We are proud to invite you to the Skoltech Colloquium!
Speaker: Dr Dmitri (Mitya) O Pushkin graduated from the Moscow Institute of Physics and Technology in 1996. After a yearlong internship at the ABB Research Centre, Switzerland he joined a PhD program at the Department of Theoretical and Applied Mechanics of the University of Illinois at Urbana-Champaign (TAM, UIUC). His research focused on fundamental problems of cluster aggregation and on complex fluids. In particular, for a broad class of scale-free cluster aggregation processes that includes coagulation of colloidal particles, rain formation, growing networks and even bank mergers, he derived the steady self-similarity spectra. His PhD thesis won the best thesis award from TAM, UIUIC in 2004. Upon graduation Dmitri returned to his native Minsk, Belarus and had eventually become a business development director for an engineering IT company, Applied Systems Ltd. However, in 2010 he resumed active research at the Microgravity Research Centre, Université Libre de Bruxelles and moved to The Rudolf Peierls Centre for Theoretical Physics, University of Oxford, a year later. His recent results that include a novel physical mechanism of self-organisation of small particles in time-periodic flows and elucidating fundamentals of mixing in suspensions of microogranisms have been published in prestigious journals, such as Physical Review Letters, and led him to being an invited speaker at a number of international conferences in Europe and the United Kingdom.
Abstract: Suspensions of active particles, such as swimming microorganisms, turn out to be efficient stirrers of the surrounding fluid. This fact may be directly relevant to the feeding and evolutionary strategies of swimming cells. Microfluidic devices exploring swimmers-induced mixing have been proposed. The possibility of a significant biogenic contribution to the ocean circulation is currently under intense debate. However, understanding fluctuations and the effective tracer diffusion coefficient in such non-equilibrium systems remains a challenge for modern theoretical physics. In this talk we focus on the fundamentals of these processes. We start by explaing why the theoretical approach based on the notion of the effective temperature of the bacterial bath and the ideas of the fluctuation–dissipation theorem, such as the Stokes–Einstein relation, breaks down in active suspensions. Next, we discuss the impediments to stirring by force-free swimmers and give a classification of possible stirring mechanisms. We show that fluid entrainment by individual swimmers and the effects of their trajectories curvature give rise to independent mixing mechanisms. We discuss their relative strength in dilute suspensions of active swimers and derive a simple expression for the effective tracer diffusion coefficient as a function of the swimmer parameters. During the discussion we demonstrate an interplay of topological, fluid mechanical and statistical physics concepts, such as closedness of tracer trajectories, the net fluid volume displaced by a moving body (also known as the Darwin drift) and properties of non-Gaussian random walks.
Transfers:
Shuttle bus Hypercube – Institute of Gene Biology RAS at 3 pm
Shuttle bus MSM (Karacorum) – Institute of Gene Biology RAS at 3:10 pm
How to get to Institute of Gene Biology RAS:
Address: Vavilova street 34/5 (ул. Вавилова 34/5)
Map: http://www.genebiology.ru/institute/way.shtml
If you like to participate and for further information or questions, please Liliya Abaimova
We look forward to seeing you.
