Problemi gerarchici di punti di Nash: Esistenza e approssimazione nel caso di unicita al livello inferiore

In this paper a two level optimization problem, in which the problem of inferior level is a Nash-problem with general constraints (rappresented by multifunctions) and with a unique solution, is considered. On the problem of inferior level approximation results of the solution are proved, on the problem of superior level existence and approximation results of the solutions are proved.      

Annealing effects on the magnetization of Co–Ni–B amorphous nanoparticles

Chemically prepared (Co_xNi_1−x)_1−yB_y (x=0.5, 0.75, 1; y≈0.4) amorphous fine particles were characterized by X-ray diffraction, DTA and TGA, and in situ magnetic measurement as a function of annealing temperature in an inert atmosphere. Magnetic measurement performed in as-prepared and 150°C annealed samples shows an increase of the saturation magnetization and magnetic moment after thermal treatment. Room temperature magnetization increases by factors of 3.5, 1.8, and 1.5, for x=0.5, 0.75, and 1, respectively. These measurements may indicate a local re-ordering of the amorphous phase at temperatures much lower than the full crystallization temperature.     

Solvent-dependent host–guest complexation of two homologous merocyanines by a water-soluble calix[8]arene: Spectroscopic analysis and structural calculations

The sulfonated calixarene I₈C₁₂ acts as a host for homologous merocyanines Mc1 and Mc2 in organic solvents, exhibiting neither selectivity towards the guest dyes nor solvent dependence of the complexation equilibria. In water, on the contrary, only the lower homologue, Mc1, is solubilized in the presence of the calixarene. A combination of UV–visible and fluorescence spectroscopic and photophysical analysis and MD structural simulation of the calixarene-dye complexes was employed to account for the observations, and suggests that a radical change in the complexation mode occurs upon moving from an organic to an aqueous environment.     

Numerical experiments on billiards

We investigate decay properties of correlation functions in a class of chaotic billiards. First we consider the statistics of Poincaré recurrences (induced by a partition of the billiard): the results are in agreement with theoretical bounds by Bunimovich, Sinai, and Bleher, and are consistent with a purely exponential decay of correlations out of marginality. We then turn to the analysis of the velocity-velocity correlation function: except for intermittent situations, the decay is purely exponential, and the decay rates scale in a simple way with the (uniform) curvature of the dispersing arcs. A power-law decay is instead observed when the system is equivalent to an infinite-horizon Lorentz gas. Comments are given on the behaviour of other types of correlation functions, whose decay, during the observed time scale, appears slower than exponential.     

Metastability and exponential approach to equilibrium for low-temperature stochastic Ising models

We present a proof of the exponential convergence to equilibrium of single-spin-flip stochastic dynamics for the two-dimensional Ising ferromagnet in the low-temperature case with not too small external magnetic fieldh uniformly in the volume and in the boundary conditions.     

Projections of Gibbs measures may be non-Gibbsian

Consider the + phase of the two dimensional nearest neighbor ferromagnetic Ising model at a temperature belowT _c . Let ₊ be the restriction of this measure to a coordinate axis. We prove that there is no one dimensional translation invariant summable interaction for which ₊ is a Gibbs measure. This is proven by showing that if such an interaction existed, ₊ would have large deviation properties different from those it actually has. Percolation methods are used in the proof.Work supported by the U.S. Army Research Office through the Mathematical Sciences Institute at Cornell and by a NSF grant to Cornell. This work was finished while the author was visiting Rutgers University, being supported by the NSF grant 86-12369     

Small random perturbations of finite- and infinite-dimensional dynamical systems: Unpredictability of exit times

We apply previous results on the pathwise exponential loss of memory of the initial condition for stochastic differential equations with small diffusion to the problem of the asymptotic distribution of the first exit times from an attracted domain. We show under general hypotheses that the suitably rescaled exit time converges in the zero-noise limit to an exponential random variable. Then we extend the results to an infinite-dimensional case obtained by adding a small random perturbation to a nonlinear heat equation.     

Preparation and electrochemical behavior of ordered rh adlayers on Pt(100) electrodes

Rhodium adlayers on Pt(100) substrates have been prepared by electrodeposition from dilute Rh(III) acidic solutions. The initially disordered layer is electrochemically annealed by applying a polarization program consisting of high-sweep-rate multicycle sequences between 0.05 and 0.78 V(RHE) in 0.1 M H(2)SO(4). In this way, a pseudomorphic Rh monolayer can be prepared on Pt(100) substrates. The degree of order of the electrochemically annealed layer has been evidenced not only through voltammetric experiments but also by means of scanning tunneling microscopy with atomic resolution for iodine-protected adlayers, which show a c(2 x 2) structure. The electrochemically induced ordering of the Rh adlayer appears to be a consequence of the repeated cycles of adsorption/desorption of H and, especially, oxygenated species. Voltammetry in sulfuric acid solutions permits examination of the energetics of H/anions and OH/O adsorption as a function of the Rh coverage. The first monolayer adsorbs both hydrogen and oxygenated species more strongly than the second one. This can be explained through an electronic effect caused by the underlying Pt(100) substrate.     

The effect of the anion on the physical properties of trihalide-based N,N-dialkylimidazolium ionic liquids

Low viscosity, high density trihalide-based 1-n-butyl-3-methylimidazolium ionic liquids have been prepared and characterised. Key physical properties (density, conductivity, melting point, refractive index, surface tension and diffusion coefficient) of the ionic liquids have been determined and are compared with those of other 1,3-dialkylimidazolium molten salts. The relationship between anion identity and the physical properties of the ionic liquids under investigation is discussed.