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Current Colloquia & Seminars

  1. Hamiltonian Colloquium: Curious Instances of Geodesics on SO(3)

    Location: MSRI: Simons Auditorium
    Speakers: Oliver O'Reilly

    Geodesics on the group of rotations SO(3) manifest in disparate fields ranging from the kinematics of the human eye to rigid body dynamics to computer graphics. In kinematics of the human eye, where the motion of the eye is assumed to be subject to Listings law, they manifest as motions of constant angular velocity rotations which can be used to interpret saccadic motions of the eye. In computer graphics, they appear as great circles on the 3-sphere that are used as the basis for realistic interpolations using Shomake's SLERP algorithm. In rigid body dynamics, geodesics on SO(3) can be used to provide the simplest realization of the dependency of the geodesic on the metric used for the configuration manifold.


    In this talk, we present a quaternion-based treatment of geodesics on SO(3). We find a simple set of differential equations that characterize these motions. The solutions to these integrable equations are readily interpreted as great circles on the 3-sphere. We also show how they can be projected onto Steiner's Roman Surface using a transformation developed by Apery.  Applying our results to the human eye shows some remarkable consequences of Listing's law for the dynamics of this system.


    The work presented in this talk is based on two papers that were coauthored with Alyssa Novelia: one appeared in Nonlinear Dynamics (https://doi.org/10.1007/s11071-015-1945-0) and the other in Regular and Chaotic Dynamics (https://doi.org/10.1134/S1560354715060088)


    Brief Biosketch:

    Oliver M. O’Reilly is a professor in the Department of Mechanical Engineering at the University of California at Berkeley. His research and teaching feature a wide range of problems in the dynamics of mechanical systems.  He received his B.E. in Mechanical Engineering from the National University of Ireland, Galway (NUIG). Subsequently, he received his M.S. and Ph.D. degrees in Theoretical and Applied Mechanics from Cornell University.  O’Reilly has received multiple teaching awards, including the Distinguished Teaching Award from U.C. Berkeley, published over 90 archival journal articles, written three textbooks and is a co-inventor on two patents. His latest book, coauthored with Alyssa Novelia and Khalid Jawed is a Primer on the Kinematics of Discrete Elastic Rods (Springer, 2018).

    Updated on Oct 12, 2018 10:16 AM PDT
  2. Chancellor Course: Topics in Analysis

    Location: UC Berkeley: Evans Hall, Room 748
    Speakers: Wilfrid Gangbo (University of California, Los Angeles)

    This is a graduate level course, to cover some of the analytical aspects of Mean Field Games. In the recent years, the number of areas of applications of the Mean Field Games theory have exploded, especially because the theory provides the simplest method to handle control problems with several agents. This includes communication networks, data networks, power systems, crowd motion, trade crowding and learning in Mean FieldGames. Despite the recent pioneer work by Cardialaguet–Delarue–Lasry–Lions, the theoryof Mean Field Games is not yet out of its infancy. We will briefly cover the needed stochastic analysis aspect at the undergraduate course level. Other useful geometric concepts will be briefly mentioned in order to quickly get to the heart of the matter.

    This course will be taught by visiting Chancellor's Professor Wilfrid Gangbo.

    Updated on Aug 17, 2018 03:35 PM PDT
  3. Weak KAM Theory, Homogenization and Symplectic Topology

    Location: UC Berkeley Math
    Speakers: Fraydoun Rezakhanlou (University of California, Berkeley)

    In this course we will explore the connection between Hamilton-Jacobi PDE, Hamiltonian ODE and Symplectic Topology. Hamiltonian systems of ordinary differential equations appear in celestial mechanics to describe the motion of planets. We regard a Hamiltonian system  completely integrable if there exists a change of coordinates such that our Hamiltonian system in new coordinates is still Hamiltonian but now associated with a Hamiltonian function that is independent of position. For completely integrable systems the new momentum coordinates are conserved and the set of points at which the new momentum takes a fixed vector is invariant for the flow of our system. These invariant sets are homeomorphic to tori in many classical examples of completely integrable systems. According to Kolmogorov-Arnold-Moser (KAM) Theory, many of the invariant tori survive when a completely integrable system  is slightly perturbed. Aubry-Mather Theory construct a family of invariant sets provided that the Hamiltonian function is convex in the momentum variable.  A. Fathi uses viscosity solutions of the associated Hamilton-Jacobi PDE to construct Aubry-Mather invariant measures. Recently there have been several interesting works to understand the connection between Aubry-Mather Theory and Symplectic Topology. The hope is to use tools from Symplectic Topology to construct interesting invariant sets/measures for Hamiltonian systems associated with non-convex Hamiltonian functions. In this course, we also explore the connection between Aubry-Mather Theory and the homogenization phenomena for Hamilton-Jacobi PDEs when the Hamiltonian function is selected randomly according to a translation invariant probability measure.

    Created on Aug 24, 2018 03:42 PM PDT