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The second H.E.S.S. gamma-ray burst catalogue: 15 years of observations with the H.E.S.S. telescopes
No full textInternational audienceRecent observational efforts using imaging atmospheric Cherenkov telescopes (IACTs) have led to firm detections of very-high-energy (VHE) signals from bright gamma-ray bursts (GRBs), often at moderate redshifts. This work presents 15 years of H.E.S.S. GRB observations and examines their implications through population comparisons and selected modelling cases. GRBs are a key science target of the High Energy Stereoscopic System (H.E.S.S.). With a low-energy threshold (100 GeV) and rapid repointing capabilities, H.E.S.S. can begin follow-up observations within tens of seconds after a GRB trigger, covering the late prompt or early afterglow phases. We report GRB follow-up observations with H.E.S.S. from 2004 to 2019, which resulted in no significant VHE signals (aside from the detections of GRB~180720B and GRB~190829A). The resulting upper limits comprise the largest set available for GRBs at VHE. A subset of bursts with favourable conditions were selected for X-ray analysis and emission modelling. Population studies were performed to compare detected and non-detected GRBs. The results indicate that VHE-detected GRBs are not a distinct population, but tend to feature luminous X-ray emission and favourable redshift and observing conditions. This highlights the potential of next-generation IACTs such as the Cherenkov Telescope Array Observatory (CTAO), whose lower energy threshold will enhance the detection of fainter and more distant GRBs
ÉVALUATION DE L'ÉQUILIBRE ÉLECTRIQUE DU SCÉNARIO NÉGAWATT 2022 À L'AIDE DU MODÈLE OPEN SOURCE EOLES
No full textInternational audienceWe present the latest version of the open-source energy system optimisation model Eoles and use it to study whether the energy mix of the négaWatt 2022 scenario manages to meet demand for 2050 in France, for 19 weather-years. We find that even without recourse to interconnections, electricity demand only exceeds production for 3 to 4 hours a year on average, which is only just above the fault criteria of the French Energy Code. To prevent all hours of failure and fulfill reserves requirements, an additional 13.8~GW of dispatchable technologies is required, which corresponds to a 39\% increase compared to the négaWatt scenario. We then study the addition of three disptachable technologies: methane turbines, hydrogen turbines and batteries, that are all close in terms of total system cost. Moreover, electricity balance can be achieved even if the rooftop photovoltaic capacity is reduced compared to the négaWatt scenario. The associated gain (€3.4~bn./year) is higher than the additional cost of the dispatchable capacity mentioned above (around €1~bn./year).Nous présentons la dernière version du modèle d'optimisation du système énergétique open source Eoles et nous l'utilisons pour évaluer dans quelle mesure le mix énergétique du scénario négaWatt 2022 peut satisfaire la demande d'énergie en France à l'horizon 2050, pour 19 années météorologiques. Nous obtenons que même sans recours aux interconnexions, la demande d'électricité n'excède la production que 3 à 4 heures par an en moyenne, ce qui ne dépasse que de très peu les critères de défaillance du Code de l'énergie. Pour éliminer toute heure de défaillance et assurer les besoins de réserves, une puissance supplémentaire de technologies pilotables de 13,8 GW est nécessaire, soit une augmentation de 39 % par rapport au scénario négaWatt. Nous étudions l'ajout de trois technologies pilotables : turbines à gaz (méthane ou hydrogène) et batteries, qui sont toutes proches en termes de coût total du système énergétique. Par ailleurs, l'équilibre électrique peut être atteint même en réduisant la capacité photovoltaïque sur toitures par rapport au scénario négaWatt. Le gain associé (3,4 Md€/an) est plus élevé que le surcoût entraîné par les capacités pilotables mentionnées ci-dessus (environ 1 Md€/an)
Classifying Covering Types in Homotopy Type Theory
No full textInternational audienceCovering spaces are a fundamental tool in algebraic topology because of the close relationship they bear with the fundamental groups of spaces. Indeed, they are in correspondence with the subgroups of the fundamental group: this is known as the Galois correspondence. In particular, the covering space corresponding to the trivial group is the universal covering, which is a "1-connected" variant of the original space, in the sense that it has the same homotopy groups, except for the first one which is trivial. In this article, we formalize this correspondence in homotopy type theory, a variant of Martin-Löf type theory in which types can be interpreted as spaces (up to homotopy). Along the way, we develop an n-dimensional generalization of covering spaces. Moreover, in order to demonstrate the applicability of our approach, we formally classify the covering of lens spaces and explain how to construct the Poincaré homology sphere
Combined Temperature and Photobleaching Effects on P‐Doped Optical Fibers
No full textInternational audienceIn this paper, we investigate the combined effects of temperature and photobleaching (PB) on multimode phosphorus‐doped (P‐doped) optical fibers (OFs) response under irradiation. To achieve this purpose, we investigate the kinetics of the radiation‐induced attenuation (RIA) in the visible spectral range (450–800 nm) under X‐ray irradiation up to 5Gy(SiO 2 ) with a dose rate of 10 mGy(SiO 2 )/s, varying the temperature of irradiation from −80°C to +80°C. This study is part of a recent series of investigations on the regeneration of these radiation‐sensitive optical fibers after they have served as dosimeters. The spectral range investigated allows us to study absorbing defects such as the metastable and stable phosphorus oxygen hole centers (POHC) and the P2 point defects. Our data suggests that thermally‐assisted bleaching has an impact during and after irradiation on the RIA. It is clear that thermal bleaching is relevant, especially for wavelengths below 580 nm; its contribution remains minor compared to that of the PB by 408 nm laser. Furthermore, thermal bleaching appears to be negligible for wavelengths above 580 nm. This work provides further understanding of the combined temperature and photobleaching effects on the regeneration of transmission capability of P‐doped fiber dosimeters in the visible range
Refractive indices of photochemical haze analogs for Solar System and exoplanet applications: A cross-laboratory comparative study between the PAMPRE and COSmIC experimental setups
No full textInternational audiencePrevious observations of Titan, Pluto, and Solar System gas giants, along with recent observations of exoplanet atmospheres with the James Webb Space Telescope, have taught us that photochemical hazes are ubiquitous and form in a variety of temperature, gas composition, and irradiation environments. Despite their crucial role in understanding their impact on observations and on the planetary radiative budget, the refractive indices of these haze particles remain unknown and are strongly influenced by changes in gas-phase chemistry. In this study, we performed a cross-laboratory investigation to assess the effect of the experimental setup and gas composition on the refractive indices of Titan, Pluto, and exoplanet haze analogs. We report new data in a broad spectral range from UV to far-IR (up to 200 µm) for future use in climate models and retrieval frameworks. We compare the refractive indices of laboratory haze analogs produced from six different gas compositions, in which we varied the relative abundances N 2 /CH 4 and CH 4 /CO in the initial gas mixture, using the PAMPRE (LATMOS, France) and COSmIC (NASA Ames Research Center, USA) experimental setups. We observed strong variations in the k values in the spectral range from UV to near-IR between the different analogs, which are caused by both the experimental setup and changes in the gas N 2 /CH 4 ratio. We find that the gas N 2 /CH 4 ratio has a stronger influence on the haze refractive indices in the entire spectral range compared to the gas CH 4 /CO ratio. The experimental setup is the primary factor affecting the refractive indices, confirming that the gas residence time, irradiation, pressure, and gas temperature are important parameters influencing the composition of the solid analog. The higher n and k values in the UV-visible range, along with the stronger amine, alkene, aromatic, and/or hetero-aromatic signatures in the mid-IR for the COSmIC analogs, are consistent with a greater incorporation of nitrogen into the COSmIC solid analogs compared to the PAMPRE analogs, even at similar nitrogen abundances in the gas phase. Haze analogs produced in gas mixtures without nitrogen, similar to the stratospheres of Solar System gas giants and the H 2 -dominated atmospheres of sub-Neptunes, are generally more transparent with lower n values across the entire spectral range from UV to mid-IR and should therefore be carefully considered in climate and observational applications. The variations in IR absorption features between hazes produced with and without nitrogen could help constrain the presence of N 2 in exoplanet atmospheres
Sampling from multi-modal distributions on Riemannian manifolds with training-free stochastic interpolants
No full textIn this paper, we propose a general methodology for sampling from un-normalized densities defined on Riemannian manifolds, with a particular focus on multi-modal targets that remain challenging for existing sampling methods. Inspired by the framework of diffusion models developed for generative modeling, we introduce a sampling algorithm based on the simulation of a non-equilibrium deterministic dynamics that transports an easy-to-sample noise distribution toward the target. At the marginal level, the induced density path follows a prescribed stochastic interpolant between the noise and target distributions, specifically constructed to respect the underlying Riemannian geometry. In contrast to related generative modeling approaches that rely on machine learning, our method is entirely training-free. It instead builds on iterative posterior sampling procedures using only standard Monte Carlo techniques, thereby extending recent diffusion-based sampling methodologies beyond the Euclidean setting. We complement our approach with a rigorous theoretical analysis and demonstrate its effectiveness on a range of multi-modal sampling problems, including high-dimensional and heavy-tailed examples
Selective Disruption of Plasmodium falciparum mitochondrial DNA via G-Quadruplex-Binding Ligand RHPS4 Provides a Novel Antimalarial Strategy
No full textInternational audienceABSTRACT Malaria caused by Plasmodium falciparum remains a major health threat, killing over 600,000 people annually. The spread of resistance to all major antimalarials, including artemisinins, highlights the urgent need for new drugs with distinct mechanisms of action. Here we show that the G-quadruplex ligand RHPS4, an acridine derivative, displays strong antiplasmodial activity against both drug-sensitive and -resistant P. falciparum strains and clinical isolates. RHPS4 primarily targets the trophozoite stage and induces major mitochondrial alterations, including reduction of mitochondrial DNA (mtDNA) and transcriptional dysfunctions. Bioinformatic analyses identified at least eight putative G4-forming sequences within the parasite’s mtDNA. Biophysical studies confirmed G4 folding of at least one sequence and its interaction with RHPS4. These findings indicate that RHPS4 disrupts P. falciparum mitochondrial metabolism through G4 stabilization, leading to parasite death, and establish mtDNA G4 structures as novel therapeutic targets for antimalarial development
La captation audiovisuelle enmathématiques
No full textWe describe an experimental activity involving the recording of mathematical work sessions, aimed at documenting the work of mathematicians and contributing to an archive of the daily aspects of research. The feedback from the filmed images provides a new investigative tool and a source of reflection on our practices.Nous décrivons une activité expérimentale de captation de séances de travail mathématiques, qui a pour but de documenter le travail du mathématicien, en contribuant à nourrir un fonds d’archive sur les aspects quotidiens de l’activité de recherche. Le retour d’expérience de l’image filmée offre un nouvel outil d’investigation et une source de réflexions sur nos pratiques.</div
Measurement and effective field theory interpretation of the photon-fusion production cross section of a pair of W bosons in proton-proton collisions at = 13 TeV
No full textInternational audienceThis analysis presents an observation of the photon-fusion production of W boson pairs using the CMS detector at the LHC. The total cross section of the WW production in photon fusion is measured using proton-proton collision data with an integrated luminosity of 138 fb collected with the CMS detector in 20162018 at a center-of-mass energy of = 13 TeV. Events are selected in the final state with one isolated electron and one isolated muon, and no additional tracks associated with the electron-muon production vertex. The total and fiducial production cross sections are 643 fb and 3.96 fb, respectively, in agreement with the standard model predictions of 631 126 fb and 3.87 0.77 fb. This agreement enables stringent constraints to be imposed on anomalous quartic gauge couplings within a dimension-8 effective field theory framework
Machine learning techniques for jet reconstruction at LHCb and application to the search for and in TeV collisions
No full textInternational audienceTwo machine learning techniques for jet measurements at the LHCb experiment are presented: a regression-based method for jet-energy calibration and a deep neural network algorithm for jet flavour tagging, distinguishing between -quark, -quark, and light parton jets. These techniques are applied to a search for inclusive H \to \bbbar and H \to c\barcc decays using a LHCb dataset corresponding to an integrated luminosity of 1.6\invfb. The observed (expected) 95% confidence level upper limits correspond to 6.6 (11.1) times the SM cross-section for the process, and 1003 (1834) times the SM cross-section for the process