Contributions to the geomagnetic secular variation from a reanalysis of core surface dynamics

We invert for motions at the surface of Earth's core under spatial and temporal constraints that depart from the mathematical smoothings usually employed to ensure spectral convergence of the flow solutions. Our spatial constraints are derived from geodynamo simulations. The model is advected in time using stochastic differential equations coherent with the occurrence of geomagnetic jerks. Together with a Kalman filter, these spatial and temporal constraints enable the estimation of core flows as a function of length and time-scales. From synthetic experiments, we find it crucial to account for subgrid errors to obtain an unbiased reconstruction. This is achieved through an augmented state approach. We show that a significant contribution from diffusion to the geomagnetic secular variation should be considered even on short periods, because diffusion is dynamically related to the rapidly changing flow below the core surface. Our method, applied to geophysical observations over the period 1950-2015, gives access to reasonable solutions in terms of misfit to the data. We highlight an important signature of diffusion in the Eastern equatorial area, where the eccentric westward gyre reaches low latitudes, in relation with important up/down-wellings. Our results also confirm that the dipole decay, observed over the past decades, is primarily driven by advection processes. Our method allows us to provide probability densities for forecasts of the core flow and the secular variation.Comment: Geophysical Journal International publication; Earth core; Data assimilation; Core flows inversion; 22 pages; 14 figure

Control of programmed cell death during zebrafish embryonic development

Programmed cell death (PCD) is a conserved cellular process, which is essential during embryonic development, morphogenesis and tissue homeostasis. PCD participates in the elimination of unwanted or potentially harmful cells, and contributes in this way to the precise shaping of the developing embryo. In this review the current knowledge related to the role of PCD during zebrafish development was described and an overview was provided about the main actors that induce, control and execute the apoptosis pathways during zebrafish development. Finally, we point out some important issues regarding the regulation of apoptosis during the early stages of zebrafish development

The Apoptotic Regulator Nrz Controls Cytoskeletal Dynamics via the Regulation of Ca2+ Trafficking in the Zebrafish Blastula

SummaryBcl-2 family members are key regulators of apoptosis. Their involvement in other cellular processes has been so far overlooked. We have studied the role of the Bcl-2 homolog Nrz in the developing zebrafish. Nrz was found to be localized to the yolk syncytial layer, a region containing numerous mitochondria and ER membranes. Nrz knockdown resulted in developmental arrest before gastrulation, due to free Ca2+ increase in the yolk cell, activating myosin light chain kinase, which led to premature contraction of actin-myosin cables in the margin and separation of the blastomeres from the yolk cell. In the yolk syncytial layer, Nrz appears to prevent the release of Ca2+ from the endoplasmic reticulum by directly interacting with the IP3R1 Ca2+ channel. Thus, the Bcl-2 family may participate in early development, not only by controlling apoptosis but also by acting on cytoskeletal dynamics and cell movements via Ca2+ fluxes inside the embryo

Cytoskeleton dynamics in early zebrafish development: A matter of phosphorylation?

Early morphogenic movements are an important feature of embryonic development in vertebrates. During zebrafish gastrulation, epiboly progression is driven by the coordinated remodeling of the YSL microtubule network and F-actin cables. We recently described the implication of Nrz, an anti-apoptotic Bcl-2 homolog, in the control of the YSL cytoskeleton dynamics. Nrz knock-down induces premature actin-myosin ring formation leading to margin constriction, epiboly arrest and embryo lethality. At the molecular level, the Nrz protein controls the actin-myosin dynamics through IP3R-dependent calcium levels variation. Here, we discuss these novel findings and propose a model in which reversible phosphorylation of the Nrz/IP3R complex modulates the permeability of the IP3R calcium channel and thus may explain the Nrz-dependent control of IP3R opening required for proper epiboly completion

Reionisation time fields reconstruction from 21 cm signal maps

During the Epoch of reionisation, the intergalactic medium is reionised by the UV radiation from the first generation of stars and galaxies. One tracer of the process is the 21 cm line of hydrogen that will be observed by the Square Kilometre Array (SKA) at low frequencies, thus imaging the distribution of ionised and neutral regions and their evolution. To prepare for these upcoming observations, we investigate a deep learning method to predict from 21 cm maps the reionisation time field (treion(r)), i.e. the time at which each location has been reionised. treion(r) encodes the propagation of ionisation fronts in a single field, gives access to times of local reionisation or to the extent of the radiative reach of early sources. Moreover it gives access to the time evolution of ionisation on the plane of sky, when such evolution is usually probed along the line-of-sight direction. We trained a convolutional neural network (CNN) using simulated 21 cm maps and reionisation times fields produced by the simulation code 21cmFAST . We also investigate the performance of the CNN when adding instrumental effects. Globally, we find that without instrumental effects the 21 cm maps can be used to reconstruct the associated reionisation times field in a satisfying manner: the quality of the reconstruction is dependent on the redshift at which the 21 cm observation is being made and in general it is found that small scale (<10cMpc/h) features are smoothed in the reconstructed field, while larger scale features are well recovered. When instrumental effects are included, the scale dependance of reconstruction is even further pronounced, with significant smoothing on small and intermediate scales

Objets connectés et mobilité urbaine : visualiser les déplacements des usagers de Twitter avec des graphes dynamiques

Avec le tournant numérique, les données issues des objets connectés constituent une ressource nouvelle pour la compréhension des rythmes urbains et des mobilités dans la ville. À l’aide des messages géolocalisés (1 540 000 tweets) des usagers du réseau social Twitter enregistrés durant l’année 2015, cet article présente un outil de visualisation des mobilités parisiennes en s’appuyant sur des graphes dynamiques. Nous montrons comment un algorithme de clustering nous permet de passer d’un message géolocalisé à un déplacement individuel puis à des trajectoires collectives. Ces dernières illustrent les mobilités préférentielles des usagers du réseau social dans Paris, ainsi que des zones de concentration et pôles d’intérêt.With the digital turn, data from connected devices are a new resource for understanding urban rhythms and mobility. Using the geolocated messages (1, 540, 000 tweets) of Twitter social network users recorded in 2015, this article uses dynamic graphs to visualize Parisian mobilities. Using a clustering algorithm, we show how to move from a geolocated message to an individual displacement and on to collective trajectories. These trajectories illustrate the preferential mobility of users of the social network in Paris, as well as the areas of concentration and poles of interest.La transformación o giro digital facilita el acceso a la información de los dispositivos electrónicos conectados. Es un nuevo recurso para comprender los ritmos urbanos y la movilidad en la ciudad. Este artículo presenta una herramienta con gráficos de flujos dinámicos para visualizar la movilidad en París. Para ello utiliza los mensajes de los usuarios de la red social de Twitter registrados y geolocalizados durante el año 2015 (1,540,000 tweets), y mediante un algoritmo de agrupamiento convierte en flujos dinámicos colectivos un mensaje geolocalizado con una trayectoria individual. De este modo se puede visualizar movilidades preferidas, áreas de interés y de concentración de los usuarios de redes sociales en París

La mobilité parisienne des usagers de Twitter

International audienceThis paper, based on recorded geolocated Twitter messages, attempts to identify urban patterns by separating various modes of urban events from urban routine. We set out to identify relationships between types of user, types of event and the transmission of messages on the Twitter social network for Paris and the Île-de-France region. To do so, we used a graph method making it possible to combine spatial and temporal simplifications. This method highlights the spatiotemporal variations of nodes and flows over long time series of spatial situations. Beyond preferential trajectories of Twitter users, Parisian clusters appear: hotspots, crossing points, clusters during a specific event. Dynamics graph can reveal the " ephemeral city " and the behaviours development of Twitter users in Paris.Cet article, fondé sur le traitement des messages Twitter géolocalisés, tente d'identifier des configurations réticulaires de l'espace urbain à partir des déplacements des émetteurs de tweets dans Paris et l'Île-de-France. Nous nous appuyons sur une méthode algorithmique de réalisation de graphes dynamiques, pour révéler des mobilités en combinant des regroupements spatiaux et des séries temporelles. Cette méthode met en évidence les variations spatiotemporelles de mobilité sous forme de polarités ou de vacuités récurrentes. Au-delà des trajectoires préférentielles empruntées par les usagers, des clusters parisiens émergent de ces graphes, révélant des hubs récurrents, des points de passage et des polarisations à l'occasion d'un événement particulier. Les graphes dynamiques permettent de traduire la « ville éphémère » et l'évolution des comportements des usagers du réseau social Twitter

Inhibitors of the Cellular Trafficking of Ricin

Throughout the last decade, efforts to identify and develop effective inhibitors of the ricin toxin have focused on targeting its N-glycosidase activity. Alternatively, molecules disrupting intracellular trafficking have been shown to block ricin toxicity. Several research teams have recently developed high-throughput phenotypic screens for small molecules acting on the intracellular targets required for entry of ricin into cells. These screens have identified inhibitory compounds that can protect cells, and sometimes even animals against ricin. We review these newly discovered cellular inhibitors of ricin intoxication, discuss the advantages and drawbacks of chemical-genetics approaches, and address the issues to be resolved so that the therapeutic development of these small-molecule compounds can progress