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The Chair Allocation problem
No full textInternational audienceWe introduce the Chair Allocation problem, a three-sided matching market where researchers apply for a chair in a university, and universities request chairs (composed of a university and a research topic) to a central authority. We propose a new algorithm, the Chair Nested Deferred Acceptance algorithm, and show that it is fair, undominated by other fair assignments, and strategy-proof for researchers
Bubbles and Crashes with Partially Sophisticated Investors
No full textNational audienceWe analyze bubbles and crashes in a model in which some investors are partially sophisticated. While the expectations of such investors are endogenously determined in equilibrium, these are based on a coarse understanding of the market dynamics. We highlight how such investors may endogenously switch from euphoria to panic and how this may lead to equilibrium bubbles and crashes even in a purely speculative market in which information is complete and it is commonly understood that the bubble cannot grow forever. We also show how this setting can match stylized empirical facts, and we investigate whether bubbles may last longer when the share of fully rational traders increases
Relever les défis environnementaux et sociaux liés à la mobilité dans les zones rurales: De nouvelles solutions pour de nouveaux acteurs ?
No full textInternational audienceWhile rural mobilities are facing socio, economical and environmental challenges in France and in Europe, the French government passes a law to cover its whole territory of authorities responsible for organising mobilities so local authorities could address some responses to those diderent challenges. This reorganisation of mobility competences in France is leading to the arrival of new actors in those territories, namely some inter-municipal authorities. These actors are part of a complex and multiscalar system influenced by directives from the top and needs from the bottom. At the same time, the „repertoire of available solutions” appears to be evolving in rural areas. Indeed, rural territories are seeing the emergence of amenities previously absent around the road network: small multimodal hubs. What mobility projects can be observed now in rural areas? To what extent can we talk about changes in the repertoire of available solutions? Are those projects really new? In more general terms: what dynamics exist in the repertoire of available solutions for stakeholders in rural mobility? To answer, a literature review is completed by a multi-criteria analysis of the discourses of local authorities working on mobility in low-density areas. A sample of discourses is selected with the purpose of collecting data before and after stakeholders restructuring. We argue in this article that this law reinforces the local role of inter-municipal authorithies in local action through mobility. Nevertheless, those areas which where not lacking actors and inter-muncicipal authorithies should now find its place in a pre-existent system. Besides, the state keeps an important role behind the scene and pulls the strings of those local public policies. Our analysis will first allow us to understand the introduction of inter-municipal authorities as new players in the local mobility stakeholder system. Second, this work will give us a greater comprehension of restructuring and its impacts on public action at the local scale. Finally, we’ll see the state's role remaining in local policies.Alors que les mobilités rurales sont confrontées à des défis sociaux, économiques et environnementaux en France et en Europe, le gouvernement français adopte une loi visant à couvrir l'ensemble de son territoire par des autorités chargées d'organiser les mobilités. L'objectif est que les collectivités locales puissent apporter des réponses concrètes à ces problèmes mis à l'agenda local. Cette réorganisation des compétences en matière de mobilité en France conduit à l'arrivée de nouveaux acteurs dans le système des mobilités, notamment les communautés de communes. Ces acteurs font partie d'un système complexe et multiscalaire influencé par les directives venant d'en haut et les besoins venant d'en bas mais aussi des initiatives locales et des dépendances nationales. En même temps, le « répertoire des solutions disponibles » semble évoluer dans les zones rurales. En effet, les territoires ruraux voient apparaître des équipements qui n'existaient pas auparavant autour du réseau routier : de petits pôles multimodaux. Quels projets de mobilité peut-on observer aujourd'hui dans les zones rurales ? Dans quelle mesure peut-on parler d'évolution du répertoire des solutions disponibles ? Ces projets sont-ils vraiment nouveaux ? Plus généralement, quelles sont les dynamiques qui existent dans le répertoire des solutions disponibles pour les acteurs de la mobilité rurale ? Pour répondre à ces questions, une revue de la littérature est complétée par une analyse multicritères des discours des autorités locales travaillant sur la mobilité dans les zones à faible densité. Un échantillon de discours est sélectionné dans le but de collecter des données avant et après la restructuration des acteurs. Nous soutenons dans cet article que cette loi renforce le rôle local des autorités intercommunales dans l'action locale en matière de mobilité. Néanmoins, les zones qui ne manquaient pas d'acteurs et d'autorités intercommunales doivent désormais trouver leur place dans un système préexistant. En outre, l'État conserve un rôle important en coulisses et tire les ficelles de ces politiques publiques locales. Notre analyse nous permettra tout d'abord de comprendre l'introduction des autorités intercommunales en tant que nouveaux acteurs dans le système local des acteurs de la mobilité. Ensuite, ce travail nous permettra de mieux comprendre la restructuration et ses impacts sur l'action publique à l'échelle locale. Enfin, nous verrons que le rôle de l'État reste présent dans les politiques locales.Miközben a vidéki mobilitás társadalmi, gazdasági és környezeti kihívásokkal szembesül Franciaországban és Európában, a francia kormány olyan törvényt fogadott el, amely valamennyi mobilitás szervezéséért felelős hatóságok tevékenységére kiterjed. Mindezt annak érdekében, hogy a helyi hatóságok megfelelő válaszokat adhassanak a mobilitással kapcsolatos kihívásokra. A mobilitási hatáskörök újraszervezése Franciaországban új szereplők, nevezetesen néhány önkormányzatközi hatóság megjelenéséhez vezet ezeken a területeken. Ezek a szereplők egy összetett és többszintű rendszer részét képezik, amelyet felülről jövő irányelvek és alulról jövő igények befolyásolnak. Ugyanakkor úgy tűnik, hogy a vidéki területeken a „rendelkezésre álló megoldások repertoárja” fejlődik. A vidéki területeken ugyanis egyre inkább megjelennek a korábban a közúthálózat körül nem létező létesítmények: kis multimodális csomópontok. Milyen mobilitási projektek figyelhetők meg most a vidéki területeken? Milyen mértékben beszélhetünk az elérhető megoldások repertoárjának változásáról? Valóban újak ezek a projektek? Általánosabban fogalmazva: milyen dinamikák figyelhetők meg a vidéki mobilitásban érdekelt szereplők számára elérhető megoldások repertoárjában? A kérdés megválaszolásához jelen tanulmány a szakirodalom áttekintését az alacsony sűrűségű területeken a mobilitással foglalkozó helyi hatóságok diskurzusainak több szempontú elemzésével egészíti ki. A diskurzusok egy mintáját azzal a céllal választottuk ki, hogy adatokat gyűjtsünk az érdekelt felek átszervezése előtt és után. A tanulmány amellett érvel, hogy a törvény megerősíti a településközi hatóságok helyi szerepét a mobilitáson keresztül történő helyi cselekvésben. Mindazonáltal azoknak a területeknek, ahol nem hiányoznak a szereplők és a településközi hatóságok, most egy már létező rendszerben kell megtalálniuk a helyüket. Emellett az állam továbbra is fontos szerepet játszik a színfalak mögött, és mozgatja a helyi közpolitikák szálait. Az elemzés először is lehetővé teszi, hogy megértsük a településközi hatóságok mint a helyi mobilitási érdekképviseleti rendszer új szereplőinek megjelenését, az átszervezés részleteit és hatásait a helyi szintű közintézkedésekre. A tanulmány kiemeli az állam helyi politikákban továbbra is fennálló meghatározó szerepét
How key features of early development shape deep convective systems
No full textInternational audienceDeep Convective Systems (DCSs) reaching scales of 100-1000 km play a pivotal role as the primary precipitation source in the tropics. Those systems can have large cloud shields, and thus not only affect severe precipitation patterns but also play a crucial part in modulating the tropical radiation budget. Understanding the complex factors that control how these systems grow and how they will behave in a warming climate remain fundamental challenges. Research efforts have been directed, on one hand, towards understanding the environmental control on these systems, and on the other hand, towards exploring the internal potential of systems to develop and self-aggregate in idealized simulations. However, we still lack understanding on the relative role of the environment and internal feedbacks on DCS mature size and why. The novel high-resolution global SAM simulation from the DYAMOND project, combined with the TOOCAN Lagrangian tracking of DCSs and machine learning tools, offers an unprecedented opportunity to explore this question. We find that a system's growth rate during the first 2 h of development predicts its final size with a Pearson correlation coefficient of 0.65. Beyond this period, growth rate emerges as the strongest predictor. However, in the early stages, additional factors-such as ice water path heterogeneity, migration distance, interactions with neighboring systems, and deep shear-play a more significant role. Our study quantitatively assesses the relative influence of internal versus external factors on the mature cloud shield size. Our results show that system-intrinsic properties exert a stronger influence than environmental conditions, suggesting that the initial environment does not strictly constrain final system size, particularly for larger systems where internal dynamics dominate
Géopolitiques des infrastructures. Temporalités, imaginaires, matérialités
No full textInternational audienceLe tournant spatial de l’histoire, c’est-à-dire l’attention renouvelée à l’espace comme concept par lequel écrire l’histoire, rencontre la question des temporalités des dynamiques spatiales qui travaille la recherche urbaine. La ville comme l’espace tient du temps comprimé (Gaston Bachelard) et cette concrétion du temps invite à saisir la profondeur de ses strates et de ses mémoires pour comprendre les sociétés contemporaines. Les questions actuelles sont scrutées dans leur historicité tandis que le passé est rouvert dans sa compréhension de l’espace comme palimpseste des représentations que les sociétés ont projetées au fil du temps. Au croisement de ces itinéraires de recherche, l’infrastructure figure un objet-frontière (Susan Leigh Star) que l’on peut entendre selon une triple acception : matérielle, sociale, imaginaire. Dans leur course pour consolider les empires, étendre les influences, conquérir les espaces, les réalisations infrastructurelles manifestent des géopolitiques dont nous nous attacherons, à travers des projets transfrontaliers ou mondiaux, à saisir des clés de lecture. Qu’il s’agisse de la mer, de l’air ou du globe, les infrastructures qui entendent maîtriser ou transcender les frontières terrestres, façonnent des matérialités dont les traces politiques et vernaculaires affectent sur la durée les environnements, au risque de leur habitabilité
Integrated Study of Martian Dust: Detection of Local Dust Storms, Estimation of Vertical Distribution, and Surface Pressure Analysis Using OMEGA Observations
No full textInternational audienceUnderstanding the Martian dust cycle is essential for clarifying the atmospheric circulation and meteorological phenomena. Unlike Earth, Mars has a thin atmosphere primarily composed of CO2, where atmospheric dust plays a dominant role in regulating the energy balance and driving atmospheric motion. Among various dust-related phenomena, Local Dust Storms (LDS), defined as storms that span less than 1.6 × 106 km2 or last fewer than three Martian days (Cantor et al., 2001), are particularly important for studying localized dust lifting and its potential connection to regional or global dust events (Martin and Zurek, 1993; Cantor et al., 2001; Hinson and Wang, 2010; Wang and Richardson, 2015). However, due to their limited spatial extent and short lifetimes, LDS have remained challenging to detect and characterize comprehensively.In this study, we developed a method for identifying LDS using data from the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) imaging spectrometer onboard Mars Express (Bibring et al., 2004). Specifically, we used the strong CO₂ absorption band at 2.77 µm to retrieve dust optical depth. This band is sensitive to altitudes around 20–30 km and offers the critical advantage of being largely insensitive to surface reflectance properties. Applying this retrieval method to data from Martian Years (MY) 27 through 29, we detected 146 LDS events. Our statistical analysis revealed clear seasonal and diurnal patterns. LDS occurrences were most frequent during southern summer (Ls = 270°–360°), consistent with past findings that identify this season as conducive to dust activity (e.g., Smith, 2004; Montabone et al., 2015). However, we also observed an anomalously high frequency of LDS during northern summer in MY27 (Ls = 130°–150°), a period not typically associated with elevated dust activity. Furthermore, a noticeable increase in LDS activity was detected just before the onset of the Global Dust Storm (GDS) in MY28. Diurnally, LDS were most often observed near noon, implying that storm initiation may begin in the morning hours. Their spatial distribution varied significantly with season. During Ls = 0°–180°, LDS tended to be confined to specific regions such as Chryse Planitia and southern Acidalia. In contrast, during Ls = 180°–360°, LDS appeared more widely across mid-latitudes, with a notable absence in the northern high-latitude region (above 40°N). These results offer new insight into the role of LDS in the broader Martian dust cycle, particularly their potential influence on triggering regional or global events
‘Warehouse Policy Index’. A framework for the analysis of relationships between warehousing indicators and local policy. International urban Freight
No full textInternational audienc
Differentiable constitutive modeling in a machine learning-compatible framework
No full textInternational audienceThe field of computational mechanics is increasingly converging with machine learning, particularly in the area of constitutive modeling. Constitutive models, which are inherently data-driven, share formal similarities with neural network layers. Beyond learning constitutive models from data, there is significant potential in developing implementations of traditional constitutive models that are compatible with machine learning frameworks. Automatic differentiation (AD) has transformed machine learning by enabling complex computations to be composed from simpler operations while automating the calculation of derivatives. In this talk, we will explore the application of AD to constitutive modeling, with a special emphasis on two key areas: efficient tangent operator computation and material parameter sensitivity. First, AD can be used to automatically derive consistent tangent operators, which are essential for the efficient integration of constitutive models in large-scale simulations. We will discuss various strategies for obtaining these operators, including applying AD directly to the unrolled algorithm or using the more efficient method of implicit differentiation. Second, AD can also be leveraged to compute sensitivities of material parameters, enabling more efficient model calibration. Finally, we will delve into how AD and implicit differentiation can be extended to handle more complex constitutive models, such as multi-surface plasticity, which require advanced nonlinear solvers
Infrastructures as urban solutions? Critical perspectives on transformative socio-technical change
No full textInternational audienceThis introduction to the special issue critically explores the pervasive logic of solutionism in infrastructure-led urban development and planning -a logic marked not only by the strong belief in the transformative power of infrastructures but also by a tendency to reframe how urban problems are prioritised and governed. Although infrastructures are increasingly positioned as key tools for urban decarbonisation, circularity, resilience or smartness, this introduction critically questions dominant solutionist approaches to complex urban problems. Drawing on recent urban scholarship, it explores infrastructures as ongoing, relational, and contested sociotechnical processes, rethinking transformative urban change as a situated, incremental, and ambiguous process shaped by local politics, materiality, and everyday repair and patching. Contributions to this issue highlight how infrastructural initiatives, even when partial or unrealised, can challenge dominant interests and practices and open space for alternative urban futures. Rather than repudiating infrastructural solutions, therefore, we suggest that the special issue foregrounds infrastructures' contested potential to enable progressive, transformative change. We pull out four transversal themes from the papers, around rethinking governance, repoliticising infrastructure development, embracing incremental and context-sensitive approaches and expanding conceptions of justice