Journal De Physique 

About: Journal De Physique is an academic journal. The journal publishes majorly in the area(s): Liquid crystal & Scattering. It has an ISSN identifier of 0302-0738. Over the lifetime, 4891 publications have been published receiving 106251 citations.

Adsorption of chain molecules with a polar head a scaling description

Abstract: The adsorption of chain molecules at an interface is investigated assuming that the molecule has both a polar head type of attraction localized on the chain and a uniform interaction of the chain monomers with the surface. A scaling description of the chain configurations and interactions is used. It is shown that the presence of a uniform surface attraction changes the phase diagram drastically. Both a low density two-dimensional regime and a high density phase with the chains confined in narrow cylinders can occur. The transition between the two phases is first order. Power laws for the surface density, layer thickness and surface pressure are derived. The qualitative similarity with the behaviour observed for short chain lipids and surfactants is also noted and it is suggested that a uniform surface interaction may also play an important role there.

Star shaped polymers : a model for the conformation and its concentration dependence

Abstract: We propose a model giving the conformation of a star shaped polymer by taking into account the radial variation of the monomer concentration ϕ( r). For an isolated star when increasing r (at the centre of the star r = 0), the variation of ϕ (r) is first given by a constant value (r f1/2 ν-1 l); wh ere f is the number of branches, N the number of monomers in a branch and ν and l are the excluded volume and the length associated to a monomer. For all these cases, it is shown that the size of a branch is always larger than that of a linear polymer made of N monomers. Beyond the overlapping concentration the star conformation is obtained from two characteristic lengths essentially : χ(c ) a radius inside which the branches of the other stars do not penetrate, this radius defines a domain where the conformation of a star is similar to that of an isolated one. Beyond χ(c) the interpenetration of branches is characterized by a screening length ξ(c) very similar to that found for semi-dilute solutions of linear polymers. For all these regimes the variation of the size of a star is predicted as a function of N, f, v and c.

Modèle de fonction aléatoire de couverture applicable aux phénomènes de filiation à base poissonnienne

Abstract: On etudie un modele statistique applicable aux phenomenes de filiation radioactive a plusieurs etages. Chaque evenement se traduisant par une realisation d'une impulsion aleatoire, on determine les statistiques des deux premiers ordres de la fonction de couverture associee au phenomene global, en fonction des differentes lois des retards aleatoires introduits par le phenomene de filiation.

Diagonalisation d'une classe d'hamiltoniens de spin

Abstract: On diagonalise une classe a 2 N parametres d'hamiltoniens quadratiques dependant de N spins de grandeur arbitraire. Diverses extensions et applications sont donnees, en particulier celle de l'oscillateur couple a une collection de systemes independants a deux niveaux.

Kondo effect in real metals

Abstract: Starting from the most general form of the Anderson hamiltonian, the behaviour of magnetic impurities in real metals is considered, taking into account the orbital structure of the local impurity electrons, crystal field and spin orbit splittings. The analysis is carried out in an atomic limit, in which the impurity has a well defined integer valency (a Schrieffer Wolff transformation is then valid). The main steps of a scaling procedure are described in detail. As the temperature goes down, the excited states of the ground state configuration decouple one after the other. The hierarchy of these decouplings, and their interplay with Kondo singularities are analyzed. When a Fermi liquid picture applies as T → 0, the number of independent parameters may be reduced considerably using symmetry and universality arguments which bypass the numerical description of the crossover region. That first part sets a language in which to describe specific problems. We apply that language to the case where the atomic ground state is an orbital singlet. In the absence of anisotropies, the only parameters are the impurity spin S and the number of orbital channels n. We show that an anomalous fixed point occurs at finite coupling when n > 2 S. That fixed point is unstable with respect to anisotropies. The scaling trajectories are discussed for a cubic crystal field for several choices of valencies. The universality of the low temperature behaviour is clarified. A similar analysis is carried out when the atomic ground state only has one electron (or hole). The influence of crystal field and spin orbit interactions is analyzed — and their relevance to the Kondo crossover and to universality is ascertained.