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201.
Pierre Lesaffre Steven A. Balbus Henrik Latter 《Monthly notices of the Royal Astronomical Society》2009,396(2):779-787
We run mean-field shearing-box numerical simulations with a temperature-dependent resistivity and compare them to a reduced dynamical model. Our simulations reveal the co-existence of two quasi-steady states, a 'quiet' state and an 'active' turbulent state, confirming the predictions of the reduced model. The initial conditions determine on which state the simulation ultimately settles. The active state is strongly influenced by the geometry of the computational box and the thermal properties of the gas. Cubic domains support permanent channel flows, bar-shaped domains exhibit eruptive behaviour, and horizontal slabs give rise to infrequent channels. Meanwhile, longer cooling time-scales lead to higher saturation amplitudes. 相似文献
202.
Matthias
Van GINNEKEN Luigi FOLCO Carole CORDIER Pierre ROCHETTE 《Meteoritics & planetary science》2012,47(2):228-247
Abstract– On the basis of morphological and petrographic characteristics, eight “giant” unmelted micrometeorites in the 300–1100 μm size range were selected from the Transantarctic Mountain micrometeorite collection, Victoria Land, Antarctica. Mineralogical and geochemical data obtained by means of scanning electron microscopy, electron probe microanalyses, and synchrotron X‐ray diffraction allow their classification as chondritic micrometeorites. The large size of the micrometeorites increases considerably the amount of mineralogical and geochemical information compared to micrometeorites in smaller size fractions, therefore allowing a better definition of their parent material. A large variety of material is observed: five micrometeorites are related to unequilibrated and equilibrated ordinary chondrite, one to CV chondrite, one to CM chondrite, and one to CI chondrite parent materials. Besides reporting the first occurrence of a CV‐like micrometeorite, our study shows that the abundance of chondritic material supports observations from recent studies on cosmic spherules that a large part of the micrometeorite flux in this size range is of asteroidal origin. 相似文献
203.
Nicolas Rascle Fabrice Ardhuin Pierre Queffeulou Denis Croiz-Fillon 《Ocean Modelling》2008,25(3-4):154-171
Ocean surface mixing and drift are influenced by the mixed layer depth, buoyancy fluxes and currents below the mixed layer. Drift and mixing are also functions of the surface Stokes drift Uss, volume Stokes transport TS, a wave breaking height scale Hswg, and the flux of energy from waves to ocean turbulence Φoc. Here we describe a global database of these parameters, estimated from a well-validated numerical wave model, that uses traditional forms of the wave generation and dissipation parameterizations, and covers the years 2003–2007. Compared to previous studies, the present work has the advantage of being consistent with the known physical processes that regulate the wave field and the air–sea fluxes, and also consistent with a very large number of in situ and satellite observations of wave parameters. Consequently, some of our estimates differ significantly from previous estimates. In particular, we find that the mean global integral of Φoc is 68 TW, and the yearly mean value of TS is typically 10–30% of the Ekman transport, except in well-defined regions where it can reach 60%. We also have refined our previous estimates of Uss by using a better treatment of the high frequency part of the wave spectrum. In the open ocean, Uss 0.013U10, where U10 is the wind speed at 10 m height. 相似文献
204.
Neodymium isotopic analyses have been measured on nine ophiolites and four orogenic lherzolites. εNd varies from +12 to +3 in the ophiolites and from +18 to +2 in the orogenic lherzolites. The majority of the analyses plot on a εNd-εSr correlation line as defined by Nd and Sr isotopic analyses of oceanic basalts. However, certain ophiolitic and lherzolitic samples exhibit high87Sr/86Sr ratios and as such lie to the right of the correlation line towards seawater compositions.From these data one can postulate several origins for ophiolites including that of mid-ocean ridges and ocean islands. If the orogenic lherzolites are interpreted as representative of the mantle occurring below active ridges a more complex model is required involving mantle heterogeneity and multi-episodic chemical fractionation starting prior to 2 Ga ago. 相似文献
205.
Benoı̂t Waeles Pierre Le Hir Ricardo Silva Jacinto 《Comptes Rendus Geoscience》2004,336(11):1025-1033
Numerical experiments were performed to simulate the profile evolution of an intertidal mudflat with a 1D cross-shore morphodynamical model. First, the hydrodynamical forcing is a cross-shore tidal current due to semi-diurnal variations of the free surface elevation at the open boundary. Further, considering the conservation of the action density of surface gravity waves, a wave height (and resulting bottom shear stress) calculation is added to the morphodynamical model. Results of the numerical experiments show that the shape of the profile reaches equilibrium. The mudflat progrades continually when the forcing is tide only, whereas it can be steady under the simultaneous action of tide and waves. To cite this article: B. Waeles et al., C. R. Geoscience 336 (2004). 相似文献
206.
Pierre Schiano Bernard Bourdon Robert Clocchiatti Dominique Massare Maria E. Varela Yan Bottinga 《Earth and Planetary Science Letters》1998,160(3-4):537-550
The study of glass inclusions inside mantle minerals provides direct information about the chemistry of naturally occurring mantle-derived melts and the fine-scale complexity of the melting process responsible for their genesis. Minerals in a spinel lherzolite nodule from Grande Comore island contain glass inclusions which, after homogenization by heating, exhibit a continuous suite of chemical compositions clearly distinct from that of the host basanitic lava. The compositions range from silicic, with nepheline–olivine normative, 64 wt% SiO2 and 11 wt% alkali oxides, to almost basaltic, with quartz normative, 50 wt% SiO2 and 1–2 wt% alkali oxides. Within a single mineral phase, olivine, the inferred primary melt composition varies from 54 to 64 wt% SiO2 for MgO content ranging from 8 to 0.8 wt%. An experimental study of the glass and fluid inclusions indicates that trapped melts represent liquids that are in equilibrium with their host phases at moderate temperature and pressure (T≈1230°C and P≈1.0 Gpa for melts trapped in olivine). Quantitative modelling of the compositional trends defined in the suite shows that all of the glasses are part of a cogenetic set of melts formed by fractional melting of spinel lherzolite, with F varying between 0.2 and 5%. The initial highly silicic, alkali-rich melts preserved in Mg-rich olivine become richer in FeO, MgO, CaO and Cr2O3 and poorer in SiO2, K2O, Na2O, Al2O3 and Cl with increasing melt fractions, evolving toward the basaltic melts found in clinopyroxene. These results confirm the connection between glass inclusions inside mantle minerals and partial mantle melts, and indicate that primary melts with SiO2 >60 wt%, alkali oxides >11%, FeO <1 wt% and MgO <1 wt% are generated during incipient melting of spinel peridotite. The composition of the primary melts is inferred to be dependent on pressure, and to reflect both the speciation of dissolved CO2 and the effect of alkali oxides on the silica activity coefficient in the melt. At pressures around 1 GPa, low-degree melts are characterized by alkali and silica-rich compositions, with a limited effect of dissolved CO2 and a decreased silica activity coefficient caused by the presence of alkali oxides, whereas at higher pressures alkali oxides form complexes with carbonates and, consequently, alkali-rich silica-poor melts will be generated. 相似文献
207.
208.
Faiza Menjour Toufik Remmal Mustapha Hakdaoui Fouad El Kamel Kawtar Lakroud Fouad Amraoui Iz-Eddine El Amrani El Hassani Benjamin Van wyk de vries Pierre Boivin 《Journal of the Indian Society of Remote Sensing》2017,45(6):1015-1030
Karst formation geometry can be controlled by fractures and faults, and by other lithologies. Here we show the organization of kastic collapse features related to structures and to extensive basaltic lava flows in the Middle Atlas of Morocco. A lineament map of major faults and fractures has been created for the Middle Atlas using Landsat 7 ETM+ satellite images. This shows a dominant NE–SW regional direction and less prominent NNW–SSE and ENE–WSE directions. All these directions coincide with the alignments of karstic depressions that have formed in the Liassic limestones. The basaltic flows covering these formations on the Middle Atlas limestone plateau, have allowed the generation of cryptokarst, geometrically organized a long these major lineament directions. Karst landforms probabaly existed before the eruption of the lavas, but there were partly invaded by intrusions and volcanism. The extensive basaltic flows allowed for increased infiltration, and subsurface water flow, increasing the rate of kast formation after eruptions. Some basins show evidence of increased subsidence after lava emplacement (Aguelmam Sidi Ali Lake) and some maar-like craters also have subsided after eruption, by karts formation. We lay out the structural and lithological controls on Karstic formation in an intraplate volcanic field based on limestones and evaporites. 相似文献
209.
R. P. Pierre Lejay 《Journal of Geodesy》1949,23(2):121-142
Sans résumé
Elu Président de la Section IV—Gravimétrie à l'issue de l'Assemblée générale, en remplacement du Prof.Vening Meinesz élu Président de l'Union. Le nouveau Secrétaire de la Section estM. B. C. Browne, de Cambridge (Grande-Bretagne). 相似文献
210.