Chaos and Taub-NUT related spacetimes

The occurrence of chaos for test particles moving in a Taub-NUT spacetime with a dipolar halo perturbation is studied using Poincar\'e sections. We find that the NUT parameter (magnetic mass) attenuates the presence of chaos.Comment: 10 pages, 5 Postscript figure

Leveraging different meronym discovery methods for bridging resolution in French

International audienceThis paper presents a statistical system for resolving bridging descriptions in French, a language for which current lexical resources have a very low overage. The system is similar to that developed for English by Poesio but it was enriched to integrate meronymic information extracted automatically from both web queries and raw text using syntactic patterns. Through various experiments on the DEDE corpus, we show that although still mediocre the performance of our system compare favorably to those obtained by Poesio for English. In addition, our evaluation indicates that the different meronym extraction methods have a cumulative effect, but that the text pattern-based extraction method is more robust and leads to higher accuracy than the web-based approach

Chaos and Rotating Black Holes with Halos

The occurrence of chaos for test particles moving around a slowly rotating black hole with a dipolar halo is studied using Poincar\'e sections. We find a novel effect, particles with angular momentum opposite to the black hole rotation have larger chaotic regions in phase space than particles initially moving in the same direction.Comment: 9 pages, 4 Postscript figures. Phys. Rev. D, in pres

Chaotic Motion Around Prolate Deformed Bodies

The motion of particles in the field of forces associated to an axially symmetric attraction center modeled by a monopolar term plus a prolate quadrupole deformation is studied using Poincare surface of sections and Lyapunov characteristic numbers. We find chaotic motion for certain values of the parameters, and that the instability of the orbits increases when the quadrupole parameter increases. A general relativistic analogue is briefly discussed.Comment: RevTEX, 7 eps figures, To appear in Phys Rev E (March 2001