Chemical behavior of tungstate solutions. Part 1. A spectroscopic survey of the species involved

This study is focused on the composition and the evolution of tungstate ions solutions as a function of pH and increasing concentrations. The Raman analysis showed that, during the titration of the tungstate solutions, WO4 2−, HWO4 − ions and probably W2O7 2−, HW2O7 2− and H2W2O7 solvated species could exist in aqueous solutions. For diluted solutions, additions of a strong acid does not cause any precipitation, whereas the formation of the unstable solid tungstic acid (H2WO4 or WO3·H2O) could occur in concentrated solutions

From Vlasov-Poisson and Vlasov-Poisson-Fokker-Planck Systems to Incompressible Euler Equations: the case with finite charge

We study the asymptotic regime of strong electric fields that leads from the Vlasov-Poisson system to the Incompressible Euler equations. We also deal with the Vlasov-Poisson-Fokker-Planck system which induces dissipative effects. The originality consists in considering a situation with a finite total charge confined by a strong external field. In turn, the limiting equation is set in a bounded domain, the shape of which is determined by the external confining potential. The analysis extends to the situation where the limiting density is non-homogeneous and where the Euler equation is replaced by the Lake Equation, also called Anelastic Equation.Comment: 39 pages, 3 figure

A maximum entropy principle explains quasi-stationary states in systems with long-range interactions: the example of the Hamiltonian Mean Field model

A generic feature of systems with long-range interactions is the presence of {\it quasi-stationary} states with non-Gaussian single particle velocity distributions. For the case of the Hamiltonian Mean Field (HMF) model, we demonstrate that a maximum entropy principle applied to the associated Vlasov equation explains known features of such states for a wide range of initial conditions. We are able to reproduce velocity distribution functions with an analytical expression which is derived from the theory with no adjustable parameters. A normal diffusion of angles is detected and a new dynamical effect, two oscillating clusters surrounded by a halo, is also found and theoretically justified.Comment: 4 pages, 3 figs, submitted to Phys. Rev. Let

Discussion of agglomeration mechanisms between hydrate particles in water in oil emulsions.

International audienceLine blockage due to gas hydrate formation in water/oil emulsions can be understood by considering the increase in the effective volume fraction of dispersed particles in the hydrate slurry. This increase is the result of an agglomeration process that takes place during hydrate formation. Two mechanisms of agglomeration reported in the literature are discussed. The first one is the contact-induced agglomeration mechanism for which the crystallization-agglomeration process is described as the result of the contact between a water droplet and a hydrate particle. The second one is the shear-limited agglomeration mechanism for which the balance between hydrodynamic force and adhesive force is considered. It is proposed to gather these two mechanisms in a unified model in order to predict the evolution of the viscosity of the slurry during hydrate formation. Such a model can be based on a Population Balance Model in which the agglomeration kernel is related to the contact-induced mechanism and the fragmentation kernel is related to the shear-limited mechanism

Clustering in a model with repulsive long-range interactions

A striking clustering phenomenon in the antiferromagnetic Hamiltonian Mean-Field model has been previously reported. The numerically observed bicluster formation and stabilization is here fully explained by a non linear analysis of the Vlasov equation.Comment: 8 pages, 5 Fig

Clustering and ensembles inequivalence in the phi-4 and phi-6 mean-field Hamiltonian models

We investigate a model of globally coupled conservative oscillators. Two different algebraic potentials are considered that display in the canonical ensemble either a second ($\phi^{4}$) or both a second and a first order phase transition separated by tricritical points ($\phi^{6}$). The stability of highly clustered states appearing in the low temperature/energy region is studied both analytically and numerically for the $\phi^{4}$-model. Moreover, long-lived out-of-equilibrium states appear close to the second order phase transition when starting with "water-bag" initial conditions, in analogy with what has been found for the Hamiltonian Mean Field (HMF) model. The microcanonical simulations of the $\phi^{6}$-model show strong hysteretic effects and metastability near the first-order phase transition and a narrow region of negative specific heat.Comment: To appear in the proceedings of the workshop "Chaotic Transport and Complexity in classical and quantum dynamics", Communications in Nonlinear Science and Numerical Simulation (2003

Large deviation techniques applied to systems with long-range interactions

We discuss a method to solve models with long-range interactions in the microcanonical and canonical ensemble. The method closely follows the one introduced by Ellis, Physica D 133, 106 (1999), which uses large deviation techniques. We show how it can be adapted to obtain the solution of a large class of simple models, which can show ensemble inequivalence. The model Hamiltonian can have both discrete (Ising, Potts) and continuous (HMF, Free Electron Laser) state variables. This latter extension gives access to the comparison with dynamics and to the study of non-equilibri um effects. We treat both infinite range and slowly decreasing interactions and, in particular, we present the solution of the alpha-Ising model in one-dimension with $0\leq\alpha<1$

Synthesis and anti-HIV activity of thiocholesteryl-coupled phosphodiester antisense oligonucleotides incorporated into immunoliposomes

Encapsulation of oligonucleotides in antibody-targeted liposomes (immunoliposomes) which bind to target cells permits intracellular delivery of the oligonucleotides. This approach circumvents problems of extracellular degradation by nucleases and poor membrane permeability which free phosphodiester oligonucleotides are subject to, but leaves unresolved the inefficiency of encapsulation of oligonucleotides in liposomes. We have coupled oligonucleotides to cholesterol via a reversible disulfide bond. This modification of oligonucleotides improved their association with immunoliposomes by a factor of about 10 in comparison to unmodified oligonucleotides. The presence of cholesteryl-modified oligonucleotides incorporated in the bilayer of liposomes did not interfere with the coupling of the targeting protein to the liposome surface. Free or cholesterol coupled oligonucleotides associated with liposomes and directed against the tat gene of HIV-1 were tested for inhibition of HIV-1 proliferation in acutely infected cells. We demonstrate that the cholesteryl-modified as well as unmodified oligonucleotides acquire the target specificity of the antibody on the liposome. Their antiviral activity when delivered into cells is sequence-specific. The activity of these modified or unmodified oligonucleotides to inhibit the replication of HIV was the same on an equimolar basis (EC50 around 0.1 μM). Cholesterol coupled oligonucleotides thus offer increased liposome association without loss of antiviral activity

Out-of-equilibrium states as statistical equilibria of an effective dynamics

We study the formation of coherent structures in a system with long-range interactions where particles moving on a circle interact through a repulsive cosine potential. Non equilibrium structures are shown to correspond to statistical equilibria of an effective dynamics, which is derived using averaging techniques. This simple behavior might be a prototype of others observed in more complicated systems with long-range interactions, like two-dimensional incompressible fluids or self-gravitating systems.Comment: 4 figure