Un schéma centré pour l'hydrodynamique Lagrange bidimensionnelle

Dans ce rapport nous présentons un nouveau schéma numérique pour l'hydrodynamique Lagrange bidimensionnelle. Ce schéma colocatif est basé sur une formulation en energie totale. La vitesse des noeuds et le calcul des flux aux faces du maillage sont obtenus de manì ere cohérente par un solveur nodal. La construction de ce solveur repose sur les deux principes fondamentaux de conservation de la quantité de mouvement et d'inégalité en-tropique. Ce solveur s'interpr ete comme une extension bidimensionnelle du solveur acous-tique de Godunov. Les résultats numériques correspondants a des cas-tests représentatifs de l'hydrodynamique FCI montrent la robustesse et la précision de ce schéma

Detector Characterization of a Near-Infrared Discrete Avalanche Photodiode 5x5 Array for Astrophysical Observations

We present detector characterization of a state-of-the-art near-infrared (950nm - 1650 nm) Discrete Avalanche Photodiode detector (NIRDAPD) 5x5 array. We designed an experimental setup to characterize the NIRDAPD dark count rate, photon detection efficiency (PDE), and non-linearity. The NIRDAPD array was illuminated using a 1050 nm light-emitting diode (LED) as well as 980 nm, 1310 nm, and 1550 nm laser diodes. We find a dark count rate of 3.3x10$^6$ cps, saturation at 1.2x10$^8$ photons per second, a photon detection efficiency of 14.8% at 1050 nm, and pulse detection at 1 GHz. We characterized this NIRDAPD array for a future astrophysical program that will search for technosignatures and other fast (>1 Ghz) astrophysical transients as part of the Pulsed All-sky Near-infrared Optical Search for Extraterrestrial Intelligence (PANOSETI) project. The PANOSETI program will consist of an all-sky optical (350 - 800 nm) observatory capable of observing the entire northern hemisphere instantaneously and a wide-field NIR (950 - 1650 nm) component capable of drift scanning the entire sky in 230 clear nights. PANOSETI aims to be the first wide-field fast-time response near-infrared transient search.Comment: 8 pages, 7 figures, 1 tabl

Three-dimensional analysis of a tensile test on a propellant with digital volume correlation

International audienceA full three-dimensional study of a tensile test on a sample made of polymerbonded propellant is presented. The analysis combines different tools, namely, X-ray microtomography of an in situ experiment, image acquisition and treatment, 3D volume correlation to measure three-dimensional displacement fields. It allows for global and local strain analyses prior to and after the peak load. By studying the correlation residuals, it is also possible to analyze the damage activity during the experiment

In-situ X-ray tomographic monitoring of gypsum plaster setting

International audienceThe first in-situ monitoring of plaster hydration using X-ray tomography is reported in this paper. Dissolution of hemihydrate particles and formation of a network of gypsum needles can be observed in 3D. A 3D quantitative analysis based on the microstructure evolution allows the determination of the degree of reaction. In particular, the size of hemihydrate particles is shown to have an influence both on the hydration kinetics and on the final microstructure of the set plaster. This work paves the way to the understanding of the relationship between microstructure evolution, chemical degree of reaction and mechanical strength development for material processed through a setting reaction

Ice-Templating of Alumina Suspensions: Effect of Supercooling and Crystal Growth During the Initial Freezing Regime

International audienceWe investigate the ice-templating behavior of alumina suspensions by in situ X-ray radiography and tomography. We focus herein on the formation and structure of the transitional zone, occurring during the initial instants of freezing. For many applications, this zone is undesirable as the resulting porosity is heterogeneous in size, morphology, and orientation. We investigate the influence of the composition of alumina suspensions on the formation of the transitional zone. Alumina particles are dispersed by three different dispersants, in various quantities, or by hydrochloric acid. We show that the dimensions and the morphology of the transitional zone are determined by the growth of large dendritic ice-crystals growing in a supercooled state much faster than the cellular freezing front. When the freezing temperature decreases, the degree of supercooling increases. This results in an initial faster freezing front velocity and increase in the dimensions of the transitional zone. It is therefore possible to adjust the dimensions of the transitional zone by changing the composition of alumina suspensions. The counter-ion Na+ has the most dramatic effect on the freezing temperature of suspensions, yielding a predominance of cellular ice crystals instead of the usual lamellar crystals

Ice Shaping Properties, Similar to That of Antifreeze Proteins, of a Zirconium Acetate Complex

The control of the growth morphologies of ice crystals is a critical issue in fields as diverse as biomineralization, medicine, biology, civil or food engineering. Such control can be achieved through the ice-shaping properties of specific compounds. The development of synthetic ice-shaping compounds is inspired by the natural occurrence of such properties exhibited by antifreeze proteins. We reveal how a particular zirconium acetate complex is exhibiting ice-shaping properties very similar to that of antifreeze proteins, albeit being a radically different compound. We use these properties as a bioinspired approach to template unique faceted pores in cellular materials. These results suggest that ice-structuring properties are not exclusive to long organic molecules and should broaden the field of investigations and applications of such substances