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Mise en évidence de la connectivité fonctionnelle des réseaux d'astrocytes grâce à AstroNet, un algorithme de reconstruction de graphes couplé au traitement d'images.
No full textInternational audienceAstrocytes form extended intercellular networks, displaying complex calcium activity. However, the specific organization of these astrocytic networks and the precise extent of their functional connectivity in different brain areas remain unexplored. To unveil the functional architecture of astrocytic networks, we developed, using a datadriven methodology, a novel algorithm called AstroNet that uses two-photon calcium imaging to map temporal correlations in activation events among neighboring astrocytes. Our approach involves reconstructing functional astrocytic networks by organizing individual astrocyte activation events chronologically. This chronological order creates activity paths that enable the extraction of local astrocyte functional correlations. Ultimately, by tallying the occurrences of direct co-activations between pairs of cells along these pathways, we construct a graph that mirrors the underlying astrocyte functional network. By applying this method to two distinct brain regions (CA1 hippocampus and motor cortex), we identified notable differences in local network organizations in sub-regions of around 20-40 astrocytes. Specifically, the cortex exhibited a lower connectivity, while astrocytes in the hippocampus displayed stronger connections. Moreover, we found that in both regions, astrocytic networks consist of smaller, tightly connected sub-networks embedded within a larger, more loosely connected one. Altogether, our innovative method enables the identification of activation paths among astrocytes, facilitates the characterization of local network functional connectivity, and quantifies distinct connectivity patterns among astrocytes from different brain regions. This approach sheds light on the heterogeneous functional organization of astrocytic networks within the brain, pointing to region-specific astrocyte connectivity
Algorithm for computing perturbation series of dynamical mean field theory
No full textInternational audienceWe show how to use diagrammatic techniques to compute the weak-coupling perturbation series of the self-consistent solution to a Dynamical Mean Field Theory (DMFT) problem. This approach constitutes an alternative to using diagrammatic techniques directly as an impurity solver. It allows one to bypass the need of multiple perturbative series resummations within the DMFT self-consistency loop. It can be applied at or out of equilibrium, with any diagrammatic formalism, such as real times, imaginary times, or Matsubara frequencies formalisms. As a proof of principle, we illustrate our method with the half-filled Hubbard model on the Bethe lattice in the DMFT approximation, using Quantum Quasi-Monte Carlo (QQMC) to obtain the impurity perturbation series on the real time axis
Application of Hard X-Ray and Gamma-Ray TES Microcalorimeter at Accelerator Facility
No full textInternational audienceThe X-ray spectroscopy of the muonic atom has attracted atomic, nuclear, and particle physicists since its discovery. The properties of a muonic atom, such as its binding energy or atomic radius, are different from an ordinary atom because of the difference in the mass between the muon and electron. Our collaboration has employed superconductor transition-edge sensor (TES) microcalorimeters for the x-ray spectroscopy of the muonic atom. Thanks to the recent detector development, the 44-keV lines from muonic Ar, which is important for the precision test of bound-state quantum electrodynamics, and the 76-keV lines from muonic Si, which is of interest from the viewpoint of the measurement of nuclear radii, have been reached by the dynamic range of the state-of-art TES microcalorimeters. An accelerator facility that can produce a high-intensity muon beam is necessary for such spectroscopic experiments. We performed a commissioning experiment of the hard x-ray and gamma-ray TES microcalorimeter at the J-PARC MLF MUSE muon beam line. The energy resolution, gain stability, and performance of timing selection of the pulses were evaluated in the environment of a large-scale accelerator facility
Ottoman Fake: An Essay on Forgers, Bureaucrats, and Philologists (18th-20th Centuries)
No full textInternational audienceCoins, notes, fats, oils, soda waters, teas and wines, dyes and medicines, diplomas, certificates, patents and titles… Fakes were everywhere in the late Ottoman world. Did anyone care?As this book shows, calls to “discriminate the true from the fake”, a founding motto of philological practice from the 16th century onwards, prompted many encounters between forgers and bureaucrats in the late Ottoman world. Each tells a different story about how fakes occurred. Quoted and translated in full, reports of these forgery affairs shed new light on Ottoman state-society relations. They show that the taming of the fake has been crucial to the reforming of the state
Présentation dynamique de l’évolution intraindividuelle des δ 15N, δ 13C, δ 34S de 5 individus columnatiens, capsiens et néolithiques
No full textPrésentation dynamique de l’évolution intraindividuelle des δ15N, δ13C, δ34S de 5 individus columnatiens, capsiens et néolithiques du site de Columnata (XI-IXe mill. BP, Tiaret, Algérie). Illustration utilisée dans Chaid-Saoudi, Y., Bédécarrats, S., Larbi, I., Sayle, K.L., Couvrat, M., Lambert, A., Spanneut, L., Guihou, A., Power, R.C., Mariot, H., Vidal, L., Deschamps, P., Sonzogni, C., Bouby, L., Sitouah, B., Bray, F., Salazar Garcia, D.C., Deviese, T., Au Yang, D., Leduc, G., Rottier, S., Goude, G., 2025. Naître et grandir dans l’Algérie préhistorique. Premières approches biogéochimiques sur des sépultures du site de Columnata (XIe-IXe mill. BP, Tiaret, Algérie), in: 1850es Journées de La Société d’Anthropologie de Paris.1850es Journées de la Société d’Anthropologie de Paris, Bulletins et mémoires de la Société d’Anthropologie de Paris, Paris, France. https://hal.science/hal-0478227
Mass and light in galaxy clusters: The case of Abell 370
No full textInternational audienceIn the cold dark matter (CDM) paradigm, an association between the hypothetic dark matter (DM) and its stellar counterpart is expected. However, parametric strong-lensing studies of galaxy clusters often display misleading features: DM components on the group or cluster scale without any stellar counterpart, offsets between the two components that are larger than what might be allowed by CDM or self-interacting DM models, or significant unexplained external shear components. This is the case in the galaxy cluster Abell 370, whose mass distribution has been the subject of several studies that were motivated by a wealth of data. The cluster was described parametrically with strong-lensing techniques by a model with four dark matter clumps and galaxy-scale perturbers, and with a significant external shear component, whose physical origin remains a challenge. The dark matter distribution features a mass clump without a stellar counterpart and a significant offset between one of the dark matter clumps and its associated stellar counterpart. This paper is based on BUFFALO data, and we begin by revisiting this mass model. Sampling this complex parameter space with Markov chain Monte Carlo (MCMC) techniques, we find a solution that does not require any external shear and provides a slightly better root mean square (RMS) than previous models (0.7″ compared to 0.9″). Investigating this new solution further, in particular, by varying the parameters that lead the MCMC sampler, we present a class of models that can accurately reproduce the strong-lensing data, but whose parameters for the dark matter component are poorly constrained. This limits any insights into its properties. We then developed a model in which each large-scale dark matter component must be associated with a stellar counterpart. This model with three dark matter clumps cannot reproduce the observational constraints with an RMS smaller than 2.3″, and the parameters describing this dark matter component remain poorly constrained. Examining the total projected mass maps, we find a good agreement between the total mass and the stellar distribution, which are both bimodal to first order. We interpret the misleading features of the mass model with four dark matter clumps and the failure of the mass model with three dark matter clumps as being symptomatic of the lacking realism of a parametric description of the dark matter distribution in such a complex merging cluster. We encourage caution and attention on the outputs of parametric strong-lensing modelling. We briefly discuss the implications of our results for using Abell 370 as a gravitational telescope. With the class of models that reproduce the strong- lensing data, we computed the magnifications for background Lyα emitters, and we present the critical curves obtained for the redshift of the Dragon arc, whose recent observations with the James Webb Space Telescope prompted interest. Finally, in light of our results, we discuss the strategy of choosing merging (multi-modal) clusters as gravitational telescopes compared to simple (unimodal) clusters
Stress induces oxytocin-Gαi-dependent remodeling of astrocytes to shape neuronal response in the amygdala
No full textInternational audienceAnticipated reactions to stressful situations are vital for the survival and well-being of organisms, and abnormal reactions results in stress-related disorders. The neuropeptide oxytocin is a key modulator ensuring well-adapted stress responses. Oxytocin acts on both neurons and astrocytes, but the molecular and cellular mechanisms mediating stress response remain poorly understood. Here, we focus on the amygdala, a crucial hub that integrates and processes sensory information through oxytocin-dependent mechanisms. Using an acute stress paradigm in mice, genetic and pharmacological manipulations combined with proteomic, morphological, electrophysiological and behavioral approaches, we reveal that oxytocinergic modulation of the freezing response to stress is mediated by transient Gαi-dependent retraction of astrocytic processes, followed by enhanced neuronal sensitivity to extracellular potassium in the amygdala. Our findings elucidate a pivotal role for astrocytes morphology-dependent modulation of brain circuits that is required for proper anticipated behavioral response to stressful situations
Automatic characterization of the border deterioration in Byzantine seals
No full textInternational audienceByzantine seals were attached to official documents to authenticate the sender, thus enclosing a valuable part of the Byzantine Empire's history. With the aim to provide computational models to help historians in the seal interpretation, this paper proposes a method to automatically determine the level of deterioration of the seal borders from their photographs, i.e., a non-destructive inspection. The method consists of a segmentation step based on Morphological Geodesic Active Contours, a feature extraction step, and a classification step that groups the seals into four border deterioration categories. Our best results reached 0.80 in accuracy, 0.73 in Cohen's Kappa statistics score, and 0.80 in the macro F1 score
The Elusive Original: Differentiation and Identity in Byzantine scientific illustrations
No full textInternational audienceBy reducing the meaning of the word ‘mimesis’ to the perfect imitation of reality, modern scholars have too often focused on the degree of realism of an image. We then start thinking that, for many Greek and Latin scholars, the ultimate intention of artists was the ὁμοίωσις (or similitudo) between a copy and the original. Inexorably we end up believing that a representation individualises a subject by differentiating it from all others and can lead us to that same subject. In other words, we think we can find the original through a copy, and we view negatively images that cannot do this. My paper assesses whether the notion of visual species individualisation, particularly amongst representations of plants in Greek scientific manuscripts, had any currency for Byzantine scholars. More specifically, after a brief introduction to mimesis of reality in art and its reception in Byzantium, I first focus on how certain images of plants (especially from Dioscorides’ De materia medica) are depicted. Secondly, I present some of the ideas of Byzantine scholars that undoubtedly influenced the way in which certain images were depicted in scientific manuscripts. Finally, I consider the importance of captions (textual and visual) in individualisation, in terms of recognising the subject depicted and contributing to the creation of a diachronic identification
