14,679 research outputs found

    Flammability study of materials in oxygen environments

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    Report presents flame-propagation rates and flammability ratings of 780 specimens of commercially available plastics, elastomers, coatings, fabrics, and other sheet materials. Test results are also given for over 1970 samples of most commonly used electrical harnesses, connectors, and potting compounds

    Viscosity and density of methanol/water mixtures at low temperatures

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    Viscosity and density are measured at low temperatures for three methanol/water mixtures. Viscosity is determined by a modified falling cylinder method or a calibrated viscometer. Density is determined by the volume of each mixture contained in a calibrated glass cell placed in a constant-temperature bath

    A Peptide Core Motif for Binding to Heterotrimeric G Protein α Subunits

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    Recently, in vitro selection using mRNA display was used to identify a novel peptide sequence that binds with high affinity to G{alpha}i1. The peptide was minimized to a 9-residue sequence (R6A-1) that retains high affinity and specificity for the GDP-bound state of G{alpha}i1 and acts as a guanine nucleotide dissociation inhibitor (GDI). Here we demonstrate that the R6A-1 peptide interacts with G{alpha} subunits representing all four G protein classes, acting as a core motif for G{alpha} interaction. This contrasts with the consensus G protein regulatory(GPR) sequence, a 28-mer peptide GDI derived from the GoLoco (G{alpha}i/0-Loco interaction)/GPR motif that shares no homology with R6A-1 and binds only to G{alpha}i1-3 in this assay. Binding of R6A-1 is generally specific to the GDP-bound state of the G{alpha} subunits and excludes association with G{beta}{gamma}. R6A-G{alpha}i1 complexes are resistant to trypsin digestion and exhibit distinct stability in the presence of Mg2+, suggesting that the R6A and GPR peptides exert their activities using different mechanisms. Studies using G{alpha}i1/G{alpha}s chimeras identify two regions of G{alpha}i1 (residues 1–35 and 57–88) as determinants for strong R6A-Gi{alpha}1 interaction. Residues flanking the R6A-1 peptide confer unique binding properties, indicating that the core motif could be used as a starting point for the development of peptides exhibiting novel activities and/or specificity for particular G protein subclasses or nucleotide-bound states

    Experiments on Visual Acuity and the Visibility of Markings on the Ground in Long-duration Earth-Orbital Space Flight

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    Visual acuity and visibility of markings on ground in long duration earth orbital space fligh

    Comparative Surface Heat Transfer Measurements in Hypervelocity Flow

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    Reliable prediction of the high heat transfer rates experienced during the hypersonic portion of planetary entry and descent is critical to vehicle survival. Two types of sensors that can be used to measure surface heat flux are coaxial thermocouple gages and thin film resistance thermometers. Individually, both types of gages have been used successfully in a number of studies [1–19]. Both thermocouple and thin film gages measure surface temperature from which heat transfer can be calculated. Both have µs response times, and can be flush-mounted in models. Coaxial thermocouples are robust, can survive challenging experimental conditions, and are typically used in higher enthalpy flows. Thin film resistance gages typically provide improved signal levels, but are less robust, have to be individually calibrated, and are typically used in lower enthalpy flows. As a result, there are few studies which directly compare measurements from the two types of gages. In the present work, we perform experimental measurements at a range of intermediate enthalpies in hypervelocity flow and make direct comparisons between temperature histories and heat flux data obtained from thermocouple and thin film gages

    Scaling of heat transfer augmentation due to mechanical distortions in hypervelocity boundary layers

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    We examine the response of hypervelocity boundary layers to global mechanical distortions due to concave surface curvature. Surface heat transfer and visual boundary layer thickness data are obtained for a suite of models with different concave surface geometries. Results are compared to predictions using existing approximate methods. Near the leading edge, good agreement is observed, but at larger pressure gradients, predictions diverge significantly from the experimental data. Up to a factor of five underprediction is reported in regions with greatest distortion. Curve fits to the experimental data are compared with surface equations. We demonstrate that reasonable estimates of the laminar heat flux augmentation may be obtained as a function of the local turning angle for all model geometries, even at the conditions of greatest distortion. This scaling may be explained by the application of Lees similarity. As a means of introducing additional local distortions, vortex generators are used to impose streamwise structures into the boundary layer. The response of the large scale vortices to an adverse pressure gradient is investigated. Surface streak evolution is visualized over the different surface geometries using fast response pressure sensitive paint. For a flat plate baseline case, heat transfer augmentation at similar levels to turbulent flow is measured. For the concave geometries, increases in heat transfer by factors up to 2.6 are measured over the laminar values. The scaling of heat transfer with turning angle that is identified for the laminar boundary layer response is found to be robust even in the presence of the imposed vortex structures

    Two- and three-dimensional simulations of core-collapse supernovae with CHIMERA

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    Ascertaining the core-collapse supernova mechanism is a complex, and yet unsolved, problem dependent on the interaction of general relativity, hydrodynamics, neutrino transport, neutrino-matter interactions, and nuclear equations of state and reaction kinetics. Ab initio modeling of core-collapse supernovae and their nucleosynthetic outcomes requires care in the coupling and approximations of the physical components. We have built our multi-physics CHIMERA code for supernova modeling in 1-, 2-, and 3-D, using ray-by-ray neutrino transport, approximate general relativity, and detailed neutrino and nuclear physics. We discuss some early results from our current series of exploding 2D simulations and our work to perform computationally tractable simulations in 3D using the "Yin-Yang" grid.Comment: Proceedings of the 12th Symposium on Nuclei in the Cosmos. 5-12 August 2012. Cairns, Australia. Published online at http://pos.sissa.it/archive/conferences/146/208/NIC%20XII_208.pdf Corrected typ

    Towards practical classical processing for the surface code: timing analysis

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    Topological quantum error correction codes have high thresholds and are well suited to physical implementation. The minimum weight perfect matching algorithm can be used to efficiently handle errors in such codes. We perform a timing analysis of our current implementation of the minimum weight perfect matching algorithm. Our implementation performs the classical processing associated with an nxn lattice of qubits realizing a square surface code storing a single logical qubit of information in a fault-tolerant manner. We empirically demonstrate that our implementation requires only O(n^2) average time per round of error correction for code distances ranging from 4 to 512 and a range of depolarizing error rates. We also describe tests we have performed to verify that it always obtains a true minimum weight perfect matching.Comment: 13 pages, 13 figures, version accepted for publicatio
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