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  • Lunar and Planetary Science and Exploration  (2)
  • 2020-2022
  • 2015-2019  (2)
  • 1995-1999
  • 1950-1954
  • 1945-1949
  • 1935-1939
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  • 2020-2022
  • 2015-2019  (2)
  • 1995-1999
  • 1950-1954
  • 1945-1949
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  • 1
    Publication Date: 2019-07-13
    Description: This chapter presents a neural-network-based technique that allows for the reconstruction of the global, time-varying distribution of some physical quantity Q, that has been sparsely sampled at various locations within the magnetosphere, and at different times. We begin with a general introduction to the problem of prediction and specification, and why it is important and difficult to achieve with existing methods. We then provide a basic introduction to neural networks, and describe our technique using the specific example of reconstructing the electron plasma density in the Earth's inner magnetosphere on the equatorial plane. We then show more advanced uses of the technique, including 3D reconstruction of the plasma density, specification of chorus and hiss waves, and energetic particle fluxes. We summarize and conclude with a general discussion of how machine learning techniques might be used to advance the state-of-the-art in space weather prediction, and insight discovery.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN63232 , Machine Learning Techniques for Space Weather; 279-300
    Format: text
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  • 2
    Publication Date: 2019-09-28
    Description: X-ray microcomputed tomography is a useful means of characterizing cosmochemical samples such as meteorites or robotically returned samples. However, there are occasional concerns that the use of CT may be detrimental to the organic components of a chondrite. Small organic compounds such as amino acids comprise up to ~10% of the total solvent extractable carbon in CM carbonaceous chondrites. We irradiated three samples of the Murchison CM carbonaceous chondrite under conditions akin to and harsher than those typically used during typical benchtop x-ray CT imaging experiments to determine if detectable changes in the amino acid abundance and distribution relative to a non-exposed Murchison control sample occurred. After subjecting three meteorite samples to ionizing radiation dosages between ~300 Gray (Gy) and 3 kGy with bremstrahlung X-rays, we analyzed the amino acid content of each sample. Within sampling and analytical errors, we found no differences in the amino acid abundances and amino acid enantiomeric ratios when comparing the control samples (non-exposed Murchison) and the irradiated samples. We conclude that a polychromatic X-ray CT experiment has no detectable effect on the amino acid content of a CM type carbonaceous chondrite.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN60096 , Meteoritics & Planetary Science (ISSN 1086-9379) (e-ISSN 1945-5100); 54; 1; 220-228
    Format: application/pdf
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