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Sciences : où sont les femmes ?
No full textLe monde de la recherche scientifique souffre de la sous-représentation des femmes, particulièrement forte dans certaines disciplines, qui le prive d’une partie de ses talents à différents niveaux et dans différents corps de métiers de la science et de l’ingénierie.Consciente du rôle qu’elle a à jouer aux côtés des nombreuses institutions, sociétés savantes ou encore associations qui agissent pour corriger ce déséquilibre préjudiciable à toute la société, l’Académie des sciences souhaite ici apporter sa réflexion, ses propositions et recommandations quant à quatre causes bien établies. Sans complaisance ni anachronisme, elle rend également compte de la situation passée et actuelle des femmes parmi ses membres, avant de présenter les actions qu’elle met en place aujourd’hui en son sein pour accompagner la dynamique collective visant la parité du monde scientifique
L'hydrogène aujourd'hui et demain
No full textThe prospects offered by hydrogen as part of the energy transition and the decarbonization of the energy system are major topical issues. Although sources of natural hydrogen have been identified in various parts of the world, it is not possible to estimate at this time the potential of these sources, nor to assess their exploitation capacities without further exploration. Thus, hydrogen is not a primary energy source but should only be considered as an energy carrier. Most of this hydrogen, produced today from fossil resources mainly for industrial usage (including oil refining and ammonia synthesis), will have to be obtained tomorrow from decarbonized processes and used more widely for other industrial applications (notably to reduce the carbon footprint of steel and cement production) and for heavy mobility. Given that hydrogen production must be guided primarily by the need to reduce greenhouse gas emissions, this report aims to define what is meant by "decarbonized" hydrogen, which must take precedence over all carbon-based hydrogen. The aim of this report is to clarify how hydrogen can be produced with minimal emissions of greenhouse gases, consider the significant needs it will generate in terms of electrical energy production1, on this basis identify the most appropriate uses for it in the future and derive estimates of a reasonable level of hydrogen production and consumption.The production of hydrogen by water electrolysis, which appears to be a key element in terms of carbon dioxide emissions (CO2), is really decarbonized if the electricity employed for its production is low carbon (nuclear or renewable), which is far from being the case in Europe or at a worldwide level. For the time being, the European electricity mix is largely carbon-based, and its use to power electrolyzers would lead to CO2 emissions twice as high as those of the conventional methane synthesis process. With its remarkably low carbon electricity mix, France has a major asset in playing a pioneering role in the deployment of low carbon hydrogen, provided that the new electricity production capacities required are rapidly available and themselves low carbon.The present analysis underlines the importance of the industrial competitiveness challenge of developing electrolyzers with the highest possible performance, in the service of national energy sovereignty. Efforts in this field deserve to be supported by scientific and technological research into the energy efficiency of electrolyzers and fuel cells, issues relating to reducing the environmental footprint of these components, improving their stability and lifespan, and, more generally, all the elements in the value chain (tanks, new materials, materials and molecules for storing and transporting hydrogen, etc.). The report also highlights the need to guide choices and developments through life-cycle analyses carried out across the entire value chain. The safety issues in using hydrogen are of major importance. New scientific and technological knowledge is essential if one wishes to define safe hydrogen applications. For applications envisaged outside industrial areas, one has to ensure that protocols and regulations remain compatible with their dissemination.Analysis of the future uses of carbon-free hydrogen indicates that, applications should initially be mainly in: (i) the industrial field, essentially to defossilize the industrial processes that emit the largest amounts of greenhouse gases (notably steel and cement production) and to replace grey hydrogen in current industrial uses (synthesis of ammonia and methanol); (ii) the field of heavy transport (sea or air), notably by enabling the synthesis of alternative fuels to replace current fossil fuels
L'hydrogène aujourd'hui et demain.
No full textThe prospects offered by hydrogen as part of the energy transition and the decarbonization of the energy system are major topical issues. Although sources of natural hydrogen have been identified in various parts of the world, it is not possible to estimate at this time the potential of these sources, nor to assess their exploitation capacities without further exploration. Thus, hydrogen is not a primary energy source but should only be considered as an energy carrier. Most of this hydrogen, produced today from fossil resources mainly for industrial usage (including oil refining and ammonia synthesis), will have to be obtained tomorrow from decarbonized processes and used more widely for other industrial applications (notably to reduce the carbon footprint of steel and cement production) and for heavy mobility. Given that hydrogen production must be guided primarily by the need to reduce greenhouse gas emissions, this report aims to define what is meant by "decarbonized" hydrogen, which must take precedence over all carbon-based hydrogen. The aim of this report is to clarify how hydrogen can be produced with minimal emissions of greenhouse gases, consider the significant needs it will generate in terms of electrical energy production1, on this basis identify the most appropriate uses for it in the future and derive estimates of a reasonable level of hydrogen production and consumption.The production of hydrogen by water electrolysis, which appears to be a key element in terms of carbon dioxide emissions (CO2), is really decarbonized if the electricity employed for its production is low carbon (nuclear or renewable), which is far from being the case in Europe or at a worldwide level. For the time being, the European electricity mix is largely carbon-based, and its use to power electrolyzers would lead to CO2 emissions twice as high as those of the conventional methane synthesis process. With its remarkably low carbon electricity mix, France has a major asset in playing a pioneering role in the deployment of low carbon hydrogen, provided that the new electricity production capacities required are rapidly available and themselves low carbon.The present analysis underlines the importance of the industrial competitiveness challenge of developing electrolyzers with the highest possible performance, in the service of national energy sovereignty. Efforts in this field deserve to be supported by scientific and technological research into the energy efficiency of electrolyzers and fuel cells, issues relating to reducing the environmental footprint of these components, improving their stability and lifespan, and, more generally, all the elements in the value chain (tanks, new materials, materials and molecules for storing and transporting hydrogen, etc.). The report also highlights the need to guide choices and developments through life-cycle analyses carried out across the entire value chain. The safety issues in using hydrogen are of major importance. New scientific and technological knowledge is essential if one wishes to define safe hydrogen applications. For applications envisaged outside industrial areas, one has to ensure that protocols and regulations remain compatible with their dissemination.Analysis of the future uses of carbon-free hydrogen indicates that, applications should initially be mainly in: (i) the industrial field, essentially to defossilize the industrial processes that emit the largest amounts of greenhouse gases (notably steel and cement production) and to replace grey hydrogen in current industrial uses (synthesis of ammonia and methanol); (ii) the field of heavy transport (sea or air), notably by enabling the synthesis of alternative fuels to replace current fossil fuels.Les perspectives offertes par l’hydrogène dans le cadre de la transition énergétique et de la décarbonation du système énergétique constituent un sujet d’actualité majeur. Des sources d’hydrogène naturel ont été repérées en divers points du globe. Mais, à l’heure actuelle,il n’est pas possible de donner une estimation du potentiel en énergie primaire de ces sources, ni d’évaluer les capacités d’exploitation correspondantes. Les explorations doivent être poursuivies. L’hydrogène aujourd’hui disponible n’est pas une source d’énergie primaire mais un vecteur énergétique, produit à partir de ressources fossiles pour une utilisation essentiellement industrielle (raffinage du pétrole et synthèse d’ammoniac). Demain, il faudra décarboner cet hydrogène et l’utiliser plus largement pour d’autres applications industrielles (notamment pour diminuer l’empreinte carbone de la production d’acier et du ciment) et pour la mobilité lourde. Étant donné que la production de l’hydrogène doit principalement être guidée par le gain de réduction des émissions de gaz à effet de serre, ce présent rapport vise à définir ce qu’est l’hydrogène dit décarboné, qui doit prévaloir sur tout hydrogène carboné. Il s’agira ainsi de préciser comment il est produit, de mieux identifier quels pourraient être, à l’avenir, ses usages les plus appropriés, et de recommander un niveau raisonnable de consommation d’hydrogène, notamment en prenant en compte les besoins induits en termes de production d’énergie électrique, qui seront considérables . La production d’hydrogène par électrolyse de l’eau, qui apparaît comme un élément clé en termes d’émissions de dioxyde de carbone (CO2), n’est décarbonée que si l’électricité utilisée est effectivement bas carbone (nucléaire ou renouvelable), ce qui est loin d’être le cas en Europe ou dans le monde. Pour le moment, l’électricité au niveau du mix européen est très largement carbonée et son utilisation pour alimenter les électrolyseurs conduirait à des émissions de CO2 deux fois supérieures à celles du procédé de synthèse classique à partir du méthane. Avec un mix électrique remarquablement bas carbone, la France dispose d’un atout majeur pour jouer un rôle pionnier dansle déploiement de l’hydrogène décarboné, à condition que les nouvelles capacités de production électrique nécessaires soient rapidement disponibles et elles-mêmes bas carbone. L’analyse réalisée souligne l’importance de l’enjeu de compétitivité industrielle constitué par la mise au point d’électrolyseurs disposant des meilleures performances possibles, au service d’une souveraineté énergétique nationale. L’effort dans ce domaine mérite d’être soutenu par unerecherche scientifique et technologique sur l’efficacité énergétique des électrolyseurs et des piles à combustible, les questions de réduction de l’empreinte environnementale de ses éléments, l’amélioration de leur stabilité et de leur durée de vie, et, plus généralement, tous les éléments de la chaîne de valeur (réservoirs, nouveaux matériaux, matériaux et molécules de stockage et transport de l’hydrogène, etc.). Le rapport met également en évidence la nécessité de guider les choix et les développements par des analyses de cycles de vie effectuées sur l’ensemble de la chaîne de valeur. Les questions de sécurité soulevées par l’utilisation de l’hydrogène sont majeures. Il est absolument nécessaire de les traiter avec attention, et des connaissances scientifiques et technologiques nouvelles sont indispensables pour définir des applications sûres de l’hydrogène. En particulier, pour les applications envisagées en dehors des espaces industriels, il faudra s’assurer que les protocoles et les règlements restent compatibles avec leur diffusion.L’analyse des usages futurs de l’hydrogène décarboné indique que, dans un premier temps, les applications devraient être principalement faites dans : (i) le domaine industriel, en particulier pour défossiliser les procédés industriels les plus émetteurs de gaz à effet de serre (notamment laproduction d’acier et de ciment) et pour remplacer l’hydrogène gris dans les usages industriels actuels (synthèse de l’ammoniac et du méthanol) ; (ii) le domaine des transports lourds (maritime ou aérien), notamment en permettant la synthèse de carburants alternatifs pour remplacer les combustibles fossiles actuels
Large Satellite Constellations: Challenges and Impact
No full textThe New Space Age (NewSpace) marks the advent of a new era in the use ofspace, characterized by the opening of space to new players, the use of new spacetechnologies, new functionalities for satellites in orbit, and the development of satelliteconstellations, mainly in the fields of communications and Earth observation.These developments are underpinned by first-rate scientific and technological advances,as well as considerable public and private investment, in particular in theUSA, China and, to a lesser extent, Europe. Fleets of small low- and medium-orbitsatellites are replacing or complementing the large geostationary satellites that predominatedin the previous period. Whereas space used to be reserved to a smallnumber of states and major industrial groups, one is now witnessing the emergenceof new space states, new industrial groups such as SpaceX or Amazon, and manystart-ups. One also observes the emergence of companies with launching and satellitemanufacturing capacities, which are also taking on the role of telecommunicationoperators and content producers.The most visible result of the deployment of these new space networks is theability to provide high-speed, low-latency Internet connections to any point on theglobe. Combined with Earth observation capabilities, these new communicationsresources also enable real-time action to be taken in any region, including thosewith no equipment other than terminals. In addition, these space networks areremarkably resilient compared with terrestrial networks. Geostrategic and militaryconsiderations combine with rapidly evolving business models to explain the massiveinvestments currently being made in this domain.However, the lack of international regulation in the field is leading to a race tooccupy orbits and frequencies, which has already had serious consequences for awhole range of scientific activities. These constellations have a potentially negativeimpact on astronomy in the visible and infrared optical domains, as well as on radioastronomy. They also raise a major problem in terms of space congestion, with anincrease in the amounts of satellite debris resulting from launches or collisions betweensatellites, and the possibility of reaching a phase of chain reaction collisions. Inaddition, from an environmental point of view, the consequences of the proliferationof launches and uncontrolled re-entries into the atmosphere are equally worrying.What’s more, the lack of regulation in the field also leads to a loss of sovereignty,since these new satellite communication networks do not comply with any of therules that states impose on terrestrial communication networks operating on theirterritories. A sustainable, global solution must be found to these problems, beforemajor and potentially irreversible damage is inflicted on the planet’s environment,geostrategic balances, democracy, and science.While the Acad´emie des Sciences considers that France and Europe need to stepup their scientific and industrial actions in this field in order to benefit from theremarkable advances of these new networks, and ultimately leverage the benefitsof a resilient and secure communications network, the Acad´emie also recommendsworking in parallel to strengthen regulation of the field with the aim of assuringsustainable access to orbital and frequency resources, as well as protection for negativelyimpacted fields, foremost among which are astronomy and the environment
Is the Earth’s Magnetic Field a Constant? A Legacy of Poisson
No full textInternational audienceIn the report he submitted to the Académie des Sciences, Poisson imagined a set of concentric spheres at the origin of Earth’s magnetic field. It may come as a surprise to many that Poisson as well as Gauss both considered the magnetic field to be constant. We propose in this study to test this surprising assertion for the first time, evoked by Poisson in 1826. First, we present a development of Maxwell’s equations in the framework of a static electric field and a static magnetic field in order to draw the necessary consequences for the Poisson hypothesis. In a second step, we see if the observations can be in agreement with Poisson. To do so, we choose to compare (1) the polar motion drift and the secular variation of Earth’s magnetic field, (2) the seasonal pseudo-cycles of day length together with those of the sea level recorded by different tide gauges around the globe and those of Earth’s magnetic field recorded in different magnetic observatories. We then propose a mechanism, in the spirit of Poisson, to explain the presence of the 11-year cycle in the magnetic field. We test this mechanism with observations, and finally, we study closely the evolution of the g1,0 coefficient of the International Geomagnetic Reference Field (IGRF) over time
Application of spin glass ideas in social sciences, economics and finance
No full textContribution to the edited volume "Spin Glass Theory & Far Beyond - Replica Symmetry Breaking after 40 Years", World Scientific, 2023International audienceClassical economics has developed an arsenal of methods, based on the idea of representative agents, to come up with precise numbers for next year's GDP, inflation and exchange rates, among (many) other things. Few, however, will disagree with the fact that the economy is a complex system, with a large number of strongly heterogeneous, interacting units of different types (firms, banks, households, public institutions) and different sizes. Now, the main issue in economics is precisely the emergent organization, cooperation and coordination of such a motley crowd of micro-units. Treating them as a unique "representative" firm or household clearly risks throwing the baby with the bathwater. As we have learnt from statistical physics, understanding and characterizing such emergent properties can be difficult. Because of feedback loops of different signs, heterogeneities and non-linearities, the macro-properties are often hard to anticipate. In particular, these situations generically lead to a very large number of possible equilibria, or even the lack thereof.Spin-glasses and other disordered systems give a concrete example of such difficulties. In order to tackle these complex situations, new theoretical and numerical tools have been invented in the last 50 years, including of course the replica method and replica symmetry breaking, and the cavity method, both static and dynamic. In this chapter we review the application of such ideas and methods in economics and social sciences. Of particular interest are the proliferation (and fragility) of equilibria, the analogue of satisfiability phase transitions in games and random economies, and condensation (or concentration) effects in opinion, wealth, etc
François, Henri et Paul Ellenberger, trois frères d'exception
No full textInternational audienceFrançois Ellenberger, geologist, Henri Ellenberger, psychiatrist, Paul Ellenberger, pastor, all three born in South Africa into a Protestant missionary family, had exceptional lives in their own way. A few biographical details help us to better understand their destinies.François Ellenberger, géologue, Henri Ellenberger, psychiatre, Paul Ellenberger, pasteur, tous trois nés en Afrique du Sud au sein d'une famille de missionnaires protestants, eurent chacun à leur manière des vies exceptionnelles. Quelques données biographiques permettent de mieux connaître leurs destinées
Innovations d’édition ouverte : partenariat Académie des sciences – centre Mersenne
No full textNational audiencePrésentation du partenariat entre l'Académie des Sciences et le centre Mersenne autour des deux projets Traductions et MarginaliAS faite lors de la session de l'après-midi dédiée aux innovations éditoriales rendues possibles par la science ouverte
The eXtreme Mesh deformation approach (X-MESH) for the Stefan phase change model
No full textInternational audienceThe eXtreme Mesh deformation approach (X-MESH) is a new paradigm to follow sharp interfaces without remeshing and without changing the mesh topology. Even though the mesh does not change its topology, it can follow interfaces that do change their topology (nucleation, coalescence, splitting) and that possibly travel over long distances. To make this possible, the key X-MESH idea is to allow elements to reach zero measure. This permits interface relaying between nodes as well as interface annihilation and seeding in a time continuous manner. The paper targets the Stefan phase change model in which the interface (front) is at a given temperature. Several examples demonstrate the capability of the approach
Unlearnable Games and "Satisficing'' Decisions: A Simple Model for a Complex World
No full textInternational audienceAs a schematic model of the complexity economic agents are confronted with, we introduce the ``SK-game'', a discrete time binary choice model inspired from mean-field spin-glasses. We show that even in a completely static environment, agents are unable to learn collectively-optimal strategies. This is either because the learning process gets trapped in a sub-optimal fixed point, or because learning never converges and leads to a never ending evolution of agents intentions. Contrarily to the hope that learning might save the standard ``rational expectation'' framework in economics, we argue that complex situations are generically unlearnable and agents must do with satisficing solutions, as argued long ago by Herbert Simon (Simon 1955). Only a centralized, omniscient agent endowed with enormous computing power could qualify to determine the optimal strategy of all agents. Using a mix of analytical arguments and numerical simulations, we find that (i) long memory of past rewards is beneficial to learning whereas over-reaction to recent past is detrimental and leads to cycles or chaos; (ii) increased competition destabilizes fixed points and leads first to chaos and, in the high competition limit, to quasi-cycles; (iii) some amount of randomness in the learning process, perhaps paradoxically, allows the system to reach better collective decisions; (iv) non-stationary, ``aging'' behaviour spontaneously emerge in a large swath of parameter space of our complex but static world. On the positive side, we find that the learning process allows cooperative systems to coordinate around satisficing solutions with rather high (but markedly sub-optimal) average reward. However, hyper-sensitivity to the game parameters makes it impossible to predict ex ante who will be better or worse off in our stylized economy