École Polytechnique

Beamstop-free small-angle X-ray scattering for multiscale structure measurement of high-energy-density plasma

The advent of free-electron lasers has enabled in-situ small-angle X-ray scattering (SAXS) measurements of laser-produced high-energy-density plasma at solid density, with nanometer- and femtosecond-scale resolution. Such plasmas generally exhibit gentle density gradients, which...

Nonlinear interpolation and the flow map of quasilinear equations

We prove an interpolation theorem for nonlinear functionals defined on scales of Banach spaces that generalize Besov spaces. It applies to functionals defined only locally, requiring only some weak Lipschitz conditions, extending those introduced by Lions and Peetre. Our analysis...

Nonclassical condensation pathways revealed by the multivariable theory of nucleation

Classical nucleation theory (CNT) provides a simple conceptual framework for nucleation but often fails to quantitatively reproduce experimental and numerical observations. In this work, we extend the theory by explicitly incorporating the multidimensional nature of nucleation an...

Nonparametric Hazard Rate Estimation With Associated Kernels and Minimax Bandwidth Choice

ABSTRACT In this paper, we introduce a general theoretical framework for nonparametric hazard rate estimation using associated kernels, whose shapes depend on the point of estimation. Within this framework, we establish rigorous asymptotic results, including a second‐order expans...

Plasma-Assisted and Green Routes to Silicon and Carbon Quantum Dots: A Critical Comparison of Synthesis–Structure–Property Relationships

Silicon quantum dots (SiQDs) and carbon quantum dots (CQDs) are often discussed as related heavy-metal-free luminescent nanomaterials, although the mechanisms governing their formation and emission differ fundamentally. Rather than combining two parallel bodies of literature, thi...

Subadditivity and optimal matching of unbounded samples

We obtain new bounds for the optimal matching cost for empirical measures with unbounded support. For a large class of radially symmetric and rapidly decaying probability laws, we prove for the first time the asymptotic rate of convergence for the whole range of power exponents p...

Multivariate quadratic Hawkes processes—part II: non-parametric empirical calibration

This is the second part of our work on Multivariate Quadratic Hawkes (MQHawkes) Processes, devoted to the calibration of the model defined and studied analytically in Aubrun, C., Benzaquen, M., & Bouchaud, J. P., Quantitative Finance, 23(5), 741-758 (2023). We propose a non-param...

Scattering and inverse scattering for multipoint potentials at high energies

Abstract We consider the solvable Schrödinger equation with a multipoint potential of Bethe–Peierls–Thomas–Fermi type. For this singular potential, we develop scattering and inverse scattering at high energies. In particular, in this framework, our results include analogs of the...

Hyperbolic form factors for Yukawa interactions, and applications to the Earth

Abstract We define the hyperbolic form factor of a density distribution as its bilateral Laplace transform, related by duality or analytic continuation to its ordinary form factor. For a sphere it is given by $$\Phi (x \!= \! kR) =\langle \,\cosh \,\vec k.\vec r\,\rangle = \langl...

SuperMoTo: an integrated monitoring matrix, room correction and Ambisonics decoding plugin for audio production and immersive listening rooms

SuperMoTo is an open-source audio plugin (VST3, AU and Standalone) that puts a studio’s monitoringsignal chain into one plugin instance. From that instance it routes up to 32 inputs to 32 outputs througha configurable gain-and-EQ matrix, applies per-loudspeaker FIR correction fil...

Validation of EarthCARE CPR reflectivity using the ACTRIS cloud radar network

The Earth Cloud, Aerosol, and Radiation Explorer (EarthCARE) satellite carries a cloud profiling radar (CPR) designed to observe global cloud properties. In this study, we assess the calibration of CPR reflectivity profiles by comparing them with seven calibrated ground-based clo...

Ligand-Mediated Control of Zn x Se y Intermediates for Defect-Free ZnSe Heteroepitaxy on Quantum Dots

Abstract ZnSe is a cornerstone shell material for enhancing the efficiency and stability of quantum dots (QDs). However, the chemical mechanisms governing detrimental zinc vacancy (VZn) formation remain unclear, limiting the predictive synthesis of high-quality heterostructures....

On discrete X-ray transform

We consider a discrete version of X-ray transform going back, in particular, to Strichartz (1982). We suggest non-overdetermined reconstruction for this discrete transform. Extensions to weighted (attenuated) analogues are given. Connections to the continuous case are presented.

The Cold-Air Outbreaks in the Marine Boundary Layer Experiment model-observation intercomparison project (COMBLE-MIP) – Part 1: Model specification, observational constraints, and preliminary findings

Models struggle to represent the coupled microphysical, turbulent and radiative processes within widespread, long-lived marine cold-air outbreak (CAO) cloud fields, contributing to forecast and climate biases. Here we combine ground-based and satellite measurements to initialize...

Polygonal Faber-Krahn inequality: local minimality via validated computing

The main result of the paper shows that the regular [Formula: see text]-gon is a local minimizer for the first Dirichlet-Laplace eigenvalue among [Formula: see text]-gons having fixed area for [Formula: see text]. The eigenvalue is seen as a function of the coordinates of the ver...

Toeplitz‐Based Spectral Methods for Data‐driven Dynamical Systems

ABSTRACT We introduce a Toeplitz‐based framework for data‐driven spectral estimation of linear evolution operators in dynamical systems. Focusing on transfer and Koopman operators from equilibrium trajectories without access to the underlying equations of motion, our method appli...

Evaluation of ASCAT soil moisture retrievals and their potential to detect intraday variability

Accurate sub-daily soil moisture (SM) retrievals from satellite observations remain a major challenge due to sparse temporal sampling and retrieval uncertainties. This study introduces a localized convolutional neural network (CNN-l) framework designed to enhance SM estimates fro...

Evidence for the impact of fire activity on daily variations of IASI mid-tropospheric CO 2 anomalies at 8–11 km over South America: a pyroconvective fingerprint

Biomass burning is a major, highly variable source of atmospheric CO 2 , but its impact on the free troposphere remains difficult to quantify because of uncertainties in injection heights and transport. In the tropics, intense fires can trigger pyroconvective plumes that loft com...

Efficient Hamiltonian, structure and trace distance learning of Gaussian states

Abstract When learning descriptions of many-body quantum systems, assuming locality of interactions can dramatically reduce the required number of observations and computational time compared to unstructured approaches. In this work, we uncover an infinite-dimensional instance of...

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...