Inference on the Nature and the Mass of Earth's Late Veneer from Noble Metals and Gases

Noble metals and gases are very sensitive to the late accretion to the Earth of asteroids and comets. We present mass balance arguments based on these elements that indicate that 0.7E22-2.7E22 kg of extraterrestrial bodies struck the Earth after core formation and that comets comprised less than 1E-5 by mass of the impacting population. These results imply that the dynamics of asteroids and comets changed drastically with time and that biogenic elements and prebiotic molecules were not delivered to the Earth by comets but rather by carbonaceous asteroids.Comment: 10 pages, 2 figures, 1 table, submitted to JG

A Collaborative Workflow for Computer-Aided Design in Ambient Assisted Living: The ASIM Project

International audienceIn 2014, the worldwide context is that the population is increasingly both expanding and aging inindustrial countries. In contrast, the personal health levels of individuals could decrease. Although retirementhomes and health-care centers assume most of the demand, they will most probably overflow in thenext few years. One of the current solutions is e-Health, which involves biomedical monitoring but also homeautomation functions to compensate for disabilities that tend to increase with age. In this context, severaldomains have to be merged while respecting the entire ecosystem: the users, their needs and environment,but also all the various actors/experts involved in this process. The issue, however, is that enormous effortis required to combine the multiple expert domains because these can be antinomic. Hence, this paper proposesa collaborative workflow that brings together these different actors and generates the control/commandapplication. Applying model-driven engineering, this workflow makes a clear distinction between people ’ shealth requirements, the home automation functions, and the user interface points of view. Thus, it allowsexperts in each field to adapt their system in terms of the user ’ s needs, disability, and health state

Regulation of ERK signalling pathway in the developing mouse blastocyst

International audience14 Activation of the ERK signalling pathway is essential for the differentiation of the inner cell mass (ICM) 15 during mouse preimplantation. We show here that ERK phosphorylation is present in ICM precursor cells, 16 in differentiated Primitive Endoderm (PrE) cells as well as in the mature, formative state Epiblast (Epi). We 17 further show that DUSP4 and ETV5, factors often involved in negative feedback loops of the FGF pathway 18 are differently regulated. While DUSP4 expression in PrE cells clearly depends on ERK activity, ETV5's 19 localises mainly to Epi cells. Unexpectedly, ETV5 expression does not depend on ERK activation but 20 requires NANOG expression. Indeed ETV5, like Fgf4, is not expressed in Nanog mutant embryos. Our 21 results lead us to propose that in naïve pluripotent Epi cells, NANOG induces both Fgf4 and ETV5 to 22 enable the differentiation of neighbouring cells into PrE while protecting the Epi identity from autocrine 23 signalling. 24

Time-resolved photoluminescence as a probe of internal electric fields in GaN-(GaAl)N quantum wells.

International audienceVery strong coefficients for spontaneous and piezoelectric polarizations have recently been predicted for III-V nitride semiconductors with natural wurtzite symmetry. Such polarizations influence significantly the mechanisms of radiative emissions in quantum-confinement heterostructures based on these materials. The photoluminescence decay time of excitons is used as a probe of internal electric fields in GaN-(Ga, Al)N quantum wells in various configurations of strain, well widths, and barrier widths. The measured decays are not only controlled by radiative lifetimes, which depend on the fields inside GaN wells but also on the nonradiative escape of carriers through Ga1−xAlyN barriers, which depends on their widths and on the electric field in these layers. It is shown in particular that the magnitude of the field in the wells is not a simple function of the strain of these layers via the only piezoelectric effect, but rather the result of the interplay of spontaneous and piezoelectric polarizations in both well and barrier materials

Observation of long-lived oblique excitons in GaN-AlGaN multiple quantum wells.

International audienceThe 2-K recombination dynamics of coupled GaN-AlGaN multiple quantum wells reveals a composite nature in terms of the joint contributions of short-lived direct excitons and long-lived oblique ones. The possibility to observe these oblique excitons, which produce a unusual blueshift of the photoluminescence at long decay times is found to be in straightforward correlation with the presence of internal electric fields together with the existence of a slight disorder at the monolayer scale

A Nanog-dependent gene cluster initiates the specification of the pluripotent epiblast

Posté sur BioRxiv le 18 juillet 2019Summary The epiblast (Epi) is the source of embryonic stem (ES) cells and all embryonic tissues. It differentiates alongside the primitive endoderm (PrE) in a randomly distributed “salt and pepper” pattern from the inner cell mass (ICM) during preimplantation of the mammalian embryo. NANOG and GATA6 are key regulators of this binary differentiation event, which is further modulated by heterogeneous FGF signalling. When and how Epi and PrE lineage specification is initiated within the developing embryo is still unclear. Here we generated NANOG and GATA6 double KO ( DKO ) mouse embryos and performed single-cell expression analyses. We found that the ICM was unable to differentiate in the DKO mice, allowing us to characterize the ICM precursor state. The normally heterogeneous expression of Fgf4 between cells was significantly reduced in DKO ICMs, impairing FGF signalling. In contrast, several pluripotency markers did still display cell-to-cell expression variability in DKO ICMs. This revealed a primary heterogeneity independent of NANOG, GATA6 and FGF signalling that may also be conserved in humans. We found that NANOG is key in the initiation of epiblast specification already between the 16- and 32-cell stages, enabling the cell-clustered expression of many pluripotency genes. Our data uncover previously unknown biology in the early mouse embryo with potential implications for the field of pluripotent stem cells in human and other mammals

Cw and time-resolved spectroscopy in homoepitaxial GaN films and GaN-GaAlN quantum wells grown by molecular beam epitaxy.

International audienceWe have grown GaN films and GaN–AlGaN quantum wells (QWs) on homoepitaxial substrates, by molecular beam epitaxy using ammonia. Both the GaN film and the QW are found to have superior excitonic recombination properties which are extremely promising for the development of indium free ultra-violet lasers based on nitrides

Effects of GaAlN barriers and of dimensionality on optical recombination processes in InGaN quantum wells and quantum boxes.

International audienceWe compare several InGaN-based low-dimensional systems, by time-resolved photoluminescence (PL), versus temperature (8<T<280 K). We investigate the influence of growing or not an AlGaN barrier on top of the active layer. We address the differences between quantum wells and quantum boxes 5–10 nm in diameter and 2 nm in height. Our results are consistent with carrier localization on potential fluctuations with spatial extension much smaller than the size of the quantum boxes. Growing an AlGaN barrier reduces the carrier mobility between fluctuations, thus maintaining an effective PL dominated by localized carriers up to room temperature

High internal electric field in a graded-width InGaN/GaN quantum well: Accurate determination by time-resolved photoluminescence spectroscopy.

International audienceTime-resolvedphotoluminescence (PL), at T=8 K, is used to study a graded-width InGaN/GaN quantum well. Across the sample, the well width continuously varies from ∼5.5 to 2.0 nm corresponding to PL peak energies varying between 2.0 and 2.9 eV and to PL decay rates covering four orders of magnitude. The plot of decay times versus PL energies is very well fitted by a calculation of the electron–hole recombination probability versus well width. The only fitting parameter is the electric field in the well, which we find equal to 2.45±0.25 MV/cm, in excellent agreement with experimental Stokes shifts for this type of samples