過去の記録

過去の記録 ~11/19本日 11/20 | 今後の予定 11/21~

2017年11月16日(木)

数理人口学・数理生物学セミナー

16:30-18:00   数理科学研究科棟(駒場) 123号室
中林潤 氏 (横浜市立大学 先端医科学研究センター )
Human Immunodeficiency Virus (HIV) の細胞内複製ダイナミクスと感染個体内における進化 (JAPANESE)
[ 講演概要 ]
今回のセミナーではHuman Immunodeficiency Virus (HIV) の細胞内複製ダイナミクスと感染個体内における進化を取り扱った研究を紹介する。
HIVは+鎖RNAをゲノムとして持つレンチウイルス属に属するレトロウイルスである。RNAを鋳型として逆転写酵素によって産生されたウイルスDNAが、ホストのゲノムにintegrateされ、そこからウイルス遺伝子産物が産生され、最終的にウイルス粒子が複製される。HAART (Highly Active Antiretroviral Therapy) によってHIV感染患者の予後は劇的に改善されたが、いったんintegrateされたprovirusが休眠状態で残存し、何らかのきっかけで再びウイルスを産生することがあり、これがHIV治療の大きな妨げとなっている。Integration siteの決定機構を解明することは、HIVの治療戦略を検討するのに重要である。
HIVのintegration siteはホストのゲノム中に一様ではなく偏って分布していることが知られている。HIV細胞内複製を記述する数理モデルと、これを用いた進化シミュレーションを使って、HIV integration siteの選好性がどのように決定されるか検討した。またデータベースに登録されたHIV integration siteの情報と、ホストのepigenomeデータを統合して網羅的な解析を行い、integration site特異的な塩基配列について検討したので、これらの結果について紹介したい。

統計数学セミナー

13:00-16:00   数理科学研究科棟(駒場) 123号室
二宮嘉行 氏 (九州大学)
スパース推定法における自由度について
[ 講演概要 ]
スパース推定では、どれだけスパースに推定するかを決める、つまり罰則項の強弱を決めるチューニングパラメータの値を選択する必要がある。そして、その選択のための情報量規準で用いられる自由度が、主に正規線形回帰モデルの設定のもとで計算されている。本発表では、その自由度について紹介した後、それを形式上一般化線形モデルなどに拡張する情報量規準を導く。具体的には、古典的な統計的漸近理論に基づき、AIC型の情報量規準を導出する。

2017年11月15日(水)

PDE実解析研究会

10:30-11:30   数理科学研究科棟(駒場) 056号室
※ 通常と曜日が異なります。
Kaj Nyström 氏 (Uppsala University)
Boundary value problems for parabolic equations with measurable coefficients (English)
[ 講演概要 ]
In recent joint works with P. Auscher and M. Egert we establish new results concerning boundary value problems in the upper half-space for second order parabolic equations (and systems) assuming only measurability and some transversal regularity in the coefficients of the elliptic part. To establish our results we introduce and develop a first order strategy by means of a parabolic Dirac operator at the boundary to obtain, in particular, Green's representation for solutions in natural classes involving square functions and non-tangential maximal functions, well-posedness results with data in $L^2$-Sobolev spaces together with invertibility of layer potentials, and perturbation results. In addition we solve the Kato square root problem for parabolic operators with coefficients of the elliptic part depending measurably on all variables. Using these results we are also able to solve the $L^p$-Dirichlet problem for parabolic equations with real, time-dependent, elliptic but non-symmetric coefficients. In this talk I will briefly describe some of these developments.

2017年11月14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
Meng Chen 氏 (Fudan )
A characterization of the birationality of 4-canonical maps of minimal 3-folds (English)
[ 講演概要 ]
We explain the following theorem: For any minimal 3-fold X of general type with p_g>4, the 4-canonical map is non-birational if and only if X is birationally fibred by a pencil of (1,2) surfaces. The statement fails in the case of p_g=4.

数値解析セミナー

16:50-18:20   数理科学研究科棟(駒場) 002号室
石川歩惟 氏 (神戸大学大学院システム情報学研究科)
変分原理に基づくエネルギー保存数値解法と無制約最適化問題への応用 (Japanese)
[ 講演概要 ]
構造保存型数値解法は, 方程式のもつ力学的構造に着目し, その力学的性質を保つようにしてスキームを設計する数値計算法である. 特に, エネルギー保存則を厳密に保つような数値解法はエネルギー保存数値解法と呼ばれ, 離散勾配法などが知られている. 離散勾配法とは, 勾配の性質を引き継ぐよう定義された離散勾配と呼ばれるものをスキームに用いる方法で, この方法によるスキームは安定性に優れたものとなることが多い. その一方, 多くの場合に陰的になり, また, 解析力学における基本原理である変分原理との対応も明らかではない. また, 離散勾配自体の導出も, 容易でない場合もある.
 そこで, 我々は, 離散勾配法の枠組みに変分原理を取り入れたエネルギー保存数値解法を提案してきた. 本講演では, この手法について紹介したのち, 変分原理を活かしたエネルギー散逸系に対する方法への拡張方法について述べる. また, これと離散勾配を自動的に導出する自動離散微分という方法を組み合わせ, 無制約最適化問題の近似解法を設計する. 最後に, 最近の話題として, Lie群上でのスキーム設計手法についても述べる.

2017年11月13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) 128号室
和田 正樹 氏 (福島大学 人間発達文化学類)
シュレディンガー形式における基本解の評価について (JAPANESE)
[ 講演概要 ]
シュレディンガー形式は、マルコフ過程に対応するディリクレ形式に摂動項を加えて得られる。本研究ではシュレディンガー形式における基本解を、元のマルコフ過程の推移確率密度関数(対応するディリクレ形式における基本解と同義)と比較することを目的としている。特に、摂動項が十分大きくなったとき(臨界的という)の基本解の挙動が、元のマルコフ過程の推移確率密度関数とどのように異なるのか、現時点で判明していることを紹介する。

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
Georg Schumacher  氏 (Philipps-Universität Marburg)
Relative Canonical Bundles for Families of Calabi-Yau Manifolds
[ 講演概要 ]
We consider holomorphic families of Calabi-Yau manifolds (here being defined by the vanishing of the first real Chern class). We study induced hermitian metrics on the relative canonical bundle, which are related to the Weil-Petersson form on the base. Under a certain condition the total space possesses a Kähler form, whose restriction to fibers are equal to the Ricci flat metrics. Furthermore we prove an extension theorem for the Weil-Petersson form and give applications.

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
Juan Orendain 氏 (UNAM)
Globularily generated double categories: On the problem of existence of internalizations for decorated bicategories (English)

2017年11月10日(金)

東京無限可積分系セミナー

17:00-18:30   数理科学研究科棟(駒場) 122号室
Fabio Novaes 氏 (International Institute of Physics (UFRN))
Chern-Simons, gravity and integrable systems. (ENGLISH)
[ 講演概要 ]
It is known since the 80's that pure three-dimensional gravity is classically equivalent to a Chern-Simons theory with gauge group SL(2,R) x SL(2,R). For a given set of boundary conditions, the asymptotic classical phase space has a central extension in terms of two copies of Virasoro algebra. In particular, this gives a conformal field theory representation of black hole solutions in 3d gravity, also known as BTZ black holes. The BTZ black hole entropy can then be recovered using CFT. In this talk, we review this story and discuss recent results on how to relax the BTZ boundary conditions to obtain the KdV hierarchy at the boundary. More generally, this shows that Chern-Simons theory can represent virtually any integrable system at the boundary, given some consistency conditions. We also briefly discuss how this formulation can be useful to describe non-relativistic systems.
[ 講演参考URL ]
http://www.iip.ufrn.br/eventslecturer?inf==0EVRpXTR1TP

2017年11月09日(木)

Kavli IPMU Komaba Seminar

13:30-14:30   数理科学研究科棟(駒場) 056号室
Edouard Brezin 氏 (lpt ens, Paris)
Various applications of supersymmetry in statistical physics (English)
[ 講演概要 ]
Supersymmetry is a fundamental concept in particle physics (although it has not been seen experimentally so far). But it is although a powerful tool in a number of problems arising in quantum mechanics and statistical physics. It has been widely used in the theory of disordered systems (Efetov et al.), it led to dimensional reduction for branched polymers (Parisi-Sourlas), for the susy classical gas (Brydges and Imbrie), for Landau levels with impurities. If has also many powerful applications in the theory of random matrices. I will briefly review some of these topics.

2017年11月08日(水)

代数学コロキウム

18:00-19:00   数理科学研究科棟(駒場) 056号室
Xin Wan 氏 (Morningside Center for Mathematics)
Iwasawa theory and Bloch-Kato conjecture for modular forms (ENGLISH)
[ 講演概要 ]
Bloch and Kato formulated conjectures relating sizes of p-adic Selmer groups with special values of L-functions. Iwasawa theory is a useful tool for studying these conjectures and BSD conjecture for elliptic curves. For example the Iwasawa main conjecture for modular forms formulated by Kato implies the Tamagawa number formula for modular forms of analytic rank 0.
In this talk I'll first briefly review the above theory. Then we will focus on a different Iwasawa theory approach for this problem. The starting point is a recent joint work with Jetchev and Skinner proving the BSD formula for elliptic curves of analytic rank 1. We will discuss how such results are generalized to modular forms. If time allowed we may also explain the possibility to use it to deduce Bloch-Kato conjectures in both analytic rank 0 and 1 cases. In certain aspects such approach should be more powerful than classical Iwasawa theory, and has some potential to attack cases with bad ramification at p.

(本講演は「東京北京パリ数論幾何セミナー」として,インターネットによる東大数理,Morningside Center of Mathematics と IHES の双方向同時中継で行います.今回は北京からの中継です.)

2017年11月07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
林 晋 氏 (産総研・東北大オープンイノベーションラボラトリ)
On an explicit example of topologically protected corner states (JAPANESE)
[ 講演概要 ]
In condensed matter physics, topologically protected (codimension-one) edge states are known to appear on the surface of some insulators reflecting some topology of its bulk. Such phenomena can be understood from the point of view of an index theory associated to the Toeplitz extension and are called the bulk-edge correspondence. In this talk, we consider instead the quarter-plane Toeplitz extension and index theory associated with it. As a result, we show that topologically protected (codimension-two) corner states appear reflecting some topology of the gapped bulk and two edges. Such new topological phases can be obtained by taking a ``product’’ of two classically known topological phases (2d type A and 1d type AIII topological phases). By using this construction, we obtain an example of a continuous family of bounded self-adjoint Fredholm quarter-plane Toeplitz operators whose spectral flow is nontrivial, which gives an explicit example of topologically protected corner states.

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
村山 匠 氏 (ミシガン大学)
Characterizations of projective space and Seshadri constants in arbitrary characteristic
[ 講演概要 ]
Mori and Mukai conjectured that projective space should be the only n-dimensional Fano variety whose anti-canonical bundle has degree at least n + 1 along every curve. While this conjecture has been proved in characteristic zero, it remains open in positive characteristic. We will present some progress in this direction by giving another characterization of projective space using Seshadri constants and the Frobenius morphism. The key ingredient is a positive-characteristic analogue of Demailly’s criterion for separation of higher-order jets by adjoint bundles, whose proof gives new results for adjoint bundles even in characteristic zero.

2017年11月06日(月)

FMSPレクチャーズ

17:00-18:00   数理科学研究科棟(駒場) 118号室
V. G. Romanov 氏 (Sobolev Institute of Mathematics)
Phaseless inverse problems for Maxwell equations (ENGLISH)
[ 講演概要 ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Romanov2.pdf
[ 講演参考URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Romanov2.pdf

2017年11月02日(木)

統計数学セミナー

14:00-15:10   数理科学研究科棟(駒場) 052号室
Tudor Ciprian 氏 (Université Lille 1)
Hermite processes and sheets
[ 講演概要 ]
The Hermite process of order $\geq 1$ is a self-similar stochastic process with stationary increments living in the $q$th Wiener chaos. The class of Hermite processes includes the fractional Brownian motion (for $q=1$) and the Rosenblatt process (for $q=2$). We present the basic properties of these processes and we introduce their multiparameter version. We also discuss the behavior with respect to the self-similarity index and the possibility so solve stochastic equations with Hermite noise.

2017年11月01日(水)

離散数理モデリングセミナー

17:00-18:00   数理科学研究科棟(駒場) 056号室
Basile Grammaticos 氏 (Université de Paris VII・XI)
Discrete Painlevé equations associated with the E8 group (ENGLISH)
[ 講演概要 ]
I'll present a summary of the results of the Paris-Tokyo-Pondicherry group on equations associated with the affine Weyl group E8. I shall review the various parametrisations of the E8-related equations, introducing the trihomographic representation and the ancillary variable. Several examples of E8-associated equations will be given including what we believe is the simplest form for the generic elliptic discrete Painlevé equation.

2017年10月31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
Yash Lodha 氏 (École Polytechnique Fédérale de Lausanne)
Nonamenable groups of piecewise projective homeomorphisms (ENGLISH)
[ 講演概要 ]
Groups of piecewise projective homeomorphisms provide elegant examples of groups that are non amenable, yet do not contain non abelian free subgroups. In this talk I will present a survey of these groups and discuss their striking properties. I will discuss properties such as (non)amenability, finiteness properties, normal subgroup structure, actions by various degrees of regularity and Tarski numbers.

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
Zhan Li 氏 (Beijing)
ACC for log canonical threshold polytopes (English)
[ 講演概要 ]
We show that the log canonical threshold polytopes of varieties with log canonical singularities satisfy the ascending chain condition. This is a joint work with Jingjun Han and Lu Qi.

離散数理モデリングセミナー

16:30-17:30   数理科学研究科棟(駒場) 126号室
Basile Grammaticos 氏 (Université de Paris VII・XI)
The end of the World (ENGLISH)
[ 講演概要 ]
This is not a seminar on astrophysics or cosmology. I am not going to talk about something that will happen in billions of years. I will rather explain the menace to our civilisation and to the human species. Inspired from the works of several authors I will explain the existing risks. I will also present mathematical models which show that a general collapse is possible in the decades that follow.

離散数理モデリングセミナー

15:30-16:30   数理科学研究科棟(駒場) 126号室
Fon-Che Liu 氏 (National Taiwan University)
A hierarchy of approximate regularity of functions (ENGLISH)
[ 講演概要 ]
A hierarchy of a certain weakly sensed regularity of functions defined on subsets of Euclidean n-space which originated from the well-known Lusin theorem that characterizes measurable functions in terms of approximate continuity will be introduced. Its intimate relations with the ordinary hierarchy of regularity in terms of order of continuous differentiability will be exposed and explained.

FMSPレクチャーズ

16:00-17:00   数理科学研究科棟(駒場) 118号室
V. G. Romanov 氏 (Sobolev Institute of Mathematics)
Some Geometric Aspects in Inverse Problems (ENGLISH)
[ 講演概要 ]
We consider inverse problems related to recovering coefficients in partial differential equations of the second order. It is supposed that some measurements of solutions to direct problems are produced on convenient sets. A study of some inverse problems for hyperbolic equations leads to geometric problems: recovering a function from its integrals along geodesic lines of the Riemannian metric or recovering the Riemannian metric inside a domain from given distances between arbitrary points of the domain boundary. Our main goal here is to demonstrate how such geometric problems arise for equations of parabolic and elliptic types.
[ 講演参考URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Romanov.pdf

2017年10月30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) 128号室
伊藤 悠 氏 (京都産業大学 理学部数理科学科)
Integration of controlled rough paths via fractional calculus (JAPANESE)
[ 講演概要 ]
本研究は非整数階微積分に基づいたラフパス理論の研究である。非整数階微積分に基づいたラフパス理論の研究は、Y.Hu-D.Nualart(2009)に始まり、ラフ積分と呼ばれるラフパス理論における積分概念に特徴がある。通常のラフ積分は、補正されたRiemann-Stieltjes和の極限として与えられるが、非整数階微積分に基づいたものは、非整数階微分による明示的な表現式として与えられる。本講演では、M.Gubinelli(2004)が導入したラフ積分に対し、そのような表現式を導出するとともに、導出過程において、M.Zähle(1998)の議論が有効に働くことを説明する。

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
澤田友佑 氏 (名大多元数理)
The bicategory of $W^*$-bimodules

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
加藤 昌英 氏 (上智大学)
Odd dimensional complex analytic Kleinian groups
[ 講演概要 ]
In this talk, I would explain an idea to construct a higher dimensional analogue of the classical Kleinian group theory. For a group $G$ of a certain class of discrete subgroups of $\mathrm{PGL}(2n+2,\mathbf{C})$ which act on $\mathbf{P}^{2n+1}$, there is a canonical way to define the region of discontinuity, on which $G$ acts properly discontinuously. General principle in the discussion is to regard $\mathbf{P}^{n}$ in $\mathbf{P}^{2n+1}$ as a single point. We can consider the quotient space of the discontinuity region by the action of $G$. Though the Ahlfors finiteness theorem is hopeless because of a counter example, the Klein combination theorem and the handle attachment can be defined similarly. Any compact quotients which appear here are non-Kaehler. In the case $n=1$, we explain a new example of compact quotients which is related to a classical Kleinian group.

代数幾何学セミナー

10:30-12:00   数理科学研究科棟(駒場) 123号室
Roberto Svaldi 氏 (Cambridge)
Towards birational boundedness of elliptic Calabi-Yau varieties (English)
[ 講演概要 ]
I will discuss new results towards the birational boundedness of
low-dimensional elliptic Calabi-Yau varieties, joint work with Gabriele
Di Certo.
Recent work in the minimal model program suggests that pairs with trivial log canonical
class should satisfy some boundedness properties.
I will show that 4-dimensional Calabi-Yau pairs which are not birational to a product are
indeed log birationally bounded. This implies birational boundedness of elliptically fibered
Calabi-Yau manifolds with a section, in dimension up to 5.
If time allows, I will also try to discuss a first approach towards boundedness of rationally
connected CY varieties in low dimension.

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