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  • 1
    Publication Date: 1991-02-01
    Print ISSN: 0022-0248
    Electronic ISSN: 1873-5002
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Elsevier
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  • 2
    Publication Date: 1991-02-01
    Print ISSN: 0022-0248
    Electronic ISSN: 1873-5002
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Elsevier
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  • 3
    Publication Date: 2011-08-24
    Description: The growth of InP by metalorganic chemical vapor deposition (MOCVD) in a horizontal reactor is being modeled with a commercially available computational fluid dynamics modeling code. The mathematical treatment of the MOCVD process has four primary areas of concern: 1) transport phenomena, 2) chemistry, 3) boundary conditions, and 4) numerical solution methods. The transport processes involved in CVD are described by conservation of total mass, momentum, energy, and atomic species. Momentum conservation is described by a generalized form of the Navier-Stokes equation for a Newtonian fluid and laminar flow. The effect of Soret diffusion on the transport of particular chemical species and on the predicted deposition rate is examined. Both gas-phase and surface chemical reactions are employed in the model. Boundary conditions are specified at the inlet and walls of the reactor for temperature, fluid flow and chemical species. The coupled set of equations described above is solved by a finite difference method over a nonuniform rectilinear grid in both two and three dimensions. The results of the 2-D computational model is presented for gravity levels of zero- and one-g. The predicted growth rates at one-g are compared to measured growth rates on fused silica substrates.
    Keywords: MATERIALS PROCESSING
    Type: In: Crystal growth in space and related optical diagnostics; Proceedings of the Meeting, San Diego, CA, July 22, 23, 1991 (A93-33051 12-29); p. 54-59.
    Format: text
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  • 4
    Publication Date: 2011-08-19
    Description: A two-dimensional model for metalorganic chemical vapor deposition of GaAs in a horizontal reactor is presented. The model is characterized by the following parameters: reactor geometry and operating pressure, thermal boundary conditions, ratio of reactants, chemical reactions, total inlet gas flow rate, as well as molecular weights, thermal conductivities, heat capacities, viscosities, and binary diffusion coefficients of the gas-phase species. Film thickness profiles predicted by the model are compared with those of GaAs thin films grown in the modeled reactor. Results obtained show a good agreement between the predictions and data over the entire length of the deposition region for the low pressure and high flow rate run. Attention is also given to the reactor design and growth conditions.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Crystal Growth (ISSN 0022-0248); 109; 241-245
    Format: text
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  • 5
    Publication Date: 2011-08-19
    Description: A combined modeling and experimental approach is used to quantify the effects of various manifold components on the switching speed in metalorganic chemical vapor deposition (MOCVD). In particular, two alternative vent-run high-speed switching manifold designs suitable for either continuous or interrupted growth have been investigated. Both designs are incorporated in a common manifold, instrumented with a mass spectrometer. The experiments have been performed using nitrogen as the transport gas and argon as the simulated source gas. The advantages and limitations of two designs are discussed. It is found that while constant flow manifold switching systems may have fluid dynamic advantages, care must be taken to minimize sections of the supply manifold with low flow rates if rapid changes in alloy composition are required.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Crystal Growth (ISSN 0022-0248); 109; 246-251
    Format: text
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  • 6
    Publication Date: 2013-08-31
    Description: Although space research is still in an embryonic state, a combination of Earth based and space flight experiments are being coupled to yield a better understanding of the complex interaction of heat and fluid flow on the dynamics of crystal growth. Continued efforts on the ground as well as additional flight opportunities are needed to continue the drive to fully understand the advantages, both scientifically and economically, of microgravity crystal growth.
    Keywords: MATERIALS PROCESSING
    Type: NASA, Washington, Microgravity Science and Applications Flight Programs, January - March 1987, Selected Papers, Volume 1; p 391-407
    Format: application/pdf
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  • 7
    Publication Date: 2013-08-31
    Description: The physical scales of velocity, length, time, thermal gradient magnitude likely to be involved in gas-solid multiphase flight experiments are assessed for 1-100 micron particles.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, Second Microgravity Fluid Physics Conference; p 279-284
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  • 8
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    In:  CASI
    Publication Date: 2016-06-07
    Description: This research seeks to identify the experiment design parameters for future flight experiments to better resolve the effects of thermal and velocity gradients on gas-solid flows. By exploiting the reduced body forces and minimized thermal convection current of reduced gravity experiments, features of gas-solid flow normally masked by gravitationally induced effects can be studied using flow regimes unattainable under unigravity. This paper assesses the physical scales of velocity, length, time, thermal gradient magnitude, and velocity gradient magnitude likely to be involved in laminar gas-solid multiphase flight experiments for 1-100 micro-m particles.
    Keywords: Materials Processing
    Type: Third Microgravity Fluid Physics Conference; 227-232; NASA-CP-3338
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  • 9
    Publication Date: 2019-01-25
    Description: Twenty pyroelectric type infrared detectors were flown onboard the Long Duration Exposure Facility (LDEF). The detector chips were of three different pyroelectric materials: lithium-tantalate, strontium-barium-niobate, and triglycine-sulfide. The experiment was passive; no measurements were taken during the flight. Performance of the detectors was measured before and after flight. Postflight measurements revealed that detectors made of lithium-tantalate and strontium-barium-niobate suffered no measureable loss in performance. Detectors made of triglycine-sulfide suffered complete loss of performance, but so did the control samples of the same material. Repoling of the triglycine-sulfide failed to revive the detectors.
    Keywords: NONMETALLIC MATERIALS
    Type: First LDEF Post-Retrieval Symposium Abstracts; p 107
    Format: text
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  • 10
    Publication Date: 2019-07-13
    Description: This paper provides an overview of the research and development efforts of the Lidar and Electro-Optics element of NASA's Aviation Safety Program. This element is seeking to improve the understanding of the atmospheric environments encountered by aviation and to provide enhanced situation awareness for atmospheric hazards. The improved understanding of atmospheric conditions is specifically to develop sensor signatures for atmospheric hazards. The current emphasis is on kinetic air hazards such as turbulence, aircraft wake vortices, mountain rotors, and windshear. Additional efforts are underway to identify and quantify the hazards arising from multi-phase atmospheric conditions including liquid and solid hydrometeors and volcanic ash. When the multi-phase conditions act as obscurants that result in reduced visual awareness, the element seeks to mitigate the hazards associated with these diminished visual environments. The overall purpose of these efforts is to enable safety improvements for air transport class and business jet class aircraft as the transition to the Next Generation Air Transportation System occurs.
    Keywords: Air Transportation and Safety
    Type: NF1676L-14908 , 4th AIAA Atmospheric and Space Environments Conference; Jun 25, 2012 - Jun 28, 2012; New Orleans, LA; United States
    Format: application/pdf
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