Logic, methodology and philosophy of science VIII proceedings of the eighth international congress of logic, methodology and philosophy of science, and philosophy of science proceedings) ( PDFDrive ) 51

ILYA PRIGOGINE 32 diS = Thermal flow + Antidiffusion dr 20 20 LO dJ = "order" + "disorder" dT Fig Thermodiffusion effect: under thermal constraint (TI # T2),the distribution of H2 and N, becomes inhomogeneous modes This creation of non-equilibrium structures is well known here in Moscow, as the Russian school has played an important role in their exploration in many situations such as chemical oscillations or hydrodynamical instabilities Let us consider the Rayleigh-BCnard instability If I have choosen this example, it is because it has paved the way to some recent numerical and KESTEMONT experiments I refer to the work done by MARESCHAL (1987, 1987) on molecular dynamics of non-equilibrium systems Usually, molecular dynamics deals only with equilibrium systems; but the recent years have witnessed a development of simulations in non-equilibrium fluids, due to the huge increase of computing power offered by 'supercomputers' The work of Mareschal and Kestemont deals with the RayleighBCnard instability 'we have just mentioned The system consists of an assembly of 5400 hard disks enclosed in a rectangle; vertical sides are reflecting boundaries, whereas horizontal sides are thermal reservoirs An external force (similar to gravitation) acts downward on the fluid's particles, and the temperature of the bottom's reservoir is set higher than the top's reservoir's one The behaviour of this model fluid is integrated over time on a computer Figures 3b and 3c refer to the same system after about lo6 collisions They differ by the thermal gradient, which is larger in Fig 3c than in Fig 3b Figure 3b corresponds to constraints below the hydrodynamical macroscopic instability Still, coherent patterns are already present However, they fluctuate violently in time (see Fig 3) It is quite remarkable that a relatively small system exhibits a behaviour which can be understood in terms of macroscopic hydrodynamics However, the results of the simulation go beyond hydrodynamics proper,