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Robust a posteriori estimation of probit-lognormal seismic fragility curves via sequential design of experiments and constrained reference prior
No full textInternational audienceA seismic fragility curve expresses the probability of failure of a structure conditional to an intensity measure (IM) derived from seismic signals. When only limited data is available, the practitioner often refers to the probit-lognormal model coupled with maximum likelihood estimation (MLE) to obtain estimates of these curves. This means that only a binary indicator of the state (BIS) of the structure is known, namely a failure or non-failure state indicator, when it is subjected to a seismic signal with an intensity measure IM. In this context, the objective of this work is to propose a method for optimally estimating such curves by obtaining the most precise estimate possible with the minimum of data. The novelty of our work is twofold. First, we present and show how to mitigate the likelihood degeneracy problem which is ubiquitous with small data sets and hampers frequentist approaches such as MLE. Second, we propose a novel strategy for sequential design of experiments (DoE) that selects seismic signals from a large database of synthetic or real signals via their IM values, to be applied to structures to evaluate the corresponding BISs. This strategy relies on a criterion based on information theory in a Bayesian framework. It therefore aims to sequentially designate the IM value such that the pair (IM, BIS) has on average, with respect to the BIS of the structure, the greatest impact on the posterior distribution of the fragility curve. The methodology is applied to a case study from the nuclear industry. The results demonstrate its ability to efficiently and robustly estimate the fragility curve, and to avoid degeneracy even with a limited amount of data, i.e., less than 100. Furthermore, we demonstrate that the estimates quickly reach the model bias induced by the probit-lognormal modeling. Eventually, two criteria are suggested to help the user stop the DoE algorithm
Evidence of Fukushima fallout in the area affected by wildfires in Kamaishi (Iwate Prefecture, Tohoku Region, Japan): Implications for future environmental research using radionuclide tracers
No full textInternational audienceSignificant deposition of radiocesium including 134Cs and 137Cs occurred in March 2011 following the Fukushima nuclear accident across vast regions of Northeastern Japan. However, as most studies focused on fallout that took place in the Fukushima Prefecture, much less information is available on the situation that prevails further to the North, in other parts of the Tohoku Region of Japan. In this context, the current research investigated the occurrence of fallout radionuclides (including natural 210 Pb-xs as well as artificial 134Cs and 137Cs) in burned and unburned soil profiles as well as in a range of surface soil and sediment samples collected in the region of Kamaishi (Iwate Prefecture, Tohoku Region, Japan) affected by wildfires in 2017. Results show that 210Pb-xs and 137Cs may be used as tracers of sediment sources across landscapes affected by wildfires in this region. Furthermore, the soil profile analysis demonstrated that all analysed fallout radionuclides were found enriched in the burned vs. unburned profiles, due to the incorporation of radionuclides trapped by vegetation into the ash after the fire. The detection of 134 Cs in the uppermost 0-5 cm depth layer in all investigated soil profiles also allowed to demonstrate the occurrence of significant Fukushima fallout of 134Cs and 137Cs in this region (roughly of the same order of magnitude as the fallout associated with the nuclear atmospheric tests in the 1960s). In the future, both sources of fallout should be considered to provide relevant interpretations when examining radionuclide data found in environmental samples collected in vast regions of Northeastern Japan. The analysis of 134Cs should also be encouraged to document the sources of fallout in these regions as long as this short-lived radionuclide remains detectable (i.e., theoretically by 2031)
Towards Efficient Nuclear Data Uncertainty Quantification in Radiation Shielding Calculations
No full textInternational audienceThis study explores methodologies for propagating nuclear data uncertainties in radiation shielding calculations. The work is motivated by the aging of Pressurized Water Reactor (PWR) vessels, where quantifying uncertainties can contribute to improved risk assessment; in this context, the present analysis serves as a preliminary step toward more complex, application-specific scenarios. Two approaches are considered: First-Order Second-Moment (FOSM) sensitivity analysis and Monte Carlo Sampling (MCS), both implemented through MCNP6.3. In the FOSM approach, we examine the use of variance reduction in combination with sensitivity calculations, while the MCS method is optimized to address its higher computational demand. Our analysis revealed discrepancies in certain cases when applying variance reduction with sensitivity calculations, which may compromise its applicability under certain conditions. Conversely, the MCS approach, using Sobol and Latin Hypercube Sampling (LHS) with fast Total Monte Carlo or fast GRS techniques, yielded results comparable to FOSM. These findings suggest that using MCS for propagating nuclear data uncertainties in shielding problems should be feasible, while maintaining computational demand similar to that of traditional first-order methods. Future work will test this approach in more complex, realistic configurations
QFT as a set of ODEs
No full textInternational audienceCorrelation functions of local operators in Quantum Field Theory (QFT) on hyperbolic space can be fully characterized by the set of QFT data . These are the scaling dimensions of boundary operators , the boundary Operator Product Expansion (OPE) coefficients and the Boundary Operator Expansion (BOE) coefficients that characterize how each bulk operator can be expanded in terms of boundary operators .For simplicity, we focus on two dimensional QFTs and derive a universal set of first order Ordinary Differential Equations (ODEs) that encode the variation of the QFT data under an infinitesimal change of a bulk relevant coupling. In principle, our ODEs can be used to follow a Renormalization Group (RG) flow starting from a solvable QFT into a strongly coupled phase and to the flat space limit
Searches for extra-dimensional excitations in light-by-light scattering
No full textInternational audienceWe present a comprehensive phenomenological analysis of the Radion in the Randall-Sundrum model, focusing on its production via light-by-light scattering in ultra-peripheral proton-proton collisions at the LHC. We provide a consistent derivation of the effective couplings to Standard Model fields, clarifying the normalization of the trace anomaly-induced coupling to photons and the role of kinetic mixing with the Higgs boson. We demonstrate that while the pure gravitational coupling is loop-suppressed relative to Axion-Like Particles (ALPs), making the unmixed Radion elusive, the non-minimal mixing with the Higgs sector can induce constructive interference that enhances the signal by orders of magnitude. Using forward proton tagging to select exclusive high-mass events, we reinterpret recent experimental limits on ALPs to derive the first exclusion contours for the Radion in the plane, showing that mixing scenarios are beginning to be constrained by current LHC data
Effect of local environment on Ly line profile in DESI/ODIN LAEs
No full textInternational audienceLyman-Alpha Emitters (LAEs) are star-forming galaxies with significant Ly emission and are often used as tracers of large-scale structure at high redshift. We explore the relationship between the Ly line profile and environmental density with spectroscopy from the Dark Energy Spectroscopic Instrument (DESI) of LAEs selected with narrow-band photometry through the One-hundred-deg DECam Imaging in Narrowbands (ODIN) survey. We use LAE surface density maps in the N419 (z 2.45) and N501 (z 3.12) narrow bands to probe the relationship between local environmental density and the Ly line profile. In both narrow bands, we stack the LAE spectra in bins of environmental density and inside and outside of protocluster regions. The N501 data shows 15% higher Ly line luminosity for galaxies in protoclusters, suggesting increased star formation in these regions. However, the line luminosity is not appreciably greater in protocluster galaxies in the N419 band, suggesting a potential redshift evolution of this effect. The shape of the line profile itself does not vary with environmental density, suggesting that line shape changes are caused by local effects independent of a galaxy's environment. These data indicate a potential relationship between LAE local environmental density, ionized gas distribution, and Ly line luminosity
The BIOMASP+ project on biosphere-atmosphere exchanges and their role in air pollution in the subtropical megacity of São Paulo: motivations, methods and preliminary observations
No full textInternational audienceAir pollution, especially in urban areas, is the result of a complex mixture of natural and anthropogenic emissions and their atmospheric processing. It causes millions of premature deaths worldwide and affects plant metabolism, which in turn alters the emissions of Biogenic Volatile Organic Compound (BVOCs) by plants. By taking the subtropical Metropolitan Area of São Paulo (MASP) as a natural laboratory, the BIOMASP+ project (BIOsphere-atmosphere interactions in the Metropolitan Area of São Paulo - plus) a ims to evaluate the interplay between the biosphere and secondary pollution (ozone and SOA formation and aging). The Brazilian Atlantic Forest (Mata Atlântica) is the target ecosystem as the fifth biodiversity hotspot in the world. Here we present the scientific motivations of the project, its methodology and the preliminary observations from the Special Observation Periods of year 2023 (SOP1, 2, 3 and 4). BIOMASP+ is (i) integrative, by combining in-situ/remote/laboratory observations andmodeling, (ii) multidisciplinary, addressing micrometeorology, urban climate, atmospheric chemistry and biology. The project involves multiple nested scales: from leaf to above-canopy levels, from very short time (microseconds) to multi-year scale, from few millimeters (turbulence scale) to synoptic scale. In particular, the experimental effort relies on the implementation of two contrasting supersites (primary forest and urban forest) with a 30-m and 20-m flux towers, respectively, and a variety of state-of-the-art instruments. Ambient observations and the quantification of BVOC emissions have highlighted the complex interactions between meteorology, atmospheric composition of pollution, biogenic emissions of representative remnants of the Atlantic Forest and anthropogenic emissions
Can galactic magnetic fields diffuse into the voids?
No full textInternational audienceCosmic voids are magnetized at the level of at least G on Mpc scales, as implied by blazar observations. We show that an electrically conducting plasma is present in the voids, and that, because of the plasma, \emph{diffusion} into the voids of galactic fields generated by a mean-field dynamo is far too slow to explain the present-day void magnetization. Indeed, we show that even in the presence of turbulence in the voids, dynamo-generated galactic fields diffuse out to a galactocentric radius of only 200-400 kpc. Therefore, it is challenging to meet the required volume filling-factor of the void magnetic field. We conclude that a primordial origin remains the most natural explanation to the space-filling weak fields in voids
Tuning band gap and optical properties of Ce-doped ZnO nanorods via electrodeposition and DFT analysis for solar energy applications
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Exploring lignin conformation in organic and deep eutectic solvents using small-angle neutron scattering
No full textInternational audienceLignin, a structurally intricate and heterogeneous phenolic biopolymer, holds considerable promise as a sustainable alternative to petrochemical-derived materials across diverse applications in the energy and materials sectors. However, precise lignin molecular weight and structure determination remains challenging due to its intrinsic tendency to aggregate in solution and the absence of chemically analogous polymer standards for chromatographic techniques. By employing small-angle neutron scattering, this study aims at precise measurement of lignin's polymeric conformation, aggregation behavior, and radius of gyration in organic gel permeation chromatography/NMR solvent, tetrahydrofuran (THF), and in an emerging class of solvent systems known as deep eutectic solvents (DES). These "designer" solvents, formed from tailored hydrogen bond donors and acceptors, are gaining importance for lignin extraction from biomass and analytical characterization. However, their influence on lignin conformation in solutions remains unexplored. Our study reveals that both organosolv and Indulin AT kraft lignin in THF exhibit loosely associated polymeric conformations. Upon D 2 O addition, Indulin AT undergoes moderate swelling, suggestive of partial dissolution, while organosolv lignin undergoes substantial elongation with directional ordering, resulting in flexible rod-like structures. Lignin oil from a reductive catalytic fractionation process (RCF), in contrast, remains well-dispersed in THF and shows minimal structural change with solvent polarity modulation via D 2 O addition. Indulin AT and organosolv lignin solvated in the choline chloride/oxalic acid/ethylene glycol DES adopt dense, cylindrical morphologies. These structures show moderate temperature sensitivity and notable resistance to D 2 O-induced structural perturbation, highlighting strong lignin-DES interactions. Additionally, lignin extracted from cocoa bean shells using a diol-based DES and subsequently dissolved in the same solvent demonstrates a fractal-like morphology, which evolves with D 2 O content and temperature, revealing a complex solvation landscape. These results offer molecular-level insight into lignin's solvent-dependent structural transitions, enabling more accurate molecular weight estimation and supporting optimization of lignin processing for high-performance biobased formulations and advanced materials