# Seminars & Colloquia

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구글 Calendar나 iPhone 등에서 구독하면 세미나 시작 전에 알림을 받을 수 있습니다.

A coherent sheaf F on a projective variety X is Ulrich if its pushforward by a finite degree map is trivial. Since they naturally appears in several different theories, the study of Ulrich bundles becomes important. In this talk, I will discuss two different approaches to construct Ulrich bundles on the intersection of two 4-dimensional quadrics: via Serre correspondence and via derived categories. I will also briefly explain an unexpected connection between generalized theta series. This is a joint work with Y. Cho and K.-S.Lee.

Host: 곽시종     To be announced     2017-09-20 14:19:29
We will discuss some basic idea of the Deligne-Rapoport model of modular curves.  Then, we will introduce the special fiber of the Neron model of modular Jacobian variety at some prime p. Mainly, we will focus on the component group of this special fiber. (It can be computed by the monodromy exact sequence due to the semistable reduction theorem by Grothendieck.) The structure of this component group is already known but some Hecke actions are missing.
We will complete this understanding, namely, we will compute all the Hecke actions on this group.
(This is a joint work with Taekyung Kim.)

Host: Bo-Hae Im     To be announced     2017-09-04 11:32:53

In combinatorial and computational geometry, the complexity of a system of sets is often studied via its shatter function. I will introduce these functions, and discuss how their asymptotic growth rate is governed from a single of its values, in the spirit of the classical notion of “Vapnik-Chernonenkis dimension” of hypergraphs. In particular, I will describe a probabilistic construction that refutes a conjecture of Bondy and Hajnal. This is joint work with Boris Bukh (https://arxiv.org/abs/1701.06632). The talk will start from first principles.

Host: 엄상일     To be announced     2017-09-18 09:31:35

The main aim of the lectures is to show some recent applications of
positive characteristic version of non-abelian Hodge theory to study
of algebraic varieties and their invariants in positive and zero characteristics.
I will also review classical Simpson's correspondence and relate
it to recent developments.

Host: 이용남     English     2017-09-07 10:37:11

In these two talks, I will introduce geometric problems related to mass in general relativity, such as a series of geometric inequalities, and
conjectures regarding a notion of quasi-local mass proposed by Bartnik.

The geometric inequalities we consider include the angular momentum-mass
inequality for axially symmetric initial data for the Einstein equations.
Note that the special cases treating maximal data have been proved by Dain
et al. Here I will explain how to reduce the general (non-maximal) case to
the known maximal case, and then discuss the solvability of the system of
Elliptic PDEs arose in the process, for near maximal case.

The second part of the talk will mainly provide an introduction to the
static/stationary metric extension conjectures, related to Bartnik
quasi-local mass. I will briefly discuss some known results for the static
metric extension conjecture by Anderson, Anderson/Khuri, Miao et al., and
show a local existence theorem for the solutions of axially symmetric,
stationary vacuum Einstein equations.

Host: 백형렬     English     2017-09-18 08:51:12

We show how to compute for n-vertex planar graphs in roughly O(n^(11/6)) expected time the diameter and the sum of the pairwise distances. These are the first algorithms for these problems using time O(n^c) for some constant c<2, even when restricted to undirected, unweighted planar graphs.

Host: 엄상일     English     2017-09-19 09:20:41
In this talk, we study a dynamical instability of liquid crystals under applied magnetic fields, which is the so-called Freedericksz transition. More precisely, we show that if the magnetic field strength exceeds the threshold, any global solution to the simplified Ericksen-Leslie system subject to the magnetic field converges exponentially to a unique nontrivial equilibrium, provided that a nontrivial initial orientation angle lies between $0$ and $\pi$. It is also proved that below the threshold, the equilibrium of the orientation angle is the zero state. This is based on joint work with Yuan Chen and Yong Yu.

Host: 권순식     To be announced     2017-09-20 10:30:02

The main aim of the lectures is to show some recent applications of
positive characteristic version of non-abelian Hodge theory to study
of algebraic varieties and their invariants in positive and zero characteristics.
I will also review classical Simpson's correspondence and relate
it to recent developments.

Host: 이용남     English     2017-09-07 10:38:36

The main aim of the lectures is to show some recent applications of
positive characteristic version of non-abelian Hodge theory to study
of algebraic varieties and their invariants in positive and zero characteristics.
I will also review classical Simpson's correspondence and relate
it to recent developments.

Host: 이용남     To be announced     2017-09-07 10:39:40

빅데이터(Big-Data), 단어는 많이 들어보았는데 과연 빅데이터의 본질은 무엇일까? Volume, Velocity, Variety의 3V로 정의되는 빅데이터는 과연 우리의 미래를 예측할 수 있을까? 이번 강연에서는 우리가 살고 있는 복잡한 사회를 이해하는 도구로서의 빅데이터와 네트워크 과학에 관한 설명과 함께, 그 성공적 응용사례로 구글의 검색엔진을 이용한 선거의 예측, N-gram 프로젝트를 통한 과거의 검색엔진 개발, 알파고의 AI 알고리즘, 대규모 특허분석을 통한 기술예측, 인문학 및 예술에서의 빅데이터 분석사례 등을 소개하고자 합니다. 또한 성공의 이면에 숨겨있던 빅데이터의 한계점과 어두운 그림자까지 빅데이터의 모든 것을 함께 고민하고 이를 통해 우리의 미래의 가능성을 살짝 엿보고자 합니다.

Host: 임미경     Korean     2017-09-01 16:36:42

We calculate the global log canonical thresholds of log del Pezzo surfaces embedded in weighted projective spaces as codimension two. As important applications, we show that most of them are weakly exceptional and admit K\"ahler-Einstein metrics. This is a joint work with Joonyeong Won.

Host: 신용주     To be announced     2017-09-20 10:48:04

The spatially varying coefficient process model is a nonstationary approach to explaining spatial heterogeneity by allowing coefficients to vary across space. To accommodate geographically hierarchical data, we develop a methodology for generalizing this model. We consider two-level hierarchical structures and allow for the coefficients of both low-level and high-level units to vary over space. We assume that the spatially varying low-level coefficients follow the multivariate Gaussian process, and the spatially varying high-level coefficients follow the multivariate simultaneous autoregressive model that we develop by extending the standard simultaneous autoregressive model to incorporate multivariate data. We apply the proposed model to transaction data of houses sold in 2014 in a part of the city of Los Angeles. The results show that the proposed model predicts housing prices and fits the data effectively.

Host: 황강욱     Korean     2017-09-01 16:38:31

2017년 제5회 정오의 수학산책

일시: 10월 13일(금) 12:00 - 13:15

장소: KAIST 수리과학과 E6-1 3435호

강연자: 임선희 교수 (서울대)

제목: On the work of Mirzakhani : from counting geodesics to the classification of measures

(미르자카니의 결과들 : 측지선의 개수부터 측도의 분류까지)

내용: TBA

등록: 아래 링크를 통해 사전등록 바랍니다.

https://goo.gl/forms/DbAazUTgVwyc7vQp1

Host: 이지운 교수     Contact: 김현수 (8545)     To be announced     2017-09-14 10:13:48

In this talk, we will introduce a notion of a noncommutative probability space and useful properties.

Then we will discuss various convergence results of weighted sums in a noncommutative probability space, e.g., weak law of large numbers, convergence rates and precise asymptotics, etc.

Also, we will discuss some noncommutative inequalities, e.g., Fuk-Nagaev inequalities, Bennett inequality and Rosenthal inequality, etc

Host: 폴정     To be announced     2017-09-20 14:14:09

Starting with introducing a general Newtonian Boltzmann theory, we will establish global-in-time well-posedness and stability results for solutions nearby the relativistic Maxwellian to the special relativistic Boltzmann equation without angular cutoff.  We assume the generic soft-potential conditions on the collision kernel in that were derived by Dudynski and Ekiel-Jezewska (Commun Math Phys 115(4):607--629, 1985). In this physical situation, the angular function in the collision kernel is not locally integrable, and the collision operator behaves like a non-isotropic fractional diffusion operator.

Host: 권순식     To be announced     2017-09-20 10:43:55

Right-angled Artin groups (RAAGs) are defined from finite simplicial graphs.

It is a fundamental question whether or not, given two RAAGs, there is an embedding from one group to the other.

Extension graphs are useful in solving this problem.

In this talk, I will briefly review RAAGs and extension graphs,

and show some results on solving the embeddability problem in RAAGs by using extension graphs.

Host: 고기형     Korean     2017-09-01 16:40:06

Let K be a finite extension of Qp. It is believed that one can attach a smooth Fp-representation of GLn(K) (or a packet of such representations) to a continuous Galois representation Gal(Qp/K) → GLn(Fp) in a natural way, that is called mod p Langlands program for GLn(K). This conjecture is known only for GL2(Qp): one of the main difficulties is that there is no classification of such smooth representations of GLn(K) unless K = Qp and n = 2. However, for a given continuous Galois representation ρ0 : Gal(Qp/Qp) → GLn(Fp), one can define a smooth Fp-representation Π0 of GLn(Qp) by a space of mod p automorphic forms on a compact unitary group, which is believed to be a candidate on the automorphic side corresponding to ρ0 for mod p Langlands correspondence in the spirit of Emerton. The structure of Π0 is very mysterious as a representation of GLn(Qp), and it is not known that ρ0 and Π0 determine each other. In this talk, we discuss that Π0 determines ρ0 , provided that ρ0 is ordinary and generic. More precisely, we prove that the tamely ramified part of ρ0 is determined by the Serre weights attached to ρ0 , and the wildly ramified part of ρ0 is obtained in terms of refined Hecke actions on Π0. The talk is based on a joint work with Zicheng Qian.

Host: Bo-Hae Im     To be announced     2017-09-20 13:17:42

In these two talks, I will introduce geometric problems related to mass in general relativity, such as a series of geometric inequalities, and
conjectures regarding a notion of quasi-local mass proposed by Bartnik.

The geometric inequalities we consider include the angular momentum-mass
inequality for axially symmetric initial data for the Einstein equations.
Note that the special cases treating maximal data have been proved by Dain
et al. Here I will explain how to reduce the general (non-maximal) case to
the known maximal case, and then discuss the solvability of the system of
Elliptic PDEs arose in the process, for near maximal case.

The second part of the talk will mainly provide an introduction to the
static/stationary metric extension conjectures, related to Bartnik
quasi-local mass. I will briefly discuss some known results for the static
metric extension conjecture by Anderson, Anderson/Khuri, Miao et al., and
show a local existence theorem for the solutions of axially symmetric,
stationary vacuum Einstein equations.

Host: 백형렬     English     2017-09-15 09:54:51

It was shown by Schaffer that for a dense class of compactly supported smooth initial data,the number of shock curves is finite for large time. It was not known if there is a smooth data for which the number of shock curves is unbounded. In this talk, using the structure of entropy solutions, one can construct a smooth initial data for which the number of shocks curves is infinite.

Host: 김용정     English     2017-09-11 10:42:15

We classify minimal projective $3$-folds of general type with the geometric genus $p_g= 1, 2$ or $3$ by studying the birationality of $\varphi_{16},\ \varphi{6}$ and $\varphi{5}$. This is a joint work with Meng Chen and Matteo Penegini.

Host: 신용주     English     2017-08-21 08:58:33

For a motivation of stochastic integrals, we start with stochastic (random) versions of deterministic systems and then we discuss  the Ito integral as a non-anticipating (adapted) stochastic integral.

Based on the quantum decomposition of Brownian motion, we study the Skorohod integral and Stratonovich integral as anticipating (non-adapted) stochastic integrals.

Note that the Skorohod integral is the adjoint action of the Malliavin derivative.

Host: 황강욱     Korean     2017-09-01 16:16:42

I discuss recent progress in the classification of simply
connected Godeaux surfaces. There are two parts. The first
describes remarkable recent work of Isabel Stenger
(Kaiserslautern). She constructs an 8-dimensional rationally
parametrised moduli family of "general" surfaces, for which
the bicanonical pencil has no hyperelliptic fibres. Her
family contains a 7-dimensional subfamily with a single
hyperelliptic fibre and a 6-dimensional subfamily with two
hyperelliptic fibres. The second part describes my different
attack on the same problem, on which there has been some
progress over the last 25 years.

Host: 이용남     English     2017-09-05 13:51:16