Selective grafting of amine groups on polyethylene by means of NH3−H2 RF glow discharges

Plasma treatments in Radio Frequency Glow Discharges fed with NH₃−H₂ mixtures have been performed for modifying polyethylene surfaces. Treatment kinetics and the role of species present in the glow have been investigated. Actinometric Optical Emission Spectroscopy has been utilized as a plasma diagnostic technique. Electron Spectroscopy for Chemical Analysis has been utilized for studying surface composition of treated substrates, which have been examined both astreated and after derivatization of amine-functionalities with 4-trifluoromethylbenzaldehyde vapors. It has been found that experimental plasma parameters and plasma density of active species can be controlled to achieve selective grafting of-NH₂ among all other nitrogen-containing groups.     

Statistical physics, optimization and source coding

The combinatorial problem of satisfying a given set of constraints that depend on N discrete variables is a fundamental one in optimization and coding theory. Even for instances of randomly generated problems, the question “does there exist an assignment to the variables that satisfies all constraints?” may become extraordinarily difficult to solve in some range of parameters where a glass phase sets in. We shall provide a brief review of the recent advances in the statistical mechanics approach to these satisfiability problems and show how the analytic results have helped to design a new class of message-passing algorithms — the survey propagation (SP) algorithms — that can efficiently solve some combinatorial problems considered intractable. As an application, we discuss how the packing properties of clusters of solutions in randomly generated satisfiability problems can be exploited in the design of simple lossy data compression algorithms.     

A convenient synthesis of unsymmetrically substituted terphenyls of biologically active stilbenes via a double Suzuki cross-coupling protocol

A double Suzuki cross-coupling protocol has been devised as a practical route to a variety of terphenyls. Good chemoselectivity was observed. Unsymmetrically substituted triphenylenes were also easily prepared.     

Diffusion of interacting particles in one-dimensional heterogeneous systems

The equilibrium and transport properties of interacting ad-particles on bivariate heterogeneous chains are studied by combining analytical and simulation approaches. Heterogeneity is introduced in the way of patches of shallow and deep adsorbing sites distributed in a deterministic alternating way. Adsorption isotherms and mean-square fluctuations of the surface coverage, as well as the jump and collective diffusion coefficients, are calculated for different values of lateral interactions between ad-particles and substrate heterogeneity. In addition, different elementary jump mechanisms are introduced and their influence in the coverage dependence of the collective diffusion coefficient is investigated.     

Nonlinear dynamics in a Fabry-Perot resonator

We develop a general formalism to describe the dynamical behavior of an ensemble of two-level systems in a Fabry-Perot cavity. Our main result is a set of space and time-dependent, integro-differential equations for the slowly varying radiation and atomic variables, which we derive through a precise analysis of the slowly-varying amplitude approximation in the presence of counter-propagating fields. With the help of new and properly chosen variables we recast these equations in a form that makes their boundary conditions formally identical to those of an ideal Fabry-Perot resonator, and introduce in a natural way a modal structure even for systems with arbitrary mirror reflectivity. We derive simplified forms of these equations in the uniform field limit and within the more general single-frequency approximation. Finally, we extend our formulation to include driven systems such as optically bistable devices and the laser with an injected signal.     

Exact Statics and Approximate Dynamics of Adhering Lipid Tubules

In this paper we are concerned with the adhesion of lipid tubules to a plane wall: we treat both the statics and the dynamics of this phenomenon. Though we provide an exact solution to the equilibrium problem, our treatment of the dynamical problem is approximate, as it is based on a simplified model, which, nevertheless allows us to obtain quantitative information about the detachment dynamics of tubules. Received September 1, 1997     

Experimental determination of cw dye laser parameters by loss variation

The behavior of a cw dye laser under variation of the output coupling has been investigated. By studying the dependence of laser threshold, output power and slope efficiency on the degree of outcoupling, numerical values for macroscopic and microscopic laser parameters have been obtained. The macroscopic data comprise values for internal cavity losses and mode matching conditions, the microscopic data refer to molecular parameters of the dye used, such as cross-sections for stimulated emission and triplet-triplet absorption.