## Seminar information archive

Seminar information archive ～02/01｜Today's seminar 02/02 | Future seminars 02/03～

#### thesis presentations

9:15-10:30 Room #126 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

10:45-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

12:45-14:00 Room #126 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

14:15-15:30 Room #126 (Graduate School of Math. Sci. Bldg.)

### 2020/01/30

#### thesis presentations

10:45-12:00 Room #118 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

12:45-14:00 Room #118 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

14:15-15:30 Room #118 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

15:45-17:00 Room #118 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

9:15-10:30 Room #122 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

12:45-14:00 Room #122 (Graduate School of Math. Sci. Bldg.)

#### thesis presentations

13:45-15:00 Room #126 (Graduate School of Math. Sci. Bldg.)

### 2020/01/29

#### Operator Algebra Seminars

13:00-14:30 Room #002 (Graduate School of Math. Sci. Bldg.)

Horn's problem, polytope volumes and tensor product decompositions (English)

**Colin McSwiggen**(Brown Univ.)Horn's problem, polytope volumes and tensor product decompositions (English)

#### Operator Algebra Seminars

16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)

Stationary actions of higher rank lattices on von Neumann algebras (English)

**Cyril Houdayer**(Univ. Paris-Sud)Stationary actions of higher rank lattices on von Neumann algebras (English)

### 2020/01/28

#### Tuesday Seminar on Topology

17:00-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)

Existence problems for fibered links (JAPANESE)

**Nozomu Sekino**(The University of Tokyo)Existence problems for fibered links (JAPANESE)

[ Abstract ]

It is known that every connected orientable closed 3-manifold has a fibered knot. However, finding (and classifying) fibered links whose fiber surfaces are fixed homeomorphism type in a given 3-manifold is difficult in general. We give a criterion of a simple closed curve on a genus 2g Heegaard surface being a genus g fibered knot in terms of its Heegaard diagram. As an application, we can prove the non-existence of genus one fibered knots in some Seifert manifolds.

There is one generalization of fibered links, homologically fibered links. This requests that the complement of the "fiber surface" is a homologically product of a surface and an interval. We give a necessary and sufficient condition for a connected sums of lens spaces of having a homologically fibered link whose fiber surfaces are some fixed types as some algebraic equations.

It is known that every connected orientable closed 3-manifold has a fibered knot. However, finding (and classifying) fibered links whose fiber surfaces are fixed homeomorphism type in a given 3-manifold is difficult in general. We give a criterion of a simple closed curve on a genus 2g Heegaard surface being a genus g fibered knot in terms of its Heegaard diagram. As an application, we can prove the non-existence of genus one fibered knots in some Seifert manifolds.

There is one generalization of fibered links, homologically fibered links. This requests that the complement of the "fiber surface" is a homologically product of a surface and an interval. We give a necessary and sufficient condition for a connected sums of lens spaces of having a homologically fibered link whose fiber surfaces are some fixed types as some algebraic equations.

#### Tuesday Seminar on Topology

18:00-19:00 Room #056 (Graduate School of Math. Sci. Bldg.)

Fibred cusp b-pseudodifferential operators and its applications (JAPANESE)

**Jun Watanabe**(The University of Tokyo)Fibred cusp b-pseudodifferential operators and its applications (JAPANESE)

[ Abstract ]

Melrose's b-calculus and its variants are important tools to study index problems on manifolds with singularities. In this talk, we introduce a new variant "fibred cusp b-calculus", which is a generalization of fibred cusp calculus of Mazzeo-Melrose and b-calculus of Melrose. We discuss the basic property of this calculus and give a relative index formula. As its application, we prove the index theorem for a Z/k manifold with boundary, which is a generalization of the mod k index theorem of Freed-Melrose.

Melrose's b-calculus and its variants are important tools to study index problems on manifolds with singularities. In this talk, we introduce a new variant "fibred cusp b-calculus", which is a generalization of fibred cusp calculus of Mazzeo-Melrose and b-calculus of Melrose. We discuss the basic property of this calculus and give a relative index formula. As its application, we prove the index theorem for a Z/k manifold with boundary, which is a generalization of the mod k index theorem of Freed-Melrose.

#### Lie Groups and Representation Theory

10:00-16:40 Room # (Graduate School of Math. Sci. Bldg.)

Relationship between orbit decomposition on the flag varieties and multiplicities of induced representations (English)

TBA (English)

From Symmetry breaking toward holographic transform in representation theory (English)

Cells of Harish-Chandra modules

(English)

**Taito Tauchi**(The University of Tokyo) 10:00-11:00Relationship between orbit decomposition on the flag varieties and multiplicities of induced representations (English)

**Mikhail Kapranov**(Kavli IPMU) 11:20-12:20TBA (English)

**Michael Pevzner**(University of Reims) 14:00-15:00From Symmetry breaking toward holographic transform in representation theory (English)

**Leticia Barchini**(Oklahoma University) 15:40-16:40Cells of Harish-Chandra modules

(English)

### 2020/01/27

#### Seminar on Geometric Complex Analysis

10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)

Canonical measure and it’s applications

**Hajime Tsuji**(Sophia Univ.)Canonical measure and it’s applications

[ Abstract ]

The canonical measure is a natural generalization of K\”ahler-Einstein metrics to the case of projective manifolds with nonnegative Kodaira dimension. In this talk we consider the variation of canonical measures under projective deformations and give some applications.

The canonical measure is a natural generalization of K\”ahler-Einstein metrics to the case of projective manifolds with nonnegative Kodaira dimension. In this talk we consider the variation of canonical measures under projective deformations and give some applications.

#### Lie Groups and Representation Theory

9:30-16:30 Room # (Graduate School of Math. Sci. Bldg.)

TBA (English)

Regular Representations on Homogeneous Spaces (English)

The adapted hyper-K\"ahler structure on the tangent bundle of a Hermitian symmetric space (English)

UNIVERSAL NATURE OF THE HOROSPHERICAL TRANSFORM IN SYMMETRIC SPACES (English)

**Joseph Bernstein**(Tel Aviv and The University of Tokyo) 10:00-11:00TBA (English)

**Toshiyuki Kobayashi**(The University of Tokyo) 11:20-12:20Regular Representations on Homogeneous Spaces (English)

**Laura Geatti**(University of Roma) 14:00-15:00The adapted hyper-K\"ahler structure on the tangent bundle of a Hermitian symmetric space (English)

**Simon Gindikin**(Rutgers University) 15:30-16:30UNIVERSAL NATURE OF THE HOROSPHERICAL TRANSFORM IN SYMMETRIC SPACES (English)

### 2020/01/22

#### FMSP Lectures

17:00-18:00 Room #128 (Graduate School of Math. Sci. Bldg.)

Complex principal type operators in inverse conductivity problem (ENGLISH)

http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_SamuliSiltanen.pdf

**Samuli Siltanen**(University of Helsinki)Complex principal type operators in inverse conductivity problem (ENGLISH)

[ Abstract ]

Stroke is a leading cause of death all around the world. There are two main types of stroke: ischemic (blood clot preventing blood flow to a part of the brain) and hemorrhagic (bleeding in the brain). The symptoms are the same, but treatments very different. A portable "stroke classifier" would be a life-saving equipment to have in ambulances, but so far it does not exist. Electrical Impedance Tomography (EIT) is a promising and harmless imaging method for stroke classification. In EIT one attempts to recover the electric conductivity inside a domain from electric boundary measurements. This is a nonlinear and ill-posed inverse problem. The so-called Complex Geometric Optics (CGO) solutions have proven to be a useful computational tool for reconstruction tasks in EIT. A new property of CGO solutions is presented, showing that a one-dimensional Fourier transform in the spectral variable provides a connection to parallel-beam Xray tomography of the conductivity. One of the consequences of this “nonlinear Fourier slice theorem” is a novel capability to recover inclusions within inclusions in EIT. In practical imaging, measurement noise causes strong blurring in the recovered profile functions. However, machine learning algorithms can be combined with the nonlinear PDE techniques in a fruitful way. As an example, simulated strokes are classified into hemorrhagic and ischemic using EIT measurements.

[ Reference URL ]Stroke is a leading cause of death all around the world. There are two main types of stroke: ischemic (blood clot preventing blood flow to a part of the brain) and hemorrhagic (bleeding in the brain). The symptoms are the same, but treatments very different. A portable "stroke classifier" would be a life-saving equipment to have in ambulances, but so far it does not exist. Electrical Impedance Tomography (EIT) is a promising and harmless imaging method for stroke classification. In EIT one attempts to recover the electric conductivity inside a domain from electric boundary measurements. This is a nonlinear and ill-posed inverse problem. The so-called Complex Geometric Optics (CGO) solutions have proven to be a useful computational tool for reconstruction tasks in EIT. A new property of CGO solutions is presented, showing that a one-dimensional Fourier transform in the spectral variable provides a connection to parallel-beam Xray tomography of the conductivity. One of the consequences of this “nonlinear Fourier slice theorem” is a novel capability to recover inclusions within inclusions in EIT. In practical imaging, measurement noise causes strong blurring in the recovered profile functions. However, machine learning algorithms can be combined with the nonlinear PDE techniques in a fruitful way. As an example, simulated strokes are classified into hemorrhagic and ischemic using EIT measurements.

http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_SamuliSiltanen.pdf

### 2020/01/21

#### Algebraic Geometry Seminar

15:30-17:00 Room #118 (Graduate School of Math. Sci. Bldg.)

(Few) rational curves on K3 surfaces (English)

**Matthias Schütt**(Universität Hannover)(Few) rational curves on K3 surfaces (English)

[ Abstract ]

Rational curves play a fundamental role for the structure of a K3 surface. I will first review the general theory before focussing on the case of low degree curves where joint work with S. Rams (Krakow) extends bounds of Miyaoka and Degtyarev. Time permitting, I will also discuss the special case of smooth rational curves as well as applications to Enriques surfaces.

Rational curves play a fundamental role for the structure of a K3 surface. I will first review the general theory before focussing on the case of low degree curves where joint work with S. Rams (Krakow) extends bounds of Miyaoka and Degtyarev. Time permitting, I will also discuss the special case of smooth rational curves as well as applications to Enriques surfaces.

#### Lie Groups and Representation Theory

14:00-16:00 Room #126 (Graduate School of Math. Sci. Bldg.)

On Plancherel measure (English)

**Joseph Bernstein**(Tel Aviv University)On Plancherel measure (English)

### 2020/01/20

#### Numerical Analysis Seminar

16:50-18:20 Room #056 (Graduate School of Math. Sci. Bldg.)

Isogeometric Hierarchical Model Reduction: from analysis to patient-specific simulations (English)

**Yves A. B. C. Barbosa**(Politecnico di Milano)Isogeometric Hierarchical Model Reduction: from analysis to patient-specific simulations (English)

[ Abstract ]

In the field of hemodynamics, numerical models have evolved to account for the demands in speed and accuracy of modern diagnostic medicine. In this context, we studied in detail Hierarchical Model Reduction technique combined with Isogeometric Analysis (HigaMOD), a technique recently developed in [Perotto, Reali, Rusconi and Veneziani (2017)]. HigaMod is a reduction procedure used to downscale models when the phenomenon at hand presents a preferential direction of flow, e.g., when modelling the blood flow in arteries or the water flow in a channel network. The method showed a significant improvement in reducing the computational power and simulation time, while giving enough information to analyze the problem at hand.

Recently, we focused our work in solving the ADR problem and the Stokes problem in a patient-specific framework. Specifically, we evaluate the computational efficiency of HigaMod in simulating the blood flow in coronary arteries and cerebral arteries. The main goal is to assess the

mprovement that 1D enriched models can provide, with respect to traditional full models, when dealing with demanding 3D CFD simulations. The results obtained, even though preliminary, are promising [Brandes, Barbosa and Perotto (2019); Brandes, Barbosa, Perotto and Suito (2020)].

In the field of hemodynamics, numerical models have evolved to account for the demands in speed and accuracy of modern diagnostic medicine. In this context, we studied in detail Hierarchical Model Reduction technique combined with Isogeometric Analysis (HigaMOD), a technique recently developed in [Perotto, Reali, Rusconi and Veneziani (2017)]. HigaMod is a reduction procedure used to downscale models when the phenomenon at hand presents a preferential direction of flow, e.g., when modelling the blood flow in arteries or the water flow in a channel network. The method showed a significant improvement in reducing the computational power and simulation time, while giving enough information to analyze the problem at hand.

Recently, we focused our work in solving the ADR problem and the Stokes problem in a patient-specific framework. Specifically, we evaluate the computational efficiency of HigaMod in simulating the blood flow in coronary arteries and cerebral arteries. The main goal is to assess the

mprovement that 1D enriched models can provide, with respect to traditional full models, when dealing with demanding 3D CFD simulations. The results obtained, even though preliminary, are promising [Brandes, Barbosa and Perotto (2019); Brandes, Barbosa, Perotto and Suito (2020)].

#### Seminar on Geometric Complex Analysis

10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)

Diederich-Fornaess and Steinness indices for abstract CR manifolds

**Masanori Adachi**(Shizuoka Univ.)Diederich-Fornaess and Steinness indices for abstract CR manifolds

[ Abstract ]

The Diederich-Fornaes and Steinness indices are estimated for weakly pseudoconvex domains in complex manifolds in terms of the D'Angelo 1-form of the boundary CR manifolds. In particular, CR invariance of these indices is shown when the domain is Takeuchi 1-convex. This is a joint work with Jihun Yum (Pusan National University).

The Diederich-Fornaes and Steinness indices are estimated for weakly pseudoconvex domains in complex manifolds in terms of the D'Angelo 1-form of the boundary CR manifolds. In particular, CR invariance of these indices is shown when the domain is Takeuchi 1-convex. This is a joint work with Jihun Yum (Pusan National University).

### 2020/01/16

#### Information Mathematics Seminar

16:50-18:35 Room #122 (Graduate School of Math. Sci. Bldg.)

Foundation of Quantum Annealing (Japanese)

**Hirotaka Irie**(DENSO CORPORATION/RIKEN iTHEMS)Foundation of Quantum Annealing (Japanese)

[ Abstract ]

Explanation of Quantum Annealing

Explanation of Quantum Annealing

### 2020/01/14

#### Tuesday Seminar on Topology

17:00-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)

SO(3)-invariant G

**Ryohei Chihara**(The University of Tokyo)SO(3)-invariant G

_{2}-geometry (JAPANESE)
[ Abstract ]

Berger's classification of holonomy groups of Riemannian manifolds includes exceptional cases of the Lie groups G

Berger's classification of holonomy groups of Riemannian manifolds includes exceptional cases of the Lie groups G

_{2}and Spin(7). Many authors have studied G_{2}- and Spin(7)-manifolds with torus symmetry. In this talk, we generalize the celebrated examples due to Bryant and Salamon and study G_{2}-manifolds with SO(3)-symmetry. Such torsion-free G_{2}-structures are described as a dynamical system of SU(3)-structures on an SO(3)-fibration over a 3-manifold. As a main result, we reduce this system into a constrained Hamiltonian dynamical system on the cotangent bundle over the space of all Riemannian metrics on the 3-manifold. The Hamiltonian function is very similar to that of the Hamiltonian formulation of general relativity.< Previous 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176 Next >