Operator splitting and upwinding for the Navier-Stokes equations

We present an operator splitting scheme for the unsteady Navier-Stokes equations for incompressible viscous fluid flow. Like other operator splitting methods applied to these equations, the difficulties associated with the nonlinearity and the incompressibility condition are decoupled. At each time step we obtain two subproblems of Stokes type and a linear one of elliptic type. The linear problem gives us uncoupled scalar problems of transport type; then, we may take advantage of well known upwind techniques for such kind of problems in order to handle large Reynolds numbers flow with coarse meshes. To show the efficiency of the scheme we report numerical results up to Reynolds numbers Re=4000 obtained with very coarse meshes.     

Theoretical and numerical aspects of some semilinear hyperbolic problems

In this paper the existence of a generalized solution is proved for the Cauchy problem of the semilinear wave equation u_tt−Δu+f(u)=0, using finite differences. The finite difference scheme that we use extends the one initially introduced by other authors and leads to a numerical implementation based on a fixed point iterative process. This scheme is able to solve tridimensional problems (in space) fast and accurately. Numerical results showing the effectiveness of the scheme are given.     

FIPA — Towards a Standard for Software Agents

Software agent technology will have a significant impact on the shape of the global information society in the next millennium. This branch of systems engineering is rapidly becoming a viable and exploitable technology where BT is well placed as both a potential user and provider of agent-based services and products.The highly interactive nature of multi-agent systems points to the need for consensus on agent interfaces in order to support interoperability between different agent systems. The completion and adoption of such a standard is a prerequisite to the commercialisation and successful exploitation of agent technology.This paper describes FIPA (Foundation for Intelligent Physical Agents) and its organisation. It provides an overview and guide to the FIPA97 specification. It discusses how FIPA relates to other agent standards activities and concludes with FIPA's plans for 1998.     

The far infra-red spectrum of crystalline polytetrafluoroethylene

The far infra-red spectrum of highly crystalline polytetrafluoroethylene has been shown to contain a new band near 33cm^?1, the band at 55cm^?1 has been shown to be a close doublet and two further bands at 291 and 308cm^?1 have been observed. These results strongly support the conclusions of Boerio and Koenig from Raman observations that the unit cell contains at least two molecular segments.     

A determination of the products of reaction betweer various sulfide minerals and aqueous xanthate solution,and a correlation of the products with electrode rest potentials

The surface reaction products formed when sulfide minerals react with xanthates were analyzed by spectrophotometric methods. These products were found to be predominantly either metal xanthate or dixanthogen, depending on the particular sulfide mineral. Dixanthogen is formed on those minerals that, in a solution of xanthate, assume a rest potential greater than the equilibrium potential for the reduction of dixanthogen or xanthate.     

A far infra-red study of conformational disorder in PTFE

The examination of the 250–350 cm^?1 region of the infra-red spectrum of polytetrafluoroethylene (PTFE) has been extended by studies of thermally degraded and sintered material. We conclude that a band at 277 cm^?1 does not arise from a true mode of the crystal but has its origin in regions where the chain has a bent conformation. Our previous speculation that bands at 292 cm^?1 and 312¹ cm^?1 (Raman active only, for the isolated chain) acquire their weak activity in the infra-red through conformational disorder is confirmed. It is likely that the conformational disorder in question arises from chain folding in the polymer crystal.