Calculations of activity-composition relations in multi-site solid solutions: the example of AB2O4 spinels     

Jean Lehmann  Jacques Roux 《Contributions to Mineralogy and Petrology》1984,87(4):328-336

A model to calculate activities in multisite solutions like spinels, from a general expression of the Gibbs free energy is developped. The free energy is written as that of a solution with ideal mixing of cations on each sublattice corrected by any suitable higher order terms. It is shown that activities of i^th end-member can be simply written: $${\text{act (}}i{\text{) = (}}\gamma _i {\text{/}}\gamma _i^{\text{0}} {\text{)}}\mathop \prod \limits_j (N_j /N_j^0 )^{P(j,{\text{ }}i)} .$$ N _j are site occupancy fractions; the γ _i are equal to one for the ideal multisite model and depend only on the higher order corrections to this model; ⁰ indicate values for the i ^th end member. The exponents in the matrix P are integers and constants. The activities cannot be expressed explicitly as function of the macroscopic composition. The site occupancy fractions which minimize the Gibbs free energy must be calculated first solving a set of non linear equations which define the internal equilibrium conditions. The (Fe²⁺, Mg) (Al, Cr, Fe³⁺) spinel are used to illustrate these calculations. For multicomponent AB₂O₄ spinels activity expressions derived for the reference ideal multisite mixing model are: $${\text{act (AB}}_{\text{2}} {\text{O}}_{\text{4}} {\text{) = }}\frac{{({\text{A}})[{\text{B}}]^2 }}{{({\text{A}})_0 [{\text{B}}]_0^2 }}$$ (A): fraction of tetrahedral sites occupied by A²⁺; [B]: fraction of octahedral sites occupied by B³⁺. Because the site occupancy fractions at equilibrium are not independent (but related by the internal equilibrium relations) many equivalent expressions of the activities can be obtained. Finally approximations proposed in the literature to obtain simple explicit activity-concentration relationships are discussed.  相似文献   

On forecasting abnormal climatic events in the tropical Atlantic Ocean     

Jacques Servain  Sabine Arnault 《Annales Geophysicae》1995,13(9):995-1008

Modelling and observational evidence indicate that interannual variabilities of dynamic height and sea surface temperature (SST) in the eastern part of the tropical Atlantic Ocean (Gulf of Guinea) are largely induced by preceding fluctuations in wind stress, mainly in the western equatorial basin. A wind-driven linear ocean model is used here to test the possibility of forecasting the abnormal dynamic heights. A control run of the model, forced by 1964–1993 wind stress monthly means, is first conducted. Yearly test runs (1964-1994) are subsequently performed from January to August by forcing the model with observed winds from January to May, and then by forcing with the May wind assumed to persist from June to August. During the last three decades the largest deviations of dynamic height simulated by the control run in the Gulf of Guinea in boreal summer would have been correctly forecast from wind data related only to conditions in May of each year. However, for weak climatic anomalies, the model may forecast overestimated values. For the most part (about 20 times during the last 30 years), the sign of the observed SST anomaly in the centre of the Gulf of Guinea during the boreal summer is identical to the sign of simulated anomalies of dynamic height deduced from both control and test runs. Along the eastern equatorial waveguide, the sea level forecasting skill slowly decreases from the first 2 weeks of June until the second 2 weeks of August, but remains high on both sides of the equator throughout boreal summer, as is expected from the adjustment in a linear ocean model. It is established that throughout the year in the Gulf of Guinea the accuracy of the 1-month forecast dynamic height anomaly provided by the simple linear method is greater than that of the 1-month forecast assuming persistence.  相似文献   

“Na and Cr contents in clinopyroxenes from peridotites: a possible discriminant between ‘sub-continental’ and ‘sub-oceanic’ mantle”—a reply to G. Sen     

Jacques Kornprobst  D. Ohnenstetter  M. Ohnenstetter 《Earth and Planetary Science Letters》1982,60(3):455-459

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Fracturation tertiaire et évolution des contraintes en Bavière orientale: le Jura franconien et la forêt bavaroise (R.F.A.)     

Dr. Françoise Bergerat  Jacques Geyssant 《International Journal of Earth Sciences》1983,72(3):935-953

Résumé L'analyse géométrique et cinématique de la fracturation dans le Jura franconien et la bordure occidentale du Massif bohémien met en évidence les mécanismes de la tectonique cassante d'âge teriaire, essentiellement ceux des grands accidents SE-NW (lignes de Pfahl et de Franconie) qui ont présenté successivement des jeux en coulissement dextre, en faille normale et en faille inverse. Cinq états de contrainte ont été caractérisés et comparés à ceux définis antérieurement dans le Jura souabe, en liaison avec la cinématique des plaques Europe et Afrique: compression N-S, distension E-W, compression NE-SW puis E-W, distension N-S.

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The analysis of both the geometric and the kinematic cenozoic faulting in the Franconian Jura and in western Bohemia enables to characterize the mechanisms of cenozoic tectonics. More especially dextral strike-slip, normal fault and reverse fault have successively occurred along large SE-NW fault line, as the Pfahl and the Franconian fault systems. Five main stress patterns have thus been identified and then compared with those previously described in Swabian Jura. They are related to the kinematic of Europe and Africa plates, i. e.: (1) N-S compression, (2) E-W distension, (3) SW-NE compression, (4) E-W compression, (5) N-S distension.

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Zusammenfassung Durch die geometrische und kinematische Analyse der Brüche wird die tertiäre Bruchtektonik (tectonique cassante) im Fränkischen Jura und am westlichen Rand des Böhmischen Massifs belegt. Es handelt sich im wesentlichen um die großen SE-NW orientierten Störungen der Linie von Pfahl und der Fränkischen Linie, die nacheinander als dextrale Blattverschiebungen, als Normalverwerfungen und als inverse Verwerfungen wirkten. Fünf Spannungszustände können charakterisiert und mit jenen, die bereits im Schwäbischen Jura definiert wurden, verglichen werden. Sie spiegeln die verschiedenen Stadien der kinematischen Entwicklung der europäischen und afrikanischen Platte wider: Kompression N-S, Zerrung E-W, Kompression NE-SW, sodann E-W, Zerrung N-S.

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(tectonique cassante) . , , SE-NW , , , . 5 . : - , - , - , - - .

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A Seeing Monitor for Solar and Other Extended Object Observations     

Jacques M. Beckers 《Experimental Astronomy》2001,12(1):1-20

In this article I describe a site survey facility, which measures the signals of the solar equivalent of a Differential Image Motion Monitor (S-DIMM) and of a six element linear array of solar scintillometers. Combining the S-DIMM r _o andscintillometer _I observations allows the determination of the fractions of the seeing in the free atmosphere and in the ground/lake layer. From the scintillometer array observations C _n ² (h) is determined for heights corresponding to the first 500 m along the line-of-sight. With minor changes this seeing monitor can also be used for other extended objects like the Moon and planets.  相似文献   

Comparative Solar Seeing and Scintillation Studies at the Fuxian Lake Solar Station   总被引：1，自引：0，他引：1  

Liu Zhong  Jacques M. Beckers 《Solar physics》2001,198(1):197-209

Starting November 1999 we are carrying out simultaneous seeing observations with the Solar Differential Image Motion Monitor (S-DIMM) at the Fuxian Lake station of the Yunnan Observatory and a solar scintillometer of the type used in the recent site survey by one of us (Beckers et al., 1997). The purpose was to compare the two methods of assessing the daytime atmospheric seeing for a lake site. We report here the first results of this comparison. We find that the relation between the seeing as measured by the S-DIMM (the Fried parameter r ₀) and the scintillation in the solar irradiance (_I) differs greatly from the relation found by Seykora (1993) for NSO/Sac Peak. We conclude that the _I measurements give a good indication for the amount of near-Earth seeing but that they are a poor proxy for the total atmospheric seeing. We interpret the simultaneous (r ₀, _I) observations in terms of an atmospheric seeing model and find good quantitative agreement with a model in which a fraction () of the seeing originated near the Earth (ground or water) and the rest (1–) originates at higher layers. For lake sites is small all day and the seeing is determined primarily by the refractive index variations at higher atmospheric layers. For land sites is small in the early morning but rapidly increases as the day progresses, near-Earth seeing dominating there most of the time.  相似文献   

Fault propagation and climatic control of sedimentation on the Ghoubbet Rift Floor: insights from the Tadjouraden cruise in the western Gulf of Aden     

L. Audin  I. Manighetti  P. Tapponnier  F. Métivier  E. Jacques  P. Huchon 《Geophysical Journal International》2001,144(2):391-413

A detailed geophysical survey of the Ghoubbet Al Kharab (Djibouti) clarifies the small-scale morphology of the last submerged rift segment of the propagating Aden ridge before it enters the Afar depression. The bathymetry reveals a system of antithetic normal faults striking N130°E, roughly aligned with those active along the Asal rift. The 3.5 kHz sub-bottom profiler shows how the faults cut distinct layers within the recent, up to 60 m thick, sediment cover on the floor of the basin. A large volcanic structure, in the centre of the basin, the 'Ghoubbet' volcano, separates two sedimentary flats. The organization of volcanism and the planform of faulting, with en echelon subrifts along the entire Asal–Ghoubbet rift, appear to confirm the westward propagation of this segment of the plate boundary. Faults throughout the rift have been active continuously for the last 8400 yr, but certain sediment layers show different offsets. The varying offsets of these layers, dated from cores previously retrieved in the southern basin, imply Holocene vertical slip rates of 0.3–1.4 mm yr⁻¹ and indicate a major decrease in sedimentation rate after about 6000 yr BP, and a redistribution of sediments in the deepest troughs during the period that preceded that change.  相似文献   

Routine Analyses of Trace Elements in Geological Samples using Flow Injection and Low Pressure On-Line Liquid Chromatography Coupled to ICP-MS: A Study of Geochemical Reference Materials BR, DR-N, UB-N, AN-G and GH   总被引：6，自引：0，他引：6  

Jean Carignan  Pascal Hild  Guy Mevelle  Jacques Morel  Delphine Yeghicheyan 《Geostandards and Geoanalytical Research》2001,25(2-3):187-198

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One-station estimates of seismic moments from the mantle magnitudeM m: The case of the regional field (1.5°≤Δ≤15°)     

Jacques Talandier  Emile A. Okal 《Pure and Applied Geophysics》1992,138(1):43-60

We extend to the regional field of distances the procedure of one-station estimation of seismic moments using the mantle magnitudeM _m, as introduced earlier in the case of teleseismic events. A theoretical analysis of the validity of the asymptotic expansion of normal modes in terms of surface waves, which was used in the development ofM _m, upholds the validity of the algorithm for distances as short as 1.5°. This is confirmed by the analysis of a dataset of 149 GEOSCOPE records obtained at distances ranging from 1.5 to 15°, from earthquakes with moments between 10²⁴ and 2.5×10²⁷ dyn-cm. The performance ofM _m as measured in terms of average residual with respect to published values ofM ₀, and standard deviation of the residuals, is not degraded in this distance range, with respect to the teleseismic case. This indicates that the mantle magnitudeM _mcan be reliably used at regional distances, notably for tsunami warning applications.  相似文献   

Volcanism and uranium mineralizations: the concept of source rock and concentration mechanism   总被引：1，自引：0，他引：1  

Jacques L. Leroy  Brigitte George-Aniel 《Journal of Volcanology and Geothermal Research》1992,50(3)

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