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Extracting quantum field theory dynamics from an approximate ground state
No full textWe develop a linear-programming method to extract dynamical information from static ground-state correlators in quantum field theory. We recast the K¨all´en–Lehmann inversion as a convex optimization problem, in a spirit similar to the recent approach of Lawrence [2408.11766]. This produces robust estimates of the smeared spectral density, the real-time propagator, and the mass gap directly from an approximate equal-time two-point function, and simultaneously yields an a posteriori lower bound on the correlation-function error. We test the method on the 1 + 1-dimensional ϕ4 model, using a variational approximation to the vacuum—relativistic continuous matrix product states—that provides accurate correlators in the continuum and thermodynamic limits. The resulting mass gaps agree with renormalized Hamiltonian truncation and Borel-resummed perturbation theory across a wide range of couplings, demonstrating that accurate dynamical data can berecovered from a single equal-time slice
Design-driven roadmapping: structuring collective action for sustainability transitions in public transport
No full textInternational audienc
New results of the Ecorc’Air citizen science project: Biomonitoring of Vehicular Air Pollution in Cologne, Germany
No full textInternational audienc
Image generation of short glass fibre composite microstructures: From control to optimisation and damage prediction
No full textInternational audienc
Hydration mechanisms in Roman seawater concrete: Archaeological analogue for validation of long-term ageing reactive transport model
No full textInternational audienceCement-based materials are considered for sealing plugs in deep geological disposal of radioactive waste. Ensuring their long-term durability is critical for safety over millennia. The Roman Concrete (RoC) project uses ancient Roman underwater concretes as analogues to validate reactive transport models for long-term ageing.This study focuses on hydration mechanisms in Roman concrete made with Phlegrean pozzolan, slaked lime, and seawater. Various techniques (XRD, SEM-EDS, NMR, nanoindentation, microtomography, ICP-OES, ion chromatography) were used to characterize hydration products. Casting underwater led to aragonite and brucite layers with a 60 GPa Young's modulus, protecting the concrete from further degradation. In the core, pozzolanicreactions produce C-(A)-S-H phases (Ca/Si = 1.2; Al/Si = 0.2) with a modulus of 12 GPa. HYTEC modeling confirmed the mechanism: incongruent pozzolan dissolution releases ions (K+, SiO₄ 4− , Al3+, Na+), promoting C-(A)-S-H formation and portlandite consumption
McClear_Radiance physical model for estimating clear sky downwelling and upwelling solar irradiance on tilted surfaces
No full textInternational audienceAccurate prediction of downwelling and upwelling surface solar irradiance for various plane orientations is crucial for several solar energy applications, particularly bifacial photovoltaic systems and the architectural design of energy-efficient buildings. In this study, a fast and physical model providing downwelling and upwelling surface solar irradiance under clear skies on any tilted plane is developed and validated, entitled McClear_Radiance. This new model is inspired by the McClear clear sky model, which utilizes reference look-up tables established using the radiative transfer code libRadtran and atmospheric variables from the Copernicus Atmosphere Monitoring Service to estimate global, beam, and diffuse irradiance on a horizontal plane. McClear_Radiance uses look-up tables of sky radiance matched to atmospheric conditions extracted from output variables of McClear. The resulting sky radiances are complemented by a detailed angular representation of surface optical properties based on the Ross-Li Bidirectional Reflectance Distribution Function for non-Lambertian surfaces. McClear_Radiance is approximately 200 times faster than radiative transfer computations. Validations against high-quality pyranometric measurements from the Plataforma Solar de Almería in Spain demonstrate strong agreement. The downwelling global tilted irradiance, for planes with tilt angles from 20 • to 45 • oriented south or southwest, showed bias and root mean square error values from +1 to +2 % and 2 to 3 %, respectively, relative to the mean reference. A correlation coefficient of 0.998 was obtained. The diffuse tilted irradiance exhibited respective values of +13 to +18 %, 26 to 30 %, and 0.867 to 0.881. These results are comparable to the widely used All-Weather Model of Perez et al.</div
Damage evolution in thermal barrier coating under thermal gradient mechanical fatigue loading
No full textInternational audienc
Generation of Electric Vehicle Charging Profiles for Grid Studies in Distribution Systems
No full textInternational audienceElectrification of transport is essential to decarbonization. However, electric vehicles (EVs) integration is a challenge for power grids, as EV charging requires a high power supply compared to other appliances. This paper proposes a modelling strategy to study the impact of EVs on distribution grids, based on open data, to have realistic case studies. The methodology relies on the generation of travel events from mobility survey data. These events are then converted into charging power profiles by defining charging strategies. The power profiles are then connected to the grid nodes to assess the impact on the grid. The results show that EV charging increases the power peak on distribution grids, leading to expensive grid investments. To limit the power peak, reducing the charging frequency, by using larger batteries or by reducing the distance travelled, is effective. Indeed, larger batteries are charged less frequently, limiting the simultaneous charging of vehicles. Another solution to limit the power demand during peak hours is that distribution system operators define preferential charging time slots during low-demand hours
Comportement et caractérisation de la formation de la croûte dans l'autoclave lors de la lixiviation du minerai de latérite de nickel dans des conditions HPAL
No full textInternational audienceScale formation on reactor walls remains a major operational challenge in high-pressure acid leaching (HPAL) of nickel laterites, leading to reduced heat transfer efficiency, increased maintenance, and process downtime. This study investigates the influence of slurry solid content and acid-to-ore (A/O) ratio on autoclave scale formation during laterite leaching. Experiments performed under typical HPAL conditions (265 °C and ∼50 bar) with laterite ore examined how these parameters affect metal extraction, scale quantity, and mineralogical composition. Scale deposits were quantified and analysed to determine their composition and to evaluate the precipitation tendency of potential scale-forming minerals through solution speciation and supersaturation behaviour during HPAL leaching. The results show that increasing slurry solids significantly promotes scale formation, producing denser and more strongly adherent deposits, while higher acid dosage further enhances precipitation of sulphate-bearing phases. Mineralogical analyses indicate that the scales are primarily composed of hematite, hydronium alunite, and magnesium sulphates, whose formation is driven by solution supersaturation during leaching. High solids content also promotes incorporation of valuable metals into the scale matrix, leading to reduced nickel and cobalt recovery. In contrast, operation at moderate solids content and near-stoichiometric acid addition limits scale accumulation while maintaining high metal extraction. These findings highlight the coupling between HPAL operating conditions, solution chemistry, and fouling behaviour, and suggest an operational window for reducing scale formation without the use of chemical additives that may interfere with downstream processing
Plant diversity estimates of Mediterranean islands differ among biodiversity databases
No full textInternational audienceLarge‐scale biodiversity databases encompass three main types of data for plants, namely single species point occurrences, co‐occurrences in vegetation plots, and checklists for specific areas. Evidence shows that such data types exhibit specific biases, reporting different species assemblages at local scales. We used the Mediterranean Basin, a global biodiversity hotspot with more than 2200 islands larger than 0.01 km 2 , to compare island vascular plant diversity patterns emerging from occurrence data (Global Biodiversity Information Facility; GBIF), vegetation plots (European Vegetation Archive; EVA), and species checklists (Global Inventory of Flora and Traits; GIFT). We aggregated plant data at the island level and compared geographic coverage, inventory completeness, and taxonomic coverage among these data sources. The combined databases accounted for 8702 species distributed on 790 islands (35.6% of the target islands). Data availability increased from small (26.8%) over medium (75.7%) to large islands (100.0%). Spatial coverage of databases on a 30 × 30 km grid was high for GBIF (52.8%) and EVA (45.4%), and low for GIFT (21.7%). GIFT provided higher native and alien species richness values for most of the islands, whereas GBIF and EVA consistently missed a considerable fraction of the expected species richness. Taking GIFT as reference, GBIF, and to a lesser extent EVA, showed a positive bias towards perennial species and an underrepresentation of annuals. Despite their lower taxonomic coverage, GBIF and EVA data can complement our knowledge on Mediterranean islands' plant diversity, providing data for islands lacking plant inventories. Moreover, GBIF and EVA's large datasets can be used for investigating other levels of ecological organisation and modelling single species (GBIF) or population (EVA) trends over space and time. Finally, our results advocate for a coordinated effort to fill the knowledge gaps through data collection and digitisation, possibly integrating data collected by experts by means of citizen science initiatives