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Velocity fields and turbulence from cosmic filaments to galaxy clusters
No full textInternational audienceGalaxy clusters are currently the endpoint of the hierarchical structure formation; they form via the accretion of dark matter and cosmic gas from their local environment. In particular, filaments contribute greatly by accreting gas from cosmic matter sheets and underdense regions and by feeding it to the galaxy clusters. Along the way, the gas in the filaments is shocked and heated. Together with the velocity structure within the filament, this induces swirling, and thus, turbulence. We studied a constrained hydrodynamical simulation replica of the Virgo cluster at redshift z = 0 to characterise the velocity field in the two cosmic filaments that are connected to the cluster with unprecedented high resolution. First, we qualitatively examined slices extracted from the simulation. We studied the temperature and the velocity field. We then derived quantities in longitudinal cuts to study the general structure of the filaments and in transverse cuts to study their inner organisation and connection to cosmic matter sheets and underdense regions. Then, we quantitatively studied velocities in the Virgo filaments by computing the 2D power spectrum from 1 and 5 Mpc square maps extracted from the slices and centred on the core of the filaments. We show that the total power spectrum in the filaments gains in amplitude and steepens towards Virgo. Moreover, the velocity field evolves from mostly compressive far in the filaments to mostly solenoidal in the Virgo core
Absolute Quantum Gravimeter AQG-B01 of PIN PGravi : characterisation and use in 2025
No full textInternational audienc
Temps universel coordonné continu adopté par l'UIT
No full textInternational audienceThe work reported is one of the activities of the International Telecommunication Union - Radiocommunication Sector (ITU-R) Study Group 7 (SG 7) (Science Services), Working Party 7A (WP 7A) (Time Signals and Frequency Standard Emissions). As a result of technical time scale issues raised by Sector Members of the ITU-R about thirty years ago and a letter from the Director of the Bureau international des poids et mesures (BIPM) to the Secretary General of the ITU in 2000, a new question ITU-R 236/7 on The Future of the Coordinated Universal Time UTC time scale was generated by WP 7A in 2001. Question 236/7 was structured to address the future definition and use of UTC in the ITU-R recommendations, and was updated over time. Major technical changes to UTC clearly have a potentially significant impact on communications networks, navigation systems, time/frequency distribution systems and virtually all aspects of civil/military timekeeping. The year 2023 was a significant and decisive year as the ITU unanimously succeeded in achieving the main objective of moving towards a continuous UTC when WRC-23, held in Dubai in November - December, endorsed the BIPM decision on this matter
Cold plasma treatment of cholangiocarcinoma: investigating skin tissue as a barrier to electric field propagation and reactive species diffusion
No full textJe procède à cette soumission dans le cadre de la présentation d'un poster.International audienc
Modeling the formation of N2 and CH4 frost on the Pluto slopes
No full textInternational audienceContext . The equatorial region of Cthulhu as revealed by New Horizons appears to be generally dark and largely devoid of volatiles because its surface albedo is low. Localized bright patches, however, which are interpreted as CH4 frost, are observed on crater rims and slopes. Aims . Previous studies suggested that these frosts might result from the peculiar insolation driven by the geometry of these slopes, but this has never been tested quantitatively. We investigated the origin, stability, and potential role of these localized frost deposits in the volatile cycle of Pluto. Methods . We implemented a new subgrid-scale slope parameterization in the volatile transport model for Pluto, which accounts for the specific solar irradiation and the resulting surface and subsurface temperatures on sloped terrains. This parameterization also allows the condensation and sublimation of volatiles (either N2 or CH4 ) on slopes, including the effect of large-scale transport of these species. This is key to determining the amount of frost that forms or disappears. Results . Our simulations reproduce the observed CH4 frost on north-facing slopes as seasonal deposits that currently sublimate, predict perennial CH4 frost on south-facing slopes, and show that the slope microclimates are not expected to alter global volatile cycles. Conclusions . Seasonal and perennial N2 and CH4 frosts can form on the Pluto slopes, even in its darkest and warmest regions, because the locally sunlight received on inclined terrain is reduced. Despite the abundance of sloped surfaces on Pluto, the slope microclimates still only appear to have a minor effect on the global volatile cycles of the planet
AKR Observations From All Local Times Indicate Substorm Activity
No full textInternational audienceAuroral Kilometric Radiation (AKR) is known to present emission at lower frequencies near substorm onset, corresponding to activation of higher altitude sources along auroral magnetic field lines and acting as a proxy of the vertical distribution of acceleration processes during these events. While remote observations are more difficult to relate to ionospheric activity than those made in situ due to the illumination of the instrument by multiple AKR sources, there is a question of how the association of a particular observation with substorm activity can change with observer local time (LT) and more generally whether AKR observations can track geomagnetic activity in the same way as other proxies. This study addresses these questions by computing binary contingency tables and classification statistics including the Matthews Correlation Coefficient (MCC), using automatically selected AKR observations from Wind/WAVES and substorm event lists. AKR observations made on the dusk and dawn flanks present the greatest balance between true positive and negative associations with substorm activity, where active acceleration regions due to the enhanced substorm current wedge are distinct from typical nightside activity. Observations from the dayside and L1 can also be a reliable indicator, with AKR rarely observed from this region outside of substorm activity. Our results show that observations of AKR below 70 kHz (corresponding to active source regions above ∼12,000 km at an L-shell of 7) can act as a good discriminator of substorm activity, particularly for observations from LTs near midnight.Plain Language Summary Auroral Kilometric Radiation (AKR) is terrestrial radio emission that is produced along magnetic field lines above the auroral oval. It coincides with acceleration of electrons into the upper atmosphere and is colocated with bright, discrete optical and UV aurora. Substorms, a global process of energy transfer in the terrestrial magnetosphere, are related to the production of low frequency AKR. Due to the beaming pattern of AKR sources the spacecraft position must be considered when relating remote observations to magnetospheric processes. We address the question of how remote AKR observations from different positions can be associated with substorms. Through binary classification analyses of AKR observations and substorm event lists from 1995 to 2005, we show that observations from all local times can indicate substorm activity. Observations made on the flanks of the magnetosphere show positive correlation, with AKR occurring frequently with events due to morphological changes in the ionosphere during substorms. Observations near noon have a high probability of coinciding with extended auroral features during substorms and can also be a reliable indicator. While midnight observations have weaker correlation due to the spatial distribution of typical auroral activity, but low frequencies improve the correlation
Adaptive and Multi-Source Entity Matching for Name Standardization of Astronomical Observation Facilities
No full textInternational audienceThis ongoing work focuses on the development of a methodology for generating a multi-source mapping ofastronomical observation facilities. To compare two entities, we compute scores with adaptable criteria andNatural Language Processing (NLP) techniques (Bag-of-Words approaches, sequential approaches, and surfaceapproaches) to map entities extracted from eight semantic artifacts, including Wikidata and astronomy-orientedresources. We utilize every property available, such as labels, definitions, descriptions, external identifiers, andmore domain-specific properties, such as the observation wavebands, spacecraft launch dates, funding agencies,etc. Finally, we use a Large Language Model (LLM) to accept or reject a mapping suggestion and provide ajustification, ensuring the plausibility and FAIRness of the validated synonym pairs. The resulting mapping iscomposed of multi-source synonym sets providing only one standardized label per entity. Those mappings willbe used to feed our Name Resolver API and will be integrated into the International Virtual Observatory Alliance(IVOA) Vocabularies and the OntoPortal-Astro platform
Multi-layer frozen profiler from single conjugated adaptive optics telemetry: novel approach and potential applications
No full textInternational audienceNew generations of adaptive optics (AO) systems give access to an unprecedented stream of data at spatial and temporal resolutions never before achieved for routine scientific operations. This is for example the case for the GRAVITY+ AO (GPAO) system upgrade: the four 8 meters units of the Very Large Telescope were equipped with 43x43 deformable mirrors (DM, 1432 actuators) as well as new 40x40 visible and 30x30 laser guide star Shack-Hartmann wavefront sensors (SH-WFS). By its number of measures and controlled actuators, GPAO prefigures those of the AO systems of future giant telescopes. However, so far, the AO telemetry from these systems remains largely underexploited beyond pure real-time AO applications. In this work, we present a novel turbulence profiler working on single-conjugated AO telemetry (SCAO). Under the assumption that the atmosphere is composed of mixed frozen flow layers (but without assumption on their structure function), it jointly retrieves the individual wind speed, direction, and strength (Cn2 coefficient) of the main contributors to the turbulence. Only their height remains unknown as a result of the lack of stereoscopic information in SCAO systems. Our model successfully fits standard conditions at the Paranal Observatory, disentangling up to eight independent layers. Straightforwardly, it can be used to refine the atmospheric monitor of the real-time computer: Fried’s parameters r0, tau0, v0 or seeing and residual variances of AO. Our work shows that single-layer-frozen flow is not a realistic approximation for most situations and demonstrates that the dominant multi-layers can be effectively reconstructed from operational telemetry. As such, our method paves the way towards more transformative applications, such as (i) the debiasing of DM/WFS misregistration estimators based on AO telemetry whose performances are undermined by strong winds, or (ii) more excitingly, to a piston reconstructor, the ultimate limit of ground-based interferometers
Spectroscopic Data at High Temperature for Exoplanetary Studies: The e-PYTHEAS Project
No full textInternational audienceThe field of exoplanetary studies has immensely expanded in the past years, and the analysis of the acquired observations necessitates an improved understanding of the radiative properties of hot gaseous media. Our project, e-PYTHEAS, started in 2016 and associates both experimental and theoretical high-temperature spectroscopies of molecular species detected in exoplanets by five French laboratories and international partners to support modeling of exoplanet data. The method we use starts with theoretical research that we support and confirm with laboratory experiments yielding infrared laboratory data of methane, ethane, acetylene and ethylene between 500 and 2500 K. The outcome is then injected into models of the atmospheres of the giant gaseous planets in our solar and other exoplanetary systems helping refine thermal profiles and atmospheric composition. The results will permit to more effectively analyze data and interpret observations of space missions such as ESA's M4 ARIEL, to be launched in 2029
Influence of chemical and morphological properties on the mid-infrared refractive indices of Titan aerosol analogs
No full textInternational audienceIn the atmosphere of Saturn's largest satellite, Titan, the solid particles in suspension (photochemistry organic aerosols) play an important role notably to the attenuation of the solar spectrum by absorption and scattering. To constrain these interactions, the optical properties of Titan’s atmospheric aerosols, refractive index n and extinction coefficient k were recovered from observations [1, 2, 3, 4]. The refractive indices database has been expanded using solid analogs of Titan's aerosols produced and analyzed in laboratory [5, 6, 7]. The experimental data are generally consistent with the optical properties derived from Titan’s aerosols, including the contribution to the extinction and albedo of Saturn's moon [5, 7, 8]. However, comparisons of vibrational modes in the mid-infrared (MIR) suggest a difference in composition between laboratory analogs and Titan’s aerosols [9, 10]. These discrepancies in the refractive indices of solids can originate from their morphological and chemical properties. Indeed, numerous experimental studies have revealed the variability in the morphology and chemical composition of solid analogs formed in simulations of Titan's atmospheric chemistry