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Fall 2021 G&A ZoominarWednesdays @ 4pm California Time[Direct Link]
Meeting ID: 933 9188 4256
Passcode: seminar[Give feedback]For further information please contactProfessor Kasia Jankiewicz
Schedule (click dates for title and abstract)



10/6 
Joey Zou 
UC Santa Cruz 



10/20 
Xiaodong Wang 
Michigan State University 



11/3 
Bo Zhu

University of Minnesota 



11/17 
Kyle Miller 
UC Santa Cruz 



12/1 
Yang Zhang 
University of Washington 
Wednesday, Oct 6, at 4pm PST
Joey Zou, UC Santa Cruz
Microlocal Analysis with Applications to Seismic Inverse Problems
I will discuss the travel time tomography problem for elastic media, which asks to recover the composition of an elastic material given the data of the travel times of the material's elastic waves. This problem is particularly important in the transversely isotropic setting, as transverse isotropy forms a common model for the composition of the Earth's interior. The mathematical study of this problem relates to Xray tomography and boundary rigidity problems studied by de Hoop, Stefanov, Uhlmann, Vasy, et al., which reduce the inverse problems to the microlocal analysis (i.e. analysis in phase space) of certain operators obtained from a pseudolinearization argument; however in this setting the analysis is more subtle, as the operators obtained are somewhat degenerate (they resemble parabolic operators in a particular sense, rather than elliptic operators in previous works). In this talk, I will explain how to reduce the travel time tomography problem to a problem in microlocal analysis, as well as the analysis required to accommodate the operators involved.
Wednesday, Oct 20, at 4pm PST
Xiaodong Wang, Michigan State University
Uniqueness Results on a geometric PDE in Riemannian and CR Geometry Revisited
I will discuss some uniqueness results for a geometric nonlinear PDE related to the scalar curvature in Riemannian geometry and CR geometry. In the Riemannian case I will present a new proof of the uniqueness result assuming only a positive lower bound for Ricci curvature. I will explain how the same principle can be used in the CR case to establish a JerisonLee identity in a more general setting and a stronger uniqueness result.
Wednesday, Nov 3, at 4pm PST
Bo Zhu, University of Minnesota
Geometry of positive scalar curvature on complete 3manifolds
In this talk, we first introduce some conjectures related to scalar curvature in the context of size geometry. Then, we will particularly discuss how the strictly positive scalar curvature affects the volume growth of the geodesic ball in complete threedimensional manifolds with nonnegative scalar curvature. We will also cover related progress on this topic if time permits.
Wednesday, Nov 17, at 4pm PST
Kyle Miller, UC Santa Cruz
The homological arrow polynomial
The Kauffman bracket polynomial is an invariant of framed unoriented knots and links in the 3sphere, giving the Jones polynomial via skein relations. Applying these skein relations to links in other 3manifolds yields invariants in the Kauffman bracket skein module, which is a relatively complicated object. I will talk about a multivariable polynomial invariant for links in thickened surfaces that is obtained as a functional on the skein module, an evaluation of which coincides with the arrow polynomial of Kauffman and Dye. This polynomial is an invariant of virtual links (i.e., it is unchanged under destabilization along vertical annuli in the complement), and it has applications to checkerboard colorability and in proving nonexistence of essential vertical annuli.
Wednesday, Dec 1, at 4pm PST
Yang Zhang, UC Santa Cruz
Inverse boundary value problems for nonlinear hyperbolic equations on Lorentzian manifolds
Inverse problems of recovering the metric and nonlinear terms were originated in the work by Kurylev, Lassas, and Uhlmann for the semilinear wave equation \(square_g u(x) + a(x)u^2(x) = f(x)\) in a manifold without boundary. The idea is to use the linearization and the nonlinear interactions of distorted plane waves to produce point source like singularities in an observable set. In this talk, I will discuss joint work with Gunther Uhlmann which considers the recovery of the metric and nonlinear terms for a quadratic derivative nonlinear wave equation on a Lorentzian manifold with boundary. The main difficulty that we need to handle here is caused by the presence of the boundary. I will first overview two related inverse boundary problems for semilinear wave equations considered by Hintz, Uhlmann, and Zhai. Our work builds on these previous results and then I will discuss our methods to overcome the difficulties