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  • 11
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    Effects of multiquantum transitions on molecular populations in grain-forming circumstellar environments (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Simplification of astrophysical calculations can be achieved by invoking the condition of local thermodynamic equilibrium; however, recent investigations suggest that this assumption may not be valid for certain astrophysical regions. To examine the effects of multiquantum translation to vibration transitions in expanding circumstellar envelopes, vibrational populations of the lowest 20 levels of CO have been calculated as a function of pressure and radiation density for H atom-CO collisions. Significant departure from local thermodynamic equilibrium is indicated, which implies lower dissociation rates for molecular components and a subsequent enhancement in the rate of grain formation by many orders of magnitude. Stabilization of intermediate species before they can dissociate may facilitate the formation of refractory grain cores in very hot, dilute outflows. As the present calculations indicate, laboratory measurements of state-to-state translation to vibration rates are needed for a more complete understanding of circumstellar chemistry.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 463-469
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  • 12
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    FT-IR spectroscopic studies of polycyclic aromatic hydrocarbons (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Proper assessment of the hypothesis which correlates polycyclic aromatic hydrocarbons (PAHs) with the unidentified infrared emission bands requires additional experimental laboratory data. In order to address this need, thermal infrared emission studies were performed on a subset of PAHs suggested to be of astrophysical importance. It was proposed that infrared emission from interstellar PAHs occurs following absorption of an ultraviolet photon. Since energy transfer to the ground electronic state can be rapid for a species in which intersystem crossing is negligible, the emission spectrum may be viewed as resulting from an equilibrium vibrational temperature (Leger and d'Hendecourt, 1987). This has been the basis for using infrared absorption spectra to calculate the corresponding emission spectra at various temperatures. These calculations were made using room temperature infrared absorption coefficients instead of those at the temperature of interest because of the latter's unavailability. The present studies are designed to address the differences between the calculated and experimental thermal emission spectra and to provide information which will be useful in future ultraviolet induced infrared fluorescence studies. The emission spectra have been obtained for temperatures up to 825K using an emission cell designed to mount against an external port of an FT-IR spectrometer. These spectra provide information concerning relative band intensities and peak positions which is unavailable from previous calculations.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA, Ames Research Center, Carbon in the Galaxy: Studies from Earth and Space; p 341
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  • 13
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    Evaluation and certification of heater assemblies developed for thermal vacuum acceptance testing (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Preparation of Rockwell International's Thermal Vacuum Chamber for acceptance testing of a mass produced satellite required the development of unique quartz lamp and hot wire heater assemblies. Testing performed on the basic elements of these heaters is described, as is the final testing done to certify that the heater assemblies meet the thermal requirements for acceptance testing. The methods and procedures of thermal mapping used during the development and final certification of these heater assemblies are presented. The absence of a definitive standard for determining flux distribution and heating boundaries for heaters of this type required the development of a test plan incorporating several thermal mapping techniques. These techniques include the development of heat flux using a multiple calorimeter array for both vacuum and ambient test conditions, and a photographic method for detecting heating boundaries. The test plan and thermal mapping techniques are discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA- Goddard Space Flight Center, Greenbelt, Md. Fourteenth Space Simulation Conference: Testing for a Permanent Presence in Space; p 275
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  • 14
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    The aeronomy of vibrationally excited ozone (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Theoretical calculations show that above 80 km in the earth's atmosphere the production of vibrationally excited ozone by chemical processes leads to number densities which are usually larger than those expected for local thermodynamic equilibrium. Quenching of highly excited molecules produced in O+O2+M, O3+M provided a significant source of the lower lying states above the mesopause while the 9.6 microns emission of O3 (0,0,1) was a major sink. Analysis of available laboratory results implied that reactions involving excited ozone play a significant role in the global ozone balance despite the relatively small abundance of the molecule. However, this effect is implicit in many of the rate coefficients currently used in stratospheric calculations. In the upper mesosphere and lower thermosphere, where the excited state populations differ from those for thermal equilibrium, published reaction rate data are not necessarily applicable to aeronomic calculations.
    Keywords: GEOPHYSICS
    Type: NASA-TM-82025
    Format: application/pdf
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  • 15
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    Towards an Imaging Mid-Infrared Heterodyne Spectrometer (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We are developing a concept for a compact, low-mass, low-power, mid-infrared (MIR; 5- 12 microns) imaging heterodyne spectrometer that incorporates fiber optic coupling, Quantum Cascade Laser (QCL) local oscillator, photomixer array, and Radio Frequency Software Defined Readout (RFSDR) for spectral analysis. Planetary Decadal Surveys have highlighted the need for miniaturized, robust, low-mass, and minimal power remote sensing technologies for flight missions. The drive for miniaturization of remote sensing spectroscopy and radiometry techniques has been a continuing process. The advent of MIR fibers, and MEMS techniques for producing waveguides has proven to be an important recent advancement for miniaturization of infrared spectrometers. In conjunction with well-established photonics techniques, the miniaturization of spectrometers is transitioning from classic free space optical systems to waveguide/fiber-based structures for light transport and producing interference effects. By their very nature, these new devices are compact and lightweight. Mercury-Cadmium-Telluride (MCT) and Quantum Well Infrared Photodiodes (QWIP) arrays for heterodyne applications are also being developed. Bulky electronics is another barrier that precluded the extension of heterodyne systems into imaging applications, and our RFSDR will address this aspect.
    Keywords: Astronomy
    Type: GSFC.CPR.6751.2012 , International Workshop on Instrumentation for Planetary Missions; Oct 10, 2012 - Oct 12, 2012; Greenbelt, MD; United States
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  • 16
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    Nucleation experiments in a microgravity environment (1986)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A simple experimental apparatus is described in which a wide variety of vapor phase nucleation studies of refractory materials could be performed aboard NASA's KC-135 Research Aircraft. The chief advantage of a microgravity environment for these studies is the expected absence of thermally driven convective motions in the gas. The absence of convection leads to much more accurate knowledge of both the temperature distribution in the system and the time evolution of the refractory vapor concentration as a function of distance from the crucible.The evolution of the apparatus will be described as more experience is gained with the microgravity environment. Such experiments will be used to prepare for similar ones carried out aboard either the shuttle or Space Station where considerably longer duration experiments are possible.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: NASA. Lyndon B. Johnson Space Center Space Station Planetology Experiments (SSPEX); 2 p
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  • 17
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    New techniques in television to provide research in three-dimensional real-time or near real-time imagery and reduced cost systems for teleconferencing and educational uses, part 1 (1979)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The results are presented of a continuing research and development program the objective of which is to develop a reduced bandwidth television system and a technique for television transmission of holograms. The result of the former is a variable frame rate television system, the operation of which was demonstrated for both black-and-white and color signals. This system employs a novel combination of the inexpensive mass storage capacity of a magnetic disc with the reliability of a digital system for time expansion and compression. Also reported are the results of a theoretical analysis and preliminary feasibility experiment of an innovative system for television transmission of holograms using relatively conventional TV equipment along with a phase modulated reference wave for production of the original interference pattern.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-158099
    Format: application/pdf
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