The observation of an incommensurate diffraction pattern in urea inclusion compounds by neutron diffraction is reported. It reveals for the first time in these compounds the existence of all kinds of reflections expected for an intermodulated composite. The superspace analysis together with the temperature evolution of some characteristic reflections are presented

Ha -Flow in channels. PACS. 83.80.Iz -Emulsions and foams. PACS. 83.85.Jn -Viscosity measurements.Abstract. -We study experimentally the pressure drop needed to push a bubble train in a millimetric channel, as a function of the velocity. For dry liquid foams, the influence of the amount of liquid and of the bubble size is pointed out and we predict theoretically that this influence is closely related to the power law obtained for the force/velocity relation. This model is in fair agreement with our experimental data and provides a new interpretation of previous results.c EDP Sciences

We present neutron scattering investigations of the structural dynamical properties of the aperiodic layered compound, Bi2Sr2CaCu2O 8+δ . Acoustic phonons behave identically around the assumed average structure Bragg reflection and around the first satellite. This observation proves that the collective dynamics related to the incommensurate structure are quite different from what is expected in a modulated incommensurate model. Our data indicate two acoustic-like longitudinal branches along the incommensurate direction. Such behavior is compatible with a composite incommensurate structure where these two Bragg peaks correspond to the main reflections of each subsystem.