Levich Institute Seminar Announcement, 03/13/2007

Tuesday, 03/13/2007
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Professor Michael Graham
University of Wisconsin
Chemical and Biological Engineering

"Jiggling Genes and Dancing Bacteria: Two Problems in Biologically-Inspired Hydrodynamics"

ABSTRACT


Emerging micro- and nanofluidic approaches to single molecule analysis of genomic DNA have fueled considerable interest in the structure and dynamics of solutions of long-chain polymers in confined geometries. In the first part of this talk we describe simulation, theory and experimental studies of the hydrodynamics of solutions of long DNA molecules in microchannels. A key feature of this problem is the cross-stream migration of the large molecules—migration has been widely observed in polymer solutions but heretofore poorly understood. We elucidate the various mechanisms that drive migration: the dominant effect arises from the fluid motion induced by a DNA molecule as it tumbles around in the flow, and cannot be captured if the hydrodynamic effects of confinement are ignored.

The second part of this talk describes very recent work motivated by observations that populations of swimming bacteria exhibit a fascinating variety of flow phenomena, whose mechanisms are not understood. We propose a simple model of a swimming organism that is amenable to direct simulations of large populations. Hydrodynamic coupling between the swimmers leads to coherent motions in the flow that are consistent with experimental observations. At low concentrations, swimmers propelled from behind (like spermatozoa) strongly migrate toward solid surfaces in agreement with simple theoretical considerations. At higher concentrations this localization is disrupted by the coherent motions. Correspondingly, at large concentrations the swimmers move with velocities significantly larger than they could achieve in isolation.

BRIEF ACADEMIC/PROFESSIONAL BACKGROUND

  • B.S. 1986, Univ. of Dayton (Chemical Engineering)
  • Ph. D. 1992 Cornell University
  • Postdoc 1992 Univ of Houston (Dan Luss)
  • Postdoc 1993 Princeton (Yannis Kevrekidis)
  • At UW-Madison since Jan 1994
  • Chair since July 2006
CURRENT RESEARCH INTERESTS

Generally: flowing complex fluids. Specifically: instabilities, nonlinear dynamics and turbulence in polymer solutions; fluid and polymer dynamics at small scales and under confinement; collective dynamics in swimming microorganisms.