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Correction: Tree rings reveal the correlation between the Kaindy Lake submerged forest and the historical 1889 M 8.2 Chilik earthquake (Kazakhstan)
No full textInternational audienc
State of the art and for remote sensing monitoring of carbon dynamics in African tropical forests
No full textInternational audienceAfrican tropical forests play a crucial role in global carbon dynamics, biodiversity conservation, and climate regulation, yet monitoring their structure, diversity, carbon stocks and changes remains challenging. Remote sensing techniques, including multi-spectral data, lidar-based canopy height and vertical structure detection, and radar interferometry, have significantly improved our ability to map forest composition, estimate height and biomass, and detect degradation and deforestation features at a finer scale. Machine learning approaches further enhance these capabilities by integrating multiple data sources to produce improved maps of forest attributes and track changes over time. Despite these advancements, uncertainties remain due to limited ground-trut
Proton inelastic scattering on 56Fe: Insights from the 9-MV Tandem Accelerator measurements @ IFIN-HH
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On Einer Steemann Nielsen’s 1952 “The Use of Radio-active Carbon (C14) for measuring Organic Production in the Sea”
No full textInternational audienceEiner Steemann Nielsen's 1952 methods paper describing the use of C 14 to measure photosynthesis in the journal now known as the ICES Journal of Marine Research was a landmark publication. It is still regularly cited today. Here, in a brief account, the story of Einer Steemann Nielsen (1907-1989), and his major publication is given, along with evidence of its enduring value
Discovery of 15 new pulsars at high Galactic Latitudes with FAST
No full textInternational audienceWe present the discovery and timing results of 15 pulsars discovered in a high Galactic latitude survey conducted with the Five-hundred-meter Aperture Spherical Telescope (FAST). The survey targeted a region as close as possible to the Galactic Center, encompassing an area near the Galactic Bulge. The newly discovered pulsars consist of eleven normal pulsars and four millisecond pulsars (MSPs). Among the MSPs, three are identified in binary systems with orbital periods of ~3.1, 4.6 and 12.5 days, respectively. We have successfully obtained coherent timing solutions for three of the normal pulsars (PSRs J1745-0059, J1746-0156 and J1800-0059). Furthermore, within our data set we found that four pulsars (three new and one known) show mode-changing and/or subpulse drifting phenomena. Comparing our discoveries with simulations of the Galactic disk and Bulge MSP populations indicates that these new pulsars are most likely located in the disk. Nonetheless, our discoveries demonstrate that deep surveys at high Galactic latitudes have significant potential to enhance our understanding of the MSP population in the direction of the Bulge
Limits and challenges of the detection of cluster-scale diffuse radio emission at high redshift: The Massive and Distant Clusters of WISE Survey (MaDCoWS) in LoTSS-DR2
No full textInternational audienceDiffuse radio emission in galaxy clusters is a tracer of ultra-relativistic particles and G-level magnetic fields, and is thought to be triggered by cluster merger events. In the distant Universe (i.e. z>0.6), such sources have been observed only in a handful of systems, and their study is important to understand the evolution of large-scale magnetic fields over the cosmic time. Previous studies of nine {\it Planck} clusters up to suggest a fast amplification of cluster-scale magnetic fields, at least up to half of the current Universe's age, and steep spectrum cluster scale emission, in line with particle re-acceleration due to turbulence. In this paper, we investigate the presence of diffuse radio emission in a larger sample of galaxy clusters reaching even higher redshifts (i.e. ). We selected clusters from the Massive and Distant Clusters of {\it WISE} Survey (MaDCoWS) with richness \lambda_{15}>40 covering the area of the second data release of the LOFAR Two-Meter Sky Survey (LoTSS-DR2) at 144 MHz. These selected clusters are in the redshift range (with a median value of 1.05). We detect the possible presence of diffuse radio emission, with the largest linear sizes of kpc, in 5 out of the 56 clusters in our sample. If this diffuse radio emission is due to a radio halo, these radio sources lie on or above the scatter of the radio halo correlations (at 150 MHz and 1.4 GHz) found at z<0.6, depending on the mass assumed. We also find that these radio sources are at the limit of the detection by LoTSS, and therefore deeper observations will be important for future studies
A toy model of turbulent shear flow using vortons
No full textInternational audienceWe introduce a novel toy model for shear flows, exploiting the spatial intermittency and the scale separation between large-scale flows and small-scale structures. The model is highly sparse, focusing exclusively on the most intense structures, which are represented by vortons—dynamically regular-ized quasi-singularities that experience rapid distortion from the large-scale shear. The vortons, in turn, influence the large-scale flow through the sub-grid stress tensor. Despite its simplicity, the model displays an interesting transition between two distinct regimes: (i) a laminar regime, where dissipation is entirely attributed to the large-scale flow, and the vortons dynamics is essentially diffusive, and (ii) a turbulent regime, in which most of the dissipation arises from the vortons. These regimes correspond to different scalings of dissipation and the Grashof number as functions of the Reynolds number, with power-law relationships that resemble those observed in classical turbulence
The Massive Open Online Course: 'Atmospheric Research Infrastructures: Sharing the Future of Our Atmosphere' as an Innovative Tool for Atmospheric Science & Climate Change Education
No full textInternational audienceAs part of the ATMO-ACCESS project, an innovative two-week Massive Open Online Course (MOOC) was hosted on the FUN (France Université Numérique) MOOC platform from January 20 to February 16, 2025. This course offered an engaging and interactive platform for learners interested in exploring critical challenges related to air pollution and climate change. The first week provided participants with in-depth knowledge about atmospheric constituents such as reactive trace gases and greenhouse gases, aerosols and clouds, their sources, impacts, and complex interactions. The MOOC emphasised the crucial importance of data sharing and collaborative networks within the research community while showcasing advanced atmospheric research methodologies. Additionally, the second week introduced three key Atmospheric Research Infrastructures (ARIs): ACTRIS, IAGOS, and ICOS, providing participants with insights into their high-quality operational workflows. To support active learning, participants could self-assess their knowledge through several quizzes and earn an open badge by successfully completing a final quiz. Feedback from participants and analysis of the MOOC's concluding survey revealed valuable insights into learner expectations, which will be presented during the session. These suggestions will guide the development of future iterations of the course, aiming at delivering a more effective, impactful and engaging learning experience
Moment-based Characterization of Spatially Distributed Sources in SAR Tomography
No full textInternational audienceThis paper presents a non-parametric method for 3-D imaging of natural volumes using Synthetic Aperture Radar tomography. This array processing-based technique aims at characterizing a spatially distributed density of incoherent sources, whose shape is imprecisely known. The proposed technique estimates the moments of the reflectivity density using a low-complexity covariance matching approach, and retrieves the mean location, dispersion, and power of the distributed source. Numerical simulations of realistic tomographic scenarios show that the proposed model-free scheme achieves better accuracy than slightly misspecified maximum likelihood estimators, derived from approximately known distribution shapes
Correlation of long-term optical color variability of radio-loud quasars with their VLBI astrometric characteristics
No full textInternational audienceAims. The International Celestial Reference Frame (ICRF) is realized through geodetic very long baseline interferometry (VLBI) positions of thousands of extragalactic objects, mainly radio-loud active galactic nuclei. As previous studies have suggested a link between the optical variability of these sources and optical-radio position offsets and variability, we want to explore the possible relationships between these astrometric quantities and the color variability that characterizes VLBI sources.Methods. We computed the BP/RP and color-magnitude correlations of 2584 ICRF sources using the Gaia DR3 photometric time series at the GBP (BP), GRP (RP), and G bands, and we compared them with astrometric properties (Gaia-VLBI optical-radio offsets and positional variability derived from VLBI coordinate time series). We also searched for possible biases coming from the length of the photometric series, the magnitude, the redshift, and the jet viewing angle when available as well as correlations between the color variability and the central engine properties (black hole mass and accretion luminosity).Results. We find that the most astrometrically stable sources and the sources with smaller optical-radio shifts have lower values of BP/RP correlation and low color-magnitude correlations, corresponding to the undefined-when-brighter (or redder-stable-when-brighter and bluer-stable-when-brighter) classes of optical variability. These preferred astrometric objects often belong to the spectral class FSRQ and have a z of about one and higher. We found a significant correlation for both of the astrometric stability measures with the jet viewing angle. The shorter optical-radio offsets occur in active galactic nuclei that contain more massive black holes and more luminous accretion disks, which may be caused by the tendency of smaller viewing angles to be associated with higher redshifts.Conclusions. Our results strengthen the hypothesis that the Doppler boosting effect on luminosity and geometry is the driving physical mechanism at the origin of the observed optical-radio position offsets and the astrometric variability suggested by previous studies. The results define additional predictors of absolute astrometric performance of reference frame candidates, and they supplement the optical variability criterion. Moreover, this work demonstrates that the relatively short time span (a few years) and irregular sampling of the Gaia light curves are sufficient to predict the astrometric stability of new reference frame objects. This study also shows that absolute astrometry with the geodetic VLBI is a valuable tool to gain new insight into the physical processes responsible for quasar activity in the inner parts of the relativistic engines