Nickel layers on indium arsenide

We report here on the preparation and characterization of InAs substrates for in situ deposition of ferromagnetic contacts, a necessary precursor for semiconductor devices based on spin injection. InAs has been grown on InAs(111)A and (100) substrates by molecular-beam epitaxy and then metalized in situ in order to better understand the mechanisms that inhibit spin injection into a semiconductor. Initial x-ray characterization of the samples indicate the presence of nickel arsenides and indium–nickel compounds forming during deposition at temperatures above room temperature. Several temperature ranges have been investigated in order to determine the effect on nickel-arsenide formation. The presence of such compounds at the interface could greatly reduce the spin-injection efficiency and help elucidate previous unsuccessful attempts at measuring spin injection into InAs

Three-dimensional analysis of the Pratt and Whitney alternate design SSME fuel turbine

The three dimensional viscous time-mean flow in the Pratt and Whitney alternate design space shuttle main engine fuel turbine is simulated using the average passage Navier-Stokes equations. The migration of secondary flows generated by upstream blade rows and their effect on the performance of downstream blade rows is studied. The present simulation confirms that the flow in this two stage turbine is highly three dimensional and dominated by the tip leakage flow. The tip leakage vortex generated by the first blade persists through the second blade and adversely affects its performance. The greatest mixing of the inlet total temperature distortion occurs in the second vane and is due to the large leakage vortex generated by the upstream rotor. It is assumed that the predominant spanwise mixing mechanism in this low aspect ratio turbine is the radial transport due to the deterministically unsteady vortical flow generated by upstream blade rows. A by-product of the analysis is accurate pressure and heat loads for all blade rows under the influence of neighboring blade rows. These aero loads are useful for advanced structural analysis of the vanes and blades

Effect of Buffer Layer and III/V Ratio on the Surface Morphology of GaN Grown by MBE

The surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and "loop" defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than 1 nm RMS

Reconstructing glacial outburst floods (jökulhlaups) from geomorphology: challenges, solutions, and an enhanced interpretive framework

Glacial outburst floods (jökulhlaups) have been significant drivers of landscape change across Earth throughout the Quaternary and are a contemporary hazard in Arctic and alpine regions worldwide. Geomorphologic evidence is a foundation for reconstructing past and contemporary flood events and using additional analytical methods such as geochronology and paleohydraulics. Yet, accurate interpretation of jökulhlaup landforms and depositional sequences poses a persistent challenge due to complex controls on flood hydraulics and landscape evolution. Researchers have developed numerous strategies to reduce or resolve these challenges, but a comprehensive, globally applicable model to interpret flood evidence outside of sedimentary environments is lacking. This article synthesizes existing case studies to describe jökulhlaup geomorphologic interpretive challenges, discuss strategies to resolve them, and present a conceptual model of flood landform assemblages to illustrate hydraulic and environmental controls on resultant geomorphologic impacts. This enhanced interpretive framework aids researchers in identifying, interpreting, and testing geomorphologic evidence to reconstruct past jökulhlaups and predict future flood impacts as robustly as possible at a global, landscape-wide scale. Understanding jökulhlaup geomorphology yields insight into glacial lake and ice margin dynamics, the role of extreme events in landscape evolution, and interactions between climate, ice sheets, and hydrology. Moreover, it is increasingly important as glacial outburst floods may become more frequent due to climate-driven ice retreat, advancing predictive capacities to mitigate societal risk downstream.</div

Analysis of the role of Ser1/Ser2/Thr9 phosphorylation on myosin II assembly and function in live cells

<p>Abstract</p> <p>Background</p> <p>Phosphorylation of non-muscle myosin II regulatory light chain (RLC) at Thr18/Ser19 is well established as a key regulatory event that controls myosin II assembly and activation, both in vitro and in living cells. RLC can also be phosphorylated at Ser1/Ser2/Thr9 by protein kinase C (PKC). Biophysical studies show that phosphorylation at these sites leads to an increase in the Km of myosin light chain kinase (MLCK) for RLC, thereby indirectly inhibiting myosin II activity. Despite unequivocal evidence that PKC phosphorylation at Ser1/Ser2/Thr9 can regulate myosin II function in vitro, there is little evidence that this mechanism regulates myosin II function in live cells.</p> <p>Results</p> <p>The purpose of these studies was to investigate the role of Ser1/Ser2/Thr9 phosphorylation in live cells. To do this we utilized phospho-specific antibodies and created GFP-tagged RLC reporters with phosphomimetic aspartic acid substitutions or unphosphorylatable alanine substitutions at the putative inhibitory sites or the previously characterized activation sites. Cell lines stably expressing the RLC-GFP constructs were assayed for myosin recruitment during cell division, the ability to complete cell division, and myosin assembly levels under resting or spreading conditions. Our data shows that manipulation of the activation sites (Thr18/Ser19) significantly alters myosin II function in a number of these assays while manipulation of the putative inhibitory sites (Ser1/Ser2/Thr9) does not.</p> <p>Conclusions</p> <p>These studies suggest that inhibitory phosphorylation of RLC is not a substantial regulatory mechanism, although we cannot rule out its role in other cellular processes or perhaps other types of cells or tissues in vivo.</p

Deterministic blade row interactions in a centrifugal compressor stage

The three-dimensional viscous flow in a low-speed centrifugal compressor stage is simulated using an average passage Navier-Stokes analysis. The Introduction Recent experimental and computational studies have shed considerable light on the problem of blade row interactions in axial flow turbomachinery. However, blade row interactions in centrifugal machines have not received much attention. Many numerical simulations of isolated centrifugal impeller flows have been made, e.g., The average passage equations are similar to the steady Reynolds-averaged Navier-Stokes equations except that body forces, energy sources, and a metal blockage factor are included to introduce the effect of neighboring blade rows. In addition, the Reynolds stress is augmented by two additional stresses. The first additional stress includes the effect of spatial aperiodicity on the average passage flow and the second includes the effect of deterministic unsteadiness on the time