Department of Mathematics,
University of California San Diego

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Group Actions Seminar

Minju Lee - Graduate student
Yale University

Invariant measures for horospherical actions and Anosov groups

Abstract:

Let $\Gamma$ be an Anosov subgroup of a connected semisimple real linear Lie group $G$. For a maximal horospherical subgroup $N$ of $G$, we show that the space of all non-trivial $NM$-invariant ergodic and $A$-quasi-invariant Radon measures on $\Gamma \backslash G$, up to proportionality, is homeomorphic to $\mathbb{R}^{\mathrm{rank} (G)-1}$, where $A$ is a maximal real split torus and $M$ is a maximal compact subgroup which normalizes $N$.
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This is joint work with Hee Oh.

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Zoom ID 967 4109 3409 (email Nattalie Tamam or Brandon Seward for the password)

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Department of Mathematics,
University of California San Diego

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Center for Computational Mathematics Seminar

Stephanie Wang
Department of Computer Science and Engineering, UC San Diego

Capturing Surfaces with Differential Forms

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Zoom Meeting ID: 950 6794 9984

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Department of Mathematics,
University of California San Diego

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Math 292 - Topology Seminar

Jianfeng Lin
UC San Diego

Isotopy of the Dehn twist on $K3\#K3$ after a single stabilization

Abstract:

Kronheimer-Mrowka recently proved that the Dehn twist along a 3-sphere in the neck of $K3\#K3$ is not smoothly isotopic to the identity. This provides a new example of self-diffeomorphisms on 4-manifolds that are isotopic to the identity in the topological category but not smoothly so. (The first such examples were given by Ruberman.)
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In this talk, we study the Bauer-Furuta invariant as an element in the Pin(2)-equivariant stable homotopy group of spheres. We use it to show that this Dehn twist is not smoothly isotopic to the identity even after a single stabilization (connected summing with the identity map on S2 cross S2). This gives the first example of exotic phenomena on simply-connected smooth 4-manifolds that do not disappear after a single stabilization. In particular, it implies that one stabilization is not enough in the diffeomorphism isotopy problem for 4-manifolds. It gives an interesting comparison with Auckly-Kim-Melvin-Ruberman-Schwartz's theorem that one stabilization is enough in the surface isotopy problem.

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Zoom information: Meeting ID: 933 6734 4286 Password: topology

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Department of Mathematics,
University of California San Diego

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Zoom for Thought

Sam Spiro - Ph.D. Candidate
UC San Diego

Some Selected Picks from Extremal Combinatorics

Abstract:

In this talk things will get extreme, but not with number fields or schemes. Instead we'll focus on combinatorics, though we won't discuss clever tricks. We speak only of glorious theorems, as well as some notorious problems. And for all those that attend, there is a surprise at the end!

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Please see email with subject ``Zoom for Thought Information."

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Department of Mathematics,
University of California San Diego

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Math 296 - Graduate Colloquium

David Stapleton
UC San Diego

Projective space, hypersurfaces, and algebraic geometry

Abstract:

We give a quick and friendly introduction to projective space and then introduce and explore some of the most elementary and fundamental examples in algebraic geometry: hypersurfaces in projective space (especially cubic hypersurfaces).

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Contact Elham Izadi for Zoom link

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Department of Mathematics,
University of California San Diego

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Math 258 - Differential Geometry Seminar

Riccardo Tione
EPFL

Anisotropic energies: examples, rectifiability and regularity

Abstract:

Anisotropic energies are functionals defined by integrating over a generalized surface (such as a current or a varifold) an integrand depending on the tangent plane to the surface. In the case of a constant positive integrand, one obtains the area functional, and hence one can see anisotropic energies as a generalization of it. A long standing question in geometric measure theory is to establish regularity properties of critical points to such functionals. In this talk, I will discuss some recent developments on this theory, addressing in particular the question of rectifiability of stationary points and regularity of stationary Lipschitz graphs.
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The talk is based on joint work with Antonio De Rosa.

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Zoom link: Meeting ID: 988 8132 1752

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Department of Mathematics,
University of California San Diego

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Math 278C - Optimization and Data Science Seminar

Li Wang
University of Texas at Arlington

A Self-Consistent-Field Iteration for Orthogonal Canonical Correlation Analysis

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Meeting ID: 982 9781 6626 Password: 278CWn21

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Department of Mathematics,
University of California San Diego

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Math 288 - Probability and Statistics Seminar

Dan Daniel Erdmann-Pham
UC Berkeley

Hydrodynamics of the inhomogeneous l-TASEP and its Application to Protein Synthesis

Abstract:

The inhomogeneous l-TASEP is an interacting particle process wherein particles stochastically enter, unidirectionally traverse, and finally exit a one-dimensional lattice segment at rates that may depend on a particle's location within the lattice. Its homogeneous version is known to exhibit various phase transitions in macroscopic observables like particle density and current, with fluctuations governed by what is known as the KPZ equation. In this talk, we begin to extend such results to the inhomogeneous setting by developing the so-called hydrodynamic limit, which governs the system dynamics on an LLN-type scale. If time permits, we apply our results to elucidate the key determinants of protein synthesis, which motivated the introduction of TASEP fifty years ago.
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This is based on joint work with Khanh Dao Duc and Yun S. Song.

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For zoom ID and password email: bau@ucsd.edu

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Department of Mathematics,
University of California San Diego

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Probability Corner

First Probability Corner meeting

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Zoom: https://ucsd.zoom.us/j/93627682585 E-mail Todd Kemp tkemp@ucsd.edu for the password

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Department of Mathematics,
University of California San Diego

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Math 209 - Number Theory Seminar

Aranya Lahiri
Indiana University

Resolutions of locally analytic principal series representations of $GL_2(F)$

Abstract:

Locally analytic representations of $p$-adic analytic groups
have played a crucial role in many areas of arithmetic and
representation theory (including in $p$-adic local Langlands program)
since their introduction by Schneider and Teitelbaum. In this talk we
will briefly review some aspects of the theory of locally analytic
representations. Then, for a locally analytic representation $V$ of
$GL_2(F)$ we will construct a coefficient system attached to the
Bruhat-Tits tree of $Gl_2(F)$. Finally we will use this coefficient
system to construct a resolution for locally analytic principal series
of $GL_2(F)$.

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Location: see https://www.math.ucsd.edu/\~{}nts/

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Department of Mathematics,
University of California San Diego

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Math 218 - Seminars on Mathematics for Complex Biological Systems

Philippe Robert
INRIA, Paris

Stochastic Models of Neural Synaptic Plasticity

Abstract:

In neuroscience, learning and memory are usually associated to long-term changes of neuronal connectivity. Synaptic plasticity refers to the set of mechanisms driving the dynamics of neuronal connections, called synapses and represented by a scalar value, the synaptic weight. Spike-Timing Dependent Plasticity (STDP) is a biologically-based model representing the time evolution of the synaptic weight as a functional of the past spiking activity of adjacent neurons.
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In this talk we present a new, general, mathematical framework to study synaptic plasticity associated to different STDP rules. The system composed of two neurons connected by a single synapse is investigated and a stochastic process describing its dynamical behavior is presented and analyzed. We show that a large number of STDP rules from neuroscience and physics can be represented by this formalism. Several aspects of these models are discussed and compared to canonical models of computational neuroscience. An important sub-class of plasticity kernels with a Markovian formulation is also defined and investigated via averaging principles.
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Joint work with Gaetan Vignoud

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Contact Bo Li at bli@math.ucsd.edu for the Zoom info

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Department of Mathematics,
University of California San Diego

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Math 288C - Stochastic Systems Seminar

Sam Babichenko - Undergraduate student
UC San Diego

``Mean Field Games and Interacting Particle Systems'' following David Lacker.

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For Zoom information, please email Professor Ruth Williams

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Department of Mathematics,
University of California San Diego

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Math 208 - Algebraic Geometry Seminar

Roberto Svaldi
EPFL

Applications of birational geometry to holomorphic foliations, part 2

Abstract:

This will be the continuation to Calum's talk. The plan,
building on what Calum explained, is to discuss some recent work
building towards the birational classification of holomorphic foliations
on projective varieties (particularly 3folds) in the spirit of the
Minimal Model program.
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We will explain some applications of these ideas to the study of the
dynamics and geometry of foliations and foliation singularities.
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Features works of C. Spicer and P. Cascini and joint work with C. Spicer.

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Contact David Stapleton, dstapleton@ucsd.edu, for zoom access

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