and disappeared but the ice edge remained within a 100-km-wide zone. The ice pack behind this alternately diffuse and compact edge underwent rapid and pronounced variations in ice concentration over a 200-km-wide zone. The high-resolution ice concentration distributions obtained in the aircraft images agree well with the low-resolution distributions of SMMR images.

On the wake flow of asymmetrically beveled trailing edges

NASA Astrophysics Data System (ADS)

Guan, Yaoyi; Pröbsting, Stefan; Stephens, David; Gupta, Abhineet; Morris, Scott C.

2016-05-01

Trailing edge and wake flows are of interest for a wide range of applications. Small changes in the design of asymmetrically beveled or semi-rounded trailing edges can result in significant difference in flow features which are relevant for the aerodynamic performance, flow-induced structural vibration and aerodynamically generated sound. The present study describes in detail the flow field characteristics around a family of asymmetrically beveled trailing edges with an enclosed trailing-edge angle of 25° and variable radius of curvature R. The flow fields over the beveled trailing edges are described using data obtained by particle image velocimetry (PIV) experiments. The flow topology for different trailing edges was found to be strongly dependent on the radius of curvature R, with flow separation occurring further downstream as R increases. This variation in the location of flow separation influences the aerodynamic force coefficients, which were evaluated from the PIV data using a control volume approach. Two-point correlations of the in-plane velocity components are considered to assess the structure in the flow field. The analysis shows large-scale coherent motions in the far wake, which are associated with vortex shedding. The wake thickness parameter yf is confirmed as an appropriate length scale to characterize this large-scale roll-up motion in the wake. The development in the very near wake was found to be critically dependent on R. In addition, high-speed PIV measurements provide insight into the spectral characteristics of the turbulent fluctuations. Based on the time-resolved flow field data, the frequency range associated with the shedding of coherent vortex pairs in the wake is identified. By means of time-correlation of the velocity components, turbulent structures are found to convect from the attached or separated shear layers without distinct separation point into the wake.

Evaluation of pressure and thermal data from a wind tunnel test of a large-scale, powered, STOL fighter model

NASA Technical Reports Server (NTRS)

Howell, G. A.; Crosthwait, E. L.; Witte, M. C.

1981-01-01

A STOL fighter model employing the vectored-engine-over wing concept was tested at low speeds in the NASA/Ames 40 by 80-foot wind tunnel. The model, approximately 0.75 scale of an operational fighter, was powered by two General Electric J-97 turbojet engines. Limited pressure and thermal instrumentation were provided to measure power effects (chordwise and spanwise blowing) and control-surface-deflection effects. An indepth study of the pressure and temperature data revealed many flow field features - the foremost being wing and canard leading-edge vortices. These vortices delineated regions of attached and separated flow, and their movements were often keys to an understanding of flow field changes caused by power and control-surface variations. Chordwise blowing increased wing lift and caused a modest aft shift in the center of pressure. The induced effects of chordwise blowing extended forward to the canard and significantly increased the canard lift when the surface was stalled. Spanwise blowing effectively enhanced the wing leading-edge vortex, thereby increasing lift and causing a forward shift in the center of pressure.

Dimensionless, Scale Invariant, Edge Weight Metric for the Study of Complex Structural Networks

PubMed Central

Colon-Perez, Luis M.; Spindler, Caitlin; Goicochea, Shelby; Triplett, William; Parekh, Mansi; Montie, Eric; Carney, Paul R.; Price, Catherine; Mareci, Thomas H.

2015-01-01

High spatial and angular resolution diffusion weighted imaging (DWI) with network analysis provides a unique framework for the study of brain structure in vivo. DWI-derived brain connectivity patterns are best characterized with graph theory using an edge weight to quantify the strength of white matter connections between gray matter nodes. Here a dimensionless, scale-invariant edge weight is introduced to measure node connectivity. This edge weight metric provides reasonable and consistent values over any size scale (e.g. rodents to humans) used to quantify the strength of connection. Firstly, simulations were used to assess the effects of tractography seed point density and random errors in the estimated fiber orientations; with sufficient signal-to-noise ratio (SNR), edge weight estimates improve as the seed density increases. Secondly to evaluate the application of the edge weight in the human brain, ten repeated measures of DWI in the same healthy human subject were analyzed. Mean edge weight values within the cingulum and corpus callosum were consistent and showed low variability. Thirdly, using excised rat brains to study the effects of spatial resolution, the weight of edges connecting major structures in the temporal lobe were used to characterize connectivity in this local network. The results indicate that with adequate resolution and SNR, connections between network nodes are characterized well by this edge weight metric. Therefore this new dimensionless, scale-invariant edge weight metric provides a robust measure of network connectivity that can be applied in any size regime. PMID:26173147

Dimensionless, Scale Invariant, Edge Weight Metric for the Study of Complex Structural Networks.

PubMed

Colon-Perez, Luis M; Spindler, Caitlin; Goicochea, Shelby; Triplett, William; Parekh, Mansi; Montie, Eric; Carney, Paul R; Price, Catherine; Mareci, Thomas H

2015-01-01

High spatial and angular resolution diffusion weighted imaging (DWI) with network analysis provides a unique framework for the study of brain structure in vivo. DWI-derived brain connectivity patterns are best characterized with graph theory using an edge weight to quantify the strength of white matter connections between gray matter nodes. Here a dimensionless, scale-invariant edge weight is introduced to measure node connectivity. This edge weight metric provides reasonable and consistent values over any size scale (e.g. rodents to humans) used to quantify the strength of connection. Firstly, simulations were used to assess the effects of tractography seed point density and random errors in the estimated fiber orientations; with sufficient signal-to-noise ratio (SNR), edge weight estimates improve as the seed density increases. Secondly to evaluate the application of the edge weight in the human brain, ten repeated measures of DWI in the same healthy human subject were analyzed. Mean edge weight values within the cingulum and corpus callosum were consistent and showed low variability. Thirdly, using excised rat brains to study the effects of spatial resolution, the weight of edges connecting major structures in the temporal lobe were used to characterize connectivity in this local network. The results indicate that with adequate resolution and SNR, connections between network nodes are characterized well by this edge weight metric. Therefore this new dimensionless, scale-invariant edge weight metric provides a robust measure of network connectivity that can be applied in any size regime.

Enabling Colloidal Synthesis of Edge-Oriented MoS2 with Expanded Interlayer Spacing for Enhanced HER Catalysis.

PubMed

Sun, Yugang; Alimohammadi, Farbod; Zhang, Dongtang; Guo, Guangsheng

2017-03-08

By selectively promoting heterogeneous nucleation/growth of MoS 2 on graphene monolayer sheets, edge-oriented (EO) MoS 2 nanosheets with expanded interlayer spacing (∼9.4 Å) supported on reduced graphene oxide (rGO) sheets were successfully synthesized through colloidal chemistry, showing the promise in low-cost and large-scale production. The number and edge length of MoS 2 nanosheets per area of graphene sheets were tuned by controlling the reaction time in the microwave-assisted solvothermal reduction of ammonium tetrathiomolybdate [(NH 4 ) 2 MoS 4 ] in dimethylformamide. The edge-oriented and interlayer-expanded (EO&IE) MoS 2 /rGO exhibited significantly improved catalytic activity toward hydrogen evolution reaction (HER) in terms of larger current density, lower Tafel slope, and lower charge transfer resistance compared to the corresponding interlayer-expanded MoS 2 sheets without edge-oriented geometry, highlighting the importance of synergistic effect between edge-oriented geometry and interlayer expansion on determining HER activity of MoS 2 nanosheets. Quantitative analysis clearly shows the linear dependence of current density on the edge length of MoS 2 nanosheets.

A Ranking Approach on Large-Scale Graph With Multidimensional Heterogeneous Information.

PubMed

Wei, Wei; Gao, Bin; Liu, Tie-Yan; Wang, Taifeng; Li, Guohui; Li, Hang

2016-04-01

Graph-based ranking has been extensively studied and frequently applied in many applications, such as webpage ranking. It aims at mining potentially valuable information from the raw graph-structured data. Recently, with the proliferation of rich heterogeneous information (e.g., node/edge features and prior knowledge) available in many real-world graphs, how to effectively and efficiently leverage all information to improve the ranking performance becomes a new challenging problem. Previous methods only utilize part of such information and attempt to rank graph nodes according to link-based methods, of which the ranking performances are severely affected by several well-known issues, e.g., over-fitting or high computational complexity, especially when the scale of graph is very large. In this paper, we address the large-scale graph-based ranking problem and focus on how to effectively exploit rich heterogeneous information of the graph to improve the ranking performance. Specifically, we propose an innovative and effective semi-supervised PageRank (SSP) approach to parameterize the derived information within a unified semi-supervised learning framework (SSLF-GR), then simultaneously optimize the parameters and the ranking scores of graph nodes. Experiments on the real-world large-scale graphs demonstrate that our method significantly outperforms the algorithms that consider such graph information only partially.

Large-Scale Wind-Tunnel Tests of an Airplane Model with an Unswept, Aspect-Ratio-10 Wing, Two Propellers, and Blowing Flaps

NASA Technical Reports Server (NTRS)

Griffin, Roy N., Jr.; Holzhauser, Curt A.; Weiberg, James A.

1958-01-01

An investigation was made to determine the lifting effectiveness and flow requirements of blowing over the trailing-edge flaps and ailerons on a large-scale model of a twin-engine, propeller-driven airplane having a high-aspect-ratio, thick, straight wing. With sufficient blowing jet momentum to prevent flow separation on the flap, the lift increment increased for flap deflections up to 80 deg (the maximum tested). This lift increment also increased with increasing propeller thrust coefficient. The blowing jet momentum coefficient required for attached flow on the flaps was not significantly affected by thrust coefficient, angle of attack, or blowing nozzle height.

Large Format Transition Edge Sensor Microcalorimeter Arrays

NASA Technical Reports Server (NTRS)

Chervenak, J. A.; Adams, J. A.; Bandler, S. b.; Busch, S. E.; Eckart, M. E.; Ewin, A. E.; Finkbeiner, F. M.; Kilbourne, C. A.; Kelley, R. L.; Porst, J. P.;

Diffusion, Dispersion, and Uncertainty in Anisotropic Fractal Porous Media

NASA Astrophysics Data System (ADS)

Monnig, N. D.; Benson, D. A.

2007-12-01

Motivated by field measurements of aquifer hydraulic conductivity (K), recent techniques were developed to construct anisotropic fractal random fields, in which the scaling, or self-similarity parameter, varies with direction and is defined by a matrix. Ensemble numerical results are analyzed for solute transport through these 2-D "operator-scaling" fractional Brownian motion (fBm) ln(K) fields. Contrary to some analytic stochastic theories for monofractal K fields, the plume growth rates never exceed Mercado's (1967) purely stratified aquifer growth rate of plume apparent dispersivity proportional to mean distance. Apparent super-stratified growth must be the result of other demonstrable factors, such as initial plume size. The addition of large local dispersion and diffusion does not significantly change the effective longitudinal dispersivity of the plumes. In the presence of significant local dispersion or diffusion, the concentration coefficient of variation CV={σc}/{\\langle c \\rangle} remains large at the leading edge of the plumes. This indicates that even with considerable mixing due to dispersion or diffusion, there is still substantial uncertainty in the leading edge of a plume moving in fractal porous media.

Edge effects, not connectivity, determine the incidence and development of a foliar fungal plant disease.

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

Johnson, Brenda, L.; Haddad, Nick, M.

2011-08-01

Using a model plant-pathogen system in a large-scale habitat corridor experiment, we found that corridors do not facilitate the movement of wind-dispersed plant pathogens, that connectivity of patches does not enhance levels of foliar fungal plant disease, and that edge effects are the key drivers of plant disease dynamics. Increased spread of infectious disease is often cited as a potential negative effect of habitat corridors used in conservation, but the impacts of corridors on pathogen movement have never been tested empirically. Using sweet corn (Zea mays) and southern corn leaf blight (Cochliobolus heterostrophus) as a model plant-pathogen system, we testedmore » the impacts of connectivity and habitat fragmentation on pathogen movement and disease development at the Savannah River Site, South Carolina, USA. Over time, less edgy patches had higher proportions of diseased plants, and distance of host plants to habitat edges was the greatest determinant of disease development. Variation in average daytime temperatures provided a possible mechanism for these disease patterns. Our results show that worries over the potentially harmful effects of conservation corridors on disease dynamics are misplaced, and that, in a conservation context, many diseases can be better managed by mitigating edge effects.« less

Undermining position effects in choices from arrays, with implications for police lineups.

PubMed

Palmer, Matthew A; Sauer, James D; Holt, Glenys A

2017-03-01

Choices from arrays are often characterized by position effects, such as edge-aversion. We investigated position effects when participants attempted to pick a suspect from an array similar to a police photo lineup. A reanalysis of data from 2 large-scale field studies showed that choices made under realistic conditions-closely matching eyewitness identification decisions in police investigations-displayed edge-aversion and bias to choose from the top row (Study 1). In a series of experiments (Studies 2a-2c and 3), participants guessing the location of a suspect exhibited edge-aversion regardless of whether the lineup was constructed to maximize the chances of the suspect being picked, to ensure the suspect did not stand out, or randomly. Participants favored top locations only when the lineup was constructed to maximize the chances of the suspect being picked. In Studies 4 and 5, position effects disappeared when (a) response options were presented in an array with no obvious center, edges, or corners, and (b) instructions stated that the suspect was placed randomly. These findings show that position effects are influenced by a combination of task instructions and array shape. Randomizing the location of the suspect and modifying the shape of the lineup array may reduce misidentification. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

Removal of millimeter-scale rolled edges using bevel-cut-like tool influence function in magnetorheological jet polishing.

PubMed

Yang, Hao; Cheng, Haobo; Feng, Yunpeng; Jing, Xiaoli

2018-05-01

Subaperture polishing techniques usually produce rolled edges due to edge effect. The rolled edges, especially those in millimeter scale on small components, are difficult to eliminate using conventional polishing methods. Magnetorheological jet polishing (MJP) offers the possibility of the removal of these structures, owing to its small tool influence function (TIF) size. Hence, we investigate the removal characters of inclined MJP jetting models by means of computational fluid dynamics (CFD) simulations and polishing experiments. A discrete phase model (DPM) is introduced in the simulation to get the influence of abrasive particle concentration on the removal mechanism. Therefore, a more accurate model for MJP removal mechanisms is built. With several critical problems solved, a small bevel-cut-like TIF (B-TIF), which has fine acentric and unimodal characteristics, is obtained through inclined jetting. The B-TIF proves to have little edge effect and is applied in surface polishing of thin rolled edges. Finally, the RMS of the experimental section profile converges from 10.5 nm to 1.4 nm, and the rolled edges are successfully suppressed. Consequently, it is validated that the B-TIF has remarkable ability in the removal of millimeter-scale rolled edges.

Active flow control for a blunt trailing edge profiled body

NASA Astrophysics Data System (ADS)

Naghib Lahouti, Arash

Flow in the wake of nominally two-dimensional bluff bodies is dominated by vortex shedding, beyond a very small threshold Reynolds number. Vortex shedding poses challenges in the design of structures, due to its adverse effects such as cyclic aerodynamic loads and fatigue. The wake vortices are often accompanied by large- and small-scale secondary instabilities, which manifest as dislocations in the primary wake vortices, and/or pairs of counter-rotating streamwise vortices, depending on the dominant instability mode(s), which in turn depends on the profile geometry and Reynolds number. The secondary instabilities interact with the wake vortices through several mechanisms. Therefore, manipulation of the secondary instabilities can be used as a means to alter the wake vortices, in order to reduce their adverse effects. In the present study, flow in the wake of a blunt trailing edge profiled body, composed of an elliptical leading edge and a rectangular trailing edge, has been studied at Reynolds numbers ranging from Re(d) = 500 to 2150 where d is thickness of the body, to identify the secondary instabilities. Various tools, including numerical simulations, Laser Induced Fluorescence (LIF), and Particle Image Velocimetry (PIV) have been used for this study. Proper Orthogonal Decomposition (POD) has been applied to analyze the velocity field data. The results indicate the existence of small-scale instabilities with a spanwise wavelength of 2.0d to 2.5d in the near wake. The mechanism of the instability is similar to the Mode-A instability of a circular cylinder; however, it displays features that are specific to the blunt trailing edge profiled body. An active three-dimensional flow control mechanism based on the small-scale instabilities has been designed and evaluated. The mechanism comprises a series of trailing edge injection ports, with a spanwise spacing equal to the wavelength of the small-scale instabilities. Following preliminary evaluation of the control mechanism through numerical simulations, and experimental study of the effect of injection flow rate, extensive PIV experiments have been conducted to investigate the effectiveness of the flow control mechanism, and its effects on the wake flow structure, at Reynolds numbers ranging from Re(d ) = 700 to 1980. Measurements have been carried out at multiple spanwise locations, to establish a comprehensive image of the effect of the flow control mechanism on parameters such as drag force, wake width, and formation length. POD analysis and frequency spectrums are used to describe the process by which the mechanism affects the wake parameters and drag force. The results indicate that the flow control mechanism is able to reduce drag force by 10%. It is also shown that the best effectiveness in terms of suppression of the drag component resulting from velocity fluctuations is achieved when the flow control actuation wavelength closely matches the wavelength of the small-scale instabilities. KEYWORDS: Blunt Trailing Edge Profiled Body, Vortex Shedding, Wake Instability, Streamwise Vortex, Flow Control, Drag Reduction, Particle Image Velocimetry (PIV), Laser Induced Fluorescence (LIF), Flow Visualization, Numerical Simulation

Freeze-Drying Process Development and Scale-Up: Scale-Up of Edge Vial Versus Center Vial Heat Transfer Coefficients, Kv.

PubMed

Pikal, Michael J; Bogner, Robin; Mudhivarthi, Vamsi; Sharma, Puneet; Sane, Pooja

2016-11-01

This report presents calculations of the difference between the vial heat transfer coefficient of the "edge vial" and the "center vial" at all scales. The only scale-up adjustment for center vials is for the contribution of radiation from the shelf upon which the vial sits by replacing the emissivity of the laboratory dryer shelf with the emissivity of the production dryer shelf. With edge vials, scales-up adjustments are more complex. While convection is not important, heat transfer from the wall to the bands (surrounding the vial array) by radiation and directly from the band to the vials by both radiation and conduction is important; this radiation heat transfer depends on the emissivity of the vial and the bands and is nearly independent of the emissivity of the dryer walls. Differences in wall temperatures do impact the edge vial effect and scale-up, and estimates for wall temperatures are needed for both laboratory and manufacturing dryers. Auto-loading systems (no bands) may give different edge vial heat transfer coefficients than when operating with bands. Satisfactory agreement between theoretical predictions and experimental values of the edge vial effect indicate that results calculated from the theory are of useful accuracy. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Neat monolayer tiling of molecularly thin two-dimensional materials in 1 min

PubMed Central

Matsuba, Kazuaki; Wang, Chengxiang; Saruwatari, Kazuko; Uesusuki, Yusuke; Akatsuka, Kosho; Osada, Minoru; Ebina, Yasuo; Ma, Renzhi; Sasaki, Takayoshi

2017-01-01

Controlled arrangement of molecularly thin two-dimensional (2D) materials on a substrate, particularly into precisely organized mono- and multilayer structures, is a key to design a nanodevice using their unique and enhanced physical properties. Several techniques such as mechanical transfer process and Langmuir-Blodgett deposition have been applied for this purpose, but they have severe restrictions for large-scale practical applications, for example, limited processable area and long fabrication time, requiring skilled multistep operations. We report a facile one-pot spin-coating method to realize dense monolayer tiling of various 2D materials, such as graphene and metal oxide nanosheets, within 1 min over a wide area (for example, a 30-mmφ substrate). Centrifugal force drives the nanosheets in a thin fluid layer to the substrate edge where they are packed edge to edge all the way to the central region, without forming overlaps. We investigated the relationship between precursor concentration, rotation speed, and ultraviolet-visible absorbance and developed an effective method to optimize the parameters for neat monolayer films. The multilayer buildup is feasible by repeating the spin-coating process combined with a heat treatment at moderate temperature. This versatile solution-based technique will provide both fundamental and practical advancements in the rapid large-scale production of artificial lattice-like films and nanodevices based on 2D materials. PMID:28695198

Superwind Outflows in Seyfert Galaxies? : Large-Scale Radio Maps of an Edge-On Sample

NASA Astrophysics Data System (ADS)

Colbert, E.; Gallimore, J.; Baum, S.; O'Dea, C.

1995-03-01

Large-scale galactic winds (superwinds) are commonly found flowing out of the nuclear region of ultraluminous infrared and powerful starburst galaxies. Stellar winds and supernovae from the nuclear starburst provide the energy to drive these superwinds. The outflowing gas escapes along the rotation axis, sweeping up and shock-heating clouds in the halo, which produces optical line emission, radio synchrotron emission, and X-rays. These features can most easily be studied in edge-on systems, so that the wind emission is not confused by that from the disk. We have begun a systematic search for superwind outflows in Seyfert galaxies. In an earlier optical emission-line survey, we found extended minor axis emission and/or double-peaked emission line profiles in >~30% of the sample objects. We present here large-scale (6cm VLA C-config) radio maps of 11 edge-on Seyfert galaxies, selected (without bias) from a distance-limited sample of 23 edge-on Seyferts. These data have been used to estimate the frequency of occurrence of superwinds. Preliminary results indicate that four (36%) of the 11 objects observed and six (26%) of the 23 objects in the distance-limited sample have extended radio emission oriented perpendicular to the galaxy disk. This emission may be produced by a galactic wind blowing out of the disk. Two (NGC 2992 and NGC 5506) of the nine objects for which we have both radio and optical data show good evidence for a galactic wind in both datasets. We suggest that galactic winds occur in >~30% of all Seyferts. A goal of this work is to find a diagnostic that can be used to distinguish between large-scale outflows that are driven by starbursts and those that are driven by an AGN. The presence of starburst-driven superwinds in Seyferts, if established, would have important implications for the connection between starburst galaxies and AGN.

Subharmonic edge waves on a large, shallow island

NASA Astrophysics Data System (ADS)

Foda, Mostafa A.

1988-08-01

Subharmonic resonance of edge waves by incident and reflected waves has been studied thus far for the case of a plane infinite beach. The analysis will be extended here to the case of a curved coastline, with a large radius of curvature and slowly varying beach slope in the longshore direction. It will be shown that the effects of such slow beach slope changes on a propagating edge wave are similar to the familiar shoaling effects on incident waves. The case of subharmonic edge wave generation on large shallow islands will be discussed in detail. The nonlinear analysis will show that within a certain range of island sizes, the generation mechanism can produce a stable standing edge wave around the island. For larger islands the solution disintegrates into two out-of-phase envelopes of opposite-going edge waves. For still larger islands, the generated progressive edge waves become unstable to sideband modulations.

Lidar Measurements of Tropospheric Wind Profiles with the Double Edge Technique

NASA Technical Reports Server (NTRS)

Gentry, Bruce M.; Li, Steven X.; Korb, C. Laurence; Mathur, Savyasachee; Chen, Huailin

1998-01-01

Research has established the importance of global tropospheric wind measurements for large scale improvements in numerical weather prediction. In addition, global wind measurements provide data that are fundamental to the understanding and prediction of global climate change. These tasks are closely linked with the goals of the NASA Earth Science Enterprise and Global Climate Change programs. NASA Goddard has been actively involved in the development of direct detection Doppler lidar methods and technologies to meet the wind observing needs of the atmospheric science community. A variety of direct detection Doppler wind lidar measurements have recently been reported indicating the growing interest in this area. Our program at Goddard has concentrated on the development of the edge technique for lidar wind measurements. Implementations of the edge technique using either the aerosol or molecular backscatter for the Doppler wind measurement have been described. The basic principles have been verified in lab and atmospheric lidar wind experiments. The lidar measurements were obtained with an aerosol edge technique lidar operating at 1064 nm. These measurements demonstrated high spatial resolution (22 m) and high velocity sensitivity (rms variances of 0.1 m/s) in the planetary boundary layer (PBL). The aerosol backscatter is typically high in the PBL and the effects of the molecular backscatter can often be neglected. However, as was discussed in the original edge technique paper, the molecular contribution to the signal is significant above the boundary layer and a correction for the effects of molecular backscatter is required to make wind measurements. In addition, the molecular signal is a dominant source of noise in regions where the molecular to aerosol ratio is large since the energy monitor channel used in the single edge technique measures the sum of the aerosol and molecular signals. To extend the operation of the edge technique into the free troposphere we have developed a variation of the edge technique called the double edge technique. In this paper a ground based aerosol double edge lidar is described and the first measurements of wind profiles in the free troposphere obtained with this lidar will be presented.

Large-scale wind-tunnel investigation of a close-coupled canard-delta-wing fighter model through high angles of attack

NASA Technical Reports Server (NTRS)

Stoll, F.; Koenig, D. G.

1983-01-01

Data obtained through very high angles of attack from a large-scale, subsonic wind-tunnel test of a close-coupled canard-delta-wing fighter model are analyzed. The canard delays wing leading-edge vortex breakdown, even for angles of attack at which the canard is completely stalled. A vortex-lattice method was applied which gave good predictions of lift and pitching moment up to an angle of attack of about 20 deg, where vortex-breakdown effects on performance become significant. Pitch-control inputs generally retain full effectiveness up to the angle of attack of maximum lift, beyond which, effectiveness drops off rapidly. A high-angle-of-attack prediction method gives good estimates of lift and drag for the completely stalled aircraft. Roll asymmetry observed at zero sideslip is apparently caused by an asymmetry in the model support structure.

Full-scale wind-tunnel investigation of the effects of wing leading-edge modifications on the high angle-of-attack aerodynamic characteristics of a low-wing general aviation airplane

NASA Technical Reports Server (NTRS)

Johnson, J. L., Jr.; Newsom, W. A.; Satran, D. R.

1980-01-01

The paper presents the results of a recent investigation to determine the effects of wing leading-edge modifications on the high angle-of-attack aerodynamic characteristics of a low-wing general aviation airplane in the Langley Full-Scale Wind Tunnel. The investigation was conducted to provide aerodynamic information for correlation and analysis of flight-test results obtained for the configuration. The wind-tunnel investigation consisted of force and moment measurements, wing pressure measurements, flow surveys, and flow visualization studies utilizing a tuft grid, smoke and nonintrusive mini-tufts which were illuminated by ultra-violet light. In addition to the tunnel scale system which measured overall forces and moments, the model was equipped with an auxiliary strain-gage balance within the left wing panel to measure lift and drag forces on the outer wing panel independent of the tunnel scale system. The leading-edge modifications studied included partial- and full-span leading-edge droop arrangements as well as leading-edge slats.

Using landscape ecology to test hypotheses about large-scale abundance patterns in migratory birds

USGS Publications Warehouse

Flather, C.H.; Sauer, J.R.

1996-01-01

The hypothesis that Neotropical migrant birds may be undergoing widespread declines due to land use activities on the breeding grounds has been examined primarily by synthesizing results from local studies. Growing concern for the cumulative influence of land use activities on ecological systems has heightened the need for large-scale studies to complement what has been observed at local scales. We investigated possible landscape effects on Neotropical migrant bird populations for the eastern United States by linking two large-scale inventories designed to monitor breeding-bird abundances and land use patterns. The null hypothesis of no relation between landscape structure and Neotropical migrant abundance was tested by correlating measures of landscape structure with bird abundance, while controlling for the geographic distance among samples. Neotropical migrants as a group were more 'sensitive' to landscape structure than either temperate migrants or permanent residents. Neotropical migrants tended to be more abundant in landscapes with a greater proportion of forest and wetland habitats, fewer edge habitats, large forest patches, and with forest habitats well dispersed throughout the scene. Permanent residents showed few correlations with landscape structure and temperate migrants were associated with habitat diversity and edge attributes rather than with the amount, size, and dispersion of forest habitats. The association between Neotropical migrant abundance and forest fragmentation differed among physiographic strata, suggesting that land-scape context affects observed relations between bird abundance and landscape structure. Finally, associations between landscape structure and temporal trends in Neotropical migrant abundance were negatively correlated with forest habitats. These results suggest that extrapolation of patterns observed in some landscapes is not likely to hold regionally, and that conservation policies must consider the variation in landscape structure associations observed among different types of bird species and in physiographic strata with varying land use histories.

Reduced-Scale Transition-Edge Sensor Detectors for Solar and X-Ray Astrophysics

NASA Technical Reports Server (NTRS)

Datesman, Aaron M.; Adams, Joseph S.; Bandler, Simon R.; Betancourt-Martinez, Gabriele L.; Chang, Meng-Ping; Chervenak, James A.; Eckart, Megan E.; Ewin, Audrey E.; Finkbeiner, Fred M.; Ha, Jong Yoon;

Edge effects in the primate community of the biological dynamics of Forest Fragments Project, Amazonas, Brazil.

PubMed

Lenz, Bryan B; Jack, Katharine M; Spironello, Wilson R

2014-11-01

While much is known about abiotic and vegetative edge effects in tropical forests, considerably less is known about the impact of forest edges on large mammals. In this study, we examine edge effects in a primate community to determine: 1) the distance from the edge over which edge effects in primate density are detectable, 2) whether individual species exhibit edge effects in their density, and 3) whether biological characteristics can be used to predict primate presence in edge habitats. Given their importance to many primate species, we also examine the influence of the number of large trees. We found edge penetration distances of 150 m for the five species that experienced edge effects, suggesting that primates respond to edge-related changes in the plant community that are known to be strongest over the first 150 m. Four species had higher edge densities: Alouatta macconnelli (folivore-frugivore), Chiropotes chiropotes (frugivorous seed predator), Saguinus midas (frugivore-faunivore), and Sapajus apella apella (frugivore-faunivore); one species' density was lower: Ateles paniscus (frugivore); and the final species, Pithecia chrysocephala (frugivorous seed predator), did not show an edge-related pattern. The lone significant relationship between the biological characteristics examined (body weight, diet, group size, and home range size) and primate presence in edge habitats was a negative relationship with the amount of fruit consumed. Though we did not examine primate responses to edges that border a denuded matrix, we have shown that edges influence primate distribution even following decades of secondary forest regeneration at habitat edges. © 2014 Wiley Periodicals, Inc.

Task-Related Edge Density (TED)—A New Method for Revealing Dynamic Network Formation in fMRI Data of the Human Brain

PubMed Central

Lohmann, Gabriele; Stelzer, Johannes; Zuber, Verena; Buschmann, Tilo; Margulies, Daniel; Bartels, Andreas; Scheffler, Klaus

2016-01-01

The formation of transient networks in response to external stimuli or as a reflection of internal cognitive processes is a hallmark of human brain function. However, its identification in fMRI data of the human brain is notoriously difficult. Here we propose a new method of fMRI data analysis that tackles this problem by considering large-scale, task-related synchronisation networks. Networks consist of nodes and edges connecting them, where nodes correspond to voxels in fMRI data, and the weight of an edge is determined via task-related changes in dynamic synchronisation between their respective times series. Based on these definitions, we developed a new data analysis algorithm that identifies edges that show differing levels of synchrony between two distinct task conditions and that occur in dense packs with similar characteristics. Hence, we call this approach “Task-related Edge Density” (TED). TED proved to be a very strong marker for dynamic network formation that easily lends itself to statistical analysis using large scale statistical inference. A major advantage of TED compared to other methods is that it does not depend on any specific hemodynamic response model, and it also does not require a presegmentation of the data for dimensionality reduction as it can handle large networks consisting of tens of thousands of voxels. We applied TED to fMRI data of a fingertapping and an emotion processing task provided by the Human Connectome Project. TED revealed network-based involvement of a large number of brain areas that evaded detection using traditional GLM-based analysis. We show that our proposed method provides an entirely new window into the immense complexity of human brain function. PMID:27341204

Task-Related Edge Density (TED)-A New Method for Revealing Dynamic Network Formation in fMRI Data of the Human Brain.

PubMed

Lohmann, Gabriele; Stelzer, Johannes; Zuber, Verena; Buschmann, Tilo; Margulies, Daniel; Bartels, Andreas; Scheffler, Klaus

2016-01-01

The formation of transient networks in response to external stimuli or as a reflection of internal cognitive processes is a hallmark of human brain function. However, its identification in fMRI data of the human brain is notoriously difficult. Here we propose a new method of fMRI data analysis that tackles this problem by considering large-scale, task-related synchronisation networks. Networks consist of nodes and edges connecting them, where nodes correspond to voxels in fMRI data, and the weight of an edge is determined via task-related changes in dynamic synchronisation between their respective times series. Based on these definitions, we developed a new data analysis algorithm that identifies edges that show differing levels of synchrony between two distinct task conditions and that occur in dense packs with similar characteristics. Hence, we call this approach "Task-related Edge Density" (TED). TED proved to be a very strong marker for dynamic network formation that easily lends itself to statistical analysis using large scale statistical inference. A major advantage of TED compared to other methods is that it does not depend on any specific hemodynamic response model, and it also does not require a presegmentation of the data for dimensionality reduction as it can handle large networks consisting of tens of thousands of voxels. We applied TED to fMRI data of a fingertapping and an emotion processing task provided by the Human Connectome Project. TED revealed network-based involvement of a large number of brain areas that evaded detection using traditional GLM-based analysis. We show that our proposed method provides an entirely new window into the immense complexity of human brain function.

The Explorer of Diffuse Galactic Emission (EDGE): Determination of Large-Scale Structure Evolution from Measurement of the Anisotropy of the Cosmic Infrared Background

NASA Technical Reports Server (NTRS)

Silverberg, R. F.; Cheng, E. S.; Cottingham, D. A.; Fixsen, D. J.; Meyer, S. S.; Wilson, G. W.

2004-01-01

The formation of the first objects, stars and galaxies and their subsequent evolution remain a cosmological unknown. Few observational probes of these processes exist. The Cosmic Infrared Background (CIB) originates from this era, and can provide information to test models of both galaxy evolution and the growth of primordial structure. The Explorer of Diffuse Galactic Emission (EDGE) is a proposed balloon-borne mission designed to measure the spatial fluctuations in the CIB from 200 micrometers to 1 millimeter on 6' to 3 degree scales with 2 microKelvin sensitivity/resolution element. Such measurements would provide a sensitive probe of the large-scale variation in protogalaxy density at redshifts approximately 0.5-3. In this paper, we present the scientific justification for the mission and show a concept for the instrument and observations.

Numerical analysis of the impact of permeability on trailing-edge noise

NASA Astrophysics Data System (ADS)

Koh, Seong Ryong; Meinke, Matthias; Schröder, Wolfgang

2018-05-01

The impact of porous surfaces on the near-wall turbulent structures and the generated trailing-edge noise is analyzed for several trailing-edge shapes of finite thickness using a high resolution large-eddy simulation (LES)/computational aeroacoustics (CAA) method. The porous surface of the trailing edge is defined by the porosity and the viscous permeability determined by the solution of a turbulent flat plate boundary layer at a Reynolds number 1280 based on the displacement thickness in the inflow cross section. The volume-averaged approach for the homogeneous porous medium shows that the porous impedance scales linearly with the porosity and exponentially with the mean structure size of a porous medium. The drag induced by the porous surface changes the friction velocity and the permeability Reynolds number ReK which determines the porous impedance Rs scaled by ReK-2/3. The trailing-edge noise is analyzed for three solid and three porous trailing edges. The effect of a finite span is investigated by the spanwise correlation model based on the measured coherence distribution. The acoustic prediction shows a good agreement with measurements of the broadband spectrum and the strong tone generated by a finite trailing-edge thickness. The pressure gradient inside the porous media is redistributed by the Darcy drag defined by the viscous permeability and the porosity. The mean pressure increases in the upstream direction inside the porous medium such that the flow acceleration involved in the acoustic generation is reduced inside the porous medium. The noise reduction by a porous medium reaches 11 dB for the trailing-edge shape which possesses a sharp corner for the solid surface. The porous surface applied to a semi-circular trailing edge achieves a 4 dB noise reduction. The directivity pattern for individual components of the acoustic spectrum shows that the massive noise reduction is determined at the tone. Enhanced wave diffraction by the thick flat plate changes the directivity pattern in the high frequency range.

Robustness of Controllability for Networks Based on Edge-Attack

PubMed Central

Nie, Sen; Wang, Xuwen; Zhang, Haifeng; Li, Qilang; Wang, Binghong

2014-01-01

We study the controllability of networks in the process of cascading failures under two different attacking strategies, random and intentional attack, respectively. For the highest-load edge attack, it is found that the controllability of Erdős-Rényi network, that with moderate average degree, is less robust, whereas the Scale-free network with moderate power-law exponent shows strong robustness of controllability under the same attack strategy. The vulnerability of controllability under random and intentional attacks behave differently with the increasing of removal fraction, especially, we find that the robustness of control has important role in cascades for large removal fraction. The simulation results show that for Scale-free networks with various power-law exponents, the network has larger scale of cascades do not mean that there will be more increments of driver nodes. Meanwhile, the number of driver nodes in cascading failures is also related to the edges amount in strongly connected components. PMID:24586507

Robustness of controllability for networks based on edge-attack.

PubMed

Nie, Sen; Wang, Xuwen; Zhang, Haifeng; Li, Qilang; Wang, Binghong

2014-01-01

We study the controllability of networks in the process of cascading failures under two different attacking strategies, random and intentional attack, respectively. For the highest-load edge attack, it is found that the controllability of Erdős-Rényi network, that with moderate average degree, is less robust, whereas the Scale-free network with moderate power-law exponent shows strong robustness of controllability under the same attack strategy. The vulnerability of controllability under random and intentional attacks behave differently with the increasing of removal fraction, especially, we find that the robustness of control has important role in cascades for large removal fraction. The simulation results show that for Scale-free networks with various power-law exponents, the network has larger scale of cascades do not mean that there will be more increments of driver nodes. Meanwhile, the number of driver nodes in cascading failures is also related to the edges amount in strongly connected components.

Large and small-scale structures in Saturn's rings

NASA Astrophysics Data System (ADS)

Albers, N.; Rehnberg, M. E.; Brown, Z. L.; Sremcevic, M.; Esposito, L. W.

2017-09-01

Observations made by the Cassini spacecraft have revealed both large and small scale structures in Saturn's rings in unprecedented detail. Analysis of high-resolution measurements by the Cassini Ultraviolet Spectrograph (UVIS) High Speed Photometer (HSP) and the Imaging Science Subsystem (ISS) show an abundance of intrinsic small-scale structures (or clumping) seen across the entire ring system. These include self-gravity wakes (50-100m), sub-km structure at the A and B ring edges, and "straw"/"ropy" structures (1-3km).

Piecing together the fragments: Elucidating edge effects on forest carbon dynamics

NASA Astrophysics Data System (ADS)

Hutyra, L.; Smith, I. A.; Reinmann, A.; Marrs, J.; Thompson, J.

2017-12-01

Forest fragmentation is pervasive throughout the world's forests, impacting growing conditions and carbon dynamics through edge effects that produce gradients in microclimate, biogeochemistry, and stand structure. Despite the majority of the world's forests being <1km from an edge, our understanding of forest carbon dynamics is largely derived from intact forest systems. In the northeastern USA, we find that over 23% of the current forest area is just 30m from an agricultural or developed edge. Edge effects on the carbon cycle vary in their magnitude by biome, but current forest carbon accounting methods and ecosystem models largely do not include edge effects, highlighting an important gap in our understanding of the terrestrial carbon cycle. Characterizing the role of forest fragmentation in regional and global biogeochemical cycles necessitates advancing our understanding of how shifts in microenvironment at the forest edge interact with local prevailing drivers of global change and limitations to microbial activity and forest growth. This study synthesizes the literature related to edge effects and the carbon cycle, considering how fragmentation affects the growing conditions of the world's remaining forests based on risks and opportunities for forests near the edge.

Could the stellar magnetic field explain the structures in the AU Mic debris disk?

NASA Astrophysics Data System (ADS)

Sezestre, Élie; Augereau, Jean-Charles

2016-05-01

Recent SPHERE and reprocessed HST images of the edge-on AU Mic debris disk have revealed arch-like structures moving away from the star on unbound trajectories. No model in the literature can readily explain these features. Here, we explore the effect of the large-scale, stellar magnetic field on the dust dynamics. We show that our study may place constraints on the dust production location.

Stagnation Region Heat Transfer Augmentation at Very High Turbulence Levels

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

Ames, Forrest; Kingery, Joseph E.

A database for stagnation region heat transfer has been extended to include heat transfer measurements acquired downstream from a new high intensity turbulence generator. This work was motivated by gas turbine industry heat transfer designers who deal with heat transfer environments with increasing Reynolds numbers and very high turbulence levels. The new mock aero-combustor turbulence generator produces turbulence levels which average 17.4%, which is 37% higher than the older turbulence generator. The increased level of turbulence is caused by the reduced contraction ratio from the liner to the exit. Heat transfer measurements were acquired on two large cylindrical leading edgemore » test surfaces having a four to one range in leading edge diameter (40.64 cm and 10.16 cm). Gandvarapu and Ames [1] previously acquired heat transfer measurements for six turbulence conditions including three grid conditions, two lower turbulence aero-combustor conditions, and a low turbulence condition. The data are documented and tabulated for an eight to one range in Reynolds numbers for each test surface with Reynolds numbers ranging from 62,500 to 500,000 for the large leading edge and 15,625 to 125,000 for the smaller leading edge. The data show augmentation levels of up to 136% in the stagnation region for the large leading edge. This heat transfer rate is an increase over the previous aero-combustor turbulence generator which had augmentation levels up to 110%. Note, the rate of increase in heat transfer augmentation decreases for the large cylindrical leading edge inferring only a limited level of turbulence intensification in the stagnation region. The smaller cylindrical leading edge shows more consistency with earlier stagnation region heat transfer results correlated on the TRL (Turbulence, Reynolds number, Length scale) parameter. The downstream regions of both test surfaces continue to accelerate the flow but at a much lower rate than the leading edge. Bypass transition occurs in these regions providing a useful set of data to ground the prediction of transition onset and length over a wide range of Reynolds numbers and turbulence intensity and scales.« less

Trade-off between competition and facilitation defines gap colonization in mountains

PubMed Central

Lembrechts, Jonas J.; Milbau, Ann; Nijs, Ivan

2015-01-01

Recent experimental observations show that gap colonization in small-stature (e.g. grassland and dwarf shrubs) vegetation strongly depends on the abiotic conditions within them. At the same time, within-gap variation in biotic interactions such as competition and facilitation, caused by distance to the gap edge, would affect colonizer performance, but a theoretical framework to explore such patterns is missing. Here, we model how competition, facilitation and environmental conditions together determine the small-scale patterns of gap colonization along a cold gradient in mountains, by simulating colonizer survival in gaps of various sizes. Our model adds another dimension to the known effects of biotic interactions along a stress gradient by focussing on the trade-off between competition and facilitation in the within-gap environment. We show that this trade-off defines a peak in colonizer survival at a specific distance from the gap edge, which progressively shifts closer to the edge as the environment gets colder, ultimately leaving a large fraction of gaps unsuitable for colonization in facilitation-dominated systems. This is reinforced when vegetation size and temperature amelioration are manipulated simultaneously with temperature in order to simulate an elevational gradient more realistically. Interestingly, all other conditions being equal, the magnitude of the realized survival peak was always lower in large than in small gaps, making large gaps harder to colonize. The model is relevant to predict effects of non-native plant invasions and climate warming on colonization processes in mountains. PMID:26558706

A unified framework of image latent feature learning on Sina microblog

NASA Astrophysics Data System (ADS)

Wei, Jinjin; Jin, Zhigang; Zhou, Yuan; Zhang, Rui

2015-10-01

Large-scale user-contributed images with texts are rapidly increasing on the social media websites, such as Sina microblog. However, the noise and incomplete correspondence between the images and the texts give rise to the difficulty in precise image retrieval and ranking. In this paper, a hypergraph-based learning framework is proposed for image ranking, which simultaneously utilizes visual feature, textual content and social link information to estimate the relevance between images. Representing each image as a vertex in the hypergraph, complex relationship between images can be reflected exactly. Then updating the weight of hyperedges throughout the hypergraph learning process, the effect of different edges can be adaptively modulated in the constructed hypergraph. Furthermore, the popularity degree of the image is employed to re-rank the retrieval results. Comparative experiments on a large-scale Sina microblog data-set demonstrate the effectiveness of the proposed approach.

Natural and artificial spectral edges in exoplanets

NASA Astrophysics Data System (ADS)

Lingam, Manasvi; Loeb, Abraham

2017-09-01

Technological civilizations may rely upon large-scale photovoltaic arrays to harness energy from their host star. Photovoltaic materials, such as silicon, possess distinctive spectral features, including an 'artificial edge' that is characteristically shifted in wavelength shortwards of the 'red edge' of vegetation. Future observations of reflected light from exoplanets would be able to detect both natural and artificial edges photometrically, if a significant fraction of the planet's surface is covered by vegetation or photovoltaic arrays, respectively. The stellar energy thus tapped can be utilized for terraforming activities by transferring heat and light from the day side to the night side on tidally locked exoplanets, thereby producing detectable artefacts.

Forests on the edge: Microenvironmental drivers of carbon cycle response to edge effects

NASA Astrophysics Data System (ADS)

Reinmann, A.; Hutyra, L.; Smith, I. A.; Thompson, J.

2017-12-01

Twenty percent of the world's forest is within 100 m of a forest edge, but much of our understanding of forest carbon (C) cycling comes from large, intact ecosystems, which creates an important mismatch between the landscapes we study and those we aim to characterize. The temperate broadleaf forest is the most heavily fragmented forest biome in the world and its growth and carbon storage responses to forest edge effects appear to be the opposite of those in the tropical and boreal regions. We used field measurements to quantify the drivers of temperate forest C cycling response to edge effects, characterizing vegetative growth, respiration, and forest structure. We find large gradients in air and soil temperature from the forest interior to edge (up to 4 and 10° C, respectively) and the magnitude of this gradient is inversely correlated to the size of the forest edge growth enhancement. Further, leaf area index increases with proximity to the forest edge. While we also find increases in soil respiration between the forest interior and edge, this flux is small relative to aboveground growth enhancement near the edge. These findings represent an important advancement in our understanding of forest C cycle response to edge effects and will greatly improve our capacity to constrain biogenic C fluxes in fragmented and heterogeneous landscapes.

Edge Currents and Stability in DIII-D

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

Thomas, D M; Fenstermacher, M E; Finkenthal, D K

2005-05-05

Understanding the stability physics of the H-mode pedestal in tokamak devices requires an accurate measurement of plasma current in the pedestal region with good spatial resolution. Theoretically, the high pressure gradients achieved in the edge of H-mode plasmas should lead to generation of a significant edge current density peak through bootstrap and Pfirsh-Schlueter effects. This edge current is important for the achievement of second stability in the context of coupled magneto hydrodynamic (MHD) modes which are both pressure (ballooning) and current (peeling) driven [1]. Many aspects of edge localized mode (ELM) behavior can be accounted for in terms of anmore » edge current density peak, with the identification of Type 1 ELMs as intermediate-n toroidal mode number MHD modes being a natural feature of this model [2]. The development of a edge localized instabilities in tokamak experiments code (ELITE) based on this model allows one to efficiently calculate the stability and growth of the relevant modes for a broad range of plasma parameters [3,4] and thus provides a framework for understanding the limits on pedestal height. This however requires an accurate assessment of the edge current. While estimates of j{sub edge} can be made based on specific bootstrap models, their validity may be limited in the edge (gradient scale lengths comparable to orbit size, large changes in collisionality, etc.). Therefore it is highly desirable to have an actual measurement. Such measurements have been made on the DIII-D tokamak using combined polarimetry and spectroscopy of an injected lithium beam. [5,6]. By analyzing one of the Zeeman-split 2S-2P lithium resonance line components, one can obtain direct information on the local magnetic field components. These values allow one to infer details of the edge current density. Because of the negligible Stark mixing of the relevant atomic levels in lithium, this method of determining j(r) is insensitive to the large local electric fields typically found in enhanced confinement (H-mode) edges, and thus avoids an ambiguity common to MSE measurements of B{sub pol}.« less

Analysis and modeling of photomask edge effects for 3D geometries and the effect on process window

NASA Astrophysics Data System (ADS)

Miller, Marshal A.; Neureuther, Andrew R.

2009-03-01

Simulation was used to explore boundary layer models for 1D and 2D patterns that would be appropriate for fast CAD modeling of physical effects during design. FDTD simulation was used to compare rigorous thick mask modeling to a thin mask approximation (TMA). When features are large, edges can be viewed as independent and modeled as separate from one another, but for small mask features, edges experience cross-talk. For attenuating phase-shift masks, interaction distances as large as 150nm were observed. Polarization effects are important for accurate EMF models. Due to polarization effects, the edge perturbations in line ends become different compared to a perpendicular edge. For a mask designed to be real, the 90o transmission created at edges produces an asymmetry through focus, which is also polarization dependent. Thick mask fields are calculated using TEMPEST and Panoramic Technologies software. Fields are then analyzed in the near field and on wafer CDs to examine deviations from TMA.

Implementing a Parallel Image Edge Detection Algorithm Based on the Otsu-Canny Operator on the Hadoop Platform.

PubMed

Cao, Jianfang; Chen, Lichao; Wang, Min; Tian, Yun

2018-01-01

The Canny operator is widely used to detect edges in images. However, as the size of the image dataset increases, the edge detection performance of the Canny operator decreases and its runtime becomes excessive. To improve the runtime and edge detection performance of the Canny operator, in this paper, we propose a parallel design and implementation for an Otsu-optimized Canny operator using a MapReduce parallel programming model that runs on the Hadoop platform. The Otsu algorithm is used to optimize the Canny operator's dual threshold and improve the edge detection performance, while the MapReduce parallel programming model facilitates parallel processing for the Canny operator to solve the processing speed and communication cost problems that occur when the Canny edge detection algorithm is applied to big data. For the experiments, we constructed datasets of different scales from the Pascal VOC2012 image database. The proposed parallel Otsu-Canny edge detection algorithm performs better than other traditional edge detection algorithms. The parallel approach reduced the running time by approximately 67.2% on a Hadoop cluster architecture consisting of 5 nodes with a dataset of 60,000 images. Overall, our approach system speeds up the system by approximately 3.4 times when processing large-scale datasets, which demonstrates the obvious superiority of our method. The proposed algorithm in this study demonstrates both better edge detection performance and improved time performance.

Aerodynamic Characteristics of a 0.5-Scale Model of the Fairchild XSAM-N-2 Lark Missile at High Subsonic Speeds

NASA Technical Reports Server (NTRS)

Martin, Andrew; Hunter, Harlo A.

1949-01-01

An investigation was conducted to determine the longitudinal- and lateral-stability characteristics of a 0.5-scale moue1 of the Fairchild Lark missile, The model was tested with 0 deg and with 22.5 deg of roll. Three horizontal wings having NACA 16-009, 16-209, and 64A-209 sections were tested. Pressures were measured on both pointed and blunt noses. The wind-tunnel-test data indicate that rolling the missile 22.5 deg. had no serious effect on the static longitudinal stability. The desired maneuvering acceleration could not be attained with any of the horizontal wings tested, even with the horizontal wing flaps deflected 50 deg. The flaps on the 64A-209 wing (with small trailing-edge angles and flat sides) were effective at all flap deflections, while the flaps on the 16-series wings (with large trailing-edge angles) lost effectiveness at small flap deflections. The data showed that rolling moment existed when the vertical wing flaps were deflected with the model at other than zero angle of attack. A similar rolling moment probably would be found . with the horizontal wing flaps deflected and the model yawed.

Small scale model static acoustic investigation of hybrid high lift systems combining upper surface blowing with the internally blown flap

NASA Technical Reports Server (NTRS)

Cole, T. W.; Rathburn, E. A.

1974-01-01

A static acoustic and propulsion test of a small radius Jacobs-Hurkamp and a large radius Flex Flap combined with four upper surface blowing (USB) nozzles was performed. Nozzle force and flow data, flap trailing edge total pressure survey data, and acoustic data were obtained. Jacobs-Hurkamp flap surface pressure data, flow visualization photographs, and spoiler acoustic data from the limited mid-year tests are reported. A pressure ratio range of 1.2 to 1.5 was investigated for the USB nozzles and for the auxiliary blowing slots. The acoustic data were scaled to a four-engine STOL airplane of roughly 110,000 kilograms or 50,000 pounds gross weight, corresponding to a model scale of approximately 0.2 for the nozzles without deflector. The model nozzle scale is actually reduced to about .17 with deflector although all results in this report assume 0.2 scale factor. Trailing edge pressure surveys indicated that poor flow attachment was obtained even at large flow impingement angles unless a nozzle deflector plate was used. Good attachment was obtained with the aspect ratio four nozzle with deflector, confirming the small scale wind tunnel tests.

Optimization of a resazurin-based microplate assay for large-scale compound screenings against Klebsiella pneumoniae.

PubMed

Kim, Hyung Jun; Jang, Soojin

2018-01-01

A new resazurin-based assay was evaluated and optimized using a microplate (384-well) format for high-throughput screening of antibacterial molecules against Klebsiella pneumoniae . Growth of the bacteria in 384-well plates was more effectively measured and had a > sixfold higher signal-to-background ratio using the resazurin-based assay compared with absorbance measurements at 600 nm. Determination of minimum inhibitory concentrations of the antibiotics revealed that the optimized assay quantitatively measured antibacterial activity of various antibiotics. An edge effect observed in the initial assay was significantly reduced using a 1-h incubation of the bacteria-containing plates at room temperature. There was an approximately 10% decrease in signal variability between the edge and the middle wells along with improvement in the assay robustness ( Z ' = 0.99). This optimized resazurin-based assay is an efficient, inexpensive, and robust assay that can quantitatively measure antibacterial activity using a high-throughput screening system to assess a large number of compounds for discovery of new antibiotics against K. pneumoniae .

Edge-localized mode avoidance and pedestal structure in I-mode plasmas

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

Walk, J. R., E-mail: jrwalk@psfc.mit.edu; Hughes, J. W.; Hubbard, A. E.

I-mode is a high-performance tokamak regime characterized by the formation of a temperature pedestal and enhanced energy confinement, without an accompanying density pedestal or drop in particle and impurity transport. I-mode operation appears to have naturally occurring suppression of large Edge-Localized Modes (ELMs) in addition to its highly favorable scalings of pedestal structure and overall performance. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to themore » structure and ELM stability of I-mode pedestals. Analysis of I-mode discharges prepared with high-resolution pedestal data from the most recent C-Mod campaign reveals favorable pedestal scalings for extrapolation to large machines—pedestal temperature scales strongly with power per particle P{sub net}/n{sup ¯}{sub e}, and likewise pedestal pressure scales as the net heating power (consistent with weak degradation of confinement with heating power). Matched discharges in current, field, and shaping demonstrate the decoupling of energy and particle transport in I-mode, increasing fueling to span nearly a factor of two in density while maintaining matched temperature pedestals with consistent levels of P{sub net}/n{sup ¯}{sub e}. This is consistent with targets for increased performance in I-mode, elevating pedestal β{sub p} and global performance with matched increases in density and heating power. MHD calculations using the ELITE code indicate that I-mode pedestals are strongly stable to edge peeling-ballooning instabilities. Likewise, numerical modeling of the KBM turbulence onset, as well as scalings of the pedestal width with poloidal beta, indicates that I-mode pedestals are not limited by KBM turbulence—both features identified with the trigger for large ELMs, consistent with the observed suppression of large ELMs in I-mode.« less

Edge-localized mode avoidance and pedestal structure in I-mode plasmasa)

NASA Astrophysics Data System (ADS)

Walk, J. R.; Hughes, J. W.; Hubbard, A. E.; Terry, J. L.; Whyte, D. G.; White, A. E.; Baek, S. G.; Reinke, M. L.; Theiler, C.; Churchill, R. M.; Rice, J. E.; Snyder, P. B.; Osborne, T.; Dominguez, A.; Cziegler, I.

2014-05-01

I-mode is a high-performance tokamak regime characterized by the formation of a temperature pedestal and enhanced energy confinement, without an accompanying density pedestal or drop in particle and impurity transport. I-mode operation appears to have naturally occurring suppression of large Edge-Localized Modes (ELMs) in addition to its highly favorable scalings of pedestal structure and overall performance. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to the structure and ELM stability of I-mode pedestals. Analysis of I-mode discharges prepared with high-resolution pedestal data from the most recent C-Mod campaign reveals favorable pedestal scalings for extrapolation to large machines—pedestal temperature scales strongly with power per particle Pnet/n ¯e, and likewise pedestal pressure scales as the net heating power (consistent with weak degradation of confinement with heating power). Matched discharges in current, field, and shaping demonstrate the decoupling of energy and particle transport in I-mode, increasing fueling to span nearly a factor of two in density while maintaining matched temperature pedestals with consistent levels of Pnet/n ¯e. This is consistent with targets for increased performance in I-mode, elevating pedestal βp and global performance with matched increases in density and heating power. MHD calculations using the ELITE code indicate that I-mode pedestals are strongly stable to edge peeling-ballooning instabilities. Likewise, numerical modeling of the KBM turbulence onset, as well as scalings of the pedestal width with poloidal beta, indicates that I-mode pedestals are not limited by KBM turbulence—both features identified with the trigger for large ELMs, consistent with the observed suppression of large ELMs in I-mode.

The effects of patch shape and connectivity on nest site selection and reproductive success of the Indigo Bunting.

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

Weldon, Aimee Jean

2004-07-01

Description – Ph.D Dissertation. North Carolina State University. Raleigh, North Carolina. 135 pp. Abatract - Habitat fragmentation and its associated effects have been blamed for the recent population declines of many Neotropical migratory bird species. Increased predation and parasitism resulting from edge-related effects have been implicated for poor nesting success in many studies, mostly of forest interior species. However, little attention has been devoted to disturbance-dependent birds. In this study, I examine how patch shape and connectivity in fragmented landscapes affects the reproductive success of disturbance-dependent bird species, specifically the Indigo Bunting (Passerina cyanea). I conducted my study in amore » landscape-scale experimental system of similar-area habitat patches that differed in connectivity and in shape. Shapes differed between edgy and rectangular forms, where edgy patches contained 50% more edge than rectangular patches. I tested whether edgy patches function as ecological traps for species with strong edge preferences, by leading them to select dangerous habitats. Indigo Buntings preferentially selected edgy patches over rectangular patches, but experienced significantly lower reproductive success in edgy patches early in the season. Although predation pressure intensified in rectangular patches late in the season, seasonal fecundity was still significantly lower in edgy patches, providing the first empirical evidence that edges can function as ecological traps for Indigo Buntings. A second objective of my study was to evaluate the efficacy of conservation corridors for disturbance-dependent bird species. Conservation corridors have become a popular strategy to preserve biodiversity and promote gene flow in fragmented landscapes, but corridors may also have negative consequences. I tested the hypothesis that corridors can increase nest predation risk in connected patches relative to unconnected patches. Nest predation rates increased significantly in connected patches compared to unconnected rectangular patches, but were similar between connected patches and unconnected edgy patches. This suggests that the increase in predator activity in connected patches is largely attributable to edge effects incurred through the addition of a corridor. This is the first landscape-scale study to experimentally demonstrate the potential negative effects of conservation corridors.« less

Imbibition of a textured surface decorated by short pillars with rounded edges.

PubMed

Obara, Noriko; Okumura, Ko

2012-08-01

Imbibition of micropatterned surfaces can have broad technological and fundamental implications for areas ranging from biomedical devices and fuel transport to writing with ink. Despite rapidly growing interests aimed at various applications, a fundamental physical understanding of the imbibition dynamics is still in its infancy. Recently, two simple scaling regimes for the dynamics have been established for a textured surface decorated with long pillars whose top and bottom edges are sharp. Here, we study the imbibition dynamics of textured surfaces decorated by short pillars with rounded edges, to find a different scaling regime. Interestingly, this regime originates not from the balance of two effects but from the hybrid balance of three effects. Furthermore, this scaling law can be universal or independent of the details of the texture geometry. We envision that this potentially universal scaling regime might be ubiquitous and will be useful in the handling and transportation of a small amount of liquid.

The cosmology large angular scale surveyor (CLASS): 40 GHz optical design

NASA Astrophysics Data System (ADS)

Eimer, Joseph R.; Bennett, Charles L.; Chuss, David T.; Marriage, Tobias; Wollack, Edward J.; Zeng, Lingzhen

2012-09-01

The Cosmology Large Angular Scale Surveyor (CLASS) instrument will measure the polarization of the cosmic microwave background at 40, 90, and 150 GHz from Cerro Toco in the Atacama desert of northern Chile. In this paper, we describe the optical design of the 40 GHz telescope system. The telescope is a diffraction limited catadioptric design consisting of a front-end Variable-delay Polarization Modulator (VPM), two ambient temperature mirrors, two cryogenic dielectric lenses, thermal blocking filters, and an array of 36 smooth-wall scalar feedhorn antennas. The feed horns guide the signal to antenna-coupled transition-edge sensor (TES) bolometers. Polarization diplexing and bandpass definition are handled on the same microchip as the TES. The feed horn beams are truncated with 10 dB edge taper by a 4 K Lyot-stop to limit detector loading from stray light and control the edge illumination of the front-end VPM. The field-of-view is 19° x 14° with a resolution for each beam on the sky of 1.5° FWHM.

The Cosmology Large Angular Scale Surveyor (CLASS): 40 GHz Optical Design

NASA Technical Reports Server (NTRS)

Eimer, Joseph R.; Bennett, Charles L.; Chuss, David T.; Marriage, Tobias; Wollack, Edward J.; Zeng, Lingzhen

2012-01-01

The Cosmology Large Angular Scale Surveyor (CLASS) instrument will measure the polarization of the cosmic microwave background at 40, 90, and 150 GHz from Cerro Toco in the Atacama desert of northern Chile. In this paper, we describe the optical design of the 40 GHz telescope system. The telescope is a diffraction limited catadioptric design consisting of a front-end Variable-delay Polarization Modulator (VPM), two ambient temperature mirrors, two cryogenic dielectric lenses, thermal blocking filters, and an array of 36 smooth-wall scalar feedhorn antennas. The feed horns guide the signal to antenna-coupled transition-edge sensor (TES) bolometers. Polarization diplexing and bandpass definition are handled on the same microchip as the TES. The feed horn beams are truncated with 10 dB edge taper by a 4 K Lyot-stop to limit detector loading from stray light and control the edge illumination of the front-end VPM. The field-of-view is 19 deg x 14 deg with a resolution for each beam on the sky of 1.5 deg. FWHM.

Dynamo-driven plasmoid formation from a current-sheet instability

DOE PAGES

Ebrahimi, F.

2016-12-15

Axisymmetric current-carrying plasmoids are formed in the presence of nonaxisymmetric fluctuations during nonlinear three-dimensional resistive MHD simulations in a global toroidal geometry. In this study, we utilize the helicity injection technique to form an initial poloidal flux in the presence of a toroidal guide field. As helicity is injected, two types of current sheets are formed from the oppositely directed field lines in the injector region (primary reconnecting current sheet), and the poloidal flux compression near the plasma edge (edge current sheet). We first find that nonaxisymmetric fluctuations arising from the current-sheet instability isolated near the plasma edge have tearingmore » parity but can nevertheless grow fast (on the poloidal Alfven time scale). These modes saturate by breaking up the current sheet. Second, for the first time, a dynamo poloidal flux amplification is observed at the reconnection site (in the region of the oppositely directed magnetic field). This fluctuation-induced flux amplification increases the local Lundquist number, which then triggers a plasmoid instability and breaks the primary current sheet at the reconnection site. Finally, the plasmoids formation driven by large-scale flux amplification, i.e., a large-scale dynamo, observed here has strong implications for astrophysical reconnection as well as fast reconnection events in laboratory plasmas.« less

Heat pipes for wing leading edges of hypersonic vehicles

NASA Technical Reports Server (NTRS)

Boman, B. L.; Citrin, K. M.; Garner, E. C.; Stone, J. E.

1990-01-01

Wing leading edge heat pipes were conceptually designed for three types of vehicle: an entry research vehicle, aero-space plane, and advanced shuttle. A full scale, internally instrumented sodium/Hastelloy X heat pipe was successfully designed and fabricated for the advanced shuttle application. The 69.4 inch long heat pipe reduces peak leading edge temperatures from 3500 F to 1800 F. It is internally instrumented with thermocouples and pressure transducers to measure sodium vapor qualities. Large thermal gradients and consequently large thermal stresses, which have the potential of limiting heat pipe life, were predicted to occur during startup. A test stand and test plan were developed for subsequent testing of this heat pipe. Heat pipe manufacturing technology was advanced during this program, including the development of an innovative technique for wick installation.

Full-scale semispan tests of a business-jet wing with a natural laminar flow airfoil

NASA Technical Reports Server (NTRS)

Hahne, David E.; Jordan, Frank L., Jr.

1991-01-01

A full-scale semispan model was investigated to evaluate and document the low-speed, high-lift characteristics of a business-jet class wing that utilized the HSNLF(1)-0213 airfoil section and a single-slotted flap system. Also, boundary-layer transition effects were examined, a segmented leading-edge droop for improved stall/spin resistance was studied, and two roll-controlled devices were evaluated. The wind-tunnel investigation showed that deployment of single-slotted, trailing-edge flap was effective in providing substantial increments in lift required for takeoff and landing performance. Fixed-transition studies to investigate premature tripping of the boundary layer indicated no adverse effects in lift and pitching-moment characteristics for either the cruise or landing configuration. The full-scale results also suggested the need to further optimize the leading-edge droop design that was developed in the subscale tests.

Modelling the possible interaction between edge-driven convection and the Canary Islands mantle plume

NASA Astrophysics Data System (ADS)

Negredo, A. M.; Rodríguez-González, J.; Fullea, J.; Van Hunen, J.

2017-12-01

The close location between many hotspots and the edges of cratonic lithosphere has led to the hypothesis that these hotspots could be explained by small-scale mantle convection at the edge of cratons (Edge Driven Convection, EDC). The Canary Volcanic Province hotspot represents a paradigmatic example of this situation due to its close location to the NW edge of the African Craton. Geochemical evidence, prominent low seismic velocity anomalies in the upper and lower mantle, and the rough NE-SW age-progression of volcanic centers consistently point out to a deep-seated mantle plume as the origin of the Canary Volcanic Province. It has been hypothesized that the plume material could be affected by upper mantle convection caused by the thermal contrast between thin oceanic lithosphere and thick (cold) African craton. Deflection of upwelling blobs due to convection currents would be responsible for the broader and more irregular pattern of volcanism in the Canary Province compared to the Madeira Province. In this study we design a model setup inspired on this scenario to investigate the consequences of possible interaction between ascending mantle plumes and EDC. The Finite Element code ASPECT is used to solve convection in a 2D box. The compositional field and melt fraction distribution are also computed. Free slip along all boundaries and constant temperature at top and bottom boundaries are assumed. The initial temperature distribution assumes a small long-wavelength perturbation. The viscosity structure is based on a thick cratonic lithosphere progressively varying to a thin, or initially inexistent, oceanic lithosphere. The effects of assuming different rheologies, as well as steep or gradual changes in lithospheric thickness are tested. Modelling results show that a very thin oceanic lithosphere (< 30 km) is needed to generate partial melting by EDC. In this case partial melting can occur as far as 700 km away from the edge of the craton. The size of EDC cells is relatively small (diameter about 300 km) for lithosphere/asthenosphere viscosity contrasts of 1000. In contrast, models assuming temperature-dependent viscosity and large viscosity variations evolve to large-scale (upper mantle) convection cells, with upwelling of hot material being enhanced by cold downwellings at the edge of cratonic lithosphere.

A Novel Coarsening Method for Scalable and Efficient Mesh Generation

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

Yoo, A; Hysom, D; Gunney, B

2010-12-02

In this paper, we propose a novel mesh coarsening method called brick coarsening method. The proposed method can be used in conjunction with any graph partitioners and scales to very large meshes. This method reduces problem space by decomposing the original mesh into fixed-size blocks of nodes called bricks, layered in a similar way to conventional brick laying, and then assigning each node of the original mesh to appropriate brick. Our experiments indicate that the proposed method scales to very large meshes while allowing simple RCB partitioner to produce higher-quality partitions with significantly less edge cuts. Our results further indicatemore » that the proposed brick-coarsening method allows more complicated partitioners like PT-Scotch to scale to very large problem size while still maintaining good partitioning performance with relatively good edge-cut metric. Graph partitioning is an important problem that has many scientific and engineering applications in such areas as VLSI design, scientific computing, and resource management. Given a graph G = (V,E), where V is the set of vertices and E is the set of edges, (k-way) graph partitioning problem is to partition the vertices of the graph (V) into k disjoint groups such that each group contains roughly equal number of vertices and the number of edges connecting vertices in different groups is minimized. Graph partitioning plays a key role in large scientific computing, especially in mesh-based computations, as it is used as a tool to minimize the volume of communication and to ensure well-balanced load across computing nodes. The impact of graph partitioning on the reduction of communication can be easily seen, for example, in different iterative methods to solve a sparse system of linear equation. Here, a graph partitioning technique is applied to the matrix, which is basically a graph in which each edge is a non-zero entry in the matrix, to allocate groups of vertices to processors in such a way that many of matrix-vector multiplication can be performed locally on each processor and hence to minimize communication. Furthermore, a good graph partitioning scheme ensures the equal amount of computation performed on each processor. Graph partitioning is a well known NP-complete problem, and thus the most commonly used graph partitioning algorithms employ some forms of heuristics. These algorithms vary in terms of their complexity, partition generation time, and the quality of partitions, and they tend to trade off these factors. A significant challenge we are currently facing at the Lawrence Livermore National Laboratory is how to partition very large meshes on massive-size distributed memory machines like IBM BlueGene/P, where scalability becomes a big issue. For example, we have found that the ParMetis, a very popular graph partitioning tool, can only scale to 16K processors. An ideal graph partitioning method on such an environment should be fast and scale to very large meshes, while producing high quality partitions. This is an extremely challenging task, as to scale to that level, the partitioning algorithm should be simple and be able to produce partitions that minimize inter-processor communications and balance the load imposed on the processors. Our goals in this work are two-fold: (1) To develop a new scalable graph partitioning method with good load balancing and communication reduction capability. (2) To study the performance of the proposed partitioning method on very large parallel machines using actual data sets and compare the performance to that of existing methods. The proposed method achieves the desired scalability by reducing the mesh size. For this, it coarsens an input mesh into a smaller size mesh by coalescing the vertices and edges of the original mesh into a set of mega-vertices and mega-edges. A new coarsening method called brick algorithm is developed in this research. In the brick algorithm, the zones in a given mesh are first grouped into fixed size blocks called bricks. These brick are then laid in a way similar to conventional brick laying technique, which reduces the number of neighboring blocks each block needs to communicate. Contributions of this research are as follows: (1) We have developed a novel method that scales to a really large problem size while producing high quality mesh partitions; (2) We measured the performance and scalability of the proposed method on a machine of massive size using a set of actual large complex data sets, where we have scaled to a mesh with 110 million zones using our method. To the best of our knowledge, this is the largest complex mesh that a partitioning method is successfully applied to; and (3) We have shown that proposed method can reduce the number of edge cuts by as much as 65%.« less

The influence of anthropogenic edge effects on primate populations and their habitat in a fragmented rainforest in Costa Rica.

PubMed

Bolt, Laura M; Schreier, Amy L; Voss, Kristofor A; Sheehan, Elizabeth A; Barrickman, Nancy L; Pryor, Nathaniel P; Barton, Matthew C

2018-05-01

When a forest is fragmented, this increases the amount of forest edge relative to the interior. Edge effects can lead to loss of animal and plant species and decreased plant biomass near forest edges. We examined the influence of an anthropogenic forest edge comprising cattle pasture, coconut plantations, and human settlement on the mantled howler (Alouatta palliata), white-faced capuchin (Cebus capucinus), Central American spider monkey (Ateles geoffroyi), and plant populations at La Suerte Biological Research Station (LSBRS), Costa Rica. We predicted that there would be lower monkey encounter rate, mean tree species richness, and diameter at breast height (DBH) in forest edge versus interior, and that monkeys would show species-specific responses to edge based on diet, body size, and canopy height preferences. Specifically, we predicted that howler monkeys would show positive or neutral edge effects due to their flexible folivorous diet, large body size, and preference for high canopy, capuchins would show positive edge effects due to their diverse diet, small body size, and preference for low to middle canopy, and spider monkeys would show negative edge effects due their reliance on ripe fruit, large body size, and preference for high upper canopy. We conducted population and vegetation surveys along edge and interior transects at LSBRS. Contrary to predictions, total monkey encounter rate did not vary between the forest edge and forest interior. Furthermore, all three species showed neutral edge effects with no significant differences in encounter rate between forest edge and interior. Interior transects had significantly higher mean tree species richness than edge transects, and interior trees had greater DBH than edge trees, although this difference was not significant. These results suggest that forest edges negatively impact plant populations at La Suerte but that the monkeys are able to withstand these differences in vegetation.

Shifts in Plant Assemblages Reduce the Richness of Galling Insects Across Edge-Affected Habitats in the Atlantic Forest.

PubMed

Souza, Danielle G; Santos, Jean C; Oliveira, Marcondes A; Tabarelli, Marcelo

2016-10-01

Impacts of habitat loss and fragmentation on specialist herbivores have been rarely addressed. Here we examine the structure of plant and galling insect assemblages in a fragmented landscape of the Atlantic forest to verify a potential impoverishment of these assemblages mediated by edge effects. Saplings and galling insects were recorded once within a 0.1-ha area at habitat level, covering forest interior stands, forest edges, and small fragments. A total of 1,769 saplings from 219 tree species were recorded across all three habitats, with differences in terms of sapling abundance and species richness. Additionally, edge-affected habitats exhibited reduced richness of both host-plant and galling insects at plot and habitat spatial scale. Attack levels also differed among forest types at habitat spatial scale (21.1% of attacked stems in forest interior, 12.4% in small fragments but only 8.5% in forest edges). Plot ordination resulted in three clearly segregated clusters: one formed by forest interior, one by small fragments, and another formed by edge plots. Finally, the indicator species analysis identified seven and one indicator plant species in forest interior and edge-affected habitats, respectively. Consequently, edge effects lead to formation of distinct taxonomic groups and also an impoverished assemblage of plants and galling insects at multiple spatial scales. The results of the present study indicate that fragmentation-related changes in plant assemblages can have a cascade effects on specialist herbivores. Accordingly, hyperfragmented landscapes may not be able to retain an expressive portion of tropical biodiversity. © The Authors 2016. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

A Reynolds Number Study of Wing Leading-Edge Effects on a Supersonic Transport Model at Mach 0.3

NASA Technical Reports Server (NTRS)

Williams, M. Susan; Owens, Lewis R., Jr.; Chu, Julio

1999-01-01

A representative supersonic transport design was tested in the National Transonic Facility (NTF) in its original configuration with small-radius leading-edge flaps and also with modified large-radius inboard leading-edge flaps. Aerodynamic data were obtained over a range of Reynolds numbers at a Mach number of 0.3 and angles of attack up to 16 deg. Increasing the radius of the inboard leading-edge flap delayed nose-up pitching moment to a higher lift coefficient. Deflecting the large-radius leading-edge flap produced an overall decrease in lift coefficient and delayed nose-up pitching moment to even higher angles of attack as compared with the undeflected large- radius leading-edge flap. At angles of attack corresponding to the maximum untrimmed lift-to-drag ratio, lift and drag coefficients decreased while lift-to-drag ratio increased with increasing Reynolds number. At an angle of attack of 13.5 deg., the pitching-moment coefficient was nearly constant with increasing Reynolds number for both the small-radius leading-edge flap and the deflected large-radius leading-edge flap. However, the pitching moment coefficient increased with increasing Reynolds number for the undeflected large-radius leading-edge flap above a chord Reynolds number of about 35 x 10 (exp 6).

BFL: a node and edge betweenness based fast layout algorithm for large scale networks

PubMed Central

Hashimoto, Tatsunori B; Nagasaki, Masao; Kojima, Kaname; Miyano, Satoru

2009-01-01

Background Network visualization would serve as a useful first step for analysis. However, current graph layout algorithms for biological pathways are insensitive to biologically important information, e.g. subcellular localization, biological node and graph attributes, or/and not available for large scale networks, e.g. more than 10000 elements. Results To overcome these problems, we propose the use of a biologically important graph metric, betweenness, a measure of network flow. This metric is highly correlated with many biological phenomena such as lethality and clusters. We devise a new fast parallel algorithm calculating betweenness to minimize the preprocessing cost. Using this metric, we also invent a node and edge betweenness based fast layout algorithm (BFL). BFL places the high-betweenness nodes to optimal positions and allows the low-betweenness nodes to reach suboptimal positions. Furthermore, BFL reduces the runtime by combining a sequential insertion algorim with betweenness. For a graph with n nodes, this approach reduces the expected runtime of the algorithm to O(n2) when considering edge crossings, and to O(n log n) when considering only density and edge lengths. Conclusion Our BFL algorithm is compared against fast graph layout algorithms and approaches requiring intensive optimizations. For gene networks, we show that our algorithm is faster than all layout algorithms tested while providing readability on par with intensive optimization algorithms. We achieve a 1.4 second runtime for a graph with 4000 nodes and 12000 edges on a standard desktop computer. PMID:19146673

The importance of leading edge vortices under simplified flapping flight conditions at the size scale of birds.

PubMed

Hubel, Tatjana Y; Tropea, Cameron

2010-06-01

Over the last decade, interest in animal flight has grown, in part due to the possible use of flapping propulsion for micro air vehicles. The importance of unsteady lift-enhancing mechanisms in insect flight has been recognized, but unsteady effects were generally thought to be absent for the flapping flight of larger animals. Only recently has the existence of LEVs (leading edge vortices) in small vertebrates such as swifts, small bats and hummingbirds been confirmed. To study the relevance of unsteady effects at the scale of large birds [reduced frequency k between 0.05 and 0.3, k=(pifc)/U(infinity); f is wingbeat frequency, U(infinity) is free-stream velocity, and c is the average wing chord], and the consequences of the lack of kinematic and morphological refinements, we have designed a simplified goose-sized flapping model for wind tunnel testing. The 2-D flow patterns along the wing span were quantitatively visualized using particle image velocimetry (PIV), and a three-component balance was used to measure the forces generated by the wings. The flow visualization on the wing showed the appearance of LEVs, which is typically associated with a delayed stall effect, and the transition into flow separation. Also, the influence of the delayed stall and flow separation was clearly visible in measurements of instantaneous net force over the wingbeat cycle. Here, we show that, even at reduced frequencies as low as those of large bird flight, unsteady effects are present and non-negligible and have to be addressed by kinematic and morphological adaptations.

Implementing a Parallel Image Edge Detection Algorithm Based on the Otsu-Canny Operator on the Hadoop Platform

PubMed Central

Wang, Min; Tian, Yun

2018-01-01

The Canny operator is widely used to detect edges in images. However, as the size of the image dataset increases, the edge detection performance of the Canny operator decreases and its runtime becomes excessive. To improve the runtime and edge detection performance of the Canny operator, in this paper, we propose a parallel design and implementation for an Otsu-optimized Canny operator using a MapReduce parallel programming model that runs on the Hadoop platform. The Otsu algorithm is used to optimize the Canny operator's dual threshold and improve the edge detection performance, while the MapReduce parallel programming model facilitates parallel processing for the Canny operator to solve the processing speed and communication cost problems that occur when the Canny edge detection algorithm is applied to big data. For the experiments, we constructed datasets of different scales from the Pascal VOC2012 image database. The proposed parallel Otsu-Canny edge detection algorithm performs better than other traditional edge detection algorithms. The parallel approach reduced the running time by approximately 67.2% on a Hadoop cluster architecture consisting of 5 nodes with a dataset of 60,000 images. Overall, our approach system speeds up the system by approximately 3.4 times when processing large-scale datasets, which demonstrates the obvious superiority of our method. The proposed algorithm in this study demonstrates both better edge detection performance and improved time performance. PMID:29861711

On the generation of side-edge flap noise. [part span trailing edge flaps

NASA Technical Reports Server (NTRS)

Howe, M. S.

1981-01-01

A theory is proposed for estimating the noise generated at the side edges of part span trailing edge flaps in terms of pressure fluctuations measured just in-board of the side edge of the upper surface of the flap. Asymptotic formulae are developed in the opposite extremes of Lorentz contracted acoustic wavelength large/small compared with the chord of the flap. Interpolation between these limiting results enables the field shape and its dependence on subsonic forward flight speed to be predicted over the whole frequency range. It is shown that the mean width of the side edge gap between the flap and the undeflected portion of the airfoil has a significant influence on the intensity of the radiated sound. It is estimated that the noise generated at a single side edge of a full scale part span flap can exceed that produced along the whole of the trailing edge of the flap by 3 dB or more.

Cross Flow Effects on Glaze Ice Roughness Formation

NASA Technical Reports Server (NTRS)

Tsao, Jen-Ching

2004-01-01

The present study examines the impact of large-scale cross flow on the creation of ice roughness elements on the leading edge of a swept wing under glaze icing conditions. A three-dimensional triple-deck structure is developed to describe the local interaction of a 3 D air boundary layer with ice sheets and liquid films. A linear stability analysis is presented here. It is found that, as the sweep angle increases, the local icing instabilities enhance and the most linearly unstable modes are strictly three dimensional.

Performance of Large Format Transition Edge Sensor Microcalorimeter Arrays

NASA Technical Reports Server (NTRS)

Chervenak, J. A.; Adams, J. A.; Bandler, S. B.; Busch, S. E.; Eckart, M. E.; Ewin, A. E.; Finkbeiner, F. M.; Kilbourne, C. A.; Kelley, R. L.; Porst, J. P.;

Numerical investigation of roughness effects in aircraft icing calculations

NASA Astrophysics Data System (ADS)

Matheis, Brian Daniel

2008-10-01

Icing codes are playing a role of increasing significance in the design and certification of ice protected aircraft surfaces. However, in the interest of computational efficiency certain small scale physics of the icing problem are grossly approximated by the codes. One such small scale phenomena is the effect of ice roughness on the development of the surface water film and on the convective heat transfer. This study uses computational methods to study the potential effect of ice roughness on both of these small scale phenomena. First, a two-dimensional condensed layer code is used to examine the effect of roughness on surface water development. It is found that the Couette approximation within the film breaks down as the wall shear goes to zero, depending on the film thickness. Roughness elements with initial flow separation in the air induce flow separation in the water layer at steady state, causing a trapping of the film. The amount of trapping for different roughness configurations is examined. Second, a three-dimensional incompressible Navier-Stokes code is developed to examine large scale ice roughness on the leading edge. The effect on the convective heat transfer and potential effect on the surface water dynamics is examined for a number of distributed roughness parameters including Reynolds number, roughness height, streamwise extent, roughness spacing and roughness shape. In most cases the roughness field increases the net average convective heat transfer on the leading edge while narrowing surface shear lines, indicating a choking of the surface water flow. Both effects show significant variation on the scale of the ice roughness. Both the change in heat transfer as well as the potential change in surface water dynamics are presented in terms of the development of singularities in the surface shear pattern. Of particular interest is the effect of the smooth zone upstream of the roughness which shows both a relatively large increase in convective heat transfer as well as excessive choking of the surface shear lines at the upstream end of the roughness field. A summary of the heat transfer results is presented for both the averaged heat transfer as well as the maximum heat transfer over each roughness element, indicating that the roughness Reynolds number is the primary parameter which characterizes the behavior of the roughness for the problem of interest.

Trade-off between competition and facilitation defines gap colonization in mountains.

PubMed

Lembrechts, Jonas J; Milbau, Ann; Nijs, Ivan

2015-11-10

Recent experimental observations show that gap colonization in small-stature (e.g. grassland and dwarf shrubs) vegetation strongly depends on the abiotic conditions within them. At the same time, within-gap variation in biotic interactions such as competition and facilitation, caused by distance to the gap edge, would affect colonizer performance, but a theoretical framework to explore such patterns is missing. Here, we model how competition, facilitation and environmental conditions together determine the small-scale patterns of gap colonization along a cold gradient in mountains, by simulating colonizer survival in gaps of various sizes. Our model adds another dimension to the known effects of biotic interactions along a stress gradient by focussing on the trade-off between competition and facilitation in the within-gap environment. We show that this trade-off defines a peak in colonizer survival at a specific distance from the gap edge, which progressively shifts closer to the edge as the environment gets colder, ultimately leaving a large fraction of gaps unsuitable for colonization in facilitation-dominated systems. This is reinforced when vegetation size and temperature amelioration are manipulated simultaneously with temperature in order to simulate an elevational gradient more realistically. Interestingly, all other conditions being equal, the magnitude of the realized survival peak was always lower in large than in small gaps, making large gaps harder to colonize. The model is relevant to predict effects of non-native plant invasions and climate warming on colonization processes in mountains. Published by Oxford University Press on behalf of the Annals of Botany Company.

Earthquakes in the Laboratory: Continuum-Granular Interactions

NASA Astrophysics Data System (ADS)

Ecke, Robert; Geller, Drew; Ward, Carl; Backhaus, Scott

2013-03-01

Earthquakes in nature feature large tectonic plate motion at large scales of 10-100 km and local properties of the earth on the scale of the rupture width, of the order of meters. Fault gouge often fills the gap between the large slipping plates and may play an important role in the nature and dynamics of earthquake events. We have constructed a laboratory scale experiment that represents a similitude scale model of this general earthquake description. Two photo-elastic plates (50 cm x 25 cm x 1 cm) confine approximately 3000 bi-disperse nylon rods (diameters 0.12 and 0.16 cm, height 1 cm) in a gap of approximately 1 cm. The plates are held rigidly along their outer edges with one held fixed while the other edge is driven at constant speed over a range of about 5 cm. The local stresses exerted on the plates are measured using their photo-elastic response, the local relative motions of the plates, i.e., the local strains, are determined by the relative motion of small ball bearings attached to the top surface, and the configurations of the nylon rods are investigated using particle tracking tools. We find that this system has properties similar to real earthquakes and are exploring these ``lab-quake'' events with the quantitative tools we have developed.

Magnetic Stress at the Marginally Stable Orbit: Altered Disk Structure, Radiation, and Black Hole Spin Evolution

NASA Astrophysics Data System (ADS)

Agol, Eric; Krolik, Julian H.

2000-01-01

Magnetic connections to the plunging region can exert stresses on the inner edge of an accretion disk around a black hole. We recompute the relativistic corrections to the thin-disk dynamics equations when these stresses take the form of a time-steady torque on the inner edge of the disk. The additional dissipation associated with these stresses is concentrated relatively close outside the marginally stable orbit, scaling as r-7/2 at large radius. As a result of these additional stresses, spin-up of the central black hole is retarded; the maximum spin-equilibrium accretion efficiency is 36% and occurs at a/M=0.94 the disk spectrum is extended toward higher frequencies; line profiles (such as Fe Kα) are broadened if the line emissivity scales with local flux; limb brightening, especially at the higher frequencies, is enhanced; and the returning radiation fraction is substantially increased, up to 58%. This last effect creates possible explanations for both synchronized continuum fluctuations in active galactic nuclei and polarization rises shortward of the Lyman edge in quasars. We show that no matter what additional stresses occur, when a/M<0.36, the second law of black hole dynamics sets an absolute upper bound on the accretion efficiency.

Spatiotemporal complexity of 2-D rupture nucleation process observed by direct monitoring during large-scale biaxial rock friction experiments

NASA Astrophysics Data System (ADS)

Fukuyama, Eiichi; Tsuchida, Kotoyo; Kawakata, Hironori; Yamashita, Futoshi; Mizoguchi, Kazuo; Xu, Shiqing

2018-05-01

We were able to successfully capture rupture nucleation processes on a 2-D fault surface during large-scale biaxial friction experiments using metagabbro rock specimens. Several rupture nucleation patterns have been detected by a strain gauge array embedded inside the rock specimens as well as by that installed along the edge walls of the fault. In most cases, the unstable rupture started just after the rupture front touched both ends of the rock specimen (i.e., when rupture front extended to the entire width of the fault). In some cases, rupture initiated at multiple locations and the rupture fronts coalesced to generate unstable ruptures, which could only be detected from the observation inside the rock specimen. Therefore, we need to carefully examine the 2-D nucleation process of the rupture especially when analyzing the data measured only outside the rock specimen. At least the measurements should be done at both sides of the fault to identify the asymmetric rupture propagation on the fault surface, although this is not perfect yet. In the present experiment, we observed three typical types of the 2-D rupture propagation patterns, two of which were initiated at a single location either close to the fault edge or inside the fault. This initiation could be accelerated by the free surface effect at the fault edge. The third one was initiated at multiple locations and had a rupture coalescence at the middle of the fault. These geometrically complicated rupture initiation patterns are important for understanding the earthquake nucleation process in nature.

Boundaries in ground beetle (Coleoptera: Carabidae) and environmental variables at the edges of forest patches with residential developments

PubMed Central

Davis, Doreen E.

2018-01-01

Background Few studies of edge effects on wildlife objectively identify habitat edges or explore non-linear responses. In this paper, we build on ground beetle (Coleoptera: Carabidae) research that has begun to address these domains by using triangulation wombling to identify boundaries in beetle community structure and composition at the edges of forest patches with residential developments. We hypothesized that edges are characterized by boundaries in environmental variables that correspond to marked discontinuities in vegetation structure between maintained yards and forest. We expected environmental boundaries to be associated with beetle boundaries. Methods We collected beetles and measured environmental variables in 200 m by 200 m sampling grids centered at the edges of three forest patches, each with a rural, suburban, or urban context, in Charlotte, North Carolina, USA. We identified boundaries within each grid at two spatial scales and tested their significance and overlap using boundary statistics and overlap statistics, respectively. We complemented boundary delineation with k-means clustering. Results Boundaries in environmental variables, such as temperature, grass cover, and leaf litter depth, occurred at or near the edges of all three sites, in many cases at both scales. The beetle variables that exhibited the most pronounced boundary structure in relation to edges were total species evenness, generalist abundance, generalist richness, generalist evenness, and Agonum punctiforme abundance. Environmental and beetle boundaries also occurred within forest patches and residential developments, indicating substantial localized spatial variation on either side of edges. Boundaries in beetle and environmental variables that displayed boundary structure at edges significantly overlapped, as did boundaries on either side of edges. The comparison of boundaries and clusters revealed that boundaries formed parts of the borders of patches of similar beetle or environmental condition. Discussion We show that edge effects on ground beetle community structure and composition and environmental variation at the intersection of forest patches and residential developments can be described by boundaries and that these boundaries overlap in space. However, our results also highlight the complexity of edge effects in our system: environmental boundaries were located at or near edges whereas beetle boundaries related to edges could be spatially disjunct from them; boundaries incompletely delineated edges such that only parts of edges were well-described by sharp transitions in beetle and/or environmental variables; and the occurrence of boundaries related to edges was apparently influenced by individual property management practices, site-specific characteristics such as development geometry, and spatial scale. PMID:29333346

Boundaries in ground beetle (Coleoptera: Carabidae) and environmental variables at the edges of forest patches with residential developments.

PubMed

Davis, Doreen E; Gagné, Sara A

2018-01-01

Few studies of edge effects on wildlife objectively identify habitat edges or explore non-linear responses. In this paper, we build on ground beetle (Coleoptera: Carabidae) research that has begun to address these domains by using triangulation wombling to identify boundaries in beetle community structure and composition at the edges of forest patches with residential developments. We hypothesized that edges are characterized by boundaries in environmental variables that correspond to marked discontinuities in vegetation structure between maintained yards and forest. We expected environmental boundaries to be associated with beetle boundaries. We collected beetles and measured environmental variables in 200 m by 200 m sampling grids centered at the edges of three forest patches, each with a rural, suburban, or urban context, in Charlotte, North Carolina, USA. We identified boundaries within each grid at two spatial scales and tested their significance and overlap using boundary statistics and overlap statistics, respectively. We complemented boundary delineation with k -means clustering. Boundaries in environmental variables, such as temperature, grass cover, and leaf litter depth, occurred at or near the edges of all three sites, in many cases at both scales. The beetle variables that exhibited the most pronounced boundary structure in relation to edges were total species evenness, generalist abundance, generalist richness, generalist evenness, and Agonum punctiforme abundance. Environmental and beetle boundaries also occurred within forest patches and residential developments, indicating substantial localized spatial variation on either side of edges. Boundaries in beetle and environmental variables that displayed boundary structure at edges significantly overlapped, as did boundaries on either side of edges. The comparison of boundaries and clusters revealed that boundaries formed parts of the borders of patches of similar beetle or environmental condition. We show that edge effects on ground beetle community structure and composition and environmental variation at the intersection of forest patches and residential developments can be described by boundaries and that these boundaries overlap in space. However, our results also highlight the complexity of edge effects in our system: environmental boundaries were located at or near edges whereas beetle boundaries related to edges could be spatially disjunct from them; boundaries incompletely delineated edges such that only parts of edges were well-described by sharp transitions in beetle and/or environmental variables; and the occurrence of boundaries related to edges was apparently influenced by individual property management practices, site-specific characteristics such as development geometry, and spatial scale.

Theory based scaling of edge turbulence and implications for the scrape-off layer width

NASA Astrophysics Data System (ADS)

Myra, J. R.; Russell, D. A.; Zweben, S. J.

2016-11-01

Turbulence and plasma parameter data from the National Spherical Torus Experiment (NSTX) [Ono et al., Nucl. Fusion 40, 557 (2000)] is examined and interpreted based on various theoretical estimates. In particular, quantities of interest for assessing the role of turbulent transport on the midplane scrape-off layer heat flux width are assessed. Because most turbulence quantities exhibit large scatter and little scaling within a given operation mode, this paper focuses on length and time scales and dimensionless parameters between operational modes including Ohmic, low (L), and high (H) modes using a large NSTX edge turbulence database [Zweben et al., Nucl. Fusion 55, 093035 (2015)]. These are compared with theoretical estimates for drift and interchange rates, profile modification saturation levels, a resistive ballooning condition, and dimensionless parameters characterizing L and H mode conditions. It is argued that the underlying instability physics governing edge turbulence in different operational modes is, in fact, similar, and is consistent with curvature-driven drift ballooning. Saturation physics, however, is dependent on the operational mode. Five dimensionless parameters for drift-interchange turbulence are obtained and employed to assess the importance of turbulence in setting the scrape-off layer heat flux width λq and its scaling. An explicit proportionality of the width λq to the safety factor and major radius (qR) is obtained under these conditions. Quantitative estimates and reduced model numerical simulations suggest that the turbulence mechanism is not negligible in determining λq in NSTX, at least for high plasma current discharges.

Theory based scaling of edge turbulence and implications for the scrape-off layer width

DOE PAGES

Myra, J. R.; Russell, D. A.; Zweben, S. J.

2016-11-01

Turbulence and plasma parameter data from the National Spherical Torus Experiment (NSTX) is examined and interpreted based on various theoretical estimates. In particular, quantities of interest for assessing the role of turbulent transport on the midplane scrape-off layer heat flux width are assessed. Because most turbulence quantities exhibit large scatter and little scaling within a given operation mode, this paper focuses on length and time scales and dimensionless parameters between operational modes including Ohmic, low (L), and high (H) modes using a large NSTX edge turbulence database. These are compared with theoretical estimates for drift and interchange rates, profile modificationmore » saturation levels, a resistive ballooning condition, and dimensionless parameters characterizing L and H mode conditions. It is argued that the underlying instability physics governing edge turbulence in different operational modes is, in fact, similar, and is consistent with curvature-driven drift ballooning. Saturation physics, however, is dependent on the operational mode. Five dimensionless parameters for drift-interchange turbulence are obtained and employed to assess the importance of turbulence in setting the scrape-off layer heat flux width λ q and its scaling. An explicit proportionality of the width λ q to the safety factor and major radius (qR) is obtained under these conditions. Lastly, quantitative estimates and reduced model numerical simulations suggest that the turbulence mechanism is not negligible in determining λ q in NSTX, at least for high plasma current discharges.« less

Small-Scale Transonic Investigation of the Effects of Partial-Span Leading-Edge Camber on the Aerodynamic Characteristics of a 50 Deg 38' Sweptback Wing of Aspect Ratio 2.98

NASA Technical Reports Server (NTRS)

Alford, William J., Jr.; Byrnes, Andrew L., Jr.

1952-01-01

A small-scale transonic investigation of two semispan wings of the same plan form was made in the Langley high-speed 7- by 10-foot tunnel through a Mach number range of 0.70 to 1.10 and a mean-test Reynolds number range of 745,000 to 845,000 to determine the effects of partial-span leading-edge camber on the aerodynamic characteristics of a swept-back wing. This paper presents the results of the investigation of wing-alone and wing-fuselage configurations of the two wings; one, was an uncambered wing and the other had the forward 45 percent of the chord cambered over the outboard 55 percent of the span. The semispan wings had 50deg 38ft sweepback of their quarter-chord lines, aspect ratio of 2.98, taper ratio of 0.45, and modified NACA 64A-series airfoil sections tapered in thickness ratio. Lift, drag, pitching moment, and root-bending moment were obtained for these configurations. The results indicated that, for the wing-alone configuration, use of the partial-span leading-edge camber provided an increase in maximum lift-drag ratios up to a Mach number of 0.95, after which no gain was realized. For the wing-fuselage combination, the partial-span leading-edge camber appeared to cause no gain in maximum lift-drag ratio throughout the test range of Mach numbers. The lift-curve slopes of the partial-span leading-edge camber configurations indicated no significant change over the basic configurations in the subsonic range but resulted in slight reductions at the higher Mach numbers. No significantly large changes in pitching-moment-curve slopes or lateral center of additional loading were indicated because of the modification.

Detecting Multi-scale Structures in Chandra Images of Centaurus A

NASA Astrophysics Data System (ADS)

Karovska, M.; Fabbiano, G.; Elvis, M. S.; Evans, I. N.; Kim, D. W.; Prestwich, A. H.; Schwartz, D. A.; Murray, S. S.; Forman, W.; Jones, C.; Kraft, R. P.; Isobe, T.; Cui, W.; Schreier, E. J.

1999-12-01

Centaurus A (NGC 5128) is a giant early-type galaxy with a merger history, containing the nearest radio-bright AGN. Recent Chandra High Resolution Camera (HRC) observations of Cen A reveal X-ray multi-scale structures in this object with unprecedented detail and clarity. We show the results of an analysis of the Chandra data with smoothing and edge enhancement techniques that allow us to enhance and quantify the multi-scale structures present in the HRC images. These techniques include an adaptive smoothing algorithm (Ebeling et al 1999), and a multi-directional gradient detection algorithm (Karovska et al 1994). The Ebeling et al adaptive smoothing algorithm, which is incorporated in the CXC analysis s/w package, is a powerful tool for smoothing images containing complex structures at various spatial scales. The adaptively smoothed images of Centaurus A show simultaneously the high-angular resolution bright structures at scales as small as an arcsecond and the extended faint structures as large as several arc minutes. The large scale structures suggest complex symmetry, including a component possibly associated with the inner radio lobes (as suggested by the ROSAT HRI data, Dobereiner et al 1996), and a separate component with an orthogonal symmetry that may be associated with the galaxy as a whole. The dust lane and the x-ray ridges are very clearly visible. The adaptively smoothed images and the edge-enhanced images also suggest several filamentary features including a large filament-like structure extending as far as about 5 arcminutes to North-West.

Wind-tunnel investigation of a large-scale VTOL aircraft model with wing root and wing thrust augmentors. [Ames 40 by 80 foot wind tunnel

NASA Technical Reports Server (NTRS)

Aoyagi, K.; Aiken, T. N.

1979-01-01

Tests were conducted in the Ames 40 by 80 foot wind tunnel to determine the aerodynamic characteristics of a large-scale V/STOL aircraft model with thrust augmentors. The model had a double-delta wing of aspect ratio 1.65 with augmentors located in the wing root and the wing trailing edge. The supply air for the augmentor primary nozzles was provided by the YJ-97 turbojet engine. The airflow was apportioned approximately 74 percent to the wing root augmentor and 24 percent to wing augmentor. Results were obtained at several trailing-edge flap deflections with the nozzle jet-momentum coefficients ranging from 0 to 7.9. Three-component longitudinal data are presented with the agumentor operating with and without the horizontal tail. A limited amount of six component data are also presented.

Supplementary Free-Spinning-Tunnel Tests of a 1/16-Scale Model of the McDonnell XB-85 Airplane Equipped with a Conventional-Tail Arrangement

NASA Technical Reports Server (NTRS)

Klinar, Walter J.

1947-01-01

Spin tests have been conducted in the Langley free-spinning tunnel on a 1/16-scale model of the McDonnell XP-85 airplane with the normal X-tail replaced with a short-coupled conventional tail arrangement. The effect of the conventional tail arrangement and the effects of various modifications upon the spin and recovery characteristics of the model were determined. The results of the tests indicated that installation of the conventional tail arrangement wil not provide satisfactory recoveries from spins of the airplane. Satisfactory recoveries will be obtainable, however, either by installing in addition a very large ventral fin (17.94 sq ft, full-scale) below the tail or by decreasing the width of the fuselage and making it flat sided rearward of the wing trailing edge.

Spatial and temporal patterns of microclimates at an urban forest edge and their management implications.

PubMed

Li, Yingnan; Kang, Wanmo; Han, Yiwen; Song, Youngkeun

2018-01-23

Fragmented forests generate a variety of forest edges, leading to microclimates in the edge zones that differ from those in the forest interior. Understanding microclimatic variation is an important consideration for managers because it helps when making decisions about how to restrict the extent of edge effects. Thus, our study attempted to characterize the changing microclimate features at an urban forest edge located on Mt. Gwanak, Seoul, South Korea. We examined edge effects on air temperature, relative humidity, soil temperature, soil moisture, and photosynthetically active radiation (PAR) during the hottest three consecutive days in August 2016. Results showed that each variable responded differently to the edge effects. This urban forest edge had an effect on temporal changes at a diurnal scale in all microclimate variables, except soil moisture. In addition, all variables except relative humidity were significantly influenced by the edge effect up to 15 m inward from the forest boundary. The relative humidity fluctuated the most and showed the deepest extent of the edge effect. Moreover, the edge widths calculated from the relative humidity and air temperature both peaked in the late afternoon (16:00 h). Our findings provide a reference for forest managers in designing urban forest zones and will contribute to the conservation of fragmented forests in urban areas.

Dynamic Edge Effects in Small Mammal Communities across a Conservation-Agricultural Interface in Swaziland

PubMed Central

Hurst, Zachary M.; McCleery, Robert A.; Collier, Bret A.; Fletcher, Robert J.; Silvy, Nova J.; Taylor, Peter J.; Monadjem, Ara

2013-01-01

Across the planet, high-intensity farming has transformed native vegetation into monocultures, decreasing biodiversity on a landscape scale. Yet landscape-scale changes to biodiversity and community structure often emerge from processes operating at local scales. One common process that can explain changes in biodiversity and community structure is the creation of abrupt habitat edges, which, in turn, generate edge effects. Such effects, while incredibly common, can be highly variable across space and time; however, we currently lack a general analytical framework that can adequately capture such spatio-temporal variability. We extend previous approaches for estimating edge effects to a non-linear mixed modeling framework that captures such spatio-temporal heterogeneity and apply it to understand how agricultural land-uses alter wildlife communities. We trapped small mammals along a conservation-agriculture land-use interface extending 375 m into sugarcane plantations and conservation land-uses at three sites during dry and wet seasons in Swaziland, Africa. Sugarcane plantations had significant reductions in species richness and heterogeneity, and showed an increase in community similarity, suggesting a more homogenized small mammal community. Furthermore, our modeling framework identified strong variation in edge effects on communities across sites and seasons. Using small mammals as an indicator, intensive agricultural practices appear to create high-density communities of generalist species while isolating interior species in less than 225 m. These results illustrate how agricultural land-use can reduce diversity across the landscape and that effects can be masked or magnified, depending on local conditions. Taken together, our results emphasize the need to create or retain natural habitat features in agricultural mosaics. PMID:24040269

Effect of spanwise blowing on leading-edge vortex bursting of a highly swept aspect ratio 1.18 delta wing

NASA Technical Reports Server (NTRS)

Scantling, W. L.; Gloss, B. B.

1974-01-01

An investigation was conducted in the Langley 1/8-scale V/STOL model tunnel on a semispan delta wing with a leading-edge sweep of 74 deg, to determine the effectiveness of various locations of upper surface and reflection plane blowing on leading-edge vortex bursting. Constant area nozzles were located on the wing upper surface along a ray swept 79 deg, which was beneath the leading-edge vortex core. The bursting and reformation of the leading-edge vortex was viewed by injecting helium into the vortex core, and employing a schlieren system.

The catalog of edge-on disk galaxies from SDSS. I. The catalog and the structural parameters of stellar disks

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

Bizyaev, D. V.; Kautsch, S. J.; Mosenkov, A. V.

We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS). A visual inspection of the g, r, and i images of about 15,000 galaxies allowed us to split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-on galaxies, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects either show signs of interaction and warps, or nearby bright stars project on it. We added more candidate galaxies from RFGC, EFIGI, RC3, andmore » Galaxy Zoo catalogs found in the SDSS footprints. Our final sample consists of 5747 genuine edge-on galaxies. We estimate the structural parameters of the stellar disks (the stellar disk thickness, radial scale length, and central surface brightness) in the galaxies by analyzing photometric profiles in each of the g, r, and i images. We also perform simplified three-dimensional modeling of the light distribution in the stellar disks of edge-on galaxies from our sample. Our large sample is intended to be used for studying scaling relations in the stellar disks and bulges and for estimating parameters of the thick disks in different types of galaxies via the image stacking. In this paper, we present the sample selection procedure and general description of the sample.« less

Aerodynamic Inner Workings of Circumferential Grooves in a Transonic Axial Compressor

NASA Technical Reports Server (NTRS)

Hah, Chunill; Mueller, Martin; Schiffer, Heinz-Peter

2007-01-01

The current paper reports on investigations of the fundamental flow mechanisms of circumferential grooves applied to a transonic axial compressor. Experimental results show that the compressor stall margin is significantly improved with the current set of circumferential grooves. The primary focus of the current investigation is to advance understanding of basic flow mechanics behind the observed improvement of stall margin. Experimental data and numerical simulations of a circumferential groove were analyzed in detail to unlock the inner workings of the circumferential grooves in the current transonic compressor rotor. A short length scale stall inception occurs when a large flow blockage is built on the pressure side of the blade near the leading edge and incoming flow spills over to the adjacent blade passage due to this blockage. The current study reveals that a large portion of this blockage is created by the tip clearance flow originating from 20% to 50% chord of the blade from the leading edge. Tip clearance flows originating from the leading edge up to 20% chord form a tip clearance core vortex and this tip clearance core vortex travels radially inward. The tip clearance flows originating from 20% to 50% chord travels over this tip clearance core vortex and reaches to the pressure side. This part of tip clearance flow is of low momentum as it is coming from the casing boundary layer and the blade suction surface boundary layer. The circumferential grooves disturb this part of the tip clearance flow close to the casing. Consequently the buildup of the induced vortex and the blockage near the pressure side of the passage is reduced. This is the main mechanism of the circumferential grooves that delays the formation of blockage near the pressure side of the passage and delays the onset of short length scale stall inception. The primary effect of the circumferential grooves is preventing local blockage near the pressure side of the blade leading edge that directly determines flow spillage around the leading edge. The circumferential grooves do not necessarily reduce the over all blockage built up at the rotor tip section.

Edge control in a computer controlled optical surfacing process using a heterocercal tool influence function.

PubMed

Hu, Haixiang; Zhang, Xin; Ford, Virginia; Luo, Xiao; Qi, Erhui; Zeng, Xuefeng; Zhang, Xuejun

2016-11-14

Edge effect is regarded as one of the most difficult technical issues in a computer controlled optical surfacing (CCOS) process. Traditional opticians have to even up the consequences of the two following cases. Operating CCOS in a large overhang condition affects the accuracy of material removal, while in a small overhang condition, it achieves a more accurate performance, but leaves a narrow rolled-up edge, which takes time and effort to remove. In order to control the edge residuals in the latter case, we present a new concept of the 'heterocercal' tool influence function (TIF). Generated from compound motion equipment, this type of TIF can 'transfer' the material removal from the inner place to the edge, meanwhile maintaining the high accuracy and efficiency of CCOS. We call it the 'heterocercal' TIF, because of the inspiration from the heterocercal tails of sharks, whose upper lobe provides most of the explosive power. The heterocercal TIF was theoretically analyzed, and physically realized in CCOS facilities. Experimental and simulation results showed good agreement. It enables significant control of the edge effect and convergence of entire surface errors in large tool-to-mirror size-ratio conditions. This improvement will largely help manufacturing efficiency in some extremely large optical system projects, like the tertiary mirror of the Thirty Meter Telescope.

Quantized edge modes in atomic-scale point contacts in graphene

NASA Astrophysics Data System (ADS)

Kinikar, Amogh; Phanindra Sai, T.; Bhattacharyya, Semonti; Agarwala, Adhip; Biswas, Tathagata; Sarker, Sanjoy K.; Krishnamurthy, H. R.; Jain, Manish; Shenoy, Vijay B.; Ghosh, Arindam

2017-07-01

The zigzag edges of single- or few-layer graphene are perfect one-dimensional conductors owing to a set of gapless states that are topologically protected against backscattering. Direct experimental evidence of these states has been limited so far to their local thermodynamic and magnetic properties, determined by the competing effects of edge topology and electron-electron interaction. However, experimental signatures of edge-bound electrical conduction have remained elusive, primarily due to the lack of graphitic nanostructures with low structural and/or chemical edge disorder. Here, we report the experimental detection of edge-mode electrical transport in suspended atomic-scale constrictions of single and multilayer graphene created during nanomechanical exfoliation of highly oriented pyrolytic graphite. The edge-mode transport leads to the observed quantization of conductance close to multiples of G0 = 2e2/h. At the same time, conductance plateaux at G0/2 and a split zero-bias anomaly in non-equilibrium transport suggest conduction via spin-polarized states in the presence of an electron-electron interaction.

Quantized edge modes in atomic-scale point contacts in graphene.

PubMed

Kinikar, Amogh; Phanindra Sai, T; Bhattacharyya, Semonti; Agarwala, Adhip; Biswas, Tathagata; Sarker, Sanjoy K; Krishnamurthy, H R; Jain, Manish; Shenoy, Vijay B; Ghosh, Arindam

2017-07-01

The zigzag edges of single- or few-layer graphene are perfect one-dimensional conductors owing to a set of gapless states that are topologically protected against backscattering. Direct experimental evidence of these states has been limited so far to their local thermodynamic and magnetic properties, determined by the competing effects of edge topology and electron-electron interaction. However, experimental signatures of edge-bound electrical conduction have remained elusive, primarily due to the lack of graphitic nanostructures with low structural and/or chemical edge disorder. Here, we report the experimental detection of edge-mode electrical transport in suspended atomic-scale constrictions of single and multilayer graphene created during nanomechanical exfoliation of highly oriented pyrolytic graphite. The edge-mode transport leads to the observed quantization of conductance close to multiples of G 0  = 2e 2 /h. At the same time, conductance plateaux at G 0 /2 and a split zero-bias anomaly in non-equilibrium transport suggest conduction via spin-polarized states in the presence of an electron-electron interaction.

Morphology, Structure, and Origin of Island Paterae on Io

NASA Astrophysics Data System (ADS)

Howell, R. R.; Lopes, R. M.

2011-12-01

We are investigating both the small and large scale morphology of those paterae on Jupiter's moon Io which show central islands. At small scales a variety of features may be evidence of volatile transport processes. For example Loki Patera contains small bright spots colloquially known as sulfur bergs, which we suspect are fumarole deposits. They are near the limit of the best spatial resolution obtained in Voyager I images. Our preliminary results indicate their reflectance is consistent with sulfur (but not sulfur dioxide) as would be expected based on the temperatures seen in the infrared. At large scales we are beginning to model the stress patterns which could produce the overall morphology of island paterae. As discussed by Radebaugh (Ph.D. Dissertation, 2005) and Black (M.S. thesis, 2007), of 428 cataloged patera on Io, 35 contain bright islands. Most of these islands are irregularly shaped and may simply be regions not yet covered by lava. However several paterae, in particular Loki and Tupan, show more regular structure. Both patera have one straight edge, and in the case of Loki the most volcanically active part of the patera is located near that edge. As Turtle et al. (2001 JGR 106: 33175) and others have suggested, those straight edges may be faults which relieve the expected global compressive stresses and also act as magma conduits. Radebaugh (2005) has suggested that some of these large islands might be analogs of resurgent domes. We are investigating whether a hybrid stress model may be able to explain the overall morphology.

Non-steady wind turbine response to daytime atmospheric turbulence.

PubMed

Nandi, Tarak N; Herrig, Andreas; Brasseur, James G

2017-04-13

Relevant to drivetrain bearing fatigue failures, we analyse non-steady wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and the rotating blades of a GE 1.5 MW wind turbine using a unique dataset from a GE field experiment and computer simulation. Time-resolved local velocity data were collected at the leading and trailing edges of an instrumented blade together with generator power, revolutions per minute, pitch and yaw. Wind velocity and temperature were measured upwind on a meteorological tower. The stability state and other atmospheric conditions during the field experiment were replicated with a large-eddy simulation in which was embedded a GE 1.5 MW wind turbine rotor modelled with an advanced actuator line method. Both datasets identify three important response time scales: advective passage of energy-dominant eddies (≈25-50 s), blade rotation (once per revolution (1P), ≈3 s) and sub-1P scale (<1 s) response to internal eddy structure. Large-amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the aerofoil plane, modulated by eddy passage at longer time scales. Generator power responds strongly to large-eddy wind modulations. We show that internal dynamics of the blade boundary layer near the trailing edge is temporally modulated by the non-steady external flow that was measured at the leading edge, as well as blade-generated turbulence motions.This article is part of the themed issue 'Wind energy in complex terrains'. © 2017 The Author(s).

Non-steady wind turbine response to daytime atmospheric turbulence

PubMed Central

Nandi, Tarak N.; Herrig, Andreas

2017-01-01

Relevant to drivetrain bearing fatigue failures, we analyse non-steady wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and the rotating blades of a GE 1.5 MW wind turbine using a unique dataset from a GE field experiment and computer simulation. Time-resolved local velocity data were collected at the leading and trailing edges of an instrumented blade together with generator power, revolutions per minute, pitch and yaw. Wind velocity and temperature were measured upwind on a meteorological tower. The stability state and other atmospheric conditions during the field experiment were replicated with a large-eddy simulation in which was embedded a GE 1.5 MW wind turbine rotor modelled with an advanced actuator line method. Both datasets identify three important response time scales: advective passage of energy-dominant eddies (≈25–50 s), blade rotation (once per revolution (1P), ≈3 s) and sub-1P scale (<1 s) response to internal eddy structure. Large-amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the aerofoil plane, modulated by eddy passage at longer time scales. Generator power responds strongly to large-eddy wind modulations. We show that internal dynamics of the blade boundary layer near the trailing edge is temporally modulated by the non-steady external flow that was measured at the leading edge, as well as blade-generated turbulence motions. This article is part of the themed issue ‘Wind energy in complex terrains’. PMID:28265026

Edge reconstruction in armchair phosphorene nanoribbons revealed by discontinuous Galerkin density functional theory.

PubMed

Hu, Wei; Lin, Lin; Yang, Chao

2015-12-21

With the help of our recently developed massively parallel DGDFT (Discontinuous Galerkin Density Functional Theory) methodology, we perform large-scale Kohn-Sham density functional theory calculations on phosphorene nanoribbons with armchair edges (ACPNRs) containing a few thousands to ten thousand atoms. The use of DGDFT allows us to systematically achieve a conventional plane wave basis set type of accuracy, but with a much smaller number (about 15) of adaptive local basis (ALB) functions per atom for this system. The relatively small number of degrees of freedom required to represent the Kohn-Sham Hamiltonian, together with the use of the pole expansion the selected inversion (PEXSI) technique that circumvents the need to diagonalize the Hamiltonian, results in a highly efficient and scalable computational scheme for analyzing the electronic structures of ACPNRs as well as their dynamics. The total wall clock time for calculating the electronic structures of large-scale ACPNRs containing 1080-10,800 atoms is only 10-25 s per self-consistent field (SCF) iteration, with accuracy fully comparable to that obtained from conventional planewave DFT calculations. For the ACPNR system, we observe that the DGDFT methodology can scale to 5000-50,000 processors. We use DGDFT based ab initio molecular dynamics (AIMD) calculations to study the thermodynamic stability of ACPNRs. Our calculations reveal that a 2 × 1 edge reconstruction appears in ACPNRs at room temperature.

Applications of Proteomic Technologies to Toxicology

EPA Science Inventory

Proteomics is the large-scale study of gene expression at the protein level. This cutting edge technology has been extensively applied to toxicology research recently. The up-to-date development of proteomics has presented the toxicology community with an unprecedented opportunit...

Study of the Unsteady Flow Features on a Stalled Wing

NASA Technical Reports Server (NTRS)

Yon, Steven A.; Katz, Joseph

1997-01-01

The occurrence of large scale structures in the post stall flow over a rectangular wing at high angles of attack was investigated in a small-scale subsonic wind tunnel. Mean and time dependent measurements within the separated flow field suggest the existence of two distinct angle of attack regimes beyond wing stall. The shallow stall regime occurs over a narrow range of incidence angles (2-3 deg.) immediately following the inception of leading edge separation. In this regime, the principal mean flow structures, termed stall cells, are manifested as a distinct spanwise periodicity in the chordwise extent of the separated region on the model surface with possible lateral mobility not previously reported. Within the stall cells and on the wing surface, large amplitude pressure fluctuations occur with a frequency much lower than anticipated for bluff body shedding, and with minimum effect in the far wake. In the deep stall regime, stall cells are not observed and the separated region near the model is relatively free of large amplitude pressure disturbances.

Scale-free characteristics of random networks: the topology of the world-wide web

NASA Astrophysics Data System (ADS)

Barabási, Albert-László; Albert, Réka; Jeong, Hawoong

2000-06-01

The world-wide web forms a large directed graph, whose vertices are documents and edges are links pointing from one document to another. Here we demonstrate that despite its apparent random character, the topology of this graph has a number of universal scale-free characteristics. We introduce a model that leads to a scale-free network, capturing in a minimal fashion the self-organization processes governing the world-wide web.

Observational evidence for cloud cover enhancement over western European forests.

PubMed

Teuling, Adriaan J; Taylor, Christopher M; Meirink, Jan Fokke; Melsen, Lieke A; Miralles, Diego G; van Heerwaarden, Chiel C; Vautard, Robert; Stegehuis, Annemiek I; Nabuurs, Gert-Jan; de Arellano, Jordi Vilà-Guerau

2017-01-11

Forests impact regional hydrology and climate directly by regulating water and heat fluxes. Indirect effects through cloud formation and precipitation can be important in facilitating continental-scale moisture recycling but are poorly understood at regional scales. In particular, the impact of temperate forest on clouds is largely unknown. Here we provide observational evidence for a strong increase in cloud cover over large forest regions in western Europe based on analysis of 10 years of 15 min resolution data from geostationary satellites. In addition, we show that widespread windthrow by cyclone Klaus in the Landes forest led to a significant decrease in local cloud cover in subsequent years. Strong cloud development along the downwind edges of larger forest areas are consistent with a forest-breeze mesoscale circulation. Our results highlight the need to include impacts on cloud formation when evaluating the water and climate services of temperate forests, in particular around densely populated areas.

Low-speed wind-tunnel investigation of the longitudinal characteristics of a large-scale variable wing-sweep fighter model in the high-lift configuration

NASA Technical Reports Server (NTRS)

Eckert, W. T.; Maki, R. L.

1973-01-01

The low-speed characteristics of a large-scale model of the U. S. Navy/Grumman F-14A aircraft were studied in tests conducted in the Ames Research Center 40- by 80-Foot Wind Tunnel. The primary purpose of the program was the determination of lift and stability levels and landing approach attitude of the aircraft in its high-lift configuration. Tests were conducted at wing angles of attack between minus 2 deg and 30 deg with zero yaw. Data were taken at Reynolds numbers ranging from 3.48 million to 9.64 million based on a wing mean aerodynamic chord of 7.36 ft. The model configuration was changed as required to show the effects of glove slat, wing slat leading-edge radius, cold flow ducting, flap deflection, direct lift control (spoilers), horizontal tail, speed brake, landing gear and missiles.

Observational evidence for cloud cover enhancement over western European forests

PubMed Central

Teuling, Adriaan J.; Taylor, Christopher M.; Meirink, Jan Fokke; Melsen, Lieke A.; Miralles, Diego G.; van Heerwaarden, Chiel C.; Vautard, Robert; Stegehuis, Annemiek I.; Nabuurs, Gert-Jan; de Arellano, Jordi Vilà-Guerau

2017-01-01

Forests impact regional hydrology and climate directly by regulating water and heat fluxes. Indirect effects through cloud formation and precipitation can be important in facilitating continental-scale moisture recycling but are poorly understood at regional scales. In particular, the impact of temperate forest on clouds is largely unknown. Here we provide observational evidence for a strong increase in cloud cover over large forest regions in western Europe based on analysis of 10 years of 15 min resolution data from geostationary satellites. In addition, we show that widespread windthrow by cyclone Klaus in the Landes forest led to a significant decrease in local cloud cover in subsequent years. Strong cloud development along the downwind edges of larger forest areas are consistent with a forest-breeze mesoscale circulation. Our results highlight the need to include impacts on cloud formation when evaluating the water and climate services of temperate forests, in particular around densely populated areas. PMID:28074840

An investigation of rooftop STOL port aerodynamics

NASA Technical Reports Server (NTRS)

Blanton, J. N.; Parker, H. M.

1972-01-01

An investigation into aerodynamic problems associated with large building rooftop STOLports was performed. Initially, a qualitative flow visualization study indicated two essential problems: (1) the establishment of smooth, steady, attached flow over the rooftop, and (2) the generation of acceptable crosswind profile once (1) has been achieved. This study indicated that (1) could be achieved by attaching circular-arc rounded edge extensions to the upper edges of the building and that crosswind profiles could be modified by the addition of porous vertical fences to the lateral edges of the rooftop. Important fence parameters associated with crosswind alteration were found to be solidity, fence element number and spacing. Large scale building induced velocity fluctuations were discovered for most configurations tested and a possible explanation for their occurrence was postulated. Finally, a simple equation relating fence solidity to the resulting velocity profile was developed and tested for non-uniform single element fences with 30 percent maximum solidity.

Research in VLSI Systems. Heuristic Programming Project and VLSI Theory Project. A Fast Turn Around Facility for Very Large Scale Integration (VLSI)

DTIC Science & Technology

1982-11-01

to occur). When a rectangle is inserted, all currently selected items are de -selected, and the newly inserted rectangle is selected. This makes it...Items are de - * selected before the selection takes place. A selected symbol instance is displayed with a bold outline, and a selected rectangle edge...symbol instance or set of rectangle edges, everything previously selected is first de -selected. If the selected object is a reference point the old

Large discrete jumps observed in the transition between Chern states in a ferromagnetic topological insulator

PubMed Central

Liu, Minhao; Wang, Wudi; Richardella, Anthony R.; Kandala, Abhinav; Li, Jian; Yazdani, Ali; Samarth, Nitin; Ong, N. Phuan

2016-01-01

A striking prediction in topological insulators is the appearance of the quantized Hall resistance when the surface states are magnetized. The surface Dirac states become gapped everywhere on the surface, but chiral edge states remain on the edges. In an applied current, the edge states produce a quantized Hall resistance that equals the Chern number C = ±1 (in natural units), even in zero magnetic field. This quantum anomalous Hall effect was observed by Chang et al. With reversal of the magnetic field, the system is trapped in a metastable state because of magnetic anisotropy. We investigate how the system escapes the metastable state at low temperatures (10 to 200 mK). When the dissipation (measured by the longitudinal resistance) is ultralow, we find that the system escapes by making a few very rapid transitions, as detected by large jumps in the Hall and longitudinal resistances. Using the field at which the initial jump occurs to estimate the escape rate, we find that raising the temperature strongly suppresses the rate. From a detailed map of the resistance versus gate voltage and temperature, we show that dissipation strongly affects the escape rate. We compare the observations with dissipative quantum tunneling predictions. In the ultralow dissipation regime, two temperature scales (T1 ~ 70 mK and T2 ~ 145 mK) exist, between which jumps can be observed. The jumps display a spatial correlation that extends over a large fraction of the sample. PMID:27482539

Dynamic mode decomposition of separated flow over a finite blunt plate: time-resolved particle image velocimetry measurements

NASA Astrophysics Data System (ADS)

Liu, Yingzheng; Zhang, Qingshan

2015-07-01

Dynamic mode decomposition (DMD) analysis was performed on a large number of realizations of the separated flow around a finite blunt plate, which were determined by using planar time-resolved particle image velocimetry (TR-PIV). Three plates with different chord-to-thickness ratios corresponding to globally different flow patterns were particularly selected for comparison: L/D = 3.0, 6.0 and 9.0. The main attention was placed on dynamic variations in the dominant events and their interactive influences on the global fluid flow in terms of the DMD analysis. Toward this end, a real-time data transfer from the high-speed camera to the arrayed disks was built to enable continuous sampling of the spatiotemporally varying flows at the frequency of 250 Hz for a long run. The spectra of the wall-normal velocity fluctuation, the energy spectra of the DMD modes, and their spatial patterns convincingly determined the energetic unsteady events, i.e., St = 0.051 (Karman vortex street), 0.109 (harmonic event of Karman vortex street) and 0.197 (leading-edge vortex) in the shortest system L/D = 3.0, St = 0.159 (Karman vortex street) and 0.242 (leading-edge vortex) in the system L/D = 6.0, and St = 0.156 (Karman vortex street) and 0.241 (leading-edge vortex) in the longest system L/D = 9.0. In the shortest system L/D = 3.0, the first DMD mode pattern demonstrated intensified entrainment of the massive fluid above and below the whole plate by the Karman vortex street. The phase-dependent variation in the low-order flow field elucidated that this motion was sustained by the consecutive mechanisms of the convective leading-edge vortices near the upper and lower trailing edges, and the large-scale vortical structures occurring immediately behind the trailing edge, whereas the leading-edge vortices were entrained and decayed into the near wake. For the system L/D = 6.0, the closely approximated energy spectra at St = 0.159 and 0.242 indicated the balanced dominance of dual unsteady events in the measurement region. The Karman vortex street was found to induce considerable localized movement of the fluid near the trailing edges of the plate. However, the leading-edge vortices near the trailing edge were found to detach away from the plate and fully decay around 0.5 D behind the trailing edge, where a well-ordered origination of the downstream large-scale vortical structures (the Karman vortex street) was established and might be locally energized by the decayed leading-edge vortex. In the longest system L/D = 9.0, the phase-dependent variations in the low-order flow disclosed a rapid decay of the leading-edge vortices beyond the reattachment zone, reaching the fully diffused state near the trailing edges. Accordingly, no clear signature of the interaction between the Karman vortex street and the leading-edge vortex could be found in the dynamic process of the leading-edge vortex.

CHIPPING FRACTURE RESISTANCE OF DENTURE TOOTH MATERIALS

PubMed Central

Quinn, G. D.; Giuseppetti, A. A.; Hoffman, K. H.

2014-01-01

Objective The applicability of the edge chipping method to denture tooth materials was assessed. These are softer materials than those usually tested by edge chipping. The edge chipping fracture resistances of polymethylmethacrylate (PMMA) based and two filled resin composite denture tooth materials were compared. Methods An edge chipping machine was used to chip rectangular blocks and flattened anterior denture teeth. Force versus edge distance data were collected over a broad range of forces and distances. Between 20 and 65 chips were made per condition depending upon the material, the scatter, and the indenter type. Different indenter types were used including Rockwell C, sharp conical 120°, Knoop, and Vickers. The edge toughness, Te, was evaluated for different indenter types. Results The edge chipping data collected on the blocks matched the data collected from flattened teeth. High scatter, particularly at large distances and loads, meant that many tests (up to 64) were necessary to compare the denture tooth materials and to ascertain the appropriate data trends. A linear force – distance trend analysis was adequate for comparing these materials. A power law trend might be more appropriate, but the large scatter obscured the definitive determination of the precise trend. Different indenters produce different linear trends, with the ranking of: sharp conical 120°, Rockwell C, and Knoop, from lowest to highest edge toughness. Vickers indenter data were extremely scattered and a sensible trend could not be obtained. Edge toughness was inversely correlated to hardness. Significance Edge chipping data collected either from simple laboratory scale test blocks or from actual denture teeth may be used to evaluate denture materials. The edge chipping method’s applicability has been extended to another class of restorative materials. PMID:24674342

Full-scale semi-span tests of an advanced NLF business jet wing

NASA Technical Reports Server (NTRS)

Hahne, David E.; Jordan, Frank L., Jr.; Davis, Patrick J.; Muchmore, C. Byram

1987-01-01

An investigation has been conducted in the NASA Langley Research Center's 30- by 60-Foot Wind Tunnel on a full-scale semispan model to evaluate and document the low-speed, high-lift characteristics of a business-jet class wing utilizing the HSNLF(1)-0213 airfoil section and a single slotted flap system. In addition to the high-lift studies, evaluations of boundary layer transition effects, the effectiveness of a segmented leading-edge droop for improved stall/spin resistance, and roll control effectiveness with and without flap deflection were made. The wind-tunnel investigation showed that deployment of a single-slotted trailing-edge flap provided substantial increments in lift. Fixed transition studies indicated no adverse effects on lift and pitching-moment characteristics for either the cruise or landing configuration. Subscale roll damping tests also indicated that stall/spin resistance could be enhanced through the use of a properly designed leading-edge droop.

Ion Heating During Local Helicity Injection Plasma Startup in the Pegasus ST

NASA Astrophysics Data System (ADS)

Burke, M. G.; Barr, J. L.; Bongard, M. W.; Fonck, R. J.; Hinson, E. T.; Perry, J. M.; Reusch, J. A.

2015-11-01

Plasmas in the Pegasus ST are initiated either through standard, MHD stable, inductive current drive or non-solenoidal local helicity injection (LHI) current drive with strong reconnection activity, providing a rich environment to study ion dynamics. During LHI discharges, a large amount of impurity ion heating has been observed, with the passively measured impurity Ti as high as 800 eV compared to Ti ~ 60 eV and Te ~ 175 eV during standard inductive current drive discharges. In addition, non-thermal ion velocity distributions are observed and appear to be strongest near the helicity injectors. The ion heating is hypothesized to be a result of large-scale magnetic reconnection activity, as the amount of heating scales with increasing fluctuation amplitude of the dominant, edge localized, n =1 MHD mode. An approximate temporal scaling of the heating with the amplitude of higher frequency magnetic fluctuations has also been observed, with large amounts of power spectral density present at several impurity ion cyclotron frequencies. Recent experiments have focused on investigating the impurity ion heating scaling with the ion charge to mass ratio as well as the reconnecting field strength. The ion charge to mass ratio was modified by observing different impurity charge states in similar LHI plasmas while the reconnecting field strength was modified by changing the amount of injected edge current. Work supported by US DOE grant DE-FG02-96ER54375.

Superwind Outflow in Seyfert Galaxies? : Optical Observations of an Edge-On Sample

NASA Astrophysics Data System (ADS)

Colbert, E.; Gallimore, J.; Baum, S.; O'Dea, C.; Lehnert, M.

1994-12-01

Large-scale galactic winds (superwinds) are commonly found flowing out of the nuclear region of ultraluminous infrared and powerful starburst galaxies. Stellar winds and supernovae from the nuclear starburst are thought to provide the energy to drive these superwinds. The outflowing gas escapes along the rotation axis, sweeping up and shock-heating clouds in the halo, which produces optical line emission, X-rays and radio synchrotron emission. These features can most easily be studied in edge-on systems, so that the wind emission is not confused by that from the disk. Diffuse radio emission has been found (Baum et al. 1993, ApJ, 419, 553) to extend out to kpc-scales in a number of edge-on Seyfert galaxies. We have therefore launched a systematic search for superwind outflows in Seyferts. We present here narrow-band optical images and optical spectra for a sample of edge-on Seyferts. These data have been used to estimate the frequency of occurence of superwinds. Approximately half of the sample objects show evidence for extended emission-line regions which are preferentially oriented perpendicular to the galaxy disk. It is possible that these emission-line regions may be energized by a superwind outflow from a circumnuclear starburst, although there may also be a contribution from the AGN itself. A goal of this work is to find a diagnostic that can be used to distinguish between large-scale outflows that are driven by starbursts and those that are driven by an AGN. The presence of starburst-driven superwinds in Seyferts, if established, would have important implications for the connection between starburst galaxies and AGN.

Gyro-Landau-Fluid Theory and Simulations of Edge-Localized-Modes

NASA Astrophysics Data System (ADS)

Xu, X. Q.

2012-10-01

We report on the theory and simulations of edge-localized-modes (ELMs) using a gyro-Landau-fluid (GLF) extension of the BOUT++ code. Consistent with the two-fluid model (including 1st order FLR corrections), large ELMs, which are low-to-intermediate toroidal mode number (n) peeling-ballooning (P-B) modes, are suppressed by finite Larmor radius (FLR) effects as the ion temperature increases, while small ELMs (at intermediate n's) remain unstable. This result is good news for high ion temperatures in ITER due to the large stabilizing effects of FLR. Because the FLR effects are proportional to both Ti and n, the maximum growth rate is inversely proportional to Ti and the P-B mode is stabilized at high n. Nonlinear gyro-fluid simulations show results similar to those from the two-fluid model, namely that the P-B modes trigger magnetic reconnection, which drives the collapse of the pedestal pressure. Hyper-resistivity limits the radial spreading of ELMs by facilitating magnetic reconnection. The gyro-fluid ion model further limits the radial spreading of ELMs due to FLR-corrected nonlinear ExB convection of the ion gyro-center density. A gyro-fluid ETG model is being developed to self-consistently calculate the hyper-resistivity. Zonal magnetic fields arise from an ELM event and finite beta drift-wave turbulence when electron inertia effects are included. These lead to current generation and self-consistent current transport as a result of ExB convection in the generalized Ohm's law. Because edge plasmas have significant spatial inhomogeneities and complicated boundary conditions, we have developed a fast non-Fourier method for the computation of Landau-fluid closure terms based on an accurate and tunable approximation. The accuracy and the fast computational scaling of the method are demonstrated.

Effect of dynamical phase on the resonant interaction among tsunami edge wave modes

USGS Publications Warehouse

Geist, Eric L.

2018-01-01

Different modes of tsunami edge waves can interact through nonlinear resonance. During this process, edge waves that have very small initial amplitude can grow to be as large or larger than the initially dominant edge wave modes. In this study, the effects of dynamical phase are established for a single triad of edge waves that participate in resonant interactions. In previous studies, Jacobi elliptic functions were used to describe the slow variation in amplitude associated with the interaction. This analytical approach assumes that one of the edge waves in the triad has zero initial amplitude and that the combined phase of the three waves φ = θ1 + θ2 − θ3 is constant at the value for maximum energy exchange (φ = 0). To obtain a more general solution, dynamical phase effects and non-zero initial amplitudes for all three waves are incorporated using numerical methods for the governing differential equations. Results were obtained using initial conditions calculated from a subduction zone, inter-plate thrust fault geometry and a stochastic earthquake slip model. The effect of dynamical phase is most apparent when the initial amplitudes and frequencies of the three waves are within an order of magnitude. In this case, non-zero initial phase results in a marked decrease in energy exchange and a slight decrease in the period of the interaction. When there are large differences in frequency and/or initial amplitude, dynamical phase has less of an effect and typically one wave of the triad has very little energy exchange with the other two waves. Results from this study help elucidate under what conditions edge waves might be implicated in late, large-amplitude arrivals.

Effect of Dynamical Phase on the Resonant Interaction Among Tsunami Edge Wave Modes

NASA Astrophysics Data System (ADS)

Geist, Eric L.

2018-02-01

Different modes of tsunami edge waves can interact through nonlinear resonance. During this process, edge waves that have very small initial amplitude can grow to be as large or larger than the initially dominant edge wave modes. In this study, the effects of dynamical phase are established for a single triad of edge waves that participate in resonant interactions. In previous studies, Jacobi elliptic functions were used to describe the slow variation in amplitude associated with the interaction. This analytical approach assumes that one of the edge waves in the triad has zero initial amplitude and that the combined phase of the three waves φ = θ 1 + θ 2 - θ 3 is constant at the value for maximum energy exchange (φ = 0). To obtain a more general solution, dynamical phase effects and non-zero initial amplitudes for all three waves are incorporated using numerical methods for the governing differential equations. Results were obtained using initial conditions calculated from a subduction zone, inter-plate thrust fault geometry and a stochastic earthquake slip model. The effect of dynamical phase is most apparent when the initial amplitudes and frequencies of the three waves are within an order of magnitude. In this case, non-zero initial phase results in a marked decrease in energy exchange and a slight decrease in the period of the interaction. When there are large differences in frequency and/or initial amplitude, dynamical phase has less of an effect and typically one wave of the triad has very little energy exchange with the other two waves. Results from this study help elucidate under what conditions edge waves might be implicated in late, large-amplitude arrivals.

Effect of Dynamical Phase on the Resonant Interaction Among Tsunami Edge Wave Modes

NASA Astrophysics Data System (ADS)

Geist, Eric L.

2018-04-01

Different modes of tsunami edge waves can interact through nonlinear resonance. During this process, edge waves that have very small initial amplitude can grow to be as large or larger than the initially dominant edge wave modes. In this study, the effects of dynamical phase are established for a single triad of edge waves that participate in resonant interactions. In previous studies, Jacobi elliptic functions were used to describe the slow variation in amplitude associated with the interaction. This analytical approach assumes that one of the edge waves in the triad has zero initial amplitude and that the combined phase of the three waves φ = θ 1 + θ 2 - θ 3 is constant at the value for maximum energy exchange ( φ = 0). To obtain a more general solution, dynamical phase effects and non-zero initial amplitudes for all three waves are incorporated using numerical methods for the governing differential equations. Results were obtained using initial conditions calculated from a subduction zone, inter-plate thrust fault geometry and a stochastic earthquake slip model. The effect of dynamical phase is most apparent when the initial amplitudes and frequencies of the three waves are within an order of magnitude. In this case, non-zero initial phase results in a marked decrease in energy exchange and a slight decrease in the period of the interaction. When there are large differences in frequency and/or initial amplitude, dynamical phase has less of an effect and typically one wave of the triad has very little energy exchange with the other two waves. Results from this study help elucidate under what conditions edge waves might be implicated in late, large-amplitude arrivals.

Scale-invariant streamline equations and strings of singular vorticity for perturbed anisotropic solutions of the Navier-Stokes equation

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

Libin, A., E-mail: a_libin@netvision.net.il

2012-12-15

A linear combination of a pair of dual anisotropic decaying Beltrami flows with spatially constant amplitudes (the Trkal solutions) with the same eigenvalue of the curl operator and of a constant velocity orthogonal vector to the Beltrami pair yields a triplet solution of the force-free Navier-Stokes equation. The amplitudes slightly variable in space (large scale perturbations) yield the emergence of a time-dependent phase between the dual Beltrami flows and of the upward velocity, which are unstable at large values of the Reynolds number. They also lead to the formation of large-scale curved prisms of streamlines with edges being the stringsmore » of singular vorticity.« less

Improved Edge Performance in MRF

NASA Technical Reports Server (NTRS)

Shorey, Aric; Jones, Andrew; Durnas, Paul; Tricard, Marc

2004-01-01

The fabrication of large segmented optics requires a polishing process that can correct the figure of a surface to within a short distance from its edges-typically, a few millimeters. The work here is to develop QED's Magnetorheological Finishing (MRF) precision polishing process to minimize residual edge effects.

Semiclassical electron transport at the edge of a two-dimensional topological insulator: Interplay of protected and unprotected modes

NASA Astrophysics Data System (ADS)

Khalaf, E.; Skvortsov, M. A.; Ostrovsky, P. M.

2016-03-01

We study electron transport at the edge of a generic disordered two-dimensional topological insulator, where some channels are topologically protected from backscattering. Assuming the total number of channels is large, we consider the edge as a quasi-one-dimensional quantum wire and describe it in terms of a nonlinear sigma model with a topological term. Neglecting localization effects, we calculate the average distribution function of transmission probabilities as a function of the sample length. We mainly focus on the two experimentally relevant cases: a junction between two quantum Hall (QH) states with different filling factors (unitary class) and a relatively thick quantum well exhibiting quantum spin Hall (QSH) effect (symplectic class). In a QH sample, the presence of topologically protected modes leads to a strong suppression of diffusion in the other channels already at scales much shorter than the localization length. On the semiclassical level, this is accompanied by the formation of a gap in the spectrum of transmission probabilities close to unit transmission, thereby suppressing shot noise and conductance fluctuations. In the case of a QSH system, there is at most one topologically protected edge channel leading to weaker transport effects. In order to describe `topological' suppression of nearly perfect transparencies, we develop an exact mapping of the semiclassical limit of the one-dimensional sigma model onto a zero-dimensional sigma model of a different symmetry class, allowing us to identify the distribution of transmission probabilities with the average spectral density of a certain random-matrix ensemble. We extend our results to other symmetry classes with topologically protected edges in two dimensions.

Wake profile measurements of fixed and oscillating flaps

NASA Technical Reports Server (NTRS)

Owen, F. K.

1984-01-01

Although the potential of laser velocimetry for the non-intrusive measurement of complex shear flows has long been recognized, there have been few applications in other small, closely controlled laboratory situations. Measurements in large scale, high speed wind tunnels are still a complex task. To support a study of periodic flows produced by an oscillating edge flap in the Ames eleven foot wind tunnel, this study was done. The potential for laser velocimeter measurements in large scale production facilities are evaluated. The results with hot wire flow field measurements are compared.

Yukawa unification in an SO(10) SUSY GUT: SUSY on the edge

NASA Astrophysics Data System (ADS)

Poh, Zijie; Raby, Stuart

2015-07-01

In this paper we analyze Yukawa unification in a three family SO(10) SUSY GUT. We perform a global χ2 analysis and show that supersymmetry (SUSY) effects do not decouple even though the universal scalar mass parameter at the grand unified theory (GUT) scale, m16, is found to lie between 15 and 30 TeV with the best fit given for m16≈25 TeV . Note, SUSY effects do not decouple since stops and bottoms have mass of order 5 TeV, due to renormalization group running from MGUT. The model has many testable predictions. Gauginos are the lightest sparticles and the light Higgs boson is very much standard model-like. The model is consistent with flavor and C P observables with the BR (μ →e γ ) close to the experimental upper bound. With such a large value of m16 we clearly cannot be considered "natural" SUSY nor are we "split" SUSY. We are thus in the region in between or "SUSY on the edge."

Large-scale fluctuations in the cosmic ionizing background: the impact of beamed source emission

NASA Astrophysics Data System (ADS)

Suarez, Teresita; Pontzen, Andrew

2017-12-01

When modelling the ionization of gas in the intergalactic medium after reionization, it is standard practice to assume a uniform radiation background. This assumption is not always appropriate; models with radiative transfer show that large-scale ionization rate fluctuations can have an observable impact on statistics of the Lyman α forest. We extend such calculations to include beaming of sources, which has previously been neglected but which is expected to be important if quasars dominate the ionizing photon budget. Beaming has two effects: first, the physical number density of ionizing sources is enhanced relative to that directly observed; and secondly, the radiative transfer itself is altered. We calculate both effects in a hard-edged beaming model where each source has a random orientation, using an equilibrium Boltzmann hierarchy in terms of spherical harmonics. By studying the statistical properties of the resulting ionization rate and H I density fields at redshift z ∼ 2.3, we find that the two effects partially cancel each other; combined, they constitute a maximum 5 per cent correction to the power spectrum P_{H I}(k) at k = 0.04 h Mpc-1. On very large scales (k < 0.01 h Mpc-1) the source density renormalization dominates; it can reduce, by an order of magnitude, the contribution of ionizing shot noise to the intergalactic H I power spectrum. The effects of beaming should be considered when interpreting future observational data sets.

Homogenization techniques for population dynamics in strongly heterogeneous landscapes.

PubMed

Yurk, Brian P; Cobbold, Christina A

2018-12-01

An important problem in spatial ecology is to understand how population-scale patterns emerge from individual-level birth, death, and movement processes. These processes, which depend on local landscape characteristics, vary spatially and may exhibit sharp transitions through behavioural responses to habitat edges, leading to discontinuous population densities. Such systems can be modelled using reaction-diffusion equations with interface conditions that capture local behaviour at patch boundaries. In this work we develop a novel homogenization technique to approximate the large-scale dynamics of the system. We illustrate our approach, which also generalizes to multiple species, with an example of logistic growth within a periodic environment. We find that population persistence and the large-scale population carrying capacity is influenced by patch residence times that depend on patch preference, as well as movement rates in adjacent patches. The forms of the homogenized coefficients yield key theoretical insights into how large-scale dynamics arise from the small-scale features.

Recent Developments in Transition-Edge Strip Detectors for Solar X-Rays

NASA Technical Reports Server (NTRS)

Rausch, Adam J.; Deiker, Steven W.; Hilton, Gene; Irwin, Kent D.; Martinez-Galarce, Dennis S.; Shing, Lawrence; Stern, Robert A.; Ullom, Joel N.; Vale, Leila R.

2008-01-01

LMSAL and NIST are developing position-sensitive x-ray strip detectors based on Transition Edge Sensor (TES) microcalorimeters optimized for solar physics. By combining high spectral (E/ delta E approximately equals 1600) and temporal (single photon delta t approximately equals 10 micro s) resolutions with imaging capabilities, these devices will be able to study high-temperature (>l0 MK) x-ray lines as never before. Diagnostics from these lines should provide significant new insight into the physics of both microflares and the early stages of flares. Previously, the large size of traditional TESs, along with the heat loads associated with wiring large arrays, presented obstacles to using these cryogenic detectors for solar missions. Implementing strip detector technology at small scales, however, addresses both issues: here, a line of substantially smaller effective pixels requires only two TESs, decreasing both the total array size and the wiring requirements for the same spatial resolution. Early results show energy resolutions of delta E(sub fwhm) approximately equals 30 eV and spatial resolutions of approximately 10-15 micron, suggesting the strip-detector concept is viable.

Investigation of a driven fermionic system and detecting chiral edge modes in an optical lattice

NASA Astrophysics Data System (ADS)

Görg, Frederik; Messer, Michael; Jotzu, Gregor; Sandholzer, Kilian; Desbuquois, Rémi; Goldman, Nathan; Esslinger, Tilman

2017-04-01

Periodically driven systems of ultracold fermions in optical lattices allow to implement a large variety of effective Hamiltonians through Floquet engineering. An important question is whether this method can be extended to interacting systems. We investigate driven two-body systems in an array of double wells and measure the double occupancy and the spin-spin correlator in the large frequency limit and when driving resonantly to an energy scale of the underlying static Hamiltonian. We analyze whether the emerging states of the driven system can be adiabatically connected to states in the unshaken lattice. In addition, we measure the amplitude of the micromotion which describes the short time dynamics of the system and compare it directly to theory. In another context we propose a method to create topological interfaces and detect chiral edge modes in a two dimensional optical lattice. We illustrate this through an optical lattice realization of the Haldane model for cold atoms, where an additional spatially-varying lattice potential induces distinct topological phases in separated regions of space.

Tempest simulations of kinetic GAM mode and neoclassical turbulence

NASA Astrophysics Data System (ADS)

Xu, X. Q.; Dimits, A. M.

2007-11-01

TEMPEST is a nonlinear five dimensional (3d2v) gyrokinetic continuum code for studies of H-mode edge plasma neoclassical transport and turbulence in real divertor geometry. The 4D TEMPEST code correctly produces frequency, collisionless damping of GAM and zonal flow with fully nonlinear Boltzmann electrons in homogeneous plasmas. For large q=4 to 9, the Tempest simulations show that a series of resonance at higher harmonics v||=φGqR0/n with n=4 become effective. The TEMPEST simulation also shows that GAM exists in edge plasma pedestal for steep density and temperature gradients, and an initial GAM relaxes to the standard neoclassical residual with neoclassical transport, rather than Rosenbluth-Hinton residual due to the presence of ion-ion collisions. The enhanced GAM damping explains experimental BES measurements on the edge q scaling of the GAM amplitude. Our 5D gyrokinetic code is built on 4D Tempest neoclassical code with extension to a fifth dimension in toroidal direction and with 3D domain decompositions. Progress on performing 5D neoclassical turbulence simulations will be reported.

Elementary dispersion analysis of some mimetic discretizations on triangular C-grids

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

Korn, P., E-mail: peter.korn@mpimet.mpg.de; Danilov, S.; A.M. Obukhov Institute of Atmospheric Physics, Moscow

2017-02-01

Spurious modes supported by triangular C-grids limit their application for modeling large-scale atmospheric and oceanic flows. Their behavior can be modified within a mimetic approach that generalizes the scalar product underlying the triangular C-grid discretization. The mimetic approach provides a discrete continuity equation which operates on an averaged combination of normal edge velocities instead of normal edge velocities proper. An elementary analysis of the wave dispersion of the new discretization for Poincaré, Rossby and Kelvin waves shows that, although spurious Poincaré modes are preserved, their frequency tends to zero in the limit of small wavenumbers, which removes the divergence noisemore » in this limit. However, the frequencies of spurious and physical modes become close on shorter scales indicating that spurious modes can be excited unless high-frequency short-scale motions are effectively filtered in numerical codes. We argue that filtering by viscous dissipation is more efficient in the mimetic approach than in the standard C-grid discretization. Lumping of mass matrices appearing with the velocity time derivative in the mimetic discretization only slightly reduces the accuracy of the wave dispersion and can be used in practice. Thus, the mimetic approach cures some difficulties of the traditional triangular C-grid discretization but may still need appropriately tuned viscosity to filter small scales and high frequencies in solutions of full primitive equations when these are excited by nonlinear dynamics.« less

Natural vegetation cover in the landscape and edge effects: differential responses of insect orders in a fragmented forest.

PubMed

González, Ezequiel; Salvo, Adriana; Valladares, Graciela

2017-10-01

Human activities have led to global simplification of ecosystems, among which Neotropical dry forests are some of the most threatened. Habitat loss as well as edge effects may affect insect communities. Here, we analyzed insects sampled with pan traps in 9 landscapes (at 5 scales, in 100-500 m diameter circles) comprising cultivated fields and Chaco Serrano forests, at overall community and taxonomic order level. In total 7043 specimens and 456 species of hexapods were captured, with abundance and richness being directly related to forest cover at 500 m and higher at edges in comparison with forest interior. Community composition also varied with forest cover and edge/interior location. Different responses were detected among the 8 dominant orders. Collembola, Hemiptera, and Orthoptera richness and/or abundance were positively related to forest cover at the larger scale, while Thysanoptera abundance increased with forest cover only at the edge. Hymenoptera abundance and richness were negatively related to forest cover at 100 m. Coleoptera, Diptera, and Hymenoptera were more diverse and abundant at the forest edge. The generally negative influence of forest loss on insect communities could have functional consequences for both natural and cultivated systems, and highlights the relevance of forest conservation. Higher diversity at the edges could result from the simultaneous presence of forest and matrix species, although "resource mapping" might be involved for orders that were richer and more abundant at edges. Adjacent crops could benefit from forest proximity since natural enemies and pollinators are well represented in the orders showing positive edge effects. © 2016 Institute of Zoology, Chinese Academy of Sciences.

Scale-free effect of substitution networks

NASA Astrophysics Data System (ADS)

Li, Ziyu; Yu, Zhouyu; Xi, Lifeng

2018-02-01

In this paper, we construct the growing networks in terms of substitution rule. Roughly speaking, we replace edges of different colors with different initial graphs. Then the evolving networks are constructed. We obtained the free-scale effect of our substitution networks.

Many-Body Localization and Quantum Nonergodicity in a Model with a Single-Particle Mobility Edge.

PubMed

Li, Xiaopeng; Ganeshan, Sriram; Pixley, J H; Das Sarma, S

2015-10-30

We investigate many-body localization in the presence of a single-particle mobility edge. By considering an interacting deterministic model with an incommensurate potential in one dimension we find that the single-particle mobility edge in the noninteracting system leads to a many-body mobility edge in the corresponding interacting system for certain parameter regimes. Using exact diagonalization, we probe the mobility edge via energy resolved entanglement entropy (EE) and study the energy resolved applicability (or failure) of the eigenstate thermalization hypothesis (ETH). Our numerical results indicate that the transition separating area and volume law scaling of the EE does not coincide with the nonthermal to thermal transition. Consequently, there exists an extended nonergodic phase for an intermediate energy window where the many-body eigenstates violate the ETH while manifesting volume law EE scaling. We also establish that the model possesses an infinite temperature many-body localization transition despite the existence of a single-particle mobility edge. We propose a practical scheme to test our predictions in atomic optical lattice experiments which can directly probe the effects of the mobility edge.

Diffraction-based analysis of tunnel size for a scaled external occulter testbed

NASA Astrophysics Data System (ADS)

Sirbu, Dan; Kasdin, N. Jeremy; Vanderbei, Robert J.

2016-07-01

For performance verification of an external occulter mask (also called a starshade), scaled testbeds have been developed to measure the suppression of the occulter shadow in the pupil plane and contrast in the image plane. For occulter experiments the scaling is typically performed by maintaining an equivalent Fresnel number. The original Princeton occulter testbed was oversized with respect to both input beam and shadow propagation to limit any diffraction effects due to finite testbed enclosure edges; however, to operate at realistic space-mission equivalent Fresnel numbers an extended testbed is currently under construction. With the longer propagation distances involved, diffraction effects due to the edge of the tunnel must now be considered in the experiment design. Here, we present a diffraction-based model of two separate tunnel effects. First, we consider the effect of tunnel-edge induced diffraction ringing upstream from the occulter mask. Second, we consider the diffraction effect due to clipping of the output shadow by the tunnel downstream from the occulter mask. These calculations are performed for a representative point design relevant to the new Princeton occulter experiment, but we also present an analytical relation that can be used for other propagation distances.

Entanglement convertibility by sweeping through the quantum phases of the alternating bonds XXZ chain

PubMed Central

Tzeng, Yu-Chin; Dai, Li; Chung, Ming-Chiang; Amico, Luigi; Kwek, Leong-Chuan

2016-01-01

We study the entanglement structure and the topological edge states of the ground state of the spin-1/2 XXZ model with bond alternation. We employ parity-density matrix renormalization group with periodic boundary conditions. The finite-size scaling of Rényi entropies S2 and S∞ are used to construct the phase diagram of the system. The phase diagram displays three possible phases: Haldane type (an example of symmetry protected topological ordered phases), Classical Dimer and Néel phases, the latter bounded by two continuous quantum phase transitions. The entanglement and non-locality in the ground state are studied and quantified by the entanglement convertibility. We found that, at small spatial scales, the ground state is not convertible within the topological Haldane dimer phase. The phenomenology we observe can be described in terms of correlations between edge states. We found that the entanglement spectrum also exhibits a distinctive response in the topological phase: the effective rank of the reduced density matrix displays a specifically large “susceptibility” in the topological phase. These findings support the idea that although the topological order in the ground state cannot be detected by local inspection, the ground state response at local scale can tell the topological phases apart from the non-topological phases. PMID:27216970

Entanglement convertibility by sweeping through the quantum phases of the alternating bonds XXZ chain.

PubMed

Tzeng, Yu-Chin; Dai, Li; Chung, Ming-Chiang; Amico, Luigi; Kwek, Leong-Chuan

2016-05-24

We study the entanglement structure and the topological edge states of the ground state of the spin-1/2 XXZ model with bond alternation. We employ parity-density matrix renormalization group with periodic boundary conditions. The finite-size scaling of Rényi entropies S2 and S∞ are used to construct the phase diagram of the system. The phase diagram displays three possible phases: Haldane type (an example of symmetry protected topological ordered phases), Classical Dimer and Néel phases, the latter bounded by two continuous quantum phase transitions. The entanglement and non-locality in the ground state are studied and quantified by the entanglement convertibility. We found that, at small spatial scales, the ground state is not convertible within the topological Haldane dimer phase. The phenomenology we observe can be described in terms of correlations between edge states. We found that the entanglement spectrum also exhibits a distinctive response in the topological phase: the effective rank of the reduced density matrix displays a specifically large "susceptibility" in the topological phase. These findings support the idea that although the topological order in the ground state cannot be detected by local inspection, the ground state response at local scale can tell the topological phases apart from the non-topological phases.

Edge type affects leaf-level water relations and estimated transpiration of Eucalyptus arenacea.

PubMed

Wright, Thomas E; Tausz, Michael; Kasel, Sabine; Volkova, Liubov; Merchant, Andrew; Bennett, Lauren T

2012-03-01

While edge effects on tree water relations are well described for closed forests, they remain under-examined in more open forest types. Similarly, there has been minimal evaluation of the effects of contrasting land uses on the water relations of open forest types in highly fragmented landscapes. We examined edge effects on the water relations and gas exchange of a dominant tree (Eucalyptus arenacea Marginson & Ladiges) in an open forest type (temperate woodland) of south-eastern Australia. Edge effects in replicate woodlands adjoined by cleared agricultural land (pasture edges) were compared with those adjoined by 7- to 9-year-old eucalypt plantation with a 25m fire break (plantation edges). Consistent with studies in closed forest types, edge effects were pronounced at pasture edges where photosynthesis, transpiration and stomatal conductance were greater for edge trees than interior trees (75m into woodlands), and were related to greater light availability and significantly higher branch water potentials at woodland edges than interiors. Nonetheless, gas exchange values were only ∼50% greater for edge than interior trees, compared with ∼200% previously found in closed forest types. In contrast to woodlands adjoined by pasture, gas exchange in winter was significantly lower for edge than interior trees in woodlands adjoined by plantations, consistent with shading and buffering effects of plantations on edge microclimate. Plantation edge effects were less pronounced in summer, although higher water use efficiency of edge than interior woodland trees indicated possible competition for water between plantation trees and woodland edge trees in the drier months (an effect that might have been more pronounced were there no firebreak between the two land uses). Scaling up of leaf-level water relations to stand transpiration using a Jarvis-type phenomenological model indicated similar differences between edge types. That is, transpiration was greater at pasture than plantation edges in summer months (most likely due to greater water availability at pasture edges), resulting in significantly greater estimates of annual transpiration at pasture than plantation edges (430 vs. 343lm(-2)year(-1), respectively). Our study highlights the need for landscape-level water flux models to account for edge effects on stand transpiration, particularly in highly fragmented landscapes.

Impact of Periodic Unsteadiness on Performance and Heat Load in Axial Flow Turbomachines

NASA Technical Reports Server (NTRS)

Sharma, Om P.; Stetson, Gary M.; Daniels, William A,; Greitzer, Edward M.; Blair, Michael F.; Dring, Robert P.

1997-01-01

Results of an analytical and experimental investigation, directed at the understanding of the impact of periodic unsteadiness on the time-averaged flows in axial flow turbomachines, are presented. Analysis of available experimental data, from a large-scale rotating rig (LSRR) (low speed rig), shows that in the time-averaged axisymmetric equations the magnitude of the terms representing the effect of periodic unsteadiness (deterministic stresses) are as large or larger than those due to random unsteadiness (turbulence). Numerical experiments, conducted to highlight physical mechanisms associated with the migration of combustor generated hot-streaks in turbine rotors, indicated that the effect can be simulated by accounting for deterministic stress like terms in the time-averaged mass and energy conservation equations. The experimental portion of this program shows that the aerodynamic loss for the second stator in a 1-1/2 stage turbine are influenced by the axial spacing between the second stator leading edge and the rotor trailing edge. However, the axial spacing has little impact on the heat transfer coefficient. These performance changes are believed to be associated with the change in deterministic stress at the inlet to the second stator. Data were also acquired to quantify the impact of indexing the first stator relative to the second stator. For the range of parameters examined, this effect was found to be of the same order as the effect of axial spacing.

Potential negative ecological effects of corridors.

PubMed

Haddad, Nick M; Brudvig, Lars A; Damschen, Ellen I; Evans, Daniel M; Johnson, Brenda L; Levey, Douglas J; Orrock, John L; Resasco, Julian; Sullivan, Lauren L; Tewksbury, Josh J; Wagner, Stephanie A; Weldon, Aimee J

2014-10-01

Despite many studies showing that landscape corridors increase dispersal and species richness for disparate taxa, concerns persist that corridors can have unintended negative effects. In particular, some of the same mechanisms that underlie positive effects of corridors on species of conservation interest may also increase the spread and impact of antagonistic species (e.g., predators and pathogens), foster negative effects of edges, increase invasion by exotic species, increase the spread of unwanted disturbances such as fire, or increase population synchrony and thus reduce persistence. We conducted a literature review and meta-analysis to evaluate the prevalence of each of these negative effects. We found no evidence that corridors increase unwanted disturbance or non-native species invasion; however, these have not been well-studied concerns (1 and 6 studies, respectively). Other effects of corridors were more often studied and yielded inconsistent results; mean effect sizes were indistinguishable from zero. The effect of edges on abundances of target species was as likely to be positive as negative. Corridors were as likely to have no effect on antagonists or population synchrony as they were to increase those negative effects. We found 3 deficiencies in the literature. First, despite studies on how corridors affect predators, there are few studies of related consequences for prey population size and persistence. Second, properly designed studies of negative corridor effects are needed in natural corridors at scales larger than those achievable in experimental systems. Third, studies are needed to test more targeted hypotheses about when corridor-mediated effects on invasive species or disturbance may be negative for species of management concern. Overall, we found no overarching support for concerns that construction and maintenance of habitat corridors may result in unintended negative consequences. Negative edge effects may be mitigated by widening corridors or softening edges between corridors and the matrix. Other negative effects are relatively small and manageable compared with the large positive effects of facilitating dispersal and increasing diversity of native species. © 2014 Society for Conservation Biology.

Study on installation of the submersible mixer

NASA Astrophysics Data System (ADS)

Tian, F.; Shi, W. D.; He, X. H.; Jiang, H.; Xu, Y. H.

2013-12-01

Study on installation of the submersible mixer for sewage treatment has been limited. In this article, large-scale computational fluid dynamics software FLUENT6.3 was adopted. ICEM software was used to build an unstructured grid of sewage treatment pool. After that, the sewage treatment pool was numerically simulated by dynamic coordinate system technology and RNG k-ε turbulent model and PIOS algorithm. Agitation pools on four different installation location cases were simulated respectively, and the external characteristic of the submersible mixer and the velocity cloud of the axial section were respectively comparatively analyzed. The best stirring effect can be reached by the installation location of case C, which is near the bottom of the pool 600 mm and blade distance the bottom at least for 200 mm wide and wide edge and narrow edge distance by 4:3. The conclusion can guide the engineering practice.

DNA molecules on periodically microstructured lipid membranes: Localization and coil stretching

NASA Astrophysics Data System (ADS)

Hochrein, Marion B.; Leierseder, Judith A.; Golubović, Leonardo; Rädler, Joachim O.

2007-02-01

We explore large scale conformations of DNA molecules adsorbed on curved surfaces. For that purpose, we investigate the behavior of DNA adsorbed on periodically shaped cationic lipid membranes. These unique membrane morphologies are supported on grooved, one-dimensionally periodic microstructured surfaces. Strikingly, we find that these periodically structured membranes are capable to stretch DNA coils. We elucidate this phenomenon in terms of surface curvature dependent potential energy attained by the adsorbed DNA molecules. Due to it, DNA molecules undergo a localization transition causing them to stretch by binding to highly curved sections (edges) of the supported membranes. This effect provides a new venue for controlling conformations of semiflexible polymers such as DNA by employing their interactions with specially designed biocompatible surfaces. We report the first experimental observation of semiflexible polymers unbinding transition in which DNA molecules unbind from one-dimensional manifolds (edges) while remaining bound to two-dimensional manifolds (cationic membranes).

Flexible sampling large-scale social networks by self-adjustable random walk

NASA Astrophysics Data System (ADS)

Xu, Xiao-Ke; Zhu, Jonathan J. H.

2016-12-01

Online social networks (OSNs) have become an increasingly attractive gold mine for academic and commercial researchers. However, research on OSNs faces a number of difficult challenges. One bottleneck lies in the massive quantity and often unavailability of OSN population data. Sampling perhaps becomes the only feasible solution to the problems. How to draw samples that can represent the underlying OSNs has remained a formidable task because of a number of conceptual and methodological reasons. Especially, most of the empirically-driven studies on network sampling are confined to simulated data or sub-graph data, which are fundamentally different from real and complete-graph OSNs. In the current study, we propose a flexible sampling method, called Self-Adjustable Random Walk (SARW), and test it against with the population data of a real large-scale OSN. We evaluate the strengths of the sampling method in comparison with four prevailing methods, including uniform, breadth-first search (BFS), random walk (RW), and revised RW (i.e., MHRW) sampling. We try to mix both induced-edge and external-edge information of sampled nodes together in the same sampling process. Our results show that the SARW sampling method has been able to generate unbiased samples of OSNs with maximal precision and minimal cost. The study is helpful for the practice of OSN research by providing a highly needed sampling tools, for the methodological development of large-scale network sampling by comparative evaluations of existing sampling methods, and for the theoretical understanding of human networks by highlighting discrepancies and contradictions between existing knowledge/assumptions of large-scale real OSN data.

Large-scale 3D modeling of projectile impact damage in brittle plates

NASA Astrophysics Data System (ADS)

Seagraves, A.; Radovitzky, R.

2015-10-01

The damage and failure of brittle plates subjected to projectile impact is investigated through large-scale three-dimensional simulation using the DG/CZM approach introduced by Radovitzky et al. [Comput. Methods Appl. Mech. Eng. 2011; 200(1-4), 326-344]. Two standard experimental setups are considered: first, we simulate edge-on impact experiments on Al2O3 tiles by Strassburger and Senf [Technical Report ARL-CR-214, Army Research Laboratory, 1995]. Qualitative and quantitative validation of the simulation results is pursued by direct comparison of simulations with experiments at different loading rates and good agreement is obtained. In the second example considered, we investigate the fracture patterns in normal impact of spheres on thin, unconfined ceramic plates over a wide range of loading rates. For both the edge-on and normal impact configurations, the full field description provided by the simulations is used to interpret the mechanisms underlying the crack propagation patterns and their strong dependence on loading rate.

The Atacama B-Mode Search: CMB Polarimetry with Transition-Edge-Sensor Bolometers

NASA Astrophysics Data System (ADS)

Essinger-Hileman, T.; Appel, J. W.; Beal, J. A.; Cho, H. M.; Fowler, J.; Halpern, M.; Hasselfield, M.; Irwin, K. D.; Marriage, T. A.; Niemack, M. D.; Page, L.; Parker, L. P.; Pufu, S.; Staggs, S. T.; Stryzak, O.; Visnjic, C.; Yoon, K. W.; Zhao, Y.

2009-12-01

The Atacama B-mode Search (ABS) experiment is a 145 GHz polarimeter designed to measure the B-mode polarization of the Cosmic Microwave Background (CMB) at large angular scales. The ABS instrument will ship to the Atacama Desert of Chile fully tested and ready to observe in 2010. ABS will image large-angular-scale CMB polarization anisotropies onto a focal plane of 240 feedhorn-coupled, transition-edge sensor (TES) polarimeters, using a cryogenic crossed-Dragone design. The ABS detectors, which are fabricated at NIST, use orthomode transducers to couple orthogonal polarizations of incoming radiation onto separate TES bolometers. The incoming radiation is modulated by an ambient-temperature half-wave plate in front of the vacuum window at an aperture stop. Preliminary detector characterization indicates that the ABS detectors can achieve a sensitivity of 300 μK√s in the field. This paper describes the ABS optical design and detector readout scheme, including feedhorn design and performance, magnetic shielding, focal plane architecture, and cryogenic electronics.

Landscape heterogeneity reduces coyote predation on white-tailed deer fawns

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

Gulsby, William D.; Kilgo, John C.; Vukovich, Mark

Coyote (Canis latrans) predation on white-tailed deer (Odocoileus virginianus) fawns in southeastern North America has led to deer population declines in some areas. Research or management efforts initiated in response to coyote predation on fawns have primarily focused on implementation of reduced antlerless deer harvest or coyote control to mitigate population declines. Vegetation characteristics may influence coyote hunting efficiency, but the potential influence of land cover at large scales in the southeastern United States is underexplored. We investigated whether mortality risk was affected by landscape characteristics within fawn home ranges for a sample of 165 fawns on the United Statesmore » Department of Energy’s Savannah River Site (SRS), South Carolina, 2007–2012. We monitored fawns every 8 hours to ≥ 4 weeks of age and 1–3 times daily to 12 weeks of age. We included only surviving or coyote-predated fawns in the dataset. The most supported model describing hazard ratios included the length of edge (i.e., area where 2 land cover types joined) in fawn home ranges. Probability of coyote predation increased 1.26 times for each 968-m decrease in edge within a fawn’s simulated home range (29.1-ha circular buffer) under this model. Further, fawns with the least edge in their home ranges were >2 times more likely to be depredated by a coyote than fawns with the greatest edge availability. Support for other models was relatively low, but informative variables (e.g., mean patch fractal dimension, Shannon’s diversity index, mean forest patch size) supported a general trend that as fawn home ranges became more homogeneous and contained larger patches with less edge and fewer cover types, predation risk increased. These findings are consistent with similar work in the midwestern United States, despite landscape differences between regions. The combined weight of evidence suggests maintenance of a heterogeneous landscape consisting of relatively small dispersed patches may reduce fawn losses to coyotes. In conclusion, this information may also be used to identify areas susceptible to greater fawn predation rates across large spatial scales. However, the relatively long forestry rotation lengths and large scale of consistent forest management on the SRS are uncommon in the southeastern United States and the mechanism for the pattern we observed is unclear. Therefore, our results may not be applicable to sites with different forest management practices.« less

Landscape heterogeneity reduces coyote predation on white-tailed deer fawns

DOE PAGES

Gulsby, William D.; Kilgo, John C.; Vukovich, Mark; ...

2017-03-07

Coyote (Canis latrans) predation on white-tailed deer (Odocoileus virginianus) fawns in southeastern North America has led to deer population declines in some areas. Research or management efforts initiated in response to coyote predation on fawns have primarily focused on implementation of reduced antlerless deer harvest or coyote control to mitigate population declines. Vegetation characteristics may influence coyote hunting efficiency, but the potential influence of land cover at large scales in the southeastern United States is underexplored. We investigated whether mortality risk was affected by landscape characteristics within fawn home ranges for a sample of 165 fawns on the United Statesmore » Department of Energy’s Savannah River Site (SRS), South Carolina, 2007–2012. We monitored fawns every 8 hours to ≥ 4 weeks of age and 1–3 times daily to 12 weeks of age. We included only surviving or coyote-predated fawns in the dataset. The most supported model describing hazard ratios included the length of edge (i.e., area where 2 land cover types joined) in fawn home ranges. Probability of coyote predation increased 1.26 times for each 968-m decrease in edge within a fawn’s simulated home range (29.1-ha circular buffer) under this model. Further, fawns with the least edge in their home ranges were >2 times more likely to be depredated by a coyote than fawns with the greatest edge availability. Support for other models was relatively low, but informative variables (e.g., mean patch fractal dimension, Shannon’s diversity index, mean forest patch size) supported a general trend that as fawn home ranges became more homogeneous and contained larger patches with less edge and fewer cover types, predation risk increased. These findings are consistent with similar work in the midwestern United States, despite landscape differences between regions. The combined weight of evidence suggests maintenance of a heterogeneous landscape consisting of relatively small dispersed patches may reduce fawn losses to coyotes. In conclusion, this information may also be used to identify areas susceptible to greater fawn predation rates across large spatial scales. However, the relatively long forestry rotation lengths and large scale of consistent forest management on the SRS are uncommon in the southeastern United States and the mechanism for the pattern we observed is unclear. Therefore, our results may not be applicable to sites with different forest management practices.« less

Application of Approximate Pattern Matching in Two Dimensional Spaces to Grid Layout for Biochemical Network Maps

PubMed Central

Inoue, Kentaro; Shimozono, Shinichi; Yoshida, Hideaki; Kurata, Hiroyuki

2012-01-01

Background For visualizing large-scale biochemical network maps, it is important to calculate the coordinates of molecular nodes quickly and to enhance the understanding or traceability of them. The grid layout is effective in drawing compact, orderly, balanced network maps with node label spaces, but existing grid layout algorithms often require a high computational cost because they have to consider complicated positional constraints through the entire optimization process. Results We propose a hybrid grid layout algorithm that consists of a non-grid, fast layout (preprocessor) algorithm and an approximate pattern matching algorithm that distributes the resultant preprocessed nodes on square grid points. To demonstrate the feasibility of the hybrid layout algorithm, it is characterized in terms of the calculation time, numbers of edge-edge and node-edge crossings, relative edge lengths, and F-measures. The proposed algorithm achieves outstanding performances compared with other existing grid layouts. Conclusions Use of an approximate pattern matching algorithm quickly redistributes the laid-out nodes by fast, non-grid algorithms on the square grid points, while preserving the topological relationships among the nodes. The proposed algorithm is a novel use of the pattern matching, thereby providing a breakthrough for grid layout. This application program can be freely downloaded from http://www.cadlive.jp/hybridlayout/hybridlayout.html. PMID:22679486

KRISTINA: Kinematic rib-based structural system for innovative adaptive trailing edge

NASA Astrophysics Data System (ADS)

Pecora, R.; Amoroso, F.; Magnifico, M.; Dimino, I.; Concilio, A.

2016-04-01

Nature teaches that the flight of the birds succeeds perfectly since they are able to change the shape of their wings in a continuous manner. The careful observation of this phenomenon has re-introduced in the recent research topics the study of "metamorphic" wing structures; these innovative architectures allow for the controlled wing shape adaptation to different flight conditions with the ultimate goal of getting desirable improvements such as the increase of aerodynamic efficiency or load control effectiveness. In this framework, the European research project SARISTU aimed at combining morphing and smart ideas to the leading edge, the trailing edge and the winglet of a large commercial airplane (EASA CS25 category) while assessing integrated technologies validation through high-speed wind tunnel test on a true scale outer wing segment. The design process of the adaptive trailing edge (ATED) addressed by SARISTU is here outlined, from the conceptual definition of the camber-morphing architecture up to the assessment of the device executive layout. Rational design criteria were implemented in order to preliminarily define ATED structural layout and the general configuration of the embedded mechanisms enabling morphing under the action of aerodynamic loads. Advanced FE analyses were then carried out and the robustness of adopted structural arrangements was proven in compliance with applicable airworthiness requirements.

Application of approximate pattern matching in two dimensional spaces to grid layout for biochemical network maps.

PubMed

Inoue, Kentaro; Shimozono, Shinichi; Yoshida, Hideaki; Kurata, Hiroyuki

2012-01-01

For visualizing large-scale biochemical network maps, it is important to calculate the coordinates of molecular nodes quickly and to enhance the understanding or traceability of them. The grid layout is effective in drawing compact, orderly, balanced network maps with node label spaces, but existing grid layout algorithms often require a high computational cost because they have to consider complicated positional constraints through the entire optimization process. We propose a hybrid grid layout algorithm that consists of a non-grid, fast layout (preprocessor) algorithm and an approximate pattern matching algorithm that distributes the resultant preprocessed nodes on square grid points. To demonstrate the feasibility of the hybrid layout algorithm, it is characterized in terms of the calculation time, numbers of edge-edge and node-edge crossings, relative edge lengths, and F-measures. The proposed algorithm achieves outstanding performances compared with other existing grid layouts. Use of an approximate pattern matching algorithm quickly redistributes the laid-out nodes by fast, non-grid algorithms on the square grid points, while preserving the topological relationships among the nodes. The proposed algorithm is a novel use of the pattern matching, thereby providing a breakthrough for grid layout. This application program can be freely downloaded from http://www.cadlive.jp/hybridlayout/hybridlayout.html.

A first large-scale flood inundation forecasting model

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

Schumann, Guy J-P; Neal, Jeffrey C.; Voisin, Nathalie

2013-11-04

At present continental to global scale flood forecasting focusses on predicting at a point discharge, with little attention to the detail and accuracy of local scale inundation predictions. Yet, inundation is actually the variable of interest and all flood impacts are inherently local in nature. This paper proposes a first large scale flood inundation ensemble forecasting model that uses best available data and modeling approaches in data scarce areas and at continental scales. The model was built for the Lower Zambezi River in southeast Africa to demonstrate current flood inundation forecasting capabilities in large data-scarce regions. The inundation model domainmore » has a surface area of approximately 170k km2. ECMWF meteorological data were used to force the VIC (Variable Infiltration Capacity) macro-scale hydrological model which simulated and routed daily flows to the input boundary locations of the 2-D hydrodynamic model. Efficient hydrodynamic modeling over large areas still requires model grid resolutions that are typically larger than the width of many river channels that play a key a role in flood wave propagation. We therefore employed a novel sub-grid channel scheme to describe the river network in detail whilst at the same time representing the floodplain at an appropriate and efficient scale. The modeling system was first calibrated using water levels on the main channel from the ICESat (Ice, Cloud, and land Elevation Satellite) laser altimeter and then applied to predict the February 2007 Mozambique floods. Model evaluation showed that simulated flood edge cells were within a distance of about 1 km (one model resolution) compared to an observed flood edge of the event. Our study highlights that physically plausible parameter values and satisfactory performance can be achieved at spatial scales ranging from tens to several hundreds of thousands of km2 and at model grid resolutions up to several km2. However, initial model test runs in forecast mode revealed that it is crucial to account for basin-wide hydrological response time when assessing lead time performances notwithstanding structural limitations in the hydrological model and possibly large inaccuracies in precipitation data.« less

The effect of butterfly scales on flight efficiency and leading edge vortex formation

NASA Astrophysics Data System (ADS)

Lang, Amy; Wilroy, Jacob; Wahidi, Redha; Slegers, Nathan; Heilman, Micahel; Cranford, Jacob

2016-11-01

It is hypothesized that the scales on a butterfly wing lead to increased flight efficiency. Recent testing of live butterflies tracked their motion over 246 flights for 11 different specimens. Results show a 37.8 percent mean decrease in flight efficiency and a flapping amplitude reduction of 6.7 percent once the scales were removed. This change could be largely a result of how the leading edge vortex (LEV) interacts with the wing. To simplify this complex flow problem, an experiment was designed to focus on the alteration of 2-D vortex development with a variation in surface patterning. Specifically, the secondary vorticity generated by the LEV interacting at the patterned surface was studied, as well as the subsequent effect on the LEV's growth rate and peak circulation. For this experiment butterfly inspired grooves were created using additive manufacturing and were attached to a flat plate with a chordwise orientation, thus increasing plate surface area. The vortex generated by the grooved plate was then compared to a smooth case as the plate translated vertically through a tow tank at Re = 1500, 3000, and 6000. Using DPIV, the vortex formation was documented and a maximum vortex formation time of 4.22 was found based on the flat plate travel distance and chord length. Results indicate that the patterned surface slows down the growth of the vortex which corroborates the flight test results. Funding from NSF CBET Fluid Dynamcis is gratefully acknowledged.

Primary control of a Mach scale swashplateless rotor using brushless DC motor actuated trailing edge flaps

NASA Astrophysics Data System (ADS)

Saxena, Anand

The focus of this research was to demonstrate a four blade rotor trim in forward flight using integrated trailing edge flaps instead of using a swashplate controls. A compact brushless DC motor was evaluated as an on-blade actuator, with the possibility of achieving large trailing edge flap amplitudes. A control strategy to actuate the trailing edge flap at desired frequency and amplitude was developed and large trailing edge flap amplitudes from the motor (instead of rotational motion) were obtained. Once the actuator was tested on the bench-top, a lightweight mechanism was designed to incorporate the motor in the blade and actuate the trailing edge flaps. A six feet diameter, four bladed composite rotor with motor-flap system integrated into the NACA 0012 airfoil section was fabricated. Systematic testing was carried out for a range of load conditions, first in the vacuum chamber followed by hover tests. Large trailing edge flap deflections were observed during the hover testing, and a peak to peak trailing edge flap amplitude of 18 degree was achieved at 2000 rotor RPM with hover tip Mach number of 0.628. A closed loop controller was designed to demonstrate trailing edge flap mean position and the peak to peak amplitude control. Further, a soft pitch link was designed and fabricated, to replace the stiff pitch link and thereby reduce the torsional stiffness of the blade to 2/rev. This soft pitch link allowed for blade root pitch motion in response to the trailing edge flap inputs. Blade pitch response due to both steady as well as sinusoidal flap deflections were demonstrated. Finally, tests were performed in Glenn L. Martin wind tunnel using a model rotor rig to assess the performance of motor-flap system in forward flight. A swashplateless trim using brushless DC motor actuated trailing edge flaps was achieved for a rotor operating at 1200 RPM and an advance ratio of 0.28. Also, preliminary exploration was carried out to test the scalability of the motor driven trailing edge flap concept. In conclusion, the concept of using brushless DC motors as on-blade actuators, actuating trailing edge flaps has the potential to replace the current mechanically complex swashplate with a hydraulic-free swashplateless system and thereby reduce overall weight and hub drag.

Turbulent Structures in a Pine Forest with a Deep and Sparse Trunk Space: Stand and Edge Regions

NASA Astrophysics Data System (ADS)

Dupont, Sylvain; Irvine, Mark R.; Bonnefond, Jean-Marc; Lamaud, Eric; Brunet, Yves

2012-05-01

Forested landscapes often exhibit large spatial variability in vertical and horizontal foliage distributions. This variability may affect canopy-atmosphere exchanges through its action on the development of turbulent structures. Here we investigate in neutral stratification the turbulent structures encountered in a maritime pine forest characterized by a high, dense foliated layer associated with a deep and sparse trunk space. Both stand and edge regions are considered. In situ measurements and the results of large-eddy simulations are used and analyzed together. In stand conditions, far from the edge, canopy-top structures appear strongly damped by the dense crown layer. Turbulent wind fluctuations within the trunk space, where the momentum flux vanishes, are closely related to these canopy-top structures through pressure diffusion. Consequently, autocorrelation and spectral analyses are not quite appropriate to characterize the vertical scale of coherent structures in this type of canopy, as pressure diffusion enhances the actual scale of structures. At frequencies higher than those associated with canopy-top structures, wind fluctuations related to wake structures developing behind tree stems are observed within the trunk space. They manifest themselves in wind velocity spectra as secondary peaks in the inertial subrange region, confirming the hypothesis of spectral short-cuts in vegetation canopies. In the edge region specific turbulent structures develop just below the crown layer, in addition to canopy-top structures. They are generated by the wind shear induced by the sub-canopy wind jet that forms at the edge. These structures provide a momentum exchange mechanism similar to that observed at the canopy top but in the opposite direction and with a lower magnitude. They may develop as in plane mixing-layer flows, with some perturbations induced by canopy-top structures. Wake structures are also observed within the trunk space in the edge region.

Dynamics of edge currents in a linearly quenched Haldane model

NASA Astrophysics Data System (ADS)

Mardanya, Sougata; Bhattacharya, Utso; Agarwal, Amit; Dutta, Amit

2018-03-01

In a finite-time quantum quench of the Haldane model, the Chern number determining the topology of the bulk remains invariant, as long as the dynamics is unitary. Nonetheless, the corresponding boundary attribute, the edge current, displays interesting dynamics. For the case of sudden and adiabatic quenches the postquench edge current is solely determined by the initial and the final Hamiltonians, respectively. However for a finite-time (τ ) linear quench in a Haldane nanoribbon, we show that the evolution of the edge current from the sudden to the adiabatic limit is not monotonic in τ and has a turning point at a characteristic time scale τ =τ0 . For small τ , the excited states lead to a huge unidirectional surge in the edge current of both edges. On the other hand, in the limit of large τ , the edge current saturates to its expected equilibrium ground-state value. This competition between the two limits lead to the observed nonmonotonic behavior. Interestingly, τ0 seems to depend only on the Semenoff mass and the Haldane flux. A similar dynamics for the edge current is also expected in other systems with topological phases.

A continental scale trophic cascade from wolves through coyotes to foxes.

PubMed

Newsome, Thomas M; Ripple, William J

2015-01-01

Top-down processes, via the direct and indirect effects of interspecific competitive killing (no consumption of the kill) or intraguild predation (consumption of the kill), can potentially influence the spatial distribution of terrestrial predators, but few studies have demonstrated the phenomenon at a continental scale. For example, in North America, grey wolves Canis lupus are known to kill coyotes Canis latrans, and coyotes, in turn, may kill foxes Vulpes spp., but the spatial effects of these competitive interactions at large scales are unknown. Here, we analyse fur return data across eight jurisdictions in North America to test whether the presence or absence of wolves has caused a continent-wide shift in coyote and red fox Vulpes vulpes density. Our results support the existence of a continental scale cascade whereby coyotes outnumber red foxes in areas where wolves have been extirpated by humans, whereas red foxes outnumber coyotes in areas where wolves are present. However, for a distance of up to 200 km on the edge of wolf distribution, there is a transition zone where the effects of top-down control are weakened, possibly due to the rapid dispersal and reinvasion capabilities of coyotes into areas where wolves are sporadically distributed or at low densities. Our results have implications for understanding how the restoration of wolf populations across North America could potentially affect co-occurring predators and prey. We conclude that large carnivores may need to occupy large continuous areas to facilitate among-carnivore cascades and that studies of small areas may not be indicative of the effects of top-down mesopredator control. © 2014 The Authors. Journal of Animal Ecology © 2014 British Ecological Society.

Detailed film cooling effectiveness and three component velocity field measurements on a first stage turbine vane subject to high freestream turbulence

NASA Astrophysics Data System (ADS)

Polanka, Marcus Damian

1999-11-01

This experimental program studied the effects of high freestream turbulence on film cooling for a turbine vane. This investigation focussed on the showerhead and pressure surface of an airfoil. An emphasis of this study was to acquire highly detailed film cooling effectiveness and velocity measurements in the showerhead region. Acquisition of both pieces of information resulted in detailed knowledge of the physics involved in the interaction of the coolant jets and the freestream flow in this region of an airfoil. By generating a 18% turbulence level at the leading edge of the airfoil, the impact of elevated freestream turbulence was also studied. Of further interest was the affect of a highly turbulent flow resulting from both the freestream flow as well as that generated from the showerhead jets themselves, further downstream. The impact of this turbulent approach flow will have significant consequence on downstream film cooling designs. In order to achieve the desired goals, modification to the existing closed loop wind tunnel facility was required. The new tunnel consisted of a test section containing a center, instrumented airfoil with inner and outer walls positioned to match the flow parameters around the center airfoil. The center airfoil was built at a nine times scale ratio. In utilizing this large scale vane and still matching the engine conditions, a better understanding of leading edge film cooling was gained. This was a result of the high spatial resolution of the flow field gained from the large scale of the airfoil. This benefited both the Laser Doppler Velocimeter (LDV) system for velocity measurements and the infrared camera used for thermal field measurements. High effectiveness levels were measured throughout the showerhead region. This was attributed to a build up of coolant along the span of the airfoil. The introduction of a high freestream turbulence level increased the uniformity at the expense of lower overall effectiveness levels. Velocity field measurements verified that a core of coolant existed in the near wall region of the airfoil. This showerhead coolant flow dominated the flow at the downstream coolant row.

Aerodynamic forces and flow structures of the leading edge vortex on a flapping wing considering ground effect.

PubMed

Van Truong, Tien; Byun, Doyoung; Kim, Min Jun; Yoon, Kwang Joon; Park, Hoon Cheol

2013-09-01

The aim of this work is to provide an insight into the aerodynamic performance of the beetle during takeoff, which has been estimated in previous investigations. We employed a scaled-up electromechanical model flapping wing to measure the aerodynamic forces and the three-dimensional flow structures on the flapping wing. The ground effect on the unsteady forces and flow structures were also characterized. The dynamically scaled wing model could replicate the general stroke pattern of the beetle's hind wing kinematics during takeoff flight. Two wing kinematic models have been studied to examine the influences of wing kinematics on unsteady aerodynamic forces. In the first model, the angle of attack is asymmetric and varies during the translational motion, which is the flapping motion of the beetle's hind wing. In the second model, the angle of attack is constant during the translational motion. The instantaneous aerodynamic forces were measured for four strokes during the beetle's takeoff by the force sensor attached at the wing base. Flow visualization provided a general picture of the evolution of the three-dimensional leading edge vortex (LEV) on the beetle hind wing model. The LEV is stable during each stroke, and increases radically from the root to the tip, forming a leading-edge spiral vortex. The force measurement results show that the vertical force generated by the hind wing is large enough to lift the beetle. For the beetle hind wing kinematics, the total vertical force production increases 18.4% and 8.6% for the first and second strokes, respectively, due to the ground effect. However, for the model with a constant angle of attack during translation, the vertical force is reduced during the first stroke. During the third and fourth strokes, the ground effect is negligible for both wing kinematic patterns. This finding suggests that the beetle's flapping mechanism induces a ground effect that can efficiently lift its body from the ground during takeoff.

An evaluation of edge effects in nutritional accessibility and availability measures: a simulation study

PubMed Central

2010-01-01

Background This paper addresses the statistical use of accessibility and availability indices and the effect of study boundaries on these measures. The measures are evaluated via an extensive simulation based on cluster models for local outlet density. We define outlet to mean either food retail store (convenience store, supermarket, gas station) or restaurant (limited service or full service restaurants). We designed a simulation whereby a cluster outlet model is assumed in a large study window and an internal subset of that window is constructed. We performed simulations on various criteria including one scenario representing an urban area with 2000 outlets as well as a non-urban area simulated with only 300 outlets. A comparison is made between estimates obtained with the full study area and estimates using only the subset area. This allows the study of the effect of edge censoring on accessibility measures. Results The results suggest that considerable bias is found at the edges of study regions in particular for accessibility measures. Edge effects are smaller for availability measures (when not smoothed) and also for short range accessibility Conclusions It is recommended that any study utilizing these measures should correct for edge effects. The use of edge correction via guard areas is recommended and the avoidance of large range distance-based accessibility measures is also proposed. PMID:20663199

Direct measurements of local bed shear stress in the presence of pressure gradients

NASA Astrophysics Data System (ADS)

Pujara, Nimish; Liu, Philip L.-F.

2014-07-01

This paper describes the development of a shear plate sensor capable of directly measuring the local mean bed shear stress in small-scale and large-scale laboratory flumes. The sensor is capable of measuring bed shear stress in the range 200 Pa with an accuracy up to 1 %. Its size, 43 mm in the flow direction, is designed to be small enough to give spatially local measurements, and its bandwidth, 75 Hz, is high enough to resolve time-varying forcing. Typically, shear plate sensors are restricted to use in zero pressure gradient flows because secondary forces on the edge of the shear plate caused by pressure gradients can introduce large errors. However, by analysis of the pressure distribution at the edges of the shear plate in mild pressure gradients, we introduce a new methodology for correcting for the pressure gradient force. The developed sensor includes pressure tappings to measure the pressure gradient in the flow, and the methodology for correction is applied to obtain accurate measurements of bed shear stress under solitary waves in a small-scale wave flume. The sensor is also validated by measurements in a turbulent flat plate boundary layer in open channel flow.

Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster

NASA Astrophysics Data System (ADS)

Nguyen-Luong, Q.; Anderson, L. D.; Motte, F.; Kim, Kee-Tae; Schilke, P.; Carlhoff, P.; Beuther, H.; Schneider, N.; Didelon, P.; Kramer, C.; Louvet, F.; Nony, T.; Bihr, S.; Rugel, M.; Soler, J.; Wang, Y.; Bronfman, L.; Simon, R.; Menten, K. M.; Wyrowski, F.; Walmsley, C. M.

2017-08-01

We report the first map of large-scale (10 pc in length) emission of millimeter-wavelength hydrogen recombination lines (mm-RRLs) toward the giant H II region around the W43-Main young massive star cluster (YMC). Our mm-RRL data come from the IRAM 30 m telescope and are analyzed together with radio continuum and cm-RRL data from the Karl G. Jansky Very Large Array and HCO+ 1-0 line emission data from the IRAM 30 m. The mm-RRLs reveal an expanding wind-blown ionized gas shell with an electron density ˜70-1500 cm-3 driven by the WR/OB cluster, which produces a total Lyα photon flux of 1.5× {10}50 s-1. This shell is interacting with the dense neutral molecular gas in the W43-Main dense cloud. Combining the high spectral and angular resolution mm-RRL and cm-RRL cubes, we derive the two-dimensional relative distributions of dynamical and pressure broadening of the ionized gas emission and find that the RRL line shapes are dominated by pressure broadening (4-55 {km} {{{s}}}-1) near the YMC and by dynamical broadening (8-36 {km} {{{s}}}-1) near the shell’s edge. Ionized gas clumps hosting ultra-compact H II regions found at the edge of the shell suggest that large-scale ionized gas motion triggers the formation of new star generation near the periphery of the shell.

Where the woodland ends: How edges affect landscape structure and physiological responses of Quercus agrifolia

NASA Astrophysics Data System (ADS)

de Chant, Timothy Paul

Forests and woodlands are integral parts of ecosystems across the globe, but they are threatened by a variety of factors, including urbanization and introduced forest pathogens. These two forces are fundamentally altering ecosystems, both by removing forest cover and reshaping landscapes. Comprehending how these two processes have changed forest ecosystems is an important step toward understanding how the affected systems will function in the future. I investigated the range of edge effects that result from disturbance brought about by forest pathogens and urbanization in two coastal oak woodlands in Marin County, California. Oak woodlands are a dynamic part of California's landscape, reacting to changes in their biotic and abiotic environments across a range of spatial and temporal scales. Sudden Oak Death, caused by the introduced forest pathogen Phytophthora ramorum, has led to widespread mortality of many tree species in California's oak woodlands. I investigated how the remaining trees respond to such rapid changes in canopy structure (Chapter 2), and my results revealed a forest canopy quick to respond to the new openings. Urbanization, another disturbance regime, operates on a longer time scale. Immediately following urban development, forest edges are strikingly linear, but both forest processes and homeowner actions likely work in concert to disrupt the straight edge (Chapter 3). Forest edges grew more sinuous within 14 years of the initial disturbance, and continued to do so for the remainder of the study, another 21 years. Individual Quercus agrifolia trees also respond to urban edges decades after disturbance (Chapter 4), and their reaction is reflected in declining stable carbon isotope values (delta13C). This change suggests trees may have increased their stomatal conductance in response to greater water availability, reduced their photosynthetic rate as a result of stress, or some combination of both. Edges have far reaching and long lasting effects on forest structure and function. Investigations of their impacts on multiple spatial and temporal scales are important in determining the range of effects they have on forest ecosystems. Studies that combine remote sensing, geographic information systems, and field studies may help us understand the ecological consequences of forest edges.

Helicopter rotor noise investigation during ice accretion

NASA Astrophysics Data System (ADS)

Cheng, Baofeng

An investigation of helicopter rotor noise during ice accretion is conducted using experimental, theoretical, and numerical methods. This research is the acoustic part of a joint helicopter rotor icing physics, modeling, and detection project at The Pennsylvania State University Vertical Lift Research Center of Excellence (VLRCOE). The current research aims to provide acoustic insight and understanding of the rotor icing physics and investigate the feasibility of detecting rotor icing through noise measurements, especially at the early stage of ice accretion. All helicopter main rotor noise source mechanisms and their change during ice accretion are discussed. Changes of the thickness noise, steady loading noise, and especially the turbulent boundary layer - trailing edge (TBL-TE) noise due to ice accretion are identified and studied. The change of the discrete frequency noise (thickness noise and steady loading noise) due to ice accretion is calculated by using PSU-WOPWOP, an advanced rotorcraft acoustic prediction code. The change is noticeable, but too small to be used in icing detection. The small thickness noise change is due to the small volume of the accreted ice compared to that of the entire blade, although a large iced airfoil shape is used. For the loading noise calculation, two simplified methods are used to generate the loading on the rotor blades, which is the input for the loading noise calculation: 1) compact loading from blade element momentum theory, icing effects are considered by increasing the drag coefficient; and 2) pressure loading from the 2-D CFD simulation, icing effects are considered by using the iced airfoil shape. Comprehensive rotor broadband noise measurements are carried out on rotor blades with different roughness sizes and rotation speeds in two facilities: the Adverse Environment Rotor Test Stand (AERTS) facility at The Pennsylvania State University, and The University of Maryland Acoustic Chamber (UMAC). In both facilities the measured high-frequency broadband noise increases significantly with increasing surface roughness heights, which indicates that it is feasible to quantify helicopter rotor ice-induced surface roughness through acoustic measurements. Comprehensive broadband noise measurements based on different accreted ice roughness at AERTS are then used to form the data base from which a correlation between the ice-induced surface roughness and the broadband noise level is developed. Two parameters, the arithmetic average roughness height, Ra, and the averaged roughness height, based on the integrated ice thickness at the blade tip, are introduced to describe the ice-induced surface roughness at the early stage of the ice accretion. The ice roughness measurements are correlated to the measured broadband noise level. Strong correlations (absolute mean deviations of 9.3% and 11.2% for correlation using Ra and the averaged roughness height respectively) between the ice roughness and the broadband noise level are obtained, which can be used as a tool to determine the accreted ice roughness in the AERTS facility through acoustic measurement. It might be possible to use a similar approach to develop an early ice accretion detection tool for helicopters, as well as to quantify the ice-induced roughness at the early stage of rotor ice accretion. Rotor broadband noise source identification is conducted and the broadband noise related to ice accretion is argued to be turbulent boundary layer - trailing edge (TBL-TE) noise. Theory suggests TBL-TE noise scales with Mach number to the fifth power, which is also observed in the experimental data. The trailing edge noise theories developed by Ffowcs Williams and Hall, and Howe both identify two important parameters: boundary layer thickness and turbulence intensity. Numerical studies of 2-D airfoils with different ice-induced surface roughness heights are conducted to investigate the extent that surface roughness impacts the boundary layer thickness and turbulence intensity (and ultimately the TBL-TE noise). The results show that boundary layer thickness and turbulence intensity at the trailing edge increase with the increased roughness height. Using Howe's trailing edge noise model, the increased sound pressure level (SPL) of the trailing edge noise due to the increased displacement thickness and normalized integrated turbulence intensity are 6.2 dB and 1.6 dB for large and small accreted ice roughness heights, respectively. The estimated increased SPL values agree well with the experimental results, which are 5.8 dB and 2.6 dB for large and small roughness height, respectively. Finally a detailed broadband noise spectral scaling for all measured broadband noise in both AERTS and UMAC facilities is conducted. The magnitude and the frequency spectrum of the measured broadband noise are scaled on characteristic velocity and length. The peak of the laminar boundary layer - vortex shedding (LBL-VS) noise coalesces well on the Strouhal scaling in those cases. For the measured broadband noise from a rotor with relatively large roughness heights, no contribution of the LBL-VS noise is observed. The velocity scaling shows that the TBL-TE noise, which is the dominant source mechanism, scales with Mach number to the fifth power based on the absolute frequency. The length scaling shows that the TBL-TE noise scales well on the absolute roughness height based on Howe's TE noise theory.

STOL Characteristics of a Propeller-Driven, Aspect-Ratio-10, Straight-Wing Airplane with Boundary-Layer Control Flaps, as Estimated from Large-Scale Wind-Tunnel Tests

NASA Technical Reports Server (NTRS)

Weiberg, James A; Holzhauser, Curt A.

1961-01-01

A study is presented of the improvements in take-off and landing distances possible with a conventional propeller-driven transport-type airplane when the available lift is increased by propeller slipstream effects and by very effective trailing-edge flaps and ailerons. This study is based on wind-tunnel tests of a 45-foot span, powered model, with BLC on the trailing-edge flaps and controls. The data were applied to an assumed airplane with four propellers and a wing loading of 50 pounds per square foot. Also included is an examination of the stability and control problems that may result in the landing and take-off speed range of such a vehicle. The results indicated that the landing and take-off distances could be more than halved by the use of highly effective flaps in combination with large amounts of engine power to augment lift (STOL). At the lowest speeds considered (about 50 knots), adequate longitudinal stability was obtained but the lateral and directional stability were unsatisfactory. At these low speeds, the conventional aerodynamic control surfaces may not be able to cope with the forces and moments produced by symmetric, as well as asymmetric, engine operation. This problem was alleviated by BLC applied to the control surfaces.

A leading edge heating array and a flat surface heating array: Final design. [for testing the thermal protection system of the space shuttle

NASA Technical Reports Server (NTRS)

1975-01-01

A heating array is described for testing full-scale sections of the leading edge and lower fuselage surfaces of the shuttle. The heating array was designed to provide a tool for development and acceptance testing of leading edge segments and large flat sections of the main body thermal protection system. The array was designed using a variable length module concept to meet test requirements using interchangeable components from one test configuration in another configuration. Heat generating modules and heat absorbing modules were employed to achieve the thermal gradient around the leading edge. A support was developed to hold the modules to form an envelope around a variety of leading edges; to supply coolant to each module; the support structure and to hold the modules in the flat surface heater configuration. An optical pyrometer system mounted within the array was designed to monitor specimen surface temperatures without altering the test article's surface.

Active edge control in the precessions polishing process for manufacturing large mirror segments

NASA Astrophysics Data System (ADS)

Li, Hongyu; Zhang, Wei; Walker, David; Yu, Gouyo

2014-09-01

The segmentation of the primary mirror is the only promising solution for building the next generation of ground telescopes. However, manufacturing segmented mirrors presents its own challenges. The edge mis-figure impacts directly on the telescope's scientific output. The `Edge effect' significantly dominates the polishing precision. Therefore, the edge control is regarded as one of the most difficult technical issues in the segment production that needs to be addressed urgently. This paper reports an active edge control technique for the mirror segments fabrication using the Precession's polishing technique. The strategy in this technique requires that the large spot be selected on the bulk area for fast polishing, and the small spot is used for edge figuring. This can be performed by tool lift and optimizing the dell time to compensate for non-uniform material removal at the edge zone. This requires accurate and stable edge tool influence functions. To obtain the full tool influence function at the edge, we have demonstrated in previous work a novel hybrid-measurement method which uses both simultaneous phase interferometry and profilometry. In this paper, the edge effect under `Bonnet tool' polishing is investigated. The pressure distribution is analyzed by means of finite element analysis (FEA). According to the `Preston' equation, the shape of the edge tool influence functions is predicted. With this help, the multiple process parameters at the edge zone are optimized. This is demonstrated on a 200mm crosscorners hexagonal part with a result of PV less than 200nm for entire surface.

Parallel Algorithms for Switching Edges in Heterogeneous Graphs.

PubMed

Bhuiyan, Hasanuzzaman; Khan, Maleq; Chen, Jiangzhuo; Marathe, Madhav

2017-06-01

An edge switch is an operation on a graph (or network) where two edges are selected randomly and one of their end vertices are swapped with each other. Edge switch operations have important applications in graph theory and network analysis, such as in generating random networks with a given degree sequence, modeling and analyzing dynamic networks, and in studying various dynamic phenomena over a network. The recent growth of real-world networks motivates the need for efficient parallel algorithms. The dependencies among successive edge switch operations and the requirement to keep the graph simple (i.e., no self-loops or parallel edges) as the edges are switched lead to significant challenges in designing a parallel algorithm. Addressing these challenges requires complex synchronization and communication among the processors leading to difficulties in achieving a good speedup by parallelization. In this paper, we present distributed memory parallel algorithms for switching edges in massive networks. These algorithms provide good speedup and scale well to a large number of processors. A harmonic mean speedup of 73.25 is achieved on eight different networks with 1024 processors. One of the steps in our edge switch algorithms requires the computation of multinomial random variables in parallel. This paper presents the first non-trivial parallel algorithm for the problem, achieving a speedup of 925 using 1024 processors.

Parallel Algorithms for Switching Edges in Heterogeneous Graphs☆

PubMed Central

Khan, Maleq; Chen, Jiangzhuo; Marathe, Madhav

2017-01-01

An edge switch is an operation on a graph (or network) where two edges are selected randomly and one of their end vertices are swapped with each other. Edge switch operations have important applications in graph theory and network analysis, such as in generating random networks with a given degree sequence, modeling and analyzing dynamic networks, and in studying various dynamic phenomena over a network. The recent growth of real-world networks motivates the need for efficient parallel algorithms. The dependencies among successive edge switch operations and the requirement to keep the graph simple (i.e., no self-loops or parallel edges) as the edges are switched lead to significant challenges in designing a parallel algorithm. Addressing these challenges requires complex synchronization and communication among the processors leading to difficulties in achieving a good speedup by parallelization. In this paper, we present distributed memory parallel algorithms for switching edges in massive networks. These algorithms provide good speedup and scale well to a large number of processors. A harmonic mean speedup of 73.25 is achieved on eight different networks with 1024 processors. One of the steps in our edge switch algorithms requires the computation of multinomial random variables in parallel. This paper presents the first non-trivial parallel algorithm for the problem, achieving a speedup of 925 using 1024 processors. PMID:28757680

Paraxial ray optics cloaking.

PubMed

Choi, Joseph S; Howell, John C

2014-12-01

Despite much interest and progress in optical spatial cloaking, a three-dimensional (3D), transmitting, continuously multidirectional cloak in the visible regime has not yet been demonstrated. Here we experimentally demonstrate such a cloak using ray optics, albeit with some edge effects. Our device requires no new materials, uses isotropic off-the-shelf optics, scales easily to cloak arbitrarily large objects, and is as broadband as the choice of optical material, all of which have been challenges for current cloaking schemes. In addition, we provide a concise formalism that quantifies and produces perfect optical cloaks in the small-angle ('paraxial') limit.

The Superior-Edge-of-the-Knee Incision Method in Lymphaticovenular Anastomosis for Lower Extremity Lymphedema.

PubMed

Seki, Yukio; Yamamoto, Takumi; Yoshimatsu, Hidehiko; Hayashi, Akitatsu; Kurazono, Arito; Mori, Masanori; Kato, Yoichi; Koshima, Isao

2015-11-01

Lymphatic vessel diameter and lymph flow are important for accurate anastomosis and effective lymph-to-venous flow in lymphaticovenular anastomosis. The authors developed a reliable method, the superioredge-of-the-knee incision method, for detecting and making the best use of high-flow lymphatic vessels in the distal medial thigh between the deep and superficial fascia, where movement of the knee, combined with compression between these fascial layers, theoretically results in upward propulsion of lymphatic fluid. Intraoperative detection of large lymphatic vessels and of venous reflux and postoperative lymphedematous volume reduction were compared between 15 patients in whom lymphaticovenular anastomoses with the superior-edge-of-the-knee incision method were undergone and 15 in whom conventional lymphaticovenular anastomoses were undergone. Lymphaticovenular anastomosis at the thigh yielded 30 anastomoses in the superior-edge-of-the-knee incision group and 32 anastomoses in the non-superior-edge-of-the-knee incision group. Large lymphatic vessels were more frequently found in the superior-edge-of-the-knee incision group than in the non-superior-edge-of-the-knee incision group (60.0 percent versus 18.8 percent; p = 0.002). Venous reflux occurred less frequently in the superior-edge-of-the-knee incision group than in the non-superior-edge-of-the-knee incision group (10.0 percent versus 65.6 percent; p < 0.001). Reduction of the lower extremity lymphedema index was significantly greater in the superior-edge-of-the-knee incision group than in the non-superior-edge-of-the-knee incision group (24.427 ± 12.400 versus 0.032 ± 20.535; p < 0.001). The superior-edge-of-the-knee incision method facilitates detection and use of large, high-flow lymphatic vessels in the distal medial thigh, both of which are important for optimum therapeutic effects in patients with lower extremity lymphedema. Therapeutic, III.

Large-Scale Stratospheric Transport Processes

NASA Technical Reports Server (NTRS)

Plumb, R. Alan

2001-01-01

The paper discusses the following: 1. The Brewer-Dobson circulation: tropical upwelling. 2. Mixing into polar vortices. 3. The latitudinal structure of "age" in the stratosphere. 4. The subtropical "tracer edges". 5. Transport in the lower troposphere. 6. Tracer modeling during SOLVE. 7. 3D modeling of "mean age". 8. Models and measurements II.

Single shot near edge x-ray absorption fine structure spectroscopy in the laboratory

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

Mantouvalou, I., E-mail: ioanna.mantouvalou@tu-berlin.de; Witte, K.; Martyanov, W.

With the help of adapted off-axis reflection zone plates, near edge X-ray absorption fine structure spectra at the C and N K-absorption edge have been recorded using a single 1.2 ns long soft X-ray pulse. The transmission experiments were performed with a laser-produced plasma source in the laboratory rendering time resolved measurements feasible independent on large scale facilities. A resolving power of E/ΔE ∼ 950 at the respective edges could be demonstrated. A comparison of single shot spectra with those collected with longer measuring time proves that all features of the used reference samples (silicon nitrate and polyimide) can be resolved in 1.2 ns.more » Hence, investigations of radiation sensitive biological specimen become possible due to the high efficiency of the optical elements enabling low dose experiments.« less

Simulation of Acoustic Scattering from a Trailing Edge

NASA Technical Reports Server (NTRS)

Singer, Bart A.; Brentner, Kenneth S.; Lockard, David P.; Lilley, Geoffrey M.

1999-01-01

Three model problems were examined to assess the difficulties involved in using a hybrid scheme coupling flow computation with the the Ffowcs Williams and Hawkings equation to predict noise generated by vortices passing over a sharp edge. The results indicate that the Ffowcs Williams and Hawkings equation correctly propagates the acoustic signals when provided with accurate flow information on the integration surface. The most difficult of the model problems investigated inviscid flow over a two-dimensional thin NACA airfoil with a blunt-body vortex generator positioned at 98 percent chord. Vortices rolled up downstream of the blunt body. The shed vortices possessed similarities to large coherent eddies in boundary layers. They interacted and occasionally paired as they convected past the sharp trailing edge of the airfoil. The calculations showed acoustic waves emanating from the airfoil trailing edge. Acoustic directivity and Mach number scaling are shown.

Weighted Scaling in Non-growth Random Networks

NASA Astrophysics Data System (ADS)

Chen, Guang; Yang, Xu-Hua; Xu, Xin-Li

2012-09-01

We propose a weighted model to explain the self-organizing formation of scale-free phenomenon in non-growth random networks. In this model, we use multiple-edges to represent the connections between vertices and define the weight of a multiple-edge as the total weights of all single-edges within it and the strength of a vertex as the sum of weights for those multiple-edges attached to it. The network evolves according to a vertex strength preferential selection mechanism. During the evolution process, the network always holds its total number of vertices and its total number of single-edges constantly. We show analytically and numerically that a network will form steady scale-free distributions with our model. The results show that a weighted non-growth random network can evolve into scale-free state. It is interesting that the network also obtains the character of an exponential edge weight distribution. Namely, coexistence of scale-free distribution and exponential distribution emerges.

Thermodynamics of the Coma Cluster Outskirts

NASA Astrophysics Data System (ADS)

Simionescu, A.; Werner, N.; Urban, O.; Allen, S. W.; Fabian, A. C.; Mantz, A.; Matsushita, K.; Nulsen, P. E. J.; Sanders, J. S.; Sasaki, T.; Sato, T.; Takei, Y.; Walker, S. A.

2013-09-01

We present results from a large mosaic of Suzaku observations of the Coma Cluster, the nearest and X-ray brightest hot (~8 keV), dynamically active, non-cool core system, focusing on the thermodynamic properties of the intracluster medium on large scales. For azimuths not aligned with an infalling subcluster toward the southwest, our measured temperature and X-ray brightness profiles exhibit broadly consistent radial trends, with the temperature decreasing from about 8.5 keV at the cluster center to about 2 keV at a radius of 2 Mpc, which is the edge of our detection limit. The southwest merger significantly boosts the surface brightness, allowing us to detect X-ray emission out to ~2.2 Mpc along this direction. Apart from the southwestern infalling subcluster, the surface brightness profiles show multiple edges around radii of 30-40 arcmin. The azimuthally averaged temperature profile, as well as the deprojected density and pressure profiles, all show a sharp drop consistent with an outwardly-propagating shock front located at 40 arcmin, corresponding to the outermost edge of the giant radio halo observed at 352 MHz with the Westerbork Synthesis Radio Telescope. The shock front may be powering this radio emission. A clear entropy excess inside of r 500 reflects the violent merging events linked with these morphological features. Beyond r 500, the entropy profiles of the Coma Cluster along the relatively relaxed directions are consistent with the power-law behavior expected from simple models of gravitational large-scale structure formation. The pressure is also in agreement at these radii with the expected values measured from Sunyaev-Zel'dovich data from the Planck satellite. However, due to the large uncertainties associated with the Coma Cluster measurements, we cannot yet exclude an entropy flattening in this system consistent with that seen in more relaxed cool core clusters.

Edge fires drive the shape and stability of tropical forests.

PubMed

Hébert-Dufresne, Laurent; Pellegrini, Adam F A; Bhat, Uttam; Redner, Sidney; Pacala, Stephen W; Berdahl, Andrew M

2018-06-01

In tropical regions, fires propagate readily in grasslands but typically consume only edges of forest patches. Thus, forest patches grow due to tree propagation and shrink by fires in surrounding grasslands. The interplay between these competing edge effects is unknown, but critical in determining the shape and stability of individual forest patches, as well the landscape-level spatial distribution and stability of forests. We analyze high-resolution remote-sensing data from protected Brazilian Cerrado areas and find that forest shapes obey a robust perimeter-area scaling relation across climatic zones. We explain this scaling by introducing a heterogeneous fire propagation model of tropical forest-grassland ecotones. Deviations from this perimeter-area relation determine the stability of individual forest patches. At a larger scale, our model predicts that the relative rates of tree growth due to propagative expansion and long-distance seed dispersal determine whether collapse of regional-scale tree cover is continuous or discontinuous as fire frequency changes. © 2018 The Authors. Ecology Letters published by CNRS and John Wiley & Sons Ltd.

Enhanced heat transfer is dependent on thickness of graphene films: the heat dissipation during boiling

PubMed Central

Ahn, Ho Seon; Kim, Jin Man; Kim, TaeJoo; Park, Su Cheong; Kim, Ji Min; Park, Youngjae; Yu, Dong In; Hwang, Kyoung Won; Jo, HangJin; Park, Hyun Sun; Kim, Hyungdae; Kim, Moo Hwan

2014-01-01

Boiling heat transfer (BHT) is a particularly efficient heat transport method because of the latent heat associated with the process. However, the efficiency of BHT decreases significantly with increasing wall temperature when the critical heat flux (CHF) is reached. Graphene has received much recent research attention for applications in thermal engineering due to its large thermal conductivity. In this study, graphene films of various thicknesses were deposited on a heated surface, and enhancements of BHT and CHF were investigated via pool-boiling experiments. In contrast to the well-known surface effects, including improved wettability and liquid spreading due to micron- and nanometer-scale structures, nanometer-scale folded edges of graphene films provided a clue of BHT improvement and only the thermal conductivity of the graphene layer could explain the dependence of the CHF on the thickness. The large thermal conductivity of the graphene films inhibited the formation of hot spots, thereby increasing the CHF. Finally, the provided empirical model could be suitable for prediction of CHF. PMID:25182076

Characterizing Atacama B-mode Search Detectors with a Half-Wave Plate

NASA Astrophysics Data System (ADS)

Simon, S. M.; Appel, J. W.; Campusano, L. E.; Choi, S. K.; Crowley, K. T.; Essinger-Hileman, T.; Gallardo, P.; Ho, S. P.; Kusaka, A.; Nati, F.; Palma, G. A.; Page, L. A.; Raghunathan, S.; Staggs, S. T.

2016-08-01

The Atacama B-Mode Search (ABS) instrument is a cryogenic (˜ 10 K) crossed-Dragone telescope located at an elevation of 5190 m in the Atacama Desert in Chile that observed for three seasons between February 2012 and October 2014. ABS observed the cosmic microwave background (CMB) at large angular scales (40<ℓ <500) to limit the B-mode polarization spectrum around the primordial B-mode peak from inflationary gravity waves at ℓ ˜ 100. The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers. They are coupled to orthogonal polarizations from a planar ortho-mode transducer and observe at 145 GHz. ABS employs an ambient-temperature, rapidly rotating half-wave plate (HWP) to mitigate systematic effects and move the signal band away from atmospheric 1 / f noise, allowing for the recovery of large angular scales. We discuss how the signal at the second harmonic of the HWP rotation frequency can be used for data selection and for monitoring the detector responsivities.

3D two-fluid simulations of turbulence in LAPD

NASA Astrophysics Data System (ADS)

Fisher, Dustin M.

The Large Plasma Device (LAPD) is modeled using a modified version of the 3D Global Braginskii Solver code (GBS) for a nominal Helium plasma. The unbiased low-flow regime is explored in simulations where there is an intrinsic E x B rotation of the plasma. In the simulations this rotation is caused primarily by sheath effects with the Reynolds stress and J x B torque due to a cross-field Pederson conductivity having little effect. Explicit biasing simulations are also explored for the first time where the intrinsic rotation of the plasma is modified through boundary conditions that mimic the biasable limiter used in LAPD. Comparisons to experimental measurements in the unbiased case show strong qualitative agreement with the data, particularly the radial dependence of the density fluctuations, cross-correlation lengths, radial flux dependence outside of the cathode edge, and camera imagery. Kelvin Helmholtz (KH) turbulence at relatively large scales is the dominant driver of cross-field transport in these simulations with smaller-scale drift waves and sheath modes playing a secondary role. Plasma holes and blobs arising from KH vortices are consistent with the scale sizes and overall appearance of those in LAPD camera images. The addition of ion-neutral collisions in the unbiased simulations at previously theorized values reduces the radial particle flux due to a modest stabilizing contribution of the collisions on the KH-modes driving the turbulent transport. In the biased runs the ion-neutral collisions have a much smaller effect due to the modification of the potential from sheath terms. In biasing the plasma to increase the intrinsic rotation, simulations show the emergence of a nonlinearly saturated coherent mode of order m = 6. In addition, the plasma inside of the cathode edge becomes quiescent due to the strong influence of the wall bias in setting up the equilibrium plasma potential. Biasing in the direction opposite to the intrinsic flow reduces the effective shear and leads to a stronger presence of drift modes that are seen to saturate when the KH drive has been suppressed. Both biasing cases show a moderate density confinement similarly seen in the experiment.

Influence of the Bermuda High on interannual variability of summertime ozone in the Houston-Galveston-Brazoria region

NASA Astrophysics Data System (ADS)

Wang, Yuxuan; Jia, Beixi; Wang, Sing-Chun; Estes, Mark; Shen, Lu; Xie, Yuanyu

2016-12-01

The Bermuda High (BH) quasi-permanent pressure system is the key large-scale circulation pattern influencing summertime weather over the eastern and southern US. Here we developed a multiple linear regression (MLR) model to characterize the effect of the BH on year-to-year changes in monthly-mean maximum daily 8 h average (MDA8) ozone in the Houston-Galveston-Brazoria (HGB) metropolitan region during June, July, and August (JJA). The BH indicators include the longitude of the BH western edge (BH-Lon) and the BH intensity index (BHI) defined as the pressure gradient along its western edge. Both BH-Lon and BHI are selected by MLR as significant predictors (p < 0.05) of the interannual (1990-2015) variability of the HGB-mean ozone throughout JJA, while local-scale meridional wind speed is selected as an additional predictor for August only. Local-scale temperature and zonal wind speed are not identified as important factors for any summer month. The best-fit MLR model can explain 61-72 % of the interannual variability of the HGB-mean summertime ozone over 1990-2015 and shows good performance in cross-validation (R2 higher than 0.48). The BH-Lon is the most important factor, which alone explains 38-48 % of such variability. The location and strength of the Bermuda High appears to control whether or not low-ozone maritime air from the Gulf of Mexico can enter southeastern Texas and affect air quality. This mechanism also applies to other coastal urban regions along the Gulf Coast (e.g., New Orleans, LA, Mobile, AL, and Pensacola, FL), suggesting that the BH circulation pattern can affect surface ozone variability through a large portion of the Gulf Coast.

Forest edges: Effects on vegetation, environmental gradients and local avian communities in the Sierra Juarez, Oaxaca, Mexico

NASA Astrophysics Data System (ADS)

Burcsu, Theresa Katherine

Edge effects are among the most serious threats to forest integrity because as global forest cover decreases overall, forest edge influence increases proportionally, driving habitat change and loss. Edge effects occur at the division between adjacent habitat types. Our understanding of edge effects comes mainly from tropical wet, temperate and boreal forests. Because forest structure in moisture-limited forests differs from wetter forest types, edge dynamics are likely to differ as well. Moreover, dry forests in the tropics have been nearly eliminated or exist only as forest fragments, making edge influence an important conservation and management concern for remaining dry forests. This study addresses this gap in the edge influence knowledge by examining created, regenerating edges associated with forest management in a seasonally dry pine-oak forest of Oaxaca, creating a new data point in edge effects research. In this study I used Landsat TM imagery and a modified semivariance analysis to estimate the distance of edge influence for vegetation. I also used field methods to characterize forest structure and estimate edge influence on canopy and subcanopy vegetation. To finalize the project I extended the study to bird assemblages to identify responses and habitat preferences to local-scale changes associated with regenerating edges created by group-selection timber harvest. Remote sensing analysis estimated that the distance of edge influence was 30-90 m from the edge. Vegetation analysis suggested that edge effects were weak relative to wetter forest types and that remote sensing data did not provide an estimate that was directly applicable to field-measured vegetative edge effects. The bird assemblages likewise responded weakly to habitat change associated with edge effect. Open canopy structure, simple vertical stratigraphy, and topographic variation create forest conditions in which small openings do not create a high contrast to undisturbed forest. Thus, in this seasonally dry, open forest, vegetation and bird communities respond less to small openings than they do in wetter, more closed-canopy forests. Management practices and historical land-use interact and interfere with the detectability of edge influence in our study area. These results support hypotheses proposed for open forest types and suggest that patterns in edge influence in wet forest types may not be applicable to dry sites.

Effect of LES models on the entrainment of a passive scalar in a turbulent planar jet

NASA Astrophysics Data System (ADS)

Chambel Lopes, Diogo; da Silva, Carlos; Reis, Ricardo; Raman, Venkat

2011-11-01

Direct and large-eddy simulations (DNS/LES) of turbulent planar jets are used to study the role of subgrid-scale models in the integral characteristics of the passive scalar mixing in a jet. Specifically the effect of subgrid-scale models in the jet spreading rate and centreline passive scalar decay rates are assessed and compared. The modelling of the subgrid-scale fluxes is particularly challenging in the turbulent/nonturbulent (T/NT) region that divides the two regions in the jet flow: the outer region where the flow is irrotational and the inner region where the flow is turbulent. It has been shown that important Reynolds stresses exist near the T/NT interface and that these stresses determine in part the mixing and combustion rates in jets. The subgrid scales of motion near the T/NT interface are far from equilibrium and contain an important fraction of the total kinetic energy. Model constants used in several subgrid-scale models such as the Smagorinsky and the gradient models need to be corrected near the jet edge. The procedure used to obtain the dynamic Smagorinsky constant is not able to cope with the intermittent nature of this region.

Electron correlations in L-subshell photoionization of intermediate-Z elements (47<=Z<=51)

NASA Astrophysics Data System (ADS)

Jitschin, W.; Stötzel, R.

1998-08-01

The x-ray mass attenuation of 48Cd, 49In, 50Sn, and 51Sb in the energy regime of the L-subshell edges has been measured. For a comparison of the data of neighboring elements, these were scaled to 47Ag. The scaled data were compared with theoretical calculations of photoionization cross sections by Scofield, which use the common single electron approach. The comparison reveals minor but significant deviations between measurement and calculation: The measured cross sections are smaller than the prediction in the regime between the L3 and L2 edges, they have a flatter slope in the regime between the L2 and L1 edges, and they exhibit a decrease just above the L3 and L2 edges. All observed deviations can be explained as electron correlation effects originating from a polarization of the whole electron cloud by the ionizing radiation, since they are qualitatively reproduced by comparative calculations of the ionization process either omitting (independent particle approach) or including (in the linear response approximation) the electron correlations. However, the comparative calculations quantitatively overestimate the electron correlation effects.

Dependence of the L-Mode scrape-off layer power fall-off length on the upper triangularity in TCV

NASA Astrophysics Data System (ADS)

Faitsch, M.; Maurizio, R.; Gallo, A.; Coda, S.; Eich, T.; Labit, B.; Merle, A.; Reimerdes, H.; Sieglin, B.; Theiler, C.; the Eurofusion MST1 Team; the TCV Team

2018-04-01

This paper reports on experimental observations on TCV with a scan in upper triangularity {δ }up}, including negative triangularity, focusing on the power fall-off length {λ }{{q}} in L-Mode. The upper triangularity is scanned from -0.28 to 0.47. Smaller {λ }{{q}}out} is measured at the outer divertor target for decreasing {δ }up} together with higher edge temperature {T}{{e},{edge}} leading to increased confinement. This effect is observed for both magnetic drift directions for discharges in deuterium and helium. In helium larger {λ }{{q}} values are observed compared to deuterium. The power fall-off length at the inner divertor target {λ }{{q}}in} has a non-monotonic behaviour with changing triangularity. The largest values are around {δ }up}=0. The ratio {λ }{{q}}in}/{λ }{{q}}out} increases for decreasing {δ }up} for positive triangularity and is approximately constant for negative triangularity. {λ }{{q}}out} is compared to available scaling laws. Partial agreement is only observed for a scaling law containing a proxy for {T}{{e},{edge}} at ASDEX Upgrade (Sieglin 2016 Plasma Phys. Control. Fusion 58 055015). Extending this scaling to TCV and using {T}{{e},{edge}} at {ρ }pol}=0.95 suggests that {λ }{{q}}out} is independent of machine size {λ }{{q}}{{L} - {Mode}} ({mm}) = 165\\cdot {B}pol}{({{T}})}-0.66\\cdot A{({{u}})}-0.15\\cdot {T}{{e},{edge}}{({eV})}-0.93\\cdot R{({{m}})}-0.03. Possible explanations for smaller {λ }{{q}}out} for decreasing {δ }up} is a reduction in turbulence or a direct effect of increasing {T}{{e},{edge}}.

Near-edge wrack effects on bare sediments: Small scale variation matters in the monitoring of sandy beaches.

PubMed

MacMillan, Mitchell R; Tummon Flynn, Paula; Duarte, Cristian; Quijón, Pedro A

2016-12-01

The influence of wrack on sandy beach communities is well-documented but its effect on bare sediments located immediately beyond its edge has not yet been tested. This study aimed to explore these effects by surveying bare sediments located at increasing distances (0.5-2 m) from the wrack in five sandy beaches on Prince Edward Island, Atlantic Canada. In addition, we tested the influence of wrack with a field manipulation using wrack patches made up of rockweed bundles. The survey indicated that a modest but significant number of amphipods and beetles occupied bare sediments located 0.5 m from the edge of the wrack, but that those numbers dropped in sediments 1 m away and farther. The outcome of the field manipulation showed a similar pattern. Although small in spatial scale, our results have implications for the monitoring sandy beaches affected by scattered as well as heavy wrack input. Copyright © 2016 Elsevier Ltd. All rights reserved.

Synergistic interactions between edge and area effects in a heavily fragmented landscape.

PubMed

Ewers, Robert M; Thorpe, Stephen; Didham, Raphael K

2007-01-01

Both area and edge effects have a strong influence on ecological processes in fragmented landscapes, but there is little understanding of how these two factors might interact to exacerbate local species declines. To test for synergistic interactions between area and edge effects, we sampled a diverse beetle community in a heavily fragmented landscape in New Zealand. More than 35,000 beetles of approximately 900 species were sampled over large gradients in habitat area (10(-2) 10(6) ha) and distance from patch edge (2(0)-2(10) m from the forest edge into both the forest and adjacent matrix). Using a new approach to partition variance following an ordination analysis, we found that a synergistic interaction between habitat area and distance to edge was a more important determinant of patterns in beetle community composition than direct edge or area effects alone. The strength of edge effects in beetle-species composition increased nonlinearly with increasing fragment area. One important consequence of the synergy is that the slopes of species area (SA) curves constructed from habitat islands depend sensitively on the distance from edge at which sampling is conducted. Surprisingly, we found negative SA curves for communities sampled at intermediate distances from habitat edges, caused by differential edge responses of matrix- vs. forest-specialist species in fragments of increasing area. Our data indicate that distance to habitat edge has a consistently greater impact on beetle community composition than habitat area and that variation in the strength of edge effects may underlie many patterns that are superficially related to habitat area.

An exact and efficient first passage time algorithm for reaction-diffusion processes on a 2D-lattice

NASA Astrophysics Data System (ADS)

Bezzola, Andri; Bales, Benjamin B.; Alkire, Richard C.; Petzold, Linda R.

2014-01-01

We present an exact and efficient algorithm for reaction-diffusion-nucleation processes on a 2D-lattice. The algorithm makes use of first passage time (FPT) to replace the computationally intensive simulation of diffusion hops in KMC by larger jumps when particles are far away from step-edges or other particles. Our approach computes exact probability distributions of jump times and target locations in a closed-form formula, based on the eigenvectors and eigenvalues of the corresponding 1D transition matrix, maintaining atomic-scale resolution of resulting shapes of deposit islands. We have applied our method to three different test cases of electrodeposition: pure diffusional aggregation for large ranges of diffusivity rates and for simulation domain sizes of up to 4096×4096 sites, the effect of diffusivity on island shapes and sizes in combination with a KMC edge diffusion, and the calculation of an exclusion zone in front of a step-edge, confirming statistical equivalence to standard KMC simulations. The algorithm achieves significant speedup compared to standard KMC for cases where particles diffuse over long distances before nucleating with other particles or being captured by larger islands.

Tunable resonances due to vacancies in graphene nanoribbons

NASA Astrophysics Data System (ADS)

Bahamon, D. A.; Pereira, A. L. C.; Schulz, P. A.

2010-10-01

The coherent electron transport along zigzag and metallic armchair graphene nanoribbons in the presence of one or two vacancies is investigated. Having in mind atomic scale tunability of the conductance fingerprints, the primary focus is on the effect of the distance to the edges and intervacancies spacing. An involved interplay of vacancies sublattice location and nanoribbon edge termination, together with the spacing parameters lead to a wide conductance resonance line-shape modification. Turning on a magnetic field introduces a new length scale that unveils counterintuitive aspects of the interplay between purely geometric aspects of the system and the underlying atomic scale nature of graphene.

Multiscale infrared and visible image fusion using gradient domain guided image filtering

NASA Astrophysics Data System (ADS)

Zhu, Jin; Jin, Weiqi; Li, Li; Han, Zhenghao; Wang, Xia

2018-03-01

For better surveillance with infrared and visible imaging, a novel hybrid multiscale decomposition fusion method using gradient domain guided image filtering (HMSD-GDGF) is proposed in this study. In this method, hybrid multiscale decomposition with guided image filtering and gradient domain guided image filtering of source images are first applied before the weight maps of each scale are obtained using a saliency detection technology and filtering means with three different fusion rules at different scales. The three types of fusion rules are for small-scale detail level, large-scale detail level, and base level. Finally, the target becomes more salient and can be more easily detected in the fusion result, with the detail information of the scene being fully displayed. After analyzing the experimental comparisons with state-of-the-art fusion methods, the HMSD-GDGF method has obvious advantages in fidelity of salient information (including structural similarity, brightness, and contrast), preservation of edge features, and human visual perception. Therefore, visual effects can be improved by using the proposed HMSD-GDGF method.

Tetrapods on the EDGE: Overcoming data limitations to identify phylogenetic conservation priorities

PubMed Central

Gray, Claudia L.; Wearn, Oliver R.; Owen, Nisha R.

2018-01-01

The scale of the ongoing biodiversity crisis requires both effective conservation prioritisation and urgent action. As extinction is non-random across the tree of life, it is important to prioritise threatened species which represent large amounts of evolutionary history. The EDGE metric prioritises species based on their Evolutionary Distinctiveness (ED), which measures the relative contribution of a species to the total evolutionary history of their taxonomic group, and Global Endangerment (GE), or extinction risk. EDGE prioritisations rely on adequate phylogenetic and extinction risk data to generate meaningful priorities for conservation. However, comprehensive phylogenetic trees of large taxonomic groups are extremely rare and, even when available, become quickly out-of-date due to the rapid rate of species descriptions and taxonomic revisions. Thus, it is important that conservationists can use the available data to incorporate evolutionary history into conservation prioritisation. We compared published and new methods to estimate missing ED scores for species absent from a phylogenetic tree whilst simultaneously correcting the ED scores of their close taxonomic relatives. We found that following artificial removal of species from a phylogenetic tree, the new method provided the closest estimates of their “true” ED score, differing from the true ED score by an average of less than 1%, compared to the 31% and 38% difference of the previous methods. The previous methods also substantially under- and over-estimated scores as more species were artificially removed from a phylogenetic tree. We therefore used the new method to estimate ED scores for all tetrapods. From these scores we updated EDGE prioritisation rankings for all tetrapod species with IUCN Red List assessments, including the first EDGE prioritisation for reptiles. Further, we identified criteria to identify robust priority species in an effort to further inform conservation action whilst limiting uncertainty and anticipating future phylogenetic advances. PMID:29641585

Groundlayer vegetation gradients across oak woodland canopy gaps

USGS Publications Warehouse

Pavlovic, N.B.; Grundel, R.; Sluis, W.

2006-01-01

Frequency of groundlayer plants was measured across oak woodland canopy gaps at three sites in northwest Indiana to examine how vegetation varied with gap size, direction along the gap edge, and microhabitat. Microhabitats were defined as under the canopy adjacent to the gap, along the gap edge, and within the gap. Gap-sites consisted of gaps plus adjacent tree canopy. Gaps were classified as small (16 ± 1 m2), medium (97 ± 8), and large (310 ± 32). Neither richness nor diversity differed among microhabitats, gap sizes, or edges. Similarity between microhabitats wthin a gap-site increased as the distance between plots decreased and as the difference in PAR decreased, the latter explaining twice the variation in percent dissimilarity compared to Mg concentration, A horizon depth, and litter cover. Diervilla lonicera, Frageria virginiana, Helianthus divaricatus, Polygonatum pubescens, Quercus velutina, Smilacena stellata, and Tradescantia ohiensis decreased, whileTephrosia virginiana and legumes increased in frequency, from canopy to gap, and C4 grasses peaked at the gap edge, independent of gap size. Additional species frequency varied across the microhabitat gradient within specific sites. Sorghastrum nutans was three times more frequent in gaps at large sites than elsewhere. The vegetation in medium-sized gap-sites was more variable than within small and large gap-sites, suggesting greater environmental heterogeneity at that scale. Within gap-sites, vegetation was more heterogeneous within edges and canopies than in gaps. Edges were more similar in composition to gaps than to canopy groundlayer within gap-sites. Few species varied significantly in frequency around the gap edge. The oak woodland groundlayer on sandy substrates can be characterized as a mosaic of forb dominated vegetation that varies across light gradients associated with canopy gaps, transitioning to islands of grassland vegetation when gaps exceed 160 m2.

Annual Research Briefs

NASA Technical Reports Server (NTRS)

Spinks, Debra (Compiler)

1997-01-01

This report contains the 1997 annual progress reports of the research fellows and students supported by the Center for Turbulence Research (CTR). Titles include: Invariant modeling in large-eddy simulation of turbulence; Validation of large-eddy simulation in a plain asymmetric diffuser; Progress in large-eddy simulation of trailing-edge turbulence and aeronautics; Resolution requirements in large-eddy simulations of shear flows; A general theory of discrete filtering for LES in complex geometry; On the use of discrete filters for large eddy simulation; Wall models in large eddy simulation of separated flow; Perspectives for ensemble average LES; Anisotropic grid-based formulas for subgrid-scale models; Some modeling requirements for wall models in large eddy simulation; Numerical simulation of 3D turbulent boundary layers using the V2F model; Accurate modeling of impinging jet heat transfer; Application of turbulence models to high-lift airfoils; Advances in structure-based turbulence modeling; Incorporating realistic chemistry into direct numerical simulations of turbulent non-premixed combustion; Effects of small-scale structure on turbulent mixing; Turbulent premixed combustion in the laminar flamelet and the thin reaction zone regime; Large eddy simulation of combustion instabilities in turbulent premixed burners; On the generation of vorticity at a free-surface; Active control of turbulent channel flow; A generalized framework for robust control in fluid mechanics; Combined immersed-boundary/B-spline methods for simulations of flow in complex geometries; and DNS of shock boundary-layer interaction - preliminary results for compression ramp flow.

Edge enhancement improves disruptive camouflage by emphasising false edges and creating pictorial relief

PubMed Central

Egan, John; Sharman, Rebecca J.; Scott-Brown, Kenneth C.; Lovell, Paul George

2016-01-01

Disruptive colouration is a visual camouflage composed of false edges and boundaries. Many disruptively camouflaged animals feature enhanced edges; light patches are surrounded by a lighter outline and/or a dark patches are surrounded by a darker outline. This camouflage is particularly common in amphibians, reptiles and lepidopterans. We explored the role that this pattern has in creating effective camouflage. In a visual search task utilising an ultra-large display area mimicking search tasks that might be found in nature, edge enhanced disruptive camouflage increases crypsis, even on substrates that do not provide an obvious visual match. Specifically, edge enhanced camouflage is effective on backgrounds both with and without shadows; i.e. this is not solely due to background matching of the dark edge enhancement element with the shadows. Furthermore, when the dark component of the edge enhancement is omitted the camouflage still provided better crypsis than control patterns without edge enhancement. This kind of edge enhancement improved camouflage on all background types. Lastly, we show that edge enhancement can create a perception of multiple surfaces. We conclude that edge enhancement increases the effectiveness of disruptive camouflage through mechanisms that may include the improved disruption of the object outline by implying pictorial relief. PMID:27922058

Edge enhancement improves disruptive camouflage by emphasising false edges and creating pictorial relief.

PubMed

Egan, John; Sharman, Rebecca J; Scott-Brown, Kenneth C; Lovell, Paul George

2016-12-06

Disruptive colouration is a visual camouflage composed of false edges and boundaries. Many disruptively camouflaged animals feature enhanced edges; light patches are surrounded by a lighter outline and/or a dark patches are surrounded by a darker outline. This camouflage is particularly common in amphibians, reptiles and lepidopterans. We explored the role that this pattern has in creating effective camouflage. In a visual search task utilising an ultra-large display area mimicking search tasks that might be found in nature, edge enhanced disruptive camouflage increases crypsis, even on substrates that do not provide an obvious visual match. Specifically, edge enhanced camouflage is effective on backgrounds both with and without shadows; i.e. this is not solely due to background matching of the dark edge enhancement element with the shadows. Furthermore, when the dark component of the edge enhancement is omitted the camouflage still provided better crypsis than control patterns without edge enhancement. This kind of edge enhancement improved camouflage on all background types. Lastly, we show that edge enhancement can create a perception of multiple surfaces. We conclude that edge enhancement increases the effectiveness of disruptive camouflage through mechanisms that may include the improved disruption of the object outline by implying pictorial relief.

Discriminating the Drivers of Edge Effects on Nest Predation: Forest Edges Reduce Capture Rates of Ship Rats (Rattus rattus), a Globally Invasive Nest Predator, by Altering Vegetation Structure

PubMed Central

Ruffell, Jay; Didham, Raphael K.; Barrett, Paul; Gorman, Nic; Pike, Rhonda; Hickey-Elliott, Andrée; Sievwright, Karin; Armstrong, Doug P.

2014-01-01

Forest edges can strongly affect avian nest success by altering nest predation rates, but this relationship is inconsistent and context dependent. There is a need for researchers to improve the predictability of edge effects on nest predation rates by examining the mechanisms driving their occurrence and variability. In this study, we examined how the capture rates of ship rats, an invasive nest predator responsible for avian declines globally, varied with distance from the forest edge within forest fragments in a pastoral landscape in New Zealand. We hypothesised that forest edges would affect capture rates by altering vegetation structure within fragments, and that the strength of edge effects would depend on whether fragments were grazed by livestock. We measured vegetation structure and rat capture rates at 488 locations ranging from 0–212 m from the forest edge in 15 forest fragments, seven of which were grazed. Contrary to the vast majority of previous studies of edge effects on nest predation, ship rat capture rates increased with increasing distance from the forest edge. For grazed fragments, capture rates were estimated to be 78% lower at the forest edge than 118 m into the forest interior (the farthest distance for grazed fragments). This relationship was similar for ungrazed fragments, with capture rates estimated to be 51% lower at the forest edge than 118 m into the forest interior. A subsequent path analysis suggested that these ‘reverse’ edge effects were largely or entirely mediated by changes in vegetation structure, implying that edge effects on ship rats can be predicted from the response of vegetation structure to forest edges. We suggest the occurrence, strength, and direction of edge effects on nest predation rates may depend on edge-driven changes in local habitat when the dominant predator is primarily restricted to forest patches. PMID:25412340

Discriminating the drivers of edge effects on nest predation: forest edges reduce capture rates of ship rats (Rattus rattus), a globally invasive nest predator, by altering vegetation structure.

PubMed

Ruffell, Jay; Didham, Raphael K; Barrett, Paul; Gorman, Nic; Pike, Rhonda; Hickey-Elliott, Andrée; Sievwright, Karin; Armstrong, Doug P

2014-01-01

Forest edges can strongly affect avian nest success by altering nest predation rates, but this relationship is inconsistent and context dependent. There is a need for researchers to improve the predictability of edge effects on nest predation rates by examining the mechanisms driving their occurrence and variability. In this study, we examined how the capture rates of ship rats, an invasive nest predator responsible for avian declines globally, varied with distance from the forest edge within forest fragments in a pastoral landscape in New Zealand. We hypothesised that forest edges would affect capture rates by altering vegetation structure within fragments, and that the strength of edge effects would depend on whether fragments were grazed by livestock. We measured vegetation structure and rat capture rates at 488 locations ranging from 0-212 m from the forest edge in 15 forest fragments, seven of which were grazed. Contrary to the vast majority of previous studies of edge effects on nest predation, ship rat capture rates increased with increasing distance from the forest edge. For grazed fragments, capture rates were estimated to be 78% lower at the forest edge than 118 m into the forest interior (the farthest distance for grazed fragments). This relationship was similar for ungrazed fragments, with capture rates estimated to be 51% lower at the forest edge than 118 m into the forest interior. A subsequent path analysis suggested that these 'reverse' edge effects were largely or entirely mediated by changes in vegetation structure, implying that edge effects on ship rats can be predicted from the response of vegetation structure to forest edges. We suggest the occurrence, strength, and direction of edge effects on nest predation rates may depend on edge-driven changes in local habitat when the dominant predator is primarily restricted to forest patches.

Shark teeth as edged weapons: serrated teeth of three species of selachians.

PubMed

Moyer, Joshua K; Bemis, William E

2017-02-01

Prior to European contact, South Pacific islanders used serrated shark teeth as components of tools and weapons. They did this because serrated shark teeth are remarkably effective at slicing through soft tissues. To understand more about the forms and functions of serrated shark teeth, we examined the morphology and histology of tooth serrations in three species: the Tiger Shark (Galeocerdo cuvier), Blue Shark (Prionace glauca), and White Shark (Carcharodon carcharias). We show that there are two basic types of serrations. A primary serration consists of three layers of enameloid with underlying dentine filling the serration's base. All three species studied have primary serrations, although the dentine component differs (orthodentine in Tiger and Blue Sharks; osteodentine in the White Shark). Smaller secondary serrations are found in the Tiger Shark, formed solely by enameloid with no contribution from underlying dentine. Secondary serrations are effectively "serrations within serrations" that allow teeth to cut at different scales. We propose that the cutting edges of Tiger Shark teeth, equipped with serrations at different scales, are linked to a diet that includes large, hard-shelled prey (e.g., sea turtles) as well as smaller, softer prey such as fishes. We discuss other aspects of serration form and function by making analogies to man-made cutting implements, such as knives and saws. Copyright © 2016 Elsevier GmbH. All rights reserved.

Measurements of the Influence of Integral Length Scale on Stagnation Region Heat Transfer

NASA Technical Reports Server (NTRS)

Vanfossen, G. James; Ching, Chang Y.

1994-01-01

The purpose was twofold: first, to determine if a length scale existed that would cause the greatest augmentation in stagnation region heat transfer for a given turbulence intensity and second, to develop a prediction tool for stagnation heat transfer in the presence of free stream turbulence. Toward this end, a model with a circular leading edge was fabricated with heat transfer gages in the stagnation region. The model was qualified in a low turbulence wind tunnel by comparing measurements with Frossling's solution for stagnation region heat transfer in a laminar free stream. Five turbulence generating grids were fabricated; four were square mesh, biplane grids made from square bars. Each had identical mesh to bar width ratio but different bar widths. The fifth grid was an array of fine parallel wires that were perpendicular to the axis of the cylindrical leading edge. Turbulence intensity and integral length scale were measured as a function of distance from the grids. Stagnation region heat transfer was measured at various distances downstream of each grid. Data were taken at cylinder Reynolds numbers ranging from 42,000 to 193,000. Turbulence intensities were in the range 1.1 to 15.9 percent while the ratio of integral length scale to cylinder diameter ranged from 0.05 to 0.30. Stagnation region heat transfer augmentation increased with decreasing length scale. An optimum scale was not found. A correlation was developed that fit heat transfer data for the square bar grids to within +4 percent. The data from the array of wires were not predicted by the correlation; augmentation was higher for this case indicating that the degree of isotropy in the turbulent flow field has a large effect on stagnation heat transfer. The data of other researchers are also compared with the correlation.

Living beyond the edge: Higgs inflation and vacuum metastability

DOE PAGES

Bezrukov, Fedor; Rubio, Javier; Shaposhnikov, Mikhail

2015-10-13

The measurements of the Higgs mass and top Yukawa coupling indicate that we live in a very special universe, at the edge of the absolute stability of the electroweak vacuum. If fully stable, the Standard Model (SM) can be extended all the way up to the inflationary scale and the Higgs field, nonminimally coupled to gravity with strength ξ, can be responsible for inflation. We show that the successful Higgs inflation scenario can also take place if the SM vacuum is not absolutely stable. This conclusion is based on two effects that were overlooked previously. The first one is associatedmore » with the effective renormalization of the SM couplings at the energy scale M P/ξ, where M P is the Planck scale. Lastly, the second one is a symmetry restoration after inflation due to high temperature effects that leads to the (temporary) disappearance of the vacuum at Planck values of the Higgs field.« less

Long-lived Dust Asymmetries at Dead Zone Edges in Protoplanetary Disks

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

Miranda, Ryan; Li, Hui; Li, Shengtai

A number of transition disks exhibit significant azimuthal asymmetries in thermal dust emission. One possible origin for these asymmetries is dust trapping in vortices formed at the edges of dead zones. We carry out high-resolution, two-dimensional hydrodynamic simulations of this scenario, including the effects of dust feedback. We find that, although feedback weakens the vortices and slows down the process of dust accumulation, the dust distribution in the disk can nonetheless remain asymmetric for many thousands of orbits. We show that even after 10{sup 4} orbits, or 2.5 Myr when scaled to the parameters of Oph IRS 48 (a significantmore » fraction of its age), the dust is not dispersed into an axisymmetric ring, in contrast to the case of a vortex formed by a planet. This is because accumulation of mass at the dead zone edge constantly replenishes the vortex, preventing it from being fully destroyed. We produce synthetic dust emission images using our simulation results. We find that multiple small clumps of dust may be distributed azimuthally. These clumps, if not resolved from one another, appear as a single large feature. A defining characteristic of a disk with a dead zone edge is that an asymmetric feature is accompanied by a ring of dust located about twice as far from the central star.« less

Amount and type of forest cover and edge are important predictorsof golden-cheeked warbler density

Treesearch

Rebecca G. Peak; Frank R. III. Thompson

2013-01-01

Considered endangered by the U.S. Fish and Wildlife Service, the Golden-cheeked Warbler (Setophaga chrysoparia) breeds exclusively in the juniper--oak (Juniperus ashei--Quercus spp.) woodlands of central Texas. Large-scale, spatially explicit models that predict population density as a function of habitat and landscape variables...

Study Gives Edge to 2 Math Programs

ERIC Educational Resources Information Center

Viadero, Debra

2009-01-01

This article reports that two programs for teaching mathematics in the early grades--Math Expressions and Saxon Math--emerged as winners in early findings released last week from a large-scale federal experiment that pits four popular, and philosophically distinct, math curricula against one another. But the results don't promise to end the…

Broadband rotor noise analyses

NASA Technical Reports Server (NTRS)

George, A. R.; Chou, S. T.

1984-01-01

The various mechanisms which generate broadband noise on a range of rotors studied include load fluctuations due to inflow turbulence, due to turbulent boundary layers passing the blades' trailing edges, and due to tip vortex formation. Existing analyses are used and extensions to them are developed to make more accurate predictions of rotor noise spectra and to determine which mechanisms are important in which circumstances. Calculations based on the various prediction methods in existing experiments were compared. The present analyses are adequate to predict the spectra from a wide variety of experiments on fans, full scale and model scale helicopter rotors, wind turbines, and propellers to within about 5 to 10 dB. Better knowledge of the inflow turbulence improves the accuracy of the predictions. Results indicate that inflow turbulence noise depends strongly on ambient conditions and dominates at low frequencies. Trailing edge noise and tip vortex noise are important at higher frequencies if inflow turbulence is weak. Boundary layer trailing edge noise, important, for large sized rotors, increases slowly with angle of attack but not as rapidly as tip vortex noise.

An Automated Method of Scanning Probe Microscopy (SPM) Data Analysis and Reactive Site Tracking for Mineral-Water Interface Reactions Observed at the Nanometer Scale

NASA Astrophysics Data System (ADS)

Campbell, B. D.; Higgins, S. R.

2008-12-01

Developing a method for bridging the gap between macroscopic and microscopic measurements of reaction kinetics at the mineral-water interface has important implications in geological and chemical fields. Investigating these reactions on the nanometer scale with SPM is often limited by image analysis and data extraction due to the large quantity of data usually obtained in SPM experiments. Here we present a computer algorithm for automated analysis of mineral-water interface reactions. This algorithm automates the analysis of sequential SPM images by identifying the kinetically active surface sites (i.e., step edges), and by tracking the displacement of these sites from image to image. The step edge positions in each image are readily identified and tracked through time by a standard edge detection algorithm followed by statistical analysis on the Hough Transform of the edge-mapped image. By quantifying this displacement as a function of time, the rate of step edge displacement is determined. Furthermore, the total edge length, also determined from analysis of the Hough Transform, combined with the computed step speed, yields the surface area normalized rate of the reaction. The algorithm was applied to a study of the spiral growth of the calcite(104) surface from supersaturated solutions, yielding results almost 20 times faster than performing this analysis by hand, with results being statistically similar for both analysis methods. This advance in analysis of kinetic data from SPM images will facilitate the building of experimental databases on the microscopic kinetics of mineral-water interface reactions.

Relative role of subinertial and superinertial modes in the coastal long wave response forced by the landfall of a tropical cyclone

NASA Astrophysics Data System (ADS)

Ke, Ziming; Yankovsky, Alexander E.

2011-06-01

A set of numerical experiments has been performed in order to analyze the long-wave response of the coastal ocean to a translating mesoscale atmospheric cyclone approaching the coastline at a normal angle. An idealized two-slope shelf topography is chosen. The model is forced by a radially symmetric atmospheric pressure perturbation with a corresponding gradient wind field. The cyclone's translation speed, radius, and the continental shelf width are considered as parameters whose impact on the long wave period, modal structure, and amplitude is studied. Subinertial continental shelf waves (CSW) dominate the response under typical forcing conditions and on the narrower shelves. They propagate in the downstream (in the sense of Kelvin wave propagation) direction. Superinertial edge wave modes have higher free surface amplitudes and faster phase speeds than the CSW modes. While potentially more dangerous, edge waves are not as common as subinertial shelf waves because their generation requires a wide, gently sloping shelf and a storm system translating at a relatively high (˜10 m s -1 or faster) speed. A relatively smaller size of an atmospheric cyclone also favors edge wave generation. Edge waves with the highest amplitude (up to 60% of the forced storm surge) propagate upstream. They are produced by a storm system with an Eulerian time scale equal to the period of a zero-mode edge wave with the wavelength of the storm spatial scale. Large amplitude edge waves were generated during Hurricane Wilma's landfall (2005) on the West Florida shelf with particularly severe flooding occurring upstream of the landfall site.

Aerodynamic Effects of Simulated Ice Accretion on a Generic Transport Model

NASA Technical Reports Server (NTRS)

Broeren, Andy P.; Lee, Sam; Shah, Gautam H.; Murphy, Patrick C.

2012-01-01

An experimental research effort was begun to develop a database of airplane aerodynamic characteristics with simulated ice accretion over a large range of incidence and sideslip angles. Wind-tunnel testing was performed at the NASA Langley 12-ft Low-Speed Wind Tunnel using a 3.5 percent scale model of the NASA Langley Generic Transport Model. Aerodynamic data were acquired from a six-component force and moment balance in static-model sweeps from alpha = -5deg to 85deg and beta = -45 deg to 45 deg at a Reynolds number of 0.24 x10(exp 6) and Mach number of 0.06. The 3.5 percent scale GTM was tested in both the clean configuration and with full-span artificial ice shapes attached to the leading edges of the wing, horizontal and vertical tail. Aerodynamic results for the clean airplane configuration compared favorably with similar experiments carried out on a 5.5 percent scale GTM. The addition of the large, glaze-horn type ice shapes did result in an increase in airplane drag coefficient but had little effect on the lift and pitching moment. The lateral-directional characteristics showed mixed results with a small effect of the ice shapes observed in some cases. The flow visualization images revealed the presence and evolution of a spanwise-running vortex on the wing that was the dominant feature of the flowfield for both clean and iced configurations. The lack of ice-induced performance and flowfield effects observed in this effort was likely due to Reynolds number effects for the clean configuration. Estimates of full-scale baseline performance were included in this analysis to illustrate the potential icing effects.

Ocean-shelf interaction and exchange (Fridtjof Nansen Medal Lecture)

NASA Astrophysics Data System (ADS)

Huthnance, John M.

2016-04-01

A brief review will be given of physical processes where shallow shelf seas border the deep ocean, including waves that travel and propagate responses around the ocean boundary. Some implications for ocean-shelf exchange of water and its physical and biochemical contents will be discussed, along with an outline of some studies estimating these exchanges. There will be an emphasis on the north-west European shelf edge. A recent study is the project FASTNEt: "Fluxes across sloping topography of the North East Atlantic". This aims to resolve seasonal, interannual and regional variations. Novel and varied measurements have been made in three contrasting sectors of shelf edge: the Celtic Sea south-west of Britain, the Malin-Hebrides shelf west of Scotland and the West Shetland shelf north of Scotland. Previous studies established the existence of flow along the continental slope in these areas, more persistently poleward in northern sectors. Modelling aims to diagnose and estimate the contribution of various processes to transports and to exchange along and across the slope. Estimates obtained so far will be presented; overall transport from drifters and moored current meters; effective "diffusivity" from drifter dispersion and salinity surveys; other estimates of velocity variance contributing to exchange. In addition to transport by the along-slope flow, possible process contributions which may be estimated include internal waves and their Stokes drift, tidal pumping, eddies and Ekman transports, in a wind-driven surface layer and in a bottom boundary layer. Overall estimates of exchange across the shelf edge here are large by global standards, several m**2/s (Sverdrups per 1000 km). However, the large majority of this exchange is in tides and other motion of comparably short period, and is only effective for water properties or contents that evolve on a time-scale of a day or less.

Losing your edge: climate change and the conservation value of range-edge populations.

PubMed

Rehm, Evan M; Olivas, Paulo; Stroud, James; Feeley, Kenneth J

2015-10-01

Populations occurring at species' range edges can be locally adapted to unique environmental conditions. From a species' perspective, range-edge environments generally have higher severity and frequency of extreme climatic events relative to the range core. Under future climates, extreme climatic events are predicted to become increasingly important in defining species' distributions. Therefore, range-edge genotypes that are better adapted to extreme climates relative to core populations may be essential to species' persistence during periods of rapid climate change. We use relatively simple conceptual models to highlight the importance of locally adapted range-edge populations (leading and trailing edges) for determining the ability of species to persist under future climates. Using trees as an example, we show how locally adapted populations at species' range edges may expand under future climate change and become more common relative to range-core populations. We also highlight how large-scale habitat destruction occurring in some geographic areas where many species range edge converge, such as biome boundaries and ecotones (e.g., the arc of deforestation along the rainforest-cerrado ecotone in the southern Amazonia), can have major implications for global biodiversity. As climate changes, range-edge populations will play key roles in helping species to maintain or expand their geographic distributions. The loss of these locally adapted range-edge populations through anthropogenic disturbance is therefore hypothesized to reduce the ability of species to persist in the face of rapid future climate change.

Cloud-edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds

NASA Astrophysics Data System (ADS)

Kumar, Bipin; Bera, Sudarsan; Prabha, Thara V.; Grabowski, Wojceich W.

2017-03-01

A direct numerical simulation (DNS) with the decaying turbulence setup has been carried out to study cloud-edge mixing and its impact on the droplet size distribution (DSD) applying thermodynamic conditions observed in monsoon convective clouds over Indian subcontinent during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX). Evaporation at the cloud-edges initiates mixing at small scale and gradually introduces larger-scale fluctuations of the temperature, moisture, and vertical velocity due to droplet evaporation. Our focus is on early evolution of simulated fields that show intriguing similarities to the CAIPEEX cloud observations. A strong dilution at the cloud edge, accompanied by significant spatial variations of the droplet concentration, mean radius, and spectral width, are found in both the DNS and in observations. In DNS, fluctuations of the mean radius and spectral width come from the impact of small-scale turbulence on the motion and evaporation of inertial droplets. These fluctuations decrease with the increase of the volume over which DNS data are averaged, as one might expect. In cloud observations, these fluctuations also come from other processes, such as entrainment/mixing below the observation level, secondary CCN activation, or variations of CCN activation at the cloud base. Despite large differences in the spatial and temporal scales, the mixing diagram often used in entrainment/mixing studies with aircraft data is remarkably similar for both DNS and cloud observations. We argue that the similarity questions applicability of heuristic ideas based on mixing between two air parcels (that the mixing diagram is designed to properly represent) to the evolution of microphysical properties during turbulent mixing between a cloud and its environment.

Edge Response and NIIRS Estimates for Commercial Remote Sensing Satellites

NASA Technical Reports Server (NTRS)

Blonski, Slawomir; Ryan, Robert E.; Pagnutti, mary; Stanley, Thomas

2006-01-01

Spatial resolution of panchromatic imagery from commercial remote sensing satellites was characterized based on edge response measurements using edge targets and the tilted-edge technique. Relative Edge Response (RER) was estimated as a geometric mean of normalized edge response differences measured in two directions of image pixels at points distanced from the edge by -0.5 and 0.5 of ground sample distance. RER is one of the engineering parameters used in the General Image Quality Equation to provide predictions of imaging system performance expressed in terms of the National Imagery Interpretability Rating Scale (NIIRS). By assuming a plausible range of signal-to-noise ratio and assessing the effects of Modulation Transfer Function compensation, the NIIRS estimates were made and then compared with vendor-provided values and evaluations conducted by the National Geospatial-Intelligence Agency.

Quantifying edge effect extent and its impacts on carbon stocks across a degraded landscape in the Amazon using airborne lidar.

NASA Astrophysics Data System (ADS)

dos-Santos, M. N.; Keller, M.; Morton, D. C.; Longo, M.; Scaranello, M. A., Sr.; Pinagé, E. R.; Correa Pabon, R.

2017-12-01

Ongoing tropical forest degradation and forest fragmentation increases forest edge area. Forest edges experience hotter, drier, and windier conditions and greater exposure to fires compared to interior areas, which elevate rates of tree mortality. Previous studies have suggested that forests within 100 m from the edge may lose 36% of biomass during the first two decades following fragmentation, although such estimates are based on a limited number of experimental plots. Degraded forests behave differently from intact forests and quantifying edge effect extension in a degraded forest landscape is more challenging compared to experimental studies. To overcome these limitations, we used airborne lidar data to quantify changes in forest structure near 91 edges in a heavily degraded tropical forest in Paragominas Municipality, eastern Brazilian Amazon. Paragominas was a center of timber production in the 1990s. Today, the landscape is a mosaic of different agricultural uses, degraded, secondary and unmanaged forests. A total of 3000 ha of high density (mean density of 17.9 points/m2) lidar data were acquired in August/September 2013 and June/July 2014 over 30 transects (200 x 5000m), systematically distributed over the study area, using the Optech Orion M-200 laser scanning system. We adopted lidar-measured forest heights as the edge effect criteria and found that mean extent of edge effect was highly variable across degraded forests (150 ± 354m) and secondary forest fragments (265 ± 365m). We related the extent of forest edges to the historical disturbances identified in Landsat imagery since 1984. Contrary to previous studies, we found that carbon stocks along forest edges were not significantly lower than forest core biomass when edges were defined by previously estimated range of 100 and 300m. In frontier forests, ecological edge effect may be masked by the cumulative impact of historic forest degradation - an anthropogenic edge effect that extends beyond the scale of changes in forest microclimate from fragmentation.

Edge Effects along a Seagrass Margin Result in an Increased Grazing Risk on Posidonia australis Transplants.

PubMed

Statton, John; Gustin-Craig, Samuel; Dixon, Kingsley W; Kendrick, Gary A

2015-01-01

A key issue in habitat restoration are the changes in ecological processes that occur when fragments of habitat are lost, resulting in the persistence of habitat-degraded margins. Margins often create or enhance opportunities for negative plant-herbivore interactions, preventing natural or assisted re-establishment of native vegetation into the degraded area. However, at some distance from the habitat margin these negative interactions may relax. Here, we posit that the intensity of species interactions in a fragmented Posidonia australis seagrass meadow may be spatially dependent on proximity to the seagrass habitat edge, whereby the risk of grazing is high and the probability of survival of seagrass transplants is low. To test this, transplants were planted 2 m within the meadow, on the meadow edge at 0m, and at 2m, 10m, 30m, 50m and 100m distance from the edge of the seagrass meadow into the unvegetated sand sheet. There was an enhanced grazing risk 0-10m from the edge, but decreased sharply with increasing distances (>30m). Yet, the risk of grazing was minimal inside the seagrass meadow, indicating that grazers may use the seagrass meadow for refuge but are not actively grazing within it. The relationship between short-term herbivory risk and long-term survival was not straightforward, suggesting that other environmental filters are also affecting survival of P. australis transplants within the study area. We found that daily probability of herbivory was predictable and operating over a small spatial scale at the edge of a large, intact seagrass meadow. These findings highlight the risk from herbivory can be high, and a potential contributing factor to seagrass establishment in restoration programs.

Edge Effects along a Seagrass Margin Result in an Increased Grazing Risk on Posidonia australis Transplants

PubMed Central

Statton, John; Gustin-Craig, Samuel; Dixon, Kingsley W.; Kendrick, Gary A.

2015-01-01

A key issue in habitat restoration are the changes in ecological processes that occur when fragments of habitat are lost, resulting in the persistence of habitat-degraded margins. Margins often create or enhance opportunities for negative plant-herbivore interactions, preventing natural or assisted re-establishment of native vegetation into the degraded area. However, at some distance from the habitat margin these negative interactions may relax. Here, we posit that the intensity of species interactions in a fragmented Posidonia australis seagrass meadow may be spatially dependent on proximity to the seagrass habitat edge, whereby the risk of grazing is high and the probability of survival of seagrass transplants is low. To test this, transplants were planted 2 m within the meadow, on the meadow edge at 0m, and at 2m, 10m, 30m, 50m and 100m distance from the edge of the seagrass meadow into the unvegetated sand sheet. There was an enhanced grazing risk 0-10m from the edge, but decreased sharply with increasing distances (>30m). Yet, the risk of grazing was minimal inside the seagrass meadow, indicating that grazers may use the seagrass meadow for refuge but are not actively grazing within it. The relationship between short-term herbivory risk and long-term survival was not straightforward, suggesting that other environmental filters are also affecting survival of P. australis transplants within the study area. We found that daily probability of herbivory was predictable and operating over a small spatial scale at the edge of a large, intact seagrass meadow. These findings highlight the risk from herbivory can be high, and a potential contributing factor to seagrass establishment in restoration programs. PMID:26465926

Arthropods on plants in a fragmented Neotropical dry forest: a functional analysis of area loss and edge effects.

PubMed

González, Ezequiel; Salvo, Adriana; Valladares, Graciela

2015-02-01

Loss and fragmentation of natural ecosystems are widely recognized as the most important threats to biodiversity conservation, with Neotropical dry forests among the most endangered ecosystems. Area and edge effects are major factors in fragmented landscapes. Here, we examine area and edge effects and their interaction, on ensembles of arthropods associated to native vegetation in a fragmented Chaco Serrano forest. We analyzed family richness and community composition of herbivores, predators, and parasitoids on three native plant species in 12 fragments of varying size and at edge/interior positions. We also looked for indicator families by using Indicator Species Analysis. Loss of family richness with the reduction of forest fragment area was observed for the three functional groups, with similar magnitude. Herbivores were richer at the edges without interaction between edge and area effects, whereas predators were not affected by edge/interior position and parasitoid richness showed an interaction between area and position, with a steeper area slope at the edges. Family composition of herbivore, predator, and parasitoid assemblages was also affected by forest area and/or edge/interior situation. We found three indicator families for large remnants and five for edges. Our results support the key role of forest area for conservation of arthropods taxonomic and functional diversity in a highly threatened region, and emphasize the need to understand the interactions between area and edge effects on such diversity. © 2014 Institute of Zoology, Chinese Academy of Sciences.

Introduction of High Throughput Magnetic Resonance T2-Weighted Image Texture Analysis for WHO Grade 2 and 3 Gliomas.

PubMed

Kinoshita, Manabu; Sakai, Mio; Arita, Hideyuki; Shofuda, Tomoko; Chiba, Yasuyoshi; Kagawa, Naoki; Watanabe, Yoshiyuki; Hashimoto, Naoya; Fujimoto, Yasunori; Yoshimine, Toshiki; Nakanishi, Katsuyuki; Kanemura, Yonehiro

2016-01-01

Reports have suggested that tumor textures presented on T2-weighted images correlate with the genetic status of glioma. Therefore, development of an image analyzing framework that is capable of objective and high throughput image texture analysis for large scale image data collection is needed. The current study aimed to address the development of such a framework by introducing two novel parameters for image textures on T2-weighted images, i.e., Shannon entropy and Prewitt filtering. Twenty-two WHO grade 2 and 28 grade 3 glioma patients were collected whose pre-surgical MRI and IDH1 mutation status were available. Heterogeneous lesions showed statistically higher Shannon entropy than homogenous lesions (p = 0.006) and ROC curve analysis proved that Shannon entropy on T2WI was a reliable indicator for discrimination of homogenous and heterogeneous lesions (p = 0.015, AUC = 0.73). Lesions with well-defined borders exhibited statistically higher Edge mean and Edge median values using Prewitt filtering than those with vague lesion borders (p = 0.0003 and p = 0.0005 respectively). ROC curve analysis also proved that both Edge mean and median values were promising indicators for discrimination of lesions with vague and well defined borders and both Edge mean and median values performed in a comparable manner (p = 0.0002, AUC = 0.81 and p < 0.0001, AUC = 0.83, respectively). Finally, IDH1 wild type gliomas showed statistically lower Shannon entropy on T2WI than IDH1 mutated gliomas (p = 0.007) but no difference was observed between IDH1 wild type and mutated gliomas in Edge median values using Prewitt filtering. The current study introduced two image metrics that reflect lesion texture described on T2WI. These two metrics were validated by readings of a neuro-radiologist who was blinded to the results. This observation will facilitate further use of this technique in future large scale image analysis of glioma.

The effects of leading edge modifications on the post-stall characteristics of wings

NASA Technical Reports Server (NTRS)

Winkelmann, A. E.; Barlow, J. B.; Saini, J. K.; Anderson, J. D., Jr.; Jones, E.

1980-01-01

An investigation of the effects of leading edge modifications on the post-stall characteristics of two rectangular planform wings in a series of low speed wind tunnel tests is presented. Abrupt discontinuities in the leading edge shape of the wings were produced by placing a nose glove over a portion of the span or by deflecting sections of a segmented leading edge flap. Six component balance data, oil flow visualization photographs, and pressure distribution measurements were obtained, and tests made to study the development of flow separation at stall on small scale planform wing models. Results of oil flow visualization tests at and beyond stall showed the formation of counter-rotating swirl patterns on the upper surface of the '2-D' and '3-D' wings, and results of a numerical lifting line technique applied to wings with leading edge modifications are included.

Deterministic object tracking using Gaussian ringlet and directional edge features

NASA Astrophysics Data System (ADS)

Krieger, Evan W.; Sidike, Paheding; Aspiras, Theus; Asari, Vijayan K.

2017-10-01

Challenges currently existing for intensity-based histogram feature tracking methods in wide area motion imagery (WAMI) data include object structural information distortions, background variations, and object scale change. These issues are caused by different pavement or ground types and from changing the sensor or altitude. All of these challenges need to be overcome in order to have a robust object tracker, while attaining a computation time appropriate for real-time processing. To achieve this, we present a novel method, Directional Ringlet Intensity Feature Transform (DRIFT), which employs Kirsch kernel filtering for edge features and a ringlet feature mapping for rotational invariance. The method also includes an automatic scale change component to obtain accurate object boundaries and improvements for lowering computation times. We evaluated the DRIFT algorithm on two challenging WAMI datasets, namely Columbus Large Image Format (CLIF) and Large Area Image Recorder (LAIR), to evaluate its robustness and efficiency. Additional evaluations on general tracking video sequences are performed using the Visual Tracker Benchmark and Visual Object Tracking 2014 databases to demonstrate the algorithms ability with additional challenges in long complex sequences including scale change. Experimental results show that the proposed approach yields competitive results compared to state-of-the-art object tracking methods on the testing datasets.

Copper intercalation at the interface of graphene and Ir(111) studied by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Sicot, M.; Fagot-Revurat, Y.; Kierren, B.; Vasseur, G.; Malterre, D.

2014-11-01

We report on the intercalation of a submonolayer of copper at 775 K underneath graphene epitaxially grown on Ir(111) studied by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) at 77 K. Nucleation and growth dynamics of Cu below graphene have been investigated, and, most importantly, the intercalation mechanism has been identified. First, LEED patterns reveal the pseudomorphic growth of Cu on Ir under the topmost graphene layer resulting in a large Cu in-plane lattice parameter expansion of about 6% compared to Cu(111). Second, large-scale STM topographs as a function of Cu coverage show that Cu diffusion on Ir below graphene exhibits a low energy barrier resulting in Cu accumulation at Ir step edges. As a result, the graphene sheet undergoes a strong edges reshaping. Finally, atomically-resolved STM images reveal a damaged graphene sheet at the atomic scale after metal intercalation. Point defects in graphene were shown to be carbon vacancies. According to these results, a Cu penetration path beneath graphene is proposed to occur via metal aided defect formation with no or poor self healing of the graphene sheet. This work illustrates the fact that Cu intercalation is harmful for graphene grown on Ir(111) at the atomic scale.

Effect of Hardwood Sawmill Edging and Trimming Practices on Furniture Part Production

Treesearch

D. Earl Kline; Carmen Regalado; Eugene M. Wengert; Fred M. Lamb; Philip A. Araman

1993-01-01

In a recent edging and trimming study at three hardwood sawmills, it was observed that the lumber volume produced was approximately 10 percent less than would be necessary to make the most valuable lumber. Furthermore, the excess portion of wood that was removed from the edging and trimming process contained a large percentage of clear wood. In light of rising costs...

An Adaptive Immune Genetic Algorithm for Edge Detection

NASA Astrophysics Data System (ADS)

Li, Ying; Bai, Bendu; Zhang, Yanning

An adaptive immune genetic algorithm (AIGA) based on cost minimization technique method for edge detection is proposed. The proposed AIGA recommends the use of adaptive probabilities of crossover, mutation and immune operation, and a geometric annealing schedule in immune operator to realize the twin goals of maintaining diversity in the population and sustaining the fast convergence rate in solving the complex problems such as edge detection. Furthermore, AIGA can effectively exploit some prior knowledge and information of the local edge structure in the edge image to make vaccines, which results in much better local search ability of AIGA than that of the canonical genetic algorithm. Experimental results on gray-scale images show the proposed algorithm perform well in terms of quality of the final edge image, rate of convergence and robustness to noise.

Maximizing algebraic connectivity in air transportation networks

NASA Astrophysics Data System (ADS)

Wei, Peng

In air transportation networks the robustness of a network regarding node and link failures is a key factor for its design. An experiment based on the real air transportation network is performed to show that the algebraic connectivity is a good measure for network robustness. Three optimization problems of algebraic connectivity maximization are then formulated in order to find the most robust network design under different constraints. The algebraic connectivity maximization problem with flight routes addition or deletion is first formulated. Three methods to optimize and analyze the network algebraic connectivity are proposed. The Modified Greedy Perturbation Algorithm (MGP) provides a sub-optimal solution in a fast iterative manner. The Weighted Tabu Search (WTS) is designed to offer a near optimal solution with longer running time. The relaxed semi-definite programming (SDP) is used to set a performance upper bound and three rounding techniques are discussed to find the feasible solution. The simulation results present the trade-off among the three methods. The case study on two air transportation networks of Virgin America and Southwest Airlines show that the developed methods can be applied in real world large scale networks. The algebraic connectivity maximization problem is extended by adding the leg number constraint, which considers the traveler's tolerance for the total connecting stops. The Binary Semi-Definite Programming (BSDP) with cutting plane method provides the optimal solution. The tabu search and 2-opt search heuristics can find the optimal solution in small scale networks and the near optimal solution in large scale networks. The third algebraic connectivity maximization problem with operating cost constraint is formulated. When the total operating cost budget is given, the number of the edges to be added is not fixed. Each edge weight needs to be calculated instead of being pre-determined. It is illustrated that the edge addition and the weight assignment can not be studied separately for the problem with operating cost constraint. Therefore a relaxed SDP method with golden section search is developed to solve both at the same time. The cluster decomposition is utilized to solve large scale networks.

Size effects of nano-spaced basal stacking faults on the strength and deformation mechanisms of nanocrystalline pure hcp metals

NASA Astrophysics Data System (ADS)

Wang, Wen; Jiang, Ping; Yuan, Fuping; Wu, Xiaolei

2018-05-01

The size effects of nano-spaced basal stacking faults (SFs) on the tensile strength and deformation mechanisms of nanocrystalline pure cobalt and magnesium have been investigated by a series of large-scale 2D columnar and 3D molecular dynamics simulations. Unlike the strengthening effect of basal SFs on Mg alloys, the nano-spaced basal SFs are observed to have no strengthening effect on the nanocrystalline pure cobalt and magnesium from MD simulations. These observations could be attributed to the following two reasons: (i) Lots of new basal SFs are formed before (for cobalt) or simultaneously with (for magnesium) the other deformation mechanisms (i.e. the formation of twins and the < c + a > edge dislocations) during the tensile deformation; (ii) In hcp alloys, the segregation of alloy elements and impurities at typical interfaces, such as SFs, can stablilise them for enhancing the interactions with dislocation and thus elevating the strength. Without such segregation in pure hcp metals, the < c + a > edge dislocations can cut through the basal SFs although the interactions between the < c + a > dislocations and the pre-existing SFs/newly formed SFs are observed. The nano-spaced basal SFs are also found to have no restriction effect on the formation of deformation twins.

Augmentation of Stagnation Region Heat Transfer Due to Turbulence From a DLN Can Combustor

NASA Technical Reports Server (NTRS)

VanFossen, G. James; Bunker, Ronald S.

2000-01-01

Heat transfer measurements have been made in the stagnation region of a flat plate with a circular leading edge. Electrically heated aluminum strips placed symmetrically about the leading edge stagnation region were used to measure spanwise averaged heat transfer coefficients. The maximum Reynolds number obtained, based on leading edge diameter, was about 100,000. The model was immersed in the flow field downstream of an approximately half scale model of a can-type combustor from a low NO(x), ground based power-generating turbine. The tests were conducted with room temperature air; no fuel was added. Room air flowed into the combustor through six vane type fuel/air swirlers. The combustor can contained no dilution holes. The fuel/air swirlers all swirled the incoming airflow in a counter clockwise direction (facing downstream). A 5-hole probe flow field survey in the plane of the model stagnation point showed the flow was one big vortex with flow angles up to 36' at the outer edges of the rectangular test section. Hot wire measurements showed test section flow had very high levels of turbulence, around 28.5 percent, and had a relatively large axial-length scale-to-leading edge diameter ratio of 0.5. X-wire measurements showed the turbulence to be nearly isotropic. Stagnation heat transfer augmentation over laminar levels was around 77 percent and was about 14 percent higher than predicted by a previously developed correlation for isotropic grid generated turbulence.

Fundamental edge broadening effects during focused electron beam induced nanosynthesis

DOE PAGES

Schmied, Roland; Fowlkes, Jason Davidson; Winkler, Robert; ...

2015-02-16

In this study, we explore lateral broadening effects of 3D structures fabricated through focused electron beam induced deposition using MeCpPt(IV)Me 3 precursor. In particular, the scaling behavior of proximity effects as a function of the primary electron energy and the deposit height is investigated through experiments and validated through simulations. Correlated Kelvin force microscopy and conductive atomic force microscopy measurements identified conductive and non-conductive proximity regions. It was determined that the highest primary electron energies enable the highest edge sharpness while lower energies contain a complex convolution of broadening effects. In addition, it is demonstrated that intermediate energies lead tomore » even more complex proximity effects that significantly reduce lateral edge sharpness and thus should be avoided if desiring high lateral resolution.« less

SOL and Edge Flows in DIII-D

NASA Astrophysics Data System (ADS)

Boedo, J. A.; Degrassie, J. S.; Grierson, B. A.; Rudakov, D. A.

2015-11-01

Recent measurements at DIII-D edge plasmas at the outer midplane show that, in the absence of external torque, the edge and near-SOL plasma flow is largely dominated by the intrinsic source of rotation most likely due to thermal ion loss. We also show that when NBI heating is present, the core momentum competes with the edge intrinsic momentum and can overwhelm it, in short, NBI-heated discharges at high power tend to determine edge and near SOL flows. Experiments performed in the DIII-D tokamak with OH heated, ECH-heated and NBI-heated discharges are diagnosed for core plasma flow with CER and edge/SOL plasma flow with Mach probes. We have changed the amount of NBI, OH and ECH heating while scanning the discharge collisionality. We have compared the experimental measurements to two complementary thermal ion loss theories that explain most of the observed features, including a scaling with Ti. One theory considers passing and trapped particles that are lost via a loss cone purely due to drifts and the other considers turbulence-enhanced loss of passing particles. Work supported by the US DOE under DE-FC02-04ER54698, DE-FG02-07ER54917 and DE-AC02-09CH111466.

An edge-based solution-adaptive method applied to the AIRPLANE code

NASA Technical Reports Server (NTRS)

Biswas, Rupak; Thomas, Scott D.; Cliff, Susan E.

1995-01-01

Computational methods to solve large-scale realistic problems in fluid flow can be made more efficient and cost effective by using them in conjunction with dynamic mesh adaption procedures that perform simultaneous coarsening and refinement to capture flow features of interest. This work couples the tetrahedral mesh adaption scheme, 3D_TAG, with the AIRPLANE code to solve complete aircraft configuration problems in transonic and supersonic flow regimes. Results indicate that the near-field sonic boom pressure signature of a cone-cylinder is improved, the oblique and normal shocks are better resolved on a transonic wing, and the bow shock ahead of an unstarted inlet is better defined.

Amount of Future Forest Edge at a 2 Hectare Scale

EPA Pesticide Factsheets

Forests provide economic and ecological value. High amounts of forest edge indicates a highly fragmented forest, which generally diminishes those economic and ecological values. EDGE2 is the percent of forest that is classified as edge using a 2 ha scale. More information about these resources, including the variables used in this study, may be found here: https://edg.epa.gov/data/Public/ORD/NERL/ReVA/ReVA_Data.zip.

Amount of Future Forest Edge at a 65 Hectare scale

EPA Pesticide Factsheets

Forests provide economic and ecological value. High amounts of forest edge indicates a highly fragmented forest, which generally diminishes those economic and ecological values. EDGE65 is the percent of forest that is classified as edge using a 65 ha scale. More information about these resources, including the variables used in this study, may be found here: https://edg.epa.gov/data/Public/ORD/NERL/ReVA/ReVA_Data.zip.

Amount of Forest Edge at a 2 Hectare Scale

EPA Pesticide Factsheets

Forests provide economic and ecological value. High amounts of forest edge indicates a highly fragmented forest, which generally diminishes those economic and ecological values. EDGE2 is the percent of forest that is classified as edge using a 2 ha scale. More information about these resources, including the variables used in this study, may be found here: https://edg.epa.gov/data/Public/ORD/NERL/ReVA/ReVA_Data.zip.

Amount of Forest Edge at a 65 Hectare Scale

EPA Pesticide Factsheets

Forests provide economic and ecological value. High amounts of forest edge indicates a highly fragmented forest, which generally diminishes those economic and ecological values. EDGE65 is the percent of forest that is classified as edge using a 65 ha scale. More information about these resources, including the variables used in this study, may be found here: https://edg.epa.gov/data/Public/ORD/NERL/ReVA/ReVA_Data.zip.

Enhanced viscous flow drag reduction using acoustic excitation

NASA Technical Reports Server (NTRS)

Nagel, R. T.

1988-01-01

Large eddy break up devices (LEBUs) constitute a promising method of obtaining drag reduction in a turbulent boundary layer. Enhancement of the LEBU effectiveness by exciting its trailing edge with acoustic waves phase locked to the large scale structure influencing the momentum transfer to the wall is sought. An initial estimate of the required sound pressure level for an effective pulse was obtained by considering the magnitude of the pressure perturbations at the near wake of a thin plate in inviscid flow. Detailed skin friction measurments were obtained in the flow region downstream of a LEBU excited with acoustic waves. The data are compared with skin friction measurements of a simply manipulated flow, without acoustic excitation and with a plain flow configuration. The properties and the scales of motion in the flow regime downstream of the acoustically excited LEBU are studied. A parametric study based upon the characteristics of the acoustic input was pursued in addition to the careful mapping of the drag reduction phenomenon within the acoustically manipulated boundary layer. This study of boundary layer manipulation has lead to improved skin friction drag reduction and further understanding of the turbulent boundary layer.

A study on efficient detection of network-based IP spoofing DDoS and malware-infected Systems.

PubMed

Seo, Jung Woo; Lee, Sang Jin

2016-01-01

Large-scale network environments require effective detection and response methods against DDoS attacks. Depending on the advancement of IT infrastructure such as the server or network equipment, DDoS attack traffic arising from a few malware-infected systems capable of crippling the organization's internal network has become a significant threat. This study calculates the frequency of network-based packet attributes and analyzes the anomalies of the attributes in order to detect IP-spoofed DDoS attacks. Also, a method is proposed for the effective detection of malware infection systems triggering IP-spoofed DDoS attacks on an edge network. Detection accuracy and performance of the collected real-time traffic on a core network is analyzed thru the use of the proposed algorithm, and a prototype was developed to evaluate the performance of the algorithm. As a result, DDoS attacks on the internal network were detected in real-time and whether or not IP addresses were spoofed was confirmed. Detecting hosts infected by malware in real-time allowed the execution of intrusion responses before stoppage of the internal network caused by large-scale attack traffic.

Plant biodiversity in French Mediterranean vineyards

NASA Astrophysics Data System (ADS)

Cohen, Marianne; Bilodeau, Clelia; Alexandre, Frédéric; Godron, Michel; Gresillon, Etienne

2017-04-01

In a context of agricultural intensification and increasing urbanization, the biodiversity of farmed plots is a key to improve the sustainability of farmed landscapes. The medium life-duration of the vineyards as well as their location in Mediterranean region are favorable to plant biodiversity. We studied 35 vineyards and if present, their edges, located in three French Mediterranean terroirs: Bandol, Pic Saint Loup and Terrasses du Larzac. We collected botanical information (floral richness et diversity, biological traits), and analyzed their relationships with different factors: social (management, heritage or professional concern), environmental (slope, exposition, geology), spatial (edges, surrounding landscape in a 500 meters radius, distance to the nearest large city). Vineyards are generally heavily disturbed by intensive practices like tilling and application of herbicides, and for this reason their floral diversity is low. This is particularly true in Bandol terroir, in accordance with the standards of the Bandol PDO wine sector. Farmed landscapes and proximity to a large town impact on functional groups, generalist species being overrepresented. If vineyards are surrounded with natural edges, it doubles the floral richness at the plot and edges scale. Species present in vineyards edges are perennial herbaceous species with Euro- Asian and Mediterranean distribution ranges characteristic of prairie and wasteland stages, increasing the functional diversity of vineyards (generalist species). Environmental factors have a lower influence: vineyards are generally located on flat lands. These results suggest that some practices should be encouraged to avoid the biological degradation of vineyards: conservation of tree-lined edges and their extensive management, reduction of chemical weeding, grass-growing using non-cosmopolitan species. These recommendations should also contribute to soil conservation.

Novel analysis technique for measuring edge density fluctuation profiles with reflectometry in the Large Helical Device.

PubMed

Creely, A J; Ida, K; Yoshinuma, M; Tokuzawa, T; Tsujimura, T; Akiyama, T; Sakamoto, R; Emoto, M; Tanaka, K; Michael, C A

2017-07-01

A new method for measuring density fluctuation profiles near the edge of plasmas in the Large Helical Device (LHD) has been developed utilizing reflectometry combined with pellet-induced fast density scans. Reflectometer cutoff location was calculated by proportionally scaling the cutoff location calculated with fast far infrared laser interferometer (FIR) density profiles to match the slower time resolution results of the ray-tracing code LHD-GAUSS. Plasma velocity profile peaks generated with this reflectometer mapping were checked against velocity measurements made with charge exchange spectroscopy (CXS) and were found to agree within experimental uncertainty once diagnostic differences were accounted for. Measured density fluctuation profiles were found to peak strongly near the edge of the plasma, as is the case in most tokamaks. These measurements can be used in the future to inform inversion methods of phase contrast imaging (PCI) measurements. This result was confirmed with both a fixed frequency reflectometer and calibrated data from a multi-frequency comb reflectometer, and this method was applied successfully to a series of discharges. The full width at half maximum of the turbulence layer near the edge of the plasma was found to be only 1.5-3 cm on a series of LHD discharges, less than 5% of the normalized minor radius.

Novel analysis technique for measuring edge density fluctuation profiles with reflectometry in the Large Helical Device

NASA Astrophysics Data System (ADS)

Creely, A. J.; Ida, K.; Yoshinuma, M.; Tokuzawa, T.; Tsujimura, T.; Akiyama, T.; Sakamoto, R.; Emoto, M.; Tanaka, K.; Michael, C. A.

2017-07-01

A new method for measuring density fluctuation profiles near the edge of plasmas in the Large Helical Device (LHD) has been developed utilizing reflectometry combined with pellet-induced fast density scans. Reflectometer cutoff location was calculated by proportionally scaling the cutoff location calculated with fast far infrared laser interferometer (FIR) density profiles to match the slower time resolution results of the ray-tracing code LHD-GAUSS. Plasma velocity profile peaks generated with this reflectometer mapping were checked against velocity measurements made with charge exchange spectroscopy (CXS) and were found to agree within experimental uncertainty once diagnostic differences were accounted for. Measured density fluctuation profiles were found to peak strongly near the edge of the plasma, as is the case in most tokamaks. These measurements can be used in the future to inform inversion methods of phase contrast imaging (PCI) measurements. This result was confirmed with both a fixed frequency reflectometer and calibrated data from a multi-frequency comb reflectometer, and this method was applied successfully to a series of discharges. The full width at half maximum of the turbulence layer near the edge of the plasma was found to be only 1.5-3 cm on a series of LHD discharges, less than 5% of the normalized minor radius.

A study of high-lift airfoils at high Reynolds numbers in the Langley low-turbulence pressure tunnel

NASA Technical Reports Server (NTRS)

Morgan, Harry L., Jr.; Ferris, James C.; Mcghee, Robert J.

1987-01-01

An experimental study was conducted in the Langley Low Turbulence Pressure Tunnel to determine the effects of Reynolds number and Mach number on the two-dimensional aerodynamic performance of two supercritical type airfoils, one equipped with a conventional flap system and the other with an advanced high lift flap system. The conventional flap system consisted of a leading edge slat and a double slotted, trailing edge flap with a small chord vane and a large chord aft flap. The advanced flap system consisted of a leading edge slat and a double slotted, trailing edge flap with a large chord vane and a small chord aft flap. Both models were tested with all elements nested to form the cruise airfoil and with the leading edge slat and with a single or double slotted, trailing edge flap deflected to form the high lift airfoils. The experimental tests were conducted through a Reynolds number range from 2.8 to 20.9 x 1,000,000 and a Mach number range from 0.10 to 0.35. Lift and pitching moment data were obtained. Summaries of the test results obtained are presented and comparisons are made between the observed aerodynamic performance trends for both models. The results showing the effect of leading edge frost and glaze ice formation is given.

Evolving network simulation study. From regular lattice to scale free network

NASA Astrophysics Data System (ADS)

Makowiec, D.

2005-12-01

The Watts-Strogatz algorithm of transferring the square lattice to a small world network is modified by introducing preferential rewiring constrained by connectivity demand. The evolution of the network is two-step: sequential preferential rewiring of edges controlled by p and updating the information about changes done. The evolving system self-organizes into stationary states. The topological transition in the graph structure is noticed with respect to p. Leafy phase a graph formed by multiple connected vertices (graph skeleton) with plenty of leaves attached to each skeleton vertex emerges when p is small enough to pretend asynchronous evolution. Tangling phase where edges of a graph circulate frequently among low degree vertices occurs when p is large. There exist conditions at which the resulting stationary network ensemble provides networks which degree distribution exhibit power-law decay in large interval of degrees.

Mapping of the Resistance of a Superconducting Transition Edge Sensor as a Function of Temperature, Current, and Applied Magnetic Field

NASA Technical Reports Server (NTRS)

Zhang, Shou; Eckart, Megan E.; Jaeckel, Felix; Kripps, Kari L.; McCammon, Dan; Zhou, Yu; Morgan, Kelsey M.

2017-01-01

We have measured the resistance R (T, I, B(sub ext) of a superconducting transition edge sensor over the entire transition region on a fine scale, producing a four-dimensional map of the resistance surface. The dimensionless temperature and current sensitivities (alpha equivalence partial derivative log R/partial derivative log T|(sub I) and beta equivalence partial derivative log R/partial derivative log I|(sub T) of the TES resistance have been determined at each point. alpha and beta are closely related to the sensor performance, but show a great deal of complex, large amplitude fine structure over large portions of the surface that is sensitive to the applied magnetic field. We discuss the relation of this structure to the presence of Josephson weak link fringes.

Competitive adsorption of a binary CO2-CH4 mixture in nanoporous carbons: effects of edge-functionalization.

PubMed

Lu, Xiaoqing; Jin, Dongliang; Wei, Shuxian; Zhang, Mingmin; Zhu, Qing; Shi, Xiaofan; Deng, Zhigang; Guo, Wenyue; Shen, Wenzhong

2015-01-21

The effect of edge-functionalization on the competitive adsorption of a binary CO2-CH4 mixture in nanoporous carbons (NPCs) has been investigated for the first time by combining density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulation. Our results show that edge-functionalization has a more positive effect on the single-component adsorption of CO2 than CH4, therefore significantly enhancing the selectivity of CO2 over CH4, in the order of NH2-NPC > COOH-NPC > OH-NPC > H-NPC > NPC at low pressure. The enhanced adsorption originates essentially from the effects of (1) the conducive environment with a large pore size and an effective accessible surface area, (2) the high electronegativity/electropositivity, (3) the strong adsorption energy, and (4) the large electrostatic contribution, due to the inductive effect/direct interaction of the embedded edge-functionalized groups. The larger difference from these effects results in the higher competitive adsorption advantage of CO2 in the binary CO2-CH4 mixture. Temperature has a negative effect on the gas adsorption, but no obvious influence on the electrostatic contribution on selectivity. With the increase of pressure, the selectivity of CO2 over CH4 first decreases sharply and subsequently flattens out to a constant value. This work highlights the potential of edge-functionalized NPCs in competitive adsorption, capture, and separation for the binary CO2-CH4 mixture, and provides an effective and superior alternative strategy in the design and screening of adsorbent materials for carbon capture and storage.

Edge-induced Schottky barrier modulation at metal contacts to exfoliated molybdenum disulfide flakes

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

Nouchi, Ryo, E-mail: r-nouchi@21c.osakafu-u.ac.jp

2016-08-14

Ultrathin two-dimensional semiconductors obtained from layered transition-metal dichalcogenides such as molybdenum disulfide (MoS{sub 2}) are promising for ultimately scaled transistors beyond Si. Although the shortening of the semiconductor channel is widely studied, the narrowing of the channel, which should also be important for scaling down the transistor, has been examined to a lesser degree thus far. In this study, the impact of narrowing on mechanically exfoliated MoS{sub 2} flakes was investigated according to the channel-width-dependent Schottky barrier heights at Cr/Au contacts. Narrower channels were found to possess a higher Schottky barrier height, which is ascribed to the edge-induced band bendingmore » in MoS{sub 2}. The higher barrier heights degrade the transistor performance as a higher electrode-contact resistance. Theoretical analyses based on Poisson's equation showed that the edge-induced effect can be alleviated by a high dopant impurity concentration, but this strategy should be limited to channel widths of roughly 0.7 μm because of the impurity-induced charge-carrier mobility degradation. Therefore, proper termination of the dangling bonds at the edges should be necessary for aggressive scaling with layered semiconductors.« less

Installation to Production of a Large-Scale General Purpose Graphics Processing Unit (GPGPU) Cluster at the U.S. Army Research Laboratory: Thufir

DTIC Science & Technology

2014-09-01

semiempirical and ray-optical models. For example, the semiempirical COST-Walfisch- Ikegami model (3) estimates the received power predominantly on the...Books: Philadelphia, PA, 1965. 2. Rick, T .; Mathur, R. Fast Edge-Diffraction-Based Radio Wave Propagation Model for Graphics Hardware. Proceedings of

Large-deflection theory for end compression of long rectangular plates rigidly clamped along two edges

NASA Technical Reports Server (NTRS)

Levy, Samuel; Krupen, Philip

1943-01-01

The von Karman equations for flat plates are solved beyond the buckling load up to edge strains equal to eight time the buckling strain, for the extreme case of rigid clamping along the edges parallel to the load. Deflections, bending stresses, and membrane stresses are given as a function of end compressive load. The theoretical values of effective width are compared with the values derived for simple support along the edges parallel to the load. The increases in effective width due to rigid clamping drops from about 20 percent near the buckling strain to about 8 percent at an edge strain equal to eight times the buckling strain. Experimental values of effective width in the elastic range reported in NACA Technical Note No. 684 are between the theoretical curves for the extremes of simple support and rigid clamping.

Quality detection system and method of micro-accessory based on microscopic vision

NASA Astrophysics Data System (ADS)

Li, Dongjie; Wang, Shiwei; Fu, Yu

2017-10-01

Considering that the traditional manual detection of micro-accessory has some problems, such as heavy workload, low efficiency and large artificial error, a kind of quality inspection system of micro-accessory has been designed. Micro-vision technology has been used to inspect quality, which optimizes the structure of the detection system. The stepper motor is used to drive the rotating micro-platform to transfer quarantine device and the microscopic vision system is applied to get graphic information of micro-accessory. The methods of image processing and pattern matching, the variable scale Sobel differential edge detection algorithm and the improved Zernike moments sub-pixel edge detection algorithm are combined in the system in order to achieve a more detailed and accurate edge of the defect detection. The grade at the edge of the complex signal can be achieved accurately by extracting through the proposed system, and then it can distinguish the qualified products and unqualified products with high precision recognition.

Using Multiple Watershed-scale Dye Tracing Tests to Study Water and Solute Transport in Naturally Obstructed Stream Channels

NASA Astrophysics Data System (ADS)

Jin, L.; Meeks, J. L.; Hubbard, K. A.; Kurian, L. M.; Siegel, D. I.; Lautz, L. K.; Otz, M. H.

2007-12-01

Temporary storage of surface water at channel sides and pools significantly affects water and solute transport downstream in watersheds. Beavers, natural "stream channel engineers", build dams which obstruct stream flow and temporarily store water in small to large ponds within stream channels. These ponds substantially delay water movement and increase the water residence time in the system. To study how water and solutes move through these obstructed stream channels, we did multiple dye tracing tests at Cherry Creek, a main tributary to Red Canyon Creek (Wind River Range, Wyoming). First we surveyed beaver dam distributions in detail within the study reaches. We then introduced dyes four times from July 2nd to 6th, 2007 using a scale-up approach. The observation site was fixed at the mouth of Cherry Creek, and 1.5 grams of Rhodamine WT (RWT) dye was injected sequentially at upstream sites with increasing test reach length. The reach lengths scaled up from 500m to 2.5 km. A field fluorometer recorded RWT concentrations every 15 seconds. The results show non-linear decreases of the peak concentration of the dye tracing cloud as the reach scaled up. Also, the times to 1.) the arrivals of the leading edges (Tl), 2.) the peak concentrations (Tp) and 3.) the tailing edges (Tt) and 4) the durations of the tracer cloud (Td) behaved non-linearly as function of length scale. For example, plots of arrivals of leading edges and tailing edges with scale distance appear to define curves of the form; Tl=27.665e1.07× Distance (r2=0.99) and Tt=162.62e0.8551× Distance (r2=0.99), respectively. The greatest non-linearity occurred for the time of tailing and the least for the time of leading edge. These observations are consistent with what would be expected with greater density of dams and/or storage volumes as the reach length increased upgradient. To come to a first approximation, we are currently modeling the breakthrough curves with the solute transport code OTIS to address the relative differences in average travel velocity, longitudinal dispersion, and storage parameters from the mouth to the headwaters of the creek.

Quasi-steady solar wind dynamics

NASA Technical Reports Server (NTRS)

Pizzo, V. J.

1983-01-01

Progress in understanding the large scale dynamics of quasisteady, corotating solar wind structure was reviewed. The nature of the solar wind at large heliocentric distances preliminary calculations from a 2-D MHD model are used to demonstrate theoretical expectations of corotating structure out to 30 AU. It is found that the forward and reverse shocks from adjacent CIR's begin to interact at about 10 AU, producing new shock pairs flanking secondary CIR's. These sawtooth secondary CIR's interact again at about 20 AU and survive as visible entities to 30 AU. The model predicts the velocity jumps at the leading edge of the secondary CIR's at 30 AU should be very small but there should still be sizable variations in the thermodynamic and magnetic parameters. The driving dynamic mechanism in the distant solar wind is the relaxation of pressure gradients. The second topic is the influence of weak, nonimpulsive time dependence in quasisteady dynamics. It is suggested that modest large scale variations in the coronal flow speed on periods of several hours to a day may be responsible for many of the remaining discrepancies between theory and observation. Effects offer a ready explanation for the apparent rounding of stream fronts between 0.3 and 1.0 AU discovered by Helios.

3-D plasma boundary and plasma wall interaction research at UW-Madison

NASA Astrophysics Data System (ADS)

Schmitz, Oliver; Akerson, Adrian; Bader, Aaron; Barbui, Tullio; Effenberg, Florian; Flesch, Kurt; Frerichs, Heinke; Green, Jonathan; Hinson, Edward; Kremeyer, Thierry; Norval, Ryan; Stephey, Laurie; Waters, Ian; Winters, Victoria

2016-10-01

The necessity of considering 3-D effects on the plasma boundary and plasma wall interaction (PWI) in tokamaks, stellarators and reversed field pinches has been highlighted by abundant experimental and numerical results in the recent past. Prominent examples with 3-D boundary situations are numerous: ELM controlled H-modes by RMP fields in tokamaks, research on boundary plasmas and PWI in stellarators in general, quasi-helical states in RFPs, asymmetric fueling situations, and structural and wall elements which are not aligned with the magnetic guiding fields. A systematic approach is being taken at UW-Madison to establish a targeted experimental basis for identifying the most significant effects for plasma edge transport and resulting PWI in such 3-D plasma boundary situations. We deploy advanced 3-D modeling using the EMC3-EIRENE, ERO and MCI codes in combination with laboratory experiments at UW-Madison to investigate the relevance of 3-D effects in large scale devices with a concerted approach on DIII-D, NSTX-U, and Wendelstein 7-X. Highlights of experimental results from the on-site laboratory activities at UW-Madison and the large scale facilities are presented and interlinks will be discussed. This work was supported by US DOE DE-SC0013911, DE-SC00012315 and DE-SC00014210.

Area-based tests for association between spatial patterns

NASA Astrophysics Data System (ADS)

Maruca, Susan L.; Jacquez, Geoffrey M.

Edge effects pervade natural systems, and the processes that determine spatial heterogeneity (e.g. physical, geochemical, biological, ecological factors) occur on diverse spatial scales. Hence, tests for association between spatial patterns should be unbiased by edge effects and be based on null spatial models that incorporate the spatial heterogeneity characteristic of real-world systems. This paper develops probabilistic pattern association tests that are appropriate when edge effects are present, polygon size is heterogeneous, and the number of polygons varies from one classification to another. The tests are based on the amount of overlap between polygons in each of two partitions. Unweighted and area-weighted versions of the statistics are developed and verified using scenarios representing both polygon overlap and avoidance at different spatial scales and for different distributions of polygon sizes. These statistics were applied to Soda Butte Creek, Wyoming, to determine whether stream microhabitats, such as riffles, pools and glides, can be identified remotely using high spatial resolution hyperspectral imagery. These new ``spatially explicit'' techniques provide information and insights that cannot be obtained from the spectral information alone.

Temperate forest fragments maintain aboveground carbon stocks out to the forest edge despite changes in community composition.

PubMed

Ziter, Carly; Bennett, Elena M; Gonzalez, Andrew

2014-11-01

Edge effects are among the primary mechanisms by which forest fragmentation can influence the link between biodiversity and ecosystem processes, but relatively few studies have quantified these mechanisms in temperate regions. Carbon storage is an important ecosystem function altered by edge effects, with implications for climate change mitigation. Two opposing hypotheses suggest that aboveground carbon (AGC) stocks at the forest edge will (a) decrease due to increased tree mortality and compositional shifts towards smaller, lower wood density species (e.g., as seen in tropical systems) or, less often, (b) increase due to light/temperature-induced increases in diversity and productivity. We used field-based measurements, allometry, and mixed models to investigate the effects of proximity to the forest edge on AGC stocks, species richness, and community composition in 24 forest fragments in southern Quebec. We also asked whether fragment size or connectivity with surrounding forests altered these edge effects. AGC stocks remained constant across a 100 m edge-to-interior gradient in all fragment types, despite changes in tree community composition and stem density consistent with expectations of forest edge effects. We attribute this constancy primarily to compensatory effects of small trees at the forest edge; however, it is due in some cases to the retention of large trees at forest edges, likely a result of forest management. Our results suggest important differences between temperate and tropical fragments with respect to mechanisms linking biodiversity and AGC dynamics. Small temperate forest fragments may be valuable in conservation efforts based on maintaining biodiversity and multiple ecosystem services.

Edge effects on morphometrics and body mass in two sympatric species of mouse lemurs in Madagascar.

PubMed

Burke, Ryan J; Lehman, Shawn M

2014-01-01

Edge effects are an inevitable and important consequence of forest loss and fragmentation. These effects include changes in species biology and biogeography. Here we examine variations in body mass and morphometrics for 2 sympatric species of mouse lemurs (Microcebus murinus and M. ravelobensis) between edge and interior habitats in the dry deciduous forest at Ankarafantsika National Park. Between May and August 2012, we conducted mark-recapture experiments on mouse lemurs trapped along edge and interior forest transects within continuous forest adjacent to a large savannah. Of the 34 M. murinus captured during our study, 82% (n = 28) were trapped in interior habitats. Conversely, 72% (n = 47) of M. ravelobensis were captured in edge habitats. We found that mean body mass of M. murinus and M. ravelobensis did not differ between edge and interior habitats. However, female M. ravelobensis weighed significantly more in edge habitats (56.09 ± 1.74 g) than in interior habitats (48.14 ± 4.44 g). Our study provides some of the first evidence of sex differences in edge responses for a primate species. © 2015 S. Karger AG, Basel.

Global-scale patterns of forest fragmentation

USGS Publications Warehouse

Riitters, K.; Wickham, J.; O'Neill, R.; Jones, B.; Smith, E.

2000-01-01

We report an analysis of forest fragmentation based on 1-km resolution land-cover maps for the globe. Measurements in analysis windows from 81 km 2 (9 ?? 9 pixels, "small" scale) to 59,049 km 2 (243 ?? 243 pixels, "large" scale) were used to characterize the fragmentation around each forested pixel. We identified six categories of fragmentation (interior, perforated, edge, transitional, patch, and undetermined) from the amount of forest and its occurrence as adjacent forest pixels. Interior forest exists only at relatively small scales; at larger scales, forests are dominated by edge and patch conditions. At the smallest scale, there were significant differences in fragmentation among continents; within continents, there were significant differences among individual forest types. Tropical rain forest fragmentation was most severe in North America and least severe in Europe - Asia. Forest types with a high percentage of perforated conditions were mainly in North America (five types) and Europe - Asia (four types), in both temperate and subtropical regions. Transitional and patch conditions were most common in 11 forest types, of which only a few would be considered as "naturally patchy" (e.g., dry woodland). The five forest types with the highest percentage of interior conditions were in North America; in decreasing order, they were cool rain forest, coniferous, conifer boreal, cool mixed, and cool broadleaf. Copyright ?? 2000 by The Resilience Alliance.

An Amazonian rainforest and its fragments as a laboratory of global change.

PubMed

Laurance, William F; Camargo, José L C; Fearnside, Philip M; Lovejoy, Thomas E; Williamson, G Bruce; Mesquita, Rita C G; Meyer, Christoph F J; Bobrowiec, Paulo E D; Laurance, Susan G W

2018-02-01

We synthesize findings from one of the world's largest and longest-running experimental investigations, the Biological Dynamics of Forest Fragments Project (BDFFP). Spanning an area of ∼1000 km 2 in central Amazonia, the BDFFP was initially designed to evaluate the effects of fragment area on rainforest biodiversity and ecological processes. However, over its 38-year history to date the project has far transcended its original mission, and now focuses more broadly on landscape dynamics, forest regeneration, regional- and global-change phenomena, and their potential interactions and implications for Amazonian forest conservation. The project has yielded a wealth of insights into the ecological and environmental changes in fragmented forests. For instance, many rainforest species are naturally rare and hence are either missing entirely from many fragments or so sparsely represented as to have little chance of long-term survival. Additionally, edge effects are a prominent driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage and a diversity of fauna. Even within our controlled study area, the landscape has been highly dynamic: for example, the matrix of vegetation surrounding fragments has changed markedly over time, succeeding from large cattle pastures or forest clearcuts to secondary regrowth forest. This, in turn, has influenced the dynamics of plant and animal communities and their trajectories of change over time. In general, fauna and flora have responded differently to fragmentation: the most locally extinction-prone animal species are those that have both large area requirements and low tolerance of the modified habitats surrounding fragments, whereas the most vulnerable plants are those that respond poorly to edge effects or chronic forest disturbances, and that rely on vulnerable animals for seed dispersal or pollination. Relative to intact forests, most fragments are hyperdynamic, with unstable or fluctuating populations of species in response to a variety of external vicissitudes. Rare weather events such as droughts, windstorms and floods have had strong impacts on fragments and left lasting legacies of change. Both forest fragments and the intact forests in our study area appear to be influenced by larger-scale environmental drivers operating at regional or global scales. These drivers are apparently increasing forest productivity and have led to concerted, widespread increases in forest dynamics and plant growth, shifts in tree-community composition, and increases in liana (woody vine) abundance. Such large-scale drivers are likely to interact synergistically with habitat fragmentation, exacerbating its effects for some species and ecological phenomena. Hence, the impacts of fragmentation on Amazonian biodiversity and ecosystem processes appear to be a consequence not only of local site features but also of broader changes occurring at landscape, regional and even global scales. © 2017 Cambridge Philosophical Society.

Anisotropic scene geometry resampling with occlusion filling for 3DTV applications

NASA Astrophysics Data System (ADS)

Kim, Jangheon; Sikora, Thomas

2006-02-01

Image and video-based rendering technologies are receiving growing attention due to their photo-realistic rendering capability in free-viewpoint. However, two major limitations are ghosting and blurring due to their sampling-based mechanism. The scene geometry which supports to select accurate sampling positions is proposed using global method (i.e. approximate depth plane) and local method (i.e. disparity estimation). This paper focuses on the local method since it can yield more accurate rendering quality without large number of cameras. The local scene geometry has two difficulties which are the geometrical density and the uncovered area including hidden information. They are the serious drawback to reconstruct an arbitrary viewpoint without aliasing artifacts. To solve the problems, we propose anisotropic diffusive resampling method based on tensor theory. Isotropic low-pass filtering accomplishes anti-aliasing in scene geometry and anisotropic diffusion prevents filtering from blurring the visual structures. Apertures in coarse samples are estimated following diffusion on the pre-filtered space, the nonlinear weighting of gradient directions suppresses the amount of diffusion. Aliasing artifacts from low density are efficiently removed by isotropic filtering and the edge blurring can be solved by the anisotropic method at one process. Due to difference size of sampling gap, the resampling condition is defined considering causality between filter-scale and edge. Using partial differential equation (PDE) employing Gaussian scale-space, we iteratively achieve the coarse-to-fine resampling. In a large scale, apertures and uncovered holes can be overcoming because only strong and meaningful boundaries are selected on the resolution. The coarse-level resampling with a large scale is iteratively refined to get detail scene structure. Simulation results show the marked improvements of rendering quality.

Spatial Variation in Transpiration Within a Small Forest Patch in Hoa Binh, Northern Vietnam

NASA Astrophysics Data System (ADS)

Giambelluca, T. W.; Ziegler, A. D.; Nullet, M. A.; Dao, T. M.

2001-12-01

We conducted measurements of small-scale variations in microclimate and sapflow within and near a small forest patch in Ban Tat Hamlet, Hoa Binh, northern Vietnam. Our observations provide evidence of the influences of surrounding clearings on forest patch microclimate and transpiration. The effects of proximity to the forest edge can be seen in the gradients in temperature, humidity, wind, and soil moisture content. Sapflow measurements in sample trees strongly indicate that transpiration rates are higher near the edge of the patch (edge effect). This effect is seen in the averages for the whole study period, despite infrequent wind flow into the instrumented edge of the patch. Edge effect is observed during both dry and wet periods, but is most apparent on days when solar and net radiation are high, relative humidity is low, or wind direction is from the clearing into the forest edge. These conditions are conducive to high positive heat advection from the clearing to the forest edge. Transpiration in both edge and interior trees is highly correlated with conditions in the clearing. Our results suggest that greater land-cover fragmentation tends to increase regional evaporative flux, i.e. fragmentation of remaining forested areas partly reverses the reduction in regional evaporation due to deforestation. We can infer from the distance-to-edge dependency of transpiration that the magnitude of this regional effect depends on the size, shape, and spatial distribution of landscape patches. It is also likely that the replacement land cover and moisture status of the clearings affect this process. Although we found slightly greater edge effect during the dry period of our observations, it is possible that under more prolonged or severe dry conditions, the soil moisture storage at the forest edge would become depleted leading to a reversal the transpiration pattern. >http://webdata.soc.hawaii.edu/climate/Frags/Frags.html

Facebook and its effects on users' empathic social skills and life satisfaction: a double-edged sword effect.

PubMed

Chan, Terri H

2014-05-01

This study examines how Facebook usage affects individual's empathic social skills and life satisfaction. Following the self-presentational theory, the study explores a key component of the Internet paradox-whether Facebook suppresses or enhances users' interpersonal competence (specifically empathic social skills), given their respective personality makeup. Going further, the study assesses these events' subsequent impacts on users' psychological well-being. Analogous to a double-edged sword, Facebook activities are hypothesized to suppress the positive effect of a user's extraversion orientation on empathic social skills but lessen the negative effect of neuroticism on these skills. The study examines a sample of college-aged Facebook users (n=515), who responded to a large-scale online survey. The findings from a structural equation modeling analysis indicate that while empathic social skills are positively associated with life satisfaction, Facebook activities mainly exert suppression effects. Only upon low usage can Facebook activities lessen the negative effect of neuroticism on empathic social skills, suggesting that Facebook may appear as a less threatening platform for social interactions among neurotics. Yet, results in general suggest that undesirable effects may occur at high levels of Facebook usage whereby both extroverted and neurotic users displace real world social ties to online ones. The findings point to the complex ways in which social media usage may impact the livelihood of users.

Drought and heatwaves in Europe: historical reconstruction and future projections

NASA Astrophysics Data System (ADS)

Samaniego, Luis; Thober, Stephan; Kumar, Rohini; Rakovec, Olda; Wood, Eric; Sheffield, Justin; Pan, Ming; Wanders, Niko; Prudhomme, Christel

2017-04-01

Heat waves and droughts are creeping hydro-meteorological events that may bring societies and natural systems to their limits by inducing large famines, increasing health risks to the population, creating drinking and irrigation water shortfalls, inducing natural fires and degradation of soil and water quality, and in many cases causing large socio-economic losses. Europe, in particular, has endured large scale drought-heat-wave events during the recent past (e.g., 2003 European drought), which have induced enormous socio-economic losses as well as casualties. Recent studies showed that the prediction of droughts and heatwaves is subject to large-scale forcing and parametric uncertainties that lead to considerable uncertainties in the projections of extreme characteristics such as drought magnitude/duration and area under drought, among others. Future projections are also heavily influenced by the RCP scenario uncertainty as well as the coarser spatial resolution of the models. The EDgE project funded by the Copernicus programme (C3S) provides an unique opportunity to investigate the evolution of droughts and heatwaves from 1950 until 2099 over the Pan-EU domain at a scale of 5x5 km2. In this project, high-resolution multi-model hydrologic simulations with the mHM (www.ufz.de/mhm), Noah-MP, VIC and PCR-GLOBWB have been completed for the historical period 1955-2015. Climate projections have been carried out with five CMIP-5 GCMs: GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, MIROC-ESM-CHEM, NorESM1-M from 2006 to 2099 under RCP2.6 and RCP8.5. Using these multi-model unprecedented simulations, daily soil moisture index and temperature anomalies since 1955 until 2099 will be estimated. Using the procedure proposed by Samaniego et al. (2013), the probabilities of exceeding the benchmark events in the reference period 1980-2010 will be estimated for each RCP scenario. References http://climate.copernicus.eu/edge-end-end-demonstrator-improved-decision-making-water-sector-europe Samaniego, L., R. Kumar, and M. Zink, 2013: Implications of parameter uncertainty on soil moisture drought analysis in Germany. J. Hydrometeor., 14, 47-68, doi:10.1175/JHM-D-12-075.1. Samaniego, L., et al. 2016: Propagation of forcing and model uncertainties on to hydrological drought characteristics in a multi-model century-long experiment in large river basins. Climatic Change. 1-15.

The Effects of the Critical Ice Accretion on Airfoil and Wing Performance

NASA Technical Reports Server (NTRS)

Selig, Michael S.; Bragg, Michael B.; Saeed, Farooq

1998-01-01

In support of the NASA Lewis Modern Airfoils Ice Accretion Test Program, the University of Illinois at Urbana-Champaign provided expertise in airfoil design and aerodynamic analysis to determine the aerodynamic effect of ice accretion on modern airfoil sections. The effort has concentrated on establishing a design/testing methodology for "hybrid airfoils" or "sub-scale airfoils," that is, airfoils having a full-scale leading edge together with a specially designed and foreshortened aft section. The basic approach of using a full-scale leading edge with a foreshortened aft section was considered to a limited extent over 40 years ago. However, it was believed that the range of application of the method had not been fully exploited. Thus a systematic study was being undertaken to investigate and explore the range of application of the method so as to determine its overall potential.

Finding community structure in very large networks

NASA Astrophysics Data System (ADS)

Clauset, Aaron; Newman, M. E. J.; Moore, Cristopher

2004-12-01

The discovery and analysis of community structure in networks is a topic of considerable recent interest within the physics community, but most methods proposed so far are unsuitable for very large networks because of their computational cost. Here we present a hierarchical agglomeration algorithm for detecting community structure which is faster than many competing algorithms: its running time on a network with n vertices and m edges is O(mdlogn) where d is the depth of the dendrogram describing the community structure. Many real-world networks are sparse and hierarchical, with mtilde n and dtilde logn , in which case our algorithm runs in essentially linear time, O(nlog2n) . As an example of the application of this algorithm we use it to analyze a network of items for sale on the web site of a large on-line retailer, items in the network being linked if they are frequently purchased by the same buyer. The network has more than 400 000 vertices and 2×106 edges. We show that our algorithm can extract meaningful communities from this network, revealing large-scale patterns present in the purchasing habits of customers.

Isotope effects on L-H threshold and confinement in tokamak plasmas

NASA Astrophysics Data System (ADS)

Maggi, C. F.; Weisen, H.; Hillesheim, J. C.; Chankin, A.; Delabie, E.; Horvath, L.; Auriemma, F.; Carvalho, I. S.; Corrigan, G.; Flanagan, J.; Garzotti, L.; Keeling, D.; King, D.; Lerche, E.; Lorenzini, R.; Maslov, M.; Menmuir, S.; Saarelma, S.; Sips, A. C. C.; Solano, E. R.; Belonohy, E.; Casson, F. J.; Challis, C.; Giroud, C.; Parail, V.; Silva, C.; Valisa, M.; Contributors, JET

2018-01-01

The dependence of plasma transport and confinement on the main hydrogenic ion isotope mass is of fundamental importance for understanding turbulent transport and, therefore, for accurate extrapolations of confinement from present tokamak experiments, which typically use a single hydrogen isotope, to burning plasmas such as ITER, which will operate in deuterium-tritium mixtures. Knowledge of the dependence of plasma properties and edge transport barrier formation on main ion species is critical in view of the initial, low-activation phase of ITER operations in hydrogen or helium and of its implications on the subsequent operation in deuterium-tritium. The favourable scaling of global energy confinement time with isotope mass, which has been observed in many tokamak experiments, remains largely unexplained theoretically. Moreover, the mass scaling observed in experiments varies depending on the plasma edge conditions. In preparation for upcoming deuterium-tritium experiments in the JET tokamak with the ITER-like Be/W Wall (JET-ILW), a thorough experimental investigation of isotope effects in hydrogen, deuterium and tritium plasmas is being carried out, in order to provide stringent tests of plasma energy, particle and momentum transport models. Recent hydrogen and deuterium isotope experiments in JET-ILW on L-H power threshold, L-mode and H-mode confinement are reviewed and discussed in the context of past and more recent isotope experiments in tokamak plasmas, highlighting common elements as well as contrasting observations that have been reported. The experimental findings are discussed in the context of fundamental aspects of plasma transport models.

Full-scale-wind-tunnel Tests of a 35 Degree Sweptback Wing Airplane with High-velocity Blowing over the Training-edge Flaps

NASA Technical Reports Server (NTRS)

Kelley, Mark W; Tolhurst, William H JR

1955-01-01

A wind-tunnel investigation was made to determine the effects of ejecting high-velocity air near the leading edge of plain trailing-edge flaps on a 35 degree sweptback wing. The tests were made with flap deflections from 45 degrees to 85 degrees and with pressure ratios across the flap nozzles from sub-critical up to 2.9. A limited study of the effects of nozzle location and configuration on the efficiency of the flap was made. Measurements of the lift, drag, and pitching moment were made for Reynolds numbers from 5.8 to 10.1x10(6). Measurements were also made of the weight rate of flow, pressure, and temperature of the air supplied to the flap nozzles.The results show that blowing on the deflected flap produced large flap lift increments. The amount of air required to prevent flow separation on the flap was significantly less than that estimated from published two-dimensional data. When the amount of air ejected over the flap was just sufficient to prevent flow separation, the lift increment obtained agreed well with linear inviscid fluid theory up to flap deflections of 60 degrees. The flap lift increment at 85 degrees flap deflection was about 80 percent of that predicted theoretically.With larger amounts of air blown over the flap, these lift increments could be significantly increased. It was found that the performance of the flap was relatively insensitive to the location of the flap nozzle, to spacers in the nozzle, and to flow disturbances such as those caused by leading-edge slats or discontinuities on the wing or flap surfaces. Analysis of the results indicated that installation of this system on an F-86 airplane is feasible.

Scalable Preconditioners for Structure Preserving Discretizations of Maxwell Equations in First Order Form

DOE PAGES

Phillips, Edward Geoffrey; Shadid, John N.; Cyr, Eric C.

2018-05-01

Here, we report multiple physical time-scales can arise in electromagnetic simulations when dissipative effects are introduced through boundary conditions, when currents follow external time-scales, and when material parameters vary spatially. In such scenarios, the time-scales of interest may be much slower than the fastest time-scales supported by the Maxwell equations, therefore making implicit time integration an efficient approach. The use of implicit temporal discretizations results in linear systems in which fast time-scales, which severely constrain the stability of an explicit method, can manifest as so-called stiff modes. This study proposes a new block preconditioner for structure preserving (also termed physicsmore » compatible) discretizations of the Maxwell equations in first order form. The intent of the preconditioner is to enable the efficient solution of multiple-time-scale Maxwell type systems. An additional benefit of the developed preconditioner is that it requires only a traditional multigrid method for its subsolves and compares well against alternative approaches that rely on specialized edge-based multigrid routines that may not be readily available. Lastly, results demonstrate parallel scalability at large electromagnetic wave CFL numbers on a variety of test problems.« less

Scalable Preconditioners for Structure Preserving Discretizations of Maxwell Equations in First Order Form

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

Phillips, Edward Geoffrey; Shadid, John N.; Cyr, Eric C.

Here, we report multiple physical time-scales can arise in electromagnetic simulations when dissipative effects are introduced through boundary conditions, when currents follow external time-scales, and when material parameters vary spatially. In such scenarios, the time-scales of interest may be much slower than the fastest time-scales supported by the Maxwell equations, therefore making implicit time integration an efficient approach. The use of implicit temporal discretizations results in linear systems in which fast time-scales, which severely constrain the stability of an explicit method, can manifest as so-called stiff modes. This study proposes a new block preconditioner for structure preserving (also termed physicsmore » compatible) discretizations of the Maxwell equations in first order form. The intent of the preconditioner is to enable the efficient solution of multiple-time-scale Maxwell type systems. An additional benefit of the developed preconditioner is that it requires only a traditional multigrid method for its subsolves and compares well against alternative approaches that rely on specialized edge-based multigrid routines that may not be readily available. Lastly, results demonstrate parallel scalability at large electromagnetic wave CFL numbers on a variety of test problems.« less

Material/element-dependent fluorescence-yield modes on soft X-ray absorption spectroscopy of cathode materials for Li-ion batteries

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

Asakura, Daisuke; Hosono, Eiji; Nanba, Yusuke

2016-03-07

Here, we evaluate the utilities of fluorescence-yield (FY) modes in soft X-ray absorption spectroscopy (XAS) of several cathodematerials for Li-ion batteries. In the case of total-FY (TFY) XAS for LiNi 0.5Mn 1.5O 4, the line shape of the Mn L 3-edge XAS was largely distorted by the self-absorption and saturation effects, while the distortions were less pronounced at the Ni L 3 edge. The distortions were suppressed for the inverse-partial-FY (IPFY) spectra. We found that, in the cathodematerials, the IPFY XAS is highly effective for the Cr, Mn, and Fe L edges and the TFY and PFY modes are usefulmore » enough for the Ni L edge which is far from the O K edge.« less

THERMODYNAMICS OF THE COMA CLUSTER OUTSKIRTS

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

Simionescu, A.; Werner, N.; Urban, O.

2013-09-20

We present results from a large mosaic of Suzaku observations of the Coma Cluster, the nearest and X-ray brightest hot ({approx}8 keV), dynamically active, non-cool core system, focusing on the thermodynamic properties of the intracluster medium on large scales. For azimuths not aligned with an infalling subcluster toward the southwest, our measured temperature and X-ray brightness profiles exhibit broadly consistent radial trends, with the temperature decreasing from about 8.5 keV at the cluster center to about 2 keV at a radius of 2 Mpc, which is the edge of our detection limit. The southwest merger significantly boosts the surface brightness,more » allowing us to detect X-ray emission out to {approx}2.2 Mpc along this direction. Apart from the southwestern infalling subcluster, the surface brightness profiles show multiple edges around radii of 30-40 arcmin. The azimuthally averaged temperature profile, as well as the deprojected density and pressure profiles, all show a sharp drop consistent with an outwardly-propagating shock front located at 40 arcmin, corresponding to the outermost edge of the giant radio halo observed at 352 MHz with the Westerbork Synthesis Radio Telescope. The shock front may be powering this radio emission. A clear entropy excess inside of r{sub 500} reflects the violent merging events linked with these morphological features. Beyond r{sub 500}, the entropy profiles of the Coma Cluster along the relatively relaxed directions are consistent with the power-law behavior expected from simple models of gravitational large-scale structure formation. The pressure is also in agreement at these radii with the expected values measured from Sunyaev-Zel'dovich data from the Planck satellite. However, due to the large uncertainties associated with the Coma Cluster measurements, we cannot yet exclude an entropy flattening in this system consistent with that seen in more relaxed cool core clusters.« less

Vortex Flows at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Wood, Richard M.; Wilcox, Floyd J., Jr.; Bauer, Steven X. S.; Allen, Jerry M.

2003-01-01

A review of research conducted at the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) into high-speed vortex flows during the 1970s, 1980s, and 1990s is presented. The data are for flat plates, cavities, bodies, missiles, wings, and aircraft with Mach numbers of 1.5 to 4.6. Data are presented to show the types of vortex structures that occur at supersonic speeds and the impact of these flow structures on vehicle performance and control. The data show the presence of both small- and large-scale vortex structures for a variety of vehicles, from missiles to transports. For cavities, the data show very complex multiple vortex structures exist at all combinations of cavity depth to length ratios and Mach number. The data for missiles show the existence of very strong interference effects between body and/or fin vortices. Data are shown that highlight the effect of leading-edge sweep, leading-edge bluntness, wing thickness, location of maximum thickness, and camber on the aerodynamics of and flow over delta wings. Finally, a discussion of a design approach for wings that use vortex flows for improved aerodynamic performance at supersonic speeds is presented.

Characterisation of edge turbulence in relation to edge magnetic field configuration in L-mode plasmas in the Mega Amp Spherical Tokamak.

NASA Astrophysics Data System (ADS)

Dewhurst, J.; Hnat, B.; Dudson, B.; Dendy, R. O.; Counsell, G. F.; Kirk, A.

2007-12-01

Almost all astrophysical and magnetically confined fusion plasmas are turbulent. Here, we examine ion saturation current (Isat) measurements of edge plasma turbulence for three MAST L-mode plasmas that differ primarily in their edge magnetic field configurations. First, absolute moments of the coarse grained data are examined to obtain accurate values of scaling exponents. The dual scaling behaviour is identified in all samples, with the temporal scale τ ≍ 40-60 μs separating the two regimes. Strong universality is then identified in the functional form of the probability density function (PDF) for Isat fluctuations, which is well approximated by the Fréchet distribution on temporal scales τ ≤ 40μs. For temporal scales τ > 40μs, the PDFs appear to converge to the Gumbel distribution, which has been previously identified as a universal feature of many other complex phenomena. The optimal fitting parameters k=1.15 for Fréchet and a=1.35 for Gumbel provide a simple quantitative characterisation of the full spectrum of fluctuations. We conclude that, to good approximation, the properties of the edge turbulence are independent of the edge magnetic field configuration.

Characterization of edge turbulence in relation to edge magnetic field configuration in Ohmic L-mode plasmas in the Mega Amp Spherical Tokamak

NASA Astrophysics Data System (ADS)

Hnat, B.; Dudson, B. D.; Dendy, R. O.; Counsell, G. F.; Kirk, A.; MAST Team

2008-08-01

Ion saturation current (Isat) measurements of edge plasma turbulence are analysed for six MAST L-mode plasmas that differ primarily in their edge magnetic field configurations. The analysis techniques are designed to capture the strong nonlinearities of the datasets. First, absolute moments of the data are examined to obtain accurate values of scaling exponents. This confirms dual scaling behaviour in all samples, with the temporal scale τ ≈ 40-60 µs separating the two regimes. Strong universality is then identified in the functional form of the probability density function (PDF) for Isat fluctuations, which is well approximated by the Fréchet distribution on temporal scales τ <= 40 µs. For temporal scales τ > 40 µs, the PDFs appear to converge to the Gumbel distribution, which has been previously identified as a universal feature of many other complex phenomena. The optimal fitting parameters k = 1.15 for Fréchet and a = 1.35 for Gumbel provide a simple quantitative characterization of the full spectrum of fluctuations. It is concluded that, to good approximation, the properties of the edge turbulence are independent of the edge magnetic field configuration.

The effects of patch shape on indigo buntings. Evidence for an ecological trap

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

Weldon, Aimee J.; Haddad, Nick M.

2005-01-01

Weldon, Aimee, J., and Nick M. Haddad. 2005. The effect of patch shape on indigo buntings: Evidence for an ecological trap. Ecology 86(6):1422-1431. Abstract. Habitat loss and fragmentation have led to a widespread increase in the proportion of edge habitat in the landscape. Disturbance-dependent bird species are widely assumed to benefit from these edges. However, anthropogenic edges may concentrate nest predators while retaining habitat cues that birds use to select breeding habitat. This may lead birds to mistakenly select dangerous habitat a phenomenon known as an ecological trap. We experimentally demonstrated how habitat shape, and thus amount of edge, canmore » adversely affect nest site selection and reproductive success of a disturbance-dependent bird species, the Indigo Bunting (Passerina cyanea). We did so within a landscape-scale experiment composed of equal-area habitat patches that differed in their amount of edge. Indigo Buntings preferentially selected edgy patches, which contained 50% more edge than more compact rectangular patches. Further, buntings fledged significantly fewer young per pair in edgy patches than in rectangular patches. These results provide the first experimental evidence that edges can function as ecological traps.« less

Investigation of Prussian Blue Analogs by XMCD at the K-edge of transition metals

NASA Astrophysics Data System (ADS)

Bordage, A.; Nataf, L.; Baudelet, F.; Bleuzen, A.

2016-05-01

Despite transition metal (TM) K-edge x-ray magnetic circular dichroism (XMCD) seems an interesting tool to get magnetic and structural information at the atomic scale, the effects originating this signal are still poorly understood. We thus initiated a deep investigation of the TM K-edge XMCD using Prussian Blue analogs (PBA) as model-compounds. In a recent study of the NiFe PBA family, we demonstrated that the XMCD signals at the TM K-edges strongly vary with external (mechanical) or internal (chemical) pressure and so that they are highly sensitive to small structural distortions. Following these first results, we extended this approach to the MnFe and CoFe families to evaluate the effect of electronic parameters (number of unpaired electrons of the M II TM) on the XMCD signal. All the results set milestones in the disentanglement of the components originating the XMCD signals at the K-edge of TM and will eventually help in a better understanding of the photomagnetic properties of PBAs.

Restricted cross-scale habitat selection by American beavers.

PubMed

Francis, Robert A; Taylor, Jimmy D; Dibble, Eric; Strickland, Bronson; Petro, Vanessa M; Easterwood, Christine; Wang, Guiming

2017-12-01

Animal habitat selection, among other ecological phenomena, is spatially scale dependent. Habitat selection by American beavers Castor canadensis (hereafter, beaver) has been studied at singular spatial scales, but to date no research addresses multi-scale selection. Our objectives were to determine if beaver habitat selection was specialized to semiaquatic habitats and if variables explaining habitat selection are consistent between landscape and fine spatial scales. We built maximum entropy (MaxEnt) models to relate landscape-scale presence-only data to landscape variables, and used generalized linear mixed models to evaluate fine spatial scale habitat selection using global positioning system (GPS) relocation data. Explanatory variables between the landscape and fine spatial scale were compared for consistency. Our findings suggested that beaver habitat selection at coarse (study area) and fine (within home range) scales was congruent, and was influenced by increasing amounts of woody wetland edge density and shrub edge density, and decreasing amounts of open water edge density. Habitat suitability at the landscape scale also increased with decreasing amounts of grass frequency. As territorial, central-place foragers, beavers likely trade-off open water edge density (i.e., smaller non-forested wetlands or lodges closer to banks) for defense and shorter distances to forage and obtain construction material. Woody plants along edges and expanses of open water for predator avoidance may limit beaver fitness and subsequently determine beaver habitat selection.

Restricted cross-scale habitat selection by American beavers

PubMed Central

Taylor, Jimmy D; Dibble, Eric; Strickland, Bronson; Petro, Vanessa M; Easterwood, Christine; Wang, Guiming

2017-01-01

Abstract Animal habitat selection, among other ecological phenomena, is spatially scale dependent. Habitat selection by American beavers Castor canadensis (hereafter, beaver) has been studied at singular spatial scales, but to date no research addresses multi-scale selection. Our objectives were to determine if beaver habitat selection was specialized to semiaquatic habitats and if variables explaining habitat selection are consistent between landscape and fine spatial scales. We built maximum entropy (MaxEnt) models to relate landscape-scale presence-only data to landscape variables, and used generalized linear mixed models to evaluate fine spatial scale habitat selection using global positioning system (GPS) relocation data. Explanatory variables between the landscape and fine spatial scale were compared for consistency. Our findings suggested that beaver habitat selection at coarse (study area) and fine (within home range) scales was congruent, and was influenced by increasing amounts of woody wetland edge density and shrub edge density, and decreasing amounts of open water edge density. Habitat suitability at the landscape scale also increased with decreasing amounts of grass frequency. As territorial, central-place foragers, beavers likely trade-off open water edge density (i.e., smaller non-forested wetlands or lodges closer to banks) for defense and shorter distances to forage and obtain construction material. Woody plants along edges and expanses of open water for predator avoidance may limit beaver fitness and subsequently determine beaver habitat selection. PMID:29492032

SPIDER: CMB Polarimetry from the Edge of Space

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

Gualtieri, R.; et al.

SPIDER is a balloon-borne instrument designed to map the polarization of the millimeter-wave sky at large angular scales. SPIDER targets the B-mode signature of primordial gravitational waves in the cosmic microwave background (CMB), with a focus on mapping a large sky area with high fidelity at multiple frequencies. SPIDER's first longduration balloon (LDB) flight in January 2015 deployed a total of 2400 antenna-coupled Transition Edge Sensors (TESs) at 90 GHz and 150 GHz. In this work we review the design and in-flight performance of the SPIDER instrument, with a particular focus on the measured performance of the detectors and instrumentmore » in a space-like loading and radiation environment. SPIDER's second flight in December 2018 will incorporate payload upgrades and new receivers to map the sky at 285 GHz, providing valuable information for cleaning polarized dust emission from CMB maps.« less

Scalable Triadic Analysis of Large-Scale Graphs: Multi-Core vs. Multi-Processor vs. Multi-Threaded Shared Memory Architectures

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

Chin, George; Marquez, Andres; Choudhury, Sutanay

2012-09-01

Triadic analysis encompasses a useful set of graph mining methods that is centered on the concept of a triad, which is a subgraph of three nodes and the configuration of directed edges across the nodes. Such methods are often applied in the social sciences as well as many other diverse fields. Triadic methods commonly operate on a triad census that counts the number of triads of every possible edge configuration in a graph. Like other graph algorithms, triadic census algorithms do not scale well when graphs reach tens of millions to billions of nodes. To enable the triadic analysis ofmore » large-scale graphs, we developed and optimized a triad census algorithm to efficiently execute on shared memory architectures. We will retrace the development and evolution of a parallel triad census algorithm. Over the course of several versions, we continually adapted the code’s data structures and program logic to expose more opportunities to exploit parallelism on shared memory that would translate into improved computational performance. We will recall the critical steps and modifications that occurred during code development and optimization. Furthermore, we will compare the performances of triad census algorithm versions on three specific systems: Cray XMT, HP Superdome, and AMD multi-core NUMA machine. These three systems have shared memory architectures but with markedly different hardware capabilities to manage parallelism.« less

CFD-based aero-optical analysis of flow fields over two-dimensional cavities with active flow control

NASA Astrophysics Data System (ADS)

Tan, Yan

Prediction and control of optical wave front distortions and aberrations in a high energy laser beam due to interaction with an unsteady highly non-uniform flow field is of great importance in the development of directed energy weapon systems for Unmanned Air Vehicles (UAV). The unsteady shear layer over the weapons bay cavity is the primary cause of this distortion of the optical wave front. The large scale vortical structure of the shear layer over the cavity can be significantly reduced by employing an active flow control technique combined with passive flow control. This dissertation explores various active and passive control methods to suppress the cavity oscillations and thereby improve the aero-optics of cavity flow. In active flow control technique, a steady or a pulsed jet is applied at the sharp leading edge of cavities of different aspect ratios L/D (=2, 4, 15), where L and D are the width and the depth of a cavity respectively. In the passive flow control approach, the sharp leading or trailing edge of the cavity is modified into a round edge of different radii. Both of these active and passive flow control approaches are studied independently and in combination. Numerical simulations are performed, with and without active flow control for subsonic free stream flow past two-dimensional sharp and round leading or trailing edge cavities using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a two-equation Shear Stress Transport (SST) turbulence model or a hybrid SST/Large Eddy Simulation (LES) model. Aero-optical analysis is developed and applied to all the simulation cases. Index of refraction and Optical Path Difference (OPD) are compared for flow fields without and with active flow control. Root-Mean-Square (RMS) value of OPD is calculated and compared with the experimental data, where available. The effect of steady and pulsed blowing on buffet loading on the downstream face of the cavity is also computed. Using the numerical simulations, the most effective approach for controlling the cavity oscillations and aero-optical signatures is determined.

An Examination of Not-For-Profit Stakeholder Networks for Relationship Management: A Small-Scale Analysis on Social Media.

PubMed

Wyllie, Jessica; Lucas, Benjamin; Carlson, Jamie; Kitchens, Brent; Kozary, Ben; Zaki, Mohamed

2016-01-01

Using a small-scale descriptive network analysis approach, this study highlights the importance of stakeholder networks for identifying valuable stakeholders and the management of existing stakeholders in the context of mental health not-for-profit services. We extract network data from the social media brand pages of three health service organizations from the U.S., U.K., and Australia, to visually map networks of 579 social media brand pages (represented by nodes), connected by 5,600 edges. This network data is analyzed using a collection of popular graph analysis techniques to assess the differences in the way each of the service organizations manage stakeholder networks. We also compare node meta-information against basic topology measures to emphasize the importance of effectively managing relationships with stakeholders who have large external audiences. Implications and future research directions are also discussed.

An Examination of Not-For-Profit Stakeholder Networks for Relationship Management: A Small-Scale Analysis on Social Media

PubMed Central

Carlson, Jamie; Kitchens, Brent; Kozary, Ben; Zaki, Mohamed

2016-01-01

Using a small-scale descriptive network analysis approach, this study highlights the importance of stakeholder networks for identifying valuable stakeholders and the management of existing stakeholders in the context of mental health not-for-profit services. We extract network data from the social media brand pages of three health service organizations from the U.S., U.K., and Australia, to visually map networks of 579 social media brand pages (represented by nodes), connected by 5,600 edges. This network data is analyzed using a collection of popular graph analysis techniques to assess the differences in the way each of the service organizations manage stakeholder networks. We also compare node meta-information against basic topology measures to emphasize the importance of effectively managing relationships with stakeholders who have large external audiences. Implications and future research directions are also discussed. PMID:27711236

Structural characteristics of the shock-induced boundary layer separation extended to the leading edge

NASA Astrophysics Data System (ADS)

Tao, Y.; Liu, W. D.; Fan, X. Q.; Zhao, Y. L.

2017-07-01

For a better understanding of the local unstart of supersonic/hypersonic inlet, a series of experiments has been conducted to investigate the shock-induced boundary layer separation extended to the leading edge. Using the nanoparticle-based planar laser scattering, we recorded the fine structures of these interactions under different conditions and paid more attention to their structural characteristics. According to their features, these interactions could be divided into four types. Specifically, Type A wave pattern is similar to the classic shock wave/turbulent boundary layer interaction, and Type B wave configuration consists of an overall Mach reflection above the large scale separation bubble. Due to the gradual decrease in the size of the separation bubble, the separation bubble was replaced by several vortices (Type C wave pattern). Besides, for Type D wave configuration which exists in the local unstart inlet, there appears to be some flow spillage around the leading edge.

Beta diversity at different spatial scales: plant communities in organic and conventional agriculture.

PubMed

Gabriel, Doreen; Roschewitz, Indra; Tscharntke, Teja; Thies, Carsten

2006-10-01

Biodiversity studies that guide agricultural subsidy policy have generally compared farming systems at a single spatial scale: the field. However, diversity patterns vary across spatial scales. Here, we examined the effects of farming system (organic vs. conventional) and position in the field (edge vs. center) on plant species richness in wheat fields at three spatial scales. We quantified alpha-, beta-, and gamma-diversity at the microscale in 800 plots, at the mesoscale in 40 fields, and at the macroscale in three regions using the additive partitioning approach, and evaluated the relative contribution of beta-diversity at each spatial scale to total observed species richness. We found that alpha-, beta-, and gamma-diversity were higher in organic than conventional fields and higher at the field edge than in the field center at all spatial scales. In both farming systems, beta-diversity at the meso- and macroscale explained most of the overall species richness (up to 37% and 25%, respectively), indicating considerable differences in community composition among fields and regions due to environmental heterogeneity. The spatial scale at which beta-diversity contributed the most to overall species richness differed between rare and common species. Total richness of rare species (present in < or = 5% of total samples) was mainly explained by differences in community composition at the meso- and macroscale (up to 27% and 48%, respectively), but only in organic fields. Total richness of common species (present in > or = 25% of total samples) was explained by differences in community composition at the micro- and mesoscale (up to 29% and 47%, respectively), i.e., among plots and fields, independent of farming system. Our results show that organic farming made the greatest contribution to total species richness at the meso (among fields) and macro (among regions) scale due to environmental heterogeneity. Hence, agri-environment schemes should exploit this large-scale contribution of beta-diversity by tailoring schemes at regional scales to maximize dissimilarity between conservation areas using geographic information systems rather than focusing entirely at the classical local-field scale, which is the current practice.

Modeling carbon production and transport during ELMs in DIII-D

NASA Astrophysics Data System (ADS)

Hogan, J.; Wade, M.; Coster, D.; Lasnier, C.

2004-11-01

Large-scale Type I ELM events could provide a significant C source in ITER, and C production rates depend on incident D flux density and surface temperature, quantities which can vary significantly during an ELM event. Recent progress on DIII-D has improved opportunities for code comparison. Fast time-scale measurements of divertor CIII evolution [1] and fast edge CER measurements of C profile evolution during low-density DIII-D LSN ELMy H-modes (type I) [2] have been modeled using the solps5.0/Eirene99 coupled edge code and time dependent thermal analysis codes. An ELM model based on characteristics of MHD peeling-ballooning modes reproduces the pedestal evolution. Qualitative agreement for the CIII evolution during an ELM event is found using the Roth et al annealing model for chemical sputtering and the sensitivity to other models is described. Significant ELM-to-ELM variations in observed maximum divertor target IR temperature during nominally identical ELMs are investigated with models for C emission from micron-scale dust particles. [1] M Groth, M Fenstermacher et al J Nucl Mater 2003, [2] M Wade, K Burrell et al PSI-16

Landscape And Edge Effects On The Distribution Of Mammalian Predators In Missouri

Treesearch

William D. Dijak; Frank R. Thompson III

2000-01-01

Raccoons (Procyon lotor), opossums (Didelphis virginiana), and striped skunks (Mephitis mephitis) are predators of forest songbird eggs and nestlings. We examined the relative abundance of these predators at landscape and local scales to better understand predation risks. At the landscape scale, we examined the...

Multispectral Image Enhancement Through Adaptive Wavelet Fusion

DTIC Science & Technology

2016-09-14

13. SUPPLEMENTARY NOTES 14. ABSTRACT This research developed a multiresolution image fusion scheme based on guided filtering . Guided filtering can...effectively reduce noise while preserving detail boundaries. When applied in an iterative mode, guided filtering selectively eliminates small scale...details while restoring larger scale edges. The proposed multi-scale image fusion scheme achieves spatial consistency by using guided filtering both at

Connection between plasma response and resonant magnetic perturbation (RMP) edge localized mode (ELM) suppression in DIII-D [Connection between plasma response and RMP ELM suppression in DIII-D

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

Wingen, Andreas; Ferraro, Nathaniel M.; Shafer, Morgan W.

Calculations of the plasma response to applied non-axisymmetric fields in several DIII-D discharges show that predicted displacements depend strongly on the edge current density. This result is found using both a linear two-fluid-MHD model (M3D-C1) and a nonlinear ideal-MHD model (VMEC). Furthermore, it is observed that the probability of a discharge being edge localized mode (ELM)-suppressed is most closely related to the edge current density, as opposed to the pressure gradient. It is found that discharges with a stronger kink response are closer to the peeling–ballooning stability limit in ELITE simulations and eventually cross into the unstable region, causing ELMsmore » to reappear. Thus for effective ELM suppression, the RMP has to prevent the plasma from generating a large kink response, associated with ELM instability. Experimental observations are in agreement with the finding; discharges which have a strong kink response in the MHD simulations show ELMs or ELM mitigation during the RMP phase of the experiment, while discharges with a small kink response in the MHD simulations are fully ELM suppressed in the experiment by the applied resonant magnetic perturbation. The results are cross-checked against modeled 3D ideal MHD equilibria using the VMEC code. The procedure of constructing optimal 3D equilibria for diverted H-mode discharges using VMEC is presented. As a result, kink displacements in VMEC are found to scale with the edge current density, similar to M3D-C1, but the displacements are smaller. A direct correlation in the flux surface displacements to the bootstrap current is shown.« less

Connection between plasma response and resonant magnetic perturbation (RMP) edge localized mode (ELM) suppression in DIII-D [Connection between plasma response and RMP ELM suppression in DIII-D

DOE PAGES

Wingen, Andreas; Ferraro, Nathaniel M.; Shafer, Morgan W.; ...

2015-09-03

Calculations of the plasma response to applied non-axisymmetric fields in several DIII-D discharges show that predicted displacements depend strongly on the edge current density. This result is found using both a linear two-fluid-MHD model (M3D-C1) and a nonlinear ideal-MHD model (VMEC). Furthermore, it is observed that the probability of a discharge being edge localized mode (ELM)-suppressed is most closely related to the edge current density, as opposed to the pressure gradient. It is found that discharges with a stronger kink response are closer to the peeling–ballooning stability limit in ELITE simulations and eventually cross into the unstable region, causing ELMsmore » to reappear. Thus for effective ELM suppression, the RMP has to prevent the plasma from generating a large kink response, associated with ELM instability. Experimental observations are in agreement with the finding; discharges which have a strong kink response in the MHD simulations show ELMs or ELM mitigation during the RMP phase of the experiment, while discharges with a small kink response in the MHD simulations are fully ELM suppressed in the experiment by the applied resonant magnetic perturbation. The results are cross-checked against modeled 3D ideal MHD equilibria using the VMEC code. The procedure of constructing optimal 3D equilibria for diverted H-mode discharges using VMEC is presented. As a result, kink displacements in VMEC are found to scale with the edge current density, similar to M3D-C1, but the displacements are smaller. A direct correlation in the flux surface displacements to the bootstrap current is shown.« less

Efficient L1 regularization-based reconstruction for fluorescent molecular tomography using restarted nonlinear conjugate gradient.

PubMed

Shi, Junwei; Zhang, Bin; Liu, Fei; Luo, Jianwen; Bai, Jing

2013-09-15

For the ill-posed fluorescent molecular tomography (FMT) inverse problem, the L1 regularization can protect the high-frequency information like edges while effectively reduce the image noise. However, the state-of-the-art L1 regularization-based algorithms for FMT reconstruction are expensive in memory, especially for large-scale problems. An efficient L1 regularization-based reconstruction algorithm based on nonlinear conjugate gradient with restarted strategy is proposed to increase the computational speed with low memory consumption. The reconstruction results from phantom experiments demonstrate that the proposed algorithm can obtain high spatial resolution and high signal-to-noise ratio, as well as high localization accuracy for fluorescence targets.

Habitat fragmentation in the temperate zone: a perspective for managers

Treesearch

John Faaborg; Margaret Brittingham; Therese Donovan; John Blake

1993-01-01

Habitat fragmentation occurs when a large, fairly continuous tract of vegetation is converted to other vegetation types such that only scattered fragments of the original type remain. Problems associated with habitat fragmentation include overall habitat loss, increase in edge habitat and edge effects (particularly higher parasitism and nest predation rates), and...

Graphene microsheets enter cells through spontaneous membrane penetration at edge asperities and corner sites

PubMed Central

Li, Yinfeng; Yuan, Hongyan; von dem Bussche, Annette; Creighton, Megan; Hurt, Robert H.; Kane, Agnes B.; Gao, Huajian

2013-01-01

Understanding and controlling the interaction of graphene-based materials with cell membranes is key to the development of graphene-enabled biomedical technologies and to the management of graphene health and safety issues. Very little is known about the fundamental behavior of cell membranes exposed to ultrathin 2D synthetic materials. Here we investigate the interactions of graphene and few-layer graphene (FLG) microsheets with three cell types and with model lipid bilayers by combining coarse-grained molecular dynamics (MD), all-atom MD, analytical modeling, confocal fluorescence imaging, and electron microscopic imaging. The imaging experiments show edge-first uptake and complete internalization for a range of FLG samples of 0.5- to 10-μm lateral dimension. In contrast, the simulations show large energy barriers relative to kBT for membrane penetration by model graphene or FLG microsheets of similar size. More detailed simulations resolve this paradox by showing that entry is initiated at corners or asperities that are abundant along the irregular edges of fabricated graphene materials. Local piercing by these sharp protrusions initiates membrane propagation along the extended graphene edge and thus avoids the high energy barrier calculated in simple idealized MD simulations. We propose that this mechanism allows cellular uptake of even large multilayer sheets of micrometer-scale lateral dimension, which is consistent with our multimodal bioimaging results for primary human keratinocytes, human lung epithelial cells, and murine macrophages. PMID:23840061

Structure Discovery in Large Semantic Graphs Using Extant Ontological Scaling and Descriptive Statistics

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

al-Saffar, Sinan; Joslyn, Cliff A.; Chappell, Alan R.

As semantic datasets grow to be very large and divergent, there is a need to identify and exploit their inherent semantic structure for discovery and optimization. Towards that end, we present here a novel methodology to identify the semantic structures inherent in an arbitrary semantic graph dataset. We first present the concept of an extant ontology as a statistical description of the semantic relations present amongst the typed entities modeled in the graph. This serves as a model of the underlying semantic structure to aid in discovery and visualization. We then describe a method of ontological scaling in which themore » ontology is employed as a hierarchical scaling filter to infer different resolution levels at which the graph structures are to be viewed or analyzed. We illustrate these methods on three large and publicly available semantic datasets containing more than one billion edges each. Keywords-Semantic Web; Visualization; Ontology; Multi-resolution Data Mining;« less

Low speed wind tunnel test of ground proximity and deck edge effects on a lift cruise fan V/STOL configuration, volume 1

NASA Technical Reports Server (NTRS)

Stewart, V. R.

1979-01-01

The characteristics were determined of a lift cruise fan V/STOL multi-mission configuration in the near proximity to the edge of a small flat surface representation of a ship deck. Tests were conducted at both static and forward speed test conditions. The model (0.12 scale) tested was a four fan configuration with modifications to represent a three fan configuration. Analysis of data showed that the deck edge effects were in general less critical in terms of differences from free air than a full deck (in ground effect) configuration. The one exception to this was when the aft edge of the deck was located under the center of gravity. This condition, representative of an approach from the rear, showed a significant lift loss. Induced moments were generally small compared to the single axis control power requirements, but will likely add to the pilot work load.

Radiocesium interaction with clay minerals: Theory and simulation advances Post-Fukushima.

PubMed

Okumura, Masahiko; Kerisit, Sebastien; Bourg, Ian C; Lammers, Laura N; Ikeda, Takashi; Sassi, Michel; Rosso, Kevin M; Machida, Masahiko

2018-04-14

Insights at the microscopic level of the process of radiocesium adsorption and interaction with clay mineral particles have improved substantially over the past several years, triggered by pressing social issues such as management of huge amounts of waste soil accumulated after the Fukushima Dai-ichi nuclear power plant accident. In particular, computer-based molecular modeling supported by advanced hardware and algorithms has proven to be a powerful approach. Its application can now generally encompass the full complexity of clay particle adsorption sites from basal surfaces to interlayers with inserted water molecules, to edges including fresh and weathered frayed ones. On the other hand, its methodological schemes are now varied from traditional force-field molecular dynamics on large-scale realizations composed of many thousands of atoms including water molecules to first-principles methods on smaller models in rather exacting fashion. In this article, we overview new understanding enabled by simulations across methodological variations, focusing on recent insights that connect with experimental observations, namely: 1) the energy scale for cesium adsorption on the basal surface, 2) progress in understanding the structure of clay edges, which is difficult to probe experimentally, 3) cesium adsorption properties at hydrated interlayer sites, 4) the importance of the size relationship between the ionic radius of cesium and the interlayer distance at frayed edge sites, 5) the migration of cesium into deep interlayer sites, and 6) the effects of nuclear decay of radiocesium. Key experimental observations that motivate these simulation advances are also summarized. Furthermore, some directions toward future solutions of waste soil management are discussed based on the obtained microscopic insights. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

The BALDER Beamline at the MAX IV Laboratory

NASA Astrophysics Data System (ADS)

Klementiev, K.; Norén, K.; Carlson, S.; Sigfridsson Clauss, K. G. V.; Persson, I.

2016-05-01

X-ray absorption spectroscopy (XAS) includes well-established methods to study the local structure around the absorbing element - extended X-ray absorption fine structure (EXAFS), and the effective oxidation number or to quantitatively determine the speciation of an element in a complex matrix - X-ray absorption near-edge structure (XANES). The increased brilliance and intensities available at the new generation of synchrotron light sources makes it possible to study, in-situ and in-operando, much more dilute systems with relevance for natural systems, as well as the micro-scale variability and dynamics of chemical reactions on the millisecond time-scale. The design of the BALDER beamline at the MAX IV Laboratory 3 GeV ring has focused on a high flux of photons in a wide energy range, 2.4-40 keV, where the K-edge is covered for the elements S to La, and the L 3-edge for all elements heavier than Sb. The overall design of the beamline will allow large flexibility in energy range, beam size and data collection time. The other focus of the beamline design is the possibility to perform multi-technique analyses on samples. Development of sample environment requires focus on implementation of auxiliary methods in such a way that techniques like Fourier transform infrared (FTIR) spectroscopy, UV-Raman spectroscopy, X-ray diffraction and/or mass spectrometry can be performed simultaneously as the XAS study. It will be a flexible system where different instruments can be plugged in and out depending on the needs for the particular investigation. Many research areas will benefit from the properties of the wiggler based light source and the capabilities to perform in-situ and in-operando measurements, for example environmental and geochemical sciences, nuclear chemistry, catalysis, materials sciences, and cultural heritage.

On the interplay between neoclassical tearing modes and nonlocal transport in toroidal plasmas

NASA Astrophysics Data System (ADS)

Ji, X. Q.; Xu, Y.; Hidalgo, C.; Diamond, P. H.; Liu, Yi; Pan, O.; Shi, Z. B.; Yu, D. L.

2016-09-01

This Letter presents the first observation on the interplay between nonlocal transport and neoclassical tearing modes (NTMs) during transient nonlocal heat transport events in the HL-2A tokamak. The nonlocality is triggered by edge cooling and large-scale, inward propagating avalanches. These lead to a locally enhanced pressure gradient at the q = 3/2 (or 2/1) rational surface and hence the onset of the NTM in relatively low β plasmas (βN < 1). The NTM, in return, regulates the nonlocal transport by truncation of avalanches by local sheared toroidal flows which develop near the magnetic island. These findings have direct implications for understanding the dynamic interaction between turbulence and large-scale mode structures in fusion plasmas.

A new genus and species of xenodermatid snake (Squamata: Caenophidia: Xenodermatidae) from northern Lao People's Democratic Republic.

PubMed

Teynié, Alexandre; David, Patrick; Lottier, Anne; Le, Minh Duc; Vidal, Nicolas; Nguyen, Truong Quang

2015-03-09

A male snake collected in Louangphabang Province and a second specimen observed in Houaphan Province, North Laos, share morphological characters with the Asian genus Fimbrios Smith, 1921, including erected edges on the first supra- and infralabial scales, but differ in the following morphological characters: fewer dorsal scale rows (25-27 vs. 30-33), fewer maxillary teeth (27 vs. 30-35), posterior teeth progressively slightly enlarged, and especially the correspondence of two dorsal scale rows per ventral plate throughout the body (i.e. the first dorsal scale row made of a small scale above the fore part of a ventral, followed by a much larger scale above its hind part), a condition known only in Xenodermus Reinhardt, 1836. As the Laotian specimens differ in morphological characters from other genera and species in the family Xenodermatidae, and on the basis of molecular analyses showing a large genetic divergence from the genus Fimbrios (p-distance ≥14.7 %, mitochondrial COI gene), we place these specimens in a new genus, Parafimbrios gen. nov., and describe them as a new species, Parafimbrios lao sp. nov. Besides the characters mentioned above, the new species is diagnosed by a combination of the following ones: small, strongly keeled dorsal scales; rostral and first four supra- and infralabials with raised, erected edges; horizontal tissue ridges above the rostral; loreal single, large, elongate; ventral scales 177-189; subcaudals 55-56, undivided; dorsal colour purplish-grey, neck with a broad, very pale grey collar reaching downwards the pale grey colour of the venter. The morphological characters of the new genus are compared with those of the genera Fimbrios Smith, 1921, Xenodermus Reinhardt, 1836, Stoliczkaia Jerdon, 1870, Achalinus Peters, 1869, and Xylophis Beddome, 1878. A key to the genera Achalinus, Fimbrios and Parafimbrios gen. nov. is provided. Parafimbrios laos spec. nov. is the 111th snake species currently recorded from Laos.

Scaling analysis of the non-Abelian quasiparticle tunneling in [Formula: see text] FQH states.

PubMed

Li, Qi; Jiang, Na; Wan, Xin; Hu, Zi-Xiang

2018-06-27

Quasiparticle tunneling between two counter propagating edges through point contacts could provide information on its statistics. Previous study of the short distance tunneling displays a scaling behavior, especially in the conformal limit with zero tunneling distance. The scaling exponents for the non-Abelian quasiparticle tunneling exhibit some non-trivial behaviors. In this work, we revisit the quasiparticle tunneling amplitudes and their scaling behavior in a full range of the tunneling distance by putting the electrons on the surface of a cylinder. The edge-edge distance can be smoothly tuned by varying the aspect ratio for a finite size cylinder. We analyze the scaling behavior of the quasiparticles for the Read-Rezayi [Formula: see text] states for [Formula: see text] and 4 both in the short and long tunneling distance region. The finite size scaling analysis automatically gives us a critical length scale where the anomalous correction appears. We demonstrate this length scale is related to the size of the quasiparticle at which the backscattering between two counter propagating edges starts to be significant.

Bootstrap Current for the Edge Pedestal Plasma in a Diverted Tokamak Geometry

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

Koh, S.; Chang, C. S.; Ku, S.

The edge bootstrap current plays a critical role in the equilibrium and stability of the steep edge pedestal plasma. The pedestal plasma has an unconventional and difficult neoclassical property, as compared with the core plasma. It has a narrow passing particle region in velocity space that can be easily modified or destroyed by Coulomb collisions. At the same time, the edge pedestal plasma has steep pressure and electrostatic potential gradients whose scale-lengths are comparable with the ion banana width, and includes a magnetic separatrix surface, across which the topological properties of the magnetic field and particle orbits change abruptly. Amore » driftkinetic particle code XGC0, equipped with a mass-momentum-energy conserving collision operator, is used to study the edge bootstrap current in a realistic diverted magnetic field geometry with a self-consistent radial electric field. When the edge electrons are in the weakly collisional banana regime, surprisingly, the present kinetic simulation confirms that the existing analytic expressions [represented by O. Sauter et al. , Phys. Plasmas 6 , 2834 (1999)] are still valid in this unconventional region, except in a thin radial layer in contact with the magnetic separatrix. The agreement arises from the dominance of the electron contribution to the bootstrap current compared with ion contribution and from a reasonable separation of the trapped-passing dynamics without a strong collisional mixing. However, when the pedestal electrons are in plateau-collisional regime, there is significant deviation of numerical results from the existing analytic formulas, mainly due to large effective collisionality of the passing and the boundary layer trapped particles in edge region. In a conventional aspect ratio tokamak, the edge bootstrap current from kinetic simulation can be significantly less than that from the Sauter formula if the electron collisionality is high. On the other hand, when the aspect ratio is close to unity, the collisional edge bootstrap current can be significantly greater than that from the Sauter formula. Rapid toroidal rotation of the magnetic field lines at the high field side of a tight aspect-ratio tokamak is believed to be the cause of the different behavior. A new analytic fitting formula, as a simple modification to the Sauter formula, is obtained to bring the analytic expression to a better agreement with the edge kinetic simulation results« less

Bootstrap current for the edge pedestal plasma in a diverted tokamak geometry

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

Koh, S.; Choe, W.; Chang, C. S.

The edge bootstrap current plays a critical role in the equilibrium and stability of the steep edge pedestal plasma. The pedestal plasma has an unconventional and difficult neoclassical property, as compared with the core plasma. It has a narrow passing particle region in velocity space that can be easily modified or destroyed by Coulomb collisions. At the same time, the edge pedestal plasma has steep pressure and electrostatic potential gradients whose scale-lengths are comparable with the ion banana width, and includes a magnetic separatrix surface, across which the topological properties of the magnetic field and particle orbits change abruptly. Amore » drift-kinetic particle code XGC0, equipped with a mass-momentum-energy conserving collision operator, is used to study the edge bootstrap current in a realistic diverted magnetic field geometry with a self-consistent radial electric field. When the edge electrons are in the weakly collisional banana regime, surprisingly, the present kinetic simulation confirms that the existing analytic expressions [represented by O. Sauter et al., Phys. Plasmas 6, 2834 (1999)] are still valid in this unconventional region, except in a thin radial layer in contact with the magnetic separatrix. The agreement arises from the dominance of the electron contribution to the bootstrap current compared with ion contribution and from a reasonable separation of the trapped-passing dynamics without a strong collisional mixing. However, when the pedestal electrons are in plateau-collisional regime, there is significant deviation of numerical results from the existing analytic formulas, mainly due to large effective collisionality of the passing and the boundary layer trapped particles in edge region. In a conventional aspect ratio tokamak, the edge bootstrap current from kinetic simulation can be significantly less than that from the Sauter formula if the electron collisionality is high. On the other hand, when the aspect ratio is close to unity, the collisional edge bootstrap current can be significantly greater than that from the Sauter formula. Rapid toroidal rotation of the magnetic field lines at the high field side of a tight aspect-ratio tokamak is believed to be the cause of the different behavior. A new analytic fitting formula, as a simple modification to the Sauter formula, is obtained to bring the analytic expression to a better agreement with the edge kinetic simulation results.« less

Three-dimensional estimates of tree canopies: Scaling from high-resolution UAV data to satellite observations

NASA Astrophysics Data System (ADS)

Sankey, T.; Donald, J.; McVay, J.

2015-12-01

High resolution remote sensing images and datasets are typically acquired at a large cost, which poses big a challenge for many scientists. Northern Arizona University recently acquired a custom-engineered, cutting-edge UAV and we can now generate our own images with the instrument. The UAV has a unique capability to carry a large payload including a hyperspectral sensor, which images the Earth surface in over 350 spectral bands at 5 cm resolution, and a lidar scanner, which images the land surface and vegetation in 3-dimensions. Both sensors represent the newest available technology with very high resolution, precision, and accuracy. Using the UAV sensors, we are monitoring the effects of regional forest restoration treatment efforts. Individual tree canopy width and height are measured in the field and via the UAV sensors. The high-resolution UAV images are then used to segment individual tree canopies and to derive 3-dimensional estimates. The UAV image-derived variables are then correlated to the field-based measurements and scaled to satellite-derived tree canopy measurements. The relationships between the field-based and UAV-derived estimates are then extrapolated to a larger area to scale the tree canopy dimensions and to estimate tree density within restored and control forest sites.

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

Fisher, Dustin M., E-mail: dustin.m.fisher.gr@dartmouth.edu; Rogers, Barrett N., E-mail: barrett.rogers@dartmouth.edu; Rossi, Giovanni D.

The Large Plasma Device (LAPD) is modeled using the 3D Global Braginskii Solver code. Comparisons to experimental measurements are made in the low-bias regime in which there is an intrinsic E × B rotation of the plasma. In the simulations, this rotation is caused primarily by sheath effects and may be a likely mechanism for the intrinsic rotation seen in LAPD. Simulations show strong qualitative agreement with the data, particularly the radial dependence of the density fluctuations, cross-correlation lengths, radial flux dependence outside of the cathode edge, and camera imagery. Kelvin Helmholtz (KH) turbulence at relatively large scales is the dominant drivermore » of cross-field transport in these simulations with smaller-scale drift waves and sheath modes playing a secondary role. Plasma holes and blobs arising from KH vortices in the simulations are consistent with the scale sizes and overall appearance of those in LAPD camera images. The addition of ion-neutral collisions in the simulations at previously theorized values reduces the radial particle flux by about a factor of two, from values that are somewhat larger than the experimentally measured flux to values that are somewhat lower than the measurements. This reduction is due to a modest stabilizing contribution of the collisions on the KH-modes driving the turbulent transport.« less

Static friction boost in edge-driven incommensurate contacts

NASA Astrophysics Data System (ADS)

Mandelli, Davide; Guerra, Roberto; Ouyang, Wengen; Urbakh, Michael; Vanossi, Andrea

2018-04-01

We present a numerical investigation of the size scaling of static friction in incommensurate two-dimensional contacts performed for different lateral loading configurations. Results of model simulations show that both the absolute value of the force Fs and the scaling exponent γ strongly depend on the loading configuration adopted to drive the slider along the substrate. Under edge loading, a sharp increase of static friction is observed above a critical size corresponding to the appearance of a localized commensurate dislocation. Noticeably, the existence of sublinear scaling, which is a fingerprint of superlubricity, does not conflict with the possibility to observe shear-induced localized commensurate regions at the contact interface. Atomistic simulations of gold islands sliding over graphite corroborate these findings, suggesting that similar elasticity effects should be at play in real frictional contacts.

Learning from Our Global Competitors: A Comparative Analysis of Science, Technology, Engineering and Mathematics (STEM) Education Pipelines in the United States, Mainland China and Taiwan

ERIC Educational Resources Information Center

Chow, Christina M.

2011-01-01

Maintaining a competitive edge within the 21st century is dependent on the cultivation of human capital, producing qualified and innovative employees capable of competing within the new global marketplace. Technological advancements in communications technology as well as large scale, infrastructure development has led to a leveled playing field…

Experimental Space Shuttle Orbiter Studies to Acquire Data for Code and Flight Heating Model Validation

NASA Technical Reports Server (NTRS)

Wadhams, T. P.; Holden, M. S.; MacLean, M. G.; Campbell, Charles

2010-01-01

In an experimental study to obtain detailed heating data over the Space Shuttle Orbiter, CUBRC has completed an extensive matrix of experiments using three distinct models and two unique hypervelocity wind tunnel facilities. This detailed data will be employed to assess heating augmentation due to boundary layer transition on the Orbiter wing leading edge and wind side acreage with comparisons to computational methods and flight data obtained during the Orbiter Entry Boundary Layer Flight Experiment and HYTHIRM during STS-119 reentry. These comparisons will facilitate critical updates to be made to the engineering tools employed to make assessments about natural and tripped boundary layer transition during Orbiter reentry. To achieve the goals of this study data was obtained over a range of Mach numbers from 10 to 18, with flight scaled Reynolds numbers and model attitudes representing key points on the Orbiter reentry trajectory. The first of these studies were performed as an integral part of Return to Flight activities following the accident that occurred during the reentry of the Space Shuttle Columbia (STS-107) in February of 2003. This accident was caused by debris, which originated from the foam covering the external tank bipod fitting ramps, striking and damaging critical wing leading edge heating tiles that reside in the Orbiter bow shock/wing interaction region. During investigation of the accident aeroheating team members discovered that only a limited amount of experimental wing leading edge data existed in this critical peak heating area and a need arose to acquire a detailed dataset of heating in this region. This new dataset was acquired in three phases consisting of a risk mitigation phase employing a 1.8% scale Orbiter model with special temperature sensitive paint covering the wing leading edge, a 0.9% scale Orbiter model with high resolution thin-film instrumentation in the span direction, and the primary 1.8% scale Orbiter model with detailed thin-film resolution in both the span and chord direction in the area of peak heating. Additional objectives of this first study included: obtaining natural or tripped turbulent wing leading edge heating levels, assessing the effectiveness of protuberances and cavities placed at specified locations on the orbiter over a range of Mach numbers and Reynolds numbers to evaluate and compare to existing engineering and computational tools, obtaining cavity floor heating to aid in the verification of cavity heating correlations, acquiring control surface deflection heating data on both the main body flap and elevons, and obtain high speed schlieren videos of the interaction of the orbiter nose bow shock with the wing leading edge. To support these objectives, the stainless steel 1.8% scale orbiter model in addition to the sensors on the wing leading edge was instrumented down the windward centerline, over the wing acreage on the port side, and painted with temperature sensitive paint on the starboard side wing acreage. In all, the stainless steel 1.8% scale Orbiter model was instrumented with over three-hundred highly sensitive thin-film heating sensors, two-hundred of which were located in the wing leading edge shock interaction region. Further experimental studies will also be performed following the successful acquisition of flight data during the Orbiter Entry Boundary Layer Flight Experiment and HYTHIRM on STS-119 at specific data points simulating flight conditions and geometries. Additional instrumentation and a protuberance matching the layout present during the STS-119 boundary layer transition flight experiment were added with testing performed at Mach number and Reynolds number conditions simulating conditions experienced in flight. In addition to the experimental studies, CUBRC also performed a large amount of CFD analysis to confirm and validate not only the tunnel freestream conditions, but also 3D flows over the orbiter acreage, wing leading edge, and controlurfaces to assess data quality, shock interaction locations, and control surface separation regions. This analysis is a standard part of any experimental program at CUBRC, and this information was of key importance for post-test data quality analysis and understanding particular phenomena seen in the data. All work during this effort was sponsored and paid for by the NASA Space Shuttle Program Office at the Johnson Space Center in Houston, Texas.

Full-Field Calcium K-Edge X-ray Absorption Near-Edge Structure Spectroscopy on Cortical Bone at the Micron-Scale: Polarization Effects Reveal Mineral Orientation.

PubMed

Hesse, Bernhard; Salome, Murielle; Castillo-Michel, Hiram; Cotte, Marine; Fayard, Barbara; Sahle, Christoph J; De Nolf, Wout; Hradilova, Jana; Masic, Admir; Kanngießer, Birgit; Bohner, Marc; Varga, Peter; Raum, Kay; Schrof, Susanne

2016-04-05

Here, we show results on X-ray absorption near edge structure spectroscopy in both transmission and X-ray fluorescence full-field mode (FF-XANES) at the calcium K-edge on human bone tissue in healthy and diseased conditions and for different tissue maturation stages. We observe that the dominating spectral differences originating from different tissue regions, which are well pronounced in the white line and postedge structures are associated with polarization effects. These polarization effects dominate the spectral variance and must be well understood and modeled before analyzing the very subtle spectral variations related to the bone tissue variations itself. However, these modulations in the fine structure of the spectra can potentially be of high interest to quantify orientations of the apatite crystals in highly structured tissue matrices such as bone. Due to the extremely short wavelengths of X-rays, FF-XANES overcomes the limited spatial resolution of other optical and spectroscopic techniques exploiting visible light. Since the field of view in FF-XANES is rather large the acquisition times for analyzing the same region are short compared to, for example, X-ray diffraction techniques. Our results on the angular absorption dependence were verified by both site-matched polarized Raman spectroscopy, which has been shown to be sensitive to the orientation of bone building blocks and by mathematical simulations of the angular absorbance dependence. As an outlook we further demonstrate the polarization based assessment of calcium-containing crystal orientation and specification of calcium in a beta-tricalcium phosphate (β-Ca3(PO4)2 scaffold implanted into ovine bone. Regarding the use of XANES to assess chemical properties of Ca in human bone tissue our data suggest that neither the anatomical site (tibia vs jaw) nor pathology (healthy vs necrotic jaw bone tissue) affected the averaged spectral shape of the XANES spectra.

High-frequency and meso-scale winter sea-ice variability in the Southern Ocean in a high-resolution global ocean model

NASA Astrophysics Data System (ADS)

Stössel, Achim; von Storch, Jin-Song; Notz, Dirk; Haak, Helmuth; Gerdes, Rüdiger

2018-03-01

This study is on high-frequency temporal variability (HFV) and meso-scale spatial variability (MSV) of winter sea-ice drift in the Southern Ocean simulated with a global high-resolution (0.1°) sea ice-ocean model. Hourly model output is used to distinguish MSV characteristics via patterns of mean kinetic energy (MKE) and turbulent kinetic energy (TKE) of ice drift, surface currents, and wind stress, and HFV characteristics via time series of raw variables and correlations. We find that (1) along the ice edge, the MSV of ice drift coincides with that of surface currents, in particular such due to ocean eddies; (2) along the coast, the MKE of ice drift is substantially larger than its TKE and coincides with the MKE of wind stress; (3) in the interior of the ice pack, the TKE of ice drift is larger than its MKE, mostly following the TKE pattern of wind stress; (4) the HFV of ice drift is dominated by weather events, and, in the absence of tidal currents, locally and to a much smaller degree by inertial oscillations; (5) along the ice edge, the curl of the ice drift is highly correlated with that of surface currents, mostly reflecting the impact of ocean eddies. Where ocean eddies occur and the ice is relatively thin, ice velocity is characterized by enhanced relative vorticity, largely matching that of surface currents. Along the ice edge, ocean eddies produce distinct ice filaments, the realism of which is largely confirmed by high-resolution satellite passive-microwave data.

Real Gas Scale Effects on Hypersonic Laminar Boundary-Layer Parameters Including Effects of Entropy-Layer Swallowing

DTIC Science & Technology

1975-12-01

crossed the essentially normal portion of the bow shock is swallowed by the boundary layer. The flow along the edge of the boundary layer on the aft...portions hf the body will then have passed through an oblique part of the bow shock and will be in a different state than had it passed through a normal...determination of the local edge flow conditions may be improvedby taking into con- sideration the inclination of the bow shock where the local flow stream- line

Experimental investigation of forebody and wing leading-edge vortex interactions at high angles of attack

NASA Technical Reports Server (NTRS)

Erickson, G. E.; Gilbert, W. P.

1983-01-01

An experimental investigation was conducted to assess the vortex flow-field interactions on an advanced, twin-jet fighter aircraft configuration at high angles of attack. Flow-field surveys were conducted on a small-scale model in the Northrop 0.41 - by 0.60-meter water tunnel and, where appropriate, the qualitative observations were correlated with low-speed wind tunnel data trends obtained on a large-scale model of the advanced fighter in the NASA Langley Research Center 30- by 60-foot (9.1- by 18.3-meter) facility. Emphasis was placed on understanding the interactions of the forebody and LEX-wing vortical flows, defining the effects on rolling moment variation with sideslip, and identifying modifications to control or regulate the vortex interactions at high angles of attack. The water tunnel flow visualization results and wind tunnel data trend analysis revealed the potential for strong interactions between the forebody and LEX vortices at high angles of attack. In particular, the forebody flow development near the nose could be controlled by means of carefully-positioned radome strakes. The resultant strake-induced flow-field changes were amplified downstream by the more powerful LEX vortical motions with subsequent large effects on wing flow separation characteristics.

Nonlinear Dynamical Analysis of Fibrillation

NASA Astrophysics Data System (ADS)

Kerin, John A.; Sporrer, Justin M.; Egolf, David A.

2013-03-01

The development of spatiotemporal chaotic behavior in heart tissue, termed fibrillation, is a devastating, life-threatening condition. The chaotic behavior of electrochemical signals, in the form of spiral waves, causes the muscles of the heart to contract in an incoherent manner, hindering the heart's ability to pump blood. We have applied the mathematical tools of nonlinear dynamics to large-scale simulations of a model of fibrillating heart tissue to uncover the dynamical modes driving this chaos. By studying the evolution of Lyapunov vectors and exponents over short times, we have found that the fibrillating tissue is sensitive to electrical perturbations only in narrow regions immediately in front of the leading edges of spiral waves, especially when these waves collide, break apart, or hit the edges of the tissue sample. Using this knowledge, we have applied small stimuli to areas of varying sensitivity. By studying the evolution of the effects of these perturbations, we have made progress toward controlling the electrochemical patterns associated with heart fibrillation. This work was supported by the U.S. National Science Foundation (DMR-0094178) and Research Corporation.

Helicons, magnetoplasma edge, and faraday rotation in solid state plasmas at microwave frequencies.

PubMed

Furdyna, J K

1967-04-01

The effect of magnetic field on propagation of electromagnetic waves through free carrier plasmas in semiconductors is discussed. The Faraday configuration and the parameter ranges omega(c),omega(p) > omega and omega(c) > tau(-1) are specifically considered. Dispersion of helicon waves, propagation near the magnetoplasma edge (omega(p)(2) = omegaomega(c)), and the Faraday rotation are developed in terms of the one-electron Drude theory. Microwave transmission measurements at 35 Gc/s on n-type InSb are presented. Experiments near the magnetoplasma edge yield the value of the static dielectric constant of the InSb lattice K(l) = 19.3 +/- 0.8. Faraday rotation, observed beyond the edge, is found to be extremely large. Some practical possibilities for this effect are considered.

End Effects and Load Diffusion in Composite Structures

NASA Technical Reports Server (NTRS)

Horgan, Cornelius O.; Ambur, D. (Technical Monitor); Nemeth, M. P. (Technical Monitor)

2002-01-01

The research carried out here builds on our previous NASA supported research on the general topic of edge effects and load diffusion in composite structures. Further fundamental solid mechanics studies were carried out to provide a basis for assessing the complicated modeling necessary for large scale structures used by NASA. An understanding of the fundamental mechanisms of load diffusion in composite subcomponents is essential in developing primary composite structures. Specific problems recently considered were focussed on end effects in sandwich structures and for functionally graded materials. Both linear and nonlinear (geometric and material) problems have been addressed. Our goal is the development of readily applicable design formulas for the decay lengths in terms of non-dimensional material and geometric parameters. Analytical models of load diffusion behavior are extremely valuable in building an intuitive base for developing refined modeling strategies and assessing results from finite element analyses. The decay behavior of stresses and other field quantities provides a significant aid towards this process. The analysis is also amenable to parameter study with a large parameter space and should be useful in structural tailoring studies.

Ground Motion Simulation for a Large Active Fault System using Empirical Green's Function Method and the Strong Motion Prediction Recipe - a Case Study of the Noubi Fault Zone -

NASA Astrophysics Data System (ADS)

Kuriyama, M.; Kumamoto, T.; Fujita, M.

2005-12-01

The 1995 Hyogo-ken Nambu Earthquake (1995) near Kobe, Japan, spurred research on strong motion prediction. To mitigate damage caused by large earthquakes, a highly precise method of predicting future strong motion waveforms is required. In this study, we applied empirical Green's function method to forward modeling in order to simulate strong ground motion in the Noubi Fault zone and examine issues related to strong motion prediction for large faults. Source models for the scenario earthquakes were constructed using the recipe of strong motion prediction (Irikura and Miyake, 2001; Irikura et al., 2003). To calculate the asperity area ratio of a large fault zone, the results of a scaling model, a scaling model with 22% asperity by area, and a cascade model were compared, and several rupture points and segmentation parameters were examined for certain cases. A small earthquake (Mw: 4.6) that occurred in northern Fukui Prefecture in 2004 were examined as empirical Green's function, and the source spectrum of this small event was found to agree with the omega-square scaling law. The Nukumi, Neodani, and Umehara segments of the 1891 Noubi Earthquake were targeted in the present study. The positions of the asperity area and rupture starting points were based on the horizontal displacement distributions reported by Matsuda (1974) and the fault branching pattern and rupture direction model proposed by Nakata and Goto (1998). Asymmetry in the damage maps for the Noubi Earthquake was then examined. We compared the maximum horizontal velocities for each case that had a different rupture starting point. In the case, rupture started at the center of the Nukumi Fault, while in another case, rupture started on the southeastern edge of the Umehara Fault; the scaling model showed an approximately 2.1-fold difference between these cases at observation point FKI005 of K-Net. This difference is considered to relate to the directivity effect associated with the direction of rupture propagation. Moreover, it was clarified that the horizontal velocities by assuming the cascade model was underestimated more than one standard deviation of empirical relation by Si and Midorikawa (1999). The scaling and cascade models showed an approximately 6.4-fold difference for the case, in which the rupture started along the southeastern edge of the Umehara Fault at observation point GIF020. This difference is significantly large in comparison with the effect of different rupture starting points, and shows that it is important to base scenario earthquake assumptions on active fault datasets before establishing the source characterization model. The distribution map of seismic intensity for the 1891 Noubi Earthquake also suggests that the synthetic waveforms in the southeastern Noubi Fault zone may be underestimated. Our results indicate that outer fault parameters (e.g., earthquake moment) related to the construction of scenario earthquakes influence strong motion prediction, rather than inner fault parameters such as the rupture starting point. Based on these methods, we will predict strong motion for approximately 140 to 150 km of the Itoigawa-Shizuoka Tectonic Line.

Survey of techniques for reduction of wind turbine blade trailing edge noise.

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

Barone, Matthew Franklin

2011-08-01

Aerodynamic noise from wind turbine rotors leads to constraints in both rotor design and turbine siting. The primary source of aerodynamic noise on wind turbine rotors is the interaction of turbulent boundary layers on the blades with the blade trailing edges. This report surveys concepts that have been proposed for trailing edge noise reduction, with emphasis on concepts that have been tested at either sub-scale or full-scale. These concepts include trailing edge serrations, low-noise airfoil designs, trailing edge brushes, and porous trailing edges. The demonstrated noise reductions of these concepts are cited, along with their impacts on aerodynamic performance. Anmore » assessment is made of future research opportunities in trailing edge noise reduction for wind turbine rotors.« less

Statistical properties of edge plasma turbulence in the Large Helical Device

NASA Astrophysics Data System (ADS)

Dewhurst, J. M.; Hnat, B.; Ohno, N.; Dendy, R. O.; Masuzaki, S.; Morisaki, T.; Komori, A.

2008-09-01

Ion saturation current (Isat) measurements made by three tips of a Langmuir probe array in the Large Helical Device are analysed for two plasma discharges. Absolute moment analysis is used to quantify properties on different temporal scales of the measured signals, which are bursty and intermittent. Strong coherent modes in some datasets are found to distort this analysis and are consequently removed from the time series by applying bandstop filters. Absolute moment analysis of the filtered data reveals two regions of power-law scaling, with the temporal scale τ ≈ 40 µs separating the two regimes. A comparison is made with similar results from the Mega-Amp Spherical Tokamak. The probability density function is studied and a monotonic relationship between connection length and skewness is found. Conditional averaging is used to characterize the average temporal shape of the largest intermittent bursts.

Bending of Rectangular Plates with Large Deflections

NASA Technical Reports Server (NTRS)

Levy, Samuel

1942-01-01

The solution of von Karman's fundamental equations for large deflections of plates is presented for the case of a simply supported rectangular plate under combined edge compression and lateral loading. Numerical solutions are given for square plates and for rectangular plates with a width-span ratio of 3:1. The effective widths under edge compression are compared with effective widths according to von Karman, Bengston, Marguerre, and Cox and with experimental results by Ramberg, McPherson, and Levy. The deflections for a square plate under lateral pressure are compared with experimental and theoretical results by Kaiser. It is found that the effective widths agree closely with Marguerre's formula and with the experimentally observed values and that the deflections agree with the experimental results and with Kaiser's work.

Dimensionless size scaling of intrinsic rotation in DIII-D

DOE PAGES

deGrassie, John S.; Solomon, Wayne M.; Rice, J. E.; ...

2016-08-01

A dimensionless empirical scaling for intrinsic toroidal rotation is given; M A ~β Nρ*, where M A is the toroidal velocity divided by the Alfvén velocity, β N the usual normalized β value, and ρ* is the ion gyroradius divided by the minor radius. This scaling describes well experimental data from DIII-D, and also some published data from C-Mod and JET. The velocity used in this scaling is in an outer location in minor radius, outside of the interior core and inside of the large gradient edge region in H-mode conditions. Furthermore, this scaling establishes the basic magnitude of themore » intrinsic toroidal rotation and its relation to the rich variety of rotation profiles that can be realized for intrinsic conditions is discussed.« less

Quantum phase transitions in effective spin-ladder models for graphene zigzag nanoribbons

NASA Astrophysics Data System (ADS)

Koop, Cornelie; Wessel, Stefan

2017-10-01

We examine the magnetic correlations in quantum spin models that were derived recently as effective low-energy theories for electronic correlation effects on the edge states of graphene nanoribbons. For this purpose, we employ quantum Monte Carlo simulations to access the large-distance properties, accounting for quantum fluctuations beyond mean-field-theory approaches to edge magnetism. For certain chiral nanoribbons, antiferromagnetic interedge couplings were previously found to induce a gapped quantum disordered ground state of the effective spin model. We find that the extended nature of the intraedge couplings in the effective spin model for zigzag nanoribbons leads to a quantum phase transition at a large, finite value of the interedge coupling. This quantum critical point separates the quantum disordered region from a gapless phase of stable edge magnetism at weak intraedge coupling, which includes the ground states of spin-ladder models for wide zigzag nanoribbons. To study the quantum critical behavior, the effective spin model can be related to a model of two antiferromagnetically coupled Haldane-Shastry spin-half chains with long-ranged ferromagnetic intrachain couplings. The results for the critical exponents are compared also to several recent renormalization-group calculations for related long-ranged interacting quantum systems.

Patch size and edge proximity are useful predictors of brood parasitism but not nest survival of grassland birds.

PubMed

Benson, Thomas J; Chiavacci, Scott J; Ward, Michael P

2013-06-01

Declines of migratory birds have led to increased focus on causative factors for these declines, including the potential adverse effects of habitat fragmentation on reproductive success. Although numerous studies have addressed how proximity to a habitat edge, patch size, or landscape context influence nest survival or brood parasitism, many have failed to find the purported effects. Furthermore, many have sought to generalize patterns across large geographic areas and habitats. Here, we examined evidence for effects of edge proximity, patch size, and landscape context on nest survival and brood parasitism of grassland birds, a group of conservation concern. The only consistent effect was a positive association between edge proximity and brood parasitism. We examined effects of patch size on nest survival (37 studies) and brood parasitism (30 studies) representing 170 and 97 different estimates, respectively, with a total sample size of > 14000 nests spanning eastern North America. Nest survival weakly increased with patch size in the Great Plains, but not in the Midwestern or Eastern United States, and brood parasitism was inversely related to patch size and consistently greater in the Great Plains. The consistency in brood parasitism relative to nest survival patterns is likely due to parasitism being caused by one species, while nest survival is driven by a diverse and variable suite of nest predators. Often, studies assume that predators responsible for nest predation, the main driver of nest success, either are the same or exhibit the same behaviors across large geographic areas. These results suggest that a better mechanistic understanding of nest predation is needed to provide meaningful conservation recommendations for improving grassland bird productivity, and that the use of general recommendations across large geographic areas should only be undertaken when sufficient data are available from all regions.

Spin-transfer-torque efficiency enhanced by edge-damage of perpendicular magnetic random access memories

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

Song, Kyungmi; Lee, Kyung-Jin, E-mail: kj-lee@korea.ac.kr; Department of Materials Science and Engineering, Korea University, Seoul 136-713

2015-08-07

We numerically investigate the effect of magnetic and electrical damages at the edge of a perpendicular magnetic random access memory (MRAM) cell on the spin-transfer-torque (STT) efficiency that is defined by the ratio of thermal stability factor to switching current. We find that the switching mode of an edge-damaged cell is different from that of an undamaged cell, which results in a sizable reduction in the switching current. Together with a marginal reduction of the thermal stability factor of an edge-damaged cell, this feature makes the STT efficiency large. Our results suggest that a precise edge control is viable formore » the optimization of STT-MRAM.« less

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

NASA Astrophysics Data System (ADS)

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

2012-10-01

The effects of convex curvature on the outer structure of a Mach 4.9 turbulent boundary layer (Reθ = 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.

LOGISTIC NETWORK REGRESSION FOR SCALABLE ANALYSIS OF NETWORKS WITH JOINT EDGE/VERTEX DYNAMICS

PubMed Central

Almquist, Zack W.; Butts, Carter T.

2015-01-01

Change in group size and composition has long been an important area of research in the social sciences. Similarly, interest in interaction dynamics has a long history in sociology and social psychology. However, the effects of endogenous group change on interaction dynamics are a surprisingly understudied area. One way to explore these relationships is through social network models. Network dynamics may be viewed as a process of change in the edge structure of a network, in the vertex set on which edges are defined, or in both simultaneously. Although early studies of such processes were primarily descriptive, recent work on this topic has increasingly turned to formal statistical models. Although showing great promise, many of these modern dynamic models are computationally intensive and scale very poorly in the size of the network under study and/or the number of time points considered. Likewise, currently used models focus on edge dynamics, with little support for endogenously changing vertex sets. Here, the authors show how an existing approach based on logistic network regression can be extended to serve as a highly scalable framework for modeling large networks with dynamic vertex sets. The authors place this approach within a general dynamic exponential family (exponential-family random graph modeling) context, clarifying the assumptions underlying the framework (and providing a clear path for extensions), and they show how model assessment methods for cross-sectional networks can be extended to the dynamic case. Finally, the authors illustrate this approach on a classic data set involving interactions among windsurfers on a California beach. PMID:26120218

LOGISTIC NETWORK REGRESSION FOR SCALABLE ANALYSIS OF NETWORKS WITH JOINT EDGE/VERTEX DYNAMICS.

PubMed

Almquist, Zack W; Butts, Carter T

2014-08-01

Change in group size and composition has long been an important area of research in the social sciences. Similarly, interest in interaction dynamics has a long history in sociology and social psychology. However, the effects of endogenous group change on interaction dynamics are a surprisingly understudied area. One way to explore these relationships is through social network models. Network dynamics may be viewed as a process of change in the edge structure of a network, in the vertex set on which edges are defined, or in both simultaneously. Although early studies of such processes were primarily descriptive, recent work on this topic has increasingly turned to formal statistical models. Although showing great promise, many of these modern dynamic models are computationally intensive and scale very poorly in the size of the network under study and/or the number of time points considered. Likewise, currently used models focus on edge dynamics, with little support for endogenously changing vertex sets. Here, the authors show how an existing approach based on logistic network regression can be extended to serve as a highly scalable framework for modeling large networks with dynamic vertex sets. The authors place this approach within a general dynamic exponential family (exponential-family random graph modeling) context, clarifying the assumptions underlying the framework (and providing a clear path for extensions), and they show how model assessment methods for cross-sectional networks can be extended to the dynamic case. Finally, the authors illustrate this approach on a classic data set involving interactions among windsurfers on a California beach.

Hartree-Fock study of the Anderson metal-insulator transition in the presence of Coulomb interaction: Two types of mobility edges and their multifractal scaling exponents

NASA Astrophysics Data System (ADS)

Lee, Hyun-Jung; Kim, Ki-Seok

2018-04-01

We investigate the role of Coulomb interaction in the multifractality of Anderson metal-insulator transition, where the Coulomb interaction is treated within the Hartree-Fock approximation, but disorder effects are taken into account exactly. An innovative technical aspect in our simulation is to utilize the Ewald-sum technique, which allows us to introduce the long-range nature of the Coulomb interaction into Hartree-Fock self-consistent equations of order parameters more accurately. This numerical simulation reproduces the Altshuler-Aronov correction in a metallic state and the Efros-Shklovskii pseudogap in an insulating phase, where the density of states ρ (ω ) is evaluated in three dimensions. Approaching the quantum critical point of a metal-insulator transition from either the metallic or insulting phase, we find that the density of states is given by ρ (ω ) ˜|ω| 1 /2 , which determines one critical exponent of the McMillan-Shklovskii scaling theory. Our main result is to evaluate the eigenfunction multifractal scaling exponent αq, given by the Legendre transformation of the fractal dimension τq, which characterizes the scaling behavior of the inverse participation ratio with respect to the system size L . Our multifractal analysis leads us to identify two kinds of mobility edges, one of which occurs near the Fermi energy and the other of which appears at a high energy, where the density of states at the Fermi energy shows the Coulomb-gap feature. We observe that the multifractal exponent at the high-energy mobility edge remains to be almost identical to that of the Anderson localization transition in the absence of Coulomb interactions. On the other hand, we find that the multifractal exponent near the Fermi energy is more enhanced than that at the high-energy mobility edge, suspected to result from interaction effects. However, both the multifractal exponents do not change even if the strength of the Coulomb interaction varies. We also show that the multifractality singular spectrum can be classified into two categories, confirming the appearance of two types of mobility edges.

Effects of Small-scale Vegetation-related Roughness on Overland Flow and Infiltration in Semi-arid Grassland and Shrublands

NASA Astrophysics Data System (ADS)

Bedford, D.

2012-12-01

We studied the effects of small-scale roughness on overland flow/runoff and the spatial pattern of infiltration. Our semi-arid sites include a grassland and shrubland in Central New Mexico and a shrubland in the Eastern Mojave Desert. Vegetation exerts strong controls on small-scale surface roughness in the form of plant mounds and other microtopography such as depressions and rills. We quantified the effects of densely measured soil surface heterogeneity using model simulations of runoff and infiltration. Microtopographic roughness associated with vegetation patterns, on the scale of mm-cm's in height, has a larger effect on runoff and infiltration than spatially correlated saturated conductivity. The magnitude and pattern of the effect of roughness largely depends on the vegetation and landform type, and rainfall depth and intensity. In all cases, runoff and infiltration amount and patterns were most strongly affected by depression storage. In the grassland we studied in central New Mexico, soil surface roughness had a large effect on runoff and infiltration where vegetation mounds coalesced, forming large storage volumes that require filling and overtopping in order for overland flow to concentrate into runoff. Total discharge over rough surfaces was reduced 100-200% compared to simulations in which no surface roughness was accounted for. For shrublands, total discharge was reduced 30-40% by microtopography on gently sloping alluvial fans and only 10-20% on steep hillslopes. This difference is largely due to the lack of storage elements on steep slopes. For our sites, we found that overland flow can increase infiltration by up to 2.5 times the total rainfall by filling depressions. The redistribution of water via overland flow can affect up to 20% of an area but varies with vegetation type and landform. This infiltration augmentation by overland flow tends to occur near the edges of vegetation canopies where overland flow depths are deep and infiltration rates are moderate. Infiltration augmentation is greatest in microtopographic depressions and flow threads. These results show that some vegetation-landform settings are efficient at trapping and concentrating the primary limiting resource, and demonstrate the importance of micro-scale soil characteristics for the ecohydrologic function of semi-arid environments. Since other essential attributes for plant ecosystems, such as nutrients, likely co-vary with water availability, further research is needed to elucidate ecosystem dynamics that may lead to self-organized behavior and determine thresholds for ecosystem stability.

Controlled vortical flow on delta wings through unsteady leading edge blowing

NASA Technical Reports Server (NTRS)

Lee, K. T.; Roberts, Leonard

1990-01-01

The vortical flow over a delta wing contributes an important part of the lift - the so called nonlinear lift. Controlling this vortical flow with its favorable influence would enhance aircraft maneuverability at high angle of attack. Several previous studies have shown that control of the vortical flow field is possible through the use of blowing jets. The present experimental research studies vortical flow control by applying a new blowing scheme to the rounded leading edge of a delta wing; this blowing scheme is called Tangential Leading Edge Blowing (TLEB). Vortical flow response both to steady blowing and to unsteady blowing is investigated. It is found that TLEB can redevelop stable, strong vortices even in the post-stall angle of attack regime. Analysis of the steady data shows that the effect of leading edge blowing can be interpreted as an effective change in angle of attack. The examination of the fundamental time scales for vortical flow re-organization after the application of blowing for different initial states of the flow field is studied. Different time scales for flow re-organization are shown to depend upon the effective angle of attack. A faster response time can be achieved at angles of attack beyond stall by a suitable choice of the initial blowing momentum strength. Consequently, TLEB shows the potential of controlling the vortical flow over a wide range of angles of attack; i.e., in both for pre-stall and post-stall conditions.

Generation algorithm of craniofacial structure contour in cephalometric images

NASA Astrophysics Data System (ADS)

Mondal, Tanmoy; Jain, Ashish; Sardana, H. K.

2010-02-01

Anatomical structure tracing on cephalograms is a significant way to obtain cephalometric analysis. Computerized cephalometric analysis involves both manual and automatic approaches. The manual approach is limited in accuracy and repeatability. In this paper we have attempted to develop and test a novel method for automatic localization of craniofacial structure based on the detected edges on the region of interest. According to the grey scale feature at the different region of the cephalometric images, an algorithm for obtaining tissue contour is put forward. Using edge detection with specific threshold an improved bidirectional contour tracing approach is proposed by an interactive selection of the starting edge pixels, the tracking process searches repetitively for an edge pixel at the neighborhood of previously searched edge pixel to segment images, and then craniofacial structures are obtained. The effectiveness of the algorithm is demonstrated by the preliminary experimental results obtained with the proposed method.

Edge-related loss of tree phylogenetic diversity in the severely fragmented Brazilian Atlantic forest.

PubMed

Santos, Bráulio A; Arroyo-Rodríguez, Víctor; Moreno, Claudia E; Tabarelli, Marcelo

2010-09-08

Deforestation and forest fragmentation are known major causes of nonrandom extinction, but there is no information about their impact on the phylogenetic diversity of the remaining species assemblages. Using a large vegetation dataset from an old hyper-fragmented landscape in the Brazilian Atlantic rainforest we assess whether the local extirpation of tree species and functional impoverishment of tree assemblages reduce the phylogenetic diversity of the remaining tree assemblages. We detected a significant loss of tree phylogenetic diversity in forest edges, but not in core areas of small (<80 ha) forest fragments. This was attributed to a reduction of 11% in the average phylogenetic distance between any two randomly chosen individuals from forest edges; an increase of 17% in the average phylogenetic distance to closest non-conspecific relative for each individual in forest edges; and to the potential manifestation of late edge effects in the core areas of small forest remnants. We found no evidence supporting fragmentation-induced phylogenetic clustering or evenness. This could be explained by the low phylogenetic conservatism of key life-history traits corresponding to vulnerable species. Edge effects must be reduced to effectively protect tree phylogenetic diversity in the severely fragmented Brazilian Atlantic forest.

Langley Full-scale-tunnel Investigation of Maximum Lift and Stability Characteristics of an Airplane Having Approximately Triangular Plan Form (DM-1 Glider)

NASA Technical Reports Server (NTRS)

Lovell, J Calvin; Wilson, Herbert A JR

1947-01-01

An investigation of the DM-1 Glider, which had approximately triangular plan form, an aspect ratio of 1.8 and a 60 degree sweptback leading edge, has been conducted in the Langley full-scale tunnel. The investigation consisted of the determination of the separate effects of the following modifications made to the glider on its maximum lift and stability characteristics: (a) installation of sharp leading edges over the inboard semispan of the wing, (b) removal of the vertical fin, (c) sealing of the elevon control-balance slots, (d) installation of redesigned thin vertical surfaces, (e) installation of faired sharp leading edges, and (f) installation of canopy. The maximum lift coefficient of the DM-1 glider was increased from 0.61 to 1.01 by the installation of semispan sharp leading edges, and from 1.01 to 1.24 by the removal of the vertical fin and sealing of the elevon control-balance slots. The highest maximum lift coefficient (1.32) was obtained when the faired sharp leading edges and the thin vertical surfaces were attached to the glider. The original DM-1 glider was longitudinally stable. The semispan sharp leading edges shifted the neutral point forward approximately 3 percent of the root chord at moderate lift coefficients, and the glider configuration with these sharp leading edges attached was longitudinally unstable, for the assumed center-of-gravity location, at lift coefficients above 0.73. Sealing the elevon control-balance slots and installing the faired sharp leading edges, the thin vertical surfaces, and the canopy shifted the neutral point forward approximately 8 percent of the root chord.

Functional renormalization group approach to the Yang-Lee edge singularity

DOE PAGES

An, X.; Mesterházy, D.; Stephanov, M. A.

2016-07-08

Here, we determine the scaling properties of the Yang-Lee edge singularity as described by a one-component scalar field theory with imaginary cubic coupling, using the nonperturbative functional renormalization group in 3 ≤ d ≤ 6 Euclidean dimensions. We find very good agreement with high-temperature series data in d = 3 dimensions and compare our results to recent estimates of critical exponents obtained with the four-loop ϵ = 6 - d expansion and the conformal bootstrap. The relevance of operator insertions at the corresponding fixed point of the RG β functions is discussed and we estimate the error associated with O(∂more » 4) truncations of the scale-dependent effective action.« less

Functional renormalization group approach to the Yang-Lee edge singularity

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

An, X.; Mesterházy, D.; Stephanov, M. A.

Here, we determine the scaling properties of the Yang-Lee edge singularity as described by a one-component scalar field theory with imaginary cubic coupling, using the nonperturbative functional renormalization group in 3 ≤ d ≤ 6 Euclidean dimensions. We find very good agreement with high-temperature series data in d = 3 dimensions and compare our results to recent estimates of critical exponents obtained with the four-loop ϵ = 6 - d expansion and the conformal bootstrap. The relevance of operator insertions at the corresponding fixed point of the RG β functions is discussed and we estimate the error associated with O(∂more » 4) truncations of the scale-dependent effective action.« less

Fabrication of ultra-fine nanostructures using edge transfer printing.

PubMed

Xue, Mianqi; Li, Fengwang; Cao, Tingbing

2012-03-21

The exploration of new methods and techniques for application in diverse fields, such as photonics, microfluidics, biotechnology and flexible electronics is of increasing scientific and technical interest for multiple uses over distance of 10-100 nm. This article discusses edge transfer printing--a series of unconventional methods derived from soft lithography for nanofabrication. It possesses the advantages of easy fabrication, low-cost and great serviceability. In this paper, we show how to produce exposed edges and use various materials for edge transfer printing, while nanoskiving, nanotransfer edge printing and tunable cracking for nanogaps are introduced. Besides this, different functional materials, such as metals, inorganic semiconductors and polymers, as well as localised heating and charge patterning, are described here as unconventional "inks" for printing. Edge transfer printing, which can effectively produce sub-100 nm scale ultra-fine structures, has broad applications, including metallic nanowires as nanoelectrodes, semiconductor nanowires for chemical sensors, heterostructures of organic semiconductors, plasmonic devices and so forth. This journal is © The Royal Society of Chemistry 2012

Containment of a silicone fluid free surface in reduced gravity using barrier coatings

NASA Technical Reports Server (NTRS)

Pline, Alexander D.; Jacobson, Thomas P.

1988-01-01

In support of the Surface Tension Driven Convection Experiment planned for flight aboard the Space Shuttle, tests were conducted under reduced gravity in the 2.2-sec Drop Tower and the 5.0-sec Zero-G facility at the NASA Lewis Research Center. The dynamics of controlling the test fluid, a 10-cSt viscosity silicone fluid in a low gravity environment were investigated using different container designs and barrier coatings. Three container edge designs were tested without a barrier coating; a square edge, a sharp edge with a 45-deg slope, and a sawtooth edge. All three edge designs were successful in containing the fluid below the edge. G-jitter experiments were made in scaled down containers subjected to horizontal accelerations. The data showed that a barrier coating is effective in containing silicone fluid under g-levels up to 10 sup -1 sub g sub 0. In addition, a second barrier coating was found which has similar anti-wetting characteristics and is also more durable.

Vortex stretching in self-gravitating protoplanetary discs

NASA Astrophysics Data System (ADS)

Regály, Zs.; Vorobyov, E.

2017-10-01

Horseshoe-shaped brightness asymmetries of several transitional discs are thought to be caused by large-scale vortices. Anticyclonic vortices efficiently collect dust particles, therefore they can play a major role in planet formation. Former studies suggest that the disc self-gravity weakens vortices formed at the edge of the gap opened by a massive planet in discs whose masses are in the range of 0.01 ≤ Mdisc/M* ≤ 0.1. Here, we present an investigation on the long-term evolution of the large-scale vortices formed at the viscosity transition of the discs' dead zone outer edge by means of two-dimensional hydrodynamic simulations taking disc self-gravity into account. We perform a numerical study of low-mass, 0.001 ≤ Mdisc/M* ≤ 0.01, discs, for which cases disc self-gravity was previously neglected. The large-scale vortices are found to be stretched due to disc self-gravity even for low-mass discs with Mdisc/M* ≳ 0.005, where initially the Toomre Q-parameter was ≲ 50 at the vortex distance. As a result of stretching, the vortex aspect ratio increases and a weaker azimuthal density contrast develops. The strength of the vortex stretching is proportional to the disc mass. The vortex stretching can be explained by a combined action of a non-vanishing gravitational torque caused by the vortex and the Keplerian shear of the disc. Self-gravitating vortices are subject to significantly faster decay than non-self-gravitating ones. We found that vortices developed at sharp viscosity transitions of self-gravitating discs can be described by a Goodman - Narayan - Goldreich (GNG) model as long as the disc viscosity is low, I.e. αdz ≤ 10-5.

Full particle simulations of short large-amplitude magnetic structures (SLAMS) in quasi-parallel shocks

NASA Astrophysics Data System (ADS)

Tsubouchi, K.; LembèGe, B.

2004-02-01

Dynamics of SLAMS (short large-amplitude magnetic structures) is investigated by the use of one-dimensional, full particle electromagnetic simulations. As previous hybrid simulations and analysis of experimental observations suggested, present results confirm that the SLAMS patterns result from the steepening of long wavelength magnetosonic waves which are excited by diffuse ions (representing the field-aligned reflected ion beam) interacting with the upstream ambient plasma. Five successive phases have been identified in the SLAMS dynamics: ULF wave growth and symmetric, asymmetric, spiky, and late SLAMS. The present accessibility to high-resolution (electron) scales leads to the following new features: (1) the leading edge of the SLAMS steepens over a spatial scale from which a large-amplitude whistler precursor is emitted; (2) this whistler departs from the SLAMS edge and behaves as a new shock front; (3) the spiky SLAMS phase is characterized by the build-up of a strong spiky electrostatic field (its width is about 0.5 ion inertial length) within the whistler precursor and is intermittent with a lifetime less than one inverse ion gyroperiod; (4) the new shock front suffers a local self-reformation typical of a quasi-perpendicular shock in supercritical regime during the late-SLAMS phase. The features of the spiky SLAMS phase can be used as a typical signature in the time history of the SLAMS dynamics. Spatial/time scales of SLAMS have been measured throughout the different phases and are found in good agreement with results issued from previous hybrid simulations and with experimental measurements made by AMPTE UKS/IRM satellites; these are also compared with recent results from Cluster-2 space mission.

EDGE(3): a web-based solution for management and analysis of Agilent two color microarray experiments.

PubMed

Vollrath, Aaron L; Smith, Adam A; Craven, Mark; Bradfield, Christopher A

2009-09-04

The ability to generate transcriptional data on the scale of entire genomes has been a boon both in the improvement of biological understanding and in the amount of data generated. The latter, the amount of data generated, has implications when it comes to effective storage, analysis and sharing of these data. A number of software tools have been developed to store, analyze, and share microarray data. However, a majority of these tools do not offer all of these features nor do they specifically target the commonly used two color Agilent DNA microarray platform. Thus, the motivating factor for the development of EDGE(3) was to incorporate the storage, analysis and sharing of microarray data in a manner that would provide a means for research groups to collaborate on Agilent-based microarray experiments without a large investment in software-related expenditures or extensive training of end-users. EDGE(3) has been developed with two major functions in mind. The first function is to provide a workflow process for the generation of microarray data by a research laboratory or a microarray facility. The second is to store, analyze, and share microarray data in a manner that doesn't require complicated software. To satisfy the first function, EDGE3 has been developed as a means to establish a well defined experimental workflow and information system for microarray generation. To satisfy the second function, the software application utilized as the user interface of EDGE(3) is a web browser. Within the web browser, a user is able to access the entire functionality, including, but not limited to, the ability to perform a number of bioinformatics based analyses, collaborate between research groups through a user-based security model, and access to the raw data files and quality control files generated by the software used to extract the signals from an array image. Here, we present EDGE(3), an open-source, web-based application that allows for the storage, analysis, and controlled sharing of transcription-based microarray data generated on the Agilent DNA platform. In addition, EDGE(3) provides a means for managing RNA samples and arrays during the hybridization process. EDGE(3) is freely available for download at http://edge.oncology.wisc.edu/.

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

Zhang, Fangyan; Zhang, Song; Chung Wong, Pak

Effectively visualizing large graphs and capturing the statistical properties are two challenging tasks. To aid in these two tasks, many sampling approaches for graph simplification have been proposed, falling into three categories: node sampling, edge sampling, and traversal-based sampling. It is still unknown which approach is the best. We evaluate commonly used graph sampling methods through a combined visual and statistical comparison of graphs sampled at various rates. We conduct our evaluation on three graph models: random graphs, small-world graphs, and scale-free graphs. Initial results indicate that the effectiveness of a sampling method is dependent on the graph model, themore » size of the graph, and the desired statistical property. This benchmark study can be used as a guideline in choosing the appropriate method for a particular graph sampling task, and the results presented can be incorporated into graph visualization and analysis tools.« less

Edge detection of optical subaperture image based on improved differential box-counting method

NASA Astrophysics Data System (ADS)

Li, Yi; Hui, Mei; Liu, Ming; Dong, Liquan; Kong, Lingqin; Zhao, Yuejin

2018-01-01

Optical synthetic aperture imaging technology is an effective approach to improve imaging resolution. Compared with monolithic mirror system, the image of optical synthetic aperture system is often more complex at the edge, and as a result of the existence of gap between segments, which makes stitching becomes a difficult problem. So it is necessary to extract the edge of subaperture image for achieving effective stitching. Fractal dimension as a measure feature can describe image surface texture characteristics, which provides a new approach for edge detection. In our research, an improved differential box-counting method is used to calculate fractal dimension of image, then the obtained fractal dimension is mapped to grayscale image to detect edges. Compared with original differential box-counting method, this method has two improvements as follows: by modifying the box-counting mechanism, a box with a fixed height is replaced by a box with adaptive height, which solves the problem of over-counting the number of boxes covering image intensity surface; an image reconstruction method based on super-resolution convolutional neural network is used to enlarge small size image, which can solve the problem that fractal dimension can't be calculated accurately under the small size image, and this method may well maintain scale invariability of fractal dimension. The experimental results show that the proposed algorithm can effectively eliminate noise and has a lower false detection rate compared with the traditional edge detection algorithms. In addition, this algorithm can maintain the integrity and continuity of image edge in the case of retaining important edge information.

Anomalous Ion Heating, Intrinsic and Induced Rotation in the Pegasus Toroidal Experiment

NASA Astrophysics Data System (ADS)

Burke, M. G.; Barr, J. L.; Bongard, M. W.; Fonck, R. J.; Hinson, E. T.; Perry, J. M.; Redd, A. J.; Thome, K. E.

2014-10-01

Pegasus plasmas are initiated through either standard, MHD stable, inductive current drive or non-solenoidal local helicity injection (LHI) current drive with strong reconnection activity, providing a rich environment to study ion dynamics. During LHI discharges, a large amount of anomalous impurity ion heating has been observed, with Ti ~ 800 eV but Te < 100 eV. The ion heating is hypothesized to be a result of large-scale magnetic reconnection activity, as the amount of heating scales with increasing fluctuation amplitude of the dominant, edge localized, n = 1 MHD mode. Chordal Ti spatial profiles indicate centrally peaked temperatures, suggesting a region of good confinement near the plasma core surrounded by a stochastic region. LHI plasmas are observed to rotate, perhaps due to an inward radial current generated by the stochastization of the plasma edge by the injected current streams. H-mode plasmas are initiated using a combination of high-field side fueling and Ohmic current drive. This regime shows a significant increase in rotation shear compared to L-mode plasmas. In addition, these plasmas have been observed to rotate in the counter-Ip direction without any external momentum sources. The intrinsic rotation direction is consistent with predictions from the saturated Ohmic confinement regime. Work supported by US DOE Grant DE-FG02-96ER54375.

Fabrication of Silicon Backshort Assembly for Waveguide-Coupled Superconducting Detectors

NASA Technical Reports Server (NTRS)

Crowe, E.; Bennett, C. L.; Chuss, D. T.; Denis, K. L.; Eimer, J.; Lourie, N.; Marriage, T.; Moseley, S. H.; Rostem, K.; Stevenson, T. R.;

A new method of edge detection for object recognition

USGS Publications Warehouse

Maddox, Brian G.; Rhew, Benjamin

2004-01-01

Traditional edge detection systems function by returning every edge in an input image. This can result in a large amount of clutter and make certain vectorization algorithms less accurate. Accuracy problems can then have a large impact on automated object recognition systems that depend on edge information. A new method of directed edge detection can be used to limit the number of edges returned based on a particular feature. This results in a cleaner image that is easier for vectorization. Vectorized edges from this process could then feed an object recognition system where the edge data would also contain information as to what type of feature it bordered.

Climate Dynamics and Hysteresis at Low and High Obliquity

NASA Astrophysics Data System (ADS)

Colose, C.; Del Genio, A. D.; Way, M.

2017-12-01

We explore the large-scale climate dynamics at low and high obliquity for an Earth-like planet using the ROCKE-3D (Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics) 3-D General Circulation model being developed at NASA GISS as part of the Nexus for Exoplanet System Science (NExSS) initiative. We highlight the role of ocean heat storage and transport in determining the seasonal cycle at high obliquity, and describe the large-scale circulation and resulting regional climate patterns using both aquaplanet and Earth topographical boundary conditions. Finally, we contrast the hysteresis structure to varying CO2 concentration for a low and high obliquity planet near the outer edge of the habitable zone. We discuss the prospects for habitability for a high obliquity planet susceptible to global glaciation.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Novel Route to Fabrication of Metal-Sandwiched Nanoscale Tapered Structures

NASA Astrophysics Data System (ADS)

Zhang, Yang; Yu, Da-Peng

2009-08-01

Tapered dielectric structures in metal have exhibited extraordinary performance in both surface plasmon polariton (SPP) waveguiding and SPP focusing. This is crucial to plasmonic research and industrial plasmonic device integration. We present a method that facilitates easy fabrication of smooth-surfaced sub-micron tapered structures in large scale simply with electron beam lithography (EBL). When a PMMA layer is spin-coated on previously-EBL-defined PMMA structures, steep edges can be transformed into a declining slope to form tapered PMMA structures, scaled from 10 nm to 1000 nm. Despite the simplicity of our method, patterns with PMMA surface smoothness can be well-positioned and replicated in large numbers, which therefore gives scientists easy access to research on the properties of tapered structures.

Illustrative visualization of 3D city models

NASA Astrophysics Data System (ADS)

Doellner, Juergen; Buchholz, Henrik; Nienhaus, Marc; Kirsch, Florian

2005-03-01

This paper presents an illustrative visualization technique that provides expressive representations of large-scale 3D city models, inspired by the tradition of artistic and cartographic visualizations typically found in bird"s-eye view and panoramic maps. We define a collection of city model components and a real-time multi-pass rendering algorithm that achieves comprehensible, abstract 3D city model depictions based on edge enhancement, color-based and shadow-based depth cues, and procedural facade texturing. Illustrative visualization provides an effective visual interface to urban spatial information and associated thematic information complementing visual interfaces based on the Virtual Reality paradigm, offering a huge potential for graphics design. Primary application areas include city and landscape planning, cartoon worlds in computer games, and tourist information systems.

Infering and Calibrating Triadic Closure in a Dynamic Network

NASA Astrophysics Data System (ADS)

Mantzaris, Alexander V.; Higham, Desmond J.

In the social sciences, the hypothesis of triadic closure contends that new links in a social contact network arise preferentially between those who currently share neighbours. Here, in a proof-of-principle study, we show how to calibrate a recently proposed evolving network model to time-dependent connectivity data. The probabilistic edge birth rate in the model contains a triadic closure term, so we are also able to assess statistically the evidence for this effect. The approach is shown to work on data generated synthetically from the model. We then apply this methodology to some real, large-scale data that records the build up of connections in a business-related social networking site, and find evidence for triadic closure.

Low-speed longitudinal and lateral-directional aerodynamic characteristics of the X-31 configuration

NASA Technical Reports Server (NTRS)

Banks, Daniel W.; Gatlin, Gregory M.; Paulson, John W., Jr.

1992-01-01

An experimental investigation of a 19 pct. scale model of the X-31 configuration was completed in the Langley 14 x 22 Foot Subsonic Tunnel. This study was performed to determine the static low speed aerodynamic characteristics of the basic configuration over a large range of angle of attack and sideslip and to study the effects of strakes, leading-edge extensions (wing-body strakes), nose booms, speed-brake deployment, and inlet configurations. The ultimate purpose was to optimize the configuration for high angle of attack and maneuvering-flight conditions. The model was tested at angles of attack from -5 to 67 deg and at sideslip angles from -16 to 16 deg for speeds up to 190 knots (dynamic pressure of 120 psf).

Coherent structures and flow topology of transitional separated-reattached flow over two and three dimensional geometrical shapes

NASA Astrophysics Data System (ADS)

Diabil, Hayder Azeez; Li, Xin Kai; Abdalla, Ibrahim Elrayah

2017-09-01

Large-scale organized motions (commonly referred to coherent structures) and flow topology of a transitional separated-reattached flow have been visualised and investigated using flow visualisation techniques. Two geometrical shapes including two-dimensional flat plate with rectangular leading edge and three-dimensional square cylinder are chosen to shed a light on the flow topology and present coherent structures of the flow over these shapes. For both geometries and in the early stage of the transition, two-dimensional Kelvin-Helmholtz rolls are formed downstream of the leading edge. They are observed to be twisting around the square cylinder while they stay flat in the case of the two-dimensional flat plate. For both geometrical shapes, the two-dimensional Kelvin-Helmholtz rolls move downstream of the leading edge and they are subjected to distortion to form three-dimensional hairpin structures. The flow topology in the flat plate is different from that in the square cylinder. For the flat plate, there is a merging process by a pairing of the Kelvin-Helmholtz rolls to form a large structure that breaks down directly into many hairpin structures. For the squire cylinder case, the Kelvin-Helmholtz roll evolves topologically to form a hairpin structure. In the squire cylinder case, the reattachment length is much shorter and a forming of the three-dimensional structures is closer to the leading edge than that in the flat plate case.

Aerodynamics of a translating comb-like plate inspired by a fairyfly wing

NASA Astrophysics Data System (ADS)

Lee, Seung Hun; Kim, Daegyoum

2017-08-01

Unlike the smooth wings of common insects or birds, micro-scale insects such as the fairyfly have a distinctive wing geometry, comprising a frame with several bristles. Motivated by this peculiar wing geometry, we experimentally investigated the flow structure of a translating comb-like wing for a wide range of gap size, angle of attack, and Reynolds number, Re = O(10) - O(103), and the correlation of these parameters with aerodynamic performance. The flow structures of a smooth plate without a gap and a comb-like plate are significantly different at high Reynolds number, while little difference was observed at the low Reynolds number of O(10). At low Reynolds number, shear layers that were generated at the edges of the tooth of the comb-like plate strongly diffuse and eventually block a gap. This gap blockage increases the effective surface area of the plate and alters the formation of leading-edge and trailing-edge vortices. As a result, the comb-like plate generates larger aerodynamic force per unit area than the smooth plate. In addition to a quasi-steady phase after the comb-like plate travels several chords, we also studied a starting phase of the shear layer development when the comb-like plate begins to translate from rest. While a plate with small gap size can generate aerodynamic force at the starting phase as effectively as at the quasi-steady phase, the aerodynamic force drops noticeably for a plate with a large gap because the diffusion of the developing shear layers is not enough to block the gap.

Improving performance of armchair graphene nanoribbon field effect transistors via boron nitride doping

NASA Astrophysics Data System (ADS)

Goharrizi, A. Yazdanpanah; Sanaeepur, M.; Sharifi, M. J.

2015-09-01

Device performance of 10 nm length armchair graphene nanoribbon field effect transistors with 1.5 nm and 4 nm width (13 and 33 atoms in width respectively) are compared in terms of Ion /Ioff , trans-conductance, and sub-threshold swing. While narrow devices suffer from edge roughness wider devices are subject to more substrate surface roughness and reduced bandgap. Boron Nitride doping is employed to compensate reduced bandgap in wider devices. Simultaneous effects of edge and substrate surface roughness are considered. Results show that in the presence of both the edge and substrate surface roughness the 4 nm wide device with boron nitride doping shows improved performance with respect to the 1.5 nm one (both of which incorporate the same bandgap AGNR as channel material). Electronic simulations are performed via NEGF method along with tight-binding Hamiltonian. Edge and surface roughness are created by means of one and two dimensional auto correlation functions respectively. Electronic characteristics are averaged over a large number of devices due to statistic nature of both the edge and surface roughness.

Room Temperature Quantum Spin Hall Insulator in Ethynyl-Derivative Functionalized Stanene Films

PubMed Central

Zhang, Run-wu; Zhang, Chang-wen; Ji, Wei-xiao; Li, Sheng-shi; Yan, Shi-shen; Hu, Shu-jun; Li, Ping; Wang, Pei-ji; Li, Feng

2016-01-01

Quantum spin Hall (QSH) insulators feature edge states that topologically protected from backscattering. However, the major obstacles to application for QSH effect are the lack of suitable QSH insulators with a large bulk gap. Based on first-principles calculations, we predict a class of large-gap QSH insulators in ethynyl-derivative functionalized stanene (SnC2X; X = H, F, Cl, Br, I), allowing for viable applications at room temperature. Noticeably, the SnC2Cl, SnC2Br, and SnC2I are QSH insulators with a bulk gap of ~0.2 eV, while the SnC2H and SnC2F can be transformed into QSH insulator under the tensile strains. A single pair of topologically protected helical edge states is established for the edge of these systems with the Dirac point locating at the bulk gap, and their QSH states are confirmed with topological invariant Z2 = 1. The films on BN substrate also maintain a nontrivial large-gap QSH effect, which harbors a Dirac cone lying within the band gap. These findings may shed new light in future design and fabrication of large-gap QSH insulators based on two-dimensional honeycomb lattices in spintronics. PMID:26728874

Effect of interaction strength on robustness of controlling edge dynamics in complex networks

NASA Astrophysics Data System (ADS)

Pang, Shao-Peng; Hao, Fei

2018-05-01

Robustness plays a critical role in the controllability of complex networks to withstand failures and perturbations. Recent advances in the edge controllability show that the interaction strength among edges plays a more important role than network structure. Therefore, we focus on the effect of interaction strength on the robustness of edge controllability. Using three categories of all edges to quantify the robustness, we develop a universal framework to evaluate and analyze the robustness in complex networks with arbitrary structures and interaction strengths. Applying our framework to a large number of model and real-world networks, we find that the interaction strength is a dominant factor for the robustness in undirected networks. Meanwhile, the strongest robustness and the optimal edge controllability in undirected networks can be achieved simultaneously. Different from the case of undirected networks, the robustness in directed networks is determined jointly by the interaction strength and the network's degree distribution. Moreover, a stronger robustness is usually associated with a larger number of driver nodes required to maintain full control in directed networks. This prompts us to provide an optimization method by adjusting the interaction strength to optimize the robustness of edge controllability.

Observability of planet-disc interactions in CO kinematics

NASA Astrophysics Data System (ADS)

Pérez, Sebastián; Casassus, S.; Benítez-Llambay, P.

2018-06-01

Empirical evidence of planets in gas-rich circumstellar discs is required to constrain giant planet formation theories. Here we study the kinematic patterns which arise from planet-disc interactions and their observability in CO rotational emission lines. We perform three-dimensional hydrodynamical simulations of single giant planets, and predict the emergent intensity field with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes and vortices bear strong kinematic counterparts. The iso-velocity contours in the CO(2-1) line centroids vo reveal large-scale perturbations, corresponding to abrupt transitions from below sub-Keplerian to super-Keplerian rotation along with radial and vertical flows. The increase in line optical depth at the edge of the gap also modulates vo, but this is a mild effect compared to the dynamical imprint of the planet-disc interaction. The large-scale deviations from the Keplerian rotation thus allow the planets to be indirectly detected via the first moment maps of molecular gas tracers, at ALMA angular resolutions. The strength of these deviations depends on the mass of the perturber. This initial study paves the way to eventually determine the mass of the planet by comparison with more detailed models.

TESTING SCALING RELATIONS FOR SOLAR-LIKE OSCILLATIONS FROM THE MAIN SEQUENCE TO RED GIANTS USING KEPLER DATA

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

Huber, D.; Bedding, T. R.; Stello, D.

2011-12-20

We have analyzed solar-like oscillations in {approx}1700 stars observed by the Kepler Mission, spanning from the main sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power ({nu}{sub max}), the large frequency separation ({Delta}{nu}), and oscillation amplitudes. We show that the difference of the {Delta}{nu}-{nu}{sub max} relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M){sup s} scaling nor the revised scaling relation by Kjeldsen andmore » Bedding is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main sequence to red giants to a precision of {approx}25%. The residuals show an offset particularly for unevolved stars, suggesting that an additional physical dependency is necessary to fully reproduce the observed amplitudes. We investigate correlations between amplitudes and stellar activity, and find evidence that the effect of amplitude suppression is most pronounced for subgiant stars. Finally, we test the location of the cool edge of the instability strip in the Hertzsprung-Russell diagram using solar-like oscillations and find the detections in the hottest stars compatible with a domain of hybrid stochastically excited and opacity driven pulsation.« less

MoS2 edges and heterophase interfaces: energy, structure and phase engineering

NASA Astrophysics Data System (ADS)

Zhou, Songsong; Han, Jian; Sun, Jianwei; Srolovitz, David J.

2017-06-01

The transition metal dichalcogenides exhibit polymorphism; i.e. both 2H and 1T‧ crystal structures, each with unique electronic properties. These two phases can coexist within the same monolayer microstructure, producing 2H/1T‧ interfaces. Here we report a systematic investigation of the energetics of the experimentally most important MoS2 heterophase interfaces and edges. The stable interface and edge structures change with chemical potential (these edges/interfaces are usually non-stoichiometric). Stable edges tend to be those of highest atomic density and the stable interfaces correspond to those with local atomic structure very similar to the 2H crystal. The interfacial energies are lower than those of the edges, and the 1T‧ edges have lower energy than the 2H edges. Because the 1T‧ edges have much lower energy than the 2H edges, a sufficiently narrow 1T‧ ribbon will be more stable than the corresponding 2H ribbon (this critical width is much larger in MoTe2 than in MoS2). Similarly, a large 2H flake have an equilibrium strip of 1T‧ along its edge (again this effect is much larger in MoTe2 than in MoS2). Application of tensile strains can increase the width of the stable 1T‧ strip or the critical thickness below which a ribbon favors the 1T‧ structure. These effects provide a means to phase engineer transition metal dichalcogenide microstructures.

Spatial vision processes: From the optical image to the symbolic structures of contour information

NASA Technical Reports Server (NTRS)

Jobson, Daniel J.

1988-01-01

The significance of machine and natural vision is discussed together with the need for a general approach to image acquisition and processing aimed at recognition. An exploratory scheme is proposed which encompasses the definition of spatial primitives, intrinsic image properties and sampling, 2-D edge detection at the smallest scale, the construction of spatial primitives from edges, and the isolation of contour information from textural information. Concepts drawn from or suggested by natural vision at both perceptual and physiological levels are relied upon heavily to guide the development of the overall scheme. The scheme is intended to provide a larger context in which to place the emerging technology of detector array focal-plane processors. The approach differs from many recent efforts in edge detection and image coding by emphasizing smallest scale edge detection as a foundation for multi-scale symbolic processing while diminishing somewhat the importance of image convolutions with multi-scale edge operators. Cursory treatments of information theory illustrate that the direct application of this theory to structural information in images could not be realized.

Impact of a large density gradient on linear and nonlinear edge-localized mode simulations

DOE PAGES

Xi, P. W.; Xu, X. Q.; Xia, T. Y.; ...

2013-09-27

Here, the impact of a large density gradient on edge-localized modes (ELMs) is studied linearly and nonlinearly by employing both two-fluid and gyro-fluid simulations. In two-fluid simulations, the ion diamagnetic stabilization on high-n modes disappears when the large density gradient is taken into account. But gyro-fluid simulations show that the finite Larmor radius (FLR) effect can effectively stabilize high-n modes, so the ion diamagnetic effect alone is not sufficient to represent the FLR stabilizing effect. We further demonstrate that additional gyroviscous terms must be kept in the two-fluid model to recover the linear results from the gyro-fluid model. Nonlinear simulations show that the density variation significantly weakens the E × B shearing at the top of the pedestal and thus leads to more energy loss during ELMs. The turbulence spectrum after an ELM crash is measured and has the relation ofmore » $$P(k_{z})\\propto k_{z}^{-3.3}$$ .« less

Robust light transport in non-Hermitian photonic lattices

PubMed Central

Longhi, Stefano; Gatti, Davide; Valle, Giuseppe Della

2015-01-01

Combating the effects of disorder on light transport in micro- and nano-integrated photonic devices is of major importance from both fundamental and applied viewpoints. In ordinary waveguides, imperfections and disorder cause unwanted back-reflections, which hinder large-scale optical integration. Topological photonic structures, a new class of optical systems inspired by quantum Hall effect and topological insulators, can realize robust transport via topologically-protected unidirectional edge modes. Such waveguides are realized by the introduction of synthetic gauge fields for photons in a two-dimensional structure, which break time reversal symmetry and enable one-way guiding at the edge of the medium. Here we suggest a different route toward robust transport of light in lower-dimensional (1D) photonic lattices, in which time reversal symmetry is broken because of the non-Hermitian nature of transport. While a forward propagating mode in the lattice is amplified, the corresponding backward propagating mode is damped, thus resulting in an asymmetric transport insensitive to disorder or imperfections in the structure. Non-Hermitian asymmetric transport can occur in tight-binding lattices with an imaginary gauge field via a non-Hermitian delocalization transition, and in periodically-driven superlattices. The possibility to observe non-Hermitian delocalization is suggested using an engineered coupled-resonator optical waveguide (CROW) structure. PMID:26314932

Coriolis effect on dynamic stall in a vertical axis wind turbine

NASA Astrophysics Data System (ADS)

Tsai, Hsieh-Chen; Colonius, Tim

2013-11-01

The immersed boundary method is used to simulate the flow around a two-dimensional rotating NACA 0018 airfoil at moderate (sub-scale) Reynolds number in order to investigate separated flow occurring on a vertical-axis wind turbine (VAWT). The influence of dynamic stall on the forces is characterized as a function of tip-speed ratio. The influence of the Coriolis effect is also investigated by comparing the rotating airfoil to one undergoing a surging and pitching motion that produces an equivalent speed and angle-of-attack variation over the cycle. While the Coriolis force produces only small differences in the averaged forces, it plays an important role during dynamic stall. Due to the fact that the Coriolis force deflects the fluid and propagates the vortices differently, the wake-capturing phenomenon of the trailing edge vortex is observed in the flow around the rotating airfoil during a certain range of azimuthal angle. This wake-capturing of the trailing edge vortex leads to a large decrease in lift. However, because of the phase difference between each wake-capturing, there are only small differences in the average forces. The simulations are also compared to results from companion water-tunnel experiments at Caltech. This project is supported by the Gordon and Betty Moore Foundation.

Experimental study on the crack detection with optimized spatial wavelet analysis and windowing

NASA Astrophysics Data System (ADS)

Ghanbari Mardasi, Amir; Wu, Nan; Wu, Christine

2018-05-01

In this paper, a high sensitive crack detection is experimentally realized and presented on a beam under certain deflection by optimizing spatial wavelet analysis. Due to the crack existence in the beam structure, a perturbation/slop singularity is induced in the deflection profile. Spatial wavelet transformation works as a magnifier to amplify the small perturbation signal at the crack location to detect and localize the damage. The profile of a deflected aluminum cantilever beam is obtained for both intact and cracked beams by a high resolution laser profile sensor. Gabor wavelet transformation is applied on the subtraction of intact and cracked data sets. To improve detection sensitivity, scale factor in spatial wavelet transformation and the transformation repeat times are optimized. Furthermore, to detect the possible crack close to the measurement boundaries, wavelet transformation edge effect, which induces large values of wavelet coefficient around the measurement boundaries, is efficiently reduced by introducing different windowing functions. The result shows that a small crack with depth of less than 10% of the beam height can be localized with a clear perturbation. Moreover, the perturbation caused by a crack at 0.85 mm away from one end of the measurement range, which is covered by wavelet transform edge effect, emerges by applying proper window functions.

Robust light transport in non-Hermitian photonic lattices.

PubMed

Longhi, Stefano; Gatti, Davide; Della Valle, Giuseppe

2015-08-28

Combating the effects of disorder on light transport in micro- and nano-integrated photonic devices is of major importance from both fundamental and applied viewpoints. In ordinary waveguides, imperfections and disorder cause unwanted back-reflections, which hinder large-scale optical integration. Topological photonic structures, a new class of optical systems inspired by quantum Hall effect and topological insulators, can realize robust transport via topologically-protected unidirectional edge modes. Such waveguides are realized by the introduction of synthetic gauge fields for photons in a two-dimensional structure, which break time reversal symmetry and enable one-way guiding at the edge of the medium. Here we suggest a different route toward robust transport of light in lower-dimensional (1D) photonic lattices, in which time reversal symmetry is broken because of the non-Hermitian nature of transport. While a forward propagating mode in the lattice is amplified, the corresponding backward propagating mode is damped, thus resulting in an asymmetric transport insensitive to disorder or imperfections in the structure. Non-Hermitian asymmetric transport can occur in tight-binding lattices with an imaginary gauge field via a non-Hermitian delocalization transition, and in periodically-driven superlattices. The possibility to observe non-Hermitian delocalization is suggested using an engineered coupled-resonator optical waveguide (CROW) structure.

TCA High Lift Preliminary Assessment

NASA Technical Reports Server (NTRS)

Wyatt, G. H.; Polito, R. C.; Yeh, D. T.; Elzey, M. E.; Tran, J. T.; Meredith, Paul T.

1999-01-01

This paper presents a TCA (Technology Concept Airplane) High lift Preliminary Assessment. The topics discussed are: 1) Model Description; 2) Data Repeatability; 3) Effect of Inboard L.E. (Leading Edge) Flap Span; 4) Comparison of 14'x22' TCA-1 With NTF (National Transonic Facility) Modified Ref. H; 5) Comparison of 14'x22' and NTF Ref. H Results; 6) Effect of Outboard Sealed Slat on TCA; 7) TCA Full Scale Build-ups; 8) Full Scale L/D Comparisons; 9) TCA Full Scale; and 10) Touchdown Lift Curves. This paper is in viewgraph form.

The shock/shear platform for planar radiation-hydrodynamics experiments on the National Ignition Facility

DOE PAGES

Doss, F. W.; Kline, J. L.; Flippo, K. A.; ...

2015-04-17

An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130 μm/ns shocks into a CH foam-filled shock tube (~ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for >10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment tomore » the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.« less

Mechanical and thermal buckling analysis of sandwich panels under different edge conditions

NASA Technical Reports Server (NTRS)

Ko, William L.

1993-01-01

By using the Rayleigh-Ritz method of minimizing the total potential energy of a structural system, combined load (mechanical or thermal load) buckling equations are established for orthotropic rectangular sandwich panels supported under four different edge conditions. Two-dimensional buckling interaction curves and three dimensional buckling interaction surfaces are constructed for high-temperature honeycomb-core sandwich panels supported under four different edge conditions. The interaction surfaces provide easy comparison of the panel buckling strengths and the domains of symmetrical and antisymmetrical buckling associated with the different edge conditions. Thermal buckling curves of the sandwich panels also are presented. The thermal buckling conditions for the cases with and without thermal moments were found to be identical for the small deformation theory. In sandwich panels, the effect of transverse shear is quite large, and by neglecting the transverse shear effect, the buckling loads could be overpredicted considerably. Clamping of the edges could greatly increase buckling strength more in compression than in shear.

Dynamic Stall Characteristics of Drooped Leading Edge Airfoils

NASA Technical Reports Server (NTRS)

Sankar, Lakshmi N.; Sahin, Mehmet; Gopal, Naveen

2000-01-01

Helicopters in high-speed forward flight usually experience large regions of dynamic stall over the retreating side of the rotor disk. The rapid variations in the lift and pitching moments associated with the stall process can result in vibratory loads, and can cause fatigue and failure of pitch links. In some instances, the large time lag between the aerodynamic forces and the blade motion can trigger stall flutter. A number of techniques for the alleviation of dynamic stall have been proposed and studied by researchers. Passive and active control techniques have both been explored. Passive techniques include the use of high solidity rotors that reduce the lift coefficients of individual blades, leading edge slots and leading edge slats. Active control techniques include steady and unsteady blowing, and dynamically deformable leading edge (DDLE) airfoils. Considerable amount of experimental and numerical data has been collected on the effectiveness of these concepts. One concept that has not received as much attention is the drooped-leading edge airfoil idea. It has been observed in wind tunnel studies and flight tests that drooped leading edge airfoils can have a milder dynamic stall, with a significantly milder load hysteresis. Drooped leading edge airfoils may not, however, be suitable at other conditions, e.g. in hover, or in transonic flow. Work needs to be done on the analysis and design of drooped leading edge airfoils for efficient operation in a variety of flight regimes (hover, dynamic stall, and transonic flow). One concept that is worthy of investigation is the dynamically drooping airfoil, where the leading edge shape is changed roughly once-per-rev to mitigate the dynamic stall.

Conduction Band-Edge Non-Parabolicity Effects on Impurity States in (In,Ga)N/GaN Cylindrical QWWs

NASA Astrophysics Data System (ADS)

Haddou El, Ghazi; Anouar, Jorio

2014-02-01

In this paper, the conduction band-edge non-parabolicity (NP) and the circular cross-section radius effects on hydrogenic shallow-donor impurity ground-state binding energy in zinc-blende (ZB) InGaN/GaN cylindrical QWWs are reported. The finite potential barrier between (In,Ga)N well and GaN environment is considered. Two models of the conduction band-edge non-parabolicity are taking into account. The variational approach is used within the framework of single band effective-mass approximation with one-parametric 1S-hydrogenic trial wave-function. It is found that NP effect is more pronounced in the wire of radius equal to effective Bohr radius than in large and narrow wires. Moreover, the binding energy peak shifts to narrow wire under NP effect. A good agreement is shown compared to the findings results.

Effect of RANS-Type Turbulence Models on Adiabatic Film Cooling Effectiveness over a Scaled Up Gas Turbine Blade Leading Edge Surface

NASA Astrophysics Data System (ADS)

Yepuri, Giridhara Babu; Talanki Puttarangasetty, Ashok Babu; Kolke, Deepak Kumar; Jesuraj, Felix

2016-06-01

Increasing the gas turbine inlet temperature is one of the key technologies in raising gas turbine engine power output. Film cooling is one of the efficient cooling techniques to cool the hot section components of a gas turbine engines in turn the turbine inlet temperature can be increased. This study aims at investigating the effect of RANS-type turbulence models on adiabatic film cooling effectiveness over a scaled up gas turbine blade leading edge surfaces. For the evaluation, five different two equation RANS-type turbulent models have been taken in consideration, which are available in the ANSYS-Fluent. For this analysis, the gas turbine blade leading edge configuration is generated using Solid Works. The meshing is done using ANSYS-Workbench Mesh and ANSYS-Fluent is used as a solver to solve the flow field. The considered gas turbine blade leading edge model is having five rows of film cooling circular holes, one at stagnation line and the two each on either side of stagnation line at 30° and 60° respectively. Each row has the five holes with the hole diameter of 4 mm, pitch of 21 mm arranged in staggered manner and has the hole injection angle of 30° in span wise direction. The experiments are carried in a subsonic cascade tunnel facility at heat transfer lab of CSIR-National Aerospace Laboratory with a Reynolds number of 1,00,000 based on leading edge diameter. From the Computational Fluid Dynamics (CFD) evaluation it is found that K-ɛ Realizable model gives more acceptable results with the experimental values, compared to the other considered turbulence models for this type of geometries. Further the CFD evaluated results, using K-ɛ Realizable model at different blowing ratios are compared with the experimental results.

A robotic platform for studying sea lion thrust production

NASA Astrophysics Data System (ADS)

Leftwich, Megan; Patel, Rahi; Kulkarni, Aditya; Friedman, Chen

California Sea Lions are agile swimmers and, uniquely, use their foreflippers (rather than hind flipper undulation) to generate thrust. Recently, a sea lion flipper from a deceased subject was externally scanned in high detail for fluid dynamics research. The flipper's geometry is used in this work to build an accurate scaled down flipper model (approximately 68% of the full size span). The flipper model is placed in a water flume to obtain lift and drag force measurements. The unique trailing edge features are then examined for their effect on the measured forces by comparing to similar flipper models with a smooth trailing edge, sinusoidal trailing edge, and a saw-tooth trailing edge. Additionally, a robotic flipper is being designed and built, replicating the sea lion foreflipper anatomical structure. The robot is actuated by a set of servo motors and replicates the sea lion flipper clap motion based on previously extracted kinematics. The flipper tip speed is designed to match typical full scale Reynolds numbers for an acceleration from rest maneuver. The model is tested in the water flume as well to obtain the forces and flow structures during the thrust production phase of the flipper motion.

Is there a common orientational order for the liquid phase of tetrahedral molecules?

PubMed

Rey, Rossend

2009-08-14

The title question is addressed with molecular dynamics simulations for a broad set of molecules: methane (CH4), neopentane (C(CH3)4), carbon tetrafluoride (CF4), carbon tetrachloride (CCl4), silicon tetrachloride (SiCl4), vanadium tetrachloride (VCl4), tin tetrachloride (SnCl4), carbon tetrabromide (CBr4), and tin tetraiodide (SnI4). In all cases the sequence of most populated relative orientations, for increasing distances, is found to be identical: The closest distances correspond to face-to-face followed by a dominant role of edge-to-face, while for larger distances the main configuration is edge-to-edge. The corner-to-face configuration plays an almost negligible role. The range of orientational order is also similar, with remnants of orientational correlation discernible up to the fourth solvation shell. The equivalence does not only hold in the qualitative terms just stated but is also quantitative to a large extent once the center-center distance is properly scaled.

Is there a common orientational order for the liquid phase of tetrahedral molecules?

NASA Astrophysics Data System (ADS)

Rey, Rossend

2009-08-01

The title question is addressed with molecular dynamics simulations for a broad set of molecules: methane (CH4), neopentane (C(CH3)4), carbon tetrafluoride (CF4), carbon tetrachloride (CCl4), silicon tetrachloride (SiCl4), vanadium tetrachloride (VCl4), tin tetrachloride (SnCl4), carbon tetrabromide (CBr4), and tin tetraiodide (SnI4). In all cases the sequence of most populated relative orientations, for increasing distances, is found to be identical: The closest distances correspond to face-to-face followed by a dominant role of edge-to-face, while for larger distances the main configuration is edge-to-edge. The corner-to-face configuration plays an almost negligible role. The range of orientational order is also similar, with remnants of orientational correlation discernible up to the fourth solvation shell. The equivalence does not only hold in the qualitative terms just stated but is also quantitative to a large extent once the center-center distance is properly scaled.

Summer Drivers of Atmospheric Variability Affecting Ice Shelf Thinning in the Amundsen Sea Embayment, West Antarctica

NASA Astrophysics Data System (ADS)

Deb, Pranab; Orr, Andrew; Bromwich, David H.; Nicolas, Julien P.; Turner, John; Hosking, J. Scott

2018-05-01

Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves.

Computer simulation and evaluation of edge detection algorithms and their application to automatic path selection

NASA Technical Reports Server (NTRS)

Longendorfer, B. A.

1976-01-01

The construction of an autonomous roving vehicle requires the development of complex data-acquisition and processing systems, which determine the path along which the vehicle travels. Thus, a vehicle must possess algorithms which can (1) reliably detect obstacles by processing sensor data, (2) maintain a constantly updated model of its surroundings, and (3) direct its immediate actions to further a long range plan. The first function consisted of obstacle recognition. Obstacles may be identified by the use of edge detection techniques. Therefore, the Kalman Filter was implemented as part of a large scale computer simulation of the Mars Rover. The second function consisted of modeling the environment. The obstacle must be reconstructed from its edges, and the vast amount of data must be organized in a readily retrievable form. Therefore, a Terrain Modeller was developed which assembled and maintained a rectangular grid map of the planet. The third function consisted of directing the vehicle's actions.

Crystallographic analysis of the solid-state dewetting of polycrystalline gold film using automated indexing in a transmission electron microscope

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

Jang, S. A.; Lee, H. J.; Oh, Y. J., E-mail: yjoh@hanbat.ac.kr

We analyzed the effect of crystallographic anisotropy on the morphological evolution of a 12-nm-thick gold film during solid-state dewetting at high temperatures using automated indexing tool in a transmission electron microscopy. Dewetting initiated at grain-boundary triple junctions adjacent to large grains resulting from abnormal grain growth driven by (111) texture development. Voids at the junctions developed shapes with faceted edges bounded by low-index crystal planes. The kinetic mobility of the edges varied with the crystal orientation normal to the edges, with a predominance of specific edges with the slowest retraction rates as the annealing time was increased.

Multiscale properties of weighted total variation flow with applications to denoising and registration.

PubMed

Athavale, Prashant; Xu, Robert; Radau, Perry; Nachman, Adrian; Wright, Graham A

2015-07-01

Images consist of structures of varying scales: large scale structures such as flat regions, and small scale structures such as noise, textures, and rapidly oscillatory patterns. In the hierarchical (BV, L(2)) image decomposition, Tadmor, et al. (2004) start with extracting coarse scale structures from a given image, and successively extract finer structures from the residuals in each step of the iterative decomposition. We propose to begin instead by extracting the finest structures from the given image and then proceed to extract increasingly coarser structures. In most images, noise could be considered as a fine scale structure. Thus, starting the image decomposition with finer scales, rather than large scales, leads to fast denoising. We note that our approach turns out to be equivalent to the nonstationary regularization in Scherzer and Weickert (2000). The continuous limit of this procedure leads to a time-scaled version of total variation flow. Motivated by specific clinical applications, we introduce an image depending weight in the regularization functional, and study the corresponding weighted TV flow. We show that the edge-preserving property of the multiscale representation of an input image obtained with the weighted TV flow can be enhanced and localized by appropriate choice of the weight. We use this in developing an efficient and edge-preserving denoising algorithm with control on speed and localization properties. We examine analytical properties of the weighted TV flow that give precise information about the denoising speed and the rate of change of energy of the images. An additional contribution of the paper is to use the images obtained at different scales for robust multiscale registration. We show that the inherently multiscale nature of the weighted TV flow improved performance for registration of noisy cardiac MRI images, compared to other methods such as bilateral or Gaussian filtering. A clinical application of the multiscale registration algorithm is also demonstrated for aligning viability assessment magnetic resonance (MR) images from 8 patients with previous myocardial infarctions. Copyright © 2015. Published by Elsevier B.V.

Computational Evaluation of the Steady and Pulsed Jet Effects on the Performance of a Circulation Control Wing Section

NASA Technical Reports Server (NTRS)

Liu, Yi; Sankar, Lakshmi N.; Englar, Robert; Ahuja, K.; Gaeta, R.

2003-01-01

Circulation Control Wing (CCW) technology is a very effective way of achieving very high lift coefficients needed by aircraft during take-off and landing. This technology can also be used to directly control the flow field over the wing. Compared to a conventional high-lift system, a Circulation Control Wing (CCW) can generate the required values of lift coefficient C(sub L,max) during take-off/landing with fewer or no moving parts and much less complexity. Earlier designs of CCW configurations used airfoils with a large radius rounded trailing edge to maximize the lift benefit. However, these designs also produced very high drag. These high drag levels associated with the blunt, large radius trailing edge can be prohibitive under cruise conditions when Circulation Control is no longer necessary. To overcome this difficulty, an advanced CCW section, i.e., a circulation hinged flap was developed to replace the original rounded trailing edge CC airfoil. This concept developed by Englar is shown. The upper surface of the CCW flap is a large-radius arc surface, but the lower surface of the flap is flat. The flap could be deflected from 0 degrees to 90 degrees. When an aircraft takes-off or lands, the flap is deflected as in a conventional high lift system. Then this large radius on the upper surface produces a large jet turning angle, leading to high lift. When the aircraft is in cruise, the flap is retracted and a conventional sharp trailing edge shape results, greatly reducing the drag. This kind of flap does have some moving elements that increase the weight and complexity over an earlier CCW design. But overall, the hinged flap design still maintains most of the Circulation Control high lift advantages, while greatly reducing the drag in cruising condition associated with the rounded trailing edge CCW design. In the present work, an unsteady three-dimensional Navier-Stokes analysis procedure has been developed and applied to this advanced CCW configuration. The solver can be used in both a 2-D and a 3-D mode, and can thus model airfoils as well as finite wings. The jet slot location, slot height, and the flap angle can all be varied easily and individually in the grid generator and the flow solver. Steady jets, pulsed jets, the leading edge and trailing edge blowing can all be studied with this solver.

Generation of Artificial Ionospheric Irregularities in the Midlatitude Ionosphere Modified by High-Power High-Frequency X-Mode Radio Waves

NASA Astrophysics Data System (ADS)

Frolov, V. L.; Bolotin, I. A.; Komrakov, G. P.; Pershin, A. V.; Vertogradov, G. G.; Vertogradov, V. G.; Vertogradova, E. G.; Kunitsyn, V. E.; Padokhin, A. M.; Kurbatov, G. A.; Akchurin, A. D.; Zykov, E. Yu.

2014-11-01

We consider the properties of the artificial ionospheric irregularities excited in the ionospheric F 2 region modified by high-power high-frequency X-mode radio waves. It is shown that small-scale (decameter) irregularities are not generated in the midlatitude ionosphere. The intensity of irregularities with the scales l ⊥ ≈50 m to 3 km is severalfold weaker compared with the case where the irregularities are excited by high-power O-mode radio waves. The intensity of the larger-scale irregularities is even stronger attenuated. It is found that the generation of large-scale ( l ⊥ ≈5-10 km) artificial ionospheric irregularities is enhanced at the edge of the directivity pattern of a beam of high-power radio waves.

The Relationship Between Fusion, Suppression, and Diplopia in Normal and Amblyopic Vision.

PubMed

Spiegel, Daniel P; Baldwin, Alex S; Hess, Robert F

2016-10-01

Single vision occurs through a combination of fusion and suppression. When neither mechanism takes place, we experience diplopia. Under normal viewing conditions, the perceptual state depends on the spatial scale and interocular disparity. The purpose of this study was to examine the three perceptual states in human participants with normal and amblyopic vision. Participants viewed two dichoptically separated horizontal blurred edges with an opposite tilt (2.35°) and indicated their binocular percept: "one flat edge," "one tilted edge," or "two edges." The edges varied with scale (fine 4 min arc and coarse 32 min arc), disparity, and interocular contrast. We investigated how the binocular interactions vary in amblyopic (visual acuity [VA] > 0.2 logMAR, n = 4) and normal vision (VA ≤ 0 logMAR, n = 4) under interocular variations in stimulus contrast and luminance. In amblyopia, despite the established sensory dominance of the fellow eye, fusion prevails at the coarse scale and small disparities (75%). We also show that increasing the relative contrast to the amblyopic eye enhances the probability of fusion at the fine scale (from 18% to 38%), and leads to a reversal of the sensory dominance at coarse scale. In normal vision we found that interocular luminance imbalances disturbed binocular combination only at the fine scale in a way similar to that seen in amblyopia. Our results build upon the growing evidence that the amblyopic visual system is binocular and further show that the suppressive mechanisms rendering the amblyopic system functionally monocular are scale dependent.

Evaluation of subgrid-scale models in large-eddy simulations of turbulent flow in a centrifugal pump impeller

NASA Astrophysics Data System (ADS)

Yang, Zhengjun; Wang, Fujun; Zhou, Peijian

2012-09-01

The current research of large eddy simulation (LES) of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale (SGS) model to simulate turbulent flow, which aims at obtaining the flow field in pump. The selection of SGS model is usually not considered seriously, so the accuracy and efficiency of the simulation cannot be ensured. Three SGS models including Smagorinsky-Lilly model, dynamic Smagorinsky model and dynamic mixed model are comparably studied by using the commercial CFD code Fluent combined with its user define function. The simulations are performed for the turbulent flow in a centrifugal pump impeller. The simulation results indicate that the mean flows predicted by the three SGS models agree well with the experimental data obtained from the test that detailed measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The comparable results show that dynamic mixed model gives the most accurate results for mean flow in the centrifugal pump impeller. The SGS stress of dynamic mixed model is decompose into the scale similar part and the eddy viscous part. The scale similar part of SGS stress plays a significant role in high curvature regions, such as the leading edge and training edge of pump blade. It is also found that the dynamic mixed model is more adaptive to compute turbulence in the pump impeller. The research results presented is useful to improve the computational accuracy and efficiency of LES for centrifugal pumps, and provide important reference for carrying out simulation in similar fluid machineries.

Cosmology Large Angular Scale Surveyor (CLASS) Focal Plane Development

NASA Technical Reports Server (NTRS)

Chuss, D. T.; Ali, A.; Amiri, M.; Appel, J.; Bennett, C. L.; Colazo, F.; Denis, K. L.; Dunner, R.; Essinger-Hileman, T.; Eimer, J.;

Cosmology Large Angular Scale Surveyor (CLASS) Focal Plane Development

NASA Astrophysics Data System (ADS)

Chuss, D. T.; Ali, A.; Amiri, M.; Appel, J.; Bennett, C. L.; Colazo, F.; Denis, K. L.; Dünner, R.; Essinger-Hileman, T.; Eimer, J.; Fluxa, P.; Gothe, D.; Halpern, M.; Harrington, K.; Hilton, G.; Hinshaw, G.; Hubmayr, J.; Iuliano, J.; Marriage, T. A.; Miller, N.; Moseley, S. H.; Mumby, G.; Petroff, M.; Reintsema, C.; Rostem, K.; U-Yen, K.; Watts, D.; Wagner, E.; Wollack, E. J.; Xu, Z.; Zeng, L.

2016-08-01

The Cosmology Large Angular Scale Surveyor (CLASS) will measure the polarization of the Cosmic Microwave Background to search for and characterize the polarized signature of inflation. CLASS will operate from the Atacama Desert and observe ˜ 70 % of the sky. A variable-delay polarization modulator provides modulation of the polarization at ˜ 10 Hz to suppress the 1/ f noise of the atmosphere and enable the measurement of the large angular scale polarization modes. The measurement of the inflationary signal across angular scales that spans both the recombination and reionization features allows a test of the predicted shape of the polarized angular power spectra in addition to a measurement of the energy scale of inflation. CLASS is an array of telescopes covering frequencies of 38, 93, 148, and 217 GHz. These frequencies straddle the foreground minimum and thus allow the extraction of foregrounds from the primordial signal. Each focal plane contains feedhorn-coupled transition-edge sensors that simultaneously detect two orthogonal linear polarizations. The use of single-crystal silicon as the dielectric for the on-chip transmission lines enables both high efficiency and uniformity in fabrication. Integrated band definition has been implemented that both controls the bandpass of the single-mode transmission on the chip and prevents stray light from coupling to the detectors.

Edge states in the climate system: exploring global instabilities and critical transitions

NASA Astrophysics Data System (ADS)

Lucarini, Valerio; Bódai, Tamás

2017-07-01

Multistability is a ubiquitous feature in systems of geophysical relevance and provides key challenges for our ability to predict a system’s response to perturbations. Near critical transitions small causes can lead to large effects and—for all practical purposes—irreversible changes in the properties of the system. As is well known, the Earth climate is multistable: present astronomical and astrophysical conditions support two stable regimes, the warm climate we live in, and a snowball climate characterized by global glaciation. We first provide an overview of methods and ideas relevant for studying the climate response to forcings and focus on the properties of critical transitions in the context of both stochastic and deterministic dynamics, and assess strengths and weaknesses of simplified approaches to the problem. Following an idea developed by Eckhardt and collaborators for the investigation of multistable turbulent fluid dynamical systems, we study the global instability giving rise to the snowball/warm multistability in the climate system by identifying the climatic edge state, a saddle embedded in the boundary between the two basins of attraction of the stable climates. The edge state attracts initial conditions belonging to such a boundary and, while being defined by the deterministic dynamics, is the gate facilitating noise-induced transitions between competing attractors. We use a simplified yet Earth-like intermediate complexity climate model constructed by coupling a primitive equations model of the atmosphere with a simple diffusive ocean. We refer to the climatic edge states as Melancholia states and provide an extensive analysis of their features. We study their dynamics, their symmetry properties, and we follow a complex set of bifurcations. We find situations where the Melancholia state has chaotic dynamics. In these cases, we have that the basin boundary between the two basins of attraction is a strange geometric set with a nearly zero codimension, and relate this feature to the time scale separation between instabilities occurring on weather and climatic time scales. We also discover a new stable climatic state that is similar to a Melancholia state and is characterized by non-trivial symmetry properties.

The effect of short ground vegetation on terrestrial laser scans at a local scale

NASA Astrophysics Data System (ADS)

Fan, Lei; Powrie, William; Smethurst, Joel; Atkinson, Peter M.; Einstein, Herbert

2014-09-01

Terrestrial laser scanning (TLS) can record a large amount of accurate topographical information with a high spatial accuracy over a relatively short period of time. These features suggest it is a useful tool for topographical survey and surface deformation detection. However, the use of TLS to survey a terrain surface is still challenging in the presence of dense ground vegetation. The bare ground surface may not be illuminated due to signal occlusion caused by vegetation. This paper investigates vegetation-induced elevation error in TLS surveys at a local scale and its spatial pattern. An open, relatively flat area vegetated with dense grass was surveyed repeatedly under several scan conditions. A total station was used to establish an accurate representation of the bare ground surface. Local-highest-point and local-lowest-point filters were applied to the point clouds acquired for deriving vegetation height and vegetation-induced elevation error, respectively. The effects of various factors (for example, vegetation height, edge effects, incidence angle, scan resolution and location) on the error caused by vegetation are discussed. The results are of use in the planning and interpretation of TLS surveys of vegetated areas.

Myosin II activity is required for functional leading-edge cells and closure of epidermal sheets in fish skin ex vivo.

PubMed

Morita, Toshiyuki; Tsuchiya, Akiko; Sugimoto, Masazumi

2011-09-01

Re-epithelialization in skin wound healing is a process in which epidermal sheets grow and close the wound. Although the actin-myosin system is thought to have a pivotal role in re-epithelialization, its role is not clear. In fish skin, re-epithelialization occurs around 500 μm/h and is 50 times faster than in mammalian skin. We had previously reported that leading-edge cells of the epidermal outgrowth have both polarized large lamellipodia and "purse string"-like actin filament cables in the scale-skin culture system of medaka fish, Oryzias latipes (Cell Tissue Res, 2007). The actin purse-string (APS) is a supracellular contractile machinery in which adherens junctions (AJs) link intracellular myosin II-including actin cables between neighboring cells. In this study, we developed a modified "face-to-face" scale-skin culture system as an ex vivo model to study epidermal wound healing, and examined the role of the actin-myosin system in the rapid re-epithelialization using a myosin II ATPase inhibitor, blebbistatin. A low level of blebbistatin suppressed the formation of APS and induced the dissociation of keratocytes from the leading edge without attenuating the growth of the epidermal sheet or the migration rate of solitary keratocytes. AJs in the superficial layer showed no obvious changes elicited by blebbistatin. However, two epidermal sheets without APSs did not make a closure with each other, which was confirmed by inhibiting the connecting AJs between the superficial layers. These results suggest that myosin II activity is required for functional leading-edge cells and for epidermal closure.

Multifractal analysis of line-edge roughness

NASA Astrophysics Data System (ADS)

Constantoudis, Vassilios; Papavieros, George; Lorusso, Gian; Rutigliani, Vito; van Roey, Frieda; Gogolides, Evangelos

2018-03-01

In this paper, we propose to rethink the issue of LER characterization on the basis of the fundamental concept of symmetries. In LER one can apply two kinds of symmetries: a) the translation symmetry characterized by periodicity and b) the scaling symmetry quantified by the fractal dimension. Up to now, a lot of work has been done on the first symmetry since the Power Spectral Density (PSD), which has been extensively studied recently, is a decomposition of LER signal into periodic edges and quantification of the `power' of each periodicity at the real LER. The aim of this paper is to focus on the second symmetry of scaling invariance. Similarly to PSD, we introduce the multifractal approach in LER analysis which generalizes the scaling analysis of standard (mono)fractal theory and decomposes LER into fractal edges characterized by specific fractal dimensions. The main benefit of multifractal analysis is that it enables the characterization of the multi-scaling contributions of different mechanisms involved in LER formation. In the first part of our work, we present concisely the multifractal theory of line edges and utilize the Box Counting method for its implementation and the extraction of the multifractal spectrum. Special emphasis is given on the explanation of the physical meaning of the obtained multifractal spectrum whose asymmetry quantifies the degree of multifractality. In addition, we propose the distinction between peak-based and valley-based multifractality according to whether the asymmetry of the multifractal spectrum is coming from the sharp line material peaks to space regions or from the cavities of line materis (edge valleys). In the second part, we study systematically the evolution of LER multifractal spectrum during the first successive steps of a multiple (quadruple) patterning lithography technique and find an interesting transition from a peak-based multifractal behavior in the first litho resist LER to a valley-based multifractality caused mainly by the effects of etch pattern transfer steps.

Spatial Variation of Pressure in the Lyophilization Product Chamber Part 2: Experimental Measurements and Implications for Scale-up and Batch Uniformity.

PubMed

Sane, Pooja; Varma, Nikhil; Ganguly, Arnab; Pikal, Michael; Alexeenko, Alina; Bogner, Robin H

2017-02-01

Product temperature during the primary drying step of freeze-drying is controlled by a set point chamber pressure and shelf temperature. However, recent computational modeling suggests a possible variation in local chamber pressure. The current work presents an experimental verification of the local chamber pressure gradients in a lab-scale freeze-dryer. Pressure differences between the center and the edges of a lab-scale freeze-dryer shelf were measured as a function of sublimation flux and clearance between the sublimation front and the shelf above. A modest 3-mTorr difference in pressure was observed as the sublimation flux was doubled from 0.5 to 1.0 kg·h -1 ·m -2 at a clearance of 2.6 cm. Further, at a constant sublimation flux of 1.0 kg·h -1 ·m -2 , an 8-fold increase in the pressure drop was observed across the shelf as the clearance was decreased from 4 to 1.6 cm. Scale-up of the pressure variation from lab- to a manufacturing-scale freeze-dryer predicted an increased uniformity in drying rates across the batch for two frequently used pharmaceutical excipients (mannitol and sucrose at 5% w/w). However, at an atypical condition of shelf temperature of +10°C and chamber pressure of 50 mTorr, the product temperature in the center vials was calculated to be a degree higher than the edge vial for a low resistance product, thus reversing the typical edge and center vial behavior. Thus, the effect of local pressure variation is more significant at the manufacturing-scale than at a lab-scale and accounting for the contribution of variations in the local chamber pressures can improve success in scale-up.

Structural evolution dynamics in fusion of sumanenes and corannulenes: defects formation and self-healing mechanism

NASA Astrophysics Data System (ADS)

Sorkin, Anastassia; Su, Haibin

2018-06-01

The fusion processes of structures consisting of various combinations between sumanene and corannulene, leading to the formation of graphene nanoribbons (GNRs) under heating are simulated by density-functional-based tight-binding molecular dynamics. Distinct stages are unraveled in the course of GNR formation. Firstly, the carbon fragments coalescence into highly strained framework. Secondly, structural reconstruction invokes breaking most strained bonds to form a GNR structure containing numerous defects. Lastly, defects are remedied by the delicate ‘edge-facilitated self-healing’ process through two synergized edge-related effects: elevated mobility of defects and promoted structure reconstructions owing to the remarkable dynamics associated with edges. Importantly, detailed dynamics in the course of forming GNRs with defects and grain boundaries simulated in this work is valuable to provide better understanding at the atomistic scale of defect formation as well as self-healing in the context of the sp2 carbon network. In particular, edges play important roles in not only generating Stone–Wales (SW), 5-8-5 types of defects, 8-5-5-8 and pentagon–heptagon grain boundaries. In addition, our simulations predict the existence of one novel defect, coined as the Inverse SW defect, which is to be confirmed in future experimental studies. This study of dynamic structural evolution reveals that edges are prone to intrinsic and extrinsic modifications such as atomic-scale defects, structural distortions and inhomogeneity.

Large-scale Graph Computation on Just a PC

DTIC Science & Technology

2014-05-01

edges for several vertices simultaneously). We compared the performance of GraphChi-DB to Neo4j using their Java API (we discuss MySQL comparison in the...75 4.7.6 Comparison to RDBMS ( MySQL ) . . . . . . . . . . . . . . . . . . . . . 75 4.7.7 Summary of the...Windows method, GraphChi. The C++ implementation has circa 8,000 lines of code. We have also de- veloped a Java -version of GraphChi, but it does not

Iron Polymerization and Arsenic Removal During In-Situ Iron Electrocoagulation in Synthetic Bangladeshi Groundwater

NASA Astrophysics Data System (ADS)

van Genuchten, C. M.; Pena, J.; Addy, S.; Gadgil, A.

2010-12-01

Millions of people worldwide are exposed to arsenic-contamination in groundwater drinking supplies. The majority of affected people live in rural Bangladesh. Electrocoagulation (EC) using iron electrodes is a promising arsenic removal strategy that is based on the generation of iron precipitates with a high affinity for arsenic through the electrochemical dissolution of a sacrificial iron anode. Many studies of iron hydrolysis in the presence of co-occurring ions in groundwater such as PO43-, SiO44-, and AsO43- suggest that these ions influence the polymerization and formation of iron oxide phases. However, the combined impact of these ions on precipitates generated by EC is not well understood. X-ray absorption spectroscopy (XAS) was used to examine EC precipitates generated in synthetic Bangladeshi groundwater (SBGW). The iron oxide structure and arsenic binding geometry were investigated as a function of EC operating conditions. As and Fe k-edge spectra were similar between samples regardless of the large range of current density (0.02, 1.1, 5.0, 100 mA/cm2) used during sample generation. This result suggests that current density does not play a large role in the formation EC precipitates in SBGW. Shell-by-shell fits of Fe K-edge data revealed the presence of a single Fe-Fe interatomic distance at approximately 3.06 Å. The absence of longer ranged Fe-Fe correlations suggests that EC precipitates consist of nano-scale chains (polymers) of FeO6 octahedra sharing equatorial edges. Shell-by-shell fits of As K-edge spectra show arsenic bound in primarily bidentate, binuclear corner sharing complexes. In this coordination geometry, arsenic prevents the formation of FeO6 corner-sharing linkages, which are necessary for 3-dimensional crystal growth. The individual and combined effects of other anions, such as PO43- and SiO44- present in SBGW are currently being investigated to determine the role of these ions in stunting crystal growth. The results provided by this study are useful in explaining the large adsorption capacity of EC precipitates. This study will also lead to better predictions of arsenic removal efficiency during EC and a better understanding of the long-term stability of arsenic-laden EC sludge.

Automated divertor target design by adjoint shape sensitivity analysis and a one-shot method

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

Dekeyser, W., E-mail: Wouter.Dekeyser@kuleuven.be; Reiter, D.; Baelmans, M.

As magnetic confinement fusion progresses towards the development of first reactor-scale devices, computational tokamak divertor design is a topic of high priority. Presently, edge plasma codes are used in a forward approach, where magnetic field and divertor geometry are manually adjusted to meet design requirements. Due to the complex edge plasma flows and large number of design variables, this method is computationally very demanding. On the other hand, efficient optimization-based design strategies have been developed in computational aerodynamics and fluid mechanics. Such an optimization approach to divertor target shape design is elaborated in the present paper. A general formulation ofmore » the design problems is given, and conditions characterizing the optimal designs are formulated. Using a continuous adjoint framework, design sensitivities can be computed at a cost of only two edge plasma simulations, independent of the number of design variables. Furthermore, by using a one-shot method the entire optimization problem can be solved at an equivalent cost of only a few forward simulations. The methodology is applied to target shape design for uniform power load, in simplified edge plasma geometry.« less

Resolution factors in edgeline holography.

PubMed

Trolinger, J D; Gee, T H

1971-06-01

When an in-line Fresnel hologram of an object such as a projectile in flight is made, the reconstruction comprises an image of the outside edge of the object superimposed upon a Fresnel diffraction pattern of the edge and an unmodulated portion of the reconstruction beam. When the reconstructed image is bandpass filtered, the only remaining significant contribution is that of a diffraction pattern which is symmetrical about an edgeline gaussian image of the object. The present paper discusses the application of this type of holography in accurately locating the edge of a large dynamic object, the position of which is not accurately known in any dimension. A theoretical and experimental analysis was performed to study the effects of motion, hologram size, film type, and practical limitations upon the attainable resolution in the reconstructed image. The bandlimiting effect of motion is used to relate the motion effected resolution limit of holography to that of photography. The study shows that an edgeline can be accurately located even at high velocity normal to the edge.

Historical harvests reduce neighboring old-growth basal area across a forest landscape.

PubMed

Bell, David M; Spies, Thomas A; Pabst, Robert

2017-07-01

While advances in remote sensing have made stand, landscape, and regional assessments of the direct impacts of disturbance on forests quite common, the edge influence of timber harvesting on the structure of neighboring unharvested forests has not been examined extensively. In this study, we examine the impact of historical timber harvests on basal area patterns of neighboring old-growth forests to assess the magnitude and scale of harvest edge influence in a forest landscape of western Oregon, USA. We used lidar data and forest plot measurements to construct 30-m resolution live tree basal area maps in lower and middle elevation mature and old-growth forests. We assessed how edge influence on total, upper canopy, and lower canopy basal area varied across this forest landscape as a function of harvest characteristics (i.e., harvest size and age) and topographic conditions in the unharvested area. Upper canopy, lower canopy, and total basal area increased with distance from harvest edge and elevation. Forests within 75 m of harvest edges (20% of unharvested forests) had 4% to 6% less live tree basal area compared with forest interiors. An interaction between distance from harvest edge and elevation indicated that elevation altered edge influence in this landscape. We observed a positive edge influence at low elevations (<800 m) and a negative edge influence at moderate to high elevations (>800 m). Surprisingly, we found no or weak effects of harvest age (13-60 yr) and harvest area (0.2-110 ha) on surrounding unharvested forest basal area, implying that edge influence was relatively insensitive to the scale of disturbance and multi-decadal recovery processes. Our study indicates that the edge influence of past clearcutting on the structure of neighboring uncut old-growth forests is widespread and persistent. These indirect and diffuse legacies of historical timber harvests complicate forest management decision-making in old-growth forest landscapes by broadening the traditional view of stand boundaries. Furthermore, the consequences of forest harvesting may reach across ownership boundaries, highlighting complex governance issues surrounding landscape management of old-growth forests. © 2017 by the Ecological Society of America.

Experimental investigation of large-scale vortices in a freely spreading gravity current

NASA Astrophysics Data System (ADS)

Yuan, Yeping; Horner-Devine, Alexander R.

2017-10-01

A series of laboratory experiments are presented to compare the dynamics of constant-source buoyant gravity currents propagating into laterally confined (channelized) and unconfined (spreading) environments. The plan-form structure of the spreading current and the vertical density and velocity structures on the interface are quantified using the optical thickness method and a combined particle image velocimetry and planar laser-induced fluorescence method, respectively. With lateral boundaries, the buoyant current thickness is approximately constant and Kelvin-Helmholtz instabilities are generated within the shear layer. The buoyant current structure is significantly different in the spreading case. As the current spreads laterally, nonlinear large-scale vortex structures are observed at the interface, which maintain a coherent shape as they propagate away from the source. These structures are continuously generated near the river mouth, have amplitudes close to the buoyant layer thickness, and propagate offshore at speeds approximately equal to the internal wave speed. The observed depth and propagation speed of the instabilities match well with the fastest growing mode predicted by linear stability analysis, but with a shorter wavelength. The spreading flows have much higher vorticity, which is aggregated within the large-scale structures. Secondary instabilities are generated on the leading edge of the braids between the large-scale vortex structures and ultimately break and mix on the lee side of the structures. Analysis of the vortex dynamics shows that lateral stretching intensifies the vorticity in the spreading currents, contributing to higher vorticity within the large-scale structures in the buoyant plume. The large-scale instabilities and vortex structures observed in the present study provide new insights into the origin of internal frontal structures frequently observed in coastal river plumes.

Abnormal blueshift of the absorption edge in graphene nanodots

NASA Astrophysics Data System (ADS)

Sheng, Weidong

2018-06-01

In a conventional semiconductor, when the dielectric screening effect is suppressed, the exciton binding energy increases and the corresponding excitonic transition would exhibit a redshift in the spectrum. In this work, I study the optical properties of hexagonal graphene nanodots by using a configuration interaction approach and reveal that the edge of the absorption spectrum shows an abnormal blueshift as the environmental dielectric constant ɛr decreases. The two dominant many-body effects in the nanodot: the quasiparticle and excitonic effects are both found to scale almost linearly with ɛr-1. The former is shown to have a larger proportionality constant and thus accounts for the blueshift of the absorption edge. In contrast to the long-range Coulomb interaction, the on-site Coulomb energy is found to have a negative impact on the bright excitonic states. In the presence of a strong dielectric screening effect, a strong short-range Coulomb interaction is revealed to be responsible for the disintegration of the bright exciton.

Communicating Emerging Issues in Ocean Hypoxia (or Suffocating in Your Own Home)

NASA Astrophysics Data System (ADS)

Whitney, F. A.; Tunnicliffe, V.; Diaz, R. J.

2009-12-01

Some large regions of our interior oceans are losing oxygen both from the impacts of human uses of coastal margins and the impacts that climate change is having on ocean circulation. As oxygen minimum zones expand, impacts are especially noticed along the edges of continents. Ecosystems are being affected in ways that result in habitat compression or forced migrations. Looking into the future, we foresee large scale disruptions to habitat that, in some cases, will dramatically impact fish productivity. As waters become more hypoxic, energy fixed by marine plants will be less available to support higher trophic levels (e.g. fish and marine mammals). Communicating concern about hypoxia has its challenges: the word itself is poorly know to those on land who live in an oxygen-rich world. Thus, crucial factors in effective communication include illustrating: i) how many ocean animals live “on the edge”, ii) how ocean organisms respond to hypoxia iii) the long-term effects on ocean ecosystems and iv) causes and mitigation. For media that respond to visual stimulation, good graphics, evocative analogies and focussed examples are important.

Postbreeding resource selection by adult black-footed ferrets in the Conata Basin, South Dakota

USGS Publications Warehouse

Eads, D.A.; Millspaugh, J.J.; Biggins, D.E.; Livieri, T.M.; Jachowski, D.S.

2011-01-01

We investigated postbreeding resource selection by adult black-footed ferrets (Mustela nigripes) on a 452-ha black-tailed prairie dog (Cynomys ludovicianus) colony in the Conata Basin of South Dakota during 20072008. We used resource selection functions (RSFs) to evaluate relationships between numbers of ferret locations and numbers of prairie dog burrow openings (total or active), distances to colony edges, and connectivity of patches of burrow openings. In both years ferrets selected areas near edges of the prairie dog colony where active burrow openings were abundant. In the interior of the colony ferrets selected areas with low abundance of active burrow openings. At times, prairie dog productivity (i.e., pup abundance) might be greatest at colony edges often characterized by grasses; ferrets are likely to select areas where refuge and vulnerable prey are abundant. Ferrets could have used interior areas with few active burrow openings as corridors between edge areas with many active burrow openings. Also, in areas with few active burrow openings ferrets spend more time aboveground during movements and, thus, are likely to be more easily detected. These results complement previous studies demonstrating importance of refuge and prey in fine-scale resource selection by ferrets and provide insight into factors that might influence edge effects on ferret space use. Conservation and restoration of colonies with areas with high densities of burrow openings and prairie dogs, and corridors between such areas, are needed for continued recovery of the black-footed ferret. RSFs could complement coarse-scale habitat evaluations by providing finer-scale assessments of habitat for the black-footed ferret. ?? 2011 American Society of Mammalogists.

Development of a cyber physical apparatus for investigating fluid structure interaction on leading edge vortex evolution

NASA Astrophysics Data System (ADS)

Raghu Gowda, Belagumba Venkatachalaiah

This dissertation examines how simple structural compliance impacts a specific transient vortex phenomenon that occurs on high angle of attack lifting surfaces termed dynamic stall. In many Fluid structure interaction (FSI) research efforts, a purely physical or purely computational approach is taken. In this work a low cost cyber-physical (CPFD) system is designed and developed for representing the FSI in the leading edge vortex (LEV) development problem. The leading edge compliance appears to be favorable in a specific spring constant range for a given wing. When the leading edge compliance prescribed via CPFD system is too low compared with the moment due to dynamic pressure or fluid unsteady effect, the LEV behavior is similar to that of a rigid wing system. When the leading edge compliance is too high, excessive compliance is introduced into the wing system and the leading edge vortex evolution is affected by the large change in wing angle. At moderate leading edge compliance, a balance appears to be achieved in which the leading edge vorticity shedding rate supports the long term evolution of the leading edge vortex. Further investigation is required to determine specific parameters governing these leading edge compliance ranges.

Electrical Current Leakage and Open-Core Threading Dislocations in AlGaN-Based Deep Ultraviolet Light-Emitting Diodes.

DOE PAGES

Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; ...

2014-08-04

Electrical current transport through leakage paths in AlGaN-based deep ultraviolet (DUV) lightemitting diodes (LEDs) and their effect on LED performance are investigated. Open-core threading dislocations, or nanopipes, are found to conduct current through nominally insulating Al0.7Ga0.3N layers and limit the performance of DUV-LEDs. A defect-sensitive phosphoric acid etch reveals these opencore threading dislocations in the form of large, micron-scale hexagonal etch pits visible with optical microscopy, while closed-core screw-, edge-, and mixed-type threading dislocations are represented by smaller and more numerous nanometer-scale pits visible by atomic-force microscopy. The electrical and optical performances of DUV-LEDs fabricated on similar Si-doped Al0.7Ga0.3N templatesmore » are found to have a strong correlation to the density of these nanopipes, despite their small fraction (<0.1% in this study) of the total density of threading dislocations.« less

The Edge States of the BF System and the London Equations

NASA Astrophysics Data System (ADS)

Balachandran, A. P.; Teotonio-Sobrinho, P.

It is known that the 3D Chern-Simons interaction describes the scaling limit of a quantum Hall system and predicts edge currents in a sample with boundary, the currents generating a chiral U(1) Kac-Moody algebra. It is no doubt also recognized that, in a somewhat similar way, the 4D BF interaction (with B a two-form, dB the dual *j of the electromagnetic current, and F the electromagnetic field form) describes the scaling limit of a superconductor. We show in this paper that there are edge excitations in this model as well for manifolds with boundaries. They are the modes of a scalar field with invariance under the group of diffeomorphisms (diffeos) of the bounding spatial two-manifold. Not all diffeos of this group seem implementable by operators in quantum theory, the implementable group being a subgroup of volume-preserving diffeos. The BF system in this manner can lead to the w1+∞ algebra and its variants. Lagrangians for fields on the bounding manifold which account for the edge observables on quantization are also presented. They are the analogs of the (1+1)-dimensional massless scalar field Lagrangian describing the edge modes of an Abelian Chern-Simons theory with a disk as the spatial manifold. We argue that the addition of “Maxwell” terms constructed from F∧*F and dB∧*dB does not affect the edge states, and that the augmented Lagrangian has an infinite number of conserved charges—the aforementioned scalar field modes—localized at the edges. This Lagrangian is known to describe London equations and a massive vector field. A (3+1)-dimensional generalization of the Hall effect involving vortices coupled to B is also proposed.

EDGE3: A web-based solution for management and analysis of Agilent two color microarray experiments

PubMed Central

Vollrath, Aaron L; Smith, Adam A; Craven, Mark; Bradfield, Christopher A

2009-01-01

Background The ability to generate transcriptional data on the scale of entire genomes has been a boon both in the improvement of biological understanding and in the amount of data generated. The latter, the amount of data generated, has implications when it comes to effective storage, analysis and sharing of these data. A number of software tools have been developed to store, analyze, and share microarray data. However, a majority of these tools do not offer all of these features nor do they specifically target the commonly used two color Agilent DNA microarray platform. Thus, the motivating factor for the development of EDGE3 was to incorporate the storage, analysis and sharing of microarray data in a manner that would provide a means for research groups to collaborate on Agilent-based microarray experiments without a large investment in software-related expenditures or extensive training of end-users. Results EDGE3 has been developed with two major functions in mind. The first function is to provide a workflow process for the generation of microarray data by a research laboratory or a microarray facility. The second is to store, analyze, and share microarray data in a manner that doesn't require complicated software. To satisfy the first function, EDGE3 has been developed as a means to establish a well defined experimental workflow and information system for microarray generation. To satisfy the second function, the software application utilized as the user interface of EDGE3 is a web browser. Within the web browser, a user is able to access the entire functionality, including, but not limited to, the ability to perform a number of bioinformatics based analyses, collaborate between research groups through a user-based security model, and access to the raw data files and quality control files generated by the software used to extract the signals from an array image. Conclusion Here, we present EDGE3, an open-source, web-based application that allows for the storage, analysis, and controlled sharing of transcription-based microarray data generated on the Agilent DNA platform. In addition, EDGE3 provides a means for managing RNA samples and arrays during the hybridization process. EDGE3 is freely available for download at . PMID:19732451

New Perspectives on the Dynamical State of Extraplanar Diffuse Ionized Gas Layers

NASA Astrophysics Data System (ADS)

Boettcher, Erin; Zweibel, Ellen; Gallagher, John S.; Benjamin, Robert A.

2018-01-01

Gaseous, disk-halo interfaces are an important boundary in the baryon cycle in galaxies like the Milky Way, and their structure, support, and kinematics carry clues about the star formation feedback and accretion processes that produce them. Due to their unexpectedly large scale heights, which are often several times greater than their thermal scale heights, it is unclear whether they are in dynamical equilibrium, or are evidence of a galactic fountain, wind, or accretion flow. In the nearby, edge-on disk galaxies NGC 891 and NGC 5775, we test a dynamical equilibrium model of the extraplanar diffuse ionized gas (eDIG) layer by quantifying the thermal, turbulent, magnetic field, and cosmic ray pressure gradients using optical emission-line spectroscopy from the SparsePak IFU at the WIYN Observatory and the Robert Stobie Spectrograph on the Southern African Large Telescope and radio continuum observations from Continuum Halos in Nearby Galaxies - an EVLA Survey. The vertical pressure gradients are too shallow to produce the observed scale heights at the moderate galactocentric radii where the gas is believed to be found (R < 8 kpc). For the low-inclination galaxy M83, we develop a Markov Chain Monte Carlo method to decompose the [NII]λλ6548, 6583, Hα, and [SII]λλ6717, 6731 emission lines into multiple components, and identify eDIG emission based on its rotational velocity lag and elevated [NII]/Hα and [SII]/Hα line ratios. The median, line-of-sight velocity dispersion of the eDIG layer, σ = 96 km/s, greatly exceeds the horizontal velocity dispersions observed in edge-on eDIG layers (σ = 20 - 60 km/s), presenting the possibility that these layers have anisotropic random motions. The role of an anisotropic velocity dispersion in producing eDIG scale heights, as well as the absence of evidence for large-scale inflow or outflow, motivates further study of eDIG dynamics in face-on galaxies with a range of star formation rates. This work was supported by the NSF GRFP under Grant No. DGE-1256259.

Helicopter rotor trailing edge noise. [noise prediction

NASA Technical Reports Server (NTRS)

Schlinker, R. H.; Amier, R. K.

1981-01-01

A two dimensional section of a helicopter main rotor blade was tested in an acoustic wind tunnel at close to full-scale Reynolds numbers to obtain boundary layer data and acoustic data for use in developing an acoustic scaling law and testing a first principles trailing edge noise theory. Results were extended to the rotating frame coordinate system to develop a helicopter rotor trailing edge noise prediction. Comparisons of the calculated noise levels with helicopter flyover spectra demonstrate that trailing edge noise contributes significantly to the total helicopter noise spectrum at high frequencies. This noise mechanism is expected to control the minimum rotor noise. In the case of noise radiation from a local blade segment, the acoustic directivity pattern is predicted by the first principles trailing edge noise theory. Acoustic spectra are predicted by a scaling law which includes Mach number, boundary layer thickness and observer position. Spectrum shape and sound pressure level are also predicted by the first principles theory but the analysis does not predict the Strouhal value identifying the spectrum peak.

Scaling analysis of the non-Abelian quasiparticle tunneling in Z}}_k FQH states

NASA Astrophysics Data System (ADS)

Li, Qi; Jiang, Na; Wan, Xin; Hu, Zi-Xiang

2018-06-01

Quasiparticle tunneling between two counter propagating edges through point contacts could provide information on its statistics. Previous study of the short distance tunneling displays a scaling behavior, especially in the conformal limit with zero tunneling distance. The scaling exponents for the non-Abelian quasiparticle tunneling exhibit some non-trivial behaviors. In this work, we revisit the quasiparticle tunneling amplitudes and their scaling behavior in a full range of the tunneling distance by putting the electrons on the surface of a cylinder. The edge–edge distance can be smoothly tuned by varying the aspect ratio for a finite size cylinder. We analyze the scaling behavior of the quasiparticles for the Read–Rezayi states for and 4 both in the short and long tunneling distance region. The finite size scaling analysis automatically gives us a critical length scale where the anomalous correction appears. We demonstrate this length scale is related to the size of the quasiparticle at which the backscattering between two counter propagating edges starts to be significant.

Large and small-scale structures and the dust energy balance problem in spiral galaxies

NASA Astrophysics Data System (ADS)

Saftly, W.; Baes, M.; De Geyter, G.; Camps, P.; Renaud, F.; Guedes, J.; De Looze, I.

2015-04-01

The interstellar dust content in galaxies can be traced in extinction at optical wavelengths, or in emission in the far-infrared. Several studies have found that radiative transfer models that successfully explain the optical extinction in edge-on spiral galaxies generally underestimate the observed FIR/submm fluxes by a factor of about three. In order to investigate this so-called dust energy balance problem, we use two Milky Way-like galaxies produced by high-resolution hydrodynamical simulations. We create mock optical edge-on views of these simulated galaxies (using the radiative transfer code SKIRT), and we then fit the parameters of a basic spiral galaxy model to these images (using the fitting code FitSKIRT). The basic model includes smooth axisymmetric distributions along a Sérsic bulge and exponential disc for the stars, and a second exponential disc for the dust. We find that the dust mass recovered by the fitted models is about three times smaller than the known dust mass of the hydrodynamical input models. This factor is in agreement with previous energy balance studies of real edge-on spiral galaxies. On the other hand, fitting the same basic model to less complex input models (e.g. a smooth exponential disc with a spiral perturbation or with random clumps), does recover the dust mass of the input model almost perfectly. Thus it seems that the complex asymmetries and the inhomogeneous structure of real and hydrodynamically simulated galaxies are a lot more efficient at hiding dust than the rather contrived geometries in typical quasi-analytical models. This effect may help explain the discrepancy between the dust emission predicted by radiative transfer models and the observed emission in energy balance studies for edge-on spiral galaxies.

The source location of mantle plumes from 3D spherical models of mantle convection

NASA Astrophysics Data System (ADS)

Li, Mingming; Zhong, Shijie

2017-11-01

Mantle plumes are thought to originate from thermal boundary layers such as Earth's core-mantle boundary (CMB), and may cause intraplate volcanism such as large igneous provinces (LIPs) on the Earth's surface. Previous studies showed that the original eruption sites of deep-sourced LIPs for the last 200 Myrs occur mostly above the margins of the seismically-observed large low shear velocity provinces (LLSVPs) in the lowermost mantle. However, the mechanism that leads to the distribution of the LIPs is not clear. The location of the LIPs is largely determined by the source location of mantle plumes, but the question is under what conditions mantle plumes form outside, at the edges, or above the middle of LLSVPs. Here, we perform 3D geodynamic calculations and theoretical analyses to study the plume source location in the lowermost mantle. We find that a factor of five decrease of thermal expansivity and a factor of two increase of thermal diffusivity from the surface to the CMB, which are consistent with mineral physics studies, significantly reduce the number of mantle plumes forming far outside of thermochemical piles (i.e., LLSVPs). An increase of mantle viscosity in the lowermost mantle also reduces number of plumes far outside of piles. In addition, we find that strong plumes preferentially form at/near the edges of piles and are generally hotter than that forming on top of piles, which may explain the observations that most LIPs occur above LLSVP margins. However, some plumes originated at pile edges can later appear above the middle of piles due to lateral movement of the plumes and piles and morphologic changes of the piles. ∼65-70% strong plumes are found within 10 degrees from pile edges in our models. Although plate motion exerts significant controls over the large-scale mantle convection in the lower mantle, mantle plume formation at the CMB remains largely controlled by thermal boundary layer instability which makes it difficult to predict geographic locations of most mantle plumes. However, all our models show consistently strong plumes originating from the lowermost mantle beneath Iceland, supporting a deep mantle plume origin of the Iceland volcanism.

Studies of numerical algorithms for gyrokinetics and the effects of shaping on plasma turbulence

NASA Astrophysics Data System (ADS)

Belli, Emily Ann

Advanced numerical algorithms for gyrokinetic simulations are explored for more effective studies of plasma turbulent transport. The gyrokinetic equations describe the dynamics of particles in 5-dimensional phase space, averaging over the fast gyromotion, and provide a foundation for studying plasma microturbulence in fusion devices and in astrophysical plasmas. Several algorithms for Eulerian/continuum gyrokinetic solvers are compared. An iterative implicit scheme based on numerical approximations of the plasma response is developed. This method reduces the long time needed to set-up implicit arrays, yet still has larger time step advantages similar to a fully implicit method. Various model preconditioners and iteration schemes, including Krylov-based solvers, are explored. An Alternating Direction Implicit algorithm is also studied and is surprisingly found to yield a severe stability restriction on the time step. Overall, an iterative Krylov algorithm might be the best approach for extensions of core tokamak gyrokinetic simulations to edge kinetic formulations and may be particularly useful for studies of large-scale ExB shear effects. The effects of flux surface shape on the gyrokinetic stability and transport of tokamak plasmas are studied using the nonlinear GS2 gyrokinetic code with analytic equilibria based on interpolations of representative JET-like shapes. High shaping is found to be a stabilizing influence on both the linear ITG instability and nonlinear ITG turbulence. A scaling of the heat flux with elongation of chi ˜ kappa-1.5 or kappa-2 (depending on the triangularity) is observed, which is consistent with previous gyrofluid simulations. Thus, the GS2 turbulence simulations are explaining a significant fraction, but not all, of the empirical elongation scaling. The remainder of the scaling may come from (1) the edge boundary conditions for core turbulence, and (2) the larger Dimits nonlinear critical temperature gradient shift due to the enhancement of zonal flows with shaping, which is observed with the GS2 simulations. Finally, a local linear trial function-based gyrokinetic code is developed to aid in fast scoping studies of gyrokinetic linear stability. This code is successfully benchmarked with the full GS2 code in the collisionless, electrostatic limit, as well as in the more general electromagnetic description with higher-order Hermite basis functions.

Interpreting Brightness Asymmetries in Transition Disks: Vortex at Dead Zone or Planet-carved Gap Edges?

NASA Astrophysics Data System (ADS)

Regály, Zs.; Juhász, A.; Nehéz, D.

2017-12-01

Recent submillimeter observations show nonaxisymmetric brightness distributions with a horseshoe-like morphology for more than a dozen transition disks. The most-accepted explanation for the observed asymmetries is the accumulation of dust in large-scale vortices. Protoplanetary disks’ vortices can form by the excitation of Rossby wave instability in the vicinity of a steep pressure gradient, which can develop at the edges of a giant planet–carved gap or at the edges of an accretionally inactive zone. We studied the formation and evolution of vortices formed in these two distinct scenarios by means of two-dimensional locally isothermal hydrodynamic simulations. We found that the vortex formed at the edge of a planetary gap is short-lived, unless the disk is nearly inviscid. In contrast, the vortex formed at the outer edge of a dead zone is long-lived. The vortex morphology can be significantly different in the two scenarios: the vortex radial and azimuthal extensions are ∼1.5 and ∼3.5 times larger for the dead-zone edge compared to gap models. In some particular cases, the vortex aspect ratios can be similar in the two scenarios; however, the vortex azimuthal extensions can be used to distinguish the vortex formation mechanisms. We calculated predictions for vortex observability in the submillimeter continuum with ALMA. We found that the azimuthal and radial extent of the brightness asymmetry correlates with the vortex formation process within the limitations of α-viscosity prescription.

RADIO AND DEEP CHANDRA OBSERVATIONS OF THE DISTURBED COOL CORE CLUSTER ABELL 133

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

Randall, S. W.; Nulsen, P. E. J.; Forman, W. R.

2010-10-10

We present results based on new Chandra and multi-frequency radio observations of the disturbed cool core cluster Abell 133. The diffuse gas has a complex bird-like morphology, with a plume of emission extending from two symmetric wing-like features. The plume is capped with a filamentary radio structure that has been previously classified as a radio relic. X-ray spectral fits in the region of the relic indicate the presence of either high-temperature gas or non-thermal emission, although the measured photon index is flatter than would be expected if the non-thermal emission is from inverse Compton scattering of the cosmic microwave backgroundmore » by the radio-emitting particles. We find evidence for a weak elliptical X-ray surface brightness edge surrounding the core, which we show is consistent with a sloshing cold front. The plume is consistent with having formed due to uplift by a buoyantly rising radio bubble, now seen as the radio relic, and has properties consistent with buoyantly lifted plumes seen in other systems (e.g., M87). Alternatively, the plume may be a gas sloshing spiral viewed edge-on. Results from spectral analysis of the wing-like features are inconsistent with the previous suggestion that the wings formed due to the passage of a weak shock through the cool core. We instead conclude that the wings are due to X-ray cavities formed by displacement of X-ray gas by the radio relic. The central cD galaxy contains two small-scale cold gas clumps that are slightly offset from their optical and UV counterparts, suggestive of a galaxy-galaxy merger event. On larger scales, there is evidence for cluster substructure in both optical observations and the X-ray temperature map. We suggest that the Abell 133 cluster has recently undergone a merger event with an interloping subgroup, initialing gas sloshing in the core. The torus of sloshed gas is seen close to edge-on, leading to the somewhat ragged appearance of the elliptical surface brightness edge. We show that the additional buoyant force from a passing subcluster can have a significant effect on the rise trajectories of buoyant bubbles, although this effect alone cannot fully explain the morphology of Abell 133. The radio observations reveal a large-scale double-lobed structure not previously identified in the literature. We conclude that this structure represents a previously unreported background giant radio galaxy at z = 0.293, the northern lobe of which overlies the radio relic in the core of Abell 133. A rough estimate indicates that the contribution of this background lobe to the total radio emission in the region of the relic is modest (<13%).« less

Strain-Dependent Edge Structures in MoS2 Layers.

PubMed

Tinoco, Miguel; Maduro, Luigi; Masaki, Mukai; Okunishi, Eiji; Conesa-Boj, Sonia

2017-11-08

Edge structures are low-dimensional defects unavoidable in layered materials of the transition metal dichalcogenides (TMD) family. Among the various types of such structures, the armchair (AC) and zigzag (ZZ) edge types are the most common. It has been predicted that the presence of intrinsic strain localized along these edges structures can have direct implications for the customization of their electronic properties. However, pinning down the relation between local structure and electronic properties at these edges is challenging. Here, we quantify the local strain field that arises at the edges of MoS 2 flakes by combining aberration-corrected transmission electron microscopy (TEM) with the geometrical-phase analysis (GPA) method. We also provide further insight on the possible effects of such edge strain on the resulting electronic behavior by means of electron energy loss spectroscopy (EELS) measurements. Our results reveal that the two-dominant edge structures, ZZ and AC, induce the formation of different amounts of localized strain fields. We also show that by varying the free edge curvature from concave to convex, compressive strain turns into tensile strain. These results pave the way toward the customization of edge structures in MoS 2 , which can be used to engineer the properties of layered materials and thus contribute to the optimization of the next generation of atomic-scale electronic devices built upon them.

Large-scale uniform bilayer graphene prepared by vacuum graphitization of 6H-SiC(0001) substrates

NASA Astrophysics Data System (ADS)

Wang, Qingyan; Zhang, Wenhao; Wang, Lili; He, Ke; Ma, Xucun; Xue, Qikun

2013-03-01

We report on the preparation of large-scale uniform bilayer graphenes on nominally flat Si-polar 6H-SiC(0001) substrates by flash annealing in ultrahigh vacuum. The resulting graphenes have a single thickness of one bilayer and consist of regular terraces separated by the triple SiC bilayer steps on the 6H-SiC(0001) substrates. In situ scanning tunneling microscopy reveals that suppression of pit formation on terraces and uniformity of SiC decomposition at step edges are the key factors to the uniform thickness. By studying the surface morphologies prepared under different annealing rates, it is found that the annealing rate is directly related to SiC decomposition, diffusion of the released Si/C atoms and strain relaxation, which together determine the final step structure and density of defects.

Large-scale uniform bilayer graphene prepared by vacuum graphitization of 6H-SiC(0001) substrates.

PubMed

Wang, Qingyan; Zhang, Wenhao; Wang, Lili; He, Ke; Ma, Xucun; Xue, Qikun

2013-03-06

We report on the preparation of large-scale uniform bilayer graphenes on nominally flat Si-polar 6H-SiC(0001) substrates by flash annealing in ultrahigh vacuum. The resulting graphenes have a single thickness of one bilayer and consist of regular terraces separated by the triple SiC bilayer steps on the 6H-SiC(0001) substrates. In situ scanning tunneling microscopy reveals that suppression of pit formation on terraces and uniformity of SiC decomposition at step edges are the key factors to the uniform thickness. By studying the surface morphologies prepared under different annealing rates, it is found that the annealing rate is directly related to SiC decomposition, diffusion of the released Si/C atoms and strain relaxation, which together determine the final step structure and density of defects.

Fusion of infrared polarization and intensity images based on improved toggle operator

NASA Astrophysics Data System (ADS)

Zhu, Pan; Ding, Lei; Ma, Xiaoqing; Huang, Zhanhua

2018-01-01

Integration of infrared polarization and intensity images has been a new topic in infrared image understanding and interpretation. The abundant infrared details and target from infrared image and the salient edge and shape information from polarization image should be preserved or even enhanced in the fused result. In this paper, a new fusion method is proposed for infrared polarization and intensity images based on the improved multi-scale toggle operator with spatial scale, which can effectively extract the feature information of source images and heavily reduce redundancy among different scale. Firstly, the multi-scale image features of infrared polarization and intensity images are respectively extracted at different scale levels by the improved multi-scale toggle operator. Secondly, the redundancy of the features among different scales is reduced by using spatial scale. Thirdly, the final image features are combined by simply adding all scales of feature images together, and a base image is calculated by performing mean value weighted method on smoothed source images. Finally, the fusion image is obtained by importing the combined image features into the base image with a suitable strategy. Both objective assessment and subjective vision of the experimental results indicate that the proposed method obtains better performance in preserving the details and edge information as well as improving the image contrast.

The Emergence of Figural Effects in the Watercolor Illusion

NASA Astrophysics Data System (ADS)

Pinna, Baingio; Penna, Maria Pietronilla

The watercolor illusion is characterized by a large-scale assimilative color spreading (coloration effect) emanating from thin colored edges. The watercolor illusion enhances the figural properties of the colored areas and imparts to the surrounding area the perceptual status of background. This work explores interactions between cortical boundary and surface processes by presenting displays and psychophysical experiments that exhibit new properties of the watercolor illusion. The watercolor illusion is investigated as supporting a new principle of figure-ground organization when pitted against principles of surroundedness, relative orientation, and Prägnanz. The work demonstrated that the watercolor illusion probes a unique combination of visual processes that set it apart from earlier Gestalt principles, and can compete successfully against them. This illusion exemplifies how long-range perceptual effects may be triggered by spatially sparse information. All the main effects are explained by the FACADE model of biological vision, which clarifies how local properties control depthful filling-in of surface lightness and color.

Full-scale wind-tunnel tests of high-lift system modifications on a carrier based fighter aircraft

NASA Technical Reports Server (NTRS)

Meyn, Larry A.; Zell, Peter T.; Hagan, John L.; Schoch, David

1993-01-01

Modifications to the high-lift system of a full-scale F/A-I8A were tested in the 80- by 120-Foot Wind Tunnel of the National Full-Scale Aerodynamics Complex at the NASA Ames Research Center in Moffett Field, California. The objective was to measure the effect of simple modifications on the aerodynamic performance of the high-lift system. The modifications included the placement of a straight fairing in the shroud cove above the trailing-edge flap and the addition of seals to prevent air leakage through the hinge lines of the leading-edge flap, the trailing-edge shroud, and the wing fold. The test was carried out on an actual F/A-18A with it's flaps deployed in the landing approach configuration. The angle of attack ranged from 0 to 16 degrees and the wind speed was 100 knots. At an angle of attack of 8 degrees, the trimmed lift coefficient was improved by 0.09 with all wing seals in place. This corresponds to a reduction in the approach speed for the F/A-I8A of about 5 knots. The seal along the wing fold hinge, a feature present on many naval aircraft, provided one third of the total increment in trimmed lift. A comparison of the full-scale wind-tunnel results with those obtained from flight test is also presented.

Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors

NASA Technical Reports Server (NTRS)

Sadleir, John E.; Smith, Stephen J.; Bandler, SImon R.; Chervenak, James A.; Clem, John R.

2009-01-01

We have found experimentally that the critical current of a square superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. The observed behavior has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. We have observed the proximity effect in these devices over extraordinarily long lengths exceeding 100 microns.

Loitering of the retreating sea ice edge in the Arctic Seas.

PubMed

Steele, Michael; Ermold, Wendy

2015-12-01

Each year, the arctic sea ice edge retreats from its winter maximum extent through the Seasonal Ice Zone (SIZ) to its summer minimum extent. On some days, this retreat happens at a rapid pace, while on other days, parts of the pan-arctic ice edge hardly move for periods of days up to 1.5 weeks. We term this stationary behavior "ice edge loitering," and identify areas that are more prone to loitering than others. Generally, about 20-25% of the SIZ area experiences loitering, most often only one time at any one location during the retreat season, but sometimes two or more times. The main mechanism controlling loitering is an interaction between surface winds and warm sea surface temperatures in areas from which the ice has already retreated. When retreat happens early enough to allow atmospheric warming of this open water, winds that force ice floes into this water cause melting. Thus, while individual ice floes are moving, the ice edge as a whole appears to loiter. The time scale of loitering is then naturally tied to the synoptic time scale of wind forcing. Perhaps surprisingly, the area of loitering in the arctic seas has not changed over the past 25 years, even as the SIZ area has grown. This is because rapid ice retreat happens most commonly late in the summer, when atmospheric warming of open water is weak. We speculate that loitering may have profound effects on both physical and biological conditions at the ice edge during the retreat season.

Transonic Free-Flight Investigation of the Longitudinal Aerodynamic Characteristics of a 1/10-Scale Steel-Wing Model of the Northrop MX-775A Missile with Leading-Edge Extensions, Inboard Trailing-Edge Flaps, and a Speed Brake on the Vertical Tail

NASA Technical Reports Server (NTRS)

Arbic, R. G.

1955-01-01

Results are presented of a free-flight investigation between Mach numbers of 0.7 to 1.3 and Reynolds numbers of 3.1 x 10(exp 6) to 7.0 x 10(exp 6) to determine the longitudinal aerodynamic characteristics of the Northrop MX-775A missile. This missile has a weng, body, and vertical tail, but has no horizontal tail. The basic wing plan form has an aspect ratio of 5.5, 45 deg of sweepback of the 0.406 streamwise chord line, and a taper ratio of 0.4. A 1/10-scale steel-wing model of the missile was flown with modifications to the basic wing plan form consisting of leading-edge chord-extensions deflected 7 deg downward together with the forward 15 percent of the wing chord, and inboard trailing-edge flaps deflected 5 deg downward. In addition, the model had a static-pressure tube mounted at the tip of the vertical tail for position-error measurements and had a speed brake also mounted on the vertical tail to trim the model to positive lift coefficients and to permit determination of the trim and drag effectiveness of the brake. The data are uncorrected for the effects of wing elasticity, but experimental wing influence coefficients are presented.

Shock formation induced by poloidal flow and its effects on the edge stability in tokamaks

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

Seol, J.; Aydemir, A. Y.; Shaing, K. C.

2016-04-15

In the high confinement mode of tokamaks, magnitude of the radial electric field increases at the edge. Thus, the poloidal flow inside the transport barrier can be sonic when the edge pressure gradient is not steep enough to make the poloidal flow subsonic. When the poloidal Mach number is close to unity, a shock appears in the low field side and causes a large density perturbation. In this study, we describe a shock induced by the sonic poloidal plasma flow. Then, an entropy production across the shock is calculated. Finally, we introduce a simple model for Type III edge localizedmore » modes using the poloidal density variation driven by the sonic poloidal flow.« less

Pest Control and Pollination Cost-Benefit Analysis of Hedgerow Restoration in a Simplified Agricultural Landscape.

PubMed

Morandin, L A; Long, R F; Kremen, C

2016-05-11

Field edge habitat in homogeneous agricultural landscapes can serve multiple purposes including enhanced biodiversity, water quality protection, and habitat for beneficial insects, such as native bees and natural enemies. Despite this ecosystem service value, adoption of field border plantings, such as hedgerows, on large-scale mono-cropped farms is minimal. With profits primarily driving agricultural production, a major challenge affecting hedgerow plantings is linked to establishment costs and the lack of clear economic benefits on the restoration investment. Our study documented that hedgerows are economically viable to growers by enhancing beneficial insects and natural pest control and pollination on farms. With pest control alone, our model shows that it would take 16 yr to break even from insecticide savings on the US$4,000 cost of a typical 300-m hedgerow field edge planting. By adding in pollination benefits by native bees, where honey bees (Apis mellifera L.) may be limiting, the return time is reduced to 7 yr. USDA cost share programs allow for a quicker return on a hedgerow investment. Our study shows that over time, small-scale restoration can be profitable, helping to overcome the barrier of cost associated with field edge habitat restoration on farms. Published by Oxford University Press on behalf of Entomological Society of America 2016. This work is written by US Government employees and is in the public domain in the United States.

Effects of Blade Boundary Layer Transition and Daytime Atmospheric Turbulence on Wind Turbine Performance Analyzed with Blade-Resolved Simulation and Field Data

NASA Astrophysics Data System (ADS)

Nandi, Tarak Nath

Relevant to utility scale wind turbine functioning and reliability, the present work focuses on enhancing our understanding of wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and rotating blades of a GE 1.5 MW wind turbine using a unique data set from a GE field experiment and computer simulations at two levels of fidelity. Previous studies have shown that the stability state of the lower troposphere has a major impact on the coherent structure of the turbulence eddies, with corresponding differences in wind turbine loading response. In this study, time-resolved aerodynamic data measured locally at the leading edge and trailing edge of three outer blade sections on a GE 1.5 MW wind turbine blade and high-frequency SCADA generator power data from a daytime field campaign are combined with computer simulations that mimic the GE wind turbine within a numerically generated atmospheric boundary layer (ABL) flow field which is a close approximation of the atmospheric turbulence experienced by the wind turbine in the field campaign. By combining the experimental and numerical data sets, this study describes the time-response characteristics of the local loadings on the blade sections in response to nonsteady nonuniform energetic atmospheric turbulence eddies within a daytime ABL which have spatial scale commensurate with that of the turbine blade length. This study is the first of its kind where actuator line and blade boundary layer resolved CFD studies of a wind turbine field campaign are performed with the motivation to validate the numerical predictions with the experimental data set, and emphasis is given on understanding the influence of the laminar to turbulent transition process on the blade loadings. The experimental and actuator line method data sets identify three important response time scales quantified at the blade location: advective passage of energy-dominant eddies (≈25 - 50 s), blade rotation (1P, ≈3 s) and sub-1P scale (< 1 s) response to internal eddy structure. Large amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the airfoil plane, modulated by eddy passage at longer time scales. Generator power is found to respond strongly to large-eddy wind modulations. The experimental data show that internal dynamics of blade boundary layer near the trailing edge is temporally modulated by the nonsteady external ABL flow that was measured at the leading edge, as well as blade generated turbulence motions. A blade boundary layer resolved CFD study of a GE 1.5MW wind turbine blade is carried out using a hybrid URANS/LES framework to quantify the influence of transition on the blade boundary layer dynamics and subsequent loadings, and also to predict the velocity magnitude data set measured by the trailing edge rakes in the experiment. A URANS based transition model is used as the near-wall model, and its ability to predict nonsteady boundary layer dynamics is assessed for flow over an oscillating airfoil exhibiting varying extents of nonsteady behavior. The CFD study shows that, at rated conditions, the transition and separation locations on the blade surface can be quite dynamic, but the transitional flow has negligible influence on the determination of the separation location and the overall pressure distribution at various blade sections, and subsequently the power output. But this conclusion should be accepted with caution for wind turbines running in off-design conditions (e.g. with significant yaw error, off-design pitch or rapid changes in pitch), where massive separation and dynamic stall may occur. Analysis of the near-blade flow field shows strong three dimensional flow in the inboard regions, which can possibly weaken the chordwise flow in the relatively outboard regions and make them more prone to separation. The trailing edge velocity profiles show qualitative resemblance with some specific cycles observed in the field experiment. The factors leading to the observed differences from the experimental data are also mentioned.

Statistical analysis of Hasegawa-Wakatani turbulence

NASA Astrophysics Data System (ADS)

Anderson, Johan; Hnat, Bogdan

2017-06-01

Resistive drift wave turbulence is a multipurpose paradigm that can be used to understand transport at the edge of fusion devices. The Hasegawa-Wakatani model captures the essential physics of drift turbulence while retaining the simplicity needed to gain a qualitative understanding of this process. We provide a theoretical interpretation of numerically generated probability density functions (PDFs) of intermittent events in Hasegawa-Wakatani turbulence with enforced equipartition of energy in large scale zonal flows, and small scale drift turbulence. We find that for a wide range of adiabatic index values, the stochastic component representing the small scale turbulent eddies of the flow, obtained from the autoregressive integrated moving average model, exhibits super-diffusive statistics, consistent with intermittent transport. The PDFs of large events (above one standard deviation) are well approximated by the Laplace distribution, while small events often exhibit a Gaussian character. Furthermore, there exists a strong influence of zonal flows, for example, via shearing and then viscous dissipation maintaining a sub-diffusive character of the fluxes.

Local curvature entropy-based 3D terrain representation using a comprehensive Quadtree

NASA Astrophysics Data System (ADS)

Chen, Qiyu; Liu, Gang; Ma, Xiaogang; Mariethoz, Gregoire; He, Zhenwen; Tian, Yiping; Weng, Zhengping

2018-05-01

Large scale 3D digital terrain modeling is a crucial part of many real-time applications in geoinformatics. In recent years, the improved speed and precision in spatial data collection make the original terrain data more complex and bigger, which poses challenges for data management, visualization and analysis. In this work, we presented an effective and comprehensive 3D terrain representation based on local curvature entropy and a dynamic Quadtree. The Level-of-detail (LOD) models of significant terrain features were employed to generate hierarchical terrain surfaces. In order to reduce the radical changes of grid density between adjacent LODs, local entropy of terrain curvature was regarded as a measure of subdividing terrain grid cells. Then, an efficient approach was presented to eliminate the cracks among the different LODs by directly updating the Quadtree due to an edge-based structure proposed in this work. Furthermore, we utilized a threshold of local entropy stored in each parent node of this Quadtree to flexibly control the depth of the Quadtree and dynamically schedule large-scale LOD terrain. Several experiments were implemented to test the performance of the proposed method. The results demonstrate that our method can be applied to construct LOD 3D terrain models with good performance in terms of computational cost and the maintenance of terrain features. Our method has already been deployed in a geographic information system (GIS) for practical uses, and it is able to support the real-time dynamic scheduling of large scale terrain models more easily and efficiently.

An intercomparison of GCM and RCM dynamical downscaling for characterizing the hydroclimatology of California and Nevada

NASA Astrophysics Data System (ADS)

Xu, Z.; Rhoades, A.; Johansen, H.; Ullrich, P. A.; Collins, W. D.

2017-12-01

Dynamical downscaling is widely used to properly characterize regional surface heterogeneities that shape the local hydroclimatology. However, the factors in dynamical downscaling, including the refinement of model horizontal resolution, large-scale forcing datasets and dynamical cores, have not been fully evaluated. Two cutting-edge global-to-regional downscaling methods are used to assess these, specifically the variable-resolution Community Earth System Model (VR-CESM) and the Weather Research & Forecasting (WRF) regional climate model, under different horizontal resolutions (28, 14, and 7 km). Two groups of WRF simulations are driven by either the NCEP reanalysis dataset (WRF_NCEP) or VR-CESM outputs (WRF_VRCESM) to evaluate the effects of the large-scale forcing datasets. The impacts of dynamical core are assessed by comparing the VR-CESM simulations to the coupled WRF_VRCESM simulations with the same physical parameterizations and similar grid domains. The simulated hydroclimatology (i.e., total precipitation, snow cover, snow water equivalent and surface temperature) are compared with the reference datasets. The large-scale forcing datasets are critical to the WRF simulations in more accurately simulating total precipitation, SWE and snow cover, but not surface temperature. Both the WRF and VR-CESM results highlight that no significant benefit is found in the simulated hydroclimatology by just increasing horizontal resolution refinement from 28 to 7 km. Simulated surface temperature is sensitive to the choice of dynamical core. WRF generally simulates higher temperatures than VR-CESM, alleviates the systematic cold bias of DJF temperatures over the California mountain region, but overestimates the JJA temperature in California's Central Valley.

Electrically driving large magnetic Reynolds number flows on the Madison plasma dynamo experiment

NASA Astrophysics Data System (ADS)

Weisberg, David; Wallace, John; Peterson, Ethan; Endrezzi, Douglass; Forest, Cary B.; Desangles, Victor

2015-11-01

Electrically-driven plasma flows, predicted to excite a large-scale dynamo instability, have been generated in the Madison plasma dynamo experiment (MPDX), at the Wisconsin Plasma Astrophysics Laboratory. Numerical simulations show that certain topologies of these simply-connected flows may be optimal for creating a plasma dynamo and predict critical thresholds as low as Rmcrit =μ0 σLV = 250 . MPDX plasmas are shown to exceed this critical Rm , generating large (L = 1 . 4 m), warm (Te > 10 eV), unmagnetized (MA > 1) plasmas where Rm < 600 . Plasma flow is driven using ten thermally emissive LaB6 cathodes which generate a J × B torque in Helium plasmas. Detailed Mach probe measurements of plasma velocity for two flow topologies will be presented: edge-localized drive using the multi-cusp boundary field, and volumetric drive using an axial Helmholtz field. Radial velocity profiles show that edge-driven flow is established via ion viscosity but is limited by a volumetric neutral drag force (χ ~ 1 / (ντin)), and measurements of velocity shear compare favorably to Braginskii transport theory. Volumetric flow drive is shown to produce stronger velocity shear, and is characterized by the radial potential gradient as determined by global charge balance.

Ultrashort Nucleic Acid Duplexes Exhibit Long Wormlike Chain Behavior with Force-Dependent Edge Effects

NASA Astrophysics Data System (ADS)

Whitley, Kevin D.; Comstock, Matthew J.; Chemla, Yann R.

2018-02-01

Despite their importance in biology and use in nanotechnology, the elastic behavior of nucleic acids on "ultrashort" (<15 nt ) length scales remains poorly understood. Here, we use optical tweezers combined with fluorescence imaging to observe directly the hybridization of oligonucleotides (7-12 nt) to a complementary strand under tension and to measure the difference in end-to-end extension between the single-stranded and duplex states. Data are consistent with long-polymer models at low forces (<8 pN ) but smaller than predicted at higher forces (>8 pN ), the result of the sequence-dependent duplex edge effects.

The Inner Structure of OH Megamaser Galaxies: The Genesis of the Unified Scheme of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Axon, David

OH megamaser galaxies (OHMG) represent a key post-merger phase in the evolution of the Ultra-Luminous Infrared Galaxies (ULIRGs) population, in which an edge-on circum-nuclear gas disk (proto-torus) has already formed. Detailed interferometric mapping of maser sources implies that they originate in dense edge-on rotating molecular gas within a few tens of parsecs of the AGN. In addition, the OH lines are often broad (Doppler widths ~ 1000 km/s), implying large dynamical masses in the central few parsecs. In many systems the OH lines also show high velocity asymmetric tails suggesting large-scale outflows that could be clearing away enshrouding dense molecular material. Taken together this evidence points to a picture in which an OHMG hosts a nascent QSO surrounded by a flattened distribution of dense molecular gas that is in the process of being cleared away along the rotation axis of the maser disk. A great advantage of studying OHMG systems over the general ULIRG population is that the circum-nuclear disks are effectively "fixed" at an edge on orientation, thereby breaking the degeneracy between the number of clumps and inclination in state of the art clumpy torus models. We have been awarded HST time in cycle 17 to conduct a comprehensive study of structure of the circum-nuclear gas, and its relationship to the radio structure and that of the maser disk, of large sample (80) of OHMG. This work is supported by ground-based spectropolarimetry, integral field spectroscopy and new radio continuum observations, Our overall objective is to probe the final stages of evolution immediately before the full- emergence of an enshrouded AGN as the circum-nuclear dust is dispersed by starburst and AGN-induced outflows. The specific scientific goals of this ADP proposal are to retrieve and analyze the Spitzer thermal-IR 5-70 micron imaging and IRS spectra of the subset of 72 of our targets for which Spitzer observations are available in the archive. We aim to establish the relationship between host and circum-nuclear ionized gas and dust structures in different OHMG spectroscopic types (AGN, Starburst, Composite) and model the AGN and starburst contributions to the mid-IR SED. Combining these with our other data we will address a number of important questions: is the mid-IR SED consistent with an edge-on circum-nuclear dust structure, as expected from the maser observations? What is the relative orientation of the Maser molecular structure and the ionized gas? Is there a connection between AGN heating of the circum-nuclear dust and wind or radiation driven outflows from the nucleus? How does the bolometric luminosity of the AGN relate to the OH line luminosity, FWHM and line shape? In turn these will relate the ionizing luminosity to the covering factor of the torus and the enclosed dynamical mass. When complete, this study should provide new insights on the relationships between the fundamental physical parameters of the AGN, including black hole mass, accretion and mass outflow rates, and the large scale properties of the host galaxy.

Load Diffusion in Composite and Smart Structures

NASA Technical Reports Server (NTRS)

Horgan, C. O.

2003-01-01

The research carried out here builds on our previous NASA supported research on the general topic of edge effects and load diffusion in composite structures. Further fundamental solid mechanics studies were carried out to provide a basis for assessing the complicated modeling necessary for the multi-functional large scale structures used by NASA. An understanding of the fundamental mechanisms of load diffusion in composite subcomponents is essential in developing primary composite structures. Some specific problems recently considered were those of end effects in smart materials and structures, study of the stress response of pressurized linear piezoelectric cylinders for both static and steady rotating configurations, an analysis of the effect of pre-stressing and pre-polarization on the decay of end effects in piezoelectric solids and investigation of constitutive models for hardening rubber-like materials. Our goal in the study of load diffusion is the development of readily applicable results for the decay lengths in terms of non-dimensional material and geometric parameters. Analytical models of load diffusion behavior are extremely valuable in building an intuitive base for developing refined modeling strategies and assessing results from finite element analyses. The decay behavior of stresses and other field quantities provides a significant aid towards this process. The analysis is also amenable to parameter study with a large parameter space and should be useful in structural tailoring studies. Special purpose analytical models of load diffusion behavior are extremely valuable in building an intuitive base for developing refined modeling strategies and in assessing results from general purpose finite element analyses. For example, a rational basis is needed in choosing where to use three-dimensional to two-dimensional transition finite elements in analyzing stiffened plates and shells. The decay behavior of stresses and other field quantities furnished by this research provides a significant aid towards this element transition issue. A priori knowledge of the extent of boundary-layers induced by edge effects is also useful in determination of the instrumentation location in structural verification tests or in material characterization tests.

Full-field Strain Methods for Investigating Failure Mechanisms in Triaxial Braided Composites

NASA Technical Reports Server (NTRS)

Littell, Justin D.; Binienda, Wieslaw K.; Goldberg, Robert K.; Roberts, Gary D.

2008-01-01

Composite materials made with triaxial braid architecture and large tow size carbon fibers are beginning to be used in many applications, including composite aircraft and engine structures. Recent advancements in braiding technology have led to commercially viable manufacturing approaches for making large structures with complex shape. Although the large unit cell size of these materials is an advantage for manufacturing efficiency, the fiber architecture presents some challenges for materials characterization, design, and analysis. In some cases, the static load capability of structures made using these materials has been higher than expected based on material strength properties measured using standard coupon tests. A potential problem with using standard tests methods for these materials is that the unit cell size can be an unacceptably large fraction of the specimen dimensions. More detailed investigation of deformation and failure processes in large unit cell size triaxial braid composites is needed to evaluate the applicability of standard test methods for these materials and to develop alternative testing approaches. In recent years, commercial equipment has become available that enables digital image correlation to be used on a more routine basis for investigation of full field 3D deformation in materials and structures. In this paper, some new techniques that have been developed to investigate local deformation and failure using digital image correlation techniques are presented. The methods were used to measure both local and global strains during standard straight-sided coupon tensile tests on composite materials made with 12 and 24 k yarns and a 0/+60/-60 triaxial braid architecture. Local deformation and failure within fiber bundles was observed, and this local failure had a significant effect on global stiffness and strength. The matrix material had a large effect on local damage initiation for the two matrix materials used in this investigation. Premature failure in regions of the unit cell near the edge of the straight-sided specimens was observed for transverse tensile tests in which the braid axial fibers were perpendicular to the specimen axis and the bias fibers terminated on the cut edges in the specimen gage section. This edge effect is one factor that could contribute to a measured strength that is lower than the actual material strength in a structure without edge effects.

Kinetic simulation of edge instability in fusion plasmas

NASA Astrophysics Data System (ADS)

Fulton, Daniel Patrick

In this work, gyrokinetic simulations in edge plasmas of both tokamaks and field reversed. configurations (FRC) have been carried out using the Gyrokinetic Toroidal Code (GTC) and A New Code (ANC) has been formulated for cross-separatrix FRC simulation. In the tokamak edge, turbulent transport in the pedestal of an H-mode DIII-D plasma is. studied via simulations of electrostatic driftwaves. Annulus geometry is used and simulations focus on two radial locations corresponding to the pedestal top with mild pressure gradient and steep pressure gradient. A reactive trapped electron instability with typical ballooning mode structure is excited in the pedestal top. At the steep gradient, the electrostatic instability exhibits unusual mode structure, peaking at poloidal angles theta=+- pi/2. Simulations find this unusual mode structure is due to steep pressure gradients in the pedestal but not due to the particular DIII-D magnetic geometry. Realistic DIII-D geometry has a stabilizing effect compared to a simple circular tokamak geometry. Driftwave instability in FRC is studied for the first time using gyrokinetic simulation. GTC. is upgraded to treat realistic equilibrium calculated by an MHD equilibrium code. Electrostatic local simulations in outer closed flux surfaces find ion-scale modes are stable due to the large ion gyroradius and that electron drift-interchange modes are excited by electron temperature gradient and bad magnetic curvature. In the scrape-off layer (SOL) ion-scale modes are excited by density gradient and bad curvature. Collisions have weak effects on instabilities both in the core and SOL. Simulation results are consistent with density fluctuation measurements in the C-2 experiment using Doppler backscattering (DBS). The critical density gradients measured by the DBS qualitatively agree with the linear instability threshold calculated by GTC simulations. One outstanding critical issue in the FRC is the interplay between turbulence in the FRC. core and SOL regions. While the magnetic flux coordinates used by GTC provide a number of computational advantages, they present unique challenges at the magnetic field separatrix. To address this limitation, a new code, capable of coupled core-SOL simulations, is formulated, implemented, and successfully verified.

Universal shocks in the Wishart random-matrix ensemble.

PubMed

Blaizot, Jean-Paul; Nowak, Maciej A; Warchoł, Piotr

2013-05-01

We show that the derivative of the logarithm of the average characteristic polynomial of a diffusing Wishart matrix obeys an exact partial differential equation valid for an arbitrary value of N, the size of the matrix. In the large N limit, this equation generalizes the simple inviscid Burgers equation that has been obtained earlier for Hermitian or unitary matrices. The solution, through the method of characteristics, presents singularities that we relate to the precursors of shock formation in the Burgers equation. The finite N effects appear as a viscosity term in the Burgers equation. Using a scaling analysis of the complete equation for the characteristic polynomial, in the vicinity of the shocks, we recover in a simple way the universal Bessel oscillations (so-called hard-edge singularities) familiar in random-matrix theory.

Quasi-periodic oscillations and the global modes of relativistic, MHD accretion discs

NASA Astrophysics Data System (ADS)

Dewberry, Janosz W.; Latter, Henrik N.; Ogilvie, Gordon I.

2018-05-01

The high-frequency quasi-periodic oscillations that punctuate the light curves of X-ray binary systems present a window on to the intrinsic properties of stellar-mass black holes and hence a testbed for general relativity. One explanation for these features is that relativistic distortion of the accretion disc's differential rotation creates a trapping region in which inertial waves (r-modes) might grow to observable amplitudes. Local analyses, however, predict that large-scale magnetic fields push this trapping region to the inner disc edge, where conditions may be unfavourable for r-mode growth. We revisit this problem from a pseudo-Newtonian but fully global perspective, deriving linearized equations describing a relativistic, magnetized accretion flow, and calculating normal modes with and without vertical density stratification. In an unstratified model we confirm that vertical magnetic fields drive r-modes towards the inner edge, though the effect depends on the choice of vertical wavenumber. In a global model we better quantify this susceptibility, and its dependence on the disc's vertical structure and thickness. Our calculations suggest that in thin discs, r-modes may remain independent of the inner disc edge for vertical magnetic fields with plasma betas as low as β ≈ 100-300. We posit that the appearance of r-modes in observations may be more determined by a competition between excitation and damping mechanisms near the ISCO than by the modification of the trapping region by magnetic fields.

Compressibility effects on dynamic stall of airfoils undergoing rapid transient pitching motion

NASA Technical Reports Server (NTRS)

Chandrasekhara, M. S.; Platzer, M. F.

1992-01-01

The research was carried out in the Compressible Dynamic Stall Facility, CDSF, at the Fluid Mechanics Laboratory (FML) of NASA Ames Research Center. The facility can produce realistic nondimensional pitch rates experienced by fighter aircraft, which on model scale could be as high as 3600/sec. Nonintrusive optical techniques were used for the measurements. The highlight of the effort was the development of a new real time interferometry method known as Point Diffraction Interferometry - PDI, for use in unsteady separated flows. This can yield instantaneous flow density information (and hence pressure distributions in isentropic flows) over the airfoil. A key finding is that the dynamic stall vortex forms just as the airfoil leading edge separation bubble opens-up. A major result is the observation and quantification of multiple shocks over the airfoil near the leading edge. A quantitative analysis of the PDI images shows that pitching airfoils produce larger suction peaks than steady airfoils at the same Mach number prior to stall. The peak suction level reached just before stall develops is the same at all unsteady rates and decreases with increase in Mach number. The suction is lost once the dynamic stall vortex or vortical structure begins to convect. Based on the knowledge gained from this preliminary analysis of the data, efforts to control dynamic stall were initiated. The focus of this work was to arrive at a dynamically changing leading edge shape that produces only 'acceptable' airfoil pressure distributions over a large angle of attack range.

The impact of forest structure and spatial scale on the relationship between ground plot above ground biomass and GEDI lidar waveforms

NASA Astrophysics Data System (ADS)

Armston, J.; Marselis, S.; Hancock, S.; Duncanson, L.; Tang, H.; Kellner, J. R.; Calders, K.; Disney, M.; Dubayah, R.

2017-12-01

The NASA Global Ecosystem Dynamics Investigation (GEDI) will place a multi-beam waveform lidar instrument on the International Space Station (ISS) to provide measurements of forest vertical structure globally. These measurements of structure will underpin empirical modelling of above ground biomass density (AGBD) at the scale of individual GEDI lidar footprints (25m diameter). The GEDI pre-launch calibration strategy for footprint level models relies on linking AGBD estimates from ground plots with GEDI lidar waveforms simulated from coincident discrete return airborne laser scanning data. Currently available ground plot data have variable and often large uncertainty at the spatial resolution of GEDI footprints due to poor colocation, allometric model error, sample size and plot edge effects. The relative importance of these sources of uncertainty partly depends on the quality of ground measurements and region. It is usually difficult to know the magnitude of these uncertainties a priori so a common approach to mitigate their influence on model training is to aggregate ground plot and waveform lidar data to a coarser spatial scale (0.25-1ha). Here we examine the impacts of these principal sources of uncertainty using a 3D simulation approach. Sets of realistic tree models generated from terrestrial laser scanning (TLS) data or parametric modelling matched to tree inventory data were assembled from four contrasting forest plots across tropical rainforest, deciduous temperate forest, and sclerophyll eucalypt woodland sites. These tree models were used to simulate geometrically explicit 3D scenes with variable tree density, size class and spatial distribution. GEDI lidar waveforms are simulated over ground plots within these scenes using monte carlo ray tracing, allowing the impact of varying ground plot and waveform colocation error, forest structure and edge effects on the relationship between ground plot AGBD and GEDI lidar waveforms to be directly assessed. We quantify the sensitivity of calibration equations relating GEDI lidar structure measurements and AGBD to these factors at a range of spatial scales (0.0625-1ha) and discuss the implications for the expanding use of existing in situ ground plot data by GEDI.

ESnet: Large-Scale Science and Data Management ( (LBNL Summer Lecture Series)

ScienceCinema

Johnston, Bill

2017-12-09

Summer Lecture Series 2004: Bill Johnston of Berkeley Lab's Computing Sciences is a distinguished networking and computing researcher. He managed the Energy Sciences Network (ESnet), a leading-edge, high-bandwidth network funded by DOE's Office of Science. Used for everything from videoconferencing to climate modeling, and flexible enough to accommodate a wide variety of data-intensive applications and services, ESNet's traffic volume is doubling every year and currently surpasses 200 terabytes per month.

The effect of split pixel HDR image sensor technology on MTF measurements

NASA Astrophysics Data System (ADS)

Deegan, Brian M.

2014-03-01

Split-pixel HDR sensor technology is particularly advantageous in automotive applications, because the images are captured simultaneously rather than sequentially, thereby reducing motion blur. However, split pixel technology introduces artifacts in MTF measurement. To achieve a HDR image, raw images are captured from both large and small sub-pixels, and combined to make the HDR output. In some cases, a large sub-pixel is used for long exposure captures, and a small sub-pixel for short exposures, to extend the dynamic range. The relative size of the photosensitive area of the pixel (fill factor) plays a very significant role in the output MTF measurement. Given an identical scene, the MTF will be significantly different, depending on whether you use the large or small sub-pixels i.e. a smaller fill factor (e.g. in the short exposure sub-pixel) will result in higher MTF scores, but significantly greater aliasing. Simulations of split-pixel sensors revealed that, when raw images from both sub-pixels are combined, there is a significant difference in rising edge (i.e. black-to-white transition) and falling edge (white-to-black) reproduction. Experimental results showed a difference of ~50% in measured MTF50 between the falling and rising edges of a slanted edge test chart.

Meniscus-assisted solution printing of large-grained perovskite films for high-efficiency solar cells

NASA Astrophysics Data System (ADS)

He, Ming; Li, Bo; Cui, Xun; Jiang, Beibei; He, Yanjie; Chen, Yihuang; O'Neil, Daniel; Szymanski, Paul; Ei-Sayed, Mostafa A.; Huang, Jinsong; Lin, Zhiqun

2017-07-01

Control over morphology and crystallinity of metal halide perovskite films is of key importance to enable high-performance optoelectronics. However, this remains particularly challenging for solution-printed devices due to the complex crystallization kinetics of semiconductor materials within dynamic flow of inks. Here we report a simple yet effective meniscus-assisted solution printing (MASP) strategy to yield large-grained dense perovskite film with good crystallization and preferred orientation. Intriguingly, the outward convective flow triggered by fast solvent evaporation at the edge of the meniscus ink imparts the transport of perovskite solutes, thus facilitating the growth of micrometre-scale perovskite grains. The growth kinetics of perovskite crystals is scrutinized by in situ optical microscopy tracking to understand the crystallization mechanism. The perovskite films produced by MASP exhibit excellent optoelectronic properties with efficiencies approaching 20% in planar perovskite solar cells. This robust MASP strategy may in principle be easily extended to craft other solution-printed perovskite-based optoelectronics.

Realizing Large-Scale, Electronic-Grade Two-Dimensional Semiconductors.

PubMed

Lin, Yu-Chuan; Jariwala, Bhakti; Bersch, Brian M; Xu, Ke; Nie, Yifan; Wang, Baoming; Eichfeld, Sarah M; Zhang, Xiaotian; Choudhury, Tanushree H; Pan, Yi; Addou, Rafik; Smyth, Christopher M; Li, Jun; Zhang, Kehao; Haque, M Aman; Fölsch, Stefan; Feenstra, Randall M; Wallace, Robert M; Cho, Kyeongjae; Fullerton-Shirey, Susan K; Redwing, Joan M; Robinson, Joshua A

2018-02-27

Atomically thin transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics. Here, we demonstrate device-ready synthetic tungsten diselenide (WSe 2 ) via metal-organic chemical vapor deposition and provide key insights into the phenomena that control the properties of large-area, epitaxial TMDs. When epitaxy is achieved, the sapphire surface reconstructs, leading to strong 2D/3D (i.e., TMD/substrate) interactions that impact carrier transport. Furthermore, we demonstrate that substrate step edges are a major source of carrier doping and scattering. Even with 2D/3D coupling, transistors utilizing transfer-free epitaxial WSe 2 /sapphire exhibit ambipolar behavior with excellent on/off ratios (∼10 7 ), high current density (1-10 μA·μm -1 ), and good field-effect transistor mobility (∼30 cm 2 ·V -1 ·s -1 ) at room temperature. This work establishes that realization of electronic-grade epitaxial TMDs must consider the impact of the TMD precursors, substrate, and the 2D/3D interface as leading factors in electronic performance.

Meniscus-assisted solution printing of large-grained perovskite films for high-efficiency solar cells

PubMed Central

He, Ming; Li, Bo; Cui, Xun; Jiang, Beibei; He, Yanjie; Chen, Yihuang; O’Neil, Daniel; Szymanski, Paul; EI-Sayed, Mostafa A.; Huang, Jinsong; Lin, Zhiqun

2017-01-01

Control over morphology and crystallinity of metal halide perovskite films is of key importance to enable high-performance optoelectronics. However, this remains particularly challenging for solution-printed devices due to the complex crystallization kinetics of semiconductor materials within dynamic flow of inks. Here we report a simple yet effective meniscus-assisted solution printing (MASP) strategy to yield large-grained dense perovskite film with good crystallization and preferred orientation. Intriguingly, the outward convective flow triggered by fast solvent evaporation at the edge of the meniscus ink imparts the transport of perovskite solutes, thus facilitating the growth of micrometre-scale perovskite grains. The growth kinetics of perovskite crystals is scrutinized by in situ optical microscopy tracking to understand the crystallization mechanism. The perovskite films produced by MASP exhibit excellent optoelectronic properties with efficiencies approaching 20% in planar perovskite solar cells. This robust MASP strategy may in principle be easily extended to craft other solution-printed perovskite-based optoelectronics. PMID:28685751

Application of the multi-scale finite element method to wave propagation problems in damaged structures

NASA Astrophysics Data System (ADS)

Casadei, F.; Ruzzene, M.

2011-04-01

This work illustrates the possibility to extend the field of application of the Multi-Scale Finite Element Method (MsFEM) to structural mechanics problems that involve localized geometrical discontinuities like cracks or notches. The main idea is to construct finite elements with an arbitrary number of edge nodes that describe the actual geometry of the damage with shape functions that are defined as local solutions of the differential operator of the specific problem according to the MsFEM approach. The small scale information are then brought to the large scale model through the coupling of the global system matrices that are assembled using classical finite element procedures. The efficiency of the method is demonstrated through selected numerical examples that constitute classical problems of great interest to the structural health monitoring community.

Full scale wind turbine test of vortex generators mounted on the entire blade

NASA Astrophysics Data System (ADS)

Bak, Christian; Skrzypiński, Witold; Gaunaa, Mac; Villanueva, Hector; Brønnum, Niels F.; Kruse, Emil K.

2016-09-01

Measurements on a heavily instrumented pitch regulated variable speed Vestas V52 850 kW wind turbine situated at the DTU Risø Campus are carried out, where the effect of vortex generators mounted on almost the entire blade is tested with and without leading edge roughness. The measurements are compared to the predictions carried out by a developed design tool, where the effect of vortex generators and leading edge roughness is simulated using engineering models. The measurements showed that if vortex generators are mounted there is an increase in flapwise blade moments if the blades are clean, but also that the loads are almost neutral when vortex generators are installed if there is leading edge roughness on the blades. Finally, it was shown that there was a good agreement between the measurements and the predictions from the design tool.

Fungal biomineralization of montmorillonite and goethite to short-range-ordered minerals

NASA Astrophysics Data System (ADS)

Li, Huan; Hu, Shuijin; Polizzotto, Matthew L.; Chang, Xiaoli; Shen, Qirong; Ran, Wei; Yu, Guanghui

2016-10-01

Highly reactive nano-scale minerals, e.g., short-range-ordered minerals (SROs) and other nanoparticles, play an important role in soil carbon (C) retention. Yet, the mechanisms that govern biomineralization from bulk minerals to highly reactive nano-scale minerals remain largely unexplored, which critically hinders our efforts toward managing nano-scale minerals for soil C retention. Here we report the results from a study that explores structural changes during Aspergillus fumigatus Z5 transformation of montmorillonite and goethite to SROs. We examined the morphology and structure of nano-scale minerals, using high-resolution transmission electron microscopy, time-resolved solid-state 27Al and 29Si NMR, and Fe K-edge X-ray absorption fine structure spectroscopy combined with two dimensional correlation spectroscopy (2D COS) analysis. Our results showed that after a 48-h cultivation of montmorillonite and goethite with Z5, new biogenic intracellular and extracellular reactive nano-scale minerals with a size of 3-5 nm became abundant. Analysis of 2D COS further suggested that montmorillonite and goethite were the precursors of the dominant biogenic nano-scale minerals. Carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectra and their deconvolution results demonstrated that during fungus Z5 growth, carboxylic C (288.4-289.1 eV) was the dominant organic group, accounting for approximately 34% and 59% in the medium and aggregates, respectively. This result suggested that high percentage of the production of organic acids during the growth of Z5 was the driving factor for structural changes during biomineralization. This is, to the best of our knowledge, the first report of the structural characterization of nano-scale minerals by 2D COS, highlighting its potential to elucidate biomineralization pathways and thus identify the precursors of nano-scale minerals.

Fragmentation, topography, and forest age modulate impacts of drought on a tropical forested landscape in eastern Puerto Rico

NASA Astrophysics Data System (ADS)

Uriarte, M.; Schwartz, N.; Budsock, A.

2017-12-01

Naturally regenerating second-growth forests account for ca. 50% of tropical forest cover and provide key ecosystem services. Understanding climate impacts on these ecosystems is critical for developing effective mitigation programs. Differences in environmental conditions and landscape context from old-growth forests may exacerbate climate impacts on second-growth stands. Nearly 70% of forest regeneration is occurring in hilly, upland, or mountain regions; a large proportion of second-growth forests are also fragmented. The effects of drought at the landscape scale, however, and the factors that modulate landscape heterogeneity in drought impacts remain understudied. Heterogeneity in soil moisture, light, and temperature in fragmented, topographically complex landscapes is likely to influence climate impacts on these forests. We examine impacts of a severe drought in 2015 on a forested landscape in Puerto Rico using two anomalies in vegetation indices. The study landscape is fragmented and topographically complex and includes old- and second-growth forests. We consider how topography (slope, aspect), fragmentation (distance to forest edge, patch size), and forest age (old- vs second-growth) modulate landscape heterogeneity of drought impacts and recovery from drought. Drought impacts were more severe in second-growth forests than in old-growth stands. Both topography and forest fragmentation influences the magnitude of drought impacts. Forest growing in steep areas, south facing slopes, small patches, and closer to forest edges exhibited more marked responses to drought. Forest recovery from drought was greater in second-growth forests and south facing slopes but slower in small patches and closer to forest edges. These findings are congruent with studies of drought impacts on tree growth in the study region. Together these results demonstrate the need for a multi-scalar approach to the study of drought impacts on tropical forests.

Giant edge spin accumulation in a symmetric quantum well with two subbands

NASA Astrophysics Data System (ADS)

Khaetskii, Alexander; Egues, J. Carlos

We have studied the edge spin accumulation due to an electric current in a high mobility two-dimensional electron gas formed in a symmetric well with two subbands. This study is strongly motivated by recent experiments which demonstrated the spin accumulation near the edges of a symmetric bilayer GaAs structure in contrast to no effect in a single-layer configuration. The intrinsic mechanism of the spin-orbit interaction we consider arises from the coupling between two subband states of opposite parities. Following the method developed in, we show that the presence of a gap in the system (i.e., the energy separation between the two subband bottoms) changes drastically the picture of the edge spin accumulation. We obtain a parametrically large magnitude of the edge spin density for a two-subband well as compared to the usual single-subband structure, and show that by changing the gap from zero up to 1 ÷2 K, the magnitude of the effect changes by three orders of magnitude. It opens up the possibility for the design of new interesting spintronic devices. We acknowledge financial support from FAPESP.

Edge effects resulting from forest fragmentation enhance carbon uptake and its vulnerability to climate change in temperate broadleaf forests

NASA Astrophysics Data System (ADS)

Reinmann, A.; Hutyra, L.

2016-12-01

Forest fragmentation resulting from land use and land cover change is a ubiquitous, ongoing global phenomenon with profound impacts on the growing conditions of the world's remaining forest. However, our understanding of forest carbon dynamics and their response to climate largely comes from unfragmented forest systems, which presents an important mismatch between the landscapes we study and those we aim to characterize. The temperate broadleaf forest makes a large contribution to the global terrestrial carbon sink, but is also the most heavily fragmented forest biome in the world. We use field measurements and geospatial analyses to characterize carbon dynamics in temperate broadleaf forest fragments. We show that forest growth and biomass increase by 89 ± 17% and 64 ± 12%, respectively, from the forest interior to edge. These ecosystem edge enhancements are not currently captured by models or approaches to quantifying regional C balance, but across southern New England, USA it increases carbon uptake and storage by 12.5 ± 2.9% and 9.6 ± 1.4%, respectively. However, we also find that forest growth near the edge declines three times faster than in the interior in response to heat stress during the growing season. Using climate projections, we show that future heat stress could reduce the forest edge growth enhancement by one-third by the end of the century. These findings contrast studies of edge effects in the world's other major forest biomes and indicate that the strength of the temperate broadleaf forest carbon sink and its capacity to mitigate anthropogenic carbon emissions may be stronger, but also more sensitive to climate change than previous estimates suggest.

Ultrahigh-rate supercapacitors with large capacitance based on edge oriented graphene coated carbonized cellulous paper as flexible freestanding electrodes

NASA Astrophysics Data System (ADS)

Ren, Guofeng; Li, Shiqi; Fan, Zhao-Xia; Hoque, Md Nadim Ferdous; Fan, Zhaoyang

2016-09-01

Large-capacitance and ultrahigh-rate electrochemical supercapacitors (UECs) with frequency response up to kilohertz (kHz) range are reported using light, thin, and flexible freestanding electrodes. The electrode is formed by perpendicularly edge oriented multilayer graphene/thin-graphite (EOG) sheets grown radially around individual fibers in carbonized cellulous paper (CCP), with cellulous carbonization and EOG deposition implemented in one step. The resulted ∼10 μm thick EOG/CCP electrode is light and flexible. The oriented porous structure of EOG with large surface area, in conjunction with high conductivity of the electrode, ensures ultrahigh-rate performance of the fabricated cells, with large areal capacitance of 0.59 mF cm-2 and 0.53 mF cm-2 and large phase angle of -83° and -80° at 120 Hz and 1 kHz, respectively. Particularly, the hierarchical EOG/CCP sheet structure allows multiple sheets stacked together for thick electrodes with almost linearly increased areal capacitance while maintaining the volumetric capacitance nearly no degradation, a critical merit for developing practical faraday-scale UECs. 3-layers of EOG/CCP electrode achieved an areal capacitance of 1.5 mF cm-2 and 1.4 mF cm-2 at 120 Hz and 1 kHz, respectively. This demonstration moves a step closer to the goal of bridging the frequency/capacitance gap between supercapacitors and electrolytic capacitors.

The effects of leading-edge serrations on reducing flow unsteadiness about airfoils, an experimental and analytical investigation

NASA Technical Reports Server (NTRS)

Schwind, R. G.; Allen, H. J.

1973-01-01

High frequency surface pressure measurements were obtained from wind-tunnel tests over the Reynolds number range 1.2 times one million to 6.2 times one million on a rectangular wing of NACA 63-009 airfoil section. Measurements were also obtained with a wide selection of leading-edge serrations added to the basic airfoil. Under a two-dimensional laminar bubble very close to the leading edge of the basic airfoil there is a large apatial peak in rms pressure. Frequency analysis of the pressure signals in this region show a large, high-frequency energy peak which is interpreted as an oscillation in size and position of the bubble. The serrations divide the bubble into segments and reduce the peak rms pressures. A low Reynolds number flow visualization test on a hydrofoil in water was also conducted. A von Karman vortex street was found trailing from the rear of the foil. Its frequency is at a much lower Strouhal number than in the high Reynolds number experiment, and is related to the trailing-edge and boundary-layer thicknesses.

Propagative selection of tilted array patterns in directional solidification

NASA Astrophysics Data System (ADS)

Song, Younggil; Akamatsu, Silvère; Bottin-Rousseau, Sabine; Karma, Alain

2018-05-01

We investigate the dynamics of tilted cellular/dendritic array patterns that form during directional solidification of a binary alloy when a preferred-growth crystal axis is misoriented with respect to the temperature gradient. In situ experimental observations and phase-field simulations in thin samples reveal the existence of a propagative source-sink mechanism of array spacing selection that operates on larger space and time scales than the competitive growth at play during the initial solidification transient. For tilted arrays, tertiary branching at the diverging edge of the sample acts as a source of new cells with a spacing that can be significantly larger than the initial average spacing. A spatial domain of large spacing then invades the sample propagatively. It thus yields a uniform spacing everywhere, selected independently of the initial conditions, except in a small region near the converging edge of the sample, which acts as a sink of cells. We propose a discrete geometrical model that describes the large-scale evolution of the spatial spacing profile based on the local dependence of the cell drift velocity on the spacing. We also derive a nonlinear advection equation that predicts the invasion velocity of the large-spacing domain, and sheds light on the fundamental nature of this process. The models also account for more complex spacing modulations produced by an irregular dynamics at the source, in good quantitative agreement with both phase-field simulations and experiments. This basic knowledge provides a theoretical basis to improve the processing of single crystals or textured polycrystals for advanced materials.

Preliminary Assessment of Microwave Readout Multiplexing Factor

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

Croce, Mark Philip; Koehler, Katrina Elizabeth; Rabin, Michael W.

2017-01-23

Ultra-high resolution microcalorimeter gamma spectroscopy is a new non-destructive assay technology for measurement of plutonium isotopic composition, with the potential to reduce total measurement uncertainty to a level competitive with destructive analysis methods [1-4]. Achieving this level of performance in practical applications requires not only the energy resolution now routinely achieved with transition-edge sensor microcalorimeter arrays (an order of magnitude better than for germanium detectors) but also high throughput. Microcalorimeter gamma spectrometers have not yet achieved detection efficiency and count rate capability that is comparable to germanium detectors, largely because of limits from existing readout technology. Microcalorimeter detectors must bemore » operated at low temperature to achieve their exceptional energy resolution. Although the typical 100 mK operating temperatures can be achieved with reliable, cryogen-free systems, the cryogenic complexity and heat load from individual readout channels for large sensor arrays is prohibitive. Multiplexing is required for practical systems. The most mature multiplexing technology at present is time-division multiplexing (TDM) [3, 5-6]. In TDM, the sensor outputs are switched by applying bias current to one SQUID amplifier at a time. Transition-edge sensor (TES) microcalorimeter arrays as large as 256 pixels have been developed for X-ray and gamma-ray spectroscopy using TDM technology. Due to bandwidth limits and noise scaling, TDM is limited to a maximum multiplexing factor of approximately 32-40 sensors on one readout line [8]. Increasing the size of microcalorimeter arrays above the kilopixel scale, required to match the throughput of germanium detectors, requires the development of a new readout technology with a much higher multiplexing factor.« less