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Adenine formation in prebiotic conditions from ab initio machine learning calculations
No full textInternational audienceThe prebiotic formation of nucleobases remains a fundamental question in the field of the origins of life. The reaction between 4-amino-5-cyanoimidazole (AICN) and hydrogen cyanide (HCN) has been proposed as a possible step in the HCN oligomerization pathway forming adenine, a nucleobase found in RNA and DNA. In this work, we employ machine learning interatomic potentials combined with enhanced sampling simulations to investigate this reaction in aqueous solution. This approach allows the identification of reaction pathways and a detailed exploration of the associated free energy landscape, explicitly accounting for solvent effects. The data efficiency of the employed machine learning architecture enables modelling at a hybrid DFT level of theory, which would otherwise be computationally too expensive using conventional ab initio methods. Our results show that, although the overall transformation is thermodynamically favorable, the high free-energy barriers make it difficult to proceed 1 efficiently in bulk water. This observation agrees with the low yields typically reported in experimental syntheses of adenine from HCN
Stability and renormalization of Jackson networks with non-idling mobile servers
No full textA tandem of two queues sharing a pool of servers, where users take the time to switch to thesecond queue, is used to model a typical pathway through an emergency department (ED), wherepatients undergo two consultations separated by diagnostic tests. In this article, explicit conditionsfor ergodicity and transience are given and proven via Foster’s criterion, using a linear Lyapunovfunction. This result is extended to a Jackson network, with the key difference that the nodes sharea pool of servers, with a non-idling service policy. Further, the delay times for customers to movefrom one node to another must be taken into account. This covers some of the main features ofmodels for emergency departments, namely priorities (triage) between patients. In the case of thetandem queue, by scaling the arrival rate and the number of servers by N, we obtain a renormalizedprocess converging to the solution of an ordinary differential equation (ODE) subject to boundaryconditions. When the system is ergodic, we discuss the solution of this ODE as t → ∞
Research Engine by Seintinelles: A participatory platform to foster science–society dialogue and inform research priorities in cancer research
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A synthetic approach to comparison principles for variational problems, with applications to optimal transport
No full textWe develop a synthetic, variational framework for deriving comparison principles in infinite-dimensional Banach spaces. Unlike traditional approaches that rely on the regularity of minimizers and Euler--Lagrange equations, our method exploits the order-theoretic structure of the energy. Central to our analysis is the notion of submodularity and its convex dual, substitutability, which we extend here to the infinite-dimensional setting. We prove a duality theorem establishing that a convex functional is submodular if and only if its conjugate is substitutable. We apply these results to problems in optimal transport, and derive comparison principles for Kantorovich potentials in standard, entropic, and unbalanced settings without requiring regularity assumptions on the cost or domain. Finally, we prove that general transport costs are substitutable, yielding comparison principles for JKO schemes driven by internal energies
Accounting for exposure in 3D spatiotemporally contiguous heatwaves in Europe 1975-2024
No full textHeatwaves are becoming more common, intense, and widespread as climate change accelerates, increasing their effects on infrastructure, economies, and health. However, heatwaves' material and human effects cannot be adequately captured by their meteorological characteristics alone. In order to address this challenge, we propose a new heatwave index (HWMId_pop), which combines population exposure and meteorological data to provide a more accurate representation of heatwave impacts. Heatwaves are detected using a 3D-event framework, which considers heatwaves as spatiotemporal events that transcend conventional, spatially limited definitions. We validate this new index by comparing it to the impacts of heatwaves recorded in the EM-DAT disaster database for Europe from 1975 to 2021. Our results show that HWMId_pop outperforms traditional heatwave indices by correlating more closely with mortality data and demonstrating a superior ability to identify significant heatwave events. We also examine trends in several commonly used heatwave indices between 1975 and 2024, finding that our proposed index shows a significant increasing trend. We highlight that the increasing affected population, driven by the expanding spatial extent of heatwaves and the rising European population, poses growing health risks. Additionally, we argue that this index can be used as a guide to carry out gap-filling in heatwaves impacts database such as EM-DAT
Evidence of mutually exclusive outflow forms from a black hole X-ray binary
No full textInternational audienceAccretion onto black holes often leads to the launch of outflows that significantly influence their surrounding environments. The two primary forms of these outflows are X-ray disk winds-hot, ionized gases ejected from the accretion disk-and relativistic jets, which are collimated streams of particles often expelled along the rotational axis of the black hole. While previous studies have revealed a general association between spectral states and different types of outflows, the physical mechanisms governing wind and jet formation remain debated. Here, using coordinated NICER and MeerKAT observations of the recurrent black hole X-ray binary 4U 1630-472, we identify a clear anti-correlation between X-ray disk winds and jets: during three recent outbursts, only one type of outflow is detected at a time. Notably, this apparent exclusivity occurs even as the overall accretion luminosity remains within the range expected for a standard thin disk, characteristic of the canonical soft state. These results suggest a competition between outflow channels that may depend on how the accretion energy is partitioned between the disk and the corona. Our findings provide new observational constraints on jet and wind formation in X-ray binaries and offer a fresh perspective on the interplay between different modes of accretion-driven feedback
Upper Limits on the Isotropic Gravitational-Wave Background from the first part of LIGO, Virgo, and KAGRA's fourth Observing Run
No full textInternational audienceWe present results from the search for an isotropic gravitational-wave background using Advanced LIGO and Advanced Virgo data from O1 through O4a, the first part of the fourth observing run. This background is the accumulated signal from unresolved sources throughout cosmic history and encodes information about the merger history of compact binaries throughout the Universe, as well as exotic physics and potentially primordial processes from the early cosmos. Our cross-correlation analysis reveals no statistically significant background signal, enabling us to constrain several theoretical scenarios. For compact binary coalescences which approximately follow a 2/3 power-law spectrum, we constrain the fractional energy density to (95% cred.), a factor of 1.7 improvement over previous results. Scale-invariant backgrounds are constrained to , representing a 2.1x sensitivity gain. We also place new limits on gravity theories predicting non-standard polarization modes and confirm that terrestrial magnetic noise sources remain below detection threshold. Combining these spectral limits with population models for GWTC-4, the latest gravitational-wave event catalog, we find our constraints remain above predicted merger backgrounds but are approaching detectability. The joint analysis combining the background limits shown here with the GWTC-4 catalog enables improved inference of the binary black hole merger rate evolution across cosmic time. Employing GWTC-4 inference results and standard modeling choices, we estimate that the total background arising from compact binary coalescences is at 90% confidence, where the largest contribution is due to binary black holes only,
Exploring the relationships between Electron Spin Resonance (ESR)/Luminescence (OSL/TL) properties and trace element composition from quartz in various bedrocks (Strengbach catchment, Vosges)
No full textInternational audienceQuartz Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) offer valuable quantitative tools both for understanding sediment provenance and surface processes. However, the variability of quartz sensitivity remains an issue, attributed either to the intrinsic properties of source bedrock, to processes during sediment transport and deposition, or to both. This study addresses these questions by investigating quartz from magmatic, metamorphic, and sedimentary formations in the Strengbach catchment (Vosges Massif, France). Using a combination of ESR, TL, OSL, and LA-ICPMS (Laser-Ablation Inductively Coupled Plasma Mass Spectrometry) trace element analyses, our study reveals significant relationships between quartz TL-OSL/ESR sensitivities and source bedrock characteristics, such as lithology, crystallization conditions, and deformation histories. ESR Ti-centre and TL-OSL signals are notably influenced by trace elements like Al, Li, and Ti. Quartz that underwent high pressure during metamorphism along with those located in the tectonic shear zone show both lowest TL-OSL and ESR intensities, while higher sensitivities are observed in quartz from plutonic rocks and sandstones. This suggests that (i) pressure can be one of the prevailing factors driving changes in quartz TL-OSL/ESR sensitivities (ii) enhanced quartz TL-OSL sensitivity in mature and recycled sediments (sandstones) highlight the importance of sedimentary transport and reworking on TL-OSL and ESR signals.Our results highlight the need for careful interpretation of ESR and TL-OSL signals, both for dating or sourcing, particularly in sediments derived from metamorphic terrains.</p
