Search NASA⌕ Search

SEARCH · Search NASA

Results for “As-73”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

111 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Cold Conditions Promote Mg and Si Incorporation in Fe/Si-Rich and Al-Poor X-Ray Amorphous Material in Mars-Relevant Field Environments

X-ray amorphous material that is variably Fe/Si-rich, Al-poor, and volatile containing is prevalent (~15-73 wt.%) within ancient fluvial-lacustrine and eolian sediments examined by the CheMin instrument in Gale crater. Al-rich X-ray amorphous material within Mars-analog environments on Earth has previously been proposed to result from aqueous alteration under cold and icy conditions. However, to the best of our knowledge, no work to date has examined the effects of climate upon the formation of Al-poor and Fe/Si-rich X-ray amorphous material. This study therefore investigates the production of Al-poor and Fe-containing X-ray amorphous material and the chemical heterogeneity within that material under varying temperature conditions to better interpret the formation of Fe-containing X-ray amorphous material detected on Mars.

A D Feldman↗
NASA NTRS2001

Composition and physical properties of starch in microgravity-grown plants

The effect of spaceflight on starch development in soybean (Glycine max L., BRIC-03) and potato (Solanum tuberosum, Astroculture-05) was compared with ground controls by biophysical and biochemical measurements. Starch grains from plants from both flights were on average 20-50% smaller in diameter than ground controls. The ratio delta X/delta rho (delta X --difference of magnetic susceptibilities, delta rho--difference of densities between starch and water) of starch grains was ca. 15% and 4% higher for space-grown soybean cotyledons and potato tubers, respectively, than in corresponding ground controls. Since the densities of particles were similar for all samples (1.36 to 1.38 g/cm3), the observed difference in delta X/delta rho was due to different magnetic susceptibilities and indicates modified composition of starch grains. In starch preparations from soybean cotyledons (BRIC-03) subjected to controlled enzymatic degradation with alpha-amylase for 24 hours, 77 +/- 6% of the starch from the flight cotyledons was degraded compared to 58 +/- 12% in ground controls. The amylose content in starch was also higher in space-grown tissues. The good correlation between the amylose content and delta X/delta rho suggests, that the magnetic susceptibility of starch grains is related to their amylose content. Since the seedlings from the BRIC-03 experiment showed elevated post-flight ethylene levels, material from another flight experiment (GENEX) which had normal levels of ethylene was examined and showed no difference to ground controls in size distribution, density, delta X/delta rho and amylose content. Therefore the role of ethylene appears to be more important for changes in starch metabolism than microgravity. c2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

NASA Experiment Number 9305014 2/2↗