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Measurement and control of main spatio-temporal couplings in a CPA laser chain
No full textInternational audienceWe report a straightforward method to control main spatio-temporal couplings in a chirped pulse amplification (CPA) laser chain system using a specially designed chromatic doublet in a divergent beam configuration. The centering of the doublet allows for the control of the spatial chirp of the CPA laser chain, while its longitudinal position in the divergent beam enables the control of the amount of longitudinal chromatism in a wide dynamic range. The performance of this technique is evaluated by measuring main spatio-temporal couplings with a simple method, based on an ultrafast pulse shaper, which allows for a selection of narrow windows of the spectrum
Securing a High-Level Language Virtual Machine Through its ISA: Pharo as a Case Study
No full textInternational audienceManaged languages such as Python, C#, Java or JavaScript are the most popular when looking at the PYPL (PopularitY of Programming Language) index. These languages come with modern engines called virtual machines (VMs) composed of performant and intricate pieces of software such as garbage collectors or just-in-time compilers. As these components need to be extremely performant, they have grown in size and complexity. They are also powerful tools that could become an important breach if exploited maliciously. Using vulnerabilities in a JIT compiler can lead to code injection or JIT spraying attacks, often needing no more than a carefully written input program. Enforcing memory security has been a hot topic for several years; our goal is to extend the RISC-V instruction set to enforce this memory isolation dynamically. This work-in-progress focuses on Pharo, a metacircular VM extended to the RISC-V ISA. We believe that the concepts applied to this VM should be applicable to other implementations
Numerical and Experimental Comparison of Spinnaker Aerodynamics Close to Curling
No full textInternational audienceWhen sailing downwind with a spinnaker, the “verge of curling” is one of the common recommendations that sailors follow for efficient sailing. Wind tunnel experiments on spinnaker models conducted by Aubin et al. (2017) in the Twisted Flow Wind Tunnel of the Yacht Research Unit of the University of Auckland have shown that curling can be related to better performance at Apparent Wind Angle ≥ 100°. In the present article, we will focus on the aerodynamic performance jump observed at Apparent Wind Angle AWA = 100°, where the drive force increases up to 15% when the sail starts to flap. Thanks to four triggered HD cameras and coded targets stuck on the sail, three flying shapes of the spinnaker are reconstructed by photogrammetry for different sheet lengths from over trimmed to flapping occurrence. The pimpleFOAM solver from OpenFOAM is used to simulate the aerodynamics of the three rigid extracted flying shapes. Results highlight the ability of the model to simulate the experimental jump observed closed to curling and the significant confinement effect of the roof of the wind tunnel
Smoothness of densities for path-dependent SDEs under Hörmander's condition
No full textInternational audienceWe establish the existence of smooth densities for solutions to a broad class of path-dependent SDEs under a Hörmander-type condition. The classical scheme based on the reduced Malliavin matrix turns out to be unavailable in the path-dependent context. We approach the problem by lifting the given n-dimensional path-dependent SDE into a suitable Lp-type Banach space in such a way that the lifted Banach-space-valued equation becomes a state-dependent reformulation of the original SDE. We then formulate Hörmander’s bracket condition in Rnfor non-anticipative SDE coefficients defining the Lie brackets in terms of vertical derivatives in the sense of the functional Itô calculus. Our pathway to the main result engages an interplay between the analysis of SDEs in Banach spaces, Malliavin calculus, and rough path techniques
Ubérisation, espace public et parties prenantes : vers une nouvelle configuration des relations d’emploi et de travail dans les territoires ?
No full textEUV and Hard X-ray Hartmann Wavefront Sensing for Optical Metrology, Alignment and Phase Imaging
No full textInternational audienceFor more than 15 years, Imagine Optic have developed Extreme Ultra Violet (EUV) and X-ray Hartmann wavefront sensors for metrology and imaging applications. These sensors are compatible with a wide range of X-ray sources: from synchrotrons, Free Electron Lasers, laser-driven betatron and plasma-based EUV lasers to High Harmonic Generation. In this paper, we first describe the principle of a Hartmann sensor and give some key parameters to design a high-performance sensor. We also present different applications from metrology (for manual or automatic alignment of optics), to soft X-ray source optimization and X-ray imaging
General-purpose kernel regularization of boundary integral equations via density interpolation
No full textInternational audienceThis paper presents a general high-order kernel regularization technique applicable to all four integral operators of Calder\'on calculus associated with linear elliptic PDEs in two and three spatial dimensions. Like previous density interpolation methods, the proposed technique relies on interpolating the density function around the kernel singularity in terms of solutions of the underlying homogeneous PDE, so as to recast singular and nearly singular integrals in terms of bounded (or more regular) integrands. We present here a simple interpolation strategy which, unlike previous approaches, does not entail explicit computation of high-order derivatives of the density function along the surface. Furthermore, the proposed approach is kernel- and dimension-independent in the sense that the sought density interpolant is constructed as a linear combination of point-source fields, given by the same {Green's function} used in the integral equation formulation, thus making the procedure applicable, in principle, to any PDE with known {Green's function}. For the sake of definiteness, we focus here on Nystr\"om methods for the (scalar) Laplace and Helmholtz equations and the (vector) elastostatic and time-harmonic elastodynamic equations. The method's accuracy, flexibility, efficiency, and compatibility with fast solvers are demonstrated by means of a variety of large-scale three-dimensional numerical examples