Seminars and Colloquia by Series

Monday, March 14, 2011 - 11:00 , Location: Skiles 005 , Weishi Liu , University of Kansas , , Organizer: Shui-Nee Chow
They may flow like fluids but under constraints of mechanical energies from their crystal aspects. As a result, they exhibit very rich phenomena that grant them  tremendous applications in modern technology.  Based on works of Oseen, Z\"ocher,  Frank and others, a continuum theory (not most general but satisfactory to a great extent) for liquid-crystals was formulated by Ericksen and Leslie in 1960s.  We will  first give a brief introduction to this classical theory and then focus on various important special settings in both static and dynamic cases. These special flows are rather simple for classical fluids but are quite  nonlinear for liquid-crystals.  We are able to apply abstract theory of nonlinear dynamical systems upon  revealing specific structures of the problems at hands.
Friday, March 11, 2011 - 11:00 , Location: Skiles 005 , Weiping Li , Oklahoma State University , Organizer: Haomin Zhou
In this talk, I will explain the correspondence between the Lorenz periodic solution and the topological knot in 3-space.The effect of small random perturbation on the Lorenz flow will lead to a certain nature order developed previously by Chow-Li-Liu-Zhou. This work provides an answer to an puzzle why the Lorenz periodics are only geometrically simple knots.
Monday, March 7, 2011 - 11:00 , Location: Skiles 005 , Qinglan Xia , University of California Davis , Organizer: Haomin Zhou
An optimal transport path may be viewed as a geodesic in the space of probability measures under a suitable family of metrics. This geodesic may exhibit a tree-shaped branching structure in many applications such as trees, blood vessels, draining and irrigation systems. Here, we extend the study of ramified optimal transportation between probability measures from Euclidean spaces to a geodesic metric space. We investigate the existence as well as the behavior of optimal transport paths under various properties of the metric such as completeness, doubling, or curvature upper boundedness. We also introduce the transport dimension of a probability measure on a complete geodesic metric space, and show that the transport dimension of a probability measure is bounded above by the Minkowski dimension and below by the Hausdorff dimension of the measure. Moreover, we introduce a metric, called "the dimensional distance", on the space of probability measures. This metric gives a geometric meaning to the transport dimension: with respect to this metric, the transport dimension of a probability measure equals to the distance from it to any finite atomic probability measure.
Monday, December 6, 2010 - 11:00 , Location: Skiles 169 , John Mallet-Paret , Brown University , Organizer: Chongchun Zeng
We examine a variety of problems in delay-differential equations. Among the new results we discuss are existence and asymptotics for multiple-delay problems, global bifurcation of periodic solutions, and analyticity (or lack thereof) in variable-delay problems. We also plan to discuss some interesting open questions in the field.
Monday, November 29, 2010 - 11:00 , Location: Skiles 169 , Federico Bonetto , Georgia Tech , Organizer: Chongchun Zeng
Modern Economic Theory is largely based on the concept of Nash Equilibrium. In its simplest form this is an essentially statics notion. I'll introduce a simple model for the use of money (Kiotaki and Wright, JPE 1989) and use it to introduce a more general (dynamic) concept of Nash Equilibrium and my understanding of its relation to Dynamical Systems Theory and Statistical Mechanics.
Monday, November 22, 2010 - 11:00 , Location: Skiles 169 , Nan Lu , Georgia Tech , Organizer: Chongchun Zeng
We consider a dynamical system, possibly infinite dimensional or non-autonomous, with fast and slow time scales which is oscillatory with high frequencies in the fast directions. We first derive and justify the limit system of the slow variables. Assuming a steady state persists, we construct the stable, unstable, center-stable, center-unstable, and center manifolds of the steady state of a size of order $O(1)$ and give their leading order approximations. Finally, using these tools, we study the persistence of homoclinic solutions in this type of normally elliptic singular perturbation problems.
Monday, November 15, 2010 - 11:00 , Location: Skiles 169 , Björn Sandstede , Brown University , Organizer: Chongchun Zeng
In this talk, I will discuss localized stationary 1D and 2D structures such as hexagon patches, localized radial target patterns, and localized 1D rolls in the Swift-Hohenberg equation and other models. Some of these solutions exhibit snaking: in parameter space, the localized states lie on a vertical sine-shaped bifurcation curve so that the width of the underlying periodic pattern, such as hexagons or rolls, increases as we move up along the bifurcation curve. In particular, snaking implies the coexistence of infinitely many different localized structures. I will give an overview of recent analytical and numerical work in which localized structures and their snaking or non-snaking behavior is investigated.
Monday, November 8, 2010 - 11:00 , Location: Skiles 169 , Shu-Ming Sun , Virginia Tech , Organizer: Chongchun Zeng
The talk concerns the mathematical aspects of solitary waves (i.e. single hump waves) moving with a constant speed on water of finite depth with surface tension using fully nonlinear Euler equations governing the motion of the fluid flow. The talk will first give a quick formal derivation of the solitary-wave solutions from the Euler equations and then focus on the mathematical theory of existence and stability of two-dimensional solitary waves. The recent development on the existence and stability of various three-dimensional waves will also be discussed.
Monday, October 25, 2010 - 11:00 , Location: Skiles 114 , Shouhong Wang , Indiana University , Organizer: Chongchun Zeng
Gas-liquid transition is one of the most basic problem to study in equilibrium phase transitions. In the pressure-temperature phase diagram, the gas-liquid coexistence curve terminates at a critical point C, also called the Andrews critical point. It is, however, still an open question why the Andrews critical point exists and what is the order of transition going beyond this critical point. To answer this basic question, using the Landau's mean field theory and the Le Chatelier principle,  a dynamic model for the gas-liquid phase transitions is established. With this dynamic model, we are able to derive a theory on the Andrews critical point C: 1) the critical point is a switching point where the phase transition changes from the first order with latent heat to the third order, and 2) the liquid-gas phase transition going beyond Andrews point is of the third order. This clearly explains why it is hard to observe the liquid-gas phase transition going beyond the Andrews point. In addition, the study suggest an asymmetry principle of fluctuations, which appears also in phase transitions in ferromagnetic systems. The analysis is based on the dynamic transition theory we have developed recently with the philosophy to search the complete set of transition states. The theory has been applied to a wide range of nonlinear problems. A brief introduction for this theory will be presented as well. This is joint with Tian Ma.
Monday, April 26, 2010 - 11:00 , Location: Skiles 269 , Mark Pollicott , University of Warwick , Organizer: Yingfei Yi
We consider a shift transformation and a Gibbs measure and estimate the drop in entropy caused by deleting an arbitrarily small (cylinder) set. This extends a result of Lind. We also estimate the speed at which the Gibbs measure escapes into the set, which relates to recent work of Bunimovich-Yurchenko and Keller-Liverani. This is joint with Andrew Ferguson.