The acceleration of the universe and the physics behind it

Using a general classification of dark enegy models in four classes, we discuss the complementarity of cosmological observations to tackle down the physics beyond the acceleration of our universe. We discuss the tests distinguishing the four classes and then focus on the dynamics of the perturbations in the Newtonian regime. We also exhibit explicitely models that have identical predictions for a subset of observations.     

Beyond the Microscale: Advances in Surface Nanopatterning by Laser-Driven Self-Organization

Designing complex local properties that seamlessly integrate efficient functions into processed materials presents a formidable challenge. A promising solution has emerged in the form of ultrafast laser-surface structuring. Through time-controlled polarization ultrafast irradiation at the picosecond timescale, spontaneous self-organization of surfaces can be induced. The thermal gradient length scale unfolds on the micro- and nanoscale, instigating thermoconvection that leads to structured surfaces upon quenching. Convective instabilities dynamically shape intricate yet self-regulated periodic relief structures. The ability to achieve laser-induced self-organization in both surface dimensions holds immense scientific importance, as it unlocks the potential to create uniform periodic 2D patterns by harnessing the inherent regulation of nonlinear dynamics processes in fluids. This comprehensive review explores recent advances in understanding and leveraging ultrafast laser-induced self-organization for precise patterning across versatile scales and applications. The insights herein hold the potential to drive significant advancements in nanoscale manufacturing through 2D laser-induced periodic surface structures.     

Rigorous computation of smooth branches of equilibria for the three dimensional Cahn–Hilliard equation

In this paper, we propose a new general method to compute rigorously global smooth branches of equilibria of higher-dimensional partial differential equations. The theoretical framework is based on a combination of the theory introduced in Global smooth solution curves using rigorous branch following (van den Berg et al., Math. Comput. 79(271):1565–1584, 2010) and in Analytic estimates and rigorous continuation for equilibria of higher-dimensional PDEs (Gameiro and Lessard, J. Diff. Equ. 249(9):2237–2268, 2010). Using this method, one can obtain proofs of existence of global smooth solution curves of equilibria for large (continuous) parameter ranges and about local uniqueness of the solutions on the curve. As an application, we compute several smooth branches of equilibria for the three-dimensional Cahn–Hilliard equation.     

Conservation laws for cosmological perturbations

We briefly recall the problem of defining conserved quantities such as energy in general relativity, and the solution given by introducing a symmetric background. We apply the general formalism to perturbed Robertson-Walker spacetimes with de Sitter geometry as background. We relate the obtained conserved quantities to Traschen's integral constraints and mention a few applications in cosmology.     

Etude du chromatisme d'un systeme optique par photographie “speckle”

Speckle photography experiments have been used for studying optical systems and more recently we have used image speckle photography to measure displacements and deformations of a partial diffuser. The same method is now used for studying chromatic aberrations of a lens system. Experimental results are given for three optical lenses.     

Influence des parametres experimentaux sur la restitution du sinus de la phase en interferometrie

Combination of phase-modulation interferometry and scanning of the object is capable of restoring the sine of the phase everywhere in the object field. So, information on the direction of the surface relief is obtained. The influences of the analysing surface characteristics and of the process of scanning are studied.     

Sur la restitution du signe de la phase en interferometrie

Phase variations are transformed into intensity variations by means of interferometry. It is then possible to form a visible image of a pure phase object. But then information on the sign of the phase or the direction of surface relief is lost. Principles of a method for extracting only the imaginary part of the complex amplitude of the object, which is an odd function of the phase, are studied. From this it is possible to obtain the sign of the phase.     

Interferometrie a double plage par photographie “speckle”

The image of a partial diffusor is recorded on a holographic plate. After development, the hologram is repositioned to observe “live fringes”. Half of the aperture of the optical system has been masked during the exposure, but the full aperture is used for the reconstruction. Two separate reconstructed images of the half aperture show two different interferograms. This set up can be used to measure displacements of objects, or defocusing.