Low Entropy and the Mean Curvature Flow with Surgery

Speaker: 

Alex Mramor

Institution: 

UC, Irvine

Time: 

Tuesday, October 16, 2018 - 4:00pm to 5:00pm

Host: 

Location: 

RH 306

In this talk we will discuss the mean curvature flow with surgery and how to extend it to the low entropy, mean convex setting. An application to the topology of low entropy self shrinkers will also be discussed. This is a joint work with Shengwen Wang.

Joint Los Angeles Topology Seminar at Caltech

Institution: 

Joint Seminar

Time: 

Monday, November 5, 2018 - 4:00pm to 6:00pm

Location: 

Linde 310

Chris Gerig (Harvard): SW = Gr
Whenever the Seiberg-Witten (SW) invariants of a 4-manifold X are defined, there exist certain 2-forms on X which are symplectic away from some circles. When there are no circles, i.e. X is symplectic, Taubes' ``SW=Gr'' theorem asserts that the SW invariants are equal to well-defined counts of J-holomorphic curves (Taubes' Gromov invariants). In this talk I will describe an extension of Taubes' theorem to non-symplectic X: there are well-defined counts of J-holomorphic curves in the complement of these circles, which recover the SW invariants. This ``Gromov invariant'' interpretation was originally conjectured by Taubes in 1995.

Biji Wong (CIRGET Montreal): A Floer homology invariant for 3-orbifolds via bordered Floer theory
Using bordered Floer theory, we construct an invariant for 3-orbifolds with singular set a knot that generalizes the hat flavor of Heegaard Floer homology. We show that for a large class of 3-orbifolds the orbifold invariant behaves like HF-hat in that the orbifold invariant, together with a relative Z_2-grading, categorifies the order of H_1^orb. When the 3-orbifold arises as Dehn surgery on an integer-framed knot in S^3, we use the {-1,0,1}-valued knot invariant epsilon to determine the relationship between the orbifold invariant and HF-hat of the 3-manifold underlying the 3-orbifold.

Joint Los Angeles Topology Seminar at UCLA

Institution: 

Joint Seminar

Time: 

Monday, October 15, 2018 - 4:00pm to 6:00pm

Location: 

MS 6627

Lei Chen (Caltech): Section problems
In this talk, I will discuss a direction of study in topology: Section problems. There are many variations of the problem: Nielsen realization problems, sections of a surface bundle, sections of a bundle with special property (e.g. nowhere zero vector field). I will discuss some techniques including homology, Thurston-Nielsen classification and dynamics. Also I will share many open problems. Some of the results are joint work with Nick Salter.

Lisa Piccirillo (UT Austin): TBA

Combinatorics of orbit configuration spaces

Speaker: 

Christin Bibby

Institution: 

University of Michigan

Time: 

Monday, October 29, 2018 - 4:00pm to 5:00pm

Host: 

Location: 

RH 340P

From a group action on a space, define a variant of the configuration space by insisting that no two points inhabit the same orbit. When the action is almost free, this "orbit configuration space'' is the complement of an arrangement of subvarieties inside the cartesian product, and we use this structure to study its topology. We give an abstract combinatorial description of its poset of layers (connected components of intersections from the arrangement) which turns out to be of much independent interest as a generalization of partition and Dowling lattices. The close relationship to these classical posets is then exploited to give explicit cohomological calculations akin to those of (Totaro '96). Joint work with Nir Gadish.

Nilpotent structures and collapsing Ricci-flat metrics on K3 surfaces

Speaker: 

Jeff Viaclovsky

Institution: 

UC Irvine

Time: 

Tuesday, October 2, 2018 - 4:00pm

Location: 

RH 306

I will discuss a new construction of families of Ricci-flat Kahler metrics on K3 surfaces which collapse to an interval, with Tian-Yau and Taub-NUT metrics occurring as bubbles. There is a corresponding singular fibration from the K3 surface to the interval, with regular fibers diffeomorphic to either 3-tori or Heisenberg nilmanifolds. This is joint work with Hans-Joachim Hein, Song Sun, and Ruobing Zhang.

Using active learning to engage students in the learning process

Speaker: 

Matthew Mahavongtrakul

Institution: 

Division of Teaching Excellence and Innovation UC Irvine

Time: 

Friday, October 5, 2018 - 4:00pm

Location: 

PSCB 140

In this session, we will cover the use of active learning techniques in the classroom to engage students in the learning process. We will begin with a short discussion on considerations for active learning, followed by how to create buy-in for students. Afterwards, we will go over different techniques depending on content goals and group sizes. We will finish by designing a lesson plan that integrates 1-2 active learning techniques that you can use in your own discussions. Participants interested in learning more are encouraged to visit the Division of Teaching Excellence and Innovation (DTEI) website at www.dtei.uci.edu.

Spectral transitions for Schr\"odinger operators with decaying potentials and Laplacians on asymptotically flat (hyperbolic) manifolds

Speaker: 

Wencai Liu

Institution: 

UCI

Time: 

Friday, October 26, 2018 - 3:00pm

Location: 

RH 440R

We apply piecewise constructions and gluing  techniques  to  construct

asymptotically flat (hyperbolic) manifolds such that associated

Laplacians have dense embedded eigenvalues or singular continuous

spectra.  The method also allows us to provide various examples of

operators with embedded singular spectra. With additional perturbation theory,    several sharp

spectral transitions (even criteria) for singular spectra are obtained.

In this talk, I will focus on two models-Laplacians on manifolds and Stark operators.

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