École Polytechnique

Geometry-driven jets underlie dispersal of plants and fungi by raindrops

The impact of droplets on concave surfaces is poorly understood, although it is relevant to a mode of dispersal of reproductive units that has evolved independently in several species of plants and fungi. This mode of dispersal relies on splash-cups, specialized organs that use r...

Strong coupling between RF photons and plasmons of electrons on liquid helium

Plasmons, arising from the collective motion of electrons, can interact strongly with electromagnetic fields or photons; this capability has been exploited across a broad range of applications, from chemical reactivity to biosensing. Recently, there has been growing interest in p...

Strongly coupled stimulated Brillouin amplification with flying focus

Damage to compression gratings poses a fundamental limit to chirped pulse amplification in high-power laser systems. Plasma-based compressors using strongly coupled stimulated Brillouin scattering (scSBS) offer a damage-free alternative, but their effectiveness has been hindered...

Convergence Analysis of a High-Order Multiscale Finite Element Method (MsFEM) for Stokes Flows in Heterogeneous Media

Abstract. An enriched nonconforming Multiscale Finite Element Method (MsFEM) to solve viscous incompressible flow problems in genuine heterogeneous or porous media was proposed in [Q. Feng, G. Allaire, and P. Omnes, Multiscale Model. Simul., 20 (2022), pp. 462–492]. The main feat...

State Spaces of Multifactor Approximations of Nonnegative Volterra Processes

We show that the state spaces of multifactor Markovian processes, coming from approximations of nonnegative Volterra processes, are given by explicit linear transformations of the nonnegative orthant. We demonstrate the usefulness of this result for applications, including simula...

Resource competition between buoyancy‐regulating and sinking phytoplankton species along a stratified water column

Abstract In temperate lakes plankton dynamics are closely linked to seasonal shifts in water stratification, following air temperature. The onset of summer stratification typically coincides with spring bloom for-mation of algae in the well mixed surface layer (epilimnion). Howev...

Beyond wind-induced upwelling: diverse drivers of future productivity in eastern boundary upwelling systems

Abstract. Eastern Boundary Upwelling Systems (EBUS) contribute disproportionately to global marine productivity and fisheries, yet their response to climate change remains poorly understood. Given the essential ecosystem services they support, improving projections of future EBUS...

A nested factor model for equity markets: reconciling multifractal stock returns and rough index volatilities

The Nested factor model was introduced by Chicheportiche et al. to represent non-linear correlations between stocks. Stock returns are explained by a standard factor model, but the (log)-volatilities of factors and residuals are themselves decomposed into factor modes, with a com...

A barycenter-based approach for the multi-model ensembling of subseasonal forecasts

Abstract. Ensemble forecasts and their combination are examined from the perspective of probability spaces. By treating ensemble forecasts as discrete probability distributions, multi-model ensemble (MME) forecasts are reformulated as barycenters of these distributions. We consid...

Bellman Search in Arbitrary Finite Dimension: A Self-Similar Cell Theorem and Effective Computability of Planar Shoreline Search

A shoreline-search path starts at the origin and must meet an unknown affine line, without knowing either its normal or its distance. We first establish a self-similar reduction theorem for homogeneous search problems whose historical information is a record profile updated by po...

Bellman Search in Arbitrary Finite Dimension: A Self-Similar Cell Theorem and Effective Computability of Planar Shoreline Search

A shoreline-search path starts at the origin and must meet an unknown affine line, without knowing either its normal or its distance. We first establish a self-similar reduction theorem for homogeneous search problems whose historical information is a record profile updated by po...

Neural network–augmented Pfaffian wave-functions for scalable simulations of interacting fermions

Developing accurate numerical methods for strongly interacting fermions is crucial for improving our understanding of various quantum many-body phenomena, especially unconventional superconductivity. Recently, neural quantum states have emerged as a promising approach for studyin...

4D Printing of Magneto‐Active Soft Elastomers via Efficient Active Mixing Direct Ink Writing

ABSTRACT 4D printing relies on the 3D printing of materials that respond to various stimuli after printing. Among these, magneto‐active elastomers readily react to magnetic fields, particularly at high magnetic particle loadings. For soft silicones with high particle contents, di...

Noise through an Additional Variable for Mean Field Games Master Equation on Finite State Space

Abstract. This paper provides a mathematical study of the well-posedness of a master equation with terms modeling common noise on finite state space. In this setting, the solution of the master equation depends on an additional variable modeling the value of a stochastic process...

A Survey on Clustered Federated Learning: Taxonomy, Analysis and Applications

As Federated Learning (FL) expands, the challenge of non-independent and identically distributed (non-IID) data becomes critical. Clustered Federated Learning (CFL) addresses this by training multiple specialized models, each representing a group of clients with similar data dist...

Characterization of tensile and torsional fatigue behaviors of additively manufactured super duplex stainless steel SAF 2507

Abstract Super duplex stainless steels (SDSSs) are well known for their good mechanical properties and corrosion resistance inherited from the dual-phase microstructure with equivalent proportion of ferrite and austenite. The development of additive manufacturing has given rise t...

Itō and Itō-Wentzell chain rule for flows of conditional laws of continuous semimartingales: an easy approach

We provide a general Itō-Wentzell formula for a random field of maps on the Wasserstein space of probability measures, defined by continuous semimartingales, and evaluated along the flow of conditional distributions of another continuous semimartingale. Our method follows standar...

Ultra-compact plasma photocathode in a hybrid wakefield accelerator

Abstract Plasma-based particle accelerators, realized by driving plasma waves with either an intense laser pulse or particle beam, offer accelerating fields orders of magnitude higher than conventional accelerators. This enables sources of highly relativistic electron beams with...

dd-RCMA-ES: CMA-ES with Projection-Based Restricted Covariance Matrix Adaptation for High-Dimensional Problems

This paper addresses the computational challenges of the covariance matrix adaptation evolution strategy (CMA-ES) in high-dimensional optimization of an objective function \(f:\mathbb{R}^{n}\to\mathbb{R}\) where \(n\gg 100\) , particularly for problems exhibiting sparse-sensitivi...

Thermohaline gradients and frontal regimes in the northwestern Tropical Atlantic

Abstract. At the edge of the Amazon River plume, stirring by the North Brazil Current (NBC) and its eddies creates sharp surface thermohaline gradients on scales of O(1–100) km. This study provides a comprehensive picture of these gradients and fronts associated with the region's...