A 16 moments model in relativistic extended thermodynamics of rarefied polyatomic gas

A model with 16 moments is here presented in the framework of RET of polyatomic gases. It furnishes as principal subsystem the relativistic counterpart of a work by Arima T., Ruggeri T., Sugiyama M.; this is present in literature and treats the non relativistic case which incorporates relaxation processes of molecular rotation and vibration. Another principal subsystem is the natural extension of the 14 moments model by Pennisi S. and Ruggeri T.; this is also present in literature in the relativistic framework but where the trace of the third balance equation is neglected. Its extension is found here for the case when this trace isn’t neglected.

     

Chemically controlled pattern formation in phase-separating materials

Summary The role of chemical reactions in the selection of patterns in phase-separating mixtures is presented. Linearized theory and computer simulation show that the initial long-wavelength instability characteristic of spinodal decomposition is suppressed by chemical reactions, which restrict domain growth to intermediate length scales even in the late stages of phase separation. Our findings suggest that chemical reactions may provide a novel way to stabilize and tune the steady-state morphology of phase-separating materials. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Interfaces and typical Gibbs configurations for one-dimensional Kac potentials

Summary We consider a one dimensional Ising spin system with a ferromagnetic Kac potential J(|r|),J having compact support. We study the system in the limit, »0, below the Lebowitz-Penrose critical temperature, where there are two distinct thermodynamic phases with different magnetizations. We prove that the empirical spin average in blocks of size ^–1 (for any positive ) converges, as »0, to one of the two thermodynamic magnetizations, uniformly in the intervals of size ^–p , for any given positivep1. We then show that the intervals where the magnetization is approximately constant have lengths of the order of exp(c ^–1),c>0, and that, when normalized, they converge to independent variables with exponential distribution. We show this by proving large deviation estimates and applying the Ventsel and Friedlin methods to Gibbs random fields. Finally, if the temperature is low enough, we characterize the interface, namely the typical magnetization pattern in the region connecting the two phases.The research has been partially supported by CNR, GNFM, GNSM and by grant SC1CT91-0695 of the Commission of European Communities     

Quantum mechanical description of electrode reactions: Part II. Treatment of compact layer structure at platinum electrodes by means of the extended Hückel molecular orbital method. Pt(111) surfaces

The Iteraltive Extended Hückel Molecular Orbital method has been adapted to calculation of the properties of an electrode and compact layer. Predictions of the stablest orientations, on the Pt(111) surface of species such as H₂O, Pt, OH^?, H, and the halides, F^?, Cl^?, Br^? and I^?, based upon calculation of the total energy corresponding to various internuclear distances, are reported. The calculations correctly predict self-adsorption of Pt on the Pt(111) surface at the face-centered cubic closest-packing position. The H₂O molecule is predicted to locate itself above three adjoining Pt atoms, with the O atom closest to the surface and the H atoms opposite the O. Similar results were obtained for OH^? and the halides. Atomic H, however, is predicted to drop into the plane of centers of the Pt surface atoms, where it would lie between, three adjacent Pt atoms. Application of the method to electrode studies requires only modest amounts of computer time but produces surprisingly reliable qualitative predictions. Compulation of electrochemical quantities such as charge, differential capacitance, surface tension and potential energy as a function of electrode potential will be described in future work.     

Semiempirical Potential in Kinetics Calculations on the HC3N + CN Reaction

The reaction between the cyano radical CN and cyanoacetylene molecule HC3N is of great interest in different astronomical fields, from star-forming regions to planetary atmospheres. In this work, we present a new synergistic theoretical approach for the derivation of the rate coefficient for gas phase neutral-neutral reactions. Statistic RRKM calculations on the Potential Energy Surface are coupled with a semiempirical analysis of the initial bimolecular interaction. The value of the rate coefficient for the HC3N + CN → H + NCCCCN reaction obtained with this method is compared with previous theoretical and experimental investigations, showing strengths and weaknesses of the new presented approach.     

Ionization of O3 in Excess N2: A New Route to N2O via Intermediate N2O3+ Complexes

No Abstract     

Extended approaches to covariant Maxwell electrodynamics

The field equations of covariant Maxwell electrodynamics are a set I of 8 equations for the determination of 6 variables, i.e., the independent components of the skew-symmetric Maxwell tensorF . Obviously 2 of these equations are not evolutive; however they cannot be eliminated without losing manifest covariance. This paper presents a new hyperbolic set S of 8 equations in the 8 variablesF ,x, y, wherex, y are new auxiliary quantities. The solutions of S withx =y = 0 are those of the set I. Moreover, S is expressed in covariant form and is equivalent to a symmetric hyperbolic system.     

Extended thermodynamics of the Blotekjaer hydrodynamical model for semiconductors

The Blotekjaer hydrodynamical model for charge carriers transport in semiconductors is reconsidered from the viewpoint of extended thermodynamics. In particular the Blotekjaer original closure of the moment equations is shown to be equivalent to that obtained by applying the entropy principle.Work partially supported by C.N.R. (MMI-P.S IPPMI, U.O Mathematical Models of Semiconductors)