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 Wendy Zhang, email address, and Leo Kadanoff, email address.

 A photo of M51 Galaxy

Whirlpool Galaxy M51
July 30, 2008
Robert Deegan, University of Michigan
e-mail: email address, Faculty contact: Leo Kadanoff, email address
Fingers and Holes in Shear Thickening Fluids
The simplest models of matter posit a linear relationship between the stress and deformation, as for example in Hooke's law. However, many useful and important fluids (such as shampoos, industrial slurries, geophysical fluids, polymeric melts) exhibit a nonlinear response to stress. I will discuss the behavior of shear thickening fluids subjected to vertical vibrations in the context of pattern forming systems. I will show that a mixture of cornstarch/water or glass beads/water vibrated above a critical acceleration (approximately 10 g) is unstable to perturbations. At low accelerations a small indentation of the fluid surface will grow until it reaches the bottom of the container, forming a circular hole. At higher accelerations the rim of the hole becomes unstable and develops an upward growing tongue. At even higher accelerations, the entire layer writhes in a disordered manner. The mechanism for these instabilities is unknown. I will present experimental correlations between these instabilities and the fluid's rheological proprieties and attempts to model this phenomenon.
August 6, 2008
Maximino Aldana Gonzalez, Universidad Nacional Autonoma de Mexico
e-mail: email address, Faculty contact: Leo Kadanoff, email address
Critical Dynamics in Genetic Networks: Examples from Four Kingdoms
The coordinated expression of the different genes in an organism is essential to sustain functionality under the random external perturbations to which the organism might be subjected. To cope with such external variability, the global dynamics of the genetic network must possess two central properties. (a) It must be robust enough as to guarantee stability under a broad range of external conditions, and (b) it must be flexible enough to recognize and integrate specific external signals that may help the organism to change and adapt to different environments. This compromise between robustness and adaptability has been observed in dynamical systems operating at the brink of a phase transition between order and chaos. Such systems are termed critical. Thus, criticality, a precise, measurable, and well characterized property of dynamical systems, makes it possible for robustness and adaptability to coexist in living organisms. In this talk I investigate the dynamical properties of the gene transcription networks reported for S. cerevisiae, E. coli, and B. subtilis, as well as the network of segment polarity genes of D. melanogaster, and the network of flower development of A. thaliana. By analyzing hundreds of microarray experiments to infer the nature of the regulatory interactions among genes, and implementing these data into the Boolean models of the genetic networks, I will show that, to the best of the current experimental data available, the five networks under study indeed operate close to criticality. The generality of this result suggests that criticality at the genetic level might constitute a fundamental evolutionary mechanism that generates the great diversity of dynamically robust living forms that we observe around us.
August 13, 2008
Norman Lebovitz, University of Chicago
e-mail: email address, Faculty contact: Leo Kadanoff, email address
Subcritical Instability in Shear Flows: the Shape of the Basin Boundary
The boundary of the basin of attraction of the stable 'laminar' point is investigated for several of the dynamical systems modeling subcritical instability. In the cases thus far considered, this boundary contains a linearly unstable structure (equilibrium point or periodic orbit). The stable manifold of this unstable structure coincides at least locally with the basin boundary. The unstable structure plays a decisive role in mediating the transition in that transition orbits cluster tightly around its (one-dimensional) unstable manifold, illustrating a scenario proposed by Waleffe. The picture that emerges augments the bypass scenario for transition and reconciles it with Waleffe's scenario.
We consider a model proposed by Waleffe (W97) for which an unstable equilibrium point U lies on the boundary. We find numerically that all orbits staring near U decay toward the origin, whereas 'half' of them should remain permanently bounded away from the origin. We offer an interpretation of this tendency toward decay based on the structure of the basin boundary.
August 20, 2008 (&)
(open date)
August 27, 2008 (&)
(open date)
September 3, 2008
(open date)
September 10, 2008
(open date)
September 17, 2008
Michael Marder, University of Texas
e-mail: email address, Faculty contact: Leo Kadanoff, email address
September 24, 2008
Lee Smolin, Perimeter Institute for Theoretical Physics
e-mail: email address, Faculty contact: Leo Kadanoff, email address
October 1, 2008
Doug Smith
e-mail: email address, Faculty contact: Leo Kadanoff, email address
October 8, 2008
Leo Kadanoff, University of Chicago
e-mail: email address
October 15, 2008
Dmitri Talapin, University of Chicago
e-mail: email address
October 22, 2008
Berni Alder, Lawrence Livermore National Laboratory
e-mail: email address, Faculty contact: Leo Kadanoff, email address
October 29, 2008 (^)
(open date)
November 5, 2008 (^)
Benoit Roman, Ecole Superieure de Physique et de Chimie Industrielles
e-mail: email address, Faculty contact: Wendy Zhang, email address
November 12, 2008 (^)
(open date)
November 19, 2008
(open date)
November 21, 2008 (Special Seminar: 12:30 in KPTC 206)
Detlef Lohse, University of Twente
e-mail: email address, Faculty contact: Leo Kadanoff, email address
December 3, 2008
V. Ramanathan, University of California, San Diego
e-mail: email address, Faculty contact: Leo Kadanoff, email address
January 7, 2009
(open date)
January 14, 2009
Marcelo Magnasco, Rockefeller University
e-mail: email address, Faculty contact: Leo Kadanoff, email address
January 21, 2009
Margaret Gardel, University of Chicago
e-mail: email address
January 28, 2009
(open date)
February 4, 2009
(open date)
February 11, 2009
(open date)
February 18, 2009
(open date)
February 25, 2009
(open date)
March 4, 2009
(open date)
March 11, 2009
(open date)
March 18, 2009 (During APS March Meeting)
(open date)
March 25, 2009
(open date)

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

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

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