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The value of Iberian Margin paleotemperature records with a novel organic proxy to revisit the bipolar seesaw model
No full textInternational audienceThe last glacial cycle provides the opportunity to investigate large changes in the Atlantic Meridional Overturning Circulation (AMOC) beyond the small fluctuations evidenced from modern measurements. Paleotemperature records from Greenland and the North Atlantic, including the Iberian Margin, show an abrupt variability, called Dansgaard–Oeschger (DO) events, which is associated with abrupt changes of the AMOC. These DO events also have Southern Hemisphere counterparts via the thermal bipolar seesaw, a concept describing the meridional heat transport leading to asynchronous temperature changes between both hemispheres. However, temperature records from the North Atlantic, notably the Iberian Margin, show more pronounced DO cooling events during massive releases of icebergs known as Heinrich (H) events, contrary to ice-core–based temperature records from Greenland. We present high-resolution temperature records over the last 160 kyr using several independent organic proxies (e.g., RI-OH′, TEX86, and UK′37) from three deep-sea sediment cores located in a north-south transect along the Iberian Margin (cores MD99-2331, MD95-2040, and MD95-2042). Over the 160–45 ka BP period, the recent RI-OH′ proxy yields faithful temperature records along the Iberian Margin in comparison with established paleotemperature proxies (e.g., TEX86 and UK′37; Davtian et al., 2021 Paleoceano. Paleoclim. https://doi.org/10.1029/2020PA004077). In the southern Iberian Margin (core MD95-2042), the RI-OH′ and UK′37 proxies faithfully reflect the contrasting DO cooling amplitudes with and without H events over the last glacial cycle (Davtian et al., 2021; Davtian and Bard, 2023 PNAS https://doi.org/10.1073/pnas.2209558120). We also revisit the thermal bipolar seesaw model using two independent temperature records (RI-OH′ and UK′37) from the southern Iberian Margin (core MD95-2042; Davtian and Bard, 2023). We show that temperature records from the southern Iberian Margin better support the classical thermal bipolar seesaw model than do ice-core–based temperature records from Greenland. We also introduce an extended thermal bipolar seesaw model that considers the contrasting DO cooling amplitudes with and without H events in the southern Iberian Margin, and a Bipolar Seesaw Index to distinguish DO cooling events with and without H events. Our data-model comparison emphasizes the role of the thermal bipolar seesaw in the abrupt temperature variability of both hemispheres with a clear enhancement during DO cooling events with H events, implying a relationship that is more complex than a simple flip-flop between two climate states linked to a tipping point threshold
Exploration de dynamique de gaz de Bose à température nulle : mesure de la fraction superfluide et observation d'oscillations de Bloch d'un soliton magnétique
No full textAt sufficiently high phase space densities, the many-body state of a degenerate Bose gas can be described by a single macroscopic wavefunction that undergoes nonlinear dynamics. Ultracold Bose gases are a prominent platform in the field of nonlinear physics, enabling the study of stable stationary wavepackets, known as solitons. In these platforms, atom interactions are often weak and treated within a mean-field approach. However, interactions play a crucial role in the physics of these Bose gases and explain for example the formation mechanism of solitons or the emergence of a remarkable phase of matter: superfluidity. This thesis describes investigations on peculiar dynamics of ultracold Bose gases, which are approximated by zero-temperature physics. After introducing our experimental setup and its theoretical characterization, we discuss the survival of the superfluid property in spatially modulated systems, in connection with Leggett's seminal work in 1970 and the spectacular supersolid phase of matter. We then explore the physics of a specific type of 1D soliton that emerges in a weakly-immiscible two-component mixture, known as the magnetic soliton. Its name originates from its appearance in 1D ferromagnetic spin chains. Magnetic solitons exhibit a captivating periodic motion under a uniform force field, similar to the Bloch oscillations of electrons in solids. Finally, we introduce a new experimental setup for studying Rydberg excitations and the realization of an all-optical Bose-Einstein-Condensate.Pour des densités dans l'espace des phases suffisamment grandes, l'état à N corps d'un gaz de Bose dégénéré peut se décrire par une unique fonction d'onde macroscopique qui obéit à une dynamique non linéaire. Les gaz de bosons ultrafroids sont devenus une plateforme de choix pour la mise en évidence de phénomènes non linéaires, permettant l'étude des solitons, des paquets d'onde stationnaires ayant des propriétés de stabilité remarquables. Les interactions entre atomes dans cette plateforme sont souvent faibles et peuvent être traitées dans une approche de champ moyen. Malgré cela, les interactions jouent un rôle prépondérant dans la physique de ces gaz et permettent d'expliquer notamment le mécanisme de formation des solitons, mais aussi l'émergence d'un état superfluide de la matière à basse température. Cette thèse décrit de récentes études de dynamique de gaz de Bose, menées à température nulle. Après avoir introduit la plateforme expérimentale utilisée ainsi qu'une description théorique de ces gaz de Bose, nous discutons le devenir de la propriété de superfluidité en présence d'une modulation spatiale. Ce travail est en lien direct avec les travaux menés par Leggett en 1970 et avec un état spectaculaire de la matière, connu sous le nom de supersolide. Nous explorons ensuite la physique d'un type spécifique de soliton unidimensionnel, qui apparaît dans des mélanges de spin faiblement immiscibles à deux composantes et qui est connu sous le nom de soliton magnétique. Cette désignation provient d'un autre contexte dans lequel ce soliton apparaît: une chaîne ferromagnétique de spins. Les solitons magnétiques répondent de manière spectaculaire à l'application d'une force uniforme: ils oscillent périodiquement dans le temps, de manière similaire au mouvement d'électrons dans le potentiel périodique créé par des solides, connu sous le nom d'oscillations de Bloch. Pour finir, nous discuterons le début de la construction d'une nouvelle plateforme expérimentale, visant dans le futur à étudier des excitations Rydberg, et la réalisation d'un condensat de Bose-Einstein sans utiliser de pièges magnétiques
Éditorial: Usages de Bergson : la Scandinavie du moment 1900, l’éducation créatrice au XXe siècle, et leurs enjeux aujourd’hui
No full textInternational audienc
Vu depuis l’au-delà. Le monde selon Jacques de Néa Skètè
No full textInternational audienceIakovos of Nea Skete († 1869) is an unclassifiable author, whose work belongs to popular theology. Facing Heliocentrism, going through an intense gnoseological crisis, he elaborates a paradoxical cosmology, both moral and metaphysical. His guide is neither a Father of the Church nor, of course, a ‘physiologist’, but Andrew the Fool in Christ, the holy hero of a Byzantine edifying tale. Transported to the afterlife, enlightened, Andrew provides a panoptic vision of the universe, to which Iakovos gives the credit of a first-hand account. This paper aims to describe the universe as Iakovos conceives it, but also to address the question of what this cosmological elaboration tells us about its author, a hesychast monk startled by modernity.Jacques de Néa Skètè (†1869) est un auteur inclassable, dont l’œuvre relève de la théologie populaire. Confronté à l’héliocentrisme, traversant une véritable crise gnoséologique, il élabore une cosmologie paradoxale, à la fois morale et métaphysique. Dans celle-ci, son guide n’est ni un Père de l’Église, ni bien sûr un « physiologue », mais André le Fol-en-Christ, saint héros d’un roman d’édification byzantin. Transporté dans l’au-delà, illuminé, ce dernier propose une vision panoptique de l’univers, à laquelle Jacques confère le crédit d’un témoignage issu de l’expérience. La présente contribution se propose de décrire le monde tel que Jacques le conçoit, mais aussi de répondre à la question de savoir ce que cette élaboration cosmologique nous dit sur son auteur, un moine hésychaste surpris par la modernité
Smoking changes adaptive immunity with persistent effects
No full textInternational audienceIndividuals differ widely in their immune responses, with age, sex and genetic factors having major roles in this inherent variability 1–6 . However, the variables that drive such differences in cytokine secretion—a crucial component of the host response to immune challenges—remain poorly defined. Here we investigated 136 variables and identified smoking, cytomegalovirus latent infection and body mass index as major contributors to variability in cytokine response, with effects of comparable magnitudes with age, sex and genetics. We find that smoking influences both innate and adaptive immune responses. Notably, its effect on innate responses is quickly lost after smoking cessation and is specifically associated with plasma levels of CEACAM6, whereas its effect on adaptive responses persists long after individuals quit smoking and is associated with epigenetic memory. This is supported by the association of the past smoking effect on cytokine responses with DNA methylation at specific signal trans -activators and regulators of metabolism. Our findings identify three novel variables associated with cytokine secretion variability and reveal roles for smoking in the short- and long-term regulation of immune responses. These results have potential clinical implications for the risk of developing infections, cancers or autoimmune diseases
Reconstructing human brown fat developmental trajectory in vitro
No full textInternational audienceThe loss of pancreatic β-cell identity has emerged as an important feature of type 2 diabetes development, but the molecular mechanisms are still elusive. Here, we explore the cell-autonomous role of the cell-cycle regulator and transcription factor E2F1 in the maintenance of β-cell identity, insulin secretion, and glucose homeostasis. We show that the β-cell–specific loss of E2f1 function in mice triggers glucose intolerance associated with defective insulin secretion, altered endocrine cell mass, downregulation of many β-cell genes, and concomitant increase of non–β-cell markers. Mechanistically, epigenomic profiling of the promoters of these non–β-cell upregulated genes identified an enrichment of bivalent H3K4me3/H3K27me3 or H3K27me3 marks. Conversely, promoters of downregulated genes were enriched in active chromatin H3K4me3 and H3K27ac histone marks. We find that specific E2f1 transcriptional, cistromic, and epigenomic signatures are associated with these β-cell dysfunctions, with E2F1 directly regulating several β-cell genes at the chromatin level. Finally, the pharmacological inhibition of E2F transcriptional activity in human islets also impairs insulin secretion and the expression of β-cell identity genes. Our data suggest that E2F1 is critical for maintaining β-cell identity and function through sustained control of β-cell and non–β-cell transcriptional programs. Article Highlights β-Cell–specific E2f1 deficiency in mice impairs glucose tolerance. Loss of E2f1 function alters the ratio of α- to β-cells but does not trigger β-cell conversion into α-cells. Pharmacological inhibition of E2F activity inhibits glucose-stimulated insulin secretion and alters β- and α-cell gene expression in human islets. E2F1 maintains β-cell function and identity through control of transcriptomic and epigenetic programs
"GUIDES TO THE VIEW" (LTA KHRID): TIBETAN BUDDHIST MANUALS OF PHILOSOPHICAL CONTEMPLATION
No full textInternational audienceA brief introduction to the Tibetan contemplative and philosophical genre of "Guides to the View." This was written for an audience of theologians and published in a volume entitled "To Know God." But that's in fact not quite my theme here - I've never been comfortable with the idea of "theology" in a Buddhist context - and the article may be of some interest to those studying Tibetan Buddhism alone. Pierre Hadot's thinking on "spiritual exercise" is also referenced, however