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  • 1
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    Modeling of the float zone process (1981)
    In:  CASI
    Details
    Publication Date: 2006-07-02
    Description: The interaction of heat, mass, and momentum transport in the floating zone method for growing single crystals from the melt is examined. Methods for detailed numerical simulation of the transport phenomena in a floating zone are developed. Results of the calculations are combined with experiments to determine the effects of solidification induced, surface tension driven, and buoyancy driven convection in establishing dopant redistribution in the melt and the roles of heat transfer in crystal and melt and melt/solid interface shape in determining crystal quality. State of the art finite element techniques were developed for calculating the influence of natural convection in the melt on the shape of a melt/crystal interface and dopant segregation in the crystal. These techniques are demonstrated for solidification by the Bridgman technique. Numerical techniques are developed that calculate the shapes of both the melt/solid and melt/gas interfaces simultaneously with the thermal fields in melt and solid. Models for the fluid flows due to the rotation of the feed and crystal rods are completed and the effects of these flows on dopant segregation are studied, especially in the case of zones longer than can be achieved on Earth.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: NASA. Marshall Space Flight Center Float Zone Workshop; p 175-199
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  • 2
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    Some developments in improved methods for the measurements of the spectral irradiances of solar simulators (1963)
    In:  CASI
    Details
    Publication Date: 2019-05-23
    Description: Measurement of spectral emission from solar simulators - photoelectric photometry
    Keywords: SPACE RADIATION
    Type: NASA-CR-201
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  • 3
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    Triton's global heat budget (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Internal heat flow from radioactive decay in Triton's interior along with absorbed thermal energy from Neptune total 5 to 20 percent of the insolation absorbed by Triton, thus comprising a significant fraction of Triton's surface energy balance. These additional energy inputs can raise Triton's surface temperature between approx. 0.5 to 1.5 K above that possible with absorbed sunlight alone, resulting in a factor of approx. 1.5 to 2.5 increase in Triton's basal atmospheric pressure. If Triton's internal heatflow is concentrated in some areas, as is likely, local effects such as enhanced sublimation with subsequent modification of albedo could be quite large. Furthermore, indications of recent albedo change on Triton suggest that Triton's surface temperature and pressure may not now be in steady state, further suggesting that atmospheric pressure on Triton was as much as 10 times higher in the recent past.
    Keywords: SPACE RADIATION
    Type: NASA-CR-188178 , NAS 1.26:188178
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  • 4
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    Solutal Convection and Its Effects on Crystal Growth and Segregation in Binary and Pseudo-Binary System with Large Liquidus-Solidus Separation (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This research program is composed of theoretical and experimental studies of solutal convection and its effects on crystal growth and segregation in binary and pseudo-binary systems with large liquidus-solidus separation. The theoretical program has resulted in the development of a transient simulation of the growth of concentrated alloys in microgravity and has been used to study the dynamics of GeSi, PbSnTe, HgCdTe growth. Finite element analysis has also been developed for studying the interactions of buoyancy-driven convection in the melt caused by temperature and concentration variations with melt-solid interface morphology and alloy segregation in the grown crystal. These calculations are being compared directly to experimental measurements of segregation and interface shape for GeSi growth and GaGe growth. The results for SiGe indicate that careful design of the thermal system can result in almost diffusion-controlled growth on Earth because of the stablizing influence of the concentration gradient ahead of the solidification front.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: NASA, Washington Microgravity Sci. and Appl. Program Tasks; p 11
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  • 5
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    Modelling of Laser-Enhanced Chemical Vapor Deposition (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Research is directed at development of a detailed model of mass and heat transfer and chemical reaction in the pyrolysis of silane for the growth of thin amorphous silicon substrates incorporating laser heating of the gas phase above the film. The model will be the basis for evaluation of the relative importances of the decomposition of SiH4 in the vapor phase, mass transfer of the intermediate species, e.g., SiH2, and the evolution of hydrogen gas. Plans are also underway for developing a model for homogeneous nucleation of Si in the vapor phase to model the rate limitations observed at high gas-phase temperatures and high partial pressures of silane. Work was concentrated on an almost one-dimensional model for the coupling of the CO2 laser beam for heat transfer of the vapor phase with simple kinetic models for SiH4 decomposition and subsequent absorption of Si vapor on the substrate. Mass transfer in the vapor phase is assumed to be solely by diffusion. The role of convection in the vapor phase caused by the large changes in density in and around the center of the laser beam will be analyzed to evaluate the potential of microgravity experiments for increasing the uniformity of the film and the deposition rate.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: NASA, Washington Microgravity Sci. and Appl. Program Tasks; p 94
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  • 6
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    Cosmic ray neutrino tests for heavier weak bosons and cosmic antimatter (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A program for using high energy neutrino astronomy with large neutrino detectors to directly test for the existence of heavier weak intermediate vector bosons (ivb) and cosmic antimatter is described. Such observations can provide a direct test of baryon symmetric cosmologies. Changes in the total cross section for nu(N) yields mu(X) due to additional propagators are discussed and higher mass resonances in the annihilation channel bar-nu sub e e(-) yields X are analyzed. The annihilation channel is instrumental in the search for antimatter, partcularly if heavier IVB's exist.
    Keywords: SPACE RADIATION
    Type: NASA-TM-83878 , NAS 1.15:83878
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  • 7
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    Fluid Flow in Crystal Growth: Analysis of the Verticle Bridgman and Floating Zone Process (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Research is aimed at the fundamental understanding of the interactions of heat and mass transport and fluid mechanics in crystal growth from the melt, especially in how it pertains to experiments supported by the Microgravity Science and Applications program. Emphasis has been on studies of the vertical Bridgman system, on small-scale floating zone systems proposed for space flight, and on quantitative prediction of nonlinear transitions in melt/solid interface morphologies leading to the formation of dendrites in directional solidification. The analysis of vertical Bridgman growth has lead to the complete numerical analysis of transport phenomena in directional solidification and to a detailed comparison of calculations to the GaGe growth experiments of Wang and Witt. Calculations show the central role of the ampoule material in determining the radial temperature gradients in the melt and thus, the intensity of convection. Results indicate that diffusion-controlled growth can not be achieved on Earth with conventional growth systems, but are feasible in microgravity
    Keywords: ASTRONAUTICS (GENERAL)
    Type: NASA, Washington Microgravity Sci. and Appl. Program Tasks; p 8-10
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  • 8
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    Auroral zone electron precipitation accompanying a sudden impulse in the geomagnetic field (1967)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Auroral zone electron precipitation accompanying sudden commencement of geomagnetic storms
    Keywords: SPACE RADIATION
    Type: NASA-CR-82982
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  • 9
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    Temporal and spectral features of an intense auroral zone X-ray event in the 4-5 second period range (1966)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Temporal and spectral features of intense auroral zone X-ray event in 4 to 5 second period range - electron precipitation
    Keywords: SPACE RADIATION
    Type: NASA-CR-82984
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  • 10
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    Observed correlations between electron bursts in the magnetotail and electron precipitation in the auroral zone. (1968)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Electron bursts in magnetotail and electron precipitation in auroral zone correlations, discussing balloons and Vela satellites observations
    Keywords: SPACE RADIATION
    Format: text
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