The implications of resonant x-ray scattering data on the physics of the insulating phase of V_2O_3

We have performed a quantitative analysis of recent resonant x-ray scattering experiments carried out in the antiferromagnetic phase of V_2O_3 by means of numerical ab-initio simulations. In order to treat magnetic effects, we have developed a method based on multiple scattering theory (MST) and a relativistic extension of the Schr\"{o}dinger Equation, thereby working with the usual non relativistic set of quantum numbers $l,m,\sigma$ for angular and spin momenta. Electric dipole-dipole (E1-E1), dipole-quadrupole (E1-E2) and quadrupole-quadrupole (E2-E2) transition were considered altogether. We obtain satisfactory agreement with experiments, both in energy and azimuthal scans. All the main features of the V K edge Bragg-forbidden reflections with $h+k+l=$odd can be interpreted in terms of the antiferromagnetic ordering only, {\it ie}, they are of magnetic origin. In particular the ab-initio simulation of the energy scan around the (1,1,1)-monoclinic reflection excludes the possibility of any symmetry reduction due to a time-reversal breaking induced by orbital ordering.Comment: 11 pages, 6 figure

On the size of the Fe II emitting region in the AGN Akn 120

We present a reverberation analysis of the strong, variable optical Fe II emission bands in the spectrum of Akn 120, a low-redshift AGN which is one of the best candidates for such a study. On time scales of several years the Fe II line strengths follow the variations in the continuum strength. However, we are unable to measure a clear reverberation lag time for these Fe II lines on any time scale. This is due to the very broad and flat-topped nature of the Fe II cross correlation functions, as compared to the H-beta response which is much more sharply localized in time. Although there is some suggestion in the light curve of a 300-day response time, our statistical analysis does not pick up such a feature. We conclude that the optical Fe II emission does not come from a photoionization-powered region similar in size to the H-beta emitting region, but we cannot say for sure where it does come from. Our results are generally consistent either with emission from a photoionized region several times larger than the H-beta zone, or with emission from gas heated by some other means, perhaps responding only indirectly to the continuum variations.Comment: Accepted for publication in the Ap

Wetting on Nanorough Surfaces

We present in this Letter a free-energy approach to the dynamics of a fluid near a nanostructured surface. The model accounts both for the static phase equilibrium in the vicinity of the surface (wetting angles, Cassie-Wenzel transition) and the dynamical properties like liquid slippage at the boundary. This method bridges the gap between phenomenological phase-field approaches and more macroscopic lattice-Boltzmann models

La représentation sociale du football chez des jeunes adultes issus d’un milieu social défavorisé

Soccer is a team sport, practiced as a recreational physical activity by amateurs or professionally with elite players. This popular sport has several advantages such as integration of diverse styles and simple rules (Defrance, 1995). A psycho-sociological perspective is adopted in this article, exploring soccer as an object of social representation (Moscovici, 1961/76) with young, adult amateurs from a disadvantaged social background. The results obtained using the free association method and the characterization questionnaire show that there is a social representation of soccer. If, for young amateurs, this representation is based on the values of team sport, the one given to parents is rooted in the professional world. In addition, this study adds to an original phenomenon of the hidden” area of social representations. Between amateurism and professionalism, the reference to “Zinedine Zidane” adds to the controversial nature of this representation for young people

Resonant inelastic x-ray scattering probes the electron-phonon coupling in the spin-liquid kappa-(BEDT-TTF)2Cu2(CN)3

Resonant inelastic x-ray scattering at the N K edge reveals clearly resolved harmonics of the anion plane vibrations in the kappa-(BEDT-TTF)2Cu2(CN)3 spin-liquid insulator. Tuning the incoming light energy at the K edge of two distinct N sites permits to excite different sets of phonon modes. Cyanide CN stretching mode is selected at the edge of the ordered N sites which are more strongly connected to the BEDT-TTF molecules, while positionally disordered N sites show multi-mode excitation. Combining measurements with calculations on an anion plane cluster permits to estimate the sitedependent electron-phonon coupling of the modes related to nitrogen excitation

Raisons et pratiques de la pendularité intensive : le temps de trajet, entre temps subi et temps choisi

Cet article étudie les raisons conduisant certains individus à consacrer des temps importants à leur mobilité, par une approche mixte, en mobilisant les méthodologies quantitatives et qualitatives. Dans la littérature, le temps de trajet est traditionnellement considéré comme un temps inutile et non-productif, voire comme le pire temps de la journée. Dans ces conditions, le comportement des pendulaires intensifs qui passent plus de deux heures quotidiennes à se déplacer, constitue sinon une remise en question, du moins un contre-exemple à cette conception du temps de trajet. Tout d'abord, une analyse quantitative des budgets-temps de transport (BTT) dans huit villes (Berne, Bruxelles, Genève, Grenoble, Lyon, Rennes, Strasbourg et Zurich) explore les temps de transport dans ces villes par la méthode des modèles de durées. Un premier résultat est qu’environ 20% des individus de l'échantillon de chaque ville font face à des déplacements de longue durée (plus de 100 minutes). Ensuite, le modèle de durées estimé suggère un comportement atypique de ces individus, qui n’est pas explicable uniquement par leurs caractéristiques renseignées dans les enquêtes de mobilités.Ensuite, les résultats des entretiens qualitatifs d’individus, dont les BTT sont supérieurs à deux heures sont présentés. Diverses dimensions illustrent les choix ou les obligations qui causent ces BTT extrêmes. L’approche sociologique qualitative complète l’approche économétrique quantitative et illustre que l’allocation de temps au transport n’est pas uniquement déterminée par l’activité à destination et les modes de transport, mais aussi par d’autres éléments tels que les convictions personnelles, les interactions avec les autres membres du ménage, la perception de ce temps de transport, etc. Notamment, le temps de transport peut être perçu comme un temps support d’autres activités (ex. travailler, écouter de la musique, etc.).TEMPS DE TRANSPORT;PENDULARITE;APPROPRIATION DES TEMPS DE TRANSPORT;MODELE DE SURVIE;APPROCHE MIXTE

Derivation of the Zakharov equations

This paper continues the study of the validity of the Zakharov model describing Langmuir turbulence. We give an existence theorem for a class of singular quasilinear equations. This theorem is valid for well-prepared initial data. We apply this result to the Euler-Maxwell equations describing laser-plasma interactions, to obtain, in a high-frequency limit, an asymptotic estimate that describes solutions of the Euler-Maxwell equations in terms of WKB approximate solutions which leading terms are solutions of the Zakharov equations. Because of transparency properties of the Euler-Maxwell equations, this study is led in a supercritical (highly nonlinear) regime. In such a regime, resonances between plasma waves, electromagnetric waves and acoustic waves could create instabilities in small time. The key of this work is the control of these resonances. The proof involves the techniques of geometric optics of Joly, M\'etivier and Rauch, recent results of Lannes on norms of pseudodifferential operators, and a semiclassical, paradifferential calculus

Predicted FeII Emission-Line Strengths from Active Galactic Nuclei

We present theoretical FeII emission line strengths for physical conditions typical of Active Galactic Nuclei with Broad-Line Regions. The FeII line strengths were computed with a precise treatment of radiative transfer using extensive and accurate atomic data from the Iron Project. Excitation mechanisms for the FeII emission included continuum fluorescence, collisional excitation, self-fluorescence amoung the FeII transitions, and fluorescent excitation by Lyman-alpha and Lyman-beta. A large FeII atomic model consisting of 827 fine structure levels (including states to E ~ 15 eV) was used to predict fluxes for approximately 23,000 FeII transitions, covering most of the UV, optical, and IR wavelengths of astrophysical interest. Spectral synthesis for wavelengths from 1600 Angstroms to 1.2 microns is presented. Applications of present theoretical templates to the analysis of observations are described. In particular, we discuss recent observations of near-IR FeII lines in the 8500 Angstrom -- 1 micron region which are predicted by the Lyman-alpha fluorescence mechanism. We also compare our UV spectral synthesis with an empirical iron template for the prototypical, narrow-line Seyfert galaxy I Zw 1. The theoretical FeII template presented in this work should also applicable to a variety of objects with FeII spectra formed under similar excitation conditions, such as supernovae and symbiotic stars.Comment: 33 pages, 15 postscript figure