Virtual Compton scattering off nuclei in the Δ\Delta-resonance region

Virtual Compton scattering in the $\Delta$-resonance region is considered in the case of a target nucleus. The discussion involves generalized polarizabilities and is developed for zero-spin nuclei, focusing on the new information coming from virtual Compton scattering in comparison with real Compton scattering.Comment: 8 pages, LaTeX, 3 figures available from the author

Anisotropic elasticity in confocal studies of colloidal crystals

We consider the theory of fluctuations of a colloidal solid observed in a confocal slice. For a cubic crystal we study the evolution of the projected elastic properties as a function of the anisotropy of the crystal using numerical methods based on the fast Fourier transform. In certain situations of high symmetry we find exact analytic results for the projected fluctuations.Comment: 6 pages, 7 figure

The space-time structure of hard scattering processes

Recent studies of exclusive electroproduction of vector mesons at JLab make it possible for the first time to play with two independent hard scales: the virtuality Q^2 of the photon, which sets the observation scale, and the momentum transfer t to the hadronic system, which sets the interaction scale. They reinforce the description of hard scattering processes in terms of few effective degrees of freedom relevant to the Jlab-Hermes energy range.Comment: 4 pages; 5 figure

Harmonics detection in a vibration spectrum by image processing methods

This paper presents a problem of signal analysis which is treated by methods issued from image processing, mainly mathematical morphology . It concerns spectrum analysis of rotating machines vibrations . We propose a method for extracting harmonics families from an autospectrum, without any previous knowledge about it . It allows as well to detect local lack of resolution in the spectrum .Dans cet article nous abordons un problème posé par l'analyse des signaux temporels à l'aide d'une méthode dérivée du traitement des images. Nous l'avons développée pour l'analyse des spectres de vibrations engendrées par des machines tournantes . Nous proposons ici une méthode qui extrait les familles d'harmoniques d'un autospectre sans aucune connaissance a priori sur celui-ci . Elle permet également de reconnaître des fréquences sur lesquelles il y a manque de résolution

Non-diffractive mechanisms in the ϕ\phi meson photoproduction on nucleons

We examine the non-diffractive mechanisms in the $\phi$ meson photoproduction from threshold up to a few GeV using an effective Lagrangian in a constituent quark model. The new data from CLAS at large angles can be consistently accounted for in terms of {\it s}- and {\it u}-channel processes. Isotopic effects arising from the reactions $\gamma p\to \phi p$ and $\gamma n\to \phi n$, are investigated by comparing the cross sections and polarized beam asymmetries. Our result highlights an experimental means of studying non-diffractive mechanisms in $\phi$ meson photoproduction.Comment: 4 eps figures, version accepted by Phys. Lett.

Color quantization and image analysis

The aim of this paper is to provide an up-to-date review of the numerous aspects and technics of color quantization used in image analysis. This synthesis is all the more necessary that this field of study is in high expansion . In this article, we also propose several criteria and study parameters linked to visual analysis in order to improve the existing color quantization methods or to define new more accurate methods.L'objectif de cet article est de faire une synthèse sur les multiples aspects et techniques de quantification couleur développés en analyse d'image. Cette synthèse s'avère d'autant plus nécessaire que cette voix de recherche est en plein essor et que de multiples techniques peuvent être utilisées. Cet article propose également plusieurs critères et paramètres d'étude, fondés sur l'analyse visuelle, afin d'améliorer les méthodes de quantification couleur existantes ou de définir de nouvelles méthodes plus pertinentes

Pion emission in 2H, 12C, 27Al, gamma pi+ reactions at threshold

The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.Comment: 19 pages, 7 figure

Image segmentation using local-base pyramids

This paper describes an approach to image segmentation. ne methods intended for images where local topographie irregularities contrast with their noisy backgrounds . Since the method bas to bel localized and adoptive, the description of each object uses a local-base pyramid, called "local pyramid" . It simulates the human vision in its attention focusing . Using such a tool, each object is described independently and with respect to the image texture .Dans cet article, nous abordons un problème de segmentation d'images, caractérisées par des irrégularités topographiques qui n'émergent que localement d'un fond bruité. Dans ce cas, la méthode de segmentation ne peut être que localisée et adaptative. Pour cela, la description d'un objet se fait par l'utilisation d'une pyramide à base locale - appelée «pyramide locale» - simulant la focalisation de l'œil sur les zones sensibles de l'image. Ainsi, chaque objet est analysé indépendamment et en fonction de la texture intrinsèque de l'imag

Adolescent drug use escalation and de-escalation: a 3-year follow-up study [Abstract]

This study aims to assess adolescents drug use with a longitudinal perspective in order to identify factors interacting with drug use onset and course. Supported by the Swiss Federal Office of Public Health, the study was initiated in 1999 with a follow-up in 2001 and 2002. The first objective was to measure risk factors for substance use initiation. The second objective was to analyse the co-variation of substance use with environmental, social, relational, medical and psychological factors. A total of 102 adolescents, aged 14-19 years, were recruited for the study in the French-speaking part of Switzerland. Results clearly show that substance use is not a disorder per se in adolescence, but that it is part of a multidimensional complex of problems that some adolescents may encounter: increase and decrease in substance use is paralleled with an increase or decrease in the other areas. This implies that prevention of substance use should not be focused mainly on substances but should consider the adolescent's environment and significant life area

Multipole analysis of spin observables in vector meson photoproduction

A multipole analysis of vector meson photoproduction is formulated as a generalization of the pseudoscalar meson case. Expansion of spin observables in the multipole basis and behavior of these observables near threshold and resonances are examined.Comment: 15 pages, latex, 2 figure