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Abstract An analytical spectral model of the barotropic divergent equations on a sphere is developed using the potential-stream function formulation and the normal modes as basic functions. Explicit expressions of the coefficients of nonlinear interaction are obtained in the asymptotic case of a slowly rotating sphere, i.e. when the normal modes can be expressed as single spherical harmonics. 相似文献
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Encased embryos of spotted dogfish Scyliorhinus canicula absorbed six radio-isotopes (241Am, 109Cd, 57Co, 134Cs, 54Mn and 65Zn) directly from seawater during short-term experimental exposure, demonstrating the permeability of the egg-case to these contaminants. Embryo to water concentration factors (CFs) ranged from 0.14 for 134Cs to 7.4 for 65Zn. The 65Zn and 57Co CFs increased exponentially with embryo length, whereas the CF for 109Cd declined with length. Among different components of the encased embryo the egg case was the major repository (69-99%) of all six radio-isotopes that were distributed throughout its wall. Egg-case CFs were as high as 10(3) for 57Co and 65Zn, making it the major source of gamma radiation exposure to the embryo and potentially of radio-isotopes for continued absorption by the embryo, following the uptake phase of the experiment. The patterns of uptake by the egg-case approximated linearity for most isotopes and loss rates were isotope-specific; egg-case biokinetics were not greatly affected by the viability of the contained embryo. Within the embryo initial data on radio isotopic distribution show that the skin is their major site of uptake, as previously demonstrated for juveniles. 相似文献
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金属丰度与星系光度是星系的重要特征参量,研究它们之间的关系有助于理解星系中恒星质量与金属成分的累积过程。评述了星系的光度-金属丰度关系的最新研究进展,包括对近邻星系、中等红移星系(0.42)的研究结果.由于观测样本跨越较宽的宇宙学时标,可以由此来探讨这一关系的演化过程,从而帮助理解星系演化的整体图景。 相似文献
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Marcus?FreiseEmail author Francois?Holtz Jürgen?Koepke James?Scoates Hervé?Leyrit 《Contributions to Mineralogy and Petrology》2003,145(6):659-672
Phase relations of a phonolite (K1) and a tephri-phonolite (K2) from the Upper Miocene lavas in the Southeast Province of the Kerguelen Archipelago have been investigated in the P/T range 100–500 MPa and 700–900 °C at two fO2 conditions (~ NNO and ~ NNO+2.3) to clarify the differentiation and pre-eruptive conditions of these magmas. Crystallization experiments were performed in cold seal pressure vessels (CSPV) and internally heated pressure vessels (IHPV) at various XH2O, under reducing (log fO2 ~ NNO) and oxidizing conditions (log fO2 ~ NNO+2.3). Under reducing conditions, the resulting phase assemblage for K1 was: titanomagnetite, nepheline, alkali feldspar, clinopyroxene and biotite; under oxidizing conditions, the assemblage was: magnetite, plagioclase, alkali feldspar, nepheline, titanite (minerals given in the order of appearance with decreasing T at 200 MPa for 4 wt% water in the melt). It is emphasized that an effect of fO2 on the phase stability of feldspars and feldspathoides was observed. Comparison of the natural and experimental phase assemblages shows that the pre-eruptive conditions for K1 must have been in the log fO2 range NNO+1–NNO+2, at pressures above 200–250 MPa. Assuming a temperature of 800 °C, the water content of the melt is constrained to be between 4 and 6 wt% H2O. The pre-eruptive fO2 conditions for the less evolved sample K2 are more oxidizing with log fO2 close to NNO+2.3. The experimental results show that the enrichment of alkalis in residual melts during differentiation of tephri-phonolites is enhanced at high fO2.Editorial responsibility: J. Hoefs 相似文献
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Ralph C. Foster Francois Vianey Philippe Drobinski Pierre Carlotti 《Boundary-Layer Meteorology》2006,120(2):229-255
The near-surface flow of a well-resolved large-eddy simulation of the neutrally-stratified planetary boundary layer is used to explore the relationships between coherent structures and the vertical momentum flux. The near-surface flow is characterized by transient streaks, which are alternating bands of relatively higher and lower speed flow that form parallel to the mean shear direction in the lower part of the boundary layer. Although individual streaks are transient, the overall flow is in a quasi-equilibrium state in which the streaks form, grow, decay and regenerate over lifetimes on the order of tens of minutes. Coupled with the streaky flow is an overturning circulation with alternating bands of updrafts and downdrafts approximately centered on the streaks. The surface stress is dominated by upward ejections of slower moving near-surface air and downward sweeps of higher speed air from higher in the boundary layer. Conditional sampling of the ejection and sweep events shows that they are compact, coherent structures and are intimately related to the streaks: ejections (sweeps) preferentially form in the updrafts (downdrafts) of the three-dimensional streak flow. Hence, consistent with other recent studies, we propose that the streak motion plays an important role in the maintenance of the surface stress by establishing the preferential conditions for the ejections and sweeps that dominate the surface stress. The velocity fluctuation spectra in the model near the surface have a k
−1 spectral slope over an intermediate range of wavenumbers. This behaviour is consistent with recent theoretical predictions that attempt to evaluate the effects of organized flow, such as near-surface streaks, on the variance spectra. 相似文献
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Mathieu Schuster Philippe Duringer Jean‐Francois Ghienne Patrick Vignaud Alain Beauvilain Hassan Taisso Mackaye Michel Brunet 《地球表面变化过程与地形》2003,28(10):1059-1069
This paper reports on a study dealing with the rhyolitic inselbergs of Hadjer el Khamis that formed palaeoislands during Lake Mega‐Chad events. Field observations have shown that: (1) conglomeratic patches of immature to mature clasts are preserved at the feet of the Hadjer el Khamis inselbergs; (2) in cross‐section, their pro?le reveals a well de?ned cliff–platform junction at a constant elevation (325 m). The monolithological clasts show all degrees of roundness, from angular cobbles to well rounded pebbles. This wide range of maturity suggests a coastal origin for these cobbles. The system was permanently fed with angular clasts, which were progressively worn by waves. Cobbles that were wave‐worked for the longest time are the best rounded. The cliff–platform junction is the result of erosion by waves, which attacked and undercut the inselberg cliffs during Lake Mega‐Chad events. Asymmetrical erosion pro?les moreover suggest a wind regime dominated by SW to NE oriented winds. These interpretations have two implications. The elevation of the cliff–platform junction is an indication of the highest water level of Lake Mega‐Chad at 320–325 m, which is in agreement with other observations elsewhere in the basin. The SW to NE oriented winds show that monsoon‐related winds were prevalent during Lake Mega‐Chad events, suggesting the Inter‐Tropical Convergence Zone was located higher in latitude than today. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献