Inter-diffusion coefficients parallel to the C-Axis in iron-rich clinopyroxenes calculated from microstructures     

Frans J. M. Rietmeijer 《Contributions to Mineralogy and Petrology》1983,83(1-2):169-176

Subsolidus marginal zoning in calcium-poor clinopyroxenes and intermediate zoning in discontinuously zoned subcalcic- to calcium-rich clinopyroxenes from ironrich igneous rocks is used to calculate the interdiffusion coefficient, D_Ca?(Fe,Mg), parallel to the crystallographic caxis. Wagner's mathematical models describing the displacement of interfaces in solids as the result of isothermal diffusion are adopted. The steady-state heat flow equation is used to approximate the diffusion times. The calculated interdiffusion coefficients are of a reasonable order of magnitude, viz. 6.0×10^?20?2.0×10^?17cm²· sec^?1 at about 900° C.  相似文献   

The Earliest Chemical Dust Evolution in the Solar Nebula     

Frans J.M. Rietmeijer   《Chemie der Erde / Geochemistry》2002,62(1):1-45

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The stable carbon isotopes in enstatite chondrites and Cumberland Falls     

Peter Deines  Frans E. Wickman 《Geochimica et cosmochimica acta》1985,49(1):89-95

The carbon isotopic composition of the total carbon in the enstatite chondrites Indarch, Abee, St. Marks, Pillistfer, Hvittis and Daniel's Kuil and the enstatite achondrite Cumberland Falls has been measured. The empirical relationhip between carbon isotopic composition and total carbon content is distinct from that of carbonaceous and ordinary chondrites. Within the enstatite chondrite group the average ¹³C content increases with petrographic type: E4 < E5 < E6. Daniel's Kuil shows the largest ¹³C enrichment in the bulk carbon of any meteorite. The carbon isotopic composition is most clearly correlated with the abundance of the elements Zn, Cd and In. Insofar as these elements may hold the key to the understanding of enstatite chondrites, more detailed combined carbon isotope and trace element studies of these meteorites will play an important role in the deciphering of their history.  相似文献   

Carbon in Meteoroids: Wild 2 Dust Analyses, IDPs and Cometary Dust Analogues     

Alessandra Rotundi  Frans J. M. Rietmeijer 《Earth, Moon, and Planets》2008,102(1-4):473-483

Assuming that similar organic components as in comet 81P/Wild 2 are present in incoming meteoroids, we try to anticipate the observable signatures they would produce for meteor detection techniques. In this analysis we consider the elemental and organic components in cometary aggregate interplanetary dust particles and laboratory analyses of inter- and circumstellar carbon dust analogues. On the basis of our analysis we submit that (semi) quantitative measurements of H, N and C produced during meteor ablation will open an entire new aspect to using meteoroids as tracers of these volatile element abundances in active comets and their contributions to the mesospheric metal layers.  相似文献   

Comparison of benthic foraminifera and macrofaunal indicators of the impact of oil-based drill mud disposal   总被引：1，自引：0，他引：1  

Mariéva Denoyelle  Frans J. Jorissen  Daniel Martin 《Marine pollution bulletin》2010,60(11):2007-2021

We compare foraminifera and macrofauna as bio-indicators of oil-based drill mud disposal site off Congo. The most polluted sites are characterized by poor faunas, dominated by some very tolerant taxa. Slightly further from the disposal site, there is an area with strongly increased densities, heavily dominated by opportunistic taxa. Still further, macrofauna appears to be similar to that at the reference area, but the foraminiferal meiofauna still suggests a slight environmental perturbation. The foraminiferal FIEI index, based on the species distribution in the study area, appears to be more discriminative than the macrofaunal ITI index, based on a priori definitions of the trophic guilds of the various taxa. Our comparative approach allows us to point out the benefits of (1) the use of macrofauna and foraminifera together and (2) the definition of the species groups used in biotic indices on the basis of observations made directly in the study area.  相似文献   

A zone-specific fish-based biotic index as a management tool for the Zeeschelde estuary (Belgium)     

Jan Breine  Paul Quataert  Frans Ollevier  Ericia Van den Bergh 《Marine pollution bulletin》2010,60(7):1099-233

Fish-based indices monitor changes in surface waters and are a valuable aid in communication by summarising complex information about the environment (Harrison and Whitfield, 2004). A zone-specific fish-based multimetric estuarine index of biotic integrity (Z-EBI) was developed based on a 13 year time series of fish surveys from the Zeeschelde estuary (Belgium). Sites were pre-classified using indicators of anthropogenic impact. Metrics showing a monotone response with pressure classes were selected for further analysis. Thresholds for the good ecological potential (GEP) were defined from references. A modified trisection was applied for the other thresholds. The Z-EBI is defined by the average of the metric scores calculated over a one year period and translated into an ecological quality ratio (EQR). The indices integrate structural and functional qualities of the estuarine fish communities. The Z-EBI performances were successfully validated for habitat degradation in the various habitat zones.  相似文献   

Determination of repose-period patterns of volcanoes from sequences of ash layers     

Frans E. Wickman 《Mathematical Geology》1970,2(3):277-283

The repose-period patterns of volcanoes have been studied earlier from the historical records of their eruptions. This paper analyzes the necessary conditions for using observed sequences of ash layers instead of such records. The temporal distribution of preserved ash falls at a point is a function of: (1) the number of active volcanoes of the region; (2) their locations within the region; (3) the regional wind pattern; and of accidental erosion and redeposition at the point. The distribution of ash layers is derived if only one volcano must be considered and factor (4) can be neglected. Explicit functions are complicated; ash falls from a “Poissonian volcano” are, however, also Poissonian but with a different wind pattern-dependent parameter. A correction for factor (3) is rarely possible because the present wind pattern may differ from the pattern at the time of ash falls. By determining the chronostratigraphy of the ash falls all around the volcano, factor (3) may be eliminated. The example of several volcanoes producing origin-indistinguishable ash layers, is briefly discussed. The time sequence of such “pooled” ash falls practically always shows pronounced memory effects of previous eruptions.  相似文献   

Kimberlites and their xenoliths | J.B. Dawson, 1980. Minerals and Rocks,No. 15. Springer Verlag,Berlin, xii+252 pp., DM88.00, approx. US $52.00     

Frans E. Wickman 《Earth》1982,18(2):185-186

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Modeling Steady Sea Water Intrusion with Single‐Density Groundwater Codes     

Mark Bakker  Frans Schaars 《Ground water》2013,51(1):135-144

Steady interface flow in heterogeneous aquifer systems is simulated with single‐density groundwater codes by using transformed values for the hydraulic conductivity and thickness of the aquifers and aquitards. For example, unconfined interface flow may be simulated with a transformed model by setting the base of the aquifer to sea level and by multiplying the hydraulic conductivity with 41 (for sea water density of 1025 kg/m³). Similar transformations are derived for unconfined interface flow with a finite aquifer base and for confined multi‐aquifer interface flow. The head and flow distribution are identical in the transformed and original model domains. The location of the interface is obtained through application of the Ghyben‐Herzberg formula. The transformed problem may be solved with a single‐density code that is able to simulate unconfined flow where the saturated thickness is a linear function of the head and, depending on the boundary conditions, the code needs to be able to simulate dry cells where the saturated thickness is zero. For multi‐aquifer interface flow, an additional requirement is that the code must be able to handle vertical leakage in situations where flow in an aquifer is unconfined while there is also flow in the aquifer directly above it. Specific examples and limitations are discussed for the application of the approach with MODFLOW. Comparisons between exact interface flow solutions and MODFLOW solutions of the transformed model domain show good agreement. The presented approach is an efficient alternative to running transient sea water intrusion models until steady state is reached.  相似文献