196 research outputs found
Contribution à l’étude du Mésolithique dans la moyenne vallée de la Vilaine
Le programme de prospection thématique mené en 1998 a subi quelques aménagements. En effet, nous avons au cours de cette année réduit le volume des prospections destinées à la recherche de nouveaux gisements et réorienté une partie des recherches vers la réalisation de sondages. Par ailleurs, des prospections complémentaires ont été effectuées afin d’enrichir des séries déjà existantes. Les prospections ont néanmoins permis de localiser sept nouveaux sites mésolithiques. Une quinzaine de poin..
Impact of Climate Change on HeatWave Risk
International audienceWe study a new risk measure inspired from risk theory with a heat wave risk analysis motivation. We show that this risk measure and its sensitivities can be computed in practice for relevant temperature stochastic processes. This is in particular useful for measuring the potential impact of climate change on heat wave risk. Numerical illustrations are given
Genetic control of plasticity of oil yield for combined abiotic stresses using a joint approach of crop modeling and genome-wide association
Understanding the genetic basis of phenotypic plasticity is crucial for
predicting and managing climate change effects on wild plants and crops. Here,
we combined crop modeling and quantitative genetics to study the genetic
control of oil yield plasticity for multiple abiotic stresses in sunflower.
First we developed stress indicators to characterize 14 environments for
three abiotic stresses (cold, drought and nitrogen) using the SUNFLO crop model
and phenotypic variations of three commercial varieties. The computed plant
stress indicators better explain yield variation than descriptors at the
climatic or crop levels. In those environments, we observed oil yield of 317
sunflower hybrids and regressed it with three selected stress indicators. The
slopes of cold stress norm reaction were used as plasticity phenotypes in the
following genome-wide association study.
Among the 65,534 tested SNP, we identified nine QTL controlling oil yield
plasticity to cold stress. Associated SNP are localized in genes previously
shown to be involved in cold stress responses: oligopeptide transporters, LTP,
cystatin, alternative oxidase, or root development. This novel approach opens
new perspectives to identify genomic regions involved in
genotype-by-environment interaction of a complex traits to multiple stresses in
realistic natural or agronomical conditions.Comment: 12 pages, 5 figures, Plant, Cell and Environmen
High-order harmonic transient grating spectroscopy of SF6 molecular vibrations
special issue : Ultrafast electron and molecular dynamicsInternational audienceStrong field transient grating spectroscopy has shown to be a very versatile tool in time-resolved molecular spectroscopy. Here we use this technique to investigate the high-order harmonic generation from SF6 molecules vibrationally excited by impulsive stimulated Raman scattering. Transient grating spectroscopy enables us to reveal clear modulations of the harmonic emission. This heterodyne detection shows that the harmonic emission generated between 14 to 26 eV is mainly sensitive to two among the three active Raman modes in SF6, i.e. the strongest and fully symmetric nu 1-A1g mode (774 cm-1, 43 fs) and the slowest mode nu5-T2g (524 cm-1, 63 fs). A time-frequency analysis of the harmonic emission reveals additional dynamics: the strength and central frequency of the nu 1 mode oscillate with a frequency of 52 cm-1 (640 fs). This could be a signature of the vibration of dimers in the generating medium. Harmonic 11 shows a remarkable behavior, oscillating in opposite phase, both on the fast (774 cm-1) and slow (52 cm-1) timescales, which indicates a strong modulation of the recombination matrix element as a function of the nuclear geometry. These results demonstrate that the high sensitivity of high-order harmonic generation to molecularvibrations, associated to the high sensitivity of transient grating spectroscopy, make their combination a unique tool to probe vibrational dynamics
Spatial variability of potassium in agricultural soils of the canton of Fribourg, Switzerland
Potassium (K) is a crucial element for plant nutrition and its availability and spatial distribution in agricultural soils is influenced by many agro-environmental factors. In Switzerland, a soil monitoring network (FRIBO) was established in 1987 with 250 sites distributed over the whole of the canton of Fribourg (representing 4% of the surface area of Switzerland), whose territory is shared between the Swiss Midlands and the Western Alp foothills. In this study area, diverse geological deposits (sandstone, marlstone, silts and calcareous rocks), soil types (Cambisols, Gleysols, Rendzinas, Luvisols and Fluvisols) and land uses (cropland, permanent grassland and mountain pasture) are present, making the network interesting for assessing the relative contribution of environmental variables and land use management on soil properties. The aims of the present study were to (i) characterize the soil K status in the Fribourg canton according to four different extraction methods; (ii) analyse the spatial variability of soil K in relation to land use, soil type, soil parent material and topography; (iii) evaluate the spatial predictability of K at the canton level; and (iv) analyse the implications for K fertilization management. The overall amount of soil total K averaged 13.6 g.kg-1 with significant variations across the sites (5.1-22.1 g.kg-1). The spatial distribution of total K was particularly influenced by soil parent materials, as suggested by a significant global spatial autocorrelation measure (Moran’s I10km = 0.43) and significant differences observed among soil types and soil parent materials. On the other hand, available mean K forms were significantly different among land uses, with the highest mean values of available K encountered in permanent grasslands, from 46.3 mg.kg-1 (water extraction) to 198 mg.kg-1 (acetate ammonium + EDTA extraction). All K forms showed similar spatial regional patterns for all spatial interpolation methods, with areas dominated by permanent grassland and crops presenting higher values. However, these trends were less pronounced for the available K forms due to the prevalence of on-farm management practices for these K forms and their high temporal variability. This hypothesis was supported by spatial clustering of low and/or high K fertility status that could be related to local particular farming practices. Grasslands require particular attention with regard to overall high K fertility status
Successful Leptogenesis in SO(10) Unification with a Left-Right Symmetric Seesaw Mechanism
We study thermal leptogenesis in a broad class of supersymmetric SO(10)
models with a left-right symmetric seesaw mechanism, taking into account
flavour effects and the contribution of the next-to-lightest right-handed
neutrino supermultiplet. Assuming M_D = M_u and a normal hierarchy of light
neutrino masses, we show that four out of the eight right-handed neutrino mass
spectra reconstructed from low-energy neutrino data can lead to successful
leptogenesis with a reheating temperature in the (10^9 - 10^10) GeV range. In
the remaining four solutions, leptogenesis is dominated by N_2 decays, as in
the type I seesaw case. We find that some of these spectra can generate the
observed baryon asymmetry for reheating temperatures above 10^10 GeV, in
contrast to the type I case. Together with flavour effects, an accurate
description of charged fermion masses turns out to be a crucial ingredient in
the analysis.Comment: 32 pages, 23 figures. v2: 2 comments [below Eq. (53) and at the end
of the conclusions] and 1 reference added, typos corrected. Version to be
published in Nucl. Phys.
New insights into stop codon recognition by eRF1
In eukaryotes, translation termination is performed by eRF1, which recognizes stop codons via its N-terminal domain. Many previous studies based on point mutagenesis, cross-linking experiments or eRF1 chimeras have investigated the mechanism by which the stop signal is decoded by eRF1. Conserved motifs, such as GTS and YxCxxxF, were found to be important for termination efficiency, but the recognition mechanism remains unclear. We characterized a region of the eRF1 N-terminal domain, the P1 pocket, that we had previously shown to be involved in termination efficiency. We performed alanine scanning mutagenesis of this region, and we quantified in vivo readthrough efficiency for each alanine mutant. We identified two residues, arginine 65 and lysine 109, as critical for recognition of the three stop codons. We also demonstrated a role for the serine 33 and serine 70 residues in UGA decoding in vivo. NMR analysis of the alanine mutants revealed that the correct conformation of this region was controlled by the YxCxxxF motif. By combining our genetic data with a structural analysis of eRF1 mutants, we were able to formulate a new model in which the stop codon interacts with eRF1 through the P1 pocket
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Laser-Induced Electron Diffraction in Chiral Molecules
Strong laser pulses enable probing molecules with their own electrons. The oscillating electric field tears electrons off a molecule, accelerates them, and drives them back toward their parent ion within a few femtoseconds. The electrons are then diffracted by the molecular potential, encoding its structure and dynamics with angstrom and attosecond resolutions. Using elliptically polarized laser pulses, we show that laser-induced electron diffraction is sensitive to the chirality of the target. The field selectively ionizes molecules of a given orientation and drives the electrons along different sets of trajectories, leading them to recollide from different directions. Depending on the handedness of the molecule, the electrons are preferentially diffracted forward or backward along the light propagation axis. This asymmetry, reaching several percent, can be reversed for electrons recolliding from two ends of the molecule. The chiral sensitivity of laser-induced electron diffraction opens a new path to resolve ultrafast chiral dynamics
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