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On a geometric graph-covering problem related to optimal safety-landing-site location
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Nonlinear model calibration through bifurcation curves
No full textInternational audienceNonlinear systems exhibit a plethora of complex dynamic behaviours that are difficult to model and predict accurately. This difficulty often arises from a lack of knowledge of the physics that induces the nonlinear behaviours and the strong sensitivity of the nonlinear dynamics to parameter variation. We introduce in this paper a methodology to carry out nonlinear model updating based on bifurcations. The proposed approach involves minimising the distance between experimental and numerical bifurcation curves, which are key dynamic features that define stability boundaries and regions of multi-stability. For the model, bifurcation curves are computed via standard numerical bifurcation tracking analyses. In the experiment, we use control-based continuation to obtain the data. The approach is first demonstrated on a Duffing and a beam system using synthetic data, before being applied to experimental data collected on a base-excited energy harvester with magnetic nonlinearity
Community challenge towards consensus on characterization of biological tissue: C4Bio’s first findings
No full textInternational audienceThis study investigates methodological variability across various expert laboratories worldwide, with regards to characterizing the mechanical properties of biological tissues. Two testing rounds were conducted on the specific use case of uniaxial tensile testing of porcine aorta. In the first round, 24 labs were invited to apply their established methods to assess inter-laboratory variability. This revealed significant methodological diversity and associated variability in the stress–stretch results, underscoring the necessity for a standardized approach. In the second round, a consensus protocol was collaboratively developed and adopted by 19 labs in an attempt to minimize variability. This involved standardized sample preparation and uniformity in testing protocol, including the use of a common cutting and thickness measurement tool. Despite protocol harmonization, significant variability persisted across labs, which could not be solely attributed to inherent biological differences in tissue samples. These results illustrate the challenges in unifying testing methods across different research settings, underlining the necessity for further refinement of testing practices. Enhancing consistency in biomechanical experiments is pivotal when comparing results across studies, as well as when using the resulting material properties for in silico simulations in medical research
Measurement of asymmetry in decays with the LHCb Upgrade I detector
No full textInternational audienceA measurement of asymmetry in decays is reported, based on a data sample of proton-proton collisions collected with the LHCb Upgrade I detector in 2024 at a centre-of-mass energy of TeV, corresponding to an integrated luminosity of . The decay is used as calibration channel to cancel residual detection and production asymmetries. The time-integrated asymmetry for the mode is measured to be where the first uncertainty is statistical, and the second is systematic. This is the most precise determination of this quantity to date
Utilizing simulated event lists in IACT gamma-ray astronomy
No full textInternational audienceWe present a new approach for calculating the IACT detector response of high-level analyses with publicly available software based on dedicated simulations of the individual observations. For each of them, a corresponding event list is exported, paralleling the event list of the actual data. The information contained in these simulated lists can be utilized flexibly, without the need for but also being able to reduce it to the standard IRF scheme. We show that standard IRFs from simulated event lists yield consistent results, illustrating the validity of the concept. To improve on the standard response generation, we then demonstrate how to calculate the final IRFs for a given analysis geometry directly from the simulated event lists. The result is a more accurate description, where the change in IRF methodology leads to considerable differences. Finally, we introduce a new method of generating background models based on simulated event lists. By properly considering observation and detector conditions, the new approach provides an accurate description of the γ-like background, exhibiting good stability and a moderate systematics level
Topological Signatures of Magnetic Phase Transitions with Majorana Fermions through Local Observables and Quantum Information
No full textInternational audienceThe one-dimensional (1D) quantum spin model can be viewed as a strong-coupling analogue of the Schrieffer-Su-Heeger model with two inequivalent alternating Ising couplings along the wire, associated to the physics of resonating valence bonds. Similar to the quantum Ising model, which differently presents a long-range Neel ordered phase, this model also maps onto a p-wave superconducting wire which shows a topological phase transition with the emergence of low-energy Majorana fermions. We show how signatures of the topological phase transition for the p-wave superconducting wire, i.e. a half Skyrmion, are revealed through local (short-range) spin observables and their derivatives related to the capacitance of the pairing fermion model. Then, we present an edge correspondence through the edge spin susceptibility in the model revealing that the topological phase transition is a metal of Majorana fermions. We justify that the spin magnetization at an edge at very small transverse magnetic field is a good marker of the topological invariant. We identify a correspondence between the quantum information of resonating valence bonds and the charge fluctuations in a p-wave superconductor through our method ``the bipartite fluctuations''. This system may be realized in materials and engineered in quantum circuits, optical lattices
Properties of Magnetic Switchbacks in the Near-Sun Solar Wind
No full textInternational audienceMagnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into "patches". We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies
A method for luminosity determination based on real-time hit reconstruction with the LHCb silicon pixel detector
No full textInternational audienceThe data acquisition system of the upgraded LHCb experiment includes the fast reconstruction of all hits in the vertex locator (VELO) pixel detector at the beam-crossing rate of 40 MHz, implemented as on-the-fly clustering embedded in the firmware of the readout board FPGAs. The availability of a high rate of reconstructed clusters in real time enables a new fast approach for measuring luminosity and monitoring the LHCb luminous region, directly at the detector readout level. This methodology has been implemented as an array of real-time cluster counters in the VELO readout FPGAs and has been in operation since the start of the 2024 physics run of LHCb. This paper describes the methodology and its features and performance, both on proton-proton and lead-lead collision data. The method shows a statistical resolution better than the percent level, and a sensitivity to variable running conditions of the same level. This is achieved with an intrinsic time granularity better than 100 ms , undersampled to 3 s for analysis purposes. Nonlinear behaviour is compatible with zero in a luminosity range including the LHCb Run 3 operating point
Pliocene contrasted climate conditions in space and over time: A unique pollen dataset from the NW Mediterranean Region for comparison with climate models
No full textInternational audienceA set of 62 Pliocene pollen records and reconstructed climate parameters across the Northwestern Mediterranean Region, together with palaeoclimate simulations from the IPSL earth system model, provide a unique opportunity to study the Pliocene, especially the early Piacenzian Cooling (ePC) and the mid-Piacenzian Warm Period (mPWP). Vegetation reconstructed from pollen records documents strong spatial contrasts in the area. It reveals a retreat of the subtropical broad-leaved evergreen forest to the advantage of Mediterranean sclerophyllous ecosystems.This study is a first attempt to compare observation-based data with model simulations in the Northwestern Mediterranean Region. It reveals substantial discrepancies with encouraging results, pointing out the need to expand the work of data -model comparisons to other regions. The mid-Piacenzian warm period appears to be an interesting past analogue for the ongoing anthropogenic global warming, including its regional impacts. We observe that two areas (Northern Catalonia and the Southern Alps-Liguria) were affected by increased precipitation during brief episodes in the mid-Piacenzian, while the Roussillon-Languedoc-Provence area experienced drier conditions. Such a spatial pattern seems comparable with the present-day context. The significance of ecosystems composed of some Cupressaceae (Cupressus-Juniperus-type) is interpreted partially as subtropical forest, and partially as Mediterranean vegetation. This regional study provides valuable data and interpretations to improve the contribution of past records to such evaluations, and inspires future palaeoclimate simulations with finer resolution
Mechanisms driving mesoscale latent heat flux variations and mixed layer heat content evaluation in the Northwest Tropical Atlantic
No full textInternational audienceIn this study, a high-resolution ocean-atmosphere coupled simulation is used to assess the effects of sea surface temperature (SST), surface currents, and ocean vertical stratification on the spatial variability of latent heat flux (LHF) and the stability of the marine atmospheric boundary layer (MABL) in the Northwest Tropical Atlantic during January and February 2020. The analysis focuses on the ocean mesoscale (O(50–250 km)) across the Northwest Tropical Atlantic (referred to as the EURECA region in this study) and within three sub-regions characterized by different ocean dynamical regimes: Amazon, Downstream, and Tradewind. Results indicate that the coupling between SST and wind speed (and specific humidity) is stronger (weaker) in the Amazon and Downstream regions, influenced by the warm coastal North Brazil Current eddy corridor and the Amazon River plume, than in the Tradewind region, representative of the open ocean, consistent with previous remote sensing studies. Overall, warmer SSTs are associated with increased wind speeds and variations in specific humidity, deviating from Clausius–Clapeyron expectations. We interpret this as the result of active ocean processes modifying the near-surface atmosphere, enhancing vertical motion in the MABL, and transporting momentum and drier air from the free troposphere toward the surface. To further investigate the impact of mesoscale SST features on LHF, we apply a linear, SST-based downscaling method. Results show that these mesoscale SST structures induce a substantial increase in LHF, 46.8 Wm-2K-1 on average in the Amazon and Downstream regions (warm eddy corridor). In the Tradewind region, the LHF sensitivity to SST is smaller, at about 35 Wm-2K-1. For the Amazon region, of the 46.7 Wm-2K-1 change in LHF associated with SST, approximately 7.8 Wm-2K-1 is attributed to direct mesoscale SST changes (thermodynamic contribution), while the remainder is linked to mesoscale SST-induced modifications in near-surface atmospheric circulation (dynamic contribution), mainly due to the mesoscale SST-induced humidity undersaturation imbalances. The influence of surface currents on LHF is weaker, with deviations not exceeding 15 W m−2. Finally, we focus on the SST mesoscale anomalies linked to the Amazon freshwater plume. We find them to be persistent throughout the period of study affecting LHF by the mechanisms described above. Lateral advection and heat loss to the atmosphere tend to dilute them with their environment by the end of the period of study. This work underscores the importance of a regionalized approach to mesoscale air-sea interaction studies in the Northwest Tropical Atlantic, as LHF sensitivity to SST and surface currents exhibits strong spatial variability driven by distinct oceanic dynamics. Submesoscale LHF sensitivity to SST and currents is not addressed here and will be the subject of future research