Coherent backscattering in nonlinear atomic media: quantum Langevin approach

In this theoretical paper, we investigate coherence properties of the near-resonant light scattered by two atoms exposed to a strong monochromatic field. To properly incorporate saturation effects, we use a quantum Langevin approach. In contrast to the standard optical Bloch equations, this method naturally provides the inelastic spectrum of the radiated light induced by the quantum electromagnetic vacuum fluctuations. However, to get the right spectral properties of the scattered light, it is essential to correctly describe the statistical properties of these vacuum fluctuations. Because of the presence of the two atoms, these statistical properties are not Gaussian : (i) the spatial two-points correlation function displays a speckle-like behavior and (ii) the three-points correlation function does not vanish. We also explain how to incorporate in a simple way propagation with a frequency-dependent scattering mean-free path, meaning that the two atoms are embedded in an average scattering dispersive medium. Finally we show that saturation-induced nonlinearities strongly modify the atomic scattering properties and, as a consequence, provide a source of decoherence in multiple scattering. This is exemplified by considering the coherent backscattering configuration where interference effects are blurred by this decoherence mechanism. This leads to a decrease of the so-called coherent backscattering enhancement factor.Comment: 19 pages, 1 figur

Analytical and numerical study of uncorrelated disorder on a honeycomb lattice

We consider a tight-binding model on the regular honeycomb lattice with uncorrelated on-site disorder. We use two independent methods (recursive Green's function and self-consistent Born approximation) to extract the scattering mean free path, the scattering mean free time, the density of states and the localization length as a function of the disorder strength. The two methods give excellent quantitative agreement for these single-particle properties. Furthermore, a finite-size scaling analysis reveals that all localization lengths for different lattice sizes and different energies (including the energy at the Dirac points) collapse onto a single curve, in agreement with the one-parameter scaling theory of localization. The predictions of the self-consistent theory of localization however fail to quantitatively reproduce these numerically-extracted localization lengths.Comment: 19 pages, 25 figure

Influence of local mechanical loadings paths on the oxidation assisted crack initiation of alloy 718

At high temperatures, alloy 718, like many other nickel-based superalloys, is sensitive to an oxidation-assisted intergranular crack (OAIC) growth mechanism. Former studies have pointed out that even if intergranular oxidation still occurred, intergranular crack initiation was inhibited due to specific mechanical loadings which were identified as Portevin-Le Châtelier (PLC) plastic instabilities. In the present work, key parameters triggering crack initiation or PLC instabilities in the [550–700°C] temperature range were determined for the studied grade by means of tensile tests on smooth specimens. Then, in order to assess the applicability of such a finding at a scale compatible with the material microstructure, a dedicated tensile V-shaped specimen was designed to generate different surface and sub-surface strain and strain rate histories. Thanks to a dual approach based on the observation of crack initiation location on this specific experimental specimen together with associated FE calculations, the critical mechanical loading paths inducing OAIC initiation have been specified. Thus, assuming that the metallurgical state is homogenous at the structure scale, a mapping of intergranular crack initiation is then obtainable

Tips for making the most of 64-bit architectures in langage design, libraries or garbage collection

The 64-bit architectures that have become standard today offer unprecedented low-level programming possibilities. For the first time in the history of computing, the size of address registers far exceeded the physical capacity of their bus.After a brief reminder of the possibilities offered by the small size of addresses compared to the available 64 bits,we develop three concrete examples of how the vacant bits of these registers can be used.Among these examples, two of them concern the implementation of a library for a new statically typed programming language.Firstly, the implementation of multi-precision integers, with the aim of improving performance in terms of both calculation speed and RAM savings.The second example focuses on the library's handling of UTF-8 character strings.Here, the idea is to make indexing easier by ignoring the physical size of each UTF-8 characters.Finally, the third example is a possible enhancement of garbage collectors, in particular the mark \& sweep for the object marking phase

Inondations dans le Gard : bilan

Le 9 septembre 2002, le canal de la Fontaine à Nîmes débordait, inondant les quatre étages de la bibliothèque-Carré-d’Art : questions à Benoît Lecoq, directeur

Relationship between the volume of the unit cell of hexagonal-close-packed Ti, hardness and oxygen content after α-case formation in Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy

In this study, the influence of oxygen diffusion on the physical properties of Ti–6Al–2Sn–4Zr–2Mo–0.1Si was examined. Measurements were carried out directly on sample cross sections which were preoxidized at high temperature. The lattice parameter evolution was measured using synchrotron X-ray diffraction and was coupled with microhardness and electron probe microanalyzer results with the aim of highlighting their relationships. The results show that the hardness and oxygen gradients along the oxygen diffusion zone in the alloy are similar to the evolution of the [alpha]α-phase unit-cell volume quantified by X-ray diffraction. Linear relationships were found between these three parameters

Proposal of an Eco-design Framework based on a Design Education Perspective

AbstractIn order to overspread a successful sustainable design of products and services, it is necessary to educate engineering designers at university and along life. Although literature already provides eco-design processes, frameworks, methods and tools, it does not seem to take into consideration the need for a progressive education to eco-design practice. This research proposes a framework based on six fundamental dimensions fractioned into multiple levels: Choice and management of criteria; Modeling of life cycles; Management of the eco-design process; Levels of calling into question of products and services; Integration of industrial stakeholders; Integration of civil stakeholders. The eco-design framework is finally illustrated through its usefulness in describing tools and supporting eco-design education trajectories