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Near-field imaging of local interference in radio interferometric data: Impact on the redshifted 21 cm power spectrum
No full textInternational audienceRadio-frequency interference (RFI) is a major systematic limitation in radio astronomy, particularly for science cases requiring high sensitivity, such as 21 cm cosmology. Traditionally, RFI is dealt with by identifying its signature in the dynamic spectra of visibility data and flagging strongly affected regions. However, for RFI sources that do not occupy narrow regions in the time-frequency space, such as persistent local RFI, modeling these sources could be essential to mitigating their impact. This paper introduces two methods for detecting and characterizing local RFI sources from radio interferometric visibilities: matched filtering and maximum a posteriori (MAP) imaging. These algorithms use the spherical wave equation to construct three-dimensional near-field image cubes of RFI intensity from the visibilities. The matched filter algorithm can generate normalized maps by cross-correlating the expected contributions from RFI sources with the observed visibilities, while the MAP method performs a regularized inversion of the visibility equation in the near field. We developed a full polarization simulation framework for RFI and demonstrated the methods on simulated observations of local RFI sources. The stability, speed, and errors introduced by these algorithms were investigated, and, as a demonstration, the algorithms were applied to a subset of NenuFAR observations to perform spatial, spectral, and temporal characterization of two local RFI sources. We used simulations to assess the impact of local RFI on images, the uv plane, and cylindrical power spectra, and to quantify the level of bias introduced by the algorithms in order to understand their implications for the estimated 21 cm power spectrum with radio interferometers. The near-field imaging and simulation codes are publicly available in the Python library nfis
Ordinal pattern-based mode decomposition: A new approach to time series analysis
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Non-thermal energy release in the post-impulsive phase of the May 9, 2021 event
No full textInternational audienceContext. In the standard model of solar flares, a magnetic flux rope erupts and gets ejected from the Sun. The current sheets that form in its wake are the seat of magnetic reconnection, which is thought to power energy release throughout the long-lasting decay phase of the thermal X-ray emission. This model has been broadly tested with plasma diagnostics at soft X-ray, EUV, and Hα wavelengths.Aims. The primary aim of the present investigation is to shed light on the acceleration of non-thermal electrons in the post-impulsive phase through hard X-ray (HXR) radiation and radio spectroscopic imaging at decimeter-to-meter wavelengths. We focus our study on the case of a C4.0 class flare on May 9, 2021.Methods. This event was fully observed by multiple instruments from three different vantage points in space. We analyzed the spectrum and the source configuration of X-ray emission with the Spectrometer-Telescope for Imaging X-rays (STIX) on board the Solar Orbiter spacecraft, complemented by the Gamma-Ray Burst Monitor (GBM) aboard the Fermi mission, and the radio emission with Nançay Radioheliograph (NRH) and the ORFEES spectrograph. The extreme ultraviolet images from both Solar TErrestrial RElations Observatory (STEREO-A) and Solar Dynamics Observatory (SDO) were applied to trace the evolution of thermal plasma and coronal magnetic structures.Results. The radio spectrum at decimeter-to-meter wavelengths shows broadband continuum emission (type IV burst), which is a well-known radio signature of time-extended electron acceleration in eruptive flares. Both moving and stationary radio sources were identified. Energetic electrons were observed in X-rays up to 20 keV, displaying a significant correlation with the time evolution of the stationary type IV radio burst during the long duration decay phase, which lasted over 50 minutes. The X-ray photon spectral index is relatively steep with a value of around – 7.5 and the integrated electron flux above 30 keV is on the order of 1.6 × 1032 electron s−1.Conclusions. This case study provides for the first time evidence that HXR emission accompanies the onset of a stationary type IV radio burst. It ties together several pieces of evidence to support that non-thermal electrons are released into large-scale magnetic flux ropes during the post-impulsive phase of eruptive solar flares. The energies of the non-thermal electrons inferred from the X-ray spectral analysis confirm indirect estimates from radio observations. Electron acceleration processes appear as a significant signature of post-impulsive energy release, with energies in the range from several to tens of kiloelectron volts (keV)
Phraséologie contrastive théorique et appliquée : phraséographie, phraséotraduction et phraséodidactique numériques (Préfaces du Prof. Jean Pruvost et du Prof. Alain Peyraube): Expressions idiomatiques en français et en chinois relatives au corps humain et aux animaux
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Prescription d’aide technique à la marche aux personnes âgées par les masseurs-kinésithérapeutes : apports de la didactique professionnelle
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Points de vue et perspectives, formation et recherche en sciences de la rééducation et réadaptation
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Strong impact of orally administered BCR4 defensin on aphid survival, embryo development and symbiotic cells in three Acyrthosiphon pisum parthenogenetic lines
No full textAbstract Aphids are major crop pests capable of colonizing the main plants grown for human consumption. They have specialized cells, the bacteriocytes, which house the obligatory symbionts Buchnera aphidicola that provide them with essential nutrients missing from their diet. Bacteriocyte-specific cysteine-rich peptides (BCRs) are encoded by a defensin gene family exclusively present in aphids and specifically expressed in bacteriocyte. One BCR family member, BCR4, has been shown to have insecticidal properties against the pea aphid, Acyrthosiphon pisum (Hemiptera: Aphididae). In the present study, we exposed the pea aphid to different doses of BCR4 and examined the impact on aphid survival, mass, anatomy, fecundity, as well as on bacterial symbiosis. As different pea aphid lines with various symbiotic status may be differently affected by stress, we investigated the effect of BCR4 ingestion on three different A. pisum lines: LL01 and YR2-amp, that are mono-infected with B. aphidicola , and YR2- Ri , that is genetically identical to YR2-amp but also contains the extracellular facultative symbionts Regiella insecticola . Our results show a strong dose-response effect of BCR4 on LL01 survival and a more moderate effect on both YR2 lines, while an impact on the mass was observed in the three lines. Histological analyses revealed severe embryonic developmental defects due to the treatment. Finally, BCR4 treatment reduced symbiont quantity, with B. aphidicola being more affected than R. insecticola . This study supports the idea that BCR4 could act as a key regulator of aphid symbiosis and development, and highlights its potential as a candidate bioinsecticide for pest control
Timing of Contractional Stress Propagation, From the Pyrenean Orogen to the Intraplate Domain, Evidenced by U‐Pb Dating of Syn‐Kinematic Calcite
No full textInternational audienceAbstract The Mediterranean region provides a natural laboratory for studying complex deformation resulting from body forces and interactions between the convergence of the Africa and Eurasia plates since the Cretaceous. These interactions led to the formation of a mosaic of basins and orogenic domains, whose intrinsically complex evolution over time is still subject to debate. Investigating the timing of deformation recorded on both sides of an orogen, and within the intraplate domain, links local‐scale processes to regional geodynamic events. This study combines microstructural analysis and U‐Pb dating of syn‐kinematic calcite with implications for the timing of contractional stress propagation in the Pyrenean orogen and the whole of western Europe. While many U‐Pb dating studies on syn‐kinematic calcite have been conducted in the western intraplate domain, the northern part of the Pyrenees remains to be investigated, and, therefore, a strategic study area. This study highlights (a) continuous deformation from ca. 48 Ma to 30 Ma, marking the phase of continental collision between Iberia and Eurasia and (b) a newly evidenced post‐orogenic Miocene deformation episode, spanning from ca. 16 to 11 Ma. (c) Through a comparison of U‐Pb geochronological data from syn‐kinematic calcite in the pro‐foreland basin and the intraplate domain, this study shows that deformation occurred simultaneously at the plate boundaries and within a large part of the intraplate domain of the overriding plate. These results provide insights into the geodynamic evolution of the Pyrenean orogen and its implications for Mediterranean geodynamics
The 1956 eruption of Bezymianny volcano (Kamchatka)—part I: petrological constraints on magma storage and eruptive dynamics
No full textInternational audienceBezymianny volcano (Kamchatka, Russia) is an andesitic island arc stratovolcano that started to erupt in 1955 after ~ 1000 years of dormancy. On March 30, 1956, the climactic phase of the eruption was preceded by a 4-month-long emplacement of a shallow cryptodome, which triggered a flank collapse violently decompressing the magma into a laterally directed blast followed by an explosive phase emplacing extensive pumice concentrated pyroclastic density currents (pumice C-PDC). Aiming at constraining the plumbing system below Bezymianny volcano prior to the 1956 eruption, we performed a multiphase textural and petrological study using dense to vesiculated clasts of the blast and pumice samples from the post-blast C-PDC deposits. We inferred the pressure and temperature conditions of magma storage using sample vesicularity, amphibole destabilization rims, volatile contents in melt inclusions, microlite textures, and phase compositions (phenocrysts, microlites, and glasses). We propose a three-level magma storage characterized by a deep reservoir (≥ 200–350 MPa, ≥ 840 °C, ~ 4.0–8.0 wt% H2O and CO2 up to 1500 ppm, where amphibole is stable), a shallow reservoir (50–100 MPa, 850–900 °C, 1.5–4.0 wt% H2O and CO2 < 250 ppm, where amphibole is unstable and quartz crystallizes) in which the pre-cryptodome magma resided and from which the post-blast pumiceous magma originated, and a subsurface cryptodome (< 25 MPa, ~ 900 °C, cristobalite crystallized) from which the blast was initiated. This plumbing system provides the framework for constraining the timescales of the 1956 eruptive dynamics (companion paper). The three-stage architecture proposed for the 1956 andesitic reservoir compares to the present-day plumbing system emitting mafic lavas, thus suggesting that the timescales of the eruptive dynamics (e.g., magma residence time and ascent rate) may be the key to determining evolved or mafic magmas