Tonight’s talk will be given by Prof Tim Pedley.

**Talk**

Speaker: Prof Tim Pedley

Title: Spherical squirmers – models for swimming micro-organisms: how a Tripos question led to a new field of research.

Abstract: In 1952, Sir James Lighthill (FT) introduced the simplest possible model of a swimming microorganism of finite size, intended as a model of a single-celled protozoan covered in beating cilia. The model consisted of a sphere, on the surface of which material points undergo small-amplitude oscillations. In 1971, Lighthill’s student, John Blake (FT), completed the calculations and in particular showed how to model the ‘metachronal’ wave patterns exhibited by beating cilia. In 1986 the speaker set a Part II Tripos question, to analyse an even simpler model consisting of a sphere whose surface moves tangentially with timeindependent velocity: a steady spherical squirmer. This has led to a substantial body of research on the optimisation pf the swimming and nutrient uptake of individual squirmers (Eric Lauga, FT), and on the hydrodynamic interactions between pairs of steady squirmers and their influence on self-diffusion in suspensions. The final topic describes measurements and modelling of metachronal waves in Volvox, the only truly spherical multicelled ‘organism’, culminating in the prediction of the mean swimming speed and angular velocity of free-swimming Volvox. The predictions are compared with experimental observations. [FT ≡ Fellow of Trinity]

The talk will take place at 8:30PM on Monday 20 February in the Winstanley Lecture Theatre. As usual there will be free port and juice served before the talk at 8:15PM. This talk is for members only, but there will be a chance to sign up for TMS life membership for £2.50.