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Landais A.,CEA Saclay Nuclear Research Center | Dreyfus G.,CEA Saclay Nuclear Research Center | Dreyfus G.,Princeton University | Capron E.,CEA Saclay Nuclear Research Center | And 7 more authors.
Quaternary Science Reviews | Year: 2010

The isotopic composition of atmospheric oxygen (δ18Oatm) is a complex marker that integrates changes in global sea-level, water cycle, and biosphere productivity. A strong signature of orbital precession has been identified leading to the use of low-resolution measurements of δ18Oatm to date ice core records. However, the drivers of these δ18Oatm variations are still poorly known. Here, we combine records of millennial and orbital scale variations on the NorthGRIP, Vostok, and EPICA Dome C (EDC) ice cores to explore the origin of δ18Oatm variations. We show that, superimposed on the dominant precession signal, millennial δ18Oatm variations record systematic decreases during warm phases of the Dansgaard-Oeschger events and systematic increases during the cold phases. We show that at both timescales δ18Oatm is strongly related to the monsoon activity itself influenced by precessional and millennial shifts in InterTropical Convergence Zone (ITCZ). Then, we show that despite its simplicity, the Dole effect defined as the difference between δ18Oatm and δ18O of global sea-level enables one to remove the obliquity signal within the δ18Oatm record and is a good indicator of hydrological cycle and biosphere productivity. Finally, we compare the δ18Oatm records to past changes in atmospheric composition recorded in ice cores and conclude that δ18Oatm responds much more than CH4 to precession signal, in contrast with earlier views. Similarities observed at orbital timescales between CO2 and δ18Oatm reveal a stronger coupling than previously thought between the carbon and the oxygen cycles. © 2009 Elsevier Ltd. All rights reserved. Source

Pohl A.,Max Planck Institute for Astronomy | Pohl A.,University of Heidelberg | Pinilla P.,Leiden University | Benisty M.,University Grenoble alpes | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

Scattered light images of transition discs in the near-infrared often show non-axisymmetric structures in the form of wide-open spiral arms in addition to their characteristic low-opacity inner gap region. We study self-gravitating discs and investigate the influence of gravitational instability on the shape and contrast of spiral arms induced by planet-disc interactions. Twodimensional non-isothermal hydrodynamical simulations including viscous heating and a cooling prescription are combined with three-dimensional dust continuum radiative transfer models for direct comparison to observations. We find that the resulting contrast between the spirals and the surrounding disc in scattered light is by far higher for pressure scaleheight variations, i.e. thermal perturbations, than for pure surface density variations. Self-gravity effects suppress any vortex modes and tend to reduce the opening angle of planet-induced spirals, making them more tightly wound. If the disc is only marginally gravitationally stable with a Toomre parameter around unity, an embedded massive planet (planet-to-star mass ratio of 10-2) can trigger gravitational instability in the outer disc. The spirals created by this instability and the density waves launched by the planet can overlap resulting in large-scale, more open spiral arms in the outer disc. The contrast of these spirals is well above the detection limit of current telescopes. © 2015 The Authors. Source

The aim of the study was to evaluate the photodynamic therapy (PDT) effect on root canals contaminated with Enterococcus faecalis using a light emitting diode (LED) light and a curcumin solution (CUR) as photosensitizer (PS). Eighty root canals from uniradicular human teeth were prepared with Protaper Universal rotary system and contaminated with E. faecalis for 21 days. They were divided as: GIa-PDT (CUR, pre-irradiation for 5 + 5 min of irradiation); GIb-PDT (CUR, pre-irradiation for 5 + 10 min of irradiation); GIIa-(CUR, pre-irradiation for 5 + 5 min without irradiation); GIIb-(CUR pre-irradiation for 5 + 10 min of irradiation); GIIIa-(physiological solution and irradiation for 5 min); and GIIIb-(physiological solution and irradiation for 10 min); positive and negative control groups. Collections from root canals were made at time intervals of 21 days after contamination, immediately after treatment, and 7 days after treatment, and submitted to colony forming units per milliter (CFU mL−1) counts. The data were submitted to ANOVA and Tukey multiple comparison tests, at a level of significance of 5 %. In the immediate post-treatment collection, group GIa showed greater bacterial reduction in comparison with GIIa, GIIb, GIIIa, GIIIb, and positive control (P < 0.05). At 7 days post-treatment, GIa showed significant bacterial reduction only in comparison with GIIIa (P < 0.05). Curcumin as sensitizer was effective by 5 min LED irradiation but not by 10 min irradiation PDT using LED light, and curcumin as PS was not effective in eliminating E. faecalis. No difference was observed for periods of irradiation. © 2014, Springer-Verlag London. Source

Gerber S.,Princeton University | Gerber S.,University of Florida | Hedin L.O.,Princeton University | Keel S.G.,Princeton University | And 3 more authors.
Geophysical Research Letters | Year: 2013

Our understanding of Earth's carbon climate system depends critically upon interactions between rising atmospheric CO2, changing land use, and nitrogen limitation on vegetation growth. Using a global land model, we show how these factors interact locally to generate the global land carbon sink over the past 200 years. Nitrogen constraints were alleviated by N2 fixation in the tropics and by atmospheric nitrogen deposition in extratropical regions. Nonlinear interactions between land use change and land carbon and nitrogen cycling originated from three major mechanisms: (i) a sink foregone that would have occurred without land use conversion; (ii) an accelerated response of secondary vegetation to CO2 and nitrogen, and (iii) a compounded clearance loss from deforestation. Over time, these nonlinear effects have become increasingly important and reduce the present-day net carbon sink by ∼40% or 0.4 PgC yr-1. Key Points Interactions between land-use and CO2 response curtail the land carbon uptake Successional dynamics of land-use recovery affect nitrogen supply and CO2 sink ©2013. American Geophysical Union. All Rights Reserved. Source

Schicker R.,Physics Institute
AIP Conference Proceedings | Year: 2011

The ALICE experiment consists of a central barrel in the pseudorapidity range -0.9<η<0.9 and of additional detectors covering about 3 units of pseudorapidity on either side of the central barrel. Such a geometry allows the tagging of single and double gap events. The status of the analysis of such diffractive events in proton-proton collisions at √s = 7 TeV is presented. © 2011 American Institute of Physics. Source

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