Computations on the interaction of an interplanetary shock with the Earth's magnetosphere     

Imke de Pater  Wim J. Weber 《Astrophysics and Space Science》1977,51(1):217-224

We present the results of a one-dimensional computer simulation of the interaction between interplanetary shocks and the Earth's magnetosphere. The position of the bowshock as a function of solar wind velocity and interplanetary field direction is studied.  相似文献   

Effects of arrival time errors on traveltime tomography     

Axel H.E. Röhm  Harmen Bijwaard  Wim Spakman  & Jeannot Trampert 《Geophysical Journal International》2000,142(1):270-276

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Isotope mixing models require individual isotopic tracer content for correct quantification of sediment source contributions          下载免费PDF全文

Hari Ram Upadhayay  Samuel Bodé  Marco Griepentrog  Roshan Man Bajracharya  William Blake  Wim Cornelis  Pascal Boeckx 《水文研究》2018,32(7):981-989

The use of isotopic tracers for sediment source apportionment is gaining interest with recent introduction of compound‐specific stable isotope tracers. The method relies on linear mixing of source isotopic tracers, and deconvolution of a sediment mixture initially quantifies the contribution of sources to the mixture's tracer signature. Therefore, a correction to obtain real sediment source proportions is subsequently required. As far as we are aware, all published studies to date have used total isotopic tracer content or a proxy (e.g., soil carbon content) for this post‐unmixing correction. However, as the relationship between the isotopic tracer mixture and the source mixture is different for each isotopic tracer, post‐unmixing corrections cannot be carried out with one single factor. This contribution presents an isotopic tracer model structure—the concentration‐dependent isotope mixing model (CD‐IMM)—to overcome this limitation. Herein, we aim to clarify why the “conventional” approach to converting isotopic tracer proportions to source proportions using a single factor is wrong. In an initial mathematical assessment, error incurred by not using CD‐IMM (NCD‐IMM) in unmixing two sources with two isotopic tracers showed a complex relation as a function of relative tracer contents. Next, three artificial mixtures with different proportions of three soil sources were prepared and deconvoluted using ¹³C of fatty acids using CD‐IMM and NCD‐IMM. Using NCD‐IMM affected both accuracy (mean average error increased up to a threefold compared with the CD‐IMM output) and precision (interquartile range was up to 2.5 times larger). Finally, as an illustrative example, the proportional source contribution reported in a published study was recalculated using CD‐IMM. This resulted in changes in estimated source proportions and associated uncertainties. Content of isotopic tracers is seldom reported in published work concerning use of isotopic tracers for sediment source partitioning. The magnitude of errors made by miscalculation in former studies is therefore difficult to assess. With this contribution, we hope the community will acknowledge the limitations of prior approaches and use a CD‐IMM in future studies.  相似文献   

LavAtmos: An open-source chemical equilibrium vaporization code for lava worlds     

Christiaan P. A. van Buchem  Yamila Miguel  Mantas Zilinskas  Wim van Westrenen 《Meteoritics & planetary science》2023,58(8):1149-1161

To date, over 500 short-period rocky planets with equilibrium temperatures above 1500 K have been discovered. Such planets are expected to support magma oceans, providing a direct interface between the interior and the atmosphere. This provides a unique opportunity to gain insight into their interior compositions through atmospheric observations. A key process in doing such work is the vapor outgassing from the lava surface. LavAtmos is an open-source code that calculates the equilibrium chemical composition of vapor above a dry melt for a given composition and temperature. Results show that the produced output is in good agreement with the partial pressures obtained from experimental laboratory data as well as with other similar codes from literature. LavAtmos allows for the modeling of vaporization of a wide range of different mantle compositions of hot rocky exoplanets. In combination with atmospheric chemistry codes, this enables the characterization of interior compositions through atmospheric signatures.  相似文献   

Trace element partitioning between ilmenite, armalcolite and anhydrous silicate melt: Implications for the formation of lunar high-Ti mare basalts     

Mirjam van Kan Parker  Wim van Westrenen 《Geochimica et cosmochimica acta》2011,75(15):4179-4193

We performed a series of experiments at high pressures and temperatures to determine the partitioning of a wide range of trace elements between ilmenite (Ilm), armalcolite (Arm) and anhydrous lunar silicate melt, to constrain geochemical models of the formation of titanium-rich melts in the Moon. Experiments were performed in graphite-lined platinum capsules at pressures and temperatures ranging from 1.1 to 2.3 GPa and 1300-1400 °C using a synthetic Ti-enriched Apollo ‘black glass’ composition in the CaO-FeO-MgO-Al₂O₃-TiO₂-SiO₂ system. Ilmenite-melt and armalcolite-melt partition coefficients (D) show highly incompatible values for the rare earth elements (REE) with the light REE more incompatible compared to the heavy REE ( 0.0020 ± 0.0010 to 0.069 ± 0.010 for ilmenite; 0.0048 ± 0.0023 to 0.041 ± 0.008 for armalcolite). D values for the high field strength elements vary from highly incompatible for Th, U and to a lesser extent W (for ilmenite: 0.0013 ± 0.0008, 0.0035 ± 0.0015 and 0.039 ± 0.005, and for armalcolite 0.008 ± 0.003, 0.0048 ± 0.0022 and 0.062 ± 0.03), to mildly incompatible for Nb, Ta, Zr, and Hf (e.g. 0.28 ± 0.05 and : 0.76 ± 0.07). Both minerals fractionate the high field strength elements with D_Ta/D_Nb and D_Hf/D_Zr between 1.3 and 1.6 for ilmenite and 1.3 and 1.4 for armalcolite. Armalcolite is slightly more efficient at fractionating Hf from W during lunar magma ocean crystallisation, with D_Hf/D_W = 12-13 compared to 6.7-7.5 for ilmenite. The transition metals vary from mildly incompatible to compatible, with the highest compatibilities for Cr in ilmenite (D ∼ 7.5) and V in armalcolite (D ∼ 8.1). D values show no clear variation with pressure in the small range covered.Crystal lattice strain modelling of D values for di-, tri- and tetravalent trace elements shows that in ilmenite, divalent elements prefer to substitute for Fe while armalcolite data suggest REE replacing Mg. Tetravalent cations appear to preferentially substitute for Ti in both minerals, with the exception of Th and U that likely substitute for the larger Fe or Mg cations. Crystal lattice strain modelling is also used to identify and correct for very small (∼0.3 wt.%) melt contamination of trace element concentration determinations in crystals.Our results are used to model the Lu-Hf-Ti concentrations of lunar high-Ti mare basalts. The combination of their subchondritic Lu/Hf ratios and high TiO₂ contents requires preferential dissolution of ilmenite or armalcolite from late-stage, lunar magma ocean cumulates into low-Ti partial melts of deeper pyroxene-rich cumulates.  相似文献   

Hydrogeology and groundwater flow in a basalt-capped Mesozoic sedimentary series of the Ethiopian highlands     

Ine Vandecasteele  Jan Nyssen  Wim Clymans  Jan Moeyersons  Kristine Martens  Marc Van Camp  Tesfamichael Gebreyohannes  Florimond Desmedt  Jozef Deckers  Kristine Walraevens 《Hydrogeology Journal》2011,19(3):641-650

A hydrogeological study was undertaken in the Zenako-Argaka catchment, near Hagere Selam in Tigray, northern Ethiopia, during the rainy season of 2006. A geological map was produced through geophysical measurements and field observations, and a fracture zone identified in the north west of the catchment. A perched water table was found within the Trap Basalt series above the laterized upper Aram Aradam Sandstones. A map of this water table was compiled. Water-level variation during the measurement period was at least 4.5?m. Variation in basal flow for the whole catchment for the measurement period was between 12 and 276?m³/day. A groundwater flow model was produced using Visual MODFLOW, indicating the general direction of flow to be towards the south, and illustrating that the waterways have only a limited influence on groundwater flow. The soil water budget was calculated for the period 1995?C2006, which showed the important influence of the distribution of rainfall in time. Although Hagere Selam received some 724?mm of rainfall per year over this period, the strong seasonal variation in rainfall meant there was a water deficit for on average 10?months per year.  相似文献   

Tomographic images of the upper mantle below central Europe and the Mediterranean     

Wim Spakman 《地学学报》1990,2(6):542-553

Results from delay time tomography of the European-Mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes. Slab-like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath Spain, the Tyrrhenian basin, and the Aegean. These structures are interpreted as images of subducted slabs. Large aseismic regions with positive velocity anomalies are found beneath the Western Mediterranean, Italy, the Alps, Dinarides, the Pannonian basin, northern Greece, and the Aegean. These anomalies can also be linked to subducted lithosphere. From the anomaly patterns it is deduced that subduction occurred below the Western Mediterranean and along both sides of the Adriatic micro-plate. Beneath the Dinarides and northern Greece the velocity structures suggest detachment of the slab from the surface.  相似文献   

On the wind momentum problem of O-type stars in the galaxy     

G. Israelian  K. Vyverman 《Astrophysics and Space Science》1997,254(1):51-60

We have examined the wind momentum problem of O-type stars in the Galaxy. It is shown that the discrepancy between theoretical and empirical mass loss rates and terminal velocities can be reversed by using recently updated values of force multiplier parameters. With these new values, the momentum problem found by former investigators is reversed so that there now appears to be more than enough radiation force in order to accelerate the stellar winds of a sample of Galactic O-type stars. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Delay-time tomography of the upper mantle below Europe, the Mediterranean, and Asia Minor   总被引：3，自引：0，他引：3  

Wim Spakman 《Geophysical Journal International》1991,107(2):309-332

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Characterization of mesostasis regions in lunar basalts: Understanding late‐stage melt evolution and its influence on apatite formation          下载免费PDF全文

Nicola J. Potts  Romain Tartèse  Mahesh Anand  Wim van Westrenen  Alexandra A. Griffiths  Thomas J. Barrett  Ian A. Franchi 《Meteoritics & planetary science》2016,51(9):1555-1575

Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile‐bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk‐rock basaltic composition and that of bulk‐mesostasis regions, indicating that bulk‐rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late‐stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO₂ abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite‐melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts.  相似文献