Portail HAL du Collège de France
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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
Programme ERC Consolidator Grant ChrIs-cross Entangled Christianities in Jerusalem and the Middle East: A cross-cultural bottom-up approach (12th-16th centuries). Grant Agreement n°101124193
No full textProgramme ERC Consolidator Grant 2024-2029 PI Camille Rouxpetel CNRS/IFAOChrIs-cross will produce the first comprehensive study of Christianities in Jerusalem and the Middle East from the 12th to the 16th c., in the face of shifting rulership structures, first Frankish, then Islamic, and religious affiliations. It will envisage them from a bottom-up, practice oriented and connected perspective, on the assumption that inter-Christian and Christian-Muslim relations were more conductive to fluidity than to boundary-setting. A multidisciplinary and multilingual team will study a forgotten and so far, inaccessible archive—the archives of the Christian Patriarchates in Jerusalem—and develop an overarching database including interactive maps and editing texts. Open-access metadata will be in English and Arabic. In so doing, it will resituate the history of Christianities within the Islamicate world by reassessing the concept of “minority”, historicise communities’ construction by comparing conquest-induced reconfigurations, with and without a change in religious dominance, and spatialise these processes by examining their interplay, with Jerusalem as a specific urban space in tension with the wider regional area.The project has three main objectives: it aims to address the currently compartmentalised academic study of the diverse Frankish- and Islamic-ruled societies, by shifting the focus of inquiry from the internal history of separate groups to their areas of contact; to empower local Christian communities by documenting their deep-rootedness in these complex societies, and to contribute new knowledge of the diversity of the Islamic-ruled world as a historical reality by expanding digital inclusiveness. By achieving its various objectives, ChrIs-cross will realize what arguably is an unprecedented exploration. It will thus have a major scholarly and social impact, both for the many Christian communities now facing extinction, and for people in the so-called West, which faces an inflation in essentialist discourses on religion
Couvrir ou se protéger ? La catastrophe de Fukushima vue par les journalistes sur le terrain
No full textInternational audienc
Kakemono Rouleau à suspendre lors de la réunion du thé : selon les "Notes sur le thé" Chafu.
No full textInternational audienceIl existe une continuité traditionnelle des liens entre la voit du thé et l'art en général. Le rouleau à suspendre kakémono est l'une des principales décorations de la pièce du thé au moment des réunions du thé chakai. Le sujet présenté par la calligraphie ou par la peinture est tiré des oeuvres littéraire ou religieuses, -surtout bouddhique-, chinoises ainsi que japonaises . Au japon, les réunion du thé sont considérés comme une pratique essentiel de la vie culturelle. pendant cette réunion, l'hôte offre le thé vert en poudre macha à ses invités. Elle se déroule dans un cadre destiné à ce but. Quoique la sobriété soit un principe à respecter, l'hôte prépare avec soin la pièce. D'où l'importance du kakémono suspendu au mur comme indice d'une place d'honneur.Nous examinons dans cette étude un ouvrage intitulé " Notes sur le thé " Chafu, écrit par un auteur anonyme, vers la fin du XVIe siècle. Il s'agit d'une sorte de manuel illustré , spécialisé sur la voit du thé .C'est un manuscrit de 18 volumes dont le quatrième est consacré à kakémono.Vis-à vis de celui-si se trouvent les approches différentes et variées des amateurs du thé. Elles montrent les deux aspects de cet objet: esthétique comme oeuvre d'art ; indication philosophique, ou même religieux
Two thousand years of garden urbanism in the Upper Amazon
No full textA dense system of pre-Hispanic urban centers has been found in the Upano Valley of Amazonian Ecuador, in the eastern foothills of the Andes. Fieldwork and light detection and ranging (LIDAR) analysis have revealed an anthropized landscape with clusters of monumental platforms, plazas, and streets following a specific pattern intertwined with extensive agricultural drainages and terraces as well as wide straight roads running over great distances. Archaeological excavations date the occupation from around 500 BCE to between 300 and 600 CE. The most notable landscape feature is the complex road system extending over tens of kilometers, connecting the different urban centers, thus creating a regional-scale network. Such extensive early development in the Upper Amazon is comparable to similar Maya urban systems recently highlighted in Mexico and Guatemala
Well-founded recursion done right
No full textInternational audienceSeveral Coq libraries and extensions support the definition of non-structural recursive functions using well-founded orderings for termination. After pointing out some drawbacks of these existing approaches, we advocate going back to the basics and defining recursive functions by explicit structural induction on a proof of accessibility of the principal recursive argument
Recontextualizing the Bronze Object: The Performative Power of Decoration and the Ritual Experience
No full textInternational audienc
Cold molecules in H I 21 cm absorbers across redshifts ∼0.1–4
No full textInternational audienceAbsorption lines at high-redshift in front of quasars are quite rare in the millimeter (mm) domain. Only five associated and five intervening systems have been reported in the literature. Nevertheless, these discoveries provide very useful information that is complementary to emission lines, allowing, for instance, to distinguish between inflows and outflows. These lines are also good candidates for studying the variations of the fundamental constants of physics. Here we report the findings of our search for CO and other molecules in emission and absorption in front of a sample of 30 targets, comprising 16 associated and 14 intervening H I 21 cm absorbers. The observations were made with the IRAM-30 m telescope simultaneously at 3 mm and 2 mm, exploring several lines of the CO ladder and HCO+, depending on the redshift. We detected eight targets in emission, of which five are new. The derived molecular gas masses range from 109 to 7 × 1011 M⊙ and the highest redshift detection (z = 3.387) corresponds to a relatively average-metallicity damped Lyman-α absorber for this redshift. We also report four new detections in absorption. Two of the associated CO absorption line detections at high-redshift (z = 1.211 and 1.275) result from high-spatial-resolution follow-up observations with NOEMA. The disparity between the mm molecular and H I 21 cm absorption lines for these and another intervening system detected in HNC at z = 1.275 is attributable to radio and mm sight lines tracing different media. We compare the atomic and molecular column densities of 14 known high-redshift (z > 0.1) molecular absorption line systems. The associated H I absorption lines are broad and exhibit multiple components, and the molecular absorption generally corresponds to the broader and weaker 21 cm absorption component. This indicates two distinct phases: one near galaxy centers with a larger CO-to-H I abundance ratio, and another with lower molecular abundance in the outer regions of the galaxy. In comparison, intervening absorption profiles correspond primarily to H I-dominated gas structure in galaxy outskirts, except for gas at low impact parameters in gravitationally lensed systems. The comparison of interferometric and single-dish observations presented here shows that the detection of absorption requires sufficient spatial resolution to overcome the dilution by emission and will be an important criterion for mm follow-up of 21 cm absorbers from ongoing large-scale surveys
The International Law of Regional Organizations: Mapping the Issues
No full textInternational audienc
