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Three-dimensional deformations in single-layer antimonene and interaction with a Au(111) surface from first principles
No full textUsing density functional theory, we investigate the electronic structure of the alpha phase of an antimony monolayer in its isolated form and in contact to the (111) surface of gold. We demonstrate that the isolated single-layer actually displays a slightly modulated puckering that stabilizes the monolayer, not a uniform one as often assumed. Moreover, it has dramatic consequences on the electronic band structure: the material is a semiconductor with low-dispersing bands near the Brillouin zone center. By further application of about 12% strain on the armchair direction, a double-cone features develops wherein an electronic bandgap of about 21~meV is found. When in contact with a Au(111) surface, a strong interaction with gold arises, as it appears clearly from (i) substantial atomic displacements compared to the isolated form, and (ii) hybridization of Sb and Au orbitals. The latter profoundly modifies the electronic band structure by strengthening the spin-orbit splitting of hybridized bands and spoiling the double-cone feature whose manipulation through substrate-induced strain appears therefore questionable, at least in the simulated epitaxial implementation
Selective band engineering of Bi/Si(111) by boron segregation
No full textAtomically thin layers of metals deposited on semiconductors display a variety of physical properties such as superconductivity, charge density waves, topological phases, strong spin-orbit (Rashba) splitting, among others. To access these exotic phases and induce new ones, it is necessary to control and tune the energies of the electronic states of those heterostructures. In this work we investigate the engineering of the band structure of the two-dimensional Bi/Si(111) -phase using a modulation doping approach based on boron segregation at the surface. We demonstrate that the Bi-induced Rashba bands can be displaced in energy by up to 200 meV without altering their strong Rashba parameter. Importantly, while the Bi states shift upward, the underlying Si valence states remain essentially fixed, which rules out a simple band-bending scenario. Our density functional theory calculations reveal that the displacement originates from changes in the hybridization of Si states near the surface, induced by the presence of B atoms. This selective mechanism halves the distance of the Rashba-split states from the Fermi level, opening the way to their exploitation in transport and spintronic devices and highlighting the broader potential of modulation doping as a band-engineering strategy for two-dimensional metals on semiconductors
Sensitivity-based optimization of test configurations for parameters identification using full field measurements
No full textInternational audienceIn dynamic, the material properties are typically established through the implementation of testing methodologies based on homogeneous stress/strain states. Recent advances in optical technology have enabled the identification of dynamic material parameters through the use of full-field measurement and inverse methods. In this approach, the specimen design is crucial, as it must be sensitive to the various parameters to be identified. Different methodologies have been developed to optimize the geometry of the specimen based on the sensitivity of the material properties [1][2]. The primary limitation of these approaches is the calculation cost that strongly increases with the number of parameters. This cost becomes prohibitive when identifying complex non-linear laws, commonly used in dynamics. This work proposes an innovative method based on the use of surrogate models and high-performance computing to optimize a specimen geometry by its sensitivity to material parameters. In this purpose, a surrogate model based on a parametrized specimen geometry and its mechanical response is built. The configurations are then assessed through their sensitivity level, characterized by the covariance matrix of the displacement sensitivity to material parameters to be identified. Finally, the geometry is modified until the richness is considered sufficient for a robust material parameter identification
Étude numérique de l'influence de la géométrie et du jeu sur le comportement en matage d'un composite PRFC
No full textInternational audienceÉtude numérique de l'influence de la géométrie et du jeu sur le comportement en matage d'un composite PRF
Characterisation and modelling of interscale energy transfers in high-Reynolds boundary layers
No full textHigh-Reynolds effects of wall-bounded flows, involving interscale energy transfers between small and larges scales of turbulence within and between the inner and outer regions, challenge the classical description of the structure of these flows and the ensuing turbulence models. The two-scale Reynolds stress model recently proposed by Chedevergne et al. (2024) was able to reproduce the small and large scales contributions in turbulent channel flows that follows the scale separation performed by Lee & Moser (2019) by partitioning energy spectra at a given wavelength. However, the interscale interactions within the inner region were modelled in an ad hoc manner, but without physical relevance, making the two-scale RSM model less and less accurate for boundary layer applications as the Reynolds was increased. In this study, by re-analyzing DNS data from Lee & Moser (2019) with the objective of modelling these scale interactions, crucial observations on energy transfers between large and small scales could be made. In particular, the analysis reveals the important role played by the spanwise component of the Reynolds stress in the logarithmic region. From the analysis undertaken, a revisit version of the two-scale model was thus proposed, focusing efforts on interscale transfer modelling. The resulting model is then successfully tested on high-Reynolds number boundary layer configurations without pressure gradient, up to Re τ = 20000. The excellent agreement reflects the good prediction capabilities of the proposed model and, above all, the relevance of the modelling of the energy transfers within and between the inner and outer regions of wall-bounded flows
Spectrally multimode SU(1,1) interferometer operating in the sub-nanosecond regime and the 1.57/3.3µm range
No full textInternational audienceA non-linear interferometer is implemented using 1.57/3.3µm Spontaneous Parametric Down-conversion (SPDC) pumped by a 1.064µm sub-ns pulsed laser source. The interference pattern due to induced coherence is observed in the high gain regime and on the intensity of the signal spectrum
Numerical investigation of engine position effects on contrail formation and evolution in the near-field of a realistic aircraft configuration
No full textInternational audienceThe present study investigates the impact of engine position on contrail formation and near-field evolution in a realistic three-dimensional aircraft configuration. Detailed numerical simulations are conducted using a Reynolds-Averaged Navier-Stokes (RANS) approach coupled with mesh adaptation techniques. A Eulerian microphysical model is used to characterize contrail ice crystal properties and their evolution under varying dilution conditions. The setup is based on a Boeing 777-like geometry, including fuselage, wings, engines, and tailplane. Two microphysical activation scenarios are considered: one incorporating adsorption-based ice nucleation and the other assuming fully activated soot particles. The latter for two soot number emission indices. The dilution process and wake structure exhibit a strong dependence on engine placement, which significantly influences plume saturation. In highly diluted configurations, enhanced early-stage mixing reduces plume temperature and increases relative humidity, favoring the growth of larger ice crystals. Depending on the soot number concentration, vapor depletion effects may outweigh dilution-driven changes in water vapor availability. In adsorption-limited activation scenarios, increased dilution reduces the concentration of sulfur species, leading to a lower activation fraction and the formation of smaller ice crystals. Additionally, across the scenarios, the modified jet-vortex interaction alters particle distribution and their access to water vapor, further shaping their growth. These effects ultimately impact the contrail's optical properties, particularly its optical thickness
Comparaison des méthodes multi-échelles pour la modélisation de la plaque perforée dans les calculs de structures
No full textInternational audienceComparaison des méthodes multi-échelles pour la modélisation de la plaque perforée dans les calculs de structure
L'effet de la turbulence sur une aile flexible finie : forces, déflexions et tourbillon de bout d'aile
No full textInternational audienceThe impact of freestream turbulence (FST) on the aerodynamic performance of a flexible finite wing and the produced wingtip vortex was investigated. The wing had a NACA 4412 airfoil profile and the chord-based Reynolds number was 1.4×10^5. The experiments were conducted in a closed-loop wind tunnel with four different inflow turbulence intensities ( 0.2%, 3%, 8% and 13%) generated using an active turbulence grid. Force balance measurements revealed that increasing the scale of the FST increased the maximum lift and delayed stall. Digital image correlation (DIC) measured deflections of the wing’s structure. Spanwise bending was found to be the dominant deformation. While the wing vibrated at its natural frequency in all conditions, FST increased the amplitude of the vibrations. A similar spectral signature was observed in the lift force fluctuations as well. Stereoscopic particle image velocimetry measurements were obtained two chord lengths downstream of the trailing edge simultaneously with DIC. FST decreased the vortex strength, and marginally increased vortex diffusion and size. It also increased the vortex meandering amplitude, while reducing the meandering frequency band. For the cases with a turbulence intensity of 8% and 13%, the frequency of meandering and the wing’s vibration were similar and a phase relation between the two motions was observed. Proper orthogonal decomposition of the vortex (after removing meandering) and the subsequent velocity field reconstruction revealed temporal fluctuations in the vortex strength at the same frequency as the wing’s vibration. This was linked to the lift force fluctuations induced by the wing’s deformations.L'impact de la turbulence à écoulement libre (FST) générée par une grille de turbulence active sur les performances aérodynamiques d'une aile flexible finie et sur le tourbillon d'extrémité d'aile dans son sillage proche est étudié. L'aile a un profil NACA 4412 et le nombre de Reynolds basé sur la corde était de 1,4 × 10^5. Les expériences ont été menées dans une soufflerie en boucle fermée avec quatre intensités de turbulence différentes (0,2 %, 3 %, 8 % et 13 %) générées à l'aide d'une grille active. Les mesures de l'équilibre des forces ont révélé que l'augmentation de la FST augmentait la portance maximale et retardait le décrochage. La corrélation d'images numériques (DIC) a permis de mesurer les déformations de la structure de l'aile. La flexion dans le sens de la largeur s'est avérée être la déformation dominante. Bien que l'aile ait vibré à sa fréquence naturelle dans toutes les conditions, la FST a augmenté l'amplitude des vibrations. Une signature spectrale similaire a également été observée dans les fluctuations de la force de portance. Des mesures de vélocimétrie par images de particules stéréoscopiques ont été obtenues à deux longueurs de corde en aval du bord de fuite, en même temps que la DIC. La FST a diminué la force des tourbillons et a légèrement augmenté la diffusion et la taille des tourbillons. Elle a également augmenté l'amplitude des mouvements d'oscillation du tourbillon, tout en réduisant la fréquence associée. Dans les cas où l'intensité de la turbulence était de 8 % et 13 %, la fréquence des mouvements du tourbillon et la vibration de l'aile étaient similaires et une relation de phase entre les deux mouvements a été observée. La décomposition orthogonale du tourbillon (après élimination des mouvements d'oscillation) et la reconstruction ultérieure du champ de vitesse ont révélé des fluctuations temporelles de la force du tourbillon à la même fréquence que les vibrations de l'aile. Ce phénomène est lié aux fluctuations de la force de portance induites par les déformations de l'aile