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Calibration and Uncertainty for multiRater Volume Assessment in multiorgan Segmentation (CURVAS) challenge results
No full textInternational audienceDeep learning (DL) has become the dominant approach for medical image segmentation, yet ensuring the reliability and clinical applicability of these models requires addressing key challenges such as annotation variability, calibration, and uncertainty estimation. This is why we created the Calibration and Uncertainty for multiRater Volume Assessment in multiorgan Segmentation (CURVAS), which highlights the critical role of multiple annotators in establishing a more comprehensive ground truth, emphasizing that segmentation is inherently subjective and that leveraging inter-annotator variability is essential for robust model evaluation. Seven teams participated in the challenge, submitting a variety of DL models evaluated using metrics such as Dice Similarity Coefficient (DSC), Expected Calibration Error (ECE), and Continuous Ranked Probability Score (CRPS). By incorporating consensus and dissensus ground truth, we assess how DL models handle uncertainty and whether their confidence estimates align with true segmentation performance. Our findings reinforce the importance of well-calibrated models, as better calibration is strongly correlated with the quality of the results. Furthermore, we demonstrate that segmentation models trained on diverse datasets and enriched with pre-trained knowledge exhibit greater robustness, particularly in cases deviating from standard anatomical structures. Notably, the best-performing models achieved high DSC and well-calibrated uncertainty estimates. This work underscores the need for multi-annotator ground truth, thorough calibration assessments, and uncertainty-aware evaluations to develop trustworthy and clinically reliable DL-based medical image segmentation models
Is one vote really enough? Vote privacy with revoting and a dishonest ballot box
No full textInternational audienceElectronic voting promises the possibility of convenient and efficient systems for recording and tallying votes in an election. To be widely adopted, ensuring the security of the cryptographic protocols used in e-voting is of paramount importance. However, the security analysis of this type of protocols raises a number of challenges, and they are often out of reach of existing verification tools. In this paper, we study vote privacy, a central security property that should be satisfied by any e-voting system. More precisely, we propose the first formalisation of the recent BPRIV notion in the symbolic setting. To ease the formal security analysis of this notion, we propose a reduction result allowing one to bound the number of voters and ballots needed to mount an attack. We first consider the case where voters do not revote, and the ballot box is trusted before relaxing these two conditions. Our result applies on a number of case studies including several versions of Helios, Belenios, JCJ/Civitas, and Prêt-à-Voter. For some of these protocols, thanks to our result, we are able to conduct the analysis relying on the automatic tool Proverif
Cryptanalyse de schémas de cryptographie à clé publique
No full textCryptanalysis of public-key cryptosystems is based on algorithmic and algebraic techniques in number theory. In the first part of this thesis, we present improvements to the LLL algorithm, originally designed by Lenstra, Lenstra, and Lovasz in the eighties to reduce a Euclidean lattice, i.e. to reduce the norm and orthogonalize the basis vectors as possible. We also show how to use this algorithm to reduce rank-2 module lattices in a cyclotomic number field with subfields using symplectic matrices. Indeed, some schemes such as NTRU or Falcon, whose security relies on this difficult problem, have been proposed in post-quantum cryptography and for homomorphic encryption. We also improve linear algebra techniques and propose better algorithms when the matrix is diagonally dominant. These advanced methods allow us to set new records in the computation of number fields: class number, generators of the unit group, generator of a principal ideal. In the second part, we study various classical problems in number theory: we improve algorithms for testing the primality of an integer, and in particular, the cyclotomic test initially proposed by Adleman and developed by Mihailescu. Then, we study different algorithms in a so-called black-box ring model, i.e. we study the number of additions and multiplications in the ring, without looking at how the elements are represented and how the computations are performed in the ring. This allows us in the final chapter, to instantiate these algorithms in different rings in order to propose efficient algorithms for cryptanalysis. In doing so, we are able to more easily distribute the computations of the entire algorithm, while so-called index-calculus algorithms use a linear algebra step which is difficult to parallelize.La cryptanalyse de schémas de cryptographie à clé publique repose sur un ensemble de techniques algorithmiques et algébriques en théorie des nombres. Dans une première partie de cette thèse, nous présentons des améliorations de l’algorithme LLL, dû à Lenstra, Lenstra et Lovasz pour réduire un réseau euclidien, c’est-à-dire réduire la norme et orthogonaliser le plus possible les vecteurs de la base. Nous montrons aussi comment utiliser cet algorithme pour réduire des réseaux modules en rang 2 dans un corps de nombres cyclotomique ayant des sous-corps. En effet, certains schémas comme NTRU ou Falcon, dont la sécurité repose sur ce problème difficile, ont été proposés en cryptographie post-quantique et pour du chiffrement homomorphe. Nous améliorons aussi les techniques d’algèbre linéaire creuse et proposons de meilleurs algorithmes lorsque la matrice est à diagonale dominante. Ces avancées nous permettent de réaliser de nouveaux records de calculs de corps de nombres : nombre de classes, générateurs du groupe des unités, générateur d’un idéal principal. Dans une seconde partie, nous étudions différents problèmes classiques en théorie des nombres : nous améliorons différents algorithmes pour tester la primalité d’un entier et en particulier, le test cyclotomique initialement proposé par Adleman et dernièrement développé par Mihailescu. Puis, nous étudions différents algorithmes dans un modèle dit de l’anneau en boîte noire, c’est-à-dire que nous étudions le nombre d’additions et de multiplications dans l’anneau, sans nous intéresser à la façon de représenter et de faire les calculs dans cet anneau. Ceci nous permet dans le dernier chapitre, d’instancier ces algorithmes en fonction de différents anneaux pour proposer des algorithmes efficaces en cryptanalyse. Ce faisant, nous sommes capables de distribuer plus facilement les calculs de tout l’algorithme, alors que les algorithmes dit de calcul d’indice utilisent une étape d’algèbre linéaire qu’il est difficile de paralléliser
Benchmarking the Modular Structural Analysis Algorithm
No full textInternational audienceIn a 2023 Modelica Conference paper, we proposed a novel method for the modular structural analysis of DAE systems, in which the structural analysis is not performed on flattened models, but rather at the class level. A new notion of structural interface was proposed, in which classes are enriched with context information. That paper developed our approach based on a few illustrative examples.In this paper, we provide the details of our algorithm. Its performance depends on the system architecture: the analysis of models having a small number of classes (possibly instantiated many times), with a low treewidth system architecture, scales up very efficiently with this approach. We then present additional benchmarks, among which a urban heating network, a representative real-life example on which a near-logarithmic scaling up is shown.</p
Culture, Epistemic Kinship, and Epistemic Solidarity in Didactic Activity.
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Neural correlates of approach-avoidance tendencies toward physical activity and sedentary stimuli: An MRI study
No full textInternational audienceAutomatic tendencies toward physical activity and sedentary stimuli are involved in the regulation of physical activity behavior. However, the brain regions underlying these automatic tendencies remain largely unknown. Here, we used an approach-avoidance task and magnetic resonance imaging (MRI) in 42 healthy young adults to investigate whether cortical and subcortical brain regions underpinning reward processing and executive function are associated with these tendencies. At the behavioral level, results showed more errors when avoiding sedentary stimuli (i.e., avatars in a sitting position) than physical activity stimuli (i.e., avatars in a running position). At the brain level, avoiding sedentary stimuli was associated with more activation of the motor control network (dorsolateral-prefrontal cortex, primary and secondary motor cortices, somatosensory cortex). In addition, increased activation of the bilateral parahippocampal gyrus and local hypertrophy of the right hippocampus were associated with a stronger tendency to approach sedentary stimuli. Together, these results suggest that avoiding sedentary stimuli requires higher levels of behavioral control than avoiding physical activity stimuli
AQUI-FR: Une plateforme de modélisation hydrogéologique nationale
No full textNational audienceLa plateforme de modélisation hydrogéologique Aqui-Fr repose sur une collaboration entre différents organismes de recherches impliqués dans la caractérisation du comportement des aquifères du territoire national dans un contexte de changement climatique (ENS, Mines Paris, MétéoFrance, Geosciences Rennes, Lyhges, BRGM et OFB). Un ensemble de modèles numériques maillés mono et/ou multicouches pour les eaux souterraines, ou de modèles globaux pour les sources karstiques est intégré dans une plate-forme de modélisation gérée et opérée par Météo-France. Cette plate-forme offre des services de prévisions saisonnières et de projections climatiques qui permettent de cartographier la variation des niveaux piézométriques sous la forme d’indices de piézométrie standardisée (IPS). La plateforme couvre actuellement une grande partie du bassin parisien depuis le Nord Pas de Calais jusqu’en région Poitou Charente, ainsi qu’un modèle sur la partie Tarn et Garonne et un autre sur le sud de la plaine d’Alsace. La phase 4 du projet a pour vocation de mettre à jour la calibration des modèles existants et d’étendre l’emprise territoriale des modèles vers d’autres zones du territoire encore non couverte comme la région Aquitaine ainsi que le couloir Saône-Rhône jusqu’à la région PACA. Cette modélisation hydrogéologique a pour objectif de fournir des informations fines à l’échelle nationale, notamment compatibles avec les masses d’eau de la DCE, sans pour autant remplacer les applications détaillées à l’échelle régionale. Un des principaux intérêts du modèle est d’améliorer la diffusion opérationnelle d’informations sur les aquifères et leurs relations avec la surface. Les résultats pertinents sont les niveaux piézométriques, les flux échangés entre les couches aquifères ainsi qu’entre les nappes et les rivières. Quatre types d’applications sont actuellement envisagés : la ré-analyse historique, le suivi en temps réel, la prévision saisonnière et les projections climatique
Write on Paper and Get the Online Digital Trace: A New Era for Handwriting
No full textInternational audienceCapturing the digital trace of handwriting usually requires a specific stylus and a compatible substrate, be it a capacitive touchscreen, an ElectroMagnetic Resonance (EMR) tablet as used in Wacom systems or special paper. While writing on regular paper offers rich haptics, no latency and is well known for improving information retention, no low-cost and widely accepted, effective solution exists to digitize such a pen trace. The challenge is to accurately track the pen's trajectory without an external reference system while allowing unrestricted freedom of pen movement across a surface. We propose an innovative solution that combines a digital pen, advanced artificial intelligence algorithms, and adaptive AI techniques to reconstruct the digital trace of handwriting. Our approach integrates hardware development, focusing on a sensor-equipped pen, with software innovations to optimize trajectory reconstruction and processing in real time using an embedded AI. This work aims to advance the state-of-the-art in automated trace reconstruction of handwriting, enabling a seamless connection between traditional handwriting on paper and capturing the trace digitally
Wave scattering from graphene-covered circular dielectric wire collections analysed using the single-wire part inversion: diffraction radiation case
No full textInternational audienceWe consider infrared (IR)-range diffraction radiation (DR) from finite configurations of circular graphene-covered dielectric nanowires excited by the density-modulated beam of charged particles. The beam velocity is assumed constant, and its field in the free space is considered as the incident one. The characterization of graphene employs the quantum-theory Kubo formalism and the resistive-sheet boundary conditions involving the frequency-dependent graphene surface impedance. To transform the problem into a well-conditioned algebraic equation for the field expansion coefficients, we use the separation of variables in the local coordinates and the addition theorem for the cylindrical functions. This leads to explicit inversion of the single-wire part of the problem, i.e. to the regularization, provides easy control of the accuracy and enables us to study fine resonance effects associated with the natural modes of the wire collections as open resonators.This article is part of the theme issue 'Analytically grounded full-wave methods for advances in computational electromagnetics'