Objetivo 2 experimental configuration causing the chaotic behaviour in a single mode carbon dioxide laser are investigated. The first involves a position feedback of the cavity losses where the effect of a delay time in the feedback loop is considered. The second configuration consists of a carbon dioxide laser with sinusoidal modulation applied to the cavity loss parameter.By using first passage time statistics the transient behaviour of a single mode of a carbon dioxide laser near threshold has been characterized.Spatiotemporal instabilities due to a nonlinear coupling between 2 or more transverse modes are investigated for a carbon dioxide laser. Several techniques to detect the profile of a carbon dioxide laser beam have been developed.The transition from a hexagonal to a roll pattern has been experimentally studied in Rayleigh-Benard convection under non-Boussinesq conditions (ie when the fluid parameters are function of temperature). The finite size effects have been analyzed in detail by comparing the experimental results with those of a Landau-Ginzburg amplitude equation. The topology of the defects in these patterns have been studied both theoretically and experimentally. The unstable phase is found to be present in the defects core. The wave number selection properties in thus geometry have been studied. The statistical properties of the Fourier spectra have been analyzed. It has been found that after the transition for space times chaos that the statistical distribution changes in a substantial way. Above the transition for space time chaos the Fourier mode amplitude distribution tends to a Gaussian shape. A tentative comparison of the properties of this transition with those of a system near thermal equilibrium has been made and a generalized temperature has been defined.The construction of a large cell in which it is possible to reach very high Rayleigh-Benard number (108) has been carried out. This cell will allow the study of the transition from chaos to fully developed turbulence which has only been analyzed in a few experiments.The fragmentation of a liquid drop falling in miscible fluid has been investigated. Independent of the nature of the fluid and of the size of drop. the phenomenon displays a universality ruled by a nondimensional fragmentation number.A method for measuring the vorticity field by means of sound waves has been studied. In surface waves experiments the possibilities of characterizing the transition to space time chaos by means of global parameters has been investigated. This last study is correlated with the one explained for Rayleigh-Benard convection.A conjecture on the fractal dimension of subsets of long chains of coupled maps has been accurately checked and its inconsistency proved. The standard algorithm on the estimate of distances from nearest neighbours has been improved to handle large sets of data points as required by the need to work in high dimensional spaces.The analogy between the evolution in the tangent space and the evolution of the discrete Schroedinger operator in the presence of a time dependent potential has been stressed. As a consequence an analytic solution of the Lyapunou spectrum of piece wise linear maps has been found. The samemethod has been successively extended to 2-dimensional maps and used to build a sort of mean field theory.A new method to approximate 2-dimensional maps (such as the Henon map) in terms of increasingly accurate 1-dimensional maps has been introduced. It is now possible to determine all forbidden words of the associated symbol sequences up to very long lengths (around 50 to 60 iterates). The limitations follow essentially from the round off error of the computer. The technique is very powerful since it allows the characterization of the topological properties of 2-dimensional maps (and, in turn, the metric structure) with very high accuracy, thus solving the problems associated with the methods based on periodic orbits.A 3-state cellular automation has been investigated, exploring operational regimes where algorithmic complexity and physical complexity (block entropy) have completely different behaviour.The aim was to characterize the transition to spatiotemporal chaos observed experimentally. The theoretical predications qualitatively agree with the main features of the phase transition. By a further refined numerical analysis it has been possible to observe some disagreement with the critical properties of directed percolating phenomena. A more phenomenological probabilistic automation model has been analyzed with a probability look up table directly extracted from experimental data. Relevant results have been obtained for the relationship of the dependence of the critical behaviour on the size of the sampling (finite size scaling analysis). A model has been studied of coupled map lattices, apt to describe the turbulent behaviours in reaction diffusion processes. Interesting numerical and anatylical results have been obtained. Firstly the relevance has been shown of the existence of periodic attractors in connection with the main dynamical features of such a class of models. Secondly the presence of choatic transients has been analyzed growing as a function of the number (N) of coupled maps. Numerical studies have been made of the Lyapunou spectrum of these dynamical systems, thus characterizing the full chaoticity of the model when exponentially growing transients are observed as N is increased. This approach seems quite promising for the understanding of turbulent phenomena as an effect of transient chaos. The study of violation of ergodicity in Hamiltonian models of nonlinearly coupled oscillators has continued mainly by improving the quality of the numerical simulations. A very clear indication was obtained on the presence of both stochasticity and equipartition threshold in such models. The design and construction has proceeded of a dedicated electronic machine for simulating the evolution of cellular automaton rules. The prototype of the machine has a modular structure with a memory matrix 256 x 256 x 8 which is updated in 0.01 s.The operating environment is as follows :The software has been written in C language. The hardware is the SUN 386 which is also used as a data processor. Ámbito científico natural sciencesmathematicspure mathematicstopologynatural sciencesmathematicsapplied mathematicsdynamical systemsnatural sciencesmathematicspure mathematicsgeometrynatural sciencesmathematicsapplied mathematicsnumerical analysisnatural sciencesphysical sciencesopticslaser physics Programa(s) FP2-SCIENCE - Programme plan (EEC) to stimulate the international cooperation and interchange needed by European research scientists (SCIENCE), 1988-1992 Tema(s) Data not available Convocatoria de propuestas Data not available Régimen de financiación CSC - Cost-sharing contracts Coordinador Centre National de la Recherche Scientifique (CNRS) Aportación de la UE Sin datos Dirección Parc Valrose 06034 Nice Francia Ver en el mapa Coste total Sin datos Participantes (5) Ordenar alfabéticamente Ordenar por aportación de la UE Ampliar todo Contraer todo AUTONOMOUS UNIVERSITY OF BARCELONA España Aportación de la UE Sin datos Dirección Campus Universitari Bellaterra 08193 BELLATERRA Ver en el mapa Coste total Sin datos Commissariat à l'Energie Atomique (CEA) Francia Aportación de la UE Sin datos Dirección Centre d'Études de Saclay 91191 Gif-sur-Yvette Ver en el mapa Coste total Sin datos ECOLE NORMALE SUPERIEURE DE LYON Francia Aportación de la UE Sin datos Dirección Allee d'Italie 45-47 69364 LYON Ver en el mapa Coste total Sin datos ISTITUTO NAZIONALE DI OTTICA APPLICATA Italia Aportación de la UE Sin datos Dirección Largo Enrico Fermi 6 50125 FIRENZE Ver en el mapa Coste total Sin datos UNIVERSITY OF FLORENCE Italia Aportación de la UE Sin datos Dirección Largo Enrico Fermi 2 50125 FIRENZE Ver en el mapa Coste total Sin datos
