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  • 1
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    Xenon spallation systematics in Angra dos Reis (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Literature Xe data for the Angra dos Reis meteorite have been resolved into constituent spallation, fission and trapped components. The spallation Xe compositions vary over a range wider than observed in any other samples, including lunar samples. These variations are due to the mixing of spallation Xe from Ba and rare earth element targets. It is possible to infer the Ba and rare earth spallation Xe compositions. Angra dos Reis spallation Xe compositions are systematically different from those observed in lunar samples, possibly because of differences in the irradiation conditions (geometry and shielding). Thus the Angra dos Reis data appear to be superior to lunar data for predicting spallation Xe compositions in other meteorites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 45; Oct. 198
    Format: text
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  • 2
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    Statistical analysis of the modal properties of large structural systems. (1971)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A theory is developed to predict eigenvalue and eigenvector uncertainty in large dynamic models. The uncertainty is based on physical property uncertainty and should not be confused with numerical roundoff, although the method can be extended to include the latter. The theory, when implemented on a computer, is used to analyze the uncertainties in frequencies and mode shapes based on uncertainties in mass, stiffness, modulus of elasticity, etc. The method incorporates a linear statistical model which is quite adequate for handling property uncertainties of 10% or more. The model is not limited to small systems but uses certain statistical assumptions as well as selective matrix manipulations to keep the size of all matrix operations to within the number of degrees of freedom of the system. Examples are given for two longitudinal vibration problems, and the results are supported by a Monte Carlo analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: SAE PAPER 710785 , Society of Automotive Engineers, National Aeronautic and Space Engineering and Manufacturing Meeting; Sept. 28-30, 1971; Los Angeles, CA
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  • 3
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    Structural model optimization using statistical evaluation (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The results of research in applying statistical methods to the problem of structural dynamic system identification are presented. The study is in three parts: a review of previous approaches by other researchers, a development of various linear estimators which might find application, and the design and development of a computer program which uses a Bayesian estimator. The method is tried on two models and is successful where the predicted stiffness matrix is a proper model, e.g., a bending beam is represented by a bending model. Difficulties are encountered when the model concept varies. There is also evidence that nonlinearity must be handled properly to speed the convergence.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-123575
    Format: application/pdf
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  • 4
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    Bending vibrational data accuracy study (1970)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Computer program for predicting structural bending vibrational data
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-102974 , TR-70-1066
    Format: application/pdf
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  • 5
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    Argon ages for lunar breccias 14064 and 15405 (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 13, 1978 - Mar 17, 1978; Houston, TX
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  • 6
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    The excess fission xenon problem in lunar samples (1976)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper presents noble-gas (neon, krypton, and xenon) data obtained in stepwise heating of five lunar breccias: 14063, 14082, 15205, 15405, and 15445. These data are discussed in terms of spallation gas content, cosmic-ray exposure ages, and content of fission xenon. None of these samples is rich in solar-wind gases, and none contains more fission xenon than would be expected for in situ fission of U-238 and Pu-244. The essential features of the excess-fission-xenon phenomenon seen in several Apollo 14 samples are reviewed, as are models which might account for this phenomenon and criteria by which these models may be evaluated. The lack of excess fission xenon in 14063 and 14082 eliminates models relying on microscale xenon redistribution. A model is proposed in which the excess fission xenon originates in local material and percolates through and is adsorbed on regolith material.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Science Conference; Mar 15, 1976 - Mar 19, 1976; Houston, TX
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  • 7
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    I-129/I-127 variations among enstatite chondrites (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The iodine isotopic compositions and corresponding I-Xe ages were obtained for eight enstatite chondrites, bringing the total number of enstatite chondrites examined by the I-Xe technique to 11. Iodine isotopic compositions of these 11 chondrites indicate a well-defined hiatus correlated with the hiatus in chemical composition defining the two distinct enstatite groups: EH(4,5) and EL(6). Judging by the I-129/I-127 ratios and assuming that both the EH and EL groups originated from a reservoir with a uniform initial iodine isotopic composition, the EH(4,5) chondrites were estimated to be about 4 mln older than the El chondrites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 52; 101-111
    Format: text
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  • 8
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    Fission xenon in troctolite 76535 (1980)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Xenon released in stepwise heating of troctolite 76535 shows remarkable similarity to that from the gas-rich breccias. The low temperature fractions are highly enriched in fissiogenic xenon from Pu-244. Although the quantity of fission xenon is not inconsistent with reported age data, release patterns demonstrate that this component is not due to in situ decay. However, in contrast with the gas-rich breccias, the parentless radionuclear component in 76535 is not accompanied by solar wind xenon. Mechanisms for the emplacement of this component in 76535 cannot, therefore, involve exposure on the lunar surface but most likely involve adsorption along intergranular boundaries or thermally driven redistribution. The fact that xenon released from a gas-poor igneous cumulate can mimic that from gas-rich breccias, except for the presence of solar wind xenon in the latter, suggests that direct exposure to space is not required for the incorporation of these weakly bound, surface-correlated, parentless radionuclear components in lunar samples.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Conference on the Lunar Highlands Crust; Nov 14, 1979 - Nov 16, 1979; Houston, TX
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  • 9
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    Shock disturbance of the I-Xe system (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Three separate samples of the meteorite Bjurbole were artificially shocked at pressures of 70 kb, 200 kb, and 400 kb. Analysis of xenon released in stepwise heating shows that the I-Xe system of the 400 kb sample is substantially altered by the shock loading, and it is no longer possible to infer an age or trapped xenon composition for that sample. The 200-kb and 70-kb samples display isotopic structures progressively less altered demonstrating the gradations in shock disturbance likely to be found in natural systems. Interpretations of the I-Xe and Ar-40-Ar-39 systems for several naturally shocked meteorites are also presented. New data for Arapahoe do not confirm the previously reported age and trapped xenon composition, demonstrating instead that its I-Xe structure has been strongly disturbed by shock.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 15, 1982 - Mar 19, 1982; Houston, TX
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  • 10
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    Noble gas component organization in 14301 (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A study is conducted of the organization of noble gases in the Apollo 14 breccia 14301, giving particular attention to xenon from the extinct radionuclides I-129 and Pu-244. An essential ingredient of this work is the intercomparison between noble gases released in single-stage melts of grain size fractions and those released in stepwise extractions. This approach resolves 'functional' noble gas components, which are organized by siting, into the specific genetic contributions on the basis of the 'activation energies' for diffusive loss. The procedure makes it possible to resolve various genetic components on the basis of the chemical and structural differences in their specific locations. Consequently, distinctions can be made among components acquired by different processes and among components which have undergone different regolith histories.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 17, 1980 - Mar 21, 1980; Houston, TX
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