Poétique et politique : Nouvelles lectures d'Euripide

International audienc

Correct tout seul, sûr à plusieurs

National audienceLe mémoire concurrent de OCaml 5 est conçu pour garantir la sûreté du typage et la sûreté mémoire même en présence de courses critiques (data races) entre fils d'exécution. Ce choix de conception impose des choix techniques précis dans l'implémentation du compilateur et de l'environnement d'exécution du langage. Mais il impose aussi, et c'est le sujet du présent article, des changements dans la façon d'écrire les programmes utilisateurs qui utilisent des constructions non sûres comme Array.unsafe_get et Array.unsafe_set pour des raisons de performance. Même si une structure de données est conçue pour être utilisée de façon séquentielle uniquement, le documente et ne fournit aucune garantie sur un usage concurrent incorrect, elle doit faire les bons choix d'implémentation pour préserver la sûreté mémoire même dans ce cas d'usage incorrect. Des implémentations parfaitement correctes pour OCaml 4 deviennent invalides en OCaml 5. Nous présentons ici une partie de l'implémentation du module Dynarray de tableaux redimensionnables qui a été intégré à la bibliothèque standard de OCaml 5.2. Nous expliquons comment plusieurs choix d'implémentation habituels chez les utilisateurs experts du langage deviennent invalides dans un contexte concurrent. Nous présentons une façon de raisonner sur ces implémentations (≪correct tout seul, sûr à plusieurs≫), comme un modèle mental informel que nous avons utilisé pour écrire ce code, mais aussi dans une formalisation Coq utilisant la logique de séparation Iris. Nous avons développé et vérifié le noyau de Dynarray en Iris, et montrons comment organiser les spécifications pour exprimer et vérifier de façon simple et claire cette nouvelle propriété de correction

Chimeric identities and reduced stiffness characterise the shoot apex of Arabidopsis stem cell mutants

Abstract Stem cell homeostasis in the shoot apical meristem involves a core regulatory feedback loop between the signalling peptide CLAVATA3, produced in stem cells, and the transcription factor WUSCHEL, expressed in the underlying organising centre. Compromised CLAVATA activity leads to massive meristem overgrowth, which is thought to be caused by stem cell overproliferation. However, it is unknown how uncontrolled stem cell divisions lead to the specific changes observed in clavata mutants. Here we first quantitatively characterise these mutants, to reveal underlying tissue curvature defects. We use analytical models to show how perturbed mechanical properties and/or growth rates may contribute to altered meristem morphology. Indeed, we find that clavata meristems are softer than the wild type, and that stereotypical meristem organisation is lost, with cells instead simultaneously expressing multiple domain markers. Furthermore, we show that mutant meristematic cells are auxin-responsive, suggesting that they are functionally different from wild-type stem cells. We propose that the clavata phenotype is not caused by stem cell overproliferation, but rather by the disruption of a more complex regulatory framework that is key to maintaining distinct genetic and functional domains at the shoot apex. Summary statement Mechanical, genetic and functional evidence supported by theoretical models call into question the current definition of stem cells in the shoot apex

Barcode entropy of geodesic flows

41 pagesInternational audienceWe introduce and study the barcode entropy for geodesic flows of closed Riemannian manifolds, which measures the exponential growth rate of the number of not-too-short bars in the Morse-theoretic barcode of the energy functional. We prove that the barcode entropy bounds from below the topological entropy of the geodesic flow and, conversely, bounds from above the topological entropy of any hyperbolic compact invariant set. As a consequence, for Riemannian metrics on surfaces, the barcode entropy is equal to the topological entropy. A key to the proofs and of independent interest is a crossing energy theorem for gradient flow lines of the energy functional

Efficient learning of the structure and parameters of local Pauli noise channels

The unavoidable presence of noise is a crucial roadblock for the development of large-scale quantum computers and the ability to characterize quantum noise reliably and efficiently with high precision is essential to scale quantum technologies further. Although estimating an arbitrary quantum channel requires exponential resources, it is expected that physically relevant noise has some underlying local structure, for instance that errors across different qubits have a conditional independence structure. Previous works showed how it is possible to estimate Pauli noise channels with an efficient number of samples in a way that is robust to state preparation and measurement errors, albeit departing from a known conditional independence structure. We present a novel approach for learning Pauli noise channels over n qubits that addresses this shortcoming. Unlike previous works that focused on learning coefficients with a known conditional independence structure, our method learns both the coefficients and the underlying structure. We achieve our results by leveraging a groundbreaking result by Bresler for efficiently learning Gibbs measures and obtain an optimal sample complexity of O(log(n)) to learn the unknown structure of the noise acting on n qubits. This information can then be leveraged to obtain a description of the channel that is close in diamond distance from O(poly(n)) samples. Furthermore, our method is efficient both in the number of samples and postprocessing without giving up on other desirable features such as SPAM-robustness, and only requires the implementation of single qubit Cliffords. In light of this, our novel approach enables the large-scale characterization of Pauli noise in quantum devices under minimal experimental requirements and assumptions

Inferring the arrow of time in quantum spatiotemporal correlations

We consider how to tell the time-ordering associated with measurement data from quantum experiments at two times and any number of qubits. We define an arrow of time inference problem. We consider conditions on the initial and final states that are symmetric or asymmetric under time reversal. We represent the spatiotemporal measurement data via the pseudo density matrix space-time state. There is a forward process which is CPTP and a reverse process which is obtained via a novel recovery map based on inverting unitary dilations. For asymmetric conditions, the protocol determines whether the data is consistent with the unitary dilation recovery map or the CPTP map. For symmetric conditions, the recovery map yields a valid unitary and the experiment may have taken place in either direction. We also discuss adapting the approach to the Leifer-Spekkens or Process matrix space-time states

Papyri Universitatis Lupiensis. I. Papiri ieratici e greci

International audienc

Louise Labé. La rime féminine

International audienceQui est Louise Labé, écrivaine au livre unique, surnommée « La Cordière de Lyon » ? Comment une fille et épouse de cordiers illettrés a-t-elle pu se ménager un espace de liberté tel qu'elle donne naissance à des textes savants qui résonnent toujours, quatre cent cinquante ans après sa mort ? C'est entre Rhône et Saône, à Lyon, haut lieu de la Renaissance française, que naît et vit l'autrice du réjouissant « Débat de Folie et d'Amour » et d'un émouvant ensemble de poèmes amoureux, précédés d'une épître aux accents féministes étonnamment modernes. Démêlant la légende et l'histoire, ce petit livre synthétise et met en perspective les apports de la recherche la plus récente afin de soulever un peu le voile du « mystère Louise Labé »

Cosmogenic (un-)steadiness revealed by paired-nuclide catchment-wide denudation rates in the formerly half-glaciated Vosges Mountains (NE France)

International audienceAlthough catchment-wide denudation rates inferred from in situ cosmogenic nuclide concentrations measured in stream sediments has represented a ground-breaking progress in geomorphology over the last three decades, most of these studies rely on 10Be concentrations only. It seems that this current and routine one-nuclide approach to infer catchment-wide denudation rates has somehow overshadowed two key assumptions that are cosmogenic steady-state and short sediment transit time at the catchment scale. Although a paired-nuclide approach allow testing these assumptions, it is rarely performed on stream sediments and this can become highly problematic in slow-eroding, formerly glaciated contexts. In this study, we thus measure both 10Be and 26Al in stream sediments pertaining to twenty-one rivers draining an entire low mountain range: the Vosges Massif (NE France). The latter exhibits a sharp gradient between its southern and northern part in terms of lithology, morphometry and climate. Moreover, if its northern part remained void of glacial cover during Quaternary cold stages, its southern part was significantly and repeatedly glaciated. We aim to assess the factors that control the denudation of the Vosges Mountains and to quantitatively explore the impact of both repeated glacial cover and storage of glacially derived sediments on 26Al/10Be ratios, hence cosmogenic (un-)steadiness in modern river samples. Our results first show that elevation, slope, channel steepness and precipitation are primarily organised along a N-S increasing trend. 10Be- and 26Al-derived catchment-wide denudation rates accordingly range from 34 ± 1 to 66 ± 2, and 41 ± 3 to 73 ± 7 mm/ka, respectively, in thirteen investigated catchments that are in cosmogenic equilibrium. Lithological contrasts may control the pattern of denudation with a higher erodibility of the sandstone-dominated catchment to the north compared to the crystalline-dominated catchments to the south.Our results also show that catchments in strong cosmogenic disequilibrium (26Al/10Be ratios from 1.4 to 5.2) spatially cluster in the SW part of the Vosges Mountains that was the most intensively glaciated during Quaternary cold stages. If this precludes any conclusion about controlling factors at the whole massif scale, this study is the first to quantify the impact of past glaciations on cosmogenic (un-)steadiness measured in stream sediments. A statistically significant relationship between the degree of depletion of the 26Al/10Be ratios and the spatial pattern of glaciation is found: the larger the former glacial cover in each catchment, the lower the 26Al/10Be ratio. Equally important is the significant correlation reported between the degree of depletion of the 26Al/10Be ratios and the proportion of glacial and fluvio-glacial deposits within each catchment. These two relationships underline the link between cosmogenic unsteadiness in the stream cosmogenic signal and long-lasting and repetitive ice shielding, and complex sediment routing systems in glacial environments, respectively. We thus argue to systematically measure 26Al in complement to 10Be and to test the steady-state assumption when it comes to infer catchment-wide denudation rates from modern stream sediments, especially in slow eroding, formerly glaciated landscapes

Φύλαιος (Pseudo-Arcadius 167.2 Roussou ≈ Hérodien 1.133.4 Lentz) et la formation et l’accentuation des anthroponymes grecs en -αιος

International audienceDocumented in two passages attributed to Herodian, the hapax φλαιος can be interpreted as a personal name (Φλαιος). Two hypotheses may be proposed in order to explain its origin: a) a nominalization (conversion) of the adjective φῡλαῖος 'concerning the tribe', which is confirmed by the month names Φῡλαῖος (Lisos) and Φῡλαιών (Iasos); b) a derivation of *Φλᾱς / *Φῡλᾶς (stem in-ᾱ-), an abbreviated form of a compound like Φλαρχος and a flexional variant of Φλᾱς (stem in-αντ-). The proparoxytonesis of Φύλαιος is consistent with that of personal names of the type Ἀθήναιος, Ἥραιος, etc., that exhibit a recessive accentuation vis-à-vis the corresponding paroxyton adjectives (Ἀθηναῖος, Ἡραῖος, etc.), and have exerted an influence on the accentuation of other abbreviated personal names (Τµαιος, Φίλαιος, etc