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A Γ-convergence result for 2D type-I superconductors
No full textInternational audienceWe consider a 2D non-standard Modica-Mortola type functional. This functional arises from the Ginzburg-Landau theory of type-I superconductors in the case of an infinitely long sample and in the regime of comparable penetration and coherence lengthes. We prove that the functional Γ-converges to the perimeter functional. This result is a first step in understanding how to extend the results of Conti, Goldman, Otto, Serfaty (2018) to the regime of non vanishing Ginzburg-Landau parameter κ
Distinguishing carriers' and lattice's temperatures through photoluminescence analysis
No full textInternational audienceWe report the direct and independent measurement of the lattice and the electrons temperatures in a nanocooler device (asymmetric double-barrier semiconductor heterostructure) at different operating points. Both temperatures are estimated from photoluminescence measurements -the former through the shift of the absorptivity profile, the latter through the shape of the blackbody baseline. The device's cooling feature results from the thermionic extraction of electrons injected in a quantum well through an energy selective barrier. While electrons exhibit a spectacular cooling for resonant injection, the lattice temperature remains essentially unaffected, with a temperature decrease at the resolution limit. Further from resonance, both systems show an identical thermal behavior governed by Joule's heating. The similarities and discrepancies of the temperature profiles illustrate the complex thermal behavior of the system, epitomize the need of reliable thermometry method and showcase the ability of photoluminescence to do so
SAG-SCI: the Real-time, High-level Analysis Software for Array Control and Data Acquisition of the Cherenkov Telescope Array Observatory
No full textInternational audienceThe Cherenkov Telescope Array Observatory (CTAO) is going to be the leading observatory for very-high-energy gamma-rays over the next decades. Its unique sensitivity, wide field of view, and rapid slewing capability make the CTAO especially suited to study transient astrophysical phenomena. The CTAO will analyse its data in real-time, responding to external science alerts on transient events and issuing its own. The Science Alert Generation (SAG) automated pipeline, a component of the Array Control and Data Acquisition (ACADA) software, is designed to detect and issue candidate science alerts. In this work, we present the current development status of SAG-SCI, the SAG component responsible for the real-time, high-level analysis of CTAO data. The SAG-SCI pipelines receive gamma-ray data from multiple reconstruction lines, merge them, store them in a database, and trigger several parallel scientific analyses on the latest data. These analyses include estimating target significance and flux, producing sky maps and light curves, and conducting blind searches for sources within the field of view. We execute SAG-SCI on a set of simulated gamma-ray data, detecting the simulated sources and accurately reconstructing their flux and position. We also estimate the systematic errors introduced by the analysis and discuss the results in relation to the generation of candidate science alerts
Contraintes de théorie de l'information en gravité et cosmologie quantique
No full textPerhaps the greatest success of the holographic principle is its explicit realization in Anti-de Sitter (AdS) spacetime, whose quantum description is equivalent to a conformal field theory (CFT) defined on its boundary. Despite the success of AdS/CFT, an analogous holographic description of expanding spacetimes, such as our own, remains elusive. Fundamental difficulties arise from the closed spatial topology of de Sitter (dS) spacetime. Resolving this problem would be a crucial step towards a deeper understanding of the early history of our universe.In parallel, key progress has been made through the discovery of the connection between quantum information and the geometry of spacetime. Stemming from black hole thermodynamics, this idea has shed light on fundamental problems in the description of black holes and the AdS/CFT correspondence. Remarkably, quantum information appears to be a natural language for describing quantum effects in gravity that extend beyond the framework of AdS/CFT and black holes. In this thesis, we present new results on quantum information constraints in gravity that are of interest to cosmological models and demonstrate how this approach sheds light on cosmological holography.A remarkable example of this framework is Bousso's conjecture that the number of degrees of freedom necessary for the description of a spatial region is bounded by the area of its boundary divided by 4Ghbar with G being Newton's constant. As the Bousso bound can be violated by quantum effects, it has been proposed that one should replace ext{Area}/4Ghbar by the generalized entropy S_{m gen}= ext{Area}/4Ghbar + S_{m out} where S_{m out} is the entropy of quantum fields outside the spatial region, leading to a quantum Bousso bound. Another crucial conjecture is quantum focusing, which generalizes the classical property that light must focus in the presence of matter. It can be related to the quantum Bousso bound and forbids the existence of pathological spacetimes. We show that Jackiw-Teitelboim gravity — a toy model of quantum gravity that provides a controlled setting for exploring quantum gravitational effects — can be used to study the validity of these conjectures. In particular, we prove the quantum Bousso bound in this framework. We also prove a weakened version of quantum focusing that is sufficient for all of its applications. Interestingly, we find violations of the unrestricted formulation of quantum focusing in this model.A crucial implication of the Bousso bound is the static patch holography conjecture, where the causal region of an observer in dS space is fully described by a dual theory living on the cosmological horizon. We propose a generalization of this conjecture to a broad class of closed Friedmann-Lemaître-Robertson-Walker (FLRW) spacetimes. We introduce a covariant prescription for computing holographic entanglement entropy in this holographic framework, leading to a formulation of subregion-subregion duality. In particular, we argue that entangling the holographic theories associated with complementary observers gives rise to the emergence of the inflationary region in de Sitter space. The FLRW generalization provides a cosmological and time-dependent realization of the idea that entanglement constructs spacetime.Finally, we discuss the Connected Wedge Theorem, which establishes a relation between the causal structure of spacetime and information-theoretic constraints in the holographic dual. The gravitational counterpart of this statement derives from quantum focusing. We argue that maintaining the consistency of static patch holography with this theorem leads to constraints on the causal structure of the dual theory. Our results suggest a novel relation between static patch holography and the dS/CFT correspondence, an alternative approach to cosmological holography.Le principe holographique trouve son plus grand succès dans l’espace-temps d’Anti-de Sitter (AdS), où la description quantique équivaut à une théorie conforme des champs (CFT) sur son bord. Cependant, une description holographique d’un espace-temps en expansion, comme le nôtre, demeure insaisissable. L’espace-temps de de Sitter (dS), en raison de sa topologie spatiale fermée, pose des défis fondamentaux. Les résoudre permettrait une meilleure compréhension des premiers instants de l’univers.Parallèlement, le lien entre information quantique et géométrie d’espace-temps a ouvert de nouvelles perspectives. Issue de la thermodynamique des trous noirs, cette connexion a permis des avancées majeures dans la correspondance AdS/CFT et au-delà. L’information quantique semble être un langage naturel pour décrire la gravité quantique. Dans cette thèse, nous explorons les contraintes imposées par l’information quantique et leur rôle dans l’holographie cosmologique.Un exemple clé est la conjecture de Bousso, selon laquelle les degrés de liberté d’une région spatiale sont limités par l’aire de son bord divisée par 4Ghbar. Toutefois, des effets quantiques peuvent briser cette borne, menant à l’introduction de l’entropie généralisée S_{m gen}=ext{Aire}/4Ghbar+S_{m out}, où S_{m out} représente l’entropie des champs quantiques extérieurs. Cette formulation donne naissance à une borne de Bousso quantique. Une autre conjecture essentielle est le principe de focalisation quantique, qui généralise la propriété classique de convergence de la lumière sous l’effet de la matière. Directement lié à la borne de Bousso quantique, il interdit certains espaces-temps pathologiques. Nous utilisons la gravité de Jackiw-Teitelboim, modèle simplifié de gravité quantique, pour tester ces conjectures. Nous démontrons la validité de la borne de Bousso quantique et prouvons une version restreinte du principe de focalisation quantique, suffisante pour ses applications. Toutefois, la version non restreinte de ce principe est violée dans ce cadre.La borne de Bousso conduit à la conjecture holographique du patch statique, affirmant que la région causale d’un observateur en dS est entièrement décrite par une théorie duale sur l’horizon cosmologique. Nous généralisons cette conjecture à des espaces-temps fermés de type FLRW. Nous introduisons une prescription covariante pour calculer l’entropie holographique d’intrication dans ce cadre, formalisant une dualité sous-région/sous-région. Nous soutenons que l’intrication entre théories holographiques associées à des observateurs complémentaires donne naissance à la région inflationnaire en dS. La généralisation aux espaces FLRW fournit une vision cosmologique de l’idée selon laquelle l’intrication construit l’espace-temps.Enfin, nous établissons une relation entre la structure causale de l’espace-temps et des contraintes issues de la théorie de l’information dans le cadre holographique. L’analogue gravitationnel découle du principe de focalisation quantique. Nous soutenons que la cohérence de l’holographie du patch statique avec ce théorème impose des contraintes sur la structure causale de la théorie duale. Ces résultats suggèrent une nouvelle connexion entre l’holographie du patch statique et la correspondance dS/CFT, une approche alternative de l’holographie cosmologique
Ansa -effects in alkaline earth metal octaphenylmetallocenophanes and a derived ansa -ferrocene
No full textInternational audienceThe synthesis and structural characterisation of a series of alkaline earth ansa-octaphenylmetallocenes (Mg, Ca, Sr, Ba) bearing an ethylene bridge are described. The complexes [AE(C5Ph4CH2)2(thf)n] (AE = Mg (1), Ca (2) n = 1; AE = Sr (3), Ba (4), n = 2) were obtained through reductive dimerisation of 1,2,3,4-tetraphenylfulvene, facilitated by zero-valent metals and fully characterised by NMR spectroscopy. Singlecrystal XRD studies reveal distinct binding differences of the Cp ligands to Mg in complex 1 compared to the heavier analogues (η3 vs. η5). Complex 3 is the first structurally characterised ansa-metallocene complex of Sr. An ansa-effect was observed for the Ba complex 4 which showed good stability at room temperature in contrast to the previously described non-bridged analogue. Efficient transmetallation from the Ca ansa complex 2 to FeCl2 provided the new ansa-ferrocene complex [Fe(C5Ph4CH2)2] (5). Structural, spectroscopic and electrochemical properties of this bent ferrocenophane complex were compared to those of the known unbridged octaphenylferrocene
Group-Level Imitation May Stabilize Cooperation
No full textInternational audienceStabilizing cooperation among self-interested individuals presents a fundamental challenge in evolutionary theory and social science. While classical models predict the dominance of defection in social dilemmas, empirical and theoretical studies have identified various mechanisms that promote cooperation, including kin selection, reciprocity, and spatial structure. In this work, we investigate the role of localized imitation in the evolutionary dynamics of cooperation within an optional Public Goods Game (PGG). We introduce a model where individuals belong to distinct groups and adapt their strategies based solely on comparisons within their own group. We identify different dynamical regimes, including stable fixed points, limit cycles, and Rock-Scissors-Paper-type oscillations. Our analysis, grounded in a replicator-type framework, reveals that such group-level imitation can stabilize cooperative behavior, provided that groups are not initially polarized around a single strategy. In other words, restricting imitation to group-level interactions mitigates the destabilizing effects of global competition, providing a potential explanation for the resilience of cooperation in structured populations.</div
Yet another differential shape lemma
No full textRecently, Kauers, Koutschan, and Verron proved a non-commutative version of the classical shape lemma in the theory of Gröbner bases. Their result requires the ideal to be D-radical. In this note, we prove a new non-commutative shape lemma that does not require this assumption
Bayesian model averaging of AI models for the high resolution mapping of the forest canopy height
No full textInternational audienceThe development of high resolution mapping models of forest attributes based on employing machine or deep learning techniques has&#160;increasingly accelerated in the last couple of years. The consequence of this is the widespread availability of multiple sources of information, which can either lead to a potential&#160;confusion, or to a possibility to get an "extended&#8221; insight into the state of our forests by interpreting these sources jointly. This contribution aims at addressing the latter, by relying on the Bayesian model averaging (BMA) approach. BMA is a method that can be used in building a consensus from an ensemble of different model predictions. It can be seen as weighted mean of different predictions with weights reflecting the predictive performances of different models, or as a finite mixture model which estimates the probability that each observation from the independent validation dataset has been generated by one of the models belonging to the ensemble. BMA can thus be used to diagnose and understand the difference in the predictions and to possibly interpret them. The predictions in our case are the forest canopy height estimations for the metropolitan France coming from 5 different AI models [1-5], while the independent validation dataset comes from the French National Forest Inventory (NFI) disposing with some 6000 plots per year, distributed across the territory of interest. For every plot we have several measurements/estimations of the forest canopy height out of which the following two are considered in this study: h_m &#8211; the maximum total height (from the tree's base level to the terminal bud of the tree's main stem) measured within the plot, and h_dom &#8211; the average height of the seven largest dominant trees per hectare. In this contribution we present for every considered plot the dominant model with respect to both references i.e. the model having the highest probability to be the one generating measurements/estimations at NFI plot (h_m and h_dom). We present as well as the respective inter-model and the intra-model variance estimations, allowing us to propose a series of hypotheses concerning the established differences between predictions of individual models in function of their specificities. [1] Schwartz, M., et al.: FORMS: Forest Multiple Source height, wood volume, and biomass maps in France at 10 to 30&#8201;m resolution based on Sentinel-1, Sentinel-2, and Global Ecosystem Dynamics Investigation (GEDI) data with a deep learning approach, Earth Syst. Sci. Data, 15, 4927&#8211;4945,&#160;2023, https://doi.org/10.5194/essd-15-4927-2023 [2] Lang, N., et al.: A high-resolution canopy height model of the Earth,&#160;Nat Ecol&#160;Evol&#160;7, 1778&#8211;1789, 2023. https://doi.org/10.1038/s41559-023-02206-6 [3] Morin, D. et al.: Improving Heterogeneous Forest Height Maps by Integrating GEDI-Based Forest Height Information in a Multi-Sensor Mapping Process, Remote Sens.,&#160;14, 2079. 2022, https://doi.org/10.3390/rs14092079 [4] Potapov, P.,&#160;et al.: Mapping global forest canopy height through integration of GEDI and Landsat data, Remote Sensing of Environment, 253, 2021, https://doi.org/10.1016/j.rse.2020.112165. [5] Liu, S.&#160;et al.: The overlooked contribution of trees outside forests to tree cover and woody biomass across Europe, Sci. Adv. 9, eadh4097, 2023, 10.1126/sciadv.adh4097
Large smooth twins from short lattice vectors
No full textFinding the largest pair of consecutive -smooth integers is computationally challenging. Current algorithms to find such pairs have an exponential runtime -- which has only be provably done for and heuristically for 100 < B \leq 113. We improve this by detailing a new algorithm to find such large pairs. The core idea is to solve the shortest vector problem (SVP) in a well constructed lattice. With this we are able to significantly increase and notably report the heuristically largest pair with which has -bits. By slightly modifying the lattice, we are able to find larger pairs for which one cannot conclusively say whether it is the largest or not for a given . This notably includes a -bit pair with which is the largest pair found in this work