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Andreas Poll 《Astrophysics and Space Science》1994,216(1-2):333-335
The system of ordinary differential equations derived from the hydrodynamical equations of a radially symmetric flow has a one dimensional manifold of critical points if there is mass loading in the flow or if the heating and cooling rates are taken to be independent of the thermodynamic variables as is usual. 相似文献
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Rolf?S.?ArvidsonEmail author Cornelius?Fischer Andreas?Luttge 《Aquatic Geochemistry》2015,21(5):415-422
We compare the canonical treatment of calcite’s dissolution rate from the literature in a closed system, particle batch reactor, with the alternative approach suggested by Truesdale (Aquat Geochem, 2015). We show that the decay of rate over time can be understood in terms of the evolution and distribution of reactive sites on the surface of these particles. We also emphasize that interpretation of observed rates must not exclude the fundamental role of crystal defects, whose importance is already implicitly reflected in the common form of rate laws in geochemistry. The empirical behavior of overall rate in closed systems, such as those described by Truesdale, may thus reflect relationships between defect centers and the generation of steps over the calcite surface (previously documented for silicates), such that below a critical free energy limit, there is insufficient driving force to open hollow cores and thus a loss of reaction mechanism. Dissolution in this very-near-equilibrium regime will be dependent on the distribution of extant steps and the energetics of new kink site nucleation. However, these sensitivities are complicated in the case of particle systems by grain boundaries, edges, corners, and other terminations. Such discontinuities constitute a defect class whose overall kinetic importance will be strongly tied to particle diameter and which can act independently of the internal strain field imposed by screw and edge dislocations. 相似文献
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Fe and O isotope composition of meteorite fusion crusts: Possible natural analogues to chondrule formation? 下载免费PDF全文
Dominik C. Hezel Graeme M. Poole Jack Hoyes Barry J. Coles Catherine Unsworth Nina Albrecht Caroline Smith Mark Rehkämper Andreas Pack Matthew Genge Sara S. Russell 《Meteoritics & planetary science》2015,50(2):229-242
Meteorite fusion crust formation is a brief event in a high‐temperature (2000–12,000 K) and high‐pressure (2–5 MPa) regime. We studied fusion crusts and bulk samples of 10 ordinary chondrite falls and 10 ordinary chondrite finds. The fusion crusts show a typical layering and most contain vesicles. All fusion crusts are enriched in heavy Fe isotopes, with δ56Fe values up to +0.35‰ relative to the solar system mean. On average, the δ56Fe of fusion crusts from finds is +0.23‰, which is 0.08‰ higher than the average from falls (+0.15‰). Higher δ56Fe in fusion crusts of finds correlate with bulk chondrite enrichments in mobile elements such as Ba and Sr. The δ56Fe signature of meteorite fusion crusts was produced by two processes (1) evaporation during atmospheric entry and (2) terrestrial weathering. Fusion crusts have either the same or higher δ18O (0.9–1.5‰) than their host chondrites, and the same is true for Δ17O. The differences in bulk chondrite and fusion crust oxygen isotope composition are explained by exchange of oxygen between the molten surface of the meteorites with the atmosphere and weathering. Meteorite fusion crust formation is qualitatively similar to conditions of chondrule formation. Therefore, fusion crusts may, at least to some extent, serve as a natural analogue to chondrule formation processes. Meteorite fusion crust and chondrules exhibit a similar extent of Fe isotope fractionation, supporting the idea that the Fe isotope signature of chondrules was established in a high‐pressure environment that prevented large isotope fractionations. The exchange of O between a chondrule melt and an 16O‐poor nebula as the cause for the observed nonmass dependent O isotope compositions in chondrules is supported by the same process, although to a much lower extent, in meteorite fusion crusts. 相似文献
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Andreas Hoy Jaak Jaagus Mait Sepp Jörg Matschullat 《Theoretical and Applied Climatology》2013,112(1-2):73-88
Air pressure field and circulation pattern frequencies were investigated to (1) locate and compare positions of the underlying pressure fields, (2) analyse the spatial dimension of affected areas, (3) create schematic maps of important circulation types and (4) compare the classification types in their response to the data. Two manual classifications were used, selected for the length of their time series and their applicability to a larger region: the Grosswetterlagen classification (GWLc) and the Vangengeim–Girs classification (VGc). Their time series were correlated with a global set of gridded monthly sea-level pressure data. Results show the different conceptual orientation of VGc (hemispheric) and GWLc (continental). The highest correlation values and the largest affected areas are visible in winter, where patterns frequently extended into northern Africa and western Asia. Schematic maps, illustrating the average location of main pressure centres, are provided for basic classes of both classifications. Re-arranging GWLc subtypes increases the classifications comparability with the VGc. Analysis of moving correlation coefficients reveals high fluctuations in the relation of both classifications over time. 相似文献