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From plasma to quantum: the journey of nanodiamonds with color centers
No full textInternational audienceDiamond, a solid composed of carbon atoms, is an extremely interesting material for its technological and scientific applications, including those in nuclear physics and power electronics. Recent progress in controlling diamond synthesis has made it possible to produce very pure crystals and to incorporate and control atomic impurities and carbon vacancies in the crystal lattice. The appropriate impurity-vacancy combinations can give rise to special defects known as color centers, such as the nitrogen-vacancy (NV) or the silicon-vacancy (SiV), which exhibit exceptional quantum properties with spins that are optically addressable. The use of diamond containing color centers has paved the way for the development of innovative quantum technologies, such as very high-resolution magnetometry and quantum information processing [1-3]. Nevertheless, the development of quantum sensors at the nanometric scale remains one of the most interesting challenges. In this context, the development of a reliable nanoparticle synthesis technique that allows the desired defects to be incorporated and their quantum optical properties to be modulated is crucial. In this seminar, an efficient and recent method to produce diamond nanoparticles containing NV, SiV and germanium-vacancy (GeV) centers is proposed through direct plasma assisted chemical vapour deposition (CVD) growth [4, 5]. This technique allows good control of both nanoparticle growth processes and color centers formation. The optimization of the CVD nanodiamond growth process is presented, showing the impact of different plasma parameters and gas phase composition on nanoparticle crystallinity, size and shape. Morphological characterizations reveal the production of small (around 100 nm) and well faceted nanodiamond particles. In addition, the SiV and GeV color centers incorporation can be tuned within this material by varying the gas phase composition which emphasizes the high flexibility of the CVD growth technique. Finally, the quantum properties of the incorporated color centers have been successfully investigated under extreme pressure conditions (up to ~ 180 GPa) showing a monotonic blue shift of their optical zero-phonon line. Since their luminescence remains stable, SiV and GeV centers emerge as high-pressure nanosensors [6]. References[1] G. Villaret, L. Mayer, M. Schmidt, S. Magaletti, M. De Feudis, M. Markham, A. Edmonds, J.-F. Roch, T. Debuisschert, Applied Physics Letters 122, 194001 (2023).[2] A. Hilberer, L. Toraille, C. Dailledouze, M.-P. Adam, L. Hanlon, G. Weck, M. Schmidt, P. Loubeyre, J.-F. Roch, Physical Review B 107, L220102 (2023).[3] M. Pompili, S. L. N. Hermans, S. Baier, H. K. C. Beukers, P. C. Humphreys, R. N. Schouten, R. F. L. Vermeulen, M. J. Tiggelman, L. dos Santos Martins, B. Dirkse, S. Wehner, R. Hanson, Science 372, 259–264 (2021).[4] M. De Feudis, A. Tallaire, L. Nicolas, O. Brinza, P. Goldner, G. Hétet, F. Bénédic, J. Achard, Advanced Materials Interfaces 7, 1901408 (2019).[5] A. Tallaire, O. Brinza, M. De Feudis, A. Ferrier, N. Touati, L. Binet, L. Nicolas, T. Delord, G. Hétet, T. Herzig, S. Pezzagna, P. Goldner, J. Achard, ACS Applied Nano Materials 2, 5952 (2019).[6] B. Vindolet, M.-P. Adam , L. Toraille, M. Chipaux, A. Hilberer, G. Dupuy, L. Razinkovas, A. Alkauskas, G. Thiering, A. Gali, M. De Feudis, M. W. Ngandeu Ngambou, J. Achard, A. Tallaire, M. Schmidt, C. Becher, J.-F. Roch, Physical Review B 106, 214109 (2022)
The golden age of solar magnetography at Paris-Meudon observatory in the second half of the twentieth century
No full textThis paper describes advances in solar magnetography and developments in instrumental techniques of polarimetry and spectroscopy made at Paris-Meudon observatory in the second half of the twentieth century. The adventure started from Lyot expertise and extended progressively to the measurement of vector magnetic fields using various and improving polarimetric techniques (such as beam exchange or grid) or new spectroscopic methods (such as the MSDP imaging slicer), at Meudon and Pic du Midi, ending by the achievement of the state-of-the-art optimized and polarization free telescope THEMIS in 1999
UN DISPOSITIF À TROIS NIVEAUX POUR LA FORMATION EN MATHÉMATIQUES ET TECHNOLOGIES NUMÉRIQUES : VERS UNE THÉORIE DES SITUATIONS DIDACTIQUES CURRICULAIRE ET SYSTÉMIQUE
No full textInternational audienceThis paper proposes an extension of the Theory of Didactic Situations (TDS) to the domain of curricular teacher education, through the design and implementation of a three-level professional development system involving trainers, teachers, and students. Anchored in a geometric task and structured through the Lesson Study approach, the framework facilitates the analysis of knowledge circulation across embedded didactic environments. The study is grounded in the DAaT-DP theoretical model (Double Approach Adapted to Technologies for Professional Development), which articulates systemic and local tensions within training processes. It shows how key TDS concepts—such as milieu, didactic contract, devolution, and institutionalization—are recontextualized to support the professional learning of both teachers and teacher educators in digital mathematics education.Cette communication propose une extension de la Théorie des Situations Didactiques (TSD) au champ de la formation curriculaire, à partir d'un dispositif à trois niveaux articulant formateurs, enseignants et élèves. Fondé sur une tâche géométrique et structuré par des Lesson Study, ce dispositif permet d'observer la circulation des savoirs dans des milieux didactiques emboîtés. L'analyse repose sur le cadre original DAaT-DP (Double Approche Adaptée aux Technologies pour le Développement Professionnel) et montre comment les concepts de la TSD sont réinvestis dans la formation à enseigner et à former
A panchromatic view of N2CLS GOODS-N: The evolution of the dust cosmic density since z ∼ 7
No full textInternational audienceTo understand early star formation, it is essential to determine the dust mass budget of high-redshift galaxies. Sub-millimeter rest-frame emission, dominated by cold dust, is an unbiased tracer of dust mass. The New IRAM KID Arrays 2 (NIKA2) conducted a deep blank field survey at 1.2 and 2.0 mm in the GOODS-N field as part of the NIKA2 Cosmological Legacy Survey (N2CLS), detecting 65 sources with S/N ≥ 4.2. Thanks to a dedicated interferometric program with NOEMA and other high-angular resolution data, we identified the multi-wavelength counterparts of these sources and resolved them into 71 individual galaxies. We built detailed spectral energy distributions (SEDs) and assigned a redshift to 68 of them over the range 0.6 < z < 7.2. We fit these SEDs using modified blackbody and Draine & Li (2007, ApJ, 657, 810) models and the panchromatic approaches MAGPHYS, CIGALE, and SED3FIT, thus deriving their dust mass (Mdust), infrared luminosity (LIR), and stellar mass (M⋆). Eight galaxies require an active galactic nucleus torus component, and another six require an unextinguished young stellar population. A significant fraction of our galaxies are classified as starbursts based on their position on the M⋆ versus star formation rate plane or their depletion timescales. We computed the dust mass function in three redshift bins (1.6 < z ≤ 2.4, 2.4 < z ≤ 4.2 and 4.2 < z ≤ 7.2) and determined the Schechter function that best describes it. The dust cosmic density, ρdust, increases by at least an order of magnitude from z ∼ 7 to z ∼ 1.5, as predicted by theoretical works. At lower redshifts, the evolution flattens. Nonetheless, significant differences exist between results obtained with different selections and methods. The superb GOODS-N data set enabled a systematic investigation into the dust properties of distant galaxies. N2CLS holds promise for combining these deep field findings with the wide COSMOS field into a self-consistent analysis of dust in galaxies both near and far
Building without income mixing: Public housing quotas in France
No full textWe study the effects of the SRU law introduced in France in December 2000 to support scattered development of public housing in cities and favor social mixity. This law imposes 20% of public dwellings to all medium and large municipalities of large-enough cities, with fees for those not abiding by the law. Using exhaustive fiscal data, we evaluate the effects of the law over the 1996-2008 period using a difference-in-differences approach at the municipality and neighborhood levels. We find that the law stimulated public housing construction in treated municipalities, but only slightly increased the presence of low-income households. Indeed, new public dwellings enter categories to which medium-income are eligible and most additional occupants are not poor. Within municipalities, the policy decreased public housing segregation but it barely decreased low-income segregation. This comes from local authorities increasing over time the presence of public dwellings in neighborhoods away from existing public housing but in places concentrating low-income households
Territoires délaissés : table ronde [avec Y. Amsellem-Mainguy, B. Coquard, E. Guéraut, V. Sala Pala et F. Vincent ; propos recueillis par V. Béal, R. Epstein, T. Kirszbaum et S. Zappi]
No full textTable ronde avec Yaëlle Amsellem-Mainguy, Benoît Coquard, Elie Guéraut, Valérie Sala Pala et Fanny Vincent Propos recueillis par Vincent Béal, Renaud Epstein, Thomas Kirszbaum et Sylvia ZappiTable ronde avec Yaëlle Amsellem-Mainguy, Benoît Coquard, Elie Guéraut, Valérie Sala Pala et Fanny Vincent / propos recueillis par Vincent Béal, Renaud Epstein, Thomas Kirszbaum et Sylvia Zappi , Mouvements, 13/01/2025International audiencehttps://mouvements.info/table-ronde-territoires-delaisses/ Pour accompagner la publication du dossier « Politiques des territoires délaissées », Mouvements a organisé une table ronde avec cinq chercheurs et chercheuses qui ont investi différents types de territoires délaissés au fil de leurs parcours personnels et de leurs travaux scientifiques. Yaëlle Amsellem-Mainguy, Benoît Coquard, Elie Guéraut, Valérie Sala Pala et Fanny Vincent débattent de cette notion de « territoires délaissés » et des enjeux qu’elle recouvre
Quasi-Thermal Noise Spectroscopy in Magnetized Space Plasma: Theory and Model
No full textCaSciModOT federation at the Centre deCalcul Scientifique in the Centre‐Val deLoire region, France.International audienceThe quasi-thermal noise measured by an electric antenna is routinely used to characterize space plasmas, mainly measuring the electrons' properties. To employ this diagnostic technique, instrumental models are required to turn the instrumental output into physically meaningful measurements. Such models have been developed mainly under the assumption that no magnetic field is present in the plasma. This limit case is not met in planetary magnetospheres, for example, Earth, Mercury. The latter is the objective of the European Space Agency/Japan Aerospace Exploration Agency BepiColombo mission, that has a dedicated quasi-thermal noise experiment. The aim of this work is to extend the current state-of-the-art in quasi-thermal noise modeling by taking into account the magnetic field, therefore providing a plasma diagnostic in this magnetized regime. To achieve this goal, we developed a model for the quasi-thermal noise in a magnetized plasma. We explore four cases: for a Maxwellian and double Maxwellian electron distributions, both in the collisionless limit and in the presence of weak electron-neutral collisions. Our model is validated against known behaviors of the magnetized quasi-thermal noise spectrum, including: the characteristic frequency of maxima and minima, the modulation from the antenna spinning around the magnetic field, the electron temperature(s) influence. We explored parameter ranges that were not accessible to previous quasi-thermal noise models, in particular the high magnetization regime. The model we developed will enable using quasi-thermal noise experiments for the diagnostic of magnetospheric space plasmas, including but not limited to the Hermean and terrestrial magnetospheres, with foreseen applications to future space missions
Euclid Quick Data Release (Q1): VIS processing and data products
No full textInternational audienceThis paper describes the VIS Processing Function (VIS PF) of the Euclid ground segment pipeline, which processes and calibrates raw data from the VIS camera. We present the algorithms used in each processing element, along with a description of the on-orbit performance of VIS PF, based on Performance Verification (PV) and Q1 data. We demonstrate that the principal performance metrics (image quality, astrometric accuracy, photometric calibration) are within pre-launch specifications. The image-to-image photometric scatter is less than , and absolute astrometric accuracy compared to Gaia is mas Image quality is stable over all Q1 images with a full width at half maximum (FWHM) of . The stacked images (combining four nominal and two short exposures) reach (, measured as the variance of diameter apertures). We also describe quality control metrics provided with each image, and an appendix provides a detailed description of the provided data products. The excellent quality of these images demonstrates the immense potential of Euclid VIS data for weak lensing. VIS data, covering most of the extragalactic sky, will provide a lasting high-resolution atlas of the Universe
Euclid Quick Data Release (Q1). NIR processing and data products
No full textInternational audienceThis paper describes the near-infrared processing function (NIR PF) that processes near-infrared images from the Near-Infrared Spectrometer and Photometer (NISP) instrument onboard the Euclid satellite. NIR PF consists of three main components: (i) a common pre-processing stage for both photometric (NIR) and spectroscopic (SIR) data to remove instrumental effects; (ii) astrometric and photometric calibration of NIR data, along with catalogue extraction; and (iii) resampling and stacking. The necessary calibration products are generated using dedicated pipelines that process observations from both the early performance verification (PV) phase in 2023 and the nominal survey operations. After outlining the pipeline's structure and algorithms, we demonstrate its application to Euclid Q1 images. For Q1, we achieve an astrometric accuracy of 9-15 mas, a relative photometric accuracy of 5 mmag, and an absolute flux calibration limited by the 1% uncertainty of the Hubble Space Telescope (HST) CALSPEC database. We characterise the point-spread function (PSF) that we find very stable across the focal plane, and we discuss current limitations of NIR PF that will be improved upon for future data releases
Video-Based Analysis of the Mechanical Design Process in a Student Dyadic Activity
No full textInternational audienceThe aim of this study is to rationalize the dyadic collaborative design activity of students. It explores the characteristics of the process underway in a mechanical design activity, from the point of view of the nature of actions initiated and external representations mobilized. This work is based on video recordings of the collaborative activity of six dyads of students engaged in designing solutions to improve an existing mechanical system. The workspace of each dyad is filmed by a camera and synchronized with the capture of the modelling actions on the dyads’ computer screens. The coding of the video recordings is, on the one hand, based on the characteristics of the external representations used. On the other hand, it is inspired a priori by the micro-strategies defined by Purcell et al. [1] and adopted by Gero and McNeil [2]. The identified categories of actions are enriched a posteriori by anchoring them to the data. By implementing the cSPADE algorithm to search for patterns, our study was able to identify the most frequent sequences of action categories and the most frequent sequences of mobilized external representations. In addition, a CBA classification algorithm makes it possible to detect which external representations are most frequently mobilized to support which categories of actions. These results therefore help to initiate a characterization of the design activity under study