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The summertime haze transported from the Gulf Coast northward in maritime tropical air masses is partially formed from emissions in the midwestern and northeastern United States. Several cases are documented in which sulfate particulates, formed from emissions in the Midwest and Northeast, traveled to the Gulf of Mexico and, in some cases, returned to their source regions. 相似文献
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Since the induction of sister chromatid exchanges in cultured cells has been shown to be the most sensitive mammalian system to detect the effects of mutagenic carcinogens, Chinese hamster ovary cells and human lymphocytes were exposed to the sodium saccharin found to induce bladder cancer in rats. Both that saccharin and a highly purified extract of it increased the yield of sister chromatid exchanges in both types of cells. The results, which were repeatable and statistically highly significant, indicated that the weak carcinogen, saccharin, is also mutagenic in the sense that it induces cytogenetic changes. 相似文献
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Lemmon MT Wolff MJ Smith MD Clancy RT Banfield D Landis GA Ghosh A Smith PH Spanovich N Whitney B Whelley P Greeley R Thompson S Bell JF Squyres SW 《Science (New York, N.Y.)》2004,306(5702):1753-1756
A visible atmospheric optical depth of 0.9 was measured by the Spirit rover at Gusev crater and by the Opportunity rover at Meridiani Planum. Optical depth decreased by about 0.6 to 0.7% per sol through both 90-sol primary missions. The vertical distribution of atmospheric dust at Gusev crater was consistent with uniform mixing, with a measured scale height of 11.56 +/- 0.62 kilometers. The dust's cross section weighted mean radius was 1.47 +/- 0.21 micrometers (mm) at Gusev and 1.52 +/- 0.18 mm at Meridiani. Comparison of visible optical depths with 9-mm optical depths shows a visible-to-infrared optical depth ratio of 2.0 +/- 0.2 for comparison with previous monitoring of infrared optical depths. 相似文献
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Christensen PR Ruff SW Fergason RL Knudson AT Anwar S Arvidson RE Bandfield JL Blaney DL Budney C Calvin WM Glotch TD Golombek MP Gorelick N Graff TG Hamilton VE Hayes A Johnson JR McSween HY Mehall GL Mehall LK Moersch JE Morris RV Rogers AD Smith MD Squyres SW Wolff MJ Wyatt MB 《Science (New York, N.Y.)》2004,305(5685):837-842
The Miniature Thermal Emission Spectrometer (Mini-TES) on Spirit has studied the mineralogy and thermophysical properties at Gusev crater. Undisturbed soil spectra show evidence for minor carbonates and bound water. Rocks are olivinerich basalts with varying degrees of dust and other coatings. Dark-toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy (+/-5 to 10%) of 45% pyroxene (20% Ca-rich pyroxene and 25% pigeonite), 40% sodic to intermediate plagioclase, and 15% olivine (forsterite 45% +/-5 to 10). Two spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. Diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0.5 to 3 mm in soils. 相似文献
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Under astronomically favorable circumstances, photographs do not reveal excess light near the triangular libration points of the earth-moon system. We find that the visible surface brightness of anomalous dust populations, if these populations do exist, is less than 10(-9) candela per square centimeter. 相似文献