Parallel geodesics and minimal stable length of random groups

21 pagesWe show that for any pair of long enough parallel geodesics in a random group G(m, d) with m generators at density d < 1/6, there is a van Kampen diagram having only one layer of faces. Using this result, we give an upper bound, depending only on d, of the number of pairwise parallel geodesics in G(m, d) when d < 1/6. As an application, we show that the minimal stable length of a random group at density d < 1/6 is exactly 1

VIP Virtual Imaging Platform (séminaire invité CRNL, avril 2026)

Présentation de la plateforme VIP dans le cadre d'un séminaire au Centre de Recherche en Neurosciences de LyonInternational audienc

A comprehensive characterization of sepiolite clays for isopropanol dehydration to propylene

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Biochemical components of chicken primordial germ cells are modified by cryopreservation: original analysis by Fourier Transform Infrared (FTIR) microspectroscopy

International audienceChicken primordial germ cells (cPGCs) are a highly valuable resource for preserving chicken genetics and poultry biodiversity, as these diploid stem cells, derived from both male and female genotypes, can be maintained in long-term in vitro culture and are still capable of producing germline-transmitting progeny. However, the cryopreservation process, which guarantees that these cells can be used to maintain genetic resources, raises various questions about their quality after thawing. We assessed cryo-induced biological alterations in cPGCs derived from Lueng Hang Khao (LK), a Thai native chicken breed, using both Fourier transform infrared (FTIR) microspectroscopy along with traditional biological and molecular assays. Established male and female cPGC lines were cryopreserved for ≥ 2 weeks and assessed at day 10 and day 20 post-thawing against fresh control. The main findings of this study were that i) cryopreservation induced a transient decrease in viability and proliferation, while germ-cell gene markers remained stable in both sexes, ii) pluripotency markers in female cPGCs were more sensitive than in males, and more interestingly, iii) FTIR analysis of male cPGCs showed that cryopreservation induced biochemical changes. Those include membrane remodeling—increased lipid peroxidation, greater saturation and acyl-chain packing, and reduced unsaturation—with lipid accumulation that is most evident at day 20 post-thawing, suggesting a long-term effect. Additionally, a marked reduction of the ester C=O (∼1740 cm⁻1) band was also observed in cryopreserved cPGCs, suggesting constant modifications of key molecules. Concordantly, secondary-structure analysis indicated a shift toward native-like α-helical states, and nucleic-acid/carbohydrate signatures declined. These results highlight the overall post-thawing recovery of cPGCs and establish FTIR as a practical, label-free readout to complement standard assays, informing quality control and optimization of the quality of germ-cell biobanking

Méthodes quantitatives sous Python

This course aims to introduce you to data manipulation using the Python language.Over the course of our three sessions together, we will cover:- The fundamentals of how the Python language works- Getting started with Jupyter Notebook environments- Exploring data manipulation libraries: - Numpy - Pandas - Matplotlib - Seaborn- Exploring data visualization libraries- Using a Vico dataset (Life during lockdown)Ce cours a pour but de vous introduire à la manipulation de données, à travers de le langage python.Tout au long de nos trois cours ensembles, nous verrons : - Les rudiments du fonctionnement du langage python- La prise en main des environnements de type Jupyter Notebook - La découverte des bibliothèques de manipulation de données : - Numpy - Pandas - Matplotlib - Seaborn- La découverte de bibliothèques de visualisation des données- Exploitation d'un jeu de données Vico (La vie pendant le confinement

Photodecomposition of the uricosuric drug benzbromarone under natural sunlight

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Measurement of the Z →\toμ+μ−μ^+μ^- angular coefficients in pp collisions at s\sqrt{s} = 13 TeV as functions of transverse momentum and rapidity

International audienceA measurement of the eight angular polarization coefficients, $A_0$ to $A_7$, in the cross section for the Drell$-$Yan production of two muons is presented. The analysis is based on proton-proton (pp) collision data recorded with the CMS detector at the LHC at a center-of-mass energy of $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 140 fb$^{-1}$. The coefficients are determined double differentially in eight intervals of transverse momentum and two intervals of rapidity of the muon pair $μ^+μ^-$. The results are presented for the $μ^+μ^-$ invariant mass range 81$-$101 GeV and are compared with theoretical predictions calculated at next-to-next-to-leading order in perturbative quantum chromodynamics. The measurement provides relevant information about the underlying partonic dynamics and the Z boson production mechanisms

The SPHINX public data release: II. Using low-ionisation absorption lines and dust attenuation to predict Lyman continuum escape

International audienceContext. Low-ionisation state (LIS) metal absorption lines, such as Si II λ 1526, are widely used to trace the properties and dynamics of the interstellar medium (ISM) in galaxies. These lines provide crucial insights into galaxy evolution, including feedback mechanisms, metal enrichment, and the escape fraction of ionising photons ( f esc ) during the epoch of reionisation. Aims. We expand our understanding of LIS absorption lines as diagnostic tools for ISM properties and f esc . Using the high-resolution SPHINX 20 cosmological radiation-hydrodynamics simulation, we generated a comprehensive synthetic dataset of LIS absorption lines and tested their predictive power for f esc in star-forming galaxies. Methods. Synthetic ISM absorption lines, focusing on Si II λ 1260 and Si II λ 1526, were computed with the radiative transfer code RASCAS , incorporating resonant scattering of photons, fluorescent emission, and interactions with dust grains. The simulated data enhance the public SPHINX 20 dataset with high-resolution LIS lines for the full 1380 galaxies and ten viewing angles per galaxy. We analysed correlations between line properties (width, depth, and Doppler shift), dust attenuation, and f esc , extending previous single-galaxy studies to a statistically significant mock galaxy sample. We also tested our predictions on observed data using the LzLCS and CLASSY surveys. Results. We found a strong correlation between the dust-corrected residual flux of Si II λ 1526, R ∼ ≡ R flux 1526 · 10 −0.4 A 1500 , and f esc . More precisely, we found f esc ≈ 1.041 R ∼ 1.887 −0.002, with an average absolute error of 0.02. When we applied observational conditions, the error increased, but the escape fraction was still well recovered. In particular, the measurement of residual fluxes required a very high spectral resolution, and the dust attenuation is not directly observable. We show by applying common tools for fitting the spectral energy distribution to our mock data that the inferred dust attenuation is often far from the correct value, with a tendency to underestimate the attenuation when the effect of dust is strongest. Conclusions. Our results demonstrate that the residual flux of Si II λ 1526 is a powerful predictor of the escape fraction of ionising photons when it is corrected for dust. The spectra, line measurements, and escape fraction values used in this work are made publicly available

Euclid Quick Data Release (Q1). AgileLens: A scalable CNN-based pipeline for strong gravitational lens identification

International audienceWe present an end-to-end, iterative pipeline for efficient identification of strong galaxy--galaxy lensing systems, applied to the Euclid Q1 imaging data. Starting from VIS catalogues, we reject point sources, apply a magnitude cut (I$_E$$\leq$ 24) on deflectors, and run a pixel-level artefact/noise filter to build 96 $\times$ 96 pix cutouts; VIS+NISP colour composites are constructed with a VIS-anchored luminance scheme that preserves VIS morphology and NISP colour contrast. A VIS-only seed classifier supplies clear positives and typical impostors, from which we curate a morphology-balanced negative set and augment scarce positives. Among the six CNNs studied initially, a modified VGG16 (GlobalAveragePooling + 256/128 dense layers with the last nine layers trainable) performs best; the training set grows from 27 seed lenses (augmented to 1809) plus 2000 negatives to a colour dataset of 30,686 images. After three rounds of iterative fine-tuning, human grading of the top 4000 candidates ranked by the final model yields 441 Grade A/B candidate lensing systems, including 311 overlapping with the existing Q1 strong-lens catalogue, and 130 additional A/B candidates (9 As and 121 Bs) not previously reported. Independently, the model recovers 740 out of 905 (81.8%) candidate Q1 lenses within its top 20,000 predictions, considering off-centred samples. Candidates span I$_E$ $\simeq$ 17--24 AB mag (median 21.3 AB mag) and are redder in Y$_E$--H$_E$ than the parent population, consistent with massive early-type deflectors. Each training iteration required a week for a small team, and the approach easily scales to future Euclid releases; future work will calibrate the selection function via lens injection, extend recall through uncertainty-aware active learning, explore multi-scale or attention-based neural networks with fast post-hoc vetters that incorporate lens models into the classification

Quantitative honesty in snakes: acoustic warning is influenced by sex, personality and correlates with bite risk in the nose-horned viper

International audienceAposematism has evolved as a strategy to warn predators of potential danger. While visual signals have received considerable attention, acoustic signals remain less studied despite their flexibility across contexts and individuals. We investigated defensive behaviours (hissing and biting) in the nose-horned viper (Vipera ammodytes). First, we assessed the repeatability of defensive behaviours under standardized conditions. Second, we quantified responses in a test arena simulating increasing threat levels: (i) no stimulation, (ii) visual stimulation, and (iii) combined visual and tactile stimulation. Hissing and biting were highly repeatable within individuals but varied markedly among them. Males showed a higher likelihood of exhibiting defensive behaviours than females. In the test arena, hissing and its acoustic variables (duration, intensity) increased with threat level. Biting occurred only during the visual and combined stimulation phases, and its frequency increased between the two periods. Consistent with the hypothesis of quantitative signal honesty, we found that hissing characteristics (number of hisses and hiss intensity) were positively correlated with the number of bites. Overall, our results reveal that defensive behaviour expression is influenced by personality traits, sex and threat level, highlighting the complexity of acoustic warning signals in snakes and their potential role as honest indicators of defensive capacity