Planet gaps in the dust layer of 3D proto-planetary disks: Observability with ALMA

Among the numerous known extrasolar planets, only a handful have been imaged directly so far, at large orbital radii and in rather evolved systems. The Atacama Large Millimeter/submillimeter Array (ALMA) will have the capacity to observe these wide planetary systems at a younger age, thus bringing a better understanding of the planet formation process. Here we explore the ability of ALMA to detect the gaps carved by planets on wide orbits.Comment: 2 pages, 2 figures, to appear in the Proceedings of IAU Symp. 299: Exploring the Formation and Evolution of Planetary Systems (Victoria, Canada

Evitement scolaire : la fuite des collégiens vers Paris

Avoidance of the legal school-area spreads in both space and society. The object of this paper is to analyse the flow of pupils who live in the suburban area and (illegally) choose their secondary schools in the inner-Paris. Since it is not usual, this behaviour has great consequences on social structures, as factorial analysis says. Some interviews with parents and school administrators show that the avoidant families are moving for different reasons; moreover, the benefit may vary: better social integration not always occurs.L'évitement scolaire (l'ensemble des pratiques des familles qui scolarisent leurs enfants dans un autre établissement que celui de l'aire de recrutement à laquelle appartient leur domicile) se diffuse rapidement dans l'espace et la société. On cherche ici à cerner le mouvement des élèves banlieusards qui viennent s'inscrire au collège à Paris intra-muros. Ces « migrants » sont peu nombreux, mais les conséquences locales de l'évitement peuvent être très importantes, notamment en affectant la composition sociale des établissements : c'est ce que montrent les résultats d'une Analyse Factorielle des Correspondances. Des entretiens avec les parents d'élèves et les responsables de l'administration scolaire permettent enfin de montrer que les motifs des migrants sont divers et leur réussite inégale : l'accès à Paris n'est pas synonyme d'intégration sociale automatique

Les évolutions récentes de la division sociale de l'espace francilien: observation des discontinuités structurelles par l'analyse discriminante

International audienceIn order to understand how the social divisions of residential space in Île-de-France evolved between 1990 and 1999, the problem of measuring discontinuities was tackled. To measure major social change in space, this paper proposes an approach combining smoothing and discriminant analysis. The data used (socio-professional categories from INSEE's censuses of 1990 and 1999 at the level of each IRIS district) show that the two socially opposed spaces are extremely compact and are becoming even more so as small existing centres merge. Mapping also shows a clear trend towards a reinforcement and linearisation of the discontinuities surrounding the more disadvantaged spaces. Conversely, the discontinuities observed around the edges of the most advantaged spaces followed various patterns between 1990 and 1999.Lorsque l'on cherche à comprendre comment a évolué la division sociale de l'espace résidentiel francilien entre 1990 et 1999, on est confronté au problème de la mesure des discontinuités. Pour mesurer la brutalité du changement social dans l'espace, on propose une démarche combinant le lissage et l'analyse discriminante. D'après les données utilisées (catégories socioprofessionnelles des recensements 1990 et 1999 de l'INSEE à l'échelon du quartier IRIS), on remarque une grande compacité des deux espaces socialement opposés, compacité tendant à se renforcer par la coalescence des petits pôles existants. La cartographie montre également une très nette tendance au renforcement, à la linéarisation des discontinuités circonscrivant les espaces globalement les moins favorisés. À l'opposé, les discontinuités que l'on pouvait observer aux bords des espaces les plus favorisés ont connu des évolutions diverses entre 1990 et 1999

Steganography: a class of secure and robust algorithms

This research work presents a new class of non-blind information hiding algorithms that are stego-secure and robust. They are based on some finite domains iterations having the Devaney's topological chaos property. Thanks to a complete formalization of the approach we prove security against watermark-only attacks of a large class of steganographic algorithms. Finally a complete study of robustness is given in frequency DWT and DCT domains.Comment: Published in The Computer Journal special issue about steganograph

Steganography: a Class of Algorithms having Secure Properties

Chaos-based approaches are frequently proposed in information hiding, but without obvious justification. Indeed, the reason why chaos is useful to tackle with discretion, robustness, or security, is rarely elucidated. This research work presents a new class of non-blind information hidingalgorithms based on some finite domains iterations that are Devaney's topologically chaotic. The approach is entirely formalized and reasons to take place into the mathematical theory of chaos are explained. Finally, stego-security and chaos security are consequently proven for a large class of algorithms.Comment: 4 pages, published in Seventh International Conference on Intelligent Information Hiding and Multimedia Signal Processing, IIH-MSP 2011, Dalian, China, October 14-16, 201