Horizontal Cylindrical Structures in an Unconsolidated Quaternary Deposit at Saint-Joachim, Near Québec City (Canada)

Two series of six horizontal cylindrical structures (pipes) were discovered recently in a Late Pleistocene (11‑10 ka BP) emerged delta deposit about 40 km NE of Québec City, Canada. The pipes occur at a depth of 19 m in a slightly oxydized layer of fine sand which is interlayered with two strata of compact blue silty clay, respectively 35 and 45 cm in thickness. The maximum length of the pipes is not known, but the remaining exhumed pipes measure 34 to 59 cm. Their diameter ranges from 6.5 to 14.5 cm. The pipe core generally consists of clean and loose medium to coarse sand whereas the outer ring, made of oxydized fine sand, is semi-consolidated. Pipes are the result of water flow in a permeable sand layer enclosed between two non-permeable layers; water enclosed in a shallow basin created by local collapsing was under hydraulic pressure and forced to drain out on the delta front. These water escape features are possibly the first known site of horizontal cylindrical structures observed in unconsolidated Quaternary sediments.Deux séries de structures cylindriques horizontales ont été observées récemment dans un dépôt deltaïque émergé mis en place à la fin du Pléistocène (11‑10 ka BP), à une quarantaine de kilomètres au nord-est de la municipalité de Québec. Sises à 19 m de profondeur, les structures cylindriques occupent un lit de sable fin, légèrement oxydé, inséré entre deux couches d’argile silteuse, bleue, compacte, respectivement de 35 et 45 cm d’épaisseur. La longueur maximale atteinte par les structures est inconnue en raison de l’exploitation avancée de la gravière. Toutefois, dans la partie restante, dégagée manuellement, elles ont une longueur minimale comprise entre 34 et 59 cm. Le centre des cylindres est composé de sable, moyen à grossier, non stratifié alors que l’enveloppe extérieure de quelques centimètres d’épaisseur est constituée de sable fin, oxydé et semi-induré. Les structures horizontales ont été formées après la mise en place du dépôt par un écoulement souterrain d’eau sous pression hydraulique provenant d’une cuvette peu profonde produite par un affaissement local. La pression a été suffisamment forte pour créer des cavités de type suffosion. Lors de la baisse de pression, elles ont été comblées par des sédiments plus grossiers que la couche encaissante. L’eau, qui a migré parallèlement aux couches, devait s’écouler sur le front du delta. Ces structures cylindriques horizontales semblent les premières du genre à avoir été observées dans un dépôt meuble quaternaire

Density functional calculations of the formation and migration enthalpies of monovacancies in Ni: Comparison of local and nonlocal approaches

We examine in this work the potential and the functional to be used in a density functional theory approach in order to describe correctly the formation and migration energies of monovacancies in nickel. As the formation enthalpy is not well-known experimentally at 0 K, we choose in a first step to determine some structural, magnetic, and elastic properties of the bulk, which are well-established experimentally. The comparison between both approaches, i.e., the local spin density approximation LSDA and the generalized gradient approximation GGA exchange-correlation functionals is analyzed. We conclude that the contribution of nonlocal GGA terms in order to describe correctly the electronic density is necessary to determine the formation and migration enthalpies and activation energy of monovacancy. The calculated formation Hv f and migration Hv m enthalpies differ significantly between both approaches. The overestimation of the LSDA approximation is of 0.25 eV for Hv f and of 0.23 eV for Hv m with respect to the GGA one, leading to a gap of 0.48 eV between both methods for the activation energy Q1. We show that the GGA results are comparable with experimental data if the thermal expansion contribution is taken into account through the lattice parameter variation. Finally, it is shown that the activation energy is nearly independent of the thermal expansion effects; thus we can expect that the curvature of the Arrhenius plot of the diffusion factor near the melting point is essentially due to the contribution of divacancies

CCCP: A CCD Controller for Counting Photons

CCCP, a CCD Controller for Counting Photons, is presented. This new controller uses a totally new clocking architecture and allows to drive the CCD in a novel way. Its design is optimized for the driving of EMCCDs at up to 20MHz of pixel rate and fast vertical transfer. Using this controller, the dominant source of noise of EMCCDs at low flux level and high frame rate, the Clock Induced Charges, were reduced to 0.001 - 0.0018 electron/pixel/frame (depending of the electron multiplying gain), making efficient photon counting possible. CCCP will be deployed in 2009 on the ESO NTT through the 3D-NTT1 project and on the SOAR through the BTFI project.Comment: 10 pages, 10 figures, to appear in "Ground-based and Airborne Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200