# Department Seminars & Colloquia

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In this work, we investigate optimal control problems in heterogeneous porous media. Based on the partial differential equation constraint connecting the state and the control, we produce the associated control as a dependent quantity of the state. Then, we introduce the reduced optimal control problem which contains only the state variable. Here we employ $C^0$ interior penalty finite element methods for the spatial discretization to solve the reduced optimal control problem resulting in a fourth-order variational inequality. We provide a priori error estimates and stability analyses. Several numerical examples validate and illustrate the capabilities of the proposed algorithm.

Knot homology theories revolutionized the study of knots and links, much like (simplicial or singular) homology theory revolutionized the study of topological spaces. One of the major knot homology theories, Khovanov homology, was introduced by M. Khovanov in 2000 as a "categorification of the Jones polynomial." One notable feature of Khovanov homology is its ability to detect the unknot, a feature not known to be possessed by the Jones polynomial. Recently, it has found notable applications in low-dimensional topology, including the detection of exotic surfaces in the 4-ball.
Day 1: Jones polynomial and its categorification.

In this lecture, we will discuss the formal/mathematical connection between the Boltzmann equation and the compressible Euler equation. For the mathematical justification we study the convergence of real analytic solutions of Boltzmann equations toward smooth solutions of the compressible Euler equation (before shock). This lecture will be accessible to graduate students.

We introduce a version of Heegaard diagrams for 5-dimensional cobordisms with 2- and 3-handles, 5-dimensional 3-handlebodies, and closed 5-manifolds. We show that every such 5-manifold can be represented by a Heegaard diagram, and two Heegaard diagrams represent diffeomorphic 5-manifolds if and only if they are related by certain moves. As an application, we construct Heegaard diagrams for 5-dimensional cobordisms from the standard 4-sphere to the Gluck twists along knotted 2-spheres. This provides some equivalent statements regarding the Gluck twists being diffeomorphic to the standard 4-sphere.

Knot homology theories revolutionized the study of knots and links, much like (simplicial or singular) homology theory revolutionized the study of topological spaces. One of the major knot homology theories, Khovanov homology, was introduced by M. Khovanov in 2000 as a "categorification of the Jones polynomial." One notable feature of Khovanov homology is its ability to detect the unknot, a feature not known to be possessed by the Jones polynomial. Recently, it has found notable applications in low-dimensional topology, including the detection of exotic surfaces in the 4-ball.
Day 2: Numerical invariants from Khovanov homology and their applications.

Knot homology theories revolutionized the study of knots and links, much like (simplicial or singular) homology theory revolutionized the study of topological spaces. One of the major knot homology theories, Khovanov homology, was introduced by M. Khovanov in 2000 as a "categorification of the Jones polynomial." One notable feature of Khovanov homology is its ability to detect the unknot, a feature not known to be possessed by the Jones polynomial. Recently, it has found notable applications in low-dimensional topology, including the detection of exotic surfaces in the 4-ball.
Day 3: Recent developments of Khovanov homology and its applications to low-dimensional topology.

Mr. Saqib Mushtaq Shah, a KAIX visiting graduate student from ISI Bangalore who will stay at KAIST for 8 weeks, is going to give a series of weekly talks on the Milnor K-theory from the beginning. It is part of his KAIX summer internship works.

This is part of an informal seminar series to be given by Mr. Jaehong Kim, who has been studying the book "Hodge theory and Complex Algebraic Geometry Vol 1 by Claire Voisin" for a few months. It will summarize about 70-80% of the book.

Kahn-Sujatha's birational motive is a variant of Chow motive that synthesis the ideas of birational geometry and motives. We explain our result saying that the unramified cohomology is a universal invariant for torsion motives of surfaces. We also exhibit examples of complex varieties violating the integral Hodge conjecture. If time permits, we discuss a pathology in positive characteristic.
(Joint work with Kanetomo Sato.)

For motivational purposes, we begin by explaining the classical Satake isomorphism from which we deduce the unramified local Langlands correspondence. Then we explain a geometric interpretation of the Satake isomorphism. More precisely, we explain how one can view Hecke operators as global functions on the moduli space of unramified L-parameters. This viewpoint arises from the categorical local Langlands correspondence. The main content of the talk is p-adic and mod p analogues of this interpretation, where the space of unramified L-parameters is replaced by certain loci in the moduli stack of p-adic Galois representations (so-called the Emerton-Gee stack). We will also discuss their relationship with the categorical p-adic local Langlands program.

Let S be a simply-connected rational homology complex projective plane with quotient singularities. The algebraic Montgomery-Yang problem conjectures that the number of singular points of S is at most three. In this talk, we leverage results from the study of smooth 4-manifolds, such as the Donaldson diagonalization theorem, to establish additional conditions for S. As a result, we eliminate the possibility of a rational homology complex projective plane of specific types with four singularities. We also identify infinite families of singularities that satisfy properties in algebraic geometry, including the orbifold BMY inequality, but are obstructed from being a rational homology complex projective plane due to smooth conditions. Additionally, we discuss experimental results related to this problem. This is joint work with Jongil Park and Kyungbae Park.

In this talk, I will talk about isotopy problems of Seifert surfaces pushed in to the 4-ball. In particular, I will prove that every Seifert surface of a non-split alternating link become isotopic in the 4-ball. This is a joint work with Maggie Miller and Jaehoon Yoo.

In the first part of the talk, I will discuss the asymptotic expansions of the Euclidean Φ^4-measure in the low-temperature regime. Consequently, we derive limit theorems, specifically the law of large numbers and the central limit theorem for the Φ^4-measure in the low-temperature limit. In the second part of the talk, I will focus on the infinite volume limit of the focusing Φ^4-measure. Specifically, with appropriate scaling, the focusing Φ^4-measure exhibits Gaussian fluctuations around a scaled solitary wave, that is, the central limit theorem.
This talk is based on joint works with Benjamin Gess, Pavlos Tsatsoulis, and Philippe Sosoe.

In general relativity, spacetime is described by a (1+3)-dimensional Lorentzian manifold satisfying the Einstein equations, and initial data sets (i.e., fixed-time configurations) correspond to embedded spacelike hypersurfaces. The initial data sets are required to satisfy underdetermined PDEs called constraint equations -- in the language of differential geometry, these are exactly the Gauss and Codazzi equations. The goal of my talk will be to elucidate the flexibility of these objects -- specific results to be presented include extension, gluing, asymptotics-prescription, and parametrization of asymptotically flat initial data sets, often with sharp assumptions. Basic to our approach is a novel way to construct solution operators for divergence-type equations with prescribed support properties, which should be of independent interest. This part is based on joint work with Phil Isett (Caltech), Yuchen Mao (UC Berkeley), and Zhongkai Tao (UC Berkeley).

In this talk, we will discuss cylindrical and hypoelliptic extensions of Hardy, Sobolev, Rellich, Caffarelli-Kohn-Nirenberg, and other related functional inequalities. We will then concentrate on discussing their best constants, ground states for higher-order hypoelliptic Schrödinger-type equations, and solutions to the corresponding variational problems.

In the 1980's Casson and Gordon produced the first non slice knots which are trivial in Levine's algebraic concordance group, and in 2003 Cochran-Orr-Teichner produced the first no slice knots undetectable by Casson and Gordon's invariants. They do so by producing a filtration of the concordance group by subgroups a knot in the 1.5th term of this filtration has vanishing Casson-Gordon invariants. Since then this work has been central to the study of knot concordance. We will introduce this filtration and review just enough of the theory of L^2 homology to prove that the successive quotients of this filtration are nontrivial.

In the 1970's J. Levine produced a surjection from the knot concordance group to the so called algebraic concordance group. This captured the known features of the knot concordance group to that point and classifies high dimensional concordance. During this survey talk we will explore the construction of the algebraic concordance group and explain some of its consequences.

The analysis on the limiting behavior of solution is pivotal for equations in geometric analysis, mathematical physics and application in optimization. In 80s, Rene Thom conjectured that if an analytic gradient flow has a limit, then it approaches to the limit along a unique asymptotic direction. This represents a next-order question following the seminal works by Lojasiewicz and L. Simon. In 2000, Thom's conjecture was affirmatively proved by Kurdyka, Mostowski, and Parusinski for finite dimensional gradient flows. In this first part, we will discuss about the basics about theory of Lojasiewicz concerning the uniqueness of limits. Then we explore vast applications in PDEs which were initiated by Leon Simon.

Following the brief introduction to Lojasiewicz's theory in the first part, in the second part we discuss Thom's gradient conjecture and our recent joint work with Pei-Ken Hung where we generalized this conjecture to the class of PDEs. The result classifies the next-order asymptotics by revealing both the rate and the direction of convergence to the limit. Finally we talk about possible future applications and working directions.