# Bending and tumbling dynamics of semi-flexible molecules: a talk by Emmanuel Plan of Universite Nice Sophia Antipolis

September 3, 2016 Leave a comment

by Mark Loyola

You are cordially invited to attend the talk of Mr. Emmanuel Lance Christopher VI M. Plan on “Bending and tumbling dynamics of semi-flexible molecules” on September 6, 2016, 5:00 – 6:30 PM, at SECA 303A. Undergraduate and graduate students are also invited to attend the talk.

**Abstract**

This talk will address two different questions on the dynamics of the simplest semi-flexible model, namely the *trumbbell*, in a flow. The trumbbell consists of three beads joined by two rigid connectors and of an elastic hinge at the central bead.

First, we show that the trumbbell performs a random end-over-end tumbling motion in an extensional flow. The trumbbell spends a significant amount of time extended and oriented along the stretching direction of the flow; occasionally, a favorable sequence of thermal fluctuations make the trumbbell fold, reverse its orientation and unfold. The mean time separating two reversals grows with the Weissenberg number Wi (the product of the amplitude of the velocity gradient and the relaxation time of the spring), and the growth is exponential. This phenomenon is explained by performing a stability analysis of the dynamical system describing the configuration of the trumbbell and by applying the large deviation theory to it.

In the second part of the talk, the Lagrangian dynamics of the trumbbell in homogeneous and isotropic turbulent flows is studied by means of analytically solvable stochastic models and direct numerical simulations. The stationary statistics of the bending angle shows a strong dependence on the dimension of the flow. In two-dimensional turbulence, particles are either found in a fully extended or in a fully folded configuration; in three dimensions, the predominant configuration is the fully extended one. Such a sensitivity of the bending statistics on the dimensionality of the flow is peculiar to fluctuating flows and is not observed in laminar stretching flows.

**About the Speaker**

Emmanuel L. C. VI M. Plan finished his undergraduate studies in Mathematics in the Ateneo de Manila University in 2010. He obtained his Master of Science degree from the National University Singapore in 2013. He is currently finishing his doctorate in physics from Universite Nice Sophia Antipolis. He has also served as a lecturer in the Loyola Schools Mathematics Department in 2011 and 2013.