HAL-Université de Bretagne Occidentale
Not a member yet
75442 research outputs found
Sort by
Reliable machine learning initialization methods for the calibration of Dynamic Energy Budget models
No full textInternational audienc
Hydrological regime shifts in Sahelian watersheds: an investigation with a simple dynamical model driven by annual precipitation
No full textInternational audienceAbstract. The Sahel, the semi-arid fringe south of the Sahara, experienced severe meteorological droughts in the 1970s–1980s. During and after these droughts, watersheds in the Central Sahel have experienced an increase in the annual runoff coefficient (annual runoff normalized by annual precipitation). We hypothesize that these increases correspond to regime shifts. To investigate the timing of these regime shifts, we introduce a lumped model that represents feedbacks between soil, water and vegetation at the watershed scale and the annual time step. This model relies on runoff coefficient as a constraint for the state variable and precipitation as unique external forcing. Four watersheds (Gorouol, Dargol, Nakanbé and Sirba), with pluri-decennial observations (1950s–2010s), are modeled. For each watershed, one million parameterizations of this model are sampled and run, and an ensemble of one thousand best parameterizations is selected based on observed runoff coefficients. Our results show that this model can reproduce the trend of runoff coefficients. For all watersheds, almost all selected parameterizations from the ensemble are bistable. We define two alternative runoff coefficient regimes (a low and a high regime) by splitting with a threshold the bifurcation diagram of bistable parameterizations. Most selected parameterizations undergo regime shifts: simulated runoff coefficients belong to the low regime in 1965 and to the high regime in 2014. Finally, we find that the year of the regime shift, defined as the year when the number of regime shifts is maximized, was 1971, 1972, 1973, 1983 for the Gorouol, Nakanbé, Dargol and Sirba watershed, respectively. These results were obtained with a parsimonious model which deliberately neglects fine-scale processes of Sahelian hydrology. It would therefore be wise to supplement this analysis with other models – with varying levels of complexity – that also allow regime shifting. Overall, this article proposes simple ideas toward improving the modelling and characterization of hydrological regime shifts
A microbiome assessment of healthy and bleached Halymenia floresii (Clemente) C.Agardh (Rhodophyta, Florideophyceae)
No full textInternational audienceAbstract Macroalgae serve as critical habitat-formers and primary producers in coastal ecosystems, functioning across near-subtidal and intertidal zones in three distinct states: substrate-attached, free-floating (drift), and beach-cast. While substrate-attached macroalgae are susceptible to infectious diseases with significant ecological implications, diseases affecting drift macroalgal communities remain virtually unstudied. Here, we investigated bleaching disease - one of the most common macroalgal afflictions - in the drift rhodophyte Halymenia floresii from the Gulf of Mexico. Using 16S rRNA gene high-throughput sequencing and scanning electron microscopy, we characterized the bacterial community structure and composition associated with the free-floating healthy, bleached and degrading H. floresii to understand how bacterial partners respond to host health status. Principal Coordinate Analysis based on UniFrac distance revealed distinct clustering of bacterial communities according to host health condition. Shannon diversity indices showed distinct patterns ranging from 1.14 – 3.15 for healthy, bleached, and degrading samples, while Simpson indices ranged from 0.62 to 0.91, reflecting substantial variation in community evenness. In healthy samples, Cyanobacteria (17 – 52%) and Pseudomonadota (previously, Proteobacteria) (41 – 81%) dominated, and the bleached samples were characterized by elevated Bacteroidota (formerly, Bacteroidetes) (5 – 35%) and Pseudomonadota (41 – 88%). Notably, Novosphingobium (25 – 49%) dominated healthy hosts while showing lower abundance in degrading (13 – 17%) and bleached (18 – 22%) specimens. Conversely, Reinekea emerged as a dominant genus (22.5%) specifically in bleached samples, suggesting a potential role in disease pathogenesis. Microbial network analysis using NetCoMi revealed three distinct bacterial clusters corresponding to health states: a healthy-associated cluster dominated by Novosphingobium and uncultured Cyanobacterial with predominantly positive associations, and two disease-associated clusters enriched in opportunistic genera including Reinekea , Vibrio , Colwellia , and Alteromonas , indicating network reorganization from cooperative to exploitative interactions. This study provides the first descriptive assessment of microbiome transitions associated with bleaching disease in a drift macroalga and highlights the importance of considering free-floating macroalgal diseases and their potential impacts on coastal ecosystem health
Behind the Scenes - Preferential Circulation and the Micro-Geography of Innovation in Off Off Broadway Theater (1950s-1970s)
No full textInternational audienc
Shaping nonreciprocal caustic spin-wave beams
No full textInternational audienceCaustics are intricate and challenging to control near-field interference patterns that exist in a wide range of physical systems, and which usually exhibit a reciprocal wave propagation. Here, we utilize the highly anisotropic dispersion and inherent non-reciprocity of a magnonic system to shape non-reciprocal emission of caustic like spin wave beams in an extended yttrium iron garnet (YIG) film from a nano-constricted waveguide. We introduce a near-field diffraction model to study spin wave beamforming in homogeneous in-plane magnetized thin films, and reveal the propagation of non-reciprocal spin wave beams directly emitted from the nanoconstriction by spatially resolved microfocused Brillouin light spectroscopy. The experimental results agree well with both micromagnetic simulation, and the near-field diffraction model. The proposed method can be readily implemented to study spin wave interference at the sub-µm scale, which is central to the development of wave-based computing applications and magnonic devices
The Design Multiverse: A Scientific Model for Design Evolution and Co-evolution
No full textInternational audienceModel-Based Systems Engineering lacks a formal model that treats design evolution, with its inherent branching, rework, and contextsensitivity, as a first-class citizen. Current approaches reduce rich design trajectories to repository artifacts, losing the semantics of design decisions. This paper calls for a scientific model for design evolution and introduces the Design Multiverse that frames design dynamics as a context-sensitive, nondeterministic transition system, while orthogonally separating observational link theories (e.g., conformance, refinement) for consistency reasoning. We demonstrate the model's explanatory power through co-evolution. Furthermore, we outline a research agenda grounded by Design Multiverse Experiments (DMX), which enable empirical validation and pave the way for scalable, history-aware modeling environments.</div
Émotion et subjectivité simulée : entre art, humanités numériques et intelligence artificielle
No full textInternational audienceFar from disappearing in the face of technoscientific rationality, the marvellous is today undergoing a profound reconfiguration through digital, immersive, and computational arts. Building on Alfred Gell’s perspective on the “technologies of enchantment,” we look at how contemporary artistic dispositifs—interactive installations, generative algorithms, immersive interfaces—reinvent the modalities of appearance. It is no longer simply a matter of representing the extraordinary, but of bringing it to life in the viewer's sensory experience, through technical processes that confuse the senses and blur the distinctions between nature and artifice, reality and virtuality. By analyzing works such as Refik Anadol’s Melting Memories and Ryoichi Kurokawa’s Subassemblies, the study highlights how the unexpected, metamorphosis, and surprise unfold in an environment saturated with data and non-human agents. These dispositifs do not merely produce a spectacular effect: they engage a critical reflection on perception, cognition, and the fabrication of imagination in the algorithmic age. The marvellous thus becomes an aesthetic and epistemological operation, both poetic and critical, capable of re-enchanting sensory experience while revealing the ideological stakes of technicality. The article argues that today’s technoscientific arts, beyond limiting themselves to illusion, redefine the role of the spectator as an actor in a hybrid experience, where wonder constitutes both a mode of appearance and a tool of lucidity in the face of the potentialities—and ambiguities and disillusionments—of this digitized world.Le merveilleux, loin d’avoir disparu face à la rationalité technoscientifique, connaît à présent une reconfiguration profonde à travers les arts numériques, immersifs et computationnels. En nous inscrivant dans la perspective ouverte par Alfred Gell sur les « technologies de l’enchantement », nous nous penchons sur la manière dont les dispositifs artistiques contemporains – installations interactives, algorithmes génératifs, interfaces immersives – réinventent les modalités de l’apparition. Il ne s’agit plus seulement de représenter l’extraordinaire, mais de le faire surgir dans l’expérience sensible du spectateur, par le biais de processus techniques qui troublent les sens et estompent les distinctions entre nature et artifice, réel et virtuel. En analysant des œuvres comme Melting Memories de Refik Anadol ou Subassemblies de Ryoichi Kurokawa, l’étude met en lumière comment l’inattendu, la métamorphose et la surprise se déploient dans un environnement saturé de données et d’agents non humains. Ces systèmes ne produisent pas uniquement un effet spectaculaire : ils engagent une réflexion critique sur la perception, la cognition et la fabrique de l’imaginaire à l’ère des algorithmes. Le merveilleux y devient une opération esthétique et épistémologique, simultanément poétique et critique, capable de réenchanter l’expérience sensible tout en révélant les enjeux idéologiques de la technicité. L’article vise ainsi à montrer que les arts technoscientifiques actuels, loin de se limiter à l’illusion, redéfinissent le rôle du spectateur comme acteur d’une expérience hybride, où l’émerveillement constitue à la fois une forme d’apparition et un outil de lucidité face aux potentialités – et aux ambiguïtés et désillusions – de ce monde digitalisé
Mise en œuvre des méthodologies scientifiques et Techniques dans une exposition muséale: Le projet ANR LAB in Virtuo
No full textInternational audienceLes objectifs du projet Lab In Virtuo sont de permettre une meilleure élicitation des Connaissances liées à la sauvegarde de dispositifs techniques et la création de nouveaux types de scénarios de médiation. Le projet s’appuie sur les technologies de la Réalité Virtuelle et Augmentée.En effet, nous estimons que l’implication du corps favorise les fonctions cognitives, que ce soit dans la création ou l’acquisition de nouvelles connaissances. Lors de la phase de création des connaissances, la Réalité Virtuelle et Augmentée permet d’immerger le corps d’experts ou d’anciens utilisateurs dans une scène reconstituant l’objet d’étude. Nous considérons que cette situation permettra une meilleure élicitation des connaissances. Pour utiliser un tel système en tant qu’interface de création de connaissances, nous devons alors nous appuyer sur un langage suffisamment formel pour être traité automatiquement et pour stocker les informations créées. Lors de la phase de restitution des connaissances, durant un scénario de médiation, nous considérons également que l’utilisation de ces technologies amélioré l’acquisition de ces connaissances par l’utilisateur. Cela est dû non seulement à une meilleure implication des utilisateurs grâce aux nouvelles technologies, mais surtout à l’immersion de l’utilisateur dans un environnement reconstitué et à ses capacités ‘interaction avec le système, ce qui n’est pas possible dans la réalité. Le projet est financé par l’ANR, est toujours en cours et se terminera fin 2025. Nous allons présenter ici l’architecture et le flot de conception proposés ainsi que la mise en place d’une exposition permettant d’éxpérimenter nos méthodologies
Evaluating AI for Palm Tree Disease Detection: A Comparative Study of YOLOv8 Object Detection and U-Net Segmentation Using UAV Imagery
No full textInternational audienceAbstract. Agriculture is a cornerstone of economic stability and food security, particularly in regions like Morocco, where palm trees are vital to the environment and local livelihoods. The Figuig oasis, known for its extensive palm plantations, faces significant threats from the spread of palm tree diseases, which can lead to substantial agricultural losses. Early and accurate disease detection is critical to mitigating these impacts. This study evaluates the effectiveness of deep learning models YOLOv8 for object detection and U-Net for segmentation in detecting and segmenting healthy and diseased palm trees using Unmanned Aerial Vehicle (UAV) imagery. A dataset of 400 UAV images was annotated and divided into training (70%), validation (20%), and test (10%) sets. YOLOv8 achieved an accuracy of 78.48%, with a precision of 58.38% and a recall of 47.70%, demonstrating robust object detection capabilities but highlighting the need for improved recall to reduce false negatives. On the other hand, U-Net excelled in segmentation, achieving an overall precision of 0.8746, recall of 0.8713, and F1-score of 0.8727, with powerful performance in delineating diseased regions. The results underscore the complementary strengths of YOLOv8 and U-Net, with YOLOv8 offering efficient detection and U-Net providing detailed segmentation for precise health assessment. This study highlights the potential of integrating UAV imagery and deep learning for automated palm tree health monitoring, paving the way for early disease detection and sustainable agricultural practices. Future work will focus on optimizing model performance, expanding the dataset, and exploring advanced architectures to further enhance accuracy and recall
The role of livestock farming in the conservation of wet grasslands and the ecosystem services they provide
No full textLe résumé de la journéeThis issu follows on from the Carrefour de l'innovation agronomique, forum dedicated to Grazing livestock : the contribution of biodiversity, from soils to landscapes event that took place on 12 December 2024 at the Institut Agro in Rennes, France. It provide an update on knowledge and feedback showing the trajectories of agroecological livestock farms that make the most of wild and domestic biodiversity and the interactions between them. The development of agroecological practices is necessary to adapt agri-food systems to climate change and its impacts, and to mitigate their environmental impact. Biodiversity has been identified as a key factor in the sustainability of farming systems in their environmental ecosystems, combining the genetic diversity of domestic species with that of wild species. This Agronomic Innovation Forum will present results on domestic biodiversity in herbivore farming and the environmental biodiversity impacted and mobilised, from the scale of soils to that of landscapes.International audienceWet grasslands are managed for livestock farming. They have been heavily drained in the past and their abandonment is now the main threat. Extensive management allows the conservation of these open ecosystems and the ecosystem services they provide, such as hosting a diverse fauna and flora, the production of quality fodder, the regulation of water flows and quality, pollination and carbon storage. The services are not all synergistic and there is no ideal habitat for all the services provided. However, the diversity of habitats, sometimes within the same marsh, makes it possible to offer interesting levels of services at the landscape scale. Wet grassland conservation depends above all on maintaining livestock farming with extensive management in marshy areas