Coffee Meeting Log

2020-06-26

Observational study of suprenova remnants

Naomi Tsuji (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

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

Akinori Tanaka (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

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?

Tomoya Naito (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).

2020-05-29

Knot theory and topological semimetals

Ching-Kai Chiu (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.

2020-05-15

Basics of evolution and the evolution of Sars-CoV-2

Jeffrey Fawcett (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

2020-05-08

Next-generation method to derive the basic reproduction number of infectious disease models

Ryosuke Iritani (Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

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

Ryusuke Hamazaki (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / RIKEN Hakubi Team Leader, Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team, RIKEN Cluster for Pioneering Research (CPR))

2020-04-17

On COVID-19 spreading

Pascal Naidon (Senior Research Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

2020-04-03

Multi-meesenger Search for sources of high energy neutrino

Haoning He (ABBL)

2020-03-27

Mathematical models of epidemics

Takemasa Miyoshi (Deputy Program Director, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Team Leader, Data Assimilation Research Team, RIKEN Center for Computational Science (R-CCS))

2020-02-21

Motivic homotopy theory and modular representation theory

Shane Kelly (Tokyo Institute of Technology)

2020-02-14

On the geodesics of regular polyhedra

Hiroki Kodama (Visiting Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / Assistant Professor, Advanced Institute for Materials Research (AIMR), Tohoku University)

2020-01-31

Report on RIKEN iTHEMS - Berkeley Math Visiting Scholar Program (Lunch Meeting)

Keita Mikami (Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

2020-01-24

Algorithms for point set processes

Martin Skrodzki (Visiting Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) / 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)

2019-12-13

TBA

Nagisa Hiroshima (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

2019-12-06

Introduction to genetics

Jeffrey Fawcett (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

2019-11-29

Pruning brunches of deep learning

Masato Taki (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

2019-11-22

The new SI units

Tomoki Ozawa (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))