2,446 research outputs found
On Drinfel'd associators
In 1986, in order to study the linear representations of the braid group
coming from the monodromy of the Knizhnik-Zamolodchikov differential
equations,Drinfel'd introduced a class of formal power series 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
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
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
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
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