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« Médias, transmission du savoir et engagement politique chez Carlo L. Ragghianti »
No full textInternational audienc
The unexpected dewetting during growth of silicene flakes with dendritic pyramids
No full textInternational audienceSilicene growth on graphene has emerged as a novel method for fabricating silicon-based van der Waals heterostructures. However, the silicene flakes produced in this manner are the result of an exotic growth mode characterized by metastable nanostructures with varying degrees of deviation from equilibrium, with large two-dimensional flakes surrounded by a rim that coexist with small 3D islands, and, at large deposits, thick dendritic pyramids separated by a denuded zone. In order to rationalize and control this growth, a model is derived that revisits the dewetting thermodynamics and considers generally ignored adsorption and step-edge energies. The model is investigated using kinetic Monte-Carlo simulations and mean-field rate equations, and implemented by close inspection of microscopy images. This model perfectly reproduces the experimental outcomes, unveiling an anomalous growth mode, and provides guidelines on experimental conditions for high-quality silicene growth.</div
Workload Shifting Techniques: From Digital Inebriation to Sobriety
No full textInternational audienceComputing demand in cloud environments has grown exponentially over the past decade, due to the increase in cloud workload related to new services such as artificial intelligence, autonomous vehicles, augmented reality, etc. As a result, the ICT sector has seen its carbon emissions increase. It is possible to adopt less energy-intensive strategies and consume electricity produced by renewable energy to limit the increase in carbon emissions. In this paper, we present a review of the workload-shifting techniques available for sustainable workload deployment, providing an innovative framework that can be used to analyze energy-aware approaches that apply any type of shifting technique. We identified three main concepts: compute a workload at a different time, deploy a workload and/or its data in a different location, or use alternative processing to provide a good-enough option for a workload. A definition and some examples are given for each shifting concept, and then we explore the opportunities and challenges of combining different shifting techniques
50 Years of Giese Reaction - a Personal View
No full textInternational audience50 years ago, a synthetic method was discovered, in which alkyl radical precursors, alkenes and hydrogen donors selectively yield 1:1:1-addition products in cyclic chain reactions. This paved the way for many variants of three-component syntheses, which became standard procedures for C,C-bond formation. For successful syntheses the different chain carrying radicals have to follow reactivity and selectivity rules. This requires knowledge of the substituent influence on substrate-, regio- and stereoselectivities of intermolecular radical reactions. These rules were experimentally elucidated, and the synthetic method was coined “Giese reaction”. Twenty years after its discovery in the chemical laboratory, biologists observed that microorganisms use the same synthetic strategy, which triggered our studies on biological cells. Although chemical rules in laboratory vessels and biological cells are the same, their different set-ups lead to very different features. Syntheses in homogeneous solution of a laboratory vessel is driven by kinetic effects. In contrast, most reactions in biological cells occur at protein/water interfaces, where thermodynamic interactions with enzymatic amino acids establish close contact between the educts. In addition, biochemical processes often start with radicals that don’t react with educts but generate the productive radicals at the interface by long-distane electron transfer
Front-surface cooling of infrared thermophotovoltaic cells
No full textInternational audienceThis paper proposes a front-surface cooling method for thermophotovoltaic (TPV) cells utilizing microfluidic channels for efficient heat dissipation. Unlike conventional back-surface cooling, front-surface cooling minimizes thermal resistance by directly cooling the top surface of the cell. The microfluidic channel layer also functions as an antireflection layer through the gradual change in the refractive index. The proposed cooling method was evaluated using a thermo-fluid analysis, considering factors such as the emitter temperature, cell reflectance, thermal resistance, and fluid optical properties. We examined liquids with ideal absorption characteristics and actual liquids whose absorption coefficients were measured. The results showed that front-surface cooling significantly outperformed back-surface cooling in terms of the net power density. This method is particularly advantageous for high emitter temperatures or in cases where the thermal resistance between the cell and backsurface liquid is high. Moreover, this study highlights the potential application of the cooling method in bifacial TPV cells, which can generate electricity from thermal radiation incident on both sides. Bifacial cells offer higher power generation per unit area but face cooling challenges. The proposed cooling technique addresses these challenges, paving the way for innovative TPV system configurations and improved performance
Optimal energy management in multi energy microgrid with combined heat and power system and demand side response integration
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Environmental impacts of supercritical fluids processes: A critical review of life cycle assessment studies
No full textInternational audienceThe application of supercritical fluids (SCF) in industrial and research processes has gained attention in recent years for their unique properties and potential environmental benefits. Frequently described as "green solvents", SCF can reduce of replace the use of conventional organic solvents. However, broader adoption requires a clear understanding of their full life cycle environmental impacts. Life cycle assessment (LCA) has been widely used to evaluate the environmental performance of SCF technologies.This study critically reviews 70 LCA studies of SCF processes across various applications through the four phases of LCA: goal and scope definition, life cycle inventory, life cycle impact assessment, and interpretation to identify methodological gaps and trends in energy use, solvent consumption, and environmental impacts. Despite variability in modelling approaches, process-level trends emerge: for gasification, global warming results range from -0.2 to 5 kg CO2eq.kg; for extraction from 0.2 to 153 kg CO2eq.kg depending on feed and scale. Contribution analyses highlight that energy is the main hotspot, especially in supercritical water gasification and transesterification, even though yielding higher-quality output and lower solvent consumption. Benchmarking results are mixed: 27 studies reporting lower environmental impacts for SCF processes, while 18 studies report higher impacts, especially in extraction applications. Sensitivity analyses highlight the influence of electricity mix, feed concentration, and solvent recycling on LCA outcomes. This review provides targeted recommendations to enhance consistency and accuracy in future LCA studies. By synthesizing current findings, it supports the development of more sustainable SCF technologies from early stage to support their broader adoption
L'idée de « Sciences « humaines. » »
No full textInternational audienceSi les sciences humaines posent un certain nombre de problèmes conceptuels, épistémologiques, institutionnels, méthodologiques, normatifs, typologiques, sémantiques, elles posent également de fortes interrogations scientifiques quant à leurs présupposés, leurs histoires, leurs fonctions et la nature des connaissances et des savoirs disciplinaires et interdisciplinaires qu'elles peuvent recouvrir. A leur décharge, les sciences dites « humaines » et les discours scientifiques comme théories et pratiques intellectuelles posent également une multiplicité d’interrogations fondamentales parmi les suivantes : qu’est-ce qui caractérise foncièrement le concept de « pensées scientifiques » ? A quels degrés de certitude, la connaissance, les savoirs et les champs disciplinaires peuvent-ils accéder étant donné les moyens dont nous disposons ? Quelle(s) sorte(s) de vérité(s) proposent-ils ? A partir de quelles caractéristiques et selon quels critères conférons-nous le qualificatif de « science(s) » et d’épithète « humaines » à un genre de la connaissance prétendument relatif à la sphère et aux dimension humaines ? C’est pourquoi, par-delà nos conceptions peu ou prou univoque ou plurivoque de l’idée de science(s) humaine(s), en définitive, le propos de notre communication cherchera fondamentalement à répondre aux questions suivantes : qu'est-ce qu’une « Science(s) dite « humaine(s) » prétend faire en termes de connaissances et quels types de savoirs produit-elle ? Quels sont les modes possibles d’être des choses et des affaires humaines en termes disciplinaires et scientifiques? Dans quelle mesure une science humaine peut-elle ou non enrichir l’ontologie des sciences dites « non ou autre(s) qu’humaine(s) », à l’aune des théories, pratiques, discours et récits expérientiels dont témoigne irréfragablement le caractère humain de toute activité scientifique ? Autrement dit, en quels sens l’idée de « science(s) humaine(s) » peut-elle être conceptualisée, définit et comprise dans ses dimensions de convergence, de divergence et de complémentarité avec ce qui, supposément, ne se définirait pas en termes de discipline comme une « science « humaine » »
Hydrodynamics of a gas-liquid microreactor designed for the oxidation kinetics of organic compounds
No full textInternational audienceLiquid phase oxidation reactions are widely studied and optimized for industrial processes of interest such as the oxidation of cyclohexane. The slow oxidation of hydrocarbons, which takes place throughout their chain of use, is the cause of fuel deterioration known as fuel ageing. In recent years, the use of microfluidic tools for the investigation of such processes is expanding with the development of the technologies. Microfluidics enables the use of explosive conditions in a safer way than traditional processes and these tools can be adapted for the kinetic study of the oxidation of ground fuels and jet fuels. Their kinetics of oxidation are slow, and their study requires long residence times, which are not usually reached in the microfluidic field. The PEEK-ACHU rig, a microfluidic device with a heated silicon/glass microfluidic reactor designed for long residence times (from 16 min up to 230 min) and high pressure (up to 40 bar), was developed for the study of slow oxidation reactions of organic compounds. This work presents the design of the reactor and proposes a hydrodynamic study of the gas-liquid Taylor flow implemented in this tool to enable the study of oxidation reactions of fuels. A good understanding of the different diphasic flow regimes as a function of gas bubble generation was obtained for conditions in the explosive range. A correlation was found between the density and viscosity of a fuel and the length of gas bubbles and liquid slugs. The thickness of the residual liquid film at the wall and the reaction regime were characterized and demonstrate that the design of our microreactor enables the kinetic study of organic compounds oxidation, without oxygen mass transfer limitations, at high temperature and high pressure, for very long residence times