Collective Hydrodynamics of Swimming Micro-Organisms

Add to your list(s) Download to your calendar using vCal

• Tim Pedley (Department of Applied Mathematics and Theoretical Physics)
• Wednesday 21 May 2008, 11:20-12:05
• MR2, Centre for Mathematical Sciences, Wilberforce Road, Cambridge.

If you have a question about this talk, please contact Danielle Stretch.

Since the work of Kessler in the 1980s, and before, there has been considerable interset among fluid dynamicists and physicists in the collective behaviour of swimming micro-organisms in suspension. Since all such cells are denser than the water in which they swim, bioconvection patterns result from upswimming of cells in a chamber of finite depth and from gyrotaxis of bottom-heavy cells in a uniform fluid. Bioconvection has been analysed for dilute suspensions; the theory will be briefly re-examined with emphasis on the additional stress induced by the cells’ swimming motions (each cell can be regarded as a force-dipole, or stresslet), because of the new instabilities revealed by Simha & Ramaswamy (2002) for uniform suspensions in the absence of gravity.

Even more fascinating coherent structures arise in concentrated suspensions, of bacteria for example, in which cell-cell interactions cannot be ignored. The hypothesis is that such structures emerge from purely hydrodynamic interactions between cells. A variety of models have been developed, which are outlined briefly, but particular attention will be paid to our own model in which cells are represented as inertia-free “spherical squirmers”, whose behaviour is dominated by near-field hydrodynamics. Pairwise interactions are computed precisely, and Stokesian dynamics in a periodic box is used to simulate an infinite suspension. Trajectories are computed deterministically, but the long-time spreading of a 3D suspension, from random initial conditions, is diffusive; scaling arguments can be used to estimate the effective diffusivity. However, in 2D there is a strong tendency towards aggregation into clumps or bands. [Recent work reported here has been performed in collaboration with T Ishikawa and J T Locsei.]

This talk is part of the One Day Meeting: Fourth Annual Symposium of the Cambridge Computational Biology Institute series.

This talk is included in these lists:

• All CMS Events
• All Talks (aka the CURE list)
• Biology
• CamBridgeSens
• Cambridge talks
• Computational and Systems Biology
• Graduate-Seminars
• Life Science Interface Seminars
• Life Sciences
• Life Sciences
• ME Seminar
• MR2, Centre for Mathematical Sciences, Wilberforce Road, Cambridge
• One Day Meeting: Fourth Annual Symposium of the Cambridge Computational Biology Institute
• PMRFPS's
• School of Physical Sciences
• Trust & Technology Initiative - interesting events
• custom
• my_list
• other talks
• se393's list

Note that ex-directory lists are not shown.