We consider a nonconforming streamline-diiusion nite element method for solving convection-diiusion problems. The theoretical and numerical investigation for triangular and tetrahedral meshes recently given by John, Maubach and Tobiska has shown that the usual application of the SDFEM gives not a suucient stabilization. Additional parameter dependent jump terms have been proposed which preserve...

A molecular dynamics study of atomic self-diiusion in Frank-Kasper type do-decagonal quasicrystals is presented. It is found that the quasicrystal-speciic ip mechanism for atomic diiusion, predicted by Kalugin and Katz, indeed occurs in this system. However, in order to be eeective, this mechanism needs to be catalyzed by other defects, such as half-vacancies. For this reason, it is diicult to ...

The behaviour of a system comprising two competitive autocatalytic processes, A ] B] 2B, and A] C] 2C, rate \ k1a6 b 6 where and represent the concentrations of the various species, is considered. In a well-stirred batch reactor, the rate \ 2 a6 c6 , a6 , b 6 c6 Ðnal equilibrium composition always corresponds to a mixture of the two product species B and C, with their respective equilibrium con...

The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG 1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens as the star cools. In the temperature range of the pulsating DB white dwarfs (Teff ∼ 25, 000 K) this transformation is still taking place, ...

We establish L convergence of a viscous splitting method for nonlinear possibly strongly degenerate convection-di usion problems. Since we allow the equations to be strongly degenerate, solutions can be discontinuous and they are not, in general, uniquely determined by their data. We thus consider entropy weak solutions realized by the vanishing viscosity method. This notion is broad enough to ...

We study reaction-di¤usion systems of propagator-controller type in the one-dimensional unit interval. When propagator di¤uses slowly, we establish the existence of transition layer equilibria by using singular perturbation expansions and a Lyapunov-Schmidt reduction method. Our approach to the existence also enables us to simultaneously obtain a stability criterion for the layer equilibria.

Signalling pathways allow cells to perceive and exchange information under the form of chemical signals. Such a signal generates a response of the cell through the crucial stages of reception and transduction. Di erent types of protein interact in a structured manner as a cascade of reactions that relay the signal from the exterior to the interior of the cell, notably through the membrane. Sign...

A simple and robust approach is proposed for the parametric estimation of scalar homogeneous stochastic di¤erential equations. We specify a parametric class of di¤usions and estimate the parameters of interest by minimizing criteria based on the integrated squared di¤erence between kernel estimates of the drift and di¤usion functions and their parametric counterparts. The procedure does not req...

We prove long time di usive behavior (homogenization) for convection-di usion in a turbulent ow that it incompressible and has a stationary and square integrable stream matrix. Simple shear ow examples show that this result is sharp for ows that have stationary stream matrices.

We synthesize robust nonlinear static output feedback controllers for systems of quasi-linear parabolic partial di!erential equations with time-dependent spatial domains and uncertain variables. The controllers are successfully applied to a typical di!usion}reaction process with moving boundary and uncertainty. ( 2000 Elsevier Science Ltd. All rights reserved.