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Exclusive four pion photoproduction in ultraperipheral Pb-Pb collisions at TeV
No full textInternational audienceThe intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. The measurement of coherently photoproduced final states in ultraperipheral Pb-Pb collisions at TeV is presented for the first time. The cross section, d/d, times the branching ratio () is found to be mb in the rapidity interval . The invariant mass distribution is not well described with a single Breit-Wigner resonance. The production of two interfering resonances, and , provides a good description of the data. The values of the masses () and widths () of the resonances extracted from the fit are MeV/, MeV/, MeV/ and MeV/, respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions
Simulation of shockless spalling fragmentation using the Discrete Element Method (DEM)
No full textInternational audienceIn the present study a Discrete Element Method (DEM) is considered to model the dynamic behaviour and fragmentation mechanisms of alumina ceramic under high strain-rate shockless loading. GEPI (high-pulsed power) spalling experiments are simulated. The DEM allows to take into account the accurate propagation and interaction of stress waves within the samples upon calibration of microscopic bond parameters. The results indicate that a standard failure criterion can effectively represent the spalling phenomenon, though discrepancies with experimental data increase at higher strain rates. To address this, the study combines the DEM approach with a damage law, specifically the first and second order Kachanov damage law, tomodel crack initiation and propagation. Comparative analysis with experimental rear face velocity profiles validates the approach. The strain-rate sensitivity of the present DEM model is explored using loading pulses of increasing intensity that induce different strain-rate levels. This research demonstrates that the DEM approach can effectively model dynamic behaviour in brittle solids leading to a multiple fragmentation sensitive to the strain rate
Validation of a lipopetide approach to a Safe-and-Sustainable-by-Design strategy on nano-TiO2 UV filters
No full textInternational audienceTitanium dioxide (TiO2) nanoparticles are well suited for cosmetics and polymer films because they efficiently absorb UV light while remaining transparent to visible light. Their widespread use requires strategies for managing potential human and environmental risks. Implementing the Safe and Sustainable by Design (SSbD) methodology to advanced chemicals and materials is a major global challenge and a concept that is included in several EU research projects. This study employed a SSbD strategy by functionalizing the surface of TiO2 nanoparticles with a lipopeptide-based biosurfactant (Sodium Surfactin, SS). A colloidal heterocoagulation approach was used to produce SS-modified TiO2 nanoparticles. Different design options (TiO2 source, order of addition, TiO2/SS weight ratio) were investigated, and the properties were compared by measuring the UV filtering capability, photoreactivity, dustiness index, biological and ecotoxicological endpoints. This allowed us to estimate the safety and sustainability profile in agreement with the steps suggested by the JRC SSbD framework. The lipopeptide-based coating was essential for managing UV light-induced photoactivity and significantly lowering both in vitro cytotoxicity and ecotoxicity while simultaneously enhancing photostability when applied in cosmetic formulations. These results demonstrate that a colloidal process, which can be easily scaled up for industrial purposes, is a promising and exploitable SSbD strategy for the design and implementation of nano-TiO2 based UV filters
Digital electronics upgrade of the INDRA <math altimg="si2.svg" display="inline" id="d1e354"><mrow><mn>4</mn><mi>π</mi></mrow></math> charged particle detection array and resulting performance improvements
No full textInternational audienceINDRA is a 4π charged particle detection array in use since 1993 for the study of nuclear collisions at bombarding energies from a few 10s to a few 100s of MeV/nucleon. Originally equipped with custom electronics using the VXI standard, the entire acquisition system was recently upgraded to a fully digital system using commercially-available modules supplied by mesytec GmbH & Co. KG. At the same time, both low and high voltage supplies and all cabling and signal routing outside of the reaction chamber have also been replaced. The new electronics were used for the first time in 2022 in an experiment at GANIL coupling INDRA with 12 blocks of FAZIA telescopes placed at forward angles. The full details of the upgraded system, and the resulting improvements in performance, stability, dead time and identification capabilities are presented in this article
Validation of the DESI DR2 Ly BAO analysis using synthetic datasets
No full textInternational audienceThe second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI), containing data from the first three years of observations, doubles the number of Lyman- (Ly) forest spectra in DR1 and it provides the largest dataset of its kind. To ensure a robust validation of the Baryonic Acoustic Oscillation (BAO) analysis using Ly forests, we have made significant updates compared to DR1 to both the mocks and the analysis framework used in the validation. In particular, we present CoLoRe-QL, a new set of Ly mocks that use a quasi-linear input power spectrum to incorporate the non-linear broadening of the BAO peak. We have also increased the number of realisations used in the validation to 400, compared to the 150 realisations used in DR1. Finally, we present a detailed study of the impact of quasar redshift errors on the BAO measurement, and we compare different strategies to mask Damped Lyman- Absorbers (DLAs) in our spectra. The BAO measurement from the Ly dataset of DESI DR2 is presented in a companion publication
Magnetic aftereffect and Barkhausen effect in thin films of the altermagnetic candidate Mn<sub>5</sub>Si<sub>3</sub>
No full textAltermagnetism as a third distinct type of collinear magnetic ordering lately attracts vivid attention. We here study the Hall effect response of micron-scale Hall bars patterned into Mn5Si3 thin films, an altermagnet candidate material. Recording transport data as a function of time, at fixed magnetic field magnitude, we observe a time-dependent relaxation of the Hall voltage qualitatively and quantitatively similar to the magnetic viscosity response well established in ferromagnetic films. In addition, the Hall voltage time traces feature clear unilateral steps, which we interpret as Barkhausen steps, i.e., as experimental evidence for abrupt reorientations of magnetic (Hall vector) domains in the altermagnetic candidate material. A quantitative analysis yields a Barkhausen length of around 18nm in the Hall bar devices with the smallest width of 100 nm
Multi-Messenger Studies with High-Energy Neutrinos and Gamma Rays: The WST Opportunity
No full textInternational audienceThe search for the sources of ultra-high-energy cosmic rays (UHECRs) using high-energy neutrinos represents a frontier in high-energy astrophysics. However, a critical bottleneck remains: the ability to rapidly survey the sizable sky areas defined by the localization uncertainties of neutrino detectors and to provide rapid spectroscopic classification of the multitude of optical transients found within them. By deploying a large field-of-view with high-multiplex Multi-Object Spectroscopy (MOS) on a large aperture telescope, one can instantaneously cover neutrino error circles, thus providing crucial spectroscopic classifications of potential counterparts discovered, for example, by the Vera C. Rubin Observatory (LSST) with unprecedented efficiency. Furthermore, simultaneous operation of a giant panoramic central Integral Field Spectrograph (IFS) would allow for detailed kinematic and environmental characterization of primary candidates. This facility would unlock deep synergies between next-generation neutrino telescopes (IceCube-Gen2, KM3NeT) and gamma-ray observatories (CTAO), transforming unique multi-messenger alerts into a comprehensive physical understanding
Highstand, drop and stillstand: reconstructing MIS 5.5 sea-level changes in the central Mediterranean
No full textInternational audienc
Screening of materials in NaCl-MgCl2 at 600 °C– a comparative study leading to a new corrosion-resistance criterion
No full textInternational audienceThe behavior of several materials in molten NaCl-MgCl2 at 600°C during 168h was studied. In order to ensure the comparison of their respective corrosion resistance, a dedicated experimental set up and protocol were designed both for the control of the impurity level in the salt and for the corrosion testing. The salt was purified only through thermal steps and with the removal of precipitated MgO layer after solidification. Electrochemistry techniques (OCV and CV) were performed to ensure a good reproductibility in terms of amount of impurity. Regarding the corrosion testing, IN625 was used as a reference sample in every test, leading to a qualitative comparison between the different alloys. In these conditions, the SiC showed the best resistance while TA6V and 316L suffered the most. For Ni-based alloys Hastelloy G35 seemed to provide the best compromise despite its high chromium content. A coupling effect between Cr and Mo has been evidenced to explain Mo dissolution
Tara Polaris expeditions: seasonal and long-term contaminant monitoring in the changing central Arctic
No full textInternational audienceThe central Arctic atmosphere, cryosphere, hydrosphere and biosphere, is heavily impacted by anthropogenic activities. While some contaminants originate from local activities, the majority are transported over long distances via rivers, ocean currents, and atmospheric pathways. Contaminants can have adverse effects on the environment, ecosystems, and human health, which are expected to intensify with continued emissions and warming climate. This article outlines the objectives for new studies on contaminants in the Arctic Ocean, in particular during the Tara Polaris expedition, with an emphasis on year-round long-term contaminant dynamics and associated ecotoxicological risks. Mercury contamination remains a major concern in the Arctic, especially in the form of methylmercury, which is primarily produced by marine microbes. Methylmercury bioconcentrates, bioaccumulates and biomagnifies to harmful levels in Arctic wildlife and threatens indigenous communities. Anthropogenic lead (Pb), though low in Arctic waters, remains toxic and may be remobilized by climate change. Plastic pollution, from nano-to macro-scales, is widespread across all Arctic compartments, closely interacting with planktonic communities and posing ingestion risks to invertebrates, fish, seabirds and mammals (including humans). Chemicals of Emerging Arctic Concern (CEAC), including newly recognized persistent organic pollutants inherited from past industrial activities (e.g., per-and polyfluoroalkyl substances (PFAS)), are more recalcitrant in the environment than many other synthetic compounds, raising serious questions about their long-term ecological and health effects. In this context, the Tara Polaris expeditions aim to produce high-resolution, year-round observational data in the central Arctic to deepen our understanding of contaminant sources, transport, internal cycling and environmental fate. These data will also support the development and refinement of numerical models for contaminant dynamics in the context of both Arctic and global environmental change