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Burnett's conjecture in generalized wave coordinates
No full textWe prove Burnett's conjecture in general relativity when the metrics satisfy a generalized wave coordinate condition, i.e., suppose is a sequence of Lorentzian metrics (in arbitrary dimensions ) satisfying a generalized wave coordinate condition and such that in a suitably weak and "high-frequency" manner, then the limit metric satisfies the Einstein--massless Vlasov system. Moreover, we show that the Vlasov field for the limiting metric can be taken to be a suitable microlocal defect measure corresponding to the convergence. The proof uses a compensation phenomenon based on the linear and nonlinear structure of the Einstein equations
Original Adverse Outcome Pathway linking neuronal exposure to nanoparticles to the onset of Alzheimer’s disease
No full textInternational audienc
ADAM Sheddase Activity Promotes the Detachment of Small Extracellular Vesicles From the Plasma Membrane
No full textInternational audienceSmall extracellular vesicles (SEVs) are involved in diverse functions in normal and pathological situations, including intercellular communication, immunity, metastasis and neurodegeneration. Cell release of SEVs is assumed to occur passively right after multivesicular bodies of the endocytic pathway fuse with the plasma membrane. We show here that the completion of SEV release depends on membrane‐bound ADAM10 and ADAM17 sheddases that promote the detachment of SEVs from the cell surface by catalysing the cleavage of adhesion proteins of the SEV membrane. The intensity of ADAM10/17‐mediated release of SEVs depends on a balanced control of 3‐phosphoinositide–dependent kinase 1 (PDK1) and ERK1/2 signalling pathways converging on 90‐kDa ribosomal S6 kinase‐2 (RSK2), which, in turn, fine‐tunes ADAM17 bioavailability and ADAM10/17 enzymatic activities at the plasma membrane, according to a mechanism that relies, at least in part, on variation of the rhomboid‐like pseudoprotease iRhom2 cell surface level. By identifying a new proteolytic step involved in the basal release of SEVs, our work may help understand how the deregulation of ADAM10/17‐mediated discharge of SEVs contributes to several pathological states
New representation of sea ice salt dynamics within NEMO-SI3: Evaluation and impacts
No full textInternational audienceMany large-scale sea ice models represent salt dynamics, yet, these remain insufficiently evaluated, with large uncertainty on several parameterization choices. To address this, we conduct global 1° resolution ice-ocean simulations with NEMO-SI3 v5, forced by climatological atmospheric data, and evaluate them against a new compilation of >1,200 ice-core observations. We specifically investigate the effects of (1) the treatment of vertical ice salinity variations (diagnostic vs. prognostic), (2) gravity drainage parameterization type (brine fraction–based vs. Rayleigh number–based), and (3) key parameter values. We show that mean ice salinity can be simulated within 0.1 g/kg (Arctic) and 0.4 g/kg (Antarctic) of the observed mean, provided careful adjustment of parameters. In particular, using a high value for the new ice liquid fraction parameter (75%) proves critical to simulate high salinity in the thin ice range. With appropriately adjusted parameters, the model captures the key large-scale ice salinity features, including the Arctic-Antarctic contrast, seasonal cycle, vertical profiles, and salinity-thickness relationship. A prognostic treatment of vertical salinity increases the variance of ice salinity and ice-ocean salt fluxes, yielding vertically-averaged salinity more in line with observations, however only in the Arctic. The choice of gravity drainage parameterization is influential through interactions with melt ponds, with Rayleigh number–based parameterizations performing best. While salt dynamics strongly affect sea ice mass budget terms, they moderately affect sea ice volume and the ocean due to compensation effects. Uncertainties are larger than in the Antarctic than in Arctic, reflecting less mature process understanding and possibly higher observational biases
Consensus guidelines for cellular label-free optical metabolic imaging: ensuring accuracy and reproducibility in metabolic profiling
No full textInternational audienceSignificance: Cellular metabolism plays a central role in health and disease, making its study critical for advancing diagnostics and therapies. Label-free optical metabolic imaging using endogenous fluorescence from reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] and flavin adenine dinucleotide (FAD) provides nondestructive, high-resolution insights into metabolic function and heterogeneity from the sub-cellular to the tissue level. Standardized approaches are essential to ensure reproducibility and comparability across studies.Aim: We aim to establish a consensus framework for the acquisition, calibration, and reporting of microscopic imaging metabolic function assessments based on fluorescence intensity and lifetime measurements of NAD(P)H and FAD.Approach: We present best practices for calibrating, analyzing, and reporting fluorescence intensity-based optical redox ratios and fluorescence lifetime data using multiexponential fitting and phasor analysis. Guidelines for validation experiments and cross-system standardization are provided to improve accuracy and reproducibility.Results: We demonstrate the importance of calibration procedures and normalization strategies for intensity-based optical redox measurements. We highlight needed calibration, signal-to-noise ratio considerations, and the impact of distinct analytical approaches on fluorescence lifetime-based metabolic function metrics.Conclusion: We recommend a consistent, practical framework for reproducible, label-free, optical metabolic imaging, facilitating robust comparisons across studies and supporting the broader adoption of optical metabolic imaging technologies for biomedical research and clinical translation
L'énergie photovoltaïque sous concentration: des cellules solaires sous «stéroïdes »?
No full textInternational audienc
Signature approach for pricing and hedging path-dependent options with frictions
No full textWe introduce a novel signature approach for pricing and hedging path-dependent options with instantaneous and permanent market impact under a mean-quadratic variation criterion. Leveraging the expressive power of signatures, we recast an inherently nonlinear and non-Markovian stochastic control problem into a tractable form, yielding hedging strategies in (possibly infinite) linear feedback form in the time-augmented signature of the control variables, with coefficients characterized by non-standard infinite-dimensional Riccati equations on the extended tensor algebra. Numerical experiments demonstrate the effectiveness of these signature-based strategies for pricing and hedging general path-dependent payoffs in the presence of frictions. In particular, market impact naturally smooths optimal trading strategies, making low-truncated signature approximations highly accurate and robust in frictional markets, contrary to the frictionless case
CoHiRF: A Scalable and Interpretable Clustering Framework for High-Dimensional Data
No full textClustering high-dimensional data poses significant challenges due to the curse of dimensionality, scalability issues, and the presence of noisy and irrelevant features. We propose Consensus Hierarchical Random Feature (CoHiRF), a novel clustering method designed to address these challenges effectively. CoHiRF leverages random feature selection to mitigate noise and dimensionality effects, repeatedly applies K-Means clustering in reduced feature spaces, and combines results through a unanimous consensus criterion. This iterative approach constructs a cluster assignment matrix, where each row records the cluster assignments of a sample across repetitions, enabling the identification of stable clusters by comparing identical rows. Clusters are organized hierarchically, enabling the interpretation of the hierarchy to gain insights into the dataset. CoHiRF is computationally efficient with a running time comparable to K-Means, scalable to massive datasets, and exhibits robust performance against state-of-the-art methods such as SC-SRGF, HDBSCAN, and OPTICS. Experimental results on synthetic and real-world datasets confirm the method's ability to reveal meaningful patterns while maintaining scalability, making it a powerful tool for high-dimensional data analysis
Adversarial Bandits Against Arbitrary Strategies
No full textInternational audienceWe study the adversarial bandit problem against arbitrary strategies, where the difficulty is captured by an unknown parameter , which is the number of switches in the best arm in hindsight. To handle this problem, we adopt the master-base framework using the online mirror descent method (OMD). We first provide a master-base algorithm with simple OMD, achieving , in which comes from the variance of loss estimators. To mitigate the impact of the variance, we propose using adaptive learning rates for OMD and achieve , where is a variance term for loss estimators
Enhanced short-duration precipitation and divergent rainfall spatial patterns of Typhoon Nida (2016) under the impact of urbanization
No full textInternational audienceTropical cyclones (TCs), when approaching coasts and after landfalling, may exhibit significant interactions with heavily urbanized surfaces. Despite numerous studies, the effects of urbanization on TCs and their landfalling processes remain insufficiently explored. Typhoon Nida, landfalling in the Pearl River Delta region on August 1, 2016, provides an interesting case for us to revisit the issue. We use the Weather Research and Forecasting model in paired numerical experiments to isolate the urban effects. Urban land cover has a small impact on the track and the intensity of the typhoon. Urban effect on landfalling precipitation in this event is mainly profound in changing rainfall spatial patterns rather than the average rain rate. The accumulated precipitation and the rain rate of the major urban area are reduced. During different stages of the TC rapid movement, enhanced precipitation is observed at the downwind and upwind regions within a short duration. The increase in surface temperature and sensible heat flux enhances thermal circulation; however, this effect is weakened under the strong synoptic background during landfall. Increasing urban surface roughness decelerates airflows and enhances updrafts along the urban boundaries, producing enhanced water vapor convergence and bifurcated winds, increasing downwind precipitation with a maximum value of 46.17 mm in 6 h. Throughout the TC rapid movement, urban modification on precipitation patterns displays high spatial variability over short periods. The study raises concern about more extreme hazards occurring in multiple locations over urban areas caused by urban-induced TC rainfall redistribution