Impact of trailing wake drag on the statistical properties and dynamics of finite-sized particle in turbulence

We study by means of an Eulerian-Lagrangian model the statistical properties of velocity and acceleration of a neutrally-buoyant finite-sized particle in a turbulent flow statistically homogeneous and isotropic. The particle equation of motion, beside added mass and steady Stokes drag, keeps into account the unsteady Stokes drag force - known as Basset-Boussinesq history force - and the non-Stokesian drag based on Schiller-Naumann parametrization, together with the finite-size Faxen corrections. We focus on the case of flow at low Taylor-Reynolds number, Re_lambda ~ 31, for which fully resolved numerical data which can be taken as a reference are available (Homann & Bec 651 81-91 J. Fluid Mech. (2010)). Remarkably, we show that while drag forces have always minor effects on the acceleration statistics, their role is important on the velocity behavior. We propose also that the scaling relations for the particle velocity variance as a function of its size, which have been first detected in fully resolved simulations, does not originate from inertial-scale properties of the background turbulent flow but it is likely to arise from the non-Stokesian component of the drag produced by the wake behind the particle. Furthermore, by means of comparison with fully resolved simulations, we show that the Faxen correction to the added mass has a dominant role in the particle acceleration statistics even for particle with size in the inertial range.Comment: 9 pages, 9 figure

Acceleration statistics of finite-sized particles in turbulent flow: the role of Faxen forces

The dynamics of particles in turbulence when the particle-size is larger than the dissipative scale of the carrier flow is studied. Recent experiments have highlighted signatures of particles finiteness on their statistical properties, namely a decrease of their acceleration variance, an increase of correlation times -at increasing the particles size- and an independence of the probability density function of the acceleration once normalized to their variance. These effects are not captured by point particle models. By means of a detailed comparison between numerical simulations and experimental data, we show that a more accurate model is obtained once Faxen corrections are included.Comment: 10 pages, 4 figure

: THE BRONZE AGE PAINTED CAVE OF " LES FRAUX ", DORDOGNE (FRANCE)

International audienceFor six years, an interdisciplinary team of archaeologists, surveyors, environmentalists and archaeometrists have jointly carried out the study of a Bronze Age painted cave, registrered in the French Historical Monuments. The archaeological cave of Les Fraux (Saint-Martin-de-Fressengeas, Dordogne) forms a wide network of galleries, characterized by the exceptional richness of its archaeological remains such as ceramic and metal deposits, parietal representation and about domestic fireplaces. This cave is the only protohistorical site in Europe wherein are gathered testimonies of domestic, spiritual and artistic activities. Fortunately, the cave was closed at the end of the Bronze Age, following to the collapse of its entrance. The site was re-discovered in 1989 and its study started in 2007. The study in progress takes place in a new kind of tool founded by the CNRS's Institute of Ecology and Environment. The purpose of this observatory is the promotion of new methodologies and experimental studies in Global Ecology. In that framework, 3D models of the cave constitute the common work support and the best way for scientific communication for the various studies conducted on the site by nearly forty researchers. In this specific context, a partnership among archaeologists and surveyors from INSA Strasbourg allows the team to develop, in an interdisciplinary way, new methods of data acquiring based on contact-free measurements techniques in order to acquire a full 3D-documentation. This work is conducted in compliance with the integrity of the site. Different techniques based on Terrestrial Laser Scanning, Digital Photogrammetry and Spatial Imaging System have been used in order to generate a geometric and photorealistic 3D model from the combination of point clouds and photogrammetric images, for both visualization and accurate documentation purposes. Various scales of acquiring and diverse resolutions have been applied according to the subject: global volume cave, parietal representations, deposits... The aim of this paper is to issue a statement of the different 3D technologies tested in this outstanding site and the integration of magnetic measurements in the models

Thermal characterization of ancient hearths from the cave of Les Fraux (Dordogne, France) by thermoluminescence and magnetic susceptibility measurements

International audienceNumerous sorts of evidence of fires were observed in the cave of Les Fraux (Dordogne, France) and in particular the effects of fire on sediment were studied for a better understanding of their use centuries ago. Our present objective is the evaluation of the firing intensity by determining the past temperature (paleotemperature) attained by the topmost sediment of the archaeological fires. The principle of paleotemperature determination is based on the thermoluminescence (TL) properties of quartz and the magnetic susceptibility of the sediment. By comparing the TL signal of anciently heated quartz to the TL signal of thermal references made in the laboratory, we were able to obtain a maximal equivalent temperature attained for each sample extracted from ancient fires. The magnetic susceptibility (previously measured on the hearth surface) could thus be estimated as a function of temperature. The main result of this study is the temperature mapping of the hearth which can be used as meaningful information about the ancient firing intensity

Caractérisation thermique de foyers de l'âge du Bronze de la grotte des Fraux (Dordogne)

International audienceThe Les Fraux cave (Dordogne, France) was occupied during the Bronze Age. It contained numerous hearth features. The questions related to the function of the cave and more particularly of the hearth features involved a multidisciplinary study of these remains. The aim of this paper is to present the methods applied for the study of the hearths. The analysis combined thermoluminescence (TL) of the quartz grains and magnetic susceptibility principally registered by the iron oxides contained in the sediments (whether heated or not). For each sample, the TL permits to obtain the corresponding temperature (palaeotemperature) by comparison between the TL curves of the samples and those of the thermal references. The relationship established between the palaeotemperature and the magnetic susceptibility allows converting magnetic susceptibility to palaeotemperatures reached by the sediment on a larger surface. This permits to characterize the intensity of heat attained in these hearths and to contribute to the determination of the function of this site through the comparison with experimental firesLa grotte des Fraux (Dordogne, France), occupée à l'âge du Bronze, présente de nombreuses structures de combustion. Les questions relatives à la fonction du site et plus particulièrement des foyers, ont entrainé la mise en place d'une étude pluridisciplinaire de ces structures. L'objet de cet article est de présenter la méthodologie mise en oeuvre pour l'étude de ces foyers. Elle s'appuie sur un couplage entre la thermoluminescence (TL) des grains de quartz et la susceptibilité magnétique principalement portée par les oxydes de fer contenus dans les sédiments (chauffés ou non). Pour chaque prélèvement, la TL permet d'obtenir une température équivalente (paléotempérature) par comparaison entre les courbes TL correspondantes et celles de références thermiques. La relation établie entre la paléotempérature et la susceptibilité magnétique permet de traduire la carte de susceptibilité magnétique en paléotempératures atteintes par le sédiment sur une surface étendue. L'objectif est de caractériser l'intensité de chauffe de ces foyers et, par une comparaison avec des feux expérimentaux, de contribuer à préciser la fonction de ce site

Characterisation of iron (II) sulfides in wet archaeological woods: the wreck of Mandirac (IV th century, antique ports of Narbonne, France)

International audienceThe wreck of Mandirac (Narbonne, France, IV century) was excavated in 2013 and 2014 from waterlogged soil. A magnetic prospection campaign performed in 2014 revealed that the wood was abnormally magnetic. A plank extracted from the hull, containing an iron nail, was analysed using Environmental Scanning Electron Microscopy, micro-Raman spectroscopy, X-Ray diffraction and magnetic characterization methods in order to identify the mineral composition inside the wood and of the nail. Results revealed an accumulation of greigite and pyrite in the wood around the nail, where the pH was measured below 3. The nail was completely corroded into pyrite and siderite, with no metal left. Marcasite was also identified far from the nail, where the pH was measured around 5. Greigite was the only phase responsible of the magnetic signal emitted from the wood and proved to be present in varying amounts throughout the entire wreck. The iron sulfides were probably formed via anaerobic sulphidogenic bacteria influenced corrosion processes, which occurred on the nails. These results are very different from those obtained from more recent shipwrecks (XIX century). So the nature of these iron sulfides in wet archaeological woods is discussed

Assemblages bois-fer et biocorrosion : étude des sulfures de fer formés en conditions anoxiques dans des bois d'épaves

International audienceLes conséquences de la corrosion des renforts de fer dans les assemblages de bois peuvent compromettre la durabilité d'une structure. Si le bois est gorgé d'eau, les conditions à la surface du métal deviennent anoxiques. La présence de fer et l'activité microbiologique favorisée par la présence de matière organique font des systèmes composites bois-fer des milieux propices à l'apparition de sulfures de fer. Or ces derniers se transforment soit en milieux anaérobies sulfurés, soit lorsque l'oxygène diffuse dans le bois, soit lors d'une remise à l'air de la structure, avec pour conséquence de contribuer à la dégradation du bois. Afin de mieux comprendre les mécanismes impliqués, nous étudions des bois d'épaves archéologiques. Cet article sera illustré par des exemples d'époques récentes (18 è s. 19 è s.) et antiques et par une approche analytique multi-techniques originale. La mackinawite, la greigite et la pyrite ont été identifiées et il semble que la nature des sulfures de fer présents soit liée à l'âge du vestige conformément aux schémas proposés dans la littérature d'évolution de ces composés. La greigite est intéressante à considérer. Seule phase détectée quel que soit l’âge, elle peut s’avérer un bon marqueur de la biocorrosion du fer dans les assemblages bois-fer

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

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

Adaptive Lagrangian–Eulerian computation of propagation and rupture of a liquid plug in a tube

Liquid plug propagation and rupture occurring in lung airways can have a detrimental effect on epithelial cells. In this study, a numerical simulation of a liquid plug in an infinite tube is conducted using an Eulerian–Lagrangian approach and the continuous interface method. A reconstruction scheme is developed to allow topological changes during plug rupture by altering the connectivity information about the interface mesh. Results prior to the rupture are in reasonable agreement with the study of Fujioka et al . in which a Lagrangian method is used. For unity non‐dimensional pressure drop and a Laplace number of 1000, rupture time is shown to be delayed as the initial precursor film thickness increases and rupture is not expected for thicknesses larger than 0.10 of tube radius. During the plug rupture process, a sudden increase of mechanical stresses on the tube wall is recorded, which can cause tissue damage. The peak values of those stresses increase as the initial precursor film thickness is reduced. After rupture, the peaks in mechanical stresses decrease in magnitude as the plug vanishes and the flow approaches a fully developed behavior. Increasing initial pressure drop is shown to linearly increase maximum variations in wall pressure and shear stress. Decreasing the pressure drop and increasing the Laplace number appear to delay rupture because it takes longer for a fluid with large inertial forces to respond to the small pressure drop. Copyright © 2010 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/88023/1/2422_ftp.pd

Projected SO(5) Hamiltonian for Cuprates and Its Applications

The projected SO(5) (pSO(5)) Hamiltonian incorporates the quantum spin and superconducting fluctuations of underdoped cuprates in terms of four bosons moving on a coarse grained lattice. A simple mean field approximation can explain some key feautures of the experimental phase diagram: (i) The Mott transition between antiferromagnet and superconductor, (ii) The increase of T_c and superfluid stiffness with hole concentration x and (iii) The increase of antiferromagnetic resonance energy as sqrt{x-x_c} in the superconducting phase. We apply this theory to explain the ``two gaps'' problem found in underdoped cuprate Superconductor-Normal- Superconductor junctions. In particular we explain the sharp subgap Andreev peaks of the differential resistance, as signatures of the antiferromagnetic resonance (the magnon mass gap). A critical test of this theory is proposed. The tunneling charge, as measured by shot noise, should change by increments of Delta Q= 2e at the Andreev peaks, rather than by Delta Q=e as in conventional superconductors.Comment: 3 EPS figure