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Fifty years of research on resource-constrained project scheduling explored from different perspectives
No full textInternational audienceThe resource-constrained project scheduling problem is one of the most investigated problems in the project scheduling literature, and has a rich history. This article provides a perspective on this challenging scheduling problem, without having the ambition to provide a complete overview. Instead, the article does aim to summarize a number of reasons why this problem has been so intensely investigated from different perspectives.It will be shown that this scheduling problem has many faces, and therefore deserves a lot of research time from a computational and theoretical point of view as well as from a practical point of view. An overview of possible extensions to other problems and a detailed overview of the used (both heuristic and exact) solution methods will be given. In addition, the data used will be discussed and interesting avenues for further research will be mentioned throughout the different sections.</div
Swarm dynamics for global optimisation on finite sets
No full textInternational audienceConsider the global optimisation of a function defined on a finite set endowed with an irreducible and reversible Markov generator.By integration, we extend to the set of probability distributions on and we penalise it with a time-dependent generalised entropy functional.Endowing with a Maas' Wasserstein-type Riemannian structure, enables us to consider an associated time-inhomogeneous gradient descent algorithm.There are several ways to interpret this \cP(V)-valued dynamical system as the time-marginal laws of a time-inhomogeneous non-linear Markov process taking values in , each of them allowing for interacting particle approximations.This procedure extends to the discrete framework the continuous state space swarm algorithm approach of Bolte, Miclo and Villeneuve \cite{Bolte}, but here we go further by considering more general generalised entropy functionals for which functional inequalities can be proven.Thus in the full generality of the above finite framework, we give conditions on the underlying time dependence ensuring the convergence of the algorithm toward laws supported by the set of global minima of .Numerical simulations illustrate that one has to be careful about the choice of the time-inhomogeneous non-linear Markov process interpretation
Embrittlement after high-temperature exposure to air of a near-γ TiAl alloy
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Simulation numérique directe de la combustion d'une particule d'aluminium isolée sous divers environnements
No full textThe authors acknowledge the French Defense Agency for funding L.P.’s scholarship and CALMIP supercomputing centre in Toulouse (France) for providing us computational resources.International audienceThis study presents a comprehensive numerical investigation of single aluminum particle combustion under varying convective oxidizing flow conditions, using Direct Numerical Simulations. A three-dimensional, boundary-layer-resolved model is developed to capture the complex interplay of gas-phase chemistry, surface reactions, and multiphase transport phenomena. The model incorporates aluminum evaporation, aluminum suboxide reactions at the particle's surface, and alumina formation both on the surface and in the gas phase. It also introduces an original scheme to account for the dissolution of alumina into the molten particle, based on parameters derived from molecular dynamics simulations. The model was validated against experimental burn time data. The unsteady combustion of a 125 μm-aluminum particle in various flowing O2/N2 conditions is then investigated in terms of standoff flame distance, gas-phase temperature and chemistry, particle temperature and surface chemistry. The results demonstrate that gas-phase reactions remain the dominant source of heat release, although surface reactions, particularly under highly oxygenated environments, play a significant role in modulating local combustion kinetics. The formation of liquid alumina at the particle's surface, its partial dissolution into the molten aluminum, and the limited surface coverage even at high O2 concentrations highlight the importance of coupling surface chemistry with thermal transport. While this mathematical model successfully reproduces the main macroscopic characteristics such as flame temperature, burn time-radius relationship, gas-phase composition, and fluxes, some discrepancies appear near the particle surface, i.e. at the microscale. These deviations can be attributed to radiative heat transfer effects which are not considered or to an incomplete understanding of surface reactions
Low-latency online estimation of human upper-limb pose and kinematics from a single 360 camera
No full textInternational audienceWe present a fully online framework for streaminghuman upper-limb kinematics estimation from a single 360camera. Incoming frames are processed sequentially throughvertical-boundary-aware tracking, pseudo-perspective rendering,and Neural Localizer Fields to estimate a sparse set of 3Danatomical landmarks in real time. These landmarks are mappedto an OpenSim-compatible biomechanical model, with jointangles computed on the fly via an online inverse kinematicssolver. The system achieves end-to-end latencies as low as22.9 ms on a high-performance setup. Evaluated in a single-participant scenario involving an initial T-pose calibration andrepeated object displacement toward the camera, it demonstratesrobust performance under moderate self-occlusion and sphericaldistortion. While tested in a constrained setting, its modular, real-time design makes it a promising candidate for human–robotinteraction and other motion analysis applications, enablingminimal, markerless, and anatomically interpretable upper-limbtracking from omnidirectional vision
Influence of tow-preg composition on microstructure and mechanical behaviour of oxide/oxide CMCs
No full textInternational audienceCeramic matrix composites could soon be used in an ever-increasing number of high-temperature applications. This study explores the potential of a new tow-preg process for the manufacturing of oxide-based ceramic matrix composites. With these techniques, the choice of impregnation slurries is crucial for the quality of the materials. This study focuses on the development of several grades of alumina matrices CMCs. The impact of the slurry composition on the CMCs microstructure and mechanical behaviour is evaluated. The benefits of a minimum amount of boehmite, a gel-forming agent which is a precursor of alumina, on inter-ply cohesion have been demonstrated
Diffusive gradient in thin film for ultra-trace methylmercury measurements in the coastal and open sea
No full textInternational audienceMonomethylmercury (MMHg) is a potent neurotoxin causing neurodevelopmental delays and cardiovascular and immunological issues. Human exposure primarily occurs through seafood consumption due to MMHg bioaccumulation and biomagnification from seawater into marine organisms. Determining MMHg in seawater at ultratrace concentrations poses logistical and analytical challenges. Diffusive Gradient in Thin-film (DGT) samplers represent a promising solution, which captures time-averaged concentrations by preconcentrating in situ MMHg over a defined exposure time. DGT manufactured with 3-mercaptopropyl-functionalized silica (3MFS) in agarose and polyacrylamide gels were tested and compared for the determination of MMHg present in open ocean and coastal waters. Different elution methods using acidic thiourea were tested to reach precise, accurate and quantitative elution of MMHg from the binding gel. We found that polyacrylamide-3MFS binding gels display a higher elution efficiency (94 ± 3 %), precision and better handling compared to agarose-3MFS gels (41 ± 6 %). A unique mooring line installed in the South Western Tropical Pacific Ocean, provided monthly DGT-MMHg concentrations over a year showing potential seasonal differences in MMHg concentrations ranging between 18 and 106 fM. DGT were also deployed in shallow Peruvian coastal waters, exhibiting higher MMHg concentrations (170 ± 97, n = 26) with typical benthopelagic gradients. DGT-MMHg concentrations were in good agreement with discrete water samples analyzed by reference methods using isotope dilution. DGTs offer complementary advantages over oceanographic cruises, notably in situ preconcentration, low blanks, minimal logistical requirements and cost-effectiveness. DGTs represent a valuable tool for studying the marine MMHg cycle for evaluating the implementation of the Minamata Convention
Role of the amine monomer in polymer/metal interaction: application to the DGEBA-DETA-TA6V system
No full textInternational audienc
Gas permeability of concrete under compressive creep during drying–wetting cycles
No full textInternational audienceGas permeability is used as an indicator of concrete durability due to its strong correlation with material porosity. However, permeability is typically measured on unloaded specimens or under loading conditions that are not representative of actual structural applications. This experimental investigation aims to enhance the understanding of the impact of mechanical stress on the gas permeability and, by extension, concrete durability, under conditions approaching those of structural applications. For this purpose, a novel experimental setup was designed to measure radial gas flow through hollow concrete specimens under compressive creep loading. The setup was validated by comparing the measured gas permeabilities to those obtained using a Cembureau constant-head permeameter. The impact of two levels of compressive creep on the gas permeability of initially saturated concrete specimens was investigated over a 150-day drying period at 20 °C and 50 % relative humidity. Subsequently, the specimens were immersed in water until constant mass was reached and then dried a second time under identical hygro-mechanical conditions, in order to distinguish the effect of water saturation from that of hygro-mechanical cracking. The results show that sustained loading to 30 % of the concrete compressive strength has no significant impact on gas flow. However, loading concrete to 60 % of its compressive strength leads to a tenfold increase in measured gas permeability, compared to unloaded specimens. Monitoring the mass of the specimens revealed that the studied stress levels do not significantly impact drying kinetics. Therefore, the observed increase in gas permeability is attributed to hygro-mechanical damage
Insight into cooling requirements for thermophotovoltaic devices
No full textInternational audiencePerformance of thermophotovoltaic conversion devices depends on the operating temperature of the cell, and thus on how heat generated in the cell is dissipated. The present research examines the cooling requirements that allow the cell to operate at a specified temperature, based on the parameters influencing electrical power generation. A detailed balance approach and a simple thermal model involving an effective heat transfer coefficient are used. Key parameters, such as emitter temperature, view factor, in-band transmission and out-of-band transmission functions, and external radiative efficiency, are systematically varied to evaluate their influence on pairwise efficiency and power density, and on the required effective heat transfer coefficient to ensure that the cell operates at selected temperatures. Although thermophotovoltaic cells are typically presumed to function at close to ambient, our findings indicate that maintaining this operating temperature necessitates a cooling system with a substantially high effective heat transfer coefficient (∼ 10^3 -10^4 Wm -2 K -1 ). The cooling challenge grows when the cell bandgap diminishes, due to the interplay of rising power density and decreasing pairwise efficiency. The cooling requirements increase with the temperature of the emitter and the view factor. Nevertheless, they can be mitigated by reducing both in-band and out-of-band transmission functions. They are underestimated, and the bandgap optimizing pairwise efficiency or power density is inadequately predicted when the cell is assumed to operate in the radiative limit. These insights into cooling requirements imply that they should be considered from the initial stages of thermophotovoltaic device design