My main interest has been the relation between microscopic (statistical mechanical) and macroscopic (non-equilibrium thermodynamic) description of transport of mass, heat and momentum in fluids. I have worked on methods for calculating mobility, diffusion, thermal conductivity and viscosity from intermolecular pair potentials by theory or simulation, I have measured mobility and diffusion with high precision and I have used transport coefficients to constrain intermolecular pair potentials.

subsection{Dilute gases, experiments and theory} In dilute gases (as in the higher atmosphere, ionosphere) the molecular interactions are essentially pairwise. In these conditions the Boltzmann equation gives a good description of linear transport. At the heart of the Boltzmann equation is the collision integral. For different types of transport different moments of the two-body scattering are important. During my master thesis~\cite{diplom} I measured diffusion coefficients of Li$^+$ ions in H$_2$ gas (using an existing, high precision drift tube), developed a Fokker-Planck expansion of the collision integral with quantized inelastic scattering and concieved a model of the elastic and non-elastic collisions. By comparing the measured diffusion coefficients with the solution to the Boltzmann equation we could demonstrate the effect of the quantized rotation exitation in hydrogen on diffusion~\cite{Roeggen2002a}.

subsection{Dense fluid mixtures, experiments and theory} For my dr.ing.\ thesis~\cite{doktor} I continued to work on diffusion, but in dense fluid mixtures. Knowledge of hydrocarbon transport properties is important to the petroleum industry. Most of my work went into refining an instrument for measuring diffusion at high temperatures ($<$150$^\circ$C) and pressures ($<$60~MPa). The instrument, using Mach-Zehnder interferometry, was at the time the most accurate ever made for these conditions.~\cite{Dysthe1995b} I also participated in enhancing the performance of a high pressure self diffusion instrument using pulsed field gradient spin echo NMR.~\cite{Helbak1996a} I used the instruments especially in the supercritical region of mixtures of methane and n-decane and studied the thermodynamic effects of the critical demixing line~\cite{Dysthe1995a} and the microscopic foundations of universal correlations for diffusion in mixtures. My supervisor, Hafskjold, is a theoretician and during my dr.ing.\ work I became an independent experimentalist.

I enclose the following document: \begin{itemize} \item {\rm Dysthe, D.~K., Hafskjold, B., Breer, J., {\rm and} \v{C}ejka, D.} \newblock {\em Interferometric-technique for measuring interdiffusion at high pressures\/}. \newblock J. Phys. Chem., {\bf 99} 11230 (1995). \end{itemize}

\subsection{Dense fluid mixtures, simulation} After 4 years of experimental work I wanted to do more theory and simulation again. I spent 2 years in Paris doing molecular dynamics (MD) simulations on dense mixtures of hydrocarbons using flexible, multicentre pair interaction models. The position was payed by Total and the prediction of hydrocarbon mixture properties by MD has become ever more important. I studied the capabilities of equilibrium MD and linear response theory and found that contrary to common belief this method (when carried out carefully) is as efficient as non equilibrium MD at high density / high temperature fluid states.~\cite{Dysthe1999a} I also studied the effectiveness of different pair interaction potentials~\cite{Dysthe2000a} and size and number dependecy of simulation results and the limits to how many different components in a mixture could be represented in a small system.~\cite{Dysthe1998a,Dysthe1999b} Finally I participated in the study of thermal diffusion (mass diffusion due to a thermal gradient) mechanisms~\cite{Simon1998a,Simon1999a}.

I enclose the following document: \begin{itemize} \item {\rm Dysthe, D.~K., Fuchs, A.~H., {\rm and} Rousseau, B.} \newblock {\em Fluid transport properties by equilibrium molecular dynamics. {I}. {M}ethodology at extreme fluid states\/}. \newblock J. Chem. Phys., {\bf 110} 4047 (1999). \end{itemize}