Un projet du Centre International Blaise Pascal : l’édition électronique des Pensées

International audienceLe projet d’une édition électronique des Pensées de Pascal remonte aujourd’hui à près de six ans. La mode est actuellement aux éditions électroniques commerciales, destinées soit à offrir des photographies d’exemplaires inaccessibles à la vente, soit à fournir des textes saisis en vue de permettre des recherches lexicales aisées par ordinateur. Le défaut de telles entreprises et évidemment de se réduire à des reproductions ou des retranscriptions dépourvues de toute réflexion sur la nature particulière des textes. Cela n’a en soi rien de surprenant : entamer une réflexion analytique de fond qui permette de créer un outil informatique particulier exige de très longs délais, un engagement financier et humain lourd, et surtout une connaissance critique approfondie des textes. Or nous avons la chance à Clermont de pouvoir faire coopérer un chercheur littéraire et un analyste informatique

The structure and dynamics of the AC114 galaxy cluster revisited

We present a dynamical analysis of the galaxy cluster AC114 based on a catalogue of 524 velocities. Of these, 169 (32%) are newly obtained at ESO (Chile) with the VLT and the VIMOS spectrograph. Data on individual galaxies are presented and the accuracy of the measured velocities is discussed. Dynamical properties of the cluster are derived. We obtain an improved mean redshift value z= 0.31665 +/- 0.0008 and velocity dispersion \sigma= 1893+73-82 \kms. A large velocity dispersion within the core radius and the shape of the infall pattern suggests that this part of the cluster is in a radial phase of relaxation with a very elongated radial filament spanning 12000 \kms. A radial foreground structure is detected within the central 0.5/h Mpc radius, recognizable as a redshift group at the same central redshift value. We analyze the color distribution for this archetype Butcher-Oemler galaxy cluster and identify the separate red and blue galaxy sequences. The latter subset contains 44% of confirmed members of the cluster, reaching magnitudes as faint as R_{f}= 21.1 (1.0 magnitude fainter than previous studies). We derive a mass M_{200}= (4.3 \pm 0.7) x 10^15 Msun/h. In a subsequent paper we will utilize the spectral data presented here to explore the mass-metallicity relation for this intermediate redshift cluster.Comment: 17 pages, 11 figures, 4 tables, accepted for publication in MNRA

Molecular Signature of Polyoxometalates in Electron Transport of Silicon-based Molecular Junctions

Polyoxometalates (POMs) are unconventional electro-active molecules with a great potential for applications in molecular memories, providing efficient processing steps onto electrodes are available. The synthesis of the organic-inorganic polyoxometalate hybrids [PM$_{11}$O$_{39}$(Sn(C$_6$H$_4$)C$\equiv$C(C$_6$H$_4$)N$_2$)]$^{3-}$ (M = Mo, W) endowed with a remote diazonium function is reported together with their covalent immobilization onto hydrogenated n-Si(100) substrates. Electron transport measurements through the resulting densely-packed monolayers contacted with a mercury drop as a top electrode confirms their homogeneity. Adjustment of the current-voltage curves with the Simmons equation gives a mean tunnel energy barrier of 1.8 eV and 1.6 eV, for the Silicon-Molecules-Metal (SMM) junctions based on the polyoxotungstates (M = W) and polyoxomolybdates (M = Mo), respectively. This follows the trend observed in the electrochemical properties of POMs in solution, the polyoxomolybdates being easier to reduce than the polyoxotungstates, in agreement with lowest unoccupied molecular orbitals (LUMOs) of lower energy. The molecular signature of the POMs is thus clearly identifiable in the solid-state electrical properties and the unmatched diversity of POM molecular and electronic structures should offer a great modularity

Un projet du Centre International Blaise Pascal : l’édition électronique des Pensées

I/ Présentation du projet Le projet d’une édition électronique des Pensées de Pascal remonte aujourd’hui à près de six ans. La mode est actuellement aux éditions électroniques commerciales, destinées soit à offrir des photographies d’exemplaires inaccessibles à la vente, soit à fournir des textes saisis en vue de permettre des recherches lexicales aisées par ordinateur. Le défaut de telles entreprises et évidemment de se réduire à des reproductions ou des retranscriptions dépourvues de toute ..

Structure and dynamics of the supercluster of galaxies SC0028-0005

According to the standard cosmological scenario, superclusters are objects that have just passed the turn around point and are collapsing. The dynamics of very few superclusters have been analysed up to now. In this paper we study the supercluster SC0028-0005, at redshift 0.22, identify the most prominent groups and/or clusters that make up the supercluster, and investigate the dynamic state of this structure. For the membership identification, we have used photometric and spectroscopic data from SDSS-DR10, finding 6 main structures in a flat spatial distribution. We have also used a deep multi-band observation with MegaCam/CFHT to estimate de mass distribution through the weak-lensing effect. For the dynamical analysis, we have determined the relative distances along the line of sight within the supercluster using the Fundamental Plane of early-type galaxies. Finally, we have computed the peculiar velocities of each of the main structures. The 3D distribution suggests that SC0028-005 is indeed a collapsing supercluster, supporting the formation scenario of these structures. Using the spherical collapse model, we estimate that the mass within $r = 10$~Mpc should lie between 4 and $16 \times 10^{15} M_\odot$. The farthest detected members of the supercluster suggest that within $\sim 60$~Mpc the density contrast is $\delta \sim 3$ with respect to the critical density at $z=0.22$, implying a total mass of $\sim 4.6$--$16 \times 10^{17} M_\odot$, most of which in the form of low-mass galaxy groups or smaller substructures.Comment: 12 pages, 9 figures, Accepted for publication in MNRA

Structure and dynamics of the Shapley Supercluster

We present results of our wide-field redshift survey of galaxies in a 285 square degree region of the Shapley Supercluster (SSC), based on a set of 10529 velocity measurements (including 1201 new ones) on 8632 galaxies obtained from various telescopes and from the literature. Our data reveal that the main plane of the SSC (v~ 14500 km/s) extends further than previous estimates, filling the whole extent of our survey region of 12~degrees by 30~degrees on the sky (30 x 75~h-1 Mpc). There is also a connecting structure associated with the slightly nearer Abell~3571 cluster complex (v~ 12000km/s. These galaxies seem to link two previously identified sheets of galaxies and establish a connection with a third one at V= 15000 km/s near R.A.= 13h. They also tend to fill the gap of galaxies between the foreground Hydra-Centaurus region and the more distant SSC. In the velocity range of the Shapley Supercluster (9000 km/s < cz < 18000 km/s), we found redshift-space overdensities with b\_j < 17.5 of ~5.4 over the 225 square degree central region and ~3.8 in a 192 square degree region excluding rich clusters. Over the large region of our survey, we find that the intercluster galaxies make up 48 per cent of the observed galaxies in the SSC region and, accounting for the different completeness, may contribute nearly twice as much mass as the cluster galaxies. In this paper, we discuss the completeness of the velocity catalogue, the morphology of the supercluster, the global overdensity, and some properties of the individual galaxy clusters in the Supercluster.Comment: Accepted for publication in Astronomy and Astrophysic

FLAIR-II spectroscopy of two DENIS J-band galaxy samples

As a pilot survey for the forthcoming 6dF Galaxy Redshift Survey, spectroscopy of galaxies selected in J (1.2 mu) with the DENIS survey was performed at the UKST using the FLAIR II multi-object spectroscope. 69 galaxy redshifts (z's) were obtained in a high |b| field and an additional 12 z's in a low latitude (b=-17 deg), obscured field. This study illustrates the feasibility of obtaining z's with optical spectra on galaxies selected at much longer wavelengths. It validated a very preliminary algorithm for star/galaxy separation for high |b| DENIS objects, with 99% reliability for J < 13.9. However, the FLAIR II z determinations required substantially longer integration times to achieve 90% completeness than expected from previous optical surveys at comparable depth. This is mainly due to a degradation in overall fibre throughput due to known problems with ageing of the prism-cement-fibre interface with exposure to UV light. Our low |b| (high extinction) field required 2.5 times more exposure time for less than 50% of successful z measurements. Among the J <= 13.9 galaxies with measured z's, only 37+/-6% display emission lines, in comparison with 60% of emission-line galaxies (ELGs) in optical samples of comparable depth. The ELGs are, on average, 0.5 mag bluer in B-J than non-ELGs of the same luminosity. We confirm a previous optically-based result that the fraction of ELGs increases rapidly with decreasing galaxy luminosity. The J-band luminosity function is estimated. Our high latitude field displays a concentration of galaxies at cz ~ 38000 km/s suggesting a possible supercluster. A radial velocity is reported for a galaxy lying near the projected centre of the Abell 1434 cluster of galaxies, for which no cluster z is currently available.Comment: Accepted in PASA, 21 pages, 9 figure

Multiscale analysis of waves reflected by complex interfaces: Basic principles and experiments

International audience[1] This paper considers the reflection of waves by multiscale interfaces in the framework of the wavelet transform. First, we show how the wavelet transform is efficient to detect and characterize abrupt changes present in a signal. Locally homogeneous abrupt changes have conspicuous cone-like signatures in the wavelet transform from which their regularity may be obtained. Multiscale clusters of nearby singularities produce a hierarchical arrangement of conical patterns where the multiscale structure of the cluster may be identified. Second, the wavelet response is introduced as a natural extension of the wavelet transform when the signal to be analyzed (i.e., the velocity structure of the medium) can only be remotely probed by propagating wavelets into the medium instead of being directly convolved as in the wavelet transform. The reflected waves produced by the incident wavelets onto the reflectors present in the medium constitute the wavelet response. We show that both transforms are equivalent when multiple scattering is neglected and that cone-like features and ridge functions can be recognized in the wavelet response as well. Experimental applications of the acoustical wavelet response show how useful information can be obtained about remote multiscale reflectors. A first experiment implements the synthetic cases discussed before and concerns the characterization of planar reflectors with finite thicknesses. Another experiment concerns the multiscale characterization of a complex interface constituted by the surface of a layer of monodisperse glass beads immersed in water. Citation: Le Gonidec, Y., D. Gibert, and J.-N. Proust , Multiscale analysis of waves reflected by complex interfaces: Basic principles and experiments

An integrated geochemical and mineralogical approach for the evaluation of Zn distribution in long-term sludge-amended soil

International audienceThis research work was designed to compare the Zn distribution in a long-term sludge-amended soil with that in a control soil. Two complementary approaches were performed: (1) a geochemical approach at the metric scale of the bulk soil horizons and (2) a mineralogical approach at the micrometric scale of the primary minerals weathering microsites. The geochemical approach reveals that Zn in the control soil is inherited from the weathering parent-rock. Its concentration is always lower than in the amended soil where Zn is supplied at the surface by the spread sludges and moves downwards. The mineralogical approach shows that the clay minerals, produced by the weathering of the primary minerals (amphiboles and plagioclases), or filling the fissure network are made up of smectites (saponite and montmorillonite) at the bottom and kaolinite at the top of the two soil profiles. Each clay mineral, with its specific sorption capacity, controls the Zn distribution within the soil: the smectites produced by the amphiboles have high sorption capacity and favor Zn retention in the upper horizons of the soil. Conversely, the kaolinites produced by the plagioclases have lower sorption capacity, do not retain Zn in the surface horizons, and allow it to migrate to deeper horizons where it is sorbed onto the montmorillonites

L'archéoastronomie à Rapa Nui

International audienceUntil its discovery on April 4, 1722 (Easter Day), Rapa Nui Island lived in total autarky, developing a culture and knowledge in direct relation to the movement of planets, stars and the appearance of temporary celestial phenomena (comets, novae and supernovae). Sheltered from any external influence, the inhabitants have thus developed over the generations a culture and a way of life based on the celestial calendar.Jusqu'à sa découverte, le 4 avril 1722 (jour de Pâques), l'île Rapa Nui vécut en totale autarcie, développant une culture et une connaissance en relation directe avec le mouvement des planètes, des étoiles et l'apparition de phénomènes célestes temporaires (comètes, novae et supernovae). A l'abri de toute influence extérieure, les habitants ont ainsi développé au cours des générations une culture et un mode de vie basé sur le calendrier céleste