100 research outputs found

    APRÈS LE DÉLUGE : ÉVOLUTION GÉOMORPHOLOGIQUE DU DELTA DU DANUBE APRÈS LA RECONNEXION MER NOIRE - MÉDITERRANÉE ET SES IMPLICATIONS SUR LE PEUPLEMENT ÉNÉOLITHIQUE / CHALCOLITHIQUE

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    International audienceIn this work, we document the evolution of the upper Danube delta (i.e. blocked delta) using archaeological, geomorphological and geoarchaeological approaches, after the discovery, in the 90's, of the oldest human settlement (Eneolithic/Chalcolithic) close to Mila 23 district. In-site and out-site fieldwork allows us to refine the Danube delta early evolution from 5,600 to 4,000 cal. yr BC. During this period, it functions like a fresh bayhead delta, flowing into a huge lagoon isolated from the open sea by the Letea-Caraorman spit. Then, lagoon water level rose rapidly due to an eustatic rise, and possibly from an unusual highstand of sealevel resulting from wet conditions. The settlement was then partially flooded and abandoned around 4,450 cal. yr BC.Dans ce travail, l'évolution de la zone interne du delta du Danube est appréhendée à partir de travaux géoarchéologiques et géomorphologiques réalisés dans le district de Mila 23, suite à la découverte de la plus vieille occupation humaine (énéolithique/ chalcolithique) du delta dans les années 90. Les travaux sur site et hors site ont permis de préciser les stades précoces de l'évolution du delta entre 5 600 et 4 000 ans cal. av. J.-C. Celui-ci évolue comme un delta lagunaire en eau douce, s'épandant dans un large lagon séparé de la mer par la ride de Letea-Caraorman. La remontée rapide du niveau lagunaire, sous l'effet de la remontée eustatique et peut-être d'une sur cote liée à un événement humide, ont conduit à une submersion partielle du site et probablement à son abandon vers 4 450 ans cal. av. J.-C

    The long cross-over dynamics of capillary imbibition

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    Spontaneous capillary imbibition is a classical problem in interfacial fluid dynamics with a broad range of applications, from microfluidics to agriculture. Here we study the duration of the cross-over between an initial linear growth of the imbibition front to the diffusive-like growth limit of Washburn's law. We show that local-resistance sources, such as the inertial resistance and the friction caused by the advancing meniscus, always limit the motion of an imbibing front. Both effects give rise to a cross-over of the growth exponent between the linear and the diffusive-like regimes. We show how this cross-over is much longer than previously thought - even longer than the time it takes the liquid to fill the porous medium. Such slowly slowing-down dynamics is likely to cause similar long cross-over phenomena in processes governed by wetting

    The long cross-over dynamics of capillary imbibition

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    Spontaneous capillary imbibition is a classical problem in interfacial fluid dynamics with a broad range of applications, from microfluidics to agriculture. Here we study the duration of the cross-over between an initial linear growth of the imbibition front to the diffusive-like growth limit of Washburn's law. We show that local-resistance sources, such as the inertial resistance and the friction caused by the advancing meniscus, always limit the motion of an imbibing front. Both effects give rise to a cross-over of the growth exponent between the linear and the diffusive-like regimes. We show how this cross-over is much longer than previously thought - even longer than the time it takes the liquid to fill the porous medium. Such slowly slowing-down dynamics is likely to cause similar long cross-over phenomena in processes governed by wetting

    Collisional dark matter density profiles around supermassive black holes

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    We solve the spherically symmetric time dependent relativistic Euler equations on a Schwarzschild background space-time for a perfect fluid, where the perfect fluid models the dark matter and the space-time background is that of a non-rotating supermassive black hole. We consider the fluid obeys an ideal gas equation of state as a simple model of dark matter with pressure. Assuming out of equilibrium initial conditions we search for late-time attractor type of solutions, which we found to show a constant accretion rate for the non-zero pressure case, that is, the pressure itself suffices to produce stationary accretion regimes. We then analyze the resulting density profile of such late-time solutions with the function A/rκA/r^{\kappa}. For different values of the adiabatic index we find different slopes of the density profile, and we study such profile in two regions: a region one near the black hole, located from the horizon up to 50MM and a region two from ∼800M\sim 800M up to ∼1500M\sim 1500M, which for a black hole of 109M⊙10^{9}M_{\odot} corresponds to ∼0.1\sim 0.1pc. The profile depends on the adiabatic index or equivalently on the pressure of the fluid and our findings are as follows: in the near region the density profile shows values of κ<1.5\kappa <1.5 and in the limit of the pressure-less case κ→1.5\kappa \rightarrow 1.5; on the other hand, in region two, the value of κ<0.3\kappa<0.3 in all the cases we studied. If these results are to be applied to the dark matter problem, the conclusion is that, in the limit of pressure-less gas the density profile is cuspy only near the black hole and approaches a non-cuspy profile at bigger scales within 1pc. These results show on the one hand that pressure suffices to provide flat density profiles of dark matter and on the other hand show that the presence of a central black hole does not distort the density profile of dark matter at scales of 0.1pc.Comment: 7 pages, 8 eps figures, accepted for publication in MNRA

    Electrodynamics of black hole magnetospheres

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    Numerical simulations combined with simple analytical arguments are used to reach a number of important conclusions on the nature of the Blandford-Znajek mechanism. We show that, just like in the Penrose mechanism and in the MHD models of Punsly and Coroniti, the key role in this mechanism is played by the black hole ergosphere. The poloidal currents are driven by the gravitationally induced electric field which cannot be screened within the ergosphere by any static distribution of the electric charge of locally created pair plasma. Contrary to what is expected in the Membrane paradigm, the energy and angular momentum are extracted not only along the magnetic field lines penetrating the event horizon but along all field lines penetrating the ergosphere. In dipolar magnetic configurations symmetric relative to the equatorial plane the force-free approximation breaks down within the ergosphere where a strong current sheet develops along the equatorial plane. This current sheet supplies energy and angular momentum at infinity to the surrounding force-free magnetosphere. The Blandford-Znajek monopole solution is found to be asymptotically stable and causal. The so-called horizon boundary condition of Znajek is shown to be a regularity condition at fast critical surface.Comment: 1) MNRAS in press 2) corrected typos and added reference

    Aftermath of the flooding : geomorphological evolution of the Danube delta after the black sea-mediterranean reconnection and its implications on eneolithic settlements

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    International audienceIn this article we document the evolution of the internal area of the Danube Delta (i.e. the blocked delta) starting from the geo-archaeological and geomorphological investigations performed at Mila 23 district, following the discovery of the oldest human settlement in the Delta. The in-site and out-site field work and coring allowed us to specify the delta's early stages of evolution from 5600 to 4000 CAL BC. During this period, the site evolves as a freshwater bay-head delta flowing into a huge lagoon isolated from the open sea by Letea-Caraorman spits. The rapid sedimentation rate in the lagoon is interpreted as a response to base-level rise and overflooding as a result of humid conditions during 6-5 ky RCC, leading to the partial submersion of the site and probably to its abandonment around 4450 CAL BC

    Construction of a subgenomic CV-B3 replicon expressing emerald green fluorescent protein to assess viral replication of a cardiotropic enterovirus strain in cultured human cells

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    Coxsackieviruses B (CV-B) (Picornaviridae) are a common infectious cause of acute myocarditis in children and young adults, a disease, which is a precursor to 10-20% of chronic myocarditis and dilated cardiomyopathy (DCM) cases. The mechanisms involved in the disease progression from acute to chronic myocarditis phase and toward the DCM clinical stage are not fully understood but are influenced by both viral and host factors. Subgenomic replicons of CV-B can be used to assess viral replication mechanisms in human cardiac cells and evaluate the effects of potential antiviral drugs on viral replication activities. Our objectives were to generate a reporter replicon from a cardiotropic prototype CV-B3/28 strain and to characterize its replication properties into human cardiac primary cells. To obtain this replicon, a cDNA plasmid containing the full CV-B3/28 genome flanked by a hammerhead ribozyme sequence and an MluI restriction site was generated and used as a platform for the insertion of sequences encoding emerald green fluorescent protein (EmGFP) in place of those encoding VP3. In vitro transcribed RNA from this plasmid was transfected into HeLa cells and human primary cardiac cells and was able to produce EmGFP and VP1-containing polypeptides. Moreover, non-structural protein biological activity was assessed by the specific cleavage of eIF4G1 by viral 2A(pro). Viral RNA replication was indirectly demonstrated by inhibition assays, fluoxetine was added to cell culture and prevented the EmGFP synthesis. Our results indicated that the EmGFP CV-B3 replicon was able to replicate and translate as well as the CV-B3/28 prototype strain. Our EmGFP CV-B3 replicon will be a valuable tool to readily investigate CV-B3 replication activities in human target cell models

    Numerical hydrodynamics in general relativity

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    The current status of numerical solutions for the equations of ideal general relativistic hydrodynamics is reviewed. With respect to an earlier version of the article the present update provides additional information on numerical schemes and extends the discussion of astrophysical simulations in general relativistic hydrodynamics. Different formulations of the equations are presented, with special mention of conservative and hyperbolic formulations well-adapted to advanced numerical methods. A large sample of available numerical schemes is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. A comprehensive summary of astrophysical simulations in strong gravitational fields is presented. These include gravitational collapse, accretion onto black holes and hydrodynamical evolutions of neutron stars. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances on the formulation of the gravitational field and hydrodynamic equations and the numerical methodology designed to solve them.Comment: 105 pages, 12 figures. The full online-readable version of this article, including several animations, will be published in Living Reviews in Relativity at http://www.livingreviews.or

    Numerical Hydrodynamics and Magnetohydrodynamics in General Relativity

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