No abstract available

[en] Using long time-series counting in a neutron scattering experiment, hydrodynamic fluctuations were studied near the Rayleigh-Benard instability in para-azoxyanisole. Critical enhancement was observed and the coupling to inner orientational fluctuations of the nematic liquid crystal was demonstrated through the response of the signal to an external magnetic field. The similarity of the experimental curves to those of critical scattering in equilibrium physics lends support to the phase-transition analogy of hydrodynamic instabilities. (orig.) 891 EZ/orig. 892 MB

No abstract available

[en] Polarized neutron provide the only possibility for accurately measuring the critical indices β, γ and delta by neutron scattering. The method has been used in a study of the magnetic phase transition in Fe₃O₄, for which the critical indices of each of the two sublattices were measured and found equal. The results will be discussed in the context of universality and scaling. (orig.)

[en] Employing a real-time method, neutron scattering has been used in the investigation of nonlinear convection and the development of chaos in a nematic liquid crystal. Features of the experimental method are explained. The data processing involved in obtaining the autocorrelation function, the power spectrum, the phase portrait and the fractal dimension of strange attractors is demonstrated. The convective system under study is shown to be a rich nonequilibrium system, displaying multicritically, multistability, period doubling and chaos. (orig.)

No abstract available

[en] Published in summary form only

[en] Eventually conventional neutron spectroscopy has to fail when the neutron passage time over a correlation range becomes shorter than the characteristic time that we are trying to measure. We shall discuss below the merits of a complementary method, a real-time method, which in principle works when the conventional method fails. It seems worthwhile to seriously consider this method as much of the scientific interest moves to mesoscopic and to nonequilibrium systems. We have used this method for some years in the study of convection instabilities in nematic liquid crystals. Probably we have discovered more problems than we have solved, but perhaps a presentation of them is justified at a workshop where we are discussing the problems of tomorrow

No abstract available

No abstract available