Chaotic Mixing in Three Dimensional Porous Media

Under steady flow conditions, the topological complexity inherent to all random 3D porous media imparts complicated flow and transport dynamics. It has been established that this complexity generates persistent chaotic advection via a three-dimensional (3D) fluid mechanical analogue of the baker's map which rapidly accelerates scalar mixing in the presence of molecular diffusion. Hence pore-scale fluid mixing is governed by the interplay between chaotic advection, molecular diffusion and the broad (power-law) distribution of fluid particle travel times which arise from the non-slip condition at pore walls. To understand and quantify mixing in 3D porous media, we consider these processes in a model 3D open porous network and develop a novel stretching continuous time random walk (CTRW) which provides analytic estimates of pore-scale mixing which compare well with direct numerical simulations. We find that chaotic advection inherent to 3D porous media imparts scalar mixing which scales exponentially with longitudinal advection, whereas the topological constraints associated with 2D porous media limits mixing to scale algebraically. These results decipher the role of wide transit time distributions and complex topologies on porous media mixing dynamics, and provide the building blocks for macroscopic models of dilution and mixing which resolve these mechanisms.Comment: 36 page

The non dissipative damping of the Rabi oscillations as a "which-path" information

Rabi oscillations may be viewed as an interference phenomenon due to a coherent superposition of different quantum paths, like in the Young's two-slit experiment. The inclusion of the atomic external variables causes a non dissipative damping of the Rabi oscillations. More generally, the atomic translational dynamics induces damping in the correlation functions which describe non classical behaviors of the field and internal atomic variables, leading to the separability of these two subsystems. We discuss on the possibility of interpreting this intrinsic decoherence as a "which-way" information effect and we apply to this case a quantitative analysis of the complementarity relation as introduced by Englert [Phys. Rev. Lett. \textbf{77}, 2154 (1996)].Comment: 5 pages, 2 figure

Les forêts de montagne de la Nouvelle-Calédonie

L'existence d'un gradient local de température plus prononcé près des montagnes isolées abaisse l'altitude moyenne de formation des masses nuageuses, créant ainsi des conditions propices au développement des forêts de montagne en Nouvelle-Calédonie à des altitudes inférieures à 1 600 m. Ces forêts sont d'une grande importance pour la biodiversité et la compréhension de la phytogéographie et phylogénie de certains groupes, comme celui des conifères ou ceux des genres Metrosideros (Myrtaceae) et Cunonia (Cunoniaceae). Elles constituent aussi des refuges pour la faune menacée et jouent un rôle de régulateur hydrologique non négligeable. Relativement bien protégées, elles sont peu menacées par l'exploitation forestière, un peu plus par les activités minières. Le plus grand risque semble, toutefois, être le réchauffement climatique global, qui pourrait entraîner une disparition des conditions écologiques particulières nécessaires à leur existence. (Résumé d'auteur

Continuum limit of amorphous elastic bodies (III): Three dimensional systems

Extending recent numerical studies on two dimensional amorphous bodies, we characterize the approach of elastic continuum limit in three dimensional (weakly polydisperse) Lennard-Jones systems. While performing a systematic finite-size analysis (for two different quench protocols) we investigate the non-affine displacement field under external strain, the linear response to an external delta force and the low-frequency harmonic eigenmodes and their density distribution. Qualitatively similar behavior is found as in two dimensions. We demonstrate that the classical elasticity description breaks down below an intermediate length scale $\xi$, which in our system is approximately 23 molecular sizes. This length characterizes the correlations of the non-affine displacement field, the self-averaging of external noise with distance from the source and gives the lower wave length bound for the applicability of the classical eigenfrequency calculations. We trace back the "Boson-peak" of the density of eigenfrequencies (obtained from the velocity auto-correlation function) to the inhomogeneities on wave lengths smaller than $\xi$.Comment: 27 pages, 11 figures, submitted to Phys. Rev.

Worst-Case Optimization of a Digital Link for Wearable Electronics in a Stochastic Framework

This paper demonstrates an optimization strategy for systems affected by uncertainties in the case of a textile interconnect line. Rather than simply conducting stochastic analysis at the end of the design process, tolerances are accounted for from the early stages of the flow. An unsupervised approach, used to describe the stochastic behavior of the line, isintegrated within a heuristic optimization algorithm with the aim of selecting the optimal parameters of a passive equalizer

Realization of a semiconductor-based cavity soliton laser

The realization of a cavity soliton laser using a vertical-cavity surface-emitting semiconductor gain structure coupled to an external cavity with a frequency-selective element is reported. All-optical control of bistable solitonic emission states representing small microlasers is demonstrated by injection of an external beam. The control scheme is phase-insensitive and hence expected to be robust for all-optical processing applications. The motility of these structures is also demonstrated

Inhomogeneous elastic response of silica glass

Using large scale molecular dynamics simulations we investigate the properties of the {\em non-affine} displacement field induced by macroscopic uniaxial deformation of amorphous silica,a strong glass according to Angell's classification. We demonstrate the existence of a length scale $\xi$ characterizing the correlations of this field (corresponding to a volume of about 1000 atoms), and compare its structure to the one observed in a standard fragile model glass. The "Boson-peak'' anomaly of the density of states can be traced back in both cases to elastic inhomogeneities on wavelengths smaller than $\xi$, where classical continuum elasticity becomes simply unapplicable