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41.
42.
Jan Hertogen Marie-Josée Janssens H. Takahashi John W. Morgan Edward Anders 《Geochimica et cosmochimica acta》1983,47(12):2241-2255
We have analyzed by RNAA 3 EH and 3 EL chondrites for 20 trace elements. Interelement correlations were examined visually and by factor analysis, to assess the effects of nebular fractionation and metamorphism.Refractory siderophiles (Ir, Os, Re) correlate with “normal siderophiles” (Ni, Pd, Au, Sb, and Ge) in EL's but not EH's; presumably these two element groups originally condensed on separate phases (CAI and metal), but then concentrated in metal during metamorphism. Sb and Ge are more depleted than the other three elements of the “normal” group, presumably by volatilization during chondrule formation.Volatiles are consistently more depleted in EL's than EH's, by factors >10× for the more volatile elements. Some of the stronger correlations are found for In-Tl, Tl-Bi, and Zn-Cd-In. These correlations are about equally consistent with predicted condensation curves for the solar nebula (especially for host phases with negative heats of solution, or for P = 0.1?1 atm) and with volatilization curves for artificially heated Abee, as determined by M E. Lipschutz and coworkers at Purdue. No decisive test between these alternatives is available at present, but the close correlation of Zn, Cd, In may eventually provide a crucial test.Factor analysis shows that 3 factors account for 93% of the variance; they seem to reflect volatile (F1), siderophile (F2), and chalcophile (F3) behavior. The element groupings agree largely with those recognized visually; they are listed with the inferred host phases. F1 (minor sulfide, probably ZnS): Zn, Cd, In, Br; F2 (CAI, later metal): Ir, Os. Re; F1, F2 (metal): Ni, Pd, Au, Ge, Sb; F3, F1 (FeS): Se, Te, Bi, Tl. These correlations differ to some extent from those obtained by Shaw (1974) in an earlier factor analysis, presumably because the new data are more homogeneous and extensive, especially for siderophiles. The new correlations also show that the cosmochemical behavior of some volatiles in E-chondrites differs from that predicted for ordinary chondrites, so that condensation curves for the latter are not strictly applicable. 相似文献
43.
T. J. Janssens 《Solar physics》1972,25(1):237-241
A design is presented for an instrument to measure solar oblateness without forming a solar image and having two identical prisms as the only optical elements. Feasibility calculations indicate that this might be sensitive and quite free from instrumental induced errors. 相似文献
44.
45.
Numerical simulation of upwelling currents in pockmarks,and data from the Inner Oslofjord,Norway 总被引:5,自引:3,他引:2
The deflection of oceanic or tidal currents into pockmarks has been studied by both general three-dimensional computational
fluid dynamics simulations and acoustic measurements in a number of pockmarks in the Inner Oslofjord, Norway. The modeling
demonstrates upstream convergence of flow lines, followed by upwelling over the pockmark. This upwelling is an effect of deflected
regional currents, not of expulsion of fluids or gas from the seafloor, and is sufficiently strong to prevent the settling
of fine particles. The field measurements, although noisy at low vertical velocities, are consistent with the hypothesis of
upwelling. The reduction in sedimentation rate inferred over the pockmarks (relative to that of the flat surrounding seabed)
can explain the maintenance, or even deepening of pockmarks in the absence of fluid or gas seepage. The current pattern may
also have consequences for the marine biology of pockmarks. 相似文献
46.
The O2 3?-Y3+ center in fluorite-type structures (CaF2 and SrF2) has been investigated at the density functional theory (DFT) level using the CRYSTAL06 code. Our calculations were performed by means of the hybrid B3PW method in which the Hartree–Fock exchange is mixed with the DFT exchange functional, using Becke’s three parameter method, combined with the non-local correlation functionals by Perdew and Wang. Our calculations confirm the stability and the molecular character of the O2 3?-Y3+ center. The unpaired electron is shown to be almost exclusively localized on and equally distributed between the two oxygen atoms that are separated by a bond distance of 2.47 Å in CaF2 and 2.57 Å in SrF2. The calculated 17O and 19F hyperfine constants for of the O2 3?-Y3+ center are in good agreement with their corresponding experimental values reported by previous electron paramagnetic resonance and electron nuclear double resonance studies, while discrepancies are notable for the 89Y hyperfine constants. 相似文献
47.
Christophe Grenier Damien Régnier Emmanuel Mouche Hakim Benabderrahmane François Costard Philippe Davy 《Hydrogeology Journal》2013,21(1):257-270
The impact of glaciation cycles on groundwater flow was studied within the framework of nuclear waste storage in underground geological formations. The eastern section of the Paris Basin (a layered aquifer with impervious/pervious alternations) in France was considered for the last 120 ka. Cold periods corresponded with arid climates. The issue of talik development below water bodies was addressed. These unfrozen zones can maintain open pathways for aquifer recharge. Transient thermal evolution was simulated on a small-scale generic unit of the landscape including a “river” and “plain”. Coupled thermo-hydraulic modeling and simplified conductive heat transfer were considered for a broad range of scenarios. The results showed that when considering the current limited river dimensions and purely conductive heat transfer, taliks are expected to close within a few centuries. However, including coupled advection for flows from the river to the plain (probably pertinent for the eastern Paris Basin aquifer recharge zones) strongly delays talik closure (millennium scale). The impact on regional underground flows is expected to vary from a complete stop of recharge to a reduced recharge, corresponding to the talik zones. Consequences for future modeling approaches of the Paris Basin are discussed. 相似文献
48.
The cause of the desiccation of the Mediterranean Sea during the Messinian Salinity Crisis has been widely debated, but its re-flooding remains poorly investigated. Interpretations generally involve tectonic collapse of the Strait of Gibraltar or global sea-level rise, or even a combination of both. The dramatic sea-level fall in the Mediterranean has induced deep fluvial incision all around the desiccated basin. We investigate erosion dynamics related to this base level drop by using the numerical simulator EROS. We show that intense regressive erosion develops inevitably in the Gibraltar area eventually inducing the piracy of the Atlantic waters by an eastward-flowing stream and the subsequent re-flooding of the Mediterranean. 相似文献
49.
50.
Herbert Palme Marie-Josée Janssens H. Takahashi Edward Anders Jan Hertogen 《Geochimica et cosmochimica acta》1978,42(3):313-323
Sixteen crater samples were analyzed by radiochemical neutron activation analysis for Ge, Ir, Ni, Os, Pd and Re. Two impact melt rock samples from Clearwater East (22 km) showed strong, uniform enrichments in all elements except Ge, corresponding to 7.4% C1 chondrite material. Interelement ratios suggest that the meteorite was a C1 (or C2) chondrite, not an iron, stony iron, or chondrite of another type. An Ivory Coast tektite (related to the 10 km Bosumtwi crater) was enriched in Ir + Os and Ni to about 0.04 and 1.6% of C1 chondrite levels, but in the absence of data on country rocks, the meteorite cannot yet be characterized.Impact melt rock samples from Clearwater West (32km), Manicouagan (70km), and Mistastin (28 km) showed no detectable meteoritic component. Upper limits, as Cl chondrite equivalent, were Os ≤ 2 × 10?3% (~0.01 ppb), Ni ≤ 2 × 10?1% (~20ppm). Possible causes are high impact velocity and/or a chemically inconspicuous meteorite (achondrite, Ir,Os-poor iron or stony iron). However, a more likely reason is that some fraction of the impact melt remains meteorite-free, especially at craters with central peaks.Clearwater East is the first terrestrial impact crater found to be associated with a stony meteorite. Apparently the consistent absence of stony projectiles at small craters (< 1 km diameter) reflects their destruction in the atmosphere, as proposed by Öpik. 相似文献