Georges Benko  Ulf Strohmayer 《GeoJournal》1993,31(4):467

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Book review     

John C. Davis  David B. Kitts  Georges Verly 《Mathematical Geology》1992,24(5):577-586

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Normalisation des systèmes linéaires canoniques et application au problème restreint des trois corps     

Jacques Roels  Georges Louterman 《Celestial Mechanics and Dynamical Astronomy》1970,3(1):129-140

An algorithm is given for normalizing conservative linear Hamiltonian systems. This one generalizes Siegel's method to the cases where the eigenvalues are multiple. We obtain by a canonical transformation a normal form of two blocks, one of which is the upper Jordan form, and the other, the lower Jordan form. We select real solutions from the solutions of these equations, and we apply the result to the restricted three body problem in the vicinity of the triangular points for Routh's critical mass ratio.

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_n est la matrice unité d'ordren,O _n est la matrice nulle d'ordren.  相似文献   

Geology and geochemistry of the Changba SEDEX Pb-Zn deposit,Qinling orogenic belt,China   总被引：8，自引：0，他引：8  

Guoliang?Ma  Georges?BeaudoinEmail author  Sijing?Qi  Ying?Li 《Mineralium Deposita》2004,39(3):380-395

The Changba Pb-Zn SEDEX deposit occurs in the Middle Devonian sequence of the Anjiaca Formation of the Western Qinling Hercynian Orogen in the Gansu Province, China. The Changba-II orebody is hosted in biotite quartz schist and is the largest of 143 stratiform orebodies that are hosted either in biotite quartz schist or marble. The Changba-II comprises two types of mineralization: a bedded facies and an underlying breccia lens. The bedded section exhibits three sulfide sub-facies zoned from bottom to top: 1) banded sphalerite intercalated with quartz albitite; 2) interbedded massive pyrite and sphalerite ore; and 3) banded sphalerite ore intercalated with banded baritite. Major metallic minerals are sphalerite, pyrite, galena, with minor arsenopyrite, pyrrhotite, boulangerite, and rare chalcopyrite. The bedded sulfides are underlain by a lens of brecciated and albitized biotite-quartz schists cemented by sulfides and tourmaline.Massive and bedded sulfide ³⁴S values range from 8.1 to 29.3, whereas barite ³⁴S values range from 20.8 to 31.5. Disseminated pyrite in footwall schists has ³⁴S values ranging from 8.1 to 10.6, and increase to values ranging from 11.1 to 14.7 in the hangingwall. The lower ³⁴S values for massive and bedded sulfides are interpreted to be derived from progressive bacterial sulfate reduction (BSR) of Devonian seawater in a sulfate-restricted sub-basin. The higher ³⁴S values for massive and bedded sulfides could be a product of quantitative BSR but this is incompatible with barite being more abundant above the bedded sulfides. Instead, it is more likely that thermochemical sulfate reduction of seawater sulfate or of evaporite was the source of heavy hydrothermal sulfur. Heavy hydrothermal sulfur was injected into a sulfate-restricted sub-basin where it mixed with low ³⁴S BSR sulfide to form the massive and bedded sulfides. The REE patterns of sulfide layers and associated quartz albitite and baritite are similar to those of the host biotite quartz schists, suggesting that the hydrothermal fluids leached REE from the underlying rocks. Pb isotope ratios in galena form an array between the Upper Crust and the Mantle reservoir curves, which indicates that the lead is derived from upper crustal rocks comprising mafic igneous units. The Sr⁸⁷/Sr⁸⁶ ratio of 0.7101 for carbonate within the sulfide layers also suggests that Sr is derived from the mixing of Sr leached from upper crustal rocks with Middle Devonian seawater Sr. A Rb-Sr isochron age of 389.4 ± 6.4 Ma for sulfide layers and the interbedded hydrothermal sediments is consistent with the age of host Mid-Devonian strata. Ar³⁹/Ar⁴⁰ plateau age at 352.8 ± 3.5 Ma and Ar³⁹-Ar⁴⁰ isochron age of 346.6 ± 6.4 Ma for albite in the quartz albitite intercalated with sulfide layers indicate either albite formation after the sulfides or thermal resetting of the Rb-Sr system at about 350 Ma, the age of collision between the North China and Yangtze cratons.Editorial handling: E. Frimmel  相似文献   

Lander radioscience for obtaining the rotation and orientation of Mars     

Veronique Dehant  William Folkner  Etienne Renotte  Daniel Orban  Sami Asmar  Georges Balmino  Jean-Pierre Barriot  Jeremy Benoist  Richard Biancale  Jens Biele  Frank Budnik  Stefaan Burger  Olivier de Viron  Bernd Häusler  Özgur Karatekin  Sébastien Le Maistre  Philippe Lognonné  Michel Menvielle  Michel Mitrovic  Martin Pätzold  Marie Yseboodt 《Planetary and Space Science》2009,57(8-9):1050-1067

The paper presents the concept, the objectives, the approach used, and the expected performances and accuracies of a radioscience experiment based on a radio link between the Earth and the surface of Mars. This experiment involves radioscience equipment installed on a lander at the surface of Mars. The experiment with the generic name lander radioscience (LaRa) consists of an X-band transponder that has been designed to obtain, over at least one Martian year, two-way Doppler measurements from the radio link between the ExoMars lander and the Earth (ExoMars is an ESA mission to Mars due to launch in 2013). These Doppler measurements will be used to obtain Mars’ orientation in space and rotation (precession and nutations, and length-of-day variations). More specifically, the relative position of the lander on the surface of Mars with respect to the Earth ground stations allows reconstructing Mars’ time varying orientation and rotation in space.Precession will be determined with an accuracy better by a factor of 4 (better than the 0.1% level) with respect to the present-day accuracy after only a few months at the Martian surface. This precession determination will, in turn, improve the determination of the moment of inertia of the whole planet (mantle plus core) and the radius of the core: for a specific interior composition or even for a range of possible compositions, the core radius is expected to be determined with a precision decreasing to a few tens of kilometers.A fairly precise measurement of variations in the orientation of Mars’ spin axis will enable, in addition to the determination of the moment of inertia of the core, an even better determination of the size of the core via the core resonance in the nutation amplitudes. When the core is liquid, the free core nutation (FCN) resonance induces a change in the nutation amplitudes, with respect to their values for a solid planet, at the percent level in the large semi-annual prograde nutation amplitude and even more (a few percent, a few tens of percent or more, depending on the FCN period) for the retrograde ter-annual nutation amplitude. The resonance amplification depends on the size, moment of inertia, and flattening of the core. For a large core, the amplification can be very large, ensuring the detection of the FCN, and determination of the core moment of inertia.The measurement of variations in Mars’ rotation also determines variations of the angular momentum due to seasonal mass transfer between the atmosphere and ice caps. Observations even for a short period of 180 days at the surface of Mars will decrease the uncertainty by a factor of two with respect to the present knowledge of these quantities (at the 10% level).The ultimate objectives of the proposed experiment are to obtain information on Mars’ interior and on the sublimation/condensation of CO₂ in Mars’ atmosphere. Improved knowledge of the interior will help us to better understand the formation and evolution of Mars. Improved knowledge of the CO₂ sublimation/condensation cycle will enable better understanding of the circulation and dynamics of Mars’ atmosphere.  相似文献   

Behaviour of REE and mass balance calculations in a lateritic profile over chlorite schists in South Cameroon     

Veronique Kamgang Kabeyene Beyala  Estelle Ndome Effoudou Priso  Georges Emmanuel Ekodeck 《Chemie der Erde / Geochemistry》2009,69(1):61-13

An in situ weathering profile overlying chlorite schists in the Mbalmayo-Bengbis formations (South Cameroon) was chosen for the study of the behaviour of REE and the evaluation of geochemical mass balance. After physical and mineralogical studies, the chlorite schists and the undisturbed weathered materials were chemically analyzed for major elements (X-ray fluorescence and titrimetry) and REE (ICP-MS). The behaviour of the REE in the Mbalmayo weathering system was established in comparison with the REE of the reference parent rock. Mass balance calculations were applied to both major elements and REE. The mineralogy of the materials was determined with the aid of a Philips 1720, diffractometer. The chlorite schists of the Mbalmayo sector show low REE contents (Σ=153.44 ppm). These rocks are relatively rich in LREE (about 125 times the chondritic value) and relatively poor in HREE (about 20 times the chondritic value). The REE diagram normalized to chondrites shows a slightly split graph ((La/Yb)_N=6.18) with marked enrichment in LREE (LREE/HREE=9.50) in relation to HREE. Moreover, these spectra do not present any Ce anomaly, but a slightly positive Eu anomaly. The imperfectly evolved profile, whose materials are genetically linked, shows an atypical behaviour of REE. In effect, the LREE are more mobile than the HREE during weathering ((La/Yb)NASC<1) with weak Ce anomalies. This has been rarely reported in lateritic profiles characterized by higher HREE mobility than LREE during weathering processes with high Ce anomalies. This is either due to the difference in the stability of REE-bearing minerals, or to the weak acidic to basic pH conditions (6.70<pH<7.80), or even due to the average evolution of the weathering materials. The pathway of the REE along the profile is as follows: (1) leaching in the saprolites and summit of the profile, except for Ce, which precipitates very weakly in the nodular materials and the coarse saprolite materials, (2) at the base of the profile, solutions come in contact with chlorite schist formations, at this level, the pH increases (pH=7.79), HREE and a part of LREE partially void of Ce precipitate and (3) the other part of LREE precipitates further up in the profile. The geochemical mass balance calculations reveal that these elements are leached in the same phases as the relatively high Si, Al, K and Fe²⁺ contents.  相似文献   

Arsenite sequestration at the surface of nano-Fe(OH)₂, ferrous-carbonate hydroxide, and green-rust after bioreduction of arsenic-sorbed lepidocrocite by Shewanella putrefaciens     

Georges Ona-Nguema  Guillaume Morin  Yuheng Wang  Farid Juillot  Giuliana Aquilanti  Christian Ruby  François Guyot  Gordon E. Brown Jr. 《Geochimica et cosmochimica acta》2009,73(5):1359-1446

X-ray Absorption Fine Structure (XAFS) spectroscopy was used in combination with high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), X-ray energy dispersive spectroscopy (XEDS), X-ray powder diffraction, and Mössbauer spectroscopy to obtain detailed information on arsenic and iron speciation in the products of anaerobic reduction of pure and As(V)- or As(III)-adsorbed lepidocrocite (γ-FeOOH) by Shewanella putrefaciens ATCC 12099. We found that this strain of S. putrefaciens is capable of using Fe(III) in lepidocrocite and As(V) in solution or adsorbed on lepidocrocite surfaces as electron acceptors. Bioreduction of lepidocrocite in the absence of arsenic resulted in the formation of hydroxycarbonate green rust 1 [Fe^II₄Fe^III₂(OH)₁₂CO₃: GR1(CO₃)], which completely converted into ferrous-carbonate hydroxide (Fe^II₂(OH)₂CO₃: FCH) over nine months. This study thus provides the first evidence of bacterial reduction of stoichiometric GR1(CO₃) into FCH. Bioreduction of As(III)-adsorbed lepidocrocite also led to the formation of GR1(CO₃) prior to formation of FCH, but the presence of As(III) slows down this transformation, leading to the co-occurrence of both phases after 22-month of aging. At the end of this experiment, As(III) was found to be adsorbed on the surfaces of GR1(CO₃) and FCH. After five months, bioreduction of As(V)-bearing lepidocrocite led directly to the formation of FCH in association with nanometer-sized particles of a minor As-rich Fe(OH)₂ phase, with no evidence for green rust formation. In this five-month experiment, As(V) was fully converted to As(III), which was dominantly sorbed at the surface of the Fe(OH)₂ nanoparticles as oligomers binding to the edges of Fe(OH)₆ octahedra at the edges of the octahedral layers of Fe(OH)₂. These multinuclear As(III) surface complexes are characterized by As-As pairs at a distance of 3.32 ± 0.02 Å and by As-Fe pairs at a distance of 3.50 ± 0.02 Å and represent a new type of As(III) surface complex. Chemical analyses show that the majority of As(III) produced in the experiments with As present is associated with iron-bearing hydroxycarbonate or hydroxide solids, reinforcing the idea that, at least under some circumstances, bacterial reduction can promote As(III) sequestration instead of mobilizing it into solution.  相似文献   

An overview of Mediterranean Ridge collisional accretionary complex as deduced from multichannel seismic data     

J. Mascle  E. Chaumillon 《Geo-Marine Letters》1998,18(2):81-89

 The Mediterranean Ridge (eastern Mediterranean) is a large accretionary complex that results from the Africa–Europe–Aegean plates convergence. Multichannel seismic data, combined with previous results showed that the ridge comprises distinct major structural domains facing different forelands: (1) An outer domain is bounded to the south by the ridge toe. Underneath the Ionian and Levantine outer Ridge, Messinian evaporites act as a major decollement level. (2) An axial, or crestal, ridge domain with mud diapiric and mud volcano activity is bounded to the north by backthrust. (3) A less tectonized inner Ridge domain, possibly a series of former forearc basins, abuts the Hellenic Trench. The ridge displays strong along-strike variations. These variations can be interpreted as consequences of an ongoing collision against the Libyan continental promontory.  相似文献   

Presumed magnetic biosignatures observed in magnetite derived from abiotic reductive alteration of nanogoethite     

Jessica L. Till  Yohan Guyodo  France Lagroix  Guillaume Morin  Nicolas Menguy  Georges Ona-Nguema 《Comptes Rendus Geoscience》2017,349(2):63-70

The oriented chains of nanoscale Fe-oxide particles produced by magnetotactic bacteria are a striking example of biomineralization. Several distinguishing features of magnetite particles that comprise bacterial magnetosomes have been proposed to collectively constitute a biosignature of magnetotactic bacteria (Thomas-Keprta et al., 2001). These features include high crystallinity, chemical purity, a single-domain magnetic structure, well-defined crystal morphology, and arrangement of particles in chain structures. Here, we show that magnetite derived from the inorganic breakdown of nanocrystalline goethite exhibits magnetic properties and morphologies remarkably similar to those of biogenic magnetite from magnetosomes. During heating in reducing conditions, oriented nanogoethite aggregates undergo dehydroxylation and transform into stoichiometric magnetite. We demonstrate that highly crystalline single-domain magnetite with euhedral grain morphologies produced abiogenically from goethite meets several of the biogenicity criteria commonly used for the identi?cation of magnetofossils. Furthermore, the suboxic conditions necessary for magnetofossil preservation in sediments are conducive to the reductive alteration of nanogoethite, as well as the preservation of detrital magnetite originally formed from goethite. The findings of this study have potential implications for the identification of biogenic magnetite, particularly in older sediments where diagenesis commonly disrupts the chain structure of magnetosomes. Our results indicate that isolated magnetofossils cannot be positively distinguished from inorganic magnetite on the basis of their magnetic properties and morphology, and that intact chain structures remain the only reliable distinguishing feature of fossil magnetosomes.  相似文献   

Collocation resolution of the oceanic geoid based on satellite altimetry     

Georges Blaha  Robert P. Bessette  George Hadgigeorge 《Marine Geodesy》2013,36(2):131-168

The approach presented is directed toward a specific adaptation of the least‐squares collocation with noise, yielding smooth predictions of geophysical quantities. The smoothing corresponds here to a truncated gravity field equivalent to an (n’, n') spherical‐harmonic expansion. This is reflected in the truncation, at the degree n‘, of the pertinent covariance and cross‐covariance functions in most (but not all) instances. The smooth predictions of geophysical quantities, made in an equilateral grid corresponding to the truncation degree n‘, serve in constructing contour maps after having been densified for the needs of a contour routine. Such a densification is carried out efficiently via errorless collocation with the degree truncation n‘ throughout. Consistent with this procedure, “residuals” at observation points (i.e., discrepancies between the contour map and the data) are computed using the same algorithm. The complete collocation approach is utilized for a 2° resolution of the earth's gravity field with emphasis on the oceanic geoid, based on the residuals from a global spherical‐harmonic adjustment of SEASAT altimetry. The presented results include contour maps of geoid undulations and gravity anomalies. They are compared to the results of a point‐mass adjustment, another technique based on the spherical‐harmonic adjustment. The agreement between these two techniques is found to be excellent.  相似文献