Seminars

Math-Fi seminar on 9 Jan.

2020.01.07 Tue up
  • Date: 9 Jan. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:00-19:00


  • First Speaker: Katsushi Nakajima (Ritsumeikan Asia Pacific University)
  • Time: 16:00-17:30
  • Title: TBA

  • Second Speaker: Koya Sakakibara (Kyoto University)
  • Time: 17:30-19:00
  • Title: Numerical analysis of interface problem
  • Abstract:
​ The interface appears in several problems, such as fluid dynamics between two different liquids. To study its evolution and dynamics forms the basis of the research in natural science. Although there are several mathematical studies for interfacial phenomena, they are, in general, so difficult, and numerical study becomes an essential tool in this field.
 In this talk, I will talk about the numerical analysis of interface problem, and especially consider two issues: The Hele-Shaw problem and grain boundary. The Hele-Shaw problem describes the motion of viscous fluid in a quasi-two-dimensional space, which started from a short paper by Henry Selby Hele-Shaw (1854–1941). It is now recognized as a basic mathematical model to study the fingering phenomena (also known as the Saffman–Taylor instability), and several researchers have studied this problem; however, there are still several open questions. A problem on the grain boundary appears in the field of material science. A grain boundary is an interface between two grains, or crystallites, in a polycrystalline material. It is the two-dimensional defect in the crystal structure. The study of grain boundaries and their effects on the mechanical, electrical, and other properties of materials forms an essential topic in material science. My study aims to understand the mechanism of grain boundaries from mathematical and numerical points of view.
 In the first half of this talk, I will explain this problem and construct some efficient numerical scheme based on the method of fundamental solutions and the asymptotic uniform distribution method. I will also briefly survey the geometric numerical integration, which aims to construct a numerical scheme which inherits properties of the original problem in some discrete sense. In the second half of this talk, I will move on to the problem on grain boundaries and consider manifold-valued total variation flows. I will introduce spatially discretized total variation flow and construct a numerical scheme using the exponential map of the manifold. I will also present an energy dissipation property and convergence result.

Ritsumeikan University Geometry Seminar (16/December/2019)

2019.12.10 Tue up
<<Ritsumeikan University Geometry Seminar>>

Date: 16/December/2019, Monday, 16:30-18:00

Title: Semitoric systems in geometry and dynamics

Speaker: Sonja Hohloch (University of Antwerp)

Abstract: PDF-file

Room: Ritsumeikan University, Biwako-Kusatsu Campus, Westwing, 6th floor, Colloquium Room

Ritsumeikan University Geometry Seminar (09/December/2019)

2019.12.04 Wed up
<<Ritsumeikan University Geometry Seminar>>

Date: 09/December/2019, Monday, 16:30-17:30

Title: BV structures on moduli spaces of flat connections

Speaker: Pavol Severa （University of Geneva）

Abstract:
Loops (or rather their homotopy classes) on an oriented surface form a Lie algebra, originally discovered by Goldman.The Lie bracket is given by a simple formula involving intersection points of two loops. This Lie algebra can be interpreted as the Poisson bracket on a moduli space of flat connections (given by the famous Atiyah-Bott symplectic form), if to each loop we assign the trace of the holonomy along the loop. Loops come also with another operation, a Lie cobracket discovered by Turaev, given by a very similar formula. I will explain what is the corresponding geometric structure on the moduli space. I will also try to explain why this structure is interesting and how it relates to the Kashiwara-Vergne problem in Lie theory. Based on a joint work in progress with Anton Alekseev, Florian Naef, and Jan Pulmann.

Room: Ritsumeikan University, Biwako-Kusatsu Campus, Westwing 6th floor, Colloquium Room.

Ritsumeikan Geometry Seminar

2019.10.24 Thu up
Date: 2 December (Mon) 16:20-17:50
Place: Colloquium Room, West-Wing 6th floor, Biwako-Kusatsu Campus, Ritsumeikan University
Speaker: Jesús Antonio Álvarez López (University of Santiago de Compostela)
Title: Topological Molino’s theory
Abstract: (joint work with Ramón Barral Lijó and Manuel Moreira Galicia) Molino’s description of Riemannian foliations on compact manifolds is generalized to the setting of compact equicontinuous foliated spaces, in the case where the leaves are dense. In particular, a structural local group is associated to such a foliated space. As applications, we obtain a partial generalization of results by Carrière and Breuillard-Gelander, relating the structural local group to the growth of the leaves, and a description of foliated homogeneous spaces.

Ritsumeikan Geometry Seminar

2019.10.23 Wed up
Place: Colloquium Room, West-Wing 6th floor, Biwako-Kusatsu Campus, Ritsumeikan University
Speaker: Olga Lukina (University of Vienna)

Talk 1

Date: 25 November (Mon) 16:20-17:50
Title: Introduction to group actions on Cantor sets
Abstract: In this talk, we consider basic tools and properties which we use in the subsequent talks to study minimal equicontinuous group actions on Cantor sets. The tools include chains of finite index subgroups. An important property is the local quasi-analyticity of an action, introduced by Alvarez Lopez and Candel. We illustrate the concepts and methods using examples.

Talk 2

Date: 28 November (Thu) 10:40-12:10
Title: Invariants of Cantor group actions
Abstract: In this talk, we consider two direct limit invariants which can be associated to a Cantor group action, introduced in a recent joint work with Steve Hurder, and the corresponding classification of Cantor group actions. It is recommended that the participants attend Talk 1 as a preparation for this talk.

Math-Fi seminar on 10 Oct.

2019.10.07 Mon up
  • Date: 10 Oct. (Thu.) 
  • Place: W.W. 6th-floor, Colloquium Room 
  • Time: 16:30-18:00 
  • Speaker: Dan Crisan (Imperial College London) 
  • Title: second lecture 

Math-Fi seminar on 3 Oct.

2019.09.30 Mon up
  • Date: 3 Oct. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:30-18:00
  • Speaker: Dan Crisan (Imperial College London)
  • Title: Modelling multi-period carbon markets using singular forward backward SDEs
  • Abstract:
I will introduce a model the evolution of emissions and the price of emissions allowances in a carbon market such as the European Union Emissions Trading System (EU ETSP). The model accounts for multiple trading periods (and phases) and multiple times at which compliance can occur. At the end of each trading period, the participating firms must surrender allowances for the emissions made during that period, but any excess allowances can be used for compliance in the following periods. We show that the multi-period allowance pricing problem is well-posed for various mechanisms linking the trading periods (such as banking, borrowing and withdrawals). The results are based on the analysis of a forward-backward stochastic differential equation with the following special characteristics: i. the forward and backward components are coupled,  ii. the final condition is singular and iii. the forward component of the model is degenerate. I will also introduce an infinite period model, that is, a model for carbon market with a sequence of compliance times and no end date. I will show that, under appropriate conditions, the value function for the multi-period pricing problem converges, as the number of periods increases, to a value function for this infinite period model. This is joint work with Jean-Francois Chassagneux (Paris Diderot) and Hinesh Chotai (Citybank).
 

Math-Fi seminar on 12 Sep.

2019.09.09 Mon up
  • Date: 12 Sep. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:30-18:00
  • Speaker: José Manuel Corcuera (Universitat de Barcelona)
  • Title: Contingent Convertibles (final lecture)
 

Math-Fi seminar on 29 Aug.

2019.08.05 Mon up
  • Date: 29 Aug. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:00-18:00
  • Speaker: Wei Zhu/Maoqi Hu (University of Liverpool)
  • Title: Introduction to Ruin Theory (final lecture)
  • Abstract:
Risk theory in general and ruin probabilities in particular are traditionally considered as part of insurance mathematics, and has been an active area of research from the days of Lundberg all the way up to today. One of the central topics in the risk theory literature is deriving the probability of ruin in the collective risk model. The classical risk model and renewal risk models will be focused in this course, where the claim number processes are assumed to be Poisson counting processes and any general renewal counting processes, respectively.
 
The first part of this course is about the classical risk model. Different approaches to derive the ruin probability will be shown and explained. The natural extension of the classical risk model leads to the renewal risk model. Very general assumptions on interarrival times are possible for the renewal risk model, which includes the classical risk model, Erlang risk model and fractional Poisson risk model. A new family of differential operators are defined in order to construct the fractional integro-differential equations for ruin probabilities in such renewal risk models. Through the characteristic equation approach, specific fractional differential equations for the ruin probabilities can be solved explicitly, allowing for the analysis of the ruin probabilities

Math-Fi seminar on 22 Aug.

2019.08.05 Mon up
  • Date: 22 Aug. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:00-18:00
  • Speaker: Wei Zhu/Maoqi Hu (University of Liverpool)
  • Title: Some Aspects about Life Insurance and Life Expectancy in China (second lecture)
  • Abstract: 
​Life insurance has undergone enormous change in the last two to three decades. Given the changes occurring in the interconnected worlds of finance and life insurance, we believe that this is a good time to recast the mathematics of life contingent risk to be better adapted to the products, science and technology that are relevant to current and future actuaries. Pension, a part of the life insurance, is an importance insurance in our life. However, most countries face the challenge in pension. Population aging and life expectancy both of these will influence the pension system. The course will first introduce the background and give some basial theories about life insurance and pension. Then the course will discuss the influence factors of life expectancy and also use Spatial Statistical tools to assess mortality differences in China.

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