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Bimodal Depth-First Search for Scalable GAC for AllDifferent
No full textInternational audienceWe propose a version of DFS designed for Constraint Programming, called bimodal DFS, that scales to both sparse and dense graphs. It runs in O(n + ~m) time, where ~m is the sum, for each vertex v, of the minimum between the numbers of successors and non-successors of v. Integrating it into Régin’s GAC algorithm for the AllDifferent constraint results in faster performance as the problem size increases, outperforming a GPU-accelerated version. In the vast majority of our tests, GAC now performs similarly to BC in terms of speed, but is able to solve more problems
Influence of Alclad layers on mechanical properties of friction stir welded 2024-T3 aluminium alloy thin sheets
No full textInternational audienceAlclad sheets are used in aeronautics to resist corrosion. This paper presents the investigation of the effect of the Alclad on the mechanical properties of thin friction stir welds of 2024-T3 aluminium alloy (3 mm and 1 mm). The friction stir welding process is carried out on sheet metal without any surface preparation. Tensile tests, micro-hardness measurements, optical microscopy and scanning electron microscopy observations are performed to identify the behaviour of the friction stir welds at local and macroscopic scales. The evolution of micro-hardness through the welds associated with literature results reliably describe precipitates in each area of the welds. Tensile test results combined with micrographic observations reveal that the Alclad layer is introduced by the pin into the alloy in a pointed shape. The weld fractures are clearly located in Alclad insertion zones. Independently of the state of the precipitates due to the friction stir welding parameters, Alclad insertions are responsible for the decrease in ductility of the welds
A digital twin-based decision support system for managing an operating room
No full textInternational audienceThe objective of our research is to optimize the operating schedule in order to help hospitals develop a performant, resilient, and robust OR organization. We assess performance using key metrics such as staff workload (overtime), patient satisfaction (waiting times), and operational efficiency (OR utilization). We define a robust organization as one that can maintain performance levels despite inherent variability (i.e. surgery duration variability), while a resilient one can withstand significant disruptions (i.e. non-elective case arrival) without compromising performance.We investigate the following general research question: “How can we promote and maintain the performance of a surgical suite’s organization under uncertainties?”. To answer this, we analyze the operational schedule across three key stages: before, during, and after execution—corresponding to its provisional, ongoing, and completed states. This abstract focuses on the prospective and retrospective analyses, as they represent the most advanced features of the tool we developed. Specifically, we propose: (1) a methodology for the prospective analysis of the provisional schedule, and (2) a methodology for the retrospective analysis of the completed schedule. To implement these analyses on real-world OR schedules, we develop a digital twin-based decision support system (DT-DSS). We illustrate our work on a study case inspired from our partner, the Hôpital Privé de La Baie (GIE Vivalto Santé, France
Experimental VLE Data and Thermodynamic Modeling of the Ethane + Hexafluoropropylene Oxide (HFPO) System
No full textInternational audienceThis study presents experimental vapor-liquid equilibrium (VLE) data for two fluorinated-based systems. Experimental VLE data for the R116 + propane system at 292.22 and 296.93 K were initially undertaken to validate the experimental setup and procedure. Subsequently, VLE data for the ethane + HFPO system were measured at five isotherms (283.39, 290.32, 298.67, 308.42, and 318.45 K), encompassing three below and two above the critical temperature of ethane, the more volatile component. The measurements were conducted using a static-analytical setup, with equilibrium-phase sampling performed via a capillary sampler and composition analysis carried out using gas chromatography. The uncertainties in the measurements were estimated to be within 0.07 K for temperature, 11 kPa for pressure, and 0.009 and 0.008 mole fractions for the liquid- and vapor-phase compositions, respectively. Thermodynamic modeling of VLE data for the two systems was undertaken using the homogeneous "Phi-Phi" approach, employing the Peng-Robinson equation of state with the Mathias-Copeman alpha function. A combination of the Wong-Sandler mixing rule with the nonrandom two-liquid activity coefficient model was utilized to account for fluid mixture behavior. This modeling approach yielded satisfactory results, as shown by AAD xy and bias xy values of less than 3%
Heptafluorobutyronitrile (C<sub>4</sub>F<sub>7</sub>N), Hydrolysis, a Density Functional Theory (DFT) Investigation
No full textInternational audienceHeptafluorobutyronitrile (C4F7N) has received much consideration as an effective substitute to sulfur hexafluoride (SF6) in the electrical industrial sector over the last decade. However, liability is the key to emerging technology, and the thermoelectric aging of the insulation gases may produce unavoidable consequences that raise concerns for the operator and human safety. Recently, numerous pieces of literature mentioned the production of crystals in the form of amide and dimer (ligand) generated from the aging of C4F7N with few water molecules. It was found that the hydrolysis of fluoronitrile chemical reactions initial with the production of amide (C4H2F7NO) and following, with the addition of C4F7N molecules, accelerates the reaction to produce dimer (C8H2F14N2O) and further is the possibility to generate various range of byproducts. Thermodynamically, C4F7NH2O + C4F7N → C8H2F14N2O is the favourable chemical reaction with a 23 kcal/mol energy barrier that generates a dimer molecule. Furthermore, in presence of paramagnetic ion (typically Cu (II)), a Cooper based complex (as purple crystals) may appear. Gibbs free energy at elevated temperature indicates the driving force is needed to accelerate the reaction except C8H2F14N2O + H2O → C12H2F21N3O, whose energy values throughout remain consistent. Theoretical calculations reveal the water acts as a strong catalytic that can abruptly reduce the energy barrier of the initial reaction from 59 to 10 kcal mol-1 and open the pathway to generate other byproducts
Liquid-Liquid Equilibria for Aromatic Extraction from Fuel Oil Using Deep Eutectic Solvents: Evaluating Hansen Solubility Parameters for Phase Equilibrium Prediction
No full textInternational audienceThe separation of aromatic hydrocarbons from fuel oil is a crucial process in the petrochemical industry and is driven by economic and environmental considerations. Deep eutectic solvents (DESs) have gained attention as sustainable alternatives to conventional solvents because of their tunable properties, low toxicity, and biodegradability. This study explores the calculation of liquid-liquid equilibria (LLE) for aromatic extraction from fuel oil using choline chloride-based DESs. The focus is on the evaluation of Hansen solubility parameters (HSPs) for phase equilibrium prediction. HSPs, which account for dispersive, polar, and hydrogen bonding interactions, were utilized to assess the solubility of aromatic and aliphatic hydrocarbons in DESs using HSPiP software®. Two DES systems were investigated, a binary system (ChCl:U 1:2) and a ternary system (ChCl:U:EG 1:2:1), using quantum-based DFT calculations to elucidate the molecular interactions governing their behavior. Tie-line data were obtained using Simulis thermodynamic software® for the ternary mixtures (Toluene + Heptane + ChCl:U or ChCl:U:EG and Benzene + Hexane + ChCl:U or ChCl:U:EG) at T = 303.15 and 313.15 K under atmospheric pressure from experimental data. The phase equilibrium predictions from the Hansen-based model were correlated with the NRTL and COSMO-SAC models and compared with experimental data in the literature, as shown in Figure 1. These findings demonstrate the effectiveness of HSPs as a predictive tool for optimizing DES selection and process conditions, providing insights into the selectivity and efficiency of aromatic extraction. This study highlighted the potential of DESs as green solvents for sustainable separation processes in the petrochemical industry
Evolution of surface layers during the sliding wear of wheel and rail steel under very high load
No full textWOM 2025 - 25th International Conference on Wear of Materials, Sitges, Espagne, 13-17 avril 2025International audienceThe near-surface regions of the wheel-rail contact experience complex thermomechanical phenomena. In sharp curves, the sliding contact between the wheel flange and rail gauge corner is associated with elevated stresses and catastrophic wear. Understanding the evolution of tribologically transformed layers (TTLs) beneath the contact is key to explaining wear behavior. However, replicating the extreme conditions of this contact in laboratory tests remains a challenge. Conventional sliding wear testing setups, such as pin-on-disc, often fail to produce TTLs as thick as those found in serviced wheels due to limited normal loads. To achieve thicker TTLs, sliding wear tests were carried out under an 8 kN normal load (604 MPa) using a ring-on-disc configuration (disc: AAR Class D pearlitic wheel steel, 353 ± 7 HBW; ring: high-strength rail steel, 378 ± 3 HBW). The tests were carried out over increasing sliding distances, at 0.1 and 0.2 m/s. The evolution of the TTLs was observed through optical and scanning electron microscopy, and their hardnesses and thicknesses were evaluated. Average TTL thicknesses in the order of 100 μm were observed across tests, even at the smaller sliding distances. Significant hardening was observed in TTLs, with the presence of a hardness gradient towards the surface. The friction coefficient revolved around 0.3 in the steady state, and the wear data showed a large dispersion. At 0.1 m/s, seizure occurred at 132 m of sliding, marked by heavily oxidized wear tracks, severe wear, the thickest TTLs and a sudden increase in friction and temperature. These results indicate that high-load ring-on-disc tests can more accurately reproduce surface layers found in serviced wheels and rails
Optimisation models for the design of multiple self-consumption loops in semi-rural areas
No full textCollective electricity self-consumption gains increasing interest in a context where localised consumption of energy is a lever of sustainable development. While easing energy distribution networks, collective self-consumption requires complementary prosumers' profiles. Before determining the proper energy exchanges happening between these prosumers, one must ensure their compatibility in the context of collective self-consumption. Motivated by real use cases from a solar power producer, this article proposes network flow-based linear models to solve both the design aspect of the problem and the attribution of distribution flows between the involved prosumers. Two main models are proposed, handling (i) single collective self-consumption loop creation and (ii) multiple loop creation. One of the objectives of this work is to provide models that can be applied at a strategic level which implies their extension to large time scale and large spatial scale. To do so, associated Benders and Dantzig-Wolfe decompositions are proposed to ensure model scalability along temporal and spatial dimensions. The proposed models are tested on realistic use cases to assess their performances
Biochar-based catalytic upgrading of plastic waste into liquid fuels towards sustainability
No full textInternational audienceAs the demand for single-use plastics rises, sustainable plastic management has become a pressing concern. Transforming plastic waste into value-added fuels is a promising waste-to-energy strategy that benefits environmental and energy security. In recent years, biochar-based catalysts (BBCs) have attracted increasing attention for their cost-effectiveness, well-developed pore structure, and effective surface functional groups in catalytic conversions of plastic waste into fuels. Many researchers have documented the successful utilization of biochar catalysts for efficient plastic waste valorization. However, a systematic review of biochar-based catalytic valorization of plastic waste into useful fuels is still missing. We assessed practical applications of biochar-based catalytic pyrolysis and advanced oxidation technologies, evaluating their performance from life-cycle and techno-economic perspectives. Machine learning was also introduced to design high-performance BBCs and optimize the plastic upcycling system. This eco-friendly innovation supports several UN SDGs and provides valuable insights for the UN Treaty on Plastic Pollution
Ontological framework for horizon scanning of business continuity of essential services
No full textInternational audienceKeeping up essential operations in the face of more complicated disruptions from crises that impact essential services such as healthcare, public transit, and government operations is a major challenge for business continuity (BC) research. Taking up this issue in the midst of increased academic discussion emphasizes how urgent it is to create a thorough reference on BC principles. This paper uses a recently developed BC ontological framework to give a comprehensive review of the literature focused on BC research. The report summarizes a comprehensive investigation of important BC aspects, including technological aspects and the urgent difficulties in maintaining BC sustainability. Through the integration of many viewpoints, this study advances a unified awareness of BC dynamics, promoting a general understanding that is necessary for risk management which is both efficient and lasting for organizations