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Generalized perimeters and gradient estimates
No full textWe use a variational formulation to define a generalized notion of perimeter, from which we derive abstract isoperimetric Cheeger's inequalities via gradient estimates on solutions of Poisson equations. Our abstract framework unifies many existing results and in particular allows us to recover the transport inequality, which strengthens the usual transport-information inequality. Conversely, we also prove that Cheeger's inequality implies certain first order Calderón-Zygmund-type gradient estimates
Local Drivers of Antarctic Spring Sea Ice Retreat
No full textInternational audienceAntarctic sea ice has changed significantly over the past four decades; yet limited understanding of fundamental processes, including its seasonal cycle, hinders our ability to interpret these changes. Here, we examine the processes determining the moment when sea ice locally disappears each spring, defined as the retreat date, using satellite observations over 1994–2020. We find that climatological retreat date is driven by sea ice melt in most of the seasonal ice zone and strongly constrained by the seasonal maximum ice thickness. Ice removal due to drifting ice export predominantly drives retreat only in coastal polynyas. At interannual timescales, retreat date anomalies are also preconditioned by prior maximum ice thickness, which affects melt‐driven spring ice loss through the ice‐albedo feedback, though this effect appears limited to specific regions. Winds emerge as a primary driver of interannual variability in the retreat date, influencing both drift‐ and melt‐related spring ice removal processes
Méthodes approchées pour le partage de livraisons dans les circuits courts alimentaires
No full textInternational audienc
Controlling radiative properties of circular atomic arrays through nanofiber guided modes
No full textInternational audienceWe theoretically investigate the collective emission of one and two circular arrays of two-level atomssurrounding an optical nanofiber. We show that the radiation eigenmodes of a single ring selectively coupleto specific guided modes of the fiber, according to their symmetry, and study how the physical parameters of thesystem control their nature. In particular, we identify situations in which the emission toward radiation modesis highly suppressed with respect to fiber guided modes while the lifetime of the atomic excitation is enhanced.We further address the case of two identical rings positioned at a distance from each other along the nanofiber.By contrast to free-space configurations, the rings can exchange an excitation even at large separation throughnanofiber guided modes resulting in enhanced sub- and supper-radiance with respect to the single-ring case.Our findings suggest that the ring configuration is promising for the implementation of efficient and versatilelight-matter nanofiber-based interfaces and the achievement of waveguide quantum electrodynamics
Unveiling renovation patterns in the French building stock using archetype classification and energy performance certificates data
No full textInternational audienceThe energy renovation of buildings plays a pivotal role in mitigating greenhouse gas emissions and adapting cities to climate change. However, the pace of renovation in the European building stock remains relatively slow. The objective of this study is to enhance our understanding of the renovation status of the French building stock by cross-analysing multiple databases. In order to assess the levels of renovation, a methodology is proposed which combines Energy Performance Certificate (EPC) data with Danube, an archetypal architectural database. By mapping the Danube archetypes to the EPC geospatial data, an examination of the renovation status across different buildings can be conducted, taking into account factors such as construction period, building usage, urban form, and geographical location. The methodology employed entails the establishment of a correspondence between the aforementioned databases, the calculation of U-values for building envelope components of the Danube database, and the conduct of a comparative analysis of their thermal performances with the EPC referential. The findings of this study reveal a complex pattern of renovation rates across different construction periods and housing types. Notably, buildings constructed after the Second World War exhibit the highest rates of renovation. Additionally, individual dwellings undergo more extensive roof renovations than collective housing. This research makes a significant contribution to the understanding of the complexities of building renovations in urban environments, and provides insights that can inform the development of effective strategies for enhancing urban sustainability and resilience
When Knockoffs fail: diagnosing and fixing non-exchangeability of Knockoffs
No full textInternational audienceKnockoffs are a popular statistical framework that addresses the challenging problem of conditional variable selection in high-dimensional settings with statistical control. Such statistical control is essential for the reliability of inference. However, knockoff guarantees rely on an exchangeability assumption that is difficult to test in practice, and there is little discussion in the literature on how to deal with unfulfilled hypotheses. This assumption is related to the ability to generate data similar to the observed data. To maintain reliable inference, we introduce a diagnostic tool based on Classifier Two-Sample Tests. Using simulations and real data, we show that violations of this assumption occur in common settings for classical knockoff generators, especially when the data have a strong dependence structure. As a consequence, knockoff-based inference suffers from a massive inflation of false positives. We show that the diagnostic tool correctly detects such behavior. We show that an alternative knockoff construction, based on constructing a predictor of each variable based on all others, solves the issue. We also propose a computationally-efficient variant of this algorithm and show empirically that this approach restores error control on simulated data and semi-simulated experiments based on neuroimaging data
SERVOVALVES MODELS FOR CUSTOMERS
No full textInternational audienceThis communication deals with the modelling of 2-stage servovalves from a customer's point of view. The main objective is to propose a model which parameters can be easily identified from the servovalve datasheet, and that reproduces well the key servovalve performances. The first step focusses on the power stage and the servovalve hydraulic static characteristic. The second step is dedicated to the servovalve dynamics and its sensitivity to the input current magnitude. Additional considerations are provided about the influence of the supply pressure and the modelling of internal faults
Non-destructive evaluation (NDE) via Acoustic Emission (AE) simulation: Response and modelling of AE transmitting sensor
No full textInternational audienceAcoustic Emission (AE) method is a monitoring technique that detects transient elastic waves generated by therapid release of energy from localised sources within materials. It is widely used for non-destructive evaluationand health monitoring of structures. However, interpreting AE signals is challenging, requiring a comprehensiveunderstanding of the AE measurement chain, including excitation sources, propagation mediums, sensors andtheir coupling conditions, acquisition systems and signal processing. To address these challenges, a combinationof simulation and experimental approaches is essential. In this study, the modelling of the AE measurementchain, with particular emphasis on excitation sources, was developed by using highly reliable and reproducibleemission waves from piezoelectric sensors. To achieve this, the velocity response across the entire active surfaceof typical AE sensors (R3α, R6α, R15α, and F15α, from Physical Acoustics, USA) was first identified experi-mentally, using a laser vibrometer. Then, 3D models incorporating these AE sources were established throughboth experiment and simulation, with a configuration using a metallic plate, to study the wave propagation andthe influence of the AE measurement chain. Several parameters were studied, including the relationship betweenthe sensor’s response and excitation pulse characteristics, aperture effect of AE sensors, and main parameters ofAE signals. The results demonstrated a very good agreement in both signal waveform and key characteristicsbetween simulations and experiments obtained using a laser vibrometer. These findings are essential for un-derstanding sensor characteristics, controlling artificial source generation, performing AE sensor calibrationtests, and advancing models for the entire AE measurement chain
Structural comparison of homomolecular systems on surfaces using a fingerprint-based method
No full textInternational audienceThis work presents an adaptation of the Smooth Overlap of Atomic Positions (SOAP) method to improve the efficiency of (dis)similarity quantification in homogeneous molecular (homomolecular) systems. SOAP, a fingerprint-based approach, is widely used to measure molecular similarity. We propose variants of SOAP kernels that leverage the structural architecture of homomolecular systems to minimize irrelevant comparisons of atomic environments. To evaluate its performance, we apply this adapted SOAP-based method to a synthetic dataset consisting of two identical tripeptides deposited on a copper surface, simulating different molecular states. The results demonstrate that the adapted method not only improves computational efficiency but also yields more meaningful clustering outcomes by better capturing the key structural differences between states. These findings suggest that the proposed method is well-suited for the study of homomolecular systems, particularly those involving surface interactions, and has the potential to enhance the use of diverse types of molecular modeling and analysis methods that rely on (dis)similarity measures
Action concertée transverse 2 èmes Journées nationales du Packaging -20-21 mai 2025 -FEMTO-ST -Besançon
No full textNational audienceTravaux de l'ACPAC du PEPR électronique lors des deuxièmes journées nationales du packagin