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Alright, thank you very much. Good afternoon ladies and gentlemen. I want first to thank

Willy Mets and you Alexander for organizing this for my friend and that you invited me

to his party. I was very pleasantly surprised when I got the email and I do apologize to

the previous speakers that I'm so late because I hate it when you come halfway, basically

you only go to your own talk, but I will be here tomorrow as well so it's not that bad.

But anyway, that's because of the Dutch Railroad system. So, Peter Knabner. So I do everything

out of my head so I hope I have the dates correct. Maybe there is a year or a month

here and there, not correct, but I thought that we met for the first time last month,

30 years ago in Maupil-Visson. At that time there was a community of applied mathematicians

in Europe, Karl-Heinz Hofman, Mario Primitierio, John Ockenden, Juan Luis Vasquez and I'm

sure I forget a few. And they organized the free boundary meetings every three years.

There was a first one in 81 in Monte-Cattini and this was the second one in the south of

France. And there I met Peter, he was an assistant at that time and he invited me to Augsburg

because he was working there with Karl-Heinz Hofman and for me that was my first visit

to Germany. And I was actually before that I was oriented very much towards the west,

so atlantically oriented, had not so much to do with Germany. But since that invitation

and my visit to Augsburg and many visits followed, he really opened up Germany. I mean I write

here Sebastian Hofner, everybody knows who that is, he's an historian, he died unfortunately

but he wrote great books and German history became one of my hobbies. He wrote great books,

I have them all. Herbert Krönemeyer of course, all the music, alcohol is the dressing for

Deine Kopf Salat, Peter. I wasn't drinking at that time, I picked that up later again.

And of course football by a mention, but let's not talk about football, okay. So Peter invited

me to Augsburg, I visited him there many times and I was working in Delft at that time and

he returned to visit and that was made possible because that was quite unique. We had with

five cities a first European project with Madrid, with Augsburg, Oxford, Leiden and

Delft. And that gave us actually a lot of freedom to travel around, to invite people

and do work together. And so that was the start of our cooperation and Peter was looking

for a subject for his Haberli Tatjons and so he said, well is it okay because we were

already working on that. I remember that you asked me that, is it okay that I do this on

reactive flow and transport in porous media and of course it became very successful. And

as I said we became good friends, I attended his wedding with my wife in Bayreuth, I remember

that and also the baptisms I think of the daughters and you visited me at home of course

with Mieke and the boys many, many times. But since I'm a rector it is a bit difficult

to travel for mathematical purposes. I do travel but it has another purpose. And our

collaboration was basically around this topic, solute transport, reactive solute transport

in porous media. I think the title of the colloquium, vrij, porous, reactif, that is

precisely what this is. Our first paper was in a conference proceeding in ESA. ESA that

was the third free boundary conference, ESA little town south of Germany, organised by

Karl Heinz Hoffman. And it was about the pointer. So it was about a system of equations, so

a PDE coupled with an ODE and that was typically the stuff that we were looking at in these

years and where U is the concentration of dissolved solutes and V is the concentration

absorbed on the grains. So you have in a volume you have fluid and grains and so you have

two types of concentrations so it appears in the capacity, so in the PDE and in the

ODE there is this ton linearity, the phi of U minus V, phi is an increasing Lipschitz

function and it's generally concave. And we developed theory for such equations, later

on I will show you more general expressions. And then for instance we spent days on issues

like is it concave or is it strict concave. And remember that we went to once, we went

together to Kaufhof in Augsburg and I bought a skateboard for one of the boys and that

skateboard was not strictly concave but it was radical concave. Anyway, so typically