The hydrogen balmer lines and the structure of the quiet solar chromosphere     

Pierre Mein  Nicole Mein 《Solar physics》1975,40(2):317-328

Spectra of Hα, Hβ and Hδ have been taken under good seeing conditions with the vacuum tower telescope of Sacramento Peak Observatory. Intensity curves are given at various wavelengths in these lines to permit further comparison with a theoretical model. Moreover, considering in each case the range of height in which the lines are almost optically thin and using a few approximations, the following results are derived: between 2000 and 6000 km above the limb the average thermal + turbulent velocity of the atoms is found to increase from 20 km s^?1 to 30 km s^?1 and the mean number of hydrogen atoms per cm³ in level 2 is given by $$\log n_2 {\text{ = }}4.5{\text{ }} - {\text{ 0}}{\text{.00056(}}z - 2000)$$ z being the altitude above the limb in km. For line profile computations a new interpolation formula is presented; it gives good profiles with a small number of scans, saving microphotometer time.  相似文献   

Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)     

Vinciane Debaille  Dominique Weis  Pierre Schiano 《Geochimica et cosmochimica acta》2006,70(3):723-741

Many studies have argued for the contribution of at least three components, namely the mantle wedge, the subducted oceanic crust, and its sediment cover, to describe the geochemistry of island arc volcanics. However, isotope correlations reflecting a simple binary mixing can be observed at the scale of a single arc island or volcano. Here we investigate the possibility that these trends reflect pseudo-binary mixing relationships in a three-component system. We present a simplified, two-stage model for the systematic isotope modelling of a cogenetic suite of arc lavas. This includes metasomatism of portions of the mantle wedge by hydrous phases released from the down-going oceanic crust, and sediments, followed by progressive mixing and melting. A consequence of this model is that it leads to a two end-member mixing process from the mantle wedge, oceanic crust, and sediment components. To solve the model we reduce it to a step-by-step procedure combined with a Monte-Carlo simulation. The procedure consists of: (i) producing a large number of random values on each variable of the model; (ii) using the computed values to calculate the isotopic compositions of lavas; and (iii) comparing the obtained isotopic compositions with measured data. Applied to a new set of Sr, Nd, and Pb isotope data for volcanics (basalts, basaltic andesites, trachybasalts, and basaltic trachyandesites) from Merapi volcano (Java island, Sunda arc), the model successfully reproduces the binary mixing relationships previously documented for the medium-K and high-K lava series from this volcano, thus giving further support to the hypothesis that this distinction is inherited from the primary magmas and primarily reflects a property of the mantle source. The results allow identification of a set of numerical values for bulk partition coefficients (solid/hydrous fluid, and solid/H₂O-rich melt) and variables (e.g., the mass ratio between the metasomatizing phase and the mantle wedge), which can be used for quantitative arc-lava petrogenetic calculations. They also require a direct relationship between dehydration of the slab and melting of the metasomatized mantle wedge. Finally, our evaluation shows that for isotope modelling of the Merapi lavas, the two-stage procedure is controlled more by the considered source components (mantle wedge, oceanic crust, sediments, and their derivatives) than by the various processes involved (dehydration, melting, and mixing).  相似文献   

Response to the Comment by G. Druschel and M. Borda on “Pyrite dissolution in acidic media”     

Michael Descostes  Pierre Vitorge 《Geochimica et cosmochimica acta》2006,70(20):5251-5252

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Comment on “The Moroccan Hercynides” by Hoepffner et al. (Journal of African Earth Sciences, vol. 43, pp. 144–165)     

Martin Roddaz  Jean-Claude Soula  Mohamed Ben Abbou  Stphane Brusset  Pierre Debat  Ahmed Ntarmouchant  Youssef Driouch  Didier Bziat 《Journal of African Earth Sciences》2006,45(4-5):515-517

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Review: Microbial biocenoses in pristine aquifers and an assessment of investigative methods   总被引：2，自引：6，他引：2  

Nico Goldscheider  Daniel Hunkeler  Pierre Rossi 《Hydrogeology Journal》2006,14(6):926-941

The current knowledge of microbial biocenoses (communities) in pristine aquifers is presented in a review, which also discusses their relevance for questions of groundwater protection. Aquifers are heterogeneous on all scales and structured in a variety of habitats. The void spaces in many aquifers are small. The biocenoses are thus predominantly composed of microorganisms and, often, microinvertebrates. Larger voids and macroorganisms occur in karst cavities. Due to the absence of light, the biocenoses depend on chemical energy resources, which are, however, scarce in non-contaminated groundwater. The microorganisms thus show small cell sizes, low population densities and reduced activity; they developed specific strategies to survive oligotrophic conditions. The review also discusses the impact of contamination on the biocenoses, and the potential use of the biocenoses or specific organisms as indicators for groundwater quality, and the limits of this approach. Bacteria are either planktonic or attached to aquifer material, which requires both fluid and solid phase sampling. Most groundwater bacteria are viable but non-culturable. Consequently, cultivation techniques give an incomplete picture of the biocenoses, while methods from molecular microbiology provide genetic fingerprints of the entire community. Different analytical methods are available to count microorganisms, identify species, characterise microbial diversity, and measure activity.  相似文献   

Mathematical modelling is a necessary step in biology and in environmental sciences     

Pierre Auger  Jean-Christophe Poggiale 《Comptes Rendus Geoscience》2006,338(4):223-224

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Atténuation de l'intensité macrosismique pour la France métropolitaine : importance de l'intensité épicentrale     

Pierre Arroucau  Antoine Mocquet  Pierre Vacher 《Comptes Rendus Geoscience》2006,338(9):596-605

The main result of this work is to show that macroseismic intensity decay with distance strongly depends on the epicentral intensity. An attenuation law that takes this parameter into account is proposed for Metropolitan France, from the analysis of SISFRANCE macroseismic database. Such a model significantly reduces the difference between observed and theoretical intensities. A map of the attenuation variations is also set up for Metropolitan France. No major site effects are observed, but at a broad scale, young Alpine regions display a stronger attenuation than old Hercynian regions. To cite this article: P. Arroucau et al., C. R. Geoscience 338 (2006).  相似文献   

Variscan to eo-Alpine events recorded in European lower-crust zircons sampled from the French Massif Central and Corsica, France     

Philippe Rossi  Alain Cocherie  C. Mark Fanning  tienne Deloule 《Lithos》2006,87(3-4):235-260

Ion-microprobe U–Pb zircon dating of lower-crust metasedimentary granulite are reported on samples from two localities in Europe in order to determine (a) how this environment recorded the Variscan and eo-Alpine events, and (b) whether the transition between the two orogenic cycles was continuous or separated by a gap. The samples come from enclaves hosted by Miocene volcanoes at Bournac in the French Massif Central, and from the granulitic metasedimentary basement of the Alpine Santa Lucia nappe in Corsica, on the South European paleomargin of the Ligurian branch of the Tethys Sea. The zircon ages from Bournac range between 630 and 430 Ma and between 380 and 150 Ma with a major frequency peak at 285 Ma; the zircons older than 430 Ma are interpreted as detrital, whereas those younger than 380 Ma are considered to have formed by metamorphic processes after burial in the lower crust. Zircon ages from Santa Lucia range from to 356 to 157 Ma, with exception of one inherited Archean grain, and are interpreted like the younger Bournac zircons as having been formed by metamorphic processes.

In a granulite metamorphic environment, as opposed to an anatectic environment, new zircon growth can occur in the solid state. Once Zr has been incorporated into zircon, however, it is difficult to remobilize without dissolution; thus Zr available for new zircon growth must result from the breakdown of Zr-bearing minerals during prograde and/or retrograde events. In this light, the U–Pb zircon-age probability curves are interpreted as markers for major tectonometamorphic events, as suggested by the close correspondence between peaks in the curve and geological events recorded in the upper-crust, such as magma emplacement and basin subsidence.

Evidence of a tectonometamorphic gap between the Variscan and Alpine orogeneses is provided by the Santa Lucia zircon-age probability curve, which reveals a probable interlude during the Variscan–Alpine transition between 240 and 210 Ma. Here, the peak at 240 Ma is interpreted as the very beginning of crustal extension and the low at 210 Ma as a period of quiescence prior to the formation of an active margin and oceanization.  相似文献   

A north-south section across the Queyras Schistes lustrés (Piedmont zone, Western Alps): Syn-collision refolding of a subduction wedge     

Pierre Tricart  Stephane Schwartz 《Eclogae Geologicae Helvetiae》2006,99(3):429-442

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Will the river Irtysh survive the year 2030? Impact of long-term unsuitable land use and water management of the upper stretch of the river catchment (North Kazakhstan)     

Zbyněk Hrkal  Alain Gadalia  Pierre Rigaudiere 《Environmental Geology》2006,50(5):717-723

The Irtysh river basin all the way from river spring in China across Kazakhstan as far as the Russian part of Siberia is among the most ecologically endangered and affected regions on our planet. The study provides a summary of the historical reasons for anthropological interventions in this area, which began with the construction of plants of the military—industrial complexes in the forties of the last century during World War II. These plants have a major share in extreme high concentrations of heavy metals in surface as well in groundwaters locally. The Semipalatinsk nuclear polygon plays a specific role as a source of contamination of local waters. The release of top secret data enabled us to gain knowledge about serious problems related to high radioactivity of groundwaters, which should spread uncontrollably through a system of secondary fissures activated by nuclear blasts. Another serious problem in this region is the quantitative aspect of contamination. Model simulations of water balance indicate that large industrial development in the spring area in China and continuously increasing water consumption in Kazakhstan may lead to desiccation of the lower stretch of this large river in Siberia during the summer months of 2030.  相似文献