On Drinfel'd associators

In 1986, in order to study the linear representations of the braid group $B\_n$coming from the monodromy of the Knizhnik-Zamolodchikov differential equations,Drinfel'd introduced a class of formal power series $\Phi$on noncommutative variables. These formal series can be considered as a class of associators. We here give an interpretation of them as well as some new tools over Noncommutative Evolution Equations. Asymptotic phenomena are also discussed

Phantom Black Holes in Einstein-Maxwell-Dilaton Theory

We obtain the general static, spherically symmetric solution for the Einstein-Maxwell-dilaton system in four dimensions with a phantom coupling for the dilaton and/or the Maxwell field. This leads to new classes of black hole solutions, with single or multiple horizons. Using the geodesic equations, we analyse the corresponding Penrose diagrams revealing, in some cases, new causal structures.Comment: Latex file, 32 pages, 15 figures in eps format. Typo corrected in Eq. (3.18

Phantom Black Holes and Sigma Models

We construct static multicenter solutions of phantom Einstein-Maxwell-dilaton theory from null geodesics of the target space, leading to regular black holes without spatial symmetry for certain discrete values of the dilaton coupling constant. We also discuss the three-dimensional gravitating sigma models obtained by reduction of phantom Einstein-Maxwell, phantom Kaluza-Klein and phantom Einstein-Maxwell-dilaton-axion theories. In each case, we generate by group transformations phantom charged black hole solutions from a neutral seed.Comment: 19 page

Sea level and dynamic topography in the Western Pacific during 1982-83 El Nino

Pendant le fort El Nino 1982-1983, deux réseaux d'observations océanographiques ont fourni des données continues dans le Pacifique tropical : le réseau de mesure du niveau de la mer créé et maintenu par l'Université d'Hawaii et le réseau XTB - navires marchands du groupe SURTROPAC, Centre ORSTOM de Nouméa - La topographie dynamique mensuelle 0-400 db est calculée le long de la route Nouméa-Japon (20°S-20°N, 150°E-165°E), en utilisant des relations T-S réelles, pour faire ressortir les anomalies interannuelles. Cette topographie est comparée aux valeurs mensuelles du niveau de la mer. Ce très bon accord obtenu entre les variations spatio-temporelles déduites des deux réseaux montre qu'ils se complètent utilement dans la surveillance des anomalies climatiques. (Résumé d'auteur

Infrared problem for the Nelson model on static space-times

We consider the Nelson model with variable coefficients and investigate the problem of existence of a ground state and the removal of the ultraviolet cutoff. Nelson models with variable coefficients arise when one replaces in the usual Nelson model the flat Minkowski metric by a static metric, allowing also the boson mass to depend on position. A physical example is obtained by quantizing the Klein-Gordon equation on a static space-time coupled with a non-relativistic particle. We investigate the existence of a ground state of the Hamiltonian in the presence of the infrared problem, i.e. assuming that the boson mass tends to 0 at infinity

Effect of growth conditions on optical properties of CdSe/ZnSe single quantum dots

In this work, we have investigated the optical properties of two samples of CdSe quantum dots by using submicro-photoluminescence spectroscopy. The effect of vicinal-surface GaAs substrates on their properties has been also assessed. The thinner sample, grown on a substrate with vicinal surface, includes only dots with a diameter of less than 10 nm (type A islands). Islands of an average diameter of about 16 nm (type B islands) that are related to a phase transition via a Stranski-Krastanow growth process are also distributed in the thicker sample grown on an oriented substrate. We have studied the evolution of lineshapes of PL spectra for these two samples by improving spatial resolution that was achieved using nanoapertures or mesa structures. It was found that the use of a substrate with the vicinal surface leads to the suppression of excitonic PL emitted from a wetting layer.Comment: 2pages, 2 figures, Proceedings of International Conference On Superlattices Nano-Structures And Nano-Devices, July, Toulouse, France, to appear in the special issue of Physica