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Low Cost Quasi Gauss-Newton Algorithm Implementation for 2D ML-DoA Estimation using a Sparse Representation of Array Covariance
No full textInternational audienceMaximum Likelihood (ML) Direction-of-Arrival (DoA) estimation on the Vectorized Covariance Matrix Model (VCMM) exhibits enhanced performances. However, its implementation remains challenging as highly non-convex multidimensional optimization is required. To mitigates this, we recently propose to employ a sparse estimator for which we shown equivalence with the ML after a pre-whitening transform. Nevertheless, the sparse estimator yields an intricate objective function whose optimization is restricted to first-order methods such as the Forward-Backward Splitting (FBS) algorithm. The high correlation between the dictionary matrix vectors leads to slow convergence and thereby refrains the estimator practical use.To tackle this issue, the pre-whitening transform benefits are leveraged using a variable stepsize algorithm. The transform is shown to significantly improve the stepsize by decorrelating the dictionary matrix vectors in the sources directions and thus, yielding consequent acceleration. Furthermore, the last iterations of the algorithm are shown to be equivalent with a more computationally demanding second-order algorithm.Numerical simulations confirm the predicted speed improvements in the case of 2D DoA estimation
Pratiques enseignantes dans un contexte interdisciplinaire en sciences.
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Analyse de séances conçues dans le cadre d’un dispositif de formation portant sur l’usage de l’histoire des mathématiques à l’école primaire
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Evidence for a sub-Jovian planet in the young TWA 7 disk
No full textInternational audiencePlanets are thought to form from dust and gas in protoplanetary disks, with debris disks being the remnants of planet formation. Aged a few million up to a few billion years, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies1,2. Tens of debris disks, with sizes of tens, sometimes hundreds, of astronomical units have been resolved with high-spatial-resolution, high-contrast imagers at optical and near-infrared or (sub)millimetre interferometers3,4. They commonly show cavities, ring-like structures and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals2,5. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2–10 MJ) of high-contrast imaging instruments (see, for example, refs. 6,7,8,9) before the James Webb Space Telescope. Here we have used the unprecedented sensitivity of the James Webb Space Telescope’s Mid-Infrared Instrument10,11 in the thermal infrared to search for such planets in the disk of the approximately 6.4-Myr-old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arcsec from the star, which is best interpreted as a cold, sub-Jupiter-mass planet. Its estimated mass (about 0.3 MJ) and position (about 52 au, de-projected) can thoroughly account for the main disk structures
Recent Evolution of the Northern Caribbean Plate Boundary Insights from Seismic Reflection Data from the Northern Hispaniola Margin
No full textInternational audienceThe northern margin of Hispaniola is characterised by a complex morpho-structure shaped by the interplay of geodynamic, tectonic, and sedimentary processes. The Haiti Seismic Investigation (HAITISIS) of the northern Caribbean plate boundary reveals evidence of oblique convergence. It elucidates the relationships among fault-driven tectonic activity, seafloor morphology, and the effects of transpressional deformation. The markedly different morpho-structural characteristics of the seafloor and sedimentation patterns in the Eastern and Western domains of the northern Hispaniola margin originated during the Upper Miocene-Pliocene tectonic reorganisation of the northern Caribbean Plate boundary. This regional reorganisation is associated with the onset of the oblique collision between the Caribbean and North American Plates that carried Hispaniola to the transpressive plate boundary opposite the Bahamas Carbonate Platform. This tectonic process led to the formation of an accretionary prism and activated segments of the eastern strand of the Septentrional-Oriente Fault Zone (SOFZ), resulting in lateral sediment source displacements and influencing sedimentary infill and deformation patterns. A mass transport deposit (MTD) in the Eastern domain is thought to have formed during this period of tectonic instability. Differential compaction and remobilisation of recent seismic units caused by the MTD have influenced the seafloor morphology of the Eastern domain. The MTD is absent in the Western domain, as are the canyons found in the Eastern domain. Our interpretation of the early Miocene initiation of the SOFZ and its evolution differs from previous studies that assume continuous eastward propagation. Morphologic features, such as the lateral displacement of canyons, provide a chronology for the development of strike-slip and thrust faults prior to the initiation of the SOFZ.
1D modelling of pegmatite migration
No full textInternational audiencePegmatites and rare metal granites are granitic igneous rocks distinguished by their texture, which is dominated by crystal growth. These rocks are frequently enriched in rare elements (e.g., Li, Cs, Be, Nb, Ta) and represent economically significant deposits, classified among the critical raw materials identified by the European Commission. Our objective is to better constrain the tectonic parameters that govern the emplacement of pegmatites within the continental crust, including their migration rates and durations, with a particular emphasis on the role of temperature in these crustal migration processes. To model those fluid migrations, two-phase flow in Julia, based on porosity waves with compressible fluid is used. The porosity is interpreted as melt [1]. To improve the yet existing codes [2], we implement temperature in our two phase flow formulation from energy conservation. Temperature allow a thermomechanical coupling with rock viscosity. A first equation with a simple exponential coupling is used to understand thermal implication on viscosities. The model represents a continental crust with partial melting occurring within the lowermost 5 km, where temperature is maintained at 750°C due to underplating. A constant geothermal gradient is applied from this depth to the surface. A 10% porosity anomaly is introduced in the partially molten zone, while a baseline porosity of 1% is applied throughout the model to ensure numerical stability. The fluid viscosity is set at 10^4 Pa.s, while at 750°C, the rock viscosity is 10^16 Pa.s. A constant permeability of 10^-11 m² is applied throughout the model. Thermomechanical couplings of varying strength are implemented to assess their impact on migration processes. Accordingly, the rock viscosity at 450°C is varied between 10^16Pa.s and 10^21 Pa.s.Models reveals two distinct mechanisms that halt migration. The first occurs when the thermomechanical coupling is low (soft and hot crust). Allowing rock viscosity to remain low, so melt migration can outpace thermal diffusivity. Enabling the melt to be in an undercooling state. This means that the magma can migrate beyond the point at which the surrounding rock reaches the crystallization temperature of the melt, a necessary condition for pegmatite formation. The second case arises when thermomechanical coupling is strong, causing the surrounding rock's viscosity to become too high for the magma to reach undercooling condition. In this scenario, the magma crystallizes as soon as it reaches the surrounding rock at its crystallization temperature, potentially becoming trapped by a viscous layer (of different or colder nature).The use of a geothermal gradient more representative of a metamorphic core complex, along with an improved thermomechanical coupling, should refine the estimates of migration time and distance. Similarly, the introduction of viscous heterogeneity would help highlight the geological structures that may or may not facilitate the migration of these magmas to shallower levels of the crust. References:[1] L. Räss, T. Duretz & Y.Y. Podladchikov (2020). https://doi.org/10.1093/gji/ggz239[2] A. Plunder & al. (2022). https://doi.org/10.1016/j.lithos.2022.10665
Extreme flood event and their depositonal signatures: the case of the Storm Alex in the Roya Valley
No full textInternational audienceThis study examines sedimentary deposits from Storm Alex (2 October 2020) in the Roya Valley, focusing on three different sub-valley (Dente, Consciente and Caïros) to understand flow processes and associated lithofacies. Key factors controlling sediment transport include lithology, slope, and sediment supply, which influence the occurrence of bedload, suspension, or debris flows. A notable ~5 wt% difference in fines (clay + silt) was observed between debris flows in the Dente sub-valley and bedload/hyperconcentrated flows in other areas.In the Dente, extensive reworking of glacial and colluvial deposits triggered debris flows that transitioned into hyperconcentrated and bedload flows, culminating in sheetflood deposits on the Viévola fan. The Consciente sub-valley exhibited bedload and hyperconcentrated flows, with debris flows linked to lateral inputs from landslides. The Caïros sub-valley, characterised by gentler slopes and a wider valley floor, was dominated by bedload processes with localized debris flows originating from right-bank tributaries or natural dams.Hydraulic reconstructions using empirical discharge, unit stream power, shear stress, and clast size estimates provided insights into event intensity, offering valuable reference points for understanding extreme hydro-sedimentary events. Spatial and temporal variability was significant, highlighting the challenges in interpreting fossil deposits without precise temporal context, since a single extreme rainfall event (>1000-year return period) produced a wide range of facies.This case study underscores the complexity of flow transitions (debris flows to bedload) and the importance of lithological and topographic constraints. The findings emphasize the value of interdisciplinary, multi-scale approaches in documenting and understanding extreme hydro-sedimentary events in mountainous region
Confinement determines transport of a reaction-diffusion active matter front
No full textInternational audienceCouplings between biochemical and mechanical processes have a profound impact on embryonic development. However, in-vitro studies capable of quantifying these interactions have remained elusive. Here, we investigate a synthetic system where a DNA reaction-diffusion (RD) front is advected by a turbulent flow generated by active matter (AM) flows in a quasi-one-dimensional geometry. Whereas the dynamics of simple RD fronts solely depend on the reaction and diffusion rates, we show that RD-AM front propagation is also influenced by the confinement geometry. We first experimentally dissected the different components of the reaction-diffusion-advection process by knocking out reaction or advection and observed how RD-AM allows for faster transport over large distances, avoiding dilution. We then show how confinement impacts active matter flow: while changes in instantaneous flow velocities are small; correlation times are dramatically increased with decreasing confinement. As a result, RD-AM front speed increased 3 to 9-fold compared to a RD one. This RD-AM experimental model provides a framework for the rational engineering of complex spatiotemporal processes observed in living systems. It will reinforce our understanding of how macro-scale patterns and structures emerge from microscopic components in non-equilibrium systems
Detection of an orthogonal alignment between parsec scale AGN jets and their host galaxies
No full textInternational audienceThe relationship between galaxies and their supermassive black holes (SMBHs) is an area of active research. One way to investigate this is to compare parsec-scale jets formed by SMBHs with the projected shape of their kiloparsec-scale host galaxies. We analyse Very Long Baseline Interferometry (VLBI) images of Active Galactic Nuclei (AGN) and optical images of their host galaxies. We compare the inner-jet position angle in VLBI-detected radio sources with the optical shapes of galaxies as measured by several large optical surveys. In total 6273 galaxy-AGN pairs were found. We carefully account for the systematics of the cross-matched sources and find that Dark Energy Spectroscopic Instrument Legacy Imaging Surveys data (DESI LS) is significantly less affected by them. Using DESI LS, with which 5853 galaxy-AGN pairs were cross-matched, we find a weak but significant alignment signal (with a p-value 0.01) between the parsec-scale AGN jet and the kpc projected minor axis of the optical host galaxy in sources with measured spectroscopic redshifts. Our results show that the observed source properties are connected over 3 orders of magnitude in scale. This points towards an intimate connection between the SMBH, their host galaxies and their subsequent evolution
Techno-solutionism and sustainable development: the activity analysis as a way of reintroducing the primacy of the “Living” over technology. Proceedings of the 22nd triennial congress of the international ergonomics association
No full textInternational audienceThis contribution challenges the techno-solutionism that dominates public policies for sustainable development. A cross-discussion of two sectors studied in the field of constructive ergonomics provides a better understanding of the - non-automatic - link between technological solutions, appropriation pro- cess and the transformation of activities to make them more sustainable