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  • Astrophysics  (2)
  • Lunar and Planetary Science and Exploration  (2)
  • [abr] CSNB; congential stationary night blindness  (2)
  • [abr] OA; ocular albinism  (2)
  • [abr] ad; autosomal dominant  (2)
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Publisher
Years
  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Current Opinion in Genetics & Development 2 (1992), S. 459-466 
    ISSN: 0959-437X
    Keywords: [abr] AIED; Aland island eye disease ; [abr] CSNB; congential stationary night blindness ; [abr] HR; hereditary retinoschisis ; [abr] OA; ocular albinism ; [abr] OAT; ornithine aminotransferase ; [abr] OED; Oregon eye disease ; [abr] RP; retinitis pigmentosa ; [abr] RS; retinoschisis ; [abr] TCD; tapetochoroidal dystrophy ; [abr] XL; X-linked ; [abr] YAC; yeast artificial chromosome ; [abr] ad; autosomal dominant ; [abr] ar; autosomal recessive
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Current Opinion in Genetics & Development 2 (1992), S. 459-466 
    ISSN: 0959-437X
    Keywords: [abr] AIED; Aland island eye disease ; [abr] CSNB; congential stationary night blindness ; [abr] HR; hereditary retinoschisis ; [abr] OA; ocular albinism ; [abr] OAT; ornithine aminotransferase ; [abr] OED; Oregon eye disease ; [abr] RP; retinitis pigmentosa ; [abr] RS; retinoschisis ; [abr] TCD; tapetochoroidal dystrophy ; [abr] XL; X-linked ; [abr] YAC; yeast artificial chromosome ; [abr] ad; autosomal dominant ; [abr] ar; autosomal recessive
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-07-19
    Description: Comets and asteroids are subjected to extremely cold conditions throughout their lifetimes. During their sojourns in the solar system, they are subjected to collisions at speeds that are easily capable of generating shock waves in their constituent materials. In addition to ices, more common silicate minerals such as olivines and pyroxenes are important components of these objects. The collision-induced shocks could affect the spectral signatures of those mineral components, which could in turn be detected telescopically. We have embarked on a project to determine how impact-generated shock might affect the reflectance spectra and structures of select silicates as both impact speed and target temperature are varied systematically. While the effects of impact speed (in the form of shock stress) on numerous materials have been and continue to be studied, the role of target temperature has received comparatively little attention, presumably because of the operational difficulties it can introduce to experimentation. Our experiments were performed with the vertical gun in the Experimental Impact Laboratory of the Johnson Space Center. A liquid-nitrogen system was plumbed to permit cooling of the target container and its contents under vacuum to temperatures as low as -100 C (173 K). Temperatures were monitored by thermocouples mounted on the outside of the target container. Because those sensors were not in contact with the target material at impact, the measured temperatures are treated as lower limits for the actual values. Peridot (Mg-rich olivine) and enstatite (Mg-rich orthopyroxene) were used as targets, which involved the impact of alumina (Al2O3) spheres at speeds of 2.0 - 2.7 km s(exp -1) and temperatures covering 25 C to -100 C (298 K to 173 K). We have begun collecting and analyzing data in the near to mid-IR with a Fourier-transform infrared spectrometer, and preliminary analyses show that notable differences in absorption-band strength and position occur as functions of both impact speed (peak shock stress) and initial temperature.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-34417 , Annual Meeting of the Division of Planetary Sciences American Astronomical Society; Nov 08, 2015 - Nov 13, 2015; Fort Washington, MD; United States
    Format: application/pdf
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  • 4
    Publication Date: 2019-07-13
    Description: Impacts into forsterite and orthoenstatite at speeds typically encountered by comets demonstrate that shock imparted by collisions is detectable in the infrared signatures of their dust. The spectral signatures can be traced to physical alterations in their crystalline structures, as observed in TEM imaging and modeled using a dipole approximation. These results yield tantalizing insights into the collisional history of our solar system, as well as the history of individual comets and Trojan asteroids.
    Keywords: Astrophysics
    Type: JSC-CN-26222 , Asteroids, Comets, Meteors 2012; May 16, 2012 - May 20, 2012; Niigata; Japan
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  • 5
    Publication Date: 2019-07-13
    Description: Comets and asteroids have weathered dynamic histories, as evidenced by their rough surfaces. The Nice model describes a violent reshuffling of small bodies during the Late Heavy Bombardment, with collisions acting to grind these planetesimals away. This creates an additional source of impact material that can re-work the surfaces of the larger bodies over the lifetime of the solar system. Here, we investigate the possibility that signatures due to impacts (e.g. from micrometeoroids or meteoroids) could be detected in their spectra, and how that can be explained by the physical manifestation of shock in the crystalline structure of minerals. All impact experiments were conducted in the Johnson Space Center Experimental Impact Laboratory using the vertical gun. Impact speeds ranged from approx.2.0 km/s to approx.2.8 km/s. All experiments were conducted at room temperature. Minerals found in comets and asteroids were chosen as targets, including diopside (MgCaSi2O6, monoclinic pyroxene), magnesite (MgCO3, carbonate), and fayalite (FeSiO4, olivine). Impacted samples were analyzed using a Fourier Transform Infrared Spectrometer (FTIR) and a Transmission Electron Microscope (TEM). Absorbance features in the 8-13 m spectral region demonstrate relative amplitude changes as well as wavelength shifts. Corresponding TEM images exhibit planar shock dislocations in the crystalline structure, attributed to deformation at high strain and low temperatures. Elongating or shortening the axes of the crystalline structure of forsterite (Mg2SiO4, olivine) using a discrete dipole approximation model (Lindsay et al., submitted) yields changes in spectral features similar to those observed in our impacted laboratory minerals.
    Keywords: Astrophysics
    Type: JSC-CN-26880 , 44th Annual Meeting of the Division of Planetary Sciences American Astronomical Society; Oct 14, 2012 - Oct 19, 2012; Reno, NV; United States
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  • 6
    Publication Date: 2019-07-19
    Description: A new paradigm has emerged where 3.9 Gyr ago, a violent reshuffling reshaped the placement of small bodies in the solar system (the Nice model). Surface properties of these objects may have been affected by collisions caused by this event, and by collisions with other small bodies since their emplacement. These impacts affect the spectrographic observations of these bodies today. Shock effects (e.g., planar dislocations) manifest in minerals allowing astronomers to better understand geophysical impact processing that has occurred on small bodies. At the Experimental Impact Laboratory at NASA Johnson Space Center, we have impacted forsterite and enstatite across a range of velocities. We find that the amount of spectral variation, absorption wavelength, and full width half maximum of the absorbance peaks vary non-linearly with the velocity of the impact. We also find that the spectral variation increases with decreasing crystal size (single solid rock versus granular). Future analyses include quantification of the spectral changes with different impactor densities, temperature, and additional impact velocities. Results on diopside, fayalite, and magnesite can be found in Lederer et al., this meeting.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-26881 , 44th Annual Meeting of the Division of Planetary Sciences American Astronomical Society; Oct 14, 2012 - Oct 19, 2012; Reno, NV; United States
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