Hal - Université Grenoble Alpes
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Integrating functional accessibility and pedestrian environmental comfort: A spatially explicit framework for urban walkability evaluation
No full textInternational audienceUrban walkability is central to sustainable urban development and, at the city scale, is increasingly viewed as shaped by both functional accessibility and pedestrian environmental comfort (PEC). However, most citywide assessments remain predominantly function-oriented, and few provide explicit behavioral validation using observed walking patterns. This study addresses this gap by proposing a spatially explicit, dual-dimensional framework that treats functional accessibility and PEC as co-equal components of walkability. Using Nantes, France, as a case study, we implement the framework on a uniform 150 m × 150 m grid and derive three composite indices—Traditional Walkability Score (TWS), a PEC index, and a PEC-enhanced Walkability Score (PEWS)—from GIS indicators standardized and combined using entropy-based weighting. Our analysis reveals a systematic spatial mismatch between functional and environmental dimensions: TWS concentrates in amenity-rich and well-connected areas, whereas PEC is highest along blue–green corridors. The integrated PEWS induces a targeted spatial re-ranking, deprioritizing functionally rich but environmentally harsh central areas while upgrading nature-rich peripheral zones. We then behaviorally validate the framework using observed pedestrian counts and gridded resident population data from INSEE, operationalized as a deviation metric comparing observed flows with population-based expectations. Blue–green features (trees, rivers, and green spaces) are associated with higher-than-expected pedestrian activity, whereas proximity to major motorized roads is associated with lower-than-expected activity. These findings support PEC as a necessary component of city-scale walkability assessment and provide actionable guidance for planning interventions
Strain pattern and active faults' compatibility across the Western Alps revealed by 25 years of GNSS measurements
No full textUpdated GNSS solutions integrating 25 years of GNSS data allow to evaluate deformation rates of 0.1–1 mm/yr in the WesternAlps, and in particular to compare the High Durance fault (HDF) activity (internal zones) with the Belledonne Fault (BDF)(external zone). Strain rate estimates are larger across HDF (19 ± 3 nanostrain/yr EW extension) than BDF (5 ± 1 nanostrain/yr EW compression). Fault slip rates indicate dominant dextral strike-slip motion on BDF (0.2 ± 0.1 mm/yr), whileHDF exhibits major extensional motion (0.3 ± 0.1 mm/yr). These two faults represent therefore the broader kinematics of theW-Alps characterized by seismicity showing mainly extensional deformation in the internal zones (HDF) and strike-slip motionin the external zone (BDF). Finally, a rigid 3-blocks model explains 29% of the observed GNSS velocity field and confirms theHDF and BDF deformation styles and their interconnected roles in the W-Alpine deformation framework
New insight on the properties of the superconducting iron spin ladder BaFe<sub>2</sub>S<sub>3</sub>
No full textInternational audienceBaFe2S3 and BaFe2Se3 are the only two quasi-one-dimensional iron-based compounds that become superconductors under pressure. Interestingly, these two compounds exhibit different symmetries and properties. While more detailed and recent studies on BaFe2S3 using single crystals have advanced the field towards a more universal description of this family, such a study is still lacking for the compound BaFe2S3 . Here, we present a detailed study of the crystalline and magnetic structures performed on single crystals using X-ray and neutron diffraction. We demonstrate a polar structure at room temperature within the Cm2m followed by a structural transition at TS = 130 K to the polar Pb21m space group, space group. This space group remains unchanged across the magnetic transition at TN = 95 K, revealing multiferroic characteristics with a weak magnetoelastic coupling. The determined magnetic structure is monoclinic (Pam ), with non-collinear Fe magnetic moments, tilted from the rung axis. This reexamination of the temperature-dependent properties of BaFe2S3 provides new insights into the physics of this system from multiple key perspectives
A Detailed Study of NiFe2O4-PVDF Magnetic Composites: Structural Stability and Superior Magnetic Properties for Functional Applications
No full textInternational audienceIn this work, PVDF-based magnetic nanocomposites reinforced with NiFe2O4 nanoparticles were successfully fabricated through a two-step process, involving nanoparticle synthesis at controlled pH values (10, 11, and 12) followed by composite preparation via solvent casting. The influence of particle size, loading, and inter-particles interaction on the structural, mechanical, and magnetic properties of the magnetic polymer composite was systematically investigated. SEM analysis revealed that higher nanoparticle loadings and larger particle sizes increased surface roughness due to aggregation and chain disruption, yet the magnetic polymer composite material maintained structural integrity without phase separation or defects. Mechanical performance was also strongly governed by nanoparticle characteristics: PVDF/30-NF11 showed the highest stiffness, while PVDF/30-NF10, containing smaller particles (26.7 nm), achieved the best balance of stiffness, strength, and strain. Magnetic behavior was optimized in PVDF/30-NF11, where particle size (42 nm) enabled strong inter-particle interactions and enhanced structural stability, yielding superior magnetic response. These findings highlight how particle size, the filler content in the PVDF matrix, and the inter-particle interactions, collectively govern the overall performance of PVDF based magnetic composite, offering a clear pathway to guide the optimized design of high-performance polymer-based magnetic materials for applications in sensors, actuators, and electromagnetic devices
Weak Lensing Mass Calibration of the ACT DR5 Galaxy Clusters with the DES Year 3 Weak Lensing Data
No full textInternational audienceWe use weak gravitational lensing measurements from Year 3 Dark Energy Survey data to calibrate the masses of 443 galaxy clusters selected via the Sunyaev-Zel'dovich effect from Atacama Cosmology Telescope Data Release 5 maps of the cosmic microwave background. We incorporate redshift and SZ measurements for individual clusters into a hierarchical model for the stacked lensing signals and perform Bayesian analyses to constrain the hydrostatic mass bias of the clusters. Our treatment of systematic uncertainties includes a prescription for measuring and accounting for the weak lensing boost factor, consideration of a miscentering effect, as well as marginalization over uncertainties in the source galaxy photometric redshift distributions and shear calibration. The resultant constraints on the normalization of the mass-observable relation have a precision of approximately 7%, with the mean WL halo mass of . We measure the bias between the true cluster mass and the mass estimated from the SZ signal based on an X-ray--calibrated scaling relation assuming hydrostatic equilibrium, to be over the full sample. When splitting the clusters into high (=0.43-0.70) and low (=0.15-0.43) redshift bins, we measure and , respectively. When introducing additional freedom in redshift and mass to the hydrostatic bias model, we find that decreases with redshift (with the power law of , 99.95% confidence), consistent with findings from other recent studies, while we do not find any significant trend in mass. We also demonstrate that our result is robust against various systematics. The weak-lensing mass calibration presented in this study will be a useful tool for using the ACT clusters as probes of astrophysics and cosmology
Communal coping in high-level sports teams: A mixed-method investigation
No full textInternational audienceCommunal coping, defined as collectively perceiving and addressing stressors as "our problem," plays a critical role in teams’ ability to manage stressful situations. By using a mixed-method approach this study examined (1) the extent to which athletes share their appraisals of stressful match situations, (2) the degree to which they perceive coping strategies as collectively enacted, and (3) psychosocial and contextual factors that may facilitate or hinder these shared processes. Forty-nine elite athletes from four high-level sports teams (basketball, football, and ice hockey) participated in this study. Quantitative data were analyzed using descriptive statistics, whereas qualitative data from the focus groups were analyzed using thematic analysis. The quantitative results indicated variability in athletes' shared appraisals of stress intensity and revealed differential use of communal coping strategies across teams and situations. Focus groups provided in-depth qualitative insights into the factors that influenced these processes. The findings highlight that communal coping is a complex social phenomenon influenced by communication, leadership, emotional expression, and environmental contexts such as competition stakes and timing. This study underscores the necessity for mixed methods approaches in future communal coping research, especially in ecological settings, emphasizing both shared appraisal and communal action dimensions. Recommendations for future research include employing larger samples, evaluating both primary and secondary appraisals, and explicitly examining perceptions of stress ownership to enhance understanding of communal coping among sports team
CP4SBI: Local Conformal Calibration of Credible Sets in Simulation-Based Inference
No full textInternational audienceCurrent experimental scientists have been increasingly relying on simulation-based inference (SBI) to invert complex non-linear models with intractable likelihoods. However, posterior approximations obtained with SBI are often miscalibrated, causing credible regions to undercover true parameters. We develop CP4SBI, a model-agnostic conformal calibration framework that constructs credible sets with local Bayesian coverage. Our two proposed variants, namely local calibration via regression trees and CDF-based calibration, enable finite-sample local coverage guarantees for any scoring function, including HPD, symmetric, and quantile-based regions. Experiments on widely used SBI benchmarks demonstrate that our approach improves the quality of uncertainty quantification for neural posterior estimators using both normalizing flows and score-diffusion modeling
Mg2NiH4 under stress: Coupling transition metal doping with structural deformation for improved hydrogen storage
No full textInternational audienceWe use first-principles DFT to assess transition-metal substitution (Ag, Co, Mn) and uniaxial strain (−3% to +3%) as dual levers to improve Mg2NiH4 for hydrogen storage. Among the dopants, Mn is most effective: the formation enthalpy shifts from −63 to −38 kJ.mol−1.H2 under compressive strain, near the DOE target (≈−40 kJ.mol−1.H2). The corresponding decomposition temperature drops from 502 to 282 K, aligning with the PEMFC operating window (≈289–393 K). Structurally, compressive strain increases the volumetric hydrogen density without compromising reversibility. Kinetically, the H migration barrier decreases from 0.50 to 0.42 eV in the Mn-substituted phase, especially under tensile strain, indicating faster diffusion. These results demonstrate that combining chemical substitution with strain engineering tunes both thermodynamics and kinetics, positioning Mn-doped Mg2NiH4 under ±1% compressive/tensile strain as a practical candidate for low-temperature, fuel-cell-compatible hydrogen storage
Altermagnétisme : la face cachée du monde magnétique
No full textInternational audienceQuand nous pensons à un matériau magnétique, nous imaginons instinctivement un aimant et le champ magnétique qu’il produit de lui-même. C’est en effet cette propriété qui est exploitée dans de nombreuses applications de la vie courante : transformateurs électriques, moteurs, générateurs, capteurs, appareils médicaux, électroménagers, stockage de données... Cependant, il existe de nombreux matériaux qui ne sont pas spontanément aimantés et qui, pourtant, possèdent microscopiquement un ordre magnétique bien déterminé. Cet article met en lumière une famille de matériaux de ce genre, découverte récemment : les altermagnétiques. Leurs propriétés, supérieures par bien des aspects à celles des aimants usuels, élargissent le spectre des applications des matériaux magnétiques, notamment dans le domaine de l’électronique de spin
