コーヒーミーティング過去ログ
2020-07-10
What should we do about COVID-19?
カトゥリン・ボシゥメン (数理創造プログラム 客員主管研究員 / Professor, Department of Physics, Ryerson University, Canada)
We have been analyzing and modelling the data for COVID-19 cases in Tokyo and Saitama. We have built mathematical models to analyze the data and make predictions about where the case counts can be expected to go next, and what the consequences could be. For a while, things were going better and better, and daily cases were going down. With the increasing case count in Tokyo, Saitama, Osaka, etc., we now have some concerns. We would like an opportunity to show you some of our results and observations and hear your thoughts. How do you feel about the recent increases? If you were in charge, what decision would you take? As scientists, do we have a responsibility to make sure this information is provided to the general public so they have a clear understanding of the situation? We hope you will join us and share your thoughts.
Public2020-07-03
Morse theory and Floer theory
谷口 正樹 (数理創造プログラム 基礎科学特別研究員)
In a study of topology, Morse theory provides a way to decompose a manifold into elementary parts. We first review a fundamental method in Morse theory. In Floer theory, we consider infinite-dimensional versions of Morse theory for nice functionals. We explain an idea of Floer theory.
2020-06-26
Observational study of suprenova remnants
辻 直美 (数理創造プログラム 特別研究員)
Supernova remnants, leftovers of supernova explosion, are believed to be factories of heavy elements and high-energy particles (cosmic rays). These ideas can be probed by observations of electromagnetic waves from supernova remnants. I will give a review talk of the observational studies; what we can learn from observations.
2020-06-19
Markdown - the next generation markup language
田中 章詞 (数理創造プログラム 上級研究員)
Markdown is a lightweight markup language. Important features are easy to use, beautiful document output, and TeX rendering support. Thanks to these fascinating features, Markdown has been already one of common markup languages at least in engineering perspectives. But, I guess, there will be benefits even in scientific research perspectives. So, I would like to introduce how to use it and its applications.
2020-06-05
Does Neutron Finite Size Affect Nuclear Structure?
内藤 智也 (U Tokyo/QHP)
Atomic nuclei consist of protons and neutrons, which interact via Coulomb and nuclear interactions. Since protons and neutrons have finite charge radii instead of point particles, these finite-size effects for the Coulomb interaction should be considered in the theoretical calculations. Nevertheless, since the contribution of the Coulomb interaction to the nuclear properties is weaker than that of the nuclear force, it was not considered properly. Recently, we have taken the finite-size effect to the Coulomb interaction into account for the calculation of nuclear structures. We found that the finite-size effects give a non-negligible contribution to the nuclear binding energy [1]. [1] T. Naito, X. Roca-Maza, G. Colò, and H. Liang. Phys. Rev. C Accepted (arXiv: 2003.03177).
Public2020-05-29
Knot theory and topological semimetals
邱 靖凱 (Senior Research Associate, Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, China)
Topological nodal line semimetals host stable chained, linked, or knotted line degeneracies in momentum space protected by symmetries. We use the Jones polynomial as a general topological invariant to capture the global knot topology of the oriented nodal lines. We show that every possible change in Jones polynomial is attributed to the local evolutions around every point where two nodal lines touch. As an application of our theory, we show that nodal chain semimetals with four touching points can evolve to a Hopf link. We extend our theory to 3D non-Hermitian multiband exceptional line semimetals and provide a recipe to understand the transition of the knot topology for protected nodal lines.
2020-05-08
Next-generation method to derive the basic reproduction number of infectious disease models
入谷 亮介 (数理創造プログラム 研究員)
In response to the recent, increasing interest in epidemiology, I will talk about the mathematical framework to derive the basic reproductive number for compartmental disease models: the Next-Generation Theorem (NGT). In general, whether diseases spread or not is determined by the leading eigenvalue (spectral radius) of a disease-free steady state(s). For an SI-model, for instance, the conventional wisdom is that the instability of (S, I) =(S_0, 0) around the ODE for the model is determined by the real part of the eigenvalue. As the number of infected-class compartments grows, however, it becomes increasingly difficult to determine the spectral radius of the associated matrix. NGT partially resolves this issue by (i) reducing the size of the matrix or dimension, (ii) making the matrix relatively sparse, and (iii) clarifying the biological meaning. I will talk about this theorem per se, though do not give its proof, with some illustrative applications (one of which is actually unsolved and therefore a quiz for you all!) as well as why graph-theory and stochastic analyses may be of great use in the discipline of epidemiology. The purpose of this talk is to facilitate future interactions between biologists including me and theoreticians who are interested in graph theory, matrix calculus, and/or dynamical systems.
2020-04-24
Quantum physicists now study non-Hermiticity
濱崎 立資 (数理創造プログラム 上級研究員 / 理化学研究所 開拓研究本部 (CPR) 濱崎非平衡量子統計力学理研白眉研究チーム 理研白眉研究チームリーダー)
2020-04-17
On COVID-19 spreading
パスカル・ネドン (理化学研究所 仁科加速器科学研究センター (RNC) 量子ハドロン物理研究室 専任研究員)
2020-04-03
Multi-meesenger Search for sources of high energy neutrino
Haoning He (ABBL)
2020-03-27
Mathematical models of epidemics
三好 建正 (数理創造プログラム 副プログラムディレクター / 理化学研究所 計算科学研究センター (R-CCS) データ同化研究チーム チームリーダー)
2020-02-21
Motivic homotopy theory and modular representation theory
Shane Kelly (Tokyo Institute of Technology)
2020-01-31
Report on RIKEN iTHEMS - Berkeley Math Visiting Scholar Program (Lunch Meeting)
三上 渓太 (数理創造プログラム 研究員)
2020-01-24
Algorithms for point set processes
スクロツキ マーティン (数理創造プログラム 客員研究員 / Fellow, German Academic Scholarship Foundation, Germany)
2020-01-17
Balancing Thermodynamics and Kinetics to Achieve Maximum Rates in Catalysis
Hideshi Ooka (CSRS)
2020-01-10
Spintronics: Spin current propagation or susceptibility?
Gen Tatara (CEMS/CPR)