15,101 research outputs found

    Electron capture rates in a plasma

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    A new general expression is derived for nuclear electron capture rates within dense plasmas. Its qualitative nature leads us to question some widely accepted assumptions about how to calculate the effects of the plasma on the rates. A perturbative evaluation, though not directly applicable to the strongly interacting case, appears to bear out these suspicions.Comment: 9 page

    Life considerations of the shuttle orbiter densified-tile thermal protection system

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    The Shuttle orbiter themal protection system (TPS) incorporates ceramic reusable surface insulation tiles bonded to the orbiter substructure through a strain isolation pad. Densification of the bonding surface of the tiles increases the static strength of the tiles. The densification proces does not, however, necessarily lead to an equivalent increase in fatigue strength. Investigation of the expected lifetime of densified tile TPS under both sinusoidal loading and random loading simulating flight conditions indicates that the strain isolation pads are the weakest components of the TPS under fatigue loading. The felt pads loosen under repetitive loading and, in highly loaded regions, could possibly cause excessive step heights between tiles causing burning of the protective insulation between tiles. A method of improving the operational lifetime of the TPS by using a strain isolation pad with increased stiffness is presented as is the consequence of the effect of increased stiffness on the tile inplane strains and transverse stresses

    Glycyl-L-proline hemihydrate at 298 K

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    Generation of long time creep data of refractory alloys at elevated temperatures Eleventh quarterly report, 26 Dec. 1965 - 26 Mar. 1966

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    Creep tests of arc-cast and vapor deposited tungsten, molybdenum alloys, niobium, and tantalum base alloys for use in advanced power system

    Turbulence, combustion, pollutant, and stability characterization of a premixed, step combustor

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    A two dimensional combustion tunnel was constructed to study a lean premixed turbulent propane/air flame stablized behind a rearward facing step. Studied were: (1) the existence and importance of large coherent structures in turbulent reacting and nonreacting free shear layers behind the steps; (2) the effect of inlet temperature and reference velocity on combustion efficiency; (3) CO, NO2 and NO sub x production in the flame; and (4) the blowout and upstream propagation of the flame. In the ranges studied, the large coherent structures dominated both the reacting and the nonreacting free shear layers behind the step. The growth of the vortices and the propagation of the flamer were intimately linked. Vortex pairing was observed to be one of the mechanisms for introduction of fresh reactants into the shear layer and growth of the shear layer. Probe composition measurements of the flame showed that, in the recirculation zone, the reaction was above 99 percent complete, CO and unburnt hydrocarbons were above the equilibrium level NO sub x concentration was far below the equilibrium level and NO2 comprised a negligible fraction of NO sub x

    Nuclear radiation problems, unmanned thermionic reactor ion propulsion spacecraft

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    A nuclear thermionic reactor as the electric power source for an electric propulsion spacecraft introduces a nuclear radiation environment that affects the spacecraft configuration, the use and location of electrical insulators and the science experiments. The spacecraft is conceptually configured to minimize the nuclear shield weight by: (1) a large length to diameter spacecraft; (2) eliminating piping penetrations through the shield; and (3) using the mercury propellant as gamma shield. Since the alumina material is damaged by the high nuclear radiation environment in the reactor it is desirable to locate the alumina insulator outside the reflector or develop a more radiation resistant insulator

    Generation of long time creep data on refractory alloys at elevated temperatures eighth quarterly report

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    Creep resistance of refractory alloys at elevated temperatures under ultrahigh vacuum condition
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