PubMed · 9536755
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J Scott. Fast-track slips.. https://pubmed.ncbi.nlm.nih.gov/9536755/
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The Clementine mission has revived interest in the possibility that ice exists in shadowed craters near the lunar poles. Theoretically, the problem is complex, with several possible sources of water (meteoroid, asteroid, comet impact), several possible loss mechanisms (impact vaporization, sputtering, photoionization), and burial by meteorite impact. Opinions of modelers have ranged from no ice to several times 10(16) g of ice in the cold traps. Clementine bistatic radar data have been interpreted in favor of the presence of ice, while Arecibo radar data do not confirm its presence. The Lunar Prospector mission, planned to be flown in the fall of 1997, could gather new evidence for the existence of ice. If ice is present, both scientific and utilitarian objectives would be addressed by a lunar polar rover, such as that proposed to the NASA Discovery program, but not selected. The lunar polar rover remains the best way to understand the distribution and characteristics of lunar polar ice.
Quantitative characteristics of degenerative succession in Festuca sinensis sowing grassland in the alpine pastoral area were studied. The results showed that with the succession developing, number of species, richness index, diversity index, and evenness index were all increased, but ecological dominance was decreased. Analysis on important values, niche width, and niche overlaps proved that some herb species such as Ajania tenuifolia and Polygomum sibiricum were pioneer plants invading sowing grassland in the succession process. The pioneer plants had wider niche widths than other species, and their important values increased with the succession developing. Niche overlaps between Festuca sinensis and other species were smaller than that between two latifoliate herbs species in most case. The invasion of latifoliate herbs was one of the most important factors, which made the sowing grassland more degenerative.