Gianne Derks visited the Universiteit Twente in Enschede on Friday 27 March to give one of the four invited lectures at the Retirement Symposium of Professor E. (Brenny) van Groesen.  Her talk was on “Viscosity-induced instability for Euler and averaged Euler equations in a circular domain“.  On 25-26 March she visited the Universiteit Leiden for research interaction: working on inhomogeneous wave equations (with Arjen Doelman), on mathematical pharmacology (with Piet van der Graaf and Vivi Rottschafer), and to discuss the organisation of the upcoming Lorentz Center Workshop on Mathematical Pharmacology.