# 세미나 및 콜로퀴엄

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

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E6-1, ROOM 1409
Discrete Math
Brendan Rooney (KAIST)
Eigenpolytopes, Equitable Partitions, and EKR-type Theorems

_{n}due to Godsil and Meagher. Along the way we will see some useful tools from algebraic graph theory. Namely, a bound on the maximum size of an independent set in a graph, equitable partitions, and eigenpolytopes.

Let X be a smooth projective rational surface over an algebraically closed field. One version of a long standing conjecture asks whether the set of self-intersections of reduced curves is bounded below. This question can be reduced to studying singular plane curves. One approach is to measure how singular the curve is using a recently introduced quantity called an H-constant. This has raised some new open problems I will discuss.

2017 제2회 정오의 수학산책

강연자: 이윤원 (인하대)

일시: 2017년 4월 28일(금) 12:00 ~ 13:15

장소: 카이스트 자연과학동 E6-1 3435호

제목: Atiyah-Singer index theorem

내용: TBA

등록: 2017년 4월 26일(수) 오후 3시까지

https://goo.gl/forms/0lqSboiW5A9vv9rd2

문의: hskim@kias.re.kr / 내선:8545

Probabilistic methods in geometric group theory have recently gained in importance. In the course I will focus on the setting where a countable group G acts on a (possibly nonproper) Gromov hyperbolic space X. Examples include a mapping class group acting on the associated curve complex, or Out(F_n) acting on the complex of free factors, or a group acting on the contact graph of a CAT(0) cube complex it acts on. Under minor assumptions, Maher-Tiozzo show that a random walk on G, projected to X, almost surely converges to a point in the Gromov boundary of X. I will discuss the proof of this theorem. As an application, we will see that "generic" elements of mapping class groups are pseudo-Anosov, and (following Horbez) we will give a random walk proof of the classical theorem of Ivanov classifying subgroups of mapping class groups.

Probabilistic methods in geometric group theory have recently gained in importance. In the course I will focus on the setting where a countable group G acts on a (possibly nonproper) Gromov hyperbolic space X. Examples include a mapping class group acting on the associated curve complex, or Out(F_n) acting on the complex of free factors, or a group acting on the contact graph of a CAT(0) cube complex it acts on. Under minor assumptions, Maher-Tiozzo show that a random walk on G, projected to X, almost surely converges to a point in the Gromov boundary of X. I will discuss the proof of this theorem. As an application, we will see that "generic" elements of mapping class groups are pseudo-Anosov, and (following Horbez) we will give a random walk proof of the classical theorem of Ivanov classifying subgroups of mapping class groups.

Probabilistic methods in geometric group theory have recently gained in importance. In the course I will focus on the setting where a countable group G acts on a (possibly nonproper) Gromov hyperbolic space X. Examples include a mapping class group acting on the associated curve complex, or Out(F_n) acting on the complex of free factors, or a group acting on the contact graph of a CAT(0) cube complex it acts on. Under minor assumptions, Maher-Tiozzo show that a random walk on G, projected to X, almost surely converges to a point in the Gromov boundary of X. I will discuss the proof of this theorem. As an application, we will see that "generic" elements of mapping class groups are pseudo-Anosov, and (following Horbez) we will give a random walk proof of the classical theorem of Ivanov classifying subgroups of mapping class groups.

This talk will review previous work on quadrupedal gaits and recent work on a generalized model for binocular rivalry proposed by Hugh Wilson. Both applications show how rigid phase-shift synchrony in periodic solutions of coupled systems of differential equations can help understand high level collective behavior in the nervous system.

2017 제3회 정오의 수학산책

강연자: 이수준(경희대)

일시: 2017년 5월 12일(금) 12:00 ~ 13:15

장소: 카이스트 자연과학동 E6-1 3435호

제목: 양자정보이론 소개 : 디지털정보 vs 양자정보

내용: TBA

등록: 2017년 5월 10일(수) 오후 3시까지

https://goo.gl/forms/TnDIENKzVJAnxy9v2

문의: hskim@kias.re.kr / 내선:8545

In the talk, I discuss previous works on the arithmetic of various twisted special $L$-values and dynamical phenomena behind them. Main emphasis will be put on the problem of estimating several exponential sums such as Kloosterman sums and its relation to the problem of non-vanishing of special $L$-values with cyclotomic twists. A distribution of homological cycles on the modular curves will also be discussed and as a consequence, some results on a conjecture of Mazur-Rubin-Stein about the distribution of period integrals of elliptic modular forms will be presented.

In this talk, I will introduce the distribution of eigenvalues of random normal matrix ensembles. Specifically, I will discuss the existence and universality of scaling limits for the eigenvalues at a bulk singularity, an isolated point in the interior at which the equilibrium density vanishes. I will describe how to find a suitable scale and how the rescaled ward’s identity can be used to prove the universality. This is joint work with Yacin Ameur.

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E6-1, ROOM 1409
Discrete Math
Dieter Spreen (Universität Siegen, Siegen, Germany)
Bi-Topological Spaces and the Continuity Problem

The continuity problem is the question when effective (or Markov computable) maps between effectively given topological spaces are effectively continuous. It will be shown that this is always the case if the the range of the map is effectively bi-regular. As will be shown, such spaces appear quite naturally in the context of the problem.

Evolutionary games of cyclic competitions have been extensively studied

to gain insights into one of the most fundamental phenomena in nature:

biodiversity that seems to be excluded by the principle of natural selection.

The Rock-Paper-Scissors (RPS) game of three species and

its extensions [e.g., the Rock-Paper-Scissors-Lizard-Spock (RPSLS) game] are

paradigmatic models in this field.

In all previous studies, the intrinsic symmetry associated with the cyclic competitions imposes

a limitation on the resulting coexistence states, leading to only selective types of such states.

We investigate the effect of nonuniform intraspecific competitions on coexistence and

find that a wider spectrum of coexistence states can emerge and persist.

This surprising finding is substantiated using three classes of cyclic game models through stability analysis,

Monte Carlo simulations and patterns of continuous spatiotemporal dynamical evolution.

Our finding indicates that intraspecific competitions or alternative symmetry-breaking mechanisms

can promote biodiversity to a broader extent than previously thought.

Recent development of high throughput sequencing and CRISPR genome editing technology have brought great advances in the understanding of molecular mechanisms underlying diseases. We studied infertility in Drosophila model: deep sequencing analyses of small RNA, mRNA, and RNA immunoprecipitation sequencing (RIP-seq) showed that a conserved mRNA export factor, Thoc5, represses the expression of transposable elements, which are deleterious mobile genetic elements that cause genome instability and germ cell death. We also found that Thoc5 binds nascent RNAs and facilitates biogenesis of small RNAs, which in turn regulated transposable elements. Furthermore, we used CRISPR-Cpf1, a recently found class 2/type V CRISPR RNA-guided endonuclease that is distinct from the common CRISPR-Cas9, to generate mutant mice. Whole genome analyses of the mutant mice showed precise alteration of DNA sequence at the target genomic locus with no detectable off-target mutation. We generated a cell line with a single base change in Isocitrate Dehydrogenase I (IDH1), a gain-of-function mutation widely found in glioma patients. We further applied CRISPR genome editing to pathogenic bacteria to generate bacterial strains with mutations in genes required for quorum sensing, which is an intercellular communication system for detection cell density. The quorum sensing mutant strains showed reduced biofilm formation, and changes in expression profile of genes in the metabolic pathway.

Among the most well-known examples of L-functions are the Riemann zeta

function and the L-functions associated to classical modular forms.

Less well known, but equally important, are the L-functions associated

to Maass forms, which are eigenfunctions of the Laplace-Beltrami

operator on a hyperbolic surface. Named after H. Maass, who discovered

some examples in the 1940s, Maass forms remain largely mysterious.

Fortunately, there are concrete tools to study Maass forms: trace

formulas, which relate the spectrum of the Laplace operator on a

hyperbolic surface to its geometry. After Selberg introduced his

famous trace formula in 1956, his ideas were generalised, and various

trace formulas have been constructed and studied. However, there are

few numerical results from trace formulas, the main obstacle being

their complexity. Various types of trace formulas are investigated,

constructed and used to understand automorphic representations and

their L-functions from a theoretical point of view, but most are not

explicit enough to implement in computer code.

Having explicit computations of trace formulas makes many potential

applications accessible. In this talk, I will explain the

computational aspects of the Selberg trace formula for GL(2) for

general levels and applications towards the Selberg eigenvalue

conjecture and classification of 2-dimensional Artin representations

of small conductor.

This is a joint work with Andrew Booker and Andreas Strömbergsson.

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E6-1, ROOM 1409
Discrete Math
Otfried Cheong (School of Computing, KAIST)
Putting your coin collection on a shelf

Imagine you want to present your collection of n coins on a shelf, taking as little space as possible – how should you arrange the coins?