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A 7-Year Record Of Vertical Profiles Of Radar Measurements And Precipitation Estimates At Dumont D'Urville, Adélie Land, East Antarctica
No full textInternational audienceStudying precipitation falling over Antarctica is crucial as snowfall represents the main water input term for the polar cap. However, precipitation observations still remain scarce – and, more particularly, in the atmospheric column – due to numerous experimental issues related to the white continent. This paper aims at helping to close this observation gap by presenting 7 years of Micro Rain Radar (Metek MRR-2) data at the Dumont d'Urville station in coastal Adélie Land, East Antarctica. Statistics are calculated on three radar variables (equivalent reflectivity, mean Doppler velocity and signal-to-noise ratio (SNR)) to outline the main characteristics of the radar dataset. Seasonal and interannual variabilities are also investigated, but no significant temporal trends are detected, except for the seasonal mean Doppler velocity, which is higher in summer and lower in winter. We then use the snowfall rate (S) data from a collocated snow gauge to estimate the MRR precipitation profile from the radar equivalent reflectivity (Ze) through a locally derived Ze–S relation. We find the relation Ze=43.3S0.88. The processing method used to obtain this relation, data quality and uncertainty considerations are discussed in the paper. In order to give an example of application of the dataset, a brief statistical comparison of the MRR precipitation rate along the vertical with model data from the ERA5 reanalysis and the LMDZ climate model is performed, which notably shows that models underestimate heavy precipitation events
Quantitative feasibility study of sequential neutron captures using intense lasers
No full textInternational audienceDeciphering the conditions under which neutron captures occur in the Universe to synthesize heavy elements is an endeavor pursued since the 1950s, but has proved elusive up to now due to the experimental difficulty of generating the extreme neutron fluxes required. It has been evoked that laser-driven (pulsed) neutron sources could produce neutron beams with characteristics suitable to achieve nucleosynthesis in the laboratory. In this scheme, the laser first generates an ultra-high-current, high-energy proton beam, which is subsequently converted into a dense neutron beam. Here we model, in a self-consistent manner, the transport of laser-accelerated protons through the neutron converter, the subsequent neutron generation and propagation, and finally the neutron capture reactions in gold (Au197), chosen as an illustrative example. Using the parameters of present-day available lasers, as well as of those foreseeable in the near future, we find that the final yield of the isotopes containing two more neutrons than the seed nuclei is negligible. Our investigation highlights that the areal density of the laser-driven neutron source is a critical quantity and that it would have to be increased by several orders of magnitude over the current state of the art in order to offer realistic prospects for laser-based generation of neutron-rich isotopes
Search for a scalar or pseudoscalar dilepton resonance produced in association with a massive vector boson or top quark-antiquark pair in multilepton events at = 13 TeV
No full textInternational audienceA search for beyond the standard model spin-0 bosons, , that decay into pairs of electrons, muons, or tau leptons is presented. The search targets the associated production of such bosons with a W or Z gauge boson, or a top quark-antiquark pair, and uses events with three or four charged leptons, including hadronically decaying tau leptons. The proton-proton collision data set used in the analysis was collected at the LHC from 2016 to 2018 at a center-of-mass energy of 13 TeV, and corresponds to an integrated luminosity of 138 fb. The observations are consistent with the predictions from standard model processes. Upper limits are placed on the product of cross sections and branching fractions of such new particles over the mass range of 15 to 350 GeV with scalar, pseudoscalar, or Higgs-boson-like couplings, as well as on the product of coupling parameters and branching fractions. Several model-dependent exclusion limits are also presented. For a Higgs-boson-like model, limits are set on the mixing angle of the Higgs boson with the boson. For the associated production of a boson with a top quark-antiquark pair, limits are set on the coupling to top quarks. Finally, limits are set for the first time on a fermiophilic dilaton-like model with scalar couplings and a fermiophilic axion-like model with pseudoscalar couplings
Pump-laser-wavelength dependence of population inversion in N 2 +
No full textInternational audienceWe investigate the pump wavelength dependence of population inversion in a nitrogen ion when nitrogen gas is irradiated by a femtosecond laser pulse in the wavelength range from ultraviolet to near-infrared. It is found that the population inversions corresponding to the transitions at 391 and 428 nm are very sensitive to the laser wavelength, with extreme values near 400 and 1000 nm. For the ultraviolet pump, the population inversions for 391 and 428 nm transitions occur at different wavelengths: a maximum inversion for the first corresponds to a minimum for the second. This is attributed to the near-resonance single-photon transition combined with the Raman process. A significantly stronger inversion is observed for the near-infrared laser, with the maximum depending on the laser intensity, ascribed to the ac Stark effect. The Floquet theory confirms this conclusion and reveals that the three-photon transition assisted by the strong laser field leads to this enhanced population inversion. This study provides the optimal conditions for air lasing based on ionic transitions of nitrogen molecules
Scaling laws of the plasma velocity in visco-resistive magnetohydrodynamic systems
No full textInternational audienceWe consider a visco-resistive magnetohydrodynamic modeling of a steady-state incompressible tokamak plasma with a prescribed toroidal current drive, featuring constant resistivity η and viscosity ν. It is shown that the plasma velocity root-mean-square behaves as η f (H) as long as the inertial term remains negligible, where H stands for the Hartmann number H ≡ (ην)^-1/2 , and that f (H) exhibits power-law behaviours in the limits H ≪ 1 and H ≫ 1. In the latter limit, we establish that f (H) scales as H^1/4 , which is consistent with numerical results
Spatial modeling of telomere intra-nuclear distribution reveals non-random organization that varies during cell cycle and depends on LAP2 and BAF
No full textAbstract Genome organization within the 3D nuclear volume influences major biological processes but is completely lost during mitosis, which represents a major challenge to maintain cellular identity and cell fate. To restore a functional G1 nucleus for the next cell cycle, it is imperative to reestablish genome organization during post-mitotic nuclear assembly. Importantly, the configuration of linear chromosomes has been shown to directly impact spatial genome architecture. Both centromeres and telomeres are known to associate with nuclear structures, such as the nuclear envelope, and support chromatin distribution. Here, using high-resolution 3D imaging combined with 3D spatial statistics and modeling, we showed that telomeres generally followed a regular distribution compared to what is expected under a random organization. While the preferential localization of telomeres at nuclear periphery was restricted to early G1, we found a strong clustering of centromeres in addition to their predominant peripheral localization at all cell cycle stages. We then conducted a targeted screen using MadID to identify the molecular pathways driving or maintaining telomere anchoring to the nuclear envelope. Among these factors, we could show that LAP2α transiently localizes to telomeres in anaphase, at a stage where LAP2α initiates the reformation of the nuclear envelope. Moreover, co-depletion of LAP proteins and their partner BAF impacted telomere redistribution in the next interphase. There results suggest that in addition to their crucial role in genome protection, telomeres also participate in reshaping functional G1 nuclei after mitosis
Dense and nondense limits for uniform random intersection graphs
No full textWe obtain the scaling limits of random graphs drawn uniformly in three families of intersection graphs: permutation graphs, circle graphs, and unit interval graphs. The two first families typically generate dense graphs, in these cases we prove a.s. convergence to an explicit deterministic graphon. Uniform unit interval graphs are nondense and we prove convergence in the sense of Gromov-Prokhorov after normalization of the distances: the limiting object is the interval [0,1] endowed with a random metric defined through a Brownian excursion. Asymptotic results for the number of cliques of size k (k fixed) in a uniform random graph in each of these three families are also given.In all three cases, an important ingredient of the proof is that, for indecomposable graphs in each class (where the notion of indecomposability depends on the class), the combinatorial object defining the graph (permutation, matching, or intervals) is essentially unique
Explore2 – Rapport de synthèse sur les projections climatiques régionalisées
No full textCe deuxième rapport sur le climat vise à préciser les évolutions climatiques projetées par l’ensemble élaboré dans le cadre du projet Explore2, d’en caractériser les incertitudes et de proposer des modes d’exploration de ces données.Dans un premier temps, les simulations individuelles sélectionnées à partir de l’ensemble EURO-CORDEX et corrigées par les méthodes ADAMONT et CDF-t sont évaluées selon des critères de changement en température et précipitation sur la France par rapport à l’ensemble CMIP6 complet au pas de temps saisonnier (hiver et été). La comparaison réalisée sur le scénario RCP8.5 à l’horizon fin de siècle met en évidence la concordance globale de ces simulations à l’exception de deux simulations hors de la dispersion CMIP6 en été (à la fois en température et précipitation). Le projet a décidé de rejeter ces deux simulations de l’ensemble final afin de pouvoir garantir une cohérence avec les changements proposés par CMIP6 sur la France. Une sélection de 17 couples GCM/RCM compose finalement l’ensemble baptisé « Explore2-2024 » dont les simulations (10 sous RCP2.6, 9 sous RCP4.5 et 17 sous RCP8.5) sont corrigées par les méthodes ADAMONT et CDF-t.Au-delà d'une caractérisation statistique des propriétés de l'ensemble Explore2-2024, un travail a également été mené pour identifier des simulations particulières proposant des futurs climatiques contrastés sur la France. Cette approche narrative ou « storyline » en anglais a conduit à sélectionner de manière experte quatre simulations pour leurs impacts attendus sur l’hydrologie. Les principales caractéristiques de ces narratifs sont détaillées et accompagnées de cartes. Il est à noter que la sélection de narratifs a aussi été comparée aux résultats d’une approche objective par classification hiérarchique ascendante (fournie en Annexe 1).Une grande partie de ce livrable est consacrée à l’analyse des évolutions climatiques proposées par l’ensemble Explore2-2024 à partir d’une liste synthétique d’indicateurs climatiques d’intérêt pour l’hydrologie. Les incertitudes sur les changements projetés sont évaluées selon des critères de robustesse pour chaque simulation et d’accord de signe pour l’ensemble. Pour chaque indicateur, des cartes des paramètres de distribution (médiane, min et max) sont fournies en identifiant pour chaque maille les simulations de l’ensemble portant ce signal. Les figures et tableaux de valeur (pour les changements France entière, moitié Nord, moitié Sud) sont aussi complétés par des commentaires donnant les messages clé sur les évolutions attendues.Un chapitre spécifique est proposé pour l’analyse des quatre narratifs sélectionnés par le projet avec des visualisations synthétiques, mettant en avant la variabilité inter annuelle en complément des moyennes par horizon
Acceleration of an interplanetary shock through the magnetosheath: a global hybrid simulation
No full textInternational audienceAccording to most observations and simulations, interplanetary shocks slow down when they propagate through the magnetosheath. In this article, we present results from a self-consistent global hybrid PIC simulation of an interplanetary shock which, by contrast, accelerates as it propagates through the magnetosheath. In this simulation, the solar wind upstream of the interplanetary shock is set up with an Alfvén Mach number M A = 4.5 and the interplanetary magnetic field (IMF) is set up to be almost parallel to the y direction in GSE coordinate system. The ‘planet’ is modelled as a magnetic dipole with no tilt: the dipole is in the GSE’s z direction. In the ecliptic plane (Oxy), which contains the interplanetary magnetic field (IMF), the magnetic field lines are piling up against the magnetopause, and the velocity of the interplanetary shock decreases from 779 ± 48 km/s in the solar wind down to 607 ± 48 km/s in the magnetosheath. By contrast, in the noon-meridian plane (Oxz), which is perpendicular to the IMF, the velocity of the interplanetary shock in the magnetosheath can reach values up to 904 ± 48 km/s. This study suggests that interplanetary shocks can accelerate as they propagate through the magnetosheath. This finding, reported here for the first time, could have important implications for space weather, as it corresponds to the case where an interplanetary shock catches up with a low Alfvén Mach number solar transient such as an interplanetary coronal mass ejection
Unveiling the Initiation Route of Coronal Mass Ejections through Their Slow Rise Phase
No full textInternational audienceUnderstanding the early evolution of coronal mass ejections (CMEs), in particular their initiation, is the key to forecasting solar eruptions and induced disastrous space weather. Although many initiation mechanisms have been proposed, a full understand- ing of CME initiation, which is identified as a slow rise of CME progenitors in kine- matics before the impulsive acceleration, remains elusive. Here, with a state-of-the-art thermal-magnetohydrodynamics simulation, we determine a complete CME initiation route in which multiple mainstream mechanisms occur in sequence yet are tightly cou- pled. The slow rise is first triggered and driven by the developing hyperbolic flux tube (HFT) reconnection. Subsequently, the slow rise continues as driven by the coupling of the HFT reconnection and the early development of torus instability. The end of the slow rise, i.e., the onset of the impulsive acceleration, is induced by the start of the fast magnetic reconnection coupled with the torus instability. These results unveil that the CME initiation is a complicated process involving multiple physical mechanisms, thus being hardly resolved by a single initiation mechanism