Petrographical and geochemical characterization of Comblanchien limestone (Bourgogne,France): A fingerprint of the building stone provenance     

Claudine Malfilatre  Philippe Boulvais  Marie-Pierre Dabard  Sylvie Bourquin  Erwan Hallot  Didier Pallix  Denis Gapais 《Comptes Rendus Geoscience》2012,344(1):14-24

The Comblanchien limestone is a well-known building stone that deserves a quantitative characterization in order to be able to certify its origin. We compare petrographical and geochemical characteristics of limestones commercialized under the name of Comblanchien to those of one of their competitors (VATC, a Portuguese coated grain-bearing limestone). From macroscopic and microscopic observations, the distinction is somehow difficult but the coated grain-bearing Comblanchien samples have δ¹³C values (from +1.75 to +2.25‰) different from those of the VATC sample (negative δ¹³C value). As an example of application of these results, three samples from a building site near Paris are also studied in order to verify their provenance. We conclude that they do not come from quarries from the Comblanchien area, but likely from Portugal. The study shows that a detailed analysis of building limestones may provide a robust tool for discriminating between currently mined stones of different provenances, and thus open the possibility to attach to a given limestone a fingerprint, an identity card, and if required a commercial label.  相似文献   

The Fresnel imager: instrument numerical model     

Denis Serre 《Experimental Astronomy》2011,30(2-3):111-121

The methodology used in the end-to-end numerical model of the Fresnel Interferometric Imager is presented. This Instrument Numerical Model (INM) performs plane-to-plane Fresnel propagation, starting from the Fresnel array and ending at the achromatic focal plane, and has been written in c so that it can handle various instrument configurations (sizes of Fresnel arrays from cm to m, from a few Fresnel zones to a few hundred, and for various wavelengths) with a standard desktop computer (a few GHz processor(s) speed, a few GB of memory, execution time per wavelength spanning from few minutes to few hours in the most extreme cases). The INM is used to estimate the performances of the Fresnel Imager: angular resolution, photometric dynamic range, transmission, for on and off-axis sources.  相似文献   

Estimated energy balance in the jovian upper atmosphere during an auroral heating event     

Henrik Melin  Tom Stallard  Denis Grodent 《Icarus》2006,181(1):256-265

We present an analysis of a series of observations of the auroral/polar regions of Jupiter, carried out between September 8 and 11, 1998, making use of the high-resolution spectrometer, CSHELL, on the NASA InfraRed Telescope Facility (IRTF), Mauna Kea, Hawaii; these observations spanned an “auroral heating event.” This analysis combines the measured line intensities and ion velocities with a one-dimensional model vertical profile of the jovian thermosphere/ionosphere. We compute the model line intensities both assuming local thermodynamic equilibrium (LTE) and, relaxing this condition (non-LTE), through detailed balance calculations, in order to compare with the observations. Taking the model parameters derived, we calculate the changes in heating rate required to account for the modelled temperature profiles that are consistent with the measured line intensities. We compute the electron precipitation rates required to give the modelled ion densities that are consistent with the measured line intensities, and derive the corresponding Pedersen conductivities. We compute the changes in heating due to Joule heating and ion drag derived from the measured ion velocities, and modelled conductivities, making use of ion-neutral coupling coefficients derived from a 3-D global circulation model. Finally, we compute the cooling due to the downward conduction of heat and the radiation-to-space from the molecular ion and hydrocarbons. Comparison of the various heating and cooling terms enables us to investigate the balance of energy inputs into the auroral/polar atmosphere. Increases in Joule heating and ion drag are sufficient to explain the observed heating of the atmosphere; increased particle precipitation makes only a minor heating contribution. But local cooling effects—predominantly radiation-to-space—are shown to be too inefficient to allow the atmosphere to relax back to pre-event thermal conditions. Thus we conclude that this event provides observational, i.e. empirical, evidence that heat must be transported away from the auroral/polar regions by thermally or mechanically driven winds.  相似文献   

A 3-D coastal tidal rectification process: observations, theory and experiments     

Denis Aelbrecht  Gabriel Chabert d'Hires  Dominique Renouard 《Continental Shelf Research》1999,19(15-16)

In homogeneous rotating fluid, when there is an oscillating forcing in the interior fluid with a period long enough for an Ekman layer to develop, there is an interaction between the oscillatory Ekman layer and the vertical wall, since the latter imposes an alternating adjustment flow confined near the wall. As a result, this coastal rectification process leads to a Lagrangian transport along the coast. The Ekman number, the Rossby number and the temporal Rossby number of the forcing flow are the governing parameters of that mechanism which can be described by a simplified analytical model taking into account both the vertical time-dependent structure of the current and the presence of the wall. The model shows that the residual (rectified) current flowing with the coast to its right results from the strong nonlinear interaction between along- and cross-shore tidal currents leading to asymmetrical momentum exchanges between the Ekman bottom layer and the coastal boundary layer. The model provides simple scaling laws for the maximum intensity and width of the residual current. The latter is significantly larger than the friction (Stokes) lateral boundary layer of the forcing flow. A comprehensive set of experiments is performed in the 13 m diameter rotating tank by oscillating an 8 m×2 m horizontal plate and vertical wall in a homogeneous fluid at rest in solid-body rotation and measuring the two horizontal components of the current at several locations and depths above the central part of the plate. The predicted and experimentally measured maximum intensity and width of the residual current are in very good agreement, within the range of validity of the model, i.e. when the Ekman number is sufficiently small. However experiments also show that the residual current still occurs when the Ekman layer thickness is of the same order as the fluid depth, but it is then confined to a narrower band along the vertical wall. The flow structure found experimentally is also correctly described by a numerical model developed by Zhang et al. (1994). Current measurements in the Eastern part of the English Channel near the French coast reveal a significant coastal residual current flowing Northward and the coastal rectification process described here may account for part of it.  相似文献   

Subglacial deformation and water-pressure cycles as a key for understanding ice stream dynamics: evidence from the Late Ordovician succession of the Djado Basin (Niger)     

Michael Denis  M. Guiraud  M. Konat��  J.-F. Buoncristiani 《International Journal of Earth Sciences》2010,99(6):1399-1425

Subglacial deformation is crucial to reconstructing glacier dynamics. Sediments associated with the Late Ordovician ice sheet in the Djado Basin, Niger, exhibit detailed structures of the subglacial shear zone. Three main types of subglacial shear zones (SSZ) are discriminated. The lowermost SSZ, developed on sandstones, displays Riedel macrostructures and cataclastic microstructures. These resulted from brittle deformation associated with strong glacier/bed coupling and low pore-water pressure. Where they developed on a clay-rich bed, the overlying SSZ display S–C to S–C′ fabrics, sheath folds, and dewatering structures. These features indicate high ductile shear strain and water overpressure. On fine-grained sand beds, the SSZ exhibit homogenized sand units with sand stringers, interpreted as fluidized sliding beds. The succession of subglacial deformation processes depends on fluid-pressure behavior in relation to subglacial sediment permeability. Fluid overpressure allows subglacial sediment shear strength and ice/bed coupling to be lowered, leading to ice streaming.  相似文献   

The discovery of a persistent quasi-periodic oscillation in the intermediate polar TX Col     

N. Mhlahlo  D. A. H. Buckley  V. S. Dhillon  S. B. Potter  B. Warner  P. Woudt  G. Bolt  J. McCormick  R. Rea  Denis J. Sullivan  F. Velhuis 《Monthly notices of the Royal Astronomical Society》2007,380(1):133-141

We report on the detection of an ∼5900 s quasi-periodic variation in the extensive photometry of TX Col spanning 12 yr. We discuss five different models to explain this period. We favour a mechanism where the quasi-periodic variation results from the beating of the Keplerian frequency of the 'blobs' orbiting in the outer accretion disc with the spin frequency and from modulated accretion of these 'blobs' taking place in a shocked region near the disc/magnetosphere boundary.  相似文献   

Experimental study of the heterogeneous reactivity between atomic chlorine and palmitic acid films     

Raluca Ciuraru  Michael Ward  Maxence Mendez  Sylvie Gosselin  Nicolas Visez  Denis Petitprez 《Journal of Atmospheric Chemistry》2013,70(4):341-355

The present study focuses on the heterogeneous reaction between gaseous atomic chlorine and solid palmitic acid films, used as a proxy of the fatty acids detected in atmospheric airborne particles. This reaction is investigated in a coated wall flow tube reactor coupled to a molecular beam mass spectrometer. The reactive surfaces were prepared by coating the inner surface of the reactor. The initial Cl˙ and Cl₂ uptake coefficient measured for these heterogeneous reactions is found to be fast: γ_o ^Cl?=?0.07. The rapid formation of hydrogen chloride corresponding with the disappearance of atomic chlorine is highlighted. Furthermore, the formation of new chlorinated species on the solid substrate has been detected by TOF SIMS analysis leading to an ageing process of the surface. A heterogeneous recombination of Cl atoms to Cl₂ molecules was observed for aged surfaces.  相似文献   

Spaces of uncertainty: A model of mobile space in the Sahel     

Denis Retaillé  Olivier Walther 《Singapore journal of tropical geography》2011,32(1):85-101

This paper presents a model of mobile space in the Sahel based on the two logics of circulation and production. An overview of the epistemological origins of the model shows how spatial structuring in (and of) the Sahel has been progressively transformed by the territorial action of economic actors, colonial powers, states and development programmes. The particular focus is on nomadic and cross‐border spaces – configurations that offer an ideal perspective on the mobility of space. The model confirms the hypothesis that economic actors, states and development agencies all aim to improve the way uncertainty is managed, but remain profoundly divided over what strategies to adopt. Whereas free flows allow economic actors to obtain products wherever these may be available, states and development agencies conceive of territory as a resource that must drive the specialization of production. The proposed model also suggests that mobile space is not peculiar to the Sahel and that the spatial logics of circulation and production in the Sahel are also present in the process of globalization. It provides conceptual resources that could lead to other models potentially applicable to understanding uncertainty in a highly mobile, globalized world.  相似文献   

Crustal thickening and lateral flow during compression of hot lithospheres,with particular reference to Precambrian times     

Florence Cagnard  Nicolas Durrieu  Denis Gapais  Jean‐Pierre Brun  Carl Ehlers 《地学学报》2006,18(1):72-78

Many ancient deformation belts, especially of Archean and Palaeoproterozoic age, show large areas marked by primary flat‐lying fabrics associated with rather monotonous metamorphic conditions of HTLP type and affected by steep transpressive zones involving vertical stretch. These features do not support strain localization along large‐scale thrusts and (or) extensional detachments, as common in modern orogens. Instead, they are consistent with hot and weak lithospheres where gravity‐driven horizontal flow may compete with distributed thickening from early stages of collisional processes. Relevant deformation features are reviewed and highlighted by lithosphere‐scale analogue models involving low‐viscosity lower crust and sub‐Moho mantle. Both nature and models argue that compression of such lithospheres may induce combined distributed thickening and lateral channel flow of the ductile crust accommodated by transpressive zones.  相似文献   

Optimal Routefinding with Unlimited Possible Directions of Movement     

Denis J. Dean 《Transactions in GIS》2011,15(1):87-107

Finding optimal paths through raster databases is limited by the very nature of the raster data itself. This limitation restricts the possible directions of movement through the database from the infinite possibilities found in the real world to a finite number of possibilities defined by the cell‐to‐cell movement that characterizes raster databases. A Triangulated Irregular Network (TIN)‐based alternative optimization model that allows unlimited possible directions of movement is presented. While not without its own limitations, this new approach offers a viable alternative to raster‐based optimal routefinding.  相似文献