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Traffic prediction by combining macroscopic models and Gaussian processes
No full textInternational audienceWe propose a physics informed statistical framework for traffic travel time prediction. On one side, the discrepancy of the considered mathematical model is represented by a Gaussian process. On the other side, the traffic simulator is fed with boundary data predicted by a Gaussian process, forced to satisfy the mathematical equations at virtual points, resulting in a multi-objective optimization problem. This combined approach has the merit to address the shortcomings of the purely model-driven or data-driven approaches, while leveraging their respective advantages. Indeed, models are based on physical laws, but cannot capture all the complexity of real phenomena. On the other hand, pure statistical outputs can violate basic characteristic dynamics. We validate our approach on both synthetic and real world data, showing that it delivers more reliable results compared to other methods.“This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible.
Share the ride: The determinants of long-distance carpooling pricing strategies in France
No full textInternational audienceThis paper investigates the pricing strategies used in long-distance carpooling in France. We investigate how several factors affect carpooling prices using a comprehensive dataset of BlaBlaCar trips combined with sociodemographic and intermodal competition data. The analysis identifies two distinct pricing patterns within the platform: one characterized by standardized and consistent pricing, and another marked by more flexible, market-responsive price setting. By focusing on price per minute, we examine how trip characteristics, competitive conditions, and demand heterogeneity affect these pricing behaviors. The results show that variables such as the number of stopovers, trip length, airport or cross-border connections, and the presence of alternative transport modes influence pricing, but with contrasting effects across the two patterns. The standardized approach tends to reflect cost-sharing principles and reinforces network effects, while the more flexible approach adapts dynamically to local competition and demand
Organic geochemical investigations of an MIS 5 fire in the Palaeolithic deposits of Ormesson (Seine-et-Marne, France): Anthropic or natural?
No full textInternational audienceDespite the central role of fire in Pleistocene and Palaeolithic lifeways, the relationship among hominins, fire, and their environment remains unclear. Ancient combustion residues hold a wealth of molecular data that may help to resolve some of these questions, yet standardised guidelines for reconstructing past fire traces are notably lacking. In this study, we examine extensive combustion residues overlying Middle Palaeolithic deposits from the open-air site of Ormesson (France). To determine whether the combustion residues are of natural or human origin, multiproxy approaches including anthracology, lipid biomarker, and benzene polycarboxylic acid (BPCA) analyses are applied. These techniques are used to characterise organic matter and pyrogenic carbon compositions in the deposits, providing insights into surrounding vegetation, palaeoenvironmental shifts, and the production parameters involved in the formation of the char assemblage. Lipid biomarker evidence suggests that the pre-fire local environment featured abundant coniferous vegetation (e.g., Pinaceae taxa), which is supported by anthracological evidence for a predominance of Pinus cf. sylvestris/nigra complemented by Betula sp. taxa. The post-fire environment saw a contraction of coniferous vegetation, concurrent with an expansion of deciduous taxa, grasses and herbaceous material. The combustion event, which resulted in 67 % of the charcoal assemblage exhibiting vitrification, produced PyC contents of up to 362 g/kg OC in soil samples and 443 g/kg OC in charcoal samples, with aromatic condensation values of up to 34 %. BPCA-derived predictions of heat treatment temperatures yielded values of approximately 300–400 °C for charcoal samples and 400–550 °C for soil samples in the burned layer, constituting the first instance in which quantitative temperature estimations are obtained from BPCA results. Based on the integrated evidence, we accept the null hypothesis that the studied combustion residues are natural in origin. However, the similarity of archaeometric and geochemical signatures from natural and human-controlled fires underscores the need for interdisciplinary, multiproxy efforts to improve the identification of past fire regimes
Seeing yew for the forest: a call to action for improving conservation and restoration of the European yew (Taxus baccata L.)
No full textInternational audienceThe European yew (Taxus baccata L.) is a long-lived conifer of ecological, cultural, and historical importance across Eurasia. Despite its remarkable resilience, wide distribution, and symbolic importance, the species has experienced a long-term decline due to a complex interplay of climatic fluctuations, megafaunal extinctions, human exploitation, and insufficient regeneration. Recent studies in palaeoecology, archaeology, dendroecology, and conservation have revealed a species with greater ecological plasticity and a broader historical distribution than previously assumed. However, many fundamental questions remain unresolved, particularly regarding its biogeographical history, population dynamics, recruitment processes, and the drivers of its decline.This review stems from prior investigations of yew in the French Pyrenees and, more broadly, across Europe. These efforts led to a transdisciplinary seminar and opened a collaboration uniting >30 researchers across Eurasia. By synthesizing a wide array of data and perspectives, the article highlights key knowledge gaps and outlines emerging research priorities. These are organized thematically—past, present, and future—and include 25 questions on the species' ecological niche, life-history strategies, human interactions, genetic resilience, and conservation under global change. The article advocates for a shift towards integrative and long-term conservation strategies that embrace the historical legacies of yew populations, the general ecology of the species along with local ecological context dependence, and the urgency of future threats. By identifying pressing research needs, this review seeks to lay the foundation for new collaborative initiatives and to support evidence-based conservation of this emblematic yet understudied species
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
Neighbor selection strategies in the wild for CDN/V2V WebRTC live streaming: Can we learn what a good neighbor is?
No full textInternational audienceA hybrid CDN/Viewer-to-Viewer (V2V) architecture is an attractive solution for HTTP (HLS) and MPEG-DASH-based live streaming providers. It combines a traditional CDN with a V2V overlay for exchanging video fragments, reducing the CDN costs while maintaining the quality of experience. This work explores machine learning models to address the key challenge of neighbor selection. Our goal is to predict the connection quality between two arbitrary viewers using features such as locality, access providers, operating systems, past CDN, and V2V throughput. The proposed solutions are validated using an A/B testing approach on our production system and demonstrate a significant improvement in key system metrics compared to the traditional locality-based methods. We observe 17% higher V2V throughput, 26% lower delay, 37% fewer lost chunks, 39% fewer rebuffering, and 20% fewer quality switches.</div
De Métal Hurlant à Mœbius : Jean Giraud et l’Italie dans une conversation graphique transalpine (1975–1987)
No full textInternational audienceFrom Métal Hurlant to Moebius: Jean Giraud and Italy in a Transalpine Graphic Conversation (1975–1987). Jean Giraud, also known by his pseudonym Moebius, stands as one of the most influential figures in twentieth-century comics. From the 1970s to the present day, his artistic vision and narrative innovations have left an indelible mark on the medium, not only in Europe but also in North America and Asia—particularly Japan. Yet it is in Italy that he found fertile ground to deepen his aesthetic exploration, reimagine his artistic practice, and give form to his most dreamlike landscapes. The connections between Moebius, the French magazine Métal Hurlant, and the Italian comics scene chart an original cultural geography—one shaped by inspiration, adaptation, and imaginative exploration. (1) A Franco-Italian Graphic Revolution. In 1975, Giraud co-founded Métal Hurlant alongside Philippe Druillet and Jean-Pierre Dionnet, under the auspices of Les Humanoïdes Associés. Far from a conventional publication, it functioned as an experimental laboratory and a radical platform, breaking with the traditions of the Franco-Belgian school. Through a bold interplay of graphic excess and non-linear narrative, Moebius introduced a universe devoid of moral didacticism, populated by metaphysical wanderers, desert worlds, cosmic odysseys, and fluid, minimalist lines. His drawings, suspended in space and silence, his rarefied language, and his poetic pacing all reflected a personal quest, both spiritual and artistic. Soon, Métal Hurlant crossed French borders to take root in Italy. From 1977 onwards, it was published in translation by L’Eternauta and later by Métal Hurlant Italia under Edizioni Nuova Frontiera. These Italian editions disseminated the works of Moebius and his French contemporaries to a readership attuned to cultural change. Italy, then undergoing a transformation of artistic and moral codes, particularly in cinema and the underground comics scene, offered a resonant terrain for such radical aesthetics. (2) Moebius and Italy: A Shared Artistic Dialogue. Moebius’s impact on Italian comic artists is both direct and profound. Renowned figures such as Guido Buzzelli—who published work in Métal Hurlant—Milo Manara, Sergio Toppi, Andrea Pazienza, and Tanino Liberatore (creator of RanXerox) all recognised in him a liberating force, allowing them to break free from conventional narratives and editorial constraints. His work was quickly championed by major Italian publishers such as Mondadori, Rizzoli, and Nuova Frontiera. Even beyond publishing, his influence spread to design: Elio Fiorucci, a major figure in Italian fashion, drew heavily on the Métal Hurlant aesthetic in his visual experiments. Italian readers discovered a radically different kind of comic in Arzach, Le Garage Hermétique, and L’Incal (co-authored with Jodorowsky)—hybrid works at the crossroads of contemporary art, science fiction, philosophy, and avant-garde cinema. These albums elevated the comic strip to a form of total art. (3) Italy in the Worlds of Moebius This relationship was by no means unidirectional. Italy—land of the Renaissance and the Baroque, birthplace of Fellini’s cinema (Fellini was a friend of Giraud), of opera, Futurism, and industrial design—offered a reservoir of imagery and thought that nourished Moebius’s own universe. In numerous interviews, the artist cited the influence of Italian masters, both classical and modern, from the metaphysical visions of De Chirico to the poetic realism of Pasolini. The ruins of Rome, the statuary of antiquity, and the frescoed walls of Renaissance palaces informed the dreamscapes and architectural compositions of his imaginary worlds. His visit to Venice left a lasting impression, inspiring ethereal visions of floating illusions and mineral labyrinths—motifs clearly visible in The World of Edena and in panels from 40 Days in the Desert B. His reflective journey through Italian culture echoes the paths of aristocratic travellers undertaking the Grand Tour, with Naples in particular acting as a locus of introspection and artistic reverie. (4) A Poetic and Graphic Bridge. In conclusion, the relationship between Moebius and Italy was not one of mere admiration or artistic exchange, but rather of deep cultural interfacing. Moebius served as a vector for new forms of storytelling in Italian comics, while Italy provided an aesthetic legacy that allowed French bande dessinée to be reimagined as a total artwork. This transalpine conversation, at once poetic and graphic, continues to resonate today—as evidenced by the recent exhibitions dedicated to Moebius in Venice, Naples, and Pordenone, all celebrating this enduring and vital dialogue. The work of Jean Giraud transcends borders and genres, drawing shared pathways toward imagination, time, and the lyricism of landscapes.De Métal Hurlant à Mœbius : Jean Giraud et l’Italie dans une conversation graphique transalpine (1975–1987). Jean Giraud, alias Moebius, représente par excellence la figure majeure de la bande dessinée du XXe siècle de par son influence et sa résonnance à l’échelle mondiale des années 1970 à nos jours. Il modifie pour toujours par son esthétisme et sa capacité à renouveler l’art de la narration la BD européenne et bien au-delà en Amérique et en Asie (Japon). Mais c’est en Italie qu’il découvre et trouve un terreau fertile au renouvellement de ses pratiques, de ses rêves et de sa capacité à travailler les paysages oniriques. D’ailleurs, les liens entre Moebius, la revue Métal Hurlant et la scène italienne de la BD amorcent une géographie culturelle singulière, entre inspiration, adaptation et exploration. (1) Une révolution graphique partagée France - Italie s’observe. En 1975, Giraud cofonde le magazine Métal Hurlant, publié par Les Humanoïdes Associés avec entre autres Druillet et Dionnet. Laboratoire expérimental, force de proposition jamais connue auparavant, rupture et démesure, graphisme et narration viennent très souvent (mais pas totalement) en rupture avec l’école franco-belge. Moebius y pourfend un imaginaire sans concession entre mondes désertiques, espace et aventure SF, collaboration cinématographique et caractères métaphysiques, dans des récits ni linéaires ni vertueux. Son dessin épuré, tout en apesanteur, jouant avec le vide, voire une fluidité des mots ou mouvements sont une réponse à sa quête personnelle. Or, cet artiste et sa revue - maison d’édition Humanoïdes Associés - dépassent les frontières françaises pour « toucher terre » en Italie avec Métal Hurlant diffusé dès 1977 par L’Eternauta, puis par Métal Hurlant Italia Edizioni Nuova Frontiera, qui traduisent et diffusent les œuvres de Moebius et de ses amis. Ces publications obtiennent un écho immédiat dans une Italie en pleine mutation culturelle, marquée par la libéralisation des mœurs et l’émergence de nouveaux modes d’expression artistique, notamment dans le cinéma de science-fiction et la BD underground. (2) Les liens forts entre Moebius et l’Italie : un dialogue artistique partagé. L’influence de Moebius sur les auteurs italiens est considérable. Des figures comme Guido Buzzelli (publiant une histoire dans Métal) Milo Manara, Sergio Toppi, Andrea Pazienza ou encore Tanino Liberatore (le créateur de RanXerox), reconnaissent en lui un modèle qui leur permet d’écrire différemment des histoires trop classiques et sans interdits éditoriaux – étatiques (ou presque). Des éditeurs comme Mondadori, Rizzoli et Edizioni Nuova Frontiera publient ses œuvres dès la fin des années 1970 (sans oublier le designer comme Elio Fiorucci s’inspirant fortement de Métal hurlant pour ces créations…). À travers des éditions de qualité d’Arzach, Le Garage hermétique ou L’Incal (coécrit avec Jodorowsky), le lecteur italien découvre une BD radicalement différente, à la croisée de l’art contemporain, du cinéma, de la philosophie et de la SF. (3) L’Italie dans Les Mondes de Moebius. C’est d’une réciprocité des perspectives dont il est question, L’Italie - pays de la Renaissance et du baroque, berceau du cinéma de Fellini (ami de Jean Giraud), de l’opéra, du futurisme et du design industriel - nourrit l’imaginaire de Moebius. Nombreux sont les interviews de l’artiste qui soulignent l’influence des maîtres italiens (de la peinture moderne comme contemporaine De Chirico, cinéma de Pasolini…). D’ailleurs, des ruines romaines, l’art statuaire antique ou les fresques inspirent grandement l’auteur pour ces décors - paysages. Son voyage à Venise le marque profondément, inspirant des atmosphères étranges, entre illusions lacustres et dédales minéraux, visibles dans Le Monde d’Edena (les grands panoramas et fresques murales) ou dans certaines planches de 40 jours dans le désert B. Quant à sa démarche réflexive, elle trouve un écho dans l’héritage humaniste italien avec des détours comme vers la ville de Naples à la manière des aristocrates visitant l’Italie lors de leur Grand Tour. (4) Une passerelle poétique et graphique. En conclusion, il ne s’agit pas simplement d’initiation ou d’enthousiasme réciproque, mais bien d’une interface culturelle que nous relaterons. Moebius a fait office de « véhicule » pour le compte des artistes italiens, l’Italie de « patrimoine esthétique » pour une nouvelle forme de la BD comme art total profitable pour le français. La conversation entre Moebius et l’Italie est d’une richesse exceptionnelle comme en témoigne les dernières expositions internationales à son sujet à Venise, Naples et Pordenone facteurs et héritages de la vitalité de ce lien transalpin. L’œuvre de Jean Giraud, au-delà des frontières et des styles continue de tracer des chemins d’imagination partagés à la recherche du temps et de la poésie des paysages
Tensor Decompositions for Signal Processing: Theory, Advances, and Applications
No full textInternational audienceIn the era of big data, rapid advancements in technology and data collection methods have led to the generation and accessibility of vast amounts of multi-modal, high-dimensional data across a diverse range of disciplines. Tensor methods have emerged as essential tools in signal processing, providing powerful frameworks to model and analyze such complex data effectively. This survey offers a comprehensive overview of tensor factorization techniques and their applications in key areas. We explore their role in remote sensing, focusing on tensor-based methods for analyzing hyperspectral and multispectral images, tackling challenges such as recovering super-resolution images and addressing spectral unmixing. In wireless communication, we examine tensor methods used for signal modulation in unsourced massive random access communication, which achieve strong performance in multi-antenna channel and signal modeling. We also discuss tensor applications in network compression, where they reduce the computational demands of deep neural networks, making them more feasible for edge devices. Additionally, we highlight the use of tensor methods in high-dimensional missing data completion problems, showcasing their versatility across various domains. Furthermore, we explore applications in image analysis and computer vision, where tensors are effectively utilized for motion and object tracking, 3D modeling, analysis of satellite imaging, and medical imaging. By bridging theoretical advancements with practical applications, this survey aims to guide researchers in leveraging tensor methods to tackle emerging challenges in signal processing
Bigraded Castelnuovo-Mumford regularity and Groebner bases
No full textInternational audienceWe study the relation between the bigraded Castelnuovo-Mumford regularity of abihomogeneous ideal in the coordinate ring of the product of two projective spaces and the bidegrees of a Groebner basis of with respect to the degree reverse lexicographical monomial order in generic coordinates. For the single-graded case, Bayer and Stillman unraveled all aspects of this relationship forty years ago and these results led to complexity estimates for computations with Groebner bases. We build on this work to introduce a bounding region of the bidegrees of minimal generators of bihomogeneous Groebner bases for . We also use this region to certify the presence of some minimalgenerators close to its boundary. Finally, we show that, up to a certain shift, this region is related to the bigraded Castelnuovo-Mumford regularity of
New insights into Glasser-Manna integrals and the harmonic zeta function
No full textInternational audienceUsing a new representation of the harmonic zeta function (also known as the Apostol-Vu zeta function), we establish an interesting connection between the special values of this function and a certain type of complex logarithmic integrals previously introduced by Glasser and Manna which proved to be useful in the study of the Laplace transform of the digamma function. To our knowledge, this unexpected connection has never been noticed before