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  • 21
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    On the theory of Gamma Ray Amplification through Stimulated Annihilation Radiation (GRASAR) (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The theory of photon emission, absorption, and scattering in a relativistic plasma of positrons, electrons, and photon was studied. Expressions for the emissivities and absorption coefficients of pair annihilation, pair production, and Compton scattering are given and evaluated numerically. The conditions for negative absorption were investigated. In a system of photons and e(+) - e(-) pairs, an emission line at at approximately 0.43 MeV can be produced by grasar action provided that the pair chemical potential exceeds approximately 1 MeV. At a temperature of approximately 10 to the 9th power. This requires a pair density approximately 10 to the 30th power cm to the (-3) power a value much larger than the thermodynamic equilbrium pair density at this temperature. This emission line could account without a gravitational redshift for the observed lines at this energy from gamma ray bursts.
    Keywords: SPACE RADIATION
    Type: NASA-TM-83857
    Format: application/pdf
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  • 22
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    The Considere Condition and Rapid Stretching of Linear and Branched Polymer Melts (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We analyze the onset of "necking" and subsequent filament failure during the transient uniaxial elongation of viscoelastic fluid samples in extensional rheometers. In the limit of rapid elongation (such that no molecular relaxation occurs), the external work applied is all stored elastically and the Considere criterion originally developed in solid mechanics can be used to quantitatively predict the critical Hencky strain to failure. By comparing the predictions of the Doi-Edwards model for linear homopolymer melts with those of the "Pom-Pom" model for prototypical branched melts we show that the critical strain to failure in rapid elongation of a rubbery material is intimately linked to the molecular topology of the chain, especially the degree of chain branching. The onset of necking instability is monotonically shifted to larger Hencky strains as the number of branches is increased. Numerical computations at finite Deborah numbers also show that there is an optimal range of deformation rates over which homogeneous extensions can be maintained to large strain. We also consider other rapid homogeneous stretching deformations, such as biaxial and planar stretching, and show that the degree of stabilization afforded by inclusion of material with long-chain branching is a sensitive function of the imposed mode of deformation.
    Keywords: Nonmetallic Materials
    Type: Journal of Rheology (ISSN 0148-6055); 43; 5; 1195-1212
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  • 23
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    Preliminary Findings from the SHERE ISS Experiment (2009)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The Shear History Extensional Rheology Experiment (SHERE) is an International Space Station (ISS) glovebox experiment designed to study the effect of preshear on the transient evolution of the microstructure and viscoelastic tensile stresses for monodisperse dilute polymer solutions. The SHERE experiment hardware was launched on Shuttle Mission STS-120 (ISS Flight 10A) on October 22, 2007, and 20 fluid samples were launched on Shuttle Mission STS-123 (ISS Flight 10/A) on March 11, 2008. Astronaut Gregory Chamitoff performed experiments during Increment 17 on the ISS between June and September 2008. A summary of the ten year history of the hardware development, the experiment's science objectives, and Increment 17's flight operations are discussed in the paper. A brief summary of the preliminary science results is also discussed.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: E-18249 , 47th AIAA Aerospace Sciences Meeting and Exhibit; Jan 05, 2009 - Jan 08, 2009; Orlando, FL; United States
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  • 24
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    Shear History Extensional Rheology Experiment II (SHERE II) Microgravity Rheology with Non-Newtonian Polymeric Fluids (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The primary objective of SHERE II is to study the effect of torsional preshear on the subsequent extensional behavior of filled viscoelastic suspensions. Microgravity environment eliminates gravitational sagging that makes Earth-based experiments of extensional rheology challenging. Experiments may serve as an idealized model system to study the properties of lunar regolith-polymeric binder based construction materials. Filled polymeric suspensions are ubiquitous in foods, cosmetics, detergents, biomedical materials, etc.
    Keywords: Mechanical Engineering
    Type: GRC-E-DAA-TN7182 , American Society for Gravitational and Space Research (ASGSR); Nov 28, 2012 - Dec 02, 2012; New Orleans, LA; United States
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  • 25
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    A unique type 3 ordinary chondrite containing graphite-magnetite aggregates - Allan Hills A77011 (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: ALHA 77011, which is the object of study in the present investigation, is a chondrite of the 1977 meteorite collection from Allan Hills, Antarctica. It contains an opaque and recrystallized silicate matrix (Huss matrix) and numerous aggregates consisting of micron- and submicron-sized graphite and magnetite. It is pointed out that no abundant graphite-magnetite aggregates could be observed in other type 3 ordinary chondrites, except for Sharps. Attention is given to the results of a modal analysis, relations between ALHA 77011 and other type 3 ordinary chondrites, and the association of graphite-magnetite and metallic Fe, Ni. The discovery of graphite-magnetite aggregates in type 3 ordinary chondrites is found to suggest that this material may have been an important component in the formation of ordinary chondrites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 16, 1981 - Mar 20, 1981; Houston, TX
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  • 26
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    Mariner Jupiter/Saturn 1977 navigation strategy (1975)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper presents selected navigational aspects of the Mariner Jupiter/Saturn 1977 mission. Emphasis is given to the trajectory correction strategy. In addition to science return and propellant costs, specific considerations affecting the strategy include a large number of candidate trajectories, relatively close satellite flybys, use of trajectory correction maneuvers for trajectory shaping, and the requirement for an optical data type to achieve precision satellite encounters. Finally, important error sources and mission constraints are identified, and their impact on the strategy is discussed.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 75-1098 , American Institute of Aeronautics and Astronautics, Guidance and Control Conference; Aug 20, 1975 - Aug 22, 1975; Boston, MA
    Format: text
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  • 27
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    An engineering study of onboard checkout techniques. Task 1: Requirements analysis and concepts (1971)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Concepts and requirements analysis for automated onboard checkout of manned space station
    Keywords: SPACE VEHICLES
    Type: NASA-CR-115128 , IBM-71W-00111
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  • 28
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    Composition and origin of enstatite in E chondrites (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A petrologic and electron-probe study of enstatite in six EH3, 4, and 5 chondrites, including the previously undescribed Allan Hills A77156, provides no support for Leitch and Smith's (1982) model in which crystals and liquids from two chemically distinct, partially molten planetesimals are mixed. It is found that Cr and Mn concentrations in enstatite grains in matrix and chondrules are not uniquely defined by their cathodoluminescence color. Wide variations in enstatite compositions among chondrules may partly reflect heterogeneities in the precursor material. However, correlated variations of Cr, Mn, and Fe concentrations in enstatite are probably largely due to fractionation during chondrule crystallization. The inverse correlation of petrologic type with minor element concentrations in enstatite appears to be a metamorphic effect.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 89; B567-B57
    Format: text
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  • 29
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    Apollo 16 - Impact melt sheets, contrasting nature of the Cayley plains and Descartes mountains, and geologic history (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Apollo 16 stations four and five rake samples have been examined petrographically and by electron microprobe and INAA. Lithologic abundances support the idea (Korontev, 1981) that the variation of soil composition at Apollo 16 results from mixing between a component represented by station five and components much like either the dimict breccias or feldspathic fragmental breccias in composition. Pyroxene, olivine, and coexisting plagioclase compositions from within the anorthosite portions of dimict breccias bridge the gap between the Mg-rich and ferroan anorthosite fields. Analyses from associated cumulate and granulitic clasts indicate that they are the source of the intermediate material. Dimict breccias formed about 3.92 b.y. ago, the nectaris event occurred 3.84-3.92 b.y. ago, and the Cayley plains were deposited as a result of the Imbrium event sometime later than 3.84 b.y.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 89; B513-B52
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  • 30
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    Discovery of Pulsation Dropout and Turn-on During the High State of the Accreting X-Ray Pulsar LMC X-4 (2018)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the luminous X-ray pulsar LMC X-4 in2015 October and November captured several bright accretion flares from this source, which has a long history of stable pulse and superorbital behavior. We present a timing analysis of these data in which we detect a rapid pulse "turn-on" in association with the accretion flares, during which the source reaches super-Eddington luminosities.Pulsations, which are normally seen from this source, are found to only occur for approximately one hour before and during the bright flares. Beyond one hour before and after the flares, we find pulsations to be weak or nonexistent, with fractional rms amplitudes of less than 0.05. At the onset of the flare, the pulse profiles exhibit a phase shift of 0.25 cycles that could be associated with a change in the emission geometry. This increase in pulse strength occurring well before the flare cannot be explained by the propeller effect, and potentially offers a connection between the magnetic properties of pulsars that accrete close to their Eddington limits and ultraluminous X-ray pulsars.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN59888 , The Astrophysical Journal Letters (ISSN 2041-8205) (e-ISSN 2041-8213); 861; 1
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