過去の記録

過去の記録 ~11/11本日 11/12 | 今後の予定 11/13~

2018年07月18日(水)

代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室
普段と違う水曜日にセミナーを行います。The seminar will be held on Wednesday. This is a different day from usual.
Jun-Muk Hwang 氏 (KIAS)
Normal Legendrian singularities (English)
[ 講演概要 ]
A germ of a Legendrian subvariety in a holomorphic contact manifold
is called a Legendrian singularity. Legendrian singularities are usually not normal.
We look at some examples of normal Legendrian singularities and discuss their rigidity under deformation.

数理人口学・数理生物学セミナー

15:00-16:00   数理科学研究科棟(駒場) 118号室
Malay Banerjee 氏 (Department of Mathematics & Statistics, IIT Kanpur)
Effect of demographic stochasticity on large amplitude oscillation
[ 講演概要 ]

Classical Rosenzweig-MacArthur model exhibits two types of stable coexistence, steady-state and oscillatory coexistence. The oscillatory coexistence is the result of super-critical Hopf-bifurcation and the Hopf-bifurcating limit cycle remains stable for parameter values beyond the bifurcation threshold. The size of the limit cycle grows with the increase in carrying capacity of prey and finally both the populations show high amplitude oscillations. Time evolution of prey and predator population densities exhibit large amplitude peaks separated by low density lengthy valleys. Persistence of both the populations at low population density over a longer time period is more prominent in case of fast growth of prey and comparatively slow growth of predator species due to slow-fast dynamics. In this situation, small amount of demographic stochasticity can cause the extinction of one or both the species. Main aim of this talk is to explain the effect of demographic stochasticity on the high amplitude oscillations produced by two and higher dimensional interacting population models.

博士論文発表会

15:30-16:45   数理科学研究科棟(駒場) 128号室
張 龍傑 氏 (東京大学大学院数理科学研究科)
Mean curvature flow with driving force
(駆動力付きの平均曲率流方程式)
(JAPANESE)

FMSPレクチャーズ

10:15-12:15   数理科学研究科棟(駒場) 118号室
集中講義901-118「数物先端科学X」として行われます(7/18,20,23,24,25の全5回)。
Christian Schnell 氏 (Stony Book University)
Singular hermitian metrics and morphisms to abelian varieties (ENGLISH)
[ 講演概要 ]
Consider a morphism from a smooth projective variety to an abelian variety (over the field of complex numbers). After reviewing what is known about the pushforward of the canonical bundle under such a morphism, we will try to extend these results to the case of pluricanonical bundles (= the tensor powers of the canonical bundle). Along the way, we will learn about three important tools: generic vanishing theory; Viehweg's cyclic covering trick; and some new results from complex analysis about metrics with singularities. As an application, we will discuss the proof of Iitaka's conjecture (about the subadditivity of the Kodaira dimension in algebraic fiber spaces) over abelian varieties, following Cao and Paun.
[ 講演参考URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Schnell.pdf

2018年07月17日(火)

トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
石川 昌治 氏 (慶應義塾大学)
Positive flow-spines and contact 3-manifolds (JAPANESE)
[ 講演概要 ]
A contact structure is a smooth distribution of hyperplanes on an odd-dimensional manifold that is non-integrable everywhere. In the case of dimension 3, there is a nice relationship between open book decompositions of 3-manifolds and contact structures up to contactomorphisms, called Giroux correspondence. A flow-spine is a spine of a 3-manifold admitting a flow such that it is transverse to the spine and the flow in the complement of the spine is diffeomorphic to a constant flow in an open ball. In this talk, we introduce some results in progress that give a correspondence between contact structures and positive flow-spines by regarding Reeb vector fields as flows of spines. This is a joint work with Y. Koda (Hiroshima) and H. Naoe (Tohoku).

博士論文発表会

15:30-16:45   数理科学研究科棟(駒場) 128号室
三浦 達彦 氏 (東京大学大学院数理科学研究科)
Mathematical analysis of evolution equations in curved thin domains or on moving surfaces
(曲がった薄膜領域や動く曲面上の発展方程式の数学解析)
(ENGLISH)

東京無限可積分系セミナー

16:00-17:00   数理科学研究科棟(駒場) 002号室
Valerii Sopin 氏 (Higher School of Economics (Moscow))
Operator algebra for statistical model of square ladder (ENGLISH)
[ 講演概要 ]
In this talk we will define operator algebra for square ladder on the basis
of semi-infinite forms.

Keywords: hard-square model, square ladder, operator algebra, semi-infinite
forms, fermions, quadratic algebra, cohomology, Demazure modules,
Heisenberg algebra.

2018年07月13日(金)

談話会・数理科学講演会

15:30-16:30   数理科学研究科棟(駒場) 056号室
DINH Tien Cuong 氏 (National University of Singapore )
Pluripotential theory and complex dynamics in higher dimension

[ 講演概要 ]
Positive closed currents, the analytic counterpart of effective cycles in algebraic geometry, are central objects in pluripotential theory. They were introduced in complex dynamics in the 1990s and become now a powerful tool in the field. Challenging dynamical problems involve currents of any dimension. We will report recent developments on positive closed currents of arbitrary dimension, including the solutions to the regularization problem, the theory of super-potentials and the theory of densities. Applications to dynamics such as properties of dynamical invariants (e.g. dynamical degrees, entropies, currents, measures), solutions to equidistribution problems, and properties of periodic points will be discussed.

2018年07月11日(水)

作用素環セミナー

17:15-18:45   数理科学研究科棟(駒場) 126号室
George Elliott 氏 (Univ. Toronto)
Recent progress in the classification of amenable C*-algebras (cont'd)

2018年07月10日(火)

代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 002号室
いつもと部屋が違います。The room is different from usual.
賴青瑞 氏 (国立成功大学)
The effective bound of anticanonical volume of Fano threefolds (English)
[ 講演概要 ]
According to Mori's program, varieties covered by rational curves are
built up from anti-canonically polarized varieties, aka Fano varieties. After fixed the
dimension and singularity type, Fano varieties form a bounded family by Birkar's proof (2016)
of Borisov-Alexeev-Borisov conjecture, which In particular implies that the anticanonical
volume -K^\dim is bounded. In this talk, we focus on canonical Fano threefolds,
where boundedness was established by Koll\'ar-Miyaoka-Mori-Takagi (2000).
Our aim is to find an effective bound of the anticanonical volume -K^3, which is
not explicit either from the work of Koll\'ar-Miyaoka-Mori-Takagi or Birkar. We will discuss
some effectiveness results related to this problem and prove that -K_X^3\leq 72 if \rho(X)\leq 2.
This partially extends early work of Mori, Mukai, Y. Prokhorov, et al.

講演会

15:00-16:00   数理科学研究科棟(駒場) 128号室
Canceled!! (諸事情により,講演は取りやめとなりました.)
Sam Nariman 氏 (Northwestern University)
On the moduli space of flat symplectic surface bundles
[ 講演概要 ]
There are at least three different approaches to construct characteristic invariants of flat symplectic bundles. Reznikov generalized Chern-Weil theory for finite dimension Lie groups to the infinite dimensional group of symplectomorphisms. He constructed nontrivial invariants of symplectic bundles whose fibers are diffeomorphic to complex projective spaces. Kontsevich used formal symplectic geometry to build interesting classes that are not yet known to be nontrivial. Also for surface bundles whose holonomy groups preserve the symplectic form, Kotschick and Morita used the flux homomorphism to construct many nontrivial stable classes.

In this talk, we introduce infinite loop spaces whose cohomolgy groups describe the stable characteristic invariants of symplectic flat surface bundles. As an application, we give a homotopy theoretic description of
Kotschick and Morita's classes and prove a result about codimension 2 foliations that implies the nontriviality of KM classes.

トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
Emmy Murphy 氏 (Northwestern University)
Loose Legendrians and arboreal singularities (ENGLISH)
[ 講演概要 ]
Given a Stein manifold X, under what conditions can we ensure that X is symplectomorphic to C^n? For n>2 the condition of X being diffeomorphic to C^n does not suffice, and many counterexamples have been constructed which are detected by symplectic cohomology and the Fukaya category. One might conjecture that the diffeomorphism type together with a vanishing Fukaya category characterizes C^n. While this question is currently well of of reach, we present some new partial results. The main tools we'll discuss are arboreal singularities, constructable sheaf theory, and loose Legendrians -- and how they fit together to approach this question.

数値解析セミナー

16:50-18:20   数理科学研究科棟(駒場) 126号室
松本純一 氏 (産業技術総合研究所)
直交基底気泡関数有限要素法による自由表面流れ
(Japanese)
[ 講演概要 ]
非構造格子(三角形と四面体)に適用が可能な直交基底気泡関数要素による有限要素法を用いた2次元浅水流れと3次元気液二相流れについて解説する。2次元浅水流れでは、浅水長波方程式とBoussinesq方程式おける数値安定性を考慮した陽的および陰的有限要素法について説明する。計算例として、浅水長波方程式では風応力を考慮した自由表面問題および河床摩擦を考慮した跳水現象の厳密解との比較、波の分散を考慮したBoussinesq方程式では孤立波の近似解および実験結果と計算結果との比較を示す。3次元気液二相流れでは、界面関数を扱うPhase-FieldモデルとしてAllen-Cahn方程式、Cahn-Hilliard方程式の双方を取り上げ、Navier-Stokes方程式とPhase-Field界面モデルを採用した直交基底気泡関数要素安定化法について解説する。さらに、2次元(2D)浅水流れと3次元(3D)気液二相流れにおける双方向の流れを考慮した結合法について述べ2D-3D連成問題について計算例を示す。

2018年07月09日(月)

複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室
Casey Kelleher 氏 (Princeton University)
Rigidity results for symplectic curvature flow (ENGLISH)
[ 講演概要 ]
We continue studying a parabolic flow of almost Kähler structure introduced by Streets and Tian which naturally extends Kähler-Ricci flow onto symplectic manifolds. In a system consisting primarily of quantities related to the Chern connection we establish clean formulas for the evolutions of canonical objects. Using this we give an extended characterization of fixed points of the flow.

2018年07月03日(火)

トポロジー火曜セミナー

17:00-18:00   数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
吉田 純 氏 (東京大学大学院数理科学研究科)
Symmetries on algebras and Hochschild homology in view of categories of operators (JAPANESE)
[ 講演概要 ]
The categorical construction of Hochschild homology by Connes reveals that the symmetric structure on the tensor product of abelian groups is essential. It means that the categorical meaning of ad-hoc generalizations of Hochschild homology in less symmetric monoidal abelian categories remains unclear. In this talk, I will propose formulation of this problem in terms of group operads introduced by Zhang. Moreover, for each group operad G, G-symmetric versions of categories of operators will be discussed. The notion plays a key role in defining Hochschild homology for homotopy algebras; such as topological Hochschild homology.

代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室
Xun Yu 氏 (Tianjin University)
Surface automorphisms and Salem numbers (English)
[ 講演概要 ]
The entropy of a surface automorphism is either zero or the
logarithm of a Salem number.
In this talk, we will discuss which Salem numbers arise in this way. We
will show that any
supersingular K3 surface in odd characteristic has an automorphism the
entropy of which is
the logarithm of a Salem number of degree 22. In particular, such
automorphisms are
not geometrically liftable to characteristic 0.

2018年07月02日(月)

東京確率論セミナー

16:00-17:30   数理科学研究科棟(駒場) 126号室
世良 透 氏 (京都大学大学院理学研究科)
間欠力学系に関する種々の分布極限定理 (JAPANESE)
[ 講演概要 ]
間欠力学系とは,中立不動点を持つ一次元写像力学系のことである.この力学系は様々な非平衡系に現れる間欠現象のモデルとして,統計物理学などの観点から広く研究されてきた.間欠現象とは,ほぼ周期的かつ持続的な「安定状態」が,非周期的かつ一時的に生ずる「不安定状態」によって繰り返し中断される,という現象を指す.Lorenz(1963)は熱対流の微分方程式モデルを研究し,解軌道の数値プロットから間欠力学系を抽出した.Pomeau--Manneville(1980)は「熱対流の安定状態」を「間欠力学系の中立不動点」と見なして,間欠力学系を介してLorenzの熱対流モデルが持つ間欠性を考察している.

また,間欠力学系は無限エルゴード理論などの観点からも研究され,Markov過程論のアナロジーから種々の分布極限定理が得られてきた.本講演では間欠力学系に関する分布極限定理として,中立不動点から離れた場所(不安定状態)への滞在に関するAaronson(1981)&(1986),Owada--Samorodnitsky(2015)の結果,および中立不動点近傍(安定状態)への滞在に関するThaler(2002),S.--Yano(2017+)の結果を紹介する.そしてこれらを統合・精密化した講演者の最近の結果について述べる.間欠力学系の滞在時間のスケール極限として,マルチレイ上を走る歪みBessel拡散過程の原点局所時間や各レイごとの滞在時間が現れる.証明の鍵は周遊理論およびTyran-Kaminska(2010)による定常増分過程の関数型極限定理である.

複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室
松崎克彦 氏 (早稲田大学)
Rigidity of certain groups of circle homeomorphisms and Teichmueller spaces (JAPANESE)
[ 講演概要 ]
In this talk, I explain a complex analytic method and its applications for the study of quasisymmetric homeomorphisms of the circle by extending them to the unit disk quasi-conformally. In RIMS conference "Open Problems in Complex Geometry'' held in 2010, I gave a talk entitled "Problems on infinite dimensional Teichmueller spaces", and mentioned several problems on the fixed points of group actions on the universal Teichmueller space and its subspaces, and the rigidity of conjugation of certain groups of circle homeomorphisms. I will report on the development of these problems since then.

PDE実解析研究会

10:30-11:30   数理科学研究科棟(駒場) 056号室
通常の曜日と異なります。
László Székelyhidi Jr. 氏 (Universität Leipzig)
Convex integration in fluid dynamics (English)
[ 講演概要 ]
In the talk we present the technique of convex integration for constructing weak solutions to various equations in fluid mechanics.
We will focus on the recent resolution of Onsagers conjecture, but also discuss further directions and in particular the applicability to dissipative systems.

2018年06月29日(金)

談話会・数理科学講演会

15:30-16:30   数理科学研究科棟(駒場) 056号室
石毛和弘 氏 (東京大学大学院数理科学研究科)
放物型方程式の解の冪凸性 (日本語)
[ 講演概要 ]
放物型方程式の解の凸冪性の研究は、Brascamp-Lieb (1976), Korevaar (1983)らの研究を契機として大きく進展し、例えば、正値な値をもつ初期関数の対数が上に凸であるとき、熱流はその凸性を保つこと等が解明されてきた。
本講演では、これら一連の研究を概観した後、Paolo Salani 氏らとの共同研究に基づき、放物型冪凸という概念の導入とその応用、放物型方程式系の解の冪凸性等について述べ、さらに近年の研究の進展について触れる。

2018年06月27日(水)

作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 126号室
Seung-Hyeok Kye 氏 (Seoul National Univ.)
未定

2018年06月26日(火)

代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室
渡辺究 氏 (埼玉)
Varieties with nef diagonal (English)
[ 講演概要 ]
For a smooth projective variety $X$, we consider when the diagonal $Δ _X$ is nef as a
cycle on $X \times X$. In particular, we give a classication of complete intersections and smooth
del Pezzo varieties where the diagonal is nef. We also study the nefness of the diagonal for
spherical varieties. This is a joint work with Taku Suzuki.

解析学火曜セミナー

16:50-18:20   数理科学研究科棟(駒場) 128号室
小川卓克 氏 (東北大学)
移流拡散方程式の初期値問題について (日本語)
[ 講演概要 ]
We consider the Cauchy problem of the drift-diffusion system in the whole space. Introducing the scaling critical case, we consider the solvability of the drift-diffusion system in the whole space and give some large time behavior of solutions. This talk is based on a collaboration with Masaki Kurokiba and Hiroshi Wakui.

2018年06月25日(月)

東京確率論セミナー

16:00-17:30   数理科学研究科棟(駒場) 126号室
濱口 雄史 氏 (京都大学大学院理学研究科)
BSDEs driven by cylindrical martingales with application to approximate hedging in bond markets (JAPANESE)
[ 講演概要 ]
金利マーケットや商品先物市場では、フォワードカーブのランダムな時間発展挙動を連続関数空間上の無限次元確率過程として記述する手法が用いられる。このモデルでは形式的に非加算無限個の取引可能財が存在するため、ボンドの満期を表す区間上の符号付測度に値を取るポートフォリオを考えることとなる。本講演では、無限次元マーケットにおけるクレームのヘッジに関連して、無限次元マルチンゲール(連続関数空間上のcylindrical martingale)により駆動するリプシッツ型BSDEの解の存在と一意性を示す。さらに、この解が対応する有限次元BSDEの解によって近似できることを示す。これにより、無限次元マーケットにおけるクレームの形式的なヘッジ戦略が、有限次元部分マーケットにおけるFollmer-Schweizer分解、すなわち局所リスク最少戦略の極限として得られることが従う。

離散数理モデリングセミナー

17:30-18:30   数理科学研究科棟(駒場) 056号室
Anton Dzhamay 氏 (University of Northern Colorado)
Gap Probabilities and discrete Painlevé equations
[ 講演概要 ]
It is well-known that important statistical quantities, such as gap probabilities, in various discrete probabilistic models of random matrix type satisfy the so-called discrete Painlevé equations, which provides an effective way to computing them. In this talk we discuss this correspondence for a particular class of models, known as boxed plane partitions (equivalently, lozenge tilings of a hexagon). For uniform probability distribution, this is one of the most studied models of random surfaces. Borodin, Gorin, and Rains showed that it is possible to assign a very general elliptic weight to the distribution, with various degenerations of this weight corresponding to the degeneration cascade of discrete polynomial ensembles, such as Racah and Hahn ensembles and their q-analogues. This also correspond to the degeneration scheme of discrete Painlevé equations, due to Sakai. In this talk we consider the q-Hahn and q-Racah ensembles and corresponding discrete Painlevé equations of types q-P(A_{2}^{(1)}) and q-P(A_{1}^{(1)}).
This is joint work with Alisa Knizel (Columbia University)

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