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Results for “Chloride Channels”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1986

Design and performance of the halogen occultation experiment (HALOE) remote sensor

HALOE is an optical remote sensor that measures extinction of solar radiation caused by the earth's atmosphere in eight channels, ranging in wavelength from 2.5 to 10.1 microns. These measurements, which occur twice each satellite orbit during solar occultation, are inverted to yield vertical distributions of middle atmosphere ozone (O3), water vapor, nitrogen dioxide, nitric oxide, hydrogen fluoride, hydrogen chloride, and methane. A channel located in the 2.7 region is used to infer the tangent point pressure by measuring carbon dioxide absorption. The HALOE instrument consists of a two-axis gimbal system, telescope, spectral discrimination optics and a 12-bit data system. The gimbal system tracks the solar radiometric centroid in the azimuthal plane and tracks the solar limb in the elevation plane, placing the instrument's instantaneous field-of-view 4 arcmin down from the solar top edge. The instrument gathers data for tangent altitudes ranging from 150 km to the earth's horizon. Prior to an orbital sunset and after an orbital sunrise, HALOE automatically performs calibration sequences to enhance data interpretation. The instrument is presently being tested at the NASA Langley Research Center in preparation for launch on the Upper Atmosphere Research Satellite near the end of this decade. This paper describes the instrumenmt design, operation, and functional performance.

Baker, R. L.↗

NASA NTRS1984

The mechanisms of formation and prevention of channel segregation during alloy solidification

Using a base chilled configuration, conditions for the formation and prevention of segregation channels are studied in the ammonium chloride-water and lead-tin systems. Such channels develop when the rejected solute is less dense than the solvent and are therefore a result of density inversion, but slow (less than 5 rpm) rates of mold rotation, about axes inclined to the vertical by 20 to 30 deg, throughout the time of solidification, effectively prevent the formation or propagation of these channels. In experiments with artificially created or blocked channels, a simultaneous solute plume in the bulk liquid must be present in order for a channel to develop. The results indicate that channels originate not within the dendritic array, but immediately ahead of the growth front as a result of perturbation from the less dense boundary layer into the bulk liquid. The effect of mold movement is to translate laterally the bulk liquid relative to the growth front so that perturbations are sheared off. The nature of the liquid movement is considered and shown to be a function of the mold dimensions.

Hellawell, A.↗

NASA NTRS1985

Transient proton inflows during illumination of anaerobic Halobacterium halobium cells

The roles of bacteriorhodopsin (bR), halorhodopsin (hR), and the H(+)-ATPase in the proton uptake in intact cells are examined. The Halobacterium halobium strains and solutions utilized in the experiment, and the techniques for measuring extracellular pH changes and intracellular K(+) concentrations are described. It is observed that in Halobacterium halobium strain R1, containing bR and hR, the light-driven proton uptake is divided into three transient inflows superimposed on the larger proton outflow. Under anaerobic conditions early proton uptake consists of an inflow which can be blocked with Dio-9 and a second inflow that can be eliminated by low concentrations (less than 125 nm) of triphenyltin chloride (TPT). The effects of Dio-9 and TPT on the passive proton-hydroxyl permeability of the cell membrane are investigated. A third transient light-driven proton flow observed at later times of illumination is studied. The data reveal that the first proton inflow correlates with proton dependent ATP synthesis; the second inflow is a passive uptake through an unidentified channel in response to electrogenic chloride pumping by bR and/or hR; and the third inflow correlates with the Na(+)/H(+) antiporter function.

Helgerson, S. L.↗

NASA NTRS1988

Convective effects on directional solidification of a simulated metal alloy

The first significant results of a ground-based experimental program which supports a low gravity space processing Spacelab experiment are reported. The phenomena which precipitate pluming and thus freckling in a metal alloy analog (ammonium chloride and water) are studied in detail and the sequential events leading to massive channeling and convection are optically documented. The pluming is shown to be other than a random burst of unstable fluid from a preferred channel but rather a natural occurrence resulting from a fundamental (Rayleigh-Benard) fluid dynamic instability at the density inversion interface. This extrapolates to critical size parameters appropriate to processing of actual metal alloys.

Mccay, T. D.↗

NASA NTRS1988

Soft X-ray and extreme utraviolet quantum detection efficiency of potassium chloride photocathode layers on microchannel plates

The quantum detection efficiency (QDE) of KCl photocathodes in the 44-1460 A range was investigated. An opaque layer of KCl, about 15,000-A-thick, was evaporated and applied the surface of a microchannel plate (MCP), and the contribution of the photocathode material in the channels (and on the interchannel web) to the QDE was measured using a Z stack MCP detector. It is shown that KCl is a relatively stable photocathode material, with the QDE equal to 30-40 percent in the EUV. At wavelengths above 200 A, the QDE is slightly better than the QDE of CsI, as reported by Siegmund et al. (1986). While the shape of the QDE curve as a function of wavelength is similar to those reported for CsI and KBr, KCl was found to lack the high QDE peak found in the curves of CsI and KBr at about 100 A. A simple QDE model is described, the predictions of which were found to agree with the measurements on the KCl photocathode.

Siegmund, Oswald H. W.↗

NASA NTRS1980

Hydrothermal alteration of impact melt sheets with implications for Mars

A model of the interaction of water with an impact melt sheet is constructed to explain the presence of hydrothermal alteration, fluid flow channels, and the redistribution of volatile elements in terrestrial melt sheets. A calculation of the amount of water vaporized beneath a melt sheet with a large fraction of melt results in a maximum total steam/melt sheet ratio of 23% by weight. The model also applies to Martian impact melt sheets, which have a total volume greater than a global layer 60 m thick. Hydrothermal circulation of steam in Martian melt sheets may have produced iron-rich alteration clays, ferric hydroxides, and near-surface accumulations of salts. The ability of vapor-dominated hydrothermal systems to concentrate sulfate relative to chloride is consistent with the high sulfate to chloride ratio found in the Martian soil by the Viking landers. A major fraction of the Martian soil may consist of the erosion products of hydrothermally altered impact melt sheets.

Newsom, H. E.↗