Impact of Oyster Farming on Diagenetic Processes and the Phosphorus Cycle in Two Estuaries (Brittany,France)     

Françoise Andrieux-Loyer  Afi Azandegbé  Florian Caradec  Xavier Philippon  Roger Kérouel  Agnès Youenou  Jean-Louis Nicolas 《Aquatic Geochemistry》2014,20(6):573-611

This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size and organic matter parameters) and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations in sulfide and Fe concentrations in pore waters, as well as Fe–P concentrations in the solid phase, highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulfate reduction (beneath oyster). This could be partly explained by the increase in labile organic matter (i.e., biodeposits) beneath oysters, whose mineralization by sulfate led to high sulfide concentrations in pore waters (up to 4,475 µmol l^?1). In turn, sulfide caused an enhanced release of phosphate in the summer, as adsorption sites for phosphate decreased through the formation of iron–sulfide compounds (FeS and FeS₂). In the Aber Benoît, dissolved Fe/PO₄ ratios could be used as an indicator of phosphate release into oxic water. Low Fe/PO₄ ratios in the summer indicated higher effluxes of phosphate toward the water column (up to 47 µmol m^?2 h^?1). At other periods, Fe/PO₄ ratios higher than 2 mol/mol indicated very low phosphate fluxes. In contrast, in the Rivière d’Auray, the occurrence of macroalgae, stranding regularly all over the site, clearly masked the impact of oyster cultures on sediment properties and the phosphorus cycle and made the use of Fe/PO₄ ratios more difficult in terms of indicators of phosphate release.  相似文献   

Shatter cones and planar deformation features confirm Santa Marta in Piauí State,Brazil, as an impact structure     

Grace Juliana Gonçalves de Oliveira  Marcos Alberto Rodrigues Vasconcelos  Alvaro Penteado Crósta  Wolf Uwe Reimold  Ana Maria Góes  Astrid Kowitz 《Meteoritics & planetary science》2014,49(10):1915-1928

A total of 184 confirmed impact structures are known on Earth to date, as registered by the Earth Impact Database . The discovery of new impact structures has progressed in recent years at a rather low rate of about two structures per year. Here, we introduce the discovery of the approximately 10 km diameter Santa Marta impact structure in Piauí State in northeastern Brazil. Santa Marta is a moderately sized complex crater structure, with a raised rim and an off‐center, approximately 3.2 km wide central elevated area interpreted to coincide with the central uplift of the impact structure. The Santa Marta structure was first recognized in remote sensing imagery and, later, by distinct gravity and magnetic anomalies. Here, we provide results obtained during the first detailed ground survey. The Bouguer anomaly map shows a transition from a positive to a negative anomaly within the structure along a NE–SW trend, which may be associated with the basement signature and in parts with the signature developed after the crater was formed. Macroscopic evidence for impact in the form of shatter cones has been found in situ at the base around the central elevated plateau, and also in the interior of fractured conglomerate boulders occurring on the floor of the surrounding annular basin. Planar deformation features (PDFs) are abundant in sandstones of the central elevated plateau and at scattered locations in the inner part of the ring syncline. Together, shatter cones and PDFs provide definitive shock evidence that confirms the impact origin of Santa Marta. Crystallographic orientations of PDFs occurring in multiple sets in quartz grains are indicative of peak shock pressures of 20–25 GPa in the rocks exposed at present in the interior of the crater. In contrast to recent studies that have used additional, and sometimes highly controversial, alleged shock recognition features, Santa Marta was identified based on well‐understood, traditional shock evidence.  相似文献   

Investigation of the relationship between ground and engineering bedrock at northern part of the Gulf of İzmir by borehole data supported geophysical works     

Mustafa Akgün  Tolga Gönenç  Oya Pamukçu  Şenol Özyalin 《Journal of Earth System Science》2014,123(3):545-564

Loss of life and property that may occur as a result of a possible earthquake can be reduced by earthquake resistant building designs. In order to investigate possible ground motion amplification in earthquake resistant building design, relationship between the ground and engineering bedrock must be ensured. In order to provide this relation, structure, basic characteristics, and thickness of the ground are investigated. In this context, calculating ground transfer function, obtaining horizontal earthquake acceleration changes, calculating Vs values and defining the engineering bedrock are necessary. In this study, Menemen plain, the nothern part of Izmir metropolitan located in active earthquake zone and its immediate vicinity have been examined to define the structure, ground, engineering and bedrock relation. In this context, Menemen plain has been investigated by geophysical methods, which are supported with borehole data (microtremor, MASW – multichannel analysis of surface waves, microgravity measurements, and vertical electrical sounding–VES). Microtremor method was conducted at 377 points in average in the investigation area to define fundamental period and empirical transfer function; after that in order to create basin model and to define the shallow subsurface geometry, microgravity measurements were carried out by using Scintrex CG-5. Also, MASW measurements were carried out in approximately 277 profiles and Schlumberger VES measurements were conducted at approximately 7 points in the investigation area. The existence of a linear relation between H/V peak period values obtained by microtremor measurements and ground thickness in the investigation area is also supported by geothermal drilling logs (depth of 600 m) with microgravity survey. Also, in some parts of the investigation area, it was observed that high S velocity (Vs) values affected H/V peak period values in sections of the ground close to the surface and there was an inversely correlated relation between this ground thickness and peak period values. This event occurring in shallow depths is supported by both VES sections and 2nd order vertical gravity derivative. As a result, depth of the engineering bedrock was obtained between 200 and 700 m and this unit was proposed as Bornova Melange for the investigation area in the scope of the works carried out. Also, it is observed that the area from ground to the engineering bedrock consists of four different layers which were defined by individual S velocities and densities. According to all results, characterictics of the shallow subsurface show that there is a high heterogeneity. Therefore, according to Eurocode8 (EC8 2004) regulations, soil characteristic of the Menemen plain and its vicinity are in the S1–S2 soil class.  相似文献   

Hollow Cylinder Tests on Boom Clay: Modelling of Strain Localization in the Anisotropic Excavation Damaged Zone     

Bertrand François  Vincent Labiouse  Arnaud Dizier  Ferdinando Marinelli  Robert Charlier  Frédéric Collin 《Rock Mechanics and Rock Engineering》2014,47(1):71-86

Boom Clay is extensively studied as a potential candidate to host underground nuclear waste disposal in Belgium. To guarantee the safety of such a disposal, the mechanical behaviour of the clay during gallery excavation must be properly predicted. In that purpose, a hollow cylinder experiment on Boom Clay has been designed to reproduce, in a small-scale test, the Excavation Damaged Zone (EDZ) as experienced during the excavation of a disposal gallery in the underground. In this article, the focus is made on the hydro-mechanical constitutive interpretation of the displacement (experimentally obtained by medium resolution X-ray tomography scanning). The coupled hydro-mechanical response of Boom Clay in this experiment is addressed through finite element computations with a constitutive model including strain hardening/softening, elastic and plastic cross-anisotropy and a regularization method for the modelling of strain localization processes. The obtained results evidence the directional dependency of the mechanical response of the clay. The softening behaviour induces transient strain localization processes, addressed through a hydro-mechanical second grade model. The shape of the obtained damaged zone is clearly affected by the anisotropy of the materials, evidencing an eye-shaped EDZ. The modelling results agree with experiments not only qualitatively (in terms of the shape of the induced damaged zone), but also quantitatively (for the obtained displacement in three particular radial directions).  相似文献   

Gravitational lensing in quasar samples     

Jean-François Claeskens  Jean Surdej 《Astronomy and Astrophysics Review》2002,10(4):263-311

The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field of research. This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications in cosmology and astrophysics, as well as numerous important results achieved so far. The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect. 2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions are summarized in the last section. We have tried to avoid duplication with existing (and excellent) introductions to the field of gravitational lensing. For this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a broad view on gravitational lensing in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with lensing by galaxy clusters; microlensing in the Galaxy and the local group is reviewed by Paczyński (1996) and a general panorama on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field. Received 4 April 2000 / Published online 9 August 2000  相似文献   

Metals from star-forming dwarfs: retention or ejection?     

Daniel Kunth  Françcois Legrand  Guillermo Tenorio-Tagle  Sergey Silich  J. Miguel Mas-Hesse  Miguel Cerviño 《Astrophysics and Space Science》2002,281(1-2):261-266

We show evidences that gas outflows occur in starburst galaxies as superbubbles evolve. We then question whether hot gas will be expelled and enrich the IGM with metals or be retained within the host galaxy. For this purpose we construct three extreme scenarios of the star formation histories for a sample of dwarf galaxies using either their present metallicity or their luminosity. The three scenarios imply different mechanical energy input rates, those are compared with theoretical lower limits for the ejection of processed matter out of host galaxies. The comparison strongly points at the existence of extended gaseous haloes acting as a barrier that allows these galaxies to retain their metals and enhance their abundance. Our findings strongly point that continuous star-forming processes, rather than coeval bursts, must contribute to the overall metallicity in our galaxy sample. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

A search for starlight reflected from HD 75289b     

Christopher Leigh  rew Collier Cameron  Stephane Udry  Jean-François Donati  Keith Horne  David James  Alan Penny 《Monthly notices of the Royal Astronomical Society》2003,346(2):L16-L20

We have used a Doppler tomographic analysis to conduct a deep search for the starlight reflected from the planetary companion to HD 75289. In four nights on VLT(UT2)/UVES in 2003 January, we obtained 684 high-resolution echelle spectra with a total integration time of 26 h. We establish an upper limit on the geometric albedo of the planet   p < 0.12  (to the 99.9 per cent significance level) at the most probable orbital inclination   i ≃ 60°  , assuming a grey albedo, a Venus-like phase function and a planetary radius   R _p= 1.6 R_Jup  . We are able to rule out some combinations of the predicted planetary radius and atmospheric albedo models with high, reflective cloud decks.  相似文献   

Pyroxene microstructure in the Northwest Africa 856 martian meteorite     

Hugues Leroux  Bertrand Devouard  Patrick Cordier  Franois Guyot 《Meteoritics & planetary science》2004,39(5):711-722

Abstract— Transmission electron microscopy was used to examine pyroxene microstructure in the Northwest Africa (NWA) 856 martian meteorite to construct its cooling and shock histories. All pyroxenes contain strained coherent pigeonite/augite exsolution lamellae on (001). The average width and periodicity of lamellae are 80 and 400 nm, respectively, indicating a cooling rate below 0.1 °C/hr for the parent rock. Pigeonite and augite are topotactic, with strained coherent interfaces parallel to (001). The closure temperature for Ca‐Fe, Mg interdiffusion, estimated from the composition at the augite pigeonite interface, is about 700 °C. Tweed texture in augite reveals that a spinodal decomposition occurred. Locally, tweed evolved toward secondary pigeonite exsolutions on (001). Due to the decreasing diffusion rate with decreasing temperature, “M‐shaped” concentration profiles developed in augite lamellae. Pigeonite contains antiphase boundaries resulting from the C2/c to P2₁/c space group transition that occurred during cooling. The reconstructive phase transition from P2₁/c clinopyroxene to orthopyroxene did not occur. The deformation (shock) history of the meteorites is revealed by the presence of dislocations and mechanical twins. Dislocations are found in glide configuration, with the [001](100) glide system preferentially activated. They exhibit strong interaction with the strained augite/pigeonite interfaces and did not propagate over large distances. Twins are found to be almost all parallel to (100) and show moderate interaction with the augite/pigeonite interfaces. These twins are responsible for the plastic deformation of the pyroxene grains. Comparison with microstructure of shocked clinopyroxene (experimentally or naturally shocked) suggests that NWA 856 pyroxenes are not strongly shocked.  相似文献   

Future supernovae data and quintessence models     

Elisa Di Pietro  Jean-François Claeskens 《Monthly notices of the Royal Astronomical Society》2003,341(4):1299-1310

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Comparison of neural network and McNish and Lincoln methods for the prediction of the smoothed sunspot index     

Françoise Fessant  Catherine Pierret  Pierre Lantos 《Solar physics》1996,168(2):423-433

In this paper we propose a comparison between two methods for the problem of long-term prediction of the smoothed sunspot index. These two methods are first the classical method of McNish and Lincoln (as improved by Stewart and Ostrow), and second a neural network method. The results of these two methods are compared in two periods, during the ascending and the declining phases of the current cycle 22 (1986–1996). The predictions with neural networks are much better than with the McNish and Lincoln method for the atypical ascending phase of cycle 22. During the second period the predictions are very similar, and in agreement with observations, when the McNish and Lincoln method is based on the data of declining phases of the cycles.  相似文献