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Lectures
Seminar information archive ～03/22｜Next seminar｜Future seminars 03/23～
Seminar information archive
2011/03/03
14:45-15:45 Room #270 (Graduate School of Math. Sci. Bldg.)
Hirofumi Osada (Kyushu Univ.)
Singularity and absolute continuity of Palm measures of Ginibre random fields
(ENGLISH)
Hirofumi Osada (Kyushu Univ.)
Singularity and absolute continuity of Palm measures of Ginibre random fields
(ENGLISH)
[ Abstract ]
The Ginibre random point field is a probability measure on the configuration space over the complex plane $\\mathbb{C}$, which is translation and rotation invariant. Intuitively, the interaction potential of this random point field is the two dimensional Coulomb potential with $\\beta = 2 $. This fact is justified by the integration by parts formula.
Since the two dimensional Coulomb potential is quite strong at infinity, the property of the Ginibre random point field is different from that of Gibbs measure with Ruelle class potentials. As an instance, we prove that the Palm measure of the Ginibre random point field is singular to the original Ginibre random point field. Moreover, all Palm measures conditioned at $x \\in \\mathbb{C}$ are mutually absolutely continuous.
The Ginibre random point field is a probability measure on the configuration space over the complex plane $\\mathbb{C}$, which is translation and rotation invariant. Intuitively, the interaction potential of this random point field is the two dimensional Coulomb potential with $\\beta = 2 $. This fact is justified by the integration by parts formula.
Since the two dimensional Coulomb potential is quite strong at infinity, the property of the Ginibre random point field is different from that of Gibbs measure with Ruelle class potentials. As an instance, we prove that the Palm measure of the Ginibre random point field is singular to the original Ginibre random point field. Moreover, all Palm measures conditioned at $x \\in \\mathbb{C}$ are mutually absolutely continuous.
2011/03/03
16:00-16:30 Room #270 (Graduate School of Math. Sci. Bldg.)
Yuu Hariya (Tohoku Univ.)
A proof of the Brascamp-Lieb inequality based on Skorokhod embedding (ENGLISH)
Yuu Hariya (Tohoku Univ.)
A proof of the Brascamp-Lieb inequality based on Skorokhod embedding (ENGLISH)
[ Abstract ]
In this talk, we provide a probabilistic approach to the Brascamp-Lieb inequality based on Skorokhod embedding. An extension of the inequality to non-convex potentials will also be discussed.
In this talk, we provide a probabilistic approach to the Brascamp-Lieb inequality based on Skorokhod embedding. An extension of the inequality to non-convex potentials will also be discussed.
2011/02/28
17:00-18:00 Room #470 (Graduate School of Math. Sci. Bldg.)
Ying Tan (The University of Melbourne)
Extremum Seeking Control: history and recent developments (ENGLISH)
Ying Tan (The University of Melbourne)
Extremum Seeking Control: history and recent developments (ENGLISH)
[ Abstract ]
A control system which is to determine and maintain the extremum value of a function is called extremum seeking control. The first extremum seeking control application appeared in 1922, in which the extremum seeking control was applied to electric railways. The first rigorous local stability analysis for an ESC scheme was recently proved in 2000 and later extended to semi-global stability analysis 2006.. This has spurred a renewed interest in this research area, leading to numerous practical implementations of the scheme. This talk will first revisit the history of extremum seeking control. It is followed by an explanation how the extremum seeking works. Finally, it will focus on the latest unifying framework that combines arbitrary continuous optimization algorithms with an estimator for derivatives of the unknown reference-to-output steady state map that contains an extremum.
A control system which is to determine and maintain the extremum value of a function is called extremum seeking control. The first extremum seeking control application appeared in 1922, in which the extremum seeking control was applied to electric railways. The first rigorous local stability analysis for an ESC scheme was recently proved in 2000 and later extended to semi-global stability analysis 2006.. This has spurred a renewed interest in this research area, leading to numerous practical implementations of the scheme. This talk will first revisit the history of extremum seeking control. It is followed by an explanation how the extremum seeking works. Finally, it will focus on the latest unifying framework that combines arbitrary continuous optimization algorithms with an estimator for derivatives of the unknown reference-to-output steady state map that contains an extremum.
2011/02/02
16:30-17:30 Room #002 (Graduate School of Math. Sci. Bldg.)
Yong Jung Kim (Korea Advanced Institute of Science and Technology (KAIST))
Connectedness of a level set and a generalization of Oleinik and Aronson-Benilan type one-sided inequalities (ENGLISH)
Yong Jung Kim (Korea Advanced Institute of Science and Technology (KAIST))
Connectedness of a level set and a generalization of Oleinik and Aronson-Benilan type one-sided inequalities (ENGLISH)
[ Abstract ]
The one-sided Oleinik inequality provides the uniqueness and a sharp regularity of solutions to a scalar conservation law. The Aronson-Benilan type one-sided inequalities also play a similar role. We will discuss about their generalization to a general setting.
The one-sided Oleinik inequality provides the uniqueness and a sharp regularity of solutions to a scalar conservation law. The Aronson-Benilan type one-sided inequalities also play a similar role. We will discuss about their generalization to a general setting.
2011/02/02
15:15-16:15 Room #002 (Graduate School of Math. Sci. Bldg.)
Guanghui ZHANG (Graduate School of Mathematical Sciences, the University of Tokyo)
Regularity of two dimensional capillary gravity water waves (ENGLISH)
Guanghui ZHANG (Graduate School of Mathematical Sciences, the University of Tokyo)
Regularity of two dimensional capillary gravity water waves (ENGLISH)
[ Abstract ]
We consider the two-dimensional steady capillary water waves with vorticity. In the case of zero surface tension, it is well known that the free surface of a wave of maximal amplitude is not smooth at a free surface point of maximal height, but forms a sharp crest with an angle of 120 degrees. When the surface tension is not zero, physical intuition suggests that the corner singularities should disappear. In this talk we prove that for suitable weak solutions, the free surfaces are smooth. On a technical level, solutions of our problem are closely related to critical points of the Mumford-Shah functional, so that our main task is to exclude cusps pointing into the water phase. This is a joint work with Georg Weiss.
We consider the two-dimensional steady capillary water waves with vorticity. In the case of zero surface tension, it is well known that the free surface of a wave of maximal amplitude is not smooth at a free surface point of maximal height, but forms a sharp crest with an angle of 120 degrees. When the surface tension is not zero, physical intuition suggests that the corner singularities should disappear. In this talk we prove that for suitable weak solutions, the free surfaces are smooth. On a technical level, solutions of our problem are closely related to critical points of the Mumford-Shah functional, so that our main task is to exclude cusps pointing into the water phase. This is a joint work with Georg Weiss.
2010/12/16
13:00-14:30 Room #123 (Graduate School of Math. Sci. Bldg.)
Sebastien Hitier (BNP Paribas, Head of Quantitative Research, Credit Asia)
Credit Derivatives Modelling and the concept of Background Intensity I (ENGLISH)
Sebastien Hitier (BNP Paribas, Head of Quantitative Research, Credit Asia)
Credit Derivatives Modelling and the concept of Background Intensity I (ENGLISH)
[ Abstract ]
Session 1: Introducing background intensity models
- Motivation for the concept of background intensity
- The default realisation marker
- Definition of background filtration and background intensity
- Reformulating the H hypothesis, and Kusuoka’s “remark”
- Generalised HJM formula and Credit Risk neutral dynamics
Session 2: Five useful properties of background intensity models
- Generalised HJM formula for credit
- Definition of conditionally independent defaults
- Diversification effects: results on forward loss distribution
- Stronger conditional independence effect for spot loss
- Existence of a canonical copula
- Properties of the portfolio loss copula
Session 1: Introducing background intensity models
- Motivation for the concept of background intensity
- The default realisation marker
- Definition of background filtration and background intensity
- Reformulating the H hypothesis, and Kusuoka’s “remark”
- Generalised HJM formula and Credit Risk neutral dynamics
Session 2: Five useful properties of background intensity models
- Generalised HJM formula for credit
- Definition of conditionally independent defaults
- Diversification effects: results on forward loss distribution
- Stronger conditional independence effect for spot loss
- Existence of a canonical copula
- Properties of the portfolio loss copula
2010/12/16
14:40-16:10 Room #123 (Graduate School of Math. Sci. Bldg.)
Sebastien Hitier (BNP Paribas, Head of Quantitative Research, Credit Asia)
Credit Derivatives Modelling and the concept of Background Intensity II (ENGLISH)
Sebastien Hitier (BNP Paribas, Head of Quantitative Research, Credit Asia)
Credit Derivatives Modelling and the concept of Background Intensity II (ENGLISH)
[ Abstract ]
Session 1: Introducing background intensity models
- Motivation for the concept of background intensity
- The default realisation marker
- Definition of background filtration and background intensity
- Reformulating the H hypothesis, and Kusuoka’s “remark”
- Generalised HJM formula and Credit Risk neutral dynamics
Session 2: Five useful properties of background intensity models
- Generalised HJM formula for credit
- Definition of conditionally independent defaults
- Diversification effects: results on forward loss distribution
- Stronger conditional independence effect for spot loss
- Existence of a canonical copula
- Properties of the portfolio loss copula
Session 1: Introducing background intensity models
- Motivation for the concept of background intensity
- The default realisation marker
- Definition of background filtration and background intensity
- Reformulating the H hypothesis, and Kusuoka’s “remark”
- Generalised HJM formula and Credit Risk neutral dynamics
Session 2: Five useful properties of background intensity models
- Generalised HJM formula for credit
- Definition of conditionally independent defaults
- Diversification effects: results on forward loss distribution
- Stronger conditional independence effect for spot loss
- Existence of a canonical copula
- Properties of the portfolio loss copula
2010/11/04
10:40-12:10 Room #123 (Graduate School of Math. Sci. Bldg.)
Jean Meyer, Yasuko HISAMATSU (Risk Capital Market Tokyo, BNP Paribas)
Market, Liquidity and Counterparty Risk (ENGLISH)
Jean Meyer, Yasuko HISAMATSU (Risk Capital Market Tokyo, BNP Paribas)
Market, Liquidity and Counterparty Risk (ENGLISH)
[ Abstract ]
1. Introduction to the market risk
- Introduction to the Risk Management
in the Financial institutions
- Overview of the main market risks
2. Market & Liquidity Risks –Basics
-Presentation of the main Greeks
-Focus on volatility risk
-Focus on correlation risk
-Conclusion (common features of the market risks)
3. Risk measure
- Stress test
- Value at risk
- Risks measure for counterparty risk
1. Introduction to the market risk
- Introduction to the Risk Management
in the Financial institutions
- Overview of the main market risks
2. Market & Liquidity Risks –Basics
-Presentation of the main Greeks
-Focus on volatility risk
-Focus on correlation risk
-Conclusion (common features of the market risks)
3. Risk measure
- Stress test
- Value at risk
- Risks measure for counterparty risk
2010/11/02
13:00-16:10 Room #122 (Graduate School of Math. Sci. Bldg.)
Vladimir Bogachev (Moscow)
The Malliavin calculus on configuration spaces and applications (ENGLISH)
Vladimir Bogachev (Moscow)
The Malliavin calculus on configuration spaces and applications (ENGLISH)
[ Abstract ]
It is planned to discuss first a general scheme of the Malliavin
calculus on an abstract measurable
manifold with minimal assumptions about the manifold.
Then a practical realization of this scheme will be discussed in
several concrete examples with emphasis
on configuration spaces, i.e., spaces of locally finite configurations
in a given manifold (for example, just
a finite-dimensional Euclidean space), which can be alternatively
described as the spaces of integer-valued
discrete measures equipped with suitable differential structures.
No acquaintance with the Malliavin calculus and differential geometry
is assumed.
It is planned to discuss first a general scheme of the Malliavin
calculus on an abstract measurable
manifold with minimal assumptions about the manifold.
Then a practical realization of this scheme will be discussed in
several concrete examples with emphasis
on configuration spaces, i.e., spaces of locally finite configurations
in a given manifold (for example, just
a finite-dimensional Euclidean space), which can be alternatively
described as the spaces of integer-valued
discrete measures equipped with suitable differential structures.
No acquaintance with the Malliavin calculus and differential geometry
is assumed.
2010/11/01
16:00-18:15 Room #270 (Graduate School of Math. Sci. Bldg.)
Michel Cristofol (マルセイユ大学) 16:00-17:00
Inverse problems in non linear parabolic equations : Two differents approaches (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~kengok/abstractTokyo.pdf
Patricia Gaitan (マルセイユ大学) 17:15-18:15
Inverse Problems for parabolic System
(ENGLISH)
Michel Cristofol (マルセイユ大学) 16:00-17:00
Inverse problems in non linear parabolic equations : Two differents approaches (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~kengok/abstractTokyo.pdf
Patricia Gaitan (マルセイユ大学) 17:15-18:15
Inverse Problems for parabolic System
(ENGLISH)
[ Abstract ]
I will present a review of stability and controllability results for linear parabolic coupled systems with coupling of first and zeroth-order terms by data of reduced number of components. The key ingredients are global Carleman estimates.
I will present a review of stability and controllability results for linear parabolic coupled systems with coupling of first and zeroth-order terms by data of reduced number of components. The key ingredients are global Carleman estimates.
2010/10/28
10:40-12:10 Room #123 (Graduate School of Math. Sci. Bldg.)
Jean Meyer, Yasuko HISAMATSU (Risk Capital Market Tokyo, BNP Paribas)
Market, Liquidity and Counterparty Risk (ENGLISH)
Jean Meyer, Yasuko HISAMATSU (Risk Capital Market Tokyo, BNP Paribas)
Market, Liquidity and Counterparty Risk (ENGLISH)
[ Abstract ]
1. Introduction to the market risk
- Introduction to the Risk Management
in the Financial institutions
- Overview of the main market risks
2. Market & Liquidity Risks –Basics
-Presentation of the main Greeks
-Focus on volatility risk
-Focus on correlation risk
-Conclusion (common features of the market risks)
3. Risk measure
- Stress test
- Value at risk
- Risks measure for counterparty risk
1. Introduction to the market risk
- Introduction to the Risk Management
in the Financial institutions
- Overview of the main market risks
2. Market & Liquidity Risks –Basics
-Presentation of the main Greeks
-Focus on volatility risk
-Focus on correlation risk
-Conclusion (common features of the market risks)
3. Risk measure
- Stress test
- Value at risk
- Risks measure for counterparty risk
2010/09/09
16:30-18:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Bernhard Mühlherr (Justus-Liebig-Universität Gießen)
Mini-course on Buildings (3/3) (ENGLISH)
Bernhard Mühlherr (Justus-Liebig-Universität Gießen)
Mini-course on Buildings (3/3) (ENGLISH)
[ Abstract ]
The goal of this course is to provide an overview on the theory of buildings which was developed by Jacques Tits.
The third lecture will be then devoted to classification results,
mainly the classification of spherical buildings. However, I will try to say some words on the classification of affine buildings and twin buildings as well.
This is Part 3 of a 3-part lecture.
The goal of this course is to provide an overview on the theory of buildings which was developed by Jacques Tits.
The third lecture will be then devoted to classification results,
mainly the classification of spherical buildings. However, I will try to say some words on the classification of affine buildings and twin buildings as well.
This is Part 3 of a 3-part lecture.
2010/09/04
09:30-11:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Bernhard Mühlherr (Justus-Liebig-Universität Gießen)
Mini-course on Buildings (1/3) (ENGLISH)
Bernhard Mühlherr (Justus-Liebig-Universität Gießen)
Mini-course on Buildings (1/3) (ENGLISH)
[ Abstract ]
The goal of this course is to provide an overview on the theory of buildings which was developed by Jacques Tits.
In my first lecture I will begin by introducing generalized polygons, namely rank two spherical buildings, and discussing several aspects of them which will be generalized later, and then move on to defining Coxeter complexes and giving the classical definition of buildings as simplicial complexes. I will try to include as many examples as possible.
This is Part 1 of a 3-part lecture. The second lecture will follow after a ten-minute break.
The goal of this course is to provide an overview on the theory of buildings which was developed by Jacques Tits.
In my first lecture I will begin by introducing generalized polygons, namely rank two spherical buildings, and discussing several aspects of them which will be generalized later, and then move on to defining Coxeter complexes and giving the classical definition of buildings as simplicial complexes. I will try to include as many examples as possible.
This is Part 1 of a 3-part lecture. The second lecture will follow after a ten-minute break.
2010/09/04
11:10-12:40 Room #126 (Graduate School of Math. Sci. Bldg.)
Bernhard Mühlherr (Justus-Liebig-Universität Gießen)
Mini-course on Buildings (2/3) (ENGLISH)
Bernhard Mühlherr (Justus-Liebig-Universität Gießen)
Mini-course on Buildings (2/3) (ENGLISH)
[ Abstract ]
The goal of this course is to provide an overview on the theory of buildings which was developed by Jacques Tits.
In my second lecture I will start with chamber systems and coset
geometries, introducing some special properties of chamber systems in order to give another definition of a building. This definition is less standard but it will give some results on presentations of groups acting on buildings for free. In particular it will enable me to present a sketch of a proof of the Curtis-Tits theorem for Chevalley groups and to formulate Tits' extension theorem.
This is Part 2 of a 3-part lecture. Part 1 takes place ealier on the same day. Part 3 will take place on Thursday, September 9.
The goal of this course is to provide an overview on the theory of buildings which was developed by Jacques Tits.
In my second lecture I will start with chamber systems and coset
geometries, introducing some special properties of chamber systems in order to give another definition of a building. This definition is less standard but it will give some results on presentations of groups acting on buildings for free. In particular it will enable me to present a sketch of a proof of the Curtis-Tits theorem for Chevalley groups and to formulate Tits' extension theorem.
This is Part 2 of a 3-part lecture. Part 1 takes place ealier on the same day. Part 3 will take place on Thursday, September 9.
2010/09/03
14:30-15:30 Room #370 (Graduate School of Math. Sci. Bldg.)
Luc Robbiano (University of Versailles)
Carleman estimates and boundary problems. (JAPANESE)
Luc Robbiano (University of Versailles)
Carleman estimates and boundary problems. (JAPANESE)
[ Abstract ]
In this presentation, based on joint works with Jerome LeRousseau and Matthieu Leautaud, we consider boundary problems for elliptic/parabolic operators. We prove Carleman estimates in such cases. One of the interest for such an estimate is the implied controllability of (semi-linear) heat equations.
One of the main aspects of the proof is a microlocal decomposition separating high and low tangential frequencies.
If time permits, we will present how such an approach can be used to prove Carleman estimates in the case of non smooth coefficients at an interface, possibly with an additional diffusion process along the interface.
In this presentation, based on joint works with Jerome LeRousseau and Matthieu Leautaud, we consider boundary problems for elliptic/parabolic operators. We prove Carleman estimates in such cases. One of the interest for such an estimate is the implied controllability of (semi-linear) heat equations.
One of the main aspects of the proof is a microlocal decomposition separating high and low tangential frequencies.
If time permits, we will present how such an approach can be used to prove Carleman estimates in the case of non smooth coefficients at an interface, possibly with an additional diffusion process along the interface.
2010/08/06
15:30-17:45 Room #370 (Graduate School of Math. Sci. Bldg.)
Leevan Ling (Hong Kong Baptist University) 15:30-16:30
A Spectral Method for Space--
Time Fractional Diffusion Equation (ENGLISH)
Mourad Choulli (University of Metz) 16:45-17:45
A multidimensional Borg-Levinson theorem (ENGLISH)
Leevan Ling (Hong Kong Baptist University) 15:30-16:30
A Spectral Method for Space--
Time Fractional Diffusion Equation (ENGLISH)
Mourad Choulli (University of Metz) 16:45-17:45
A multidimensional Borg-Levinson theorem (ENGLISH)
2010/08/05
16:30-17:30 Room #370 (Graduate School of Math. Sci. Bldg.)
Yongzhi Steve Xu (University of Louisville, USA)
Radiation Conditions for Wave in Stratified Medium and Related Inverse
Problems (ENGLISH)
Yongzhi Steve Xu (University of Louisville, USA)
Radiation Conditions for Wave in Stratified Medium and Related Inverse
Problems (ENGLISH)
2010/08/05
16:30-17:30 Room #370 (Graduate School of Math. Sci. Bldg.)
Yongzhi Steve Xu (University of Louisville, USA)
Radiation Conditions for Wave in Stratified Medium and Related Inverse Problems (ENGLISH)
Yongzhi Steve Xu (University of Louisville, USA)
Radiation Conditions for Wave in Stratified Medium and Related Inverse Problems (ENGLISH)
2010/06/26
10:00-16:10 Room #056 (Graduate School of Math. Sci. Bldg.)
Yoshimichi Ueda (Kyushu Univ.) 10:00-11:00
On the predual of non-commutative $H^\\infty$ (ENGLISH)
Hiroki Matui (Chiba Univ.) 11:20-12:20
${\\mathbf Z}^N$-actions on UHF algebras of infinite type (ENGLISH)
Feng Xu (UC Riverside) 13:50-14:50
On a subfactor generalization of Wall's conjecture (ENGLISH)
Masaki Izumi (Kyoto Univ.) 15:10-16:10
Group actions on Kirchberg algebras (ENGLISH)
Yoshimichi Ueda (Kyushu Univ.) 10:00-11:00
On the predual of non-commutative $H^\\infty$ (ENGLISH)
Hiroki Matui (Chiba Univ.) 11:20-12:20
${\\mathbf Z}^N$-actions on UHF algebras of infinite type (ENGLISH)
Feng Xu (UC Riverside) 13:50-14:50
On a subfactor generalization of Wall's conjecture (ENGLISH)
Masaki Izumi (Kyoto Univ.) 15:10-16:10
Group actions on Kirchberg algebras (ENGLISH)
2010/06/25
15:00-17:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Narutaka Ozawa (Univ. Tokyo) 15:00-16:00
Quasi-homomorphism rigidity with noncommutative targets (ENGLISH)
Yoshiko Ogata (Univ. Tokyo) 16:30-17:30
Ruelle-Lanford functions for quantum spin systems (ENGLISH)
Narutaka Ozawa (Univ. Tokyo) 15:00-16:00
Quasi-homomorphism rigidity with noncommutative targets (ENGLISH)
Yoshiko Ogata (Univ. Tokyo) 16:30-17:30
Ruelle-Lanford functions for quantum spin systems (ENGLISH)
2010/05/12
15:30-17:00 Room #123 (Graduate School of Math. Sci. Bldg.)
Luc Illusie (東京大学/Paris南大学)
Independence of families of $\\ell$-adic representations and uniform constructibility (ENGLISH)
Luc Illusie (東京大学/Paris南大学)
Independence of families of $\\ell$-adic representations and uniform constructibility (ENGLISH)
[ Abstract ]
Let $k$ be a number field, $\\overline{k}$ an algebraic closure of $k$, $\\Gamma_k = \\mathrm{Gal}(\\overline{k}/k)$. A family of continuous homomorphisms $\\rho_{\\ell} : \\Gamma_k \\rightarrow G_{\\ell}$, indexed by prime numbers $\\ell$, where $G_{\\ell}$ is a locally compact $\\ell$-adic Lie group, is said to be independent if $\\rho(\\Gamma_k) = \\prod \\rho_{\\ell}(\\Gamma_k)$, where $\\rho = (\\rho_{\\ell}) : \\Gamma_k \\rightarrow \\prod G_{\\ell}$. Serre gave a criterion for such a family to become independent after a finite extension of $k$. We will explain Serre's criterion and show that it applies to families coming from the $\\ell$-adic cohomology (or cohomology with compact support) of schemes separated and of finite type over $k$. This application uses a variant of Deligne's generic constructibility theorem with uniformity in $\\ell$.
Let $k$ be a number field, $\\overline{k}$ an algebraic closure of $k$, $\\Gamma_k = \\mathrm{Gal}(\\overline{k}/k)$. A family of continuous homomorphisms $\\rho_{\\ell} : \\Gamma_k \\rightarrow G_{\\ell}$, indexed by prime numbers $\\ell$, where $G_{\\ell}$ is a locally compact $\\ell$-adic Lie group, is said to be independent if $\\rho(\\Gamma_k) = \\prod \\rho_{\\ell}(\\Gamma_k)$, where $\\rho = (\\rho_{\\ell}) : \\Gamma_k \\rightarrow \\prod G_{\\ell}$. Serre gave a criterion for such a family to become independent after a finite extension of $k$. We will explain Serre's criterion and show that it applies to families coming from the $\\ell$-adic cohomology (or cohomology with compact support) of schemes separated and of finite type over $k$. This application uses a variant of Deligne's generic constructibility theorem with uniformity in $\\ell$.
2010/05/07
16:00-17:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Luc Illusie (東京大学/Paris南大学)
Independence of families of $\\ell$-adic representations and uniform constructibility
Luc Illusie (東京大学/Paris南大学)
Independence of families of $\\ell$-adic representations and uniform constructibility
[ Abstract ]
Let $k$ be a number field, $\\overline{k}$ an algebraic closure of $k$, $\\Gamma_k = \\mathrm{Gal}(\\overline{k}/k)$. A family of continuous homomorphisms $\\rho_{\\ell} : \\Gamma_k \\rightarrow G_{\\ell}$, indexed by prime numbers $\\ell$, where $G_{\\ell}$ is a locally compact $\\ell$-adic Lie group, is said to be independent if $\\rho(\\Gamma_k) = \\prod \\rho_{\\ell}(\\Gamma_k)$, where $\\rho = (\\rho_{\\ell}) : \\Gamma_k \\rightarrow \\prod G_{\\ell}$. Serre gave a criterion for such a family to become independent after a finite extension of $k$. We will explain Serre's criterion and show that it applies to families coming from the $\\ell$-adic cohomology (or cohomology with compact support) of schemes separated and of finite type over $k$. This application uses a variant of Deligne's generic constructibility theorem with uniformity in $\\ell$.
Let $k$ be a number field, $\\overline{k}$ an algebraic closure of $k$, $\\Gamma_k = \\mathrm{Gal}(\\overline{k}/k)$. A family of continuous homomorphisms $\\rho_{\\ell} : \\Gamma_k \\rightarrow G_{\\ell}$, indexed by prime numbers $\\ell$, where $G_{\\ell}$ is a locally compact $\\ell$-adic Lie group, is said to be independent if $\\rho(\\Gamma_k) = \\prod \\rho_{\\ell}(\\Gamma_k)$, where $\\rho = (\\rho_{\\ell}) : \\Gamma_k \\rightarrow \\prod G_{\\ell}$. Serre gave a criterion for such a family to become independent after a finite extension of $k$. We will explain Serre's criterion and show that it applies to families coming from the $\\ell$-adic cohomology (or cohomology with compact support) of schemes separated and of finite type over $k$. This application uses a variant of Deligne's generic constructibility theorem with uniformity in $\\ell$.
2010/04/28
16:00-17:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Luc Illusie (東京大学/Paris南大学)
Independence of families of $\\ell$-adic representations and uniform constructibility
Luc Illusie (東京大学/Paris南大学)
Independence of families of $\\ell$-adic representations and uniform constructibility
[ Abstract ]
Let $k$ be a number field, $\\overline{k}$ an algebraic closure of $k$, $\\Gamma_k = \\mathrm{Gal}(\\overline{k}/k)$. A family of continuous homomorphisms $\\rho_{\\ell} : \\Gamma_k \\rightarrow G_{\\ell}$, indexed by prime numbers $\\ell$, where $G_{\\ell}$ is a locally compact $\\ell$-adic Lie group, is said to be independent if $\\rho(\\Gamma_k) = \\prod \\rho_{\\ell}(\\Gamma_k)$, where $\\rho = (\\rho_{\\ell}) : \\Gamma_k \\rightarrow \\prod G_{\\ell}$. Serre gave a criterion for such a family to become independent after a finite extension of $k$. We will explain Serre's criterion and show that it applies to families coming from the $\\ell$-adic cohomology (or cohomology with compact support) of schemes separated and of finite type over $k$. This application uses a variant of Deligne's generic constructibility theorem with uniformity in $\\ell$.
Let $k$ be a number field, $\\overline{k}$ an algebraic closure of $k$, $\\Gamma_k = \\mathrm{Gal}(\\overline{k}/k)$. A family of continuous homomorphisms $\\rho_{\\ell} : \\Gamma_k \\rightarrow G_{\\ell}$, indexed by prime numbers $\\ell$, where $G_{\\ell}$ is a locally compact $\\ell$-adic Lie group, is said to be independent if $\\rho(\\Gamma_k) = \\prod \\rho_{\\ell}(\\Gamma_k)$, where $\\rho = (\\rho_{\\ell}) : \\Gamma_k \\rightarrow \\prod G_{\\ell}$. Serre gave a criterion for such a family to become independent after a finite extension of $k$. We will explain Serre's criterion and show that it applies to families coming from the $\\ell$-adic cohomology (or cohomology with compact support) of schemes separated and of finite type over $k$. This application uses a variant of Deligne's generic constructibility theorem with uniformity in $\\ell$.
2010/04/19
16:00-17:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Cyrill Muratov (New Jersey Institute of Technology)
Droplet phases in non-local Ginzburg-Landau models with Coulomb repulsion in two dimensions
Cyrill Muratov (New Jersey Institute of Technology)
Droplet phases in non-local Ginzburg-Landau models with Coulomb repulsion in two dimensions
[ Abstract ]
In this talk I will present an analysis of the behavior of the minimal energy in non-local Ginzburg-Landau models with Coulomb repulsion in two space dimensions near the onset of multi-droplet patterns. As a first step, I will show that under suitable scaling the energy of minimizers becomes asymptotically equal to that of a sharp interface energy with screened Coulomb interaction. I will then show that the minimizers of the corresponding sharp interface energy consist of nearly identical circular droplets of small size separated by large distances. Finally, I will show that in a suitable limit these droplets become uniformly distributed throughout the domain. The analysis allows to obtain precise asymptotic behaviors of the bifurcation threshold, the minimal energy, the droplet radii, and the droplet density in the considered limit.
In this talk I will present an analysis of the behavior of the minimal energy in non-local Ginzburg-Landau models with Coulomb repulsion in two space dimensions near the onset of multi-droplet patterns. As a first step, I will show that under suitable scaling the energy of minimizers becomes asymptotically equal to that of a sharp interface energy with screened Coulomb interaction. I will then show that the minimizers of the corresponding sharp interface energy consist of nearly identical circular droplets of small size separated by large distances. Finally, I will show that in a suitable limit these droplets become uniformly distributed throughout the domain. The analysis allows to obtain precise asymptotic behaviors of the bifurcation threshold, the minimal energy, the droplet radii, and the droplet density in the considered limit.
2010/03/25
17:00-18:00 Room #370 (Graduate School of Math. Sci. Bldg.)
Dr Bangti Jin (Center for Industrial Mathematics University of Bremen, Germany)
Heuristic Choice Rules for Convex Variational Regularization
Dr Bangti Jin (Center for Industrial Mathematics University of Bremen, Germany)
Heuristic Choice Rules for Convex Variational Regularization
[ Abstract ]
In this talk we shall consider heuristic rules for choosing regularization parameters for general convex variational regularization of linear inverse problems. Several rules of recent origin are described, and some theoretical issues, e.g. existence, convergence, and a posteriori error estimates, are discussed. Numerical examples will be presented to demonstrate their accuracy and practical utility.
In this talk we shall consider heuristic rules for choosing regularization parameters for general convex variational regularization of linear inverse problems. Several rules of recent origin are described, and some theoretical issues, e.g. existence, convergence, and a posteriori error estimates, are discussed. Numerical examples will be presented to demonstrate their accuracy and practical utility.
