
Model, 1. modul, 2009/10, id:390  
Vejleder:  Bernhelm BoossBavnbek 
Findes på RUb:  Ja 
English abstract
Mathematical modelling of isomorphs in IPLliquids The purpose of this project is to investigate, in part whether group theory, can be used as a model for isomorphic curves in IPLliquids, and in part whether the explanation of isomorphic behaviour can be found as symmetry in solutions to the, for this project unknown, differential equations that controls the dynamics in simulations of vicous liquids By analysing the IPLmodel with group theory a transformation group GIPL was suggested as a way of describing the equivalence relation r1n/3 /T1 = r2n/3/T2. From this it was shown, that isomorphic curves can be described as orbits in the (T, r)plane, where each of the orbits can be identified as elements in the quotient space by means of isochors and isotherms. From this it is concluded, that orbits can be used as a model for isomorphs, since these capture some of the isomorphic characteristics. As a frame of reference to the unknown differential equations, the heat equation is used as a simple example of a system of differential equations. Based on Olver [1993] a symmetry group Gi is established, for which the solution T(x, t) = je?(x?Kt) is group invariant. From the parameters (k, c, r), which define the contant K, an equivalence relation is created along with a group, Geq, that describes this relation. From this it is shown, that solutions to the heat equation are invariant to transformation by Geq. From the analysis of the heat equaiton in respect to symmetry groups, group invariant solutions and invariance towards transformations of the parameters in the heat equation it is postulatet, that the existence of isomorphs imply the presence of solutions that are invariant to the transformation of the underlying system of differential equations. Such an invariance should thus be pressent in all liquids that exhibit isomorphic behaviour. For IPLliquids it is surmised that the equivalence relation given by a constant ratio between r n/3 and T along isomophic curves has a relation to this invariance.