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JWST imaging of the Pleiades: anisotropy of turbulence in the cold neutral medium
No full textInternational audienceInterstellar medium studies rely on magnetohydrodynamic (MHD) turbulence as a framework for interpretation. In this context, the statistical characterization of interstellar observations is of prime importance. We open a new perspective on diffuse interstellar matter by analyzing James Webb Space Telescope (JWST) observations of the Pleiades nebula with NIRCam. These observations are remarkable in that they provide a microscope view at the cold neutral medium (CNM) with a spatial resolution of 0.2 mpc (40 au). A two-dimensional Fourier analysis is used to characterize the structure of PAH emission in regions near and far from the Pleiades star Merope. To produce maps of the interstellar emission, stars and galaxies are filtered out. The final step in the data cleaning involves subtracting a component, in Fourier space, which we infer to be a residual of the near-infrared cosmic background. The PAH emission power spectra are highly anisotropic. They are well fitted with a break-free power-law, suggesting that we do not observe a specific scale for energy dissipation. Power-law indices are -3.5 near Merope and -3 in the more distant field. The magnetic field orientation, as derived from the Planck dust polarization data, aligns with the PAH anisotropy. The power anisotropy is constant across scales. These findings are discussed in relation to interstellar turbulence that may be driven by the Pleiades stars. The JWST observations of the Pleiades offer a new viewpoint for comparing observations and theoretical models, as they examine physical scales at which turbulence in the CNM is subsonic and decoupled from the thermal instability. The observations may indicate that the turbulent energy cascade in the CNM is anisotropic
Capillary Drainage in Horizontal Soap Films: Theoretical Review and Experimental Illustrations
No full textInternational audienceSoap films and bubbles are inherently unstable systems that evolve over time. Their thickness is primarily governed by the competition between capillary and viscous forces. The presence of surfactants introduces Marangoni stresses, which limit interfacial extension and significantly increase film lifetime. While the bulk flow is typically well-described by a simple Poiseuille profile between the two interfaces, the interfacial dynamics can induce complex behaviors, even in the simple case of horizontal film drainage, which is used as a paradigmatic example in this review. The interfacial velocity is dictated by the thickness gradients and by the interfacial rheology, which, in many practical cases, reduces to the condition of an incompressible interface. This simplified framework allows for analytical predictions and scaling laws in axisymmetric flows. It is also consistent with the spontaneous symmetry breaking that may be observed in horizontal films—a phenomenon associated with the marginal regeneration process, which remains only partially understood. This review presents the most elementary theoretical frameworks capable of capturing the essential features of these flows and provides quantitative comparisons with available experimental data
Iron Sulfides Produced by Thermococcales: An Iron Detoxification Mechanism
No full textInternational audienceThermococcales, sulfur-reducing archaea inhabiting the hottest parts of hydrothermal vents, have evolved to thrive in environments rich in iron and sulfide species. In this study, using experimental analogues of sulfur-rich hydrothermal chimneys, we confirm previous suggestions that the precipitation of iron sulfide minerals promoted by Thermococcales contributes to a population-wide adaptation to reactive species induced by the presence of high levels of iron. In parallel with mineral phases identification, cellular metabolic activity was monitored during mineralization, revealing a mechanism in which a subpopulation of cells does not survive mineralization and becomes encrusted in pyrite, while the remaining living cells exhibit a gene expression profile focused on DNA repair and metal excess associated detoxification. Compared to abiotic conditions, Thermococcales induce a faster precipitation of dissolved iron, immobilising excess metal. Our results clarify the role of mineralizing cells in this survival mechanism, suggesting that this biomineralization process allows resilience to extreme chemical stress. Upon drastic levels of toxic dissolved iron, thanks to a population of mineralizing cells, the surviving Thermococcales are thus more likely to endure those still harsh environments. This complex mechanism is likely a key factor in the adaptation of microorganisms to the hottest environments of hydrothermal vents
NIKA2 Cosmological Legacy Survey. First measurement of the confusion noise at the IRAM 30 m telescope
No full textInternational audienceThe NIKA2 Cosmological Legacy Survey (N2CLS) is a large programme using the NIKA2 dual-band camera on the IRAM 30 m telescope. Its goal is to improve our understanding of the physics of distant Dusty Star Forming Galaxies (DSFGs) by carrying out deep surveys of two fields, GOODS-North and COSMOS. This work is focussed on GOODS-North, which was observed for 78.2 hours, simultaneously at 1.2 and 2 mm, with a field of view of ∼240 arcmin 2 . With such a deep integration, we were able to measure, for the first time, the confusion noise limits at the 30 m telescope using the best sampled ∼62 arcmin 2 and masking sources with a flux greater than 0.54 or 0.17 mJy at 1.2 or 2 mm, respectively. We found a confusion noise of 139.1 +15.9 -19.2 ± 11.9 µJy/beam at 1.2 mm and 38.6 +9.6 -13.1 ± 3.7 µJy/beam at 2 mm (the first uncertainty is statistical, the second is the cosmic variance). In this region, this corresponds to half the instrumental noise. To derive these estimates, we devised a novel estimator, referred to as the cross variance, which also enabled us to estimate the correlated confusion noise between the two bands. Thus, we obtained a result of 49.6 +15.9-24.8 ± 6.4 µJy/beam. These values are consistent with the state of the art Simulated Infrared Dusty Extragalactic Sky (SIDES) model.</div
Dark Energy Survey Year 6 Results: Galaxy-galaxy lensing
No full textInternational audienceWe present galaxy--galaxy lensing (GGL) measurements from the full six years of data from the Dark Energy Survey (DES Y6), covering and used in the DES Y6 pt cosmological analysis. We use the MagLim++ lens sample, containing million galaxies divided into six redshift bins, and the Metadetection source catalog, including million galaxies divided into four redshift bins. The mean tangential shear signal achieves a total signal-to-noise ratio (S/N) of , corresponding to a improvement over DES Y3. After applying the scale cuts used in the cosmological analysis, with () for the linear (nonlinear) galaxy-bias model, the S/N is reduced to (90). A comprehensive suite of validation tests demonstrates that the measurement is robust against observational and astrophysical systematics at the statistical precision required for the DES Y6 analysis. Although not used in the main cosmological analysis, we extract high--signal-to-noise geometric shear-ratio measurements from the galaxy--galaxy lensing signal on small angular scales. These measurements provide an internal consistency check on the photometric redshift distributions and shear calibration used in the pt analysis
Space-time evolution of particle emission in pPb collisions at TeV with 3D kaon femtoscopy
No full textInternational audienceThe measurement of three-dimensional femtoscopic correlations between identical charged kaons (KK) produced in pPb collisions at center-of-mass energy per nucleon pair TeV with ALICE at the LHC is presented for the first time. This measurement, supplementary to those in pp and PbPb collisions, allows understanding the particle-production mechanisms at different charged-particle multiplicities and provides information on the dynamics of the source of particles created in pPb collisions, for which a general consensus does not yet exist. It is shown that the measured source sizes increase with charged-particle multiplicity and decrease with increasing pair transverse momentum. These trends for KK are similar to the ones observed earlier in identical charged-pion and KK correlations in PbPb collisions at various energies and in correlations in pPb collisions at TeV. At comparable multiplicity, the source sizes measured in pPb collisions agree within uncertainties with those observed in pp collisions, and there is an indication that they are smaller than those observed in PbPb collisions. The obtained results are also compared with predictions from the hadronic interaction model EPOS~3, which tends to underestimate the source size for the most central collisions and agrees with the data for semicentral and peripheral events. Furthermore, the time of maximal emission for kaons is extracted. It turns out to be comparable with the value obtained in highly peripheral PbPb collisions at the same energy, indicating that the kaon emission evolution is similar to that in pPb collisions
The Network for the Detection of Atmospheric Composition Change at 35 Years: Achievements and Future Strategy
No full textInternational audienceSince 1991, continuous, consistently calibrated and openly archived ground-based measurements from the Network for the Detection of Atmospheric Composition Change (NDACC) have been collected to investigate processes responsible for decadal-scale changes, anomalies in atmospheric composition, and to validate satellite observations and model simulations. These measurements, from nearly 120 stations, support fundamental research in the area of stratospheric and tropospheric processes impacting ozone chemistry, greenhouse gases, atmospheric radiative forcing, air quality, and interactions with solar radiation and the entire Earth system. NDACC data are supplemented by observations from 11 global Cooperating Networks. The operational principles of Cooperating Networks are well aligned with NDACC objectives and protocols, focusing on data that (a) are high-quality, uniformly processed and traceable to reference standards; and (b) capture short-term (daily to interannual) anomalies and long-term trends. This paper summarizes the NDACC organizational structure. We review the major accomplishments of NDACC since De Mazière et al. (2018), collaborative research with Cooperating Networks, and interactions with the satellite and modeling communities. Ground-based atmospheric composition monitoring is at a crossroads. Challenges include sustainability of human and financial resources required for complex and intensive data collection, technical issues including aging instrumentation, requirements for FAIR (findable, accessible, interoperable, reusable) data, and lack of data over most of Asia, Africa and South America. NDACC is well-positioned to adopt a three-pronged strategy going forward: protecting and modernizing existing stations; promoting the growing use of NDACC data; expanding the number of measured species and network coverage in under-sampled or under-reporting regions
Predicting rolling shear failure of cross-laminated panels using a multiscale domain decomposition approach
No full textInternational audienceCross-laminated timber (CLT) is gaining popularity as a sustainable building material due to its favorable structural performance and low environmental impact. This study introduces a multiscale domain decomposition method, known as the LaTIn strategy, to predict the out-of-plane behavior and failure of CLT panels. The proposed approach incorporates cohesive zone models to capture inter-and intralaminar damage using a cohesive parameter identification based on strength values reported in the literature. By aligning domain partitioning with principal stress directions and leveraging parallel computations, the method reduces degrees of freedom and the number of subdomains by up to 55% and 70%, respectively. Additional algorithmic enhancements allow for a 70% reduction of iterations. Validation with experimental data confirms the model's ability to predict rolling shear failure with high accuracy. These results demonstrate the potential of the strategy for efficient and reliable simulation of timber structures, in line with the needs of multiscale nonlinear analysis in structural engineering
Functionalized Anti-Cryptophane-A as a Platform for Type II Porous Ionic Liquids
No full textInternational audienceType II porous ionic liquids could be prepared at room temperature by dissolving up to 5 wt% of anti-cryptophane-A derivatives functionalized with alkyl or fluorinated alkyl chains in phosphonium- and pyrrolidinium-based ionic liquids. In this study, we provide the first direct experimental evidence that these molecular cages retain their internal free volume when dissolved in ionic liquids. At 303 K and 1 bar, the porous ionic liquids prepared as solutions of anti-cryptophane-A grafted with a ten-carbon alkyl chain in the ionic liquids [P6,6,6,14][NTf2] (1:36), [P6,6,6,14][DCA] (1:52) and [C1C3pyrr][NTf2] (1:50) absorb 1 3.0, 3.5 and 11 times more methane than the pure ionic liquid, respectively. The solution of anti-cryptophane-A grafted with a fluorinated alkyl chain in [P6,6,6,14][NTf2] (1:73) absorbs in turn 1.8 times more methane than the pure ionic liquid. We show that 97(2)% of the cryptophane dissolved in [P6,6,6,14][NTf2] can encapsulate one molecule of methane, whereas only 60(1)% of the cavities in solid cryptophane are available for gas encapsulation. The presence of permanent porosity in the liquid solution is further supported by controlled atmosphere 1H NMR spectroscopy that allows to distinguish between free and caged methane thus providing molecular-level evidence that the gas is encapsulated in the free cryptophane cavities
