Helium and point defect accumulation: (ii) kinetic modelling

The main outstanding issues regarding modeling He diffusion and defect accumulation in α-iron are reviewed. During recent years, first principles calculations have provided a better understanding of defect stability and migration properties in pure α-iron, and accurate values of energetics of He migration and He-vacancy interactions. Such information has been used by several authors to study damage evolution under different irradiation conditions using both kinetic Monte Carlo and rate theory models. In this article a review of the main results is provided, in particular for He desorption. The influence of impurities such as carbon is discussed as well as the main challenges ahead for modeling. To cite this article: M.J. Caturla et al., C. R. Physique 9 (2008).     

Discrete dislocation dynamics: an important recent break-through in the modelling of dislocation collective behaviour

Recent results obtained by 3D discrete Dislocation Dynamics (DD) simulations are reviewed. Firstly, in the case of fatigued AISI 316L stainless steel, it is shown how DD simulations can both explain the formation of persistent slip bands and give a criterion for crack initiation. The same study is performed in the case of precipitate hardened metals where the precipitate size plays a crucial role. Secondly, we show how molecular dynamics (MD) simulations can feed the DD simulations for two applications. The first concerns the modelling of BCC Fe for which the dislocation mobility is derived from MD simulations. The second considers the modelling of irradiated stainless steels (FCC), where MD is used to define the local rules of interactions between dislocations and Frank loops. To cite this article: M.C. Fivel, C. R. Physique 9 (2008).     

Nucleation problems in metallurgy of the solid state: recent developments and open questions

Nucleation processes play a key role in the microstructure evolution of metallic alloys during thermomechanical treatments. These processes can involve phase transformations (such as precipitation) and structural instabilities (such as recrystallisation). Although the word ‘nucleation’ is used in both cases, the situation is profoundly different for precipitation and for recrystallisation on which this article is focussed. In the case of precipitation, species are conserved and the underlying physics is stochastic fluctuations, allowing the apparition of critical germs of the new phase. In the case of recrystallisation, the underlying physical phenomenon is the progressive growth of subgrain structures leading to an unstable configuration, allowing a dislocation free grain to grow at the expense of a dislocated one. The two cases require different types of modelling which are presented in the article. To cite this article: Y. Bréchet, G. Martin, C. R. Physique 7 (2006).     

FALCON: multi-object AO

FALCON is a wide-field, multi-object integral field spectrograph equipped with adaptive optics. It is dedicated to the study of the formation process of primordial galaxies. The AO system uses natural guide stars, and the high sky coverage required for these studies is obtained using tomographic techniques for the wavefront analysis. The structure of the OA system is very new, and particularly suited for a future implementation on extremely large telescopes. To cite this article: E. Gendron et al., C. R. Physique 6 (2005).     

Exploring the electronic band structure of individual carbon nanotubes under 60 T

Nano-sciences, and in particular nano-physics, constitute a fascinating world of investigations where the experimental challenges are to synthesize, to address (for instance optically or electrically) to explore and promote the remarkable physical properties of new nano-materials. Somehow, one of the most promising realization of nano-sciences lies in carbon-based nano-materials with sp² covalent bonds. In particular, carbon nanotubes, graphene and more recently ultra-narrow graphene nano-ribbons are envisioned as elementary bricks of the future of nano-electronics. However, prior to such an achievement, the first steps consist in understanding their fundamental electronic properties when they constitute the drain–source channel of a gated device or inter-connexion elements. In this article, we present the richness of challenging experiments combining single-object measurements with an extreme magnetic environment. We demonstrate that an applied magnetic field (B), along with a control of the electrostatic doping, drastically modifies the electronic band structure of a carbon nanotube based transistor. Several examples will be addressed in this presentation. When B is applied parallel to the tube axis, a quantum flux threading the tube induces a giant Aharonov–Bohm conductance modulation mediated by Schottky barriers whose profile is magnetic field dependent. In the perpendicular configuration, the applied magnetic field breaks the revolution symmetry along the circumference and non-conventional Landau states develop in the high field regime. By playing with a carbon nanotube based electronic Fabry–Perot resonator, the field dependence of the resonant states of the cavity reveals the onset of the first Landau state at zero energy. These experiments enlighten the outstanding efficiency of magneto-conductance experiments to probe the electronic properties of carbon based nano-materials. To cite this article: S. Nanot et al., C. R. Physique 10 (2009).     

Radiation effects in concentrated alloys and compounds: equilibrium and kinetics of driven systems

What organization of condensed matter does resist irradiation, as a function of irradiation conditions? How to characterize the latter? We survey the advances in the field during the past three decades, when irradiation effects reduce to nuclear collisions. While in simple cases (structure defined by a scalar order parameter) one may define a stochastic potential, which yields the stationary states of the compounds under irradiation and their respective stability, in more general cases, we are left with brute force atomistic simulations to explore materials' behaviour as a function of irradiation conditions. Special attention is given to the kinetics of concentration fields under irradiation, a question with several practical implications. We conclude that irradiation conditions are best defined by three parameters: the cascade features (number of displacements and replacements, length of replacement sequences, …), the frequency of cascade occurrence, and the cumulated dose. We suggest cascade features be named ‘(elementary) dose’ and the cascade occurrence frequency ‘dose rate’. To cite this article: G. Martin, P. Bellon, C. R. Physique 9 (2008).     

Jules Horowitz Reactor: a high performance material testing reactor

The physical modelling of materials' behaviour under severe conditions is an indispensable element for developing future fission and fusion systems: screening, design, optimisation, processing, licensing, and lifetime assessment of a new generation of structure materials and fuels, which will withstand high fast neutron flux at high in-service temperatures with the production of elements like helium and hydrogen.JANNUS and other analytical experimental tools are developed for this objective. However, a purely analytical approach is not sufficient: there is a need for flexible experiments integrating higher scales and coupled phenomena and offering high quality measurements; these experiments are performed in material testing reactors (MTR). Moreover, complementary representative experiments are usually performed in prototypes or dedicated facilities such as IFMIF for fusion. Only such a consistent set of tools operating on a wide range of scales, can provide an actual prediction capability. A program such as the development of silicon carbide composites (600–1200 °C) illustrates this multiscale strategy.Facing the long term needs of experimental irradiations and the ageing of present MTRs, it was thought necessary to implement a new generation high performance MTR in Europe for supporting existing and future nuclear reactors. The Jules Horowitz Reactor (JHR) project copes with this context. It is funded by an international consortium and will start operation in 2014. JHR will provide improved performances such as high neutron flux (10¹⁵ n/cm²/s above 0.1 MeV) in representative environments (coolant, pressure, temperature) with online monitoring of experimental parameters (including stress and strain control). Experimental devices designing, such as high dpa and small thermal gradients experiments, is now a key objective requiring a broad collaboration to put together present scientific state of art, end-users requirements and advanced instrumentation. To cite this article: D. Iracane et al., C. R. Physique 9 (2008).     

Time-reversed waves and super-resolution

Time-reversal mirrors (TRMs) refocus an incident wavefield to the position of the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz microwaves to MHz ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting for a broadband pulse, in a refocusing quality that does not depend on the TRM aperture.Moreover, when the complex environment is located in the near field of the source, time-reversal focusing opens completely new approaches to super-resolution. We will show that, for a broadband source located inside a random metamaterial, a TRM located in the far field radiated a time-reversed wave that interacts with the random medium to regenerate not only the propagating but also the evanescent waves required to refocus below the diffraction limit. This focusing process is very different from that developed with superlenses made of negative index material only valid for narrowband signals. We will emphasize the role of the frequency diversity in time-reversal focusing. To cite this article: M. Fink et al., C. R. Physique 10 (2009).     

Radiation aging of nonmetallic materials: specific aspects

Under irradiation, all materials experience various forms of structural evolution, from the simplest, associated with point defect creation and accumulation, to complex phase changes, either towards equilibrium or nonequilibrium structures. In nonmetallic ceramics the same processes are known or probable; however, the nature of bonding, partly ionic and partly covalent, as well as the complexity associated with the long range character of the Coulomb interaction, have long posed great difficulties in defect and aging studies under irradiation. Our aim here is to review the current state of knowledge, stressing the specific characteristics of nonmetallic materials, from primary defect creation to collective behavior, with respect to both experimental facts as well as to modeling perspectives. Given the broad field covered, we will illustrate the problem by choosing a few model materials, mostly oxides, in which the whole spectrum of phenomena has been handled. We will begin with threshold energy studies, then go to microstructure formation and evolution, radiation enhanced diffusion results, and lastly to phase changes. To cite this article: Y. Limoge, C. R. Physique 9 (2008).     

Cloaking by plasmonic resonance among systems of particles: cooperation or combat?

We study quasistatic cloaking by the mechanism of plasmonic resonance, for systems of coated cylinders. Our focus is on the nature of the resonant cloaking interaction: whether systems of particles can be made to cooperate in cloaking a polarizable particle from an applied uniform field. We show that in fact if the cloaking regions of the systems of particles overlap, then they tend to interact in a fashion detrimental to their cloaking of the polarizable particle. If the cloaking regions touch but do not overlap, then the system of particles can cloak a larger region than each would in isolation. To cite this article: R.C. McPhedran et al., C. R. Physique 10 (2009).     

Magnetization dynamics: ultra-fast and ultra-small

Ultrafast magnetic processes are of great scientific interest but also form the basis of high density magnetic recording applications. We demonstrate the uniqueness of time resolved, high resolution magnetic X-ray microscopy, and show that the motion of a magnetic vortex core can be imaged. The vortex core direction is hidden to most experimental techniques, but has a decisive influence on the dynamics of the magnetic structure.We imaged the switching of a ferromagnetic nanostructure by a spin polarized current pulse using time resolved X-ray microscopy. As opposed to the common uniform switching process due to Néel and Stoner–Wohlfarth, the magnetization in spin injection devices does not switch uniformly, but involves the motion of a magnetic vortex. To cite this article: Y. Acremann, C. R. Physique 9 (2008).     

First principles calculations in iron: structure and mobility of defect clusters and defect complexes for kinetic modelling

Predictive simulations of the defect population evolution in materials under or after irradiation can be performed in a multi-scale approach, where the atomistic properties of defects are determined by electronic structure calculations based on the Density Functional Theory and used as input for kinetic simulations covering macroscopic time and length scales. Recent advances obtained in iron are presented. The determination of the 3D migration of self-interstitial atoms instead of a fast one-dimensional glide induced an overall revision of the widely accepted picture of radiation damage predicted by previously existing empirical potentials. A coupled ab initio and mesoscopic kinetic Monte Carlo simulation provided strong evidence to clarify controversial interpretations of electrical resistivity recovery experiments concerning the mobility of vacancies, self-interstitial atoms, and their clusters. The results on the dissolution and migration properties of helium in α-Fe were used to parameterize Rate Theory models and new inter-atomic potentials, which improved the understanding of fusion reactor materials behavior. Finally, the effects of carbon, present in all steels as the principal hardening element, are also shown. To cite this article: C.C. Fu, F. Willaime, C. R. Physique 9 (2008).     

Resonant Inelastic X-ray Scattering: From band mapping to inter-orbital excitations

Resonant inelastic X-ray scattering (also known as resonant X-ray Raman spectroscopy when only valence and conduction states are involved in the final state excitation) has developed into a major tool for understanding the electronic properties of complex materials. Presently it provides access to electron excitations in the few hundred meV range with element and bulk selectivity. Recent progress in X-ray optics and synchrotron radiation engineering have opened up new perspectives for this powerful technique to improve resolving power and efficiency. We briefly present the basics of the method and illustrate its potential with examples chosen from the literature. To cite this article: J. Lüning, C.F. Hague, C. R. Physique 9 (2008).     

Semiclassical relativistic strings in and long scalar operators in SYM theory

We review recent progress in quantitative checking of AdS/CFT duality in the sector of ‘semiclassical’ string states dual to ‘long’ scalar N=4 super Yang–Mills operators. In particular, we describe the effective action approach, in which the same sigma model type action describing coherent states is shown to emerge from the AdS₅×S⁵ string action and from an integrable spin chain Hamiltonian representing the SYM dilatation operator. To cite this article: A.A. Tseytlin, C. R. Physique 5 (2004).

Résumé

Nous passons en revue les progrès récents sur les vérifications quantitatives de la dualité AdS/CFT dans le régime où les états « semiclassiques » de cordes sont du aux « longs » opérateurs scalaires de la théorie de super Yang–Mills N=4. En particulier, nous décrivons l'approche effective, dans laquelle le modèle sigma décrivant les états cohérents est montré émerger de l'action de la corde sur AdS₅×S⁵ et de l'Hamiltonien d'une chaîne de spin intégrable représentant l'opérateur de dilatation en SYM. Pour citer cet article : A.A. Tseytlin, C. R. Physique 5 (2004).     

Introduction to the physics of nucleation

In this introductory article, I review the theory of nucleation by thermal activation and by quantum tunneling. The effect of heterogeneous nucleation at surfaces is discussed and a brief survey of experimental techniques is given. To cite this article: H.J. Maris, C. R. Physique 7 (2006).     

Cavitation in water: a review

Liquid water can be brought beyond the liquid–vapor equilibrium line into a metastable state, before nucleation of bubbles (cavitation) occurs. We review the experimental work on cavitation in water, focusing on the determination of the ultimate degree of metastability at which liquid water can exist. We also present practical applications of metastability and cavitation. To cite this article: F. Caupin, E. Herbert, C. R. Physique 7 (2006).     

Metamaterials and invisibility

Metamaterials have significantly extended the range of electromagnetic properties available to device designers. An interesting application of these new materials is to the problem of cloaking, where the goal is to render an object invisible to electromagnetic radiation within a certain frequency range. Here, I review the concepts behind recently-proposed invisibility cloaks, and the way in which metamaterials can allow these designs to be realized. To cite this article: B. Wood, C. R. Physique 10 (2009).     

Holographic dynamics of unstable branes in AdS

The gauge theory dual to the decay of an unstable D-particle in AdS is analysed in terms of coherent states. We discuss in detail how to count the number of particles in the decay product. We find, in agreement with the analysis in flat space, that the emission amplitude is suppressed as the mass of the radiated particles increases. To cite this article: M. Zamaklar, K. Peeters, C. R. Physique 5 (2004).

Résumé

La théorie de jauge duale à la désintégration de D-particules instables dans AdS est analysée en termes d'état cohérents. Nous discutons en détails le comptage du nombre de particule dans le produit de désintégration. Nous trouvons, en accord avec l'analyse en espace plat, que le taux d'émission est supprimé quand la masse de la particule augmente. Pour citer cet article : M. Zamaklar, K. Peeters, C. R. Physique 5 (2004).