Radiative, magnetic and numerical feedbacks on small-scale fragmentation

Radiative feedback and magnetic field are understood to have a strong impact on the protostellar collapse. We present high resolution numerical calculations of the collapse of a 1 solar mass dense core in solid body rotation, including both radiative transfer and magnetic field. Using typical parameters for low-mass cores, we study thoroughly the effect of radiative transfer and magnetic field on the first core formation and fragmentation. We show that including the two aforementioned physical processes does not correspond to the simple picture of adding them separately. The interplay between the two is extremely strong, via the magnetic braking and the radiation from the accretion shock.Comment: 4 pages, 2 figures ; to appear in "IAU Symposium 270: Computational Star formation", Eds. J. Alves, B. Elmegreen, J. Girart, V. Trimbl

The LoReLi database: 21 cm signal inference with 3D radiative hydrodynamics simulations

The Square Kilometer array is expected to measure the 21cm signal from the Epoch of Reionization (EoR) in the coming decade, and its pathfinders may provide a statistical detection even earlier. The currently reported upper limits provide tentative constraints on the astrophysical parameters of the models of the EoR. In order to interpret such data with 3D radiative hydrodynamics simulations using Bayesian inference, we present the latest developments of the \textsc{Licorice} code. Relying on an implementation of the halo conditional mass function to account for unresolved star formation, this code now allows accurate simulations of the EoR at $256^3$ resolution. We use this version of \textsc{Licorice} to produce the first iteration of \textsc{LoReLi}, a public dataset now containing hundreds of 21cm signals computed from radiative hydrodynamics simulations. We train a neural network on \textsc{LoReLi} to provide a fast emulator of the \textsc{Licorice} power spectra, \textsc{LorEMU}, which has $\sim 5\%$ rms error relative to the simulated signals. \textsc{LorEMU} is used in a Markov Chain Monte Carlo framework to perform Bayesian inference, first on a mock observation composed of a simulated signal and thermal noise corresponding to 100h observations with the SKA. We then apply our inference pipeline to the latest measurements from the HERA interferometer. We report constraints on the X-ray emissivity, and confirm that cold reionization scenarios are unlikely to accurately represent our Universe.Comment: 15 figures, 15 pages. Accepted by A&

Berry phase in superconducting multiterminal quantum dots

We report on the study of the non-trivial Berry phase in superconducting multiterminal quantum dots biased at commensurate voltages. Starting with the time-periodic Bogoliubov-de Gennes equations, we obtain a tight binding model in the Floquet space, and we solve these equations in the semiclassical limit. We observe that the parameter space defined by the contact transparencies and quartet phase splits into two components with a non-trivial Berry phase. We use the Bohr-Sommerfeld quantization to calculate the Berry phase. We find that if the quantum dot level sits at zero energy, then the Berry phase takes the values $\varphi_B=0$ or $\varphi_B=\pi$. We demonstrate that this non-trivial Berry phase can be observed by tunneling spectroscopy in the Floquet spectra. Consequently, the Floquet-Wannier-Stark ladder spectra of superconducting multiterminal quantum dots are shifted by half-a-period if $\varphi_B=\pi$. Our numerical calculations based on Keldysh Green's functions show that this Berry phase spectral shift can be observed from the quantum dot tunneling density of states.Comment: 15 pages, 7 figures. Supplemental Material as ancillary file (3 pages, 5 figures), manuscript in final for

Probing the concept of line tension down to the nanoscale

A novel mechanical approach is developed to explore by means of atom-scale simulation the concept of line tension at a solid-liquid-vapor contact line as well as its dependence on temperature, confinement, and solid/fluid interactions. More precisely, by estimating the stresses exerted along and normal to a straight contact line formed within a partially wet pore, the line tension can be estimated while avoiding the pitfalls inherent to the geometrical scaling methodology based on hemispherical drops. The line tension for Lennard-Jones fluids is found to follow a generic behavior with temperature and chemical potential effects that are all included in a simple contact angle parameterization. Former discrepancies between theoretical modeling and molecular simulation are resolved, and the line tension concept is shown to be robust down to molecular confinements. The same qualitative behavior is observed for water but the line tension at the wetting transition diverges or converges towards a finite value depending on the range of the solid/fluid interactions at play.Comment: 8 pages, 7 figure

Enhancement of radiation trapping for quasi-resonant scatterers at low temperature

We present a transport equation for the incoherent propagation of radiation inside a quasi-resonant atomic gas at low temperature. The derivation is based on a generalized Bethe-Salpeter equation taking into account the motion of the atoms. The obtained equation is similar to the radiative transfer equation. It is solved numerically by an original Monte Carlo approach in the case of a slab geometry. The partial frequency redistribution caused by the small velocity of the scatterers make the emitted flux outside the system and the energy density inside the medium to behave differently than in the case of complete frequency redistribution. In particular, the long time dependence of the specific intensity (escape factor) is slightly different from the Holstein prediction.Comment: 17 pages, 6 figure

Time-Resolved Tomo-PIV Measurements to Study 3D Coherent Structures in a Pulsed Jet in Cross-flow

International audienceThe recent tomo-PIV technique is presented and applied to a pulsed jet in cross-flow. This technique gives the instantaneous three-dimensional velocity field in a fat sheet (typically the depth of the measurement volume is a tenth of the other dimensions). The results presented here show the applicability of the technique to the characterization of a complex three-dimensional flow

Transfert de couleurs et colorisation guidés par la texture

National audienceCet article se concentre sur deux problèmes de manipulation de couleurs liés : le transfert de couleurs qui modifie les couleurs d'une image, et la colorisation qui ajoute des couleurs à une image en niveaux de gris. Les méthodes automatiques pour ces deux applications modifient l'image d'entrée à l'aide d'une image de référence contenant les couleurs désirées. Les approches précédentes visent rarement les deux problèmes simultanement et souffrent de deux principales limitations : les correspondances créées entre les images d'entrée et de référence sont incorrectes ou approximatives, et une mauvaise cohérence spatiale autour des structures de l'image. Dans cet article, nous proposons un pipeline unifiant les deux problèmes, basé sur le contenu texturel des images pour guider le transfert ou la colorisation. Notre méthode introduit un descripteur de textures préservant les contours de l'image, basé sur des matrices de covariance, permettant d'appliquer des transformations de couleurs locales. Nous montrons que notre approche est capable de produire des résultats comparables ou meilleurs que d'autres méthodes de l'état de l'art dans les deux applications

Influence of geometric parameters and image preprocessing on tomo-PIV results

International audienceThe tomography-PIV is using multiple camera views for a full tomographic reconstruction of the object space, which is represented by a 3-D voxel structure with a resolution adapted to the camera resolution. Influences of different parameters such as the images pre-processing, the volume discretization and the weighting matrix, the algorithm initialization and the cameras angles, the volume thickness and the particle density are studied on synthetic and real images