Large scale simulation of turbulence using a hybrid spectral/finite difference solver

Performing Direct Numerical Simulation (DNS) of turbulence on large-scale systems (offering more than 1024 cores) has become a challenge in high performance computing. The computer power increase allows now to solve flow problems on large grids (with close to 10^9 nodes). Moreover these large scale simulations can be performed on non-homogeneous turbulent flows. A reasonable amount of time is needed to converge statistics if the large grid size is combined with a large number of cores. To this end we developed a Navier-Stokes solver, dedicated to situations where only one direction is heterogeneous, and particularly suitable for massive parallel architecture. Based on an hybrid approach spectral/finite-difference, we use a volumetric decomposition of the domain to extend the FFTs computation to a large number of cores. Scalability tests using up to 32K cores as well as preliminary results of a full simulation are presented

Direct numerical simulation of unsheared turbulence diffusing toward a free-slip or no-slip surface

The physics involved in the interaction between statistically steady, shearless turbulence and a blocking surface is investigated with the aid of direct numerical simulation. The original conguration introduced by Campagne et al. [ECCOMAS CFD 2006] serves as the basis for comparing cases in which the blocking surface can be either a free-slip surface or a no-slip wall. It is shown that in both cases, the evolutions of the anisotropy state are the same throughout the surface-influenced layer (down to the surface), despite the essentially different natures of the inner layers. The extent of the blocking effect can thereby be measured through a local (surface) quantity identically defined in the two cases. Examination of the evolution and content of the pressure-strain correlation brings information on the mechanisms by which energy is exchanged between the normal and tangential directions: In agreement with an earlier analysis by Perot and Moin [J. Fluid Mech. 295 (1995)], it appears that the level of the pressure strain correlation is governed by a splat/antisplat disequilibrium which is larger in the case of the solid wall due to viscous effects. However, in contradiction with the latter, the pressure-strain correlation remains as a signicant contributor to both Reynolds-stress budgets; it is argued that the net level of the splat/antisplat disequilibrium is set, in the first place, by the normal-velocity skewness of the interacting turbulent field. The influence of viscous friction on the intercomponent energy transfer at the solid wall only comes in the second place and part of it can also be measured by the skewness. The remainder seems to originate from interactions between the strain field and ring-like vortices in the vicinity of the splats

The structure of a statistically steady turbulent boundary layer near a free-slip surface

The interaction between a free-slip surface with unsheared but sustained turbulence is investigated in a series of direct numerical simulations. By changing (i) the distance between the (plane) source of turbulence and the surface, and (ii) the value of the viscosity, a set of five different data sets has been obtained in which the value of the Reynolds-number varies by a factor of 4. The observed structure of the interaction layer is in agreement with current knowledge, being made of three embedded sublayers: a blockage layer, a slip layer, and a Kolmogorov layer. Practical measures of the different thicknesses are proposed that lead to a new Reynolds-number scaling based on easy-to-evaluate surface quantities. This scaling is consistent with previous proposals but makes easier the comparison between free-surface flows when they differ by the characteristics of the distant turbulent field. Its use will be straightforward in a turbulence-modeling framework

Etude par simulation directe de l'interaction turbulence/surface plane sans cisaillement en vue de l'analyse des transferts intercomposantes

Cette communication présente une simulation directe de l'interaction turbulence/surface plane sans cisaillement. L'originalité de la configuration étudiée tient au fait que la turbulence est entretenue à distance par un forçage aléatoire localisé au voisinage d'un plan de l'espace parallèle à la surface. L'écoulement est donc statistiquement stationnaire et la couche de surface continûment alimentée par diffusion turbulente. On donne les premiers résultats de simulation obtenus. On discute de la pertinence de ces résultats pour l'interprétation des mécanismes de transfert énergétique intercomposantes au voisinage d'une surface de blocage

Study of the Phylloceratoidea fauna of the Valanginian marls of Senez-Lioux (Al-pes-de-Haute-Provence, France). Comparison with some Drôme and Ardèche Valanginian localities

The recent "Révision de la Paléontologie française de d'ORBIGNY (1840-42, tome premier, Terrains crétacés)" has allowed a better understanding of Ammonites calypso (d'ORBIGNY, 1841), so that a more accurate age of the species is known at its type-locality. At first the authors of this memoir had searched for other specimens in the Valanginian marls of Senez-Lioux in order to give it the most correct age. The Phylloceratoidea do not give a precise age of the strata from which the specimens were collected so the authors have determined the ammonites from five successive horizons. This work has shown the Lower Valanginian and two zones of Upper Valanginian (the zone with Verrucosum and the zone with Peregrinus ?, the presence of this last zone is less certain). The zone with Furcillata of Upper Valangi-nian has not been proved. The Phylloceratoidea are abundant in Senez-Lioux. Six species have been identified: Phylloceras (Hypo-phylloceras) serum (OPPEL, 1865), Phylloceras (Hypophylloceras) tethys (d'ORBIGNY, 1841), Sowerby-ceras calypso (d'ORBIGNY, 1841), Ptychophylloceras (Semisulcatoceras) semisulcatum semisulcatum (d'ORBIGNY, 1841), Ptychophylloceras (Semisulcatoceras) semisulcatum (d'ORBIGNY, 1841) diphyllum (d'ORBIGNY, 1841), Phyllopachyceras rogersi (KITCHIN, 1908) and a new species: Phylloceras (Goreto-phylloceras) liouxense n. sp. This new species was found in the Alpes-de-Haute-Provence (material collected by Philippe MERCIER and Bernard JOLY) and in the Drôme area (material collected by Laurent VAREILLES and Philippe MERCIER). These ammonites are small (diameter 5-28 mm) and seem to belong to the juvenile stage. For a long time the Vocontian basin seems to have been the egg-laying area of these Cephalopods. In the Valangi-nian marls there are specimens whose diameter is less than 5 mm. They have not been determined in this study. However their presence is significant. The pyritic specimens and the iron oxide specimens (for example the limonitic specimens) are not necessarily small in size. In the marly facies there are very large pyritic specimens, which are among the largest known (JOLY, 2000, p. 173). In Senez-Lioux the smallest specimens are not the nuclei of the largest ones. They are not small adults because we are unable to see the contraction of the last septa showing the slowing down of their growth. The beginning of the body chamber, which is present in many of the specimens, proves that these specimens were merely not nuclei and definitely they have not attained sexual maturity. The many specimens gathered permitted a statistical study of the populations especially of the species Phylloceras (Hypophylloceras) serum (OPPEL, 1865), Phylloceras (Hypophylloceras) tethys (d'ORBIGNY, 1841), Phylloceras (Goretophylloceras) liouxense n. sp., Ptychophylloceras (Semisulcatoceras) semi-sulcatum semisulcatum (d'ORBIGNY, 1841), and Ptychophylloceras (Semisulcatoceras) semisulcatum (d'ORBIGNY, 1841) diphyllum (d'ORBIGNY, 1841). The species Sowerbyceras calypso (d'ORBIGNY, 1841) and Phyllopachyceras rogersi (KITCHIN, 1908) are represented by very few specimens. The fossils gathered in some deposits from the Drôme and Ardèche area have allowed us to further our knowledge about the Valanginian faunas of the Vocontian Basin. In particular they have permitted the statistical study of a population of the very rare species Ptychophylloceras (Semisulcatoceras) semi-sulcatum semisulcatum (d'ORBIGNY, 1841) as only one specimen was identified among the fossils gathe-red in the deposits of Senez-Lioux but is more abundant in the Valanginian from the Drôme.La récente révision critique de la Paléontologie française de d'ORBIGNY (1840-42, tome pre-mier, texte et atlas, Terrains crétacés) ayant permis de mieux fixer le statut de l'Ammonites calypso (d'ORBIGNY, 1841), il s'avérait utile de préciser l'âge de l'espèce, au moins dans sa localité-type. Les auteurs de la présente note ont eu d'abord comme objectif de rechercher d'autres spécimens de l'espè-ce calypso dans les marnes valanginiennes de Senez-Lioux afin de lui attribuer un âge le plus fiable possible. Les Phylloceratoidea ne permettant pas une datation précise des niveaux de récolte des spécimens les auteurs ont déterminé les ammonites sur cinq niveaux successifs. Ce travail a permis de mettre en évi-dence le Valanginien inférieur et deux zones du Valanginien supérieur (zone à Verrucosum et zone à Peregrinus ?), la présence de cette dernière étant moins certaine. La zone à Furcillata, du Valanginien supérieur, n'a pas été mise en évidence. Les Phylloceratoidea abondent à Senez-Lioux. Six espèces ont pu être identifiées : Phylloceras (Hypo-phylloceras) serum (OPPEL, 1865), Phylloceras (Hypophylloceras) tethys (d'ORBIGNY, 1841), Sowerbyce-ras calypso (d'ORBIGNY, 1841), Ptychophylloceras (Semisulcatoceras) semisulcatum semisulcatum (d'ORBIGNY, 1841), Ptychophylloceras (Semisulcatoceras) semisulcatum (d'ORBIGNY, 1841) diphyllum (d'ORBIGNY, 1841), Phyllopachyceras rogersi (KITCHIN, 1908), ainsi qu'une nouvelle espèce Phylloceras (Goretophylloceras) liouxense n. sp. Cette espèce a été mise en évidence grâce au matériel récolté dans les Alpes-de-Haute-Provence et dans la Drôme (où le matériel a été récolté par Laurent VAREILLES et Philippe MERCIER). Toutes ces ammonites sont de petite taille de 5 à 28 mm. Dans les marnes valanginiennes il existe aussi des spécimens de diamètre inférieur à 5 mm, ils n'ont pu être déterminés et ne figurent pas dans cette étude. Cet ensemble paraît avoir été constitué par le naissain et de jeunes individus, le Bassin vo-contien ayant été longtemps, semble-t-il, l'un des lieux de reproduction des Céphalopodes. La petite taille des spécimens n'est pas liée à leur nature pyriteuse ou en pyrite transformée en oxydes de fer, limonite par exemple. Il existe dans les faciès marneux de très grands spécimens pyriteux, parmi les plus grands connus (JOLY, 2000, p. 173). Les plus petits spécimens de Senez-Lioux ne sont pas des adultes de petite taille, on n'observe pas le resserrement des dernières cloisons témoignant du ralentis-sement de croissance des adultes. Le début de la loge présent chez beaucoup de spécimens prouve que ces spécimens n'étaient pas des nuclei de spécimens plus grands. Ils n'avaient certainement pas atteint la maturité sexuelle. Le grand nombre de spécimens récoltés a permis une étude statistique des populations (ou assembla-ges, terme préférable en paléontologie) surtout pour les espèces Phylloceras (Hypophylloceras) serum (OPPEL, 1865), Phylloceras (Hypophylloceras) tethys (d'ORBIGNY, 1841), Phylloceras (Goretophylloceras) liouxense n. sp., Ptychophylloceras (Semisulcatoceras) semisulcatum semisulcatum (d'ORBIGNY, 1841) et Ptychophylloceras (Semisulcatoceras) semisulcatum (d'ORBIGNY, 1841) diphyllum (d'ORBIGNY, 1841). Les espèces Sowerbyceras calypso (d'ORBIGNY, 1841) et Phyllopachyceras rogersi (KITCHIN, 1908) sont représentées par de plus rares spécimens. Les récoltes de la Drôme et l'Ardèche ont permis de complé-ter nos connaissances sur les faunes valanginiennes du Bassin vocontien. En particulier, c'est le cas pour l'espèce Ptychophylloceras (Semisulcatoceras) semisulcatum semisulcatum (d'ORBIGNY, 1841) très rare (un seul spécimen identifié à Senez-Lioux) mais plus abondante dans les gisements valanginiens de la Drôme

Aptian and Albian Phylloceratids (Ammonoidea) from the Vocontian Basin (SE France)

More than 2,200 pyritized ammonites of the Superfamily Phylloceratatoidea have been collected in consonance with the scale of the ammonite zonation of the expanded Marnes Bleues Fm in the Vocontian Basin (SE France). This abundant material allows the description and the figuration (specimens and sutures) of 28 taxa of which 4 are new: • Phylloceras (Hypophylloceras) moriezense SAYN, 1920 subsp. tenuicostulata nov. Diagnosis: variant of P. (H.) moriezense distinguished by a subrectangular section of the whorl and a flattening of the sides less accentuated than on the typical form, with a very fine costulation that descends almost to the middle of the side (early late Aptian); • Phylloceras (Goretophylloceras) vocontium nov. sp. Diagnosis: thick shell, convex sides, rounded and compressed venter, maximum thickness of the whorl near the umbilicus, open umbilicus, constrictions at least at the beginning of the last whorl, oval whorl section, suture line of subgenus Goretophylloceras (mid middle Aptian to earliest Albian); • Salfeldiella (Gyrophyllites) falloti nov. sp. Diagnosis: shell with a finely costulate test, smooth internal mold, open umbilicus, nearly flat sides, rounded venter, subquadratic whorl section, proverse constrictions of the internal mold, radial constrictions in small specimens, a ventral sinus in the largest specimens, suture line like that of the genus Gyrophyllites (late Early Aptian to late Aptian); • Phyllopachyceras brehereti nov. sp. Diagnosis: thick shell, flat sides, venter flat or slightly convex, whorl quadratic in section, suture lines like those of the genus Phyllopachyceras with tetraphyllic spatulate elongated saddles (early mid-Aptian to early late Aptian). Owing to the abundance of the Phylloceratoidea and the variations of specific diversity in 9 fossiliferous levels ranging in age from the late Early Aptian to the end of the Albian it is possible to identify 3 peaks of abundance: • peak 1 during the early mid-Aptian (base of the Martini zone), • peak 2 near the Aptian and Albian boundary, a few meters below the anoxic PAQUIER level, • peak 3 during the latest Albian (Blancheti zone). Of these 3 peaks the first is the most important probably because the Vocontian Basin attained its maximum depth during this time. The peaks appear to be correlated with the maximum flooding intervals of depositional sequences. But high sea-levels were not always favourable for the Phylloceratoidea. The very fossiliferous PAQUIER level, although it took place during a high in sea-level, is characterised by the virtual absence of the deep-water ammonites, e.g. Phylloceratids, Tetragonids and Lytoceratids. This fact is explained by the presence of a deep-water anoxia. Another depletion of Phylloceratoidea in conjonction with a great abundance of Desmoceratid and Mortoniceratid ammonites and benthic fauna (Inoceramids Bivalves) occurred during the early Late Albian. At that time, the Vocontian area appears to have reached a minimal depth resulting from a pause in the rate of subsidence associated with an influx of siliciclastic material that attained the center of the basin. After a last episode during the Early Cenomanian of the Vocontian Basin when the Phylloceratoidea occurred in significant numbers, this group of ammonites shows a drastic decrease in abundance. This evolution is correlated with the filling of the basin from west to east, thus restricting the Phylloceratoidea and the other deep-water ammonites to a small eastern area (Leiostraca area of THOMEL, 1965, 1980).L'étude de plus de 2200 spécimens de Phylloceratoidea (Cephalopoda, Ammonoidea) récoltés dans les dépôts aptiens et albiens du bassin vocontien (Sud-Est de la France) a permis l'identification et la description de 28 taxons repérés stratigraphiquement à l'échelle de la zone d'ammonite. Quatre nouveaux taxons sont décrits : Phylloceras (Hypophylloceras) moriezense SAYN, 1920 tenuicostulata nov. subsp. (base de l'Aptien supérieur), Phylloceras (Goretophylloceras) vocontium nov. sp. (sommet de l'Aptien moyen à base de l'Albien inférieur), Salfeldiella (Gyrophyllites) falloti nov. sp. (sommet de l'Aptien inférieur à base de l'Aptien supérieur), Phyllopachyceras brehereti nov. sp. (base de l'Aptien moyen à base de l'Aptien supérieur)

Independence of first- and second-order memories in newborn rabbits.

WOS:000291649400006International audienceThe mammary pheromone promotes the acquisition of novel odorants (CS1) in newborn rabbits. Here, experiments pinpoint that CS1 becomes able to support neonatal learning of other odorants (CS2). We therefore evaluated whether these first- and second-order memories remained dependent after reactivation. Amnesia induced after CS2 recall selectively blocked this memory, when recall and amnesia of CS1 left the souvenir of CS2 safe; this finding partially differed from results obtained in adult mammals. Thus, in this model of neonatal appetitive odor learning, second-order memory seems to depend on first-order memory for its formation but not for its maintenance

Approche multivariée des facteurs influençant le bilan de masse d’un glacier arctique

National audienceL’Arctique est la zone géographique où la modification du climat au cours du XXIieme siècle sera la plus forte de la planète. La totalité de la cryosphère (banquise, glaciers, pergélisol, etc.) subira de profondes altérations qui se traduiront spatialement par des évolutions majeures. Les glaciers sont de bons indicateurs de ces changements, aussi bien à une échelle locale que globale, car leur dynamique est très sensible au climat. Cette étude porte sur un glacierdu Spitsberg où il a été observé que des conditions climatiques et nivologiques contrastées d’une année sur l’autre avaient des conséquences multiples, et parfois inattendues, sur les bilans de masse