Journal De Physique Ii 

About: Journal De Physique Ii is an academic journal. The journal publishes majorly in the area(s): Liquid crystal & Phase (matter). It has an ISSN identifier of 1155-4312. Over the lifetime, 914 publications have been published receiving 19378 citations.

Boundary flow condition analysis for the three-dimensional lattice Boltzmann model

Abstract: In the continuum limit, the velocity of a Newtonian fluid should vanish at a solid wall. This condition is studied for the FCHC lattice Boltzmann model with rest particles. This goal is achieved by expanding the mean populations up to the second order in terms of the ratio e between the lattice unit and a characteristic overall size of the medium. This expansion is applied to two extreme flow situations. In Poiseuille flow, the second eigenvalue of the collision matrix can be chosen so that velocity vanishes at the solid walls with errors smaller than e2 ; however the choice depends on the angle between the channel walls and the axes of the lattice. In a plane stagnation flow, the tangential and normal velocities do not vanish at the same point, except for particular choices of the parameters of the model ; this point does not coincide with the solid wall. It is concluded that the boundary conditions are as a matter of fact imposed with errors of second order.

Dynamic coupling between stress and composition in polymer solutions and blends

Abstract: Phenomenological hydrodynamic equations are proposed for entangled polymer blends as generalization of those for polymer solutions. They can describe coupling between macroscopic flow and relative diffusion. The key concept we use is the "tube velocity" introduced by Brochard in the problem of mutual diffusion in polymer blends. As applications, (I) we give a general expression for the time-correlation function of the polymer concentration around equilibrium and examine its relaxation in some typical cases. It can be strongly influenced by the viscoelastic effect when the two polymers have different lengths. Our expression can also be used for gelling solutions and explains previous dynamic light scattering experiments at the sol-gel transition. (ii) Detailed calculations are performed for the case of a single rheological relaxation time (the Maxwell model). The steady state structure factor is obtained to Iinear order in macroscopic flow. (iii) We predict that composition inhomogeneity is created in mixtures oflong and short polymers undergoing nonuniform flow. Its origin is that the longer chains support stress more than the shorter ones and the resultant imbalance of stress causes relative motion of the two polymers. These results are applicable both to solutions and blends.

Effect of shear on a lyotropic lamellar phase

Abstract: We present a series of experiments, using different techniques such as light scattering, conoscopy, neutron scattering and microscopic observations, to determine the orientation of lyotropic lamellar phases under shear. Three states of orientation are observed, depending upon both the shear rate and the inter-membrane separation. These steady states are separated by dynamic transitions. Among the states described, we focus our attention on a state made of monodisperse close-packed multilayered vesicles whose size is precisely fixed by the shear rate.

Budding of membranes induced by intramembrane domains

Abstract: . — Membranes are often composed of a mixture of amphiphilic molecules whichaggregate into clusters or domains. A simple theoretical model is introduced which predictsthat flat or weakly curved domains become unstable at a certain limiting size and then undergoa budding or invagination process. This shape transformation is primarily driven by the linetension of the domain edge. It is also predicted that the budding domain can rupture themembrane and then pinch off from the matrix. The size of the bud and the time scales involvedin the budding dynamics are estimated for model membranes composed of lipid mixtures. Thisinstability mechanism should also be effective for the budding of biomembranes. 1. Introduction. Membranes such as lipid bilayers are highly flexible and thus can easily change their shape.Recently, a variety of shape transformations have been observed by phase contrast microscopyof giant lipid vesicles [1-7]. It was found that these vesicles can exhibit budding or invaginationprocesses in which small vesicles bud off from a larger membrane surface. These processescan be simply induced by a change in temperature. Such temperature-induced budding canbe understood theoretically if one assumes that the lipid bilayer of the vesicle is laterallyhomogeneous. Its shape is then determined, to a large extent, by the area to volume ratio.The thermal expansivity of the bilayer membrane is large compared to that of the water.Therefore, as the temperature is increased, the bilayer membrane expands more rapidly thanthe enclosed water, and the area to volume ratio of the vesicles is increased.In biological cells, budding is a rather frequent event since it represents the first step inthe production of transport vesicles which shuttle between different compartments of the cell[8-11]. Two budding processes can be distinguished: (i) Endocytosis of the plasma membrane,i.e., budding of the plasma membrane towards the

The Feynman path integral approach to atomic interferometry: A tutorial

Abstract: Many problems of current interest in atomic interferometry lend themselves to a path integral treatment. We present a practical guide to solving such problems, taking as examples the gravitational experiments of Kasevich and Chu, and the atomic equivalents of the Sagnac and Aharonov-Bohm effects. Atomic interferometry is a new and rapidly-developing field of research, concerned with physical phenomena in which the wave-nature of neutral atoms plays an important role ill. The wide variety of internal degrees of freedom of an atom opens up new possibilities for investigation which do not exist in the more traditional types of interferometry using photons, electrons and neutrons. The development of atomic interferometry has been aided by recent technical advances, particularly in the manipulation of atoms. New mechanisms for slowing, deflecting, cooling and trapping atoms allow control of both their position and momentum. Also important has been the birth of "atomic optics", a range of mechanisms providing the equivalent of mirrors, beamsplitters and lenses for atoms. Recently it has been pointed out that certain high-resolution spectroscopy techniques which avoid the Doppler effect amount to realizing an atomic interferometer (2). These methods have since been adapted to measure inertial fields (due to rotation and gravitation) by atomic interferometry. The situation encountered in atomic interferometry experiments is often close to the classical limit. When this is the case a path integral approach to the analysis is very appropriate since it reduces to a calculation of integrals along classical paths. Further simplifications can be made if the Lagrangian is quadratic, as is true for a particle in a gravitational field or a rotating (*) The Laboratoire Kastler Brossel is associated with the CNRS and the Universit4 Pierre et Marie