441 research outputs found
Neue Beiträge zur Macrolepidopteren-Fauna Oberandalusiens aus den Provinzen Granada, AlmerÃa und Málaga (Südspanien)
Current-Induced Spin Polarization in Gallium Nitride
Electrically generated spin polarization is probed directly in bulk GaN using
Kerr rotation spectroscopy. A series of n-type GaN epilayers are grown in the
wurtzite phase both by molecular beam epitaxy (MBE) and metalorganic chemical
vapor deposition (MOCVD) with a variety of doping densities chosen to broadly
modulate the transverse spin lifetime, T2*. The spin polarization is
characterized as a function of electrical excitation energy over a range of
temperatures. Despite weak spin-orbit interactions in GaN, a current-induced
spin polarization (CISP) is observed in the material at temperatures of up to
200 K.Comment: 16 pages, 3 figure
Effect of Seagrass on Current Speed: Importance of Flexibility vs. Shoot Density
Water flow through seagrass beds transports nutrients, affects sediment stability and chemistry, and imposes hydrodynamic forces on shoots that alter canopy configuration. Past studies done under diverse conditions yielded conflicting results about the effects of shoot density on flow through seagrass bed canopies. We used eelgrass, Zostera marina, to study how the density of flexible shoots affect the hydrodynamics of seagrass beds in unidirectional water flow. By exposing randomly-arranged shoots of uniform length to current velocities controlled in a flume, the effects of shoot density and distance downstream from the bed edge could be determined without confounding factors. Comparison of velocity profiles within beds to those upstream of beds showed that flow was slower in the beds. However, shoot density, downstream distance, and current velocity did not affect the percent reduction in flow velocity in a bed. Turbulence enhances mixing of substances carried in the water. Here, turbulence intensity (index of the importance of turbulent velocity fluctuations relative to average current velocity) was lower when ambient flow was faster, but was not affected by shoot density or downstream position, Drag (hydrodynamic force on a shoot that bends it over in the flow direction) provides another measure of how the canopy affects flow experienced by a shoot. Drag was not affected by current velocity, shoot density, or downstream position in the bed. Gaps between shoots can enhance light and flow penetration into the canopy, but when shoots are bent over by flow, they can cover gaps. Faster ambient currents caused greater gap closure, which at each current speed was greater for high shoot densities. Thus, canopy gap closure did not correlate with percent flow reduction in grass beds or with drag on individual shoots, both of which were independent of shoot density and ambient current velocity. Since changing shoot density does not affect the flow in a grass bed exposed to a given ambient current, our results are inconsistent with the hypothesis that the high shoot densities observed in grass beds in habitats exposed to rapid flow are due to a direct, adaptive response of the grass to the flow environment
An investigation of the reaction of titanium with hydrogen Summary report
Hydrogen gas reaction with titanium and titanium alloys determined at low temperatures and pressure
Self consistent determination of plasmonic resonances in ternary nanocomposites
We have developed a self consistent technique to predict the behavior of
plasmon resonances in multi-component systems as a function of wavelength. This
approach, based on the tight lower bounds of the Bergman-Milton formulation, is
able to predict experimental optical data, including the positions, shifts and
shapes of plasmonic peaks in ternary nanocomposites without using any ftting
parameters. Our approach is based on viewing the mixing of 3 components as the
mixing of 2 binary mixtures, each in the same host. We obtained excellent
predictions of the experimental optical behavior for mixtures of Ag:Cu:SiO2 and
alloys of Au-Cu:SiO2 and Ag-Au:H2 O, suggesting that the essential physics of
plasmonic behavior is captured by this approach.Comment: 7 pages and 4 figure
Accuracy of side-chain prediction upon near-native protein backbones generated by ab initio folding methods
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Potential of the acousto-ultrasound method to characterize the strength of hot gas filter materials.
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Development of nondestructive evaluation methods for structural ceramics
Nondestructive evaluation (NDE) methods using three-dimensional microfocus X-ray computed tomographic imaging (3DXCT) were employed to map axial and radial density variations in hot-gas filters and heat exchanger tubes. 3D XCT analysis was conducted on (a) two 38-mm-OD, 6.5-mm wall, SiC/SiC heat exchanger tubes infiltrated by CVI; (b) eight 10 cm diam. oxide/oxide heat exchanger tubes; and (c) one 26-cm-long Nextel fiber/SiC matrix hot-gas filter. The results show that radial and axial density uniformity as well as porosity, can be assessed by 3D XCT. NDE methods are also under development to assess thermal barrier coatings which are under development as methods to protect gas-turbine first-stage hot section metallic substrates. Further, because both shop and field joining of CFCC materials will be necessary, work is now beginning on development of NDE methods for joining
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