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Convective-absolute and dripping-jetting transitions in core-annular flow within fuel cells
No full textInternational audienceLiquid/vapour water flows are encountered in a variety of fields, such as in Proton Exchange Membrane Fuel Cell (PEMFC), an emerging technology for energy decarbonation. In PEMFC, two-phase core-annular water flows are observed in the gas fuel channels (GFC) used to supply the reactive species to the cell. Formation of liquid plugs may occur via the Plateau-Rayleigh instability in these millimeter-size GFC [1]. This instability is however modified by the presence of an imposed core gas flow which may non-linearly saturate its development and prevent the formation of plugs [3]. Both convective and absolute instabilities are observed under these conditions. A 2D-axisymmetrical two-phase lubrication model is developed to investigate this instability transition. It is solved numerically for two configurations: (1) in an open domain with a finite-difference scheme allowing to simulate the spatio-temporal evolution of the flow; (2) in a periodic domain using the continuation software Auto-07p which allows to track nonlinear travelling-wave solutions corresponding to the most dangerous instability mode. By comparing these approaches, it is observed that, while both methods predict similar results for a convective instability, significant differences in the predicted wave-length are observed for an absolute instability. Notably, a transition from dripping to jetting is observed; in the dripping regime, the wavelength is selected by the boundary condition. Similar results are also obtained when inertial effects are accounted for by using a WRIBL model [2] implemented in Auto-07p and an open-domain Direct Numerical Simulation solved with TRUST/TrioCFD. The goal of the current work is to understand the dripping regime under the conditions of the absolute instability in order to obtain correlations between the input parameters (liquid/gas flow rates Ql,g and inlet film thickness) and the travelling-wave variables (celerity, maximum/minimum film thickness, wavelength, plug width, etc.). Ultimately, the global pressure drop over a full channel length shall be predicted by this model, enabling the construction of a macroscopic 1D channel model to be coupled to electrochemical and transport models in an integrative model of the fuel cell
Communiquer sur les risques (péri)glaciaires ? Pistes de réflexion à partir des recherches en sciences sociales sur les risques naturels
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Towards a unified view of uncertainty quantification methods for full waveform inversion
No full textInternational audienceFull Waveform Inversion (FWI) is a strongly ill-posed and computationally intensive inverse problem. Effective uncertainty quantification (UQ) for FWI has long remained beyond the reach of computational capabilities but is critically important due to the pronounced non-uniqueness of the FWI inversion.In this study, we explore techniques for propagating and assessing uncertainties related to the model reconstruction within a Bayesian framework. We discuss the relationships between Monte Carlo and Variational inference approaches. Specifically, we examine Ensemble Kalman and Stein Variational Gradient Descent methods, contextualizing them with a state-space model for Bayesian filtering.By adopting a probabilistic perspective, grounded in principles of optimal transport and gradient flows, we propose a novel unified view to understand uncertainty quantification. This perspective inspires new algorithms and numerical experiments towards a more robust and efficient uncertainty quantification in FWI
Precision measurement of CP violation and branching fractions in decays and search for the rare decay
No full textInternational audienceAn analysis of the decays and is performed using proton--proton collision data collected by the LHCb experiment at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4fb. The CP asymmetries are determined to be and , and the branching-fraction ratio is measured to be , where the first uncertainties are statistical and the second systematic. These results are the most precise measurements of these quantities to date. A search for the rare decay is also performed. No significant signal is observed, and the upper limit on the product of the branching-fraction ratio and the fragmentation-fraction ratio is set to be 0.015 (0.016) at the 90% (95%) confidence level
Operando detection of lithium plating and stripping in fast charging Li-ion cells with a reference electrode
No full textInternational audienceUnderstanding degradation mechanisms in Li-ion cells is essential for advancing fast-charging technologies. One of the primary limitations of fast charging is the risk of lithium plating, driven by the negative electrode potential. In this study, a reference electrode was integrated into 30 mAh pouch cells to investigate aging under various charging regimes. This three-electrode setup allowed us to monitor the potential of both electrodes, with a particular focus on the negative electrode. By coupling operando data with post-mortem analysis, we linked the cell's electrical behavior to physical phenomena occurring within the cell. During fast charging at 2C, changes in the incremental capacity profile (ICA) were observed and correlated with a critical threshold in the negative electrode potential, measured using the reference electrode. Post-mortem analysis confirmed that these changes are indicative of lithium plating. Furthermore, an additional current during the potentiostatic phase of the charge was identified, correlating with a rise in the potentials of both electrodes. This current bump is interpreted as evidence of a lithium stripping process. These findings highlight the importance of monitoring the negative electrode potential using a reference electrode to detect and mitigate the risk of lithium plating during fast charging, contributing to the optimization of battery performance and safety
Energetically expensive dynamo action in Earth’s basal magma ocean
No full textInternational audiencePrevious studies focusing on the electrical conductivity and thermal evolution of an early magma ocean at the base of Earth’s mantle have found that basal magma ocean (BMO) convection could have produced the ancient geomagnetic field. By advances in high-resolution dynamo modeling, we find that convection in a thin BMO-like spherical shell is able to sustain strong magnetic fields, including axial dipolar fields similar to current day field structure. However, integrating our dynamo results with improved thermal evolution models and taking the planet’s rapid rotation into account using rotating convective turbulence models implies that an Earth-like magnetic field was unlikely to have been generated in the BMO, a finding relevant to the interpretation of ancient paleomagnetic signatures, Earth’s global-scale dynamics, and long-term planetary evolution. Large uncertainties still remain, calling for refined models of deep Earth thermal and mineralogical processes, accurate determination of prefactors in convective scaling laws, and fully coupled core-BMO dynamo simulations. Nonetheless, our work highlights that BMO-type dynamos intrinsically require a larger product of electrical conductivity and velocity than core-type dynamos, and that they are similarly rotationally constrained, so that velocities are significantly reduced compared to nonrotating estimates
From ancient agricultural practices to living traditions in southern Uzbekistan: Insights from Archaeobotany and Ethnobotany in the Kayrit Oasis
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Rupture of the 1949 Khait Earthquake on a Cryptic Fault: Implications for Earthquake Hazard
No full textInternational audienceAbstract The 1949 M w 7.6 Khait earthquake, Tajikistan, was one of the most destructive of the Pamir—Tien Shan region, killing over 7,000 people by building collapse and landsliding. It occurred at the transition between the Pamir and Tien Shan mountain ranges, which converge along the narrow Vashkh river valley. Therefore, it is important in understanding the tectonic and structural development at the junction of these two major mountain ranges, as well as yielding important information regarding hazard and risk to local populations and infrastructure. Although widespread landsliding and intensities of shaking were recorded, no surface ruptures were mapped, and the earthquake epicenter and source are poorly known. To determine the location, magnitude, and focal mechanism of the 1949 earthquake we combine calibrated earthquake relocations with body‐wave amplitude ratios from digitized paper seismograms. Our analysis shows that the earthquake nucleated within the Tien Shan basement with strike slip kinematics. Using high‐resolution digital elevation models and orthophotos derived from high‐resolution satellite imagery, we identify earthquake ruptures within the epicentral zone consistent with NW‐SE right‐lateral faulting. Relocated aftershocks and later seismicity also follow a NW‐SE trend through the Tien Shan north of the Vakhsh river. Mapping tectonically offset moraines dated in previous literature, we find a Vakhsh Fault slip rate of only half the present day strain accumulation rate derived from GNSS. Our results suggest a significant proportion of the regional deformation may occur away from the geomorphologically well expressed Vakhsh and Darvaz faults, and on faults with little prior expression of activity
Search for and measurement of in vector-boson fusion production with the ATLAS Detector
No full textInternational audienceA search for Standard Model (SM) Higgs bosons produced via vector-boson fusion at the Large Hadron Collider and decaying into a charm quark-antiquark pair () is presented. The datasets used correspond to integrated luminosities of 37.5 fb and 51.5 fb and were collected by the ATLAS detector from proton-proton collisions at =13 and 13.6 TeV, respectively. The observed (expected) upper limit on the production cross-section times branching ratio is 41 (28) times the SM prediction at 95% confidence level. Combining this search with the previous search in associated production with a or boson yields an observed (expected) limit on the Higgs-charm Yukawa coupling modifier of < 4.7 (3.9). Higgs bosons decaying into a bottom quark-antiquark pair () are measured simultaneously using the 51.5 fb dataset at =13.6 TeV, with an observed signal strength of 0.97 relative to the SM expectation. When combined with previous results at 13 TeV, the observed (expected) significance reaches 3.2 (3.6) standard deviations, providing evidence for events from vector-boson fusion
JITI: Dynamic Model Serving for Just-in-Time Traffic Inference
No full textInternational audienceAccurate and efficient inference on network traffic through machine learning models is important for many management tasks, from traffic prioritization to anomaly detection. Existing ML inference pipelines differ primarily in their feature design: those based on summary flow statistics (e.g., packet sizes, inter-arrival times) are lightweight and efficient, though they may be less accurate for fine-grained classification, whereas pipelines that consume features directly from raw packet capture data can achieve higher accuracy but at significantly greater computational and resource cost. In this paper, we develop Just-in-Time Traffic Inference(JITI), a model serving system to support fast and accurate network traffic inference in raw packet-capture-based machine learning inference pipelines. Offline, JITI builds a curated pool of diverse trained models with varied feature and performance requirements. Online, JITI responds to traffic fluctuations via an adaptive scheduler that selects the model from the pool that offers the highest accuracy-to-efficiency ratio within system resource limits, thereby providing inference accuracy comparable to the more complex and resource-intensive packet-capture-based methods, with minimal efficiency compromise. Using traffic application inference as an example task, our evaluation shows that JITI improves inference performance by 18% over flow-statistics-based methods; when benchmarked against state-of-the-art packet-capture-based methods, JITI results in a worst-case drop in F1-Score of only 12.3%, while reducing the average inference decision time by ~127x