Computations in Science Seminars

Wednesdays at KPTC 206, unless otherwise specified

The Kersten Physics Teaching Center is on the corner of 57th Street and Ellis Avenue.

Discussion over bag-lunch at 12:15 PM. Talk starts at 12:30 PM.

INFORMATION FOR SPEAKERS

Upcoming seminars

Previous seminars

This seminar series is organized by David Biron, email address, Wendy Zhang, email address, and Leo Kadanoff, email address.

 A photo of M51 Galaxy

Whirlpool Galaxy M51
July 8, 2009 (&)
James Martin, Sandia National Laboratories
e-mail: email address
Formation of an advection lattice with biaxial magnetic fields: A powerful new method of heat and mass transfer
In recent years we have become interested in the dynamics of magnetic particle suspensions subjected to biaxial and triaxial ac magnetic fields. For suspensions of spherical particles we have convinced ourselves (through theory, simulation and experiment) that we understand what is going on, including some pretty weird stuff. We have now started to study suspensions of magnetic platelets and have observed, under some very particular field conditions, the formation of extraordinary flow patterns and surface instabilities. We have no idea of what is going on, but we have made a lot of interesting videos that are fun to puzzle over.
Biaxial and triaxial ac magnetic fields are spatially uniform, time-dependent fields whose direction explores either two or three dimensions, with typical field component frequencies in the range of 100 - 1000 Hz and magnitudes from 0.005 - 0.05 T. In spherical particles suspensions a biaxial field creates negative dipolar interactions that lead to particle sheets, which are static structures of little interest. All of the really interesting phenomena -- fluid mixing [1], molecular-like particle clusterings [2], the formation of composites with exotic structures [3] -- occur in triaxial fields, which create complex many-body interactions.
We have discovered that magnetic platelets behave very differently, probably because of their tendency to rotate so as to confine the field vector to their plane. The resultant particle fluttering apparently creates complex flow because of hydrodynamic coupling. In the simplest case the flow can be described as a diagonal square lattice (relative to the directions of the field components) of "antiferromagnetic" flow cells, with the flow in each cell normal to the field plane. More complex flows can be stimulated, including helical flows, and these depend critically on both the frequency ratios of the field components and their phase relation. Understanding these flows is probably going to be a computational challenge of the first order, but their utility is clear: we can magnetically transport heat and mass at a terrific rate without a thermal gradient or gravity, and without pumps, hoses, connectors, seals or any moving parts. This has significant implications for cooling in space, or in any other circumstance where convection does not occur.
[1] J. E. Martin, Theory of strong intrinsic mixing of particle suspensions in vortex magnetic fields, Phys. Rev. E 79, 011503 (2009).
[2] J. E. Martin, E. Venturini, G. L. Gulley,* and J. Williamson, Using triaxial magnetic fields to create high susceptibility particle composites, Phys. Rev. E 69, 021508 (2004).
[3] J. E. Martin, R. A. Anderson, and R. L. Williamson, Generating strange magnetic and dielectric interactions: Classical molecules and particle foams, J. Chem. Phys. 118, (2003).
*Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the UnitedStates Department of Energy under Contract No. DE-AC04-94AL85000. This work was supported by the Office of Basic Energy Research, DOE.
July 15, 2009 (&)
Robert Schroll, University of Chicago
e-mail: email address
The Impact of Viscous Liquid Drops
The phenomenon of drop impact displays a rich variety of behaviors throughout its large parameter space. Here, we focus on the specific regime of viscous liquid drops impacting on a smooth dry substrate. After impact, these drops form a thin pancake of uniform thickness. Using Volume-of-Fluid simulations, we find that this thickness is set by the growth of a viscous boundary layer, due to the no-slip conditions at the solid wall. The upper surface of the drop flattens down onto this interface, starting near the rim and moving inwards.
July 22, 2009 (&)
Tom Witten, University of Chicago
e-mail: email address
Fadeout profile of a stain, Chiral sedimentation: two novel shaped responses via creeping flow.
Remarkably, the evaporation of a droplet containing a nonvolatile solute creates a singular deposition profile: an arbitrarily large fraction of the solute becomes concentrated at the the perimeter. The density profile has a distinctive form, with a smooth fadeout at the trailing edge. We present a mechanism that predicts a power-law form for this profile. For the simplest and most common case, the predicted power is -7 as recently shown by Rui Zheng. This power can readily be varied. The power law is governed by the stagnation region of the lateral flow as the drop evaporates. It suffices to know two quantities: a) the evaporating flux J(0) at this stagnation point relative to its average over the drop and b) the height at the stagnation point relative to its average. We describe conditions for achieving a range of power laws. For a noncircular drop a single power law characterizes the deposition over the whole perimeter, despite the anisotropy of the stagnation flow. Another kind of novel controlled motion happens when an irregular object falls through a viscous liquid. These objects twist as they fall. Sufficiently extended objects twist in a way that depends on their shape but not their initial conditions, Nathan Krapf, Nathan Keim and I have shown.
July 29, 2009
Fred Streitz, Lawrence Livermore National Laboratory
e-mail: email address, Faculty contact: Robert Rosner, email address
August 5, 2009
Michael Hagan, Brandeis University
e-mail: email address, Faculty contact: Leo Kadanoff, email address
August 12, 2009 (#)
Eric Brown, University of Chicago
e-mail: email address
August 19, 2009 (#)
Satish Kumar, University of Minnesota
e-mail: email address, Faculty contact: Wendy Zhang, email address
Squishy, Frozen, and Elastic Interfaces: Instabilities and Applications
Hydrodynamic instabilities at fluid interfaces are usually undesirable because of the detrimental effect they have on practical applications such as polymer processing and liquid-film coating. In this talk, two examples will be given in which such instabilities can actually be exploited for scientific and technological purposes. In the first example, we consider an instability that arises when a fluid flows past a soft elastic solid. Experiments and theory suggest that this instability may be responsible for certain rheological phenomena observed in surfactant solutions, and that it can also be useful for enhancing mixing in small-scale flows. In the second example, we gain insight into the surface-freezing phenomenon by considering an instability that occurs when the free surface of a liquid is oscillated vertically. Experiments show an abrupt change in instability characteristics at the onset of surface freezing, and theory indicates that this change corresponds to a transition from a free surface allowing slip to one where slip is absent. We also show that the instability can arise in viscoelastic liquids even in the absence of inertia, and derive a simple Mathieu equation which reveals that elasticity introduces an effective inertia.
August 26, 2009 (#)
(open date)
September 2, 2009 (#)
(open date)
September 9, 2009 (#)
(open date)
September 16, 2009
Will Ryu, University of Toronto
e-mail: email address, Faculty contact: David Biron, email address
September 23, 2009
Stephen Morris, University of Toronto
e-mail: email address, Faculty contact: Wendy Zhang, email address
September 30, 2009
Lenka Zdeborova, Los Alamos National Laboratory
e-mail: email address, Faculty contact: Wendy Zhang, email address
October 7, 2009
Henry Abarbanal, University of California, San Diego
e-mail: email address
October 14, 2009
Philippe Guyot-Sionnest, University of Chicago
e-mail: email address
October 21, 2009
Boris Shraiman, University of California, Santa Barbara
e-mail: email address, Faculty contact: Leo Kadanoff, email address
October 28, 2009
Zheng-Tian Lu, Argonne National Laboratory
e-mail: email address, Faculty contact: Wendy Zhang, email address
November 4, 2009
Subir Sachdev, Harvard University
e-mail: email address, Faculty contact: Leo Kadanoff, email address
November 11, 2009
(open date)
November 18, 2009
Penger Tong, Hong Kong University of Science and Technology
e-mail: email address, Faculty contact: Leo Kadanoff, email address
December 2, 2009
(open date)
December 9, 2009
Benny Davidovitch, University of Massachusetts, Amherst
e-mail: email address, Faculty contact: Ka Yee Lee, email address
January 13, 2010
(open date)
January 20, 2010
Michael Foote, University of Chicago
e-mail: email address, Faculty contact: Leo Kadanoff, email address
January 27, 2010
Steve Berry, University of Chicago
e-mail: email address
February 3, 2010
Heinrich Jaeger, University of Chicago
e-mail: email address
February 10, 2010
(open date)
February 17, 2010
(open date)
February 24, 2010
(open date)
March 3, 2010
Daniel Rothman, Massachusetts Institute of Technology
e-mail: email address, Faculty contact: Leo Kadanoff, email address
March 10, 2010
(open date)
March 17, 2010
(open date)
April 7, 2010
David Chandler, University of California, Berkeley
e-mail: email address, Faculty contact: Leo Kadanoff, email address

(&) : When Wendy Zhang is unavailable for the seminar.

(^) : When Leo Kadanoff is unavailable for the seminar.

(#) : When David Biron is unavailable for the seminar.

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