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  • 1
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    Cellular interface morphologies in directional solidification. II - The effect of grain boundaries (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A singular perturbation analysis valid for small grain-boundary slopes is used with the one-sided model for solidification to show that grain boundaries introduce imperfections into the symmetry of the developing cellular interfaces which rupture the junction between the family of planar shapes and the bifurcating cellular families. Undulating interfaces are shown to develop first near grain boundaries, and to evolve with decreasing temperature gradient either by a smooth transition from the almost planar family or by a sudden jump to moderate-amplitude cellular forms, depending on the growth rate.
    Keywords: SOLID-STATE PHYSICS
    Type: Physical Review B, 3rd Series (ISSN 0163-1829); 30; 3993-399
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Ball Aerospace AMSD Ambient and Cryogenic Test Plans (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The planned testing of the Advanced Mirror System Demonstrator program being performed by Ball Aerospace are presented.
    Keywords: Instrumentation and Photography
    Type: 2nd Annual Technology Days; May 22, 2002 - May 24, 2002; Huntsville, AL; United States
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  • 3
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    Ball Aerospace SBMD Coating Test Results (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The Sub-scale Beryllium Mirror Demonstrator that was successfully tested to demonstrate cryogenic figuring of a bare mirror has been coated with a protected gold reflective surface and retested at cryogenic temperatures. Results showing less than 9 nm rms surface distortion attributable to the added coating are presented.
    Keywords: Instrumentation and Photography
    Type: 2nd Annual Technology Days; May 22, 2002 - May 24, 2002; Huntsville, AL; United States
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  • 4
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    Ball Aerospace AMSD Progress Update (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The current status of the Advanced Mirror System Demonstrator program being performed by Ball Aerospace is presented. The hexagonal low-areal density Beryllium mirror blank has been fabricated and undergoing polishing at the time of this presentation.
    Keywords: Instrumentation and Photography
    Type: 2nd Annual Technology Days; May 22, 2002 - May 24, 2002; Huntsville, AL; United States
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  • 5
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    Perspectives on integrated modeling of transport processes in semiconductor crystal growth (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The wide range of length and time scales involved in industrial scale solidification processes is demonstrated here by considering the Czochralski process for the growth of large diameter silicon crystals that become the substrate material for modern microelectronic devices. The scales range in time from microseconds to thousands of seconds and in space from microns to meters. The physics and chemistry needed to model processes on these different length scales are reviewed.
    Keywords: SOLID-STATE PHYSICS
    Type: In: Heat and mass transfer in materials processing (A93-10826 01-31); p. 137-153.
    Format: text
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  • 6
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    Optimized program completeness (2005)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Overall program completeness is optimized by selecting the ordered set of observations and targets that maximizes the efficiency for the ensemble of stars. We describe the optimization approach and report on completeness sensitivity to instrument throughput, inner working angle, instrument sensitivity, observational overhead, exo-zodiacal brightness, and target revisit constraints.
    Keywords: Instrumentation and Photography
    Type: Terrestrial Planet Finder - Coronagraph STDT #5; Nov 30, 2005; Pasadena, CA; United States
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  • 7
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    Single visit completeness optimization (2005)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The Terrestrial Planet Finder Coronagraph (TPF-C) is a NASA pre-phase. A orbiting telescope with the goal of detecting and characterizing visible and near-IR light refelected from terrestrial planets. We use observational completeness, defined as the fraction of potentially observable planets that are detected, to determine how well the proposed telescope meets the mission goals. Single visit completeness is optimized by slecting the length of observation per target that maximizes the completeness for the ensemble of stars. In this memo we describe the integration time calculations and two approaches to single visit optimization.
    Keywords: Instrumentation and Photography
    Type: Terrestrial Planet Finder - Coronagraph STDT #5; Nov 30, 2005; Pasadena, CA; United States
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  • 8
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    Rate limits in silicon sheet growth - The connections between vertical and horizontal methods (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Meniscus-defined techniques for the growth of thin silicon sheets fall into two categories: vertical and horizontal growth. The interactions of the temperature field and the crystal shape are analyzed for both methods using two-dimensional finite-element models which include heat transfer and capillarity. Heat transfer in vertical growth systems is dominated by conduction in the melt and the crystal, with almost flat melt/crystal interfaces that are perpendicular to the direction of growth. The high axial temperature gradients characteristic of vertical growth lead to high thermal stresses. The maximum growth rate is also limited by capillarity which can restrict the conduction of heat from the melt into the crystal. In horizontal growth the melt/crystal interface stretches across the surface of the melt pool many times the crystal thickness, and low growth rates are achievable with careful temperature control. With a moderate axial temperature gradient in the sheet a substantial portion of the latent heat conducts along the sheet and the surface of the melt pool becomes supercooled, leading to dendritic growth. The thermal supercooling is surpressed by lowering the axial gradient in the crystal; this configuration is the most desirable for the growth of high quality crystals. An expression derived from scaling analysis relating the growth rate and the crucible temperature is shown to be reliable for horizontal growth.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Crystal Growth (ISSN 0022-0248); 82; 1-2; 1-9
    Format: text
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