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Structure factor of fractal aggregates based on pair correlation modeling : comparison with current modeling and impacts
No full textInternational audienceThe characterization of nanoparticle aerosols is of vital importance for many applications, such as nanomaterials synthesis, aircraft engine emissions, pollution, climate change and health impact. Optical techniques based on light scattering have the great advantage of being sensitive, in-situ and capable of covering spatial scales ranging from a few millimeters to a few kilometers. The processing of these collected signals is often based on Mie theory, but it is well known that this is not suitable for fractal aggregates such as soot and black carbon. Cross-sections can be evaluated numerically using T-matrix or DDA approaches, but they are computationally expensive. To overcome these constraints and enable real-time analysis, approximate models that take account of the fractal nature have been developed to directly interpret scattering patterns (Rayleigh Debye Gans theory for fractal aggregates for static light scattering in the visible range, Beaucage unified model [1] for small-angle X-ray scattering (SAXS), both constructed in q reciprocal space). Both models establish a link between size and morphology via Guinier and Porod regimes, which can be repeated at different scales for SAXS measurements (e.g. primary spheres and aggregates for mass fractal aggregates, as is the case in the present study). However, by definition, the scattered signal corresponds to the Fourier transform of the pair correlation of the particles [2], allowing an alternative model based on the pair correlation function itself [3]. This approach has recently been demonstrated to cover polydisperse aggregates composed of any number of primary spheres, providing a theoretical decomposition of the scaling originally proposed by Beaucage. In the present study, we aim at comparing the two modeling approaches and explore the impact of the parameters of the analytical pair correlation model on the scattering structure factor. We will study the extent to which the nature of the aggregates can affect the Porod regime at large q and potentially affect the measurement of the primary sphere size distribution with conventional approaches. To this end, both approaches are applied to SAXS data of soot particles in a laminar ethylene diffusion flame measured at the European Synchrotron Radiation Facility (ESRF) [4] and processed via Abel inversion.[1] Beaucage, G. and Schaefer, D.W, Journal of non-crystalline solids, 172, 797–805 (1994).[2] Sorensen, C.M, JAerosol Science & Technology, 35, 648–687 (2001).[3] Yon, J. and Morán, J. and Ouf, F-X and Mazur, M. and Mitchell, J.B, Journal of Aerosol Science, 151, 105627 (2021).[4] T. Narayanan, M. Sztucki, T. Zinn, J. Kieffer, A. Homs-Puron, J. Gorini, P. Van Vaerenbergh and P. Boesecke, J.Appl. Cryst., 55, 98 (2022)
Apport de l’analyse thermique au suivi du vieillissement de films polymeres pour applications ballons stratospheriques
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Performance Assessment of Counter-Drone Systems using Bayesian Networks
No full textInternational audienceThis paper proposes a method to model and analyze the performance of a Counter-Drone System (CDS) using Bayesian Networks (BN). Quantitative performance indexes related to the sensor and tracking algorithm used in the CDS are proposed. They are used in a BN which also accounts for CDS functions related to alert, localization and engagement of neutralization means. A case study is proposed to illustrate how performance of the CDS can be evaluated under various scenario conditions, including different types of drones and influences of the environment. To illustrate how BN can also help for design considerations of a CDS, influence of the sensor location is also analyzed
Extension de CBBA par intercession d'offre pour favoriser l'initiative mixte
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The SPHERE infrared survey for exoplanets (SHINE): IV. Complete observations, data reduction and analysis, detection performances, and final results
No full textInternational audienceContext. Over the past decade, large surveys with state-of-the-art planet-finder instruments such as Spectro-Polarimetric High-contrast Exoplanet REsearch on board Very Large Telescope (SPHERE@VLT), coupled with coronagraphic devices and extreme adaptive optics (AO) systems, have unveiled around 20 planetary mass companions at a semi-major axis greater than 10 astronomical units (au). Since direct imaging is the only detection technique with the ability to probe this outer region of planetary systems, the SPHERE infrared survey for exoplanets (SHINE) was designed and conducted from 2015 to 2021 to study the demographics of such young gas giant planets around 400 young nearby solar-type stars. The analysis of the first part of the survey focused on 150 stars (SHINE F150) was already published in a series of papers in 2021. An additional filler campaign called snapSHINE was conducted to acquire second epoch data, using shallow observations. Aims. In this paper, we present the observing strategy, data quality, and point source analysis of the full SHINE statistical sample as well as snapSHINE. Methods. Both surveys used the SPHERE@VLT instrument with the IRDIS dual band imager in conjunction with the integral field spectrograph (IFS) and the angular differential imaging observing technique. All SHINE data (650 datasets), corresponding to 400 stars, including the targets of the F150 survey, are processed in a uniform manner, with an advanced post-processing algorithm called PACO ASDI. An emphasis is put on the classification and identification of the most promising candidate companions. Results. Compared to the previous early analysis SHINE F150, the use of advanced post-processing techniques significantly improved the contrast detection limits by one or two magnitudes (x3-x6), which will allow us to put even tighter constraints on the radial distribution of young gas giants. This increased sensitivity directly sets SHINE apart as the largest and deepest direct imaging survey ever conducted. We detected and classified more than 3500 physical sources. One additional substellar companion was confirmed during the second phase of the survey (HIP 74865 B) and several new promising candidate companions are awaiting follow-up epoch confirmations
Investigation of perovskite solar cells stability under vacuum and AM0 exposure with in situ measurements
No full textInternational audienceAs the new space revolution unfolds, the need for cost-effective space photovoltaics is growing. In this context, alternative solar technologies, in particular, perovskites, are gaining attention since they hold promises of price competitiveness, high specific power, and compatibility with rollable/foldable solar arrays. However, strong R&D effort remains before perovskites can effectively power a space mission; for instance, better understanding of space constraints related degradation modes is of utmost importance. In that sense, while much literature is investigating perovskite solar cells’ radiation hardness against various spectra of electrons and protons, far fewer are tackling the topic of vacuum impact, which remains a major constraint in this environment. In this work, we focus on four perovskite cell architectures, three bare cells and one encapsulated, and quantify their behavior against AM0/dark and air/vacuum sequences using in situ Voc monitoring. Those observations are confronted with existing literature hypotheses, and possible vacuum-related perovskite solar cell degradation mechanisms are discussed
Worst-Case Finite-Frequency H 2 -Norm Analysis of Uncertain Linear Systems
No full textInternational audienceThe H 2 norm is a fundamental design metric in many control applications and it is therefore important to evaluate how it is affected by uncertainties in the model. In the space domain, the H 2 norm is particularly significant when the Pointing Error Source (PES) of a satellite can be approximated by a white noise, which is often the case for microvibrations and acoustic disturbances. The present paper discusses a new method to identify a set of real parametric uncertainties which maximizes (resp. minimizes) the finite-frequency H 2 norm of an uncertain Multiple-Input Multiple-Output (MIMO) linear system. To do so, the analytical expression of the finite-frequency H 2 norm is first approximated as a sum of contributions on a discrete frequency grid. A constrained nonlinear optimization is then performed to maximize (resp. minimize) the so-obtained function. The proposed worst-case finite-frequency H 2 -norm analysis paves the way to a wide range of possible applications, specially when integrated into the Verification and Validation (V&V) process of space missions requiring high pointing performances. The theoretical results derived in the paper are implemented and successfully tested on models of increasing complexity
Analyse des performances et charges du rotor UH-60A à grand paramètre d'avancement avec des méthodes rapides
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Covariance Fitting Interferometric Phase Linking: Modular Framework and Optimization Algorithms
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A finite element-based simulation of the microstructure evolution through a 3D finite strain Cosserat-phase-field model
No full textInternational audienceThis paper proposes a computational framework for microstructure evolution in three dimensions by coupling large deformation Cosserat isotropic hyperelasticity with a phase-field model to take into account grain boundary motion. At the microscale level, each material point has an associated crystal lattice orientation described through the Cosserat micro-rotation to which a parametrization has been assigned to tackle all possible singularities. Discretization by finite elements leads to a strongly nonlinear, coupled system that can be resolved using the classic Newton-Raphson method. In order to reduce computation time and effort, a parallel computing mechanism based on domain decomposition is adopted. To avoid the ill-conditioning inherent to the monolithic coupled system, an iterative staggered scheme was implemented to solve the approximate problem, whose convergence is achieved by setting a fixed point criterion characterized by stagnation of the phase-field variable