세미나 및 콜로퀴엄

2018-11
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구글 Calendar나 iPhone 등에서 구독하면 세미나 시작 전에 알림을 받을 수 있습니다.

I will discuss the Ramsey problem for {x,y,z:x+y=p(z)} for polynomials p over ℤ. This is joint work with Peter Pach and Csaba Sandor.

Host: 엄상일     미정     2018-12-06 09:22:47

This series of lecture will introduce the study of groups acting on the circle and the line, the moduli spaces of such actions, and the role of these spaces in questions of geometric topology, dynamics, and foliation theory.  I will focus on new rigidity results in low regularity, surveying important techniques, geometrically motivated examples, and open problems. 

Host: 백형렬     영어     2018-12-07 08:36:39

We propose a novel class of Hawkes-based model that assesses two types of systemic risk in high-frequency price processes: the endogenous systemic risk within a single process and the interactive systemic risk between a couple of processes. We examine the existence of systemic risk at a microscopic level via an empirical analysis of the futures markets of the West Texas Intermediate (WTI) crude oil and gasoline and perform a comparative analysis with the conditional value-at-risk as a benchmark measure of the proposed model. Throughout the analysis, we uncover remarkable empirical findings in terms of the high-frequency structure of the two markets: for the past decade, the level of endogenous systemic risk in the WTI market was significantly higher than that in the gasoline market. Moreover, the level at which the gasoline price affects the WTI price was constantly higher than in the opposite case.  Although the two prices interact with each other at the transaction-unit level, the degree of relative influences on the two markets, that is, from the WTI to the gasoline and vice versa, was very asymmetric, but that difference has reduced gradually over time.

Host: 최건호     한국어     2018-12-10 08:58:40

Hierarchical Risk Parity approach 관련 논문과 논문 내용의 실제 데이터 적용 결과 및 문제점에 대해 살펴본다.     

Host: 최건호     한국어     2018-12-10 08:59:37

This series of lecture will introduce the study of groups acting on the circle and the line, the moduli spaces of such actions, and the role of these spaces in questions of geometric topology, dynamics, and foliation theory.  I will focus on new rigidity results in low regularity, surveying important techniques, geometrically motivated examples, and open problems. 

Host: 백형렬     영어     2018-12-07 08:35:21

Let H be a planar graph. By a classical result of Robertson and Seymour, there is a function f(k) such that for all k and all graphs G, either G contains k vertex-disjoint subgraphs each containing H as a minor, or there is a subset X of at most f(k) vertices such that G−X has no H-minor. We prove that this remains true with f(k)=ck log k for some constant c depending on H. This bound is best possible, up to the value of c, and improves upon a recent bound of Chekuri and Chuzhoy. The proof is constructive and yields the first polynomial-time O(log 𝖮𝖯𝖳)-approximation algorithm for packing subgraphs containing an H-minor.

This is joint work with Wouter Cames van Batenburg, Gwenaël Joret, and Jean-Florent Raymond.

Host: 엄상일     미정     2018-12-05 09:52:03

This series of lecture will introduce the study of groups acting on the circle and the line, the moduli spaces of such actions, and the role of these spaces in questions of geometric topology, dynamics, and foliation theory.  I will focus on new rigidity results in low regularity, surveying important techniques, geometrically motivated examples, and open problems. 

Host: 백형렬     영어     2018-12-07 08:34:18

I will recall some basic facts in the syzygy theory, with emphasis on connections with Koszul cohomology, and I will present a vanishing result for Koszul modules.

 

Host: 곽시종     미정     2018-12-05 15:43:52

I will introduce the syzygy schemes of a canonical curve and compute a few examples.

Host: 곽시종     미정     2018-12-05 15:45:46

Let X be a compact Kahler manifold of dimension n > 0. Let G be a group of zero entropy automorphisms of X.

Let G_0 be the set of elements in G which are isotopic to the identity. We prove that after replacing G by a suitable finite-index subgroup,

G/G_0 is a unipotent group of derived length at most n-1. This is a corollary of an optimal upper bound of length involving the Kodaira dimension.

We also study the algebro-geometric structure of X when it admits a group action with maximal derived length n-1.

This is a joint work with Dinh and Oguiso.

Host: 이용남     영어     2018-11-26 08:47:25

Given a group G and a manifold M, can one describe all the actions of G on M? This is a basic, natural question in geometric topology, but also a very difficult one -- even in the case where M is 1-dimensional, and G is a familiar, finitely generated group.  
This talk will introduce the theory of groups acting on 1-manifolds, through the study of orderable groups.  I will describe some connections between this theory and themes in topology and dynamics (like rigidity and foliation theory ), some current open problems, and indicate new approaches coming from recent joint work with C. Rivas.

Host: 백형렬     영어     2018-08-22 11:32:45

본 발표에서는 Deep learning 방법을 위시한 인공지능 기술이 X-ray CT 영상
연구에 어떤 기여를 해왔고 또 할 수 있는지 살펴보고자 한다. Domain knowledge
영역에서 영상 재구성 및 아티팩트 제거를 위한 패러다임이 인공지능의 새로운
패러다임에서 어떤 역할을 할 수 있을지도 함께 고찰해 보고 향후 CT 영상 기술
발전의 outlook을 AI 프레임에서 논의해 보고자 한다.

Host: 이창옥     미정     2018-11-30 16:32:47

심 사 위 원 장 : 변재형

 

심  사  위  원 : 권순식, 임미경, 박진해(충남대 수학과), 석진명(경기대 수학과) 

한국어     2018-11-20 15:08:26

For a graph G, let f2(G) denote the largest number of vertices in a 2-regular subgraph of G. We determine the minimum of f2(G) over 3-regular n-vertex simple graphs G.

To do this, we prove that every 3-regular multigraph with exactly c cut-edges has a 2-regular subgraph that omits at most max{0,⎣(c-1)/2⎦} vertices.
More generally, every n-vertex multigraph with maximum degree 3 and m edges has a 2-regular subgraph that omits at most max{0, ⎣(3n-2m+c-1)/2⎦} vertices.
These bounds are sharp; we describe the extremal multigraphs. 
This is joint work with Ringi Kim, Alexandr V. Kostochka, Boram Park, and Douglas B. West.
 
Host: 엄상일     미정     2018-11-19 09:38:14

심 사 위 원 장 : 이용남

 

심  사  위  원 : 곽시종, 배성한, 신동수(충남대 수학과), 정기룡(경북대 수학교육학과)

한국어     2018-11-20 15:04:04

Direct sampling method (DSM) is a well-known, non-iterative imaging technique in inverse scattering problem. Throughout various researches, DSM has been applied various research area e.g., diffusion tomography, electrical impedance tomography, source detection in stratified ocean waveguide, etc.; however, due to the small number of incident fields or sources, further improvements are still required. In this presentation, we carefully identify mathematical structure of indicator function of DSM to show the feasibilities and limitations, design a method of improvement, and apply in real-world microwave imaging. Simulations results with synthetic and experimental data are shown for supporting identified structure.

Host: 임미경     한국어 (필요한 경우 영어 가능) ( )     2018-11-16 10:35:31

 

심 사 위 원 장 : 황강욱

 

 

심  사  위  원 : 김성호, 정연승, 김재경,  김윤배(ETRI 선임연구원) 

한국어     2018-11-20 14:52:58

This talk introduces one of surprising empirical regularities observed in economics: Pareto distributions are everywhere. Wealth and income, the size of cities and firms, stock market returns, to list but a few, are all known to follow a Pareto distribution. I first highlight key empirical facts and describe some economic theories that have been proposed to explain the regularity. To be more specific, I will put emphasis on inequality in income distributions. A simple mechanism as well as more complex random growth models that give rise to Pareto distributions will be discussed to explore dynamics of income inequality.

Host: 정연승     영어     2018-08-22 11:31:40

We discuss a sensitivity analysis of long-term cash flows. The price of the cash flow at time zero is given by the pricing operator of a Markov diffusion acting on the cash flow function. We study the extent to which the price of the cash flow is affected by small perturbations of the underlying Markov diffusion. The main tool is the Hansen--Scheinkman decomposition, which is a method to express the cash flow in terms of eigenvalues and eigenfunctions of the pricing operator. By incorporating techniques of Malliavin calculus, the sensitivities of long-term cash flows can be represented via simple expressions in terms of the eigenvalue and the eigenfunction.

Host: 최건호     한국어     2018-11-14 16:44:01

 

One fairly standard version of the Riemann Hypothesis (RH) is that a specific probability density on the real line has a moment generating function (Laplace transform) that, as an analytic function on the complex plane, has all its zeros pure imaginary. We'll review a series of results that span the period from the 1920's to 2018 concerning a perturbed version of the RH. In that perturbed version, due to Polya, the log of the probability density is modified by a quadratic term.

 

This gives rise to an implicitly defined real constant known as the de Bruijn-Newman Constant, Lambda. The conjecture and now theorem (Newman 1976, Rodgers and Tao 2018) that Lambda is greater than or equal to zero is complementary to the RH which is equivalent to Lambda less than or equal to zero; The conjecture/theorem is a version of the dictum that the RH, if true, is only barely so. Until very recently, the best upper bound, was a 2009 result of Ki, Kim and Lee that Lambda is strictly less than 1/2.

 

Host: Paul Jung     영어     2018-10-23 10:49:48

심사위원장: 최 건 호

 

심사위원: 곽도영, 이성연, 김동석(경영공학부),

                    이억균(화학과)

 

 

한국어     2018-10-24 16:26:52

A wallspace, which is named by Haglund-Paulin, has been used as a powerful tool for geometric group theory. The dual cube complex of a wallspace is the CAT(0) cube complex whose pocset structure is identical to the wallspace. In this talk, we will focus on dual cube complexes from the hyperbolic plane with finitely many simple closed geodesics in a finite-area hyperbolic surface, construct a Dehn-twist-like quasi-isometry, and give an answer to the problem suggested by Koberda.

Host: 백형렬     영어     2018-11-05 13:13:15

In the k-cut problem, we are given an edge-weighted graph G and an integer k, and have to remove a set of edges with minimum total weight so that G has at least k connected components. This problem has been studied various algorithmic perspectives including randomized algorithms, fixed-parameter tractable algorithms, and approximation algorithms. Their proofs of performance guarantees often reveal elegant structures for cuts in graphs.
It has still remained an open problem to (a) improve the runtime of exact algorithms, and (b) to get better approximation algorithms. In this talk, I will give an overview on recent progresses on both exact and approximation algorithms. Our algorithms are inspired by structural similarities between k-cut and the k-clique problem.

Host: 엄상일     미정     2018-11-06 09:29:42

In this talk, I'll generalize the proper base change theorem in étale cohomology to space-valued sheaves, and provide two applications to the étale homotopy theory: the profinite étale homotopy type functor commutes with finite products and the symmetric powers of proper schemes over a separably closed field, respectively. In particular, the commutativity of the étale fundamental groups with finite products will be extended to all higher homotopy groups. In the applications, we'll see the advantage of the infinity categorical approach in étale homotopy theory over the model categorical one. 

Host: 박진현     영어     2018-10-26 18:20:04

 1. 학과 및 학생명 : 수리과학과 장부식

 

  2. 심 사 위 원 장 : 한상근

 

  3. 심  사  위  원 : 황강욱, 채수찬(기술경영학부), 엄재용(기술경영학부),

                          이주형(가천대 소프트웨어학과)

 

  4. 논    문    명 : 세 계층으로 나뉘어진 빅데이터 마켓 모델

 

                          Three Hierarchical Levels of Big-data Market Model

                          over Multiple Data Sources for the Internet

                          of Things

 

  5. 심  사  일  시 : 2018.11.12(월), 16:00

 

  6. 심  사  장  소 : KAIST 산업경영학동 3221호. 끝.   

미정     2018-10-16 13:14:08

In this talk we outline the construction of certain higher Chow cycles on Abelian surfaces. The existence of these cycles is predicted by certain conjectures on special values of L-functions in the local case and by the existence of certain modular forms in the case of the universal family over a Shimura curve - providing evidence for the conjecture described in the first talk. The construction uses beautiful 19th century constructions of Kummer and Humbert. 

Host: 박진현     영어     2018-10-11 15:13:52

심사위원장: 임 미 경

심사위원:  김용정, 변재형, 이은정(연세대 수학과),

              김성환(한밭대 수학과)

 

한국어     2018-10-24 16:19:50

Gross and Zagier made a conjecture on the algebraicity of values of certain `higher' Greens functions at special points. Mellit proved a few cases by linking it to the existence of certain higher Chow cycles. Viazovska proved a few cases by linking it to Borcherds lifts of modular forms. We formulate a conjecture linking modular forms and higher Chow cycles which relates the two approaches and also describe a construction of higher Chow cycles which allows us to prove special cases of the Gross-Zagier conjecture as well as provide evidence for our conjecture. 

Host: 박진현     영어     2018-08-22 11:30:37

심사위원장: 임 미 경

심사위원: 김용정, 변재형, 이은정(연세대 수학과),

              김성환(한밭대 수학과)

 

한국어     2018-10-24 16:24:04

Some reaction-diffusion systems appearing in chemistry have a natural entropy structure. In a series of works with K. Fellner and B. Q. Tang, we studied the effect of this structure on the large time behavior of the solutions of those systems. In some cases it is possible to obtain an explicit and quantitative estimate of convergence towards the equilibrium. We propose to explain the estimates starting from explicit examples of chemical networks.

 

Host: 김용정     미정     2018-10-29 10:04:51

The extremal number ex(n,F) of a graph F is the maximum number of edges in an n-vertex graph not containing F as a subgraph. A real number r∈[1,2] is realisable if there exists a graph F with ex(n , F) = Θ(nr). Several decades ago, Erdős and Simonovits conjectured that every rational number in [1,2] is realisable. Despite decades of effort, the only known realisable numbers are 1,7/5,2, and the numbers of the form 1+(1/m), 2-(1/m), 2-(2/m) for integers m≥1. In particular, it is not even known whether the set of all realisable numbers contains a single limit point other than two numbers 1 and 2.
We discuss some recent progress on the conjecture of Erdős and Simonovits. First, we show that 2-(a/b) is realisable for any integers a,b≥1 with b>a and b≡±1 (mod a). This includes all previously known ones, and gives infinitely many limit points 2-(1/m) in the set of all realisable numbers as a consequence.
Secondly, we propose a conjecture on subdivisions of bipartite graphs. Apart from being interesting on its own, we show that, somewhat surprisingly, this subdivision conjecture in fact implies that every rational number between 1 and 2 is realisable.
This is joint work with Jaehoon Kim and Hong Liu.

Host: 엄상일     미정     2018-10-29 09:34:58

Recently, there has been considerable interest in both inference and predictions for compartmental epidemic models on multiple physical scales. For instance, one could be interested in analyzing response of immune system to infection within a single host or in  describing infectuous interactions in a population of hosts. Both viral invasions and global pandemics are often described by similar mathematical constructs known as SIR models. In this talk I will review some basic concepts related to such models across scales and present a simple unifying framework that allows to conceptually connect both deterministic (e.g., population level) and stochastic (e.g., molecular level) SIR models with the help of tools of statistical theory of survival analysis. 

Host: 김재경     영어     2018-08-22 11:22:33