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41.
The polarimetric survey of electrons in the K-corona initiated at Pic-du-Midi and Meudon Observatories in 1964 now covers a full solar cycle of activity. The measurements are photometrically calibrated in an absolute scale.In June 1967 a persistent coronal feature was fan-shaped as a lame coronale above quiescent prominences. We deduce an electron density of N
0 = 1.5 × 108 at 60 000 km above the photosphere, a total number of 14 × 1039 electrons, a hydrostatic temperature of 1.7 × 106 K, and a total thermal energy 3N
eKT = 1.0 × 1031 ergs. When a center of activity appeared, a major localized condensation developed to replace the old elongated feature, with N
0 = 4.5 × 108, a total of 4.5 × 1039 electrons and the same temperature of 1.7 × 106 K.Also, a fan-shaped feature of exceptional intensity was analysed on 8 September 1966, with N
0 = 6 × 108 and a total of 24 × 1039 electrons.Fan-shaped features are frequent above quiescent prominences. They degenerate above a height of 2R
into thinner isolated columns or blades with temperatures also around 1.7 × 106 K. 相似文献
42.
J. P. De Grève 《Astrophysics and Space Science》1982,84(2):447-456
The remaining core hydrogen burning lifetime after case B of mass transfer of the secondary (mass gaining) component in a medium mass close binary star is estimated, for mediummass binaries with primaries in the mass range 5M
to 9M
. From the comparison of this quantity with the helium burning time-scale of the remnant primary a critical mass ratioq
c is derived such that for larger values ofq, mass transfer from the secondary towards the primary starts before the latter has evolved into a white dwarf. Consequences for the advanced stages of medium mass binaries are discussed. 相似文献
43.
The results of evolutionary computations for massive binary systems (initial masses of the primary 10M
) with mass ratios between 0.3 and 0.8 are summarized and compared with observations in order to verify how far one can go with the conservative assumption of mass exchange. It is found that conservative mass exchange leads to acceptable first-order models of W-R and massive X-ray binaries. However, the comparison between this theory and observation reveals that for the observed systems (W-R and X-ray binaries) a preference exists for low intial mass ratios; moreover, the X-ray luminosities of the theoretical models are systematically too low, though this may be due to the adopted wind model. In addition, the influences of several parameters (distance between the components, chemical composition, primary mass, mass ratio and atmosphere) are examined. These parameters influence the remnant mass and any further evolution only marginally. Attention is also given to the effect on the system parameters of a supernova explosion of the remnant of the mass-losing component. For a large range of systems a disruption probability smaller than 25% is found. 相似文献
44.
Jacques Boulègue 《Geochimica et cosmochimica acta》1978,42(9):1439-1445
Careful measurements of rest potentials of platinum electrodes (Eh) in the H2S-H2O system were made together with measurements of the pH and the potentials of Ag-Ag2S electrodes (Es2?). The potentials of the platinum electrode are characteristic of H2S chemisorption followed by H2S discharge on the platinum. The relations between Eh, Es2? and pH are characteristic of the H2S-H2O system and of the hydrogen sulfide concentration. Thus these parameters can be employed to distinguish H2S-H2O systems from H2S-S8-H2O systems. Field measurements on hot sulfurous springs are in agreement with laboratory data. 相似文献
45.
Yves Goddéris Louis M. François Jacques Schott David Labat 《Geochimica et cosmochimica acta》2006,70(5):1128-1147
A numerical model of chemical weathering in soil horizons and underlying bedrock (WITCH) has been coupled to a numerical model of water and carbon cycles in forest ecosystems (ASPECTS) to simulate the concentration of major species within the soil horizons and the stream of the Strengbach granitic watershed, located in the Vosges Mountains (France). For the first time, simulations of solute concentrations in soil layers and in the catchment river have been performed on a seasonal basis. The model is able to reproduce the concentrations of most major species within the soil horizons, as well as catching the first-order seasonal fluctuations of aqueous calcium, magnesium and silica concentrations. However, the WITCH model underestimates concentrations of Mg2+ and silica at the spring of the catchment stream, and significantly underestimates Ca2+ concentration. The deficit in calculated calcium can be compensated for by dissolution of trace apatite disseminated in the bedrock. However, the resulting increased Ca2+ release yields important smectite precipitation in the deepest model layer (in contact with the bedrock) and subsequent removal of large amount of silica and magnesium from solution. In contrast, the model accurately accounts for the concentrations of major species (Ca, Mg and silica) measured in the catchment stream when precipitation of clay minerals is not allowed. The model underestimation of Mg2+ and H4SiO4 concentrations when precipitation of well crystallized smectites is allowed strongly suggests that precipitation of well crystallized clay minerals is overestimated and that more soluble poorly crystallized and amorphous materials may be forming. In agreement with observations on other watersheds draining granitic rocks, this study indicates that highly soluble trace calcic phases control the aqueous calcium budget in the Strengbach watershed. 相似文献
46.
In order to better understand condensation processes that took place in the solar nebula and to evaluate the effect of kinetics on the condensed matter, we have built an experimental apparatus for studying condensation of multi-elemental refractory gases at high-temperature and low-pressure. The condensation of a Mg-Si-rich gas, with solar interelement ratios of Ca, Al, Mg and Si, and of a Ca-Al-rich gas under a total pressure of ∼4 × 10−3 bar at temperatures from 1045 to 1285 °C and for run times of 4-60 min results in direct formation of crystalline oxides or silicates such as corundum, spinel, anorthite, melilite, Al-diopside, forsterite and enstatite. The mineralogy of the condensates, close to that predicted at equilibrium, varies with the duration of an experiment and the temperature of condensation. The chemical reactions between gas and condensates are rapid enough to attain a steady state in less than one hour. The condensation results in chemical fractionation of the gas, i.e. a depletion of the gas in refractory elements at high temperature. Finally, besides revealing the textures of refractory crystals, which condense from a gas of complex chemical composition, this study shows that certain phases, such as spinel, have favored kinetics of condensation. Our experimental results confirm that refractory inclusions in primitive meteorites could have formed by condensation from a hot nebular gas. Similarly, we confirm that crystalline grains can condense at high temperature in the outflows of evolved stars. In both cases, our results indicate that kinetic processes certainly influence grain mineralogy. Kinetic processes must thus be taken into account in modeling the pressure-temperature conditions of circumstellar environments. 相似文献
47.
H. Thveniaut C. Delor J.M. Lafon P. Moni P. Rossi D. Lahondre 《Precambrian Research》2006,150(3-4):221-256
We present a comprehensive paleomagnetic study on Paleoproterozoic (2173–2060 Ma) plutonic and metamorphic rocks from French Guiana, representative of the full range of the main Transamazonian tectonothermal steps. Twenty-seven groups of directions and poles were obtained from combination of 102 sites (613 samples) based on age constraint, similar lithology and/or geographical proximity. Paleomagnetic results show variations between rocks of different ages which are supposed to be characteristic of magnetizations acquired during uplift and cooling of successive plutonic pulses and metamorphic phases. This is also reinforced by positive field tests (baked contact and reversal tests). Recent U/Pb and Pb/Pb on zircon and complementary 40Ar/39Ar on amphibole and biotite allow questioning the problem of magnetic ages relative to rock formation ages. Estimated magnetic ages, based on amphibole dating as a proxy, enable us to construct a Guiana Shield apparent polar wander path for the 2155–1970 Ma period. It is also possible to present paleolatidudinal evolution and continental drift rates related to specific Transamazonian tectonic regimes.French Guiana and probably the Guiana Shield were located at the Equator from ca. 2155 to 2130 Ma during the Meso-Rhyacian D1 magmatic accretion phase, related to subduction of Eorhyacian oceanic crust. After closure of the Eorhyacian Ocean and collision of West African and Amazonian plates, the Guiana Shield moved. The first evolution towards 60° latitude, occurs after 2080 Ma, during the Neorhyacian D2a post collisional sinistral transcurrent phase. During the Late Rhyacian D2b phase, up to 2050 Ma, the Guiana Shield reaches the pole and starts to move to lower latitudes on an opposite meridian. By the Orosirian D2c phase, from ca. 2050 to 1970 Ma, the Guiana Shield reaches the Equator.Based on the amphibole 40Ar/39Ar dates, we estimate the continental drift between 12 and 16 cm/y for the Meso to Late Rhyacian period followed by a lower rate between 9 and 14 cm/y up to Orosirian time. This study highlights rock ages and magnetic ages are prerequisite to any continental reconstruction especially when it is shown continental drift is important for a 100–200 Ma time period. Our results confirm the possibility of APWP construction on Paleoproterozoic plutonic rocks but suggest improvement will rely on the combination with multidisciplinary approaches such as structural geology and multi-method radiometric dating. 相似文献
48.
The Kelçyra area is emplaced in a foreland fold-and-thrust belt (FFTB), characterized by a westward thrusting with the Triassic evaporites as the major décollement level. Several secondary features related with this evolution, like backthrusting, folding, duplex structures, evaporite diapirism are present. During the FFTB evolution, the study area has been subjected to several fracturing events with associated stages of fluid migration. During the pre-deformational stage, complex textures such as crack-and-seal features most likely reflect expulsion of overpressured fluids. These fluids were dominantly host-rock buffered. Within the post-deformational stage, a meteoric fluid caused cementation and development of a karst network during a period of emergence after the thrust emplacement. Subsequently, Mg calcite reprecipitated in the more stable carbonate phase calcite and dolomite, which filled part of the karts network. The latter is finally dedolomitized and locally partially dissolved by a second meteoric fluid flow, which greatly increased the secondary porosity. 相似文献
49.
Bérengère Laslandes Florence Sylvestre Abdelfettah Sifeddine Bruno Turcq Ana Luiza S. Albuquerque Jorge Abrão 《Comptes Rendus Geoscience》2006,338(10):667-675
This study concerns a core collected in Brejo do Espinho's lagoon from Cabo Frio littoral (Brazil) submitted to dry influence of local upwelling controlled by north-east trade winds from the South Atlantic and particularly strengthened during El Niño events. Diatoms study supported by sedimentological and isotopic analyses shows dry phases infrequent before 4000 yr, a highly variable climatic phase between 3600 and 2900 yr and from 2400 yr onward a dryness enhancement. To cite this article: B. Laslandes et al., C. R. Geoscience 338 (2006). 相似文献
50.
A framework for an optimised groundwater monitoring network and aggregated indicators 总被引:1,自引:0,他引:1
The implementation of the Water Framework Directive (EU 2000) requires a groundwater quality monitoring. It is used for characterisation of the ‘good’ chemical status of each groundwater body and for the restoration or protection purposes of those bodies already at ‘good’ status. Interpretative aspects are lying in the design of monitoring network and in the way of building global indicators. Attention is given here to the global chemical status of the groundwater bodies and to the role of diffuse pollution, much of which is brought via groundwater to surface water. Monitoring ‘local’ pollution associated with individual sites is not addressed. Groundwater bodies with different contrasted hydrogeology conditions, land use and topography have been considered to establish an approach for choosing an optimised monitoring network. Then, a quality assessment system has been developed and applied for qualifying the general status of each groundwater body. The use of non-dimensional indexes allows us to process with all kinds of chemical parameters in a normalised way and, by means of adequate aggregation rules, to qualify the general quality status of a groundwater body. The obtained diagnostic, even if not fully validated, is closely linked to the pragmatic objectives contained in the EU Water Directive. 相似文献